Bert Moore
Even the most powerful process-control computers can't control what they don't know about. But the traditional method of tagging pieces and parts as they wend their way through the manufacturing process -- the venerable bar code -- doesn't work when the size of the bar code is substantially larger than the part itself.
Enter 2-D bar code symbologies. Able to encode up to 2000 characters in a single symbol measuring no more than a few square inches, these efficient symbologies offer new possibilities for automated data collection in manufacturing. Companies are currently exploring and implementing 2-D symbols for item identification, lot/batch tracking, production history, safety inform
ation, and even machine programming.
For manufacturing-data collection, the two leading symbologies are Data Matrix (developed by International Data Matrix) and PDF417 (developed by Symbol Technologies). Both symbologies are already in use, are in the public domain, and have recommendations from draft-industry or national standards.
SmithKlein Beecham is using Data Matrix to comply with new FDA regulations that require verification of label content for all pharmaceuticals, including over-the-counter medications. The UPC bar code on such a product identifies the product but does not indicate the label content. The Data Matrix symbol, meanwhile, has both.
The semiconductor industry has selected Data Matrix for wafer tracking during production. In addition, a draft Electronics Industry Association (EIA) standard recommends it for component marking and Automotive Industry Action Group (AIAG) production history. Data Matrix may become the symbology of choice for all small-parts identification.
The automotive industry is also interested in PDF417 for production-history documentation. A single PDF417 symbol can contain up to 2000 data characters and still take up no more than a few square inches (the actual size depends on the options selected). Volvo is using this symbology in Sweden to program manufacturing-testing equipment, and Casappa S.p.A. in Italy uses it to enter data into automatic engraving equipment. In addition, the U.S. Department of Energy uses PDF417 for Material Safety Data Sheet information on drums of hazardous waste.
Data Matrix is an example of a matrix symbology (
see the photo
), which uses fixed-size light and dark elements (typically squares) to represent data characters in a predetermined arrangement. Matrix symbols require special imaging readers (typically linear or 2-D charge-coupled devices [CCDs]) but need less contrast, which makes them ideal for molding, etching, or casting into an item.
PDF417 is an example of a stacked bar co
de, which is just that: short bar codes stacked on top of each other, with special bar code characters in each row to indicate its sequence within the symbol. As with regular bar codes, symbols can vary in length and height. Stacked bar codes offer the advantage of being readable with many existing bar code readers and CCD imagers.
The major 2-D symbologies all provide special features, such as full ASCII encoding, multiple ISO code page selection, the ability to append data from multiple symbols in the correct order, and user-selectable levels of Reed-Solomon or convolution codes for error detection and erasure correction to read even badly damaged symbols (
see the photo
).
It's true that 2-D symbologies won't replace UPC symbols in the supermarket or in many other existing applications. Yet for manufacturing-data collection, they offer tremendous opportunities for marking small items or conveying large amounts of data efficiently.
photo_link (14 Kbytes)
The Data Matrix symbol on SmithKlein Beecham's Tums label, for FDA compliance.
photo_link (92 Kbytes)
Despite obvious damage, this PDF417 symbol is still readable.
Bert Moore is director of IDAT Consulting & Education, a Pittsburgh
-based firm specializing in automatic data-collection technologies. You can reach him at
72620.1677@compuserve.com
or
IDATconslt@aol.com
, or on BIX c/o "editors."
A New Dimension in Bar Codes
