Inverse Projected-fringe-technique

Fast and robust 3D shape inspection is of big importance for industrial quality control. The three-dimension sensing methods with structured light illumination, such as moire topography, phase measurement profilometry (PMP), Fourier transform profilometry (FTP), and modulation measurement profilometry (MMP), have received great attention in recent years. However, there are some problems such as phase unwrapping, shadows and low speed when these techniques are used for on-line and batch inspection.Inverse projected-fringe-technique is a novel technique that aims at fast on-line and batch inspection. Common fringe projection setups use straight fringe patterns, which are projected onto an object to record deformed fringe patterns. But inverse fringe projection inverts the whole process. The inverse fringe pattern is generated according to the absolute phase measurement on the master object and the wanted image (optimized sine fringe) defined on the recording plan. During the inspection process, the inverse fringe is projected on the test object. If the test object and the master object are identical, an optimized sine fringe is got on the camera. Otherwise, every faulty area of the test object causes distortions of the fringe. Therefore, the deformations become obvious and can be evaluated quantitatively by simple Fourier transformation and phase unwrapping. The peculiarity of this technique is to put the processing of the complex object surface into the measurement of the master object before the inspection, and to process the deformation separately during the processing. Only one frame of fringe pattern is adequate for inspection, therefore the...