bar code

the concept of bar code

a bar code or barcode is a graphic identifier that arranges a plurality of black bars and blanks with different widths according to certain coding rules to express a group of information. The common bar code is a parallel line pattern composed of black bars (referred to as bars) and white bars (referred to as spaces) with great differences in reflectivity. Barcode can indicate the country of production, manufacturer, commodity name, date of production, book classification number, starting and ending place of mail, category, date and many other information, so it has been widely used in many fields such as commodity circulation, book management, postal management, banking system and so on.

[ Edit this paragraph] I. The history of bar code

Bar code technology was first produced in the turbulent 192s 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 very novel.

His idea is to mark the envelope with a bar code, and the information in the bar code is the address of the recipient, just like today's postal code. For this reason, Comander invented the earliest bar code identification, and the design scheme is very simple (note: this method is called modular comparison method), that is, one bar represents the number "1", two bars represent the number "2", and so on. Then, he invented a bar code reading device composed of basic components: a scanner (which can emit light and receive reflected light); A method for measuring the reflection signal strip and space, that is, 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, and "bar" reflects a weak signal. Different from today's high-speed electronic components, Comander uses magnetic coils to measure "bars" and "spaces". It's 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 a switch when it receives an "empty" signal, and releases the switch and connects the circuit when it receives a "bar" signal. Therefore, 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 "strips" printed on the envelope. In this way, the bar code symbol directly sorts the letters.

shortly thereafter, Douglas Young, Comander's collaborator, made some improvements on Comander's code.

Comande code contains very little information, and it is difficult to compile more than ten different codes. Yang code, on the other hand, uses fewer bars, but takes advantage of the size change of the spaces between bars, just like UPC barcode symbols today use four different bar sizes. The new bar code symbol can code 1 different regions in the same size space, while Comander code can only code 1 different regions.

it was not until 1949 that the omni-directional bar code symbols invented by Norm Woodland and Bernard Searwar were recorded for the first time in the patent documents. before that, there was no record of bar code technology and no precedent for practical application. Noam Woodland and Bernard Searwar's idea is to use Comander's and Yang's vertical "strips" and "spaces" and bend them into rings, much like the target of archery. In this way, the scanner can decode the bar code symbol by scanning the center of the graph, regardless of the orientation of the bar code symbol direction.

in the process of constantly improving this patented technology, Isaac Azimov, a science fiction writer, described an example of automatic identification using a new method of information coding in his book The Naked Sun. At that time, people thought that the bar code symbol in this book looked like a chessboard of Fang Gezi, but today's bar code professionals will immediately realize that it is a two-dimensional matrix bar code symbol. Although this bar code symbol has no direction, positioning and timing, it is obvious that it represents digital coding with high information density.

it was not until the "two-dimensional code" was developed by Iterface Mechanisms in 197 that the printing and reading equipment of two-dimensional matrix bar code was available at an affordable price. At that time, two-dimensional matrix bar codes were used to automate the typesetting process of newspapers. 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 the paper tape or not, and combines them to generate a high-density information pattern. 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 enters the market, the complete set of equipment including printing and reading equipment will cost about $5,.

shortly thereafter, with the continuous development of LED (light emitting diode), microprocessor and laser diode, a new symbol (symbolism) and its big explosion were ushered in, which was called "barcode industry". Today, it is rare to find companies or individuals who have not been directly exposed to the fast and accurate barcode technology. As the technical progress and development in this field is very rapid, and more and more application fields are developed every day, it won't be long before bar codes become as popular as light bulbs and transistor radio, which will make everyone's life easier and more convenient.

[ Edit this paragraph] II. Recognition principle of bar code

To convert a 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 its reflected light. White objects can reflect visible light of various wavelengths, while black objects absorb visible light of various wavelengths. Therefore, when the light emitted by the light source of the barcode scanner is reflected on the barcode, the reflected light shines on the photoelectric converter inside barcode scanner, and the photoelectric converter converts it into corresponding electrical signals according to the reflected light signals with different intensities. According to the difference of principle, scanners can be divided into three types: light pen, CCD and laser. The electric signal is output to the amplification circuit of 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. Then the decoder determines the number of bars and spaces by measuring the number of pulse digital electrical signals and 1. By measuring the duration of ,1 signal, the width of bar and space can be judged. At this time, the data obtained is still chaotic. To know the information contained in the bar code, it is necessary to change the bar symbol into the corresponding number 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 for data processing and management.

[ Edit this paragraph] III. Advantages of barcode

1. Strong reliability. The reading accuracy of bar code far exceeds that of manual recording, with an average error every 15, characters.

2. High efficiency. The reading speed of bar code is very fast, which is equivalent to 4 characters per second.

3. low cost. Compared with other automatic identification technologies, bar code technology only needs a small sticker and a relatively simple optical scanner, and the cost is quite low.

4. easy to make. Bar code is very simple to write and only needs to be printed, so it is called "printable computer language".

5. Easy to operate. Bar code recognition equipment is simple in structure and convenient to use.

6. Flexible and practical. Bar code symbols can be entered by manual keyboard, and can also be combined with related equipment to realize automatic identification, and can also be linked with other control equipment to realize automatic management of the whole system.

[ Edit this paragraph] IV. Scanning of bar code

The scanning of bar code requires 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 zone, start character, data character and end character. Some barcodes also have a check character between the data character and the termination character.

▲ quiet zone: as the name implies, an area that does not carry any information, which plays a prompting role.

▲ Start character: the first character with a special structure. When the scanner reads this character, the code will be officially read.

▲ data character: the main content of bar code.

▲ check character: check whether the read data is correct. Different coding rules may have different checking rules.

▲ Termination character: the last character, which also has a special structure, is used to inform static code analysis that it is finished, and also plays the role of only checking calculation.

in order to facilitate bidirectional scanning, the starting and ending characters have an asymmetric structure. Therefore, the scanner can automatically rearrange the bar code information when scanning. There are three kinds of light pen, CCD and laser in barcode scanner

▲ Light pen: the most primitive scanning method requires manual movement of light pen and contact with 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.

line type: mostly used for hand-held scanners, with long range and high accuracy.

all angles: mostly horizontal, with high degree of automation, which can automatically read bar codes in all directions.

[ Edit this paragraph] V. Advantages of barcode technology

Barcode is by far the most economical and practical automatic identification technology. Bar code technology has the following advantages

A. Fast input speed: compared with keyboard input, bar code input speed is five times that of keyboard input, and it can realize "instant data input".

B. High reliability: the error rate of keyboard input data is 1: 3, that of optical character recognition technology is 1: 1, and that of bar code technology is less than 1: 1.

C. A large amount of information is collected: the traditional one-dimensional bar code can collect dozens of characters at a time, and the two-dimensional bar code can carry thousands of characters, and it has certain automatic error correction ability.

D. Flexible and practical: Bar code identification can be used alone as a means of identification, can also be combined with relevant identification equipment to realize automatic identification, and can also be connected with other control equipment to realize automatic management.

In addition, bar code labels are easy to make, and there are no special requirements for equipment and materials. The identification equipment is easy to operate, and it does not need special training, and the equipment is relatively cheap.

[ Edit this paragraph] VI. Coding rules of bar codes

Uniqueness: the same product with the same specification corresponds to the same product code, and the same product with different specifications should correspond to different product codes. According to the different properties of products, such as weight, packaging, specifications, smell, color, shape, etc., different commodity codes are given.

permanence: once the product code is assigned, it will not be changed, and it is lifelong. When this product is no longer produced, its corresponding product code can only be shelved and cannot be reused and redistributed to other commodities.

meaningless: in order to ensure that the code has enough capacity to meet the needs of frequent product updates, it is best to use meaningless sequence codes.

formula of barcode check code:

1. First, number the barcode from right to left as "... 4, 3, 2, 1." Add and sum all the numbers on even-numbered bits starting from the second serial number, multiply the calculated sum by 3, then add and sum all the numbers on odd-numbered bits starting from the third serial number, add the calculated sum with the product of the sum of the numbers on even-numbered bits multiplied by 3, and then get the sum. Subtract this sum by a multiple of 1 greater than the minimum sum to get the check code.

For example:

This barcode is: 97716712161X(X is the check code).

1, 1+6+2+7+1+7=24

2, 24× 3 = 72

3, +1+1+6+7+9=24

4 and 72+24=96

5. This barcode is 977167121614.

[ Edit this paragraph] VII. The coding difference of bar code

UPC: (Uniform product code)

It can only indicate that there are four versions of numbers: A, B, C, D and E. The last digit of the A-12 digit version E-7 digit is a parity bit with a width of 1.5 "and a clear background. It is mainly used in the United States and Canada for When UPC is decoded as twelve bits, The definition is as follows: the first digit = digital identification (established by UCC (Unified Code Committee)). The 2nd-6th digits = the identification number of the manufacturer (including the first digit), the 7th-11th digits = the 12th digit of the unique manufacturer's product code = check digit (used for error detection)

Code 3 of 9:

can represent letters, Numbers and other symbols ***43 characters: A-Z, -9,-.$/+%.The length of PACE barcode can be changed. Usually, the "*" is used as the starting and ending symbol. The code density of the check code is 3-9.4 characters/inch, and the blank area is 1 times that of the narrow bar. It is used in industry, books and automatic ticket management.

Code 128:

represents high-density data, with variable-length strings and symbols containing check codes. There are three different versions: A, B, and C, with 128 characters, respectively, in the three string sets of A, B, or C, which are used in industry, warehouse, retail and wholesale.

Interleaved 2-of-5 (I2 of 5):

It can only represent numbers -9, and it is a continuous bar code. All bars and spaces represent codes. The first number starts with bars, and the second number consists of spaces, and the blank area is 1 times wider than the narrow bar. It is used in commodity wholesale, warehouse, airport, production/packaging identification, and industry to read bar codes.