365 research outputs found
Cooperation of unmanned systems for agricultural applications: A theoretical framework
Agriculture 4.0 comprises a set of technologies that combines sensors, information systems, enhanced machinery, and informed management with the objective of optimising production by accounting for variabilities and uncertainties within agricultural systems. Autonomous ground and aerial vehicles can lead to favourable improvements in management by performing in-field tasks in a time-effective way. In particular, greater benefits can be achieved by allowing cooperation and collaborative action among unmanned vehicles, both aerial and ground, to perform in-field operations in precise and time-effective ways. In this work, the preliminary and crucial step of analysing and understanding the technical and methodological challenges concerning the main problems involved is performed. An overview of the agricultural scenarios that can benefit from using collaborative machines and the corresponding cooperative schemes typically adopted in this framework are presented. A collection of kinematic and dynamic models for different categories of autonomous aerial and ground vehicles is provided, which represents a crucial step in understanding the vehicles behaviour when full autonomy is desired. Last, a collection of the state-of-the-art technologies for the autonomous guidance of drones is provided, summarising their peculiar characteristics, and highlighting their advantages and shortcomings with a specific focus on the Agriculture 4.0 framework. A companion paper reports the application of some of these techniques in a complete case study in sloped vineyards, applying the proposed multi-phase collaborative scheme introduced here
Tube-based Robust MPC Processor-In-the-Loop Validation for Fixed-Wing UAVs
Real systems, as Unmanned Aerial Vehicles (UAVs),
are usually subject to environmental disturbances, which could
compromise the mission accomplishment. For this reason, the
main idea proposed in this research is the design of a robust
controller, as autopilot control system candidate for a fixedwing
UAV. In detail, the inner loop of the autopilot system
is designed with a tube-based robust model predictive control
(TRMPC) scheme, able to handle additive noise. Moreover, the
navigation outer loop is regulated by a proportional-integralderivative
controller. The proposed TRMPC is composed of two
parts: (i) a linear nominal dynamics, evaluated online with an
optimization problem, and (ii) a linear error dynamics, which
includes a feedback gain matrix, evaluated offline. The key
aspects of the proposed methodology are: (i) offline evaluation
of the feedback gain matrix, and (ii) robustness to random,
bounded disturbances. Moreover, a path-following algorithm is
designated for the guidance task, which provides the reference
heading angle as input to the control algorithm. Software-in-theloop
and processor-in-the-loop simulations have been performed
to validate the proposed approach. The obtained performance
have been evaluated in terms of tracking capabilities and
computational load, assessing the real-time implementability
compliance with the XMOS development board, selected as
continuation of previous works
A Survey of path following control strategies for UAVs focused on quadrotors
The trajectory control problem, defined as making a vehicle follow a pre-established path in space, can be solved by means of trajectory tracking or path following. In the trajectory tracking problem a timed reference position is tracked. The path following approach removes any time dependence of the problem, resulting in many advantages on the control performance and design. An exhaustive review of path following algorithms applied to quadrotor vehicles has been carried out, the most relevant are studied in this paper. Then, four of these algorithms have been implemented and compared in a quadrotor simulation platform: Backstepping and Feedback Linearisation control-oriented algorithms and NLGL and Carrot-Chasing geometric algorithms.Peer ReviewedPostprint (author's final draft
A review of path following control strategies for autonomous robotic vehicles: theory, simulations, and experiments
This article presents an in-depth review of the topic of path following for
autonomous robotic vehicles, with a specific focus on vehicle motion in two
dimensional space (2D). From a control system standpoint, path following can be
formulated as the problem of stabilizing a path following error system that
describes the dynamics of position and possibly orientation errors of a vehicle
with respect to a path, with the errors defined in an appropriate reference
frame. In spite of the large variety of path following methods described in the
literature we show that, in principle, most of them can be categorized in two
groups: stabilization of the path following error system expressed either in
the vehicle's body frame or in a frame attached to a "reference point" moving
along the path, such as a Frenet-Serret (F-S) frame or a Parallel Transport
(P-T) frame. With this observation, we provide a unified formulation that is
simple but general enough to cover many methods available in the literature. We
then discuss the advantages and disadvantages of each method, comparing them
from the design and implementation standpoint. We further show experimental
results of the path following methods obtained from field trials testing with
under-actuated and fully-actuated autonomous marine vehicles. In addition, we
introduce open-source Matlab and Gazebo/ROS simulation toolboxes that are
helpful in testing path following methods prior to their integration in the
combined guidance, navigation, and control systems of autonomous vehicles
Prohibited Volume Avoidance for Aircraft
This thesis describes the development of a pilot override control system that prevents aircraft
entering critical regions of space, known as prohibited volumes. The aim is to prevent another
9/11 style terrorist attack, as well as act as a general safety system for transport aircraft.
The thesis presents the design and implementation of three core modules in the system; the
trajectory generation algorithm, the trigger mechanism for the pilot override and the trajectory
following element. The trajectory generation algorithm uses a direct multiple shooting strategy
to provide trajectories through online computation that avoid pre-defi ned prohibited volume
exclusion regions, whilst accounting for the manoeuvring capabilities of the aircraft. The trigger
mechanism incorporates the logic that decides the time at which it is suitable for the override to
be activated, an important consideration for ensuring that the system is not overly restrictive
for a pilot. A number of methods are introduced, and for safety purposes a composite trigger
that incorporates di fferent strategies is recommended. Trajectory following is best achieved via
a nonlinear guidance law. The guidance logic sends commands in pitch, roll and yaw to the
control surfaces of the aircraft, in order to closely follow the generated avoidance trajectory.
Testing and validation is performed using a full motion simulator, with volunteers
flying a
representative aircraft model and attempting to penetrate prohibited volumes.
The proof-of-concept system is shown to work well, provided that extreme aircraft manoeuvres
are prevented near the exclusion regions. These hard manoeuvring envelope constraints allow
the trajectory following controllers to follow avoidance trajectories accurately from an initial
state within the bounding set. In order to move the project closer to a commercial product,
operator and regulator input is necessary, particularly due to the radical nature of the pilot
override system
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