Machine Vision Sorts It All Out

There’s a good chance that machine vision helped deliver nearly 100% of the letters to Santa, Saint Nicholas and Pere Noel - and more than a few Christmas, Hanukkah and Kwanzaa presents - that passed through local post offices last month. High-speed line scan cameras connected to powerful PCs running image processing libraries are an integral part to modern postal and shipping operations as logistics companies, internal warehouse operations and government agencies all seek logistic efficiency in a tough global economy.

Parcel or Post?
When it comes to sorting letters and boxes, machine vision handles the three most common types: post (or letter); parcel, usually measuring up to 40 inches on a side; and carton, which contain multiple parcels, products, etc. These three applications can be further characterized as 2D and 3D applications. Letters, envelopes and other “postal” products lay flat on conveyors. Postal applications may require the vision system to measure the size of the envelop to confirm a shipping rate, but mainly these applications use Optical Character Recognition (OCR) to read either hand written or machine written addresses, as well as some barcode or data matrix reading for bulk mail. This information is then used to automatically sort the mail according to its destination. Color is an emerging requirement for these applications.

Parcel and carton sorting use OCR and barcode reading, but also require the vision system to accurately and expeditiously measure the dimensions of the box because this is integral to determine the accurate shipping rate. Potential customers include logistics and transportation companies, as well as warehouse and distribution companies, and just about any large manufacturer trying to squeeze efficiency out of their shipping and logistics departments.

In A Flat World
Whether it’s 2D post, or 3D parcel/carton sorting, customers typically want the same things from their machine vision suppliers: faster, more accurate sorting of letters and boxes but without increasing the price of the equipment as each generation brings more capability. And as usual, vision suppliers struggle and succeed to deliver on their customer’s conflicting desires of more capability for less money.

Basler Vision Technologies (Ahrensburg, Germany) recently designed and introduced the Sprint family of line scan cameras with postal sorting in mind. “The Sprint camera is the first camera in the history of Basler that we have had designed by a sensor specialist exclusively for us,” explains Erik Lohse, Product Manager at Basler Vision Technolgoies. “In the past, we had 2k line scan cameras, but their speed was only 30 kHz. Resolution and speed are often the bottlenecks when it comes to postal sorting. The new Sprint CMOS cameras are either 2k, 4k or 8k, and can operate at speeds up to 140 kHz.”

Because image quality is critical to high-speed postal sorting applications - success depends on the ability to find and read the address on envelops at speeds approaching 75 pieces per second - postal sorting applications have used CCD cameras in the past because of their high image quality. New CMOS sensor designs improve on the non-uniformity issues that have plagued these sensors in the past, while allowing for cheaper construction and higher-speed read out electronics compared to CCD designs. CMOS manufacturing processes are also more conducive to large linear arrays with 100% fill factor.

“OCR is successful based on the resolution of the image without doing something special with custom processing and algorithms to clean up the image,” explains Jay Stone, Vice President of Sales and Marketing for VITRONIC Machine Vision Ltd. (Louisville, KY). “The more dots per inch you have, the easier the image is to decode. Lower resolution images mean lower accuracies as you increase other factors like speed, packaging variations, etc.”

As cameras work faster to keep up with automated sorting applications, having enough light becomes a more important issue. Unfortunately, according to Basler’s Lohse, plastic windows on utility bills and fancy envelopes can wreak havoc with traditional high output line lights typically used with line scan cameras. “To avoid blooming and reflections from these windows, you have to use a hybrid dark field illumination along with diffuse illumination,” Lohse explains. “Integrators are moving to ‘dome’ designs that have a small angle between the incoming light and the conveyor.”

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One Image, Many Colors
Color is also becoming increasingly important for high-speed sorting applications. Basler’s new Sprint cameras come in a dual line, color configuration using a Bayer filter approach, delivering good contrast color images.

“The best situation you get is black writing on a white envelope, but that doesn’t always happen,” explains Dr. Joachim Linkemann, Basler Vision Product Manager. “Especially around the holidays, when people like to use red ink on green envelopes, for instance. This is why more OEMs in the postal sorting industry are moving towards color cameras for their next generation machine vision sorting system. Because resolution is also critical, we can collect full-resolution color images without binning pixels together to generate a true, RGB image. Sorting applications use color, but do not need absolute color values as you do with printing applications.”

Cameras that combine high-resolution with color at a reasonable cost are also helping to deliver a new trend among OEMs of using a single camera to capture all information on the letter. “At a recent postal sorting exhibit in Germany last year, more OEMs were saying they wanted to capture all information from the letter at once, rather than use different cameras to capture different parts of the letter along the conveyor,” adds Dr. Linkemann. If you can capture a single image with the address, the stamp, company logos, etc., regardless of whether it’s printed in black and white or color ink, you’re simplifying the process. You’re also in a better position to troubleshoot the process.  For instance, in the case of bulk mail coming from a telephone company where high percentages of their bills are failing the automated sort, costing the customer money.  A single image that captures address information and the company logo can provide information back to the customer about what is going wrong with their billing operations and why some letters could not be delivered to their recipients.”

To the Edge and Back
VITRONIC Machine Vision Ltd. has targeted the entire sorting supply chain, starting with it’s handheld Vicam product that can automatically locate and identify everything from handwritten addresses and partial barcodes, to Vipac, a fully automated post, parcel and carton sorting system complete with network-based telecoding to insure 100% sorts without manual intervention.

“Vipac has four main features,” explains Stone. “It can capture the dimensions of the packages, barcode information OCR and image processing with remote terminal telecoding to deliver a 100% sort solution.” Telecoding collects images of letters, parcels and cartons that the vision system could not read.  It then passes those images to centralized locations where operators can see the box and input the missing information without pulling the parcel from the conveyor.

Vipac’s standard configuration solves the “0 to 40” requirement, a common automated sorting system specification that means the system can handle any package from 0” to 40” tall. “If someone needs less, we can build that system for them too, which is something the large, turnkey sorting companies will not do unless there is very large volume,” says VITRONIC’s Stone.

When confronted with a new customer application, Stone says he considers the total system operation before designing a solution, including minimum and maximum carton sizes, separation between packages, conveyor belt speeds, the types of conveyor (solid, cross, layered), types of encoding and how the data is used among other considerations.

“More and more customers outside of the traditional logistics and shipping companies are looking at automated sorting applications,” explains Stone. “In today’s market, everyone is trying to streamline and automate processes while squeezing out value. This means that in addition to the large sorting applications, we’re seeing more automated equipment installed closer to the edge of the supply network, in smaller facilities, with different requirements. With the flexibility of VITRONIC sorting systems, we’re well positioned to support automation in both large and small facilities.”