Image-based barcode readers improve package sorting efficiency

Positioned between simple applications requiring laser-type bar-code readers and high-end applications that use line scan image-based systems lies an entire range of projects that currently use laser-based scanners but could benefit from migrating to new image-based techniques.

08/28/2011


The high volume and frequency of orders placed over the Internet, combined with the explosion in the sheer number of products shipped from retailers, makes automated scanning at logistics centers more important than ever. Improving barcode scanning is a key way major retailers and parcel hubs can reduce costs by allowing automated equipment to handle the highest possible number of packages, rather than diverting the package to a manual station, increasing overhead and reducing profit margins.

In the past, many large retailers and parcel distribution centers have relied on laser barcode reading systems, which are easy to set up, connect and aim, and can read codes fast enough to accommodate high speeds. Unfortunately, the laser method limits the read rate (the percentage of codes that a scanner reads correctly) because the laser frequently fails to read poorly printed codes.

The alternative, image-based, line scan systems, provides greatly improved read rates, but their cost and complexity have previously limited their use to high-volume distribution centers. Now a new generation of image-based readers has been developed, offering high speed at a price comparable to most mid-range laser scanners. The technology allows automated equipment to read ID barcodes during the first pass, resulting in higher efficiency that will cut costs by permitting higher throughput and more packages per hour.

Because the system is camera-based, operators capture an image, which gives them data about failed package reads that will allow them to improve their process and support ongoing continuous improvement initiatives. Finally, with no moving parts, the new image-based technology is much more durable than laser systems.

Logistics status quo – laser scanning

Laser barcode scanning is a simple, easy-to-use and affordable process that offers a large scanning area and working range. The generation of laser systems now in use at many logistics operations provides high read rates with good-quality printed barcodes when labels are undamaged, but they have difficulty reading codes under less than ideal conditions.

A laser scanner reads a barcode by measuring the size of printed modules using light reflected from the code. This method in and of itself limits the read rate, because printed barcode quality can vary dramatically depending on the amount that the package is handled, the printing technology, label geometry, and point of origin, among other factors. A laser scanner may fail to read poorly printed codes, as well as codes that have been damaged, distorted, blurred, scratched, or codes with low height. Because a laser scanner attempts to decipher the code along a single laser line, light or specular reflections or damage to the portion of the code being scanned may dramatically reduce the scanner’s ability to read the code successfully. Some laser scanners attempt to solve this issue by stitching multiple scan lines together to reconstruct a damaged code. This method works well in some cases, but not when damage is severe. Figure 1 shows examples of poorly printed barcode labels, which may not be read correctly by laser scanners. 

An unread code requires diverting the package to a manual station, where an operator either directs the package to its destination, or replaces the defective barcode, and resends the package back through the sorting system. This increases labor and material costs and reduces the efficiency of automated sorting equipment, because packages are handled more than once. The result is a negative impact on the bottom line, resulting in increased overhead and lost margins.

To cope with these limitations, the logistics industry has designed special labels that maximize read rates and equipment specifically optimized to handle high numbers of no reads. Nevertheless, with rapid growth, distribution centers must handle escalating package volumes, an increasing number of sources and destinations, and a greater package mix. All these factors exacerbate the need for better efficiency and higher read rates.

Image-based barcode reading systems offer advantages

The new high-speed, area-array, image-based reader captures an entire image in a single snapshot, eliminating the need for precise encoder input or very bright, always-on illumination. Also, area scan technology is not susceptible to distortion or other undesirable image artifacts. Several recent advances in the technology now enable area scan readers to keep pace with the speeds required by package conveyors.

Also fundamental to this new generation of area scan image-based readers is new autofocus liquid lens technology. The automatic adjusting focus of the liquid lens provides the maximum depth of field for even the highest speed applications. Liquid lenses focus much more quickly and with greater range than the mechanical variety – with no moving parts. The liquid lens technology means that the size and position of a package on a conveyor need no longer compromise either throughput or read accuracy. Also, liquid lens technology simplifies installation, setup and maintenance by allowing focal-length adjustment without the need for anyone to touch the lens.

Image-based barcode reading systems offer several advantages over the laser-based variety. First, because a picture is worth a thousand scans, image-based readers begin with more information about the barcode. This advantage allows them to successfully read codes degraded by damage, orientation or distortion. To compensate for damage to the code or light reflections from the package, the analysis software can reconstruct the data of interest from any legible portion of the image.

Image-based systems can also store images for later retrieval and analysis. Archiving this information helps a distribution facility to determine the root cause for any unread barcodes and implement corrective actions, reducing the number of subsequent misreads and thereby improving process efficiency.

For example, consider a distribution facility that achieves read rates of only 98 percent. Reviewing images of unread packages might show that package handling issues caused a portion of the no-reads, and supervisors could then modify the operators’ procedures for loading packages onto the sorting conveyor to improve the read rate. If the read rate is improved to 99 percent, the reduction in the number of packages that needed to be re-read following a failure reduces the number of packages manually sorted by hundreds or even thousands per day.

Image-based systems offer additional setup advantages over lasers. For example, when setting up a laser scanner to maximize read rates, users cannot see the image that the scanner is attempting to read. They have difficulty determining whether the scanner is positioned optimally, especially in omni-directional applications where the rotational position of the code is unknown. During operation, laser scanners provide no information to help the user determine why a read was unsuccessful. Data from the scanner indicates only the number of packages that were not read successfully, making any attempts to respond reflect pure guesswork rather than data-driven corrective action.

On the other hand, an image-based system can display the scanner image on a monitor or industrial display in real time. As the user sets the system up, the display shows exactly what the scanner sees, ensuring that the images will be in focus and that the image will include all codes on any package that comes down the conveyor. Both initial setup and later adjustments to improve the scanner’s read rate require little specialized knowledge, minimizing setup and maintenance times.

As a result, image-based readers are easier to maintain and support than are laser scanners. Vendors provide support, of course, but with easy review of “no-read” images, users can quickly and easily identify and rectify problems and support the systems themselves with little training. Or, they can provide most of the support themselves and call in the vendor only when absolutely necessary. The convenience of not needing to schedule, wait for and pay for vendor-supplied service can significantly reduce downtime and the accompanying costs.

Image-based readers also offer better uptime because laser scanners use motors and other mechanical mechanisms to move the laser spot across the code. These moving parts wear out over time, thereby limiting the system’s useful life. In contrast, area-array image-based readers contain no moving parts, typically resulting in a useful life that is two to three times longer than that of laser scanners.

The first image-based reader to be able to successfully accomplish logistics applications that were traditionally dominated by laser scanners is the new Cognex DataMan 500. The DataMan 500 contains patented chip technology that enables the reader to acquire and analyze images at up to 1,000 frames per second (fps) and process them in real time, so the reader can adapt to wide variations in package size. This technology allows DataMan 500 to reliably read ID barcodes on packages moving at speeds up to 500 feet per minute (2.5 meters per second) without an external trigger or complicated setup procedure. Figure 2 is a picture of the new image-based reader, while Figure 3 demonstrates the wide range of operations the system is designed to handle. 

The unit is also the first barcode reader for the logistics industry to introduce liquid lens autofocus technology for the maximum depth of field for even the highest speed applications. The optional accessory is fast and reliable and offers good optical quality with low power consumption.

The DataMan 500 also offers Power over Ethernet (PoE) technology, which simplifies wiring in the system. Originally invented for use in enterprise phone systems, PoE reduces cost by eliminating the need for a local DC power supply and individual 120 V power drops at the scanning location.

Longer life of image-based systems, attractive capital purchase

Most companies are struggling to reduce capital costs and want to invest for the long term. They do not want the equipment they buy to become obsolete prematurely. In this environment, image-based systems’ longer life represents a considerable advantage. 

Another future trend in the logistics industry is the introduction of two-dimensional (2D) codes like Data Matrix and QR. The pharmaceutical industry will be required to start using these codes for unit level serialization to combat drug counterfeiting. The amount of information 2D codes can store makes them very attractive for a wide range of other applications. Image-based scanners are required to read these codes.

Retail distribution centers require meticulous stock control, which includes careful management of purchasing, shipping and warehouse inventory. Capital equipment acquisitions that improve read rates, such as this new generation of high-speed area array image-based readers, enjoy short payback times that can be measured in months. As large retailers and Internet fulfillment centers consider capital equipment purchases to add capacity or increase throughput, raising barcode read rates by just 1 percent can significantly shorten payback schedules and increase return on investment.

- Jorge F. Schuster, Cognex Corporation, Director of ID Sales, Americas; Edited by Chris Vavra, Control Engineering, www.controleng.com



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