JPS6251003A - Magnetic recording erasion system - Google Patents

Abstract

PURPOSE:To attain the magnetic recording erasion with no residual magnetic field by providing an erasion signal generating circuit, an amplitude reducing circuit and a spindle motor drive control system. CONSTITUTION:A reference oscillator 20 transmits a reference signal fS and an M-divider 21 divides the signal fS and produces an erasion signal fEO. Here T=(m+0.5)Tm is satisfied between the revolving cycle T of a magnetic disk 2 and the cycle Tm of the signal fEO (m:integer). Thus the signal fEO inverts its phase for each cycle T. The erasion signal fE1 serving as the output signal of an AGC amplifier 23 is turned into such a signal obtained by reducing the amplitude of the signal fEO for each rotation of the disk 2. This signal is supplied to a coil 4 of a magnetic head 3 via a power amplifier 25. While the signal fS is supplied also to an N-divider 26 for production of a reference signal fM for control of a spindle motor 13 which drives the disk 2.

Description

DETAILED DESCRIPTION OF THE INVENTION <Field of Industrial Application> The present invention relates to an erasing method in magnetic recording. The present invention particularly relates to erasing information recorded on concentric tracks on a magnetic recording medium track by track using a recording or reproducing magnetic head. This allows high-frequency recording signals to be erased well.

<Prior Art> The alternating current erasure method is a well-known method for erasing information recorded on a magnetic recording medium such as a magnetic tape or a magnetic disk. This is a method in which an alternating magnetic field is applied to a magnetic recording medium so that it gradually decreases from the saturation level, as shown in FIG. Due to this gradually decreasing alternating magnetic field, the hysteresis loop of the magnetization of the magnetic recording medium gradually becomes smaller, and eventually the magnetization becomes zero. In other words, once the magnetic flux is saturated, it draws a loop to the magnetic neutral point, converges, and erases the residual magnetism. In Figure 6, 100 is an alternating magnetic field, and 10
1 is a hysteresis loop, 102 (indicates a change in magnetic flux).

Common methods for AC erasing include (1) a method using a pulse eraser, and (2) a method using a magnetic head exclusively for erasing. In a method using a bulk eraser, the amplitude of the alternating current magnetic field generated by the bulk eraser itself is usually attenuated gradually. On the other hand, in a method using an erasing-only magnetic head, the amplitude of the magnetic head does not need to change, but the magnetic field generated by the magnetic head during the time when any point on the magnetic recording medium passes over the gap of the magnetic head. The polarity of the signal must alternate many times. Therefore, the gap of the erase-only magnetic head is, for example, about several tens of micrometers.
Extremely spacious. That is, as shown in FIG. 7, the component Hx of the magnetic field H that the magnetic recording medium 104 receives from the magnetic head 103 in the medium longitudinal direction is maximum at the center of the gap 105, and gradually attenuates as it moves away from the center of the gap. . Therefore, if the polarity of the magnetic field is alternated many times during the time that an arbitrary point on the magnetic recording medium 104 passes over the gap 105, the magnetic field received by that point will be 100 in FIG.
The alternating current magnetic field gradually decreases in the same way as the waveform shown in , and after the magnetic flux is once saturated near the gap center, as it moves away from the gap center, it draws a loop and converges to the magnetic neutral point, and the residual magnetism disappears. As a result, AC cancellation is performed.

However, in the bulk eraser method (1), all tracks of the magnetic recording medium are erased, so it cannot be used for erasing each track.

On the other hand, according to the method 2) using an erasing-only magnetic head, erasing can be performed on a track-by-track basis.

However, since a magnetic head separate from the recording or reproducing head is required, the cost of the magnetic recording or reproducing apparatus increases and miniaturization of the apparatus is hindered. especially,
Recently developed electronic still cameras and recording devices that record video signals on concentric tracks using magnetic disks as small as 47 mm in diameter, as well as 8 tan V T
R is not practical because it is difficult to secure a space for installing a magnetic head dedicated to erasing.

Therefore, it would be convenient if erasing as described in (2) above could be performed using a recording or reproducing magnetic head.

However, this is not a major problem for devices that record or play back signals in a relatively low frequency band, such as audio tape recorders, but for devices that record or play back signals in a relatively low frequency band, such as VTRs and magnetic disk electronic still cameras. In this device, since the gap of the recording or reproducing magnetic head is on the order of 0.1 μm, AC erasing is virtually impossible. For example, in an electronic still camera system that rotates a 47 m+++φ magnetic disk at 60 revolutions per second and records video signals in one field per track using the low carrier FM method on concentric tracks, it is possible to record high frequency signals of about 10 MHz. , the gap of the recording or reproducing video head is 0.25-035 μm. Therefore, in order to perform erasing as described in (2) above using such a narrow gap video head, the video head must be able to operate at an extremely high frequency that clearly exceeds the upper limit of the recording or playback frequency of 50 to 100 MHz. In addition, a magnetic field with a sufficiently large amplitude must be generated. However, with current technology, it is not easy to make a recording or reproducing video head that can generate such an ultra-high frequency magnetic field, and it is also extremely expensive. Moreover, even if an ultra-high frequency magnetic field is generated, because it is an ultra-high frequency, the magnetic field will only reach the extremely shallow surface layer of the magnetic recording medium, and the IMH frequency that is recorded even in the deep layer.
Low frequency signals below this level are not erased and remain.

For the reasons mentioned above, AC erasure using a video head has not been put to practical use.

On the other hand, as a method for performing track-by-track erasing using a magnetic head, there is a method in which a relatively high single frequency signal within the recording or reproduction frequency band is recorded over the track to be erased. Although this method also erases a portion of the previously recorded signal, it cannot be said that erasing has actually taken place since a large amount of the subsequently recorded signal remains as a matter of course. Furthermore, when the previously recorded signal has a wide frequency band, such as a video signal, there is a drawback that a considerably large amount of low frequency components remains.

<Problems to be Solved by the Invention> In view of the above-mentioned prior art, the present invention solves the following problems when erasing each concentric recording track using a recording or reproducing magnetic head. It is an object of the present invention to provide an erasing method for magnetic recording in which magnetic flux is once saturated and then converged in a loop to a magnetic neutral point to perform erasing without residual magnetism.

Means for Solving the Problems The present invention achieves the above object by providing a recording or reproducing magnetic head that scans concentric tracks of a magnetic recording medium many times, and a magnetic head that is included in this magnetic head. a coil that generates a magnetic field in the longitudinal direction of the track in the gap of , an erase signal generating circuit that generates an erase signal whose phase is reversed every rotation of the recording medium at at9, and an amplitude that gradually decreases the amplitude of the erase signal supplied to the coil. It has a reduction circuit and a control system that controls the rotation of a spindle motor that rotates the magnetic recording medium so that the zero-crossing point of the erase signal written on the magnetic recording medium coincides with each rotation of the magnetic recording medium. It is characterized by:

Function> Now, in the coil 4 of the recording or reproducing magnetic head 3 of the recording device using the magnetic disk 2 as shown in Fig. 2,
Assume that an erase signal 1 having a waveform as shown in FIG. 1 is applied before the recording mode. Here, 5 is a video signal input terminal,
6 is a recording signal processing circuit including FM modulation, 7 is a recording amplifier, 8 is a reproduction amplifier, 9 is a reproduction signal processing circuit including FM demodulation, 10 is an output terminal for the reproduced video signal,
11 is a generation circuit for erasing signal 1; 12 is a switch; 13 is a spindle motor that rotates the magnetic disk at 60 revolutions per second;
14 is a head positioning device.

Further, FIG. 3 shows a plan view of the magnetic disk viewed from the direction ``■'' in FIG. 2. In the figure, 15 is a concentric track;
Reference numeral 16 indicates the head movement direction, and 17 indicates the disk rotation direction.

The erasing signal 1 shown in FIG.
The phase is reversed every rotation of the magnetic disk 2, with one cycle being 5 ec), and the amplitude is gradually decreased. Considering a single point on the track 15 when such an erase signal 1 is supplied to the coil 4 of the magnetic head 3, this point is an erase signal of opposite polarity and smaller amplitude every rotation of the magnetic disk 2. magnetized by This phenomenon occurs for several lines at all other points on the track 15, and is therefore equivalent to performing AC cancellation as explained based on FIG.

Embodiments Hereinafter, embodiments of the present invention will be described in detail based on the drawings. As shown in FIG. 4, the reference oscillator 20 sends out a reference signal fS. The M frequency divider 21 divides the frequency of the reference signal fS to generate an erase signal f6°.

At this time, the rotation period T of the magnetic disk 2 and the erase signal fEo
The following relationship is established between the period Tm and the period Tm.

Tm (m+0.5)Tm (where m is an integer) ・■
As a result, the erase signal fEO becomes a signal whose phase is inverted every rotation period T. This erase signal fl:.

is A via a PLL circuit 22 consisting of a phase comparator 22a10, a pass filter 22b and a voltage controlled oscillator 22c.
The signal is supplied to the GC amplifier 23.

This AGC amplifier 23 is connected to an amplitude reduction circuit 2 which will be described in detail later.
4, the gain is reduced each time the magnetic disk 2 rotates. Therefore, the erase signal fii, which is the output signal of the AGC amplifier 23, is generated by the erase signal f every one revolution of the magnetic disk 2.
I:. A signal having a reduced amplitude, that is, a signal having the same waveform as the erasing signal 1 shown in FIG. 1, is supplied to the coil 4 of the magnetic head 3 via the power amplifier 25.

On the other hand, the reference signal f6 is also supplied to the N frequency divider 26, and provides a reference signal f for controlling the spindle motor 13 that rotates the magnetic disk 2. That is, spindle motor 1
3. A servo system is composed of a frequency generator 27a, a phase comparator 27b, and a low-pass filter 27c, and the output signal of the frequency generator 27a, which transmits a signal with a frequency proportional to the rotation speed of the spindle motor 13, and the reference signal f6. The rotation of the spindle motor 13 is controlled so that the phases of the two are matched by phase comparison @27b. Thus, as shown in FIG. 1, the zero cross point of the first cycle of the second rotation of the magnetic disk 2 is "02'"
is the previous time, that is, the zero cross of the first cycle, point a
. l'''II on track 15.

This relationship holds true for all other zero cross points as well.

In addition, in this embodiment, the magnetic disk? The following relationship holds between the rotation period T and the reference signal f, .

T=nT, (however; n is an integer)
・・・・・・■ Therefore, M frequency divider type 21 and N frequency divider 2
The frequency division ratio of 6 can be determined, for example, by the following method. That is, from formulas ■ and ■, T= (m+0.5) Tl1= n T.

......■ From formula 0, m + 0.5 N = -M 1 ......For both M and N to be integers from formula 00, M must be a multiple of n, and - is It is sufficient if it is a multiple of 2.

Now, m=3. n=6. If M=60, then from formula 0, N=
It becomes 35. That is, in this case M: N=12: 7
The number of revolutions of the magnetic disk 2 (usually 360
0 rpm) is determined, the frequency division ratio of the frequency dividers 21 and 26 and the reference signal f.

The frequency of can also be easily determined.

FIG. 5 fal is a circuit diagram showing a specific circuit configuration of the amplitude reduction circuit 24. In the figure, 24a is an erase switch;
4b is a sampling switch, 24c and 24d are capacitors, and 24e.

24f is a resistor and 24g is a buffer amplifier.

In this amplitude reduction circuit 24, the erase switch 24a
When the voltage is turned on, the power supply voltage ■cC is applied to the point a, and as a result, a voltage with a gradually decreasing waveform forming an exponential curve determined by a time constant based on the values of the capacitor 24c and the resistor 24f is generated at the point A. The voltage waveform at point b is shown in FIG. 5 (bl). The voltage at point b is sampled by the sampling pulse PG shown in FIG. is held.

As a result, a stepped waveform voltage input is obtained at point C, which gradually decreases every rotation T of the magnetic disk 2.

The waveform of this voltage v8 is shown in FIG. 5(C). Thereafter, the voltage V is supplied to the AGC amplifier 23 via the buffer amplifier 24g. As a result, the erase signal fEl, which is the output signal of the AGC amplifier 23, becomes a waveform signal whose level is reduced every rotation.

In this embodiment, sampling is performed every rotation using the sampling pulse PG, but it is not necessarily necessary to form it in this manner. If the attenuation step is small, you can use an analog switch to obtain a voltage that gradually decreases by switching the analog switch, or if the time constant is large enough, you can directly use the AGC amplifier with the voltage waveform shown in Figure 5 (bl). 23 may be controlled.

In addition, in this embodiment, the relationship of equation 0 is established between the rotation period T of the magnetic disk 2 and the period - of the erasing signal f5o.
The phase of the erase signal f is inverted every rotation of the magnetic disk 2. This is done by passing the erase signal having the relationship T=m-T□ alternately through a 180° phase shifter every rotation. It can also be obtained by Furthermore, the control system does not need to be limited to the servo system of this embodiment, and the rotation speed of the spindle motor 13 changes following fluctuations in the erasing signal fEO, or the erasing signal follows fluctuations in the rotation of the spindle motor 13. f
It is sufficient if the phase of the phase changes.

<Effects of the Invention> According to the present invention, the recording or reproducing magnetic head is operated to once saturate the magnetic flux for each concentric track, and then draw a loop to the magnetic neutral point to converge and erase without residual magnetism. be able to. Furthermore, it is possible to erase even deep parts of a track. Furthermore, erasing can be performed without using special circuit elements.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of the erasing current waveform according to the present invention, and FIG.
The figure is a block diagram of a recording device using a magnetic disk cited as an example to which the present invention is applied, Figure 3 is a plan view of the magnetic disk seen from the direction ■ in Figure 2, and Figure 4 is an implementation of the present invention. A block diagram showing an example, FIG. 5 (at is a circuit diagram more specifically showing the amplitude reduction circuit in the above embodiment, FIG. 5 tb +
Figure 5 fd) is a waveform diagram showing the voltage waveforms of each part, and Figure 6
The figure is an explanatory diagram of the principle of AC erasing, and FIG. 7 is an explanatory diagram of the magnetic field applied by the magnetic head to the magnetic recording medium. In the drawing, 1 is an erase signal, 2 is a magnetic disk, 3 is a magnetic head, 4 is a coil, 15 is a track, f is a reference signal, 'l:o' 1ml is an erase signal, fl and l are control standards. It's a signal.

Claims (1)

[Claims] A recording or reproducing magnetic head that scans concentric tracks of a magnetic recording medium many times, a coil that is included in this magnetic head and generates a magnetic field in the longitudinal direction of the track in the gap between the magnetic heads, and an erasing signal generation circuit that generates an erasing signal whose phase is inverted; an amplitude reduction circuit that gradually reduces the amplitude of the erasing signal supplied to the coil; and a zero-crossing point of the erasing signal written on the magnetic recording medium. and a control system for controlling the rotation of a spindle motor that rotates a magnetic recording medium so that the rotation of the magnetic recording medium coincides with each rotation of the magnetic recording medium.