The impact of local masses and inertias on the dynamic modelling of flexible manipulators

After a brief review of the recent literature dealing with flexible multi-body modelling for control design purpose, the paper first describes three different techniques used to build up the dynamic model of SECAFLEX, a 2 d.o.f. flexible in-plane manipulator driven by geared DC motors : introduction of local fictitious springs, use of a basis of assumed Euler-Bernouilli cantilever-free modes and of 5th order polynomial modes. This last technique allows to take easily into account local masses and inertias, which appear important in real-life experiments. Transformation of the state space models obtained in a common modal basis allows a quantitative comparison of the results obtained, while Bode plots of the various interesting transfer functions relating input torques to output in-joint and tip mea-surements give rather qualitative results. A parametric study of the effect of angular configuration changes and physical parameter modifications (including the effect of rotor inertia) shows that the three techniques give similar results up to the first flexible modes of each link when concentrated masses and inertias are present. From the control point of view, “pathological” cases are exhibited : uncertainty in the phase of the non-colocated transfer functions, high dependence of the free modes in the rotor inertia value. Robustness of the control to these kinds of uncertainties appears compulsory

Flexible joint control : robustness analysis of the collocated and non-collocated feedbacks

In this paper, we propose a discussion on the robustness and performance properties of a proportional-derivative controller applied to a very flexible joint. Because of the flexible mode due to in-joint compliance, the classical collocated control does not allow to obtain good rigid mode dynamics with a correct phase margin in low and high frequency, and the non-collocated control does not allow to damp correctly the rotor mode. The simultaneous analysis of discrete root loci and Nichols plots leads to a phase control law with a derivative term built from both input and output velocities. Simulations taking into account various real non-linearities and measurement imperfections are proposed to validate this improved control design

Note de lecture sur "Anne Cornet, Politiques de santé et contrôle social au Rwanda. 1920-1940, Karthala, 2011, 472p."

International audienceLa politique sanitaire et médicale belge au Rwanda sous la colonisation : aspects sociaux, rôles respectifs des missions chrétiennes et de l'administration

Six-axis decentralized control design for spacecraft formation flying mission

This contribution addresses the control design for the three-spacecraft formation flying interferometry mission Pegase. The operational mode considered is the high-precision nulling phase. The control design has as major objective the minimization of the variance of the controlled outputs, e.g. the optical path difference. The payload performance demands are shown to be fulfilled in spite of orbital disturbances, solar radiation pressure as well as sensor and actuator noise. Furthermore, a novel iterative algorithm is proposed, capable of designing decentralized H2-suboptimal controllers. These controllers consist of a set of individual closed loops on board the different spacecraft which only use locally available measurements, forces and torques. This approach reduces communication bandwidth and enhances robustness concerning faulty communication links. Finally, the performance loss due to decentralization is investigated

Les communautés indiennes au Burundi sous les colonisations allemande et belge

Depuis le début du xxe siècle des commerçants indiens, venus de la côte swahilie, sont établis sur les rives du lac Tanganyika. Au Burundi, ils passent de vingt en 1914 sous l’administration allemande à près de cinq cents en 1946 sous la tutelle belge. Ces « Indiens », à majorité masculine, jeune et mobile, travaillent à leur compte ou pour des firmes installées dans l’Est africain britannique. Ils se regroupent en réseaux à la fois économiques, familiaux et religieux (hindous, musulmans chiites, notamment ismaéliens, sunnites, catholiques goanais), et entretiennent des rapports distants avec les Africains et ambigus avec les colonisateurs. Cette microhistoire démographique et sociale est éclairée par les archives coloniales.Desde o início do século XX, alguns comerciantes, vindos da costa suaile, estabeleceram-se nas margens do lago Tanganyika. No Burundi, eles passam de vinte em 1914 sob a administração alemã para cerca de quinhentos em 1946 sob a tutela belga. Estes « Indianos », de maioria masculina, jovem e com uma grande mobilidade, trabalham por conta própria ou para empresas implantadas na África oriental britânica. Eles agrupam-se em redes ao mesmo tempo económicas, familiares e religiosas (hindus, muçulmanos chiitas, especialmente ismaelitas, sunitas, católicos goeses), mantêm relações distantes com os Africanos e ambíguas com os colonizadores. Esta micro-história demográfica e social está baseada nos arquivos coloniais.From the beginning of the 20th Century, Indian traders from the Swahili coast settled on the shores of Lake Tanganyika. In Burundi, their number grew from twenty in 1914 under the German administration, to almost five hundred in 1946 under the Belgians. These young, mobile, mostly male “Indians” were self-employed or worked for firms based in British East Africa. They formed networks based on economic, family and religious ties (Hindus, Muslims, Shiites, in particular Ismailis, Sunnites, Goan Catholics) and had distant relations with the Africans and ambiguous ones with the colonisers. The colonial archives illustrate this demographic and social micro-history

Les communautés indiennes au Burundi sous les colonisations allemande et belge

Depuis le début du xxe siècle des commerçants indiens, venus de la côte swahilie, sont établis sur les rives du lac Tanganyika. Au Burundi, ils passent de vingt en 1914 sous l’administration allemande à près de cinq cents en 1946 sous la tutelle belge. Ces « Indiens », à majorité masculine, jeune et mobile, travaillent à leur compte ou pour des firmes installées dans l’Est africain britannique. Ils se regroupent en réseaux à la fois économiques, familiaux et religieux (hindous, musulmans chiites, notamment ismaéliens, sunnites, catholiques goanais), et entretiennent des rapports distants avec les Africains et ambigus avec les colonisateurs. Cette microhistoire démographique et sociale est éclairée par les archives coloniales.Desde o início do século XX, alguns comerciantes, vindos da costa suaile, estabeleceram-se nas margens do lago Tanganyika. No Burundi, eles passam de vinte em 1914 sob a administração alemã para cerca de quinhentos em 1946 sob a tutela belga. Estes « Indianos », de maioria masculina, jovem e com uma grande mobilidade, trabalham por conta própria ou para empresas implantadas na África oriental britânica. Eles agrupam-se em redes ao mesmo tempo económicas, familiares e religiosas (hindus, muçulmanos chiitas, especialmente ismaelitas, sunitas, católicos goeses), mantêm relações distantes com os Africanos e ambíguas com os colonizadores. Esta micro-história demográfica e social está baseada nos arquivos coloniais.From the beginning of the 20th Century, Indian traders from the Swahili coast settled on the shores of Lake Tanganyika. In Burundi, their number grew from twenty in 1914 under the German administration, to almost five hundred in 1946 under the Belgians. These young, mobile, mostly male “Indians” were self-employed or worked for firms based in British East Africa. They formed networks based on economic, family and religious ties (Hindus, Muslims, Shiites, in particular Ismailis, Sunnites, Goan Catholics) and had distant relations with the Africans and ambiguous ones with the colonisers. The colonial archives illustrate this demographic and social micro-history

Le droit à la recherche sur les génocides et sur les négationnismes

Discutant le cas du génocide des Tutsi du Rwanda en 1994 dans le contexte des controverses sur les « lois mémorielles » et à la lumière du débat sur la loi Boyer, l’auteur plaide pour le droit à la recherche sur les génocides et sur les négationnismes en soulignant les problèmes actuellement posés par l’absence d’un positionnement politique officiel et clair à ce sujet en France.Discussing current debates on “memory laws” in France, the author analyses the absence of a clear and official political position about the genocide of Rwandese Tutsi in 1994, and its consequences for denial and research on denials

La mise à mort des masses

L'époque qui voit naître les masses va aussi être le témoin de leurs destructions. L'auteur montre que la Première Guerre mondiale inaugure les destructions massives d'hommes conçus comme de pures entités numériques. Mais déjà, dans les «gazages», en particulier, s'annoncent les mises à mort massives de l'extermination des Camps de la Seconde Guerre mondiale. Ce type d'annihilation constitue un anéantissement virtuel de l'humanité comme masse des masses et de l'humanité de l'homme dans son être. Les conséquences examinées portent pour finir sur la possibilité de construire une théorie du Survivant comme théorie du pouvoir à l'époque des masses

Dexterous external space manipulation: serial or parallel concepts comparison

Within the external space manipulation framework, we compare two concepts to achieve an accurate positioning of the manipulator end effector. The first one involves a serial mini-manipulator inserted between the external space manipulator (macro-manipulator) and the end effector. Then, an anchorage mechanism is required to provide a hold point to the macro / mini manipulators interface. This solution can be called: static positioning of the minimanipulator base. The anchorage system stiffness is then discussed. In the second concept,the mini-manipulator serial architecture is replaced by a light parallel architecture. The macro manipulator is then used to provide a dynamic positioning to the mini-manipulator base by the mean of a coordinated control scheme between both manipulators

CAT: Robust attitude control of a telescope with flexible modes

The requirements concerning satellite optical instruments pointing stability are getting more and more stringent. To put up with a disturbed dynamic environment, the Line-of-Sight (LOS) control laws have to be efficient over a large bandwidth. One of the main performance limitation comes from the flexible modes of these optical payloads and their variations w.r.t host satellite configuration. To solve this problem, both classical frequency domain and modern H2/H1 syntheses have been performed and validated on the CAT experimental test facility (CAT: Contrôle d’Attitude de Télescope)