Ford Motor Co.'s (Dearborn, MI) production center in Cuautitlan, Mexico, produces between 300,000 and 400,000 cars and trucks each year. It uses modern production approaches such as just-in-time-supply and is one of the company's largest foreign assembly plants.

In the past, Ford used a manual coding system to track auto and truck frames as they went through the final assembly, paint and body shop areas of the production line. However, the system was prone to error. Paper identification sheets were continually being lost, switched and ruined, making quality control difficult.

To solve the problem, Ford implemented a radio frequency identification (RFID) tracking system from Escort Memory Services (Scotts Valley, CA), a company that had worked with Ford in the past on an engine production line. The system is built around a number of reusable, reprogrammable RFID tags that can each be secured to an individual vehicle skid. After being programmed with a serial number, each tag keeps track of what has been done to its attendant vehicle as it travels along the production line. Information regarding customized features such as body color and interior trim options can also be easily referenced by using a serial number programmed into the tag.

Because the tags need to travel through paint ovens that reach temperatures up to 220 C, Ford selected the EMS LRP250HT tag, which is built to withstand high temperatures. Although Ford was originally unsure how many bytes would be needed per tag, the LRP250HT's 48-byte memory and 1,200 bytes-per-second transfer rate were more than adequate for what eventually became serial numbers up to 23 digits long.

Because metal interferes with their read-write capabilities, the tags are attached to the skids with Teflon brackets. Upon completion of a vehicle, each tag is cleared of all information, so it will be ready to attach to another skid.

To read the tags, Ford uses a number of LRP-08 antennas, wired using the RS485 transmission protocol. In all, there are five in the body production area, 12 in the paint shop and three in the final assembly area. These antennas are set into the floor below the conveyor belt in a nylon, explosion-proof enclosure.

As a tag passes over an antenna, its serial number is sent to a battery of LRP820 readers that are interfaced with Ford's operating system using Lantronix MSS100 and EMS MM80 modules.

Different portions of the serial number describe the characteristics of the car or truck being produced, including model, body color and performance options. As the vehicle passes through the different workstations, the serial number is automatically referenced, indicating what needs to be done.

The RFID tag is also updated as it moves down the line, so that steps are neither skipped nor executed twice-a common problem when a paper-based worksheet had to be updated by hand. For example, if a vehicle gets to the paint oven, but has not undergone the necessary modifications in final assembly, the system will alert operators that there is a problem.

For more information on RFID systems, call 800-626-3993, visit or eInquiry 3.