JPH0623570B2 - Magnetic bearing device for double structure rotating body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to an active magnetic field applied to a rotor having a double structure such as a turbo molecular pump, or a rotor having a nearly double structure such as a flywheel. It relates to bearings.

(Prior Art) There is a magnetic bearing using an electromagnet as a means for floatingly holding a rotating body. This magnetic bearing has a smaller loss than the conventional fluid lubrication bearing, and the bearing is made dry and the atmosphere is clean, and is particularly useful in a vacuum state.

FIG. 6 shows a structural diagram of a rotating body having a double structure and its support base. The rotating body 5 is composed of an outer cylinder 7 having a function of performing work and the like, an inner shaft 8 having a function of driving, and a disk 9 connecting the outer cylinder 7 and the inner shaft 8.
In the figure, the work function and the drive function are omitted.

The support portion of the rotating body 5 is composed of a support cylinder 10 to which the magnetic bearing 6 is attached and a mount 11 for fixing the support cylinder 10.

The supporting cylinder 10 is often formed into a cylindrical shape depending on the length of the outer cylinder 7. In FIG. 6, at least a magnetic bearing 6 is used for the two journal bearings, and a total of four axes are controlled in two directions, horizontal and perpendicular.

In this magnetic bearing, as a means for setting the levitation position of the rotating body 5, the levitation position of the rotating body 5 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 is a means to determine.

FIG. 7 is a block diagram showing the means. In FIG. 7, a position sensor 1 is a sensor for measuring the position of a floating object, and an eddy current displacement meter or the like is an example thereof. The position feedback gain 2 is for proportionally multiplying the magnitude of the signal obtained by the position sensor 1 to the required magnitude. The controller 3 comprises a processing circuit for inputting the signal obtained by the position feedback gain 2 into the electromagnet 4 in an appropriate form. As this processing circuit, for example, PID
There are (proportional, integral, differential) circuits, phase compensation circuits, and their combination circuits. The electromagnet 4 is formed by winding a coil around an iron core, and generates a magnetic force for levitation according to the current input from the controller 3.

Consider the simplest position feedback system in which the controller 3 is composed of only proportional elements (P elements). Input I of electromagnet 4
The transfer function between the output and the magnetic force F, which is the output, becomes the following first-order lag system due to the resistance and inductance of the coil, the iron core, and the like.

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, and S is the 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) where K _F is the position feedback gain 2 and K _P is the proportional gain of the controller 3, respectively. In order to see the frequency characteristics of (force F) / (displacement D) of the position feedback system, the Laplace operator S = j2πf is set, and the Laplace operator S = j2πf is substituted into the equation (2).
Here, f is the frequency (H _z), Is. (Force F) / (Displacement D) is a complex number and is set as follows.

F / D = K _R (f) + j · K _I (f) ……………… (3) The real part of (Force F) / (Displacement D) in Eq. (3) is frequency f.
And the imaginary part means damping depending on the frequency f. The first-order lag as shown in Eq. (2) always has a negative imaginary part, which is a destabilizing force against the levitated object, which is the opposite of damping.

FIG. 8 is a diagram showing the relationship between (force F) / (displacement D), that is, the value of the imaginary part of the equation (3) and the frequency f. The dotted line A shown in FIG. 8 corresponds to the equation (2) and shows the above-mentioned state. When the value of the natural frequency fc composed of the floating object and the position feedback system is large, especially when the value of the frequency f = fc shown in Fig. 8 is larger than that of the floating object, the natural frequency fluctuates divergently. , I can't drive.

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

(Differential element) = K _D S / 1 + T _D S (4) where K _D is the gain of the differential element and T _D is the time constant.
The (force F) / (displacement D) of the position feedback system having only the differential element 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 the equation (5) is the first order of S. Since the denominator is a quadratic of S,
The imaginary part of the equation (5) becomes like the one-dot chain line B shown in FIG.
That is, in the low frequency region, the damping effect on the floating object,
It has a destabilizing effect in the high region. In order to hold the position of the floating object, the controller 3 needs to have a proportional element and a derivative element. The (force F) / (displacement D) of the position feedback system of the controller 3 is F / D = K _F · {K _P + K _D · S / (1 + T _D · S)} · K _M / (1 + T _M・ S) (6), which is like the solid line C shown in FIG. 8 and has the same characteristics as described above. If the natural frequency fc composed of the floating object and the position feedback system is placed in a low frequency region having a damping effect, stability can be secured and operation can be performed without generating vibration.

Considering the case where the magnetic bearing having such characteristics is used as the bearing 6 of the double structure rotating body 5 shown in FIG. 6 to levitate the rotating body 5, the following phenomenon is exhibited. Rotating body 5
Has an infinite number of natural frequencies as shown in FIGS. 9 (b) (c) (d) (e). The damping of the material of the rotating body 5 itself acts to destabilize the natural frequency below the rotational frequency, and acts as a damping effect to the natural frequency above the rotational frequency.

Therefore, (force F) / of the position feedback system of the magnetic bearing
It is necessary to bring the natural frequency equal to or lower than the rotation speed into the frequency range having the damping effect of (displacement D). However, since the natural frequency of the rotating body 5 is infinite as shown in FIG. 9 (b) (c) (d) (e), the destabilizing action of (force F) / (displacement D) The natural frequency is in the frequency domain having. Therefore,
If the destabilizing action of the position feedback system of the magnetic bearing becomes larger than the damping of the natural frequency due to the rotating body 5 itself, it becomes unstable, and the vibration becomes divergently large and it becomes impossible to rotate.

In particular, the damping characteristic of the third natural frequency, which is usually higher than the maximum rotation speed of the rotating body 5, is small, and is easily divergently vibrated by the destabilizing action of the position feedback system of the magnetic bearing. As a countermeasure, even if the damping action region is extended to the third natural frequency by the magnetic bearing, a larger destabilizing action is brought about in the frequency region higher than that, and the fourth natural frequency is the next divergent vibration. Will be caused. Also,
An electromagnet 4 and a position sensor 1 are attached to the support cylinder 10,
The position sensor 1 measures the relative displacement between the inner shaft 8 of the rotating body and the support cylinder 10, and the reaction force of the force generated by the electromagnet 4 is also applied to the support cylinder 10. Therefore, the magnetic bearing 6 has the same effect on the supporting cylinder 10 as on the rotating body 5, and the supporting cylinder 10 also has an infinite natural frequency as a beam, which is also unstable. Vibration occurs.

(Problems to be Solved by the Invention) As described above, in the conventional device, the position of the floating object is measured to hold the position of the floating object, and the signal is fed back to generate the force from the electromagnet 4. However,
This force becomes a destabilizing force that vibrates the floating object. Even if the controller 3 is subjected to processing such as PID and phase compensation, it has a stabilizing (damping) force in the low frequency region, but still has a large destabilizing force in the middle and high frequency regions. Therefore, in a floating object having an infinite number of natural frequencies such as the rotating body 5, the natural frequency always exists in the region that becomes the destabilizing force, and the magnetic bearing causes divergent vibration.

As a countermeasure against this, for example, the damping region of the magnetic bearing is extended to the bending primary natural frequency (third order) of the inner shaft, which has the least damping for the double rotating body. However, with respect to the secondary bending frequency (fourth order), the destabilizing force further increases, and the secondary bending frequency causes divergent vibration.

Therefore, the present invention can change the destabilizing force generated by the magnetic bearing into a stabilizing force (damping force) for the bending primary natural frequency that is most important for the rotating body, and prevents divergent vibration generation. Therefore, a magnetic bearing device having a simple structure capable of stably levitating the rotating body is provided, and the supporting portion of the double rotating body is a one-sided cylinder, so that the primary natural frequency of the supporting portion is It is an object of the present invention to provide a magnetic bearing device that can be changed to a stabilizing force even in the secondary natural frequency by putting it in the damping region of the magnetic bearing.

(Means for Solving Problems) The present invention has taken the following means in order to solve the above problems and achieve the object. That is, the signal from the position sensor for the rotating body is fed back to the magnetic bearing, and the PID
In a magnetic bearing device in which the magnetic bearing is actively used by controlling (proportional, integral, differential), phase compensation, etc., two sets of journal magnetic bearings are placed on the left and right with respect to the center of gravity of a rotating body having a double structure. And the position sensor and the electromagnet in the bearing element of the journal magnetic bearing farther from the disk with the outer cylinder, the node point in the vibration mode of the free-free secondary natural frequency mainly of the inner shaft of the rotating body. On the other hand, when the support is cylindrical, the position sensor of the journal magnetic bearing on the disk side and the electromagnet are axially arranged with respect to the node point in the vibration mode of the free secondary natural frequency of the support when the support is cylindrical. It is configured to be arranged according to the direction.

(Operation) By taking such means, the following operation is exhibited. Active type with phase compensation (stabilization) for frequencies including the primary natural frequency of the rotating body, the secondary natural frequency, the bending primary natural frequency, and the primary natural frequency of the support. In the magnetic bearing, the position sensor and the electromagnet are free-free secondary natural frequency of the rotating body and free-of-support 1
As a result of being arranged in consideration of the vibration mode of the next natural frequency, phase reversal occurs also in the secondary natural frequency of bending of the rotating body and the secondary natural frequency of the support outside the phase compensation range, and the frequency range is stable. It is changed to the ability.

(Examples) Examples of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing the configuration of the first embodiment of the present invention. The parts having the same functions as those shown in FIGS. 6 to 9 are designated by the same reference numerals. FIG. 1 shows a rotary body 5 (the outer cylinder 7 is omitted for half) and two sets of journal magnetic bearings 6A, 6
The positional relationship between B, a secondary natural frequency when the free bearing portion of the rotating body 5 (hereinafter, referred to as a free-free secondary natural frequency.) Shown in response to the vibration mode F ₀ in FIG. Is. As shown in FIG. 1, two sets of journal magnetic bearings 6
A and 6B are arranged separately at the left and right positions of the center of gravity G of the rotating body 5. In the figure, the journal magnetic bearing 6A arranged on the left side includes a position sensor 1L, a position feedback gain 2L, a control circuit 3L, and four bearing elements.
The journal magnetic bearing 6B, which has an electromagnet 4L and is arranged on the right side, also has a position sensor as four bearing elements.
1R to electromagnet 4R. The position sensor 1L and the electromagnet 4L, which are bearing elements of the journal magnetic bearing 6A, are in the vibration mode F ₀ of the free-free secondary natural frequency of the rotor 5.
Are arranged so as to be sandwiched between the node points P in FIG. Since the rotor 5 has a double structure, the characteristics of the inner shaft 8 are similar to a cantilever beam, and in the free-free second-order natural frequency, in the vibration mode having one node point P near the tip of the inner shaft 8. is there.

FIG. 2 is a diagram showing the relationship between the vibration modes F1, F2, F3 and F4 of the primary, secondary, tertiary and quaternary natural frequencies of the rotor 5 and the journal magnetic bearings 6A and 6B. Is.

Since the rigidity of the rotor 5 is higher than the rigidity generated by the magnetic bearing 6 as shown in FIG. 2, the vibration mode of the fourth natural frequency has the shape of the free-free second natural vibration shown in FIG. It has the same shape as the number vibration mode. As can be seen from FIG. 2, the position sensor 1L and the electromagnet 4L, and the position sensor 1R and the electromagnet 4 in each journal magnetic bearing 6A, 6B.
R is located within a vibration mode in which the first, second, and third natural frequencies swing in the same direction.

However for the Fourth pieces chromatic frequency, the vibration mode F4 of the fourth-order natural frequency is the same waveform as the vibration mode F ₀ of the free-free Fourth natural frequency, the position sensor 1L bearing 6A The electromagnet 4L and the electromagnet 4L are positioned in a vibration mode in which they swing in opposite directions.
4R is located in a part that cannot shake together. As the two controllers 3L and 3R, those capable of giving phase compensation so as to exhibit attenuation in the low frequency region as shown by a solid line C in FIG. 8 are used. Thus, the first-order, second-order, and third-order natural frequencies of the rotating body 5 are placed in the frequency region that gives damping, and the fourth-order natural frequency is placed in the frequency region that gives destabilizing force.

By the way, when the (force F) / (displacement D) of the journal magnetic bearing 6A is expressed by the equation (3), the primary natural frequency, the secondary natural frequency and the tertiary natural frequency are The characteristics remain unchanged from Eq. (3), but for the fourth natural frequency, it is reversed from Eq. (3): F / D = -K _R (fc ₄ ) -j · K ₁ (fc ₄ ) and the destabilizing force changes to the damping force. Note that fc ₄ is the fourth natural frequency. Therefore, the characteristic for the rotating body 5 has damping for each of the first-order, second-order, third-order, and fourth-order natural frequencies as shown by the solid line D _C in FIG. For the journal magnetic bearing 6B, refer to No. 4
Since it is arranged in a place where the vibration mode does not shake at all with respect to the fourth natural frequency, no destabilizing force is given to the fourth natural frequency.

Thus, according to the present embodiment, the controller that gives damping only to the first, second, and third natural frequencies is used, but as the most destabilizing force at the fourth natural frequency, The working area can be changed to damping force (stabilizing force). Therefore, the problem of medium- and high-frequency hunting of the rotating body 5 is reduced, and it is possible to operate up to the bending secondary critical velocity (corresponding to the third natural frequency). It should be noted that there is almost no problem for the fifth and higher natural frequencies since the destabilizing force is in the frequency region where the destabilizing force is small.

Next, the arrangement of the support base and the journal bearing 6B will be described. As shown in FIG. 6, when the outer cylinder 7 becomes longer, the bearing support becomes a cylinder 10 and is attached to the mount 11. Only when such a support is used, the positions of the position sensor 1R and the electromagnet 4R, which are the bearing elements of the journal bearing 6B, are restricted. FIG. 3 is for explaining an embodiment of the present invention with respect to such a support base, and shows the positional relationship between the rotating body 5 and the two sets of journal magnetic bearings 6A and 6B under the above-mentioned arrangement conditions. FIG. 7 is a diagram corresponding to the vibration modes FS-1 and FS-2 of the primary and secondary natural frequencies (hereinafter referred to as free primary and secondary natural frequencies) when the is set to be free.

As shown in FIG. 3, among the bearing elements 1R to 4R of the journal bearing 6B close to the coupling disk 9, the position sensor 1R and the electromagnet 4R mounted on the support cylinder 10 are the vibration modes FS of the free secondary natural frequency of the support base. -The node point Q at -2 is sandwiched between the left and right. Since the rigidity of the support is higher than the rigidity generated by the magnetic bearing 6, the actual natural frequency is the same as the free natural frequency mode. This is exactly the same as the relationship between the bending primary and bending secondary natural frequencies of the rotating body 5, and the primary natural frequency of the support is placed in the frequency region that gives the damping of the magnetic bearing 6, The secondary natural frequency is placed in the frequency range that gives the destabilizing force, but by disposing the journal bearing 6B, damping capacity can be provided up to the secondary natural frequency of the support as shown in FIG. Resonance problems and divergent vibrations of the table can be reduced.

(Effects of the Invention) According to the present invention, phase compensation (stabilizing action) is performed for frequencies including the primary, secondary, and tertiary natural frequencies of the rotor and the primary natural frequency of the support. In an active magnetic bearing, two sets of journal magnetic bearings are arranged separately to the left and right with respect to the center of gravity of the rotating body, and the position sensor and the electromagnet, which are bearing elements of each journal magnetic bearing, are respectively free and free of rotation. Next natural frequency and free base of support base Since the node points in the vibration mode of the secondary natural frequency are distributed to the left and right, the rotor is out of phase compensation range. Phase inversion also occurs with respect to the secondary natural frequency of the. As a result, the rotating body can be stabilized up to the frequency range in which the primary natural frequency of bending is present by the magnetic bearing without the problem of high frequency hunting, and at the same time, the vibration of the support can be eliminated and the high speed rotation can be achieved. Can be driven stably,
In addition, it is possible to enable operation at a bending primary critical speed or higher.

[Brief description of drawings]

FIGS. 1 to 5 show a typical embodiment of the present invention, and FIGS. 1 and 2 show a free and free secondary and first and second rotary bodies.
FIG. 3 is a schematic explanatory view showing a magnetic bearing arrangement relationship with respect to vibration modes of 2, 3, and 4 natural frequencies, and FIG. 3 shows a magnetic bearing arrangement with respect to vibration modes of free primary and secondary natural frequencies of a support base. FIG. 4 and FIG. 5 are schematic explanatory diagrams showing the relationship, FIG. 4 and FIG. 5 are damping characteristic diagrams of the magnetic bearing with respect to the rotating body and the supporting base, respectively, FIGS. 6 to 9 show conventional examples, and FIG. FIG. 7 is a block diagram of the components of the magnetic bearing, FIG. 8 is a damping characteristic diagram of the magnetic bearing, and FIG.
(a)-(e) is explanatory drawing which shows the rotating body and the kind of natural frequency. Description of main parts of the drawing 1L, 1R ... Position sensor 2L, 2R ... Position feedback gain 3L, 3R ... Controller 4L, 4R ... Electromagnet, 5 ... Rotating body 6A, 6B ... Magnetic bearing, 7 ... … Cylinder 8 …… Inner shaft, 9 …… Disk 10 …… Supporting cylinder, G …… Center of gravity of the rotating body P …… Nodal point of vibration mode

Claims (1)

[Claims] 1. A double structure rotating body having a shaft arranged at the center and one end of which is connected to an end of a cylindrical body via a disk, and a signal from a position sensor for the rotating body is fed back to obtain a magnetic force. In a rotating structure comprising a support body that supports the rotating body via a journal magnetic bearing that is actively controlled by changing the angle, two sets of the journal magnetic bearings are arranged in the axial direction across the center of gravity of the rotating body. Among the two sets of the journal magnetic bearings, one set on the side opposite to the disk is provided with a position sensor and an electromagnet, which are bearing elements constituting the journal magnetic bearing, on the rotary body free-free shaft.
A magnetic bearing device for a double structure rotating body, wherein the magnetic bearing device is arranged so as to be axially distributed with respect to a node point in a vibration mode of a next natural frequency.