The tiniest mobile robot ever has been created by US researchers. It is a sliver of silicon one hundredth of a millimetre thick that can be precisely steered like a remote-control car to move in any direction across the surface of a special plate.
Powered by a grid of electrodes underneath a surface layer and steered by its tiny silicon paddle, the bot crawls around at a speed of about 200 micrometres per second and can push specks of dust, or other “dead” robots.
“I believe this is the smallest untethered mobile silicon structure in a dry environment,” says Ron Fearing, a micro-roboticist at the University of California, Berkeley. “I would certainly consider it a robot – it does a lot more than a simple actuator.”
At 250 by 60 micrometres, the bot is narrower than a human hair and shorter than a full stop at the end of a sentence. It could be deployed to build or prototype other robots or micro-electromechanical systems.
Its creators lead by Bruce Donald of Dartmouth University in Hanover, New Hampshire will present it at the International Symposium for Robotics Research on 14 October. To see movies of the micro-robot moving click here.
Although micro-scale objects have been steered to move previously, they either required suspension in water or were made partially of animal muscle cells and so could not be fuelled indefinitely and were difficult to control.
Other micro-bots, also known as “walking chips”, consist of a computer chip equipped with legs and a solar panel, but are over 10 times bigger than the new robot – it is just a small, flat sheet of silicon, bent asymmetrically like the letter L.
It requires no motor to move, but instead sits on the surface of an electronic plate with the corner pointing upwards and only its two ends touching the surface. The plate is a zebra crossing of alternating positive and negative gold electrodes. When the electrodes are charged, the full length of the robot becomes oppositely charged. The plate and the robot attract each other so that the L-shape of the robot suddenly stretches out to maximise the attraction, flattening its shape (see image).
To unstretch the robot, the charge in the plate is switched off, and then the corner of the L pops back up. And because it is asymmetric, the robot always ends up about 12 nanometres closer to the short end than it was before it snapped up. Each of these up-down motions is a tiny robot step. “These things just go and go and go,” says co-creator Christopher Levey.
In 2003, Donald’s group demonstrated this type of motion on untethered robots, but the bots could only move in straight lines. Now they can be steered around the surface of the plate in any direction just by tuning the voltage. “Moving anywhere we want to in 2D is the most important feat we have accomplished,” says Levey.
The secret is to add a tiny silicon paddle coated on the upside with chromium which allows the robot to turn with a changing voltage. The paddle’s motion can be controlled separately to that of the main body of the robot as it only responds to a larger voltage. At a higher voltage the paddle becomes charged and uncurls so it can stretch out along the surface too, acting like a pivot to turn the robot.
The same principle could be used to steer several robots on the same plate at the same time, says Levey. However, they will always be limited in what they can do because they only work when sitting on a special grid of electrodes, he adds.