Md. Emdadul Hoque

Development of a three-axis active vibration isolator using zero-power control

This paper presents the development of an active 3-degree-of-freedom (DoF) vibration isolation system using zero-power magnetic suspension. The developed system is capable to suppress direct disturbances and isolate ground vibrations of the 3-DoF motions, associated with vertical translational and rotational modes. Two categories of control strategy for the actuators are proposed, i.e., local control and mode control. The latter method allows to overcome limitations of the poor performances for rotational modes exhibited by the former. A mathematical model of the system is derived and each DoF motion is treated separately for the control system. It is demonstrated analytically that the infinite stiffness to static direct disturbances can be generated and the resonance peak due to floor vibration can effectively be suppressed for the system. Moreover, the experiments have been carried out to measure the static and dynamic responses of the isolation table to direct disturbances, and transmissibility characteristic of the isolator from the floor. The results indicate good vibration isolation and attenuation performances, and show the efficacy of the developed isolator for industrialization

Development of an Active Vibration Isolation System Using Linearized Zero-Power Control With Weight Support Springs

This paper presents a hybrid vibration isolation system using linearized zero-power control with weight support springs. The isolation system, fundamentally, is developed by linking a mechanical spring in series with a negative stiffness spring realized by zero-power control in order to insulate ground vibration as well as to reject the effect of on-board-generated direct disturbances. In the original system, the table is suspended from the middle table solely by the attractive force produced by the magnets and therefore, the maximum supporting force on the table is limited by the capacity of the permanent magnets used for zero-power control. To meet the growing demand to support heavy payload on the table, the physical model is extended by introducing an additional mechanism-weight support springs, in parallel with the above system. However, the nonlinearity of the zero-power control instigates a nonlinear vibration isolation system, which leads to a deviation from zero compliance to direct disturbance. Therefore, a nonlinear compensator for the zero-power control is employed furthermore to the system to meet the ever-increasing precise disturbance rejection requirements in the hitechnology systems. The fundamental characteristics of the system are explained analytically and the improved control performances are demonstrated experimentally.

Design of a mode-based controller for 3-DOF vibration isolation system

This paper presents an active suspension technique for a three-degrees-of-freedom (3-DOF) vibration isolation system using negative stiffness. A mode-based digital controller is designed based on a theoretical model to generate negative stiffness by active suspension. The active suspension mechanism, in conjunction with a conventional spring in series, can generate infinite stiffness against direct disturbances on the isolation table. Three-axis motions of the isolation table in the vertical directions are actively controlled by the proposed system. Experimental results show that the active suspension system using the proposed controller well evaluates and describes the zero-compliance against direct disturbances.

VIBRATION ISOLATION SYSTEM USING ZERO-POWER MAGNETIC SUSPENSION WITH A WEIGHT SUSPENSION MECHANISM

Abstract Vibration isolation system using zero-power magnetic suspension is modified to be equipped with a weight support mechanism. The original system has a problem that the whole weight of the isolation table must be supported solely by the attractive force produced by permanent magnets. It is an obstacle to develop large isolation tables. In order to overcome this obstacle, a weight support mechanism is introduced in parallel with the serial connection of a zero-power magnetic suspension system and a normal spring. It can reduce the static load force that the zero-power magnetic suspension has to support. The basic characteristics of the modified system are shown analytically. Experimental study demonstrates that the modified system maintains infinite stiffness against direct disturbance even if such a weight support mechanism is added.

Development of a Six-Axis Hybrid Vibration Isolation System Using Zero-Power Control

This paper presents a six-axis hybrid vibration isolation system by an active zero-power control in combination with a passive weight support mechanism in order to develop a large vibration isolation table. The use of active zero-power control and weight support mechanism is the salient feature of the proposed system which enables to develop a vibration isolator with low power consumption and low cost. The system is capable to isolate as well as to control vibrations from different sources in addition to suppress large payloads or support large table. The basic characteristics of the developed system are elaborately discussed analytically. The proposed control technique can control all the motions of the system. The performance of the controller is evaluated by conducting several experiments

A Nonlinear Compensator for Zero-Power Control and Its Application to Vibration Isolation System

This paper presents a nonlinear compensation of zero-compliance system using zero-power magnetic suspension. Realization of negative stiffness by zero-power control is an integral part of vibration isolation system. Zero-compliance to direct disturbance is achieved by connecting a negative stiffness suspension in series with a normal positive stiffness spring. However, zero-power control system itself has inherently nonlinear characteristics and thus, makes the zero-compliance system nonlinear. In this paper, a nonlinear zero-power controller is designed and applied to vibration isolation system. The experimental results show that the proposed controller could effectively reduce the nonlinearity of the zero-power control, as well as vibration isolation system.Copyright

A 3-DOF modular vibration isolation system using zero-power magnetic suspension with adjustable negative stiffness

This paper presents a 3-DOF vibration isolation system combining three vibration isolation modules. Each vibration isolation module is constructed by connecting a positive stiffness spring in series with a negative stiffness spring. The positive and negative spring is realized by an active controlled magnetic suspension. In the previous system, conventional zero-power control system has been used to generate negative stiffness, and the stiffness depends on the capacity of the permanent magnets or the gap-force coefficient of the magnets. This is one of the bottlenecks in the fields of application of zero-power control where the adjustment of stiffness is necessary. On the other hand, the suspension system was used in the vertical and horizontal directions, which made the system complicated. To overcome the above problems, a vibration isolation system is developed with three modules connected by parallel mechanism. Some experiments have been carried out to measure the efficacy of the control system, as well as the vibration isolation system.

A Modular-Type Three-Axis Vibration Isolation System Using Negative Stiffness

A vibration isolation system is presented in this paper which is developed by the combination of multiple vibration isolation modules. Each module is fabricated by connecting a positive stiffness suspension in series with a negative stiffness suspension. Each vibration isolation module can be considered as a self-sufficient single-degree-of-freedom vibration isolation system. 3-DOF vibration isolation system can be developed by combining three modules. As the number of motions to be controlled and the number of actuators are equal, there is no redundancy in actuators in such vibration isolation systems. Experimental results are presented to verify the proposed concept of the development of MDOF vibration isolation system using vibration isolation modules.Copyright

A MODEL-BASED CONTROLLER FOR A VIBRATION ISOLATION SYSTEM WITH WEIGHT SUPPORT SPRINGS

Abstract This paper is aimed to design a zero-power controller based on the theoretical model and to implement it into a vibration isolation system. To develop the vibration isolation system which is able to isolate ground vibrations as well as to suppress direct disturbance, a positive passive suspension is connected in series with an active negative spring at the outset. The system is further reinforced by using a weight support mechanism to enhance the performance for supporting heavy payloads and/ or developing large isolation table. The characteristic of the developed system is treated analytically and the efficacy of the controller performances is verified experimentally.