Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the head
Reexamination Certificate
2000-05-19
2002-08-13
Sniezek, Andrew L. (Department: 2651)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the head
C360S077020
Reexamination Certificate
active
06433950
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to magnetic storage devices and, more particularly, to magnetic storage devices which employ shielded magneto-resistive (MR) transducer heads.
BACKGROUND OF THE INVENTION
Manufacturers of disk drives have relatively recently moved from using thin-film inductive (“TFI”) heads to magneto-resistive (“MR”) heads to perform the disk drive's read functions. One of the main reasons for the switch is due to the greater sensitivity of MR heads over TFI heads. As a result, areal densities have dramatically increased.
Due to their sensitivity, however, MR heads sometimes pickup spurious signals emitted by power transformers, motors and the like. In an effort to reduce or eliminate the pickup of the aforementioned spurious signals, disk drive manufactures have placed shields around the MR heads. Such shields, however, have caused additional problems.
Specifically, the shields have been found to be susceptible to variations in their magnetic states. These variations can be magnetically coupled to the MR head which can cause unwanted shield-related side readings. For the most part, the data regions of the magnetic disk have not caused problematic variations in the magnetic state of the shield because the information placed on the disk is written in the data regions in a relatively random fashion. However, the servo regions of the disk have caused problematic magnetic variations in the shields and, hence, problematic shield-related side readings, due to the fact that servo-burst patterns are written in a radially coherent manner.
The above-described shield-related side readings can cause, among other things, a decrease in (1) the linear range of the MR head when reading off-track servo information; and, (2) the off-track signal-to-noise ratio. Furthermore, in extreme cases, the shield-related side readings can cause the disk drive to completely malfunction.
Accordingly, there is a need to minimize and/or eliminate the magnetic variations in the shields which can cause shield-related side readings. The present invention is designed to overcome the aforementioned problems and meet the aforementioned, and other, needs.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a variable-phase servo-burst pattern which can increase: (1) the linear range of the MR head when reading off-track servo information; and, (2) the off-track signal-to-noise ratio.
In accordance with the invention, a disk which incorporates variable-phase servo burst pattern is disclosed. The disk has servo information thereon. In a preferred embodiment, the servo information includes a first servo burst pattern written on a first track and a second servo burst pattern written on a second track. Both the first servo burst pattern and the second servo burst pattern include a plurality of transition pulses. The corresponding transition pulses of the first servo burst pattern and the second servo burst pattern are 180 degrees out of phase from one another.
A method of writing servo-information which is used to position a magneto-resistive head on a centerline of a track is also disclosed. The method includes the steps of (1) writing a first servo burst pattern on a first track, the first servo burst pattern having a plurality of transition pulses; and (2) writing a second servo burst pattern on a second track, the second servo burst pattern having a plurality of transition pulses, wherein the corresponding transition pulses of the first servo burst pattern and the second servo burst pattern are 180 degrees out of phase from one another.
Other objects, features and advantages of the invention will be apparent from the following specification taken in conjunction with the following drawings.
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Feng, “Cross Talk in Shielded Magnetoresistive Sensors,” 2 pages.
Shi et al., “Shield-Related Side Reading in MR Heads,” 3 pages.
Min et al., “Track Position Dependence of Performance Attributes in Permanent Magnet Biased MR/SAL Heads,” IEEE Transactions on Magnetics, pp. 67-73, vol. 32, No. 1 (Jan. 1996).
Zhu et al., “Narrow Track Recording Characteristics in Thin Film Media,” IEEE Transactions on Magnetics, pp. 984-989, vol. 33, No. 1 (Jan. 1997).
Maxtor Corporation
Sigmond David M.
Sniezek Andrew L.
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