Time to Danger, an Alternative to Passive Safety for the Locomotion of a Biped Robot in a Crowd

A biped robot walking in a crowd must avoid falls and collisions at the same time. The latter is usually addressed through Passive Safety (PS), which guarantees that the robot is at rest when a collision is inevitable. Since PS may limit the robot's mobility, the purpose of this work is to introduce and explore the novel concept of Time To Danger (TTD) as an alternative. For a given robot motion, TTD is the time where the robot enters the region that a person can potentially occupy in the future. After having studied the properties of TTD, a novel locomotion strategy is proposed, which computes an optimal locomotion plan that guarantees balance preservation and TTD maximization, following a receding horizon Model Predictive Control scheme. Controlled experiments in a challenging simulated crowd scenario demonstrate how the novel locomotion strategy outperforms a Passive Safety-based locomotion strategy from a collision avoidance point of view.