JPS6348604A - Erasing method for magnetic record - Google Patents

Abstract

PURPOSE:To prevent an erasure signal from remaining in the frequency band of a video signal by scanning a magnetic head on a track to be erased and supplying an erasure current which decreases gradually from an initial amplitude level to the magnetic head. CONSTITUTION:While a floppy disk 5 is rotated, the magnetic head 4 is scanned on a track 5a and the erasure current I is supplied to the magnetic head 4. Then, the initial amplitude level of the erasure current I is large, so the track 5a is saturated magnetically with the erasure current I and its video signal is erased, so that the remaining level decreases to nearly the same extent with bulk erasure. Further, the amplitude of the erasure current I decreases gradually, so the residual level of the erasure signal by the erasure current I also decreases gradually. When an attenuation time T is set to >=1sec, the residual level of the erasure signal further drops low enough to disregard.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to seven methods of erasing in magnetic recording, and is devised to eliminate good erasure without leaving any erasure signal within the frequency band of the video signal. It is something.

<Prior Art> Various techniques have been proposed in the past as methods for erasing one track in iH magnetic recording of video signals, particularly in magnetic recording using a floppy disk as a magnetic recording medium in an electric still camera system. One of these methods is called a sweep erase method. The sweep cancellation method is to first erase a frequency within the video signal band (for example, 6M
1lz) is written onto a track of a magnetic recording medium on which a video signal has already been written, such as a magnetic disk, and the frequency of this erasing signal is increased continuously, and the same writing is repeated. , the frequency of erasure No. 13 is finally brought out of the band of the video signal. By this sweep method, the track is erased (the frequency of 2r
Since it is out of the signal band, it can be cut by a filter during playback, and only the necessary video can be played back.In other words, many erasing signals with different frequencies can be removed from the original signal. Overlap the track on which the video signal is written δ
By doing so, the original video signal is essentially erased. At this time, the deep layer of the magnetic recording medium is erased with a relatively low frequency erase signal, and the surface layer is erased with a relatively high frequency erase signal.

<Problem to be solved by the invention> However, in the sweep erasing method according to the above-mentioned prior art,
When the erasing time is shortened (for example, 2 seconds or less), there is a problem that the erasure No. 17 itself remains at a large level within the frequency band of the video signal, and the noise level is higher than that erased by the bulk eraser. Ta.

In view of the above drawbacks of the prior art, the present invention prevents the erased signal from remaining within the frequency band of the video signal, and lowers the noise level in the entire band after erasing to the level of bulk erase erase. The purpose of the present invention is to provide an erasing method in magnetic recording that can be performed.

<Means to Solve the Interval Reversal> The structure of the present invention that achieves the above object is a method for erasing a video signal written by a magnetic head on a track of a rotating magnetic recording medium, which comprises: is scanned by the magnetic head, and an erase current whose frequency is higher than the recording band frequency of the video signal and whose amplitude level is higher than the optimum recording current level of the magnetic head decreases from an initial amplitude level, It is characterized in that it is caused to flow through the magnetic head.

<Operation> The video signal is erased by the erasure signal, and the erasure signal itself almost disappears outside the recording band of Video No. 45.

Embodiments Hereinafter, embodiments of the present invention will be described in detail based on the drawings. FIG. 1 is a block diagram illustrating a 711 apparatus implementing an embodiment of the present invention.

In the figure, 1 is an oscillator, 2 is an attenuation circuit, 3 is a recording amplifier, 4 is a magnetic head, 5 is a floppy disk which is a magnetic recording medium, and 6 is a control circuit. Of these, oscillator 1
receives the oscillation control signal S from the control circuit 6, oscillates, and outputs an oscillation signal S2 which is a sine wave. The frequency of this oscillation signal S2 is the recording band frequency of the video signal (approximately 0 to 1
2Mtlz), specifically 14MHz. The attenuation circuit 2 converts the oscillation signal S2 into I! l is decreased to obtain 'a reduction signal S3. In this case, the time required for the level of the Wk reduced total oscillation signal S3 to become sufficiently small, that is, the decay time, may be determined in relation to the rotational speed of the floppy disk 5. In this case, 60 degrees of rotation is appropriate. The recording amplifier 3 receives the recording control signal S from the control circuit 6.
4, the erase current I is obtained by amplifying the gradual oscillation signal S3. The initial amplitude level of this erase current I is set larger than the optimum recording current of the magnetic head 4. In this example, the initial amplitude level of the erase current I is set to 100 mA p-p, and the optimum recording current value of the magnetic head 4 is 80 mA p-p.
This is an increase of 25%. In the case of magnetic disks for electronic still cameras, the optimum recording current means that the spectrum of the recorded signal is 7.
Since it is distributed with a peak near MHz, in practical terms it refers to the recording current of a value that maximizes the reproduction output when recording at a frequency of 7 MHz. As a result, the erasing current I, which gradually decreases from an initial amplitude level whose frequency is higher than the recording band frequency of the video signal and whose amplitude is larger than the optimum recording current level of the magnetic head 4, is applied to the magnetic head 4.
flow to.

Next, a method of the present invention using such an apparatus will be explained. For example, in order to erase a video signal recorded by the magnetic head 4 on the track 5a of the floppy disk 5, the floppy disk 5 is rotated and the magnetic head 4 moves over the track 5a.
At the same time, the erasing current I is applied to the magnetic head 4. Since the initial amplitude level of 711 is large, the track 5a is magnetically saturated by the erasing current I, and the video signal is After erasing, the residual level drops to the same level as bulk erase. Also, the erase current I
Since the amplitude of the erase signal gradually decreases, the residual level of the erase signal caused by the erase current I in the track 5a also gradually decreases. If the decay time T is set to 1 second or more, the residual level of the erased signal is further reduced to a level that does not pose a problem. Furthermore, even if the erased signal remains, since its frequency is higher than the recording band frequency of the video signal, it is normally rewritten to a new spectrum by the rewritten signal, so there is no problem.

Next, data of various experiments conducted using the apparatus shown in FIG. 1 will be shown. Note that the track 5a to be erased has a power of 80 mA.
I) A single frequency signal of 7M11z at -p and a single frequency signal of 1.25MIIz at a level of -17 dB with respect to this signal level '-'i is applied to evaluate the erasure rate', q. A simulated video of the words was recorded.

Figures 2, 3, and 4 show the erasure rate: AI 60+n8p-p, 80mA p-p, ! 00mA
When p-p, the reduction Q time of the erase current (■) is 15 seconds.

Change it to 10 seconds or 0.5 seconds and delete it? : Shows the erasure rate of luminance A5 fY when the frequency of L flow I is changed. From these figures, it can be seen that the decay time is long, the frequency is high,
It is understood that the erase rate is large for warts with a thick erase current value, and that the erase current value in particular has a large influence Δ on the erase rate.

That is, when the erase current value is 60 mA p-p, the erasure rate is -3
It's around 0dB, but when it's over 80mA p-p -5
0dl] or more -L erasing performance can be obtained. Also 100mA
If you set it to Mllz from pp to m, it becomes almost the bulk...r laser level (-60dB).

Figures 'f25, 6 and 7 show the erase current I of 50mA p-p, 80ffl8p-p, 100m
The decay time of the dissipation current I when A pp is 1.
5 seconds.

The erasing rate of the color signal f is shown when changing the frequency of the erasing current (2) to 1.0 seconds, 0.5 sand, and changing the frequency of the erasing current (2).

From these figures, it can be seen that the effect of the erase current value is the greatest, similar to the above-mentioned erasure of the luminance signal. That is, the erase current value is 60m8p and pte is -10dBii7r? , 4
．． 80m 8p to p Teher 20~-25d [about l, l0
At 0iA 1p, it becomes -40dBH*.

Figures 8, 9 and 1o show residual levels other than a single spectrum. From these diagrams, you can understand the following. In other words, the current dependence is 60[11A p-p''
C: Does the residual level become small? 80mΔp-p,
＋00+nA p-p TEHAP] し、J- The residual level becomes smaller.

Regarding frequency dependence, the higher the frequency, the lower the residual level. The dependence on the decay time is that the residual level is large at 0.5 seconds, and becomes small at 1.0 seconds and 1.5 seconds.

Next, the following table shows a comparison of the S/N ratio between bulk erase and the method of the present invention. In the method of the present invention, 14MHz,
+00mA p-p, erasure of "j+ r<i 1.
Decayed for 0 seconds.

Table (S/N ratio, unit dB) From the above, it was confirmed that according to the method of the present invention, erasing comparable to bulk erasing can be achieved.

<Effects of the Invention> As specifically explained above in conjunction with the embodiments, according to the present invention, signals within the video signal frequency band can be erased as well as when bulk erasing is performed.

[Brief explanation of drawings]

Figure 1 is a block diagram showing a device for realizing the direction lighting of the present invention, Figures 2 to 4 are data diagrams showing the erasure rate of luminance (iE), and Figures 5 to 7 are data diagrams showing the erasure rate of color signals. (data diagram showing
FIGS. 8 to 10-1 are theta diagrams showing residual levels other than the middle spectrum. In the drawing, 1 is an oscillator, 2 is a decay circuit, 3 is a recording head, 4 is a magnetic head, 5 is a floppy disk, 6 is a control circuit, and 1 is a decay current.

Claims (1)

[Claims] A method for erasing a video signal written by a magnetic head on a track of a rotating magnetic recording medium, comprising: scanning the track to be erased with the magnetic head, and adjusting the frequency of the recording of the video signal. An erasing method in magnetic recording, characterized in that an erasing current that gradually decreases from an initial amplitude level higher than a band frequency and larger than an optimum recording current level of the magnetic head is passed through the magnetic head.