JPH0798928A - Spindle motor - Google Patents

Abstract

PURPOSE:To obtain a small-sized spindle motor which is used for disk rotary driving on an HDD equipment in an OA field and which does not have difficulty in reading and writing on a magnetic disk. CONSTITUTION:This motor has a hub 1 mounting the magnetic disk and rotating, two ball bearings 2 rotatably bearing the hub, and a fixed shaft 3a supporting the ball bearings 2; the hub and the fixed shaft are constituted of members having different coefficients of thermal expansion; and a counter bore part 12 having an aperture part on an inside diameter side and a counter bore part 14 opening outward are provided in the hub. Thus, the spindle motor in which preload caused by the temperature change of the ball bearing can be constant, and which does not have difficulty in reading and writing on the magnetic disk can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spindle motor mainly used in a magnetic disk drive device.

[0002]

2. Description of the Related Art In recent years, HDD devices in the field of office automation have been increasing in density, and spindle motors (hereinafter abbreviated as motors) for rotating disks are required to have extremely stable rotation accuracy at the same time. , That level is getting tougher year by year.

The structure of a conventional motor will be described below with reference to FIG. As shown in the figure, there are two ball bearings 2 that allow the hub 1 to rotate, and the ball bearings 2 are supported by a fixed shaft 3a. A yoke 4 is installed on the inner surface of the hub 1 so as to face the fixed shaft 3 a, and a magnet 5 is installed on the inner surface of the yoke 4. The fixed shaft 3a supports the stator core 6, and the Hall element 7 detects the position of the rotary hub 1. There are two magnetic fluid seals 8 at both ends of the hub 1, one of which is supported by a magnetic fluid holder 9. The reinforcing plate 10a is installed on the outer surface of the fixed shaft 3a, and the reinforcing plate 10a supports the printed wiring board 11,
The motor is supported by being clamped in the disk enclosure 13.

[0004]

[Problems to be Solved by the Invention]

(1) In such a conventional motor, since the members of the hub 1 and the fixed shaft 3a are different and the coefficients of thermal expansion are different, the ball bearing 2 connecting the hub 1 and the fixed shaft 3a is deformed by the temperature and the ball bearing. Since the preload acting on No. 2 cannot be made constant, the support rigidity of the magnetic disk may change, and reading and writing may not be performed normally.

(2) Also, the fixed shaft 3a and the reinforcing plate 1
Since a step is formed at the joint portion of 0a, the dimension L between the printed wiring board 11 and the disk enclosure 13 cannot be reduced. Therefore, there is a problem in that the reliability of the strength of the bonded portion is lacking.

The present invention solves the above-mentioned problems, and prevents the change in the supporting rigidity of the hub 1 by keeping the preload acting on the ball bearing 2 constant, and is small in size and highly reliable without obstructing reading and writing of the magnetic disk. The purpose is to provide a motor.

[0007]

In order to achieve the above object, a spindle motor according to the present invention has a hub inner diameter between an outer peripheral portion of a magnetic disk mounting side ball bearing and a hub outer peripheral portion corresponding to the outer peripheral portion of the ball bearing. Reinforced on the inner surface of the hollow cylindrical part of the fixed shaft, with a counterbore part that opens to the side, and a counterbore part between the outer peripheral part of this ball bearing and the hub holding part that holds this ball bearing. It has a configuration in which a joint portion with a plate is provided.

[0008]

According to this structure, the change in the hub ball bearing support rigidity caused by the difference in the coefficient of thermal expansion between the hub and the fixed shaft made of different materials is transferred to the deformation of the thin bearing holding portion of the hub. By eliminating it relatively, the preload acting on the ball bearing is made constant, and as a result, reading and writing from and to the magnetoelectric disk can be performed normally.

Further, by providing the joint portion with the reinforcing plate on the inner surface of the fixed shaft, there is no step between the outer surface of the fixed shaft and the reinforcing plate, and as a result, the cylinder which is the joint portion of the reinforcing plate to the disk enclosure. The influence of the shaped portion is eliminated, and the dimension L between the printed wiring board and the disk enclosure can be reduced.

Further, since the cylindrical portion which is the joint portion of the reinforcing plate is inside the fixed shaft, it is not affected by the disk enclosure, and therefore the cylindrical portion which is the joint portion of the reinforcing plate is lengthened. This makes it possible to increase the joint strength between the fixed shaft and the reinforcing plate.

[0011]

【Example】

(Embodiment 1) An embodiment of the present invention will be described below with reference to FIG.

As shown in the figure, the hub 1 rotatably supported by two ball bearings 2 is made of aluminum and corresponds to the outer peripheral portion of the magnetic disk mounting side ball bearing 2 and the outer peripheral portion thereof. A counterbore 12 having a structure having a thin wall portion with the outer peripheral portion of the hub 1, and a counterbore provided between the outer peripheral portion of the ball bearing 2 and a part of the ball bearing holding portion of the hub 1. Each section 14 is provided. On the inner surface of the hub 1,
A yoke 4 that supports the other ball bearing 2 and a magnet 5 are installed on the inner surface of the yoke 4.

A fixed shaft 3a made of iron supports a stator core 6 and a Hall element 7. A magnetic fluid seal 8 and a magnetic fluid holder 9 are provided at the end of the hub 1. Reference numeral 10a is a reinforcing plate, 11 is a printed wiring board, and 13 is a disk enclosure.

The characteristics of the preload of the motor according to the present embodiment and the preload of the conventional motor are shown in FIG. 4 by comparing their characteristics with respect to temperature. In FIG. 4, the preload applied to the ball bearing 2 at room temperature (23 degrees) is taken as a reference value, and the change of the preload with temperature is shown by the ratio of the preload to the reference value.

As is apparent from FIG. 4, the preload applied to the ball bearing 2 according to this embodiment has an excellent effect in that it is stable against temperature changes.

As described above, according to this embodiment, the counterbore portion 12 is provided on the support portion of the hub 1 supported by the ball bearing 2, and the counterbore portion is provided between the ball bearing 2 and the ball bearing holding portion. By using the portion 14, a bearing holding portion having a structure having a thin wall portion is provided, and the preload acting on the ball bearing 2 is made constant with respect to temperature change to prevent displacement of the hub 1 due to temperature change. It is possible to provide a motor that does not hinder reading and writing of a magnetic disk over the entire temperature range.

(Second Embodiment) A second embodiment of the present invention will be described below with reference to the drawings.

2 is different from that of FIG. 1 in that the joint between the fixed shaft 3a and the reinforcing plate 11a in FIG.
This is the point that supported 0b.

As described above, by providing the joint portion with the reinforcing plate 10b on the inner surface of the hollow cylindrical portion of the fixed shaft 3b, there is no step between the outer surface of the fixed shaft 3b and the reinforcing plate 10b, and the printed wiring board 11 and The dimension L of the disk enclosure 13 can be reduced. Further, since the length of the joint portion between the reinforcing plate 10b and the fixed shaft 3b can be sufficiently secured, the strength of the joint portion can be increased, and the reliability of the joint strength can be improved.

In the first embodiment, the fixed shaft 3a is made of different materials such as iron and the hub 1 is made of aluminum, but the fixed shaft 3a and the hub 1 are made of the same material having different thermal expansion coefficients. It may be. Further, the materials of the fixed shaft 3a and the hub 1 are not limited to the above-mentioned two materials, and can be applied to all materials having different thermal expansion coefficients.

[0021]

As is apparent from the above-described embodiments, the present invention provides the hub with the counterbore to stabilize the preload applied to the ball bearing against temperature changes, and also to fix the hollow of the fixed shaft. By providing the joint portion with the reinforcing plate on the inner surface of the cylindrical portion, it is possible to provide a motor having a small length dimension and capable of normally reading and writing to the magnetic disk.

[Brief description of drawings]

FIG. 1 is a vertical sectional side view of a spindle motor according to a first embodiment of the present invention.

FIG. 2 is a vertical sectional side view of a spindle motor according to a second embodiment of the present invention.

FIG. 3 is a vertical sectional side view of a conventional spindle motor.

FIG. 4 is a characteristic diagram showing a preload against temperature of a spindle motor in one embodiment of the present invention in comparison with a preload in a conventional spindle motor.

[Explanation of symbols]

 1 Hub 2 Ball Bearing 3a, 3b Fixed Shaft 4 Yoke 5 Magnet 6 Stator Core 7 Hall Element 8 Magnetic Fluid Seal 9 Magnetic Fluid Holder 10a, 10b Reinforcing Plate 11 Printed Wiring Board 12, 14 Counterbore 13 Disk Enclosure

Claims (3)

[Claims] 1. A spindle motor having a cylindrical hub for mounting and rotating a magnetic disk, two ball bearings for rotatably supporting the hub, and a fixed shaft for supporting the ball bearing, comprising: A spindle motor characterized in that a counterbore portion that opens toward the inner diameter side of the hub is provided between the outer peripheral portion of the mounting side ball bearing and the outer peripheral portion of the hub corresponding to the outer peripheral portion of the ball bearing. 2. A counterbore opening to the outside of the hub is provided between an outer peripheral portion of a mounting side ball bearing of the magnetic disk and a holding portion of a hub that holds the ball bearing. The spindle motor according to claim 1. 3. A hub which carries a magnetic disk and rotates,
Two ball bearings that rotatably support the hub, a fixed shaft that supports the ball bearings and has a hollow cylindrical portion, a reinforcing plate that is fixed on the inner surface of the hollow portion of the fixed shaft, and the reinforcing plate. Spindle motor with fixed printed wiring board.