Soichi Ibaraki, Kyoto University

There is no methodology established in today's industries to measure two-dimensional motion errors, such as the straightness error or the squareness error, of high-precision and ultra-precision machine tools. The cross grid encoder is a diffraction grating type optical encoder that can measure two-dimensional position of a optical head by using a grid plate where grids are aligned orthogonal to each other. As a basis to establish a measurement methodology of two-dimensional motion accuracy of high-precision and ultra-precision machine tools by using the cross grid encoder, this paper presents a self-calibration scheme of a measurement error of the cross grid encoder caused mainly by the misalignement of grids. The measurement error corresponding to the location on the grid plate is calibrated by comparing three measurements taken with different orientation of the grid plate. It is experimentally validated that the measurement error of the cross grid encoder is reduced by about 80% by applying the self-calibration and the compensation of measurement errors.