Fast Calibration Based Photometric Stereo for Multiscale Metallic Surface Measurement

Multiscale analysis and characterizations of metallic surface topographies is a crucial task in advanced manufacturing and precision engineering. In this paper, we present a multiscale measurement technique based on photometric stereo for accurately reconstructing surface topographies at different scales. Our system employs a zoom lens and LED illuminators, providing the flexibility to adjust the measurement scale. To ensure efficiency and accuracy during scale transition, a fast light source calibration method using a Lambertian sphere is proposed to obtain the position and orientation of the LED precisely and simultaneously. A surface reconstruction algorithm is designed through modeling the light propagation process, enabling the identification of surface features at different levels of detail. The system is calibrated using an Edmund USAF resolution target, which demonstrate the accuracy of our method with the minimum deviation as low as 4 mu m. The proposed approach is applied to investigate the multiscale surface topography produced by metal additive manufacturing (AM) technique, achieving an accurate representation from contour to roughness. The results are compared with those obtained from a commercial 3D scanner from Keyence, which validate the effectiveness of our method and show its great potential in quality control and optimization of manufacturing processes.