Moving Platform Landing Control Method Of Small-scale Unmanned Helicopters

Unmanned helicopters are widely used in modern military operations.The role they play is becoming increasingly important.With the complexity and diversity of flight missions keep growing,the capability to land on moving platforms autonomously shows vital necessity.This paper studies the flight control method of small-scale unmanned helicopters.Aiming at autonomous landing on moving platform,the research focuses on three parts: low cost attitude estimation method,guidance method and attitude control method.The helicopter dynamics is studied and analyzed.A nonlinear dynamic model of a single-rotor helicopter including flapping motion is presented.The relationship between control forces,control moments and control inputs is clarified.A compound gradient descent(CGD)attitude estimation method for high dynamic environment is constructed.The method is based on MEMS measurement to address the internal space and cost limitations of small-scale unmanned helicopters.It is evolved from basic gradient descent method by adding virtual reference vector,load compensation and dual-antenna information fusion mechanisms.Simulation is conducted.Performance of the new CGD method is compared with that of the existing method.In order to satisfy the velocity and acceleration limitations during the flight mission,the asymmetric tracking differentiator(ATD)is derived from the basic tracking differentiator.Velocity and acceleration limits of the tracking signal in opposite directions can be configured separately in the new asymmetric tracking differentiator.Based on the new asymmetric tracking differentiator,a fal ESO disturbance observer is added to construct the attitude and rotation controller.The transient progress of the controller can be configured explicitly through parameter setting.In order to set control parameters more reasonably,a control gain coefficient estimation method based on forgetting-factor least square method is proposed.An inertia parameter estimation method utilizing CAD design data and helicopter dynamics is proposed.On this basis,a gain scheduling control parameter tuning mechanism is established.Based on the asymmetric tracking differentiator,the guidance algorithms of unmanned helicopters in altitude and horizontal directions are established.A two-layer guidance system is structured.The first layer is the reference trajectory generator and the second layer is the collective pitch command generator or attitude command generator.Guidance algorithms for straight line reference path,circular reference path and moving target are described in detail.The guidance and attitude control methods proposed in this paper are tested and validated by means of mathematical simulation.The whole progress of autonomous landing on a moving platform including three stages,approaching,following and landing,is exercised in the same scenario.Motion and error data obtained under different wave heights and periods is analyzed.Range of safe landing conditions is derived from the analysis.Approach and corresponding cost of expanding the range of safe landing conditions are given.