Force sensitive hook for epiretinal membrane peeling in eye surgery

This project addresses the design, construction and evaluation of a peeling hook with force measurement capability for in-vivo intra-ocular vitreoretinal surgery. The force sensor consists of a miniature multi-degree-offreedom flexure where deformations induced by contact forces are measured using optical fiber white light interferometry. This instrument will be used for epiretinal membrane peeling procedures and should then lead to the creation of a new generation of force sensitive surgical tools

IsoSpring : vers la montre sans échappement

Depuis son introduction en 1675, le balancier-spiral est la base de temps exclusive de la montre mécanique. Or cet oscillateur présente deux difficultés limitatives qui n'ont jusqu'à présent pas été contournées : un facteur de qualité limité (en particulier par des phénomènes tribologiques), ainsi que la nécessité d'un échappement, mécanisme complexe au rendement limité. Cet article pré-sente un nouvel oscillateur appelé IsoSpring, qui améliore le facteur de qualité grâce au recours aux guidages flexibles et élimine complètement l'échappement. Le concept de ce nouvel oscillateur qui est doté de deux degrés de liberté remonte à Issac Newton. Il est replacé dans le contexte historique des principales avancées conceptuelles en horlogerie mécanique. La résolution des équa-tions du mouvement démontre que l'inertie desorganes tournants perturbe l'isochronisme. Pour pallier cette limitation, des architec-tures de mécanismes à guidages flexibles supprimant l'essentiel de l’inertie des organes tournants sont proposées. Le movement bidimensionnel de cet oscillateur n’est plus alterné, mais unidirectionnel. Ainsi, un mécanisme de maintien continu constitué d'une manivelle transmet le couple à l'oscillateur et l'échappement disparaît

Flexure-based multi-degrees-of-freedom in-vivo force sensors for medical instruments

This paper presents novel multi-degrees-of-freedom force sensors based on flexures used as mecano-optical transducers (named flexure body) and white light interferometers used as opto-electrical transducers. Together, these transducers make up a load cell exploiting the nanometric accuracy of Fabry-Pérot interferometric measurement to reach milli-Newton force accuracy. The design focuses on the flexure body composed of three sections: a base (attached to the measuring device), a compliant section which deforms under applied forces and a pointed rigid section whose tip touches tissues during surgery. The fiber interferometer measures the distal displacement with respect to the base using one 125 μm diameter optical fiber for each load cell DOF. The key advantages of this design are: compact design (1 to 4 mm diameter shaft), simple optical alignment during assembly, scalability from Newton down to milli-Newton force levels, insensitivity to electrical charge and compatibility with sterilization procedure. These properties satisfy the requirements of in-vivo force measurements during surgery. The paper presents analytical stiffness estimation of 1 DOF flexure bodies and finite element stiffness analysis of multiple-DOF structures followed by the design, manufacturing and assembly process. The realized sensors are then characterized experimentally on a specifically designed motorized test-bench, which allows application of calibrated forces from various directions onto the senor tip. A specific calibration strategy was developed improving measurement accuracy of the sensor

Flexure-based mecano-optical multi-degree-of-freedom transducers dedicated to medical force sensing instruments

This thesis develops novel multi-degrees-of-freedom flexure-based force sensors by exploiting white light interferometry. Fabry-Pérot interferometry measurement has nanometric accuracy which yields sub milli-Newton force sensing accuracy. Such force sensing accuracy can be advantageously utilisized for medical applications. Using these techniques, this thesis develops the first monolithically fabricated medical instrument having submillimetric diameter, a peeling hook used to treat epiretinal membranes in the eye. The thesis describes the concepts, design, simulation, fabrication and characterization of this type of instrument. The results of this thesis pave the way for new techniques in Minimally Invasive Surgery (MIS). The study starts with systematization of sensor manufacturing, which is followed by catalogue of proposed sensor topologies. These structures are then dimensioned using Finite Element Analysis (FEA), with emphasis on two medical applications: biopsy needles and intraocular surgery. Selected designs were manufactured and characterized on a motorized test bench with automatic and repetitive measurement. Sensor calibration methods were developed and tested and characterization methods were also evaluated. Manufacturing and measurement error were also described. The test results showed a significant reduction of sensor calibration error in the selected workspace, as compared to industry solutions. The tool developed in this thesis is an epiretinal membrane peeling hook for minimally invasive intraocular surgery. It was fabricated using Electro Discharge Machining (EDM), and was at the limit of the feature size of this method. The novel methods developed in this thesis open new horizons for designing submillimetric tools having complex kinematic force sensing and thereby significantly advance delicate surgical procedures

Isotropic springs based on parallel flexure stages

We define isotropic springs to be central springs having the same restoring force in all directions. In previous work, we showed that isotropic springs can be advantageously applied to horological time bases since they can be used to eliminate the escapement mechanism [7]. This paper presents our designs based on planar serial 2-DOF linear isotropic springs. We propose two architectures, both based on parallel leaf springs, then evaluate their isotropy defect using firstly an analytic model, secondly finite element analysis and thirdly experimental data measured from physical prototypes. Using these results, we analyze the isotropy defect in terms of displacement, radial distance, angular separation, stiffness and linearity. Based on this analysis, we propose improved architectures stacking in parallel or in series duplicate copies of the original mechanisms rotated at specific angles to cancel isotropy defect. We show that using the mechanisms in pairs reduces isotropy defect by one to two orders of magnitude. (C) 2015 The Authors. Published by Elsevier Inc