Keeping Track With Symbology
These last couple of years have seen much progress in bar code reading reliability (98% is not unusual), longer reading distances (tens of feet for laser-based scanning), and all-encompassing bar code data collection, says Kevin Prouty, Research Director, Manufacturing Strategy for Boston-based AMR Research. Now for the inevitable "but": There really haven't been any earth-shaking changes in how bar code technology really works.
That's not to say nothing has been happening. The big news is that the automotive industry–particularly General Motors (GM)–is implementing standards to use two-dimensional (2D) code symbologies in day-to-day supply chain and production operations. This is a natural situation. Bar code technology tends to lead the industry, and now the industry is catching up by gravitating toward PDF417 for shipping labels and Data Matrix for direct part marking (DPM).
The main automotive 2D codes are either stacked codes, such as PDF417, or matrix codes, such as Data Matrix and QR Code.
PDF417 (sponsor: Symbol Technologies Inc.) is a high-capacity 2D bar code symbology. It can encode up to 1,850 ASCII or 2,725 numeric characters per symbol, or approximately 900 characters per square inch—more than 100 times the data than a conventional linear bar code.
Data Matrix (sponsor: RVSI Acuity CiMatrix) looks like a checkerboard—a square made up of multiple squares of equal size or dots. This checkerboard can be quite small—as small as 0.1 in.—which is ideal for tight spaces. The symbol typically contains up to 500 characters per square inch and it has little redundancy; almost all of it is meant for data or error correction. The solid-bar finder patterns are minimal, which winds up being the symbol's Achilles heel: Damaging one of those lines can make the code unscannable.PDF417 is best read by a rastering laser scanner (the laser pattern envelopes the entire bar code). Overhead built into the symbology tells the scanner where each row is—those picket fences—in terms of height. Because of that, you can cut a PDF417 label into horizontal slices, jumble those slices up, pull them out one at a time, and have the scanner put the jumbled mess back together. This makes PDF417 virtually bulletproof. Really. You have to shoot a lot of bullets into a PDF417 bar code or mark it up a lot before it's unscannable.
To read this matrix code, an imager takes a snapshot of the entire symbol. Imaging algorithms locate the finder patterns within that snapshot, and then apply decoding algorithms. Readability depends on proper and consistent lighting and contrast across the checkerboard pattern, as well as sophisticated image processing hardware and algorithms. The imagers themselves are still an immature technology, costly, and don't feature nearly the depth of field that laser scanners offer.
Because Data Matrix can be printed simply as individual squares or dots, versus bars as required by PDF417, it can be directly etched, stamped, or peened onto metal, plastic, and other materials.
Other 2D codes do exist. About 60% of Japan's automotive industry uses QR Code (Quick Response Code; sponsor: Nippondenso Company). QR code is a 2D matrix code that can encode up to 2,509 numeric or 1,520 alphanumeric characters. The symbol has locator patterns in three corners, three levels of error detection, and 32 standard sizes. The smallest QR Code measures 21 x 21 cells (each cell encodes one bit) and can grow in increments of four cells to a maximum of 105 x 105 cells.
MaxiCode (sponsor: United Parcel Service) looks like a honeycomb (888 hexagonal cells) with a bull's-eye target in the middle for an imager to locate. It is limited to 100 alphanumeric characters and is used for high-speed sortation. While MaxiCode is in the public domain, the symbol is used almost exclusively by UPS, mostly for political rather than technical reasons.
Many of the people interviewed for this article felt that the symbology-standards wars have been fought. Unless a code brings some unique capability to the table, then the feeling is that the various standards bodies—AIAG, AIM, and ISO, etc.—are not going to consider the new symbology for an industry standard.
How do you read this stuff?
Laser scanners are typically used for reading linear bar codes. A conventional laser-based, linear bar code scanner operates at 36 scans per second and costs under $1,000. In the middle market, high-speed linear laser scanners operate at 100 to 200 scans per second. These devices output a straight scan line; however, they can read PDF417 if this scan line is waved over the symbology. At the high end are laser scanners that can output a raster pattern if they recognize a PDF417 symbol. Read rates are less than a second. Because the scanning requires two degrees of freedom, the device contains a more complex and expensive central processor.
2D imagers involve camera technology, specifically some sort of lens system. Therein lies the problem: currently, all image readers on the market are fixed focus; imagers are optimized for one point in space, which is typically between 7 in. and 10 in., though reading from up to 2 ft. is not unusual with the proper lens system. In fact, the depth of field in imagers is a multivariable function depending on lighting, lens system, code size, and imager speed.
Most imagers are based on charge-coupled device (CCD) technology. A low-end CCD imager includes a linear CCD array of about 500 to 600 pixels by 1 pixel. Such scanners are basically contact reading devices. On the high-end side, 640 x 480 element imagers have to crunch through an image weighing in at 300 KB or more to extract the symbol. Such image processing often uses a processor powerful enough to drive a low-end Macintosh computer.
In the past two years, imagers based on complimentary metal oxide semiconductor (CMOS) sensor technology have hit the market. Compared with CCD imagers, CMOS imagers are faster, consume less power, more expensive by a few hundred dollars, and still evolving.
Vision systems can also read bar code symbologies. These systems have tended to be overkill for bar code reading and they are generally more expensive than bar code scanning devices, whether laser or CCD. Plus, they have all the same lens and lighting problems that imagers have. However, their prices have been dropping, making them more competitive for fixed-mount applications.
A global shipping label
Now for the big news. In late 1999, GM introduced GM1724 specification, "Common Global Shipping Label Template." This was subsequently superseded by GM1724-A, "Individual Container Label."* (The "A" extension differentiates the individual container standard from the master-label standards, "-B," and mixed-label standards, "-C.")
This specification came about because the word came from on high to "get commonality wherever possible." Truth is, says Larry Graham, GM's Global Manager for Automatic Identification Technologies, coming up with a standard shipping label is not just a GM issue; it's an industry issue involving suppliers, carriers, third-party logistics providers, as well as GM and all the other automakers.
GM also realized it had to develop a shipping label system that could work with and without technology. Strange, huh? Even Graham admits that. However, in some parts of the world where GM is building new facilities (such as in Thailand and China), scanning, electronic data interchange (EDI) and other technologies we take for granted don't exist. Plus, these technologies can be cost-prohibitive in those regions.
GM1724-A is very automation-oriented. GM's previous shipping labels used as many as five or more Code 39 linear bar codes. These are replaced by a single line of PDF417, which acts as a paper-based EDI transmission. Oxymoron aside, it turns out that many manufacturing companies batch their EDI transactions for transmission at the end of the day. In just-in-time environments, this transmission can sometimes be six hours after the truck arrives at the customer site. By scanning essentially the same EDI information—now in a bar code—incoming shipments don't have to wait at the receiving dock.
GM1724-A also specifies such things as standard data locations, standard fonts, upper case lettering, and human readable data—all in a 4 in. by 6 in. label. "It turns out that the real scanners that move things are not the technology scanners, but the human eye," says Graham.
MACHINE VISION SEES SYMBOLOGIES AT AN AFFORDABLE PRICE
Here's a Data Matrix symbol dot peened directly on a metal part, as seen by a vision system. The symbol could have been just as easily laser etched, chemically etched, even ink jet printed. And the part could have been made of plastic, glass, or just about anything else that's solid.
The label contains ship to/from addresses, made/assembled in information, material handling codes, part numbers, shipment dates, part bin, special handling requirements, container type, and gross weight. A descriptor block contains information known only by the supplier, such as quantity, part description, or revision or engineering change date. A license-plate linear bar code using Code 128—that's right, GM is moving away from Code 39 for space efficiency—holds up to 22 characters. These include a new "J Series" international data identifier for describing the container load type (mixed load) plus a DUNS number for vendor identification. (In Europe, ODETTE, the European automotive standards group, would be used instead of DUNS.) Other blocks on the label provide reference information, such as pack or production dates. And there's even a block exclusively for suppliers to use.
GM1724-A was okayed back in July 1999. Starting March 31, 2000, all GM suppliers were to use this label standard when shipping production parts to GM's facilities, including the designated receiving locations for passenger and truck vehicle assembly operations (e.g., GMNA, Saturn, Opel, and Saab), component operations (e.g., powertrain and metal fab), and service parts operations (e.g., GMSPO). GM started issuing PR&Rs (Problem Report & Resolutions) on December 1, 2000.
According to Graham, ODETTE stopped working on a next-generation shipping label when it saw GM1724-A. In April, JAMA (the Japanese counterpart of the AIAG) is expected to offer some final edits to the specification. At that time, the auto industry will have a common, global transport label.
Overall, GM expects the single global label will streamline GM's receiving operations to the tune of at least $100 million per year.
The next step: Direct part marking
So much for in-transit part marking. The next step is direct part marking (DPM). Note the difference here. Part marking usually involves other media, be that a sticky label, a tag, riveted metal tag, a tag chained to the part, or, for parts too small to individually mark, a box of nuts and bolts. DPM is as advertised: the mark is directly on the part. Another difference, explains Bill Hoffman, manager of Industrial Solutions, Automotive, for Intermec Technologies Corp. (Oxford, MI), DPM is serialized data for the express purpose of tracking the individual part, not just the type of part.
"All the top tiers in the automotive industry have DPM projects going on," says Jim Hahn, president of AutoImage ID, Inc. (Cherry Hill, NJ). GM, for instance, has DPM pilots involving airbags, engine blocks, heads, and camshafts. Actually, DPM applications are plenty: cradle-to-grave track-and-trace, recalls, theft protection and fighting gray-market theft, and error proofing. Spark plugs are a simple example where DPM might prove indispensable. The spark plug might screw into an engine without a problem, but its spark gap directly affects engine performance. So, given the speed of car manufacturing these days, a mislabeled box of spark plugs can create havoc. "In less than a second, a perfectly good shipment of spark plugs can turn into bad parts!" says Graham. Not only would each of thousands of engines have to be inspected for the wrong spark plugs, but the spark-plug supplier would somehow pay the price.
At the end of the day
Graham harkens back to his retail days when he talks about the GM1724-A shipping label. "Many people think of these labels as a nuisance. In fact, they are a very important. They are an extension of your image. The containers coming in the door are our first impression of you as a supplier. Look at the container labels and ask yourself, ‘Would I send this out on my letterhead or my business card?' If you start thinking about that, I think we can eliminate a lot—a lot—of issues we have in shipping labels."
*If you're one of the 30,000 vendors to General Motors, there's a surprise awaiting you regarding the GM1724-A, "Individual Container Label." The specification calls for some non-printable characters. Well, maybe they are printable on your printer, but you won't know that until your printer is certified, as well as the related firmware, software, and infrastructure, to meet the design goals of GM1724-A.
GM appointed Intermec Technologies Corp. (Everett, WA) as a certifying agent for GM1724-A. Intermec assures GM1724-A compliance by certifying each Intermec printer used to print this label. Then Intermec officially notifies GM about certification.
Certification involves two steps. The first step, pay $75.00 per printer for firmware updates, if required; any required maintenance affecting certification; and a label print test. The second step requires that actual shipping data be printed using the vendor's Level 1-certified printer and verified in compliance. Once this Level II certification is passed, the vendor is authorized to go into production.
Given the number of GM suppliers—and their printers—involved, the name of the game now is to get some PR&R (Problem Report & Resolutions) relief, urges Intermec's Bill Hoffman, Manager of Industrial Solutions, Automotive. "You can keep shipping your label as long as you're registered and just waiting to be certified." Information about Intermec's GM1724-A compliance certification process is available at www.GM1724.intermec.com/, or call 800-815-3363.