Experimental study on low velocity friction compensation and tracking control

Abstract

Stick-slip phenomenon is often associated with the control of low velocity motion because of the positional dependency of friction and negative damping friction that decreases as the motion speed increases. In this paper, smooth low velocity tracking control of a commercial robot joint is demonstrated experimentally using a combination of high gain PID control, fast sampling rate and high position sensor resolution. The experimental results also reveal that the main source of instability is not negative damping friction but position dependant friction that has been widely neglected. The short sampling period and a high resolution encoder have allowed us to compensate for the position dependant friction with a PID controller with sufficiently high gains.