| Printed Circuit Board (PCB) is information carriers integrating various electronic components. It is also the key unit of electronic products. With the continuous progress in technology and industry,electronic products are becoming lighter,thinner,shorter and smaller,which facilitate the development of PCB manufacturing technology with high density. The precise positioning of PCB benchmark hole is the key to PCB processing accuracy.In terms of the current situation and coupled with the help of documents as well as extensive market research,the automatic positioning system based on FPGA benchmark hole is developed.This system is mainly composed of single computer,CCD camera,step motor and computer system.Based on special image signal of PCB benchmark hole, it is proposed that automatic positioning system of PCB benchmark hole is designed in control of SCM SST89E516RD as master computer and two SCM AT89C2051s as slave computer.The image of PCB benchmark hole is taken and transmitted to output after turning into video signal. It is then stored in image memory after digital process, Master computer processes it and sends information of central position of benchmark hole to slave computers. Slave computers control how long and how fast the two- dimension platform moves to realize positioning at highspeed and accuracy, which insures accuracy and speed of positioning of PCB benchmark hole.The difficulties of this system lie in how to sample video image signal and how to do image process with SCM to identify immediately and locate precisely benchmark hole from many images,how to control two-dimension platform to position at high speed,accuracy and steadiness. By deep researches on ways of binary value process for CCD video image signal, sampling frequency and method of video image, image filter arithmetics,identification and located arithmetics of benchmark hole, way of speed control for step motor. It is proposed that binary value process is realized by making use of PWM to improve benchmark voltage for weak video signal to get the best image;Circuits of video signal sampling and synthesizing are designed to realize automatic sampling for video signal and display image and menu on LCD,which resolves contradiction between resolving power of video signal and speed of CPU running; Arithmetic based on SCM to process image fast is proposed, including identification and pairing of boundary points, filter and finding the center coordinate;The relation between moment and speed of step motor are analysed to determine the best curve of control speed by experiments,hardware and software designs of located system are finished to realize automatic position of PCB benchmark hole. Practices have proved that many new ideas of image process and positioning control based on SCM are proposed by these analysises and designs.Compared with similar product, it shows bigger application prospect because it has abandoned industry control machine and image sampling adapter, which greatly reduces the cost and volume of the system. |
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