Barcode

Barcode technology was first developed in the turbulent 1920s and was born in Westinghouse's laboratory. An eccentric inventor named John Kermode "whimsically" wanted to automatically sort postal documents. At that time, every idea about the application of electronic technology was very novel.

His idea was to mark envelopes with barcodes. The information in the barcode was the address of the recipient, much like today's postal code. For this reason, Kermode invented the earliest barcode identification. The design scheme is very simple (note: this method is called the module comparison method), that is, one "bar" represents the number "1", and two "bars" represent the number "2". And so on. He then invented a barcode reading device consisting of basic components: a scanner (capable of emitting light and receiving reflected light); a method of measuring the reflected signal strips and voids, the edge positioning coil; and a device that uses the measurement results. method, the decoder.

Kermode's scanner used a then-newly invented photovoltaic cell to collect reflected light. The "empty" reflection is a strong signal, and the "bar" reflection is a weak signal. Unlike today's high-speed electronic components applications, Kermode uses magnetic coils to measure "bars" and "empties." It's like a child connecting a wire to a battery and wrapping it around a nail to clip paper. Kermode uses a coil with an iron core to attract a switch when it receives an "empty" signal, and when it receives a "bar" signal, it releases the switch and completes the circuit. As a result, the earliest barcode readers were noisy. The switch is controlled by a series of relays, and "on" and "off" are determined by the number of "strips" printed on the envelope. With this method, barcode symbols sort letters directly.

Shortly thereafter, Kermode collaborator Douglas Young made some improvements based on the Kermode code.

The amount of information contained in Kermode codes is quite low, and it is difficult to compile more than ten different codes. The Young code uses fewer bars, but takes advantage of the size variation of the spaces between the bars, just like today's UPC bar code symbols use four different bar space sizes. The new barcode symbology can encode a hundred different regions in the same size space, while the Kermode code can only encode ten different regions.

It was not until the patent documents of 1949 that the omnidirectional barcode symbol invented by Norm Woodland and Bernard Silver was recorded for the first time. Before that, there was no record of barcode technology in the patent documents, and there was no A precedent for practical application. Norm Woodland and Bemard Silver's idea was to take the vertical "bars" and "voids" of Kermode and YOung and bend them into a ring, much like an archery target. In this way, the scanner can decode the barcode symbol by scanning the center of the pattern, regardless of the direction of the barcode symbol.

In the process of continuously improving it using this patented technology, a science fiction writer Isaac-Azimov in his book "The Naked Sun" tells about the implementation of new methods using information encoding Examples of automatic identification. At that time, people thought that the barcode symbology in this book looked like a checkerboard with square tiles, but today's barcode professionals will immediately realize that it is a two-dimensional matrix barcode symbology. Although this barcode symbol has no direction, positioning or timing, it is clear that it represents a high information density digital encoding.

It wasn’t until 1970, when Iterface Mechanisms developed the “QR code”, that there were printing and reading equipment for two-dimensional matrix barcodes that were affordable for sale. At that time, two-dimensional matrix barcodes were used to automate the typesetting process in newspapers. Two-dimensional matrix barcodes are printed on paper tape and scanned and read by today's one-dimensional CCD scanners. The light emitted by the CCD shines on the paper tape, and each photocell is aimed at a different area of ??the paper tape.

Each photocell outputs a different pattern depending on whether the barcode is printed on the paper tape, and the combination produces a high-density information pattern. In this way a single character can be printed in the same size space as a single bar in early Kermode codes. Timing information is also included, so the whole process is reasonable. When the first systems hit the market, the complete set of equipment, including printing and reading equipment, cost approximately $5,000.

Shortly thereafter, with the continuous development of LEDs (light-emitting diodes), microprocessors and laser diodes, there was an explosion of new identification symbols (symbolism) and their applications, which people called "Barcode Industry". Today it is rare to find a company or individual who has not been directly exposed to fast and accurate barcoding technology. Due to the rapid technological progress and development in this field, and more and more application fields are being developed every day, it will not be long before barcodes are as popular as light bulbs and semiconductor radios, and will make every one of our lives All become easier and more convenient.

Bar code is a group of bar and space symbols arranged according to certain coding rules to represent information composed of certain characters, numbers and symbols. The barcode system is an automatic identification system consisting of barcode symbol design, production, and scanning and reading.

What is a barcode?

Barcode:

Barcode technology is a technology that is produced and developed in computer applications and practices and is widely used in commerce, postal services, library management, warehousing, industrial production process control, and transportation. Automatic identification technology in other fields has the advantages of fast input speed, high accuracy, low cost, strong reliability, etc., and occupies an important position in today's automatic identification technology.

The concept of barcode

A barcode is a mark composed of a set of regularly arranged bars, spaces and corresponding characters. The "bar" refers to the part with low light reflectivity, " "Empty" refers to the part with high light reflectivity. The data composed of these bars and spaces express certain information and can be read by specific equipment and converted into binary and decimal information compatible with computers. Usually, for each item, its code is unique. For ordinary one-dimensional barcodes, the corresponding relationship between the barcode and product information must be established through a database. When the barcode data is transmitted to the computer, it is processed by the computer. Applications operate and process data. Therefore, ordinary one-dimensional barcodes are only used as identification information during use, and their meaning is achieved by extracting the corresponding information from the database of the computer system.

Advantages of barcode technology

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

A. Fast input speed: Compared with keyboard input, barcode input is 5 times faster and can achieve "instant data input".

B. High reliability: the error rate of keyboard input data is one in 300, the error rate of using optical character recognition technology is one in 10,000, and the error rate of using barcode technology is less than one in a million.

C． Large amount of information collected: Traditional one-dimensional barcodes can collect information of dozens of characters at a time, while two-dimensional barcodes can carry information of thousands of characters and have certain automatic error correction capabilities.

D. Flexible and practical: Barcode identification can be used alone as a means of identification, or it can form a system with related identification equipment to achieve automated identification, and can also be connected with other control equipment to achieve automated management.

In addition, barcode labels are easy to produce and have no special requirements for equipment and materials. The identification equipment is easy to operate and does not require special training, and the equipment is relatively cheap.

Encoding rules

Uniqueness: Products of the same type and specifications should correspond to the same product code, and products of the same type and specifications should correspond to different product codes. Different product codes are assigned according to the different properties of the product, such as weight, packaging, specifications, smell, color, shape, etc. Permanence: Once a product code is assigned, it cannot be changed and is lifelong.

When such a product is no longer produced, its corresponding product code can only be put on hold and cannot be reused or allocated to other products. Meaningless: In order to ensure that the code has enough capacity to adapt to the needs of frequent product updates, it is best to use meaningless sequence codes.

The difference between barcode coding systems

UPC: (Unified Product Code) can only represent numbers. There are four versions: A, B, C, D, and E. Version A - 12-digit version E - The last digit of the 7-digit number is the check digit. The size is 1.5" wide and 1" high, and the background must be clear. It is mainly used in the United States and Canada, and is used in industry, medicine, warehouses and other sectors.lt;BRgt; lt; BRgt; When UPC is decoded as twelve digits, the definition is as follows: The first digit = numeric identification (has been established by the UCC (Uniform Code Committee)). The 2-6th digit = the manufacturer's identification number (including the One digit) No. 7-11 = unique manufacturer product code No. 12 = check digit (used for error detection)

Code 3 of 9: can represent letters, numbers and other symbols*** 43 characters: A -Z, 0 - 9, -.$/, the length of the pace barcode is variable. Usually "*" is used as the starting and ending character. The check code is not used. The code density is between 3 and 9.4 characters. /The blank area per inch is 10 times that of the narrow strip. It is used in industry, books, and ticket automation management

Code 128: Represents high-density data, string variable length symbol contains check code There are three different versions: A, B, and C. The available 128 characters are used in three string sets A, B, or C for industry, warehouse, retail and wholesale.

Interleaved 2-of-5 (I2 of 5): Can only represent numbers 0-9. Variable-length continuous barcodes. All bars and spaces represent codes. The first number starts with a bar and the second number consists of spaces. The blank area is 10 wider than the narrow bar. It has a high reading rate for barcodes in wholesale goods, warehouses, airports, production/packaging identification, and industry. It can be used for fixed scanners to scan reliably. It has the highest density among all one-dimensional barcodes

Codabar ( Qudba barcode): can represent numbers 0-9, characters, -, and four characters a, b, c d which can only be used as start/terminator

Variable length has no check Bits are used in material management, libraries, blood stations and current airport parcel delivery. The blank area is 10 times wider than the narrow strips of non-continuous barcodes. Each character is represented as 4 strips and 3 spaces.

PDF417 (two QR code): A multi-line barcode does not need to be connected to a database and can store a large amount of data. It is used in: hospitals, driver's licenses, material management, and cargo transportation. When the barcode is damaged to a certain extent, error correction can enable the barcode to be correctly decoded PDF417, It is a product developed by Symbol Technology Company in 1990. It is a multi-line, continuous, variable-length symbolic identifier that contains a large amount of data. Each barcode has 3-90 lines, and each line has a start part, data part, and end part. Its character set includes all 128 characters, and the maximum data content is 1850 characters.

One-dimensional barcodes only express information in one direction (usually the horizontal direction), but do not express any information in the vertical direction. Their certain height is usually to facilitate the alignment of the reader.

The application of one-dimensional barcodes can increase the speed of information entry and reduce the error rate, but one-dimensional barcodes also have some shortcomings:

* Small data capacity: 30 characters Left and right

* Can only contain letters and numberslt;BRgt;* Barcode size is relatively large (low space utilization)

* Barcode cannot be read after it is damaged

A barcode that stores information in two-dimensional space in the horizontal and vertical directions is called a 2-dimensional bar code.

Like one-dimensional barcodes, two-dimensional barcodes also have many different encoding methods, or coding systems. In terms of the coding principles of these code systems, they can usually be divided into the following three types

1. Linear stacked QR codes are based on the coding principles of one-dimensional barcodes, combining multiple one-dimensional codes. Produced by vertical stacking. Typical code systems include: Code 16K, Code 49, PDF417, etc.

2. Matrix QR code is encoded in a rectangular space through the different distribution of black and white pixels in the matrix. Typical code systems include: Aztec, Maxi Code, QR Code, Data Matrix, etc.

3. Postal code is encoded through bars of different lengths, mainly used for mail encoding, such as: Postnet, BPO 4-State.

Among many types of two-dimensional barcodes, commonly used code systems are: Data Matrix, Maxi Code, Aztec, QR Code, Vericode, PDF417, Ultracode, Code 49, Code 16K, etc., among which: lt; BRgt;* Data Matrix is ??mainly used for marking small parts in the electronics industry. For example, this code is printed on the back of Intel's Pentium processor. lt;BRgt;* Maxi Code was developed by the United Parcel Service (UPS) and is used for parcel sorting and tracking.

* Aztec is launched by the American Welch Allyn Company and can accommodate up to 3832 numbers or 3067 alphabetic characters or 1914 bytes of data.

Below, we take the PDF417 code as an example to introduce the characteristics and characteristics of the two-dimensional barcode.

1) Introduction to PDF417

The PDF417 code was invented by Dr. Wang Yinjing (sound), a Chinese student studying in the United States. PDF is the abbreviation of the three words Portable Data File in English, which means "portable data file". Because each symbol character that makes up a barcode is composed of 4 bars and 4 spaces, if the narrowest bar or space that makes up the barcode is called a module, then the total number of modules of the above 4 bars and 4 spaces is one. It is set as 17, so it is called 417 code or PDF417 code.

2) Characteristics of PDF417

1. Large information capacity. In addition to letters, numbers, and ASCII characters, PDF417 codes can also express binary numbers. In order to make the encoding more compact and increase the information density, PDF417 has three formats when encoding:

* Extended alphanumeric compression format can accommodate 1850 characters;

* Binary/ASCII format Can hold 1108 bytes;

* Number compressed format can hold 2710 numbers.

2. Error correction capability One-dimensional barcodes usually have a verification function to prevent misreading. Once the barcode is defaced, it will be rejected. The two-dimensional barcode can not only prevent errors, but also correct them. Even if the barcode is partially damaged, the correct information can be restored.

3. The printing requirements are not high. It can be printed with ordinary printing equipment, and faxes can also be read.

4. Can be read with a variety of reading devices. PDF417 codes can be read with laser readers with gratings, linear and area scanning image readers.

5. The size is adjustable to adapt to different printing spaces

6. The disclosure of code system has formed an international standard, and our country has also formulated a national standard of 417 codes.

3) Error correction function of PDF417

The error correction function of 2D barcode is achieved by repeatedly representing part of the information (redundancy). For example, in the PDF417 code, in addition to the information of this line, a certain line also contains information that reflects characters (error correction codes) in other positions. In this way, even if part of the barcode is damaged, its information can be restored through the error correction code that exists elsewhere.

The error correction ability of PDF417 is divided into 0~8***9 levels according to the number of error correction code words. See Figure 4. The higher the level, the more correction code words and the stronger the correction ability. Barcode Also bigger. When the correction level is 8, even if the barcode is stained 50%, it can still be read correctly, as shown in Figure 5.

4) Several deformations of PDF417

As shown in Figure 6, there are several deformed coding forms of PDF417:

* PDF417 truncation code is relatively In a "clean" environment, where the likelihood of barcode corruption is low, the line indicator on the right can be omitted and the terminators reduced.

* PDF417 microcode further reduced PDF code.

* Macro PDF417 code When the file content is too long and cannot be represented by one PDF417 code, it can be represented by a macro PDF417 code containing multiple (1~99999) barcode blocks.

Advantages of two-dimensional barcodes

As can be seen from the above introduction, two-dimensional barcodes have obvious advantages compared with one-dimensional barcodes, which can be summarized in the following aspects:

1) Larger data capacity

The PDF417 code in the picture contains all the text in the text box.

2) Beyond the limitations of alphanumeric characters

3) The barcode is relatively small in size

4) It is resistant to damage