Experimental implementation of integrator backstepping and passive nonlinear controllers on the RTAC testbed

The rotational/translational actuator (RTAC) provides a low-dimensional nonlinear system for investigating nonlinear control techniques. The lossless formulation of this problem involves coupling of an undamped oscillator with a rotational rigid body mode. Stabilization and disturbance rejection objectives for this problem have been formulated as a benchmark problem. We implement four nonlinear controllers on the RTAC, including an integrator backstepping controller and three passivity-based controllers. The integrator backstepping design is based on the work of Wan et al. (1996). This approach requires that the equations of motion be reformulated by partial feedback linearization. Integrator backstepping is then used to produce a family of globally asymptotically stabilizing control laws. Next, three passivity-based controllers are developed for the RTAC. These controllers have intuitively appealing energy-dissipative properties and thus also inherent stability robustness to plant and disturbance uncertainty. Two of these controllers are encompassed by the classical passivity framework. The final controller is based upon the novel concept of resetting absorbers