Passive cooling through permeable frame eliminates dedicated cooling infrastructure

Kengoro


Researchers from the University of Tokyo’s JSK Lab have come
up with an efficient way to cool off waters hard at work, by “sweating” water
right out of their exoskeleton. Demonstrating the technology at the IEEE/RSJ
Internal Conference on Intelligent Robots and Systems (IROS), Professor Masayuki Inaba and his team built Kengoro, a humanoid robot capable of performing
pushups.

Like humans generate heat as a byproduct of locomotion, humanoid robots and other dynamic machines
place near-constant torque demands on their motors to point where heat becomes a
major design constraint. But unlike
humans who evolved sweat glands to cool off, machines require robust cooling infrastructures
made up of fans, heat sinks, and radiators.

The 1.7-meter tall, 56-kilogram (123.5-lbs) musculoskeletal
humanoid Kengoro requires 108 motors to
move, leaving almost no additional space for the dozens of fans, heat sinks,
tubes, and radiators required in an active water cooling system.

 

Kengoro_internals

Inaba and his team resolved the issue by using the robot’s very own
skeletal structure as a coolant delivery
system. Instead of circulating water throughout the frame, a solution requiring
a pump and radiator, the team went with a passive technique that allows water
to “seep out through the frame” around the motor, cooling it while evaporating—similar
to “sweating.”

Kengoro’s frame was
laser sintered from aluminum powder to achieve the right level of permeability
needed for the solution to work. By altering the energy density of the laser
during fabrication, the team could dictate the level of permeability of the end
product and build seamless structures containing microchannels of both high and
low permeability. This allows water to
seep from an inner porous layer into a more porous layer near the surface of
the frame where it can evaporate.

In testing, the passive method of cooling worked three times
better than air cooling, and “significantly better” than solely circulating
water through the interior change, although not as efficient as radiator
cooling. A cup of deionized water supplies Kengoro
with enough coolant to do 11 minutes worth of continuous push-ups without overheating
its motors. Like it us, it needs to keep itself hydrated to stay cool.

Source: IEEE
Spectrum