As you know, the round thing has to go into the square thing. But not with RoboKeeper, a development of the Fraunhofer Institute for Material Flow and Logistics (IML) in Dortmund. In most cases, the artificial goalkeeper is the winner - and this facing players of all performance levels.
The boundary conditions of the project, which started in 2005, differ slightly from those of a real soccer match: The player shoots from around 9 m and the goal measures 2.0 x 4.0 m². The scientific assistant Thomas Albrecht at Fraunhofer IML and project manager of RoboKeeper development explains: »The aim of the development was to keep the balls safe even when they were shot flat into the lower right or left corner of the goal at a speed of 100 km/h«. This corresponds to the maximum distance for the goalkeeper, who stands upright and in the middle of the goal during the shot. According to Albrecht, the pure flight time of the ball at this speed is about 360 ms.
»During this time, the estimated trajectory and point of arrival of the ball in the goal plane must be extrapolated and the complete movement of the goalkeeper including all acceleration and deceleration processes of the motor must be completed in order to prevent a goal,« says Albrecht. The accuracy requirements are in the range of a few centimetres, as it is not certain that the goalkeeper figure hits the middle of the ball: »The RoboKeeper only has to hit the ball so that it is repelled and does not land in the goal«.
The RoboKeeper uses a fast image processing system as »eyes«. Two Prosilica GC655C color area scan cameras from Allied Vision with Gigabit Ethernet interfaces and a resolution of 659 x 493 pixels are mounted laterally above the door. They aim at the ball and follow its trajectory. The color of the ball must stand out from its surroundings.
The cameras each deliver up to 90 images per second, which are then evaluated by image processing software developed by Fraunhofer IML on a dual-core processor system from Kontron. If a movement towards the goal is detected during the evaluation of three consecutive images, the first data responsible for the movement of the RoboKeeper and positioning the goalkeeper is transmitted to the motor control.
Based on the calculations and with the help of a high-performance motor, the RoboKeeper only takes about 300 ms to reach the calculated defense position. It accelerates about 20 times faster than a Formula 1 racing car. The system has seven different difficulty levels and thus adapts to the performance level of the players.
If the system is set up outdoors, the sunlight and thus the illuminance of the scene varies considerably during the day. For this reason, camera systems were used which are equipped with automatic iris control and a video signal-controlled motorized iris. Goyo Optical's CVO GAT23516AC lenses with a focal length of 3.5 mm are wide enough to ensure correct ball detection from launch to goal.
The image processing setup consisting of the two cameras, the associated motorized lenses, and the cables is from Stemmer Imaging.
Fancy a duel? During the 2018 World Cup, fans can try their luck on the Red Square in Moscow. In addition to the system described, other versions are also available: a smaller version with a shorter shooting distance and reduced goal size, as well as variants for hockey, ice hockey, and handball.