JPH09177872A - Precise vibration isolation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance vibration isolation effect of a higher harmonic component of vibration by supporting an apparatus placement table above a base table, coupling this placement table and the base table by means of a passive vibration isolation mechanism, and supporting the base table so that the table can be vibration isolated by means of a servo actuator. SOLUTION: A base table 1 is supported on a placement floor 3, the base end part of a servo actuator 4 is fixed to the placement floor 3, and the tip end part of a piston rod is coupled to the base table 1. This device is provided with a vibration sensor 6a sensitive to vibration of the placement floor 3, a vibration sensor 6b sensitive to vibration of the base table 1, and a displacement sensor 6c for detecting displacement of the movable part of the servo actuator 4, and vibration of the base table 1 is restricted by means of a computer 7 based on these output signals. An apparatus placement table 9 is mounted above this base table 1 via an elastic mount 8, and the base table 1 and the placement table 9 are coupled together by means of a viscous damper 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a precision vibration isolator used for the purpose of mounting precision equipment such as an LSI reduction exposure device, an electron microscope or a scanning tunneling microscope. Related to technical improvement to suppress.

[0002]

2. Description of the Related Art As is well known, the following precision vibration isolator is used in LSI factories and the like. A table on which an electron microscope or the like is placed is supported on the installation floor via an appropriate elastic mount and servo actuator. The output of the vibration sensor for detecting the vibration is processed by a computer, and the servo actuator is driven according to the processing result to suppress the vibration of the table. This is a well-known active damping technique. The active vibration suppression control system drives the actuator according to the output of the vibration sensor sensitive to the vibration of the table, and drives the actuator according to the output of the vibration sensor sensitive to the vibration of the installation floor. There is a feedforward control system. Although a device having only one control system is also known, it generally includes both feedback and feedforward control systems.

[0003]

With the active vibration damping mechanism as described above, when it is attempted to suppress the vibration of the table to the micron level or less, the accuracy of the micron order or less from a low frequency to an infinitely high frequency. An actuator that can control the displacement is required. An actuator (piezo actuator, etc.) that follows a relatively high frequency has a high rigidity of the actuator itself, and the vibration of the higher frequency component of the floor that the actuator cannot follow is transmitted to the vibration isolation table through the actuator. become. Furthermore, in the case of such an actuator, vibration is transmitted at a low frequency due to insufficient stroke of the actuator. Further, in a pneumatic actuator or the like having a low rigidity of the actuator itself, there is a problem in that the vibration isolating table has poor followability at high secondary and tertiary frequencies, and effective vibration damping cannot be performed.

The present invention has been made in view of the above-mentioned problems. It has a coarse precision, but is sufficiently large in terms of stroke and uses a very general actuator that follows from a low frequency to a relatively high frequency. An object of the present invention is to provide a precision vibration isolator capable of controlling to a level below a level and exerting a large vibration isolation effect on harmonic vibration components.

[0005]

A schematic structure of a precision vibration isolator according to an embodiment of the present invention is shown in FIG. Base table 1 is elastic mount 2 such as laminated rubber or air spring
It is supported by the installation floor 3 via. A base end portion (cylinder portion) of a servo actuator 4 formed of a servo hydraulic cylinder is fixed to the installation floor 3, and a tip end portion of a piston rod is connected to the base table 1 via a coupling spring 5. In the figure, only one servo actuator 4 is shown, and it seems that the base table 1 is excited only in the horizontal one-axis direction, but this is for the sake of simplicity. Of course, usually, two systems of actuator mechanisms for exciting the base table 1 in two orthogonal directions on a horizontal plane are provided, and an actuator mechanism for exciting the base table 1 in the vertical direction is often added. However, in the following description, it is explained that there is only the actuator 4 in the horizontal 1-axis direction. However, in the case of performing two-dimensional or three-dimensional active vibration suppression control, the configuration of the control system described below corresponds to two axes or three. It suffices to provide the axes.

A vibration sensor 6a sensitive to the vibration of the installation floor 3 directly below the base table 1 and a vibration sensor 6b sensitive to the vibration of the base table 1 are additionally provided. Also,
A displacement sensor 6c for detecting the displacement of the movable portion (piston or piston rod) of the servo actuator 4 is additionally provided. The computer 7, which is the center of the active vibration suppression control, reads the outputs of the vibration sensors 6a and 6b and the displacement sensor 6c, performs feedforward control and feedback control arithmetic processing according to the set algorithm, and drives the servo actuator 4. Vibration of the base table 1 is suppressed.

The driving force of the servo actuator 4 is not directly transmitted to the base table 1, but is transmitted through the coupling spring 5. The coupling spring 5 is an extremely soft spring (having an extremely large elastic modulus and an extremely small rigidity), and has a rigidity of about 1 / 10,000 of the displacement rigidity of the elastic mount 2 supporting the base table 1. As a result, even if the servo actuator 4 is reciprocally displaced with a large amplitude on the order of centimeters, the base table 1
Will only be displaced with an amplitude below the micron order. Further, vibration isolation with a very high frequency that the actuator 4 cannot follow is passively isolated by the coupling spring 5 attached to the actuator 4.

The vibration characteristics (vibration isolation performance) of the active vibration damping mechanism attached to the base table 1 described above will be described in detail using a mathematical model.

The equation of vibration when the vibration of the installation floor 3 and the damping force of the actuator 4 act on the base table 1 is represented by the equation 1.

[0010]

[Equation 1] If this is put together by the response (z + y) seen from the absolute coordinates, the following formula 2 is obtained.

[0011]

[Equation 2] Here, if c = 0 for simplification, it is necessary to satisfy Expression 3 in order to cancel the external force term on the right side of Expression 2 of the absolute response by the displacement z of the actuator 4.

[0012]

(Equation 3) If the rigidity Ks of the coupling spring 5 is 1/1000 of the rigidity K of the elastic mount 2, the stroke of the actuator 4 can be expanded and used for the movement of 10,000 times the vibration y of the installation floor 3. This description relates to feedforward control (input cancellation) for floor vibration, but also in the case of feedback control in which the movement of the base table 1 is sensed and controlled, the amplitude (x + y) can be expanded and controlled. Where C'is the control damping,

(Equation 4) In order to realize the characteristic of Expression 4 by the stroke control of the actuator 4, the stroke of only the feedback term becomes Expression 5.

[0013]

(Equation 5) Finally, the stroke of the actuator 4 that satisfies the equation 4 becomes the equation 6 by adding the equation 3.

[0014]

(Equation 6) These mathematical expressions also show that the stroke Z of the actuator 4 increases as ks decreases with respect to (k + ks). That is, the vibration of the table 1 can be controlled to the micron order or less by the large amplitude operation of the actuator 4.

Further, as shown in FIG. 1, in the present invention, the precision instrument 11 is not placed directly on the base table 1. A device mounting table 9 is mounted on the base table 1 via an elastic mount 8 such as laminated rubber or an air spring. The precision instrument 11 is placed on the table 9. The device mounting table 9 has a smaller mass than the base table 1, and the elastic mount 8 has a softer characteristic than the elastic mount 2. Further, the base table 1 and the equipment mounting table 9 are connected by a viscous damper 10 as a passive vibration damping mechanism. The passive damping mechanism is not limited to the viscous damper 10 and various types of dampers can be used. This passive vibration damping mechanism absorbs the vibration of the device mounting table 9 with respect to the base table 1 (particularly high frequency components of 100 Hz or higher).

As shown in FIG. 1, a vibration sensor 6d that is sensitive to the vibration of the equipment mounting table 9 is provided, and the computer 7 uses the output information of this sensor 6d to perform the above-described active vibration suppression control. If so, a better vibration damping effect can be realized.

[0017]

According to the present invention, table vibration can be suppressed to a micron order or less by using a high-power servo actuator such as a hydraulic cylinder whose displacement control accuracy is not so high, and an electron microscope having a large mass can be mounted. It exhibits extremely excellent vibration isolation performance as a precision vibration isolation device. Further, in the precision vibration isolator of the present invention, in addition to suppressing the vibration of the base table by the active vibration control mechanism, the passive vibration control that couples the vibration of the equipment mounting table mounted on the base table between the two is performed. It is suppressed by a shaking mechanism.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a precision vibration isolator according to an embodiment of the present invention.

[Explanation of symbols]

 1 Table 2 Elastic Mount 3 Installation Floor 4 Servo Actuator 5 Coupling Spring 6a, 6b, 6d Vibration Sensor 6c Displacement Sensor 7 Computer 8 Elastic Mount 9 Equipment Mounting Table 10 Viscous Damper (Passive Vibration Control Mechanism) 11 Precision Equipment

Claims (2)

[Claims] 1. A base table supported on an installation floor via an elastic mount, a servo actuator having a base end fixed to the installation floor, and a modulus of elasticity much higher than that of the elastic mount. A coupling spring that connects the tip of the servo actuator and the base table, a vibration sensor that is sensitive to the vibration of the installation floor, a vibration sensor that is sensitive to the vibration of the table, and a displacement of the movable portion of the servo actuator is detected. Displacement sensor, active vibration damping control means for driving the servo actuator according to the outputs of these three sensors to suppress the vibration of the table, and a device supported on the main table via an elastic mount. A mounting table and a passive vibration damping mechanism for connecting the equipment mounting table and the base table are provided. Precision vibration isolation device characterized by 2. The active damping control means according to claim 1, further comprising a control system for driving the servo actuator according to an output of an acceleration sensor which is sensitive to a vibration of the equipment mounting table. Precision vibration isolation device.