Research On Techniques And Applications For Phase Retrieval Based Three-dimensional Profile Testing With Complex-channel

Technique based on phase retrieval with complex channels for three-dimensional profile measurement which combines the modulation/demodulation of phase and complex channels has the advantanges of huge information acquirement, high measurement precision, etc. Hence it has been applied in many fields, including aeronautics and astronautics, machine vision, reverse engineering, and micro-structure-device manufacturing. With the development of this technique, a series of related scientific and technical problems are still needed to be solved. This dissertation mainly focuses fringe projection and white light interference with the emphasis on the key techniques for complex-channel measurement and the unit key techniques for extended profile measurement, which includes the following aspects:To correct phase retrieval errors occuring in complex-channel measurement with single-frame color phase-shifiting fringe projection, a hybrid blind correction technique based on multi-dimensional Hilbert transform and carrier squeezing interferometry (CSI) is proposed. The phase demodulation errors caused by the gamma effect and the color coupling phenomenon of the used electronic devices can be effectively suppressed without an extra system pre-calibration. A single-frame measurement with a sub-millimeter accuracy for the target has been achieved and the precision of the proposed technique is better than λeq/38.To high precisely demodulate the interested physical values in complex-channel measurement with color white light interference, a novel least-square strategy to estimate zero-order position based on Windowed Fourier transform ridge (WFTR) and phase-crossing techniques is proposed after an in-depth analysis of the inner relationship between the phase values of the signals in color channels and the position of zero-order white-light fringe. Compared with existing techniques, the proposed technique takes full advantages of the color information of the captured fringes and hence has a better immunity to the intensity noises and the color-coupling. Furthermore the center wavelength of the used light source and the refractive index of the test object are not required in advance. A higher precise result for the profile measurement of micro-structure-device with a deviation less than3.5nm can be finally attained.For the gamma distortion problem in profile measurement with fringe projection, an accurate and simple correction technique which is based on the principle of Fourier spectrum analysis (FSA) for gamma coefficient pre-calibration is proposed. Compared with other existing methods, a similar result has been obtained by the proposed strategy which only needs two pre-encoded fringe patterns while others≥32frames. Therefore, in principle, the proposed technique can be applied in profile measurement using traditional phase-shifting algorithms and has a potential in rapid/dynamic profile measurement.For the lens distortion problem in profile measurement using fringe projection, a flexible nonlinear-iterative profile measurement technique based on a simple red/blue checkerboard is proposed, which has fully considered the distortion of the projector-camera lens. Compared with existing techniques, the proposed method has no restrict requirement for the geometry of the measurement system which is convenience to the system adjustment. The distortion model can be easily extended as long as the profile measurement needs. The measurement errors caused by the lens distortion are able to be corrected during the iterative reconstruction for the desired three-dimensional morphology. Experimental works show that the reconstructed root mean square (RMS) error of the proposed algorithm is less than0.040mm, the location error is no more than1‰, and the measurement precision is improved over8times compared with existing linear-model-method.For the profile measurement using white light interference, an in-depth analysis of the inner-relationships between the frequency and phase of the interference signals, the center wavelength of the used light source, the scanning interval of the micro-transducer device and the position of zero-order white-light fringe is given. Windowed Fourier transform (WFT) with a good anti-noise and partially analysis ability is introduced to process gray white light interferograms. Two different techniques, single-point-phase compensation and multi-point-phase least-square estimation, are hence proposed. Compared with previous envelope peak location methods, the proposed two strategies have a better robustness and immunity to noise. In addition, the center wavelength of the used light source and the refractive index of the test object are not needed. High-precision results with a deviation no more than6nm can be finally achieved.The aforementioned related key techniques have been successfully applied into the multi-view profile measurement for transient moving targets. A multi-view measurement system with a hexagonal configuration for three-dimensional profile measurement based on complex-channel fringe projection profilometry is proposed and designed in this thesis. High quality fringes are instantaneously projected onto a test surface and the distorted fringe patterns are synchronously captured through imaging devices. The desired phase information is retrieved by continuous wavelet transform which has a good robustness and anti-noise ability. A precise three-dimensional profile of the transient moving target is then achieved which will provide helpful experimental foundations for the research of transient testing.