High-precision contouring control of table drive system in machine tools using lost motion compensation based on static characteristics of ball screws

Abstract

Lost motion is the center of major disturbance to the contouring accuracy of NC machine tools as conventional compensation often causes over-compensation resulting in undesirable slits in reversal motion. This paper describes a model of the table drive system of a ball screw with loss of elastic energy brought by ball wedging in the nut. A simplified compensation method for that lost motion is derived from the model. The performance has been evaluated by ball bar measurement in a test machine under various conditions including the table position, movable load and feedrate. The ball bar measurement on a large double column machining center shows the generality of the proposed method.