Bar Code Technology
Invented early in the 1950s, barcodes accelerate the flow of information and products through the worldwide business community. Barcode technology excels over keyboard data entry by greatly improving the accuracy of data, so barcode systems are now critical to the conduct of business in the global economy. This technology consists of the symbologies to encode data that can be optically read, the programs that print symbols to be read by machines, the scanning and decoding equipment that creates visual images of the symbols and converts them into digital data compatible with computers, and the verifiers of symbol quality.
Each of the many barcode symbologies (languages) has its own rules for encoding character (e.g., number, punctuation, letter), decoding and printing, checking for errors, and other features.
The numerous barcode symbologies differ in their data representation and in the kind of data they are able to encode. Some encode only numbers; others letters, numbers, and a very few punctuation marks; still others encode both ASCII sets, the 128-character and 256-character. The newest languages have options to code several languages in the same symbol; to allow encoding, defined by the user, of additional or special data; and even to build in redundancies to permit reconstruction of data if a symbol is damaged. There are more than 225 known barcode symbologies; however, only a few are currently in use and even fewer are still widely used.
Barcode symbols are created by marking directly with laser or ink jet printing, or more often by printing or imaging the barcode symbol on individual labels. In any case, "printer" and "print" indicate the production of a barcode image whether or not it is imaged, etched, or printed. Precise barcode printing is of most importance; the success of all of the integrated technologies in the entire barcode system depends on the print quality of the barcode.
On-site printing usually is located near or at the location of use. Encoded data is generally variable. It is either downloaded by the system computer or entered by a keyboard operator. For on-site applications, the most used barcode print technologies are as follows:
- Dot Matrix Impact — Equipped with one or several hammers in vertical rows, the printhead makes many passes over a ribbon, creating an image with rows of overlapped dots on the required substrate. Serial dot matrix printers lay down images one character at a time. Higher volume line printers can print a whole line in a single pass.
- Direct Thermal — In the printhead, selected heating elements are heated to form a pattern of overlapping dots on a substrate that is sensitive to heat.
- Thermal Transfer — Although it uses a printhead similar to that in the direct thermal process, a ribbon impregnated with either hot wax- or resin-based ink transfers the desired image onto the substrate.
- Ink Jet — Through tiny orifices, a stationary printhead projects tiny ink droplets onto a substrate to print an image consisting of overlapping dots. Ink jet printers are most useful for direct, in-line marking on containers or products.
- Laser — The xerographic process employs a controlled laser beam to create an image on a photo-conductive drum that is electrostatically charged. Toner particles are attracted to charged areas, transferred, and then fused to the substrate.
On-site barcode printers are available in many configurations and in a range of technologies:
- For jobs to suit variable demands, thermal transfer, direct thermal, laser, or desk-top dot matrix printers.
- For high-volume jobs, ink jet printers used in-line, dot matrix line printers as large as copy machines, or thermal transfer printers used in-line.
- For field and portable applications, thermal transfer printers or wireless direct thermal printers.
With so many choices, users must consider the parameters of their application carefully before selecting a barcode printer.
Most often, printing at your site requires the purchase of software for label design, along with the printer hardware. Barcode printers have their own built-in programming languages to support the most often used symbologies, and thereby are able to print serialized barcode labels and uncomplicated data-static labels.
However, if labels must have more complex graphics, multiple fields, or formatted text, a separate software package for label design is required. Currently, over 100 packages are designed to work on a number of platforms with many more features. Label design no longer requires programmers and can be easily executed with WYSIWYG graphical interfaces.
Commercial printers can produce consistently better-quality labels because they use digital, laser etching, hot stamping, photocomposition, rotogravure, offset lithographic, letterpress, or flexographic processes. A commercial supplier of labels is usually the better choice if the contents of the barcode symbol are already known, but such labels have a downside. They must be ordered and stocked and inventoried so they are not appropriate for companies whose product lines or labels are frequently changed.
Barcode scanners work electro-optically to illuminate the symbol and measure the reflected light. Analog data from this light waveform is then converted to digital so it can be processed by the decoder (which can be built into a separate plugged-in device or into the scanner) and transmitted to application software in the computer.
Scanners can be either on a fixed mount or handheld. Handheld scanners read barcodes on items that are stationary. Scanners on fixed mounts read barcoded items that pass by the scanner, for example, on an industrial conveyor belt or by hand in a retail setting.
Handheld scanners present a choice of three different technologies: a contact wand, a laser, and a charge-coupled device (CCD):
- The contact wand, a pen-shaped wand with a light aperture tip, is drawn across the barcode by the user. They require practice to learn the proper angle (about 30 degrees) and speed to read successfully. They are the least costly device for scanning barcode, although not commonly used these days.
- One step above in cost are CCD scanners. They use a strong stationary flood light, generally light-emitting diodes (LEDs), to bounce the image of the symbol back to a photosensor array. Depth of field (DOF), the best reading distance between the CCD scanner and the barcode, is generally 0 to 6 inches, although greater depth of field has been successfully achieved. Because there are no moving parts in CCD scanners, they are more rugged than are laser scanners. Handheld image readers that are CCD-based (see machine vision systems below) are able to read 2D matrix as well as 1D codes and stacked codes.
- Laser scanners operate with a laser diode-created beam swept in a horizontal arc by a swiftly moving mirror at about 40 scans per second. If the light is in a visible spectrum it looks like a single line. When a laser scanner operates in the invisible infrared spectrum, some type of auxiliary lighting equips users to aim the laser beam. Oscillating mirrors or revolving polygons might also be used to produce a more complex moving-beam starburst, cross-hatched, or rastered pattern to improve readability or omnidirectional laser scanning. Laser scanning offers several advantages, including a bigger field of view and depth of field, which is generally 6 to 12 inches but can operate up to 35 feet with the use of special long-range labels that are reflective. Laser scanners are best at tolerating symbol skew and are thought by some users to be the easiest to use because of their broad field of view and DOF. However, they are costlier than CCDs. The latest technology for handheld laser scanning is rastered scanning that can read 2D stacked codes. Scanners on a fixed mount operate with either CCD technology, usually called "vision-based" or "machine vision" technology when fixed-mounted) or moving-beam laser technology. Laser fixed-mount scanners are used widely at grocery checkouts, distribution, shipping and warehousing centers, and work-in-process (WIP) manufacturing.
Extremely small fixed-mount scanners are often used in process control and laboratory applications. In all types of industries, side-mounted or overhead laser scanners are common, but vision-based fixed-mount scanners are gaining favor, most notably in very high-speed sortation.
Now that AIDC applications are becoming more critical to the success of a company, a barcode scanning failure is all the more costly. Such huge retailers as Wal-Mart, for example, are famous for fining suppliers with fines of $50,000 or more if their labels are not consistently readable. As a result, systems for barcode verification, once used only by label vendors and printers, are now common for on-site printing. Verifiers grade a symbol as either unacceptable or acceptable by varying degrees based on ANSI’s Bar Code Print Quality Guideline.
Verification devices can stand alone to audit batches of labels, attach to a printer to monitor quality of each label, or integrate into the work flow.
No matter how verification is performed, it cannot always catch barcode performance problems. However, verification provides quantifiable metrics on print contrast, derives wide-to-narrow ratios, and checks the conformance of the printed symbol against the standards of symbology print quality.
Linear (One-Dimensional) Barcode Symbologies
Key Attributes and Limitations
- A demonstrated optical, read-only technology
- Inexpensive symbol formation on labels using a number of techniques
- Little capacity, generally only 15 to 50 characters, depending on symbol set and form. Best for “license plate” use, i.e., coded to indicate stored data located elsewhere
- Accurate machine-read coding, compatible with symbologies that offer different detection/protection levels
- Symbologies to accommodate ASCII, alphanumeric, numeric, and other characters
- A number of symbologies meet AIM Symbology Specifications, including several open-system, area-specific applications which are designed for specific symbologies
- A variety of techniques for forming barcodes (i.e., printing requirements for barcode labels, composite and impressed, and pierced metal
- Many types of labels and substrates and symbol types to meet the needs of most applications and end-user environments
- Line-of-sight, fast, machine-reading capability, with a large selection of equipment to accommodate a wide range of distances from zero to several meters, dependent on the system and the size of the barcode symbols
- Large range of symbol-writing software, label products, printer hardware, fixed and portable scanning systems, and verifiers to assess the quality of symbols
- Technical variants of barcode labels available for specialized applications, often requiring specialized read systems, e.g., security symbols using holographics and extremely rugged pierced-metal barcodes for harsh environments
Now used for more than 25 years, barcodes are familiar as a series of parallel spaces and bars in varying widths. These linear one dimensional (1D) symbologies are still the most used technology for optical recognition. More than 100 other symbologies or encodation schemes have been created, but the most used 1D symbologies are Codabar, employed in the early years by blood banks; Code 39, invented by the automotive and defense industries; the Universal Product Code (UPC), initiated in 1973 by the supermarket industry; Code 128; and Interleaved 2-of-5 (ITF).
Depending on the symbology, barcodes might encode numeric data only (UPC and ITF) or they might encode part or all of the American National Standard Code for Information Interchange (ASCII) character set (e.g., Codes 39 and 128) by the bar widths and usually by the space widths as well. As a scanner moves across the symbols, the widths of the bars and spaces are analyzed to retrieve the data originally encoded.
The narrowest space or bar is called the X dimension, usually measured in thousandths of an inch, called mils. The X dimension regulates the widths of all of the other spaces and bars, and ultimately the barcode’s length. Wider X dimensions are easier to scan; however, easy readability is offset by the higher cost of larger labels. For ease of scanning, almost all barcodes have, at one end or the other, a clear space (quiet zone) measuring at least 10 times the X dimension of the barcode.
Barcode labels employ special start and stop characters at each end to identify the symbology used and also to help the scanner read in either direction while decoding data in its intended order. A check digit is often included at the end of a barcode to validate that all characters are correctly decoded. The check digit is assigned by an algorithm that is based on preceding characters.
Almost all barcodes include human-readable characters below the symbol. Called an interpretation line, it translates the encoded data into text that humans can read. It is notable that barcode technology made the “human readable” term necessary. Formerly, humans were the only readers.
Industry standardization continues to be vital to continue the incredible growth and worldwide adoption of barcode technology. Barcode standards are now applied to printing and scanning, and to verification of symbologies. AIM, the leading organization for developing standards for the AIDC industry, has published specifications for many symbology standards. In addition, EAN and the Uniform Code Council (UCC) have determined specifications for the EAN/UPC symbology.
These widely distributed standards permit AIDC vendors to produce all of the elements of their integrated systems in a wide-open business environment. Standardized barcode label formats, under the auspices of the American National Standards Institute (ANSI), ISO/IEC, and CEN, have brought efficiencies and cost savings to manufacturers, warehousers, and distribution centers across industries through the entire supply chain.
Two Dimensional (2D) Barcode Symbologies
The necessity of encoding more information in smaller spaces is driving the innovation, standardization, and increasing usage of 2D barcodes. While 1D barcodes are more like a license plate referring to information in a database, 2D codes can perform the same function in much less space or can also serve as a database itself, assuring complete portability for items labeled with 2D.
Two symbologies of 2D barcodes are in use: matrix and stacked codes.
Stacked symbologies developed as Code 128 and Code 39 1D codes stacked in layers horizontally to create two new multi-row symbologies, Code 16K and Code 49, respectively. In 1990, PDF417 followed with additional features that expanded data capacity, increased data density, and boosted a scanner’s reading reliability. These features offered decoding by scanning many adjacent rows simultaneously, and included capability to detect errors and make corrections. PDF417 can encode the entire ASCII character up to about 2000 characters to four square inches. AIM makes available the uniform symbol specifications for PDF417, Code16K, and Code 49. Also available is SuperCode, which is a stacked code capable of breaking data down into small packets and creating variously shaped symbols.
Key Attributes and Limitations
- Printable similar techniques to linear barcodes
- Well founded read only optical technology
- Variety of labels and other substrate forms and symbol realizations to suit a variety of applications and user environments
- Many symbologies support up to 2000 or more characters
- Readable by laser scan technology and image capture systems
- Most symbologies capable of handling international character sets using 'extended channel interpretation' system
- Error detection and correction capabilities in most symbologies
In most cases, matrix symbologies can offer greater data densities than stacked codes, as well as scanning that is independent of orientation. A matrix code consists of an arrangement of cells in circular, hexagonal, or square shapes. The relative positions of the dark and light areas are used to encode the data, and encoding schemes employ error detection and correction technology to improve decoding reliability and to read partly damaged symbols. Matrix codes can be scaled and are suited for use as small product IDs and on conveyor-scannable packages for shipping.
Key Attributes and Limitations
- Printable similar techniques to linear barcodes
- Well founded read only optical technology
- Variety of symbol forming techniques (printing methods for label-based
symbols, pierced metal, impressed and composite formed symbols
- Error detection and correction capabilities essential
- Range of symbologies with capacities up to 2000 or more characters
- Handle international character sets either natively or through extended
Composite Barcode Symbologies
Composite barcode symbologies are in a new class of symbology which prints two symbols very close to one another and containing linked data. Generally, one symbol is linear and the other either a matrix or a multi-row symbol.
These symbologies are meant for applications in which different pieces of information might be needed at different points in the item's use. They are also used when the amount of available space is too restricted to allow placement of a linear barcode.
The UCC.EAN composite symbol, the emerging major application for composite barcoding, was invented to meet needs of such industries as pharmaceuticals, which must encode a great deal of information--identification, batch number, expiration date-- in a very small space on their packaging. These symbols encompass a standard UCC.EAN linear code family such as UPC-A or EAN- 13, a UCC.EAN 128 symbol, or one of the RSS reduced-space symbologies, combined with a related multi-row 2D symbol. Tight rules govern the structure and the related positions of the two symbols. Normally, linkages are encoded in each symbol to prompt the decoder to look for the other symbol. Some users of composite barcodes might need only the item identification in the linear symbol; others might require all of the supplementary information in the 2D composite area of the barcode.
Bar code technology became widespread in supermarkets about 20 years ago and was so successful that almost all grocery suppliers now print the UPC symbol on packaging to facilitate point-of-sale (POS) scanning. Mass merchandisers and a vast range of retailers noticed the grocers’ success and POS scanning is now ubiquitous in retailing.
About fifteen years ago, the Department of Defense began requiring a Code 39 barcode on the packaging of all products received. This DOD mandate caused rapid adoption of manufacturing barcode applications from shipping dock to the factory floor. Barcode technology was employed in factories for inventory control, time-and-attendance, labor reporting, work in process (WIP), and other WIP processes like quality control, lot and process control, and finished goods inventory. Soon barcode technology moved into the warehouse to aid in receiving goods, stocking shelves, picking orders, and packing for shipment.
Recent economic conditions and pressing global competition have caused downsizing across most industries. Managers’ efforts to cut costs and boost productivity made barcode technology a priority in industries from health care to utilities, especially in logistics. Retailers that had only used barcodes at the point of sale copied Wal-Mart’s lead and automated their transportation and warehousing operations, reaping huge cost benefits.
Extensive use of barcode technology is also found in such applications as asset tracking, access control, hazardous waste tracking, book and files cataloging in libraries and archives, package tracking and delivery, document management, and vehicle identification and control.
See our solutions page for industry specific applications.