Control of a swinging juggling robot

We present a control strategy for a robot that juggles a ball with a single actuated paddle that is attached to the tip of a pendulum-like mechanism. The robot juggles the ball from side-to-side by striking the ball with the paddle when the pendulum reaches its peak angles. Sustained juggling is only possible if the pendulum motion is synchronized to the ball motion. We propose adapting the paddle motion to achieve synchronization. Specifically, we exploit the dynamic coupling between the pendulum and the paddle, which is essentially a moving mass at the tip of the pendulum. Optimal control is used to compute paddle motions that synchronize the pendulum to the ball. Feedback is introduced with a lookup table that maps a measured state to an appropriate paddle motion. In experiments, the proposed feedback strategy enables the robot to juggle at various amplitudes.