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Soft Actuators Go From Squishy to Stiff (and Back Again)

Jamming layers give a soft actuator adjustable stiffness

2 min read
Soft Actuators Go From Squishy to Stiff (and Back Again)
Photo: Evan Ackerman/IEEE Spectrum

Soft actuators are appealing for robotics because they’re cheap (made out of plastics or polymers and air), inherent compliant and relatively safe for humans to interact with, and able to adapt themselves to grip a wide range of objects. Being soft does tend to make them by definition bad at being hard, so for those times when you need an actuator with some stiffness, well, that’s just too bad.

Or is it?

Researchers at Technische Universitat Berlin led by Professor Oliver Brock have combined soft pneumatic actuators with a jammingsystem that results in a variable-stiffness actuator that’s soft when you want and hard when you want.

The researchers tested three different jamming systems, including the traditional coffee grounds, as well as two other designs based on scales and interleaved layers [see image below]. They eventually settled on the interleaved layers for the final design, because it requires far less pressure to jam, although it’s more complex to manufacture. In principle, it works in a similar manner: when the interleaved layers have air between them, they can slide against eachother, allowing the actuator to flex. When the air is pumped out, the layers compress against eachother, and the actuator is stiffened. You can do this by hand with a syringe, or using a pump or autonomous operation.

imgThe three jamming systems tested by the researchers: granular jamming; layer jamming with overlapping fish-scale-like layers; and layer jamming with stacks of interleaved layers. The jamming chambers are indicated by dashed lines, and the Pneuflex actuator is shown on the bottom. (a) Unjammed chambers result in flexible actuators. (b) Jammed chambers result in stiff actuators.Image: TU Berlin

Overall, the jammed actuator exhibited a stiffness increase of 8x, resulting in an application of force increase of 2.3x, which is pretty significant. Incidentally, you can make these actuators yourself for free: they’re called Pneuflex actuators, and instructions are available here.

“Selective Stiffening of Soft Actuators Based on Jamming,” by Vincent Wall, Raphael Deimel, and Oliver Brock from the Robotics and Biology Laboratory at TU Berlin was presented at ICRA 2015 in Seattle, Wash.

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The Bionic-Hand Arms Race

The prosthetics industry is too focused on high-tech limbs that are complicated, costly, and often impractical

12 min read
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A photograph of a young woman with brown eyes and neck length hair dyed rose gold sits at a white table. In one hand she holds a carbon fiber robotic arm and hand. Her other arm ends near her elbow. Her short sleeve shirt has a pattern on it of illustrated hands.

The author, Britt Young, holding her Ottobock bebionic bionic arm.

Gabriela Hasbun. Makeup: Maria Nguyen for MAC cosmetics; Hair: Joan Laqui for Living Proof
DarkGray

In Jules Verne’s 1865 novel From the Earth to the Moon, members of the fictitious Baltimore Gun Club, all disabled Civil War veterans, restlessly search for a new enemy to conquer. They had spent the war innovating new, deadlier weaponry. By the war’s end, with “not quite one arm between four persons, and exactly two legs between six,” these self-taught amputee-weaponsmiths decide to repurpose their skills toward a new projectile: a rocket ship.

The story of the Baltimore Gun Club propelling themselves to the moon is about the extraordinary masculine power of the veteran, who doesn’t simply “overcome” his disability; he derives power and ambition from it. Their “crutches, wooden legs, artificial arms, steel hooks, caoutchouc [rubber] jaws, silver craniums [and] platinum noses” don’t play leading roles in their personalities—they are merely tools on their bodies. These piecemeal men are unlikely crusaders of invention with an even more unlikely mission. And yet who better to design the next great leap in technology than men remade by technology themselves?

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