JP4154378B2 - Magnetic disk unit - Google Patents

Description

  The present invention relates to a magnetic disk apparatus, and in particular, an angle formed by a relative movement direction between a magnetic head that performs an information recording / reproducing operation and a recording medium that stores information, and a magnetization reversal region that is recorded and formed on the recording medium. The present invention relates to prevention of deterioration of the head off-track characteristic due to the left-right asymmetry of the erase bandwidth that occurs when the skew angle (hereinafter referred to as skew angle) is not 0 degree.

  FIG. 2 shows the result of observation with a magnetic force microscope of the recording state recorded on the disk by the head. Here, data 1 is recorded on data 3 written as a base. As shown in FIG. 2, there are erase bands 2 (areas in which information is not recorded but the background is erased) on both sides of the track width of the recorded data 1. Normally, the adjacent track is not erased when positioned on the target track (following state), but the recording operation is performed before the vibration (settling vibration) is sufficiently established immediately after seeking from another track. When recording is performed in a state where a large offset is generated due to an external impact, the erase band 2 erases information on an adjacent track. In order to prevent such erroneous data erasure, in the current magnetic disk apparatus, an offset larger than the write inhibit slice value determined by the apparatus usually occurs on the target recording track based on the position signal obtained every moment. If this happens, do not perform the recording operation.

  FIG. 3 shows a rotary actuator system which is the mainstream system of the current magnetic disk apparatus. In the rotary actuator system, the actuator 6 that supports the head 5 rotates around a point A in the figure to move the inner and outer tracks on the disk 4 that stores information. As shown in FIG. 4, in the rotary actuator system, the relative movement direction between the magnetic head 5 that performs information recording / reproducing operation and the disk 4 that stores information, the element position of the head 4, and the rotary actuator rotation center A are determined. The angle φ formed by the connecting straight direction changes as it moves from the inner periphery to the outer periphery. Therefore, as shown in FIG. 5, an angle θ (hereinafter referred to as a skew angle) formed by the traveling direction of the disk and the reversal region of the magnetization 9 recorded and formed on the disk changes as it moves from the inner periphery to the outer periphery. . It has been reported that the erase band becomes asymmetric due to the presence of the skew angle [K. Wiesen et al., IEEE Trans. Magn., Vol. 29, pp. 4002, 1993].

  FIG. 6 shows a schematic diagram of the recording state on the disc when the self track and the adjacent tracks on both sides are recorded with the skew angle being 0 degree. Here, it is assumed that the self track is recorded first, the inner peripheral side adjacent track is recorded, and the outer peripheral side adjacent track is finally recorded. When the effective recorded track width is Tww as shown in FIG. 6 and the left and right erase band widths (equal to the inner and outer peripheral sides) are set to EB, the track is erased at the left end and the right end of the own track. There is no difference in the width of the area.

  On the other hand, assuming that the skew angle takes a finite value other than 0 degrees, FIG. 7 shows a schematic diagram of the recording state on the disc when the self track and the adjacent tracks on both sides are recorded as in FIG. Here, as in FIG. 6, it is assumed that the self track is recorded first, the inner peripheral side adjacent track is recorded, and finally the outer peripheral side adjacent track is recorded. The effective recording track width is Tww (s), the inner erase band width is EB (s) in, and the outer erase band width is EB (s) out. FIG. 7 shows a state where the inner peripheral side erase band EB (s) in is larger than EB (s) out. As shown in FIG. 7, when the adjacent tracks on both sides of the own track are recorded at a track pitch position separated by Tww (s) + EB (s) out, the erase band of the outer peripheral side adjacent track becomes the data track area of the own track. The self-data is destroyed due to the outer periphery adjacent to a smaller track pitch. However, the adjacent track on the inner circumference recorded at the same distance does not yet destroy the data track area of the self track. From this, it can be seen that if the inner erase band and the outer erase band of the track to be recorded are asymmetric, the recording data is destroyed from one side of the adjacent track as the track pitch is reduced.

Based on the above recording state, the 747 curve [JK Lee et al., IEEE Trans. Magn., Vol. 26, pp. 2475, 1990] is affected by the presence or absence of erase band asymmetry.
FIG. 8 shows an example in which the erase band asymmetry dependence of the 747 curve is calculated using the algorithm disclosed in the paper [F. Tomiyama et al., IEEE Trans. Magn., Vol.34, pp.1970, 1998]. Shown in It can be seen that the off-track capability decreases in the region where the track pitch is small due to the erase band asymmetry. This is because the larger erase band on the left and right attacks the adjacent track and starts erasing part of the information recorded on the adjacent track.

  Due to asymmetry with respect to the erase band, the left and right write inhibit slice values are the same as before even if the larger erase band on the left and right erases adjacent track data and the Off-Track Capability decreases. Below, the write-inhibit slice value must only be reduced and tightened from the point of view of data protection. However, if the write inhibit slice value is set to a small value, the write operation is frequently prohibited due to temporary deterioration of positioning accuracy due to a slight disturbance, so that the frequency of rotation waiting increases and the performance of the device decreases. There is a fear. From the viewpoint of securing device performance, it is necessary to minimize the write inhibit slice value.

The same is true for the seek complete slice level as well as the write inhibit slice value. As shown in FIG. 9, the seek completion slice level refers to a predetermined seek completion slice level and the head distance to the target track position when approaching the target track during seek, and seek completion is performed. This is a slice level at which seek completion is determined when the distance is smaller than the slice level. Similar to the write inhibit slice value, even if there is a residual vibration with the same amplitude at the same time in the seek from the inner circumference to the outer circumference and the seek from the outer circumference to the inner circumference, if erase band asymmetry exists, There is a difference in the possibility of destruction of adjacent data. For this reason, it is necessary to set the seek completion condition to be small in accordance with the direction in which data corruption is likely to occur for both seeks. Since reducing the seek completion slice level leads to an increase in seek time, there is a possibility that the apparatus performance may deteriorate.
As in the case of the write inhibit slice value, it is necessary to minimize the seek completion slice level from the viewpoint of device performance.

K. Wiesen et al., IEEE Trans. Magn., Vol. 29, pp. 4002, 1993

  In view of the above background, it is an object of the present invention to prevent deterioration in head off-track characteristics and apparatus performance even when there is an erase band asymmetry caused by a skew angle.

  At locations where the inner peripheral erase band is larger than the outer erase band, the adjacent track on the outer peripheral side can easily erase its own track, so that the write inhibit slice for the inner peripheral offset is changed to the write inhibit for the outer peripheral offset. Make it smaller than a slice.

  Conversely, where the outer periphery side erase band is larger than the inner periphery side erase band, this is dealt with by reversing the inner periphery and the outer periphery in the description of the problem solving means described above.

  Similarly, the seek completion slice level can be set to a different value between the seek from the inner circumference to the outer circumference and the seek from the outer circumference to the inner circumference, and the seek condition on the side where the adjacent track can be easily erased can be handled. Is possible.

 By implementing the present invention, the access time to the target track can be reduced without erroneously erasing adjacent tracks.

(Example 1)
In this embodiment, a rotary actuator type magnetic disk device is used. This magnetic disk apparatus has a structure in which an actuator 6 that supports a head 5 moves on a disk 4 that stores information by rotating around a point A in the figure. Since the rotary actuator system is used, the angle formed by the relative movement direction between the magnetic head 5 that performs the information recording / reproducing operation and the disk 4 that stores the information, and the linear direction that connects the element position of the head 4 and the rotation center A of the rotary actuator. φ changes as it moves from the inner periphery to the outer periphery. FIG. 1 is a flowchart showing a first embodiment of the present invention. After receiving a recording command on the target recording track from the controller, it is determined whether or not the inner erase band is larger than the outer erase band in the target track. This determination is performed, for example, by storing information on erase band asymmetry on the inner and outer circumferences in a table. When the inner erase band is larger than the outer erase band, the write inhibit slice level Sin for the inner offset and the write inhibit slice level Sout for the outer offset are set.
Sin <Sout (Formula 1)
Set to be. Then, seek is performed on the target track, and when the seek operation is completed, the recording operation is performed. This setting is performed so that the data on the adjacent track on the inner periphery side is not destroyed by the large erase band on the inner periphery side. If the write inhibit slice is small, data can be securely protected when settling residual vibration or abnormal vibration occurs, but the time required to start the recording operation becomes long. Assuming the above equation 1 as in this embodiment, the average access time in the entire apparatus can be improved as compared with the case where both the write inhibit slices to the inner and outer circumferential offsets are both reduced in the worst case. . On the contrary, even when the outer peripheral side erase band is larger than the inner peripheral side erase band, the above-described contents can be similarly achieved by replacing the “inner periphery” and the “outer periphery” and rereading them.

(Example 2)
The discriminating routine for comparing the sizes of the inner and outer erase bands in the first embodiment is larger or smaller than the skew angle of the adjacent track on the outer circumference than the magnitude of the skew angle on the target track to be recorded. It may be changed to such a determination. That is, as can be easily estimated from FIG. 4, the radius dependence of the skew angle usually changes continuously. When it is larger, the write inhibit slice for the inner circumferential offset may be made smaller than the write inhibit slice for the outer circumferential offset. On the contrary, when it is small, the write inhibit slice for the outer peripheral offset may be made smaller than the write inhibit slice for the inner peripheral offset.

Example 3
When a settling response waveform as shown in FIG. 9 is shown in a magnetic disk apparatus having an algorithm for determining a seek completion by obtaining an offset amount with respect to a target track from a position signal and comparing it with a predetermined seek completion slice level. When the position error becomes smaller than the seek completion slice level, the recording operation can be performed. In other words, this means that recording is performed with a position error corresponding to the seek completion slice level. As in Example 1 and the like, in a track where the size of the erase band on the inner peripheral side and the outer peripheral side is not equal, such as a track whose skew angle is not 0 degrees, the larger erase band tends to erase the adjacent track. The data is protected by keeping the seek completion slice level on the larger erase band side smaller than the slice level on the opposite side, and the seek completion slice level for both inner and outer offsets is adjusted to match the larger erase band. Rather than setting both to the same exact value, the average seek time is reduced.

Example 4
Assume that at the time when the recording command reaches the head with respect to the target track, the head is located at a position separated from the target track by the number of tracks on the inner peripheral side, and then seek toward the target track is started. In general, with respect to a seek to be a target track, with respect to a seek that crosses the same number of tracks, there is no difference in seek time depending on a mechanical factor in terms of seek from the inner periphery to the outer periphery and seek from the outer periphery to the inner periphery.
However, if the number of tracks traversed by the seek is different, there will be a difference in seek time due to a difference in seek distance and a difference in bearing characteristics. When a target recording track is a track whose skew angle is not 0 degree, adjacent data erase is likely to occur due to erase band asymmetry when seeking from the inner circumference to the outer circumference and seeking from the outer circumference to the inner circumference across the same number of tracks. By making the seek time in the direction larger than the seek time in the opposite direction, you can wait until the settling vibration is well established for the seek in the direction that tends to disappear, so you can perform the recording operation The average seek time can be shortened without causing deterioration of the off-track characteristic, as compared with the case where the seek time in both directions is set to be the same so that the erase is not caused in both directions.

(Example 5)
When a rotational impact as shown in FIG. 10 is applied to the magnetic disk device while performing the recording operation, the head moves and is offset with respect to the disk in the direction opposite to the direction of angular acceleration applied to the device. Therefore, in order to correct the offset in the apparatus, the head position is restored based on the detected position signal.
When a track whose skew angle is not 0 degrees is set as a target recording track, if an offset exceeding the write-inhibit slice occurs due to application of angular acceleration, the offset in the direction in which adjacent track data is likely to be erased due to erase band asymmetry is generated. In order not to cause erasure, when an impact is detected by an acceleration sensor incorporated in the device in advance, the offset in that direction is set so that recording can be started after the offset is well established. Increasing the time is safer, and better performance is obtained for both offset directions than waiting for the time that is more difficult to offset.

The flowchart which shows one Example of this invention. The figure which shows the data recording state on the disk using a head. The figure which shows the structure of the magnetic disk apparatus of a rotary actuator system. FIG. 4 is a schematic diagram showing the relationship between the magnetic disk and the head in FIG. 3. The figure which defines a skew angle. FIG. 5 is a schematic diagram of a data recording state at a skew angle of 0 degree. The schematic diagram of the recording state of the data in the state in which a skew angle exceeds 0 degree | times. 747 curve calculation result with or without erase band asymmetry. Explanatory drawing of the time response of the position error at the time of a seek, and a seek completion slice level. 1 is a diagram illustrating a magnetic disk device according to the present invention.

Explanation of symbols

1 ... Recorded data 2 ... Erase band 3 ... Background data 4 ... Disk
5 .... Head, 6 .... Rotary actuator, 7 .... Inner track,
8 .. Outer track, 9... Direction of recording magnetization 10... Recording head core

Claims (2)

  A table of seek completion slice levels to be set for each track is provided for a magnetic disk device having an algorithm for determining completion of seek by obtaining an offset amount for a target track from a position signal and comparing it with a predetermined seek completion slice level. And a seek completion slice level is set with reference to the table during recording.   A magnetic disk apparatus having an algorithm for determining a seek completion by obtaining an offset amount with respect to a target track from a position signal and comparing it with a predetermined seek completion slice level. And a seek completion slice level when seeking from the inner circumference to the outer circumference and a seek completion slice level from the outer circumference to the inner circumference are set to different values.

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