High-speed flexible arm to reduce the effect of spinning ball in table tennis

Table-tennis robots struggle to return a spinning ball to the opponent' s court because the direction of bound depends on the direction and magnitude of the spin. We aim to solve this problem using a swing motion that is robust over a large range of spin patterns without accurate recognition of the spin. Specifically, we examine the relation between the swing speed and direction of return. When the racket speed is 7 m/s, the difference in the return direction is only 20 % of that when the racket is not swung for the ball spinning in the range from -20 to 20 rev/s. In addition, we investigate the increase in swing speed of the racket due to flexibility of the swinging arm. We find that a flexible arm swings more rapidly than a rigid arm throughout the range of motion when exploiting the joint angle limit.