Vector control method applied to a traveling wave in a finite beam

This paper presents the closed-loop control of exciters to produce a traveling wave in a finite beam. This control is based on a dynamical modeling of the system established in a rotating reference frame. This method allows dynamic and independent control of the phase and amplitude of two vibration modes. The condition to obtain the traveling wave is written in this rotating frame, and requires having two vibration modes with the same amplitude, and imposing a phase shift of 90° between them. The advantage of the method is that it allows easy implementation of a closed loop control that can handle parameter drift of the system, after a temperature rise, for example. The modeling is compared with measurement on an experimental test bench which also implements real-time control. We managed to experimentally obtain a settling time of 250 ms for the traveling wave, and a standing wave ratio (SWR) of 1.3

Analysis of the energy harvesting performance of a piezoelectric bender outside its resonance

When the frequency of the source of vibration of a piezolectric generator is significantly different from its eigenfrequency, the dielectric power losses become prominent and decrease the amount of power which is practically harvested. For off-resonance vibrating frequencies, the optimal operating conditions can be obtained with a Maximum Power Point Tracking method. This paper introduces complex phasors in the study of power conversion for piezoelectric generators. These complex phasors are used to describe three strategies which help simplify the tracking of the optimal generator output power for vibration frequencies which are away from resonance. Experimental results obtained on a prototype illustrate and confirm the approach with the phasor approaches illustrate and confirm the success of the proposed optimal power tracking strategies. Finally, we show that the efficiency results of each strategy depend on whether they are used inside or outside a frequency bandwidth around the eigenfrequency, and that the length of this bandwidth depends on the excitation amplitude.IRCICA Stimtac Project, INRIA Mint Project

Mechanical Behavior of AA6061 Aluminum in the Semisolid State Obtained by Partial Melting and Partial Solidification

International audienceThe tensile properties of a 6061 aluminum alloy have been studied in the semisolid state at large solid fractions. The tests have been carried out either after a partial melting treatment or after partial solidification. Results show the following: (1) the mechanical behavior depends on the liquid-phase distribution and, therefore, on the way the semisolid state has been achieved (melting or solidification); (2) there is a critical solid fraction range where the semisolid alloy is relatively brittle; and (3) the mushy alloy exhibits viscoplastic behavior with the occurrence of micro-superplasticity at low strain rate. Modeling of this behavior is carried out by considering either the area fraction of grain boundaries wetted by the liquid or a cohesion parameter of the solid phase, which depends on solid fraction and thermal treatment

Control of a multi-degree of freedom worktool for vibrations assisted forging

This paper addresses the control of a tool developed to superimpose vibrations along several directions on a piece during forging. Piezoelectric actuators are used to provide the required forces and speeds. Due to the minute displacements of the actuators, flexible hinges are used in a special arrangement in order realize the specified movements and to ensure controllability. The experimental results confirm the approach

Preliminary design of a multi-touch ultrasonic tactile stimulator

This paper presents a method to control ultrasonic waves on a beam, allowing to obtain a Multi-touch ultrasonic tactile stimulation in two points, to give the sensation to two fingers, from two piezoelectric transducers. The multi-modal approach and the vector control method are used to regulate the vibration amplitude, in order to modulate the friction coefficient with the fingers. An analytical modelling is presented, with experimental validation. Finally a psychophysical experiment shows that a multi-touch ultrasonic tactile stimulation is possible.This work has been carried out within the framework of the project StimTac of IRCICA (institut de recherche sur les composants logiciels et matériel pour la communication avancée), and the Project Mint of Inria

Modelling, identification and control of a Langevin transducer

The control of the vibration amplitude, and the resonance frequency tracking for ultrasonic transducer have been established. However, some applications require to control the vibration amplitude and its relative phase at a fixed frequency as the generation of travelling wave. In this paper, the transducer is modelled in rotating frame, and the decoupling according to two-axis allows to obtain a double independent closed loop control to address this issue. It is possible to control the transducer vibration amplitude and its relative phase, in steady state even in transient by acting on the amplitude of the supply voltage. Thanks to vector control method. This approach will be confirmed with experimental and simulation results.This work has been carried out within the framework of the project StimTac of IRCICA (institut de recherche sur les composants logiciels et matériel pour la communication avancée), and the Project Mint of Inria

« Question noire » et mémoire de l’esclavage

RésuméCe texte est une réaction contre la racialisation croissante des phénomènes sociaux qui est opérée aujourd’hui dans la société française en général et dans les sciences sociales en particulier. Une tendance dont l’émergence d’une « question noire » et d’un des principaux corollaires de celle-ci (au moins pour ce qui est des populations des départements d’Outre-mer), l’activation d’une mémoire de l’esclavage des «nègres», sont ici considérées comme un exemple des plus significatifs.Cette tendance se développe au risque que soient occultés ou, pour le moins, travestis les enjeux, les stratégies et les mécanismes proprement sociaux qui sont au fondement des discriminations racistes qu’affrontent effectivement les « Noirs » en France et que soient finalement brisées — sous le poids de la concurrence de victimes de l’histoire exigeant réparation — les solidarités transcommunautaires de diverses sortes qui, seules, peuvent enrayer ces discriminations et les dynamiques les déterminant.Elle a pour un de ses principaux moteurs des stratégies d’élites qui, toutes, consistent à constituer le racialisme en un moyen d’ascension sociale. Des stratégies dans lesquelles et pour lesquelles des groupes d’individus — convenablement dotés en capitaux de différentes sortes (économique, culturel et « racial ») — se révèlent donc particulièrement aptes à capter à leur seul profit les mobilisations identitaires ou mémorielles qu’ils ont souvent contribué à déclencher mais dont d’autres, moins bien dotés, forment la grande masse des fantassins.Concernant les populations des départements d’Outre-mer, les stratégies en question sont portées par des élites nationalistes ou indigénistes en mal de reconnaissance et renvoient à une même logique argumentative qui, sous couvert d’une dénonciation de l’aliénation coloniale (sous les espèces de « l’aveuglement à la couleur » ou de « l’oubli généralisé de l’esclavage »), est opposée à tous ceux qui, désireux de construire une citoyenneté française enfin « véritable », ne veulent pas se laisser enfermer dans « le piège de la race » ou dans celui d’une mémoire sacralisée du passé servile.AbstractThis paper is a reaction against the growing “racialization” of social issues occurring today in French society in general, and in the social sciences in particular. The emergence of a “black question” is one of the main corollaries of this trend (at least where populations in the French overseas departments is concerned). Here we consider that activating a memory of “negro” slavery it one of the most significant examples.The risk of this trend developing is that it may conceal (or at least misrepresent), the issues, strategies and purely social mechanisms that are the cornerstone of the racial discrimination to which “blacks” in France are subjected, and that the trans-community solidarity of various kinds that alone can curb these discriminations, and the dynamics that determine them, will collapse under the weight of the competing victims of history demanding reparation.Among the driving forces of this trend are the elite strategies that consist of making racism a means of social advancement. Using these strategies, groups of individuals — properly equipped with various kinds of capital (economic, cultural and “racial”) — appear to be particularly adept at seizing for themselves the benefits of the identity or memorial mobilisation that they themselves often helped trigger, away from the mass of less well equipped “footsoldiers”.Where populations in the French overseas departments are concerned, these strategies are promoted by the nationalist elite or indigénistes in need of recognition, and refer to the same argumentative logic that, under guise of denouncing colonial alienation (of the “colour blindness” or “the widespread forgetting of slavery” type) oppose all those who want to build a “true” French citizenship at last and do not want to be ensnared by the “race trap”, or a sanctified memory of a servile past

Présentation

Alors que les effets négatifs de la « mondialisation libérale » renforcent leurs traits un peu partout et déstabilisent la vie physique, économique, sociale et politique d’un grand nombre de pays, les sociétés caraïbéennes dans leur ensemble paraissent - tels des fétus de paille face à la tornade- bien mal armées pour tenter de relever les défis que constituent ces effets. Elles sont, en effet, de taille très modeste ou même, concernant certaines, minuscule, sont situées à l’écart des grands ..

La créolisation

Aucun des discours de la créolisation n’évite l’écueil d’une mise en œuvre double de ce concept. Ainsi le terme « créolisation » y renvoie-t-il à la fois à un phénomène historique singulier et à une pure procédure particulière de la dynamique culturelle en général. Sans que, le plus souvent, ces deux dimensions sémantiques – en vérité bien différentes l’une de l’autre – ne soient clairement distinguées. C’est là la principale faiblesse des discours en question. En ce que l’absence d’une telle..