Barcodes - 2D & 3D
A barcode to most is a pattern of black stripes that communicate the product identification t
o a computer via a scanner. This type of barcode is just the tip of the iceberg. The sophistication of barcodes goes way beyond this basic common one.
Traditional barcodes are basically machine-readable license plates. Each label contains a unique serial number coded in black and white bars that is a key into a database containing detailed information. Ordinary bar code is "vertically redundant", meaning that the same information is repeated vertically. It is in fact a one-dimensional code. The heights of the bars can be truncated without any lose of information. However, the vertical redundancy allows a symbol with printing defects, such as spots or voids, to still be read. The higher the bar heights, the more probability that at least one path along the bar code will be readable.
Yet many end users wanted to code more information. They wanted the bar code to be a portable database rather than just a database key.
2-D Barcodes
A two-dimensional code stores information along the height as well as the length of the symbol. In fact, all human alphabets are two-dimensional codes. Since both dimensions contain information, at least some of the vertical redundancy is gone. Other techniques must be used to prevent misreads and to produce an acceptable read rate. Misread prevention is relatively easy. Most two-dimensional codes use check words to insure accurate reading.
Two-dimensional code systems have become more feasible with the increased use of moving beam laser scanners, and Charge Coupled Device (CCD) scanners. The 2-D symbol can be read with hand held moving beam scanners by sweeping the horizontal beam down the symbol. However, this way of reading such a symbol brings us full circle back to the way 1D bar code was read -- by sweeping a contact wand across the symbol. The speed of sweep, resolution of the scanner, and symbol/reader distance take on the same criticality as with contact readers and one-dimensional bar code.
Initially, two-dimensional symbologies were developed for applications where only a small amount of space was available for an automatic ID symbol. The first application for such symbols was unit-dose packages in the healthcare industry. These packages were small and had little room to place a bar code. The electronics industry also showed an early interest in very high density bar codes, and two-dimensional symbologies, since free space on electronics assemblies was scarce. More recently, the ability to encode a portable database has made two-dimensional symbologies attractive in applications where space is not at a premium. A good example is found in the service and maintenance of equipment such as that found in a manufacturing environment. The servicing data is stored in a 2-D symbol on the equipment and the field engineer uses a portable reader to retrieve the information rather than dialling up the home office's computer.
There are well over 20 different 2-D symbologies available today.
3-D or Bumpy Barcodes
One of the problems facing the 1-D & 2-D systems is that they cannot withstand harsh treatment, such as cleaning solutions, high heat treatment or coolant spays that most metal parts routinely undergo.
Also, A 1-D and 2-D barcodes typically require a white background, so when applied directly to the metal there is often not enough contrast for a conventional barcode scanner to read the code.
The solution therefore was to develop a barcode that could be either raised from or impressed into the surface of the part. This means it can be integrally cast or moulded into the part at the time of manufacturing. Alternatively it can be etched, stamped or impressed onto the part following manufacturing or applied to a metal tags that can then be attached.
This latest development is illuminated with a laser which captures the reflected image in a two-dimensional closed coupled device (CCD). The angular displacement between the laser and CCD array allows detection of the differences in height across the 3D Bar Code. Once captured, the reflected image is digitised and processed by an onboard Digital Signal Processor. The BBC process requires no contrast of colour, therefore parts can often be scanned even though they have been painted.
One major benefit of this technology is that manufacturers are now able to identify individual parts rather than just simply identify batches. By being able to identify individual parts it avoids the huge expenses associated with massive recalls of cars, refrigerators, tires, etc, as it avoids the problem of not being able to determine whether a particular problem affected just a few parts or the entire day’s production.”
Machinery Automation & Robotics
1/101 Derby Street
Silverwater NSW 2128
Phone: (61) 2 9748 7001
http://www.machineryautomation.com.au