JPH09112482A - Turbo-molecular pump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a magnetic bearing stably support a rotor shaft and to check any adverse effect due to vibration in the power frequency of a driving motor of an auxilairy pump even in the case where the vibration in the power frequency of the auxiliary pump is transmitted to this magnetic bearing. SOLUTION: In this turbo-molecular pump, some ingredients in and around the frequency fc of an output signal of a position sensor 41 secured by a band- pass filter 54 having another center frequency fc in the said power frequency is added to an output signal of a main control circuit 53 performing three- element control (PID) on the basis of the output signal of the position sensor 41 by an addition circuit 55 at a magnetic bearing control part 52 controlling a magnetic bearing 40, and a driving circuit 56 is driven by the output signal. A control characteristic is enhanced of its gain in and around the frequency fc, whereby rigidity in the magnetic bearing 40 is well improved, and thus any adverse effect of vibration is controllable.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a turbo molecular pump used in a vacuum exhaust device used in a semiconductor manufacturing apparatus.

[0002]

2. Description of the Related Art In general, the above vacuum evacuation device is provided with the above turbo molecular pump as a high vacuum pump and an auxiliary pump such as a vane pump connected to an exhaust port of the turbo molecular pump through a pipe. The turbo molecular pump has a magnetic bearing that rotatably supports a rotor shaft to which exhaust blades are attached in a non-contact manner.

[0003]

However, the magnetic bearing may be vibrated, which may adversely affect the turbo molecular pump. As a result of pursuing this cause, the applicant of the present application has obtained the following findings. That is, when the above-mentioned auxiliary pump is driven by a drive motor using a normal commercial power supply, the power supply frequency of the drive motor is 5
Vibrations having a main component at 0 Hz or 60 Hz may occur. This vibration is transmitted to the turbo molecular pump through the pipe, and the magnetic bearing is excited.

Therefore, an object of the present invention is to provide a turbo-molecular pump in which adverse effects due to vibration at the power supply frequency of the drive motor for the auxiliary pump are suppressed.

[0005]

In order to achieve the above-mentioned object, (1) a turbo-molecular pump according to a first aspect of the present invention rotatably supports a rotor shaft, to which exhaust blades are attached, in a non-contact manner. Based on the detection signal of the turbo molecular pump main body having a magnetic bearing and the position sensor that detects the position of the rotor shaft,
A turbo molecular pump having a control unit for controlling the magnetic bearing, wherein an auxiliary pump driven by a drive motor is connected to the exhaust port of the turbo molecular pump body.
The control unit is characterized by having a control characteristic in which the gain at the power supply frequency of the drive motor is increased so as to increase the rigidity of the magnetic bearing against the vibration of the auxiliary pump.

According to the above structure, since the magnetic bearing has the rigidity at the power supply frequency of the drive motor increased by the control portion, it is possible to reduce the influence even when the power supply frequency is vibrated. Therefore, even if the vibration at the power supply frequency of the auxiliary pump is transmitted to the magnetic bearing, the magnetic bearing can stably support the rotor shaft, and the operation of the turbo-molecular pump is unlikely to be adversely affected.

(2) A turbo molecular pump according to a second aspect of the present invention is the turbo molecular pump according to the first aspect, wherein the detection signal of the position sensor is input to the control unit, and the detection signal is transferred to a predetermined transfer function. Based on the main control circuit to perform arithmetic processing and output, the detection signal of the position sensor is input, the band pass filter whose center frequency is set to the power supply frequency, the output signal of the main control circuit, and the band pass filter The present invention is characterized by including an adder circuit for adding and outputting the output signal and a drive circuit for receiving the output signal of the adder circuit and driving the magnetic bearing.

According to the above configuration, the output signal of the adder circuit is the output signal of the main control circuit added with the signal in the vicinity of the power supply frequency. Therefore, the control unit determines the control characteristic of the main control circuit. In comparison, it is possible to realize the same control characteristic as that in which the gain near the power supply frequency is increased. Therefore, it is possible to obtain the same operation as that of the invention according to claim 1.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION A first embodiment of the present invention will be described below in detail with reference to the accompanying drawings, taking a vacuum exhaust device using this turbo molecular pump as an example. FIG.
It is a schematic diagram of the schematic structure of the said vacuum exhaust apparatus. In this vacuum exhaust device, a vacuum chamber 1 which is partitioned from the surroundings in order to realize a vacuum, and a suction port communicating with the inside of the vacuum chamber 1 and a turbo as a high vacuum pump for sucking air molecules in the vacuum chamber 1 The molecular pump main body 2, an auxiliary pump 3 composed of a vane pump connected to the exhaust port 31 (see FIG. 2) of the turbo molecular pump main body 2 via a pipe 6, and the auxiliary pump 3 is a commercial AC of a predetermined power supply frequency. As a part for controlling the drive motor 4 driven by the electric power from the power source and the turbo molecular pump main body 2, a magnetic bearing control part 52 described later, a drive circuit (not shown) of the built-in motor 21, and the like, and a vacuum exhaust device. And a power supply unit 5 having a power supply circuit.

A turbo molecular pump 7 is constituted by the portion of the power supply section 5 for controlling the turbo molecular pump main body 2 and the turbo molecular pump main body 2. Hereinafter, the turbo molecular pump 7 will be described. FIG. 2 is a partial cross-sectional front view of the turbo molecular pump body 2. The turbo molecular pump main body 2 has a substantially cylindrical casing 23 that defines a rotor chamber 22 therein, and a rotor shaft 2 that extends in a vertical direction and is rotatably supported in a central portion of the casing 23.
6, a rotor 25 having a substantially cylindrical shape that is coaxially attached to a rotor shaft 26, has a large number of blades 24 for exhaust provided on its peripheral surface, and that exhausts by rotating in a rotor chamber 22. The rotor chamber 22 is partitioned between the rotor chamber 2 and the casing 23 and is located below and between the shaft 26 and the casing 23.
Lower casing 27 having the exhaust port 31 from inside 2
And

The following components are attached to the lower casing 27 around the rotor shaft 26 from above. That is, a so-called touchdown bearing 28 that is a protective bearing of the rotor shaft 26, a radial position sensor 29 that detects a displacement of the rotor shaft 26 in a direction orthogonal to the axis line,
A radial magnetic bearing 30 that rotatably supports the rotor shaft 26 in a direction orthogonal to the axis line in a non-contact manner by a magnetic force, the built-in motor 21 that rotates the rotor shaft 26, the radial magnetic bearing 30, and the radial displacement sensor. Two
9 and the touchdown bearing 28.

Also, around the lower end of the rotor shaft 26,
An axial magnetic bearing 33 that rotatably supports the rotor shaft 26 in the axial direction by a magnetic force without contact, and the rotor shaft 26.
And an axial position sensor 34 for detecting the axial displacement of the. The axial magnetic bearing 33 is composed of a pair of electromagnets arranged axially opposite to each other with the disc 32 fixed to the rotor shaft 26 interposed therebetween. The axial position sensor 34 is arranged so that the displacement of the rotor shaft 26 in the axial direction in the vicinity thereof can be detected.

Further, the radial magnetic bearing 30 has the rotor shaft 2 along a predetermined direction orthogonal to the axial direction of the rotor shaft 26.
It is composed of a pair of electromagnets that are arranged so as to face each other with 6 in between,
A total of four pairs are provided on the upper and lower sides of the rotor shaft 26 so that predetermined directions are orthogonal to each other. The radial position sensor 29 is arranged near each of them so that the displacement of the rotor shaft 26 can be detected in a predetermined direction.

As described above, each of the axial magnetic bearing 33 and the radial magnetic bearing 30 (hereinafter referred to as "magnetic bearing") has either the axial position sensor 34 or the radial position sensor 29 (hereinafter " Position sensor ") is arranged. This position sensor uses an eddy current type sensor that detects displacement by a change in proximity capacitance due to a minute gap formed with the surface of the rotor shaft 26. The detection signal is input to the magnetic bearing control unit 52 and used for controlling the magnetic bearing.

FIG. 3 is a block diagram of the magnetic bearing control unit 52. The magnetic bearing control unit 52 is provided for each of the above magnetic bearings and the corresponding position sensor. The magnetic bearing control unit 52 receives the detection signal of the position sensor 41, performs arithmetic processing based on a predetermined transfer function, and outputs the processed signal to perform control, for example, a main control circuit 53 that performs PID control,
A detection signal of the position sensor 41 is input, and a central frequency fc of a signal band to be passed is set to a power supply frequency of the drive motor 4, for example, a frequency of a commercial AC power supply of 60 Hz, and a bandpass filter (BPF) 54, and a main control. Circuit 5
3 and the output signal of the bandpass filter 54 are added and output, and the drive circuit 56 which receives the output signal of the addition circuit 55 and drives the magnetic bearing 40.

Next, the operation of the magnetic bearing control unit 52 will be specifically described. FIG. 4 is a control characteristic diagram of the magnetic bearing control unit 52. FIG. 4A shows the output of the main control circuit 53.
Regarding the output of the bandpass filter 54 in (b),
Regarding the output of the adding circuit 55, the horizontal axis represents frequency,
The vertical axis shows the gain. The detection signal of the position sensor 41 is input to the main control circuit 53. The main control circuit 53 is
When the position of the rotor shaft 26 moves, the detection signal is arithmetically processed to output the command signal to the drive circuit 56 so as to return the position to the original position. This output characteristic is, for example, as shown in FIG.
It is as shown in (a).

Conventionally, the drive circuit 56 drives the magnetic bearing 40 in response to this command signal. Note that FIG.
The output characteristic of (a) is set as in the conventional case. The feature of the present invention is that the output signal of the bandpass filter 54 is added to the command signal as described below. That is, the detection signal of the position sensor 41 is also input to the bandpass filter 54. As a result, as shown in FIG. 4B, the bandpass filter 54 outputs only the frequency component near the center frequency fc. When this output signal is added to the command signal by the adder circuit 55,
As for the output characteristic, as shown in FIG. 4C, the gain near the center frequency fc is increased as compared to the characteristic of FIG. 4A, and as a result, a command signal in which the frequency component near the center frequency fc is increased is obtained. . The drive circuit 56 responds to the command signal by
The magnetic force of the magnetic bearing 40 with respect to the rotor shaft 26 is controlled by changing the magnitude of the current flowing through the electromagnet of the magnetic bearing 40.

According to the above control characteristics, the magnetic force of the magnetic bearing 40 is strengthened at a frequency near the center frequency fc with respect to a constant magnitude of the detection signal of the position sensor 41 which is an input signal. Therefore, in order to give a predetermined displacement amount to the rotor shaft 26 of the turbo molecular pump 7, the rotor shaft 2
The force acting on 6 becomes larger. This indicates that the rigidity of the magnetic bearing 40, which is the supporting rigidity of the rotor shaft 26, increases.

FIG. 5 shows a frequency characteristic diagram of rigidity of the radial magnetic bearing 30 of the turbo molecular pump 7. Here, the rigidity of the radial magnetic bearing 30 means the magnitude of the force applied to the rotor shaft 26 in order to obtain a predetermined displacement amount in a predetermined direction with respect to a predetermined direction that supports the rotor shaft 26 of the radial magnetic bearing 30. It is represented by As described above, since this rigidity is proportional to the gain of the magnetic bearing control unit 52, the frequency characteristic has the same tendency. As shown in FIG. 5, the rigidity of the radial magnetic bearing 30 is a frequency characteristic of the rigidity of the magnetic bearing in the conventional turbo molecular pump (shown by a chain line C2 in FIG. 5).
On the other hand, it is increased in the vicinity of 60 Hz which is the power supply frequency of the drive motor 4. The same applies to the frequency characteristic of rigidity of the axial magnetic bearing 33.

As described above, since the rigidity of the magnetic bearing 40 is high in the vicinity of the power supply frequency of the drive motor 4, even if vibration having a component of this frequency acts on the magnetic bearing 40, its influence can be reduced. . Therefore, even if the vibration of the auxiliary pump 3 having a component in the power supply frequency is transmitted to the magnetic bearing 40, the magnetic bearing 40 can stably support the rotor shaft 26, and the turbo molecular pump 7 operates. Can be suppressed.

Further, since the rigidity of each magnetic bearing is increased only near the power source frequency, the rigidity at other frequencies and the change in the control characteristics of the magnetic bearing are small. Therefore, it is less likely that a new problem will occur due to the suppression of the vibration. Next, a second embodiment of the present invention will be described. In the present embodiment, a magnetic bearing control unit 60 is used instead of the magnetic bearing control unit 52 in the first embodiment, and the other parts are the same. Therefore, the first
The same parts as those in the embodiment are given the same reference numerals.

FIG. 6 is a block diagram of the magnetic bearing control unit 60. The magnetic bearing control unit 60 receives the detection signal of the position sensor 41, receives the output signal of the DSP 61, and a digital signal processor (DSP) 61 that performs control by calculating and outputting based on a predetermined transfer function. Drive circuit 56 for driving the magnetic bearing 40.

The DSP 61 is a signal processing circuit element, and hardware and software can be set in advance so as to perform desired signal processing by a built-in CPU, hardware, software and the like. In the present embodiment, the DSP 61 has an output characteristic obtained by a portion including the main control circuit 53, the bandpass filter 54, and the adder circuit 55 described in the first embodiment, specifically, FIG. Are set so as to have the characteristics of the transfer function.

Therefore, since the control characteristics of the magnetic bearing control unit 60 can be the same as those of the magnetic bearing control unit 52 of the first embodiment, the frequency characteristic of the rigidity of the magnetic bearing 40 of the turbo molecular pump 7 can be realized. Also has the same characteristics and has the same effects as those of the first embodiment. As described above, the addition of the bandpass filter 54 and the addition circuit 55 for suppressing the influence of vibration, the program change of the DSP 61, and the like may be performed by another method such as the pipe 6,
This can be performed more easily than changing the auxiliary pump 3 or the like. Therefore, the vacuum evacuation device using this turbo molecular pump 7 can be easily operated stably.

The transfer shown in FIG. 4C is performed by the circuits such as the bandpass filter 54 and the adder circuit 55 in the first embodiment, and by the DSP 61 in the second embodiment. Although the characteristic of the function is realized, the method is not limited as long as this characteristic can be obtained. Further, the frequency of which the gain is increased in the magnetic bearing control units 52 and 60, for example, the center frequency fc of the bandpass filter 54 of the first embodiment is set as the power supply frequency of the drive motor 4 to the commercial AC power supply. The frequency was set,
It is not limited to this. For example, the drive motor 4
When the commercial AC power source is converted into direct current and is driven by using an inverter that converts this direct current into a predetermined alternating current, the frequency with the increased gain may be the frequency converted by the inverter.

Further, the magnetic bearing control units 52 and 60 described above are used.
Is a radial magnetic bearing 30 and an axial magnetic bearing 33.
However, the rigidity of any one of the magnetic bearings may be increased. In addition, various design changes can be made without changing the gist of the present invention.

[0027]

According to the invention of claim 1, since the rigidity of the magnetic bearing is increased by the control unit at the power supply frequency of the drive motor, the magnetic bearing is affected by the vibration at the power supply frequency of the auxiliary pump. It is hard to receive and can support a rotor shaft stably. Therefore, the turbo molecular pump can also be operated stably.

According to the invention of claim 2, since the bandpass filter and the adder circuit can realize the control characteristic with the increased gain in the vicinity of the power supply frequency, the same effect as that of the invention of claim 1 can be realized. The effect of can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a schematic configuration of a vacuum exhaust device using a turbo molecular pump according to a first embodiment of the present invention.

FIG. 2 is a partial cross-sectional front view of a turbo molecular pump body.

FIG. 3 is a block diagram of a magnetic bearing control unit.

4A and 4B are control characteristic diagrams of the control unit, in which FIG. 4A shows the control characteristic of the main control circuit, FIG. 4B shows the output characteristic of the bandpass filter, and FIG. 4C shows the characteristic of the output signal of the addition circuit. . The horizontal axis represents frequency and the vertical axis represents gain.

FIG. 5 is a characteristic diagram of dynamic rigidity of a magnetic bearing of a turbo molecular pump.

FIG. 6 is a block diagram of a magnetic bearing control unit according to a second embodiment.

[Explanation of symbols]

 2 Turbo molecular pump main body 3 Auxiliary pump 4 Drive motor 7 Turbo molecular pump 24 Blade 26 Rotor shaft 29 Radial displacement sensor (position sensor) 30 Radial magnetic bearing (magnetic bearing) 31 Exhaust port 33 Axial magnetic bearing (magnetic bearing) 34 Axial Displacement sensor (position sensor) 40 Magnetic bearing 41 Position sensor 52 Magnetic bearing control unit (control unit) 53 Main control circuit 54 Bandpass filter 55 Addition circuit 56 Drive circuit 60 Magnetic bearing control unit (control unit)

Claims (2)

[Claims] 1. A turbo-molecular pump main body having a magnetic bearing for rotatably supporting a rotor shaft, to which exhaust blades are attached, in a non-contact manner, and a position sensor for detecting the position of the rotor shaft. A turbo molecular pump comprising: a control unit for controlling a magnetic bearing; and an auxiliary pump driven by a drive motor connected to the exhaust port of the turbo molecular pump body. On the other hand, a turbo molecular pump having a control characteristic in which the gain at the power frequency of the drive motor is increased so as to increase the rigidity of the magnetic bearing. 2. The turbo molecular pump according to claim 1, wherein the control unit receives a detection signal of the position sensor, and performs a calculation process on the detection signal based on a predetermined transfer function to output the main control circuit. , A detection signal of the position sensor is input, a bandpass filter whose center frequency is set to the power supply frequency, an adder circuit that adds and outputs the output signal of the main control circuit and the output signal of the bandpass filter, A turbo molecular pump comprising: a drive circuit that receives the output signal of the adder circuit and drives the magnetic bearing.