A Tank-Based Approach to Impedance Control with Variable Stiffness

In this paper, we present a new impedance control strategy that allows to reproduce a time-varying stiffness. By properly controlling the energy exchanged during the action, we guarantee the system passivity for any choice of the stiffness matrix, especially in case of time-varying stiffness, and therefore a stable behavior of the robot both in free motion and in interaction with an environment. A possible application of the presented algorithm is the reproduction of surgeon’s behavior during a puncturing task. In this application, the stiffness is changed depending on the layer of the human body the needle is crossing. To demonstrate the validity of the proposed method we conducted several simulations. Then, in order to prove the effec- tive useless of the proposed strategy, we built an experimental setup reproducing the puncturing scenario and implemented the algorithm by means of a 7 degree of freedom (DOF) robot manipulator.