Flying Control Study For Quadcopter Used For Ground Object Tracking And Simulation System Development

Quadrotor UAVs(unmanned aerial vehicle)have attracted great attention because of the agility and the capability of vertical take-off and landing(VTOL)and flying in various environments.Their applications can be widely found in military,industry and civil operations,especially in the fields like aerial photography and inspection,target detection and tracking and so on.These applications require that UAVs have autonomous space navigation capability.Meanwhile the complexity of flying environment also demands better flight control to achieve flight stability.During operations,the flight of UAV is often affected by the surrounding situation,especially by the wind.It becomes important to make quick adjustment of flight trajectory and attitude to ensure flight stability when the flying conditions of environment change.Clearly,it is necessary to study the precise flight trajectory tracking control of UAV in adverse flying environments,for example,those with wind interference.The main study here includes:The quadrotor UAV here is coupled with vision system.The function modules are designed and components are determined and selected according to requirements,and the test platform of quadrotor UAV is designed for the purpose of the ground object(target)tracking.The structure and motion characteristics are analyzed based on the previous design.The altitude of UAV in the coordinate system of the earth is calculated by the construction of global and body coordinate systems,respectively,and then the coordinate system transformation.The motion model of UAV is formulated using the Newton-Euler method.Wind influences the flight stability greatly in the study.In order to analyze the influence of wind during the flight,the mathematical model of wind field has been built and the wind interference has been factored and included in the motion model of UAV.Since the trajectory of UVA consists of two components,i.e.,the position and the altitude,accordingly the model for the UAV is also divided into two sub-models for the position and the altitude respectively for the study of trajectory control.Due to the coupling relationship between the position control and altitude control,the position control can be realized through altitude angle control.The control structure consists of the inner and outer closed loops to decouple the inter closed loop control and outer closed loop control.Inner and outer closed loops are for the control of the altitude and position,respectively.Based on the sliding mode algorithm,an algorithm for trajectory tracking is formulated for outer closed loop control by proposing an exponential approximation method including a robust term to achieve the stable flight control for the cases of wind interference.Similar methodology is also applied for inner closed loop control,and in this way both the altitude angle and angle velocity controls are realized for real-time trajectory tracking.Integral term for the attitude angle tracking error is added when designing the attitude sliding mode surface to improve the robustness of the UAV attitude control system.In addition,the Lyapunov stability criterion is used to mathematically prove control stability of this control strategy for UAV.Both the algorithms of proposed here and traditional sliding mode are used to compare the efficiency and accuracy of trajectory tacking and the simulation results using MATLAB software reveal that the proposed one has clear advantage over the traditional one.For the purpose of simulation,the three-dimensional CAD model of the UAV is imported into Simscape and flight scenarios are completed.Then comparisons of the trajectory tracking using dual PID control algorithm and the algorithm proposed here are made by analyzing the simulation results and evaluating the control performance.GUIs are developed to display the trajectory and the states of UAV during the flight and to realize the information exchange between users and the system.Finally,based on the design architecture of UAV platform coupled with vision module,a UAV flight test system is developed and constructed.System tests are designed and made to evaluate the reliability and practicability of this system.