Joint torque control by a direct feedback for industrial robots

Abstract

Two joints of an industrial robot have been redesigned and fabricated to include torque sensing capability by means of strain gauges. The resulting control systems reduced the effective frictional torques of the joints from 1072 oz.-inches to 33.5 oz-inches. The stability of the closed-loop systems was analyzed by means of the describing function for limit cycles exhibited in the system, which can be removed by an insertion of phased-lead series compensating networks.