Passivity-based variable impedance control for redundant manipulators

Kinematic redundancy significantly improves the dexterity and flexibility of robotic manipulators. The redundant degrees of freedom can be exploited to fulfill additional tasks that can be executed without disturbing the primary task. In this work, we investigate how a time varying impedance behavior can be embedded into redundant manipulators where it is desired to achieve such a behavior both for the primary and null space tasks. A passivity based controller is developed, relying on the concept of energy tanks which are filled by the dissipated power in the system, and compensate for non-passive control actions. This guarantees that the system remains passive, which ensures stable interactions with any passive environment. The method is validated in simulations where the interactive behavior of the main and null space tasks is specified by a time varying stiffness profile.