THE ability to scale walls and hang off the ceiling with gecko-like ease may be within reach 鈥� for robots at least.
and Ozgur Unver of Carnegie Mellon University in Pittsburgh, Pennsylvania, say their new robots 鈥� a sticky-tracked wall climber and a 16-legged ceiling walker 鈥� could tackle many jobs in the home including painting ceilings and clearing cobwebs. They could also play a part in exploration, inspection, repair and even search and rescue.
鈥淭he robots could play a part in exploration, inspection, repair and even search and rescue鈥�
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Previous wall and ceiling climbers have used suction for locomotion. But suction has drawbacks: it requires lots of energy to drive a vacuum pump, and motion is limited to smooth surfaces like glass.
The new robots, however, rely on a 鈥渟ticky鈥� elastic polymer, or elastomer, that can adhere to a variety of surfaces, including wood, metal, glass and brick. The idea is to mimic the mechanism which geckos use to climb walls and walk upside down.
Geckos can cling fast, and also detach themselves easily to move on, thanks to millions of tiny hairs called setae on their toe pads. Engineers at the University of California at Berkeley, including Sitti, showed in 2002 that the geckos鈥� setae do this by harnessing van der Waals forces, a weak electrostatic attraction which operates only at an intermolecular level. Although each hair鈥檚 attraction is tiny, the combined force provided by the huge number of hairs is enough to support the weight of the lizard.
Since then, Sitti has been experimenting with squishy elastomers to mimic the forces that geckos鈥� setae use (New 杏吧原创, 17 May 2003, p 15). One method uses a nanoscale probe in an electron microscope to punch indentations in a wax mould. When filled with a liquid polymer, it sets to create hairs of the right size. Each has the same attractive force as a gecko hair.
Now it is time to try out such biomimetic technologies in robots, Sitti will tell delegates at the annual (ICRA) in Kobe, Japan, in mid-May.
Both his robots use sticky elastomers, though not in the form of hairs, to grip surfaces using van der Waals forces. Their wall-climbing robot is a palm-sized, 60-gram machine with a tacky elastomer tank track on either side of it. Called , its trick is to keep its tracks in close contact with the surface whilst continuously 鈥渦npeeling鈥� itself.
To make this rolling attachment and detachment happen, Tankbot has a spring-loaded U-shaped 鈥渢ail鈥�, which trails behind the robot pressing down on the surface. The tails keeps the rear end of the track clear of the ground, so the full length of the track is never in contact with the surface. This leaves the front of the tracks doing the gripping while the track gradually unpeels towards the rear.
In tests, (see image) Tankbot deftly scales walls and even carries small payloads. However, its 鈥渁dhesion falls short for upside-down ceiling climbing鈥�, Sitti says.
So for scampering on ceilings, the pair are working on another design with stronger adhesion: the . This has four tough plastic bars that move parallel to one another driven by a motor (see diagram). Each bar has four tacky elastomer footpads, mounted in pairs on rockers. When the eight footpads on the interior bars are stuck to a surface, the outer bars unpeel their footpads and move forwards. When they are safely restuck, the inner bars unpeel and move forwards.
In tests, Sitti and Unver got the robot to move 30 metres upside down. But one problem with both robots is that their elastomers can clog with dirt and dust and lose their crucial tackiness. Sitti hopes to overcome this on future bots by using his hairy gecko-like elastomers. Ultrafine nanoscale hairs do not provide micro-scale dirt particles with enough contact 鈥� so they simply roll off.
Other researchers reckon the climbing technology has potential. 鈥淭hese robots could extend the work of robotic builder鈥檚 assistants. And there are often diagnostic and repair jobs for plumbers and electricians that are tricky to reach,鈥� says Noel Sharkey at the University of Sheffield in the UK. Tony Pipe at the University of the West of England in Bristol envisages the robots in search and rescue. 鈥淎 small robot that can negotiate contorted spaces from any angle, whilst carrying a significant payload of medicines and other recovery equipment, could be very useful.鈥�
There could be sinister uses though: 鈥淎 less palatable idea would be a surveillance robot that hugs the ceiling,鈥� Sharkey adds.
