A Reachability-based planner for sequences of acyclic contacts in cluttered environments

International audienceMultiped locomotion in cluttered environments is addressed as the problem of planning acyclic sequences of contacts, that characterize the motion. In order to overcome the inherent combinatorial difficulty of the problem, we separate it in two subproblems: first, planning a guide trajectory for the root of the robot and then, generating relevant contacts along this trajectory. This paper proposes theoretical contributions to these two subproblems. We propose a theoretical characterization of the guide trajectory, named " true feasibility " , which guarantee that a guide can be mapped into the contact manifold of the robot. As opposed to previous approaches, this property makes it possible to assert the relevance of a guide trajectory without explicitly computing contact configurations. This property can be efficiently checked by a sample-based planner (e.g. we implemented a visibility PRM). Since the guide trajectories that we characterized are easily mapped to a valid sequence of contacts, we then focused on how to select a particular sequence with desirable properties, such as robustness, efficiency and naturalness, only considered for cyclic locomotion so far. Based on these novel theoretical developments, we implemented a complete acyclic contact planner and demonstrate its efficiency by producing a large variety of movements with three very different robots (humanoid, insectoid, dexterous hand) in five challenging scenarios. The planner is very efficient in quality of the produced movements and in computation time: given a computed RB-PRM, a legged figure or a dexterous hand can generate its motion in real time. This result outperforms any previous acyclic contact planner