Accurate control of Aerial Manipulators outdoors. A reliable and self-coordinated nonlinear approach

Abstract

In recent years, standard Unmanned Aerial Vehicles have been enhanced in order to execute manipulation tasks, named Aerial Manipulators and composed of an Unmanned Aerial Vehicle and a Robot Manipulator. These aerial vehicles are extremely demanding on the flight control system, which needs to keep flight stability while autonomously executing complex tasks. This work continues a recent line of research where a nonlinear control strategy is proposed to comply with outdoor high-level demands to achieve enhanced accuracy and safety. This solution combines nonlinear control subsystems with decentralized priorities but coordinating their relative movements to allow the aerial vehicle to accommodate itself while reaching the manipulator target. The complete strategy is composed of: a passive nonlinear dynamic controller for the UAV, an integral kinematic multi-task controller for the manipulator, and an optimizer to coordinate their relative movements. Theoretical stability results are reported, along with implementation-oriented add-ons and an extensive analysis in realistic simulations. These include aerodynamic effects (e.g. unsteady wind disturbances and rotor propulsion models), collision avoidance, grasping and a comparison with a standard strategy on a benchmark mission complex enough for validation.