Материал: Крючков Фундаменталс оф Нуцлеар Материалс Пхысицал Протецтион 2011

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UPC/EAN Code (UPC – Uniform Product Code, EAN – European Article Code). Has a highly common use in all retail and worldwide trade applications. This code has several versions. In its basic versions, this is a digital, continuous code with a fixed number of characters (basic version has 12 characters, inclusive of the check character). The highest possible record density is 5.5 characters per cm.

The code symbol has two halves. The left-hand half contains the manufacturer number as specified in the Unified Commercial Code (UCC), and the right-hand one contains the manufacturer-assigned product number. The code includes self-testing based on the checking character and by parity. The symbol’s left-hand half is tested for oddity and the right-hand half is checked for parity. Figure 9.3 shows the structure of characters in UPC-A code’s right-hand half. A symbol’s right-hand half has characters beginning with a bar and ending in spacing, the symbol’s left-hand half having, contrarily, each character beginning with spacing and ending in a bar.

UPC– A code

∙Character length – 7 Х

∙Character comprises 2 bars and 2 intervals

∙Bar or spacing width is a multiple of Х and may equal Х, 2Х, 3Х, 4Х.

Fig. 9.3. Structure of the UPC–A code’s right-hand characters.

PDF417 Code is a barcode with a high data density in excess of the standard density by about a factor of 100. Code PDF417 is a commonly accessible barcode standard with a capability to record comparatively large arrays of data. It includes the complete set of ASCII–codes and is used as a compact data file with product documentation, medical data and so on. Symbols are placed on labels and tags. The highest possible record density

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is 360 characters per cm. The message is capable of comprising up to 1850 characters.

Printing and reading of barcode symbols

Barcode symbols may be applied to the whole range of materials, including paper, plastic, metal, glass, wood and others. Symbol application requires printers with respective software. Symbols may be applied both to articles and to special tags and labels that are attached to articles. Thus, Figure 9.4 shows the design of a standard sticker. This represents a multilayer sandwich of at least 3 layers.

покрытиеcoating

face

лицевой материалmaterial

adhesive

клеящийся материалmaterial

защитнаяsafety прокладкаlining

Fig. 9.4. Composite layers of a barcode sticker

Various technologies are used to print barcode symbols: conventional (offset lithography), matrix, thermal and other print technologies. Offset lithography is the best process to produce large numbers of one symbol, this requiring a print matrix to be made with the image transposed then from the matrix onto the drum. All labels obtained are identical but cheap to make.

Thermal printing uses a matrix of heating elements. The elements are switched on and off selectively for image generation. Zebra S–500, a thermal printer by Zebra Technologies Corporation, is convenient to use to make self-adhesive labels with a high print quality. It supports printing of

barcodes using 15 symbologies, including PDF–417. T he printing speed is 5÷15 cm per second and the resolution is about 8 dots per mm. Labels are

relatively cheap to print if batches thereof are not large. A special basis is however required for printing.

Barcode symbols applied directly to articles are more durable and harder to falsify as compared to labels and tags. Still, this marking application

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technique may involve process complexities. Choosing a technology to apply barcodes to articles requires further operational environments for these to be accounted for. Inter alia, this includes a potentiality of the coating to which the barcode is applied to be damaged or wear out, the requirement of decontamination, restrictions with respect to adding harmful substances and so on. So, practically, barcodes are applied to pretreated metal surfaces using:

∙laser-beam surface treatment;

∙jet printers;

∙extrusion;

∙etching, etc.

Ink-jet technology, which is contactless, may be used to apply marking to different surfaces, including abrasive, fragile and rough ones. One example is Willet 3940, an ink-jet printer that applies images by an electronically controlled ink jet directed onto the surface. The complexity of the jet control system confines uses of Willet 3040 to applications not accessible to other printers.

Therefore, there is a range of technologies and respective devices to apply barcode symbols to articles. Quality requirements and potential operation environments are what selection of techniques to apply symbols to articles relies on. Developed printing software provides automation of respective processes.

Readers are used to read barcodes with data transmitted further to a computer via an interface. Readers receive a standard electric signal that matches in time the symbol’s spatial image and convert this signal to ASCII–coded words. Readers have two component devic es:

∙a scanner that emits a controlled luminous flux, receives and measures the reflected light, and generates the electric signal;

∙a decoder that analyzes the electric signal from the scanner and converts the signal to an ASCII–code form.

Nowadays, there are many barcode readers in a range from elementary scanners to multi-channel, high-speed data capture and handling terminal devices.

Scanners differ in light sources (LED, laser), beam movements (scanning and fixed-beam), type of contact with the barcode symbol (contact or contactless) and type of installation (portable or fixed).

Decoder functions are:

∙recognition of the scanned item as a barcode;

∙determination of the wide bar/narrow bar width ratios;

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