Pneumatic Isolation Research Articles

Low vibration laboratory with a single-stage vibration isolation for microscopy applications.

The construction and the vibrational performance of a low vibration laboratory for microscopy applications comprising a 100 ton floating foundation supported by passive pneumatic isolators (air springs), which rest themselves on a 200 ton solid base plate, are discussed. The optimization of the air spring system leads to a vibration level on the floating floor below that induced by an acceleration of 10 ng for most frequencies. Additional acoustic and electromagnetic isolation is accomplished by a room-in-room concept.

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.

Acoustic buffeting by infrasound in a low vibration facility.

Measurement instruments and fabrication tools with spatial resolution on the atomic scale require facilities that mitigate the impact of vibration sources in the environment. One approach to protection from vibration in a building's foundation is to place the instrument on a massive inertia block, supported on pneumatic isolators. This opens the questions of whether or not a massive floating block is susceptible to acoustic forces, and how to mitigate the effects of any such acoustic buffeting. Here this is investigated with quantitative measurements of vibrations and sound pressure, together with finite element modeling. It is shown that a particular concern, even in a facility with multiple acoustic enclosures, is the excitation of the lowest fundamental acoustic modes of the room by infrasound in the low tens of Hz range, and the efficient coupling of the fundamental room modes to a large inertia block centered in the room.

Control of input delayed pneumatic vibration isolation table using adaptive fuzzy sliding mode

PNEUMATIC ISOLATORS ARE PROMISING CANDIDATES FOR INCREASING THE QUALITY OF THE PRECISION INSTRUMENTS. FOR THIS PURPOSE, HOWEVER, HIGHER PERFORMANCE OF SUCH ISOLATORS IS A PREREQUISITE. IN THIS PAPER AN ADAPTIVE FUZZY SLIDING MODE CONTROLLER IS PROPOSED TO IMPROVE THE PERFORMANCE OF A PNEUMATIC ISOLATOR IN THE LOW FREQUENCY RANGE, I.E., WHERE THE PASSIVE TECHNIQUES HAVE OBVIOUS SHORTCOMINGS. THE MAIN IDEA IS TO COMBINE THE ADAPTIVE FUZZY CONTROLLER WITH ADAPTIVE PREDICTOR AS A NEW TIME DELAY CONTROL TECHNIQUE. THE ADAPTIVE FUZZY SLIDING MODE CONTROL AND THE ADAPTIVE FUZZY PREDICTOR HELP TO CIRCUMVENT THE INPUT DELAY AND NONLINEARITIES IN SUCH ISOLATORS. THE MAIN ADVANTAGE OF THE PROPOSED METHOD IS THAT THE CLOSED-LOOP SYS-TEM STABILITY IS GUARANTEED UNDER CERTAIN CONDITIONS. SIMULATION RESULTS ARE COMPARED TO THE RESULTS OF TDC TECHNIQUE TO VERIFY THE EFFECTIVENESS OF THE PROPOSED METHOD.

離散値入力を伴う空圧式除振台のモデル予測制御

離散値入力を伴う空圧式除振台のモデル予測制御

이중챔버를 이용한 공압가진기의 주파수 범위 확장

Pneumatic exciters can be good replacements of electrodynamic, piezoelectric and hydraulic exciters owing to simple structure and large exciting force. One problem to be solved is a slow response caused by compressibility of air. Desirable frequency response characteristics of exciter are constant magnitude and zero degree phase, because users want no time delay between input signal and output force. For this reason, frequency range of pneumatic exciters is limited about 0~1 Hz. Therefore, expansion of frequency range is an important issue when designing the pneumatic exciter. In this paper, the pneumatic exciter which has same structure with active pneumatic isolator is dealt with. The dynamic characteristics are presented, and its limitation of expanding frequency range is shown based on analytical studies. Then the pneumatic exciter with dual-chamber is suggested to overcome this problem. Based on simulation study, a design method is presented.

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.

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.

Flow Disturbance Compensation Based on Off-Line Estimated Signal for a Pneumatic Isolation Table

Flow Disturbance Compensation Based on Off-Line Estimated Signal for a Pneumatic Isolation Table

Control of a Pneumatic Isolation Table Including Non-linear Quantizer

Control of a Pneumatic Isolation Table Including Non-linear Quantizer

Vibration Suppression Control for a Pneumatic Isolation Table with Three Degrees-of-Freedom Using On-Off Valves

Pneumatic isolation tables are generally used in the fields of manufacturing and measuring precision components, and several methods by which to achieve active control of pneumatic isolation tables have been proposed. In these studies, the internal pressure of the air springs is actively controlled by using servo valves in order to suppress micro-level vibration. On the other hand, so as to suppress millimeter-level vibration and obtain low cost equipment, several methods by which to achieve active control using on-off valves instead of servo valves have been proposed. In these investigations, a switching control method based on the Lyapunov function exhibits performances that are superior to the other methods. However, the switching control method suppresses vibrations in only the vertical direction. Therefore, improvement of the vibration suppression performance is required in not only the vertical direction but also the rolling and pitching directions. Thus, the purpose of this study is to obtain high vibration suppression performance for a pneumatic isolation table with three degrees-of-freedom using on-off valves. The switching control method is extended to multi-input system, and it is shown that the extended method is suitable for control of a pneumatic isolation table with three degrees-of-freedom. The effects of the extended method are verified by numerical simulations and experiments.

C12 On-off操作駆動を伴う空圧式除振台のモデル予測制御(M-OS7-1:精密・情報・産業機器の制御,M-OS7 精密・情報・産業機器の制御,「海を越え,国を越え,世代を超えて!」)

C12 On-off操作駆動を伴う空圧式除振台のモデル予測制御(M-OS7-1:精密・情報・産業機器の制御,M-OS7 精密・情報・産業機器の制御,「海を越え,国を越え,世代を超えて!」)

228 サーボ系における過渡応答改善方法の提案と空圧式除振台への応用

It is well known that the servo system sometimes provides undesirable overshoot in transient responses for temporary disturbance such as the impulse disturbance. The response is caused from the action of the servo system which sweeps out the state variable of the integrator. In such cases, the transient response performance becomes worse in comparison to the one by the regulator system. In the present paper, a method for improvement of the transient response of the servo system based on the disturbance estimation and switching the control action is proposed. The effectiveness of the proposed method is verified by the pneumatic isolation table by numerical simulations.

Compensation for the effect of feedforward controller's switching on isolation table using flow meter

This paper considers a control scheme for the suppression of pneumatic isolation table’s fluctuation induced by switching of the feedforward controller. The table acceleration and feedforward paths are added and the combined signal is sent to a damping integrator and gain. The damping integrator, besides generating a damping signal from acceleration signal, also avoids a large jump/drop of the feedforward signal during switching of the feedforward controller. Performance of this control scheme is evaluated by experiments while comparing with conventional control schemes. In addition, retuning of the feedforward compensator’s gains is investigated. Based on the experimental results, it is shown that this control scheme can suppress both flow disturbances and switching of the feedforward controller.

The Leveling Position Control of a Four-Axial Active Pneumatic Isolation System Using PWM-Driving Parallel Dual-On/Off Valves

This study aims to develop a leveling position control of an active PWM-controlled pneumatic isolation table system. A novel concept using parallel dual-on/off valves with PWM control signals is implemented to realize active control and to improve the conventional pneumatic isolation table that supported by four pneumatic cushion isolators. In this study, the cushion isolators are not only passive vibration isolation devices, but also pneumatic actuators in active position control. Four independent closed-loop position feedback control system are designed and implemented for the four axial isolators. In this study, on/off valves are used, and PWM is realized by software. Therefore, additional hardware circuit is not required to implement PWM and not only cost down but also reach control precision of demand. In the controller design, the Fourier series-based adaptive sliding-mode controller with H∞ tracking performance is used to deal with the uncertainty and time-varying problems of pneumatic system. Finally, the experiments on the pneumatic isolation table system for synchronous position and trajectory tracking control, including no-load and loading conditions, and synchronous position control with master-slave method, are implemented in order to verify that the controller for each cushion isolator can realize good position and trajectory tracking performance.

Analysis of Pneumatic Vibration Isolator Considering Diaphragm Stiffness

An accurate model of pneumatic isolators is important for its structure optimization and controller design. Previous researches show that an isolator model including the diaphragm effect which is neglected before can predict the isolator response more accurately. Since the diaphragm is often made of reinforced rubber material and has an irregular shape, it is not easy to obtain its parameters with experimental or computing method. A finite element analysis method for estimating the diaphragm stiffness is proposed in this paper, and experimental results suggest that a new model including the diaphragm stiffness correspond to the isolator behaviors more accurately.

A111 入力むだ時間を有するOn-Off制御系に対する量子化誤差情報に基づいた空圧式除振台の制御系設計(OS9 フルードパワーの基礎と応用2)

A111 入力むだ時間を有するOn-Off制御系に対する量子化誤差情報に基づいた空圧式除振台の制御系設計(OS9 フルードパワーの基礎と応用2)

Research on Whole-spacecraft Vibration Isolation based on Predictive Control

Launch vehicles will impart high levels of vibration to satellite during launch. Whole-spacecraft vibration isolation is a better choice to reduce the magnitude of launch dynamic loads. In this paper, active vibration isolation technology based on predictive control for whole-spacecraft vibration isolation is studied. Considering the special environment of the rocket, pneumatic isolation system is applied. In order to improve the dynamic characteristics of the isolation system, a cascade control with double loop structure and predictive control algorithm for pressure tracking control of inner loop are proposed. A pneumatic servo system exhibits strong nonlinearity. To resolve this problem, the control method of multi-models combined with MPC is put forward and applied in this paper, where piecewise linear models, on which controllers are built, are obtained by integrating the models with data at the work points. To enhance the tracking speed, a strategy of switching ahead is proposed, whose feasibility and effectiveness are proved by experiments. In addition, by resetting the predictive horizon and the weighting matrices of the MPC algorithm, influences of the considerable time delay, which is caused by a long pipeline, on the control system performance are effectively suppressed. With these newly proposed approaches, the pressure tracking performance is significantly improved. Thus with this design, the real-time pressure tracking can be guaranteed and so that the active control system can work at higher frequency range. The experiment results of isolation system with the double loop controller showed that the overshoot appears near the natural frequency was decreased greatly.

圧力微分計を用いた空気ばね式除振台の外乱補償制御(機械力学,計測,自動制御)

The purpose of this research is to suppress the inclination of the pneumatic isolation table caused by the relatively quick movement of the servo stage set on the isolation table. Pneumatic isolation tables are widely used in ultra precision machineries, such as steppers and precision measurement apparatuses. This is because they can support a high payload with a relatively low energy. Recently, pneumatic isolation tables for the semiconductor manufacturing devices have required higher performance as the line widths of semiconductors become finer. Therefore, the size of isolation table including the counter-mass is becoming larger, and the characteristics of the air springs are becoming softer. When the servo stage on a soft isolation table quickly moves, the table inclines and the recovery takes some long time. In this paper, a new compensation method of the inclination of isolation table using pressure differentiators is proposed. The pressure change in the air spring is detected with the pressure differentiator and it is positively fed back to realize higher pressure response. The performance of the proposed method is evaluated using an isolation table having 4 air springs in vertical direction, and a pneumatic driven servo stage on it. The effectiveness of the proposed method is demonstrated experimentally.