JPH06117481A - Vibration isolator - Google Patents

Abstract

PURPOSE:To improve the effect of suppressing vibration caused by disturbance in a vibration isolator for precision instrument or the like by feeding the detected vibration caused by distrubance back to an actuator, and changing the gain of a position control compensator for feeding the displacement of a vibration isolating table back to the actuator. CONSTITUTION:When disturbing force Fd acts upon a vibration isolating table 1 by the acceleration/deceleration of a stage 2 to generate vibration cuased by disturbance, the vibration of the vibration isolating table 1 is detected by a vibration detecting sensor 5 and fed back to an actuator 4 through a vibration control compensator 6. At this time, the gain of a position control compensator 8 for compensating the output of a displacement sensor 7 to feed it back to the actuator 4 is made high by the output of the vibration detecting sensor 5 so as to enlarge the resilience of a vibration system. When the vibration caused by disturbance is settled, the gain is made small inversely to make the resilience small.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anti-vibration device which has improved vibration-damping effect without impairing the anti-vibration effect as compared with the prior art.

[0002]

2. Description of the Related Art With the increase in precision of precision instruments such as electron microscopes, STM surface roughness meters, optical instruments, and steppers, micro-vibration caused by micro-vibration transmitted to these instruments from the installation floor.
There is a need to insulate at the (milligal) level. In order to insulate minute vibrations transmitted to equipment from a frequency as low as possible, it is basically necessary to install them on a vibration isolation table having a support mechanism with low rigidity (spring constant) and low viscosity. However, when the precision instrument itself generates vibrations that cause disturbances, low-frequency resonance, which is determined by the rigidity of the support mechanism and the mass of the instrument and the vibration isolation table, excites overall vibration, which increases the rigidity and viscosity. Can't be made smaller. Therefore, in consideration of the trade-off between insulation of vibrations transmitted from the floor (vibration isolation) and suppression of disturbance vibrations generated inside the equipment (vibration suppression) (vibration transmissibility range of 5 to 30%), appropriate rigidity and viscosity are set. The anti-vibration device has been selectively used.

There are various types of vibration isolation supporting devices, but the air spring vibration isolation device can be widely used for supporting precision equipment because it can set a small spring constant and can insulate vibrations of about 5 Hz or more. Has been done. Further, recently, in order to break through the limitations of the passive vibration isolator as described above, an active vibration isolator has been put into practical use. This is an active vibration isolation device that detects the vibration of the vibration isolation table with a sensor and uses a feedback circuit to control the vibration using an actuator or a mass damper. Ideal vibration isolation effect with no resonance peak in the low frequency band. It is possible to have.

For example, the active control precision vibration damping base disclosed in Japanese Patent Application Laid-Open No. 1-210634 controls vibration by detecting the vibration of the vibration damping base with a sensor and adjusting the air pressure in the air spring via a control valve. It is a pneumatic active vibration isolator using an air spring as an actuator. As shown in FIG. 3A, a control system of such an active vibration isolation device generally detects a vibration isolation table vibration (for example, acceleration) and mainly adds viscosity to control the vibration, and a vibration control loop. It has a position control loop that controls the level fluctuation of the vibration isolation table by detecting the relative displacement of the oscillation table and the floor.

3 (b) and 3 (c) show an active vibration isolator in which such conventional actuators are arranged at four corners and precision equipment (XY stage) is mounted. This active vibration isolation system includes a vibration isolation table 1 and an isolation table 1
It is equipped with sensors 10, 12, 14, 16, 16, 24 and 26 and actuators 9, 11, 13, 15, 15, 23 and 25 that are installed at the four corners of the vibration isolation table 1 to control the movement of the vibration isolation table 1 in six degrees of freedom, and it is isolated from floor vibration. (Vibration isolation) and the disturbance vibration generated inside the XY stages 17 and 20 are suppressed (vibration suppression). There are a total of eight actuators, and the arrangement details are four in the vertical Z direction, two in the horizontal X direction, and two in the horizontal Y direction.

The XY stages 17 and 2 will be described below with reference to FIG.
The operation of the vibration isolator when 0 is driven in the X direction will be described. First, it is assumed that the X stage 17 is driven in the + X direction via the X axis ball screw 18 by the rotation of the X axis motor 12. At this time, the vibration isolation table 1 is displaced in the −X direction by the reaction force of the drive, and the vibration isolation table 1 mainly vibrates in the X direction. Next, this vibration is detected by the sensors 12 and 16 and is controlled by the actuators 11 and 15 arranged in the horizontal X direction via a feedback circuit. That is, the disturbance force acting on the vibration isolation table 1 by the reaction force of the drive of the X stage 17 is supported by the two horizontal X-direction actuators 11 and 15. The same applies to the Y direction, and the Y stage 2
The disturbance force acting on the vibration isolation table 1 by the reaction force of 0 driving is supported by the two horizontal Y-direction actuators 9 and 13.

[0007]

In the vibration isolator, the rigidity of the support mechanism is set as low as possible in order to enhance the insulation (vibration isolation) effect of floor vibration. Therefore, the rigidity of the actuator (mechanical rigidity and electrical rigidity) must be reduced. This is because the actuator also becomes a part of the support mechanism. However, when the precision equipment mounted on the vibration isolation table as shown in FIG. 3 is an equipment such as an XY stage that performs large acceleration / deceleration, the vibration isolation table is oscillated with a large amplitude due to disturbance force. Even with an active vibration isolator, it takes time to settle the disturbance vibration. This disturbance vibration adversely affects precision equipment as well as floor vibration, so we want to minimize it. In this case, the following three methods can be considered as methods for suppressing (damping) the disturbance vibration.

(1) Enlarge the actuator.

(2) Increase the control loop gain.

(3) Add more actuators.

However, since all of these are equivalent to increasing the mechanical or electrical rigidity of the vibration isolation support mechanism, the vibration isolation effect is enhanced but the vibration isolation effect is deteriorated. In order to improve the performance of precision equipment, it is necessary to eliminate the trade-off between vibration isolation and vibration suppression.

That is, when the compensator gain of the vibration control loop is increased in order to quickly suppress this vibration, if it is set too high, the stability of the closed loop will be impaired, so there is a limit. Further, when the compensator gain of the position control loop is increased, the spring constant of the support mechanism is equivalently increased, and the damping effect is enhanced but the vibration isolation effect is deteriorated. In particular, the pneumatic active vibration isolator has a problem that the high-speed response of the air spring actuator is poor due to the compressibility of air, and it is not possible to sufficiently follow the shocking disturbance vibration when the XY stage is driven. However, since the support of precision equipment by the air spring has a high effect of insulating (vibrating) floor vibration, it is desired to improve the effect of suppressing disturbance vibration (vibration suppression) that occurs when the XY stage is driven, without impairing this characteristic.

In view of the above problems, it is an object of the present invention to improve the effect of suppressing disturbance vibration (damping) without damaging the effect of insulating (vibrating) floor vibration in a vibration isolator.

[0014]

In order to achieve this object, a vibration isolator according to a first aspect of the present invention comprises a vibration isolation table on which a precision instrument having a drive means is mounted, and an elastic support for elastically supporting the vibration isolation table. Means, an actuator for supporting the vibration isolation table, a vibration sensor for detecting the vibration of the vibration isolation table, a vibration control compensating means for compensating the output of the vibration sensor and feeding back to the actuator, a displacement sensor for detecting the displacement of the vibration isolation table, a displacement Position control compensating means for compensating the output of the sensor and feeding back to the actuator, and for disturbance vibration of large amplitude based on the output of the vibration sensor, position control compensating means has a high gain and for floor vibration of small amplitude. The position control compensating means is provided with a control means for making the gain low.

According to the second aspect of the present invention, in a vibration isolation device equipped with a vibration isolation table on which a precision instrument having a drive means is mounted, and an elastic support means for supporting the vibration isolation table, the vibration isolation device has a degree of freedom in the direction of freedom. The direction of the degree of freedom of precision equipment has an angle so that they do not match.

[0016]

In the conventional vibration isolator, suppression of disturbance vibration with large amplitude and insulation of floor vibration with small amplitude are controlled by the same closed loop structure. In this structure, insulation of floor vibration (vibration isolation) is performed. There is a limit to improving both the effect and the suppression (damping) effect of the main body vibration. That is, when the gain of the position control loop is increased, the springiness (responsiveness) of the system is increased and the vibration damping effect is improved, but the vibration damping effect is deteriorated. In order to solve this problem, the present inventors have found that suppression of disturbance vibration having a large amplitude and insulation of floor vibration having a small amplitude may be controlled by different closed loop configurations. In the first invention, the vibration sensor Based on the output, the position control compensating means is controlled to have a high gain for the disturbance vibration having a large amplitude, and the position control compensating means is controlled to have a low gain for the floor vibration having a small amplitude. That is,
For example, an actuator such as a voice coil motor (VCM) having a quick response is installed in parallel with an air spring, and a sensor detects vibration of the vibration isolation table. When the vibration is large, this actuator is driven with a high gain to If the gain is small, the gain of the position control compensator is changed according to a certain function depending on the vibration level, such as driving with a low gain. This is because when the precision equipment such as the XY stage on the vibration isolation table is driven, the spring constant of the support mechanism is increased to enhance the vibration damping effect, and when it is not driven, the spring constant is decreased to reduce the vibration isolation. It works to increase the effect. In this way, by providing an actuator with a quick response and varying the gain of the position control compensator according to the vibration level of the vibration isolation table, the vibration damping effect is improved without impairing the vibration isolation effect.

Further, a vibration isolation device used to support precision equipment and a precision equipment mounted on the vibration isolation table (for example, X
The Y stage) was not arranged in consideration of each other's freedom of movement. On the other hand, in the second invention, in consideration of the degrees of freedom between the vibration isolation device and the equipment mounted thereon, an angle is provided between the directions of these degrees of freedom, and the directions are shifted,
Even though the rigidity of the vibration isolation table support means such as the actuator does not change, the disturbance force generated by the precision equipment is dispersed to more support means because of the optimal arrangement, and as a result, the disturbance force acts in the direction in which it acts. On the other hand, the rigidity is improved, and
The vibration damping effect is improved without impairing the vibration damping effect.

[0018]

Embodiment 1 FIG. 1 is a schematic diagram showing the structure of a vibration isolation device according to a first embodiment of the present invention. As shown in the figure, this device includes a vibration isolation table 1, an air spring 3 supporting the vibration isolation table 1, an actuator 4 installed in parallel with the air spring 3, and a vibration sensor 5 for detecting vibration of the vibration isolation table 1. , A vibration control compensator 6 that compensates the output of the vibration sensor 5 and feeds it back to the actuator 4.
A displacement sensor 7 that detects a relative displacement (x−x ₀ ) between the floor and the vibration isolation table 1, and a position control compensator 8 that compensates the output of the displacement sensor 7 and feeds it back to the actuator 4 are provided.
The vibration sensor 4, the vibration control compensator 6, and the vibration control loop by the actuator 4, and the displacement sensor 7,
The position control compensator 8 and the position control loop by the actuator 4 are configured, and for the disturbance vibration having a large amplitude indicated by the output of the vibration sensor 5, the position control loop is set to a high gain,
Floor vibration with small amplitude is controlled by setting the position control loop to low gain. Reference numeral 2 is a stage mounted on the vibration isolation table 1.

Now, it is assumed that the disturbance force F _d acts on the vibration isolation table 1 due to the acceleration / deceleration of the stage 2 to generate disturbance vibration.
In this case, the vibration detection sensor 5 detects the vibration of the vibration isolation table 1 (for example, acceleration d ² x / dt ² ) and this is fed back to the actuator 4 via the vibration control compensator 6. As a result, the actuator 4 mainly serves to add viscosity to the vibration system. Further, the output of the vibration detection sensor 5 at this time increases the gain of the position control compensator 8 to increase the elasticity of the vibration system, so that the disturbance vibration is quickly settled.

Next, when the acceleration / deceleration of the stage 2 is completed and the disturbance vibration is substantially settled, the floor vibration x ₀ must be insulated this time. In this case, the vibration detection sensor 5 lowers the gain of the position control compensator 8 to reduce the springiness of the system, thereby insulating the floor vibration. The function for changing the gain of the position control compensator 8 may be simple proportional or non-linear.

FIG. 2 is a block diagram of the apparatus configuration of FIG. In the following, the effect of varying the gain of the position control compensator will be confirmed using an equation. For simplification, the configurations of the vibration control compensator 6 and the position control compensator 8 are considered only with the proportional element (gain). In FIG. 2, the absolute displacement x of the vibration isolation table is expressed by the following formula 1.

[0022]

[Equation 1]

Here, F _d is the disturbance force acting on the vibration isolation table 1, A is the gain of the actuator, m is the mass of the vibration isolation table 1 and the stage 2, H _a is the gain of the vibration control compensator 47, and g _p is the gain of the position control compensator 8, x ₀ is the absolute displacement of the floor vibration, k is the spring constant of the air spring 3, and c is the air spring 3.
Is the viscosity coefficient of. As the role of the vibration isolator, even if the disturbance force F _d and the floor vibration x ₀ act in the above equation, the vibration isolation table 1
It suffices if the absolute displacement x of is as small as possible (ideally 0).

First, the acceleration / deceleration of the stage 2 causes disturbance force F.
_{Since the} disturbance vibration is dominant over the floor vibration when _d is acting, the floor vibration x ₀ can be ignored (x ₀ = 0). In this case, if the position control compensator gain g _p is increased in the above equation, the equation 2 holds in the limit, and the disturbance force F _d
Will no longer be affected by. That is, it can be seen that the position control compensator gain g _p can be increased to reduce the influence of the disturbance force F _d .

[0025]

[Equation 2]

Next, when the disturbance vibration is almost settled,
Since the disturbance force F _d can be ignored (F _d = 0), the floor vibration x ₀ becomes dominant. In this case, if the position control compensator gain g _p is reduced in the equation (1), (VC
When M is turned off), Formula 3 is established, the influence of the position control compensator gain g _p is eliminated, and the numerator polynomial of the second term of Formula 1 can be reduced. That is, it can be understood that the position control compensator gain g _p can be reduced to reduce the influence of the floor vibration x ₀ .

[0027]

[Equation 3]

In this embodiment, the control in the vertical direction is described, but the present invention is not limited to this, and the control can be similarly performed in the horizontal direction. In this case, the precision device may be supported by an air spring for vibration isolation, the actuator may be installed in the horizontal direction, and the vibration detection sensor and the displacement sensor may be installed so that each of the horizontal components can be detected.

A signal for driving a device such as a stage installed on the vibration isolation table can be derived from, for example, a stage drive circuit. This signal includes information on the stage acceleration / deceleration magnitude and drive timing. Therefore, as shown in FIG. 4, the signal from the stage drive circuit 27 may be fed forward to change the gain of the position control compensator of the vibration isolation device.

Embodiment 2 FIG. 5 is a schematic plan view showing the structure of an active vibration isolation device equipped with XY stages having actuators arranged at the four corners according to the second embodiment of the present invention. Degrees of freedom of the anti-vibration device (O-X _B -Y _B) an XY stage 10, 13
The degrees of freedom (O-X _S -Y _S ) are shifted by 45 degrees. Other configurations are the same as those of the conventional example shown in FIGS.

Hereinafter, according to the figure, the X stage 17 moves to the X direction.
_The operation of the vibration isolation device when driven in the _S direction will be described. First, it is assumed that the X stage 17 is driven in the + X direction via the X axis ball screw 18 by the rotation of the X axis motor 19.
At this time, the vibration isolation table 1 is displaced in the −X _S direction by the reaction force of the drive, and the vibration isolation table 1 mainly vibrates in the X _S direction. next,
This vibration is detected by four sensors 10, 12, 14, 16 and passes through a feedback circuit to the horizontal X direction and Y direction.
Actuators 9, 11, 1 arranged in one direction
3,15 controlled. In this case, the disturbance force acting on the vibration isolation table 1 by the reaction force of the stage drive is supported by the four actuators 9, 11, 13, 15. Since degrees of freedom (O-X _B -Y _B) and the XY stage optional direction of vibration isolator (O-X _S -Y _S) are offset 45 degrees, shown in FIG. 3 (b) Compared to the conventional arrangement, even though the rigidity of the vibration isolation table support mechanism (actuator) remains unchanged, the rigidity is 2 ^1/2 times the disturbance force when the stage is driven. That is, by improving this rigidity, it is possible to improve only the vibration damping effect without impairing the vibration damping effect.

Embodiment 3 FIG. 6 is a schematic plan view showing the structure of an active vibration isolator equipped with an XY stage according to another embodiment of the present invention. Again, degrees of freedom of the anti-vibration device (O-X _B -
Y _B) with the XY stage optional direction (O-X _S -Y _S)
Are shifted by 45 degrees, and the same effect as that of the above-described embodiment can be obtained. That is, the deviation between the direction of the vibration isolation device and the direction of the installed device may be relative.

In the above-mentioned Embodiments 2 and 3, the case of the active vibration isolator was explained, but also in the passive vibration isolator, there is an angle between the direction of the freedom of the vibration isolator and the direction of the freedom of the mounted equipment. By doing so, the same effect can be obtained.

[0034]

As described above, according to the first invention,
By changing the gain of the position control loop according to the vibration level of the vibration isolation table, the gain is increased when the disturbance vibration is dominant, and the gain is decreased when the floor vibration is dominant. The vibration isolation effect can be improved together. In addition, it can be considered that the vibration isolation is left to the air spring and the vibration damping is left to the actuator. Therefore, it is not necessary to consider the trade-off between vibration isolation and vibration suppression with one actuator as in the conventional case, and it is possible to design the vibration isolation device. The time required and the adjustment time after installation can be shortened. Further, since the vibration isolation effect is not impaired and the response speed is sufficiently higher than that of the air spring actuator, it is possible to support high-speed driving of precision equipment installed on the vibration isolation table. Furthermore, even a precision instrument that has already been vibration-isolated and supported by an air spring can be applied to the present invention because it is only necessary to add an actuator. Moreover, since the actuator mounting position does not have to be in the vicinity of the air spring, there is considerable freedom.

Further, according to the second aspect of the invention, since the direction of the freedom of the vibration isolation device and the direction of the degree of freedom of the precision equipment have an angle, even if the rigidity of the vibration isolation table support mechanism such as the actuator does not change, the precision is high. It is possible to disperse the disturbance force generated by the device in a larger number of support mechanisms, improve the rigidity in the direction in which the disturbance force acts, and improve only the damping effect without impairing the vibration isolation effect. Therefore, it is possible to achieve high-speed driving of the precision equipment installed on the vibration isolation table or downsizing of the support mechanism. Further, in the active vibration isolator, the disturbance force when the precision device is driven can be distributed to more actuators, so that the number of actuators not in operation can be reduced and the operation efficiency can be improved. Moreover, since no new support mechanism needs to be improved, replaced or added, it can be economically implemented.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration of a vibration isolation device according to a first embodiment of the present invention.

FIG. 2 is a block diagram illustrating the principle of the device of FIG.

FIG. 3 is a schematic diagram showing a configuration of a vibration isolation device according to a conventional example,
FIG. 3 is a top view and a side view of an active vibration isolation device equipped with precision equipment (XY stage).

FIG. 4 is a schematic diagram of the device of FIG. 4 configured to feed forward a signal from a stage drive circuit.

FIG. 5 is a schematic plan view showing the configuration of an active vibration isolation device equipped with an XY stage according to the first embodiment of the present invention.

FIG. 6 is a schematic plan view showing a configuration of an active vibration isolation device equipped with an XY stage according to a second embodiment of the present invention.

[Explanation of symbols]

1: Vibration isolation table, 9, 11, 13, 15, 23, 25: Actuator, 10, 12, 14, 16, 24, 26: Sensor, 17: X stage, 18: X axis ball screw, 1
9: X-axis motor, 20: Y stage, 21: Y-axis ball screw, 22: Y-axis motor, 3: Air spring, 4: Actuator, 5: Vibration detection sensor, 6: Vibration control compensator,
7: displacement sensor, 8: position control compensator, 2: stage,
27: Stage drive circuit.

Claims (2)

[Claims] 1. An anti-vibration table on which a precision instrument having a driving means is mounted, elastic supporting means for elastically supporting the anti-vibration table, an actuator for driving the anti-vibration table, and a vibration sensor for detecting vibration of the anti-vibration table. A vibration control compensating means for compensating the output of the vibration sensor and feeding back to the actuator, a displacement sensor for detecting the displacement of the vibration isolation table, a position control compensating means for compensating the output of the displacement sensor and feeding back to the actuator, and a vibration sensor. On the basis of the output of the position control compensation means, the position control compensation means has a high gain for the disturbance vibration having a large amplitude, and the position control compensation means has a low gain for the floor vibration having a small amplitude. Shaking device. 2. A vibration isolator equipped with a precision device having a drive means mounted thereon, and an elastic support means for supporting the vibration isolator, comprising: a direction of freedom of the vibration isolator and freedom of the precision device. An anti-vibration device characterized by having an angle with the degree direction and not matching.