Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Document formatted into pages; contains xxi, 261 p.; also includes graphics (some col.). Includes bibliographical references (p. 244-254). Available online via OhioLINK's ETD Center

Thesis (Ph.D.) - University of St Andrews, September 2007. / Restricted until 14th September 2009.

Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Document formatted into pages; contains xvii, 213 p.; also includes graphics (some col.). Includes bibliographical references (p. 206-213). Available online via OhioLINK's ETD Center

Automotive active suspension, advanced seismic testing, and force/torque emulations of space manipulators are examples of applications, where the hydraulic actuator force control is required. In double-rod hydraulic actuators, the actuator force is the differential pressure across the actuator multiplied by the piston effective area. The focus of this work is to control the actuator force of a double-rod hydraulic actuator by controlling the differential pressure across the actuator. The double-rod hydraulic actuator of this study is run by two independent circuits: 1) electro-hydraulic actuation and 2) electro-hydrostatic actuation. In general, developing controllers for hydraulic actuators is challenging due to the presence of parametric uncertainties and uncertain nonlinearities. Also, a specific challenge in force control of hydraulic actuators is the limiting effect of environment dynamics on the maximum achievable tracking bandwidth. Considering the above challenges, in this research for the first time, quantitative feedback theory (QFT) is employed to control the hydraulic actuator force. Using QFT, a robust, linear, fixed-gain, and low-order controller is designed for each actuation system which: (i) keeps the closed-loop response within desired tracking bounds (ii) guarantees the closed-loop stability around desired operating points, (iii) rejects disturbance, and (iv) achieves desired tracking bandwidth. Among the performance criteria, special attention is paid to achieve high tracking bandwidth. Trade-offs between different performance criteria towards achieving high tracking bandwidth, are discussed. Experimental results are presented to validate that the performance criteria are satisfied by the designed QFT controllers. The QFT controllers are synthesized based on the families of frequency responses of the hydraulic actuation systems, which limits the stability results of the closed-loop system, only for these families of the frequency responses. In this thesis, to investigate the nonlinear stability of the closed-loop systems with QFT controllers, for the first time, Takagi-Sugeno (T-S) fuzzy modeling and its corresponding stability theory are used. The stability conditions are presented in the form of linear matrix inequalities (LMIs). As a result, the nonlinear stability of the designed QFT controllers for both the actuation systems is proven in the presence of parametric uncertainties. / February 2016

Thesis (MScEng)--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: A unified method is proposed to treat saturation in both Multi-Input-Multi-Output MIMO and Single-Input-Single-Output controllers. This method offers superior performance over existing MIM 0 anti-saturation schemes. The anti-saturation problem is posed as a linear programming problem. A practical and efficient implementation of the algorithm is developed by transforming the problem into its dual linear programming form. The problem, in dual form, is then solved using the dual simplex method rather than the primal simplex method. The nature of the problem when expressed in dual form and the properties of the dual simplex method are harmonised to guarantee an initial basic feasible solution and an optimal bounded final solution in a finite, predictable and minimal number of iterations. The resultant controller never saturates, hence cannot windup. Furthermore the resultant controller always applies the optimal control effort to the plant to minimise the error signal input as follows: • The controller is governed such that while the future free response combined with the present forced response of the controller results in no saturation limits being exceeded, now or at some time in the future, the normal linear response of the controller prevails. • When the future free response combined with the present forced response of the controller will result in a saturation limit being reached, now or at some time in the future, the present time input signal into the controller is optimally governed to prevent the saturation limit from being exceeded at any future time. / AFRIKAANSE OPSOMMING: 'n Metode word voorgestel waarmee versadiging in enkel-inset enkel-uitset en meer-inset meeruitset (MIMU) stelsels beheer kan word. Die metode presteer beter as ander huidige teenversadiging- maatreels vir (MIMU) beheerders. Die teen-versadigings-probleem word as 'n lineere programmeringsprobleem herformuleer. 'n Praktiese en effektiewe implementering van die algoritme word verkry deur die probleem na die duale vorm te transformeer. Die probleem, in duale vorm, word opgelos met die duale simplex metode, in plaas van die direkte metode. Die eienskappe van hierdie formulering is 'n gewaarborgde, aanvanklike, bereikbare oplossing en 'n optimale, begrensde, finale oplossing in 'n eindige, voorspelbare en minimum aantal stappe. Die uiteindelike beheerder versadig nooit nie, en wen gevolglik nie op nie. Die beheerder wend altyd die optimale aanleg-inset aan om die foutsein te minimeer soos volg: • Wanneer die nul-inset gedrag saam met die huidige inset-gedrag geen beperkings nou of in die toekoms saloorskry nie, word geen beperkende aksie geneem nie, en tree die beheerder dus lineer op. • Sodra die toekomstige nul-inset gedrag saam met die huidige inset-gedrag, nou of later versadiging sou veroorsaak, word die huidige inset tot die beheerder optimaal begrens om latere versadiging te voorkom.

Les systèmes microélectromécaniques (MEMS) sont des dispositifs de taille micrométrique capables de transformer un signal mécanique en un signal électrique et vice-versa. Ils sont aujourd'hui largement répandus dans notre vie quotidienne pour la détection, la transformation de l'énergie et l'actionnement de dispositifs grâce à leur faible dissipation énergétique, leur réponse ultra-rapide et leur grande sensibilité. Même si depuis plusieurs décennies, les progrès technologiques ont entraîné la miniaturisation des ces dispositifs, il reste nombreux challenges à surmonter dont l'un des plus importantes est l'intégration à l'échelle nanométrique d'actionneurs à base des matériaux dit " intelligents " (à ces dimensions, les matériaux habituellement utilisés perdent leurs propriétés d'actionnement). Dans ce contexte, ce travail de thèse avait pour objectif d'explorer l'utilisation des matériaux moléculaires à transition de spin pour le développement d'actionneurs électromécaniques. Dans ce but, nous avons conçu des microleviers en silicium que nous avons recouvert par différentes molécules à transition de spin soit par sublimation, soit par " spray-coating ". Les MEMS ont été caractérisés à température et pression variables en modes dynamique et statique à l'aide d'un unique dispositif expérimental. Les résultats obtenus démontrent que les molécules à transition de spin peuvent être intégrées, à l'aide de différents procédés de fabrication, dans des dispositifs MEMS et qu'il est possible de réaliser l'actionnement à l'aide d'une source d'énergie thermique (chauffage et refroidissement) et/ou lumineuse. Simultanément, cette étude a également permis d'évaluer les propriétés mécaniques des matériaux à transition de spin (module de Young, coefficient de Poisson) qui restent mal connues. / Microelectromechanical systems (MEMS) are micrometric devices able to transform a mechanical signal into an electrical one and vice-versa. In the past years they have been successfully employed in different fields of our everyday life for sensing, transducing different forms of energy and for actuating purposes thanks to their low energy dissipation, fast response and high sensibility. Even if recent technological progress has allowed a considerable miniaturization of these devices, several challenges remain. In particular the integration of smart actuating materials at the nanometric scale remains arduous because in most cases they lose their actuating properties at reduced sizes. In this context, this thesis work aimed for exploring the possibility of using molecular spin crossover materials for the development of electromechanical actuators. To this aim we have conceived silicon microcantilevers, which have been coated by various spin crossover molecules using either thermal evaporation or spray-coating methods. The MEMS have been characterized at variable temperature and pressure both in dynamical and static modes using a single experimental setup. The results prove that spin crossover molecules can be successfully integrated into silicon MEMS devices using different fabrication processes and their actuation can be achieved using either a thermal energy source or light irradiation. In parallel, this work has allowed us to extract relevant mechanical properties of spin crossover materials (Young's modulus, Poisson's ratio), which have been largely unknown previously.

The control of complex robotic platforms is a challenging task, especially in designs with high levels of kinematic redundancy. Novel variable impedance actuators (VIAs) have recently demonstrated that, by allowing the ability to simultaneously modulate the output torque and impedance, one can achieve energetically more efficient and safer behaviour. However, this adds further levels of actuation redundancy, making planning and control of such systems even more complicated. VIAs are designed with the ability to mechanically modulate impedance during movement. Recent work from our group, employing the optimal control (OC) formulation to generate impedance policies, has shown the potential benefit of VIAs in tasks requiring energy storage, natural dynamic exploitation and robustness against perturbation. These approaches were, however, restricted to systems with smooth, continuous dynamics, performing tasks over a predefined time horizon. When considering tasks involving multiple phases of movement, including switching dynamics with discrete state transitions (resulting from interactions with the environment), traditional approaches such as independent phase optimisation would result in a potentially suboptimal behaviour. Our work addresses these issues by extending the OC formulation to a multiphase scenario and incorporating temporal optimisation capabilities (for robotic systems with VIAs). Given a predefined switching sequence, the developed methodology computes the optimal torque and impedance profile, alongside the optimal switching times and total movement duration. The resultant solution minimises the control effort by exploiting the actuation redundancy and modulating the natural dynamics of the system to match those of the desired movement. We use a monopod hopper and a brachiation system in numerical simulations and a hardware implementation of the latter to demonstrate the effectiveness and robustness of our approach on a variety of dynamic tasks. The performance of model-based control relies on the accuracy of the dynamics model. This can deteriorate significantly due to elements that cannot be fully captured by analytic dynamics functions and/or due to changes in the dynamics. To circumvent these issues, we improve the performance of the developed framework by incorporating an adaptive learning algorithm. This performs continuous data-driven adjustments to the dynamics model while re-planning optimal policies that reflect this adaptation. The results presented show that the augmented approach is able to handle a range of model discrepancies, in both simulation and hardware experiments using the developed robotic brachiation system.

Thesis (MTech (Mechanical Engineering))--Peninsula Technikon, Cape Town, 2002 / Distributed Piezoelectric Actuator (DPA) is one kind of actuator in the smart technology field. Firstly, DPA is one kind of solid-state actuator, and can be embedded in the structure. Secondly, it can be controlled by the electrical signal with high bandwidth and high precision. So it can be applied in the many different fields, such as high-resolution positioning, noise and vibration detection and shape control. Up to now, all of the DPA theory investigations and the product designs are based on applying the approximate electrical field. And only the rectangular shape DPA has been studied. The accurate distribution and intensity of electrical and mechanics field, and the numerical imitation for the DPA products with rectangular and other shapes have never been discussed and studied. Therefore, the development of DPA to be used in the micro application, such as in the Micro Electro-Mechanical System (MEMS), has been limited. This thesis has developed the analytical analysis models for two types of DPA elements and the part circular shape DPA element. The MathCAD and MATLAB program have been used to develop the analytical models. The ABAQUS program has also been used to compare the results between the analytical models and Finite Element Method (FEM). Finally, the accuracy and reliability of analytical models have been proved by results comparison between the analytical models, FEM and the product testing data from the industry. This thesis consists of five chapters. Chapter 1 is the introduction of smart structure. The characterizations of constituent materials, including the piezoelectric material and matrix epoxy material have been discussed in Chapter 2. In Chapter 3, the analytical models for two type of DPA element have been developed and the comparisons have also been completed. The analytical models for part circular shape DPA element have been developed in Chapter 4. The conclusions and recommendations are included in Chapter 5.

O estudo da força de radiação acústica é de extrema importância para compreender o fenômeno da levitação acústica, tendo em vista que ela é que permite a levitação de objetos no interior de uma cavidade acústica. A cavidade acústica é uma região do espaço delimitada pelas faces de um transdutor e de um refletor, onde é produzida uma onda estacionária de alta intensidade. Nesta técnica, conhecida como levitação por ondas estacionárias, pequenos objetos são aprisionados nos nós de pressão da onda estacionária. Além desta, também existe uma outra técnica de levitação onde não há a necessidade de se utilizar um refletor, técnica conhecida como levitação de campo próximo, na qual se tem apenas um transdutor e o objeto de face plana que se deseja levitar. Nesta técnica há uma pequena região com ar entre o transdutor e o objeto, sendo que a espessura da camada de ar é muito menor que o comprimento de onda. Neste trabalho foi feito um estudo numérico e experimental da força de radiação acústica em levitadores acústicos de onda estacionária e em levitadores de campo próximo. As simulações foram realizadas no software de elementos finitos COMSOL Mutiphysics. No estudo experimental foi utilizada uma balança eletrônica para medir a força de radiação acústica e uma câmera de alta velocidade para observar o comportamento oscilatório de objetos esféricos no interior da cavidade acústica. O estudo da força de radiação acústica resultou em três principais contribuições. A primeira contribuição está relacionada com a caracterização de efeitos não lineares em um levitador acústico, como o fenômeno de salto (jump phenomenon) e o fenômeno de histerese. A segunda contribuição está relacionada com o estudo numérico e experimental da força de radiação acústica que atua no refletor de um levitador acústico. Por último também foi feito um estudo da força de radiação acústica que atua no refletor para a região do campo próximo. Neste último estudo foi verificado que quando o diâmetro da face do transdutor é pequeno em comparação com o comprimento de onda, surge uma força atrativa sobre o refletor, e esta força pode ser utilizada para levitar um objeto plano em baixo da face do transdutor, sem haver necessidade de utilizar refletores. / The study of the acoustic radiation force is of high relevance to understand the acoustic levitation, since it is responsible for the levitation of small objects in the interior of an acoustic cavity. The acoustic cavity is the region delimited by the surfaces of the transducer and the reflector, where it is generated an acoustic standing wave field of high intensity. In this technique, called standing wave acoustic levitation, small objects are entrapped at the pressure nodes of the standing wave. In addition, there is also another levitation technique where there is no need to use a reflector. This technique is known as near-field levitation, in which there is only one transducer and the flat-faced object to be levitated. In this technique there is a small region with air between the transducer and the object, with the thickness of the air layer being much smaller than the wavelength. In this work, a numerical and experimental study of the acoustic radiation force in acoustic wave levitators and near-field levitators was done. The simulations were performed in the finite element software COMSOL Mutiphysics. In the experimental results, an electronic scale was used to measure the acoustic radiation force and a high speed camera was applied to observe the oscillatory behavior of spherical objects inside the acoustic cavity. The study of acoustic radiation strength resulted in three main contributions. The first contribution is related to the characterization of nonlinear effects in an acoustic levitator, such as the jump phenomenon and the hysteresis phenomenon. The second contribution is related to the numerical and experimental study of the acoustic radiation force that acts on the reflector of an acoustic levitator. Finally, a study of the acoustic radiation force that acts on the reflector for the near field region was also made. In this last study, it was verified that when the transducer is small in comparison with the wavelength, an attractive force appears on the reflector. This force can be used to levitate a flat object below the transducer face, without requiring a reflector.

Considerando que o petróleo quando extraído dos poços em águas profundas chega a ter teor de água superior a 50% e que antes de ser enviado à refinaria deve ter uma quantidade de água inferior a 1%, torna-se necessário o uso de técnicas de redução da quantidade de água. Durante a extração do petróleo formam-se emulsões de água em óleo que são muito estáveis devido a um filme interfacial contendo asfaltenos e/ou resinas ao redor das gotas de água. Nesse trabalho é apresentada a utilização de ondas estacionárias de ultrassom para realizar a quebra dessas emulsões. Quando gotículas de água com dimensões da ordem de 10m, muito menores que o comprimento de onda, são submetidas a um campo acústico estacionário em óleo, a força de radiação acústica empurra as gotículas para os nós de pressão da onda. Uma célula de coalescência com frequência central ao redor de 1 MHz, constituída por quatro camadas sendo uma piezelétrica, uma de acoplamento sólido, uma com o líquido e outra refletora, foi modelada empregando o método da matriz de transferência, que permite calcular a impedância elétrica em função da frequência. Para minimizar o efeito do gradiente de temperatura entre a entrada e a saída da cavidade da célula, quando está em operação, foram utilizados dois transdutores piezelétricos posicionados transversalmente ao fluxo que são excitados e controlados independentemente. Foi implementado um controlador digital para ajustar a frequência e a potência de cada transdutor. O controlador tem como entrada o módulo e a fase da corrente elétrica no transdutor e como saída a amplitude da tensão elétrica e a frequência. Para as células desenvolvidas, o algoritmo de controle segue um determinado pico de ressonância no interior da cavidade da célula no intervalo de frequência de 1,09 a 1,15 MHz. A separação acústica de emulsões de água em óleo foi realizada em uma planta de laboratório de processamento de petróleo no CENPES/PETROBRAS. Foram testados a variação da quantidade de desemulsificante, o teor inicial de água na emulsão e a influência da vazão do sistema, com uma potência de 80 W. O teor final de água na emulsão mostrou que a aplicação de ultrassom aumentou a coalescência de água da emulsão, em todas as condições testadas, quando comparada a um teste sem aplicação de ultrassom. Identificou-se o tempo de residência no interior da célula de separação como um fator importante no processo de coalescência de emulsões de água e óleo. O uso de desemulsificante químico é necessário para realizar a separação, porém, em quantidades elevadas implicaria no uso de processos adicionais antes do repasse final do petróleo à refinaria. Os teores iniciais de água na emulsão de 30 e 50% indicam que o uso da onda estacionária na coalescência de emulsões não tem limitação quanto a esse parâmetro. De acordo com os resultados obtidos em laboratório, essa técnica seria indicada como uma alternativa para integrar um sistema de processamento primário em conjunto com um separador eletrostático. / Considering that oil when extracted from the wells in deep water have water content greater than 50%, and that before to be sent to the refinery must have a quantity of water less than 1%, it becomes necessary to use water amount reduction techniques. During the oil extraction are formed water-in-oil emulsions that are highly stable due to an interfacial film containing asphaltenes and / or resins around the water droplets. This work presents the use of ultrasonic standing waves to perform that emulsion break. When water droplets with dimensions about 10m, much smaller than the wavelength, are placed in a standing acoustic field in oil, the acoustic radiation force pushes the water droplets to the pressure wave nodes. A coalescing chamber with frequency about 1 MHz, with four layers comprising a piezoelectric, a solid coupling, one with the liquid, and another reflector, was modeled using the matrix transfer method, that allows calculating the electrical impedance as a function of frequency. To minimize the effect of the temperature gradient between the inlet and the outlet of the chamber cavity, when it is operating, were used two groups of piezoelectric transducers positioned transverse to the flow which are excited and controlled independently. A digital controller has been implemented to adjust the frequency and the power of each transducer. The controller has as input the modulus and phase of electrical current of the transducer and as output the amplitude of voltage and the frequency. For developed cells, the control algorithm follows an specific resonance peak within the chambers cavity in the frequency range 1.09 to 1.15 MHz. Acoustic separation of water in oil emulsions was carried out on a laboratory oil processing plant. Tests were performed by varying the amount of the chemical demulsifier, the initial water content in the emulsion. The system flow rate was kept constant at 80 W using the control system. Residence time within the separation chamber was identified as an important factor in the water in oil emulsions coalescence process. The use of chemical demulsifier is required to perform the separation, however in large quantities, it implies the use of additional processes before the oil final transfer to the refinery. Initial water contents in the emulsion about 30 and 50% indicate that the use of the acoustic standing wave in the emulsion coalescence has not limitation on this parameter. According to the results obtained in laboratory, this technique would be indicated as an alternative to integrate a primary processing system together with an electrostatic separator.