JPS6251002A - Method and device for erasing magnetic recording - Google Patents

Abstract

PURPOSE:To attain the magnetic recording erasion with no residual magnetic field by converging the magnetic flux in a loop up to a magnetic neutral point after saturating once the magnetic flux for each concentric track by means of a recording or reproducing magnetic head. CONSTITUTION:An erasion current 1 having such a waveform as shown in the diagram is supplied to a coil 4 of a recording or reproducing magnetic head 3 of a video recording device using a magnetic disk 2 before a recording mode. Thus a magnetic field having the alternating magnetic polarities and the amplitude decreasing gradually affects always any point on a track 15 in the lengthwise direction of the track owing to rotations since T+alpha>T is satisfied. Here the initial value I1 of the current 1 is set at such a level that can magnetize the disk 2 up to a saturating level.

Description

DETAILED DESCRIPTION OF THE INVENTION <Field of Industrial Application> The present invention relates to an erasing method and an erasing device 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 and converges to the magnetic neutral point, thereby eliminating residual magnetism. In Figure 6, 100 is an AC magnetic field, 1
01 indicates a hysteresis loop, and 102 indicates a change in magnetic flux.

For AC erasing, there are generally two methods: (1) using a bulk eraser and (2) 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 Hz in the medium longitudinal direction of the magnetic field H that the magnetic recording medium 10.4 receives from the magnetic head 103 is maximum at the center of the gap 105, and gradually increases as it moves away from the center of the gap. Attenuate. 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 10 in FIG.
The alternating current magnetic field gradually decreases in the same way as the waveform indicated by 0, and after the magnetic flux is once saturated near the gap center, it converges in a loop to the magnetic neutral point as it moves away from the gap center, and residual magnetism disappears. As a result, AC cancellation is performed.

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

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 m VTRs, require less space to install magnetic heads dedicated to erasing. It is difficult to secure, so it is not practical.

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 47III1φ magnetic disk at 60 revolutions per second and records video signals 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 video head for recording or playback is 0.25-035μm
It is. Therefore, in order to perform the erasure described in (2) above using such a narrow gap video head, the video head must be able to operate at an extremely high frequency of 50 to 100 MHz, which far exceeds the upper limit of the recording or playback frequency. 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 will not reach the low frequencies below about IMHz that are recorded even in the deep layers. The signal remains without being erased. 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. Even with this method, the previously recorded signal is erased to some extent, but since a large amount of the subsequently recorded signal remains as a matter of course, it cannot be said that erasure has actually taken place. 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 has been developed in such a way that when erasing each concentric recording track using a recording or reproducing magnetic head, the magnetic flux is first saturated and then the magnetic flux is saturated. The object of the present invention is to provide a method and apparatus capable of drawing and converging a loop to a neutral point and performing erasing without residual magnetism.

Means for Solving the Problems> The erasing method according to the present invention that achieves the above-mentioned object consists of scanning concentric tracks of a magnetic recording medium multiple times with a recording or reproducing magnetic head, and using the magnetic head to perform erasing. A magnetic field is generated in the longitudinal direction of the track in the gap of the magnetic head by passing an erasing current, and the waveform of the erasing current changes its polarity and gradually decreases its amplitude over a period longer than the scanning period of one round of the track. In addition, this is a method of erasing data from a magnetic recording medium for each concentric track by creating a waveform with a substantially constant amplitude between adjacent polarity changes.

Further, the erasing device of the present invention which achieves the above-mentioned object includes a recording or reproducing magnetic head that scans a concentric track of a magnetic recording medium many times, and a recording or reproducing magnetic head that scans a concentric track of a magnetic recording medium many times, and a recording or reproducing magnetic head that is provided with a recording or reproducing magnetic head that scans a concentric track of a magnetic recording medium many times. A coil for generating a magnetic field, a voltage generating means for generating a DC voltage whose magnitude gradually decreases from a certain value over a period sufficiently longer than the scanning period of one round of the track, and a gradually decreasing DC voltage output from the voltage generating means. A sample/hold means for sampling and holding a period longer than the scanning period of one track rotation, a voltage/current conversion means for outputting a current proportional to the output voltage of the sample/hold means, and a voltage/current converting means for outputting a current proportional to the output voltage of the sample/hold means. A device comprising: a polarity switching means for switching the polarity of the output current of the converting means in synchronization with the sampling period and supplying the polarity to the coil of the magnetic head; and a timing pulse generating means for generating timing pulses necessary for the operation of each part. It is.

Operation> Now, an erasing current 1 having a waveform as shown in FIG. 1 is applied to the coil 4 of the recording or reproducing magnetic head 3 of a recording device using a magnetic disk 2 as shown in FIG. 2 in the recording mode. Suppose you run it before. Here, 5 is a video signal input terminal, 6
1 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, 1
Reference numeral 1 designates a generation circuit for erasing current 1, 12 a switch, 13 a motor that rotates the magnetic disk at 60 revolutions per second, and 14 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, 16 is a head movement direction, and 17 is a disc rotation direction.

The erase current 1 shown in FIG. 1 alternates in polarity with a period of T+α, and its amplitude gradually decreases.

However, within each period of T+α, the amplitude is constant. T
is the period during which the magnetic head 3 scans the track 15 once (for example, T = 11 sec), and 0<α<<T.

When such an erasing current 1 is applied to the coil 4 of the magnetic head 3, since it is T10〉T, at any point on the track 15 there is always a change in polarity and a gradual decrease in amplitude as the track rotates. A magnetic field acts. In this case, the initial value 11 of the erase current 1 is set to a value that can generate a magnetic field sufficient to magnetize the magnetic disk 2 to a saturation level. Further, it is desirable that the amplitude of the erase current 1 attenuates as slowly as possible in a region close to zero.

The erase current 1 with the waveform shown in FIG. 1 is shown in FIG.
It is generated as shown in FIG. First, a DC voltage v8 having a gradually decreasing waveform as shown in FIG. 4(a) is sampled and held using a sampling pulse 62 having a cycle of T+α shown in FIG. 4(b). Then, Figure 4 (
A gradually decreasing step waveform voltage V as shown in cl is obtained.

Figure 4 (If the voltage of cl is converted to current, Figure 4 fd)
A gradually decreasing step waveform current IT is obtained as shown in FIG.

When the polarity of the current lA of FIG. 4(dl) is changed at the timing shown in FIG. 4(el), the polarity of the current lA of FIG.
An erase current 1 having a waveform similar to that shown in the figure is obtained. However, the timing of the polarity change is synchronized with the sampling pulse 62.

Embodiment> An embodiment of the present invention will be described with reference to FIGS. 4(a) to (g) and FIG. 5. FIG. 5 is a circuit diagram showing an example of an erasing device. In the figure, 20 is a gradually decreasing DC voltage generation circuit, 30 is a sample/hold circuit, 40 is a voltage/current conversion circuit, 50 is a polarity switching circuit, and 60 is a timing pulse generation circuit.

In the voltage generation circuit 20, a voltage source 21, a switch 22, a capacitor C, and a resistor R are connected in series.

When the switch 22 is turned on, a gradually decreasing DC voltage VR is generated between the terminals of the resistor R as shown in FIG.

In this embodiment, the recording apparatus shown in FIG. 2 is targeted, and considering the case where the scanning period T for one round of the track is T-s o see, T+a=16.
．． 7ms>71sec. Therefore, 16.7 shoes S
CR=71.6m5ec is set so that the erase current attenuates by 20% in each ec period and the polarity changes about 15 times. The switch 22 is normally an electronic type, and is turned on for about 300 m5θC by a control signal 61 from a timing pulse generation circuit 60.

The sample and hold circuit 30 may be any conventionally used circuit. Sampling pulse 62 given from timing pulse generation circuit 60 (Koyotte, Kono@J@3
If 0, the outside of the gradually decreasing DC voltage is sampled every T+a=16.7 ms and held. This circuit 30 outputs a voltage V having a staircase waveform shown in FIG. 4 (q).

The voltage/current conversion circuit 40 may also be one that is conventionally used. However, in this embodiment, the initial value VS1 of the gradually decreasing staircase wave voltage V5 output from the sample-and-hold circuit 30 is set to 50
It is designed to convert to mA.

The polarity switching port $50 has two switches 51 and 52. These two switches 51, 52 are typically electronic switches. Both switches 51° and 52 are timing pulse generation ports! It is controlled by a control signal 63 from l560. As shown in FIG. 4, this control signal 63 is an on/off signal with a period of 2 (T + a ) = 33.4 msec and a duty of 50%.The on/off timing is determined by the sampling pulse 62. When the control signal 63 is on, both switches 51 and 52 are closed to contact a, and current flows through the coil 4 of the magnetic head 3 in the direction of arrow P.On the contrary, when the control signal 63 is off, both switches 51 and 52 are closed to their contacts, and current flows through the coil 4 of the magnetic head 3 in the opposite direction indicated by the arrow N. As a result, the polarity of the erase current 1 changes to T+a=16. It changes every 7m5ec.The resistor 53 is for damping.In addition, the polarity conversion circuit 50
is connected to the magnetic head 3 by the switch 12 shown in FIG. 2, but is not shown in FIG.

<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. Additionally, it is possible to erase even the deepest 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 configuration diagram of a recording device using a magnetic disk cited as an example of the application of the present invention, FIG. 3 is a plan view of the magnetic disk seen from the direction ■ in FIG. FIG. 5 is a block diagram showing one embodiment of the erasing device, FIG. 6 is a diagram explaining the principle of AC erasing, and FIG. 7 is a diagram explaining the magnetic field applied to the magnetic recording medium by the magnetic head. In the drawing, 1 is an erase current, 2 is a magnetic disk, 3 is a recording or reproducing magnetic head, 4 is a coil, 15 is a concentric track, 20 is a gradually decreasing DC voltage generation circuit, 30 is a sample/hold circuit, 40 is a voltage/current conversion circuit, 5
0 is a polarity switching circuit, and 60 is a timing pulse generation circuit.

Claims (2)

[Claims] (1) Scanning concentric tracks of a magnetic recording medium multiple times with a recording or reproducing magnetic head, passing an erasing current through the magnetic head to generate a magnetic field in the longitudinal direction of the track in the gap between the magnetic heads, and , by making the waveform of the erasing current such that the amplitude gradually decreases as the polarity changes over a period longer than the scanning period of one round of the track, and the waveform has a substantially constant amplitude between adjacent polarity changes. , a method of erasing a magnetic recording medium concentrically on a track-by-track basis. (2) 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 Voltage generating means for generating a DC voltage whose magnitude gradually decreases from a certain value over a period sufficiently longer than a scanning period; and a voltage generating means for generating a DC voltage whose magnitude gradually decreases from a certain value over a period sufficiently longer than the scanning period of one track revolution; sample/hold means for sampling and holding as a period; voltage/current conversion means for outputting a current proportional to the output voltage of the sample/hold means; and output of the voltage/current conversion means for synchronizing the output of the voltage/current conversion means with the sampling period. An erasing device comprising a polarity switching means for switching the polarity and supplying the polarity to the coil of the magnetic head, and a timing pulse generation means for generating timing pulses necessary for the operation of each part.