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Personne# Ilan Vardi

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Personnes menant des recherches similaires (130)

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Oscillation

Une oscillation est un mouvement ou une fluctuation périodique autour d'une position d'équilibre stable. Les oscillations sont soit régulières (périodiques) soit décroissantes (amorties). Elles répon

Oscillateur harmonique quantique

L'oscillateur harmonique quantique correspond au traitement par les outils de la mécanique quantique de l'oscillateur harmonique classique.
De façon générale, un oscillateur est un système dont l'évo

Échappement (horlogerie)

Dans les horloges et les montres mécaniques, l'échappement est un mécanisme placé entre la source d'énergie (ressort, poids, etc.) et le résonateur (Pendule, balancier-spiral, etc.). C'est le mécanis

Publications associées (42)

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Simon Nessim Henein, Ilan Vardi

Since the invention of the pendulum clock by Christiaan Huygens in 1657, precision timekeepers have been regulated by oscillators. Although the pendulum is not an isochronous oscillator, its introduction as a time basis for clock regulation led to a significant increase in accuracy. Indeed, numerous clocks were subsequently retrofitted with pendulums to replace the foliot time base. Oscillators have defined revolutions in accuracy, as seen by the terms quartz watch and atomic clock. Observation of a rocking chair and its mathematical modelling shows that it provides oscillatory motion and can therefore theoretically be used as a clock time base. This led to the study, design, and fabrication of a rocker oscillator for the regulation of a table clock. The demonstrator consists of a rocker oscillator designed to replace the original pendulum of a commercial precision table clock. Two identical clocks were used to compare the operation of the modified clock with that of the original one. The rocker oscillator was dimensioned so that its natural frequency as well as its quality factor fit those of the original pendulum. The performance of both clocks was then the subject of an experimental study. This project serves as a demonstration of how new oscillators can be retrofitted to existing timekeepers.

2021Patrick Robert Flückiger, Simon Nessim Henein, Ilan Vardi

The Foucault pendulum is a well-known mechanism used to demonstrate the rotation of the Earth. It consists in a pendulum launched on linear orbits and, following Mach’s Principle, this line of oscillation will remain fixed with respect to absolute space but appear to slowly precess for a terrestrial observer due to the turning of the Earth. The theoretical proof of this phenomenon uses the fact that, to first approximation, the Foucault pendulum is a harmonic isotropic two degree of freedom (2-DOF) oscillator. Our interest in this mechanism follows from our research on flexure-based implementations of 2-DOF oscillators for their application as time bases for mechanical timekeeping. The concept of the Foucault pendulum therefore applies directly to 2-DOF flexure based harmonic oscillators. In the Foucault pendulum experiment, the rotation of the Earth is not the only source of precession. The unavoidable defects in the isotropy of the pendulum along with its well-known intrinsic isochronism defect induce additional precession which can easily mask the precession due to Earth rotation. These effects become more prominent as the frequency increases, that is, when the length of the pendulum decreases. For this reason, short Foucault pendulums are difficult to implement, museum Foucault pendulum are typically at least 7 meters long. These effects are also present in our flexure based oscillators and reducing these parasitic effects, requires decreasing their frequency. This paper discusses the design and dimensioning of a new flexure based 2-DOF oscillator which can reach low frequencies of the order of 0.1[Hz]. The motion of this oscillator is approximatelyplanar, like the classical Foucault pendulum, and will have the same Foucault precession rate. The construction of a low frequency demonstrator is underway and will be followed by quantitative measurements which will examine both the Foucault effect as well as parasitic precession.

2020Simon Nessim Henein, Mohammad Hussein Kahrobaiyan, Etienne Frédéric Gabriel Thalmann, Ilan Vardi

The most important property for accurate mechanical time bases is isochronism: the independence of period from oscillation amplitude. This paper develops a new concept in isochronism adjustment for flexure-based watch oscillators. Flexure pivot oscillators, which would advantageously replace the traditional balance wheel-spiral spring oscillator used in mechanical watches due to their significantly lower friction, exhibit nonlinear elastic properties that introduce an isochronism defect. Rather than minimizing this defect, we are interested in controlling it to compensate for external defects such as the one introduced by escapements. We show that this can be done by deriving a formula that expresses the change of frequency of the oscillator with amplitude, i.e., isochronism defect, caused by elastic nonlinearity. To adjust the isochronism, we present a new method that takes advantage of the second-order parasitic motion of flexures and embody it in a new architecture we call the co-RCC flexure pivot oscillator. In this realization, the isochronism defect of the oscillator is controlled by adjusting the stiffness of parallel flexures before fabrication through their length Lp, which has no effect on any other crucial property, including nominal frequency. We show that this method is also compatible with post-fabrication tuning by laser ablation. The advantage of our design is that isochronism tuning is an intrinsic part of the oscillator, whereas previous isochronism correctors were mechanisms added to the oscillator. The results of our previous research are also implemented in this mechanism to achieve gravity insensitivity, which is an essential property for mechanical watch time bases. We derive analytical models for the isochronism and gravity sensitivity of the oscillator and validate them by finite element simulation. We give an example of dimensioning this oscillator to reach typical practical watch specifications and show that we can tune the isochronism defect with a resolution of 1 s/day within an operating range of 10% of amplitude. We present a mock-up of the oscillator serving as a preliminary proof-of-concept.

2020