KR100608202B1 - Combined radial-axial magnetic bearing - Google Patents

Abstract

The present invention relates to a first leg extending radially with a gap between the rotary shaft and a second leg extending parallel to the first leg at a position axially spaced from the first leg and an axial direction connecting them. A first core pair consisting of a pair of cores composed of a yoke and disposed at positions symmetrical about the rotation axis, each of the first and first legs extending radially with a gap therebetween; A second core consisting of a pair of cores arranged in axially spaced positions, the second legs extending parallel to the first legs and the axial yokes connecting them and symmetrical about the axis of rotation; The cores of the first core pair and the second core pair are circumferentially arranged in a circumferential direction, so that the magnetic flux can be formed between two adjacent cores in the circumferential direction The circumferential yoke connecting incense, the first coil wound over the first leg and the second leg, the second coil wound respectively on the first leg and the second leg, and when the rotation axis is displaced radially and axially Disclosed is a radial-axial composite electromagnetic bearing comprising control means for controlling the magnitude and direction of current flowing through the first and second coils to return the axis of rotation to the center.

Magnetic, Bearing, Active, Lorentz, Damping, Small, Cross Section, Long Section

Description

Radial-Axial Composite Electromagnetic Bearings {COMBINED RADIAL-AXIAL MAGNETIC BEARING}

1 and 2 are cross-sectional and longitudinal cross-sectional views of a prior art electromagnetic bearing.

3 and 4 are cross-sectional and longitudinal cross-sectional views of the electromagnetic bearing of the present invention.

<Explanation of symbols for the main parts of the drawings>

40: magnetic bearing

41: axis of rotation

42: core

43a: first coil

43b: second coil

44: cross-sectional flux

45: longitudinal magnetic flux

46, 47: virtual coil

The present invention relates to a magnetic bearing, and more particularly, to an active magnetic bearing capable of simultaneously controlling the rotational axis displacement in the radial and axial direction in one bearing unit.

1 and 2 show cross-sectional and longitudinal cross-sectional views of prior art magnetic bearings capable of controlling both radial and axial rotational displacements. The prior art shown is introduced in the Proceedings of DETC '03; Bulletin No. VIB-48542.

The illustrated magnetic bearing 30 consists of a first unit 31a, a second unit 31b and a housing 39. The first unit 31a and the second unit 31b each include four U-shaped cores 32 connected to each other in the circumferential direction. A radial control coil 34 and an axial control coil 35 are wound on the outer circumferential surface of the core 32, and a permanent magnet 33 is disposed on the radially outer side of the core.

The permanent magnets 33 of the first unit 31a are all N-pole type, and the permanent magnets 33 of the second unit are all S-pole type, and they are the U-shaped core 32 and the magnetic housing 39. And a bias magnetic flux 38 in the closed circuit via the rotation shaft 31. The bias magnetic flux 38 is formed by the permanent magnet, has a predetermined size and magnetic flux direction, and is formed at a position symmetrical about the axis about the rotation axis 31 to act as an equilibrium attraction force with respect to the rotation axis 31.

Referring to FIG. 1, when a current is applied to the radial control coil 34, a cross section magnetic flux 36 is formed. The cross-sectional magnetic flux 36 cooperates with the bias magnetic flux 38 to exert a magnetic force that pulls the rotational axis 31 radially. For example, when the rotary shaft 31 is downwardly displaced in a radial direction, an electric current increased by a predetermined magnitude is applied to the radial control coil 34 of the U-shaped core 32 located upward in the drawing, and By applying the electric current reduced by the same magnitude to the opposing lower radial control coil 34, the rotating shaft 31 can be raised and returned to its original position.

As shown in FIG. 2, the current applied to the axial control coil 35 of each core 32 forms a longitudinal magnetic flux 37. The longitudinal magnetic flux 37 and the bias magnetic flux 38 interact to exert a force to move the rotational axis 31 in the axial direction.

The magnetic bearing 30 thus constructed has the advantage of low power consumption because it is advantageous in providing miniaturized bearings and uses permanent magnets, but only one bearing unit cannot be used independently and the control forces of the two bearing units are related to each other. In order to form a bias magnetic flux path, the housing and the shaft have to be made of a magnetic material, and thus have a limitation in weight reduction.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and an object thereof is to provide an active magnetic bearing which can be miniaturized by simultaneously performing rotation axis displacement control in a radial direction and an axial direction in a single bearing unit.

The above object and another object of the present invention are to extend in parallel with the first leg at a position axially spaced from the first leg and a first leg extending radially with a gap between the rotational axis, respectively. A first core pair consisting of a pair of cores disposed at positions symmetrical about a rotation axis with each other, each having a gap therebetween in the radial direction with a gap therebetween. A first leg that is extended and a second leg that extends in parallel with the first leg at a position axially spaced from the first leg, and an axial yoke connecting them, the positions being symmetric about a rotation axis with each other A second core pair consisting of a pair of cores disposed in the core, wherein the cores of the first core pair and the second core pair are disposed angularly in the circumferential direction, two adjacent in the circumferential direction A circumferential yoke for circumferentially connecting the core so that magnetic flux can be formed between the cores of the core, a first coil wound over the first leg and the second leg, and wound around each of the first leg and the second leg. And a control means for controlling the magnitude and direction of current flowing through the first coil and the second coil to return the rotation shaft to the center when the rotation shaft is displaced radially and axially. This can be achieved by providing an electromagnetic bearing.

The Lorentz force is a force acting on the coil by the correlation between the magnetic flux caused by the current and the magnetic field when a current is applied to the coil located in the magnetic field. This force is expressed as a vector product of the strength of the magnetic field (magnetic flux density), the current flowing through the coil, the length of the coil, etc., and its direction of operation follows Fleming's left hand law. In the magnetic bearing proposed in the present invention, the axial control basically uses this Lorentz force, and the radial control uses the same Maxwell force as the conventional magnetic bearing.

In the description of the present invention, "axial direction" means the longitudinal direction of the axis of rotation and "radial direction" is a direction near or away from the center of the axis of rotation in a plane with the axial direction normal, "circumferential direction" is the axis It means the direction perpendicular | vertical to the said radial direction in the plane which makes a direction normal. In addition, "cross section" means the cross section which took the plane which made the said axial direction normal as a cut surface, and "longitudinal cross section" is the cross section which made the plane parallel to the said axial direction a cut surface.

Hereinafter, with reference to the accompanying drawings, preferred embodiments of the present invention and its operation will be described in detail.

3 and 4 show cross-sectional and longitudinal cross-sectional views, respectively, of a composite electromagnetic bearing capable of controlling displacement in the radial and axial directions of the present invention.

Referring to FIG. 3, the electromagnetic bearing 40 of the present invention includes a total of four “C” shaped cores 42, 43, 44, and 45. The number of cores can vary from eight to ten.

As shown in FIG. 4, the U-shaped core 42 has a first leg 42a and a first leg 42a extending radially in the rotation axis with a gap 41a between the rotation shaft 41, respectively. It consists of the 2nd leg 42c extended in parallel with the 1st leg 42a, and the yoke 42b which connects these in the position spaced apart from the axial direction. The yoke 42b is also configured to connect between adjacent cores 43, 44, 45 in the circumferential direction so that magnetic flux can be formed between the core and the core. They can all be formed of magnetic material to form a magnetic path.

One core 42 operates in pairs or pairs with corresponding cores disposed at positions symmetrical about the axis of rotation. For example, as shown in FIG. 3, when four cores 42, 43, 44, and 45 are disposed at right angles in the circumferential direction, the core 42 and the core ( 44 may be paired (hereinafter, the pair of cores 42 and 44 are referred to as “first core pairs 42 and 44”) and cores disposed at positions symmetrical about an axis of rotation ( 43 and the core 45 may be paired (hereinafter, the pair of the core 43 and the core 45 are referred to as “second core pairs 43 and 45”). The arrangement of another core 44 symmetrically about the axis of rotation with respect to one core 42 provides the advantage that it is easy to control when the axis of rotation is displaced radially from the center of the bearing. In the case where the magnetic bearing comprises a plurality of core pairs, each core is preferably arranged equilaterally in the circumferential direction, and according to the present invention, various numbers of core pairs are possible.

In a preferred embodiment of the invention, each core 42 comprises a coil pair wound in a multilayer structure.

The first coil 46a, which is disposed outward in the radial direction, forms four cross-sectional magnetic flux 47 as shown in FIG. The cross-sectional magnetic flux 47 is formed to exit radially inward at one core and exit radially outward at an adjacent core and again through the core to radially inward through the magnetic yoke 42b. At this time, in one core pair, magnetic fluxes are formed in the same direction in the radial direction inward or outward in the radial direction, and current is applied to the core pairs adjacent in the circumferential direction to form opposite polarities.

As shown in FIG. 4, the first coil 46a is wound to form one circular or approximately square closed curve over the first leg 42a and the second leg 42c of the core. Therefore, the magnetic flux of the same direction in the radial direction is formed in the 1st leg 42a and the 2nd leg 42c.

The second coil 46b disposed further inward in the radial direction forms a longitudinal magnetic flux 48 as shown in FIG. 4. The longitudinal magnetic flux 48 is formed in a direction radially inward on one leg and radially outward through the other leg. The second coil 46b is wound around the first and second legs 42a and 42c of the core 42 to form the longitudinal magnetic flux 48, respectively. In order to form the longitudinal magnetic flux, currents in opposite directions are applied to the respective second coils 46b of the first and second legs 42a and 42c so that the magnetic flux can form a closed circuit. In a preferred embodiment of the present invention, the first leg 42a → void 41a → rotation shaft 41 → void 41a → second leg 42c → yoke 42b → first leg 42a is connected. A longitudinal cross section magnetic flux 48 is formed.

 As such, it can be regarded that the virtual equivalent coils 49a and 49b exist as shown in FIG. 4 with respect to the longitudinal magnetic flux 48 formed by the two second coils 46b. It can be assumed that the equivalent coil 49a or 49b flows a current forming the longitudinal cross-sectional magnetic flux 48.

Meanwhile, in the drawing, the equivalent coil 49a means a direction coming out of the ground, and the equivalent coil 49b means a current direction entering the ground.

The composite electromagnetic bearing of the present invention having such a configuration includes a controller (not shown) that controls each component for positioning the rotational axis 41 in the radial and axial centers. Referring to the first and second embodiments of the present invention according to the operation method of the controller as follows.

First embodiment

As the first embodiment, the controller performs the radial rotation axis displacement control by adding and subtracting a control current thereto while making the cross-sectional magnetic flux 47 a bias magnetic flux, and forming a longitudinal magnetic flux 49 to control the axial direction of the rotation shaft 41. Perform

In this embodiment, the bias magnetic flux forming current (hereinafter referred to as “bias current”) is applied to the four first coils 46a via a current amplifier (not shown) to make the cross-sectional magnetic flux 47 a bias magnetic flux. do. The bias magnetic flux provides the basic force by which the axis of rotation 41 can be held in the center of the bearing. At this time, all the legs 42a and 42c of one core 42 are formed with the same radial magnetic flux, and all the legs 43a of the pair of cores 43 and 45 circumferentially adjacent to the core 42 are formed. 43c, 45a, and 45c generate radial magnetic flux opposite thereto to form a closed loop magnetic flux 47.

If the axis of rotation during rotation or stationary is displaced in the radial direction, for example in the vertical direction in FIG. 3, the controller applies current from the first coil 46a to the first pair of cores 42, 44 in the vertical direction. The rotary shaft 41 is returned to the center again. That is, a current reduced by a control current of ΔI in a bias current is applied to the first coil of the core in which the gap 41a is narrowed when the rotation axis 41 is displaced, and a current increased by ΔI is applied to the symmetric core of the core. To return the rotating shaft 41 to the center.

In addition, when the rotary shaft 41 is eccentrically in the left and right radial direction in FIG. 3, a current changed by a control current is applied to the first coils of the second core pairs 43 and 45 in the left and right directions to displace the rotated shaft 41. Return to the center. It is possible to return the rotating shaft 41 in a faster time by changing the value of ΔI applied according to the displacement amount of the rotating shaft. For example, a control current having a magnitude proportional thereto may be applied according to the displacement amount.

In order to return the rotational shaft 41 displaced in the axial direction to the initial center position, the controller generates a longitudinal magnetic flux 48 by applying a control current to the second coil 46b. When the longitudinal magnetic flux 45 is formed, it can be understood that a current flows through the equivalent coils 49a and 49b of the virtual longitudinal magnetic flux 45. When there is an equivalent coil 46 through which electric current flows in the state where the cross-sectional magnetic flux 44 is formed, the virtual coil 46 is forced by the principle of Lorentz's force.

For example, in Fig. 4, the imaginary equivalent coil 49a in which a current flows in a state in which the cross-sectional magnetic flux 47, which is a bias magnetic flux, is inward radially inward in the first leg and the second leg 42a, 42c. Once formed, the equivalent coil 49a is forced in the right axial direction in FIG. 4 by the principle of the Lorentz force. However, since the actual coil in the magnetic bearing is mounted on the stator, the rotating shaft 41 moves in the left axial direction as shown by the arrow in response to the Lorentz force acting on the equivalent coil 49a. In order to adjust the force and direction applied to the rotating shaft 41, the magnitude and direction of the current applied to the second coil are adjusted to generate the Lorentz force by Fleming's left-hand law.

Here, since the sum of the currents flowing through the equivalent coils with or without the radial control magnetic flux is constant, it can be seen that the axial control can be made independently by the cross-sectional magnetic flux.

Second embodiment

The operation of the controller according to the second embodiment of the present invention will be described below.

In the second embodiment, the longitudinal magnetic flux 48 forms a basic bias magnetic flux for supporting the rotational shaft 41, and applies radially controlled current by applying or subtracting the control current, and performs the cross-sectional magnetic flux under the influence of the bias magnetic flux. 47) to control the axial displacement of the rotary shaft 41.

A current for forming the bias magnetic flux is applied to the second coil 46b to form the longitudinal magnetic flux 48. As a result, a basic force capable of supporting the shaft is generated. At this time, the second coil 46b wound around the first leg 42a and the second leg 42b based on one core 42 has the first leg 42a of the core 42 → gap 41a. → a current is applied such that a closed loop radial magnetic flux is passed through the axis 41 → the gap 41a → the second leg 42b of the core → the yoke 42 → the first leg 42a of the core.

When the axis of rotation in rotation or stationary is displaced in the radial direction, for example in the vertical direction in FIG. 3, the controller applies a current equal to or less than the control current to the bias current for the first pair of cores 42 and 44 in the vertical direction. The rotary shaft 41 is returned to the center by being applied to the second coil 46b. That is, a current reduced by ΔI in the bias current is applied to the second coil 46b of the core in which the gap 41a is narrowed when the rotation axis 41 is displaced, and a current increased by ΔI is applied to the symmetric core of the core. 2 is applied to the coil 46b to return the rotating shaft 41 to the center. In addition, when the rotating shaft 41 is eccentric in the left and right radial directions, the rotating shaft displaced by applying a current changed by a control current from the bias current to the second coil 46b of the second core pairs 43 and 45 in the left and right directions. Return 41 to the center. It is possible to return the rotating shaft 41 in a faster time by changing the value of ΔI applied according to the displacement amount of the rotating shaft. For example, a control current having a magnitude proportional thereto may be applied according to the displacement amount.

 In order to control the axial direction of the rotating shaft 41, a control current is applied to the first coil 46a to generate the cross-sectional magnetic flux 47. As an example of axial control, in FIG. 4, the cross-sectional magnetic flux 47 generated in the two legs 42a and 42c of the upper core 42 has the same direction, and a current flowing by the longitudinal magnetic flux 48 of the bias magnetic flux flows. The virtual equivalent coil 49a is forced by the Lorentz principle between the virtual equivalent coil 49a and the cross-sectional magnetic flux 47. This is due to the presence of the equivalent coil 49a in the constant cross-sectional magnetic flux 47, but the Lorentz force should be applied to the coil. However, since the coil is attached to the stator, the rotating shaft 41 moves in the left axial direction as indicated by the arrow. Will move. The magnitude and intensity of the current applied to the first coil 46a are adjusted to adjust the strength and direction of the force applied to the rotating shaft.

In addition, it is possible to change the magnitude of the control current applied according to the displacement amount of the rotating shaft to return the shaft to the initial position in the axial direction within a shorter time.

According to the first and second embodiments of the present invention described above, four coils for the minimum cross-sectional magnetic flux and one for the longitudinal cross-sectional magnetic flux are used to enable the control of the rotational axis in a total of two degrees of freedom in radial two degrees of freedom and one degree of freedom in the axial direction. Five power amplifiers are needed to drive the coil.

As a variant of the composite electromagnetic bearing according to the present invention, the legs 42a and 42c of each core may be configured to have only one coil. In this case, the coil is wound independently of a total of eight legs of four U-shaped cores, and the controller calculates and applies currents necessary for radial and axial control in advance. In this case, there is an advantage in that efficiency is increased by eliminating mutual inductance between coils, but eight channels of a D / A converter and a power amplifier are required.

On the other hand, by applying the same principle as described above, for example, eight cores may be employed, and they may be disposed at right angles in the circumferential direction to form a composite electromagnetic bearing. As described above, since one core operates in pairs with a corresponding core disposed at a position symmetric about the rotation axis, the first core is paired with a fifth core disposed at a position symmetric about the rotation axis. It can be a core pair, the second and sixth cores can be the second core pair, the third and seventh cores can be the third core pair, and the fourth and eighth cores can be the fourth core pair. . In this case, the odd-numbered core pairs have a cross-sectional flux such that the even-numbered core pairs have radial magnetic fluxes in the same direction, and the even-numbered core pairs have opposite radial magnetic fluxes, and the first and second legs of each core are opposite to each other. It is also possible to form a composite electromagnetic bearing by forming a longitudinal section magnetic flux to have a radial magnetic flux of.

According to the present invention, it is possible to implement a composite electromagnetic bearing having a simple structure and capable of radial and axial control.

Since the composite electromagnetic bearing of the present invention can be manufactured as described above with only one bearing unit, the overall size can be reduced, thereby enabling the implementation of a magnetic bearing for a compact system.

The composite electromagnetic bearing of the present invention can be applied to a high precision position control device and a high speed rotation device requiring a small space and radial control and an axial control, for example, to an artificial heart pump, a turbo cooler, a hard disk, and a high precision imaging device. Applicable

The present technology can be utilized for various purposes in accordance with the development trend of the technology represented by small size, light weight, simplification, precision, optimization, high reliability and the like.

Claims (5)

A first leg extending radially with a gap between the rotary shaft and a second leg extending parallel to the first leg at a position axially spaced from the first leg and an axial yoke connecting them A first core pair consisting of a pair of cores arranged in a position symmetric about a rotation axis of each other, A first leg extending radially with a gap between the rotary shaft and a second leg extending parallel to the first leg at a position axially spaced from the first leg and an axial yoke connecting them A second core pair consisting of a pair of cores arranged in a position symmetric about an axis of rotation of each other, wherein the cores of the first core pair and the second core pair are circumferentially arranged in a circumferential direction, Circumferential yoke for connecting the core in a circumferential direction so that magnetic flux can be formed between two adjacent cores in the circumferential direction, A first coil wound over the first leg and the second leg, A second coil wound around the first leg and the second leg, and Control means for controlling the magnitude and direction of current flowing through the first coil and the second coil to return the rotation shaft to the center when the rotation shaft is displaced in the radial and axial directions Composite electromagnetic bearing comprising a. The method of claim 1, The control means applies a bias current having a predetermined magnitude for forming a bias magnetic flux to the second coil so that radial magnetic fluxes in opposite directions are formed on the first leg and the second leg, The second coil of the core of which the gap with the rotation shaft is narrowed when the rotation shaft is moved in the radial direction is applied to the second coil of the core paired with the core, the current reduced by a predetermined amount of control current The second coil is applied with a current increased by a predetermined magnitude from the bias current, The first coil so that when the axis of rotation is displaced in the axial direction, radial magnetic flux in the same direction is formed in all legs of the first core pair and at the same time radial magnetic flux in the opposite direction is formed in all legs of the second core pair. To apply a control current  Composite electromagnetic bearing. The method of claim 1, The control means is a constant for forming a bias magnetic flux in the first coil so that the radial magnetic flux in the same direction is formed on all the legs of the first core pair and at the same time the magnetic flux in the opposite direction is formed on all legs of the second core pair. Apply a bias current of magnitude, When the rotary shaft is displaced in the radial direction, the first coil of the core of which the gap with the rotary shaft is narrowed is applied a current reduced by the control current in the bias current, and the first coil of the core mating with the core Current is increased by the control current from the bias current, And a control current is applied to the second coil such that radial magnetic fluxes in opposite directions are formed on the first leg and the second leg when the rotation axis is displaced in the axial direction. The method of claim 2 or 3, The magnitude of the control current is a composite electromagnetic bearing, characterized in that the magnitude proportional to the displacement amount of the rotating shaft. The method according to any one of claims 1 to 3, And a third core pair having the same configuration as the first core pair, and a fourth core pair having the same configuration as the second core pair, wherein the first to fourth core pairs are arranged in the circumferential direction. A composite electromagnetic bearing, characterized in that it is disposed at an angle.

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