Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2006. / An analysis of the attitude determination and control system required for a small geostationary satellite is performed in this thesis. A three axis quaternion feedback reaction wheel control system is the primary control system used to meet the stringent accuracy requirements. A momentum bias controller is also evaluated to provide redundancy and to extend actuator life. Momentum dumping is preformed by magnetic torque rods using a crossproduct controller. Performance of three axis thruster control is also evaluated. A full state Extended Kalman filter is used to determine attitude and body angular rates during normal operation whereas a Multiplicative Extended Kalman Filter is used during attitude manoeuvres. An analytical orbit control study is also performed to calculate the propellant required to perform station-keeping, for a specific sub-satellite location over a ten year period. Finally an investigation on the effects caused by thruster misalignment, on satellite attitude is also performed.

A three-rotational degree of freedom attitude control system has been developed for the NASA Jet Propulsion Laboratory’s INSPIRE Project by the Texas Spacecraft Laboratory at The University of Texas at Austin. Using 3D plastic printing manufacturing techniques, a cold gas thruster system was created in order to detumble and maintain the attitude of two 3U CubeSats traveling through interplanetary space. A total of four thruster units were produced, including two engineering designs and two flight units. The units feature embedded sensors and millisecond level thrust control while using an inert, commercially-available refrigerant as a propellant. The thrust, minimum impulse bit, and specific impulse performance of the cold gas units was characterized using a ballistic pendulum test stand within a microtorr vacuum chamber. A heating element was used to change the temperature conditions of the propellant and determine the relationship between temperature and performance. The flight units were delivered in January of 2014 and the INSPIRE satellites are expected to launch in the upcoming year. / text

This thesis investigates the possibility of using reinforcement learning (RL) techniques to create a flight controller for a quadrotor Micro Aerial Vehicle (MAV). A capable flight control system is a core requirement of any unmanned aerial vehicle. The challenging and diverse applications in which MAVs are destined to be used, mean that considerable time and effort need to be put into designing and commissioning suitable flight controllers. It is proposed that reinforcement learning, a subset of machine learning, could be used to address some of the practical difficulties. While much research has delved into RL in unmanned aerial vehicle applications, this work has tended to ignore low level motion control, or been concerned only in off-line learning regimes. This thesis addresses an area in which accessible information is scarce: the performance of RL when used for on-policy motion control. Trying out a candidate algorithm on a real MAV is a simple but expensive proposition. In place of such an approach, this research details the development of a suitable simulator environment, in which a prototype controller might be evaluated. Then inquiry then proposes a possible RL-based control system, utilising the Q-learning algorithm, with an adaptive RBF-network providing function approximation. The operation of this prototypical control system is then tested in detail, to determine both the absolute level of performance which can be expected, and the effect which tuning critical parameters of the algorithm has on the functioning of the controller. Performance is compared against a conventional PID controller to maximise the usability of the results by a wide audience. Testing considers behaviour in the presence of disturbances, and run-time changes in plant dynamics. Results show that given sufficient learning opportunity, a RL-based control system performs as well as a simple PID controller. However, unstable behaviour during learning is an issue for future analysis. Additionally, preliminary testing is performed to evaluate the feasibility of implementing RL algorithms in an embedded computing environment, as a general requirement for a MAV flight controller. Whilst the algorithm runs successfully in an embedded context, observation reveals further development would be necessary to reduce computation time to a level where a controller was able to update sufficiently quickly for a real-time motion control application. In summary, the study provides a critical assessment of the feasibility of using RL algorithms for motion control tasks, such as MAV flight control. Advantages which merit interest are exposed, though practical considerations suggest at this stage, that such a control system is not a realistic proposition. There is a discussion of avenues which may uncover possibilities to surmount these challenges. This investigation will prove useful for engineers interested in the opportunities which reinforcement learning techniques represent.

The subject of the thesis is the design and implementation of a modular control system environment, which could be used in robotics. Both autonomous and guided robots are supported. The higher-level software com- ponents like localization, steering, decision making, etc. are effectively sepa- rated from the underlying hardware devices and their communication protocols in the environment. Based on the layered design, hardware-independent algo- rithms can be implemented. These can run on different hardware platforms just by exchanging specific device drivers. Written in C++ using standard libraries, the final software is highly portable and extensible. Support for new platforms and hardware modules can be implemented easily. The whole sys- tem was tested on two robots and the particular instances of the systems built using this development environment are included in the solution and partially described in the thesis.

I arbetet undersöks behovet av ökad kontroll i stålbyggnadskonstruktioner med avseende på utförandefel. Riksdagen beslutade 1 juni 1994 att förändra Plan- och bygglagen (PBL) där förändringen trädde i kraft 1995 och bland annat innebar att hela ansvaret för en byggnads uppförande och kontroll lades på byggherren. Efter vintrarna 2009/10 och 2010/11 där flera tak rasade av snötyngden uppdagades en rad dimensionerings- och utförandefel. Under examensarbetet undersöktes vad som händer med säkerheten i byggnadskonstruktioner i stål som genomgår förändringar under dess livslängd och en jämförelse mot gällande regelverk genomfördes. En fältstudie och flera intervjuer genomfördes där fokus låg på utförandefel och hur förändringar av regelverk lett fram till dagens egenkontrollsystem som påverkat antalet utförandefel. Arbetets resultat visar att det kan finnas ett behov av att se över dagens kontrollsystem och att antalet allvarliga utförandefel i fallstudieobjektet ökat efter 1995. / In the work the need of increased inspections of steel structures with respect to errors of execution was examined. On 1 June 1994, the Swedish parliament decided to change the Planning and Building Act (PBL) and the changes came into force in 1995, where the entire responsibility for the construction and control of a building was placed on the developer. After the winters of 2009/10 and 2010/11, when several roofs collapsed by the snow weight, a number of design and execution faults were discovered. During the thesis work it was investigated what happens to the safety of building structures in steel that undergo changes during its lifetime and a comparison with current regulations was made. A field study and several interviews were conducted where the focus was on execution errors and how changes in regulations led to today's self-control systems that affect the number of execution errors. The results of the work show that there may be a need to review the current control system and that the number of serious execution errors in the case study object increased after 1995.

O Motor Assíncrono Tubular para Aplicação na Extração de Óleo do Subsolo MATÆOS foi desenvolvido na Escola Politécnica da Universidade de São Paulo (EPUSP) com a função de acionar diretamente uma bomba de sucção, instalada no fundo de um poço de petróleo em terra. Dando continuidade aos trabalhos realizados na EPUSP envolvendo sistemas de levitação magnética, foi desenvolvido um mancal magnético ativo (AMB - Active Magnetic Bearing), aplicado ao protótipo do motor em substituição ao mancal mecânico tradicional existente. O projeto abrange a construção de um protótipo de mancal magnético composto das partes mecânicas, elétricas e de software necessárias ao funcionamento do sistema. O projeto do eletroímã foi realizado por meio do método dos elementos finitos (MEF), para análise da densidade de fluxo e da relação entre a força radial e a corrente elétrica nas bobinas. O controle da levitação do mancal é realizado por meio de controlador digital com placas conversoras AD/DA e algoritmo de controle implementado em hardware FPGA. Utilizando o modelo do sistema, os controladores são sintonizados para atender aos requisitos de estabilidade e rejeição de perturbações, que desviem o entreferro do seu valor nominal. Na configuração do AMB, ao invés do sistema tradicional com oito pólos, um conceito diferente é adotado. Neste, uma máquina primitiva bearingless é excitada com corrente contínua e usada como mancal magnético. Os resultados experimentais obtidos com o protótipo em funcionamento mostram que o sistema em malha fechada é estável e apresenta uma resposta transitória satisfatória. / A tubular linear induction motor applied to onshore oil exploitation, named MATÆOS (which is in the Portuguese acronym for Tubular Asynchronous Motor for Onshore Oil Exploitation) was built at Escola Politécnica da Universidade de São Paulo (EPUSP). Its purpose is to directly drive the sucker-rod pump installed in the down hole of the oil well. In continuing the research accomplished at EPUSP concerning magnetic levitation systems, an Active Magnetic Bearing (AMB) was developed and applied to the prototype of the motor in substitution to the existing traditional bearing. The design includes the construction of the magnetic bearing prototype composed of mechanical, electric and software components required to the operation of the system. The electromagnet design was accomplished using the Finite Element Method (FEM) in the analysis of both the flux density and the relationship between the radial force and the suspension winding current. The magnetic bearing levitation control is executed by a digital controller using an AD/DA converter and a control algorithm implemented in FPGA hardware. Using the system model, the controllers are tuned to provide both stability and rejection of disturbances that tend to move the air gap from its nominal value. Instead of the usual eight-pole AMB, a different concept is adopted where a DC-excited primitive bearingless machine is used as a magnetic bearing. The experimental results obtained with the prototype in operation show that the closed-loop system is stable and exhibits a satisfactory transient response.

Contabilidade Gerencial e a Estratégia têm em comum a questão do desempenho organizacional, a primeira tem como objetivo medir o desempenho, a segunda se preocupa em como as organizações podem obter desempenho por meio de vantagens competitivas. Uma abordagem utilizada pela Estratégia é a Visão Baseada em Recursos, nessa ótica, o desempenho é potencializado pelas competências organizacionais da empresa, mas, nessa busca pelas competências, as organizações utilizam-se do Sistema de Controle Gerencial - SCG. Dependendo de como o SCG é utilizado, diagnóstica ou interativamente, ou uma combinação dos ambos, este pode contribuir para o desenvolvimento das competências e balancear as Tensões Dinâmicas e, indiretamente, influenciar o desempenho organizacional. Fundamentado no modelo teórico de Henri (2006), o objetivo deste trabalho foi contribuir para o entendimento deste relacionamento nas 1.000 maiores empresas brasileiras, utilizando a técnica estatística multivariada Modelagem de Equações Estruturais com o método de estimação Partial Least Square PLS. Os resultados em um total de 104 empresas indicam que (i) não existem evidências de relacionamento negativo entre o Uso Diagnóstico e o desenvolvimento de competências organizacionais, sugerindo que, no Brasil, o Uso Diagnóstico pode ter um menor componente disfuncional, e também, que este pode ser visto como uma rotina organizacional necessária para manter a organização dentro de um caminho planejado, o que não é incompatível com o desenvolvimento das competências; (ii) não existem relacionamentos significativos positivos entre desenvolvimento de competências e desempenho econômico, medido pelo Retorno sobre Patrimônio Líquido, o que é coerente com o estudo de Henri (2006), sugerindo que devem existir outras variáveis não contempladas no modelo, ou ainda que o indicador RSPL possa não ser uma proxy adequada de desempenho nos anos de 2005 a 2007; (iii) existe relacionamento positivo entre o Uso Interativo e o desenvolvimento de competências, com exceção do Empreendedorismo, o que é consistente com os resultados de Henri (2006); (iv) existe relacionamento positivo entre as Tensões Dinâmicas e as competências, o que está em linha com Henri (2006) e valida a teoria de que as tensões são importantes para busca da eficácia organizacional; (v) Uso Diagnóstico e Uso Interativo do SCG influenciam positivamente as Tensões Dinâmicas, podendo configurar o SCG como um recurso complementar na ótica da VBR; (vi) quando o desempenho é medido por auto-avaliação, ocorre uma alteração nos resultados dos relacionamentos entre competências e desempenho, com as competências Aprendizagem Organizacional e Orientação para Mercado influenciando positivamente o desempenho, indicando que estas duas competências/orientações devem ser estimuladas pelo uso do SCG. Os resultados da pesquisa estão sujeitos a algumas limitações, a principal delas refere-se ao fato que as respostas refletem a percepção dos profissionais de controladoria e finanças das empresas e a análise dos dados também não considerou a estratificação por setores econômicos. Estas limitações ensejam futuras pesquisas, como a sua replicação utilizando outro perfil de respondente, a realização de estudos de casos em empresas com diferentes culturas e desempenhos, bem como estudos que aprofundem a dimensão uso com competências específicas e mesmos construtos oriundos de outros campos de conhecimento. / Managerial Accounting and the Strategy have in common the issue of organizational performance; the first has as the objective of performance measuring the second focuses on how the organizations can obtain performance through competitive advantages. An approach used by the Strategy is the Resource-Based View, through this point of view, the performance is maximized by the company organizational competences, but in this competences search, the organizations use the Management Control System - MCS. Depending on how the MCS is used diagnostically or interactively, or in a combination of both, this can contribute to the competences development and the dynamic tensions balance and indirectly, influence the organizational performance. Originated by the Henri (2006) theoretical model this study proposal is to contribute for this relationship understanding in the 1,000 Brazilian biggest companies, using the multivariate statistic technique Structural Equation Modeling with the estimation method Partial Least Square PLS. The result in a total of 104 companies indicates that (i) there are no evidences of negative relationship between the diagnostic use and the organizational competences development, suggesting that in Brazil, the diagnostic use can have a minor dysfunctional component, and also, that the diagnostic use can be seen as an organizational routine needed to maintain the organization in a planned path, which is not incompatible with the competences development ; (ii) there are no meaningful positive relationships between the competence development and the economical performance, measured by the Return on Equity, which is coherent with the Henri (2006), suggesting that there must be other variables not contemplated in the model, or even that the indicator ROE might not be an adequate proxy of development in the years of 2005-2007; (iii) there is a relationship between the interactive use and the development of competences, excepting the enterprising, which is consistent with Henri (2006) results; there is a positive relation between the dynamic tensions and the competences, which is aligned with Henri (2006) and validates the theory that the tensions are important for the search of the organizational effectiveness (v) diagnostic use and interactive use of the MCS have a positive influence on the dynamic tensions, being able to configure the MCS as an additional resource in the RBV framework ; (vi) when the development measurement is made by self-evaluation, there happens a results change of the relations between competences and performance, with the organizational learning competences and market orientation having a positive influence on the performance, indicating that this two competences/orientations must be stimulates by the MCS use. The research results have some limitation; the main one is that the answers reflect the perception of corporate controllers and finance managers The data analyses did not take in account the stratification by economical sector. These limitations enhance future researches, such as its reply using others professional profiles ; the use cases study methodology in companies with different cultural and performance profiles, and more accurate studies of the usage dimension of specific competences and the same construct deriving from other fields of knowledge.

Entender a influência que o Sistema de Controle Gerencial (SCG) exerce nos funcionários é de suma importância para que uma empresa consiga alcançar seus objetivos. Entretanto, o foco das pesquisas sobre os efeitos dos SCG nos indivíduos tem tido forte incidência no comportamento disfuncional (Birnberg, Turopolec, & Young, 1983; Chenhall, 2006; Hartmann, 2000). Portanto, é urgente a necessidade de um novo olhar sobre o SCG, enfatizando o quanto o SCG pode aprimorar o potencial dos indivíduos, fazendo com que eles se empenhem para que a organização alcance seus objetivos. Assim, esta tese investiga os relacionamentos entre o Sistema de Controle Gerencial, o Capital Psicológico e satisfação no trabalho e o comprometimento organizacional. Fundamentado no framework das alavancas de controle de Simons (1995), este estudo tem por hipótese uma associação positiva entre o SCG e o Capital Psicológico, que é definido como um estado psicológico positivo de um indivíduo, que enfatiza o desenvolvimento de forças individuais, caracterizado por: autoeficácia, esperança, otimismo e resiliência. Ademais, investigou-se a hipótese de que há uma associação positiva entre o Capital Psicológico e a satisfação no trabalho e o comprometimento organizacional. Para alcançar os objetivos da pesquisa, realizou-se um survey single entity em uma empresa brasileira de grande porte do setor alimentício. Foram utilizadas duas técnicas de coleta de dados, questionário e entrevistas, a fim de obter uma análise ampla do fenômeno a ser estudado. As entrevistas foram realizadas com doze diretores e gerentes da empresa, com o objetivo de buscar uma compreensão mais profunda sobre o sistema de controle gerencial, a fim de agregar informações adicionais sobre os achados quantitativos. O questionário foi aplicado a uma amostra de 132 respondentes de uma população de 404, abrangendo gerentes e coordenadores de diversas áreas da organização. Os dados coletados pelo survey foram submetidos a técnicas estatística de análise descritiva e análise de equações estruturais (PLS-SEM). Os resultados indicaram que há uma forte associação entre o SCG e o Capital Psicológico, que, por sua vez, está relacionado com a satisfação no trabalho e o comprometimento organizacional. Esse resultado é relevante, ao demonstrar empiricamente o quanto o Sistema de Controle Gerencial pode aprimorar o potencial dos indivíduos, uma vez que o Capital Psicológico produz motivação e perseverança em direção à realização de metas, promovendo atitudes e comportamentos desejáveis e ajudando a aplacar resultados atitudinais e comportamentais indesejáveis (Avey, Reichard, et al., 2011; Luthans et al., 2015), contribuindo para que a organização adquira vantagem competitiva. / The understanding of the influence that the Management Control System (MCS) exerts on the employees is of paramount importance for the company to achieve its objectives. However, the focus of research on the effects of MCS on individuals has had a strong incidence on dysfunctional behavior (Birnberg, Turopolec, & Young, 1983; Chenhall, 2006; Hartmann, 2000). Therefore, there is a need for a new look at MCS, emphasizing how MCS can enhance individuals\' potential by making them strive for the organization to achieve its intended goals. Thus, this thesis investigates the relationships between the Management Control System, the Psychological Capital and job satisfaction and the organizational commitment. Based on the Levers of Control framework of Simons (1995), this study hypothesizes a positive association between MCS and Psychological Capital, which is defined as a positive psychological state of an individual that emphasizes the development of individual forces, characterized by self-efficacy, hope, optimism and resilience. In addition, was investigated the hypothesis that there is a positive association between Psychological Capital and job satisfaction and organizational commitment. To achieve the research objectives, a survey single entity was conducted in a large Brazilian company in the food sector. Two techniques of data collection, questionnaire and interviews, were used in order to obtain a broad analysis of the phenomena to be studied. The interviews were conducted with twelve directors and managers of the company, with the objective of seeking a deeper understanding of the company\'s management control system in order to aggregate additional information about the quantitative findings. The questionnaire was applied to a sample of 132 respondents from a population of 404, comprising managers and coordinators from various areas of the organization. The data collected by the survey were submitted to statistical techniques of descriptive analysis and analysis of structural equations (PLS-SEM). The results indicated that there is a strong association between MCS and Psychological Capital, which, in turn, is related to job satisfaction and organizational commitment. This result is relevant, by empirically demonstrating how the Management Control System can improve individuals\' potential, since Psychological Capital produces motivation and perseverance towards achieving goals by promoting desirable attitudes and behaviors and helping to placate undesirable attitudinal and behavioral outcomes (Avey, Reichard, et al., 2011; Luthans et al., 2015), contributing to the organization gaining competitive advantage.

Le cadre de cette thèse est l'étude des systèmes contrôlés en réseau sans fil (SCRSF) qui utilise la technologie IEEE 802.15.4. Le premier objectif est d'étudier la pertinence de l'utilisation du réseau de type IEEE 802.15.4 pour les SCRSF puis de proposer et d'évaluer des mécanismes pour garantir la Qualité de Service (QdS) offerte par le réseau au système contrôlé. Nous analysons l'utilisation des slots temporels réservés (GTS) dans le cadre des SCRSF et les contraintes qui en découlent. De plus, nous proposons des mécanismes de gestion de la QdS avec priorité aussi bien pour le mode avec balise que pour le mode sans balise du protocole IEEE 802.15.4. Ces propositions ont été validées par des simulations et une partie de manière analytique. Notre deuxième objectif est de concevoir, d'une manière conjointe, les SCRSF pour pouvoir régler en ligne la QdS offerte par le réseau en fonction de la Qualité de Contrôle (QdC) du système contrôlé. Nous proposons des protocoles d'adaptation en ligne de la QdS du réseau qui prennent en compte la QdC du système contrôlé. Ces protocoles ont été validés par simulations et une implémentation réelle de chacun d'eux est proposée / In this thesis, we study wireless networked control systems (WNCS) which use the IEEE 802.15.4 technology. The first objective is to study the pertinence of the use of the IEEE 802.15.4 for the WNCS, then to propose and evaluate QoS management mechanisms which guarantee the Quality of Service (QoS) offered by network to the controlled system. We analyse the use of the guaranteed temporel slots (GTS) for WNCS and in which conditions it is possible. We propose QoS management mechanisms with priority for both the beacon enabled mode and the non-beacon enabled mode of the IEEE 802.15.4 protocol. These proposals are validated through simulations and partially with analytical approach. The second objective is to design the WNCS so that the QoS offered by the network is adated online depending on the Quality of Control (QoC) on the controlled system. We propose QoS online adaptation protocols which take as parameter the QoC of the system. These protocols are validated through simulations and a realistic implementation of them is proposed

The present thesis deals with the analysis of Environmental Control System (ECS) as a part of the aircraft conceptual design. The research focuses on developing methods for modelling, simulation and optimization of current and future cooling technologies suitable for aircraft applications. The work started with a pre-study in order to establish the suitability of different cooling technologies for ECS application. Therefore, five technologies namely, Bootstrap (BS), Reverse-Bootstrap (RBS), vapour cycle system (VCS), magnetic cooling (MC) and thermo-electric cooling (EC), were assessed from a theoretical point of view by the method of benchmarking. This resulted into the selection of three most suitable technologies that were further modelled and simulated in Dymola. In order to compare the optimum designs for each technology, the models were optimized using the modeFRONTIER software. The comparison was performed based on the optimum ratio of maximum power of cooling and minimum fuel penalty. The results showed that VCS has the “best” performances compared to BS and RBS. In addition to the active technologies, passive cooling methods such as liquid cooling by means of jet-fuel and poly-alpha-olefin were considered to address high heat transfer rates. In order to apply the cooling technologies in the ECS, concept system architectures were formulated using the functional analysis. This led to the identification of basic functions, components and sub-systems interaction. Based on the comparison carried out previously and the functional analysis, two ECS architectures were developed. Design optimization procedure was applied further in order to assess each concept and also to study the differences between the two concept architectures. The results depict the complex interaction of different key parameters of the architectures and their influence on the outcome. The study culminated with a proposed methodology for formulation of systems architecture using information from the optimization results and a robust functional analysis method. To sum up, the thesis proposes a simulation-based optimization method that allows inclusion of ECS system in aircraft conceptual design phase. The study also proves the complexity of the conceptual design stage for ECS architectures which highly influences the design of the combat aircraft.