JPH0326450B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is suitable for magnetic disk storage devices, etc.
The present invention relates to a track position shift detection method for causing a playback head to follow a track recorded with a guard band.

It is a well-known fact that in recent years, as information processing capabilities have improved, there has been an increasing need for increased recording capacity, and the recording density of recording media has been increasing year by year. In order to increase the recording density, it is necessary to increase the linear recording density in the direction of movement of the recording medium and the track density in the direction perpendicular to this. For large magnetic disk storage devices, track densities have increased from 500 to 700 tracks per inch over the last decade.
The number has increased to 800, and it is expected that the number will exceed 1,000 by around 1985. Therefore, the track pitch, which was about 50 μm, has become 32 or 32 μm.
It becomes narrower to 36 μm, and furthermore, it has no choice but to become about 25 μm.

On the other hand, as the track density increases in this manner, an increase in noise due to positional deviation of the reproducing head with respect to the track becomes a problem. These problems will be explained in detail below.

FIG. 1 is an explanatory diagram showing the mechanism of noise generation due to misalignment of the reproducing head with respect to the track.

In FIG. 1, if we consider two tracks 1 and 2 that are adjacent to each other, these tracks 1 and 2 are naturally recorded by recording heads, but when recording information, the recording medium and the recording head are connected. A relative displacement occurs between them, so that the tracks 1 and 2 are no longer parallel, but move toward or away from each other.

Therefore, the track pitch is set as W _P , and the relative maximum positional deviation between the recording medium and the recording head is ΔS.
Then, the track width W _W is set to W _W = W _P −2ΔS (1), and tracks 1 and 2 are recorded so that a guard band 3 with a width of 2ΔS is formed between the tracks. Tracks 1 and 2 can then be recorded without interfering with each other.

On the other hand, in a magnetic disk storage device, when data is to be recorded, a data signal is supplied to the recording head to saturate the recording medium, and the data is read along the track where old data is recorded while erasing the old data. New data is being recorded to form a new track.

Now, regarding track 1, when the old data was recorded, the recording head was misaligned, so the old data track 1' was recorded in a winding manner as shown by the dotted line, and then the new data track 1''' is recorded along the old data track 1', and it is assumed that it is recorded in a meandering manner as shown by the solid line. In the portions 4 and 5 where the recording tracks 1' and 1'' are shifted from each other, Old data will remain without being deleted.

When reproducing track 1'' recorded in this way, the reproducing head is also assumed to be displaced from the track by the maximum positional displacement amount ΔS in the same way as the recording head. When the playback head is in a playback state where the old data remains, the playback head also scans the portion 4 where the old data remains;
A new data signal in an amount proportional to W _W −ΔS and an old data signal in an amount proportional to ΔS are obtained.
Furthermore, when the playback head is in the playback state as indicated by 6', the playback head also scans the portion 5 where the old data remains, and generates a new data signal of an amount proportional to W _W -2ΔS and a new data signal proportional to 2ΔS. This means that the amount of old data signals will be obtained. Since the old data signal is noise, the S/N ratio in this case is W _W -2ΔS/2ΔS, and if W _P = 25.4 μm and ΔS = 1.5 μm, from equation (1) above, the S/N is It is about 6.47, which does not reach the 20 to 30 dB required for the equipment.

Reduces noise caused by unerased old data and improves S/
In order to improve N, the gap width of the reproducing head is changed to the track width W _W as shown by the reference numeral 6'' in FIG.
Even if the playback head is misaligned by ±ΔS with respect to the track, the track will be narrowed by 2ΔS.
Just make sure it does not protrude beyond 1″. However,
In this case, the effective reproduction width W _R of track 1'' is W _R = W _P -6ΔS. If W _P and ΔS are set to the above values, W _R = 16.4 μm, which is significantly This has the drawback that the amplitude of the reproduced signal is significantly reduced.

Therefore, it is necessary to make the playback head follow the track. For this purpose, the positional deviation of the reproducing head with respect to the track may be detected, and the position of the reproducing head may be adjusted using a control signal corresponding to the positional deviation. Conventionally, as a means for detecting the positional deviation of the playback head, positional deviation detection heads are provided on both sides of the playback head in the track width direction, and the amplitudes of the playback signals obtained from each of the positional deviation detection heads are compared. The technology is known (Japanese Unexamined Patent Publication No. 119973/1973). However, in this prior art, as shown in FIG. 1, if there are portions 4 and 5 along the track 1'' where the old data has not been erased, even though the playback head is misaligned, Since the old data is reproduced by one of the positional deviation detection heads, an error occurs in the detection of the positional deviation of the reproducing head, resulting in a disadvantage that the reproducing head cannot accurately follow the track.

The purpose of the present invention is to eliminate the drawbacks of the above-mentioned prior art,
To provide a track position deviation detection method which allows a reproducing head to always accurately follow a track and obtains a reproduced signal having a large amplitude and an improved S/N ratio.

In order to achieve this object, the present invention provides positional deviation detection heads on both sides of a playback head with a gap width slightly narrower than the track width in the track width direction, and detects the positional deviation detection head in response to the playback signal from the playback head. The present invention is characterized in that it is possible to detect the presence or absence of correlation between the respective reproduction signals from the recording head, and to detect the positional deviation of the reproduction head based on the presence or absence of such correlation.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is an explanatory diagram showing an embodiment of the track position deviation detection method according to the present invention, in which 7 is a track, 8 is an unerased portion of old data, 9 is a reproduction head, and 10 and 11 are position deviation detection heads. It is.

In the figure, it is assumed that there is an unerased portion 8 of old data on one side of the track 7, and that the recording medium is being transported in the direction of arrow X. The playback head 9 that scans the track 7 is formed so that its gap width is slightly narrower than the width of the track 7, and positional deviation detection heads 10 and 11 are provided on both sides of the playback head 9 in the track width direction, respectively. Head 9,
The positional deviation detection heads 10 and 11 form a composite head. Positional deviation detection heads 10, 11
The gap widths of the playback head 9 are set to be equal, and in state A where the center of the playback head 9 in the track width direction coincides with the track center line 0, the positional deviation detection head 1
0 and 11 scan both ends of the track 7 over the same width to reproduce data signals of the same amplitude, and at the same time, the reproduction head 9 and the phase shift detection heads 10 and 1
The gap with 1 is on the same straight line in the track width direction, and the positional deviation with respect to the playback head 9 is detected so that the phases of the playback signals obtained from the respective heads 9, 10, and 11 by scanning the track 7 match. The arrangement of heads 10 and 11 is set.

As mentioned earlier, the compound head is a track 7
On the other hand, there are state A in which there is no track position deviation, state B in which the track position is deviated in one direction, and state C in which the track position is deviated in the other direction. , the amplitude of the reproduction signal obtained from the positional deviation detection heads 10, 11 changes.

Therefore, the amount of positional deviation x of the center line of the reproducing head 9 in the track width direction with respect to the center line 0 of the track 7
In contrast, the playback head 9 and the positional deviation detection head 1
The amplitudes of the respective output signals from 0 and 11 vary as shown in FIG.

In FIG. 3, the horizontal axis represents the amount of positional deviation x, and the vertical axis represents the amplitude of each reproduction signal, and the solid line a represents the reproduction head 9.
represents the change in the amplitude of the reproduced signal, and is symmetrical about the x=0 axis. The one-dot chain line b shows the change in the amplitude of the reproduction signal of the positional deviation detection head 11 when there is no unerased portion 8 (FIG. 2) of the old data, and the two-dot chain line c shows the change in the amplitude of the reproduction signal of the positional deviation detection head 10. represents changes in amplitude, and these amplitude changes are x
Since they are mutually symmetrical with respect to the axis of =0, it is possible to detect the positional deviation of the reproducing head 9 by comparing the amplitudes of the reproduced signals from the positional deviation detection heads 10 and 11, and the amplitude of these reproduced signals can be detected. By adjusting the position of the reproducing head 9 so that the numbers are equal to each other, the reproducing head 9 can be made to follow the track 7 so that the positional deviation becomes zero.

However, in reality, as shown in FIG. 2, there is an unerased portion 8 of the old data, so when the positional deviation detection head 11 scans this portion 8, it is natural that a reproduced signal will be obtained. Become.
Therefore, the change in amplitude of the reproduced signal obtained from the positional deviation detection head 11 is as shown by the dotted line d in FIG.
When comparing the amplitude of the playback signal from is not performed accurately, and the ability to follow the track deteriorates.

Furthermore, as mentioned earlier, the positional deviation x is 1 μm.
Or, if it is attempted to be lower than that, the absolute value of the reproduction signal of the positional deviation detection heads 10, 11 becomes small. For example, even in the case of the current most sensitive magnetoresistive magnetic head, the output voltage per 1 μm is at most about 30 μV _rns , while the input equivalent noise of the amplifier is about 4 μV _rns , so the resolution is less than 1/8 μm. is difficult to obtain.

Incidentally, in FIG. 2, the reproduction signals obtained by scanning the track 7 by the reproduction head 9 and the positional deviation detection heads 10 and 11 are all in phase. On the other hand, the old data in the unerased portion 8 has a random phase with respect to the new data recorded on the track 7, and there is no correlation between the new and old data.

Therefore, the reproduction signal from the reproduction head 9 and the reproduction signal from the positional deviation detection head 10 are multiplied to obtain a product signal, and the reproduction signal from the reproduction head 9 and the reproduction signal from the positional deviation detection head 11 are multiplied. The product signals are obtained by multiplication, and these product signals are integrated by an integrating circuit having a time constant sufficiently large with respect to the period of the data signal. The amplitudes of the respective signals obtained from the integrating circuit vary depending on the correlation of the two reproduced signals to be multiplied.

Next, regarding this point, Figure 4 a, b, c,
This will be explained in more detail in d and e.

4a shows the reproduction signal from the reproduction head 9 (FIG. 2), and FIG. 4b shows the reproduction signal from the positional deviation detection head 10.
The reproduction signal obtained by scanning the track 7 from (Fig. 2) is shown in Fig. 2c.
1 (FIG. 2), reproduced signals obtained by scanning the unerased portion 8 of the old data are shown. Since the reproduction signal from the positional deviation detection head 10 is in phase with the reproduction signal from the reproduction head 9, when these reproduction signals are multiplied by the multiplier circuit, the obtained product signal is as shown in FIG. 4d. , resulting in a positive amplitude signal. Therefore, by integrating this product signal using an integrating circuit with a sufficiently large time constant, an output signal with a large amplitude can be obtained. On the other hand, since the reproduction signal from the positional deviation detection head 11 (FIG. 4c) has a random phase with respect to the reproduction signal from the reproduction head 9 (FIG. 4a), these reproduction signals are multiplied by a multiplier. When multiplied, the obtained product signal becomes a signal whose amplitude changes from positive to negative, as shown in FIG. 4e. Therefore, by integrating this product signal using an integrating circuit with a sufficiently large time constant, an output signal with a small amplitude close to zero can be obtained.

Now, in FIG. 2, if a positional deviation occurs in the x>0 direction, the greater the positional deviation in this direction, the greater the amplitude of the reproduction signal from the positional deviation detection head 10, and the greater the Since the amplitude of the reproduced signal due to scanning the unerased portion 8 of the old data from 11 also increases, the amplitude of the output signal obtained by integrating the signal shown in FIG. 4d increases, and as shown in FIG. 4e. The amplitude of the output signal obtained by integrating the signal shown in will become smaller and smaller. Conversely, when a positional deviation occurs in the x<0 direction, the larger the positional deviation in this direction becomes, the smaller the amplitude of the output signal obtained by integrating the signal shown in FIG. 4d becomes. The amplitude of the output signal obtained by integrating the signal shown in FIG. 4e becomes larger and larger. Therefore, by comparing the amplitudes of the output signals from the respective integrating circuits, the positional deviation of the reproducing head 9 with respect to the track 7 can be detected.

As for the time constant of the above-mentioned integrating circuit, the frequency of the recorded data is approximately several hundred kHz to 10 MHz, whereas the frequency of the signal for which the track position deviation is to be corrected may be at most several kHz. Figure 4 d,
Set so that hundreds to thousands of pulses of the waveform shown in e can be integrated. In this way, the product signals in Figure 4 d and e are integrated with a very long time constant relative to the pulse period, so the amplitude ratio of the output signals from each integrating circuit becomes extremely large, making it possible to reproduce them with high accuracy. The position of the head 9 can be adjusted, and the influence of noise can be sufficiently suppressed, resulting in a high S/N ratio.

It should be noted that if there is no unerased portion 8 of the old data, the positional deviation detection heads 10 and 11 will obtain a reproduced signal resulting from scanning the track 7.
The amplitude of each reproduction signal differs depending on the positional deviation, and the reproduction head 9 and the positional deviation detection head 10
The product signal of the reproduction signal of the reproduction head 9 and the reproduction signal of the displacement detection head 9 are both positive amplitude signals as shown in FIG. The amplitudes differ from each other depending on size and direction. Therefore, the amplitudes of the output signals obtained by integrating the respective product signals are also different from each other, and by comparing the amplitudes of these output signals, it is possible to detect the positional deviation of the reproducing head.

FIGS. 5a and 5b are plan views showing specific examples of composite heads, respectively, as viewed from the side that contacts the recording medium.

Figure 5a shows a specific example of an inductive head, 1
2, 13, 14, 15, 16, 17 are magnetic cores,
18, 19, 20 are gap, 21, 22, 23
is a winding.

The reproducing head 9 has magnetic cores 12 and 13 and a winding 2.
1, and a gap 18 having a width slightly narrower than the track width is formed. The positional deviation detection head 10 includes magnetic cores 14 and 15 and a winding 22.
The positional deviation detection head 11 is composed of magnetic cores 16 and 17 and a winding 23, and a gap 20 is formed therein. The gaps 19, 20 of the positional deviation detection heads 10, 11 have the same width, and are arranged on the same straight line as the gap 18 of the reproducing head 9.

FIG. 5b shows a specific example of a magnetoresistive head, with magnetoresistive sensors 24, 25, and 26;
7 and 28 are magnetic shields, and 29 and 30 are gaps.

The reproducing head 9 has gaps 29, 28 by a magnetoresistive sensor 24 and magnetic shields 27,28.
The misalignment detection head 10 is composed of a magnetoresistive sensor 25 and magnetic shields 27, 28 forming gaps 29, 30.
1 is a magnetoresistive effect sensor 26 and a magnetic shield 2
7 and 28 form gaps 29 and 30. The width of the magnetoresistive sensor 24 is made slightly narrower than the track width, and the widths of the magnetoresistive sensors 25 and 26 are made equal. and,
The magnetoresistive sensors 24, 25, 26 are arranged on the same straight line, and the magnetic shields 27, 28
are arranged parallel to the magnetoresistive sensors 24, 25, and 26. With this configuration, the magnetic shields 27 and 28 can be used in common for the reproducing head 9 and the positional deviation detecting heads 10 and 11.

As described above, when the track 7 (Fig. 2) is scanned by configuring the composite head,
Reproduction signals having the same phase can be obtained from the reproduction head 9 and the positional deviation detection heads 10 and 11. It is clear that the composite head is not limited to the specific examples shown in FIGS. 5a and 5b.

It is clear that the present invention is applicable not only to magnetic disk storage devices, but also to other recording and reproducing devices, such as video tape recorders, which require position adjustment of the reproducing head relative to the track.

As explained above, according to the present invention, even if there is an unerased portion of the old information signal, it is possible to detect the positional deviation of the reproducing head with respect to the track with a high S/N ratio and with high accuracy. The head can be made to follow the track very accurately, and a large amplitude, high S/N information signal can be reproduced from the track, and the track position has an excellent function except for the drawbacks of the above-mentioned prior art. A shift detection method can be provided.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the noise generation mechanism due to positional deviation of the playback head with respect to the track, FIG. 2 is an explanatory diagram showing an embodiment of the track position deviation detection method according to the present invention, and FIG. Characteristic diagrams showing changes in the amplitude of the reproduced signal of each head with respect to track position deviation; Figures 4a, b, c, d, and e are signal waveform diagrams for explaining the operation of Figure 2; Figures 5a, b
FIG. 2 is a plan view showing a specific example of a composite head. 7...Track, 8...Unerased portion of old data, 9...Reproduction head, 10, 11... Position shift detection head.

Claims (1)

[Scope of Claims] 1. In a track position deviation detection method for causing a playback head to follow a track recorded with a guard band, the gap width of the playback head is made slightly narrower than the width of the track to perform the playback. First and second positional deviation detection heads are provided on both sides of the head in the track width direction, and a first and second positional deviation detection head is provided on both sides of the head in the track width direction, and a first and second positional deviation detection head is provided to express the correlation of the reproduction signal from the first and second positional deviation detection heads with respect to the reproduction signal from the reproduction head. 1. A track position deviation detection method, characterized in that a second signal is obtained, and the position deviation of the reproducing head with respect to the track can be detected using the first and second signals. 2. In claim 1, the first,
The second signal is characterized in that the second signal is a signal obtained by multiplying the reproduction signal from the reproduction head by the reproduction signal from the first and second positional deviation detection heads, respectively, and integrating the respective reproduction signals. Track position deviation detection method.