JPS61194351A - Magnetic medium flaw detection system - Google Patents

Abstract

PURPOSE:To attain to enhance detection accuracy, by allowing a flaw detection level to follow the envelope of a reading signal. CONSTITUTION:At first, a specific pattern is written in a magnetic disc 1 through a control circuit 4 and a head 2 and the written pattern is subsequently applied to an envelope converter circuit 8 through the head 2, the control circuit 4 and a filter circuit 6 to take out an envelope which is, in turn, held for a definite period by peak hold circuits 11, 12 while peak sensing is alternately performed. Exchange timing performing peak sensing is changed over on the basis of head position detecting information from a servo head 3. The held peak value sets the level synthesized prior to a magnetization reversal position in a synthesizer circuit 13 and said level is shifted corresponding to a condition to be outputted as a flaw detection level and a flaw is detected from a reading signal.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a method for detecting physical defects in magnetic media, and is particularly applicable to media such as magnetic disks and magnetic tapes that cannot accurately trace the same trajectory. The present invention relates to a suitable defect detection method.

[Background of the invention]

When reading information magnetically recorded on a magnetic disk such as a magnetic disk, if there is a physical defect on the disk, the location cannot be read accurately. Therefore, it is necessary to register such defects on the disc in advance on the track and skip this location when using the disc.

Conventionally, a method for detecting defects in magnetic disks, magnetic tapes, etc. is to extract information as two signals with a 180° phase difference, pulse these difference signals at an error detection level, and then add the sum of these signals. (see Japanese Unexamined Patent Publication No. 56-37828), or by adding a detection signal read from the medium to an error detection circuit.
An inspection device that detects defects in the medium at different levels by selecting a plurality of slice levels of this circuit (Japanese Unexamined Patent Publication No. 5B-1
(Refer to Publication No. t5378).

In the former case, as shown in FIG. 6, after amplifying the reproduced signal read from the medium, it is added to a low-pass filter to obtain output signals A and B having a 180° phase difference.

Next, difference signals AB and BA of these signals are obtained. Further, these signals are double-wave rectified and integrated, and the error-check level is superimposed to obtain signals C and D.

These signals are applied to a comparator in reverse phase to generate pulse signals E,
Get an F. Error pulses gt t g2y g3 can be obtained at locations where the pulses of these signals are missing.

In the latter case, as shown in FIG. 7, the comparison circuit 24 compares the average output value 26 obtained by amplifying the readout signal with the slice level from the D/A converter 23, and detects the location where the dip occurs. to determine magnetic defects. In that case, by storing a plurality of slice levels in the register 22 and using the initial signal provided for each track of the magnetic recording/reproducing disk as a set pulse, the slice level output from the register 22 is sequentially changed. Detecting defects at different slice levels・This allows 1.
Even if the slicing level varies somewhat depending on the device that mounts the disk, an appropriate level can be used.

However, in both of the above methods, although the magnetically recorded trajectory is repeatedly read, it is impossible to obtain exactly the same read envelope each time. Furthermore, since the timing of the envelope undulations changes due to head vibrations, etc., there is a limit to the defect detection accuracy in a method in which defect slice calculation and defect detection are performed separately during repeated reading operations.

[Purpose of the invention]

An object of the present invention is to solve such conventional problems and to detect physical defects in magnetic media with high precision.

Another object of the present invention is to provide a magnetic medium defect detection method that can perform defect detection processing at high speed.

[Summary of the invention]

In order to achieve the above object, the magnetic medium defect detection method of the present invention writes a basic pattern on a magnetic medium and detects the defect position on the magnetic medium in the process of accurately reading the written basic pattern. 5 in a magnetic medium defect detection device
head position detection means for detecting the position of the reading head; switching means for switching the reading output at intervals controlled by the head position detection means; and the above at the switched intervals.

It has two or more peak hold means for peak sensing and holding the read output, and a combining means for combining each portion held by the means, and in the combining means, the signals are combined before the magnetization reversal position of the read signal. The present invention is characterized in that a level is set, and this level is shifted according to the detection conditions to be output as a defect detection slice level, and defects are detected from the read signal using the slice level.

[Embodiments of the invention]

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 3 shows read signals for one track and one rotation of the magnetic disk device and an enlarged view thereof.

Figure 3 (a) shows the index signal.

It represents the beginning and end of one track. The figure (b) shows the read signal for one track, and the figure (c) shows the read signal for one track.
This is an enlarged part of the image. The read level for each magnetization reversal position is checked, and those below a certain level as shown in (d) are detected and the defect position is registered. The part (d) is the signal level at a defective location due to, for example, a scratch. Conventionally, the calculation of the defect slice level and the detection of the defect are performed separately, but in the present invention, the calculation of the defect detection level and the defect detection are performed using the same waveform.

That is, the read envelope for creating defect detection standards and the read envelope for defect detection are performed in one read.

FIGS. 4(a) and 4(b) are comparison diagrams of defect detection slice signals of the conventional method and the method of the present invention.

In FIG. 4, in the conventional case (e) is one of the read signals.
The average voltage, (f) is a part of the envelope waveform of the defect detection read signal, and (g) is the defect slice level,
Level KV, which is obtained by multiplying the value of one round average voltage (e) by a certain constant
It is. Further, (h) in the present invention is a part of the envelope waveform of the defect detection read signal, and is the same as (h) above.

(S) is a part of the trajectory of the section average obtained by dividing the readout signal of one round. (x) is the defect detection slice level in the present invention, and is a part of the locus obtained by multiplying a part of the two envelope waveforms by a certain constant.

As described above, the present invention is completely different from the conventional method in that the slice level is not constant and is made to follow the envelope of the read signal.

In a magnetic disk drive, the undulation of a read signal is about 10%, and the most significant factor is head vibration. Since this is synchronized to the resonant frequency of the head assembly, it can be treated as a nearly sinusoidal wave. In the present invention,
A servo head is set on the same track as the reading head and detects in which area of the approximately 1000 divisions of the track the reading head is located. The reading output is switched every time, detecting each pimple and following the undulations so that software processing can be executed. Then, fluctuations in the hold values of the detected peaks are combined and shifted according to preset detection conditions to obtain a defect detection slice level. The stiffness provides a slice level that follows the envelope caused by fluctuations such as head vibration. Therefore, detection accuracy can be improved, and since defect detection and slice calculation are performed using the same waveform, processing speed can also be improved.

FIG. 5 is a diagram showing an example of error ranges in the conventional method and the method of the present invention.

(R) in FIG. 5 is a curve showing the error range of defective bits detected by the conventional method, that is, the defect detection slice level (G) in FIG. , that is, a curve showing the error range of defective bits detected at the defect detection slice level (nu) in FIG. 4(b).

As mentioned above, the undulation of the read signal due to head vibration is about 10%, so when defects are detected at the straight slice level as in the conventional method.

Naturally, errors will occur. In the present invention, assuming that the number of peak holds is approximately 800 times/track, the respective detection errors are plotted as shown in (R) and (E) in FIG. In the model shown in Figure 5, for the defect detection level set to 6,
Conventionally, the error range was ±5%, and this detection accuracy was 40%.
However, the present invention has an error range of ±1.2%,
Since this detection accuracy is about 90%, the detection accuracy is improved compared to the conventional method.

FIG. 1 is a block diagram of a medium defect detection device showing one embodiment of the present invention, and FIG. 2 is a signal time chart of FIG. 1.

In FIG. 1, ■ is a magnetic disk, 2 is a write/read head, 3 is a head position detection head (servo head),
4 is a write/read control circuit, 5 is a head position detection circuit, 6 is a filter circuit, 7 is a timing generation circuit, 8 is an envelope conversion circuit, 9.10 is an analog switch, 1
1.12 is a peak hold circuit, 13 is a peak hold synthesis circuit 214 is a defect detection slice setting circuit, 15 is a comparator, 16 is a defect mode determiner, 17 is a pass line, and 18 is a write control circuit.

First, the write control circuit 18 writes and reads data onto the magnetic disk l from the read control circuit 4. and write a specific pattern via the head 2. Next, the written pattern is read via the head 2 and the write/read control circuit 4, the noise level is removed by the filter circuit 6, and the envelope of the read signal is extracted by the envelope conversion circuit 8. This signal is alternately peak sensed by peak hold circuits 11 and 12 and held for a certain period. Servo head 3 determines peak sensing replacement timing.
Switching is performed based on the head position detection information from. That is,
Here, one track is divided into approximately 800 sections to form one section, the servo head 3 detects the current section, analog switches 9 and 10 switch each section, and peak hold circuits 11 and 12 sense the peak value in each section. do.

In FIG. 2, (a) is an index signal indicating the beginning and end of one track, and (b) is a defect detection invalid section, that is, only in this section, no defect detection is performed. (c)
is the peak hold sense interval, that is, 8 within this interval.
Perform peak sense 00 times. (d) is a defect detection valid section, that is, defects are detected in this section. (a)
, (f) is the switching timing of the analog switch 9.10, (g) is the output (envelope waveform) of the envelope conversion circuit 8, (h), (i) is the peak hold circuit LL.
, 12 output, (j) is the output of the peak hold synthesis circuit 13 (that is, defect detection slice level waveform), (k)
is the magnetization reversal position timing signal, (h'), (i
').

(j') is an enlarged timing diagram of (hL (iL O)).

Using the index signal shown in Fig. 2(a) as a trigger (
The signals b), (c), (d), (e), and (f) are generated. Using the signal 2 of (e) and (f), that is, the switching timing, the analog switches 9 and 10 are controlled on and off, and the hold value of each span held in the peak hold @ path 11° 12 is output. . The output of the envelope conversion circuit 8 is.

Since the envelope is shown in (g), the output value of each span is the read envelope (g) as shown in (h) and (i).
It becomes a staircase waveform that follows. By combining these staircase waveforms (h) and (g) in a peak hold combining circuit 13, a defect detection slice output (j) is obtained. In order to detect the read level for each magnetization reversal position, it is necessary that the detection slice level is determined before the reversal position. Therefore, upon receiving a signal (k) synchronized with the magnetization reversal position from the timing generation circuit 7, the synthesis timing of the peak hold synthesis circuit 13 is controlled. That is,
As is clear from the enlarged view, by shifting the rising edge of the slice signal (j') by half a period from the timing signal (k), the composite output (slice signal) is established before the magnetization reversal position.

The defect detection slice setting circuit 14 is a circuit that sets this slice output to detection conditions corresponding to the product. This circuit 14 levels-shifts the output of the peak hold synthesis circuit 13 based on program information corresponding to the detection conditions from the pass line 17 and outputs the level-shifted output. The output slice signal and the output signal from the filter circuit 6 are connected to a comparator 15.
Defects can be detected by inputting and comparing the results here. Finally, the defect mode determiner 16.

The detected defects are classified according to their contents and outputted via the pass line 17.

In this way, in this embodiment, the deviation of the reading locus,
Alternatively, error fluctuations in the detection slice due to positional deviation of envelope undulations due to head vibration or the like are reduced, so the detection rate of defect detection can be significantly improved compared to conventional methods.

Furthermore, since the number of read rotations for calculating the defect detection level can be reduced, the processing speed can be improved by 20% or more compared to the conventional method.

〔Effect of the invention〕

As explained above, according to the present invention, physical defects in magnetic media can be detected with high precision, and the number of circumferential rotations for defect detection is reduced by one rotation/track, improving processing speed. can be measured.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a medium defect detection device showing an embodiment of the present invention, FIG. 2 is a signal time chart of FIG. 1, and FIG.
Figure 4 shows a read signal for one track of a magnetic disk drive, Figure 4 is a comparison diagram of the defect detection slice signal between the conventional method and the method of the present invention, and Figure 5 shows the error range of the conventional method and the method of the present invention. 6 and 7 are explanatory diagrams of conventional magnetic medium defect detection methods, respectively. 1: Magnetic disk, 2: Write/read head, 3: Head position detection head (servo head), 4: Write/read control circuit, 5: Head position detection circuit, 6: Filter circuit, 7: Timing generation circuit, 8: Envelope Conversion circuit, 9, 10: analog switch, 11, 12: peak hole 1: circuit, 13; peak hold synthesis circuit, 14:
Defect detection slice setting circuit, 15: Comparator, 16
= defective mode determiner, 17: pass line, 18: control circuit including f. Figure 1 Figure 2 Figure 3 Figure 4 (IL) Figure 5 Figure 6 g1-g3 Figure 7

Claims (1)

[Claims] (1) In a magnetic medium defect detection device that detects a defect position on the magnetic medium in the process of writing a basic pattern on the magnetic medium and accurately reading the written basic pattern,
head position detection means for detecting the position of the reading head; switching means for switching the read output at intervals controlled by the head position detection means; and 2 for peak sensing and holding the read output at the switched intervals. It has the above peak hold means and a synthesis means for synthesizing each value held by the means, and the synthesis means sets the synthesized level before the magnetization reversal position of the read signal, and sets this as a detection condition. 1. A magnetic medium defect detection method characterized in that a defect detection slice level is output by shifting the signal by a value of 1, and a defect is detected from a read signal using the slice level.