JPH0612827U - Magnetic bearing device - Google Patents

Abstract

(57) [Summary] [Object] To provide a magnetic bearing device capable of suppressing oscillation of a rotor shaft even when the device temperature changes. [Configuration] The temperature of the device is detected by a temperature sensor 50.
Then, the oscillation frequency of the rotor shaft 18 at the device temperature is determined from the data stored in the ROM, and the corresponding frequency component is cut by the notch filter arranged in the correction circuit (PID) 82. A switching element that functions equivalently as a variable resistance by switching a capacitor is arranged in the resistance portion of the notch filter. Then, the frequency band to be cut is changed by changing the switching frequency of the switching element according to the device temperature detected by the temperature sensor 50.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a magnetic bearing device, and more particularly to a magnetic bearing device that suppresses oscillation of a rotor shaft.

[0002]

[Prior art]

For example, in an etching process or a CVD process in semiconductor manufacturing, a vacuum pump is used to secure a vacuum state and discharge a process gas. In this case, if a contact-type vacuum pump using lubricating oil is used, the lubricating oil may affect the process gas such as SiH ₄ , PH ₃ , B ₂ H ₆ , and _AS H ₃ , A magnetic bearing device using a non-contact bearing is often used.

A magnetic bearing device secures a vacuum state with rotor blades attached to a rotor shaft by rotating the rotor shaft with a high-frequency motor while magnetically levitating the rotor shaft in the axial and radial directions by an electromagnet. It is like this. In the magnetic bearing device, when the rotor shaft is magnetically levitated in the axial direction and the radial direction by an electromagnet, in order to hold the rotor shaft at a predetermined position, a sensor for detecting the radial direction and the axial position of the rotor shaft is provided. It is arranged. The radial and axial sensors detect the rotor shaft position, calculate the rotor shaft correction value from the detected position detection signal, and perform feedback control so that the rotor shaft is held at a predetermined position such as the shaft center. The position is controlled by.

In general, a feedback control system becomes unstable when the open loop gain g is 0 dB or more and the phase delay is 180 ° or more. In the control system of the magnetic bearing device, the open loop transfer function may have a gain g> 0 dB and a phase delay of 180 ° or more at the natural frequency ω of the rotor. In such a case, the control system becomes unstable and oscillation occurs at the frequency ω that matches the natural frequency.

Therefore, in the control system of the conventional magnetic bearing device, a notch filter that cuts the frequency corresponding to the natural frequency ω of the rotor shaft is provided in the position correction circuit to lower the gain at the frequency ω. The oscillation of the rotor shaft is suppressed.

[0006]

[Problems to be solved by the device]

 By the way, the natural frequency ω of a substance is proportional to the square root of the Young's modulus E when k is a constant, as shown in the following equation (1). ω = k√E (1) Since this Young's modulus E changes in response to changes in temperature, if the temperature of the components of the pump body, such as the rotor and shaft, changes, their natural frequencies also change. To do. Further, the rotor and the like thermally expand due to the temperature change, which also changes the natural frequency. In this way, the natural frequency ω of the substance fluctuates due to thermal expansion and changes in the Young's modulus E due to temperature changes. For example, when this magnetic bearing device is used as a magnetic levitation type vacuum pump connected to a semiconductor connection device, when the device is started up or when the chamber of the semiconductor connection device is in a vacuum state and no load is applied, etc. In, the temperature is lower than in normal operation when the process gas is discharged.

However, in a filter used in a position correction circuit of a conventional magnetic bearing device, a predetermined frequency band to be cut is fixed, so that an appropriate frequency is always cut by a temperature change. I didn't. Therefore, an object of the present invention is to provide a magnetic bearing device capable of suppressing the oscillation of the rotor shaft even when the device temperature changes.

[0008]

[Means for Solving the Problems]

 In the present invention, based on a rotor shaft having magnetism, a high-frequency motor for rotating the rotor shaft, a plurality of position detection sensors for detecting the position of the rotor shaft, and a detection signal from the position detection sensor, Control signal output means for outputting a control signal for holding the rotor shaft at a predetermined position, and generating a magnetic field according to the control signal output by the control signal output means to bring the rotor shaft into non-contact. A magnetic levitation electromagnet that magnetically levitates to a predetermined position, a temperature detection unit that detects the temperature at a predetermined position in the device, and a frequency that cuts a control signal in a predetermined frequency band from the control signal output from the control signal output unit. The magnetic bearing device is provided with cutting means and changing means for changing the predetermined frequency band cut by the frequency cutting means according to the temperature detected by the temperature detecting means. To achieve the above purpose.

[0009]

[Action]

 In the magnetic bearing device of the present invention, the device temperature is detected by temperature detecting means such as a thermistor, and the control signal in the band which is the oscillation frequency of the rotor shaft at the device temperature is cut by frequency cutting means such as a notch filter. Then, the frequency band cut by the notch filter is also changed according to the change in the device temperature.

[0010]

【Example】

 A preferred embodiment of the magnetic bearing device of the present invention will be described in detail with reference to FIGS. 1 to 6 when it is used in a magnetic levitation type vacuum pump. FIG. 1 shows the overall structure of the magnetic bearing device.

This magnetic bearing device is installed in, for example, a semiconductor manufacturing apparatus or the like, and discharges process gas from a chamber or the like. In this example, a flange 11 is formed on the upper end of a cylindrical outer casing 10 and is connected to a semiconductor manufacturing apparatus by a bolt or the like.

A plurality of stator blades 12 are arranged inside the outer casing 10, and a plurality of rotor blades 14 are arranged between the respective stator blades 12. The rotor blades 14 are provided on the outer peripheral wall of the rotor 15, and the rotor 15 is fixed to the rotor shaft 18 by bolts 19 so as to rotate in conjunction with the rotor shaft 18 made of a magnetic material.

The rotor 15 uses a so-called magnetic bearing, and two pairs of radial electromagnets 20 are arranged above the rotor shaft 18 so as to face each other with the rotor shaft 18 interposed therebetween. Are arranged so as to be orthogonal to each other. Two pairs of radial sensors 22 are provided adjacent to the radial electromagnet 20 so as to face each other with the rotor shaft 18 interposed therebetween.

Further, two pairs of radial electromagnets 24 are similarly arranged under the rotor shaft 18, and the radial electromagnets 24 are also provided with two pairs of radial sensors 26 adjacent to each other. . By supplying an exciting current to the radial electromagnets 20 and 24, the rotor shaft 18 is magnetically levitated. This exciting current is controlled in response to position detection signals from the radial direction sensors 22 and 26 during magnetic levitation, whereby the rotor shaft 18 is held at a predetermined position in the radial direction.

Further, a high frequency motor 30 is arranged between the radial direction sensor 22 and the radial direction sensor 26 inside the exterior body 10. When the high frequency motor 30 is energized, the rotor shaft 18 and the rotor blades 14 fixed to the rotor shaft 18 rotate.

A disc-shaped metal disk 31 made of a magnetic material is fixed to the lower portion of the rotor shaft 18, and the pair of axial electromagnets 32, 34 that sandwich the metal disk 31 and face each other. Are arranged. Further, an axial sensor 36 is arranged facing the cut end of the rotor shaft 18.

The exciting currents of the axial electromagnets 32 and 34 are controlled according to the position detection signal from the axial sensor 36, so that the rotor shaft 18 is held at a predetermined axial position. There is. A rotation sensor 38 for detecting the number of rotations of the rotor shaft is arranged at the lower end of the rotor shaft 18.

An exhaust port 52 for exhausting process gas or the like from the semiconductor manufacturing apparatus is arranged in the lower portion of the outer casing 10 of the magnetic bearing device. A temperature sensor 50 such as a thermistor is arranged near the exhaust port 52 to measure the temperature of the spacer (fixed portion).

Each of these parts is connected in a cable to a signal processing system including a magnetic bearing controller, a main controller and the like through a connector 44 provided near the axial electromagnets 32 and 34. FIG. 2 shows the electrical configuration of the magnetic bearing device.

The magnetic bearing device is mainly configured by a system controller 70 mainly using a microprocessor unit (MPU) and a magnetic levitation controller 80. The system controller 70 stores a CPU (Central Processing Unit) 70a for performing various controls such as the judgment operation according to the present embodiment, and a program and data for executing various controls in the CPU 70a, in addition to performing overall control of the magnetic bearing device. ROM (Read Only Memory) 70b, RAM (Random Access Memory) 70c used as working memory, Keyboard Interface (I / F) 70d, Display I / F 70e, I / O 70f , 70g, 70h, 70i, and these units are connected to a bus line 70j such as a data bus.

The keyboard I / F 70d is connected to a keyboard 74 for performing various operation instructions and other operations. Further, the display I / F 70e is connected with a display 76 such as a CRT or LCD for displaying the operating state from the keyboard 74, the floating state of the rotor shaft 18, and the operating state of the magnetic bearing device. .

A magnetic levitation controller 80 is connected to the I / O 70f. The magnetic levitation controller 80 includes PIDs (correction circuits) 82a to 82e to which the position detection signals from the radial direction sensors 22 and 26 and the axial direction sensor 36 are input. Each of these PIDs 82a to 82e is provided with a frequency variable notch filter, which will be described later, and a clock generation circuit that outputs a clock signal for changing the center frequency cut by this notch filter. The clock generation circuit generates a clock having an output frequency corresponding to the signal supplied from the CPU 70a and supplies it to the notch filter.

Amplifiers 84a to 84e are connected to the output terminals of the PIDs 82a to 82e, respectively. Radial electromagnets 20 and 24 formed of a pair of coils are connected to the output terminals of the amplifiers 84a to 84d. The output terminals of the amplification section 84e are connected to the axial electromagnets 32 and 34, which are each composed of a pair of coils.

The magnetic levitation controller 80 magnetically levitates the rotor shaft 18 in the radial direction by supplying an exciting current to the radial electromagnets 20 and 24, and outputs the position detection signals from the radial direction sensors 22 and 26. Accordingly, the amplification factors of the amplifiers 84a to 84d are changed so as to hold the rotor shaft 18 at a predetermined position in the radial direction, and control is performed to change the exciting current supplied.

At the same time, the magnetic levitation controller 80 magnetically levitates the rotor shaft 18 in the axial direction by supplying an exciting current to the axial electromagnets 32 and 34, and in response to a position detection signal from the axial sensor 36. The amplification factor of the amplifier 84e is changed so as to hold the rotor shaft 18 at a predetermined position in the axial direction, and the exciting current to be supplied is changed.

A rotation sensor 38 is connected to the I / O 70g, and a pulse signal from the rotation sensor 38 is read by the CPU 70a to detect the rotation speed of the rotor shaft 18. A motor driver 77 for rotating the high frequency motor 30 is connected to the I / O 70h. The motor driver 77 converts an AC power source (not shown) into a direct current by a converter, and then converts it into a three-phase alternating current by an inverter so as to supply a current according to a load to the high frequency motor 30.

FIG. 3 shows a configuration of a frequency variable notch filter arranged in the correction circuits (PID) 82a to 82e. This notch filter includes four operational amplifiers 101, 103, 105 and 107 whose non-inverting terminals are grounded.

One end of the resistor 121 and one end of the resistor 111 are connected to the inverting input terminal of the operational amplifier 101, and the other end of the resistor 111 is connected to the input terminal ei of the notch filter. The output terminal of the operational amplifier 101 is connected to one ends of the resistors 113 and 115, and the other end of the resistor 113 is connected to the inverting input terminal of the operational amplifier 101.

The other end of the resistor 115, one end of the resistor 125, and one end of the resistor 117 are connected to the inverting input terminal of the operational amplifier 103, and the output terminal of the operational amplifier 103 has the other end of the resistor 117 and one of the variable resistors Rf. It is connected to the terminal a. The other terminal b of the variable resistor Rf is connected to the inverting input terminal of the operational amplifier 105 and one end of the capacitor 119 having the capacity C. The output terminal of the operational amplifier 105 is connected to the other end of the capacitor 119, the other end of the resistor 121, and one terminal a of the variable resistor Rf. The other terminal b of the variable resistor Rf is connected to the inverting input terminal of the operational amplifier 107 and one end of the capacitor 123 having the capacitance C. The output terminal of the operational amplifier 107 is connected to the other end of the capacitor 123 and the other end of the resistor 125.

FIG. 4 shows the characteristics of this notch filter. As shown in FIG. 4, the notch filter cuts the frequency component of the center frequency f0. This center frequency f0 is expressed by the following equation (2), where R is the resistance of the variable resistor RF of the notch filter shown in FIG. 3 and C is the capacitance of the capacitors 119 and 123.

F0 = 1 / (2πCR) (2) Therefore, the center frequency f0 is variable by the resistance value of the variable resistor RF. FIG. 5 shows a switching element used equivalently to the variable resistor RF in this embodiment.

As shown in FIG. 5, the switching element includes two switches, and a capacitor having a capacitance C1 is connected between the switches. Both switches perform switching operation by the external clock fc, and as shown in FIG. 5, the input terminal a, the capacitor, and the ground are connected in series, and by switching, the ground, the capacitor C1, and the output terminal b are connected. It is designed to be connected in series.

An equivalent resistance value Req of this switching element is expressed by the following equation (3). Req = 1 / (C1 · fc) (3) Therefore, the center frequency f0 to be cut by the notch filter is changed by changing the switching frequency by the external clock fc from the expressions (2) and (3). Is possible.

FIG. 6 shows an example of the relationship between the temperature of the magnetic bearing device shown in FIG. 1 and the natural frequency ω 0 of the rotor shaft 18. As shown in FIG. 6, the natural frequency ω0 of the rotor 18 decreases as the temperature t increases. Data indicating the relationship between the temperature t and the natural frequency ω0 is stored in the ROM 70b shown in FIG.

Next, the operation of the magnetic bearing device thus configured with respect to temperature changes will be described. When an instruction to start the operation of the magnetic bearing device is input from the keyboard 74, a start instruction signal is supplied to the CPU 70a via the keyboard I / F 70d, and the CPU 70a sends it to the magnetic levitation controller 80 via the I / O 70f. Magnetic levitation of the rotor shaft 18 is instructed.

Upon receiving an instruction from the CPU 70 a, the magnetic levitation controller 80 supplies an exciting current to the radial electromagnets 20, 24 and the axial electromagnets 32, 34 to magnetically levitate the rotor shaft 18. In this case, in the magnetic levitation controller 80, the exciting current is controlled by the PIDs 82a to 82e and the amplifiers 84a to 84e based on the position detection signals from the radial direction sensors 22 and 26 and the axial direction sensor 36. The rotor shaft 18 is held at the shaft center.

Further, the CPU 70a instructs the motor driver 77 to start rotation of the high frequency motor 30 via the I / O 70h. Upon receiving this instruction, the high-frequency motor 30 outputs the converted three-phase alternating current, which causes the high-frequency motor 30 to start high-speed rotation. Along with this, the rotor shaft 18 and the rotor blades 14 also start to rotate at high speed.

Here, the CPU 70a measures the device temperature t of the magnetic bearing device based on the signal supplied from the temperature sensor 50 via the I / O 70i. Then, the value of the natural frequency ω0 at the measured temperature t is read from the data on the temperature-natural frequency curve (FIG. 6) stored in the ROM 70b.

From the equations (2) and (3), the CPU 70a determines the frequency fc of the external clock at which the center frequency f0 to be cut by the notch filter is equal to this natural frequency ω0, and the corresponding control signal is I / It supplies to each PID82a-82e of the controller 80 for magnetic levitation via O70f. In each PID 82, a clock circuit (not shown) outputs a clock signal having a predetermined frequency fc divided by a well-known frequency dividing means and supplies it to the switching element shown in FIG. 5 as an external clock.

By repeating the switching operation at the frequency fc of the supplied external clock, the switching element functions equivalently to the resistance element having the resistance value Req shown in the equation (3). Here, the frequency fc of the external clock is selected so that the value of f0 obtained by the equation (2) matches the oscillation frequency ω0 of the rotor shaft, so that the notch filter (FIG. 3) arranged in each PID is used. , The optimum frequency component corresponding to the device temperature will be cut.

In the embodiment described above, the notch filter and the switching element shown in FIGS. 3 and 4 are used as the frequency cutting means, but the present invention is not limited to this configuration, and the variable resistor RF having another configuration is used. May be used. Further, the configuration of the notch filter is not limited to the notch filter shown in FIG. 3 as long as it can cut a specific frequency. For example, the frequency cut means may be configured by combining band pass filters that pass only a specific frequency band. Thus, a filter that cuts a specific frequency and a configuration that can change the frequency band to be cut may be used.

Further, although the temperature sensor is arranged in the vicinity of the exhaust port 52 in the embodiment described above, it may be arranged at another position as long as it can measure the temperature of the spacer (fixed portion). For example, if it is arranged between the connector 44 and the rotor blade 12 and there is a space between the outer casing 10 and the stator blade 12, the temperature sensor on the stator blade side at this space. May be arranged.

Although a contact type thermometer such as a thermistor was used as the temperature sensor, a non-contact type thermometer, for example, a sensor part of a radiation thermometer was attached to each position described above, and the thermometer body was connected to the connector 44. It may be arranged in the existing signal processing system.

Further, in the embodiment described above, the magnetic bearing device is applied to the magnetic levitation type vacuum pump, but in the present invention, the magnetic bearing spindle or the like used for the grindstone or the like may be used. It can also be used for.

[0045]

[Effect of device]

 In the magnetic bearing device of the present invention, the device temperature is detected by the temperature detecting device, and the control signal in the predetermined frequency band at the device temperature is cut by the frequency cutting device and also cut by the frequency cutting device according to the change of the device temperature. Since the frequency band to be changed is changed, an appropriate frequency component can be cut even if the device temperature changes.

Therefore, the oscillation of the rotor shaft can be suppressed even if the device temperature changes.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of a magnetic bearing device of the present invention.

FIG. 2 is a block diagram showing an electrical configuration of the embodiment.

FIG. 3 is a configuration diagram of a notch filter according to the embodiment.

FIG. 4 is an explanatory diagram showing characteristics of the notch filter of the embodiment.

FIG. 5 is a configuration diagram of a switching element equivalently used as the variable resistance RF of the embodiment.

FIG. 6 is an explanatory diagram showing a relationship between an apparatus temperature and a natural frequency ω0 according to the embodiment.

[Explanation of symbols]

 10 Exterior Body 12 Stator Blade 13 Rotor Blade 15 Rotor 18 Rotor Shaft 20, 24 Radial Electromagnet 22, 26 Radial Sensor 30 High Frequency Motor 32, 34 Axial Electromagnet 36 Axial Sensor 50 Temperature Sensor 52 Exhaust Port 70 System Controller 70a CPU 70b ROM 74 keyboard 77 motor driver 80 magnetic levitation controller 82 PID

Claims (1)

[Scope of utility model registration request] 1. A magnetic rotor shaft, a high-frequency motor for rotating the rotor shaft, a plurality of position detecting sensors for detecting the position of the rotor shaft, and a detection signal from the position detecting sensor. Control signal output means for outputting a control signal for holding the rotor shaft at a predetermined position, and a predetermined position at which the rotor shaft is brought into non-contact by generating a magnetic field according to the control signal output by the control signal output means. A magnetic levitation electromagnet to magnetically levitate, a temperature detecting means for detecting a temperature at a predetermined position in the apparatus, a frequency cutting means for cutting a control signal in a predetermined frequency band from a control signal output from the control signal output means, And a changing unit for changing the predetermined frequency band cut by the frequency cutting unit according to the temperature detected by the temperature detecting unit. Gas-bearing device.