JPH0724936Y2 - Spindle motor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a spindle motor for a disk.

[Conventional technology]

In a conventional in-hub type fixed shaft spindle motor, a cylindrical back yoke made of steel is fixed inside a hub made of aluminum or the like over the entire axial length.

[Problems to be solved by the invention] In the conventional spindle motor, when the temperature changes during use, it behaves like bimetal due to the difference in thermal expansion between the hub and the back yoke, and the radius with respect to the center of the shaft part. There is a case where a directional distortion occurs and a magnetic disk read malfunction by a magnetic head-so-called off-track-is caused. In addition, the expansion and contraction amount of the fixed shaft due to temperature change in the axial direction and the expansion and contraction amount of the rotor portion including the hub and the back yoke in the axial direction are different, and an unreasonable force acts on the bearing, or the reverse In addition, there is a problem that the balls of the bearing are loose.

[Means for Solving the Problems]

The present invention is an in-hub type spindle motor in which a cylindrical back yoke and a permanent magnet are provided inside a hub on which a magnetic disk is mounted, and a stator core provided on a fixed shaft is surrounded by the hub. And an outer flange portion for receiving the magnetic disk at one end, and an inner flange portion for fitting the first bearing at the other end, respectively, is formed in a hat shape, and the inner flange portion at the other end of the hub is formed. Is pivotally attached to one end of the steel fixed shaft via the first bearing, and only the inner end portion of the outer peripheral surface of the steel back yoke is close to the inner flange portion of the inner peripheral surface of the hub. A small void portion or an elastic material filled in the minute void portion between 70% to 90% of the height of the back yoke and the inner peripheral surface of the hub. A free stretchable part is formed, and the above-mentioned structure is formed on the outer end of the inner surface of the back yoke. A second bearing is fitted or directly fitted with an auxiliary ring made of a non-ferrous metal having a shape substantially the same as that of the inner flange portion, and the one end of the hub is fixed with steel through the second bearing. Pivotally attached to the other end of the shaft.

[Action]

The hub and the back yoke, which have different coefficients of thermal expansion, expand and contract according to the coefficient of thermal expansion due to temperature changes. Therefore, both can freely expand and contract in the minute void portion provided between the hub and the back yoke or in the mutual free expanding and contracting portion in which the elastic material is filled.

And both of them are in the axial direction, and the height of the back yoke is
Only 10% to 30% are fitted and fixed. Therefore, the stress that causes strain due to the difference in thermal expansion between the two is extremely small for the entire hub.

That is, in response to this strain, the strain acting on the hub due to the stress is itself very small. In addition to this,
This strain itself is further smoothed as a strain in the minute void portion or the mutual free expansion and contraction portion provided in the axial direction. As a result, virtually no strain acts on the entire hub. Therefore, the off-track phenomenon can be prevented. In addition, the space between the first and second bearings of the fixed shaft expands and contracts due to temperature changes according to the coefficient of thermal expansion of the steel fixed shaft itself. On the other hand, on the other hand, the corresponding portion between the first and second bearings in the axial direction on the hub side is mostly except for a small portion of the inner flange portion when the auxiliary ring is not interposed. It is composed of a steel back yoke. Therefore, the hub side also expands and contracts substantially in accordance with the thermal expansion coefficient of steel, similarly to the fixed shaft side. In addition, the corresponding portion between the first and second bearings is the same as above, except for a small part of the inner collar part and a small part of the auxiliary ring when the auxiliary ring is interposed. Most of them are composed of a steel back yoke, so that they substantially expand and contract according to the coefficient of thermal expansion of steel.

As a result, in the axial direction between the fixed shaft side and the hub side, there is substantially no difference in thermal expansion due to temperature changes, and stress acting in the axial direction is substantially not generated.

The auxiliary ring has substantially the same shape as the inner collar portion. Therefore, the effect of expansion and contraction due to temperature change as a difference in thermal expansion in the axial direction of the fixed shaft and the hub is further reduced.

Thus, no stress is generated in the fixed shaft and the hub in the axial direction, and thus the off-track phenomenon due to the distortion of the hub does not occur. In addition, damage to the first and second bearings is avoided, and rattling of the bearings is prevented.

〔Example〕

An embodiment will be described with reference to the drawings. FIG. 1 is a view showing an embodiment in which the left and right halves are different from each other. First, the configuration common to the left half and the right half will be described, and then each characteristic To be referred to.

Reference numeral 1 denotes a hub, on which a plurality of magnetic disks (not shown) can be mounted. Inside the hub 1, a cylindrical back yoke 2 and a permanent magnet 3 are provided. Reference numeral 4 denotes a fixed shaft, which is erected on a bracket 5 and a stator core 6 is fixed to the fixed shaft 4, and the inner peripheral surface of the permanent magnet 3 corresponds to the outer peripheral surface of the stator core 6 with a predetermined gap. The permanent magnet 3 is fitted and fixed to the inner peripheral surface of the cylindrical back yoke 2. In this way, the fixed shaft 4
FIG. 1 shows an in-hub type spindle motor in which the stator core 6 provided in the above is surrounded by the hub 1.

The hub 1 is made of a non-ferrous metal such as aluminum, and has an outer flange 8 for receiving a magnetic disk at one end 7 and an inner flange 10 for fitting a steel first bearing 10 such as a ball bearing at the other end 9. It is a hat type provided with each section 11.

The inner flange 11 on the other end 9 side of the hub 1 is rotatably attached to one end 12 of the fixed shaft 4 via a first bearing 10. The fixed shaft 4 is made of steel such as stainless steel.

The cylindrical back yoke 2 has an inner end portion 13 of the outer peripheral surface 13.
Only a is fitted to the inner peripheral surface 14 of the hub 1 close to the inner flange portion 11 and fixed by an adhesive or the like.

H indicates the height of the back yoke 2. h is back yoke 2
The inner end 13a of the outer peripheral surface indicates the axial dimension of the fitting portion 15 fitted and fixed to the inner peripheral surface 14 of the hub 1, and the dimension h is set so that the following relational expression is established. To do.

0.1 · H ≦ h ≦ 0.3 · H ... Then, the inner peripheral surface 14 of the hub 1 is formed with an escape portion 16 having a slightly larger diameter over the range of the remaining portion (H-h) excluding the fitting portion 15. Between the outer surface 13 of the fitted back yoke 2,
A minute void portion 17 is formed (see the embodiment shown in the right half of FIG. 1). Therefore, according to the spindle motor of the present invention,
The hub 1 and the back yoke 2 having different thermal expansion coefficients expand and contract in accordance with the thermal expansion coefficient thereof due to the temperature change, and both can expand and contract freely in the minute void portion 17. The fitting portion 15 in which the hub 1 and the back yoke 2 are fixed, that is, bundled, has a small ratio of 0.1H to 0.3H with respect to the height of 1H of the back yoke 2.

Therefore, the stress that causes strain due to the difference in thermal expansion between the hub 1 and the back yoke 2 is extremely small, in other words, the strain that occurs in the entire hub 1 is extremely small.

That is, the strain acting on the hub 1 due to this stress is very small in itself. In addition to this, the strain itself is further smoothed by a sufficiently long distance (that is, 0.7H to 0.9H) (with respect to the fitting portion 15) in the axial direction of the minute void portion 17. As a result, substantially no strain acts on the entire hub 1. Therefore, as one of the causes of the above-mentioned off-track phenomenon in the magnetic disk device, there is an accident that the disk fitted to the hub 1 and the head cause an error due to the distortion or tilting of the hub 1 in the axial direction. It can be prevented.

Therefore, the smaller the axial dimension of the fitting portion 15 between the hub 1 and the back yoke 2 is, the less the influence of the strain is reduced, while the holding / fixing strength of the fixed hub 1 and the back yoke 2 is increased. Based on the need to secure at least
It is desirable to set within the range of the above relational expression. In this case, it can be arbitrarily selected depending on the fitting strength per unit area of the fitting portion 15 or the adhesive strength of the adhesive.

Then, as in the embodiment shown in the left half of FIG. 1, it is also preferable to fill the minute voids 17 with an elastic material to form the mutual free stretchable portions 18. Here, the elastic material refers to elastic rubber or soft plastic. As a result, the effect of vibration isolation / vibration is obtained (see another embodiment shown in the left half of FIG. 1). As described above, the axial direction dimension of the minute void portion 17 or the free stretchable portion 18 occupies 0.7H to 0.9H.

An auxiliary ring 19 made of non-ferrous metal such as aluminum is fitted and fixed to the outer end portion 20a of the inner peripheral surface 20 of the back yoke 2 with an adhesive or the like. Then, a second bearing 21 such as a steel ball bearing is interposed between the inner peripheral surface of the auxiliary ring 19 and the outer peripheral surface of the fixed shaft 4. That is, one end 7 of the hub 1 is rotatably attached to the other end 22 of the fixed shaft 4 via the back yoke 2, the auxiliary ring 19 and the second bearing 21.

The non-ferrous metal auxiliary ring 19 is formed with notches 23 and 24 as shown in the figure, so that the auxiliary ring 19 having a coefficient of thermal expansion different from that of steel is provided between the second bearing 21 and the back yoke 2. Even if it is interposed between them, the strain caused by the difference in thermal expansion is prevented.

That is, the notch 23 opens downward in the axial direction and is provided with the auxiliary ring 19 over the entire circumference. Therefore, the auxiliary ring 19 can easily absorb the stress acting in the radial direction.

Further, the cutout portion 24 is opened outward in the radial direction, the auxiliary ring 19 is similarly provided over the entire circumference, and this opening is fixed to the inner peripheral surface 20 of the back yoke 2. In this case, the auxiliary ring 19 can easily absorb the stress acting in the axial direction.

Then, as shown in FIG. 1 by the stars, points A and B are shown on the fixed axis, and positions a and b are shown on the hub 1 side.
Between A and B is the coefficient of thermal expansion of steel, which is the material of the fixed shaft 4 itself, while between A and B on the hub 1 side (excluding a small part of the inner collar part 11 and a small part of the auxiliary ring 19). Most of them are steel parts with similar coefficient of thermal expansion.
Therefore, even if the temperature changes when using the motor,
The fixed shaft 4 side and the hub 1 side expand and contract according to substantially the same coefficient of thermal expansion. Therefore, there is no difference in thermal expansion between the fixed shaft 4 and the hub 1, and the dimension between AB and the dimension between ab are substantially equal.

Therefore, the stress acting in the axial direction of the fixed shaft 4 and the hub 1 is not generated, and therefore the hub 1 is not tilted with respect to the fixed shaft 4, so that the accident such as the off-track described above can be prevented.

Further, since the stress does not act on the bearings 10 and 21, the bearings 10 and 21 are not damaged, and the preload is not released to cause rattling or vibration. For this reason bearings 10,21
The durability of can be improved and high rotation accuracy can be maintained. Further, in the embodiment shown in FIG. 1, since the auxiliary ring 19 has substantially the same shape and size as the inner collar portion 11, the radial thermal strains of the bearings 10 and 21 are also substantially equal. Therefore, the influence of expansion and contraction due to temperature change as a difference in thermal expansion in the axial direction between the fixed shaft 4 and the hub 1 is further reduced, which is preferable.

Further, by using the auxiliary ring 19 having the above-mentioned cutouts 23 and 24, the strain can be reduced due to the difference in thermal expansion.

It should be noted that the design can be changed freely in addition to the embodiment shown in the drawings. For example, the auxiliary ring 19 may be omitted and the second bearing 21 having a large outer diameter may be used to directly back the outer ring of the second bearing 21. It is also possible to fit it on the outer end portion 20a of the inner peripheral surface of the yoke 2. With this configuration, since the second bearing 21 and the back yoke 2 are made of steel, there is no difference in thermal expansion between them and no distortion occurs.

[Effect of device]

Since the spindle motor of the present invention has the above-described structure, the hub on which the magnetic disk is mounted is not distorted or tilted even when the spindle motor itself or the ambient temperature changes. Therefore, the off-track phenomenon can be prevented in advance. Since damage, rattling and vibration of the bearing that rotatably supports the hub are prevented, durability and high rotational accuracy can be maintained.

As described above, according to the present invention, a spindle motor with high stability and reliability can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view showing two embodiments of the present invention together. 1 ... Hub, 2 ... Back yoke, 3 ... Magnet, 4 ... Fixed shaft, 6 ... Stator core, 7 ... One end, 8 ... Outer collar part, 9 ...
The other end, 10 ... First bearing, 11 ... Inner collar part, 12 ... One end, 13a ... Inner end part, 14 ... Inner peripheral surface, 17 ... Micro void part, 18 ... Mutual free expansion and contraction part, 19 ... Auxiliary ring, 20a ... Outer end, 21 ... Second bearing, 22
... The other end, H ... The height of the back yoke, h ... The axial dimension of the fitting portion.

Claims (1)

[Scope of utility model registration request] 1. An in-hub type spindle motor in which a cylindrical back yoke 2 and a permanent magnet 3 are provided inside a hub 1 for mounting a magnetic disk, and a stator core 6 provided on a fixed shaft 4 is surrounded by the hub 1. And the hub 1 is made of non-ferrous metal, and the one end 7 is provided with an outer flange portion 8 for receiving a magnetic disk, and the other end 9 is provided with an inner flange portion 11 into which the first bearing 10 is fitted. The inner flange 11 of the other end 9 of the hub 1 is pivotally attached to the one end 12 of the fixed shaft 4 made of steel through the first bearing 10 and the back yoke 2 made of steel is Only the inner end portion 13a of the outer peripheral surface is fitted and fixed to the inner peripheral surface 14 of the hub 1 near the inner flange portion 11, and 70% to 90% of the height H of the back yoke 2 is secured.
% And the inner peripheral surface 14 of the hub 1, a minute void portion 17 or a mutual free stretchable portion 18 in which the minute void portion 17 is filled with an elastic material is formed. The second bearing 21 is fitted to the outer end portion 20a of the inner peripheral surface of the second bearing 21 by directly or indirectly interposing an auxiliary ring 19 of a non-ferrous metal having substantially the same shape as that of the inner collar portion 11. The one end 7 of the hub 1 is pivotally attached to the other end 22 of the steel-made fixed shaft 4 via the spindle motor.