Global output-feedback tracking for a benchmark nonlinear system

The output-feedback global tracking problem is solved for the well-known nonlinear benchmark RTAC (rotational-translational actuator) system, where one of the unmeasured states appears quadratically in the state equations. Our observer-controller backstepping design yields a nonlinear output-feedback controller that forces the translational displacement to globally asymptotically track an appropriate time-varying signal. The proposed solution is new even for the case of global output-feedback stabilization, namely when the reference signal is zero.