JPH03313A - Bearing unit - Google Patents

Abstract

PURPOSE:To allow a period of shaft deflection, due to the revolving movement of a rolling element and the unbalanced centrifugal force acting on a supporting shaft to coincide with one rotation of a shaft, by setting a ratio of the turning angular velocity of the shaft to the revolving angular velocity of a rolling element turning and revolving when the shaft is rotated. CONSTITUTION:Balls of n in quantity, for example, six balls 181 to 186, are arranged between inner and outer rings 16 and 17 at equal intervals. When the outer diameter of the inner ring 16 is assumed R1, the diameter of the balls 181 to 186 is assumed Rb, and the inner diameter R2 of the outer ring 17 is assumed R2, these dimensions are so that a ratio of the turning angular velocity omegas of a shaft 20 to the revolving angular velocity omegaB of the balls 181 to 186 may be omegas:omegaB=n:m (m is an integer smaller than n). Accordingly, when the shaft 20 is rotated by one turn, the arrangement condition of a rolling element viewed at a specified position is the same as that before one rotation is started. Thus, the same deflection mode of the shaft is repeated for each shaft rotation and its period coincides with one rotation of the shaft.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a bearing device including a plurality of rolling elements provided between an outer ring and an inner ring.

(Prior Art) For example, in a hard disk drive motor, the shaft of a rotor to which a hard disk is attached is supported by a ball bearing. These ball bearings are made with small asynchronous runout (runout that is not synchronized with rotation), with minimal variations in the sphericity of the balls serving as rolling elements and the curvature of both the inner and outer wheels. No equivalent consideration was given to the orbital speed.

By the way, in a hard disk drive motor, the rotational speed of the rotor is as high as about 3600 rpra, so when a disk is attached, even if the unbalanced load is minute, the minute unbalanced load causes local centrifugation. A large portion of the force is generated, and the centrifugal force causes a small displacement (runout) of the bearing and thus the rotor (disc). There is a difference in the minute displacement of the bearing between when the ball, which revolves as the rotor rotates, is located in the direction of action of this centrifugal force and when it is not, which causes asynchronous runout. The amount of this asynchronous runout is about 0.2μ.

The above-mentioned asynchronous runout will be explained with reference to FIG. FIG. 6 shows an example in which the number of balls is six, and the outer ring 1 is attached to the housing, and the inner ring 2 is attached to the shaft of the rotor. In this bearing, the rotational angular velocity ωS of the shaft and the balls 3 that revolve while rotating on their own axis as the shaft rotates.
The ratio of revolution angular velocity ω8 of 1 to 36 is ω5:ωB of 6:2.
．． 5. Under this condition, the sixth
Figure 6(a) shows the case where the ball 31 is located in the direction where a locally large centrifugal force Fv acts, and Figures 6(b) to 6(d) show a 1/4 rotation from the state of Figure 6(a). The states of 1/2 rotation and 1 rotation are shown, respectively. As is clear from FIG. 6, it is not possible to obtain a state in which any of the balls 3□ to 36 is located at point A when the inner ring 2 rotates once.

FIG. 7 shows the results of measuring the amount of displacement (runout) of the bearing at point A in FIG. 6. In this FIG. 7, the curve Va
indicates the displacement due to the revolution of the balls 2□ to 26, the curve vb indicates the displacement due to the centrifugal force, and the curve Vc indicates the combined displacement of the biconvex lines Va and vb, and this combined displacement appears as asynchronous runout of the bearing. As is clear from this curve Vc, ωB:
When ω8 has a relationship of 6:2.5, the asynchronous runout is in a mode in which one cycle is two rotations of the rotor.

For example, if an asynchronous runout occurs that repeats the same mode every two rotations of the rotor, the trajectory T of the magnetic head with respect to the disk 4 will be different for each adjacent track, as shown in FIG. 8, which will hinder reading and writing. Come.

(Problems to be Solved by the Invention) As mentioned above, in conventional bearing devices, the orbital angular velocity of the balls is not equally taken into account, and therefore the rotational velocity of the balls is caused by the unbalanced centrifugal force acting on the orbital motion of the rolling elements and the supporting shaft. The mode of vibration differs for each rotation, and when used as a bearing device for a motor for driving a hard disk, for example, a problem arises in that the locus of the magnetic head relative to the disk differs for each track.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a bearing device in which the period of runout caused by the revolving motion of rolling elements and the unbalanced centrifugal force acting on a supporting shaft can be made to coincide with one revolution of the shaft, resulting in synchronous runout. There is something to do.

[Structure of the Invention (Means for Solving the Problems) The bearing device of the present invention includes n rolling elements provided between an outer ring and an inner ring, one of the inner and outer rings is attached to a housing, and the other is attached to a housing. In a device that is attached to a shaft, the ratio ωS of the rotational angular velocity ω5 of the shaft to the revolution angular velocity ωB of the rolling element that revolves while rotating as the shaft rotates: ωB is ω
B:ωB=n:m (m is an integer smaller than n).

(Function) Ratio ω of the rotational angular velocity of the shaft ωS and the revolution angular velocity ω8 of the rolling elements
Since S=ωB is set to n:m, when the shaft makes one rotation, the arrangement of the rolling elements seen at a fixed point becomes the same arrangement as at the start of that one rotation. For this reason, the runout mode repeats the same mode every rotation of the shaft,
The period becomes equal to one revolution of the axis.

(Example) An example of the present invention applied to a bearing device for a hard disk drive motor will be described below with reference to FIGS. 1 to 5.

First, the overall structure of the hard disk drive motor is as shown in FIG.
A stator 14 having a coil 13 wound thereon is fitted and fixed.

On the other hand, inside the sleeve 12, two ball bearings 15 serving as a bearing device according to the present invention are arranged at intervals in the axial direction. This ball bearing 15 is made up of balls 18 as rolling elements arranged between an inner ring 16 and an outer ring 17. They are fitted and attached so that the shaft 20 rotates integrally with the inner ring 16. Further, a spring 21 is provided between the sleeve 12 and the inner ring 16 of the upper ball bearing 15, and this spring 21 urges the inner ring 16 of both ball bearings 15 upward, giving a so-called preload. is in a state. A hub 22 surrounding the stator 14 is fixed to the upper end of the shaft 20.
A rotor yoke 24 having a rotor magnet 23 on the inner periphery of the rotor yoke 2 is fitted and fixed. And the above /% b22
A hard disk 25 (see FIG. 5) is fixed to the outside of the disk.

Now, in the ball bearing 15, n balls 18 are arranged at equal intervals between the inner and outer wheels 16 and 17, but in this embodiment, as shown in FIG.
For example, six balls 181 to 186 are arranged at equal angular intervals of 60 degrees and held by a holder (not shown).

These balls 181 to 186 are connected to the inner ring 16 and the shaft 20.
It revolves while rotating as the inner ring 16 rotates, but now the inner ring 16
The outer diameter of the ball is R1, the diameter of the balls 18□~186 is R11,
When the inner diameter of the outer ring 17 is R2, these dimensions are determined by the rotational angular velocity ω5 of the shaft 20 and the balls 18. The ratio of ~186 to the orbital angular velocity ωB is ω5 :ωB−n:m [where m is an integer smaller than n]
......(1) It is set so that.

That is, the revolution angular velocity ω3 of the balls 18□ to 186 is (IJB − [Rt / CR1+R2) ] ×lu
Since gs ++ is expressed as (2), the above equation (1) is ws : ωB 禦(R, +R2) : R, -n : m...
...(3) becomes. Therefore, from R,-(R2-R1)/2, while considering the diameter R1 of the balls 181 to 186, ωS:
R1 and R2 are appropriately set so that ωB −(R1+R2) : Rt −n :m.

In this embodiment, R2H2 and Rb are set to m-2 for the number n-6 of balls 18□ to 186.

By the way, in ball bearings, the radius r is generally from the center of the inner ring 16 to the centers of the balls 181 to 186. and ball 18. Since it is represented by the radius r of ~186, the above (3
) expression r. and radius r, it becomes ωS :ωe""(ro rb):2ro-n:m.

Next, the operation of the above structure will be explained with reference to FIG.

First, it is assumed that the shaft 20 (inner ring 16) is rotating in a counterclockwise direction, and that a large centrifugal force acting locally due to an unbalanced load is acting at a position indicated by Fv. Now, in Fig. 1(a), the centrifugal force Fv is
This figure shows the state in which it is acting on position 1, and (b) and (c)
) and (d) show states in which the shaft 20 has rotated 1/4, 1/2, and 1 turn from the state shown in (a) of the figure. In this embodiment, ωS is set to ωB-6:2, so ωS:ω
a=6:2-360:120. This means that the balls 181 to 186 revolve 120 degrees while the shaft 20 rotates 360 degrees, that is, one rotation. Therefore, in FIG. 1(b) where the shaft 20 has rotated 1/4, the balls 181 to 186 have revolved 30 degrees, and the shaft 20 has rotated 1/2
In the rotated state of FIG. 1(c), the balls 18, ~186
The balls 181 to 186 revolve by 120 degrees in the state shown in FIG. 1(d) in which the shaft 20 rotates once. Since the balls 18□ to 186 are arranged at equal angular intervals of 60 degrees, when viewed from a fixed point indicated by A in FIG.
are in the same arrangement state (the same state is achieved even with a 1/2 rotation of the shaft 20).

In such a device, when the displacement at the position indicated by A in FIG. 1 is measured, the result is as shown in FIG. 2. In this FIG. 2, the curve Va is the ball 18. 186, the curve vb shows the displacement due to the centrifugal force Fv, and the curve Vc shows the combined displacement of both circuits Va and vb.

However, in the case of this embodiment, as is clear from the curve Vc, the resultant displacement is in the same mode for each rotation of the shaft 20, and the displacement eventually becomes a synchronous movement that is synchronized with the rotation of the shaft 20. Therefore, as shown in FIG. 5, the trajectory T of the magnetic head with respect to the disk 25 becomes parallel between the tracks, making it possible to prevent as much as possible any hindrance to reading and writing.

In the above embodiment, the number of balls has been described as six, but the number is not limited to this, and it goes without saying that the value of m is not limited to two.

In addition, the present invention is not limited to the embodiments described above and shown in the drawings, and can be widely applied, for example, not only to bearing devices for hard disk drive motors, but also to bearing devices where asynchronous runout is a problem. Depending on the object, the inner ring may be attached to the housing and the outer ring may be attached to the shaft, and various modifications can be made without departing from the gist of the invention.

[Effects of the Invention] As is clear from the above explanation, according to the bearing device of the present invention, the arrangement state of the rolling elements as seen from a fixed point is the same for each rotation of the shaft, so that the rotational movement and the rotational movement of the rolling elements are the same. The period of runout caused by unbalanced centrifugal force acting on the supported shaft can be made to coincide with one revolution of the shaft, resulting in synchronous runout.

[Brief explanation of the drawing]

1 to 5 show an embodiment of the present invention,
Fig. 1 is a ball arrangement state diagram showing changes in the arrangement state of balls during one revolution of the shaft, Fig. 2 is a runout mode diagram, Fig. 3 is an enlarged cross-sectional plan view of the main part, and Fig. 4 is a hard disk drive. 5 shows the locus of the magnetic head on the disk, FIG. 6 is a diagram corresponding to FIG. 1 showing a conventional example, FIG. 7 is a diagram equivalent to FIG. 2, and FIG. is a diagram equivalent to Figure 5. In the figure, 12 is a sleeve (housing), 15 is a ball bearing (bearing device), 16 is an inner ring, 17 is an outer ring, 18
1 to 186 are balls (rolling elements), and 20 is a shaft. Applicant: Toshiba Corporation

Claims (1)

[Claims] 1.In a device in which n rolling elements are provided between an outer ring and an inner ring, and one of the inner and outer rings is attached to a housing and the other is attached to a shaft, the rotational angular velocity ω_S of the shaft and the rotation of this shaft are The ratio ω_S:ω_B to the revolution angular velocity ω_B of the rolling element that revolves while rotating on its own axis is ω_S:ω
A bearing device characterized in that _B=n:m (m is an integer smaller than n).