New suction-cup system spins water to stick to rough surfaces
While there already are powered suction-cup devices that allow people or robots to climb walls, they only work on smooth surfaces. Chinese scientists, however, have now developed a system that sticks to rough surfaces via spinning water.
Known as "zero-pressure difference" (ZPD), the technology is being developed by a team at Zhejiang University, led by Xin Li and Kaige Shi.
It still incorporates soft rubber cups, but each one contains a ring of water that's rotating at high speed along its periphery, at the boundary between the cup and the rough surface to which it's applied. The resulting inertial force generates a steep pressure gradient, allowing a high vacuum to be maintained at the center of the cup's vacuum zone, while letting the pressure at the boundary remain equal to the atmospheric pressure.
On a regular powered suction cup, because there is a big pressure difference at that boundary, the vacuum will easily leak and fail when placed on surfaces that aren't completely smooth. Because that difference is eliminated in the new system, though, such leaks don't occur – no matter how textured the surface.
And as an added bonus, as compared to traditional systems, ZPD requires much less power to maintain a given amount of suction. The whole unit is also smaller and lighter than conventional models.
So far, ZPD cups of three sizes have been successfully tested on a robotic arm that can grip objects, a "Spiderman-like" device that could be used by people to climb walls, and a hexapod wall-climbing robot – the researchers are particularly intrigued by the latter.
"Compared to other wall-climbing robots, the robot with our ZPD-based suction unit achieves surprising improvement in performance," says Li. "The next step in this research is to cut down the water consumption. If the water consumption can be reduced, the suction unit will work for a very long time with little water so that the wall-climbing robot could carry its own water instead of being connected to a supply."
A paper on the research was recently published in the journal Physics of Fluids.