JPS6319734B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of controlling magnetic attraction force in an opposed control type magnetic bearing device.

The opposed type controlled magnetic bearing device is composed of two electromagnets 2 and 3, 4 and 5, 6 and 7, 8 arranged oppositely to sandwich a rotating object 1 or a controlled object as shown in FIG. A device for suspending and supporting a rotating object 1 or a controlled object in the air by the magnetic attraction forces of 9, 10, and 11, which does not cause wear and therefore has a long life and does not require lubricating oil. Although it has such excellent features, it has the problem that stable aerial support is difficult.

Note that "opposed type" is used to distinguish from a hanging type using a single magnet, and "controlled type" is used to distinguish from a non-controlled type using a permanent magnet.

Conventional opposed-type controlled magnetic bearing devices are simply a combination of two suspended-type controlled magnetic bearings, and even in the suspended type, stable aerial support performance has not been achieved with conventional technology. Naturally, good control performance was not obtained even with the opposed type.

To facilitate understanding, a conventional example will be explained with reference to FIG. 2.

The figure shows the controlled object 21 (rotating or not,
If rotating, use axial support type (thrust type)
This figure conceptually shows that electromagnets 22 and 23 are provided to sandwich the electromagnets 22 and 23 (regardless of whether they are of the radial or radial support type) and that the electromagnets are supported in the air by their magnetic attractive force.

This control system is controlled so that the detected gap x ₁ detected by the gap detector 24 matches the target gap x ₀ of the control system, and the gap deviation Δx is
Currents _I 1 and I 2 are input to the current converters 26 and 27 through the PID controller 25 and are to be passed to the electromagnets 22 and ₂₃ .
It is configured to be converted to

In FIG. 2, a current converter 27 and an electromagnet 23
If the electromagnet 22 is removed and the electromagnet 22 is placed vertically above the controlled body 21, it becomes a hanging type, so it can be seen that the conventional facing type is simply a combination of two hanging types.

By the way, the force with which an electromagnet attracts an object is as follows (1)
It is well known that it is expressed by the following formula.

F≒B ² A/2μ ₀ ≒μ ₀ A/8 (NI/x) ² ≡K _F (I/x) ²
...(1) However, F: Electromagnetic attractive force B: Magnetic flux density A: Magnetic pole area μ ₀ : Vacuum permeability N: Number of turns I: Current x: Gap (distance between electromagnet and object) K _F ≡μ ₀ AN ² / 8. Figure 3 also represents the part of equation (1) above as a block diagram.

Block 28 is a transfer function in which the mass of the controlled body 21 is m, the input is F, and the output is Δx. Blocks 29 and 30 are multipliers (in this case, they are multipliers because the same input is multiplied). ), block 3
x ₁ and x ₂ of 1,32 are x ₀ +△x, x ₀ -△ respectively
The dotted arrow indicates that it is determined by x.

That is, the current and the electromagnetic attraction force, and the gap and the electromagnetic attraction force each have a nonlinear relationship. It is also a well-known fact that this nonlinear characteristic is a major cause of unstable control.

The present invention was made to solve the above-mentioned conventional problems, and is a feature of an opposed magnetic bearing device. This method cleverly utilizes the fact that the force acting on the controlled object is the sum of the electromagnetic attraction forces of the two electromagnets to eliminate nonlinear characteristics.

A specific example will be described below with reference to FIG.

In the conventional device, the control current command _I0 , which is the output of the PID controller 25, is directly transmitted to the current converters 26 and 27.
However, in the present invention, the multiplier 33,
34 and a bias current command unit 35, and inputs the value obtained by adding the bias current command Ib to the control current command _I0 multiplied by the gap _x1 to the current conversion unit 26,
The current converter 27 calculates the value obtained by subtracting the bias current command Ib from the control current command I ₀ and multiplying it by the gap x ₂ .
It is configured so that it can be input.

With this configuration, the control current command I ₀ and the force F acting on the controlled body 21 have a linear relationship. Now, the transfer function G of the current converters 26 and 27
To simplify (S), let G(S) = 1, then I ₁ = (I ₀ + Ib) × x ₁ ... (2) I ₂ = (I ₀ - Ib) × x ₂ ... (3) Become.

From equation (1), the force F acting on the controlled body 21 is F=F ₁ −F ₂ =K _F {(I ₁ /x ₁ ) ² −(I ₂ /x ₂ ) ² } ...(4), Substituting equations (2) and (3) into equation (4), F=K _F {x ₁ ² (I ₀ + Ib) ² /x ₁ ² −x ₂ ² (I ₀ −Ib) ² /x ₂ ² } =K _F {(I ₀ + Ib) ² − (I ₀ − Ib) ² } = 4K _F IbI ₀ ...(5). That is, since K _F and Ib are both constants, a linear relationship is obtained between the force F acting on the controlled object 21 and the control current command I ₀ .

Note that block 36 is a multiplier that converts x ₂ into the formula 2x ₀ −
Since it is intended to lead by _{x 1} , it is equipped with its own gap detector for x ₂ , and
It is not necessary if you input it into .

As described above, according to the present invention, since the control current command and the force acting on the controlled object can be linearized, the stability of control can be greatly improved, so that an extremely high-performance magnetic bearing device can be provided.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an example of a magnetic bearing device;
FIG. 2 is a block diagram of a conventional control method, FIG. 3 is a detailed block diagram of the conventional example, and FIG. 4 is a block diagram of a specific embodiment of the present invention. 21... Controlled object, 22, 23... Electromagnet, 2
4...Gap detector, 25...PID
Controller, 26, 27...Current converter, 29, 3
0, 33, 34... Multiplier, 35... Bias current command device, 36... Multiplier.

Claims (1)

[Claims] 1 In an opposed control type magnetic bearing device, the command current given to one electromagnet is the gap value between that electromagnet and the controlled object multiplied by the control current command plus the bias current command. , the command current given to the other electromagnet is given by multiplying the gap value between the electromagnet and the controlled object by the value obtained by subtracting the bias current command from the control current command. Method.