Compensation and measurement of external cylindrical thread geometric errors based on machine vision and optical micrometer

Conventional non-contact thread measurement methods face limitations in addressing profile occlusion distortion caused by the helix angle and in accurately quantifying critical geometric errors such as pitch diameter runout. This paper, from a metrological viewpoint, proposes a novel high-precision collaborative measurement methodology that integrates multimodal machine vision with an optical micrometer. The core innovation of this approach is twofold: first, it combines a traceable physical datum provided by the optical micrometer with high-resolution profile analysis from machine vision, enabling the synergistic measurement of both macroscopic dimensions and microscopic features. Second, a mathematical model is developed and validated to compensate for the occlusion distortion inherent in vertical projection, thereby eliminating a significant systematic measurement error. The findings indicate a high degree of precision, with repeatability standard deviations of 1.3 µm for the major diameter and 1.25 µm for the pitch diameter. Furthermore, the system demonstrates exceptional efficiency, capable of completing a full-dimensional inspection of a single cross-section in under one second. These combined strengths in precision and speed confirm that the proposed methodology meets the stringent requirements for high-throughput industrial thread inspection.