Electrothermal actuators propel small robot like an inchworm

Researchers at the University of Toronto have used electrothermal actuators to create a small robot that can crawl like an inchworm. The engineers said that the materials technology could have implications for smart wearables and aviation.

Prof. Hani Naguib and his team at the university’s Smart Polymers & Composites Laboratory specialize in smart materials. Part of their research focuses on electrothermal actuators, which are made of specialized polymers that can be programmed to physically respond to electrical or thermal changes.

For example, an electrothermal actuator could be programmed to mimic muscle reflexes, tensing up when cold and relaxing when hot.

Naguib and his group are applying this technology to build soft robots that can crawl and curl. They said that such robots could one day replace the bulky and metal-plated machines found in manufacturing and other industries.

“Right now, the robots you’ll find in industry are heavy, solid, and caged off from workers on the factory floor because they pose safety hazards,” explained Naguib.

“But the manufacturing industry is modernizing to meet demand,” he added. “More and more, there’s an emphasis on incorporating human-robot interactions. Soft, adaptable robots can leverage that collaboration.”

Novel approach to programming electrothermal actuators

Although responsive materials have been studied for decades, the team has discovered a novel approach to programming them, resulting in the inchworm motion demonstrated in a paper recently published in Scientific Reports.

“Existing research documents the programming of ETAs [electrothermal actuators] from a flat resting state,” explained Yu-Chen (Gary) Sun, a Ph.D. student and the paper’s lead author. “The shape-programmability of a two-dimensional structure is limited, so the response is just a bending motion.”

By contrast, Sun and his co-authors created an electrothermal actuator with a three-dimensional resting state.

They used a thermal-induced, stress-relaxation and curing method that opens far more possibilities in shape and movement.

“What’s also novel is the power required to induce the inchworm motion,” Sun said. “Ours is more efficient than anything that has existed in research literature so far.”

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Wide applications possible

Naguib claimed that such programmable shape-shifting soft robots won’t just revolutionize manufacturing industries; they could also be useful in fields including security, aviation, surgery, and wearable electronics.

“In situations where humans could be in danger — a gas leak or a fire — we could outfit a crawling robot with a sensor to measure the harmful environment,” he said. “In aerospace, we could see smart materials being the key to next-generation aircrafts with wings that morph.”

Although morphed-wing aircraft are probably some time away from realization, Naguib said that wearable technology could be affected much sooner by electrothermal actuators.

“We’re working to apply this material to garments. These garments would compress or release based on body temperature, which could be therapeutic to athletes,” he said. The University of Toronto researchers are also studying whether smart garments could be beneficial for treating spinal cord injuries.

Over the next year, Naguib’s team plans to focus on speeding up the responsive crawling motion and looking at other configurations.

“In this case, we’ve trained it to move like a worm,” he said. “But our innovative approach means we could train robots to mimic many movements — like the wings of a butterfly.”