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‘Venus flytrap’ soft robot gets a grip

Autonomous light-powered device inspired by the carnivorous plant grabs reflective objects

by Bethany Halford
May 26, 2017 | A version of this story appeared in Volume 95, Issue 22

Two panels showing the optical flytrap in its open and closed states.
Credit: Adapted from Nat. Commun.
An open optical flytrap closes when a reflective “insect” enters its field of view, causing light to scatter onto the liquid crystalline elastomer actuator, which bends in response, trapping the insect.

Pity the poor insect that wanders onto a Venus flytrap. Just a couple false steps into the carnivorous plant’s trigger hairs, and the leaves snap shut, dooming the bug. Inspired by the Venus flytrap’s ability to distinguish between insects and other stray bits of matter, Tampere University of Technology scientists Arri Priimagi, Hao Zeng, and Owies M. Wani have created a soft robot that acts with the same sort of autonomy. Their optical flytrap distinguishes between objects that reflect or scatter light and those that do not before grabbing the reflective ones.

“It’s very difficult in soft robotics to develop systems that make decisions by themselves,” says Priimagi, who led the research team. Most soft robots, he says, don’t react to their environment but instead require some sort of external activation.

An optical flytrap closes only on objects that reflect or scatter light.
Credit: Nat. Commun.

An optical flytrap closes only on objects that reflect or scatter light.
Credit: Nat. Commun.

His team’s solution was to incorporate an optical fiber into a liquid crystalline elastomer. When the light strikes a reflective object, it reflects back onto the liquid crystalline elastomer, triggering a photochemical isomerization in the elastomer’s azobenzene components. The isomerization events release heat, causing the liquid crystals to lose their orientation and bend the elastomer, which makes the device grip the reflective object in as little as 200 microseconds (Nat. Commun. 2017, DOI: 10.1038/ncomms15546).

Jian Chen, an expert in soft robotics at the University of Wisconsin, Milwaukee, says Priimagi and coworkers’ use of an optical feedback loop to make their soft robot autonomous is creative. “This work represents very significant progress in the field of soft robotics,” Chen says.

Priimagi explains that the optical flytrap was originally developed out of scientific curiosity. But the device might find use in quality control during microfabrication, gripping and removing tiny objects that don’t reflect light as they should. The optical flytrap can currently clamp down on objects hundreds of times as heavy as the elastomer, but Priimagi would like to boost that by an order of magnitude. He’d also like to create grippers that distinguish between differently colored objects and ones that snap shut as quickly as Venus flytraps—about twice as fast as the current optical flytrap.



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