JPH09166176A - Precise vibration resistant device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain vibration to be under a micron level by respectively detecting vibration and displacement of a table elastically supported on an installation floor and a servo actuator of which base end is fixed, so as to control vibration of the table. SOLUTION: A table 1 is supported on an installation floor 3 through elastic mounts 2 such as laminated rubber. The base end part of a servo actuator 4 is fixed to the installation floor 3, and the extreme end part of a piston rod is connected to the table 1 through a connecting spring 5. A vibration sensor 6a acting upon vibration of the installation floor 3 directly under the table 1, a vibration sensor 6b acting upon vibration of the table 1, and a displacement sensor 6c detecting displacement of the movable part of the actuator 4 are provided. A computer 7 reads output of the vibration sensors 6a, 6b and the displacement sensor 6c, performs computing process of feedforward control and feedback control according to set algorism, and restrains vibration of the table 1.

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 that the vibration isolating table has a 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 uses a very general actuator that is coarse in accuracy but sufficiently large in terms of stroke and follows from a low frequency to a relatively high frequency. An object is to provide a precision vibration isolator that can be controlled below a level.

[0005]

A precision vibration isolator according to the present invention includes a table supported on an installation floor via an elastic mount, a servo actuator having a base end fixed to the installation floor, and A coupling spring that has a spring constant much smaller than that of an elastic mount and that connects the tip of the servo actuator and the table, a vibration sensor that is sensitive to the vibration of the installation floor, and a vibration sensor that is sensitive to the vibration of the table. A displacement sensor for detecting a displacement of a movable portion of the servo actuator, and an active vibration damping control means for driving the servo actuator according to outputs of these three sensors to suppress vibration of the table. is there.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a schematic structure of a precision vibration isolator according to an embodiment of the present invention. The table 1 is supported on an installation floor 3 via an elastic mount 2 such as laminated rubber or an air spring. 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 table 1 via a coupling spring 5. In the figure, only one servo actuator 4 is shown, and it seems that the table 1 is excited only in the horizontal uniaxial direction, but this is for the sake of simplicity. Of course, usually, a two-system actuator mechanism that excites the table 1 in two orthogonal directions on a horizontal plane is provided, and an actuator mechanism that excites the table 1 in the vertical direction is often added. However, in the following description, there is only one horizontal uniaxial actuator 4, but 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 axes. You only have to set the amount.

A vibration sensor 6a sensitive to the vibration of the installation floor 3 directly below the table 1 and a vibration sensor 6b sensitive to the vibration of the table 1 are additionally provided. In addition, the movable part of the servo actuator 4 (piston or piston rod)
A displacement sensor 6c for detecting the displacement of is attached. 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 table 1 is suppressed.

The driving force of the servo actuator 4 is not directly transmitted to the table 1, but is transmitted through the coupling spring 5. The coupling spring 5 is an extremely soft spring (having a very large elastic modulus and a very small rigidity), and has a rigidity of about 1 / 10,000 of the displacement rigidity of the elastic mount 2 supporting the table 1. Accordingly, even if the servo actuator 4 is reciprocally displaced with a large amplitude of centimeter order, the table 1 is displaced only with an amplitude of micron order or less.

Further, vibration isolation at a very high frequency that the actuator cannot follow is passively isolated by a coupling spring attached to the actuator.

Next, the vibration characteristics (vibration isolation performance) of the table 1 in the above embodiment will be described 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 table 1 is represented by the equation 1.

[0012]

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

[0013]

(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.

[0014]

(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. Although this description relates to feedforward control (input cancellation) for floor vibration, the amplitude (x + y) can be expanded and controlled also in the case of feedback control in which the movement of the table 1 is detected 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.

[0015]

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

[0016]

(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.

[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.

[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 springs 6a and 6b vibration sensor 6c displacement sensor 7 computer

Claims (1)

[Claims] 1. A table supported on an installation floor via an elastic mount, a servo actuator having a base end portion 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 actuator and the 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 that detects the displacement of the movable portion of the servo actuator. A precision vibration isolator, comprising: a sensor; and active vibration suppression control means for driving the servo actuator according to the outputs of these three sensors to suppress vibration of the table.