Often, RFID is associated with retail and distribution applications, such as well-publicized efforts involving Gillette Co. (Boston), Procter & Gamble Co. (Cincinnati) and Wal-Mart Stores Inc. (Bentonville, AR). But, the technology has traditionally been used to track farm animals, semitrailers and railroad cars.

The widespread move toward RFID is being fueled by Wal-Mart, which is requiring its suppliers to place electronic tags on shipping pallets and cases. It currently operates more than 500 stores equipped with RF readers that can automatically track out-of-stock items.

Wal-Mart plans to have 1,000 stores and more than 600 suppliers using the technology by the end of this year. A recent study conducted by the University of Arkansas (Fayetteville, AR) discovered that RFID-enabled stores are 63 percent more effective in replenishing out-of-stock items than traditional stores.

However, RFID also has huge potential on the plant floor, where the technology is slowly catching on. Indeed, more and more manufacturers are harnessing the power of wireless systems to improve supply chain efficiency, address traceability issues and solve error-proofing problems.

"Today, most of the emphasis is at the end of the assembly line to label products for tracking into the consumer market, with a secondary emphasis on tracking material to the beginning of the assembly line," says Bob Eckles, industrial goods director at Intermec Technologies Corp. (Everett, WA). "Although RFID on the assembly line is [still] fairly limited, the integration of the technology and the industrial Ethernet world of PLCs will change that significantly."

According to the 2005 State of the Profession survey conducted by ASSEMBLY magazine, RFID is currently used by 25 percent of manufacturers. Activity is strongest in the consumer goods industry, with 39 percent of respondents claiming to use wireless technology. Other industries that are actively using RFID for production applications include machinery manufacturing (30 percent) and transportation equipment (26 percent).

The technology is also popular with food and pharmaceutical manufacturers. But, its widest use is in the automotive industry, where OEMs such as DaimlerChrysler (Auburn Hills, MI), Ford Motor Co. (Dearborn, MI) and General Motors Corp. (GM, Detroit), and Tier 1 suppliers such as Johnson Controls Inc. (Milwaukee), have invested millions of dollars in wireless equipment and software.

For instance, GM has deployed RFID for more than 20 years. It uses the technology to identify and sequence parts on its assembly lines, and keep track of finished vehicles. By attaching tags to engines, chassis, bodies, seats and other subassemblies, automakers can quickly record the completion of each assembly process and trace potential warranty problems.

Kenworth Truck Co. (Renton, WA), the recipient of the inaugural Assembly Plant of the Year award sponsored by ASSEMBLY magazine, began experimenting with RFID in 2004. The technology is used for product tracking and power-and-free conveyor management in the plant's paint shop.

"It enables us to quickly receive and locate parts throughout the production line and produce cost savings through dunnage reduction," says Doug Baugh, plant manager. "RFID reduces the retrieval time of parts being painted. It has proven to be more reliable than the optical-based sensor system it replaced."

In addition, RFID has been successfully implemented by nonautomotive manufacturers such as Airbus S.A.S. (Toulouse, France), Boeing Co. (Chicago), Hewlett-Packard Co. (Palo Alto, CA), HomeCrest Cabinetry (Goshen, IN) and International Business Machines Corp. (IBM, Armonk, NY). Both Airbus and Boeing are developing standards for using RFID equipment in their assembly processes. In fact, the new Airbus A380 boasts 10,000 parts equipped with wireless tags.

Boeing recently unveiled an RFID initiative that is expected to affect hundreds of suppliers and trickle down the aerospace supply chain. It plans to use robust RF tags on engines and other maintenance-intensive parts of its new 787 jetliner. The wireless system will enable aircraft mechanics to use handheld readers to access critical components without having to dismantle bulkheads or panels. Tags will store and transmit information such as assembly date, part number and hours in service.

These tags will not be like those used in traditional retail-based systems. Boeing is specifying RF tags that can withstand severe changes in humidity, pressure and temperature, in addition to interference from metallic surfaces. The initiative is expected to spawn new RFID technology and create a new class of tags that will be ideal for industrial applications.

According to IDTechEx Ltd. (Cambridge, England), the global market for RFID systems is currently $2 billion. However, it's predicted to reach $7 billion by 2008 and $24 billion by 2015. Yankee Group Research Inc. (Boston) claims that 1 million active RF tags, which are widely used for manufacturing applications, will be tracked worldwide by 2007. And, the company predicts that there will be 10 million tags in use by 2009.

More than Just Bar Coding

The basic technology behind RFID is not new. Indeed, it traces its roots to World War II, where it was used with radar signals to distinguish friendly aircraft from enemy aircraft.

An RFID system uses radio frequency waves to transfer data between a reader and items that have electronic tags affixed. The tags contain a microchip and antenna that operate at internationally recognized standard frequencies. Tags are typically embedded in epoxy and plastic. However, inlays can also be embedded within label material and attached directly to cartons, containers, parts bins, racks and totes.

Tags come in many different sizes and shapes. The shape, size and cost of each tag varies with how much memory it has, how far it can send and receive data, and how it will be used.

Tags are typically used for either product identification or carrier identification. The former is commonly used by retailers and consumer goods manufacturers that want to track shelf life or buying patterns. Most RFID applications in manufacturing apply to carrier identification.

An RF tag can be either active or passive. Passive tags draw their electrical power from the radio waves generated by the reader and antenna. Active tags are powered by a battery. Passive tags last longer and are less expensive than active tags. However, active tags have more memory and a longer radio range than passive tags.

"The primary difference between the two are cost and read range," says Damon Bramble, general manager of solution center services at Alien Technology Corp. (Morgan Hill, CA). "Active technology is generally used in higher value or closed-loop applications [such as assembly lines], while passive technology is used more in open-loop applications [such as retail or distribution] and can be used anywhere."

An antenna sends and receives data from RF tags. It emits a radio signal at a certain frequency. In an assembly environment, it can be mounted above or alongside a conveyor, or it can be a handheld wand.

The antenna's maximum transmission distance is directly proportional to its size and signal frequency. For example, a large antenna broadcasting a high-frequency signal has a longer range than a small antenna broadcasting a low-frequency signal.

For assembly line applications, the distance between the antenna and the tag is usually less than 18 inches and rarely exceeds 6 feet. Tags do not have to be directly in sight of the antenna, but they must be within the antenna's broadcast range.

"The type of tag used for assembly line applications depends on the application, including the reading distance and accuracy required," says Andreas Somogyi, global program manager of wireless warehouse solutions at Rockwell Automation Inc. (Milwaukee). "For assembly lines, we use mostly 13.56-megahertz technology. This [allows] tighter integration to other control systems like PLCs, due to standard network adoptions on the RFID reader.

"In assembly applications, a short reading distance from 1 to 5 inches is often desired," adds Somogyi. "In retail and distribution applications, you need a longer reading distance-up to 15 feet-which is achieved by deploying 915-megahertz technology."

Similar to a bar code, an RF tag stores data but offers enhanced data collection and significant advantages such as being able to read without a direct view of the RF label and a dynamic read-write capability. With RFID, end users can identify and receive a wide array of information about products moving down assembly lines, stored in shipping containers or sitting on store shelves.

One- and two-dimensional identification codes are widely used in manufacturing, either on packaging or directly on products. However, traditional bar codes have limitations. For instance, they can be damaged if they become dirty or get scraped on the plant floor. In addition, readers and scanners must have a direct line of sight to the codes.

Unlike printed codes, RF tags can be reused and they can withstand harsh environments. However, metal can pose a big problem. That's why RFID systems are easier to implement in a warehouse than in an assembly plant. "There is much more potential for interference on an assembly line," notes Chantal Polsonetti, vice president of ARC Advisory Group Inc. (Dedham, MA). "RF signals reflect off metal, which can make it a challenge to use around machinery."

If a tag is mounted on a metallic surface, such as a conveyor, a plastic carrier will be necessary to separate the tag slightly from the equipment or part. This will prevent the radio wave from reflecting off the metal.

Depending on the tag and its application, each memory address can be overwritten thousands of times. So, a tag can ride down an assembly line on a pallet or fixture; be removed at the end of the line; be decoded; and placed back on another carrier.

Bar codes are a one-time use technology. Once the code is printed, information cannot be added to it and the code cannot be reused. Unlike traditional bar codes, RF tags contain much more detailed information. For instance, the typical bar code contains 14 to 16 digits vs. 96 to 256 digits for RF tags. That allows manufacturers to capture much more data that can be used to identify products by shift, machine and operator.

With RFID, "parts can automatically ‘talk' about when and where they are made, how much they cost, and where they are at any given moment in the warehouse or on the production floor," says Scot Sharland, executive director of the Automotive Industry Action Group (AIAG, Southfield, MI), which has been spearheading RFID implementation among automakers.

Assembly Applications

Radio frequency identification technology is ideal for many assembly applications. It can be used to sequence the delivery of outsourced components, monitor and track work in process, error-proof build instructions, ensure correct tool usage, trace the history of parts, improve product quality and operate kanban systems.

According to Rockwell Automation's Somogyi, RFID can play a huge role in improving assembly line efficiency and productivity. "RFID reduces human mistakes and guarantees correct data tracking," he points out. "It has the potential of providing new streams of real-time data that can support existing lean and Six Sigma initiatives on the plant floor.

"RFID information can be used to ensure that the correct labor, machine, tooling and components are available and ready to use at each processing step, thereby eliminating paperwork and reducing downtime," adds Somogyi. "As raw materials are consumed and assemblies created, triggers can be set off, controlling inbound materials and impacting work-in-process inventory or post-process inventory."

One of the biggest benefits of RFID is ensuring the accuracy of build instructions in a manual assembly environment. Traditionally, work orders and build sheets must be updated at every workstation. With RFID, updates can be written to the tag so that it is constantly being updated without risk of operator error. That means critical tasks aren't skipped or executed incorrectly.

"A few companies have begun to realize of value of [RFID] technology on the shop floor," notes Michel Baudin, a consultant at the Manufacturing Management & Technology Institute (MMTI, Palo Alto, CA). They have begun to use the technology to "track tools, fixtures or pallets, to trigger the picking of kits, or to trace products.

"These applications, however, have barely scratched the surface," adds Baudin. "RFID can [also] be used to mistake-proof mixed-flow assembly of products. In different forms, the combination of RFID with kanbans also offers opportunities for smoother integration with the overall information system."

According to Chris Huff, marketing specialist at Escort Memory Systems (Scotts Valley, CA), RFID can play a key role in developing and maintaining flexible assembly lines. For instance, he points to the experience of Johnson Controls, a leading supplier of automotive seats and interior modules. One of its seat plants located near a Big 3 automaker was experiencing problems using traditional clipboards and checklists that were located at each workstation. The company invested in RFID to eliminate human error and production mistakes. Manufacturing engineers considered using bar codes, but quickly determined that they would be more susceptible to misreads because of operating conditions.

Johnson Controls installed RF tags on the bottom of seat pallets. As each seat progresses down the assembly line, the pallet passes over an antenna at each workstation. Operators reference a touchscreen PLC that indicates seat type as well as needed alterations.

If a seat requires work, the operating system won't let the seat continue down the line until the operator has made and verified all necessary adjustments. The antenna then writes to the tag, updating it with whatever modifications have been made to the seat.

The process continues until the seat reaches the final workstation where its build instructions are verified with the actual assembly record. If they match up, the seats are transferred to the shipping area and are sequenced for delivery to the automaker's assembly line.

Previously, each type of car and truck seat had to be separated and sent through the assembly line in matching groups. But, the RFID system allows Johnson Controls operators to assemble many different types of seats on the same production line.

In addition to the automotive industry, electronics manufacturers have successfully implemented RFID on assembly lines. For example, CompControl GmbH (Gersfeld, Germany) recently started using RF tags to provide full traceability of printed circuit boards (PCBs) in the manufacturing process and throughout the entire lifecycle of a product.

"With today's PCB industry witnessing tougher international regulations regarding traceability, recycling and maintenance of high-value electronic units, there is a need to introduce more highly automated manufacturing and tracking processes," says Egon Konopitzky, vice president of Sokymat, a supplier of RFID transponders.

CompControl uses 125-kilohertz transponders in its tracking system. The tags are mounted on the PCB at the beginning of the production process. The RFID transponder, which is used throughout the life of the PCB to identify and access information about the product, is assembled onto the board using standard surface-mount equipment.

According to Konopitzky, the application allows operators to have full visibility over the entire process down to the level of the individual parts. Each product has a unique ID that can also be used for stock control, production planning and control systems, manufacturing, production control and optimization.

IBM's semiconductor plant in East Fishkill, NY, also features RFID readers that automatically trace wafer carriers. In the past, engineers manually read the labels on wafer carriers and then physically transported them to the appropriate workstation. The inefficient process often resulted in errors, such as transposing carrier ID numbers.

In the new system, readers scan the carrier's RF tags as it moves along overhead tracks to different fabrication stations. The readers validate the carrier's location and instruct each assembly device to perform the necessary fabrication steps.

Numerous Challenges

Radio frequency identification systems offer many benefits. But, before implementing the technology, manufacturing engineers must clear several hurdles, such as addressing numerous misperceptions. One of the biggest myths surrounding RFID is the cost of tags.

According to Kevin Prouty, senior director of Symbol Technologies Inc. (Holtsville, NY), the cost of RF tags is dropping dramatically. He says tags that cost 25 cents one year ago now range in price from 8 cents to 15 cents.

In addition, Prouty says most assembly applications are closed-loop systems, where tags remain under the control of a single company, eliminating compatibility issues that exist in retailing and distribution, which use many more tags than a manufacturing plant. Because tags are typically reused in a closed-loop environment, they become less expensive to use.

"A simple chart showing the life cycle of a tag vs. its cost is an easy way to address this issue," says Escort Memory Systems's Huff. "After a few hundred thousand read-write cycles, your cost per cycle is comparable to even bar codes."

"While the price is coming down with increasing demand and acceptance, a cheap RFID tag is still 10 times more expensive than a bar code label," argues MMTI's Baudin.

Another challenge is weighing the pros and cons of RFID vs. bar coding. "The current price of RFID technology suggests that a complete replacement of bar codes is unlikely," says Priyanka Gouthaman, a research analyst at Frost & Sullivan Inc. (San Antonio). "Coexistence of both technologies is expected for the next 10 years."

"The main obstacle to the spread of RFID in manufacturing is the success of bar codes," adds Baudin. However, he points out that in most applications, reading bar codes requires human intervention, a clean, high-contrast environment, and often more than one attempt.

"In many applications, the functional potential of RFID may not yet beat the low cost of bar codes," explains Baudin. "But, it is only a matter of time before it does."

Another challenge facing manufacturing engineers is deciding what to tag and when, in addition to determining what data to record or collect, and how the data will be converted into useful information. According to Rockwell Automation's Somogyi, tagging reusable assets, such as machines, forklifts, tools, fixtures and material handling devices, is one of the easiest ways for manufacturers to test RFID in a closed-loop environment.

"The best opportunities for RFID [in assembly applications] are where bar coding is so pervasive that operators spend a perceptible fraction of their time scanning bar codes," adds Baudin. "Such a situation is found in computer assembly, for pick validation and component serialization. A switch to RFID in this context can be the vehicle to help the technology cross the chasm from a sprinkling of pilot systems to mass adoption."

Another challenge is determining what department has jurisdiction over the RFID initiative on the plant floor: IT or engineering. According to a recent study conducted by AMR Research Inc. (Boston), the IT department is more than twice as likely to make the final decision regarding RFID applications. Of course, what department assumes responsibility will vary from company to company and application to application.

"This gets into some interesting dynamics," notes Intermec's Eckles. "The primary means of connectivity on the plant floor is via industrial Ethernet equipment. This world is typically controlled by the operations organization.

"There is a great amount of crossover now with the implementation of manufacturing execution systems and the concept of plant-to-business (P2B) transactions, so the IT organization is getting more involved," explains Eckles. "These two entities will ultimately end up blending around these applications."

No matter who's in charge of implementing RFID systems, engineers should be prepared to deal with a deluge of data. Radio frequency identification readers collect vast amounts of information, which can lead to data management and data storage challenges.

"You'll be receiving a lot more data than you were previously," warns Huff. "Sometimes, managing that data and making sense of it takes a while to figure out."

"The [one] thing that we see in any RFID implementation are systems that are not prepared to deal with the volume of data that will be delivered for processing," concludes Eckles.