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Fathi H. Ghorbel - One of the best experts on this subject based on the ideXlab platform.
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Modeling and set point control of Closed-Chain mechanisms: Theory and experiment
IEEE Transactions on Control Systems Technology, 2000Co-Authors: Fathi H. Ghorbel, Ruvinda Gunawardana, Olivier Chételat, Roland LongchampAbstract:We derive a reduced model, that is, a model in terms of\nindependent generalized coordinates, for the equations of motion of\nClosed-Chain mechanisms. We highlight the fact that the model has two\nspecial characteristics which make it different from models of\nopen-Chain mechanisms. First, it is defined locally in the generalized\ncoordinates. We therefore characterize the domain of validity of the\nmodel in which the mechanism satisfies the constraints and is not in a\nsingular configuration. Second, it is an implicit model, that is, parts\nof the equations of motion are not expressed explicitly. Despite the\nimplicit nature of the equations of motion, we show that Closed-Chain\nmechanisms still satisfy a skew symmetry property, and that proportional\nderivative (PD)-based control with so-called simple gravity compensation\nguarantees (local) asymptotic stability. We discuss the computational\nissues involved in the implementation of the proposed controller. The\nproposed modeling and PD control approach is illustrated experimentally\nusing the Rice planar delta robot which was built to experiment with\nClosed-Chain mechanisms
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PD Control of Closed-Chain Mechanical Systems: An Experimental Study
IFAC Proceedings Volumes, 1997Co-Authors: Ruvinda Gunawardana, Fathi H. GhorbelAbstract:Abstract In this paper, we briefly review recent results by the authors on the formulation of the equations of motion of Closed-Chain mechanisms and the development of PD control strategies with guaranteed Lyapunov asymptotic stability. We then introduce and derive the equations of motion of the Rice Planar Delta Robot which was designed and built at Rice University as a test bed to perform control experiments for Closed-Chain mechanisms. Finally, we present simulation as well as experimental results to illustrate the successful application of PD plus simple gravity control strategy for this class of dynamical systems.
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and PD Control of Closed-Chain Mechanical Systems
1995Co-Authors: Fathi H. GhorbelAbstract:In this paper, we review the structure of a reduced model for Closed-Chain mechanical systems originally proposed in [2], and highlight the fact that the model has two special characteristics which make it different from models of opendain mechanical systems. First, it is defined locally, and second it is an implicit model. We show that Closed-hain systems satisfy the property of skew symmetry. We therefore propose PD-based control strategies with full as well as simple gravity compensation and discuss and compare the computational issues involved in the implementation of both controllers.
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Modeling and PD control of Closed-Chain mechanical systems
Proceedings of 1995 34th IEEE Conference on Decision and Control, 1Co-Authors: Fathi H. GhorbelAbstract:In this paper, we review the structure of a reduced model for Closed-Chain mechanical systems originally proposed by Ghorbel, Chetelat and Longchamp (1994), and highlight the fact that the model has two special characteristics which make it different from models of open-Chain mechanical systems. First, it is defined locally, and second it is an implicit model. We show that Closed-Chain systems satisfy the property of skew symmetry. We therefore propose PD-based control strategies with full as well as simple gravity compensation and discuss and compare the computational issues involved in the implementation of both controllers.
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A validation study of PD control of a Closed-Chain mechanical system
Proceedings of the 36th IEEE Conference on Decision and Control, 1Co-Authors: Fathi H. Ghorbel, Ruvinda GunawardanaAbstract:In this paper, we briefly review recent results by the authors on the formulation of the equations of motion of Closed-Chain mechanisms and the development of PD control strategies with guaranteed Lyapunov asymptotic stability. We then introduce and derive the equations of motion of the Rice Planar Delta Robot which was designed and built at Rice University as a test bed to perform control experiments for Closed-Chain mechanisms. Finally, we present simulation as well as experimental results to illustrate the successful application of PD plus simple gravity control strategy for this class of dynamical systems.
B. Andrei Bernevig - One of the best experts on this subject based on the ideXlab platform.
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Parafermionic phases with symmetry breaking and topological order
Physical Review B, 2016Co-Authors: A. Alexandradinata, Nicolas Regnault, Chen Fang, Matthew J. Gilbert, B. Andrei BernevigAbstract:Parafermions are the simplest generalizations of Majorana fermions that realize topological order. We propose a less restrictive notion of topological order in 1D open Chains, which generalizes the seminal work by Fendley [J. Stat. Mech., P11020 (2012)]. The first essential property is that the groundstates are mutually indistinguishable by local, symmetric probes, and the second is a generalized notion of zero edge modes which cyclically permute the groundstates. These two properties are shown to be topologically robust, and applicable to a wider family of topologically-ordered Hamiltonians than has been previously considered. An an application of these edge modes, we formulate a new notion of twisted boundary conditions on a Closed Chain, which guarantees that the Closed-Chain groundstate is topological, i.e., it originates from the topological manifold of degenerate states on the open Chain. Finally, we generalize these ideas to describe symmetry-breaking phases with a parafermionic order parameter. These exotic phases are condensates of parafermion multiplets, which generalizes Cooper pairing in superconductors. The stability of these condensates are investigated on both open and Closed Chains.
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Parafermionic phases with symmetry breaking and topological order
Phys.Rev.B, 2016Co-Authors: A. Alexandradinata, Nicolas Regnault, Chen Fang, Matthew J. Gilbert, B. Andrei BernevigAbstract:Parafermions are the simplest generalizations of Majorana fermions that realize topological order. We propose a less restrictive notion of topological order in one-dimensional open Chains, which generalizes the seminal work by Fendley [J. Stat. Mech. (2012) P1102010.1088/1742-5468/2012/11/P11020]. The first essential property is that the ground states are mutually indistinguishable by local, symmetric probes, and the second is a generalized notion of zero edge modes which cyclically permute the ground states. These two properties are shown to be topologically robust, and applicable to a wider family of topologically ordered Hamiltonians than has been previously considered. As an application of these edge modes, we formulate a notion of twisted boundary conditions on a Closed Chain, which guarantees that the Closed-Chain ground state is topological, i.e., it originates from the topological manifold of the open Chain. Finally, we generalize these ideas to describe symmetry-breaking phases with a parafermionic order parameter. These exotic phases are condensates of parafermion multiplets, which generalize Cooper pairing in superconductors. The stability of these condensates is investigated on both open and Closed Chains.
Sungbok Kim - One of the best experts on this subject based on the ideXlab platform.
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ICRA - Joint actuation switching in Closed-Chain mechanisms for high task adaptability
Proceedings 1999 IEEE International Conference on Robotics and Automation (Cat. No.99CH36288C), 1Co-Authors: Sungbok KimAbstract:Presents the smooth joint actuation switching in a Closed Chain mechanism for achieving high task adaptability. First, the kinematic characteristics of a Closed-Chain mechanism possibly with actuational redundancy is formulated, and the effect of the distribution of actuating joints is analyzed. Next, with respect to the task compatibility in control efficiency or accuracy, the joint actuation switching of a Closed-Chain mechanism is optimized, and the discontinuity in joint torque incurred due to the abrupt joint actuation switching is described. Then, the smooth transition in joint actuation of a Closed-Chain mechanism is proposed, based on the redundancy resolution associated with the augmented statics defined for a short transition interval. Simulation results for a planar Closed-Chain mechanism are given.
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ICRA - Adjustable manipulability of Closed-Chain mechanisms through joint freezing and joint unactuation
Proceedings. 1998 IEEE International Conference on Robotics and Automation (Cat. No.98CH36146), 1Co-Authors: Sungbok KimAbstract:This paper presents the adjustment of the manipulability of a Closed-Chain mechanism using joint freezing/releasing and joint unactuation/actuation, leading to the improved task adaptability. A Closed-Chain mechanism under consideration consists of multiple redundant subChains and individual joints can be put into frozen, actuated or unactuated mode, as needed. First, the joint freezing and joint unactuation allowed for a Closed-Chain mechanism are examined, which limits the possible combinations of joint modes. Second, the kinematics of a Closed-Chain mechanism is formulated, taking into account joint freezing and joint unactuation. Third, the manipulability ellipsoids of a Closed-Chain mechanism with/without joint freezing and/or joint unactuation are defined and compared. Finally, the wide range of the manipulability of a Closed-Chain mechanism due to the changes of joint modes is exemplified.
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IROS - Optimal redundant actuation of Closed-Chain mechanisms for high operational stiffness
Proceedings. 2000 IEEE RSJ International Conference on Intelligent Robots and Systems (IROS 2000) (Cat. No.00CH37113), 1Co-Authors: Sungbok KimAbstract:This paper presents the optimal redundant actuation of Closed-Chain mechanisms for robotic applications requiring a high degree of operational stiffness, as well as the balance of force applicability and dexterity. First, by taking into account the distribution of active joints, the statics and the operational stiffness of a Closed-Chain mechanism are formulated with the analysis on the effects of actuation redundancy. Second, for given joint torque limit, task force, allowable disturbance, and allowable deflection, the task execution conditions of a Closed-Chain mechanism are derived along with the efficient testing formulas. Third, to achieve high stiffness while maintaining dexterity, the active joint distribution and the internal joint torque of a Closed-Chain mechanism is optimized. Finally, the simulation results for the optimal redundant actuation of a planar Closed-Chain mechanism are given.
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IROS - Improved task adaptability of open/Closed Chain mechanisms through continuous joint mode conversion
Proceedings 1999 IEEE RSJ International Conference on Intelligent Robots and Systems. Human and Environment Friendly Robots with High Intelligence and, 1Co-Authors: Sungbok Kim, Jong Gap ChoiAbstract:Presents a simple and effective way of improving the task adaptability of redundant open/Closed Chain mechanisms based on joint locking/unactuation and continuous joint mode conversion. The joint locking/unactuation in an open/Closed Chain mechanism is incorporated in the kinematics/statics of the mechanism, and the varying kinematic characteristics depending on the distribution of frozen/passive joints is analyzed. The discontinuity in joint velocity/torque of an open/Closed Chain mechanism, incurred when the joint mode switching is done abruptly, is described. Two methods of the continuous joint mode conversion for a short transition interval are proposed and compared. Finally, simulation results for a planar redundant open Chain mechanism employing joint locking are given.
Ruvinda Gunawardana - One of the best experts on this subject based on the ideXlab platform.
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Modeling and set point control of Closed-Chain mechanisms: Theory and experiment
IEEE Transactions on Control Systems Technology, 2000Co-Authors: Fathi H. Ghorbel, Ruvinda Gunawardana, Olivier Chételat, Roland LongchampAbstract:We derive a reduced model, that is, a model in terms of\nindependent generalized coordinates, for the equations of motion of\nClosed-Chain mechanisms. We highlight the fact that the model has two\nspecial characteristics which make it different from models of\nopen-Chain mechanisms. First, it is defined locally in the generalized\ncoordinates. We therefore characterize the domain of validity of the\nmodel in which the mechanism satisfies the constraints and is not in a\nsingular configuration. Second, it is an implicit model, that is, parts\nof the equations of motion are not expressed explicitly. Despite the\nimplicit nature of the equations of motion, we show that Closed-Chain\nmechanisms still satisfy a skew symmetry property, and that proportional\nderivative (PD)-based control with so-called simple gravity compensation\nguarantees (local) asymptotic stability. We discuss the computational\nissues involved in the implementation of the proposed controller. The\nproposed modeling and PD control approach is illustrated experimentally\nusing the Rice planar delta robot which was built to experiment with\nClosed-Chain mechanisms
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PD Control of Closed-Chain Mechanical Systems: An Experimental Study
IFAC Proceedings Volumes, 1997Co-Authors: Ruvinda Gunawardana, Fathi H. GhorbelAbstract:Abstract In this paper, we briefly review recent results by the authors on the formulation of the equations of motion of Closed-Chain mechanisms and the development of PD control strategies with guaranteed Lyapunov asymptotic stability. We then introduce and derive the equations of motion of the Rice Planar Delta Robot which was designed and built at Rice University as a test bed to perform control experiments for Closed-Chain mechanisms. Finally, we present simulation as well as experimental results to illustrate the successful application of PD plus simple gravity control strategy for this class of dynamical systems.
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A validation study of PD control of a Closed-Chain mechanical system
Proceedings of the 36th IEEE Conference on Decision and Control, 1Co-Authors: Fathi H. Ghorbel, Ruvinda GunawardanaAbstract:In this paper, we briefly review recent results by the authors on the formulation of the equations of motion of Closed-Chain mechanisms and the development of PD control strategies with guaranteed Lyapunov asymptotic stability. We then introduce and derive the equations of motion of the Rice Planar Delta Robot which was designed and built at Rice University as a test bed to perform control experiments for Closed-Chain mechanisms. Finally, we present simulation as well as experimental results to illustrate the successful application of PD plus simple gravity control strategy for this class of dynamical systems.
Wenjun Zhang - One of the best experts on this subject based on the ideXlab platform.
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tracking control of a Closed Chain five bar robot with two degrees of freedom by integration of an approximation based approach and mechanical design
Systems Man and Cybernetics, 2012Co-Authors: Long Cheng, Zengguang Hou, Min Tan, Wenjun ZhangAbstract:The trajectory tracking problem of a Closed-Chain five-bar robot is studied in this paper. Based on an error transformation function and the backstepping technique, an approximation-based tracking algorithm is proposed, which can guarantee the control performance of the robotic system in both the stable and transient phases. In particular, the overshoot, settling time, and final tracking error of the robotic system can be all adjusted by properly setting the parameters in the error transformation function. The radial basis function neural network (RBFNN) is used to compensate the complicated nonlinear terms in the Closed-loop dynamics of the robotic system. The approximation error of the RBFNN is only required to be bounded, which simplifies the initial “trail-and-error” configuration of the neural network. Illustrative examples are given to verify the theoretical analysis and illustrate the effectiveness of the proposed algorithm. Finally, it is also shown that the proposed approximation-based controller can be simplified by a smart mechanical design of the Closed-Chain robot, which demonstrates the promise of the integrated design and control philosophy.
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adaptive tracking control of hybrid machines a Closed Chain five bar mechanism case
IEEE-ASME Transactions on Mechatronics, 2011Co-Authors: Long Cheng, Zengguang Hou, Min Tan, Yingzi Lin, Jian Huang, Wenjun ZhangAbstract:This paper considers the trajectory tracking problem of hybrid machines. A hybrid machine here refers to a machine that is driven by the constant velocity (CV) motors and servomotors in a proper configuration. The hybrid machine is a meaningful tradeoff between task flexibility and power capacity. However, this system has brought a new challenge to control due to the velocity fluctuation in the CV motor. The velocity fluctuation problem is caused mainly by the uncontrollable input current and the time-varying workload. In addition, the dynamic parameters are uncertain, which further increases the control difficulty. In this paper, we propose an adaptive control law for the trajectory tracking and demonstrate the effectiveness of this control law on a 2-DOF Closed-Chain five-bar hybrid mechanism driven by one servomotor and one CV motor. The principle of the proposed controller is to properly design the servomotor control input that can compensate not only the uncertainty in the servomotor but also the uncertainty in the CV motor. By the proposed adaptive control law, it can be theoretically proved that the position/velocity tracking errors of the joint associated with the servomotor and the velocity tracking error of the joint associated with the CV motor are convergent to zero as time goes to infinity. Finally, the simulation examples are given to illustrate the effectiveness of the proposed method.