Study on the nature of stick–slip motion for high-precision table

Abstract

Friction is one of the important factors resulting in the contour error of feed servo systems for high-precision computer numerical control machine tools. The beginning criterion of friction compensation is usually based on the recognition that reverse axis velocity reaches zero at quadrant boundary in circular motion. In fact, reverse velocity cannot reach zero at quadrant boundary. This article investigates the dynamics question behind stick–slip motion, based on re-understanding friction and closed-loop control. Here, the stick–slip motions were distinguished as three kinds: positive, negative and full reversals. Moreover, it is also considered that closed-loop control system must produce inhibition to inner disturbance as to friction. The conclusion that friction compensation should take place before the velocity decreases to zero is obtained. The simulation result well illustrates the theoretical analysis of the nature of stick–slip motion. Compensation experiment shows that friction compensation considering negative friction can easily further decrease friction error in high speed.