How to solve deadlock situations within the plan-merging paradigm for multi-robot cooperation

Our approach in proposing the plan-merging paradigm as a cooperation scheme was to allow an efficient distribution of the decisions for a better reactivity to contingencies for multi-robot applications with loosely coupled tasks. The paradigm proved to be quite efficient because it exploits the fact that most conflicts can be solved locally and because it allows a finer overlapping between plan refinement, plan coordination and execution. We develop in this paper the mechanisms which allow one to extend this paradigm in order to obtain a scheme which distributes as much as possible the decision processes for planning and coordination while maintaining two key features: the coherence of the global system and the ability to detect the situations where it is not applicable; and a localized management of the planning and coordination processes with, in particularly intricate situations, a progressive transition to more global schemes which may "degrade" to a unique and centralized planning activity.