Unified passivity-based Cartesian force/impedance control for rigid and flexible joint robots via task-energy tanks

In this paper we propose a novel hybrid Cartesian force/impedance controller that is equipped with energy tanks to preserve passivity. Our approach overcomes the problems of (hybrid) force control, impedance control, and set-point based indirect force control. It allows accurate force tracking, full compliant impedance behavior, and safe contact resemblance simultaneously by introducing a controller shaping function that robustly handles unexpected contact loss and avoids chattering behavior that switching based approaches suffer from. Furthermore, we propose a constructive way of initiating the energy tanks via the concept of task energy. This represents an estimate of the energy consumption of a given force control task prior to execution. The controller can be applied to both rigid body and flexible joint dynamics. To show the validity of our approach, several simulations and experiments with the KUKA/DLR LWR-III are carried out.