Friction and disturbance compensation for speed control of servo control systems

Generally, friction/disturbance compensation is an important issue in high-precision motion control applications. In particular, when the system under control undergoes low-speed or reversal motions, the friction force and external disturbances will degrade motion accuracy. Therefore, to achieve satisfactory motion performance, it is necessary to simultaneously compensate for the friction force and external disturbances. In this paper, an integrated motion control scheme consists of a PI-type feedback controller, a friction compensator based on the LuGre model, and a Virtual Plant Disturbance Compensator (VPDC) is developed. In particular, the VPDC is proposed to replace the PI-type Closed-loop Torque Observer (PICTO) since the latter may provide inaccurate information when used in disturbance compensation. Several experiments on load torque estimation and speed control are conducted in order to evaluate the performance of the proposed approach. Experimental results demonstrate the effectiveness of the proposed approach.