1. College of Metrology and Measurement Engineering, China Jiliang University, Hangzhou, Zhejiang 310018, China
2. Shanghai Institute of Measurement and Testing Technology, Shanghai 201203, China
Abstract：The accurate determination of the central axis of the thread is one of the important factors that determine whether the three-dimensional measurement result of the thread is accurate. The inclination and offset of the central axis will introduce errors in the measurement operations, such as setting up the workpiece coordinate system, reconstructing the three-dimensional thread, and inspecting the parameters.Based on three-dimensional point cloud, the least squares fitting algorithm is proposed to develop the fitting method of the central axis of the thread. According to the point cloud data of the thread surface, the least square mathematical model is established by using the characteristic relationship between the thread surface and the central axis, and the three-dimensional convex hull of the point cloud data is calculated to filter out the fitting error brought by the three-dimensional structure of the thread itself, so the measurement is more accurate. Through simulation experiments, the distance between the straight line fitted by the least square fitting algorithm based on the three-dimensional point cloud and the three-dimensional point cloud has a variance of 0.34, the maximum distance between the two ends of the straight line determined by the projection method within the twist length is 0.15μm, which meets the high-precision standard for three-dimensional measurement. It shows that the least squares fitting algorithm based on the three-dimensional point cloud is a fast and accurate fitting method of the thread central axis.
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2020, Vol. 41 
