JPH0816498B2 - Vibration isolation device - Google Patents

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, and in particular, a levitation table equipped with an anti-vibration device such as an electron microscope or a semiconductor manufacturing device that is not sensitive to vibration is suspended by magnetic force,
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vibration isolation device that removes vibrations from a floor on which the vibration isolation device is installed.

[0002]

2. Description of the Related Art Conventionally, vibration-eliminating devices, that is, mechanical devices such as electron microscopes and semiconductor manufacturing devices, which are extremely reluctant to vibrate,
It was mounted on a vibration isolation device. As a conventional vibration isolation device, a vibration isolation device by magnetic levitation that can realize high-performance vibration isolation has been developed in place of the one using an air spring and rubber, and the details thereof are disclosed in, for example, Japanese Unexamined Patent Publication No. 2-203040. ing.

FIG. 6 is a block diagram of a control system of a conventional vibration isolator. In FIG. 6, reference numeral 1 is a casing, and an electromagnet stator 2 having an exciting coil 3 is fixed to the casing 1. On the other hand, a levitation disk 5 made of a magnetic material is fixed to the levitation table 4. A displacement sensor 6 is arranged adjacent to the levitation disk 5, and a current is passed through the coil 3 based on the output signal from the displacement sensor 6 by the compensation circuit 7 and the power amplifier 8 to float the magnetic material. A magnetic attraction force is applied between the disk 5 and the electromagnet stator 2.

Next, the operation of the magnetic bearing device having this structure will be described. The displacement sensor 6 detects the displacement of the levitation disk 5, and the compensation circuit 7 generates a compensation signal based on the deviation between the position target value of the levitation table and the displacement signal detected by the displacement sensor 6. The power amplifier 8 is driven by the generated signal, a current is caused to flow through the coil 3 of the electromagnet stator 2 fixed to the casing 1, and a magnetic attraction force is applied between the levitation disk 5 and the electromagnet stator 2 to levitate. Levitate the table 4 to the target position.

[0005]

However, in the conventional magnetic vibration isolator, as shown in spectrum S-1 of FIG. 6, some natural vibration modes of the levitating table system equipped with the vibration isolator are shown. Therefore, there was a problem that vibration and oscillation occur at those natural frequencies. In other words, since the natural frequency of the levitating table system is relatively high, the compensation circuit cannot perform sufficient phase lead compensation.
There is a problem in that unnecessary gain control causes vibration and oscillation.

As a countermeasure for this, conventionally, a filter that advances the phase at the local frequency, or a notch filter that lowers the gain at the local frequency is used. However, these filters must measure the natural frequency of the levitating table system and make the filters accordingly. What is more difficult is that the natural frequency of the floating table system also changes depending on the vibration eliminator mounted on the floating table. Since the above filters are tuned to the local frequency, if the natural frequency changes due to the above-mentioned vibration-eliminating device, the natural frequencies will go out of the range of these filters, causing problems such as vibration and oscillation. Is often caused.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to eliminate the above-mentioned problems and to change the natural frequency of a levitation table system equipped with an anti-vibration device from a design value. An object of the present invention is to provide a vibration isolation device by magnetic levitation that can automatically correct a circuit even if it changes and prevent unnecessary control by a natural frequency and solve problems of vibration and oscillation.

[0008]

According to the present invention, in a vibration eliminator by magnetic levitation, a transfer function setting unit for determining a transfer function of a predetermined levitation table system and a transfer function setting unit for simulating this transfer function are provided. An adaptive digital filter that generates a pseudo signal by the output signal of the power amplifier,
A high-pass circuit that is provided on the input side or output side of this adaptive digital filter and passes only a pseudo signal having a frequency higher than the control frequency (for example, natural vibration frequency) and a signal obtained by subtracting or adding the pseudo signal from the displacement signal. Based on this, the magnetic attraction force between the electromagnet stator and the levitation disk is controlled.

In the present invention, the transmission of the levitating table system on which the vibration isolator is mounted is transmitted by calculation or other means, or by the signal from the pulse generator and the displacement sensor, or the output of the compensation circuit or the power amplifier and the sensor signal. A function is obtained, this transfer function is simulated by an adaptive digital filter, and a pseudo signal is generated by adding the output signal of the compensation circuit or power amplifier to this, and only the frequency higher than the control frequency is passed, and it is detected by the displacement sensor. The current of the coil 3 is controlled by the compensation circuit and the power amplifier based on the signal obtained by subtracting the pseudo signal from the displacement signal. Also, the identification error detection circuit may be provided, and the adaptive digital filter may be sequentially corrected so that the error between the displacement signal and the pseudo signal is reduced by feeding back to the adaptive digital filter. Furthermore, when the adaptive digital filter is not sufficiently modified, a pulse can be generated by the pulse generator so that the transfer function can be set again.

[0010]

Since the present invention is constructed as described above, even if the natural frequency of the levitation table system equipped with the vibration eliminator changes, the adaptive digital filter follows the circuit characteristics sequentially or at any time. By changing and removing the frequency component of the bending natural vibration mode of the levitating table which is a problem by subtraction, or by adding a damping force by addition, vibration at the natural frequency of the levitating table in any operating state, The levitation table can be stably controlled without causing oscillation.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A control system of a magnetic levitation vibration isolator according to the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows an embodiment of the present invention. In FIG. 1, reference numeral 1 is a casing, to which an electromagnet stator 2 having an exciting coil 3 is fixed. On the other hand, a levitation disk 5 is fixed to the levitation table 4. A displacement sensor 6 is arranged adjacent to the levitation disk 5, and the displacement sensor 6 measures changes in the vertical position of the levitation table 4.

The vibration isolator comprises a system identification circuit 10,
The system identification circuit 10 is composed of a transfer function setting unit 11 and a canceller 14. The displacement signal from the displacement sensor 6 is input to the transfer function measuring device 12 and the adder 21. Further, the transfer function setting unit 11 includes a pulse generator 13, and the pulse from the pulse generator is input to the adder 23 and the power amplifier 8.

On the other hand, the canceller 14 is provided with an adaptive digital filter 15 and a high-pass circuit 16, and the transfer function of the levitating table system measured by the transfer function measuring device 12 is inputted to the adaptive digital filter 15 and this adaptive digital filter 15 is used. Simulates the transfer function of this floating table system. The output signal of the compensation circuit 7 or the power amplifier 8 (not shown) is input to the adaptive digital filter 15, and a pseudo signal according to the transfer function peculiar to the floating table system is generated. The high-pass circuit 16 cuts the low-frequency component of this pseudo signal, and only the high-frequency component is subtracted and input to the adder 21. Here, the high-pass circuit allows only a control frequency, for example, a frequency component higher than the natural frequency of the floating table system to pass.
Therefore, in the adder 21, the output signal of the compensating circuit 7 or the power amplifier 8 is applied to the displacement signal of the displacement sensor by the adaptive digital filter 15, and the signal is simulated by the number of transmissions peculiar to the floating table system and passed through the high pass circuit. Components above the control frequency are subtracted and applied.

The output signal of the adder 21 is input to the identification error detection circuit 17, and the identification error detection circuit 17 is supplied.
The output signal of is input to the adaptive digital filter 15,
As a result, the adaptive digital filter 15 is configured so that a signal obtained by subtracting the pseudo signal from the displacement signal is judged by the identification error detection circuit 17 and is sequentially corrected so that the error becomes smaller.

Next, the operation of the vibration isolator by magnetic levitation constructed as described above will be explained. The pulse generated by the pulse generator 13 in the transfer function setting unit 11 is the third adder 2
3, a current is applied to the exciting coil 3 wound around the electromagnet stator 2 fixed to the casing via the power amplifier 8 to give a disturbance to the levitation table 4 by the electromagnetic force from the electromagnet stator 2 at that time. The displacement of the floating table 4 is measured by the displacement sensor 6. And here, the pulse generator 13
The pulse generated by is a system identification pulse, white noise, or a chirp signal, and the transfer function of the flying table system is measured by the transfer function measuring device 12, and the measured transfer function is applied to the adaptive digital filter 15. Is entered. Adaptive digital filter 15
Generates a pseudo signal based on a transfer function, and the high pass circuit 16 cuts a low frequency portion below a control frequency, for example, a rotation frequency, and a pseudo signal having only a high frequency component is subtracted and input to an adder 21.

In the adder 21, the pseudo signal which is the output signal of the canceller 14 is subtracted from the displacement signal which is the output signal of the displacement sensor 6, and the subtracted signal is input to the identification error signal detection circuit 17, which causes displacement. The adaptive digital filter 15 is sequentially modified so that the error between the signal and the pseudo signal becomes small. Further, the signal subtracted by the adder 21 is input to the adder 22, where the floating table 4
Is subtracted from the target position value, and the subtracted signal is input to the compensating circuit 7. The power amplifier 8 is operated by the output of the compensating circuit 7 to cause a current to flow through the exciting coil 3 and the electromagnet stator 2 and the levitation device. The position of the floating table 4 is controlled by the electromagnetic attraction force generated between the disks 5.

In this way, the signal after the displacement signal is subtracted by the pseudo signal mainly has a component below the control frequency necessary for the levitation control of the levitation table, and levitation is controlled based on this signal. As a result, the bending eigenmode component of the high-frequency component, which has been a problem in the past, is eliminated, so unnecessary control is not performed, and as a result, the problem of vibration and oscillation of the levitating table is eliminated. The controlled control can be performed.

In FIG. 1, S-1 indicates the spectrum of the displacement signal detected by the displacement sensor 6, and S-2 indicates the spectrum of the pseudo signal. The peak in the high frequency region of S-1 indicates the pole due to the bending eigenmode of the floating table system. In S-2, it is shown that the pole of the bending eigenmode of the levitating table system higher than the control frequency is formed by simulating the adaptive digital filter 15, and the low-frequency component is removed by the high-pass filter 16. S-3 is a spectrum obtained by subtracting the pseudo signal from the displacement signal. At a frequency lower than the control frequency, the displacement signal that is originally necessary for the levitation control of the levitation table remains as it is. There is no eigenmode peak, or conversely a depressed spectrum.

In the above description, in the adder 21,
This is a case where the pseudo signal is subtracted from the displacement signal. In the adder 21, a pseudo signal is added to the displacement signal, and the compensating circuit 7 performs sufficient phase compensation such as phase advancement to give a strong damping force to the natural vibration mode of the floating table system. You can also

Next, a second embodiment of the present invention will be described with reference to FIG. 2, constituent elements having the same functions and functions as those of the constituent elements of FIG. 1 are designated by the same reference numerals and the description thereof will be omitted. In this embodiment, a transfer function setting device 31 is provided in place of the transfer function measuring device 12 and the pulse generator 13 of the first embodiment, and the transfer function setting device 31 is provided.
Generates a transfer function of a predetermined floating table system, which is calculated or obtained by another means. The transfer eigenmode of the bending eigenmode of the floating table system can be calculated by a separate computer simulation or the like. Also, in the vibration isolator of the same type, if the transfer function is experimentally measured for one floating table, the transfer function can be experimentally inferred for similar ones. According to this transfer function setting device, an expensive pulse generator and transfer function measuring device are unnecessary, which is economical.

Next, a third embodiment of the present invention will be described with reference to FIG. In FIG. 3, constituent elements having the same operations and functions as those of the constituent elements of FIGS. 1 and 2 are designated by the same reference numerals, and description thereof will be omitted. This embodiment differs from the second embodiment shown in FIG. 2 in that the identification error detection circuit 17 is omitted. The identification error detection circuit 17 evaluates the error obtained by subtracting the pseudo signal generated by the canceller circuit 14 from the displacement signal of the displacement sensor 6, and modifies the parameters of the adaptive digital filter so as to reduce the error. is there. Since the bending eigenmode of the levitation table system changes depending on the vibration-eliminating device mounted, strictly speaking, the adaptive digital filter must also reduce its error by changing its parameters in response to these changes. However, in practice, it may not be necessary to change the parameters of the adaptive digital filter, and at this time, the identification error detection circuit 17 becomes unnecessary.

Next, a fourth embodiment of the present description will be described with reference to FIG. 4, constituent elements having the same functions and functions as those of the constituent elements of FIG. 1 are designated by the same reference numerals and the description thereof will be omitted. The present embodiment is different from the first embodiment shown in FIG. 1 in that the pulse generator is omitted and the output of the compensation circuit or the power amplifier is input to the transfer function measuring device 12. The transfer function measuring device 12 estimates the transfer function of the levitation table from the output of the compensation circuit 7 or the power amplifier 8 and the displacement signal of the displacement sensor 6, and corrects the parameter of the adaptive digital filter 15.

Secondly, the transfer function of the levitation table system is composed of a plurality of transfer function measuring devices and an adaptive digital filter, and the output signal of another compensation circuit or power amplifier of the levitation table system and the displacement of the levitation table system. It is obtained by superimposing it from the signal and simulated. Therefore, as shown in the figure,
When the present invention is applied between four electromagnetic actuators and four sensors, 16 sets such as a transfer function measuring device and an adaptive digital filter are required. Such plucking control is effective because it has a correlation with the transfer function of the floating table system.

Next, a fifth embodiment of the present invention will be described with reference to FIG. 5, constituent elements having the same operations and functions as those of the constituent elements of FIG. 1 are designated by the same reference numerals and the description thereof will be omitted. The present embodiment differs from the first embodiment shown in FIG. 1 in that, firstly, the transfer function setting unit is the eigenmode measuring instrument 25. The eigenmode measuring device 25 estimates the eigenvibration mode of the floating table system from the displacement signal of the displacement sensor 6 and superimposes it by an adaptive digital filter to simulate it. With such a configuration, if the variation range of the natural frequency is known in advance, it can be dealt with by preparing an adaptive digital filter corresponding to each natural frequency. Will be needed.

[0026]

As described above, according to the present invention, the transfer function of the levitation table system equipped with the vibration eliminator is simulated by the adaptive digital filter, and the low frequency component is removed to obtain the high frequency bending eigenmode component. Is added to the displacement signal of the floating table by processing such as subtraction. Therefore, the peak on the spectrum of the high-frequency component higher than the control frequency, which is the cause of the vibration and oscillation due to the bending eigenmode of the conventional levitating table, is removed, so that the levitating table can be stably levitated. A vibration isolation device using magnetic levitation has been realized. This device is an adaptive digital filter that simulates the transfer function of the levitation table system, eliminating the need for a conventional local notch filter, etc., and changing parameters even for magnetic anti-vibration devices of various shapes and capacities. Since it can be handled only by itself, it is extremely versatile. Further, a magnetic levitation vibration eliminator capable of automatically responding to fluctuations in the transfer function of the levitation table system due to changes in the capacity and mounting position of the vibration eliminator by detecting an identification error has been realized.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a control system of a magnetic levitation vibration isolator according to the present invention.

FIG. 2 is a block diagram showing a second embodiment of the control system of the magnetic levitation vibration isolator according to the present invention.

FIG. 3 is a block diagram showing a third embodiment of the control system of the magnetic levitation vibration isolator according to the present invention.

FIG. 4 is a block diagram showing a fourth embodiment of the control system of the magnetic levitation type vibration isolation device according to the present invention.

FIG. 5 is a block diagram showing a fifth embodiment of the control system of the magnetic levitation vibration isolator according to the present invention.

FIG. 6 is a block diagram showing a control system of a conventional magnetic levitation vibration isolator.

[Explanation of symbols]

 1 Casing 2 Electromagnet Stator 3 Coil 4 Levitation Table 5 Levitation Disk 6 Displacement Sensor 7 Compensation Circuit 8 Power Amplifier 10 System Identification Circuit 11 Transfer Function Setting Section 12 Transfer Function Measuring Device 13 Pulse Generator 14 Canceller 15 Adaptive Digital Filter 16 High Pass Circuit 17 Identification error detection circuit 21, 22, 23 Adder 25 Eigenmode measuring instrument 31 Transfer function setter

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuhide Watanabe 4-2-1 Honfujisawa, Fujisawa-shi, Kanagawa Ebara Research Institute Ltd. No. 1 stock company within EBARA Research Institute

Claims (7)

[Claims] 1. A levitation table on which a mechanical device that dislikes vibration is mounted, and a levitation disk fixed to the levitation table,
An electromagnet stator attached to the casing at a distance of a minute gap from the levitation disk, and a displacement sensor for measuring relative displacement between the levitation disk and the electromagnet stator,
In a vibration isolation device having a power amplifier and a compensation circuit that controls a magnetic attraction force acting between the levitation disk and the electromagnet stator based on a displacement signal from the displacement sensor, the predetermined levitation A transfer function setting unit for setting the transfer function of the table, an adaptive digital filter for simulating the transfer function set by the transfer function setting unit and generating a pseudo signal by inputting the output of the compensation circuit or the power amplifier, A high-pass circuit provided on the input side or output side of the adaptive digital filter, and controlling the magnetic attraction force based on a signal obtained by subtracting or adding the pseudo signal from the displacement signal. apparatus. 2. A system identification circuit is further provided which detects a signal obtained by subtracting the pseudo signal from the displacement signal by an identification error detection circuit and sequentially corrects the adaptive digital filter so as to reduce the error. The vibration isolator according to claim 1. 3. The transfer function setting unit is composed of a transfer function measuring device and a pulse generator, and a pulse generated by the pulse generator is input to a power amplifier to give a disturbance to the levitation table. The vibration isolation device according to claim 1 or 2, wherein a displacement signal of the levitation table is detected by the displacement sensor, and a transfer function of the levitation table system is obtained from the displacement signal. 4. The vibration isolator according to claim 1, wherein the transfer function setting unit includes a transfer function setting device that sets a transfer function obtained by calculation or other means. . 5. When the identification error detecting circuit detects an error and adaptively corrects the adaptive digital filter, when the error gradually increases and correction becomes difficult, a pulse is regenerated by the pulse generator. 3. The vibration isolator according to claim 2, wherein the transfer function is set again. 6. The transfer function setting unit is composed of a transfer function measuring device, estimates the transfer function of the levitating table system from the output of the compensating circuit or power amplifier and the displacement signal of the displacement sensor, and levitating table system. The transfer function of is determined by multiple transfer function measuring instruments and adaptive digital filters.
The vibration isolation device according to claim 1 or 2, wherein the vibration isolation device is obtained by superimposing it from an output signal of another compensating circuit of the levitation table system or a power amplifier and is simulated. 7. The transfer function setting unit is composed of an eigenmode measuring device of a levitation table system, estimates the eigenmode of the levitation table system from the displacement signal of the displacement sensor, and uses the adaptive digital filter to generate the eigenmode frequency. 3. A pseudo signal for simulating a component is generated, and a transfer function of a levitating table system is simulated by being superposed by a plurality of eigenmode measuring devices and an adaptive digital filter. Anti-vibration device.