Dynamic magnetic information storage or retrieval – General processing of a digital signal – Data in specific format
Reexamination Certificate
2000-07-25
2003-03-04
Faber, Alan T. (Department: 2651)
Dynamic magnetic information storage or retrieval
General processing of a digital signal
Data in specific format
C360S049000, C360S077080, C360S078140, C360S016000, C360S135000
Reexamination Certificate
active
06529341
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a magnetic recording/reproduction device with high recording density and large capacity.
BACKGROUND ART
The recording density of magnetic recording/reproduction apparatus is constantly increasing to realize small size and large capacity. Especially, in the field of hard disk drives, which are typical magnetic writing devices, an areal recording density of more than 1 Gbit/in
2
is already available on the market, and an areal recording density of 10 Gbit/in
2
is expected within a couple of years. The technology proceeds with a rapid pace.
One of the primary technical factors that has enabled such high recording densities is the increase of linear recording density, due to improvements of the magnetic recording medium, the head-disk interface performance, and new signal processing methods such as “partial response”. However, in recent years, the rate of increase of the track density has exceeded that of the linear recording density, and has therefore become a primary factor when it comes to increasing the areal recording density. Practical use of magnetoresistive heads, whose read-back signal performance is superior to that of conventional inductive type heads, has contributed to the progress in the track density. At present, it is possible to read signals from tracks of only a few microns width with good S/N ratio by using a magnetoresistive type head. Furthermore, it is expected that with further improvement of the head performance, the track pitch will reach the sub-micron range in the near future.
To read a signal with high S/N ratio by tracing such a narrow track, the tracking servo technique for the magnetic head plays a very important role. For example, a conventional hard disk has areas that are distributed at predetermined angles over an entire revolution of the disk, i.e. 360 degrees. Signals such as a tracking servo signal, an address signal and a clock signal are written into these areas. In this specification, these signals are referred to as “preformat” signals. A magnetic head can monitor its position by reading these signals in predetermined intervals, and correctly trace a track while correcting any displacement in the radial direction of the magnetic disk.
The preformat signals, i.e. tracking servo signal, address signal, clock signal etc., serve as reference signals for precisely tracing a track with the magnetic head. Therefore, precise track positioning is required for these information signals. Present hard disk drives are equipped with a built-in magnetic head that records the tracking servo signal, the address signal, the clock signal etc. by using a special servo-track writing device, after the magnetic disks and the magnetic heads have been installed in the drive. The track positioning can be realized with the necessary precision when the recording is performed while precisely controlling the position of the built-in magnetic head with an external actuator, which is part of the servo-track writing device.
To this date, there were the following problems with preformat recordings of servo signals, address information signals, and clock signals with a magnetic head using the above-described dedicated servo track recording device.
First of all, recording with a magnetic head is basically linear recording based on the relative motion between the head and the recording medium. Therefore, with the above method of recording while precisely controlling the position of the magnetic head using a dedicated servo-track recording device, not only is a lot of time required for the preformat recording, but also the dedicated servo track recording device is relatively expensive, which leads to a considerable increase in cost.
Secondly, because of the widening of the recording field caused by the spacing between head and medium and the pole-shaped recording head, the magnetization transition of the preformat-recorded track edges lacks sharpness. The current tracking servo technology is to detect the misplacement of the magnetic head in the radial direction of the disk with the change in the reproduction output amplitude when scanning the disk with the head at a distance from the track. Consequently, there is a need not only for a good S/N ratio when precisely tracking the track with the head when reproducing the data information signal recorded between the preformatted recording areas, but also for a sharp change in the reproduction output amplitude when the head is misplaced away from the track (i.e. the off-track characteristics). The above-mentioned problem goes against this need, and makes the realization of precise tracking servo technology for future sub-micron track recordings very difficult.
On the other hand, in the specification of Tokkai Hei 10-40544 (international application number: PCT/JP97/02519), the inventors of the present invention proposed a preformatting technology, wherein a magnetization pattern corresponding to a pattern in the surface of a master information carrier is recorded on a magnetic recording medium by contacting the surface of the magnetic recording medium with the surface of the master information carrier, which has an orderly ferromagnetic pattern corresponding to a preformat information signal formed on the surface of a substrate.
With the configuration disclosed in the specification of Tokkai Hei 10-40544, a magnetization pattern corresponding to the ferromagnetic film pattern on the master information carrier is recorded on the magnetic recording medium with the recording magnetic field generated by the ferromagnetic film pattern on the master information carrier, which is magnetized in one direction. In other words, by forming a ferromagnetic film pattern corresponding to the tracking servo signal, the address information signal, and the clock signal on the surface of the master information carrier, a preformat recording corresponding to these signals can be recorded on the magnetic recording medium.
The characteristic feature of this configuration is the static en-bloc recording without relative movement between the master information carrier and the recording medium. Due to this feature, the technique disclosed in Tokkai Hei 10-40544 displays the following useful effects with regard to the problems of prior preformat recording.
Firstly, because the surface is recorded en bloc, the time required for the preformat recording is much shorter than in conventional recording methods using a magnetic head. Moreover, an expensive servo recording device for recording while precisely controlling the position of the magnetic head is unnecessary. Consequently, it is possible to increase the productivity of the preformat recording considerably, and to reduce the production costs.
Secondly, because the recording is static without a relative movement between the master information carrier and the recording medium, the spacing between the two during recording can be minimized by contacting the surface of the master information carrier with the surface of the magnetic recording medium. Moreover, there is no widening of the magnetic recording field due to the pole shape of the magnetic head, as there is in the case of recording with a magnetic head. Thus, the magnetization transition at the preformat-recorded track edges is much sharper than with conventional recording with a magnetic head, so that a more precise tracking becomes possible.
Several preferable configurations have been suggested to let the preformat-recorded signal pattern provide optimum performance for handling tracking servo signals, address signals and clock signals. However, since in these conventional techniques, which use a special servo-track writing device, a separate magnetic head is built into the drive, there are severe limitations to the magnetization pattern of the preformat-recorded signal.
For example, the recording track width of a magnetic head in a magnetic recording/reproduction device, such as a hard disk drive, is usually narrower than the track pitch, and a guard band of a certain width is provided between adj
Hamada Taizou
Ishida Tatsuaki
Miyata Keizou
Ryonai Hiroshi
Tohma Kiyokazu
Faber Alan T.
Rosenthal & Osha L.L.P.
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