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Machine vision inspection related issues

2020-09-09  Visits:46

       The machine vision industry is extensive and profound. For beginners, there are many problems. For example, bottle cap inspection is the use of machine vision. Yuzhen technology has sorted out some machine vision entry-level problems to help everyone understand machine vision inspection. 

       1. Imaging process

       The principle of photoelectric conversion between CCD and CMOS image sensor is the same, and their main difference lies in the different signal reading process; In CMOS chip, each pixel has its own signal amplifier, which converts charge to voltage, so the signal output is not the same. However, in order to read the whole image signal, CCD requires a wide signal bandwidth of the output amplifier. In CMOS chip, the bandwidth requirement of the amplifier in each pixel is lower, which greatly reduces the power consumption of the chip. This is the main reason why the power consumption of CMOS chip is lower than that of CCD. Although the power consumption is reduced, the difference of many amplifiers brings high fixed noise, which is the inherent disadvantage of CMOS compared with CCD.

       2. Integration

       From the point of view of manufacturing process, the circuit and device in CCD are integrated in semiconductor single crystal material suppliers, and the process is complex. Only a few manufacturers in the world can produce CCD crystal elements, such as DALSA, Sony, Panasonic, etc. CCD can only output analog electrical signal, which needs the following address decoder, analog converter, image signal processor processing, and also needs to provide three groups of different voltage power supply synchronous clock control circuit, the integration is very low. However, CMOS is integrated on the plate monomer material called metal oxide. This process is the same as the process of producing many semiconductor integrated circuits such as computer chips and memory devices, so the cost of sound field CMOS is much lower than that of CCD. At the same time, CMOS chip can integrate image signal amplifier, signal reading circuit, a / D conversion circuit, image signal processor and controller into one chip. As long as one chip can realize the basic functions of the camera, the integration is very high, and the concept of chip level camera is generated from this. With the development of CMOS imaging, more and more companies can provide good CMOS imaging chips, including micron, CMOS is, cypress, etc.      

       3. Speed

       The CCD of bottle cap detection equipment uses one by one photosensitive output, which can only output according to the prescribed program, and the speed is slow. CMOS has multiple charge voltage converters and row and column switch control, so the readout speed is much faster. At present, most of the high-speed cameras above 500fps are CMOS cameras. In addition, the address gate switch of CMOS can sample randomly to realize sub window output, which can achieve high speed when only sub window image is output.      

        4. Noise

        CCD, which is used for bottle cap detection, is developed earlier and more mature. It uses PN junction or silicon dioxide (SiO2), and its imaging quality is better than that of CMOS photoelectric sensor. Because of the high integration of CMOS image sensor, the distance between components and circuits is very close, the interference is serious, and the noise has a great impact on the image quality. In recent years, with the development of CMOS circuit denoising, it provides a good condition for the production of high density and good CMOS image sensor.

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