Three-dimensional profile stitching measurement for large aspheric surface during grinding process with sub-micron accuracy

A novel measurement method is proposed to realize three-dimensional (3D) profile stitching for large aspheric surface. The proposed method is based on the multiple sub-regions stitching technology applying a four-axis fixture and a commercial small-range profiler. The partition of sub-regions is due to the effective profiler's range and the characteristic parameters of aspheric surface, and the measurement for each sub-region within the profiler's range is achieved through the fixture to translate and rotate the aspheric surface. Then a stitching algorithm including the multi-body theory, the invariability of curvature radiuses and the least square principle is established to reconstruct the full 3D profile. Simulations of multiple sub-regions stitching for different aspheric surfaces are performed to predict the stitching accuracy of proposed method and analyze the influence of alignment errors in Y direction caused by the rotation error along Z direction (Δβw,g). The stitching accuracy of proposed method is verified by measuring the 3D profile of an off-axis parabolic surface and an axisymmetric aspheric surface. The experimental standard deviations of stitching errors are 0.16 μm and 0.42 μm, which are less than the form errors of aspheric surface during grinding process. The results show that the proposed method achieves 3D profile stitching for large aspheric surface with sub-micron accuracy.