Dynamic magnetic information storage or retrieval – General recording or reproducing – Specifics of biasing or erasing
Reexamination Certificate
2001-05-14
2003-07-15
Faber, Alan T (Department: 2651)
Dynamic magnetic information storage or retrieval
General recording or reproducing
Specifics of biasing or erasing
C360S137000, C361S149000
Reexamination Certificate
active
06594099
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a device for erasing data, for example, servo data stored on a magnetic disk.
2. Description of the Related Art
A typical disk device comprises a magnetic disk; a spindle motor for rotating the magnetic disk; a head for writing/reading data on/from the magnetic disk, etc. Such a disk device also has a case referred to as an enclosure case used to house the magnetic disk, the spindle motor, the head, etc. On the magnetic disk is formed a data storing layer by means of sputtering. The data storing layer consists of a magnetic thin film formed on the surface of a substrate consisting of glass or such a non-magnetic material as Al or the like. Generally, the enclosure case comprises a box-like base having an opening and a plate-like top cover for covering the opening of the base.
The disk device, after assembling the magnetic disk, the spindle motor, and other components in the base, is completed by covering the opening of the base with the top cover. After this assembling, servo data, which is position data of the magnetic disk, is written on the magnetic disk together with other necessary data. The disk device, when such servo data is written thereon, is put to various performance tests in prior to the delivery. Some disk devices are judged as defective ones in these tests. Defective disk devices are disassembled so that non-defective parts are collected and reused. Before a magnetic disk is reused, however, the servo data must be erased from the disk so as to prevent the servo data written newly on the disk from interference with the old one. And, if the servo data itself is judged to be imperfect, the servo data must also be erased. Some data is also written in the above tests and such test data must be erased from the defective disk devices.
The official gazette of Japanese Published Unexamined Patent Application No. 7-29106 discloses an effective technique for erasing such data from a magnetic disk. According to the technique, a rod provided with a permanent magnet is inserted between rotating magnetic disks, thereby erasing data from those magnetic disks. Although the method disclosed in Application No. 7-29106 is effective, it is premised here that a rod provided with a permanent magnet is inserted between magnetic disks. Consequently, when magnetic disks are loaded in the above disk device, the enclosure case of the disk device becomes an obstacle, so that the rod provided with the permanent magnet cannot be inserted between the magnetic disks. In some case, therefore, the magnetic disks are unloaded from the disk device so as to erase data therefrom. For example, imperfectly written servo data can be erased while magnetic disks are loaded in the disk device. Thus, the technique disclosed in Application No. 7-29106 cannot respond to necessary requirements.
A disk device that can erase data from magnetic disks loaded in a disk device is disclosed in International Publication WO98/49674. This disk device will be described below with reference to
FIGS. 11 through 13
.
As shown in
FIG. 11
, a data eraser
400
comprises an upper magnet fixer
402
, a lower magnet fixer
404
, and a linkage
406
. The upper magnet fixer
402
fixes permanent magnets
412
and
414
and the lower magnet fixer
404
fixes permanent magnets
416
and
418
. The permanent magnets
412
and
414
are adjoining so that their different poles attract each other. The permanent magnets
416
and
418
are also adjoining so that their different poles attract each other. The permanent magnets
412
and
416
face each other in the vertical direction while different poles are disposed on opposed surfaces of the permanent magnet
412
and the permanent magnet
416
. The permanent magnets
414
and
418
also face each other in the vertical direction, but different poles are disposed on opposed surfaces of the permanent magnet
414
and the permanent magnet
418
.
FIG. 12
is an explanatory view of a magnetic field formed by the data eraser
400
shown in FIG.
11
. As shown in
FIG. 12
, the magnetic field is generated almost in the center of the data eraser
400
, mainly oriented in the horizontal direction. At present, the horizontal magnetic recording method is employed for magnetic disks. In order to erase data from such a magnetic disk, therefore, a magnetic field must be applied in the direction parallel to the magnetic disk. In addition, the strength of the magnetic field must be larger than the coercive force of the magnetic disk.
FIG. 13
shows a method for erasing data stored on a magnetic disk
22
with use of the data eraser
400
. In
FIG. 13
, the top cover is removed so as to show the movement of the components in the disk device clearly. A magnetic disk
22
is rotated at first. A spindle motor in the disk device
10
is driven to rotate the magnetic disk
22
. Next, the disk device
10
is inserted into a gap between the upper and lower magnet fixers
402
and
404
of the data eraser
400
. At this time, the data eraser
400
is inserted so that its side where a head slider S does not exist is inserted between both fixers
402
and
404
and the head slider S is retreated as shown with an arrow in FIG.
13
. This is to block the influence of a magnetic field generated by the data eraser
400
. In this state, if the magnetic disk
22
is kept rotated, a magnetic field is applied to the whole surface of the magnetic disk
22
in parallel, thereby data is erased from the magnetic disk
22
.
In order to erase data stored on a magnetic disk, a magnetic field that is over the coercive force of the magnetic disk must be applied onto the magnetic disk. In recent years, the recording density of such the magnetic disk has been improved remarkably, thereby the coercive force of the magnetic disk is also increased significantly. This is why a magnetic field is required that has enough strength to erase data stored on the magnetic disk.
In some cases, a magnetic disk is unloaded from the object disk device when data is also erased from the disk. As described above, however, data is erased from a magnetic disk loaded in the disk device, of course. The disk device has a spindle motor for rotating the magnetic disk and this spindle motor has a permanent magnet. The spindle motor is disposed in the center of the rotation of the magnetic disk. Consequently, if a strong magnetic field is applied to the magnetic disk so as to erase data therefrom, the magnetic field becomes a demagnetizing field of the permanent magnetic of the spindle motor, thereby it causes the characteristics of the spindle motor to be degraded. In order to improve the coercive force of the magnetic disk, it is just required to apply a stronger magnetic field to the magnetic disk, but this causes the characteristics of the spindle motor to further be degraded at the same time.
Under such circumstances, it is an object of the present invention to provide a data eraser that can apply a strong magnetic field to the magnetic disk while suppressing the strength of the magnetic field to be applied to the spindle motor.
SUMMARY OF THE INVENTION
The present invention provides a data eraser that erases data stored on a magnetic disk as described above. The data eraser comprises magnetic field generating means having two permanent magnets, each of which forms different poles, are disposed so that different poles adjoin on both an obverse and a reverse thereof; and a yoke disposed on a surface except either the obverse or the reverse of the magnetic field generating means. This data eraser erases data from the magnetic disk with use of a leaked magnetic flux from each of the obverse and the reverse on which different poles are adjoining. Consequently, the magnetic flux from either the obverse or reverse of the magnetic field generating means is not required originally so as to erase data. And, it is important to block such the unnecessary leaked magnetic flux that will affect the permanent magnet of the spindle motor.
To avoid such the problem, therefore, the data era
Faber Alan T
Martin Robert B.
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