There are limits to the flexibility of both human and robotic arms. The joints are often rather bulky and connect rigid bones or mechanical assemblies. Motion is typically restricted to certain spatial directions. In contrast, an elephant trunk or an octopus tentacle offer far greater agility. The presence of tens of thousands of muscles enables these creatures to move the trunk or tentacle in all directions, to bend it to just the right degree, and to grip things with great power.
Researchers have developed flexible robot arms constructed using ‘muscles’ made from shape-memory wires that can bend in almost any direction and wind themselves around corners. The flexible arms are powered electrically, eliminating pneumatic equipment or other bulky accessories. As the shape-memory alloy itself has sensor properties, the arms can be controlled without the need for additional sensors. The new technology can be used to build large robotic arms with the flexibility of an elephant’s trunk, or ultrafine tentacles for use in endoscopic operations.
Precisely controlled artificial tentacles could be used as guide wires in cardiac surgery or as an endoscope in gastroscopic and colonoscopic procedures. The artificial tentacles are equipped with additional functions such as a gripper or a tip with adjustable stiffness that delivers an improved pushing force. The technology can also be scaled up to produce large robotic arms not dissimilar to an elephant’s trunk.
The ‘muscles’ are composed of ultrafine nickel-titanium (nitinol) wires that are able to contract and lengthen in a controlled manner. The ultrafine nitinol wires contract like real muscles, depending on whether an electric current is flowing or not. Nickel-titanium is known as a shape memory alloy, which means that it is able to remember its shape and return to that original shape after being deformed. If an electric current flows through a nitinol wire, the material heats up, causing it to adopt a different crystal structure with the result that the wire becomes shorter. If the current is switched off, the wire cools down and lengthens again.
Bundles of these wires act as artificial muscle fibers. Multiple ultrathin wires provide a large surface area through which they can transfer heat, which means they contract more rapidly. The wires have the highest energy density of all known drive mechanisms. And they can exert a very high tensile force over a short distance. A range of applications for these wires includes novel cooling systems to new types of valves and pumps.
For more information, contact Dr. Stefan Seelecke, Intelligent Material Systems Lab, at