JPH0712175A - Precision vibration control device - Google Patents

Abstract

PURPOSE:To dispense with a servo accelerometer by feeding back the output of a position sensor as a driving signal through a high-pass filter with cut-off frequency of specific times or more of the vibration control object frequency of a vibration control object and through a low-pass filter with cut-off frequency not less than the cut-off frequency of the high-pass filter. CONSTITUTION:A controller 8 passes the position signal of a surface plate 5, detected by a position detecting sensor 6, through a secondary high-pass filter 3 and further through a compensating element 4 (Gc2(s)) so as to make it a command to a servo valve 7. The compensating element 4 is formed of one or two or the whole combination of a proportional element, an integral element and a derivative element, and a low-pass filter. The high-pass filter 3 has cut-off frequency ten times or more of the vibration control object frequency of the surface plate 5. When the vibration control object frequency (surface plate characteristic frequency) is 2Hz, for instance, the cut-off frequency of the high-pass filter becomes 20Hz or more. A servo accelerometer is thereby dispensed with so as to reduce the cost of a device while improving the reliability of the device.

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 semiconductor manufacturing equipment, optical measuring instruments, precision machine tools and the like.

[0002]

2. Description of the Related Art Conventionally, a control method for a precision anti-vibration device and its circuit are usually constructed as described in JP-A-3-121328 and JP-A-4-254025.
FIG. 4 is a block diagram showing the configuration. In the figure, 5 is a surface plate having a certain viscosity C and springiness K, 6 is a position sensor for detecting the position of the surface plate 5 and outputting the position signal x, 10 is the acceleration of the surface plate 5 and its acceleration An acceleration sensor that outputs a signal α, 11 is an air actuator that suppresses vibration of the surface plate 5, 7 is a servo valve that controls the air pressure of the air actuator 11, and 9 is a servo valve that takes in the position and acceleration signals and performs control calculation. 7 is a control controller that outputs a control value to 7.

FIG. 3 is a control block diagram of the apparatus shown in FIG. In the figure, 1 is a control target. The input voltage and output characteristics of the air actuator 11 including the servo valve 7 are shown in FIG.
And can be expressed by equation 1.

[0004]

[Equation 1] When the weight of the surface plate 5 is M, the transfer function of the controlled object 1 is
It can be expressed by Equation 2.

[0005]

[Equation 2] Here, the input is the command voltage [V] to the servo valve, and the output is the displacement of the surface plate. The vibration frequency of the surface plate of a semiconductor exposure apparatus or the like is usually about 2 to 5 Hz. For the controlled object 1, the output of the acceleration sensor 10
2 (G _c1 (s)) to be a command to the servo valve 7. Further, the output of the position sensor 6 is calculated from the reference position x _r, and the servo valve 7 is passed through the compensating element 2 (G _c (s)).
Command to. The compensating element 12 may be one or two or all combinations of proportional, integral or derivative elements, and the compensating element 2 may be proportional or proportional and integral elements.
The vibration amplitude of the controlled object 1 is suppressed. For example, when the time constant T _M of the air actuator 11 is sufficiently large, the transfer function of the controlled object 1 is expressed by Equation 3.

[0006]

[Equation 3] Compensating elements 12 and 2 are each proportional and G _c
Command position x _r when (s) = a and G _c1 (s) = b
And the transfer function of the platen position x can be expressed by Equation 4.

[0007]

[Equation 4] M = 3000kg, C = 2262kgs / N, K = 4
In the case of 73700 kg / N and K _A / T _M = 300 N / V, the frequency response when b = 0 and a = 1,2,4 is shown in FIG. 6 (a), where a = 4 and b = 0,1. , 6 the frequency response is shown in FIG. From this, when the proportional gain a of G _c (s) is increased, the control band is expanded as shown in FIG. 6A, but if the natural vibration resonance peak of the surface plate is amplified and the proportional gain a is increased too much. It oscillates. However, by increasing the proportional gain b of G _c1 (s), the resonance of the surface plate can be suppressed as shown in FIG. Thus, the feedback of the position sensor expands the control band, and the feedback of the acceleration sensor has the effect of suppressing the amplitude of the natural vibration frequency of the surface plate.

[0008]

However, in the above-mentioned conventional example, a highly sensitive servo accelerometer is required, which increases the cost of the entire apparatus. In addition, the servo accelerometer itself is very vulnerable to large vibrations, and therefore has the drawback that it requires careful handling.

In view of the problems of this prior art, it is an object of the present invention to eliminate the need for a servo accelerometer in a precision vibration isolation device, thereby reducing the cost and improving the reliability of the device.

[0010]

In order to achieve this object, a precision vibration damping device of the present invention comprises an actuator unit for controlling the vibration of a vibration-damping target based on a given control signal,
A position sensor for detecting the position of the image stabilization target, and means for outputting the control signal based on the output of the position sensor,
A means for feeding back the output of the position sensor to the drive signal through a high-pass filter having a cut-off frequency which is 10 times or more the frequency of the vibration-damping target object and a low-pass filter having a cut-off frequency higher than the cut-off frequency; It is characterized by including.

Here, the position of the image stabilization target detected by the position sensor is usually the position of the image stabilization target in the horizontal and vertical directions. The actuator unit is provided with, for example, an air spring actuator and a servo valve for controlling the air pressure, and the high pass filter has 2
This is the next high-pass filter.

[0012]

In this structure, when the vibration-proof object vibrates and is displaced from the reference position, a drive signal corresponding thereto is given to the actuator unit to suppress the vibration of the vibration-proof object. Is fed back to the drive signal via the low-pass filter and the high-pass filter, the resonance peak of the vibration suppression target frequency is suppressed, and the same effect as in the feedback using the servo accelerometer can be obtained. Therefore, it is not necessary to use a servo accelerometer which is expensive, weak against vibration and easily damaged, and the cost of the device can be reduced and the reliability can be improved.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. 1 and 2 are a control block diagram and a configuration diagram of a precision vibration damping device according to an embodiment of the present invention. The difference from the conventional example of FIGS. 3 and 4 is that the controller is different because the acceleration sensor 10 is not provided. The controller 8 of the present embodiment passes the position signal of the surface plate 5 detected by the position detection sensor 6 to the servo valve 7 through the secondary high-pass filter 3 and the compensating element 4 (G _c2 (s)). It is a command. The compensation element 4 is composed of a low-pass filter and a combination of one or two or all of a proportional element, an integral element and a derivative element. The high-pass filter 3 has a cut-off frequency that is 10 times or more the frequency of the vibration suppression target of the surface plate 5. For example, in the case of FIG. 6A, the vibration suppression target frequency (natural frequency of the surface plate) is 2 Hz, so the cutoff frequency of the high-pass filter 3 is 20 Hz or higher.
The cut-off frequency of the low-pass filter is equal to or higher than the cut-off frequency of the high-pass filter 3, and is equal to or higher than 20 Hz.

For example, the transfer function of the high pass filter can be expressed by the equation (5).

[0015]

[Equation 5] Here, ω _h is the cutoff frequency of the high-pass filter, and ζ _h is the viscous damping coefficient ratio. Then, when the compensation elements 2 and 4 are made proportional and G _c (s) = a and G _c2 (s) = b, the transfer function of the command position x _r and the surface plate position x can be expressed by Equation 6. it can.

[0016]

[Equation 6]Comparing with Equation 4, s² The coefficients of are different. This person
The difference in the numbers is whether or not there is a formula 7.

[0017]

[Equation 7] This is a second-order low-pass filter, which has a value of 1 at low frequencies. Since the target platen has a natural frequency of 2 Hz, which is lower than the cutoff frequency of this filter, this value is almost 1, which is the same as the equation (4).

A phase lead or phase lead / lag circuit may be added to the compensating element 4 in order to improve the phase of the frequency to be damped on the surface plate 5.

In this way, by feeding back the output of the position sensor 6 to the control system through the secondary high-pass filter 3, the same effect as the conventional example can be obtained.
That is, as shown in FIG. 6B, since the resonance peak of the vibration suppression target frequency becomes small, the vibration can be suppressed. Therefore, it is not necessary to use an expensive and fragile servo accelerometer, so that the cost of the device is low.

[0020]

As described above, according to the present invention, the output of the position sensor is set to 10% of the vibration suppression target frequency of the vibration suppression target object.
Since the feedback is provided to the drive signal through the high-pass filter having the cut-off frequency which is more than double and the low-pass filter having the cut-off frequency higher than the cut-off frequency, the same effect as the case of the feedback using the servo accelerometer is obtained You can Therefore, it is possible to reduce the cost of the device and improve the reliability of the device by eliminating the need for the servo accelerometer.

[Brief description of drawings]

FIG. 1 is a block diagram of a control system of a precision anti-vibration device according to an embodiment of the present invention.

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

FIG. 3 is a block diagram of a control system of a precision vibration control device according to a conventional example.

FIG. 4 is a block diagram of the apparatus of FIG.

5 is a characteristic diagram of an air actuator in the apparatus of FIG. 1. FIG.

FIG. 6 is a frequency response characteristic diagram when the value of the compensation element of the control system is changed.

[Explanation of symbols]

1: Control object, 2, 4, 12: Compensation element, 3: Secondary high-pass filter, 5: Surface plate, 6: Position sensor, 7: Servo valve, 8, 9: Control controller, 10: Acceleration sensor, 11 : Pneumatic actuator.

Claims (3)

[Claims] 1. An actuator unit for controlling the vibration of an image stabilization target based on a given control signal, a position sensor for detecting the position of the image stabilization target, and the control signal output based on the output of this position sensor. Means, a high-pass filter having a cut-off frequency that is 10 times or more the vibration-damping target frequency of the vibration-damping target, and a low-pass filter having a cut-off frequency that is equal to or higher than the cut-off frequency, and the output of the position sensor to the drive signal A precision anti-vibration device comprising: means for feeding back. 2. The precision image stabilization device according to claim 1, wherein the position of the image stabilization target detected by the position sensor is the position of the image stabilization target in the horizontal and vertical directions. 3. The precision unit according to claim 1, wherein the actuator unit includes an air spring actuator and a servo valve for controlling the air pressure thereof, and the high-pass filter is a second-order high-pass filter. Anti-vibration device.