Compliant grasping device for robotized medical applications

Needle manipulation is a very common need in several specialties. This paper presents the development of NGDs (needle grasping devices) capable of handling elongated objects such as surgical needles. After describing the main demands of medical needle-based procedures, a requirement list for a typical NGD is presented. Some solution principles for a grasping device are generated, combined and then classified to obtain a set of principle variant solutions. The design study of some of these variant solutions is then developed and a discussion on two device candidates constructed using either interconnected rigid bodies or compliant parts will be presented. The mechanical behavior of the compliant mechanism acting on a needle barrel is simulated with a FEM analysis including the model of non-linearities induced by large deformations and the contact between the needle and the grasping device. Functional prototypes of both NGDs have been constructed and a first experimental assessments of their service capability are finally exposed

Détermination des déformations 3D de pièces thermoplastiques chargées fibres de verre courtes

Le but de ce travail de thèse est la prédiction des retraits et déformations de pièces injectées en thermoplastique chargé fibres de verre courtes. Le matériau utilisé a été premièrement caractérisé sous des conditions proches de celles appliquées en injection, les résultats étant ensuite intégrés au calcul. Deuxièmement, la simulation 3D du cycle d injection a permis de définir l orientation des fibres au sein des pièces injectées. Les retraits et déformations après éjection ont ensuite été calculés avec deux types de loi de comportement, élastique orthotrope et viscoélastique isotrope transverse. Les propriétés d orientation dues à l injection ont été transférées grâce à une interface vers un logiciel de calcul de structure. Enfin, les résultats ont été comparés avec des mesures expérimentales des déformations. À terme, on souhaite ainsi remplacer la phase expérimentale et itérative de détermination des paramètres optimaux du procédé par les prédictions de la simulation.The aim of this work is to predict the shrinkage and warpage of short fiber reinforced thermoplastic parts produced through injection molding. The material used was first characterized under conditions approaching process conditions. Results were then integrated to the calculation. Moreover, a 3D simulation of the process allowed the definition of the fiber orientation in the parts. Shrinkage and warpage after ejection were then calculated with two material models (orthotropic elastic and transversal isotropic viscoelastic). Orientation properties due to injection were transferred to structural analysis thanks to an interface. Finally, the results have been compared to experimental warpage measurements. On a long term, the experimental and iterative phase necessary to determine the optimal process parameters should be replaced by the predictions of the simulation on this way.STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

Etude de la résistance au choc de tubes PVC tri-couches

Actuellement, la tenue aux chocs des tubes PVC à parois structurées utilisés dans le domaine de l'assainissement n'est pas garantie. Une étude de la résistance aux chocs a été menée dans l'optique d'améliorer la qualité du produit fini. Nous avons dans un premier temps analysé l'influence du procédé de fabrication sur la résistance aux chocs. Cette analyse montre que la structure du tube n'est pas homogène sur sa circonférence. Des expériences supplémentaires ont été menées qui mettent en évidence des zones de plus faible résistance : les lignes de recollement. Ces lignes se créent en production lors de l'écoulement de la matière dans la tête d'extrusion. Pour comprendre la formation de ces lignes et limiter leur influence, l'écoulement de la matière a été étudié par voie numérique grâce au logiciel Polyflow

An automatic differentiation-based gradient method for inversion of the shear wave equation in magnetic resonance elastography: specific application in fibrous soft tissues

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Design and Modeling of a Polymer Force Sensor

International audienceThis article presents the design, modeling, force correction strategies and experimental validation of a force sensor designed for robotized medical applications. The proposed sensor offers a new solution for force measurement in the presence of specific constraints such as medical imaging transparency, limited size, satisfactory rigidity and measurement performance. More specifically, the presented prototype has been purposely adapted to comply with the requirements of needle insertion applications, in the context of interventional radiology. A systematic viscoelastic model identification method is discussed for choosing the best time-dependent model for the force sensor. A novel compensation law is proposed based on the chosen model to correct for the viscoelastic effects of the utilized polymer material. The developed compensation law is inexpensive, stable to noise and can be applied in real-time to the sensor signal. A comparative assessment of the experimental results, obtained from quasi-static to dynamic experiments including harmonic analysis, shows the efficacy of the proposed compensation law, as compared to calibration with static gain and without compensation. The improvement in the sensor response results in decreased hysteresis levels and increased bandwidth, which are improved by more than a factor of 4

Investigation of PVC plastisol tissue-mimicking phantoms for MR-and ultrasound-elastography

International audienceObjective: Realistic tissue-mimicking phantoms are essential for the development, the investigation and the calibration of medical imaging techniques and protocols. Because it requires taking both mechanical and imaging properties into account, the development of robust, calibrated phantoms is a major challenge in elastography. Soft polyvinyl chloride gels in a liquid plasticizer (plastisol or PVCP) have been proposed as soft tissue-mimicking phantoms (TMP) for elasticity imaging. PVCP phantoms are relatively low-cost and can be easily stored over long time periods without any specific requirements. In this work, the preparation of a PVCP gel phantom for both MR and ultrasoundelastography is proposed and its acoustic, NMR and mechanical properties are studied.Material and methods: The acoustic and magnetic resonance imaging properties of PVCP are measured for different mass ratios between ultrasound speckle particles and PVCP solution, and between resin and plasticizer. The linear mechanical properties of plastisol samples are then investigated over time using not only indentation tests, but also MR and ultrasound-elastography clinical protocols. These properties are compared to typical values reported for biological soft tissues and to the values found in the literature for PVCP gels.Results and conclusions: After a period of two weeks, the mechanical properties of the plastisol samples measured with indentation testing are stable for at least the following 4 weeks (end of follow-up period 43 days after gelation-fusion). Neither the mechanical nor the NMR properties of plastisol gels were found to be affected by the addition of cellulose as acoustic speckle. Mechanical properties of the proposed gels were successfully characterized by clinical, commercially-available MR Elastography and sonoelastography protocols. PVCP with a mass ratio of ultrasound speckle particles of 0.6% to 0.8% and a mass ratio between resin and plasticizer between 50 and 70% appears as a good TMP candidate that can be used with both MR and ultrasound-based elastography methods

Investigation of PolyVinyl Chloride Plastisol Tissue-Mimicking Phantoms for MR- and Ultrasound-Elastography

Objective: Realistic tissue-mimicking phantoms are essential for the development, the investigation and the calibration of medical imaging techniques and protocols. Because it requires taking both mechanical and imaging properties into account, the development of robust, calibrated phantoms is a major challenge in elastography. Soft polyvinyl chloride gels in a liquid plasticizer (plastisol or PVCP) have been proposed as soft tissue-mimicking phantoms (TMP) for elasticity imaging. PVCP phantoms are relatively low-cost and can be easily stored over long time periods without any specific requirements. In this work, the preparation of a PVCP gel phantom for both MR and ultrasound-elastography is proposed and its acoustic, NMR and mechanical properties are studied.Materials and methods: The acoustic and magnetic resonance imaging properties of PVCP are measured for different mass ratios between ultrasound speckle particles and PVCP solution, and between resin and plasticizer. The linear mechanical properties of plastisol samples are then investigated over time using not only indentation tests, but also MR and ultrasound-elastography clinical protocols. These properties are compared to typical values reported for biological soft tissues and to the values found in the literature for PVCP gels.Results and conclusions: After a period of two weeks, the mechanical properties of the plastisol samples measured with indentation testing are stable for at least the following 4 weeks (end of follow-up period 43 days after gelation-fusion). Neither the mechanical nor the NMR properties of plastisol gels were found to be affected by the addition of cellulose as acoustic speckle. Mechanical properties of the proposed gels were successfully characterized by clinical, commercially-available MR Elastography and sonoelastography protocols. PVCP with a mass ratio of ultrasound speckle particles of 0.6%–0.8% and a mass ratio between resin and plasticizer between 50 and 70% appears as a good TMP candidate that can be used with both MR and ultrasound-based elastography methods