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Going Postal with Vision Systems
by Winn Hardin, Contributing Editor - AIA Posted 02/27/2002
Vision-based multiline optical character readers (MLOCR) and remote barcoding systems (RBCS) have helped the US Postal Service cut $2 billion in operating deficits in recent years. These systems read handwritten addresses and spray the Zip+4 bar code on letters, which represent 70 percent of the postal service's traffic, greatly reducing the number of times a letter must be handled.
Although still a market maker, the US Postal Service is but one example of an institution depending on vision systems to aid in parcel sorting. Fed-Ex, UPS, DHL and many other smaller transportation companies have also turned to vision systems to help them with their shipping and transportation handling systems.
'Of our industrial sales into the transportation market, about 20 percent is for postal and 80 percent for private companies,' said Andy D'Amelio, director of strategic sales at Metrologic (Blackwood, NJ). Metrologic is not alone. Bell & Howell's (Irving, TX) executive director of the imaging division, Mark Woolston added, 'Right now, our business probably has a 20/80 split between US Postal and the commercial market primarily because of [a recent contract], but in general, the private market is bigger overall…The market appears to be moving towards inbound applications where the mail is coming into companies instead of outbound processing. The commercial outbound sorting is a mature market. It's been around for a long time and the players have converged -- it's getting to be more of a replacement market.' Inbound applications refer to sorting of mail for large companies prior to delivery to individual employees, reducing mailroom staff requirements for this purpose.
Other trends impacting the parcel and postal sorting market include a move away from 1D, laser-based barcode readers to vision systems capable of 2D matrix reading and optical character recognition (OCR); tunnel scanners and other systems that require singulation but not orientation while reducing optical distortion; high-speed conveyors approaching 825 feet per minute and rotary tilt tray sorters close to 400 feet per minute or higher. Higher speed conveyor lines challenge every link of the sorting system, pushing the limits of the camera, processor, optics and light budget. As a result, OEM suppliers to this market use a number of techniques from high brightness (300W+) halogen lamps, to coherent light, to TDI linear array cameras to maximize the light budget in high-speed conveyor applications.
Speed versus light
'We're seeing a big trend to using vision systems versus laser scanners,' said Dave Wurz, Chief Operating Officer of ACCU-SORT Systems Inc. (Telford, PA). 'You can get a better read rate especially on damaged labels and labels under plastic, which are very common in postal/parcel applications. There's more data because laser scanner is working at 500 to 600 scans per second versus a line-scan camera that scans at 12k+ scans per second. You can also read 2D bar codes with a camera, which are becoming more popular. Lastly, vision gives you more ability beyond bar codes: dimensioning the parcel, detecting side by side parcels, capturing images of no-reads for diagnostic purposes or videocoding.'
Although traditionally a laser scanner supplier, Metrologic's D'Amelio said he also sees a trend toward camera-based systems. However, Jeff Yorsz, president of Metrologic's subsidiary Adaptive Optics Associates (Blackwood, NJ) believes that lasers still have a place in vision systems used for sorting. 'A system using a high-pressure sodium lamp wastes a lot of the light. You're only illuminating something on the [conveyor] with a pixel size of a couple hundred microns. Our object is to put light where it needs to be and no where else.'
Metrologic's iQ180 uses a 20-mW red diode lasers to illuminate the packages rather than high-brightness halogen lamps. 'It's more cost efficient,' added Metrologic's D'Amelio. 'Laser illumination consumes much less power over the long run.
Conveyors running at 165 inches per second sometimes need up to 400 W of illuminating power, but even that much illumination is sometimes not enough. Bell & Howell's Woolston uses DALSA (Waterloo, Ontario, Canada) multitap TDI linear arrays that essentially combine the signal from several line-scan cameras to boost the accumulated light per pixel of the final image. 'If you're below 100 inches per second, you can get away with LEDS or fluorescent illumination using standard line-scan technology. Typically, if you see LEDS or fluorescent lamps, they're running TDI technology or slow - one or the other.' As LED prices continue to drop, more systems will use this type of illumination, added ACCU-SORT's Wurz. In addition, LED's are safer and more user-friendly.
Bell & Howell is looking for CMOS sensors that will be cheaper but meet the dynamic range of the CCD linear arrays. So far, only Basler Vision Components (Exton, PA) has produced a CMOS line scan prototype that might meet the sensitivity standards of high-speed parcel inspection, Woolston said.
Pushing the processor
As with most other vision applications, postal and parcel vision OEMs take advantage of improved processor speeds in the PC market to boost the performance of their systems. 'Our older systems are VME based and they're going obsolete,' said Bell & Howell's Woolston. 'We now use a standard PC with a frame grabber and use DMA transfer to load the video directly into the PC's memory…We tend to go with Dell. We analyzed others, but Dells are the most consistent between upgrades. It's a BIOS and PCI chipset issue.' Both Bell & Howell and Metrologic use commercially available framegrabbers, although they declined to identify the brand. However, Metrologic's Yorsz said the company is considering using proprietary technology for this purpose in the future.
Processing power is always a concern when dealing with imaging systems. Woolston uses three OCR approaches to read an address, with the final result represented by the highest probability developed by all three OCR engines.
ACCU-SORT's Wurz estimates that image transfers into the PC's memory run at 100 MB/s. Wurz uses standard PCs, not only for running the vision system, but also as videocoding workstations when the system determines an illegal operation, such as unreadable labels or side-by-side packages. The PC also controls a unique focusing mechanism that uses a moving mirror or sensor to adapt the focal length for maximum resolution, rather than slower zoom lenses.
Metrologic actually brings the PC inside the box with its iQ180. 'One of the major obstacles at sorting facilities is running wires and trying to maintain several pieces of equipment, adding to the overall failure points. If your solution is in one box, it's better for everyone,' explained D'Amelio.
Flexible vision just beginning
According to industry insiders, PC/vision-based sorting systems will continue to gain market share as companies and OEMs devise new ways to use vision data. Bell & Howell is developing vision systems to locate and analyze all parameters associated with mail processing and automation. Sorting houses that use ACCU-SORT equipment use stored images of rejected parcels to educate corporate consumers on poor labeling practices, increasing efficiency. 'With vision, there's always going to be new applications in the parcel sorting area as customers discover new ways to use the data. I'm sure there's more to come,' Wurz said.
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