TechArchive

Original article date: May 2000

With the small data capacity of bar codes increasingly limiting their usefulness, Omron’s SEAN ELEY looks at the emergence of the 2D code, and the equipment to print and detect it

The humble bar code has been meeting data portability requirements industry-wide for decades, unmatched in its ease of application and of data extraction, and untouchable in its cost-effectiveness. It is not without its detractors, who point out the fragility of the print quality in aggressive environments and the implications for quality control, and who champion the applications for read/write technology, but still the bar code marches on largely unchallenged. It may be a read-only technology, but in numerous market sectors, that is exactly what is required.

But still, the bar code we know and love is starting to show its age. In this information society, the amounts of data we try to carry around on products have been escalating wildly, reaching and exceeding the limits of the bar code’s capacity. At the same time, as data requirements rise, so does the need for providing error checking on that data – something again to which the traditional bar code has no answer.

And so a new challenger is emerging – the 2D code. Whilst a conventional bar code encodes information in one direction only, the 2D code extends this with a matrix across both the X and Y axes.

For the standard bar code, the only way to add more information is to greatly extend the length of the bar code, making it much more difficult to read. At the same time, there is no mechanism for redundancy, and a very high contrast (80% or more) is required to ensure accurate reading of the code. As a result, it doesn’t take much degrading of the print of the bar code before it becomes unreadable.

By contrast, the 2D code, offering expansion in two directions, can hold a much higher volume of information. For a given ‘area’ of code, where the bar code can hold say 20 bytes of information, a 2D code of the same area can contain some 2000 bytes. In addition it provides redundancy by error checking, and, impressively, requires only a 20% contrast to ensure accurate reading, so misreading is almost impossible. And against the subjective blandness of the bar code, there is a certain aesthetic appeal about the 2D code.

Of the many flavours of 2D code, the ‘data matrix’ code is now becoming a standard across Europe and the US, with advantages of size and higher safety in reading over other types. A key advantage of the data matrix code, however, from the user’s point of view, is that it is extremely easy to print. You can select from either round dots or square cells, and can employ either a square or rectangular matrix. Any type of output device can be used to print the code, from inkjet, laser etch and dot matrix printers, to thermal transfer, web press and laser printers. The qualities of the data matrix code mean that the stringent print quality requirements of traditional bar codes can be relaxed..

The format also assures ease of reading. Continuous orientation bars around two sides of the mark provide information for orientation. Alternate light and dark cells around the remaining two sides define the number of rows and columns. A further mark gives identification data for the centre of the cell. Having registered all this, the pattern decoder can then set about extracting the coded data.

As the data matrix code has evolved, the error correction capabilities have greatly improved. It is now the only symbology to offer both Reed-Solomon and Convolutional code error correction..

Importantly, the technology to read and decode the 2D mark is both affordable and easy to use. Omron has recently launched a system built around its F150 visual inspection system, but with a dedicated operating system and tailored software for 2D code reading applications. The resulting V530-R150 system is an extremely compact solution combining high performance with ease of use, and at a fraction of the cost of a traditional vision system.

At a cost which makes using 2D codes viable for just about any application, the V530-R150 system meets the requirements of 2D code reading by combining pattern matching with greyscale inspection.

With its advancement of the cause of the bar code, 2D coding looks set to become the portable information medium of choice in a whole host of applications where the limits of the conventional bar code have been reached. In particular, in sectors where technologies such as RFID tagging still have too great an implied cost, the 2D code at last offers a viable, high performance alternative.

• Omron

May 2000