Radio-tagged pallets permit pinpoint control of production, staging, and sequential shipping in a JIT-driven environment.
s with nearly every component in a modern vehicle, today's car and truck seating systems have evolved radically from the utilitarian units of yore, and now include such features as adjustable air-cell contouring for a custom fit, massage systems, cooling fans, and simulators that provide a walking-like motion as an aid to circulation. Manufacturing complex units such as these, in volume, requires equally complex production techniques.
Johnson Controls of Livermore, CA, produces state-of-the-art automotive seats for New United Motor Manufacturers Inc. (NUMMI), a production facility jointly operated by Toyota and General Motors. At its own modern plant, Johnson Controls manufactures a variety of car and truck seats for the NUMMI plant, which is located roughly 20 miles away, in Fremont, CA.
NUMMI uses just-in-time technology to produce various cars and trucks. A basic tenet of JIT is, of course, the elimination of large inventories of production parts. Instead, parts are ordered from suppliers on an as-needed basis. And while JIT minimizes—or eliminates entirely—over-ordering and the storage of outdated materials, it also requires rigid, accurate ordering and delivery. The bottom line is that Johnson Controls makes as many as 12 deliveries each day to the NUMMI plant, with each truck unloading new seats directly at pre-designated points along the assembly lines.
On an hourly basis, Johnson Controls receives seat orders via modem transmission from NUMMI, in the form of a serial-number list. These hourly lists, carefully correlated with the sequence of vehicles production at the NUMMI plant, dictate the order in which seats are loaded onto the trucks at Johnson Controls.
Naturally, any inaccuracy in the loading/unloading sequence would create big-time problems. For instance, if the NUMMI plant has an order that specifies a sequence of "car-truck-car," and Johnson Controls loads the shipment in the order of "car-truck-truck," NUMMI's production line will be brought to a standstill, because a vehicle-in-progress cannot continue on NUMMI's production line without seats, or with the wrong type of seats. Which means that Johnson Controls, as a key supplier, must have its act together at all times.
No Room for Error
Johnson Controls has two production lines—one that produces truck cab seats, and another that produces car seats. When the finished seats reach the inventory/packing stage, the two lines merge, mixing truck and car seats together on the same conveyer. And since there are numerous different models of both truck and car seats being sifted together, the potential exists for a disastrous—and expensive—mix-up. NUMMI allows only a certain amount of mistakes each year, and for that reason, Johnson Controls decided to invest in a radio frequency identification (RFID)-based control system.
"Our previous ID system involved basic clipboards and checklists, located with operators at each station of production, inventory, and shipping" explained Fred Zaske, electrical engineer at Johnson Controls. "The main reason we invested in RFID was to eliminate the human error [inherent] with [a manual] ID system."
"We looked first at a bar code system, but because of the dirty and often abrasive conditions on the production floor, we were worried about bar codes being dirtied or scraped, rendering them useless," recounted Mr. Zaske. "Bar codes were also more susceptible to misreads, and would cost us a great deal of time to troubleshoot while on the line."
Not long afterwards, at a trade show, Mr. Zaske stopped at the booth of Escort Memory Systems, a California-based manufacturer of RFID systems. The conversation covered the relative merits and simplicity of RFID, and the booth visit eventually turned into a sale.
EMS recommended its HMS series of products initially, and Johnson Controls installed that system on its truck-seat assembly line and also in the inventory/shipping section of the plant. HMS tags, installed on the bottom of the truck-seat pallets, are "written to" during the first stage of production, the data containing the seat's detailed job order or "recipe."
Two of EMS's CM 52 interface modules link the 16 HMS and RS antennas to the server, a Rockwell AB PLC5S. Each interface supports eight antennas, integrated into the production lines. The plant uses MFG/PRO, an MRP package from QAD Inc., to orchestrate its overall operation.
As the seat continues down the production line, the pallet passes over an HMS827-04 antenna, one of which is located at each operator's station. Operators use touchscreen-equipped programmable logic controllers (PLCs) at their respective stations; the PLCs verify seat type and indicate any alterations that may be necessary.
If a seat requires work at a given station, the operating system won't let the seat continue down the line until the operator has made—and verified—all the required modifications/enhancements. The antenna then writes to the tag, updating it with whatever work has been completed on the seat.
The process continues until the seat reaches the final station, where its recipe is compared with the record of the work that was actually completed. If they match up, the seat is transferred to the plant's storage/shipping area.
As with the truck seat line, the finished-product storage area was also outfitted with several HMS827-04 antennas, mounted on the conveyer line. Following final inspection, an automated system selects and lines up the stored seats to create a loading sequence for the delivery trucks, based on the sequential serial numbers specified by NUMMI.
As a final checkpoint, a reader, installed on the conveyer leading into the delivery trucks, confirms the loading sequence. Before an operator can load a seat into the delivery truck, he or she must first pass the seat over the antenna-equipped conveyer, at which point a touchscreen-equipped computer displays the type of seat being loaded. The computer also references the serial number lineup provided by NUMMI, thereby reconfirming a match-up.
Life in the Fast Lane
With the RFID system successfully installed on the truck-seat line, Mr. Zaske's engineering team looked for ways to leverage their new wireless technology, which led them to the car seat production line. This application, however, required a different type of RFID: "read-only" tags and complementary antennas. "RS series" readers and "ES series" tags, also from EMS, were selected for two reasons.
First, car seats require many more assembly steps than do truck seats. By using read-only technology, the pallets can move faster over the readers than with HMS, because the writing function is not being executed.
Secondly, the tags are purchased with custom-programmed serial numbers—Johnson Controls uses numbers "1" through "32"—and each tag number corresponds with specifications for a specific car seat; these specs are stored in the main server.
The company's car seat line utilizes a network of motorized, overhead tracks to shuttle "raw," pre-formed car seats out to the shop floor. The levitated seats are ferried to a predetermined spot, at which point they begin their descent and, upon reaching the shop floor, are fitted to small metal pallets, each of which is fitted with an RF tag. Ready for assembly, the seats head down the production line, where headrests are attached, seat belts secured, and other necessary steps are performed. At each station, an antenna mounted on the conveyer reads the tag attached to the bottom of the pallet.
In pre-RFID days, car seats went through the assembly line in matching groups. But now, the firm is able to mix and match at will on the same production line. As a seat reaches a station, its tag is read, and if the tag number indicates that the seat doesn't need to undergo a particular station's modification, the system will tell the conveyer to simply bypass the station.
As a built-in precaution, the power tools at each station will not operate until the operator has verified the type of seat and the appropriate modifications and materials for that particular station. Such RFID-assisted safeguards have enabled Johnson Controls to minimize production error.
Once assembled, the seats go through a series of quality tests, including flexibility, strength, and airbag inspection. Here again, RFID provides positive monitoring of each car seat, allowing all units to be routed through one testing line, regardless of the order in which they are received.
Following the testing phase, the seats are wrapped in plastic, removed from the small metal pallets and secured to larger pallets made of plastic, identical to the pallets used on the truck production line. The second pallet accompanies the seat until it is ready to actually be installed in a vehicle on NUMMI's production line.
When the seats are swapped from metal to plastic pallets, their digitized serial numbers are wirelessly transferred with them. After a tag is attached to the bottom of the plastic pallet, the unit passes over an HMS827-04 antenna, located at the beginning of the inventory line. Moments earlier, when the seat exited the production/testing line, the read-only tag was read, with the computer relaying the data to the inventory line's antenna-equipped station, telling it what seat it should be expecting next. Then, when the car seat passes over the antenna at the head of the inventory line, the new read/write tag is written to, receiving the seat's ID number and production-testing history. This automated, tag-to-tag data-transfer replaces the previous process whereby an operator used a touchscreen to identify each seat coming off the line before it could be moved into storage.
Clever Problem-Solving
In the early stages of application implementation, Johnson Controls ran into a read-alignment problem whenever the pallets would rotate 90 degrees on the conveyer line; this meant that the tags on the bottom of the pallet would not pass directly over antennas sunk into the conveyer bed—because they had rotated too far. Engineers came up with a simple solution—they simply installed four tags per pallet, one per side. This ensured that at least one tag would pass over the antenna, regardless of the pallet's orientation.
Time Savings
Johnson Controls represents a new order of RFID-enhanced manufacturing, where multi-step production and pick-pack-ship is rigorously yet smoothly controlled in real time. The end result, says Mr. Zaske, is significant savings in time and a large gain in plant floor flexibility.
