Pneumatic Vibration Isolation Research Articles

Static and dynamic stability of pneumatic vibration isolators and systems of isolators

Abstract Pneumatic vibration isolation is the most widespread effective method for creating vibration-free environments that are vital for precise experiments and manufacturing operations in optoelectronics, life sciences, microelectronics, nanotechnology and other areas. The modeling and design principles of a dual-chamber pneumatic vibration isolator, basically established a few decades ago, continue to attract attention of researchers. On the other hand, behavior of systems of such isolators was never explained in the literature in sufficient detail. This paper covers a range of questions essential for understanding the mechanics of pneumatic isolation systems from both design and application perspectives. The theory and a model of a single standalone isolator are presented in concise form necessary for subsequent analysis. Then the dynamics of a system of isolators supporting a payload is considered with main attention directed to two aspects of their behavior: first, the static stability of payloads with high positions of the center of gravity; second, dynamic stability of the feedback system formed by mechanical leveling valves. The direct method of calculating the maximum stable position of the center of gravity is presented and illustrated by three-dimensional stability domains; analytic formulas are given that delineate these domains. A numerical method for feedback stability analysis of self-leveling valve systems is given, and the results are compared with the analytical estimates for a single isolator. The relation between the static and dynamic phenomena is discussed.

Active suppression of pneumatic vibration isolators using adaptive sliding controller with self-tuning fuzzy compensation

This paper develops intelligent control schemes for a diaphragm-type pneumatic vibration isolation system. The active-control schemes are applied to the pneumatic isolator to enhance isolation performances in the low-frequency range where passive techniques usually have difficulties in remaining effective, especially at the resonance frequency. The functional approximation technique (FAT) is integrated with a sliding-mode control (SMC) design to capture unknown system dynamics and release the requirement of mathematical modeling. To deal with approximation error and system dynamics variation, an adaptive fuzzy sliding-mode controller (AFSMC) is employed as a compensator of the FAT-based SMC. Lyapunov stability theory is used not only to ensure the closed-loop stability, but also to formulate the updating laws for weighting coefficients of expansion basis and fuzzy tuning parameters. To validate the proposed method, a composite control scheme using pressure and velocity measurements as feedback signals is implemented. Experimental explorations indicate that isolation performances obtained using the proposed FAT-based sliding control augmented with AFSMC compensation (FA + AFSMC) are evidently better than those of the traditional proportional integral-derivative control and solely AFSMC scheme.

Active Pneumatic Vibration Control by Using Pressure and Velocity Measurements and Adaptive Fuzzy Sliding-Mode Controller

This paper presents an intelligent control strategy to overcome nonlinear and time-varying characteristics of a diaphragm-type pneumatic vibration isolator (PVI) system. By combining an adaptive rule with fuzzy and sliding-mode control, the method has online learning ability when it faces the system's nonlinear and time-varying behaviors during an active vibration control process. Since the proposed scheme has a simple structure, it is easy to implement. To validate the proposed scheme, a composite control which adopts both chamber pressure and payload velocity as feedback signal is implemented. During experimental investigations, sinusoidal excitation at resonance and random-like signal are input on a floor base to simulate ground vibration. Performances obtained from the proposed scheme are compared with those obtained from passive system and PID scheme to illustrate the effectiveness of the proposed intelligent control.

Dynamics and stability of pneumatically isolated systems

Pneumatic vibration isolation is the most widespread effective method for creating vibration-free environments that are vital for precise experiments and manufacturing operations in optoelectronics, life sciences, microelectronics, nanotechnology, and other areas. The modeling and design principles of a dual-chamber pneumatic vibration isolator continue to attract attention of researchers. On the other hand, behavior of systems of such isolators was never explained in the literature in sufficient detail. After a brief summary of the theory and a model of a single standalone isolator, the dynamics of a system of isolators supporting a payload is considered with main attention directed to three aspects of their behavior: first, the static stability of payloads with high positions of the center of gravity; second, role of gravity terms in the vibration transmissibility; third, the dynamic stability of the feedback system formed by mechanical leveling valves. The direct method of calculating the maximum stable position of the center of gravity is presented and illustrated by three-dimensional stability domains. A numerical method for feedback stability analysis of self-leveling valve systems is provided, and the results are compared with the analytical estimates for a single isolator. The relation between the static and dynamic phenomena is discussed.

Systematic design of a magneto-rheological fluid embedded pneumatic vibration isolator subject to practical constraints

A systematic design of a magneto-rheological fluid embedded pneumatic vibration isolator (MrEPI) considering practical constraints and optimal performance is proposed. The design procedure basically consists of three steps, i.e. system level design, component level design and practical realization. The system level design involves synthesizing appropriate non-dimensional system parameters of pneumatic spring and MR damper elements based on parameter sensitivity analysis considering requirements for compact and efficient hardware utilization. The component level design involves optimal design of the MR valve by minimizing an objective function in terms of non-dimensional geometric, material and excitation parameters, and guaranteeing required performance in the worst cases. Then practical realization involves determining actual plant parameters from the non-dimensional analysis in system and component level designs with the considerations of practical requirements/constraints. To verify the effectiveness of this optimization procedure, the semi-active vibration control performance of the optimized MrEPI subject to harmonic disturbances is evaluated, which shows good isolation performance in all tested cases. This study actually provides a systematic method for the optimal analysis and design of all those nonlinear vibration isolators consisting of pneumatic spring and MR damper elements. This is achieved firstly by developing effective sensitivity analysis of dominant design parameters upon the adjustable stiffness and damping capacity irrespective of bulky or small system mass configuration and subsequently via a systematic realization design with the consideration of practical constraints in applications.

이동 질량을 포함하는 능동형 공압제진대에 대한 시간지연제어기법의 적용 검토

As applying an active control technique to a pneumatic vibration isolation system, the settling time for the payload excitation could be remarkably reduced as well as the improvement of isolation performance for the ground vibration. Some previous researches were dealt with the settling time through the simulation or experiment but, the discussion on the simulation or experimental results including moving parts, such as a XY-stage, on the isolation table rarely exists. As considering the moving part, the dynamic model could be time varying system and in such a case the force imposed on pneumatic vibration isolation table could be described by inertial forces of moving parts according to Newton's 3rd law, the action and reaction law. In this paper, the simulation procedure of the 3-DOF active pneumatic vibration isolation system including moving parts by TDC(time delay control) technique is proposed and the effectiveness through simulation results are also shown.

A magnetorheological fluid embedded pneumatic vibration isolator allowing independentlyadjustable stiffness and damping

A magnetorheological (MR) fluid embedded pneumatic vibration isolator (MrEPI) withhybrid and compact connection of pneumatic spring and MR damping elements is proposedin this study. The proposed MrEPI system allows independent nonlinear stiffness anddamping control with considerable maneuverable ranges. Meanwhile, it allows convenientswitching between different passive and active vibration control modes, thus providingmore flexibility and versatility in applications. To demonstrate the advantageous dynamicperformance of the MrEPI, a nonlinear non-dimensional dynamic model is developed withfull consideration of the nonlinear elements involved. A systematic analysis is thereforeconducted which can clearly reveal the influence on system output performance caused byeach physically important parameter and provide a useful insight into the analysisand design of nonlinear vibration isolators with pneumatic and MR elements.

Modeling and analysis of dual-chamber pneumatic spring with adjustable damping for precision vibration isolation

Dual-chamber pneumatic spring with adjustable damping (DCPS-AD) employs a variable orifice mechanism (VOM) to obtain the adjustable stiffness and damping characteristics. These adjustable characteristics are aimed at improving the performance of the pneumatic vibration isolation system (VIS). In order to understand thoroughly how the adjustable parameter of VOM affects the behavior of DCPS-AD, the model of DCPS-AD is derived analytically and validated experimentally. The influence of VOM on the performance of DCPS-AD is analyzed quantitatively. All the results demonstrate that VOM has the ability to vary complex stiffness distribution in frequency domain. Based on these results, the approach optimizing the performance of VIS is proposed, which is realized by adjusting VOM actively. Performance experimental measurements of VIS in frequency domain are carried out under different payload masses. The measurement results validate the proposed approach, which can optimize the performance of VIS when some application conditions varying.

Investigation on Harmonic Response of Pneumatic Vibration Isolation System with Single and Double-Frequency Excitations

In this paper, a nonlinear model of pneumatic vibration isolator was established, considering the volumetric compressibility of air. Based on this, simulation analyses were done using matlab/simulink software. The response to two different types of disturbances is studied: single-frequency excitation and double-frequency excitation. Single-frequency excitation can induce harmonic frequency response and offset response at the zero frequency. When the frequency is near to the the linearized natural frequency, the harmonic frequency response become stronger. Nonlinear characters have much to do with the drive amplitude. When the drive amplitude become large, the nonlinear characters are more obvious. Double-frequency excitation can induce combination resonance. When the two drive frequencys are close, combination resonance are more strong.

Modeling and sensitivity analysis of a pneumatic vibration isolation system with two air chambers

This paper aims at accurate modeling and sensitivity analysis for a pneumatic vibration isolation system (PVIS) as a foundation for practical design. Even though the PVIS is widely used for its effective performance in vibration isolation, its design has depended largely on trial-and-error methods. In previous studies, nonlinear characteristics of the diaphragm and the air flow restrictor, which significantly affect the performance of a PVIS, have been investigated. However, several hurdles, such as the absence of a mathematical model for the diaphragm, still remain with regard to the model-based prediction of performance. Therefore, a fractional derivative model for the diaphragm and a quadratic damping model for the air flow restrictor are newly developed based on the careful examination of previous studies. Then, sensitivities of vibration isolation performance indices with regard to major design variables are analyzed and new approximation formulas are created based on the dynamic characteristics of the PVIS. Our models with a transmissibility-computing algorithm are verified by comparison with experimental data. The sensitivity analyses and approximation formulas are expected to be useful for practical PVIS design owing to their simplicity and accuracy.

Three Degrees of Freedom Active Control of Pneumatic Vibration Isolation Table by Pneumatic and Time Delay Control Technique

Based on previous feasibility study on one degree of freedom (1DOF) pneumatic active control of pneumatic springs, this paper presents procedures and results of a more realistic 3DOF active control of a pneumatic vibration isolation table. The 3DOF motion of the pneumatic table, consisting of heaving, rolling, and pitching, is controlled directly by adjusting air pressure in four pneumatic cylinders in a dynamic manner with pneumatic valves, without any external actuator such as an electromagnet or voice coil. The time delay control, which is a software chosen in this study, together with the hardware, i.e., the pneumatic actuator, is shown to be very powerful in enhancing the performance of vibration isolation for ground excitation as well as in settling time reduction for payload excitation through simulations and measurements on the 3DOF motion control system. New key results found in the experimental approach are that the pneumatic actuator shows a dynamic behavior of a second-order system, instead of a first-order system, which has been used in existing literatures so far, and that just feed-forward control of the pneumatic actuator by the second-order model can compensate for the inherently slow response characteristics of the pneumatic actuator very successfully. Effectiveness of the proposed active pneumatic control technique in the multi-input and multi-output system is shown via singular value decomposition analysis on the transmissibility matrix. Promising future of the proposed control and performance analysis technique is further discussed based on the results in the case of payload excitations as well.

Concrete pier foundation and building design for electron microscope installations with vibration disturbances from train, truck, and bus traffic.

A university microscopy and imaging center housing nine instruments including scanning electron microscopes and transmission electron microscopes was proposed for a site near an active railroad and roadways. Low-frequency sound and vibration from trains, trucks, and buses can affect the performance and use of electron microscopes, by disturbing the stability and resolution of the specimen’s image. On-site observations and spectrum measurements were conducted to determine the ambient and transient ground borne vibration conditions. Measurements showed that disturbances from trains as well as bus and truck traffic on campus roads significantly exceeded allowable floor vibration tolerances for many of the instruments. Soils exhibited response to disturbances at dominant frequencies around 5 and 10 Hz. This paper addresses the potential for concrete pier-supported floor vibration and structural resonance contributions to ground borne vibration levels and solutions proposed to mitigate the disturbances for sensitive instrument installations. Graphic diagrams of structural design concepts and results from on-site measurements prior to construction will be discussed. The designs and effectiveness of the microscope rooms, structural treatments, and actively damped, pneumatic vibration isolation systems are discussed, along with post-construction vibration measurement results and photographs.

Effective suppression of pneumatic vibration isolators by using input–output linearization and time delay control

This paper presents a new state space representation of pneumatic vibration isolators (PVIs) and a design of a robust control, Time Delay Control (TDC), based on it. The new state space model, derived by using the input–output linearization method, is of the phase variable form with the air mass-flow as the control input. This model offers a framework that enables simultaneous suppression of both seismic vibration and direct disturbance (or payload disturbance) with an accelerometer only. Based on this model, TDC is designed and verified with experiments on a single chamber PVI with an accelerometer only. In the experiment, the PVI with TDC successfully suppresses seismic vibration and direct disturbance, both individually and simultaneously. Faced with seismic vibration, the transmissibility of the PVI with TDC has virtually no resonance peak at low frequency; under direct disturbance, the former achieves a 68 percent reduction in settling time of the latter. The final analysis of experimental result shows that TDC effectively estimates the modeling error along with other uncertainties and cancels them, while achieving desired closed-loop dynamics.

Pneumatically Isolated Inertia Base with Active Damping for a Transmission Electron Microscope (TEM)

Low frequency sound and vibration affects the performance and use of electron microscopes, by disturbing the stability and resolution of the specimen's video image. A transmission electron microscope (TEM) addition was proposed to an existing research suite that had three scanning electron microscopes (SEM). The TEM, which is very heavy, rather tall and has a high center of gravity, is very sensitive to floor vibrations. This case study presents sources of disturbing vibration with spectrum measurements. The designs of the microscope room and an actively damped, pneumatic vibration isolation system are discussed. Post-installation vibration measurement results to validate performance are presented in spectral analysis charts versus criteria. Drawings and photographs illustrate the installation.

A new, high precision, quick response pressure regulator for active control of pneumatic vibration isolation tables

Abstract Pressure regulators are important elements in pneumatic systems. Relief-type precision pressure regulators are commonly used to control the supply pressure to actively controlled pneumatic vibration isolators. Herein, a high precision, quick response pneumatic pressure regulator is proposed. This consists of an isothermal chamber, a servo valve, a pressure sensor, a quick response laminar flow sensor (QFS), and a pressure differential sensor (PD sensor) as developed by the authors. Slight changes of pressure in the chamber can be detected by the PD sensor and are fed back to the servo valve to maintain the pressure at a desired value. The performance of this regulator was confirmed experimentally in comparison with one available commercially. The regulator was then applied to the supply pressure regulation of an actively controlled pneumatic vibration isolation table. The superior performance of the regulator is clearly shown in the experimental results, especially in terms of avoiding effects from upstream or downstream disturbances.

A method of transmissibility design for dual-chamber pneumatic vibration isolator

Dual-chamber pneumatic vibration isolators have a wide range of applications for vibration isolation of vibration-sensitive equipment. Recent advances in precision machine tools and instruments such as medical devices and those related to nano-technology require better isolation performance, which can be efficiently achieved by precise modeling- and design- of the isolation system. This paper discusses an efficient transmissibility design method of a pneumatic vibration isolator wherein a complex stiffness model of a dual-chamber pneumatic spring developed in our previous study is employed. Three design parameters, the volume ratio between the two pneumatic chambers, the geometry of the capillary tube connecting the two pneumatic chambers, and, finally, the stiffness of the diaphragm employed for prevention of air leakage, were found to be important factors in transmissibility design. Based on a design technique that maximizes damping of the dual-chamber pneumatic spring, trade-offs among the resonance frequency of transmissibility, peak transmissibility, and transmissibility in high frequency range were found, which were not ever stated in previous researches. Furthermore, this paper discusses the negative role of the diaphragm in transmissibility design. The design method proposed in this paper is illustrated through experimental measurements.

Performance enhancement of pneumatic vibration isolation tables in low frequency range by time delay control

As environmental vibration requirements on precision equipment become more stringent, the use of pneumatic isolators has become more popular and their performance is subsequently required to be further improved. Dynamic performance of passive pneumatic isolators is related to various design parameters in a complicated manner and that in low-frequency range is limited by resonance frequency or volume of pneumatic chambers in practice. In this study, an active control technique, called as time delay control, is applied to a pneumatic isolator to enhance the isolation performance in the low frequency range where the passive techniques have difficulties. This time delay control technique is taken especially because it is known to be useful for the low frequency control. The procedure of applying the time delay control technique to the pneumatic isolator is presented, together with how to resolve distortion problems in actuator dynamics in implementing the active control technique into a pneumatic system. Effectiveness of the technique in enhancement of transmissibility performance is shown based on simulation as well as experiments. Comparisons with passive pneumatic isolators are also presented.

Active control of electro-rheological fluid embedded pneumatic vibration isolator

Vibration isolation is crucial to better product quality in precision machinery, and can be achieved through either passive or active vibration control systems. Although passive pneumatic vibration...

Active control of electro-rheological fluid embedded pneumatic vibration isolator

Vibration isolation is crucial to better product quality in precision machinery, and can be achieved through either passive or active vibration control systems. Although passive pneumatic vibration isolators have excellent isolation characteristics a

지반진동절연을 위한 공압제진대의 전달률 설계기법

Pneumatic vibration isolator has a wide application for ground-vibration isolation of vibration-sensitive equipments. Recent advances In precision machine tools and instruments such as nano-technology or medical devices require a better isolation performance, which can be efficiently done by precise modeling- and design- of the isolation system. This paper will discuss an efficient transmissibility design method for pneumatic vibration isolator by employing the complex stiffness model of dual-chamber pneumatic spring developed in our previous research. Three design parameters of volume ratio between the two pneumatic chambers, the geometry of capillary tube connecting the two pneumatic chambers and finally the stiffness of diaphragm necessarily employed for prevention of air leakage were found to be important factors in transmissibility design. Based on design technique that maximizes damping of dual-chamber pneumatic spring, trade-off among the resonance frequency of transmissibility, peak transmissibility and transmissibility in high frequency range was found, which was not ever stated in previous researches. Furthermore this paper will discuss about negative role of diaphragm in transmissibility design. Then the design method proposed in this paper will be illustrated through experiment at measurements.