Dynamic magnetic information storage or retrieval – Record copying – Contact transfer
Reexamination Certificate
2002-05-01
2004-11-02
Hudspeth, David (Department: 2853)
Dynamic magnetic information storage or retrieval
Record copying
Contact transfer
Reexamination Certificate
active
06813106
ABSTRACT:
BACKGROUND
The invention relates generally to magnetic printing and, more particularly, to magnetic printing of storage media.
Various servo techniques or approaches have been developed to reduce the effects of tracking error and thus improve track density. Although known servo techniques vary somewhat, most involve mechanisms for dynamically moving the read head laterally to continually re-position it over the recorded data track. They also use servo heads to provide corrective positioning information.
One approach stores servo information in the form of a pattern of servo marks (or “spokes”) on a surface of a storage medium, such as a disk, and reads the recorded servo information to produce a position error signal for accurate head positioning. The servo information can be dedicated (that is, located on a continuous track of servo information) or embedded within the user data.
One well-known mechanism that is used to record the servo pattern is the servo writer process, which formats the surface of the disk with the servo pattern, typically during disk manufacturing. For high track density storage media, the servo writer process can be quite time-consuming, as it requires “N” revolutions (where N is the number of tracks per inch times the number of servo marks per track) to complete.
Another servo writing mechanism is the servo self-write process. The servo self-write process constructs a servo pattern from a reference pattern that is printed on the disk's surface. One type of print process involves the use of a master disk with ferromagnetic teeth. Typically, the disk (or “product” disk) surface is pre-magnetized with a field that is opposite to the printing field. The master disk is brought into contact with the product disk and a printing field is applied to the master disk. The application of the printing field causes magnetization in the direction of the printing field to occur on the product disk in the regions that are not shielded by the master disk teeth. In the regions under the teeth (the shielded regions), the magnetization is unchanged. The magnetic transitions, that is, the borders between the regions under the teeth and regions between teeth, are used by the servo self-write process to construct the servo pattern. Contributions of the field under the teeth to the regions both under and between the teeth, however, can cause an imperfect printing to occur. An imperfect printing, in turn, can result in weak signals, false readings (subpulses) and extra noise, all of which interfere with normal data storage operations. The printing process may be improved through decreased teeth spacing and increased teeth thickness (for better shielding), but such improvements are limited by master disk manufacturing process capabilities.
SUMMARY
In one aspect, the invention provides a method of and apparatus for printing on a storage medium. The method includes applying preconditioning fields to the storage medium to precondition the storage medium prior to applying a printing field, one of the preconditioning fields magnetizing the storage medium in a direction of the printing field and at least another of the preconditioning fields magnetizing the storage medium in a direction opposite to the direction of the printing field. The method further includes applying the printing field to the preconditioned storage medium to produce a pattern of magnetic transitions thereon.
Embodiments of the invention may include one or more of the following features.
Applying the preconditioning fields includes applying a first field of a first magnitude to magnetize a first population of grains of the material in the surface of the medium in the direction of the printing field, applying a second field of a second magnitude to magnetize a second population of grains of the material in the surface of the medium in a direction opposite to the direction of the printing field and applying a third field of a third magnitude to magnetize a third population of grains of the material in the surface in the direction of the printing field.
The first, second and third magnitudes are chosen so that magnetization of only a portion of the second population is changed by the application of the printing field.
The first magnitude is greater than the magnitude of a saturation field, the second magnitude is less than the magnitude of the saturation field and greater than a magnitude of the printing field, and the third magnitude is less than the magnitude of the printing field but greater than a magnitude of a field below which little change in magnetization occurs.
The first field, the third field and the printing field are reverse fields, and the second field is a forward field.
Applying the printing field includes providing a master having ferromagnetic teeth formed thereon, placing the ferromagnetic teeth into proximity with the surface of the storage medium after applying the preconditioning fields and applying the printing field to cause a change in magnetization only in regions on the surface of the medium between the teeth to produce the pattern of magnetic transitions.
The pattern is a reference pattern from which a servo pattern is constructed.
In another aspect, the invention provides for a media printing system that includes a printing device configured to generate a pattern on a magnetic storage medium, the pattern comprising a pattern of magnetic transitions, and a preconditioning device configured to precondition the magnetic storage medium to reduce the range of magnetic switching fields required to generate the pattern from the range of magnetic switching fields required to generate the pattern without the preconditioning.
Particular implementations of the invention may provide one or more of the following advantages.
Undesirable subpulses are eliminated without requiring further advances in the master manufacturing process capabilities. As a result of the preconditioning, all of the “easy-to-switch” grains (i.e., the sources of subpulses under master disk teeth) and “hard-to-switch” grains (i.e., the sources of subpulses between the master disk teeth) are premagnetized in the direction of the printing field. At the same time, grains with intermediate switching fields are magnetized in a direction opposite to the direction of the printing field. Only these intermediate switching grains change orientation in response to the printing field. Therefore, the range of the switching fields needed to cause switching between the teeth and prevent switching under the teeth is reduced by removing both the high field and the low field tails of the switching distribution, making it easier to achieve a clean printed pattern.
Other features and advantages of the invention will be apparent from the following detailed description and from the claims.
REFERENCES:
patent: 6433944 (2002-08-01), Nagao et al.
Cesari and McKenna LLP
Davidson Dan I
Hudspeth David
Maxtor Corporation
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