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Research On Reference-plane-based Calibration Techniques And Hybrid Phase Unwrapping Algorithms Of Multi-frequency-segment And Phase-shift

Posted on:2011-09-04Degree:DoctorType:Dissertation
Country:ChinaCandidate:S C CuiFull Text:PDF
GTID:1118330338485834Subject:Physical Electronics
Abstract/Summary:PDF Full Text Request
The calibration techniques, phase unwrapping algorithms and noise compensation methods in the structure light measuring system are investigated in this work Calibration techniques are important generalized techniques used in all the measuring systems.In this thesis, a generalized reference-plane-based calibration method is proposed by exploring projection ray tracing method and image ray tracing method of the structrure light measuring systems. The pin-hole camera model is used to model the camera and the projector, and parallel plane model is used to model the reference and test planes. The camera, projector and planes can be in arbitrary positions and directions. The reciprocal of the height and the reciprocal of the phase shift (or pixel position vertical distance) are in linear relationship. For the line stripe measuring profilometry and the phase shift measuring profilometry, the calibration equations coincide and have fewer coefficients than the traditional calibration method, so the computation in the calculation of height is less and this method is more efficient. Experiments are conducted to verify the proposed method.The traditional calibration method for laser galvanometric scanning (LGS) system is tedious and less accuracy, to solve this problem, a new calibration method is proposed for LGS system by adapting the camera model to model the LGS system. The similarity between the camera system and the LGS system has been investigated and exploited. A twelve coefficients distortion model is proposed in this thesis to model the LGS distortions and the distortion parameters are acquired by solving a nonlinear least square problem. The efficiency of the calibration is improved. Experiments are conducted to verify the proposed model.Phase unwrap algorithms are important generalized techniques in the structure light measuring fields. When surfaces contain large discontinuities, the existing phase unwrap methods always fail, to solve this problem, a hybrid phase unwrapping method based on the multiple-frequency segments and phase shift method is proposed. In this method, the common commercial digital camera and projector are used. The red channel of the camera (projector) is defined as the background channel, and the blue channel is defined as the measuring channel. The phase space resolution of the background channel is larger than the measuring channel. In the proposed method, the phase of background channel is firstly unwrapped by traditional phase unwrap algorithms, and then the unwrapped information of background channel is used to determine the phase order in the measuring channel. This algorithm is noise-immune, so it is robust. The phase shift method is also implemented to solve the phase unwrapping problems at the edge areas. So there is no need to explore the relationship of the phase area anymore, thus the computing speed is fast and the method is more efficient.The noise filter algorithm is also an important technique in the structure light measuring system. The projected light intensity of the digital projector exhibits an exponential translation characteristic in the low level illumination environment, and lager multiple noises are also found, so the measuring accuracy degrades. To solve this problem, a noise compensation method based on theπ/ 3phase shift is proposed. The noise intensity is correlated to the signal amplitude. After theπ/ 3phase shift, the amplitude of signal alternates, so the noise level will alternate too, which are averaged to compensate the noises. The algorithm is simple and feasible. Experiments show that the multiple noises can be compensated mostly and the accuracy is highly improved. Image feature extraction method, as an import composition of the software in the structure light measuring systems, is also mentioned.After the above generalized technique being investigated, three different measuring systems, Laser Tin Thickness Measuring System, Portrait Measuring System and Electrics Grid Object Measuring System are constructed by the benefit of the non-touch, effective and efficient characteristic of the structure light measuring system.
Keywords/Search Tags:Structure light measuring, Calibration technique, Phase unwrapping algorithm, Noise compensation method, Phase measurement, Distortion model
PDF Full Text Request
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