Passivity-based unification of force and impedance control via energy tanks for rigid joint robots

In this paper a novel hybrid Cartesian force/impedance controller is porposed that is equipped with energy tanks to preserve passivity. The approach overcomes the problems of (hybrid) force control, impedance control and set-point based indirect force control. It simultaneously allows accurate force tracking, full compliant impedance behavior and safe contact resemblance by introducing a controller shaping function. This robustly handles unexpected contact loss and avoids chattering behavior that other switching based approaches suffer from. Furthermore, a constructive way to initiate energy tanks via the concept of task energy is proposed, where the energy consumption of a given force control task is estimated prior to execution. To show the validity of our approach, several simulations and experiments with a 7-degree-of-freedom robot are carried out.