Dominic Frutiger doesn’t really go in for football. That is unless the players are micron-sized robots, the pitch is smaller than a wrist watch date display and the ball consists of a tiny silica disk. Frutiger and his project partners from the ETH Zurich Institute of Robotics and Intelligent Systems (IRIS) are world class in this field. At the RoboCup in Atlanta in July they won first prize in the “Nanogram” league, which was being contested for the first time

Fully automatic dribblers

Their “players”, measuring only 300 x 300 microns, had to complete three tasks: a 2 millimetre sprint from one goal to the other, dribbling around obstacles from one goal to the other and shooting as many goals as possible inside three minutes. The robots were required to derive their propulsion energy from the environment and were not allowed to be connected to a cable or guide lead. The robot can be controlled by computer mouse and keyboard. However, in the competition the control of the robot had to be implemented fully automatically so the robot dribbled the ball around static opponents and conveyed it to the goal autonomously.

In this respect the micro-robots, the three project managers and their students from ETH Zurich displayed their world class skill. Their team was the only one of five groups to successfully solve all three tasks. As an additional demonstration they guided their robot through a labyrinth of polymer walls like in the original “Pac Man” computer game. Frutiger says, not without pride: “We were the only ones who created something reliable in the short time remaining for preparation.” They did not hear about the football competition until November 2006. In only six months they had designed a prototype of the micro-robot based on fundamental mechanisms of the kind being researched at IRIS and, according to Frutiger, developed it further “into a Ferrari”.

Forwards without a motor

The researchers have already filed a patent application for the basic principle. The micro-robot itself consists of a frame and a meander spring made of gold together with two rectangular nickel blocks that can be magnetised. The frame rests on the playing field and one of the blocks is suspended on the frame. The other block hangs 8 microns above the playing field on the spring, which is in turn rigidly attached to the frame. In a magnetic field this “vehicle” aligns itself along the common longitudinal axis of the two pieces of nickel, which are now polarised.

To enable the micro-robot to move even though it has no motor, the researchers apply a magnetic field. This exerts an attractive force on the two polarised blocks. As a result the spring is deflected and the gap between the pieces of nickel narrows. As soon as the magnetic field is removed, the attraction disappears down to the level of the magnetic attraction between the two nickel pieces and the tensioned spring makes the pieces of nickel swing back. In an oscillating magnetic field at about the resonant frequency the spring starts vibrating rhythmically, causing the blocks to strike against one another. The whole complex moves forward a small distance in a jerky fashion each time.

Fast, agile, robust

The researchers can control the movement direction by using an electrostatic potential that can also be switched on and off: because of the electrostatic attraction, the robot adheres to the substrate for a brief moment and the spring force cannot move it from the spot. The skilful trick in this respect is to co-ordinate and combine the magnetic field and the electrostatic potential together in such a way that the robot moves forwards or backwards at a continuous speed in a controllable manner.

The ETH Zurich scientists were completely successful in this feat. At the RoboCup it became clear that the IRIS team’s robot is robust and fast, the control functions reliably and the robot moves very purposefully. For example it can cover 1.25 centimetres in one second – more than 40 times its own length. The process can also be repeated any number of times. On the other hand the competition from the USA and Canada relied on the technology that the competition organiser would have liked to see implemented. However, Frutiger and his project partners quickly realised that this is not very promising in the long term because it allows the micro-robots to be controlled only with difficulty and the technology is inherently doomed to remain on a specially designed two-dimensional substrate.

From toy to medical aid?

"We wanted to defend the world reputation of our laboratory and ETH Zurich at the RoboCup," is how Dominic Frutiger describes his team’s motivation for the special effort they made for their entry in the RoboCup. He says "So our victory is also a proof of performance for Switzerland and for ETH Zurich.” Above all it also showed that Switzerland has a lead over other countries in microtechnology and nanotechnology. However, no decision has yet been taken as to whether he and his team-mates will be there to defend the title again next year.

Frutiger says "What we have created here is a nice game application.” However, he says it is a foundation for new and serious applications in the three-dimensional area, e.g. in bio-medicine. For example the researcher is thinking of mini-robots that can move autonomously in the blood stream or in the intestine, can find target objects such as organs or vessels and can administer locally dosed medicines. However, the IRIS star strikers are still a long way from that. He asks us to bear in mind that "Those problems are far more complex than playing football.”

The robot championship

The RoboCup has been held annually since 1997, most recently in 2006 in Bremen and this July in Atlanta (USA). The football tournament is an ideal arena in which to demonstrate the progress and possibilities of mobile robotics and artificial intelligence. Playing football needs a multitude of key competences of artificial intelligence and robotics. For example robots must be able to recognise objects autonomously (opponent and ball) and behave purposefully (kicking goals) and cooperatively (involving team-mates). The Nanogram League was contested for the first time this year. The name refers to the weight of the robots.