Hybrid position force control of robot manipulator with an instrumented compliant wrist

Abstract

A six DOF compliant wrist which combines passive compliance and active sensing has been developed to provide the necessary flexibility for force and contact control as well as being accurately controllable in position. This paper describes the compliant wrist and sensing mechanism design. Utilizing the sensed information from this wrist allows the apparent stiffness of the end-effector to be increased in unconstrained mode and decreased in constrained modes where the contact force is controlled. An active feedback control scheme for both position and force control is presented and the dynamic behavior of the system is analyzed. As the manipulator is partially constrained by the environment, a new hybrid control algorithm with consideration of passive compliance is proposed. The applicability of the method is demonstrated by experimental results. The entire system performance is analyzed under conditions with variable environment characteristics, controller parameters, and contact force, etc. A sinusoid surface tracking experiment was performed as an application of the hybrid control scheme and some useful results were obtained. The velocity discontinuity as the robot makes contact with, or breaks from, the environment is accommodated by the passive compliance of the wrist. The method shown is simple, economical, and applicable in industry.