Precision machine system feedback-controlled with hexapod-type measurement device for six-degree-of-freedom relative motions between tool and workpiece

Evaluation of length measurement accuracy of passively-extensible strut

Abstract

This study deals with a feedback-controlled precision machine system based on six-degree-of-freedom (6 DOF) relative motion errors between the tool and workpiece, which are measured by a hexapod-type measurement device. The device installed between the tool spindle and surface plate measures the relative motions because the hexapod consists of six passive extensible struts equipped with linear scale units. This paper describes length measurement accuracy compared with a laser interferometer length measurement system in a test apparatus when a strut is expanded and contracted in the linear motion stage. We show measured repeatability and systematic error of the length measurement. Moreover, effects of angular motions of the linear scale unit on the length measurement error is discussed.