Optimal exposure selection of high dynamic range-based reflection compensation for printed circuit board reconstruction using structured light 3D measurement system

Structured light (SL) scanning in industrial metrology offers the advantages of non-contact measurement, high-speed operation, and high precision. However, fringes may exhibit excessive modulation when measuring highly reflective metal parts, leading to the calculation of invalid phases and the reconstruction of abnormal point clouds. High dynamic range (HDR) scanning is a commonly used approach to address this issue, but the optimal exposure time using this method is usually influenced by the reflective properties of the object. In this paper, we propose an optimal exposure time selection method based on the clustering of images in the fringe modulation. Firstly, we acquire modulation degree images containing only objects. Subsequently, the K-Means method is employed to cluster the modulation degree images. The K best exposure times are calculated based on the average maximum gray value of the fringe images in each cluster. Finally, K sets of fused fringe images are captured and utilized to reconstruct three-dimensional (3D) information with enhanced coverage. Using our method, the three-dimensional information of the printed circuit board (PCB) is reconstructed, achieving an improved coverage rate of 98.1% compared to the 88.3% coverage rate obtained from a single-shot capture. Additionally, our method achieves a measurement accuracy of 0.08mm. Experimental results demonstrate that the proposed method efficiently selects the optimal fusion exposure time, making it suitable for measuring highly reflective PCBs.