Nonlinear observer-based tracking control of link stress and elevation for a tethered aerial robot using inertial-only measurements

This work deals with a comprehensive version of the tethered aerial vehicle problem including all the three possible link cases: cable, strut, and bar. We prove the dynamic feedback linearizability and differential flatness of the system with respect to the elevation of the vehicle and the stress applied to the link. Moreover we prove the observability of the system using only on-board inertial sensors (i.e., only a gyroscope plus an accelerometer). We design a globally convergent nonlinear controller based on the concurrent use of a dynamic feedback linearization control and a state estimator based on a nonlinear state/output transformation and a high gain observer scheme. The controller/observer algorithm is thus able to globally control elevation and stress (both tension and compression) along independent time-varying trajectories only resorting to inertial measurements. The stability of the controlled system is theoretically proven and its behavior is shown by means of extensive dynamical simulations.