Pneumatic Vibration Isolation Research Articles

A semi-active adaptive pneumatic vibration isolator based on frequency response analysis and nonlinear control

In this work, an adaptive nonlinear error feedback controller based on fuzzy state observer is proposed to a novel rubber pneumatic vibration isolator (PVI) system. First, a novel rubber PVI system is designed and developed. Harmonic balance method is applied to establish the dynamic model of the PVI system, so as to analyze the frequency response characteristics of the system. Second, to improve the PVI performance in low-frequency vibration, a nonlinear state error feedback control system based on fuzzy state observer is designed for the active PVI system. Furthermore, the experiment system is established. Finally, through the experimental comparison under 5 Hz, 7 Hz, 20 Hz, and 40 Hz, an adaptive PVI strategy is proposed. The experimental results demonstrate that the adaptive PVI shows better performance in vibration isolation.

A Compound Regulative Pneumatic Vibration Isolator With Quasi-Zero Stiffness Mechanism For Load Variable Instruments

A Compound Regulative Pneumatic Vibration Isolator With Quasi-Zero Stiffness Mechanism For Load Variable Instruments

Research on the Pressure Regulator Effect on a Pneumatic Vibration Isolation System

The pneumatic vibration isolator (PVI) plays an increasingly important role in precision manufacturing. In this paper, aiming to detect the performance of the pressure regulator in the PVI system, a PVI testing system with a pressure regulator is designed and developed. Firstly, the structure of the pneumatic spring is presented and analyzed, and the nonlinear stiffness is obtained based on the ideal gas model and material mechanics. Then, according to the working principle and continuity equations of ideal airflow, a dynamic model of the PVI system with a pressure regulator is established. Through the simulation analysis, the vibration isolation performance is improved with the efficient and precise pressure regulator. The average values of both the vibration velocity and transmission rate decrease when the vibration is set to 4, 10, 20 and 40 Hz, respectively. The experiments demonstrate the reliability and effectiveness of the pressure regulator. This achievement will become an important basis for future research concerning precision manufacturing.

Highly damped single-chamber pneumatic vibration isolator using effects of thermal conductivity in the air volume

State-of-the-art pneumatic isolators have a two-chamber design with metered orifices between the chambers. This arrangement produces energy dissipation necessary to avoid excessive resonance vibration [1]. However, this leads to reduced isolation performance at high frequencies compared to a single-chamber isolator of equivalent total volume. Analysis shows that, while the dynamic process of the air compression in the pneumatic chamber is adiabatic for geometric parameters usually employed in vibration isolators, substantial dissipation of mechanical energy can be achieved by introducing certain thermally conductive features into the chamber. That makes practical a single-chamber design with sufficient damping. The paper presents the optimization of the geometry of thermally conductive features aimed at maximizing the loss factor at the resonance frequency of the isolation system. Experimental results illustrate the concept [2] and demonstrate the increased isolation effect. [1] V. M. Ryaboy, Vibration Control for Optomechanical Systems (World Scientific, 2022), p. 280. [2] Vibration isolation apparatus with thermally conductive pneumatic chamber, and method of manufacture, U.S. patent application No. 17/721834, USPTO, 2022.

Dynamic Analysis of Quasi-Zero Stiffness Pneumatic Vibration Isolator

This paper focuses on analyzing the dynamic response of an innovated quasi-zero stiffness pneumatic vibration isolator (QZSPVI) using two mechanisms, including wedge and semicircle cam. Different from other studies relating quasi-zero stiffness isolation system, the pneumatic cylinder in this paper works as an air spring in order to easily adjust the dynamic stiffness of the proposed system according to the change of the isolated load through regulating the pressure. Firstly, the dynamic stiffness of the QZSPVI will be analyzed. Then, the condition for which the minimum dynamic stiffness is quasi-zero around the equilibrium position is also determined. The fundamental resonance response of the QZSPVI subjected to the externally harmonic force is analyzed through multi-scale method and the numerical simulations are verified. Secondly, due to exiting relative sliding frictional phenomenon between the cylinder and piston, instead of an experiment, another key content of this work is to identify the friction force model of the cylinder through virtual prototyping model. From this identified result, the complex dynamic response of the QZSPVI and coexistence of multiple solutions will be discovered by realizing the direct integration of the original dynamic equation through using the 5th-order Runge–Kutta algorithm. The analysis and simulation results clearly show the advantages of the proposed model against the equivalent pneumatic vibration isolator (EPVI), which only employs the wedge mechanism. This research will offer a useful insight into design and QZSPVI in practice.

Analytical study of a pneumatic vibration isolation platform featuring adjustable stiffness

This paper proposed a pneumatic vibration isolation platform (named VIP) with adjustable stiffness characteristics in which two opposite stiffness mechanisms are introduced. One with positive stiffness is formed by the wedge-roller mechanism used to support the load, which is named the load bearing mechanism (LBM), the other (called stiffness correction mechanism-SCM) generating negative stiffness in vertical direction, constructed by the cam-roller mechanism, is used for correction of the total stiffness of the VIP. Instead of using coil spring, the rubber air spring is employed, hence the stiffness of the VIP can be easily adjusted to adapt to the change of the isolated load as well as improve the isolation effectiveness in low frequency region. The force model of the rubber air spring generated by the compressed air, friction and viscoelastic is then built and identified via the experiment. Next, the dynamic stiffness model of the VIP will be established and analyzed. The primary resonant response of the proposed model subjected to harmonically excited base will be analyzed by employing the normal form technique. The effects of the configurative parameters on the amplitude-frequency curve are investigated. Furthermore, due to the nonlinear dynamical system, the complex dynamical analysis including coexistence solution, bifurcation and so on is necessary to explore in this work by using the numerical integration and Poincaré map. Finally, the isolation response of the VIP subjected to the random excitation is also evaluated and compared with that of the equivalent linear isolator (named ELI in which the SCM is removed). The result shows clearly the advantages of the VIP against the ELI. This work will furnish a useful insight into the design and manufacture of the low frequency vibration isolation systems.

Dynamics and isolation properties for a pneumatic near-zero frequency vibration isolator with nonlinear stiffness and damping

Aiming to isolate disturbance vibration for heavy machines with low frequency, a novel hydro-pneumatic vibration isolator with high-static and low-dynamic (HSLD) stiffness is proposed, which contains bellows structure as elastic element and pressurized gas and incompressible liquid as working media. Due to that the natural frequency of isolation system with such isolator is close to zero and loading capacity can be adjusted by the gas pressure, the proposed device is termed as pneumatic near-zero frequency (NZF) vibration isolator. To obtain the mathematical model of isolator’s stiffness, the quasi-static derivation based on gas state equation is carried out first. Results prove that the presented isolator possesses ideal high-static and low-dynamic stiffness, which is also verified by the experimental data measured by a quasi-static test. The proportion of gas volume to total volume of gas and liquid media, respectively, in bellows and cylinder chambers are significant physical parameters, which dominate the nonlinearity extent of isolator’s stiffness. Different from most existing isolators, the proposed isolator includes fluidic damping and friction damping. The former is expressed by classic square-velocity-type nonlinear model, and the latter is modeled as Coulomb damping. To obtain dynamic response and vibration isolation transmissibility, the harmonic balance method is applied. A direct current term is added in the trial solution, which reflects the asymmetry of dynamic response. In respect of transmissibility analysis, square-velocity nonlinear damping brings a favorable advantage that it can ensure the fine force transmissibility in both resonance region and effective isolation band. This conclusion holds consistently under base motion excitation. Friction damping cannot give the same conclusion. Further comparison with a linear vibration isolator exhibits that the HSLD stiffness characteristics of the NZF isolator breaks through the trade-off between large loading capacity and small static deformation, and the square nonlinearity of fluid damping is able to overcome the dilemma that weak linear vicious damping is beneficial for isolation performance within the effective isolation frequency band, but cannot suppress resonance amplitude and transmissibility. And the experimental transmissibility is in good agreement with the analytical result. Besides, the influences of excitation variation on isolation performance are estimated theoretically. Due to the hardening stiffness, overload acceleration will cause the increase in linearized natural frequency of NZF isolator system, and thus, isolation effectiveness will be reduced.

Active optical table tilt stabilization.

We show that a simple modification to an optical table with pneumatic vibration isolation can be used to actively reduce the long term drift in the tilt of the table by nearly a factor of 1000. Without active stabilization, we measure a root-mean-square (rms) tilt variation of 270 µrad over three days. The active stabilization can be used to limit the tilt to 0.35 µrad rms over the same time period. This technique can be used to minimize drift in tilt-sensitive experiments.

Adaptive pneumatic vibration isolation platform

Abstract A novel adaptive pneumatic vibration isolation platform (APVIP) which is built by combining two opposite stiffness mechanisms is proposed. The positive stiffness mechanism including the wedge, the roller and the air spring is used to support the load (named load bearing mechanism LBM) meanwhile the dynamic stiffness of the APVIP can be reduced by introducing a stiffness correction mechanism (SCM) configured the negative stiffness comprising the cam, the roller and the air spring. The significant feature of the APVIP is explored that both its easily adjusted stiffness according to the mass variation of the isolated object and its improved isolation effectiveness. The paper presents theoretical and experimental analyses of the proposed system. Firstly, the pneumatic-mechanical model of the LBM and SCM is analytically expressed, then, the original and approximate restoring forces of the proposed model are found. Secondly, the dynamic equation of the platform is obtained and the Normal form method is used to analyze the primary resonance response of the APVIP. Simultaneously, due to the nonlinear dynamic system, the numerical integration and Poincare map are employed to analyze the complex dynamical equation including coexistence of solutions and bifurcation phenomena. Next, an experimental apparatus has been set up to verify theoretical model and simulation. Finally, the results demonstrate that the APVIP outperforms the equivalent isolation platform without SCM (shorten platform without SCM).

An Analytical Model for a Pneumatic Vibration Isolator with the Stiffness Effect of the Elastomeric Diaphragm

The elastomeric diaphragm is widely used in pneumatic vibration isolators, and the relevant model is often ignored due to its complexity. Considering that the ignored model of the elastomeric diaphragm in pneumatic vibration isolators plays an important role in the discrepancy between the predicted and practical behavior, this paper develops an analytical model for the elastomeric diaphragm using the Mooney‐Rivlin modeling method and elastomeric theory. Specifically, the elastomeric diaphragm consists of several segments in the axial section. After considering the structural restriction, each segment can be simplified as uniaxial stretching, and the force‐strain equation can be established for each segment. By combining the equations of all segments, an analytical model of the elastomeric diaphragm can be built and solved via numerical methods. The developed model is added to the standard model of pneumatic cylinders to supply a complete analytical model for pneumatic vibration isolators. The experimental results demonstrate that the analytically predicted behavior is similar to the practical behavior. The proposed analytical model can be used as a guide for the parameter design of pneumatic isolators in practice.

Versatile variable temperature and magnetic field scanning probe microscope for advanced material research.

We have built a variable temperature scanning probe microscope (SPM) that covers 4.6 K-180 K and up to 7 T whose SPM head fits in a 52 mm bore magnet. It features a temperature-controlled sample stage thermally well isolated from the SPM body in good thermal contact with the liquid helium bath. It has a 7-sample-holder storage carousel at liquid helium temperature for systematic studies using multiple samples and field emission targets intended for spin-polarized spectroscopic-imaging scanning tunneling microscopy (STM) study on samples with various compositions and doping conditions. The system is equipped with a UHV sample preparation chamber and mounted on a two-stage vibration isolation system made of a heavy concrete block and a granite table on pneumatic vibration isolators. A quartz resonator (qPlus)-based non-contact atomic force microscope (AFM) sensor is used for simultaneous STM/AFM operation for research on samples with highly insulating properties such as strongly underdoped cuprates and strongly correlated electron systems.

The dynamic behavior of pneumatic vibration isolators

The ubiquity of pneumatic vibration isolators, especially in heavy road vehicle suspensions and in passenger rail vehicle secondary suspensions, has boosted research interest in these systems. Thermodynamic models have been used in order to inform and support engineering design decisions. Most models assume that the air inside the system undergoes a polytropic transformation during the compression/expansion cycle, but the necessary polytropic index value is often guessed at and seldom measured. This paper presents measured polytropic indexes that contradict the traditional assumptions with respect to its value. On a different note, the work presented in this paper also investigates the air flow through the restrictor (a component that is often used in suspension applications to introduce damping and adapt the frequency response function). The results show that this flow can be analyzed with utterly simple models.

Active control for non-autonomous diaphragm-type pneumatic isolation system by using an augmented adaptive sliding-mode controller

An augmented adaptive sliding-mode controller is proposed in this paper for a diaphragm-type pneumatic vibration isolation (PVI) system containing nonlinear characteristics and time-varying uncertainties with unknown bounds. To capture and deal with the time-varying uncertainties, a controller design based primarily on the functional approximation (FA) technique complemented with an adaptive fuzzy sliding-mode control (AFSMC) is adopted. The resultant hybrid design is denoted as FA+AFSMC to differentiate itself from other attempting solutions. Lyapunov stability theory is utilized not only to stabilize the closed-loop system but also to formulate updating laws for weighting coefficients of the FA and tuning parameters of the AFSMC. This developed scheme has online learning ability when it faces the system’s nonlinear and time-varying behaviors. Experimental explorations which incorporates both pressure and velocity measurements as feedback signals reveals that the proposed FA+AFSMC scheme outperforms other attempting solutions, such as passive isolation and pure AFSMC scheme, by a significant margin.

LDI 노광기용 초정밀 스테이지의 진동 저감 기구에 관한 연구

Recently, Laser Direct Imaging (LDI) has been used to replace lithography in Flexible Printed Circuit Board (FPCB) manufacturing. However, repeated motion of a linear motor caused residual vibration in the granite on which the workpiece was placed when the motor either accelerated or decelerated. Because the residual vibration made positioning less accurate, there were more defective products and worse productivity. This paper proposes a way to reduce vibration in the granite during the precision stage. First, the frequency domain of the vibrations of a pneumatic vibration isolator is identified. Second, we present the design of the mechanism using a voice coil actuator and a capacitive displacement sensor. Third, we apply a feedback control algorithm based on PID to cancel displacement. Consequently, we are able to propose an optimal way to reduce vibration for the laser direct imaging equipment. The amount of vibration reduction is evaluated in terms of amplitude and settling time.

Adaptive wavelet neural network controller for active suppression control of a diaphragm-type pneumatic vibration isolator

This paper applies an intelligent control scheme to investigate a diaphragm-type pneumatic vibration isolation (PVI) problem. Adaptive wavelet neural network (AWNN) control is employed to control the PVI system which has inherited nonlinear and time-varying system characteristics. Since AWNN has excellent approximation capability originating from wavelet decomposition property and online learning ability stemming from neural networks, the method is especially suitable for the PVI control applications. In this paper, the adaptive learning rates are derived based on the Lyapunov stability theorem. Therefore, the stability of the closed-loop system can be assured. To validate the proposed method, a composite control scheme using pressure and velocity measurements as feedback signals is implemented. During experimental investigations, sinusoidal excitation with the excitation frequency close to the resonance and random-like signal are input on a floor base to simulate ground vibrations. Performances obtained from the proposed control scheme are compared with those obtained from passive isolation and PID scheme to illustrate the effectiveness of the proposed intelligent control.

Control Algorithm Design of the Active Pneumatic Vibration Isolator

The background for the proposed vibration isolation method is based on the principle of active pressure control, minimizing the cyclic load transmitted to the system base through elastic pneumatic element. The paper presents a research on effectiveness of PID-control algorithm with back-calculation of integrator part. Pressure pulsation inside the pneumatic element of the vibration isolator is studied in the frequency range that includes its sub-resonant and resonant frequencies. Spectral analysis is conducted in order to analyze the harmonic excitation response of an active pneumatic isolation system and a passive one, with disabled valves control. The minimal bore size and response rate of the control valve are defined to achieve at least a double advantage of the active system over the passive one in the frequency range including the vibration isolator resonant frequency. As expected, the proposed control algorithm demonstrated a decent decrease of pressure pulsation amplitude at a low frequency range of a Hertz-level excitation signal. The calculation data analysis shows that PID-control algorithm with back-calculation of integrator part can be effectively used for active pneumatic vibration isolator, if the control valve parameters are within specified ranges.

Design of a Miniaturized Pneumatic Vibration Isolator With High-Static-Low-Dynamic Stiffness

In the ultraprecision vibration isolation systems, it is desirable for the isolator to have a larger load bearing capacity and a broader isolation bandwidth simultaneously. Generally, pneumatic spring can bear large load and achieve relatively low natural frequency by enlarging its chamber volume. However, the oversized isolator is inconvenient to use and might cause instability. To reduce the size, a miniaturized pneumatic vibration isolator (MPVI) with high-static-low-dynamic stiffness (HSLDS) is developed in this paper. The volume of proposed isolator is minimized by a compact structure design that combines two magnetic rings in parallel with the pneumatic spring. The two magnetic rings are arranged in the repulsive configuration and can be mounted into the chamber to provide the negative stiffness. Then dynamic model of the developed MPVI is built and the isolation performances are analyzed. Finally, experiments on the isolator with and without the magnetic rings are conducted. The final experimental results are consistent with the dynamical model and verify the effectiveness of the developed vibration isolator.

Effect of External Excitation on Dynamic Characteristics of Vibro-Isolating Table

Performance of optical table with pneumatic vibration isolators is analyzed within 2–50 Hz frequency range. Specific vibrational excitation platform with a vibrator of the frequency range of 1–50 Hz in one of three directions were tested.The following pneumatic vibration isolator dynamic parameters were identified:transmissibility of vertical oscillation characteristics at 50 Hz frequency range;resonant frequency (vertical direction);damping efficiency at 5 Hz to 10 Hz for excitation frequencies.

Generic vibration criteria–based dual-chamber pneumatic spring vibration isolation table design

Dual-chamber pneumatic spring vibration isolation tables are commonly used as the base of precision equipment to isolate vibrations from the floor. During the design of dual-chamber pneumatic spring vibration isolation table, transmissibility is often taken as the performance measure, which does not represent the precision requirements directly and could not be adapted to different floor vibration conditions. In this article, a new performance measure is developed to obtain an optimum isolation performance during the design of a dual-chamber pneumatic spring vibration isolation table. Based on the generic vibration criteria, the weighted root-mean-square velocity of platform vibration in one-third octave bands resulting from the floor excitations is used as the new measure. The platform vibration is predicted by establishing a model of dual-chamber pneumatic spring vibration isolation table, which consists of a platform and four dual-chamber pneumatic springs. The model disturbance inputs are actual random floor excitations (7.98 µm/s, vibration criteria-C level), which are obtained by vibration acquisition test in a typical laboratory. The genetic algorithm is applied to solve this nonlinear optimization problem. The maximum weighted root-mean-square velocity of platform with the optimum design isolation table decreases to 2.35 µm/s, which provides a vibration criteria-E level environment.

Active pneumatic vibration isolation system using negative stiffness structures for a vehicle seat

Abstract In this paper, an active pneumatic vibration isolation system using negative stiffness structures (NSS) for a vehicle seat in low excitation frequencies is proposed, which is named as an active system with NSS. Here, the negative stiffness structures (NSS) are used to minimize the vibratory attraction of a vehicle seat. Owing to the time-varying and nonlinear behavior of the proposed system, it is not easy to build an accurate dynamic for model-based controller design. Thus, an adaptive intelligent backstepping controller (AIBC) is designed to manage the system operation for high-isolation effectiveness. In addition, an auxiliary control effort is also introduced to eliminate the effect of the unpredictable perturbations. Moreover, a radial basis function neural network (RBFNN) model is utilized to estimate the optimal gain of the auxiliary control effort. Final control input and the adaptive law for updating coefficients of the approximate series can be obtained step by step using a suitable Lyapunov function. Afterward, the isolation performance of the proposed system is assessed experimentally. In addition, the effectiveness of the designed controller for the proposed system is also compared with that of the traditional backstepping controller (BC). The experimental results show that the isolation effectiveness of the proposed system is better than that of the active system without NSS. Furthermore, the undesirable chattering phenomenon in control effort is quite reduced by the estimation mechanism. Finally, some concluding remarks are given at the end of the paper.