Expansion of measurement area of hand-scraped surface using stitching method for oblique-incident interferometer

Precision flat surfaces are required for the precision surface plates of measurement instruments and the sliding components of precision machine tools. Precision flat surfaces measuring several tens of millimeters square or more are often created via hand-scraping, which is a hand-finished work. Since a hand-scraped surface is rough, the surface form cannot be measured easily using a typical vertical incident interferometer. An oblique-incident interferometer based on Abramson interferometry has been developed previously for the surface form measurement of hand-scraped surfaces. However, the field of view of the developed oblique-incident interferometer is limited to dozens of millimeters square owing to the size of the optical components and imaging sensor; consequently, the field of view is smaller than the size of the entire hand-scraped surface. A stitching method is introduced herein to expand the size of measuring area of the oblique-incident interferometer. The surface forms of a hand-scraped surface with a partially overlapped area are obtained using an oblique-incident interferometer, and the discrepancies of the inclination and height offset between the surface form data are corrected to calculate the synthetic surface form. Pattern matching is performed when aligning the overlapping area, which reduces the alignment error of the optical system. The effectiveness of the stitching method for the oblique incident interferometer is evaluated based on the cross-correlation coefficient between the datum and corrected profiles.