Bar Code Technology

Since their invention in the early 1950s barcodes have accelerated the flow of products and information throughout the global business community. Coupled with the improvements in data accuracy that accompanies the adoption of barcode technology over keyboard data entry, barcode systems are critical elements in conducting business in today’s global economy. Bar code technology encompasses the symbologies that encode data to be optically read, the printing technologies that produce machine-readable symbols, the scanners and decoders that capture visual images of the symbologies and convert them to computer-compatible digital data, and the verifiers that validate symbol quality.

There are many different barcode symbologies, or languages. Each symbology has its own rules for character (e.g. letter, number, punctuation) encodation, printing and decoding requirements, error checking, and other features.

The various barcode symbologies differ both in the way they represent data and in the type of data they can encode: some only encode numbers; others encode numbers, letters, and a few punctuation characters; still others offer encodation of the 128-character, and even 256-character, ASCII sets. The newest symbologies include options to encode multiple languages within the same symbol; allow user-defined encodation of special or additional data; and can even allow (through deliberate redundancies) reconstruction of data if the symbol is damaged.

At the last count, there were about 225 known barcode symbologies but only a handful of these are in current use and fewer still are widely used.

Barcode Printing

Barcode symbols may be produced in a variety of ways: by direct marking, as with laser etching or with ink jet printing; or, more commonly by imaging or printing the barcode symbol onto a separate label. For our purposes, the terms "print" and "printer" refer to the production of a bar code whether the image is printed, etched, or imaged. The importance of precise bar code printing cannot be overstated; success of the whole set of integrated technologies that comprise an entire barcode system depends upon barcode print quality.

On-site Printing

On-site printing generally takes place at or near the point of use. The data encoded is usually variable, entered by an operator through a keyboard or downloaded from the host computer. The most common bar code print technologies for on-site use are:

• Direct Thermal — Heating elements in the printhead are selectively heated to form an image made from overlapping dots on a heat-sensitive substrate.
• Thermal Transfer — Thermal transfer technology uses much the same type of printhead as direct thermal, except that an intervening ribbon with resin-based or wax-based ink is heated and transfers the image from the ribbon to the substrate.
• Dot Matrix Impact — A moving printhead, with one or more vertical rows of hammers, produces images by multiple passes over a ribbon. These passes create rows of overlapping dots on the substrate to form an image. Serial dot matrix printers produce images character by character; high-volume dot matrix line printers print an entire line in one pass.
• Ink Jet — This technology uses a fixed printhead with a number of tiny orifices that project tiny droplets of ink onto a substrate to form an image made up of overlapping dots. Ink jet printers are used for in-line direct marking on products or containers.
• Laser (Xerographic) — The image is formed on an electrostatically charged, photo-conductive drum using a controlled laser beam. The charged areas attract toner particles that are transferred and fused onto the substrate.

On-site barcode printers come in a range of configurations as well as a wide variety of technologies. Users’ choices include:

• Large copy-machine-size dot matrix line printers, in-line ink jet printers, or in-line thermal transfer printer applicators for high-volume applications
• Desk-top dot matrix, laser, direct thermal, and thermal transfer printers for variable-demand print jobs
• Wireless direct thermal or thermal transfer printers for portable and field applications

Clearly, with the staggering range of choices available, users need to carefully determine their application parameters before going to purchase a bar code printer.

On-site printing most often involves purchasing label-design software as well as printer hardware. Barcode printers come with their own proprietary programming languages that support all the standard symbologies, and they are capable of printing simple data-static or serialized barcode labels on their own. However, labels that require additional formatted text, graphics, or multiple fields will require a separate label-design software package. Currently, more than 100 packages exist that are designed for a wide range of platforms and have a wider range of features. Once the purview of programmers, label design can now be accomplished by nonprogrammers via easy-to-use WYSIWYG graphical interfaces.

Off-site Printing

Generally speaking, commercial label printers may use flexographic, letterpress, offset lithographic, rotogravure, photocomposition, hot stamping, laser etching, or digital processes to produce a consistently higher-grade label than those labels produced by on-site printers. If the content of the barcode symbol is known ahead of use, a commercial label supplier is generally the best choice. However, there are tradeoffs. Commercially supplied labels have to be ordered, stocked, and placed in inventory. A business with frequent product line changes and/or label changes will have to weigh its options carefully.

BarCode Scanning

Barcode scanners are electro-optical systems that include a means of illuminating the symbol and measuring reflected light. The light waveform data is converted from analog to digital, in order to be processed by a decoder (which is either built into the scanner, or a separate plug-in device), and then transmitted to the computer-based application software.

Scanners are either handheld or fixed-mount. Handheld scanners are used to read bar codes on stationary items. With fixed-mount scanners, items having a barcode are passed by the scanner — by hand as in retail scanning applications, or by conveyor belt in many industrial applications.

Handheld scanners offer three different technology choices: contact wands, CCD (charge-coupled device), and laser. A wand is a pen-shaped device with a light aperture tip that the user draws across the bar code. Contact wands require some practice to achieve the proper degree of tilt (typically 30 degrees) and correct motion speed for a successful read, but they are the least expensive barcode scanning device.

At the next price level are CCD scanners that use a stationary flood of light [usually Light Emitting Diodes (LEDs)] to reflect the symbol image back to an array of photosensors. Depth of field (DOF), the optimal distance for the scanner to read the barcode, ranges from contact to six inches, though greater DOF has been achieved. Because CCD scanners contain no moving parts, they tend to be more rugged than laser scanners. CCD-based handheld image readers (see machine vision systems below), lately coming to market, are capable of reading 2D matrix as well as stacked and 1D codes.

Laser scanners employ a beam created by a laser diode that is spread into a horizontal arc by means of a rapidly moving mirror. Though the light sweeps at about 40 scans per second, it appears (if it is in the visible light spectrum) as a single line. Laser scanners that operate in the invisible infrared spectrum use some means of auxiliary lighting that enables users to aim the laser beam. Revolving polygons or oscillating mirrors may also be employed to produce a more sophisticated moving-beam rastered, cross hatched, or starburst pattern for improved readability and omnidirectional laser scanning.

The advantages of laser scanning include a larger field of view and also DOF, which averages 6 to 12 inches but can achieve distances of 35 feet (with special reflective long-range labels). Laser scanners can best tolerate symbol skew and are perceived by some as the easiest to use because of their DOF and broader field of view. The tradeoff, however, is a cost which is somewhat more expensive than CCDs. The latest development in handheld laser scanning technology is rastering scanners that read 2D stacked codes.

Fixed-mount scanners use either moving-beam laser or CCD technology (often referred to as "machine vision" or "vision-based" technology in the fixed-mount configuration). Laser fixed-mount scanners are most familiar at grocery checkout. They are also used widely in work-in-process (WIP) manufacturing applications and in warehousing and distribution sortation and shipping applications. Very small fixed-mount scanners are commonly used in laboratory and process control applications. Overhead or side-mounted laser scanners are most commonly used across all industries, but fixed-mount vision-based scanners are beginning to gain favor, especially in high-speed sortation.

Barcode Verification

As AIDC applications become more and more critical to a company’s success, the cost of barcode scanning failure becomes more significant. Such giant merchandisers as Wal-Mart, for example, have become famous for leveling whopping fines of $50,000 or more on suppliers whose product labels repeatedly misread. Consequently, bar code verification systems, once exclusively used by printers and label vendors, are now commonly used for on-site printing. Verifiers will grade a symbol unacceptable or by degrees of acceptability based upon ANSI’s published criteria, known as the Bar Code Print Quality Guideline. Verification devices can be integrated in-line, attached to the printer while monitoring the quality of every printed label or they can be used in a standalone configuration to audit batches of labels. In either case, verification can’t completely eliminate barcode performance problems. Verification can, however, provide a quantitative measure of print contrast and derive wide-to-narrow ratios, checking printed symbol conformance against symbology print quality standards.

Linear (One-Dimensional) Barcode Symbologies

Key Attributes and Limitations

• Well established, read-only, optical-read technology
• Low cost, label-based symbol formation by a variety of techniques
• Low capacity, typically 15-to-50 character carrying capability, depending upon symbology and the symbol form, favoring 'license plate' usage (code to locate data stored elsewhere)
• Accurate means of machine-readable coding, with different symbologies offering different levels of error detection/protection
• Symbologies available to accommodate numeric, alphanumeric, ASCII and other characters
• A range of symbologies supported by AIM Symbology Specifications, with a number of area-specific, open systems, applications adopting particular symbologies
• Variety of symbol (barcode) forming techniques (printing methods for bar code labels, pierced metal, impressed and composite formed symbols)
• Variety of labels and other substrate forms and symbol realizations to suit a variety of applications and user environments
• Fast, line-of-sight machine-readability, with a wide range of equipment available accommodating distances from direct contact to several meters, depending upon system and size of barcode symbols
• Wide range of symbol formation software, printer hardware, label products, scanning systems (portable and fixed position) and verifiers for assessing symbol quality
• Technical barcode label variants available to satisfy specialist applications (often with specialist read systems) - e.g. holographic security symbols and pierced metal bar codes for extremely harsh conditions

Barcodes in their most familiar format — a series of varying-width parallel bars and spaces — have been with us for over 25 years. These linear, or 1D (one dimensional as opposed to two dimensional barcodes discussed below) symbologies continue to be the most widely used optical recognition technology. Well over 100 encodation schemes or symbologies have been invented over the years, but the most common 1D symbologies are Code 39, pioneered by the defense and automotive industries; the Universal Product Code (U.P.C.), first employed by the supermarket industry in 1973; Codabar, used early on by blood banks, Interleaved 2-of-5 (ITF), and Code 128.

Depending upon which symbology is used, bar codes may encode only numeric data (U.P.C. and ITF, for example), or all or part of the American National Standard Code for Information Interchange (ASCII) character set (e.g., Codes 39 and 128) by the width of the bars, and in most cases by the width of the spaces as well. As a scanning device is moved across the symbol, the width pattern of the bars and spaces is analyzed to extract the original encoded data.

The width of the narrowest bar or space is referred to as the X dimension, usually given in mils (thousandths of an inch). The X dimension dictates the width of all other bars and spaces, and ultimately the length of the barcode. The greater the X dimension, the more easily a barcode will scan; however, the tradeoff for easier readability is the greater cost of bigger labels. For proper scanning, most barcodes have a quiet zone, i.e., clear space, at either end whose width is at least 10 times the barcode’s X dimension.

All barcodes use special patterns at each end, called start and stop characters. These characters identify the symbology and also enable the scanner to read the symbol bidirectionally, decoding the data in the correct order. Bar codes also often include a check digit at the end that is determined according to an algorithm based upon the preceding characters. The check digit validates that all characters have been decoded correctly.

Most bar codes include an interpretation line — the encoded data printed in human readable characters directly below the symbol. It is interesting to note that barcode technology made necessary the "human readable" designation for what used to be called simply numbers or text when humans were the only "readers."

Standardization within and across industries has been, and continues to be, essential to the phenomenal growth and widespread implementation of barcode technology. Barcode standards apply to printing, scanning, and verification of barcode symbologies. AIM, the leading standards developing organization for the AIDC industry, has published standard specifications for many symbologies. Additionally, the Uniform Code Council (UCC) and EAN has published specifications for the EAN/U.P.C. symbology.

These publicly available specifications allow AIDC vendors to produce labels, printers, scanners, verifiers, and entire integrated systems that can interact in an open business environment. The standardization of bar code label formats, under the aegis of ANSI (American National Standards Institute), CEN, and ISO/IEC has resulted in manufacturing, warehousing, and distribution cost savings and efficiencies across industries throughout the supply chain.

Two Dimensional (2D) Barcode Symbologies

The need to encode more information in a smaller space has driven the development, standardization, and growing use of 2D barcodes. Where traditional 1D bar codes act as a license plate to reference information stored in a database, 2D codes can fulfill the same function while taking up significantly less space. Or 2D codes can function as the database itself, and therefore assure complete portability for 2D labeled items.

There are two types of 2D barcodes in current use: stacked codes and matrix codes.

Stacked Symbologies

Stacked symbologies evolved as 1D codes — Code 39 and Code 128 — stacked in horizontal layers to create the multirow symbologies, Code 49 and Code 16K, respectively. PDF417 followed in 1990 with added features that increased data capacity, improved data density, and strengthened reading reliability by a scanner. These features enabled decoding from scan paths that span multiple adjacent rows while incorporating error detection and correcting techniques. PDF417 encodes the full ASCII character set at a maximum of about 2000 characters to four square inches. Uniform Symbol Specifications for Code 49, Code16K, and PDF417 are available from AIM. SuperCode, a stacked code that can break data into small packets and create various shaped symbols, is also available

Key Attributes and Limitations

• Well founded read only optical technology
• Printable similar techniques to linear barcodes
• Variety of labels and other substrate forms and symbol realizations to suit a variety of applications and user environments
• Readable by laser scan technology and image capture systems
• Range of symbologies with capacities up to 2000 or more characters
• Error detection and correction capabilities in most symbologies
• Most symbologies capable of handling international character sets using 'extended channel interpretation' system

Matrix Symbologies

Matrix symbologies offer higher data densities than stacked codes in most cases, as well as orientation-independent scanning. A matrix code is made up of a pattern of cells that can be square, hexagonal, or circular in shape. Data is encoded via the relative positions of these light and dark areas, and encoding schemes use error detection and correction techniques to improve reading reliability and enable reading of partially damaged symbols. Matrix codes are scaleable and well-suited both as small ID marks on products and as conveyor- scannable symbols on shipped packages.

Key Attributes and Limitations

• Well founded read only optical technology
• Printable similar techniques to linear barcodes
• Variety of symbol forming techniques (printing methods for label-based symbols, pierced metal, impressed and composite formed symbols
• Range of symbologies with capacities up to 2000 or more characters
• Error detection and correction capabilities essential
• Handle international character sets either natively or through extended channel interpretation

Composite Barcode Symbologies

This is a newly-emerging class of symbology in which two symbols are printed in close proximity (fixed relative positions) to each other and contain linked data.  Typically, one component is a linear symbol and the other either a multi-row or a matrix symbol.

These are intended for applications where different parts of the information may be required at different points of the item's life, and in cases where there are restrictions on the amount of space available in which, for example, a second linear barcode could be placed.

The major application will be that of the UCC.EAN composite symbol, which was originated to meet the needs of industries like pharmaceuticals where both product identification and supplementary information such as batch number and expiration date need to be encoded in a small space on a package.  These symbols comprise one of the standard UCC.EAN family of linear codes such as EAN- 13 or UPC-A, or a UCC.EAN 128 symbol, or the new RSS family of 'reduced space' symbologies together with an associated two-dimensional multi-row symbol.  There are tight rules governing the structure and positional relationship of the two symbols and there are normally also linkages encoded in each to indicate the need to look for the other component during the decoding process.  Certain users of these codes will need only to read the item identification in the linear symbol; others may need the full supplementary information carried in the two dimensional composite component.

Common Applications

Widespread use of bar code technology began 20 years ago in the supermarket industry and succeeded to the degree that virtually every grocery supplier now uses the U.P.C. symbol on product packaging to enable point-of-sale (POS) scanning. Mass merchandisers as well as a wide range of nongrocery retailers have followed grocers’ leads so that POS scanning is now a common fact of retail life.

Fifteen years ago, the Department of Defense required all incoming products to include a Code 39 barcode on packaging. This mandate ushered in a wave of manufacturers' implementations of barcode systems beginning at the shipping dock and quickly spreading to the factory floor. On the factory floor, bar code technology was used for time-and-attendance and labor reporting, work in process (WIP), inventory control, and various WIP applications like lot and process control, quality control, and finished goods inventory. Barcode technology then moved to the warehouse for receiving, putaway, picking, and packing applications.

Recent economic pressures, as well as increasing global competition, brought a giant wave of downsizing across a range of industries. In an effort to decrease costs and improve productivity, barcode technology became a priority for nearly every industry — from utilities to health care — especially in materials management (a.k.a. logistics) applications. Retail businesses that previously used barcodes only at POS followed Wal-Mart’s lead to automate their warehousing and transportation functions and reaped tremendous cost benefits.

Bar code technology is also used extensively for such applications as access control, asset tracking, cataloging of books and files by libraries and archives, document management, hazardous waste tracking, package tracking/delivery, and vehicle control/identification.

See our solutions page for industry specific applications.