Defect detection and classification on metallic parts

The topic of this research is to the study the feasibility of a machine vision prototype for the control of metallic tubes (used in water pomp). Nine different kinds of defects located everywhere on the tube have to be detected: The defects are: on the top: little hollows, bumps, and excesses of material on the body: horizontal bumps, vertical bumps, vertical scratches and finally on the bottom: vertical ridges, holes, and bumps. As the defects on the top of the tube are very small, a grazing angle is used to light the tube. The camera is set on the opposite side of the tube with the same angle. Hollows and bumps are both detected by a vertical Sobel gradient. For the third defects, the excess of material projects its shadow on the top of the tube, and defects are detected by looking for a dark region instead of a lighted one. To inspect the rest of the tubes, a neon tube with a diffuser is employed to homogenously light the body and the bottom of the tubes. Association of gradient operators, threshold procedures enables to find all the defects.