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PCB hole holes detection system image processing algorithm

Author: PuLiang
Tutor: YeYuTang
School: University of Electronic Science and Technology
Course: Optical Engineering
Keywords: Printed Circuit Board Automatic Optics Inspection Image Processing Image Registration Random Sample Consensus
CLC: TP391.41
Type: Master's thesis
Year: 2011
Downloads: 75
Quote: 1
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Abstract


The hole is one of the most important elements in printed circuit board. Its inspection method has a significant impact on the quality of the printed circuit board. The automatic optical hole inspection system which uses digital image processing technology has many advantages, such as high accuracy, large inspection range, non-contact, flexible. It has become an important technique of printed circuit board automated inspection. As the core of the automatic optical hole inspection system, the printed circuit board image processing algorithms have great influence on the accuracy and efficiency of the system. They have important research value.The digital image processing algorithms are analyzed in this dissertation, and the structure, composition modules, algorithms, system performance of the automatic optical hole inspection is introduced.Firstly, by comparing the conventional inspection methods, many advantages of automated inspection technology are introduced, and a detailed of the composition modules of the automatic optical hole inspection are described. Secondly, the image preprocessing algorithms of the system are discussed in this dissertation. In the preprocessing stage, distinguishing the hole type is important. The accuracy of traditional rectangle detection method is low, and does not have rotational invariance. Based on the research of ellipse fitting and other methods, the distance variance method which can determine the hole type accurately and efficiently is proposed. In the image registration stage, former method requires special locating holes, and has certain restrictions on the shooting angle of circuit board. To solve this problem, the comparative study of the Hough transform, template matching and other methods are completed, and the image registration method based on random sample consensus principle is adopted. This method selects matching points randomly under certain restrictions, then it computes the transformation matrix though coarse matching and precise matching stages without locating holes. The experimental results show that this method can perform any angle registration and completely meets the requirements of high speed inspection. In the information comparing stage, the area comparing method which has low accuracy is analyzed, and the logic algorithm is discussed according to the defects of printed circuit board. The method is accurate, stable and repeatable according to the experimental results. Finally, the algorithms are tested in the automatic optical hole inspector. The results indicate that the detection efficiency is 1.1 million holes per minute, the minimum detection aperture is 0.1 mm and the accurate rate is 99.5%. The performance of the algorithm are consistent with production requirements. The algorithms have great value in the application of printed circuit board inspection field. In addition, the distance variance method and the image registration method based on random sample consensus principle, to our knowledge, is first adopted for the automatic optical hole inspection system.

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CLC: > Industrial Technology > Automation technology,computer technology > Computing technology,computer technology > Computer applications > Information processing (information processing) > Pattern Recognition and devices > Image recognition device
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