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International audience; These last years, the additive manufacturing and 3D printing technologies have known some major break- throughs. The motion of a printer head can be made with cable transmission. The deployment of the cable- driven parallel robots (CDPR) in the industry is studied in very various application fields for their low cost and large workspace. Furthermore, the use of cables for the transmission induces a reduction of the mobile parts’ masses, compared to a rigid transmission, which enables to reach higher accelerations. Moreover, the structure of a CDPR is modular and reconfigurable thanks to the repositioning of the actuators’ anchor points. However, the lack of rigidity of a CDPR raises issues of accuracy and the rise of vibrations, which can be generated by the trajectory of the mobile parts, the actuators, the friction between pulleys and cables or disturbances. Several dynamic models of cables have been studied to understand the vibrating behaviour of a CDPR: a simple elastic model of springs with positive tensions, a lumped mass-spring model and a finite elements model based on a continuous one for the cables dynamics. The numerical simulation of the dynamic behaviour of the CDPR with these models enables the analysis of an appropriate control system and the design of a controller. It aims at ensuring an accurate positioning and a decrease of vibrations. In this contribution, we will firstly present the dynamic behaviour’s model and the issue of the actuation’s redundancy, systematically present on these robots to guarantee stiffness with the tension in the cables. A comparison will be done between the effects of the models on the conception and the performance of the controller. Thus, we explain that significant decreases in the vibration levels may be observed with the use of PID controllers. The generalisation of the command, the use of active control technologies and an experimental validation will be the next steps of this study.

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International audience; This paper reports on the design of a cm-scale double spring membrane used in a two degree-of-fre edom electromagnetic vibration energy harvester for railway monitoring applications. This type of membrane design enables to achieve very low stiffness for the springs (typically between 1N.mm-1 up to 10N.mm-1 ) in one piece, which reduces manufacturing los ses and greatly simplify the system assembly. In addition, they are very thin, resulting in extremely compact devices, which is very important in energy harvesting. The mechanical modelling of different types of membranes was performed using a finite element approach in order to highlight the best geometry. A series of membranes have been manufactured by machining into a non-magnetic steel and tested with the entire energy harvester.

International audience; The objective of the PyDAMP project is to develop a hybrid mechanical suspension to reduce the vibrations transmission on a wide frequency band. The undesired vibrations are generated by small electric motors (few kilograms). The concept of suspension is inspired by a Class IV flextensionnel transducer [1-3]. Flextensional transducers are a class of mechanical amplifiers composed of an active part, usually piezoelectric (bars, discs, rings), or magnetostrictive, and a shell that radiates in the surrounding fluid [4–6]. The suspension with piezoelectric pillar is developped by PYTHEAS Technology. A finite element study has been achieved to ensure the validity of the concept in terms of maximum admissible Von Mises stress, maximum displacement and modes shapes. An electromechanical model of the piezoelectrical suspension has been developed. Mechanical elements are converted in electrical components and an equivalent electrical circuit can be found. The electromechanical coupling of the transducer allows the introduction of mechanical damping and electric damping with different shunts based on resistor and negative capacitance [7, 8]. The simulation and the shunt optimisation are facilitated with only one physic, taking into account the whole dynamic behaviour of the piezoeletrical suspension.The piezoelectrical suspension is compared to a conventional viscoelastic suspension in terms of performances in the audible frequency range and validated using experimental tests.

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International audience

Astronomy is driven by the quest for higher sensitivity and improved angular resolution in order to detect fainter or smaller objects. The far-infrared to submillimeter domain is a unique probe of the cold and obscured Universe, harboring for instance the precious signatures of key elements such as water. Space observations are mandatory given the blocking effect of our atmosphere. However the methods we have relied on so far to develop increasingly larger telescopes are now reaching a hard limit, with the JWST illustrating this in more than one way (e.g. it will be launched by one of the most powerful rocket, it requires the largest existing facility on Earth to be qualified). With the Thinned Aperture Light Collector (TALC) project, a concept of a deployable 20 m annular telescope, we propose to break out of this deadlock by developing novel technologies for space telescopes, which are disruptive in three aspects: • An innovative deployable mirror whose topology, based on stacking rather than folding, leads to an optimum ratio of collecting area over volume, and creates a telescope with an eight times larger collecting area and three times higher angular resolution compared to JWST from the same pre-deployed volume; • An ultra-light weight segmented primary mirror, based on electrodeposited Nickel, Composite and Honeycomb stacks, built with a replica process to control costs and mitigate the industrial risks; • An active optics control layer based on piezo-electric layers incorporated into the mirror rear shell allowing control of the shape by internal stress rather than by reaction on a structure. We present in this paper the roadmap we have built to bring these three disruptive technologies to technology readiness level 3. We will achieve this goal through design and realization of representative elements: segments of mirrors for optical quality verification, active optics implemented on representative mirror stacks to characterize the shape correction capabilities, and mechanical models for validation of the deployment concept. Accompanying these developments, a strong system activity will ensure that the ultimate goal of having an integrated system can be met, especially in terms of (a) scalability toward a larger structure, and (b) verification philosophy.

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International audience; During the last three decades, several active damping strategies have been proposed, based on the so-called passivity concept, or equivalently, on the power port concept. One of them, known as Integral Force Feedback (IFF) is reviewed in this paper. Actually, the main drawback of the IFF is that high active damping is obtained at the cost of a degradation of the compliance at low frequency, compromising the capability of disturbance rejection. Classically, a trade-off between damping and stiffness can be reached by adequately high pass filtering the control signal. However, the high pass filter poles and zeros often interfere with the plant dynamics, which in turn compromises the guaranteed stability of the IFF. In this paper, a novel type of high pass filter is proposed. It is shown that this modification makes the controller unconditionally stable, and increases drastically the achievable modal damping. Analytic formulas are derived, and illustrated using simple numerical models. The characteristics of the proposed controller are discussed in terms of maximum modal damping and transmissibility.

International audience; The identification of time varying parameters of mechanical systems is a typical case of inverse problem treated in engineering. Parameter variations have various origins (crack apparition/propagation, temperature variation, ice deposit, etc…) and can be sources of serious problems as well as good indicators for system monitoring. The detection and quantification of these variations is essential before any analysis is performed on the system. The present contribution is then dedicated to the identification of time varying mechanical parameters for vibrating structures (illustrated by a time varying rotational stiffness). In many identification techniques, space/time derivatives and noise sensitivity are recurring problems. Displacements (angle) and accelerations are necessary in the differential equation governing the mechanical behavior of the structure. In rotating systems, angular sensors are commonly used and the angle is directly measured but the acceleration has to be estimated. In the proposed approach, the time derivatives of the recorded signals are computed using the Lanczos’ generalized derivatives for higher orders. This kind of differentiation byintegration methods allows an accurate and robust estimation of the acceleration of the measured input. Thanks to these estimated derivatives, the differential equation of motion of the structure can be partially reconstructed at each time step. Then, using short sliding windows where the unknown parameter is fit by a polynomial function, the coefficients defining these functions are computed using a weighted least square estimate. The unknown parameter and its time variation are then estimated by association of these polynomial expansions. First, the approach is presented and tuned in simulation. Many parameters,including the length of the integration domain and the size of the polynomial expansion, have to be optimized through the analysis of simulated results. Then, the method is applied to experimental data obtained from an equilateral beam excited in torsion while one beam support location is changed over time, creating a time varying torsional stiffness (1-DOF mechanical system). Finally, approach and results areanalyzed and compared to another method based on the derivative formulation of the Chebyshev polynomial basis. This general method can as well be extended to system identification, structure identification, damage detection, etc

International audience; This paper considers the control of a helicopter gearbox electromagnetic suspension for a complete multibody model of the structure. As the new generation of helicopters includes variable engine RPM during flight, it becomes relevant to add active control in their suspension systems. Most of active system performances derive directly from the controller construction, its optimization to the system controlled and the disturbances expected. An investigation on a FXLMS control algorithm has been made to optimize it in terms of narrow band disturbance rejection. In this paper an active suspension based on DAVI principle is evaluated. Firstly, a multibody model is set up to estimate realistic acceleration levels inside the cabin. Then multiple controllers are tested, minimizing vibrations on different parts of the helicopter structure. The simulations tend to prove that it is possible to implement an effective active suspension with a low power actuator and obtain a significant vibration reduction level for a frequency bandwidth centered at the natural frequency of the original DAVI.

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International audience; The aim of this study is to estimate structural parameters such as material properties (density, Young Modulus...) or geometrical properties (inertia, cross-section...) and structural damping. The identification method is based on a three steps process. Firstly, the recorded displacement field is recorded an expanded on the Chebyshev orthogonal basis. Thanks to this expansion the partial derivatives of the signal are computed. Finally, the partial derivatives are used to reconstruct the partial differential equation of motion of the structure. The three steps process will be directly illustrated by an example, even if this method could be applied to any kind of structure. The example is a simply-supported bar. The free response of this bar is the input signal used in our identification process. The identification process will be tested by simulation in noisy condition through a Monte Carlo test. The influence of the truncation order and the wave number will be discussed. With 5% of noise the structural damping is estimated with an error smaller than 0.001%

International audience; Previous studies by the authors show that energy regenerative vibration control systems can be realized by using piezoelectric elements as actuators and class D amplifiers as drivers of the piezoelectric elements. This paper shows a novel control method suitable for the energy regenerative vibration control systems. The control method is a kind of modal control and adapts modal feedback gains to maximize control performance under the following two constraints. One constraint is the condition for the balance of the regenerated energy and the energy losses in the systems. The condition is satisfied passively by using capacitors as the power sources of the amplifiers. The other is the input constraint of the class D amplifiers and satisfied by using gain adaptation mechanisms of controllers. The mechanisms need an index of the vibration amplitude of each mode and the modal energy is used as the index. The validity of the proposed method is shown by numerical simulations of a cantilever beam with piezoelectric elements.

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International audience; This study deals with the localization of damage in a beam, using methods which are insensitive to environmental variability. For this purpose, it considers the problem of adapting force identification techniques to the requirements of damage localization. Damage, when considered as a set of forces, creates a singularity in the structure, which can appear as a discontinuity in the spatial derivative of its transverse displacements. Damage or force localization methods attempt to locate and quantify such discontinuities. However, the damage effects are very small, when compared to those arising from forces, and can disappear due to the influence of low-level measurement noise. These considerations have led us to improve the conventional force identification techniques, in order to reduce their sensitivity to noise. The RIFF method ("Résolution Inversée Fenêtrée Filtrée"), which uses finite difference methods to compute highly noise sensitive spatial derivatives, is used to localize the forces. One major improvement proposed here is the use of curvature sensors (in the form of PVDF films), instead of displacements sensors, thereby avoiding the determination of two spatial derivatives and significantly increasing the noise robustness. Moreover, the derivatives are computed using the finite element method, rather than finite differences, which also improves the localization accuracy. When using these new sensors and calculus, the force identification techniques need to be rewritten, to enable damage to be localized, and new phenomena are detected. The aim of this study is to understand how force identification techniques can be used to locate damage, and to determine the improvements that could be made, in particular when using piezoelectric sensors as curvature sensors. Various numerical simulations of academic case studies illustrate the limitations and advantages of this approach.

National audience; The purpose of this study is to show that it is possible to use continuous time identification method with a signal discretized either in space or in time domains. The partial differential equations, and particularly those governing continuous mechanical system behaviour, can be transformed into algebraic equations by using the well known properties of orthogonal functions. Before any identification, it is crucial to perform a good expansion of the signals onto an orthogonal basis. A criterion will be studied to minimize the difference between the projected and the recorded signals. After this expansion step, the identification is performed through a very classical Least Square process. To validate the formalism, two different tests will be carried out: one for a bar in longitudinal motion and a second one with a bending beam. This study shows that it is possible to calculate immeasurable quantities and that this identification is robust to noise. The proposed methodologies and formulations can be easily extended to other orthogonal functions in association with partial differential transformations

Lightweight designs in engineering applications give rise to flexible structures with extremely low internal damping. Vibrations of these flexible structures due to an unwanted excitation of system resonances may lead to high cycle fatigue failure and noise propagation. A common method to suppress the vibrations is to increase the damping of the system using one of the classical control techniques i.e. passive, active, and/or hybrid. Passive techniques are those control systems that are simply integrated into the structures with no need of external power source for their operations, like viscoelastic damping, piezoelectric and electromagnetic shunt damping, tuned mass damper, etc. However, the control performance of these systems, in terms of the damping ratio and the robustness to uncertainties, is highly limited to the system properties. For example, viscoelastic damping may not perform well at low frequencies and the performance of shunt damping is dependent on the electromechanical coupling between the structure and the transducer. To overcome the limitations associated with passive controls, it has been proposed to use active control systems, which are less sensitive to the system's parameters, to improve the control performance. It requires an integration of sensors and actuators with a feedback loop containing control laws. However, the high requirement of the external power source is not favorable for engineering applications where energy efficiency is the key parameter. The combination of active and passive strategies, known as hybrid control systems, can provide a fail-safe configuration with a high control performance and low power consumption. The price to pay for such configurations is the complexity of the design. This doctoral thesis first investigates the conceptual designs of all kinds of classical control systems for a simplified mechanical system. They include 1) the passive shunt using an electromagnetic transducer, 2) the active control system using positive and negative feedback, and 3) the hybrid electromagnetic shunt damper using both an active voltage source as well as an active current source. The next part of this thesis is focused on bladed structures as real-life applications which highly require vibration control due to their low internal damping. Because of practical reasons, piezoelectric transducers are used for the application of control systems. The finite element model of the structure is made first without piezoelectric patches to optimize the best locations of piezoelectric patches. Then, the model is updated with the piezoelectric patches to numerically simulate different control strategies. The experiments are performed to validate the numerical designs., Doctorat en Sciences de l'ingénieur et technologie, info:eu-repo/semantics/nonPublished