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A series of tags and reader/writers
from Escort Memory Systems Inc. monitor the position and destination of
several part-carrying carts on an 800-ft track in an assembly plant.
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Hexcel Corp. builds body parts for the Chevrolet Avalanche truck, but due to
the large size of the parts, a traditionally sized conveyor system to move components
during assembly would be too costly and cumbersome. As an alternative, Hexcel
Corp., Stamford, Conn., turned to Ward Systems Inc. in Grass Valley, Calif.,
for one of its PowerPallet systems. PowerPallet uses intelligent, motorized
pallets running on a simple track. But to get the pallets where they need to
go, the system needed one more layer of intelligence. Engineers added radio-frequency
identification devices (RFIDs) from Escort Memory Systems in Scotts Valley,
Calif.
The units, passive reader/writers mounted on the carts and passive ID tags
mounted at various intersections along the track, let the carts determine where
they are and download approach information for their next programmed stop. This
information is used to decelerate and stop at scheduled stations. Since the
devices use RF, there's no need for sensor or actuator wiring, no proximity
detectors or motors to connect, and RFIDs resist dirt, oil and dust. RFIDs can
also be reliably read by the carts despite their speed.