Monotonicity and the Roy Model

In this note we study the implications on a bivariate normal Roy Model of two sets of monotonicity hypotheses proposed recently by Manski and Pepper (2000). In that simple context, we show that these hypotheses imply strong restrictions on the correlations structure between the decision and the rewards.Roy Model; Monotonicity Conditions

Improving rotation behaviour of robotic structures for micro-assembly.

International audienceSerial micro-assembly requires high precision robots able to produce translations and rotations to position and orient objects during assembly. In micro-scale, the translation ranges required are typically up to the millimeter and can be obtained with smart devices (piezomotor, etc...). In the other hand, the rotation ranges stay identical to the macroscale (eg. 90°) and require standard guidings like ball bearings which induce disturbances on the linear position. Thus, the ability to produce high precision robots where translations and rotations are découpled is currently one of the major stake in microassembly. This paper deals with an original modeling of the coupling between rotation and linear position. The geometrical model is presented and two calibration methods are discussed. Our method were tested on a 3 DOF planar robotic systems and the coupling was reduced by 93 %

La cicatrisation du tendon et la récupération des amplitudes articulaires après chirurgie de la coiffe des rotateurs par arthroscopie: influence d'un protocole de rééducation précoce comparé à un protocole d'immobilisation : revue de la littérature : travail de Bachelor

Introduction : Dans le domaine des pathologies de l’épaule, la plus rencontrée est la rupture de/des tendons de la coiffe des rotateurs. Après chirurgie réparatrice par arthroscopie différents protocoles de rééducation sont appliqués. Récemment cités comme la cause des récidives, ces protocoles de rééducation sont au cœur d’une controverse sur les résultats cliniques post-opératoires. L’objectif de cette revue est d’identifier les répercussions d’un protocole de rééducation incluant de la mobilisation passive précoce (J1) comparé à un protocole d’immobilisation, après chirurgie réparatrice de la coiffe des rotateurs par arthroscopie, sur la cicatrisation tendineuse et les amplitudes articulaires, avec un recul d’une année. Problématique : «La mobilisation immédiate passive (J1) après chirurgie de la coiffe des rotateurs par arthroscopie, est-elle préjudiciable à la cicatrisation complète du/des tendon(s), augmente t-elle le risque de récidive et est-elle bénéfique à la récupération des amplitudes articulaires ?» Méthode : Nous avons effectué notre recherche sur les bases de données suivantes : Medline, Cochrane library, PEDro, et Kinédoc. Nous avons inclus 4 études de design RCT analysant des patients ayant bénéficié d’une chirurgie réparatrice effectuée par arthroscopie et comprenant la comparaison d’un protocole de rééducation précoce avec un protocole d’immobilisation. Résultats : Ces 4 publications ne reportent aucun avantage significatif dans l’application d’un protocole précoce comparé à un protocole d’immobilisation. Cependant, l’application d’un protocole d’immobilisation a tendance à induire une meilleure cicatrisation sans effets néfastes sur la récupération des amplitudes articulaires. Conclusion : Des résultats presque similaires sont obtenus avec les deux protocoles de rééducation après une année. Les auteurs se questionnent maintenant sur l’application de protocoles individualisés à chaque patient.Introduction : The most common pathologies encountered in the area of shoulder disorders are rotators cuff’s tendons tears. After reconstructive surgery by arthroscopy, several rehabilitation protocols can be applied. Those protocols have been identified by some in the literature as the cause of recurrence and are therefore at the heart of a controversy about the post-operation outcomes. The goal of this review is to identify the effects of two types of protocols. The two protocols differ in terms of the timing of the mobilization after reconstructive surgery of the cuff by arthroscopy. We will discuss the effects of an early mobilization versus immobilization on the healing of the tendon and the range of motion one year after the operation. Main questions : "Is the immediate passive mobilization (J1) detrimental to the complete healing of the tendon? Does an immediate mobilization increase the risk of recurrence and is it beneficial in terms of the amplitude of the shoulder motion?” Methods : We reviewed the literature by including publications found in the following databases: Cochrane library, PEDro and Kinedoc. We have concentrated in particular on four design RCT studies that analyze patients having benefited from a reconstructive surgery by arthroscopy. Those studies compare an early versus late mobilization protocol in the rehabilitation stage. Results : In all four studies there is no evidence of a significant improvement of an early mobilization versus immobilization protocol. Nevertheless, late protocols tend to result in a better healing with no negative impact on the range motion at one year. Conclusion : Based on those four studies, it is not possible to favor one rehabilitation protocol. The authors therefore discuss a future area of research, mainly the establishment of a protocol specific to each patient

Nonlinear Hamiltonian modelling of magnetic shape memory alloy based actuators.

International audienceThis paper proposes an application of the Lagrangian formalism and its Hamiltonian extension to design, model and control a mechatronic system using Magnetic Shape Memory Alloys. In this aim, an original dynamical modelling of a Magnetic Shape Memory Alloy based actuator is presented. Energy-based techniques are used to obtain a coherent modelling of the magnetical, mechanical and thermodynamic phenomena. The Lagrangian formalism, well suited in such a case, is introduced and used to take into account the dynamical effects. Hamilton equations are deduced and used for the computation of the theoretical behaviour of this actuator. These numerical simulations are compared with some experimental measurements permitting the validation of the proposed modelling. Beyond the work presented here, these results will be used to design an energy shaping nonlinear control well-adapted for a strongly nonlinear active material

Modelling Rearrangement Process of Martensite Platelets in a Magnetic Shape Memory Alloy Ni2MnGa Single Crystal under Magnetic Field and (or) Stress Action

International audienceThe aim of the paper is the modelling of the rearrangement process between martensite variants in order to use Magnetic alloys (MSMs) as actuators. In the framework of the thermodynamic of irreversible processes, an efficient choice of the internal variables in order to take into account the magnetic and the mechanical actions and a free energy function are stated. The behaviour is chosen as magnetically reversible and mechanically irreversible. An equivalence between magnetic field action H and uniaxial stress action o for the initiation of the rearrangement is established. Finally, moel predictions are compared with experimental measurements

Modeling and control of micro-mechatronic devices : application of variational and energetic methods for micro-actuator design.

International audienceThis paper is focused on a modeling procedure wellsuited for the design of micro-mechatronic systems and especially for micro-actuators. The purpose of this publication is to show that the variational and energetical methods is not only wellsuited to model classical micro-mechatronic devices but that they are also well-suited to include complex dynamical behaviour such as non-linearity and hysteretical behaviour. This procedure is applied to the design of a new actuator using one of the relatively new smart materials, the Magnetic Shape Memory Alloys (MSMAs). It should be stressed that the presented approach can be extented to a great range of other smart materials and that the description can be easily extented up to the control level

Conversion d'Energie Magnéto-Thermo-Mécanique dans les Alliages à Mémoire de Forme Magnétiques.

National audienceLes alliages à mémoire de forme magnétiques sont des matériaux actifs dont les caractéristiques combinent celles des alliages à mémoire de forme classiques et celles des matériaux magnétostrictifs. Ces matériaux relativement récents sont actuellement assez peu utilisés pour des applications pratiques telles que les actionneurs et les capteurs en raison des difficultés de conception et de contrôle résultant d'un comportement complexe. Cet article se propose de présenter le mode de conversion d'énergie à l'oeuvre dans ces matériaux ainsi qu'un état de l'art des principaux travaux en termes d'actionneurs. Il se propose ensuite de présenter les réalisations des auteurs ainsi que les modèles de comportement développés pour finir par une présentation des règles de conception et de contrôle mis en évidence

Magnetic shape memory alloy and actuator design.

International audienceIn the field of micromechatronics, microrobotics and specially microfactories, active materials are used in most cases. They permit high resolution and distributed actuation. In this area, Magnetic Shape Memory Alloys (MSMA) are possible candidates. If a lot of studies deal with MSMA, only few applications use them until now. MSMA are attractive active materials because they have large strain (about 10%) as the classical shape memory alloys (SMA), but can provide a 100 times shorter time response. The main disadvantages of MSMA based actuators are the brittleness of the single-crystal material, the difficulty to apply the strong magnetic field required to obtain sufficient strain and the nonlinear behaviour. We propose in this paper a novel MSMA based actuator changing the disadvantage of the hysteretic behaviour into an advantage. This device is a push-pull actuator: two pieces of MSMA material act in an opposite way. The magnetic fields are created by coils and concentrated by ferromagnetic circuits. In order to move the central part of the actuator, a current pulse in the first coil is generated. The hysteretic behaviour of the material permits to keep a stable position when no current is applied. A current pulse in the second coil permits to displace the central part in the opposite direction. The stable position depends on the magnitude and the time duration of the current pulses and an infinity of stable positions can be reached. The use of current pulses permits also a reduction of the coil heating (Joule effect losses) and a reduction of the magnetic circuit size. The performances and characteristics of MSMA are between these of classical SMA and these of piezo-electric materials. A thermo-magneto-mechanical model of our actuator is currently in development in order to design an efficient control law welladapted to the specific MSMA properties