Analysis And Study On Computer Simulation For 3-D Shape Phase Measurement And Its Spectrum Properties

Since 1980s, optical three-dimensional (3-D) shape measurement was developed sharply with its advantages: non-contact, non-damaged, high accuracy and sensitivity and full-field measurement, base on the development and broad application of laser technology, CCD image sensor, and computer image processing technology. But in actual application the problems which are urgent to solve are as following : suiting the industrial environment ; realizing phase-shifting with high accuracy ; measuring large-scale object, real-time measuring , solving the problem of shadow regions. In order to solve these problems, some advanced methods are presented by experiment and computer simulation in this paper.In this dissertation, firstly, the development, the application, the problems, the hot aspects of research and the future research trends of optical 3-D shape measurement are introduced in details. And based on these introductions, two approaches: phase-shifting profilometry and fourier transform profilometry, which are applicated broadest and researched hottest nowadays, are presented systematically, analyzed detailly, computer simulated and verificated by experiments. Then the advantages and disadvantages of the two approaches are analyzed and compared. One can only obtain the wrap phase in the (-π,π] interval due to using the arctangent function in these applications. Some typical approaches are introduced for unwrapping phase, and then the relation between the unwrapping phase and the height of reconstructed object are showed. Fourier transform profilometry is introduced in details about its radical principle, frequency spectrum feature, strain in frequency-domain, wipping off zero-frequency. They are all done due to the huge advantage which needs only to gather and deal with one deformed image. Improved methods are presented in making stringe, image processing, shape conturement, which are based on theory of optical 3-D shape measurement and MATLAB language. In all these achievements, the improvement and innovation aspects are as follows:(1) The relationship between the center of frequency spectrum and frequency of projectional fringes are proved through theoretical analyzing and computer simulating; then the relationship between the scope of fundamental frequency which carryinformation of the conturement and the gradient of the reconstructed object on the direction uprighting the stringes.(2) A method is improved to eliminate the zero-frequency. Because of the frequency spectrum of Fourier profilometry is much complex, the way is disintegrating the deformed fringes to many child fringes by the gauss window, then fourier transforming the every child fringe. The frequency spectrum of the child fringes is much simple, and it is more possible to look for the minimum between the center of zero-frequency and the center of fundamental frequency through computer program as the boundary to wipe off the zero-frequency. Then the frequency spectrum without zero-frequency was got by using the frequency spectrum of the whole fringes subtracting the zero-frequency superposed by all the zero-frequency of the child fringe. The approach is proved effective by experiment and has some worth for referring to in this field.(3) A method for large-scale object measurement is presented without phase shifter in this paper .The sinusoidal gray fringes are simulated by computer and projected on the object by the liquid-crystal light valve in this method, in with the phase-shifting is controlled by computer through changing the program parameters. Then the deformed fringes modulated by object is collected by CCD camera, so optical 3-D measurement for large-scale object can be realized more easily and freewill phase-shifting can be got conveniently, all these are proved by experiment in this dissertation .We just need to collect and process only one deformed fringe to reconstruct the object if we linking liquid-crystal light valve with Fourier profilometry, then adopting the improved approach of wiping off the zero-frequency. The result shows this measure system is very simple, performance reliable, operating convenience for large-scale object measurement.