JPS62258219A - Magnetic bearing control system - Google Patents

Abstract

PURPOSE:To stabilize a floating object, by making the signals, which are obtaind by measuring the position of the floating object from reciprocal directions by means of the first and second position sensors, pass through the filters, whose passing and interrupting-characteristics are diametrically opposite to each other, respectively, and adding both before feeding back the result. CONSTITUTION:After the signal from the first position sensor 1 passes through the first filter 8 and after the signal from the second position sensor 7 passes through the second filter 9, both signals are added by an adding machine 10 and are input into a control circuit 3 via a position feedback gain 2. Accordingly, the ratio between the signal for the force F of a magnetic bearing and that for the displacement D, or F/D, obtaind only through the route of the sensor 1 is diametrically opposite to that through the route of the sensor 7. As a result, the damping characteristics of the magnet bearing are improved as shown in the figure, i, e., the dotted line E in the frequency domain between fc1 and fc2 is replaced by the solid line D, or the stabilizing force. Therefore, the natural frequency corresponding to the above domain is stabilized, thereby preventing the divergencetrending vibration from occurring. As a result, the control over the magnetic bearing, which is used to keep a floating object afloat in a stable manner, can be ensured.

Description

[Detailed description of the invention] C Industrial application field] The present invention is a turbo molecular pump or a compressor.

The present invention relates to a control system for magnetic bearings applied to high-speed rotating bodies such as turbines and spindles for machine tools, as well as magnetic bearings for floating moving objects such as tenters.

[Conventional technology]

There are magnetic bearings that use electromagnets as a means of keeping rotating bodies and moving objects floating. This magnetic bearing has less loss than conventional fluid-lubricated bearings, allows for a dryer bearing, and a cleaner atmosphere, making it particularly useful in vacuum conditions.

In this magnetic bearing, as a means of setting the floating position of a rotating body or a running object, the position of the floating object is measured, and the current value to be passed through the electromagnet is determined based on the measurement signal, and the large magnetic force generated by the electromagnet is determined. There is a way to determine the

FIG. 6 is a block diagram showing the means.

In Fig. 6, the position sensor 1 indicates the position (displacement) of the floating object.
It is a sensor for measuring
This is an example. The position feedback gain 2 is for proportionally multiplying the magnitude of the signal obtained by the position sensor 1 to a required magnitude.

The control circuit 3 is a processing circuit for inputting the signal obtained by the position feedback gain 2 to the electromagnet 4 in an appropriate form, and examples thereof include a PID (proportional-integral-derivative) circuit, a phase compensation circuit, and a combination thereof. and so on. The electromagnet 4 has a coil wound around an iron core, and generates magnetic force for levitation in response to a current input from the control circuit 3.

Consider the simplest position feedback system in which the control circuit 3 consists of only proportional elements (P elements).

The transfer function between the human force I of the electromagnet 4 and the output magnetic force F is:
Depending on the resistance and inductance of the coil, iron core, etc.
It becomes the next lag system.

F/I-KM/(1+TM-S)...(1)
Here, KM is the gain of the electromagnet 4, TM is the time constant of the electromagnet 4, and S is the Laplace operator. Therefore, the transfer function of the force F from the displacement measured by the position feedback system to the floating object is as follows.

F/D-KF-KP-KM/(1+TM-8)...(2) Here,
KF is position feedback gain 2° KP is control circuit 3
shows the proportional gain of , respectively.

To see the frequency characteristics of (force F) and /(displacement D) of the position feedback system, set the Laplace operator 5-j2πf and substitute it into (2). Here f is the frequency (Hz)
and j=J-:]-. (Force F)/(Displacement D) is a complex number and is written as follows.

F/D −K R・(f)+j−Ki・(f
)...(3) In equation (3), the real part of (force F)/(displacement D) means stiffness that depends on the frequency f, and the imaginary part means damping that depends on the frequency If. The imaginary part of the first-order lag as shown in equation (2) is always negative, and it becomes a destabilizing force on the floating object that is opposite to damping.

FIG. 7 is a diagram showing the relationship between (force F)/(displacement D), that is, the value of the imaginary part of equation (3), and frequency f.

Dotted line A shown in FIG. 7 corresponds to equation (2),
The above state is shown. If the value of the frequency f-fc shown in Figure 7 is greater than the damping of the natural frequency fC of the floating object and the position feedback system, especially the damping of the floating object, the natural frequency will oscillate divergently. , and become unable to drive.

Therefore, the position feedback system (force F)/(displacement D)
In order to provide a damping effect to the control circuit 3, a proportional element (P
A differential element (D element) or a phase compensation element is provided in parallel with the D element. Here, a differential element will be taken as a representative example. When the differential element (D element) is realized as a circuit in the control circuit 3, the following first-order lag system is obtained.

(Differential element) -KD -S/1+TD -S... (4
) Here, KD is the gain of the differential element, and Tp is the time constant. (Force F)/( of the position feedback system with only differential elements
The displacement D) is expressed by the following formula.

F / D = K F・KD−KM−S/((1+T
D-8)(1+TM-8))...(5) Since the numerator of equation (5) is the first order of S and the denominator is the second order of S, the imaginary part of equation (5)1 is shown in Figure 7. It will look like the dashed line B shown in . That is, in the low frequency range, it has a damping effect on the object, and in the high frequency range, it has a destabilizing effect. In order to maintain the position of the floating object, the control circuit 3 must include a proportional element and a differential element. The (force F)/(displacement D) of the position feedback system of the control circuit 3 is F/D zero K.

・lKp +Ko-S/ (1+TD-S)1・KM
/(1+TM-8) . . . (6), as shown by the solid line C shown in FIG. 7, and has the same characteristics as described above.

Natural frequency fc consisting of floating object and position feedback system
By placing the damping effect in a low frequency range, stability can be ensured and operation can be performed without generating vibrations.

When a magnetic bearing having such characteristics is used as the bearing 6 of the rotating body 5 shown in FIG. 8(a) and the rotating body 5 is levitated, the following phenomenon occurs. The rotating body 5 has a fixed frequency on the infinite side as shown in FIGS. 8(b), (c), (d), (e), and (f). The damping of the material of the rotating body 5 itself acts as a destabilizing effect for natural frequencies below the rotational speed, and acts as a damping effect for natural frequencies above the rotational speed.

Therefore, the (force F
)/(displacement D) It is necessary to bring the natural frequency below the rotational speed to a frequency range that has a damping effect. However, the natural frequency of the rotating body 5 is as shown in Fig. 8 (b), (c), (d), and (e).
(f) As shown in ~, there is an infinite number of forces, so (force F)/
There is a natural frequency in the frequency region that has the destabilizing effect of (displacement D). Therefore, if the destabilizing effect of the position feedback system of the magnetic bearing is greater than the damping of the natural frequency of the rotating body 5 itself, the rotating body becomes unstable, and the vibration increases in a divergent manner, making it impossible to rotate the body.

[Problem that the invention seeks to solve]

As mentioned above, in order to maintain the position of a floating object, conventional devices measure the position of the floating object, feed back the signal, and generate force from an electromagnet.
This force becomes a destabilizing force that causes the floating object to vibrate. And PID to control circuit 3.

Even if processing such as phase compensation is performed, it becomes a stabilizing (damping) force in the low frequency range, but it still has a large destabilizing force in the middle and high frequency ranges. Therefore, in a floating object such as a rotating body whose natural frequency is angular on the infinite side, there is always a natural frequency in the region that causes destabilizing force, and the magnetic bearing will generate divergent vibrations. .

Therefore, the present invention changes the destabilizing force generated by the magnetic bearing in a specified frequency range into a stabilizing force (damping force), prevents the generation of divergent vibrations, and makes it possible to stably levitate objects. The purpose is to provide a control method for magnetic bearings.

[Means for solving problems]

In order to solve the above-mentioned problems and achieve the object, the present invention takes the following measures. In other words, in a magnetic bearing control system in which signals from a position sensor relative to a floating object are fed back to perform phase compensation and other control and are actively used, a magnetic bearing that is placed so as to measure the positive position of the floating object The signal from the first position sensor is passed through a first filter whose cutoff frequency band is a predetermined frequency band to be stabilized, and the signal from the second position sensor that measures the position on the opposite side of the floating object is transmitted. , passing through a second filter whose pass frequency band is the same as the predetermined frequency band;
1st. The signals passed through the second filter are added and the added signal is fed back to the electromagnet.

[Operation] By taking such measures, the frequency-loss band portion that causes destabilization in the signal from the first position sensor is blocked by the first filter, and the phase is reversed by 180°. The frequency band portion of the signal from the second position sensor that serves as the stabilizing force passes through the second filter, and the sum of both signals is fed back, so the force generated by the magnetic bearing becomes the stabilizing force. Be changed.

〔Example〕

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. In FIG. 1, the same parts as in FIG. 5 are given the same reference numerals. In the first cause, 7 is 1
It is the same position sensor as , 8.9 is a filter, and 10 is an adder. The first and second position sensors 1 and 7 are
As shown in the figure, they are attached to the rotating body 5 at forward and reverse positions that differ by 180 degrees. In addition, although the rotating body 5 is shown here as an example of a floating object, it is not limited thereto.

1st. The signals generated from the second position sensors 1 and 7 have completely opposite magnitudes with respect to the movement of the rotating body 5, as shown in FIGS. becomes. For example, the signal of the first position sensor 1 is +5
, the signal from the second position sensor 7 shows a value of -5.

Figures 4(a) and 4(b) are 1. FIG. 7 is a diagram showing each gain characteristic of the second filter 8°9. As shown in (a) and (b) of the figure, the first filter 8 has a predetermined frequency band to be stabilized, that is, a frequency f. 1 to frequency f. The second filter 9 has a cutoff characteristic (gain is zero) in the region 2, and as shown in FIG.
It has a pass characteristic (gain is 1) in the region of 2.

After the signal of the first position sensor 1 passes through a first filter 8 and the signal of the second position sensor 7 passes through a second filter 9, these two signals are added in an adder 10. . This addition signal then passes through position feedback gain 2 and is manually input to the control circuit 31. Therefore, (force F)/(displacement D) of the magnetic bearing is expressed by equation (3), and the first
In the path of only the position sensor 1, in the region l from f to 'C2, F/D-0... (7-1) In other regions, F/D = K R (f) +j-Kl ・(f) ...(T-2). Also, in the path of only the position sensor 7, the signal is completely opposite to that of the position sensor 1, so in the region where f is from 'CI to fC2, F/D--KR (f) -j -Kz (f)... (8-1
) f in other areas becomes F/D-0...CF3-2). And in the end, both are added together, so
In the region where f ranges from f to f, F/D--KRa
(f) -j-KI・(f)...(9-1) When f is in other areas, F/D=KR・(f) 2). Therefore, the damping characteristic of the magnetic bearing becomes as shown by the solid line in FIG. 5, and the dotted line E in the frequency range fc1 to fC2 is changed to the stabilizing force. Therefore, the natural frequency in that frequency range is stabilized, and the occurrence of divergent vibrations is prevented.

Note that the present invention is not limited to the above embodiments.

For example, in the above embodiment, an example was shown in which one frequency range from fcl to 'C2 is stabilized, but the same stabilization can be performed in multiple frequency ranges or in a range above fc1 depending on the characteristics of the floating object and magnetic bearing. is possible.

It goes without saying that various other modifications can be made without departing from the gist of the present invention.

〔Effect of the invention〕

According to the present invention, first. A second position sensor measures the position of a floating object from two directions, forward and reverse, and the measured signals are passed through filters with opposite pass/block characteristics to the signals from each sensor, and then summed. Since the destabilizing force generated by the magnetic bearing is converted into a stabilizing force, the divergent vibration of the floating object is prevented, and the magnetic bearing can be controlled to stably levitate the floating object. We can provide methods.

[Brief explanation of drawings]

1 to 5 are diagrams showing one embodiment of the present invention, in which FIG. 1 is a block diagram showing the configuration of a control system, and FIG.
Figure 3 (a) shows the installation status of the second position sensor.
(b) is the first. FIGS. 4(a) and 4(b) are diagrams showing the output signal waveforms of the second position sensor. FIG. 5 is a diagram showing the gain-frequency characteristics of the second filter, and FIG. 5 is a diagram showing the attenuation characteristics of the magnetic bearing. Figure 6 is a block diagram showing the configuration of a conventional control system, Figure 7 is a diagram showing the damping characteristics of a magnetic bearing according to a conventional control system, and Figures 8 (a) to (f) are rotating bodies and natural vibrations. FIG. 1.7... 1st. Second position sensor, 2... Position feedback gain, 3... Control circuit, 4... Electromagnet, 5... Rotating body, 6... Bearing, 8.9... First
．． Second filter, 10...adder. Applicant Sub-Agent Patent Attorney Takehiko Suzue Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] In a magnetic bearing control system that feeds back signals from a position sensor with respect to a floating object and performs control such as phase compensation, it is actively used. The signal from the position sensor is passed through a first filter whose cutoff frequency band is a predetermined frequency band to be stabilized, and the signal from the second position sensor that measures the position on the opposite side of the floating object is passed through the filter. It is characterized by passing through a second filter whose pass frequency band is the same as the predetermined frequency band, adding the passing signals of the first and second filters, and feeding the added signal back to the electromagnet. A control method for magnetic bearings.