The current researches of this group are as follows:

  • The research about finding an algorithmic method for analysis of equilibrium point of quasi-homogeneous systems as an important part of autonomous systems, related to Hilbert’s 16th problem and Arnold’s question, associated with the indirect method of Lyapunov,
  • To design robust controllers based on linear and nonlinear H_infinity methods for industrial systems such as a half-car active suspension system with hydraulic actuators and RTAC (TORA), and in addition to this, to design the controllers for the surgical robots having haptic technology, by a state-feedback control law that minimizes an infinite/finite horizon cost function within the framework of linear/nonlinear matrix inequalities, and especially, simultaneously establishes robust stability conditions presented by a Lyapunov function,
  • To develop and tailor the techniques of state-dependent Riccati equation (SDRE) filtering so as to rigorously estimate states and parameters of the nonlinear systems with uncertainty, exposed to unknown disturbance inputs, and also to apply SDRE filter such as robust SDRE filter based on the H-infinity norm minimization criterion to stochastic systems,
  • To study Neuroscience as a multidisciplinary field, which we believe it will be significantly influenced by dynamical systems theory. We have been actively engaging in the research about modeling of the neurons, especially located at V1, and optic nerves and also investigating methods for stimulation and recording of the nerve cells, including noninvasive and invasive methods, such as Steady State Visually Evoked Potential (SSVEP) stimulation, Transcranial Magnetic Stimulation (TMS), microelectrode stimulation, Optogenetics stimulation, Electroencephalogram (EEG) recording, Electrocorticography (ECoG) recording, Local Field Potential (LPF) recoding, and Spikes recording.

Current Projects

Nonlinear Analysis
Nonlinear Analysis

We apply a wide variety of mathematical methods to analyzing system nonlinear behaviors. Moreover, we try to present new useful definitions and theorems which can assist us to accomplish the goal. Additionally, we are enthusiastic about pathological behaviors which common methods fail to analyze them such as Perron effect in the largest Lyapunov exponent sign, global attractivity without stability in Liénard type systems, and aperiodic long-term behavior of a non-hyperbolic strange attractor.

Most our efforts has been around determining invariant sets and their stability. In the first place, we investigate not only various definitions of invariant sets, but also different definitions of stability so as to find the definitions which can be appropriate to the needs of the analysis. In the second place, we conduct assorted methods such as topological, geometric, and algebraic methods which have the ability to be used for studying ordinary and partial differential equations, especially in state space. Particularly, we pursue to devise algorithms in order for finding the invariant sets of polynomial systems and solving their stability problem, specifically in the sense of V. Arnold.

Figure 1: Phase portrait of a system with two centers

Control Methods
Control Methods

A wide variety of control methods are considered in the group for control analysis and synthesis of dynamical systems. Among them  robust control synthesis for delayed systems is one of the focuses of our research group. Time-delay appear in many systems and processes and is usually a source of instability. We have proposed an  PD/PI controller synthesis for linear systems with uncertain input delay which may leads to a time-delay system of retarded or neutral type. In a neutral type system, in which delay appears both in its state and the derivatives of state, the resulting delay coefficients depend on the controller gains and makes the controller synthesis more challenging. To tackle this problem a new bounded real lemma (BRL) is introduced and the design of an output feedback PD controller for a system with uncertain time-invariant input delay is addressed. This method is further extended for designing a PI controller by augmenting an integrator to the system model.

H_infinity robust control synthesis is extensively applied in many practical systems of interest in the group.  H_infinity based robust torque control of harmonic drive systems, identification of RTAC (TORA) and Robust H_infinity Control synthesis,  Impedance control of a flight simulator yoke,  Decentralized Robust Controller design for a half-car active suspension system with hydraulic actuators,  Robust  Linear Controller, Composite QFT, Nonlinear H_infinity , Robust  H_2 /H_infinity and Mixed Sensitivity Approaches, for flexible joint robots with Phase Uncertainty, may be named among them.

H_infinity robust control synthesis is also applied on 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 minimizes an infinite horizon cost function within the framework of linear matrix inequalities. In particular, it is shown that the solution of the optimization problem can stabilize 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.

Multi agent coverage control: The recent development in the autonomy and the capabilities of mobile robots greatly increases the number of applications suitable for a team of autonomous agents. Particular interest has been received by those tasks requiring continual execution, such as the monitoring of oil spills, the detection of forest fires, the track of border changes, and the patrol (surveillance) of an environment. There is a widespread belief that continuous and pervasive monitoring will be possible in the near future with large numbers of networked, mobile, and wireless sensors. Thus, we are witnessing an intense research activity that focuses on the design of efficient control mechanisms for these systems. In particular, decentralized algorithms would allow mobile sensor networks to react autonomously to changes in the environment with minimal human supervision. A substantial body of research on mobile sensor networks has concentrated on the surveillance of an area of interest requires the robots to continuously and repeatedly cover the environment. The main objective of area coverage problem is how to monitor the whole area of the network with respect to different performance criteria such as coverage ratio, minimum number of sensors providing desired coverage level during the maximum lifetime of the network. Here, robots could use a Voronoi-based coverage control framework to distribute themselves across the environment.

Figure 2: Gershgorin disks for a randomly generated  4 by 4 complex matrix

Figure 3:  Voronoi-based area coverage for a group of agents

Observer Design & Identification Methods
Observer Design and Identification Methods

State-dependent Riccati equation (SDRE) filtering techniques have been extensively used for nonlinear state/parameter estimation within a wide range of applications. The standard SDRE filter, which is set up by direct SDC parameterization, demands complete knowledge of the system model, and the disturbance inputs characteristics, which severely  degrade its performance in practical applications. We proposed a robust SDRE filter based on the H_infinity norm minimization criterion, to effectively estimate the states of nonlinear uncertain systems exposed to unknown disturbance inputs. Extension of this work in considered for exponential stability, and in stochastic domain.

Currently, for highly uncertain models the proposed robust SDRE is combined with a switching algorithm. The theoretical development of this filter and its robustness analysis is reviewed and its implementation on the uncertain nonlinear model of Lithium-Ion battery is considered. The stimulation and the implementation results verify the efficiency of the extended filter, which is quite promising to be implemented on other nonlinear and uncertain plants.

Figure 4: Generic functional block diagram of SDRE Architecture with Built-in Parameter Estimator

Brain Computer Interface (BCI)
Brain Computer Interface (BCI)

Brain-computer interface (BCI) establish a connection between the brain activities and robotic systems through converting the brain signals into perceptible control signals for machines. Such a system has been a specific area of interest in order to provide interaction of people with disabilities with the surrounding environment. Using the system, the brain patterns for a certain type of behavior is obtained and the related control commands is produced. This control signal represents a specific neuro-behavior of the brain and can be used in BCI systems. From the EEG signals, SSVEP may be retracted as a specific type of control signal which is produced at the occipital lobe of the brain in response to an external oscillating stimulus. The frequency of this signal is matched with the frequency of the input stimuli that can be identified using EEG test, which is the focus of the current research.

As the brain signals are the neurological reaction of the individuals to stimulus signals it is crucial to design a suitable stimulus system as well as investigation of its effectiveness. In our research group, a suitable visual stimulus system is designed and implemented, and its effectiveness is proved through experiments. Various statistical and pattern identification methods such as CCA, MSI and MEC for coding the main characteristics of the SSVEP signals are implemented in the test bed by recording data of several individuals. For having a physical perception of the BCI system a robotic arm is used. An integrated system comprising the robotic arm and commercial Emotiv Brainwear® is developed and the final implementation is performed on the robotic arm. The experimental results on different subjects shoes the promising horizons of using such technology for disabled people.

Figure 5 : Control of the Avatar by EEG signal

Notable Alumni

Ala Shariati

Researcher
APAC research group

Noushin Poursafar

Ph.D. Student
University of Sydney, Australia

Ali Salamati

Researcher
Niroo Research Center

Maysam Z. Pedram

K.N. Toosi University of Technology

Arsalan Rahimabadi

Freelancer
Advanced Robotics and Automated Systems (ARAS)

Hossein Beikzadeh

Researcher
Bombardier Inc. canada

Soheil Kianzad

PhD student
University of British Columbia, Canada

Related Publications

TitleAbstractYearTypePDFResearch Group
On the matching equations of kinetic energy shaping in IDA-PBC
M Reza J Harandi, Hamid D Taghirad
Abstract:

Interconnection and damping assignment passivity-based control scheme has been used to stabilize many physical systems such as underactuated mechanical systems through total energy shaping. In this method, some partial differential equations (PDEs) related to kinetic and potential energy shaping shall be solved analytically. Finding a suitable desired inertia matrix as the solution of nonlinear PDEs relevant to kinetic energy shaping is a challenging problem. In this paper, a systematic approach to solving this matching equation for systems with one degree of underactuation is proposed. A special structure for desired inertia matrix is proposed to simplify the solution of the corresponding PDE. It is shown that the proposed method is more general than that of some reported methods in the literature. In order to derive a suitable desired inertia matrix, a necessary condition is also derived. The proposed method is …

2021JournalPDFDynamical Systems Analysis and Control
Bounded Inputs Total Energy Shaping for Mechanical Systems
MRJ Harandi, A Molaei, HD Taghirad, JG Romero
arXiv preprint arXiv:2104.02337
Abstract:

Designing control systems with bounded input is a practical consideration since realizable physical systems are limited by the saturation of actuators. The actuators' saturation degrades the performance of the control system, and in extreme cases, the stability of the closed-loop system may be lost. However, actuator saturation is typically neglected in the design of control systems, with compensation being made in the form of over-designing the actuator or by post-analyzing the resulting system to ensure acceptable performance..

2021Preprint PDFDynamical Systems Analysis and Control
Offline and Online Active Fault Tolerant System For Multirotor Drones
Hussein Mazeh, Hamid D Taghirad, Jihad Sahili
Abstract:

Object localization has a vital role in any object detector, and therefore, has been the focus of attention by many researchers. In this article, a special training approach is proposed for a light convolutional neural network (CNN) to determine the region of interest (ROI) in an image while effectively reducing the number of probable anchor boxes. Almost all CNN-based detectors utilize a fixed input size image, which may yield poor performance when dealing with various object sizes.

2021ConferencePDFDynamical Systems Analysis and Control
Bounded inputs total energy shaping for a class of underactuated mechanical systems
M Reza J. Harandi, Hamid D Taghirad, Amir Molaei, Jose Guadalupe Romero
Abstract:

Designing control systems with bounded input is a practical consideration since realizable physical systems are limited by the saturation of actuators. The actuators' saturation degrades the performance of the control system, and in extreme cases, the stability of the closed‐loop system may be lost. However, actuator's saturation is typically neglected in the design of control systems, with compensation being made in the form of overdesigning the actuator or by postanalyzing the resulting system to ensure acceptable performance. The bounded input control of fully actuated mechanical systems has been investigated in multiple studies, but it is not generalized for underactuated mechanical systems. This article proposes a systematic framework for finding the upper bound of control effort in underactuated systems, based on interconnection and the damping assignment passivity based control approach. The proposed …

2021JournalPDFDynamical Systems Analysis and Control
Solution of matching equations of IDA-PBC by Pfaffian differential equations
M Reza J Harandi, Hamid D Taghirad
Abstract:

Finding the general solution of partial differential equations (PDEs) is essential for controller design in newly developed methods. Interconnection and damping assignment passivity-based control (IDA-PBC) is one of such methods in which the solution to corresponding PDEs which are called matching equations is needed to apply it in practice. In this paper, these matching equations 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 systems such as Magnetic levitation system, Pendubot, and underactuated cable-driven robot to verify its applicability.

2021JournalPDFDynamical Systems Analysis and Control

Robust IDA-PBC for a Spatial Underactuated Cable Driven Robot with Bounded Inputs

M Reza J Harandi, S Ahmad Khalilpour, Hamid Taghirad
Abstract:

Stabilization of underactuated systems is a challenging problem especially when external disturbance is applied and the actuators are limited. Interconnection and damping assignment passivity-based control (IDA-PBC) is an approach to regulate the systems represented by port Hamiltonian modeling such as underactuated robots while its application is restricted by some PDEs. In this paper, IDA-PBC is implemented on a spatial3-DOF underactuated cable driven manipulator. A robust term with respect to bounded matched disturbance is designed, non-negative tension in cables by appropriate desired potential energy is considered and stability of the system is ensured by a Lyapunov candidate. simulation results illustrate the effectiveness of the proposed controller.

2021ConferencePDFDynamical Systems Analysis and Control
On the Matching Equations of Kinetic Energy Shaping in IDA-PBC
M. Reza J. Harandi, Hamid D. Taghirad
arXiv preprint arXiv:2011.14958
Abstract:

Interconnection and damping assignment passivity-based control scheme has been used to stabilize many physical systems such as underactuated mechanical systems through total energy shaping. In this method, some partial differential equations (PDEs) arisen by kinetic and potential energy shaping, shall be solved analytically. Finding a suitable desired inertia matrix as the solution of nonlinear PDEs related to kinetic energy shaping is a challenging problem. In this paper, a systematic approach to solve this matching equation for systems with one degree of underactuation is proposed. A special structure for desired inertia matrix is proposed to simplify the solution of the corresponding PDE. It is shown that the proposed method is more general than that of some reported methods in the literature. In order to derive a suitable desired inertia matrix, a necessary condition is also derived. The proposed method is applied to three examples, including VTOL aircraft, pendubot and 2D SpiderCrane system.

2020Preprint PDFDynamical Systems Analysis and Control
Solution to IDA-PBC PDEs by Pfaffian Differential Equations
M. Reza J. Harandi, Hamid. D. Taghirad 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.

2020Preprint PDFDynamical 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.

2018ConferencePDFDynamical Systems Analysis and Control
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
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
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
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
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.

2015JournalPDFDynamical Systems Analysis and Control
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
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
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
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.

2013ConferencePDFDynamical 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
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.

2012JournalPDFDynamical Systems Analysis and Control
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
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
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
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.

2011JournalPDFDynamical Systems Analysis and Control
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
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
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
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
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.

2010ConferencePDFDynamical Systems Analysis and Control
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.

2009ConferencePDFDynamical Systems Analysis and Control
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.

2009ConferencePDFDynamical Systems Analysis and Control
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.

2009ConferencePDFDynamical Systems Analysis and Control
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
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.

2009ConferencePDFDynamical Systems Analysis and Control
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.

2008JournalPDFDynamical Systems Analysis and Control
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.

2007JournalPDFDynamical Systems Analysis and Control
Robust Hinfinity, H2/Hinfinity 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.

2006ConferencePDFDynamical Systems Analysis and Control
Nonparametric Identification and Robust Hinfinity 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.

2006ConferencePDFDynamical Systems Analysis and Control
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.

2004JournalPDFDynamical Systems Analysis and Control
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.

2004ConferencePDFDynamical Systems Analysis and Control
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.

2003ConferencePDFDynamical Systems Analysis and Control
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
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.

2001JournalPDFDynamical Systems Analysis and Control
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.

1999JournalPDFDynamical Systems Analysis and Control
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--...

1998ConferencePDFDynamical Systems Analysis and Control
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.

1998ConferencePDFDynamical Systems Analysis and Control
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

1998ConferencePDFDynamical Systems Analysis and Control
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...

1998ConferencePDFDynamical Systems Analysis and Control
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...

1998ConferencePDFDynamical Systems Analysis and Control
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.

1998JournalPDFDynamical Systems Analysis and Control
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.

1998JournalPDFDynamical Systems Analysis and Control
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

1998JournalPDFDynamical Systems Analysis and Control
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...

1997JournalPDFDynamical Systems Analysis and Control
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 ...

1997JournalPDFDynamical Systems Analysis and Control
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

1997ConferencePDFDynamical Systems Analysis and Control
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.

1997ConferencePDFDynamical Systems Analysis and Control
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.

1996ConferencePDFDynamical Systems Analysis and Control
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...

1996JournalPDFDynamical Systems Analysis and Control
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

1995ConferencePDFDynamical Systems Analysis and Control
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.

1995JournalPDFDynamical Systems Analysis and Control
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.

1995ConferencePDFDynamical Systems Analysis and Control
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