1,720,967 research outputs found
Design and implementation of nonlinear and robust control for Hamiltonian systems: the passivity-based control approach
No full textRecently, control techniques that adopt the geometrical structure and physical properties of dynamical systems have gained a lot of interest. In this thesis, we address nonlinear and robust control problems for systems represented by port-controlled Hamiltonian (PCH) models using the interconnection and damping assignment passivity-based control(IDA-PBC) methodology, which is the most notable technique facilitating the PCH framework.In this thesis, a novel constructive framework to simplify and solve the partial differential equations (PDEs) associated with IDA-PBC for a class of underactuated mechanical systems is presented. Our approach focuses on simplifying the potential energy PDEs to shape the potential energy function which is the most important procedure in the stabilization of mechanical systems. The simplification is achieved by parametrizing thedesired inertia matrix that shapes the kinetic energy function, thus achieving total energy shaping. The simplification removes some constraints (conditions and assumptions) that have been imposed in recently developed methods in literature, thus expanding the class of systems for which the methods can be applied including the separable PCH systems(systems with constant inertia matrix) and non-separable PCH systems (systems with non-constant inertia matrix). The results are illustrated through software simulations and hardware experiments on real engineering applications.We also propose an integral control and adaptive control schemes to improve the robustness of the IDA-PBC method in presence of uncertainty. We first provide some results for the case of fully-actuated mechanical systems, and then extend those results to underactuated systems which are more complex. Integral action control on both the passive and non-passive outputs in the IDA-PBC construction, a strategy to ensure the robustness of the systems by preserving its stability in face of external disturbances, is introduced, establishing the input-to-state stability (ISS) property. The results are applied to both the separable and non-separable PCH systems and illustrated via several simulations. The extension to the non-separable case exhibits more complicated design as we need to take into account the derivative of the inertia matrix.Finally, the IDA-PBC method is employed to solve an important nonlinear phenomenon called ‘pull-in’ instability associated with the electrostatically actuated microelectromechanical systems (MEMSs). The control construction is an output-feedback controller that ensures global asymptotic stability and avoids velocity measurement which may not be practically available. Furthermore, the integral, adaptive and ISS control schemes proposed in this thesis for mechanical systems are extended to facilitate the stabilization of electromechanical systems which exhibit strong coupling between different energy domains
A simplified IDA-PBC design for underactuated mechanical systems with applications
Full text linkWe develop a method to simplify the partial differential equations (PDEs) associated to the potential energy for interconnection and damping assignment passivity based control (IDA-PBC) of a class of underactuated mechanical systems (UMSs). Solving the PDEs, also called the matching equations, is the main difficulty in the construction and application of the IDA-PBC. We propose a simplification to the potential energy PDEs through a particular parametrization of the closed-loop inertia matrix that appears as a coupling term with the inverse of the original inertia matrix. The parametrization accounts for kinetic energy shaping, which is then used to simplify the potential energy PDEs and their solution that is used for the potential energy shaping. This energy shaping procedure results in a closed-loop UMS with a modified energy function. This approach avoids the cancellation of nonlinearities, and extends the application of this method to a larger class of systems, including separable and non-separable port-controlled Hamiltonian (PCH) systems. Applications to the inertia wheel pendulum and the rotary inverted pendulum are presented, and some realistic simulations are presented which validate the proposed control design method and prove that global stabilization of these systems can be achieved. Experimental validation of the proposed method is demonstrated using a laboratory set-up of the rotary pendulum. The robustness of the closed-loop system with respect to external disturbances is also experimentally verifie
Robust IDA-PBC and PID-like control for port-controlled Hamiltonian systems
No full textInterconnection and damping assignment passivity based control (IDA-PBC) is a method that has been developed to (asymptotically) stabilize nonlinear systems formulated in portcontrolled Hamiltonian (PCH) structure. This method has gained increasing popularity and has been successfully applied to a wide range of dynamical systems. However, little is known about the robustness of this method in response to the effects of uncertainty which could result from disturbances, noises, and modeling errors. This paper explores the possibility of extending the IDAPBC method by adopting a robustness perspective, with the aim of maintaining (asymptotic) stability of the system in the presence of such perturbations which exist in any realistic problem. We propose constructive results on Robust IDA-PBC and PID-like controllers for a class of PCH systems. The results extend some existing methods and provide a new framework that allows the implementation of integral action control to underactuated PCH systems that are quite commonly found in practice. The results are applied to a Quanser inertia wheel pendulum and illustrated through numerical simulation
Position-feedback integral IDA-PBC for constant matched and unmatched disturbances
No full textThis work investigates the passivity-based control of a class of underactuated mechanical systems subject to constant matched and unmatched disturbances, for which the momenta are not measured. The main contribution is a new design of the integral interconnection-and-damping assignment passivity-based control that only relies on position feedback. Numerical simulations on a disk-on-disk system, on an Acrobot system, and on a rigid-link model representative of a soft continuum manipulator demonstrate the effectiveness of the new controller
IDA-PBC with dynamic extension for momenta observation of underactuated mechanical systems
No full textThis work investigates the passivity-based control of a class of underactuated mechanical systems for which the momenta are not measurable. To this end, a port-Hamiltonian formulation and a passivity-based control approach are employed. The main contribution is a new dynamic extension of the interconnection-and-damping assignment passivity-based control that only depends on the generalized position. Numerical simulations on an Acrobot system demonstrate that the proposed approach allows stabilizing the prescribed equilibrium by relying only on position feedback
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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