HOW DO BARCODES WORK?
Different combinations of bars and spaces are used to encode characters into barcodes. Differences in light and dark and the width of the elements are the variables used for encoding. The barcode reader illuminates the symbol and measures the amount of light that is reflected back. The reader determines the pattern of light and dark or wide and narrow, then compares it to the encoding table for that type of barcode (called a symbology) and decodes the symbol.
Hundreds of barcode symbologies have been created, but less than two dozen are widely used. Each symbology has its own pattern of bars and spaces and its own rules for encoding data. There are two basic types of barcodes: linear and two-dimensional (2-D).
Linear codes encode data in bars and spaces in a single line. The U.P.C./EAN symbol is the best-known example of a linear barcode.
Two-dimensional codes encode data in an additional dimension. The two principle types of 2-D codes are stacked and matrix symbologies. Stacked symbologies resemble multiple linear symbols stacked on top of each other. Matrix symbologies feature blocks or lines in a grid or geometric pattern. There are also hybrid 2-D symbologies and other variations.
Symbologies differ primarily by the type and amount of data that they can hold. Some symbologies offer full alphanumeric encoding, while others only encode numbers. Symbologies may be fixed or variable length. However, size isn’t unlimited, because the symbol must remain compact enough to be recognized by the reader. Two-dimensional symbologies can hold significantly more data than linear codes.
The variety of barcode formats available practically ensures you can find a symbology that meets your needs. The most important variables that determine the optimal symbology are the amount of data that needs to be encoded, the space available to print the barcode and the type of data to encode.
Variable-length symbologies can be used to encode only a few characters, if desired, while 2-D codes encode thousands of characters. The data capacity of variable-length barcodes is limited by the size of the symbol, which is in turn limited by the ability of the barcode reader. For reference, a standard U.P.C./EAN symbol encodes 14 numeric digits. Many barcode applications in warehousing, distribution, manufacturing, and inventory control require a serial number of similar length, which many common symbologies can easily encode into a compact symbol.
Yes. barcode readers support multiple common symbologies. Generally, readers can recognize more linear than 2-D symbologies, but often support a few common 2-D formats. Symbology support varies by reader manufacturer and model.
Readers have a feature called autodiscrimination, which detects the symbology that is being processed and decodes it accordingly. Autodiscrimination enables readers to map the combination of bars and spaces to the correct character, thus preventing reading errors. barcode data entry is extremely accurate, with an error rate estimated at one error per more than 3 million characters.
Thermal barcode label printers support multiple symbologies. General-purpose laser and inkjet printers and software applications may not be able to natively print any barcodes or may not offer multiple symbologies. Printer specifications list symbologies that are supported.
U.P.C. and EAN barcodes are part of the EAN.UCC system, which is managed by the Uniform Code Council in the United States and EAN International in the rest of the world. Visit their Web sites for details and resources to get started with U.P.C./EAN labeling.
To print barcode labels, a label format must be created with software that supports bar coding. To print barcodes on documents or reports, the application software needs to support bar coding or additional programming will be required. After the label or form is designed, it needs to be output on a printer that is capable of producing barcodes and supports the specific symbology that is used. Because data is encoded using differences between light and dark (and narrow and wide) elements—which are measured in mils, or thousands of an inch—a good quality printer is essential for producing crisp lines and accurate, readable barcodes. Finally, the media must support barcode print quality by not bleeding, running, fading, or otherwise defacing the symbol.
Many common laser and ink jet printers are capable of producing barcodes, but need to be set up to do so. They often do not have native support for barcode symbologies and need to be upgraded with additional fonts or programming to support bar coding. They also lack many of the special features that provide excellent barcode print quality.
barcode printers are available with many common interfaces to facilitate simple integration with a variety of host computer systems. Ethernet, USB, parallel, serial, twinax, and coax cables are available. barcode printers also offer 802.11b and Bluetooth connectivity for wireless integration. Management tools enable remote monitoring, configuration, and troubleshooting for networked printers.
Zebra also offers many advanced connectivity features. These include embedded XML processors that enable printers to decode and process incoming XML data streams, interfaces for direct connectivity to SAP and Oracle enterprise resource planning systems, solutions for the IBM midrange (AS/400 and iSeries) environment and more.
Many companies require their suppliers and other trading partners to include a barcode or radio frequency identification (RFID) label on shipments, which is used to sort incoming materials and manage inventory to support the company’s automated systems. Labels produced to meet trading partner requirements are called “compliance labels” because the shipping organization applies the label to comply with a request or demand. Compliance labels usually must follow strictly defined formats for layout, content, barcode symbology, print quality, etc.
First, find out which of your facilities and production or packaging lines will be impacted in order to determine the required label volume and the number of printers that will be needed. Determine how the printers will receive the variable information they need from your enterprise system to produce the labels. This step will show the connectivity and networking support required in the printer. Review the compliance specification to understand the required label sizes, fonts, barcode symbologies, and graphics so you can choose an appropriate printer.
Software is also required to design the label formats. Many barcode and RFID label design packages include templates for compliance label formats commonly used in the retail, automotive, aerospace, defense, distribution, and other industries. Make sure the software supports the types of labels you need and the specific model of printer you have chosen. Test the entire system and send label samples to your trading partner for analysis prior to your deadline date for compliance labeling. Many systems integration companies are very experienced with compliance labeling systems and are available to assist with any phase of the project. Zebra’s white paper “Quality Assurance Steps for Preventing Label Printing Problems” explains how to meet print quality requirements for compliance labeling.
Yes, but be prepared to deal with excessive material waste and printer wear, potential jamming caused by the label adhesive, limited symbology and software support, and delays while media is changed to support label or document printing.
Narrow the field significantly by determining the size of labels that need to be printed. Analyze the conditions the label will be exposed to and its required life span to determine the print method (direct thermal or thermal transfer) and required media support. Printers also differ significantly in the interfaces and network connectivity that they offer. The symbologies, graphics, and international characters supported are other important differentiators. Durability and printing volume are also important. For most applications, 203 dots-per-inch (dpi) resolution provides sufficient print quality. However, when higher quality printing is required, such as for very small labels or some 2-D symbologies, 300 or 600 dpi printers should be used.
Yes, but the print speed listed in the printer specifications (which is expressed as inches per second, or ips) does not always give a true indication of how fast the unit will print. Some printers take a long time to process the label format before they start printing.
First label out refers to the time it takes from when the print command is sent until the first label in a print job comes out of the printer. First label out time depends on the label size and the printer’s processing power, the interface with the computer system, and the software used in the application. These factors may also result in pauses between labels that prevent full-speed, continuous printing.
Throughput is a truer measure of how quickly a printer can process a complete print job. First label out and throughput can be evaluated when printers are set up for demonstrations or trials. It is important to use the printer in your actual work conditions to determine if it has the speed and throughput to meet your needs.
There are two thermal printing methods commonly used to print barcodes: direct thermal and thermal transfer. Each method uses a thermal printhead that applies heat to the surface being marked. Thermal transfer printing uses a heated ribbon to produce durable, long-lasting images on a wide variety of materials. No ribbon is used in direct thermal printing, which creates the image directly on the label material. Thermal transfer printers can accept a wider variety of materials and are usually used for permanent or long-lasting labeling applications. Direct thermal printers are usually used to produce shipping labels, picking/putaway labels, receipts, and other common print jobs.
Besides a wide variety of label materials, barcode printers can also print on tag and ticket stock, wristbands, polyester, polypropylene, and other synthetic materials. Different colors are available, but color should be used cautiously because insufficient contrast between bars and the background space will produce unreadable barcodes. Brand protection media is available with overt and covert security features for authentication, counterfeit and diversion deterrence, and secure data encoding. Label media, coatings, and adhesives provide resistance to temperature extremes, moisture, acids, washes, UV exposure, and other hazards to label quality. Thermal printers can also print and encode smart labels, which contain a radio frequency identification (RFID) chip and antenna inlay embedded within the label media.