JPS62297533A - Magnetic bearing controller - Google Patents

Abstract

PURPOSE:To prevent divergent vibration and to float floating substances stably by separating the signals from a position sensor so as to allow one signal to pass a first filter and another signal to pass a second filter and then by adding both signals to each other for feed back. CONSTITUTION:Signals from a position sensor 1 are separated so that one signal may pass a first filter 8 directly and another signal may pass a second filter 9 after being inverted its polarity by an inversional circuit 7 and are added to each other by an adder. This added signal is input to an electromagnet 4 through a position feed back gain 2 and a control circuit 3. The filter 8 is made to have an operating characteristic in the predetermined frequency domain to be stabilized, and the filter 9 is made to have a passage characteristic. An unstabilized force produced by a magnetic bearing can, therefore, be changed to a stabilized force to float floating substances stably.

Description

[Detailed description of the invention] 3. 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 magnetic bearing control device to which El magnetic bearings are applied for high-speed rotating bodies such as turbines and spindles for machine tools, and 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, 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.
An eddy current displacement meter is one of them.
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 N magnet 4 in an appropriate form, and includes, for example, a PID (proportional-integral-derivative) circuit, a phase compensation circuit, and the like. There are combinations. The WJ magnet 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 of the input of the magnet 4 and the magnetic force F becomes the following first-order lag system due to the resistance and inductance of the coil, iron core, etc.

F/I-KM/(1+TM-8)...
-(1) Here, KM is the gain of the ivite 4, TM is the time constant of the electromagnet 4, and S is the Laplace operator. Therefore,
Force F on the floating object from the measured displacement of the position feedback system
The transfer function leading to is as follows.

F/D=KF-KP-KM/(1,000TM-8)...(2) Here,
KF is position feedback gain 2°Kp is control circuit 3
shows the proportional gain of , respectively.

In order to see the frequency characteristics of (force F)/(displacement D) of the position feedback system, we set the Laplace operator 5-j2πf,
(2) Substitute into equation. Here, f is the frequency (Hz) and j−f−=co. (Force F)/(Displacement D) is a complex number and is written as follows.

F / D = K R・(f)+j−KJ・(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. Due to the disadvantage of the natural frequency f0 consisting of the floating object and the position feedback system, especially due to the damping of the floating object, if the value at the frequency f = fc shown in Fig. 6 is large, the natural frequency of vibration becomes divergent. It vibrates and makes it impossible 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 first-order lag system is as follows.

(g1 minute element)=Ko 'S/1+To -8...(
4) Here, Ko is the gain of the differential element, and To is the time constant. The force of the position feedback system with only differential elements E)/(
The displacement D) is expressed by the following formula.

F/D=KF-KO-KM-8/((1+To-8)(1+TM-8))...(5) The numerator of equation (5) is the first order of S and the denominator is the second order of S. Therefore, the imaginary part of equation (5) becomes like the dashed 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 −K F ” (Kp +Ko −3/ (1+To −8))・
KM/(1+TM-3)...(6), 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 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.

If we consider the case where a magnetic bearing having such characteristics is used as the bearing 6 of the rotation (45) shown in FIG.
has an infinite number of natural vibrations as shown in FIGS. 7(b), (c), (cl), (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
It is necessary to bring the natural frequency below the rotational speed to a frequency range that has a damping effect of >/(displacement D). but,
The natural frequencies of the rotating body 5 are shown in Fig. 7 (b), (c), (d) (e
) (f) Since there are infinitely many as shown in ~, there is always (force F
)/(displacement D) There is a natural frequency in the frequency region that has a destabilizing effect. 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, it will become unstable, the imaging will become divergent, and rotation will no longer be possible. .

[Problem that the invention seeks to solve]

As mentioned above, in order to maintain the position of a floating object, the conventional system measures the position of the floating object, feeds back the signal, and! I am trying to generate force from magnet 4, but
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, the rotating body 5
In a floating object having an infinite number of natural frequencies, such as the above, there is always a natural frequency in a region that causes a destabilizing force, and the magnetic bearing generates divergent vibrations.

Therefore, the present invention can change the destabilizing force generated by the magnetic bearing in a specified frequency range into a stabilizing force (damping force), prevent the occurrence of divergent imaging, and stabilize floating objects. It is an object of the present invention to provide a magnetic bearing control device that can be used to control 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. That is, the signal from the position sensor is separated into two, one of the signals is passed through a first filter whose cutoff band is the frequency band to be stabilized, and the other signal is inverted positive and whose cutoff band is the passband. The two signals passed through a second filter, which passed through separate paths, were summed again and fed back to the magnetic bearing, where it was converted into force by an electromagnet.

(Effect) By taking such measures, the frequency band portion of one of the separated signals that is a destabilizing force is blocked by the first filter, and the frequency band portion of the other separated signal is blocked by the destabilizing force. The frequency band portion that becomes a stabilizing force passes through the second filter, and the sum of both signals is fed back, so that all the force generated in the magnetic bearing is changed to a stabilizing force.

〔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 FIG. 1, 7 is an inverting circuit that inverts the polarity of a signal, and 8.9 is an inverting circuit that inverts the polarity of a signal.
The second filter, 10, is an adder.

The signal from the position sensor 1 is separated into two parts; one signal passes through the first filter 8 as it is, and the other signal has its polarity inverted by the inverting circuit 7 and then passes through the second filter 9. If the signal input to the filter 8 is a, and the signal input to the second filter 9 is b, then these two signals a
, b are signals having completely opposite magnitudes with respect to the movement of the floating object, that is, the phases are shifted by 180°, as shown in FIGS. 2(a) and 2(b). Therefore, for example, if signal a indicates +5, signal S indicates a value of -5.

Figures 3(a) and 3(b) are 1. FIG. 7 is a diagram showing each gain characteristic of the second filter 8°9. As shown in the same figure (a>,
The first filter 8 has a predetermined frequency f to be stabilized. Cutoff characteristics in the gA range from l to frequency fc2 (gain is zero)
As shown in FIG. 2B, the second filter 9 has the opposite frequency f. It has a pass characteristic (gain is 1) in the region from 1 to the frequency vlfcz. The signals that have passed through the first filter 8 and the second filter 9 are added by an adder 10. This joining signal is input to the control circuit 3 via the position feedback gain 2.

Therefore, (force F)/(displacement D) of the magnetic bearing is (3)
In the formula, in the path of signal a, f is from f to fc
In the area up to 2, F/D-0...(7-1), and in the area where f is the pond, F/D=KR・(f) +j-KI・(f)...(7 -2>.Also, in the path of the signal, the signal polarity is completely opposite, so in the region where f is from fcl to fC2, F/D=KR・(Go to f-j-・(f) ...(8-1>, and in the area where f is the number, F/D-〇 ...(8-2>).And from R Hiiragi's point of view, since both are added, f
is fcl to f. F/O in areas up to 2
= −K R・(f) −J−に工・(f)・
...(9-1), and when f is in other regions, F/D=KR.(f) +J-Kx.(f)...(9-2). Therefore, the damping characteristics of the magnetic bearing are as shown in Fig. 4. D
As shown in the figure, the part indicated by the dotted line E in the frequency region of f C1 to f C2 has been changed to a 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 embodiment described above, one signal is inverted immediately after dividing the signal from the position sensor 1 into two, but that signal is inverted after the second filter 9, that is, before entering the adder 10. You can do it like this. Furthermore, in the above embodiment, f
Although we have shown an example of stabilizing one frequency band from cl to fc2, it is possible to similarly stabilize multiple frequency bands or all bands above fcI depending on the characteristics of the floating object and magnetic bearing. It's okay. 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, a signal from a position sensor is separated into two, one of the signals is passed through a first filter whose cutoff is the frequency band to be stabilized, and the other signal is inverted in polarity and The above-mentioned cutoff region is passed through a second filter whose passband is the passband, and the sum of both signals that have passed through separate paths is fed back to the magnetic bearing and converted into force by an electromagnet, so that it can be used in the specified frequency range. It is possible to provide a magnetic bearing till i device that can change the destabilizing force generated by the 1ift air bearing into a stabilizing force (damping force), prevent the generation of divergent vibrations, and stably levitate a floating object. .

[Brief explanation of the drawing]

Figures 1 to 4 are diagrams showing one embodiment of the present invention, with Figure 1 being a block diagram showing the configuration, and Figures 2 (a) and (b) showing waveforms of two filter input signals. Figure 3(a)(b)
) is the first. FIG. 4 is a diagram showing the gain-frequency characteristics of the second filter, and FIG. 4 is a diagram showing the attenuation characteristics of the magnetic bearing. Fifth
7(a) to 7(f) are diagrams showing a conventional example, FIG. 5 is a block diagram showing the configuration, FIG. 6 is a diagram showing the damping characteristics of the magnetic bearing, and FIG. 7 (a> ~(f) is a diagram showing a rotating body and a natural frequency. 1... Position sensor, 2... Position feedback gain, 3... Control circuit, 4... Electromagnet, 5... Rotating body, 6... Bearing, 7... Inverting circuit, 8... First filter, 9... Second filter, 10... Adder. Applicant's sub-agent Patent attorney Takehiko Suzue Figure 2g Figure 3 Figure 4I21 Figure 5 Figure 6

Claims (1)

[Claims] In a magnetic bearing control device that actively uses a magnetic bearing by feeding back a signal from a position sensor for a floating object to a magnetic bearing and controlling PID (proportional, integral, differential), phase compensation, etc. The signal from the sensor is divided into two, one signal is passed through a first filter whose cutoff frequency band is a predetermined frequency band to be stabilized, and the polarity of the other signal is inverted while the cutoff frequency band is passed. A magnetic bearing control device characterized in that the two signals are passed through a second filter having a frequency band, and the two signals are added together and fed back to the magnetic bearing.