Research On Measurement Technology Of Diameter And Roundness Error Of Bearing Steel Ball

Spherical parts such as bearing ball and precision probe are widely used in aerospace,automobile manufacturing,medical instruments and other fields.The precision measurement of diameter and roundness error can effectively improve the manufacturing accuracy,and then improve the performance of the instrument or device,reduce the risk of use,improve production efficiency and increase the service life in general.Therefore,it is of great significance to study the measurement of diameter and the evaluation of roundness error of spherical parts.The diameter measurement of traditional laser diffraction method is usually based on Fraunhofer diffraction theory.On account of requiring an additional optical system to meet the infinite distance between the light source and the diffraction plane to the measured object,the difficulty of adjustment of optical devices and the uncertainty of measurement are increased.This paper presents a method for measuring the diameter and roundness error of steel ball based on Fresnel diffraction.The traditional measurement method of diameter and roundness error is complicated.We proposed a method of measuring the diameter and roundness error of bearing steel ball based on Fresnel diffraction.Based on the analysis of the Fresnel diffraction characteristics of the steel ball,a measuring system was designed and built.The influences of white noise,background noise,dark current noise and distortion noise on the actual diffraction images are analyzed by studying the formation of Fresnel diffraction pattern of steel ball.In order to extract diffraction characteristic information accurately,Butterworth filter program was designed to de-noise the diffraction image,and the center and edge of the diffraction image were respectively located by Hough transform based on gradient and subpixel edge detection algorithm.Aiming at the problem that it is difficult to obtain the analytical solution of the measured feature in scalar diffraction theory,the projection contour and the position of the first stage peak in the Fresnel diffraction of steel ball were calibrated by the dot calibration plate.The distribution of the diameter of the steel ball with nominal diameter of 2mm-4mm on the measured plane was obtained by the function relation calibrated by dot calibration.According to the diameter distribution of the steel ball,the coordinates of its contour points can be obtained.The roundness error of the steel ball is evaluated by using the traditional algorithm and the particle swarm optimization algorithm respectively.The experimental results show that the measurement uncertainty of diameter and roundness error of millimeter steel ball are less than 3.1?m(confidence level 95%)and 0.091?m(confidence level 95%)respectively without considering the diffuse reflection and scattering of the steel ball surface.Compared with the traditional diameter and roundness error measurement methods,the measurement system is relatively simple,the optical path can be to adjusted easily,It also can realize non-contact measurement,which has certain practical value and application prospect in the measurement field.