Robust plan execution via reconfiguration and replanning

Acting in the real world may be a difficult task for an agent, either software or robotic, because unexpected contingencies may arise at any step of the execution. Previous approaches to robust plan execution consider propositional goals to be achieved and time constraints to be satisfied. However, realistic plans must obey to constraints on continuous/consumable resources, too. To face the complexity in handling these resources, the paper proposes the notion of Multi Modality Action (MMA). The model allows to explicitly express the multiple execution modalities in which a given action can be executed; each execution modality models requirements/consequences on the involved consumable resources when that modality is selected. Relying on the MMA notion, the paper presents how the repair problem can be seen as a problem of reconfiguring actions modalities, and how it can be solved by exploiting a CSP encoding. The MMAs are employed by a new continual planner, FLEX-RR, which, exploiting the synergy from the reconfiguration and a numeric planning mechanism, can efficiently repair on the fly the plan keeping it rather stable. An empirical analysis, performed on three numeric planning domains, confirms the large benefits of FLEX-RR in terms of competence, efficiency and stability of the repaired plan.