Locally-optimal multi-robot navigation under delaying disturbances using homotopy constraints

We study the problem of reliable motion coordination strategies for teams of mobile robots when any of the robots can be temporarily stopped by an exogenous disturbance at any time. We assume that an arbitrary multi-robot planner initially provides coordinated trajectories computed without considering such disturbances. We are interested in designing a control strategy that handles delaying disturbance such that collisions and deadlocks are provably avoided, and the travel time is minimized. The problem is analyzed in a coordination space framework, in which each dimension represents the position of a single robot along its planned trajectory. We demonstrate that to avoid deadlocks, the trajectory of the system in the coordination space must be homotopic to the trajectory corresponding to the planned solution. We propose a controller that abides this homotopy constraint while minimizing the travel time. Besides being provably deadlock-free, our experiments show that travel time is significantly smaller with our method than than with a reactive method.