Study Of Spatial-temporal Fringe-based Phase Extraction Technique And Its Applications

In the past 30 years,with the development of electronic industry and computer technology,phase extraction method is widely used in laser interferometry,surface shape measurement based on the structured light illumination and so on.However,the expansion of measured species and applications set requirement for capability of equipment's phase extraction,not only in hardware device updating,but also in algorithm.In recent years,a phase extraction method named spatio-temporal fringes(STF)is proposed.The method combines the N step phase-shifting fringe pattern into a STF pattern that contains both temporal information and spatial information.Then,the phase of the original fringe pattern can be obtained by STF pattern.The main work of this paper is to study the advantages of STF method phase extraction technology,analyze its limitations and propose corresponding improvement algorithms,so that it can adapt to the interference of random noises,harmonics and phase shift errors in fringe pattern.The characteristics of STF phase extraction method in suppression of random noise and harmonic are studied,and get the conclusion that the more the number of phase-shifting fringe patterns used to construct STF pattern,the stronger the ability of harmonic suppression.The method is applied in phase measuring deflectometry,which eliminates the random noise in phase recovery.The windowed Fourier transform technique is introduced in the phase extraction of the traditional STF pattern,which improves the measurement accuracy by 2-3 times.In addition,the measured which is not a standard rectangular will cause the edges phase recovered error.Therefore,the interferogram region spreading technology based on two-dimensional Fourier transform iteration and blocks reconstruction algorithm is researched.Thereinto,in order to solve the problem of low computational efficiency in two-dimensional Fourier transform iteration,a solution for changing the size of the filter window is proposed,which improves the iterative efficiency by nearly 10 times.An improved STF(advanced spatio-temporal fringes,ASTF)phase extraction technique is proposed.In this technique,the linear carrier frequency of the phase-shifting fringe pattern is added as a parameter to the phase-shifting step of the phase-shifting fringe pattern.In the traditional method of constructing STF pattern,there will be an interference spectrum around the signal spectrum,and the improved method can eliminate the interference spectrum.,so that the wide filtering window can be selected to extract the signal spectrum completely.The harmonic suppression characteristic of ASTF method is studied,and this property is applied to the fringe projection 3D shape measurement,which effectively suppresses the interference caused by the Gamma effect of the system.A STF random phase-shifting phase extraction method with linear carrier frequency is proposed,aimed at CSI(carrier squeesing interferometry)method c,an only extract the phase of phase shifted fringe pattern which contain a small phase shift error.The method can directly extract the frequency of the strongest signal spectrum in the STF spectrum to recover the phase when the phase shift error is small,and it can extract the peak signal spectrum at the edge of the STF spectrun to recover the phase when the phase shift error is large.The technique is applied in 600mm aperture phase-shifting interferometer and the fiber interferometric fringe projection 3D surface measurement system,which can eliminate the influence of phase shift errors caused by inaccuracy calibration of phase shifter and any disturbance as environment vibration.A phase extraction technique from two phase-shifting fringe patterns using STF method is proposed.This technology not only reduces the number of phase-shifting fringe patterns needed in the old STF method,but also shows better ability to inhibit the phase shift error.And it also shows a better suppression of harmonics when the phase error is small.In addition,the dynamic phase extraction capability of two phase-shifting STF method is studied,which shows that the phase recovered by this method equals to the average phase of the two phase shifted fringe when the phase of the second shifted fringe patterns has changed.This characteristic is applied in the measurement process of 600mm aperture phase-shifting interferometer,which can get the surface result and monitor the influence of air turbulence and other factors at the same time.Therefore,it can provide quantitative reference data for the environmental control of large aperture phase-shifting interferometer.