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High-speed phase-shifting profilometry

A microscopic 3-D shape measurement system based on a new high-speed phase shifting technique is developed and experimented. By taking advantage of the color channel switching characteristic of a commercial Digital Micromirror Device (DMD) based video projector, a potential 3-D shape measurement speed of up to 100 frames/sec can be achieved. A computer generated color fringe pattern is projected onto an object surface. The red, green and blue channels of this pattern are programmed to be sinusoidal fringe patterns with 120 degrees in phase difference. When the color filter of the projector is removed, three grayscale fringe patterns are actually projected in sequence with a cycle time of approximately 10 ms. Through a stereomicroscope, the fringe patterns generated by the DMD is projected onto a small surface area of the object and then captured by a CCD camera via the same microscope objective. The 3-D microscopic shape of the object surface is reconstructed by using a phase wrapping and unwrapping algorithm. Experimental results demonstrated the feasibility of this technique for high-speed surface profile measurement.