JP2009068718A - Magnetic bearing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic bearing device capable of preventing excessive amplitude of a rotor in changing feedback gain. <P>SOLUTION: A magnetic bearing type turbo molecular pump must experience a critical speed (rotation speed n2) from the rotor rotating start to a stationary rotation. From the rotor rotating start to a rotation speed n3, the magnetic bearing is controlled at a control gain G1 of which the rotation speed n1 is a critical speed. When the rotation speed exceeds n4, it is controlled at a regular control gain G2. In a rotation speed range n3≤n≤n4 being a gain changeover zone, the control gain G is continuously varied from G1 to G2 in response to the increase of the rotation speed. As a result, the excessive amplitude of the rotor in changing the gain can be prevented. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a magnetic bearing device used for a turbo molecular pump or the like.

Magnetic bearings are often used in devices that require high-speed rotation, such as turbomolecular pumps and machine tools. For example, in the case of a turbo molecular pump, the rotor position is detected by a displacement sensor, the sensor signal is taken into a control circuit, and the electromagnet current is controlled based on the sensor signal. In a magnetic bearing device, generally, PID control is used as a feedback control system to attenuate a steady deviation with respect to a steady disturbance.

A magnetic bearing device that supports such a rotor has two natural vibration modes. One is called a cylindrical mode, in which the rotor shaft draws a cylindrical trajectory around the bearing center axis. The second is called a conical mode, in which the rotor shaft draws a conical locus around the bearing center axis.

Because of the existence of the natural vibration mode, when the rotational speed of the rotor is increased or decreased, resonance may occur when the rotational frequency matches the natural vibration frequency, which may cause an excessive amplitude of the rotor. . As a result, the rotor contacts the protective bearing provided on the stator side, and vibration is generated in the magnetic bearing itself. As a result, problems such as dust generation from the protective bearing and damage and seizure of the protective bearing occur.

By the way, it is known that the frequency of the natural vibration mode changes according to the gain of feedback (for example, refer to Patent Document 1). For example, when the rotor rotational speed is low, the critical speed at which resonance occurs is set higher by making the feedback gain higher than the original value. Therefore, the rotor can pass through the rotational speed corresponding to the critical speed in the original feedback gain without causing resonance. If the rotor rotational speed passes the critical speed, the feedback gain is switched to lower the original gain value.

Japanese Patent Laid-Open No. 7-224839

However, if the feedback gain is suddenly changed, an excessive amplitude is generated in the rotor due to a transient response generated when the gain is switched, and in the worst case, the rotor may touch down the protective bearing.

The present invention provides a magnetic bearing device capable of preventing an excessive amplitude of a rotor at the time of feedback gain switching by continuously changing the feedback gain and switching the feedback gain.

In the magnetic bearing device having a plurality of operation states having different magnetic levitation control gains, the present invention switches from the first operation state based on the first magnetic levitation control gain to the second operation state based on the second magnetic levitation control gain. In addition, the magnetic levitation control gain includes control means for controlling the magnetic bearing device in a third operation state in which the magnetic levitation control gain continuously changes from the first magnetic levitation control gain to the second magnetic levitation control gain.
Further, the magnetic bearing device may support the rotating body in a non-contact manner with an electromagnet and switch from the first operating state to the second operating state in accordance with the rotational speed of the rotating body. In that case, in the third operating state, the magnetic levitation control gain is continuously changed from the first magnetic levitation control gain to the second magnetic levitation control gain in accordance with the change in the rotational speed of the rotating body.
Furthermore, switching from the first operating state to the second operating state may be performed within a preset switching time.

According to the present invention, when switching from the first operating state by the first magnetic levitation control gain to the second operating state by the second magnetic levitation control gain, the magnetic levitation control gain is changed from the first magnetic levitation control gain to the second magnetic levitation control gain. 2 Since the magnetic levitation control gain is continuously changed, the transient response caused by the magnetic levitation control gain switching can be avoided.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a view showing an embodiment of a magnetic bearing device according to the present invention, and shows a magnetic bearing type turbo molecular pump. FIG. 1 is a cross-sectional view of a pump body 1 of a magnetic bearing turbomolecular pump. Inside the casing 20 provided in the pump body 1, the rotor 4 having a plurality of stages of rotor blades 21 and screw groove portions 22, the stator blades 23 arranged alternately with respect to the rotor blades 21, and the above A cylindrical member 24 disposed so as to face the screw groove 22 is provided.

The electromagnet 5 that supports the rotor 4 in a non-contact manner includes electromagnets 51 and 52 that constitute a radial magnetic bearing and an electromagnet 53 that constitutes an axial magnetic bearing, and these constitute a 5-axis control type magnetic bearing. Corresponding to the radial electromagnets 51 and 52 and the axial electromagnet 53, radial displacement sensors 71 and 72 and an axial displacement sensor 73 are provided.

The pump body 1 is driven by a controller (not shown), and a cable (not shown) connecting the controller and the pump body is connected to the receptacle 25. When the rotor 4 is rotationally driven by the motor 6 while being supported in a non-contact manner by the electromagnets 51, 52, 53, the gas on the inlet flange 20 side is exhausted to the back pressure side (space S1) as shown by the arrow G1, and then exhausted to the back pressure side. The discharged gas is discharged out of the pump by an auxiliary pump connected to the exhaust port flange 26.

27 and 28 are emergency mechanical bearings. When the rotor 4 is not magnetically levitated, the rotor 4 is supported by these bearings 27 and 28. The bearing 27 constrains the movement of the rotor 4 in the radial direction (x-axis and y-axis) in an emergency, and the bearing 28 has two radial directions (x-axis and y-axis) and one axis in the thrust direction (z-axis). ). The bearings 27 and 28 also function as protective bearings that prevent the rotor 4 from contacting the stator-side electromagnet or the like when the magnetically levitated rotor 4 is greatly decentered.

FIG. 2 is a conceptual diagram of a 5-axis control type magnetic bearing, in which the rotation axis J of the rotor 4 is shown to coincide with the z-axis. The radial electromagnet 51 shown in FIG. 1 includes a pair of electromagnets 51x related to the x axis and a pair of electromagnets 51y related to the y axis. Similarly, the radial electromagnet 52 also includes a pair of electromagnets 52x related to the x axis and a pair of electromagnets 52y related to the y axis. In addition, the axial electromagnet 53 includes a pair of electromagnets 53z disposed to face each other so as to sandwich the disk 41 provided at the lower end of the rotor 4 along the z axis.

The displacement sensors 71 and 72 in FIG. 1 are also constituted by a pair of radial displacement sensors corresponding to the electromagnets 51x, 51y, 52x, and 52y. These five sets of electromagnets 51x, 51y, 52x, 52y, 53 and displacement sensors 71-73 constitute a 5-axis control type magnetic bearing.

FIG. 3 is a block diagram showing the basic configuration of the magnetic levitation control system of the magnetic bearing device, and the magnetic bearing portion is shown only on one axis in the radial direction. The electromagnet 5 is a pair of radial electromagnets 51x, and the displacement sensor 7 is a radial displacement sensor 71x corresponding to the electromagnet 51x. The displacement sensor 7 is an inductance type sensor, and converts the gap displacement into an electrical signal by utilizing the change in the sensor unit impedance caused by the change in the gap displacement. The sensor facing surface of the rotor 4 is made of a ferromagnetic material or a conductor.

A controller that drives the pump body 1 is provided with a sensor circuit 2, a control circuit 3, and an excitation amplifier 8. The control circuit 3 includes an A / D converter 301, a D / A converter 302, a DSP (digital signal processor) 307 which is an arithmetic unit, and a storage unit 306 having a ROM 304, a RAM 305, and the like.

A carrier wave of several tens of kHz is applied to the displacement sensor 7 by the sensor circuit 2, and the carrier wave is amplitude-modulated in accordance with a change in impedance of the sensor portion caused by the gap displacement. This amplitude modulated wave (AM wave) is input to the control circuit 3 via the sensor circuit 2 as a sensor signal. In the case of the radial displacement sensor 71x, the sensor circuit 2 calculates the difference between the sensor signals from each displacement sensor 71x, and the difference component is input to the control circuit 3 as a sensor signal. The rotational speed (rotational speed) of the rotor 4 is detected by the rotational speed sensor 10, and the detection signal is input to the control circuit 3.

The analog sensor signal input to the control circuit 3 is converted into a digital value by the A / D converter 301 and input to the DSP 307. In the magnetic bearing device, the excitation signal of the electromagnet 5 is controlled by feeding back the sensor signal of the displacement sensor 7 to the control system, and the control gain corresponding to the magnetic levitation system composed of the rotor 4 and the electromagnet 5 is stored in the storage unit 306 is input in advance.

FIG. 4 is a block diagram showing functions of the DSP 307 in this embodiment. The sensor signal digitally converted by the A / D converter 301 is input to the control calculation unit 310 of the DSP 307. The control calculation unit 310 calculates the excitation current that should flow through the electromagnet 5 based on the sensor signal from the displacement sensor 7 and a preset control gain. For example, when the floating position of the rotor 4 is shifted to the left side from the proper position, control is performed so that the excitation current of the right electromagnet 51x is increased to the proper position. The current control amount at this time is calculated by PID calculation.

The control calculation output of the control calculation unit 310 is input to the control output gain switching unit 311. The control output gain switching unit 311 performs gain switching by correcting the control calculation output input from the control calculation unit 310 based on the rotation number of the rotor 4 detected by the rotation number sensor 10. Details of the gain switching will be described later. The control output gain switching unit 311 outputs a control signal obtained by multiplying the control calculation output by the gain correction coefficient. The control signal is converted to an analog value by the D / A converter 302 and then input to the excitation amplifier 8.

5 and 6 are diagrams illustrating an example of gain switching in the turbo molecular pump. FIG. 5 is a diagram showing the relationship between the rotational speed of the rotor 4 and the control gain, where the vertical axis represents the gain and the horizontal axis represents the rotor rotational speed. FIG. 6 is a flowchart showing the gain switching procedure, and shows the operation of the control output gain switching unit 311.

A curve L in FIG. 5 represents a change in the control gain. When the rotation speed n of the rotor 4 is <n3, the control gain is set to G1. When the rotational speed n is n> n4, the control gain is set to G2 (<G1). The range of n3 ≦ n ≦ n4 is a gain switching section, and the control gain decreases from G1 and changes to G2 while the rotation speed n changes from n3 to n4. Switching between the gain G1 and the gain G2 is performed across the gain switching section n3 ≦ n ≦ n4. The control gain G1 at the start of rotation is a control gain stored in advance in the storage unit 306.

The control gain G2 is a control gain suitable for high-speed rotation, and the rotation speed corresponding to the critical speed when set to the control gain G2 is n2. On the other hand, the control gain G1 is larger than G2, and the rotational speed corresponding to the critical speed at that time is n1 larger than n2. When accelerating the rotor 4 to steady rotation, it is necessary to pass a critical speed corresponding to the rotation speed n2.

Conventionally, as shown in FIG. 7, acceleration is started with a control gain G1 larger than the control gain G2 during high-speed rotation. The rotational speed corresponding to the critical speed at this time is n1 as described above. If the rotor rotational speed passes through the rotational speed n2, that is, if the critical speed in the case of the control gain G2 is passed, the control gain is suddenly switched from G1 to G2 stepwise at the rotational speed n5. Since the rotation speed corresponding to the critical speed is n2 by the gain switching, the rotor has passed the critical speed. As described above, the dangerous speed (resonance point) can be quickly passed by performing such gain switching.

Returning to FIG. 5, the point that the control gain is switched from G1 to G2 and the resonance point is passed through is the same as in FIG. 7, but in this embodiment, the gain switching section (n3 ≦ n ≦ n4) is provided, and the control gain is continuously switched from G2 to G1 in the section. By the way, although the states of the gain G1 and the gain G2 are both stable, the state between the state of the gain G1 and the state of the gain G2, which is the gain switching section, is not necessarily a stable state. Therefore, if the switching from the gain G1 to the gain G2 is performed slowly over time, the state of the magnetic bearing may become unstable.

However, in the present embodiment, it is possible to prevent instability by providing the gain switching section as described above and continuously changing the gain during the divided short time. At this time, the width of the gain switching section in which the gain is continuously changed, that is, the time required for gain switching is preferably short to some extent, and is set to, for example, 1 second or less. Of course, this switching time is sufficiently long compared to the case of changing in a stepped manner as in the prior art, and no transient phenomenon occurs when changing in a stepped manner.

As the width of the gain switching section, for example, in the case of a turbo molecular pump, it is about several Hz in terms of the rotor rotational frequency (Hz). Of course, this frequency width depends on the acceleration speed and the deceleration speed of the rotor rotation, and the frequency width becomes larger as the acceleration / deceleration speed is faster even in the same switching time.

Next, the switching procedure will be described using the flowchart of FIG. The flowchart of FIG. 6 starts when the control circuit 3 (see FIG. 3) is turned on. In step S101, it is determined whether or not the power source of the control circuit 3 has been turned off. If it is determined to be off, the gain switching process is terminated, and if it is determined to be on, the process proceeds to step S102.

In step S102, it is determined whether the rotor rotational speed n is “n <n3”, “n3 ≦ n ≦ n4”, or “n> n4”. Note that n3 and n4 represent the upper and lower rotation speeds of the gain switching section as shown in FIG. If “n <n3” is determined in step S102, the process proceeds to step S103. If “n3 ≦ n ≦ n4” is determined, the process proceeds to step S104. If “n> n4” is determined, the process proceeds to step S105.

In each process of steps S103 to S105, a gain correction coefficient α corresponding to the rotor rotational speed n is calculated. When the rotor rotational speed n is “n <n3”, the correction coefficient α is set to α = 1 in step S103, and the process proceeds to step S106, where the control gain G is calculated as G = G1 · α. That is, as shown in FIG. 5, the control gain is G1 in the range of “n <n3”.

On the other hand, when the rotor rotational speed n is “n> n4”, the correction coefficient α is set to α = G2 / G1 in step S105, and the control gain G is calculated using the correction coefficient α in step S106. In this case, the control gain G is G = G2. That is, in the range of “n> n4”, the control gain is G2, as shown in FIG.

When the rotor rotational speed n is in the gain switching section “n3 ≦ n ≦ n4”, the process proceeds to step S104, and the rotor rotational speed n is substituted into the function α (n) of n to calculate the correction coefficient α. The function α (n) satisfies “1 ≧ α (n)> G2 / G1” and changes continuously and gently in the gain switching section “n3 ≦ n ≦ n4” as shown in FIG. . Further, α (n3) = 1 and α (n4) = G2 / G1 are satisfied at the upper and lower limits of the rotational speed n.

Since the control calculation unit 310 calculates the control calculation output assuming that the control gain is G1, in step S107, the control calculation output calculated by the control calculation unit 310 is changed to the control gain G calculated in step S106. Correct so that it corresponds. In FIG. 4, the corrected control calculation output is output from the control output gain switching unit 311 to the D / A converter 302. If the process of step S107 is complete | finished, it will return to step S101 and will repeat the process of step S101 to step S107 until the power supply of the control circuit 3 is turned off.

As the α (n) in the gain switching section, various things are possible without being limited to the gain change as shown in FIG. 5 as long as the instability phenomenon at the time of gain switching can be suppressed. For example, as shown in FIG. 8, G1 · α (n) may be a straight line having a constant slope β = − (G2−G1) / (n4−n3).

As described above, in the present embodiment, the gain switching section (n3 ≦ n ≦ n4) is provided, and the control gain is continuously switched from G2 to G1 in the section. The transient response associated with can be avoided. Furthermore, destabilization in the gain switching section can be prevented by shortening the switching section. As a result, it is possible to prevent the pump from being damaged due to the occurrence of an excessive amplitude during gain switching. Further, since the system does not depend on the history of changes in the rotational speed, control with an appropriate gain can be performed even if the rotational speed is changed, such as acceleration and deceleration, near the switching rotational speed.

In the embodiment described above, the gain switching at the critical speed passage in the magnetic bearing device of the turbo molecular pump has been described as an example. For example, as shown in FIGS. The present invention can also be applied to a case where the size is increased only within the range. In the example shown in FIG. 9A, the gain is continuously changed with a correction function α ′ (n) having an upwardly convex shape within a predetermined range. On the other hand, in the example shown in FIG. 9B, the correction function α1 (n) is used in the switching section A1 in which the gain is increased, and the correction function α2 (n) is used in the switching section A2 in which the gain is decreased. Further, the present invention is not limited to the magnetic bearing device of a rotating body, and can be applied to increase or decrease the control gain in various magnetic bearing devices.

In the correspondence between the embodiment described above and the elements of the claims, the control gain G1 constitutes the first magnetic levitation control gain, and the control gain G2 constitutes the second magnetic levitation control gain. In addition, the present invention is not limited to the above embodiment as long as the characteristics of the present invention are not impaired.

It is a figure which shows one Embodiment of the magnetic bearing apparatus by this invention, and is sectional drawing of a magnetic bearing type | mold turbomolecular pump. It is a conceptual diagram of a 5-axis control type magnetic bearing. It is a block diagram which shows the basic composition of a magnetic levitation control system. 3 is a block diagram showing functions of a DSP 307. FIG. It is a figure which shows the relationship between the rotation speed of the rotor 4, and a control gain. It is a flowchart which shows a gain switching procedure. It is a figure which shows the conventional gain switching. It is a figure which shows G in the case of decreasing the gain G linearly. It is a figure which shows the other example of correction | amendment function (alpha) (n), (a) shows a 1st example and (b) shows a 2nd example, respectively.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pump main body 2 Sensor circuit 3 Control circuit 4 Rotor 5, 51-53, 51x, 51y, 52x, 52y Electromagnet 6 Motor 8 Excitation amplifier 10 Rotational speed sensor 27, 28 Mechanical bearing 71, 72 Radial displacement sensor 73 Axial displacement sensor 301 A / D converter 302 D / A converter 307 DSP
306 Storage unit 310 Control operation unit 311 Control output gain switching unit G1, G2 Control gain

Claims (6)

In a magnetic bearing device having a plurality of operating states in which the rotating body is supported in a non-contact manner by an electromagnet and the magnetic levitation control gain for controlling the electromagnet is different.
At the rotational speed of the rotating body corresponding to the critical speed when set to the first magnetic levitation control gain, the magnetic bearing device is controlled in the second operation state by the second magnetic levitation control gain,
In the rotation speed of the rotating body corresponding to the critical speed when set to the second magnetic levitation control gain, the magnetic bearing device is controlled in the first operating state by the first magnetic levitation control gain,
The rotational speed of the rotating body corresponding to the critical speed when set to the first magnetic levitation control gain is sandwiched between the rotational speed of the rotating body corresponding to the critical speed when set to the second magnetic levitation control gain. When a section that is narrower than the set section is set as a gain switching section and the first operation state by the first magnetic levitation control gain and the second operation state by the second magnetic levitation control gain are switched in the section, Control means for controlling the magnetic bearing device in a third operating state in which the magnetic levitation control gain continuously changes between the first magnetic levitation control gain and the second magnetic levitation control gain. Magnetic bearing device. The magnetic bearing device according to claim 1,
In the third operating state, the magnetic levitation control gain is continuously changed between the first magnetic levitation control gain and the second magnetic levitation control gain in response to a change in the rotational speed of the rotating body. A magnetic bearing device characterized in that In the magnetic bearing device according to claim 1 or 2,
In the third operating state, the magnetic levitation control gain changes monotonically between the first magnetic levitation control gain and the second magnetic levitation control gain. The magnetic bearing device according to claim 1,
In the third operating state, the magnetic levitation control gain changes with a straight line having a certain slope between the first magnetic levitation control gain and the second magnetic levitation control gain. . The magnetic bearing device according to claim 1, wherein
The gain switching section is set with a predetermined switching time set in advance. The rotational speed of the rotating body corresponding to the critical speed when set to the first magnetic levitation control gain is a rotational speed at which natural vibration of the cylindrical mode and / or the conical mode is generated in the first operating state,
The rotational speed of the rotating body corresponding to the critical speed when set to the second magnetic levitation control gain is a rotational speed at which natural vibration of the cylindrical mode and / or the conical mode is generated in the second operating state. The magnetic bearing device according to claim 1, wherein:

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