Key Technologies Phase Shift Fringe Projection Method

The phase-shift fringe projection method has a simple system, the real-time measurement of the benefits while avoiding direct contact with the object, which is one of the commonly used shape measurement methods. However, the measurement accuracy limits its development. The phase-shift fringe projection method takes fringes as an adjunct and uses the phase shift method as the algorithm, so the generation, read and phase shift of fringes all equally affect measurement accuracy. This paper studied the above three key technologies to improve the measurement accuracy.For improving the fringe reading accuracy problems, this research studied the camera and projector calibration techniques to improve the reading accuracy. Under the conditions of unknown internal camera, we used Zhang Zhengyou camera calibration method to get internal and external calibration parameters. Under conditions of known internal camera, we used three-point calibration technique to get external calibration parameters. Target projection method was used to achieve internal and external calibration parameters of projector.For phase shift technology, instead of the traditional phase shifters, this paper used a wavelength tunable laser to eliminate error introduced by the conventional one. Then a binary code unpack phase algorithm was used to overcome the problems which can caused error by conventional methods.For the generation of fringes, depending on the size of the subject different generation way of fringes was choose. For the small size, we choose fiber-optic interferometric fringe projection method, interference fringes were formed with good sinusoidal, which improved the measurement accuracy of the system. For large size, the projector was taken to project the sinusoidal fringes, which is easy to adjust the size. We choose the Trapezoidal artifact with30mm length and10mm height. The absolute error is0.0228cm.