Omni-Directional Fall Avoidance of Bipedal Robots with Variable Stride Length and Step Duration

This paper proposes a capturability analysis method for fall avoidance of bipedal robots under arbitrary disturbances. Based on a dynamical model of the planar movement of the center-of-mass, capture region is computed numerically by discretizing the state space and the set of control inputs. The proposed method is able to handle a number of practically important elements of fall avoidance such as the relation between stride length and step duration, and kinematic limitations of foot placement, which have been neglected in conventional studies for simplification. The developed fall-avoidance controller utilizes precomputed capturable regions to filter reference foot placements produced by a foot-step planner to ensure fall-avoidance with small online computation time. Capture regions computed by the proposed method are compared with the conventional ones in case studies. The performance of the proposed fall-avoidance controller is evaluated in simulations.