The new cooling technique could be useful for soft robots in the future, especially when there are no other methods to keep the system cool. (Image Credit: Cornell University/Facebook Reality Labs/AAAS)
Humans often perspire to keep their temperature regulated, a cooling process that may be useful in soft robots. Engineers from Cornell University have replicated the method in a newly-developed soft robot muscle. By using this new technique, scientists have found a way to keep soft robots operational for long hours without overheating. The team published their findings in a paper in Science Robotics on January 29, 2020.
According to Rob Shepherd, associate professor of mechanical and aerospace engineering, researchers have been struggling to control temperatures and prevent overheating in adaptable and agile robots. The risk of overheating in soft robots drastically increases because they’re often made of synthetic materials, which can be problematic. Additionally, a robot will no longer become operational if the high-torque density motors and exothermic engines overheat.
Even though soft robots are more flexible, they often trap their own heat. Whereas robots made of metal, an excellent conductor, dissipates it on its own. Adding a fan inside a soft robot to cool it down would likely cause further issues since it would take up space and add more weight.
Shepherd’s team became inspired by how mammals sweat to build the system. The researchers collaborated with the lab of Emmanuel Giannelis, the Walter R. Read Professor of Engineering, to construct nonopolymer materials for sweating. This was done by using a 3D printing technique, known as multi-material stereolithography, that uses light to cure resin into shapes, such as fingers.
“The ability to perspire is one of the most remarkable features of humans,” said co-lead author T.J. Wallin, M.S. ’16, Ph.D. ’18, a research scientist at Facebook Reality Labs. “Sweating takes advantage of evaporated water loss to rapidly dissipate heat and can cool below the ambient environmental temperature. … So as is often the case, biology provided an excellent guide for us as engineers.”
Researchers then created fingerlike actuators that were made of two hydrogel materials that store water and react to temperature. The base layer, which is made of poly-N-isopropyl acrylamide, shrinks when it becomes exposed to temperatures above 30C (86F). Afterward, it squeezes water into the top layer of polyacrylamide that has been drilled with extremely small pores. Since these pores are sensitive to the same temperature range, they open automatically, releasing the water and closes when the temperature drops down to below 30C.
The actuator’s surface temperature is then reduced by 21 C within 30 seconds due to the evaporation of the water. Researchers discovered that this cooling process is three times more efficient than in humans. When the actuators are exposed to wind from a fan, they’re able to cool off up to six times faster.
When the team incorporated the actuator fingers to a robot hand that grabs and lifts objects, they discovered that the release of water didn’t just affect the temperature of the hand, but it made the object feel cooler too. Adding modifications to the hydrogel texture could improve the hand’s grip.
However, this new technology may slow down a robot’s mobility. Since the system is based on water, it may need to be replenished. In the future, the system may be able to drink water. A robot storing fluids could lead to methods that involve absorbing nutrients, catalyzing reactions, removing containments, and coating the robot with a protective layer.
“I think that the future of making these more biologically analogous materials and robots is going to rely on the material composition,” Shepherd said. “This brings up a point [about the importance of] multidisciplinary research in this area, where really no one group has all the answers.”
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