Two-stage calibration method for portable light pen of vision based coordinate measurement system

Portable light pen measurement technology is widely applied in manufacturing, industrial inspection, and other engineering fields. To address the decline in measurement accuracy caused by marker points localization errors and probe center displacement in light pen systems, this paper proposes a two-stage self-calibration method based on distance constraints and geometric optimization. Unlike previous methods that rely on coordinate measurement machines to obtain marker points coordinates and distance parameters, the proposed method only utilizes image-based information for calibration. In the first stage, a sensitivity analysis of the ideal marker coordinates is conducted, followed by a trust-region optimization algorithm incorporating weighting and regularization to estimate the distances between marker points and the probe center. In the second stage, bundle adjustment with geometric constraints optimizes the marker points coordinates. Experimental results indicate that the repeatability accuracy of the probe center coordinates, as determined by the proposed method, reaches 50 μm in the X, Y, and Z directions. Additionally, measurements of standard parts indicate that the distance measurement deviation is less than 70 μm.