JPH08195179A - Active vibration removing device for electronic microscope - Google Patents

Abstract

PURPOSE: To reduce the absolute acceleration and absolute displacement of an electron microscope main body by using horizontal and vertical actuator members. CONSTITUTION: A surface plate 5 supported on vertical actuators 3 and an electron microscope 40 main body are excited in the horizontal and vertical directions by floor vibrations. Since the electron microscope 40 is generally supported at the center of gravity, the vibration mode tilted against the horizontal plane is applied to the surface plate 5. A relative displacement tends to occur between an electron gun 11 in an electromagnetic lens holder 10 and a sample bed 9, for example. The output signal of a detector 12 is inputted to a DSP member 16 through an A/D converter 15, and the DSP member 16 instantaneously calculates the voltages corresponding to the control force by the vertical actuators 3 and horizontal actuators 4. The vertical actuators 3 and horizontal actuators 4 are driven by the calculated control voltages. The electron microscope 40 is suppressed by the control force of the actuators 3, 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active anti-vibration device that vibratically isolates precision equipment such as an electron microscope from floor vibration, and is particularly suitable for reducing absolute displacement or absolute acceleration of equipment. The present invention relates to an active vibration isolation device.

[0002]

2. Description of the Related Art Generally, in an electron microscope, the image accuracy may be deteriorated due to the vibration of the floor on which the equipment is installed. Therefore, the electron microscope is installed on a surface plate supported by a vibration isolation device. The vibration isolation device has a combination of a spring member made of an elastic material having low rigidity in the horizontal direction and the vertical direction, such as a coil spring, an air spring, or a vibration damping rubber, and a vibration damping member such as a viscous damper having a damping effect. Often used. The vibration isolation device is a device for reducing (vibrating) the absolute acceleration of the response of the surface plate and the equipment mounted on the surface plate by vibrating and insulating minute vibrations from the floor surface. However, the passive vibration isolator always has a natural frequency, and there is a limit to lowering the natural frequency. Generally, the natural frequency of a passive vibration isolator becomes about 1 to 3 Hz, and floor vibrations of 1.5 to 4 Hz or less are amplified by the passive vibration isolator, rather than being able to obtain the vibration isolation effect. . This is a problem of the passive vibration isolation device.

Therefore, as a method of solving such a problem, a method of actively suppressing the vibration of the surface plate against a slight vibration of the floor vibration can be considered. As described in JP-A-2-246382 and JP-A-2-228712, an active is used to suppress absolute acceleration of vibration of the surface plate by using an actuator to feed back absolute acceleration etc. on the surface plate. There is a vibration isolation device.

[0004]

According to the principle of the prior art in the active vibration isolator, the effect of significantly reducing the vibration of the surface plate on which the equipment is mounted with respect to the floor vibration can be obtained.
However, the conventional active anti-vibration device is designed independently of the on-board equipment, and since the surface plate and the pedestal are provided as the active anti-vibration device, the work table of the electron microscope becomes higher in position, resulting in poor workability. Become. Therefore, in order to secure workability, it is necessary to make the lower part of the cradle of the active vibration isolation device in which the electron microscope is installed be at the floor level.
Therefore, it is necessary to dig down the floor portion where the active vibration isolation device is provided, which increases the construction cost and limits the layout. Further, the problem with the conventional active vibration isolation device is that the vibration characteristics of the precision equipment mounted on the vibration isolation device cannot be accurately considered, so that high-precision vibration isolation / vibration suppression performance is restricted.

It is an object of the present invention to provide an active vibration isolator which highly accurately reduces the absolute vibration amount (absolute change or absolute acceleration) of a device without changing the height of the electron microscope.

[0006]

In order to achieve the above object, the present invention provides a horizontal and vertical actuator member or a horizontal and vertical actuator member provided between a surface plate and a pedestal of an electron microscope. A passive vibration isolation member provided in parallel with this, a surface plate and an electron microscope main body, are arranged on the main body of the electron microscope to detect the acceleration or displacement of these elements, and an active vibration isolation member consisting of a controller that controls the actuator member based on the detection data. Provide a shaking device. As the actuator member, a laminated piezoelectric element is used, and when the floor vibration includes a high frequency component that is not a control target, a high frequency component blocking member for removing the high frequency component is also used. Further, the vertical actuator is provided with a height adjusting member for adjusting the height.

[0007]

In general, a passive vibration isolator does not support an electron microscope at the height of its center of gravity or at a symmetrical position with respect to a vertical plane passing through the center of gravity, and therefore, when it is vibrated horizontally or vertically. , Vibrations in these directions and rotational vibrations are coupled. Further, since the natural frequency in the horizontal and vertical directions by the passive vibration isolation device is set sufficiently lower than the natural frequency of the electron microscope main body, the response to the floor vibration input is almost the same as that of the electron microscope. With a rigid body, the vibration mode in which the vibration isolator deforms is the main, and the vibration mode is a combination of the translation mode and the rotation mode.

Therefore, in the present invention, the active vibration isolator is arranged as close as possible to the height of the center of gravity of the electron microscope main body, and when the passive vibration isolation member is used together, the center of gravity and the rigid center are matched. By designing the vertical spring constant of the passive vibration isolation device, the control force generated by the actuator member can be reduced. Furthermore, the vibration mode of the electron microscope as a whole is reduced by the passive vibration isolation member, and the higher eigenmodes of the electron microscope body are not excited, so the vibration mode of the electron microscope body becomes simpler. The number of detectors for detecting the vibration state can be reduced. Further, even when only the active vibration isolation member is used, the detection of detecting the vibration state of the electron microscope main body by preventing the higher-order vibration mode of the electron microscope main body from being excited by the spring characteristic of the high frequency cutoff member. It is possible to reduce the number of vessels. For example, the detector is arranged on the surface plate and the head of the electromagnetic lens holder of the electron microscope main body at each point in the vicinity where the vertical actuator member is installed. The analog signals from these detectors are converted into digital signals using A / D converters, and based on these signals, DSP (digital signal processor) is used to control signals according to algorithms incorporated therein. Calculate fast. This control signal is converted into an analog signal using a D / A converter and amplified by an amplifier. By controlling the horizontal and vertical actuators by this control signal, the horizontal and vertical absolute accelerations or absolute displacements of the entire electron microscope can be suppressed, and the influence of floor vibration of the electron microscope can be eliminated.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIGS.

The embodiment shown in FIG. 1 is an example in which the active vibration isolator of the present invention is applied to an electron microscope 40. In the example,
A plurality of vertical actuators 3 and horizontal actuators 4 are provided on a pedestal 2 installed on the floor 1. The plurality of vertical actuators 3 support the surface plate 5. Further, the main body of the electron microscope 40 is mounted on the surface plate 5. An electron gun 11 that emits an electron beam and an electromagnetic lens 39 that converges the electron beam are provided in the electromagnetic lens holder 10 of the electron microscope 40.
The inside is evacuated by the vacuum pump 6b. Further, a stage 8 for moving the sample table 9 in the chamber 7 from outside the chamber 7 in any horizontal and vertical directions is provided in the chamber 7, and the inside of the chamber 7 is evacuated by a vacuum pump 6a. In order to control the vertical actuator 3 and the horizontal actuator 4, as shown in FIG. 1, the horizontal and vertical directions of points on the surface plate 5 installed on the vertical actuator 3 and the horizontal actuator 4 are controlled. If necessary, a plurality of detectors 11 for detecting acceleration or displacement or the like and acceleration or the like for grasping vibration of the electron microscope 40 main body to be controlled are provided. The signals from these detectors 12 are input to the DSP member 16 through the A / D converter 15, and the DSP member 16 is written with an execution program for controlling the vertical actuator 3 and the horizontal actuator 4. DSP member 16
The signal calculated at high speed is D / A converter 17, amplifier 1
8, the vertical actuator 3 and the horizontal actuator 4 are controlled. The ROM 14 sends the command signal to the DS when starting or ending the control of the vertical actuator 3 and the horizontal actuator 4.
It has a function of sending to the P member 16.

FIG. 2 is a transverse sectional view of an embodiment in which the active vibration isolator of the present invention is applied to the electron microscope 40.

Next, an embodiment of the vertical actuator 3 of the present invention will be described with reference to FIG. The basic structure of the vertical actuator 3 is a laminated piezoelectric element 29, a height adjusting member 21, and a high frequency component blocking member 30. Block members 28 are attached to both ends of the laminated piezoelectric element 29, and the block members 28 a are supported on a height adjusting member 21 screwed into the lower plate member 19 via thrust bearing members 23. The centering member 27 inserted in the convex member provided on the upper part of the height adjusting member 21 is pushed by the pushing member 22 inserted into the hole provided in the horizontal direction of the height adjusting member 21.
It is fitted in the groove of the block member 28a. The thrust bearing member 23 is composed of a large number of ball bearings 24, a casing member 25 accommodating the ball bearings 24, and a ring-shaped magnet member 26 embedded in the casing member 25. The casing member 25 is ring-shaped and has a half-split structure with respect to the horizontal plane. The cross section of the casing member 25 is concave so that the ball bearing 24 does not go out of the casing member 25.
An appropriate gap is provided between the flange of the concave portion and the ball bearing 24 so that the horizontal relative displacement between the pedestal 2 and the surface plate 5 can be absorbed. Therefore, when adjusting the height of the vertical actuator 3, the ball bearing 24 can be positioned at the center of the concave portion by the ring-shaped magnet member 26 embedded in the casing member 25. 27, the laminated piezoelectric element 2 located above the ball bearing 24
Positioning in the horizontal direction such as 9 becomes possible. The height of the vertical actuator 3 is adjusted by rotating the height adjusting member 21. That is, when the height adjusting member 21 is rotated, the height adjusting member 21 screwed into the lower plate member 19 moves up and down, and at this time, the thrust bearing member 23 gives only the vertical displacement to the block member 28a, It is possible to prevent the transmission of the torsion load to the laminated piezoelectric element 29. Multilayer piezoelectric element 29 pushed up by height adjusting member 21
Is a block member 28b, a high frequency component blocking member 30,
Further, it is pressed against the surface plate 5 through the reinforcing member 31 until an appropriate load is applied. After adjusting the height, the nut member 20 is used for fixing. Further, the pushing member 22 is attached to the height adjusting member 2
By removing from 1 and lowering the centering member 27,
The constraint on the horizontal movement of the block member 28b is released. Accordingly, since there is a gap between the ball bearing 24 of the thrust bearing member 23 and the casing member 25,
The vertical actuator 3 does not restrain the horizontal movement of the surface plate 5. The high frequency component blocking member 30 is used to remove high frequency components of the floor vibration that are not controlled. Further, the block member 28b is provided with a cover member 32 for protecting the laminated piezoelectric element 29.

The operation of this embodiment will be described with reference to FIGS. 1, 3 and 4.

Due to floor vibration, the vertical actuator 3
The surface plate 5 and the main body of the electron microscope 40 supported by are vibrated in the horizontal and vertical directions. Generally, since the electron microscope 40 is not supported by the center of gravity, the surface plate 5 vibrates inclining with respect to the horizontal plane. Mode is added. As a result, for example, relative displacement tends to occur between the electron gun 11 in the electromagnetic lens holder 10 and the sample stage 9. At this time, the actuator member 3
Acceleration or displacement of each point of the surface plate 4 on which the surface 4 is arranged, the top of the electron microscope 40 to be controlled, and the surface plate 5
The output signal of the detector 12 for detecting acceleration etc.
The DSP gain is input to the DSP member 16 through the / D converter 15, and the acceleration gain or displacement and the square value of the power of the actuator are used as the evaluation function, and the feedback gain determined so as to minimize this evaluation function is used.
The member 16 instantly calculates the voltage corresponding to the control force by the vertical actuator 3 and the horizontal actuator 4, and the calculated control voltage is passed through the D / A converter 17 and the amplifier 18 to the vertical actuator 3 and the horizontal actuator. The directional actuator 4 is driven. The control force of the vertical actuator 3 and the horizontal actuator 4 suppresses the electron microscope 40 so as to reduce the absolute acceleration or absolute displacement of the electron microscope 40.

FIG. 5 shows an embodiment in which the vertical actuator 3 or the horizontal actuator 4 and the passive vibration isolator 36 are arranged in parallel. The passive vibration isolation member 36 is mainly composed of the rubber member 35 and the spacer member 34, and in particular, can support the weight of the electron microscope 40 and reduce the control force of the vertical actuator 4. Further, even if the control becomes impossible due to a failure of the actuator or the like, it is possible to secure the vibration isolation effect to some extent only by the passive vibration isolation member 36.

Furthermore, FIG. 6 shows another embodiment. In the embodiment of FIG. 6, the vertical actuator member 3 or the horizontal actuator member 4 is arranged at the center of a hollow rubber member as the passive vibration isolating member 36 so as to be integrated and made compact.

The height adjusting member 23 is a laminated piezoelectric element 29.
Is a member for adjusting the height of the laminated plate so that it can come into contact with the platen 5 so that the control force of the laminated piezoelectric element 29 can act on the platen 5. The piezoelectric element 29 can be used as a load cell.

In the embodiment shown in FIG. 7, in order to prevent the vertical actuator 3 from being damaged when the vertical actuator 3 is attached to the electron microscope 40 and during the transportation of the electron microscope 40, the embodiment above the surface plate 5 is used. A stopper member 37 that supports the load is provided.

[0019]

According to the present invention, by using horizontal and vertical actuator members in an active vibration isolator for an electron microscope that vibrates and isolates a floor vibration input, the absolute acceleration and absolute displacement of the electron microscope main body are significantly increased. Can be reduced to

[Brief description of drawings]

FIG. 1 is a vertical sectional view of an embodiment in which an active vibration isolator according to the present invention is applied to an electron microscope.

FIG. 2 is a cross-sectional view of an embodiment in which the active vibration isolator of the present invention is applied to an electron microscope.

FIG. 3 is a cross-sectional view of an embodiment of a vertical actuator member of the present invention.

FIG. 4 is a sectional view of an embodiment of a horizontal actuator member of the present invention.

FIG. 5 is a sectional view of an embodiment in which a passive member and an actuator member of the present invention are independently arranged.

FIG. 6 is a sectional view of an embodiment in which a passive member and an actuator member of the present invention are integrally arranged.

FIG. 7 is a sectional view of an embodiment in which a stopper member is provided when mounting the horizontal and vertical actuators of the present invention.

FIG. 8 is a sectional view of an active vibration isolator according to a conventional method.

[Explanation of symbols]

1 ... Floor, 2 ... Stand, 3 ... Vertical actuator, 4 ...
Horizontal actuator, 5 ... Surface plate, 6 ... Vacuum pump,
7 ... Chamber, 8 ... Stage, 9 ... Sample stage, 10 ... Electron lens holder, 11 ... Electron gun, 12 ... Detector, 13 ... Controller, 14 ... ROM, 15 ... A / D converter, 16
... DSP, 17 ... D / A converter, 18 ... Amplifier, 39 ...
Electromagnetic lens, 40 ... Electron microscope.

Claims (7)

[Claims] 1. An active vibration isolation device for an electron microscope, comprising horizontal and vertical actuator members provided between a surface plate supporting a main body of an electromagnetic lens constituting the electron microscope and a pedestal for installation on a floor, An active vibration isolation device comprising a detector for detecting a vibration state of an electron microscope and a controller for controlling the horizontal and vertical actuator members based on a signal from the detector. 2. The active vibration isolation device according to claim 1, wherein a passive vibration isolation member including a spring member that is an elastic body and a vibration damping member that is provided as necessary is arranged in parallel with at least the vertical actuator member. 3. An active vibration isolator according to claim 1, wherein a passive vibration isolator composed of a spring member which is an elastic body and a vibration depletion member which is provided as necessary is integrated with at least the vertical actuator member. . 4. A laminated piezoelectric element and a high frequency component blocking member of an elastic body are used as the horizontal and vertical actuator members, and the vertical actuator member has a height as defined in claim 1, 2. An active vibration isolator using a height adjusting member for adjusting. 5. The thrust bearing member according to claim 4, wherein a thrust bearing member is provided in series with a screw head portion of the height adjusting member of the vertical actuator member, and the thrust bearing member includes a ball bearing and an upper portion in contact with the ball bearing. It is composed of two split casing members arranged in the lower part, and the upper and lower members of the casing member are ring-shaped and have a concave cross-section, and there is a suitable gap between the concave collar part and the ball bearing. Anti-vibration device with magnets embedded in the casing member such that the ball bearing is located in the center of the recess with a large gap. 6. The load meter according to claim 4 or 5, wherein the height adjusting member of the vertical actuator presses the laminated piezoelectric element between a surface plate side and a floor side with an appropriate load. Active vibration isolation device used. 7. The method according to claim 1, 2, 3, 4 or 5,
An active vibration isolation device in which a stopper is provided between a surface plate and a pedestal to protect the actuator when the horizontal and vertical actuators are attached and when the electron microscope is transported.