Extending, curling, snaking braids

June 1, 2008
New designer-plastic tubes resembling Chinese finger traps actually move like snakes, to deliver coordinated 3D motion and force.

If you've ever admired the elegant locomotion of a snake, then you'll appreciate this one: A new motion device can produce all the movements that a snake can — and more.

Called an electroactive polymer (EAP) structure — see how this electroactive polymer (EAP) structure works — the electrified snake-like unit is a collection of strands, made of EAP tiles surrounded by actuators, and woven to form a biaxial braid. EAPs are plastics that change shape when voltage is applied. The actuators are
electrodes that electrically stimulate individual EAP segments to stress or strain. Segments of actuators localize the control of specific tiles or tile groups, so strategically controlling which segment receives current (as well as the current's direction) controls the braid's movement and shape. For example, applying current to two overlapping segments with reversed polarizations creates a rigid area, while applying current with the same polarization creates a hump or dip.

First developed by Selahattin Ozcelik, of the department of mechanical engineering, Texas A&M University, Kingsville, with Michael Blackburn, of the Space and Naval Warfare Systems Center, San Diego, the patented EAP braid is currently being promoted by the U.S. Navy for commercial applications.

Why do such a thing?

What makes EAP structures useful is that, while individual strands can only exert force in one dimension, braids of it can cooperatively generate forces in three dimensions.

Other EAP designs do exist, but they tend to be bulky, inflexible, and offer poor local shape control. Compared to these technologies, EAP braids decrease bulk and mass for increased flexibility.

Weight savings is an ancillary benefit; the braids make normally weighty machinery lighter, from actuators and sensors to power-generating devices.

Special shapes such as cylinders, spheres, blankets, and boxes can be woven to create structures tailored to specific applications — for snaking, climbing, or even swimming deep in the ocean, for example.

Braid strength and durability can also be optimized for various applications with different EAPs and applied voltage, for both large and small-scale designs.

This snake-inspired technology is suitable for position and guide components, block or open functions, and to change mechanical and surface device properties — to release or hold objects, anchor or fix device positions, and to unfold or contract components. Specifically, EAP biaxial braids may soon find use in prosthetics, toys, surgical devices, robotics, automotive, and small electrical devices.

For more information, call (619) 553-1904 or visit and search for EAP.

About the Author

Elisabeth Eitel

Elisabeth Eitel was a Senior Editor at Machine Design magazine until 2014. She has a B.S. in Mechanical Engineering from Fenn College at Cleveland State University.

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