Engineers at Saarland University, Saarbrücken, Germany, have developed an artificial hand with “muscles” made of shape-memory wire, a material that returns to its original shape after it has been deformed, simulating the behavior of muscles. The material, made of a nickel-titanium alloy with a lattice-like structure, makes it possible to fabricate flexible and lightweight robotic hands for prosthetic and industrial applications.
The artificial muscle fibers consist of bundles of hair-thin wires that can tense and relax. When the bundles are heated with electric current, the material contracts, shortening the wires. Once the current is stopped and the wires cool, the material returns to its original shape.
“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 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.”
Strands of the intelligent wire connect the hand’s phalanges and act as the flexor and extensor muscles. “The material of the wire itself has sensory characteristics,” said professor of mechatronics Stefan Seelecke, with Saarland University and the Center for Mechatronics and Automation Technology, who led the research group. “The control unit recognizes the exact position of the wires at any time by reading the measurement data of the electrical resistance.”
Artificial hands, such as those used in assembly lines, have been dependent on equipment such as electric motors or compressed air to operate; they are heavy, inflexible, sometimes loud, and costly to fabricate. Whereas hands fabricated using artificial muscles made of shape-memory wire will not require additional equipment to operate; are lightweight, flexible, and adaptable; operate silently; and are relatively inexpensive to manufacture, said the researchers. “And these wires have the highest energy density of any known drive mechanisms; they can therefore perform powerful movements in restricted spaces,” said Seelecke.