Optical Engineering • Open AccessHigh-speed three-dimensional shape measurements using multiwavelength spatiotemporal phase shifting
Phase shifting using digital light processing (DLP) projectors enables high-speed three-dimensional (3-D) shape measurements based on a pattern projection method. However, faster phase shifting is required in industry to reduce the measurement time. For this purpose, it is necessary to precisely control the fringe pattern, but conventional DLP projectors afford limited control of the pattern due to their low-refresh rate (typically 120 Hz). Here, a multiwavelength spatiotemporal phase-shifting technique is proposed for faster 3-D shape measurements using a 3CCD camera. The projector consists of a single micro-electro-mechanical system mirror and three laser diodes of different wavelengths. The intensity modulation is transformed from the time to the spatial domain. The phases of the fringe patterns are independently controlled at each wavelength. Images are simultaneously captured of the projected patterns deformed in accord with the surface profile of the objective. The method is validated using a gray code technique for the height measurement of a sample in large steps.