Vision and RFID: Your Eyes and Ears for Tracking Inventory

Today’s information systems have an intense craving to know what’s happening up and down the supply chain.

They need lots of data to do their jobs of passing information along so that every operation in the chain can satisfy demand smoothly. These systems are only as good as the data they collect, however. To ensure the accuracy of large amounts of data, more companies are automating the process with vision sensors and radio frequency identification (RFID).

The speed and accuracy of these automatic identification technologies are especially important to medical suppliers such as SynergEyes Inc., a contact lens manufacturer in Carlsbad, Calif. Founded in 2001, the company produces hybrid contact lenses that combine the comfort of a soft lens with the high-definition of a rigid one. Because of the large number of variations in the optics, the company must track tens of thousands of stock keeping units (SKUs).

As the company grew, the old manual method of printing and reading labels became too cumbersome. “We normally make hundreds of different SKUs a day, so the potential for error is very high,” explains Joe Collins, vice president of manufacturing, and research and development. “We had to spend considerable time inspecting each [lens] vial to be sure we had the right label. Even when our company was much smaller, this process was difficult to manage.”

Automation was necessary to prevent any mislabeling that could erode the confidence of customers and lead to expensive recalls. Given the number of labels and the kind of information that must remain with the lenses, the most cost-effective solution was a 4-mm-square data matrix bar code. The 30 to 40 characters in the code include a lot number, expiration date, and, depending on the lens, five to seven optical parameters, such as power and diameter.

Because inspection occurs in a cleanroom, SynergEyes applies two bar-coded labels, a temporary and a permanent one. In the cleanroom immediately after inspection, the strictly utilitarian temporary label is put on the caps of the vials holding the lenses and some solution. After it leaves the cleanroom, a more aesthetic permanent label containing human-readable text is printed and affixed to the vial. Then the vial is shrink-wrapped.

In the old labeling method, trays of vials would come to an operator, who would read the tiny characters on the temporary label on the cap, enter them into a labeling system, print a permanent label, and apply it by hand. Inspectors would then verify that the two labels matched.

Now, a machine-vision-based labeling system designed by code-in-motion LLC, of Irvine, Calif., does this tedious task automatically. A vision sensor from Cognex Corp., of Natick, Mass., reads the bar codes on the caps. The system parses values from the bar code to determine the contents, creates a print file, and sends it to a high-resolution thermal transfer printer. As the permanent label comes off the printer, a second Cognex camera checks both the human-readable and bar code information on it. Good labels are placed on the vials, and bad ones are rejected. Only vials with good labels are shrink-wrapped.

“This automated system has reduced the cost of labeling our products by more than 90 percent,” reports Collins. “Even better, since we began using the automated system, we have not had a single labeling error.”

When the labeled vials go to the warehouse, an operator there scans the bar codes through the wrapper with a Cognex DataMan scanner and places the vials in one of the storage carousels. As medical practitioners in the field order lenses, customer service representatives type the prescription into the inventory management system to find whether it is in stock. If it is, the order goes automatically to the warehouse. The carousel moves around so the operator can remove the vial and scan it to verify that it is indeed the correct lens, and to record the shipment.

Vision versatility

As SynergEyes’ experience demonstrates, bar codes have remained a viable automatic identification technology, despite the hype over RFID five years ago when Wal-Mart and other retailers began requiring their suppliers to use it. One reason is the momentum of the huge installed base of bar code technology that has been in place for decades.

Another reason is a combination of economics and technology. “Bar coding costs fractions of a penny per label,” explains Tom Kahn, product marketing manager for vision and auto identification products at automation vendor Omron Electronics LLC, Schaumburg, Ill. RFID tags, on the other hand, are orders of magnitude more expensive. RFID inlays are available for less than a dollar, and labels containing them can cost right around a dollar. Tags used in industry, however, must be encapsulated to withstand whatever abuse they will suffer in their working environment. “These tags usually begin in the $8 range and can be as much as $100, depending how they are hardened.”

“For the foreseeable future, bar codes will have lower cost,” predicts Chris Kelley, director of RFID business strategy at Intermec Technologies Corp., an Everett, Wash.-based manufacturer of both bar code and RFID technology. “And there have been advancements in bar code technology, both in 2D symbologies that pack more data into a small space and in the scanners reading them.” Although these symbologies can encode more information than conventional linear codes, they still hold less than RFID tags can.

For the proliferation of these 2D bar codes, other important advancements include developments in the machine vision technology used to read them. “Vision systems used to be complex, with cameras going to frame-grabber boards in high-power (at least for the time) computers,” says Helge Hornis, manager of intelligent systems at vendor Pepperl+Fuchs Inc., of Twinsburg, Ohio. “This was expensive and complex.”

Today’s vision technology, on the other hand, exploits smaller, cheaper, and more powerful cameras and electronics. One of the results is a kind of self-contained smart sensor that is much easier to use and install than earlier systems. “Such vision sensors are available for around $1,000, whereas older style, multi-component solutions could run well over $10,000,” says Hornis.

More power for the money has translated into more capability, such as sophisticated algorithms that enhance feature recognition and connections to Profinet, Ethernet and other industrial networks. “It’s becoming very easy to connect devices on the factory floor,” notes Ed Housler, RFID business manager for Siemens Energy and Automation Inc., in Alpharetta, Ga. “For tracking and tracing, it means that you can install more sensors for the same or even less money. And that gives you more visibility into what is happening on the factory floor.”

The latest generation of vision systems is more flexible than its laser-based counterparts. These systems can read not only a variety of 2D symbologies, but also the more conventional 1D bar codes. They, moreover, can be configured to read permanent marks made by any of a variety of methods: ink-jet printing, laser scribing, dot peening and electrolytic chemical etching. “This allows for cradle-to-grave traceability,” notes Israel Alguindigue, automotive industry manager for Minneapolis-based vendor Sick Inc.

He adds that vision systems can archive images of the marks that they capture. Hornis at Pepperl+Fuchs agrees, pointing out that vision systems are really highly configurable inspection devices. As such, they can evaluate features on parts, as well as read bar codes. In some cases, therefore, a vision system may be able to archive images of both the identifier and the checked feature.

Overcoming limitations

Despite the advantages of vision, it has some important limitations, one of which is its need to see the code. For example, a vision system cannot read labels or marks that become damaged during manufacturing or handling. Lenses must be in focus and have adequate depth of field to generate crisp, sharp images. Lighting also is a critical consideration. “Careful consideration needs to be given to illumination to ensure proper contrast is created between the code and the background,” says Alguindigue at Sick.

RFID is one solution to these visual readability problems. “You don’t have to worry about alignments because antennas typically have much wider ranges,” offers Sal Scafidi, strategic business manager for Omron’s RFID Division. “You’re not subject to the same environmental conditions, such as dust or other phenomena that can obstruct the line of sight or destroy the code.” He points out, however, that RFID is subject to other kinds of environmental challenges, such electromagnetic interference, moisture and proximity to metal.

There are ways around the readability problems for both technologies, however. Various encapsulation techniques, for example, can solve many RFID problems. The engineering staff at World Kitchen LLC, of Reston Va., learned a few ways to overcome vision issues when it asked supply-chain systems integrator Peak Technologies Inc., of Columbia, Md., for help in improving the readability of its bar codes. Major retailers were charging the manufacturer of baking utensils, dinnerware and related housekeeping supplies $3 for each unreadable label. Because the 850,000-square-foot factory prints 500,000 bar code labels per month, even a small percentage of defective labels can eat into profits in a hurry.

Among the problems were heat and water, which were causing labels to peel off the boxes. The codes also smudged easily or were too inconsistent to read. The solution to the first problems was acrylic labels. Unlike the glued labels that the company had been using, these labels withstand exposure to water and heat. Because they are also smudge resistant, they are less likely to smear when they rub against conveyors.

Peak’s engineers solved the problem of faint and fuzzy labels by specifying better printers that can inspect their own work. As the labels come off the printer, a laser reader grades the quality of the codes according to an A-to-E evaluation scheme devised by Peak. Since most major retailers require B quality or better, the new printers reprint labels that fall below the grade. “Generally, though, the labels are As now,” says Terry Moore, a level 3 systems administrator at World Kitchen.

Because of the growing use of RFID tags among retailers, the mix of new printers includes some that can be upgraded to handle RFID tags. “It was important that our printers were upgradeable so that down the road, we could accommodate retailers and not have to spend extra money to buy all new printers,” says Moore.

Tuning-in to tags

Other manufacturing companies are doing a different, more strategic kind of planning to accommodate retailers. Because they must put RFID tags on their shipments anyway, they have decided that they may as well look for ways to use the tags in their own processes to generate some kind of return, and recoup a portion of their investments.

“This is where we’ve been seeing most of the activity in RFID over the last two years,” says Calvin Fidler, director of solutions at Peak Technology. “There isn’t as much new activity among manufacturers that are just trying to meet the mandates of the Wal-Marts, Targets, and Best Buys. The initial rush has settled down.”

Purdue Phama LP, based in Stamford, Conn., is in the new group of manufacturers looking for a return. “We wanted to go beyond the ‘slap-and-ship’ mentality of just sticking ID tags on bottles and sending them along in order to comply with the mandate,” says Chuck Nardi, information officer for commercial systems. “We saw this as an opportunity to take a broader look at RFID and the value we could get out of it.”

Because Purdue makes narcotic analgesics such as OxyContin, which is a controlled substance, security is crucial to its business. For this reason, as well as to bolster efficiency, the company decided to use the item serialization and auto-ID platform from SAP AG, of Walldorf, Germany, to track and trace its products at the item level, rather than at the pallet or case level.

Purdue’s plant in Wilson, N.C., also uses the Serialization Product Tracking application from Systech International ,of Cranbury, N.J., to give each package a unique serial number. The application also aggregates cases and provides an interface to SAP’s software.

A high-speed packaging line puts the RFID tags on each package. As the items are packed into cartons, readers collect the unique electronic product codes (EPCs) of each item. Another set of readers records the codes again as the packed cartons enter a vault for storage, and when they are shipped to the customer. Capturing EPCs at the packaging stage and linking them to delivery confirmations provide a means for minimizing theft and inadvertent diversions.

Besides serialization, the enabling technologies for this kind of tracking include the latest generation of scanners. Faster processors and other electronics allows today’s RFID scanners to read an individual tag in five milliseconds (ms) and write to one in 50 ms. Such speeds allow RFID to collect and deliver information as a tag travels through high-speed production lines. They also allow making more scans in a given amount of time, which improves the read rates for high populations of tags. “Every time you scan, you have the ability to read a tag that you didn’t read on the previous scan,” explains Scafidi at Omron.

Another enabler of RFID is standards. For example, EPCIS (for electronic product code information services), promulgated by RFID standards organization EPCglobal Inc. last year, is streamlining the exchange of RFID data across organizational boundaries. The second generation, or Gen2, standard for passive RFID tags also has done wonders for read rates in the ultrahigh frequency (UHF) band.

The difference that it made at a Daimler AG plant in Stuttgart, Germany, was stunning. In the early stages of integrating RFID into the kanban system there, SAP had installed Gen1 tags in a pilot in gearbox production. “The read rates ranged from 60 percent to 70 percent,” recalls Tobias Goetz, SAP’s director of business development for RFID. When the engineers switched to a new Gen2 tag, the read rate jumped immediately to 99 percent.
More in Control