JPS62258220A - Magnetic beraing control system - Google Patents

Abstract

PURPOSE:To widen the frequency domain, in which the damping force of a magnetic bearing is generated, and reduce the instability-oriented force which occurs in the high frequency domain, by combining every feed-back signals from both a position-sensor and a speed sensor and then feeding them back. CONSTITUTION:An adding machine 13 adds up the output signal from a control circuit 3 and the output(signal) from a speed feed-back gain 12 and inputs the result into an electromagnet 4. A comparison between the force F/displacement D(of a magnet bearing) obtained through the speed feed-back and the force F/displacement D obtained through the position feed-back system composed of derivative elements only yields that there is a time-lag of degree 1 between the two. Accordingly, in the force F/displacement D obtained through the speed feed-back, the imaginary part K1 (f) becomes positive in all the frequency domain, contributing to the stabilization(damping) of the bearing. In addition, by choosing the speed feed-back gain large enough, the generation of the damping force of the magnetic bearing can be maintained up to the remarkably high frequency domain.

Description

[Detailed description of the invention] [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, and is particularly micrometer bearing in a vacuum state.

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, the current value to be passed through the electromagnet is determined based on the measurement signal, and the magnitude of the magnetic force generated from the electromagnet is determined. There are means to determine this.

FIG. 5 is a block diagram showing the means.

In Fig. 5, the position sensor 1 indicates the position (displacement) of the floating object.
It is a sensor for measuring
This is an example. Position feedback gain 2 is position sensor 1
This is for proportionally multiplying the magnitude of the signal obtained by the 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.
These include integral (integral-integral) circuits, phase compensation circuits, and combinations thereof. The electromagnet 4 has a coil wound around an iron core, and generates a floating square magnetic force in response to a current manually applied 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 input ■ 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+T-S)...(2) Here,
KF is position feedback gain 2° KP is control circuit 3
shows the proportional gain of Position feedback system (force F)
To see the frequency characteristics of /(displacement D), set the Laplace operator 5-j2πf and substitute it into (2). Here, f is the frequency (Hz) and j=f:■. (Force F)/(Displacement D) is a complex number and is written as follows.

F/D=KR・(f)+j−Kx
- (f) - (3) In equation (3), the real part of (force F)/(displacement D) means stiffness that depends on frequency f, and the imaginary part means damping that depends on frequency f. 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. 6 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. 6 corresponds to equation (2),
The above state is shown. If the value of the frequency t-rc shown in Fig. 6 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 of some 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, K
D is the gain of the differential element, and TD is the time constant. (Force F)/(Displacement D) of a position feedback system including only differential elements is expressed by the following equation.

F/D-KF -Ko-KM◆S/+(1+TD-S)(1+TM-3)1...(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) becomes like the dashed-dotted line B shown in FIG. That is, it has a damping effect on floating objects in a low frequency range, and a destabilizing effect in a high frequency range. 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-KF・lKP+KD-8/(1+TD-8))・KM/
(1+TM-S) (6), which is as shown by the solid line C shown in FIG. 6, and has the same characteristics as described above. By placing the natural frequency fc consisting of the floating object and the position feedback system in a low frequency range that has a damping effect, 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. 7(a) and the rotating body 5 is levitated, the following phenomenon occurs. As shown in FIGS. 7(b), (c), (d), (e), and (f), the rotating body 5 has a fixed vibration frequency on the infinite side. The damping of the material of the rotating body 5 itself works to destabilize the vibration frequency of the solid body below the rotation speed, and acts as a damping effect to the vibration frequency of the solid body above the rotation 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. 7 (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 5 becomes unstable, the vibration increases divergently, and rotation becomes impossible.

[Problem that the invention seeks to solve]

As mentioned above, in conventional systems, in order to maintain the position of a floating object, the position of the floating object is measured, the signal is fed back, and force is generated 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 that has a natural frequency on the infinite side, the natural frequency is always in a region that causes a destabilizing force, and the magnetic bearing generates divergent vibrations.

Therefore, an object of the present invention is to provide a control method for a magnetic bearing that can expand the frequency range in which the magnetic bearing generates a stabilizing (damping) force and reduce the destabilizing force that occurs in the high-frequency range. .

[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 using an electromagnet, a feedback signal from a position sensor is passed through a control circuit that performs PID processing, etc., and a signal based on the output signal of the control circuit and the feedback signal from the speed sensor (feedback signal or its The signal is further added to the signal that has passed through a specific band filter), and the added signal is input to the electromagnet.

[Effect]

By adding such means, the damping force generated by the electromagnet is expanded to a high frequency range, and it becomes possible to stably levitate a floating object.

〔Example〕

FIG. 1 is a block diagram showing a first embodiment of the present invention, and FIG. 2 shows the attenuation characteristics of the electromagnet.

In FIGS. 1 and 2, the same parts as in FIGS. 5 and 6 are designated by the same reference numerals. 11 in Figure 1
A speed sensor 1 detects speed by measuring changes in magnetic flux density using a coil. 12 is a speed feedback gain, and 13 is an addition circuit. The speed feedback gain 12 is for proportionally multiplying the signal obtained by the speed sensor 11 to a required magnitude.

The adder circuit 13 adds and superimposes the output signal of the control circuit 3 and the output of the speed feedback gain 12, and the electromagnet 4 is manually operated. The transfer function of the force F from the speed V of the floating object detected by the speed sensor 11 to the floating object is F/V-Kv-KM/(1+TM- 8)...(7
).

Here, Kv indicates velocity feedback gain. The velocity ■ has the relationship V-S-D with respect to the displacement. Therefore, due to velocity feedback, (force F)/(displacement D) becomes F/D=Kv −KM −S / (1+TM−S) (8).

Comparing (8) and (5), the order of delay is one order smaller. Therefore, in (8), the imaginary part Kr (f) of (force F)/(displacement D) is positive in the entire frequency range and acts on the stable side (attenuation). Its characteristics are shown by the two-dot chain line in FIG.

In a conventional position feedback system, the imaginary part when the control circuit 3 is composed of only proportional elements! (f) is the dotted line A in Fig. 2 (same as Fig. 6), and in this case (force F
)/(displacement D)-The imaginary part K I(f) is the sum of the two-dot chain line and the dotted line A in FIG. 2, and corresponds to the solid line E. If the velocity feedback gain K y is chosen to be sufficiently large,
Magnetic bearings can generate damping force up to a fairly high frequency range.

FIG. 3 is a block diagram showing a second embodiment of the present invention. In FIG. 3, the same parts as in FIG. 1 are given the same reference numerals. The second embodiment has a filter 14 inserted after the velocity feedback gain 12 of the first embodiment.

The filter 14 allows only a signal of a certain bandwidth to pass through the output of the velocity feedback gain 12.

The 4th fM (a) (b) is an example of the characteristics of the filter 14, where (a) is a band-pass filter consisting of one band, and (b) is a high-pass filter with each gain and frequency. Show relationships.

In this embodiment, velocity feedback is performed with a filter 14 having a pass band including a natural frequency in which the unstable force due to the position feedback system is greater than the damping of the floating object. As a result, the frequency of the solid in the passband is damped or stabilized, and no vibration occurs. Furthermore, the pass band is narrowed by the filter 14, and power consumption can be reduced.

Note that the present invention is not limited to the embodiments described above, and it goes without saying that various modifications can be made without departing from the gist of the present invention.

〔Effect of the invention〕

According to the present invention, since the feed bank signal from the position sensor and the feedback signal from the speed sensor are fed back in combination, the frequency range in which the magnetic bearing generates a stabilizing (damping) force is expanded, and It is possible to provide a control method for a magnetic bearing that can reduce destabilizing forces generated in a high frequency region.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the configuration of the first embodiment of the present invention, Fig. 2 is a diagram showing the damping characteristics of the magnetic bearing according to the control system of the same embodiment, and Fig. 3 is the second embodiment of the invention. 4(a) and 4(b) are diagrams showing characteristic examples of the filter in FIG. 3, FIG. 5 is a block diagram of the conventional control system, and FIG. 6 is a block diagram showing the configuration of the filter shown in FIG. FIG. 7 is a diagram showing the damping characteristics of a conventional magnetic bearing, and FIG. 7 is a diagram showing the rotor and natural frequency. DESCRIPTION OF SYMBOLS 1... Position sensor, 2... Position feedback gain, 3... Control circuit, 4... Electromagnet, 5... Rotating body, 6... Bearing, 11... Speed sensor, 12...・・・
Speed feedback gain, 13... Adder, 14.
...It is a filter. Applicant Sub-Agent Patent Attorney Takehiko Suzutsuta Figure 3 If Figure 4 Figure 5 Figure 6; = Figure 7

Claims (1)

[Claims] In a magnetic bearing using an electromagnet, the feedback signal from the position sensor is passed through a control circuit that performs PID processing, etc., and the output signal of the control circuit is added to a signal based on the feedback signal from the speed sensor. A magnetic bearing control method characterized in that the added signal is input to an electromagnet.