In vehicles like cars, on aeroplanes, and in other machinery and equipment, space is limited. It is crucial to keep weight levels as low as possible, too, with lighter transport methods requiring less fuel and batteries in electric cars lasting longer when the load they carry is lighter. In the future, an innovative technology could help to reduce weight as well as saving energy by using smaller and lighter technical components.
A research team in Germany working under the Chair of Intelligent Material Systems at Saarland University and the Saarbrücken Center for Mechatronics and Automation Technology (Zema) is using the properties of intelligent materials to give technical components artificial muscles. These components can be used where switches are needed or rotational movements required in confined spaces.
These “strands of muscle” can perform rotational movements to extremely high quality, including at greater torques and angles of rotation, offering potential comparable to that of motors, hydraulics or compressed air. The prototype, which the research team presented at this year’s Hannover Messe trade show, uses muscle strands that are activated by electrical impulses. These strands are made of fine nickel-titanium wires that can contract and relax. The shape-memory wires have the ability to generate high tensile forces in the tightest spaces and to contract similarly to natural muscles depending on whether current is flowing or not.
The nickel-titanium alloy consists of two phases at the crystal lattice level that can be converted into one another. As a result, it can “remember” its alternative shape and switch back into it if the temperature changes, for example. When current flows through one of these wires, it heats up and its crystal structure changes, causing it to shorten. When the power is turned off, it cools down and returns to its original length.
The researchers arrange the fine wires in a similar configuration to real muscle fibres, with multiple wires giving off more heat due to their larger surface area. This allows them to contract quickly and be controlled like a natural flexor and extensor. Impressively, they do not require any additional sensors, meaning they save on space as well as energy consumption. The artificial muscles themselves simultaneously act as sensors in the system. As the wires deform, the electrical resistance changes and each deformation can be assigned a precise reading. Engineers can then quickly and accurately model and program the wires’ movement sequences based on these measurements.
The researchers design technical components that are modular and adapt them to suit a wide range of different requirements. For instance, they use the contraction of the wires to rotate something, such as pulling on a gear. In a similar manner to natural musculature, they also use opposing muscles – also known as antagonists – to allow rotations in both directions. The technology is scalable, making it also suitable for larger technical components.
Unlike electric motors, pneumatic or hydraulic machines, this method does not generate any noise or require additional equipment such as hoses, valves, pumps or compressors. Nor are rare-earth elements necessary to support it. The researchers plan to translate the results they have obtained into industrial practice and have set up a business, Mateligent GmbH, for this purpose.