Abstract:
The object of the present invention is to provide a method and apparatus configured to allow an externally generated magnetic field to simultaneously erase a portion of the information on a disk, or a plurality of disks, within a magnetic storage device. The invention allows high throughput of erased magnetic storage devices, as in a mass production environment. Additionally, the invention allows a variety of magnetic storage device configurations in that the erasing is non-intrusive to the housing of the magnetic storage device and does not depend on the number of disks within the magnetic storage device.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method and an apparatus for erasing information recorded on a disk of a magnetic disk device. More particularly, the present invention relates to a method and an apparatus for erasing servo data and test data used in fabrication steps, particularly in repairing steps, of a magnetic recording device. 
     2. Background Art 
     Servo data are written in servo data writing steps during the manufacturing process of magnetic disk devices. The manufacturing process also includes writing and testing test data. Defects in the servo data frequently cause disk drives to fail the drive tests. In these cases, generally the disk drive must be disassembled so that any reusable parts can be recovered and so as to avoid the environmental and financial costs of discarding the entire disk device. Recovering the disk is particularly important because disks are costly and it is difficult to recycle disks after they have been discarded. 
     Any servo or test data on the recovered disks generally must be erased before the disks can be incorporated into a new disk drive so as prevent interference with the new servo and test data that will be recorded on the disk. 
     Several conventional methods for erasing information recorded on a disk have been used including: 
     1. DC erase by a servo track writer; 
     2. DC erase by a dedicated erasing device; and 
     3. Erase by an erasing bar. 
     In servo track writer DC erase methods, information on the disk is erased by DC signals applied to a servo track writer write head. Although this method can completely erase the information on the disk, it is unsuitable for a mass production process since servo track writers are costly and large sized. Also servo track writer DC erase methods are comparatively slow. 
     Dedicated erasing devices provide a lower cost alternative to servo track writer DC erase methods. However, conventional dedicated erasing devices are generally too slow to be suitable for mass production processes. 
     In DC erase methods using an erasing bar, a bar on which a permanent magnet is mounted is inserted between the rotated disks to erase all of the information on the disks, as described in Japanese published patent application H7-29106. A problem with conventional erasing bar DC erase methods is that while they may be used with disk devices having a flat type base as shown in FIG. 2, the methods are not readily used with disk devices having a bath tub type base as shown in FIG. 3 since a space for inserting the erasing bar from a lateral direction is required. That is, in a disk device  200  shown in FIG. 2, a spindle motor  204  is mounted on a flat type base  202 , and magnetic disks  206  and  208  are mounted on the spindle motor  204 . Information written on disks  206  and  208  is erased by removing a top cover, not shown, and inserting the erasing bar  210  from a side of the disk device. In contradistinction, in the disk device  300  shown in FIG. 3, a spindle motor  304  is mounted on a bath tub type base  302 , and magnetic disks  306  and  308  are mounted on the spindle motor  304 . Even if a top cover, not shown, is removed, the sides of the disks are still covered by the bath tub type base  302 , thereby preventing insertion of erasing bar  310 . 
     A further drawback of DC erase methods using erasing bars is that the vertical position of the erasing bar must be precisely controlled due to the narrow spacing of the disks, and positional deviations can damage the disks. Furthermore, the space between disks is decreasing as a result of efforts to increase the storage capacity, and reduce the size of disk drives. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a method and an apparatus for erasing information recorded on disks in magnetic disk devices irrespective of the shape of the base of the disk device. 
     Another object of the present invention is to provide a method and an apparatus for rapidly and reliably erasing information recorded on disks in magnetic disk devices. 
     A further object of the present invention is to provide an inexpensive system for erasing information on disks, while ensuring the disk device does not contact the magnets. 
     A method of erasing information recorded on a disk recording medium in a magnetic disk device comprising the disk recording medium, a motor for rotating the disk recording medium, a base attached to the motor, and a magnetic head, according to one embodiment of the present invention comprises generating a magnetic field outside of the magnetic disk device, and inserting the magnetic disk device into the magnetic field, wherein the magnetic field passes through the base to erase information recorded on the disk recording medium. 
     An apparatus for erasing information recorded on a disk recording medium in a magnetic disk device comprising the disk recording medium, a motor for rotating the disk recording medium, a base attached to the motor, and a magnetic head, according to one embodiment of the present invention comprises: a magnet to generate a magnetic field, and a handler to insert the magnetic disk device into the magnetic field. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 shows a block diagram of a hard disk device (HDD) to which the present invention can be applied; 
     FIG. 2 shows a portion of a disk device with a flat type base; 
     FIG. 3 shows a portion of a disk device with a bath tub type base; 
     FIG. 4 shows an erasing apparatus for erasing information on disks in a disk device in accordance with an embodiment of the present invention; 
     FIG. 5 shows a magnetic field generated by the FIG. 4 erasing apparatus in accordance with the present invention; 
     FIGS.  6 (A) and  6 (B) show a method of erasing the information on disks in accordance with an embodiment of the present invention; 
     FIG. 7 shows a flow chart of a method of erasing information on disks in accordance with an embodiment of the present invention; 
     FIG. 8 shows an alternative embodiment for erasing information on disks in accordance with the present invention; and 
     FIG. 9 shows a further alternative embodiment for erasing the information on disks in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a block diagram of a hard disk device (HDD) to which the present invention can be applied. Disk device  100  includes a control section  110  and a disk section  130 . Control section  110  includes a host interface controller (HIC)  112  connected to a host system  10 , a hard disk controller (HDC)  114  connected to host interface controller  112  for controlling disk section  130 , a channel  116  connected to hard disk controller  114  for controlling read/write signals, MPU  118  connected to HIC  112 , HDC  114  and channel  116  for controlling them, and RAM  120  connected to MPU  118  for storing microcode executed by MPU  118 . Disk section  130  includes a motor  134  for rotating a spindle  132 . Disks  136 A and  136 B are fixed on spindle  132  for integrally rotating with spindle  132 . Two disks are shown in FIG. 1, but disk section  130  may include only one disk or more than two disks. 
     Heads  138 A,  138 B,  138 C and  138 D opposing each surface of the disks are supported by actuator arms  140 A,  140 B,  140 C and  140 D, respectively. Actuator arms  140 A through  140 D are attached to a voice coil motor (VCM)  144  through a pivot shaft  142 . Heads  138 A through  138 D are moved to a desired position along a radial direction of the disks by the pivot shaft  142  rotation. Motor  134  and VCM  144  are connected to HDC  114  which controls their operation. Heads  138 A through  138 D are connected to channel  116 , which controls the read/write signals. 
     Disk section  130  is covered by an enclosure to prevent any contamination from the outside atmosphere entering into disk section  130 . The enclosure comprises a base and a top cover, not shown. Motor  134  and VCM  144  are fixed onto the base, as shown in FIG. 2 or FIG.  3 . The flat type base, as shown in FIG. 2, or the bath tub type base, as shown in FIG. 3, are used as the base. A top portion and a side portion of the disk section  130  is covered by the top cover. 
     FIG. 4 shows an erasing apparatus  400  for erasing information on disks in a disk device in accordance with an embodiment of the present invention. Erasing apparatus  400  includes a top portion  402  to hold magnets, a bottom portion  404  to hold magnets and a connecting portion  406 . Permanent magnets  412  and  414  are fixedly attached to top portion  402 , and permanent magnets  416  and  418  are fixedly attached to bottom portion  404 . Permanent magnets  412  and  414  are adjacently positioned with their poles reversed. Permanent magnets  416  and  418  are also adjacently positioned with their poles reversed. Permanent magnets  412  and  416  are arranged on a common axis passing through them with their poles reversed along the common axis. The permanent magnets  414  and  418  are also arranged on a common axis passing through them with their poles reversed along the common axis. Connecting portion  406  couples top portion  402  and bottom portion  404  to fix the relative positions of the permanent magnets with respect to each other. Connecting portion  406  can be replaced by other means that fix the relative positions of the permanent magnets with respect to each other. In a preferred embodiment, permanent magnets  412 ,  414 ,  416  and  418  each comprise a permanent magnet of high magnetic flux density, for example Nd—Fe—B N— 42  magnet fabricated by Tokin Corp. Electromagnets can also be used in place of the permanent magnets. 
     FIG. 5 shows a magnetic field generated by erasing apparatus  400 . It is apparent that a relatively large magnetic field in a horizontal direction is generated in a center portion of the erasing apparatus  400 . In this embodiment, the magnetic field directed from the left side to the right side is used, but a magnetic field in the opposite direction can be generated by changing the arrangement of the permanent magnets. A magnetic field directed in the vertical direction can be generated for application to vertical magnetic recordings. 
     FIGS.  6 (A) and  6 (B) show a method of erasing information on disks according to an embodiment of the present invention. FIG. 7 shows a flow chart of a method of erasing information on the disks according to an embodiment of the present invention. In step  702  in FIG. 7, the disks are rotated, as shown in FIG.  6 (A). The disks can be rotated by activating motor  134 , or by an external motor. Using an external motor is preferable where the rotation of the disks being erased, may be impaired due to eddy currents, as for example may occur with disks having an aluminum substrate. In step  704 , the heads are moved to outer radial disk locations. Moving the heads in this manner away from the permanent magnets prevents adverse leakage flux in MR heads, which can damage the heads. If the heads are not vulnerable to leakage flux damage then step  704  can be omitted. In disk devices which have a load/unload mechanism for the heads, the heads can be unloaded in advance. Magnetic shields can be mounted on the side surfaces of the top portion  402  and the bottom portion  404  to prevent the magnetic flux leakage. In step  706 , disk device  100  is inserted between top portion  402  and bottom portion  404  of erasing apparatus  400  to expose the disks to the fixed direction magnetic field to erase the information recorded on the disks, as shown in FIG.  6 (B). In step  708 , after a sufficient time period to erase the information on the entire surface of the disks, disk device  100  is removed from erasing apparatus  400 . In step  710 , the heads are moved to their respective contact start stop (CSS) zones. In step  712 , disk rotation is stopped, and the erasing operation of the information on the disks is complete. Although the disk device without the top cover is shown in FIGS.  6 (A) and  6 (B), magnets sufficiently powerful to erase the disks with the top cover on can readily be used. 
     FIG. 8 shows an alternative embodiment of the present invention. This embodiment uses a U shaped top portion  802  and a U shaped bottom portion  804 , and the permanent magnets form corresponding U shapes. U shaped top and bottom portions  802  and  804  reduce the magnetic flux leakage to the motor. Reducing magnetic flux leakage to the motor can prevent adverse effects on the motor such as leakage of a fluid magnetic seal, can be effectively prevented. 
     FIG. 9 shows a further alternative embodiment of the erasing apparatus of the present invention. As shown in FIG. 9, the erasing apparatus  900  for erasing the information on the disks includes a disk device insertion/removal section  910  and a magnet section  920 . The disk device insertion/removal section  910  is connected to a control device  930  to fix the disk device by a clamp mechanism  912  and to automatically insert the disk device into the magnet section  920  or remove the disk device from the magnet section  920  by a feeding mechanism  914 . Probe pins  916  supply the power to the spindle motor of the disk device to rotate the disks. Erasing apparatus  900  provides a reliable, inexpensive system for erasing information on disks, while ensuring the disk device does not contact the magnets. 
     In accordance with the present invention, the information recorded on the disks in the magnetic disk device can be erased irrespective of the shape of the base of the disk device; the information recorded on the disks in the disk device can be rapidly and reliably erased; and an erasing apparatus provides a reliable, inexpensive system for erasing information on disks, while ensuring the disk device does not contact the magnets. 
     The present invention completely erases all of the information recorded on each of a plurality of disks in disk devices, without requiring the disk devices to be disassembled, as demonstrated experimentally. Furthermore, embodiments of the present invention completely erase all of the information recorded on each of a plurality of disks in disk devices without removing the top cover. Such embodiments allow disks to be erased outside of a clean room environment. 
     While the present invention has been described with reference to a few specific embodiments, the description is illustrative of the invention and is not to be construed as limiting the invention. Various modifications may occur to those skilled in the art without departing from the true spirit and scope of the invention as defined by the appended claims.