1,721,018 research outputs found
Técnicas computacionales para el diseño automático de mecanismos flexibles de precisión
Get PDFTesis (Doctorado en Ciencias de Ia Ingeniería)-Universidad Nacional de Córdoba - Facultadad de Ciencias Exactas Físicas y NaturalesFil: Gallardo, Alejandro. Universidad Tecnológica Nacional. Facultad Regional Córdoba; Argentina.Los mecanismos flexibles transmiten movimientos y fuerzas mediante la deformación de sus miembros flexibles. Comparados con los mecanismos rígidos, los mecanismos flexibles tienen la ventaja de eliminar la necesidad de lubricación, no poseen juegos, reducen o eliminan la fricción y el consiguiente desgaste
entre partes, y disminuyen la complejidad y los costos del proceso de ensamblaje y alineación. El diseño de mecanismos flexibles de precisión en pequeños desplazamientos es un área de investigación en constante crecimiento debido a las nuevas necesidades de generación de movimientos micro y nanométricos
para manipulaciones en investigación, desarrollo de nuevos productos y producción industrial.
El diseño de mecanismos flexibles presenta ciertos desafíos, ya que requiere conocer e integrar la flexibilidad del elemento flexor en el análisis cinemático del mecanismo. Existen varios métodos para su diseño: método de pseudo-rígidos, método de construcción por bloques, método basado en restricciones, método FACT (por las siglas en inglés de Freedom, Actuation, and Constraint Topologies), optimización topológica, entre otros. Estos métodos de diseño de mecanismos flexibles no permiten que el proceso de diseño sea automático para cualquier tipo de mecanismo, ya sea plano o tridimensional. Sin embargo, la
automatización es un tópico de investigación abierto y requerido por los diseñadores.
La aplicación de la teoría de helicoides en el método basado en restricciones es la herramienta adecuada para la sistematización del diseño de mecanismos y posibilita tanto su cálculo analítico como su implementación computacional. En esta tesis se utiliza la teoría de helicoides para la descripción de movimientos y fuerzas, en conjunto con el método basado en restricciones, para la creación de nuevas herramientas computacionales que permitan el diseño automático de mecanismos flexibles.
En el área de teoría de helicoides, se presentan nuevos procedimientos para calcular la suma, intersección y diferencia de sistemas de helicoides. Estas operaciones se aplican en una nueva metodología para el análisis cinemático y la síntesis de mecanismos de cualquier topología. Además, se propone un procedimiento automático para la síntesis de mecanismos paralelos, partiendo del espacio de libertad deseado y contemplando las restricciones espaciales de diseño. Las principales restricciones son que los flexores deben vincular dos cuerpos rígidos y que la superficie de fijación de los mismos está acotada.
Los operadores entre sistemas de helicoides y la automatización de mecanismos paralelos se aplican, en conjunto con la teoría de grafos, para el diseño de mecanismos flexibles con actuadores desacoplados, que tienen gran relevancia en la ingeniería de precisión por su controlabilidad. La metodología se ilustra
con el diseño y rediseño de tres casos de estudio. Los análisis cinemáticos y estáticos de las soluciones se realizan analíticamente y luego se validan mediante análisis de elementos finitos.
Estos avances permiten un diseño conceptual rápido de mecanismos flexibles complejos, mejorando significativamente la capacidad de análisis y síntesis de estos sistemas en diversas aplicaciones relacionadas a micro y nano posicionamiento, robótica, dispositivos hápticos y médicos, satelitales y optomecatrónica,
entre otros. Finalmente, se espera contribuir en el desarrollo de nuevas metodologías que se puedan incorporar a sistemas de diseño e ingeniería asistida por computadora (CAD/CAE) facilitando la labor creativa y reduciendo los costos y tiempos de diseño.Fil: Gallardo, Alejandro. Universidad Tecnológica Nacional. Facultad Regional Córdoba; Argentina
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Synthesis of precision flexible mechanisms using screw theory and beam constraints
Get PDFThe design of flexible parallel stages has recently been systematised for the three-dimensional space using screw theory. The relationships between the twists (motions), the wrench actuations, and constraint wrenches spaces can be manipulated by linear algebra. The use of flexible beams to constraint small motions leads to simple precision mechanisms. In a previous work by the authors, an analytical enumeration of twists and their reciprocal wrenches for any degree of freedom with zero and infinite pitches was presented and validated using finite element analysis. This work extends the methodology to account for screws with finite non-null pitches. Two synthesis problems are analytically calculated and validated using finite element analysis.Fil: Gallardo, Alejandro Gaston. Universidad Tecnológica Nacional. Facultad Regional Córdoba. Centro de Investigación en Informática para la Ingeniería; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; ArgentinaFil: Pucheta, Martín Alejo. Universidad Tecnológica Nacional. Facultad Regional Córdoba. Centro de Investigación en Informática para la Ingeniería; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentin
Synthesis of parallel flexure stages with decoupled actuators using sum, intersection, and difference of screw systems
No full textParallel flexure systems (PFS) are used in high-precision positioning systems for a wide range of scientific, medical, and industrial applications. The controllability of the flexure system is optimized when actuators are decoupled and the output of any actuator does not affect the output of the others. In this paper, Screw Theory and Linear Algebra are used to perform the synthesis of parallel flexure systems. New procedures to compute the sum, intersection, and difference of screw systems are presented. These three operations are used to formulate the synthesis of PFS with decoupled actuators completely in terms of the freedom screw systems in combination with a graph representation of the mechanism and the implementation of constraint systems using Blanding´s rules. The methodology is illustrated with the design and redesign of three case studies: (i) a 2-DOF platform with cylindrical motion, (ii) three 3-DOF tip-tilt-piston platforms, and (iii) a 3-DOF platform with planar motion. The kinematic and static analyses for the solutions are performed analytically and then validated using finite element analyses. The designed PFS have very simple structures, high precision, and controllability.Fil: Gallardo, Alejandro Gaston. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; ArgentinaFil: Pucheta, Martín Alejo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentin
Variations on the Author
Get PDF“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
Get PDFWe 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
Get PDFWe 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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