Design of an electrochemical micromachining machine

Electrochemical micromachining (μECM) is a non-conventional machining process based on the phenomenon of electrolysis. μECM became an attractive area of research due to the fact that this process does not create any defective layer after machining and that there is a growing demand for better surface integrity on different micro applications including microfluidics systems, stress-free drilled holes in automotive and aerospace manufacturing with complex shapes, etc. This work presents the design of a next generation μECM machine for the automotive, aerospace, medical and metrology sectors. It has three axes of motion (X, Y, Z) and a spindle allowing the tool-electrode to rotate during machining. The linear slides for each axis use air bearings with linear DC brushless motors and 2-nm resolution encoders for ultra precise motion. The control system is based on the Power PMAC motion controller from Delta Tau. The electrolyte tank is located at the rear of the machine and allows the electrolyte to be changed quickly. This machine features two process control algorithms: fuzzy logic control and adaptive feed rate. A self-developed pulse generator has been mounted and interfaced with the machine and a wire ECM grinding device has been added. The pulse generator has the possibility to reverse the pulse polarity for on-line tool fabrication.The research reported in this paper is supported by the European Commission within the project “Minimizing Defects in Micro-Manufacturing Applications (MIDEMMA)” (FP7-2011-NMPICT- FoF-285614)

Design of a pulse power supply unit for micro-ECM

Electrochemical micro-machining (μECM) requires a particular pulse power supply unit (PSU) to be developed in order to achieve desired machining performance. This paper summarises the development of a pulse PSU meeting the requirements of μECM. The pulse power supply provides tens of nanosecond pulse duration, positive and negative bias voltages and a polarity switching functionality. It fulfils the needs for tool preparation with reversed pulsed ECM on the machine. Moreover, the PSU is equipped with an ultrafast overcurrent protection which prevents the tool electrode from being damaged in case of short circuits. The developed pulse PSU was used to fabricate micro-tools out of 170 μm WC-Co alloy shafts via micro-electrochemical turning and drill deep holes via μECM in a disk made of 18NiCr6. The electrolyte used for both processes was a mixture of sulphuric acid and NaNO3 aqueous solutions.The research reported in this paper is supported by the European Commission within the project “Minimizing Defects in Micro-Manufacturing Applications (MIDEMMA)” (FP7-2011-NMP-ICT-FoF-285614

Visibilité et présence de l’image dans l’espace ecclésial

Cet ouvrage met au cœur de son propos une interrogation simple : dans l’organisation complexe de l’espace de l’église médiévale, les emplacements choisis pour les images qui ornent les murs et les objets n’offrent pas toujours la possibilité de voir celles-ci, d’en déchiffrer le contenu. Certaines semblent réservées à des groupes de l’assemblée stationnant dans des espaces spécifiques, d’autres ne sont pas visibles depuis les principales zones affectées aux fidèles ou aux clercs, d’autres encore sont situées trop haut. Le rapport, a priori évident, entre représentation et visibilité se trouve donc souvent démenti, appelant alors une nouvelle notion, celle de présence. Analyser la tension existant entre ces trois catégories – figuration, visibilité et présence – implique une étude croisée des œuvres figurées, des monuments et des sources écrites. Les notions de mobilité et de fixité permettent également de prendre en compte les multiples jeux d’échelles à l’œuvre dans ce lieu rituel qu’est l’église, impliquant des objets, des manuscrits, des dispositifs liturgiques, des gestes, des déplacements physiques, dialoguant avec un décor appliqué au corps même du monument, épousant l’immobilité de l’architecture. Les cinq chapitres thématiques qui organisent ce volume mettent en regard différents cas issus de l’Occident médiéval et de l’Orient byzantin, selon une chronologie longue (de l’Antiquité tardive à la fin du Moyen Âge), dans une volonté de décloisonner les disciplines et les aires géographiques afin de tirer tous les enseignements d’une approche transversale de l’image médiévale

Prior intention can locally tune inhibitory processes in the primary motor cortex: direct evidence from combined TMS-EEG

International audienceHuman subjects are able to prepare cognitively to resist an involuntary movement evoked by a suprathreshold transcranial magnetic stimulation (TMS) applied over the primary motor cortex (M1) by anticipatory selective modulation of corticospinal excitability. Uncovering how the sensorimotor cortical network is involved in this process could reveal directly how a prior intention can tune the intrinsic dynamics of M1 before any peripheral intervention. Here, we used combined TMS-EEG to study the cortical integrative processes that are engaged both in the preparation to react to TMS (Resist vs. Assist) and in the subsequent response to it. During the preparatory period, the contingent negative variation (CNV) amplitude was found to be smaller over central electrodes (FC1, C1, Cz) when preparing to resist compared with preparing to assist the evoked movement whereas a-oscillation power was similar in the two conditions. Following TMS, the amplitude of the TMS evoked-N100 component was higher in the Resist than in the Assist condition for some central electrodes (FCz, C1, Cz, CP1, CP3). Moreover, for six out of eight subjects, a single-trial-based analysis revealed a negative correlation between CNV amplitude and N100 amplitude. In conclusion, prior intention can tune the excitability of M1. When subjects prepare to resist a TMS-evoked movement, the anticipatory processes cause a decreased cortical excitability by locally increasing the inhibitory processes