Quasi-direct nonprehensile catching with uncertain object states

One of the key challenges in dynamic manipulation is to establish continuous contact between a moving object and a manipulator. Direct robotic catching is a benchmark in this context, especially without grasping devices. In this paper, we explain why it is unrewarding to aim for an ideal initial dynamic contact if only imprecise knowledge of the object states is available. Robust initial contacts are proposed such that a successful quasi-direct catch can be predicted. The proposed robustness originates in a negative relative acceleration between object and catching end-effector. Sets, for which an upper negative relative acceleration bound holds, are evaluated throughout an exemplary catching motion. Reachable set computations allow to express and visualize these sets of successful object states at any point in time before contact. The paper closes with a robot-robot experiment that shows successful quasi-direct catches without feedback on the object states for a robotic throw.