Valve cone measurement using white light interference microscopy in a spherical measurement geometry

Abstract

We describe an interference microscope for valve cone angle, roundness, straightness, and waviness using scanning white light interferometry. Our unusual test geometry creates a spherical optical measurement surface centered at an optical datum point that represents the center of curvature of the mating valve needle or ball. A radial scan locates intersections of the measurement surface with respect to the datum point, and software reconstructs the conical sample surface by means of a calibrated mapping function. This flexible approach accommodates a wide range of cone angles and diameters without a change of optics. Experimental results show promising performance, including a 0.02-μm standard deviation for cone roundness, including sample removal and replacement.