Study Of Geometric Size Measurement Technology Of Shaft Parts Based On The Telecentric Imaging

As the basic parts of machinery and equipment,shaft parts are mainly used for the transmission of load,torque and motion,and play an important role in the normal operation of the entire machinery and equipment.As technology improves,so do the requirements for the accuracy of shaft geometries.Compared to contact measurement,vision-based non-contact measurement does not damage the surface properties of the part and has the advantage of being fast and highly accurate,making it suitable for measuring geometric parameters such as shaft diameter,radial runout and roundness of shaft components.This thesis is based on telecentric imaging technology to investigate high accuracy measurement techniques for geometric parameters of shaft components.The specific work is:1)Theoretical analysis of telecentric imaging.According to the telecentric imaging principle,the camera calibration technique for telecentric measurement is analysed,the whole telecentric imaging calibration process is derived,and the calibration of camera parameters such as magnification,principal point and aberration is completed at a certain imaging distance.2)In order to improve the measurement error caused by the telecentricity of the telecentric lens,a telecentricity measurement error compensation model is established based on the radial aberration model.The assembly error of the telecentric lens leads to a small angle between the main light and the optical axis,the angle is the telecentricity.As a result of the telecentricity of the lens,the magnification of the telecentric imaging system also varies slightly with the imaging distance in the depth of field range,affecting the measurement accuracy of the system.To this end,this thesis analyses the mechanism of the telecentricity of the telecentric lens on the measurement accuracy,and establishes a telecentricity measurement error compensation model based on the aberration model of the lens.A polynomial relationship between the aberration parameter and the imaging distance is established in the model,and the measurement error caused by the telecentricity is compensated by correcting the aberration parameter for different imaging distances.In the experiments with the tessellated calibration plate as the measured object,the root mean square error of the measurement results before and after compensation in the depth-of-field range improved from about 20 μm to about 4 μm,fully verifying the necessity of the telecentricity measurement error compensation and the feasibility of the proposed compensation scheme.3)In order to overcome the influence of noise on the extraction of shaft diameter edges,a parallel line fitting method for the extraction of journal edges is proposed based on the RANSAC(Random Sample Consensus)algorithm.Template matching is used to obtain the journal region,and two parallel lines are extracted from the journal edge based on RANSAC parallel line fitting.Compared with the least squares method,the noise points in the RANSAC algorithm do not participate in the parallel line fitting calculation,which improves the robustness of the edge extraction.4)A platform for measuring the geometric parameters of shaft components has been built and the corresponding software platform has been developed to enable online inspection of the diameter,radial runout and circularity parameters of shaft components.This thesis realizes multiple geometric parameters measurement of shaft parts based on telecentric imaging machine vision technology,which enriches the application of telecentric imaging theory and lays the foundation for the subsequent development of precision equipment based on telecentric measurement.