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How do bar codes work?
Different combinations of bars and spaces are
used to encode characters into bar codes. Differences
in light and dark and the width of the elements
are the variables used for encoding. The bar
code 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 bar code (called a symbology)
and decodes the symbol. |
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How
many kinds of bar codes are there?
Hundreds of bar code 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 bar codes: 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 bar code.
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. |
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How
are symbologies different?
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. |
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What
kind of bar code should I use?
The variety of bar code 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 bar code and the type of data to
encode. |
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How
much data can a bar code hold?
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 bar codes is limited
by the size of the symbol, which is in turn limited
by the ability of the bar code reader. For reference,
a standard U.P.C./EAN symbol encodes 14 numeric
digits. Many bar code 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. |
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Can
a bar code reader process more than one type
of symbol?
Yes. Bar code 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. |
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How
does the bar code reader know which symbol
it is reading?
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. Bar code data entry is extremely
accurate, with an error rate estimated at one
error per more than 3 million characters. |
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Can
printers print more than one kind of bar code?
Thermal bar code label printers support multiple
symbologies. General-purpose laser and inkjet
printers and software applications may not be
able to natively print any bar codes or may not
offer multiple symbologies. Printer specifications
list symbologies that are supported. |
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What
do I need to print bar codes?
To print bar code labels, a label format must be created with software that
supports bar coding. To print bar codes 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 bar codes 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 bar codes. Finally, the media must support bar code
print quality by not bleeding, running, fading, or otherwise defacing the symbol.
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Do
I need a special printer to print bar codes? |
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How
can I hook up a bar code printer to my computer
system?
Bar code 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. Bar code 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. |
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What
does "compliance labeling" mean?
Many companies require their suppliers and other
trading partners to include a bar code 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,
bar code symbology, print quality, etc. |
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A
customer has asked us to start applying bar
code labels to shipments. What should I do?
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,
bar code symbologies, and graphics so you can
choose an appropriate printer.
Software is also required to design the label
formats. Many bar code 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. |
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Can
I use my laser printer to print bar code shipping
labels?
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. |
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There
are so many bar code printers. How do I choose?
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. |
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Is
print speed important?
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. |
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What
is the difference between direct thermal and
thermal transfer?
There are two thermal printing methods commonly used to print bar codes: 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.
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What
kind of materials can be used in bar code printers?
Besides a wide variety of label materials, bar code 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 bar codes. 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.
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