Design of mount quality visual inspection system for FPC stiffeners

According to the measuring requirements of mount quality for flexible printed circuit (FPC), starting from the designs of the hardware and software subsystems, an automatic mount quality inspection system based on machine vision was developed. The use of self-designed arc frame was utilized to simplify the process of calibration and reduce the influence of hardware on image acquisition. On the basis of laser triangulation method, the Laplacian of Gaussian operator and ultimate threshold segmentation methods were introduced to distinguish between centre and scattered area for the scattered light spot. And then the centric region was separated out by morphological closing operation. Meanwhile, the invariance of spatial moments was applied to ellipse fitting whose central position was converted to the change of stiffener on thickness that was easier to make observation. The results show that the fluctuation of spot center location is 1.15 pixels. Furthermore, the maximum error of location is only 0.82 pixels. And if the structure element of closed operation is 8, it can further improve the detection accuracy and efficiency.