JP2000195124A - Magnetic disk device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic disk device capable of reducing the deformation or distortion of a magnetic disk by making uniform the clamping force of the magnetic disk. SOLUTION: A clamper 46 for clamping a magnetic disk fixed in the outer peripheral surface of the hub 28 of a spindle motor 18 is formed like a disk, its outer peripheral end part constitutes an abutting part abutted on the magnetic disk, and in its center part, a center hole 67 and a hexagonal positioning projecting part protruded to the hub side are formed. In the upper end wall 34 of the hub, a hexagonal positioning recessed part 70 and a screw hole 72 are formed. The clamper is fixed on the hub while the positioning projecting part is fitted in the positioning recessed part of the hub side, and its relative rotational shift from the hub is regulated. The clamper is fixed to the hub by screwing a screw 68 through the center hole into the screw hole of the hub, and thus a disk clamping force is generated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a magnetic disk drive used for a laptop computer, a book computer, and the like.

[0002]

2. Description of the Related Art In recent years, in small portable computers such as personal computers, laptop computers, and book computers, magnetic disk devices have been widely used as memories for storing a large amount of information.

In general, a magnetic disk device includes a spindle motor for rotating a magnetic disk as a recording medium, a magnetic head for recording and reproducing data on and from the magnetic disk, and a magnetic head movably supported on the magnetic disk. And a voice coil motor (hereinafter referred to as VCM) for driving the carriage assembly to move and position the magnetic head on a desired track of the magnetic disk.

A spindle motor has a cylindrical hub functioning as a rotor, and a flange is formed at one end of the hub. And, the magnetic disk is mounted on the outer periphery of the hub, and a clamper screwed to the upper end of the hub,
It is held in a state of being sandwiched between the flange of the hub.

[0005] Usually, the clamper is formed of a disk-shaped metal plate, has a contact portion with the magnetic disk at the peripheral edge thereof, and has a central hole made of a through hole for inserting a screw at the center. ing. Further, the clamper is formed flat except for the peripheral portion, and only the peripheral portion is bent toward the magnetic disk.

In the clamper, the screw inserted into the center hole of the clamper is screwed into a screw hole formed at the upper end of the hub of the spindle motor with the contact portion abutting on the upper surface of the inner peripheral portion of the magnetic disk. The clamper is fixed to the hub by fastening the center of the clamper to the upper surface of the hub. Then, by clamping the center portion with a screw, the flat portion of the clamper is elastically deformed, and the resulting tensile stress obtains a disk clamping force.

Further, when the clamper is screwed to the hub of the motor, it is necessary to prevent relative rotation between the clamper and the hub. Therefore, the clamper has a plurality of positioning through holes provided around the through holes, and a plurality of positioning recesses are formed on the upper end surface of the hub corresponding to these through holes. At the time of assembly, a plurality of positioning pins provided on the jig are fitted into the recesses of the hub through the through holes of the clamper, and the clamper is screwed in a state where relative rotation between the clamper and the hub is prevented. ing.

[0008]

However, as described above, when a plurality of through holes are formed around the center hole of the clamper, the clamping force acting on the magnetic disk from the clamper depends on the existence of the through holes. It becomes uneven in the circumferential direction. Such non-uniformity of the clamper force has a large effect on the deformation of the magnetic disk, particularly on the in-plane distortion, and when a temperature change occurs, the magnetic force is placed at a position corresponding to the through hole of the clamper. Disk distortion occurs.

When the magnetic disk is distorted,
The ability of the magnetic head to follow the surface of the magnetic disk is reduced, causing a track shift and making it difficult to reduce the flying height of the magnetic head.

The present invention has been made in view of the above points, and an object of the present invention is to provide a magnetic disk drive capable of reducing the deformation and distortion of a magnetic disk by making the clamping force of the magnetic disk uniform. is there.

[0011]

To achieve the above object, a magnetic disk drive according to the present invention has a rotatable hub on which a magnetic disk is mounted, and a spindle motor for driving the magnetic disk to rotate. A disk-shaped disk holder attached to the hub and holding the magnetic disk, a magnetic head for recording and reproducing information on and from the magnetic disk, and a carriage supporting the magnetic head movably with respect to the magnetic disk An assembly; and a voice coil motor that moves the carriage assembly to position the magnetic head at an arbitrary position on the magnetic disk.

The hub has a substantially cylindrical main body, an upper end wall facing the disc retainer, a flange provided on the outer peripheral surface of the main body, and a positioning recess formed at the center of the upper end wall. And a screw hole formed at the bottom of the positioning recess, wherein the magnetic disk is fitted on the outer peripheral surface of the main body of the hub while being mounted on the flange, and the disk retainer is An abutting portion provided on the outer peripheral edge portion and abutting on the surface of the magnetic disk; and a central portion formed so as to protrude toward the upper end wall of the hub. A positioning projection that regulates relative rotation with the hub, a center hole formed through the positioning projection at the center and aligned with a screw hole of the hub, and a screw is inserted into the screw hole through the center hole. Screwing More, it is characterized in that it is fixed to the upper end wall of the hub.

The positioning recess and the positioning projection are:
It has a non-circular outline, for example, a polygonal or elliptical outline. According to the invention, the clamper has a non-circular fitting recess formed on the surface on the side opposite to the upper end wall of the hub and including the center hole and into which the assembly jig is fitted. ing.

Further, according to the magnetic disk drive of the present invention, the hub of the spindle motor has a substantially cylindrical main body, an upper end wall facing the disk holder, a flange provided on the outer peripheral surface of the main body, A screw hole formed at the center; and a plurality of positioning recesses formed at equal intervals along the circumferential direction around the screw hole, and the magnetic disk is mounted on the flange. In this state, the hub is fitted to the outer peripheral surface of the main body of the hub. Further, the disk retainer has an abutting portion provided on an outer peripheral edge portion and abutting on the surface of the magnetic disk, a center hole formed at the center and aligned with a screw hole of the hub, and a center portion around the center hole. A plurality of protrusions are formed at equal intervals along the circumferential direction, protrude toward the upper end wall of the hub, and are fitted into positioning recesses of the hub to regulate the relative rotation between the disc retainer and the hub. And a fixing convex portion, which is fixed to the upper end wall of the hub by screwing a screw through the center hole into the screw hole.

According to the magnetic disk drive configured as described above, when the disk retainer is fixed to the upper end wall of the hub with the screw, the positioning projection provided at the center of the disk retainer is positioned on the hub. By fitting into the recess, it is possible to screw the disk retainer in a state where the relative displacement between the disk retainer and the hub is eliminated. This eliminates the need to provide a plurality of positioning through holes in the intermediate portion of the disk holder, reduces non-uniformity of the pressing force acting on the magnetic disk from the disk holder caused by these through holes, and Deformation and distortion can be reduced.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which a magnetic disk drive of the present invention is applied to a hard disk drive (hereinafter referred to as an HDD) will be described in detail with reference to the drawings.

As shown in FIGS. 1 and 2, the HDD is
A case 10 having a case body 12 and a top cover 14 is provided. The case body 12 has a rectangular bottom wall and four side walls erected on side edges of the bottom wall.
The top cover 14 is screwed to the case main body 12 with a plurality of screws 11 and closes an upper end opening of the case main body.

In the case body 12, two magnetic disks 16a and 16b as magnetic recording media, and a spindle motor 1 for supporting and rotating these magnetic disks.
8. A plurality of magnetic head assemblies 2 each having a magnetic head for recording and reproducing information on and from a magnetic disk
0, a carriage unit 22 rotatably supporting these magnetic head assemblies, a voice coil motor 24 for rotating and positioning the carriage assembly, and a substrate unit 21 having a preamplifier and the like are housed.

A printed circuit board (not shown) for controlling operations of the spindle motor 18, the voice coil motor 24, and the magnetic head assembly 20 is screwed to the outer surface of the bottom wall of the case body 12.

As shown in FIG. 2, the spindle motor 18
Includes a bracket 26 fixed to the bottom wall of the case body 12 and functioning as a base portion, and a hub 28 rotatably supported by the bracket and functioning as a rotor. A cylindrical support sleeve 30 is integrally formed at the center of the bracket 26.

The hub 28 has a cylindrical main body 32, an upper end wall 34 having a closed upper end, and a pivot 36 projecting from the center of the upper end wall and extending simultaneously inside the main body 32.
And are integrally formed. An annular flange 38 is formed on the outer periphery of the lower end of the main body 32.

The hub 28 includes a main body 32 and a support sleeve 30.
And the pivot 36 is disposed coaxially inserted into the support sleeve 30 so that the pivot 3
A pair of ball bearings 40 are fitted between 6 and the support sleeve 30. Therefore, the hub 28 is provided with a pair of ball bearings 40.
Accordingly, the support sleeve 30 is rotatably supported by the support sleeve 30.

An annular permanent magnet 42 is coaxially fixed on the inner peripheral surface of the hub body 32, and a stator 44 having a core and a coil is disposed on the outer periphery of the support sleeve 30.
Is attached and is adjacently opposed to the permanent magnet 42. Then, by energizing the coils of the stator 44, a driving torque is generated and the hub 28 is rotationally driven.

The two magnetic disks 16a and 16bc are
The spindle motor 18 is coaxially fitted with the outer peripheral surface of the hub 28 and is laminated along the axial direction of the hub.
A spacer ring 43 fitted to the hub 28 is interposed between two adjacent magnetic disks 16a and 16b.

The magnetic disks 16a and 16b and the spacer ring 43 are sandwiched between a flange 38 and a disk-shaped clamper 46 screwed to the upper end wall 34 of the hub 28, and are fixed to the outer periphery of the hub body 32. ing. These magnetic disks 16a and 16b are connected to the spindle motor 1
8 is driven to rotate at a predetermined speed. The structure of the clamper 46 will be described later in detail.

On the other hand, as shown in FIG. 1, the carriage assembly 22 has a substantially cylindrical bearing assembly 48 fixed on the bottom wall of the case body 12, and extends from the bearing assembly toward the magnetic disk. And four arms 50. The magnetic head assembly 20 is fixed to the extending end of each arm 50.

Each magnetic head assembly 20 has an elongated suspension 52 formed by a leaf spring, and a magnetic head 54 attached to the tip of the suspension. Note that the suspension 52 may be formed integrally with the arm using the same material as the arm. Also, four arms 50 and four magnetic head assemblies 2
Numeral 0 is disposed so that two magnetic heads face each other with a magnetic disk interposed therebetween. Accordingly, when the carriage assembly 22 rotates about the bearing assembly 48, each magnetic head 54 can move to an arbitrary track of the corresponding magnetic disk.

The VCM 24 includes a lower yoke 56 fixed to the bottom wall of the case body 12, an upper yoke 57 facing the lower yoke at a predetermined distance, and a VCM 24 fixed to the inner surface of the lower yoke and facing the upper yoke. Not a permanent magnet,
It has. Further, the VCM 24 includes a voice coil (not shown) which is mounted on a support frame extending from the bearing assembly 48 of the carriage assembly 22 and is movable between the upper yoke 57 and the permanent magnet. Has become. When a current is applied to the voice coil, a magnetic field is generated, and the interaction with the magnetic field generated from the permanent magnet causes the carriage assembly 22 to rotate.

The board unit 21 provided in the case body 12 is provided with a board body 58 installed on the inner surface of the bottom wall 12a.
And a flexible wiring board 60 extending from the substrate body;
have. A plurality of electronic components are mounted on the board main body 58. The extending end of the flexible wiring board 60 is fixed to the bearing assembly 48 of the carriage assembly 22 and is connected to four magnetic heads 54 via wiring (not shown).

Next, the clamper 46 which functions as a disk holder for fixing the magnetic disks 16a and 16b to the hub 28 of the spindle motor 18 will be described in detail. As shown in FIG. 2 to FIG.
Is formed in a disk shape by pressing a metal plate. The peripheral portion of the clamper 46 is bent toward the magnetic disk to form an annular contact portion 62 that contacts the upper surface of the inner peripheral portion of the magnetic disk 16a. The contact portion 62
Is set slightly larger than the diameter of the hub body 32 of the spindle motor 18.

At the center of the clamper 46, a positioning convex portion 64 protruding toward the upper end wall 34 of the hub body 32 is formed. Since the positioning convex portion 64 is formed by press working, a concave portion 66 is formed on the back side of the convex portion 64, that is, on the center of the surface of the clamper 46 opposite to the hub body 32. The recess 66 is provided for fitting an assembly jig described later. The positioning convex portion 64 and the concave portion 66 are formed in a polygonal shape, for example, a hexagonal profile. Further, a center hole 67 for inserting a tightening screw 68 is formed at the center of the clamper 46, and extends through the bottom wall of the positioning projection 64.

On the other hand, a hexagonal positioning recess 70 corresponding to the positioning projection 64 of the clamper 46 is formed in the center of the upper end wall 34 of the hub body 32. A screw hole 72 extending coaxially with the hub body 32 is formed in the bottom wall of the positioning recess 70.

The clamper 46 is provided with the positioning projection 6.
4 is mounted on the upper end wall 34 of the hub main body in a state where it is fitted into the positioning recess 70 of the hub main body 32 and the abutment portion 62 is in contact with the upper surface of the inner peripheral portion of the magnetic disk 16a. The tightening screw 68 inserted into the center hole 67 of the hub body 32 is fixed to the upper end wall 34 by screwing it into the screw hole 72 of the hub body 32. By tightening the screw 68, the center of the clamper 46 is moved to the hub body 3.
2 slightly deforms toward the upper end wall 34 side, and as a result, the contact portion 6
2 generates a clamping force on the magnetic disks 16a and 16b.

In the HDD configured as described above,
The magnetic disk 1 is attached to the hub body 32 of the spindle motor 18.
When attaching the spacers 6a, 16b and the spacer 43, as shown in FIG. 3, first, the magnetic disk 16b, the spacer ring 43, the magnetic disk 16
a are fitted in order and placed on the flange 38. Next, the clamper 46 is placed on the upper end wall 34 of the hub main body 32, and the magnetic disks 16a and 16b and the spacer ring 4 are placed between the abutting portion 62 of the clamper and the flange 38 of the hub main body.
Hold 3 At this time, the positioning protrusion 6 of the clamper 46 is used.
4 is fitted into the positioning recess 70 on the hub body 32 side, and is initially positioned. The positioning projection 64 and the positioning recess 70 are formed in a hexagonal shape.
2, relative displacement, in particular, relative rotation is regulated.

In this state, the rotation of the clamper 46 and the hub body 32 is regulated by using the fixing jig 74. As shown in FIGS. 3 and 6, the fixing jig 74 is formed in an elongated plate shape, and a fitting projection 76 is formed in the center of one surface thereof. The fitting projection 76 has a hexagonal outline corresponding to the recess 66 of the clamper 46, and can be fitted into the recess 66. In the center of the fixing jig 74,
A through hole 78 extending through the fitting protrusion 76 is formed. Then, the fitting projection 76 is inserted into the recess 6 of the clamper 46.
The fixing jig 74 is arranged on the clamper in a state of being fitted to the clamp 6, and the rotation of the clamper 46 and the hub body 32 is regulated by pressing the fixing jig.

Then, in this state, as shown in FIG.
The fastening screw 68 is screwed into the screw hole 72 of the hub body 32 through the through hole 78 of the fixing jig 74 and the center hole 67 of the clamper 46, and the clamper 46 is fixed to the upper end wall 34 of the hub body 32. As a result, the clamping force generated in the clamper 46 acts on the magnetic disks 16a, 16b and the spacer ring 43, and these are fixed to the hub main body 32.

According to the HDD configured as described above,
The clamper 46 is connected to the hub body 32 by the tightening screw 68.
When the clamper is fixed to the upper end wall 34, the positioning protrusion 64 provided at the center of the clamper is fitted into the positioning recess 70 formed on the hub body side, so that the relative position between the clamper and the hub body is increased. Screwing can be performed in a state where the displacement is eliminated. Therefore, it is not necessary to provide a plurality of positioning through-holes in the middle portion of the clamper 46, that is, outside the center hole 67, and it is possible to reduce non-uniformity of the clamper force caused by these through-holes, and In contrast, a uniform clamping force can be applied to the magnetic disk. Thereby, deformation and distortion of the magnetic disk are reduced, and H
The thickness of the DD can be reduced, and the flying height of the magnetic head can be reduced.

Further, according to the above configuration, the clamper 46
Has a positioning recess 66 formed on the opposite side of the positioning projection 64, and includes the fastening screw 68 because the head of the fastening screw 68 is housed in the positioning recess 66. The overall height of the spindle motor 18 can be reduced, and as a result, the overall HDD can be made thinner.

In the above-described embodiment, the positioning projection 64 of the clamper 46, the positioning recess 70 of the hub body 32, and the fitting projection 76 of the fixing jig 74 are hexagonal, but the invention is not limited to this. Any polygon may be used as long as it is a non-circular shape that can prevent relative rotation, and may be another polygonal shape or an elliptical shape.

FIGS. 7 to 10 show a main part of an HDD according to another embodiment of the present invention. According to this embodiment, as shown in FIGS.
Reference numeral 6 denotes a center hole 67 penetratingly formed at the center thereof, and three positioning projections 8 formed around the center hole at regular intervals in the circumferential direction and projecting toward the hub body 32.
0. These positioning projections 80 are formed by press working, and a fitting recess 82 is formed on the opposite side of each positioning projection. When the radius of the clamper 46 is R, the positioning projection 80 is about 3 times the radius R.
It is formed in a region a having a radius of 0% or less.

On the other hand, the upper end wall 34 of the hub main body 32 is formed with a screw hole 72 located at the center thereof and three positioning recesses 84. These positioning recesses 84
Are formed around the screw hole 72 at equal intervals along the circumferential direction, and are arranged corresponding to the positioning projections 80 of the clamper 46.

The clamper 46 is provided with the positioning projection 8.
0 is mounted on the upper end wall 34 of the hub main body in a state in which each of the magnetic heads 0 is fitted into the positioning recess 84 of the hub main body 32 and the abutment portion 62 is in contact with the upper surface of the inner peripheral portion of the magnetic disk 16a, The fastening screw 68 inserted into the center hole 67 of the clamper 46 is fixed to the upper end wall 34 by screwing it into the screw hole 72 of the hub body 32. Also, screw 68
By tightening, the center of the clamper 46 is slightly deformed toward the upper end wall 34 of the hub main body 32, and as a result, the contact portion 62 generates a clamping force on the magnetic disks 16a and 16b.

In the HDD configured as described above,
The magnetic disk 1 is attached to the hub body 32 of the spindle motor 18.
When attaching the spacers 6a, 16b and the spacer 43, as shown in FIG. 3, first, the magnetic disk 16b, the spacer ring 43, the magnetic disk 16
a are fitted in order and placed on the flange 38. Next, the clamper 46 is placed on the upper end wall 34 of the hub main body 32, and the magnetic disks 16a and 16b and the spacer ring 4 are placed between the abutting portion 62 of the clamper and the flange 38 of the hub main body.
Hold 3 At this time, the three positioning projections 80 of the clamper 46 are fitted into the three positioning recesses 84 on the hub main body 32 side, respectively, to perform initial positioning. By fitting the positioning projection 80 and the positioning recess 84, the relative displacement between the clamper 46 and the hub main body 32, in particular, the relative rotation is regulated.

In this state, the rotation of the clamper 46 and the hub body 32 is regulated by using the fixing jig 74. As shown in FIGS. 8 and 10, the fixing jig 74 is formed in an elongated plate shape, and a through hole 78 is formed in the center thereof.
Also, three fitting projections 8 are provided on one surface of the fixing jig 74.
6 are protruded, and are arranged around the through hole 78 at equal intervals along the circumferential direction. These fitting projections 86 can fit into the recesses 82 of the clamper 46. Then, the fixing jig 74 is arranged on the clamper with the fitting protrusion 86 fitted in the recess 82 of the clamper 46, and the rotation of the clamper 46 and the hub body 32 is regulated by pressing the fixing jig.

In this state, a fastening screw 68 is screwed into the screw hole 72 of the hub body 32 through the through hole 78 of the fixing jig 74 and the center hole 67 of the clamper 46, and the clamper 46 is attached to the upper end wall 34 of the hub body 32. Fixed to. As a result, the clamping force generated in the clamper 46 acts on the magnetic disks 16a, 16b and the spacer ring 43, and these are fixed to the hub main body 32.

The other structure is the same as that of the above-described embodiment, and the same portions are denoted by the same reference numerals and detailed description thereof will be omitted.

In another embodiment configured as described above, when the clamper 46 is fixed to the upper end wall 34 of the hub body 32 by the tightening screw 68, the positioning projection 80 provided at the center of the clamper is used. By fitting into the positioning recess 84 formed on the hub main body side, screwing can be performed with the relative displacement between the clamper and the hub main body eliminated. Therefore, clamper 4
It is not necessary to provide a plurality of through holes for positioning in 6, and it is possible to reduce the non-uniformity of the clamper force caused by these through holes and apply a uniform clamping force to the magnetic disk in the circumferential direction. It becomes possible. As a result, deformation and distortion of the magnetic disk can be reduced, the thickness of the HDD can be reduced, and the flying height of the magnetic head can be reduced.

In another embodiment, the number of positioning projections 80 provided on the clamper 46 may be two or more, and can be increased or decreased as needed. Further, the present invention is not limited to the above-described embodiment, and can be variously modified within the scope of the present invention. For example, the number of magnetic disks can be increased or decreased to two.

[0049]

As described above in detail, according to the present invention, when the disc holder is fixed to the upper end wall of the hub by the screw, the positioning projection provided at the center of the disc holder is formed on the hub. By fitting into the positioning recess, it is possible to screw the disk retainer in a state where the relative displacement between the disk retainer and the hub is eliminated. This eliminates the need to provide a plurality of through holes for positioning in the middle portion of the disk holder, and achieves a uniform clamping force acting on the magnetic disk from the disk holder caused by these through holes, thereby deforming the magnetic disk. A magnetic disk device with reduced distortion can be provided.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view of an HDD according to an embodiment of the present invention.

FIG. 2 is a longitudinal sectional view showing a spindle motor portion of the HDD.

FIG. 3 is an exploded perspective view showing a step of attaching a magnetic disk and a clamper to the spindle motor.

FIG. 4 is a perspective view showing the bottom side of the clamper.

FIG. 5 is a plan view and a sectional view of the clamper.

FIG. 6 is a perspective view showing a rotation fixing jig.

FIG. 7 is a sectional view showing a spindle motor portion of an HDD according to another embodiment of the present invention.

FIG. 8 is an exploded perspective view showing a step of attaching a magnetic disk and a clamper to the spindle motor.

FIG. 9 is a plan view and a sectional view of the clamper.

FIG. 10 is a perspective view showing a rotation fixing jig.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Case 12 ... Case main body 16a, 16b ... Magnetic disk, 18 ... Spindle motor 20 ... Magnetic head assembly 22 ... Carriage assembly 24 ... Voice coil motor 28 ... Hub 32 ... Hub main body 34 ... Upper end wall 46 ... Clamper 54 ... Magnetic Head 62: Contact portion 64: Positioning convex portion 66: Recess 67: Center hole 74: Fixing jig 76: Fitting convex portion 78: Through hole 80: Positioning convex portion 82: Recess 84: Positioning concave

Claims (8)

[Claims] 1. A spindle motor having a rotatable hub on which a magnetic disk is mounted, for driving the magnetic disk to rotate, a disk-shaped disk holder attached to the hub and holding the magnetic disk, A magnetic head for recording / reproducing information on / from a disk, a carriage assembly supporting the magnetic head movably with respect to the magnetic disk, and moving the carriage assembly to move the magnetic head to an arbitrary position on the magnetic disk. Wherein the hub comprises a substantially cylindrical main body, an upper end wall facing the disc retainer, a flange provided on the outer peripheral surface of the main body, and a center of the upper end wall. A positioning recess formed in the portion, and a screw hole formed in the bottom of the positioning recess; The disc is fitted on the outer peripheral surface of the main body of the hub while being mounted on the flange, and the disc retainer is provided on an outer peripheral edge portion and abuts on the magnetic disc surface and a central portion. A positioning projection that is formed and protrudes toward the upper end wall of the hub and that fits into a positioning recess of the hub to regulate relative rotation between the disc retainer and the hub; And a center hole formed through the center hole and aligned with the screw hole of the hub, and fixed to the upper end wall of the hub by screwing a screw through the center hole into the screw hole. . 2. The positioning recess and the positioning projection,
2. The magnetic disk drive according to claim 1, wherein the magnetic disk drive has a non-circular contour. 3. The positioning recess and the positioning projection,
3. The magnetic disk drive according to claim 2, wherein the magnetic disk drive has a polygonal outline. 4. The positioning recess and the positioning projection,
3. The magnetic disk drive according to claim 2, wherein the magnetic disk drive has an elliptical contour. 5. The clamper has a non-circular fitting recess formed on the surface opposite to the upper end wall of the hub and including the center hole and into which an assembly jig is fitted. 5. The magnetic disk drive according to claim 1, wherein: 6. The magnetic disk drive according to claim 5, wherein the fitting recess is formed in a shape similar to the positioning projection. 7. A spindle motor having a rotatable hub on which a magnetic disk is mounted, for driving the magnetic disk to rotate, a disk-shaped disk holder attached to the hub and holding the magnetic disk, A magnetic head for recording / reproducing information on / from a disk, a carriage assembly supporting the magnetic head movably with respect to the magnetic disk, and moving the carriage assembly to move the magnetic head to an arbitrary position on the magnetic disk. The hub is formed at the center with a substantially cylindrical main body, an upper end wall facing the disc retainer, and a flange provided on the outer peripheral surface of the main body. A screw hole, and a plurality of positioning recesses formed at equal intervals along the circumferential direction around the screw hole. The magnetic disk is fitted on the outer peripheral surface of the main body of the hub in a state where the magnetic disk is mounted on the flange, and the disk retainer is provided on an outer peripheral edge portion and abuts on the surface of the magnetic disk. And a center hole formed at the center and aligned with the screw hole of the hub, and formed around the center hole at equal intervals along the circumferential direction at the center and on the upper end wall side of the hub. A plurality of positioning protrusions that protrude and fit into the positioning recesses of the hub to regulate the relative rotation of the disc retainer and the hub, and that a screw is screwed into the screw hole through the center hole. A magnetic disk drive fixed to an upper end wall of the hub. 8. The apparatus according to claim 5, wherein said plurality of positioning projections are provided in an area having a radius of about 30% or less of a radius of said magnetic disk with respect to said center hole. The magnetic disk device according to the above.