Detecting defects on corrugated plate surfaces using a differential laser triangulation method

Abstract During corrugated-plate manufacturing and associated service processes, the plates are often prone to suffering from defects such as cracks, holes and thinning. However, traditional inspection methods cannot effectively satisfy real-time requirements owing to the complexities of the examined surfaces. To solve this problem, this study develops a differential laser triangulation method based on online detection of variations in wall thicknesses, to identify surface defects (holes and thinning). This integrated system drives a pair of laser triangulation probes to capture the surface data of the plates. To compensate for the measurement errors of the triangulation probe caused by irregular surface curvatures, an empirical error model based on error evaluation is established. To improve the precision of the cross-sectional contour reconstruction, the corrected point data are segmented according to the geometrical characteristics of the examined plates, and the analytical model of the contour data in each subsection is modeled using the least-squares method. The wall thickness of each point can then be calculated using its normal equation, to characterize the surface defects. Experiments on a 203 mm × 176 mm workpiece demonstrate that the developed method not only analyzes the object dimensions, but also provides a non-destructive means to effectively detect defects on the surface of a corrugated plate.