Experimental study on the measurement of the curvature radius of a spherical grid

To ensure the manufacturing accuracy of a spherical grid, it is necessary t o accurately measure the curvature radius, which is one of its important pa rameters. A measurement system consisting of precision machinery, a microsc ope, CCD camera, an image processing unit, a grating measurement system, an d a computer control is described. By using image processing, noncontact al ignment with high speed and accuracy is achieved. The curvature radius of t he grid is obtained accurately through applying least-square fitting for mu ltiple points of the grid. The measuring principle and experiments based on the principle are described. The results show that the repeatability of th e measurement is up to +/-3 mum. (C) 2001 Society of Photo-Optical Instrume ntation Engineers.