Three-Dimensional Surface-Shape Measurement of Moving Billets Using Phase-Shifting Profilometry

Three-dimensional shape of the billet/slab surface is an import cue to detect the surface defects, but it is difficult for phase-shifting profilometry to handle moving objects with textured surface such as casting billets/slabs. There are two issues that need to be addressed together, including object tracking and phase error correction. We propose a method to deal with these two issues. A projection and imaging technique is introduced to track the objects covered with fringe patterns. Based on object tracking, we find that phase errors are mainly induced by rotations and translations of the measured object and we propose a model to describe the phase error distributions. The coefficients of the model are determined by actual phase error distributions, and algorithms for obtaining actual phase error distributions are developed. Phase error distributions provided by the proposed model with determined coefficients are used for phase error correction. Simulations and experiments are carried out to validate the proposed method. Via the proposed method, the 3-D reconstruction result of the billet surface measured in moving conditions can provide stereoscopic details as that measured in a stationary state.