108 research outputs found
Advanced control for miniature helicopters : modelling, design and flight test
Unmanned aerial vehicles (UAV) have been receiving unprecedented development during the past two decades. Among different types of UAVs, unmanned helicopters exhibit promising features gained from vertical-takeoff-and-landing, which make them as a versatile platform for both military and civil applications. The work reported in this thesis aims to apply advanced control techniques, in particular model predictive control (MPC), to an autonomous helicopter in order to enhance its performance and capability. First, a rapid prototyping testbed is developed to enable indoor flight testing for miniature helicopters. This testbed is able to simultaneously observe the flight state, carry out complicated algorithms and realtime control of helicopters all in a Matlab/Simulink environment, which provides a streamline process from algorithm development, simulation to flight tests. Next, the modelling and system identification for small-scale helicopters are studied. A parametric model is developed and the unknown parameters are estimated through the designed identification process. After a mathematical model of the selected helicopter is available, three MPC based control algorithms are developed focusing on different aspects in the operation of autonomous helicopters. The first algorithm is a nonlinear MPC framework. A piecewise constant scheme is used in the MPC formulation to reduce the intensive computation load. A two-level framework is suggested where the nonlinear MPC is combined with a low-level linear controller to allow its application on the systems with fast dynamics. The second algorithm solves the local path planning and the successive tracking control by using nonlinear and linear MPC, respectively. The kinematics and obstacle information are incorporated in the path planning, and the linear dynamics are used to design a flight controller. A guidance compensator dynamically links the path planner and flight controller. The third algorithm focuses on the further reduction of computational load in a MPC scheme and the trajectory tracking control in the presence of uncertainties and disturbances. An explicit nonlinear MPC is developed for helicopters to avoid online optimisation, which is then integrated with a nonlinear disturbance observer to significantly improve its robustness and disturbance attenuation. All these algorithms have been verified by flight tests for autonomous helicopters in the dedicated rapid prototyping testbed developed in this thesis.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
Disturbance rejection flight control for small fixed-wing unmanned aerial vehicles
Disturbance rejection flight control for small fixed-wing unmanned aerial vehicle
Dual Control for Exploitation and Exploration (DCEE) in Autonomous Search
This paper proposes an optimal autonomous search framework, namely Dual
Control for Exploration and Exploitation (DCEE), for a target at unknown
location in an unknown environment. Source localisation is to find sources of
atmospheric hazardous material release in a partially unknown environment. This
paper proposes a control theoretic approach to this autonomous search problem.
To cope with an unknown target location, at each step, the target location is
estimated by Bayesian inference. Then a control action is taken to minimise the
error between future robot position and the hypothesised future estimation of
the target location. The latter is generated by hypothesised measurements at
the corresponding future robot positions (due to the control action) with the
current estimation of the target location as a prior. It shows that this
approach can take into account both the error between the next robot position
and the estimate of the target location, and the uncertainty of the estimate.
This approach is further extended to the case with not only an unknown source
location, but also an unknown local environment (e.g. wind speed and
direction). Different from current information theoretic approaches, this new
control theoretic approach achieves the optimal trade-off between exploitation
and exploration in a unknown environment with an unknown target by driving the
robot moving towards estimated target location while reducing its estimation
uncertainty. This scheme is implemented using particle filtering on a mobile
robot. Simulation and experimental studies demonstrate promising performance of
the proposed approach. The relationships between the proposed approach,
informative path planning, dual control, and classic model predictive control
are discussed and compared
Optimization-based safety analysis of obstacle avoidance systems for unmanned aerial vehicles
The integration of Unmanned Aerial Vehicles (UAVs) in airspace requires new methods to certify collision avoidance systems. This paper presents a safety clearance process for obstacle avoidance systems, where worst case analysis is performed using simulation based optimization in the presence of all possible parameter variations. The clearance criterion for the UAV obstacle avoidance system is defined as the minimum distance from the aircraft to the obstacle during the collision avoidance maneuver. Local and global optimization based verification processes are developed to automatically search the worst combinations of the parameters and the worst-case distance between the UAV and an obstacle under all possible variations and uncertainties. Based on a 6 Degree of Freedom (6DoF) kinematic and dynamic model of a UAV, the path planning and collision avoidance algorithms are developed in 3D space. The artificial potential field method is chosen as a path planning and obstacle avoidance candidate technique for verification study as it is a simple and widely used method. Different optimization algorithms are applied and compared in terms of the reliability and efficiency
Autonomous search of an airborne release in urban environments using informed tree planning
The use of autonomous vehicles for chemical source localisation is a key
enabling tool for disaster response teams to safely and efficiently deal with
chemical emergencies. Whilst much work has been performed on source
localisation using autonomous systems, most previous works have assumed an open
environment or employed simplistic obstacle avoidance, separate to the
estimation procedure. In this paper, we explore the coupling of the path
planning task for both source term estimation and obstacle avoidance in a
holistic framework. The proposed system intelligently produces potential gas
sampling locations based on the current estimation of the wind field and the
local map. Then a tree search is performed to generate paths toward the
estimated source location that traverse around any obstacles and still allow
for exploration of potentially superior sampling locations. The proposed
informed tree planning algorithm is then tested against the Entrotaxis
technique in a series of high fidelity simulations. The proposed system is
found to reduce source position error far more efficiently than Entrotaxis in a
feature rich environment, whilst also exhibiting vastly more consistent and
robust results
Information based mobile sensor planning for source term estimation of a non-continuous atmospheric release
This paper presents a method to estimate the
original location and the mass of an instantaneous release of hazardous material into the atmosphere. It is formulated as an inverse problem, where concentration observations from a mobile sensor are fused with meteorological information and a Gaussian puff dispersion model to characterise the
source. Bayes’ theorem is used to estimate the parameters of the release taking into account the uncertainty that exists in the dispersion parameters and meteorological variables. An
information based reward is used to guide an unmanned aerial vehicle equipped with a chemical sensor to the expected most
informative measurement locations. Simulation results compare the performance between a single mobile sensor with various amounts of static sensors
Boustrophedon coverage path planning for UAV aerial surveys in wind
© 2017 IEEE. In the quickly developing world of precision agriculture UAV remote sensing, there is a need for a greater understanding of winds effect on fixed wing aerial surveying, as this is missing from current literature. This paper presents a method to define and calculate flight times in a Boustrophedon aerial survey coverage path in wind, for a given convex polygon, at a given sweep angle. It is shown that there exists no easy way to define a sweep angle relative to the wind that minimises flight time. This method is validated by comparing the numerical simulated path and times with a number of surveys run in the high fidelity X-Plane simulator
- …