From SCDigest's OnTarget e-Magazine
Feb. 22, 2012
RFID and AIDC News: Traditional Laser Scanners versus Imagers in Distribution Centers
Increased Use of 2D Bar Codes, Improved Read Range of Imagers, May Change the Selection Dynamics
SCDigest Editorial Staff
Bar code scanning is one of the foundational technologies of most advanced distribution centers, and with RFID still slow to make its way into the DC, is likely to stay that way for years if not (almost) forever.
Whether as a separate device tethered to a PC or data collection terminal, or as an integrated scan engine built into a wireless terminal, the choice of what scanner to use has become almost routine today in one sense, given the performance of today's scanning systems, which are far better than a decade ago.
SCDigest Says: |
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| More and more tech manufacturers are putting all those serial numbers for a handling unit in a single 2D bar code, requiring only one scan to capture all the information and eliminating the need to open a box or walk around a pallet scanning labels.
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What Do You Say?
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But when most people think of a scanner, they think in terms of a traditional laser scanner, in which the device generates a laser beam. An oscillating scan mirror moves the beam back and forth rapidly across the target bar code to create a laser line which reflects light back from the bar code label to a reader in the scanner.
There is another popular approach to bar code scanning, however, called imaging. Imagers work more like a camera, taking a "picture" of the bar code, translating what they see into digital form, and the encoding the data into numbers and /or text. Indeed, many imagers today can take a real photo, as is sometimes used in logistics applications relative to things like documenting freight damage or capturing a signature.
In general, imagers do a better job of reading a bar code. While this is a very general statement subject to all kinds of caveats and application specifics, imagers will usually read a bar code faster than a laser, and can handle poor quality bar codes better.
"Imagers are better able to adjust to the harsh conditions often found in the warehouse and manufacturing environment. Bad lighting, damaged labels, incorrect label types, faint or faded labels, each offer a degree of complexity when it comes to decoding the label," says Kevin McArdle, an
applications engineer at bar code and wireless solutions provider Supply Chain Services. "While the typical laser scan engine is able to decode a label of good quality quite quickly, that same laser engine may have difficulty when the label is damaged or hard to read. The knock-on effect of this difficulty is the scan engine must read and re-read the label many times to accurately decode the label (if it is able to read it at all)."
He says the reason for this is that current imager engines typically take a single snap-shot of the label, then apply aggressive algorithms to assemble the information. On damaged labels, this may involve multiple algorithms being applied similar to the additional scans by a laser scan engine. The difference lies in the speed at which these algorithms are run versus the speed of multiple attempts to decode the label by the typical laser scan engine, which uses a more physical process in the repeated scans.
So, you may ask, why not just go with an imager scanner? There are two reasons: First, imagers in general are a bit more expensive than comparable laser scanners. Those on a tight budget may opt for the less expensive lasers.
Second, critical in many warehouse applications, imagers have had a limited read range - about 8 feet, says McArdle. That meant they weren't suitable for DC or manufacturing applications that involve scanning rack or floor locations where the actual label is further away than that, scenarios handled well by extended range laser scanners.
That aside, McArdle says that absent the long read range requirement (and usually only a subset of workers need that extended range in a DC), " If all else is equal, I would likely suggest an imager engine to most clients."
Two-Dimensional Codes are Changing the Dynamics
There are now other dynamics entering the equation. One is the use of two-dimensional bar codes, such as Data Matrix or PDF417, in distribution center applications. These 2D symbols encode information in what is usually close to a square shaped size code, with the bar code marks and white spaces running in both the horizontal and vertical dimensions (hence "2D"), versus the one-dimensional nature of a traditional bar codes such as Code 39 or Code 128. While these linear bar codes of course have a vertical dimension, that height does not encode any additional information, whereas it does in a 2D code.
2D codes have been designed to encode a lot more information in a smaller space. Indeed, Data Matrix was designed for small parts marking in the electronics industry, where there often was very little space available for a label.
(RFID and AIDC Story Continued Below)
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