3D Measuremnet Based On Digital Phase-Shifting And Fringe Projection Technique

With the development of science and technology and industry, 3D measurement techniques are increasingly important in production for automation, quality control machine vision, reversal engineering, CAD/CAM and biomedical engineering, etc. Traditional contact measurement techniques have lots of flaws, such as measurement force companying with measurement process, being time-consuming, needing compensation for radius of the test head, and being unable to measure elastic or fragile material, and so on. Therefore, it can't meet demands of the development of modern industry. Optical non-contact 3D measurement techniques have become the focus of research of 3D measurement techniques in recent years because of overcoming the defects above-mentioned.A kind of new-type non-contact 3D measurement system is described in this paper. The system adopts digital phase-shifting and fringe projection techniques and its measurement has advantages of non-contact, the whole field, higher precision, and quite high speed. In traditional phase-shifting systems, the fringe patterns are usually abtained through the physical grating, and it is realized by the movement of the grating that phase-shifting of the fringe patterns is moved. However, the system described in this paper adopts the digital fringe projection system to produce the standard sinusoidal projection fringe with the high ratio of light and contrast by a computer, and thus raises the ratio of resolution of the system and precision of the measurement. Phase-shifting is controlled by software accurately and all kinds of errors caused by traditional phase-shifting systems will be avoided.The basic principle of 3D measurement method based on digital phase-shifting and fringe projection techniques is illustrated in this paper. To the questions that exist in the system with traditional structure, the traditional structure is improved to remove parallel degree required in traditional structure for higher maneuverability in system calibration and higher precision of measurement. The mechanism of the non-linear distortion of the camera lens is carried on research. A kind of optimal method of the distortion coefficients of camera lens for improving the precision of the fringe projection measurement is proposed. Based on measuring the reference plane, the approach analyses the errors of some measure points on it, finds the relationship between the errors and the distortion coefficients of camera lens. Then the distortion coefficients of camera lens are determined by iterative optimization. This methodsolves the problem of the error caused by the distortion of camera lens effectively and the method to compensate for the error caused by the distortion of camera lens is given.