Actuated MOEMS Micro-Mirror based on PMN-PT Piezoelectric Material.

International audienceThis paper investigates the use of a PMN-PT [001] piezoelectric actuator to be integrated in smart Micro-Opto-Electrical-Mechanicals Systems (MOEMS). Unlike most piezoelectric materials, PMN-PT [001] can generate large-stroke out-of-plane displacement. This is due to its very high longitudinal piezoelectric coefficient of tu to 4500 pm/V. After an introduction on MOEMS actuation and a short description of the Reconfigurable Free Space Micro-Optical Bench (RFS-MoB) in which the studied actuator may be included is presented, a bulk actuator is proposed. FEM simulations are then presented highlighting some tradeoffs : increased displacement with the reduction in size while decreasing the optical aberration. It was observed that for actuators with a smaller surface than 800 x 800 µm2 and 200 µm thick, displacement larger than 325 nm is largely achievable and that the size of the usable area of the actuator varies in size with the applied voltage

Guest Editorial Microassembly for Manufacturing at Small Scales.

International audienceMICROELECTRONICS brought an information revolution through integrating a vast number of microscopic transistors. Much progress has beenmade inminiaturization and integration of MEMS or MOEMS (Micro-(Opto-)Electro-Mechanical-Systems to produce accelerometers, inkjet printer heads, micro-mirrors, micro-relays, and pressure sensors. A new generation of MEMS is rapidly moving toward highly integrated, more complex heterogeneous microsystems with increased functionalities. Many limitations remain that are extremelydifficult to overcome, especially concerning processes and materials incompatibilities. microassembly is a natural and powerful approach to overcome these processes incompatibilities and to facilitate complex, heterogeneous, 3D, or out of plane integration. By using basic micro-scale components, microassembly constitutes a new alternative of Microsystems production that may lead to cost savings and shorter development cycle times. Because of the size of the components and of the required precision, automation is needed

Piston Motion Performance Analysis of a 3DOF Electrothermal MEMS Scanner for Medical Applications.

International audienceMEMS scanners are useful for medical applications as optical coherence tomography, and laser microsurgery. Although widespread design of MEMS scanners have been presented, their behaviour is not well known and thus their motions are not easily and efficiently controlled. This lack induces several difficulties (limited resolution, accuracy, cycle time, etc.) and to tackle this problem, the paper presents the modeling of an ISCelectrothermally actuated MEMS mirror and the experimental characterization for the piston motion. Modeling and characterization are important to implement the control.A multiphysic model is proposed and an experimental validation is performed with a good correspondence for a voltage range from 0V to 3.5V with a maximum displacement up to 200_m and with a relative tilting difference of 0.1°. The paper also presents a simple and efficient experimental setup to measure a displacement in dynamic and static mode or a mirror plane tilting in static mode

Measurement of microfibril angle in plant fibres : Comparison between X-ray diffraction, second harmonic generation and transmission ellipsometry microscopies

The orientation of cellulose microfibrils within plant fibres is one of the main factors influencing their mechanical properties. As plant fibres are more and more used as reinforcement for agro-composites, their mechanical properties have a strong influence on the final composite properties. It is, therefore, of interest to obtain reliable information about the microfibril angle (MFA) to better support the choice of fibres depending on the product requirements. In the present study, the reliability and specificities of three non-destructive methods that allow analysis on the same fibre glued on a holder; X-ray diffraction (XRD), second harmonic generation (SHG) and transmission ellipsometry (TE) microscopy; are investigated. Three types of plant fibres, with both low (nettle), and high (cotton, sisal) MFA values, are compared and their geometry and biochemical composition are characterised. The results obtained on the same fibre confirm that MFA analysis remains tedious and that despite their limitations, the methods are complementary depending on the information requested. Indeed, SHG is recommended for direct, qualitative and plane-selective mapping of heterogeneities in macrofibril orientations at various depths. However, reliable quantitative results with SHG depend on the initial image quality and could benefit from further image processing refinement. On the contrary, XRD and TE measure MFAs over the entire fibre thickness and provide variations along the fibres if a sufficient optical/spatial resolution is reached. Regarding the characterization of intrinsic defects in plant fibres, both SHG and TE suffer from uncertainties induced by the disorganization of the microfibril network and the lack of symmetry between the front and back fibre walls. Finally, all techniques prove to be dependant on the initial fibre alignment and geometry (i.e. twisting, double fibre configuration or form factor) which vary along the fibre length and should be carefully taken into account.publishedVersionPeer reviewe

Analysis of Forces during UV Glue Curing for Micro-Assembly Applications

International audience"Positional drift resulted from the glue curing may result into serious challenges towards accuracy especially for micro-assembly processes. Studying forces and positional drifts resulted from the glue curing appears as a key objective towards reaching precise micro-assemblies. For this reason, works notably investigate the forces and displacements originated from the UV glue curing. Experimental investigations demonstrates that the force induced during the glue curing is in 160 µN range against a micro-object with cross section of 500 x 500 µm, and the corresponding positional drift in the 10 µm range was obtained. Works also show that these values depend on the system and strategy used for the assembly.

Hysteresis Characterization And Modeling Of Novel Thick-Film Pzt Microactuators.

International audienceThis paper reports the characterization of the new kind of piezoelectric microactuators which shown highly nonlinear behavior, such as hysteresis and creep. In this paper we will focus on the characterization and modeling of the hysteresis of such actuators. It is shown that the gain of these thick-film microactuators exceeds 4μm/V and the related hysteresis is of 16% (Fig.1.b). A generalized Bouc-Wen model is afterwards employed to track the hysteresis. Thanks to this model, an open-loop compensation of the hysteretic behavior of the cantilever was efficiently performed

High-Precision Gluing Tasks Based on Thick Films of Glue and a Microrobotics Approach

International audienceMicro-assembly using glue is an industrial need, but at the microscale, the gluing process appears highly challenging. Especially when the thickness of the glue film is large relative to the size of components to be assembled. Moreover, the down-scaling of passive techniques used at the macroscale (such as using reference surfaces) are widespread, but require highly complex and dedicated procedures to reach the required precision (typically 1 μm or below). To address this, we propose an original approach for micro-assembly that consists of using a thick film of glue (glue thickness typically >50 μm) with an active microrobotic control. This approach enables us to have high precision positioning of the two components during the gluing task. The proposed approach appears highly versatile and flexible because it is independent of many parameters that usually influence gluing tasks. Several experiments without the use of the proposed approach show that the typical order of positional drift from curing could be of 5 to 15 μm. Finally, experimental results using the proposed approach demonstrate that a positioning accuracy of 200 nm can typically be obtained, which validates the approach and suggests its potential interest to industry

Mesures expérimentales du module d’Young transverse de fibres élémentaires de lin, chanvre et ortie

International audienceLes propriétés transverses des fibres sont importantes pour déterminer le comportement mécanique des composites les intégrant. Elles ont été déterminées jusqu’alors par méthode inverse à partir d’essais sur composites pour les fibres végétales. Cependant, pour ces fibres, l’incertitude sur les valeurs identifiées est grande car la loi des mélanges induit un manque de fiabilité inhérent. Ce travail propose de déterminer le module d’Young transverse de fibres élémentaires européennes, lin, chanvre et ortie, à partir d’essais de compression diamétrale sur fibre élémentaire.<br&gtLe protocole expérimental des campagnes d’essais repose sur un dispositif micro-mécatronique avec un capteur spécialement développé pour la compression de fibres végétales (répétabilité en force : 10μN, en déplacement : 30nm). Pour garantir la précision des mesures, le parallélisme entre les deux plateaux est contrôlé à 0.1° et l’environnement régulé à ± 0,5 % d’humidité relative. Ces travaux ont permis les premières déterminations du module d’Young transverse de fibres végétales

Investigating the influence of plant fiber geometry on apparent transverse elastic properties through finite element analysis

International audienceThis study explores the link between plant fiber geometry and its transverse behavior, focusing on the resulting apparent transverse stiffness as determined by analytical models. Using Finite Element Analysis (FEA) plant fiber transverse compression is simulated with two-dimensional models. Simplified geometric representations of common geometric features are examined, showing how distinct attributes influence behavior. The fiber lumen is shown to decrease apparent stiffness, while elliptical geometry and flat sections increase it. An adaptation of analytical models for ellipticalcross-sections yields a 93 % improvement on identification accuracy. Furthermore, the transverse compression of realistic geometries, extracted from microscopy images and presenting a blend of different features, is simulated. The lumen’s impact on apparentstiffness is shown to outweigh the effects of other features. These findings show the importance of apparent stiffness over fiber cell wall stiffness and how it may evolve under repeated loading, which has important implications for the composites sector

Force-Position Photo-Robotic Approach for the High-Accurate Micro-Assembly of Photonic Devices

International audienceRecently, micro-assembly of individual photonic elements has been highly attracting to provide new optical functionalities and products with high performances. This approach requires position control in free space and contact detection in constrained space. In both cases, getting accurate measurements remains a key lock. For this sake, the FP (Fabry-Perot) interferences happening during the active alignment of optical elements is exploited. This 1D displacement measurement is combined with multi-DoF (Degrees-of-Freedom) robotic motions and a compliant structure along a photo-robotic approach to provide high accurate estimation of both multi-DoF position and contact forces during the assembly process. This approach has been applied to the assembly of an optical lamella with respect to a fiber. An original contact detection algorithm has been proposed, which relies on correlations between the interference figure and the expected irradiance deduced from the nano-positioner internal sensors. This contact detection enables to estimate the position of the lamella with respect to the fiber along the optical axis and thus control the UV-adhesive thickness required to achieve high optical performances after assembly. Experimental investigations using this new approach shows that a positioning accuracy of 27.6 nm and 2.1 m ∘ (standard deviation values) are reached for positions and orientations respectively. The contact detection algorithm has also been studied experimentally and results shows that the contact position can be detected with a maximum error of 80 nm, which provides a very high interest for many photonic applications