Adaptive Impedance Control Subject to Torque Constraints in a Hydraulic Robot.

Abstract

This paper is concerned with the adaptive impedance control for a hydraulic robot. Because of joint torque constraints depending on the angular velocity, the parameter adaptation and the robot motion sometimes exhibit instabilities. In order to avoid the instabilities, an adaptive control scheme with a modification of Slotine's method is proposed and implemented in a 2-link articulated hydraulic robot. Stable impedance control is attained in the range of small external force input even if the dynamical parameters are unknown. The system is shown to be stable even though the saturation of the joint torque occurs due to application of large external force. Moreover, the effect of the torque control subsystem characteristics on the performance of the whole adaptive impedance control system is investigated.