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Robotic fabric combines sensing and actuation

25 September, 2014

Researchers in the US are developing an elastic fabric embedded with sensors that moves and contracts and could lead to a new class of “soft” robots with sensory skins. The fabric is a cotton material made from a flexible polymer and threadlike strands of a shape-memory alloy that return to a coiled shape when heated, causing the fabric to move.

“We have integrated both actuation and sensing, whereas most robotic fabrics currently in development feature only sensing or other electronic components that utilise conductive thread,” explains Rebecca Kramer, an assistant professor of mechanical engineering at Purdue University, where the research is being done. “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 or an inflated balloon. Orienting the fabric in one direction causes the robot to bend, producing movement like an inchworm. Orienting the fabric in a different direction causes it to compress, resulting in a peristaltic, or slithering, motion.

The aim is to make possible a class of soft robots where all of the functional elements are embedded in a stretchable skin. This skin will 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 travellers to ship lightweight, easy-to-store sheets of robotic skin for assembly once they reach their destination.

Like the robotic fabric, the skin could be wrapped around a deformable object, creating robots capable of exploring alien terrains. Other potential applications for the materials include stretchable robotic garments that people could wear for added strength and endurance, and g-suits for pilots or astronauts to counteract the effects of acceleration.

Flexing fabric: a demonstration of one of the materials being developed at Purdue University
Photo: Purdue University/Rebecca Kramer

“We will be able to design robots on the fly,” Kramer says. “Anything can be a robot because all of the robotic technology is in the fabric or skin.”

In another project, Purdue researchers are working with colleagues from the Swiss Ecole Polytechnique Federale de Lausanne to develop a fabric in which fibres of a shape-memory polymer are used to change its stiffness. The polymer goes through a phase transition when heated, causing it to become soft. The polymer is coated with a shape-memory alloy that heats up when electrical current is applied, causing it to soften.

As well as having potential robotic applications, this fabric could also be used in medical braces that lock in place for support. “Ordinarily, if we are moving a hinge joint and want to maintain a particular position, we would have to maintain a high energy input to keep the joint from relaxing,” Kramer explains. “Here, we could just lock it in place.”

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