JPH01243205A - Magnetic disk device - Google Patents

Abstract

PURPOSE:To improve the reliability of a device by performing defect detection effectively by changing the slice level of the defect detection extending over from an inner periphery to an outer periphery. CONSTITUTION:The slice level 4 of on-going defect detection is kept constant extending over the inner and outer periphery shown as SL1 and SL2. To enable minor defect to be detected in an area where the effect of the defect detection can be easy to appear, the slice level 4 is changed extending over from the inner periphery to the outer periphery. In other words, the slice level SL3 is employed so as to detect the minor defect as in a middle peripheral part with low resolution 2. As a result, no large difference in the number 5 of the whole of SDs is generated compared with that of the SL2, however, the easiness 6 of generation of an error in the middle peripheral part can be reduced remarkably compared with that of the SL2, thereby, the reliability of the device can be improved.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a magnetic disk device, and in particular, detects defects before actual use and registers the defective portion as prohibited from use, thereby improving data recording and reproduction. The present invention relates to a magnetic disk device with improved reliability.

[Conventional technology]

In conventional devices, scratches, dropouts, etc. that occur on the recording surface of a magnetic disk medium may cause errors that occur during data reproduction. For this reason, in a magnetic disk drive, a portion that is prone to errors is detected in advance as a media defect, and the position of the detected defect is recorded on a part of the medium when formatting the medium. By preventing the use of defective parts based on the above information during actual use, errors are suppressed and reliability is improved.

In the above-mentioned defect detection, the following method is used in the conventional apparatus. First, a constant frequency signal is written on a recording medium, and the written signal is read out to find the average output. Next, a portion of the signal amplitude below the specified percentage of the average output is detected as a missing pulse defect. Further, a portion where the reproduced output after DC erasure exceeds a specific percentage of the above-mentioned average output is detected as an extra pulse defect.

Here, the specific ratio of the average output is called a slice level, and is a parameter indicating the range of the size of the defect to be detected in defect detection. Therefore, by changing the slice level □, even small defects can be detected. Therefore, it is important to be able to detect defects small enough to ensure the reliability necessary for recording and playback.
Considering the fact that the number of detected defects cannot be increased significantly due to physical limitations on the number of defects that can be stored, appropriate slice levels are determined for detecting missing pulse defects and extra pulse defects. , defect detection is performed □.

Incidentally, related to the defect detection method and apparatus described above, for example, Japanese Unexamined Patent Application Publication No. 1982-058-OS3', No. 'A' is cited.

[Problem to be solved by the invention]

The above-mentioned conventional technology does not take into consideration the fact that the S/N and resolution of the reproduced waveform differ in the range from the inner circumference to the outer circumference of the recording medium in a magnetic disk device, and the following problems occurred.

First, in a magnetic disk device, the recording density of data is higher toward the inner periphery of the recording medium, and the relative speed with respect to the magnetic head is lower. Therefore, the S/N and resolution are generally lower toward the inner periphery. Therefore, even at a constant slice level, the number of detected defects increases toward the inner circumference. On the other hand, when recording and reproducing data, errors are generally more likely to occur in the inner circumference where the S/N and resolution are smaller. In such a case, it is not a problem from the viewpoint of error reduction that the number of detected defects is larger in the inner circumference. However, when a rotary actuator is used in the access system of the magnetic head, the yaw angle of the magnetic head changes from the inner circumference to the outer circumference, so the space between the head and the medium becomes maximum at the middle circumference, which reduces the resolution. may be smallest at the middle. Furthermore, due to waveform processing such as waveform equivalence, the resolution may become minimum at areas other than the innermost periphery. In this case, the location where errors are likely to occur during recording and playback is not necessarily the inner periphery, but on the other hand, the number of detected defects is greater in the inner periphery, so defect detection is not performed effectively from the perspective of error reduction. The problem was that it wasn't.

It is an object of the present invention to provide a magnetic disk device that effectively performs defect detection to reduce recording/reproducing errors and, as a result, has improved reliability.

[Means to solve the problem]

The above object is achieved by varying the slice level for defect detection from the inner circumference to the outer circumference. Specifically, in areas where errors are likely to occur due to low resolution of the reproduced waveform or large undershoot, it is difficult to detect even small defects compared to other areas.
Change the slice level continuously or stepwise. Furthermore, in order to effectively detect defects, the S/N
In the inner periphery where the resolution is poor, the resolution is set to 100% and the undershoot is approached to 0% by □ waveform processing. The slicing level is changed for the areas where defects smaller than other areas can be detected.

[Effect]

If the S/N is about the same, the resolution is small and there is undershoot.
Errors are more likely to occur in areas where 1- is large. Also,
If the S/N is poor, even a large number of minute defects become a cause of errors, making it difficult for defect detection to be effective. In other words, the effect of defect detection becomes clearer as the S/N ratio improves.

Therefore, since the effect of defect detection is difficult to be seen in areas with poor S/N, the resolution is set to 1. It is assumed that the error occurrence is suppressed by bringing O0% and underrush-1 close to 0%. On the other hand, in areas where the resolution has decreased or where undershoot has increased, defect detection works effectively because the S/N ratio is somewhat good.

Therefore, in such areas, the slice level for defect detection is made stricter to detect even minute defects and suppress the occurrence of errors. As described above, by changing the slice level to detect even minute defects in areas where the effect of defect detection is likely to appear, defect detection can be performed effectively to reduce errors.

〔Example〕

A first embodiment of the present invention will be described below with reference to FIG.

FIG. 1 shows various characteristics of a magnetic disk device using a rotary actuator, including its inner and outer circumferences. When a rotary actuator is used, since the yaw angle of the head differs between the inner and outer circumferences, the head-medium spacing is widest near the middle circumference, as shown in FIG.

Furthermore, since the recording density and peripheral speed differ between the inner and outer circumferences, the resolution 2 and S/N3 also differ between the inner and outer circumferences, as shown in FIG.

Conventionally, slice level 4 for defect detection is S L 1 or SL
2, it is constant across the inner and outer circumferences. however,
In this example, only the missing pulse defect is described. The number of defects (SD number) 5 detected at this time is highest on the inner circumference, as shown in FIG. 1, and rapidly decreases toward the outer circumference. Furthermore, the ease of error occurrence 6 at this time also differs between the inner and outer circumferences, and in the case of this embodiment, errors are most likely to occur at the middle circumference where the resolution is low, as shown in FIG.

Here, if the slice level 4 is changed from SL 1 to SL2 for the purpose of improving the reliability of the device, the SD number will be 5.
increases, and the error susceptibility 6 decreases near the inner circumference. However, the likelihood of errors occurring near the middle periphery, where errors are most likely to occur, does not decrease much, nor does the reliability of the device decrease much, meaning that the reliability of the device has not changed much. Therefore, in the magnetic disk device of the present invention, the slice level S, which detects even the smallest defects in the middle periphery where the resolution is lower, is
L3 was adopted. In this case, the SD number 5 increases at the middle circumference but hardly changes at the inner circumference, so the overall SD number does not differ much compared to the method of S L 2. However, compared to ST, 2 described above, the likelihood of errors occurring in the middle portion is reduced, so the reliability of the device is improved.

In this embodiment, the missing pulse defect has been described, but regarding the extra pulse defect, focusing on the size of the undershoot, as shown in FIG. 2, the undershoot 7
By employing the slice level ST, 3, in which smaller defects are detected in areas where errors are more likely to occur, it is possible to provide a magnetic disk drive with improved reliability in substantially the same manner as in the above embodiment.

Next, another embodiment of the present invention will be described with reference to FIG. In this embodiment, a constant frequency signal with the lowest density recorded as data is first written, and the average output is determined from the waveform 10 from which this signal is read out and is used as a reference (100%). Next, the highest density constant frequency signal recorded as data is written and reproduced, and the signal amplitude of this waveform 11 is
A portion falling below the slice level 12, which is a specific percentage of the average output, is registered as a missing pulse defect, and recording/reproduction is prohibited. In the above manner, the amplitude of the highest density waveform 11 becomes equal to the resolution 2.

Therefore, the slice level 12 defined as a specific percentage of the average output of the lowest density waveforms 1-0 changes with the resolution 2 as shown in FIG. 4 when compared with the average output of the highest density waveform 11. This substantial change in slice level 13 works to detect smaller missing pulse defects in areas with lower resolution. Therefore, similarly to the first embodiment, defect detection works effectively and the reliability of the device can be improved.

〔Effect of the invention〕

According to the present invention, the slice level is changed to detect smaller defects in areas where the effect of defect detection is more likely to appear. Therefore, it is possible to effectively reduce errors through defect detection and improve the reliability of the device. be able to.

[Brief explanation of the drawing]

Figures 1 and 2 are correlation diagrams of slice levels and various characteristics at the inner and outer circumferences used to explain the first embodiment of the present invention, and Figure 3 is used to explain the second embodiment of the present invention. FIG. 4 is a diagram showing resolution and substantial slice level changes in the second embodiment. 1... Spacing between head media, 2... Resolution, 3
...S/N, 4,8.12...Slice level, 5゜9...Number of SD, 6...Easiness of error occurrence, 7.
...undershoot, 1o...lowest density waveform, 11.
- Highest density waveform, 13... Slice level for the highest density waveform. Rod 1 Tsui Otsuzu γ sp sharp

Claims (1)

[Claims] 1. A signal written on a magnetic recording medium is read out to obtain an average output, a specific percentage of the average output is set as a first slice level, and another specific percentage of the average output is set as a second slice level. A slice level is detected, and a missing pulse defect is detected when the width of the read signal is lower than a first slice level, and a missing pulse defect is detected when the signal is erased and the output signal exceeds a second slice level. In the magnetic disk device, the defect position of at least one of the missing pulse defect and the extra pulse defect is stored, and recording/reproduction to the defect position is prohibited. A magnetic disk device characterized in that a slice level or a second slice level differs depending on the radial position of a magnetic recording medium. 2. The magnetic disk device according to claim 1, wherein the first slice level is varied so that a smaller missing pulse defect is detected at a radial position where the resolution of the reproduced waveform is lower. . 3. The above-mentioned second
2. The magnetic disk device according to claim 1, wherein the slice level of the magnetic disk device is varied. 4. A patent characterized in that, in a magnetic disk device using a rotary actuator in the access mechanism of a magnetic head, small missing pulse defects or extra pulse defects are detected at the middle circumference of the magnetic disk rather than at the innermost circumference. A magnetic disk device according to claim 1.