Contrôle d'un bras robotique flexible

Le contrôle des systèmes mécaniques, plus particulièrement des manipulateurs robotiques, est un domaine actif de la recherche appliquée. Les robots classiques utilisés dans l'industrie sont extrêmement précis mais relativement lents, massifs et exigent des moteurs puissants. Les efforts déployés dans la modélisation et le contrôle de manipulateurs flexibles sont alors motivés par la demande prévue d'un poids léger, de la précision et d'une grande vitesse des robots dans diverses applications. En fait, dans le cas d'un robot rigide, la connaissance de l'angle moteur permet d'obtenir directement la position de l'extrémité. Par contre, à cause de la flexibilité, la rotation de la base d’un bras flexible entraîne l'oscillation du bras tout entier. Le contrôle direct de l'extrémité d'un robot flexible est plus difficile que celui d'un robot rigide. D'où le besoin d'une loi de commande qui contrôle la position de l'extrémité en tenant compte des déformations de la membrure. Ceci constitue l'objectif de recherche de ce travail. Pour y arriver, on commence par développer le modèle d’un système à un bras flexible entraîné par un moteur à courant continu. Ensuite, il s'agit du développement des lois de contrôle qui assurent la régulation de l’extrémité tout en réduisant les vibrations du bras. Finalement, les performances des contrôleurs développés sont simulées sur un banc d’essai. The control of mechanical systems and particularly of robotic manipulators is an active applied research area. Most existing robots, rigid manipulators, achieve good positioning accuracy by using heavy materials. As a consequence, such robots are usually heavy which limits the speed of operation of the robot manipulation and increases the energy consumption. After the era of rigid robotics, major research activities were devoted to improving dynamic performances and to reducing the mass of robotic systems by considering structural flexibility in robot arms. However, the question of modeling and control of flexible manipulators is challenging due to precise positioning requirements. In fact, knowing the base angle of a rigid arm leads directly to knowing the tip position. In contrast, system flexibility leads to the appearance of oscillations at the tip of the link during motion. These oscillations make the control problems of such systems really difficult. Hence the need for a control law that controls the tip position and takes in consideration the deformation of the link. In this purpose, we started by modeling the system consisting of a flexible single-link drived by a DC motor. After that, we developed control laws in order to minimize the vibrations while regulating the tip position. Finally, performances of such controllers were tested by simulation and experimentally on an experimental flexible arm system

Assessment of pesticide contamination in Akkar groundwater, northern Lebanon

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Validity and Reproducibility of a Culture-Specific Food Frequency Questionnaire in Lebanon

This study aims to assess the validity and reproducibility of a culture-specific semi-quantitative food frequency questionnaire (FFQ) for Lebanese adults. The 94-item FFQ captures intake of traditional Mediterranean dishes and Western food, reflective of current Lebanese nutrition transition. Among 107 participants (18–65 years), the FFQ was administered at baseline (FFQ-1) and one year thereafter (FFQ-2); 2–3 24-h recalls (24-HRs)/season were collected for a total of 8–12 over four seasons. A subset (n = 67) provided a fasting blood sample in the fall. Spearman-correlation coefficients, Bland–Altman plots, joint-classification and (ICC) were calculated. Mean intakes from FFQ-2 were higher than from the total 24-HRs. Correlations for diet from FFQ-2 and 24-HRs ranged from 0.17 for α-carotene to 0.65 for energy. Joint classification in the same/adjacent quartile ranged from 74.8% to 95%. FFQ-2-plasma carotenoid correlations ranged from 0.18 for lutein/zeaxanthin to 0.59 for β-carotene. Intra-class correlations for FFQ-1 and FFQ-2 ranged from 0.36 for β-cryptoxanthin to 0.85 for energy. 24-HRs carotenoid intake varied by season; combining season-specific 24-HRs proximal to biospecimen collection to the FFQ-2 improved diet-biochemical correlations. By applying dietary data from two tools with biomarkers taking into consideration seasonal variation, we report a valid, reproducible Lebanese FFQ for use in diet-disease research