Research on Visual Measurement of Aperture and Hole Group Center Distance Based on Geometric Constraint

Abstract

Hole is the most common symmetrical geometric structure of mechanical parts, and aperture and hole center distance are important measured dimensions in machining. However, existing visual measurement methods often require high equipment installation accuracy and low measurement accuracy. To solve the problem of projection deformation of the measured hole: Firstly, a local coordinate system is created, and the coordinate plane of the coordinate is parallel to the end face of the measured hole. Secondly, a cone is established, the end face of the measured hole is alike to the bottom face of the cone, and the optical center of the camera is the vertex. The space equation of the cone is represented by the coordinates of the center point of the hole. Finally, a cutting plane is established near the imaging plane of the camera, and the intersection line equation between the plane and the cone is obtained, and the diameter of the measured hole and the coordinates of the center of the circle are obtained through the parameters of the intersection line equation. In order to solve the problem of errors in edge points of the hole, geometric constraints based on the center of the circle are used to improve measurement accuracy. This experiment takes the automobile insert mold as the measured part and uses the measurement model of this paper to measure the aperture and hole center distance of the mold. The measurement results show that the measurement accuracy of the aperture is 0.018 mm, the measurement accuracy of the center distance of the hole is 0.05 mm, and the maximum relative error is 2.2%.