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Gerd Hirzinger - One of the best experts on this subject based on the ideXlab platform.

  • on the passivity based impedance control of Flexible Joint robots
    IEEE Transactions on Robotics, 2008
    Co-Authors: Alin Albuschaffer, Andreas Kugi, Gerd Hirzinger
    Abstract:

    In this paper, a novel type of impedance controllers for Flexible Joint robots is proposed. As a target impedance, a desired stiffness and damping are considered without inertia shaping. For this problem, two controllers of different complexity are proposed. Both have a cascaded structure with an inner torque feedback loop and an outer impedance controller. For the torque feedback, a physical interpretation as a scaling of the motor inertia is given, which allows to incorporate the torque feedback into a passivity-based analysis. The outer impedance control law is then designed differently for the two controllers. In the first approach, the stiffness and damping terms and the gravity compensation term are designed separately. This outer control loop uses only the motor position and velocity, but no noncollocated feedback of the Joint torques or link side positions. In combination with the physical interpretation of torque feedback, this allows us to give a proof of the asymptotic stability of the closed-loop system based on the passivity properties of the system. The second control law is a refinement of this approach, in which the gravity compensation and the stiffness implementation are designed in a combined way. Thereby, a desired static stiffness relationship is obtained exactly. Additionally, some extensions of the controller to viscoelastic Joints and to Cartesian impedance control are given. Finally, some experiments with the German Aerospace Center (DLR) lightweight robots verify the developed controllers and show the efficiency of the proposed control approach.

  • a unified passivity based control framework for position torque and impedance control of Flexible Joint robots
    The International Journal of Robotics Research, 2007
    Co-Authors: Alin Albuschaffer, Gerd Hirzinger
    Abstract:

    This paper describes a general passivity-based framework for the control of Flexible Joint robots. Recent results on torque, position, as well as impedance control of Flexible Joint robots are summarized, and the relations between the individual contributions are highlighted. It is shown that an inner torque feedback loop can be incorporated into a passivity-based analysis by interpreting torque feedback in terms of shaping of the motor inertia. This result, which implicitly was already included in earlier work on torque and position control, can also be used for the design of impedance controllers. For impedance control, furthermore, potential energy shaping is of special interest. It is shown how, based only on the motor angles, a potential function can be designed which simultaneously incorporates gravity compensation and a desired Cartesian stiffness relation for the link angles. All the presented controllers were experimentally evaluated on DLR lightweight robots and their performance and robustness shown with respect to uncertain model parameters. Experimental results with position controllers as well as an impact experiment are presented briefly, and an overview of several applications is given in which the controllers have been applied.

  • a passivity based cartesian impedance controller for Flexible Joint robots part ii full state feedback impedance design and experiments
    International Conference on Robotics and Automation, 2004
    Co-Authors: Alin Albuschaffer, Christian Ott, Gerd Hirzinger
    Abstract:

    The paper presents a Cartesian impedance controller for Flexible Joint robots based on the feedback of the complete state of the system, namely the motor position, the Joint torque and their derivatives. The approach is applied to a quite general robot model, in which also a damping element is considered in parallel to the Joint stiffness. Since passivity and asymptotic stability of the controller hold also for varying damping matrices, some possibilities of designing those gain matrices (depending on the actual inertia matrix) are addressed. The passivity of the controller relies on the usage of only motor side measurements for the position feedback. A method is introduced, which provides the exact desired link side stiffness based on this motor position information. Experimental results are validating the proposed controller.

  • a globally stable state feedback controller for Flexible Joint robots
    Advanced Robotics, 2001
    Co-Authors: Alin Albuschaffer, Gerd Hirzinger
    Abstract:

    The paper addresses the problem of controlling the Joints of a Flexible Joint robot with a state feedback controller and proposes a gradual way of extending such a controller towards the complete decoupling of the robot dynamics. The global asymptotic stability for the state feedback controller with gravity compensation is proven, followed by some theoretical remarks on its passivity properties. By proper parameterization, the proposed controller structure can implement a position, a stiffness or a torque controller. Experimental results on the DLR lightweight robots validate the method.

G. Hirzinger - One of the best experts on this subject based on the ideXlab platform.

Alin Albuschaffer - One of the best experts on this subject based on the ideXlab platform.

  • on the passivity based impedance control of Flexible Joint robots
    IEEE Transactions on Robotics, 2008
    Co-Authors: Alin Albuschaffer, Andreas Kugi, Gerd Hirzinger
    Abstract:

    In this paper, a novel type of impedance controllers for Flexible Joint robots is proposed. As a target impedance, a desired stiffness and damping are considered without inertia shaping. For this problem, two controllers of different complexity are proposed. Both have a cascaded structure with an inner torque feedback loop and an outer impedance controller. For the torque feedback, a physical interpretation as a scaling of the motor inertia is given, which allows to incorporate the torque feedback into a passivity-based analysis. The outer impedance control law is then designed differently for the two controllers. In the first approach, the stiffness and damping terms and the gravity compensation term are designed separately. This outer control loop uses only the motor position and velocity, but no noncollocated feedback of the Joint torques or link side positions. In combination with the physical interpretation of torque feedback, this allows us to give a proof of the asymptotic stability of the closed-loop system based on the passivity properties of the system. The second control law is a refinement of this approach, in which the gravity compensation and the stiffness implementation are designed in a combined way. Thereby, a desired static stiffness relationship is obtained exactly. Additionally, some extensions of the controller to viscoelastic Joints and to Cartesian impedance control are given. Finally, some experiments with the German Aerospace Center (DLR) lightweight robots verify the developed controllers and show the efficiency of the proposed control approach.

  • a unified passivity based control framework for position torque and impedance control of Flexible Joint robots
    The International Journal of Robotics Research, 2007
    Co-Authors: Alin Albuschaffer, Gerd Hirzinger
    Abstract:

    This paper describes a general passivity-based framework for the control of Flexible Joint robots. Recent results on torque, position, as well as impedance control of Flexible Joint robots are summarized, and the relations between the individual contributions are highlighted. It is shown that an inner torque feedback loop can be incorporated into a passivity-based analysis by interpreting torque feedback in terms of shaping of the motor inertia. This result, which implicitly was already included in earlier work on torque and position control, can also be used for the design of impedance controllers. For impedance control, furthermore, potential energy shaping is of special interest. It is shown how, based only on the motor angles, a potential function can be designed which simultaneously incorporates gravity compensation and a desired Cartesian stiffness relation for the link angles. All the presented controllers were experimentally evaluated on DLR lightweight robots and their performance and robustness shown with respect to uncertain model parameters. Experimental results with position controllers as well as an impact experiment are presented briefly, and an overview of several applications is given in which the controllers have been applied.

  • a passivity based cartesian impedance controller for Flexible Joint robots part ii full state feedback impedance design and experiments
    International Conference on Robotics and Automation, 2004
    Co-Authors: Alin Albuschaffer, Christian Ott, Gerd Hirzinger
    Abstract:

    The paper presents a Cartesian impedance controller for Flexible Joint robots based on the feedback of the complete state of the system, namely the motor position, the Joint torque and their derivatives. The approach is applied to a quite general robot model, in which also a damping element is considered in parallel to the Joint stiffness. Since passivity and asymptotic stability of the controller hold also for varying damping matrices, some possibilities of designing those gain matrices (depending on the actual inertia matrix) are addressed. The passivity of the controller relies on the usage of only motor side measurements for the position feedback. A method is introduced, which provides the exact desired link side stiffness based on this motor position information. Experimental results are validating the proposed controller.

  • a globally stable state feedback controller for Flexible Joint robots
    Advanced Robotics, 2001
    Co-Authors: Alin Albuschaffer, Gerd Hirzinger
    Abstract:

    The paper addresses the problem of controlling the Joints of a Flexible Joint robot with a state feedback controller and proposes a gradual way of extending such a controller towards the complete decoupling of the robot dynamics. The global asymptotic stability for the state feedback controller with gravity compensation is proven, followed by some theoretical remarks on its passivity properties. By proper parameterization, the proposed controller structure can implement a position, a stiffness or a torque controller. Experimental results on the DLR lightweight robots validate the method.

Jean-jacques E. Slotine - One of the best experts on this subject based on the ideXlab platform.

  • brief paper adaptive task space regulation of rigid link Flexible Joint robots with uncertain kinematics
    Automatica, 2008
    Co-Authors: Chao Liu, Chien Chern Cheah, Jean-jacques E. Slotine
    Abstract:

    In this paper, an adaptive control scheme is proposed for the regulation problem of rigid-link Flexible-Joint (RLFJ) robots with uncertain kinematics. Existing research works in literature on RLFJ robot control assume exact knowledge of the kinematics of robot, and no result that can deal with kinematics uncertainty in RLFJ robot has been proposed so far. This paper presents the first study addressing this problem. The adaptive control scheme proposed can deal with the kinematics uncertainty and uncertainties in both link and actuator dynamics of the RLFJ robot system. A nonlinear observer is designed to avoid the use of acceleration due to the fourth-order overall dynamics. Asymptotic stability of the closed-loop system is shown and sufficient conditions are presented to guarantee the stability. Simulation results are provided to illustrate the effectiveness of the proposed control method.

  • adaptive task space regulation of rigid link Flexible Joint robots with uncertain kinematics
    International Conference on Robotics and Automation, 2006
    Co-Authors: Chao Liu, Chien Chern Cheah, Jean-jacques E. Slotine
    Abstract:

    Joint flexibility is an important factor to consider in the robot control design if high performance is expected for the robot manipulators. The research work on control of rigid-link Flexible-Joint (RLFJ) robot in the literature has assumed that the kinematics of the robot is known exactly. There have been no results so far that can deal with the kinematics uncertainty in RLFJ robot. In this paper, we present the first study on this problem and propose an adaptive regulation method which can deal with the kinematics uncertainty and uncertainties in both link and motor dynamics of the RLFJ robot system. An observer is designed to avoid the use of acceleration due to the fourth-order overall dynamics. Sufficient conditions are derived to guarantee the asymptotic stability of the closed-loop system. Simulation result illustrates the effectiveness of proposed control method

Guanrong Chen - One of the best experts on this subject based on the ideXlab platform.

  • fuzzy pid control of a Flexible Joint robot arm with uncertainties from time varying loads
    IEEE Transactions on Control Systems and Technology, 1997
    Co-Authors: Heidar A Malki, Dave Misir, D Feigenspan, Guanrong Chen
    Abstract:

    This paper presents the design and experiment of a fuzzy proportional integral derivative (PID) controller for a Flexible-Joint robot arm with uncertainties from time-varying loads. Experimental results have shown remarkable tracking performance of this fuzzy PID controller, and have convincingly demonstrated that fuzzy logic control can be used for Flexible-Joint robot arms with uncertainties and it is quite robust. In this paper, the fuzzy PID controller is first described briefly, using a simple and practical PD+I controller configuration. This configuration preserves the linear structure of the conventional PD+I controller, but has nonconstant gains: the proportional, integral, and derivative gains are nonlinear functions of their input signals, which have self-tuning (adaptive) capabilities in set-point tracking performance. Moreover, these variable gains make the fuzzy PID controller robust with faster response time and less overshoot than its conventional counterpart. The proposed design was tested using a Flexible-Joint robot arm driven by a DC motor in a laboratory, where the arm was experienced with time-varying loads. Control performance by the conventional and fuzzy PID controllers for such a laboratory robotic system are both included in this paper for comparison.

  • analytic closed form solutions for suboptimal trajectory planning of single link Flexible Joint robot arms
    International Conference on Robotics and Automation, 1992
    Co-Authors: Guanrong Chen
    Abstract:

    A suboptimal trajectory planning problem for single-link Flexible-Joint robot arms is studied. A global feedback-linearization technique is first applied to reformulate the nonlinear constrained optimization as a suboptimal interpolation problem. Then the unique analytic suboptimal solution for the problem is obtained in closed form. Simulation results are given to show the effectiveness of the method. >