Surface roughness measurement using photometric stereo method with coordinate measuring machine

Abstract

This paper presents a novel technique for surface roughness measurement using a photometric stereo method together with a coordinate measuring machine (CMM). The photometric stereo system was tested by some surface roughness standards. The roughness average (Ra) computed from the recovered surface was compared with the values measured from contacting roughness measurement. Since the illumination angles of light source have some influences on the measurement results, the CMM was used to accurately move and position the light source, so the effects of tilt and slant angles can be studied. The results of these experiments have indicated that the slant and tilt angles used in the photometric stereo method have significant effects on the accuracy of the roughness measurement. In the experiment a linear regression was applied to determine the optimum slant angles. In addition, the camera was calibrated by a standard glass scale used to verify the pixel error.