Simon Chesne

Semi-adaptive modal control of on-board electronic boards using an identification method

Modal active control, based on a state model, is an efficient method of increasing the lifetime of electronic boards by using piezoelectric components. In the case of industrial mass production, dispersions lead to changes in mechanical and electromechanical properties. Moreover, initial operating conditions such as boundary conditions can change during the lifetime of the control and modify its efficiency and stability. Therefore, a semi-adaptive modal control strategy in deferred time is proposed to attenuate these problems. Firstly modal control gains are calculated by using a classical linear quadratic Gaussian algorithm with the nominal model including mode shapes. Then control I/O data are collected by an identification system that uses on-board piezoelectric components. A subspace method is implemented to estimate modal matrices in order to update the controller. The sensitivity of control performance to modal parameter variation is presented. Estimated control frequencies and modal damping are finally used to update modal control gains. The effectiveness of the proposed method is examined through numerical simulation and experimental tests in the case of boundary condition modifications. This adaptive modal control/identification design greatly increases the nominal robustness of the controller in the case of frequency shifts.

Identification of Plate Boundary Forces From Measured Displacements

This work deals with the identification of forces at plate boundaries, by measuring displacements only. Shear force and bending moment directly depend on different spatial derivatives of displacement at plate boundaries that can be approximated from measured displacements (finite differences, modal approach, etc.), but two major difficulties occur: Derivatives are highly sensitive to measurement errors and the usual methods used to obtain them are not well adapted to boundary points. In this paper a mathematical approach is proposed to identify shear force at boundaries without any direct calculation of the displacement derivatives. The method is based on the weak form of the plate equation of motion and a test function satisfying particular boundary conditions. Following the description of the technique and the definition of the test function that permits the identification at one boundary point, numerical simulation results, including the effects of noise on displacements, are provided in order to establish the spatial and frequency limits of this method.

Identification of Boundary Forces in Beams From Measured Displacements

This paper deals with shear force and bending moment identification in a beam from measured displacement. The proposed approach, using the weak form of the equation of motion, is based on the extraction of shear force or bending moment from integral equation and choice of test functions, associated to each boundary quantity of interest. After the theorical description, numerical simulation results are shown in order to clarify limits of the method and to stress its self-regularization. Two experimentations are described, showing very good accuracy of shear force and bending moment reconstruction in comparison with direct measurements.

Experimental identification of smart material coupling effects in composite structures

Smart composite structures have an enormous potential for industrial applications, in terms of mass reduction, high material resistance and flexibility. The correct characterization of these complex structures is essential for active vibration control or structural health monitoring applications. The identification process generally calls for the determination of a generalized electromechanical coupling coefficient. As this process can in practice be difficult to implement, an original approach, presented in this paper, has been developed for the identification of the coupling effects of a smart material used in a composite curved beam. The accuracy of the proposed identification technique is tested by applying active modal control to the beam, using a reduced model based on this identification. The studied structure was as close to reality as possible, and made use of integrated transducers, low-cost sensors, clamped boundary conditions and substantial, complex excitation sources. PVDF (polyvinylidene fluoride) and MFC (macrofiber composite) transducers were integrated into the composite structure, to ensure their protection from environmental damage. The experimental identification described here was based on a curve fitting approach combined with the reduced model. It allowed a reliable, powerful modal control system to be built, controlling two modes of the structure. A linear quadratic Gaussian algorithm was used to determine the modal controller‐observer gains. The selected modes were found to have an attenuation as strong as 13 dB in experiments, revealing the effectiveness of this method. In this study a generalized approach is proposed, which can be extended to most complex or composite industrial structures when they are subjected to vibration. (Some figures may appear in colour only in the online journal)

Distributed piezoelectric sensors for boundary force measurements in Euler–Bernoulli beams

In many vibro-acoustic problems, in which structures are excited by their boundaries, the identification of boundary quantities such as bending moments and shear forces is not straightforward because these quantities are not readily accessible. Moreover, since they are proportional to the spatial derivatives of the structures displacements, their quantification using methods based on post-processing remains very sensitive to uncertainties. In this paper, a new class of distributed piezoelectric sensors is proposed, using laminate theory and the weak forms of the equation of motion for a beam. Using this approach, it is shown that the bending moments or the shear forces can be determined at the boundaries, using spatial integrations generated by piezoelectric patches (or PVDF films) with specific shapes. Following a description of the general approach, this paper provides a description for the case of bending moment identification. In this example, the calculations used to determine the adequate shapes are presented. An analytical one-dimensional (1D) simulation, together with a numerical three-dimensional (3D) simulation, taking into account the influence of uncertainties, demonstrate the accuracy of the developed sensor. The same technique can be applied to shear force identification, as shown in the last section of this paper.

Improvement of Transmission Loss Using Active Control with Virtual Modal Mass

This paper deals with an alternative modal active control approach to reduce sound transmission through a structure excited by an acoustic wave. Active control makes it possible to conserve lightness while improving acoustic performances. “Modal mass damping control” is proposed for light and small structures having slight modal overlap. The aim of this control is to modify the modal distribution of high radiation efficiency modes with active modal virtual mass and active modal damping. The active virtual mass effects lower eigen frequencies to less audible frequency range while reducing vibration amplitudes in a broad frequency range. An application of this concept is presented in a simple smart structure. It is harmonically excited on large bandwidth by a normal acoustic plane wave. Results obtained by active modal virtual mass and damping control are compared to other modal control approaches.

A development roadmap for critical technologies needed for TALC: a deployable 20m annular space telescope

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.

Enhanced Damping of Flexible Structures Using Force Feedback

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.

Reconstruction of the Instantaneous Angular Speed Variations Caused by a Spall Defect on a Rolling Bearing Outer Ring Correlated with the Length of the Defect

In the framework of monitoring of rotating machinery, this paper proposes a simple signal processing tool to reconstruct the Instantaneous Angular Speed (IAS) variations caused by the presence of spalled bearing. This tool is applied to signals obtained on a specific test bench. Associated with an angular sampling, the analysis of these variations can identify the length of the defect whatever the mode of operation, particularly in non-stationary operating conditions in rotation speed.

Hybrid active suspension system of a helicopter main gearbox

This paper considers experiments on the control of a helicopter gearbox hybrid electromagnetic suspension. As the new generation of helicopters includes variable engine revolutions per minute (RPMs) during flight, it becomes relevant to add active control to their suspension systems. Most active system performance derives directly from the controller construction, its optimization to the system controlled, and the disturbances expected. An investigation on a feedback and feedforward filtered-x least mean square (FXLMS) control applied to an active DAVI suspension has been made to optimize it in terms of narrow-band disturbance rejection. In this paper, we demonstrate the efficiency of a new hybrid active suspension by combining the advantages of two different approaches in vibration control: resonant absorbers and active suspensions. Here, a hybrid active suspension based on the passive vibration filter called DAVI is developed. The objective of this paper is to prove the relevancy of coupling a resonant vibration absorber with a control actuator in order to create an active suspension with larger bandwidth efficiency and low energy consumption. The simulations and experimentation achieved during this suspension system development support this hypothesis and illustrate the efficiency and low energy cost of this smart combination.