Study Of Cylindricity Error Measurement Technology Based On Structured Light Vision

In the field of modern machinery manufacturing,shafts are important parts of mechanical products.The error of their form and position directly affect the fit characteristics and the positioning accuracy of the parts.The cylindricity error is an important part of the form and position error,and is an important precision index for shaft parts.Accurate measurement and evaluation of cylindricity error can not only ensure the quality of shaft products,but also provide a reliable basis to improve assembly accuracy and processing accuracy of the shaft parts.Based on the geometric tolerance system,the traditional cylindricity error measurement methods mostly belong to contact measurement,which have some disadvantages including approximation,randomness,cumbersome and inefficient.Higher requirements of geometric error measurement technology are put forward along with the rapid development of digital and information technology as the core of advanced manufacturing technology.Non-contact measurements based on optical and machine vision technology are developed.Structural light vision technology is an important research content in machine vision,which is based on machine vision theory combined with optical,computer science,image processing technology and other disciplines.Based on the method,the three-dimensional geometric information of the measured object is reconstructed by obtaining the image information of the intersection of the structured light and the surface of the measured object.And the method can be applied to the three-dimensional topography measurement of complex parts with the advantages of non-contact,high precision,fast and so on.According to the geometric characteristics of the shaft parts,the paper presents a measurement method of cylindricity error based on line structure light vision technology.The measurement system is made up of a line laser sensor,a camera,lens,a computer and workbenches.Firstly,in order to improve the accuracy of the measurement system,light stripe center detection algorithm,the calibration algorithm of the camera and the sensor are studied.To improve Hession algorithm,the normalized similarity measure of ROI(region of interest)and Haar wavelet are introduced into the detection of the light stripe center,which can avoid the large-scale Gaussian convolution operation and improve the detection efficiency.Because the distortion is larger along the axial than radial in shaft images,a partition calibration model of structural light is proposed.The field of view is divided into multiple regions and each region of the distortion factors is corrected.Then the parameters of the structured light plane are estimated by the weighted least squares method.In the end,the correctness and validity of the improved method are verified by the experiments of structural light system calibration.Secondly,according to the geometrical features and the clamping method of the shaft parts,a kind of structured light irradiation mode is proposed that the light plane is approximate parallel to the axis.Based on the structured light irradiation mode,the measurement model of cylindricity error is established.According to the measurement model,the surface sampling point is reconstructed by the line structure light technique.The rapid calibration method of the rotary axis is designed,and the surface contour information of the shaft can be obtained by coordinate transformation.Combined with the characteristics of sampling information,a non-periodic spline filter for open contour is studied.On this basis,the robust spline filtering method that uses weight function by Tukey estimate is applied to the filtering of the cylindricity error measurement data for eliminating the influence of abnormal signal on spline filtering.This measurement method meets the online testing requirements,and can quickly gain a large number of cylindrical surface data.Thirdly,according to the characteristics of the measurement method,a measurement method of cylindricity error based on tectonic datum and simulation datum is proposed.In the measurement of using the simulation reference,the projection plane perpendicular to the rotation axis direction is established,and the cylindricity error is evaluated by the roundness error.In the measurement based on the construction datum,the method of measuring the reference axis is studied by fitting the contour data under the arbitrary position of the shaft.On the basis of the two methods,the roundness and cylindricity evaluation models of least squares and minimum zone are expounded.A hybrid differential evolution algorithm(PODE)is obtained combining the Powell operator and the differential evolution algorithm.The method makes full use of the strong global search ability of the difference algorithm and local fine search ability of Powell algorithm.The accuracy and speed of error evaluation are improved,when the method is applied to the minimum zone evaluation of cylindricity error.Finally,the complete morphological data of the shaft are obtained by the measurement system under the condition of higher sampling frequency in the experiment.In the process of evaluation of cylindricity error,the measurement results obtained from the new method are compared with the results measured by cylindricity measuring instrument(FMS8200)and coordinate measuring machine(ACCURA).The correctness and feasibility of the measurement method are verified,and the influencing factors for the measurement accuracy are analyzed.