Coordinated Control of a Tethered Autonomous Docking UAV

A tethered autonomous docking system, which is composed of a rope winch installed at the bottom of the unmanned aerial vehicle (UAV), a quadrotor for autonomous docking, and a connected tether, can be widely used for unmanned delivery. Frequent ups and downs can be inevitable through the deployment/retrieval of the flexible tether. Although the tether offers several advantages compared with traditional UAV transportation, new control problems can arise as well. To solve this nonlinear, underactuated, and time-varying disturbance system, a complete control scheme, including the accurate trajectory tracking of the end quadrotor under a time-varying disturbance caused by tether and the coordinated control of the rope winch, is proposed in this paper. A complete dynamics model, including the terminal quadrotor and the rope winch, is derived. A new control scheme, combining active disturbance rejection control with finite time integral backstepping, is proposed to achieve the position tracking of the quadrotor under the unknown disturbance introduced by tether and environment. In the case of obtaining the real-Time position and tether tension of the quadrotor, a position-based impedance control strategy was proposed to always keep the tether slightly tensioned. Theoretical proof and simulation are given to verify the designed control algorithm, which can provide good performance of tracking and antidisturbance.