In-Line Burr Inspection Through Backlight Vision

This paper presents a vision-based quality control system for detecting burrs (miniature metal filaments) in transverse holes of high precision turned hollow cylinders. The system performs 100% in-line quality control at the turning station. It exploits a camera with telecentric optics framing the sample from the outside in back-light condition. A specifically developed cylindrical illuminator provides radial diffuse back-light illumination over 360° and can be inserted within the part to be inspected. The possibility to detect burrs placed on both the outer and the inner surface of target holes is achieved by exploiting a customized rotating device integrated to a commercial gripping device. Overall, the system mimics the manual inspection normally performed by operators. Burrs are detected as modifications of the circular shape of each hole, through algorithms that identify the holes on grayscale images, perform circle identification by geometric matching and identify burrs through analysis of local deviations of the edge from circularity. Results acquired in a real production line over a batch of 2000 parts showed no false-positive or false-negative diagnosis.