Passivity-Based Impedance Control of a Class of Nonlinear Actuators with Internal Dynamics

Gianluca Rizzello, Paolo Roberto Massenio

Abstract: This paper presents an impedance control approach for a class of variable stiffness actuators with output nonlinearities and slow internal dynamics, representative for smart material transducers like shape memory alloys or ionic polymer-metal composites. The goal is to render in closed loop an arbitrary mechanical impedance with desired stiffness and damping properties, while also ensuring that the controlled actuator is passive with respect to its velocity-force interaction port. The problem is made challenging by the presence of nonlinearities, together with the fact that the control input does not allow instantaneous modulation of the actuator force/stiffness characteristics. Two different versions of the control law are proposed, i.e., a state feedback and an observer-based one. Numerical simulations show that the proposed approach can be used to effectively achieve motion control of actuated mechanical structures, while control laws that ignore the actuator dynamics may lead to instability.