Combined Task and Motion Planning under Partial Observability: An Optimization-Based Approach

Camille Phiquepal, Marc Toussaint

Abstract: We propose a novel approach to Combined Task and Motion Planning (TAMP) under partial observability. Previous optimization-based TAMP methods [1][2] compute optimal plans and paths assuming full observability. However, partial observability requires the solution to be a policy that reacts to the observations that the agent receives. We consider a formulation where observations introduce additional branching in the symbolic decision tree. The solution is now given by a reactive policy on the symbolic level together with a path tree that describes the branchings of optimal motion depending on the observations. Our method works in two stages: First, the symbolic policy is optimized using approximate path costs estimated from independent optimizations of trajectory pieces. Second, we fix the best symbolic policy and optimize a joint trajectory tree. We test our approach on object manipulation and autonomous driving examples. We also compare the algorithm's performance to a state-of-the-art TAMP planner in fully observable cases.