The Goalkeeper

The goalkeeper robot has both special hardware and special software. Thus, it does not switch positions or active modes like the others. The goalkeeper's physical frame is distinct from that of the other robots in that it is as long as allowed under the RoboCup-97 rules (18cm) so as to block as much of the goal as possible. The goalkeeper's role is to prevent the ball from entering the goal. It stays parallel to and close to the goal, aiming always to be directly even with the ball's lateral coordinate on the field.

Ideally, simply staying even with the ball would guarantee that the ball would never get past the goalkeeper. However, since the robots cannot accelerate as fast as the ball can, it would be possible to defeat such a behavior. Therefore, the goalkeeper continually monitors the ball's trajectory. In some cases it moves to the ball's predicted destination point ahead of time. The decision of when to move to the predicted ball position is both crucial and difficult, as illustrated in Figure 8. Our goalkeeper robot currently take into account the predicted velocity and direction of the ball to select its moves.

  
Figure 8: Goalkeeping.