Application Of PMP Based On Composite Grating In Measurement Of Rail Surface Defects

As the railway develops in the direction of high speed,heavy load and high density operation,rail wear and surface defects are increasing.Based on the composite grating's Phase Measurement Profilometry(PMP),the measurement time is shortened and the measurement efficiency is improved.In this thesis,the three-dimensional measurement of rail wear and surface defects is carried out,and the traditional PMP and composite grating-based PMP are simulated,experimentally verified and compared.At the same time,in the context of railway application,the PMP algorithm based on composite grating is improved,and the composite grating PMP based on dual frequency channel and 2+1 algorithm is derived,which reduces spectrum aliasing and improves measurement accuracy.Aiming at the specular reflection of the rail surface in practical applications,based on the Bidirectional Reflectance Distribution Function(BRDF),the optical reflection model of the 45 Mn rail surface is established.The reflection characteristics and phase transition characteristics are analyzed.At the same time,a method for avoiding the highlight effect is proposed.By establishing the BRDF model and the phase change model of the rail surface and using simulation software to simulate the relationship between the BRDF value and the phase shift of the 45 Mn rail surface and the incident angle and wavelength,the simulation is carried out by the peaks function,Stoilov phase shift algorithm and PMP.The improved results show the method of determining the incident angle at the common wavelength,preserving the phase information to avoid distortion,and the range of incident angles for avoiding the high light effect in the BRDF measurement.The thesis provides theoretical guidance and methodological reference for three-dimensional reconstruction of in-service rail.Theoretical simulation and experimental results show that the improved method can reconstruct the three-dimensional shape and surface defects of the rail better,and the measurement accuracy is significantly improved compared with the traditional composite grating.