Parallel & Cable Robotics Group

Increasing performance demands necessitate design of new types of robots with larger work space, being capable to perform at higher accelerations. In a cable-driven redundant parallel manipulator (CDRPM), the linear actuators of parallel manipulators are replaced with electrical powered cable drivers, which lead immediately to a larger work space. The idea of using cable driven redundant parallel manipulators, are not limited to only the applications where a very large work space is required, and this idea is effectively penetrated in the applications where precise and stiff robot is required to operate in high accelerations within a relatively larger work space than that attainable in conventional parallel robots. In our lab , several applications in which a CDRPM is used are introduced, and the challenging issues in the optimal kinematics structure, dynamics formulation, and control of such structure are studied.

Core Projects

Control of CDR Considering Cable Dynamics

In many former studies, cable mass have been ignored against end-effector mass. In other words, the cables have been modeled as straight massless body. This assumption is valid for robots of small size carrying light payloads, but for such large scale robots, cannot be applicable anymore. In the latter case, the mass of long cables can lead to sagging effect. In summary, the sagging effect of cables can result in following problems: (1) increasing complexity of both kinematic and dynamic analysis (2) decreasing robot stiffness (3) reducing natural frequencies and undesirable vibrations. Wave-based control (WBC), as a newly-developed technique for mechanical flexible systems is proposed by ARAS group and applied to cable driven parallel manipulators to do position control and active vibration damping at the same time.

Project Manager: Ahmad Khalilpour
Project Manager: Ahmad Khalilpour

Deployable CDRs

Over the last decade‎, ‎many researches have studied in the‎ field of cable robots‎, ‎but still their applications are very limited‎ compared to the conventional serial robots‎. ‎Introducing a simple and‎ deployable design for the cable driven robots may significantly‎ influence their wider use in industrial applications‎. ‎This causes‎ the installation of the robot is not be limited to a fixed and well‎ calibrated structure and high accuracy calibration process is no‎ longer required‎. ‎By this means the robot may be easily moved from‎ one place to another‎. ‎Such designs are considered to have rapidly‎ deployable characteristics‎, ‎which makes them more applicable‎. In deploy-able cable driven robots‎, ‎kinematic dimensions and‎ parameters of the robot is not accurately measured‎, ‎and this‎ uncertainty in the measurement will appear in the most of the robots‎ model parameters‎. ‎This introduces many challenges in terms of the‎ controller design with the required performance for the designer‎. The goal of this project is to develop a theoretical framework for robust position control of CDPMs. To develop the idea, modeling uncertainties are taken into account and robust stability of the closed-loop system with proposed control algorithm is performed.

Sensor Fusion in Control of CDRs

Embedded in everyday life, sensors are the eyes and the ears of our robots. since they are not perfect and each one of them is telling a part of the story about the surrounded world,  many researchers have tried to develop algorithms in order to fuse the data coming from many sensors into a more accurate and reliable final measurement. algorithms based on mathematical model and properties of the system under monitoring and the stochastic parameters of the sensors used. We, in CDRPM team of ARAS robotic group, are using sensors ranging from gyroscopes and accelerometers to cameras and motor load cells and encoders to calculate the required states and feedback data for controlling our suspended cable driven parallel robot using algorithms ranging from Kalman based filtering to state estimation and observer design techniques.

Project Manager: Rouhollah Khorrambakht

Related Publications

TitleAbstractYearTypePDFResearch Group
Robust cascade control of a deployable cable-driven robotIn 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
Extracting of Sagging Profile of Overhead Power Transmission Line Via Image ProcessingSagging 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 RobotDespite 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
Wave Based Control of A Deployable Cable Driven RobotCable 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
Forward Kinematics Resolution of A Deployable Cable RobotIn 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 ConstraintAdding 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
Stability Analysis and Robust PID Control of Cable-Driven Robots Considering Elasticity in CablesIn 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
Type Synthesis of 2R-T Parallel Mechanisms Based on the Screw Theory for Haptic ApplicationsaRecently 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
Adaptive robust control of fully constrained cable robots: singular perturbation approachIn 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
Optimization of KNTU Delta Robot for Pick and Place ApplicationIn 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
Adaptive robust control of fully-constrained cable driven parallel robotsIn 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
Dynamic Analysis and Control of Fully-Constrained Cable Robots with Elastic Cables: Variable Stiffness FormulationIn 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 ParametersThis 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
Online Time-Optimal Trajectory Planning in Dynamic Workspace of Cable Suspended RobotsThis 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 MethodSpherical 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 RobotAnalytic 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
Dynamic Modeling and Control of Parallel Robots With Elastic Cables: Singular Perturbation ApproachIn 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
Robust PID control of fully-constrained cable driven parallel robotsIn 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
Dynamic Modeling and Control of Parallel Robots With Elastic Cables: Singular Perturbation ApproachIn 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
Kinematic Performance Indices Analyzed on Four Planar Cable Robots via Internal AnalysisIn 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 CablesIn 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
A Positive Tensions PID Controller for a Planar Cable Robot: An Experimental StudyIn 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 AnalysisIn 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
Feasible Kinematic Sensitivity in Cable Robots Based on Interval AnalysisThe 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 RobotIn 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-SLAMParticle 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 AnalysisWorkspace 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
Dexterous Workspace Optimization of a Tricept Parallel ManipulatorThe 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
Controllable Workspace of General Cable Driven Redundant Parallel Manipulator Based on Fundamental WrenchWorkspace 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 CablesIn 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
Dynamic Aalysis and Control of Cable Driven Robots With Elastic CablesIn 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 simulations2011ConferencePDFParallel and Cable Robotics
Lagrangian Dynamics of Cable-Driven Parallel Manipulators: A Variable Mass FormulationIn 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 MechanismsThe 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
On the Optimum Design of 3-RPR Parallel MechanismsThis 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 CablesIn 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 TheoryThis 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
Modeling and Control of Cable Driven Parallel Manipulators with Elastic Cables: Singular Perturbation TheoryThis 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
Multi-Objective Scale Independent Optimization of 3-RPR Parallel MechanismsThis 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
Workspace analysis of 5-PRUR parallel mechanisms (3T2R)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
An Analytic-Iterative Redundancy Resolution Scheme for Cable-Driven Redundant Parallel ManipulatorsIn 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 ManipulatorIn 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)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
Forward Kinematic Problem and Constant Orientation Workspace of 5-RPRRR (3T2R) Parallel MechanismsThis 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 CDRPMThis 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
Forward Kinematic Analysis of A Planar Cable Driven Redundant Parallel Manipulator Using Force SensorsNewly 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 ApproachDynamic 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
Kinematic analysis of 5-RPUR (3T2R) parallel mechanismsThis 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
Wrench Feasible Workspace Analysis of Cable-Driven Parallel Manipulators Using LMI ApproachWorkspace 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
Kinematics and Jacobian Analysis of the KNTU CDRPM: A Cable Driven Redundant Parallel ManipulatorKNTU 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
Adaptive Cascade Control of the KNTU CDRPM: A Cable Driven Redundant Parallel ManipulatorThe 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 ManipulatorsOptimal 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
Dynamic Analysis of a Macro–Micro Redundantly Actuated Parallel ManipulatorIn 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 ManipulatorIn 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
Dynamics Analysis of A Redundant Parallel Manipulator Driven By Elastic CablesIn 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 ManipulatorKNTU 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
On The Control of the KNTU CDRPM: A Cable Driven Redundant Parallel ManipulatorThis 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 CDRPMKNTU 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
Dynamic and Sensitivity Analysis of KNTU CDRPM: A Cable Driven Redundant Parallel ManipulatorKNTU 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 ManipulatorsThis 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
Forward Kinematics of A Macro–Micro Parallel ManipulatorIn 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
Position Controller Synthesis for The Redundant Hydraulic Shoulder ManipulatorIn 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 lators2007ConferencePDFParallel and Cable Robotics
Dynamic Analysis of A Redundantly Actuated Parallel Manipulator:A Virtual Work ApproachIn 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
Kinematic, singularity and stiffness analysis of the hydraulic shoulder: a 3-d.o.f. redundant parallel manipulatorIn 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
Comparison of Different Methods for Computing the Forward Kinematics of a Redundant Parallel ManipulatorIn 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 ShoulderIn 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
Kinematic and Singularity Analysis of the Hydraulic ShoulderIn 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 ManipulatorIn 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
Neural Networks Approaches for Computing the Forward Kinematics of a Redundant Parallel ManipulatorIn 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
Comparison of Different Methods for Computing the Forward Kinematics of a Redundant Parallel ManipulatorIn 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 Robust Linear Controller for Flexible Joint ManipulatorsIn 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 ManipulatorIn 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
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