Simon Henein

Design of parallel robots in microrobotics

During the past few years, there has been an increasing demand in the field of precision engineering for fine motion in multi-degrees of freedom systems. These applications motivated the development of a new robotics field called microrobotics. In this paper, we review both the design guidelines for microrobots and the advantages of using parallel robots in very high precision applications. Parallel micromanipulators using elastic joints as well as structures manufactured in single solid and metallic bellows are introduced.

Harvesting Energy From a Rotating Gear Using an AFM-Like MEMS Piezoelectric Frequency Up-Converting Energy Harvester

This paper presents an analytical and experimental study of a compact configuration to harvest energy from a rotating gear using piezoelectric microelectromechanical system harvesters. The reported configuration realizes a contact-type frequency up-conversion mechanism in order to generate useful electrical energy. The up-conversion mechanism was achieved using an atomic force microscope (AFM)-like piezoelectric cantilever plucked by the teeth of the rotating gear that could be eventually driven by an oscillating mass. This paper describes relevant design guidelines for harvesting energy from the low-frequency mechanical movement of a rotating gear through analytical modeling and finite element method (FEM) simulation followed by experimental validation. Different harvester configurations are investigated to identify the optimal configuration in terms of the output energy and energy conversion efficiency. The latter results are reported for the first time because of the implementation of an original concept based on the coupling of the harvester with a rotational flywheel. The experimental results reveal that free vibrations of the harvester after plucking contribute significantly to the output energy and efficiency. By adding a proof mass, the efficiency of the system can be greatly improved. For plucking speeds between 3 and 19 r/s, average output powers in the order of tens of microwatts were obtained for continuous plucking. By combining interaction energy, friction, and energy absorption, between the harvester and inertial mass, the maximum efficiency of the impact piezoelectric harvesters was found to be 1.4%. The efficiency results obtained were compared with the noncontact magnetic plucking approach further demonstrating the potential of our concept. Finally, different tip-gear materials combinations were evaluated showing the importance of their nature on the reliability of the presented configuration.

A statistical shape model of the human second cervical vertebra

PurposeStatistical 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.MethodsThe 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.ResultsThe 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.ConclusionThe 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.

On the experimental determination of the efficiency of piezoelectric impact-type energy harvesters using a rotational flywheel

This paper demonstrates a novel methodology using a rotational flywheel to determine the energy conversion efficiency of the impact based piezoelectric energy harvesters. The influence of the impact speed and additional proof mass on the efficiency is presented here. In order to convert low frequency mechanical oscillations into usable electrical energy, a piezoelectric harvester is coupled to a rotating gear wheel driven by flywheel. The efficiency is determined from the ratio of the electrical energy generated by the harvester to the mechanical energy dissipated by the flywheel. The experimental results reveal that free vibrations of the harvester after plucking contribute significantly to the efficiency. The efficiency and output energy can be greatly improved by adding a proof mass to the harvester. Under certain conditions, the piezoelectric harvesters have an impact energy conversion efficiency of 1.2%.

Fatigue failure of thin wire-electrodischarge-machined flexure hinges

This paper inquires into the exportability of the fatigue measurements made on standard test-specimen to wire electro- discharge machined flexures with thin cross sections (50 micrometers ). It describes the results of a set of fatigue measurements made on 66 circular flexible hinges machined in steel and bronze by wire electro-discharge machining. After reminding the fatigue theory and describing the theoretical model used to calculate the stresses inside the bent hinges, the paper describes the experimental setup and the measured results. The main conclusions drawn out of this work is that the admissible stresses for the tested flexures having a low surface roughness (Ra equals 0.2 micrometers ) are at least as high as the admissible stresses for standard test specimens. This indicates that fatigue data found in literature can be used to calculate the dimensions of this kind of flexures without any reduction of the safety factor.

Tunable extended-cavity diode laser based on a novel flexure-mechanism

This article presents the design, implementation and characterization of an extended-cavity laser diode. The design of the wavelength tuning mechanism is based on a two degrees-of-freedom monolithic flexure-based mechanism. The linear stroke for cavity length tuning could be minimized by optimizing the position of the prisms. The tuning with narrowband emission line is demonstrated in the wavelength range of 837 nm to 870 nm.

Flexures: simply subtle

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

Gravity-Insensitive Flexure Pivot Oscillators

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 10 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. [DOI: 10.1115/1.4039887]

Investigating the Size-Dependent Static and Dynamic Behavior of Circular Micro-Plates Subjected to Capillary Force

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.