| Optical three-dimensional measurement techniques have advantages over others in being non-contacting and providing whole-field information, and hence been extensively studied to meet the demands of the industrial or civil applications. The phase unwrapping is a very difficult problem for profilometry of object containing depth discontinuities. The problem can be resolved with dual-frequency measurement technique. A novel technique including amendatory three-step spatial phase-shifting and dual-frequency grating for profilometry of object containing depth discontinuities is presented.In this technique, two measurements with dual different frequencies can not be contented with real-time demand. The new profilometry is based on compound grating, generated by computer software, projected by liquid crystal projector, so that the grating with different precision is easily created, conveniently changed. The same purpose is obtained as capturing two different frequencies deforming gratings. Fourier transform profilometry is used in the commonly dual-frequency grating profilometry to deal with the modulating fringes, existing the leak of carrier frequency. The amendatory three-step spatial phase-shifting eliminates the carrier-frequency leakage, and increases the range can be tested contrasting three-step phase-stepping technique. The principle of amendatory three-step spatial phase-shifting and dual-frequency grating are clarified, and the validity and performance of this algorithm are verified by computer simulations and experimental results.Aiming at the problem of inferior precision and bad maneuverability during system calibration of automatic profilometry by projected grating, a new system construction is introduced and the object-phase relation is derived in this paper. Because of without parallel and perpendicular restricted conditions in the conventional system construction, the CCD camera and the projecting device can be located arbitrarily. |
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