Occluded dark field: A new inspection technique of convex mirrored surfaces

Abstract

The inspection of shiny or chromed surfaces is usual in many industries, especially in the automotive auxiliary companies. However, the inspection over those objects is a great challenge, since the acquisition procedures require specific designs due to reflection properties of mirrored surfaces, especially if the piece is convex, or specular in many directions. The best known illumination techniques are not effective in these cases: either they overexpose the piece, missing important defects, or they require a progressive scanning using a set of images instead of only one. In this paper we present a new image acquisition technique that uses a light-absorber dome which encases a Dark Field ring illumination. The so named Occluded Dark Field allows the detection of defects on convex mirrored surfaces by acquiring one only image. This improvement saves acquisition and execution time on the inspection, allowing a fastest quality control over all the production. © 2013 Springer-Verlag.