Adaptive PID-tracking control of muscle-like actuated compliant robotic systems with input constraints

Abstract

• Simple adaptive feedback strategies to dominate an uncertain system. • Bio-inspiration/biomechanics. • Controlling a human-upper-arm-like system: double pendulum with muscle forces. • Input constraints. In this paper, adaptive control strategies are analyzed to control a compliant robot arm in form of a double pendulum structure. Powered by antagonistic, muscle-like actuators, the controller shall enable the system to track prescribed trajectories for a desired movement of the arm, as quickly and precisely as possible. But, due to the natural muscle behavior, the control variables underly prescribed bounds: the limited control inputs are generated by muscle intensities. Therefore, feedback strategies are sought which have to be limited/saturated from the very beginning. For this, at first, simulation studies of adaptive λ -tracking controllers are performed to apply the best-rated ones to the compliant robotic system . After some model adjustments concerning the mechanics of a prototype (for experimental verification), an intensity control is determined, to divide the controller variables to the respective muscle pairs. Various numerical simulations of a system with DoF=2 show the effectiveness of the saturated controllers in set-point and tracking control. The efficiency of these controllers is verified and proven in experiments of a prototype.