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. Barcodes can indicate the country of production, manufacturer, product name, production date, book classification number, starting and ending place, category and mailing date, so they are used in commodity circulation, book management, post and telecommunications management, etc. 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 (referred to as bars) and white bars (referred to as spaces) with different reflectivity.
Bar code development history
Wrigley gum is the first product with a bar code. Bar code technology was first produced in the jittery 1920s, and was born in the laboratory of Westinghouse. John Kermode, an eccentric inventor, wanted to sort postal documents automatically in a whimsical way. At that time, every idea about the application of electronic technology was novel.
His idea is to put a barcode on the envelope, and the information in the barcode is the address of the recipient, just like today's postal code. For this reason, Comander invented the earliest bar code recognition, and the design scheme is very simple (note: this method is called modular comparison method), that is, one represents the number "1", two represents the number "2", and so on. Then, he invented a bar code reading device composed of basic components: scanner (which can emit light and receive reflected light); A method for measuring the band and space of reflected signal, namely edge positioning coil; And a method of using the measurement result, namely a decoder.
Comander's scanner uses a newly invented photovoltaic cell to collect reflected light. "Empty" reflects a strong signal, while "bar" reflects a weak signal. Unlike today's high-speed electronic components, Comander uses magnetic coils to measure "bars" and "spaces". Just like a child connecting a wire to a battery and winding it around a nail to clamp paper. Comander uses a coil with an iron core to attract the switch when it receives the "empty" signal, and release the switch when it receives the "bar" signal to connect the circuit. So the earliest bar code readers were very noisy. The switch is controlled by a series of relays, and the "on" and "off" are determined by the number of "paper strips" printed on the envelope. In this way, the bar code symbol directly sorts the letters.
Shortly thereafter, douglas young, Comand's collaborator, made some improvements to the Comand code.
Comande code contains so little information that it is difficult to compile more than ten different codes. On the other hand, Yang code uses fewer bars, but takes advantage of the change of the space between bars, just like UPC barcode symbols today use four different bar sizes. The new barcode symbol can encode 100 different regions in the same space, while Comander code can only encode 10 different regions.
It was not until 1949 that the omni-directional bar code symbols invented by Norm Woodland and Bernard Searwar were first recorded in patent documents. Prior to this, there was no record of bar code technology and no precedent for practical application. The idea of Noam Woodland and Bernard Searwar is to use the vertical "strips" and "spaces" of Comander and Yang, and bend them into rings, much like archery targets. In this way, the scanner can decode the bar code symbol by scanning the center of the graph, regardless of the direction of the bar code symbol.
In the process of perfecting this patented technology, the science fiction writer Isaac Azimov described an example of automatic identification using a new information coding method in his book The Naked Sun. At that time, people thought that the barcode symbol in this book looked like Fang Gezi's chessboard, but today's barcode professionals will immediately realize that it is a two-dimensional matrix barcode symbol. Although this bar code symbol has no direction, no positioning and no timing, it is obvious that it represents a digital code with high information density.
It was not until 1970 that ITER FACE MACHINES developed "two-dimensional code", and the printing and reading equipment of two-dimensional matrix bar code came out at a price suitable for sale. At that time, two-dimensional matrix bar code was used to realize the automation of newspaper typesetting process. Two-dimensional matrix bar code is printed on paper tape and scanned and read by today's one-dimensional CCD scanner. The light emitted by CCD shines on the paper tape, and each photocell is aimed at different areas of the paper tape. Each photovoltaic cell outputs different patterns according to whether the bar code is printed on paper tape or not, and combines them to generate high-density information patterns. In this way, a single character can be printed in the same size space as a single bar in the early Comander code. Timing information is also included, so the whole process is reasonable. When the first system entered the market, the price of the whole set of equipment including printing and reading equipment was about $5,000.
Shortly thereafter, with the continuous development of LED (light emitting diode), microprocessor and laser diode, a new symbol (symbolism) and its explosion came, which was called "barcode industry". Today, it is difficult to find companies or individuals who have not been directly exposed to fast and accurate barcode technology. With the rapid technological progress and development in this field, more and more application fields are developed every day. Before long, bar codes will be as popular as light bulbs and transistor radios, which will make everyone's life easier and more convenient.
Bar code principle
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.
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 (as shown in the figure):
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