A Multi-Link-Flexible Robot Arm Catching Thrown Balls

The contribution proposes a control architecture, which enables a multi-link-flexible robot arm under gravitational influence to catch multiple balls sequentially thrown by a human. A net at the end-effector is utilized to intercept the balls when they pass the vertically oriented robot plane of motion. The ball detection, tracking as well as the prediction of the ball intercept location is based on a wall-mounted Kinect RGB-D sensor. Previously caught balls represent a varying payload, which induces also dynamic disturbances due to the pendulum motion. These disturbances as well as the coupled flexible-link vibrations are damped with a model free independent joint controller. The inverse kinematics approach is based on neural networks and augmented by an online payload estimation.