Synthesis of Whole-Body Behaviors Through Hierarchical Control of Behavioral Primitives

To synthesize whole-body behaviors interactively, multiple behavioral primitives need to be simultaneously controlled, including those that guarantee that the constraints imposed by the robot's structure and the external environment are satisfied. Behavioral primitives are entities for the control of various movement criteria, e.g. primitives describing the behavior of the center of gravity, the behaviors of the hands, legs, and head, the body attitude and posture, the constrained body parts such as joint-limits and contacts, etc. By aggregating multiple primitives, we synthesize whole-body behaviors. For safety and for efficient control, we establish a control hierarchy among behavioral primitives, which is exploited to establish control priorities among the different control categories, i.e. constraints, operational tasks, and postures. Constraints should always be guaranteed, while operational tasks should be accomplished without violating the acting constraints, and the posture should control the residual movement redundancy. In this paper, we will present a multi-level hierarchical control structure that allows the establishment of general priorities among behavioral primitives, and we will describe compliant control strategies for efficient control under contact interactions.