JPH0512764B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a tracking method effective in a magnetic recording/reproducing device having a narrow track width.

Conventional configurations and their problems With the progress in increasing the recording density in magnetic recording, there is a need to improve the linear recording density as well as the density in the track width direction.

Among the magnetic recording devices currently in use, the device with the narrowest track width is the 1/2-inch home VTR.
The track width is 30 to 50 μm. Tracking in this device is such that the video head traces the video track recorded in a fixed positional relationship with the control signal by controlling the capstan with the control signal written on the control track. Since this tracking method assumes that the video track is recorded correctly on a straight line on the tape, it cannot cope with distortion of the recorded track due to changes in the tape over time. Therefore, such a tracking method cannot be applied to a device having a track width of about 20 μm or less.

In contrast, the video head is slightly vibrated by a piezoelectric element in a direction perpendicular to its running direction, and the changes in the output of the reproduced signal and the vibration signal applied to the piezoelectric element are synchronously detected, and this signal is used to track the piezoelectric element. There is a way to control the signal. Figure 6a shows the outline, 15 is a video track,
16 is the playback head, 17 is the head gap, and C is the vibration direction of the video head. FIG. 6b shows the reproduced signal in this case. This method traces the video track while playing it, so
More accurate tracking than the first method is possible, but in this case, in order to obtain a good reproduction signal, the track width of the reproduction head and the track width to be reproduced must be approximately equal, and the vibration width must be equal to the track width. It must be sufficiently small in comparison. On the other hand, perpendicular magnetic recording can realize a recording track width of 2 to 3 μm. However, it is difficult to apply the above-described tracking method to such narrow tracks.

OBJECTS OF THE INVENTION The present invention seeks to provide a novel tracking method that can satisfactorily reproduce track widths of several microns.

Structure of the Invention The present invention relates to a perpendicular magnetic recording medium in which a signal track is recorded with a track width Tw and a track pitch Tp by direct current erasing in one direction and magnetization in the opposite direction, and a perpendicular magnetic recording medium in which a signal track is recorded with a track width Tw and a track pitch Tp. a first reproducing head which is sufficiently large and whose track width direction is substantially aligned with the longitudinal direction of the signal track; a matched second playback head and a first
and a second head in the width direction of the signal track.
a first drive means for causing vibration with an amplitude greater than Tw; a second drive means for causing relative movement in the longitudinal direction of the signal track between the first and second heads and the medium; This tracking method includes a signal processing circuit that obtains a drive signal for the first drive means from the reproduced output of the first head.

According to the present invention, the signal processing circuit obtains a control signal from the output that changes as the first reproducing head vibrated by the first drive means crosses a signal track, and the control signal is fed back to the first drive means. control so that the center of the signal track is always traced. Furthermore, since the track width of the second playback head is larger than the sum of the signal track width and the amplitude of the vibration, the output of the second playback head cannot be changed by vibrating in the track width direction. It is possible to perform tracking while keeping the output of the second head for signal reproduction constant.

DESCRIPTION OF THE EMBODIMENTS FIG. 1 shows an example in which the tracking method according to the present invention is applied to a rotating head type magnetic recording/reproducing device. Fig. 3a shows a state in which the head is attached to a rotating drum rotating in the direction of arrow A, and b is an enlarged explanatory view of the head mounting portion.

1 is a rotating drum, 2 is a head consisting of a tracking head and a signal reproducing head fixed in one case, and 3 and 3' are piezoelectric elements made of ceramic, which are bonded together to form a bimorph. ing.

In the block diagram of FIG. 1b, numeral 4 is an amplifier for amplifying the output of the tracking head, 5 is an AC voltage oscillator, and 6 is an amplifier for tracking by comparing the output of the amplifier 4 and the output of the AC voltage oscillator 5. tracking control circuit that generates a signal, 7
8 is an adder circuit, and 8 is a drive circuit. An adder circuit 7 that adds the output Y of the tracking control circuit 6 and the output X of the AC voltage oscillator 5 generates a control signal Z for vibrating the head 2, and this signal is sent to the piezoelectric elements 3, 3' by a drive circuit 8. to vibrate the head 2 in the direction of arrow B. The X, Y, and Z output waveforms are as shown in FIG. 1c. There are various input signals to the tracking control circuit 6, as shown in the embodiments described below. Note that 9 is an amplifier for amplifying the output of the signal reproducing head.

The operation of the tracking method of the present invention will be explained with reference to FIG. 2, which shows an example. Reference numeral 10 denotes a perpendicular magnetic recording medium whose entire surface is subjected to DC erasing in the direction toward the surface of the medium. On the other hand, the shaded area 11 is a signal bit magnetized in a direction away from the medium surface. 12 is a group of bits constituting one track. Tw is the track width and Tp is the track pitch. 13 is the gap or MR element (magnetoresistive element) of the tracking head;
The track width _T1 is sufficiently long compared to the wavelength of the signal bit. 14 is a gap or MR element of the head for signal bit reproduction. In the embodiment shown in FIG. 2, no MR element is used in the head. These heads 13, 14 form the already described head 2 and are shown in FIG.
By moving in the direction, the signal bit reproducing head 14 reproduces the signal bits on the track.
Further, by vibrating in the direction of arrow B in FIG. 2, the tracking head 13 reproduces the tracking signal. If the amplitude in the direction of arrow B is 2a, 2a>Tw
Then, the tracking head 13 crosses the track portion and reciprocates in the non-track portions on both sides of the track portion. 3A shows the head driving voltage, b shows the output state at this time, and U shows the output state of the head 13 when the center of the head swings toward the U side in FIG. 2. The center of vibration of the head is L from the center of the track.
When shifted to the side, the L period becomes longer and the U period becomes shorter. Therefore, it is possible to correct the center of tracking from this signal by applying feedback to the head vibration drive circuit 8 after simple signal processing. Here, the non-track part and the track bit part are magnetized in opposite directions, and T ₁ > λ
(recording wavelength), the track section has an output at an average level in the track direction. Therefore, the output of the track section is an output corresponding to "0", and the output of the non-track section is an output corresponding to "-Mr". (However, Mr is residual magnetization.) Next, if the track width T ₂ of the signal bit reproducing head 14 is set to T ₂ >Tw+2a, no change in output occurs due to vibration of the signal bit reproducing head 14 in the track width direction. Furthermore, if the relationship (Tp - Tw) > 1/2 (T ₂ - Tw) + a is satisfied, bits from adjacent tracks will not be reproduced. For example, a number that satisfies this is
Tw = 1μm, a = 1μm, T ₂ = 3.5μm, Tp = 4μm,
There is.

In the embodiment described above, the value of a had to be relatively large in order to cause the tracking head to vibrate on both sides of the signal track. Therefore, there is a drawback that the track pitch Tp is considerably larger than the track width Tw. In the second embodiment shown in FIG. 4, the track pitch Tp can be made smaller. The overall structure is similar to that of the first embodiment, but the gap length G _L of the tracking head 13 is a ring head having a value close to the track width Tw. In this way, 2a＞(Tw−G _L )
, and the amplitude 2a can be reduced. Similar equations hold true for other relational expressions, so for example, Tw=1μm,
If G _L = 0.6 μm, a = 0.3 μm, T ₂ = 1.8 μm,
Tp can be set to 2 μm.

Further, a third embodiment is shown in FIG. 13,1
3' forms a tracking head by arranging two MR elements in parallel, and if the distance between these MR elements is S, then a can be made smaller than the condition 2a>(Tw-S). That is, when the track width Tw is relatively large, a becomes large, but a can be made small by arranging the MR elements as tracking heads 13 in parallel with each other and selecting the distance a little smaller than the track width Tw. FIG. 5a shows its specific configuration.

The outputs of the MR elements 13 and 13' are as shown in FIG. 5b. Here tracking is L
This shows the reproduced waveform when it is shifted to the side.

In this case, for example, Tw = 5 μm, S = 4 μm, a
= 1 μm, T ₂ = 8 μm, and Tp = 8 μm, the above conditions are satisfied.

In the above embodiments, the case where T ₂ >Tw has been described, but it is also possible to set T ₂ <Tw. The case where T ₂ <Tw will be described below as a fourth embodiment with reference to FIG. 5.

The conditions of 2a＞(Tw−S) are the same, but the other conditions are: If T ₂ <(Tw−2a) Tp−Tw＞1/2(S+2a−Tw) is satisfied, the output of the reproduced signal No change occurs,
The tracking head is not affected by adjacent tracks. As a numerical example in this case, Tw = 5μm, S = 4μm, a = 1μm, T ₂ = 2.5μ
m, Tp = 6 μm, the above conditions are satisfied.

The track pitch Tp can be made smaller than when T ₂ >Tw.

Note that in any case, as long as the track width T ₁ is about 20 times or more of the shortest wavelength, it is sufficient if the encoding method has a small DC component.

Furthermore, although only the rotary head type has been described here, the same configuration and operation are possible in a fixed head type as well.

Effects of the Invention As described in detail above, according to the present invention, tracking of a narrow track recording/reproducing apparatus can be performed with a simple device. That is, the tracking output can be increased by increasing the track width of the tracking head, and the output of the reproducing head is not affected by vibrations for tracking. Therefore, in particular, it has been considered difficult to
This invention is extremely useful as it can successfully reproduce tracks with a narrow track width of about 10 μm or less.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram when the tracking method of the present invention is applied to a rotary head type recording/reproducing device.
is a perspective view, b is an explanatory diagram of the magnetic head installation part, and c is a waveform diagram. FIG. 2 is an explanatory diagram showing an example of the relationship between the medium and the head that constitute the tracking method of the present invention, FIG. 3 is a waveform diagram showing the operation of the first embodiment of the present invention, and FIG. This figure shows an example, in which a is a configuration explanatory diagram, b is a waveform diagram, and FIG. 5 is a third diagram.
FIG. 6A is an explanatory diagram of the configuration, FIG. 6B is a waveform diagram, and FIGS. 6A and 6B are explanatory diagrams of a conventional tracking method.

Claims (1)

[Claims] 1. A perpendicular magnetic recording medium that is erased by DC magnetization in one direction and records a signal track with track width Tw and track pitch Tp by magnetization in the opposite direction according to the signal. and a first reproducing head group whose track width is sufficiently larger than the recording wavelength of the signal and whose track width direction substantially coincides with the longitudinal direction of the signal track, and a first reproduction head group whose track width is substantially equal to the signal track width Tw. a second reproducing head whose track width direction substantially coincides with the signal track width direction; a first driving means for vibrating the first and second heads in the signal track width direction with an amplitude greater than Tw; a second drive means for causing relative movement in the longitudinal direction of the signal track between the first and second heads and the medium; and a drive signal for the first drive means from the reproduction output of the first head group. and a signal processing circuit that obtains the
the first head so that the reproduction output of the second head is constant.
A tracking method characterized by controlling a driving means of. 2. The tracking method according to claim 1, wherein the first read head group is composed of a single magnetoresistive head. 3. The tracking method according to claim 1, wherein the first read head group is constituted by a single ring-shaped head whose head gap is approximately equal to Tw. 4. The tracking method according to claim 1, wherein the first read head group is composed of two magnetoresistive heads arranged in parallel with a constant interval S smaller than Tw.