JPH05325468A - Method for attaching magnetic plate to disk substrate - Google Patents

Abstract

PURPOSE:To house and hold a magnetic plate on a disk substrate with a fixed clearance in a loosely fitted state. CONSTITUTION:In a state where the magnetic plate 5 is arranged in a magnetic plate housing recessed part 6 provided in the center of the disk substrate 2, a horn 17 which generates torsional vibration is allowed to abut on so as to form a projecting part 19 which projects toward the inner side of the recessed part 6 from the periphery of the recessed part 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for attaching a magnetic plate disposed on a disk substrate which constitutes an information signal recording disk for recording desired information signals such as an optical disk and a magneto-optical disk.

[0002]

2. Description of the Related Art Conventionally, discs for recording information signals, such as optical discs and magneto-optical discs, on which desired information signals are recorded have been proposed. This type of disc is capable of high density recording of information signals, so that a disc having an extremely small diameter has been proposed. For example, there has been proposed an optical disk or a magneto-optical disk having a diameter of about 64 mm and capable of recording a music signal for about 74 minutes.

The magneto-optical disk having such a small diameter and capable of high-density recording of information signals is mounted on a disk rotation driving device and rotated at a high speed. Then, while being driven to rotate at a high speed, a fine recording track provided on the signal recording layer formed on one main surface of the magneto-optical disk is irradiated with a light beam emitted from the optical pickup device, and a magnetic field is generated. A desired information signal is recorded by applying an external magnetic field that is magnetic field modulated according to the information signal to be recorded from an external magnetic field generator such as a head.

In order to accurately irradiate a fine recording track with a light beam while being rotationally driven at such a high speed,
The magneto-optical disk is required to be securely integrated with the disk table of the disk rotation driving device and to be mounted with the rotation center positioned with high accuracy on the axis of the disk table. In order to achieve such an object, conventionally, a metal plate made of a magnetic material is arranged on the side of the magneto-optical disk, and this is attracted by a magnet provided on the side of the disk table. A disk mounting method has been proposed in which the disk is chucked upward.

The magneto-optical disk used in the magnet chucking system utilizing the attractive force of this magnet is
As shown in FIG. 9, a disk substrate 5 formed by molding a transparent synthetic resin such as a polycarbonate resin into a disc shape.
1 is provided. One main surface 5 of the disk substrate 51
An information signal recording layer on which a desired information signal is recorded is formed on the 1a side. Then, the disc substrate 51
Defines the other main surface 51b opposite to the one main surface 51a on which the information signal recording layer is formed as an information signal writing / reading surface, and irradiates the signal recording layer with a light beam from this writing / reading surface side. Recording or reproduction of a desired information signal is performed.

A center hole 52 is formed in the center of the disk substrate 51 so that a centering member provided on the disk rotation drive side can engage with the center hole 52. Further, a disk-shaped magnetic plate 53 made of a metallic material is disposed in the center of the one main surface 51a side of the disk substrate 51 so as to close the center hole 52. The magnetic plate 53 is arranged so as to fit into a magnetic plate storage recess 54 formed on the one main surface 51a side of the disk substrate 51 so as to surround the center hole 52. And
The magnetic plate 53 disposed in the magnetic plate storage recess 54 is formed by the protrusion 55 that is formed so as to project inward of the recess 54 by ultrasonically processing the peripheral edge of the magnetic plate storage recess 54. The disc substrate 51 is housed and held.

The attachment of the magnetic plate 53 to the disk substrate 51 is performed as follows. First, as shown in FIG. 9, the disc substrate 51 is positioned and placed on the disc receiving base 56. The disk support 56
Is a magnetic plate storage recess 54 provided on the disk substrate 51.
Has a disc receiving portion 57 for accommodating the disc substrate 51 by accommodating a projecting portion 59 projecting on the outer periphery of the disc substrate, and by accommodating the projecting portion 59 in the disc receiving portion 57, 51 is positioned.

Next, a horn 58 is brought into contact with the opening peripheral edge of the magnetic plate accommodating concave portion 54 of the disc substrate 51 placed on the disc receiving portion 57, and ultrasonic vibration from an ultrasonic oscillator (not shown) is applied to this horn. 58. The ultrasonic vibration applied at this time is a direction parallel to the main surface 2a of the disk substrate 2, that is, ultrasonic transverse vibration. As a result, the portion of the magnetic plate housing recess 54 in contact with the horn 58 is melted by frictional heat, and the resin at the peripheral edge of the opening protrudes inward of the recess 54 to form the protrusion 55. As a result, the magnetic plate 53 is housed and held in the magnetic plate housing recess 54 in a loosely fitted state. It should be noted that swaging is provided at several places, for example, four places, of the magnetic plate accommodating recess 54 so that the magnetic plate 53 does not fall off from the disk substrate 51.

[0009]

However, in the ultrasonic transverse vibration, since the propagation of the disk substrate 51 in the thickness direction is small, the thickness of the protrusion 55 for preventing the magnetic plate 5 from falling is compared. Although it has an advantage that it can be controlled with extremely high precision, it has a drawback that swaging can be performed in only two places at most in one operation. Therefore, the productivity is deteriorated due to the increase in the takt time, and the strength of the protruding portions 55 provided at several places is insufficient.

For this reason, as shown in FIG.
As shown in FIG. 3, a columnar horn 58 is brought into contact with the main surface 51a of the disk substrate 51 perpendicularly, and a longitudinal vibration is applied to the horn 58. With such ultrasonic longitudinal vibration, since the annular protrusion 55 can be formed over the entire circumference of the magnetic plate accommodating recess 54 by one swaging, productivity is very good in terms of tact time.

However, since the vibration is in the direction perpendicular to the disk substrate 51, the protrusion 5 shown in FIG.
It is very difficult to control the thickness T of the magnetic plate 53.
Are easily fixed to the disc substrate 51. Magnetic plate 5
When 3 is fixed to the disk substrate 51, the magnetic plate 58 made of these metal materials and the disk substrate 5 made of synthetic resin
The disk substrate 51 may be deformed due to the difference in thermal expansion coefficient of 1. As a result, birefringence occurs in the disk substrate 51, and there is a risk that writing or reading of an information signal may be defective due to deterioration of optical characteristics.

Therefore, the present invention has been proposed in view of the above technical problem, and the magnetic plate can be housed and held in a loosely fitted state with a fixed clearance with respect to the disk substrate. An object of the present invention is to provide a method of attaching a magnetic plate to a disk substrate, which enables swaging at one time and is excellent in productivity.

[0013]

In order to achieve the above-mentioned object, the method of the present invention is an ultrasonic wave which generates a torsional vibration in a state where a magnetic plate is arranged in a magnetic plate accommodating recess provided in the center of a disk substrate. By bringing the generating means into contact with the peripheral edge of the magnetic plate accommodating recess, a protrusion is formed that protrudes inward from the peripheral edge of the magnetic plate accommodating recess, and the magnetic plate is disc-shaped by the protrusion. It is characterized by being attached to a substrate.

The frequency of the ultrasonic vibration applied at this time is set to 15 kHz to 50 kHz. In addition, the disk substrate is swaged while being pressed by the disk pressing means.

Further, in the method of the present invention, the ultrasonic wave generating means having a horn having a stepped portion at the tip thereof is arranged in the state where the magnetic plate is disposed in the magnetic plate accommodating concave portion provided at the center of the disk substrate. By abutting against the peripheral edge of the plate accommodating recess, a protrusion protruding from the peripheral edge of the magnetic plate accommodating recess toward the inside of the recess is formed, and the magnetic plate is attached to the disk substrate by this protrusion. It is a feature.

[0016]

In the method according to the present invention, the ultrasonic wave generating means for generating the torsional vibration at the peripheral edge of the magnetic plate accommodating recess is provided with the magnetic plate disposed in the magnetic plate accommodating recess provided in the center of the disk substrate. When brought into contact with each other, the peripheral edge of the magnetic plate accommodating recess is melted by the frictional heat due to the torsional vibration, and an annular projecting portion is formed on the inner peripheral side of the magnetic plate accommodating recess. Further, before the ultrasonic wave generating means comes into contact with the disk substrate, the disk holding means holds down the disk substrate and fixes the disk substrate, so that accurate swaging can be performed.

Further, in the present invention, since the step portion is provided at the tip of the horn constituting the ultrasonic wave generating means, the step portion prevents the resin melted by the torsional vibration from jumping out from the disk substrate. It

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments to which the present invention is applied will be described in detail below with reference to the drawings. The present embodiment is an example in which the present invention is applied to a magneto-optical disk having a diameter of 64 mm. First, a magneto-optical disk to which the present invention is applied will be described. Such a magneto-optical disk 1
As shown in FIG. 1, the disk substrate 2 is formed by integrally molding a transparent synthetic resin material such as a polycarbonate resin. The disc substrate 2 has a diameter of about 64 mm and is formed in a disk shape with a thickness of about 1.2 mm.

A magneto-optical disc 1 constructed by using this disc substrate 2 is one main surface 2 of the disc substrate 2.
It has a signal recording part formed with an information signal recording layer for recording a desired information signal on the a side, and the other main surface 2b on the opposite side is used as a writing / reading surface of the information signal, and The information signal is recorded / reproduced by irradiating the signal recording layer with a light beam from the writing / reading surface side.

As shown in FIG. 2, the central portion of the disc substrate 2 constituting the magneto-optical disc 1 is arranged at the central portion of the disc table constituting the disc rotation driving device arranged in the recording / reproducing apparatus. A center hole 3 is formed in which a provided centering member (not shown) is engaged. The center hole 3 is formed as a circular hole penetrating the disk substrate 2, and the center of the center hole 3 coincides with the center of curvature of a recording track formed concentrically or spirally on the signal recording layer. It is formed to let.

The other main surface 2 of the disk substrate 2
An annular projecting portion 4 is integrally formed in the center portion on the b side so as to surround the center hole 3. This protrusion 4
The center hole 3 of the centering member arranged on the side of the disk table on which the magneto-optical disk 1 is mounted, without increasing the depth of the center hole 3 formed in the thin disk substrate 2. The amount of protrusion with respect to is increased, and the centering operation for mounting the magneto-optical disk 1 with the rotation center of the magneto-optical disk 1 aligned with the axis of the disk table is performed reliably. further,
The tip surface 4a of the protruding portion 4 functions as a reference surface for mounting on the disc table.

The projecting portion 4 is formed at least in the non-signal recording area on the inner peripheral side of the disk substrate 2 where the signal recording layer is not formed, and projects with a projection amount substantially equal to the thickness of the disk substrate 2. Has been formed. Therefore, the portion of the disk substrate 2 on which the protruding portion 4 is formed is about twice as thick as the substrate body portion.

At the center of the one main surface 2a side of the disk substrate 2, there is formed an annular magnetic plate accommodating recess 6 which surrounds the center hole 3 and is provided with a magnetic plate 5 for attracting magnets. Has been formed. The magnetic plate accommodating recess 6 has a diameter smaller than the outer peripheral diameter of the protrusion 4, and the disk substrate 2
Is formed to a depth approximately equal to the thickness of. Further, the inner diameter of the opening of the magnetic plate housing recess 6 is larger than the diameter of the center hole 3. Therefore, an annular flat surface 6a is provided at the bottom of the magnetic plate storage recess 6. The flat surface 6a serves as a mounting surface on which the magnetic plate 5 is mounted.

On the other hand, the magnetic plate 5 accommodated and held in the magnetic plate accommodating recess 6 is formed by punching a metal material such as a stainless plate into a disc shape. The magnetic plate 5 is formed as a disk having a size large enough to be stored in the magnetic plate storage recess 6, and when the magnetic plate 5 is stored and held in the magnetic plate storage recess 6, the outer peripheral surface 5a thereof is the magnetic plate. It is formed in such a size that it does not come into contact with the inner peripheral wall 6b of the storage recess 6. Also, this magnetic plate 5
A small circular hole 7 used for handling in the manufacturing process is formed in the center of the.

The magnetic plate 5 formed as described above is attached to the disk substrate 2 by an attaching device having an ultrasonic wave generating means described below. As shown in FIG. 3, such a mounting device includes a disk substrate supporting table 8 which is a disk mounting means for mounting the disk substrate 2 and an ultrasonic wave generating means which is an ultrasonic wave generating means for applying an ultrasonic wave to the disk substrate 2. It is composed of a mechanical section 9.

The disc substrate support table 8 is constructed so as to position the placed disc substrate 2, and the support table body 1 has a flat plate shape.
On the upper surface side of 0, a disk substrate mounting table 11 for positioning and mounting the disk substrate 2 is provided. As shown in FIG. 4, the disc substrate mounting table 11 is formed as a disc body having a protrusion fitting concave portion 13 for fitting the protrusion 4 of the disc substrate 2 in a loosely fitted state in the central portion. .. The protrusion fitting recess 13 is formed as an annular recess sufficient to accommodate the protrusion 4 of the disk substrate 2 therein, and when the protrusion 4 is accommodated, the inner peripheral wall 13a and the protrusion 13a. A slight gap is opened between the outer peripheral surface 4b of the portion 4. Therefore, the disc substrate 2 is positioned on the disc substrate mounting table 11 by fitting the protrusion 4 provided at the center of the disc substrate 2 into the protrusion fitting recess 13.

In the state where the disc substrate 2 is positioned, the tip end surface 4a of the protrusion 4 of the disc substrate 2 is supported by the bottom surface 13b of the protrusion fitting recess 13, and the annular shape of the disc substrate mounting table 11 is formed. The main surface 2b which serves as the information signal writing / reading surface of the disk substrate 2 is supported on the upper end surface 11a. A suction mechanism for vacuum-sucking the disk substrate supporting table 8 configured as described above using a vacuum pump in order to securely fix the disk substrate 2 mounted on the disk substrate mounting table 11. (Not shown).

On the other hand, as shown in FIG. 3, the ultrasonic wave generation mechanism section 9 has an ultrasonic vibrator 15 which mainly converts electric energy generated from an ultrasonic oscillator into mechanical vibration.
And a cone 16 for amplifying the mechanical vibration of the ultrasonic transducer 15 and a horn 17 having a columnar shape for propagating the amplified mechanical vibration to the workpiece. These ultrasonic transducer 15, cone 16 and horn 17 are
In that order, the air cylinders 1 are integrated in a vertical line.
By means of 8, the disk substrate 2 can be moved up and down. In addition, the disk substrate support table 8
A control panel is provided between the ultrasonic wave oscillator and the ultrasonic oscillator to control the pressing force and amplitude of the horn 17 with respect to the disk substrate 2 and the swaging depth.

In particular, in this embodiment, the horn 1 is used.
A step portion 12 is provided at the tip of 7. The step 1
2 is provided so as to project outward from the outer peripheral edge of the welded portion 14 that swages the peripheral edge of the magnetic plate housing recess 6 of the disk substrate 2, and restricts the protrusion of the resin that melts around the welded portion 14 during swaging. Play a role. The welded portion 14 is formed as a columnar body having a size sufficient for swaging the peripheral edge of the magnetic plate housing recess 6.

Further, the ultrasonic wave generating mechanism section 9 has a disk substrate 2 mounted on a disk substrate mounting table 11.
A disc holding means 20 for securely fixing the disc is provided. The disc holding means 20 holds a disc substrate 2 directly from above and fixes the disc substrate 2, and a disc holding portion 21.
1 and a support arm 22 that supports the unit 1.

The disk pressing portion 21 is formed as a ring having an outer diameter substantially the same as the outer diameter of the disk substrate mounting table 11, and the disk pressing surface 21a is an annular flat surface. The main surface 2a of the disk substrate 2 is supported in a surface contact state. Further, the disc pressing portion 21 is adapted to press a position which does not cover the information signal recording layer formed on the disc substrate 2, and protects the information signal recording layer. On the other hand, the support arm 22
Are provided integrally with the disc holding portion 21 and are configured to move the disc holding portion 21 up and down with respect to the disc substrate 2.

In order to hold the magnetic plate 5 on the disk substrate 2 in a loosely fitted state by using the mounting device constructed as described above, the procedure is as follows. First, as shown in FIG.
The disc substrate 2 is placed on the disc substrate placing table 11. That is, the protruding portion 4 of the disk substrate 2 is housed and held in the protruding portion fitting concave portion 13 provided in the disk substrate mounting table 11. As a result, the disk substrate 2
The mounting position for the disk substrate mounting table 11 is determined.

After that, the disk substrate mounting table 11
By operating a suction mechanism built in the disk substrate 2 by vacuum suction, the disk substrate mounting table 11
Fix it on top.

Next, the magnetic plate 5 is put into the magnetic plate housing recess 6 of the disk substrate 2. As a result, the magnetic plate 5 is
As shown in FIG. 4, the bottom surface 13a of the protrusion fitting recess 13
Are held in surface contact with each other. Next, the disc holding means 20 is lowered and brought into contact with the disc substrate 2 placed on the disc substrate placing table 11. Then, a predetermined pressure is applied to the disc pressing portion 21 of the disc pressing means 20 to securely fix the disc substrate 2 on the disc substrate mounting table 11.

Thereafter, the horn 17 is lowered by the air cylinder 18, and as shown in FIG. 5, the welded portion 14 at the tip of the horn 17 is magnetized on the one main surface 2a of the disk substrate 2 on which the information signal recording layer is formed. The plate storage recess 6 is brought into contact with the peripheral edge of the opening. Next, a torsional vibration is applied to the disk substrate 2 with a predetermined pressure F being applied to the disk substrate 2 by the air cylinder 18.

The torsional vibration referred to here means a vibration generated by alternately switching the horn 17 in the clockwise direction and the counterclockwise direction about the axis O of the horn 17 as a center and rotating the horn 17 in a plane. Further, the frequency of the torsional vibration applied here is set in the range of 15 kHz to 50 kHz in consideration of the controllability of the thickness of the protrusion 19 that prevents the magnetic plate 5 from falling off from the disk substrate 2 described later. Above all,
20 kHz is more preferable. The amplitude of the torsional vibration is slightly different depending on the material of the disc substrate 2,
The range of μm to 70 μm is preferable. In this embodiment, 70
μm.

Then, as shown in FIG. 6, the peripheral edge of the opening of the magnetic plate accommodating recess 6 with which the horn 17 is in contact melts out by frictional heat. Part of the melted resin 23 is
As shown in FIG. 7, an attempt is made to pop out from the outer periphery of the welded portion 14 of the horn 17, but since the step portion 12 is provided on the horn 17, the resin 23 is formed by the step surface of the step portion 12. Can be suppressed. Further, the height of the resin 23 protruding from the main surface 2a of the disc substrate 2 can be regulated. When the height of the resin 23 is large, when the magneto-optical disk 1 is housed in a disk cartridge, the resin 23 comes into contact with the inner wall surface of the cartridge, which adversely affects the centering of the magneto-optical disk 1. However, in this embodiment, since the height of the resin 23 protruding from the peripheral edge of the welded portion 14 can be regulated, there is no problem even if it is stored in the disk cartridge.

When torsional vibration is further applied,
As shown in FIG. 7, the inner periphery of the magnetic plate storage recess 6 is formed such that the opening peripheral edge of the magnetic plate storage recess 6 forms a recess corresponding to the size of the welded portion 14 of the horn 17. Stick to the side. As a result, a protrusion 19 is formed on the peripheral edge of the opening of the magnetic plate storage recess 6 so as to project toward the inner peripheral side of the magnetic plate storage recess 6. The projecting portion 19 is formed on the outer peripheral edge portion 5 of the magnetic plate 5 housed in the magnetic plate housing recess 6.
It is formed in an annular shape so as to cover a and prevents the magnetic plate 5 from falling off the disk substrate 2. The thickness T of the protrusion 19 is highly accurate because the torsional vibration is close to so-called lateral vibration in the in-plane direction of the disk substrate 2.

After the swaging is completed, the horn 1
7 and the disc pressing means 20 are raised with respect to the disc substrate 2, the vacuum suction is released, and the disc substrate 2 is taken out. As a result, as shown in FIG. 8, the magneto-optical disk 1 in which the magnetic plate 5 is held in the disk substrate 2 in a loosely fitted state is manufactured. In such a magneto-optical disk 1, since the thickness of the protruding portion 19 formed by swaging can be made highly accurate, the protruding portion 19 and the disk substrate 2 housed in the magnetic plate housing recess 6 are separated from each other. A constant clearance C can be provided between them. That is, the magnetic plate 5 can be loosely fitted and held on the disk substrate 2 with a preset clearance C. As a result, it is possible to prevent the disk substrate 2 from being deformed due to the difference in thermal expansion coefficient between the disk substrate 2 made of synthetic resin and the magnetic plate 5 made of a metal material. Further, since the projecting portion 19 can be formed in an annular shape on the peripheral edge of the magnetic plate accommodating concave portion 6 by one swaging, the tact time is improved and the strength is also improved.

In the present embodiment, an example in which the present invention is applied to a magneto-optical disk has been described, but the present invention also has a disk substrate made of synthetic resin and a magnetic plate for magnet chucking. It is widely applicable to information signal recording discs having

[0041]

As is apparent from the above description, in the method of the present invention, the ultrasonic wave generating means is disposed in the magnetic plate accommodating recess provided in the center of the disk substrate, and the ultrasonic wave generating means is disposed in the magnetic plate accommodating recess. Since swaging is performed by bringing the disk substrate 2 into contact with the peripheral edge of the disk substrate and generating a torsional vibration that is a vibration close to a lateral vibration, the protruding portion whose thickness is controlled with high accuracy is formed by the inward projection of the disk substrate 2. Can be formed. Therefore, a certain clearance can be provided between the protrusion formed by this swaging and the disk substrate, and as a result, the magnetic plate can be housed and held in a loosely fitted state. As a result, it is possible to prevent the magnetic plate from being fixedly attached to the main surface of the disk substrate in an inclined manner, and it is caused by the difference in thermal expansion coefficient between the disk substrate made of synthetic resin and the magnetic plate made of a metal material. The deformation of the disk substrate can be prevented.

Further, in the method of the present invention, since the annular protrusion can be formed by swaging once, the tact time can be greatly reduced and the productivity can be improved. Further, since the protruding portion is formed into an annular shape, the strength is increased, and the magnetic plate can be reliably prevented from coming off from the disk substrate.

Further, in the method of the present invention, since the step portion is provided at the tip of the horn, it is possible to suppress the resin that is melted and jumped out from the peripheral portion of the horn at the time of swaging. Therefore, when the information signal recording disk composed of this disk substrate is housed in the disk cartridge, the protrusion does not come into contact with the inner wall surface of the cartridge. Therefore, it is possible to center the information signal recording disk with high accuracy.

[Brief description of drawings]

FIG. 1 is an exploded perspective view of a magneto-optical disk to which the present invention is applied.

FIG. 2 is a cross-sectional view showing a disassembled state of a magneto-optical disk to which the present invention is applied.

FIG. 3 is a front view showing a magnetic plate attachment device to which the present invention is applied.

FIG. 4 is a cross-sectional view showing a state in which a magnetic plate is placed on the disc substrate.

FIG. 5 is a cross-sectional view showing a state in which a horn is in contact with a disk substrate.

FIG. 6 is a cross-sectional view showing a swaging state.

FIG. 7 is an enlarged cross-sectional view of a main part in a swaging state.

FIG. 8 is a cross-sectional view of the magneto-optical disk after swaging is completed.

FIG. 9 is a cross-sectional view showing a state of swaging by applying lateral vibration.

FIG. 10 is a cross-sectional view showing a state of swaging by applying vertical vibration.

FIG. 11 is an enlarged cross-sectional view of a main part in a swaging state when vertical vibration is applied.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Magneto-optical disk 2 ... Disk substrate 3 ... Center hole 5 ... Magnetic plate 6 ... Magnetic plate storage recess 8 ... Disk substrate support table 9 ... Ultrasonic wave generation mechanism part 11 ... Disk substrate mounting table 12 ... Step portion 14 ... Welding portion 15 ... Ultrasonic transducer 16 ... Cone 17 ... Horn 18 ... Air cylinder 19 ... Projection Part 20: Disc holding means 21: Disc holding portion

Claims (4)

[Claims] 1. An ultrasonic wave generating means for generating a torsional vibration is brought into contact with a peripheral edge of the magnetic plate storage recess in a state where the magnetic plate is disposed in the magnetic plate storage recess provided in the center of the disk substrate. A method of attaching a magnetic plate to a disk substrate, characterized in that a protrusion is formed to protrude from the peripheral edge of the magnetic plate accommodating recess toward the inside of the recess, and the magnetic plate is attached to the disk substrate by the protrusion. 2. The frequency of ultrasonic vibration is from 15 kHz to 50 kHz.
The method of attaching a magnetic plate to a disk substrate according to claim 1, wherein the magnetic plate has a frequency of kHz. 3. The method of attaching a magnetic plate to a disc substrate according to claim 1, wherein the magnetic plate is attached to the disc substrate while the disc substrate is being held by the disc holding means. 4. An ultrasonic wave generating means comprising a horn having a stepped portion at a tip thereof in a state where the magnetic plate is arranged in a magnetic plate accommodating recess provided in the center of the disk substrate. A disk characterized by forming a protrusion protruding from the peripheral edge of the magnetic plate accommodating recess toward the inside of the recess by contacting with the peripheral edge, and attaching the magnetic plate to the disk substrate by this protrusion. How to attach a magnetic plate to a substrate.