Error separation technique for measuring aspheric surface based on dual probes

In this paper, we present an error separation method based on dual probes for the swing arm profilometer to calibrate the rotary table errors. Two probes and the rotation axis of swinging arm are in a plane. The scanning tracks cross each other as both probes scan the mirror edge to edge. Since the surface heights should ideally be the same at these scanning crossings, this crossings height information can be used to calibrate the rotary table errors. But the crossings height information contains the swing arm air bearing errors and measurement errors of probes. The errors seriously affect the correction accuracy of rotary table errors. The swing arm air bearing errors and measurement errors of probes are randomly distributed, we use least square method to remove these errors. In this paper, we present the geometry of the dual probe swing arm profilometer system, and the profiling pattern made by both probes. We analyze the influence the probe separation has on the measurement results. The algorithm for stitching together the scans into a surface is also presented. The difference of the surface heights at the crossings of the adjacent scans is used to find a transformation that describes the rotary table errors and then to correct for the errors. To prove the error separation method based on a dual probe can successfully calibrate the rotary table errors, we establish SAP error model and simulate the effect of the error separation method based on a dual probe on calibrating the rotary table errors.