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Register a new userAnalyse de la rigidite des machines outils 3 axes darchitecture parall`ele hyperstatique
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Added by
Damien Chablat
Publication date
2008
fields
Informatics Engineering
and research's language is
English
Authors
Anatoly Pashkevich
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The paper presents a new stiffness modelling method for overconstrained parallel manipulators, which is applied to 3-d.o.f. translational mechanisms. It is based on a multidimensional lumped-parameter model that replaces the link flexibility by localized 6-d.o.f. virtual springs. In contrast to other works, the method includes a FEA-based link stiffness evaluation and employs a new solution strategy of the kinetostatic equations, which allows computing the stiffness matrix for the overconstrained architectures and for the singular manipulator postures. The advantages of the developed technique are confirmed by application examples, which deal with comparative stiffness analysis of two translational parallel manipulators.
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Otologic surgery has some specificities compared to others surgeries. The anatomic working space is small, with various anatomical structures to preserve, like ossicles or facial nerve. This requires the use of microscope or endoscope. The microscope let the surgeon use both hands, but allows only direct vision. The endoscope leaves only one hand to the surgeon to use his tools, but provides a fish-eye vision. The rise of endoscopy these past few years has led to the development of numerous devices for the surgeon: the Robotol, first otological robot designed to performed some movements and hold an endoscope, or the Endofix Exo. Both devices need the hand of the surgeon to be moved. No robotic device allows the endoscope to be directed autonomously while the surgeon keeps both hands free to work, just like when he is working with a microscope. The objective of our work is to define the specific needs of the otological assistance surgery.
The aim of this study is to produce a kinematic analysis of movements of the shoulder complex when hemiparetic patients achieve the grasping of weighted objects. We propose to describe the influence of the weight on kinematic characteristics of the gesture and to establish the relevance of several quantitative indexes concerning the quality of the grasping gesture.
Two different way of assessing seismic vulnerability are available nowadays: observed or empirical and calculated vulnerability assessment methods. The first methods are based on observed damage after earthquakes correlated with the structural properties of buildings, whereas the second methods are based on numerical models more or less representing the buildings. In both cases, the trouble is the imperfect knowledge of existing buildings. We propose here a new method for estimating the vulnerability based on experimental modal parameters (resonance frequencies, modal shapes and damping ratio) estimated under ambient vibrations. They allow to build up a simplified numerical model of the elastic building behaviour. The motion produced by numerous earthquakes leads to determine its first damage level and therefore its vulnerability. An inter-story drift threshold based on HAZUS values defines the first damage level of the building. This method is applied to the Grenoble (France) city in which 60 buildings have been instrumented.
Petri-nets are a simple formalism for modeling concurrent computation. Recently, they have emerged as a powerful tool for the modeling and analysis of biochemical reaction networks, bridging the gap between purely qualitative and quantitative models. These networks can be large and complex, which makes their study difficult and computationally challenging. In this paper, we focus on two structural properties of Petri-nets, siphons and traps, that bring us information about the persistence of some molecular species. We present two methods for enumerating all minimal siphons and traps of a Petri-net by iterating the resolution of a boolean model interpreted as either a SAT or a CLP(B) program. We compare the performance of these methods with a state-of-the-art dedicated algorithm of the Petri-net community. We show that the SAT and CLP(B) programs are both faster. We analyze why these programs perform so well on the models of the repository of biological models biomodels.net, and propose some hard instances for the problem of minimal siphons enumeration.
Poincares approach to the three body problem has often been celebrated as a starting point of chaos theory in relation to the investigation of dynamical systems. Yet, Poincares strategy can also be analyzed as molded on - or casted in - some specific algebraic practices for manipulating systems of linear equations. These practices shed new light on both the novelty and the collective dimensions of Poincares Methodes nouvelles. As the structure of a cast-iron building may be less noticeable than its creative fac{c}ade, the algebraic cast of Poincares strategy is broken out of the mold in generating the novel methods of celestial mechanics. But as the various components that are mixed in some casting process can still be detected in the resulting alloy, the algebraic cast of the Methodes nouvelles points to some collective dimensions of Poincares methods. An edited version of the present preprint is to be published in the journal textit{Lastronomie} under the title Lapproche de Poincar`E sur le problEme des trois corps. This publication is an abstract in French language of a forthcoming paper - The algebraic cast of Poincar`Es textit{M`Ethodes nouvelles} - which will develop its main claims as well as the historiographical and mathematical issues raised in section 4 and section 5.
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