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Wheel Offers Omni-Directional Motion
Rim-mounted rollers move lift truck for tight maneuvering
Rick DeMeis -- Design News, July 19, 2004
Omni-directional wheel technology by Hammonton, NJ-based Airtrax provides its new lift truck with smooth, crablike moves in any direction. Such translating motion capability offers operators precise movement in tight confines, which allows using more warehouse space for storage by tightening-up open areas needed for truck access. In addition, the truck can carry long loads sideways through narrow overhead doors.
The wheel features six elliptically shaped rollers around its circumference. The roller axes are offset by 45 degrees from the plane of the wheel. A wheel is positioned at the four corners of a vehicle, but none are pivoted for steering.
Like a conventional vehicle, if all four wheels move in unison, motion is forward or backward. Driving the wheels on each side opposite those on the other side spins the vehicle about its vertical axis with the rollers accommodating slip. The big difference comes when the fore and aft wheels are rotated with equal speed in opposite directions—interaction of the rollers produces sideways motion. Synchronizing changes in speed at opposite corners and varying individual wheel speeds produces combinations of crabbing in any direction and rotation.
The original omni-directional wheel was patented in Sweden in the 1970s and eventually sold to the U.S. Navy, which considered it for vehicles that had to maneuver on crowded aircraft carrier decks. Airtrax entered into a CRADA (Cooperative Research and Development Agreement) with the service to commercialize the technology in 1995. The company holds patents on revisions to the original design, which are used on its new SIDEWINDER™ lift truck that starts shipping this summer and previously on its scissor lifts.
The first design of the wheel had the rollers supported at their ends. That structure would sometimes impact small objects on the ground, causing the rollers to lift and lose their omni-directional capability, notes Peter Amico, Airtrax president. The newer rollers are supported at their centers to always keep them in contact with the ground for consistent operation.
The Timken Co. makes the polyurethane-covered steel rollers and their tapered roller bearings. The company also furnishes the wheel hub bearings. Tapered roller bearings are used for the elliptical rollers because of their high axial and side loads, with the Timken units specifically picked for their high lifetime and lower friction, says Amico.
On the latest Airtrax wheels, engineers deliberately designed them out-of-round, according to Amico. "The wheel is then round under load," he points out, for smoother rolling action.
Hydraulics powered the original omni-directional wheels. The most recent Airtrax versions are driven electrically, which simplifies control and lowers parts count and maintenance. A Danaher Motion brushless ac induction motor and sealed transmission drive each wheel. These custom-built motors produce a constant 5 hp, with up to 11 hp on a 15 percent duty cycle possible. Hydraulics actuate the lift forks.
Airtrax engineers provide electric motor control via CANbus using a Danaher controller running patented Airtrax-developed algorithms. Operator interface is a three-axis joystick (fore/aft, left/right, and twist) to input direction, speed, and turning. This setup eliminates pedals and a steering wheel in front of the operator for a better view of the forks and load, and further reduces parts count. A second, two-axis stick governs lift hydraulics.
Safety
Amico says the joystick control is simple and thus more intuitive for greater safety, as opposed to the more complex coordination needed between pedals, steering, and throttle. Engineers allow the joystick to function as a deadman's switch-if let go, the system stops the truck, uses power to hold position, and then applies the brakes. Downhill travel is also done at constant speed.
Each omni-directional wheel weighs 320 lbs, lowering the truck's center of gravity to between 4.5 and 18 inches above the ground, depending on configuration. This position enhances stability so that the 3,000-lb rated mast can lift 2,190 lbs to its full 20-ft height. Most trucks have their rated load cut in half at full extension, says Amico.
Market impact
Bill Wahl, a NJ distributor of roofing, windows, and siding has driven a prototype and is waiting for delivery of his SIDEWINDER. He likes the omni-directional capability to allow reducing aisle space in his warehouse. "We'll still use conventional forklift trucks outside in the yard but for inside maneuvering it will be a big advantage," Wahl adds. He also cites the fact that the lateral movement that will allow his operators to move the 12-ft siding sections easily through all the warehouse's 12-ft wide doors.
"It's a unique product," says Brett Wood of the SIDEWINDER. He's chairman of the Industrial Truck Association trade group, as well as national product planning and marketing manager at Toyota Material Handling, USA, a competitor. But Wood adds, the omni-directional lift truck may be seen as a niche product for a niche market. Airtrax' Amico counters that it's not a niche product since the premium for the $36,697-priced SIDEWINDER is not "niche-like" and only 20 percent over comparable lift trucks.
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| On Deck: Airtrax' prototype Navy munitions handler permits a single operator, rather than several deck hands, to move up to 4,000 lbs of weapons in any direction on the confined deck of an aircraft carrier. |
| Web Resources | ||
| Check out the links below for more info | ||
| To view a video clip of how omni-directional wheels work, go to http://rbi.ims.ca/3852-549 |
Airtrax technology: http://rbi.ims.ca/3852-550 | Motors, transmissions, and controllers from Danaher Motion: http://rbi.ims.ca/3852-551 |
| The Timken Co. bearings: http://rbi.ims.ca/3852-552 | ||
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