If I had a hammer…

The words of psychologist Abraham Maslow in 1966 have been adopted by industry as a warning against over-reliance on a familiar tool or technology – “I suppose it is tempting, if the only tool you have is a hammer, to treat everything as if it were a nail.”

Maslow’s fascinating observation of human behaviour is particularly apt in the field of auto-identification technologies.

For more than 15 years, users in factory and warehouse automation have been confused by some claims that one auto-ident solution fits all: RFID, camera or laser.

Given that there are a range of auto-ident technologies for different tasks, let’s examine the pros and cons.

The first question should be – is a centralised solution needed with all data and production history held on central PCs and servers? Or is the production history held on the label of each product as it progresses through the process?  If a decentralised system is in operation, then RFID could be the only real choice. 

RFID offers unique benefits:

• Tags can be read from any direction, so locating the reader is not as critical as optical systems and line-of sight is unnecessary. The tag to reader range can be very large compared to the other technologies.

• For high speed throughput, reading is very rapid and many tags can be read at once.

• Tags can carry large volumes of complex data, which can be rewritten, amended or updated easily.

• RFID performs well in harsh factory environments where there is dirt, dust or high moisture levels, for example.

But RFID can be expensive. Reliable transponder tags are about ten times the cost of a printed label and many tags may be needed in the supply chain as well as in the factory; the effect on ROI (return on investment) can be significant.

RFID systems also need careful set up in areas where radio signals could be masked or reflected, for example, where multiple metal surfaces are present.

If a centralised system is acceptable, then either a barcode or 2D code is likely to be the answer. Generally the 2D code is becoming widely used because it can be read in any direction and stores a larger amount of data in a smaller space than a 1D code.

However, 2D codes need a camera to read them, which is more expensive but worthwhile if large amounts of on-pack data are necessary. A camera is also better at reading low contrast coding in 1D and 2D.

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A broad variety of cameras are available, so if this is the route for you, look closely at the cameras that for your application best. These include matrix scanner cameras and line scan cameras.

A simple laser reader will be the answer if all that is needed is to read simple SSCC (standard industry) or in-house barcodes on the side of a pallet, say, to check goods in or out. With wide scanning height and width, it can sweep the entire side of a pallet, with cell sizes down to 3mm.

Laser scanners use a laser beam directed onto a rotating polygon and reflected onto the code where it is read. Some devices use Time of Flight technology to measure the distance between the laser and the code, to achieve precise focus.

Although eye safe, the laser spot is very bright and the polygon scanning action over the code is a rapid 1200 Hz. The high power of the laser and its tightly focused spot enables reading over long range without disturbing operatives.

To achieve omnidirectional code reading, two or more laser scanning heads are required. They offer a wider and better depth of field than matrix cameras of the equivalent price, but perform less well where they is a very low contrast, poor aspect ratios or badly-printed codes.

For basic 1D code reading function laser cameras provide a low cost option with an excellent depth of field and large reading field width. They are not sensitive to external light pollution and don’t need additional illumination. Codes can be read easily whether the object is still or moving.

No one device suits all applications. With the most up-to-date software solutions, it is now much easier to integrate a wide range of auto-ident solutions in a single network. The most impartial advice is likely to come from a vendor offering all three technologies, especially where they can become part of a seamless communications network.

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