Modeling And Control Of Unmanned Multi-rotor Craft With A Cable-suspended Payload

Unmanned Aerial Vehicle(UAV)is a kind of vehicle controlled by radio remote control ap-paratuses or automatic control devices.Compared with manned aerial vehicles,UAVs can carry out more complex and dangerous tasks and have been widely applied in the various fields,such as fire fighting,rescue,circuit inspection,aerial photography,and so on.In addition,in the military field,UAVs can perform reconnaissance,strike,and transport tasks,and play an essential role in the national defense.The UAVs can be divided into multi-rotor UAV,tilt-rotor UAV,fixed-wing UAV,flapping-wing UAV,and so on.The unmanned multi-rotor crafts like quadrotor UAV and tilt-rotor UAV,which are capable of taking off and landing vertically,can instal various devices to complete different tasks.There are three methods to connect the unmanned rotorcraft with the payload: connecting the payload rigidly,grabbing the payload by robot arms,and connecting the payload by a soft cable.In contrast to the other two connection methods,connecting the payload by a soft cable possesses the following advantages: the shape and size of the payload do not need to match that of the UAVs,and the UAVs can load and unload without landing.For the above characteristics,the unmanned multi-rotor craft with a cable-suspended payload are suit-able for transportation,rescue,and survey,and have essential application values.However,the unmanned multi-rotor craft with a cable-suspended payload are a typical underactuated nonlin-ear system with parameter uncertainty,and its rotor downwash significantly influences the swing motion of the payload.The control design for this system faces significant challenges.Hence,proposing new control schemes to reduce the influence caused by the above issues and improve the control performance of the unmanned multi-rotor craft with a cable-suspended payload has great research and application value.This dissertation focuses on the modeling and control de-sign for a quadrotor UAV with a cable-suspended payload and a coaxial tilt-rotor UAV with a cable-suspended payload.The main work of this thesis is concluded as follows:1.A dynamic model of a quadrotor UAV with a cable-suspended payload is constructed by the Euler-Lagrange equation.The payload is always assumed to be a point mass in other works,which means the air drag force and the rotor downwash force on the payload is not included in modeling.However,in the case of transporting a payload with large volume,the aforemen-tioned air force will obviously influence the dynamic of the system.Hence,a dynamic model which takes the air drag force and the rotor downwash force on the payload into consideration is constructed.The models of the air drag force and rotor downwash force on the payload are constructed through mechanism modeling,experimental measurement,and parameter fitting.2.A quadrotor with a cable-suspended payload is an underactuated nonlinear system.In the transporting process,the suspended payload is susceptible to external disturbance,which will seriously influence the stability of the transportation.Based on the dynamic model above,considering the uncertainty of the payload mass and the underactuated property of the system,an adaptive control algorithm is proposed with a cascade structure to realize motion control.The proposed adaptive controller consists of three parts: inner-loop quadrotor attitude controller,middle-loop swing angle adaptive controller,and outer-loop payload velocity adaptive controller.The key to realizing stable payload transportation is to control the velocity and the swing angle of the payload accurately.Controlled by the proposed control algorithm,the quadrotor with a cable-suspended payload can track desired payload velocity and swing angle in the presence of the payload mass uncertainty.The stability of the whole closed-loop system is analyzed theoretically by the Lyapunov method.Then,an experimental platform,which is made up of a quadrotor and a newly designed suspended structure,is constructed.The suspended structure mainly consists of a Cardan joint,a gyroscope,a soft cable,and a carbon fiber tube.The gyroscope of the suspended structure is used to measure swing angle,and its measuring performance will not be influenced by the ambient light and the obstacle.The simulations and experiments show that the proposed adaptive controller can rapidly stabilize the system from different initial state and realize accurate motion control in the presence of the uncertainty of payload mass.3.In contrast to the quadrotor,the coaxial tilt-rotor UAV is faster,more agile,and also suit-able for transportation tasks by suspending the payload.However,the coaxial tilt-rotor UAV with a cable-suspended payload is an underactuated system,and the payload is easy to swing in the transport.For the problems above,the researches about the control design of the coaxial tilt-rotor UAV and the coaxial tilt-rotor UAV with a cable-suspended payload are carried out.Primarily,an experimental coaxial tilt-rotor platform is designed and constructed with compact structure and high control redundancy,whose layout is with two front tiltable coaxial rotors and a rear rotor.An adaptive control law is proposed to realize velocity and attitude control.Two adaptive laws are included in the proposed control algorithm to reduce the influence caused by the external dis-turbance.The asymptotic stability of the whole closed-loop system is proved by the Lyapunov method.The simulation tests,ground bench tests,and actual flight tests are accomplished to verify the effectiveness of the proposed control law.Then,combining the dynamic model and the control law of the coaxial tilt-rotor UAV and the quadrotor with a cable-suspended payload,a nonlinear control algorithm with cascade structure is proposed to realize motion control for the coaxial tilt-rotor with a cable-suspended payload.Several simulation tests are performed to validate the effectiveness of the proposed control scheme.The simulation results show that the proposed control law can rapidly stabilize the system from different initial states,and realize accurate motion control.Through these works,systematic researches from theoretical analysis to engineering prac-tice are completed.Based on the current researches,the future work will focus on the robust control and trajectory tracking control for the unmanned quadrotor with a cable-suspended pay-load,and the flight control for a winged coaxial tilt-rotor UAV with a cable-suspended payload.