High-precision binocular fringe reflectometry based on normal vector consistency

Modern manufacturing industry has a strong measurement demand of specular surfaces. Fringe reflection method has the advantages of simple structure, low cost, high accuracy, and is becoming more and more popular for 3D measurement of these surfaces. Most of previous methods achieve the fringe reflection measurement using a single camera, and suffer the problem of gradient-height ambiguity. Here, a binocular fringe reflectometry method is proposed with the surface normal is obtained through normal vector consistency of the measured surface. To enhance the computation efficiency, a polar constraint and bisection method are also developed to get the matching points on the two camera images. After that the normal vector and the gradient distribution can be calculated. The 3D measurement result can be obtained according to integral reconstruction algorithm subsequently. To verify the effectiveness of the method, measurements were performed on a spherical mirror. Compared with the result from interferometer, the deviation of peak to valley value is 314.3 nm, and the root mean square value is 52.8 nm, which indicates high accuracy of the method.