A Sub-pixel Location Method of Circular PCB Markers Based on Partial Area Effect
Yingyuan Yang, Xianwen Wang, Sijin Luo, Guoyuan Liang · 2023
With the rapid development of electronic manufacturing industry, automatic optical inspection (AOI) systems are widely applied to mark positioning and defect inspection of printed circuit board (PCB). As the most common mark, the accurate positioning of circle is of great importance in the wiring and assembly of the PCB. Various sub-pixel algorithms have been presented in the past decade. In this paper, we propose an improved version of sub-pixel edge location method based on partial area effect to acquire better sub-pixel points for fitting the circular marks. In stead of the simple one direction offset model, a composite offset model is adopted to diminish the positioning error as much as possible in the case of small gradient differences between horizontal and vertical directions. Besides, the constraints of both gradient magnitude and angle are also introduced for filtering the sub-pixel points at each edge pixel in order to effectively improve the quality of the fitted circle. Experiments conducted on synthetic and real PCB mark images have verified the better performance of the proposed method in terms of anti-interference and location accuracy.