Suspended load path tracking control based on zonotopic state estimation using a tilt-rotor UAV

This work addresses the problem of load transportation by a tilt-rotor unmanned aerial vehicle (UAV). In the literature, the suspended load's dynamics are often regarded as external disturbances affecting the UAV, or are handled implicitly in the equations of motion of the system, not allowing direct control of its coordinates. This work presents the formulation of the whole-body system dynamics from the load's perspective, in which the suspended load's dynamics appear explicitly in the equations of motion, while the aircraft's are handled implicitly. A nonlinear state-space representation of the system is obtained, with the load's position and orientation among the system states, allowing state-feedback strategies to directly control these variables. In real applications, available sensors provide information about the UAV's coordinates, thus the states of the present approach may not be directly measured. Then, this work also proposes a state estimation strategy, based on a set-membership, zonotopic technique, for which it is assumed that measurements are noisy and have different sampling times. Finally, a discrete-time, mixed H-2/H-infinity controller with pole placement constraints, is designed for path tracking control of the suspended load with constant disturbances rejection, and feedback from the estimated states. Simulation results are presented in order to validate the proposed approach.