JP3074284B2 - Magnetic bearing control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION << Industrial Application >> The present invention relates to a magnetic bearing used for a turbo-molecular pump or the like, and particularly to preventing resonance of the magnetic bearing.

<< Prior Art >> A radial magnetic bearing 1 generally used for a turbo molecular pump or the like is provided with an electromagnet 3 for floating a rotating rotor 2 to a target value as shown in FIG.
The comparator 5 compares the flying position of the rotor 2 fed back from the position sensor 4 with the target value, and the comparison value is processed by the control circuit 6 to drive the electromagnet 3 via the power amplifier 7. It is configured with feedback control.

Further, the above control circuit 6 are those having one gain characteristic as shown in FIG. 10, P ₁ is the resonance frequency of the magnetic bearing 1 in the gain characteristic.

Next, in the magnetic bearing 1 configured as described above will be described with reference to FIG. 11, the operation when the rotational frequency of the rotor 2 reaches the resonance frequency P ₁ of the magnetic bearing 1.

The magnetic bearing 1 can be represented by an equivalent circuit in which the electromagnet 3 (see FIG. 9) is replaced by a spring 3a as shown in FIG. According to this equivalent circuit, the rotor 2 has a resonance frequency determined by the mass of the rotor 2 and the spring constant of the spring 3a, and the frequency can be changed by a gain of a control circuit equivalent to the spring constant.
That is, when the gain is increased, the resonance frequency increases, and when the gain is decreased, the resonance frequency decreases.

Thus, the rotor 2 rotates and the rotation frequency is close to the resonance frequency P ₁ of the magnetic bearing, the spring 3a begins to vibrate up and down, its amplitude (referred mention below) gradually increases, the rotor 2 When the rotational frequency reaches the resonance frequency P ₁ of the magnetic bearing, the touch becomes maximum.

<< Problems to be Solved by the Invention >> However, in such a conventional magnetic bearing 1, the control circuit 6 constituting the magnetic bearing 1 has only one gain characteristic. resonance frequency P ₁ of the magnetic bearing 1 of the characteristic is always fixed, when the rotor 2 has reached the desired rotational speed had to be increased through the rotational frequency is always the resonance frequency P ₁ of the rotor 2 .

Therefore, the rotation frequency of the rotor 2 is equal to the resonance frequency P _1.
When the magnetic bearing 1 reaches the above-mentioned point, the above-described resonance occurs in the magnetic bearing 1, causing the rotor 2 to sway and fail to increase to a desired rotation speed, and also causes the rotor 2 and its peripheral members to be damaged. Was.

<< Means for Solving the Problems >> The present invention has been made in view of the above circumstances,
An object of the present invention is to provide a control device for a magnetic bearing in which resonance of the magnetic bearing is prevented. In order to achieve the above object, the present invention provides an electromagnet 3 as shown in FIG.
The position sensor 4 detects the floating position of the rotor 2 which is lifted and rotated by the electromagnet 3, and the electromagnet 3 determines the actual floating position of the rotor 2 detected by the position sensor 4 and the target floating position (target value) of the rotor 2. In the control device for the radial magnetic bearing of the feedback control, which is controlled by the control circuit a based on the result of the comparison operation and floats the rotor 2 to the target flying position, the rotation for detecting and outputting the rotation frequency of the rotor 2 A sensor 11; storage means b for storing a first resonance frequency of the magnetic bearing 1 when the control circuit a controls the electromagnet 3 by the first gain characteristic; and a rotation frequency detected and output by the rotation sensor 11. The control circuit a compares the first resonance frequency stored in the storage means b with the first resonance frequency.
And frequency comparing means c for outputting (via gain switching means b), and when the rotation frequency approaches the first resonance frequency from a low frequency side to a predetermined value, the output of the frequency comparing means c changes. The control means a determines that the first
From the control of the gain characteristic to the control of the second gain characteristic in which at least the gain on the higher frequency side than the vicinity of the first resonance frequency is smaller than the first gain characteristic, and the rotation frequency is changed from the first resonance frequency to the high frequency. When the distance from the frequency comparing means c changes to a predetermined value, the control means a switches from the control of the second gain characteristic to the control of the first gain characteristic.

<< Operation >> According to the present invention, when the rotation frequency of the rotor approaches the first resonance frequency from the low frequency side, the control is switched to the control of the second gain characteristic, and the resonance frequency of the magnetic bearing moves to the lower side. Even if the rotation frequency of the rotor passes the first resonance frequency, no resonance occurs. Before and after the rotation frequency of the rotor passes the first resonance frequency (including the rotation frequency used normally), the rotor is supported by the control of the first gain characteristic, the support rigidity is high, and the rotation of the rotor is stabilized. ing.

<< Embodiment >> Hereinafter, an embodiment in which the present invention is mounted on a turbo-molecular pump will be described in detail with reference to FIG. 2 to FIG.

Note that the same reference numerals are used for the same portions as those in the related art, and the detailed description is omitted.

FIG. 2 shows a turbo-molecular pump on which a control device for a magnetic bearing is mounted. A rotor 2 constituting the turbo-molecular pump surrounds a fixed portion 9 fixed in a central longitudinal direction in a housing 8. The rotor 2 is rotatably disposed. The rotor 2 is rotated by a high-frequency motor 10 provided near the center of the fixed portion 9, and the rotation frequency is detected and output by a rotation sensor 11.

The outline of the radial magnetic bearing 1 bearing the rotor 2 will now be described.
Radial electromagnet 3 and radial position sensor 4 mounted on
The radial electromagnet 3 causes the rotor 2 to float in the rotor radial direction, while the position sensor 4 measures the distance between the rotor 2 and the end face of the sensor 4 to determine the actual flying position of the rotor 2 ( The actual flying position is detected and output. Based on the detected output value and the value of the target flying position of the rotor, the rotor 2
Is configured to perform feedback control of the electromagnet 3 so that the electromagnet 3 is floated to the target flying position.

FIG. 3 is a block diagram showing a control device for a magnetic bearing that is feedback-controlled as described above.

The comparator 5 compares and calculates a target value at which the rotor 2 floats, that is, a target floating position of the rotor 2 and an actual floating detection output value of the rotor detected and output by the radial position sensor 4, and the comparison calculation value is calculated. Is output to the control circuit 6.

The control circuit 6 constituting the control means a includes a first control circuit 6a having a first gain characteristic and a second control circuit 6b having a second gain characteristic as shown in FIG. The control circuits 6a and 6b are configured to be switchable by a changeover switch 12. Both control circuits 6a and 6b perform signal processing on a comparison operation result output from the comparator 5, and process the processing result to the two control circuits 6a and 6b. Is output to the power amplifier 7 from any one of.

The power amplifier 7 amplifies the processing result output from one of the control circuits 6a and 6b, and drives the electromagnet 3.

Next, a control device for controlling the magnetic bearing 1 having the above-described configuration will be described.

The microcomputer 13 constituting the storage means b, the comparison means c, and the gain switching means d has a storage memory 14 for storing the first resonance frequency of the magnetic bearing 1 when the electromagnet 3 is controlled by the first gain characteristic in advance. And a CPU (frequency comparison means) 15. The CPU 15 compares the stored first resonance frequency with the rotation frequency of the rotor 2 detected and output by the rotation sensor 11, and based on the comparison value, 5. Execute the flowchart shown in FIG.
Switch 12

FIG. 5 shows a flowchart executed by the CPU 15. The operation of the magnetic bearing control device configured as described above will be described with reference to the flowchart shown in FIG. 5 and FIGS. This will be described with reference to FIG.

According to the present embodiment, first, the CPU 15 outputs a signal for switching the changeover switch 12 to the first control circuit 6a side,
12 is switched to the first control circuit 6a side, and the magnetic bearing 1 is subjected to feedback control using the first control circuit 6a. Then, the rotor 2 is rotated, and the rotation speed of the rotor gradually increases.
It rises from P ₀ (step 100).

Furthermore, by comparing the rotational frequency P ₂ in proximity to the low frequency side of the rotation frequency and the first resonant frequency P ₁ of the rotor 2 (Step 10
1), when the rotational frequency of the rotor 2 is the rotational frequency P ₂ less (NO), such as again of the comparison (step
Performs 101), is greater than the rotational frequency P _2, when indicating that the proximity from the low frequency side to the first resonant frequency P ₁ to a predetermined value (YES), CPU 15 has the switch 12 second
A switch signal is output to the control circuit 6b, the switch 12 is switched to the second control circuit 6b, and the magnetic bearing 1
Feedback control is performed using the control circuit 6b (step 102).

Then, by comparing the rotational frequency P ₃ in the rotation frequency and the first resonant frequency P ₁ of the rotor 2 in away position to the high-frequency side (step 103), the rotation frequency of the rotor 2 than the rotation frequency P ₃ If smaller (NO), performs such re of the comparison (step 103), is greater than the rotational frequency P _3, when indicating that away to a predetermined value to the high frequency side from the first resonant frequency P ₁ (YES), the CPU 15 outputs a signal for switching the changeover switch 12 to the first control circuit 6a side, the changeover switch 12 switches to the first control circuit 6a side, and the magnetic bearing 1 uses the first control circuit 6a. Feedback control is performed (step 104).

The rotational frequency decelerates the rotation of the rotor 2, the rotational frequency of the rotor 2 is close to the desired the rotational frequency P ₅ decreases from the high-frequency side of the rotation frequency and the first resonant frequency P ₁ of the rotor 2 comparing the P ₃ (step 105), if the rotational frequency of the rotor 2 is larger than the rotational frequency P ₃ (NO) performs such re of the comparison (step 105), less than the rotational frequency P ₃ Then (YES), CPU15
Outputs a signal for switching the changeover switch 12 to the second control circuit 6b, the changeover switch 12 switches to the second control circuit 6b, and the magnetic bearing 1 is subjected to feedback control using the second control circuit 6b. (Step 106).

Furthermore, by comparing the rotational frequency P ₂ at the position away from the rotation frequency and the first resonant frequency P ₁ of the rotor 2 to the low frequency side (step 107), the rotation frequency of the rotor 2 than the rotation frequency P ₂ If so (NO), performs such re of the comparison (step 107), becomes smaller than the rotation frequency P ₂ (YES), CPU 15 outputs a signal for switching the changeover switch 12 to the first control circuit 6a side Then, the changeover switch 12 is switched to the first control circuit 6a side, and the magnetic bearing 1 operates so that feedback control using the first control circuit 6a is performed (step 108).

Therefore, according to the above configuration, the first control circuit
6a, when the rotational frequency of the rotor 2 approaches the first resonance frequency of the magnetic bearing from a low frequency side, the first control circuit 6a
Is switched to the second control circuit 6b, the magnetic bearing 1 is feedback-controlled using the second control circuit 6b, and is switched when the rotation frequency of the rotor 2 moves away from the first resonance frequency to a higher frequency side. The second control circuit 6b is configured to be switched to the first control circuit 6a again.

That is, as shown in FIG. 4 (b), only while the rotational frequency of the rotor passes between P ₂ to P _3, the first control circuit having the first gain characteristic, first has a second gain characteristic 2
The control circuit is switched to the control circuit.
Resonance frequency P ₁ is instantaneously moved to the second resonance frequency P _4,
Since P is between ₂ to P ₃ does not exist a first resonance frequency, when the rotational frequency of the rotor passes between the P ₂ to P _3, since the rotor is touching operates normally not occur, the magnetic bearing Resonance can be prevented.

In describing the embodiment of the magnetic bearing control device shown in FIG. 6, the same reference numerals will be used for the same portions as in the prior art, and detailed description thereof will be omitted.

In this embodiment, the magnetic bearing is improved in order to solve the problems in the magnetic bearing control device shown in FIG. That is, when the gain characteristics are switched, the gain characteristics change over all frequencies. Therefore, due to the very low frequency disturbance acting on the rotor, for example, the gravity of the earth working when the rotor is rotated horizontally, the floating position of the rotor moves at the time of gain switching, causing unnecessary vibration on the rotor. was there.

Therefore, in the present embodiment, the gain characteristic on the low frequency side is not changed when the gain is switched.

In this embodiment, as shown in FIG. 6, there is provided a magnetic bearing 1 for bearing the rotor 2, and there is a control circuit 6 having two gain characteristics constituting the magnetic bearing 1. The switching by the computer 13 is the same as that of the embodiment of the magnetic bearing control device shown in FIG. 3, so that the detailed description thereof will be omitted, and only the characteristic portions will be described.

That is, in the present embodiment, the control circuit 6 having the above two gain characteristics is configured as follows.

As shown in FIGS. 6 and 7, the control circuit 6 includes a third control circuit 6c having a gain characteristic (A) forming the low frequency side and a gain characteristic (B) forming the high frequency side. ), And a fifth control circuit 6e having the gain characteristic (B) and a gain characteristic (C) having a smaller gain than the characteristic described above, which constitutes the high frequency side similarly to the above. The gain characteristic (B) and the gain characteristic (C) can be switched by a changeover switch 16.

The control circuit 6 has an adder 17 for adding the gain characteristic (A) and the gain characteristic (B) or the gain characteristic (A) and the gain characteristic (C).
By adding each of the above characteristics at 17, a first gain characteristic as shown in FIG. 8 and a second gain characteristic having a characteristic smaller on the high frequency side than the first gain characteristic are formed. .

That is, in this embodiment, the microcomputer
Switching the changeover switch 16 by means of 13 means switching between the first gain characteristic and the second gain characteristic as shown in FIG. 8. According to this switching, only the high frequency side of the first gain characteristic is Switching to the second gain characteristic having a characteristic smaller than the one gain characteristic is performed, and the switching operation is executed based on the flowchart shown in FIG. 5 in the same manner as described above.

Therefore, according to the above configuration, resonance of the magnetic bearing can be prevented, and only the high frequency side of the first gain characteristic is switched to the second gain characteristic having a characteristic smaller than the first gain characteristic. Because it is composed
Since the gain characteristic on the low frequency side is not changed before and after the switching, the stability of the magnetic bearing on the low frequency side increases.

In the above embodiment, the first gain characteristic and the second gain characteristic each use a control circuit having the characteristic. However, even one control circuit can switch two or more characteristics of the control circuit. May be configured.

The changeover switch 12 shown in FIG. 3 is connected to the control circuits 6a, 6b
May be provided on the output side of the switch.
May be provided on the output side of the control circuits 6d and 6e as described above.

Further, the switching to the first control circuit between P _{3 and} P ₅ shown in FIG. 4 (b) is achieved by reducing the number of parts, reducing cost, increasing reliability, and keeping the gain low so that the rotor rotates. It is also possible to omit the vibration due to the effect of preventing vibration from being transmitted to the fixed portion to obtain a vibration isolation effect.

<< Effect of the Invention >> According to the present invention, the control means has the first gain characteristic and the second gain characteristic as described above, and the rotation frequency of the rotor is lower than the first resonance frequency in the first gain characteristic by the gain switching means. , The first gain characteristic is switched to the second gain characteristic from the first gain characteristic, and the second gain characteristic is switched to the first gain characteristic when the rotation frequency moves away from the first resonance frequency to a higher frequency side. While the rotation frequency of the rotor passes through the first resonance frequency, the gain characteristic is switched from the first gain characteristic to the second gain characteristic. With this switching, while the rotation frequency of the rotor passes through the first resonance frequency, the second gain characteristic is switched. Since one resonance frequency does not exist, there is an effect of preventing resonance of the rotor.

In particular, the second gain characteristic switched as described above is changed to the first gain characteristic.
Since the gain characteristic has a second gain characteristic having a smaller characteristic only on the high frequency side of the characteristic, the gain characteristic on the low frequency side is not changed before and after the switching, so that the stability of the magnetic bearing on the low frequency side is increased. There are specific effects such as doing.

[Brief description of the drawings]

FIG. 1 is a diagram corresponding to claims, FIG. 2 is a turbo-molecular pump equipped with a control device for a magnetic bearing of the present application, FIG. 3 is a block diagram showing an embodiment of a control device for a magnetic bearing, and FIG. FIG. 4B is a gain characteristic diagram showing the first gain characteristic and the second gain characteristic of the first control circuit and the second control circuit, and FIG. 4B shows the relationship between the resonance frequency of the magnetic bearing and the runout of the rotor based on the gain characteristic. FIG. 5 is a flowchart executed by a CPU, FIG. 6 is a block diagram showing an embodiment of a magnetic bearing control device, and FIG. 7 is a third control circuit, a fourth control circuit, and a fifth control circuit. Gain characteristic (A)
FIG. 8 is a gain characteristic diagram showing (B) and (C), and FIG. 8 is a first characteristic diagram composed of the sum of the gain characteristic (A) and the gain characteristic (B).
FIG. 9 is a gain characteristic diagram showing a gain characteristic and a second gain characteristic constituted by the sum of the gain characteristic (A) and the gain characteristic (C). FIG. 9 is a block diagram showing a conventional magnetic bearing. FIG. 11 is a gain characteristic diagram of a conventional control circuit, and FIG. 11 is an equivalent circuit of a magnetic bearing. DESCRIPTION OF SYMBOLS 1 ... Magnetic bearing 2 ... Rotor 3 ... Electromagnet 4 ... Position sensor 6 ... Control circuit 7 ... Power amplifier 11 ... Rotation sensor 14 ... Storage memory 15 ... CPU

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-233518 (JP, A) JP-A-1-158215 (JP, A) JP-A-61-206820 (JP, A) JP-A 52-233 93852 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C05D 3/12

Claims (1)

(57) [Claims] 1. A result obtained by detecting a floating position of a rotor which is levitated and rotated by an electromagnet by a position sensor, and calculating by the electromagnet an actual floating position of the rotor detected by the position sensor and a target floating position of the rotor. In the feedback control radial magnetic bearing control device which is controlled by a control circuit based on the following, and floats the rotor to a target flying position, a rotation sensor for detecting and outputting the rotation frequency of the rotor; and Storage means for storing a first resonance frequency of the magnetic bearing when the electromagnet is controlled by the first gain characteristic; and a rotation frequency detected and output by the rotation sensor and a first resonance frequency stored in the storage means. Frequency comparing means for comparing and outputting the rotation frequency to the first resonance frequency from the low frequency side. When the output of the frequency comparison means correspondingly changes, the control circuit causes the first
Is switched from the control of the gain characteristic to the control of the second gain characteristic in which at least the gain on the frequency side higher than the vicinity of the first resonance frequency is smaller than the first gain characteristic, and the rotation frequency is changed from the first resonance frequency to a high frequency. The control circuit switches from the control of the second gain characteristic to the control of the first gain characteristic due to a corresponding change in the output of the frequency comparison means when the control circuit moves away from the control circuit to a predetermined value. A control device for a magnetic bearing.