Rotorcraft Unmanned Aerial Vehicle Research Articles

Extended state observer-based continuous finite time control for a fixed-wing vertical take-off and landing unmanned aerial vehicle

Dual system Vertical Take-Off and Landing (VTOL) fixed-wing Unmanned Aerial Vehicles (UAVs) combine the advantages of both the rotorcraft and fixed-wing UAV, characterizing horizontal and vertical flight capabilities. However, they face challenges such as aerodynamic coupling between propulsion systems, model uncertainty, and external disturbances, significantly deteriorating the tracking accuracy and robustness. This paper proposes an Extended State Observer based Continuous Finite-Time Control (ESO-CFTC) scheme to solve the attitude and trajectory tracking problem of such a VTOL fixed-wing UAV. Initially, the Nonsingular Fast Terminal Sliding Mode (NFTSM) controller guarantees the tracking errors reach a prescribed manifold in finite time with a continuous reaching law, then converge to the origin in finite time while avoiding singularities. To suppress the inherent chattering problem of the sliding mode control, an ESO technique is incorporated into the ESO-CFTC scheme, which is completely decoupled with the basic NFTSM controller. The supremum of the estimation residual set is derivated theoretically. The scheme forces the tracking errors to converge into the neighborhood of the origin in finite time without requiring prior knowledge of lumped disturbance supremum values. Finally, the numerical simulation results in a Matlab/Simulink environment demonstrate that the presented method outperforms existing benchmark in terms of disturbance estimation, tracking accuracy, convergence rate, and robustness.

Rotating 3D laser mapping system for multi-rotor drones

Accurate positional estimation is an essential prerequisite for the regular operation of an autonomous rotary-wing Unmanned Aerial Vehicles (UAV). However, the field of view (FOV) limitation problem of lidar makes it more challenging to locate the rotary-wing UAV in an unknown environment. To address rotor drones with an insufficient FOV and the observation blindness of lidar in complex environments, this paper designs a rotorcraft UAV system based on rotating 3D lidar and proposes a simultaneous localization and mapping algorithm for rotating 3D lidar. The algorithm distinguishes between planar and edge features based on the curvature value of the point cloud first. Then, to reduce the impact caused by the UAV motion and lidar rotation, messages about the Inertial Measurement Unit (IMU) and real-time rotation angles are used to compensate for these motions twice, while the IMU measurements are used for state prediction, and the error-sate iterative extended Kalman filter is used to update the residuals after matching line and surface features with sub-map. Finally, Smoother high-rate odometer data was obtained through IMU pre-integration and a first-order low-pass filter. The experimental results show that the proposed rotating lidar unit in indoor and outdoor conditions makes the rotorcraft UAV have a larger FOV, which not only improves the environmental perception capability and positional estimation accuracy of the rotorcraft but enhances the positioning reliability and flight stability of the rotorcraft UAV in complex environments.

A Novel Asymptotic Robust Tracking Control Strategy for Rotorcraft UAVs

This article proposes a novel asymptotic robust control approach for rotorcraft unmanned aerial vehicles (UAVs), which can effectively eliminate the impact of external disturbances and the model uncertainties. Different from existing works, the proposed method alleviates the assumption that disturbances should have no variations in the existing observers for uncertainties. In addition, the equilibrium point of the entire observer-controller system is asymptotically stable without the assumption of the boundness of the outer-loop signals or the time-scale separation assumption. Specifically, two observer-based estimators are designed to estimate the model uncertainty and the external disturbance for the force and torque, respectively. On this basis, a nonlinear hierarchical tracking controller is then proposed with the feedforward compensated disturbance term. Despite the nonlinear coupled dynamics and the disturbances, a generic framework for the stability analysis is proposed to yield the asymptotic stability of the equilibrium point of the entire controller-observer system. Comparative experiments are conducted to show the superior performance of the proposed approach in terms of higher tracking accuracy and stronger robustness. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Note to Practitioners</i> —Most of the existing observer-based control approaches can only govern the rotorcraft closed-loop system to be ultimately uniformly bounded. The highly coupled dynamics and mismatched uncertainties in practice make the effective asymptotic robust control of rotorcrafts very challenging. A novel robust control approach for rotorcraft UAVs is proposed to yield the asymptotic stability of the equilibrium point despite the nonlinear coupled dynamics and the disturbances. The key insight of this work to guarantee the asymptotic stability of the system is that the nominal signals (i.e., the output of the nominal auxiliary dynamics) are fed back to the controller. In addition, the attitude error signal is proved to be exponentially convergent, which can further help prove the asymptotic stability of the entire controller-observer system. Comparative experiments are conducted to show the applicability of the proposed approach.

Airflow characteristics of rotorcraft plant protection UAV operating in rice fields

Rotorcraft unmanned aerial vehicles (UAVs) cause movement of the rice crop which is an important indicator of the effectiveness of spray applications. A method of acquiring images of the effects of airflow on the spray target by video aerial photography and computer vision to process the images was examined to obtain the characteristic information in rice fields; the dimensions of the disturbed area of crop, the so-called “rice vortex”. Orthogonal experiments were designed to investigate the three factors of take-off mass, flying height and flight speed of the plant protection to assess the four indices of trailing distance, trailing stability, area and shape of the rice vortex. The results show that the influence of the three factors on the vortex trailing distance and its stability was in the order of flight speed, flight altitude and take-off mass. The effects on the vortex area and vortex shape were speed > mass > height. Analysis and discussion of the characteristics and morphological features of the airflow targets revealed that the greater the distance and longer the duration of the trailing vortex, the more easily the rice vortex was disturbed and dissipated, and the lower its stability. Changes in the shape of the rice vortex mainly occur in its length, and changes in width are smaller. The results provide a data collection method and basis for further development of flight parameter-airflow target-application effect models. The four parameters of the trailing distance, stability, vortex area, and vortex shape constitute technical parameters suitable for assessing the effects of rotorcraft plant protection UAVs operating in rice fields.

SVM-BTS Based Trajectory Identification and Prediction Method for Civil Rotorcraft UAVs

SVM-BTS Based Trajectory Identification and Prediction Method for Civil Rotorcraft UAVs

Research on Landing Stability of Four-Legged Adaptive Landing Gear for Multirotor UAVs

Rotorcraft Unmanned Aerial Vehicles (UAVs) often need to take off and land under complex working conditions. The rugged terrains may cause the UAV to tilt during takeoff and landing and even cause rollover and other accidents in severe cases. In this paper, a new four-legged landing gear of multirotor UAVs with a passive cushioning structure is designed, aiming at the landing stability requirement of rotorcraft UAVs in complex terrains. The mathematical model of the landing gear dynamics is established in MATLAB/Simulink, and the drop test simulation is carried out under different landing terrain conditions. By comparing the simulation results of the drop test multibody dynamic model in Simcenter3D dynamics software, the adaptive landing and cushioning capacity of the landing gear and the accuracy of the mathematical model are verified. Combined with the landing stability criterion and control strategy of adaptive landing gear adjustment, the landing stability of adaptive landing gear under different slope angles of landing surface and horizontal velocities is studied. The landing stability boundary under different combinations of these two parameters is found.

A data-driven fault detection approach for Modular Reconfigurable Flying Array based on the Improved Deep Forest

The Modular Reconfigurable Flying Array, as a kind of special modular rotorcraft UAV, can change its topology configurations fitting for different tasks and varying work scenarios. However, strongly nonlinear characteristics and limited uncertainties of Modular Reconfigurable Flying Array make its sensor faults happen easily and fail to be detected with higher accuracy. In the light of the potential serious losses of its sensors faults, it is valuable and challenging to detect the sensor faults of the aircraft accurately and effectively. Therefore, a data-driven multivariate regression approach based on the Improved Deep Forest is proposed to fulfill sensor faults detection. Firstly, the Deep Forest algorithm is improved by adding the enhanced cascade layer structure and redesigning the inter-layer loss function to pursuit better prediction accuracy. And then, the Improved Deep Forest algorithm is used to establish a multivariate regression model and obtains an estimation of the monitored parameter by learning the historical flight data. Finally, the residual between the actual flight data and the estimated value is calculated to achieve sensor faults detection by comparing with the statistical threshold. What is more, the proposed faults detection approach is evaluated with two real flight datasets collected from the self-made rotorcraft and the experimental results show that the average ACC and AUC are increased by 3% and 2.3% respectively compared with the approach based on the standard Deep Forest.

Rotorcraft aerial vehicle’s contact-based landing and vision-based localization research

AbstractA novel concept—the contact-based landing on a mobile platform—is proposed in this paper. An adaptive backstepping controller is designed to deal with the unknown disturbances in the interactive process, and the contact-based landing mission is implemented under the hybrid force/motion control framework. A rotorcraft aerial vehicle system and a ground mobile platform are designed to conduct flight experiments, evaluating the feasibility of the proposed landing scheme and control strategy. To the best of our knowledge, this is the first time a rotorcraft unmanned aerial vehicle has been implemented to conduct a contact-based landing. To improve system autonomy in future applications, vision-based recognition and localization methods are studied, contributing to the detection of a partially occluded cooperative object or at a close range. The proposed recognition algorithms are tested on a ground platform and evaluated in several simulated scenarios, indicating the algorithm’s effectiveness.

Online environmentally adaptive trajectory planning for rotorcraft unmanned aerial vehicles

PurposeThis paper aims to propose an environmentally adaptive trajectory planning system considering the dynamic characteristics of unmanned aerial vehicles (UAVs) and the distance between obstacles and the UAV. The system generates a smooth and safe flight trajectory online.Design/methodology/approachFirst, the hybrid A* search method considering the dynamic characteristics of the quadrotor is used to find the collision-free initial trajectory. Then, environmentally adaptive velocity cost is designed for environment-adaptive trajectory optimization using environmental gradient data. The proposed method adaptively adjusts the autonomous flight speed of the UAV. Finally, the initial trajectory is applied to the multi-layered optimization framework to make it smooth and dynamically viable.FindingsThe feasibility of the designed system is validated by online flight experiments, which are in unknown, complex situations.Practical implicationsThe proposed trajectory planning system is integrated into a vision-based quadrotor platform. It is easily implementable onboard and computationally efficient.Originality/valueA hybrid A* path searching method is proposed to generate feasible motion primitives by dispersing the input space uniformly. The proposed method considers the control input of the UAV and the search time as the heuristic cost. Therefore, the proposed method can provide an initial path with the minimum flying time and energy loss that benefits trajectory optimization. The environmentally adaptive velocity cost is proposed to adaptively adjust the flight speed of the UAV using the distance between obstacles and the UAV. Furthermore, a multi-layered environmentally adaptive trajectory optimization framework is proposed to generate a smooth and safe trajectory.

Hostile UAV Detection and Neutralization Using a UAV System

The technologies of Unmanned Aerial Vehicles (UAVs) have seen extremely rapid development in recent years. UAV technologies are being developed much faster than the means of their legislation. There have been many means of UAV detection and neutralization proposed in recent research; nonetheless, all of them have serious disadvantages. The essential problems in the detection of UAVs is the small size of UAVs, weak radio wave reflection, weak radio signal, and sound emitting. The main problem of conventional UAV countermeasures is the short detection and neutralization range. The authors propose the concept of the airborne counter-UAV platform (consisting of several vehicles) with radar. We use a low-cost marine radar with a high resolution 2 m wide antenna, embedded into the wing. Radar scanning is implemented by changing the heading of the aircraft. For the countermeasures, the authors suggest using a small rotorcraft UAV carried by a bigger fixed-wing one. A mathematical model that allows the calculation of the coordinates of the detected drone while scanning the environment in a moving UAV with radar was created. Furthermore, the results of integrated radar performance with a detected drone and the results of successful neutralization experiments of different UAVs were achieved.

A New Estimation Method for Rotor Size of UAV Based on Peak Time-Shift Effect in Micro-Doppler Lidar

The aim of this study was to solve the problem that the existing identification parameters of rotor unmanned aerial vehicles (UAVs) are few and limited by the detection mode, and an identification method for estimating the rotor blade width based on the peak time-shift effect is proposed for the first time. Taking the width of the rotor blade as the parameter to identify the rotor of UAVs, the time-shift effect and its relationship with rotor blade width are verified by theoretical analysis and simulation. The proposed time-shift method has the characteristics of high-precision extraction of rotor width, and its effectiveness is verified by simulation and experiments. The aspect ratio of the rotor is accurately extracted based on the proposed time-shift method under the condition of an unknown pitch angle. Simulation results show that the estimation accuracy of the width and aspect ratio is up to 98 and 98.4%, respectively. The experimental results show that the relative errors of the width and aspect ratio are less than 7 and 4%, respectively. This study provides the theoretical basis and technical support for the high-accuracy identification of rotorcraft UAVs.

In-Ground-Effect Model Based Adaptive Altitude Control of Rotorcraft Unmanned Aerial Vehicles

In-Ground-Effect Model Based Adaptive Altitude Control of Rotorcraft Unmanned Aerial Vehicles

Research on Cooperative Search Trajectory Planning for Rotorcraft UAVs Based on Scrolling Planning Algorithm

Abstract The UAV trajectory planning algorithm for scrolling planning is proposed for the objective of multi-UAVs searching for multiple targets in an uncertain environment. Information about the unknown environment is described using infographic, while for the huge computational effort in multi-UAVs scrolling planning, an improved genetic algorithm is used to solve the optimal solution for the UAV population. Simulation results show that the scrolling planning algorithm proposed in this paper can achieve a better search for the target in the uncertain region, and the algorithm framework is reasonable and feasible with high planning efficiency, which can be used for the cooperative search task of multi-UAVs in the uncertain area.

Optimizing scheme for tension re-allocation of two collaborative RUAVs: An experimental study

The collaborative aerial transportation (CAT) of multiple rotorcraft unmanned aerial vehicles (RUAVs) collaboratively carrying a cable-suspended payload provides a feasible way to ship a heavy load by multiple small-sized RUAVs. Usually, the formation of the RUAVs for CAT has to be pre-designed according to the tension assignment on each RUAV, and maintained via control during flight. However, in case the tension assignment needs to be adjusted during flight, the formation of the RUAVs needs to be re-allocated accordingly. This situation may occur due to the changing circumstances, such as fuel condition, maximum payload capability, payload re-assignment, etc. In this paper, we propose an optimizing scheme for the re-allocation of two-RUAV CAT (TR-CAT) system to meet the commanded tension adjustment. A novel optimization structure is formulated with respect to the adjustable tension requirement, while multiple constraints, including task, safety, as well as dynamic constraints, are provided for the optimization formulation. The differential flatness of the TR-CAT system is also analyzed and proved. Besides the simulation validations, indoor and outdoor experiments were conducted on a real CAT system to demonstrate the efficacy of the proposed scheme.

Image-Based Visual Servoing of Rotorcrafts to Planar Visual Targets of Arbitrary Orientation

This letter for the first time extends the virtual camera image-based visual servoing (IBVS) scheme to enable an underactuated rotorcraft UAV to regulate its translational motion and heading relative to a planar visual target of arbitrary orientation. The conversion from real camera images to virtual camera images of visual targets are proposed based on a set of rotation matrices. Hence, image moment features can be reused due to the simplicity and decoupled structure of the interaction matrix, and satisfactory 3D Cartesian trajectory of UAVs. In the design of the IBVS control law, the external disturbance and model uncertainties are estimated by an integral-based filter. In addition, to enable tracking of a moving visual target, a velocity estimator is developed. The global asymptotic stability of the error dynamics is proven. Both of the simulation and experimental results of tracking of a tilted moving planar target are provided to show the efficacy of the proposed IBVS scheme.

Aerodynamic Performance of Propellers for Multirotor Unmanned Aerial Vehicles: Measurement, Analysis, and Experiment

Analyzing the propeller aerodynamic performance is of vital importance for research and improvement of unmanned aerial vehicles. This paper presents the design requirements for a propeller for rotorcraft unmanned aerial vehicles and an analysis of a model for calculating propeller aerodynamic performance. Based on blade element momentum theory, the aerodynamic force of a blade element is analyzed and used. The symmetric airfoil NACA 0012 is used as an example to verify the validity of the model. An experimental system for propeller aerodynamic performance is designed and built to test the aerodynamic performance of six types of the propeller from a single manufacturer (APC). Data-processing software is also developed to draw curves and perform single-step calculations of three propellers’ parameters: airfoil resistance power, induced velocity, and efficiency. The results of the experiment indicate that both the thrust and torque of the propeller increase with rotational speed, propeller diameter, and propeller pitch. The research is of great significance to select more suitable propellers for unmanned aerial vehicles and the further improvement of the performance of unmanned aerial vehicles’ dynamical system.

군용 소형 회전익무인기 감항인증기준에 대한 연구

In modern society, the use of small rotary-wing unmanned aerial vehicles such as drones is increasing. As the military considers tactics using drones, demand for drones is increasing. However, there is still no airworthiness certification standard for drones for safety. In this paper, we proposed airworthiness certification standards for small rotorcraft unmanned aerial vehicles based on CS-LURS in Europe and STANG-4703, 4738 (draft) of the North Atlantic Treaty Organization. In addition, airworthiness certification standards have been strengthened through the case of unmanned aerial vehicle accidents in operation by the Korean military. The airworthiness certification standards for small rotary-wing unmanned aerial vehicles will be supplemented through a demonstration project.

Ground effect on rotorcraft unmanned aerial vehicles: a review

This article aims at collecting and discussing the results reached by the research community regarding the study of the ground effect on small rotorcraft unmanned aerial vehicles, especially from the modeling and control point of view. Rotorcraft performance is affected by the presence of the ground or any other boundary that alters the flow into the rotors. Specifically, the ground effect can induce perturbations in the flight stability, when operating near the ground. For a rotorcraft, an accident is likely to happen when the vehicle leaves or enters the ground effect region, which may cause crashes and property damages. Today, the use of unmanned aerial vehicles has grown widespread, which raises safety concerns when they are flying at very low altitudes and near the ground. Consequently, studying the influence of the ground over rotorcrafts is of paramount importance for general safety. Also, these investigations can be used to design systems of guidance, navigation, and control. In this review, we break down the most relevant works to date. We discuss aspects related to modeling, control, and application of the ground effect for small-scale multirotors, as well as other aerodynamic proximity effects, such as the ceiling and wall effects. We conclude by mentioning potential avenues of research when studying the ground effect from the point of view of the robotics and artificial intelligence fields.

Winter atmospheric boundary layer observations over sea ice in the coastal zone of the Bay of Bothnia (Baltic Sea)

Abstract. The Hailuoto Atmospheric Observations over Sea ice (HAOS) campaign took place at the westernmost point of Hailuoto island (Finland) between 27 February and 2 March 2020. The aim of the campaign was to obtain atmospheric boundary layer (ABL) observations over seasonal sea ice in the Bay of Bothnia. Throughout 4 d, both fixed-wing and quad-propeller rotorcraft unmanned aerial vehicles (UAVs) were deployed over the sea ice to measure the properties of the lower ABL and to obtain accompanying high-resolution aerial photographs of the underlying ice surface. Additionally, a 3D sonic anemometer, an automatic weather station, and a Halo Doppler lidar were installed on the shore to collect meteorological observations. During the UAV flights, measurements of temperature, relative humidity, and atmospheric pressure were collected at four different altitudes between 25 and 100 m over an area of ∼ 1.5 km2 of sea ice, located 1.1–1.3 km off the shore of Hailuoto's Marjaniemi pier, together with orthomosaic maps of the ice surface below. Altogether the obtained dataset consists of 27 meteorological flights, four photogrammetry missions, and continuous measurements of atmospheric properties from ground-based stations located at the coast. The acquired observations have been quality controlled and post-processed and are available through the PANGAEA repository (https://doi.org/10.1594/PANGAEA.918823, Wenta et al., 2020). The obtained dataset provides us with valuable information about ABL properties over thin, newly formed sea ice cover and about physical processes at the interface of sea ice and atmosphere which may be used for the validation and further improvement of numerical weather prediction (NWP) models.

Polygonal plot scaling method for plant protection of rotor-like UAVs

In this paper, a universal polygonal block boundary method is proposed to solve the problem of integral shrinkage and integral expansion of the boundary of the operation area when facing complex operation area boundary and obstacle boundary in the plant protection process of rotor-wing unmanned aerial vehicles (UAVs). When rotorcraft UAVs carry out plant protection operation, they cannot spray more or miss spraying, and they cannot have any collision with obstacles. Based on the method proposed in this paper, the boundary of the operation area and the boundary of the obstacles can be shrunk and expanded as a whole, so as to improve the safety factor of UAVs and the operation accuracy and efficiency.