Optical method for the calibration of raster scales

High quality techniques for the calibration of linear and circular raster scales used in photoelectric transducers and the information-measuring systems of a range of machines and scientific instruments is of particular importance, enabling them to give a more accurate performance, The most significant methods of measurement in this area are discussed in this paper, and a new approach to their calibration is presented. Most methods used for optical measurement scales apply a standard measure of angle or length and use photoelectric devices for the readout. A new half circle method for the calibration of circular scale is described. A novel idea for the measurement of linear and circular raster scales is described, given by the determination of a bias from a straight line and from a circle, respectively. This idea is implemented by applying a Moire fringe conjunction technique and the modification of Moire fringe parameters resulting. expressed by discrete functions, is discussed. (C) 2002 Elsevier Science Ltd. All rights reserved.