Antiswing Control for Aerial Transportation of the Suspended Cargo by Dual Quadrotor UAVs

Quadrotor unmanned aerial vehicles, with excellent maneuver performance and flexibility, are widely used in cargo transportation. Due to higher requirements for load capacity, dual quadrotors are expected to work cooperatively so as to transport heavy cargos. However, the aerial transportation system with dual quadrotors exhibits higher degrees of freedom, stronger nonlinearities, and more complex system couplings compared with the single quadrotor transportation system, which brings great challenges to the control of the system. This article focuses on the cooperative control of aerial transportation systems with dual quadrotors. Based on the Lagrange’s method, a redundant form of the dynamic model is constructed and presented, where the control inputs are decoupled with system dynamic. According to the cascade characteristics of the system, the inner loop subsystem on the attitude characteristics of the quadrotor, as well as the outer loop subsystem on the cargo’s swing motion and the quadrotor’s translational motion are defined. Then, a nonlinear hierarchical controller containing relative position constraints and cable tensions compensation is proposed. Specifically, by utilizing the energy-based analysis method, virtual control inputs are designed for the outer loop subsystem. Finally, LaSalle’s invariance principle is used to prove the stability of the closed-loop system. Experimental results show satisfactory control performance of the proposed controller.