Calibration of Closed Loop Controllers for Setting Impedances in Force-Reflecting Systems

Abstract

Abstract This paper discusses a new method of impedance control that has been successfully implemented on the master robot of a teleoperation system. The method involves calibrating the robot to quantify the effect of adjustable controller parameters on the impedances along its different axes. The empirical equations relating end-effector impedance to the controller’s feedback gains are obtained by performing system identification tests along individual axes of the robot. With these equations, online control of end-effector stiffness and damping is possible without having to monitor joint torques or solving complex algorithms. Hard contact conditions and compliant interfaces have been effectively demonstrated on a telemanipulation test-bed using appropriate combinations of stiffness and damping settings obtained by this method. Since the method is general in nature and can be used for finding possible relations between controllable parameters and quantifiable output behaviour of a system, it can be extended to calibrating and controlling impedances in poorly modeled robot-actuator systems. A limitation of this method is that the actuator being modeled must have very little friction.