Modelagem e controle de posição e orientação de uma Plataforma de Stewart

Este trabalho apresenta o controle de posição e orientação de um modelo não linear de Plataforma de Stewart com seis graus de liberdade construído no ambiente de sistemas multicorpos ADAMS® desenvolvido pela Mechanical Dynamics, Inc. O modelo não linear é exportado para o ambiente SIMULINK® desenvolvido pela MathWorks, Inc., onde o controle de posição e orientação é realizado a partir da linearização do modelo e a aplicação de um sistema seguidor com realimentação de estados. Utililiza-se, também o SIMULINK® para implementar a dinâmica de um sistema servoválvula e cilindro hidráulico com um servocontrole de pressão e assim simular o comportamento dinâmico de um simulador de vôo com acionamento hidráulico. A utilização destes pacotes comerciais visa obter uma economia de tempo e esforço na modelagem de sistemas mecânicos complexos e na programação para obtenção da resposta do sistema no tempo, além de facilitar a análise de várias configurações de Plataformas de Stewart

Book review : "Carbon Capture and Storage Emerging Legal and Regulatory Issues" edited by Ian Havercroft, Richard Macrory, Richard B Stewart, Oxford, Hart Publishing, 2011

As the international community struggles to find a cost-effective solution to mitigate climate change and reduce greenhouse gas emissions, carbon capture and storage (CCS) has emerged as a project mechanism with the potential to assist in transitioning society towards its low carbon future. Being a politically attractive option, legal regimes to promote and approve CCS have proceeded at an accelerated pace in multiple jurisdictions including the European Union and Australia. This acceleration and emphasis on the swift commercial deployment of CCS projects has left the legal community in the undesirable position of having to advise on the strengths and weaknesses of the key features of these regimes once they have been passed and become operational. This is an area where environmental law principles are tested to their very limit. On the one hand, implementation of this new technology should proceed in a precautionary manner to avoid adverse impacts on the atmosphere, local community and broader environment. On the other hand, excessive regulatory restrictions will stifle innovation and act as a barrier to the swift deployment of CCS projects around the world. Finding the balance between precaution and innovation is no easy feat. This is an area where lawyers, academics, regulators and industry representatives can benefit from the sharing of collective experiences, both positive and negative, across the jurisdictions. This exemplary book appears to have been collated with this philosophy in mind and provides an insightful addition to the global dialogue on establishing effective national and international regimes for the implementation of CCS projects...

Singularity-free path planning for the Stewart platform manipulator

This paper addresses the problem of singularity-free path planning for the six-degree-of-freedom parallel manipulator known as the Stewart platform manipulator. Unlike serial manipulators, the Stewart platform possesses singular configurations within the workspace where the manipulator is uncontrollable. An algorithm has been developed to construct continuous paths within the workspace of the manipulator by avoiding singularities and ill-conditioning. Given two end-poses of the manipulator, the algorithm finds out safe (well-conditioned) via points and plans a continuous path from the initial pose to the final one. When the two end-poses belong to different branches and no singularity-free path is possible, the algorithm indicates the impossibility of a valid path. A numerical example has also been presented as illustration of the path planning strategy.

A Newton-Euler formulation for the inverse dynamics of the Stewart platform manipulator

This paper presents an inverse dynamic formulation by the Newton–Euler approach for the Stewart platform manipulator of the most general architecture and models all the dynamic and gravity effects as well as the viscous friction at the joints. It is shown that a proper elimination procedure results in a remarkably economical and fast algorithm for the solution of actuator forces, which makes the method quite suitable for on-line control purposes. In addition, the parallelism inherent in the manipulator and in the modelling makes the algorithm quite efficient in a parallel computing environment, where it can be made as fast as the corresponding formulation for the 6-dof serial manipulator. The formulation has been implemented in a program and has been used for a few trajectories planned for a test manipulator. Results of simulation presented in the paper reveal the nature of the variation of actuator forces in the Stewart platform and justify the dynamic modelling for control.

An algebraic formulation of static isotropy and design of statically isotropic 6-6 Stewart platform manipulators

In this paper, we present an algebraic method to study and design spatial parallel manipulators that demonstrate isotropy in the force and moment distributions. We use the force and moment transformation matrices separately, and derive conditions for their isotropy individually as well as in combination. The isotropy conditions are derived in closed-form in terms of the invariants of the quadratic forms associated with these matrices. The formulation is applied to a class of Stewart platform manipulator, and a multi-parameter family of isotropic manipulators is identified analytically. We show that it is impossible to obtain a spatially isotropic configuration within this family. We also compute the isotropic configurations of an existing manipulator and demonstrate a procedure for designing the manipulator for isotropy at a given configuration. (C) 2008 Elsevier Ltd. All rights reserved.

An algebraic formulation of static isotropy and design of statically isotropic 6–6 Stewart platform manipulators

In this paper, we present an algebraic method to study and design spatial parallel manipulators that demonstrate isotropy in the force and moment distributions. We use the force and moment transformation matrices separately, and derive conditions for their isotropy individually as well as in combination. The isotropy conditions are derived in closed-form in terms of the invariants of the quadratic forms associated with these matrices. The formulation is applied to a class of Stewart platform manipulator, and a multi-parameter family of isotropic manipulators is identified analytically. We show that it is impossible to obtain a spatially isotropic configuration within this family. We also compute the isotropic configurations of an existing manipulator and demonstrate a procedure for designing the manipulator for isotropy at a given configuration.

A canonical formulation of the direct position kinematics problem for a general 6-6 stewart platform

This paper deals with the direct position kinematics problem of a general 6-6 Stewart platform, the complete solution of which is not reported in the literature until now and even establishing the number of possible solutions for the general case has remained an unsolved problem for a long period. Here a canonical formulation of the direct position kinematics problem for a general 6-6 Stewart platform is presented. The kinematic equations are expressed as a system of six quadratic and three linear equations in nine unknowns, which has a maximum of 64 solutions. Thus, it is established that the mechanism, in general, can have up to 64 closures. Further reduction of the system is shown arriving at a set of three quartic equations in three unknowns, the solution of which will yield the assembly configurations of the general Stewart platform with far less computational effort compared to earlier models.

A near-singular, flexure jointed, moment sensitive Stewart platform based fore-torque sensor

A force-torque sensor capable of accurate measurement of the three components of externally applied forces and moments is required for force control in robotic applications involving assembly operations. The goal in this paper is to design a Stewart platform based force torque sensor at a near-singular configuration sensitive to externally applied moments. In such a configuration, we show an enhanced mechanical amplification of leg forces and thereby higher sensitivity for the applied external moments. In other directions, the sensitivity will be that of a normal load sensor determined by the sensitivity of the sensing element and the associated electronic amplification, and all the six components of the force and torque can be sensed. In a sensor application, the friction, backlash and other non-linearities at the passive spherical joints of the Stewart platform will affect the measurements in unpredictable ways. In this sensor, we use flexural hinges at the leg interfaces of the base and platform of the sensor. The design dimensions of the flexure joints in the sensor have been arrived at using FEA. The sensor has been fabricated, assembled and instrumented. It has been calibrated for low level loads and is found to show linearity and marked sensitivity to moments about the three orthogonal X, Y and Z axes. This sensor is compatible for usage as a wrist sensor for a robot under development at ISRO Satellite Centre.

Plataforma legislativa para a biodiversidade

Trata de uma contribuição do Grupo de Trabalho criado no âmbito da Comissão de Meio Ambiente e Desenvolvimento Sustentável (CMADS) da Câmara dos Deputados com intuito de fornecer instrumento aos parlamentares e à sociedade em geral no sentido de alcançar os objetivos da Convenção sobre Diversidade Biológica. Pretende, ainda, nortear as discussões entre parlamentares e sociedade sobre as prioridades nacionais e buscar soluções criativas e inovadoras que tenham a biodiversidade e a sustentabilidade como pilares centrais das políticas públicas.

Moodle, la plataforma para la enseñanza y organización escolar

Sencilla y Potente. Ecológica y económica. “Moodle” se extiende exponencialmente por los centros de enseñanza de todo el mundo. Es muy útil como herramienta para la enseñanza. Permite la gestión de la asignatura, y son muchas sus utilidades, desde colgar los más diversos contenidos multimedia (apuntes, videos, imágenes,…,) hasta poder evaluar las diferentes tareas de nuestros alumnos o realizar exámenes online. Resulta esencial para crear “objetos de aprendizaje” o “unidades didácticas” y para fomentar el autoaprendizaje y el aprendizaje cooperativo. También es la herramienta ideal para gestionar la organización de las comunidades educativas y permitir la comunicación y el trabajo en red entre sus distintos integrantes y con otros centros. Resultando especialmente útil para la integración e implementación de los currículos, la comunicación con las familias y su uso en el ámbito extraescolar. Con este artículo se pretende explicar de una manera clara y sencilla en que consiste moodle y cuales son sus diferentes posibilidades de uso para los centros, los profesores y los alumnos, siempre desde el punto de vista de un usuario no iniciado en las nuevas tecnologías.

Los programas de fidelización como plataforma de venta directa: clasificación de los titulares según la redención de billetes aéreos

[ES] Cada vez son más numerosos los programas de fidelización que ofrecen al titular la posibilidad de comprar puntos o conseguir premios, viajes o billetes aéreos pagando una parte de los mismos con dinero. Dicha característica, unida a la propia estructura y dinámica de los programas de fidelización y a la actual coyuntura del sector turístico, ha permitido desarrollar plataformas de venta directa desde las que ofrecer servicios a los titulares.

Utilización de la plataforma virtual eKasi en la docencia de la tecnología farmacéutica

[ES] Una de las aplicaciones más interesantes de las nuevas tecnologías en la docencia, es la utilización de plataformas virtuales accesibles por el alumno a través de Internet. eKASI es una plataforma informática para el apoyo a la docencia presencial desarrollada en la Universidad del Pais Vasco, que permite la gestión de los documentos y la gestión de los estudiantes de un curso, a la vez que facilita el aprendizaje del alumno. Es una herramienta de distribución gratuita y de fácil manejo. Durante el curso 2005/2006, se ha utilizado esta plataforma como apoyo a la docencia de la asignatura Tecnología Farmacéutica I de 4º curso de la Licenciatura en Farmacia de la Universidad del País Vasco. La plataforma está accesible en la dirección de Internet http://ekasi.ehu.es mediante la introducción de una clave facilitada por el administrador del sistema. En la sección correspondiente al aula virtual de la plataforma, el alumno tiene a su disposición la información y documentos relacionados con la asignatura (plan docente, presentaciones utilizadas en las clases, cuestionarios de autoevaluación, enlaces de interés a paginas web, materiales multimedia, etc.). Por otra parte, esta plataforma permite la colaboración y discusión on line de los materiales estudiados, a través del foro y del correo electrónico y posibilita al profesor tutorizar y realizar un seguimiento del progreso de los estudiantes, mediante la realización de tests y de las diferentes tareas propuestas al grupo de alumnos. La plataforma eKASI ha supuesto un instrumento de gran utilidad como apoyo a la docencia presencial tal como se deduce de los resultados de la encuesta realizada a los alumnos al finalizar el curso académico.

Combinación de funcionalidades Gateway de bus sobre plataforma embebida

Analisis de viabilidad de la combinación de las funcionalidades de dos módulos/dispositivos GW (Gateway).Dichos módulos realizan el intercambio de datos entre los diferentes buses embarcados en un tren.