Accurate and robust sub-pixel refinement for fillet weld joint based on directional maximum projection

Embedded seam tracking system that integrates sensing and computing hardware has obvious advantages due to its miniaturization and flexibility. A core problem of the embedded seam tracking system is to obtain accurate welding seam with low-resolution structured-light images. To remove this burden, an accurate and robust sub-pixel refinement method for fillet weld joint is proposed, and it mainly includes: initial direction detection of structured-light stripes by adopting mean shift algorithm, direction refinement based on weighted least squares method with constraint, and fillet weld joint sub-pixel refinement based on directional maximum projection. The main novelties of this work include: (1) the idea of refining fillet weld joint based on directional maximum projection is proposed for the first time; (2) the proposed method is accurate and robust in heavy noise images. The proposed method is robust, universal, and accurate, and as demonstrated by the following performances: (1) average biases of noise-free, rusty, highly reflective and arc-and-spatter images are 0.51, 0.55, 0.68, and 1.21 pixels, respectively; (2) the CR (effective rate) of pure, rusty, highly reflective, and arc-and-spatter images are all 100%; and (3) the offsets of the initial pixel-level fillet weld joint are effectively rectified.