A technique of phase-shifting for 3-D measurement using spectral-transform

• A phase-shifting approach for 3-D shape measurement using spectral-transform is proposed.
• The speed of phase shift depends on the driving signal frequency of LEDs.
• The phase-shifted value is a fixed value depends on the spectral ability of the assembled projector.
• This technique is more stable, phase-shifted error free, high-speed and low-cost.

This paper presents a phase-shifting approach for three-dimensional (3-D) shape measurement using spectral-transform. In this technique, a projection system, with a simple structure and without moving parts, is used to achieve high precision and high speed phase shifts. This projection system utilizes three different wavelengths of LEDs as projection light source. When three LEDs light up individually, the light beam is collimated and vertically passes through the sinusoidal grating and an optical phase shifter, and then the sinusoidal grating image is projected onto the surface of the measured object by projection lens. Because three sinusoidal grating images are translated after through the optical phase shifter, and different wavelength of light has different offset distance; the direction of the fringes is perpendicular to the direction of translation. Therefore, three fringe patterns with phase shift which 3-D shape measurement requires are generated. The speed of phase shift depends on the driving signal frequency of LEDs. The phase-shifted value of fringe patterns between each other is a fixed value after the projection system was assembled. This technique has high stability, high phase-shifted accuracy and high scanning speed. In this paper, some evaluation experiments have been carried out. Experiment results indicate that the proposed technique is valid.