Wire rope diameter measurement based on an improved linear fitting method

Abstract The diameter of a metal wire rope is a critical parameter for assessing its structural health and safety, yet traditional measurement methods are often manual, discontinuous, and prone to error. This paper presents an improved non-contact optical method for real-time diameter monitoring of operating wire ropes. The proposed approach integrates sub-pixel boundary extraction based on gradient analysis with a coupled linear fitting algorithm that simultaneously fits both rope boundaries under a shared slope constraint, significantly improving edge localization accuracy. Furthermore, an adaptive adjustment factor is introduced to correct systematic deviations caused by object distance and perspective effects. Experimental validation on a custom optical platform demonstrates that the method achieves a diameter measurement accuracy of 0.1 mm under laboratory conditions, with fitting errors reduced by up to 28% compared to conventional pixel-based approaches. The results confirm the method’s robustness and precision, providing a reliable foundation for real-time, in-service wire rope health assessment and predictive maintenance.