Principle of an innovative visual sensor based on combined laser structured lights and its experimental verification

To promote development of sensing technology applied in the welding process and improvement of production automation in the welding manufacturing industry, an innovative multi-functional monocular visual sensor based on combined laser structured lights (single-line & cross-lines) is proposed and devised. It can realize the detection of cross-sectional size parameters of welding groove, space position and posture of welding torch relative to the weldment or welding groove by using monocular vision. Its calibration makes full use of the intrinsic parameters, such as its internal structure parameters and the focal length of industrial CCD camera. Therefore, it is unnecessary to re-calibrate when the position and posture of welding torch have some variations during the welding process or the visual sensor reassembles with the welding torch, which availably improves the adaptability of this sensor in engineering application, so that it can apply to the welding process with complex space welding trajectory. Furthermore, with the use of combined laser structured lights, it effectively eliminates the problem of information loss in depth commonly existing in usual monocular visual sensor. Meanwhile, all the detection functions of this sensor are derived from the processing results of a single image captured by industrial CCD camera, which avoids the problems of time-consuming and large amount of calculation resulting from multi-images processing (multi-vision method or multi-angle time-sharing imaging in monocular vision), and thus significantly improves its real-time performance in engineering application. Its functional detection algorithms for the cross-sectional size parameters of welding groove and the height of welding torch derived from the principle of optical triangulation are given. After establishing a test platform, we carried out a series of detecting experiments for different types or sizes of V-type butt groove. By image processing, recognition and extraction of the feature points, the cross-sectional size parameters of welding groove and the height of welding torch calculate out through the derived detection algorithms. The acquired detection results have enough accuracy and their maximum relative errors are not exceeding 3.9%, which demonstrate the rationality of the physical design for the proposed visual sensor and the validity of the derived detection algorithms.