A study on transparency of a passive manipulation mechanism : application to Neoditech Scara Parts

International audienceIn the field of 5 to 100 kg load transportation in workshops, many systems having more or less complex ar-chitectures have been developed to reduce musculo-skeletal disorders (hoists, pliers, dedicated systems). These systems offer different behaviors and human interaction is far from being the same for all of them. In recent years, the literature produced a lot of work around design thinking, user-centered approaches emphasizing notions around perception, cognition, and ergonomics to meet the needs of the end user. The development of cobotics and more generally systems allowing the interaction or co-manipulation of objects highlights the notion of transparency of the system. This transparency is expressed as the fact of feeling only a part of the physical magnitudes of the object most relevant to the user in his manipulation. In the context of this article, we study the transparency of a kinematically redundant passive mechanism based on a scara one (revolute joints parallel between them) when manipulating heavy objects on a plane. This article is based on a state of the art of different criteria in order to evaluate the behavior of a robot such as manipulability or dexterity. We will indicate the relevance of these criteria that we apply to a theoretical study. These theoretical aspects will then be evaluated on Neoditech Scara Parts arm. It is a mechanism capable of handling up to 50kg composed of a plane arm mounted on vertical linear axis itself mounted on a fixed or mobile base. This plane arm consists of 6 revolute joints having parallel axes ensuring redundancy in the architecture of the robot

Influence of the V-Y advancement flap geometry on the wound closure maximal force

International audienceIn clinical practice, the V-Y advancement flap is a widely used technique to cover human skin defect, which consists in incising; advancing and suturing a triangular flap adjacent to the base of a rectangular defect (see Figure 1a). A previous geometrical study of the V-Y flap technique allowed us to find a good compromise between the flap size and the defect width [1]. However, the geometrical approach does not consider the mechanical properties of the human skin by assuming rigid-body behaviour of the skin. The aim of the present paper deals with a numerical analysis as a complement to the geometrical one to highlight the major role of the skin elasticity in the V-Y advancement flap. A compromise between the size of the flap and the level of the closure force value has been found when varying the angle at the flap apex, noted . The sensitivity to the mechanical parameters makes the closure force dependent on the size to be covered. At the end, the successive actions of the surgeon are analyzed

Mechanics and band gaps in hierarchical auxetic rectangular perforated composite metamaterials

International audienceWe describe in this work a composite metamaterial with a hierarchical topology made by tessellating perforations that exhibit an auxetic (negative Poisson’s ratio) behaviour. We perform an analysis of the hierarchical structure by evaluating the fractal order of the topologies associated to the perforated composites. The periodic hierarchical lattice configuration shows negative Poisson’s ratio characteristics at higher levels of hierarchy, even when the baseline configuration has a topology not exhibiting an auxetic behaviour. We investigate the wave propagation characteristics of these particular hierarchical lattices by using a Bloch wave approach applied to detailed Finite Element geometries of the unit cell configurations. We show that the level of hierarchy creates new band gaps with large relative widths, and it also shifts the same bandgaps towards lower frequencies. We correlate the mechanical properties, fractal order and the dispersion characteristics of the multiscale auxetic perforated metamaterial with the parameters defining the geometry of the lattice and the hierarchy levels, and discuss the results in a nondimensional form to provide a performance map of the mechanical and dynamic properties

Numerical tools for efficient simulations of wave propagation in damped periodic structures

International audiencePeriodic structures exhibit very specific properties in terms of wave propagation. In this paper, some numerical tools for dispersion analysis of periodic structures are presented, with a focus on the ability of the methods to deal with the dissipative behavior of the systems. The classical Floquet-Bloch approach is first presented, as a reference. This technique uses proper boundary conditions on the unit cell, it is quite simple to implement but dealing with damping is not easy for 2D or 3D cases. Secondly, the Shifted-Cell Operator technique is described. It consists in a reformulation of the PDE problem by shifting in terms of wave number the space derivatives appearing in the mechanical behavior operator inside the cell, while imposing continuity boundary conditions on the borders of the domain. Damping effects can be introduced in the system and a quadratic eigenvalue problem yields to the dispersion properties of the periodic structure. Both approaches are first analyzed in terms of mesh convergence, and then a focus is proposed on tools for the post-processing of dispersion diagrams in damped configurations. The group velocityof each branch in the diagram is defined including damping effects, and it is shown that it constitutes a pertinent indicator for the branches tracking from one computational point to another

Design of smart metamaterials for vibration control: extension of Bloch approach to handle finite system boundary conditions

International audienceThe design of smart metamaterials for vibration control is usually based on the use of Bloch theorem which considers a single cell with adequate boundary conditions. These boundary conditions correspond to the infinite repetition of the unit cell in 1D, 2D or 3D. Complex geometries and composite systems can then be designed using this approach with finite elements. The control of the elastic waves can be performed by combining Bragg's (wave interferences), resonant's (resonance of a component embedded in the unit cell), damping and/or active control. The energy can then be reected, transmitted, damped, focused or confined in a specific zone of the structure. However, the practical realization of real-life 2D or 3D finite systems may lead to some situationswhere energy transfers are not in accordance with those predicted by the infinite system considered in the design, because of reections on the boundary conditions of the finite structure. The behavior of the system may be simulated by full system modelling, but this is time consuming and may lead to huge calculation costs. In this paper, we propose an extension of the Bloch approach to handle finite system boundary conditions in order to be able to identify situations in which energy transfer may arise because of re ections on the border of the elastic domain. Calculations are performed on 2 cells with adequate boundary conditions. The methodology is described and validated using full finite model and experimental tests on a 2D metamaterial structure

Parametric study of wave propagation in hierarchical auxetic perforated metamaterials

International audienceThe understanding of wave propagation in a metamaterial with hierarchical, auxetic rectangular perforations is presented in this work. The metamaterial is a 2D structure with chaining horizontal and vertical perforations exhibing auxetic in-plane behaviour. The unit cell of this lattice is identified as the reference level 0. Hierarchical structures are composed of structural elements which themselves have structure. At level 0, 4 rigid squares are present in the unit cell. In each square, the reference structure is used by applying a scale ratio to obtain the level 1. The same strategy is used to reach the upper level in each subunit. A geometric parametric investigation of these rectangular perforations using a numerical asymptotic homogenisation finite element approach is done. Some numerical eigenvalue tools are used for the dispersion analysis of this structure. It is first observed that the total width of Band gaps increases with the hierarchy. The porosity induced by the perforations is taken into account in the mechanical properties. The symmetry of the geometry in the x-y plane allow to define the entire geometry of the unit cell using only 2 parameters: the void aspect ratio, the intercell spacing and the hierarchy level. When decreasing the intercell spacing, the total width of Band gaps increases and the effective stiffness in x and y directions decrease, allowing for increased rotations of the rigid sqares, so auxetic behaviour is greater. Hierarchical levels shift from isotropic to orthotropic, hierarchical levels are always auxetic

A study on transparency of a passive manipulation mechanism : application to Neoditech Scara Parts

International audienceIn the field of 5 to 100 kg load transportation in workshops, many systems having more or less complex ar-chitectures have been developed to reduce musculo-skeletal disorders (hoists, pliers, dedicated systems). These systems offer different behaviors and human interaction is far from being the same for all of them. In recent years, the literature produced a lot of work around design thinking, user-centered approaches emphasizing notions around perception, cognition, and ergonomics to meet the needs of the end user. The development of cobotics and more generally systems allowing the interaction or co-manipulation of objects highlights the notion of transparency of the system. This transparency is expressed as the fact of feeling only a part of the physical magnitudes of the object most relevant to the user in his manipulation. In the context of this article, we study the transparency of a kinematically redundant passive mechanism based on a scara one (revolute joints parallel between them) when manipulating heavy objects on a plane. This article is based on a state of the art of different criteria in order to evaluate the behavior of a robot such as manipulability or dexterity. We will indicate the relevance of these criteria that we apply to a theoretical study. These theoretical aspects will then be evaluated on Neoditech Scara Parts arm. It is a mechanism capable of handling up to 50kg composed of a plane arm mounted on vertical linear axis itself mounted on a fixed or mobile base. This plane arm consists of 6 revolute joints having parallel axes ensuring redundancy in the architecture of the robot

Transparency Analysis of a Passive Heavy Load Comanipulation Arm

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Modeling real phononic crystals via the weighted relaxed micromorphic model with free and gradient micro-inertia

International audienceIn this paper the relaxed micromorphic continuum model with weighted free and gradient microinertia is used to describe the dynamical behavior of a real two-dimensional phononic crystal for a wide range of wavelengths arriving down to the size of the unit cell. In particular, a periodic structure with specific micro-structural topology and mechanical properties, capable of opening a phononic band-gap, is chosen with the criterion of showing a low degree of anisotropy (the band-gap is almost independent of the direction of propagation of the traveling wave). A Bloch wave analysis is performed to obtain the dispersion curves and the corresponding vibrational modes of the periodic structure. A linear-elastic, isotropic, relaxed micromorphic model including both a free micro-inertia (related to free vibrations of the microstructures) and a gradient micro-inertia (related to the motions of the microstructure which are coupled to the macro-deformation of the unit cell) is introduced and particularized to the case of plane wave propagation. The parameters of the relaxed model are then calibrated on the dispersion curves of the phononic crystal showing an excellent agreement in terms of both dispersion curves and vibrational modes. Almost all the homogenized elastic parameters of the relaxed micromorphic model result to be determined. This opens the way to the design of morphologically complex meta-structures which make use of the chosen phononic structure as the basic building block and which preserve its ability of “stopping” elastic wave propagation at the scale of the structure

Design and experimental validation of a hierarchical auxetic rectangular perforated metamaterial

International audienceThe understanding of wave propagation in a metamaterial with hierarchical, auxetic rectangular perforations is presented in this work. The metamaterial is a 2D structure with chaining horizontal and vertical perforations exhibing auxetic in-plane behaviour. Some numerical eigenvalue tools are used for the dispersion analysis of this structure. It is first observed that the total width of Band gaps increases with the hierarchy. In order to validate the design of the metamaterial, results issued from a full 3D model of a finite structure embedding an interface composed by a distributed set of the unit cells are presented. After this step, a comparison between the results obtained using the structure simulation and the experimental results are presented with critical analysis