There is little doubt that the RFID initiatives started years ago by multinational retailers, such as Wal-Mart and Marks & Spencer, has given the technology a level of visibility it did not previously possess. While much is written about RFID and how it will change the face of distribution, it is time to address several misconceptions about the technology and discuss the effects recent developments have on the discrete manufacturing sector.
The visibility RFID enjoys today is not without problems as it created significant hype and some unreasonable expectations. Possibly even more problematic is the fact many potential users actively avoid taking advantage of RFID today, hoping that these large scale initiatives will result in some obscure, super-solution at ultra-low cost. This type of wait-and-see attitude deprives the manufacturing base of a powerful method to compete globally; only better products at competitive prices will guarantee survival in the marketplace and automation is an important factor in this fight.
This article hopes to paint a clearer picture of the true state of industrial RFID while providing information to better understand what the different RFID technologies can deliver and where their specific limitations lie.
Why Should I Pay Several Dollars For A Tag?
Tags are available today for well under one dollar (US) but users must realise what they can expect from a tag at this price. They also have to understand all the ‘small print’before they can get to this price.
The tags used by Wal-Mart for example are operating in the UHF (860 –880 Mhz) band and offer very little memory: 12 bytes to be exact. These tags are specifically designed for open systems associated with high-volume logistics tracking. This means they must offer a reasonable level of readability and reliability —99 percent is considered very good, at as low a price as possible.
For a tag to be useful in the manufacturing environment it must be housed in such a way to withstand particular environments. In automation environments RFID tags must withstand aggressive fluids, shock and vibration, dirt and grime, and possibly elevated temperatures. These tags are also expected to operate for many years in these abusive applications. Finally, is 99 percent read reliability really enough for the manufacturing environment?
With this in mind, it is highly doubtful that an industrial tag satisfying the needs of industrial applications will ever be available for 20 cents. While the cost of the chips used in those tags will continue to come down, most of the cost is tied to the construction and housing material, and it is unlikely that those prices will experience significant reductions due to the wide variety of requirements.
Is EPC The Only Technology Needed For Automation?
We need to differentiate between EPC and RFID. EPC is a code —a number that will uniquely identify a product and/or group of products —that the manufacturer of consumer items must purchase from EPCglobal. EPCglobal did an excellent job pushing for a standardised data format and RFID solutions. EPC is virtually synonymous with RFID tags operating in the UHF band is retailing and logistics applications. UHF was selected because it allows tags (or rather, tag inlays) to be produced very cheaply.
UHF technology also tends to allow tags to be read while they are relatively far away from an antenna. This is an advantage, for example, when pallets need to be tracked as they are moved through a doorway, but can be big problem in automation where pallets or items located very close to each other must be read individually. EPCglobal has recently identified this inherent limitation and HF systems are now evaluated as a suitable alternative for EPC.
As far as automation is concerned, a long read/write range has never been a big issue. On most conveyor-based production lines, tagged items that range from engine blocks to tooling carriers are moved with precise accuracy. A read/write range between 20mm and 200mm is suitable for most applications. This allows two items to be placed very close together without having to worry about them being read simultaneously.
Based On Cost, Other Tagging Technologies Cannot Compete With UHF
The basic cost of growing a UHF chip is no different than growing a chip for any other RFID technology. The cost of the chip is first and foremost a function of size; and size is driven significantly by memory. UHF tags for EPC can be made cheaply simply because they have only 12 bytes of memory. On the other hand, tags typically used in manufacturing require upwards of 10 times that memory.
The second factor driving the cost of the tag inlay is the antenna. UHF tags, by virtue of their operating frequency, do not use coil antennas, but rather they use printed structures. The same is true for HF tags. Consequently UHF and HF tagging technologies can offer similarly priced tags.
Read/Write Electronics — The Forgotten Factor In RFID
While the cost of the tags appears to be the primary issue discussed in the literature, the cost of the read/write electronics is often forgotten. UHF readers are still relatively expensive. It is expected that these readers will eventually drop below the US$500 mark, but exactly when this will happen is unclear.
Conversely the cost of read/write electronics for other technologies this price threshold is not even a challenge. For devices designed to operate in the HF and LF (125 kHz) band complete solutions, including communication interfaces, can be below US$500.
Consequently, operators of closed-loop industrial systems, where tags remain attached to carriers and thus never leave the plant, should be less concerned with using an extremely cheap tag and more concerned with the total cost of ownership (cost of all hardware items, longevity and reliability of all selected items.)
Network Connections To PLC Still Rule The Industry
PLCs continue to dominate automation control in plants and manufacturing systems. The capability of PLCs continues to increase as the cost decreases. Any suitable RFID solution for the plant floor must therefore offer a reliable and easy way to connect to the dominant networks supported by those PLCs. EtherNet based protocols including ProfiNet, EtherNet/IP, ModBus/TCP and EtherCAT cover the majority of vendors and are the most popular industrial networks used with RFID technology today.
In industrial applications however there is the ever present need to support more legacy connectivity such as ProfiBus, DeviceNet and even Serial interfaces. There is no direct connection between the tag technologies and the available networking solutions, however the logistics/retail type applications are not driven by PLCs.
As things stand today, typical logistics/retail UHF tags are not suitable for tough automation applications. Consequently, reader connections to PLCs are not required in this field. Exchanging data with an ERP system is more important and the providers of these solutions have realised and addressed this need.
Recently, however, there has been much development into UHF RFID technology in factory automation applications. Ruggedised read/write head solutions have been developed along with multiple manufacturers producing more robust industrial tag types. Typically the read ranges are much greater than HF or LF and multiple tags in field can be read at once. The costs of the tags range from less than HF versions to much more expensive depending on application. In factory automation applications the key is to match the right technology with the specific application. Among the topics in factory automation RFID ‘ease of interface to the control system’is of paramount importance.
Why The Wait?
RFID is a mature technology that has been around for several decades. Many fields of automation absolutely require this technology for the purpose of error tracking and prevention as well as production control and product tractability. For users who toyed with the idea of using RFID a few years ago, but decided against it for one reason or another, it is time to take another serious look. The technology has further matured, prices have come down and connections to PLCs have gotten better and simpler. Now with the inclusion of UHF in the bag of industrial RFID options the possibilities have never been so wide.