JPH1113763A - Magnetic levitation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent control from falling into the unstable state by constituting a drive circuit in which electromagnetic current for feedback control is let flow into a pair of electromagnets so that output overlapped a constant offset current on AC component corresponding to a drive signal for feedback control is generated. SOLUTION: When a magnetic levitation device is operated, a drive signal S in made by a feedback circuit 5 in a drive circuit 3, the drive signal to which bias is added, is converted to electromagnetic current 1a by a V/I conversion circuit 6 so as to input it to an electromagnet 2a. Meanwhile, a signal added with bias after inverting the drive signal S by an inversion circuit 5a is input to an electromagnet 2b as electromagnetic current 1b by the V/I conversion circuit 6. In this case, an offset adding means 7 is provided between a bias point and the V/I conversion circuit 6, the offset is decided so that the electromagnetic current is larger than zero and smaller than bias current. Hereby the electromagnets 2a, 2b can always be effectively functioned.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to various magnetic levitation devices.

[0002]

2. Description of the Related Art As a magnetic levitation device of this type, there is a magnetic levitation type suction device using normal conduction. FIG. 6 schematically shows this, in which the magnetic body 1 and the magnetic body 1
A pair of electromagnets 2a, 2b disposed at opposing positions with respect to
And a drive circuit 3 for inputting electromagnet currents Ia and Ib for feedback control to these electromagnets 2a and 2b. Then, the magnetic body 1 is attracted to each other by the pair of electromagnets 2a and 2b in opposite directions, thereby realizing the floating of the magnetic body 1.

The conventional driving circuit 3 is composed of a magnetic material 1
A feedback signal 5 is used to generate a drive signal S for correcting the displacement of the magnetic body 1 based on a detection signal from the sensor circuit 4 for detecting the flying position of the magnetic sensor 1. / I conversion circuit 6 generates an electromagnetic current I
a, which is directly input to one of the electromagnets 2a, the drive signal S is inverted by an inverting circuit 5a, and a bias is applied thereto.
It is configured to input as b to the other electromagnet 2b. At this time, the drive circuit 3 of this type has a structure in which each part is formed of a rectifying element such as a transistor, and in a region where the drive signal S is negative, the gain of the electromagnet 2 is reversed and the control becomes unstable. As shown by the broken line in FIG.
a and Ib are configured not to actually flow (or not flow) to the electromagnets 2a and 2b. When the drive signal S is within a certain range centered on zero, both electromagnets 2a and 2b operate, and in the other range, the positive current Ia or Ib flows only to one of the electromagnets 2 and the attraction is performed. It has become.

[0004]

However, in such a configuration, only one of the electromagnets 2a or 2b can be driven in a state where a large one-side load such as gravity is applied. For this reason, since both electromagnets 2a and 2b cannot be used effectively, the control efficiency must be reduced by half.

In addition, in view of the fact that the electromagnets for magnetic bearings and the electromagnets for sensors actually have substantially the same structure, the sensor circuit 4 has recently been used to detect the sensor current from the input currents to the electromagnets 2a and 2b for magnetic bearings. A so-called sensorless type magnetic bearing capable of extracting information has also been developed, but even in such a case, in a region where the electromagnet current Ia or Ib to the electromagnets 2a and 2b becomes zero, the electromagnets 2a Since the sensor information from the sensors 2b and 2b is lost and the flying position cannot be read correctly, there is also a problem that the system becomes unstable.

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention is to reduce the current flowing through the electromagnet from zero even when a negative drive signal is input so that the current becomes zero. The electromagnet is driven by maintaining a large constant value and applying an AC component based on the drive signal to the current.

With this configuration, even if the drive signal exceeds a certain range centered on zero, none of the electromagnet currents becomes zero, and the AC component of the drive signal is superimposed on the offset current and transmitted. Therefore, both electromagnets can always function effectively. Also, in the case of sensorless, since the sensor information can be obtained from both electromagnets, it is possible to read the flying position correctly.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. FIG. 1 shows a turbo molecular pump to which the magnetic levitation device of this embodiment is applied as a magnetic bearing. In this turbo molecular pump, a rotor 13 is provided in a casing 11 while being supported by a rotor shaft 12.
A turbine cascade 14 is formed between the turbine blade cascade 14 and the inner periphery of the casing 11, and the gas sucked in from the intake port 15 with the rotation of the rotor 13 is blown off by the turbine cascade 14 and is forcibly exhausted from the exhaust port 16. is there.

In this embodiment, the magnetic levitation devices X and Y for the radial bearing for floatingly supporting the rotor shaft 12 in the radial direction, and the magnetic levitation devices for the thrust bearing for floatingly supporting the rotor shaft 12 in the thrust direction. A levitation device Z is provided. The magnetic levitation device X for a radial bearing has at least a part of the outer periphery of the rotor shaft 12 as the magnetic body 1 and the electromagnets 2a, 2b facing each other on the inner periphery of the casing 2 in two axial directions. By inputting currents Ia and Ib for feedback control from the drive circuit 3 shown in FIG. 2 to these electromagnets 2a and 2b,
The rotor shaft 12 is supported by floating in the radial direction. A magnetic levitation device Z for a thrust bearing has a thrust runner 12a fixed to the rotor shaft 12 and at least a part of the thrust runner 12a is used as the magnetic body 1. The rotor shafts 12a and 2b are floated and supported in the thrust direction by inputting feedback control currents Ia and Ib from the drive circuit 3 to the electromagnets 2a and 2b.

Hereinafter, the configuration of the drive circuit 3 of the magnetic levitation device for a thrust bearing will be described in detail. This drive circuit 3 is basically basically the same as that shown in FIG.
The difference between the bias point and the V / I conversion circuit 6 is that an offset adding means 7 is provided. This offset adding means 7 is, as shown in FIG.
A line for directly inputting the drive signal S to the V / I conversion circuit 6 and a line for inputting the drive signal S to the V / I conversion circuit 6 via the polygonal line circuit 71 and the low-pass filter 72 are provided in parallel. FIG. 4 shows a broken line circuit 71 of FIG.
5 shows the input / output characteristics. The offset is determined so that the resulting electromagnet current is greater than zero and less than the bias current. The cut-off frequency of the low-pass filter 72 is set sufficiently lower than the frequency that affects the magnetic levitation feedback characteristics.

FIG. 5 shows input / output characteristics according to this embodiment.
Conventionally, the portion where the current becomes zero is a broken line circuit 7.
1 so that at least a constant offset current flows. In terms of AC, the AC component is cut by the low-pass filter 72 after exiting the polygonal line circuit 71, and the AC component as a whole remains.
In the figure, the current value changes in the shaded range, and an AC component corresponding to the drive signal S is transmitted to the electromagnets 2a and 2b.

Therefore, according to this structure, even if the drive signal S exceeds a certain range centered at zero, neither the electromagnet current Ia nor Ib becomes zero, and the drive signal S utilizes the offset signal to make use of the offset current. The AC component by S can be effectively transmitted. Therefore, both electromagnets 2a and 2b can always function effectively. Further, even in the case of the sensorless type, since the sensor information can always be obtained from both the electromagnets 2a and 2b, it is possible to correctly read the floating position of the rotor shaft 12.

The specific configuration of each part is not limited to only the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, the same function can be obtained even if the arrangement of the broken line circuit and the low-pass filter is reversed.

[0014]

According to the present invention having the above-described structure, it is possible to always effectively supply an electromagnet current to both electromagnets to make them function. For this reason, it becomes possible to stably support the magnetic body or the rotating body attached to the magnetic body with high efficiency as compared with the related art. In particular, in the case of sensorless magnetic levitation, since position information can always be obtained effectively from the electromagnet current, it is possible to reliably eliminate the disadvantage that the sensor signal is interrupted and control is unstable.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a turbo-molecular pump to which an embodiment of the present invention is applied.

FIG. 2 is a block diagram of a magnetic levitation device used in the embodiment.

FIG. 3 is a detailed view of a main part of FIG. 2;

FIG. 4 is a graph showing input / output characteristics of the polygonal circuit in the embodiment.

FIG. 5 is a graph showing the input / output characteristics of the entire magnetic levitation device in the example.

FIG. 6 is a block diagram showing a conventional example of a magnetic levitation device.

FIG. 7 is a graph showing input / output characteristics of the entire magnetic levitation device in the conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Magnetic body 2a, 2b ... Electromagnet 3 ... Drive circuit 12 ... Rotor shaft Ia, Ib ... Electromagnet current S ... Drive signal X, Y, Z ... Magnetic levitation device

Claims (1)

[Claims] An electromagnet includes a magnetic body, a pair of electromagnets disposed at opposing positions across the magnetic body, and a drive circuit for inputting an electromagnet current for feedback control to the electromagnets. In a magnetic levitation device configured to levitate and support a magnetic body by a pair of electromagnets, the drive circuit may include an electromagnet current obtained by superimposing at least a constant offset current and an AC component corresponding to a drive signal for feedback control. A magnetic levitation device characterized by being configured to be able to input to an electromagnet.