关键词: 机器视觉, PCB缺陷检测, Hough变换, 边界分段

Abstract:

An algorithm was proposed for defect inspection of PCB bare board.It was based on comparison between the standard PCB image and the target image and analysed the boundaries of  the different regions in the target image.Multiple images were acquired for the qualified PCB at the same position,and an average was applied as the standard image.Then the target image was compared with it.On the PCB image there symmetrically distributed some vertical mark lines.First,these mark lines were detected rapidly by restricted areas Hough transform and the intersection of the lines were chosen as the feature point.Then the affine registration between the target image and the standard image could be completed.After subtraction,false defects were removed by threshold segmentation and morphological processing in the difference images.The locations of defect areas were obtained.The difference image was in the process of dilation,then the coordinate values of each defect area closed contour points could be obtained by boundary detection.The aligned target image was treated with threshold segmentation.In the processed image,the pixel values of the points whose coordinate values had been get above were obtained.According to the analysis of the pixel values and the judgment of whether the defect was lack of material or not,the type of detects could be quickly determined.The experimental results on 400 PCB images  indicate that the correction rate of detection is of 98.3%.The algorithm can accurately detect conventional defect steadily.

Key words: machine vision, printed circuit board(PCB) defect inspection, hough transform, boundary segmentation