A novel visual detecting and positioning method for screw holes

Abstract

A new visual detecting and positioning method was proposed to solve the positioning problem of screw holes in dark-colored workpieces. Firstly, a red LED lighting system was designed and built to make the screw holes distinct even under dark background of workpieces. Then an improved Hough transform was applied to detect screw holes and a template matching method based on the features of gradation histogram was used for precise positioning of screw holes. After that, a sub-pixel positioning method was adopted in order to achieve the sub-pixel accuracy of screw holes. Further, the image coordinates of screw holes were transformed to the coordinates in world coordinates system according to the camera model. Finally, the experiment results demonstrated the effectiveness, accuracy as well as robustness of the proposed method.