JP2956992B2 - Media clamp structure - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a media clamp structure for a magneto-optical disk drive.

[Prior Art and Problems to be Solved by the Invention] In this type of conventional media clamp structure, an attraction magnet used for a rotating body such as a hub or a turntable is a samarium-cobalt (Sm-Co) based magnet. Such expensive and high magnetic force materials have been used.

The reason is that near the drive unit of the magneto-optical disk device,
This is because the temperature tends to change, and the attracting force of the attracting magnet decreases as the temperature increases. That is,
Since there is a possibility that the medium-magneto-optical disk cannot be held with high accuracy and reliability, a magnet made of a normal material having poor temperature characteristics cannot be used.

The present invention reduces the temperature change of the attraction force at the position of the medium-the temperature change of the magnetic flux-and uses an inexpensive ordinary magnet (material) without using such an expensive special magnet as the attraction magnet. The purpose is to make it possible.

[Means for solving the problem]

A media clamp structure according to the present invention includes a rotating body having a medium mounting surface, an attraction magnet fixed to the rotating body and facing a portion to be attracted of the medium with a certain gap, and a predetermined magnet on a back side of the attraction magnet. A magnetic body disposed at intervals and a material fixed to the rotating body, holding the magnetic body, and having a positive coefficient of thermal expansion, and decreasing and increasing the predetermined interval in reverse to the temperature rise and fall. And an interposition member.

(Operation)

The magnetic body provided on the back surface side of the attraction magnet is held by an interposition member, which has a positive coefficient of thermal expansion and expands and contracts as the temperature rises and falls. Conversely, the predetermined distance between the back surface of the attracting magnet and the magnetic body decreases and increases, thereby changing the permeance of the magnetic circuit. In other words, if the temperature rises, the above-mentioned predetermined interval decreases, the permeance of the magnetic circuit increases, and the decrease in the attraction force of the attraction magnet accompanying this temperature rise is compensated for.
Minimal temperature change of the attraction force to the media.

If the temperature decreases, the above-mentioned predetermined interval increases, the permeance of the magnetic circuit decreases, and the increase in the attraction force of the attraction magnet due to the temperature decrease is compensated for, so that the temperature change of the attraction force on the medium is reduced. And

〔Example〕

 Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.

1 to 3, reference numeral 1 denotes a rotating body having a medium mounting surface 2 on which a medium M is mounted. In the illustrated example, the rotating body 1 is integrated with a rotor 4 of a spindle motor 3. Of the hub 5 of FIG.

The spindle motor 3 includes a cylindrical portion 7 of a bracket 6.
A rotor 4 having the hub 5 is integrally fixed to the shaft 9 via bearings 8, 8, and a stator 10 is fixed to the outer peripheral surface of the cylindrical portion 7. A rotor magnet 11 is fixed to the inner peripheral surface of the rotor 4.

The medium M is a magneto-optical disk. The disk-shaped center portion is an attracted portion 12 made of a magnetic material, and the medium is placed in a state where the tip of the shaft 9 is inserted into the center hole 13. The medium M contacts the surface 2. Reference numeral 14 denotes an attraction magnet, which is fixed to the rotating body 1. That is, the hub 5
It comprises a small cylindrical portion 5a, a large cylindrical portion 5b, and a flat plate portion 5C, and has a circular concave groove portion 15 as an opening upward in the figure, and is circular so as to cover the opening of the concave groove portion 15. A flat ring-shaped attracting magnet 14 is fixedly attached to the attracted portion of the medium M.
And 12 with a gap 16 at a constant spacing A.

A circular flat ring-shaped interposition member 17 made of a material having a positive coefficient of thermal expansion such as PBT (polybutylene terephthalate) resin is fixed to the bottom surface 15a of the concave groove portion 15 of the hub 5 by bonding or the like. A circular plate-shaped magnetic body 18 is fixed to the outer surface of the mounting member 17 by bonding or the like. That is, the magnetic material 18 is provided on the back surface 14a side of the attracting magnet 14 with a predetermined interval B.
The hub 5 is attached to the flat plate portion 5C via the interposition member 17 with this magnetic body 18.

Due to the attachment via the interposition member 17, the predetermined distance B
Decreases and increases as the temperature rises and falls, respectively. That is, when the temperature rises, as shown in FIG. 3, the thickness dimension T of the interposition member 17 increases, and the above-mentioned predetermined interval B decreases. Conversely, when the temperature falls, as shown in FIG. like,
The thickness dimension T of the interposition member 17 decreases, and the predetermined interval B increases.

FIG. 4 shows a magnetization curve (BH curve). As the temperature changes, the distance B between the attracting magnet 14 and the magnetic body 18 changes as described above, and the permeance of the magnetic circuit including the attracting magnet 14 is reduced. Change.

That is, when the interval B is large as shown in FIG. 2, the permeance is small and the flow of magnetic flux decreases. Conversely, when the interval B is small as shown in FIG. 3, the permeance is large,
The flow of magnetic flux increases.

By the way, the magnetic force of the attracting magnet 14 is large when the temperature is low (FIG. 2), and is small when the temperature is high (FIG. 3). Therefore, since the increase and decrease of the magnetic force of the attracting magnet 14 itself and the increase and decrease of the permeance of the magnetic circuit including the attracting magnet 14 are opposite to each other, the force for attracting the attracted portion 12 of the medium M as a whole is It can be seen that the compensation is made to be substantially constant.

It should be noted that the present invention is not limited to the illustrated embodiment, and it is needless to say that the design can be freely changed. The structure and shape of the spindle motor 3 can be various, and the hub and the rotor can be separated from each other. It is also desirable to fix to the rotating shaft 9,
Further, the rotating body 1 is preferably a turntable type separated from a driving source.

〔The invention's effect〕

The present invention has the following significant effects by the above configuration. That is, since the permeance of the magnetic circuit including the attraction magnet 14 is changed by the temperature change, the temperature change of the attraction force of the attraction magnet 14 (the attraction force of the medium M to the attracted portion 12) becomes small, and the reliable media M Can be held. Further, it is possible to use the attracting magnet 14 having not so good temperature characteristics, and it is possible to achieve a control down.

[Brief description of the drawings]

FIG. 1 is a cross-sectional front view showing an embodiment of the present invention, FIG. 2 is an enlarged cross-sectional view of a main part at a low temperature, FIG.
FIG. 4 is a graph for explaining characteristics. M: media, B: interval, 1 ... rotating body, 2 ... media mounting surface, 12: attracted portion, 14 ... attracted magnet, 14a ... back surface, 16 ... gap, 17 ... Interposer, 18 ...
... Magnetic material.

Claims (1)

(57) [Claims] 1. A rotating body 1 having a medium mounting surface 2, an attracting magnet 14 fixed to the rotating body 1 and facing a portion to be attracted 12 of a medium M with a certain gap 16, and a back surface of the attracting magnet 14. A magnetic body 18 disposed at a predetermined interval B on the 14a side;
A media clamp structure comprising a material 17 holding a material 18 and having a positive coefficient of thermal expansion, the interposition member 17 decreasing and increasing the predetermined interval B in reverse to the rise and fall of the temperature. .