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Focus: RFID and Automated Identification and Data Collection (AIDC)

Feature Article from Our RFID and AIDC Subject Area - See All

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:


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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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)




But now, 2D codes are spreading the application footprint into more mainstream supply chain applications. Again, though, the driver is the ability of these codes to very efficiently encode a lot of information in a small space - often much more than just a bar code license plate number (e.g., GS1 128 serialized case number) or product ID (e.g., an interleaved 2 of 5 case code).

Examples of how 2D codes are being used in DC/supply chain applications include putting the serial numbers for all of the products in a carton or on a pallet in a 2D symbol. While many companies are interested in better serial number tracking, scanning every case on a pallet takes a long time, as would opening up a carton with multiple products inside it to scan each item.

Now, 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. This provides the visibility companies seek in a very time efficient process. It should be noted, however, that capturing a whole series of serial numbers in one scan will require some modest changes to the underlying software system to process this data correctly.

The same is true for capturing much greater information relative to food-related products. The Food Safety Act and company-specific initiatives are driving the need to track lot/batch numbers, expiration dates and other information in additional to a license plate and/or product ID.

Again, a 2D symbol can come to the rescue, being capable of encoding all of that data and more in one code (again with the proviso about required changes to underlying applications). There is a need to place all the data in the symbol as opposed to just a license plate which is tied to a back end database that carries all this other information arises because as the product moves across the supply chain, systems among different trading partners may not be electronically connected. The data needs to move with the product.

Laser scanners are not able to read 2D bar codes except for PDF417. So, companies that are considering (or may be required) to read 2D codes like Data Matrix in the future - or even think there is a chance they will - might be well off make the investment in imagers if any new scanners or wireless terminals are needed.

But wait! What about the read range limit? Could that present a real barrier to using 2D symbols in a DC, if workers needed to sometimes read the codes more than 8 feet away?

Fortunately, technology changes are eliminating that concern.

New Long Range Imager from Motorola Solutions

At the recent MODEX show in Atlanta, Motorola Solutions debuted a new imaging scanner that provides something of a breakthrough in the technology. The new DS3500-ER (extended range) scanner is capable of reading both 1D and 2D codes at both short distances (sometimes a problem for long-range scanners) and long distances, up to almost 31 feet, Motorola says.

At MODEX, Motorola was demonstrating the scanner reading a Data Matrix code from a very long distance. In fact, product management Matt Kowalski said that companies are starting to look at using 2D codes for the rack location labels themselves, in addition to the other types of DC applications discussed above.

Motorola says that food manufacturer Goya Foods is using the DS3500-ER in one of its distribution centers, and has started to scan Data Matrix codes for detailed pallet tracking. (See image below.)


The Bottom Line: Improved scan performance has always made the modest price premium for imagers worth the investment in many applications, but growing use of 2D bar codes and new technology that allows longer range imaging may alter the dynamics ever more in favor of imaging versus lasers.

What thoughts do you have on laser versus imaging scanners? Will longer range imagers change market dynamics? Are you using or considering 2D bar codes in for pallets, cases or locations? Let us know your thoughts at the Feedback section below.

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