Off-axis aspheric surface measurement by coordinate contour measuring machine

A method is proposed to measure off-axis aspherical mirrors with a circular flat base,a rectangular flat base and a family of parallel lines that cut the circular flat base by a coordinate measurement machine(CMM).In response to the base features above,workpiece coordinate system is designed,and the positioning points used to establish the workpiece coordinate system are defined.The 3D-coordinates point-cloud data on the off-axis mirrors are obtained with automatic measurement of single points schema by CMM,and then,the off-axis aspheric surface data processing model for these error corrections is built.Compared with the data by the theoretical model,the surface error of an actual off-axis aspheric surface is obtained.All the pre-polishing processes are guided according to the measurement results.