Airborne collision scenario flight tests: impact of angle measurement errors on reactive vision-based avoidance control

The future emergence of many types of airborne vehicles and unpiloted aircraft in the national airspace means collision avoidance is of primary concern in an uncooperative airspace environment. The ability to replicate a pilot’s see and avoid capability using cameras coupled with vision based avoidance control is an important part of an overall collision avoidance strategy. But unfortunately without range collision avoidance has no direct way to guarantee a level of safety. Collision scenario flight tests with two aircraft and a monocular camera threat detection and tracking system were used to study the accuracy of image-derived angle measurements. The effect of image-derived angle errors on reactive vision-based avoidance performance was then studied by simulation. The results show that whilst large angle measurement errors can significantly affect minimum ranging characteristics across a variety of initial conditions and closing speeds, the minimum range is always bounded and a collision never occurs

An evolutionary computation approach to three- dimensional path planning for unmanned aerial vehicles with tactical and kinematic constraints

This paper presents a novel evolutionary computation approach to three-dimensional path planning for unmanned aerial vehicles (UAVs) with tactical and kinematic constraints. A genetic algorithm (GA) is modified and extended for path planning. Two GAs are seeded at the initial and final positions with a common objective to minimise their distance apart under given UAV constraints. This is accomplished by the synchronous optimisation of subsequent control vectors. The proposed evolutionary computation approach is called synchronous genetic algorithm (SGA). The sequence of control vectors generated by the SGA constitutes to a near-optimal path plan. The resulting path plan exhibits no discontinuity when transitioning from curve to straight trajectories. Experiments and results show that the paths generated by the SGA are within 2% of the optimal solution. Such a path planner when implemented on a hardware accelerator, such as field programmable gate array chips, can be used in the UAV as on-board replanner, as well as in ground station systems for assisting in high precision planning and modelling of mission scenarios

Minimum-time trajectory generation for quadrotors in constrained environments

In this paper, we present a novel strategy to compute minimum-time trajectories for quadrotors in constrained environments. In particular, we consider the motion in a given flying region with obstacles and take into account the physical limitations of the vehicle. Instead of approaching the optimization problem in its standard time-parameterized formulation, the proposed strategy is based on an appealing re-formulation. Transverse coordinates, expressing the distance from a frame path, are used to parameterise the vehicle position and a spatial parameter is used as independent variable. This re-formulation allows us to (i) obtain a fixed horizon problem and (ii) easily formulate (fairly complex) position constraints. The effectiveness of the proposed strategy is proven by numerical computations on two different illustrative scenarios. Moreover, the optimal trajectory generated in the second scenario is experimentally executed with a real nano-quadrotor in order to show its feasibility.Comment: arXiv admin note: text overlap with arXiv:1702.0427

AI-based Navigation and Communication Control for a Team of UAVs with Reconfigurable Intelligent Surfaces Supporting Mobile Internet of Vehicles

Unmanned aerial vehicles (UAVs) are employed in wireless communication networks (WCNs) to improve coverage and quality. The applications of UAVs become problematic in the millimeters wave fifth-generation (5G) and beyond in the optical 6G WCNs because of two reasons: 1) higher path loss which means UAVs should fly at lower altitudes to be closer to the user's equipment; 2) complexities associated with a multi-input multi-output antenna to be incorporated in the UAV as an active aerial base station. We propose equipping UAVs with a (passive) reconfigurable intelligent surface (RIS) to resolve the issues with UAV-enabled wireless communication in 5G/6G. In this paper, the trajectory planning of the RIS-equipped UAV (RISeUAV) that renders aerial LoS service (ALoSS) is elaborated. The ALoSS facilitates vehicle-to-vehicle (V2V) and vehicle-to-everything (V2X) communication in obstructed dense urban environments for Internet-of-vehicles. (IoVs). To handle the nonconvexity and computation hardness of the optimization problem we use AI-based deep reinforcement learning to effectively solve the optimality and time complexity issues. Numerical simulation results assess the efficacy of the proposed method

Adaptive nonlinear guidance law using neural networks applied to a quadrotor

© 2019IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.The NonLinear Guidance Law (NLGL) is a geometric algorithm commonly employed to solve the path following problem on different unmanned vehicles. NLGL is simple (does no depend on the model of the vehicle), effective and has only one tunning parameter. Its control parameter (L) depends on various factors, such as the velocity of the vehicle, the shape of the reference path and the dynamics of the vehicle. This paper analyses the effect of parameter L on the performance of NLGL when it is applied to a quadrotor vehicle. An Adaptive NLGL, which includes a velocity reduction term, is proposed. Stability proofs are given. Simulation results show that the proposed algorithm enhances the performance of the standard NLGL. Furthermore, it has no parameters to tune.Peer ReviewedPostprint (author's final draft

Planning Visual Inspection Tours for a 3D Dubins Airplane Model in an Urban Environment

This paper investigates the problem of planning a minimum-length tour for a three-dimensional Dubins airplane model to visually inspect a series of targets located on the ground or exterior surface of objects in an urban environment. Objects are 2.5D extruded polygons representing buildings or other structures. A visibility volume defines the set of admissible (occlusion-free) viewing locations for each target that satisfy feasible airspace and imaging constraints. The Dubins traveling salesperson problem with neighborhoods (DTSPN) is extended to three dimensions with visibility volumes that are approximated by triangular meshes. Four sampling algorithms are proposed for sampling vehicle configurations within each visibility volume to define vertices of the underlying DTSPN. Additionally, a heuristic approach is proposed to improve computation time by approximating edge costs of the 3D Dubins airplane with a lower bound that is used to solve for a sequence of viewing locations. The viewing locations are then assigned pitch and heading angles based on their relative geometry. The proposed sampling methods and heuristics are compared through a Monte-Carlo experiment that simulates view planning tours over a realistic urban environment.Comment: 18 pages, 10 figures, Presented at 2023 SciTech Intelligent Systems in Guidance Navigation and Control conferenc

A review of optimization techniques in spacecraft flight trajectory design

For most atmospheric or exo-atmospheric spacecraft flight scenarios, a well-designed trajectory is usually a key for stable flight and for improved guidance and control of the vehicle. Although extensive research work has been carried out on the design of spacecraft trajectories for different mission profiles and many effective tools were successfully developed for optimizing the flight path, it is only in the recent five years that there has been a growing interest in planning the flight trajectories with the consideration of multiple mission objectives and various model errors/uncertainties. It is worth noting that in many practical spacecraft guidance, navigation and control systems, multiple performance indices and different types of uncertainties must frequently be considered during the path planning phase. As a result, these requirements bring the development of multi-objective spacecraft trajectory optimization methods as well as stochastic spacecraft trajectory optimization algorithms. This paper aims to broadly review the state-of-the-art development in numerical multi-objective trajectory optimization algorithms and stochastic trajectory planning techniques for spacecraft flight operations. A brief description of the mathematical formulation of the problem is firstly introduced. Following that, various optimization methods that can be effective for solving spacecraft trajectory planning problems are reviewed, including the gradient-based methods, the convexification-based methods, and the evolutionary/metaheuristic methods. The multi-objective spacecraft trajectory optimization formulation, together with different class of multi-objective optimization algorithms, is then overviewed. The key features such as the advantages and disadvantages of these recently-developed multi-objective techniques are summarised. Moreover, attentions are given to extend the original deterministic problem to a stochastic version. Some robust optimization strategies are also outlined to deal with the stochastic trajectory planning formulation. In addition, a special focus will be given on the recent applications of the optimized trajectory. Finally, some conclusions are drawn and future research on the development of multi-objective and stochastic trajectory optimization techniques is discussed

Fast generation of chance-constrained flight trajectory for unmanned vehicles

In this work, a fast chance-constrained trajectory generation strategy incorporating convex optimization and convex approximation of chance constraints is designed so as to solve the unmanned vehicle path planning problem. A pathlength- optimal unmanned vehicle trajectory optimization model is constructed with the consideration of the pitch angle constraint, the curvature radius constraint, the probabilistic control actuation constraint, and the probabilistic collision avoidance constraint. Subsequently, convexification technique is introduced to convert the nonlinear problem formulation into a convex form. To deal with the probabilistic constraints in the optimization model, convex approximation techniques are introduced such that the probabilistic constraints are replaced by deterministic ones, while simultaneously preserving the convexity of the optimization model. Numerical results, obtained from a number of case studies, validate the effectiveness and reliability of the proposed approach. A number of comparative studies were also performed. The results confirm that the proposed design is able to produce more optimal flight paths and achieve enhanced computational performance than other chance-constrained optimization approaches investigated in this paper

대기바람을 고려한 비행체의 수직-접선벡터 가중치 기반 경로추종 제어

학위논문(박사) -- 서울대학교대학원 : 공과대학 기계항공공학부, 2023. 2. 김유단.In this dissertation, a versatile path-following control method for aerial vehicles that can effectively deal with an ambient wind shear is proposed. Novel equations of motion for aerial vehicles considering the effect of continuously differentiable time-varying ambient winds are derived, and a path-following control law in a three-dimensional Euclidean space, called the Weighted-Perpendicular-Tangent-based Path-Following Control (WPTPFC), that makes the vehicle asymptotically follow a given sufficiently smooth desired path is developed. The proposed equations of motion consist of the aerodynamic angles and the inertial flight path angles as state variables. The equations cover a large range of ambient wind speeds without any approximation or linearization. Two unique angles of sequential rotations called the path-relative wind angles are proposed to parametrize the difference between the air-relative velocity and the inertial velocity caused by ambient wind terms. The conventional aerodynamic roll angle is not defined in a wind condition; thus, a compatible modified version is also proposed. The resulting state equations are structured to form a cascade system, which helps designers interpret the physical and geometrical meaning of individual subsystems and efficiently design a corresponding feedback control law. The model particularly fits motion control problems such as trajectory tracking or path-following control of fixed-wing-type aerial vehicles in the presence of time-varying ambient wind. The properties and potential of the proposed formulation are discussed in depth by focusing on the meaning and use of each proposed angle and the wind estimation techniques. In the design of WPTPFC, a reference point called the perpendicular foot is proposed for path-following control as an alternative to the closest point. Though the notion of perpendicular foot suffers from a similar singularity issue that the closest point has, it guarantees the continuity of solution with respect to the motion of the vehicle provided that the point does not reach some geometrical region, and it is shown that the region can be effectively avoided by the proposed singularity avoidance strategies. A Velocity Direction Input (VDI) and Steering Input (SI), which are common input configurations for mobile robots with nonzero moving speed, are considered the inputs of the control system. In particular, a special barrier function-based method called the Barrier Weighting Method (BWM) is developed to fully utilize the characteristics of the backstepping control for a certain class of constrained systems. Using the proposed technique, it is demonstrated that the velocity direction control law can be efficiently reused for the steering input control design preserving the singularity avoidance capability. Finally, the flight control system and WPTPFC are unified based on the time-scale decomposition technique. The compatibility between the methods is investigated, and appropriate coordinate transformations and control allocation methods are developed. Numerical simulations are performed to demonstrate the effectiveness of the proposed control scheme.본 논문에서는 대기바람이 존재하는 환경에서 운용되는 비행체에 적용할 수 있는 경로추종 기법을 제안하였다. 연속 미분가능한 대기바람 속도를 고려하는 비행체 운동방정식을 유도하고, 이를 기반으로 한 비행제어 법칙을 설계하였다. 또한, 비행체가 충분히 매끈한 경로를 추종하도록 하는 수직-접선벡터 가중치 기반 경로추종 제어를 개발하고 비행제어 법칙과 통합하였다. 본 논문에서 제안한 운동방정식은 공력각과 관성 경로각을 상태변수로 가진다. 두 개의 경로대비 바람각(path-relative wind angle)을 정의하여 대기바람에 의해 발생하는 대기속도와 대지속도 벡터 성분의 차이를 매개화 하였다. 대기바람이 존재하는 상황에서 공력롤각을 정의하여 대기바람이 존재하는 환경에서도 균형선회가 수월하게 하였다. 제안한 운동방정식은 계단식 구조를 가지도록 정식화하여 제어법칙을 설계하는 데 도움이 되도록 하였다. 또한, 제안한 모델은 바람이 존재하는 상황에서도 관성 경로각의 거동을 효율적으로 표현하므로 경로추종 제어법칙을 설계하기에 유리하다. 한편, 수직-접선벡터 가중치 기반 경로추종 제어는 경로에 대한 수선의 발(perpendicular foot)을 기준점으로 채택하여, 기존 기법에서 널리 쓰이는 최단점이 가지는 특이점, 불연속성 등의 문제들을 보완하였다. 시스템 입력으로는 속도방향 벡터(velocity direction)와 조향 벡터(steering)을 고려하였다. 특히, 장벽가중치 기법(barrier weighting method)을 적용하여 조향벡터 입력 시스템에 백스텝핑 기법을 도입할 때 기준점 운동방정식이 가지는 특이점을 효과적으로 회피하도록 하였다. 위의 연구내용은 시간비례 분해기법(time-scale decomposition)을 적용하여 비행제어 법칙과 경로추종 제어기법을 통합하였다. 개별적으로 설계된 비행제어법칙 간의 호환성을 검토하고, 적절한 변환 및 조종할당 기법을 개발하였다. 본 논문에서 제안한 기법의 성능을 평가하기 위해 수치 시뮬레이션을 수행하였다.1 Introduction 1 1.1 Motivation and Objective 1 1.1.1 Effects of Wind Shear on Aerial Vehicles 1 1.1.2 Path-Following Control for Aerial Vehicles 3 1.1.3 Unification of Flight Controller and PFC 4 1.1.4 Study Objective 5 1.2 Literature Survey 6 1.2.1 Flight in Ambient Wind Shear 6 1.2.2 PFC for Aerial Vehicles 7 1.3 Research Contribution 9 1.3.1 Flight Dynamics 9 1.3.2 Weighted-Perpendicular-Tangent-based PFC 10 1.3.3 Summary 11 1.4 Dissertation Organization 13 2 Flight Dynamics Considering Time-Varying Ambient Wind 14 2.1 Derivation of Equations of Motion 15 2.1.1 External Force and Moment 20 2.1.2 Angular Velocity Dynamics 22 2.1.3 Aerodynamic Angle Dynamics 22 2.1.4 Flight Path Angle Dynamics 25 2.1.5 Airspeed Dynamics 26 2.1.6 Ground Speed Dynamics 27 2.1.7 Aerodynamic Roll Angle Dynamics 28 2.1.8 Overall Dynamics 36 2.2 Discussions 39 2.2.1 Aerodynamic Roll Angle 39 2.2.2 Path-Relative Wind Angles 40 2.2.3 Compensation of Unsteady Winds 40 2.2.4 Local Wind Field 42 2.2.5 Wind Estimation 43 3 Design of Flight Control System 49 3.1 State Representation 50 3.2 Cascade System Approximation 51 3.3 Angular Velocity Tracking Control 52 3.4 Aerodynamic Angle Tracking Control 54 3.5 Flight-path Angle Tracking Control 56 3.6 Numerical Examples 58 3.6.1 Example 3.1 59 3.6.2 Example 3.2 60 3.6.3 Example 3.3 65 4 Lyapunov Barrier Weighting Method 67 4.1 Notation 71 4.2 Mathematical Preliminary 72 4.3 Barrier Method 78 4.4 Lyapunov Barrier Weighting Method 83 5 Weighted-Perpendicular-Tangent-based Path-Following Control 90 5.1 Notation 91 5.2 Path-Following Problem 92 5.2.1 Perpendicular Foot 92 5.2.2 Vehicle Dynamics 94 5.2.3 Problem Statement 96 5.2.4 Path and Initial Position 99 5.2.5 Closest Point and Perpendicular Foot 99 5.3 Velocity Direction Control 104 5.3.1 Dynamics 104 5.3.2 Controller Design 105 5.3.3 Direct Approaching 113 5.3.4 Singularity Avoidance 114 5.3.5 Design Example 116 5.4 Steering Control 118 5.4.1 Dynamics 118 5.4.2 Controller Design 120 5.4.3 Singularity Avoidance 122 5.4.4 Design Example 125 5.5 Numerical Simulations 127 5.5.1 Rotation weighting function 127 5.5.2 Singularity Avoidance 130 5.5.3 Various Initial Position and Velocity 133 6 Unification of Flight Control System and WPTPFC 137 6.1 Parameter Normalization 138 6.2 WPTPFC: Velocity Direction Control 138 6.2.1 FPA Command Filter 140 6.3 WPTPFC: Steering Control 144 6.3.1 Normal Acceleration Control Allocation 146 6.3.2 Low-pass Filter for VDI Control 146 6.4 Numerical Simulation 147 6.4.1 Scenario 1: straight line tracking 147 6.4.2 Scenario 2: descending vertical helix tracking 153 6.4.3 Various simulation results 156 7 Conclusion 165 7.1 Concluding Remarks 165 7.2 Future Research 166 Appendices 166 A Flight Dynamics 167 A.1 Components of the Equations of Motion 167 A.2 Angle Conversion 169 B WPTPFC 172 B.1 Foot Dynamics 172 B.1.1 Curve Parametrization 172 B.1.2 Robust Foot Control 173 초록 184박

Smooth path planning with Pythagorean-hodoghraph spline curves geometric design and motion control

This thesis addresses two significative problems regarding autonomous systems, namely path and trajectory planning. Path planning deals with finding a suitable path from a start to a goal position by exploiting a given representation of the environment. Trajectory planning schemes govern the motion along the path by generating appropriate reference (path) points. We propose a two-step approach for the construction of planar smooth collision-free navigation paths. Obstacle avoidance techniques that rely on classical data structures are initially considered for the identification of piecewise linear paths that do not intersect with the obstacles of a given scenario. In the second step of the scheme we rely on spline interpolation algorithms with tension parameters to provide a smooth planar control strategy. In particular, we consider Pythagorean–hodograph (PH) curves, since they provide an exact computation of fundamental geometric quantities. The vertices of the previously produced piecewise linear paths are interpolated by using a G1 or G2 interpolation scheme with tension based on PH splines. In both cases, a strategy based on the asymptotic analysis of the interpolation scheme is developed in order to get an automatic selection of the tension parameters. To completely describe the motion along the path we present a configurable trajectory planning strategy for the offline definition of time-dependent C2 piece-wise quintic feedrates. When PH spline curves are considered, the corresponding accurate and efficient CNC interpolator algorithms can be exploited