5 research outputs found
State relativity and speed-allocated line-of-sight course control for path-following of underwater vehicles
Path-following is a primary task for most marine, air or space crafts, especially during
autonomous operations. Research on autonomous underwater vehicles (AUV) has received large interests in the last few decades with research incentives emerging from the safe, cost-effective and practical solutions provided by their applications such as search and rescue, inspection and monitoring of pipe-lines ans sub-sea structures. This thesis presents a novel guidance system based on the popular line-of-sight (LOS) guidance law for path-following (PF) of underwater vehicles (UVs) subject to environmental disturbances. Mathematical modeling and dynamics of (UVs) is presented first. This is followed by a comprehensive literature review on guidance-based path-following control of marine vehicles, which includes revised definitions of the track-errors and more detailed illustrations of the general PF problem. A number of advances on relative equations of motion are made, which include an improved understanding of the fluid FLOW frame and expression of its motion states, an analytic method of modeling the signs of forces and moments and the proofs of passivity and boundedness of relative UV systems in 3-D. The revision in the relative equations of motion include the concept of state relativity, which is an improved understanding of relativity of motion states expressed in reference frames and is also useful in incorporating environmental disturbances. In addition, the concept of drift rate is introduced along with a revision on the angles of motion in 3-D. A switching mechanism was developed to overcome a drawback of a LOS guidance law, and the linear and nonlinear stability results of the LOS guidance laws have been provided, where distinctions are made between straight and curved PF cases. The guidance system employs the unique formulation and solution of the speed allocation problem of allocating a desired speed vector into x and y components, and the course control that employs the slip angle for desired heading for disturbance rejection. The guidance system and particularly the general course control problem has been extended to 3-D with the new definition of vertical-slip angle. The overall guidance system employing the revised relative system model, course control and speed allocation has performed well during path-following under strong ocean current and/or wave disturbances and measurement noises in both 2-D and 3-D scenarios. In 2-D and 3-D 4 degrees-of-freedom models (DOF), the common sway-underactuated and fully actuated cases are considered, and in 3-D 5-DOF model, sway and heave underactuated and fully actuated cases are considered. Stability results of the LOS guidance laws include the semi-global exponential stability (SGES) of the switching LOS guidance and enclosure-based LOS guidance for straight and curved paths, and SGES of the loolahead-based LOS guidance laws for curved paths. Feedback sliding mode and PID controllers are applied during PF providing a comparison between them, and simulations are carried out in MatLab
Guidance and control of an autonomous underwater vehicle
Merged with duplicate record 10026.1/856 on 07.03.2017 by CS (TIS)A cooperative project between the Universities of Plymouth and Cranfield was aimed
at designing and developing an autonomous underwater vehicle named Hammerhead.
The work presented herein is to formulate an advance guidance and control system
and to implement it in the Hammerhead. This involves the description of Hammerhead
hardware from a control system perspective. In addition to the control system,
an intelligent navigation scheme and a state of the art vision system is also developed.
However, the development of these submodules is out of the scope of this thesis.
To model an underwater vehicle, the traditional way is to acquire painstaking mathematical
models based on laws of physics and then simplify and linearise the models to
some operating point. One of the principal novelties of this research is the use of system
identification techniques on actual vehicle data obtained from full scale in water
experiments. Two new guidance mechanisms have also been formulated for cruising
type vehicles. The first is a modification of the proportional navigation guidance for
missiles whilst the other is a hybrid law which is a combination of several guidance
strategies employed during different phases of the Right.
In addition to the modelling process and guidance systems, a number of robust control
methodologies have been conceived for Hammerhead. A discrete time linear
quadratic Gaussian with loop transfer recovery based autopilot is formulated and integrated
with the conventional and more advance guidance laws proposed. A model
predictive controller (MPC) has also been devised which is constructed using artificial
intelligence techniques such as genetic algorithms (GA) and fuzzy logic. A GA
is employed as an online optimization routine whilst fuzzy logic has been exploited
as an objective function in an MPC framework. The GA-MPC autopilot has been
implemented in Hammerhead in real time and results demonstrate excellent robustness
despite the presence of disturbances and ever present modelling uncertainty. To
the author's knowledge, this is the first successful application of a GA in real time
optimization for controller tuning in the marine sector and thus the thesis makes an
extremely novel and useful contribution to control system design in general. The
controllers are also integrated with the proposed guidance laws and is also considered
to be an invaluable contribution to knowledge. Moreover, the autopilots are used in
conjunction with a vision based altitude information sensor and simulation results
demonstrate the efficacy of the controllers to cope with uncertain altitude demands.J&S MARINE LTD., QINETIQ,
SUBSEA 7 AND SOUTH WEST WATER PL
Trajectory solutions for a game-playing robot using nonprehensile manipulation methods and machine vision
The need for autonomous systems designed to play games, both strategy-based and
physical, comes from the quest to model human behaviour under tough and
competitive environments that require human skill at its best. In the last two decades,
and especially after the 1996 defeat of the world chess champion by a chess-playing
computer, physical games have been receiving greater attention. Robocup TM, i.e.
robotic football, is a well-known example, with the participation of thousands of
researchers all over the world. The robots created to play snooker/pool/billiards are
placed in this context. Snooker, as well as being a game of strategy, also requires
accurate physical manipulation skills from the player, and these two aspects qualify
snooker as a potential game for autonomous system development research. Although
research into playing strategy in snooker has made considerable progress using
various artificial intelligence methods, the physical manipulation part of the game is
not fully addressed by the robots created so far. This thesis looks at the different ball
manipulation options snooker players use, like the shots that impart spin to the ball in
order to accurately position the balls on the table, by trying to predict the ball
trajectories under the action of various dynamic phenomena, such as impacts.
A 3-degree of freedom robot, which can manipulate the snooker cue on a par with
humans, at high velocities, using a servomotor, and position the snooker cue on the
ball accurately with the help of a stepper drive, is designed and fabricated. [Continues.
Control oriented modelling of an integrated attitude and vibration suppression architecture for large space structures
This thesis is divided into two parts. The main focus of the research, namely active vibration control for large flexible spacecraft, is exposed in Part I and, in parallel, the topic of machine learning techniques for modern space applications is described in Part II. In particular, this thesis aims at proposing an end-to-end general architecture for an integrated attitude-vibration control system, starting from the design of structural models to the synthesis of the control laws. To this purpose, large space structures based on realistic missions are investigated as study cases, in accordance with the tendency of increasing the size of the scientific instruments to improve their sensitivity, being the drawback an increase of its overall flexibility. An active control method is therefore investigated to guarantee satisfactory pointing and maximum deformation by avoiding classical stiffening methods. Therefore, the instrument is designed to be supported by an active deployable frame hosting an optimal minimum set of collocated smart actuators and sensors. Different spatial configurations for the placement of the distributed network of active devices are investigated, both at closed-loop and open-loop levels. Concerning closed-loop techniques, a method to optimally place the poles of the system via a Direct Velocity Feedback (DVF) controller is proposed to identify simultaneously the location and number of active devices for vibration control with an in-cascade optimization technique. Then, two general and computationally efficient open-loop placement techniques, namely Gramian and Modal Strain Energy (MSE)-based methods, are adopted as opposed to heuristic algorithms, which imply high computational costs and are generally not suitable for high-dimensional systems, to propose a placement architecture for generically shaped tridimensional space structures. Then, an integrated robust control architecture for the spacecraft is presented as composed of both an attitude control scheme and a vibration control system. To conclude the study, attitude manoeuvres are performed to excite main flexible modes and prove the efficacy of both attitude and vibration control architectures. Moreover, Part II is dedicated to address the problem of improving autonomy and self-awareness of modern spacecraft, by using machine-learning based techniques to carry out Failure Identification for large space structures and improving the pointing performance of spacecraft (both flexible satellite with sloshing models and small rigid platforms) when performing repetitive Earth Observation manoeuvres
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Criticism in the absence of criticism
English abstract:
Criticism is defined as the examination and judgment about someone or something. This definition includes, at first, an analytical task -with a particular methodology related to it- and, at second, a synthetic activity, translated into a value judgment on what is previously analyzed. Criticism can be done in different ways and depths: from the basic critical thinking -essentially descriptive- to the most truthful one –the poetic criticism-, that transcends pure description or analysis and refers itself to the internal coherence of the object. Any criticism that seeks to reduce the distance to the truth will address both to the intrinsic object relationships -or own laws- and to the extrinsic ones. Furthermore, an objective criticism provides a knowledge of the object regardless of the observer or frame of reference. This provides an effective method and a guaranteed way to approach to the knowledge of the object.
Does this mean that without a regular critical method no criticism is undertaken? The proposal of this paper is to
explain how a critical thought can be undertaken in the
absence of criticism, in which there is no explicit value
judgment. Taking the hypothesis that there is criticism in the absence of criticism, an architectural work –either
being a building, a writing on architecture, etc.- that implies a tacit criticism could work on two levels: as a
practical result –built, literary, etc.- and as a critical thought. The hypothesis proposes that such duality, criticism and practice, may come together in a single work. Although not in any. The existence of criticism in the absence of criticism will depend on the nature of the object and, with no doubt, on the speaker and receiver. At first glance, the guarantees provided by this criticism in the absence of criticism seem less tan through the orthodox one, in which the subject is the weakest part of the chain. However, the absence of explicit value judgment can lead to a series of stimuli –coherency, aesthetic, recreational or other- that, in certain contexts, do more viable the approach to the knowledge than through the conventional method.
Spanish abstract:
La crÃtica se define como el examen y juicio acerca de alguien o algo. Esta definición comprende, por un lado,
una tarea analÃtica -con una determinada metodologÃa
asociada- y, por otro, una actividad sintética, traducida en
un juicio de valor acerca de lo previamente analizado. La crÃtica puede hacerse de distinta forma y con distinto
grado de profundidad: desde la más básica –fundamentalmente, la crÃtica descriptiva- hasta la más veraz -la crÃtica poética-, que trasciende la descripción o el análi sis puro y se refiere a la coherencia interna del objeto de estudio. Toda crÃtica que pretenda reducir la distancia de aproximación a la verdad se ocupará tanto de las relaciones intrÃnsecas o leyes propias del objeto como de las eelaciones extrÃnsecas al mismo. Por otro lado, una crÃtica objetiva facilita el conocimiento del objeto de estudio independientemente del observador o del marco de referencia, lo que la convierte en un método eficaz y con garantÃas para la aproximación al conocimiento del objeto. Pero ¿significa esto que sin crÃtica ortodoxa no puede existir crÃtica?. La propuesta de esta comunicación es dilucidar hasta qué punto puede emprenderse una crÃtica en ausencia de crÃtica, es decir, una crÃtica en la que no sea explÃcito el juicio de valor. Tomando como hipótesis el hecho de que exista crÃtica
en ausencia de crÃtica, una obra arquitectónica –ya sea un edificio construido, un escrito sobre arquitectura, etc.- que implique una crÃtica tácita podrÃa funcionar a dos niveles: como producto práctico -edificado, literario, etc.- y como reflexión crÃtica. La hipótesis planteada propone que tal dualidad, la crÃtica y la práctica, pueda confluir en una misma obra. Aunque no en cualquiera. La existencia de crÃtica en ausencia de crÃtica dependerá de la naturaleza de la obra y, sin lugar a dudas, del emisor y el receptor del mensaje crÃtico. A primera vista, las garantÃas que ofrece la crÃtica en ausencia de crÃtica parecen menores que mediante la crÃtica ortodoxa, para la que el sujeto es la parte más débil de la cadena. Sin embargo, la ausencia de juicio de valor explÃcito puede comportar una serie de estÃmulos – de coherencia, estéticos, lúdicos, prácticos o de otra Ãndole- que, en determinados contextos, hagan más viable y clara la comprensión de la obra que a través del método convencional