A 3D vision system based on one-shot projection and phase demodulation for fast profilometry

We present a 3D vision system based on the projection of a single fringe pattern of incoherent light and on robust phase coding. A novel projection scheme is exploited: two sinusoidal gratings at different frequencies are combined into a single pattern, and phase demodulated in the natural domain of the signal. The method yields the determination of two phase maps, whose sensitivity to height variations is proportional to the frequencies of the two grating components. Robust phase unwrapping is implemented, where the phase ambiguity of the fine grating component is naturally compensated for by the phase values evaluated by using the coarse one. As a result, both a high measurement resolution and an extended height range are obtained. The method requires the projection of a static pattern. Hence, even a low-cost slide projector can be used as the projection device. Moreover, the system turns out to be suitable for dynamic and real-time measurement applications. In addition, it may be fruitfully used as the acquisition sensor in full-optical reverse engineering applications. In this paper, the measurement principle and the design issues of the instrument are presented. The measurement performances are discussed, in relation to both the input–output characteristic of the instrument and the acquisition of free-form shapes.