A machine for automatic measurement of he surface roughness of 3-dimensional cast metals using an optical noncontact method has been developed. The specimen is illuminated from eight surrounding directions with the incident angle of 60 deg and detected by a CCD camera, perpendicular to the surface. The surface roughness Ra can be obtained from the contrast C which is calculated using the image detected by the CCD camera. First, the specimen is positioned at an angle of 0deg,45deg or 90deg with respect to the x axis. Second, at each of these positions, the images of the specimen are detected by the CCD camera by rotating the specimen in steps of deg between 0 deg and 360 deg around the z' axis. The regions to calculate to calculate the contrast C for each image are obtained from the shape data of the specimen which are measured using a 3-dimensional coordinates measuring machine. In the experiment, the specimen is illuminated from eight surrounding directions using 100W halogen lamps and Fresnel lenses, and the surface roughness Ra at various regions on the specimen is calculated. As a result, the surface roughness of good or defective specimens is measured with an error less than ±25/100.
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