Researchers at Purdue University, Lafayette, Ind., report that they have developed variable stiffness fibers made from shape memory materials in which a shape-memory alloy is coated with a thin film of shape-memory polymer. The fibers, which are fabricated by a continuous feed-through process, are reduced in bending stiffness by an order of magnitude when the polymer goes through the glass transition. The transition between rubbery and glassy state is done by direct joule heating of the embedded shape memory alloy heater.
“We have integrated both actuation and sensing, whereas most robotic fabrics currently in development feature only sensing or other electronic components that utilize conductive thread,” said Dr. Rebecca Kramer, an assistant professor of mechanical engineering at Purdue. “We also use standard sewing techniques to introduce the thread-like actuators and sensors into the fabric, so they could conceivably be integrated into the existing textile manufacturing infrastructure.”
The robotic fabric can be wrapped around a block of foam as shown in the photo. Orienting the fabric in one direction causes the robot to bend, producing locomotion like an inchworm’s. Orienting the fabric in a different direction causes it to compress – producing a peristaltic – or slithering locomotion.
Materials with variable stiffness have the potential to provide a range of new functionalities, including system reconfiguration by tuning the location of rigid links and joints. In particular, wearable applications would benefit from variable stiffness materials in the context of active braces that may stiffen when necessary and soften when mobility is required.
The goal is to make possible a class of soft robots where all the functional elements are embedded in a stretchable skin. This skin would include flexible electronics that are less sensitive to vibration than conventional hardware, making them rugged enough for space missions. Such a technology could allow space travelers to ship lightweight, easy-to-store sheets of robotic skin for assembly once they reach their destination.
Like the robotic fabric, the skin might be wrapped around a deformable object, creating robots capable of exploring alien terrains.
“We will be able to design robots on the fly,” Prof. Kramer says. “Anything can be a robot because all of the robotic technology is in the fabric or skin.”
