JP2003036502A - Magnetic disk drive and medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To take countermeasures against the anticipated drop in recovery from retry errors which may be encountered following the high-density recording on a magnetic disk of the recent trend. SOLUTION: The magnetic field from the read head or the recording medium can be effectively applied to the read head by reducing the revolution of the disk when retrying for read errors.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic disk device for performing a retry error recovery operation when a read error occurs, and more particularly to a magnetic disk device having a retry error recovery means for relieving a read error due to waveform fluctuation and the same device. The present invention relates to a magnetic disk medium suitable for.

[0002]

2. Description of the Related Art Generally, when an error occurs in read data, a magnetic disk device performs data correction using an error correction code (hereinafter referred to as ECC), which is an error recovery code, in order to recover this error. When the data cannot be corrected by the ECC, the retry error recovery means is used to read the data again.

Factors that cause this data error include deterioration of the S / N ratio due to random noise, and
(1) Defects on disk, (2) Thermal failure (Therma
l Asperity; TA), (3) Waveform fluctuation,
(4) Off-track writing, (5) Characteristic change of read signal waveform due to fluctuation of operating environment, and the like.

The above-mentioned (1) defect on the disk is not limited to a data error at the defective portion depending on the size and range, but also has an automatic amplitude adjusting function (AG) of the reproducing circuit due to an amplitude change.
In some cases, C) or the phase locked loop (PLL) malfunctions to cause a deviation between the read waveform and the data decoding clock, resulting in a burst error. In particular, in recent years, a higher recording density (higher BPI) has progressed, and a small size defect which has not been a problem in the past has become a problem.

The above (2) TA is a phenomenon observed when a magnetoresistive effect element (MR element) is used for the read head.

This MR element utilizes the magnetoresistive effect in which the resistance of the element changes when the direction of magnetization of the element changes due to an external magnetic field, and a constant bias current is applied to the MR element to change the resistance of the element. A voltage change is obtained as an output signal. The TA changes the resistance of the MR element, which is a metal material, by increasing the temperature of the MR element by contact with a protrusion on the magnetic disk and friction. This is a phenomenon in which the change in resistance due to heat is superimposed on the original signal component and the waveform is deformed from its original shape.

The above-mentioned (3) waveform fluctuation is likely to occur due to the write magnetic field (magnetic field at the time of writing) exerted on the read head by the write head, and the write magnetic field at the time of writing the data causes a magnetic domain structure in the read head. This is a phenomenon that causes a transition to a different structure temporarily and causes a waveform deformation such as a change in output amplitude or an asymmetry of the waveform.

The above-mentioned (4) off-track write is a phenomenon in which a data track is written at a position offset from the position to be originally written, and it is a phenomenon that affects not only the offset track but also the adjacent track. When this track position is written with being offset from the original position, even if the data is read at the correct position, the expected read signal waveform cannot be obtained and the error rate deteriorates. This offset light is a phenomenon that becomes more and more problematic if the track density further increases in the future.

The phenomenon (5) caused by the operating environment is, for example, that the flying height of the head changes in a high temperature or low pressure state, which changes the resolution of the read waveform. In a signal processing method called partial response, which is currently the mainstream, an equalization error due to a change in resolution causes a large deterioration in error rate.

As described above, there are various factors in the read error, and the retry read for re-reading when an error occurs causes various error avoiding methods to be performed assuming the factor. The error avoiding means (3) for the waveform fluctuation will be described below.

As an error avoiding means for this waveform fluctuation, there is a method disclosed in Japanese Patent Laid-Open No. 10-134305. In this method, the problem of waveform fluctuation is that the magnetic field from the write head affects the read head. Therefore, a method is used to generate a magnetic field from the write head again to restore the read head to a stable magnetic domain structure. There is.

In this avoidance method, after the head is sought to a track in which no data is written, a write current is passed to restore the magnetic domain structure of the head to a stable state, and then the target track is sought again to read. Is to execute. The write operation for this recovery is called a dummy write because it is not a data write but a write magnetic field generation.

[0013]

According to the conventional method for the error recovery caused by the above-mentioned waveform fluctuation, the write head has a single unit in the future high density recording / reproduction, for example, in the perpendicular magnetic recording system corresponding to the high recording density. The use of a magnetic pole head has been studied, and in that case, there is concern that the efficiency of magnetic field generation effective for recovery of a read head retry error from the write head may decrease and the recovery probability due to a dummy write of the retry may decrease. There is.

An object of the present invention is to eliminate the above-mentioned concern, efficiently generate a magnetic field effective for recovery of the read head at the time of retry, and improve the error recovery probability due to waveform fluctuation at the time of retry. is there.

[0015]

In order to achieve the above object, according to the present invention, information is recorded / reproduced on / from a magnetic disk medium by a recording / reproducing separated type head, and a read error recovery operation is performed when a read error occurs. In the magnetic disk device for carrying out the above, a means for reducing the number of rotations of the disk from the number of rotations during the normal operation is included in the read error recovery operation.

Further, there is provided a means for temporarily stopping the head in the adhesion avoidance zone on the disk surface during the read error recovery operation.

Furthermore, during the above read error recovery operation,
It is desirable to include a dummy write means for supplying a dummy write current to the recording head.

At least a retry magnetic field generating means for applying a magnetic field in a random direction to the reproducing head is provided at the time of the above-mentioned retry error recovery operation.

Further, it is desirable to have a means for applying the write current while reducing the write current in the retry and a means for applying the read current in synchronization with the reduced write current.

Further, the magnetic disk medium has a data recording zone and a head temporary retraction zone at the time of retry, and the product of the residual magnetic flux density and the film thickness of the retry temporary head retraction zone is the residual magnetic flux of the recording zone. It has a value larger than the product of the density and the film thickness.

Further, it is desirable that the recording zone is formed of a perpendicular magnetic recording double layer film, and the head temporary retreat zone at the time of retry is formed of an in-plane recording film.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below in detail based on embodiments with reference to the drawings. <First Embodiment> FIG. 1 shows an example of the sequence of the retry recovery means in the present invention. When a read error occurs, the retry is first performed a predetermined number of times (steps 3 and 4) in the normal step. Here, the above (1)
Defect on disk, (2) (heat failure) (Thermal
Asperity; TA), (3) Waveform fluctuation (4) Off-track write (5) The following retries are carried out for changes in the characteristics of the read signal waveform due to changes in the operating environment. (A) Error avoidance method for defects on disk: This error avoidance method differs depending on whether the defect exists in the normal data range or in the PLO SYNC part for synchronization, but in the former case, the error of the reproducing circuit is A method of changing the gain or switching the data decoding method is adopted. In the latter case, a PLL (Phase Locked) is used.
A measure such as changing the pull-in timing of Loop) is taken. (B) Error avoiding method for TA: An error avoiding method for reducing the influence of TA takes advantage of the fact that the response of TA is slower than the frequency of the signal component, and the cutoff frequency of the high pass filter (HPF) is set to A method of removing the TA component from the read waveform by increasing the temperature is adopted. In addition, AGC (automatic gain control circuit) and PLL (Phase Loc)
In order to prevent the error from propagating to the subsequent portion due to the ked loop (data separator circuit) responding to the TA waveform, a method of holding the operation of the AGC or PLL is also performed. (C) Error avoidance method for waveform fluctuation: This waveform fluctuation avoidance method is caused by the fact that the magnetic field from the write head affects the read head. Therefore, the magnetic field is generated again from the write head to stabilize the read head in a stable magnetic domain. The method of returning to the structure is adopted. (D) Error avoidance method for off-track write: This avoidance method is sufficient if reading is performed at a position shifted from the original read position by the above-mentioned offset with respect to the data track that was written off-track. Since the offset direction and its value are not known, the retry read is performed with some offset values. (E) Other error avoidance method: This avoidance method is not an error recovery method for a specific factor, but uses information issued by the R / W channel about a place where an error has occurred, and For example, erasure correction for more effective error correction can be mentioned.

If the read is not successful in the step 2 even if the number of retries exceeds the predetermined number, the present invention controls the disk rotation speed in the step 5 and executes the predetermined number of times until the read is successful in the step 6 ( Steps 7 and 8). By reducing or stopping the number of rotations, the flying height of the head is reduced and the gap between the head and the magnetic disk is reduced. As a result, the medium magnetic field applied to the read head is increased, and the magnetic field changes and recovers the magnetization state of the read head to recover the read error. Further, the disk rotation speed control 5 may be performed during normal retry.

This embodiment is implemented in the magnetic disk device whose outline is shown in FIG. 8 by reducing the rotation speed by the rotation speed control unit 32 when the reproduced waveform fluctuation is detected during the retry.

<Second Embodiment> Next, a second embodiment of the read error recovery means due to the waveform fluctuation caused by controlling the rotational speed of the magnetic disk will be described with reference to FIG. The rotation speed control is effective also in the data zone, but in order to further improve the effect, a head temporary retreat zone 10 is provided on the magnetic disk medium 9 as shown in FIG. The product of the residual magnetic flux density Br of the medium and the film thickness t is made larger than the data zone.
As a result, the medium magnetic field applied to the read head in the temporary head retreat zone 10 at the time of retry increases, and the probability of recovery of the magnetization state of the read head increases.

<Third Embodiment> A write magnetic field is easily applied to the read head 15 via the disk medium as shown in FIG. 3 as an effect of bringing the head and the disk close to each other in the head temporary retreat zone during disk retry. Therefore, the error recovery efficiency by the conventional dummy write can be improved.

This effect of the present invention will be described in more detail with reference to FIG. 3 as a third embodiment. For example,
The write magnetic field of a single magnetic pole head, which is considered as a write head for perpendicular magnetic recording, passes from the main pole 11 to the return yoke 12 via the magnetic disk perpendicular recording layer 16, the magnetic disk backing layer 17, and the magnetic disk perpendicular recording layer 16. Here, when the flying height is large, the write magnetic field applied to the read head is small. However, for example, when the rotational speed of the disk is reduced and the head and the disk are brought closer to each other (the case where they are extremely close to each other is shown in the figure), the write magnetic field is easily applied to the read head 15 via the disks 16 and 17. Therefore, the effect of this magnetic field improves the read head recovery probability.

Further, in this case, as shown in FIG. 4, the write perpendicular magnetic field is further increased by eliminating the disk perpendicular recording layer in the head temporary retraction zone at the time of retry in the magnetic disk medium and leaving only the backing layer 17 and an in-plane recording film. It becomes easier to join. When the head rotation is stopped and the head and the disk are brought into contact with each other, it is necessary to take an adhesion prevention measure against contact between the head and the disk such as texture in the head temporary retreat zone during the retry. In this example, the tackiness prevention measure was taken by texturing the disk substrate.

Also, in the current longitudinal recording method, the write magnetic field is easily applied to the read head, and the same effect can be obtained.

<Fourth Embodiment> Next, a fourth embodiment of the present invention relating to a retry means other than disk rotation speed control will be described. One means is to use an external magnetic field. As shown in FIG. 5, a magnetic field generating means 18 such as an electromagnet is provided in the magnetic disk device, the read error head 19 is moved to the vicinity of the magnet 18, for example, to the unload position, and a magnetic field in a random direction is applied to the read head. Is added to recover the read function of the read head and recover the retry error. By utilizing the fact that the write magnetic pole or the shield film of the read head collects the magnetic field, the magnetic field generated from the magnet can be reduced and the device is not adversely affected.

<Fifth Embodiment> Another means is to reduce the magnetic field of the write head from that during normal writing and to retry while applying a magnetic field to the read head.
A fifth embodiment to which this means of the present invention is applied will be described with reference to FIG. The magnetization state 21 of the read head that has caused the read error is locally non-uniform (2
2). In such a case, the magnetization becomes uniform by applying the write magnetic field 23 in synchronization with the read current (24). At this time, if the write magnetic field is applied in the same manner as in the normal write, the information recorded on the magnetic disk medium is rewritten, so that the write magnetic field is suppressed by, for example, reducing the write current. FIG. 7 shows an example of the write current dependency of overwrite.
Shown in. From this result, in this embodiment, in order to prevent the write magnetic field from affecting the recorded information, the write current setting value at the time of data writing is 0.4 mA (indicated by reference numeral 25).
It is understood that the magnetic field application by the write current can be selected at, for example, 0.2 mA or less, which is about 1/2.

The write current control in this embodiment is shown in FIG.
In the magnetic disk device whose outline is shown in FIG. 1, when the reproduction waveform fluctuation is detected at the time of retry, by applying the magnetic field by the write current in the range allowable in the recording circuit 31 in synchronization with the read current application by the reproducing circuit 30. Be implemented.

By this method, the read error can be recovered without degrading the performance. Further, in order to prevent recurrence of the read error, it is possible to implement the method of controlling the disk rotation speed or applying an external magnetic field, for example, when the power is turned off after implementing the error recovery means.

Further, in the case of this embodiment, an R / W IC capable of reading while writing is required, but since the write current can be made smaller than that at the time of normal writing, this IC can be easily manufactured by the conventional technique. It can be manufactured.

[0035]

According to the present invention, when a read error occurs, it is possible to improve the success rate of retries and prevent the performance from deteriorating, so that a highly reliable magnetic disk device can be obtained.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a sequence of a retry unit executed when a read error occurs according to the first embodiment of the present invention.

FIG. 2 is an explanatory diagram of a second embodiment of the magnetic disk according to the present invention.

FIG. 3 is an explanatory diagram of a third embodiment of the present invention.

FIG. 4 is another explanatory diagram of the third embodiment of the present invention.

FIG. 5 is an explanatory diagram of a fourth embodiment of the present invention.

FIG. 6 is an explanatory diagram of a fifth embodiment of the present invention.

FIG. 7 is another explanatory view of the fifth embodiment of the present invention.

FIG. 8 is a schematic diagram of a magnetic disk device according to an embodiment of the present invention.

[Explanation of symbols]

1: normal retry, 2: read determination, 3: repeat count, 4: repeat determination, 5: disk rotation speed control,
6: Read judgment, 7: Repeat count, 8: Repeat judgment, 9: Magnetic disk medium, 10: Head temporary withdrawal zone during retry, 11: Main pole, 12: Return yoke, 13: Upper shield, 14: Lower shield, 1
5: read head, 16: disc vertical recording layer, 17:
Disk backing layer, 18: external magnetic field generating means, 19: read error head, 20: spindle, 21: read head magnetization state, 22: non-uniform magnetization, 23: write magnetic field,
24: uniform magnetization, 25: data write current set value, 2
6: magnetic head, 27: positioning stage, 28: reproducing amplifier, 29: positioning circuit, 30: reproducing circuit, 31:
Recording circuit, 32: rotation speed control unit, 33: controller.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G11B 5/66 G11B 5/66 5/82 5/82 F term (reference) 5D006 DA03 DA08 FA09 5D031 AA04 BB01 BB02 EE07 EE08 FF04 FF08 HH20 5D091 AA10 CC05 FF20 GG33 HH20

Claims (7)

[Claims] 1. A magnetic disk device for recording / reproducing information on / from a magnetic disk medium by a recording / reproducing separated head, and performing a read error recovery operation when a read error occurs. A magnetic disk device comprising means for reducing the number of revolutions during normal operation. 2. In a magnetic disk device for recording / reproducing information on / from a magnetic disk medium by a recording / reproducing separated head and performing a read error recovery operation when a read error occurs, the head is moved to the disk surface during the read error recovery operation. A magnetic disk drive having means for temporarily stopping the adhesion avoidance zone. 3. The magnetic disk drive according to claim 1, further comprising a dummy write means for supplying a dummy write current to the recording head during the read error recovery operation. 4. A magnetic disk device for recording / reproducing information to / from a magnetic disk medium by a recording / reproducing separated type head and performing a read error recovery operation when a read error occurs. A magnetic disk device comprising a retry magnetic field generating means for applying a magnetic field in various directions. 5. A magnetic disk device having means for recording / reproducing information with respect to a magnetic disk medium by a recording / reproducing separated type head and performing a read error recovery operation when a read error occurs, in a retry, a write current is used to write data. A magnetic disk device comprising: a means for applying the read current in synchronization with the reduced write current and a means for applying the read current in synchronization with the reduced write current. 6. The magnetic disk medium comprises a data recording zone,
And a head temporary retreat zone during retry, wherein the product of the residual magnetic flux density and the film thickness is larger than the product of the residual magnetic flux density and the film thickness of the recording zone. Magnetic disk media. 7. A magnetic disk medium has a data recording zone and a head temporary retraction zone at the time of retry, the recording zone is formed of a perpendicular magnetic recording double layer film, and the head temporary retraction zone at the time of retry is made of an in-plane recording film. A magnetic disk medium characterized by being formed.