Bar code technology was first produced in the trembling twenties, and it was born in the laboratory of Westinghouse. An eccentric inventor named John Kermode "whimsically" wants to realize the automatic sorting of postal documents. At that time, every idea about the application of electronic technology was very 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, Kermode invented the earliest bar code recognition, 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: 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.

Kermode's scanner uses a newly invented photocell to collect reflected light. "Empty" reflects a strong signal, while "bar" reflects a weak signal. Unlike today's high-speed applications of electronic components, Kermode 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. Kermode uses a coil with an iron core to attract a switch when receiving the "empty" signal, and release the switch when receiving 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, a collaborator of Kermode, made some improvements on the basis of Kermode code.

Kermode code contains so little information that it is difficult to compile more than ten different codes. Young codes use fewer bars, but the size of the space between bars changes, just as UPC barcode symbols today use four different bar sizes. The new bar code symbol can encode one hundred different regions in the same size space, while Kermode code can only encode ten different regions.

It was not until 1949 that the omni-directional bar code symbols invented by Noam Woodland and Bernard Silver were recorded for the first time. Prior to this, there was no record of bar code technology in patent literature, and there was no precedent for practical application. Noam Woodland and Bemmad Silver's idea is to use Kermode and Yang's vertical "strips" and "spaces" to bend them into a ring, 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 direction of the bar code symbol.

In the process of constantly improving this patented technology, the science fiction writer Isaac-Azimov described an example of automatic identification using a new information coding method in his book 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 Kermode 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 our life easier and more convenient.

Advantages of barcode technology

Bar code 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, which can realize "instant data input".

B High reliability: the error rate of keyboard input data is 300%, the error rate of optical character recognition technology is110000, and the error rate of barcode technology is less than110000.

C. The amount of information collected is large: 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 as a means of identification alone, can also be combined with related identification equipment to realize automatic identification, and can also be connected with other control equipment to realize automatic management.

In addition, the bar code label is simple to make, has no special requirements for equipment and materials, and the identification equipment is simple to operate without special training, and the equipment is relatively cheap.

code rule

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

Permanence: once the product code is assigned, it will not be changed, and it is lifelong. When the 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.

Code difference of bar code

Uniform product code

It can only indicate that there are four versions of a, b, c, d and e, version A- 12 and version E-7, and the last one is the check bit. The size is 1.5 "high 1" and the background is clear. Mainly used in the United States and Canada, used in industry, medicine, warehousing and other departments. When UPC is decoded into twelve bits, it is defined as follows: the first bit = digital identification (established by UCC (Unified Coding Committee)). Second-sixth digit = manufacturer's identification number (including the first digit) 7- 1 1 = unique manufacturer's product code 12 digits = parity bit (for error).

Code 3/9:

Can represent letters, numbers and other symbols ***43 characters: A-Z, 0-9,-. $/+%.The length of the pacing bar code can be changed. Usually "*" is used as the starting and ending symbols. The code density is 3-9.4 characters/inch, and the blank area is 10 times of the narrow strip, which is used for checking codes.

Code 128:

Represents high-density data, with variable string length and symbols containing check codes. There are three different versions: A, B and C can use 128 characters in the three string sets of A, B or C for industry, warehouse, retail and wholesale.

Staggered 2/5(I2/5):

It can only represent numbers 0 -9, variable length and continuous bar code. All bars and spaces represent codes. The first number begins with a bar, and the second number consists of spaces. The blank area is 10 times wider than the narrow strip. Used in commodity wholesale, warehouse, airport, production/packaging identification and industry. Bar codes have high recognition rate, can be used for reliable scanning of fixed scanners, and have the highest density among all one-dimensional bar codes.

Codabar (Kudba barcode):

It can represent the numbers 0-9, the characters $,+,-and the characters A, B and C D, and can only be used as starting and ending symbols. Its length is variable and there is no parity bit. It is used in material management, libraries, blood stations and current airport parcel delivery. The blank area is wider than the narrow column 10. It is a discontinuous bar code, and each character is represented by four bars with three spaces in the middle.

PDF4 17 (QR code):

Barcodes composed of multiple lines can store a large amount of data without connecting to a database. They are used in hospitals, driver's licenses, material management and cargo transportation. When the bar code is damaged to a certain extent, error correction can make the bar code correctly decode PDF4 17, which is a product developed by Symbol Technology Company in 1990. It is a multi-line, continuous and variable-length symbol with a large amount of data. Each bar code has 3-90 lines, and each line has a beginning part, a data part and an end part. Its character set includes all 128 characters, and the maximum data content is 1850 characters.

One-dimensional bar code only expresses information in one direction (generally horizontal direction), and does not express any information in the vertical direction. Its height is usually for readers' alignment.

The application of one-dimensional bar code can improve the speed of information input and reduce the error rate, but it also has some shortcomings:

* Small data capacity: about 30 characters.

* can only contain letters and numbers.

* Bar code size is relatively large (low space utilization)

* The bar code cannot be read after it is damaged.

Barcodes that store information in two-dimensional space in horizontal and vertical directions are called two-dimensional barcodes.

Like one-dimensional bar code, two-dimensional bar code has many different coding methods, or coding systems. As far as the coding principles of these codes are concerned, they can usually be divided into the following three types.

1. Linear stacked QR code

Based on the principle of one-dimensional bar code coding, multiple one-dimensional codes are vertically stacked. Typical coding systems are: Code 16K, Code 49, PDF4 17, etc.

2. Matrix QR code

According to the different distribution of black and white pixels in the matrix, they are coded in rectangular space. Typical coding systems include: Aztec, Maxi code, two-dimensional code, data matrix and so on.

3. Postal code

Bar codes with different lengths are mainly used for mail coding, such as Postnet and BPO 4-State.

Among many kinds of 2D barcodes, the commonly used coding systems are: Datamatrix, Maxicode, AZTEC, QR code, Vericode, PDF 4 17, Ultra Code, Code 49, Code 16K, etc. , in which:

* The data matrix is mainly used to identify small parts in the electronics industry, such as the code printed on the back of the Intel Pentium processor.

* Maxi Code was developed by United Parcel Service (UPS) to sort and track parcels.

* Aztec is introduced by Welch Allyn Company of the United States, and can accommodate up to 3832 numbers or 3067 alphabetic characters or 19 14 bytes of data.

Next, we take PDF4 17 code as an example to introduce the characteristics and characteristics of two-dimensional code.

Introduction to 1)pdf 4 17

The code PDF4 17 was invented by Dr. Wang, a China student studying in the United States. PDF is the abbreviation of English portable data file, which means "portable data file". Because each symbol character that constitutes a bar code consists of four bars and four spaces, if the narrowest bar or space that constitutes a bar code is called a module, then the total number of modules of the above four bars and four spaces must be 17, so it is called 4 17 code or PDF4 17 code.

2) Features of PDF 417

1. Large information capacity

PDF4 17 code can represent not only letters, numbers and ASCII characters, but also binary numbers. In order to make the encoding more compact and improve the information density, PDF4 17 has three formats when encoding:

* The expanded alphanumeric compression format can accommodate 1850 characters;

* binary /ASCII format can hold 1 108 bytes;

* Digital compression format can accommodate 27 10 digits.

2. Error correction ability

One-dimensional bar codes usually have verification function to prevent misreading. Once the bar codes are defaced, they will be rejected. Two-dimensional bar code can not only prevent errors, but also correct them. Even if the bar code is partially damaged, the correct information can be recovered.

3. The printing requirements are not high

Ordinary printing equipment can print and fax can read.

You can read with all kinds of reading equipment.

PDF4 17 code can be read by laser reader with grating and image reader with linear and surface scanning.

5. The size can be adjusted to suit different printing spaces.

6. The coding system has become an international standard, and China has also formulated a national standard of 4 17 code.

3) error correction function of pdf 417.

The error correction function of two-dimensional bar code is realized by repeating (redundant) some information. For example, in the PDF4 17 code, a line contains not only the information of its own line, but also some information reflecting the characters in other positions (error correction code). In this way, even when a certain part of the bar code is damaged, its information can be recovered by error correction codes existing in other places.

The error correction capability of PDF4 17 is divided into 0~8***9 levels according to the number of error correction codes, as shown in Figure 4. The higher the level, the more correction codes, the stronger the correction ability and the larger the bar code. When the correction level is 8, even if the barcode is defaced by 50%, it can be read correctly.

4) several variants of pdf 417.

PDF4 17 also has several different coding forms:

* PDF4 17 truncation code

In a relatively "clean" environment, the bar code is less likely to be damaged, so you can omit the line indicator on the right and reduce the terminator.

* PDF4 17 microcode

Further reducing the PDF code.

* macro PDF4 17 code

When the file content is too long to be represented by PDF4 17 code, it can be represented by macro PDF4 17 code containing multiple (1~99999) barcode blocks.

Advantages of two-dimensional bar code

As can be seen from the above introduction, compared with one-dimensional bar code, two-dimensional bar code has obvious advantages, which can be summarized as follows:

1) larger data capacity.

2) Exceeding the limit of alphanumeric characters.

3) The relative size of bar code is small.

4) Have the ability to resist destruction.

Reference: /view/ 13740.htm