Disturbance Observer-Based Nonlinear Friction Compensation and Application to Table Drive System

Abstract

Nonlinear friction in machine elements is one of the inherent nonlinearities, which causes stick-slip motion in very low velocity control range and tracking errors in trajectory control due to the break-away friction and Stribeck effect. Since those greatly affect the control accuracy of servo drive systems, the appropriate modeling and/or compensation for friction is indispensable to achieve the higher performance motion.
The authors have already proposed the compensation scheme for nonlinear friction by using a remarkable disturbance observer which is designed on the basis of Coulomb friction characteristic. In this paper, the dynamic characteristic of nonlinear friction is examined by means of a friction model with elastic bristles between sliding surfaces. The analysis reveals that the nonlinear friction behaves in Coulomb friction under the dynamic motion at velocity reversal and, as a result, it is concluded clearly that the proposed disturbance observer is quite useful to estimate the instantaneous friction. Experimental results using a table drive system show the significant performance improvement of the proposed scheme in precise trajectory control.