Festo usually likes to have some fun with its exhibit at the Hannover Fair. And this year was no exception. The company displayed a racing simulator, a robotic arm capable of human-like movements and a pair of remote-controlled “manta rays”—one waterborne and one that flies. Ignoring the fun factor for a minute, all of these demos have some serious engineering implications from actuation and software standpoints.
The racing simulator, robot arm and waterborne manta all make extensive use of Festo’s fluidic muscles, an alternative to pneumatic cylinders and other actuators. Consisting of an elastomer tube reinforced by aramid fibers, these actuators contract quickly and exert a pulling force when they're filled with a blast of compressed air or liquid. And much like their natural muscle counterparts, these bionic muscles experience a decay in force as they shorten.
But the initial force and speeds with which that force is reached can be significant. Elias Knubben of Festo’s Corporate Design Center reports that the company has developed muscles that can exert 6,000 N of force when filled to a pressure of 6 bar. They can respond quickly too—at frequencies up to 100 Hz. At more than 25 percent smaller than comparable pneumatic actuators, they also take up relatively little space.
Those characteristics came in handy in the impressive robotic hand and arm that Festo developed for the show. Called Airic’s Arm, it features 32 fluidic muscles and laser-sintered artificial bones that approximate the structures of a human arm—well, sort of, given that human arms and hands have more than 60 muscles. But Airic’s Arm still offers pretty much the same range of movement as a human arm and hand, according to Knubben. “It has the same degrees of freedom as a human arm,” he says, adding that it's capable of handling a 3-kg load while full extended.
Festo runs the arm's fluidic muscles with a compact collection of 72 proportional valves along with related pressure sensors and power electronics. The entire assembly weighs just 6.4 kg.
At last year's Hannover Fair, the company showed a robotic hand and partial arm that used fluidic muscle technology.This year's demo, though, is much more complex since it extends back to a fully-functioning shoulder joint. And with its extra joints, muscles and expanded range of movements—all powered by the 72 valves—the new arm required much more control software.
Fluidic muscles also help power another of Festo’s bionic demos, a remote controlled manta ray with a hydraulic drive unit. The fluidic muscles operate in antagonistic pairs to mimic the propulsive flapping of a manta ray's wings. This Aqua Ray system makes use of a compact vane pump to deliver pressure to the fluidic muscles, while Spectra cords to serve as “tendons” that transfer forces from the fluidic muscles to the wings. A tendon travel of 55 mm translates into a vertical wing amplitude of more than 550 mm.
Festo’s other ray at Hannover takes fewer cues from nature—in that it flies. Like the Aqua Ray, this helium-filled Air Ray borrows its propulsion style from a manta's flapping wings. In this case, though, the movements of the wing are servo driven.
It may be tempting to write these nature-inspired demos off as a trade-show amusement, but Festo has already come up with at least one automation system that makes use of the fluidic muscle and manta ray concept. It's a “bionic material sorting system” that uses fluidic muscles and a ray-like wing structure to sort up to seven components in one operation. “We think and hope there will be other industrial applications for biologically inspired systems in the future,” says Knubben.