New artificial hand uses smart wires as muscles

Researchers have developed an artificial hand which uses smart wires that can tense and flex as its muscles to perform extremely precise movements.
The advance by engineers at Saarland University in Germany will enable the development of flexible and lightweight robot hands for industrial applications and novel prosthetic devices.
The research team led by Professor Stefan Seelecke from Saarland University and the Center for Mechatronics and Automation Technology (ZeMA) is using a new technology based on the shape memory properties of nickel-titanium alloy.
The engineers have provided the artificial hand with muscles that are made up from very fine wires whose diameter is similar to that of a human hair and that can contract and relax.

Until now, artificial hands, such as those used in industrial production lines, have relied on a lot of complex background technology.
As a result they are dependent on other devices and equipment, such as electric motors or pneumatics, they tend to be heavy, relatively inflexible, at times loud, and also expensive.

"In contrast, tools fabricated with artificial muscles from shape-memory alloy (SMA) wire can do without additional equipment, making them light, flexible and highly adaptable. They operate silently and are relatively cheap to produce," Seelecke said.
"And these wires have the highest energy density of all known drive mechanisms, which enables them to perform powerful movements in restricted spaces," said Seelecke.

The term 'shape memory' refers to the fact that the wire is able to 'remember' its shape and to return to that original predetermined shape after it has been deformed.
"This property of nickel-titanium alloy is a result of phase changes that occur within the material. If the wire becomes warm, which happens, for instance, when it conducts electricity, the material transforms its lattice structure causing it to contract like a muscle," said Seelecke.
The engineers use 'smart' wires to play the role of muscles in the artificial hand. Multiple strands of shape-memory wire connect the finger joints and act as flexor muscles on the front-side of the finger and as extensor muscles on the rear.

In order to facilitate rapid movements, the engineers copied the structure of natural human muscles by grouping the very fine wires into bundles to mimic muscle fibres.
"The bundle can rapidly contract and relax while exerting a high tensile force," said Filomena Simone, an engineer who is working on the prototype of the artificial hand.
"Unlike a single thick wire, a bundle of very fine wires can undergo rapid contractions and extensions equivalent to those observed in human muscles. As a result, we are able to achieve fast and smooth finger movements," she said.