Visco-Elastic Structure Preserving Impedance (Ves Pi) Control For Compliantly Actuated Robots

In this paper we consider the control of robots that feature visco-elastic actuators with adjustable physical damping. Considering the link variables of the robot as output, the corresponding system dynamics has a relative degree of 3. We present a novel control approach that allows to realize a torque interface on the link side, while preserving the intrinsic visco-elastic structure and the inertial properties of the system. By means of this joint torque interface one can implement link-side position tracking and impedance tasks. For this case, we provide a stability and passivity analysis. The control approach has been verified by experiments with a visco-elastic joint testbed.