Study Of Shaft Diameter Measurement Algorithm Based On Line-structured Light Vision

The shaft is a popular component in mechanical processing, therefore on-line measurement of shaft diameter has an important role in the development of advanced machinery manufacturing technology.The system of line-structured light vision measurement is consisted of cameras and line-structured lasers for 3D measurement in line with optical triangle principle. In order to improve the measuring accuracy of shaft diameter by the line-structured light, the detection for the center point of shaft surface stripe, the calibration of line-structured light measurement system and measurement algorithm of shaft diameter are studied in the thesis.Firstly, the gray distribution of the stripe cross section is analyzed on the surface of the measured object with the various materials and shapes. According to the requirements of measuring shaft diameter, the evaluation methods for center detecting algorithm on the straight line shaped light strip and elliptic curve shaped light strip are proposed. In addition the gravity method, the Gauss fitting method and the Steger algorithm are evaluated by using these two methods. The thesis proposes light strip normalization method to improve the quality of image under the influence of surface material.Secondly, the calibration method of the line structured light measurement system is studied including calibration of the camera and the light plane. To enhance the calibration accuracy, the thesis put forward an advanced calibration method which the parameters of light plane equation are optimized with gauge blocks. The comparison of calibration precision between classical methods and improved method is presented. In the experiment, the influence of the lens aperture, the light source power and the laser power on the calibration accuracy is analyzed. Moreover the optimal combination of the parameters is obtained by the orthogonal experiment method.Thirdly, the thesis analyzes shaft diameter measurement algorithm using the least square ellipse fitting and the parameter ellipse fitting according to the geometric characteristics of the strip on the shaft. In order to solve the problem of low precision, the virtual plane that is perpendicular to the axis is established and set up the local coordinate system by using the direction vector of the measured axis. In the coordinate system, center constraint measurement algorithm is put forward for improving the measuring accuracy of the shaft diameter.Finally, the accuracy of shaft diameter measurement by center constraint algorithm is verified in the static experiment. Meanwhile the influences of location of the camera installation, the angle between the light plane and the measured axis and image noise are also studied. In the dynamic experiment, it is proved measurement precision of center constraint algorithm under the different speed, and the thesis analyzes the impact of the measured shaft speed on shaft diameter measurement accuracy and stability.The thesis is potential for further prospect in non-contact and online measurement of shaft diameter.