Researchers develop flexible and sensitive artificial hand

March 27, 2015  20:44

The prosthetic or artificial hands are useful in regaining normal hand movements. However, these prosthetic hands are made of electric motors, pneumatics or any other machinery that makes these hands, in some cases, heavy, inflexible, expensive and loud. In order to address these issues, researchers from Saarland University have developed an artificial hand made of ‘nickel-titanium alloy’ wires, also called ‘shape-memory alloy (SMA)’ wires. This relatively flexible and lightweight hand prototype moves its fingers via SMA wires that acts like natural muscles and helps the hand to perform precise and accurate movements.

The advantages of using SMA wires are that they are light, flexible, highly adaptable, operate silently, cheap to produce and can perform without additional equipment. As these wires have highest energy density of all known drive mechanisms till date, they are able to carry out powerful motions in limited spaces. Instead of using single SMA wires, the team has used many bundles of the ultrafine wires whose diameter is similar to that of a cotton thread. Moreover, these bundles have the tensile strength of a thick metal wire. While exerting a high tensile force, each bundle can quickly contract and relax owing to the rapid cooling that takes place when heat is dissipated through the individual wires having greater surface area. The speedy contractions and extensions of the bundles are equivalent to those noticed in human muscles. The multiple strands of SMA wire also connect the finger joints of the hand. They act as extensor and flexor muscles that allow each finger to both curl up and open readily.

According to Professor Stefan Seelecke, the head of the team, a semiconductor chip is used for controlling the relative motions of the SMA wires for carrying out the movements and the controller unit is able to interpret electric resistance measurement data for knowing the accurate positions of the wires. The system does not need sensors as the materials of the wires have sensor properties.

The development is at the nascent stage and the prototype requires further improvements by modelling hand movement patterns and exploiting sensor properties of SMA wire. The prototype will be showcased at Hannover Messe 2015, next month.

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