Le sens de la recherche
Bulletin de la Société Suisse de Chronométrie. 2018-12-01.
SYSTEME MULTISTABLE PROGRAMMABLE
Programmable Multistable Mechanisms: Design, modeling, characterization and applications
Lausanne, EPFL, 2018.
DOI : 10.5075/epfl-thesis-9055.
Multistable Mechanisms are mechanical devices having more than one stable state. Since these mechanisms can maintain different deformations with zero force, they are advantageous for low power environments such as wristwatches and medical devices. In this thesis, I introduce programmable multistable mechanisms (PMMs), a new family of multistable mechanisms where the number, position, and stiffness of stable states can be controlled by programming inputs modifying the boundary conditions. PMMs can be synthesized by combining bistable mechanisms. This method was used to produce the T-mechanism, a PMM consisting of two double parallelogram mechanisms (DPMs) connected orthogonally where each DPM consists of two parallel beams connected centrally by a rigid block and axially loaded by programming input. An analytical model based on Euler-Bernoulli beam theory was derived to describe qualitatively the stability behaviour of the T-mechanism. The model approximates the mechanism's stiffness by a sixth order polynomial from which the reaction force and strain energy expressions can be estimated. These explicit formulas provide analytical expressions for the number, position, and stiffness of stable and unstable states as functions of the programming inputs. The qualitative stability behavior was represented by the programming diagram, bifurcation diagrams and stiffness maps relating the number, position and stiffness of stable states with the programming inputs. In addition, I showed that PMMs have zero stiffness regions functioning as constant-force multistable mechanisms. Numerical simulations validated these results. Experimental measurements were conducted on the T-mechanism prototype manufactured using electro-discharge machining. An experimental setup was built to measure the reaction force of the mechanism for different programming inputs. I verified the possible configurations of the T-mechanism including monostability bistability, tristability, quadrastability, zero stiffness regions, validating my analytical and numerical models. Compared to classical multistable mechanisms which are displaced between their stable states by imposing a direct displacement, PMMs can be displaced by modifying mechanism strain energy. This property increases the repeatability of the mechanism as the released energy is independent of the driving parameters, which can be advantageous for mechanical watches and medical devices. Accurate timekeepers require oscillators having repeatable period independent of their energy source. However, the balance wheel spiral spring oscillator used in all mechanical watches, suffers from isochronism defect, i.e., its oscillation period depends on its amplitude. I addressed this problem by introducing novel detached constant force escapements for mechanical wristwatches based on PMMs. In the medical domain, I applied PMMs to construct a retinal vein cannulation needle for the treatment of retinal vein occlusion. PMMs based needles produce sufficient repeatable puncturing energy with a predefined stroke independent of the operator input. Numerical simulations were used to model and dimension our proposed tool and satisfy the strict requirements of ophthalmologic operations. The tool was manufactured using 3D femto-laser printing of glass. An experimental setup was built to characterize the tool's mechanical behavior and to verify my computations. The tool was applied successfully to cannulate retinal veins of pig eyes.
Programmable Multistable Mechanisms: Synthesis and Modeling
JOURNAL OF MECHANICAL DESIGN. 2018.
DOI : 10.1115/1.4038926.
Gravity-Insensitive Flexure Pivot Oscillators
Journal of Mechanical Design. 2018.
DOI : 10.1115/1.4039887.
Classical mechanical watch plain bearing pivots have frictional losses limiting the quality factor of the hairspring-balance wheel oscillator. Replacement by flexure pivots leads to a drastic reduction in friction and an order of magnitude increase in quality factor. However, flexure pivots have drawbacks including gravity sensitivity, nonlinearity, and limited stroke. This paper analyzes these issues in the case of the cross-spring flexure pivot (CSFP) and presents an improved version addressing them. We first show that the cross-spring pivot cannot be simultaneously linear, insensitive to gravity, and have a long stroke: the 10 ppm accuracy required for mechanical watches holds independently of orientation with respect to gravity only when the leaf springs cross at 12.7% of their length. But in this case, the pivot is nonlinear and the stroke is only 30% of the symmetrical (50% crossing) crossspring pivot’s stroke. The symmetrical pivot is also unsatisfactory as its gravity sensitivity is of order 104 ppm. This paper introduces the codifferential concept which we show is gravity-insensitive. It is used to construct a gravity-insensitive flexure pivot (GIFP) consisting of a main rigid body, two codifferentials, and a torsional beam. We show that this novel pivot achieves linearity or the maximum stroke of symmetrical pivots while retaining gravity insensitivity.
Horloge neuchâteloise du XXIe siècle équipée de l’oscillateur IsoSpring
Echappements à impulsion virtuelle
Bulletin de la Société Suisse de Chronométrie. 2018.
L’échappement à détente est reconnu pour sa performance chronométrique, mais il n’est pas sécurisé pour la montre-bracelet. Plusieurs échappements ont été proposés pour adapter cet échappement à la montre, dont l’échappement Robin récemment sécurisé par Audemars Piguet. George Daniels a poursuivi une démarche qui a mené à l’échappement coaxial. Nous proposons un nouveau concept, l’impulsion virtuelle, qui pourrait réunir tous les avantages de ces échappements. Notre solution est une simple modification de l’échappement Robin, nous ajoutons seulement une dent d’impulsion indirecte. Le principe de l’impulsion virtuelle consiste en une impulsion indirecte qui ne se fait qu’à l’arrêt et à faible amplitude. Ceci ajoute la contrainte du double coup, donc sécurise, et assure l’auto-démarrage. Un tracé et un démonstrateur ont été réalisés. Des observations du démonstrateur, à l’aide d’une caméra haute vitesse, démontrent la validité du concept de l’impulsion virtuelle.
Theory and design of spherical oscillator mechanisms
Precision Engineering. 2018.
DOI : 10.1016/j.precisioneng.2017.10.005.
In previous work, we showed that two degree of freedom oscillators can be advantageously applied to horological time bases since they can be used to eliminate the escapement mechanism. We subsequently examined planar two degree of freedom oscillators based on parallel flexure stages. We noted that these oscillators are strongly affected by the orientation of gravity so are not directly suitable for portable timekeepers such as wristwatches. In this paper we examine the design and performance of two degree of freedom spherical oscillators. By spherical oscillator, we mean a spherical mass having purely rotational kinematics and subject to elastic restoring torque. As opposed to our previously examined oscillators, the oscillation period of spherical oscillators is relatively insensitive to the effect of tilting the mechanism in the presence of gravity. In order to restrict spherical rotation to two degrees of freedom, we restrict the kinematics to obey Listing's law, a well–known constraint occurring in human eye movement. We show that a particular central restoring force we call the scissors law is best suited for chronometric performance and propose a number of theoretical mechanisms producing it. We then design an actual spherical oscillator based on our theoretical results. The design uses flexure springs to restrict kinematics to Listing's Law, produce the scissors law and provide the necessary suspension. Finally, we present experimental data based on a physical realization indicating promising chronometric performance.
VivoForce instrument for retinal microsurgery
2017. Surgetical 2017 , Strasbourg, France , November 20-22, 2017. p. 155-157.
The Art of Flexure Mechanism Design
Lausanne: EPFL Press.
Flexure mechanism design is an art, and this book provides the theoretical and practical foundation for scientists and engineers to express their creativity in this field. Flexure mechanisms, also known as compliant mechanisms, rely on the elasticity of matter to provide motion to mechanism linkages. Flexure mechanisms eliminate the disadvantages of classical joints: friction, wear, lubrication and play, while permitting monolithic design. Flexure-based mechanisms have gained prominence in a wide variety of fields including robotics, surgical instrumentation, aerospace, astronomy, particle accelerators, metrology and horology. This book establishes a conceptual framework for the design of flexure-based articulated structures. Topics featured deal with the theoretical foundations for the design of translational and rotational flexures, the simple kinematic analysis of flexure-based mechanisms, and advanced kinematic approaches to the design of complex flexure-based mechanisms using modules in parallel or serial arrangements. The book also features detailed examples of long stroke flexure mechanisms used in metrology applications, and a detailed example of planar flexure mechanisms having out of plane functionality and used in surgical applications. This book aims to provide scientists and engineers with a conceptual tool, an analytic methodology and the key references for their precision engineering needs.
Higher-order continuation method for the rigid-body kinematic design of compliant mechanisms
Precision Engineering-Journal Of The International Societies For Precision Engineering And Nanotechnology. 2017.
DOI : 10.1016/j.precisioneng.2017.06.021.
Compliant mechanisms are of great interest in precision engineering. In this paper we propose a higher order continuation method to help their rigid-body kinematic design. The method helps to investigate the choice of a mechanism configuration through the whole exploration of the workspace, and eases the kinematic analysis to avoid, or take advantage of, the vicinity of kinematic singularities. Such approach is relevant for planar and quasi-planar mechanisms that can be obtained with micro-manufacturing processes adapted to precision applications. The higher-order continuation method allows for a direct and accurate plotting of the input-output relationship of any mechanism by considering only its geometrical closed-loop equations, i.e. without the complex derivation of any analytical model. We show that these plots, called bifurcation diagrams, reveal essential information such as the joint velocity profile and the presence of singular configurations. Moreover, the continuous and accurate computation of the mechanism configuration in the vicinity of singularities provides detailed information about the kinematic behavior of the mechanism in its extreme positions. For the design of compliant mechanisms, the designer can advantageously use the bifurcation diagrams to evaluate the relevance of the selected mechanism, then to identify a configuration in order to obtain desired kinematic properties without the derivation of the inverse kinematic model (IKM). or the direct kinematic model (DKM). The method is exemplified with a 3 universal-joint and 3 spherical-joint mechanism (3-US), the IKM and DKM of which cannot be derived analytically. The latter has a large workspace and special kinematic behaviors consisting of a screw-like motion and a platform gyration, which have not been studied before and could lead to novel compliant devices. (C) 2017 Elsevier Inc. All rights reserved.
Une horlogerie mécanique sans tic-tac
Pour la Science. 2017.
La R&D commune entreprises-université dans l'industrie horlogère de 1900 à nos jours
Bulletin de la Société Suisse de Chronométrie. 2017.
Gravity insensitive flexure pivots for watch oscillators
2016. Congrès International de Chronométrie CIC 2016 , Montreux, Switzerland , September 28-29, 2016. p. 49-55.
Classical pivots have frictional losses leading to the limited quality factor of oscillators used as time bases in mechanical watches. Flexure pivots address these issues by greatly reducing friction. However, they have drawbacks such as gravity sensitivity and limited angular stroke. This paper analyses these problems for the cross-spring flexure pivot and presents an improved version addressing these issues. We first show that the cross spring pivot cannot be both insensitive to gravity and have a long stroke. A 10 ppm sensitivity to gravity acceptable for watchmaking applications occurs only when the leaf springs cross at about 87.3 % of their length, but the stroke is only 30.88 % of the stroke of the symmetrical cross-spring pivot. For the symmetrical pivot, gravity sensitivity is of the order of 104 ppm. Our solution is to introduce the co-differential concept which we show to be gravity insensitive. We then use the co-differential to build a gravity insensitive flexure pivot with long stroke. The design consists of a main rigid body, two co-differentials and a torsional beam. We show that our pivot is gravity insensitive and achieves 100 % of the stroke of symmetrical pivots.
Investigating The Size-Dependent Static And Dynamic Behavior Of Circular Micro-Plates Subjected To Capillary Force
2016. ASME International Design Engineering Technical Conferences and Computers and Information in Engineering Conference', u'ASME International Design Engineering Technical Conferences and Computers and Information in Engineering Conference'] , Boston, USA , August 21-24, 2016. p. V004T09A008.
The size-dependent static deflection, pull-in instability and resonant frequency of a circular microplate under capillary force have been studied using modified couple stress elasticity theory. SiZe-dependency is a phenomenon in which the normalized quantities that classical elasticity theory predicts to be independent of the structure size, such as normalized deflection or normalized frequency, vary significantly as the structure size changes. This phenomenon has been observed in micro-scale structures such as micro-electro-mechanical-systems (MEMS). Since classical elasticity theory is unable to predict the size-dependency, non-classical elasticity theories such as modified couple stress theory have been developed recently. In this paper, modified couple stress theory is used for the first time to develop the governing equation and boundary conditions of circular microplates when subjected to capillary force. Consideration of capillary force is important since it is has a significant role in the mechanical behavior and stability of micro-scale structures in the presence of a liquid bridge. We investigated the static deflection and pull-in instability of microplates using the Galerkin method to assess the effect of size-dependency for static deflection. We observed that, as the ratio of the microplate thickness to length scale parameter (an additional material property suggested in modified couple stress theory to capture the size-dependency) decreases, the normalized deflection of the microplate also decreases. We further observed that the difference between the normalized deflection predicted by classical elasticity theory and the one evaluated using modified couple stress theory is significant when thickness of the microplate is small, but diminishes as thickness increases. Furthermore, we defined a dimensionless number called the dimensionless capillary tension (DCT) as a function of the mechanical, geometrical and size-dependent properties of the microplate as well as the characteristics of the liquid bridge such as the contact angle and the interfacial tension. We showed that for DCT values greater than a threshold evaluated in this paper, pull-in instability happens and the microplate collapses to the substrate. Moreover, we evaluated the size-dependent resonant frequency of the microplate under capillary force as a function of the DCT and obtained the result that the frequency decreases as DCT increases. In addition, our investigation of size-dependency revealed that as the ratio of the microplate thickness to length scale parameter increases, the frequency decreases in a way that for large values of, the ratio, it asymptotically approaches the value predicted by classical elasticity theory.
Force sensitive hook for epiretinal membrane peeling in eye surgery
Swiss MedTech Day, Berne, Switzerland, June 7, 2016.
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.
Flexure-based multi-degrees-of-freedom in-vivo force sensors for medical instruments
2016. Euspen's 16th International Conference , Nottingham, Great Britain , May 30-Jun 03, 2016. p. 333-334.
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.
Design, analysis, testing and applications of two-body and three-body kinematic mounts
Lausanne, EPFL, 2016.
DOI : 10.5075/epfl-thesis-7005.
Kinematic couplings are used when two rigid bodies need to be repeatedly and accurately positioned with respect to each other. They allow for sub-micron positioning repeatability by suppressing play and reducing strains in the bodies. Typical applications are lens mounts, work piece mounts and docking interfaces for astrophysics, semiconductor and metrology applications. This thesis generalizes the well-known concept of two-body kinematic couplings to three-body kinematic mounts. The goal of the thesis is: To pave the way for high precision assembly using kinematic mounts by providing an exhaustive catalogue of all twobody and three-body kinematic mounts and to test key configurations experimentally. The main contributions of this thesis are: - State of the art survey of essential knowledge in the field of kinematic couplings. - Rigorous problem statement for the design of two-body and three-body kinematic mounts. - Rigorous limitation of the scope of research to three-body kinematic mounts whose contact points lie exclusively on three convergent orthogonal lines and whose constraint lines are parallel to these lines. - An exhaustive catalogue of three-body kinematic mounts consisting of seven configurations in 3D and nine configurations in 2D. - An exhaustive set of four conditions satisfied by three-body 3-dimensional kinematic mounts. - An exhaustive set of seven conditions satisfied by three-body 2-dimensional kinematic mounts. - Realization of a two-body kinematic mount and a three-body kinematic mount in metal, and precise measurement of their positioning accuracy on a 3D coordinate measurement machine at the Swiss Federal Institute of Metrology. Positioning error of 0.2 microns and 5 microradian achieved with two-body kinematic mounts. Positioning error of 1 micron and 50 microradian achieved with three-body kinematic mounts. - Realization of three-body kinematic mounts in Silicon by Deep Reactive Ion Etching processes (DRIE) and experimental measurement of their positioning error. - Physical implementation of nesting forces and assembly methods allowing for the physical construction of kinematic mounts. - Physical realizations in robotics, optics and aerospace using our new kinematic mounts.
Investigation of Size-Dependency in Free-Vibration of Micro-Resonators Based on the Strain Gradient Theory
Latin American Journal Of Solids And Structures. 2016.
DOI : 10.1590/1679-78252430.
This paper investigates the vibration behavior of micro-resonators based on the strain gradient theory, a non-classical continuum theory capable of capturing the size effect appearing in micro-scale structures. The micro-resonator is modeled as a clamped-clamped micro-beam with an attached mass subjected to an axial force. The governing equations of motion and both classical and non-classical sets of boundary conditions are developed based on the strain gradient theory. The normalized natural frequency of the micro-resonator is evaluated and the influences of various parameters are assessed. In addition, the current results are compared to those of the classical and modified couple stress continuum theories.
Refraction limit of miniaturized optical systems: a ball-lens example
Optics Express. 2016.
DOI : 10.1364/OE.24.006996.
We study experimentally and theoretically the electromagnetic field in amplitude and phase behind ball-lenses across a wide range of diameters, ranging from a millimeter scale down to a micrometer. Based on the observation, we study the transition between the refraction and diffraction regime. The former regime is dominated by observables for which it is sufficient to use a ray-optical picture for an explanation, e.g., a cusp catastrophe and caustics. A wave-optical picture, i.e. Mie theory, is required to explain the features, e.g., photonic nanojets, in the latter regime. The vanishing of the cusp catastrophe and the emergence of the photonic nanojet is here understood as the refraction limit. Three different criteria are used to identify the limit: focal length, spot size, and amount of crosspolarization generated in the scattering process. We identify at a wavelength of 642 nm and while considering ordinary glass as the ball-lens material, a diameter of approximately 10 μm as the refraction limit. With our study, we shed new light on the means necessary to describe micro-optical system. This is useful when designing optical devices for imaging or illumination.
Flexure-based multi-degree-of-freedom force and torque sensors at the milimeter scale for medical instruments
Summer School in Surgical Robotics, Montpellier, France, Sep 7-11, 2015.
Mathematics, the Language of Watchmaking
Watch Around. 2015.
Mathématiques et horlogerie
Watch Around. 2015.
La Revue POLYTECHNIQUE. 2015.
Analyse, synthèse et création d’échappements horlogers par la théorie des engrenages
Journée d'études de la Société Suisse de Chronométrie SSC, Lausanne. Switzerland, September 16, 2015.
Nous présentons la méthode du tracé primitif développée par le premier auteur dans sa thèse de doctorat. Cette nouvelle méthode donne pour la première fois une approche systématique à la problématique du tracé d’un échappement horloger. Elle revient à considérer chacune des phases cinématiques d’un échappement comme une transmission par engrenages. Puisque les engrenages sont décrits par leurs cercles primitifs, il s’ensuit que le fonctionnement d’un échappement peut être décrit par l’ensemble des arcs de cercles primitifs de ses différentes phases que nous appelons tracé primitif de l’échappement. L’étude des échappements au travers de leur tracé primitif a plusieurs implications : le tracé d’un échappement devient systématique grâce à cette formalisation du concept de tracé ; inversement, des échappements peuvent être facilement dessinés en partant d’un tracé primitif donné. C’est ainsi qu’un nouvel échappement dit « à double impulsion primitive » a été inventé. Cet échappement a été construit et ses performances sont prometteuses.
The Geometry of Eye Movement Dynamics
2015. The 18th European Conference on Eye Movements 2015 , Vienna, Austria , August 16-21, 2015. p. 65.
Eye movements consist of spherical rotations, with orientation generally constrained by Listing’s law. Our main result is a complete explicit formulation of ballistic eye movement under the Listing constraint. We present a conceptual framework for eye movement bas-ing the dynamics of Listing motion on the equator of the sphere of unit quaternions, which we call the Listing sphere. Analytical dynamics shows that ballistic Listing motion corre-sponds to free particle motion on the Listing sphere. Thus, ballistic Listing movement is greatly simplified by transposition to the Listing sphere, where it consists of shortest dis-tance trajectories. This proves that ballistic eye motion consists of constant speed rotation along circles passing through the occipital point. The relevance of the occipital point in eye movement was already noted by Helmholtz, which we explain by the fact that it cor-responds to the equator of the Listing sphere. We designed a physical mechanism produc-ing the correspondence between eye movement and particle motion on the Listing sphere. Our straightforward description of ballistic eye motion under the pure Listing kinematic constraint serves as a useful idealized benchmark in the study of actual physiological eye movements, whose orientations are known to deviate slightly from the Listing constraint.
Isotropic springs based on parallel flexure stages
Precision Engineering-Journal Of The International Societies For Precision Engineering And Nanotechnology. 2015.
DOI : 10.1016/j.precisioneng.2015.07.003.
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 . 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.
GENERAL 2 DEGREE OF FREEDOM ISOTROPIC HARMONIC OSCILLATOR AND ASSOCIATED TIME BASE WITHOUT ESCAPEMENT OR WITH SIMPLIFIED ESCAPEMENT
The mechanical isotropic harmonic oscillator comprises at least a two degrees of freedom linkage supporting an orbiting mass with respect to a fixed base with springs having isotropic and linear restoring force properties wherein the mass has a tilting motion. The oscillator may be used in a timekeeper, such a watch.
XY ISOTROPIC HARMONIC OSCILLATOR AND ASSOCIATED TIME BASE WITHOUT ESCAPEMENT OR WITH SIMPLIFIED ESCAPEMENT
The mechanical isotropic harmonic oscillator comprises at least a two degree of freedom linkage supporting an orbiting mass with respect to a fixed base with springs having isotropic and linear restoring force properties. The oscillator may be used in a timekeeper, such as a watch.
Solid on liquid deposition, a review of technological solutions
Microelectronic Engineering. 2015.
DOI : 10.1016/j.mee.2015.03.068.
Solid-on-liquid deposition (SOLID) techniques are of great interest to the MEMS and NEMS (Micro- and Nano Electro Mechanical Systems) community because of potential applications in biomedical engineering, on-chip liquid trapping, tunable micro-lenses, and replacements of gate oxides. However, depositing solids on liquid with subsequent hermetic sealing is difficult because liquids tend to have a lower density than solids. Furthermore, current systems seen in nature lack thermal, mechanical or chemical stability. Therefore, it is not surprising that liquids are not ubiquitous as functional layers in MEMS and NEMS. However, SOLID techniques have the potential to be harnessed and controlled for such systems because the gravitational force is negligible compared to surface tension, and therefore, the solid molecular precursors that typically condense on a liquid surface will not sediment into the fluid. In this review we summarize recent research into SOLID, where nucleation and subsequent cross-linking of solid precursors results in thin film growth on a liquid substrate. We describe a large variety of thin film deposition techniques such as thermal evaporation, sputtering, plasma enhanced chemical vapor deposition used to coat liquid substrates. Surprisingly, all attempts at deposition to date have been successful and a stable solid layer on a liquid can always be detected. However, all layers grown by non-equilibrium deposition processes showed a strong presence of wrinkles, presumably due to residual stress. In fact, the only example where no stress was observed is the deposition of parylene layers (poly-para-xylylene, PPX). Using all the experimental data analyzed to date we have been able to propose a simple model that predicts that the surface property of liquids at molecular level is influenced by cohesion forces between the liquid molecules. Finally, we conclude that the condensation of precursors from the gas phase is rather the rule and not the exception for SOLID techniques. (C) 2015 The Authors. Published by Elsevier B.V.
A statistical shape model of the human second cervical vertebra
International Journal Of Computer Assisted Radiology And Surgery. 2015.
DOI : 10.1007/s11548-014-1121-x.
Statistical shape and appearance models play an important role in reducing the segmentation processing time of a vertebra and in improving results for 3D model development. Here, we describe the different steps in generating a statistical shape model (SSM) of the second cervical vertebra (C2) and provide the shape model for general use by the scientific community. The main difficulties in its construction are the morphological complexity of the C2 and its variability in the population. The input dataset is composed of manually segmented anonymized patient computerized tomography (CT) scans. The alignment of the different datasets is done with the procrustes alignment on surface models, and then, the registration is cast as a model-fitting problem using a Gaussian process. A principal component analysis (PCA)-based model is generated which includes the variability of the C2. The SSM was generated using 92 CT scans. The resulting SSM was evaluated for specificity, compactness and generalization ability. The SSM of the C2 is freely available to the scientific community in Slicer (an open source software for image analysis and scientific visualization) with a module created to visualize the SSM using Statismo, a framework for statistical shape modeling. The SSM of the vertebra allows the shape variability of the C2 to be represented. Moreover, the SSM will enable semi-automatic segmentation and 3D model generation of the vertebra, which would greatly benefit surgery planning.
The value of Statistical Shape Models to Spine Surgery
Shape 2014 : Symposium on Statistical Shape Models & Applications, Delémont, Suisse, June 11-13, 2014.
The increased use of 3D models of organs or bones by the surgeon has lead to rapid development of new methods to automaKze model generaKon.
Statistical Shape Model for robotic spine surgery
Winter Slicer Porject Week 2014 (NA-MIC), Salt Lake City, Utah, USA, January 6-10,2014.
The goal of the project is to generate a 3D model of the C2 cervical vertebra for surgery planning using an atlas-based segmentation technique. A Statistical Shape Model of the C2 vertebra has been created from 91 CT scans using Statismo , a toolkit for building PCA shape models
Optical measuring element having a single-piece structure
An optical measuring element measures forces at least one direction. The measuring element has a single-piece structure. There is an outside wall with notches introduced therein. Each notch defines parallel edges, and the notches define more or less elastically flexible zones in the structure and constitute the only connection between a first region and a second region of the structure. For optical distance measurement between the two regions of the structure, one or more optical fibers are each attached with one end thereof to a region of the structures such that reflective surfaces are located close to the ends. The reflective surfaces are firmly connected to another region. The optical fibers are disposed on the outside wall.
Analyse, synthèse et création d'échappements horlogers par la théorie des engrenages
Lausanne, EPFL, 2014.
DOI : 10.5075/epfl-thesis-6189.
In principle, knowledge of watch and clock escapements is acquired through the study of the geometry and operation of numerous realizations, studied patiently one after the other. Knowing the classics, one can hope to construct a new realizations by borrowing components from one or geometry from another. Currently, there is no formal model or systematic approach which permits any other method of learning escapements and creating new ones. The purpose of this thesis is fill this gap by describing a formal model which will provide a systematic approach to escapements. We will not limit ourselves to the study of the geometry and operation of fundamental escapements but will add a formalism which has only been partially used in the past, outlining gear tooth profiles. The operation of proposed escapements will thus be characterized by an abstract geometric shape called the primitive outline. As opposed to visible escapement geometry, primitive outlines differ very little from one escapement to the other, making them an excellent basis for escapement unification. After going from existing geometries to primitive outlines we will reverse course. The method of outlining gear tooth profiles will allow us, based on existing primitive outlines, to construct new escapements. We will push this method to create a new primitive outline which, according to traditional criteria, appears to have unprecedented efficiency.
IsoSpring : vers la montre sans échappement
Journée d'étude de la Société Suisse de Chronométrie, Lausanne, Suisse, September 17, 2014.
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.
Using Singularities of Parallel Manipulators to Enhance the Rigid-Body Replacement Design Method of Compliant Mechanisms
Journal of Mechanical Design. 2014.
DOI : 10.1115/1.4026949.
The rigid-body replacement method is often used when designing a compliant mechanism. The stiffness of the compliant mechanism, one of its main properties, is then highly dependent on the initial choice of a rigid-body architecture. In this paper, we propose to enhance the efficiency of the synthesis method by focusing on the architecture selection. This selection is done by considering the required mobilities and parallel manipulators in singularity to achieve them. Kinematic singularities of parallel structures are indeed advantageously used to propose compliant mechanisms with interesting stiffness properties. The approach is first illustrated by an example, the design of a one degree of freedom compliant architecture. Then, the method is used to design a medical device where a compliant mechanism with three degrees of freedom is needed. The interest of the approach is outlined after application of the method.
Masse oscillante idéale : CQFD
2013. Congrès International de Chronométrie SSC , Montreux, Switzerland , September 25-26, 2013.
Dans les années 60, H. Kocher démontre que l'appareil Cyclotest accélère le remontage d'un système automatique d'un facteur parfaitement bien défini et précis par rapport à unporter réel. Ensuite, dans les années 70, A. Hoffmann s'attelle à la détermination des durées de remontage au Cyclotest par simulationnumérique. Il obtient des correspondances avec la pratique qui de son propre aveu ne sont "pas bonnes." Le but de cette étude est de fournir des résultats numériques compatibles avec la pratique. Partant des résultats de Kocher et appliquant des moyens de calculs actuels, nous avons déterminé pour différents systèmes automatiques des vitesses de remontage au Cyclotest. Notre approche heuristique a permis de formuler la vitesse de remontage par une expression simple; elle voit disparaître les diverses propriétés des systèmes automatiques pour ne prendre en compte que l'angle de freinage de la masse. En utilisant cette formule et connaissant les principes généraux d'un remontoir automatique, nous avons déterminé les conditions dans lesquelles une masse donnée est la plus efficace et posé des principes de construction qui permettent de dimensionner idéalement une masse oscillante sur la seule base de la puissance à la roue des secondes. Nous avons ensuite confirmé les résultats de notre théorie semi-empirique de vitesse de remontage au Cyclotest par des résultats pratiques.
Optical force sensing element and microsurgical instrument
Méthode de libération d'une pièce micromécanique et pièce micromécanique comprenant des attaches sacrificielles
Robotic system for spinal and other surgeries
The present invention relates to a method, such as a surgical method for assisting a surgeon for placing screws in the spine using a robot attached to a passive structure. The present invention also related to a method, such as a surgical method for assisting a surgeon for removing volumes in the body of a patient using a robot attached to a passive structure and to a device to carry out said methods. The present invention further concerns a device suitable to carry out the methods according to the present invention.
Short Communication: Flexure delicacies
Mechanical Sciences. 2012.
DOI : 10.5194/ms-3-1-2012.
Flexures are nowadays enjoying a new boom in numerous high-precision and extreme-environment applications. The paper presents some delicate issues concerning stiffness compensation, large reduction ratios, as well as rectilinear and circular movements in compliant mechanisms. Novel concrete technical solutions to these well-known issues are described, giving a glimpse into the vast and still largely unexploited potential of flexure mechanisms manufactured by wire-electrical-discharge machining.
Immobilizing device for a toothed wheel
Conception des guidages flexibles
Lausanne: Presses Polytechniques et Universitaires Romande.
Flexures: simply subtle
Diamond Light Source Proceedings. 2011.
DOI : 10.1017/S204482011000002X.
Flexures are enjoying a new boom in numerous high-precision and extreme-environment applications. This paper presents some general aspects of flexure design, showing simple principles, and also some subtler issues concerning kinematic design, stiffness compensation, large reduction ratios and rectilinear as well as circular movements
Flexure-based pointing mechanism with sub-microradian resolution for the Laser Interferometer Space Antenna
2010. EUSPEN 2010 , Delft, the Netherlands , May 31-June 4, 2010. p. 84.
The Point Ahead Angle Mechanism (PAAM) for ESA’s Laser Interferometer Space Antenna (LISA) mission will compensate the out-of-plane point-ahead angle between three satellites flying 5 million kilometres apart. The PAAM consists of a mirror supported by flexures allowing the mirror to rotate with a maximum stroke of ± 412 rad. The mirror is actuated in 0.14 μrad steps by two redundant linear Piezo LEGS® actuators driving a sine-bar. Since the actuators are self-locking, a special lever performing the role of a linear mechanical differential is used to provide redundancy. The angle is driven in closed loop using two capacitive sensors.
Correcteur d'isochromisme pour échappement horloger et échappement muni d'un tel correcteur
Design and development of the point-ahead angle mechanism for the lase interferometer space antenna (LISA),
2009. 13th European Space Mechanisms & Tribology Symposium , Vienna, Austria .
The Point Ahead Angle Mechanism (PAAM) for ESA’s Laser Interferometer Space Antenna (LISA) mission will compensate the out-of-plane point-ahead angle between three satellites flying 5 million kilometres apart. The PAAM consists of a mirror supported by flexures allowing the mirror to rotate with a maximum stroke of ±1 mrad. The mirror is actuated in 0.14 μrad steps by two redundant linear Piezo LEGS® actuators driving a sine-bar. Since the actuators are self-locking, a special lever performing the role of a linear mechanical differential is used to provide redundancy. The design uses high-precision flexures to minimise mirror parasitic piston displacements in the picometres range. The angle is driven in closed loop using two capacitive sensors. This paper presents the mechanism at the design stage of an elegant breadboard (EBB) ready for tests. The performance requirements are summarized, then the overall concept of the mechanism is described, at last the key aspects of the detailed design are discussed: flexures design, kinematic structure, kinematic mount, redundant piezo-actuation, sensors and control. Optimisation of the design has shown that the selected high-precision design can meet the stringent requirements of fine positioning and severe environments.
Device for converting a first motion into a second motion responsive to said first motion under a demagnification scale
Surgical navigation system
The invention relates to a surgical navigation system, comprising a microscope to which a 3D measuring apparatus is rigidly fixed, for localising objects within the field of operation. Markers are fixed to the objects the position of which is desirable to know, for example, the patient or surgical instruments, which are themselves connected to the measuring system. The change in coordinates between the measuring system and the microscope is fixed as the two devices are rigidly connected. Also, knowing the position of the markers relating to the measuring system, it is possible to calculate the change in coordinates between the markers and the image from the microscope. When the markers are recorded, in other words when the relationship between the real objects and the virtual objects is determined, the information can then be used as a navigational instrument and/or for enhanced reality. A typical application for enhanced reality is the superimposition of a 3D anatomical model of the patient on the microscope image, generated from a pre-operative scan of the patient.