<title>Digital fringe projection technique for high-speed 3D shape measurement</title>

Abstract

A high-speed phase-shifting technique for 3-D shape measurement has been developed and experimented. A DigitalMicromirror Device (DMD) based video projector is used to project sinusoidal fringe patterns onto the object surface. Its red,green, and blue (RGB) channels are programmed to be sinusoidal fringe patterns with 120-degree phase difference. Theprojector has a color filter with four segments, RGB and clear, which controls the color of the projected image. When aspecific segment is in the light path, the DMD forms the corresponding image of that color. A 24-bit color image is formedwhen the RGB color channels are sequentially projected in a cycle time of 10 ms. When the color filter in the projector isremoved, the DMD still projects the three color channels sequentially, but the actual projected images are now in grayscale.The timing control mechanism of the DMD is studied and a circuit is designed to provide an external timing signal forprojection control. When a CCD camera used to capture the fringe patterns is synchronized with the DMD, the individualchannels of RGB or the three phase-shifted fringe patterns can be captured in less than 10 ms, thus making high-speed phaseshifting possible. Experimental results demonstrated the feasibility of this technique for high-speed 3-D shape measurement.Keywords: 3-D shape measurement, fringe projection, phase shifting, video projector, CCD camera, digital lightprocessing (DLP), digital micromirror device (DMD).