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thumb|La barre de platine-iridium utilisée comme prototype du mètre de 1889 à 1960. La métrologie est la science de la mesure. Elle définit les principes et les méthodes permettant de garantir et maintenir la confiance envers les mesures résultant des processus de mesure. Il s'agit d'une science transversale qui s'applique dans tous les domaines où des mesures quantitatives sont effectuées. On peut distinguer, artificiellement, différents aspects de la métrologie pour faciliter sa compréhension :

la métrologie fondamentale, ou scientifique, qui vise à créer, développer et maintenir des étalons de référence reconnus ;
la métrologie industrielle, la plus fréquente, qui permet de garantir les mesures, par exemple d'un processus de fabrication, souvent dans le cadre d'un contrôle qualité lié à un système de management de la qualité ;
la métrologie légale, liée aux mesures sur lesquelles s'appliquent des exigences réglementaires ;
en plus d'une métrologie traditionnelle quantitati

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Résumé

la métrologie fondamentale, ou scientifique, qui vise à créer, développer et maintenir des étalons de référence reconnus ;
la métrologie industrielle, la plus fréquente, qui permet de garantir les mesures, par exemple d'un processus de fabrication, souvent dans le cadre d'un contrôle qualité lié à un système de management de la qualité ;
la métrologie légale, liée aux mesures sur lesquelles s'appliquent des exigences réglementaires ;
en plus d'une métrologie traditionnelle quantitati

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Publications associées (19)

Publications associées

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Personnes associées

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Concepts associés (44)

Concepts associés

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Cours associés (17)

Cours associés

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Séances de cours associées (29)

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High-frequency broadband laser phase noise cancellation using a delay line

Timo Zwettler

Laser phase noise remains a limiting factor in many experimental settings, including metrology, time-keeping, as well as quantum optics. Hitherto this issue was addressed at low frequencies ranging from well below 1 Hz to maximally 100 kHz. However, a wide range of experiments, such as, e.g., those involving nanomechanical membrane resonators, are highly sensitive to noise at higher frequencies in the range of 100 kHz to 10 MHz, such as nanomechanical membrane resonators. Here we employ a fiber-loop delay line interferometer optimized to cancel laser phase noise at frequencies around 1.5 MHz. We achieve noise reduction in 300 kHz-wide bands with a peak reduction of more than 10 d13 at desired frequencies, reaching phase noise of less than -160 dB(rad(2)/Hz) with a Ti:Al2O3 laser. These results provide a convenient noise reduction technique to achieve deep ground-state cooling of mechanical motion. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

OPTICAL SOC AMER2021

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Precision Positioning of Microrobots for Multi-Object Spectrographs

Luzius Gregor Kronig

How does one study the evolution of the Milky Way, or the expansion of the Universe, or explore the mysteries of Dark energy? To investigate these complex topics, astronomers require data, and a great deal of it, in the form of the spectra of stars, galaxies, and quasars. In recent years remarkable efforts have been made to develop telescopes and instruments that can measure more light spectra in parallel than ever before. One solution for building these instruments, called Multi-Object Spectrographs, requires the use of several hundreds of small precise automated robots in the telescope's focal plane. Each robot can position an optical fiber with micrometer precision along the focal surface in order to capture and transmit the light of a celestial object to a spectrograph, which then measures the spectrum with great precision. In the future, new instruments will be able to measure over 10000 celestial objects simultaneously, which would consequently require the implementation of as many optical fiber positioners. To assure the development and successful operation of the instrument, every single fiber positioner requires design and validation testing. Tools for such quality assurance have yet to be developed. This thesis proposes solutions to verify, calibrate, control, and operate optical fiber positioners with two actuated rotation axes, serially linked. A metrology system is presented which is capable of accurately measuring position and alignment of the optical fiber, and a detailed model describing the correct behavior of the positioner is introduced. Based on the model, an automated measurement procedure enables calibration and validation of the positioners. The introduced measurement procedure identifies not only flaws in performance, but also various error sources, which help to detect possible design and manufacturing problems. Finally, a method is proposed on how to operate these positioners in the focal plane. Taken together, the results of this thesis can inform the present and future manufacturer of Multi-Object Spectrographs.

EPFL2020

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Guidance, Navigation and Control for Autonomous Rendezvous and Docking of Nano-Satellites

Camille Sébastien Pirat

Is it possible to dock CubeSats in Low Earth Orbit? Challenges are associated with the level of miniaturisation: the docking accuracy is driven by the docking mechanism dimensions. The achievable docking performance with the Guidance, Navigation and Control (GNC) subsystem is constrained by the use of small sensors and actuators. A docking mechanism prototype, tailored for CubeSats was designed, built and tested in the laboratory using a simple experimental setup. Results showed that a lateral precision of 1 cm and a relative angular alignment better than 2 degrees are required to guarantee successful docking. A filtered monocular camera on the chaser satellite and various arrays of light-emitting diodes on the target vehicle were selected for the metrology, due to their potential to achieve a high relative navigation accuracy and to ensure the observability of the system throughout the final approach trajectory. Both docking mechanism and metrology system are contained within 0.5U volume and can thus be used on a wide span of satellite types. The chaser and target have a complete 3-axis attitude pointing capability and are equipped with off-the-shelf CubeSats attitude sensors and actuators, including star trackers and reaction wheels. The chaser is further equipped with a six degrees of freedom low-thrust cold gas propulsion system. The navigation and control functions rely on a linearised coupled dynamic, which includes fuel sloshing effects, and describes the 6 degrees of freedom relative motion between the chaser and target docking ports. Using this dynamic, LQR, LQI, H-Infinity and Mu-Synthesis controllers were investigated and their stability and performance assessed by mean of Mu-Analysis. A comprehensive simulation framework was developed to evaluate the performances of the navigation and control functions and the impact of actuator and sensor errors on the overall docking performance. The environmental and internal perturbations, such as atmospheric drag and fuel sloshing were taken into account. All sensors and actuators required for the docking were modelled, including realistic errors and noise characteristics. Different docking scenarios were investigated based on the different behaviour of the coupled dynamics. Worst-case scenarios such as the loss of sensor signals prior to docking are also tackled. The robustness of the proposed control schemes was assessed by the use of structured singular values. Complementary non-linear Monte-Carlo simulations were also performed to determine the complete GNC performances as well as fuel consumption. Results show that the proposed GNC is robust to the modelled sensor and actuator noises, fuel sloshing, dynamics uncertainties and that a lateral position accuracy better than 5 mm can always be obtained at docking. Furthermore, docking is not affected by the loss of star tracker signals nor by harsh illumination conditions, and can thus take place on a variety of orbits.

EPFL2018

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Système international d'unités

Le Système international d'unités (abrégé en SI), inspiré du système métrique, est le système d'unités le plus largement employé au monde ; il n'est pas officiellement utilisé aux États-Unis, au Libe

Mètre

Le mètre, de symbole m (sans point abréviatif), est l'unité de longueur du Système international (SI). C'est l'une de ses sept unités de base, à partir desquelles sont construites les unités dérivées

Kilogramme

Le kilogramme, dont le symbole est kg (en minuscules), est l'unité de base de masse dans le Système international d'unités (SI). Le kilogramme est la seule unité SI de

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