Online Rolling Motion Generation for Humanoid Falls Based on Active Energy Control Concepts

This paper introduces a novel online rolling over control technique based on energy concepts to alleviate impact forces during humanoid fall overs. To generate efficient rolling motion, critical parameters are defined by the insights drawn from a study on rolling, which are contact positions and attack angles. In addition, energy-injection velocity is proposed as an auxiliary control command to ensure sequential multiple contacts in rolling. The online rolling controller is synthesized to compute the optimal values of three rolling parameters: the first two parameters are to construct the humanoid's posture as a polyhedron by selecting suitable contacts points. This polyhedron distributes the energy gradually across multiple contacts; and the last one is to inject additional energy into the system during the fall, to overcome energy drought and tip over successive contacts, i.e., rolling. Accordingly, the proposed controller exploits energy injection, minimization, and distribution techniques and renders a rolling like motion. Numerical experiments with a segmented planar model and a full humanoid model verify that it significantly reduces impact forces.