Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the head
Reexamination Certificate
1999-01-05
2001-12-04
Sniezek, Andrew L. (Department: 2651)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the head
C360S048000, C360S077080, C360S055000
Reexamination Certificate
active
06327112
ABSTRACT:
BACKGROUND OF THE INVENTION
In a magnetic disk unit, a plurality of circular magnetic disks are fixed to the drive shaft of the spindle motor and rotated and driven together with the spindle motor. An air layer (air bearing) is generated between the surface of a rotating magnetic disk and the slider with a magnetic head mounted and the magnetic head relatively moves on the magnetic disk with a fine interval held. The surface of the magnetic disk is finely textured so as to prevent it from sticking to the slider and improve magnetic characteristics (characteristics of flying height).
When the magnetic head relatively moves on the magnetic disk, an offtrack is generated due to the fluttering phenomenon caused by vibration of the bearing in the spindle motor and a minute bending of the magnetic disk, a texture mark on the magnetic disk, and vibration of servo information which is recorded on the magnetic disk beforehand.
Therefore, the track follow-up control is executed so as to demodulate a track position signal from the reproduced servo information during data recording and reproducing and suppress the amount of offtrack on the basis of the signal. In the embedded servo system, the servo information area is arranged at each fixed interval on the same recording track as the data recording area and the pattern for detection of servo information is recorded in the area beforehand.
SUMMARY OF THE INVENTION
The present invention relates to a control system for positioning a recording head for recording tracks provided on a circular information recording medium of a magnetic disk unit or an optical disk unit and recording information and more particularly to an information storage apparatus using a function for detecting the offtrack state that the recording head is off a desired position.
Since the number of servo areas is limited because it is necessary to reserve as many data storage areas as possible, it is difficult to set a sufficiently wide track bandwidth in follow-up control. Therefore, when the amount of offtrack is suddenly changed due to vibration, a follow-up error remains due to the shortage of bandwidth in follow-up control and an occurrence of offtrack cannot be avoided.
When this offtrack becomes larger, a recorded magnetization pattern is recorded overlapped to the adjacent track. In this case the adjacent track which was recorded prior to the squeezing track becomes narrower because a part of this track is invaded by the squeezing track. Moreover, the crosstalk from the squeezing track becomes larger when reproducing this track. By these reason, a suspicion that the squeezed adjacent track cannot be reproduced without any error is enlarged.
Therefore, during recording of data, by monitoring the amount of offtrack, the recording operation (offtrack write) in the offtrack state is prevented. Namely, the technology for inhibiting the recording operation when it is detected that the amount of offtrack before recording or during recording exceeds the specified value (hereinafter, called the threshold value) is applied.
Also on an optical disk for recording and reproducing data using light or both light and magnetism, in the same way as with a magnetic disk, by demodulating a track position signal from servo information reproduced from a recording track during data recording and monitoring the amount of offtrack during recording, the recording operation in the state of offtrack is prevented.
There is an appropriate setting range for the threshold value in this technology for preventing from offtrack recording. If this value is excessively large, there is a danger that the adjacent recorded magnetization pattern is destroyed and cannot be reproduced without error. On the other hand, when the value is excessively small, it is frequently detected that the amount of offtrack exceeds this threshold value, and the recording operation is stopped, and it is necessary to wait by one rotation or more for re-recording, so that the throughput reduces substantially. Therefore, it is necessary to set the threshold value within a range that these phenomena will not be generated.
To correspond to an increase in storage capacity and a decrease in cost in a recent information storage apparatus, it is essential to improve the recording density and it is necessary to increase the recording density in the circumferential direction on a recording medium and also the track density. However, when the track pitch is narrowed, the distance between a track and its adjacent track becomes smaller, so that the track is easily overlapped with the adjacent recording track. Therefore, the upper limit of the threshold value in the aforementioned technology for preventing from offtrack recording is reduced.
Furthermore, this function for preventing from offtrack recording detects the position relation with the servo pattern recorded beforehand and does not directly detect the distance from the adjacent data track. Furthermore, this servo pattern is not identical with that of the adjacent track and the follow-up control is executed with independent servo patterns when each track is followed. Therefore, there is the possibility that the servo pattern on a track is recorded in the offtrack position due to vibration, and in this case the distance between the adjacent track and the data track becomes smaller.
Namely, the distance from the recorded magnetization pattern recorded on the adjacent track is indirectly inferred based on the standard of the servo pattern including an error and the actual distance is not known. Therefore, a worst situation that the adjacent track squeezes the data track and the servo patterns of the these two tracks are located in the offtrack position is forced to suppose. It is necessary even in this situation to make the upper limit of the threshold value more smaller so as to prevent the recorded magnetization pattern of the data track from overlapping with the recorded magnetization pattern of the adjacent track.
Under the aforementioned restriction condition, even if the track density is comparatively low, this settable range is vanished and a more narrower track pitch cannot be realized.
To solve these problems, dedicated areas (areas for recording position error checking pattern) for recording a position error checking pattern are provided at a plural locations on the same track as the data recording area on a magnetic disk and the position error checking pattern is recorded in the areas during data recording.
A recording circuit having a function for recording the above position error checking pattern with more recording current than that at general data recording time is provided. Furthermore, a reproducing circuit having a function for demodulating leakage signals (hereinafter called adjacent track position signals) from the position error checking patterns of the left and right adjacent tracks and detecting the distance from the recorded magnetization patterns on the adjacent tracks in the radial direction is provided.
The aforementioned position error checking patterns are arranged by shifting the positions in the circumferential direction from those on the adjacent tracks so as to prevent the demodulation operation of the adjacent track position signals and the recording operation of the position error checking pattern of the data track from being performed at the same time.
The present invention directly detects the distance from the recorded magnetization patterns recorded on the adjacent tracks by detecting the adjacent track position signals when recording data on the data track and judges prevention from offtrack recording. As a result, although in the conventional technology for preventing from offtrack recording, since the actual distance from the recorded magnetization patterns recorded on the adjacent tracks is not known, it is forced to reduce the upper limit of the threshold value on the assumption of a worst condition, according to the present invention, the upper limit of the threshold value can be increased and the track density can be increased.
Therefor
Hamaguchi Takehiko
Ide Hiroshi
Maruyama Yohji
Nakamura Atsushi
Nishida Yasutaka
Hitachi , Ltd.
Kenyon & Kenyon
Sniezek Andrew L.
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