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2020
TitleAbstractYearTypePDFResearch Group
Preintegrated IMU Features For Efficient Deep Inertial Odometry
R Khorrambakht, H Damirchi, HD Taghirad
arXiv preprint arXiv:2007.02929
Abstract:

MEMS Inertial Measurement Units (IMUs) are inexpensive and effective sensors that provide proprioceptive motion measurements for many robots and consumer devices. However, their noise characteristics and manufacturing imperfections lead to complex ramifications in classical fusion pipelines. While deep learning models provide the required flexibility to model these complexities from data, they have higher computation and memory requirements, making them impractical choices for low-power and embedded applications. This paper attempts to address the mentioned conflict by proposing a computationally, efficient inertial representation for deep inertial odometry. Replacing the raw IMU data in deep Inertial models, preintegrated features improves the model's efficiency. The effectiveness of this method has been demonstrated for the task of pedestrian inertial odometry, and its efficiency has been shown through its embedded implementation on a microcontroller with restricted resources.

2020JournalPDFAutonomous Robotics
ARC-Net: Activity Recognition Through Capsules
H Damirchi, R Khorrambakht, H Taghirad
arXiv preprint arXiv:2007.03063
Abstract:

Human Activity Recognition (HAR) is a challenging problem that needs advanced solutions than using handcrafted features to achieve a desirable performance. Deep learning has been proposed as a solution to obtain more accurate HAR systems being robust against noise. In this paper, we introduce ARC-Net and propose the utilization of capsules to fuse the information from multiple inertial measurement units (IMUs) to predict the activity performed by the subject. We hypothesize that this network will be able to tune out the unnecessary information and will be able to make more accurate decisions through the iterative mechanism embedded in capsule networks. We provide heatmaps of the priors, learned by the network, to visualize the utilization of each of the data sources by the trained network. By using the proposed network, we were able to increase the accuracy of the state-of-the-art approaches by 2%. Furthermore, we investigate the directionality of the confusion matrices of our results and discuss the specificity of the activities based on the provided data.

2020JournalPDFAutonomous Robotics
Solution to IDA-PBC PDEs by Pfaffian Differential Equations
MRJ Harandi, H Taghirad
arXiv preprint arXiv:2006.14983
Abstract:

Finding the general solution of partial differential equations (PDEs) is essential for controller design in some methods. Interconnection and damping assignment passivity based control (IDA-PBC) is one of such methods in which the solution to corresponding PDEs is needed to apply it in practice. In this paper, such PDEs are transformed to corresponding Pfaffian differential equations. Furthermore, it is shown that upon satisfaction of the integrability condition, the solution to the corresponding third order Pfaffian differential equation may be obtained quite easily. The method is applied to the PDEs of IDA-PBC in some benchmark problems such as Magnetic levitation system, Pendubot and underactuated cable driven robot to verify its applicability.

2020JournalPDFDynamical Systems Analysis and Control
Adaptive motion control of parallel robots with kinematic and dynamic uncertainties
MRJ Harandi, SA Khalilpour, H Taghirad, JG Romero
arXiv preprint arXiv:2003.08860
Abstract:

One of the most challenging issues in adaptive control of robot manipulators with kinematic uncertainties is requirement of the inverse of Jacobian matrix in regressor form. This requirement is inevitable in the case of the control of parallel robots, whose dynamic equations are written directly in the task space. In this paper, an adaptive controller is designed for parallel robots based on representation of Jacobian matrix in regressor form, such that asymptotic trajectory tracking is ensured. The main idea is separation of determinant and adjugate of Jacobian matrix and then organize new regressor forms. Simulation and experimental results on a 2--DOF R\underline{P}R and 3--DOF redundant cable driven robot, verify promising performance of the proposed methods.

2020JournalPDFParallel and Cable Robotics
A switched SDRE filter for state of charge estimation of lithium-ion batteries
Faraz Lotfi, Saeedeh Ziapour, Farnoosh Faraji, Hamid D. Taghirad
International Journal of Electrical Power & Energy Systems
Abstract:

Lithium-ion (Li-ion) batteries need very precise monitor of the state of charge (SOC) to ensure a long cycle life.
Hence, a knowledge of the SOC is important for Li-ion batteries. Although SOC cannot be measured directly, it can be estimated from direct measurement variables based on a model of the battery. Single-Particle-Model (SPM), a reduced-order nonlinear electrochemical model, is commonly used for this purpose. State-dependent-
Riccati-equation (SDRE) filter is chosen as the estimator due to its high-flexibility in handling the model’s nonlinearity. However, performance of this filter is limited in presence of uncertainties. To tackle this problem,
in this paper, a switching concept is induced into SDRE filter, in the form of switched estimation error covariance
matrix with a certain frequency. Thus, by changing the Riccati equation dynamic in SDRE filter and proper
adjustment of estimation error covariance matrix eigenvalues, performance and robustness of the common SDRE
filter is significantly improved for Li-ion SOC estimation. To analyze the fidelity of such a filter in further
applications, stability analysis is carried out on a class of nonlinear systems, and ultimate bound of estimation error is analytically obtained, and the influence of switching is investigated. Simulation results reveal effec-
tiveness of the proposed filter compared to common SDRE filter, extended Kalman filter and variable structure approaches. Furthermore, experimental results verify the effectiveness of the proposed method in practice.

2020JournalPDFAutonomous Robotics
A force reflection robust control scheme with online authority
adjustment for dual user haptic system

Mohammad Motaharifar, Hamid D. Taghirad
Mechanical Systems and Signal Processing
Abstract:

This article aims at developing a control structure with online authority adjustment for a
dual-user haptic training system. In the considered system, the trainer and the trainee
are given the facility to cooperatively conduct the surgical operation. The task dominance
is automatically adjusted based on the task performance of the trainee with respect to the trainer. To that effect, the average norm of position error between the trainer and the trainee is calculated in a sliding window and the relative task dominance is assigned to the operators accordingly. Moreover, a robust controller is developed to satisfy the require-
ment of position tracking. The stability analysis based on the input-to-state stability (ISS) methodology is reported. Experimental results demonstrate the effectiveness of the
proposed control approach.

2020JournalPDFSurgical Robotics
Joint-Space Position Control of a Deployable Cable Driven Robot in Joint Space Using Force Sensors and Actuator Encoders
S.A. Khalilpour, R. Khorrambakht, A. Bourbour, H.D. Taghirad
Modares Mechanical Engineering
Abstract:

Despite the intense development of cable-driven robot in recent years, they have not yet been
vastly utilized in their potential applications because of difficulties in their performing accurate
installation and calibration. This paper aims to present a suitable control method, relieving the
limitation of accurate calibration and installation requirement in the suspended cable-driven
parallel robot. In this paper, kinematics and dynamics uncertainties are investigated and based
on their bounds, a robust controller is proposed. The main innovation of this article is providing
a new control method to cost reduction by eliminating accurate measurement tools such as a
camera in position control of a deployable cable-driven robot. Using this approach, reducing
costs in building a robot and increasing the speed of installation and calibration is achieved.
Another problem investigated in this paper is the problem of joint space controllers applied
to redundant cable-driven parallel robots, namely the loosened redundant cable. To solve this
problem, the embedded force sensor and a new sliding surface for the controller is proposed. In
fact, in this paper, the conventional joint-space controllers are modified to become applicable
to the control of cable-driven robots. Finally, by conducting some experiments using ARAS
suspended cable-driven parallel robot, the proposed algorithms are verified and it is shown
that there are feasible solutions for stable robot maneuvers.

2019JournalPDFParallel and Cable Robotics
Experimental Performance of Adaptive Fast Terminal Sliding Mode Control on a Suspended Cable Robot
Mohammad Isaac Hosseini, Mohammad Reza Jafari Harandi, Seyed Ahmad Khalilpour, Hamid Taghirad
The Journal of Electrical and Computer Engineering Innovations
Abstract:

Fast-tracking of reference trajectory and performance improvement in
the presence of dynamic and kinematic uncertainties is of paramount
importance in all robotic applications. This matter is even more
important in the case of cable-driven parallel robots due to the flexibility
of the cables. Furthermore, cables are limited in the sense that they can
only apply tensile forces, for this reason, feedback control of such robots
becomes more challenging than conventional parallel robots. To address
these requirements for a suspended cable-driven parallel robot, in this
paper a novel adaptive fast terminal sliding mode controller is proposed
and then the stability of the closed-loop system is proven. In the proposed
controller, a nonlinear term as a fractional power term is used to
guarantee the convergent response at a finite time. At last, to show the
effectiveness of the proposed controller in tracking the reference
trajectory, simulations and the required experimental implementation is

performed on a suspended cable-driven robot. This robot, named ARAS-
CAM, has three degrees of transmission freedom. The obtained results

confirm the suitable performance of this method for cable robots.

2019JournalPDFParallel and Cable Robotics
Control Synthesis and ISS Stability Analysis of a Dual-User Haptic Training System Based on S-Shaped Function
Mohammad Motaharifar, Hamid D. Taghirad, Keyvan Hashtrudi-Zaad, and Seyed Farzad Mohammadi
IEEE/ASME Transactions on Mechatronics
Abstract:

The controller design and stability analysis of
a dual user training haptic system is studied. Most of the previously proposed control methodologies for this system
have not simultaneously considered special requirements
of surgery training and stability analysis of the nonlinear
closed-loop system which is the objective of this paper. In the proposed training approach, the trainee is allowed
to freely experience the task and be corrected as needed,
while the trainer maintains the task dominance. A special S-shaped function is suggested to generate the corrective force according to the magnitude of motion error between the trainer and the trainee. The closed-loop stability of the system is analyzed considering the nonlinearity of
the system components using the Input-to-State Stability approach. Simulation and experimental results show the effectiveness of the proposed approach.

2019JournalPDFSurgical Robotics
Control of Dual-User Haptic Training System With Online Authority Adjustment: An Observer-Based Adaptive Robust Scheme
Mohammad Motaharifar, Hamid D. Taghirad, Keyvan Hashtrudi-Zaad and Seyed Farzad Mohammadi
IEEE Transactions on Control Systems Technology
Abstract:

The design problem for the control a dual-user
haptic surgical training system is studied in this article. The
system allows the trainee to perform the task on a virtual environment, while the trainer is able to interfere in the operation and correct probable mistakes made by the trainee. The proposed
methodology allows the trainer to transfer the task authority to or from the trainee in real time. The robust adaptive nature
of the controller ensures position tracking. The stability of the closed-loop system is analyzed using the input-to-output stability approach and the small-gain theorem. Simulation and
experimental results are presented to validate the effectiveness
of the proposed control scheme.

2019JournalPDFSurgical Robotics
Adaptive Fast Terminal Sliding Mode Control of A Suspended Cable–Driven Robot
M Hosseini, M. J. Harandi, S. A. Khalilpour Seyedi, H.D. taghirad
2019 27th Iranian Conference on Electrical Engineering (ICEE)
Abstract:

Increasing the speed and precision of operation in
cable robots is crucial due to the flexibility of cables. On the other hand, due to the frequent dynamical uncertainties present in
cable robots, providing a robust control method is necessary. The
performance of the fast terminal sliding mode (FTSM) controller
has been investigated in various systems, which ensures that
the state of the system is rapidly converged to the equilibrium
point at a finite time. In this paper, the FTSM controller has
been developed in such a way to be able to track the optimal robot path in the presence of dynamic uncertainties at different operating speeds. The main innovation of this paper is to provide
an adaptive robust control method for controlling cable robots and analyzing the stability of the closed-loop control system
based on the Lyapunov stability theory. In order to demonstrate
the effectiveness of the proposed controller, simulation results,
as well as experimental implementation on ARAS–CAM, a four
cable suspended robot with three degrees of freedom, has been
investigated and it is shown that the proposed controller can
provide suitable tracking performance in practice.

2019ConferencePDFParallel and Cable Robotics
System identification and H-infinity based control of quadrotor attitude
Ali Noormohammadi-Asl, Omid Esrafilian, Mojtaba Ahangar Arzati, Hamid D. Taghirad
Arxiv Optimization and Control
Abstract:

The attitude control of a quadrotor is a fundamental problem, which has a pivotal role in a
quadrotor stabilization and control. What makes this problem more challenging is the
presence of uncertainty such as unmodelled dynamics and unknown parameters. In this
paper, to cope with uncertainty, an H1 control approach is adopted for a real quadrotor.
To achieve H1 controller, first a continuous-time system identification is performed on the experimental data to encapsulate a nominal model of the system as well as a multiplicative uncertainty. By this means, H1 controllers for both roll and pitch angle are synthesized. To verify the effectiveness of the proposed controllers, some real experiments
and simulations are carried out. Results verify that the designed controller does retain robust stability, and provide a better tracking performance in comparison with a well-tuned PID and a l synthesis controller.

2019JournalPDFAutonomous Robotics
A Force Reflection Impedance Control Scheme for Dual User Haptic Training System
M. Motaharifar, A. Iranfar, and H. D. Taghirad
2019 27th Iranian Conference on Electrical Engineering (ICEE)
Abstract:

In this paper, an impedance control based training scheme for a dual user haptic surgery training system is introduced. The training scheme allows the novice surgeon (trainee) to perform a surgery operation while an expert surgeon (trainer)
supervises the procedure. Through the proposed impedance control structure, the trainer receives trainee’s position to detect
his (her) wrong movements. Besides, a novel force reflection term is proposed in order to efficiently utilize trainer’s skill in the training loop. Indeed, the trainer can interfere into the procedure
whenever needed either to guide the trainee or suppress his (her)
authority due to his (her) supposedly lack of skill to continue
the operation. Each haptic device is stabilized and the closed
loop stability of the nonlinear system is investigated. Simulation
results show the appropriate performance of the proposed control
scheme.

2019ConferencePDFSurgical Robotics
Point-to-Point Motion Control of An Underactuated Planar Cable Driven Robot
Mohammad Reza Jafari Harandi, Hamed Damirchi, Seyed ahmad Khalilpour seyedi and Hamid Dokht Taghirad
2019 27th Iranian Conference on Electrical Engineering (ICEE)
Abstract:

Despite being vastly investigated for underactuated
serial robots, there is less attention paid to controller design of
underactuated parallel robots in the literature. This paper studies
regulation of an underactuated planar parallel cable-driven robot
with three degrees of freedom. First, kinematic and dynamic
equations of the robot are derived, then equilibrium points of
the robot are investigated. By analyzing dynamics of the under–
constrained robot, it is shown that zero dynamic is oscillatory, thus a control law is proposed by a composition of damping injection and sliding mode control. One of the greatest advantages
of the proposed controller is that after convergence of the robot to the desired point, which is proven by Lyapunov theorem, it is chattering free. Finally, simulation results shows the effectiveness
of the controller in practice.

2019ConferencePDFParallel and Cable Robotics
Implementation of an improved moment-based visual servoing controller on an industrial robot
Parisa Masnadi Khiabani, Javad Ramezanzadeh and Hamid D. Taghirad
International Conference on Robotics and Mechatronics
Abstract:

In this paper, robust nonlinear control of momentbased visual servoing has been proposed. Due to the nonlinear
nature of system, proportional integral sliding mode controller
could improve the performance and robustness of visual servoing.
The proposed method not only increases domain of attraction
even in extraneous image regions, but also it achieves convergence
to the target point despite of uncertainties. The stability of the
controller is analyzed by Lyapunov’s theorem. Furthermore,
Integrated control of 4 DOF camera motions in this work,
drastically improves the accuracy in compare with the kernelbased sliding mode visual servoing. Different experiments are
done to demonstrate considerable performance improvements on
5 DOF industrial robot.

2019ConferencePDFSurgical Robotics
ARAS-IREF: An Open-Source Low Cost Framework for Pose Estimation
H. Damirchi, R. Khorrambakht, H. D. Taghirad
International Conference on Robotics and Mechatronics
Despite the amount of research reported on state
estimation and sensor fusion in the field of robotics, there
are no well known low-cost solutions for a referencing system
to determine the accuracy of developed methods by providing
a suitable ground truth for them. In this paper an efficient
and accurate 6–DoF pose measurement system is proposed and
implemented on a spherical parallel robot using IR LEDs. This
approach uses the perspective-n-point algorithm to derive the
transformation matrix representing the accurate relative pose
of the end-effector with respect to an inertial frame. Exploiting
a visible light filter in front of the camera has rendered this
approach robust against illumination changes. Furthermore, it
allows for mitigating the rolling shutter effects by reducing the
exposure time. Finally, a custom made testing module is proposed
to verify the accuracy of the proposed device, and the calibration
process proves the accuracy and efficiency of the system.
2019ConferencePDFParallel and Cable Robotics
Position Estimation for Drones based on Visual SLAM and IMU in GPS-denied Environment
Hamid Didari Khamseh Motlagh, Faraz Lotfi, Saeed Bakhshi Germi, Hamid D.Taghirad
International Conference on Robotics and Mechatronics
Due to the increased rate of drone usage in various
commercial and industrial fields, the need for their autonomous
operation is rapidly increasing. One major aspect of
autonomous movement is the ability to operate safely in an
unknown environment. The majority of current works are
persistently using a global positioning system (GPS) to directly
find the absolute position of the drone. However, GPS accuracy
might be not suitable in some applications and this solution is
not applicable to all situations. In this paper, a positioning
system based on monocular SLAM and inertial measurement
unit (IMU) is presented. The position is calculated through the
semi-direct visual odometry (SVO) method alongside IMU data,
and is integrated with an extended Kalman filter (EKF) to
enhance the efficiency of the algorithm. The data is then
employed to control the drone without any requirement to any
source of external input. The experiment results for longdistance flying paths is very promising
2019ConferencePDFAutonomous Robotics
A Calibration Framework for Deployable Cable Driven Parallel Robots with Flexible Cables
R. Khorrambakht, H. Damirchi, S. A. Khalilpour∗, and H. D. Taghirad
International Conference on Robotics and Mechatronics
Due to their simple and inexpensive structures,
suspended cable driven parallel robots are suitable choices for
many real-world applications. However, only when the accurate
kinematic parameters are available, can we control the robot to
the best of its abilities. This is specially a stringent requirement
for fast deployable cable driven robots. With the aim of addressing these needs, in this paper we propose an effective framework
for calibrating the kinematic parameters of suspended cable
driven parallel robots with no requirements for expensive tools
and measurement devices. Moreover, the proposed algorithm
utilizes the existing force sensors in the cable robot to nominate
the best set of data for calibration. The integrity and effectiveness
of this framework is reported through simulation and practical
experiments, which verifies promising horizons for deployable
real-world applications.
2019ConferencePDFParallel and Cable Robotics
Coverage Control of Multi-Robot System for Dynamic Cleaning of Oil Spills
Samane Kaviri, Ahmadreza Tahsiri and Hamid D. Taghirad
International Conference on Robotics and Mechatronics
This paper addressed the dynamic cleaning of
oil spills using a multi-robot system. The cleaning process is
performed using a group of aerial agents adaptively covering
an oil spill considering its advection and spreading on the sea
surface. The concept of Voronoi Tessellation is employed to
command the autonomous vehicles on how to adapt its
configuration with the dynamic oil spill. Once the spill tracking
error reduces to the desired value, all of the agents spray
dispersant on the oil spill. This solution prevents wasting the
excess amount of dispersant that is often being sprayed in
conventional methods by aircraft. A distributed sliding mode
control scheme is proposed to navigate the agents to the nearoptimal Centroidal Voronoi Tessellation (CVT) by targeting
the thick layers. Simulation results demonstrate that the
proposed strategy can efficiently track the trajectory of the
polluted area, and adaptively cover the time-varying shape of
the oil spill.
2019ConferencePDFDynamical Systems Analysis and Control
Stabilization of Cable Driven Robots Using Interconnection Matrix: Ensuring Positive Tension
M. R. J. Harandi, S. A. Khalilpour, Hamed Damirchi and Hamid. D. Taghirad
International Conference on Robotics and Mechatronics
Cable driven parallel robots are closed-loop kinematic chains, where the end-effector is attached to the base by a
number of cables. Because of the nature of cables, a major issue
in control of these robots is ensuring positive tensions. When
the robot is not redundant, this issue is of utmost importance
for the controller synthesis. In the case of point to point motion
control, the trajectory is not specified beforehand, thus negative
tension may occur. In order to resolve this issue, interconnection
and damping assignment passivity based control (IDA-PBC) is
employed. IDA-PBC is a well-known method for control of underactuated systems where desired damping and interconnection
between subsystems are imposed. Interconnection matrix is a
skew-symmetric matrix which doesn’t have an effect on stability,
but it greatly influences the transient response of the system.
In this paper, the interconnection matrix is exploited to ensure
positive tension in fully actuated cable driven robots. The results
are verified through simulation on a 3-DOF suspended cable
driven robot.
2019ConferencePDFParallel and Cable Robotics
Robust Impedance Control for Dual User Haptic Training System
R. Heidari, M. Motaharifar and H. D. Taghirad
International Conference on Robotics and Mechatronics
In this paper, an impedance controller with switching parameters for a dual-user haptic training system is introduced. The trainer and the trainee are connected through their
haptic consoles, and the trainee performs the surgical procedure
on the environment. The trainer can intervene in the procedure
by pressing a mechanical pedal; thus, the control parameters are
switched to transfer the authority over the task from the trainee
to the trainer. The stability of each subsystem and the closed-loop
stability of the overall system are investigated. The simulation
results verify the performance of the proposed controller.
2019ConferencePDFSurgical Robotics
Skill Assessment Using Kinematic Signatures: Geomagic Touch Haptic Device
N. S. Hojati, M. Motaharifar, H. D. Taghirad, A. Malekzadeh
International Conference on Robotics and Mechatronics
he aim of t his paper is to develop a practical
skill assessment for some designed experimental tasks, retrieved
from Minimally Invasive Surgery. The skill evaluation is very
important in surgery training, especially in MIS. Most of the
previous studies for skill assessment methods are limited in the
Hidden Markov Model and some frequency transforms, such as
Discret e Fourier transform, Discrete Cosine Transform and etc.
In this paper , some features have been ext racted from timefrequency analysis with t he Discret e Wavelet Transform and
t emporal signa l ana lysis of some kinematic metrics whi ch were
compute d from Geom agic Touch kinematic data. In addition,
the k-n earest neighbors classifier are employed to detect skill
level based on ext racted features. Through cross-validation
results, it is demonstrated that t he proposed methodology has
appropriate accuracy in skill level det ection
2019ConferencePDFSurgical Robotics
Path Planning for a UAV by Considering Motion Model Uncertainty
Hossein Sheikhi Darani, Ali Noormohammadi-Asl and Hamid D. Taghirad
International Conference on Robotics and Mechatronics
Abstract:

The primary purpose of path planning for unmanned aerial vehicles (UAVs), which is a necessary prerequisite toward an autonomous UAV, is to guide the robot to
the predefined target while the chosen path is optimized. This
paper addresses the problem of path planning for an unmanned
aerial vehicle in a 2D indoor environment, considering motion uncertainty. To cope with this challenge, the problem of
motion planning is formulated in three parts. A vision-based
extended Kalman Filter (EKF) is used to localize the UAV in
the unstructured environment. To overcome motion uncertainty,
the problem is modeled as a Markov decision problem (MDP).
Finally, a novel dynamic feedback linearization based switching
controller is proposed for point-to-point motion. Simulation and
experimental results are given to show the effectiveness of the
proposed path planning method in practice

2019ConferencePDFAutonomous Robotics
2019
TitleAbstractYearTypePDFResearch Group
Control Synthesis and ISS Stability Analysis of Dual-User Haptic Training System Based on S-Shaped Function
Mohammad Motaharifar, Hamid D. Taghirad, Keyvan Hashtrudi-Zaad, Seyed Farzad Mohammadi
IEEE/ASME Transactions on Mechatronics
Abstract:

The controller design and stability analysis of dual user training haptic system is studied. Most of the previously proposed control methodologies for this system have not simultaneously considered special requirements of surgery training and stability analysis of the nonlinear closed loop system which is the objective of this paper. In the proposed training approach, the trainee is allowed to freely experience the task and be corrected as needed, while the trainer maintains the task dominance. A special S-shaped function is suggested to generate the corrective force according to the magnitude of motion error between the trainer and the trainee. The closed loop stability of the system is analyzed considering the nonlinearity of the system components using the Input-to-State Stability (ISS) approach. Simulation and experimental results show the effectiveness of the proposed approach.

2019ConferencePDFSurgical Robotics
Robust cascade control of a deployable cable-driven robot
S.A. Khalilpour, R. Khorrambakht, H.D. Taghirad, Philippe Cardou
Mechanical Systems and Signal Processing
Abstract:

In this paper, we derive the dynamic formulation of a deployable cable-driven robot that considers models of the actuator and power transmission systems, and we investigate the challenges of structural uncertainty. To accommodate the inherent uncertainty of the system, we propose a proper control topology based on a cascade structure. The inner loop of the structure controls the cable forces, and the outer loop tracks the precise position of the robot’s end-effector. For the design of the outer loop controller, we propose a robust sliding mode controller with a stability analysis that is based on the Lyapunov direct method. The main contribution of this paper is to analyze the stability of the system as a whole considering both the inner and outer loop controllers. Finally, in order to illustrate the performance of the proposed controller, we present the results of an experiment on a deployable suspended cable-driven robot, which shows the effectiveness of the proposed controller in the presence of the inherent uncertainties of the system.

2019JournalPDFParallel and Cable Robotics
Control Synthesis and ISS Stability A5Analysis of Dual-User Haptic Training System Based on S-Shaped Function
Mohammad Motaharifar, Hamid D. Taghirad, Keyvan Hashtrudi-Zaad and Seyed Farzad Mohammadi
IEEE/ASME Transactions on Mechatronics
Abstract:

The controller design and stability analysis of dual user training haptic system is studied. Most of the previously proposed control methodologies for this system have not simultaneously considered special requirements of surgery training and stability analysis of the nonlinear closed loop system which is the objective of this paper. In the proposed training approach, the trainee is allowed to freely experience the task and be corrected as needed, while the trainer maintains the task dominance. A special S-shaped function is suggested to generate the corrective force according to the magnitude of motion error between the trainer and the trainee. The closed loop stability of the system is analyzed considering the nonlinearity of the system components using the Input-to-State Stability (ISS) approach. Simulation and experimental results show the effectiveness of the proposed approach.

2019JournalPDFSurgical Robotics
Joint-Space Position Control of a Deployable Cable Driven Robot in Joint Space Using Force Sensors and Actuator Encoders
S.A. Khalilpour, R. Khorrambakht, A. Bourbour, H.D. Taghirad
Modares Mechanical Engineering
Abstract:

Despite the intense development of cable-driven robot in recent years, they have not yet been
vastly utilized in their potential applications because of difficulties in their performing accurate
installation and calibration. This paper aims to present a suitable control method, relieving the
limitation of accurate calibration and installation requirement in the suspended cable-driven
parallel robot. In this paper, kinematics and dynamics uncertainties are investigated and based
on their bounds, a robust controller is proposed. The main innovation of this article is providing
a new control method to cost reduction by eliminating accurate measurement tools such as a
camera in position control of a deployable cable-driven robot. Using this approach, reducing
costs in building a robot and increasing the speed of installation and calibration is achieved.
Another problem investigated in this paper is the problem of joint space controllers applied
to redundant cable-driven parallel robots, namely the loosened redundant cable. To solve this
problem, the embedded force sensor and a new sliding surface for the controller is proposed. In
fact, in this paper, the conventional joint-space controllers are modified to become applicable
to the control of cable-driven robots. Finally, by conducting some experiments using ARAS
suspended cable-driven parallel robot, the proposed algorithms are verified and it is shown
that there are feasible solutions for stable robot maneuvers.

2019JournalPDFParallel and Cable Robotics
Experimental Performance of Adaptive Fast Terminal Sliding Mode Control on a Suspended Cable Robot
Mohammad Isaac Hosseini, Mohammad Reza Jafari Harandi, Seyed Ahmad Khalilpour, Hamid Taghirad
The Journal of Electrical and Computer Engineering Innovations
Abstract:

Fast-tracking of reference trajectory and performance improvement in
the presence of dynamic and kinematic uncertainties is of paramount
importance in all robotic applications. This matter is even more
important in the case of cable-driven parallel robots due to the flexibility
of the cables. Furthermore, cables are limited in the sense that they can
only apply tensile forces, for this reason, feedback control of such robots
becomes more challenging than conventional parallel robots. To address
these requirements for a suspended cable-driven parallel robot, in this
paper a novel adaptive fast terminal sliding mode controller is proposed
and then the stability of the closed-loop system is proven. In the proposed
controller, a nonlinear term as a fractional power term is used to
guarantee the convergent response at a finite time. At last, to show the
effectiveness of the proposed controller in tracking the reference
trajectory, simulations and the required experimental implementation is

performed on a suspended cable-driven robot. This robot, named ARAS-
CAM, has three degrees of transmission freedom. The obtained results

confirm the suitable performance of this method for cable robots.

2019JournalPDFParallel and Cable Robotics
Control Synthesis and ISS Stability Analysis of a Dual-User Haptic Training System Based on S-Shaped Function
Mohammad Motaharifar, Hamid D. Taghirad, Keyvan Hashtrudi-Zaad, and Seyed Farzad Mohammadi
IEEE/ASME Transactions on Mechatronics
Abstract:

The controller design and stability analysis of
a dual user training haptic system is studied. Most of the previously proposed control methodologies for this system
have not simultaneously considered special requirements
of surgery training and stability analysis of the nonlinear
closed-loop system which is the objective of this paper. In the proposed training approach, the trainee is allowed
to freely experience the task and be corrected as needed,
while the trainer maintains the task dominance. A special S-shaped function is suggested to generate the corrective force according to the magnitude of motion error between the trainer and the trainee. The closed-loop stability of the system is analyzed considering the nonlinearity of
the system components using the Input-to-State Stability approach. Simulation and experimental results show the effectiveness of the proposed approach.

2019JournalPDFSurgical Robotics
Control of Dual-User Haptic Training System With Online Authority Adjustment: An Observer-Based Adaptive Robust Scheme
Mohammad Motaharifar, Hamid D. Taghirad, Keyvan Hashtrudi-Zaad and Seyed Farzad Mohammadi
IEEE Transactions on Control Systems Technology
Abstract:

The design problem for the control a dual-user
haptic surgical training system is studied in this article. The
system allows the trainee to perform the task on a virtual environment, while the trainer is able to interfere in the operation and correct probable mistakes made by the trainee. The proposed
methodology allows the trainer to transfer the task authority to or from the trainee in real time. The robust adaptive nature
of the controller ensures position tracking. The stability of the closed-loop system is analyzed using the input-to-output stability approach and the small-gain theorem. Simulation and
experimental results are presented to validate the effectiveness
of the proposed control scheme.

2019JournalPDFSurgical Robotics
Adaptive Fast Terminal Sliding Mode Control of A Suspended Cable–Driven Robot
M Hosseini, M. J. Harandi, S. A. Khalilpour Seyedi, H.D. taghirad
2019 27th Iranian Conference on Electrical Engineering (ICEE)
Abstract:

Increasing the speed and precision of operation in
cable robots is crucial due to the flexibility of cables. On the other hand, due to the frequent dynamical uncertainties present in
cable robots, providing a robust control method is necessary. The
performance of the fast terminal sliding mode (FTSM) controller
has been investigated in various systems, which ensures that
the state of the system is rapidly converged to the equilibrium
point at a finite time. In this paper, the FTSM controller has
been developed in such a way to be able to track the optimal robot path in the presence of dynamic uncertainties at different operating speeds. The main innovation of this paper is to provide
an adaptive robust control method for controlling cable robots and analyzing the stability of the closed-loop control system
based on the Lyapunov stability theory. In order to demonstrate
the effectiveness of the proposed controller, simulation results,
as well as experimental implementation on ARAS–CAM, a four
cable suspended robot with three degrees of freedom, has been
investigated and it is shown that the proposed controller can
provide suitable tracking performance in practice.

2019ConferencePDFParallel and Cable Robotics
System identification and H-infinity based control of quadrotor attitude
Ali Noormohammadi-Asl, Omid Esrafilian, Mojtaba Ahangar Arzati, Hamid D. Taghirad
Arxiv Optimization and Control
Abstract:

The attitude control of a quadrotor is a fundamental problem, which has a pivotal role in a
quadrotor stabilization and control. What makes this problem more challenging is the
presence of uncertainty such as unmodelled dynamics and unknown parameters. In this
paper, to cope with uncertainty, an H1 control approach is adopted for a real quadrotor.
To achieve H1 controller, first a continuous-time system identification is performed on the experimental data to encapsulate a nominal model of the system as well as a multiplicative uncertainty. By this means, H1 controllers for both roll and pitch angle are synthesized. To verify the effectiveness of the proposed controllers, some real experiments
and simulations are carried out. Results verify that the designed controller does retain robust stability, and provide a better tracking performance in comparison with a well-tuned PID and a l synthesis controller.

2019JournalPDFAutonomous Robotics
A Force Reflection Impedance Control Scheme for Dual User Haptic Training System
M. Motaharifar, A. Iranfar, and H. D. Taghirad
2019 27th Iranian Conference on Electrical Engineering (ICEE)
Abstract:

In this paper, an impedance control based training scheme for a dual user haptic surgery training system is introduced. The training scheme allows the novice surgeon (trainee) to perform a surgery operation while an expert surgeon (trainer)
supervises the procedure. Through the proposed impedance control structure, the trainer receives trainee’s position to detect
his (her) wrong movements. Besides, a novel force reflection term is proposed in order to efficiently utilize trainer’s skill in the training loop. Indeed, the trainer can interfere into the procedure
whenever needed either to guide the trainee or suppress his (her)
authority due to his (her) supposedly lack of skill to continue
the operation. Each haptic device is stabilized and the closed
loop stability of the nonlinear system is investigated. Simulation
results show the appropriate performance of the proposed control
scheme.

2019ConferencePDFSurgical Robotics
Point-to-Point Motion Control of An Underactuated Planar Cable Driven Robot
Mohammad Reza Jafari Harandi, Hamed Damirchi, Seyed ahmad Khalilpour seyedi and Hamid Dokht Taghirad
2019 27th Iranian Conference on Electrical Engineering (ICEE)
Abstract:

Despite being vastly investigated for underactuated
serial robots, there is less attention paid to controller design of
underactuated parallel robots in the literature. This paper studies
regulation of an underactuated planar parallel cable-driven robot
with three degrees of freedom. First, kinematic and dynamic
equations of the robot are derived, then equilibrium points of
the robot are investigated. By analyzing dynamics of the under–
constrained robot, it is shown that zero dynamic is oscillatory, thus a control law is proposed by a composition of damping injection and sliding mode control. One of the greatest advantages
of the proposed controller is that after convergence of the robot to the desired point, which is proven by Lyapunov theorem, it is chattering free. Finally, simulation results shows the effectiveness
of the controller in practice.

2019ConferencePDFParallel and Cable Robotics
Implementation of an improved moment-based visual servoing controller on an industrial robot
Parisa Masnadi Khiabani, Javad Ramezanzadeh and Hamid D. Taghirad
International Conference on Robotics and Mechatronics
Abstract:

In this paper, robust nonlinear control of momentbased visual servoing has been proposed. Due to the nonlinear
nature of system, proportional integral sliding mode controller
could improve the performance and robustness of visual servoing.
The proposed method not only increases domain of attraction
even in extraneous image regions, but also it achieves convergence
to the target point despite of uncertainties. The stability of the
controller is analyzed by Lyapunov’s theorem. Furthermore,
Integrated control of 4 DOF camera motions in this work,
drastically improves the accuracy in compare with the kernelbased sliding mode visual servoing. Different experiments are
done to demonstrate considerable performance improvements on
5 DOF industrial robot.

2019ConferencePDFSurgical Robotics
ARAS-IREF: An Open-Source Low Cost Framework for Pose Estimation
H. Damirchi, R. Khorrambakht, H. D. Taghirad
International Conference on Robotics and Mechatronics
Despite the amount of research reported on state
estimation and sensor fusion in the field of robotics, there
are no well known low-cost solutions for a referencing system
to determine the accuracy of developed methods by providing
a suitable ground truth for them. In this paper an efficient
and accurate 6–DoF pose measurement system is proposed and
implemented on a spherical parallel robot using IR LEDs. This
approach uses the perspective-n-point algorithm to derive the
transformation matrix representing the accurate relative pose
of the end-effector with respect to an inertial frame. Exploiting
a visible light filter in front of the camera has rendered this
approach robust against illumination changes. Furthermore, it
allows for mitigating the rolling shutter effects by reducing the
exposure time. Finally, a custom made testing module is proposed
to verify the accuracy of the proposed device, and the calibration
process proves the accuracy and efficiency of the system.
2019ConferencePDFParallel and Cable Robotics
Position Estimation for Drones based on Visual SLAM and IMU in GPS-denied Environment
Hamid Didari Khamseh Motlagh, Faraz Lotfi, Saeed Bakhshi Germi, Hamid D.Taghirad
International Conference on Robotics and Mechatronics
Due to the increased rate of drone usage in various
commercial and industrial fields, the need for their autonomous
operation is rapidly increasing. One major aspect of
autonomous movement is the ability to operate safely in an
unknown environment. The majority of current works are
persistently using a global positioning system (GPS) to directly
find the absolute position of the drone. However, GPS accuracy
might be not suitable in some applications and this solution is
not applicable to all situations. In this paper, a positioning
system based on monocular SLAM and inertial measurement
unit (IMU) is presented. The position is calculated through the
semi-direct visual odometry (SVO) method alongside IMU data,
and is integrated with an extended Kalman filter (EKF) to
enhance the efficiency of the algorithm. The data is then
employed to control the drone without any requirement to any
source of external input. The experiment results for longdistance flying paths is very promising
2019ConferencePDFAutonomous Robotics
A Calibration Framework for Deployable Cable Driven Parallel Robots with Flexible Cables
R. Khorrambakht, H. Damirchi, S. A. Khalilpour∗, and H. D. Taghirad
International Conference on Robotics and Mechatronics
Due to their simple and inexpensive structures,
suspended cable driven parallel robots are suitable choices for
many real-world applications. However, only when the accurate
kinematic parameters are available, can we control the robot to
the best of its abilities. This is specially a stringent requirement
for fast deployable cable driven robots. With the aim of addressing these needs, in this paper we propose an effective framework
for calibrating the kinematic parameters of suspended cable
driven parallel robots with no requirements for expensive tools
and measurement devices. Moreover, the proposed algorithm
utilizes the existing force sensors in the cable robot to nominate
the best set of data for calibration. The integrity and effectiveness
of this framework is reported through simulation and practical
experiments, which verifies promising horizons for deployable
real-world applications.
2019ConferencePDFParallel and Cable Robotics
Coverage Control of Multi-Robot System for Dynamic Cleaning of Oil Spills
Samane Kaviri, Ahmadreza Tahsiri and Hamid D. Taghirad
International Conference on Robotics and Mechatronics
This paper addressed the dynamic cleaning of
oil spills using a multi-robot system. The cleaning process is
performed using a group of aerial agents adaptively covering
an oil spill considering its advection and spreading on the sea
surface. The concept of Voronoi Tessellation is employed to
command the autonomous vehicles on how to adapt its
configuration with the dynamic oil spill. Once the spill tracking
error reduces to the desired value, all of the agents spray
dispersant on the oil spill. This solution prevents wasting the
excess amount of dispersant that is often being sprayed in
conventional methods by aircraft. A distributed sliding mode
control scheme is proposed to navigate the agents to the nearoptimal Centroidal Voronoi Tessellation (CVT) by targeting
the thick layers. Simulation results demonstrate that the
proposed strategy can efficiently track the trajectory of the
polluted area, and adaptively cover the time-varying shape of
the oil spill.
2019ConferencePDFDynamical Systems Analysis and Control
Stabilization of Cable Driven Robots Using Interconnection Matrix: Ensuring Positive Tension
M. R. J. Harandi, S. A. Khalilpour, Hamed Damirchi and Hamid. D. Taghirad
International Conference on Robotics and Mechatronics
Cable driven parallel robots are closed-loop kinematic chains, where the end-effector is attached to the base by a
number of cables. Because of the nature of cables, a major issue
in control of these robots is ensuring positive tensions. When
the robot is not redundant, this issue is of utmost importance
for the controller synthesis. In the case of point to point motion
control, the trajectory is not specified beforehand, thus negative
tension may occur. In order to resolve this issue, interconnection
and damping assignment passivity based control (IDA-PBC) is
employed. IDA-PBC is a well-known method for control of underactuated systems where desired damping and interconnection
between subsystems are imposed. Interconnection matrix is a
skew-symmetric matrix which doesn’t have an effect on stability,
but it greatly influences the transient response of the system.
In this paper, the interconnection matrix is exploited to ensure
positive tension in fully actuated cable driven robots. The results
are verified through simulation on a 3-DOF suspended cable
driven robot.
2019ConferencePDFParallel and Cable Robotics
Robust Impedance Control for Dual User Haptic Training System
R. Heidari, M. Motaharifar and H. D. Taghirad
International Conference on Robotics and Mechatronics
In this paper, an impedance controller with switching parameters for a dual-user haptic training system is introduced. The trainer and the trainee are connected through their
haptic consoles, and the trainee performs the surgical procedure
on the environment. The trainer can intervene in the procedure
by pressing a mechanical pedal; thus, the control parameters are
switched to transfer the authority over the task from the trainee
to the trainer. The stability of each subsystem and the closed-loop
stability of the overall system are investigated. The simulation
results verify the performance of the proposed controller.
2019ConferencePDFSurgical Robotics
Skill Assessment Using Kinematic Signatures: Geomagic Touch Haptic Device
N. S. Hojati, M. Motaharifar, H. D. Taghirad, A. Malekzadeh
International Conference on Robotics and Mechatronics
he aim of t his paper is to develop a practical
skill assessment for some designed experimental tasks, retrieved
from Minimally Invasive Surgery. The skill evaluation is very
important in surgery training, especially in MIS. Most of the
previous studies for skill assessment methods are limited in the
Hidden Markov Model and some frequency transforms, such as
Discret e Fourier transform, Discrete Cosine Transform and etc.
In this paper , some features have been ext racted from timefrequency analysis with t he Discret e Wavelet Transform and
t emporal signa l ana lysis of some kinematic metrics whi ch were
compute d from Geom agic Touch kinematic data. In addition,
the k-n earest neighbors classifier are employed to detect skill
level based on ext racted features. Through cross-validation
results, it is demonstrated that t he proposed methodology has
appropriate accuracy in skill level det ection
2019ConferencePDFSurgical Robotics
Path Planning for a UAV by Considering Motion Model Uncertainty
Hossein Sheikhi Darani, Ali Noormohammadi-Asl and Hamid D. Taghirad
International Conference on Robotics and Mechatronics
Abstract:

The primary purpose of path planning for unmanned aerial vehicles (UAVs), which is a necessary prerequisite toward an autonomous UAV, is to guide the robot to
the predefined target while the chosen path is optimized. This
paper addresses the problem of path planning for an unmanned
aerial vehicle in a 2D indoor environment, considering motion uncertainty. To cope with this challenge, the problem of
motion planning is formulated in three parts. A vision-based
extended Kalman Filter (EKF) is used to localize the UAV in
the unstructured environment. To overcome motion uncertainty,
the problem is modeled as a Markov decision problem (MDP).
Finally, a novel dynamic feedback linearization based switching
controller is proposed for point-to-point motion. Simulation and
experimental results are given to show the effectiveness of the
proposed path planning method in practice

2019ConferencePDFAutonomous Robotics
Extracting of Sagging Profile of Overhead Power Transmission Line Via Image Processing
Amir Molaei, Hamid D.Taghirad, Javad Dargahi
2018 IEEE Canadian Conference on Electrical & Computer Engineering (CCECE)
Abstract:

Sagging of the conductor in transmission line has a vital role in the safety, reliability and efficiency of power transmission. Transmission lines must be designed to guarantee the maximum static loading capacity. This is done by maintaining the minimum vertical clearance between the cables and the ground. However, the increase of the cable length between two tower, leads to the high cost of material and electrical energy loss, as well as increasing the possibility of intervention. On the other hand, reducing the line sagging induces high tension in the conductor, which may lead to damage of the conductor. To assure a safety sagging profile, an inspection is essential at the establishment and maintainance of the power transmission lines. In this paper firstly the mathematical formulation of long and heavy cables are developed. Then an image processing method is applied for inspection of cable sagging. To investigate the method a reconfigurable experimental setup is designed to provide various sagging profiles and the sagging profile is extracted via image processing and the result is compared to that of analytical method.

2018ConferencePDFParallel and Cable Robotics
Robust Dynamic Sliding Mode Control of a Deployable Cable Driven Robot
S. A. Khalipour, R. Khorrambakht, M. J. Harandi, H. D. D. Taghirad and Philippe Cardou
Electrical Engineering (ICEE), Iranian Conference on
Abstract:

Despite of bing intensively developed, cable driven parallel manipulators are not yet vastly used due to their requirements for accurate assembly and installation. The main goal of this paper is to propose a suitable control method by which the robot could be suitably controlled without the requirement for undergoing any accurate calibration process. Here this robot is called deployable cable driven manipulator, in which the positions of the cable attachment points are not accurately known. This uncertainty in measurements will affect many parameters in the kinematic model especially the Jacobian matrix which is used as a force distributer in the Cartesian-space control strategies. In this paper in order to overcome this problem, a robust dynamic sliding mode controller is proposed. Then robust stability of the closed-loop system is analyzed through the Lyapunov direct method and by accordingly appropriate controller gain selection is performed. In order to illustrate the performance of the proposed controller, the robot is simulated in ADAMS software and it is shown that a suitable controller performance could be achieved.

2018ConferencePDFParallel and Cable Robotics
Robust Object Tracking Based on Recurrent Neural Networks
F. Lotfi, V. Ajallooeian and H. D. Taghirad
2018 6th RSI International Conference on Robotics and Mechatronics (IcRoM)
Abstract:

Object tracking through image sequences is one of the important components of many vision systems, and it has numerous applications in driver assistance systems such as pedestrian collision avoidance or collision mitigating systems. Blurred images produced by a rolling shutter camera or occlusions may easily disturb the object tracking system. In this article, a method based on convolutional and recurrent neural networks is presented to further enhance the performance and robustness of such trackers. It is proposed to use a convolutional neural network to detect an intended object and feed the tracker with found image. Moreover, by using this structure the tracker is updated every ' n ' frames. A recurrent neural network is designed to learn the object behavior for estimating and predicting its position in blurred frames or when it is occluded behind an obstacle. Real-time implementation of the proposed approach verifies its applicability for improvement of the trackers performance.

2018ConferencePDFAutonomous Robotics
Two PID-Based Controllers for a tethered Segway on Dome Shaped Structures
Mohammad H. Salehpour Hamid D. Taghirad and Hadi Moradi
2018 6th RSI International Conference on Robotics and Mechatronics (IcRoM)
Abstract:

The UTDTR Robot is a human inspired robotic platform based on a two-wheeled mobile robot. This robot is designed for the purpose of dome shaped structures inspection and maintenance, and it is a tethered robot to stably climb steep surfaces on the top of dome structures. In this paper analysis and controller design of this robot modelled as a MIMO system is represented in order to provide the desired performance on the operating surface with minimum control effort and complexity. Two PID-based controllers are designed such that the stability and desired performance conditions are obtained. In the first design a fuzzy PID controller with self-tuning scale factors is designed to tune the controller gains is forwarded, while in the second approach a multi model gain scheduling controller based on conventional PID controller is considered. Finally, the effectiveness and simplicity of the proposed controller is verified through simulation, comparing the resulting closed loop transient and steady-state response to that of the previously proposed controllers.

2018ConferencePDFDynamical Systems Analysis and Control
Wave Based Control of A Deployable Cable Driven Robot
S. A. Khalilpour, R. Khorrambakht, H. D. Taghirad, and Philippe Cardou
2018 6th RSI International Conference on Robotics and Mechatronics (IcRoM)
Abstract:

Cable driven parallel manipulator are known by their low costs and numerous applications. However despite of all research interests and developed methods they are not yet vastly used in action. The reason for this, is their limiting requirements for accurate assembly and installation process. The main goal of this paper is to propose a suitable control method by which the robot could appropriately be controlled, requiring no accurate calibrations or precise sensors. As it is well known, uncertainty in kinematics equations can lead to loose cables in redundant robots controlled through joint space controllers. In this paper a simple but very effective joint space controller is proposed that addresses the problem of loose cables by a wave based control method by employing a novel force feedback scheme. Indeed, a new conceptual framework for controlling deployable cable driven parallel manipulators is introduced by which such robots are greatly empowered at real-world scenarios. Finally, the performance of the proposed controller and its effectiveness is verified through some practical experiments showing that the proposed controller outperforms conventional cascade topologies in terms of much smoother tracking performance.

2018ConferencePDFParallel and Cable Robotics
A Dual-User Teleoperated Surgery Training Scheme Based on Virtual Fixture
A. Iranfar, M. Motaharifar, and H. D. Taghirad
2018 6th RSI International Conference on Robotics and Mechatronics (IcRoM)
Abstract:

The widespread use of minimally invasive surgery (MIS) demands an appropriate framework to train novice surgeons (trainees) to perform MIS. One of the effective ways to establish a cooperative training system is to use virtual fixtures. In this paper, a guiding virtual fixture is proposed to correct the movements of the trainee according to trainer hand motion performing a real MIS surgery. The proposed training framework utilizes the position signals of trainer to modify incorrect movements of the trainee which leads to shaping the trainee's muscle memory. Thus, after enough training sessions the trainee gains sufficient experience to perform the surgical task without any further help from the trainer. The passivity approach is utilized to analyze the stability of system. Simulation results are also presented to demonstrate the effectiveness of the proposed method.

2018ConferencePDFSurgical Robotics
Multi-goal motion planning using traveling salesman problem in belief space
Ali Noormohammadi-Asl, Hamid D. Taghirad
Information Sciences
Abstract:

In this paper, the multi-goal motion planning problem of an environment with some background information about its map is addressed in detail. The motion planning goal is to find a policy in belief space for the robot to traverse through a number of goal points. This problem is modeled as an asymmetric traveling salesman problem (TSP) in the belief space using Partially Observable Markov Decision Process (POMDP) framework. Then, feedback-based information roadmap (FIRM) algorithm is utilized to reduce the computational burden and complexity. By generating a TSP-FIRM graph, the search policy is obtained and an algorithm is proposed for online execution of the policy. Moreover, approaches to cope with challenges such as map updating, large deviations and high uncertainty in localization, which are more troublesome in a real implementation, are carefully addressed. Finally, in order to evaluate applicability and performance of the proposed algorithms, it is implemented in a simulation environment as well as on a physical robot in which some challenges such as kidnapping and discrepancies between real and computational models and map are examined.

2018JournalPDFAutonomous Robotics
Implementation of Multi-Goal Motion Planning Under Uncertainty on a Mobile Robot
Ali Noormohammadi-Asl, Hamid D. Taghirad, Amirhossein Tamjidi
2017 5th RSI International Conference on Robotics and Mechatronics (ICRoM)
Abstract:

Multi-goal motion planning under motion and sensor uncertainty is the problem of finding a reliable policy for visiting a set of goal points. In this paper, the problem is formulated as a formidable traveling salesman problem in the belief space. To solve this intractable problem, we propose an algorithm to construct a TSP-FIRM graph which is based on the feedback-based information roadmap (FIRM) algorithm. Also, two algorithms are proposed for the online planning of the obtained policy in the offline mode and overcoming changes in the map of the environment. Finally, we apply the algorithms on a physical nonholonomic mobile robot in the presence of challenging situations like the discrepancy between the real and computation model, map updating and kidnapping.

2017ConferencePDFAutonomous Robotics
Brain Computer Interface Control of a Virtual Robotic System based on SSVEP and EEG Signal
Fatemeh Akrami, Ebrahim Abedloo and Hamid D. Taghirad
Abstract:

In brain computer interface (BCI) systems the brain patterns for a certain type of behaviour is extracted and the corresponding control commands are produced in order to control an external apparatus. SSVEP is a specific type of such control signal which is produced at the occipital lobe of the brain in response to an external oscillating stimulus. As the brain signals in SSVEP based BCI are the neurological reaction of the individuals to the presented stimulus, it is crucial to design a suitable stimulus system as well as investigation of its effectiveness. In this paper a suitable visual stimulus is designed and implemented, and its effectiveness to control the motion of a robot on a virtual robotic system is verified based on experiments. An online integrated system comprising of a virtual industrial robotic manipulator, an EEG deployment and statistical feature extraction method is developed and real time experiments to verify its accuracy and effectiveness is experimented on different subjects. The experiments shows the promising features of the developed systems for further applications.

2017ConferencePDFDynamical Systems Analysis and Control
Two PID-Based Controllers for a tethered Segway on Dome Shaped Structures
Mohammad H. Salehpour Hamid D. Taghirad and Hadi Moradi
2018 6th RSI International Conference on Robotics and Mechatronics (IcRoM)
Abstract:

The UTDTR Robot is a human inspired robotic platform based on a two-wheeled mobile robot. This robot is designed for the purpose of dome shaped structures inspection and maintenance, and it is a tethered robot to stably climb steep surfaces on the top of dome structures. In this paper analysis and controller design of this robot modelled as a MIMO system is represented in order to provide the desired performance on the operating surface with minimum control effort and complexity. Two PID-based controllers are designed such that the stability and desired performance conditions are obtained. In the first design a fuzzy PID controller with self-tuning scale factors is designed to tune the controller gains is forwarded, while in the second approach a multi model gain scheduling controller based on conventional PID controller is considered. Finally, the effectiveness and simplicity of the proposed controller is verified through simulation, comparing the resulting closed loop transient and steady-state response to that of the previously proposed controllers.

2017ConferencePDFDynamical Systems Analysis and Control
Forward Kinematics Resolution of A Deployable Cable Robot
S. A. Khalilpour , A. Bourbour, R. Khorrambakht, S. Kariminasab, H. D. Taghirad
2017 5th RSI International Conference on Robotics and Mechatronics (ICRoM)
Abstract:

In this paper, forward kinematic derivation of a deployable suspended cable robot (DSCR) is investigated. Since the positions of the cable attachment points in this robot are not accurately available, the forward kinematics of the robot would not provide an accurate estimate for the end effector position. This paper proposes two methods to improve the accuracy of the forward kinematic solutions. First, an analysis on parameter sensitivity is presented and effective parameters are extracted. Then, based on these parameters and by using the redundant equations of the DSCR, a new set of equations for forward kinematic analysis are derived. The second method proposed in this paper is based on a geometrical analysis of kinematic uncertainty bounds. Finally, using the simulation results the effectiveness of the proposed methods is verified by illustrating the significant accuracy improvement in the obtained end effector positions.

2017ConferencePDFParallel and Cable Robotics
Motion Control of an Underactuated Parallel Robot with First Order Nonholonomic Constraint
Mohammad Reza J. Harandi and Hamid. D. Taghirad
2017 5th RSI International Conference on Robotics and Mechatronics (ICRoM)
Abstract:

Adding nonholonomic constraints in parallel manipulators, allows reduction of the actuated-joint number without affecting the reachable workspace. This principle applies to wrist robot in some underactuated designs. This paper studies steady state motion control for an nS-2SPU underactuated parallel wrist robot. First, a suitable Euler angles representation is selected and a new method for forward kinematic problem without extra sensor is proposed. Next, differential kinematics of the robot is analyzed considering first order nonholonomic constraint on angular velocity of the robot. By some manipulations, the derived equations are transformed into chain form, and a hierarchical sliding mode controller is designed for the system. Closed-loop performance of the proposed controller is compared to that of a traditional controller reported in the literature through simulations.

2017ConferencePDFParallel and Cable Robotics
An Observer-Based Force Reflection Robust Control for Dual User Haptic Surgical Training System
M. Motaharifar and H. D. Taghirad
2017 5th RSI International Conference on Robotics and Mechatronics (ICRoM)
Abstract:

This paper investigates the controller design problem for the dual user haptic surgical training system. In this system, the trainer and the trainee are interfaced together through their haptic devices and the surgical operations on the virtual environment is performed by the trainee. The trainer is able to interfere into the procedure in the case that any mistakes is made by the trainee. In the proposed structure, the force of the trainer's hands is reflected to the hands of the trainee to give necessary guidance to the trainee. The force signal is obtained from an unknown input high gain observer. The position of the trainee and the contact force with the environment are sent to the trainer to give him necessary information regarding the status of surgical operations. Stabilizing control laws are also designed for each haptic device and the stability of the closed loop nonlinear system is proven. Simulation results are presented to show the effectiveness of the proposed controller synthesis.

2017ConferencePDFSurgical Robotics
A Robust Approach Toward Kernel-Based Visual Servoing
Mahsa Parsapour and Hamid D. Taghirad
2017 5th RSI International Conference on Robotics and Mechatronics (ICRoM)
Abstract:

We introduce a robust controller for kernel-based visual servoing systems. In such systems, visual features are sum of weighted-image intensities via smooth kernel functions. This information along with its derivative are input to the controller in which we have developed a sliding mode approach to generate system commands. In vision-based systems, image uncertainties affect the tracking performance and stability, and the target object may get out of the field of view. Unless considerable image uncertainties appear, such systems are able to track the object within desired precision. Hence, we have investigated the effect of the image noise as the main source of uncertainty, and encapsulated its characteristics in a proper representation. In order to fulfill the sliding condition, some bounds over image uncertainty and tracking errors are considered, and the controller gains are tuned online to keep the tracking error bounded. An application of the proposed method is experimentally tested on an industrial robot.

2017ConferencePDFVisual Robotics
Comment on: "Centers of quasi-homogeneous polynomial planar systems"
A. Rahimabadi, H.D. Taghirad
Nonlinear Analysis: Real World Applications
Abstract:

We describe a counter-example which shows that of theorem in Algaba et al. (2012) is not correct. This part of the theorem, pinpoints whether the origin of quasi-homogeneous system in Algaba et al. (2012) is a center or not. It is shown in this note that the given necessary and sufficient conditions of theorem, in Algaba et al. (2012) are not complete.

2017JournalPDFDynamical Systems Analysis and Control
Stability Analysis and Robust PID Control of Cable-Driven Robots Considering Elasticity in Cables
M. A. Khosravi, H. D. Taghirad
AUT Journal of Electrical Engineering
Abstract:

In this paper robust PID control of fully-constrained cable driven parallel manipulators with elastic cables is studied in detail. In dynamic analysis, it is assumed that the dominant dynamics of cable can be approximated by linear axial spring. To develop the idea of control for cable robots with elastic cables, a robust PID control for cable driven robots with ideal rigid cables is firstly designed and then, this controller is modified for the robots with elastic cables. To overcome vibrations caused by inevitable elasticity of cables, a composite control law is proposed based on singular perturbation theory. The proposed control algorithm includes robust PID control for corresponding rigid model and a corrective term. Using the proposed control algorithm the dynamics of the cable driven robot is divided into slow and fast subsystems. Then, based on the results of singular perturbation theory, stability analysis of the total system is performed. Finally, the effectiveness of the proposed control law is investigated through several simulations on a planar cable driven robot.

2016JournalPDFParallel and Cable Robotics
Reconstruction of B-spline curves and surfaces by adaptive group testing
Alireza Norouzzadeh Ravari, Hamid D. Taghirad
Computer-Aided Design
Abstract:

Point clouds as measurements of 3D sensors have many applications in various fields such as object modeling, environment mapping and surface representation. Storage and processing of raw point clouds is time consuming and computationally expensive. In addition, their high dimensionality shall be considered, which results in the well known curse of dimensionality. Conventional methods either apply reduction or approximation to the captured point clouds in order to make the data processing tractable. B-spline curves and surfaces can effectively represent 2D data points and 3D point clouds for most applications. Since processing all available data for B-spline curve or surface fitting is not efficient, based on the Group Testing theory an algorithm is developed that finds salient points sequentially. The B-spline curve or surface models are updated by adding a new salient point to the fitting process iteratively until the Akaike Information Criterion (AIC) is met. Also, it has been proved that the proposed method finds a unique solution so as what is defined in the group testing theory. From the experimental results the applicability and performance improvement of the proposed method in relation to some state-of-the-art B-spline curve and surface fitting methods, may be concluded.

2016JournalPDFAutonomous Robotics
Reconstruction of B-spline curves and surfaces by adaptive group testing
Alireza Norouzzadeh Ravari, Hamid D. Taghirad
Computer-Aided Design
Abstract:

Point clouds as measurements of 3D sensors have many applications in various fields such as object modeling, environment mapping and surface representation. Storage and processing of raw point clouds is time consuming and computationally expensive. In addition, their high dimensionality shall be considered, which results in the well known curse of dimensionality. Conventional methods either apply reduction or approximation to the captured point clouds in order to make the data processing tractable. B-spline curves and surfaces can effectively represent 2D data points and 3D point clouds for most applications. Since processing all available data for B-spline curve or surface fitting is not efficient, based on the Group Testing theory an algorithm is developed that finds salient points sequentially. The B-spline curve or surface models are updated by adding a new salient point to the fitting process iteratively until the Akaike Information Criterion (AIC) is met. Also, it has been proved that the proposed method finds a unique solution so as what is defined in the group testing theory. From the experimental results the applicability and performance improvement of the proposed method in relation to some state-of-the-art B-spline curve and surface fitting methods, may be concluded.

2016JournalPDFMixed Reality in Surgery
Adaptive Control of Dual User Teleoperation with Time Delay and Dynamic Uncertainty
M. Motaharifar, A. Bataleblu, and H. D. Taghirad
2016 24th Iranian Conference on Electrical Engineering (ICEE)
Abstract:

This technical note aims at proposing an adaptive control scheme for dual-master trilateral teleoperation in the presence of communication delay and dynamic uncertainty in the parameters. The majority of existing control schemes for trilateral teleoperation systems have been developed for linear systems or nonlinear systems without dynamic uncertainty or time delay. However, in the practical teleoperation applications, the dynamics equations are nonlinear and contain uncertain parameters. In addition, the time delay in the communication channel mostly exists in the real applications and can affect the stability of closed loop system. As a result, an adaptive control methodology is proposed in this paper that to guarantee the stability and performance of the system despite nonlinearity, dynamic uncertainties and time delay. Simulation results are presented to show the effectiveness of the proposed adaptive controller methodology.

2016ConferencePDFSurgical Robotics
NURBS-based Representation of Urban Environments for Mobile Robots
Alireza Norouzzadeh Ravari and Hamid D. Taghirad
2016 4th International Conference on Robotics and Mechatronics (ICROM)
Abstract:

Representation of the surrounding environment is a vital task for a mobile robot. Many applications for mobile robots in urban environments may be considered such as self-driving cars, delivery drones or assistive robots. In contrast to the conventional methods, in this paper a Non Uniform Rational B-Spline (NURBS) based technique is represented for 3D mapping of the surrounding environment. While in the state of the art techniques, the robot's environment is expressed in a discrete space, the proposed method is mainly developed for representation of environment in a continuous space. Exploiting the information theory, the generated representation has much lower complexity and more compression capability in relation to some state of the art techniques. In addition to representation in a lower dimensional space, the NURBS based representation is invariant against 3D geometric transformations. Furthermore, the NURBS based representation can be employed for obstacle avoidance and navigation. The applicability of the proposed algorithm is investigated in some urban environments through some publicly available data sets. It has been shown by some experiments that the proposed method has better visual representation and much better data compression compared to some state-of-the-art methods.

2016ConferencePDFAutonomous Robotics
NURBS-based Representation of Urban Environments for Mobile Robots
Alireza Norouzzadeh Ravari and Hamid D. Taghirad
2016 4th International Conference on Robotics and Mechatronics (ICROM)
Abstract:

Representation of the surrounding environment is a vital task for a mobile robot. Many applications for mobile robots in urban environments may be considered such as self-driving cars, delivery drones or assistive robots. In contrast to the conventional methods, in this paper a Non Uniform Rational B-Spline (NURBS) based technique is represented for 3D mapping of the surrounding environment. While in the state of the art techniques, the robot's environment is expressed in a discrete space, the proposed method is mainly developed for representation of environment in a continuous space. Exploiting the information theory, the generated representation has much lower complexity and more compression capability in relation to some state of the art techniques. In addition to representation in a lower dimensional space, the NURBS based representation is invariant against 3D geometric transformations. Furthermore, the NURBS based representation can be employed for obstacle avoidance and navigation. The applicability of the proposed algorithm is investigated in some urban environments through some publicly available data sets. It has been shown by some experiments that the proposed method has better visual representation and much better data compression compared to some state-of-the-art methods.

2016ConferencePDFMixed Reality in Surgery
Autonomous Flight and Obstacle Avoidance of a Quadrotor By Monocular SLAM
Omid Esrafilian and Hamid D. Taghirad
2016 4th International Conference on Robotics and Mechatronics (ICROM)
Abstract:

In this paper, a monocular vision based autonomous flight and obstacle avoidance system for a commercial quadrotor is presented. The video stream of the front camera and the navigation data measured by the drone is sent to the ground station laptop via wireless connection. Received data processed by the vision based ORB-SLAM to compute the 3D position of the robot and the environment 3D sparse map in the form of point cloud. An algorithm is proposed for enrichment of the reconstructed map, and furthermore, a Kalman Filter is used for sensor fusion. The scaling factor of the monocular slam is calculated by the linear fitting. Moreover, a PID controller is designed for 3D position control. Finally, by means of the potential field method and Rapidly exploring Random Tree (RRT) path planning algorithm, a collision-free road map is generated. Moreover, experimental verifications of the proposed algorithms are reported.

2016ConferencePDFAutonomous Robotics
Design of a Robust Controller for a Tethered Segway on Dome-Shaped Structures
Mohammad H. Salehpour Hamid D. Taghirad and Hadi Moradi
2016 4th International Conference on Robotics and Mechatronics (ICROM)
Abstract:

Tethered Segway is a robotic platform inspired by human climbers. It is a two-wheeled mobile platform tethered to the top of a structure in order to climb steep surfaces with varying slopes, such as domes. The unstructured environment may cause uncertainties in the dynamic behavior of the robot while operating on different parts of the dome. In this paper analysis and synthesis of a robust controller for a tethered Segway is presented in order to provide desired performance in the presence of uncertainties. To design the robust controller, structured and unstructured uncertainties of the model are encapsulated into a structured singular perturbation. A linear robust controller is designed such that the robust stability of the closed loop system is preserved in the presence of modeling uncertainties. Finally, the effectiveness of the proposed controller is verified through simulation by comparing its closed loop transient response and sufficiently suitable steady-state performance to that of a previously proposed LQR controller for the robot.

2016ConferencePDFDynamical Systems Analysis and Control
Type Synthesis of 2R-T Parallel Mechanisms Based on the Screw Theory for Haptic Applicationsa
Nahid Khajeh Ahmadi, Fateme Zarei and Hamid D.Taghirad
2016 4th International Conference on Robotics and Mechatronics (ICROM)
Abstract:

Recently haptic devices are increasingly used in industry and research. As their applications become widespread, their design is needed to be more efficient. At design stage, determinant features of haptic devices such as rigidity, force bandwidth, accuracy etc. must be considered and improved. Structurally, parallel mechanisms (PMs) are appropriate candidates for haptic devices. Due to multi legged structure of PMs and their grounded motors, inertia and stiffness feautures of them are desirable and it also made them popular for applications that require high mechanical transparency. Spherical kinematics (two rotational and one translational motion, 2R-T) is a very common type of motion in haptic devices that is also capable of general rendering. In this paper, several 3-DOF 2R-T PMs are synthesized for haptic applications by means of the screw theory. All of these mechanisms have center of motion (CM) which is a key property in variety of applications such as surgery. These mechanisms are compared qualitatively and their applications as haptic devices are discussed.

2016ConferencePDFParallel and Cable Robotics
Robust H-Infinity Control of a 2RT Parallel Robot For Eye Surgery
Abbas Bataleblu, Mohammad Motaharifar, Ebrahim Abedlu, Hamid D. Taghirad
2016 4th International Conference on Robotics and Mechatronics (ICROM)
Abstract:

This paper aims at designing a robust controller for a 2RT parallel robot for eye telesurgery. It presents two robust controllers designs and their performance in presence of actuator saturation limits. The nonlinear model of the robot is encapsulated with a linear model and multiplicative uncertainty using linear fractional transformations (LFT). Two different robust control namely, H ? and ?-synthesis are used and implemented. Results reveal that the controllers are capable to stabilize the closed loop system and to reduce the tracking error in the presence of the actuators saturation. Simulation results are presented to show that effectiveness of the controllers compared to that of conventional controller designs. Furthermore, it is observed that ?-synthesis controller has superior robust performance.

2016ConferencePDFSurgical Robotics
Particle Filters for Non-Gaussian Hunt-Crossley Model of Environment in Bilateral Teleoperation
Pedram Agand, Hamid D. Taghirad and Ali Khaki-Sedigh
2016 4th International Conference on Robotics and Mechatronics (ICROM)
Abstract:

Optimal solution for nonlinear identification problem in the presence of non-Gaussian distribution measurement and process noises is generally not analytically tractable. Particle filters, known as sequential Monte Carlo method (SMC), is a suboptimal solution of recursive Bayesian approach which can provide robust unbiased estimation of nonlinear non-Gaussian problem with desire precision. On the other hand, Hunt-Crossley is a widespread nonlinear model for modeling telesurgeries environment. Hence, in this paper, particle filter is proposed to capture most of the nonlinearities in telesergerie environment model. An online Bayesian framework with conventional Monte Carlo method is employed to filter and predict position and force signals of environment at slave side respectively to achieve transparent and stable bilateral teleoperation simultaneously. Simulation results illustrate effectiveness of the algorithm by comparing the estimation and tracking errors of sampling importance resampling (SIR) with extended Kalman filter.

2016ConferencePDFSurgical Robotics
Adaptive Control for Force-Reflecting Dual User Teleoperation Systems
Sara Abkhofte, Mohammad Motaharifar, and Hamid D. Taghirad
2016 4th International Conference on Robotics and Mechatronics (ICROM)
Abstract:

The aim of this paper is to develop an adaptive force reflection control scheme for dual master nonlinear teleoperation systems. Having a sense of contact forces is very important in applications of dual master teleopreation systems such as surgery training. However, most of the previous studies for dual master nonlinear teleoperation systems are limited in the stability analysis of force reflection control schemes. In this paper, it is assumed that the teleopreation system consists of two masters and a single slave manipulator. In addition, all communication channels are subject to unknown time delays. First, adaptive controllers are developed for each manipulator. Next, Input-to-State Stability (ISS) approach is used to analyze the stability of the closed loop system. Through simulation results, it is demonstrated that the proposed methodology is effective in a nonlinear teleopreation system.

2016ConferencePDFSurgical Robotics
An Observer-Based Adaptive Impedance-Control for Robotic Arms: Case Study in SMOS Robot
Soheil Gholami, Arash Arjmandi, and Hamid D. Taghirad
2016 4th International Conference on Robotics and Mechatronics (ICROM)
Abstract:

In this paper an adaptive output-feedback impedance control is proposed to be used in environment-machine interaction applications. The proposed control is designed to achieve a desired robot impedance in the presence of possible dynamical parameter uncertainties. A high-gain observer is utilized in the control structure to achieve this objective by using only position feedback of robot joints, which in turn, reduces implementation costs and eliminates additional sensor requirements. Stability of the overall system is analyzed through input to state stability analysis. Finally, to evaluate the presented structure, computer simulations are provided and the scheme effectiveness is verified.

2016ConferencePDFSurgical Robotics
Visual Servoing Simulator by Using ROS and Gazebo
Parisa Masnadi Khiabani, Babak Sistanizadeh Aghdam, Javad Ramezanzadeh and Hamid D. Taghirad
International Conference on Robotics and Mechatronics
Abstract:

In this paper, a simulator for five degree of freedom (DOF) visual servoing robot is presented with eye-in-hand configuration. This simulator has been developed in Robot Operating System (ROS) and Gazebo environment. The designed simulator eases the process of testing and debugging visual servoing schemes, and robot controllers. Among different methods, one of the existing Image based visual servoing schemes, image moments, has been implemented to verify the functionality and performance of designed simulator.

2016ConferencePDFVisual Robotics
A Navigation System for Autonomous Robot Operating in Unknown and Dynamic Environment: Escaping Algorithm
F. AdibYaghmaie, A. Mobarhani, H. D. Taghirad
International Journal of Robotics
Abstract:

In this study, the problem of navigation in dynamic and unknown environment is investigated and a navigation method based on force field approach is suggested. It is assumed that the robot performs navigation in unknown environment and builds the map through SLAM procedure. Since the moving objects' location and properties are unknown, they are identified and tracked by Kalman filter. Kalman observer provides important information about next paths of moving objects which are employed in finding collision point and time in future. In the time of collision detection, a modifying force is added to repulsive and attractive forces corresponding to the static environment and leads the robot to avoid collision. Moreover, a safe turning angle is defined to assure safe navigation of the robot. The performance of proposed method, named Escaping Algorithm, is verified through different simulation and experimental tests. Besides, comparison between Escaping Algorithm and Probabilistic Velocity Obstacle, based on computational complexity and required steps for finishing the mission is provided in this paper. The results show Escaping Algorithm outperforms PVO in term of dynamic obstacle avoidance and complexity as a practical method for autonomous navigation.

2016JournalPDFAutonomous Robotics
Adaptive robust control of fully constrained cable robots: singular perturbation approach
Reza Babaghasabha, Mohammad A. Khosravi, Hamid D. Taghirad
Nonlinear Dynamics
Abstract:

In this paper, adaptive robust control of fully constrained cable-driven parallel robots with elastic cables is studied in detail. A composite controller is proposed for the system under the assumption of linear axial spring model as the dominant dynamics of the cables and in presence of model uncertainties. The proposed controller which is designed based on the singular perturbation theory, consists of two main parts. An adaptive robust controller is designed to counteract the unstructured and parametric uncertainties of the robot and a fast control term which is added to control the longitudinal vibrations of the cables. Moreover, to ensure that all cables remain in tension, the proposed control algorithm benefits from internal force concept. Using the results of the singular perturbation theory, the stability of the overall closed-loop system is analyzed through Lyapunov second method, and finally, the effectiveness of the proposed control algorithm is verified through some simulations on a planar cable-driven parallel robot.

2016JournalPDFParallel and Cable Robotics
Reconstruction of B-spline curves and surfaces by adaptive group testing
Alireza Norouzzadeh Ravari, Hamid D. Taghirad
Computer-Aided Design
Abstract:

Point clouds as measurements of 3D sensors have many applications in various fields such as object modeling, environment mapping and surface representation. Storage and processing of raw point clouds is time consuming and computationally expensive. In addition, their high dimensionality shall be considered, which results in the well known curse of dimensionality. Conventional methods either apply reduction or approximation to the captured point clouds in order to make the data processing tractable. B-spline curves and surfaces can effectively represent 2D data points and 3D point clouds for most applications. Since processing all available data for B-spline curve or surface fitting is not efficient, based on the Group Testing theory an algorithm is developed that finds salient points sequentially. The B-spline curve or surface models are updated by adding a new salient point to the fitting process iteratively until the Akaike Information Criterion (AIC) is met. Also, it has been proved that the proposed method finds a unique solution so as what is defined in the group testing theory. From the experimental results the applicability and performance improvement of the proposed method in relation to some state-of-the-art B-spline curve and surface fitting methods, may be concluded.

2015JournalPDFAutonomous Robotics
Reconstruction of B-spline curves and surfaces by adaptive group testing
Alireza Norouzzadeh Ravari, Hamid D. Taghirad
Computer-Aided Design
Abstract:

Point clouds as measurements of 3D sensors have many applications in various fields such as object modeling, environment mapping and surface representation. Storage and processing of raw point clouds is time consuming and computationally expensive. In addition, their high dimensionality shall be considered, which results in the well known curse of dimensionality. Conventional methods either apply reduction or approximation to the captured point clouds in order to make the data processing tractable. B-spline curves and surfaces can effectively represent 2D data points and 3D point clouds for most applications. Since processing all available data for B-spline curve or surface fitting is not efficient, based on the Group Testing theory an algorithm is developed that finds salient points sequentially. The B-spline curve or surface models are updated by adding a new salient point to the fitting process iteratively until the Akaike Information Criterion (AIC) is met. Also, it has been proved that the proposed method finds a unique solution so as what is defined in the group testing theory. From the experimental results the applicability and performance improvement of the proposed method in relation to some state-of-the-art B-spline curve and surface fitting methods, may be concluded.

2015JournalPDFMixed Reality in Surgery
Reigon of Convergence Expansion of a Robust Model Predictive Controller
Mojgan Rostami and Hamid D. Taghirad
2015 23rd Iranian Conference on Electrical Engineering
Abstract:

In this paper a gain scheduling method is proposed for robust model predictive control of a useful class of nonlinear discrete-time systems. The system is composed of a linear model perturbed by an additive state-dependent nonlinear term. Robust model predictive controllers are designed in the literature to compensate for the uncertainty of the system. In order to enlarge the region of convergence it is assumed that system has several equilibrium points and multiple robust controllers are designed. By switching between the controllers it is verified that the region of convergence shall be enlarged, while the overall stability of the system is preserved. In the proposed method, the stability analysis based on Lyapunov functions for each level set is performed, while state feedback control law is designed by minimization of a desired cost function formed in linear matrix inequalities. The simulation results show the applicability of the proposed method.

2015ConferencePDFDynamical Systems Analysis and Control
Kinematic and Workspace Analysis of DIAMOND: An Innovative Eye Surgery Robot
Amir Molaei, Ebrahim Abedloo, Hamid D. Taghirad and Zahra Marvi
2015 23rd Iranian Conference on Electrical Engineering
Abstract:

This paper presents a new robot for eye surgeries, referred to as DIAMOND. It consists of a spherical mechanism that has a remote center of motion (RCM) point and is capable of orienting the surgical instrument about this unique point. Using the RCM as the insertion point of the surgery instruments makes the robot suitable for minimally invasive surgery applications. DIAMOND has two pairs of identical spherical serial limbs that form a closed kinematic chain leading to high stiffness. The spherical structure of the mechanism is compatible with the human head and the robot may perform the surgery upon the head without any collision with the patient. Furthermore, dexterity and having a compact size is taken into account in the mechanical design of the robot. The workspace of the robot is a complete singularity free sphere that covers the region needed for any eye surgeries. In this paper, a comparison between different types of existing eye surgery robots is presented, the structure of the mechanism is described in detail and kinematic analysis of the robot is investigated.

2015ConferencePDFSurgical Robotics
Loop Closure Detection by Compressed Sensing for Exploration of Mobile Robots in Outdoor Environments
Alireza Norouzzadeh Ravari and Hamid D. Taghirad
2015 3rd RSI International Conference on Robotics and Mechatronics (ICROM)
Abstract:

In the problem of simultaneously localization and mapping (SLAM) for a mobile robot, it is required to detect previously visited locations so the estimation error shall be reduced. Sensor observations are compared by a similarity metric to detect loops. In long term navigation or exploration, the number of observations increases and so the complexity of the loop closure detection. Several techniques are proposed in order to reduce the complexity of loop closure detection. Few algorithms have considered the loop closure detection from a subset of sensor observations. In this paper, the compressed sensing approach is exploited to detect loops from few sensor measurements. In the basic compressed sensing it is assumed that a signal has a sparse representation is a basis which means that only a few elements of the signal are non-zero. Based on the compressed sensing approach a sparse signal can be recovered from few linear noisy projections by l1 minimization. The difference matrix which is widely used for loop detection has a sparse structure, where similar observations are shown by zero distance and different locations are indicated by ones. Based on the multiple measurement vector technique which is an extension of the basic compressed sensing, the loop closure detection is performed by comparison of few sensor observations. The applicability of the proposed algorithm is investigated in some outdoor environments through some publicly available data sets. It has been shown by some experiments that the proposed method can detect loops effectively.

2015ConferencePDFAutonomous Robotics
Loop Closure Detection by Compressed Sensing for Exploration of Mobile Robots in Outdoor Environments
Alireza Norouzzadeh Ravari and Hamid D. Taghirad
2015 3rd RSI International Conference on Robotics and Mechatronics (ICROM)
Abstract:

In the problem of simultaneously localization and mapping (SLAM) for a mobile robot, it is required to detect previously visited locations so the estimation error shall be reduced. Sensor observations are compared by a similarity metric to detect loops. In long term navigation or exploration, the number of observations increases and so the complexity of the loop closure detection. Several techniques are proposed in order to reduce the complexity of loop closure detection. Few algorithms have considered the loop closure detection from a subset of sensor observations. In this paper, the compressed sensing approach is exploited to detect loops from few sensor measurements. In the basic compressed sensing it is assumed that a signal has a sparse representation is a basis which means that only a few elements of the signal are non-zero. Based on the compressed sensing approach a sparse signal can be recovered from few linear noisy projections by l1 minimization. The difference matrix which is widely used for loop detection has a sparse structure, where similar observations are shown by zero distance and different locations are indicated by ones. Based on the multiple measurement vector technique which is an extension of the basic compressed sensing, the loop closure detection is performed by comparison of few sensor observations. The applicability of the proposed algorithm is investigated in some outdoor environments through some publicly available data sets. It has been shown by some experiments that the proposed method can detect loops effectively.

2015ConferencePDFMixed Reality in Surgery
Modified Fast-SLAM For 2D Mapping And 3D Localization
Soheil Gharatappeh, Mohammad Ghorbanian, Mehdi Keshmiri, Hamid D. Taghirad
2015 3rd RSI International Conference on Robotics and Mechatronics (ICROM)
Abstract:

Fast Simultaneous Localization and Mapping (SLAM) algorithm is capable of real-time implementation due to logarithmic time complexity which results in decrease of computational cost. In this algorithm state vector of a robot merely includes planar location of the robot and its angle to the horizontal plane. It has fewer components comparing to state vector in extended Kalman filter method which consists of location of all environmental features. In existing methods for implementing this algorithm, robot movement is considered to be totally in planar movement; while if moving on a slope changes the pitch angle of the robot, it causes errors in the algorithm. Correcting these errors will lead to a precise 2D mapping and 3D localization. This paper details the modification added to conventional Fast-Slam algorithm to accommodate this requirement by using an IMU. Simulation and experimental results shows the effectiveness of such modification.

2015ConferencePDFAutonomous Robotics
Optimization of KNTU Delta robot for pick and place application
Amin Khorasani, Soheil Gholami, Hamid D. Taghirad
2015 3rd RSI International Conference on Robotics and Mechatronics (ICROM)
Abstract:

In this paper, the desired configuration for installation of Delta robot is formulated as an optimization problem and has been solved to reach to the highest rate of pick and place operation. The optimization is performed considering the actuators speed and acceleration limitation of the robot within the workspace. Furthermore, energy consumption is considered next as the other optimization objective, and it is shown that the optimal region for the first optimization problem lies within that of the latter one, and therefore, there is no need to propose a multi-objective optimization problem in this case. As a proof of concept, KNTU Delta robot is designed and implemented in practice by using the optimal configuration, and it is observed that the optimal design is very promising in practice.

2015ConferencePDFParallel and Cable Robotics
Eye-RHAS Manipulator: From Kinematics to Trajectory Control
Ebrahim Abedloo, Soheil Gholami, and Hamid D. Taghirad
2015 3rd RSI International Conference on Robotics and Mechatronics (ICROM)
Abstract:

One of the challenging issues in the robotic technology is to use robotics arm for surgeries, especially in eye operations. Among the recently developed mechanisms for this purpose, there exists a robot, called Eye-RHAS, that presents sustainable precision in vitreo-retinal eye surgeries. In this work the closed-form dynamical model of this robot has been derived by Gibbs-Appell method. Furthermore, this formulation is verified through SimMechanics Toolbox of MATLAB. Finally, the robot is simulated in a real time trajectory control in a teleoperation scheme. The tracking errors show the effectiveness and applicability of the dynamic formulation to be used in the teleoperation schemes.

2015ConferencePDFSurgical Robotics
Vision-Based Kinematic Calibration of Spherical Robots
Pedram Agand, Hamid D. Taghirad and Amir Molaee
2015 3rd RSI International Conference on Robotics and Mechatronics (ICROM)
Abstract:

In this article, a method to obtain spatial coordinate of spherical robot's moving platform using a single camera is proposed, and experimentally verified. The proposed method is an accurate, flexible and low-cost tool for the kinematic calibration of spherical-workspace mechanisms to achieve the desired accuracy in position. The sensitivity and efficiency of the provided method is thus evaluated. Furthermore, optimization of camera location is outlined subject to the prescribed cost functions. Finally, experimental analysis of the proposed calibration method on ARAS Eye surgery Robot (DIAMOND) is presented; In which the accuracy is obtained from three to six times better than the previous calibration.

2015ConferencePDFSurgical Robotics
Kernel-based sliding mode control for visual servoing system
Mahsa Parsapour, Hamid D. Taghirad
IET Computer Vision
Abstract:

In this study, a new approach to design a controller for a visual servoing (VS) system is proposed. Kernel-measurement is used to track the motion of a featureless object which is defined as sum of weighted-image value through smooth kernel functions. This approach was used in kernel-based VS (KBVS). To improve the tracking error and expand the stability region, sliding mode control is integrated with kernel measurement. Proportional-integral-type sliding surface is chosen as a suitable manifold to produce the required control effort. Moreover, the stability of this algorithm is analysed via Lyapunov theory and its performance is verified experimentally by implementing the proposed method on a five degrees of freedom industrial robot. Through experimental results, it is shown that the performance of tracking error in the proposed method is more suitable than KBVS, for a wider workspace and when the object is placed near the boundary of the camera's field of view.

2015JournalPDFVisual Robotics
Stability domains of the delay and PID coefficients for general time-delay systems
Elham Almodaresi, Mohammad Bozorg and Hamid D. Taghirad
International Journal of Control
Abstract:

Time delays are encountered in many physical systems, and they usually threaten the stability and performance of closed-loop systems. The problem of determining all stabilising proportional-integral-derivative (PID) controllers for systems with perturbed delays is less investigated in the literature. In this study, the Rekasius substitution is employed to transform the system parameters to a new space. Then, the singular frequency (SF) method is revised for the Rekasius transformed system. A novel technique is presented to compute the ranges of time delay for which stable PID controller exists. This stability range cannot be readily computed from the previous methods. Finally, it is shown that similar to the original SF method, finite numbers of singular frequencies are sufficient to compute the stable regions in the space of time delay and controller coefficients.

2015JournalPDF
3D Scene and Object Classification Based on Information Complexity of Depth Data
A. Norouzzadeh, H. D. Taghirad
Mathematics
Abstract:

In this paper the problem of 3D scene and object classification from depth data is addressed. In contrast to high-dimensional feature-based representation, the depth data is described in a low dimensional space. In order to remedy the curse of dimensionality problem, the depth data is described by a sparse model over a learned dictionary. Exploiting the algorithmic information theory, a new definition for the Kolmogorov complexity is presented based on the Earth Mover’s Distance (EMD). Finally the classification of 3D scenes and objects is accomplished by means of a normalized complexity distance, where its applicability in practice is proved by some experiments on publicly available datasets. Also, the experimental results are compared to some state-of-the-art 3D object classification methods. Furthermore, it has been shown that the proposed method outperforms FAB-Map 2.0 in detecting loop closures, in the sense of the precision and recall.

2015JournalPDFAutonomous Robotics
3D Scene and Object Classification Based on Information Complexity of Depth Data
A. Norouzzadeh, H. D. Taghirad
Mathematics
Abstract:

In this paper the problem of 3D scene and object classification from depth data is addressed. In contrast to high-dimensional feature-based representation, the depth data is described in a low dimensional space. In order to remedy the curse of dimensionality problem, the depth data is described by a sparse model over a learned dictionary. Exploiting the algorithmic information theory, a new definition for the Kolmogorov complexity is presented based on the Earth Mover’s Distance (EMD). Finally the classification of 3D scenes and objects is accomplished by means of a normalized complexity distance, where its applicability in practice is proved by some experiments on publicly available datasets. Also, the experimental results are compared to some state-of-the-art 3D object classification methods. Furthermore, it has been shown that the proposed method outperforms FAB-Map 2.0 in detecting loop closures, in the sense of the precision and recall.

2015JournalPDFMixed Reality in Surgery
Visual Tracking using Kernel Projected Measurement and Log-Polar Transformation
Fateme Bakhshande, Hamid D. Taghirad
International Journal of Robotics Theory and Applications
Abstract:

Visual Servoing is generally contained of control and feature tracking. Study of previous methods shows that no attempt has been made to optimize these two parts together. In kernel based visual servoing method, the main objective is to combine and optimize these two parts together and to make an entire control loop. This main target is accomplished by using Lyapanov theory. A Lyapanov candidate function is formed based on kernel definition such that the Lyapanov stability can be verified. The implementation is done in four degrees of freedom and Fourier transform is used for decomposition of the rotation and scale directions from 2D translation. In the present study, a new method in scale and rotation correction is presented. Log-Polar Transform is used instead of Fourier transform for these two degrees of freedom. Tracking in four degrees of freedom is synthesized to show the visual tracking of an unmarked object. Comparison between Log-Polar transform and Fourier transform shows the advantages of the presented method. KBVS based on Log-Polar transform proposed in this paper, because of its robustness, speed and featureless properties

2015JournalPDFVisual Robotics
Adaptive robust control of fully-constrained cable driven parallel robots
Reza Babaghasabha, Mohammad A. Khosravi, Hamid D. Taghirad
Mechatronics
Abstract:

In this paper, adaptive robust control (ARC) of fully-constrained cable driven parallel robots is studied in detail. Since kinematic and dynamic models of the robot are partly structurally unknown in practice, in this paper an adaptive robust sliding mode controller is proposed based on the adaptation of the upper bound of the uncertainties. This approach does not require pre-knowledge of the uncertainties upper bounds and linear regression form of kinematic and dynamic models. Moreover, to ensure that all cables remain in tension, proposed control algorithm benefit the internal force concept in its structure. The proposed controller not only keeps all cables under tension for the whole workspace of the robot, it is chattering-free, computationally simple and it does not require measurement of the end-effector acceleration. The stability of the closed-loop system with proposed control algorithm is analyzed through Lyapunov second method and it is shown that the tracking error will remain uniformly ultimately bounded (UUB). Finally, the effectiveness of the proposed control algorithm is examined through some experiments on a planar cable driven parallel robot and it is shown that the proposed controller is able to provide suitable tracking performance in practice.

2015JournalPDFParallel and Cable Robotics
Corner stability in nonlinear autonomous systems
Arsalan Rahimabadi, H. D. Taghirad
Nonlinear Dynamics
Abstract:

In most practical applications, studying the asymptotic stability of equilibrium points of a system is of utmost importance. Furthermore, in many cases, the response is restricted to only a sector of the state space. For example, positive systems that are common in chemical processes have nonnegative state variables. For such systems, stability analysis of the system using Lyapunov stability is not advised, since this stability is defined for all the points within a neighborhood of the equilibrium point. In this paper, a new notion of stability, called corner stability, is defined as more suitable for studying asymptotic stability of equilibrium points in such systems. In order to derive sufficient conditions of corner stability, a theorem is stated and proven in this paper, and corner stability of three case studies is analyzed and verified.

2015JournalPDFDynamical Systems Analysis and Control
A 3D Sliding Mode Control Approach for Position Based Visual Servoing System
Mahsa Parsapour, Soheil RayatDoost, and Hamid D. Taghirad
Scientia Iranica
Abstract:

The performance of visual servoing systems can be enhanced through nonlinear controllers. In this paper, a sliding mode control is employed for such a purpose. The controller design is based on the outputs of a pose estimator which is implemented on the scheme of the Position-Based Visual Servoing (PBVS) approach. Accordingly, a robust estimator based on unscented Kalman observer cascading with Kalman ?lter is used to estimate the position, velocity and acceleration of the target. Therefore, a PD-type sliding surface is selected as a suitable manifold. The combination of the estimator and nonlinear controller provides a robust and stable structure in PBVS approach. The stability analysis is veri?ed through Lyapunov theory. The performance of the proposed algorithm is veri?ed experimentally through an industrial visual servoing system.

2015JournalPDFVisual Robotics
Dynamic Analysis and Control of Fully-Constrained Cable Robots with Elastic Cables: Variable Stiffness Formulation
Mohammad A. Khosravi and Hamid D. Taghirad
Cable-Driven Parallel Robots
Abstract:

In this paper dynamic analysis and control of fully-constrained parallel cable robots are studied in detail. In dynamic analysis, it is assumed that the dominant dynamics of cable can be approximated by linear axial spring. Furthermore, variable stiffness formulation for the cables is employed in modeling process. To overcome vibrations caused by inevitable elasticity of cables, a composite control law is proposed based on singular perturbation theory. Using the proposed control algorithm the dynamics of the cable robot is divided into two subsystems namely slow and fast. Then, based on the results of singular perturbation theory, stability analysis of the total system is performed. Finally, the effectiveness of the proposed composite control law is investigated through several simulations on a planar parallel cable robot.

2014JournalPDFParallel and Cable Robotics
Adaptive Control of KNTU Planar Cable-Driven Parallel Robot with Uncertainties in Dynamic and Kinematic Parameters
Reza Babaghasabha, Mohammad A. Khosravi and Hamid D. Taghirad
Cable-Driven Parallel Robots
Abstract:

This paper addresses the design and implementation of adaptive control on a planar cable-driven parallel robot with uncertainties in dynamic and kinematic parameters. To develop the idea, firstly, adaptation is performed on dynamic parameters and it is shown that the controller is stable despite the kinematic uncertainties. Then, internal force term is linearly separated into a regressor matrix in addition to a kinematic parameter vector that contains estimation error. In the next step to improve the controller performance, adaptation is performed on both the dynamic and kinematic parameters. It is shown that the performance of the proposed controller is improved by correction in the internal forces. The proposed controller not only keeps all cables in tension for the whole workspace of the robot, it is computationally simple and it does not require measurement of the end-effector acceleration as well. Finally, the effectiveness of the proposed control algorithm is examined through some experiments on KNTU planar cable-driven parallel robot and it is shown that the proposed control algorithm is able to provide suitable performance in practice.

2014JournalPDFParallel and Cable Robotics
Transformation Invariant 3D Object Recognition Based On Information Complexity
Alireza Norouzzadeh Ravari and Hamid D. Taghirad
2014 Second RSI/ISM International Conference on Robotics and Mechatronics (ICRoM)
Abstract:

The 3D representation of objects and scenes as a point cloud or range image has been made simple by means of sensors such as Microsoft Kinect, stereo camera or laser scanner. Various tasks, such as recognition, modeling and classification can not be performed on raw measurements because of the curse of high dimensionality, computational and algorithm complexity. Non Uniform Rational Basis Splines (NURBS) are a widely used representation technique for 3D objects in various robotics and Computer Aided Design (CAD) applications. In this paper, a similarity measurement from information theory is employed in order to recognize an object sample from a set of objects. From a NURBS model fitted to the observed point cloud, a complexity based representation is derived which is transformation invariant in the sense of Kolmogorov complexity. Experimental results on a set of 3D objects grabbed by a Kinect sensor indicates the applicability of the proposed method for object recognition tasks. Furthermore, the results of the proposed method is compared to that of some state of the art algorithms.

2014ConferencePDFAutonomous Robotics
Transformation Invariant 3D Object Recognition Based On Information Complexity
Alireza Norouzzadeh Ravari and Hamid D. Taghirad
2014 Second RSI/ISM International Conference on Robotics and Mechatronics (ICRoM)
Abstract:

The 3D representation of objects and scenes as a point cloud or range image has been made simple by means of sensors such as Microsoft Kinect, stereo camera or laser scanner. Various tasks, such as recognition, modeling and classification can not be performed on raw measurements because of the curse of high dimensionality, computational and algorithm complexity. Non Uniform Rational Basis Splines (NURBS) are a widely used representation technique for 3D objects in various robotics and Computer Aided Design (CAD) applications. In this paper, a similarity measurement from information theory is employed in order to recognize an object sample from a set of objects. From a NURBS model fitted to the observed point cloud, a complexity based representation is derived which is transformation invariant in the sense of Kolmogorov complexity. Experimental results on a set of 3D objects grabbed by a Kinect sensor indicates the applicability of the proposed method for object recognition tasks. Furthermore, the results of the proposed method is compared to that of some state of the art algorithms.

2014ConferencePDFMixed Reality in Surgery
An Online Implementation of Robust RGB-D SLAM
M. A. Athari, H. D. Taghirad
2014 Second RSI/ISM International Conference on Robotics and Mechatronics (ICRoM)
Abstract:

This paper presents an online robust RGB-D SLAM algorithm which uses an improved switchable constraints robust pose graph slam alongside with radial variance based hash function as the loop detector. The switchable constraints robust back-end is improved by initialization of its weights according to information matrix of the loops and is validated using real world datasets. The radial variance based hash function is combined with an online image to map comparison to improve accuracy of loop detection. The whole algorithm is implemented on K. N. Toosi University mobile robot with a Microsoft Kinect camera as the RGB-D sensor and the whole algorithm is validated using this robot, while the map of the environment is generated in an online fashion.

2014ConferencePDFAutonomous Robotics
An Improved Optimization Method for iSAM2
Rana Talaei Shahir and Hamid D. Taghirad
2014 Second RSI/ISM International Conference on Robotics and Mechatronics (ICRoM)
Abstract:

There is an issue called maximum likelihood estimation in SLAM that corresponds to a nonlinear least-square problem. It is expected to earn an accurate solution for large-scale environments with high speed of convergence. Although all the applied optimization methods might be accepted in terms of accuracy and speed of convergence for small datasets, their solutions for large-scale datasets are often far from the ground truth. In this paper, a double Dogleg trust region method is proposed and adjusted with iSAM2 to level up performance and accuracy of the algorithm especially in large-scale datasets. Since the trust region methods are sensitive to their own parameters, Gould parameters are chosen to obtain better performance. Simulations are done on some large-scale datasets and the results indicate that the proposed method is more efficient compared to the conventional iSAM2 algorithm.

2014ConferencePDFAutonomous Robotics
Online Time-Optimal Trajectory Planning in Dynamic Workspace of Cable Suspended Robots
Ahmad Sharifi and Hamid D. Taghirad
2014 Second RSI/ISM International Conference on Robotics and Mechatronics (ICRoM)
Abstract:

This paper presents a method for online trajectory planning of cable suspended robots. A three degrees-of-freedom spatial cable robot is studied in this analysis. By deriving dynamic model of the robot, cable force restrictions will induce a set of algebraic inequalities in dynamic equations. Direction of required tracking acceleration reveals feasible motion of the robot, which guarantees non-violation of cable force bilateral bounds. Required tracking acceleration is in the direction of instantaneous minus desired velocity vectors with specified magnitude. Furthermore, alternative recipes are employed to decrease negative impacts of unwanted inputs and applying actuator constraints in trajectory planning. Finally, several simulations are presented to demonstrate success of the method. Proposed approach can be used in online trajectory tracking for all cable-driven parallel suspended robots akin to what is realized for the presented three degrees-of-freedom robot.

2014ConferencePDFParallel and Cable Robotics
Closed-Form Dynamic Formulation of Spherical Parallel Manipulators by Gibbs-Appell Method
Ebrahim Abedloo, Amir Molaei and Hamid D. Taghirad
2014 Second RSI/ISM International Conference on Robotics and Mechatronics (ICRoM)
Abstract:

Spherical Parallel Robot (SPR) is a complex but widely used type of manipulators that performs only rotational motion. Dynamic analysis of SPR has a vital role in mechanical design, model-based controller, identification and fault detection of such robots. Complexity of SPR kinematic structure makes traditional dynamic modeling methods such as Newton-Euler, virtual work and Lagrange formulations a prohibitive task. In this paper a new procedure for deriving closed form dynamics of general SPR using Gibbs-Appell method is presented. The proposed method does not require any recursive computation or symbolic manipulation and dynamic matrices of the robot is directly derived in an explicit form. By using the proposed method, closed form dynamic formulation of a general 3DOF SPR, known as agile wrist, is obtained and it is verified for an arbitrary trajectory. The unique feature of the method presented in this paper, makes it promising to be used for other parallel manipulators.

2014ConferencePDFParallel and Cable Robotics
Implementation of Analytic Iterative Redundancy Resolution Technique on KNTU Cable Robot
Fereshteh Sabahi, Mohammad A. Khosravi and Hamid D. Taghirad
2014 Second RSI/ISM International Conference on Robotics and Mechatronics (ICRoM)
Abstract:

Analytic Iterative Redundancy Resolution (AIRR) is a semi-analytic method for redundancy resolution in cable-driven manipulators. As all previous redundancy resolution methods were based on numerical algorithms, they impose an uncertainty to execution time which is barely acceptable in realtime implementation. In this paper, AIRR is implemented as a fast solution to redundancy resolution problem by checking a set of analytic solutions instead of using numerical algorithms. Furthermore, the performance of this method is compared to previous numerical method implemented on KNTU robot with respect to execution time and accuracy. It is shown that the realtime performance of this implementation in closed-loop control structure is at least fifteen times faster than that of previously implemented methods. Such decrease in execution time in realtime implementation is very promising for future applications.

2014ConferencePDFParallel and Cable Robotics
Sliding Impedance Control for Improving Transparency in Telesurgery
Samim Khosravi, Arash Arjmandi and Hamid D. Taghirad
2014 Second RSI/ISM International Conference on Robotics and Mechatronics (ICRoM)
Abstract:

This paper describes a novel control scheme for teleoperation with constant communication time delay and soft tissue in environment of slave side. This control scheme combine fidelity criteria with sliding impedance. Fidelity is a measure for evaluating telesurgical system when environment at slave side contains soft tissues. Sliding impedance is used to stabilize the teleoperating system with constant time delays and improve tracking performance in the presence of uncertainties in slave dynamics. The control system contains impedance and sliding impedance control in master and slave manipulators, respectively. Parameters of sliding impedance controller are obtained from fidelity optimization problem while parameters of master impedance controller are determined such that to guarantee stability of the entire teleopertaion system. Simulation results demonstrate suitable performance of position and force tracking of the telesurgical system.

2014ConferencePDFSurgical Robotics
Kernel-based sliding mode control for visual servoing system
Mahsa Parsapour, Hamid D. Taghirad
IET Computer Vision
Abstract:

In this study, a new approach to design a controller for a visual servoing (VS) system is proposed. Kernel-measurement is used to track the motion of a featureless object which is defined as sum of weighted-image value through smooth kernel functions. This approach was used in kernel-based VS (KBVS). To improve the tracking error and expand the stability region, sliding mode control is integrated with kernel measurement. Proportional-integral-type sliding surface is chosen as a suitable manifold to produce the required control effort. Moreover, the stability of this algorithm is analysed via Lyapunov theory and its performance is verified experimentally by implementing the proposed method on a five degrees of freedom industrial robot. Through experimental results, it is shown that the performance of tracking error in the proposed method is more suitable than KBVS, for a wider workspace and when the object is placed near the boundary of the camera's field of view.

2014JournalPDFVisual Robotics
Robust Control of a Steam Turbine Power Based on a Precise Nonlinear Model
S.A. Salamati, H.D. Taghirad, Ali Chaibakhsh
2014 5th Conference on Thermal Power Plants (CTPP)
Abstract:

In this paper, a precise and nonlinear model is developed for Nekka power plant turbine from its experimental data and documents. It is proposed to use boiler-turbine coordinated control system to increase effective efficiency of the steam unit. Identification procedures have been performed to obtain continuous time models of Nekka steam turbine at various loads. After determining the upper bound for uncertainty and choosing a good performance weighting function, a robust controller has been designed and implemented in closed loop for the turbine nonlinear model. Since the closed loop performance was not as required, a cascade controller structure is proposed, in which the turbine loop is closed by a PI controller in order to significantly reduce the uncertainty. Simulation results demonstrate the suitable performance of the closed loop in terms of tracking, speed of response, and damping of oscillations.

2014ConferencePDFDynamical Systems Analysis and Control
Dynamic Modeling and Control of Parallel Robots With Elastic Cables: Singular Perturbation Approach
Mohammad A. Khosravi and Hamid D. Taghirad
IEEE Transactions on Robotics
Abstract:

In this paper, control of fully-constrained parallel cable robots with elastic cables is studied in detail. In the modeling process, longitudinal vibration of cables is considered as their dominant dynamics, and the governing equations of motion are rewritten to the standard form of singular perturbation. The proposed composite controller consists of two main components. A rigid controller is designed based on the slow or rigid model of the system and a corrective term is added to guarantee asymptotic stability of the fast dynamics. Then, by using Tikhonov theorem, slow and fast variables are separated and incorporated into the stability analysis of the overall closed-loop system, and a set of sufficient conditions for the stability of the total system is derived. Finally, the effectiveness of the proposed control law is verified through simulations.

2014JournalPDFParallel and Cable Robotics
A neutral system approach to H-Infinity PD/PI controller design of processes with uncertain input delay
A. Shariati, H.D. Taghirad, A. Fatehi
Journal of Process Control
Abstract:

This paper presents a neutral system approach to the design of an H? controller for input delay systems in presence of uncertain time-invariant delay. It is shown that when proportional derivative (PD) controller is applied to a time-delay system, the resulting closed loop system is generally a time-delay system of neutral type with delay term coefficients depending on the controller parameters. A descriptor model transformation is used to derive an advantageous bounded real lemma representation for the system. Furthermore, new delay-dependent sufficient conditions for the existence of an H? PD and PI controller in presence of uncertain delay are derived in terms of matrix inequalities. Some case studies and numerical examples are given in order to illustrate the advantages of the proposed method.

2014JournalPDFDynamical Systems Analysis and Control
Robust PID control of fully-constrained cable driven parallel robots
Mohammad A. Khosravi, Hamid D. Taghirad
Mechatronics
Abstract:

In this paper dynamic analysis and robust PID control of fully-constrained cable driven parallel manipulators are studied in detail. Since in this class of manipulators cables should remain in tension for all maneuvers in their workspace, feedback control of such robots becomes more challenging than that of conventional parallel robots. In this paper, structured and unstructured uncertainties in dynamics of the robot are considered and a robust PID controller is proposed for the cable robot. To ensure that all cables remain in tension internal force concept is used in the proposed PID control algorithm. Then, robust stability of the closed-loop system with proposed control algorithm is analyzed through Lyapunov direct method and it is shown that by suitable selection of the PID controller gains, the closed-loop system would be robustly stable. Finally, the effectiveness of the proposed PID algorithm is examined through experiments on a planar cable driven robot and it is shown that the proposed control structure is able to provide suitable performance in practice.

2014JournalPDFParallel and Cable Robotics
A Square Root Unscented FastSLAM With Improved Proposal Distribution and Resampling
Ramazan Havangi, Hamid D. Taghirad, Mohammad Ali Nekoui, and Mohammad Teshnehlab
IEEE Transactions on Industrial Electronics
Abstract:

An improved square root unscented fast simultaneous localization and mapping (FastSLAM) is proposed in this paper. The proposed method propagates and updates the square root of the state covariance directly in Cholesky decomposition form. Since the choice of the proposal distribution and that of the resampling method are the most critical issues to ensure the performance of the algorithm, its optimization is considered by improving the sampling and resampling steps. For this purpose, particle swarm optimization (PSO) is used to optimize the proposal distribution. PSO causes the particle set to tend to the high probability region of the posterior before the weights are updated; thereby, the impoverishment of particles can be overcome. Moreover, a new resampling algorithm is presented to improve the resampling step. The new resampling algorithm can conquer the defects of the resampling algorithm and solve the degeneracy and sample impoverishment problem simultaneously. Compared to unscented FastSLAM (UFastSLAM), the proposed algorithm can maintain the diversity of particles and consequently avoid inconsistency for longer time periods, and furthermore, it can improve the estimation accuracy compared to UFastSLAM. These advantages are verified by simulations and experimental tests for benchmark environments.

2014JournalPDF
Loop Closure Detection By Algorithmic Information Theory: Implemented On Range And Camera Image Data
Alireza Norouzzadeh Ravari and Hamid D. Taghirad
IEEE Transactions on Cybernetics
Abstract:

In this paper the problem of loop closing from depth or camera image information in an unknown environment is investigated. A sparse model is constructed from a parametric dictionary for every range or camera image as mobile robot observations. In contrast to high-dimensional feature-based representations, in this model, the dimension of the sensor measurements' representations is reduced. Considering the loop closure detection as a clustering problem in high-dimensional space, little attention has been paid to the curse of dimensionality in the existing state-of-the-art algorithms. In this paper, a representation is developed from a sparse model of images, with a lower dimension than original sensor observations. Exploiting the algorithmic information theory, the representation is developed such that it has the geometrically transformation invariant property in the sense of Kolmogorov complexity. A universal normalized metric is used for comparison of complexity based representations of image models. Finally, a distinctive property of normalized compression distance is exploited for detecting similar places and rejecting incorrect loop closure candidates. Experimental results show efficiency and accuracy of the proposed method in comparison to the state-of-the-art algorithms and some recently proposed methods.

2014JournalPDFAutonomous Robotics
Loop Closure Detection By Algorithmic Information Theory: Implemented On Range And Camera Image Data
Alireza Norouzzadeh Ravari and Hamid D. Taghirad
IEEE Transactions on Cybernetics
Abstract:

In this paper the problem of loop closing from depth or camera image information in an unknown environment is investigated. A sparse model is constructed from a parametric dictionary for every range or camera image as mobile robot observations. In contrast to high-dimensional feature-based representations, in this model, the dimension of the sensor measurements' representations is reduced. Considering the loop closure detection as a clustering problem in high-dimensional space, little attention has been paid to the curse of dimensionality in the existing state-of-the-art algorithms. In this paper, a representation is developed from a sparse model of images, with a lower dimension than original sensor observations. Exploiting the algorithmic information theory, the representation is developed such that it has the geometrically transformation invariant property in the sense of Kolmogorov complexity. A universal normalized metric is used for comparison of complexity based representations of image models. Finally, a distinctive property of normalized compression distance is exploited for detecting similar places and rejecting incorrect loop closure candidates. Experimental results show efficiency and accuracy of the proposed method in comparison to the state-of-the-art algorithms and some recently proposed methods.

2014JournalPDFMixed Reality in Surgery
Dynamic Modeling and Control of Parallel Robots With Elastic Cables: Singular Perturbation Approach
Mohammad A. Khosravi, Member and Hamid D. Taghirad
IEEE Transactions on Robotics
Abstract:

In this paper, control of fully-constrained parallel cable robots with elastic cables is studied in detail. In the modeling process, longitudinal vibration of cables is considered as their dominant dynamics, and the governing equations of motion are rewritten to the standard form of singular perturbation. The proposed composite controller consists of two main components. A rigid controller is designed based on the slow or rigid model of the system and a corrective term is added to guarantee asymptotic stability of the fast dynamics. Then, by using Tikhonov theorem, slow and fast variables are separated and incorporated into the stability analysis of the overall closed-loop system, and a set of sufficient conditions for the stability of the total system is derived. Finally, the effectiveness of the proposed control law is verified through simulations.

2014JournalPDFParallel and Cable Robotics
System Identification and Robust Controller Design for the Autopilot of an Unmanned Helicopter
Ahmad Safaee, Hamid D. Taghirad
Control Conference
Abstract:

One of the most complex issues which are proposed in designing a controller for autopilots is robustness. This requirement is due to the dynamic model changes and also, the resistance to environmental disturbances. A main factor that changes the dynamic model of the helicopter autopilot is any change in body mass center, such as any additional load. Furthermore, wind is one of the main causes of environmental disturbances. In this paper model identification of four systems in helicopter by using real data is presented. For all systems robust H2/H-Infinity and mixed sensitivity controller are designed. The simulation results show the robustness of designed controllers in the existence of uncertainty. The designed controller was implemented on the real case study. Results demonstrate the robustness of the system.

2013ConferencePDF
An intelligent UFastSLAM with MCMC move step
Ramazan Havangi, Mohammad Ali Nekoui, Hamid D. Taghirad and Mohammad Teshnehlab
Advanced Robotics
Abstract:

FastSLAM is a framework for simultaneous localization and mapping (SLAM). However, FastSLAM algorithm has two serious drawbacks, namely the linear approximation of nonlinear functions and the derivation of the Jacobian matrices. For solving these problems, UFastSLAM has been recently proposed. However, UFastSLAM is inconsistent over time due to the loss of particle diversity that is caused mainly by the particle depletion in the resampling step and incorrect a priori knowledge of process and measurement noises. To improve consistency, intelligent UFastSLAM with Markov chain Monte Carlo (MCMC) move step is proposed. In the proposed method, the adaptive neuro-fuzzy inference system supervises the performance of UFastSLAM. Furthermore, the particle impoverishment caused by resampling is restrained after the resample step with MCMC move step. Simulations and experiments are presented to evaluate the performance of algorithm in comparison with UFastSLAM. The results show the effectiveness of the proposed method.

2013JournalPDFAutonomous Robotics
Unsupervised 3D Object Classification from Range Image Data by Algorithmic Information Theory
Alireza Norouzzadeh Ravari and Hamid D. Taghirad
2013 First RSI/ISM International Conference on Robotics and Mechatronics (ICRoM)
Abstract:

The problem of unsupervised classification of 3D objects from depth information is investigated in this paper. The range images are represented efficiently as sensor observations. Considering the high-dimensionality of 3D object classification, little attention has been paid to the curse of dimensionality in the existing state-of-the-art algorithms. In order to remedy this problem, a low-dimensional representation is defined here. The sparse model of every range image is constructed from a parametric dictionary. Employing the algorithmic information theory, a universal normalized metric is used for comparison of Kolmogorov complexity based representations of sparse models. Finally, most similar objects are grouped together. Experimental results show efficiency and accuracy of the proposed method in comparison to a recently proposed method.

2013ConferencePDFAutonomous Robotics
Unsupervised 3D Object Classification from Range Image Data by Algorithmic Information Theory
Alireza Norouzzadeh Ravari and Hamid D. Taghirad
2013 First RSI/ISM International Conference on Robotics and Mechatronics (ICRoM)
Abstract:

The problem of unsupervised classification of 3D objects from depth information is investigated in this paper. The range images are represented efficiently as sensor observations. Considering the high-dimensionality of 3D object classification, little attention has been paid to the curse of dimensionality in the existing state-of-the-art algorithms. In order to remedy this problem, a low-dimensional representation is defined here. The sparse model of every range image is constructed from a parametric dictionary. Employing the algorithmic information theory, a universal normalized metric is used for comparison of Kolmogorov complexity based representations of sparse models. Finally, most similar objects are grouped together. Experimental results show efficiency and accuracy of the proposed method in comparison to a recently proposed method.

2013ConferencePDFMixed Reality in Surgery
A New Method for Mobile Robot Navigation in Dynamic Environment: Escaping Algorithm
F. Adib Yaghmaie, A. Mobarhani and H. D. Taghirad
Robotics and Mechatronics (ICRoM)
Abstract:

This paper addresses a new method for navigation in dynamic environment. The proposed method is based on force field method and it is supposed that the robot performs SLAM and autonomous navigation in dynamic environment without any predefined information about dynamic obstacles. The movement of dynamic obstacles is predicted by Kalman filter and is used for collision detection purpose. In the time of collision detection, a modifying force is added to repulsive and attractive forces corresponding to the static environment and leads robot to avoid collision. Moreover, a safe turning angle is defined to assure safe navigation of the robot. The performance of proposed method, named Escaping Algorithm, is verified through different simulation and experimental tests. The results show the proper performance of Escaping Algorithm in term of dynamic obstacle avoidance as a practical method for autonomous navigation.

2013ConferencePDFAutonomous Robotics
Kinematic Performance Indices Analyzed on Four Planar Cable Robots via Internal Analysis
S. A. Khalipour, A. Zarif Loloei, M. Tale Masouleh and H. D. Taghirad
Robotics and Mechatronics
Abstract:

In this paper, some new kinematic performance indices are proposed and examined on four planar cable driven parallel manipulators. The main kinematic indices are based on kinematic sensitivity and controllable workspace of the robot. Interval analysis is adopted as a mathematical framework to compute feasible kinematic sensitivity and worst kinematic sensitivity indices. For determining the feasible kinematic sensitivity, the controllable workspace is combined with the desired kinematic sensitivity property. The area of the foregoing region and the worst kinematic sensitivity corresponding to it are introduced as practical design indices. Then four typical design of planar cable robot are examined by the following performance measures, and one of such designs are selected and implemented in practice.

2013ConferencePDFParallel and Cable Robotics
Robust PID Control of Cable Driven Robots with Elastic Cables
Mohammad A. Khosravi and Hamid D. Taghirad
2013 First RSI/ISM International Conference on Robotics and Mechatronics (ICRoM)
Abstract:

In this paper robust PID control of fully-constrained cable-driven robots with elastic cables is studied in detail. To develop the idea, a robust PID control for cable-driven robots with ideal rigid cables is firstly designed and then, this controller is extended for the robots with elastic cables. To overcome vibrations caused by inevitable elasticity of cables, a composite control law is proposed based on singular perturbation theory. The proposed control algorithm includes robust PID control for corresponding rigid model and a corrective term. Using the proposed control algorithm the dynamics of the cable-driven robot is divided into slow and fast subsystems. Then, based on the results of singular perturbation theory, stability analysis of the total system is performed. Finally, the effectiveness of the proposed control law is investigated through several simulations on a planar cable-driven robot.

2013ConferencePDFParallel and Cable Robotics
Position Based Sliding Mode Control for Visual Servoing System
M. Parsapour, S. RayatDoost, and H. D. Taghirad
2013 First RSI/ISM International Conference on Robotics and Mechatronics (ICRoM)
Abstract:

This paper presents a nonlinear controller for visual servoing system. Pose estimation is one of the fundamental issues in position-based visual servoing (PBVS) approach. A few researches have focused on controller synthesis under modeling uncertainty and measurement noise of estimated position. In this research, PD-type sliding surface is designed for tracking target. The control signal is obtained from the sliding surface and the stability of the algorithm is verified by Lyapunov theory. Moreover, a recent designed robust estimator based on unscented Kalman observer (UKO) cascading with Kalman filter (KF) is used to estimate the pose, velocity and acceleration of the target. The combination of the implemented estimator and the proposed controller provide a stable and robust structure in PBVS. The reported experimental results, verify the effectiveness of the proposed method in an industrial visual servoing system.

2013ConferencePDFVisual Robotics
A New Method for Mobile Robot Navigation in Dynamic Environment: Escaping Algorithm
Farnaz Adib Yaghmaie, Amir Mobarhani, and Hamid D. Taghirad
Robotics and Mechatronics
Abstract:

This paper addresses a new method for navigation in dynamic environment. The proposed method is based on force field method and it is supposed that the robot performs SLAM and autonomous navigation in dynamic environment without any predefined information about dynamic obstacles. The movement of dynamic obstacles is predicted by Kalman filter and is used for collision detection purpose. In the time of collision detection, a modifying force is added to repulsive and attractive forces corresponding to the static environment and leads robot to avoid collision. Moreover, a safe turning angle is defined to assure safe navigation of the robot. The performance of proposed method, named Escaping Algorithm, is verified through different simulation and experimental tests. The results show the proper performance of Escaping Algorithm in term of dynamic obstacle avoidance as a practical method for autonomous navigation.

2013ConferencePDFAutonomous Robotics
A Positive Tensions PID Controller for a Planar Cable Robot: An Experimental Study
Mohammad A. Khosravi, Hamid D. Taghirad and Reza Oftadeh
2013 First RSI/ISM International Conference on Robotics and Mechatronics (ICRoM)
Abstract:

In this paper design and control of planar cable-driven parallel robots are studied in an experimental prospective. Since in this class of manipulators, cable tensionability conditions must be met, feedback control of such robots becomes more challenging than for conventional robots. To meet these conditions, internal force control structure is introduced and used in addition to a PID control scheme to ensure that all cables remain in tension. A robust PID controller is proposed for partial knowledge of the robot, to keep the tracking errors bounded. Finally, the effectiveness of the proposed control algorithm is examined through experiments on K.N. Toosi planar cable-driven robot and it is shown that the proposed control structure is able to provide suitable performance in practice.

2013ConferencePDFParallel and Cable Robotics
Kinematic Performance Indices Analyzed on Four Planar Cable Robots via Interval Analysis
S. A. Khalilpour, A. Zarif Loloei, M. Tale Masouleh and H. D. Taghirad
2013 First RSI/ISM International Conference on Robotics and Mechatronics (ICRoM)
Abstract:

In this paper, some new kinematic performance indices are proposed and examined on four planar cable driven parallel manipulators. The main kinematic indices are based on kinematic sensitivity and controllable workspace of the robot. Interval analysis is adopted as a mathematical framework to compute feasible kinematic sensitivity and worst kinematic sensitivity indices. For determining the feasible kinematic sensitivity, the controllable workspace is combined with the desired kinematic sensitivity property. The area of the foregoing region and the worst kinematic sensitivity corresponding to it are introduced as practical design indices. Then four typical design of planar cable robot are examined by the following performance measures, and one of such designs are selected and implemented in practice.

2013ConferencePDFParallel and Cable Robotics
Visual Tracking in Four Degrees of Freedom Using Kernel Projected Measurement
Fateme Bakhshande and Hamid D. Taghirad
2013 First RSI/ISM International Conference on Robotics and Mechatronics (ICRoM)
Abstract:

Visual Servoing is generally comprised of feature tracking and control. According to the literature, no attempt has already been made to optimize these two parts together. In kernel based visual servoing method, the main objective is to combine and optimize the entire control loop. By kernel definition, a Lyapanov candidate function is formed and the control input is computed so that the Lyapanov stability can be verified. This is performed in four degrees of freedom. In the present study, previous kernel algorithm from the recorded literature has been implemented. We have used the KBVS for our purpose such that an object without any marker is tracked. This method is chosen because of its robustness, speed and featureless properties. Furthermore, in order to show the visual tracking performance, all four degrees of freedom have been synthesized. Experimental results verifies the effectiveness of this method implemented for four degrees of freedom movements.

2013ConferencePDFVisual Robotics
Position Based Sliding Mode Control for Visual Servoing System
M. Parsapour, S. RayatDoost, and H. D. Taghirad
2013 First RSI/ISM International Conference on Robotics and Mechatronics (ICRoM)
Abstract:

This paper presents a nonlinear controller for visual servoing system. Pose estimation is one of the fundamental issues in position-based visual servoing (PBVS) approach. A few researches have focused on controller synthesis under modeling uncertainty and measurement noise of estimated position. In this research, PD-type sliding surface is designed for tracking target. The control signal is obtained from the sliding surface and the stability of the algorithm is verified by Lyapunov theory. Moreover, a recent designed robust estimator based on unscented Kalman observer (UKO) cascading with Kalman filter (KF) is used to estimate the pose, velocity and acceleration of the target. The combination of the implemented estimator and the proposed controller provide a stable and robust structure in PBVS. The reported experimental results, verify the effectiveness of the proposed method in an industrial visual servoing system.

2013ConferencePDFVisual Robotics
A SLAM based on auxiliary marginalised particle filter and differential evolution
R. Havangi, M.A. Nekoui, M. Teshnehlab and H.D. Taghirad
International Journal of Systems Science
Abstract:

FastSLAM is a framework for simultaneous localisation and mapping (SLAM) using a Rao-Blackwellised particle filter. In FastSLAM, particle filter is used for the robot pose (position and orientation) estimation, and parametric filter (i.e. EKF and UKF) is used for the feature location's estimation. However, in the long term, FastSLAM is an inconsistent algorithm. In this paper, a new approach to SLAM based on hybrid auxiliary marginalised particle filter and differential evolution (DE) is proposed. In the proposed algorithm, the robot pose is estimated based on auxiliary marginal particle filter that operates directly on the marginal distribution, and hence avoids performing importance sampling on a space of growing dimension. In addition, static map is considered as a set of parameters that are learned using DE. Compared to other algorithms, the proposed algorithm can improve consistency for longer time periods and also, improve the estimation accuracy. Simulations and experimental results indicate that the proposed algorithm is effective.

2013JournalPDF
PD Controller Design with H-Infinity Performance for Linear Systems with Input Delay
Ala Shariati, Hamid D. Taghirad
AUR Journal of Electrical Engineering
Abstract:

This paper considers H-Infinity control problem for input-delayed systems for time-varying delays. A proportional-derivative state feedback control law is used in this paper. By this means, the resulting closed-loop system turns into a specific time-delay system of neutral type. The significant specification of this neutral system is that its delayed term coefficients depend on the controller parameters. This condition provides new challenging issues in theoretical research as well as providing new applications. In the present paper, new delay-dependent sufficient condition is derived for the existence of H-Infinity controller in terms of matrix inequalities, in presence of varying time-delays. The resulting H-Infinity controller guarantees asymptotic stability of the closed-loop system as well as a guaranteed limited system induced norm smaller than a prescribed level. Numerical examples are presented to illustrate the effectiveness of the proposed method.

2012JournalPDFDynamical Systems Analysis and Control
Feasible Kinematic Sensitivity in Cable Robots Based on Interval Analysis
S. A. Khalilpour, A. Zarif Loloei, H. D. Taghirad, and M. Tale Masouleh
Cable-Driven Parallel Robots
Abstract:

The kinematic sensitivity has been recently proposed as a unit-consistent performance index to circumvent several shortcomings of some notorious indices such as dexterity. This paper presents a systematic interval approach for computing an index by which two important kinematic properties, namely feasible workspace and kinematic sensitivity, are blended into each other. The proposed index may be used to efficiently design different parallel mechanisms, and cable driven robots. By this measure, and for parallel manipulators, it is possible to visualize constant orientation workspace of the mechanism where the kinematic sensitivity is less than a desired value considered by the designer. For cable driven redundant robots, the controllable workspace is combined with the desired kinematic sensitivity property, to determine the so-called feasible kinematic sensitivity workspace of the robot. Three case studies are considered for the development of the idea and verification of the results, through which a conventional planar parallel manipulator, a redundant one and a cable driven robot is examined in detail. Finally, the paper provides some hints for the optimum design of the mechanisms under study by introducing the concept of minimum feasible kinematic sensitivity covering the whole workspace.

2012JournalPDFParallel and Cable Robotics
Experimental Performance of Robust PID Controller on a Planar Cable Robot
M. A. Khosravi and H. D. Taghirad
Cable-Driven Parallel Robots
Abstract:

In this paper dynamic analysis and experimental performance of robust PID control for fully-constrained cable driven robots are studied in detail. Since in this class of manipulators cables should remain in tension for all maneuvers through their whole workspace, feedback control of such robots becomes more challenging than conventional parallel robots. To ensure that all the cables remain in tension, a corrective term is used in the proposed PID control scheme. In design of PID control it is assumed that there exist bounded norm uncertainties in Jacobian matrix and in all dynamics matrices. Then a robust PID controller is proposed to overcome partial knowledge of robot, and to guarantee boundedness of tracking errors. Finally, the effectiveness of the proposed PID algorithm is examined through experiments and it is shown that the proposed control structure is able to provide suitable performance in practice.

2012JournalPDFParallel and Cable Robotics
Monte Carlo Sampling of Non-Gaussian Proposal Distribution in Feature-Based RBPF-SLAM
Nina Marhamati, Hamid D. Taghirad, Kasra Khosoussi
Abstract:

Particle lters are widely used in mobile robot localization and mapping. It is well-known that choosing an appropriate proposal distribution plays a crucial role in the success of particle lters. The proposal distribution conditioned on the most recent observation, known as the optimal proposal distribution (OPD), increases the number of eective particles and limits the degeneracy of lter. Conventionally, the OPD is approximated by a Gaussian distribution, which can lead to failure if the true distribution is highly non-Gaussian. In this paper we propose two novel solutions to the problem of feature-based SLAM, through Monte Carlo approximation of the OPD which show superior results in terms of mean squared error (MSE) and number of eective samples. The proposed methods are capable of describing non-Gaussian OPD and dealing with nonlinear models. Simulation and experimental results in large-scale environments show that the new algorithms outperform the aforementioned conventional methods.

2012ConferencePDFParallel and Cable Robotics
Controllable Workspace of Cable-Driven Redundant Parallel Manipulators by Fundamental Wrench Analysis
Azadeh Zarif Loloei, Hamid D. Taghirad
Transactions- Canadian Society for Mechanical Engineering
Abstract:

Workspace analysis is always a crucial issue in robotic manipulator design. This paper introduces a set of newly defined fundamental wrenches that opens new horizons to physical interpretation of controllable workspace of a general cable-driven redundant parallel manipulator. Based on this set of fundamental wrenches, a novel tool is presented to determine configurations of cable-driven redundant parallel manipulator that belong to the controllable workspace. Analytical expressions of such workspace boundaries are obtained in an implicit form and a rigorous mathematical proof is provided for this method. Finally, the proposed method is implemented on a spatial cable-driven manipulator of interest.

2012JournalPDFParallel and Cable Robotics
SLAM Based on Intelligent Unscented Kalman Filter
R.Havangi, M.A.Nekoui, H.D.Taghirad, and M.Teshnehlab
The 2nd International Conference on Control, Instrumentation and Automation
Abstract:

The performance of SLAM based on unscented Kalman filter (UKF-SLAM) and thus the quality of the estimation depends on the correct a priori knowledge of process and measurement noise. Imprecise knowledge of these statistics can cause significant degradation in performance. In this paper, the adaptive Neuro-Fuzzy has been implemented to adapt the matrix covariance process of UKF-SLAM in order to improve its performance.

2012ConferencePDF
Feedback Error learning Control of Trajectory Tracking of Non-Holonomic Mobile Robot
Farnaz Adib Yaghmaie, Fateme Bakhshande and Hamid D.Taghirad
20th Iranian Conference on Electrical Engineering
Abstract:

In this paper a new controller for nonholonomic system is introduced. This feedback error learning controller benefits from both nonlinear and adaptive controller properties. The nonlinear controller is used to stabilize the nonholonomic behavior of the systems. This controller is a sliding mode controller which is designed based on backstepping method. The adaptive controller tries to face with uncertainty and unknown dynamic of the mobile robot. This part uses neural network controller for adaptation. The experimental results show the effectiveness of proposed controller and suitable and robust tracking performance of a mobile robot, which is significantly better than traditional controllers.

2012ConferencePDFAutonomous Robotics
Stereo-Based Visual Navigation of Mobile Robots in Unknown Environments
H. Soltani, H. D. Taghirad and A.R. Norouzzadeh Ravari
20th Iranian Conference on Electrical Engineering (ICEE2012)
Abstract:

In this paper a stereo vision-based algorithm for mobile robots navigation and exploration in unknown outdoor environments is proposed. The algorithm is solely based on stereo images and implemented on a nonholonomic mobile robot. The first step for exploration in unknown environments is construction of the map of circumference in real-time. By getting disparity image from rectified stereo images and translating its data to 3D-space, point cloud model of environments is constructed. Then by projecting points to XZ plane and put local maps together based on visual odometry, global map of environment is constructed in real-time. A* algorithm is used for investigating optimal path and nonlinear back-stepping controller guides the robot to follow the identified path. Finally, the mobile robot explores for a desired object in an unknown environment through these steps. Experimental results verify the effectiveness of the proposed algorithm in real-time implementations.

2012ConferencePDFAutonomous Robotics
Robust solution to three-dimensional pose estimation using composite extended Kalman observer and Kalman filter
H.D. Taghirad S.F. Atashzar M. Shahbazi
IET Computer Vision
Abstract:

Three-dimensional (3D) pose estimation of a rigid object by only one camera has a vital role in visual servoing systems, and extended Kalman filter (EKF) is vastly used for this task in an unstructured environment. In this study, the stability of the EKF-based 3D pose estimators is analysed in detail. The most challenging issue of the state-of-the-art EKF-based 3D pose estimators is the possibility of its divergence because of the measurement and model noises. By analysing the stability of conventional EKF-based pose estimators a composite technique is proposed to guarantee the stability of the procedure. In the proposed technique, the non-linear-uncertain estimation problem is decomposed into a non-linear-certain observation in addition to a linear-uncertain estimation problem. The first part is handled using the extended Kalman observer and the second part is accomplished by a simple Kalman filter. Finally, some experimental and simulation results are given in order to verify the robustness of the method and compare the performance of the proposed method in noisy and uncertain environment to the conventional techniques.

2012JournalPDFVisual Robotics
Robust SDRE filter design for nonlinear uncertain systems with an H-Infinity performance criterion
Hossein Beikzadeh, Hamid D. Taghirad
ISA Transactions
Abstract:

In order to remedy the effects of modeling uncertainty, measurement noise and input disturbance on the performance of the standard state-dependent Riccati equation (SDRE) filter, a new robust SDRE filter design is developed in this paper. Based on the infinity-norm minimization criterion, the proposed filter effectively estimates the states of nonlinear uncertain system exposed to unknown disturbance inputs. Moreover, by assuming a mild Lipschitz condition on the chosen state-dependent coefficient form, fulfillment of a modified performance index is guaranteed in the proposed filter. The effectiveness of the robust SDRE filter is demonstrated through numerical simulations where it brilliantly outperforms the conventional SDRE filter in presence of model uncertainties, disturbance and measurement noise, in terms of estimation error and region of convergence.

2012JournalPDF
Delay-Dependent H-Infinity Control of Linear Systems with Uncertain Input Delay Using State-Derivative Feedback
A. Shariati, H. D. Taghirad
Control Engineering and Applied Informatics
Abstract:

In some practical problems such as active vibration suppression systems, the state-derivative signals are easier to access than the state variables. This paper considers an H-Infinity -based state-derivative feedback control problem for input-delayed systems. Applying this control law, the resulting closed-loop system turns into a specific time-delay system of neutral type. The significant specification of this neutral system is that its delayed term coefficients depend on the controller parameters. The time-delay is considered as uncertain time-invariant with a known constant bound. In this paper, the delay-dependent sufficient conditions for the existence of an H-Infinity state-derivative feedback controller are derived in terms of matrix inequalities. The resulting H-Infinity controller stabilizes the closed-loop neutral system and assures that the H-Infinity -norm to be less than a prescribed level. An application example is presented to illustrate the effectiveness of the proposed method.

2012JournalPDFDynamical Systems Analysis and Control
Dexterous Workspace Optimization of a Tricept Parallel Manipulator
Mir Amin Hosseini, Hamid-Reza M. Daniali, and Hamid D. Taghirad
Advanced Robotics
Abstract:

The growing interest in the use of parallel manipulators in machining applications requires clear determination of the workspace and dexterity. In this paper, the workspace optimization of a Tricept parallel manipulator under joint constraints is performed. This parallel manipulator has complex degrees of freedom and, therefore, leads to dimensionally inhomogeneous Jacobian matrices. Here, we divide the Jacobian entries by units of length, thereby producing a new Jacobian that is dimensionally homogeneous. By multiplying the associated entries of the twist array to the same length, we made this array homogeneous as well. The workspace of the manipulator is parameterized using several design parameters and is optimized using a genetic algorithm. For the workspace of the manipulator, local conditioning indices and minimum singular values are calculated. For the optimal design, it is shown that by introducing the local conditioning indices and minimum singular values, the quality of the parallel manipulator is improved at the cost of workspace reduction.

2011JournalPDFParallel and Cable Robotics
Delay-Independent Robust Stability Analysis of Teleoperation
Masoumeh Azadegan, Sadjaad Ozgoli, and Hamid Reza Taghirad
2011 Chinese Control and Decision Conference (CCDC)
Abstract:

This paper considers the robust stability of uncertain teleoperation systems. Sufficient stability conditions are derived in terms of LMI by representing the teleoperation scheme in retarded form of time-delay systems. By choosing Lyapunov-Krasovski functional, a delay-independent robust stability criterion is presented. We show that the teleoperation system is stable and has good performance under specific LMI condition. With the given controller parameters, stability of system is guaranteed in the presence of any value of delay and admissible uncertainty. To evaluate the theoretical analysis, Numerical simulations are performed.

2011ConferencePDFDynamical Systems Analysis and Control
Controllable Workspace of General Cable Driven Redundant Parallel Manipulator Based on Fundamental Wrench
A. Zarif Loloei, H. D. Taghirad
Transactions- Canadian Society for Mechanical Engineering
Abstract:

Workspace analysis is one of the most important issues in robotic manipulator design. This paper introduces a set of newly defined fundamental wrenches that opens new horizons for physical interpretation of controllable workspace of cable driven redundant parallel manipulators. Moreover, an analytical method is proposed to specify the controllable workspace of general redundant cabledriven parallel manipulators based on this set of fundamental wrenches. In the proposed method, an analytic approach based on linear algebra is employed to derive the boundary of controllable workspace. Finally, the proposed method is illustrated through spatial example.

2011ConferencePDFParallel and Cable Robotics
Dynamic Analysis and Control of Cable Driven Robots Considering Elasticity in Cables
Mohammad A. Khosravi, Hamid. D. Taghirad
Transactions- Canadian Society for Mechanical Engineering
Abstract:

In this paper modeling and control of cable driven redundant parallel manipulators with flexible cables, are studied in detail. Based on new results, in fully constrained cable robots, cables can be modeled as axial linear springs. Considering this assumption the system dynamics formulation is developed using Lagrange approach. Since in this class of robots, all the cables should remain in tension for the whole workspace, the notion of internal forces are introduced and incorporated in the proposed control algorithm. The control algorithm is developed in cable coordinates in which the internal forces play an important role. Finally, asymptotic stability of the closed loop system is analyzed through Lyapunov theorem, and the performance of the proposed algorithm is studied by simulations.

2011ConferencePDFParallel and Cable Robotics
Analytical Passivity Analysis for Wave-based Teleoperation with Improved Trajectory Tracking
Bita Fallahi, Hamid D. Taghirad
Canadian Committee for the Theory of Machines and Mechanisms
Abstract:

In wave based teleoperation, although passivity is ensured for any time delay, tracking performance is usually distorted due to the bias term introduced by wave transmission. To improve the position tracking error, one way is to augment the forward wave with a corrective term and achieve pas-sivity by tuning the band width of a low pass filter in the forward path. However, this filter fails to meet the passivity condition in contact to stiff environments, especially at steady state. In this paper a new method is proposed and an analytical solution for passivity at steady state and a semi analytical solution for all other frequencies are represented. This method significantly reduces the complexity of the closed-loop system, ensures passivity in contact to the stiff environments, and improves trajectory tracking. Simulation results are presented to show the effectiveness of the pro-posed method.

2011ConferencePDFSurgical Robotics
Delay-Independent Stability Analysis of Internet-based Tele-operation
Masoumeh Azadegan, Sadjaad Ozgoli, Hamid Reza Taghirad
2011 International Symposium on Computer Networks and Distributed Systems (CNDS)
Abstract:

This paper presents a sufficient stability condition for internet-based tele-operation systems in terms of LMI. The tele-operation scheme is modeled in state-space as a time-delay system in retarded form and a delay-independent stability criterion is extracted. By choosing Lyapunov-Krasovski functional, we show that the internet-based tele-operation system is stable and has good performance under specific LMI condition. With the given controller design parameters, stability of system is guaranteed in the presence of any value of delay. Numerical simulations are performed to verify the theoretical results.

2011ConferencePDFDynamical Systems Analysis and Control
Dynamic Aalysis and Control of Cable Driven Robots With Elastic Cables
Mohammad A. Khosravi, Hamid D. Taghirad
Transactions- Canadian Society for Mechanical Engineering
Abstract:

In this paper modeling and control of cable driven redundant parallel manipulators with flexible cables, are studied in detail. Based on new results, in fully constrained cable robots, cables can be modeled as axial linear springs. Considering this assumption the system dynamics formulation is developed using Lagrange approach. Since in this class of robots, all the cables should remain in tension for the whole workspace, the notion of internal forces are introduced and incorporated in the proposed control algorithm. The control algorithm is developed in cable coordinates in which the internal forces play an important role. Finally, asymptotic stability of the closed loop system is analyzed through Lyapunov theorem, and the performance of the proposed algorithm is studied by simulations

2011ConferencePDFParallel and Cable Robotics
Lagrangian Dynamics of Cable-Driven Parallel Manipulators: A Variable Mass Formulation
Yousef B. Bedoustani, Pascal Bigras, Hamid D. Taghirad, Ilian A. Bonev
Transactions- Canadian Society for Mechanical Engineering
Abstract:

In this paper, dynamic analysis of cable-driven parallel manipulators (CDPMs) is performed using the Lagrangian variable mass formulation. This formulation is used to treat the effect of a mass stream entering into the system caused by elongation of the cables. In this way, a complete dynamic model of the system is derived, while preserving the compact and tractable closed-form dynamics formulation. First, a general formulation for a CDPM is given, and the effect of change of mass in the cables is integrated into its dynamics. The significance of such a treatment is that a complete analysis of the dynamics of the system is achieved, including vibrations, stability, and any robust control synthesis of the manipulator. The formulation obtained is applied to a typical planar CDPM. Through numerical simulations, the validity and integrity of the formulations are verified, and the significance of the variable mass treatment in the analysis is examined. For this example, it is shown that the effect of introducing a mass stream into the system is not negligible. Moreover, it is non linear and strongly dependent on the geometric and inertial parameters of the robot, as well as the maneuvering trajectory.

2011ConferencePDFParallel and Cable Robotics
Geometric Analysis of the Kinematic Sensitivity of Planar Parallel Mechanisms
Mohammad Hossein Saadatzi, Mehdi Tale Masouleh, Hamid D. Taghirad, Cle´ment Gosselin, Philippe Cardou
Transactions- Canadian Society for Mechanical Engineering
Abstract:

The kinematic sensitivity is a unit-consistent measure that has been recently proposed as a mechanism performance index to compare robot architectures. This paper presents a robust geometric approach for computing this index for the case of planar parallel mechanisms. The physical meaning of the kinematic sensitivity is investigated through different combinations of the Euclidean and infinity norms and by means of several illustrative examples. Finally, this paper opens some avenues to the dimensional synthesis of parallel mechanisms by exploring the meaning of the global kinematic sensitivity index.

2011JournalPDFParallel and Cable Robotics
Adaptive Robust Backstepping Control Design for A Non-minimum Phase Model of Hard Disk Drives
M. Ataollahi, H. H. Eghrari and H. D. Taghirad
2011 19th Iranian Conference on Electrical Engineering
Abstract:

In this paper, a new adaptive robust approach for non-minimum phase systems is proposed, based on the synthesis algorithm of dynamical backstepping design procedure. The previously proposed adaptive robust backstepping method has a limitation in stabilization of non-minimum phase systems, which is removed in this paper. The dynamic model of the voice coil motor actuator, which is used in the read/write head of hard disk drive, is considered as a case study to apply the proposed method. A simple but accurate model of this system is presented the proposed control method is applied onto this model. Simulations are performed for the embedded control system of hard disk drives. The obtained results verify the effectiveness of the proposed control law in terms of transient performance, tracking errors, and disturbance rejection, in both track seeking and track following modes.

2011ConferencePDFHard Disk Drives Control
On the Optimum Design of 3-RPR Parallel Mechanisms
Mohammad Hossein Saadatzi, Mehdi Tale Masouleh, Hamid D. Taghirad, Clement ´ Gosselin and Philippe Cardou
2011 19th Iranian Conference on Electrical Engineering
Abstract:

This paper deals with the optimization of 3-RPR planar parallel mechanisms based on different performance indices including the kinematic sensitivity, the workspace and the singularity locus. Since the kinematic sensitivity has been proposed only recently, more emphasis is placed on how it should be adapted for the optimization of 3-RPR parallel mechanisms. The optimization is implemented in sequence using first a single objective technique, differential evolution, and then resorting to a multi-objective optimization concept, the so-called Non-dominated sorting genetic algorithm-II. A Pareto-based multi-objective approach helps to overcome the problem of unit-inconsistent objectives in the optimization algorithm. Moreover, an Infinity-norm is used in computation of the kinematic sensitivity which has perhaps the clearest physical interpretation.

2011ConferencePDFParallel and Cable Robotics
Modelling and Control of Fully Constrained Cable Driven Robots with Flexible Cables
Mohammad A. Khosravi, and Hamid D. Taghirad
The 2nd International Conference on Control, Instrumentation and Automation
Abstract:

In this paper modelling and control of cable-driven redundant parallel manipulators (CDRPM) with flexible cables are studied in detail. In this type of manipulators the cables should remain in tension in the whole workspace. New research results have shown that in fully constrained CDRPM cable can be modelled as an axial spring. Based on this fact a new model of this type of robot is studied. Furthermore, internal forces are introduced and incorporated in the proposed control algorithm. This control algorithm is formed in cable length coordinates in which the internal forces play an important role. Finally, the closed loop system is proved to be stable, through Lyapunov analysis, and the performance of the proposed algorithm is studied through simulation.

2011ConferencePDFParallel and Cable Robotics
Modeling and Control of Cable Driven Parallel Manipulators with Elastic Cables: Singular Perturbation Theory
Alaleh Vafaei, Mohammad A. Khosravi, and Hamid D. Taghirad
ICIRA 2011: Intelligent Robotics and Applications
Abstract:

This paper presents a new approach to the modeling and control of cable driven parallel manipulators and particularly KNTU CDRPM. First, dynamical model of the cable driven parallel manipulator is derived considering the elasticity of the cables, and then this model is rewritten in the standard form of singular perturbation theory. This theory used here as an effective tool for modeling the cable driven manipulators. Next, the integrated controller, applied for control of the rigid model of KNTU CDRPM in previous researches, is improved and a composite controller is designed for the elastic model of the robot. Asymptotic stability analysis of the proposed rigid controller is studied in detail. Finally, a simulation study performed on the KNTU CDRPM verifies the closed-loop performance compared to the rigid model controller.

2011ConferencePDFParallel and Cable Robotics
Histogram Based Frontier Exploration
Amir Mobarhani, Shaghayegh Nazari, Amir H. Tamjidi, Hamid D. Taghirad
2011 IEEE/RSJ International Conference on Intelligent Robots and Systems
Abstract:

This paper proposes a method for mobile robot exploration based on the idea of frontier exploration which suggests navigating the robot toward the boundaries between free and unknown areas in the map. A global occupancy grid map of the environment is constantly updated, based on which a global frontier map is calculated. Then, a histogram based approach is adopted to cluster frontier cells and score these clusters based on their distance from the robot as well as the number of frontier cells they contain. In each stage of the algorithm, a sub-goal is set for the robot to navigate. A combination of distance transform and A* search algorithms is utilized to generate a plausible path toward the sub-goal through the free space. This way keeping a reliable distance from obstacles is guaranteed while searching for the shortest path toward the sub-goal. When such a path is generated, a B-spline interpolated and smoothed trajectory is produced as the control reference for the mobile robot to follow. The whole process is iterated until no unexplored area remains in the map. The efficiency of the method is shown through simulated and real experiments.

2011ConferencePDFAutonomous Robotics
An Adaptive Neuro-Fuzzy Rao-Blackwellized Particle Filter for SLAM
Ramazan Havangi, Mohammad Teshnehlab, Mohammad Ali Nekoui, Hamid Taghirad
2011 IEEE International Conference on Mechatronics
Abstract:

The Rao-Blackwellized particle filter SLAM (RBPF-SLAM) that is also known as FastSLAM is a framework for simultaneous localization using a Rao-Blackwellized particle filter. The performance and the quality of the estimation of the Rao-Blackwellized particle filter depends heavily on the correct a priori knowledge of the process and measurement noise covariance matrices (Qt and Rt) that are in most applications unknown. On the other hand, an incorrect a priori knowledge of Qt and Rt may seriously degrade their performance. To solve these problems, this paper presents an adaptive Neuro-Fuzzy Rao-Blackwellized particle filter. The free parameters of adaptive Neuro-Fuzzy inference systems are trained using the steepest gradient descent (GD) to minimize the differences of the actual value of the covariance of the residual with its theoretical value as much as possible.

2011ConferencePDF
The H-Infinity Fast SLAM Framework
Ramazan Havangi, Mohammad Ali Nekoui, Hamid Taghirad, Mohammad Teshnehlab
2011 IEEE International Conference on Mechatronics
Abstract:

FastSLAM is a framework using a Rao-Blackwellized particle filter. However, the performance of FastSLAM depends on correct a priori knowledge of the process and measurement noise covariance matrices (Q t and R t ) that are in most applications unknown. On the other hand, an incorrect a priori knowledge of Q t and R t may seriously degrade the performance of FastSLAM. To solve these problems, this paper presents H ? FastSLAM. In this approach, H-Infinity particle filter is used for the mobile robot position estimation and H-Infinity filter is used for the feature location's estimation. The H-Infinity FastSLAM can work in an unknown statistical noise behavior and thus it is more robust. Experimental results demonstrate the effectiveness of the proposed algorithm.

2011ConferencePDF
Robust solution to three-dimensional pose estimation using composite extended Kalman observer and Kalman filter
H.D. Taghirad S.F. Atashzar M. Shahbazi
IET Computer Vision
Abstract:

Three-dimensional (3D) pose estimation of a rigid object by only one camera has a vital role in visual servoing systems, and extended Kalman filter (EKF) is vastly used for this task in an unstructured environment. In this study, the stability of the EKF-based 3D pose estimators is analysed in detail. The most challenging issue of the state-of-the-art EKF-based 3D pose estimators is the possibility of its divergence because of the measurement and model noises. By analysing the stability of conventional EKF-based pose estimators a composite technique is proposed to guarantee the stability of the procedure. In the proposed technique, the non-linear-uncertain estimation problem is decomposed into a non-linear-certain observation in addition to a linear-uncertain estimation problem. The first part is handled using the extended Kalman observer and the second part is accomplished by a simple Kalman filter. Finally, some experimental and simulation results are given in order to verify the robustness of the method and compare the performance of the proposed method in noisy and uncertain environment to the conventional techniques.

2011JournalPDFVisual Robotics
Multi-Objective Scale Independent Optimization of 3-RPR Parallel Mechanisms
M. H. Saadatzi, M. Tale Masouleh, H. D. Taghirad, C. Gosselin, M. Teshnehlab
World Congress in Mechanism and Machine Science
Abstract:

This paper deals with the optimization of 3-RPR planar parallel mechanisms based on different per-formance indices including kinematic sensitivity, stiffness, workspace and singularity. The optimization is imple-mented in sequence using first a single objective tech-nique, differential evolution, and then resorting to a multi-objective optimization concept, the so-called nondomi-nated sorting genetic algorithm-II. The results revealed that the optimality of the mechanism under study is scale-independent for the considered optimization objectives. Moreover, based on the scale invariance property of the main objectives, it follows that different kinetoestatic ob-jective functions must be scale invariant. The relations for the kinetoestatic objective expressions as functions of mech-anism scale are derived and to circumvent the problem of unit inconsistency the rotational and translational parts of these objectives are considered separately. To overcome the problem of inconsistent objectives in optimization al-gorithm, a Pareto-based multi-objective approach is used which preserves the scale invariance property.

2011ConferencePDFParallel and Cable Robotics
Robust Internal Model Control for Impulse Elimination of Singular Systems
M. M. Share Pasandand, H. D. Taghirad
International Journal of Control Science and Engineering
Abstract:

In this paper the problem of model based internal control of singular systems is investigated. The limitations of directly extending the control schemes for normal systems to singular ones are thoroughly developed, and a robust approach is proposed in order to establish a control scheme for singular systems. The proposed method presents a general framework for robust control design of singular systems in presence of modeling uncertainties. Two simulation examples are given to how the proposed method can be implemented, and to show the effectiveness of such controllers in closed loop performance.

2011JournalPDFDynamical Systems Analysis and Control
Robust SDRE filter design for nonlinear uncertain systems with an H-Infinity performance criterion
Hossein Beikzadeh, Hamid D. Taghirad
ISA Transactions
Abstract:

In order to remedy the effects of modeling uncertainty, measurement noise and input disturbance on the performance of the standard state-dependent Riccati equation (SDRE) filter, a new robust SDRE filter design is developed in this paper. Based on the infinity-norm minimization criterion, the proposed filter effectively estimates the states of nonlinear uncertain system exposed to unknown disturbance inputs. Moreover, by assuming a mild Lipschitz condition on the chosen state-dependent coefficient form, fulfillment of a modified performance index is guaranteed in the proposed filter. The effectiveness of the robust SDRE filter is demonstrated through numerical simulations where it brilliantly outperforms the conventional SDRE filter in presence of model uncertainties, disturbance and measurement noise, in terms of estimation error and region of convergence.

2011JournalPDF
Force Control of Intelligent Laparoscopic Forceps
Soheil Kianzad, Soheil O. Karkouti, and Hamid D. Taghirad
Journal of Medical Imaging and Health Informatics
Abstract:

Actuators play an important role at the end-effectors of Minimally Invasive Surgery (MIS) robots. Having local, lightweight and powerful actuators would increase dexterity of surgeons. Shape Memory Alloy (SMA) actuators are considered as good candidates and presented significant behaviors in producing the force needed for grasping. Most of the current MIS systems provide surgeons with visual feedback. However, in many operations this information could not help surgeons to diagnose the manipulated tissue accurately. Therefore, having force and tactile information is also necessary. In order to have this information, local sensors are needed to give force feedback. This would also help to have control over the wire tension and prevent exceeding force causing tissue damages. In this paper a novel design of forceps that uses antagonistic SMA actuators is presented. This configuration helps to increase force and speed and also eliminates the bias spring used in similar works. Moreover, this antagonistic design makes it possible to place the force sensors at the back part of the forceps instead of attaching them to the jaws which results in a smaller forceps design. To control the exerted force, analytical model of system and a force control method are also presented. This enhanced design seems to address some of the existing shortcomings of similar models and remove them effectively.

2011JournalPDFSurgical Robotics
Workspace analysis of 5-PRUR parallel mechanisms (3T2R)
Mohammad Hossein Saadatzi, Mehdi Tale Masouleh, Hamid D. Taghirad
Robotics and Computer-Integrated Manufacturing
Abstract:

This paper investigates the constant-orientation workspace of five-degree-of-freedom parallel mechanisms generating the three translations and two independent rotations and comprising five identical limbs of the type. The general mechanism was proposed recently from the type synthesis performed for 5-DOF parallel mechanisms with identical limb structures. In this study, the emphasis is placed on the determination of the constant-orientation workspace using a geometric interpretation of the so-called vertex space, i.e., the motion generated by a limb for a given orientation. The geometric investigation is carried out using geometric constructive approach, which is implemented in a computer algebra system and in a CAD system. This paper shows that these two approaches are complementary tools to investigate the workspace of parallel mechanisms. The geometric constructive approach proposed in this paper bring insight into the architecture optimization and it can be regarded as a guideline for the workspace analysis of parallel mechanisms whose vertex spaces generate Bohemian dome.

2011JournalPDFParallel and Cable Robotics
Adaptive Robust Controller Design For Non-minimum Phase Systems
M. Ataollahi and H. D. Taghirad
Abstract:

Based on the synthesis algorithm of dynamical backstepping design procedure, in this paper a new adaptive robust approach for non-minimum phase systems is proposed. The proposed controller consists of two parts; a backstepping controller as the robust part and a model reference (MRAS) controller as the adaptive part. In this control scheme the daptive part acts not only as a medium to converge to suitable values for the unknown parameters and to reduce the uncertainty, but also provides a minimum-phase model for the robust controller to be well stabilized. A simulation case study is studied to show how to perform the proposed control law, and to illustrate the effectiveness of this method compared to that of conventional robust controllers.

2011ConferencePDFDynamical Systems Analysis and Control
Robust Internal Model Control For Impulse Elimination of Singular Systems
M. M. Share Pasand and H. D. Taghirad
International Journal of Control Science and Engineering
Abstract:

In this paper the problem of model based internal control of singular systems is investigated. The limitations of directly extending the control schemes for normal systems to singular ones are thoroughly developed, and a robust approach is proposed in order to establish a control scheme for singular systems. The proposed method presents a general framework for robust control design of singular systems in presence of modeling uncertainties. Two simulation examples are given to how the proposed method can be implemented, and to show the effectiveness of such controllers in closed loop performance.

2011ConferencePDFDynamical Systems Analysis and Control
An Analytic-Iterative Redundancy Resolution Scheme for Cable-Driven Redundant Parallel Manipulators
Hamid D. Taghirad and Yousef B. Bedoustani
IEEE Transactions on Robotics
Abstract:

In this paper, redundancy resolution of a cable-driven parallel manipulator is performed through an analytic-iterative scheme. The redundancy resolution scheme is formulated as a convex optimization problem with inequality constraints that are imposed by manipulator structure and cable dynamics. The Karush-Kuhn-Tucker theorem is used to analyze the optimization problem and to draw an analytic-iterative solution for it. Subsequently, a tractable and iterative search algorithm is proposed to implement the redundancy resolution of such redundant manipulators. Furthermore, it is shown through simulations that the worst case and average elapsed time that is required to implement the proposed redundancy resolution scheme in a closed-loop implementation is considerably less than that of other numerical optimization methods.

2011JournalPDFParallel and Cable Robotics
Iterative-Analytic Redundancy Resolution Scheme for A Cable-Driven Redundant Parallel Manipulator
Yousef B. Bedoustani, and Hamid D. Taghirad
2010 IEEE/ASME International Conference on Advanced Intelligent Mechatronics
Abstract:

In this paper, redundancy resolution of a cable-driven parallel manipulator is solved by an iterative-analytic scheme. The method can be applied to all kind of redundant manipulators either parallel or serial with constraint caused through their dynamics. However, for sake of simulation the proposed method is implemented on a cable-driven redundant parallel manipulator (CDRPM). The redundancy resolution problem is formulated as a convex optimization with equality and non-equality constraints caused by manipulator structure and cables dynamics. Karush-Kuhn-Tucker theorem is used to analyze the optimization problem and to find an analytic solution. Subsequently, a tractable and iterative search algorithm is proposed to solve the redundancy resolution of such redundant mechanisms. Furthermore, it is shown through the simulation that, the elapsed time required to implement the analytical redundancy resolution scheme in a closed-loop structure is considerably less than that of other numerical optimization methods.

2010ConferencePDFParallel and Cable Robotics
A Geometric Costructive Approach For The Workspace Analysis of Symmetrical 5-PRUR Parallel Mechanisms (3T2R)
Mehdi Tale Masouleh, Mohammad Hossein Saadatzi, Clement Gosselin, Hamid D. Taghirad
Proceedings of the ASME Design Engineering Technical Conference
Abstract:

This paper investigates an important kinematic property, the constant-orientation workspace, of five-degree-of-freedom parallel mechanisms generating the 3T2R motion and comprising five identical limbs of the P RUR type. The general mechanism originates from the type synthesis performed for symmetrical 5-DOF parallel mechanism. In this study, the emphasis is placed on the determination of constant-orientation workspace using geometrical interpretation of the so-called vertex space, i.e., motion generated by a limb for a given orientation, rather than relying on classical recipes, such as discretization methods. For the sake of better understanding a CAD model is also provided for the vertex space. The constructive geometric approach presented in this paper provides some insight into the architecture optimization. Moreover, this approach facilitates the computation of the evolution of the volume of the constant-orientation workspace for different orientations of the end-effector.

2010ConferencePDFParallel and Cable Robotics
Descriptor Approach to Unknown Input PI Observer Design:application to fault detection
M.M. Share Pasand, H.D. Taghirad
Control Automation and Systems (ICCAS), 2010
Abstract:

The descriptor observer approach is improved further to a more suitable observer scheme which is applicable to a more general group of faults and systems. Also a disturbance decoupling scheme is added to the mentioned observer in order to enable the observer to distinguish faults from disturbances.

2010ConferencePDFDynamical Systems Analysis and Control
Unknown Input-Proportional Integral Observer for Singular Systems: Application to fault detection
M. M. Share Pasand, M. Aliyari Sh., and H. D. Taghirad
2010 18th Iranian Conference on Electrical Engineering
Abstract:

A new approach to the observer design for descriptor continuous time systems is proposed and its application in the fault diagnosis problem is illustrated. In this observer, two features of disturbance decoupling and fault estimation are combined. Also a more general frame for fault estimation is used. Some numerical examples and simulation results are shown to justify the effectiveness of the algorithm.

2010ConferencePDFDynamical Systems Analysis and Control
Forward Kinematic Problem and Constant Orientation Workspace of 5-RPRRR (3T2R) Parallel Mechanisms
Mehdi Tale Masouleh, Clément Gosselin, Mohammad Hossein Saadatzi, Hamid D. Taghirad
Electrical Engineering (ICEE), 2010 18th Iranian Conference on
Abstract:

This paper investigates some kinematic properties of a five-degree-of-freedom parallel mechanism generating the 3T2R motion and comprising five identical limbs of the RP?UR type. In this study, two classes of simplified designs are proposed whose forward kinematic problems have either a univariate or a closed-form solution. The principal contributions of this study are the solution of the forward kinematic problem for some simplified designs—which may have more solutions than the FKP of the general 6-DOF Stewart platform with 40 solutions—and the determination of the constant orientation workspace based on algebraic geometry (Bohemian domes).

2010ConferencePDFParallel and Cable Robotics
Integrated Controller For An Over–Constrained Cable Driven Parallel Manipulator: KNTU CDRPM
Alaleh Vafaei, Mohammad M. Aref and Hamid D. Taghirad
2010 IEEE International Conference on Robotics and Automation
Abstract:

This paper presents an approach to the control of the KNTU CDRPM using an integrated control scheme. The goal in this approach is achieving accurate trajectory tracking while assuring positive tension in the cables. By the proposed controller, the inherent nonlinear behavior of the cable and the target tracking errors are simultaneously compensated. In this paper asymptotic stability analysis of the close loop system is studied in detail. Moreover, it is shown that the integrated control strategy reduces the tracking error by 80% compared to that of a single loop controller in the considered manipulator. The closed-loop performance of the control topology is analyzed by a simulation study that is performed on the manipulator. The simulation study verifies that the proposed controller is not only promising to be implemented on the KNTU CDRPM, but also being suitable for other cable driven manipulators.

2010ConferencePDFParallel and Cable Robotics
Model predictive control of non-linear discrete time systems: a linear matrix inequality approach
N. Poursafar, H.D. Taghirad, M. Haeri
IET Control Theory & Applications
Abstract:

Using a non-linear model in model predictive control (MPC) changes the control problem from a convex quadratic programme to a non-convex non-linear problem, which is much more challenging to solve. In this study, we introduce an MPC algorithm for non-linear discrete-time systems. The systems are composed of a linear constant part perturbed by an additive state-dependent non-linear term. The control objective is to design a state-feedback control law that minimises an infinite horizon cost function within the framework of linear matrix inequalities. In particular, it is shown that the solution of the optimisation problem can stabilise the non-linear plants. Three extensions, namely, application to systems with input delay, non-linear output tracking and using output-feedback, are followed naturally from the proposed formulation. The performance and effectiveness of the proposed controller is illustrated with numerical examples.

2010JournalPDFDynamical Systems Analysis and Control
Disturbance Retrieving Unknown Input Proportional Integral Observer for Generalized Linear Systems
M.M. Share Pasand and H.D. Taghirad
ICCAS 2010
Abstract:

An unknown input retrieving observer scheme is proposed which not only decouples unknown inputs in estimation but also gives an estimation of the decoupled input. The provided method benefits from its low computational cost as well as its less restrictive existence conditions compared to existing ones.

2010ConferencePDFDynamical Systems Analysis and Control
Forward Kinematic Analysis of A Planar Cable Driven Redundant Parallel Manipulator Using Force Sensors
Reza Oftadeh, Mohammad M. Aref, and Hamid D. Taghirad
IEEE/RSJ International Conference on Intelligent Robots and Systems
Abstract:

Newly developed cable driven redundant parallel manipulators (CDRPM) have numerous advantages compared to that of the conventional parallel mechanisms. However, there exist some challenging issues in over-constrained mechanisms like CDRPMs. In contrast to serial manipulators, complexity of parallel manipulator forward kinematics (FK) is one of the main issues being under study in the control of such manipulators. Moreover, using extra sensory data is a common approach in the FK solution of rigid-linked parallel manipulators, which is considered by fewer researchers for CDRPMs. In this paper, tension force sensors of the cables are used as an extra sensor to simplify analytical solution of the FK for a planar CDRPM. To find a suitable solution, geometrical and physical characteristics of the robot are analyzed. It is shown that the proposed method provides the required accuracy and significantly improves the process time compared to the conventional methods.

2010ConferencePDFParallel and Cable Robotics
Explicit Dynamics Formulation of Stewart–Gough Platform: A Newton–Euler Approach
Reza Oftadeh, Mohammad M. Aref and Hamid D. Taghirad
IEEE/RSJ International Conference on Intelligent Robots and Systems
Abstract:

Dynamic analysis of parallel manipulators plays a vital role in the design and control of such manipulators. Closed-chain kinematic structure affects the dynamics formulations by several constraints. Therefore, especially for higher degrees of freedom manipulators, manipulation of implicit and bulky dynamics formulation looses the tractability of the analysis. In this paper, a methodology and some simplification tools are introduced to achieve explicit dynamics formulation for parallel manipulators. This methodology is applied for the dynamics analysis of the most celebrated parallel manipulator, namely Stewart-Gough platform. By avoiding any recursive or component-wise derivations, the resulting dynamics formulation provides more insight for designers, and can be much easier used in any model-based control of such manipulators. In order to verify the resulting dynamics equations, Lagrange method is used to derive and compare the manipulator mass matrix. This methodology can be further used to formulate the explicit dynamics of other parallel manipulators.Dynamic analysis of parallel manipulators plays a vital role in the design and control of such manipulators. Closed-chain kinematic structure affects the dynamics formulations by several constraints. Therefore, especially for higher degrees of freedom manipulators, manipulation of implicit and bulky dynamics formulation looses the tractability of the analysis. In this paper, a methodology and some simplification tools are introduced to achieve explicit dynamics formulation for parallel manipulators. This methodology is applied for the dynamics analysis of the most celebrated parallel manipulator, namely Stewart-Gough platform. By avoiding any recursive or component-wise derivations, the resulting dynamics formulation provides more insight for designers, and can be much easier used in any model-based control of such manipulators. In order to verify the resulting dynamics equations, Lagrange method is used to derive and compare the manipulator mass matrix. This methodology can be further used to formulate the explicit dynamics of other parallel manipulators.

2010ConferencePDFParallel and Cable Robotics
Delay-Dependent H-Infinity Control of Linear Systems with input Delay Using Composite State-Derivative Feedback
A. Shariati, H. D Taghirad and B. Labibi
Iranian Conference on Electrical Engineering
Abstract:

H-Infinity control problem for input-delayed systems is considered in this paper. A composite state-derivative control law is used, in which, a composition of the state variables and their derivatives appear in the control law. Thus, the resulting closed-loop system turns into a specific time-delay system of neutral type. The significant specification of this neutral system is that its delayed term coefficients depend on the control law parameters. This condition provides new challenging issues which has its own merits in theoretical research as well as application aspects. New delay-dependent sufficient condition for the existence of H ? controller in terms of matrix inequalities is derived in the present paper. The resulting H-Infinity controller guarantees asymptotic stability of the closed-loop system as well as a guaranteed limited H ? norm smaller than a prescribed level. Numerical examples are presented to illustrate the effectiveness of the proposed methods.

2010ConferencePDFDynamical Systems Analysis and Control
Kinematic analysis of 5-RPUR (3T2R) parallel mechanisms
Mehdi Tale Masouleh, Clément Gosselin, Mohammad Hossein Saadatzi, Xianwen Kong, Hamid D. Taghirad
Parallel Manipulators
Abstract:

This paper investigates some kinematic properties of a five-degree-of-freedom parallel mechanism generating the 3T2R motion and comprising five identical limbs of the RPUR type. The general mechanism originates from the type synthesis performed for symmetrical 5-DOF parallel mechanism. In this study, two classes of simplified designs are proposed whose forward kinematic problem have either a univariate or a closed-form solution. The principal contributions of this study are the solution of the forward kinematic problem for some simplified designs—which may have more solutions than the FKP of the general 6-DOF Stewart platform with 40 solutions—and the determination of the constant-orientation workspace which is based on the topology of the vertex space (Bohemian dome) and a geometric constructive approach.

2010JournalPDFParallel and Cable Robotics
Delay-Dependent H-Infinity Control of Linear Systems with Time-Varying Delays Using Proportional-Derivative State Feedback
A. Shariati, H. D Taghirad and B. Labibi
Control & Automation (MED)
Abstract:

This paper considers H-Infinity control problem for input-delayed systems for time-varying delays. A proportional-derivative state feedback control law is used in this paper. By this means, the resulting closed-loop system turns into a specific time-delay system of neutral type. The significant specification of this neutral system is that its delayed term coefficients depend on the controller parameters. This condition provides new challenging issues in theoretical research as well as providing new applications. In the present paper, new delay-dependent sufficient condition is derived for the existence of H-Infinity controller in terms of matrix inequalities, in presence of varying time-delays. The resulting H-Infinity controller guarantees asymptotic stability of the closed-loop system as well as a guaranteed limited system induced norm smaller than a prescribed level. Numerical examples are presented to illustrate the effectiveness of the proposed method.

2010ConferencePDFDynamical Systems Analysis and Control
Identifying a two linked robot with non-symmetrical modified friction and Backlash-flexibility models
J. Bahrami, Me. Keshmiri, Mo. Keshmiri and H. D. Taghirad
2010 IEEE International Conference on Robotics and Biomimetics
Abstract:

Identifying a robotic system, especially in presence of some nonlinear phenomena, such as friction and backlash, is a troublesome problem. In this paper, initially single link parameter identification is discussed. Parameters such as actuators parameter, link inertia, friction and backlash are identified in this section. A combination of actuator's model and a model of two flexible masses in attendance of friction and backlash is utilized for this purpose. Identifying two link robot parameters will be under debate afterwards and identification results for the second link are presented in three distinct forms. Furthermore, a method is introduced for selecting best estimated parameters set, in order to be exerted on systems controller. The effects of identified friction torques and backlash modeling on controller improvement are presented. Grey box structure model, available in Matlab's system identification tool box is utilized in this research.

2010ConferencePDF
Vision-Based Fuzzy Navigation of Mobile Robots in Grassland Environments
A. R. Norouzzadeh Ravari, H. D. Taghirad, A. H. Tamjidi
Advanced Intelligent Mechatronics
Abstract:

In this paper a vision-based algorithm for mobile robot navigation in unknown outdoor environments is proposed. It is based on a simple phenomenon, that when the robot moves forward, projected images of the near obstacles grow in captured frames faster than that of the far objects. The proposed algorithm takes advantage of this property and extracts features from each grabbed frame of the camera and tracks the vertical position of the features and their speed along the Y axis of the image plane over multiple frames as the robot moves. The relative height of the features and their distance from the robot in 3D is inferred based on this data and they are fed into a fuzzy reasoning system which marks the features from safe to unsafe according to their suitability for navigation. Then a second fuzzy system summarizes these scores in different image regions and directs the robot toward the area containing more features marked as safe. Simulation and implementation results confirm the efficacy of the proposed simple algorithm for mobile robot navigation in outdoor environments.

2009ConferencePDFAutonomous Robotics
Line Matching Localization and Map Building with Least Square
E. Mihankhah, H.D. Taghirad, A. Kalantari, E. Aboosaeedan, H. Semsarilar
2009 IEEE/ASME International Conference on Advanced Intelligent Mechatronics
Abstract:

We introduce a very fast and robust localization and 2D environment representation algorithm in this paper. This innovative method matches lines extracted from the LASER range finder distance data with the lines that construct the map, in order to calculate the local translation and rotation. This matching is done with a simple least square with no iterations. The algorithm is suitable for any indoor environment with mostly polygonal structure and has proven high speed and robustness in the experimental tests on our innovatively designed tracked mobile rescue robot ldquoSilverrdquo. One experimental test is presented in the last section of this paper where the outputs are presented. These outputs are: 1-drift free raster map made of points and 2- A gallery of lines providing a linear ground truth.

2009ConferencePDFAutonomous Robotics
Wrench Feasible Workspace Analysis of Cable-Driven Parallel Manipulators Using LMI Approach
Azadeh Zarif Loloei, Mohamad M. Aref, and Hamid D. Taghirad
Advanced Intelligent Mechatronics
Abstract:

Workspace analysis is one of the most important issues in robotic manipulator design. This paper introduces a systematic method of analysis the wrench feasible workspace for general redundant cable-driven parallel manipulators. In this method, wrench feasible workspace is formulated in term of linear matrix inequalities and projective method is used for solving them. This method is one of the most efficient interior-point methods with a polynomial-time complexity. Moreover, the notion of dexterous workspace is defined, which can be determined for redundant cable driven manipulators exerting a worst case external wrench at the end effector. A detailed case study of the wrench feasible workspace and dexterous workspace determination are included for a six DOF, eight actuated cable-driven redundant parallel manipulator.

2009ConferencePDFParallel and Cable Robotics
Robust H-Infinity Filtering for Nonlinear Uncertain Systems Using State-Dependent Riccati Equation Technique
Hossein Beikzadeh and Hamid D. Taghirad
Proceedings of the IEEE Conference on Decision and Control
Abstract:

The standard state-dependent Riccati equation (SDRE) filter, which is set up by direct SDC parameterization, demands complete knowledge of the system model, and the disturbance inputs characteristics. However, this inherent dependency can severely degrade its performance in practical applications. In this paper, based on the H ¿ norm minimization criterion, a robust SDRE filter is proposed to effectively estimate the states of nonlinear uncertain systems exposed to unknown disturbance inputs. Considering a Lipschitz condition on the chosen SDC form, we guarantee fulfillment of a modified H ¿ performance index by the proposed filter. The effectiveness of the robust SDRE filter is demonstrated through numerical simulations where it brilliantly outperforms the usual SDRE filters in presence of model uncertainties as well as process and measurement noises.

2009ConferencePDF
Analysis OF First Order Systems With Variable Time Delay Using PI Controller and Smith Predictor
Abdolvahed Saeidi, Hamid D.Taghirad
Proceedings of the IASTED International Conference on Modelling, Simulation, and Identification
Abstract:

Smith predictor is one of the first structures used to compensate the time delay in closed loop systems. One of the simplest controllers which are used to control the industrial systems is PID controller. Although, we know that the derivative term is rarely used for controlling the time delay systems. Subtle identification of time delay is usually impossible in reality; on the other hand, PI controller design with smith structure is practiced upon the open loop delay free system. Therefore the structural uncertainty will be existed in open loop systems which make the designing of the PI controller very difficult. In this paper, at first, we analyze the effect of difference between modeled time delay and real time delay on the PI parameters, then the performance of the closed loop system compared with a second order delay free system is investigated; and finally, we compare the tracking of variable time delay system with fixed time delay system which both of them have the same parameters. In this analysis we assume that the fixed time delay is max of variable time delay.

2009ConferencePDF
Stability Analysis of the Discrete-Time Difference SDRE State Estimator in a Noisy Environment
Hossein Beikzadeh and Hamid D. Taghirad
2009 IEEE International Conference on Control and Automation
Abstract:

The state-dependent Riccati equation filter (SDREF) is a recent nonlinear estimation technique which has yielded a number of impressive results. However, the theoretical investigations of the filter have been carried out only in a deterministic environment. In this paper a discrete time difference SDRE-based observer for general nonlinear systems in a stochastic framework is considered, and its error behavior has been also analyzed. It is proved that, the estimation error remains bounded in mean square if the system to be observed satisfies certain conditions, and both the initial estimation error and the disturbing noise terms are small enough. Moreover, the results are verified thorough a simulation study of an example system.

2009ConferencePDF
Delay-Dependent Stabilization of Linear Input-Delayed Systems with Composite State-Derivative Feedback: Constant and Time-Varying Delays
A. Shariati, H.D Taghirad and B. Labibi
Iranian Conference on Electrical Engineering
Abstract:

This paper considers stability problem for input- delayed systems for both constant and time-varying delay case. A new composite state-derivative control law is introduced, in which, a composition of the state variables and their derivatives appear in control law. By this means, the resulting closed-loop system becomes a particular time-delay system of neutral type. The significant specification of this neutral system is that its delayed term coefficients depend on the control law's parameters. This condition provides new challenging issues which has its own merits in theoretical as well as practical aspects. In the present paper, new delay-dependent sufficient conditions are derived in presence of both constant and varying time-delay in terms of matrix inequalities. The resulting controllers guarantee asymptotic stability of the closed-loop system. Simulation studies are presented to verify the stability conditions obtained within the theorems.

2009ConferencePDFDynamical Systems Analysis and Control
Kinematics and Jacobian Analysis of the KNTU CDRPM: A Cable Driven Redundant Parallel Manipulator
Mohammad M. Aref, Reza Oftadeh and Hamid D. Taghirad
Iranian Conference on Electrical Engineering, ICEE
Abstract:

KNTU CDRPM is a cable driven redundant parallel manipulator, which is under investigation for possible implementation in large workspace applications. This type newly developed manipulator has numerous advantages compared to that of the conventional parable mechanisms. The rotational motion range is relatively large, the inherent redundancy improves dexterity of the manipulator, and the light weight structure makes the robot more energy efficient and significantly fast. However, there exist some challenging issues in the over-constrained mechanism like KNTU CDRPM. Collision avoidance, force feasibility, and linear independency of the cables are the main issues being under study in the design of such manipulators. In this paper, singularity of the KNTU CDRPM is studied in detail. To extract kinematic properties of the robot, the inverse and forward kinematics are analyzed. It is shown that singularity analysis can well describe the characteristics of the design and provide the sufficient means to the designer to improve these characteristics. Finally, a suitable design strategy is proposed to significantly reduce the singularity of the manipulator within its whole workspace. The outcomes of this strategy implemented on KNTU CDRPM result in a significant improvement of the singular free workspace of the proposed design compared to that of the latest parallel manipulators.

2009ConferencePDFParallel and Cable Robotics
Nonlinear Sensorless Speed Control of PM Synchronous Motor via an SDRE Observer Controller Combination
Hossein Beikzadeh and Hamid D. Taghirad
Industrial Electronics and Applications, ICIEA 2009
Abstract:

In this paper, a nonlinear control approach for permanent magnet synchronous motor (PMSM) drives, without mechanical sensors, is presented. The proposed method is based on a combination of the well-known nonlinear regulation technique, state-dependent Riccati equation (SDRE), and its filtering counterpart (SDREF) which is derived by constructing the dual of this control method. The SDREF is designed for online estimation of the rotor speed, position and also the load torque by only measuring the motor voltages and currents. The estimated values are applied in the controller structure as state variables. We demonstrate the performance and applicability of this new nonlinear control for PMSM derives by an illustrative simulation in presence of variable load torque. The sensitivity and robustness of the proposed method are also investigated for the motor parameters variations.

2009ConferencePDF
Adaptive Cascade Control of the KNTU CDRPM: A Cable Driven Redundant Parallel Manipulator
Pooneh Gholami, Mohammad M. Aref and Hamid D. Taghirad
Intelligent Robots and Systems, 2008. IROS
Abstract:

The challenging control problem of the cable driven redundant manipulators is due to the complexity of its dynamic and the required stringent performance for the its promising applications. This paper presents an approach to the control of the KNTU CDRPM using an adaptive cascade control scheme. The goal in this approach is achieving accurate trajectory tracking while assuring positive tension in the cables. The cascade control topology uses two loops, namely the internal and external loops. The inherent nonlinear behavior of the cable manipulator is controlled by the internal loop, while the external loop can effectively reduce the target tracking errors of the end-effector in the presence of disturbance force/torques. The cascade strategy reduces the tracking error by 80% compared to that of a single loop controller in the KNTU CDRPM. Moreover, adaptation of the cascade controller gains can significantly improve the overall tracking performance. The closed-loop performance of various control topologies are analyzed by a simulation study that is performed on the KNTU CDRPM. Since, the dynamic equations of this parallel manipulator is implicit in its general form, special integration routines are used for integration. The simulation study verifies that the proposed controller is not only promising to be implemented on the KNTU CDRPM, but also being suitable for other cable driven manipulators.

2009ConferencePDFParallel and Cable Robotics
Optimal Design of Dexterous Cable Driven Parallel Manipulators
Mohammad M. Aref, Hamid D. Taghirad and Sasan Barissi
International Journal of Robotics
Abstract:

Optimal design of parallel manipulators is known as a challenging problem especially for cable driven robots. In this paper, optimal design of cable driven redundant parallel manipulators (CDRPM) is studied in detail. Visual Inspection method is proposed as a systematic design process of the manipulator. A brief review of various design criteria shows that the optimal design of a CDRPM cannot be performed based on single objective. Therefore, a multi objective optimal design problem is formulated in this paper through an overall cost function. Furthermore, a proper weighting selection for the overall cost function is proposed, which can be viewed as a promising method to the open problem of parallel manipulator design. In order to verify the effectiveness of the proposed method, it is applied on the design of KNTU CDRPM, an eight actuated with six degrees of freedom CDRPM, which is under investigation for possible high speed and wide workspace applications in K.N. Toosi University of Technology. Finally, a combined numerical optimization algorithm is used to find the unique global optimum point. The result shows a significant enhancement in the performance characteristics of the KNTU CDRPM compared to that of the other CDRPMs. Since the proposed method is not restricted to any particular assumption on the objectives and design parameters, it can be used for optimal design of other manipulators.

2009JournalPDFParallel and Cable Robotics
On the Consistency of EKF-SLAM: Focusing on the Observation Models
Amirhossein Tamjidi, Hamid D. Taghirad, Aliakbar Aghamohammadi
Intelligent Robots and Systems
Abstract:

In this paper a new strategy for handling the observation information of a bearing-range sensor throughout the filtering process of EKF-SLAM is proposed. This new strategy is advised based on a thorough consistency analysis and aims to improve the process consistency while reducing the computational cost. At first, three different possible observation models are introduced for the EKF-SLAM solution for a robot equipped with a bearing-range sensor. General form of the covariance matrix and the level of inconsistency in the robot orientation estimate is then calculated for these variants, and based on the numerical comparison of the estimation results, it is proposed to use the bearing and range information of a feature in the initialization step of EKF-SLAM. However, it is recommended to use only the bearing information to perform other iteration steps. The simulation observations verify that the new strategy yields to more consistent estimates both for the robot and the features. Moreover, through the proposed consistency analysis, it is shown that since the source of consistency improvement is independent from the choice of the motion model, it gives us an advantage over other existing methods that assume a specific motion models for consistency improvement.

2009ConferencePDF
Fuzzy error governor: A practical approach to counter actuator saturation on flexible joint robots
S. Ozgoli, H.D. Taghirad
Mechatronics
Abstract:

In this paper, a practical method to counter actuator saturation based on a fuzzy error governor is developed and a complete case study is considered. In addition to good performance, the method has two attracting properties: It does not change the structure of the main controller, and therefore, the theoretically proven characteristics of the system are untouched, and it is simply implementable in practice. The proposed controller structure is applied on a flexible joint robot (FJR). The robust stability of the closed loop system for an n-DOF FJR is thoroughly analyzed and the proposed controller is implemented on a laboratory setup to show the ease of implementation and the resulting closed-loop performance. The main controller used for the n-DOF FJR consists of a composite structure, with a PD controller on the fast dynamics and a PID controller on the slow dynamics. The bandwidth of the fast controller is decreased during critical occasions with the fuzzy logic supervisor, which adjusts the loop gain to a proper level. Using Lyapunov direct method, the robust stability of the overall system is analyzed in presence of modeling uncertainties, and it is shown that if the PD and the PID gains are tuned to satisfy certain conditions, the closed loop system becomes UUB stable.

2009JournalPDFFlexible Robotics
A novel hybrid Fuzzy-PID controller for tracking control of robot manipulators
A. R. Norouzzadeh Ravari, H.D. Taghirad
2008 IEEE International Conference on Robotics and Biomimetics
Abstract:

In this paper, a novel hybrid fuzzy proportional-integral-derivative (PID) controller based on learning automata for optimal tracking of robot systems including motor dynamics is presented. Learning automata is used at the supervisory level for adjustment of the parameters of hybrid Fuzzy-PID controller during the system operation. The proposed method has better convergence rate in comparison with standard back-propagation algorithms, less computational requirements than adaptive network based fuzzy inference systems (ANFIS) or neural based controllers and having the ability of working in uncertain environments without any previous knowledge of environments' parameters. The proposed controller has been successfully applied in simulation to control a 6-DOF Puma 560 manipulator using robotic toolbox, and has satisfactory results. In this simulation also, external disturbance and noise are addressed. The result of simulation has also shown that the rate of convergence and robustness of the designed controller guarantees practical stability.

2009ConferencePDFAutonomous Robotics
Autonomous Staircase Detection and Stair Climbing for a Tracked Mobile Robot using Fuzzy Controller
E. Mihankhah, A. Kalantari, E. Aboosaeedan, H.D. Taghirad, and S.Ali.A. Moosavian
2008 IEEE International Conference on Robotics and Biomimetics
Abstract:

Theoretical analysis and implementation of autonomous staircase detection and stair climbing algorithms on a novel rescue mobile robot are presented in this paper. The main goals are to find the staircase during navigation and to implement a fast, safe and smooth autonomous stair climbing algorithm. Silver is used here as the experimental platform. This tracked mobile robot is a tele-operative rescue mobile robot with great capabilities in climbing obstacles in destructed areas. Its performance has been demonstrated in rescue robot league of international RoboCup competitions. A fuzzy controller is applied to direct the robot during stair climbing. Controller inputs are generated by processing the range data from two laser range finders which scan the environment one horizontally and the other vertically. The experimental results of stair detection algorithm and stair climbing controller are demonstrated at the end.

2009ConferencePDFAutonomous Robotics
Dynamic Analysis of a Macro–Micro Redundantly Actuated Parallel Manipulator
Hamid D. Taghirad and Meyer A. Nahon
Advanced Robotics
Abstract:

In this paper the dynamic analysis of a macro–micro parallel manipulator is studied in detail. The manipulator architecture is a simplified planar version adopted from the structure of the Large Adaptive Reflector (LAR), the Canadian design of next-generation giant radio telescopes. In this structure it is proposed to use two parallel redundant manipulators at the macro and micro level, both actuated by cables. In this paper, the governing dynamic equation of motion of such a structure is derived using the Newton–Euler formulation. Next, the dynamic equations of the system are used in the open-loop inverse dynamics simulations, as well as closed-loop forward dynamics simulations. In the open-loop dynamic simulations it is observed that the inertial forces of the limbs contribute only 10% of the dynamic forces required to generate a typical trajectory and, moreover, the total dynamic forces contribute only 10% of the experimentally measured disturbance forces. Furthermore, in the closed-loop simulations using decentralized PD controllers at the macro and micro levels, it is shown that the macro–micro structure results in a 10 times more accurate positioning than that in the first stage of the macro–micro structure. This convincing result promotes the use of the macro–micro structure for LAR application.

2008JournalPDFParallel and Cable Robotics
Kinematic Analysis of a Macro–Micro Redundantly Actuated Parallel Manipulator
Hamid D. Taghirad and Meyer Nahon
Advanced Robotics
Abstract:

In this paper the kinematic and Jacobian analysis of a macro–micro parallel manipulator is studied in detail. The manipulator architecture is a simplified planar version adopted from the structure of the Large Adaptive Reflector (LAR), the Canadian design of the next generation of giant radio telescopes. This structure is composed of two parallel and redundantly actuated manipulators at the macro and micro level, which both are cable-driven. Inverse and forward kinematic analysis of this structure is presented in this paper. Furthermore, the Jacobian matrices of the manipulator at the macro and micro level are derived, and a thorough singularity and sensitivity analysis of the system is presented. The kinematic and Jacobian analysis of the macro–micro structure is extremely important to optimally design the geometry and characteristics of the LAR structure. The optimal location of the base and moving platform attachment points in both macro and micro manipulators, singularity avoidance of the system in nominal and extreme maneuvers, and geometries that result in high dexterity measures in the design are among the few characteristics that can be further investigated from the results reported in this paper. Furthermore, the availability of the extra degrees of freedom in a macro–micro structure can result in higher dexterity provided that this redundancy is properly utilized. In this paper, this redundancy is used to generate an optimal trajectory for the macro–micro manipulator, in which the Jacobian matrices derived in this analysis are used in a quadratic programming approach to minimize performance indices like minimal micro manipulator motion or singularity avoidance criterion.

2008JournalPDFParallel and Cable Robotics
Parametric spectral analysis of nonstationary fluctuations of excitatory synaptic currents
M. I. Glavinovic, P. Gooria, F. Aristizabal, H. Taghirad
Biological Cybernetics
Abstract:

We assessed on Monte-Carlo simulated excitatory post-synaptic currents the ability of autoregressive (AR)-model fitting to evaluate their fluctuations. AR-model fitting consists of a linear filter describing the process that generates the fluctuations when driven with a white noise. Its fluctuations provide a filtered version of the signal and have a spectral density depending on the properties of the linear filter. When the spectra of the non-stationary fluctuations of excitatory post-synaptic currents were estimated by fitting AR-models to the segments of current fluctuations, assumed to be stationary and independent, the parameter and spectral estimates were scattered. The scatter was much reduced if the time-variant AR-models were fitted using stochastic adaptive estimators (Kalman, recursive least squares and least mean squares). The ability of time-variant AR-models to accurately fit the current fluctuations was monitored by comparing the fluctuations with predicted fluctuations, and by evaluating the model-learning rate. The median frequency of current fluctuations, which could be rapidly tracked and estimated from the individual quantal events (either Monte-Carlo simulated or recorded from pyramidal neurons of rat hippocampus), rose during the rise phase, before declining to a lower steady-state level during the decay phase of quantal event, whereas the variance showed a broad peak. The closing rate of AMPA channels directly affects the steady-state median frequency, whereas the transient peak can be modulated by a variety of factors—number of molecules released, ability of glutamate molecules to re-enter the synaptic cleft, diffusion constant of glutamate in the cleft and opening rate of AMPA channels. In each case, the effect on the amplitude and decay time of mEPSCs and on the current fluctuations differs. Each factor thus leaves its own kinetic fingerprint arguing that the contribution of such factors can be inferred from the combined kinetic properties of individual mEPSCs.

2008JournalPDF
Dynamics Analysis of A Redundant Parallel Manipulator Driven By Elastic Cables
Y. Babazadeh Bedoustani, H. D. Taghirad and M. M. Aref
2008 10th International Conference on Control, Automation, Robotics and Vision
Abstract:

In this paper the dynamic analysis of a cable-driven parallel manipulator is studied in detail. The manipulator architecture is a simplified planar version adopted from the structure of large adaptive reflector (LAR), the Canadian design of next generation giant radio telescopes. This structure consists of a parallel redundant manipulator actuated by long cables. The dynamic equations of this structure are nonlinear and implicit. Long cables, large amounts of impelling forces and high accelerations raise more concern about the elasticity of cables during dynamic analysis, which has been neglected in the preceding works. In this paper, the kinematic analysis of such manipulator is illustrated first. Then the nonlinear dynamic of such mechanism is derived using Newton-Euler formulation. Next a simple model for cable dynamics containing elastic and damping behavior is proposed. The proposed model neither ignores longitude elasticity properties of cable nor makes dynamic formulations heavily complicated like previous researches. Finally, manipulator dynamic with cable dynamic is derived, and the cable elasticity effects are compared in a simulation study. The results show significant role of elasticity in a cable-driven parallel manipulator such as the one used in LAR mechanism.

2008ConferencePDFParallel and Cable Robotics
Dynamic Analysis of the KNTU CDRPM: A Cable Driven Redundant Parallel Manipulator
Pooneh Gholami, Mohammad M. Aref and Hamid D. Taghirad
2008 IEEE/ASME International Conference on Mechtronic and Embedded Systems and Applications
Abstract:

KNTU CDRPM is a cable driven redundant parallel manipulator, which is under investigation for possible implementation of large workspace applications. This newly developed manipulators have several advantages compared to the conventional parable mechanisms. In this paper, the governing dynamic equation of motion of such structure is derived using the Newton-Euler formulation. Next, the dynamic equations of the system are used in simulations. It is shown that on the contrary to serial manipulators, dynamic equations of motion of cable-driven parallel manipulators can be only represented implicitly, and only special integration routines can be used for their simulations. In order to verify the accuracy and integrity of the derived dynamic equations, open- and closed-loop simulations for the system is performed and analyzed. Also, the effects of mechanical assembly tolerances on the closed-loop control performance of a cable driven parallel robot are studied in detail, and the sensitivity analysis of the precision in the construction and assembly of the system on the closed-loop behavior of the KNTU CDRPM is performed.

2008ConferencePDFParallel and Cable Robotics
Robust Performance Verification of Adaptive Robust Controller for Hard Disk Drives
Hamid D. Taghirad and Ehsan Jamei
IEEE Transactions on Industrial Electronics
Abstract:

An adaptive robust controller (ARC) has been recently developed for read/write head embedded control systems of hard disk drives (HDDs). This structure is applicable to both track seeking and track following modes, and it makes the mode switching control algorithms found in conventional HDD servosystems unnecessary. An Improved Desired Compensation ARC (IDCARC) scheme is proposed in this paper, in which the traditional ARC is powered by a dynamic adaptive term. In this approach the adaptation regressor is calculated using reference trajectory information. Moreover, a robust analysis of this method is developed, in which a controller designed based on a simple model of the system is verified in a closed loop performance of a more comprehensive model of the system. The simulation result verifies the significant improvement of the performance of IDCARC compared to that of ARC and its robustness for this model. It is observed that in the presence of large disturbances the proposed method preserves the stability and a suitable performance while the ARC fails even in stability.

2008JournalPDFHard Disk Drives Control
SLAM Using Single Laser Range Finder
AliAkbar Aghamohammadi, Amir H. Tamjidi, Hamid D. Taghirad
IFAC Proceedings Volumes
Abstract:

Presented method in this paper aims to develop an accurate motion model and SLAM algorithm, which is only based on the Laser Range Finder (LRF) data. Proposed method tries to overcome some practical problems in traditional motion models and SLAM approaches, such as robot slippage, and inaccuracy in parameters related to robot's hardware. Novel insights specific to process and measurement model, and making use of them in the IEKF framework, give rise to the real time method with drift-free performance in restricted environments. Furthermore, uncertainty measures, calculated through the method, are valuable information for fusion purposes and also an accurate motion model, derived in this method, can be used as a robust and an accurate localization procedure in different structured environments. These issues are validated through experimental implementations; experiments verify method's efficiency both in pure localization and in SLAM scenarios in the restricted environments, involving loop closures.

2008ConferencePDFAutonomous Robotics
A Solution for SLAM through Augmenting Vision and Range Information
Ali A. Aghamohammadi, Amir H. Tamjidi, Hamid D. Taghirad
2008 IEEE/RSJ International Conference on Intelligent Robots and Systems
Abstract:

This paper proposes a method for augmenting the information of a monocular camera and a range finder. This method is a valuable step towards solving the SLAM problem in unstructured environments free from problems of using encoderspsila data. Proposed algorithm causes the robot to benefit from a feature-based map for filtering purposes, while it exploits an accurate motion model, based on point-wise raw range scan matching rather than unreliable feature-based range scan matching, in unstructured environments. Moreover, robust loop closure detection procedure is the other consequence of this method. Experiments with a low-cost IEEE 1394 webcam and a range finder illustrate the effectiveness of the proposed method in drift-free SLAM at loop closing motions in unstructured environments.

2008ConferencePDFAutonomous Robotics
On The Control of the KNTU CDRPM: A Cable Driven Redundant Parallel Manipulator
Pooneh Gholami, Mohammad M. Aref and Hamid D. Taghirad
2008 IEEE/RSJ International Conference on Intelligent Robots and Systems
Abstract:

This paper is devoted to the control of a cable driven redundant parallel manipulator, which is a challenging problem due the optimal resolution of its inherent redundancy. Additionally to complicated forward kinematics, having a wide workspace makes it difficult to directly measure the pose of the end-effector. The goal of the controller is trajectory tracking in a large and singular free workspace, and to guarantee that the cables are always under tension. A control topology is proposed in this paper which is capable to fulfill the stringent positioning requirements for these type of manipulators. Closed-loop performance of various control topologies are compared by simulation of the closed-loop dynamics of the KNTU CDRPM, while the equations of parallel manipulator dynamics are implicit in structure and only special integration routines can be used for their integration. It is shown that the proposed joint space controller is capable to satisfy the required tracking performance, despite the inherent limitation of task space pose measurement.

2008ConferencePDFParallel and Cable Robotics
Geometrical Workspace Analysis of a Cable-Driven Redundant Parallel Manipulator: KNTU CDRPM
Mohammad M. Aref and Hamid D. Taghirad
2008 IEEE/RSJ International Conference on Intelligent Robots and Systems
Abstract:

KNTU CDRPM is a cable driven redundant parallel manipulator, which is under investigation for possible high speed and large workspace applications. This newly developed mechanisms have several advantages compared to the conventional parallel mechanisms. Its rotational motion range is relatively large, its redundancy improves safety for failure in cables, and its design is suitable for long-time high acceleration motions. In this paper, collision-free workspace of the manipulator is derived by applying fast geometrical intersection detection method, which can be used for any fully parallel manipulator. Implementation of the algorithm on the Neuron design of the KNTU CDRPM leads to significant results, which introduce a new style of design of a spatial cable-driven parallel manipulators. The results are elaborated in three presentations; constant-orientation workspace, total orientation workspace and orientation workspace.

2008ConferencePDFParallel and Cable Robotics
H-Infinity Controller Design for A Flexible Joint Robot With Phase Uncertainty
Sh. Dadashi, H. D. Taghirad
International Symposium on Robotics
Abstract:

In this paper, the design and implementation of the H-Infinity controller for flexible joint robot (FJR) is presented and the capability of the controller to deal with actuator saturation is investigated in practice. The new procedure of design is introduced to avoid an instability caused by unmodeled phase behaviour which can not be encapsulated in multiplicative uncertainty. In order to avoid instability caused by unmodeled phase behaviour, the robust controller design is divided into two stages: H-Infinity controller design and checking closed loop sensitivity function. Simulation results reveal the capability of the controller to stabilize the closed loop system and to reduce the tracking error in the presence of the actuator limitation.

2008ConferencePDFFlexible Robotics
Dynamic and Sensitivity Analysis of KNTU CDRPM: A Cable Driven Redundant Parallel Manipulator
Mohammad M. Aref, Pooneh Gholami and Hamid D. Taghirad
2008 IEEE/ASME International Conference on Mechtronic and Embedded Systems and Applications
Abstract:

KNTU CDRPM is a cable driven redundant parallel manipulator, which is under investigation for possible implementation of large workspace applications. This newly developed manipulators have several advantages compared to the conventional parable mechanisms. In this paper, the governing dynamic equation of motion of such structure is derived using the Newton-Euler formulation. Next, the dynamic equations of the system are used in simulations. It is shown that on the contrary to serial manipulators, dynamic equations of motion of cable-driven parallel manipulators can be only represented implicitly, and only special integration routines can be used for their simulations. In order to verify the accuracy and integrity of the derived dynamic equations, open- and closed-loop simulations for the system is performed and analyzed. Also, the effects of mechanical assembly tolerances on the closed-loop control performance of a cable driven parallel robot are studied in detail, and the sensitivity analysis of the precision in the construction and assembly of the system on the closed-loop behavior of the KNTU CDRPM is performed.

2008JournalPDFParallel and Cable Robotics
Task Based Optimal Geometric Design and Positioning of Serial Robotic Manipulators
Sasan Barissi and Hamid D. Taghirad
Mechtronic and Embedded Systems and Applications
Abstract:

This paper devises a multi-objective cost function which elaborates different constraints as well as an optimality criterion for design of serial robotic manipulators. In practice, inclusion of different constraints drastically limits the possible range of design parameters. The result of minimizing this multi-objective cost function is compared with another method which locates an optimal solution using a graphical representation. The effectiveness of the proposed cost function is demonstrated by a unified solution for both methods. In addition, possible tolerance of design parameters is compensated by considering a neighborhood around these parameters. Through an illustrative example, it is shown that the inclusiveness and flexibility of the proposed method makes it suitable for geometric design optimization of robotic manipulators.

2008JournalPDFParallel and Cable Robotics
Adaptive Robust Controller Design for a Dual Stage Hard Disk Drive
Hamid D. Taghirad and P. Sheykholeslami
Advanced intelligent mechatronics
Abstract:

In this paper, adaptive robust controllers are proposed for dual-stage hard disk drives. An improved desired compensation ARC (IDCARC) scheme is proposed in this paper for both actuators of the system, in which the traditional ARC is powered by a dynamic adaptive term. Moreover, a simulation study of these controllers are presented, in which the controllers designed based on simple models for the subsystem are implemented on a more comprehensive, experimentally verified models of the system. Simulation result verifies the effectiveness of the IDCARC method in providing the required tracking, in presence of unstructured uncertainty for the models.

2007ConferencePDFHard Disk Drives Control
Forward Kinematics of A Macro–Micro Parallel Manipulator
Hamid D. Taghirad and Meyer A. Nahon
Advanced intelligent mechatronics
Abstract:

In this paper the kinematic analysis of a macro-micro parallel manipulator is studied in detail. The manipulator architecture is a simplified planar version adopted from the structure of large adaptive reflector (LAR), the Canadian design of next generation giant radio telescopes. This structure is composed of two parallel and redundantly actuated manipulators at macro and micro level, which both are cable-driven. Inverse and forward kinematic analysis of this structure is presented in this paper. It is shown that unique closed form solution to the inverse kinematic problem of such structure exists. However, the forward kinematic solution is derived using numerical methods, and simulation results are reported to illustrate the integrity and accuracy of the solution.

2007ConferencePDFParallel and Cable Robotics
Parametric spectral analysis of nonstationary fluctuations of excitatory synaptic currents
M. I. Glavinovic, P. Gooria, F. Aristizabal, H. Taghirad
Biological Cybernetics
Abstract:

We assessed on Monte-Carlo simulated excitatory post-synaptic currents the ability of autoregressive (AR)-model fitting to evaluate their fluctuations. AR-model fitting consists of a linear filter describing the process that generates the fluctuations when driven with a white noise. Its fluctuations provide a filtered version of the signal and have a spectral density depending on the properties of the linear filter. When the spectra of the non-stationary fluctuations of excitatory post-synaptic currents were estimated by fitting AR-models to the segments of current fluctuations, assumed to be stationary and independent, the parameter and spectral estimates were scattered. The scatter was much reduced if the time-variant AR-models were fitted using stochastic adaptive estimators (Kalman, recursive least squares and least mean squares). The ability of time-variant AR-models to accurately fit the current fluctuations was monitored by comparing the fluctuations with predicted fluctuations, and by evaluating the model-learning rate. The median frequency of current fluctuations, which could be rapidly tracked and estimated from the individual quantal events (either Monte-Carlo simulated or recorded from pyramidal neurons of rat hippocampus), rose during the rise phase, before declining to a lower steady-state level during the decay phase of quantal event, whereas the variance showed a broad peak. The closing rate of AMPA channels directly affects the steady-state median frequency, whereas the transient peak can be modulated by a variety of factors—number of molecules released, ability of glutamate molecules to re-enter the synaptic cleft, diffusion constant of glutamate in the cleft and opening rate of AMPA channels. In each case, the effect on the amplitude and decay time of mEPSCs and on the current fluctuations differs. Each factor thus leaves its own kinetic fingerprint arguing that the contribution of such factors can be inferred from the combined kinetic properties of individual mEPSCs.

2007JournalPDF
Feature-Based Laser Scan Matching For Accurate and High Speed Mobile Robot Localization
A. A. Aghamohammadi, H. D. Taghirad, A. H. Tamjidi, and E. Mihankhah
Proceedings of the 3rd European Conference on Mobile Robots
Abstract:

This paper introduces an accurate and high speed pose tracking method for mobile robots based on matching of extracted features from consecutive scans. The feature extraction algorithm proposed in this paper uses a global information of the whole scan data and local information around feature points. Uncertainty of each feature is represented using covariance matrices determined due to observation and quantization error. Taking into account each feature's uncertainty in pose shift calculation leads to an accurate estimation of robot pose. Experiments with low range URG_X002 laser range scanner illustrate the effectiveness of the proposed method for mobile robot localization.

2007ConferencePDFAutonomous Robotics
Adaptive Robust Controller Design For Dual-Stage Hard Disk Drives
H. D. Taghirad and P. Sheykholeslami
Advanced intelligent mechatronics
Abstract:

In this paper, adaptive robust controllers are proposed for dual-stage hard disk drives. An improved desired compensation ARC (IDCARC) scheme is proposed in this paper for both actuators of the system, in which the traditional ARC is powered by a dynamic adaptive term. Moreover, a simulation study of these controllers are presented, in which the controllers designed based on simple models for the subsystem are implemented on a more comprehensive, experimentally verified models of the system. Simulation result verifies the effectiveness of the IDCARC method in providing the required tracking, in presence of unstructured uncertainty for the models.

2007ConferencePDFHard Disk Drives Control
Position Controller Synthesis for The Redundant Hydraulic Shoulder Manipulator
H. Sadjadian and H. D. Taghirad
ICEE15
Abstract:

In this paper,positioncontrol has been designed for a 3 DOF actuator redundant sphericnl parallel manipulator.A two norm minimization approach has been used to resolve the actuator redundancy problem. Robust stability of the closed loop system is analyzed considering uncertainties inherent in the dynamic model of the manipulator.A simulation study is also performed to showthe effectiveness of the proposed method. Thc results show the applicability of simple and conventional controllersto control redundant spherical parallel manip lators

2007ConferencePDFParallel and Cable Robotics
Dynamic Analysis of A Redundantly Actuated Parallel Manipulator:A Virtual Work Approach
Hamid D. Taghirad and Meyer Nahon
Advanced Robotics
Abstract:

In this paper the dynamic analysis of a macro–micro parallel manipulator is studied in detail. The manipulator architecture is a simplified planar version adopted from the structure of the Large Adaptive Reflector (LAR), the Canadian design of next-generation giant radio telescopes. In this structure it is proposed to use two parallel redundant manipulators at the macro and micro level, both actuated by cables. In this paper, the governing dynamic equation of motion of such a structure is derived using the Newton–Euler formulation. Next, the dynamic equations of the system are used in the open-loop inverse dynamics simulations, as well as closed-loop forward dynamics simulations. In the open-loop dynamic simulations it is observed that the inertial forces of the limbs contribute only 10% of the dynamic forces required to generate a typical trajectory and, moreover, the total dynamic forces contribute only 10% of the experimentally measured disturbance forces. Furthermore, in the closed-loop simulations using decentralized PD controllers at the macro and micro levels, it is shown that the macro–micro structure results in a 10 times more accurate positioning than that in the first stage of the macro–micro structure. This convincing result promotes the use of the macro–micro structure for LAR application.

2007ConferencePDFParallel and Cable Robotics
A Survey on the Control of Flexible Joint Robots
S. Ozgoli and H. D. Taghirad
Asian Journal of Control
Abstract:

The robotics literature of the last two decades contains many important advances in the control of flexible joint robots. This is a survey of these advances and an assessment for future developments, concentrated mostly on the control issues of flexible joint robots.

2006JournalPDFFlexible Robotics
Mobile Robot Navigation in an Unknown Environment
A. Jazayeri, A.Fatehi, H. Taghirad
2016 IEEE Conference on Control Applications (CCA)
Abstract:

This article focuses on the mobile robot's autonomous navigation problem in an unknown environment. Considering a robot equipped with an omnidirectional range-sensor a map of the discovered area is constructed in an iterative manner. Given a target position located in the unexplored territory, initially a motion planning scheme is employed that relies on exploration-principles of the area near the target. This is achieved by assigning an exploration cost function that indirectly attracts the robot close to target. Upon discovery of the target, the robot moves to it following the shortest-distance path. Simulation studies that prove the efficiency of the overall method are presented.

2006ConferencePDF
Stability analysis and robust composite controller synthesis for flexible joint robots
H. D. Taghirad and M. A. Khosravi
Advanced Robotics
Abstract:

The control of flexible joint manipulators is studied in detail. The model of N-axis flexible joint manipulators is derived and reformulated in the form of singular perturbations, and the integral manifold is used to separate fast dynamics from slow dynamics. A composite control algorithm is proposed for the flexible joint robots, which consists of two main parts. Fast control, u, which guarantees that the fast dynamics remains asymptotically stable, and the corresponding integral manifold remains invariant. Slow control, u, itself consists of a robust PID design based on the rigid model, and a corrective term designed based on the reduced flexible model. The stability of the overall closed loop system is proved to be UUB stable, by Lyapunov stability analysis. Finally, the effectiveness of the proposed control law is verified through simulations. It is shown that the proposed control law ensures robust stability and performance, despite the modeling uncertainties.

2006JournalPDFFlexible Robotics
Kinematic, singularity and stiffness analysis of the hydraulic shoulder: a 3-d.o.f. redundant parallel manipulator
H. Sajadian and H. D. Taghirad
Advanced Robotics
Abstract:

In this paper, kinematic modeling and singularity and stiffness analysis of a 3-d.o.f. redundant parallel manipulator have been elaborated in detail. It is known that, contrary to series manipulators, the forward kinematic map of parallel manipulators involves highly coupled non-linear equations, whose closed-form solution derivation is a real challenge. This issue is of great importance noting that the forward kinematics solution is a key element in closed-loop position control of parallel manipulators. Using the idea of inherent kinematic chains formed in parallel manipulators, both inverse and forward kinematics of the redundant parallel manipulator are fully developed, and a closed-form solution for the forward kinematic map of the parallel manipulator is derived. The closed-form solution is also obtained in detail for the Jacobian of the mechanism and singularity analysis of the manipulator is performed based on the computed Jacobian. Finally, as the first step to develop a control topology based on the overall stiffness property of the manipulator, the stiffness mapping of the manipulator is derived and its configuration dependence is analyzed. It is observed that the actuator redundancy in the mechanism is the major element to improve the Cartesian stiffness and, hence, the dexterity of the hydraulic shoulder. Moreover, loosing one limb actuation reduces the stiffness of the manipulator significantly.

2006JournalPDFParallel and Cable Robotics
Robust H’, H2/H’ Controller for Rotational/Translational Actuator (RTAC)
R. Adlgostar, H. Azimian and H. D. Taghirad
IEEE Conference on Computer Aided Control System Design
Abstract:

In this paper, robust controllers have been proposed for oscillation suppression in the RTAC benchmark problem. A nominal plant and an uncertainty model are extracted out of varieties of linear models, identified for the nonlinear system and the generalized plant for the unstructured uncertainty problem has been presented. Based on passivity, a cascade controller has been designed to reduce amount of uncertainty in lower frequencies. It is verified that through a nonlinear feedback controller in the inner loop, the uncertainty of linear estimates of the system reduces significantly, and becomes plausible to use linear robust techniques such as mixed sensitivity and H 2 /H-Infinity to design controller for the system. Finally H-Infinity and H 2 /H-Infinity controllers have been designed for new generalized plant and results are compared with the previous reports in literature.

2006ConferencePDF
Nonparametric Identification and Robust Hf Controller Synthesis for a Rotational/Translational Actuator
F.Bagheri, S. Purazarm, and H. D. Taghirad
International Journal of Control, Automation, and Systems
Abstract:

The Rotational/Translational Actuator (RTAC) benchmark problem considers a fourth-order dynamical system involving the nonlinear interaction of a translational oscillator and an eccentric rotational proof mass. This problem has been posed to investigate the utility of a rotational actuator for stabilizing translational motion. In order to experimentally implement any of the model-based controllers proposed in the literature, the values of model parameters are required which are generally difficult to determine rigorously. In this paper, an approach to the least-squares estimation of the parameters of a system is formulated and practically applied to the RTAC system. On the other hand, this paper shows how to model a nonlinear system as a linear uncertain system via nonparametric system identification, in order to provide the information required for linear robust H-Infinity control design. This method is also applied to the RTAC system, which demonstrates severe nonlinearities due to the coupling from the rotational motion to the translational motion. Experimental results confirm that this approach can effectively condense the whole nonlinearities, uncertainties, and disturbances within the system into a favorable perturbation block.

2006ConferencePDF
Designing and Implementation of Mixed H2/H-Infinity Controller for Flexible Joint Robot to Encounter Actuator Saturation
S. Ozgoli, H. D. Taghirad
Abstract:

Mixed H2/H-Infinity method is proposed to design and implement a controller for flexible joint robots considering actuator saturation by considering the control action in the mixed sensitivity. A more advanced method based on frequency weighting of the control action contribution in the mixed sensitivity function is considered here which may result higher bandwidth. But this method is also limited and to get better specifications the H2/H-Infinity method is proposed. This methods are shown to be very good remedies for problems caused by actuator saturation in practice. Experimental studies are forwarded to verify the effectiveness and the performance of the proposed controllers in practice.

2006ConferencePDFFlexible Robotics
New Wavelet Based Algorithm for Real Time Visual Tracking
Akram Bayat, Hamid R. Taghirad, Seyyed Sadegh Mottaghian
Abstract:

in this paper, we propose a new technique in wavelet domain for real time object detection and tracking in a sequence of images. The object to be tracked is identified in the first frame. Our proposed algorithm consists of two phases: the first, wavelet based edge detection is used to form ground boundary map. Then, Object dimensions estimation is implemented to determine probabilistic object areas. finally, target detection based on finding best match using feature vectors is applied. We defined dispersion of wavelet detail coefficient in object area as feature to be matched. Also we proposed a new color model for images to be used in processing algorithm. Our experimental results show that the algorithm is robust and fast. It is also insensitive to changing illumination condition and size of target

2006ConferencePDFAutonomous Robotics
Comparison of Different Methods for Computing the Forward Kinematics of a Redundant Parallel Manipulator
H. Sajadian and H. D. Taghirad
Journal of Intelligent and Robotic Systems
Abstract:

In this paper, three numerical methods are presented to solve the forward kinematics of a three DOF actuator-redundant hydraulic parallel manipulator. It is known, that on the contrary to series manipulators, the forward kinematic map of parallel manipulators involves highly coupled nonlinear equations, whose closed-form solution derivation is a real challenge. This issue is of great importance noting that the forward kinematics solution is a key element in closed loop position control of parallel manipulators. The proposed methods, namely the Neural Network Estimation, the Quasi-closed Solution, and the Taylor series approximation, are using mainly numerical computations, with different ideas to solve the problem in hand. The latter two methods are proposed for the first time in literature to solve the forward kinematics of a parallel manipulator. These methods are compared in detail and the advantages or the disadvantages of each method in computing the forward kinematic map of the given mechanism is discussed. It is shown that a 4th order Taylor series approximation to the problem provides a good compromise for practical applications compared to that of other methods considered in this paper.

2006JournalPDFParallel and Cable Robotics
Impedance Control of the Hydraulic Shoulder
H. Sajadian and H. D. Taghirad
International Conference on Robotics and Biomimetics
Abstract:

In this paper, a model-based impedance control strategy is developed for a 3 DOF parallel manipulator to manage the interaction of the robot with the environment. Kinematic and dynamic modeling of the manipulator has been analyzed in order to be used for both simulation and control purposes. The impedance controller objective and the structure of the proposed controller are introduced and controller gain selection is discussed. A simulation study evaluates the effectiveness of the proposed impedance control structure. It is observed that although the proposed controller is designed for impedance adjustment of the robot, in case of free motion, it results into desirable position tracking. Moreover, when the robot comes into contact with the environment, the interaction dynamics can be regulated regardless of the nonlinear dynamics of the robot.

2006ConferencePDFParallel and Cable Robotics
Robust Performance Verification of IDCARC Controller for Hard Disk Drives
H. D. Taghirad and E. Jamei
Abstract:

Adaptive robust controller (ARC) has been recently developed for read/write head embedded control systems of hard disk drives (HDD). This structure is applicable to both track seeking and track following modes, and it makes the mode switching control algorithms found in conventional HDD servo system unnecessary. An Improved Desired Compensation ARC (IDCARC) scheme is proposed in this paper, in which traditional ARC is powered by a dynamic adaptive term. In this approach the adaptation regressor is calculated using reference trajectory information. Moreover, a robust analysis of this method is forwarded, in which a controller designed based on a simple model of system is verified in closed loop performance of a more comprehensive model of the system. Simulation result verifies the significant improvement of the performance of IDCARC compared to that of ARC and its robustness for this model. It is observed that in the presence of large disturbances the proposed method preserves stability and performance while the ARC fails even in stability.

2006JournalPDFHard Disk Drives Control
Robust Controller with a Supervisor Implemented on a Flexible Joint Robot
Hamid D. Taghirad and S.Ozgoli
Control Applications
Abstract:

In this paper a controller for flexible joint robots (FJR) in presence of actuator saturation is proposed, its robust stability is analyzed, and it is implemented on a laboratory FJR. This controller consists of a composite structure, with a PD controller on the fast dynamics and a PID controller on slow dynamics. The need of powerful actuator is released through decrease of fast controller bandwidth at critical occasions. This is done by means of a fuzzy logic supervisory loop. The stability analysis of the overall system is then analyzed by Lyapunov theory. It is proven that UUB stability of the overall system in presence of uncertainties is guaranteed, provided that the PD and the PID gains are tuned to satisfy certain conditions. Experimental studies are forwarded to verify the effectiveness and the performance of the proposed controller

2005ConferencePDFFlexible Robotics
Composite QFT Controller Design for Flexible Joint Robots
H. D. Taghirad and H. Rahimi
Proceedings of 2005 IEEE Conference on Control Applications, 2005. CCA 2005.
Abstract:

In this paper, a practical method to design a robust controller for a flexible joint robot (FJR) using quantitative feedback theory (QFT) is proposed. In order to control fast and slow dynamics of the FJR separately, composite control scheme is considered as the basis for the design. A simple PD controller is used to stabilize the fast dynamics, and a QFT controller is used in addition to an integral manifold corrective term to perform on the slow dynamics. Because of the nonlinear dynamics of FJR and the proposed controller scheme, linear time invariant equivalent (LTIE) technique is used to assign a nominal model for the system with uncertainties templates. Design of the QFT controller, as slow part of the composite control law is performed to compromise between the required bandwidth and the controller order. Comparisons with previous works on FJR, such as robust PID and composite Hinfin, illustrate the effectiveness of the proposed controller to reduce the tracking errors despite actuator limitations

2005ConferencePDFFlexible Robotics
Nonlinear H-Infinity Controller Design for Flexible Joint Robots
H. D. Taghirad and M. Shaterian
Proceedings of the IEEE Conference on Decision and Control
Abstract:

In this paper the design of a nonlinear H-Infinity controller for flexible joint robot (FJR) is presented. An approximate solution based on Taylor series expansion is considered for the Hamilton-Jacobi-Isaac (HJI) inequality. A two-degree-of-freedom controller combined of nonlinear H-Infinity controller and inverse dynamics controller is proposed to tackle the regulation as well as tracking problem in FJR. The proposed nonlinear H-Infinity controller attenuates the disturbance with a minimum achievable control effort, despite system parameter uncertainty. Simulation comparisons for single and multiple joint manipulators, show that the proposed controller yields to superior performance such as larger domain of attraction and smaller control effort as well as better tracking characteristics, compared to that of the other methods

2005ConferencePDFFlexible Robotics
Robust Control for Flexible Joint Robots with A Supervisory Control to Remedy Actuator Saturation
S. Ozgoli, H. D. Taghirad
ICEE13
Abstract:

In this paper a controller design method for flexible joint robots (FJR), considering actuator saturation is proposed and its robust stability is thoroughly analyzed. This method consists of a composite control structure, with a PD controller on the fast dynamics and a PID controller on slow dynamics. Moreover, the need of powerful actuator is remedied by decreasing the bandwidth of the fast controller during critical occasions, with the use of a supervisory loop. Fuzzy logic is used in the supervisory law, in order to adjust the proper gain in the forward path. It is then shown that UUB stability of the overall system is guaranteed in presence of uncertainties, provided that the PD and the PID gains are tuned to satisfy certain conditions.

2005ConferencePDFFlexible Robotics
QFT Controller Synthesis For A Nonlinear Flexible Joint Robot
H. D. Taghirad and H. Rahimi
Abstract:

In this paper, a practical method to design a robust controller for a flexible joint robot (FJR) using quantitative feedback theory (QFT) is proposed. In order to control fast and slow dynamics of the FJR separately, composite control scheme is considered as the basis for the design. A simple PD controller is used to stabilize the fast dynamics, and a QFT controller is used in addition to an integral manifold corrective term to perform on the slow dynamics. Because of the nonlinear dynamics of FJR and the proposed controller scheme, linear time invariant equivalent (LTIE) technique is used to assign a nominal model for the system with uncertainties templates. Design of the QFT controller, as slow part of the composite control law, is performed to compromise between the required bandwidth and the controller order. Comparisons with previous works on FJR, such that robust PID and composite H ?, illustrate the effectiveness of the proposed controller to reduce the tracking errors despite actuator limitations.

2005ConferencePDFFlexible Robotics
Nonlinear H-Infinity Controller Synthesis for Flexible Joint Robots
H. D. Taghirad and M. Shaterian
ICEE
Abstract:

In this paper the design of an optimal nonlinear H-Infinity controller for flexible joint robot (FJR) is presented. An approximate solution based on Taylor Series expansion is considered for the Hamilton-Jacobi-Isaac (HJI) inequality. A two-degree-of-freedom controller combined of optimal nonlinear H-Infinity controller and inverse dynamics controller is proposed to tackle the regulation as well as tracking problem in FJR. The proposed optimal nonlinear H-Infinity controller attenuates the disturbance with a minimum achievable control effort, despite system parameter uncertainty. Simulation comparisons for single and multiple joint manipulators, show that the proposed controller yields to superior performance such as larger domain of attraction and smaller control effort as well as better tracking characteristics, compared to that of the others.

2005ConferencePDFFlexible Robotics
Kinematic and Singularity Analysis of the Hydraulic Shoulder
H. Sadjadian and H. D. Taghirad
Proceedings of the Second International Conference on Informatics in Control, Automation and Robotics
Abstract:

In this paper, kinematic modeling and singularity analysis of a three DOF redundant parallel manipulator has been elaborated in detail. It is known, that on the contrary to series manipulators, the forward kinematic map of parallel manipulators involves highly coupled nonlinear equations, whose closed-form solution derivation is a real challenge. This issue is of great importance noting that the forward kinematics solution is a key element in closed loop position control of parallel manipulators. Using the novel idea of kinematic chains recently developed for parallel manipulators, both inverse and forward kinematics of our parallel manipulator are fully developed, and a closed-form solution for the forward kinematic map of the parallel manipulator is derived. The closed form solution is also obtained in detail for the Jacobian of the mechanism and singularity analysis of the manipulator is performed based on the computed Jacobian.

2005ConferencePDFParallel and Cable Robotics
Kinematic Analysis of the Hydraulic Shoulder: A 3-DOF Redundant Parallel Manipulator
H. Sadjadian and H.D. Taghirad
Mechatronics and Automation
Abstract:

In this paper, kinematic modeling of a three DOF redundant parallel manipulator has been elaborated in detail. It is known, that on the contrary to series manipulators, the forward kinematic map of parallel manipulators involves highly coupled nonlinear equations, whose closed-form solution derivation is a real challenge. This issue is of great importance noting that the forward kinematics solution is a key element in closed loop position control of parallel manipulators. Using the novel idea of kinematic chains recently developed for parallel manipulators, both inverse and forward kinematics of our parallel manipulator are fully developed, and a closed-form solution for the forward kinematic map of the parallel manipulator is derived. The closed form solution is finally verified by simulated trajectories in the workspace of the manipulator.

2005ConferencePDFParallel and Cable Robotics
Identification and Robust H-Infinity Control of the Rotational/Translational Actuator System
Mahdi Tavakoli, Hamid D. Taghirad, and Mehdi Abrishamchian
International Journal of Control Automation and Systems
Abstract:

The Rotational/Translational Actuator (RTAC) benchmark problem considers a fourth-order dynamical system involving the nonlinear interaction of a translational oscillator and an eccentric rotational proof mass. This problem has been posed to investigate the utility of a rotational actuator for stabilizing translational motion. In order to experimentally implement any of the model-based controllers proposed in the literature, the values of model parameters are required which are generally difficult to determine rigorously. In this paper, an approach to the least-squares estimation of the parameters of a system is formulated and practically applied to the RTAC system. On the other hand, this paper shows how to model a nonlinear system as a linear uncertain system via nonparametric system identification, in order to provide the information required for linear robust H-Infinity control design. This method is also applied to the RTAC system, which demonstrates severe nonlinearities due to the coupling from the rotational motion to the translational motion. Experimental results confirm that this approach can effectively condense the whole nonlinearities, uncertainties, and disturbances within the system into a favorable perturbation block.

2005JournalPDFSurgical Robotics
Neural Networks Approaches for Computing the Forward Kinematics of a Redundant Parallel Manipulator
H. Sadjadian , H.D. Taghirad, A. Fatehi
Abstract:

In this paper, different approaches to solve the forward kinematics of a three DOF actuator redundant hydraulic parallel manipulator are presented. On the contrary to series manipulators, the forward kinematic map of parallel manipulators involves highly coupled nonlinear equations, which are almost impossible to solve analytically. The proposed methods are using neural networks identification with different structures to solve the problem. The accuracy of the results of each method is analyzed in detail and the advantages and the disadvantages of them in computing the forward kinematic map of the given mechanism is discussed in detail. It is concluded that ANFIS presents the best performance compared to MLP, RBF and PNN networks in this particular application.

2005JournalPDFParallel and Cable Robotics
Robust Stability Analysis of FJR Composite Controller with a Supervisory Loop
S. Ozgoli and H. D. Taghirad
2005 IEEE/RSJ International Conference on Intelligent Robots and Systems
Abstract:

In this paper, a controller design method for flexible joint robots (FJR), considering actuator saturation is proposed and its robust stability is thoroughly analyzed. This method consists of a composite control structure, with a PD controller on the fast dynamics and a PID controller on slow dynamics. Moreover, the need of powerful actuator is removed by decreasing the bandwidth of the fast controller during critical occasions, with the use of a supervisory loop. Fuzzy logic is used in the supervisory law, in order to adjust the proper gain in the forward path. It is then shown that UUB stability of the overall system is guaranteed in presence of uncertainties, provided that the PD and the PID gains are tuned to satisfy certain conditions

2005ConferencePDFFlexible Robotics
Designing H2/H-Infinity Controller for Flexible Joint Robot to Remove Instabilities due to Saturation
Sadjaad Ozgoli, H.D. Taghirad
Annual (International) Mechanical Engineering Conference
Abstract:

Mixed H 2 /H-Infinity method is proposed to design a controller for flexible joint robots (FJR) considering actuator saturation. By considering the control action in the mixed sensitivity function one can reduce the amplitude of the control action but this may affect all frequencies. A more advanced method based on frequency weighting of the control action contribution in the mixed sensitivity function is considered here which may result in higher bandwidth. But this method is also limited and to get wider bandwidth the H 2 /H-Infinity method is proposed. This method is shown to be a very good remedy to remove instabilities caused by actuator saturation.

2005ConferencePDFFlexible Robotics
Comparison of Different Methods for Computing the Forward Kinematics of a Redundant Parallel Manipulator
H. Sajadian and H. D. Taghirad
Journal of Intelligent and Robotic Systems
Abstract:

In this paper, three numerical methods are presented to solve the forward kinematics of a three DOF actuator-redundant hydraulic parallel manipulator. It is known, that on the contrary to series manipulators, the forward kinematic map of parallel manipulators involves highly coupled nonlinear equations, whose closed-form solution derivation is a real challenge. This issue is of great importance noting that the forward kinematics solution is a key element in closed loop position control of parallel manipulators. The proposed methods, namely the Neural Network Estimation, the Quasi-closed Solution, and the Taylor series approximation, are using mainly numerical computations, with different ideas to solve the problem in hand. The latter two methods are proposed for the first time in literature to solve the forward kinematics of a parallel manipulator. These methods are compared in detail and the advantages or the disadvantages of each method in computing the forward kinematic map of the given mechanism is discussed. It is shown that a 4th order Taylor series approximation to the problem provides a good compromise for practical applications compared to that of other methods considered in this paper.

2005JournalPDFParallel and Cable Robotics
A Quasi-Closed Solution Method for Computing the Forward Kinematics of a Redundant Parallel Manipulator
H. Sadjadian and H.D. Taghirad
12th Iranian Conference on Electric Engineering
Abstract:

In this paper, a quasi-closed solution method is presented to solve the forward kinematics of a three DOF actuator redundant hydraulic parallel manipulator. It is shown, that on the contrary to series manipulators, the forward kinematic map of the parallel manipulators involves highly coupled nonlinear equations, which are almost impossible to solve analytically. The proposed method uses a combination of analytical and numerical schemes to solve the problem. A simulation study is performed using a sample trajectory to identify the advantages and disadvantages of the proposed method in computing the forward kinematic map of the given mechanism. The results show that the proposed method provides us with a relatively fast solution and good tracking performance although being dependent on the initial conditions used in the solution process.

2004ConferencePDF
Design of Composite Control For Flexible Joint Robots With Saturating Actuators
S. Ozgoli, H.D. Taghirad
Iranian Conference on Fuzzy Systems
Abstract:

In this paper a method of controller design for FJRs considering actuator saturation and other practical limitations is proposed. In the proposed method the need of powerful actuator is skipped over by decreasing the bandwidth of the fast controller during critical times. In order to accomplish this, a supervisory control is employed which uses fuzzy logic to adjust the proper forward path gain. This prevents instability caused by saturation without a great change in performance. All other practical considerations to make the controller implementable are taken into account and finally the performance of the proposed controller is verified through simulation.

2004ConferencePDFFlexible Robotics
Decentralized Robust H-Infinity Controller Design For A Half-Car Active Suspension System
A. Shariati, H. D. Taghirad and A. Fatehi
Control 2004
Abstract:

In this paper an H-Infinity controller is designed for a hydraulically actuated active suspension system of a half-modeled vehicle in a cascade feedback structure. Using the proposed structure the nonlinear behavior of actuator is reduced significantly. In the controller synthesis, a proportional controller is used in the inner loop, and a robust H? controller forms the outer loop. Two H? controllers are designed for this system. First unstructured uncertainty is not considered in the design procedure and secondly, the controller is designed considering uncertainty. Each of these controllers is designed in a decentralized fashion and the vehicle oscillation in the human sensitivity frequency range is reduced to a minimum. Statistical analysis of the simulation result using random input as road roughness, illustrates the effectiveness of the proposed control algorithm for both cases. Keyword: active suspension, cascade feedback, hydraulic actuator, nonlinear model, multiplicative uncertainty, robust H? controller, disturbance input, road random input, statistical analysis.

2004JournalPDF
Adaptive Robust Controller Synthesis for Hard Disk Servo Systems
H. D. Taghirad and E. Jamei
Intelligent Robots and Systems, 2004
Abstract:

Adaptive robust controller is proposed for read/write head systems for hard disk drives (HDD). This structure can be applied to both track seeking and track following modes, and it makes the mode switching control algorithms proposed in conventional HDD servo system unnecessary. This controller theoretically guarantees a prescribed transient performance and tracking in presence of parametric uncertainties. An improved desired compensation ARC (IDCARC) scheme is then proposed, which has powered by a dynamic adaptive term compared to DCARC. The regressor is calculated using reference trajectory information. This has been done by structural vibration minimized acceleration trajectory control method. Simulation result show that the dynamic adaptation mechanism in IDCARC provide better performance compared to that of ARC, DCARC and the conventional servo system with mode switches control law.

2004ConferencePDFHard Disk Drives Control
A Robust Linear Controller for Flexible Joint Manipulators
H.D. Taghirad and M.A. Khosravi
2004 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS)
Abstract:

In this paper a new and completely linear algorithm is proposed for composite robust control of flexible joint robots. Moreover, the robust stability of the closed loop system in the presence of structured and unstructured uncertainties is analyzed. To introduce the idea, flexible joint robot with structured and unstructured uncertainties is modelled and converted into singular perturbation form. A robust linear control algorithm is proposed for the slow dynamics and its robust stability conditions are derived using Thikhonov's theorem. Then the robust stability of the total system considering the proposed composite controller is analyzed, and sufficient conditions for robust stability of system is obtained. Finally the effectiveness of the proposed controller is verified through simulations. It is shown that not only the tracking performance of the proposed controller is very suitable, but also the actuator effort is much smaller than previous result.

2004ConferencePDFParallel and Cable Robotics
Numerical Methods for Computing the Forward Kinematics of a Redundant Parallel Manipulator
H. Sadjadian and H.D. Taghirad
Abstract:

In this paper, three numerical methods are presented to solve the forward kinematics of a three DOF actuator-redundant hydraulic parallel manipulator. It is known, that on the contrary to series manipulators, the forward kinematic map of parallel manipulators involves highly coupled nonlinear equations, whose closed-form solution derivation is a real challenge. This issue is of great importance noting that the forward kinematics solution is a key element in closed loop position control of parallel manipulators. The proposed methods, namely the Neural Network Estimation, the Quasi-closed Solution, and the Taylor series approximation, are using mainly numerical computations, with different ideas to solve the problem in hand. The latter two methods are proposed for the first time in literature to solve the forward kinematics of a parallel manipulator. These methods are compared in detail and the advantages or the disadvantages of each method in computing the forward kinematic map of the given mechanism is discussed. It is shown that a 4th order Taylor series approximation to the problem provides a good compromise for practical applications compared to that of other methods considered in this paper.

2004ConferencePDFParallel and Cable Robotics
Multivariable Generalized Predictive Temprature Controller Design For Yazd Solar Power Plant
Abdolvahed Saidi and Hamid D. Taghirad
European Journal of Scientific Research
Abstract:

The Yazd Integrated Solar Combined Cycle (ISCC) Power Plant consists of two gas turbines that are generating power synchronous to Iranian national electrical network. One steam turbine will be supplied by gas units, while a parabolic through solar field is integrated with the System, as a combined cycle. In this paper an integrated model of the solar field with the purpose is presented, and a multivariable generalized predictive temperature controller is proposed for the system. As it is Illustrated in the simulation results, such a control strategy can robustly regulate both the temperature of outlet oil, and the temperature of outlet steam water of the solar boiler, despite the variation of the inherent time delays of the system and external disturbances.

2004ConferencePDF
Parametric and Nonparametric Identification and Robust Control of a Rotational/Translational Actuator
M. Tavakoli, H. D. Taghirad and M. Abrishamchian
Control and Automation
Abstract:

RTAC benchmark problem considers a nonlinear fourth-order dynamical system involving the nonlinear interaction of a translational oscillator and an eccentric rotational proof mass. This problem has been posed to investigate the utility of a rotational proof mass actuator for stabilizing translational motion. In order to implement any of the model-based controllers proposed in the literature, the values of model parameters are required which are generally difficult to determine rigorously. In this paper, an approach to the least-squares estimation of system parameters is discussed and practically applied to the benchmark problem. Next, in order to design an H-Infinity controller, the nonlinear system is modelled as a perturbed linear system using an effective identification scheme. Experimental results confirm that this approach can effectively condense the whole nonlinearities, uncertainties, and disturbances within the system into a favorable perturbation block. Finally, an effective mixed-sensitivity problem is developed for the system to satisfy all performance requirements as well as robust stability despite actuator saturation.

2003ConferencePDF
Design and Simulation of Robust Composite Controllers for Flexible Joint Robots
H.D. Taghirad and M.A. Khosravi
2003 IEEE International Conference on Robotics and Automation
Abstract:

In this paper the control of flexible joint manipulators is studied in detail. A composite control algorithm is proposed for the flexible joint robots, which consists of two main parts. Fast control, u/sub f/, which guarantees that the fast dynamics remains asymptotically stable, and the corresponding integral manifold remains invariant. Slow control, u, itself consists of a robust PID designed based on the rigid model, and a corrective term designed based on the reduced flexible model. The stability of the overall closed loop system is proved to be UUB stable, by Lyapunov stability analysis. Finally, the effectiveness of the proposed control law is verified through simulations. It is shown that the proposed control law ensure the robust stability and performance, despite the modeling uncertainties.

2003ConferencePDFFlexible Robotics
A New Sensorless Vector Control Method for Permanent Magnet Synchronus Motor Without Velocity Estimatior
H. D. Taghirad, N. Abedi, E. Noohi
7th International Workshop on Advanced Motion Control
Abstract:

In this paper, a novel vector control method for permanent magnet synchronous motors is presented. In this method, the velocity estimation is completely removed and vector control is accomplished in a new coordinate system. In conventional vector control methods, the control effort is calculated in rotating coordinates with a synchronous speed of omega. However, in the proposed method, the control effort is calculated in rotating coordinates with reference speed omega. This change of coordinate decreases the calculation effort significantly. In order to verify the applicability of the proposed control law, a Lyapunov-based stability condition is derived and the performance of the controller is verified through simulations and experiments. The obtained results illustrate the effectiveness of the proposed method despite the simplicity of its implementation.

2002ConferencePDFDynamical Systems Analysis and Control
Stability Analysis and Robust Composite Controller Synthesis for Flexible Joint Robots
H.D. Taghirad and M.A. Khosravi
Advanced Robotics
Abstract:

In this paper the control of flexible joint manipulators is studied in detail. The model of N-axis flexible joint manipulators is derived and reformulated in the form of singular perturbation theory and an integral manifold is used to separate fast dynamics from slow dynamics. A composite control algorithm is proposed for the flexible joint robots, which consists of two main parts. Fast control, u f, guarantees that the fast dynamics remains asymptotically stable and the corresponding integral manifold remains invariant. Slow control, u s, consists of a robust PID designed based on the rigid model and a corrective term designed based on the reduced flexible model. The stability of the fast dynamics and robust stability of the PID scheme are analyzed separately, and finally, the closed-loop system is proved to be uniformly ultimately bounded (UUB) stable by Lyapunov stability analysis. Finally, the effectiveness of the proposed control law is verified through simulations. The simulation results of single- and two-link flexible joint manipulators are compared with the literature. It is shown that the proposed control law ensures robust stability and performance despite the modeling uncertainties.

2002ConferencePDFFlexible Robotics
Composite-H? Controller Synthesis for Flexible Joint Robots
H. D. Taghirad, Gh. Bakhshi
Intelligent Robots and Systems
Abstract:

In this paper a robust composite control algorithm is proposed for flexible joint manipulators, with the emphasis on satisfying control effort limitations. An H-Infinity framework is used for the slow subsystem controller design, instead of robust PID synthesis introduced in the literature. Linear identification techniques are used to represent the nonlinear dynamics of the system into a linear model plus multiplicative uncertainty. An H-Infinity controller is designed in the framework of composite control, in order to optimize the required control effort, along with satisfying robust stability and desirable performance. The effectiveness of the proposed control law is compared with other methods through a simulation study. The comparison results show a significant improvement in control effort, while satisfying both stability and performance requirements.

2002ConferencePDFFlexible Robotics
Stability Analysis and Robust Composite Controller Synthesis for Flexible Joint Robots
H.D. Taghirad and M.A. Khosravi
Advanced Robotics
Abstract:

In this paper the control of flexible joint manipulators is studied in detail. The model of N-axis flexible joint manipulators is derived and reformulated in the form of singular perturbation theory and an integral manifold is used to separate fast dynamics from slow dynamics. A composite control algorithm is proposed for the flexible joint robots, which consists of two main parts. Fast control, u f, guarantees that the fast dynamics remains asymptotically stable and the corresponding integral manifold remains invariant. Slow control, u s, consists of a robust PID designed based on the rigid model and a corrective term designed based on the reduced flexible model. The stability of the fast dynamics and robust stability of the PID scheme are analyzed separately, and finally, the closed-loop system is proved to be uniformly ultimately bounded (UUB) stable by Lyapunov stability analysis. Finally, the effectiveness of the proposed control law is verified through simulations. The simulation results of single- and two-link flexible joint manipulators are compared with the literature. It is shown that the proposed control law ensures robust stability and performance despite the modeling uncertainties.

2002JournalPDFFlexible Robotics
H-Infinity Based Robust Torque Control of Harmonic Drive Systems
H.D. Taghirad, P.R. Belanger
Journal of Dynamic Systems Measurement and Control
Abstract:

In this paper, the torque control of a harmonic drive system for constrained-motion and free-motion applications is examined in detail. A nominal model for the system is obtained in each case from experimental frequency responses of the system, and the deviation of the system from the model is encapsulated by a multiplicative uncertainty. Robust torque controllers are designed using this information in an H-proportional to-framework, and implemented on two different setups. From time and frequency domain experiments, it is shown that the closed-loop system retains robust stability, while improving the tracking performance exceptionally well. To further improve the performance of the system for free-motion case, a feedforward friction-compensation algorithm is implemented in addition to the robust torque control. It is shown that friction-compensation will shrink the model uncertainty at low frequencies and hence, the performance of the closed-loop system it-ill be improved at those frequencies.

2001JournalPDF
Automobile Passenger Comfort Assured Through Lqg/Lqr Active Suspension
H. D. Taghirad, E. Esmailzadeh
Journal of Vibration and Control
Abstract:

An analytical investigation of a half-car model including passenger dynamics, subjected to random road disturbances is performed, and the advantage of active over conventional passive suspension systems are examined. Two different performance indices for optimal controller design are proposed. The performance index is a quantification of both ride comfort and road handling. Due to practical limitations, all the states required for the state-feedback controller are not measurable, and thus must be estimated with an observer. Stochastic inputs are applied to simulate realistic road surface conditions, and statistical comparisons between passive system and the two controllers, with and without state estimator, are carried out to gain a clearer insight into the performance of the controllers.The simulation results demonstrate that an optimal observer- based controller, when including passenger acceleration in the performance index, retains both excellent ride comfort and road handling characteristics.

1999JournalPDF
H-Infinity Based Robust Torque Control of Harmonic Drive Systems Under Free and Constrained Motion Applications
H.D. Taghirad, P.R. Belanger
Journal of Dynamic Systems Measurement and Control
Abstract:

A harmonic drive is a compact, light--weight and high--ratio torque transmission device which has almost zero backlash. Its unique performance features captures the attention of designers in many industrial applications, especially in robotics. However, the torque control of harmonic drive systems is still a challenging problem for researchers. In this paper the torque control of harmonic drive system for constrained motion is examined in detail. A nominal model for the system is obtained from experimented frequency responses of the system, and the deviation of the system from the model is encapsulated by multiplicative uncertainty. A robust torque controller is designed using this information in an H1 --framework, and implemented on two different setups. It is illustrated that the performance features of the closed--loop system is exceptionally good, both in time and frequency domains. I. Introduction Developed in 1955 primarily for aerospace applications, harmonic drives are high--...

1998ConferencePDF
Robust Friction Compensator For Harmonic Drive Transmission
H.D. Taghirad, P.R. Belanger
Proceedings of the 1998 IEEE International Conference on Control Applications
Abstract:

The torque control of harmonic drive system is examined in detail. An empirical nominal model for the system is obtained through experimental frequency response estimates, and the deviation of the system from the model is encapsulated by multiplicative uncertainty. A robust torque controller is subsequently designed in an H-Infinity framework and implemented using Kalman filtered torque estimates. Exceptional performance results are obtained from the time and frequency response of the closed-loop system. To further improve the performance of the system, a model-based friction-compensation algorithm is implemented in addition to the robust torque control. It is shown that the friction-compensation reduced the model uncertainty at low frequencies. Hence, the performance of the closed-loop system is improved for tracking signals with low-frequency content.

1998ConferencePDF
Electromagnetic Levitation System An Experimental Approach
H D Taghirad, M Abrishamchian, R Ghabcheloo
Abstract:

In this paper, we propose a simple method for controlling an electromagnetic levitation (Mag lev) system. The model of the Mag lev system under consideration in this paper is third order, inherently nonlinear and unstable. For designing a controller to obtain a good disturbance rejection and being insensitive to parameter variations, we use an inner-loop and an outer-loop configuration. The configuration is the key to solve this problem. By using a nonlinear state transformation in the feedback path, a cascaded PI controller and a redefined input in the inner loop, we obtain a linear second order system. Furthermore, to achieve a stable system with a good disturbance rejection, we design a Pid controller cascaded with the inner loop system in the negative unity feedback configuration in the outer loop. We show that the closed-loop system is robustly stabilized against the mass variation. Simulation results show that despite actuator saturation limits, the performance of our simple structure controller is comparable to that reported in the literature. In order to assess these results in practice, an experimental setup is designed and being constructed. The simulation analysis is based on the parameters of this experimental setup

1998ConferencePDF
A Nonlinear Model For Harmonic Drive Friction And Compliance
H.D. Taghirad, P.R. Belanger
Abstract:

Despite widespread industrial application of harmonic drives, mathematical representation of their dynamics has not been fully addressed. In this paper a systematic way to capture and rationalize the dynamic behavior of the harmonic drive systems is developed. Simple and accurate models for compliance, hysteresis, and friction are proposed, and the model parameters are estimated using least--squares approximation for linear and nonlinear regression models. A statistical measure of variation is defined, by which the reliability of the estimated parameter for different operating condition, as well as the accuracy and integrity of the proposed model is quantified. By these means, it is shown that a linear stiffness model best captures the behavior of the system when combined with a good model for hysteresis. Moreover, the frictional losses of harmonic drive are modelled at both low and high velocities. The model performance is assessed by comparing simulations with the experimental result...

1998ConferencePDF
Friction Compensation and H-Infinity Based Torque Control of Harmonic Drive Systems
H.D. Taghirad, P.R. Belanger
Abstract:

In this paper the torque control of a harmonic drive system for constrained--motion and free-- motion applications is examined in detail. A nominal model for the system is obtained in each case from experimental frequency responses of the system, and the deviation of the system from the model is encapsulated by a multiplicative uncertainty. Robust torque controllers are designed using these information in an H-Infinity framework, and implemented on two different setups. From time and frequency domain experiments, it is shown that the closed--loop system retains robust stability, while improving the tracking performance exceptionally well. To further improve the performance of the system for free-motion case, a feedforward friction--compensation algorithm is implemented in addition to the robust torque control. It is shown that friction--compensation will shrink the model uncertainty at low frequencies and hence, the performance of the closed--loop system will be improved at those frequencies...

1998ConferencePDF
Modelling and Parameter Identication of Harmonic Drive Systems
H.D. Taghirad, P.R. Belanger
Abstract:

The unique performance features of harmonic drives, such as high gear ratios and high torque capacities in a compact geometry, justify their widespread industrial application. However, harmonic drive can exhibit surprisingly more complex dynamic behavior than conventional gear transmission. In this paper a systematic way to capture and rationalize the dynamic behavior of the harmonic drive systems is developed. Simple and accurate models for compliance, hysteresis, and friction are proposed, and the model parameters are estimated using least-squares approximation for linear and nonlinear regression models. A statistical measure of variation is defined, by which the reliability of the estimated parameter for different operating condition, as well as the accuracy and integrity of the proposed model is quantified. By these means, it is shown that a linear stiffness model best captures the behavior of the system when combined with a good model for hysteresis. Moreover, the frictional losses of harmonic drive are modeled at both low and high velocities. The model performance is assessed by comparing simulations with the experimental results on two different harmonic drives. Finally, the significance of individual components of the nonlinear model is assessed by a parameter sensitivity study using simulations.

1998JournalPDF
Torque Ripple and Misalignment Torque Compensation for the Built-In Torque Sensor of Harmonic Drive Systems
H.D. Taghirad, P.R. Belanger
IEEE Transactions on Instrumentation and Measurement
Abstract:

A harmonic drive is a compact, lightweight, and high-ratio torque transmission device which is used in many electrically actuated robot manipulators. In this paper a built-in torque sensor for harmonic-drive systems is examined in detail. The method proposed by Hashimoto, in which strain gauges are directly mounted on the flexspline, is employed and improved in this paper. To minimize sensing inaccuracy, four Rosette strain gauges are used employing an accurate positioning method. To cancel the torque ripples, the oscillation observed on the measured torque and caused mainly by gear teeth meshing, Kalman filter estimation is used. A simple fourth-order harmonic oscillator proved to accurately model the torque ripples. Moreover, the error model is extended to incorporate any misalignment torque. By on-line implementation of the Kalman filter, it has been shown that this method is a fast and accurate way to filter torque ripples and misalignment torque. Hence, the intelligent built-in torque sensor is a viable and economical way to measure the harmonic-drive transmitted torque and to employ that for torque feedback strategies.

1998JournalPDF
Intelligent Built-In Torque Sensor for Harmonic Drive Systems
H.D. Taghirad, P.R. Belanger
IEEE Transactions on Instrumentation and Measurement
Abstract:

A harmonic drive is a compact, light-weight and high-ratio torque transmission device which is used in many electrically actuated robot manipulators. In many robotic control strategies it is assumed that the actuator is an ideal torque source. However, converting harmonic drive systems to ideal torque sources is still a challenging control problem for researchers. In this paper the torque control of harmonic drive system under free motion is examined in detail. A built-in torque sensor is developed in order to measure the torque, and by employing a Kalman filter the undesired torque signatures like torque ripples and misalignment torque are filtered out. An empirical nominal model for the system is obtained through experimental frequency response estimates, and the deviation of the system from the model is encapsulated by multiplicative uncertainty. A robust torque controller is subsequently designed in an H?-framework and implemented employing Kalman filtered torque estimates. From time and frequency domain experiments, it is shown that the closed-loop system retains robust stability, while improving the tracking performance exceptionally well

1998JournalPDF
Application of Kalman Filter for Intelligent Built in Torque Sensor of Harmonic Drives
H.D. Taghirad
Abstract:

A harmonic drive is a compact, light--weight and high--ratio torque transmission device which has almost zero backlash. Its unique performance features has captured the attention of designers in many industrial applications, especially in robotics. Despite widespread industrial application of harmonic drives, the torque control of this system has not been fully addressed. In this thesis the robust torque control of harmonic drive system is examined in detail. In order to measure the transmitted torque of a harmonic drive and for the purpose of a torque feedback scheme, an intelligent built--in torque sensing technique is developed in this thesis. Specifically, strain--gauges are mounted directly on the flexspline and therefore no extra flexible element is introduced into the system. To have maximum sensing accuracy, four Rosette strain gauges are employed using an accurate positioning method. Kalman filter estimation is employed to cancel the torque ripples, oscillations observed on t...

1997JournalPDF
On The Modelling and Identification of Harmonic Drive Systems
H.D. Taghirad
Abstract:

The unique performance features of harmonic drives, such as high gear ratios and high torque capacities in a compact geometry, justify their widespread industrial application, especially in robotics. However, harmonic drives can exhibit surprisingly more complex dynamic behavior than conventional gear transmissions. In this report, a systematic way to capture and rationalize the dynamic behavior of the harmonic drive systems is examined. Simple and accurate models for compliance, hysteresis, and friction are proposed, and the model parameters are estimated using least--squares approximation for linear and nonlinear regression models. A statistical measure of variation is defined, by which the reliability of the estimated parameter for different operating condition, as well as the accuracy and integrity of the proposed model is quantified. Finally, the model performance is assessed by a simulation verifying the experimental results. R' esum' e Les performances uniques de l'entrainement ...

1997JournalPDF
Intelligent Torque Sensing and Robust Torque Control of Harmonic Drive Under Free-Motion
H.D. Taghirad, P.R. Belanger
Abstract:

A harmonic drive is a compact, light-weight and high-ratio torque transmission device which is used in many electrically actuated robot manipulators. In many robotic control strategies it is assumed that the actuator is an ideal torque source. However, converting harmonic drive systems to ideal torque sources is still a challenging control problem for researchers. In this paper the torque control of harmonic drive system under free motion is examined in detail. A built-in torque sensor is developed in order to measure the torque, and by employing a Kalman filter the undesired torque signatures like torque ripples and misalignment torque are filtered out. An empirical nominal model for the system is obtained through experimental frequency response estimates, and the deviation of the system from the model is encapsulated by multiplicative uncertainty. A robust torque controller is subsequently designed in an H framework and implemented employing Kalman filtered torque estimates. From time and frequency domain experiments, it is shown that the closed-loop system retains robust stability, while improving the tracking performance exceptionally well

1997ConferencePDF
Intelligent Built-In Torque Sensor for Harmonic Drive Systems
H.D. Taghirad, A.Hemly, P.R. Belanger
Abstract:

The unique performance features of harmonic drives, such as high gear ratios and high torque capacities in a compact geometry, justify their widespread industrial application especially in many electrically actuated robot manipulators. In many robotic control strategies it is assumed that the actuator is acting as a torque source, and in order to implement such algorithms it is necessary to accurately measure the transmitted torque by the harmonic drive. In this paper a built-in torque sensor for harmonic drive systems is developed and examined in detail, in which strain-gauges are directly mounted on the harmonic drive flexspline. To minimize sensing inaccuracy, four Rosette strain gauges are used employing an accurate positioning method. To cancel the torque ripples, the oscillation observed on the measured torque and caused mainly by gear teeth meshing, Kalman filter estimation is used. A simple fourth order harmonic oscillator proved to accurately model the torque ripples. Moreover, the error model is extended to incorporate any misalignment torque. By on line implementation of the Kalman filter, it has been shown that this method is a fast and accurate way to filter torque ripples and misalignment torque. Hence, the intelligent built-in torque sensor is a viable and economical way to measure the harmonic drive transmitted torque and to employ that for torque feedback strategies.

1997ConferencePDF
An Experimental Study on Modelling and Identification of Harmonic Drive Systems
H.D. Taghirad, P.R. Belanger
Proceedings of 35th IEEE Conference on Decision and Control
Abstract:

Despite widespread industrial application of harmonic drives, mathematical representation of their dynamics has not been fully addressed. In this theoretical/experimental study of harmonic drive systems a systematic way to capture and rationalize the dynamics of the system is proposed. Simple and accurate models for compliance, hysteresis, and friction are given and the model parameters are estimated from experiments using least square approximation. A statistical measure of consistency is defined, by which the reliability of the estimated parameter for different operating condition, as well as the accuracy and integrity of the proposed model is quantified. The validity of the modelling scheme is evaluated on two different harmonic drives by comparing the experimental and simulation results.

1996ConferencePDF
An Experimental Study on Harmonic Drives
H.D. Taghirad, P.R. Belanger, A.Hemly
Abstract:

Despite widespr ad industrial application of harmonic drives, modelling and control of such systems has not been fully addressed. In this theoretical/experimental study of harmonic drive systems a systematic way to capture and rationalize the dynamics of the system is proposed. Simple and accurate models for their compliance, hysteresis, and friction are given and model parameters are estimated from experimental data using least square approximation. A statistical measure of consistency is defined, by which the reliability of the estimated parameter for different operating condition, as well as the accuracy and integrity of the proposed model is quantified. The validity of the modelling scheme is evaluated by comparing the experimental and simulation results. Two separate simulations are developed for the harmonic drive system operating in restrained and unrestrained motion. The problem of torque control of harmonic drive is addressed in the H1 controller design framework. I...

1996JournalPDF
Passenger Ride Comfort Through Observer Based Control
H. D. Taghirad, E. Esmailzadeh
Abstract:

An analytical investigation of a half-car model including passenger dynamics, subjected to random road disturbances is performed, and the advantage of active over conventional passive suspension systems are examined. Two diierent performance indices for optimal controller design are proposed. The performance index is a quantiication of both ride comfort and road handling. Due to practical limitations, all the states required for the state-feedback controller are not measurable, and thus must be estimated with an observer. Stochastic inputs are applied to simulate realistic road surface conditions, and statistical comparisons between passive system and the two controllers, with and without state estimator, are carried out to gain a clearer insight into the performance of the controllers. The simulation results demonstrate that an optimal observer-based controller, when including passenger acceleration in the performance index, retains both excellent ride comfort and road handling characteristics

1995ConferencePDF
State Feedback Control For Passenger Ride Dynamics
H. D. Taghirad, E. Esmailzadeh
Transactions- Canadian Society for Mechanical Engineering
Abstract:

An analytical investigation of a half-car model with passenger dynamics, subjected to random road disturbance, is performed. Two diierent methods of deening the performance index for optimal controller design are proposed. Nondeterministic inputs are applied to simulate the road surface conditions more realistically. Results obtained illustrate that using an optimal state-feedback controller, with passenger acceleration included in the performance index, would exhibit not only an improved passenger ride comfort, but also, a better road handling and stability.

1995JournalPDF
Ride Comfort and Roll Characteristics of Tandem Axled Trucks
E. Esmailzadeh, H. D. Taghirad
Abstract:

this paper, the ride comfort and handling characteristics of a tandem-axle truck are investigated. The equations of motion for the proposed model, with fourteen-degrees-of-freedom, are derived. Various numerical techniques are employed in order to solve the complex matrix equation. The sensitivity analysis for the parameter variations is carried out in this study and the overall effects of anti-roll bar are also examined.

1995ConferencePDF
2018
TitleAbstractYearTypePDFResearch Group
Extracting of Sagging Profile of Overhead Power Transmission Line Via Image Processing
Amir Molaei, Hamid D.Taghirad, Javad Dargahi
2018 IEEE Canadian Conference on Electrical & Computer Engineering (CCECE)
Abstract:

Sagging of the conductor in transmission line has a vital role in the safety, reliability and efficiency of power transmission. Transmission lines must be designed to guarantee the maximum static loading capacity. This is done by maintaining the minimum vertical clearance between the cables and the ground. However, the increase of the cable length between two tower, leads to the high cost of material and electrical energy loss, as well as increasing the possibility of intervention. On the other hand, reducing the line sagging induces high tension in the conductor, which may lead to damage of the conductor. To assure a safety sagging profile, an inspection is essential at the establishment and maintainance of the power transmission lines. In this paper firstly the mathematical formulation of long and heavy cables are developed. Then an image processing method is applied for inspection of cable sagging. To investigate the method a reconfigurable experimental setup is designed to provide various sagging profiles and the sagging profile is extracted via image processing and the result is compared to that of analytical method.

2018ConferencePDFParallel and Cable Robotics
Robust Dynamic Sliding Mode Control of a Deployable Cable Driven Robot
S. A. Khalipour, R. Khorrambakht, M. J. Harandi, H. D. D. Taghirad and Philippe Cardou
Electrical Engineering (ICEE), Iranian Conference on
Abstract:

Despite of bing intensively developed, cable driven parallel manipulators are not yet vastly used due to their requirements for accurate assembly and installation. The main goal of this paper is to propose a suitable control method by which the robot could be suitably controlled without the requirement for undergoing any accurate calibration process. Here this robot is called deployable cable driven manipulator, in which the positions of the cable attachment points are not accurately known. This uncertainty in measurements will affect many parameters in the kinematic model especially the Jacobian matrix which is used as a force distributer in the Cartesian-space control strategies. In this paper in order to overcome this problem, a robust dynamic sliding mode controller is proposed. Then robust stability of the closed-loop system is analyzed through the Lyapunov direct method and by accordingly appropriate controller gain selection is performed. In order to illustrate the performance of the proposed controller, the robot is simulated in ADAMS software and it is shown that a suitable controller performance could be achieved.

2018ConferencePDFParallel and Cable Robotics
Robust Object Tracking Based on Recurrent Neural Networks
F. Lotfi, V. Ajallooeian and H. D. Taghirad
2018 6th RSI International Conference on Robotics and Mechatronics (IcRoM)
Abstract:

Object tracking through image sequences is one of the important components of many vision systems, and it has numerous applications in driver assistance systems such as pedestrian collision avoidance or collision mitigating systems. Blurred images produced by a rolling shutter camera or occlusions may easily disturb the object tracking system. In this article, a method based on convolutional and recurrent neural networks is presented to further enhance the performance and robustness of such trackers. It is proposed to use a convolutional neural network to detect an intended object and feed the tracker with found image. Moreover, by using this structure the tracker is updated every ' n ' frames. A recurrent neural network is designed to learn the object behavior for estimating and predicting its position in blurred frames or when it is occluded behind an obstacle. Real-time implementation of the proposed approach verifies its applicability for improvement of the trackers performance.

2018ConferencePDFAutonomous Robotics
Two PID-Based Controllers for a tethered Segway on Dome Shaped Structures
Mohammad H. Salehpour Hamid D. Taghirad and Hadi Moradi
2018 6th RSI International Conference on Robotics and Mechatronics (IcRoM)
Abstract:

The UTDTR Robot is a human inspired robotic platform based on a two-wheeled mobile robot. This robot is designed for the purpose of dome shaped structures inspection and maintenance, and it is a tethered robot to stably climb steep surfaces on the top of dome structures. In this paper analysis and controller design of this robot modelled as a MIMO system is represented in order to provide the desired performance on the operating surface with minimum control effort and complexity. Two PID-based controllers are designed such that the stability and desired performance conditions are obtained. In the first design a fuzzy PID controller with self-tuning scale factors is designed to tune the controller gains is forwarded, while in the second approach a multi model gain scheduling controller based on conventional PID controller is considered. Finally, the effectiveness and simplicity of the proposed controller is verified through simulation, comparing the resulting closed loop transient and steady-state response to that of the previously proposed controllers.

2018ConferencePDFDynamical Systems Analysis and Control
Wave Based Control of A Deployable Cable Driven Robot
S. A. Khalilpour, R. Khorrambakht, H. D. Taghirad, and Philippe Cardou
2018 6th RSI International Conference on Robotics and Mechatronics (IcRoM)
Abstract:

Cable driven parallel manipulator are known by their low costs and numerous applications. However despite of all research interests and developed methods they are not yet vastly used in action. The reason for this, is their limiting requirements for accurate assembly and installation process. The main goal of this paper is to propose a suitable control method by which the robot could appropriately be controlled, requiring no accurate calibrations or precise sensors. As it is well known, uncertainty in kinematics equations can lead to loose cables in redundant robots controlled through joint space controllers. In this paper a simple but very effective joint space controller is proposed that addresses the problem of loose cables by a wave based control method by employing a novel force feedback scheme. Indeed, a new conceptual framework for controlling deployable cable driven parallel manipulators is introduced by which such robots are greatly empowered at real-world scenarios. Finally, the performance of the proposed controller and its effectiveness is verified through some practical experiments showing that the proposed controller outperforms conventional cascade topologies in terms of much smoother tracking performance.

2018ConferencePDFParallel and Cable Robotics
A Dual-User Teleoperated Surgery Training Scheme Based on Virtual Fixture
A. Iranfar, M. Motaharifar, and H. D. Taghirad
2018 6th RSI International Conference on Robotics and Mechatronics (IcRoM)
Abstract:

The widespread use of minimally invasive surgery (MIS) demands an appropriate framework to train novice surgeons (trainees) to perform MIS. One of the effective ways to establish a cooperative training system is to use virtual fixtures. In this paper, a guiding virtual fixture is proposed to correct the movements of the trainee according to trainer hand motion performing a real MIS surgery. The proposed training framework utilizes the position signals of trainer to modify incorrect movements of the trainee which leads to shaping the trainee's muscle memory. Thus, after enough training sessions the trainee gains sufficient experience to perform the surgical task without any further help from the trainer. The passivity approach is utilized to analyze the stability of system. Simulation results are also presented to demonstrate the effectiveness of the proposed method.

2018ConferencePDFSurgical Robotics
Multi-goal motion planning using traveling salesman problem in belief space
Ali Noormohammadi-Asl, Hamid D. Taghirad
Information Sciences
Abstract:

In this paper, the multi-goal motion planning problem of an environment with some background information about its map is addressed in detail. The motion planning goal is to find a policy in belief space for the robot to traverse through a number of goal points. This problem is modeled as an asymmetric traveling salesman problem (TSP) in the belief space using Partially Observable Markov Decision Process (POMDP) framework. Then, feedback-based information roadmap (FIRM) algorithm is utilized to reduce the computational burden and complexity. By generating a TSP-FIRM graph, the search policy is obtained and an algorithm is proposed for online execution of the policy. Moreover, approaches to cope with challenges such as map updating, large deviations and high uncertainty in localization, which are more troublesome in a real implementation, are carefully addressed. Finally, in order to evaluate applicability and performance of the proposed algorithms, it is implemented in a simulation environment as well as on a physical robot in which some challenges such as kidnapping and discrepancies between real and computational models and map are examined.

2018JournalPDFAutonomous Robotics
Two PID-Based Controllers for a tethered Segway on Dome Shaped Structures
Mohammad H. Salehpour Hamid D. Taghirad and Hadi Moradi
2018 6th RSI International Conference on Robotics and Mechatronics (IcRoM)
Abstract:

The UTDTR Robot is a human inspired robotic platform based on a two-wheeled mobile robot. This robot is designed for the purpose of dome shaped structures inspection and maintenance, and it is a tethered robot to stably climb steep surfaces on the top of dome structures. In this paper analysis and controller design of this robot modelled as a MIMO system is represented in order to provide the desired performance on the operating surface with minimum control effort and complexity. Two PID-based controllers are designed such that the stability and desired performance conditions are obtained. In the first design a fuzzy PID controller with self-tuning scale factors is designed to tune the controller gains is forwarded, while in the second approach a multi model gain scheduling controller based on conventional PID controller is considered. Finally, the effectiveness and simplicity of the proposed controller is verified through simulation, comparing the resulting closed loop transient and steady-state response to that of the previously proposed controllers.

2017ConferencePDFDynamical Systems Analysis and Control
2017
TitleAbstractYearTypePDFResearch Group
Implementation of Multi-Goal Motion Planning Under Uncertainty on a Mobile Robot
Ali Noormohammadi-Asl, Hamid D. Taghirad, Amirhossein Tamjidi
2017 5th RSI International Conference on Robotics and Mechatronics (ICRoM)
Abstract:

Multi-goal motion planning under motion and sensor uncertainty is the problem of finding a reliable policy for visiting a set of goal points. In this paper, the problem is formulated as a formidable traveling salesman problem in the belief space. To solve this intractable problem, we propose an algorithm to construct a TSP-FIRM graph which is based on the feedback-based information roadmap (FIRM) algorithm. Also, two algorithms are proposed for the online planning of the obtained policy in the offline mode and overcoming changes in the map of the environment. Finally, we apply the algorithms on a physical nonholonomic mobile robot in the presence of challenging situations like the discrepancy between the real and computation model, map updating and kidnapping.

2017ConferencePDFAutonomous Robotics
Brain Computer Interface Control of a Virtual Robotic System based on SSVEP and EEG Signal
Fatemeh Akrami, Ebrahim Abedloo and Hamid D. Taghirad
Abstract:

In brain computer interface (BCI) systems the brain patterns for a certain type of behaviour is extracted and the corresponding control commands are produced in order to control an external apparatus. SSVEP is a specific type of such control signal which is produced at the occipital lobe of the brain in response to an external oscillating stimulus. As the brain signals in SSVEP based BCI are the neurological reaction of the individuals to the presented stimulus, it is crucial to design a suitable stimulus system as well as investigation of its effectiveness. In this paper a suitable visual stimulus is designed and implemented, and its effectiveness to control the motion of a robot on a virtual robotic system is verified based on experiments. An online integrated system comprising of a virtual industrial robotic manipulator, an EEG deployment and statistical feature extraction method is developed and real time experiments to verify its accuracy and effectiveness is experimented on different subjects. The experiments shows the promising features of the developed systems for further applications.

2017ConferencePDFDynamical Systems Analysis and Control
Two PID-Based Controllers for a tethered Segway on Dome Shaped Structures
Mohammad H. Salehpour Hamid D. Taghirad and Hadi Moradi
2018 6th RSI International Conference on Robotics and Mechatronics (IcRoM)
Abstract:

The UTDTR Robot is a human inspired robotic platform based on a two-wheeled mobile robot. This robot is designed for the purpose of dome shaped structures inspection and maintenance, and it is a tethered robot to stably climb steep surfaces on the top of dome structures. In this paper analysis and controller design of this robot modelled as a MIMO system is represented in order to provide the desired performance on the operating surface with minimum control effort and complexity. Two PID-based controllers are designed such that the stability and desired performance conditions are obtained. In the first design a fuzzy PID controller with self-tuning scale factors is designed to tune the controller gains is forwarded, while in the second approach a multi model gain scheduling controller based on conventional PID controller is considered. Finally, the effectiveness and simplicity of the proposed controller is verified through simulation, comparing the resulting closed loop transient and steady-state response to that of the previously proposed controllers.

2017ConferencePDFDynamical Systems Analysis and Control
Forward Kinematics Resolution of A Deployable Cable Robot
S. A. Khalilpour , A. Bourbour, R. Khorrambakht, S. Kariminasab, H. D. Taghirad
2017 5th RSI International Conference on Robotics and Mechatronics (ICRoM)
Abstract:

In this paper, forward kinematic derivation of a deployable suspended cable robot (DSCR) is investigated. Since the positions of the cable attachment points in this robot are not accurately available, the forward kinematics of the robot would not provide an accurate estimate for the end effector position. This paper proposes two methods to improve the accuracy of the forward kinematic solutions. First, an analysis on parameter sensitivity is presented and effective parameters are extracted. Then, based on these parameters and by using the redundant equations of the DSCR, a new set of equations for forward kinematic analysis are derived. The second method proposed in this paper is based on a geometrical analysis of kinematic uncertainty bounds. Finally, using the simulation results the effectiveness of the proposed methods is verified by illustrating the significant accuracy improvement in the obtained end effector positions.

2017ConferencePDFParallel and Cable Robotics
Motion Control of an Underactuated Parallel Robot with First Order Nonholonomic Constraint
Mohammad Reza J. Harandi and Hamid. D. Taghirad
2017 5th RSI International Conference on Robotics and Mechatronics (ICRoM)
Abstract:

Adding nonholonomic constraints in parallel manipulators, allows reduction of the actuated-joint number without affecting the reachable workspace. This principle applies to wrist robot in some underactuated designs. This paper studies steady state motion control for an nS-2SPU underactuated parallel wrist robot. First, a suitable Euler angles representation is selected and a new method for forward kinematic problem without extra sensor is proposed. Next, differential kinematics of the robot is analyzed considering first order nonholonomic constraint on angular velocity of the robot. By some manipulations, the derived equations are transformed into chain form, and a hierarchical sliding mode controller is designed for the system. Closed-loop performance of the proposed controller is compared to that of a traditional controller reported in the literature through simulations.

2017ConferencePDFParallel and Cable Robotics
An Observer-Based Force Reflection Robust Control for Dual User Haptic Surgical Training System
M. Motaharifar and H. D. Taghirad
2017 5th RSI International Conference on Robotics and Mechatronics (ICRoM)
Abstract:

This paper investigates the controller design problem for the dual user haptic surgical training system. In this system, the trainer and the trainee are interfaced together through their haptic devices and the surgical operations on the virtual environment is performed by the trainee. The trainer is able to interfere into the procedure in the case that any mistakes is made by the trainee. In the proposed structure, the force of the trainer's hands is reflected to the hands of the trainee to give necessary guidance to the trainee. The force signal is obtained from an unknown input high gain observer. The position of the trainee and the contact force with the environment are sent to the trainer to give him necessary information regarding the status of surgical operations. Stabilizing control laws are also designed for each haptic device and the stability of the closed loop nonlinear system is proven. Simulation results are presented to show the effectiveness of the proposed controller synthesis.

2017ConferencePDFSurgical Robotics
A Robust Approach Toward Kernel-Based Visual Servoing
Mahsa Parsapour and Hamid D. Taghirad
2017 5th RSI International Conference on Robotics and Mechatronics (ICRoM)
Abstract:

We introduce a robust controller for kernel-based visual servoing systems. In such systems, visual features are sum of weighted-image intensities via smooth kernel functions. This information along with its derivative are input to the controller in which we have developed a sliding mode approach to generate system commands. In vision-based systems, image uncertainties affect the tracking performance and stability, and the target object may get out of the field of view. Unless considerable image uncertainties appear, such systems are able to track the object within desired precision. Hence, we have investigated the effect of the image noise as the main source of uncertainty, and encapsulated its characteristics in a proper representation. In order to fulfill the sliding condition, some bounds over image uncertainty and tracking errors are considered, and the controller gains are tuned online to keep the tracking error bounded. An application of the proposed method is experimentally tested on an industrial robot.

2017ConferencePDFVisual Robotics
Comment on: "Centers of quasi-homogeneous polynomial planar systems"
A. Rahimabadi, H.D. Taghirad
Nonlinear Analysis: Real World Applications
Abstract:

We describe a counter-example which shows that of theorem in Algaba et al. (2012) is not correct. This part of the theorem, pinpoints whether the origin of quasi-homogeneous system in Algaba et al. (2012) is a center or not. It is shown in this note that the given necessary and sufficient conditions of theorem, in Algaba et al. (2012) are not complete.

2017JournalPDFDynamical Systems Analysis and Control
2016
TitleAbstractYearTypePDFResearch Group
Stability Analysis and Robust PID Control of Cable-Driven Robots Considering Elasticity in Cables
M. A. Khosravi, H. D. Taghirad
AUT Journal of Electrical Engineering
Abstract:

In this paper robust PID control of fully-constrained cable driven parallel manipulators with elastic cables is studied in detail. In dynamic analysis, it is assumed that the dominant dynamics of cable can be approximated by linear axial spring. To develop the idea of control for cable robots with elastic cables, a robust PID control for cable driven robots with ideal rigid cables is firstly designed and then, this controller is modified for the robots with elastic cables. To overcome vibrations caused by inevitable elasticity of cables, a composite control law is proposed based on singular perturbation theory. The proposed control algorithm includes robust PID control for corresponding rigid model and a corrective term. Using the proposed control algorithm the dynamics of the cable driven robot is divided into slow and fast subsystems. Then, based on the results of singular perturbation theory, stability analysis of the total system is performed. Finally, the effectiveness of the proposed control law is investigated through several simulations on a planar cable driven robot.

2016JournalPDFParallel and Cable Robotics
Reconstruction of B-spline curves and surfaces by adaptive group testing
Alireza Norouzzadeh Ravari, Hamid D. Taghirad
Computer-Aided Design
Abstract:

Point clouds as measurements of 3D sensors have many applications in various fields such as object modeling, environment mapping and surface representation. Storage and processing of raw point clouds is time consuming and computationally expensive. In addition, their high dimensionality shall be considered, which results in the well known curse of dimensionality. Conventional methods either apply reduction or approximation to the captured point clouds in order to make the data processing tractable. B-spline curves and surfaces can effectively represent 2D data points and 3D point clouds for most applications. Since processing all available data for B-spline curve or surface fitting is not efficient, based on the Group Testing theory an algorithm is developed that finds salient points sequentially. The B-spline curve or surface models are updated by adding a new salient point to the fitting process iteratively until the Akaike Information Criterion (AIC) is met. Also, it has been proved that the proposed method finds a unique solution so as what is defined in the group testing theory. From the experimental results the applicability and performance improvement of the proposed method in relation to some state-of-the-art B-spline curve and surface fitting methods, may be concluded.

2016JournalPDFAutonomous Robotics
Reconstruction of B-spline curves and surfaces by adaptive group testing
Alireza Norouzzadeh Ravari, Hamid D. Taghirad
Computer-Aided Design
Abstract:

Point clouds as measurements of 3D sensors have many applications in various fields such as object modeling, environment mapping and surface representation. Storage and processing of raw point clouds is time consuming and computationally expensive. In addition, their high dimensionality shall be considered, which results in the well known curse of dimensionality. Conventional methods either apply reduction or approximation to the captured point clouds in order to make the data processing tractable. B-spline curves and surfaces can effectively represent 2D data points and 3D point clouds for most applications. Since processing all available data for B-spline curve or surface fitting is not efficient, based on the Group Testing theory an algorithm is developed that finds salient points sequentially. The B-spline curve or surface models are updated by adding a new salient point to the fitting process iteratively until the Akaike Information Criterion (AIC) is met. Also, it has been proved that the proposed method finds a unique solution so as what is defined in the group testing theory. From the experimental results the applicability and performance improvement of the proposed method in relation to some state-of-the-art B-spline curve and surface fitting methods, may be concluded.

2016JournalPDFMixed Reality in Surgery
Adaptive Control of Dual User Teleoperation with Time Delay and Dynamic Uncertainty
M. Motaharifar, A. Bataleblu, and H. D. Taghirad
2016 24th Iranian Conference on Electrical Engineering (ICEE)
Abstract:

This technical note aims at proposing an adaptive control scheme for dual-master trilateral teleoperation in the presence of communication delay and dynamic uncertainty in the parameters. The majority of existing control schemes for trilateral teleoperation systems have been developed for linear systems or nonlinear systems without dynamic uncertainty or time delay. However, in the practical teleoperation applications, the dynamics equations are nonlinear and contain uncertain parameters. In addition, the time delay in the communication channel mostly exists in the real applications and can affect the stability of closed loop system. As a result, an adaptive control methodology is proposed in this paper that to guarantee the stability and performance of the system despite nonlinearity, dynamic uncertainties and time delay. Simulation results are presented to show the effectiveness of the proposed adaptive controller methodology.

2016ConferencePDFSurgical Robotics
NURBS-based Representation of Urban Environments for Mobile Robots
Alireza Norouzzadeh Ravari and Hamid D. Taghirad
2016 4th International Conference on Robotics and Mechatronics (ICROM)
Abstract:

Representation of the surrounding environment is a vital task for a mobile robot. Many applications for mobile robots in urban environments may be considered such as self-driving cars, delivery drones or assistive robots. In contrast to the conventional methods, in this paper a Non Uniform Rational B-Spline (NURBS) based technique is represented for 3D mapping of the surrounding environment. While in the state of the art techniques, the robot's environment is expressed in a discrete space, the proposed method is mainly developed for representation of environment in a continuous space. Exploiting the information theory, the generated representation has much lower complexity and more compression capability in relation to some state of the art techniques. In addition to representation in a lower dimensional space, the NURBS based representation is invariant against 3D geometric transformations. Furthermore, the NURBS based representation can be employed for obstacle avoidance and navigation. The applicability of the proposed algorithm is investigated in some urban environments through some publicly available data sets. It has been shown by some experiments that the proposed method has better visual representation and much better data compression compared to some state-of-the-art methods.

2016ConferencePDFAutonomous Robotics
NURBS-based Representation of Urban Environments for Mobile Robots
Alireza Norouzzadeh Ravari and Hamid D. Taghirad
2016 4th International Conference on Robotics and Mechatronics (ICROM)
Abstract:

Representation of the surrounding environment is a vital task for a mobile robot. Many applications for mobile robots in urban environments may be considered such as self-driving cars, delivery drones or assistive robots. In contrast to the conventional methods, in this paper a Non Uniform Rational B-Spline (NURBS) based technique is represented for 3D mapping of the surrounding environment. While in the state of the art techniques, the robot's environment is expressed in a discrete space, the proposed method is mainly developed for representation of environment in a continuous space. Exploiting the information theory, the generated representation has much lower complexity and more compression capability in relation to some state of the art techniques. In addition to representation in a lower dimensional space, the NURBS based representation is invariant against 3D geometric transformations. Furthermore, the NURBS based representation can be employed for obstacle avoidance and navigation. The applicability of the proposed algorithm is investigated in some urban environments through some publicly available data sets. It has been shown by some experiments that the proposed method has better visual representation and much better data compression compared to some state-of-the-art methods.

2016ConferencePDFMixed Reality in Surgery
Autonomous Flight and Obstacle Avoidance of a Quadrotor By Monocular SLAM
Omid Esrafilian and Hamid D. Taghirad
2016 4th International Conference on Robotics and Mechatronics (ICROM)
Abstract:

In this paper, a monocular vision based autonomous flight and obstacle avoidance system for a commercial quadrotor is presented. The video stream of the front camera and the navigation data measured by the drone is sent to the ground station laptop via wireless connection. Received data processed by the vision based ORB-SLAM to compute the 3D position of the robot and the environment 3D sparse map in the form of point cloud. An algorithm is proposed for enrichment of the reconstructed map, and furthermore, a Kalman Filter is used for sensor fusion. The scaling factor of the monocular slam is calculated by the linear fitting. Moreover, a PID controller is designed for 3D position control. Finally, by means of the potential field method and Rapidly exploring Random Tree (RRT) path planning algorithm, a collision-free road map is generated. Moreover, experimental verifications of the proposed algorithms are reported.

2016ConferencePDFAutonomous Robotics
Design of a Robust Controller for a Tethered Segway on Dome-Shaped Structures
Mohammad H. Salehpour Hamid D. Taghirad and Hadi Moradi
2016 4th International Conference on Robotics and Mechatronics (ICROM)
Abstract:

Tethered Segway is a robotic platform inspired by human climbers. It is a two-wheeled mobile platform tethered to the top of a structure in order to climb steep surfaces with varying slopes, such as domes. The unstructured environment may cause uncertainties in the dynamic behavior of the robot while operating on different parts of the dome. In this paper analysis and synthesis of a robust controller for a tethered Segway is presented in order to provide desired performance in the presence of uncertainties. To design the robust controller, structured and unstructured uncertainties of the model are encapsulated into a structured singular perturbation. A linear robust controller is designed such that the robust stability of the closed loop system is preserved in the presence of modeling uncertainties. Finally, the effectiveness of the proposed controller is verified through simulation by comparing its closed loop transient response and sufficiently suitable steady-state performance to that of a previously proposed LQR controller for the robot.

2016ConferencePDFDynamical Systems Analysis and Control
Type Synthesis of 2R-T Parallel Mechanisms Based on the Screw Theory for Haptic Applicationsa
Nahid Khajeh Ahmadi, Fateme Zarei and Hamid D.Taghirad
2016 4th International Conference on Robotics and Mechatronics (ICROM)
Abstract:

Recently haptic devices are increasingly used in industry and research. As their applications become widespread, their design is needed to be more efficient. At design stage, determinant features of haptic devices such as rigidity, force bandwidth, accuracy etc. must be considered and improved. Structurally, parallel mechanisms (PMs) are appropriate candidates for haptic devices. Due to multi legged structure of PMs and their grounded motors, inertia and stiffness feautures of them are desirable and it also made them popular for applications that require high mechanical transparency. Spherical kinematics (two rotational and one translational motion, 2R-T) is a very common type of motion in haptic devices that is also capable of general rendering. In this paper, several 3-DOF 2R-T PMs are synthesized for haptic applications by means of the screw theory. All of these mechanisms have center of motion (CM) which is a key property in variety of applications such as surgery. These mechanisms are compared qualitatively and their applications as haptic devices are discussed.

2016ConferencePDFParallel and Cable Robotics
Robust H-Infinity Control of a 2RT Parallel Robot For Eye Surgery
Abbas Bataleblu, Mohammad Motaharifar, Ebrahim Abedlu, Hamid D. Taghirad
2016 4th International Conference on Robotics and Mechatronics (ICROM)
Abstract:

This paper aims at designing a robust controller for a 2RT parallel robot for eye telesurgery. It presents two robust controllers designs and their performance in presence of actuator saturation limits. The nonlinear model of the robot is encapsulated with a linear model and multiplicative uncertainty using linear fractional transformations (LFT). Two different robust control namely, H ? and ?-synthesis are used and implemented. Results reveal that the controllers are capable to stabilize the closed loop system and to reduce the tracking error in the presence of the actuators saturation. Simulation results are presented to show that effectiveness of the controllers compared to that of conventional controller designs. Furthermore, it is observed that ?-synthesis controller has superior robust performance.

2016ConferencePDFSurgical Robotics
Particle Filters for Non-Gaussian Hunt-Crossley Model of Environment in Bilateral Teleoperation
Pedram Agand, Hamid D. Taghirad and Ali Khaki-Sedigh
2016 4th International Conference on Robotics and Mechatronics (ICROM)
Abstract:

Optimal solution for nonlinear identification problem in the presence of non-Gaussian distribution measurement and process noises is generally not analytically tractable. Particle filters, known as sequential Monte Carlo method (SMC), is a suboptimal solution of recursive Bayesian approach which can provide robust unbiased estimation of nonlinear non-Gaussian problem with desire precision. On the other hand, Hunt-Crossley is a widespread nonlinear model for modeling telesurgeries environment. Hence, in this paper, particle filter is proposed to capture most of the nonlinearities in telesergerie environment model. An online Bayesian framework with conventional Monte Carlo method is employed to filter and predict position and force signals of environment at slave side respectively to achieve transparent and stable bilateral teleoperation simultaneously. Simulation results illustrate effectiveness of the algorithm by comparing the estimation and tracking errors of sampling importance resampling (SIR) with extended Kalman filter.

2016ConferencePDFSurgical Robotics
Adaptive Control for Force-Reflecting Dual User Teleoperation Systems
Sara Abkhofte, Mohammad Motaharifar, and Hamid D. Taghirad
2016 4th International Conference on Robotics and Mechatronics (ICROM)
Abstract:

The aim of this paper is to develop an adaptive force reflection control scheme for dual master nonlinear teleoperation systems. Having a sense of contact forces is very important in applications of dual master teleopreation systems such as surgery training. However, most of the previous studies for dual master nonlinear teleoperation systems are limited in the stability analysis of force reflection control schemes. In this paper, it is assumed that the teleopreation system consists of two masters and a single slave manipulator. In addition, all communication channels are subject to unknown time delays. First, adaptive controllers are developed for each manipulator. Next, Input-to-State Stability (ISS) approach is used to analyze the stability of the closed loop system. Through simulation results, it is demonstrated that the proposed methodology is effective in a nonlinear teleopreation system.

2016ConferencePDFSurgical Robotics
An Observer-Based Adaptive Impedance-Control for Robotic Arms: Case Study in SMOS Robot
Soheil Gholami, Arash Arjmandi, and Hamid D. Taghirad
2016 4th International Conference on Robotics and Mechatronics (ICROM)
Abstract:

In this paper an adaptive output-feedback impedance control is proposed to be used in environment-machine interaction applications. The proposed control is designed to achieve a desired robot impedance in the presence of possible dynamical parameter uncertainties. A high-gain observer is utilized in the control structure to achieve this objective by using only position feedback of robot joints, which in turn, reduces implementation costs and eliminates additional sensor requirements. Stability of the overall system is analyzed through input to state stability analysis. Finally, to evaluate the presented structure, computer simulations are provided and the scheme effectiveness is verified.

2016ConferencePDFSurgical Robotics
Visual Servoing Simulator by Using ROS and Gazebo
Parisa Masnadi Khiabani, Babak Sistanizadeh Aghdam, Javad Ramezanzadeh and Hamid D. Taghirad
International Conference on Robotics and Mechatronics
Abstract:

In this paper, a simulator for five degree of freedom (DOF) visual servoing robot is presented with eye-in-hand configuration. This simulator has been developed in Robot Operating System (ROS) and Gazebo environment. The designed simulator eases the process of testing and debugging visual servoing schemes, and robot controllers. Among different methods, one of the existing Image based visual servoing schemes, image moments, has been implemented to verify the functionality and performance of designed simulator.

2016ConferencePDFVisual Robotics
A Navigation System for Autonomous Robot Operating in Unknown and Dynamic Environment: Escaping Algorithm
F. AdibYaghmaie, A. Mobarhani, H. D. Taghirad
International Journal of Robotics
Abstract:

In this study, the problem of navigation in dynamic and unknown environment is investigated and a navigation method based on force field approach is suggested. It is assumed that the robot performs navigation in unknown environment and builds the map through SLAM procedure. Since the moving objects' location and properties are unknown, they are identified and tracked by Kalman filter. Kalman observer provides important information about next paths of moving objects which are employed in finding collision point and time in future. In the time of collision detection, a modifying force is added to repulsive and attractive forces corresponding to the static environment and leads the robot to avoid collision. Moreover, a safe turning angle is defined to assure safe navigation of the robot. The performance of proposed method, named Escaping Algorithm, is verified through different simulation and experimental tests. Besides, comparison between Escaping Algorithm and Probabilistic Velocity Obstacle, based on computational complexity and required steps for finishing the mission is provided in this paper. The results show Escaping Algorithm outperforms PVO in term of dynamic obstacle avoidance and complexity as a practical method for autonomous navigation.

2016JournalPDFAutonomous Robotics
Adaptive robust control of fully constrained cable robots: singular perturbation approach
Reza Babaghasabha, Mohammad A. Khosravi, Hamid D. Taghirad
Nonlinear Dynamics
Abstract:

In this paper, adaptive robust control of fully constrained cable-driven parallel robots with elastic cables is studied in detail. A composite controller is proposed for the system under the assumption of linear axial spring model as the dominant dynamics of the cables and in presence of model uncertainties. The proposed controller which is designed based on the singular perturbation theory, consists of two main parts. An adaptive robust controller is designed to counteract the unstructured and parametric uncertainties of the robot and a fast control term which is added to control the longitudinal vibrations of the cables. Moreover, to ensure that all cables remain in tension, the proposed control algorithm benefits from internal force concept. Using the results of the singular perturbation theory, the stability of the overall closed-loop system is analyzed through Lyapunov second method, and finally, the effectiveness of the proposed control algorithm is verified through some simulations on a planar cable-driven parallel robot.

2016JournalPDFParallel and Cable Robotics
Mobile Robot Navigation in an Unknown Environment
A. Jazayeri, A.Fatehi, H. Taghirad
2016 IEEE Conference on Control Applications (CCA)
Abstract:

This article focuses on the mobile robot's autonomous navigation problem in an unknown environment. Considering a robot equipped with an omnidirectional range-sensor a map of the discovered area is constructed in an iterative manner. Given a target position located in the unexplored territory, initially a motion planning scheme is employed that relies on exploration-principles of the area near the target. This is achieved by assigning an exploration cost function that indirectly attracts the robot close to target. Upon discovery of the target, the robot moves to it following the shortest-distance path. Simulation studies that prove the efficiency of the overall method are presented.

2006ConferencePDF
2015
TitleAbstractYearTypePDFResearch Group
Reconstruction of B-spline curves and surfaces by adaptive group testing
Alireza Norouzzadeh Ravari, Hamid D. Taghirad
Computer-Aided Design
Abstract:

Point clouds as measurements of 3D sensors have many applications in various fields such as object modeling, environment mapping and surface representation. Storage and processing of raw point clouds is time consuming and computationally expensive. In addition, their high dimensionality shall be considered, which results in the well known curse of dimensionality. Conventional methods either apply reduction or approximation to the captured point clouds in order to make the data processing tractable. B-spline curves and surfaces can effectively represent 2D data points and 3D point clouds for most applications. Since processing all available data for B-spline curve or surface fitting is not efficient, based on the Group Testing theory an algorithm is developed that finds salient points sequentially. The B-spline curve or surface models are updated by adding a new salient point to the fitting process iteratively until the Akaike Information Criterion (AIC) is met. Also, it has been proved that the proposed method finds a unique solution so as what is defined in the group testing theory. From the experimental results the applicability and performance improvement of the proposed method in relation to some state-of-the-art B-spline curve and surface fitting methods, may be concluded.

2015JournalPDFAutonomous Robotics
Reconstruction of B-spline curves and surfaces by adaptive group testing
Alireza Norouzzadeh Ravari, Hamid D. Taghirad
Computer-Aided Design
Abstract:

Point clouds as measurements of 3D sensors have many applications in various fields such as object modeling, environment mapping and surface representation. Storage and processing of raw point clouds is time consuming and computationally expensive. In addition, their high dimensionality shall be considered, which results in the well known curse of dimensionality. Conventional methods either apply reduction or approximation to the captured point clouds in order to make the data processing tractable. B-spline curves and surfaces can effectively represent 2D data points and 3D point clouds for most applications. Since processing all available data for B-spline curve or surface fitting is not efficient, based on the Group Testing theory an algorithm is developed that finds salient points sequentially. The B-spline curve or surface models are updated by adding a new salient point to the fitting process iteratively until the Akaike Information Criterion (AIC) is met. Also, it has been proved that the proposed method finds a unique solution so as what is defined in the group testing theory. From the experimental results the applicability and performance improvement of the proposed method in relation to some state-of-the-art B-spline curve and surface fitting methods, may be concluded.

2015JournalPDFMixed Reality in Surgery
Reigon of Convergence Expansion of a Robust Model Predictive Controller
Mojgan Rostami and Hamid D. Taghirad
2015 23rd Iranian Conference on Electrical Engineering
Abstract:

In this paper a gain scheduling method is proposed for robust model predictive control of a useful class of nonlinear discrete-time systems. The system is composed of a linear model perturbed by an additive state-dependent nonlinear term. Robust model predictive controllers are designed in the literature to compensate for the uncertainty of the system. In order to enlarge the region of convergence it is assumed that system has several equilibrium points and multiple robust controllers are designed. By switching between the controllers it is verified that the region of convergence shall be enlarged, while the overall stability of the system is preserved. In the proposed method, the stability analysis based on Lyapunov functions for each level set is performed, while state feedback control law is designed by minimization of a desired cost function formed in linear matrix inequalities. The simulation results show the applicability of the proposed method.

2015ConferencePDFDynamical Systems Analysis and Control
Kinematic and Workspace Analysis of DIAMOND: An Innovative Eye Surgery Robot
Amir Molaei, Ebrahim Abedloo, Hamid D. Taghirad and Zahra Marvi
2015 23rd Iranian Conference on Electrical Engineering
Abstract:

This paper presents a new robot for eye surgeries, referred to as DIAMOND. It consists of a spherical mechanism that has a remote center of motion (RCM) point and is capable of orienting the surgical instrument about this unique point. Using the RCM as the insertion point of the surgery instruments makes the robot suitable for minimally invasive surgery applications. DIAMOND has two pairs of identical spherical serial limbs that form a closed kinematic chain leading to high stiffness. The spherical structure of the mechanism is compatible with the human head and the robot may perform the surgery upon the head without any collision with the patient. Furthermore, dexterity and having a compact size is taken into account in the mechanical design of the robot. The workspace of the robot is a complete singularity free sphere that covers the region needed for any eye surgeries. In this paper, a comparison between different types of existing eye surgery robots is presented, the structure of the mechanism is described in detail and kinematic analysis of the robot is investigated.

2015ConferencePDFSurgical Robotics
Loop Closure Detection by Compressed Sensing for Exploration of Mobile Robots in Outdoor Environments
Alireza Norouzzadeh Ravari and Hamid D. Taghirad
2015 3rd RSI International Conference on Robotics and Mechatronics (ICROM)
Abstract:

In the problem of simultaneously localization and mapping (SLAM) for a mobile robot, it is required to detect previously visited locations so the estimation error shall be reduced. Sensor observations are compared by a similarity metric to detect loops. In long term navigation or exploration, the number of observations increases and so the complexity of the loop closure detection. Several techniques are proposed in order to reduce the complexity of loop closure detection. Few algorithms have considered the loop closure detection from a subset of sensor observations. In this paper, the compressed sensing approach is exploited to detect loops from few sensor measurements. In the basic compressed sensing it is assumed that a signal has a sparse representation is a basis which means that only a few elements of the signal are non-zero. Based on the compressed sensing approach a sparse signal can be recovered from few linear noisy projections by l1 minimization. The difference matrix which is widely used for loop detection has a sparse structure, where similar observations are shown by zero distance and different locations are indicated by ones. Based on the multiple measurement vector technique which is an extension of the basic compressed sensing, the loop closure detection is performed by comparison of few sensor observations. The applicability of the proposed algorithm is investigated in some outdoor environments through some publicly available data sets. It has been shown by some experiments that the proposed method can detect loops effectively.

2015ConferencePDFAutonomous Robotics
Loop Closure Detection by Compressed Sensing for Exploration of Mobile Robots in Outdoor Environments
Alireza Norouzzadeh Ravari and Hamid D. Taghirad
2015 3rd RSI International Conference on Robotics and Mechatronics (ICROM)
Abstract:

In the problem of simultaneously localization and mapping (SLAM) for a mobile robot, it is required to detect previously visited locations so the estimation error shall be reduced. Sensor observations are compared by a similarity metric to detect loops. In long term navigation or exploration, the number of observations increases and so the complexity of the loop closure detection. Several techniques are proposed in order to reduce the complexity of loop closure detection. Few algorithms have considered the loop closure detection from a subset of sensor observations. In this paper, the compressed sensing approach is exploited to detect loops from few sensor measurements. In the basic compressed sensing it is assumed that a signal has a sparse representation is a basis which means that only a few elements of the signal are non-zero. Based on the compressed sensing approach a sparse signal can be recovered from few linear noisy projections by l1 minimization. The difference matrix which is widely used for loop detection has a sparse structure, where similar observations are shown by zero distance and different locations are indicated by ones. Based on the multiple measurement vector technique which is an extension of the basic compressed sensing, the loop closure detection is performed by comparison of few sensor observations. The applicability of the proposed algorithm is investigated in some outdoor environments through some publicly available data sets. It has been shown by some experiments that the proposed method can detect loops effectively.

2015ConferencePDFMixed Reality in Surgery
Modified Fast-SLAM For 2D Mapping And 3D Localization
Soheil Gharatappeh, Mohammad Ghorbanian, Mehdi Keshmiri, Hamid D. Taghirad
2015 3rd RSI International Conference on Robotics and Mechatronics (ICROM)
Abstract:

Fast Simultaneous Localization and Mapping (SLAM) algorithm is capable of real-time implementation due to logarithmic time complexity which results in decrease of computational cost. In this algorithm state vector of a robot merely includes planar location of the robot and its angle to the horizontal plane. It has fewer components comparing to state vector in extended Kalman filter method which consists of location of all environmental features. In existing methods for implementing this algorithm, robot movement is considered to be totally in planar movement; while if moving on a slope changes the pitch angle of the robot, it causes errors in the algorithm. Correcting these errors will lead to a precise 2D mapping and 3D localization. This paper details the modification added to conventional Fast-Slam algorithm to accommodate this requirement by using an IMU. Simulation and experimental results shows the effectiveness of such modification.

2015ConferencePDFAutonomous Robotics
Optimization of KNTU Delta robot for pick and place application
Amin Khorasani, Soheil Gholami, Hamid D. Taghirad
2015 3rd RSI International Conference on Robotics and Mechatronics (ICROM)
Abstract:

In this paper, the desired configuration for installation of Delta robot is formulated as an optimization problem and has been solved to reach to the highest rate of pick and place operation. The optimization is performed considering the actuators speed and acceleration limitation of the robot within the workspace. Furthermore, energy consumption is considered next as the other optimization objective, and it is shown that the optimal region for the first optimization problem lies within that of the latter one, and therefore, there is no need to propose a multi-objective optimization problem in this case. As a proof of concept, KNTU Delta robot is designed and implemented in practice by using the optimal configuration, and it is observed that the optimal design is very promising in practice.

2015ConferencePDFParallel and Cable Robotics
Eye-RHAS Manipulator: From Kinematics to Trajectory Control
Ebrahim Abedloo, Soheil Gholami, and Hamid D. Taghirad
2015 3rd RSI International Conference on Robotics and Mechatronics (ICROM)
Abstract:

One of the challenging issues in the robotic technology is to use robotics arm for surgeries, especially in eye operations. Among the recently developed mechanisms for this purpose, there exists a robot, called Eye-RHAS, that presents sustainable precision in vitreo-retinal eye surgeries. In this work the closed-form dynamical model of this robot has been derived by Gibbs-Appell method. Furthermore, this formulation is verified through SimMechanics Toolbox of MATLAB. Finally, the robot is simulated in a real time trajectory control in a teleoperation scheme. The tracking errors show the effectiveness and applicability of the dynamic formulation to be used in the teleoperation schemes.

2015ConferencePDFSurgical Robotics
Vision-Based Kinematic Calibration of Spherical Robots
Pedram Agand, Hamid D. Taghirad and Amir Molaee
2015 3rd RSI International Conference on Robotics and Mechatronics (ICROM)
Abstract:

In this article, a method to obtain spatial coordinate of spherical robot's moving platform using a single camera is proposed, and experimentally verified. The proposed method is an accurate, flexible and low-cost tool for the kinematic calibration of spherical-workspace mechanisms to achieve the desired accuracy in position. The sensitivity and efficiency of the provided method is thus evaluated. Furthermore, optimization of camera location is outlined subject to the prescribed cost functions. Finally, experimental analysis of the proposed calibration method on ARAS Eye surgery Robot (DIAMOND) is presented; In which the accuracy is obtained from three to six times better than the previous calibration.

2015ConferencePDFSurgical Robotics
Kernel-based sliding mode control for visual servoing system
Mahsa Parsapour, Hamid D. Taghirad
IET Computer Vision
Abstract:

In this study, a new approach to design a controller for a visual servoing (VS) system is proposed. Kernel-measurement is used to track the motion of a featureless object which is defined as sum of weighted-image value through smooth kernel functions. This approach was used in kernel-based VS (KBVS). To improve the tracking error and expand the stability region, sliding mode control is integrated with kernel measurement. Proportional-integral-type sliding surface is chosen as a suitable manifold to produce the required control effort. Moreover, the stability of this algorithm is analysed via Lyapunov theory and its performance is verified experimentally by implementing the proposed method on a five degrees of freedom industrial robot. Through experimental results, it is shown that the performance of tracking error in the proposed method is more suitable than KBVS, for a wider workspace and when the object is placed near the boundary of the camera's field of view.

2015JournalPDFVisual Robotics
Stability domains of the delay and PID coefficients for general time-delay systems
Elham Almodaresi, Mohammad Bozorg and Hamid D. Taghirad
International Journal of Control
Abstract:

Time delays are encountered in many physical systems, and they usually threaten the stability and performance of closed-loop systems. The problem of determining all stabilising proportional-integral-derivative (PID) controllers for systems with perturbed delays is less investigated in the literature. In this study, the Rekasius substitution is employed to transform the system parameters to a new space. Then, the singular frequency (SF) method is revised for the Rekasius transformed system. A novel technique is presented to compute the ranges of time delay for which stable PID controller exists. This stability range cannot be readily computed from the previous methods. Finally, it is shown that similar to the original SF method, finite numbers of singular frequencies are sufficient to compute the stable regions in the space of time delay and controller coefficients.

2015JournalPDF
3D Scene and Object Classification Based on Information Complexity of Depth Data
A. Norouzzadeh, H. D. Taghirad
Mathematics
Abstract:

In this paper the problem of 3D scene and object classification from depth data is addressed. In contrast to high-dimensional feature-based representation, the depth data is described in a low dimensional space. In order to remedy the curse of dimensionality problem, the depth data is described by a sparse model over a learned dictionary. Exploiting the algorithmic information theory, a new definition for the Kolmogorov complexity is presented based on the Earth Mover’s Distance (EMD). Finally the classification of 3D scenes and objects is accomplished by means of a normalized complexity distance, where its applicability in practice is proved by some experiments on publicly available datasets. Also, the experimental results are compared to some state-of-the-art 3D object classification methods. Furthermore, it has been shown that the proposed method outperforms FAB-Map 2.0 in detecting loop closures, in the sense of the precision and recall.

2015JournalPDFAutonomous Robotics
3D Scene and Object Classification Based on Information Complexity of Depth Data
A. Norouzzadeh, H. D. Taghirad
Mathematics
Abstract:

In this paper the problem of 3D scene and object classification from depth data is addressed. In contrast to high-dimensional feature-based representation, the depth data is described in a low dimensional space. In order to remedy the curse of dimensionality problem, the depth data is described by a sparse model over a learned dictionary. Exploiting the algorithmic information theory, a new definition for the Kolmogorov complexity is presented based on the Earth Mover’s Distance (EMD). Finally the classification of 3D scenes and objects is accomplished by means of a normalized complexity distance, where its applicability in practice is proved by some experiments on publicly available datasets. Also, the experimental results are compared to some state-of-the-art 3D object classification methods. Furthermore, it has been shown that the proposed method outperforms FAB-Map 2.0 in detecting loop closures, in the sense of the precision and recall.

2015JournalPDFMixed Reality in Surgery
Visual Tracking using Kernel Projected Measurement and Log-Polar Transformation
Fateme Bakhshande, Hamid D. Taghirad
International Journal of Robotics Theory and Applications
Abstract:

Visual Servoing is generally contained of control and feature tracking. Study of previous methods shows that no attempt has been made to optimize these two parts together. In kernel based visual servoing method, the main objective is to combine and optimize these two parts together and to make an entire control loop. This main target is accomplished by using Lyapanov theory. A Lyapanov candidate function is formed based on kernel definition such that the Lyapanov stability can be verified. The implementation is done in four degrees of freedom and Fourier transform is used for decomposition of the rotation and scale directions from 2D translation. In the present study, a new method in scale and rotation correction is presented. Log-Polar Transform is used instead of Fourier transform for these two degrees of freedom. Tracking in four degrees of freedom is synthesized to show the visual tracking of an unmarked object. Comparison between Log-Polar transform and Fourier transform shows the advantages of the presented method. KBVS based on Log-Polar transform proposed in this paper, because of its robustness, speed and featureless properties

2015JournalPDFVisual Robotics
Adaptive robust control of fully-constrained cable driven parallel robots
Reza Babaghasabha, Mohammad A. Khosravi, Hamid D. Taghirad
Mechatronics
Abstract:

In this paper, adaptive robust control (ARC) of fully-constrained cable driven parallel robots is studied in detail. Since kinematic and dynamic models of the robot are partly structurally unknown in practice, in this paper an adaptive robust sliding mode controller is proposed based on the adaptation of the upper bound of the uncertainties. This approach does not require pre-knowledge of the uncertainties upper bounds and linear regression form of kinematic and dynamic models. Moreover, to ensure that all cables remain in tension, proposed control algorithm benefit the internal force concept in its structure. The proposed controller not only keeps all cables under tension for the whole workspace of the robot, it is chattering-free, computationally simple and it does not require measurement of the end-effector acceleration. The stability of the closed-loop system with proposed control algorithm is analyzed through Lyapunov second method and it is shown that the tracking error will remain uniformly ultimately bounded (UUB). Finally, the effectiveness of the proposed control algorithm is examined through some experiments on a planar cable driven parallel robot and it is shown that the proposed controller is able to provide suitable tracking performance in practice.

2015JournalPDFParallel and Cable Robotics
Corner stability in nonlinear autonomous systems
Arsalan Rahimabadi, H. D. Taghirad
Nonlinear Dynamics
Abstract:

In most practical applications, studying the asymptotic stability of equilibrium points of a system is of utmost importance. Furthermore, in many cases, the response is restricted to only a sector of the state space. For example, positive systems that are common in chemical processes have nonnegative state variables. For such systems, stability analysis of the system using Lyapunov stability is not advised, since this stability is defined for all the points within a neighborhood of the equilibrium point. In this paper, a new notion of stability, called corner stability, is defined as more suitable for studying asymptotic stability of equilibrium points in such systems. In order to derive sufficient conditions of corner stability, a theorem is stated and proven in this paper, and corner stability of three case studies is analyzed and verified.

2015JournalPDFDynamical Systems Analysis and Control
A 3D Sliding Mode Control Approach for Position Based Visual Servoing System
Mahsa Parsapour, Soheil RayatDoost, and Hamid D. Taghirad
Scientia Iranica
Abstract:

The performance of visual servoing systems can be enhanced through nonlinear controllers. In this paper, a sliding mode control is employed for such a purpose. The controller design is based on the outputs of a pose estimator which is implemented on the scheme of the Position-Based Visual Servoing (PBVS) approach. Accordingly, a robust estimator based on unscented Kalman observer cascading with Kalman ?lter is used to estimate the position, velocity and acceleration of the target. Therefore, a PD-type sliding surface is selected as a suitable manifold. The combination of the estimator and nonlinear controller provides a robust and stable structure in PBVS approach. The stability analysis is veri?ed through Lyapunov theory. The performance of the proposed algorithm is veri?ed experimentally through an industrial visual servoing system.

2015JournalPDFVisual Robotics
2014
TitleAbstractYearTypePDFResearch Group
Kernel-based sliding mode control for visual servoing system
Mahsa Parsapour, Hamid D. Taghirad
IET Computer Vision
Abstract:

In this study, a new approach to design a controller for a visual servoing (VS) system is proposed. Kernel-measurement is used to track the motion of a featureless object which is defined as sum of weighted-image value through smooth kernel functions. This approach was used in kernel-based VS (KBVS). To improve the tracking error and expand the stability region, sliding mode control is integrated with kernel measurement. Proportional-integral-type sliding surface is chosen as a suitable manifold to produce the required control effort. Moreover, the stability of this algorithm is analysed via Lyapunov theory and its performance is verified experimentally by implementing the proposed method on a five degrees of freedom industrial robot. Through experimental results, it is shown that the performance of tracking error in the proposed method is more suitable than KBVS, for a wider workspace and when the object is placed near the boundary of the camera's field of view.

2015JournalPDFVisual Robotics
Dynamic Analysis and Control of Fully-Constrained Cable Robots with Elastic Cables: Variable Stiffness Formulation
Mohammad A. Khosravi and Hamid D. Taghirad
Cable-Driven Parallel Robots
Abstract:

In this paper dynamic analysis and control of fully-constrained parallel cable robots are studied in detail. In dynamic analysis, it is assumed that the dominant dynamics of cable can be approximated by linear axial spring. Furthermore, variable stiffness formulation for the cables is employed in modeling process. To overcome vibrations caused by inevitable elasticity of cables, a composite control law is proposed based on singular perturbation theory. Using the proposed control algorithm the dynamics of the cable robot is divided into two subsystems namely slow and fast. Then, based on the results of singular perturbation theory, stability analysis of the total system is performed. Finally, the effectiveness of the proposed composite control law is investigated through several simulations on a planar parallel cable robot.

2014JournalPDFParallel and Cable Robotics
Adaptive Control of KNTU Planar Cable-Driven Parallel Robot with Uncertainties in Dynamic and Kinematic Parameters
Reza Babaghasabha, Mohammad A. Khosravi and Hamid D. Taghirad
Cable-Driven Parallel Robots
Abstract:

This paper addresses the design and implementation of adaptive control on a planar cable-driven parallel robot with uncertainties in dynamic and kinematic parameters. To develop the idea, firstly, adaptation is performed on dynamic parameters and it is shown that the controller is stable despite the kinematic uncertainties. Then, internal force term is linearly separated into a regressor matrix in addition to a kinematic parameter vector that contains estimation error. In the next step to improve the controller performance, adaptation is performed on both the dynamic and kinematic parameters. It is shown that the performance of the proposed controller is improved by correction in the internal forces. The proposed controller not only keeps all cables in tension for the whole workspace of the robot, it is computationally simple and it does not require measurement of the end-effector acceleration as well. Finally, the effectiveness of the proposed control algorithm is examined through some experiments on KNTU planar cable-driven parallel robot and it is shown that the proposed control algorithm is able to provide suitable performance in practice.

2014JournalPDFParallel and Cable Robotics
Transformation Invariant 3D Object Recognition Based On Information Complexity
Alireza Norouzzadeh Ravari and Hamid D. Taghirad
2014 Second RSI/ISM International Conference on Robotics and Mechatronics (ICRoM)
Abstract:

The 3D representation of objects and scenes as a point cloud or range image has been made simple by means of sensors such as Microsoft Kinect, stereo camera or laser scanner. Various tasks, such as recognition, modeling and classification can not be performed on raw measurements because of the curse of high dimensionality, computational and algorithm complexity. Non Uniform Rational Basis Splines (NURBS) are a widely used representation technique for 3D objects in various robotics and Computer Aided Design (CAD) applications. In this paper, a similarity measurement from information theory is employed in order to recognize an object sample from a set of objects. From a NURBS model fitted to the observed point cloud, a complexity based representation is derived which is transformation invariant in the sense of Kolmogorov complexity. Experimental results on a set of 3D objects grabbed by a Kinect sensor indicates the applicability of the proposed method for object recognition tasks. Furthermore, the results of the proposed method is compared to that of some state of the art algorithms.

2014ConferencePDFAutonomous Robotics
Transformation Invariant 3D Object Recognition Based On Information Complexity
Alireza Norouzzadeh Ravari and Hamid D. Taghirad
2014 Second RSI/ISM International Conference on Robotics and Mechatronics (ICRoM)
Abstract:

The 3D representation of objects and scenes as a point cloud or range image has been made simple by means of sensors such as Microsoft Kinect, stereo camera or laser scanner. Various tasks, such as recognition, modeling and classification can not be performed on raw measurements because of the curse of high dimensionality, computational and algorithm complexity. Non Uniform Rational Basis Splines (NURBS) are a widely used representation technique for 3D objects in various robotics and Computer Aided Design (CAD) applications. In this paper, a similarity measurement from information theory is employed in order to recognize an object sample from a set of objects. From a NURBS model fitted to the observed point cloud, a complexity based representation is derived which is transformation invariant in the sense of Kolmogorov complexity. Experimental results on a set of 3D objects grabbed by a Kinect sensor indicates the applicability of the proposed method for object recognition tasks. Furthermore, the results of the proposed method is compared to that of some state of the art algorithms.

2014ConferencePDFMixed Reality in Surgery
An Online Implementation of Robust RGB-D SLAM
M. A. Athari, H. D. Taghirad
2014 Second RSI/ISM International Conference on Robotics and Mechatronics (ICRoM)
Abstract:

This paper presents an online robust RGB-D SLAM algorithm which uses an improved switchable constraints robust pose graph slam alongside with radial variance based hash function as the loop detector. The switchable constraints robust back-end is improved by initialization of its weights according to information matrix of the loops and is validated using real world datasets. The radial variance based hash function is combined with an online image to map comparison to improve accuracy of loop detection. The whole algorithm is implemented on K. N. Toosi University mobile robot with a Microsoft Kinect camera as the RGB-D sensor and the whole algorithm is validated using this robot, while the map of the environment is generated in an online fashion.

2014ConferencePDFAutonomous Robotics
An Improved Optimization Method for iSAM2
Rana Talaei Shahir and Hamid D. Taghirad
2014 Second RSI/ISM International Conference on Robotics and Mechatronics (ICRoM)
Abstract:

There is an issue called maximum likelihood estimation in SLAM that corresponds to a nonlinear least-square problem. It is expected to earn an accurate solution for large-scale environments with high speed of convergence. Although all the applied optimization methods might be accepted in terms of accuracy and speed of convergence for small datasets, their solutions for large-scale datasets are often far from the ground truth. In this paper, a double Dogleg trust region method is proposed and adjusted with iSAM2 to level up performance and accuracy of the algorithm especially in large-scale datasets. Since the trust region methods are sensitive to their own parameters, Gould parameters are chosen to obtain better performance. Simulations are done on some large-scale datasets and the results indicate that the proposed method is more efficient compared to the conventional iSAM2 algorithm.

2014ConferencePDFAutonomous Robotics
Online Time-Optimal Trajectory Planning in Dynamic Workspace of Cable Suspended Robots
Ahmad Sharifi and Hamid D. Taghirad
2014 Second RSI/ISM International Conference on Robotics and Mechatronics (ICRoM)
Abstract:

This paper presents a method for online trajectory planning of cable suspended robots. A three degrees-of-freedom spatial cable robot is studied in this analysis. By deriving dynamic model of the robot, cable force restrictions will induce a set of algebraic inequalities in dynamic equations. Direction of required tracking acceleration reveals feasible motion of the robot, which guarantees non-violation of cable force bilateral bounds. Required tracking acceleration is in the direction of instantaneous minus desired velocity vectors with specified magnitude. Furthermore, alternative recipes are employed to decrease negative impacts of unwanted inputs and applying actuator constraints in trajectory planning. Finally, several simulations are presented to demonstrate success of the method. Proposed approach can be used in online trajectory tracking for all cable-driven parallel suspended robots akin to what is realized for the presented three degrees-of-freedom robot.

2014ConferencePDFParallel and Cable Robotics
Closed-Form Dynamic Formulation of Spherical Parallel Manipulators by Gibbs-Appell Method
Ebrahim Abedloo, Amir Molaei and Hamid D. Taghirad
2014 Second RSI/ISM International Conference on Robotics and Mechatronics (ICRoM)
Abstract:

Spherical Parallel Robot (SPR) is a complex but widely used type of manipulators that performs only rotational motion. Dynamic analysis of SPR has a vital role in mechanical design, model-based controller, identification and fault detection of such robots. Complexity of SPR kinematic structure makes traditional dynamic modeling methods such as Newton-Euler, virtual work and Lagrange formulations a prohibitive task. In this paper a new procedure for deriving closed form dynamics of general SPR using Gibbs-Appell method is presented. The proposed method does not require any recursive computation or symbolic manipulation and dynamic matrices of the robot is directly derived in an explicit form. By using the proposed method, closed form dynamic formulation of a general 3DOF SPR, known as agile wrist, is obtained and it is verified for an arbitrary trajectory. The unique feature of the method presented in this paper, makes it promising to be used for other parallel manipulators.

2014ConferencePDFParallel and Cable Robotics
Implementation of Analytic Iterative Redundancy Resolution Technique on KNTU Cable Robot
Fereshteh Sabahi, Mohammad A. Khosravi and Hamid D. Taghirad
2014 Second RSI/ISM International Conference on Robotics and Mechatronics (ICRoM)
Abstract:

Analytic Iterative Redundancy Resolution (AIRR) is a semi-analytic method for redundancy resolution in cable-driven manipulators. As all previous redundancy resolution methods were based on numerical algorithms, they impose an uncertainty to execution time which is barely acceptable in realtime implementation. In this paper, AIRR is implemented as a fast solution to redundancy resolution problem by checking a set of analytic solutions instead of using numerical algorithms. Furthermore, the performance of this method is compared to previous numerical method implemented on KNTU robot with respect to execution time and accuracy. It is shown that the realtime performance of this implementation in closed-loop control structure is at least fifteen times faster than that of previously implemented methods. Such decrease in execution time in realtime implementation is very promising for future applications.

2014ConferencePDFParallel and Cable Robotics
Sliding Impedance Control for Improving Transparency in Telesurgery
Samim Khosravi, Arash Arjmandi and Hamid D. Taghirad
2014 Second RSI/ISM International Conference on Robotics and Mechatronics (ICRoM)
Abstract:

This paper describes a novel control scheme for teleoperation with constant communication time delay and soft tissue in environment of slave side. This control scheme combine fidelity criteria with sliding impedance. Fidelity is a measure for evaluating telesurgical system when environment at slave side contains soft tissues. Sliding impedance is used to stabilize the teleoperating system with constant time delays and improve tracking performance in the presence of uncertainties in slave dynamics. The control system contains impedance and sliding impedance control in master and slave manipulators, respectively. Parameters of sliding impedance controller are obtained from fidelity optimization problem while parameters of master impedance controller are determined such that to guarantee stability of the entire teleopertaion system. Simulation results demonstrate suitable performance of position and force tracking of the telesurgical system.

2014ConferencePDFSurgical Robotics
Kernel-based sliding mode control for visual servoing system
Mahsa Parsapour, Hamid D. Taghirad
IET Computer Vision
Abstract:

In this study, a new approach to design a controller for a visual servoing (VS) system is proposed. Kernel-measurement is used to track the motion of a featureless object which is defined as sum of weighted-image value through smooth kernel functions. This approach was used in kernel-based VS (KBVS). To improve the tracking error and expand the stability region, sliding mode control is integrated with kernel measurement. Proportional-integral-type sliding surface is chosen as a suitable manifold to produce the required control effort. Moreover, the stability of this algorithm is analysed via Lyapunov theory and its performance is verified experimentally by implementing the proposed method on a five degrees of freedom industrial robot. Through experimental results, it is shown that the performance of tracking error in the proposed method is more suitable than KBVS, for a wider workspace and when the object is placed near the boundary of the camera's field of view.

2014JournalPDFVisual Robotics
Robust Control of a Steam Turbine Power Based on a Precise Nonlinear Model
S.A. Salamati, H.D. Taghirad, Ali Chaibakhsh
2014 5th Conference on Thermal Power Plants (CTPP)
Abstract:

In this paper, a precise and nonlinear model is developed for Nekka power plant turbine from its experimental data and documents. It is proposed to use boiler-turbine coordinated control system to increase effective efficiency of the steam unit. Identification procedures have been performed to obtain continuous time models of Nekka steam turbine at various loads. After determining the upper bound for uncertainty and choosing a good performance weighting function, a robust controller has been designed and implemented in closed loop for the turbine nonlinear model. Since the closed loop performance was not as required, a cascade controller structure is proposed, in which the turbine loop is closed by a PI controller in order to significantly reduce the uncertainty. Simulation results demonstrate the suitable performance of the closed loop in terms of tracking, speed of response, and damping of oscillations.

2014ConferencePDFDynamical Systems Analysis and Control
Dynamic Modeling and Control of Parallel Robots With Elastic Cables: Singular Perturbation Approach
Mohammad A. Khosravi and Hamid D. Taghirad
IEEE Transactions on Robotics
Abstract:

In this paper, control of fully-constrained parallel cable robots with elastic cables is studied in detail. In the modeling process, longitudinal vibration of cables is considered as their dominant dynamics, and the governing equations of motion are rewritten to the standard form of singular perturbation. The proposed composite controller consists of two main components. A rigid controller is designed based on the slow or rigid model of the system and a corrective term is added to guarantee asymptotic stability of the fast dynamics. Then, by using Tikhonov theorem, slow and fast variables are separated and incorporated into the stability analysis of the overall closed-loop system, and a set of sufficient conditions for the stability of the total system is derived. Finally, the effectiveness of the proposed control law is verified through simulations.

2014JournalPDFParallel and Cable Robotics
A neutral system approach to H-Infinity PD/PI controller design of processes with uncertain input delay
A. Shariati, H.D. Taghirad, A. Fatehi
Journal of Process Control
Abstract:

This paper presents a neutral system approach to the design of an H? controller for input delay systems in presence of uncertain time-invariant delay. It is shown that when proportional derivative (PD) controller is applied to a time-delay system, the resulting closed loop system is generally a time-delay system of neutral type with delay term coefficients depending on the controller parameters. A descriptor model transformation is used to derive an advantageous bounded real lemma representation for the system. Furthermore, new delay-dependent sufficient conditions for the existence of an H? PD and PI controller in presence of uncertain delay are derived in terms of matrix inequalities. Some case studies and numerical examples are given in order to illustrate the advantages of the proposed method.

2014JournalPDFDynamical Systems Analysis and Control
Robust PID control of fully-constrained cable driven parallel robots
Mohammad A. Khosravi, Hamid D. Taghirad
Mechatronics
Abstract:

In this paper dynamic analysis and robust PID control of fully-constrained cable driven parallel manipulators are studied in detail. Since in this class of manipulators cables should remain in tension for all maneuvers in their workspace, feedback control of such robots becomes more challenging than that of conventional parallel robots. In this paper, structured and unstructured uncertainties in dynamics of the robot are considered and a robust PID controller is proposed for the cable robot. To ensure that all cables remain in tension internal force concept is used in the proposed PID control algorithm. Then, robust stability of the closed-loop system with proposed control algorithm is analyzed through Lyapunov direct method and it is shown that by suitable selection of the PID controller gains, the closed-loop system would be robustly stable. Finally, the effectiveness of the proposed PID algorithm is examined through experiments on a planar cable driven robot and it is shown that the proposed control structure is able to provide suitable performance in practice.

2014JournalPDFParallel and Cable Robotics
A Square Root Unscented FastSLAM With Improved Proposal Distribution and Resampling
Ramazan Havangi, Hamid D. Taghirad, Mohammad Ali Nekoui, and Mohammad Teshnehlab
IEEE Transactions on Industrial Electronics
Abstract:

An improved square root unscented fast simultaneous localization and mapping (FastSLAM) is proposed in this paper. The proposed method propagates and updates the square root of the state covariance directly in Cholesky decomposition form. Since the choice of the proposal distribution and that of the resampling method are the most critical issues to ensure the performance of the algorithm, its optimization is considered by improving the sampling and resampling steps. For this purpose, particle swarm optimization (PSO) is used to optimize the proposal distribution. PSO causes the particle set to tend to the high probability region of the posterior before the weights are updated; thereby, the impoverishment of particles can be overcome. Moreover, a new resampling algorithm is presented to improve the resampling step. The new resampling algorithm can conquer the defects of the resampling algorithm and solve the degeneracy and sample impoverishment problem simultaneously. Compared to unscented FastSLAM (UFastSLAM), the proposed algorithm can maintain the diversity of particles and consequently avoid inconsistency for longer time periods, and furthermore, it can improve the estimation accuracy compared to UFastSLAM. These advantages are verified by simulations and experimental tests for benchmark environments.

2014JournalPDF
Loop Closure Detection By Algorithmic Information Theory: Implemented On Range And Camera Image Data
Alireza Norouzzadeh Ravari and Hamid D. Taghirad
IEEE Transactions on Cybernetics
Abstract:

In this paper the problem of loop closing from depth or camera image information in an unknown environment is investigated. A sparse model is constructed from a parametric dictionary for every range or camera image as mobile robot observations. In contrast to high-dimensional feature-based representations, in this model, the dimension of the sensor measurements' representations is reduced. Considering the loop closure detection as a clustering problem in high-dimensional space, little attention has been paid to the curse of dimensionality in the existing state-of-the-art algorithms. In this paper, a representation is developed from a sparse model of images, with a lower dimension than original sensor observations. Exploiting the algorithmic information theory, the representation is developed such that it has the geometrically transformation invariant property in the sense of Kolmogorov complexity. A universal normalized metric is used for comparison of complexity based representations of image models. Finally, a distinctive property of normalized compression distance is exploited for detecting similar places and rejecting incorrect loop closure candidates. Experimental results show efficiency and accuracy of the proposed method in comparison to the state-of-the-art algorithms and some recently proposed methods.

2014JournalPDFAutonomous Robotics
Loop Closure Detection By Algorithmic Information Theory: Implemented On Range And Camera Image Data
Alireza Norouzzadeh Ravari and Hamid D. Taghirad
IEEE Transactions on Cybernetics
Abstract:

In this paper the problem of loop closing from depth or camera image information in an unknown environment is investigated. A sparse model is constructed from a parametric dictionary for every range or camera image as mobile robot observations. In contrast to high-dimensional feature-based representations, in this model, the dimension of the sensor measurements' representations is reduced. Considering the loop closure detection as a clustering problem in high-dimensional space, little attention has been paid to the curse of dimensionality in the existing state-of-the-art algorithms. In this paper, a representation is developed from a sparse model of images, with a lower dimension than original sensor observations. Exploiting the algorithmic information theory, the representation is developed such that it has the geometrically transformation invariant property in the sense of Kolmogorov complexity. A universal normalized metric is used for comparison of complexity based representations of image models. Finally, a distinctive property of normalized compression distance is exploited for detecting similar places and rejecting incorrect loop closure candidates. Experimental results show efficiency and accuracy of the proposed method in comparison to the state-of-the-art algorithms and some recently proposed methods.

2014JournalPDFMixed Reality in Surgery
Dynamic Modeling and Control of Parallel Robots With Elastic Cables: Singular Perturbation Approach
Mohammad A. Khosravi, Member and Hamid D. Taghirad
IEEE Transactions on Robotics
Abstract:

In this paper, control of fully-constrained parallel cable robots with elastic cables is studied in detail. In the modeling process, longitudinal vibration of cables is considered as their dominant dynamics, and the governing equations of motion are rewritten to the standard form of singular perturbation. The proposed composite controller consists of two main components. A rigid controller is designed based on the slow or rigid model of the system and a corrective term is added to guarantee asymptotic stability of the fast dynamics. Then, by using Tikhonov theorem, slow and fast variables are separated and incorporated into the stability analysis of the overall closed-loop system, and a set of sufficient conditions for the stability of the total system is derived. Finally, the effectiveness of the proposed control law is verified through simulations.

2014JournalPDFParallel and Cable Robotics
2013
TitleAbstractYearTypePDFResearch Group
System Identification and Robust Controller Design for the Autopilot of an Unmanned Helicopter
Ahmad Safaee, Hamid D. Taghirad
Control Conference
Abstract:

One of the most complex issues which are proposed in designing a controller for autopilots is robustness. This requirement is due to the dynamic model changes and also, the resistance to environmental disturbances. A main factor that changes the dynamic model of the helicopter autopilot is any change in body mass center, such as any additional load. Furthermore, wind is one of the main causes of environmental disturbances. In this paper model identification of four systems in helicopter by using real data is presented. For all systems robust H2/H-Infinity and mixed sensitivity controller are designed. The simulation results show the robustness of designed controllers in the existence of uncertainty. The designed controller was implemented on the real case study. Results demonstrate the robustness of the system.

2013ConferencePDF
An intelligent UFastSLAM with MCMC move step
Ramazan Havangi, Mohammad Ali Nekoui, Hamid D. Taghirad and Mohammad Teshnehlab
Advanced Robotics
Abstract:

FastSLAM is a framework for simultaneous localization and mapping (SLAM). However, FastSLAM algorithm has two serious drawbacks, namely the linear approximation of nonlinear functions and the derivation of the Jacobian matrices. For solving these problems, UFastSLAM has been recently proposed. However, UFastSLAM is inconsistent over time due to the loss of particle diversity that is caused mainly by the particle depletion in the resampling step and incorrect a priori knowledge of process and measurement noises. To improve consistency, intelligent UFastSLAM with Markov chain Monte Carlo (MCMC) move step is proposed. In the proposed method, the adaptive neuro-fuzzy inference system supervises the performance of UFastSLAM. Furthermore, the particle impoverishment caused by resampling is restrained after the resample step with MCMC move step. Simulations and experiments are presented to evaluate the performance of algorithm in comparison with UFastSLAM. The results show the effectiveness of the proposed method.

2013JournalPDFAutonomous Robotics
Unsupervised 3D Object Classification from Range Image Data by Algorithmic Information Theory
Alireza Norouzzadeh Ravari and Hamid D. Taghirad
2013 First RSI/ISM International Conference on Robotics and Mechatronics (ICRoM)
Abstract:

The problem of unsupervised classification of 3D objects from depth information is investigated in this paper. The range images are represented efficiently as sensor observations. Considering the high-dimensionality of 3D object classification, little attention has been paid to the curse of dimensionality in the existing state-of-the-art algorithms. In order to remedy this problem, a low-dimensional representation is defined here. The sparse model of every range image is constructed from a parametric dictionary. Employing the algorithmic information theory, a universal normalized metric is used for comparison of Kolmogorov complexity based representations of sparse models. Finally, most similar objects are grouped together. Experimental results show efficiency and accuracy of the proposed method in comparison to a recently proposed method.

2013ConferencePDFAutonomous Robotics
Unsupervised 3D Object Classification from Range Image Data by Algorithmic Information Theory
Alireza Norouzzadeh Ravari and Hamid D. Taghirad
2013 First RSI/ISM International Conference on Robotics and Mechatronics (ICRoM)
Abstract:

The problem of unsupervised classification of 3D objects from depth information is investigated in this paper. The range images are represented efficiently as sensor observations. Considering the high-dimensionality of 3D object classification, little attention has been paid to the curse of dimensionality in the existing state-of-the-art algorithms. In order to remedy this problem, a low-dimensional representation is defined here. The sparse model of every range image is constructed from a parametric dictionary. Employing the algorithmic information theory, a universal normalized metric is used for comparison of Kolmogorov complexity based representations of sparse models. Finally, most similar objects are grouped together. Experimental results show efficiency and accuracy of the proposed method in comparison to a recently proposed method.

2013ConferencePDFMixed Reality in Surgery
A New Method for Mobile Robot Navigation in Dynamic Environment: Escaping Algorithm
F. Adib Yaghmaie, A. Mobarhani and H. D. Taghirad
Robotics and Mechatronics (ICRoM)
Abstract:

This paper addresses a new method for navigation in dynamic environment. The proposed method is based on force field method and it is supposed that the robot performs SLAM and autonomous navigation in dynamic environment without any predefined information about dynamic obstacles. The movement of dynamic obstacles is predicted by Kalman filter and is used for collision detection purpose. In the time of collision detection, a modifying force is added to repulsive and attractive forces corresponding to the static environment and leads robot to avoid collision. Moreover, a safe turning angle is defined to assure safe navigation of the robot. The performance of proposed method, named Escaping Algorithm, is verified through different simulation and experimental tests. The results show the proper performance of Escaping Algorithm in term of dynamic obstacle avoidance as a practical method for autonomous navigation.

2013ConferencePDFAutonomous Robotics
Kinematic Performance Indices Analyzed on Four Planar Cable Robots via Internal Analysis
S. A. Khalipour, A. Zarif Loloei, M. Tale Masouleh and H. D. Taghirad
Robotics and Mechatronics
Abstract:

In this paper, some new kinematic performance indices are proposed and examined on four planar cable driven parallel manipulators. The main kinematic indices are based on kinematic sensitivity and controllable workspace of the robot. Interval analysis is adopted as a mathematical framework to compute feasible kinematic sensitivity and worst kinematic sensitivity indices. For determining the feasible kinematic sensitivity, the controllable workspace is combined with the desired kinematic sensitivity property. The area of the foregoing region and the worst kinematic sensitivity corresponding to it are introduced as practical design indices. Then four typical design of planar cable robot are examined by the following performance measures, and one of such designs are selected and implemented in practice.

2013ConferencePDFParallel and Cable Robotics
Robust PID Control of Cable Driven Robots with Elastic Cables
Mohammad A. Khosravi and Hamid D. Taghirad
2013 First RSI/ISM International Conference on Robotics and Mechatronics (ICRoM)
Abstract:

In this paper robust PID control of fully-constrained cable-driven robots with elastic cables is studied in detail. To develop the idea, a robust PID control for cable-driven robots with ideal rigid cables is firstly designed and then, this controller is extended for the robots with elastic cables. To overcome vibrations caused by inevitable elasticity of cables, a composite control law is proposed based on singular perturbation theory. The proposed control algorithm includes robust PID control for corresponding rigid model and a corrective term. Using the proposed control algorithm the dynamics of the cable-driven robot is divided into slow and fast subsystems. Then, based on the results of singular perturbation theory, stability analysis of the total system is performed. Finally, the effectiveness of the proposed control law is investigated through several simulations on a planar cable-driven robot.

2013ConferencePDFParallel and Cable Robotics
Position Based Sliding Mode Control for Visual Servoing System
M. Parsapour, S. RayatDoost, and H. D. Taghirad
2013 First RSI/ISM International Conference on Robotics and Mechatronics (ICRoM)
Abstract:

This paper presents a nonlinear controller for visual servoing system. Pose estimation is one of the fundamental issues in position-based visual servoing (PBVS) approach. A few researches have focused on controller synthesis under modeling uncertainty and measurement noise of estimated position. In this research, PD-type sliding surface is designed for tracking target. The control signal is obtained from the sliding surface and the stability of the algorithm is verified by Lyapunov theory. Moreover, a recent designed robust estimator based on unscented Kalman observer (UKO) cascading with Kalman filter (KF) is used to estimate the pose, velocity and acceleration of the target. The combination of the implemented estimator and the proposed controller provide a stable and robust structure in PBVS. The reported experimental results, verify the effectiveness of the proposed method in an industrial visual servoing system.

2013ConferencePDFVisual Robotics
A New Method for Mobile Robot Navigation in Dynamic Environment: Escaping Algorithm
Farnaz Adib Yaghmaie, Amir Mobarhani, and Hamid D. Taghirad
Robotics and Mechatronics
Abstract:

This paper addresses a new method for navigation in dynamic environment. The proposed method is based on force field method and it is supposed that the robot performs SLAM and autonomous navigation in dynamic environment without any predefined information about dynamic obstacles. The movement of dynamic obstacles is predicted by Kalman filter and is used for collision detection purpose. In the time of collision detection, a modifying force is added to repulsive and attractive forces corresponding to the static environment and leads robot to avoid collision. Moreover, a safe turning angle is defined to assure safe navigation of the robot. The performance of proposed method, named Escaping Algorithm, is verified through different simulation and experimental tests. The results show the proper performance of Escaping Algorithm in term of dynamic obstacle avoidance as a practical method for autonomous navigation.

2013ConferencePDFAutonomous Robotics
A Positive Tensions PID Controller for a Planar Cable Robot: An Experimental Study
Mohammad A. Khosravi, Hamid D. Taghirad and Reza Oftadeh
2013 First RSI/ISM International Conference on Robotics and Mechatronics (ICRoM)
Abstract:

In this paper design and control of planar cable-driven parallel robots are studied in an experimental prospective. Since in this class of manipulators, cable tensionability conditions must be met, feedback control of such robots becomes more challenging than for conventional robots. To meet these conditions, internal force control structure is introduced and used in addition to a PID control scheme to ensure that all cables remain in tension. A robust PID controller is proposed for partial knowledge of the robot, to keep the tracking errors bounded. Finally, the effectiveness of the proposed control algorithm is examined through experiments on K.N. Toosi planar cable-driven robot and it is shown that the proposed control structure is able to provide suitable performance in practice.

2013ConferencePDFParallel and Cable Robotics
Kinematic Performance Indices Analyzed on Four Planar Cable Robots via Interval Analysis
S. A. Khalilpour, A. Zarif Loloei, M. Tale Masouleh and H. D. Taghirad
2013 First RSI/ISM International Conference on Robotics and Mechatronics (ICRoM)
Abstract:

In this paper, some new kinematic performance indices are proposed and examined on four planar cable driven parallel manipulators. The main kinematic indices are based on kinematic sensitivity and controllable workspace of the robot. Interval analysis is adopted as a mathematical framework to compute feasible kinematic sensitivity and worst kinematic sensitivity indices. For determining the feasible kinematic sensitivity, the controllable workspace is combined with the desired kinematic sensitivity property. The area of the foregoing region and the worst kinematic sensitivity corresponding to it are introduced as practical design indices. Then four typical design of planar cable robot are examined by the following performance measures, and one of such designs are selected and implemented in practice.

2013ConferencePDFParallel and Cable Robotics
Visual Tracking in Four Degrees of Freedom Using Kernel Projected Measurement
Fateme Bakhshande and Hamid D. Taghirad
2013 First RSI/ISM International Conference on Robotics and Mechatronics (ICRoM)
Abstract:

Visual Servoing is generally comprised of feature tracking and control. According to the literature, no attempt has already been made to optimize these two parts together. In kernel based visual servoing method, the main objective is to combine and optimize the entire control loop. By kernel definition, a Lyapanov candidate function is formed and the control input is computed so that the Lyapanov stability can be verified. This is performed in four degrees of freedom. In the present study, previous kernel algorithm from the recorded literature has been implemented. We have used the KBVS for our purpose such that an object without any marker is tracked. This method is chosen because of its robustness, speed and featureless properties. Furthermore, in order to show the visual tracking performance, all four degrees of freedom have been synthesized. Experimental results verifies the effectiveness of this method implemented for four degrees of freedom movements.

2013ConferencePDFVisual Robotics
Position Based Sliding Mode Control for Visual Servoing System
M. Parsapour, S. RayatDoost, and H. D. Taghirad
2013 First RSI/ISM International Conference on Robotics and Mechatronics (ICRoM)
Abstract:

This paper presents a nonlinear controller for visual servoing system. Pose estimation is one of the fundamental issues in position-based visual servoing (PBVS) approach. A few researches have focused on controller synthesis under modeling uncertainty and measurement noise of estimated position. In this research, PD-type sliding surface is designed for tracking target. The control signal is obtained from the sliding surface and the stability of the algorithm is verified by Lyapunov theory. Moreover, a recent designed robust estimator based on unscented Kalman observer (UKO) cascading with Kalman filter (KF) is used to estimate the pose, velocity and acceleration of the target. The combination of the implemented estimator and the proposed controller provide a stable and robust structure in PBVS. The reported experimental results, verify the effectiveness of the proposed method in an industrial visual servoing system.

2013ConferencePDFVisual Robotics
A SLAM based on auxiliary marginalised particle filter and differential evolution
R. Havangi, M.A. Nekoui, M. Teshnehlab and H.D. Taghirad
International Journal of Systems Science
Abstract:

FastSLAM is a framework for simultaneous localisation and mapping (SLAM) using a Rao-Blackwellised particle filter. In FastSLAM, particle filter is used for the robot pose (position and orientation) estimation, and parametric filter (i.e. EKF and UKF) is used for the feature location's estimation. However, in the long term, FastSLAM is an inconsistent algorithm. In this paper, a new approach to SLAM based on hybrid auxiliary marginalised particle filter and differential evolution (DE) is proposed. In the proposed algorithm, the robot pose is estimated based on auxiliary marginal particle filter that operates directly on the marginal distribution, and hence avoids performing importance sampling on a space of growing dimension. In addition, static map is considered as a set of parameters that are learned using DE. Compared to other algorithms, the proposed algorithm can improve consistency for longer time periods and also, improve the estimation accuracy. Simulations and experimental results indicate that the proposed algorithm is effective.

2013JournalPDF
2012
TitleAbstractYearTypePDFResearch Group
Comment on: "Centers of quasi-homogeneous polynomial planar systems"
A. Rahimabadi, H.D. Taghirad
Nonlinear Analysis: Real World Applications
Abstract:

We describe a counter-example which shows that of theorem in Algaba et al. (2012) is not correct. This part of the theorem, pinpoints whether the origin of quasi-homogeneous system in Algaba et al. (2012) is a center or not. It is shown in this note that the given necessary and sufficient conditions of theorem, in Algaba et al. (2012) are not complete.

2017JournalPDFDynamical Systems Analysis and Control
PD Controller Design with H-Infinity Performance for Linear Systems with Input Delay
Ala Shariati, Hamid D. Taghirad
AUR Journal of Electrical Engineering
Abstract:

This paper considers H-Infinity control problem for input-delayed systems for time-varying delays. A proportional-derivative state feedback control law is used in this paper. By this means, the resulting closed-loop system turns into a specific time-delay system of neutral type. The significant specification of this neutral system is that its delayed term coefficients depend on the controller parameters. This condition provides new challenging issues in theoretical research as well as providing new applications. In the present paper, new delay-dependent sufficient condition is derived for the existence of H-Infinity controller in terms of matrix inequalities, in presence of varying time-delays. The resulting H-Infinity controller guarantees asymptotic stability of the closed-loop system as well as a guaranteed limited system induced norm smaller than a prescribed level. Numerical examples are presented to illustrate the effectiveness of the proposed method.

2012JournalPDFDynamical Systems Analysis and Control
Feasible Kinematic Sensitivity in Cable Robots Based on Interval Analysis
S. A. Khalilpour, A. Zarif Loloei, H. D. Taghirad, and M. Tale Masouleh
Cable-Driven Parallel Robots
Abstract:

The kinematic sensitivity has been recently proposed as a unit-consistent performance index to circumvent several shortcomings of some notorious indices such as dexterity. This paper presents a systematic interval approach for computing an index by which two important kinematic properties, namely feasible workspace and kinematic sensitivity, are blended into each other. The proposed index may be used to efficiently design different parallel mechanisms, and cable driven robots. By this measure, and for parallel manipulators, it is possible to visualize constant orientation workspace of the mechanism where the kinematic sensitivity is less than a desired value considered by the designer. For cable driven redundant robots, the controllable workspace is combined with the desired kinematic sensitivity property, to determine the so-called feasible kinematic sensitivity workspace of the robot. Three case studies are considered for the development of the idea and verification of the results, through which a conventional planar parallel manipulator, a redundant one and a cable driven robot is examined in detail. Finally, the paper provides some hints for the optimum design of the mechanisms under study by introducing the concept of minimum feasible kinematic sensitivity covering the whole workspace.

2012JournalPDFParallel and Cable Robotics
Experimental Performance of Robust PID Controller on a Planar Cable Robot
M. A. Khosravi and H. D. Taghirad
Cable-Driven Parallel Robots
Abstract:

In this paper dynamic analysis and experimental performance of robust PID control for fully-constrained cable driven robots are studied in detail. Since in this class of manipulators cables should remain in tension for all maneuvers through their whole workspace, feedback control of such robots becomes more challenging than conventional parallel robots. To ensure that all the cables remain in tension, a corrective term is used in the proposed PID control scheme. In design of PID control it is assumed that there exist bounded norm uncertainties in Jacobian matrix and in all dynamics matrices. Then a robust PID controller is proposed to overcome partial knowledge of robot, and to guarantee boundedness of tracking errors. Finally, the effectiveness of the proposed PID algorithm is examined through experiments and it is shown that the proposed control structure is able to provide suitable performance in practice.

2012JournalPDFParallel and Cable Robotics
Monte Carlo Sampling of Non-Gaussian Proposal Distribution in Feature-Based RBPF-SLAM
Nina Marhamati, Hamid D. Taghirad, Kasra Khosoussi
Abstract:

Particle lters are widely used in mobile robot localization and mapping. It is well-known that choosing an appropriate proposal distribution plays a crucial role in the success of particle lters. The proposal distribution conditioned on the most recent observation, known as the optimal proposal distribution (OPD), increases the number of eective particles and limits the degeneracy of lter. Conventionally, the OPD is approximated by a Gaussian distribution, which can lead to failure if the true distribution is highly non-Gaussian. In this paper we propose two novel solutions to the problem of feature-based SLAM, through Monte Carlo approximation of the OPD which show superior results in terms of mean squared error (MSE) and number of eective samples. The proposed methods are capable of describing non-Gaussian OPD and dealing with nonlinear models. Simulation and experimental results in large-scale environments show that the new algorithms outperform the aforementioned conventional methods.

2012ConferencePDFParallel and Cable Robotics
Controllable Workspace of Cable-Driven Redundant Parallel Manipulators by Fundamental Wrench Analysis
Azadeh Zarif Loloei, Hamid D. Taghirad
Transactions- Canadian Society for Mechanical Engineering
Abstract:

Workspace analysis is always a crucial issue in robotic manipulator design. This paper introduces a set of newly defined fundamental wrenches that opens new horizons to physical interpretation of controllable workspace of a general cable-driven redundant parallel manipulator. Based on this set of fundamental wrenches, a novel tool is presented to determine configurations of cable-driven redundant parallel manipulator that belong to the controllable workspace. Analytical expressions of such workspace boundaries are obtained in an implicit form and a rigorous mathematical proof is provided for this method. Finally, the proposed method is implemented on a spatial cable-driven manipulator of interest.

2012JournalPDFParallel and Cable Robotics
SLAM Based on Intelligent Unscented Kalman Filter
R.Havangi, M.A.Nekoui, H.D.Taghirad, and M.Teshnehlab
The 2nd International Conference on Control, Instrumentation and Automation
Abstract:

The performance of SLAM based on unscented Kalman filter (UKF-SLAM) and thus the quality of the estimation depends on the correct a priori knowledge of process and measurement noise. Imprecise knowledge of these statistics can cause significant degradation in performance. In this paper, the adaptive Neuro-Fuzzy has been implemented to adapt the matrix covariance process of UKF-SLAM in order to improve its performance.

2012ConferencePDF
Feedback Error learning Control of Trajectory Tracking of Non-Holonomic Mobile Robot
Farnaz Adib Yaghmaie, Fateme Bakhshande and Hamid D.Taghirad
20th Iranian Conference on Electrical Engineering
Abstract:

In this paper a new controller for nonholonomic system is introduced. This feedback error learning controller benefits from both nonlinear and adaptive controller properties. The nonlinear controller is used to stabilize the nonholonomic behavior of the systems. This controller is a sliding mode controller which is designed based on backstepping method. The adaptive controller tries to face with uncertainty and unknown dynamic of the mobile robot. This part uses neural network controller for adaptation. The experimental results show the effectiveness of proposed controller and suitable and robust tracking performance of a mobile robot, which is significantly better than traditional controllers.

2012ConferencePDFAutonomous Robotics
Stereo-Based Visual Navigation of Mobile Robots in Unknown Environments
H. Soltani, H. D. Taghirad and A.R. Norouzzadeh Ravari
20th Iranian Conference on Electrical Engineering (ICEE2012)
Abstract:

In this paper a stereo vision-based algorithm for mobile robots navigation and exploration in unknown outdoor environments is proposed. The algorithm is solely based on stereo images and implemented on a nonholonomic mobile robot. The first step for exploration in unknown environments is construction of the map of circumference in real-time. By getting disparity image from rectified stereo images and translating its data to 3D-space, point cloud model of environments is constructed. Then by projecting points to XZ plane and put local maps together based on visual odometry, global map of environment is constructed in real-time. A* algorithm is used for investigating optimal path and nonlinear back-stepping controller guides the robot to follow the identified path. Finally, the mobile robot explores for a desired object in an unknown environment through these steps. Experimental results verify the effectiveness of the proposed algorithm in real-time implementations.

2012ConferencePDFAutonomous Robotics
Robust solution to three-dimensional pose estimation using composite extended Kalman observer and Kalman filter
H.D. Taghirad S.F. Atashzar M. Shahbazi
IET Computer Vision
Abstract:

Three-dimensional (3D) pose estimation of a rigid object by only one camera has a vital role in visual servoing systems, and extended Kalman filter (EKF) is vastly used for this task in an unstructured environment. In this study, the stability of the EKF-based 3D pose estimators is analysed in detail. The most challenging issue of the state-of-the-art EKF-based 3D pose estimators is the possibility of its divergence because of the measurement and model noises. By analysing the stability of conventional EKF-based pose estimators a composite technique is proposed to guarantee the stability of the procedure. In the proposed technique, the non-linear-uncertain estimation problem is decomposed into a non-linear-certain observation in addition to a linear-uncertain estimation problem. The first part is handled using the extended Kalman observer and the second part is accomplished by a simple Kalman filter. Finally, some experimental and simulation results are given in order to verify the robustness of the method and compare the performance of the proposed method in noisy and uncertain environment to the conventional techniques.

2012JournalPDFVisual Robotics
Robust SDRE filter design for nonlinear uncertain systems with an H-Infinity performance criterion
Hossein Beikzadeh, Hamid D. Taghirad
ISA Transactions
Abstract:

In order to remedy the effects of modeling uncertainty, measurement noise and input disturbance on the performance of the standard state-dependent Riccati equation (SDRE) filter, a new robust SDRE filter design is developed in this paper. Based on the infinity-norm minimization criterion, the proposed filter effectively estimates the states of nonlinear uncertain system exposed to unknown disturbance inputs. Moreover, by assuming a mild Lipschitz condition on the chosen state-dependent coefficient form, fulfillment of a modified performance index is guaranteed in the proposed filter. The effectiveness of the robust SDRE filter is demonstrated through numerical simulations where it brilliantly outperforms the conventional SDRE filter in presence of model uncertainties, disturbance and measurement noise, in terms of estimation error and region of convergence.

2012JournalPDF
Delay-Dependent H-Infinity Control of Linear Systems with Uncertain Input Delay Using State-Derivative Feedback
A. Shariati, H. D. Taghirad
Control Engineering and Applied Informatics
Abstract:

In some practical problems such as active vibration suppression systems, the state-derivative signals are easier to access than the state variables. This paper considers an H-Infinity -based state-derivative feedback control problem for input-delayed systems. Applying this control law, the resulting closed-loop system turns into a specific time-delay system of neutral type. The significant specification of this neutral system is that its delayed term coefficients depend on the controller parameters. The time-delay is considered as uncertain time-invariant with a known constant bound. In this paper, the delay-dependent sufficient conditions for the existence of an H-Infinity state-derivative feedback controller are derived in terms of matrix inequalities. The resulting H-Infinity controller stabilizes the closed-loop neutral system and assures that the H-Infinity -norm to be less than a prescribed level. An application example is presented to illustrate the effectiveness of the proposed method.

2012JournalPDFDynamical Systems Analysis and Control
2011
TitleAbstractYearTypePDFResearch Group
Dexterous Workspace Optimization of a Tricept Parallel Manipulator
Mir Amin Hosseini, Hamid-Reza M. Daniali, and Hamid D. Taghirad
Advanced Robotics
Abstract:

The growing interest in the use of parallel manipulators in machining applications requires clear determination of the workspace and dexterity. In this paper, the workspace optimization of a Tricept parallel manipulator under joint constraints is performed. This parallel manipulator has complex degrees of freedom and, therefore, leads to dimensionally inhomogeneous Jacobian matrices. Here, we divide the Jacobian entries by units of length, thereby producing a new Jacobian that is dimensionally homogeneous. By multiplying the associated entries of the twist array to the same length, we made this array homogeneous as well. The workspace of the manipulator is parameterized using several design parameters and is optimized using a genetic algorithm. For the workspace of the manipulator, local conditioning indices and minimum singular values are calculated. For the optimal design, it is shown that by introducing the local conditioning indices and minimum singular values, the quality of the parallel manipulator is improved at the cost of workspace reduction.

2011JournalPDFParallel and Cable Robotics
Delay-Independent Robust Stability Analysis of Teleoperation
Masoumeh Azadegan, Sadjaad Ozgoli, and Hamid Reza Taghirad
2011 Chinese Control and Decision Conference (CCDC)
Abstract:

This paper considers the robust stability of uncertain teleoperation systems. Sufficient stability conditions are derived in terms of LMI by representing the teleoperation scheme in retarded form of time-delay systems. By choosing Lyapunov-Krasovski functional, a delay-independent robust stability criterion is presented. We show that the teleoperation system is stable and has good performance under specific LMI condition. With the given controller parameters, stability of system is guaranteed in the presence of any value of delay and admissible uncertainty. To evaluate the theoretical analysis, Numerical simulations are performed.

2011ConferencePDFDynamical Systems Analysis and Control
Controllable Workspace of General Cable Driven Redundant Parallel Manipulator Based on Fundamental Wrench
A. Zarif Loloei, H. D. Taghirad
Transactions- Canadian Society for Mechanical Engineering
Abstract:

Workspace analysis is one of the most important issues in robotic manipulator design. This paper introduces a set of newly defined fundamental wrenches that opens new horizons for physical interpretation of controllable workspace of cable driven redundant parallel manipulators. Moreover, an analytical method is proposed to specify the controllable workspace of general redundant cabledriven parallel manipulators based on this set of fundamental wrenches. In the proposed method, an analytic approach based on linear algebra is employed to derive the boundary of controllable workspace. Finally, the proposed method is illustrated through spatial example.

2011ConferencePDFParallel and Cable Robotics
Dynamic Analysis and Control of Cable Driven Robots Considering Elasticity in Cables
Mohammad A. Khosravi, Hamid. D. Taghirad
Transactions- Canadian Society for Mechanical Engineering
Abstract:

In this paper modeling and control of cable driven redundant parallel manipulators with flexible cables, are studied in detail. Based on new results, in fully constrained cable robots, cables can be modeled as axial linear springs. Considering this assumption the system dynamics formulation is developed using Lagrange approach. Since in this class of robots, all the cables should remain in tension for the whole workspace, the notion of internal forces are introduced and incorporated in the proposed control algorithm. The control algorithm is developed in cable coordinates in which the internal forces play an important role. Finally, asymptotic stability of the closed loop system is analyzed through Lyapunov theorem, and the performance of the proposed algorithm is studied by simulations.

2011ConferencePDFParallel and Cable Robotics
Analytical Passivity Analysis for Wave-based Teleoperation with Improved Trajectory Tracking
Bita Fallahi, Hamid D. Taghirad
Canadian Committee for the Theory of Machines and Mechanisms
Abstract:

In wave based teleoperation, although passivity is ensured for any time delay, tracking performance is usually distorted due to the bias term introduced by wave transmission. To improve the position tracking error, one way is to augment the forward wave with a corrective term and achieve pas-sivity by tuning the band width of a low pass filter in the forward path. However, this filter fails to meet the passivity condition in contact to stiff environments, especially at steady state. In this paper a new method is proposed and an analytical solution for passivity at steady state and a semi analytical solution for all other frequencies are represented. This method significantly reduces the complexity of the closed-loop system, ensures passivity in contact to the stiff environments, and improves trajectory tracking. Simulation results are presented to show the effectiveness of the pro-posed method.

2011ConferencePDFSurgical Robotics
Delay-Independent Stability Analysis of Internet-based Tele-operation
Masoumeh Azadegan, Sadjaad Ozgoli, Hamid Reza Taghirad
2011 International Symposium on Computer Networks and Distributed Systems (CNDS)
Abstract:

This paper presents a sufficient stability condition for internet-based tele-operation systems in terms of LMI. The tele-operation scheme is modeled in state-space as a time-delay system in retarded form and a delay-independent stability criterion is extracted. By choosing Lyapunov-Krasovski functional, we show that the internet-based tele-operation system is stable and has good performance under specific LMI condition. With the given controller design parameters, stability of system is guaranteed in the presence of any value of delay. Numerical simulations are performed to verify the theoretical results.

2011ConferencePDFDynamical Systems Analysis and Control
Dynamic Aalysis and Control of Cable Driven Robots With Elastic Cables
Mohammad A. Khosravi, Hamid D. Taghirad
Transactions- Canadian Society for Mechanical Engineering
Abstract:

In this paper modeling and control of cable driven redundant parallel manipulators with flexible cables, are studied in detail. Based on new results, in fully constrained cable robots, cables can be modeled as axial linear springs. Considering this assumption the system dynamics formulation is developed using Lagrange approach. Since in this class of robots, all the cables should remain in tension for the whole workspace, the notion of internal forces are introduced and incorporated in the proposed control algorithm. The control algorithm is developed in cable coordinates in which the internal forces play an important role. Finally, asymptotic stability of the closed loop system is analyzed through Lyapunov theorem, and the performance of the proposed algorithm is studied by simulations

2011ConferencePDFParallel and Cable Robotics
Lagrangian Dynamics of Cable-Driven Parallel Manipulators: A Variable Mass Formulation
Yousef B. Bedoustani, Pascal Bigras, Hamid D. Taghirad, Ilian A. Bonev
Transactions- Canadian Society for Mechanical Engineering
Abstract:

In this paper, dynamic analysis of cable-driven parallel manipulators (CDPMs) is performed using the Lagrangian variable mass formulation. This formulation is used to treat the effect of a mass stream entering into the system caused by elongation of the cables. In this way, a complete dynamic model of the system is derived, while preserving the compact and tractable closed-form dynamics formulation. First, a general formulation for a CDPM is given, and the effect of change of mass in the cables is integrated into its dynamics. The significance of such a treatment is that a complete analysis of the dynamics of the system is achieved, including vibrations, stability, and any robust control synthesis of the manipulator. The formulation obtained is applied to a typical planar CDPM. Through numerical simulations, the validity and integrity of the formulations are verified, and the significance of the variable mass treatment in the analysis is examined. For this example, it is shown that the effect of introducing a mass stream into the system is not negligible. Moreover, it is non linear and strongly dependent on the geometric and inertial parameters of the robot, as well as the maneuvering trajectory.

2011ConferencePDFParallel and Cable Robotics
Geometric Analysis of the Kinematic Sensitivity of Planar Parallel Mechanisms
Mohammad Hossein Saadatzi, Mehdi Tale Masouleh, Hamid D. Taghirad, Cle´ment Gosselin, Philippe Cardou
Transactions- Canadian Society for Mechanical Engineering
Abstract:

The kinematic sensitivity is a unit-consistent measure that has been recently proposed as a mechanism performance index to compare robot architectures. This paper presents a robust geometric approach for computing this index for the case of planar parallel mechanisms. The physical meaning of the kinematic sensitivity is investigated through different combinations of the Euclidean and infinity norms and by means of several illustrative examples. Finally, this paper opens some avenues to the dimensional synthesis of parallel mechanisms by exploring the meaning of the global kinematic sensitivity index.

2011JournalPDFParallel and Cable Robotics
Adaptive Robust Backstepping Control Design for A Non-minimum Phase Model of Hard Disk Drives
M. Ataollahi, H. H. Eghrari and H. D. Taghirad
2011 19th Iranian Conference on Electrical Engineering
Abstract:

In this paper, a new adaptive robust approach for non-minimum phase systems is proposed, based on the synthesis algorithm of dynamical backstepping design procedure. The previously proposed adaptive robust backstepping method has a limitation in stabilization of non-minimum phase systems, which is removed in this paper. The dynamic model of the voice coil motor actuator, which is used in the read/write head of hard disk drive, is considered as a case study to apply the proposed method. A simple but accurate model of this system is presented the proposed control method is applied onto this model. Simulations are performed for the embedded control system of hard disk drives. The obtained results verify the effectiveness of the proposed control law in terms of transient performance, tracking errors, and disturbance rejection, in both track seeking and track following modes.

2011ConferencePDFHard Disk Drives Control
On the Optimum Design of 3-RPR Parallel Mechanisms
Mohammad Hossein Saadatzi, Mehdi Tale Masouleh, Hamid D. Taghirad, Clement ´ Gosselin and Philippe Cardou
2011 19th Iranian Conference on Electrical Engineering
Abstract:

This paper deals with the optimization of 3-RPR planar parallel mechanisms based on different performance indices including the kinematic sensitivity, the workspace and the singularity locus. Since the kinematic sensitivity has been proposed only recently, more emphasis is placed on how it should be adapted for the optimization of 3-RPR parallel mechanisms. The optimization is implemented in sequence using first a single objective technique, differential evolution, and then resorting to a multi-objective optimization concept, the so-called Non-dominated sorting genetic algorithm-II. A Pareto-based multi-objective approach helps to overcome the problem of unit-inconsistent objectives in the optimization algorithm. Moreover, an Infinity-norm is used in computation of the kinematic sensitivity which has perhaps the clearest physical interpretation.

2011ConferencePDFParallel and Cable Robotics
Modelling and Control of Fully Constrained Cable Driven Robots with Flexible Cables
Mohammad A. Khosravi, and Hamid D. Taghirad
The 2nd International Conference on Control, Instrumentation and Automation
Abstract:

In this paper modelling and control of cable-driven redundant parallel manipulators (CDRPM) with flexible cables are studied in detail. In this type of manipulators the cables should remain in tension in the whole workspace. New research results have shown that in fully constrained CDRPM cable can be modelled as an axial spring. Based on this fact a new model of this type of robot is studied. Furthermore, internal forces are introduced and incorporated in the proposed control algorithm. This control algorithm is formed in cable length coordinates in which the internal forces play an important role. Finally, the closed loop system is proved to be stable, through Lyapunov analysis, and the performance of the proposed algorithm is studied through simulation.

2011ConferencePDFParallel and Cable Robotics
Modeling and Control of Cable Driven Parallel Manipulators with Elastic Cables: Singular Perturbation Theory
Alaleh Vafaei, Mohammad A. Khosravi, and Hamid D. Taghirad
ICIRA 2011: Intelligent Robotics and Applications
Abstract:

This paper presents a new approach to the modeling and control of cable driven parallel manipulators and particularly KNTU CDRPM. First, dynamical model of the cable driven parallel manipulator is derived considering the elasticity of the cables, and then this model is rewritten in the standard form of singular perturbation theory. This theory used here as an effective tool for modeling the cable driven manipulators. Next, the integrated controller, applied for control of the rigid model of KNTU CDRPM in previous researches, is improved and a composite controller is designed for the elastic model of the robot. Asymptotic stability analysis of the proposed rigid controller is studied in detail. Finally, a simulation study performed on the KNTU CDRPM verifies the closed-loop performance compared to the rigid model controller.

2011ConferencePDFParallel and Cable Robotics
Histogram Based Frontier Exploration
Amir Mobarhani, Shaghayegh Nazari, Amir H. Tamjidi, Hamid D. Taghirad
2011 IEEE/RSJ International Conference on Intelligent Robots and Systems
Abstract:

This paper proposes a method for mobile robot exploration based on the idea of frontier exploration which suggests navigating the robot toward the boundaries between free and unknown areas in the map. A global occupancy grid map of the environment is constantly updated, based on which a global frontier map is calculated. Then, a histogram based approach is adopted to cluster frontier cells and score these clusters based on their distance from the robot as well as the number of frontier cells they contain. In each stage of the algorithm, a sub-goal is set for the robot to navigate. A combination of distance transform and A* search algorithms is utilized to generate a plausible path toward the sub-goal through the free space. This way keeping a reliable distance from obstacles is guaranteed while searching for the shortest path toward the sub-goal. When such a path is generated, a B-spline interpolated and smoothed trajectory is produced as the control reference for the mobile robot to follow. The whole process is iterated until no unexplored area remains in the map. The efficiency of the method is shown through simulated and real experiments.

2011ConferencePDFAutonomous Robotics
An Adaptive Neuro-Fuzzy Rao-Blackwellized Particle Filter for SLAM
Ramazan Havangi, Mohammad Teshnehlab, Mohammad Ali Nekoui, Hamid Taghirad
2011 IEEE International Conference on Mechatronics
Abstract:

The Rao-Blackwellized particle filter SLAM (RBPF-SLAM) that is also known as FastSLAM is a framework for simultaneous localization using a Rao-Blackwellized particle filter. The performance and the quality of the estimation of the Rao-Blackwellized particle filter depends heavily on the correct a priori knowledge of the process and measurement noise covariance matrices (Qt and Rt) that are in most applications unknown. On the other hand, an incorrect a priori knowledge of Qt and Rt may seriously degrade their performance. To solve these problems, this paper presents an adaptive Neuro-Fuzzy Rao-Blackwellized particle filter. The free parameters of adaptive Neuro-Fuzzy inference systems are trained using the steepest gradient descent (GD) to minimize the differences of the actual value of the covariance of the residual with its theoretical value as much as possible.

2011ConferencePDF
The H-Infinity Fast SLAM Framework
Ramazan Havangi, Mohammad Ali Nekoui, Hamid Taghirad, Mohammad Teshnehlab
2011 IEEE International Conference on Mechatronics
Abstract:

FastSLAM is a framework using a Rao-Blackwellized particle filter. However, the performance of FastSLAM depends on correct a priori knowledge of the process and measurement noise covariance matrices (Q t and R t ) that are in most applications unknown. On the other hand, an incorrect a priori knowledge of Q t and R t may seriously degrade the performance of FastSLAM. To solve these problems, this paper presents H ? FastSLAM. In this approach, H-Infinity particle filter is used for the mobile robot position estimation and H-Infinity filter is used for the feature location's estimation. The H-Infinity FastSLAM can work in an unknown statistical noise behavior and thus it is more robust. Experimental results demonstrate the effectiveness of the proposed algorithm.

2011ConferencePDF
Robust solution to three-dimensional pose estimation using composite extended Kalman observer and Kalman filter
H.D. Taghirad S.F. Atashzar M. Shahbazi
IET Computer Vision
Abstract:

Three-dimensional (3D) pose estimation of a rigid object by only one camera has a vital role in visual servoing systems, and extended Kalman filter (EKF) is vastly used for this task in an unstructured environment. In this study, the stability of the EKF-based 3D pose estimators is analysed in detail. The most challenging issue of the state-of-the-art EKF-based 3D pose estimators is the possibility of its divergence because of the measurement and model noises. By analysing the stability of conventional EKF-based pose estimators a composite technique is proposed to guarantee the stability of the procedure. In the proposed technique, the non-linear-uncertain estimation problem is decomposed into a non-linear-certain observation in addition to a linear-uncertain estimation problem. The first part is handled using the extended Kalman observer and the second part is accomplished by a simple Kalman filter. Finally, some experimental and simulation results are given in order to verify the robustness of the method and compare the performance of the proposed method in noisy and uncertain environment to the conventional techniques.

2011JournalPDFVisual Robotics
Multi-Objective Scale Independent Optimization of 3-RPR Parallel Mechanisms
M. H. Saadatzi, M. Tale Masouleh, H. D. Taghirad, C. Gosselin, M. Teshnehlab
World Congress in Mechanism and Machine Science
Abstract:

This paper deals with the optimization of 3-RPR planar parallel mechanisms based on different per-formance indices including kinematic sensitivity, stiffness, workspace and singularity. The optimization is imple-mented in sequence using first a single objective tech-nique, differential evolution, and then resorting to a multi-objective optimization concept, the so-called nondomi-nated sorting genetic algorithm-II. The results revealed that the optimality of the mechanism under study is scale-independent for the considered optimization objectives. Moreover, based on the scale invariance property of the main objectives, it follows that different kinetoestatic ob-jective functions must be scale invariant. The relations for the kinetoestatic objective expressions as functions of mech-anism scale are derived and to circumvent the problem of unit inconsistency the rotational and translational parts of these objectives are considered separately. To overcome the problem of inconsistent objectives in optimization al-gorithm, a Pareto-based multi-objective approach is used which preserves the scale invariance property.

2011ConferencePDFParallel and Cable Robotics
Robust Internal Model Control for Impulse Elimination of Singular Systems
M. M. Share Pasandand, H. D. Taghirad
International Journal of Control Science and Engineering
Abstract:

In this paper the problem of model based internal control of singular systems is investigated. The limitations of directly extending the control schemes for normal systems to singular ones are thoroughly developed, and a robust approach is proposed in order to establish a control scheme for singular systems. The proposed method presents a general framework for robust control design of singular systems in presence of modeling uncertainties. Two simulation examples are given to how the proposed method can be implemented, and to show the effectiveness of such controllers in closed loop performance.

2011JournalPDFDynamical Systems Analysis and Control
Robust SDRE filter design for nonlinear uncertain systems with an H-Infinity performance criterion
Hossein Beikzadeh, Hamid D. Taghirad
ISA Transactions
Abstract:

In order to remedy the effects of modeling uncertainty, measurement noise and input disturbance on the performance of the standard state-dependent Riccati equation (SDRE) filter, a new robust SDRE filter design is developed in this paper. Based on the infinity-norm minimization criterion, the proposed filter effectively estimates the states of nonlinear uncertain system exposed to unknown disturbance inputs. Moreover, by assuming a mild Lipschitz condition on the chosen state-dependent coefficient form, fulfillment of a modified performance index is guaranteed in the proposed filter. The effectiveness of the robust SDRE filter is demonstrated through numerical simulations where it brilliantly outperforms the conventional SDRE filter in presence of model uncertainties, disturbance and measurement noise, in terms of estimation error and region of convergence.

2011JournalPDF
Force Control of Intelligent Laparoscopic Forceps
Soheil Kianzad, Soheil O. Karkouti, and Hamid D. Taghirad
Journal of Medical Imaging and Health Informatics
Abstract:

Actuators play an important role at the end-effectors of Minimally Invasive Surgery (MIS) robots. Having local, lightweight and powerful actuators would increase dexterity of surgeons. Shape Memory Alloy (SMA) actuators are considered as good candidates and presented significant behaviors in producing the force needed for grasping. Most of the current MIS systems provide surgeons with visual feedback. However, in many operations this information could not help surgeons to diagnose the manipulated tissue accurately. Therefore, having force and tactile information is also necessary. In order to have this information, local sensors are needed to give force feedback. This would also help to have control over the wire tension and prevent exceeding force causing tissue damages. In this paper a novel design of forceps that uses antagonistic SMA actuators is presented. This configuration helps to increase force and speed and also eliminates the bias spring used in similar works. Moreover, this antagonistic design makes it possible to place the force sensors at the back part of the forceps instead of attaching them to the jaws which results in a smaller forceps design. To control the exerted force, analytical model of system and a force control method are also presented. This enhanced design seems to address some of the existing shortcomings of similar models and remove them effectively.

2011JournalPDFSurgical Robotics
Workspace analysis of 5-PRUR parallel mechanisms (3T2R)
Mohammad Hossein Saadatzi, Mehdi Tale Masouleh, Hamid D. Taghirad
Robotics and Computer-Integrated Manufacturing
Abstract:

This paper investigates the constant-orientation workspace of five-degree-of-freedom parallel mechanisms generating the three translations and two independent rotations and comprising five identical limbs of the type. The general mechanism was proposed recently from the type synthesis performed for 5-DOF parallel mechanisms with identical limb structures. In this study, the emphasis is placed on the determination of the constant-orientation workspace using a geometric interpretation of the so-called vertex space, i.e., the motion generated by a limb for a given orientation. The geometric investigation is carried out using geometric constructive approach, which is implemented in a computer algebra system and in a CAD system. This paper shows that these two approaches are complementary tools to investigate the workspace of parallel mechanisms. The geometric constructive approach proposed in this paper bring insight into the architecture optimization and it can be regarded as a guideline for the workspace analysis of parallel mechanisms whose vertex spaces generate Bohemian dome.

2011JournalPDFParallel and Cable Robotics
Adaptive Robust Controller Design For Non-minimum Phase Systems
M. Ataollahi and H. D. Taghirad
Abstract:

Based on the synthesis algorithm of dynamical backstepping design procedure, in this paper a new adaptive robust approach for non-minimum phase systems is proposed. The proposed controller consists of two parts; a backstepping controller as the robust part and a model reference (MRAS) controller as the adaptive part. In this control scheme the daptive part acts not only as a medium to converge to suitable values for the unknown parameters and to reduce the uncertainty, but also provides a minimum-phase model for the robust controller to be well stabilized. A simulation case study is studied to show how to perform the proposed control law, and to illustrate the effectiveness of this method compared to that of conventional robust controllers.

2011ConferencePDFDynamical Systems Analysis and Control
Robust Internal Model Control For Impulse Elimination of Singular Systems
M. M. Share Pasand and H. D. Taghirad
International Journal of Control Science and Engineering
Abstract:

In this paper the problem of model based internal control of singular systems is investigated. The limitations of directly extending the control schemes for normal systems to singular ones are thoroughly developed, and a robust approach is proposed in order to establish a control scheme for singular systems. The proposed method presents a general framework for robust control design of singular systems in presence of modeling uncertainties. Two simulation examples are given to how the proposed method can be implemented, and to show the effectiveness of such controllers in closed loop performance.

2011ConferencePDFDynamical Systems Analysis and Control
An Analytic-Iterative Redundancy Resolution Scheme for Cable-Driven Redundant Parallel Manipulators
Hamid D. Taghirad and Yousef B. Bedoustani
IEEE Transactions on Robotics
Abstract:

In this paper, redundancy resolution of a cable-driven parallel manipulator is performed through an analytic-iterative scheme. The redundancy resolution scheme is formulated as a convex optimization problem with inequality constraints that are imposed by manipulator structure and cable dynamics. The Karush-Kuhn-Tucker theorem is used to analyze the optimization problem and to draw an analytic-iterative solution for it. Subsequently, a tractable and iterative search algorithm is proposed to implement the redundancy resolution of such redundant manipulators. Furthermore, it is shown through simulations that the worst case and average elapsed time that is required to implement the proposed redundancy resolution scheme in a closed-loop implementation is considerably less than that of other numerical optimization methods.

2011JournalPDFParallel and Cable Robotics
Explicit Dynamics Formulation of Stewart–Gough Platform: A Newton–Euler Approach
Reza Oftadeh, Mohammad M. Aref and Hamid D. Taghirad
IEEE/RSJ International Conference on Intelligent Robots and Systems
Abstract:

Dynamic analysis of parallel manipulators plays a vital role in the design and control of such manipulators. Closed-chain kinematic structure affects the dynamics formulations by several constraints. Therefore, especially for higher degrees of freedom manipulators, manipulation of implicit and bulky dynamics formulation looses the tractability of the analysis. In this paper, a methodology and some simplification tools are introduced to achieve explicit dynamics formulation for parallel manipulators. This methodology is applied for the dynamics analysis of the most celebrated parallel manipulator, namely Stewart-Gough platform. By avoiding any recursive or component-wise derivations, the resulting dynamics formulation provides more insight for designers, and can be much easier used in any model-based control of such manipulators. In order to verify the resulting dynamics equations, Lagrange method is used to derive and compare the manipulator mass matrix. This methodology can be further used to formulate the explicit dynamics of other parallel manipulators.Dynamic analysis of parallel manipulators plays a vital role in the design and control of such manipulators. Closed-chain kinematic structure affects the dynamics formulations by several constraints. Therefore, especially for higher degrees of freedom manipulators, manipulation of implicit and bulky dynamics formulation looses the tractability of the analysis. In this paper, a methodology and some simplification tools are introduced to achieve explicit dynamics formulation for parallel manipulators. This methodology is applied for the dynamics analysis of the most celebrated parallel manipulator, namely Stewart-Gough platform. By avoiding any recursive or component-wise derivations, the resulting dynamics formulation provides more insight for designers, and can be much easier used in any model-based control of such manipulators. In order to verify the resulting dynamics equations, Lagrange method is used to derive and compare the manipulator mass matrix. This methodology can be further used to formulate the explicit dynamics of other parallel manipulators.

2010ConferencePDFParallel and Cable Robotics
2010
TitleAbstractYearTypePDFResearch Group
Iterative-Analytic Redundancy Resolution Scheme for A Cable-Driven Redundant Parallel Manipulator
Yousef B. Bedoustani, and Hamid D. Taghirad
2010 IEEE/ASME International Conference on Advanced Intelligent Mechatronics
Abstract:

In this paper, redundancy resolution of a cable-driven parallel manipulator is solved by an iterative-analytic scheme. The method can be applied to all kind of redundant manipulators either parallel or serial with constraint caused through their dynamics. However, for sake of simulation the proposed method is implemented on a cable-driven redundant parallel manipulator (CDRPM). The redundancy resolution problem is formulated as a convex optimization with equality and non-equality constraints caused by manipulator structure and cables dynamics. Karush-Kuhn-Tucker theorem is used to analyze the optimization problem and to find an analytic solution. Subsequently, a tractable and iterative search algorithm is proposed to solve the redundancy resolution of such redundant mechanisms. Furthermore, it is shown through the simulation that, the elapsed time required to implement the analytical redundancy resolution scheme in a closed-loop structure is considerably less than that of other numerical optimization methods.

2010ConferencePDFParallel and Cable Robotics
A Geometric Costructive Approach For The Workspace Analysis of Symmetrical 5-PRUR Parallel Mechanisms (3T2R)
Mehdi Tale Masouleh, Mohammad Hossein Saadatzi, Clement Gosselin, Hamid D. Taghirad
Proceedings of the ASME Design Engineering Technical Conference
Abstract:

This paper investigates an important kinematic property, the constant-orientation workspace, of five-degree-of-freedom parallel mechanisms generating the 3T2R motion and comprising five identical limbs of the P RUR type. The general mechanism originates from the type synthesis performed for symmetrical 5-DOF parallel mechanism. In this study, the emphasis is placed on the determination of constant-orientation workspace using geometrical interpretation of the so-called vertex space, i.e., motion generated by a limb for a given orientation, rather than relying on classical recipes, such as discretization methods. For the sake of better understanding a CAD model is also provided for the vertex space. The constructive geometric approach presented in this paper provides some insight into the architecture optimization. Moreover, this approach facilitates the computation of the evolution of the volume of the constant-orientation workspace for different orientations of the end-effector.

2010ConferencePDFParallel and Cable Robotics
Descriptor Approach to Unknown Input PI Observer Design:application to fault detection
M.M. Share Pasand, H.D. Taghirad
Control Automation and Systems (ICCAS), 2010
Abstract:

The descriptor observer approach is improved further to a more suitable observer scheme which is applicable to a more general group of faults and systems. Also a disturbance decoupling scheme is added to the mentioned observer in order to enable the observer to distinguish faults from disturbances.

2010ConferencePDFDynamical Systems Analysis and Control
Unknown Input-Proportional Integral Observer for Singular Systems: Application to fault detection
M. M. Share Pasand, M. Aliyari Sh., and H. D. Taghirad
2010 18th Iranian Conference on Electrical Engineering
Abstract:

A new approach to the observer design for descriptor continuous time systems is proposed and its application in the fault diagnosis problem is illustrated. In this observer, two features of disturbance decoupling and fault estimation are combined. Also a more general frame for fault estimation is used. Some numerical examples and simulation results are shown to justify the effectiveness of the algorithm.

2010ConferencePDFDynamical Systems Analysis and Control
Forward Kinematic Problem and Constant Orientation Workspace of 5-RPRRR (3T2R) Parallel Mechanisms
Mehdi Tale Masouleh, Clément Gosselin, Mohammad Hossein Saadatzi, Hamid D. Taghirad
Electrical Engineering (ICEE), 2010 18th Iranian Conference on
Abstract:

This paper investigates some kinematic properties of a five-degree-of-freedom parallel mechanism generating the 3T2R motion and comprising five identical limbs of the RP?UR type. In this study, two classes of simplified designs are proposed whose forward kinematic problems have either a univariate or a closed-form solution. The principal contributions of this study are the solution of the forward kinematic problem for some simplified designs—which may have more solutions than the FKP of the general 6-DOF Stewart platform with 40 solutions—and the determination of the constant orientation workspace based on algebraic geometry (Bohemian domes).

2010ConferencePDFParallel and Cable Robotics
Integrated Controller For An Over–Constrained Cable Driven Parallel Manipulator: KNTU CDRPM
Alaleh Vafaei, Mohammad M. Aref and Hamid D. Taghirad
2010 IEEE International Conference on Robotics and Automation
Abstract:

This paper presents an approach to the control of the KNTU CDRPM using an integrated control scheme. The goal in this approach is achieving accurate trajectory tracking while assuring positive tension in the cables. By the proposed controller, the inherent nonlinear behavior of the cable and the target tracking errors are simultaneously compensated. In this paper asymptotic stability analysis of the close loop system is studied in detail. Moreover, it is shown that the integrated control strategy reduces the tracking error by 80% compared to that of a single loop controller in the considered manipulator. The closed-loop performance of the control topology is analyzed by a simulation study that is performed on the manipulator. The simulation study verifies that the proposed controller is not only promising to be implemented on the KNTU CDRPM, but also being suitable for other cable driven manipulators.

2010ConferencePDFParallel and Cable Robotics
Model predictive control of non-linear discrete time systems: a linear matrix inequality approach
N. Poursafar, H.D. Taghirad, M. Haeri
IET Control Theory & Applications
Abstract:

Using a non-linear model in model predictive control (MPC) changes the control problem from a convex quadratic programme to a non-convex non-linear problem, which is much more challenging to solve. In this study, we introduce an MPC algorithm for non-linear discrete-time systems. The systems are composed of a linear constant part perturbed by an additive state-dependent non-linear term. The control objective is to design a state-feedback control law that minimises an infinite horizon cost function within the framework of linear matrix inequalities. In particular, it is shown that the solution of the optimisation problem can stabilise the non-linear plants. Three extensions, namely, application to systems with input delay, non-linear output tracking and using output-feedback, are followed naturally from the proposed formulation. The performance and effectiveness of the proposed controller is illustrated with numerical examples.

2010JournalPDFDynamical Systems Analysis and Control
Disturbance Retrieving Unknown Input Proportional Integral Observer for Generalized Linear Systems
M.M. Share Pasand and H.D. Taghirad
ICCAS 2010
Abstract:

An unknown input retrieving observer scheme is proposed which not only decouples unknown inputs in estimation but also gives an estimation of the decoupled input. The provided method benefits from its low computational cost as well as its less restrictive existence conditions compared to existing ones.

2010ConferencePDFDynamical Systems Analysis and Control
Forward Kinematic Analysis of A Planar Cable Driven Redundant Parallel Manipulator Using Force Sensors
Reza Oftadeh, Mohammad M. Aref, and Hamid D. Taghirad
IEEE/RSJ International Conference on Intelligent Robots and Systems
Abstract:

Newly developed cable driven redundant parallel manipulators (CDRPM) have numerous advantages compared to that of the conventional parallel mechanisms. However, there exist some challenging issues in over-constrained mechanisms like CDRPMs. In contrast to serial manipulators, complexity of parallel manipulator forward kinematics (FK) is one of the main issues being under study in the control of such manipulators. Moreover, using extra sensory data is a common approach in the FK solution of rigid-linked parallel manipulators, which is considered by fewer researchers for CDRPMs. In this paper, tension force sensors of the cables are used as an extra sensor to simplify analytical solution of the FK for a planar CDRPM. To find a suitable solution, geometrical and physical characteristics of the robot are analyzed. It is shown that the proposed method provides the required accuracy and significantly improves the process time compared to the conventional methods.

2010ConferencePDFParallel and Cable Robotics
Explicit Dynamics Formulation of Stewart–Gough Platform: A Newton–Euler Approach
Reza Oftadeh, Mohammad M. Aref and Hamid D. Taghirad
IEEE/RSJ International Conference on Intelligent Robots and Systems
Abstract:

Dynamic analysis of parallel manipulators plays a vital role in the design and control of such manipulators. Closed-chain kinematic structure affects the dynamics formulations by several constraints. Therefore, especially for higher degrees of freedom manipulators, manipulation of implicit and bulky dynamics formulation looses the tractability of the analysis. In this paper, a methodology and some simplification tools are introduced to achieve explicit dynamics formulation for parallel manipulators. This methodology is applied for the dynamics analysis of the most celebrated parallel manipulator, namely Stewart-Gough platform. By avoiding any recursive or component-wise derivations, the resulting dynamics formulation provides more insight for designers, and can be much easier used in any model-based control of such manipulators. In order to verify the resulting dynamics equations, Lagrange method is used to derive and compare the manipulator mass matrix. This methodology can be further used to formulate the explicit dynamics of other parallel manipulators.Dynamic analysis of parallel manipulators plays a vital role in the design and control of such manipulators. Closed-chain kinematic structure affects the dynamics formulations by several constraints. Therefore, especially for higher degrees of freedom manipulators, manipulation of implicit and bulky dynamics formulation looses the tractability of the analysis. In this paper, a methodology and some simplification tools are introduced to achieve explicit dynamics formulation for parallel manipulators. This methodology is applied for the dynamics analysis of the most celebrated parallel manipulator, namely Stewart-Gough platform. By avoiding any recursive or component-wise derivations, the resulting dynamics formulation provides more insight for designers, and can be much easier used in any model-based control of such manipulators. In order to verify the resulting dynamics equations, Lagrange method is used to derive and compare the manipulator mass matrix. This methodology can be further used to formulate the explicit dynamics of other parallel manipulators.

2010ConferencePDFParallel and Cable Robotics
Delay-Dependent H-Infinity Control of Linear Systems with input Delay Using Composite State-Derivative Feedback
A. Shariati, H. D Taghirad and B. Labibi
Iranian Conference on Electrical Engineering
Abstract:

H-Infinity control problem for input-delayed systems is considered in this paper. A composite state-derivative control law is used, in which, a composition of the state variables and their derivatives appear in the control law. Thus, the resulting closed-loop system turns into a specific time-delay system of neutral type. The significant specification of this neutral system is that its delayed term coefficients depend on the control law parameters. This condition provides new challenging issues which has its own merits in theoretical research as well as application aspects. New delay-dependent sufficient condition for the existence of H ? controller in terms of matrix inequalities is derived in the present paper. The resulting H-Infinity controller guarantees asymptotic stability of the closed-loop system as well as a guaranteed limited H ? norm smaller than a prescribed level. Numerical examples are presented to illustrate the effectiveness of the proposed methods.

2010ConferencePDFDynamical Systems Analysis and Control
Kinematic analysis of 5-RPUR (3T2R) parallel mechanisms
Mehdi Tale Masouleh, Clément Gosselin, Mohammad Hossein Saadatzi, Xianwen Kong, Hamid D. Taghirad
Parallel Manipulators
Abstract:

This paper investigates some kinematic properties of a five-degree-of-freedom parallel mechanism generating the 3T2R motion and comprising five identical limbs of the RPUR type. The general mechanism originates from the type synthesis performed for symmetrical 5-DOF parallel mechanism. In this study, two classes of simplified designs are proposed whose forward kinematic problem have either a univariate or a closed-form solution. The principal contributions of this study are the solution of the forward kinematic problem for some simplified designs—which may have more solutions than the FKP of the general 6-DOF Stewart platform with 40 solutions—and the determination of the constant-orientation workspace which is based on the topology of the vertex space (Bohemian dome) and a geometric constructive approach.

2010JournalPDFParallel and Cable Robotics
Delay-Dependent H-Infinity Control of Linear Systems with Time-Varying Delays Using Proportional-Derivative State Feedback
A. Shariati, H. D Taghirad and B. Labibi
Control & Automation (MED)
Abstract:

This paper considers H-Infinity control problem for input-delayed systems for time-varying delays. A proportional-derivative state feedback control law is used in this paper. By this means, the resulting closed-loop system turns into a specific time-delay system of neutral type. The significant specification of this neutral system is that its delayed term coefficients depend on the controller parameters. This condition provides new challenging issues in theoretical research as well as providing new applications. In the present paper, new delay-dependent sufficient condition is derived for the existence of H-Infinity controller in terms of matrix inequalities, in presence of varying time-delays. The resulting H-Infinity controller guarantees asymptotic stability of the closed-loop system as well as a guaranteed limited system induced norm smaller than a prescribed level. Numerical examples are presented to illustrate the effectiveness of the proposed method.

2010ConferencePDFDynamical Systems Analysis and Control
Identifying a two linked robot with non-symmetrical modified friction and Backlash-flexibility models
J. Bahrami, Me. Keshmiri, Mo. Keshmiri and H. D. Taghirad
2010 IEEE International Conference on Robotics and Biomimetics
Abstract:

Identifying a robotic system, especially in presence of some nonlinear phenomena, such as friction and backlash, is a troublesome problem. In this paper, initially single link parameter identification is discussed. Parameters such as actuators parameter, link inertia, friction and backlash are identified in this section. A combination of actuator's model and a model of two flexible masses in attendance of friction and backlash is utilized for this purpose. Identifying two link robot parameters will be under debate afterwards and identification results for the second link are presented in three distinct forms. Furthermore, a method is introduced for selecting best estimated parameters set, in order to be exerted on systems controller. The effects of identified friction torques and backlash modeling on controller improvement are presented. Grey box structure model, available in Matlab's system identification tool box is utilized in this research.

2010ConferencePDF
2009
TitleAbstractYearTypePDFResearch Group
Vision-Based Fuzzy Navigation of Mobile Robots in Grassland Environments
A. R. Norouzzadeh Ravari, H. D. Taghirad, A. H. Tamjidi
Advanced Intelligent Mechatronics
Abstract:

In this paper a vision-based algorithm for mobile robot navigation in unknown outdoor environments is proposed. It is based on a simple phenomenon, that when the robot moves forward, projected images of the near obstacles grow in captured frames faster than that of the far objects. The proposed algorithm takes advantage of this property and extracts features from each grabbed frame of the camera and tracks the vertical position of the features and their speed along the Y axis of the image plane over multiple frames as the robot moves. The relative height of the features and their distance from the robot in 3D is inferred based on this data and they are fed into a fuzzy reasoning system which marks the features from safe to unsafe according to their suitability for navigation. Then a second fuzzy system summarizes these scores in different image regions and directs the robot toward the area containing more features marked as safe. Simulation and implementation results confirm the efficacy of the proposed simple algorithm for mobile robot navigation in outdoor environments.

2009ConferencePDFAutonomous Robotics
Line Matching Localization and Map Building with Least Square
E. Mihankhah, H.D. Taghirad, A. Kalantari, E. Aboosaeedan, H. Semsarilar
2009 IEEE/ASME International Conference on Advanced Intelligent Mechatronics
Abstract:

We introduce a very fast and robust localization and 2D environment representation algorithm in this paper. This innovative method matches lines extracted from the LASER range finder distance data with the lines that construct the map, in order to calculate the local translation and rotation. This matching is done with a simple least square with no iterations. The algorithm is suitable for any indoor environment with mostly polygonal structure and has proven high speed and robustness in the experimental tests on our innovatively designed tracked mobile rescue robot ldquoSilverrdquo. One experimental test is presented in the last section of this paper where the outputs are presented. These outputs are: 1-drift free raster map made of points and 2- A gallery of lines providing a linear ground truth.

2009ConferencePDFAutonomous Robotics
Wrench Feasible Workspace Analysis of Cable-Driven Parallel Manipulators Using LMI Approach
Azadeh Zarif Loloei, Mohamad M. Aref, and Hamid D. Taghirad
Advanced Intelligent Mechatronics
Abstract:

Workspace analysis is one of the most important issues in robotic manipulator design. This paper introduces a systematic method of analysis the wrench feasible workspace for general redundant cable-driven parallel manipulators. In this method, wrench feasible workspace is formulated in term of linear matrix inequalities and projective method is used for solving them. This method is one of the most efficient interior-point methods with a polynomial-time complexity. Moreover, the notion of dexterous workspace is defined, which can be determined for redundant cable driven manipulators exerting a worst case external wrench at the end effector. A detailed case study of the wrench feasible workspace and dexterous workspace determination are included for a six DOF, eight actuated cable-driven redundant parallel manipulator.

2009ConferencePDFParallel and Cable Robotics
Robust H-Infinity Filtering for Nonlinear Uncertain Systems Using State-Dependent Riccati Equation Technique
Hossein Beikzadeh and Hamid D. Taghirad
Proceedings of the IEEE Conference on Decision and Control
Abstract:

The standard state-dependent Riccati equation (SDRE) filter, which is set up by direct SDC parameterization, demands complete knowledge of the system model, and the disturbance inputs characteristics. However, this inherent dependency can severely degrade its performance in practical applications. In this paper, based on the H ¿ norm minimization criterion, a robust SDRE filter is proposed to effectively estimate the states of nonlinear uncertain systems exposed to unknown disturbance inputs. Considering a Lipschitz condition on the chosen SDC form, we guarantee fulfillment of a modified H ¿ performance index by the proposed filter. The effectiveness of the robust SDRE filter is demonstrated through numerical simulations where it brilliantly outperforms the usual SDRE filters in presence of model uncertainties as well as process and measurement noises.

2009ConferencePDF
Analysis OF First Order Systems With Variable Time Delay Using PI Controller and Smith Predictor
Abdolvahed Saeidi, Hamid D.Taghirad
Proceedings of the IASTED International Conference on Modelling, Simulation, and Identification
Abstract:

Smith predictor is one of the first structures used to compensate the time delay in closed loop systems. One of the simplest controllers which are used to control the industrial systems is PID controller. Although, we know that the derivative term is rarely used for controlling the time delay systems. Subtle identification of time delay is usually impossible in reality; on the other hand, PI controller design with smith structure is practiced upon the open loop delay free system. Therefore the structural uncertainty will be existed in open loop systems which make the designing of the PI controller very difficult. In this paper, at first, we analyze the effect of difference between modeled time delay and real time delay on the PI parameters, then the performance of the closed loop system compared with a second order delay free system is investigated; and finally, we compare the tracking of variable time delay system with fixed time delay system which both of them have the same parameters. In this analysis we assume that the fixed time delay is max of variable time delay.

2009ConferencePDF
Stability Analysis of the Discrete-Time Difference SDRE State Estimator in a Noisy Environment
Hossein Beikzadeh and Hamid D. Taghirad
2009 IEEE International Conference on Control and Automation
Abstract:

The state-dependent Riccati equation filter (SDREF) is a recent nonlinear estimation technique which has yielded a number of impressive results. However, the theoretical investigations of the filter have been carried out only in a deterministic environment. In this paper a discrete time difference SDRE-based observer for general nonlinear systems in a stochastic framework is considered, and its error behavior has been also analyzed. It is proved that, the estimation error remains bounded in mean square if the system to be observed satisfies certain conditions, and both the initial estimation error and the disturbing noise terms are small enough. Moreover, the results are verified thorough a simulation study of an example system.

2009ConferencePDF
Delay-Dependent Stabilization of Linear Input-Delayed Systems with Composite State-Derivative Feedback: Constant and Time-Varying Delays
A. Shariati, H.D Taghirad and B. Labibi
Iranian Conference on Electrical Engineering
Abstract:

This paper considers stability problem for input- delayed systems for both constant and time-varying delay case. A new composite state-derivative control law is introduced, in which, a composition of the state variables and their derivatives appear in control law. By this means, the resulting closed-loop system becomes a particular time-delay system of neutral type. The significant specification of this neutral system is that its delayed term coefficients depend on the control law's parameters. This condition provides new challenging issues which has its own merits in theoretical as well as practical aspects. In the present paper, new delay-dependent sufficient conditions are derived in presence of both constant and varying time-delay in terms of matrix inequalities. The resulting controllers guarantee asymptotic stability of the closed-loop system. Simulation studies are presented to verify the stability conditions obtained within the theorems.

2009ConferencePDFDynamical Systems Analysis and Control
Kinematics and Jacobian Analysis of the KNTU CDRPM: A Cable Driven Redundant Parallel Manipulator
Mohammad M. Aref, Reza Oftadeh and Hamid D. Taghirad
Iranian Conference on Electrical Engineering, ICEE
Abstract:

KNTU CDRPM is a cable driven redundant parallel manipulator, which is under investigation for possible implementation in large workspace applications. This type newly developed manipulator has numerous advantages compared to that of the conventional parable mechanisms. The rotational motion range is relatively large, the inherent redundancy improves dexterity of the manipulator, and the light weight structure makes the robot more energy efficient and significantly fast. However, there exist some challenging issues in the over-constrained mechanism like KNTU CDRPM. Collision avoidance, force feasibility, and linear independency of the cables are the main issues being under study in the design of such manipulators. In this paper, singularity of the KNTU CDRPM is studied in detail. To extract kinematic properties of the robot, the inverse and forward kinematics are analyzed. It is shown that singularity analysis can well describe the characteristics of the design and provide the sufficient means to the designer to improve these characteristics. Finally, a suitable design strategy is proposed to significantly reduce the singularity of the manipulator within its whole workspace. The outcomes of this strategy implemented on KNTU CDRPM result in a significant improvement of the singular free workspace of the proposed design compared to that of the latest parallel manipulators.

2009ConferencePDFParallel and Cable Robotics
Nonlinear Sensorless Speed Control of PM Synchronous Motor via an SDRE Observer Controller Combination
Hossein Beikzadeh and Hamid D. Taghirad
Industrial Electronics and Applications, ICIEA 2009
Abstract:

In this paper, a nonlinear control approach for permanent magnet synchronous motor (PMSM) drives, without mechanical sensors, is presented. The proposed method is based on a combination of the well-known nonlinear regulation technique, state-dependent Riccati equation (SDRE), and its filtering counterpart (SDREF) which is derived by constructing the dual of this control method. The SDREF is designed for online estimation of the rotor speed, position and also the load torque by only measuring the motor voltages and currents. The estimated values are applied in the controller structure as state variables. We demonstrate the performance and applicability of this new nonlinear control for PMSM derives by an illustrative simulation in presence of variable load torque. The sensitivity and robustness of the proposed method are also investigated for the motor parameters variations.

2009ConferencePDF
Adaptive Cascade Control of the KNTU CDRPM: A Cable Driven Redundant Parallel Manipulator
Pooneh Gholami, Mohammad M. Aref and Hamid D. Taghirad
Intelligent Robots and Systems, 2008. IROS
Abstract:

The challenging control problem of the cable driven redundant manipulators is due to the complexity of its dynamic and the required stringent performance for the its promising applications. This paper presents an approach to the control of the KNTU CDRPM using an adaptive cascade control scheme. The goal in this approach is achieving accurate trajectory tracking while assuring positive tension in the cables. The cascade control topology uses two loops, namely the internal and external loops. The inherent nonlinear behavior of the cable manipulator is controlled by the internal loop, while the external loop can effectively reduce the target tracking errors of the end-effector in the presence of disturbance force/torques. The cascade strategy reduces the tracking error by 80% compared to that of a single loop controller in the KNTU CDRPM. Moreover, adaptation of the cascade controller gains can significantly improve the overall tracking performance. The closed-loop performance of various control topologies are analyzed by a simulation study that is performed on the KNTU CDRPM. Since, the dynamic equations of this parallel manipulator is implicit in its general form, special integration routines are used for integration. The simulation study verifies that the proposed controller is not only promising to be implemented on the KNTU CDRPM, but also being suitable for other cable driven manipulators.

2009ConferencePDFParallel and Cable Robotics
Optimal Design of Dexterous Cable Driven Parallel Manipulators
Mohammad M. Aref, Hamid D. Taghirad and Sasan Barissi
International Journal of Robotics
Abstract:

Optimal design of parallel manipulators is known as a challenging problem especially for cable driven robots. In this paper, optimal design of cable driven redundant parallel manipulators (CDRPM) is studied in detail. Visual Inspection method is proposed as a systematic design process of the manipulator. A brief review of various design criteria shows that the optimal design of a CDRPM cannot be performed based on single objective. Therefore, a multi objective optimal design problem is formulated in this paper through an overall cost function. Furthermore, a proper weighting selection for the overall cost function is proposed, which can be viewed as a promising method to the open problem of parallel manipulator design. In order to verify the effectiveness of the proposed method, it is applied on the design of KNTU CDRPM, an eight actuated with six degrees of freedom CDRPM, which is under investigation for possible high speed and wide workspace applications in K.N. Toosi University of Technology. Finally, a combined numerical optimization algorithm is used to find the unique global optimum point. The result shows a significant enhancement in the performance characteristics of the KNTU CDRPM compared to that of the other CDRPMs. Since the proposed method is not restricted to any particular assumption on the objectives and design parameters, it can be used for optimal design of other manipulators.

2009JournalPDFParallel and Cable Robotics
On the Consistency of EKF-SLAM: Focusing on the Observation Models
Amirhossein Tamjidi, Hamid D. Taghirad, Aliakbar Aghamohammadi
Intelligent Robots and Systems
Abstract:

In this paper a new strategy for handling the observation information of a bearing-range sensor throughout the filtering process of EKF-SLAM is proposed. This new strategy is advised based on a thorough consistency analysis and aims to improve the process consistency while reducing the computational cost. At first, three different possible observation models are introduced for the EKF-SLAM solution for a robot equipped with a bearing-range sensor. General form of the covariance matrix and the level of inconsistency in the robot orientation estimate is then calculated for these variants, and based on the numerical comparison of the estimation results, it is proposed to use the bearing and range information of a feature in the initialization step of EKF-SLAM. However, it is recommended to use only the bearing information to perform other iteration steps. The simulation observations verify that the new strategy yields to more consistent estimates both for the robot and the features. Moreover, through the proposed consistency analysis, it is shown that since the source of consistency improvement is independent from the choice of the motion model, it gives us an advantage over other existing methods that assume a specific motion models for consistency improvement.

2009ConferencePDF
Fuzzy error governor: A practical approach to counter actuator saturation on flexible joint robots
S. Ozgoli, H.D. Taghirad
Mechatronics
Abstract:

In this paper, a practical method to counter actuator saturation based on a fuzzy error governor is developed and a complete case study is considered. In addition to good performance, the method has two attracting properties: It does not change the structure of the main controller, and therefore, the theoretically proven characteristics of the system are untouched, and it is simply implementable in practice. The proposed controller structure is applied on a flexible joint robot (FJR). The robust stability of the closed loop system for an n-DOF FJR is thoroughly analyzed and the proposed controller is implemented on a laboratory setup to show the ease of implementation and the resulting closed-loop performance. The main controller used for the n-DOF FJR consists of a composite structure, with a PD controller on the fast dynamics and a PID controller on the slow dynamics. The bandwidth of the fast controller is decreased during critical occasions with the fuzzy logic supervisor, which adjusts the loop gain to a proper level. Using Lyapunov direct method, the robust stability of the overall system is analyzed in presence of modeling uncertainties, and it is shown that if the PD and the PID gains are tuned to satisfy certain conditions, the closed loop system becomes UUB stable.

2009JournalPDFFlexible Robotics
A novel hybrid Fuzzy-PID controller for tracking control of robot manipulators
A. R. Norouzzadeh Ravari, H.D. Taghirad
2008 IEEE International Conference on Robotics and Biomimetics
Abstract:

In this paper, a novel hybrid fuzzy proportional-integral-derivative (PID) controller based on learning automata for optimal tracking of robot systems including motor dynamics is presented. Learning automata is used at the supervisory level for adjustment of the parameters of hybrid Fuzzy-PID controller during the system operation. The proposed method has better convergence rate in comparison with standard back-propagation algorithms, less computational requirements than adaptive network based fuzzy inference systems (ANFIS) or neural based controllers and having the ability of working in uncertain environments without any previous knowledge of environments' parameters. The proposed controller has been successfully applied in simulation to control a 6-DOF Puma 560 manipulator using robotic toolbox, and has satisfactory results. In this simulation also, external disturbance and noise are addressed. The result of simulation has also shown that the rate of convergence and robustness of the designed controller guarantees practical stability.

2009ConferencePDFAutonomous Robotics
Autonomous Staircase Detection and Stair Climbing for a Tracked Mobile Robot using Fuzzy Controller
E. Mihankhah, A. Kalantari, E. Aboosaeedan, H.D. Taghirad, and S.Ali.A. Moosavian
2008 IEEE International Conference on Robotics and Biomimetics
Abstract:

Theoretical analysis and implementation of autonomous staircase detection and stair climbing algorithms on a novel rescue mobile robot are presented in this paper. The main goals are to find the staircase during navigation and to implement a fast, safe and smooth autonomous stair climbing algorithm. Silver is used here as the experimental platform. This tracked mobile robot is a tele-operative rescue mobile robot with great capabilities in climbing obstacles in destructed areas. Its performance has been demonstrated in rescue robot league of international RoboCup competitions. A fuzzy controller is applied to direct the robot during stair climbing. Controller inputs are generated by processing the range data from two laser range finders which scan the environment one horizontally and the other vertically. The experimental results of stair detection algorithm and stair climbing controller are demonstrated at the end.

2009ConferencePDFAutonomous Robotics
1998-2008
TitleAbstractYearTypePDFResearch Group
Preintegrated IMU Features For Efficient Deep Inertial Odometry
R Khorrambakht, H Damirchi, HD Taghirad
arXiv preprint arXiv:2007.02929
Abstract:

MEMS Inertial Measurement Units (IMUs) are inexpensive and effective sensors that provide proprioceptive motion measurements for many robots and consumer devices. However, their noise characteristics and manufacturing imperfections lead to complex ramifications in classical fusion pipelines. While deep learning models provide the required flexibility to model these complexities from data, they have higher computation and memory requirements, making them impractical choices for low-power and embedded applications. This paper attempts to address the mentioned conflict by proposing a computationally, efficient inertial representation for deep inertial odometry. Replacing the raw IMU data in deep Inertial models, preintegrated features improves the model's efficiency. The effectiveness of this method has been demonstrated for the task of pedestrian inertial odometry, and its efficiency has been shown through its embedded implementation on a microcontroller with restricted resources.

2020JournalPDFAutonomous Robotics
ARC-Net: Activity Recognition Through Capsules
H Damirchi, R Khorrambakht, H Taghirad
arXiv preprint arXiv:2007.03063
Abstract:

Human Activity Recognition (HAR) is a challenging problem that needs advanced solutions than using handcrafted features to achieve a desirable performance. Deep learning has been proposed as a solution to obtain more accurate HAR systems being robust against noise. In this paper, we introduce ARC-Net and propose the utilization of capsules to fuse the information from multiple inertial measurement units (IMUs) to predict the activity performed by the subject. We hypothesize that this network will be able to tune out the unnecessary information and will be able to make more accurate decisions through the iterative mechanism embedded in capsule networks. We provide heatmaps of the priors, learned by the network, to visualize the utilization of each of the data sources by the trained network. By using the proposed network, we were able to increase the accuracy of the state-of-the-art approaches by 2%. Furthermore, we investigate the directionality of the confusion matrices of our results and discuss the specificity of the activities based on the provided data.

2020JournalPDFAutonomous Robotics
Solution to IDA-PBC PDEs by Pfaffian Differential Equations
MRJ Harandi, H Taghirad
arXiv preprint arXiv:2006.14983
Abstract:

Finding the general solution of partial differential equations (PDEs) is essential for controller design in some methods. Interconnection and damping assignment passivity based control (IDA-PBC) is one of such methods in which the solution to corresponding PDEs is needed to apply it in practice. In this paper, such PDEs are transformed to corresponding Pfaffian differential equations. Furthermore, it is shown that upon satisfaction of the integrability condition, the solution to the corresponding third order Pfaffian differential equation may be obtained quite easily. The method is applied to the PDEs of IDA-PBC in some benchmark problems such as Magnetic levitation system, Pendubot and underactuated cable driven robot to verify its applicability.

2020JournalPDFDynamical Systems Analysis and Control
Adaptive motion control of parallel robots with kinematic and dynamic uncertainties
MRJ Harandi, SA Khalilpour, H Taghirad, JG Romero
arXiv preprint arXiv:2003.08860
Abstract:

One of the most challenging issues in adaptive control of robot manipulators with kinematic uncertainties is requirement of the inverse of Jacobian matrix in regressor form. This requirement is inevitable in the case of the control of parallel robots, whose dynamic equations are written directly in the task space. In this paper, an adaptive controller is designed for parallel robots based on representation of Jacobian matrix in regressor form, such that asymptotic trajectory tracking is ensured. The main idea is separation of determinant and adjugate of Jacobian matrix and then organize new regressor forms. Simulation and experimental results on a 2--DOF R\underline{P}R and 3--DOF redundant cable driven robot, verify promising performance of the proposed methods.

2020JournalPDFParallel and Cable Robotics
Multi-goal motion planning using traveling salesman problem in belief space
Ali Noormohammadi-Asl, Hamid D. Taghirad
Information Sciences
Abstract:

In this paper, the multi-goal motion planning problem of an environment with some background information about its map is addressed in detail. The motion planning goal is to find a policy in belief space for the robot to traverse through a number of goal points. This problem is modeled as an asymmetric traveling salesman problem (TSP) in the belief space using Partially Observable Markov Decision Process (POMDP) framework. Then, feedback-based information roadmap (FIRM) algorithm is utilized to reduce the computational burden and complexity. By generating a TSP-FIRM graph, the search policy is obtained and an algorithm is proposed for online execution of the policy. Moreover, approaches to cope with challenges such as map updating, large deviations and high uncertainty in localization, which are more troublesome in a real implementation, are carefully addressed. Finally, in order to evaluate applicability and performance of the proposed algorithms, it is implemented in a simulation environment as well as on a physical robot in which some challenges such as kidnapping and discrepancies between real and computational models and map are examined.

2018JournalPDFAutonomous Robotics
Feasible Kinematic Sensitivity in Cable Robots Based on Interval Analysis
S. A. Khalilpour, A. Zarif Loloei, H. D. Taghirad, and M. Tale Masouleh
Cable-Driven Parallel Robots
Abstract:

The kinematic sensitivity has been recently proposed as a unit-consistent performance index to circumvent several shortcomings of some notorious indices such as dexterity. This paper presents a systematic interval approach for computing an index by which two important kinematic properties, namely feasible workspace and kinematic sensitivity, are blended into each other. The proposed index may be used to efficiently design different parallel mechanisms, and cable driven robots. By this measure, and for parallel manipulators, it is possible to visualize constant orientation workspace of the mechanism where the kinematic sensitivity is less than a desired value considered by the designer. For cable driven redundant robots, the controllable workspace is combined with the desired kinematic sensitivity property, to determine the so-called feasible kinematic sensitivity workspace of the robot. Three case studies are considered for the development of the idea and verification of the results, through which a conventional planar parallel manipulator, a redundant one and a cable driven robot is examined in detail. Finally, the paper provides some hints for the optimum design of the mechanisms under study by introducing the concept of minimum feasible kinematic sensitivity covering the whole workspace.

2012JournalPDFParallel and Cable Robotics
Experimental Performance of Robust PID Controller on a Planar Cable Robot
M. A. Khosravi and H. D. Taghirad
Cable-Driven Parallel Robots
Abstract:

In this paper dynamic analysis and experimental performance of robust PID control for fully-constrained cable driven robots are studied in detail. Since in this class of manipulators cables should remain in tension for all maneuvers through their whole workspace, feedback control of such robots becomes more challenging than conventional parallel robots. To ensure that all the cables remain in tension, a corrective term is used in the proposed PID control scheme. In design of PID control it is assumed that there exist bounded norm uncertainties in Jacobian matrix and in all dynamics matrices. Then a robust PID controller is proposed to overcome partial knowledge of robot, and to guarantee boundedness of tracking errors. Finally, the effectiveness of the proposed PID algorithm is examined through experiments and it is shown that the proposed control structure is able to provide suitable performance in practice.

2012JournalPDFParallel and Cable Robotics
Forward Kinematic Analysis of A Planar Cable Driven Redundant Parallel Manipulator Using Force Sensors
Reza Oftadeh, Mohammad M. Aref, and Hamid D. Taghirad
IEEE/RSJ International Conference on Intelligent Robots and Systems
Abstract:

Newly developed cable driven redundant parallel manipulators (CDRPM) have numerous advantages compared to that of the conventional parallel mechanisms. However, there exist some challenging issues in over-constrained mechanisms like CDRPMs. In contrast to serial manipulators, complexity of parallel manipulator forward kinematics (FK) is one of the main issues being under study in the control of such manipulators. Moreover, using extra sensory data is a common approach in the FK solution of rigid-linked parallel manipulators, which is considered by fewer researchers for CDRPMs. In this paper, tension force sensors of the cables are used as an extra sensor to simplify analytical solution of the FK for a planar CDRPM. To find a suitable solution, geometrical and physical characteristics of the robot are analyzed. It is shown that the proposed method provides the required accuracy and significantly improves the process time compared to the conventional methods.

2010ConferencePDFParallel and Cable Robotics
Adaptive Cascade Control of the KNTU CDRPM: A Cable Driven Redundant Parallel Manipulator
Pooneh Gholami, Mohammad M. Aref and Hamid D. Taghirad
Intelligent Robots and Systems, 2008. IROS
Abstract:

The challenging control problem of the cable driven redundant manipulators is due to the complexity of its dynamic and the required stringent performance for the its promising applications. This paper presents an approach to the control of the KNTU CDRPM using an adaptive cascade control scheme. The goal in this approach is achieving accurate trajectory tracking while assuring positive tension in the cables. The cascade control topology uses two loops, namely the internal and external loops. The inherent nonlinear behavior of the cable manipulator is controlled by the internal loop, while the external loop can effectively reduce the target tracking errors of the end-effector in the presence of disturbance force/torques. The cascade strategy reduces the tracking error by 80% compared to that of a single loop controller in the KNTU CDRPM. Moreover, adaptation of the cascade controller gains can significantly improve the overall tracking performance. The closed-loop performance of various control topologies are analyzed by a simulation study that is performed on the KNTU CDRPM. Since, the dynamic equations of this parallel manipulator is implicit in its general form, special integration routines are used for integration. The simulation study verifies that the proposed controller is not only promising to be implemented on the KNTU CDRPM, but also being suitable for other cable driven manipulators.

2009ConferencePDFParallel and Cable Robotics
A novel hybrid Fuzzy-PID controller for tracking control of robot manipulators
A. R. Norouzzadeh Ravari, H.D. Taghirad
2008 IEEE International Conference on Robotics and Biomimetics
Abstract:

In this paper, a novel hybrid fuzzy proportional-integral-derivative (PID) controller based on learning automata for optimal tracking of robot systems including motor dynamics is presented. Learning automata is used at the supervisory level for adjustment of the parameters of hybrid Fuzzy-PID controller during the system operation. The proposed method has better convergence rate in comparison with standard back-propagation algorithms, less computational requirements than adaptive network based fuzzy inference systems (ANFIS) or neural based controllers and having the ability of working in uncertain environments without any previous knowledge of environments' parameters. The proposed controller has been successfully applied in simulation to control a 6-DOF Puma 560 manipulator using robotic toolbox, and has satisfactory results. In this simulation also, external disturbance and noise are addressed. The result of simulation has also shown that the rate of convergence and robustness of the designed controller guarantees practical stability.

2009ConferencePDFAutonomous Robotics
Autonomous Staircase Detection and Stair Climbing for a Tracked Mobile Robot using Fuzzy Controller
E. Mihankhah, A. Kalantari, E. Aboosaeedan, H.D. Taghirad, and S.Ali.A. Moosavian
2008 IEEE International Conference on Robotics and Biomimetics
Abstract:

Theoretical analysis and implementation of autonomous staircase detection and stair climbing algorithms on a novel rescue mobile robot are presented in this paper. The main goals are to find the staircase during navigation and to implement a fast, safe and smooth autonomous stair climbing algorithm. Silver is used here as the experimental platform. This tracked mobile robot is a tele-operative rescue mobile robot with great capabilities in climbing obstacles in destructed areas. Its performance has been demonstrated in rescue robot league of international RoboCup competitions. A fuzzy controller is applied to direct the robot during stair climbing. Controller inputs are generated by processing the range data from two laser range finders which scan the environment one horizontally and the other vertically. The experimental results of stair detection algorithm and stair climbing controller are demonstrated at the end.

2009ConferencePDFAutonomous Robotics
Dynamic Analysis of a Macro–Micro Redundantly Actuated Parallel Manipulator
Hamid D. Taghirad and Meyer A. Nahon
Advanced Robotics
Abstract:

In this paper the dynamic analysis of a macro–micro parallel manipulator is studied in detail. The manipulator architecture is a simplified planar version adopted from the structure of the Large Adaptive Reflector (LAR), the Canadian design of next-generation giant radio telescopes. In this structure it is proposed to use two parallel redundant manipulators at the macro and micro level, both actuated by cables. In this paper, the governing dynamic equation of motion of such a structure is derived using the Newton–Euler formulation. Next, the dynamic equations of the system are used in the open-loop inverse dynamics simulations, as well as closed-loop forward dynamics simulations. In the open-loop dynamic simulations it is observed that the inertial forces of the limbs contribute only 10% of the dynamic forces required to generate a typical trajectory and, moreover, the total dynamic forces contribute only 10% of the experimentally measured disturbance forces. Furthermore, in the closed-loop simulations using decentralized PD controllers at the macro and micro levels, it is shown that the macro–micro structure results in a 10 times more accurate positioning than that in the first stage of the macro–micro structure. This convincing result promotes the use of the macro–micro structure for LAR application.

2008JournalPDFParallel and Cable Robotics
Kinematic Analysis of a Macro–Micro Redundantly Actuated Parallel Manipulator
Hamid D. Taghirad and Meyer Nahon
Advanced Robotics
Abstract:

In this paper the kinematic and Jacobian analysis of a macro–micro parallel manipulator is studied in detail. The manipulator architecture is a simplified planar version adopted from the structure of the Large Adaptive Reflector (LAR), the Canadian design of the next generation of giant radio telescopes. This structure is composed of two parallel and redundantly actuated manipulators at the macro and micro level, which both are cable-driven. Inverse and forward kinematic analysis of this structure is presented in this paper. Furthermore, the Jacobian matrices of the manipulator at the macro and micro level are derived, and a thorough singularity and sensitivity analysis of the system is presented. The kinematic and Jacobian analysis of the macro–micro structure is extremely important to optimally design the geometry and characteristics of the LAR structure. The optimal location of the base and moving platform attachment points in both macro and micro manipulators, singularity avoidance of the system in nominal and extreme maneuvers, and geometries that result in high dexterity measures in the design are among the few characteristics that can be further investigated from the results reported in this paper. Furthermore, the availability of the extra degrees of freedom in a macro–micro structure can result in higher dexterity provided that this redundancy is properly utilized. In this paper, this redundancy is used to generate an optimal trajectory for the macro–micro manipulator, in which the Jacobian matrices derived in this analysis are used in a quadratic programming approach to minimize performance indices like minimal micro manipulator motion or singularity avoidance criterion.

2008JournalPDFParallel and Cable Robotics
Parametric spectral analysis of nonstationary fluctuations of excitatory synaptic currents
M. I. Glavinovic, P. Gooria, F. Aristizabal, H. Taghirad
Biological Cybernetics
Abstract:

We assessed on Monte-Carlo simulated excitatory post-synaptic currents the ability of autoregressive (AR)-model fitting to evaluate their fluctuations. AR-model fitting consists of a linear filter describing the process that generates the fluctuations when driven with a white noise. Its fluctuations provide a filtered version of the signal and have a spectral density depending on the properties of the linear filter. When the spectra of the non-stationary fluctuations of excitatory post-synaptic currents were estimated by fitting AR-models to the segments of current fluctuations, assumed to be stationary and independent, the parameter and spectral estimates were scattered. The scatter was much reduced if the time-variant AR-models were fitted using stochastic adaptive estimators (Kalman, recursive least squares and least mean squares). The ability of time-variant AR-models to accurately fit the current fluctuations was monitored by comparing the fluctuations with predicted fluctuations, and by evaluating the model-learning rate. The median frequency of current fluctuations, which could be rapidly tracked and estimated from the individual quantal events (either Monte-Carlo simulated or recorded from pyramidal neurons of rat hippocampus), rose during the rise phase, before declining to a lower steady-state level during the decay phase of quantal event, whereas the variance showed a broad peak. The closing rate of AMPA channels directly affects the steady-state median frequency, whereas the transient peak can be modulated by a variety of factors—number of molecules released, ability of glutamate molecules to re-enter the synaptic cleft, diffusion constant of glutamate in the cleft and opening rate of AMPA channels. In each case, the effect on the amplitude and decay time of mEPSCs and on the current fluctuations differs. Each factor thus leaves its own kinetic fingerprint arguing that the contribution of such factors can be inferred from the combined kinetic properties of individual mEPSCs.

2008JournalPDF
Dynamics Analysis of A Redundant Parallel Manipulator Driven By Elastic Cables
Y. Babazadeh Bedoustani, H. D. Taghirad and M. M. Aref
2008 10th International Conference on Control, Automation, Robotics and Vision
Abstract:

In this paper the dynamic analysis of a cable-driven parallel manipulator is studied in detail. The manipulator architecture is a simplified planar version adopted from the structure of large adaptive reflector (LAR), the Canadian design of next generation giant radio telescopes. This structure consists of a parallel redundant manipulator actuated by long cables. The dynamic equations of this structure are nonlinear and implicit. Long cables, large amounts of impelling forces and high accelerations raise more concern about the elasticity of cables during dynamic analysis, which has been neglected in the preceding works. In this paper, the kinematic analysis of such manipulator is illustrated first. Then the nonlinear dynamic of such mechanism is derived using Newton-Euler formulation. Next a simple model for cable dynamics containing elastic and damping behavior is proposed. The proposed model neither ignores longitude elasticity properties of cable nor makes dynamic formulations heavily complicated like previous researches. Finally, manipulator dynamic with cable dynamic is derived, and the cable elasticity effects are compared in a simulation study. The results show significant role of elasticity in a cable-driven parallel manipulator such as the one used in LAR mechanism.

2008ConferencePDFParallel and Cable Robotics
Dynamic Analysis of the KNTU CDRPM: A Cable Driven Redundant Parallel Manipulator
Pooneh Gholami, Mohammad M. Aref and Hamid D. Taghirad
2008 IEEE/ASME International Conference on Mechtronic and Embedded Systems and Applications
Abstract:

KNTU CDRPM is a cable driven redundant parallel manipulator, which is under investigation for possible implementation of large workspace applications. This newly developed manipulators have several advantages compared to the conventional parable mechanisms. In this paper, the governing dynamic equation of motion of such structure is derived using the Newton-Euler formulation. Next, the dynamic equations of the system are used in simulations. It is shown that on the contrary to serial manipulators, dynamic equations of motion of cable-driven parallel manipulators can be only represented implicitly, and only special integration routines can be used for their simulations. In order to verify the accuracy and integrity of the derived dynamic equations, open- and closed-loop simulations for the system is performed and analyzed. Also, the effects of mechanical assembly tolerances on the closed-loop control performance of a cable driven parallel robot are studied in detail, and the sensitivity analysis of the precision in the construction and assembly of the system on the closed-loop behavior of the KNTU CDRPM is performed.

2008ConferencePDFParallel and Cable Robotics
Robust Performance Verification of Adaptive Robust Controller for Hard Disk Drives
Hamid D. Taghirad and Ehsan Jamei
IEEE Transactions on Industrial Electronics
Abstract:

An adaptive robust controller (ARC) has been recently developed for read/write head embedded control systems of hard disk drives (HDDs). This structure is applicable to both track seeking and track following modes, and it makes the mode switching control algorithms found in conventional HDD servosystems unnecessary. An Improved Desired Compensation ARC (IDCARC) scheme is proposed in this paper, in which the traditional ARC is powered by a dynamic adaptive term. In this approach the adaptation regressor is calculated using reference trajectory information. Moreover, a robust analysis of this method is developed, in which a controller designed based on a simple model of the system is verified in a closed loop performance of a more comprehensive model of the system. The simulation result verifies the significant improvement of the performance of IDCARC compared to that of ARC and its robustness for this model. It is observed that in the presence of large disturbances the proposed method preserves the stability and a suitable performance while the ARC fails even in stability.

2008JournalPDFHard Disk Drives Control
SLAM Using Single Laser Range Finder
AliAkbar Aghamohammadi, Amir H. Tamjidi, Hamid D. Taghirad
IFAC Proceedings Volumes
Abstract:

Presented method in this paper aims to develop an accurate motion model and SLAM algorithm, which is only based on the Laser Range Finder (LRF) data. Proposed method tries to overcome some practical problems in traditional motion models and SLAM approaches, such as robot slippage, and inaccuracy in parameters related to robot's hardware. Novel insights specific to process and measurement model, and making use of them in the IEKF framework, give rise to the real time method with drift-free performance in restricted environments. Furthermore, uncertainty measures, calculated through the method, are valuable information for fusion purposes and also an accurate motion model, derived in this method, can be used as a robust and an accurate localization procedure in different structured environments. These issues are validated through experimental implementations; experiments verify method's efficiency both in pure localization and in SLAM scenarios in the restricted environments, involving loop closures.

2008ConferencePDFAutonomous Robotics
A Solution for SLAM through Augmenting Vision and Range Information
Ali A. Aghamohammadi, Amir H. Tamjidi, Hamid D. Taghirad
2008 IEEE/RSJ International Conference on Intelligent Robots and Systems
Abstract:

This paper proposes a method for augmenting the information of a monocular camera and a range finder. This method is a valuable step towards solving the SLAM problem in unstructured environments free from problems of using encoderspsila data. Proposed algorithm causes the robot to benefit from a feature-based map for filtering purposes, while it exploits an accurate motion model, based on point-wise raw range scan matching rather than unreliable feature-based range scan matching, in unstructured environments. Moreover, robust loop closure detection procedure is the other consequence of this method. Experiments with a low-cost IEEE 1394 webcam and a range finder illustrate the effectiveness of the proposed method in drift-free SLAM at loop closing motions in unstructured environments.

2008ConferencePDFAutonomous Robotics
On The Control of the KNTU CDRPM: A Cable Driven Redundant Parallel Manipulator
Pooneh Gholami, Mohammad M. Aref and Hamid D. Taghirad
2008 IEEE/RSJ International Conference on Intelligent Robots and Systems
Abstract:

This paper is devoted to the control of a cable driven redundant parallel manipulator, which is a challenging problem due the optimal resolution of its inherent redundancy. Additionally to complicated forward kinematics, having a wide workspace makes it difficult to directly measure the pose of the end-effector. The goal of the controller is trajectory tracking in a large and singular free workspace, and to guarantee that the cables are always under tension. A control topology is proposed in this paper which is capable to fulfill the stringent positioning requirements for these type of manipulators. Closed-loop performance of various control topologies are compared by simulation of the closed-loop dynamics of the KNTU CDRPM, while the equations of parallel manipulator dynamics are implicit in structure and only special integration routines can be used for their integration. It is shown that the proposed joint space controller is capable to satisfy the required tracking performance, despite the inherent limitation of task space pose measurement.

2008ConferencePDFParallel and Cable Robotics
Geometrical Workspace Analysis of a Cable-Driven Redundant Parallel Manipulator: KNTU CDRPM
Mohammad M. Aref and Hamid D. Taghirad
2008 IEEE/RSJ International Conference on Intelligent Robots and Systems
Abstract:

KNTU CDRPM is a cable driven redundant parallel manipulator, which is under investigation for possible high speed and large workspace applications. This newly developed mechanisms have several advantages compared to the conventional parallel mechanisms. Its rotational motion range is relatively large, its redundancy improves safety for failure in cables, and its design is suitable for long-time high acceleration motions. In this paper, collision-free workspace of the manipulator is derived by applying fast geometrical intersection detection method, which can be used for any fully parallel manipulator. Implementation of the algorithm on the Neuron design of the KNTU CDRPM leads to significant results, which introduce a new style of design of a spatial cable-driven parallel manipulators. The results are elaborated in three presentations; constant-orientation workspace, total orientation workspace and orientation workspace.

2008ConferencePDFParallel and Cable Robotics
H-Infinity Controller Design for A Flexible Joint Robot With Phase Uncertainty
Sh. Dadashi, H. D. Taghirad
International Symposium on Robotics
Abstract:

In this paper, the design and implementation of the H-Infinity controller for flexible joint robot (FJR) is presented and the capability of the controller to deal with actuator saturation is investigated in practice. The new procedure of design is introduced to avoid an instability caused by unmodeled phase behaviour which can not be encapsulated in multiplicative uncertainty. In order to avoid instability caused by unmodeled phase behaviour, the robust controller design is divided into two stages: H-Infinity controller design and checking closed loop sensitivity function. Simulation results reveal the capability of the controller to stabilize the closed loop system and to reduce the tracking error in the presence of the actuator limitation.

2008ConferencePDFFlexible Robotics
Dynamic and Sensitivity Analysis of KNTU CDRPM: A Cable Driven Redundant Parallel Manipulator
Mohammad M. Aref, Pooneh Gholami and Hamid D. Taghirad
2008 IEEE/ASME International Conference on Mechtronic and Embedded Systems and Applications
Abstract:

KNTU CDRPM is a cable driven redundant parallel manipulator, which is under investigation for possible implementation of large workspace applications. This newly developed manipulators have several advantages compared to the conventional parable mechanisms. In this paper, the governing dynamic equation of motion of such structure is derived using the Newton-Euler formulation. Next, the dynamic equations of the system are used in simulations. It is shown that on the contrary to serial manipulators, dynamic equations of motion of cable-driven parallel manipulators can be only represented implicitly, and only special integration routines can be used for their simulations. In order to verify the accuracy and integrity of the derived dynamic equations, open- and closed-loop simulations for the system is performed and analyzed. Also, the effects of mechanical assembly tolerances on the closed-loop control performance of a cable driven parallel robot are studied in detail, and the sensitivity analysis of the precision in the construction and assembly of the system on the closed-loop behavior of the KNTU CDRPM is performed.

2008JournalPDFParallel and Cable Robotics
Task Based Optimal Geometric Design and Positioning of Serial Robotic Manipulators
Sasan Barissi and Hamid D. Taghirad
Mechtronic and Embedded Systems and Applications
Abstract:

This paper devises a multi-objective cost function which elaborates different constraints as well as an optimality criterion for design of serial robotic manipulators. In practice, inclusion of different constraints drastically limits the possible range of design parameters. The result of minimizing this multi-objective cost function is compared with another method which locates an optimal solution using a graphical representation. The effectiveness of the proposed cost function is demonstrated by a unified solution for both methods. In addition, possible tolerance of design parameters is compensated by considering a neighborhood around these parameters. Through an illustrative example, it is shown that the inclusiveness and flexibility of the proposed method makes it suitable for geometric design optimization of robotic manipulators.

2008JournalPDFParallel and Cable Robotics
Adaptive Robust Controller Design for a Dual Stage Hard Disk Drive
Hamid D. Taghirad and P. Sheykholeslami
Advanced intelligent mechatronics
Abstract:

In this paper, adaptive robust controllers are proposed for dual-stage hard disk drives. An improved desired compensation ARC (IDCARC) scheme is proposed in this paper for both actuators of the system, in which the traditional ARC is powered by a dynamic adaptive term. Moreover, a simulation study of these controllers are presented, in which the controllers designed based on simple models for the subsystem are implemented on a more comprehensive, experimentally verified models of the system. Simulation result verifies the effectiveness of the IDCARC method in providing the required tracking, in presence of unstructured uncertainty for the models.

2007ConferencePDFHard Disk Drives Control
Forward Kinematics of A Macro–Micro Parallel Manipulator
Hamid D. Taghirad and Meyer A. Nahon
Advanced intelligent mechatronics
Abstract:

In this paper the kinematic analysis of a macro-micro parallel manipulator is studied in detail. The manipulator architecture is a simplified planar version adopted from the structure of large adaptive reflector (LAR), the Canadian design of next generation giant radio telescopes. This structure is composed of two parallel and redundantly actuated manipulators at macro and micro level, which both are cable-driven. Inverse and forward kinematic analysis of this structure is presented in this paper. It is shown that unique closed form solution to the inverse kinematic problem of such structure exists. However, the forward kinematic solution is derived using numerical methods, and simulation results are reported to illustrate the integrity and accuracy of the solution.

2007ConferencePDFParallel and Cable Robotics
Parametric spectral analysis of nonstationary fluctuations of excitatory synaptic currents
M. I. Glavinovic, P. Gooria, F. Aristizabal, H. Taghirad
Biological Cybernetics
Abstract:

We assessed on Monte-Carlo simulated excitatory post-synaptic currents the ability of autoregressive (AR)-model fitting to evaluate their fluctuations. AR-model fitting consists of a linear filter describing the process that generates the fluctuations when driven with a white noise. Its fluctuations provide a filtered version of the signal and have a spectral density depending on the properties of the linear filter. When the spectra of the non-stationary fluctuations of excitatory post-synaptic currents were estimated by fitting AR-models to the segments of current fluctuations, assumed to be stationary and independent, the parameter and spectral estimates were scattered. The scatter was much reduced if the time-variant AR-models were fitted using stochastic adaptive estimators (Kalman, recursive least squares and least mean squares). The ability of time-variant AR-models to accurately fit the current fluctuations was monitored by comparing the fluctuations with predicted fluctuations, and by evaluating the model-learning rate. The median frequency of current fluctuations, which could be rapidly tracked and estimated from the individual quantal events (either Monte-Carlo simulated or recorded from pyramidal neurons of rat hippocampus), rose during the rise phase, before declining to a lower steady-state level during the decay phase of quantal event, whereas the variance showed a broad peak. The closing rate of AMPA channels directly affects the steady-state median frequency, whereas the transient peak can be modulated by a variety of factors—number of molecules released, ability of glutamate molecules to re-enter the synaptic cleft, diffusion constant of glutamate in the cleft and opening rate of AMPA channels. In each case, the effect on the amplitude and decay time of mEPSCs and on the current fluctuations differs. Each factor thus leaves its own kinetic fingerprint arguing that the contribution of such factors can be inferred from the combined kinetic properties of individual mEPSCs.

2007JournalPDF
Feature-Based Laser Scan Matching For Accurate and High Speed Mobile Robot Localization
A. A. Aghamohammadi, H. D. Taghirad, A. H. Tamjidi, and E. Mihankhah
Proceedings of the 3rd European Conference on Mobile Robots
Abstract:

This paper introduces an accurate and high speed pose tracking method for mobile robots based on matching of extracted features from consecutive scans. The feature extraction algorithm proposed in this paper uses a global information of the whole scan data and local information around feature points. Uncertainty of each feature is represented using covariance matrices determined due to observation and quantization error. Taking into account each feature's uncertainty in pose shift calculation leads to an accurate estimation of robot pose. Experiments with low range URG_X002 laser range scanner illustrate the effectiveness of the proposed method for mobile robot localization.

2007ConferencePDFAutonomous Robotics
Adaptive Robust Controller Design For Dual-Stage Hard Disk Drives
H. D. Taghirad and P. Sheykholeslami
Advanced intelligent mechatronics
Abstract:

In this paper, adaptive robust controllers are proposed for dual-stage hard disk drives. An improved desired compensation ARC (IDCARC) scheme is proposed in this paper for both actuators of the system, in which the traditional ARC is powered by a dynamic adaptive term. Moreover, a simulation study of these controllers are presented, in which the controllers designed based on simple models for the subsystem are implemented on a more comprehensive, experimentally verified models of the system. Simulation result verifies the effectiveness of the IDCARC method in providing the required tracking, in presence of unstructured uncertainty for the models.

2007ConferencePDFHard Disk Drives Control
Position Controller Synthesis for The Redundant Hydraulic Shoulder Manipulator
H. Sadjadian and H. D. Taghirad
ICEE15
Abstract:

In this paper,positioncontrol has been designed for a 3 DOF actuator redundant sphericnl parallel manipulator.A two norm minimization approach has been used to resolve the actuator redundancy problem. Robust stability of the closed loop system is analyzed considering uncertainties inherent in the dynamic model of the manipulator.A simulation study is also performed to showthe effectiveness of the proposed method. Thc results show the applicability of simple and conventional controllersto control redundant spherical parallel manip lators

2007ConferencePDFParallel and Cable Robotics
Dynamic Analysis of A Redundantly Actuated Parallel Manipulator:A Virtual Work Approach
Hamid D. Taghirad and Meyer Nahon
Advanced Robotics
Abstract:

In this paper the dynamic analysis of a macro–micro parallel manipulator is studied in detail. The manipulator architecture is a simplified planar version adopted from the structure of the Large Adaptive Reflector (LAR), the Canadian design of next-generation giant radio telescopes. In this structure it is proposed to use two parallel redundant manipulators at the macro and micro level, both actuated by cables. In this paper, the governing dynamic equation of motion of such a structure is derived using the Newton–Euler formulation. Next, the dynamic equations of the system are used in the open-loop inverse dynamics simulations, as well as closed-loop forward dynamics simulations. In the open-loop dynamic simulations it is observed that the inertial forces of the limbs contribute only 10% of the dynamic forces required to generate a typical trajectory and, moreover, the total dynamic forces contribute only 10% of the experimentally measured disturbance forces. Furthermore, in the closed-loop simulations using decentralized PD controllers at the macro and micro levels, it is shown that the macro–micro structure results in a 10 times more accurate positioning than that in the first stage of the macro–micro structure. This convincing result promotes the use of the macro–micro structure for LAR application.

2007ConferencePDFParallel and Cable Robotics
A Survey on the Control of Flexible Joint Robots
S. Ozgoli and H. D. Taghirad
Asian Journal of Control
Abstract:

The robotics literature of the last two decades contains many important advances in the control of flexible joint robots. This is a survey of these advances and an assessment for future developments, concentrated mostly on the control issues of flexible joint robots.

2006JournalPDFFlexible Robotics
Mobile Robot Navigation in an Unknown Environment
A. Jazayeri, A.Fatehi, H. Taghirad
2016 IEEE Conference on Control Applications (CCA)
Abstract:

This article focuses on the mobile robot's autonomous navigation problem in an unknown environment. Considering a robot equipped with an omnidirectional range-sensor a map of the discovered area is constructed in an iterative manner. Given a target position located in the unexplored territory, initially a motion planning scheme is employed that relies on exploration-principles of the area near the target. This is achieved by assigning an exploration cost function that indirectly attracts the robot close to target. Upon discovery of the target, the robot moves to it following the shortest-distance path. Simulation studies that prove the efficiency of the overall method are presented.

2006ConferencePDF
Stability analysis and robust composite controller synthesis for flexible joint robots
H. D. Taghirad and M. A. Khosravi
Advanced Robotics
Abstract:

The control of flexible joint manipulators is studied in detail. The model of N-axis flexible joint manipulators is derived and reformulated in the form of singular perturbations, and the integral manifold is used to separate fast dynamics from slow dynamics. A composite control algorithm is proposed for the flexible joint robots, which consists of two main parts. Fast control, u, which guarantees that the fast dynamics remains asymptotically stable, and the corresponding integral manifold remains invariant. Slow control, u, itself consists of a robust PID design based on the rigid model, and a corrective term designed based on the reduced flexible model. The stability of the overall closed loop system is proved to be UUB stable, by Lyapunov stability analysis. Finally, the effectiveness of the proposed control law is verified through simulations. It is shown that the proposed control law ensures robust stability and performance, despite the modeling uncertainties.

2006JournalPDFFlexible Robotics
Kinematic, singularity and stiffness analysis of the hydraulic shoulder: a 3-d.o.f. redundant parallel manipulator
H. Sajadian and H. D. Taghirad
Advanced Robotics
Abstract:

In this paper, kinematic modeling and singularity and stiffness analysis of a 3-d.o.f. redundant parallel manipulator have been elaborated in detail. It is known that, contrary to series manipulators, the forward kinematic map of parallel manipulators involves highly coupled non-linear equations, whose closed-form solution derivation is a real challenge. This issue is of great importance noting that the forward kinematics solution is a key element in closed-loop position control of parallel manipulators. Using the idea of inherent kinematic chains formed in parallel manipulators, both inverse and forward kinematics of the redundant parallel manipulator are fully developed, and a closed-form solution for the forward kinematic map of the parallel manipulator is derived. The closed-form solution is also obtained in detail for the Jacobian of the mechanism and singularity analysis of the manipulator is performed based on the computed Jacobian. Finally, as the first step to develop a control topology based on the overall stiffness property of the manipulator, the stiffness mapping of the manipulator is derived and its configuration dependence is analyzed. It is observed that the actuator redundancy in the mechanism is the major element to improve the Cartesian stiffness and, hence, the dexterity of the hydraulic shoulder. Moreover, loosing one limb actuation reduces the stiffness of the manipulator significantly.

2006JournalPDFParallel and Cable Robotics
Robust H’, H2/H’ Controller for Rotational/Translational Actuator (RTAC)
R. Adlgostar, H. Azimian and H. D. Taghirad
IEEE Conference on Computer Aided Control System Design
Abstract:

In this paper, robust controllers have been proposed for oscillation suppression in the RTAC benchmark problem. A nominal plant and an uncertainty model are extracted out of varieties of linear models, identified for the nonlinear system and the generalized plant for the unstructured uncertainty problem has been presented. Based on passivity, a cascade controller has been designed to reduce amount of uncertainty in lower frequencies. It is verified that through a nonlinear feedback controller in the inner loop, the uncertainty of linear estimates of the system reduces significantly, and becomes plausible to use linear robust techniques such as mixed sensitivity and H 2 /H-Infinity to design controller for the system. Finally H-Infinity and H 2 /H-Infinity controllers have been designed for new generalized plant and results are compared with the previous reports in literature.

2006ConferencePDF
Nonparametric Identification and Robust Hf Controller Synthesis for a Rotational/Translational Actuator
F.Bagheri, S. Purazarm, and H. D. Taghirad
International Journal of Control, Automation, and Systems
Abstract:

The Rotational/Translational Actuator (RTAC) benchmark problem considers a fourth-order dynamical system involving the nonlinear interaction of a translational oscillator and an eccentric rotational proof mass. This problem has been posed to investigate the utility of a rotational actuator for stabilizing translational motion. In order to experimentally implement any of the model-based controllers proposed in the literature, the values of model parameters are required which are generally difficult to determine rigorously. In this paper, an approach to the least-squares estimation of the parameters of a system is formulated and practically applied to the RTAC system. On the other hand, this paper shows how to model a nonlinear system as a linear uncertain system via nonparametric system identification, in order to provide the information required for linear robust H-Infinity control design. This method is also applied to the RTAC system, which demonstrates severe nonlinearities due to the coupling from the rotational motion to the translational motion. Experimental results confirm that this approach can effectively condense the whole nonlinearities, uncertainties, and disturbances within the system into a favorable perturbation block.

2006ConferencePDF
Designing and Implementation of Mixed H2/H-Infinity Controller for Flexible Joint Robot to Encounter Actuator Saturation
S. Ozgoli, H. D. Taghirad
Abstract:

Mixed H2/H-Infinity method is proposed to design and implement a controller for flexible joint robots considering actuator saturation by considering the control action in the mixed sensitivity. A more advanced method based on frequency weighting of the control action contribution in the mixed sensitivity function is considered here which may result higher bandwidth. But this method is also limited and to get better specifications the H2/H-Infinity method is proposed. This methods are shown to be very good remedies for problems caused by actuator saturation in practice. Experimental studies are forwarded to verify the effectiveness and the performance of the proposed controllers in practice.

2006ConferencePDFFlexible Robotics
New Wavelet Based Algorithm for Real Time Visual Tracking
Akram Bayat, Hamid R. Taghirad, Seyyed Sadegh Mottaghian
Abstract:

in this paper, we propose a new technique in wavelet domain for real time object detection and tracking in a sequence of images. The object to be tracked is identified in the first frame. Our proposed algorithm consists of two phases: the first, wavelet based edge detection is used to form ground boundary map. Then, Object dimensions estimation is implemented to determine probabilistic object areas. finally, target detection based on finding best match using feature vectors is applied. We defined dispersion of wavelet detail coefficient in object area as feature to be matched. Also we proposed a new color model for images to be used in processing algorithm. Our experimental results show that the algorithm is robust and fast. It is also insensitive to changing illumination condition and size of target

2006ConferencePDFAutonomous Robotics
Comparison of Different Methods for Computing the Forward Kinematics of a Redundant Parallel Manipulator
H. Sajadian and H. D. Taghirad
Journal of Intelligent and Robotic Systems
Abstract:

In this paper, three numerical methods are presented to solve the forward kinematics of a three DOF actuator-redundant hydraulic parallel manipulator. It is known, that on the contrary to series manipulators, the forward kinematic map of parallel manipulators involves highly coupled nonlinear equations, whose closed-form solution derivation is a real challenge. This issue is of great importance noting that the forward kinematics solution is a key element in closed loop position control of parallel manipulators. The proposed methods, namely the Neural Network Estimation, the Quasi-closed Solution, and the Taylor series approximation, are using mainly numerical computations, with different ideas to solve the problem in hand. The latter two methods are proposed for the first time in literature to solve the forward kinematics of a parallel manipulator. These methods are compared in detail and the advantages or the disadvantages of each method in computing the forward kinematic map of the given mechanism is discussed. It is shown that a 4th order Taylor series approximation to the problem provides a good compromise for practical applications compared to that of other methods considered in this paper.

2006JournalPDFParallel and Cable Robotics
Impedance Control of the Hydraulic Shoulder
H. Sajadian and H. D. Taghirad
International Conference on Robotics and Biomimetics
Abstract:

In this paper, a model-based impedance control strategy is developed for a 3 DOF parallel manipulator to manage the interaction of the robot with the environment. Kinematic and dynamic modeling of the manipulator has been analyzed in order to be used for both simulation and control purposes. The impedance controller objective and the structure of the proposed controller are introduced and controller gain selection is discussed. A simulation study evaluates the effectiveness of the proposed impedance control structure. It is observed that although the proposed controller is designed for impedance adjustment of the robot, in case of free motion, it results into desirable position tracking. Moreover, when the robot comes into contact with the environment, the interaction dynamics can be regulated regardless of the nonlinear dynamics of the robot.

2006ConferencePDFParallel and Cable Robotics
Robust Performance Verification of IDCARC Controller for Hard Disk Drives
H. D. Taghirad and E. Jamei
Abstract:

Adaptive robust controller (ARC) has been recently developed for read/write head embedded control systems of hard disk drives (HDD). This structure is applicable to both track seeking and track following modes, and it makes the mode switching control algorithms found in conventional HDD servo system unnecessary. An Improved Desired Compensation ARC (IDCARC) scheme is proposed in this paper, in which traditional ARC is powered by a dynamic adaptive term. In this approach the adaptation regressor is calculated using reference trajectory information. Moreover, a robust analysis of this method is forwarded, in which a controller designed based on a simple model of system is verified in closed loop performance of a more comprehensive model of the system. Simulation result verifies the significant improvement of the performance of IDCARC compared to that of ARC and its robustness for this model. It is observed that in the presence of large disturbances the proposed method preserves stability and performance while the ARC fails even in stability.

2006JournalPDFHard Disk Drives Control
Robust Controller with a Supervisor Implemented on a Flexible Joint Robot
Hamid D. Taghirad and S.Ozgoli
Control Applications
Abstract:

In this paper a controller for flexible joint robots (FJR) in presence of actuator saturation is proposed, its robust stability is analyzed, and it is implemented on a laboratory FJR. This controller consists of a composite structure, with a PD controller on the fast dynamics and a PID controller on slow dynamics. The need of powerful actuator is released through decrease of fast controller bandwidth at critical occasions. This is done by means of a fuzzy logic supervisory loop. The stability analysis of the overall system is then analyzed by Lyapunov theory. It is proven that UUB stability of the overall system in presence of uncertainties is guaranteed, provided that the PD and the PID gains are tuned to satisfy certain conditions. Experimental studies are forwarded to verify the effectiveness and the performance of the proposed controller

2005ConferencePDFFlexible Robotics
Composite QFT Controller Design for Flexible Joint Robots
H. D. Taghirad and H. Rahimi
Proceedings of 2005 IEEE Conference on Control Applications, 2005. CCA 2005.
Abstract:

In this paper, a practical method to design a robust controller for a flexible joint robot (FJR) using quantitative feedback theory (QFT) is proposed. In order to control fast and slow dynamics of the FJR separately, composite control scheme is considered as the basis for the design. A simple PD controller is used to stabilize the fast dynamics, and a QFT controller is used in addition to an integral manifold corrective term to perform on the slow dynamics. Because of the nonlinear dynamics of FJR and the proposed controller scheme, linear time invariant equivalent (LTIE) technique is used to assign a nominal model for the system with uncertainties templates. Design of the QFT controller, as slow part of the composite control law is performed to compromise between the required bandwidth and the controller order. Comparisons with previous works on FJR, such as robust PID and composite Hinfin, illustrate the effectiveness of the proposed controller to reduce the tracking errors despite actuator limitations

2005ConferencePDFFlexible Robotics
Nonlinear H-Infinity Controller Design for Flexible Joint Robots
H. D. Taghirad and M. Shaterian
Proceedings of the IEEE Conference on Decision and Control
Abstract:

In this paper the design of a nonlinear H-Infinity controller for flexible joint robot (FJR) is presented. An approximate solution based on Taylor series expansion is considered for the Hamilton-Jacobi-Isaac (HJI) inequality. A two-degree-of-freedom controller combined of nonlinear H-Infinity controller and inverse dynamics controller is proposed to tackle the regulation as well as tracking problem in FJR. The proposed nonlinear H-Infinity controller attenuates the disturbance with a minimum achievable control effort, despite system parameter uncertainty. Simulation comparisons for single and multiple joint manipulators, show that the proposed controller yields to superior performance such as larger domain of attraction and smaller control effort as well as better tracking characteristics, compared to that of the other methods

2005ConferencePDFFlexible Robotics
Robust Control for Flexible Joint Robots with A Supervisory Control to Remedy Actuator Saturation
S. Ozgoli, H. D. Taghirad
ICEE13
Abstract:

In this paper a controller design method for flexible joint robots (FJR), considering actuator saturation is proposed and its robust stability is thoroughly analyzed. This method consists of a composite control structure, with a PD controller on the fast dynamics and a PID controller on slow dynamics. Moreover, the need of powerful actuator is remedied by decreasing the bandwidth of the fast controller during critical occasions, with the use of a supervisory loop. Fuzzy logic is used in the supervisory law, in order to adjust the proper gain in the forward path. It is then shown that UUB stability of the overall system is guaranteed in presence of uncertainties, provided that the PD and the PID gains are tuned to satisfy certain conditions.

2005ConferencePDFFlexible Robotics
QFT Controller Synthesis For A Nonlinear Flexible Joint Robot
H. D. Taghirad and H. Rahimi
Abstract:

In this paper, a practical method to design a robust controller for a flexible joint robot (FJR) using quantitative feedback theory (QFT) is proposed. In order to control fast and slow dynamics of the FJR separately, composite control scheme is considered as the basis for the design. A simple PD controller is used to stabilize the fast dynamics, and a QFT controller is used in addition to an integral manifold corrective term to perform on the slow dynamics. Because of the nonlinear dynamics of FJR and the proposed controller scheme, linear time invariant equivalent (LTIE) technique is used to assign a nominal model for the system with uncertainties templates. Design of the QFT controller, as slow part of the composite control law, is performed to compromise between the required bandwidth and the controller order. Comparisons with previous works on FJR, such that robust PID and composite H ?, illustrate the effectiveness of the proposed controller to reduce the tracking errors despite actuator limitations.

2005ConferencePDFFlexible Robotics
Nonlinear H-Infinity Controller Synthesis for Flexible Joint Robots
H. D. Taghirad and M. Shaterian
ICEE
Abstract:

In this paper the design of an optimal nonlinear H-Infinity controller for flexible joint robot (FJR) is presented. An approximate solution based on Taylor Series expansion is considered for the Hamilton-Jacobi-Isaac (HJI) inequality. A two-degree-of-freedom controller combined of optimal nonlinear H-Infinity controller and inverse dynamics controller is proposed to tackle the regulation as well as tracking problem in FJR. The proposed optimal nonlinear H-Infinity controller attenuates the disturbance with a minimum achievable control effort, despite system parameter uncertainty. Simulation comparisons for single and multiple joint manipulators, show that the proposed controller yields to superior performance such as larger domain of attraction and smaller control effort as well as better tracking characteristics, compared to that of the others.

2005ConferencePDFFlexible Robotics
Kinematic and Singularity Analysis of the Hydraulic Shoulder
H. Sadjadian and H. D. Taghirad
Proceedings of the Second International Conference on Informatics in Control, Automation and Robotics
Abstract:

In this paper, kinematic modeling and singularity analysis of a three DOF redundant parallel manipulator has been elaborated in detail. It is known, that on the contrary to series manipulators, the forward kinematic map of parallel manipulators involves highly coupled nonlinear equations, whose closed-form solution derivation is a real challenge. This issue is of great importance noting that the forward kinematics solution is a key element in closed loop position control of parallel manipulators. Using the novel idea of kinematic chains recently developed for parallel manipulators, both inverse and forward kinematics of our parallel manipulator are fully developed, and a closed-form solution for the forward kinematic map of the parallel manipulator is derived. The closed form solution is also obtained in detail for the Jacobian of the mechanism and singularity analysis of the manipulator is performed based on the computed Jacobian.

2005ConferencePDFParallel and Cable Robotics
Kinematic Analysis of the Hydraulic Shoulder: A 3-DOF Redundant Parallel Manipulator
H. Sadjadian and H.D. Taghirad
Mechatronics and Automation
Abstract:

In this paper, kinematic modeling of a three DOF redundant parallel manipulator has been elaborated in detail. It is known, that on the contrary to series manipulators, the forward kinematic map of parallel manipulators involves highly coupled nonlinear equations, whose closed-form solution derivation is a real challenge. This issue is of great importance noting that the forward kinematics solution is a key element in closed loop position control of parallel manipulators. Using the novel idea of kinematic chains recently developed for parallel manipulators, both inverse and forward kinematics of our parallel manipulator are fully developed, and a closed-form solution for the forward kinematic map of the parallel manipulator is derived. The closed form solution is finally verified by simulated trajectories in the workspace of the manipulator.

2005ConferencePDFParallel and Cable Robotics
Identification and Robust H-Infinity Control of the Rotational/Translational Actuator System
Mahdi Tavakoli, Hamid D. Taghirad, and Mehdi Abrishamchian
International Journal of Control Automation and Systems
Abstract:

The Rotational/Translational Actuator (RTAC) benchmark problem considers a fourth-order dynamical system involving the nonlinear interaction of a translational oscillator and an eccentric rotational proof mass. This problem has been posed to investigate the utility of a rotational actuator for stabilizing translational motion. In order to experimentally implement any of the model-based controllers proposed in the literature, the values of model parameters are required which are generally difficult to determine rigorously. In this paper, an approach to the least-squares estimation of the parameters of a system is formulated and practically applied to the RTAC system. On the other hand, this paper shows how to model a nonlinear system as a linear uncertain system via nonparametric system identification, in order to provide the information required for linear robust H-Infinity control design. This method is also applied to the RTAC system, which demonstrates severe nonlinearities due to the coupling from the rotational motion to the translational motion. Experimental results confirm that this approach can effectively condense the whole nonlinearities, uncertainties, and disturbances within the system into a favorable perturbation block.

2005JournalPDFSurgical Robotics
Neural Networks Approaches for Computing the Forward Kinematics of a Redundant Parallel Manipulator
H. Sadjadian , H.D. Taghirad, A. Fatehi
Abstract:

In this paper, different approaches to solve the forward kinematics of a three DOF actuator redundant hydraulic parallel manipulator are presented. On the contrary to series manipulators, the forward kinematic map of parallel manipulators involves highly coupled nonlinear equations, which are almost impossible to solve analytically. The proposed methods are using neural networks identification with different structures to solve the problem. The accuracy of the results of each method is analyzed in detail and the advantages and the disadvantages of them in computing the forward kinematic map of the given mechanism is discussed in detail. It is concluded that ANFIS presents the best performance compared to MLP, RBF and PNN networks in this particular application.

2005JournalPDFParallel and Cable Robotics
Robust Stability Analysis of FJR Composite Controller with a Supervisory Loop
S. Ozgoli and H. D. Taghirad
2005 IEEE/RSJ International Conference on Intelligent Robots and Systems
Abstract:

In this paper, a controller design method for flexible joint robots (FJR), considering actuator saturation is proposed and its robust stability is thoroughly analyzed. This method consists of a composite control structure, with a PD controller on the fast dynamics and a PID controller on slow dynamics. Moreover, the need of powerful actuator is removed by decreasing the bandwidth of the fast controller during critical occasions, with the use of a supervisory loop. Fuzzy logic is used in the supervisory law, in order to adjust the proper gain in the forward path. It is then shown that UUB stability of the overall system is guaranteed in presence of uncertainties, provided that the PD and the PID gains are tuned to satisfy certain conditions

2005ConferencePDFFlexible Robotics
Designing H2/H-Infinity Controller for Flexible Joint Robot to Remove Instabilities due to Saturation
Sadjaad Ozgoli, H.D. Taghirad
Annual (International) Mechanical Engineering Conference
Abstract:

Mixed H 2 /H-Infinity method is proposed to design a controller for flexible joint robots (FJR) considering actuator saturation. By considering the control action in the mixed sensitivity function one can reduce the amplitude of the control action but this may affect all frequencies. A more advanced method based on frequency weighting of the control action contribution in the mixed sensitivity function is considered here which may result in higher bandwidth. But this method is also limited and to get wider bandwidth the H 2 /H-Infinity method is proposed. This method is shown to be a very good remedy to remove instabilities caused by actuator saturation.

2005ConferencePDFFlexible Robotics
Comparison of Different Methods for Computing the Forward Kinematics of a Redundant Parallel Manipulator
H. Sajadian and H. D. Taghirad
Journal of Intelligent and Robotic Systems
Abstract:

In this paper, three numerical methods are presented to solve the forward kinematics of a three DOF actuator-redundant hydraulic parallel manipulator. It is known, that on the contrary to series manipulators, the forward kinematic map of parallel manipulators involves highly coupled nonlinear equations, whose closed-form solution derivation is a real challenge. This issue is of great importance noting that the forward kinematics solution is a key element in closed loop position control of parallel manipulators. The proposed methods, namely the Neural Network Estimation, the Quasi-closed Solution, and the Taylor series approximation, are using mainly numerical computations, with different ideas to solve the problem in hand. The latter two methods are proposed for the first time in literature to solve the forward kinematics of a parallel manipulator. These methods are compared in detail and the advantages or the disadvantages of each method in computing the forward kinematic map of the given mechanism is discussed. It is shown that a 4th order Taylor series approximation to the problem provides a good compromise for practical applications compared to that of other methods considered in this paper.

2005JournalPDFParallel and Cable Robotics
A Quasi-Closed Solution Method for Computing the Forward Kinematics of a Redundant Parallel Manipulator
H. Sadjadian and H.D. Taghirad
12th Iranian Conference on Electric Engineering
Abstract:

In this paper, a quasi-closed solution method is presented to solve the forward kinematics of a three DOF actuator redundant hydraulic parallel manipulator. It is shown, that on the contrary to series manipulators, the forward kinematic map of the parallel manipulators involves highly coupled nonlinear equations, which are almost impossible to solve analytically. The proposed method uses a combination of analytical and numerical schemes to solve the problem. A simulation study is performed using a sample trajectory to identify the advantages and disadvantages of the proposed method in computing the forward kinematic map of the given mechanism. The results show that the proposed method provides us with a relatively fast solution and good tracking performance although being dependent on the initial conditions used in the solution process.

2004ConferencePDF
Design of Composite Control For Flexible Joint Robots With Saturating Actuators
S. Ozgoli, H.D. Taghirad
Iranian Conference on Fuzzy Systems
Abstract:

In this paper a method of controller design for FJRs considering actuator saturation and other practical limitations is proposed. In the proposed method the need of powerful actuator is skipped over by decreasing the bandwidth of the fast controller during critical times. In order to accomplish this, a supervisory control is employed which uses fuzzy logic to adjust the proper forward path gain. This prevents instability caused by saturation without a great change in performance. All other practical considerations to make the controller implementable are taken into account and finally the performance of the proposed controller is verified through simulation.

2004ConferencePDFFlexible Robotics
Decentralized Robust H-Infinity Controller Design For A Half-Car Active Suspension System
A. Shariati, H. D. Taghirad and A. Fatehi
Control 2004
Abstract:

In this paper an H-Infinity controller is designed for a hydraulically actuated active suspension system of a half-modeled vehicle in a cascade feedback structure. Using the proposed structure the nonlinear behavior of actuator is reduced significantly. In the controller synthesis, a proportional controller is used in the inner loop, and a robust H? controller forms the outer loop. Two H? controllers are designed for this system. First unstructured uncertainty is not considered in the design procedure and secondly, the controller is designed considering uncertainty. Each of these controllers is designed in a decentralized fashion and the vehicle oscillation in the human sensitivity frequency range is reduced to a minimum. Statistical analysis of the simulation result using random input as road roughness, illustrates the effectiveness of the proposed control algorithm for both cases. Keyword: active suspension, cascade feedback, hydraulic actuator, nonlinear model, multiplicative uncertainty, robust H? controller, disturbance input, road random input, statistical analysis.

2004JournalPDF
Adaptive Robust Controller Synthesis for Hard Disk Servo Systems
H. D. Taghirad and E. Jamei
Intelligent Robots and Systems, 2004
Abstract:

Adaptive robust controller is proposed for read/write head systems for hard disk drives (HDD). This structure can be applied to both track seeking and track following modes, and it makes the mode switching control algorithms proposed in conventional HDD servo system unnecessary. This controller theoretically guarantees a prescribed transient performance and tracking in presence of parametric uncertainties. An improved desired compensation ARC (IDCARC) scheme is then proposed, which has powered by a dynamic adaptive term compared to DCARC. The regressor is calculated using reference trajectory information. This has been done by structural vibration minimized acceleration trajectory control method. Simulation result show that the dynamic adaptation mechanism in IDCARC provide better performance compared to that of ARC, DCARC and the conventional servo system with mode switches control law.

2004ConferencePDFHard Disk Drives Control
A Robust Linear Controller for Flexible Joint Manipulators
H.D. Taghirad and M.A. Khosravi
2004 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS)
Abstract:

In this paper a new and completely linear algorithm is proposed for composite robust control of flexible joint robots. Moreover, the robust stability of the closed loop system in the presence of structured and unstructured uncertainties is analyzed. To introduce the idea, flexible joint robot with structured and unstructured uncertainties is modelled and converted into singular perturbation form. A robust linear control algorithm is proposed for the slow dynamics and its robust stability conditions are derived using Thikhonov's theorem. Then the robust stability of the total system considering the proposed composite controller is analyzed, and sufficient conditions for robust stability of system is obtained. Finally the effectiveness of the proposed controller is verified through simulations. It is shown that not only the tracking performance of the proposed controller is very suitable, but also the actuator effort is much smaller than previous result.

2004ConferencePDFParallel and Cable Robotics
Numerical Methods for Computing the Forward Kinematics of a Redundant Parallel Manipulator
H. Sadjadian and H.D. Taghirad
Abstract:

In this paper, three numerical methods are presented to solve the forward kinematics of a three DOF actuator-redundant hydraulic parallel manipulator. It is known, that on the contrary to series manipulators, the forward kinematic map of parallel manipulators involves highly coupled nonlinear equations, whose closed-form solution derivation is a real challenge. This issue is of great importance noting that the forward kinematics solution is a key element in closed loop position control of parallel manipulators. The proposed methods, namely the Neural Network Estimation, the Quasi-closed Solution, and the Taylor series approximation, are using mainly numerical computations, with different ideas to solve the problem in hand. The latter two methods are proposed for the first time in literature to solve the forward kinematics of a parallel manipulator. These methods are compared in detail and the advantages or the disadvantages of each method in computing the forward kinematic map of the given mechanism is discussed. It is shown that a 4th order Taylor series approximation to the problem provides a good compromise for practical applications compared to that of other methods considered in this paper.

2004ConferencePDFParallel and Cable Robotics
Multivariable Generalized Predictive Temprature Controller Design For Yazd Solar Power Plant
Abdolvahed Saidi and Hamid D. Taghirad
European Journal of Scientific Research
Abstract:

The Yazd Integrated Solar Combined Cycle (ISCC) Power Plant consists of two gas turbines that are generating power synchronous to Iranian national electrical network. One steam turbine will be supplied by gas units, while a parabolic through solar field is integrated with the System, as a combined cycle. In this paper an integrated model of the solar field with the purpose is presented, and a multivariable generalized predictive temperature controller is proposed for the system. As it is Illustrated in the simulation results, such a control strategy can robustly regulate both the temperature of outlet oil, and the temperature of outlet steam water of the solar boiler, despite the variation of the inherent time delays of the system and external disturbances.

2004ConferencePDF
Parametric and Nonparametric Identification and Robust Control of a Rotational/Translational Actuator
M. Tavakoli, H. D. Taghirad and M. Abrishamchian
Control and Automation
Abstract:

RTAC benchmark problem considers a nonlinear fourth-order dynamical system involving the nonlinear interaction of a translational oscillator and an eccentric rotational proof mass. This problem has been posed to investigate the utility of a rotational proof mass actuator for stabilizing translational motion. In order to implement any of the model-based controllers proposed in the literature, the values of model parameters are required which are generally difficult to determine rigorously. In this paper, an approach to the least-squares estimation of system parameters is discussed and practically applied to the benchmark problem. Next, in order to design an H-Infinity controller, the nonlinear system is modelled as a perturbed linear system using an effective identification scheme. Experimental results confirm that this approach can effectively condense the whole nonlinearities, uncertainties, and disturbances within the system into a favorable perturbation block. Finally, an effective mixed-sensitivity problem is developed for the system to satisfy all performance requirements as well as robust stability despite actuator saturation.

2003ConferencePDF
Design and Simulation of Robust Composite Controllers for Flexible Joint Robots
H.D. Taghirad and M.A. Khosravi
2003 IEEE International Conference on Robotics and Automation
Abstract:

In this paper the control of flexible joint manipulators is studied in detail. A composite control algorithm is proposed for the flexible joint robots, which consists of two main parts. Fast control, u/sub f/, which guarantees that the fast dynamics remains asymptotically stable, and the corresponding integral manifold remains invariant. Slow control, u, itself consists of a robust PID designed based on the rigid model, and a corrective term designed based on the reduced flexible model. The stability of the overall closed loop system is proved to be UUB stable, by Lyapunov stability analysis. Finally, the effectiveness of the proposed control law is verified through simulations. It is shown that the proposed control law ensure the robust stability and performance, despite the modeling uncertainties.

2003ConferencePDFFlexible Robotics
A New Sensorless Vector Control Method for Permanent Magnet Synchronus Motor Without Velocity Estimatior
H. D. Taghirad, N. Abedi, E. Noohi
7th International Workshop on Advanced Motion Control
Abstract:

In this paper, a novel vector control method for permanent magnet synchronous motors is presented. In this method, the velocity estimation is completely removed and vector control is accomplished in a new coordinate system. In conventional vector control methods, the control effort is calculated in rotating coordinates with a synchronous speed of omega. However, in the proposed method, the control effort is calculated in rotating coordinates with reference speed omega. This change of coordinate decreases the calculation effort significantly. In order to verify the applicability of the proposed control law, a Lyapunov-based stability condition is derived and the performance of the controller is verified through simulations and experiments. The obtained results illustrate the effectiveness of the proposed method despite the simplicity of its implementation.

2002ConferencePDFDynamical Systems Analysis and Control
Stability Analysis and Robust Composite Controller Synthesis for Flexible Joint Robots
H.D. Taghirad and M.A. Khosravi
Advanced Robotics
Abstract:

In this paper the control of flexible joint manipulators is studied in detail. The model of N-axis flexible joint manipulators is derived and reformulated in the form of singular perturbation theory and an integral manifold is used to separate fast dynamics from slow dynamics. A composite control algorithm is proposed for the flexible joint robots, which consists of two main parts. Fast control, u f, guarantees that the fast dynamics remains asymptotically stable and the corresponding integral manifold remains invariant. Slow control, u s, consists of a robust PID designed based on the rigid model and a corrective term designed based on the reduced flexible model. The stability of the fast dynamics and robust stability of the PID scheme are analyzed separately, and finally, the closed-loop system is proved to be uniformly ultimately bounded (UUB) stable by Lyapunov stability analysis. Finally, the effectiveness of the proposed control law is verified through simulations. The simulation results of single- and two-link flexible joint manipulators are compared with the literature. It is shown that the proposed control law ensures robust stability and performance despite the modeling uncertainties.

2002ConferencePDFFlexible Robotics
Composite-H? Controller Synthesis for Flexible Joint Robots
H. D. Taghirad, Gh. Bakhshi
Intelligent Robots and Systems
Abstract:

In this paper a robust composite control algorithm is proposed for flexible joint manipulators, with the emphasis on satisfying control effort limitations. An H-Infinity framework is used for the slow subsystem controller design, instead of robust PID synthesis introduced in the literature. Linear identification techniques are used to represent the nonlinear dynamics of the system into a linear model plus multiplicative uncertainty. An H-Infinity controller is designed in the framework of composite control, in order to optimize the required control effort, along with satisfying robust stability and desirable performance. The effectiveness of the proposed control law is compared with other methods through a simulation study. The comparison results show a significant improvement in control effort, while satisfying both stability and performance requirements.

2002ConferencePDFFlexible Robotics
Stability Analysis and Robust Composite Controller Synthesis for Flexible Joint Robots
H.D. Taghirad and M.A. Khosravi
Advanced Robotics
Abstract:

In this paper the control of flexible joint manipulators is studied in detail. The model of N-axis flexible joint manipulators is derived and reformulated in the form of singular perturbation theory and an integral manifold is used to separate fast dynamics from slow dynamics. A composite control algorithm is proposed for the flexible joint robots, which consists of two main parts. Fast control, u f, guarantees that the fast dynamics remains asymptotically stable and the corresponding integral manifold remains invariant. Slow control, u s, consists of a robust PID designed based on the rigid model and a corrective term designed based on the reduced flexible model. The stability of the fast dynamics and robust stability of the PID scheme are analyzed separately, and finally, the closed-loop system is proved to be uniformly ultimately bounded (UUB) stable by Lyapunov stability analysis. Finally, the effectiveness of the proposed control law is verified through simulations. The simulation results of single- and two-link flexible joint manipulators are compared with the literature. It is shown that the proposed control law ensures robust stability and performance despite the modeling uncertainties.

2002JournalPDFFlexible Robotics
H-Infinity Based Robust Torque Control of Harmonic Drive Systems
H.D. Taghirad, P.R. Belanger
Journal of Dynamic Systems Measurement and Control
Abstract:

In this paper, the torque control of a harmonic drive system for constrained-motion and free-motion applications is examined in detail. A nominal model for the system is obtained in each case from experimental frequency responses of the system, and the deviation of the system from the model is encapsulated by a multiplicative uncertainty. Robust torque controllers are designed using this information in an H-proportional to-framework, and implemented on two different setups. From time and frequency domain experiments, it is shown that the closed-loop system retains robust stability, while improving the tracking performance exceptionally well. To further improve the performance of the system for free-motion case, a feedforward friction-compensation algorithm is implemented in addition to the robust torque control. It is shown that friction-compensation will shrink the model uncertainty at low frequencies and hence, the performance of the closed-loop system it-ill be improved at those frequencies.

2001JournalPDF
Automobile Passenger Comfort Assured Through Lqg/Lqr Active Suspension
H. D. Taghirad, E. Esmailzadeh
Journal of Vibration and Control
Abstract:

An analytical investigation of a half-car model including passenger dynamics, subjected to random road disturbances is performed, and the advantage of active over conventional passive suspension systems are examined. Two different performance indices for optimal controller design are proposed. The performance index is a quantification of both ride comfort and road handling. Due to practical limitations, all the states required for the state-feedback controller are not measurable, and thus must be estimated with an observer. Stochastic inputs are applied to simulate realistic road surface conditions, and statistical comparisons between passive system and the two controllers, with and without state estimator, are carried out to gain a clearer insight into the performance of the controllers.The simulation results demonstrate that an optimal observer- based controller, when including passenger acceleration in the performance index, retains both excellent ride comfort and road handling characteristics.

1999JournalPDF
H-Infinity Based Robust Torque Control of Harmonic Drive Systems Under Free and Constrained Motion Applications
H.D. Taghirad, P.R. Belanger
Journal of Dynamic Systems Measurement and Control
Abstract:

A harmonic drive is a compact, light--weight and high--ratio torque transmission device which has almost zero backlash. Its unique performance features captures the attention of designers in many industrial applications, especially in robotics. However, the torque control of harmonic drive systems is still a challenging problem for researchers. In this paper the torque control of harmonic drive system for constrained motion is examined in detail. A nominal model for the system is obtained from experimented frequency responses of the system, and the deviation of the system from the model is encapsulated by multiplicative uncertainty. A robust torque controller is designed using this information in an H1 --framework, and implemented on two different setups. It is illustrated that the performance features of the closed--loop system is exceptionally good, both in time and frequency domains. I. Introduction Developed in 1955 primarily for aerospace applications, harmonic drives are high--...

1998ConferencePDF
Robust Friction Compensator For Harmonic Drive Transmission
H.D. Taghirad, P.R. Belanger
Proceedings of the 1998 IEEE International Conference on Control Applications
Abstract:

The torque control of harmonic drive system is examined in detail. An empirical nominal model for the system is obtained through experimental frequency response estimates, and the deviation of the system from the model is encapsulated by multiplicative uncertainty. A robust torque controller is subsequently designed in an H-Infinity framework and implemented using Kalman filtered torque estimates. Exceptional performance results are obtained from the time and frequency response of the closed-loop system. To further improve the performance of the system, a model-based friction-compensation algorithm is implemented in addition to the robust torque control. It is shown that the friction-compensation reduced the model uncertainty at low frequencies. Hence, the performance of the closed-loop system is improved for tracking signals with low-frequency content.

1998ConferencePDF
Electromagnetic Levitation System An Experimental Approach
H D Taghirad, M Abrishamchian, R Ghabcheloo
Abstract:

In this paper, we propose a simple method for controlling an electromagnetic levitation (Mag lev) system. The model of the Mag lev system under consideration in this paper is third order, inherently nonlinear and unstable. For designing a controller to obtain a good disturbance rejection and being insensitive to parameter variations, we use an inner-loop and an outer-loop configuration. The configuration is the key to solve this problem. By using a nonlinear state transformation in the feedback path, a cascaded PI controller and a redefined input in the inner loop, we obtain a linear second order system. Furthermore, to achieve a stable system with a good disturbance rejection, we design a Pid controller cascaded with the inner loop system in the negative unity feedback configuration in the outer loop. We show that the closed-loop system is robustly stabilized against the mass variation. Simulation results show that despite actuator saturation limits, the performance of our simple structure controller is comparable to that reported in the literature. In order to assess these results in practice, an experimental setup is designed and being constructed. The simulation analysis is based on the parameters of this experimental setup

1998ConferencePDF
A Nonlinear Model For Harmonic Drive Friction And Compliance
H.D. Taghirad, P.R. Belanger
Abstract:

Despite widespread industrial application of harmonic drives, mathematical representation of their dynamics has not been fully addressed. In this paper a systematic way to capture and rationalize the dynamic behavior of the harmonic drive systems is developed. Simple and accurate models for compliance, hysteresis, and friction are proposed, and the model parameters are estimated using least--squares approximation for linear and nonlinear regression models. A statistical measure of variation is defined, by which the reliability of the estimated parameter for different operating condition, as well as the accuracy and integrity of the proposed model is quantified. By these means, it is shown that a linear stiffness model best captures the behavior of the system when combined with a good model for hysteresis. Moreover, the frictional losses of harmonic drive are modelled at both low and high velocities. The model performance is assessed by comparing simulations with the experimental result...

1998ConferencePDF
Friction Compensation and H-Infinity Based Torque Control of Harmonic Drive Systems
H.D. Taghirad, P.R. Belanger
Abstract:

In this paper the torque control of a harmonic drive system for constrained--motion and free-- motion applications is examined in detail. A nominal model for the system is obtained in each case from experimental frequency responses of the system, and the deviation of the system from the model is encapsulated by a multiplicative uncertainty. Robust torque controllers are designed using these information in an H-Infinity framework, and implemented on two different setups. From time and frequency domain experiments, it is shown that the closed--loop system retains robust stability, while improving the tracking performance exceptionally well. To further improve the performance of the system for free-motion case, a feedforward friction--compensation algorithm is implemented in addition to the robust torque control. It is shown that friction--compensation will shrink the model uncertainty at low frequencies and hence, the performance of the closed--loop system will be improved at those frequencies...

1998ConferencePDF
Modelling and Parameter Identication of Harmonic Drive Systems
H.D. Taghirad, P.R. Belanger
Abstract:

The unique performance features of harmonic drives, such as high gear ratios and high torque capacities in a compact geometry, justify their widespread industrial application. However, harmonic drive can exhibit surprisingly more complex dynamic behavior than conventional gear transmission. In this paper a systematic way to capture and rationalize the dynamic behavior of the harmonic drive systems is developed. Simple and accurate models for compliance, hysteresis, and friction are proposed, and the model parameters are estimated using least-squares approximation for linear and nonlinear regression models. A statistical measure of variation is defined, by which the reliability of the estimated parameter for different operating condition, as well as the accuracy and integrity of the proposed model is quantified. By these means, it is shown that a linear stiffness model best captures the behavior of the system when combined with a good model for hysteresis. Moreover, the frictional losses of harmonic drive are modeled at both low and high velocities. The model performance is assessed by comparing simulations with the experimental results on two different harmonic drives. Finally, the significance of individual components of the nonlinear model is assessed by a parameter sensitivity study using simulations.

1998JournalPDF
Torque Ripple and Misalignment Torque Compensation for the Built-In Torque Sensor of Harmonic Drive Systems
H.D. Taghirad, P.R. Belanger
IEEE Transactions on Instrumentation and Measurement
Abstract:

A harmonic drive is a compact, lightweight, and high-ratio torque transmission device which is used in many electrically actuated robot manipulators. In this paper a built-in torque sensor for harmonic-drive systems is examined in detail. The method proposed by Hashimoto, in which strain gauges are directly mounted on the flexspline, is employed and improved in this paper. To minimize sensing inaccuracy, four Rosette strain gauges are used employing an accurate positioning method. To cancel the torque ripples, the oscillation observed on the measured torque and caused mainly by gear teeth meshing, Kalman filter estimation is used. A simple fourth-order harmonic oscillator proved to accurately model the torque ripples. Moreover, the error model is extended to incorporate any misalignment torque. By on-line implementation of the Kalman filter, it has been shown that this method is a fast and accurate way to filter torque ripples and misalignment torque. Hence, the intelligent built-in torque sensor is a viable and economical way to measure the harmonic-drive transmitted torque and to employ that for torque feedback strategies.

1998JournalPDF
Intelligent Built-In Torque Sensor for Harmonic Drive Systems
H.D. Taghirad, P.R. Belanger
IEEE Transactions on Instrumentation and Measurement
Abstract:

A harmonic drive is a compact, light-weight and high-ratio torque transmission device which is used in many electrically actuated robot manipulators. In many robotic control strategies it is assumed that the actuator is an ideal torque source. However, converting harmonic drive systems to ideal torque sources is still a challenging control problem for researchers. In this paper the torque control of harmonic drive system under free motion is examined in detail. A built-in torque sensor is developed in order to measure the torque, and by employing a Kalman filter the undesired torque signatures like torque ripples and misalignment torque are filtered out. An empirical nominal model for the system is obtained through experimental frequency response estimates, and the deviation of the system from the model is encapsulated by multiplicative uncertainty. A robust torque controller is subsequently designed in an H?-framework and implemented employing Kalman filtered torque estimates. From time and frequency domain experiments, it is shown that the closed-loop system retains robust stability, while improving the tracking performance exceptionally well

1998JournalPDF
Application of Kalman Filter for Intelligent Built in Torque Sensor of Harmonic Drives
H.D. Taghirad
Abstract:

A harmonic drive is a compact, light--weight and high--ratio torque transmission device which has almost zero backlash. Its unique performance features has captured the attention of designers in many industrial applications, especially in robotics. Despite widespread industrial application of harmonic drives, the torque control of this system has not been fully addressed. In this thesis the robust torque control of harmonic drive system is examined in detail. In order to measure the transmitted torque of a harmonic drive and for the purpose of a torque feedback scheme, an intelligent built--in torque sensing technique is developed in this thesis. Specifically, strain--gauges are mounted directly on the flexspline and therefore no extra flexible element is introduced into the system. To have maximum sensing accuracy, four Rosette strain gauges are employed using an accurate positioning method. Kalman filter estimation is employed to cancel the torque ripples, oscillations observed on t...

1997JournalPDF
On The Modelling and Identification of Harmonic Drive Systems
H.D. Taghirad
Abstract:

The unique performance features of harmonic drives, such as high gear ratios and high torque capacities in a compact geometry, justify their widespread industrial application, especially in robotics. However, harmonic drives can exhibit surprisingly more complex dynamic behavior than conventional gear transmissions. In this report, a systematic way to capture and rationalize the dynamic behavior of the harmonic drive systems is examined. Simple and accurate models for compliance, hysteresis, and friction are proposed, and the model parameters are estimated using least--squares approximation for linear and nonlinear regression models. A statistical measure of variation is defined, by which the reliability of the estimated parameter for different operating condition, as well as the accuracy and integrity of the proposed model is quantified. Finally, the model performance is assessed by a simulation verifying the experimental results. R' esum' e Les performances uniques de l'entrainement ...

1997JournalPDF
Intelligent Torque Sensing and Robust Torque Control of Harmonic Drive Under Free-Motion
H.D. Taghirad, P.R. Belanger
Abstract:

A harmonic drive is a compact, light-weight and high-ratio torque transmission device which is used in many electrically actuated robot manipulators. In many robotic control strategies it is assumed that the actuator is an ideal torque source. However, converting harmonic drive systems to ideal torque sources is still a challenging control problem for researchers. In this paper the torque control of harmonic drive system under free motion is examined in detail. A built-in torque sensor is developed in order to measure the torque, and by employing a Kalman filter the undesired torque signatures like torque ripples and misalignment torque are filtered out. An empirical nominal model for the system is obtained through experimental frequency response estimates, and the deviation of the system from the model is encapsulated by multiplicative uncertainty. A robust torque controller is subsequently designed in an H framework and implemented employing Kalman filtered torque estimates. From time and frequency domain experiments, it is shown that the closed-loop system retains robust stability, while improving the tracking performance exceptionally well

1997ConferencePDF
Intelligent Built-In Torque Sensor for Harmonic Drive Systems
H.D. Taghirad, A.Hemly, P.R. Belanger
Abstract:

The unique performance features of harmonic drives, such as high gear ratios and high torque capacities in a compact geometry, justify their widespread industrial application especially in many electrically actuated robot manipulators. In many robotic control strategies it is assumed that the actuator is acting as a torque source, and in order to implement such algorithms it is necessary to accurately measure the transmitted torque by the harmonic drive. In this paper a built-in torque sensor for harmonic drive systems is developed and examined in detail, in which strain-gauges are directly mounted on the harmonic drive flexspline. To minimize sensing inaccuracy, four Rosette strain gauges are used employing an accurate positioning method. To cancel the torque ripples, the oscillation observed on the measured torque and caused mainly by gear teeth meshing, Kalman filter estimation is used. A simple fourth order harmonic oscillator proved to accurately model the torque ripples. Moreover, the error model is extended to incorporate any misalignment torque. By on line implementation of the Kalman filter, it has been shown that this method is a fast and accurate way to filter torque ripples and misalignment torque. Hence, the intelligent built-in torque sensor is a viable and economical way to measure the harmonic drive transmitted torque and to employ that for torque feedback strategies.

1997ConferencePDF
An Experimental Study on Modelling and Identification of Harmonic Drive Systems
H.D. Taghirad, P.R. Belanger
Proceedings of 35th IEEE Conference on Decision and Control
Abstract:

Despite widespread industrial application of harmonic drives, mathematical representation of their dynamics has not been fully addressed. In this theoretical/experimental study of harmonic drive systems a systematic way to capture and rationalize the dynamics of the system is proposed. Simple and accurate models for compliance, hysteresis, and friction are given and the model parameters are estimated from experiments using least square approximation. A statistical measure of consistency is defined, by which the reliability of the estimated parameter for different operating condition, as well as the accuracy and integrity of the proposed model is quantified. The validity of the modelling scheme is evaluated on two different harmonic drives by comparing the experimental and simulation results.

1996ConferencePDF
An Experimental Study on Harmonic Drives
H.D. Taghirad, P.R. Belanger, A.Hemly
Abstract:

Despite widespr ad industrial application of harmonic drives, modelling and control of such systems has not been fully addressed. In this theoretical/experimental study of harmonic drive systems a systematic way to capture and rationalize the dynamics of the system is proposed. Simple and accurate models for their compliance, hysteresis, and friction are given and model parameters are estimated from experimental data using least square approximation. A statistical measure of consistency is defined, by which the reliability of the estimated parameter for different operating condition, as well as the accuracy and integrity of the proposed model is quantified. The validity of the modelling scheme is evaluated by comparing the experimental and simulation results. Two separate simulations are developed for the harmonic drive system operating in restrained and unrestrained motion. The problem of torque control of harmonic drive is addressed in the H1 controller design framework. I...

1996JournalPDF
Passenger Ride Comfort Through Observer Based Control
H. D. Taghirad, E. Esmailzadeh
Abstract:

An analytical investigation of a half-car model including passenger dynamics, subjected to random road disturbances is performed, and the advantage of active over conventional passive suspension systems are examined. Two diierent performance indices for optimal controller design are proposed. The performance index is a quantiication of both ride comfort and road handling. Due to practical limitations, all the states required for the state-feedback controller are not measurable, and thus must be estimated with an observer. Stochastic inputs are applied to simulate realistic road surface conditions, and statistical comparisons between passive system and the two controllers, with and without state estimator, are carried out to gain a clearer insight into the performance of the controllers. The simulation results demonstrate that an optimal observer-based controller, when including passenger acceleration in the performance index, retains both excellent ride comfort and road handling characteristics

1995ConferencePDF
State Feedback Control For Passenger Ride Dynamics
H. D. Taghirad, E. Esmailzadeh
Transactions- Canadian Society for Mechanical Engineering
Abstract:

An analytical investigation of a half-car model with passenger dynamics, subjected to random road disturbance, is performed. Two diierent methods of deening the performance index for optimal controller design are proposed. Nondeterministic inputs are applied to simulate the road surface conditions more realistically. Results obtained illustrate that using an optimal state-feedback controller, with passenger acceleration included in the performance index, would exhibit not only an improved passenger ride comfort, but also, a better road handling and stability.

1995JournalPDF
Ride Comfort and Roll Characteristics of Tandem Axled Trucks
E. Esmailzadeh, H. D. Taghirad
Abstract:

this paper, the ride comfort and handling characteristics of a tandem-axle truck are investigated. The equations of motion for the proposed model, with fourteen-degrees-of-freedom, are derived. Various numerical techniques are employed in order to solve the complex matrix equation. The sensitivity analysis for the parameter variations is carried out in this study and the overall effects of anti-roll bar are also examined.

1995ConferencePDF
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