JPH0570729B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to turbomolecular pumps, compressors,
The present invention relates to a magnetic bearing device suitable for use in rotating bodies such as turbines and spindles for machine tools.

[Conventional technology]

A magnetic bearing using an electromagnet is used as a means for keeping a rotating body 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 the rotating body, the floating position of the rotating body is measured,
There is a means of determining the current value to be passed through the electromagnet based on the measurement signal and determining the magnitude of the magnetic force generated from the electromagnet.

FIG. 4 is a block diagram showing the means.
In FIG. 4, a position sensor 1 is a sensor for measuring the position of a floating object, and an example thereof is an eddy current displacement meter. Position feedback gain 2 is
This is for proportionally multiplying the magnitude of the signal obtained by the position sensor 1 to a required magnitude. The controller 3 converts the signal obtained with a position feedback gain of 2 to
It consists of a processing circuit for inputting an appropriate form to the electromagnet 4. As this processing circuit, for example, PID
There are (proportional-integral-differential) circuits, phase compensation circuits, and combination circuits thereof. 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 controller 3.

Let us consider the simplest position feedback system in which the controller 3 consists of only proportional elements (P elements). The transfer function between the input I of the electromagnet 4 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, iron core, etc.

F/I=K _M /(1+T _M ·S) (1) Here, 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 to the floating object is as follows.

F/D=K _F・K _P・K _M /(1+T _M・S) …(2) Here, K _F is position feedback gain 2,
K _P indicates 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, set the Laplace operator S=j2πf and substitute it into equation (2). Here the frequency (Hz)
So, j=√−1. (Force F)/(Displacement D) is a complex number and is written as follows.

F/D=K _R・(f)+j/K _I・(f)...(3) In equation (3), the real part of (force F)/(displacement D) is the frequency-dependent stiffness, and the imaginary part is means frequency-dependent attenuation. The imaginary part of the first-order lag as shown in equation (2) is always negative, creating a destabilizing force on the floating object that is opposite to damping.

FIG. 5 is a diagram showing the relationship between (force F)/(displacement D), that is, the value of the imaginary part of equation (3), and frequency.
The dotted line A shown in FIG. 5 corresponds to equation (2) and indicates the above-mentioned state. The damping of the natural frequency f _c consisting of the floating object and the position feedback system,
In particular, from the attenuation of floating objects, the frequency shown in Figure 5 =
If the value of f _c is large, its natural frequency will oscillate divergently, making it impossible to operate.

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

(Differential element) = K _D · S / 1 + T _D · S (4) Here, K _D is the gain of the differential element, and T _D 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=K _F・K _D・K _M・S / {(1+T _D・S) (1+T _M・S)} …(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 as shown by the dashed-dotted line B in FIG. That is, it has a damping effect on floating objects in the low frequency range, and a destabilizing effect in the high frequency range. In order to maintain the position of the floating object, the controller 3 needs to have both a proportional element and a differential 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) It becomes like the solid line C shown in FIG. 5, and has the same characteristics as described above. By placing the natural frequency f _c 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. 6a and the rotating body 5 is levitated, the following phenomenon occurs. The rotating body 5 has an infinite number of natural frequencies as shown in FIG. 6b, c, d, e, 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, it is necessary to bring the natural frequency of the magnetic bearing's position feedback system below the rotational speed into a frequency range that has a damping effect of (force F)/(displacement D). However, since the natural frequency of the rotating body 5 is infinite as shown in Figure 6b, c, d, e, f~, the frequency always has the destabilizing effect of (force F)/(displacement D). There is a natural frequency in the region. 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 becomes unstable, the vibration increases divergently, and rotation becomes impossible. It disappears. In particular, the third natural frequency, which is higher than the maximum rotational speed of the rotating body 5, normally exists in a frequency range where the damping capacity is the least and where the destabilizing effect of the position feedback system of the magnetic bearing is large. For this reason, it was impossible to operate up to the first critical bending speed corresponding to the third natural frequency.

(Problems to be Solved by the Invention) As described above, in the conventional device, 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 4. However, this force becomes a destabilizing force that causes the floating object to vibrate. Even if the controller 3 is subjected to processing such as PID and phase compensation, 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 the rotating body 5, which has an infinite number of natural frequencies, there is always a natural frequency in the region where the destabilizing force occurs, and the magnetic bearing generates divergent vibrations. .

Therefore, the present invention is capable of changing the destabilizing force generated by a magnetic bearing into a stabilizing force (damping force) for the primary bending natural frequency, which is the most important for a rotating body, and generates divergent vibrations. It is an object of the present invention to provide a magnetic bearing device with a simple configuration that can prevent the above problems and stably levitate a rotating body.

[Means for solving problems]

The present invention has taken the following measures in order to solve the above problems and achieve the objectives. In other words, the signal from the position sensor for the rotating body is fed back to the magnetic bearing, and it is used for control such as PID (proportional, integral, differential) and phase compensation, which stabilizes the first and second natural frequencies. In a magnetic bearing device that actively uses magnetic bearings by performing control to provide damping for The position sensor and electromagnet in the bearing element are connected to the third natural frequency of the rotating body (bending 1
The node points in the vibration mode of (natural frequency) are arranged to be distributed to the left and right.

[Effect]

By taking such measures, the following effects are achieved. In active magnetic bearings that perform phase compensation (stabilizing action) on frequencies that include only the primary and secondary natural frequencies of the rotating body, the position sensor and electromagnet are free to detect the vibration mode of the free primary natural frequency. As a result of the arrangement, phase inversion also occurs for the bending primary natural frequency outside the phase compensation range, and that frequency region is changed into a stabilizing force.

〔Example〕

FIG. 1 is a diagram showing the configuration of a first embodiment of the present invention. Note that parts having the same functions as those in FIGS. 4 to 6 are designated by the same reference numerals. Figure 1 shows the rotating body 5.
The arrangement relationship between the two sets of journal magnetic bearings 6A and 6B is the vibration mode F 0 of the first natural frequency (hereinafter referred to as free free first natural frequency) when the bearing part of the rotating body _{5 is} free. FIG. As shown in FIG. 1, the two sets of journal magnetic bearings 6A and 6B are arranged at left and right positions of the center of gravity G of the rotating body 5. The journal magnetic bearing 6A arranged on the left side has four bearing elements 1L to 4L, and the journal magnetic bearing 6B arranged on the right side has four bearing elements 1R.
~4R. And bearing elements 1L to 4L
The position sensor 1L and the electromagnet 4L in , and the position sensor 1R and the electromagnet 4R in the bearing elements 1R to 4R are the free-free 1 of the rotating body 5, respectively.
They are distributed to the left and right with the node point P in the vibration mode F ₀ of the next natural frequency being interposed therebetween.

FIG. 2 is a diagram showing the relationship between the vibration modes F ₁ , F ₂ , F ₃ of the first, second, and third natural frequencies of the rotating body 5 and the journal magnetic bearings 6A and 6B.
As shown in FIG. 2, the vibration mode waveform of the third natural frequency has the same shape as the vibration mode waveform of the free first natural frequency shown in FIG. As can be seen from FIG. 2, the position sensor 1L and electromagnet 4 in each journal magnetic bearing 6A, 6B
L, the position sensor 1R, and the electromagnet 4R are located in a vibration mode in which the first and second natural vibrations swing in the same direction. However, regarding the 3rd natural frequency, the vibration mode F ₃ of the 3rd natural frequency has the same waveform as the vibration mode F ₀ of the free free 1st natural frequency, so the position sensor 1L and the electromagnet 4L , the position sensor 1R, and the electromagnet 4R are located in vibration modes that swing in opposite directions. It is assumed that the controllers 3L and 3R are capable of providing phase compensation so as to exhibit attenuation in the low frequency region, as shown by the solid line C in FIG. Thus, the first order of the rotating body 5,
The second natural frequency is located in the frequency range that provides damping, and the third natural frequency is located in the frequency range that provides destabilizing forces.

By the way, when (force F)/(displacement D) of the journal magnetic bearings 6A and 6B is expressed by equation (3), the first
Regarding the 2nd natural frequency and the 2nd natural frequency, the magnetic bearing characteristics do not change and the equation (3) remains the same, but for the 3rd natural frequency, the equation (3) is reversed. Then, F/D=-K _R・(f _c3 ) −j・K _I・(f _c3 ), and the destabilizing force turns into a damping force. In addition, f _c3
is the third natural frequency. Therefore, the characteristics of the rotating body 5 are such that each of the first, second, and third natural frequencies have damping, as shown by the solid line D in FIG.

Thus, according to this embodiment, although a controller is used that damps only the first and second natural frequencies, it damps the region that acts as the most destabilizing force at the third natural frequency. force (stabilizing force)
can be changed to 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 first critical bending speed (corresponding to the third natural frequency). Note that there is almost no problem with the natural frequencies of the fourth order or higher, since they are in a frequency range where the destabilizing force is small.

Note that the present invention is not limited to the above embodiments. For example, in the above embodiment, an example was shown in which the present invention was applied to a single rotating body, but for a rotating body in which a plurality of rotating bodies are connected in tandem, each elastic coupling, such as a gear coupling,
The present invention can be applied by considering individual rotating bodies. 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, in an active magnetic bearing that performs phase compensation (stabilizing action) for frequencies including only the primary and secondary natural frequencies of a rotating body, two sets of journal magnetic bearings are connected to the rotating body. The position sensor and electromagnet in the bearing element of each journal magnetic bearing are distributed to the left and right with respect to the node point in the vibration mode of the free first natural frequency of the rotating body. Because of this arrangement, phase reversal also occurs for the first bending natural frequency outside the phase compensation range. As a result, the destabilizing force in the frequency range where the most important bending first natural frequency exists is changed to a stabilizing force, and the destabilizing force generated by the magnetic bearing is almost stabilized. It is possible to provide a magnetic bearing device with a simple configuration, which can be changed into a force (damping force), can prevent the generation of divergent vibrations, and can stably levitate a rotating body.

[Brief explanation of the drawing]

1 to 3 are diagrams showing one embodiment of the present invention, FIGS. 1 and 2 are diagrams showing the configuration, and FIG. 3 is a diagram showing the damping characteristics of the magnetic bearing. Figure 4~
Fig. 6 a to f are diagrams showing a conventional example, Fig. 4 is a block diagram showing the configuration, Fig. 5 is a diagram showing the damping characteristics of the magnetic bearing, and Fig. 6 a to f are the rotating body and natural vibration. FIG. 1, 1L, 1R...Position sensor, 2, 2L, 2
R...Position feedback gain, 3, 3L, 3
R... Controller, 4, 4L, 4R... Electromagnet, 5...
...Rotating body, 6,6A,6B...Magnetic bearing, G...
Center of gravity of the rotating body, P... Node point of vibration mode.

Claims (1)

[Claims] 1. Feedback of signals from a position sensor for a rotating body to a magnetic bearing, control of PID (proportional, integral, differential), phase compensation, etc., and controlling the first and second natural frequencies. In a magnetic bearing device that performs control to provide damping for stabilization and actively uses magnetic bearings, two sets of journal magnetic bearings are arranged on the left and right sides with respect to the center of gravity of the rotating body, The position sensor and electromagnet in the bearing element of each journal magnetic bearing are connected to the third natural frequency (bending first natural frequency) of the rotating body.
1. A magnetic bearing device characterized in that the node points in the vibration mode are arranged to be distributed to the left and right.