Shape measurement by temporal phase unwrapping and spatial light modulator-based fringe projector

A fringe projector based on a low-cost spatial light modulator has been used to measure the shapes of discontinuous objects. By changing the fringe phase and the fringe pitch, a sequence of wrapped phase maps can be acquired at different sensitivities. This sequence can then be converted to surface profile by the recently-proposed method of temporal unwrapping rather than by a conventional spatial unwrapping approach. The main advantages are that the method is simple and robust, and that objects with surface discontinuities are profiled as easily and accurately as smooth ones. Modifications to the basic temporal unwrapping method are proposed which provide significant improvements in reliability, accuracy and computation time.