Luc Gaudiller

New semi-active multi-modal vibration control using piezoceramic components

Active vibration control using piezoelectric elements has been extensively studied due to the requirement for increasingly high performances. Semi-active control, such as Synchronized Switch Damping, is an alternative technique. It consists in switching a piezoelectric element to a specific circuit synchronously with the motion of the structure, unlike active control. This method requires very low power supply, but performances remain poor in the case of broad bandwidth excitation. This article proposes a new method which is a combination of the SSDI semi-active control and technique developed for active control and has low power supply requirements. It extends semi-active control to any type of excitation, while optimizing modal damping on several targeted modes. Experimental measurements carried out on a clamped free beam are presented and a significant damping on targeted modes is demonstrated.

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.

A Nonlinear Method for Improving the Active Control Efficiency of Smart Structures Subjected to Rigid Body Motions

Smart components are commonly used for their compactness and ability to control the vibrations in an embedded flexible structure. Their relative actuation capabilities can limit the active control efficiency. This paper introduces a nonlinear method to improve their action using independent controllers for flexible modes and for rigid body modes. The nonlinear control of each flexible mode uses fuzzy logic controllers designed to improve the mechanical work of smart actuators by taking into account their actuation capabilities. The control law parameters are iteratively adjusted by taking into account the estimated disturbance levels until obtaining the desired compromise between efficiency and spillover. In addition, an independent fuzzy control for rigid body motions is then developed and adjusted in order to reduce the vibrations of the structure without decreasing the tracking efficiency. These two independent nonlinear strategies are described, implemented, and experimentally tested to control an articulated smart structure.

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)

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.

Enhanced piezoelectric voltage build-up for semi-active control of smart structures

This paper presents a combination of the SSD (Synchronized Switch Damping) semi-active control and techniques developed for active control. The principle of modal SSDI is to synchronize the piezoelectric voltage inversion or switching with the extremum of the targeted mode modal displacement. This modal displacement is estimated even in the case of complex, broadband or noisy excitation with a modal observer. The switching process control induces a non linear processing of the piezoelectric voltage which results in a cumulative self generated control voltage in phase with the mode speed, thus generating an important damping of the targeted mode. This voltage self building is optimal if the piezoelectric voltage is maximum when the modal displacement of the targeted mode is extremum. But in the case of complex excitation or when the targeted mode amplitude is lower than higher modes, the performances are altered. The proposed method consists in implementing a decision algorithm allowing waiting for the next voltage extremum before to trig the voltage inversion, the whole process being globally synchronized with the targeted modal displacement. Indeed, the targeted mode amplitude is reduced by using part of the energy of the higher modes which enhances the build up of the self generated piezoelectric control voltage. Simulations carried out on a clamped free beam are presented. Results obtained first with a bimodal excitation then in the case of pulse excitation demonstrates a large increase of the damping on the targeted mode.

Hybrid modal nodal method for multibody smart structure model reduction: application to modal feedback control

The hybrid modal nodal (HMN) method, designed for multibody smart structure model reduction and feedback control development, is based on the independent modeling of structural and electromechanical behavior. Firstly, this approach permits reducing the model of substructures independently of the electromechanical behavior. This allows choosing the most adapted component mode synthesis (CMS) method and corresponding code for any application, something that is not permitted by classical multi-physics projection-based methods. Thus, the substructuring process used in this paper is based on super-elements directly adapted for multibody dynamics modeling. Secondly, the electromechanical behavior of distributed components is introduced into the structural modal model via a nodal formulation. Its independence of any projection guarantees accuracy and its formulation is valid whatever the multibody assembly and its modal shapes. The proposed application is composed of successive developments and experiments designed to validate the model reduction method, its implementation and its use for modal feedback control, i.e. a smart beam, actively controlled by piezoelectric ceramics. It is successively clamped to illustrate the electromechanical coupling reduction, articulated to introduce the rigid-body/flexible mode coupling reduction and, finally, bi-articulated in order to deal with the nonlinear problem.

Low energy multimodal semi-active control minimizing the number of transducers

The new proposed method is the hybridization between SSDI techniques and active methods developed for modal active control such as time sharing control and modal observer in order to control several modes of a structure with a good performance but without operative energy. It is designed in order to minimize the number of control components. The principal application field is the transportation. It is based on several modal SSDI controllers which act on the same actuator voltage. They are synchronized on each extremum of the corresponding modal displacement. Modal displacements are reconstructed thanks to a modal model of the smart structure from a modal observer. In order to reduce the number of actuators, the time sharing method is adapted to SSDI techniques: all the modal SSDI are connected to the same piezoelectric actuator, but only one controller is selected to control the voltage inversion for each step time. In order to select modal SSDI controller having the most effective action for damping, a computation of modal energies is realized from the estimated modal state. A controller selector is used to connect the modal SSDI command, whose corresponding mode has the highest modal energy [6], to the switch trigger. An application on a smart clamped free beam including one actuator and two sensors is presented. Three modes are controlled and the modal responses are observed on five modes. The results show that the control reduces significantly the vibration of targeted modes. Moreover, the method is not subject to stability problems.

Semi-Active Control of a Targeted Mode of Smart Structures Submitted to Multimodal Excitation

Active control of smart structures equipped with piezoelectric elements has shown its efficiency for two decades now. However, the electric power required by amplifiers for driving actuators appeared to be a severe limitation to the development of these techniques. In order to reduce this power requirement, semi-passive techniques developments such as Synchronized Switch Damping control were carried out. These ultra-low power techniques perform very well for monomodal excitation but their performances are limited in the case of multi-modal or complex vibrations. This paper deals with the implementation of an enhanced semi-active technique using methods developed for active control. A new multimodal control technique is proposed. It is based on SSD-Inductance semi-active technique. A Luenberger observer separates themodal variables from the voltage of the piezoelectric sensors. Then, the SSDI control can be targeted separately on each mode to control the vibration. This technique does not need operative power supply. An application of the proposed method on a clamped-free smart beam is proposed. Modal dampings of the controlled smart structure are first of all predicted by simulations. then experimental results validate the proposed principle. Results obtained show the efficiency of the method and demonstrate its capabilities to control different modes on a broad frequency range.

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.