NAVIGATING "SPAGHETTI JUNCTION"
Before the AGVs arrived in the body-weld department, manned tow tractors dropped off flow racks and pallets full of parts alongside each of the robotic welding cells, which were located on both sides of a wide aisle. Team members then picked up the parts they needed from racks and pallets on both sides of the aisle. The work and material flow for parts delivery to the robotic welding cells involved 16 stops, or actions, from pickup to placement in the welding robot load positions.

Today, the storage racks and pallets are gone. Now, a driverless tow tractor pulls as many as five dollies full of auto parts from the storage area to the cells, a distance of about 950 feet. Team members retrieve the parts they need from the dollies, which are positioned parallel to the cells just a few steps away, eliminating the need to cross the aisle. Once all the parts have been unloaded, the AGV returns to the storage area for more material, while another tractor with the next batch of parts arrives just when they're needed. Instead of 16 stops, there are only nine. And because the AGVs always travel the same route at the same speed, the time from pickup to arrival at the welding cells is consistent and predictable.

To get where they're going, the tow tractors follow over two miles of magnetic strip slotted into narrow troughs in the concrete floor. Their positions are tracked by RFID tags embedded in the floor.

Navigating the high-traffic body-weld department requires care and precision. The weld stations are positioned along a 300-foot "highway" with nine routes branching off and merging into it—an area known as "spaghetti junction." In addition, the tow tractors have to share the road, so to speak, with other Toyota AGVs (such as L-cart material transporters and low-profile "Mouse" tug-carts) that motor along the same magnetic guide paths. The tow tractors also cross paths with the manned vehicles that deliver partial loads and those destined for multiple drop-off sites. Drivers are required to yield to the AGVs.

To manage the movements of the automatic vehicles, TMMK's AGV implementation team worked with ICI to develop traffic-control technology that would be compatible with the guidance systems and control devices already in place for other types of AGVs. The resulting Automated Vehicle Intersection Navigational Utility (AVINU) is "the link between the AGVs and everything else that's automated," said ICI President Tim Taylor.

The wireless system communicates with the different types of AGVs, reporting each one's location, status, and performance data—information that can be viewed on any authorized computer in the facility. AVINU assigns loads to vehicles and regulates traffic at intersections; arrival at certain RFID tags triggers wireless transmission of instructions to the AGVs. The system also monitors battery status and tells the vehicles when to head over to an opportunity charger.

REACHING A BROADER AUDIENCE
Changing the way parts are delivered and reconfiguring the robotic welding cells has cut walking distances by 978 miles a year, saving five hours of walking time per shift—the equivalent of 317 work days annually, said Paul Stafford, specialist production engineering and AGV implementation lead. Furthermore, eliminating the storage pallets and flow racks opened up nearly 37 square feet of work space adjacent to each cell, freeing up space for other activities.