Error compensation for the linear error of a universal tool microscope's scale system

The method of linear error compensation for the magnification error generated by the 1x asymmetrical optical paths in longitudinal scale system of a universal tool microscope is presented. The micro-displacements of scale images are used for the compensation of the scale's linear error based on the properties of off-axis, out of focus, and focal length inequality. The innovative optical paths design is described in the paper. A detailed analysis of the principle of error compensation is presented. Extended formula for the magnification, defocus, and off-axis errors are also derived. The relationship between the calibration result and slope of formula is obtained to benefit the analysis and application on-site. The influence caused by the change of magnification parameters also is discussed. Indication error of one-meter longitudinal coordinate can be achieved less than 2.5 um after compensation.