Research Group on the Foundations of Artificial Intelligence

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2008

• Armin Hornung and Dapeng Zhang.
  On-Line Detection of Rule Violations in Table Soccer.
  In Andreas R. Dengel, Karsten Berns, Thomas M. Breuel, Frank Bomarius and Thomas R. Roth-Berghofer, Proceedings of the 31st Annual German Conference on AI (KI 2008), pp. 217-224. Springer-Verlag 2008.
  Poster.
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  In table soccer, humans can not always thoroughly observe fast actions like rod spins and kicks. However, this is necessary in order to detect rule violations for example for tournament play. We describe an automatic system using sensors on a regular soccer table to detect rule violations in realtime. Naive Bayes is used for kick classication, the parameters are trained using supervised learning. In the on-line experiments, rule violations were detected at a higher rate than by the human players. The implementation proved its usefulness by being used by humans in real games and sets a basis for future research using probability models in table soccer.

• Dapeng Zhang and Armin Hornung.
  A Table Soccer Game Recorder.
  In Video Proceedings of the IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS 2008). Nice, France 2008.
  Digest and Video.
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  Our table soccer robot can already challenge even professional human players. Next, the robot should play games by using human-like skills. As a foundation of this research, our table soccer game recorder can save and replay games played by humans. This video shows the construction and functionality of the recording system.

  We use three types of sensors mounted on a regular game table. The movement of a game rod is measured by an optical distance sensor. Its turning is observed by a magnetic rotary encoder. Two laser measurement systems are synchronized to determine the position of the ball. The raw sensor data is smoothed by an approach using multi-model Kalman filter. We developed several software modules for the system. The modules provide a basis for the future research.

• Dapeng Zhang.
  Robot Plays Table-Soccer.
  In Proc. of Dagstuhl Seminar (08372), Computer Science in Sport - Mission and Methods 2008. 2008.
  Presentation (in .ppt) .
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  Our research focuses on learning approaches with robot KiRo. KiRo is a table soccer robot which can challenge even advanced human players. Previously, we developed a method using learning by imitation, by which KiRo can automatically acquire the demonstrated actions. Recently, we constructed a game-recorder which collects data from the human-played games. The in-process work is about explaining the recorded data, which is to classify and to evaluate human's skills. A brief overview of the previous work is addressed, and the perspective is discussed.

• Dapeng Zhang, Bernhard Nebel and Armin Hornung.
  Switching Attention Learning - A Paradigm for Introspection and Incremental Learning.
  In Proceedings of Fifth International Conference on Computational Intelligence, Robotics and Autonomous Systems (CIRAS 2008). Linz, Austria 2008.
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  Humans improve their sport skills by eliminating one recognizable weakness at a time. Inspired by this observation, we define a learning paradigm in which different learners can be plugged together. An extra attention model is in charge of iterating over them and chosing which one to improve next. The paradigm is named Switching Attention Learning (SAL). The essential idea is that improving one model in the system generates more "improvement space" for the others. Using SAL, an application for tracking the game ball in a table soccer game-recorder is implemented. We developed several models and learners which work together in the SAL framework, producing satisfying results in the experiments. The related problems, advantages, and perspective of the switching attention learning are discussed in this paper.

2007

• Dapeng Zhang and Bernhard Nebel.
  Recording and Segmenting Table Soccer Games -- Initial Results.
  In Proceedings of the 1st International Symposium on Skill Science 2007 (ISSS 2007), pp. 61-67. 2007.
  Poster.
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  Robot KiRo can play one side of a table soccer game autonomously. Our recent research focuses on learning from and acting against human actions. Therefore recording and segmenting games played by humans are motivated. In this paper, the construction of a table soccer game recorder is sketched. An intuitive segmenting algorithm is implemented to explore the properties of the recorded data. A segmentation approach using Hidden Markov Models (HMMs) is proposed.

• Dapeng Zhang and Bernhard Nebel.
  Learning a Table Soccer Robot a New Action Sequence by Observing and Imitating.
  In Proceedings of the Third Artificial Intelligence for Interactive Digital Entertainment Conference (AIIDE 2007), pp. 61-67. 2007.
  Experiment Video.
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  Star-Kick is a commercially available and fully automatic table soccer (foosball) robot, which plays table soccer games against human players on a competitive level. One of our research goals is to learn this table soccer robot skillful actions similar to a human player based on a moderate number of trials. Two independent learning algorithms are employed for learning a new lock and slide-kick action sequence by observing the performed actions and imitating the relative actions of a human player. The experiments with Star-Kick show that an effective action sequence can be learned in approximately 20 trials.

2005

• Dapeng Zhang.
  Action Selection and Action Control for Playing Table Soccer Using Markov Decision Processes.
  Master's thesis, Albert-Ludwigs-Universität, Freiburg, Germany 2005.
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  StarKick is a commercially available table soccer robot which challenges even advanced human players. However, the available set of actions for StarKick is limited and the way of selecting the actions is not flexible enough for incorporating more elaborate actions.

  In the context of this thesis, new actions for stopping and dribbling the ball are developed. Stopping is achieved by locking the ball between the playing surface and a playing figure. Dribbling makes the ball rolling at a controllable speed within the reachable area of the playing figures of one rod. By these new actions, the ball can be deliberately passed and stopped.

  To decide, which action should be taken in a given situation, an action selection scheme using Markov Decision Processes (MDPs) and reinforcement learning is developed. In order to reduce the state space, the basic actions are combined to more complex actions and the MDP is structured into four modules. Each module contains a set of states, and the actions that are applicable in these states. A simple reinforcement learning algorithm is implemented in the MDP framework. The transition probabilities are updated by counting. These updates are spread by policy iteration algorithm during a game.

  A series of experiments are carried out in real table soccer games. These experiments show that the newly developed actions are robust, the MDP model works fine, and the reinforcement learning improves the performance of StarKick in a simplified game. The attempt of making the reinforcement learning work in the whole game seems too tedious to be finished in real games.

2004

• Thilo Weigel, Dapeng Zhang, Klaus Rechert and Bernhard Nebel.
  Adaptive Vision for Playing Table Soccer.
  In S. Biundo, T. Frühwirth and G. Palm, KI 2004: Advances in Artificial Intelligence. Proceedings of the 27th Annual German Conference on Artificial Intelligence, pp. 424-438. Springer-Verlag 2004.
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  For real time object recognition and tracking often color-based methods are used. While these methods are very ecient, they usually dependent heavily on lighting conditions. In this paper we present a robust and ecient vision system for the table soccer robot KiRo. By exploiting knowledge about invariant characteristics of the table soccer game, the system is able to adapt to changing lighting conditions dynamically and to detect relevant objects on the table within a few milliseconds. We give experimental evidence for the robustness and efficiency of our approach.