Barcodes | Scanning, Printing & Quality Verification
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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. Typically, handheld scanners are used to read barcodes on stationary items. With fixed-mount scanners, items having a bar code 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:

  • CCD (charge-coupled device) scanners use a stationary flood of light [usually Light Emitting Diodes (LEDs)] to reflect the symbol image back to an array of photosensors. Many CCD-based handheld image readers are capable of reading 2D matrix as well as stacked and linear barcode symbols.

  • 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 rastered, cross hatched, or starburst pattern laser beam for improved readability and omni-directional laser scanning.

  • Contact wand is a pen-shaped device with a light aperture tip that the user draws across the bar code. Contact wands were some of the earliest bar code scanners and require some practice to achieve the proper degree of tilt and correct motion speed for a successful read. Wand scanners are not very common in the marketplace today.

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 also used in high-speed sortation.


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 barcode whether the image is printed, etched, or imaged. The importance of precise barcode printing cannot be overstated; success of the whole set of integrated technologies that comprise an entire barcode system depends upon bar code print quality.

Barcode printing applications fall into two categories:  on-site user-controlled printing or off-site label supplier-controlled 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 barcode 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

With the staggering range of choices available, users need to carefully determine their application parameters before going to purchase a barcode 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 non-programmers via easy-to-use WYSIWYG graphical interfaces.


Typically, off-site printing involves commercial label printers that 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 Quality & Verification Systems

As barcode applications have become critical to a company’s success, the cost of scanning failure becomes ever more significant. Major merchandisers like Walmart have leveled whopping fines of $50,000 or more on suppliers whose product labels repeatedly misread. Consequently, barcode verification systems, once exclusively used by printers and label vendors, are now commonly used for on-site printing.

 

Verifiers "grade” a symbol based upon published standards criteria.  Devices can be integrated in-line, attached to the printer to monitor 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.

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