A Model of Diameter Measurement Based on the Machine Vision

Qingchang Tan,Siyuan Liu,Ying Kou,Jianwei Miao,Bosen Chai

doi:10.3390/sym13020187

Abstract

If the shaft diameter can be measured in-situ during the finishing process, the closed-loop control of the shaft diameter processing process can be realized and the machining accuracy can be improved. Present work studies the measurement of shaft diameter with the structured light system composed of a laser linear light source and a camera. The shaft is a kind of part with rotationally symmetric structure. When the linear structured light irradiates the surface of the shaft, a light stripe will be formed, and the light stripe is a part of the ellipse. Therefore, the in-situ measurement of the shaft diameter can be realized by the light stripe and the rotational symmetry of the shaft. The measurement model of shaft diameter is established by the ellipse formed by the intersection of the light plane and the measured shaft surface. Firstly, in the camera coordinate system, normal vector of the light plane and the coordinates of the ellipse center are obtained by the calibration; then, the equation of oblique elliptic cone is established by taking the ellipse as the bottom and the optical center of the camera as the top. Next, the measurement model of shaft diameter is obtained by the established oblique elliptic cone equation and theoretical image plane equation. Finally, the accuracy of the measurement model of shaft diameter is tested by the checkerboard calibration plate and a lathe. The test results show that the measurement model of shaft diameter is correct, and when the shaft diameter is 36.162mm, the speed is 1250r/min, the maximum average measurement error is 0.019mm. The measurement accuracy meets the engineering requirement.

Highlights

The measurement system was mainly composed of area scanning camera, lens, LED illuminator and hood, and the imaging of defects can be improved by controlling the image acquisition environment
Wu et al [13] proposed a vision measurement method based on three-line structured light to measure the diameter of the ball
The present work studies a model of measuring shaft diameter by machine vision

Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. A shaft diameter measurement method is proposed using can realize the in-situ and on-line measurement of shaft diameter only by a single image, line structured light vision by establishing a unified model of diameter measurement. The so it features low cost and ofhigh efficiency. 1. Compared model has goodwith universality and accuracy, it is suitable for the measurements whose the existing vision measurement methods of the shaft diameter, this method can realize the in-situ on-line measurement shaft diameter only by a single image, shape is ellipse (or circle) on theand laser plane, and if theofaccuracy of the detected points onso it features low cost and high efficiency. Equation (5) is the model of shaft diameter measurement

Test and Analysis of the Shaft Diameter Measurement Model

A The Normal Vector

Test of the measurement

Findings

The tested on theimages lathe: