Calibrating system errors of large scale threedimensional profile measurement instruments by subaperture stitching method

This study presents a subaperture stitching method to calibrate system errors of several ∼2 m large scale 3D profile measurement instruments (PMIs). The calibration process was carried out by measuring a φ460 mm standard flat sample multiple times at different sites of the PMI with a length gauge; then the subaperture data were stitched together using a sequential or simultaneous stitching algorithm that minimizes the inconsistency (i.e., difference) of the discrete data in the overlapped areas. The system error can be used to compensate the measurement results of not only large flats, but also spheres and aspheres. The feasibility of the calibration was validated by measuring a φ1070 mm aspheric mirror, which can raise the measurement accuracy of PMIs and provide more reliable 3D surface profiles for guiding grinding, lapping, and even initial polishing processes.