Method for detecting hook face circular hole based on three-dimensional point cloud

Abstract

The invention provides a method for detecting a hook face circular hole based on a three-dimensional point cloud. The method comprises the steps that firstly, three-dimensional points on the edge of the circular hole to be detected on the point cloud are accurately extracted; then least square plane fitting is conducted on the edge points of the circular hole, so that an initial plane of a projection is obtained, the edge points are projected to the plane, and a coordinate system is converted, so that two-dimensional points of the projection are obtained; the radius of a least square circle and two orthogonal fixing rotary axes of the projection points are obtained; when the radius of the circle can not meet the judgment criterion of the circle, a least square plane respectively rotates around the two rotary axes, projection and iterative computation are conducted again until the radius of the circle meets the judgment criterion of the circle, so that the normal of the least square plane is the axial direction of the circular hole and the radius of the least square circle of the projection two-dimensional points is the radius of the circular hole. According to the method, the axial direction and the radius of the circular hole can be rapidly detected from the three-dimensional point cloud.

Description

technical field [0001] The invention relates to the technical field of computer vision detection, in particular to a method for detecting circular holes on curved surfaces based on three-dimensional point clouds. technical background [0002] In recent years, with the continuous development of my country's automobile industry, manufacturers have put forward higher requirements for the manufacturing precision of auto parts and the assembly precision of the whole vehicle. The assembly accuracy of a car largely depends on the size and shape accuracy of the holes on the parts. Most of the parts are cold stamped parts with large size and complex shape. These stamped parts generally have positioning holes, assembly holes and other holes. During the assembly of the whole vehicle, it is often impossible to assemble due to the deviation of the hole diameter on the stamped parts or the change of the relationship between the round holes (influenced by the rebound factor). In the insp...

AI Technical Summary

Problems solved by technology

One is to use general algorithms such as the Canny operator, and then use the least squares method to fit the boundary based on image processing. This method has spatial circular perspective projection distortion and large measurement errors

The second is to obtain three-dimensional points on the edge of the round hole based on stereo vision for fitting. It can only detect the geometric parameters of the plane round hole and cannot detect the round hole on the free-form surface.

It is obviously difficult to meet the increasingly stringent inspection requirements of automobile stamping parts by the method of plane round hole detection alone. Therefore, how to detect the size and shape accuracy of round holes on free-form surfaces has become one of the focuses of research in this field.

In the academic paper "Three-dimensional measurement of small mechanical parts under a complicated background based on stereo vision" published in the academic journal "APPLIED OPTICS" 2010, 49(10), P1789-1801, Zhiguo Ren et al proposed CAD using fixtures and components The parameters provided by the model and stereo vision calibration are used to perform least square fitting to obtain the radius of the surface hole. This method is too dependent on external conditions and cannot be detected when the workpiece has rebound

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