Isolation Tables Research Articles

Dynamic Research on Low-frequency Vibration Isolation Tables

In the paper, an establishment of dynamic characteristics of tabletops of the newly-developed optical tables is being discussed upon. Low-frequency vibration isolation systems are reviewed. Theoretical and experimental tests have been performed. Dynamic models of an optical table on a vibrating platform at different excitations have been developed, the dynamic displacement and the resonance frequencies of the system have been established and vibration transmissibility curves have been presented. The obtained dynamic characteristics of the mechanical passive low-frequency vibration isolation system show that such a system is able to isolate the vibrations effectively. The results of the performed experimental tests confirm the data of the theoretical research.

Noninteracting Control Design for 6-DoF Active Vibration Isolation Table with LMI Approach

This paper proposes a novel control strategy for six degrees-of-freedom active vibration isolation tables. In these systems, the most challenging issue is to suppress the external vibrations and isolate the internal interactions while still preserving the system’s robustness when facing uncertainties. A noninteracting controller is designed to tackle these problems. The resulting control system is completely decoupled in the sense that each system output is independently controlled to follow the corresponding reference signal. In this paper, the model of an active vibration isolation table is firstly derived. Conditions for system stability and decoupled performance are then discussed. The control law is formulated using the linear matrix inequality approach, which results in optimal control gains for the control objectives. With the proposed controller, complex system characteristics can be handled more efficiently such that an effective system is designed to obtain good control performance. Finally, simulations and comparison studies were conducted, and the results validate the efficiency of the proposed scheme.

Active Fault Diagnosis Design for Redundantly Driven Active Vibration Isolation Tables

Active Fault Diagnosis Design for Redundantly Driven Active Vibration Isolation Tables

A Setting Method of a Feedthrough Term for Pneumatic Isolation Tables Considering Difference between Bandwidth of Pressure Fluctuation and Mechanical Resonance

A Setting Method of a Feedthrough Term for Pneumatic Isolation Tables Considering Difference between Bandwidth of Pressure Fluctuation and Mechanical Resonance

A hybrid protection approaches for denial of service (DoS) attacks in wireless sensor networks

ABSTRACTWireless sensor network (WSN) contains the distributed autonomous devices with the sensing capability of physical and environmental conditions. During the clustering operation, the consumption of more energy causes the draining in battery power that leads to minimum network lifetime. Hence, the WSN devices are initially operated on low-power sleep mode to maximise the lifetime. But, the attacks arrival cause the disruption in low-power operating called denial of service (DoS) attacks. The conventional intrusion detection (ID) approaches such as rule-based and anomaly-based methods effectively detect the DoS attacks. But, the energy consumption and false detection rate are more. The absence of attack information and broadcast of its impact to the other cluster head (CH) leads to easy DoS attacks arrival. This article combines the isolation and routing tables to detect the attack in the specific cluster and broadcasts the information to other CH. The intercommunication between the CHs prevents the DoS attacks effectively. In addition, the swarm-based defence approach is proposed to migrate the fault channel to normal operating channel through frequency hop approaches. The comparative analysis between the proposed table-based intrusion detection systems (IDSs) and swarm-based defence approaches with the traditional IDS regarding the parameters of transmission overhead/efficiency, energy consumption, and false positive/negative rates proves the capability of DoS prediction/prevention in WSN.

Design of seismic isolation tables applicable to the long-period earthquake ground motion

Design of seismic isolation tables applicable to the long-period earthquake ground motion

Absence of Subharmonic Response in Vibrated Granular Systems under Microgravity Conditions

Viscous fluids are used as vibration dampers in applications ranging from isolation tables to cars; they are well understood and easy to engineer. An attractive alternative proposed for turbines, medical applications, and spacecraft is to use granular materials as dampers: Unlike fluids, they are nearly independent of temperature, can operate in harsh environments, and provide damping with no fixed anchor. Unfortunately, there are no design rules for these dampers, so the present paper characterizes effects of amplitude and frequency of oscillation on generic granular dampers. The authors determine broad operating ranges and find that, unlike their fluid counterparts, granular dampers strongly suppress higher-order dynamic resonances.

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.

Applying an Ontology to a Patrol Intrusion Detection System for Wireless Sensor Networks

With the increasing application of wireless sensor networks (WSN), the security requirements for wireless sensor network communications have become critical. However, the detection mechanisms of such systems impact the effectiveness of the entire network. In this paper, we propose a lightweight ontology-based wireless intrusion detection system (OWIDS). The system applies an ontology to a patrol intrusion detection system (PIDS). A PIDS is used to detect anomalies via detection knowledge. The system constructs the relationship of the sensor nodes in an ontology to enhance PIDS robustness. The sensor nodes preload comparison methods without detection knowledge. The system transfers a portion of the detection knowledge to detect anomalies. The memory requirement of a PIDS is lower than that of other methods which preload entire IDS. Finally, the isolation tables prevent repeated detection of an anomaly. The system adjusts detection knowledge until it converges. The experimental results show that OWIDS can reduce IDS (intrusion detection system) energy consumption.

Force Redistribution Method for Compensating Actuator-Breakdown of Vibration Isolation Tables Supported with a Redundant Number of Pneumatic Actuators

Force Redistribution Method for Compensating Actuator-Breakdown of Vibration Isolation Tables Supported with a Redundant Number of Pneumatic Actuators

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.

Six-degree of freedom active pneumatic table based on time delay control technique

Precision equipment is sensitive in general to both horizontal and vertical ground vibrations and, thus, equipment manufacturers specify limits on the vibrations of the floor so that such equipment can be operated satisfactorily. When the floor vibrations are unacceptably high, various types of passive or active vibration isolation tables can be used. A three-degree of freedom active pneumatic table with time delay control was developed for control of heaving, pitching, and rolling motions in a previous study by the authors. The isolation performances achieved were very good for both ground and table excitations in the vertical directions. Limitations of the three-degree of freedom active pneumatic table, however, were that it is vulnerable to excitations of the floor and table in the horizontal directions. Hence, a six-degree of freedom active pneumatic table was required in order to tackle ground and table excitations in the horizontal as well as vertical direction. In this paper, a study on the six-degree of freedom active pneumatic table supported by four air-springs for both vertical and horizontal vibration control is presented. Its performance is evaluated by ground and table excitation tests. The physical meaning of the singular value decomposition approach in transmissibility analysis on a multi-input/multi-output vibration isolation system is presented using a simple two-degree of freedom example and applied to the actual six-degree of freedom active pneumatic table. It is also shown that settling time in the case of table excitations in both vertical and horizontal directions can be effectively reduced by the proposed six-degree of freedom control.

322 アクチュエータ故障に対する冗長支持空気圧除振台の出力再分配法

Force redistribution method for compensating actuator-breakdown of vibration isolation tables is studied in this paper. Force of actuators can be adjusted by stepping motors in the regulator when some actuators are breaking down. The vibration isolation table in this study is supported by 8 pneumatic actuators, and has redundant number of actuators against degrees of freedom of motion. We propose a redistributing method of force which utilizes redundancy of the actuators. Effectiveness of the proposed method is examined by simulation.

Vibration Analysis of High-Precision Machine Tools Mounted on a Passive Vibration Isolation Table

Passive vibration isolation tables have been widely used to reduce the vibration of precision machine tools. However, because vibration isolators have low stiffness, vibrations are easily caused by the counter forces due to the feed motion of the machine tool. The vibration leads to the relative displacement between the tool and the workpiece that occurs in the perpendicular direction to the feed direction. This vibration is called cross talk vibration. This paper describes the analysis of the cross talk vibration by using the dynamic model of a machine tool and a vibration isolation table. First, the mechanism of the cross talk vibration is investigated by the multi-body simulation. Then, dynamic models are constructed from the multi-body simulation model by extracting a dominant structural mode of the machine tool. The analysis with the dynamic model shows that the amplitude of the cross talk vibration is in inverse proportion to the stiffness of the machine structure. The columns of the machine tool are modified to reduce the cross talk vibration. The amplitude of the vibration is reduced to approximately 1/4 as expected from the dynamic model.

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.

343 低次元システム同定法を用いた除振台の制御系自動最適化(産業機器の運動と振動の制御,OS-16 運動と振動の制御,総合テーマ「伝統を,未来へ!」)

343 低次元システム同定法を用いた除振台の制御系自動最適化(産業機器の運動と振動の制御,OS-16 運動と振動の制御,総合テーマ「伝統を,未来へ!」)

Feed-forward Control of a MIMO System for a Large-size and Lightweight Isolation Table

In this paper we propose a design method for a three-dimensional active isolation system with a low-stiffness isolation table assumed to be a large-size, lightweight isolation system. The lightweight, large-size isolation tables have been designed to be flexible. Owing to this, multi-modal vibrations appeared on the isolation table in the lower-frequency region. Therefore, a control system for considering multi-modal vibrations should be developed. We constructed a five-degree-of-freedom lumped model of the isolation table using a reduced-order physical-modeling method that is effective for controlling multi-modal vibrations. In the controller design, the performance of vibration control is obtained using a feedback controller designed using the linear—quadratic (LQ) control theory. Moreover, a feed-forward controller for a multi-input multi-output system has been added in order to obtain a high-isolation performance. Thus, a two-degree-of-freedom controller combined with LQ feed-forward controllers is designed. The usefulness of the proposed modeling method and controller are confirmed through numerical simulations and experimental results.

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.

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.

Application of Flow Rate Feedback Control to Active Controlled Pneumatic Isolation Tables

Application of Flow Rate Feedback Control to Active Controlled Pneumatic Isolation Tables