Online Detection Technique of 3D Defects for Steel Strips Based on Photometric Stereo

Abstract

2D Detection with gray level images is popularly employed in current surface inspection systems of steel strips, which lead to high false detection rate because of interference of pseudo-defects, such as iron oxide, water stains, and grease. Therefore, an online detection technique of 3D defects based on photometric stereo was developed in this paper. The acquired 3D information is utilized to distinguish real 3D defects from pseudo-defects, which can significant improve the performance of surface inspection system. The designed inspection system was equipped with lasers and linear CCD camera to scan the moving surface of steel strips, referred as the photometric stereo laser scanning system. Samples of hot and cold-rolled steels, with pseudo and real defects such as roll imprints, cracks and scratches on surface, were scanned and showed obvious distinguishment.