Bar code 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.
either handheld or fixed-mount. Typically, handheld scanners are used to read
bar codes 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 bar code 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
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.
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