Illustration by David Simonds

Correction to this article

SQUADRONS of robotic machines have taken flight in recent years, ranging from unmanned aerial vehicles which patrol in Iraq and Afghanistan to experimental machines not much bigger than insects. But it remains hard to shrink engines, batteries, mechanical actuators and control electronics to the point where they are small and light enough to fly without impairing their performance. It would be nice, therefore, if all the on-board paraphernalia of propulsion and control could be dispensed with, leaving an unencumbered device that is still capable of directed flight.

That is exactly what Behrad Khamesee and his colleagues at the University of Waterloo, in Ontario, have managed. They have built a micro-robot that levitates, rather like a Dalek in “Dr Who”. And instead of having an old sink-plunger doubling as its arm, their robot has a useful set of grippers.

The researchers use magnetic levitation to lift their robot, which is a mere 6mm tall. The process, which relies on magnetic fields attracting or repelling each other, is more usually applied to large machines such as maglev trains, and then with some kind of guide rail or tether to prevent the machine from drifting too far off track. Dr Khamesee's robot, however, is completely untethered and can be positioned to an accuracy measured in a few thousands of a millimetre.

The drive and control mechanism is an array of electromagnets that create a three-dimensional parabolic magnetic field around the robot. The interaction between this field and the permanent magnets from which the robot is constructed allows it to levitate. It is held in position using the electromagnets to concentrate the field to a focal point, much as a lens focuses light, says Dr Khamesee. By controlling the current in the array the focal point can be moved around, and with it the robot. The position of the robot is monitored by lasers and a camera, which are connected to a computer that controls the field to keep the robot steady.

Having got their robot to levitate, the researchers wanted to make it capable of work. Their first attempt used a set of grippers made from a “memory” metal, an alloy that changes shape when heated by an electric current and then returns to its original form when the current is switched off. But the watch battery the robot needed to carry around to do this quickly ran flat, so the team switched tack. Now, the grippers are made from a polymer whose thermal-expansion properties cause the jaws to open when part of the structure is heated with an external laser. The jaws close when the laser is turned off and the material cools.

Dr Khamesee thinks tiny levitating robots of this sort could manipulate small components and biological samples. Often, these manipulations are carried out in closed chambers at carefully maintained pressures and temperatures. They can also involve hazardous materials. By levitating inside such an environment the micro-robot would leave no footprints, so to speak, and need no connecting wires.

The team are now working on improving the robot's precision and expanding the volume in which it can operate. They are also looking at the possibility of using the system to control even smaller robots that could be used within the body, for drug delivery or microsurgery. Imagine opening your mouth and watching one levitate inside.





Correction: the process for lifting the robots uses magnetic attraction, as well as the magnetic repulsion to which we originally referred. And the new grippers are made from a polymer, not a metal. Sorry. These corrections were made on April 24th 2009.