Research on 3D-image Based Size Measurement Algorithm of Locomotive Brake Shoe for Locomotive Robot

Abstract

The environment of operation and maintenance of locomotives and rolling stocks is complex. Factors such as dust and reflection make point cloud missing, noise and false points, which seriously affect the accuracy of locomotive robot brake shoe image detection. To this end, this paper presents an size measurement algorithm of locomotive brake shoe for locomotive robot based on 3D image. Firstly, it realizes automatic transformation between the template region of interest (ROI) and measurement ROI according to the camera perspective transformation and point cloud registration algorithm, which makes up for the repeated positioning error of the locomotive robot to a certain extent. For the problem of point cloud missing and noise caused by reflection, RANSAC algorithm is used to fit the reference ROI in plane to make up for the loss of precision. The algorithm of automatic filtering of ordered point cloud is used to filter the point cloud between brake disc and brake shoe effectively. For the difficulty of edge discrimination by the false point cloud caused by lock brake and specular reflection of brake disc surface, this paper designs a filtering operator to preliminarily separate the edge of brake shoe and extract the ROI on the side of the brake shoe. Then, according to the imaging characteristics of the brake shoe, the gradient-based edge extraction and tracking algorithm is used to realize the accurate extraction of point cloud boundary of brake shoe and the accurate measurement of brake release gap. Finally, the accurate dimension measurement is realized by using the statistical method of sorting strategy. By the algorithm presented in this paper, accurate measurement can be realized under the condition that slack gap is less than 2mm. The method is used to measure the brake shoe in different shape, position and lighting complex environment, and the Vernier Caliper is used to measure it. The results show that the measuring accuracy of brake shoe wear size is within ±1mm range, and the algorithm has certain robustness.

Keywords

• robot
• locomotive brake shoe
• 3d image
• size algorithm
• ordered point cloud
• camera perspective transform
• filter operator
• size measurement
• complex environment
• robustness