Dynamic analysis of a novel multilink-spring mechanism for vibration isolation and energy harvesting

Due to technical limitations,existing vibration isolation and energy harvesting(VIEH)devices have poor performance at low frequency.This paper proposes a new multilink-spring mechanism(MLSM)that can be used to solve this problem.The VIEH performance of the MLSM under harmonic excitation and Gaussian white noise was analyzed.It was found that the MLSM has good vibration isolation performance for low-frequency isolation and the frequency band can be widened by adjusting parameters to achieve a higher energy harvesting power.By comparison with two special cases,the results show that the MLSM is basically the same as the other two oscillators in terms of vibration isolation but has better energy harvesting performance under multistable characteristics.The MLSM is expected to reduce the impact of vibration on high-precision sensitive equipment in some special sites such as subways and mines,and at the same time supply power to structural health monitoring devices.

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

In the semiconductor manufacturing industry,the dynamic model of a controlled object is usually obtained from a frequency sweeping method before motion control.However,the existing isolators cannot properly isolate the disturbance of the inertial force on the platform base during frequency sweeping(the frequency is between 0 Hz and the natural frequency).In this paper,an adjustable anti-resonance frequency controller for a dual-stage actuation semi-active vibration isolation system(DSASAVIS)is proposed.This system has a significant anti-resonance characteristic;that is,the vibration amplitude can drop to nearly zero at a particular frequency,which is called the anti-resonance frequency.The proposed controller is designed to add an adjustable anti-resonance frequency to fully use this unique anti-resonance characteristic.Experimental results show that the closed-loop transmissibility is less than−15 dB from 0 Hz to the initial anti-resonance frequency.Furthermore,it is less than−30 dB around an added anti-resonance frequency which can be adjusted from 0 Hz to the initial anti-resonance frequency by changing the parameters of the proposed controller.With the proposed controller,the disturbance amplitude of the payload decays from 4 to 0.5 mm/s with a reduction of 87.5%for the impulse disturbance applied to the platform base.Simultaneously,the system can adjust the anti-resonance frequency point in real time by tracking the frequency sweeping disturbances,and a good vibration isolation performance is achieved.This indicates that the DSA-SAVIS and the proposed controller can be applied in the guarantee of an ultra-low vibration environment,especially at frequency sweeping in the semiconductor manufacturing industry.

Uncertainty in the seismic performance of semi-active base isolation systems

In a conventional base isolation system,minimizing the seismic responses of the superstructure is always at the cost of increasing the isolator's response.The semi-active control of the isolator has been considered an effective solution to such a dilemma.It tunes the real-time properties of the isolator according to preset rules to further reduce the superstructure's seismic responses without increasing that of the isolator or vice versa.However,the number of ground motion records used to design and validate the controller,i.e.,the preset rules,in existing studies is usually very small and therefore is suspectable if it is adequate to address the significant uncertainty in the shaking of future earthquakes.This paper critically reviews the performance of the proportional-integralderivative(PID),linear-quadratic regulator(LQR),and fuzzy controllers in semi-active base isolation systems with magnetorheological(MR)dampers subjected to highly uncertain ground motion inputs through numerical simulations.The results show that the control performance of the controllers varies significantly with the increasing number of input records,suggesting the necessity of using at least 50 ground motion records to appropriately assess the performance uncertainty of semi-active base isolation systems.More importantly,the superior performance of the optimized controllers is not guaranteed if the system is subjected to ground motions that are new to the controller,even if the controller has been optimized for thousands of existing ground motions.It highlights the need of improving the adaptability of the semi-active systems for uncertain ground motion inputs.

A Closed-Loop Dynamic Controller for Active Vibration Isolation Working on A Parallel Wheel-Legged Robot

Serving the Stewart mechanism as a wheel-legged structure,the most outstanding superiority of the proposed wheel-legged hybrid robot(WLHR)is the active vibration isolation function during rolling on rugged terrain.However,it is difficult to obtain its precise dynamic model,because of the nonlinearity and uncertainty of the heavy robot.This paper presents a dynamic control framework with a decentralized structure for single wheel-leg,position tracking based on model predictive control(MPC)and adaptive impedance module from inside to outside.Through the Newton-Euler dynamic model of the Stewart mechanism,the controller first creates a predictive model by combining Newton-Raphson iteration of forward kinematic and inverse kinematic calculation of Stewart.The actuating force naturally enables each strut to stretch and retract,thereby realizing six degrees-of-freedom(6-DOFs)position-tracking for Stewart wheel-leg.The adaptive impedance control in the outermost loop adjusts environmental impedance parameters by current position and force feedback of wheel-leg along Z-axis.This adjustment allows the robot to adequately control the desired support force tracking,isolating the robot body from vibration that is generated from unknown terrain.The availability of the proposed control methodology on a physical prototype is demonstrated by tracking a Bezier curve and active vibration isolation while the robot is rolling on decelerate strips.By comparing the proportional and integral(PI)and constant impedance controllers,better performance of the proposed algorithm was operated and evaluated through displacement and force sensors internally-installed in each cylinder,as well as an inertial measurement unit(IMU)mounted on the robot body.The proposed algorithm structure significantly enhances the control accuracy and vibration isolation capacity of parallel wheel-legged robot.

Vibration Isolation Characteristics of Impedance-balanced Ship Equipment Foundation under Unbalanced Excitation

A new type of impedance-balanced ship equipment foundation structure based on the principle of impedance balancing using a“discontinuous panel-vibration isolation liquid layer-foundation structure”is proposed to solve the problem of poor low-frequency vibration isolation of the foundation under unbalanced excitation of shipboard equipment.Based on the finite element method,the influence of characteristic parameters of the foundation panel structure on its vibration reduction characteristics under unbalanced excitation is explored.The results show that the vibration isolation level of the impedance-balanced foundation is 10 dB higher than the traditional foundation in the low-frequency band of 10-500 Hz when subjected to combined excitation of concentrated force and moment.Increasing the thickness of the impedance-balanced foundation panel can enhance the isolation effect.Increasing the number of sub-panels can effectively reduce the vibration response of the foundation panel and enhance the isolation performance of the foundation.The connection stiffness between sub-panels has a small effect on the isolation performance of the foundation.

Seismic control of multi-degrees-of-freedom structures by vertical mass isolation method using MR dampers

Vertical mass isolation(VMI)is one of the novel methods for the seismic control of structures.In this method,the entire structure is assumed to consist of two mass and stiffness subsystems,and an isolated layer is located among them.In this study,the magnetorheological damper in three modes:passive-off,passive-on,and semi-active mode with variable voltage between zero and 9 volts was used as an isolated layer between two subsystems.Multi-degrees-of-freedom structures with 5,10,and 15 floors in two dimensions were examined under 11 pairs of near field earthquakes.On each level,the displacement of MR dampers was taken into account.The responses of maximum displacement,maximum inter-story drift,and maximum base shear in controlled and uncontrolled buildings were compared to assess the suggested approach for seismic control of the structures.According to the results,the semi-active control method can reduce the response by more than 12%compared to the uncontrolled mode in terms of maximum displacement of the mass subsystem of the structures.This method can reduce more than 16%and 20%of the responses compared to the uncontrolled mode in terms of maximum inter-story drift and base shear of the structure,respectively.

A bio-inspired spider-like structure isolator for low-frequency vibration

This paper proposes a quasi-zero stiffness(QZS)isolator composed of a curved beam(as spider foot)and a linear spring(as spider muscle)inspired by the precise capturing ability of spiders in vibrating environments.The curved beam is simplified as an inclined horizontal spring,and a static analysis is carried out to explore the effects of different structural parameters on the stiffness performance of the QZS isolator.The finite element simulation analysis verifies that the QZS isolator can significantly reduce the first-order natural frequency under the load in the QZS region.The harmonic balance method(HBM)is used to explore the effects of the excitation amplitude,damping ratio,and stiffness coefficient on the system’s amplitude-frequency response and transmissibility performance,and the accuracy of the analytical results is verified by the fourth-order Runge-Kutta integral method(RK-4).The experimental data of the QZS isolator prototype are fitted to a ninth-degree polynomial,and the RK-4 can theoretically predict the experimental results.The experimental results show that the QZS isolator has a lower initial isolation frequency and a wider isolation frequency bandwidth than the equivalent linear isolator.The frequency sweep test of prototypes with different harmonic excitation amplitudes shows that the initial isolation frequency of the QZS isolator is 3 Hz,and it can isolate 90%of the excitation signal at 7 Hz.The proposed biomimetic spider-like QZS isolator has high application prospects and can provide a reference for optimizing low-frequency or ultra-low-frequency isolators.

Active Low-frequency Vertical Vibration Isolation System for Precision Measurements

Low-fi＇equency vertical vibration isolation systems play important roles in precision measurements to reduce seismic and environmental vibration noise. Several types of active vibration isolation systems have been developed. However, few researches focus on how to optimize the test mass install position in order to improve the vibration transmissibility. An active low-frequency vertical vibration isolation system based on an earlier instrument, the Super Spring, is designed and implemented. The system, which is simple and compact, consists of two stages： a parallelogram-shaped linkage to ensure vertical motion, and a simple spring-mass system. The theoretical analysis of the vibration isolation system is presented, including terms erroneously ignored before. By carefully choosing the mechanical parameters according to the above analysis and using feedback control, the resonance frequency of the system is reduced from 2.3 to 0.03 Hz, a reduction by a factor of more than 75. The vibration isolation system is installed as an inertial reference in an absolute gravimeter, where it improved the scatter of the absolute gravity values by a factor of 5. The experimental results verifies the improved performance of the isolation system, making it particularly suitable for precision experiments. The improved vertical vibration isolation system can be used as a prototype for designing high-performance active vertical isolation systems. An improved theoretical model of this active vibration isolation system with beam-pivot configuration is proposed, providing fundamental guidelines for vibration isolator design and assembling.

Self-synchronization theory of dual motor driven vibration system with two-stage vibration isolation frame

This paper studies self-synchronization and stability of a dual-motor driven vibration system with a two-stage vibration isolation frame. Oscillation amplitude of the material box large enough can be ensured on the vibration system in order to screen materials. Reduction of the dynamic load transmitted to the foundation can also be achieved for the vibration system. A Lagrange equation is used to set up the motion differential equations of the system, and a dimensionless coupled equation of the eccentric rotors is obtained using a method of modified average small parameter. According to the existence condition of zero solution in the dimensionless coupled equation of the eccentric rotors, the precondition for commencing self-synchronization motion is achieved.The stability condition of self-synchronization is obtained based on the Routh-Hurwitz criterion. The theoretical analysis is validated by simulations and experiments.

Research and application on three-dimensional seismic and vibration isolation for building

This paper presents the study of a three-dimensional(3D) isolation system.Firstly,the authors investigated the effects of an innovative 3D isolator,which was composed of a connecting plate,a rubber pad for vibration isolation in the vertical direction and a horizontal rubber bearing for seismic isolation in both horizontal directions.Secondly,the authors designed such a vibration isolation system and installed it underneath two specific residential buildings which were built directly over an existing subway communication hub platform in Beijing.These buildings required good performance vibration and seismic isolation system to reduce the impact from the running of nearby subway trains.Finally,in situ tests were conducted for both the isolated and the non-isolated buildings for the purpose of comparison.The test results showed that the maximum acceleration response level of the isolated superstructure is reduced by 10% as compared to that of the platform.The maximum attenuation of vibration reaches up to 25 dB.The 3D system explored in this paper is very effective in control and suppression of building vibration induced by earthquakes or running of trains.

Semi-Active Control of Wave-Induced Vibration for Offshore Platforms by Use of MR Damper

The objective of the present research is to examine the effectiveness of the lateral vibration control of wave-excited response of offshore platforms with magneto-rheological (MR) damper. In this study, the offshore platform is simplified to be a singled degree-of-freedom (SDOF) system by extracting the first vibration mode of the structure. The external 'generalized' wave force is determined with a white noise via a designed filter. A semi-active control method based on optimal control theory is proposed considering that the yield stress of the MR damper can he varied continuously within a certain range. The dynamics of SDOF structure coupled with the MR damper is investigated. Numerical simulation demonstrates that the MR damper with this control strategy can significantly reduce the maximum responses and the root-mean-square (RMS) values.

Active Vibration Isolation of Micro-Manufacturing Platform Based on Neural Network

The micromation and precision of the Micro-Electromechanical System demand that its manufacturing, measuring and assembling must work in a micro-manufacturing platform with good ability to isolate vibrations. This paper develops a vibration isolation system of micro-manufacturing platform. The brains of many kinds of birds can isolate vibrations well, such as woodpecker’s brain. When a woodpecker pecks the wood at the speed as 1.6 times as the velocity of sound, its brain will tolerate the wallop 1 500 times of the weight of itself without any damage. The isolation mechanics and organic texture of woodpecker’s brain that has good isolation characteristics were studied. A structure model of vibration isolation system for the micro-manufacturing platform is established based on the bionics of the bird’s brain vibration isolation mechanism. In order to isolate effectively the high frequency vibrations from the ground, a rubber layer is used to isolate vibrations passively between the micro-manufacturing platform’s pedestal and the ground. This layer corresponds to the cartilage and muscles in the outer meninges of the bird’s brain. The active vibration isolation technique is adopted to isolate vibrations between the micro-manufacturing platform and the pedestal. Air springs are used as elastic components, which correspond to the interspaces between the outer meninges and the encephala of the bird’s brain. Actuators are made of giant magnetostrictive material, and it corresponds to the nerves and neural muscles linking the meninges and the encephala. The actuators and air springs are arranged vertically in parallel to make use of the giant magnetostrictive actuators effectively. The air springs support almost all weight of the micro-manufacturing platform and the giant magnetostrictive actuators support almost no weight. In order to realize high performance to isolate complex micro-vibration, the control method using a three-layer neural network is presented. This vibration control system takes into account the floor disturbance and the direct disturbance acting on the micro-manufacturing platform. The absolute acceleration of the micro-manufacturing platform is used as the performance index of vibration control. The performance of the control system is tested by numerical simulation. Simulation results show that the active vibration isolation system has good isolation performance against the floor disturbance and the direct disturbance acting on the micro-manufacturing platform in all the frequency range.

Vibration Control of a Composite Beam Using Self-sensing Semi-active Approach

Structural vibration control was an active research area for the past twenty years because of their potential applications in aerospace structures,civil structures,naval structures,etc.Semi-active vibration control methods based on piezoelectric actuators and synchronized switch damping on inductance（SSDI） techniques attract the attention of many researchers recently due to their advantages over passive and active methods.In the SSDI method,a switch shunt circuit is connected to the piezoelectric patch to shift the phase and amplify the magnitude of the voltage on the piezoelectric patch.The most important issue in SSDI method is to control the switching actions synchronously with the maximum vibration displacement or maximum strain.Hence,usually a displacement sensor is used to measure the vibration displacement or a collocated piezoelectric sensor is needed to measure the strain of the structure near the piezoelectric actuator.A self-sensing SSDI approach is proposed and applied to the vibration control of a composite beam,which avoids using a separate sensor.In the self-sensing technique,the same piezoelectric element functions as both a sensor and an actuator so that the total number of required piezoelectric elements can be reduced.One problem in the self-sensing actuator,which is the same as that in the traditional collocated piezoelectric sensors,is the noise generated in the sensor signal by the impact of voltage inversion,which may cause extra switching actions and deteriorate control performance.In order to prevent the shunt circuit from over-frequent on-and-off actions,a simple switch control algorithm is proposed.The results of control experiments show that the self-sensing SSDI approach combined with the improved switch control algorithm can effectively suppress over-frequent switching actions and gives good control performance by reducing the vibration amplitude by 45%,about 50% improvement from the traditional SSDI with a separate piezoelectric element and a classical switch.

Dynamic Analysis and Decoupling Control of Octo-pneumatic Actuator Vibration Isolation Platform

Control of a six-DOF vibration isolation platform is generally difficult which is due to the strong coupling among its input and output channels. The dynamic behavior and decoupling approach of a six-DOF vibration isolation platform with eight pneumatic actuators are investigated. Owing to the symmetric configuration design of the platform, the coupling among different channels is greatly weakened. When the payload＇s principal axes of inertia parallel to the platform＇s axes of symmetry and the payload＇s center of mass is at the extension line of the platform＇s central axis, the motion can be decomposed into two independent single-input single-output channels and two independent two-input two-output subsystems. The second-order subsystems are decoupled further with the simultaneous matrix diagonalization. Thus a decoupling control strategy is developed. Effectiveness of the decoupling approach is verified through experiments of the platform, and the experimental results show that vibrations of the platform are attenuated obviously owing to the active control.

A state-of-the-art review on low-frequency nonlinear vibration isolation with electromagnetic mechanisms

Vibration isolation is one of the most efficient approaches to protecting host structures from harmful vibrations,especially in aerospace,mechanical,and architectural engineering,etc.Traditional linear vibration isolation is hard to meet the requirements of the loading capacity and isolation band simultaneously,which limits further engineering application,especially in the low-frequency range.In recent twenty years,the nonlinear vibration isolation technology has been widely investigated to broaden the vibration isolation band by exploiting beneficial nonlinearities.One of the most widely studied objects is the"three-spring"configured quasi-zero-stiffness(QZS)vibration isolator,which can realize the negative stiffness and high-static-low-dynamic stiffness(HSLDS)characteristics.The nonlinear vibration isolation with QZS can overcome the drawbacks of the linear one to achieve a better broadband vibration isolation performance.Due to the characteristics of fast response,strong stroke,nonlinearities,easy control,and low-cost,the nonlinear vibration with electromagnetic mechanisms has attracted attention.In this review,we focus on the basic theory,design methodology,nonlinear damping mechanism,and active control of electromagnetic QZS vibration isolators.Furthermore,we provide perspectives for further studies with electromagnetic devices to realize high-efficiency vibration isolation.

PERFORMANCE OF ULTRA-LOW FREQUENCY PASSIVE VERTICAL VIBRATION ISOLATION SYSTEM WITH REVERSE PENDULUM

A novel long period passive vertical vibration isolatorconstructed by mounting reverse pendu- lums on two pairs of torsionsprings is presented. By theoretical analysis and numericalcalculation, it is shown that the isolator can achieve much longerresonant period due to gravitational positive feedback and is smallerin size than the current torsion spring isolators with the samegeometric parameters.

A hybrid multi-degree-of-freedom vibration isolation platform for spacecrafts by the linear active disturbance rejection control

The hybrid vibration isolation, which takes advantages of both the passive and active approaches, has been an important solution for space missions. The objective of this paper is to design a vibration isolation platform for payloads on spacecrafts with the robust, wide bandwidth, and multi-degree-of-freedom(MDOF). The proposed solution is based on a parallel mechanism with six voice-coil motors(VCMs) as the actuators. The linear active disturbance resistance control(LADRC) algorithm is used for the active control. Numerical simulation results show that the vibration isolation platform performs effectively over a wide bandwidth, and the resonance introduced by the passive isolation is eliminated. The system robustness to the uncertainties of the structure is also verified by simulation.

Barrier Vibration Isolation to Work-Place Vibration and Its Influence on Uneven Subsidence of Pillar Foundation

Aiming at practice, the wave propagation in soil has been comprehensively studied on the basis of FEM analyzing model being established. An investigation has also been performed on how to solve the problems of simulating transient vibration in actual foundation with FEM, and the result of calculating to the real transient vibration of actual foundation with FEM software ANSYS agrees with that of measuring. The vibration variation in the ground and the uneven subsidence of the factory houses’ pillars, with and without barrier vibration isolation, are calculated by employing FEM. The results show that proper barrier isolation can diminish the ground vibration displacement but likely to magnify the dynamic stress and vibration frequency within a certain region, which would aggravate the uneven subsidence of the factory house pillars.

EQUIVALENT EXCITATION METHOD FOR VIBRATION ISOLATION DESIGN:THEORETICAL ANALYSIS AND EXPERIMENTAL RESULTS

In view of difficulties concerned with direct measurement of excitationsinside source equipments and their significant influence on vibration isolation effectiveness, adynamical model, for vibration isolation of a rigid machine with six-degree-of-freedom mounted on aflexible foundation through multiple mounts, is analyzed, in which the complicated and multipledisturbances inside the machine are described as an equivalent excitation spectrum. And a method forthe estimation of the equivalent excitation spectrum according to system dynamic responses isdiscussed for the quantitative prediction of isolation effectiveness. Both theoretical analysis andexperimental results are demonstrated. Further work shows the quantitative prediction of transmittedpower flow in a flexible vibration isolation experiment system using the proposed equivalentexcitation spectrum method, by comparison with its testing results.

Active Vibration Isolation System for Sub microultra precision Turning Machine

Now vibration isolation of ultra precision machine tool is usually achieved through air springs systems. As far as HCM I sub micro turning machine developed by HIT, an active vibration isolation system that consists of air springs and electro magnetic actuators was presented. The primary function of air springs is to support the turning machine and to isolate the high frequency vibration. The electro magnetic actuators controlled by fuzzy neural networks isolate the low frequency vibration. The experiment indicates that active vibration isolation system isolates base vibration effectively in all the frequency range. So the vibration of the machine bed is controlled under 10 -6 g and the surface roughness is improved.