Robot arms are expensive to build and dangerous to operate. If a system malfunctions, people can be injured. But now, scientists in Germany have built a bionic robot arm, called ISELLA that takes inspiration from an elephant’s trunk; making it both: Kind on the purse as well gentle with people.
BUT WHY A TRUNK ?
An elephant’s trunk is biological marvel. It is long, soft, endowed with no fewer than 40,000 muscles, and extremely agile, the scientists say.
The pachyderm uses its trunk to grasp objects and for drinking.
With their trunks, the creature can tear down trees and pull heavy loads, and yet the appendage is also capable of extremely delicate manipulations.
“Its suppleness and agility gave us the idea for our bionic robot arm, ISELLA,” said Harald Staab, the researcher who invented and developed the technology at the Fraunhofer Institute for Manufacturing Engineering and Automation IPA in Stuttgart.
BACK-UP MUSCLE
Robot arms often present a risk to human operators – a technical glitch can provoke wild, uncontrolled movements. But that will never be the case with ISELLA, its developers say.
Conventional robot arms have only one motor to drive each articulated joint. ISELLA, however, has two – grouped in pairs – so that if one motor control should fail, the second takes over to prevent uncontrolled movements.
“Unlike pneumatic or hydraulic -based systems, our robot arm has a simple, low-cost ‘muscle’ mechanism that consists of a small electric motor with a drive shaft and a cord,” Staab said.
The cord links two related moving parts in the same way as a tendon attaches one muscle to another, he explained.
The mechanism’s drive shaft is attached to the midpoint of the cord, so when the shaft turns, the cord wraps around it in both directions, forming a kind of double helix.
The researchers have names this apparatus ‘DOHELIX’.
THE DOUBLE HELIX
“The shaft is no thicker than the cord, but it is strong enough to resist breaking,” Staab said. “Consequently, it has a higher transmission ratio than a conventional geared motor.”
This has been achieved using elastic materials with a very high tear strength – the type of material used to manufacture yacht sails and hang gliders. As a result, DOHELIX is much cheaper and more energy-efficient than a system of gears.
Its tensile force is many orders of magnitude greater than its own weight, and drive systems based on the DOHELIX concept could be used in applications on all scales – from micrometer-scale muscles to cranes in container seaports.
The ISELLA robot arm, which is as flexible as a human arm, consists of a total of ten DOHELIX muscles with four situated in the elbow and six in the upper arm:
“At present we are working on the elbow,” Staab said.
Possible applications for ISELLA include medical rehabilitation, for instance, in therapy to restore the use of injured limbs, and low-cost, flexible prosthetic devices.
Such devices could be commercially available within about two years, Stabb estimates.
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