High-resolution, High-speed 3D Measurement Based on Absolute Phase Measurement

A method for 3D measurement with high-resolution and high-speed is proposed. Three patterns are projected for 3D measurement. The two patterns of them are sinusoidal fringe patterns whose phases are shifted pi each other. A modified method of Fourier Transforming Profilometry is used for phase retrieve. The other pattern is used for identifying the order of sinusoidal fringe pattern. It consists of vertical slits corresponding to the period of sinusoidal fringe. Three grey levels are used to form the slits of pattern. Six symbols are encoded with these three grey levels. Then, a pseudorandom sequence is constructed with an alphabet of these six symbols. The slits are arranged according to the sequence to form the pattern. In the procedure of phase unwrapping, the position of the string which consists of symbols corresponding to three neighbor periods is worked out by string matching in the sequence. The order of sinusoidal fringe pattern is identified. So, the absolute phase can be measured. A system consists of special designed DLP projector and high-speed camera is presented. The 3D capture speed of 60 frames per second (fps), with resolution of 640x480 points and that of 120 fps, with resolution of 320x240 points was archived in experiment. The measurement results of surface change are demonstrated.