Output-Based Control of Robots with Variable Stiffness Actuation (original) (raw)
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On the control of redundant robots with variable stiffness actuation
2012
Abstract In this paper, the control of a redundant robotic manipulator with variable stiffness actuation is addressed. The problem of controlling simultaneously the end-effector position and stiffness exploiting the robot redundancy for the optimization of the robot configuration is considered, and the relation between the manipulator redundancy and the selection of both the joint and end-effector stiffness is discussed.
Stiffness Control Schemes of Redundant Actuated Manipulators
To execute high- value added operation, such as fine motion control and many other manufacture tasks, one need to incorporate into the control strategy inputs whose number is larger than the needed minimum. If the number of the actuators is larger than that of the degrees of mobility, the resulting redundancy is called "actuation redundancy". Actuation forces balance each other in a closed structure and do not execute effective work, but generate stiffness. One can use this property to design control strategies, most generally known as stiffness control by redundant actuation. In the paper are shown schemes of passive stiffness control, feedback stiffness control and stiffness control realized by means of antagonistic actuation. Examples of the last scheme are presented in the paper. They are called: open loop stiffness control; lower bound stiffness control; and stiffness control which utilizes the internal forces to modulate the stiffness at variable contact locations. T...
Output Feedback Regulation of a Flexible Joint Manipulator
IFAC Proceedings Volumes, 2007
In this work, the output feedback stabilization problem of a flexible joint manipulator is solved. It is assumed that only the angular position of the end link is measured. The employed approach consists of the asymptotic reconstruction of a full state feedback stabilizing control law, without using a Lyapunov function and by applying a separation principle. Firstly, a full information feedback linearizing controller is designed and, then, a dynamic output feedback (estimating the unmeasured state variables) is synthesized, which asymptotically recovers the full information control law. Digital simulations show excellent performance of the output feedback controlled state trajectories of the manipulator.
Dynamic control of flexible, kinematically redundant robot manipulators
IEEE Transactions on Robotics and Automation, 1992
The use of kinematic redundancy to avoid singularities, evade obstacles, and minimize joint torques, manipulator kinetic energy, endeffector contact forces, etc. has been among the most active research topics in the field of robotics in the past few years. However, these approaches have been associated mainly with rigid manipulators where there are no unpredictable flexural motions. When dealing with flexible manipulators, the flexibility of the system can cause undesired inaccuracy in end-effector motion. In this paper, we show how choosing the self-motion inherent in redundant arms is crucially important when flexibility is present. The selfmotion, by exciting or damping the flexural modes, alters the dynamic response of the arms. Kinematic redundancy can also be used in many cases to help damp out vibrations. This paper examines this issue and introduces new control algorithms designed to regulate the flexibility while maintaining precise tracking of the end-effector trajectory. The controllers are of the "computed torque'' type in end-effector space, and employ self-motion of the links to reduce the flexible effects.
Approaches of Stiffness Control of Parallel Manipulators with Actuation Redundancy
To execute high-value added operations, such as fine motion control and force control in assembly, deburring and many other manufacture tasks, one needs to design control strategies which would provide accurate and stable motion. One of the natural solutions of those tasks is to incorporate into the control strategy inputs whose number is larger than the needed minimum. If a manipulator possesses degrees of mobility that outnumber the dimensions of the task space, the redundancy thus obtained is called "kinematic redundancy". On the other hand, if the number of the actuators is larger than that of the degrees of mobility, the resulting redundancy is called "actuation redundancy" . While the kinematic redundancy is characteristic for serial manipulators, parallel manipulators are designed involving actuation redundancy. One can use kinematic redundancy control to realize gross motion, dexterity, obstacle avoidance etc. However, actuation redundancy control can be employed to enhance the load handling capacity of the manipulator, to minimize actuator torque and to obey the actuator constraints -[2]. Furthermore, actuation redundancy can also be used to reduce the force singularities of a parallel manipulator. Yet, the antagonistic actuation of redundant manipulators allows for the increase of their stiffness. Note that the internal forces balance each other in a closed structure and do not execute effective work, but generate stiffness. One can use this property to design control strategies, most generally known as stiffness control by redundant actuation . The strategies are part of impedance control schemes where one can directly follow the ratio "force/displacement", and not each quantity separately. These considerations imply the necessity to describe the desired dynamic relationship between the end-effector force and position. The present study aims at the review of known schemes of stiffness control by mean of redundant actuation. The aim of the study is to design and experiment approaches of specifying a desired stiffness whit is appropriate for the manipulator control. The present work proposes a stiffness control scheme of a serialparallel manipulator with actuation redundancy.
Feedforward control of Variable Stiffness Joints robots for vibrations suppression
2017 IEEE International Conference on Robotics and Automation (ICRA), 2017
This paper presents a new feedforward controller based on a continuous-time finite impulse response filter, designed to minimize the vibrations that usually affect robot manipulators with elastic joints. In particular, Variable Stiffness Joints (VSJ) robots are considered, since they are usually characterized by a very low level of damping which makes the problem of the oscillations quite important. The proposed approach allows to simplify the overall control structure of VSJ robots, which is based on a decentralized control of each servomotor, imposing the desired position and the desired stiffness at each joint, and on a novel feedforward control, filtering the reference signals. After analyzing some of the filter properties and the method for the parameters choice, experimental results on a VSJ robot demonstrate the importance of the proposed filtering action for minimizing vibrations and oscillations.
IEEE/RSJ International Conference on Intelligent Robots and Systems
In this paper a simple tracking controller for a variable stiffness joint is proposed. System dynamics is considered unknown. The controller guarantees link and stiffness motor position performance specifications that have been a-priori set, utilizing full state feedback. Simulation results on the previously published CompAct-VSA joint validate the efficiency of the proposed control approach.
Cartesian impedance control of redundant robots: recent results with the DLR-light-weight-arms
2003 IEEE International Conference on Robotics and Automation (Cat. No.03CH37422), 2003
This paper addresses the problem of impedance control for flexible joint robots based on a singular perturbation approach. Some aspects of the impedance controller, which turned out to be of high practical relevance during applications are then addressed, such as the implementation of nullspace stiffness for redundant manipulators, the avoiding of mass matrix decoupling and the related design of the desired damping matrix. Finally, the proposed methods are validated through measurements on the DLR robot.
Mathematical Problems in Engineering
Performance evaluation of trajectory tracking for a rotary flexible joint system is demonstrated in this paper. The robust and converse dynamic (RCD) technique is proposed and implemented for this evaluation. This control methodology is of the left inversion type, i.e., the control inputs are obtained by means of plant output error feedback. RCD control encompasses the baseline inverse (BI) control and sliding mode control-based discontinuous control element. The baseline inverse controller enforces the prescribed servo (virtual) constraints that represent the control objectives. The control objectives of the baseline inverse controller are enclosed in the form of servo (virtual) constraints which are inverted using Moore–Penrose Generalized Inverse (MPGI) to solve for the baseline control law. To boost the robust attributes against parametric uncertainties and disturbances, a discontinuous control function is augmented with baseline controller such that semiglobal practical stabili...