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 according to certain coding rules (coding system), which is used to represent a group of digital 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 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 recognition principle of bar code
Due to the different wavelengths of visible light reflected by objects of different colors, white objects can reflect visible light of various wavelengths, while black objects absorb visible light of various wavelengths. When the light emitted by the light source of barcode scanner passes through the diaphragm and convex lens 1 to irradiate the black-and-white bar code, the reflected light is focused by convex lens 2 and irradiated on the photoelectric converter. Therefore, the photoelectric converter receives reflected light signals with different intensities corresponding to white bars and black bars, and converts them into corresponding electrical signals to be output to the amplification and shaping circuit. 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. Therefore, the number of bars and spaces for bar code symbols and the corresponding width and code system can be obtained. According to the coding rules corresponding to the coding system, bar code symbols can be converted into corresponding digital and text information, and sent to the computer system for data processing through the interface circuit.
Four, bar code technology and its application
Bar code technology belongs to the category of automatic identification. It is a practical data input technology developed with the progress of electronic technology, especially the wide application of computer technology in modern production and management. From the system point of view, barcode technology involves coding technology, optical sensing technology, barcode printing technology and computer identification application technology.
Bar code is composed of a group of bars and spaces with different widths and reflectivity according to the specified coding rules, which is used to represent a group of data and symbols. Bar code technology is to study how to use bar code to represent the data needed by the computer and how to transform the data represented by bar code into data that can be automatically collected by the computer. Therefore, barcode technology mainly includes: barcode coding principle and rule standard, barcode decoding technology, photoelectric technology, printing technology, scanning technology, communication technology, computer technology and so on. Specifically, bar code is a printable machine language, which adopts the concept of binary number and represents the specific combination unit of coding through L and 0. Intuitively, commonly used bar codes are composed of a set of characters, such as numbers 0-9, letters A-E or some special symbols.
Bar code is a form of information recording. According to different coding rules, there are more than forty barcode numbering schemes. At present, the most widely used codes are: cross 25 code, 39 code, UPC code, EAN code, 128 code, etc. In recent years, there have been two-dimensional barcodes that arrange information in a matrix or stack. According to the material and color of printed bar code, it can be divided into black and white bar code, color bar code, luminous bar code (fluorescent bar code, phosphorescent bar code) and magnetic bar code.
No matter what kind of bar code, there are some similarities: the graphic structure of bar code symbols is simple; Each bar code character consists of a certain bar code symbol, occupying a certain width and printing area; Each coding scheme has its own character set; Each coding scheme matches the performance requirements of the corresponding reading device very well.
Bar code system is an automatic identification system composed of bar code symbol design, production and scanning reading. Bar code reader is the basic equipment of bar code system. Its function is to read bar code symbols, that is, to convert bar code width, interval and other signals into output signals with different time lengths, and then convert the signals into binary codes that can be recognized by the computer, and then input them into the computer. The reading device consists of a scanner and a decoder. Scanner, also known as photoelectric reader, is equipped with a beam detector to illuminate the bar code to be read, receive the reflected light of the bar code, generate analog signals, and send them to the decoder for processing after amplification and quantization. The scanner can be a light pen or a laser gun, which is operated by a person. It can also be an automatic scanner installed in a certain part, which usually includes fixed beam scanner, linear scanner, progressive scanner and omnidirectional scanner. The decoder stores the decoding algorithm of the database with the barcode coding scheme to be translated. The early recognition equipment, scanner and decoder were separated, but most of the imported equipment has been integrated in recent years, and the whole equipment is complete, convenient and dexterous.
When the computer is equipped with interface software and hardware such as network controller, this bar code system can simultaneously process the bar code information input by multiple bar code readers. The reading performance of the bar code system, that is, whether the bar code system can be successfully applied, mainly depends on the reading ability of the system and the printing quality of the bar code, which are inseparable. Bar code is powerful, and its input mode has the characteristics of high speed, high precision and strong reliability. It has been widely used in commodity circulation, industrial production, warehouse label voucher management, information service and other fields.