The Study Of Z Calibration In Fourier Transform Profilometry

Optical three-dimensional (3D) non-contact profilometry, with the excellence in high speed, high accuracy and easily controlled by computer, has been widely used and studied. In many kinds of activity 3D profilometry, Fourier Transform Profilometry(FTP) that requires only one frame of the deformed fringe pattern and one frame of reference fringe pattern makes real-time data acquiring and processing of dynamic process possible. Its foundation principle is to get the 3D shape sizes with the frequency characteristic of signal.The major contributions of this thesis include:1. The phase demodulation method was analyzed thoroughly. High harmonic error of digital projector and the nonlinear response error of the photo-detector were unified as the high harmonic error which was carefully explored through theoretical and comparative studies. It was shown that the phase-shifting with more than 5-frame algorithm would be insensitive to the detector nonlinearity.2. Temporal phase unwrapping (TPU) and its variants were compared in terms of error analysis, through which a meaningful conclusion would be drawn, showing that a generalized TPU algorithm (GTPU) could possibly eliminate the some limitations imposed on the fringe sequence for the conventional TPU algorithms. Furthermore.3. A novel calibration technique was proposed and used to calibrate 3D scanner developed in-house. With proposed calibration method, we obtained a 3-D range data with desired measurement accuracy. Experiment results showed that after the calibration the 3-D vision system was able to achieve such an accuracy as the standard deviation in X direction was 0.007mm and 0.05mm in full field, for a measuring volume of 200×150×70mm~3.4. It was found that the main error source came from system error of the vision system and this system error could be further reduced if the accuracy of calibration devices were increased.