Rapid detection of weld contour based on compound vision of projection structured light and shape from shading

With the rapid development of welding automation, manual visual detection and manual measurement of weld appearance contour are gradually transitioning to automated detection. In this paper, a compound 3D vision system of projection structured light and shape from shading is constructed, which solves the problem that the current laser scanning vision method is not applicable in the occasions with high beat requirements. The projection structured light vision system is encoded by sinusoidal fringe to realize the high-precision 3D recovery of highly reflective metal surface. The shape from shading method can obtain the high-definition gradient information of the weak fluctuation of the weld surface and the Lambert reflection theorem in this method is used to solve the problem that the reflectivity is difficult to obtain. Using the above compound vision system, taking the weld of aluminum alloy variable polarity plasma arc (VPPA) welding as an example, the relevant image processing algorithm has been developed to accurately realize the measurement of contour size and the extraction of contour defects on the face and back of the weld. In view of the features that the 3D boundary features of face of weld in VPPA welding are not obvious, the shadow recovery shape method is used to obtain the gradient image of the metal surface. Combined with the fish scale information on the weld surface, the reliable extraction of the weld boundary is realized.