The visual measurement method of the hole diameter and center-to-center distance of the box based on simplified external parameter calibration

The hole is a significant mechanical structure type. In this paper, two visual measurement models are established for chamfered and non-chamfered holes. A concentric cylinder with a known diameter is used as a calibration object to obtain the external parameters corresponding to the end face of the measured hole. This approach overcomes limitations associated with using calibration plates for external parameter calibration and aligns better with requirements in production sites. By utilizing the obtained external parameters, three-dimensional coordinates of edge points on the measured hole can be determined, and an ellipse fitting algorithm is employed to obtain aperture and center point coordinates. In the experiment, gearbox housing is used to measure hole diameter and center-to-center distance. The measurements are compared with a coordinate measuring machine, demonstrating a measurement accuracy up to 0.1 mm. The experimental results confirm both feasibility and effectiveness of measurement model while maintaining low operational complexity.