Magnetic Shape Memory Alloys

This article was published at Gizmag:

Magnetic Shape Memory Alloys to create robotic claws with nanometer precision

Robotics

May 26, 2008 Researchers at the University of the Basque Country have used ferromagnetic shape memory alloys to develop experimental devices that can position objects with an incredible accuracy of 20 nanometers. The devices do not consume energy after being put in place, and have applications ranging from medical science to positioning mirrors in high-power telescopes.

Shape memory alloys are metals that, after being bent, are triggered to return to their original state after being heated. The phenomenon was first observed in 1932, but it was only with the commercialization of the Nickel-Titanium alloy, or nitinol, that their applications were properly explored. Researchers at the Ohio State University have proposed using nitinol instead of stainless steel when reconstructing broken bones – the urge of the metal to return to its form exerts a constant pressure on bones, forcing them to stay in place. Stiquito, a small robot often used in university courses, uses the expansion and contraction of nitinol as a method of propulsion.

However, ferromagnetic shape memory alloys only transform back to their original configuration when exposed to a magnetic field. Since the application of the field is instant, the transformation is also rapid, as compared to the gradual heating and cooling of metal in regular shape memory alloy transitions. Ferromagnetic shape memory alloys do not exist commercially, and are currently only created as part of research.

The Automation Group at the Department of Electricity and Electronics of the Faculty of Science and Technology at the Leioa campus of the University of the Basque Country (UPV-EHU) is studying the stimulus-response characteristics of shape memory alloys and ferromagnetic shape memory alloys, with the aim of using them to facilitate precise movements in electrochemical systems in robotics. The researchers used shape memory alloys to build a prototype of a lightweight gripping claw - nitinol wire was placed between two elastic metal sheets, which contracted when a current was applied to the wire, gripping any objects around it. The claw has a point of precision to within a micron. The University hopes to further refine the ferromagnetic shape memory alloy actuators, which are already precise within 20 nanometers.

All these devices, currently at a laboratory stage, are useful for testing the basic characteristics of the materials, but in the future they could be end-product commercial prototypes for robotic devices and in micro and nanopositioning.

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