3-DOF Measurement Method Of Worktable Based On Non-diffracting Moire Fringes

Large-stroke precision worktable occupies an extremely important position in the field of scientific research and industrial production.The motion error of worktable in the process of processing directly affects the processing accuracy of parts.In this dissertation,non-diffracting beam is generated by liquid crystal spatial light modulator(SLM).Based on the characteristic that the size and shape of the center spot of non-diffracting beam do not change with the transmission distance,combining with the measurement and amplification of moire fringes technology,a method for measuring the 3-DOF(yaw angle,roll angle and pitch angle)motion error of the worktable is studied.The main contents are as follows:Firstly,the characteristics of non-diffracting beam and the common generation methods are introduced,and the diffraction characteristics of axicon are analyzed.The theory of simulating axicon of SLM is studied.The generation of zero-order Bessel beam and hollow annular beam is realized.The experimental results of long-distance transmission of non-diffracting beam generated by axicon and SLM are compared.The theory of moire fringes of concentric circular grating is studied,and the shape chang rules of moire fringes are analyzed.The characteristics of moire fringes of non-diffracting beam are analyzed based on the correlation between non-diffracting beam and concentric circular grating,which embodies the advantages of introducing them into 3-DOF measurement method.Secondly,using SLM as the main component to generate non-diffracting beam,a 3-DOF measuring optical path using non-diffracting moire fringe is designed.According to the change of the center position of the non-diffracting beam,a 3-DOF motion error mathematical model is established.The three motion errors of yaw angle,pitch angle and roll angle are separated by geometric analysis method,and the simultaneous measurement of 3-DOF is realized.Thirdly,aiming at the characteristics of non-diffracting beam and moire fringes,the local concentric circle region of the spot center is extracted by threshold segmentation firstly;then the initial circle center set is found by edge detection;then the initial circle center set is clustered and analyzed to determine the initial position of the spot center;finally,the more accurate central position of moire fringes of non-diffracting light is calculated by deleting abnormal point.The positioning error is controlled within 1 pixel.Finally,a 3-DOF verification system for non-diffracting light moire fringe is built by simulating the 3-DOF change of the rotary table.Designing and verifying the experiment and processing the experimental results,we can get the offset of the center of the moving beam spot,which is consistent with the theoretical analysis.The actual angular displacement is calculated by the offset of the center of the spot.Compared with the theoretical value,the angular displacement error is less than 0.01 degrees,which verifies the feasibility and correctness of the 3-DOF measurement system for non-diffracting moire fringes.