Optical method for testing the precision of linear motions.

An interferometric method for testing the accuracy of linear motions, such as that of drilling machines and lathe tools, is described. This method uses a diffraction grating fixed to the carriage to be tested. Only the first-order diffraction terms obtained by illuminating this grating with a laser beam are superimposed on each other by an imaging lens. An interference line pattern results that extends through the space of interfering beams and that can be analyzed with a microscope. Any deviations from the direction of motion, with the exception of deviations parallel to the grating lines, will be indicated by a movement of the fringe pattern and can be determined by counting the number of fringes passing the optical axis of the microscope. An application of this method for testing the chuck guidances in contact printing machines with a measurement accuracy of 0.2 micro is presented.