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Robots learn to sweat to stop overheating

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Your sweat has a purpose; now robots can do it, too

Sweat, robot, sweat, robot: a close-up of one of the soft robotic “fingers” sweating.
Image: Mishra et al

For the roboticist who has everything, here’s something new: a soft robot hand that sweats.

Designed to handle scenarios where long operating hours might lead to a robot overheating and its performance degrading, this three-fingered gripper stays cool by borrowing one of humanity’s greatest attributes: our sweat glands.

“The ability to perspire is one of the most remarkable features of humans,” material scientist T.J. Wallin, one of the gripper’s designers, told reporters during a briefing. “We’re not the fastest animals, but early humans found success as persistent hunters,” using our ability to run and stay cool via sweating to “physically exhaust our prey.”

Hollow, pressurized reservoirs inside the fingers are filled with water and connected to the surface via ducts made of heat-reactive plastic. When the plastic hits a certain temperature, the pores open and water is pushed to the surface. There, it evaporates with a cooling effect more than twice as effective as those of the sweatiest beasts in the animal kingdom.

Details of the gripper’s performance are published in a paper in Science Robotics today.

The three-fingered robot ‘hand’ was tested by grasping and picking up heated objects.
Image: Mishra et al.

But why sweat? Aren’t there easier ways to cool robots? Well, that depends.

Most robots are made from metal, which is an excellent conductor and therefore good at dispersing heat by itself. But soft robots, which are designed for delicate tasks like medical procedures and packing fruit, are made from rubber, a good insulator. If and when soft robots become commonplace, they’ll need their own ways to stay cool.

There are other advantages to sweating, too. By building sweat glands into a machine, you can cool it below the temperature of its surroundings, something you can’t achieve with environmental cooling like fans. It also means that the robot can operate independently, keeping itself cool in places where external coolants are unavailable.

The gripper’s creators, scientists from Cornell University and the Istituto Italiano di Technologia, say this could be essential for designing robots that operate untethered.

“We believe [this] is a basic building block of a general purpose, adaptive, and enduring robot,” said Robert Shepherd, associate professor of Cornell’s Sibley School of Mechanical and Aerospace Engineering and co-author of the research, during a briefing.

Shepherd also noted that sweat glands could have a dual purpose in future. As well as releasing water for cooling, they could suck up liquid from the machine’s surroundings for analysis, similar to how space rovers collect soil samples on distant planets.

But as some nervous readers will know, there are downsides to sweaty hands as well.

One is that you need to top up your liquid supply. Humans do that by drinking, but sweaty robots would need a different method. Another is that sweat isn’t helpful underwater, though in those scenarios the environment itself would aid cooling. But the biggest problem by far is that sweating causes performance issues of its own: reducing friction by lubricating the gripper’s “fingers.” Slippery hands aren’t necessarily safe ones.

The scientists have tried to compensate for this by modeling the range of temperatures in which the gripper performs best, and directing the robot to sweat sparingly to keep in that zone. “Hopefully that means that the penalty we pay is not as debilitating,” said Wallins.