I. Overview of Barcode
Bar code was first proposed by N.T.Woodland of the United States in 1949. In recent years, with the popularization of computer application, the application of bar code has been greatly developed. Barcode can indicate the country of production, manufacturer, product name, date of production, book classification number, mailing place, category, date and other information. Therefore, it is widely used in many fields, such as commodity circulation, book management, post and telecommunications management, banking system and so on. Bar code is a graphic identifier composed of bars and spaces with different widths and reflectivity, which is compiled according to certain coding rules (coding system) to represent a group of numerical or alphabetic symbol information. That is, bar code is a group of parallel lines with different thicknesses and arranged at regular intervals. Common bar codes are composed of black bars (abbreviated as bars) with different reflectivity.
Second, the composition of the bar code identification system
In order to read the information represented by bar code, a bar code recognition system is needed, which consists of bar code scanner, amplification and shaping circuit, decoding interface circuit and computer system.
Third, the principle of bar code scanner to identify bar codes
Because different colors reflect different wavelengths of visible light, white objects can reflect various wavelengths of visible light, while black objects absorb various wavelengths of visible light. Therefore, when the light emitted by the light source of the barcode scanner is irradiated onto the black and white barcode through the diaphragm and the convex lens 1, the reflected light is focused by the convex lens 2 and then irradiated onto the photoelectric converter in the barcode scanner. Therefore, the photoelectric converter receives reflected light signals with different intensities corresponding to white bars and black bars, converts them into corresponding electrical signals and outputs them to the amplification and shaping circuit of the bar code scanner. The widths of white bars and black bars are different, and the duration of corresponding electrical signals is also different. However, the electrical signal output by photoelectric converter corresponding to the bar and space of bar code is generally only about 10mV, so it cannot be used directly. Therefore, the electrical signal output by the photoelectric converter should be sent to the amplifier for amplification. The amplified electrical signal is still analog. In order to avoid false signals caused by defects and stains in bar codes, a shaping circuit should be added after the amplification circuit to convert analog signals into digital electrical signals so that the computer system can accurately interpret it. The pulse digital signal of the shaping circuit is converted into digital and character information by the decoder. It can identify the coding system and scanning direction of bar code symbols by identifying the start and end characters. By measuring the number of pulse digital electric signal 0, 1, the number of bars and spaces can be determined, and by measuring the duration of signal 0, 1, the width of bars and spaces can be determined. In this way, the number of bars and spaces used for bar code symbols and the corresponding width and code system can be obtained. According to the coding rules corresponding to the coding system, barcode scanner converts the bar code symbols into corresponding digital and literal information, and sends them to the computer system for data processing through the interface circuit.
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The application of barcode has the following advantages:
1. Reliable and accurate. It can be concluded that keyboard input has an error every 300 characters on average, while barcode input has an error every 15000 characters on average. If you add check, the error rate is one in ten million.
2. Fast data entry. Keyboard input, a typist who types 90 words per minute can input 12 characters or strings in 1.6 seconds, while using bar code, the same work takes only 0.3 seconds, which is five times faster.
3. The economy is cheap. Compared with other automatic identification technologies, the popularization and application of bar code technology takes a long time and costs less.
4. Flexible and practical. As a means of identification, bar code symbols can be used alone, or can be combined with related equipment to form an identification system to realize automatic identification, and can also be linked with other control equipment to realize automatic management of the whole system. At the same time, when there is no automatic identification device, manual keyboard input can be realized.
5. Great freedom. The degree of freedom of the relative position between the identification device and the barcode label is much greater than OCR. Barcodes usually only express information in one dimension, but the information on the same bar code is exactly the same and continuous, so that even if the label part is defective, the correct information can still be input from the normal part.
6. The equipment is simple. Bar code symbol recognition equipment is simple in structure, easy to operate and does not need special training.
7. Easy to make. Printable, called "printable computer language". Bar code labels are simple to make and have no special requirements on printing technology, equipment and materials.