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