Detection principle of PCB hole inspection machine
With the development of equipment technology, PCB hole testing machine has been widely used. Now let's introduce the working detection principle of PCB hole testing machine.
We place the circuit board to be tested on the transmission device (the maximum 360 degree tilt angle is allowed), and the transmission device sends the circuit board below the CIS to obtain the light transmission image of the light source on the circuit board (where there is a hole, there is light passing through, and the collected image is white, where there is no hole, the light is blocked, and the collected image is black). The acquired image is collected by the image acquisition card and then transmitted to the computer, The computer processes the image obtained and compares it with the standard image to determine whether the circuit board is qualified. The maximum width of the circuit board required to be tested is 610 × 650 mm. If the traditional CCD (Charge Coupled Device) is used for image acquisition, due to the limitation of the field angle, the image acquired by a single CCD will have a large distortion at the edge, making the subsequent detection more complex and the detection accuracy will decline; For example, if multiple CCD is used for acquisition, because the splicing of multiple CCD is difficult, impact, vibration and temperature have a great impact on its accuracy when it is used under bad conditions. In addition, the high price of CCD is not conducive to our detection system. Contact Image Sensor (CIS), an array of sensor ICs made by CMOS technology, came into being in the late 1980s. Compared with CCD, CIS does not require imaging optical path and has no restriction of field angle. It can be imaged 1:1 with the circuit board to be tested. This system uses a 2400dpi (dot per inch) linear array CIS, and the actual size of each pixel is 0.01058 × 0.01058mm。 The reason why machine vision can perceive the complex information of the outside world is the result of light field transmission, and illumination affects the transmission of light field. Therefore, the selection of the target LED lighting system will directly affect the definition and contrast of the image. In the application of target image processing and analysis, the definition and contrast of the image will also affect the real-time and accuracy of image processing, especially in the application of image detection, visual positioning, etc. with high requirements. Therefore, reasonable LED lighting system design is particularly important, which is an important part of the PCB photoelectric hole detector. The linear array CIS has a good absorption of red light spectrum, and LED has the advantages of no stroboscopic, low calorific value, low production cost, etc. Through the above analysis, considering that the basic components of PCB light plate image are lines and holes, as well as the spectral reflection of the surface and other reasons, in this system, we use a strip LED red light source (70cm long) with high brightness, good uniformity and good heat dissipation, and a backlight lighting scheme with a diffuser on the surface.
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