Abstract

Accurate surface contour is required in a number of metrology applications including: manufacturing tolerance verification, surface deformation assessment, surface damage detection, surface characterization. To date, no single method has been developed that is scalable across different surface materials (specular, diffuse, variable reflectance, etc.), from small (2 in. to 2 ft.) to extremely large (60 ft.) utilizes phase-shifted fringe projection and basic triangulation in order to acquire accurate contour information from a wide variety of objects and surfaces. The image of a sinusoidal grating is projected onto the measurement surface at an offset angle from a CCD area array camera. Surface contour produces deviations in the grating fringes in the camera focal plane. Three frames of data are acquired with the grating shifted by 1/4 period between frames. Phase or contour information is extracted by comparing corresponding pixels in the three images. Techniques for contouring over large deviations in surface reflectance using multiple exposure levels have been developed. Results obtained from imaging a variety of different objects and surfaces indicate that surface features and anomalies can be extracted and measured with high accuracy. Techniques for calibrating the system and for contouring extended surfaces using sub-aperture techniques will also be discussed.

© 1990 Optical Society of America