ADAPTIVE NEURAL NETWORK ATTITUDE CONTROL FOR UNMANNED HELICOPTER

Adaptive flight control technology, feedback linearization, model inversion theory are reviewed and the error dynamic characteristics are analyzed, and an adaptive on-line neural network attitude control system is presented. The model inversion is under the hover condition. And the adaptive control law based on the neural network is designed to guarantee the boundedness of tracking error and control signals. Simulation results demonstrate that the nonlinear neural network augmented model inversion can self-adapt to the uncertainty and modeling errors of unmanned helicopters. Results are compared while the parameters of PD controller and robustness items are changed.

Control System Design for an Unmanned Helicopter to Track a Ground Target

Due to potential wide applications,the problem of utilizing an unmanned helicopter to track a ground target has become one of the most active research directions in related areas.However,in most cases,it is possible for a dynamic target to implement evasive actions with strong maneuverability,such as a sudden turn during high-speed movement,to flee from the tracker,which then brings much difficulty for the design of tracking control systems.Currently,most research on this field focuses on utilizing a ground mobile robot to track a high-speed target.Unfortunately,it is very difficult to extend those developed methods to airborne applications due to much more complex dynamices of UAV-target relative motion.This study investiages thoroughly for the problem of using an unmanned helicopter to track a ground target,with particular emphasis on the avoidance of tracking failure caused by the evasive maneuvers of dynamic targets.Specifically,a novel control scheme,which consists of an innovative target tracking controller and a classical flight controller,is proposed for the helicopter-target tracking problem.Wherein,the tracking controller,whose design is the focus of the paper,aims to utilize the motion information of the helicopter and the dynamic target to construct a suitable trajectory for the helicopter,so that when it flies along this trajectory,the relative pose between the helicopter and the dynamic target will be kept consant.When designing the target tracking controller,a novel coordinate transformation is firstly introduced to convert the tracking system into a more compact form convenient for control law design,the desired velocities for the helicopter is then proposed with consideration of the dynamic constraint.The stability of the closed-loop system is finally analyzed by Lyapunov techniques.Based on Matlab/Simulink environment,two groups of simulation are conducted for the helicopter-target tracking control system where the target moves along a linear path and takes a sudden turn during high-speed movement,respectively.As shown by the simulation results,both the distance error and the pointing error are bounded during the tracking process,and they are convergent to zero when the target moves straightly.Moreover,the tracking performance can be adjusted properly to avoid tracking failure due to evasive maneuvers of the target,so as to guarantee superior tracking performance for all kinds of dynamic targets.

Nonlinear Intelligent Flight Control for Quadrotor Unmanned Helicopter

Quadrotor unmanned helicopter is a new popular research platform for unmanned aerial vehicle(UAV),thanks to its simple construction,vertical take-off and landing(VTOL)capability.Here a nonlinear intelligent flight control system is developed for quadrotor unmanned helicopter,including trajectory control loop composed of co-controller and state estimator,and attitude control loop composed of brain emotional learning(BEL)intelligent controller.BEL intelligent controller based on mammalian middle brain is characterized as self-learning capability,model-free and robustness.Simulation results of a small quadrotor unmanned helicopter show that the BEL intelligent controller-based flight control system has faster dynamical responses with higher precision than the traditional controller-based system.

Development of an Autonomous Flight Control System for Small Size Unmanned Helicopter Based on Dynamical Model

It is devoted to the development of an autonomous flight control system for small size unmanned helicopter based on dynamical model. At first, the mathematical model of a small size helicopter is described. After that simple but effective MTCV control algorithm was proposed. The whole flight control algorithm is composed of two parts: orientation controller based on the model for rotation dynamics and a robust position controller for a double integrator. The MTCV block is also used to achieve translation velocity control. To demonstrate the performance of the presented algorithm, simulation results and results achieved in real flight experiments were presented.

Adaptive Backstepping Tracking Control of a 6-DOF Unmanned Helicopter

This paper presents an adaptive backstepping control design for a class of unmanned helicopters with parametric uncertainties. The control objective is to let the helicopter track some pre-defined position and yaw trajectories. In order to facilitate the control design, we divide the helicopter's dynamic model into three subsystems. The proposed controller combines the backstepping method with online parameter update laws to achieve the control objective. The global asymptotical stability (GAS) of the closed-loop system is proved by a Lyapunov based stability analysis. Numerical simulations demonstrate that the controller can achieve good tracking performance in the presence of parametric uncertainties. © 2014 Chinese Association of Automation.

Selection of a non-localized landing region for an unmanned helicopter based on an attention model

A new landing region selection algorithm for an unmanned helicopter is proposed based on an attention model.Different from the original attention model,some properties of the possible safe landing regions（e.g.,depth,regional color and motion features）are included in the selection algorithm.Furthermore,regional color and motion features are fused directly into the saliency map because these features do not have the ＂central-peripheral＂property.Experimental results validate the feasibility and efficiency of this approach.

Angular velocity dynamics identification of small unmanned helicopter using fuzzy model

Attitude identification method for unmanned helicopter based on fuzzy model at hovering is presented. The dynamical attitude model is considered as basis for attitude control and it is very complex. To reduce the complexity of model, nonlinear model of unmanned helicopter with unknown parameters are to be determined by fuzzy system first and then derivative based gradient method is used to identify unknown parameters of model. Gradient method is used due to ability that fuzzy system is not necessarily to be linear in parameters, therefore all fuzzy sets for input and output can be adjusted. The validity of the proposed model was verified using experimental data obtained by the commercially available flight simulator X-Plane. The simulation results showed high accuracy of the modeling method and attitude dynamics data matched well with experimental data.

Robust Anti⁃swing Control for Unmanned Helicopter Slung⁃Load System with Prescribed Performance

A robust anti-swing control method based on the error transformation function is proposed,and the problem is handled for the unmanned helicopter slung-load system(HSLS)deviating from the equilibrium state due to the disturbances in the lifting process.First,the nonlinear model of unmanned HSLS is established.Second,the errors of swing angles are constructed by using the two ideal swing angle values and the actual swing angle values for the unmanned HSLS under flat flight,and the error transformation functions are investigated to guarantee that the errors of swing angles satisfy the prescribed performance.Third,the nonlinear disturbance observers are introduced to estimate the bounded disturbances,and the robust controllers of the unmanned HSLS,the velocity and the attitude subsystems are designed based on the prescribed performance method,the output of disturbance observer and the sliding mode backstepping strategy,respectively.Fourth,the Lyapunov function is developed to prove the stability of the closed-loop system.Finally,the simulation studies are shown to demonstrate the effectiveness of the control strategy.

Disturbance Observer-Based Safe Tracking Control for Unmanned Helicopters With Partial State Constraints and Disturbances

In this paper, a disturbance observer-based safe tracking control scheme is proposed for a medium-scale unmanned helicopter with rotor flapping dynamics in the presence of partial state constraints and unknown external disturbances. A safety protection algorithm is proposed to keep the constrained states within the given safe-set. A second-order disturbance observer technique is utilized to estimate the external disturbances. It is shown that the desired tracking performance of the controlled unmanned helicopter can be achieved with the application of the backstepping approach, dynamic surface control technique, and Lyapunov method. Finally, the availability of the proposed control scheme has been shown by simulation results.

Rotosonde: Acquiring Vertical Wind Profile of a Tropical Cyclone with Small Unmanned Helicopters

Spinsonde is a chute-free vertical retardation technique specifically developed for fixed-wing unmanned aircraft to acquire accurate measurement of vertical wind speed profile for meteorological applications. Key advantages of spinsonde over the expendable chute-operated dropsondes are the ability to acquire multi-cycle measurement, efficient use of payload capacity and cost-effectiveness. This work proposes the concept of “rotosonde”, which is the spinsonde equivalent for unmanned helicopters. Computer simulations are carried out to evaluate the performance of the rotosonde and results indicate that the measured speed generally correlates with the wind speed to within ±3 km·h﹣1 even for intensities in excess of 180 km·h﹣1. The profound implication of this work is that unmanned helicopters can now be considered for important field of studies such as cyclogenesis given their reliability to operate in gusty wind conditions in remote oceans, particularly during docking and launching from carriers.

Cable-driven legged landing gear for unmanned helicopter:Prototype design,optimization and performance assessment

Unmanned helicopters equipped with adaptive landing gear will dramatically extend their application especially in dealing with challenging terrains.This study presents a novel cable-driven legged landing gear(CLG)with differential transmission for unmanned helicopters in complex landing environments.To obtain the preferred configuration of the legged mechanism,a multi-objective optimization framework for the CLG is constructed by concurrently considering terrain adaptability,landing stability and reasonable linkage of internal forces.The non-dominated sorting genetic algorithmⅡis employed to numerically acquire the optimal scale parameters that guide the mechanical design of the CLG.An unmanned helicopter prototype equipped with the devised CLG is developed with key performance assessment.Experimental results show that the devised CLG can provide energy-efficient support over uneven terrains(totally driven torque demand less than 0.1 N m)in quasi-static landing tests,and favorable terrain adaptability(posture fluctuation of the fuselage less than±1°)in unknown slope landing tests.These exhibited merits give the proposed CLG the potential to enhance the landing performance of future aircraft in extreme environments.

Robust adaptive compensation control for unmanned autonomous helicopter with input saturation and actuator faults

This paper studies a robust adaptive compensation Fault Tolerant Control(FTC)for the medium-scale Unmanned Autonomous Helicopter(UAH)in the presence of external disturbances,actuator faults and input saturation.To improve the disturbance rejection capacity of the UAH system in actuator healthy case,an adaptive control method is adopted to cope with the external disturbances and a nominal controller is proposed to stabilize the system.Meanwhile,compensation control inputs are designed to reduce the negative effects derived from actuator faults and input saturation.Based on the backstepping control and inner-outer loop control technologies,a robust adaptive FTC scheme is developed to guarantee the tracking errors convergence.Under the presented FTC controller,the uniform ultimate boundedness of all closed-loop signals is ensured via Lyapunov stability analysis.Simulation results demonstrate the effectiveness of the proposed control algorithm.

Effect of wind field below unmanned helicopter on droplet deposition distribution of aerial spraying

Wind field is one of the important factors affecting the distribution characteristics of aerial spraying droplet deposition.In order to reveal the impact mechanism of droplet deposition distribution by the wind field below agricultural unmanned helicopter rotor,in this study,the wind field distribution below uniaxial single-rotor electric unmanned helicopter rotor was measured by using a wireless wind speed sensor network measurement system for unmanned helicopter.The effects of wind field in three directions(X,Y,Z)below the rotor on droplet deposition distribution were analyzed with the condition of aerial spraying droplet deposition in rice canopy,and the regression model was established via variance and regression analyses of experiment results.The results showed that,the wind field in Y direction had a significant effect on droplet deposition in effective spray area,the wind field in Z direction had an extremely significant effect on droplet deposition in effective spray area,and the corresponding significance(sig.)values were 0.011 and 0.000.Furthermore,the wind field in Z direction had a significant effect on the penetrability and uniformity of droplet deposition in effective spray area,the corresponding sig.values were 0.025 and 0.011 respectively.The wind speed in Y direction at the edge of effective spray area had a significant effect on droplet drift,the sig.value was 0.021.In addition,the correlation coefficient R of the regression model was 0.869 between droplet deposition in effective spray area and the wind speed in Y and Z directions,and 0.915 between the uniformity of droplet deposition in effective spray area and the maximum wind speed in Z direction.The result revealed the influencing mechanism of the wind field below the rotor of uniaxial single-rotor electric unmanned helicopter on the distribution of aerial spraying droplet deposition.The results can provide guidance for the actual production application of aerial spraying to reduce liquid drift and improve the utilization rate of pesticide.

Robust control for an unmanned helicopter with constrained flapping dynamics

In this paper, a neural network based adaptive prescribed performance control scheme is proposed for the altitude and attitude tracking system of the unmanned helicopter in the presence of state and output constraints. For handling the state constraints, the barrier Lyapunov function and the saturation function are employed. And, the prescribed performance method is used to deal with the flapping angle constraints for the unmanned helicopter. It is proved that the proposed control approach can ensure that all the signals of the resulting closed-loop system are bounded, and the tracking errors are within the prescribed performance bounds for all time. The numerical simulation is given to illustrate the performance of the proposed scheme.

Downwash distribution of single-rotor unmanned agricultural helicopter on hovering state

The effective coverage and velocity of downwash are directly related to the assemblage of spraying system and spraying effect.The downwash of the unmanned agricultural helicopter(UAH)N-3 was discussed in the paper.The computational fluid dynamics(CFD)methods were used to simulate and analyze the distribution of the downwash,and a wind field measurement device had been designed to test the downwash of UAH N-3.In the tests,the UAH N-3 was raised up to 5.0 m,6.0 m and 7.0 m from the ground,“annular-radial-distribution-point”method was introduced,8 directions separated by an angle of 45°(the radial direction)with the intersection point of the main rotor shaft and the ground plane as the center,0.5 m as the step length for the longitudinal(to 2.5 m)and radial(to 4.0 m)direction to set the sample points,considering the range of the rotor rotating circular area mainly.The 5 m height results of N-3 were fully discussed to describe the downwash distribution with the longitudinal altitude increased and the radial distance increased.The standard deviations of five test altitudes for eight directions were comparatively analyzed,the results showed that the total standard deviation was not greater than 0.6 m/s.The overall relative maximum margin of error calculated from the simulation and measurement data was between 0.6 and 0.7,which verified the credibility of the simulation data.High-order polynomials were used to fitting the simulation and measurement data,the fitting results showed that the polynomial coefficient of determination R^(2) met or exceeded 0.75 when the altitudes were more than 1 m,indicating the fit equation having the reference values.When the altitudes equal or less than 0.5 m,the polynomial coefficient of determination R^(2) was smaller,ranging during 0.3 to 0.7.The study would provide some foundations for the optimization of the assemblage of spraying system on the single-rotor UAH,which would promote China aviation plant protection.

Research on a full envelop controller for an unmanned ducted-fan helicopter based on switching control theory

Rotor and ducted-fan structured unmanned helicopters have shown energy efficiency in low flight speed and hovering, due to the novel ducted-fan structure. However, its aerodynamic characteristics may change dramatically when flight at higher speed,resulting in a wide flight envelope when compared with conventional structured helicopters. Hence, the flight controller is required to schedule itself based on the flight states and guarantees the overall performances of the helicopter on the entire flight envelop. This paper presents a switching system theory based approach to design the optimal controllers over a wide region of flight envelop. In the proposed method, a family of robust controller are designed based on typical operational conditions and the controller is adjusted to guarantee the stability when the switching event is trigged. A hysteresis switching logic is utilized to ensure smooth transient between specific operational subspaces. The stability of the proposed control method was analyzed through Lyapunov theory. Nonlinear simulations based flight dynamics of the prototype helicopter have demonstrated the flexibility and efficiency of the proposed work.

System Identification Method for Small Unmanned Helicopter Based on Improved Particle Swarm Optimization

This paper proposes a novel method for Small Unmanned Helicopter （SUH） system identification based on Improved Particle Swarm Optimization （IPSO）. In the proposed IPSO, every particle will do a local search as a ＂self-check＂ before up- dating the global velocity and position. Then, the global best particle is created by a certain number of elitist particles in order to get a rapid rate of convergence during calculation. Thus both the diversity and convergence speed can be taken into considera- tion during a search. Formulated by the first principles derivation, a state-space model is built for the analysis of dynamic modes of an experimental SUH. The helicopter is equipped with an Attitude Heading Reference System （AHRS） and the corresponding data storage modules, which are used for flight test data measurement and recording. After data collection and reconstruction, the input and output data are utilized to determine the corresponding aerodynamic parameters of the state-space model. The predictive accuracy and fidelity of the identified model are verified by making a time-domain comparison between the responses from the simulation model and the responses from actual flight experiments. The results show that the characteristics of the experimental SUH can be determined accurately using the identified model and the new method can be used for SUH system identification with high efficiency and reliability.

Modeling the yaw dynamics of an unmanned helicopter through modes partition method

The main difficulties in modeling yaw dynamics of a helicopter arise from the high nonlinearities,cross-couplings and dynam-ic uncertainties of these aerocraft.This paper proposes a new identification approach for yaw dynamics modeling through modes partition method(MPM) with a concentrated search space limited by implicit human factors.Working from first princi-ples and basic aerodynamics,the nonlinear equations of motion for yaw dynamics is derived.The model is linearized and transformed into a combination of dynamic modes,whose coefficients are identified from real-flight data through distributed genetic algorithm(DGA).The effectiveness of the approach is validated in terms of the identified model which can accurately capture the dynamic characters of the helicopter.Time-and frequency-domain results clearly demonstrate the potential of MPM in modeling such complex systems.

Optimal flight parameters of unmanned helicopter for tea plantation frost protection

To determine proper flight parameters of an unmanned helicopter for tea plantation frost protection,field experiments were conducted to study the impact of flight height,speed and interval on airflow disturbance and temperature rise around tea canopies based on the analysis and simulation of frost protection with a certain helicopter.The relationship between temperature rise after flight and the above flight parameters was established through a regression orthogonal experiment,based on which the optimal combination of flight parameters was obtained through the single-factor golden section method.The results showed that wind speed around tea canopies decreased with the increase of flight height when flight speed was constant.There was a multivariate linear relationship between temperature rise and flight parameters,and the sequence of flight parameters’influence on frost protection effect was flight interval,flight height,flight speed.The optimal combination of flight parameters were flight height of 4.0 m,flight speed of 6.0 m/s and flight interval of 20 min.After the flight with the above parameters air temperature around tea canopies increased 1.6℃ when background thermal inversion strength was 3.8℃.

Modified attitude factor graph fusion method for unmanned helicopter under atmospheric disturbance

The Unmanned Aerial Helicopter(UAH)has attracted increasing attention in the military and civil areas with the unique flight performance.The significant impact on the attitude measurement performance of UAHs by the strong airflow disturbance is an essential factor threatening flight safety.To improve the attitude measurement performance of UAHs under atmospheric disturbance,an attitude fusion method over the factor graph is applied and provides the plug-and-play capability.Based on the relationship between position,velocity and attitude,a new attitude correction algorithm for the Modified Attitude Factor Graph Fusion(MAFGF)navigation method is designed and constructed through the fused position and velocity information.Finally,results of simulation and experiment are given to show the effectiveness of the proposed method.