Engineers at Saarland University have developed an artificial hand with muscles made from bundles of ultrafine nickel-titanium alloy wires that are able to tense and flex. 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.
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. To facilitate rapid movements, the engineers copied the structure of natural human muscles by grouping the very fine wires into bundles to mimic muscle fibers. These bundles of wires are as fine as a thread of cotton, but have the tensile strength of a thick wire.
“The bundle can rapidly contract and relax while exerting a high tensile force,” explains Filomena Simone, an engineer who is working on the prototype of the artificial hand as part of her doctoral research. “The reason for this behavior is the rapid cooling that is possible because lots of individual wires present a greater surface area through which heat can be dissipated. 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.”
A semiconductor chip controls the relative motions of the SMA wires, allowing precise movements to be carried out. And the system does not need sensors. “The nickel-titanium alloy from which wires are made has sensor properties. The controller unit is able to interpret electric resistance measurement data so that it knows the exact position of the wires at any one time,” says Prof. Seelecke. This enables the hand and the fingers to be moved with high precision.
