284 research outputs found
Singularity-free Formation Path Following of Underactuated AUVs: Extended Version
This paper proposes a method for formation path following control of a fleet
of underactuated autonomous underwater vehicles. The proposed method combines
several hierarchic tasks in a null space-based behavioral algorithm to safely
guide the vehicles. Compared to the existing literature, the algorithm includes
both inter-vehicle and obstacle collision avoidance, and employs a scheme that
keeps the vehicles within given operation limits. The algorithm is applied to a
six degree-of-freedom model, using rotation matrices to describe the attitude
to avoid singularities. Using the results of cascaded systems theory, we prove
that the closed-loop system is uniformly semiglobally exponentially stable. We
use numerical simulations to validate the results.Comment: Extended version of a paper, to appear in Proc. 2023 IFAC World
Congress, 13 pages (9p + 4p appendices), 5 figure
COLREG-Compliant Collision Avoidance for Unmanned Surface Vehicle using Deep Reinforcement Learning
Path Following and Collision Avoidance, be it for unmanned surface vessels or
other autonomous vehicles, are two fundamental guidance problems in robotics.
For many decades, they have been subject to academic study, leading to a vast
number of proposed approaches. However, they have mostly been treated as
separate problems, and have typically relied on non-linear first-principles
models with parameters that can only be determined experimentally. The rise of
Deep Reinforcement Learning (DRL) in recent years suggests an alternative
approach: end-to-end learning of the optimal guidance policy from scratch by
means of a trial-and-error based approach. In this article, we explore the
potential of Proximal Policy Optimization (PPO), a DRL algorithm with
demonstrated state-of-the-art performance on Continuous Control tasks, when
applied to the dual-objective problem of controlling an underactuated
Autonomous Surface Vehicle in a COLREGs compliant manner such that it follows
an a priori known desired path while avoiding collisions with other vessels
along the way. Based on high-fidelity elevation and AIS tracking data from the
Trondheim Fjord, an inlet of the Norwegian sea, we evaluate the trained agent's
performance in challenging, dynamic real-world scenarios where the ultimate
success of the agent rests upon its ability to navigate non-uniform marine
terrain while handling challenging, but realistic vessel encounters
Deep Reinforcement Learning Controller for 3D Path-following and Collision Avoidance by Autonomous Underwater Vehicles
Control theory provides engineers with a multitude of tools to design
controllers that manipulate the closed-loop behavior and stability of dynamical
systems. These methods rely heavily on insights about the mathematical model
governing the physical system. However, in complex systems, such as autonomous
underwater vehicles performing the dual objective of path-following and
collision avoidance, decision making becomes non-trivial. We propose a solution
using state-of-the-art Deep Reinforcement Learning (DRL) techniques, to develop
autonomous agents capable of achieving this hybrid objective without having \`a
priori knowledge about the goal or the environment. Our results demonstrate the
viability of DRL in path-following and avoiding collisions toward achieving
human-level decision making in autonomous vehicle systems within extreme
obstacle configurations
A COLLISION AVOIDANCE SYSTEM FOR AUTONOMOUS UNDERWATER VEHICLES
The work in this thesis is concerned with the development of a novel and practical collision
avoidance system for autonomous underwater vehicles (AUVs). Synergistically,
advanced stochastic motion planning methods, dynamics quantisation approaches,
multivariable tracking controller designs, sonar data processing and workspace representation,
are combined to enhance significantly the survivability of modern AUVs.
The recent proliferation of autonomous AUV deployments for various missions such
as seafloor surveying, scientific data gathering and mine hunting has demanded a substantial
increase in vehicle autonomy. One matching requirement of such missions is
to allow all the AUV to navigate safely in a dynamic and unstructured environment.
Therefore, it is vital that a robust and effective collision avoidance system should be
forthcoming in order to preserve the structural integrity of the vehicle whilst simultaneously
increasing its autonomy.
This thesis not only provides a holistic framework but also an arsenal of computational
techniques in the design of a collision avoidance system for AUVs. The
design of an obstacle avoidance system is first addressed. The core paradigm is the
application of the Rapidly-exploring Random Tree (RRT) algorithm and the newly
developed version for use as a motion planning tool. Later, this technique is merged
with the Manoeuvre Automaton (MA) representation to address the inherent disadvantages
of the RRT. A novel multi-node version which can also address time varying
final state is suggested. Clearly, the reference trajectory generated by the aforementioned
embedded planner must be tracked. Hence, the feasibility of employing the
linear quadratic regulator (LQG) and the nonlinear kinematic based state-dependent
Ricatti equation (SDRE) controller as trajectory trackers are explored.
The obstacle detection module, which comprises of sonar processing and workspace
representation submodules, is developed and tested on actual sonar data acquired
in a sea-trial via a prototype forward looking sonar (AT500). The sonar processing
techniques applied are fundamentally derived from the image processing perspective.
Likewise, a novel occupancy grid using nonlinear function is proposed for the
workspace representation of the AUV. Results are presented that demonstrate the
ability of an AUV to navigate a complex environment.
To the author's knowledge, it is the first time the above newly developed methodologies
have been applied to an A UV collision avoidance system, and, therefore, it is
considered that the work constitutes a contribution of knowledge in this area of work.J&S MARINE LT
A Robust Reactive Static Obstacle Avoidance System for Surface Marine Vehicles
This paper is centered on the guidance systems used to increase the autonomy of unmanned surface vehicles (USVs). The new Robust Reactive Static Obstacle Avoidance System (RRSOAS) has been specifically designed for USVs. This algorithm is easily applicable, since previous knowledge of the USV mathematical model and its controllers is not needed. Instead, a new estimated closed-loop model (ECLM) is proposed and used to estimate possible future trajectories. Furthermore, the prediction errors (due to the uncertainty present in the ECLM) are taken into account by modeling the USV's shape as a time-varying ellipse. Additionally, in order to decrease the computation time, we propose to use a variable prediction horizon and an exponential resolution to discretize the decision space. As environmental model an occupancy probability grid is used, which is updated with the measurements generated by a LIDAR sensor model. Finally, the new RRSOAS is compared with other SOA (static obstacle avoidance) methods. In addition, a robustness study was carried out over a set of random scenarios. The results obtained through numerical simulations indicate that RRSOAS is robust to unknown and congested scenarios in the presence of disturbances, while offering competitive performance with respect to other SOA methods
A Novel Vector-Field-Based Motion Planning Algorithm for 3D Nonholonomic Robots
This paper focuses on the motion planning for mobile robots in 3D, which are
modelled by 6-DOF rigid body systems with nonholonomic kinematics constraints.
We not only specify the target position, but also bring in the requirement of
the heading direction at the terminal time, which gives rise to a new and more
challenging 3D motion planning problem. The proposed planning algorithm
involves a novel velocity vector field (VF) over the workspace, and by
following the VF, the robot can be navigated to the destination with the
specified heading direction. In order to circumvent potential collisions with
obstacles and other robots, a composite VF is designed by composing the
navigation VF and an additional VF tangential to the boundary of the dangerous
area. Moreover, we propose a priority-based algorithm to deal with the motion
coupling issue among multiple robots. Finally, numerical simulations are
conducted to verify the theoretical results
Collision Avoidance for Autonomous Surface Vessels using Novel Artificial Potential Fields
As the demand for transportation through waterways continues to rise, the
number of vessels plying the waters has correspondingly increased. This has
resulted in a greater number of accidents and collisions between ships, some of
which lead to significant loss of life and financial losses. Research has shown
that human error is a major factor responsible for such incidents. The maritime
industry is constantly exploring newer approaches to autonomy to mitigate this
issue. This study presents the use of novel Artificial Potential Fields (APFs)
to perform obstacle and collision avoidance in marine environments. This study
highlights the advantage of harmonic functions over traditional functions in
modeling potential fields. With a modification, the method is extended to
effectively avoid dynamic obstacles while adhering to COLREGs. Improved
performance is observed as compared to the traditional potential fields and
also against the popular velocity obstacle approach. A comprehensive
statistical analysis is also performed through Monte Carlo simulations in
different congested environments that emulate real traffic conditions to
demonstrate robustness of the approach.Comment: 28 pages, 30 figure
A multirobot platform based on autonomous surface and underwater vehicles with bio-inspired neurocontrollers for long-term oil spills monitoring
This paper describes the BUSCAMOS-Oil monitoring system, which is a robotic platform consisting of an autonomous surface vessel combined with an underwater vehicle. The system has been designed for the long-term monitoring of oil spills, including the search for the spill, and transmitting information on its location, extent, direction and speed. Both vehicles are controlled by two different types of bio-inspired neural networks: a Self-Organization Direction Mapping Network for trajectory generation and a Neural Network for Avoidance Behaviour for avoiding obstacles. The systems’ resilient capabilities are provided by bio-inspired algorithms implemented in a modular software architecture and controlled by redundant devices to give the necessary robustness to operate in the difficult conditions typically found in long-term oil-spill operations. The efficacy of the vehicles’ adaptive navigation system and long-term mission capabilities are shown in the experimental results.This work was partially supported by the BUSCAMOS Project (ref. 1003211003700) under the program DN8644 COINCIDENTE of the Spanish Defense Ministry, the “Research Programme for Groups of Scientific Excellence at Region of Murcia” of the Seneca Foundation (Agency for Science and Technology of the Region of Murcia-19895/GERM/15)”, and the Spanish Government’s cDrone (ref. TIN2013-45920-R) and ViSelTR (ref. TIN2012-39279) projects
Quadrotor path following and reactive obstacle avoidance with deep reinforcement learning
A deep reinforcement learning approach for solving the quadrotor path following and obstacle avoidance problem is proposed in this paper. The problem is solved with two agents: one for the path following task and another one for the obstacle avoidance task. A novel structure is proposed, where the action computed by the obstacle avoidance agent becomes the state of the path following agent. Compared to traditional deep reinforcement learning approaches, the proposed method allows to interpret the training process outcomes, is faster and can be safely trained on the real quadrotor. Both agents implement the Deep Deterministic Policy Gradient algorithm. The path following agent was developed in a previous work. The obstacle avoidance agent uses the information provided by a low-cost LIDAR to detect obstacles around the vehicle. Since LIDAR has a narrow field-of-view, an approach for providing the agent with a memory of the previously seen obstacles is developed. A detailed description of the process of defining the state vector, the reward function and the action of this agent is given. The agents are programmed in python/tensorflow and are trained and tested in the RotorS/gazebo platform. Simulations results prove the validity of the proposed approach.This work has been partially funded by the Spanish Government (MINECO) through the project CICYT (ref. DPI2017-88403-R).Peer ReviewedPostprint (published version
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