198 research outputs found
Algorithms for multi-robot systems on the cooperative exploration & last-mile delivery problems
La aparición de los vehículos aéreos no tripulados (UAVs) y de los vehículos terrestres no tripulados (UGVs) ha llevado a la comunidad científica a enfrentarse a problemas ideando paradigmas de cooperación con UGVs y UAVs. Sin embargo, no suele ser trivial determinar si la cooperación entre UGVs y UAVs es adecuada para un determinado problema. Por esta razón, en esta tesis, investigamos un paradigma particular de cooperación UGV-UAV en dos problemas de la literatura, y proponemos un controlador autónomo para probarlo en escenarios simulados.
Primero, formulamos un problema particular de exploración cooperativa que consiste en alcanzar un conjunto de puntos de destino en un área de exploración a gran escala. Este problema define al UGV como una estación de carga móvil para transportar el UAV a través de diferentes lugares desde donde el UAV puede alcanzar los puntos de destino. Por consiguiente, proponemos el algoritmo TERRA para resolverlo. Este algoritmo se destaca por dividir el problema de exploración en cinco subproblemas, en los que cada subproblema se resuelve en una etapa particular del algoritmo.
Debido a la explosión de la entrega de paquetes en las empresas de comercio electrónico, formulamos también una generalización del conocido problema de la entrega en la última milla. En este caso, el UGV actúa como una estación de carga móvil que transporta a los paquetes y a los UAVs, y estos se encargan de entregarlos. De esta manera, seguimos la estrategia de división descrita por TERRA, y proponemos el algoritmo COURIER. Este algoritmo replica las cuatro primeras etapas de TERRA, pero construye una nueva quinta etapa para producir un plan de tareas que resuelva el problema. Para evaluar el paradigma de cooperación UGV-UAV en escenarios simulados, proponemos el controlador autónomo ARIES. Este controlador sigue un enfoque jerárquico descentralizado de líder-seguidor para integrar cualquier paradigma de cooperación de manera distribuida.
Ambos algoritmos han sido caracterizados para identificar los aspectos relevantes del paradigma de cooperación en los problemas relacionados. Además, ambos demuestran un gran rendimiento del paradigma de cooperación en tales problemas, y al igual que el controlador autónomo, revelan un gran potencial para futuras aplicaciones reales.The emergence of Unmanned Aerial Vehicles (UAVs) and Unmanned
Ground Vehicles (UGVs) has conducted the research community to
face historical complex problems by devising UGV-UAV cooperation
paradigms. However, it is usually not a trivial task to determine
whether or not a UGV-UAV cooperation is suitable for a particular
problem. For this reason, in this thesis, we investigate a particular
UGV-UAV cooperation paradigm over two problems in the literature,
and we propose an autonomous controller to test it on simulated
scenarios.
Driven by the planetary exploration, we formulate a particular cooperative
exploration problem consisting of reaching a set of target
points in a large-scale exploration area. This problem defines the UGV
as a moving charging station to carry the UAV through different locations
from where the UAV can reach the target points. Consequently,
we propose the cooperaTive ExploRation Routing Algorithm (TERRA)
to solve it. This algorithm stands out for splitting up the exploration
problem into five sub-problems, in which each sub-problem is solved
in a particular stage of the algorithm. In the same way, driven by the
explosion of parcels delivery in e-commerce companies, we formulate
a generalization of the well-known last-mile delivery problem. This
generalization defines the same UGV’s and UAV’s rol as the exploration
problem. That is, the UGV acts as a moving charging station
which carries the parcels along several UAVs to deliver them. In this
way, we follow the split strategy depicted by TERRA to propose the
COoperative Unmanned deliveRIEs planning algoRithm (COURIER).
This algorithm replicates the first four TERRA’s stages, but it builds a
new fifth stage to produce a task plan solving the problem. In order to
evaluate the UGV-UAV cooperation paradigm on simulated scenarios,
we propose the Autonomous coopeRatIve Execution System (ARIES).
This controller follows a hierarchical decentralized leader-follower approach
to integrate any cooperation paradigm in a distributed manner.
Both algorithms have been characterized to identify the relevant
aspects of the cooperation paradigm in the related problems. Also,
both of them demonstrate a great performance of the cooperation
paradigm in such problems, and as well as the autonomous controller,
reveal a great potential for future real applications
Risk-aware Path and Motion Planning for a Tethered Aerial Visual Assistant in Unstructured or Confined Environments
This research aims at developing path and motion planning algorithms for a
tethered Unmanned Aerial Vehicle (UAV) to visually assist a teleoperated
primary robot in unstructured or confined environments. The emerging state of
the practice for nuclear operations, bomb squad, disaster robots, and other
domains with novel tasks or highly occluded environments is to use two robots,
a primary and a secondary that acts as a visual assistant to overcome the
perceptual limitations of the sensors by providing an external viewpoint.
However, the benefits of using an assistant have been limited for at least
three reasons: (1) users tend to choose suboptimal viewpoints, (2) only ground
robot assistants are considered, ignoring the rapid evolution of small unmanned
aerial systems for indoor flying, (3) introducing a whole crew for the second
teleoperated robot is not cost effective, may introduce further teamwork
demands, and therefore could lead to miscommunication. This dissertation
proposes to use an autonomous tethered aerial visual assistant to replace the
secondary robot and its operating crew. Along with a pre-established theory of
viewpoint quality based on affordances, this dissertation aims at defining and
representing robot motion risk in unstructured or confined environments. Based
on those theories, a novel high level path planning algorithm is developed to
enable risk-aware planning, which balances the tradeoff between viewpoint
quality and motion risk in order to provide safe and trustworthy visual
assistance flight. The planned flight trajectory is then realized on a tethered
UAV platform. The perception and actuation are tailored to fit the tethered
agent in the form of a low level motion suite, including a novel tether-based
localization model with negligible computational overhead, motion primitives
for the tethered airframe based on position and velocity control, and two
differentComment: Ph.D Dissertatio
MOMA: Visual Mobile Marker Odometry
In this paper, we present a cooperative odometry scheme based on the
detection of mobile markers in line with the idea of cooperative positioning
for multiple robots [1]. To this end, we introduce a simple optimization scheme
that realizes visual mobile marker odometry via accurate fixed marker-based
camera positioning and analyse the characteristics of errors inherent to the
method compared to classical fixed marker-based navigation and visual odometry.
In addition, we provide a specific UAV-UGV configuration that allows for
continuous movements of the UAV without doing stops and a minimal
caterpillar-like configuration that works with one UGV alone. Finally, we
present a real-world implementation and evaluation for the proposed UAV-UGV
configuration
Risk-aware Path and Motion Planning for a Tethered Aerial Visual Assistant in Unstructured or Confined Environments
This research aims at developing path and motion planning algorithms for a tethered Unmanned Aerial Vehicle (UAV) to visually assist a teleoperated primary robot in unstructured or confined environments. The emerging state of the practice for nuclear operations, bomb squad, disaster robots, and other domains with novel tasks or highly occluded environments is to use two robots, a primary and a secondary that acts as a visual assistant to overcome the perceptual limitations of the sensors by providing an external viewpoint. However, the benefits of using an assistant have been limited for at least three reasons: (1) users tend to choose suboptimal viewpoints, (2) only ground robot assistants are considered, ignoring the rapid evolution of small unmanned aerial systems for indoor flying, (3) introducing a whole crew for the second teleoperated robot is not cost effective, may introduce further teamwork demands, and therefore could lead to miscommunication. This dissertation proposes to use an autonomous tethered aerial visual assistant to replace the secondary robot and its operating crew. Along with a pre-established theory of viewpoint quality based on affordances, this dissertation aims at defining and representing robot motion risk in unstructured or confined environments. Based on those theories, a novel high level path planning algorithm is developed to enable risk-aware planning, which balances the tradeoff between viewpoint quality and motion risk in order to provide safe and trustworthy visual assistance flight.
The planned flight trajectory is then realized on a tethered UAV platform. The perception and actuation are tailored to fit the tethered agent in the form of a low level motion suite, including a novel tether-based localization model with negligible computational overhead, motion primitives for the tethered airframe based on position and velocity control, and two different approaches to negotiate tether with complex obstacle-occupied environments. The proposed research provides a formal reasoning of motion risk in unstructured or confined spaces, contributes to the field of risk-aware planning with a versatile planner, and opens up a new regime of indoor UAV navigation: tethered indoor flight to ensure battery duration and failsafe in case of vehicle malfunction. It is expected to increase teleoperation productivity and reduce costly errors in scenarios such as safe decommissioning and nuclear operations in the Fukushima Daiichi facility
Coordination of Cooperative Multi-Robot Teams
This thesis is about cooperation of multiple robots that have a common
task they should fulfill, i.e., how multi-robot systems behave in cooperative
scenarios. Cooperation is a very important aspect in robotics, because
multiple robots can solve a task more quickly or efficiently in many situations.
Specific points of interest are, how the effectiveness of the group of
robots completing a task can be improved and how the amount of communication
and computational requirements can be reduced. The importance
of this topic lies in applications like search and rescue scenarios, where
time can be a critical factor and a certain robustness and reliability are
required. Further the communication can be limited by various factors
and operating (multiple) robots can be a highly complicated task.
A typical search and rescue mission as considered in this thesis begins
with the deployment of the robot team in an unknown or partly known
environment. The team can be heterogeneous in the sense that it consists
of pairs of air and ground robots that assist each other. The air vehicle –
abbreviated as UAV – stays within vision range of the ground vehicle or
UGV. Therefrom, it provides sensing information with a camera or similar
sensor that might not be available to the UGV due to distance, perspective
or occlusion. A new approach to fully use the available movement range
is presented and analyzed theoretically and in simulations. The UAV
moves according to a dynamic coverage algorithm which is combined with
a tracking controller to guarantee the visibility limitation is kept.
Since the environment is at least partly unknown, an exploration method
is necessary to gather information about the situation and possible targets
or areas of interest. Exploring the unknown regions in a short amount
of time is solved by approaching points on the frontier between known
and unknown territory. To this end, a basic approach for single robot
exploration that uses the traveling salesman problem is extended to multirobot
exploration. The coordination, which is a central aspect of the
cooperative exploration process, is realized with a pairwise optimization
procedure. This new algorithm uses minimum spanning trees for cost
estimation and is inspired by one of the many multi-robot coordination
methods from the related literature. Again, theoretical and simulated as
well as statistical analysis are used as methods to evaluate the approach.
After the exploration is complete, a map of the environment with possible
regions of higher importance is known by the robot team. To stay
useful and ready for any further events, the robots now switch to a monitoring
state where they spread out to cover the area in an optimal manner.
The optimality is measured with a criterion that can be derived into a distributed
control law. This leads to splitting of the robots into areas of
Voronoi cells where each robot has a maximum distance to other robots
and can sense any events within its assigned cell. A new variant of these
Voronoi cells is introduced. They are limited by visibility and depend on
a delta-contraction of the environment, which leads to automatic collision
avoidance. The combination of these two aspects leads to a coverage
control algorithm that works in nonconvex environments and has advantageous
properties compared to related work
Autonomous landing of fixed-wing aircraft on mobile platforms
E
n esta tesis se propone un nuevo sistema que permite la operación de aeronaves
autónomas sin tren de aterrizaje. El trabajo está motivado por el interés industrial
en aeronaves con la capacidad de volar a gran altitud, con más capacidad de carga útil y
capaces de aterrizar con viento cruzado.
El enfoque seguido en este trabajo consiste en eliminar el sistema de aterrizaje de una
aeronave de ala fija empleando una plataforma móvil de aterrizaje en tierra. La aeronave y
la plataforma deben sincronizar su movimiento antes del aterrizaje, lo que se logra mediante
la estimación del estado relativo entre ambas y el control cooperativo del movimiento.
El objetivo principal de esta Tesis es el desarrollo de una solución práctica para el
aterrizaje autónomo de una aeronave de ala fija en una plataforma móvil. En la tesis se
combinan nuevos métodos con experimentos prácticos para los cuales se ha desarrollado
un sistema de pruebas específico.
Se desarrollan dos variantes diferentes del sistema de aterrizaje. El primero presta atención especial a la seguridad, es robusto ante retrasos en la comunicación entre vehículos y
cumple procedimientos habituales de aterrizaje, al tiempo que reduce la complejidad del
sistema. En el segundo se utilizan trayectorias optimizadas del vehículo y sincronización
bilateral de posición para maximizar el rendimiento del aterrizaje en términos de requerimientos de longitud necesaria de pista, pero la estabilidad es dependiente del retraso de
tiempo, con lo cual es necesario desarrollar un controlador estabilizador ampliado, basado
en pasividad, que permite resolver este problema.
Ambas estrategias imponen requisitos funcionales a los controladores de cada uno de
los vehículos, lo que implica la capacidad de controlar el movimiento longitudinal sin
afectar el control lateral o vertical, y viceversa. El control de vuelo basado en energía se
utiliza para proporcionar dicha funcionalidad a la aeronave.
Los sistemas de aterrizaje desarrollados se han analizado en simulación estableciéndose los límites de rendimiento mediante múltiples repeticiones aleatorias. Se llegó a
la conclusión de que el controlador basado en seguridad proporciona un rendimiento de
aterrizaje satisfactorio al tiempo que suministra una mayor seguridad operativa y un menor
esfuerzo de implementación y certificación. El controlador basado en el rendimiento es
prometedor para aplicaciones con una longitud de pista limitada. Se descubrió que los beneficios del controlador basado en el rendimiento son menos pronunciados para una
dinámica de vehículos terrestres más lenta.
Teniendo en cuenta la dinámica lenta de la configuración del demostrador, se eligió el
enfoque basado en la seguridad para los primeros experimentos de aterrizaje. El sistema
de aterrizaje se validó en diversas pruebas de aterrizaje exitosas, que, a juicio del autor,
son las primeras en el mundo realizadas con aeronaves reales. En última instancia, el
concepto propuesto ofrece importantes beneficios y constituye una estrategia prometedora
para futuras soluciones de aterrizaje de aeronaves.In this thesis a new landing system is proposed, which allows for the operation of
autonomous aircraft without landing gear. The work was motivated by the industrial
need for more capable high altitude aircraft systems, which typically suffer from low
payload capacity and high crosswind landing sensitivity. The approach followed in this
work consists in removing the landing gear system from the aircraft and introducing a
mobile ground-based landing platform. The vehicles must synchronize their motion prior
to landing, which is achieved through relative state estimation and cooperative motion
control. The development of a practical solution for the autonomous landing of an aircraft
on a moving platform thus constitutes the main goal of this thesis. Therefore, theoretical
investigations are combined with real experiments for which a special setup is developed
and implemented.
Two different landing system variants are developed — the safety-based landing system is
robust to inter-vehicle communication delays and adheres to established landing procedures,
while reducing system complexity. The performance-based landing system uses optimized
vehicle trajectories and bilateral position synchronization to maximize landing performance
in terms of used runway, but suffers from time delay-dependent stability. An extended
passivity-based stabilizing controller was implemented to cope with this issue. Both
strategies impose functional requirements on the individual vehicle controllers, which
imply independent controllability of the translational degrees of freedom. Energy-based
flight control is utilized to provide such functionality for the aircraft.
The developed landing systems are analyzed in simulation and performance bounds are
determined by means of repeated random sampling. The safety-based controller was found
to provide satisfactory landing performance while providing higher operational safety,
and lower implementation and certification effort. The performance-based controller
is promising for applications with limited runway length. The performance benefits
were found to be less pronounced for slower ground vehicle dynamics. Given the slow
dynamics of the demonstrator setup, the safety-based approach was chosen for first landing
experiments. The landing system was validated in a number of successful landing trials,
which to the author’s best knowledge was the first time such technology was demonstrated on the given scale, worldwide. Ultimately, the proposed concept offers decisive benefits
and constitutes a promising strategy for future aircraft landing solutions
UAV based group coordination of UGVs
Coordination of autonomous mobile robots has received significant attention during the last two decades with the emergence of small, lightweight and low power embedded systems. Coordinated motion of heterogenous robots is important due to the fact that unique advantages of di erent robots might be combined to increase the overall task efficiency of the system. In this thesis, a new coordination framework is developed for a heterogeneous robot system, composed of multiple Unmanned Ground Vehicles (UGVs) and an Unmanned Aerial Vehicle (UAV), that operates in an environment where individual robots work collaboratively in order to accomplish a predefined goal. UAV, a quadrotor, detects the target in the environment and provides a feasible trajectory from an initial configuration to a final target location. UGVs, a group of nonholonomic wheeled mobile robots, follow a virtual leader which is created as the projection of UAV's 3D position onto the horizontal plane. The UAV broadcasts its position at certain frequency to all UGVs. Two different coordination models are developed. In the dynamic coordination model, reference trajectories for each robot is generated from the motion of nodal masses located at each UGV and connected by virtual springs and dampers. Springs have adaptable parameters that allow the desired formation to be achieved In the kinematic coordination model, the position of the virtual leader and distances from the two closest neighbors are directly utilized to create linear and angular velocity references for each UGV. Several coordinated tasks are presented and the results are verified by simulations where different number of UGVs are employed and certain amount of communication delays between the vehicles are also considered. Simulation results are quite promising and form a basis for future experimental work on the topic
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