High precision measurements of small backlit objects in mechanical engineering

This paper summarizes the experience with optical gauging of small parts with high accuracy using computer vision technology. The occluding contours of the objects were measured using back illumination. Well known problems of low resolution can be partially overcome by subpixel precision algorithms. The specific problems of high precision measurement (accuracy in the range of a few microns) are caused by the presence of dust and fibres on the measured surface and by diffraction and reflection of the light used. The first problem can be eliminated by the use of robust methods. The second one can be alleviated by careful design of optics.