| With the wide application of optical three-dimensional sensing technology,the requirements of the measurement accuracy are becoming increasingly harsh.The structured light three-dimensional(3D)measurement technology raises extensively attention for researchers as it has the adventages of being high-speed,high-precision and non-contact.As an active and non-coherent optical 3D sensing technology,The structured light 3D measurement technology is measured by projecting the structured light to the tested object.The camera captures distorted strutured light images modulated by three-dimensional object surface,and then 3D topography data of the test object is reconstructed by the demodulated phase.The accuracy of the phase measurement directly affects the accuracy of the reconstructed shape.Therefore,the phase accuracy problem is one of the key and hot topics in the structured light 3D measurement technology.This paper mainly focuses on the high precision measurement of Phase Measurement Profilometry(PMP)and Phase Measuring Deflectometry(PMD).The main work is as follows:1.analysis of phase accuracy affecting factors in structured light 3D measurement technology.This thesis illustrates the basic principle,phase demodulation algorithm,phase unwrapping algorithm and height reconstruction algorithm in PMP and PMD.And the influence factors of the phase measurement accuracy of 3D measurement system with surface structure light are analyzed.These factors mainly including: the noise problem caused by phase demodulation algorithm and phase unwrapping algorithm,the system random noise,the multi-reflection problem caused by the specular reflection component of other positions,the non-linear error caused by the system non-linear Gammar response function,and so on.These factors make the phase measurement inaccurate and reduce the measurement accuracy.2.research and analysis of multiple reflective elimination methods in PMPThe multiple reflection problems in PMP are studied and analyzed.Firstly,the reason and influence of multiple reflection problems in PMP are researched.And a method based on high frequency encoded sinusoidal fringe is presented for eliminating the influence of multiple reflections on the phase of PMP,which can make phase error decreased by 1.3 times and improve phase measurement precision.3.elimination of nonlinear error in structured light 3D measurement technology.In this thesis,the influence of nonlinear Gamma effect on the accuracy of phase measurement is highlightly illustrated,and the difference of nonlinearity between the PMP and PMD is analyzed and compared.The pre-distorted fringe method and the light intensity compensation method based on cubic spline interpolation are analyzed.Based on this,a phase error compensation method based on linear fitting is proposed.The validity and reliability of the method are proved by simulations and experimental results.The method reduces the nonlinear phase error by around 20 times.In addition,several kinds of compensation methods are compared and analyzed experimentally.The experimental results show that the compensation effect of light intensity compensation based on cubic spline interpolation is the worst and the nonlinear phase error is reduced by 5 times.The proposed method can greatly decrease the nonlinear phase error and the compensation effect is the optimum.4.research and analysis of fringe quality in 3D measurement with surface structure light.The 3D measurement with surface structure light is to extract the phase information of the tested object from the deformation fringes obtained by the CCD camera,the fringe quality directly affects the phase calculation accuracy.The factors influencing the fringe quality in 3D measurement with surface structure light are studied and analyzed.In this paper,the influence factors and relations of fringe quality are analyzed,and the fringe quality analysis model is established.The computer simulations and experiments certify the reliability and correctness of the model.According to the above model,high quality fringe patterns can be obtained through optimizing the system parameters and the accuracy of phase measurement would be improved. |
