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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

Calibration of and Attitude Error Estimation for a Spaceborne Scatterometer using Measurements Over Land

Wilson, Clarence J., III 14 May 2003 (has links) (PDF)
The NASA Scatterometer (NSCAT) was launched August 20, 1996 aboard the National Space Development Agency of Japan's Advanced Earth Observing Spacecraft (ADEOS). NSCAT's primary mission was to measure radar backscatter over the world's oceans. These measurements are used to generate estimates of ocean wind speed and direction. Scatterometers must be calibrated before their measurements are scientifically useful. However, the calibration of NSCAT must be done in orbit. A new methodology for selecting land regions for use in extended target spaceborne scatterometer calibration is first developed. Next, a summary of the calibration technique used in this thesis is presented. While the foundation of this technique was previously developed theoretically, the work in this thesis is its first application for calibration/validation of an on-line spaceborne radar system. The technique is extended to estimate simultaneously NSCAT's calibration and the host spacecraft's attitude error. The attitude references reported by the attitude control system on-board ADEOS are deemed erroneous. Results of this expanded technique, applied under varying assumptions, are presented for consideration. A summary and suggestions for future research conclude this work.
12

Implementation Issues of Real-Time Trajectory Generation on Small UAVs

Kingston, Derek B. 11 March 2004 (has links) (PDF)
The transition from a mathematical algorithm to a physical hardware implementation is non-trivial. This thesis discusses the issues involved in the transition from the theory of real-time trajectory generation all the way through a hardware experiment. Documentation of the validation process as well as modifications to the existing theory as a result of hardware testing are treated at length. The results of hardware experimentation show that trajectory generation can be done in real-time in a manner facilitating coordination of multiple small UAVs.
13

Vision-Assisted Control of a Hovering Air Vehicle in an Indoor Setting

Johnson, Neil G. 22 June 2008 (has links) (PDF)
The quadrotor helicopter is a unique flying vehicle which uses the thrust from four motors to provide hover flight capability. The uncoupled nature of the longitudinal and lateral axes and its ability to support large payloads with respect to its size make it an attractive vehicle for autonomous vehicle research. In this thesis, the quadrotor is modeled based on first principles and a proportional-derivative control method is applied for attitude stabilization and position control. A unique means of using an optic flow sensor for velocity and position estimation in an indoor setting is presented with flight results. Reliable hover flight and hallway following capabilities are exhibited in GPS-denied indoor flight using only onboard sensors. Attitude angles can be reliably estimated in the short run by integrating the angular rates from MEMS gyros, but noise on the signal leads to drift which renders the measurement unsuitable to attitude estimation. Typical methods of providing vector attitude corrections such as accelerometers and magnetometers have inherent weaknesses on hovering vehicles. Thus, an additional vector measurement is necessary to correct attitude readings for long-term flights. Two methods of using image processing to determine vanishing points in a hallway are demonstrated. The more promising of the two uses a Hough transform to detect lines in the image and forms a histogram of the intersections to detect likely vanishing point candidates. Once the vanishing point is detected, it acts as a vector measurement to correct attitude estimates on the quadrotor vehicle. Results using onboard vision to estimate heading are demonstrated on a test stand. Together, these capabilities improve the utility of the quadrotor platform for flight without the need of any external sensing capability.
14

Attitude Estimation and Maneuvering for Autonomous Obstacle Avoidance by Miniature Air Vehicles

Hall, James K. 22 December 2008 (has links) (PDF)
Utilizing the Euler-Rodrigues symmetric parameters (attitude quaternion) to describe vehicle orientation, we develop a multiplicative, nonlinear (extended) variation of the Kalman filter (MEKF) to fuse data from low-cost sensors. The sensor suite is comprised of gyroscopes, accelerometers, and a GPS receiver. In contrast to the common approach of using the complete vehicle attitude as the quantities to be estimated, our filter states consist of the three components of an attitude error vector. In parallel with the time update of the attitude error estimate, we utilize the gyroscope measurements for the time propagation of the attitude quaternion. The accelerometer and the GPS sensors are used independently for the measurement update portion of the Kalman filter. For both sensors, a vector arithmetic approach is used to determine the attitude error vector. Following each measurement update, a multiplicative reset operation moves the attitude error information from the filter state into the attitude estimate. This reset operation utilizes quaternion algebra to implicitly maintain the unity-norm constraint. We demonstrate the effectiveness of our attitude estimation algorithm through flight simulations and flight tests of aggressive maneuvers such as loops and small-radius circles. We implement an approach to aerobatic maneuvering for miniature air vehicles (MAVs) using time-parameterized attitude trajectory generation and an associated attitude tracking control law. We designed two methodologies, polynomial and trigonometric, for creating functions that specify pitch and roll angles as a function of time. For both approaches, the functions are constrained by the maneuver boundary conditions of aircraft position and velocity. We construct a trajectory tracking feedback control law to regulate aircraft orientation throughout the maneuvers. The trajectory generation algorithm was used to construct several maneuvers and trajectory tracking control law successfully executed the maneuvers in the flight simulator. In addition to the simulation results, MAV flight tests verified the performance of the maneuver generation and control. To achieve obstacle avoidance maneuvering, the time parameterized trajectories were converted to spatially parameterized paths, which allowed for inertial reference frame position error to be included in the control law feedback loop. We develop a novel method to achieve the spatial parameterization using a prediction and correction approach. Additionally, the first derivative of position of the desired path is modified using a corrective parameter scheme prior to being used in the control. Using the path position error and the corrected derivative, we utilize a unit-norm quaternion framework to implement a proportional-derivative (PD) control law. This control law was demonstrated in simulation and hardware on maneuvers designed specifically to avoid obstacles, namely the Immelmann and the Close-Q, as well as a basic loop.
15

The Distributed Spacecraft Attitude Control System Simulator: From Design Concept to Decentralized Control

Schwartz, Jana Lyn 21 July 2004 (has links)
A spacecraft formation possesses several benefits over a single-satellite mission. However, launching a fleet of satellites is a high-cost, high-risk venture. One way to mitigate much of this risk is to demonstrate hardware and algorithm performance in groundbased testbeds. It is typically difficult to experimentally replicate satellite dynamics in an Earth-bound laboratory because of the influences of gravity and friction. An air bearing provides a very low-torque environment for experimentation, thereby recapturing the freedom of the space environment as effectively as possible. Depending upon con- figuration, air-bearing systems provide some combination of translational and rotational freedom; the three degrees of rotational freedom provided by a spherical air bearing are ideal for investigation of spacecraft attitude dynamics and control problems. An interest in experimental demonstration of formation flying led directly to the development of the Distributed Spacecraft Attitude Control System Simulator (DSACSS). The DSACSS is a unique facility, as it uses two air-bearing platforms working in concert. Thus DSACSS provides a pair of "spacecraft" three degrees of attitude freedom each. Through use of the DSACSS we are able to replicate the relative attitude dynamics between nodes of a formation such as might be required for co-observation of a terrestrial target. Many dissertations present a new mathematical technique or prove a new theory. This dissertation presents the design and development of a new experimental system. Although the DSACSS is not yet fully operational, a great deal of work has gone into its development thus far. This work has ranged from configuration design to nonlinear analysis to structural and electrical manufacturing. In this dissertation we focus on the development of the attitude determination subsystem. This work includes development of the equations of motion and analysis of the sensor suite dynamics. We develop nonlinear filtering techniques for data fusion and attitude estimation, and extend this problem to include estimation of the mass properties of the system. We include recommendations for system modifications and improvements. / Ph. D.
16

Vision-Based Navigation for a Small Fixed-Wing Airplane in Urban Environment

Hwangbo, Myung 01 May 2012 (has links)
An urban operation of unmanned aerial vehicles (UAVs) demands a high level of autonomy for tasks presented in a cluttered environment. While fixed-wing UAVs are well suited for long-endurance missions at a high altitude, enabling them to navigate inside an urban area brings another level of challenges. Their inability to hover and low agility in motion cause more difficulties on finding a feasible path to move safely in a compact region, and the limited payload allows only low-grade sensors for state estimation and control. We address the problem of achieving vision-based autonomous navigation for a small fixed-wing in an urban area with contributions to the following several key topics. Firstly, for robust attitude estimation during dynamic maneuvering, we take advantage of the line regularity in an urban scene, which features vertical and horizontal edges of man-made structures. The sensor fusion with gravity-related line segments and gyroscopes in a Kalman filter can provide driftless and realtime attitude for ight stabilization. Secondly, as a prerequisite to sensor fusion, we present a convenient self-calibration scheme based on the factorization method. Natural references such as gravity, vertical edges, and distant scene points, available in urban fields, are sufficient to find intrinsic and extrinsic parameters of inertial and vision sensors. Lastly, to generate a dynamically feasible motion plan, we propose a discrete planning method that encodes a path into interconnections of finite trim states, which allow a significant dimension reduction of a search space and result in naturally implementable paths integrated with ight controllers. The most probable path to reach a target is computed by the Markov Decision Process with motion uncertainty due to wind, and a minimum target observation time is imposed on the final motion plan to consider a camera's limited field-of-view. In this thesis, the effectiveness of our vision-based navigation system is demonstrated by what we call an "air slalom" task in which the UAV must autonomously search and localize multiple gates, and pass through them sequentially. Experiment results with a 1m wing-span airplane show essential navigation capabilities demanded in urban operations such as maneuvering passageways between buildings.
17

Robust adaptive control of rigid spacecraft attitude maneuvers

Dando, Aaron John January 2008 (has links)
In this thesis novel feedback attitude control algorithms and attitude estimation algorithms are developed for a three-axis stabilised spacecraft attitude control system. The spacecraft models considered include a rigid-body spacecraft equipped with (i) external control torque devices, and (ii) a redundant reaction wheel configuration. The attitude sensor suite comprises a three-axis magnetometer and three-axis rate gyroscope assembly. The quaternion parameters (also called Euler symmetric parameters), which globally avoid singularities but are subject to a unity-norm constraint, are selected as the primary attitude coordinates. There are four novel contributions presented in this thesis. The first novel contribution is the development of a robust control strategy for spacecraft attitude tracking maneuvers, in the presence of dynamic model uncertainty in the spacecraft inertia matrix, actuator magnitude constraints, bounded persistent external disturbances, and state estimation error. The novel component of this algorithm is the incorporation of state estimation error into the stability analysis. The proposed control law contains a parameter which is dynamically adjusted to ensure global asymptotic stability of the overall closedloop system, in the presence of these specific system non-idealities. A stability proof is presented which is based on Lyapunov's direct method, in conjunction with Barbalat's lemma. The control design approach also ensures minimum angular path maneuvers, since the attitude quaternion parameters are not unique. The second novel contribution is the development of a robust direct adaptive control strategy for spacecraft attitude tracking maneuvers, in the presence of dynamic model uncertainty in the spacecraft inertia matrix. The novel aspect of this algorithm is the incorporation of a composite parameter update strategy, which ensures global exponential convergence of the closed-loop system. A stability proof is presented which is based on Lyapunov's direct method, in conjunction with Barbalat's lemma. The exponential convergence results provided by this control strategy require persistently exciting reference trajectory commands. The control design approach also ensures minimum angular path maneuvers. The third novel contribution is the development of an optimal control strategy for spacecraft attitude maneuvers, based on a rigid body spacecraft model including a redundant reaction wheel assembly. The novel component of this strategy is the proposal of a performance index which represents the total electrical energy consumed by the reaction wheel over the maneuver interval. Pontraygin's minimum principle is applied to formulate the necessary conditions for optimality, in which the control torques are subject to timevarying magnitude constraints. The presence of singular sub-arcs in the statespace and their associated singular controls are investigated using Kelley's necessary condition. The two-point boundary-value problem (TPBVP) is formulated using Pontrayagin's minimum principle. The fourth novel contribution is an attitude estimation algorithm which estimates the spacecraft attitude parameters and sensor bias parameters from three-axis magnetometer and three-axis rate gyroscope measurement data. The novel aspect of this algorithm is the assumption that the state filtering probability density function (PDF) is Gaussian distributed. This Gaussian PDF assumption is also applied to the magnetometer measurement model. Propagation of the filtering PDF between sensor measurements is performed using the Fokker-Planck equation, and Bayes theorem incorporates measurement update information. The use of direction cosine matrix elements as the attitude coordinates avoids any singularity issues associated with the measurement update and estimation error covariance representation.
18

Fusion de données inertielles et magnétiques pour l’estimation de l’attitude sous contrainte énergétique d’un corps rigide accéléré / Inertial and magnetic data fusion for attitude estimation under energetic constraint for accelerated rigid body

Makni, Aida 29 March 2016 (has links)
Dans ce travail de thèse on s’intéresse à l’estimation de l’attitude d’un corps rigideen mouvement dans l’espace 3D en utilisant les quaternions comme représentation. Cetteproblématique a été largement étudiée dans la littérature sous divers domaines d’application.L’objectif de la thèse est de proposer de nouvelles méthodes de fusion de données en combinantdes mesures inertielles et magnétiques. Dans un premier temps, nous nous sommesintéressés à l’estimation de l’attitude en cas de mouvement accéléré où l’accélération linéairedu corps n’est plus négligeable devant la gravité. Deux approches ont été proposées dans cecadre. La première utilise un filtre de Kalman adaptatif pour la compensation des accélérationslinéaires. Précisément, des lois de détection ont été développées pour distinguer d’unefaçon automatique les différentes phases de mouvement (statiques et dynamiques). Ainsi, lamatrice de covariance associée à l’accélération linéaire est estimée afin d’ajuster le gain dufiltre. La deuxième approche consiste à intégrer un filtre singulier élaboré sur la base d’unnouveau modèle, dans lequel le modèle du processus est défini en se basant sur les mesuresissues de l’accéléromètre tandis que le modèle d’observation est défini par les mesures issuesdu gyromètres et du magnétomètres. Cette formulation permet de prendre en compte l’effetdes accélérations linéaires d’une manière efficace. Dans un deuxième temps, on s’est focalisésur l’estimation de l’attitude avec utilisation intermittente de gyromètres, considérés commecapteurs énergivores. Nous avons étudié dans ce cas la façon la plus adéquate afin de réduirel’acquisition des mesures de vitesse angulaire tout en gardant une qualité acceptable de l’estimationde l’attitude. Toutes les approches développées ont été validées par des simulationsnumériques ainsi que des expérimentations utilisant des données réelles. / In this PhD. thesis we deal with attitude estimation of accelerated rigid body moving in the 3D space using quaternion parameterization. This problem has been widely studied in the literature in various application areas. The main objective of the thesis is to propose new methods for data fusion to combine inertial gyros) and magnetic measurements. The first challenge concerns the attitude estimation during dynamic cases, in which external acceleration of the body is not negligible compared to the Gravity. Two main approaches are proposed in this context. Firstly, a quatenion-based adaptive Kalman filter (q-AKF) was designed in order to compensate for such external acceleration. Precisely, a smart detector is designed to decide whether the body is in static or dynamic case. Then, the covariance matrix of the external acceleration is estimated to tune the filter gain. Second, we developed descriptor filter based on a new formulation of the dynamic model where the process model is fed by accelerometer measurements while observation model is fed by gyros and magnetometer measurements. Such modeling gives rise to a descriptor system. The resulting model allows taking the external acceleration of the body into account in a very efficient way. The second challenge is related to the energy consumption issue of gyroscope, considered as the most power consuming sensor. We study the way to reduce the gyro measurements acquisition by switching on/off the sensor while maintaining an acceptable attitude estimation. The effciency of the proposed methods is evaluated by means of numerical simulations and experimental tests.
19

Estimation d'attitude et diagnostic d'une centrale d'attitude par des outils ensemblistes / Attitude central unit with accurate computation of the attitude and sensor fault detection capabilities

Nguyen, Hoang Van 24 March 2011 (has links)
L'estimation de l'attitude (ou orientation) est un problème récurrent de nombreuses applications allant de la robotique aérienne ou sous-marine en passant par des applications médicales (surveillance de patients, réhabilitation), mais aussi jeux vidéo, etc. L'objectif de cette thèse est d'évaluer l'apport des approches ensemblistes dans le cadre de l'estimation de l'attitude à partir de données issues de triaxes accéléromètres (A), magnétomètres (M) et gyromètres (G). Dans un premier temps, on s'intéresse aux mouvements "quasi-statiques" et l'estimation de l'attitude est réalisée à partir de mesures AM. On aborde ensuite le cas des mouvements dynamiques, en considérant l'ensemble des mesures AGM. Le problème du choix de la paramétrisation de l'attitude a été abordé et on a comparé les résultats obtenus et le temps calcul pour des modélisations avec les angles de Cardan et le quaternion unitaire. Les algorithmes développés ont été validés en simulation et avec des données réelles. Les résultats ont été comparés avec ceux fournis par des algorithmes de l'état de l'art, par exemple SIVIA. La deuxième partie du manuscrit est consacrée à au diagnostic des capteurs de la centrale inertielle avec des approches ensemblistes. Les algorithmes développés dans la première partie du travail sont adaptés afin de pouvoir détecter et localiser un défaut dans l'ensemble des capteurs considérés. / Attitude estimation is one of the prominent problem encountered in various application areas such as Aerial and submarine robotics, bio-medical applications (elderly people monitoring, rehabilitation) but also, video game and augmented reality. The main objective of this PhD is to assess the capabilities of set-membership estimation in the field of attitude estimation when triaxes accelerometer (A) magnetometer (M) and rate gyros (G) are used. Quasi-static movements are first considered. In this case AM measurements are taken into account. Then the dynamic case is considered with AGM measurement taken into account in the set-membership estimation algorithm. The problem of attitude parametrisation is also studied as it will have a strong in uence on the computational time. The algorithms proposed during this work have been validated with simulated and real data. The second part of the report deals with Fault Detection and Isolation based upon set-membership approaches. The algorithms that have been developed in the first part of this work have been adapted to cope with diagnosis of a faulty sensor within the Inertial Measurement Unit.
20

Modelagem e controle de um microve?culo a?reo: uma aplica??o de estabilidade robusta com a t?cnica backstepping em uma estrutura hexarrotor

Sanca, Armando Sanca 01 February 2013 (has links)
Made available in DSpace on 2014-12-17T14:55:11Z (GMT). No. of bitstreams: 1 ArmandoSS_TESE.pdf: 2110397 bytes, checksum: c6ade2a7219938325c34c1856e93d29f (MD5) Previous issue date: 2013-02-01 / In this Thesis, the development of the dynamic model of multirotor unmanned aerial vehicle with vertical takeoff and landing characteristics, considering input nonlinearities and a full state robust backstepping controller are presented. The dynamic model is expressed using the Newton-Euler laws, aiming to obtain a better mathematical representation of the mechanical system for system analysis and control design, not only when it is hovering, but also when it is taking-off, or landing, or flying to perform a task. The input nonlinearities are the deadzone and saturation, where the gravitational effect and the inherent physical constrains of the rotors are related and addressed. The experimental multirotor aerial vehicle is equipped with an inertial measurement unit and a sonar sensor, which appropriately provides measurements of attitude and altitude. A real-time attitude estimation scheme based on the extended Kalman filter using quaternions was developed. Then, for robustness analysis, sensors were modeled as the ideal value with addition of an unknown bias and unknown white noise. The bounded robust attitude/altitude controller were derived based on globally uniformly practically asymptotically stable for real systems, that remains globally uniformly asymptotically stable if and only if their solutions are globally uniformly bounded, dealing with convergence and stability into a ball of the state space with non-null radius, under some assumptions. The Lyapunov analysis technique was used to prove the stability of the closed-loop system, compute bounds on control gains and guaranteeing desired bounds on attitude dynamics tracking errors in the presence of measurement disturbances. The controller laws were tested in numerical simulations and in an experimental hexarotor, developed at the UFRN Robotics Laboratory / Nesta Tese, s?o apresentados os desenvolvimentos da modelagem din?mica de um ve?culo a?reo n?o tripulado multirrotor com capacidade de decolagem e pouso vertical, considerando as n?o linearidades de entrada e o desenvolvimento de um controlador robusto por backstepping. A formula??o do modelo din?mico ? expressa usando-se as leis de Newton-Euler, visando ? obten??o de uma melhor representa??o matem?tica do sistema mec?nico para a an?lise e projeto das leis de controle, n?o apenas quando est? pairando, como tamb?m de decolagem, de pouso, ou de voo executando uma tarefa. As n?o linearidades de entrada s?o a zona morta e a satura??o, onde o efeito gravitacional e as inerentes restri??es f?sicas dos rotores s?o relacionadas e abordadas. O microve?culo experimental est? equipado com uma unidade de medida inercial e um sonar, que devidamente instrumentada fornece as medidas da atitude e altitude. Foi desenvolvido um estimador em tempo real para atitude usando quat?rnios e baseado em filtro de Kalman estendido. Para a formula??o robusta do controlador, os sensores foram modelados como o valor real, que ? o valor ideal com a adi??o de um vi?s e mais um ru?do branco desconhecidos e limitados. Os controladores de atitude e altitude foram derivados usando-se o crit?rio globalmente uniformemente praticamente assintoticamente est?vel para sistemas reais, que permanece globalmente uniformemente assintoticamente est?vel se e somente se suas solu??es s?o globalmente uniformemente limitadas, lidando com a converg?ncia e estabilidade dentro de uma regi?o com raio n?o nula, levando em considera??o algumas suposi??es como as incertezas nas medi??es. A t?cnica de an?lise de Lyapunov foi usada para: provar a estabilidade do sistema em malha fechada; calcular os limites dos ganhos de controle, e, obter a garantia limitada pretendida sobre o erro de rastreamento da din?mica de atitude na presen?a de dist?rbios nas medi??oes. As leis de controle foram testadas em simula??es num?ricas e em um hexarrotor experimental, desenvolvido no Laborat?rio de Rob?tica da Universidade Federal do Rio Grande do Norte

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