| With the constant miniaturization of electronic components packaging, surface mounting technology has been widely used in integrated circuit plate assembly industry. As the core equipment of surface mounting technology, main functions of placement machine are pasted different electronic components on the printed-circuit board. The construction of placement machines is very complicated, and the technology of placement machines involves many subjects such as precision machinery, artificial intelligence, machine vision, automatic control and so on. Among these subjects, visual system acts as the control feedback element of placement machine and its properties directly influence the main parameters such as pasting speed and precision. Visual system is relatively independent in placement machine system, so it can be researched as an independent subsystem. A whole visual system based on each constitutional unit has been researched in the paper.In the hardware part of placement machine visual system, the function of different modules such as image acquisition system, illuminating system, and image processor has been introduced. And then the model of different constitutional units could be selected according to the properties of foreign similar products.Based on the former workings, different basic algorithms of image processing used in placement machine visual system have been comparatively studied including image smoothing filtering algorithm, edge detection and threshold segmentation algorithm, feature extraction and sub pixel level fitting algorithm of geometry construction element. This comparsion constructs the foundation of realizing Mark point location and electronic component error correcting of printed-circuit board.According to the most widely used circle Mark point in practical production, a kind of sub-pixel level circle center location algorithm is proposed in this paper. The condition of the Mark point polluted by soldering tin or oxidation has been fully considered. Experiments prove this algorithm possess enough robustness to the solder polluted Mark point and the noise polluted pictures, and satisfies the demand of intermediate speed placement machine on the speed and precision of Mark point location.Before designing processing algorithms of electronic components, we should firstly classify and settle some common standard electronic components to enhance the universality of designed algorithm. Then a kind of processing algorithm which applied to rectangle tin and ball grid array components has been put forward. Experiments proved that the algorithm has good detection speed and location precision and has sufficient robustness to disturb, and could satisfy the demand of practical application. |
