Semi-active Vibration Isolation System Research Articles

Design and control of helicopter main reducer semi-active vibration isolation system based on MR damper

In order to effectively reduce the vibration of the helicopter rotor transmitted from the main reducer to the fuselage, a semi-active vibration isolation system (SAVIS) with a magnetorheological (MR) damper was proposed and effective control strategies were designed. Firstly, the structural scheme and working principle of helicopter main reducer SAVIS were proposed. Secondly, the mechanical properties of the MR damper were tested, and the dynamic model of the MR damper was established based on the hyperbolic tangent model. In addition, the model errors of MR damper were analyzed and quantified. Thirdly, according to the design requirements and parameters of a helicopter, the structural parameters of SAVIS were designed. Then, the virtual prototype of helicopter main reducer SAVIS was established by using 3D drawing software and ADAMS software, and the vibration characteristics of three directions were analyzed. Finally, two controllers of equivalent skyhook and continuous skyhook were designed. The numerical analysis results indicate that compared with passive vibration isolation and equivalent skyhook controller, the continuous skyhook controller has the best vibration isolation performance and disturbance resistance, which can effectively reduce the vibration transmitted from helicopter rotor to fuselage.

Analysis and design of a semi-active X-structured vibration isolator with magnetorheological elastomers

This paper proposes a semi-active X-shaped vibration isolation (XSVI) system with magnetorheological elastomer (MRE) based on its field-controlled variable properties. The conceptual design of the proposed system is constructed by embedding an MRE-based device into a X-shaped structure, instead of the original XSVI’s linear spring. The proposed system could fulfill tuning capability stiffness for effective vibration mitigation in random low-frequency excitations. The theoretical modeling is developed and the static analysis of the proposed MRE-based XSVI system is studied. The dynamic equation of proposed isolation system is established and solved by harmonic balance method. The influence of key geometrical parameters and field strength on the proposed system characteristics are detailly studied and discussed, and the tunable frequency-shift properties are presented. Under the harmonic excitations in a single frequency, the displacement of the isolated objective can be reduced by 22.5% with the field strength of 0.7 T. In the presence of double-tone (2 Hz mixed with 5 Hz) external loading, the reduction ratio of excited and isolated objectives’ displacements by semi-active control are respectively 63.95% and 18.77% by comparing the passive-off state. Additionally, compared with the original XSVI system and MRE isolator, the proposed MRE-based XSVI system in semi-active controller presents outstanding isolation performances. This study indicates that the proposed MRE-based XSVI system could provide a potential method for vibration isolation tuning in wide-band low-frequency range.

Control and experimental study of 6-DOF vibration isolation platform with magnetorheological damper

Vibration is an inevitable excitation in the operation of the mechanical system, which reduces its reliability and service life. Therefore, a heavy-duty 6-DOF semi-active vibration isolation system (VIS) with magnetorheological (MR) damper was proposed in this paper. Firstly, A MR damper with large output force of 27 kN was designed. The properties test results showed that the dynamic range (the adjustable multiple of damping force) of the damper is as high as 15, which has excellent dynamic performance. And a Bouc-Wen model which can accurately describe the mechanical behavior of the MR damper was established. Secondly, the prototype of the MR 6-DOF vibration isolation platform (VIP) with cubic structure was developed. Thirdly, a on-off semi-active control strategy was proposed for the MR 6-DOF VIP. The numerical simulation results showed that the semi-active VIS can effectively isolate vibration in the working frequency domain. Finally, the vibration experiment on shaking table was carried out. The test results showed that the designed heavy-duty MR 6-DOF semi-active VIP can control the load's attitude in real-time according to the system state. Compared with the current of 0 A, the vibration isolation effect of the on-off control is improved by 63.27% in the resonance region. The MR 6-DOF VIP can effectively reduce the vibration transmitted to the isolated system through the platform.

An adjustable anti-resonance frequency controller for a dual-stage actuation semi-active vibration isolation system

An adjustable anti-resonance frequency controller for a dual-stage actuation semi-active vibration isolation system

Optimal Control of Semiactive Two-Stage Vibration Isolation Systems for Marine Engines

To improve the vibration reduction performance of two-stage vibration isolation systems for marine engines under wide frequency band and multifrequency excitation, the magnetorheological (MR) damper is introduced into the vibration isolation system and an optimal controller is designed. Taking the test results of MR damper dynamic characteristics as sample data, the forward and inverse models of the MR damper are identified by the least square method and neural network (NN) method respectively, and the identification results are applied to semiactive control of the two-stage isolation system. Based on the analysis of vibration source, a six-degree-of-freedom mechanical model of two-stage system based on the MR damper is established. The optimal controller taking the minimum force transmitted from the engine to base as the control objective is designed. The system model and numerical simulation analysis are established using MATLAB. The results show that the isolation effect of optimal control is better than that of passive vibration isolation in the whole frequency band. In addition, good control effect is achieved in the low-frequency resonance region which is most concerned in engineering, which is of great significance to further improve the vibration reduction performance of marine engines.

Design and Research of Semiactive Quasi-Zero Stiffness Vibration Isolation System for Vehicles

The vehicle-mounted equipment is easy to be disturbed by external vibration excitations during transportation, which is harmful to the measurement accuracy and performance of the equipment. Aiming at the vibration isolation of the vehicle-mounted equipment, a semiactively controlled quasi-zero stiffness (QZS) vibration isolator with positive and negative stiffness is proposed. The vertical spring is paralleled with a magnetorheological (MR) damper, and the semiactive on-off control scheme is adopted to control the vibration. The analytical expression of the isolator’s displacement transmissibility is derived via the averaging method. Then, the vibration isolation performance under different road excitations and different driving speeds is simulated and compared with the uncontrolled passive QZS vibration isolator. In addition, the mechanical structure of the semiactive QZS isolator is designed and manufactured, and the test system is built by LabVIEW software and PXI embedded system. The isolation effect of the semiactive QZS isolator is verified through test data. It is found that the proposed semiactive QZS isolator shows excellent vibration isolation performance under various road excitations, while the passive QZS isolator is effective only under harmonic excitations. The vertical acceleration of vehicle-mounted device can be decreased over 70% after isolation, and the vibration isolation effect is remarkable. The design idea and research results of the semiactive QZS isolator may provide theoretical guidance and engineering reference for vibration isolation.

DYNAMICAL ANALYSIS ON A KIND OF SEMI-ACTIVE VIBRATION ISOLATION SYSTEMS WITH DAMPING CONTROL 1)

A series of single-degree-of-freedom semi-active nonlinear vibration isolation system with cubic stiffness based on relative velocity feedback on-off control is studied. By using the averaging method, the approximate analytical solutions of the primary resonance of the system are obtained, which is controlled by the acceleration and relative velocity based acceleration drive damping control, the velocity and relative velocity based sky-hook damping control, and the displacement and relative velocity based ground-hook damping control, respectively. A further comparison between the numerical solutions and the approximate analytical solutions under different control strategies is fulfilled. And such comparison results suggest that the approximate analytical results are quite consistent with the numerical solutions, which verifies the effectiveness of the approximate analytical solutions. Moreover, the stability conditions of the steady-state solution of the system under different control strategies are analyzed by Lyapunov theory, and the influences of system parameters on the control effect are discussed. In order to compare the control performances in the three different control approaches, the amplitude-frequency response equation is conducted. The results show that the similar expressions can be found in the switching conditions in the process of the analytical analysis of the three relative velocity feedback control strategies. In the aspect of suppressing resonance response amplitude, the sky-hook damping control strategy based on velocity and relative velocity feedback has the best damping effect in low frequency band, while the acceleration drive damping control strategy based on acceleration and relative velocity feedback has the best damping effect in high frequency band. The sky-hook damping control strategy also shows good performance in reducing the amplitude response of transient response. This analytical research method can also be applied to the system with other semi-active on-off control strategies, and it provides an effective way for the control strategy research of semi-active vibration isolation system.

Modeling and controlling a semi-active nonlinear single-stage vibration isolator using intelligent inverse model of an MR damper

Semi-active systems with variable stiffness and damping have demonstrated excellent performance. The aim of this study is to investigate the new configuration of a semi-active single-stage nonlinear vibration isolation system with a Magneto-Rheological (MR) damper to reduce the magnitude of force transmissibility over the both resonant and non-resonant regions. The magnitude of force transmissibility is widely used to performance measurement for the isolation system. In current study, to achieve this reduction, two horizontal springs and one MR damper were added to the isolator. Theoretical analysis reveals that the nonlinear system with MR damper can produce ideal vibration isolation. However, due to the nonlinear characteristics behavior of the MR damper, conventional control algorithms to reach the desired are cumbersome. To address this issue, an artificial intelligent strategy using wavelet network and fuzzy logic controller is considered to be constructed to copy the inverse dynamics of the MR damper and the nonlinear isolator. Accordingly, simulation results demonstrated that the intelligent algorithm has acceptable performance.

Research on semi-active vibration isolation system based on electromagnetic spring

This paper proposes a semi-active variable stiffness vibration isolation system based on electromagnetic spring for the low-frequency vibration isolation of mass-varying objects. It is achieved by four straight leaf springs in parallel to an electromagnetic spring system composed of a single electromagnet and a permanent magnet. The equivalent magnetic circuit method is used to compute electromagnetic force of the electromagnetic spring system, and mathematical model of the semi-active vibration isolation system is established according to Maxwell's equations. The nonlinear mathematical model is linearized at the equilibrium point by using the Taylor series expansion theorem to establish linear state-space representation of the system, and then using the traditional PID control method, a double closed-loop feedback control system of the inner current loop and outer location loop is designed. By controlling the current in the coil, the equivalent stiffness and electromagnetic force of the system are variable to achieve semi-active control. Furthermore, the control block diagram of the semi-active vibration isolation system is built based on Simulink software, then make a simulation analysis to the vibration isolation performance of the system and compare the effects of vibration isolation with inner current loop control and without inner current loop control, respectively. Finally, the experiments prove the correctness of the theory. It concludes that this semi-active vibration isolation system is a vibration isolation system with broad application prospects, which has fast current response, high vibration isolation efficiency, and an excellent vibration isolation effect for the low-frequency disturbance of mass-varying objects.

Study on a new self-sensing magnetorheological elastomer bearing

The complexity of a semi-active vibration isolation system results in the difficulty of realizing its role on impact load effectively. Thus, a new self-sensing bearing based on modified anisotropic magnetorheological elastomer (MRE) is proposed in this study. This self-sensing bearing was fabricated by dispersed multi-walled carbon nanotubes and carbonyl iron particles into polydimethylsiloxane matrix under a magnetic field. The working conditions of the bearing were analyzed and decoupled. An optimal structure size of the bearing was selected and used for setting up the experiment test system. The self-sensing characteristic of the MRE bearing under the multi-field coupling of load and magnetic fields was then investigated by this test system. Results showed that the resistance of the modified MRE, in which a preload was applied by the bearing, could change approximately 28%–56% under extrusion force, mechanical force, and external magnetic field. The vibration isolation performance was tested based on the self-sensing characteristic. The bearing had excellent mechanical properties, which could reduce at least 30% of vibration. Thus, the modified MRE of the magnetorheological elastomer bearing could be simultaneously used as an actuator and a sensor.

Prediction of the vibration characteristics for wheeled tractor with suspended driver seat including air spring and MR damper

It’s essential to establish a dynamic model of a wheeled tractor with suspended driver seat including air spring and Magnetorheological (MR) damper to analyze its vibration characteristics and performance. The equivalent linearized model of the wheeled tractor always neglects the effect of nonlinear stiffness for scissors linkage driver seat and air spring with auxiliary chamber as well as dynamic characteristics of real tractor tyre and considers the driver seat as linear spring and damper elements, which causes the analysis to have a lower precision. We considered the effect of nonlinear stiffness for scissors linkage seat and air spring with auxiliary chamber as well as MR damper and dynamic characteristics of real tyre and developed a complete nonlinear dynamic model of wheeled tractor with suspended driver seat including air spring and MR damper. The experimental results demonstrate that the improved nonlinear dynamic model is more consistent with the actual state than the equivalent linearized model, and the validity of the proposed model is verified. Furthermore, the effect of forward speed, ratio of volume for air spring with respect to volume of auxiliary chamber, and area of orifice on the acceleration of wheeled tractor was also investigated, which can provide a theoretical basis for control algorithm design of semiactive vibration isolation system.

Non-linear dynamic analysis of double-layer semi-active vibration isolation systems using revised Bingham model

In this work, a revised Bingham model for magneto-rheological damper is used to investigate the primary resonance reduction in the double-layer semi-active isolation system of marine auxiliary machinery. An analytical solution for the auxiliary double-layer semi-active isolation system’s primary resonance is obtained with an averaging method, and this is verified numerically using the Maple software. The effect of model parameters of magneto-rheological damper on the system’s vibration transmissibility is studied. The research results show that the damping of magneto-rheological damper and the control force have a significant effect on the vibration transmissibility in the resonance region. The vibration transmissibility of the double-layer semi-active isolation system decreases with increase in damping of the magneto-rheological damper and control force. Yet the zero force velocity contributes very little to changes in vibration transmissibility.

Active and Semi Active Vibration Isolation Systems Based on Magnetorheological Materials

The paper presents active vibration isolation systems based on “smart” materials. Very promising “smart” materials are MR elastomers. Devices based on them have the ability to work in all vibration isolation modes (passive, semi-active and active mode). In this work we consider a construction of a damper based on the MR elastomer and the experimental research results of the damper in semi-active vibration isolation mode.

Fuzzy control of a semi-active multiple degree-of-freedom vibration isolation system

Semi-active isolation systems fill the gap between passive and active systems, delivering the versatility and adaptability of fully active systems, by expending a small amount of energy to change system parameters such as stiffness and damping. Magnetic suspension vibration isolation provides an excellent active isolation technology, and has shown useful characteristics including noncontact isolation, fast response, high reliability and long lifespan. However, because it is highly nonlinear and time variant, the control of magnetic suspension vibration isolation is an area that still requires further exploration. This paper presents a fuzzy control algorithm for a semi-active multi-degree-of-freedom vibration system. The fuzzy control is based on the minimization of the weighted sum of squared output forces. The output force response of the fuzzy, PID control semi-active vibration isolation system and passive system under the same excitation are simulated. The simulation results show that the fuzzy control system has much better performance in vibration isolation. An experimental platform is developed to test the performance of the magnetic suspension vibration isolation system and the proposed fuzzy control algorithm. The experimental results are found to be in good agreement with simulation.

Optimal controller for vibration isolation system with controlled hydraulic damper by piezoelectric stack

Piezoelectric stacks are increasingly applicable in various branches of engineering. Their work is based upon the inverse piezoelectric effect. Piezoelectric stacks are characterised by very good dynamic properties. In the presented paper a piezoelectric stack was used as an element in an operating hydraulic damper. The efficiency of a hydraulic damper was tested in a semi-active vibration isolation system. A mathematical model of a vibration isolation system with a hydraulic damper was presented. In the model it was taken into account that there is a non-linear relationship between force and velocity occurring in a hydraulic damper. Based upon the mathematical model, the synthesis of an optimum controller for vibration isolation system was carried out, taking into account the harmonic character of dependence of excitation signal from the road. Results of the simulated numeric experiments for the vibration isolation system with an optimum controller were presented.

Semi-active vibration isolation system with variable stiffness and damping control

Semi-active systems with variable stiffness and damping have demonstrated excellent performance. However, conventional devices for controlling variable stiffness are complicated and difficult to implement in most applications. To address this issue, a new configuration using two controllable dampers and two constant springs is proposed. This paper presents theoretical and experimental analyses of the proposed system. A Voigt element and a spring in series are used to control the system stiffness. The Voigt element is comprised of a controllable damper and a constant spring. The equivalent stiffness of the whole system is changed by controlling the damper in the Voigt element, and the second damper which is parallel with the other elements provides variable damping for the system. The proposed system is experimentally implemented using two magnetorheological fluid dampers for the controllable dampers. Eight different control schemes involving soft suspension, stiff suspensions with low and high damping, damping on–off (soft and stiff), stiffness on–off (low and high), and damping and stiffness on–off control are explored. The time and frequency responses of the system to sinusoidal, impulse and random excitations show that variable stiffness and damping control can be realized by the proposed system. The system with damping and stiffness on–off control provides excellent vibration isolation for a broad range of excitations.

Guidelines for low-transmissibility semi-active vibration isolation

The vibration transmissibility of passive vibration isolation systems is designed to be lowin the expected frequency range of the disturbances but is significantly higherat lower frequencies. The goal of semi-active damping systems is to reduce theisolation system transmissibility in the low-frequency range, without sacrificingperformance at high frequencies, by controlling the stiffness and damping propertiesof the isolation system via feedback measurements. In this study, experimentalimplementation of a semi-active damping system in a very small scale lightlydamped structure combines electrorheological (ER) fluids with a nonlinear analogfeedback circuit. Detailed modeling of the experiments enables the estimation ofunmeasurable internal forces in the ER damping wall, which, in turn, providesinsight into desirable stiffness and damping characteristics of semi-active dampingsystems. The guidance provided by these experiments is applied to the analysis anddesign of semi-active visco-elastic vibration isolation systems. The benefits of thecontrollable damping and controllable stiffness effects are compared in the frequencydomain through transfer function estimates computed from simulated response towide-band disturbances. Frequency response analysis of these numerical modelsfor different levels of isolation level stiffness, device stiffness, maximum devicedamping, and minimum device damping are presented to provide guidelines forthe design of low-transmissibility semi-active damping systems. The coupling ofcontrol experiments with numerical modeling illustrates that controllable dampingoffers more effective vibration isolation of base-excited structural systems andminimum device damping is the most dominant factor that controls the accelerationtransmissibility.

Signal frequency-based semi-active fuzzy control for two-stage vibration isolation system

In this paper, a novel feed forward control scheme with a fuzzy controller, based on the identification of the signal's main frequency, is proposed to control a semi-active two-stage vibration isolation system such as the floating raft isolation system, whose excitation signal changes regularly. A fuzzy controller is employed in this method to achieve the best isolation effect by analyzing the main frequency's characteristics of the excitation signal, such as amplitude and position, and a bypass electro-rheological (ER) damper is applied to achieve the best control effect more rapidly and accurately. The inputs of the fuzzy controller are the characters of the signal's main frequency and the output is the effect coefficient of the main frequency. Then, the optimal damping ratio of the ER damper and the appropriate voltage could be obtained. The experimental results indicate that the proposed feed forward control method is more effective in vibration isolation in comparison with the passive optimal system.

On invariant points and their influence on active vibration isolation

The performance of vibration isolation mounts in reducing transmission of vibrations from a machine to the large structure on which the machine is mounted is considered. The trade-offs between relative displacement, machine acceleration and structure acceleration that limit the performance of passive isolation systems are well known. Active isolation systems are also shown to suffer from some fundamental performance limitations due to the presence of invariant points. Two standard configurations––disturbance input being a force and disturbance input being a displacement––are considered. In each case, the presence of invariant points in the relative deflection and acceleration transfer functions limits the performance that can be obtained. In the case of the standard force disturbance configuration, an invariant point is shown to occur at the structural resonant frequency. In the case of the displacement disturbance input, the invariant points do not coincide with any resonant frequency and therefore good broadband performance can be obtained. An active control law that optimizes a quadratic performance index is obtained for this case. A semi-active version of the control law is implemented on a vibration test rig using a magneto-rheological fluid damper as an actuator. Experimental results confirm the predicted performance characteristics of the semi-active vibration isolation system.

Suboptimal stochastic control for semi-active vibration isolation systems

This paper describes a study of a semi-active vibration isolation system including dry-friction. A semi-active isolation system uses active dampers. The concept of 'active damper' gives rise to a control problem in that the control acts on some multiplicative parameters of the system. The main goal of this work is to find effective semi-active laws for a given performance index. The proposed procedure consists of selecting the semi-active law so that the active damper generates a given active force as long as it is dissipative. This active force is obtained from the study of performances of the associated fully active linear system under different assumptions on the feedbacks available. As an example, the suspension of a truck cab is presented.