Brenton Wilburn

Development of a Simulation Environment for Autonomous Flight Control Algorithms

A simulation environment is developed at West Virginia University to support the design and testing of algorithms for unmanned aerial vehicle (UAV) autonomous flight with advanced capabilities for abnormal conditions accommodation. A modular structure within Matlab/Simulink interfaced with FlightGear for visualization is adopted for maximum portability, flexibility, and extension capability through addition of new aircraft models and autonomous flight algorithms. Several representative UAV models are currently implemented, including subsystem failure/damage models and environmental upset conditions. Path and trajectory planning algorithms in major classes are operational as well as both conventional and adaptive trajectory tracking algorithms with significant fault-tolerant potential. The user can setup the mission configuration by defining threat zones, obstacles, and points of interest through an interactive graphical interface. The versatility and utility of the simulation environment is illustrated through example simulation results at nominal and under actuator failure conditions.

UAV Adaptive Control Laws Using Non-Linear Dynamic Inversion Augmented with an Immunity-based Mechanism

In this paper, a novel adaptive flight control system is presented, designed to handle failures and malfunctions of aircraft sub-systems as well as general environmental upset conditions. The proposed control laws use a non-linear dynamic inversion approach augmented with an artificial immune system mechanism that relies on a direct compensation inspired primarily by the biological immune system response. This work is an extension of a recently developed artificial immune system-based architecture which implements negative and positive selection algorithms for aircraft fault detection, identification, and evaluation within a hierarchical multi-self scheme. The effectiveness of the approach is demonstrated through simulation examples within the West Virginia University unmanned aerial vehicle simulation environment. The performance of the control laws is evaluated in terms of trajectory tracking errors and control activity during autonomous flight in the presence of atmospheric disturbances and actuator failures. The results show that the proposed fault tolerant adaptive control laws significantly improve the tracking performance of the vehicle at nominal conditions and under a variety of abnormal flight conditions.

Unmanned aerial vehicle trajectory tracking algorithm comparison

Purpose – The purpose of this paper is to analyze and compare the performance of several different UAV trajectory tracking algorithms in normal and abnormal flight conditions to investigate the fault‐tolerant capabilities of a novel immunity‐based adaptive mechanism.Design/methodology/approach – The evaluation of these algorithms is performed using the West Virginia University (WVU) UAV simulation environment. Three types of fixed‐parameter algorithms are considered as well as their adaptive versions obtained by adding an immunity‐based mechanism. The types of control laws investigated are: position proportional, integral, and derivative control, outer‐loop nonlinear dynamic inversion (NLDI), and extended NLDI. Actuator failures on the three channels and increased turbulence conditions are considered for several different flight paths. Specific and global performance metrics are defined based on trajectory tracking errors and control surface activity.Findings – The performance of all of the adaptive contr...

Extended Nonlinear Dynamic Inversion Control Laws for Unmanned Air Vehicles

This paper presents a novel configuration for guidance and tracking control laws for unmanned air vehicles (UAV) based on an extended nonlinear dynamic inversion (NLDI) approach. Current outer/inner loop architectures use dynamic inversion for the outer loop controller while using linear compensation-type control for inner loops. That design, although it performs well at nominal conditions, lacks robustness under certain upset flight conditions. The design proposed in this paper includes inner and outer loop control modules that both rely on the use of an NLDI control scheme. The main objective of the control laws is to minimize forward, lateral, and vertical distances with respect to a desired trajectory, and maintain stability and adequate performance in the presence of sub-system failures and upset environmental conditions. The implementation of this control laws scheme is illustrated through a simulation example using a mathematical model of the West Virginia University (WVU) YF-22 UAV. The performance of the control laws is evaluated during autonomous flight in terms of trajectory tracking errors and control activity at nominal and abnormal conditions including actuator and sensor failures and excessive turbulence. The results obtained with the WVU UAV simulation environment show that for all cases investigated the extended NLDI approach has desirable fault tolerant capabilities.

Implementation of Composite Clothoid Paths for Continuous Curvature Trajectory Generation for UAVs

This paper presents a complete methodology associated with the implementation of the 2dimensional clothoid path planner and trajectory generation algorithm for unmanned aerial vehicles (UAVs) applications. Based on previously suggested approaches for integrating the clothoid into the autonomous navigation and control architecture to produce a continuous curvature profile, the methodology presented in this paper has been extended to identify and provide a solution for the various issues encountered during a complete implementation of the clothoid planner for UAV trajectory generation. This includes a quadrant-based scheme for selecting the shortest path combination based upon the relative position and angle of the poses and a numerical solution of the nonlinear vector equations which define the ultimate path profile. The result is a ready-to-use planner that could easily be implemented on-board UAV hardware. The approach is demonstrated using the West Virginia University UAV Simulation Environment.

A modified genetic algorithm for UAV trajectory tracking control laws optimization

Purpose – The purpose of this paper is to gain trajectory-tracking controllers for autonomous aircraft are optimized using a modified evolutionary, or genetic algorithm (GA). Design/methodology/approach – The GA design utilizes real representation for the individual consisting of the collection of all controller gains subject to tuning. The initial population is generated randomly over pre-specified ranges. Alternatively, initial individuals are produced as random variations from a heuristically tuned set of gains to increase convergence time. A two-point crossover mechanism and a probabilistic mutation mechanism represent the genetic alterations performed on the population. The environment is represented by a performance index (PI) composed of a set of metrics based on tracking error and control activity in response to a commanded trajectory. Roulette-wheel selection with elitist strategy are implemented. A PI normalization scheme is also implemented to increase the speed of convergence. A flexible contr...

Implementation of a 3-Dimensional Dubins-Based UAV Path Generation Algorithm

This paper presents the implementation of a complete 3-D Dubins-based path planner, including non-coplanar and coplanar poses. Mathematical representation of a Dubins path in 3-dimensions has been extended into a complete planning methodology that provides a suitable solution to the implementation issues typically encountered for such a process. These include the numerical solution of the nonlinear implicit vector equations, as well as handling of non-coplanar and coplanar pose combinations. Since the suggested methodology breaks down for the case of coplanar poses, a complete planner is provided by diagnosing coplanar sets of poses, determining the solution within the plane containing them, and converting the 2-D solution to the 3-D environment.

Development of a Modified Voronoi Algorithm for UAV Path Planning and Obstacle Avoidance

In this paper, the development and demonstration of a modified Voronoi algorithm for unmanned aerial vehicle (UAV) path planning and obstacle avoidance is presented. This algorithm is intended to produce a flyable collision-free path through a series of obstacles/threats represented by cylindrical risk zones. A model of the West Virginia University (WVU) YF-22 research aircraft implemented within the WVU UAV simulation environment is used to demonstrate the functionality of the proposed algorithm and its effectiveness in the presence of several risk zones configurations. As compared to traditional methods, the approach is more general, coping with obstacles and risk zones of variable intensity and providing additional flexibility and better coverage of the possible solution space.

Testing of Immunity-Based Failure Detection and Identification Scheme with the NASA Generic Transport Model

In this paper, the development and testing through simulation of an integrated scheme for aircraft sub-system failure detection and identification (FDI) based on the artificial immune system (AIS) paradigm is presented. The simulation environment includes the NASA Generic Transport Model interfaced with FlightGear. A hierarchical multi-self strategy was used to develop an FDI scheme capable of handling malfunctions of actuators and aerodynamic surface damage. The performance of the FDI scheme has been evaluated in terms of false alarms and successful detection and identification over a wide flight envelope and for a large variety of abnormal conditions. For all cases investigated the performance was very good, confirming the potential of the AIS paradigm to offer a comprehensive solution to the aircraft sub-system FDI problem.

Simplified GPS model for UAV fault tolerant control laws design

Purpose – A simplified global positioning system (GPS) error model including models for a variety of abnormal operational conditions and failures is developed to provide simulation tools for the design, testing, and evaluation of autonomous flight fault tolerant control laws. The paper aims to discuss these issues. Design/methodology/approach – Analysis and experimental data are used to build simplified models for GPS position and velocity errors on all three channels. The GPS model is interfaced with West Virginia University unmanned aerial vehicles (UAV) simulation environment and its utility demonstrated through simulation for several autonomous flight scenarios including GPS abnormal operation. Findings – The proposed simplified GPS model achieves desirable levels of accuracy and realism for all components for the purpose of general UAV dynamic simulation and development of fault tolerant autonomous flight control laws. Research limitations/implications – The simplified GPS model allows investigating ...