JP2000308291A - Electric motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inhibit generation of a cogging phenomenon and vibrating noises in an electric motor. SOLUTION: This motor 10 contains permanent magnets 12, arranged to one of a rotor 16 and a stator 18 and armatures 14 arranged to the other of the rotor 16 and the stator 18. Generation of cogging phenomenon is inhibited by using skew magnetization twisted in the direction of rotation to the axis of rotation as the magnetization of the permanent magnets 12, and the generation of vibrating noises in the direction of the axis of rotation is inhibited, by having the direction of a skew in the magnetic intermediate section of a magnetizing region inverted in the direction of the axis of rotation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric motor using a permanent magnet, such as a spindle motor.

[0002]

2. Description of the Related Art Spindle motors using permanent magnets are:
Generally, a permanent magnet and an armature each having a plurality of magnetic pole portions are provided. The magnetic pole portion of the permanent magnet has an N pole and an S pole.
It is formed by magnetizing a cylindrical or ring-shaped permanent magnet material so that the poles are alternately present in the rotation direction of the rotor. The permanent magnet and the armature are arranged such that their magnetic poles are directed inward or outward, or are positioned such that their magnetic poles are directed in the direction of the rotation axis.

[0003] In a motor such as a spindle motor for a hard disk drive (HDD), which is required to have a small size, particularly a thickness dimension (dimension in a rotation axis direction), a cylindrical or ring-shaped permanent magnet is rotated. The armature is arranged as one member on the stator, and the armature is arranged as one member on the stator inside the permanent magnet.

In this type of electric motor, the direction of a current flowing through an armature is electrically or mechanically switched to periodically switch the direction of a magnetic field generated by the armature, so that Lorentz force is applied to a permanent magnet or an armature. Rotational force is obtained by acting discretely. However, in this type of electric motor, the edge of the magnetic pole portion of the permanent magnet in the rotating direction of the rotor (that is, the boundary of the magnetic pole portion of the permanent magnet) extends linearly in parallel with the rotation axis. This results in a structure in which the spatial distribution of the magnetic field formed by the magnetic pole portion of the armature and the magnetic pole portion of the armature changes abruptly. As a result, a phenomenon called cogging occurs in which the rotor does not rotate smoothly.

[0005] In order to suppress the occurrence of the cogging phenomenon, FIG.
The so-called skew magnetization in which the magnetization of the permanent magnet 100 is twisted by a predetermined angle θ in the rotation direction with respect to the rotation axis of the rotor as shown in, or the pole face of the armature is curved in the rotation direction of the rotor. By adopting a core shape, a device for smoothing the magnetic field distribution in the rotation direction has been devised.

[0006]

However, in the skew magnetizing technique, for example, the permanent magnet 100 periodically forms a rotationally symmetric torsional magnetic field with the rotation of the rotor, and a periodic force is applied in the direction of the rotation axis. As a result, although the cogging phenomenon is reduced, the rotor vibrates in the direction of the rotation axis, that is, so-called vibration noise is generated. In particular, in the case of a spindle motor using a fluid dynamic pressure bearing using a liquid as a lubricating medium, this vibration noise appears as vibration noise on the rotor. Therefore, the skew angle θ must be set to 10 degrees or less.

In the technique of bending the magnetic pole surface of the armature, the curved surface must be formed precisely.
Since a large number of thin plate-shaped core members having different curved portions must be overlapped along a desired curved surface, it is difficult to manufacture the core, and the torque is extremely small because the magnetic field utilization efficiency is low.

Therefore, it is important for a motor such as a spindle motor to suppress the occurrence of cogging and vibration noise.

[0009]

An electric motor according to the present invention includes a permanent magnet disposed on one of a rotor and a stator, and an armature disposed on the other of the rotor and the stator. The magnetization of the permanent magnet is a skew magnetization in which a skew direction is inverted at a magnetic center of a magnetization region in a rotation axis direction.

When the permanent magnet is skew-magnetized, abrupt changes in the magnetic field formed by the permanent magnet and the armature are suppressed, as in the case of simple linear skew-magnetization. It rotates and the cogging phenomenon hardly occurs.

If the skew magnetization has a skew shape in which the direction of the skew is reversed halfway, both vibration noise components generated in one side and the other side of the skewed area are opposite. Orientation, and hence both vibration noise components cancel each other out. As a result, vibration noise is smaller than in the case of simple linear skew magnetization.

Therefore, by forming the permanent magnets into a skew magnetized in the shape of a rectangle twisted in the direction of rotation with respect to the rotation axis of the rotor, both the occurrence of the cogging phenomenon and the occurrence of vibration noise are suppressed.

[0013] The reverse position of the skew direction may be a magnetic center of the magnetized region in the direction of the rotation axis. With this configuration, the two vibration noise components generated on the one side and the other side of the V-shaped region are almost the same, and the vibration noise components cancel each other, and as a result, almost no vibration noise is generated. do not do.

The skew angle with respect to the rotation axis is 4
It can be 5 degrees or less. If the skew angle is too large, both the vibration noise and the cogging phenomenon occur.
If the skew angle is too small, the effect of suppressing the occurrence of the cogging phenomenon is lost.

The permanent magnet may have a short cylindrical shape having a magnetic pole surface on an inner peripheral surface. Further, the armature can be arranged inside the permanent magnet. This makes it possible to reduce the size of the electric motor, particularly the thickness (dimension in the direction of the rotation axis), like the HDD spindle motor.

[0016] Further, it may include a shaft disposed on one of the rotor and the stator, and a fluid dynamic bearing region formed between the other of the rotor and the stator and the shaft. it can. In this manner, the occurrence of the cogging phenomenon and the vibration noise are suppressed, and the liquid dynamic pressure bearing using the lubricating oil can be used, and stable rotation at low speed can be obtained.

[0017] Further, a shaft disposed on one of the rotor and the stator, the shaft having a flange-shaped ring portion, and an annular recess opened to the rotation axis side to receive the ring portion. And a recess formed in the other of the rotor and the stator, between the inner surface of the recess and the surface of the ring portion in the direction of the rotation axis, a thrust hydrodynamic bearing region. The space between the outer peripheral surface of the ring portion and the inner bottom surface of the recess may be a radial dynamic pressure bearing region. With this configuration, the convergence of the radial fluid dynamic pressure bearing region is faster than in the case where the radial fluid bearing region is formed between the outer periphery of the shaft and the other of the rotor and the stator. Even at low speeds, sufficient dynamic pressure is generated, so that stable rotation can be obtained in either the liquid dynamic bearing region or the gas dynamic bearing region.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG.
Is a spindle motor that uses a short cylindrical or ring-shaped permanent magnet 12 and an armature 14 disposed inside the permanent magnet 12. The permanent magnet 12 is arranged on the stator 16. The armature 14 is located on the rotor 18 and is rotated about a rotation axis 20.

As shown in FIG. 2, the permanent magnet 12 includes a plurality of magnetic pole portions 22,
24 about the axis of rotation 20. The magnetic pole portions 22, 24 adjacent to the rotation direction of the rotor 18 are magnetized in opposite directions. The inner surface of each magnetic pole portion acts as the pole surface of the permanent magnet.

The magnetization of the permanent magnet 12 is a so-called skew magnetization in which the magnet is twisted by a predetermined angle θ in the rotation direction with respect to the rotation axis 20. The portions 22 and 24 (more specifically, the skew magnetized regions) are in the shape of an inverted letter at the magnetic center. In the illustrated example, the reversal position in the skew direction is the magnetic center 26 of the skew magnetized region. The boundary between adjacent polar surfaces also has a U-shaped shape.

The armature 14 has a core 28 formed by laminating a plurality of core members made of a thin metal plate such as a silicon steel plate, and an exciting coil 30 wound around each magnetic pole portion of the core 28.
Each pole face of the core 28 has a substantially rectangular shape in a developed state.

The stator 16 has a dish shape and acts as a mounting base. The stator 16 has a boss 32 at the center and a flange 34 at the outer periphery, and is screwed to an appropriate member such as a housing at the flange 34. The boss 32 has a space that opens upward. The armature 14 is attached to the outer periphery of the boss 32 so as not to rotate relatively.

The rotor 18 also has a dish shape. The rotor 18 has a shaft 36 received in the boss portion 32 at a central portion, and has an upward stepped portion 38 at an outer peripheral portion. The permanent magnet 12 is mounted inside the outer peripheral portion so as not to rotate relatively.

A ring 40 is attached to the shaft 36 so as not to rotate relatively. The ring 40 has a substantially rectangular cross-sectional shape, and has a boss portion 32 and a boss portion 32.
And is received in an annular recess 44 formed by a ring-shaped auxiliary member 42 disposed at the upper part of the ring. The auxiliary member 42 is attached to the boss 32 so as not to rotate relatively.

Both inner surfaces (upper and lower surfaces) of the recess 44 in the direction of the rotation axis 20 and corresponding two surfaces (upper and lower surfaces) of the ring 42.
Are defined as thrust dynamic pressure bearing regions 46 and 48,
A radial dynamic pressure bearing region 50 is provided between the inner bottom surface of the recess 44 and the outer peripheral surface of the ring 42. These dynamic pressure bearing areas 46, 48, 50 are filled with a liquid such as lubricating oil.

A thrust dynamic pressure groove 52 as shown in FIG. 3 is formed on both inner surfaces of the recess 44 in the direction of the rotation axis 20 or on both corresponding surfaces of the ring 42. A radial dynamic pressure groove 54 as shown in FIG. 4 is formed on the inner bottom surface of the recess 44 or the outer peripheral surface of the ring 42.

In use, a plurality of hard disks 56 are arranged on the upward step 38 of the rotor 18. When a driving current having a predetermined frequency is supplied to the exciting coil 30 of the armature 14 with a predetermined phase, the interaction between the rotating magnetic field formed by the armature 14 and the magnetic field from the permanent magnet 12 causes the rotor 18 to rotate. Is done.

When the rotor 18 is rotating, if the magnetization of the permanent magnet 12 is skew magnetization, the change in the magnetic field formed by the permanent magnet 12 and the armature 14 is greater than when the magnetization is not skew magnetization. Is reduced, the rotor 18 rotates smoothly, and the occurrence of the cogging phenomenon is suppressed.

If the skew magnetization is in a V shape, the two vibration noise components generated in the upper portion and the lower portion of the V region in the vibration noise component in the direction of the rotation axis 20 are reversed. Because of the orientation, the vibration noise components of both parts cancel each other, and as a result, the vibration noise is significantly smaller than in the case of linear skew magnetization. For this reason,
As compared with the case of linear skew magnetization, the skew angle θ with respect to the rotation axis 20 can be increased to reduce the occurrence of the cogging phenomenon, and the rotor 18 can be smoothly operated even if a fluid dynamic bearing is used. Rotate.

However, if the skew angle θ is too large,
Both occur in the vibration noise and the cogging phenomenon. Also,
If the skew angle θ is too small, the effect of suppressing the occurrence of the cogging phenomenon is lost. Therefore, the skew angle θ is 5
The angle is preferably set to about 45 to about 45 degrees, and more preferably about 10 to about 30 degrees.

In the electric motor 10 having the structure shown in FIG. 1 in which the number of magnetic pole portions of the permanent magnet 12 and the armature 14 is 12 and 9, respectively, and using a liquid dynamic bearing, the magnetization of the permanent magnet 12 is changed with respect to FIG. The cogged torque and vibration noise were measured in each case by changing the skew angle θ in various ways with the skew magnetization magnetized as described above.

As a result, when the skew angle θ was 10 degrees, the vibration noise did not stop and the cogging torque became 1/20 or less as compared with the normal linear skew magnetization. However, when the skew angle θ exceeds 45 degrees, vibration noise starts to appear, and cogging torque having a frequency higher than the rotation frequency starts to be generated. Also, the skew angle θ
Is less than 3 degrees, the effect of suppressing the cogging torque is hardly observed.

According to the above-described electric motor 10, vibration noise is generated in the direction of the rotation axis only by changing the magnetization pattern of the permanent magnet without changing the shape of the component and without using a new component. Without this, the cogging torque can be reduced. Therefore, it has become possible to provide an inexpensive electric motor with less vibration noise, particularly a spindle motor.

In the above embodiment, the skew angles of the upper portion and the lower portion of the square region in the skew magnetization are the same, but the skew angles of both portions may be different. In the skew magnetization, the skew direction is set at a position (intermediate position) other than the magnetic center in the rotation axis direction.
May be reversed, and instead of a C shape, a C shape, that is, a horizontal U shape may be used.

In the above embodiment, instead of using a liquid dynamic pressure bearing, a gas dynamic pressure bearing such as air, a ball bearing,
Other bearings such as a roll bearing may be used. Instead of disposing the permanent magnet on the rotor and disposing the armature on the stator, the permanent magnet may be disposed on the stator and the armature may be disposed on the rotor.

The present invention is not limited to the above embodiment. For example, various grooves other than the above-described embodiment may be used as the dynamic pressure grooves, and the fluid dynamic bearing region may be formed at a location other than the above-described embodiment. Therefore, the present invention can be variously modified without departing from the gist thereof.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of an electric motor according to the present invention.

FIG. 2 is a perspective view showing one embodiment of a permanent magnet used in the electric motor shown in FIG.

FIG. 3 is a diagram showing an embodiment of a thrust dynamic pressure groove.

FIG. 4 is a development view showing a part of an embodiment of the radial dynamic pressure groove.

FIG. 5 is a perspective view showing an example of a permanent magnet used in a conventional electric motor.

[Explanation of symbols]

 Reference Signs List 10 electric motor (spindle motor) 12 permanent magnet 14 armature 16 stator 18 rotor 20 rotation axis 22, 24 magnetic pole part of permanent magnet 26 magnetic center of permanent magnet in rotation axis direction 36 shaft 40 ring 42 auxiliary member 44 recess 46, 48 Thrust dynamic pressure bearing area 50 Radial dynamic pressure bearing area 52, 54 Dynamic pressure groove 56 Hard disk

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[Procedure amendment]

[Submission date] July 15, 1999 (1999.7.1)
5)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0018

[Correction method] Change

[Correction contents]

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG.
Is a spindle motor that uses a short cylindrical or ring-shaped permanent magnet 12 and an armature 14 disposed inside the permanent magnet 12. The permanent magnet 12 is located on a rotor 18 and is rotated about an axis of rotation 20. Armature 14 is arranged on stator 16.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0025

[Correction method] Change

[Correction contents]

Both inner surfaces (upper and lower surfaces) of the recess 44 in the direction of the rotation axis 20 and corresponding two surfaces (upper and lower surfaces) of the ring 40.
Are defined as thrust dynamic pressure bearing regions 46 and 48, and between the inner bottom surface of the recess 44 and the outer peripheral surface of the ring 40 is defined as a radial dynamic pressure bearing region 50. These dynamic pressure bearing areas 46, 48, 50 are filled with a liquid such as lubricating oil.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0026

[Correction method] Change

[Correction contents]

A thrust dynamic pressure groove 52 as shown in FIG. 3 is formed on both inner surfaces of the recess 44 in the direction of the rotation axis 20 or on both corresponding surfaces of the ring 40. Further, a radial dynamic pressure groove 54 as shown in FIG. 4 is formed on the inner bottom surface of the recess 44 or the outer peripheral surface of the ring 40.

Continued on the front page (72) Inventor Atsushi Ota 1-8-1, Nakase, Mihama-ku, Chiba-shi, Chiba Inside Seiko Instruments Inc. (72) Inventor Koji Nitori 1-8-1, Nakase, Mihama-ku, Chiba-shi, Chiba Seiko Instruments Inc. In-house F-term (reference) 5H607 AA04 BB01 BB09 BB14 BB17 BB25 CC01 DD02 DD16 GG01 GG02 GG09 GG12 GG15 5H621 AA02 GA01 GA04 HH05 JK08 JK15 JK18 JK19 5H622 AA02 CA01 CA05 CB05 CB06 Q05 PP17

Claims (6)

[Claims] The present invention includes a permanent magnet disposed on one of a rotor and a stator, and an armature disposed on the other of the rotor and the stator, wherein the magnetization of the permanent magnet has a skew direction. It is a skew-shaped or C-shaped skew magnetization to be reversed at the magnetic center of the magnetization region in the rotation axis direction.
Electric motor. 2. The skew direction reversal position is a magnetic center of the magnetized region in the rotation axis direction.
The electric motor according to claim 1. 3. The electric motor according to claim 1, wherein an angle of the skew with respect to the rotation axis is 45 degrees or less. 4. The permanent magnet according to claim 1, wherein the permanent magnet has a short cylindrical shape having a magnetic pole surface on an inner peripheral surface thereof, and the armature is arranged inside the permanent magnet. Electric motor. And a shaft disposed on one of the rotor and the stator, and a fluid dynamic bearing region formed between the other of the rotor and the stator and the shaft. The electric motor according to claim 1. 6. A shaft disposed on one of the rotor and the stator, the shaft having a flange-like ring portion, and an annular opening on the side of the rotation axis for receiving the ring portion. A recess formed in the other of the rotor and the stator,
Between the inner surface of the recess and the surface of the ring portion in the direction of the rotation axis is a thrust hydrodynamic bearing region,
The electric motor according to any one of claims 1 to 5, wherein a portion between an outer peripheral surface of the ring portion and an inner bottom surface of the recess is a radial dynamic pressure bearing region.