JPS62258222A - Magnet bearing control system - Google Patents

Abstract

PURPOSE:To reduce the instability-oriented force occurring in the medium & high frequency domains so as to ensure the stable floating state of a floating object, by adding the signal from the second position sensor to that from the first position sensor, after the signal from the second position sensor has passed through the high-pass filter or the bandpass filter, and then feeding back the result. CONSTITUTION:After it passes through a fitler 8, the signal from the second position sensor 7 is added by an adding machine 9 to the signal from the first position sensor 1, whose phase is deviated from that of the sensor 7 by 180 deg.. The signal thus added passes through the position feed-back gain 2 and is input into a control circuit 3. Accordingly, a relation, the force F of a magnetic bearing/displacement D of the bearing, obtained only through the route of the first position sensor 1 remains as before. On the contrary, the signal obtained only through the route of the second position sensor 7 is diametrically opposite to that obtained through the first sensor 1. However, all things considered, since both are added together, we get F/D=0 for the frequency f exceeding the cut-off frequency fc. Accordingly, the instability-oriented force is reduced, thereby decreasing the possibility of occurrence of the convergence- tending vibration. Thus, a floating object can be kept afloat in a stable manner for the medium & high frequency domains.

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 dry bearing and a cleaner atmosphere, and is particularly durable 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, 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. 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. Electromagnet 4
A coil is wound around an iron core, and it generates magnetic force for levitation according to the 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 7ti magnet 4 and the output magnetic force F becomes the following first-order lag system due to the resistance and inductance of the coil, iron core, etc.

F/I +4/(1+TM-5)...(1) Here, KM is the gain of electromagnet 4, TM is the time constant of electromagnet 4,
S is a 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=Kp-Kp.KM/(1+TM-8) (2) where KF is position feedback gain 2°Kp indicates proportional gain of control circuit 3. In order to see the frequency characteristics of (force F)/(displacement D) of the position feedback system, a Laplace operator 5-j2πf is set and substituted into (2). Here f
is j-J2:co at one frequency (Hz). (Force F)/(Displacement D) is a prime number and is written as follows.

F / D = K R・(f) 1j−Kt・(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. 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-8 (4) Here, KD is the gain of the differential element, and TD 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-KF -Ko-KuΦS /((1+TD-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) is as shown by the dashed-dotted line B 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 ・fKp +KD-S/ (1+TD-3)]・KM
/(1+TM-8) ...(6), and the seventh
It becomes like the solid line C shown in the figure, and has the same characteristics as described above. Natural frequency f consisting of floating object and position feedback system
If C is placed 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. 8(a) and the rotating body 5 is levitated, the following phenomenon occurs. The rotating body 5 has a natural 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 works to destabilize the fixed nail vibration frequency below the rotation speed, and acts as a damping effect on the natural vibration frequency above the rotation speed.

Therefore, the (force F
)/(displacement D) It is necessary to bring the natural frequency below the rotational speed to the frequency range that has the damping effect. However, the natural frequency of the rotating body 5 is as shown in Fig. 8(b)(c)<d)(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 becomes 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]

” - In the conventional magnetic bearing control system, in order to maintain the position of the floating object, the position of the floating object is measured, the signal is fed back, and force is generated from the electromagnet. It becomes a destabilizing force that causes things to vibrate. Even if the control circuit 3 performs processing such as PID and position t0 compensation, it becomes a stabilizing (damping) force in the low frequency range, but 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, there is always a fixed frequency in the region that causes destabilizing force, and the magnetic bearing causes divergent vibrations. .

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a control method for a magnetic bearing that can reduce the destabilizing force generated by the magnetic bearing in the medium and high frequency range and can prevent the generation of divergent vibrations.

[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 In addition to the first position sensor, a second position sensor is provided to determine the position on the opposite side of the floating object M1, and the signal from this second position sensor is passed through a high-pass filter or a band-pass filter. , is added to the signal from the first position sensor, and the added signal is fed back to the electromagnet of the magnetic bearing.

[Effect]

By taking such measures, in the middle and high frequency range where destabilizing force is generated, the signals from the two position sensors attached in opposite directions are added, so that the feedback signal becomes zero. As a result, the destabilizing force virtually disappears because the magnetic bearing does not generate any force.

[Embodiment] FIG. 1 is a block diagram showing a control method as an embodiment of the present invention.

In the above figure, the same parts as in FIG. 6 are given the same reference numerals. In FIG. 1, 7 is a sensor of the same order of magnitude as 1, 8 is a filter, and 9 is an adder. ”-2 1st. The second position sensors 1 and 7 are respectively attached to forward and reverse positions of the rotating body 5 that are 180 degrees apart as shown in FIG. 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 magnitude relationships with respect to the movement of the rotating body 5, as shown in FIGS. Become. If the signal of the first position sensor l indicates, for example, +5, the signal of the second position sensor 7 indicates a value of -5.

FIG. 4 is a diagram showing the gain-frequency characteristics of the filter 8. As shown in FIG. 4, this filter 8 is a high-pass filter that has a cutoff frequency fc and allows only components of frequencies higher than fc to pass. After the signal from the second position sensor 7 passes through a filter 8, it is added to the signal from the position sensor 1 in an adder 9. This added signal is input to the control circuit 3 after passing through the position feedback gain 2.

Therefore, (force F)/(displacement D) of the magnetic bearing is (3)
Using the formula, the path of only the first position sensor 1 remains the same as before, and F / D - K R · (f) + j - KI skewer at all frequencies.
(f)... (3) ゛. In the path of only the second position sensor 7, the signal is completely opposite to that of the first position sensor 1, so if [ is less than fC, F/D-0... (7-1) If f is more than fc, F/ D--KR・(f) −j-Kt・(f)...(7-2). As a whole, both are added, so when f is less than fC, F/D-KR・(f) +j-I(■・(f)...(8-1) f becomes f
c or more, F/D-0...(8-2).

FIG. 5 is a diagram showing the damping characteristics of the magnetic bearing according to this method. As shown in FIG. 5, the attenuation characteristic becomes zero at frequencies greater than fc. Therefore, when this method is applied to the conventional magnetic bearing having the damping characteristics shown by the solid line in FIG. 7, the destabilizing force is reduced and there is no possibility of divergent vibrations occurring.

Note that the present invention is not limited to the above embodiments. For example, in the embodiment described above, a high-pass filter is used for the Funilter 8, but if the frequency of vibration that becomes unstable is clear, a band-pass filter that includes that frequency may be used.

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, the position of the floating object can be determined from two directions: forward and backward.
．． Measurement is performed with a second position sensor, the signal from the second position sensor is passed through a high-pass filter or a band-pass filter, and the passed signal is added to the signal from the first position sensor and fed back. Therefore, it is possible to provide a control method for a magnetic bearing that can reduce the destabilizing force in the medium and high frequency range generated from the magnetic bearing, prevent divergent vibrations of the floating object, and levitate the floating object stably.

[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. A diagram showing the output signal waveform of the second position sensor, FIG. 4 is a diagram showing the gain-frequency characteristic of the filter,
FIG. 5 is a diagram showing the damping characteristics of the magnetic bearing. Fig. 6 is a block diagram showing the configuration of the conventional control system, Fig. 7 is a diagram showing the damping characteristics of the magnetic bearing according to the conventional control system, and Fig. 8 is a block diagram showing the configuration of the conventional control system.
Figures (a) to (f) are diagrams showing a rotating body and natural frequencies. 1.7... 1st. Second position sensor, 2... Position feedback gain, 3... Control circuit, 4... Electromagnet, 5... Rotating body, 6... Bearing, 8... Filter, 9... Addition X0 Applicant's sub-agent Patent attorney Takehiko Suzue Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 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. In addition to the position sensor, a second position sensor is provided to measure the position on the opposite side of the floating object, and the signal from the second position sensor is passed through a high-pass filter or a band-pass filter, and then the signal is passed through a high-pass filter or a band-pass filter. A control method for a magnetic bearing, characterized in that the signal is added to a signal from a position sensor, and the added signal is fed back to an electromagnet of the magnetic bearing.