Visual Servo-based Control Of UAV With A Cable Suspended Load

In recent years,the multi-rotor unmanned aerial vehicle(UAV)system with a suspended load has attracted increasing attention in logistics,construction and agriculture due to the advantages of UAV’s flexible operation,good performance and low cost.However,the UAV system with a suspended load is seriously disturbed by the load during flight,and thus it is much more complex than the UAV control.To solve the control problem of UAV with a suspended load,a method based on visual servo is proposed to realize the stability control of the UAV load system and achieve self-delivery of the load according to the visual positioning technology.Contraposing the design requirements,the dynamic model of multi-rotor UAV with a suspended load system is established by using Euler-Lagrange method;the model is applied to the design of the tracking controller.Because the base platform is not stationary during the process of UAV transportation and delivery,this dissertation proposes a visual servo tracking control method to solve the problem.Considering the distance between UAV and the ground moving target,an adaptive target tracking strategy is presented by utilizing the Open TLD and April Tag tracking algorithms.When the UAV is far away from the moving target,the visual servo controller based on the Open TLD is used.When the UAV is close to the moving target and the April Tag can be detected stably,the target position calculated by the April Tag is used as reference input to UAV flight controller.As the suspension load can cause serious interference to the control of unmanned aerial vehicles,the dissertation designs a multi-closed-loop PD controller;it is designed based on the visual-servo controller by combining the dynamic model of UAV and load.The designed controller includes a load position control loop,a load attitude control loop and a UAV attitude control loop.In order to verify the proposed UAV suspension transportation method,this dissertation applies Gazebo dynamic engine to build a simulation platform.The simulation results show that the visual servo controller can stably track the ground moving target,and stabilize the swing of the load rapidly and effectively.Finally,it is verified that the visual servo tracking controller has good tracking control effect by error analysis.In this dissertation,the research of transportation using UAV with suspended load can be extended to multiple UAVs transportations,and can provide interesting reference for the future research of UAV load transportation.