When the feed direction of the slides is changed, lost motion ensues in the feed drive system, of NC machine tools. Such lost motion is usually step type and easily compensated for by using the backlash compensation function of NC. However, special cases involve an exponential type lost motion which cannot be compensated for by this method. As a result, machining accuracy of the machine tools is adversely affected. Such lost motion often occurs in large size machine tools with linear ball guides and wiper seals. This paper presents research concerning the generation mechanism and the effective compensation method of the exponential type lost motion by using the existing large size machine tools and the teststands.
