Key Techniques Of Rail Shape 3D Measurement Based On Phase Measurement Profilometry

In the age with fast development of science and technology,optical three-dimensional(3D)measurement is gradually entering human’s production and life.As a typical representative technology of optical 3D measurement,Phase Measurement Profilometry(PMP)has the advantages of non-contact,high accuracy and fast speed,and it is widely used in many fields including industrial inspection and reverse engineering,etc..Railway industry is one of the cores of a country’s economic development.And high-speed rail is gaining strong support and promotion of governments.Therefore,railway transportation safety is becoming a very realistic issue.While the safety of rail is especially important,and the accurate measurement of rail shape is the premise of rail detection and rail safety.In this thesis,we choose to measure the 3D shape of rail based on PMP after a comprehensive analysis of optical 3D measurement technologies.And some practical key problems in measuring rail shape using PMP are studied emphatically,including fringe distortion caused by inclined projection,the difficulty of selecting and placing the reference plane plate and the specular reflection on the rail surface.To deal with the fringe distortion caused by inclined projection,two fringe pre-correction methods are proposed and studied in the thesis:Fringe Pre-correction Based on Period-Curve Analysis(PCA-FC)and Fringe Pre-correction Based on Homography Matrix(HM-FC).Through theoretical analysis and simulation experiments,PCA-FC is proved to be well effective in correcting the period distortion of fringe.HM-FC,based on an existing Homography Fringe Generation method(HFG)and a proposed Improved Homography Fringe Generation method(I-HFG),is proved not only to be able to correct the period distortion and shape distortion,but also can correct the light-intensity homogeneity distortion.Experiments about 3D shape measurement of rail show that both PCA-FC and HM-FC can make PMP get better measurement results.To deal with the difficulty of selecting and placing the reference plane plate,Phase Measurement Profilometry Based on Virtual Reference Fringe(VRF-PMP)is proposed in the thesis.By obtaining the virtual reference fringes through image interpolation,3D measurement using PMP is achieved without practical reference fringes.It means that the use of a practical reference plane plate is avoided,which overcomes the difficulty of selecting and placing the reference plane plate.Meanwhile,based on the existed New Edge-Directed Interpolation method(NEDI),the One-dimensional New Edge-Directed Interpolation method(ONEDI)is proposed to generate the virtual reference fringes.Through simulation experiments,the feasibility of VRF-PMP is proved.And experiments about 3D shape measurement of rail show that VRF-PMP can successfully measure the shape of rail without using practical reference plane plate.To deal with the problem of specular reflection on rail surface,the proposed I-HFG is used.By introducing light-intensity homogeneity correction to the original HFG method,specular reflection is suppressed.Simulations and rail surface measurement experiments show that I-HFG can eliminate the large local errors caused by specular reflection and further weaken the interference of the specular effect to a certain extent.