Most manufacturing processes produce parts that can only be correctly measured after the process cycle has been completed. Even if in-process measurement and control is possible, it is often too expensive or complex to practically implement. In this paper, a simple control scheme based on output measurement and input change after each processing cycle is proposed. It is shown to reduce the process dynamics to a simple gain with a delay, and reduce the control problem to a SISO discrete time problem. The goal of the controller is to both reduce mean output errors and reduce their variance. In so doing the process capability (e.g. Cpk) can be increased without additional investment in control hardware or in-process sensors. This control system is analyzed for two types of disturbance processes: independent (uncorrelated) and dependent (correlated). For the former the closed-loop control increased the output variance, whereas for the latter it can decrease it significantly. In both cases, proper controller design can reduce the mean error to zero without introducing poor transient performance. These finding were demonstrated by implementing Cycle to Cycle (CtC) control on a simple bending process (uncorrelated disturbance) and on an injection molding process (correlated disturbance). The results followed closely those predicted by the analysis. / Singapore-MIT Alliance (SMA)

With the ability to generate fine displacements with a resolution down to sub-nanometers, piezoelectric actuators (PEAs) have found wide applications in various nano-positioning systems. However, existence of various effects in PEAs, such as hysteresis and creep, as well as dynamics can seriously degrade the PEA performance or even lead to instability. This raises a great need to model and control PEAs for improved performance, which have drawn remarkable attention in the literature. Sliding mode control (SMC) shows its potential to the control of PEA, by which the hysteresis and other nonlinear effects can be regard as disturbance to the dynamic model and thus rejected or compensated by its switching control. To implement SMC in digital computers, this research is aimed at developing novel discrete models and discrete SMC (DSMC)-based control schemes for PEAs, along with their experimental validation. The first part of this thesis concerns with the modeling and control of one-degree of freedom (DOF) PEA, which can be treated as a single-input-single-output (SISO) system. Specifically, a novel discrete model based on the concept of auto-regressive moving average (ARMA) was developed for the PEA hysteresis; and to compensate for the PEA hysteresis and improve its dynamics, an output tracking integrated discrete proportional-integral-derivative-based SMC (PID-SMC) was developed. On this basis, by making use of the availability of PEA hysteresis models, two control schemes, named “the discrete inversion feedforward based PID-SMC” and “the discrete disturbance observer (DOB)-based PID-SMC”, were further developed. To illustrate the effectiveness of the developed models and control schemes, experiments were designed and conducted on a commercially available one-DOF PEA, as compared with the existing ones. The second part of the thesis presents the extension of the developed modeling and control methods to multi-DOF PEAs. Given the fact that details with regard to the PEA internal configurations is not typically provided by the manufacturer, a state space model based on the black box system identification was developed for the three-DOF PEA. The developed model was then integrated in the output tracking based discrete PID-SMC, with its effectiveness verified through the experiments on a commercially available three-DOF PEA. The superiority of the proposed control method over the conventional PID controller was also experimentally investigated and demonstrated. Finally, by integrating with a DOB in the discrete PID-based SMC, a novel control scheme is resulted to compensate for the nonlinearities of the three-DOF PEA. To verify its effectiveness, the discrete DOB based PID-SMC was applied in the control experiments and compared with the existing SMC. The significance of this research lies in the development of the discrete models and PID-based SMC for PEAs, which is of great help to improve their performance. The successful application of the proposed method in the control of multi-DOF PEA allows the application of SMC to the control of complicated multi-inputs-multi-outputs (MIMO) systems without details regarding the internal configuration. Also, integration of the inversion based feedforward control and the DOB in the SMC design has been proven effective for the tracking control of PEAs.

Esquemas baseados em grafos, em diferentes níveis de formalismo, são um forte apelo para a constituição de representações de sistemas complexos e de grande porte aplicados em várias áreas do conhecimento. Este fato responde pelo crescimento acentuado de métodos e representações formais baseadas em grafos e aplicadas em diferentes áreas, especialmente na Engenharia. As Redes de Petri (RdP) constituem um destes métodos, que apareceu em 1962 e desde então tem contribuído para o avanço dos métodos formais para o tratamento de sistemas de controle, sistemas discretos, logística, workflow, cadeia de fornecedores, redes de computadores, e uma variada classe de outros sistemas. Da mesma forma que outras representações formais, as primeiras tentativas de uso prático destas redes estiveram sempre ligadas ao domínio de aplicação, o que levou à criação de várias extensões. Por outro lado, a necessidade de se aplicar a representação em redes para sistemas de grande porte suscitou a discussão sobre as limitações do formalismo e sobre a necessidade de se inserir redes de alto nível. No entanto, todo este desenvolvimento, apesar de sua difusão em diferentes domínios, levantou a discussão sobre a unificação das redes. Desde 1992 a unificação do formalismo das RdPs é discutida pela comunidade acadêmica e, finalmente, no início deste século um padrão ISO/IEC foi proposto. Esta proposta conduz a dois desafios: i) mostrar que um formalismo de redes que seja candidato a ser usado na prática pertença de fato à classe de redes prescrita pelo padrão; ii) participar da discussão sobre a semântica das extensões propondo ambientes computacionais para o uso prático na modelagem e design de sistemas de grande porte. A rede GHENeSys, concebida e desenvolvida no Design Lab da Universidade de São Paulo, é uma rede estendida com conceitos de orientação a objetos, um mecanismo de hierarquia e, até o momento, parece ser uma das primeiras tentativas de prover um ambiente de modelagem e design com as propriedades de uma rede unificada, com capacidade para cobrir as diferentes variantes das RdP e suas extensões. Neste trabalho é apresentada uma proposta de ambiente integrado de modelagem para a representação de sistemas a eventos discretos (SEDs) em RdP, baseada em um formalismo enquadrado dentro da norma ISO/IEC 15909 recentemente proposta. Este formalismo é a rede GHENeSys, que terá sua definição estendida utilizando como base a definição das RdPs Coloridas (CPN) com o objetivo de permitir a representação de tipos nas marcas. Um protótipo para testes, resultado da integração de diversos trabalhos desenvolvidos separadamente por membros do D-Lab que nunca foram implementados nem integrados em formalismo único, é apresentado. Este protótipo é utilizado em um estudo de caso com a finalidade de validar de forma prática os novos elementos acrescentados à definição da rede GHENeSys para permitir a modelagem de sistemas utilizando os elementos das RdPs de alto nível. / Graph schemas are a strong approach to the representation (in dierent degrees of formality) of large and complex systems in several areas of knowledge. This fact has provided a continuous growth of methods and new formal schemas, specially in Engineering. Petri Nets(PN) are one of these methods, which appears in 1962 and since then has improved the representation of discrete control, discrete systems, logistics, workflow, supply chain, computer networks, and a variety of other systems. As any other representation, the first attempts to use it in practice were always made in a close relation between the representation and the domain of discourse, openning opportunity for several extensions. Also the need to use it in large systems brought a discussion about the formalism and the need for high level systems. However, all this development, besides the broad use in different domains, rose the need for an unified approach. Since 1992 such unification has been addressed by the scientific community and finally, in the beginning of this century, a ISO/IEC standard was proposed. That proposal also brings two new challenges: i) to show that any proposed net that belongs to Petri Net class proved itself as satisfying the requirements of the standard; ii) to enter the discussions of the semantics of extensions and also provide practical and unified system environments that can really support the design of large and complex systems. In this work, we present a proposal for the developing of an integrated modeling environment for the representation of discrete event systems using Petri Nets. This environment will use an underlying formalism framed within the rules defined recently by the ISO/IEC, in the standard 15909. The formalism to be used will be the GHENeSys net, which will have its definition extended using the definition of the Coloured PN (CPN) as a starting point in order to allow the representation of types within the net tokens. A testing prototype for this integrated modeling environment, result of the integration of several previous works of D-Lab members that were never implemented or integrated in a unique formalism, is presented. This prototype will be used in a case study in order to validate in practical way the new elements added to the definition of GHENeSys, to allow the modeling of systems using the elements of HLPNs.

Esquemas baseados em grafos, em diferentes níveis de formalismo, são um forte apelo para a constituição de representações de sistemas complexos e de grande porte aplicados em várias áreas do conhecimento. Este fato responde pelo crescimento acentuado de métodos e representações formais baseadas em grafos e aplicadas em diferentes áreas, especialmente na Engenharia. As Redes de Petri (RdP) constituem um destes métodos, que apareceu em 1962 e desde então tem contribuído para o avanço dos métodos formais para o tratamento de sistemas de controle, sistemas discretos, logística, workflow, cadeia de fornecedores, redes de computadores, e uma variada classe de outros sistemas. Da mesma forma que outras representações formais, as primeiras tentativas de uso prático destas redes estiveram sempre ligadas ao domínio de aplicação, o que levou à criação de várias extensões. Por outro lado, a necessidade de se aplicar a representação em redes para sistemas de grande porte suscitou a discussão sobre as limitações do formalismo e sobre a necessidade de se inserir redes de alto nível. No entanto, todo este desenvolvimento, apesar de sua difusão em diferentes domínios, levantou a discussão sobre a unificação das redes. Desde 1992 a unificação do formalismo das RdPs é discutida pela comunidade acadêmica e, finalmente, no início deste século um padrão ISO/IEC foi proposto. Esta proposta conduz a dois desafios: i) mostrar que um formalismo de redes que seja candidato a ser usado na prática pertença de fato à classe de redes prescrita pelo padrão; ii) participar da discussão sobre a semântica das extensões propondo ambientes computacionais para o uso prático na modelagem e design de sistemas de grande porte. A rede GHENeSys, concebida e desenvolvida no Design Lab da Universidade de São Paulo, é uma rede estendida com conceitos de orientação a objetos, um mecanismo de hierarquia e, até o momento, parece ser uma das primeiras tentativas de prover um ambiente de modelagem e design com as propriedades de uma rede unificada, com capacidade para cobrir as diferentes variantes das RdP e suas extensões. Neste trabalho é apresentada uma proposta de ambiente integrado de modelagem para a representação de sistemas a eventos discretos (SEDs) em RdP, baseada em um formalismo enquadrado dentro da norma ISO/IEC 15909 recentemente proposta. Este formalismo é a rede GHENeSys, que terá sua definição estendida utilizando como base a definição das RdPs Coloridas (CPN) com o objetivo de permitir a representação de tipos nas marcas. Um protótipo para testes, resultado da integração de diversos trabalhos desenvolvidos separadamente por membros do D-Lab que nunca foram implementados nem integrados em formalismo único, é apresentado. Este protótipo é utilizado em um estudo de caso com a finalidade de validar de forma prática os novos elementos acrescentados à definição da rede GHENeSys para permitir a modelagem de sistemas utilizando os elementos das RdPs de alto nível. / Graph schemas are a strong approach to the representation (in dierent degrees of formality) of large and complex systems in several areas of knowledge. This fact has provided a continuous growth of methods and new formal schemas, specially in Engineering. Petri Nets(PN) are one of these methods, which appears in 1962 and since then has improved the representation of discrete control, discrete systems, logistics, workflow, supply chain, computer networks, and a variety of other systems. As any other representation, the first attempts to use it in practice were always made in a close relation between the representation and the domain of discourse, openning opportunity for several extensions. Also the need to use it in large systems brought a discussion about the formalism and the need for high level systems. However, all this development, besides the broad use in different domains, rose the need for an unified approach. Since 1992 such unification has been addressed by the scientific community and finally, in the beginning of this century, a ISO/IEC standard was proposed. That proposal also brings two new challenges: i) to show that any proposed net that belongs to Petri Net class proved itself as satisfying the requirements of the standard; ii) to enter the discussions of the semantics of extensions and also provide practical and unified system environments that can really support the design of large and complex systems. In this work, we present a proposal for the developing of an integrated modeling environment for the representation of discrete event systems using Petri Nets. This environment will use an underlying formalism framed within the rules defined recently by the ISO/IEC, in the standard 15909. The formalism to be used will be the GHENeSys net, which will have its definition extended using the definition of the Coloured PN (CPN) as a starting point in order to allow the representation of types within the net tokens. A testing prototype for this integrated modeling environment, result of the integration of several previous works of D-Lab members that were never implemented or integrated in a unique formalism, is presented. This prototype will be used in a case study in order to validate in practical way the new elements added to the definition of GHENeSys, to allow the modeling of systems using the elements of HLPNs.

Discrete models are used in describing various microscopic phenomena in many branches of science, ranging from biology through chemistry to physics. Arrays of evanescently coupled, equally spaced, identical waveguides are prime examples of optical structures in which discrete dynamics can be easily observed and investigated. As a result of discretization, these structures exhibit unique diffraction properties with no analogy in continuous systems. Recently nonlinear discrete optics has attracted a growing interest, triggered by the observation of discrete solitons in AlGaAs waveguide arrays reported by Eisenberg et al. in 1998. So far, the following experiments involved systems with third order nonlinearities. In this work, an experimental investigation of discrete nonlinear wave propagation in a second order nonlinear medium is presented. This system deserves particular attention because the nonlinear process involves two or three components at different frequencies mutually locked by a quadratic nonlinearity, and new degrees of freedom enter the dynamical process. In the first part of dissertation, observation of the discrete Talbot effect is reported. In contrast to continuous systems, where Talbot self-imaging effect occurs irrespective of the pattern period, in discrete configurations this process is only possible for a specific set of periodicities. The major part of the dissertation is devoted to the investigation of soliton formation in lithium niobate waveguide arrays with a tunable cascaded quadratic nonlinearity. Soliton species with different topology (unstaggered – all channels in-phase, and staggered – neighboring channels with a pi relative phase difference) are identified in the same array. The stability of the discrete solitons and plane waves (modulational instability) are experimentally investigated. In the last part of the dissertation, a phase-insensitive, ultrafast, all-optical spatial switching and frequency conversion device based on quadratic waveguide array is demonstrated. Spatial routing and wavelength conversion of milliwatt signals is achieved without pulse distortions.

This study deals with a general method for the analysis of a semi-active control technique for a fast-shunt switching system. The benefit of the semi-active system is the reduction in power consumption, which is a significant disadvantage of a fully active system compared with a passive system. A semi-active system under consideration is a semi-actively shunted piezoelectric system, which converts the strain energy into electrical energy through strong electromechanical coupling achieved though the piezoelectric phenomenon. Our proposed semi-active approach combines a PZT-based energy harvesting with a fast switching system driven by a Pulse-Width Modulated (PWM) signal. The fast switching system enables continuous adaptation of vibration energy control/harvesting by varying the PWM duty cycle. This contrasts with a conventional capacitance switching system that can only change the capacitance at discrete values. The analysis of the current piezoelectric system combined with a fast-switching system poses a considerable challenge as it contains both continuous and discrete characteristics. The study proposes an enhanced averaging method for analyzing the piecewise linear system. The simulation of the averaged system is much faster than that of the time-varying system. Moreover, the analysis derives error bounds that characterize convergence in the time domain of the averaged system to the original system. The dissertation begins with the derivation of the equations governing the physics of a piezostructure combined with an electrical switching shunt network. The results of the averaging analysis and numerical simulation are presented in order to provide a basis for estimating the structural responses that range between open- and short-circuit conditions which constitutes two limiting conditions. An experimental study demonstrates that the capacitive shunt bimorph piezostructure coupled with a single switch can be adjusted continuously by varying the PWM duty cycle. And the behavior of such hybrid system can be well predicted by the averaging analysis. / Ph. D.

A robust servo control system based on Integral Variable Structure Model Following Control (IVSMFC) is proposed. The IVSMFC approach comprises a reference model part for specifying the design requirements and an Integral Variable Structure Control (IVSC) part for minimizing the errors between the plant and the model. Sliding mode thus obtained features robustness against external disturbances and parameter variations. Design procedures in both continuous-time and discrete-time have been detailed. The IVSMFC-based servo control system has been successfully applied to a DSP-based brushless DC motor drive for globoidal cam indexing system and to power system. Simulation and experimental results demonstrate that the proposed scheme can achieve fast and robust responses.

Στην παρούσα εργασία εξετάζεται η επίδραση του κλυδασμού στην απόκριση σφαιρικών δεξαμενών με άκαμπτα τοιχώματα για τυχαίο ποσοστό πλήρωσης, υπό οριζόντια σεισμική διέγερση. Πραγματοποιείται η ιδιομορφική ανάλυση της κίνησης του κλυδασμού χρησιμοποιώντας τη μέθοδο των πεπερασμένων στοιχείων και το πρόγραμμα ANSYS για την διατύπωση και επίλυση των εξισώσεων. Υπολογίζονται τα ιδιοδιανύσματα και εξάγονται νομογραφήματα της ιδιοσυχνότητας σε συνάρτηση με τη διάμετρο της σφαίρας, το ποσοστό πλήρωσης και την επιτάχυνση της βαρύτητας. Για την ερμηνεία της υδροδυναμικής συμπεριφοράς του περιεχόμενου υγρού υιοθετείται η καθιερωμένη θεώρηση της επαλληλίας των επιδράσεων δύο ανεξάρτητων κινήσεων: Της κίνησης της κυκλοφορούσας μάζας και της κίνησης της ωστικής μάζας του υγρού. Προτείνεται και τεκμηριώνεται μια μεθοδολογία για τον προσδιορισμό της κυκλοφορούσας και της ωστικής μάζας για κάθε μορφή δεξαμενής και κάθε ποσοστό πλήρωσης. Για την περίπτωση των σφαιρικών δεξαμενών εξάγονται νομογραφήματα που αναπαριστούν την κυκλοφορούσα και την ωστική μάζα ως συνάρτηση του ύψους πλήρωσης. Παράλληλα, παράγεται ένα ισοδύναμο σύστημα διακριτών μαζών και ελατηρίων που προσομοιώνει την υδροδυναμική συμπεριφορά του περιεχόμενου υγρού σε οριζόντια διέγερση, για κάθε στάθμη της ελεύθερης επιφάνειας. Μεταξύ άλλων, προσδιορίζονται οι κατανομές της κυκλοφορούσας και της ωστικής υδροδυναμικής πιέσης για συγκεκριμένα ποσοστά πλήρωσης και η τιμή της συνολικής πίεσης σε τυχαίο σημείο του σφαιρικού κελύφους. Τέλος, παρουσιάζονται αποτελέσματα εφαρμογών σχετικά με την σεισμική απόκριση σφαιρικών δεξαμενών, χρησιμοποιώντας το προτεινόμενο ισοδύναμο διακριτό σύστημα, και συγκρίνονται με τα αντίστοιχα άλλων εργασιών για την τεκμηρίωση της ορθότητας και της αποτελεσματικότητας του. / The present work considers the sloshing effects on the seismic response of spherical tanks with rigid walls and filled with liquid up to an arbitrary level. The sloshing eigenmode analysis is performed by means of the finite element method utilizing the ANSYS program. The eigenfunctions are computed and nomographs of the corresponding natural frequencies are obtained. Each nomograph is a multivariable function of tank diameter and filling level of the content liquid. The hydrodynamic behaviour of the liquid motion can be considered to be equivalent to the superposition of two independent motions; the motion of an impulsive and all convective masses. The main goal of the present work is the development of a methodology to determine the impulsive and the major convective masses for arbitrary tank diameter and filling level values. The accuracy of the proposed methodology is verified for the case of vertical cylindrical tanks, where the analytical solution is well known. Applying the proposed methodology to the case of spherical tanks, the impulsive and the major convective masses are computed as functions of the non-dimensional liquid filling level. It is found that the convective mass corresponding to the first eigenmode is by far more significant than all the higher order convective masses; therefore, the liquid sloshing motion is dominated by this mode. Then, the hydrodynamic behaviour of the content liquid is simulated by means of an equivalent discrete system of masses and springs. In addition, the wall distributions of convective and impulsive pressures are calculated. Finally, utilizing the obtained equivalent discrete system, numerical results of the seismic response of typical spherical tanks are presented and compared to those obtained by other semi-analytical and numerical methods.

Problems in the control and identification of structural dynamic systems can lead to multimodal optimization problems, which are difficult to solve using classical gradient based methods. In this work, optimization problems pertaining to the vibration control of smart structures and the exploration of isospectral systems are addressed. Isospectral vibrating systems have identical natural frequencies, and existence of the isospectral systems proves non-uniqueness in system identification. For the smart structure problem, the optimal location(s) of collocated actuator(s)/sensor(s) and the optimal feedback gain matrix are obtained by maximizing the energy dissipated by the feedback control system. For the isospectral system problem, both discrete and continuous systems are considered. An error function is designed to calculate the error between the spectra of two distinct structural dynamic systems. For the discrete system, the Jacobi matrix, derived from the given system, is modified and the problem is posed as an optimization problem where the objective is to minimize the non-negative error function. Isospectral spring-mass systems are obtained. For the continuous system, finite element modeling is used and an error function is designed to calculate the error between the spectra of the uniform beam and the non-uniform beam. Non-uniform cantilever beams which are isospectral to a given uniform cantilever beam are obtained by minimizing the non-negative error function. Numerical studies reveal several isospectral systems, and optimal gain matrices and sensor/actuator locations for the smart structure. New evolutionary algorithms, which do not need genetic operators such as crossover and mutation, are used for the optimization. These algorithms are: Artificial bee colony (ABC) algorithm, Glowworm swarm optimization (GSO) algorithm, Firefly algorithm (FA) and Electromagnetism inspired optimization (EIO) algorithm.

No description available.