Motion control of a robot arm using joint torque sensors

A motion control algorithm is presented for a robot arm having joint torque sensors that calculates part of the control input using the measurement of the torques at the joints. First, a dynamic model of each joint with a torque sensor is derived, which gives the inverse dynamics of the arm as recursive Newton-Euler equations consisting only of forward path computation. Then, using this model, a control law is designed by means of the computed torque method. The resultant control law is robust against parameter variations caused by loading and unloading operations and uncertainties in mass properties of links because the measured torques include information on them. The control law is experimentally applied to a second joint of a direct-drive arm with two degrees of freedom, and the experimental results illustrate the effectiveness of the proposed control algorithm