JP2575862B2 - Magnetic bearing control device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magnetic bearing for a high-speed rotating body such as a turbo-molecular pump, a compressor, a turbine, and a spindle for a machine tool.

[Technical Technique] As a means for floatingly holding a rotating body or a running object, there is a magnetic bearing using an electromagnet.

This magnetic bearing has a smaller loss than conventional fluid lubricated bearings, and allows for dry bearings and clean atmospheres.
Particularly, it is a useful bearing in a vacuum state.

In this magnetic bearing, as a means for setting the floating position of a rotating body or a moving object, the floating position of the floating object is measured, the value of the current flowing through the electromagnet is determined based on the measurement signal, and the magnitude of the magnetic force generated from the electromagnet is determined. There is a means to determine.

FIG. 8 is a block diagram showing a configuration of a control system of the means.

In FIG. 8, a position sensor 1 is a sensor for measuring the position (displacement) of a floating object, and an example thereof is an eddy current displacement meter.

The position feedback gain 2 is for multiplying the magnitude of the signal obtained by the position sensor 1 in proportion to the required magnitude.

The control circuit 3 includes a signal processing circuit for inputting a signal obtained by the position feedback gain 2 to the electromagnet 4 in an appropriate form. Examples of the signal processing circuit include a PID (proportional-integral-differential) circuit, a phase compensation circuit, and a combination circuit thereof.

The electromagnet 4 is formed by winding a coil around an iron core, and generates a magnetic force for levitation in accordance with the current supplied from the control circuit 3.

Considering the simplest position feedback system in which the control circuit 3 is composed of only the proportional element (P element), the transfer function between the input I of the electromagnet 4 and the magnetic force F which is the output is represented by the resistance or inductance of a coil or iron core. This results in the following first-order lag system.

_{F / I = K M / (} 1 + T M · S) ... (1) where, K _M is the gain of the electromagnet 4, T _M is the time constant of the electromagnet 4, S is a Laplace operator.

Therefore, the transfer function from the measured displacement D of the position feedback system to the force F on the floating object is as follows.

F / D = K _F K _P K _M / (1 + T _M S) (2) Here, K _F indicates a proportional gain of the position feedback gain 2, and K _P indicates a proportional gain of the control circuit 3, respectively.

In order to see the frequency characteristic of (force F) / (displacement D) of the position feedback system, a Laplace operator S = i2πf is set,
Substitute in equation (2).

Where f is the frequency (Hz) It is.

(Force F) / (Displacement D) is a complex number and is set as follows.

F / D = K _R (f) + j · K _I (f) (3) In equation (3), the real part of (force F) / (displacement D) means rigidity dependent on frequency f, and the imaginary part Means attenuation dependent on frequency f.

For the first-order lag as in equation (2), the imaginary part is always negative,
It becomes the destabilizing force opposite to the damping for the floating object.

FIG. 9 is a diagram showing the relationship between (force F) / (displacement D), that is, the value of the imaginary part of equation (3) and the frequency f.

A dotted line A shown in FIG. 9 corresponds to the equation (2), and indicates the above-described state.

Natural frequency f _c consisting of levitated object and position feedback system
From the attenuation of the attenuation, in particular floating matter having found the value of at the frequency f = f _c shown in FIG. 9 is large, its natural frequency vibrates divergently, can not be operated.

Therefore, in order to have a damping effect on (force F) / (displacement D) of the position feedback system, a differential element (D element) or a phase compensation element is provided in the control circuit 3 in parallel with the proportional element (P element). .

 Here, a differential element (D element) is taken as an example.

When the differential element (D element) is realized as a circuit in the control circuit 3, the following first-order lag system is added.

Here (differential _{element) = K D · S / (} 1 + T D · S) ... (4), K D is the time constant is a gain, T _D of differential elements.

(Force F) /
(Displacement D) is given by the following equation.

F / D = K _F・ K _D・ K _M・ S / {(1 + T _D・ S) (1 + T _M・ S)} (5) The numerator of equation (5) is the first order of S, and the denominator is S Since it is quadratic, the imaginary part of equation (5) is as shown by the dashed line B in FIG.

That is, it has a damping effect on flying objects in a low frequency region, and has an instability effect in a high frequency region.

In order to maintain the position of the floating object, the control circuit 3 needs to have both a proportional element and a differential element.

The (force F) / (displacement D) of the position feedback system of such a control circuit 3 is given by: F / D = K _F ｛{K _P + K _D SS / (1 + T _D ＳS)}｝ K _M / (1 + T _M S) (6), which is shown by the solid line C shown in FIG. 9, and has almost the same characteristics as the one-dot chain line B described above.

Natural frequency f _c consisting of levitated object and position feedback system
Is placed in a low frequency region having a damping effect, stability can be ensured, and operation can be performed without generating vibration.

When a magnetic bearing having such characteristics is used as the bearing 6 of the rotating body 5 shown in FIG. 10A and the rotating body 5 is levitated, the following phenomenon is exhibited.

The rotating body 5 is shown in FIGS. 10 (b) (c) (d) (e) (f)
Has an infinite number of natural frequencies. Rotating body 5
The damping due to the material itself acts to destabilize the natural frequency below the rotation speed, and acts as a damping action for the natural frequency above the rotation speed.

Therefore, it is necessary to bring a natural frequency equal to or lower than the rotation speed to a frequency region having a damping effect of (force F) / (displacement D) of the position feedback system of the magnetic bearing 6.

However, the natural frequency of the rotating body 5 is as shown in FIG.
As shown in (c), (d), (e), and (f), since there is an infinite number, there is always a natural frequency in a frequency region having a destabilizing action of (force F) / (displacement D).

Therefore, if the destabilizing action of the position feedback system of the magnetic bearing 6 becomes larger than the damping of the natural frequency caused by the rotating body 5 itself, the magnetic bearing 6 becomes unstable, the vibration diverges, and the rotation cannot be performed. .

[Problems to be Solved by the Invention] As described above, in the conventional device, in order to maintain the position of a floating object, the position of the floating object is measured by the position sensor 1, and its signal is fed back. Is generated, but this force becomes an instability that vibrates the levitating object.

Even if the control circuit 3 performs processing such as PID and phase compensation, the low frequency band becomes a stabilizing (attenuating) force, but the middle and high frequency band still has a large destabilizing force.

However, in the case of a floating object having an infinite number of natural frequencies, such as a rotating body, a natural frequency is always present in a frequency band serving as a destabilizing force. Will be.

In particular, the damping power of the third natural frequency, which is usually higher than the maximum rotational speed of the rotating body 5, is small, and the magnetic bearing is easily divergently vibrated due to the destabilizing action of the position feedback system.

As a countermeasure, even if the damping action region is extended by the magnetic bearing to the third natural frequency, a larger destabilizing effect is provided in a frequency region higher than the third natural frequency, and the fourth natural frequency then becomes divergent. Will be caused.

Therefore, the present invention provides a magnetic bearing capable of changing a destabilizing force generated by a magnetic bearing into a stabilizing force in a designated frequency band, preventing divergent vibrations, and stably holding a floating object. It is an object to provide a control device.

[Means for Solving the Problems] (First Means) A magnetic bearing control device according to the present invention feeds back a signal from a position sensor for a floating object to a magnetic bearing to actively use the magnetic bearing. In the magnetic bearing control device, (A) a first magnetic bearing and a second magnetic bearing comprising a position sensor, a position feedback gain, a control circuit, an electromagnet, a band-pass filter, a proportional circuit, and an adder (B) a signal from a position sensor constituting the first magnetic bearing is used as a first signal as it is, and (C) natural vibration between the first magnetic bearing position and the second magnetic bearing position. In the case where the number of vibration mode node points is an odd number, the signal from the position sensor of the second magnetic bearing that is an odd number of vibration mode node points having a natural frequency with respect to the first magnetic bearing position. The A bandpass filter and a proportional circuit having a center frequency near the natural frequency and a second signal is passed through a series, a signal obtained by adding (D) said first and second signals,
A feedback is provided to an electromagnet via a position feedback gain of the magnetic bearing and a control circuit.

(Second Means) A magnetic bearing control device according to the present invention is a magnetic bearing control device in which a signal from a position sensor for a floating object is fed back to the magnetic bearing to actively use the magnetic bearing. Position sensor 1, position feedback gain,
A first magnetic bearing and a second magnetic bearing comprising a control circuit, an electromagnet, a band-pass filter, a proportional circuit, and an adder; and (B) position sensors for the first and second magnetic bearings; A third position sensor and a third band-pass filter provided independently of the band-pass filter; and (C) a characteristic between the first magnetic bearing position and the second magnetic bearing position. When the number of vibration mode node points is an even number, a signal from a third position sensor sandwiching an odd number of natural frequency mode node points is transmitted to the first magnetic bearing position. A band-pass filter having a center frequency near the frequency and a proportional circuit are passed in series to form a second signal, and (D) a signal obtained by adding the first signal and the second signal,
A feedback is provided to an electromagnet via a position feedback gain of the magnetic bearing and a control circuit.

[Operation] By taking the above-described means, the following operation is exhibited.

That is, for the destabilizing force in the high frequency band of the position feedback system of the magnetic bearing, only the natural frequency component that becomes the destabilizing force is extracted by the band-pass filter in a state where the phase is inverted, and this is extracted by the proportional circuit. After being amplified, it is added to the signal of the position sensor of the magnetic bearing component, so the signal fed back is only the natural frequency component that becomes the destabilizing force, and the polarity is inverted (the phase is 180 ° different). It will be.

As a result, all the forces generated by the magnetic bearing are changed to stabilizing forces.

 Table 1 shows a comparison with the prior art.

Embodiment An embodiment of the present invention is shown in FIG. 1 to FIG.

First Embodiment FIGS. 1 to 4 show a first embodiment of the present invention.

FIG. 1 is a block diagram showing a first embodiment of the present invention, that is, a configuration of a control system relating to stabilization of an instability caused by a secondary bending natural frequency.

In FIG. 1, reference numeral 7 denotes a band-pass filter that passes a natural frequency component serving as an instability, 8 denotes a proportional circuit that amplifies a signal, and 9 denotes an addition circuit.

6L and 6R indicate two sets of magnetic bearings (first and second magnetic bearings).

The signal from the first position sensor 1L constituting the first magnetic bearing 6L is separated into two, and one of the signals is supplied as it is as a first signal aL to the (+) input terminal of the addition circuit 9L. The other signal, after the natural frequency component serving as the destabilizing force is extracted by the band-pass filter 7L and amplified by the proportional circuit 8L having a gain of α times,
Is supplied to the (+) input terminal of the adder circuit 9R as a second signal bL for the magnetic bearing 6R.

Similarly, the signal from the second position sensor 1R constituting the second magnetic bearing 6R is also separated into two, one of which is an addition circuit.
9R, and the other is supplied via a band-pass filter 7R and a proportional circuit 8R to an adder circuit 9L of the other first magnetic bearing.

The signal C after the addition is input to the control circuit 3 via the position feedback gain 2.

For simplicity, the operation when the transfer functions of the two magnetic bearings are the same will be described below.

FIG. 2 is a diagram showing typical gain characteristics of the bandpass filter 7 of the first embodiment.

As shown in FIG. 2, the band-pass filter 7 has a center frequency f ₀ near the natural frequency to be stabilized, and has a frequency f
There has pass characteristics (gain 1) when f _0.

FIG. 3 is a diagram showing a relationship between a rotating body, a bearing arrangement, and a vibration mode.

FIG. 3A shows an arrangement relationship between the rotating body 5 and the bearings (6L and 6R), and FIG. 3B shows a bending secondary vibration mode of the rotating body 5.

Position sensors 1L and 1R is an odd number the node point between the sensor since it is arranged to include (Q _L in the illustrated example, three Q _M and Q _R), signals from these positional sensors are mutually phase It is inverted.

FIGS. 4 (a), (b) and (c) are diagrams showing the relationship between (force F) / (displacement D) in each signal path, that is, the value of the imaginary part of the equation (3) and the frequency f.

FIG. 4 (a) shows the relationship between (force F) / (displacement D) and the frequency f in the path of the signal aL of one magnetic bearing 6L, as shown by the solid line C in FIG. A device capable of providing phase compensation so as to exhibit attenuation in a region is used.

Thus, the first, second, and third natural frequencies of the rotating body 5 are placed in a frequency range where damping can be given, and the fourth natural frequency is placed in a frequency range where destabilizing force is given. I will

Assuming that (force F) / (displacement D) of the first magnetic bearing 6L is expressed by Expression (3), in the path of the first signal aL, F / D = K _{R in} the entire band of the frequency f. to become _{(f) + j · K I} (f) ... (7).

FIG. 4 (b) is a diagram showing the relationship between (force F) / (displacement D) and the frequency f with respect to the magnetic bearing 6L in the path of the second magnetic bearing 6R.

Second magnetic bearing 6R, the signal of the natural frequency component f ₄ which is a destabilizing force to the magnetic bearings 6L have phase inversion, f ₄
Bandpass filter 7 with center frequency f ₀ set in the vicinity
F / D = −α · K _R (f) −jα · K _I (f) (8-1) in the vicinity of f = f ₄ , and F / D in other frequency bands. D = 0 (8-2).

Thus, in the path of the second signal bR, the fourth natural frequency of the rotating body 5 is attenuated, and in the other frequency bands, neither damping nor destabilizing force acts.

FIG. 4 (c) is a diagram showing the relationship between (force F) / (displacement D) and the frequency f in the path of the signal cL obtained by adding the first signal aL and the second signal bR.

Finally, since the second signal bR is added to the first signal aL, signal in the path of cL, f = f ₄ only near F / D = (1-α ) · K R (f) + j (1−α) · K _I (f) (9-1), and in other frequency bands, F / D = K _R (f) + j · K _I (f) (9-2) . The polarity of the sign of the value of the expression (9-1) is inverted if the gain α of the proportional circuit 8R is “1” or more.

In the present embodiment, the two position sensors are installed at positions where the amplitude values of the vibration modes of the secondary natural frequency of bending are the same as each other. Can be inverted.

Thus, the attenuation characteristics of the magnetic bearing 6L is placed in the region 4 becomes as shown by the solid line in Figure (c), bending also secondary natural frequency f ₄ which gives attenuation.

For even other magnetic bearings 6R, likewise bending the secondary natural frequency f ₄ is placed in the area to which the attenuation.

Accordingly, the destabilizing force due to the secondary natural frequency of bending is changed to a stabilizing force.

Thus, according to the present embodiment, the first, second, and third
The destabilizing force at the fourth natural frequency can be changed to a damping force (stabilizing force) while using a control circuit that gives damping only to the fourth natural frequency.

Accordingly, the medium-frequency hunting problem of the rotating body 5 is reduced, and the critical second bending speed (corresponding to the fourth natural frequency)
It is possible to drive up to.

It should be noted that there is almost no problem with the fifth or higher natural frequencies, since the frequency range is where the destabilizing force is small.

(Second Embodiment) FIGS. 5 to 7 show a second embodiment of the present invention.

FIG. 5 is a block diagram showing a second embodiment of the present invention, that is, a configuration of a control system for stabilizing the destabilizing force by the primary natural frequency of bending.

In FIG. 5, a third position sensor 1M is provided with two position sensors 1L and 1R of the magnetic bearing independently, and outputs only a signal of a frequency component which becomes an instability in the third band-pass filter 7M. After being taken out and separated into two, the proportional circuit 8L and
The signal is amplified by 8R, and as the second signals bL and bR, 2
The pair of magnetic bearings 6L and 6R are supplied to the (+) input terminals of the adders 9L and 9R.

Gain characteristics of the third bandpass filter 7M is is shown in Figure 2, the center frequency f ₀ of this embodiment is set to ₃ near the primary natural frequency f bend.

Thus, the signal from the first position sensor 1L constituting the first magnetic bearing 6L is supplied to the (+) input terminal of the addition circuit 9L as the first signal aL, and the second signal from the third position sensor 1M is supplied to the (+) input terminal. Is added to the first signal aL.

The signal cL after the addition is input to the control circuit 3L via the position feedback gain 2L.

 The same operation is performed in the second magnetic bearing 6R.

For simplicity, the operation when the transfer functions of the two magnetic bearings are the same will be described below.

FIG. 6 is a diagram showing a relationship among a rotating body, a bearing, and a vibration mode.

FIG. 6A shows an arrangement relationship between the rotating body 5 and the bearings 6L and 6R, and FIG. 6B shows a bending primary vibration mode of the rotating body 5.

The first position sensor 1L and the third position sensor 1M have an odd number of node points between the sensors (one R _{L in the} illustrated example).
The signals from these position sensors are in phase inversion with respect to each other.

Transfer function (force F) / (displacement D) of the first magnetic bearing 6L are in the bending first-order natural frequency f ₃ near (9-1)
Expressions and other bands are expressed by Expression (9-2).

(9-1) is that the gain α of the proportional circuit 8 is “1”.
If this is the case, the sign polarity is inverted.

By appropriately adjusting the gain α, the first magnetic bearing
Damping characteristics of 6L is as shown by the solid line in Figure 7, the bending first-order natural frequency f ₃ is also placed in the area to which the attenuation.

For the second magnetic bearing 6R, the primary natural frequency f ₃ of the bend as well be placed in an area to provide damping.

Therefore, the destabilizing force due to the first-order natural frequency of bending in the frequency band is changed to a stabilizing force.

As the two control circuits 3L and 3R, those which can provide phase compensation so as to exhibit attenuation in a low frequency region as shown by the solid line C in FIG. 9 are used.

In addition, it is assumed that the secondary natural frequency of bending is stable by enhancing the internal damping of the rotating body 5.

Thus, the first and second natural frequencies of the rotating body 5 are placed in the frequency region where damping is provided, and the third natural frequency is also attenuated by the above action.

According to the present embodiment, while using the control circuit that gives damping only to the first and second natural frequencies, the region acting as the destabilizing force at the third natural frequency is set to the damping force. (Stabilizing power).

Therefore, the medium-frequency hunting problem of the rotating body 5 is reduced, and the critical bending speed is primary (corresponding to the third natural frequency).
Driving becomes possible.

It should be noted that the fourth or higher natural frequency is not
The internal damping stabilizes the destabilizing force, and there is almost no problem.

The present invention is not limited to the above embodiments.

For example, in the above-described embodiment, the case where the circuit including the band-pass filter 7, the proportional circuit 8, and the adder 9 is provided between the position sensor 1 and the position feedback gain 2 is exemplified.
You may make it provide in another part in a magnetic bearing control system.

In order to reduce the destabilizing force, a notch filter having a center frequency near the frequency of the destabilizing force is generally added in the middle of the conventional path shown in FIG. Alternatively, a combination of the conventional method and the present invention may be used.

In this case, the embodiment of the present invention adds a notch filter having a center frequency near the natural frequency of the destabilizing force in the middle of the path of the signal a in FIG. 1 or FIG.

Further, the destabilizing force of the two natural frequencies may be stabilized by combining the first embodiment and the second embodiment.

It is obvious that the first embodiment can stabilize not only the bending second order but also the fourth order, sixth order,. If a plurality of center frequencies are selected, all of them can be stabilized.

Similarly, in the second embodiment, not only the primary bending but also the bending 3
The destabilizing force of the odd natural frequencies of the fifth, fifth, etc. can be stabilized.

The use of a plurality of these band-pass filters is effective when there is no internal damping of the rotating body 5 with respect to the natural frequency of the third or higher bending and the destabilizing force becomes a problem.

The shape of the rotating body 5 is not limited to those shown in FIGS. 3 and 10, and various modifications can be made without departing from the scope of the present invention.

 Table 1 shows a comparison with the prior art example.

[Effects of the Invention] Since the present invention is configured as described above, the following effects are obtained.

(1) According to the present invention, a signal from a first position sensor constituting a magnetic bearing is used as a first signal, and an odd number of node points of a vibration mode having a natural frequency are interposed with respect to the magnetic bearing position. 2, a signal from the position sensor of the magnetic bearing or a newly provided third position sensor is passed in series through a band-pass filter having a center frequency near its natural frequency and a comparison circuit to form a second signal, Since the signal obtained by adding the first signal and the second signal is fed back to the magnetic bearing, the destabilizing force can be changed to the stabilizing (damping) force for the designated frequency component, and the divergence can be obtained. It is possible to prevent the occurrence of typical vibration.

(2) Therefore, it is possible to provide a magnetic bearing control device capable of stably lifting and holding a floating object.

(3) Table 1 shows a comparison between the device of the present invention and the measures of the prior art.

[Brief description of the drawings]

1 to 4 are diagrams showing a first embodiment of the present invention, FIG. 1 is a block diagram showing a configuration of a control system, FIG. 2 is a diagram showing gain-frequency characteristics of a band-pass filter, FIG. 3 is a schematic explanatory diagram showing the relationship between the rotating body and the arrangement of the magnetic bearings and the secondary bending vibration mode, and FIG. 4 is a diagram showing the attenuation characteristics in the path of each signal. 5 to 7 show a second embodiment of the present invention. FIG. 5 is a block diagram showing the configuration of a control system. FIG. 6 is a diagram showing the arrangement of a rotating body and magnetic bearings and primary bending vibration. FIG. 7 is a schematic explanatory diagram showing the relationship between modes, and FIG. 7 is a diagram showing damping characteristics of a magnetic bearing. 8 to 10 are diagrams showing a conventional example, FIG. 8 is a block diagram showing a configuration of a control system, FIG. 9 is a diagram showing damping characteristics of a magnetic bearing, and FIG. It is a figure which shows a natural frequency. (Explanation of symbols) 1 ... Position sensor 1L ... First position sensor (6L side) 1R ... Second position sensor (6R side) 1M ... Third position sensor 2 ... Position feedback gain 2L ... ... First position feedback gain (6L side) 2R ... Second position feedback gain (6R side) 3 ... Control circuit 3L ... First control circuit (6L side) 3R ... Second control circuit ( 4R electromagnet 4L first electromagnet (6L side) 4R second electromagnet (6R side) 5 rotating body (floating object) 6 magnetic bearing 6L first magnetic Bearing 6R: second magnetic bearing 7: band-pass filter 7L: first band-pass filter (6L side) 7R: second band-pass filter (6R side) 7M: third band-pass filter 8 ... Proportional circuit 8L ... First proportional circuit (6L side) 8R ... Second proportional circuit (6R side) 9 ... Addition circuit 9L ... First addition circuit (6 L side) 9R… 2nd addition circuit (6R side) P …… node point of vibration mode Q …… node point of vibration mode

Claims (2)

(57) [Claims] 1. A magnetic bearing control device in which a signal from a position sensor for a floating object is fed back to a magnetic bearing so that the magnetic bearing is actively used. (A) A position sensor (1) and a position feedback gain ( 2), control circuit (3), electromagnet (4), band-pass filter (7), proportional circuit (8), and adder (9)
A first magnetic bearing (6L) and a second magnetic bearing (6R), and (B) a first signal as it is from a position sensor constituting the first magnetic bearing (6L). (C) when the number of node points of the vibration mode of the natural frequency between the first magnetic bearing position and the second magnetic bearing position is an odd number, the natural vibration with respect to the first magnetic bearing position The second magnetic bearing (6
R) the signal from the position sensor is passed in series through a band-pass filter having a center frequency near its natural frequency and a proportional circuit to form a second signal, and (D) the first signal and the second signal Add the signal,
A magnetic bearing control device wherein feedback is provided to an electromagnet via a position feedback gain of the magnetic bearing and a control circuit. 2. A magnetic bearing control device in which a signal from a position sensor for a floating object is fed back to a magnetic bearing so that the magnetic bearing is actively used. (A) A position sensor (1) and a position feedback gain ( 2), control circuit (3), electromagnet (4), band-pass filter (7), proportional circuit (8), and adder (9)
A first magnetic bearing (6L) and a second magnetic bearing (6R), and (B) a position sensor (1L, 1R) and a band pass of the first and second magnetic bearings (6L, 6R). A third position sensor (1M) and a third band-pass filter (7M) provided independently of the filters (7L, 7R); and (C) the first magnetic bearing position and the third In the case where the number of natural frequency mode node points between the two magnetic bearing positions is an even number, a third natural frequency mode node point is interposed with respect to the first magnetic bearing position. Position sensor (1M)
Are serially passed through a band-pass filter (7M) having a center frequency near its natural frequency and a proportional circuit (8L) to form a second signal, and (D) the first signal and the second signal The signal obtained by adding the signals of
A magnetic bearing control device wherein feedback is provided to an electromagnet via a position feedback gain of the magnetic bearing and a control circuit.