Différentiel (mécanique)

thumb|Différentiel Škoda. Un différentiel est un système mécanique qui a pour fonction de distribuer une vitesse de rotation par répartition de l'effort cinétique, de façon adaptative, immédiate et automatique, aux besoins d'un ensemble mécanique. Par exemple, il est très utile sur un véhicule automobile où il permet aux roues motrices de tourner à des vitesses différentes lors du passage d'une courbe : les roues situées à l'extérieur du virage tournent plus vite que celles situées à l'intérieur. thumb|Éclaté d'un différentiel monté sur l'axe arrière d'une automobile Histoire Le différentiel mécanique est breveté en 1827 par le mécanicien français et maître horloger Onésiphore Pecqueur, et employé dès 1860 sur les premiers véhicules routiers à vapeur. Il en existe toutefois des traces beaucoup plus anciennes dans le domaine de l'horlogerie, notamment sur une illustration de l'horloge à équation de Dauthiau, issue de l'Encyclopédie de Diderot et d'Alembert éditée de 1751

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Tibial component positioning in total knee arthroplasty: bone coverage and extensor apparatus alignment

Pierre Lemaire, Pierre-François Leyvraz, Reto Meuli, Dominique Pioletti

Correct positioning of the tibial component in total knee arthroplasty (TKA) must take into account both an optimal bone coverage (defined by a maximal cortical bearing with posteromedial and anterolateral support) and satisfactory patellofemoral tracking. Consequently, a compromise position must be found by the surgeon during the operation to simultaneously meet these two requirements. Moreover, tibial tray positioning depends upon the tibial torsion, which has been shown to act mainly in the proximal quarter of the tibia. Therefore, the correct application of the tibial tray is also theoretically related to the level of bone resection. In this study, we first quantified the torsional profile given by an optimal bone coverage for a symmetrical tibial tray design and for an asymmetrical one. Then, for the two types of tibial trays, we measured the angle difference between optimal bone coverage and an alignment on the middle of the tibial tubercule. Results showed that the values of the torsional profile given by the symmetrical tray were more scattered than those from the asymmetrical one. However, determination of the mean differential angle between the position providing optimal bone coverage and the one providing the best patellofemoral tracking indicated that the symmetrical prosthetic tray offered the best compromise between these two requirements. Although the tibiofemoral joint is known to be asymmetric in both shape and dimension, the asymmetrical tray chosen in this study was found to fulfill this compromise with more difficulty.

1997

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Crash test-based assessment of injury risks for adults and children when colliding with personal mobility devices and service robots

Aude Billard, Diego Felipe Paez Granados

Autonomous mobility devices such as transport, cleaning, and delivery robots, hold a massive economic and social benefit. However, their deployment should not endanger bystanders, particularly vulnerable populations such as children and older adults who are inherently smaller and fragile. This study compared the risks faced by different pedestrian categories and determined risks through crash testing involving a service robot hitting an adult and a child dummy. Results of collisions at 3.1 m/s (11.1 km/h/6.9 mph) showed risks of serious head (14%), neck (20%), and chest (50%) injuries in children, and tibia fracture (33%) in adults. Furthermore, secondary impact analysis resulted in both populations at risk of severe head injuries, namely, from falling to the ground. Our data and simulations show mitigation strategies for reducing impact injury risks below 5% by either lowering the differential speed at impact below 1.5 m/s (5.4 km/h/3.3 mph) or through the usage of absorbent materials. The results presented herein may influence the design of controllers, sensing awareness, and assessment methods for robots and small vehicles standardization, as well as, policymaking and regulations for the speed, design, and usage of these devices in populated areas.

2022

Chargement

Screen-printed polymer-based microfluidic and micromechanical devices based on evaporable compounds

Yannick Fournier, Caroline Jacq, Thomas Maeder, Peter Ryser, Nathalie Sophie Adeline Serra

We investigate in this work the fabrication of polymer fluidic and mechanical devices based on evaporable compounds as sacrificial layers using the screen-printing process. The combination of thermosetting polymer resins with evaporable compounds as sacrificial layers allows straightforward fabrication of polymer microfluidic and micromechanical devices. Channel, cavities and spacings are first defined by sacrificial material layers. This is followed by polymer resin deposition and polymerization / solvent removal. Removal of the sacrificial layers is then accomplished by heating at their decomposition / evaporation temperature. This process does not require an ulterior dissolution step, and systems exist where the sacrificial layer molecules escape by diffusion through the polymer at high temperature: we are therefore not limited to open structures. Furthermore, the use of screen- printed thick-film compositions is very advantageous regarding process cost and flexibility. The selected sacrificial layer must be stable at the polymer processing temperature, yet decompose / evaporate cleanly at a temperature low enough to avoid degradation of the polymer. In this work, we used polymers such as ethylcellulose and silicone resins filled with graphite to impart electrical conductivity and improve mechanical stability. The selected sacrificial materials were polyol-based and were formulated to sublime rather than evaporate, in order to preserve the structures. They were formulated as thick-film pastes using a suitable cyclohexanol-based solvent mix.

IMAPS2009

Chargement

MICRO-200: Mechanism Design I

Ce cours introduit les bases de la mécanique des structures : calcul des contraintes et déformations provoquées par les forces extérieures et calcul des déformations. Ces enseignements théoriques sont appliqués à la conception des éléments importants des mécanismes de précision.

ME-426: Micro/Nanomechanical devices

In this course we will see an overview of the exciting field of Micro and Nanomechanical systems. We will go over the dfferent scaling laws that dominate the critical parameters, how size affects material properties, how these devices are manufactured, designed and later used.

ME-251: Thermodynamics and energetics I

Introduction aux principes de la thermodynamique, propriétés thermodynamiques de la matière et à leur calcul. Les étudiants maîtriseront les concepts de conservation (chaleur, masse, quantité de mouvement) et appliqueront ces concepts au cycles thermodynamiques et systèmes de conversion d'énergie.

Engrenage

thumb|Un engrenage hélicoïdal à contact extérieur en action Un engrenage est un système mécanique composé de deux solides reliés par des dentures. Le cas particulier le plus courant étant deux roues

Automobile

Une automobile (simplification historique de l'expression « voiture légère automobile ») est un véhicule à roues, motorisé et destiné au transport terrestre de quelques personnes et de leurs bagages

Roue

thumb|Une roue à rayons en bois équipée d'un bandage plein en caoutchouc. Une roue est une pièce mécanique de forme circulaire tournant autour d'un axe passant par son centre. La roue est l'une des hu