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Based on the experimental findings of Wu and Paul 17, 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.in to 33.5 oz.in. 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.
Luh et al. (Tue,) studied this question.