Output tracking of underactuated rotary inverted pendulum by nonlinear controller

A novel tracking control law is developed for underactuated nonminimum inverted pendulum on a rotor arm by a combinated application of nonlinear backstepping, differential flatness, and small gain theorem. It has been shown that through proper input transformation, the whole system can be modified to be weak minimum phase with the external subsystem being differentially flat, and be further modified into 2 exp-ISS subsystems. Simulation and experimental results for tracking a reference signal are presented to verify the effectiveness of the proposed methodology.