Application Of CCD Imaging Technology In PCB NC Milling Machine

PCB is the core integrated part of chip and component.Its manufacturing quality determines the security and reliability of high-end equipment electronic system such as communication,high-performance computer,national defense equipment,etc.with the development of electronic components to integration,miniaturization and high performance,PCB manufacturing accuracy requirements are increasing.The contour forming in PCB manufacturing process is an important processing process,and its processing methods are mainly: cutting,die stamping and NC milling.Among the processing methods,the forming precision of PCB NC milling is the highest(± 0.1～0.06mm)。 With the development of electronic industry,the forming precision of PCB is further improved,and the forming precision of some precision PCB is up to the standard ± 0.05 mm,the existing general PCB milling machine is difficult to meet the processing requirements of such PCB.In this paper,according to the milling and forming requirements of precision PCB,based on the mainstream PCB CNC milling machine in the market,CCD image technology is introduced to PCB processing for the first time.Based on the NC Milling positioning,the research on the auxiliary positioning of PCB CNC milling machine with CCD deviation compensation is developed,The purpose of this paper is to improve the milling precision of milling machine by increasing auxiliary mechanism to eliminate or reduce PCB positioning error without changing the original machine mechanism.Firstly,according to the structure and control characteristics of PCB CNC milling machine,the technical solutions to improve its machining accuracy are compared and analyzed.From the perspective of economy and timeliness,the technical route to improve the machining accuracy of the milling machine by adding auxiliary mechanism is determined.Through the comparative analysis of auxiliary components,the final technical scheme is: adding CCD industrial camera in z-axis of milling machine,correcting the deviation value between PCB and machine tool through CCD imaging technology,effectively reducing the error caused by clamping and positioning,so as to improve the machining accuracy of milling machine.Secondly,the processing technology of PCB NC milling machine is analyzed,and the process route of PCB NC milling machine with CCD deviation compensation is determined.The process route simplifies the original process and can effectively avoid manual operation error.After determining the process route,according to the requirements of the processing site,the CCD and its accessories are selected,and the CCD measurement accuracy is tested,and the unit pixel error value is obtained,which verifies the rationality of the selection.By analyzing the common circular mark image characteristics of high-end PCB,the coordinate point recognition and transformation method are determined.According to the mark point coordinates,the actual coordinate system is established,and then the affine transformation is used to make the actual coordinate system coincide with the machine coordinate system,so as to complete the positioning work and eliminate the coarse positioning error of PCB in the fixture.Finally,according to the positioning requirements of mark points,the processing process of mark points is established,including image acquisition,image preprocessing,contour extraction and center coordinate recognition.Pretreatment includes denoising,sharpening and enhancement,binarization,corrosion and so on.This paper tests and analyzes the extraction effect of huff transform and least square method on PCB circular mark center coordinates.Through the comparison of the results of the two methods,it is confirmed that huff transform is more suitable for PCB circular mark point positioning and recognition,and can effectively improve the PCB positioning accuracy.After adopting the CCD aided positioning scheme,the forming accuracy of the PCB NC milling machine can reach ± 0.05 mm.Therefore,the research scheme of this paper can improve the forming accuracy of the PCB NC milling machine by adding the visual assistant system without changing the original structure of the PCB NC milling machine,with high economy and use value.