Ball Tracking and Trajectory Prediction for TableTennis Robots Sports robots have become a popular research topic in recent years. For tabletennis robots, ball tracking and trajectory prediction are the most important technologies. Several methods were developed in previous research efforts, and they can be divided into two categories: physical models and machine learning. The former use algorithms that consider gravity, air resistance, the Magnus effect, and elastic collision. However, estimating these external forces require high sampling frequencies that can only be achieved with highefficiency imaging equipment. This study thus employed machine learning to learn the flight trajectories of pingpong balls, which consist of two parabolic trajectories: one beginning at the serving point and ending at the landing point on the table, and the other beginning at the landing point and ending at the striking point of the robot. We established two artificial neural networks to learn these two trajectories. We conducted a simulation experiment using 200 realworld trajectories as training data. The mean errors of the proposed dualnetwork method and a singlenetwork model were 39.6 mm and 42.9 mm, respectively. The results indicate that the prediction performance of the proposed dualnetwork method is better than that of the singlenetwork approach. We also used the physical model to generate 330 trajectories for training and the simulation test results show that the trained model achieved a success rate of 97% out of 30 attempts, which was higher than the success rate of 70% obtained by the physical model. A physical experiment presented a mean error and standard deviation of 36.6 mm and 18.8 mm, respectively. The results also show that even without the time stamps, the proposed method maintains its prediction performance with the additional advantages of 15% fewer parameters in the overall network and 54% shorter training time.

Learning Optimal Parameterized Policy for High Level Strategies in a Game Setting Complex and interactive robot manipulation skills such as playing a game of table tennis against a human opponent is a multifaceted challenge and a novel problem. Accurate dynamic trajectory generation in such dynamic situations and an appropriate controller in order to respond to the incoming table tennis ball from the opponent is only a prerequisite to win the game. Decision making is a major part of an intelligent robot and a policy is needed to choose and execute the action which receives highest reward. In this paper, we address this very important problem on how to learn the higher level optimal strategies that enable competitive behaviour with humans in such an interactive game setting. This paper presents a novel technique to learn a higher level strategy for the game of table tennis using PQ Learning (a mixture of Pavlovian learning and Qlearning) to learn a parameterized policy. The cooperative learning framework of Kohenon Self Organizing Map (KSOM) along with Replay Memory is employed for faster strategy learning in this short horizon problem. The strategy is learnt in simulation, using a simulated human opponent and an ideal robot that can perform hitting motion in its workspace accurately. We show that our method is able to improve the average received reward significantly in comparison to the other stateoftheart methods.