Yuji Ishino

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 a three-axis active vibration isolation system using zero-power magnetic suspension

A three-axis active vibration isolation system using zero-power magnetic suspension was developed. A mathematical model of the apparatus was derived for discussing the control system. It was shown that the three motions could be treated separately and, in addition, each dynamics was represented in a similar form. The condition for the system to have infinite stiffness for direct disturbance was derived. This characteristic was confirmed experimentally. It was also demonstrated that the transmissibility characteristics from the floor to the isolation table were not worsened by introducing zero-power control.

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.

Realization of a Zero-compliance System by Using Displacement Cancellation Control

A control method for achieving zero compliance to direct disturbance is proposed for a vibration isolation system. The structure of the proposed zero-compliance system is as follows. A middle mass is suspended by a spring from the base. The isolation table is suspended and moved by a linear actuator that is fixed to the middle mass. When direct disturbance acts on the isolation table, the middle mass begins to move in the same direction as the disturbance. The actuator operates to move the isolation table in the opposite direction to cancel the displacement of the middle mass to the base. To verify the effectiveness of this principle, a single-axis apparatus was fabricated. In this apparatus, the isolation table and the middle mass are guided to move horizontally to study characteristics without the influence of gravity. A voice coil motor (VCM) is installed between the isolation table and the middle mass, and integral—proportional—derivative (I-PD) control is implemented to achieve displacement cancellation control. Another VCM is installed between the middle mass and the base, and PD control is implemented for realizing the prescribed stiffness and damping. The efficacy of the designed control system is confirmed experimentally.

Estimation Method and Measurement Bandwidth of Gyroscopic Sensor using Active Magnetic Bearing

A gyroscopic sensor using active magnetic bearings (AMB) is studied in this paper. The sensor utilizes the control function of AMB and works as a two-axis gyroscopic sensor and also as a three-axis servo-type accelerometer. This paper focuses on angular velocity measurement. Angular velocities are estimated from the control signals for canceling gyroscopic and inertial toques acting on the shaft of the AMB. In measuring two-axis angular velocity simultaneously, there is a limit of the measuring range. In this paper, several numerical simulations and experiments with a conventional-size AMB are used to investigate this limit. In addition, the relationship between the measurement range and the control system is shown.

Pneumatic Three-axis Vibration Isolation System Using Negative Stiffness

A three-axis active vibration isolation system with pneumatic actuators for generating negative stiffness was developed A control method of realizing a suspension with negative stiffness by the actuator was derived. It was implemented in the developed system where each actuator was controlled locally. It was demonstrated experimentally that the equalization of the amplitude of negative and positive stiffness enables the system to have zero compliance to direct disturbance.

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.

General forms of controller realizing negative stiffness

The zero-power magnetic suspension system behaves as if it has negative stiffness. Suspension with a similar characteristic can be realized by using a linear actuator such as a voice coil motor. The controllers realizing negative stiffness with a linear actuator are compared with zero-power controllers analytically. The analyses show that they have similar structures. It is pointed out that a control technique, which was effective in widening the operation range of zero-power controllers, can be applied to the controllers realizing negative stiffness.

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.

Proposal of Force Measurement Using Series Magnetic Suspension

Series magnetic suspension is applied to force measurement. In a double series magnetic suspension system, two floators are suspended with a single electromagnet. The attractive force of the electromagnet directly acts on the first floator in which a permanent magnet is installed. The motion of the second floator is controlled indirectly through the attractive force of the permanent magnet. When PID control is applied to the second floator, the first floator displaces proportionally with the external force acting on the second floator even though the second floator does not move in the steady state. Therefore, the force can be estimated for the displacement of the first floator. When the stiffness between the first and second floators is low, even small force leads to large displacement so that the proposed measurement method is suitable for noncontact measurement of micro force. An apparatus was fabricated for experimental study on the proposed measurement method. Its effectiveness was demonstrated experimentally.Copyright