Adaptive Fuzzy Consensus Control Strategy for UAS-Based Load Transportation Tasks

A control strategy for enabling a team of unmanned aircraft systems (UASs) to cooperatively transport a cable-suspended rigid-bodypayload of unknown characteristics is proposed. Considering the rigid-body payload as a disturbance with unmodeled dynamics affecting the aircraft, a fuzzy approximator is designed to identify the lumped disturbances existing in the system, which include also the forces of interaction between the aircraft. Next, a nonlinear controller is designed, which makes use of the approximator to compensate such disturbances. Making use of the fuzzy approximator and the nonlinear controller, a novel consensus-type strategy is proposed, enabling the load transportation task by means of two cooperative quad rotorcraft UASs. The stability of the proposed methodology is demonstrated making use of Lyapunov theory. The nonlinear consensus controller enhanced with fuzzy compensation is compared with respect to a feedback controller with feedforward compensation, demonstrating superior performance of the proposed technique in terms of robustness and stability. Experimental results demonstrate the applicability of the theoretical framework for executing the real-time transportation of a cable-suspended rigid-body payload by means of a team of two cooperative quad rotor UASs.

I. Introduction

Load transportation has become a popular application for multirotorcraft unmanned aircraft systems (UASs) [1]. The most common solutions for performing UAS-based load transportation tasks consist of i) enhancing the UAS with grippers for holding the load, and ii) attaching the load to the UAS by means of a cable. In the former approach, the load is maintained close to vehicle's center of gravity, which is beneficial in terms of stability. However, this solution also increases the inertia of the overall system, restricting its functionality to the execution of slow movements [2]. On the other hand, when transporting a load via a cable the agility of the multirotorcraft is preserved. However, this approach introduces additional challenges since two underactuated degrees of freedom are added to the system. Furthermore, it is known that the swinging motion of the load can trigger undesired instability in the carrier system [3], [4].