Semi-active Vibration Isolation Research Articles

New approach to semi-active vibration isolation to improve the pointing performance ofobservation satellites

A momentum-wheel installed to provide attitude-control torque actually producesundesirable force or torque disturbances owing to wheel imbalance and imperfection of theball-bearings. To improve the pointing performance of observation satellites, a vibrationisolator is used to isolate observation devices from these disturbances. This paper comparesthree types of semi-active isolators that consist of a piezoelectric material and aswitch-controlled passive circuit. Since this isolation is implemented by controlling a circuitswitch no external energy is supplied to the system, and so the system is stable even whena malfunction occurs in control. We propose a simple but effective isolation method thatneeds to know only one velocity value instead of the full state of the system. Numericalsimulations with a simple model of an observation satellite demonstrated that the proposedisolator works well to isolate an observation device from disturbances caused by themomentum-wheel, without causing any degradation in the attitude control of satellites.

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.

High-Voltage Power Supply for Semi-Active Suspension System With ER-Fluid Damper

Electrorheological (ER) fluid is a composite material sometimes applied to mechanical motion devices such as the semi-active suspension, high-speed clutch, and vibration isolator. ER fluid application needs a high-voltage power supply (HVPS) having special requirements such as sufficiently high and continuously controllable output voltage, fast dynamic performance, over-current-limiting capability, low cost, and compact size. This paper deals with the HVPS for the semi-active suspension using the ER-fluid damper. The electrical characteristics of the ER-fluid damper are analyzed and the design and implementation of the HVPS are presented. It is well demonstrated through experiments that the developed HVPS shows a satisfactory performance suitable for ER-fluid application.

112 MRダンパを用いた2自由度構造物に対するセミアクティブ免震の実験的検証(アクティブ免震・制振,OS-12:耐震・免震・制振(1))

In this paper we verify availability of semi-active vibration isolation using a large-size magneto rheological fluid (MR) damper for a two-degree-of-freedom structure. We have already proposed the design method taking account of the mechanism of a fictitious damper model to obtain the gain-scheduled controller with linear matrix inequalities for semi-active system which is classified as bi-linear system. We confirm that the proposed method has good performance in comparison with passive damping systems and other controll methods by experiments and simulations.

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.

711 ゲインスケジュールド制御による多層構造物のセミアクティブ免震

This paper proposes a design method for semi-active vibration isolation control of a structure with a semi-active damper. We formulated the linear-parameter-varying system taking account of mechanical constraints such as valve stroke of the semi-active damper and the damping coefficient restriction. The gain-scheduled control based on the linear matrix inequalities is obtained so that the closed-system is stable and has good performance. By simulations it is verified that the semi-active damper system designed is effective in comparison with either a passive damper against a non-stationary random input such as earthquakes.

211 可変減衰ダンパによる構造物制振 : 第2報(制振II)(OS 制振)

This paper describes experimental results of structural control using MR damper. First, the controller for the MR damper will be discussed. Next, device performance test results will be shown. Finally, semi-active vibration isolation controller will be applied to 3-DOF structure that supported by rubber and MR damper. Tracking control system with force feedback shows a good performance for the nonlinear controller of the MR damper. The experimental results will show that the semi-active control strategy with MR damper is fit for the sky-hook controlled vibration isolation system on broad band.

Bilinear Optimal Control Theory and its Application to Semi-Active Vibration Isolation Control.

In vibration isolation control problem, semi-active control methods in which coefficient of viscous damping or spring constant are varied effectively have been proposed and expected to realize a high performance with a little energy consumption. However, the semi-active system is classified into a bilinear system which belongs to a nonlinear system and its controller design is not easy. In this study, a bilinear optimal control theory is established by adopting the damping force in criteria function and it is applied to a semi-active base isolation problem. This study deals with 10 stories structure model corresponding to an actual building and the dynamics of an oil damper is taken into consideration by using the Maxwell model in the modelling. Moreover, the dynamics of disturbance is taken into account, and the controller is designed for the augmented bilinear system which includes both the control object and the disturbance. And the computer simulation is carried out by taking account of the delay to switch the coefficient of dampers in order to compare the performance on semi-active base isolation controls designed by the proposed method with skyhook control method and passive isolations. As a result, the usefulness of the present method was demonstrated.

Active and Semi-Active Vibration Isolation

In the five decades since the founding of the ASME Design Engineering Division, the important problem of vibration isolation has been attacked first through the design of passive spring-damper suspensions and later by the use of active and semi-active elements. This paper reviews the historical development of theoretical concepts necessary for the design of isolation systems and indicates how control theory began to influence vibration isolation in the last half of this period. Practical active and semi-active suspensions have only recently become possible with the advent of powerful but relatively inexpensive signal processors. To illustrate these developments for engineers who have not been intimately involved with active systems, only simple vibrational system models will be discussed, although some modern hardware will be shown which is now being applied to complex systems. Instead of attempting to review the many theoretical concepts which have been proposed for active systems, this article will focus on a relatively simple idea with which the author has been associated over the past thirty years; namely the “skyhook” damper. This idea came through purely theoretical studies but is now used in combination with other concepts in production suspension systems. Two quite different application areas will be discussed. The first involves stable platforms to provide extreme isolation for delicate manufacturing operations against seismic inputs and the second involves automotive suspensions. Although similar concepts are found in these two application areas, the widely varying requirements result in very different suspension hardware. The special case of the semi-active damper, which requires very little control power and is presently reaching production, will also be discussed.

Active and Semi-Active Vibration Isolation

In the five decades since the founding of the ASME Design Engineering Division, the important problem of vibration isolation has been attacked first through the design of passive spring-damper suspensions and later by the use of active and semi-active elements. This paper reviews the historical development of theoretical concepts necessary for the design of isolation systems and indicates how control theory began to influence vibration isolation in the last half of this period. Practical active and semi-active suspensions have only recently become possible with the advent of powerful but relatively inexpensive signal processors. To illustrate these developments for engineers who have not been intimately involved with active systems, only simple vibrational system models will be discussed, although some modern hardware will be shown which is now being applied to complex systems. Instead of attempting to review the many theoretical concepts which have been proposed for active systems, this article will focus on a relatively simple idea with which the author has been associated over the past thirty years; namely the “skyhook” damper. This idea came through purely theoretical studies but is now used in combination with other concepts in production suspension systems. Two quite different application areas will be discussed. The first involves stable platforms to provide extreme isolation for delicate manufacturing operations against seismic inputs and the second involves automotive suspensions. Although similar concepts are found in these two application areas, the widely varying requirements result in very different suspension hardware. The special case of the semi-active damper, which requires very little control power and is presently reaching production, will also be discussed.

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.