JP2856027B2 - Spindle motor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic disk drive, an optical disk drive, a floppy disk drive, a cylinder motor of a video tape recorder, and a holgon mirror motor of a laser beam printer.

[0002]

2. Description of the Related Art A demand for a magnetic disk drive has become smaller and smaller due to an increase in speed and downsizing of a computer main body, and an increase in size and complexity of software used for handling image information.
Large-capacity, high-speed transfer is required.
Correspondingly, the spindle motor has a small size, low vibration,
High speed rotation and long life are required. As one measure against these requirements, it has been studied to replace the conventional ball bearing with a plain bearing.

FIG. 5 shows a conventional example of a spindle motor using a sliding bearing. The shaft is fixed to a base, and two radial dynamic pressure grooves are formed in the shaft, and this serves as a bearing. Lubricating oil is injected between the hub and the radial bearing. The rotation of the hub rotates toward the wide side of the dynamic pressure groove (from left to right in FIG. 2). As a result, a large dynamic pressure is generated in the groove, and the hub is rotatably supported without contacting the shaft. In the thrust bearing, a spiral dynamic pressure groove is formed on the hub side facing the end opposite to the fixed end of the shaft, and like the radial part, this part generates a large dynamic pressure with rotation and the hub Is supported in a non-contact manner. The hub is provided with a magnet, and the fixed portion is provided with a stator coil in opposition thereto. The magnet and the stator coil form a motor, and rotate the rotary body by supplying a drive current to the stator coil.

[0004] In the radial and thrust sliding bearings, asynchronous vibrations due to ball passing vibrations and the like which are inevitable in ball bearings do not occur in principle. Further, since the lubricating oil has a large damping property, high-speed rotation with low vibration is possible.

Examples of the prior art include JP-A-2-168465 and JP-A-4-98653.

[0006]

The rigidity of a sliding bearing is determined by the viscosity of a lubricating medium, the peripheral speed, the gap ratio, and the like. These values are related to the load and cannot be specified unconditionally. When the load is equalized as compared with the bearing, the bearing stiffness of the slide bearing is reduced as compared with the ball bearing.
If the viscosity of the lubricating medium is increased and the gap ratio is reduced, the rigidity can be increased, but this time, a problem occurs in that the load increases. This problem of a decrease in rigidity and an increase in load is particularly noticeable when the disk is mounted on a small magnetic disk of 3.5 inches or less because its diameter is small and its peripheral speed is reduced. If the stiffness is low, when a vibrating force is applied to the rotating system, the gyro effect causes remarkable swinging of the magnetic disk, and the magnetic head is not correctly positioned with respect to the magnetic disk, so that accurate reading and writing of information becomes impossible.

With reference to FIG. 6, a description will be given of the generation of a swing vibration due to the gyro effect when a vibrating force is applied to a rotating system according to the prior art. If the disturbance excitation force F is applied to the rotating body, it may be considered that this force acts on the rotational center of gravity. If the center of gravity is not in the middle of the two radial bearings but in the position shown in the figure as in the prior art, each bearing k
1, k2 have the following displacements X1, X2.

[0008]

X1 = F × L2 / (L1 + L2) / K1 (Equation 1) X2 = F × L1 / (L1 + L2) / K2 In the case of the prior art, since X1 ≠ X2, the z-axis as in the following equation is obtained. A surrounding fall θ is generated.

[0009]

## EQU00002 ## .theta. = TAN-1 ((X1-X2) / (L1 + L2)) (Equation 2) Since F is a fluctuating force, .theta. Also has an angular velocity that fluctuates with time. A gyro moment L is generated around the Y axis by the angular velocity in the rotating body, and its magnitude is represented by the following equation, where the inertia moment I around the X axis and the rotational angular velocity are ω.

[0010]

L = I × ω × (dθ / dt) (Equation 3) In the case of a sliding bearing, since the bearing rigidity is lower than that of a ball bearing, the gyro moment causes a large swing motion of the magnetic disk. Might do it.

The exciting force may be an electromagnetic exciting force of a motor. In an ideal motor, the electromagnetic force should produce only rotational torque and no exciting force on the shaft. However, in actuality, an oscillating force is generated on the shaft due to eccentricity or shape error of the shaft, the stator, and the magnet. As shown in FIG. 7, when the center of the stator coil and the center of the magnet are eccentric, both the normal force vector and the tangential force vector, which should be originally balanced, are out of balance.
A force F is applied to the axis as the sum of each residual vector F1 and F2. This force F has a frequency of the number of magnet poles times the number of rotations. Considering that this force F acts at the center of the magnetic flux formed by the magnet and the stator coil, if the center of gravity and the magnetic center are shifted in the axial direction as in the related art, a rotational moment is generated around the center of gravity. Since this gives a certain angular velocity to the rotating body, a gyro moment is generated as in the case of the above-mentioned disturbance, which causes the magnetic disk to swing.

[0012]

According to the present invention, the position of the center of gravity of the rotating body is made to coincide with the position exactly between the two radial bearings. Further, the magnetic center position of the motor stator and the magnet is made to coincide with the center of gravity, and is made to coincide with the just intermediate position between the two radial bearings.

Alternatively, the position of the center of gravity or the matched center of gravity and the magnetic center position are arranged between the two radial bearings, and when a force is applied to this position, the two radial bearings have the same displacement. Set each spring stiffness so as to be as follows.

[0014]

According to the present invention, the position of the center of gravity of the rotating body, the position of the radial bearing, and the spring constant of the bearing are defined so that x1 = x2 in the equation (1). Even if it is added, the falling θ does not occur. Accordingly, no angular velocity is applied to the rotating body, and the accompanying gyro oscillation does not occur. Further, by defining the radial bearing position and the bearing rigidity so that the magnetic center and the center of gravity coincide with each other and satisfy the above-described conditions, the magnetic excitation force does not become a factor for generating a gyro force on the rotating body. Therefore, stable rotation can be realized even when a low-rigidity sliding bearing is used at high speed.

[0015]

FIG. 1 shows a first embodiment of the present invention.
In this embodiment, a 2.5-inch magnetic disk drive is assumed. The inner diameter of the magnetic disk 1 is 20 mm and the outer diameter is 65 mm. In the present embodiment, three of these are laminated. 3600 rpm
from 7200 rpm to 7200 rpm and a bearing life of 5000
It is assumed that it will be used continuously for more than 0 hours. Three magnetic disks 1 are stacked on a hub 10 via a spacer, and are fixed by a clamp 3 so as not to cause slippage during rotation. The shaft 2 is attached to the center of the hub 10 with an accurate verticality by a method such as press fitting or bonding. The shaft 2 has a lubricating medium injection hole. This hole is sealed after injection of the lubricating medium. On the inner surface of the hub 10, a cylindrical magnet 9 is attached, and several magnetic poles are formed. A stator coil 5 is formed on the bracket 6 so as to face the magnet 9, and a rotating body is driven by applying a drive current to the stator coil 5. The position of the stator coil 5 and the magnet 9 is such that the axial center of the magnetic flux formed by the stator coil 5 and the magnet 9 substantially coincides with the center of gravity of the rotating body formed by the magnetic disk 1, the hub 10, the magnet 9 and the shaft 2. Has been determined. A radial bearing bracket 14 is provided on the back surface of the stator coil 5, and radial sliding bearing surfaces 11 are formed at two upper and lower portions of the bracket 14 facing the shaft 2. This bearing 11
Is lubricated with lubricating oil or a magnetic fluid as a lubricating medium, and supports the shaft 2 by dynamic pressure generated as the shaft 2 rotates. The overall arrangement is determined so that the rotational center-of-gravity position 13 and the magnetic center position 18 are located exactly at the center of the two radial bearings 11. As a result, stable rotation can be realized even with respect to external vibration or imbalance of magnetic force. By providing a dynamic pressure groove in one or both of the bearing portions formed by the shaft 2 and the bearing bracket, the dynamic pressure can be increased and the bearing rigidity can be increased. A thrust bearing bracket 4 is provided at an end of the shaft 2 opposite to the hub 10 and a portion opposing the end, and forms a thrust bearing 16 between the shaft 2 and the end. Lubricating oil or magnetic fluid that is the same as or different from that of the radial bearing 11 is injected into the bearing 16, and the thrust load is supported by an oil film generated with rotation. Also in this part, a dynamic pressure groove can be formed on both or one of them to increase the shaft rigidity. It is also conceivable to reduce the friction torque by making the end of the shaft 2 or the bracket portion 4 spherical. At the end of the radial bearing bracket 14, a magnetic fluid seal 8 is provided.
This prevents the lubricating medium in the bearing from leaking to the outside. The magnetic fluid seal 8 is removed when the amount of leakage is small or when it is determined that the leakage medium does not deteriorate the performance of the magnetic disk 1. A thrust preload magnet 12 is provided behind the thrust bearing bracket 4 so as to magnetically attract the shaft 2 and apply a preload in the axial direction. This prevents the rotating body from coming off. As a preloading method, there is a method in which the center of the magnetic flux in the axial direction by the stator coil 5 and the center of the magnetic flux of the magnet 9 are slightly shifted from each other so that the magnetic attraction is applied in the thrust preload direction. In this case, the above-mentioned thrust preload magnet 12 becomes unnecessary.

FIG. 2 shows a second embodiment of the present invention. The present invention also assumes a 2.5 inch magnetic disk as in the case of the first embodiment. In the case of the present invention, the shaft 2 is fixed to the bracket 14, and contrary to the first embodiment, the radial bearing bracket 14 is fixed to the hub 10 and rotates. A radial dynamic pressure bearing 11 is formed between the bracket 14 and the shaft 2, and supports the rotating body in the radial direction. The center of gravity 1 of the entire rotating body such as the magnetic disk 1 and the hub 10
3 coincides with the center of magnetic flux 18 formed by the stator coil 5 and the magnet 9, and this corresponds to the radial bearing 11.
, And can rotate stably even when disturbance force and imbalance force of electromagnetic force act. At the end of the shaft 2 is a thrust disk 17 slightly larger in diameter than the shaft 2.
A dynamic pressure groove is formed on both surfaces of the thrust disk 17 so that a dynamic pressure is generated with rotation and the rotating body is supported in the thrust direction. The thrust dynamic pressure grooves may be formed on one or both surfaces of the thrust bearing bracket 4 and the radial bearing bracket 14 that oppose the thrust disk 17. According to this configuration, since the thrust disk 17 that is larger than the shaft 2 is provided, the hub 10 does not fall off even when stationary. Further, since the lubricating medium is held in a double cylindrical gap formed by the shaft 2, the bearing bracket 14, and the stator coil 5, the structure is less likely to leak. Also in this configuration, a magnetic fluid seal may be provided at the end of the bracket 14 or the end of the stator coil 5 to completely seal the leakage.

FIG. 3 shows a third embodiment of the present invention. This embodiment assumes a 1.8-inch magnetic disk. A 1.8-inch magnetic disk cannot form a motor in the hub 10. Therefore, the motor is formed at the lower end of the hub 10. The magnetic disks 1 are stacked and fixed to the hub 10 by clamps 3 via spacers 7. The shaft 2 is fixed to the hub 10 and rotates together with the hub 10. A bearing bracket 14 is formed integrally with the bracket 6. A dynamic pressure radial bearing 11 is formed on a surface of the bearing bracket 14 facing the shaft 2. The center of gravity 13 of the rotating body formed by the magnetic disk 1, the spacer 7, the hub 10, and the like.
The intermediate positions of the two radial bearings 11 are configured to substantially coincide with each other. Thereby, even when disturbance vibration is applied to the rotating system, stable rotation is compensated. At the lower end of the hub 10, a magnetic fluid seal 8 is provided.
The structure is such that the leakage of the lubricating medium in the bearing portion is stopped.
A dynamic pressure groove is formed on at least one of the end of the shaft 2 and the thrust bracket 4. Alternatively, either one is configured as a spherical surface and supports a thrust load. The preloading method in the thrust direction is the same as in the first embodiment, in which the end of the shaft 2 is magnetically attracted, and the motor stator 5 and the magnet 9 are used.
Can be considered.

FIG. 4 shows a fourth embodiment of the present invention. In this embodiment, the shaft 2 is fixed to the bracket 6, and the hub 10 and the bearing bracket 14 are integrally formed and rotate. A dynamic pressure bearing 11 is formed on a surface of the bearing bracket 14 opposite to the shaft 2 to support the rotating body. A thrust disk 17 is provided at the end of the shaft 2, and forms a thrust bearing 16 with the brackets 4 and 14. The stator coil 5 and the magnet 9 form a flat type motor. By making the motor a flat type, the overall height of the spindle motor can be reduced as compared with the conventional one. In this embodiment, the sealing effect of the lubricating medium is enhanced by making the motor coil stator 18 higher than the coil surface and forming an overlap with the bearing bracket 14. In the case of the flat motor type, since the magnetic flux is directed in the axial direction, there is no need to particularly consider the preload in the thrust direction.

FIG. 8 shows a fifth embodiment of the present invention. In this embodiment, the hub 9 is attached to the hub 10 such that the center of the magnet 9 is located at the axially intermediate position (the position of the second magnetic disk in FIG. 8) of the stacked magnetic disks 1.
Attach. A motor stator coil 18 is provided to oppose the magnet 9. Further, the intermediate position in the axial direction of the stacked magnetic disks 1 and the intermediate position of the two radial bearings 11 are matched. The magnetic seal 8 is formed below the stator coil 5 to prevent leakage of the bearing lubrication medium. It is considered that the hub 10 and the magnet 9 are cylindrical and each center of gravity 13 is located substantially at the center thereof. Since the intervals between the magnetic disks 1 are generally arranged at a constant value, the center of gravity position 13 can be considered to be substantially at the middle position of the magnetic disk by configuring as in this embodiment. Further, since the axial center 18 of the magnetic flux formed by the motor stator coil 18 and the magnet 9 coincides with the axial center of the magnet 9, the configuration according to the present invention provides the center of gravity 13.
And the center of the magnetic flux in the axial direction can be easily matched with each other, and can also be matched with the middle of the bearing. Thus, even when a disturbance exciting force or an electromagnetic exciting force is applied to the rotating body, no rotational moment is generated, and no whirling vibration is generated by the gyro. In the present invention, the shaft 2 is configured to rotate together with the hub 10, but as shown in FIG.
Even in a configuration in which the hub 10 is fixed to the bracket 6, the same effect can be obtained by installing the hub 10, the magnetic disk 1, the magnet 9, and the stator coil 5.

In each of the above embodiments, it is assumed that the center of gravity 13 or the center of gravity 13 and the magnetic flux center 18 can coincide with the middle between two radial bearings 11 having the same rigidity.
Due to the required size of the stator coil 5 and the magnet 9 due to a demand for the motor torque or the like, there may be a case where they cannot be matched. In this case, as shown in Equation 2, by increasing the rigidity of the center of gravity 13 or the bearing 11 where the center of gravity 13 and the magnetic flux center 18 are closer to each other than the other bearing rigidity, and balancing the moment around the center of gravity,
Even when disturbance vibrations or electromagnetic vibrations are applied, the gyro does not swing, and the same effect as that of the embodiment can be obtained.

In the above embodiment, the center of gravity 13 and the magnetic flux center 1
8. It was considered that the bearing can be set at an arbitrary position of the dual bearing 11. Further, it was assumed that the rigidity of the bearing 11 could be completely set. However, in the actual case, the conditions cannot be completely satisfied due to manufacturing errors, assemblability, required torque of the motor, and the like. As can be seen from Equations (1) and (2), since each condition is proportionally related to the gyro moment, an effect can be expected if it is configured to be within approximately 10%.

Although the first, second and fifth embodiments assume a spindle motor for a 2.5 inch magnetic disk, this embodiment is also applicable to a 3.5 inch magnetic disk. it can. Further, if a motor can be constructed, it can be applied to a spindle motor for a magnetic disk of 1.8 inches or less. In the third and fourth embodiments, a 1.8-inch magnetic disk spindle motor is assumed, but this configuration can also be applied to a 1.8-inch or smaller magnetic disk spindle motor. Also, this configuration can be applied to 2.5 inch and 3.5 inch magnetic disks.

The above embodiment is not limited to a magnetic disk drive, but can be applied to an optical disk drive, a floppy disk drive, a cylinder motor of a video tape recorder, and a holgon mirror motor of a laser beam printer.

[0024]

According to the present invention, stable rotation can be maintained even when disturbance or magnetic imbalance exists in the small magnetic disk.

[Brief description of the drawings]

FIG. 1 is a sectional view of a first embodiment of the present invention.

FIG. 2 is a sectional view of a second embodiment of the present invention.

FIG. 3 is a sectional view of a third embodiment of the present invention.

FIG. 4 is a sectional view of a fourth embodiment of the present invention.

FIG. 5 is a sectional view of an embodiment of the prior art.

FIG. 6 is an explanatory diagram 1 of a conventional problem.

FIG. 7 is an explanatory view 2 of a conventional problem.

FIG. 8 is a sectional view of a fifth embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Magnetic disk, 2 ... Shaft, 3 ... Clamp, 4 ...
Thrust bearing bracket, 5: stator coil, 6: bracket, 7: spacer, 8: magnetic fluid seal, 9: magnet, 10: hub, 11: radial bearing, 12: thrust preload magnet, 13: center of gravity, 14: bearing bracket , 15: oil injection hole, 17: thrust disk, 18: magnetic center.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tomoaki Inoue 502, Kandate-cho, Tsuchiura-shi, Ibaraki Pref. Machinery Research Laboratory, Hitachi, Ltd. In-house (72) Inventor Hideaki Amano 2880 Kozu, Odawara-shi, Kanagawa Prefecture Hitachi, Ltd. Storage Systems Division (56) References JP-A-2-168465 (JP, A) JP-A-59-67844 (JP, A) JP-A-4-18511 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H02K 7/08

Claims (3)

(57) [Claims] 1. A hub having one or more magnetic disks having a diameter of 3.5 inches or less laminated, a shaft providing a center of rotation, and a motor stator and a hub provided on a fixed portion for driving these rotating members. A rotating magnet and two radial bearings and a thrust bearing utilizing gas or liquid dynamic pressure to support the rotating body are used, and the center of gravity of the rotating body is located between the two radial bearings. A radial bearing closer to the position of the center of gravity, the rigidity of which is greater than the rigidity of the other bearing. 2. The apparatus according to claim 1, wherein said motor stator is formed on an inner back surface of said radial bearing, and a center position of a magnetic flux formed by said motor stator and said magnet substantially coincides with said center of gravity. Spindle motor. 3. The spindle motor according to claim 1, wherein said motor magnet is provided at a lower end of a hub, and a magnetic seal is provided between said thrust and radial bearing and said motor magnet. A spindle motor.