Characteristics and compensation of friction at velocity reversal

This paper analyzes the characteristics of pre-sliding friction of the X-Y table of a CNC machining center at velocity reversal, and presents a simple and effective method of friction compensation based on these characteristics. During velocity reversal, friction transits from the pre-sliding regime into the sliding regime, and it must not be considered as a sudden discontinuity for accurate control. In order to distinguish its regime at velocity reversal, the relationship between the transition time and the acceleration at zero velocity is investigated using the spring-like friction model. Furthermore, the experimental observations prove this relation. Using the transition time estimated from the relation without any accurate velocity information, the friction at velocity reversal can be well compensated and the experimental results show its effectiveness