Inverse projected-fringe technique based on multi projectors

The inverse projected-fringe technique based on multi projectors is proposed. By an absolute phase measurement on the master object, different inverse fringes are generated, for projectors placed in different directions. During the inspection process, inverse fringes are projected simultaneously. If the test object and the master object are identical, an optimized sine fringe is obtained on the camera. Otherwise, every faulty area of the test object causes distortions of the fringe. The deformations can be evaluated quantitatively by simple Fourier transformation and phase unwrapping. Therefore, we can complete the inspection of complex and discontinuous objects with only one fringe image, and solve the problems of shadow and break to a large extent, and consequently realize the fast on-line inspection. The principle of this technique is expatiated, and we prove the validity of it on the example of a two-projector system. The analysis of error and prerequisites of application are also presented.