Adaptive control of nonlinear resonant systems with damping

The paper describes a nonlinear controller design technique for a servo drive in the presence of: 1) nonlinear friction (or any other load torque), 2) a flexible shaft that connects the motor and the load. The shaft is characterized by the stiffness and the damping coefficients. The proposed controller is based on adaptive backstepping, modified by the use of command filtering. Although in the presence of damping the model is not in a strict-feedback form, the proposed approach allows to accomplish the rigorous proof of the closed-loop system stability. Several experiments prove the control effectiveness and robustness against un-modelled dynamics.