Nonlinear Hierarchical Control for Unmanned Quadrotor Transportation Systems

An unmanned quadrotor presents excellent mobility to fly freely in complex environments, which makes it an ideal choice for aerial transferring tasks. During the transferring process, it is very challenging to eliminate the swing since there is no direct control on the payload. The quadrotor transportation system presents the great challenge of cascaded underactuated-underactuated property, which makes it extremely difficult to simultaneously implement accurate quadrotor positioning and efficient payload swing suppression. Here, a nonlinear hierarchical control scheme is proposed for a quadrotor transportation system, which takes full advantage of the cascade property of the system, and separates the controller design for the inner loop and the outer loop respectively to facilitate the design procedure. As illustrated by experimental results, the proposed control law presents such advantages as high control precision, good robustness against external disturbances and parameter variations, and so on.