Phase Shift Fringe Projection Optical Surface Shape Measurement Technology Research

Resent years, with the rapidly developing of Electronic, Astronomy, Optical Communication, Laser Nuclear Fusion and Military Field, the manufacture and measurement precision of optical elements are facing more and more requests, while the surface measurement of optical elements is an important optical fabrication problem. Controlling the accuracy of optical surface in the course of processing is an effective way to improve the machining accuracy. Existing optical surface detection methods are usually have a slow measurement speed and easy to damage the optical surface. To overcome these problems, a non-touch optical surface measuring method based on Phase Shift Fringe Projection is proposed in this paper. Phase Shift Fringe Projection measurement has the advantages of contactless, high measure speed, huge information acquirement, well-adapted, etc. But the measurement precision needs to be improved to measuring the optical surface. At the point of improving the measurement precision, this dissertation mainly focuses on three key techniques in Phase Shift Fringe Projection:the Gamma distortion correction technique, the camera calibration and lens distortion correction technique, the phase-height calibration technique.For the Gamma distortion problem in profile measurement with Phase Shift Fringe Projection, an accurate and simple Gamma correction method is proposed by analyzing the relationship between Gamma coefficient and harmonic coefficient. The accuracy and reliability of this method has been verified through the simulation results. Finally, experimental works has been done with this method. Compared with the retrieval phase without Gamma correction, the conclusion can be made that this method can effectively restrain the Gamma distortion of the system and improve the measurement precision.For the camera calibration and lens distortion problem in profile measurement with Phase Shift Fringe Projection, the plane calibration method by Zhengyou Zhang has been used in this dissertation. Experimental works has been done to calibrate the internal and external parameters of camera and to correct the lens distortion. Results show that the measurement accuracy of this system has been improved.For the phase-height calibration problem in Phase Shift Fringe Projection measurement system, a mapping relationship of phase-height proposed by Hongwei Guo is used in this dissertation. Experimental works has been done to calibrate the phase-height conversion coefficient through calibration plane translation method. Compared with actual height distribution, the root mean square (RMS) of the fitting height reconstructed by proposed algorithm is less than0.0465mm, which verifies the accuracy and reliability of this method.Finally, the aforementioned key techniques have been successfully applied into the optical surface measurement with Phase Shift Fringe Projection. The accuracy and reliability of the method proposed in this dissertation is demonstrated by comparing the surface data obtained by our system with data from high precision profilometer.