A comparison of control laws for a cooperative robot system

A two armed master-slave robot was modeled; simulations were run with a variety of compensation schemes using a payload with a compressive spring of 10,000 N/m and a preload force of 25 N against the payload. The slave arm was at first controlled by a simple linear force controller; this was inadequate with position step commands in that the force response oscillated greatly and resulted in crushing or dropping the payload. A low pass prefilter in the position command path corrected this, but so slowed the position response that significant tasks could not be carried out. These results illustrate the two way physical linkage between position output and force regulation dynamics. A second order, band pass cross filter sending position command as input into the forward loop of the force controller, enabled adequate position control dynamics and kept the payload force excursions to a minimum.