Peidong Li

Model-free fuzzy control of a magnetorheological elastomer vibration isolation system: analysis and experimental evaluation

This paper addresses the problem of micro-vibration control of a precision vibration isolation system with a magnetorheological elastomer (MRE) isolator and fuzzy control strategy. Firstly, a polyurethane matrix MRE isolator working in the shear-compression mixed mode is introduced. The dynamic characteristic is experimentally tested, and the range of the frequency shift and the model parameters of the MRE isolator are obtained from experimental results. Secondly, a new semi-active control law is proposed, which uses isolation structure displacement and relative displacement between the isolation structure and base as the inputs. Considering the nonlinearity of the MRE isolator and the excitation uncertainty of an isolation system, the designed semi-active fuzzy logic controller (FLC) is independent of a system model and is robust. Finally, the numerical simulations and experiments are conducted to evaluate the performance of the FLC with single-frequency and multiple-frequency excitation, respectively, and the experimental results show that the acceleration transmissibility is reduced by 54.04% at most, which verifies the effectiveness of the designed semi-active FLC. Moreover, the advantages of the approach are demonstrated in comparison to the passive control and ON-OFF control.

Research on Hybrid Isolation System for Micro-Nano-Fabrication Platform

In order to obtain better vibration suppression effect, this paper designs a semiactive/fully active hybrid isolator by using magnetorheological elastomer (MRE) and piezoelectric material. Combined with multimode control scheme, full frequency vibration suppression is achieved. Firstly, series type structure is determined for the hybrid isolator, and the structure of hybrid isolator is designed. Next, the dynamic model of hybrid isolator is derived, the dynamic characteristics measurement for MRE isolator and piezoelectric stack actuator (PSA) is established, and parameters such as voltage-displacement coefficient, stiffness and damping constant are identified from the experimental results, respectively. Meanwhile, the switch frequency is determined by experimental results of PSA and MRE isolator. Lastly, influence of the stiffness of MRE, control voltage of PSA, and intermediate mass on hybrid isolator system is analyzed by simulations, and the results show that the hybrid isolator proposed is effective.

Creep and recovery behaviors of magnetorheological elastomer based on polyurethane/epoxy resin IPNs matrix

This paper mainly investigated the creep and recovery behaviors of magnetorheological elastomers (MRE) based on polyurethane/epoxy resin (EP) graft interpenetrating polymer networks (IPNs). The influences of constant stress level, content of EP, particle distribution, magnetic field and temperature on the creep and recovery behaviors were systematically investigated. As expected, results suggested that the presence of IPNs leads to a significant improvement of creep resistance of MRE, and creep and recovery behaviors of MRE were highly dependent on magnetic field and temperature. To further understand its deformation mechanism, several models (i.e., Findleys power law model, Burgers model, and Weibull distribution equation) were used to fit the measured creep and recovery data. Results showed that the modeling of creep and recovery of samples was satisfactorily conducted by using these models. The influences of content of EP and magnetic field on fitting parameters were discussed, and relevant physical mechanism was proposed to explain it qualitatively.

NARX neural network modeling and robustness analysis of magnetorheological elastomer isolator

Due to the controllability of the stiffness and damping under the applied magnetic field, magnetorheological elastomer isolator has been proved effective in the field of vibration control. For the realization of vibration control application, an accurate MRE isolator model is a non-trivial task. However, the existing parametric modeling methods are required to identify too many parameters, which are difficult to implement. Moreover, the corresponding inverse dynamic model of the isolator cannot even be obtained by the identified model inversion. Therefore, this paper proposes a nonparametric neural network approach to approximate the dynamic behaviors of magnetorheological elastomer isolator with the characteristics of nonlinearity and hysteresis. Firstly, the dynamic characteristics of the isolator in shear-compression mixed mode are experimentally tested under different loading conditions. Secondly, based on the experimental data, a NARX neural network with three-layer structure is developed to approximate the functional relationship between inputs (displacement, velocity and current) and output (force) of magnetorheological elastomer isolator. Thirdly, the effectiveness of the network model is validated by comparing the predicted force and experimental force. Finally, considering the common occurrence of inputs with noise disturbance in real application, the robustness of the network is also verified for displacement and current inputs with noise disturbance, respectively. The results of the network generalization for experimental data show that the proposed NARX network is more robust and optimal than BP network.

Development and Dynamic Characterization of a Mixed Mode Magnetorheological Elastomer Isolator

Magnetorheological elastomers (MREs) are a kind of smart material, whose mechanical properties are controllable with applied magnetic field. Moreover, there is a greater magnetorheological effect for MREs at small strain amplitude, which has attracted more attention in the field of microvibration control. In this paper, an MRE isolator with shear-compression mixed mode was developed to suppress the high-frequency and microamplitude vibration of a precision-fabrication platform. To evaluate and characterize the dynamic behavior of the MRE isolator, experiments were conducted under harmonic load and different magnetic fields, respectively. Experiments showed that the resonance frequency of the MRE isolation system shifted from 45.82 (0 A) to 82.55 Hz (1.5 A). Meanwhile, the relative change in equivalent stiffness and damping was 175% and 216%, respectively, and the relative change in isolator force was 190% from 0 to 1.5 A. The proposed mixed mode MRE isolator effectively isolated vibration at high frequency for microamplitude.

Dynamic model and parameters identification of piezoelectric stack actuators

Based on the constitutive equations of piezoelectric materials, the dynamic model of the piezoelectric stack actuators is derived. Subsequently, experimental setup for the dynamic characteristics measurement is established. Parameters such as voltage-displacement coefficient, stiffness and damping constant are identified from the experimental results by the principle of piezoelectric effect and classic automatic control theory. The effectiveness of the identification results is then verified through comparing the experimental and simulation results of step response. In addition, the influences of different parameters on the dynamic characteristics of the actuators are investigated by MATLAB simulation, which provides a basis for the piezoelectric stack actuators design and selection in practical applications. Finally, the dynamic model is applied to the analysis of the hybrid vibration isolator.

Field Directional Dependences of Magnetoelectric Behaviors in Magnetostrictive/Piezoelectric Laminate Composites

The field directional dependence of magnetoelectric (ME) behaviors in rectangular-shaped Terfenol-D and Pb(Zr,Ti)O3 laminated composites are investigated. In experiments, the DC bias field is applied along either the length or width direction of the composites respectively superimposed with a parallel or vertical AC magnetic filed. It demonstrates that: 1) the ME voltage coefficients (at 1 kHz) while the AC and the DC fields are parallel are higher than that while the fields are perpendicular; 2) the ME voltage coefficients while DC field is along the oriented direction of Terfenol-D are larger than that while DC field is perpendicular to the oriented direction; 3) the phase variation of the ME voltage coefficients is also related to the field directions; 4) in the cases of AC and DC fields perpendicular to each other, the ME voltage coefficient spectra show an additional peak near the bending resonance peak.

Enhanced sensitivity in FeCuNbSiB/FeGa/PZT laminate magnetoelectric sensor with up-conversion mechanism by square wave modulation

Magnetoelectric (ME) laminate composites have emerged as promising candidates for the development of highly sensitive magnetic field sensors at resonance frequency in recent years. Unfortunately, ME coefficient decreases dramatically and the noise level increases at low frequencies far from resonance, which leads to a significant reduction in sensitivity. For the purpose of removing these drawbacks, ME laminate composites have also been employed as weak magnetic field and current sensors at low frequencies, via a sine wave modulation technique [1]-[3]. The new technique offers the possibility to achieve resonance enhanced sensitivities at low frequencies. However, the magnetic field sensitivities of these proposed ME sensors by using sine wave modulation technique are still weak at power-line frequency of 50 Hz.

A new self-tuning fuzzy controller for vibration of a flexible structure subjected to multi-frequency excitations

This work proposes a new self-tuning fuzzy controller for vibration control of a flexible structure subjected to both single-frequency and multi-frequency excitations. A piezoelectric stack actuator is used to generate control force to attenuate vibrations in the resonant and non-resonant frequency ranges. As a first step, modal frequencies and modal shapes of the flexible beam structure are obtained via the finite element method, and these are verified through comparison with the measured values. Second, in order to attenuate multi-frequency vibration of the beam, a new fuzzy controller with self-tuning factors is proposed. This controller is independent of the structure model and very adaptive to variable excitations. Then, vibration control performances of the self-tuning fuzzy controller are experimentally investigated under two different excitation conditions: single-frequency and multi-frequency excitations. It is shown that vibration control capability of the proposed controller outperforms conventional fuzzy controller under two different excitation conditions. In addition, it is demonstrated by experimentally implementing the proposed self-tuning fuzzy controller that high performances of multi-frequency vibration control are successfully achieved in which both amplitude and frequency of sinusoidal excitations are varied.

Active/semi-active hybrid isolation system with fuzzy switching controller

This article designs an active/semi-active hybrid isolator using magnetorheological elastomer isolator and piezoelectric stack actuator to suppress the wide-frequency vibration in precision platform, which can be switched to active isolator, semi-active one, and passive one according to the spectrum signature of the excitation. First, the structure of the hybrid isolator is introduced. Then, the dynamic model of the hybrid isolation system is established, the model parameters are identified, and the switching condition for the hybrid isolator is derived by experiments. Next, considering variable amplitude and frequency vibration of the isolated system, an active and semi-active fuzzy switch controller is designed for piezoelectric stack actuator and magnetorheological elastomer hybrid isolator, which are independent of the system model, self-tuning, and robust. Finally, the numerical simulations are conducted under variable frequency excitations to evaluate the performance of the designed fuzzy switch controller, and the results show that the hybrid isolator, combined with the fuzzy switch controller, can attenuate full frequency vibration effectively.