Development and application of a system for evaluating the feed-drive errors on computer numerically controlled machine tools

This paper describes the development and application of a system for assessing the contouring characteristics of feed drives on computer numerically controlled (CNC) machine tools. The hardware comprises two linear digital displacement sensors mounted orthogonally on the work table of a CNC machine tool and operating against a precision cube, located in the spindle. Simultaneous movements of two machine axes are measured by the sensors, in conjunction with a microcomputer. Therefore, this system is capable of detecting the difference between a programmed and actual path. By using both circular and square corner programmed test paths, the system can evaluate servo-induced errors in machine tools. Application of the system to the X- and Y-axes of a machining center is undertaken, and results are shown for a range of contouring frequencies and gain settings of the axes. Comparative tests are also undertaken using a conventional double ball link bar, which is shown to be an inferior technique for characterizing the servo-errors.