The principle of recognition and scanning is as follows:
Identification principle
To convert the bar code compiled according to certain rules into meaningful information, it needs to go through two processes: scanning and decoding. The color of an object is determined by the type of light it reflects. White objects can reflect visible light of various wavelengths, while black objects absorb all kinds of light.
Bar code making
The wavelength of visible light, so when the light emitted by the light source in barcode scanner is reflected on the bar code, the reflected light shines on the photoelectric converter inside barcode scanner, and the photoelectric converter converts the reflected light signal into corresponding electrical signals according to its strength. According to different principles, scanners can be divided into four types: light pen, red CCD, laser and image. The electrical signal is output to the amplification circuit of the barcode scanner to enhance the signal, and then sent to the shaping circuit to convert the analog signal into a digital signal. The widths of white bars and black bars are different, and the duration of corresponding electrical signals is also different. The main function is to prevent the width of the dead zone from being insufficient. Then the decoder judges the number of bars and spaces by measuring the number of pulse digital electrical signals 0, 1. The width of bars and spaces is determined by measuring the duration of 0, 1 signal. The data obtained at this time is still quite confusing. In order to know the information contained in bar code, it is necessary to convert bar code symbols into corresponding digital and character information according to the corresponding coding rules (such as EAN-8 code). Finally, the detailed information of the article is identified by the computer system, and the data is processed and managed.
Scanning principle
The scanning of bar code needs a scanner. The scanner uses its own light source to illuminate the bar code, and then uses a photoelectric converter to receive the reflected light and convert the brightness of the reflected light into a digital signal. No matter what rules are adopted to print bar codes, they are all composed of dead zones, start characters, data characters and end characters. Some barcodes also have a check character between the data character and the termination character.
▲ Dead zone: Dead zone, also called blank zone, is divided into left blank zone and right blank zone. The blank space on the left is to make the scanning equipment ready for scanning, and the blank space on the right is the end mark to ensure the scanning equipment to correctly identify the barcode.
In order to prevent the left and right blank areas (static areas) from being occupied unintentionally when printing and typesetting, you can print a symbol in the blank area (when there are no numbers on the left; This symbol is called the dead zone mark. The main function is to prevent the width of the dead zone from being insufficient. As long as the width of the dead zone can be ensured, the presence or absence of this symbol will not affect the identification of bar codes.
▲ Start character: the first character with special structure. When the scanner reads this character, it begins to read the code formally.
▲ Data characters: the main content of bar code.
▲ Check the characters: check whether the read data is correct. Different coding rules may have different checking rules.
▲ Termination character: the last character, which is also a special structure, is used to inform the end of static code analysis, and also plays a role in checking calculation.
In order to facilitate bidirectional scanning, the start and stop characters have asymmetric structures. Therefore, the scanner can automatically rearrange the barcode information when scanning. There are four kinds of barcode scanners: light pen, CCD, laser and image.
▲ light pen: the most primitive scanning method requires manual movement of the light pen and contact with the bar code.
▲CCD: scanner with CCD as photoelectric converter and LED as light source. In a certain range, automatic scanning can be realized. And can read bar codes on various materials and uneven surfaces, and the cost is relatively low. But the scanning distance is shorter than that of the laser type.
▲ Laser: a scanner with laser as the light source. It can also be divided into linear, full angle and so on.
▲ Picture: Take a picture with a light source and decode it with its own hard decoding board. Usually, image scanning can scan both one-dimensional bar codes and two-dimensional bar codes, such as Honeywell engine.
Linetype: mostly used for hand-held scanners, with long action distance and high precision.
All angles: most of them are industrial-grade fixed scanning, with high degree of automation, which can automatically read bar codes, output level signals in all directions, and cooperate with sensors.