Researchers at Cornell University are one step closer to building robots that are more like humans. The innovation is one you might not expect, however: a soft robot muscle that "sweats" to regulate its temperature.
As reported in Science Robotics, the team believes this is a crucial step in building untethered high-powered robots. The sweating robots will be able to operate for an extended period of time without overheating. Metal robots are excellent heat conductors and can dissipate heat quickly. Soft robots, on the other hand, can’t do that, so the team had to brainstorm a different approach.
"The ability to perspire is one of the most remarkable features of humans," co-lead author T.J. Wallin, a research scientist at Facebook Reality Labs, said in a statement. "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."
The fingerlike actuators are 3D printed, hydraulically powered, and can be used to grab things. They are made of two hydrogel materials: a base layer of poly-N-isopropyl acrylamide covered in a perforated layer of polyacrylamide. The materials were chosen because they can retain water and respond to temperature.
When the fingers reach a temperature of 30°C (86°F), the base layer reacts by shrinking, squeezing the water through the top micron-sized pores in the top layer. The evaporation is so efficient that the surface temperature of the actuator can drop by 21°C in just 30 seconds. That's three times more efficient than in humans. When wind from a fan is thrown into the mix, they cool down around six times as fast. The evaporation also cooled the object held by the actuator hand.
"The best part of this synthetic strategy is that the thermal regulatory performance is based in the material itself," said Wallin. "We did not need to have sensors or other components to control the sweating rate. When the local temperature rose above the transition, the pores would simply open and close on their own."
While the result is exciting, it is only a first step. The sweat can make the robot hand slippery, so the team is investigating textures to improve its grip. When the sweating takes place, the robot’s mobility is also hindered and needs to replenish its water supply.
"I think that the future of making these more biologically analogous materials and robots is going to rely on the material composition," said co-lead author Rob Shepherd, an associate professor of mechanical and aerospace engineering. "This brings up a point [about the importance of] multidisciplinary research in this area, where really no one group has all the answers."
A soft robot that can sweat – and perhaps one day "drink" too – is now closer to reality.