Development of Optical Measurment for the Straightness of a Granite Bed Using Laser Beam Datum

The flatness of a granite bed as a guide of the column in a CMM (coordinate measuring machine)has a great influence upon the accuracy of the movement, and the straightness measurement of the guide surface using an electric level is a laborious task. Therefore, a new optical straightness measurement of high speed and high accuracy has been proposed in this paper. "High speed" means that a measuring time of within 3 minutes for 50 points during a 400 mm traverse was accomplished by gliding the measurement head on a granite surface by the action of an aerostatic bearing. "High accuracy" means that a repeatability of less than 0.16 μm was realized by measuring the position of a laser beam as a datum on a photosensor. The straightness was evaluated in terms of the vertical displacement and the integration of the inclination angle of the slider. As a result the integration value coincided well with the measured value using an electric level.