JPS60185207A - Erasing device of video signal - Google Patents

Abstract

PURPOSE:To erase a video signal over a wide range and to attain repeated utilization based on the rewriting of a magnetic sheet by amplifying the output of an erasing signal generating means for increasing oscillation frequency and writing the amplified signal in a magnetic disk. CONSTITUTION:A magnetic head 2 is set up so as to be abutted upon a rewriting track of a rotary megnetic sheet 1 and a switch 9 is turned to a contact (b). Control voltage generated by closing/opening a start switch 13 of a generator 11 is impressed to a power supply circuit 12 and an erasing signal generator 10, and an erasing signal for increasing the frequency is outputted from a generator 10 and impressed to the head 2 by a recording amplifier 8 as erasing current through a switch 9. Said operation makes it possible to erase the recorded signal and to rewrite a signal of high quality.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a magnetic signal erasing device, and more particularly, to a magnetic signal erasing device for selectively erasing signals recorded on a magnetic seam having a plurality of tracks for recording video signals on a trunk-by-trunk basis. The present invention relates to a video signal erasing device.

[Background of the invention]

2. Description of the Related Art Magnetic recording devices that concentrically record a plurality of signals on a rotating magnetic medium include so-called floppy disk devices used for data files and the like. In these devices, when rewriting data, a method of overwriting is used. However, in a still image recording device that records a video signal on multiple tracks of a rotating magnetic medium by superimposing a luminance signal and a color signal, the recording wavelength of the color signal is generally several times that of the recording wavelength of the luminance signal. Because it becomes long,
Layer 1. In order to improve the image quality, high coercive force such as so-called metal powder was used on the magnetic medium to improve the image quality. When using a magnetic material, the color signal remained largely unerased during overwriting, making it impractical. Therefore, when rewriting a signal, it is necessary to sufficiently erase the recorded signal in advance. The erasing method is to use a dedicated erasing head that operates at a sufficiently high frequency so as not to affect the recording band and generates a sufficient erasing magnetic field, such as in a general tape recorder. A method of erasing the signal can be considered by arranging it on the same circumference as the magnetic medium and bringing it into contact with the magnetic medium. However, the above method requires a special erasing head that can provide a sufficient erasing magnetic field at a high frequency (for example, 20 MHz or higher), and the mechanism is complicated because the erasing head must be brought into contact with the medium in addition to the recording head. This was impractical, and another, simpler method of erasing was sought.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic recording device that allows easy erasing and writing of a recording signal of an arbitrary trunk selectively among video signals of a plurality of trunks recorded concentrically.

SUMMARY OF THE INVENTION The present invention utilizes the experimental result that magnetic signals can be erased over a wide frequency band by gradually increasing the frequency of the signal applied to the magnetic head from a low frequency. An erasing signal generating means whose oscillation frequency gradually increases from the frequency of 1 to a predetermined frequency is provided, and the output of the erasing signal is amplified and then applied to the magnetic head to provide a wideband erasing device.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

Figure 1 shows the configuration of the embodiment, in which 1 is a rotating magnetic sheet made of a so-called metal magnetic sheet coated with high coercive force magnetic powder, and 2 is a metal-compatible extraction head whose magnetic circuit is composed of a metal magnetic core. , 3 is the rotating magnetic sheet 1 360
4 is a recording signal circuit system, which is composed of an FM modulator 5, a video signal circuit system 6, etc., and 7 is an input terminal of the video signal circuit system 60. 8 is a recording amplifier that supplies a recording current to the magnetic head 2; 9 is a changeover switch that switches the input signal to the recording amplifier 80; 10 is a voltage-controlled oscillator, the oscillation frequency of which is controlled by the output voltage of the control voltage generator 11; An erasure signal generator whose oscillation amplitude is controlled by a power supply circuit 12; 13 is a control voltage generator 11;
This is the start switch for starting up the .

Next, the operation will be explained. First, when recording a video signal, the image signal to be recorded is sent from the input terminal 7 to the recording signal circuit system 4.
The signal is inputted into the circuit, subjected to FM conversion through the video signal circuit system 6 and the FM modulator 5, inputted into the recording amplifier 8 through the terminal a of the changeover switch 9, and magnetically recorded on the rotating magnetic sheet 1 by the magnetic head 2. Here, the rotating magnetic sheet 1 is rotating at 3600 rpm, and the recording signal circuit system 4 operates so that one field of video signals is recorded in one recording per rotation. The magnetic head 2 is supported by a head feeding mechanism (not shown) and is configured to be movable in the radial direction of the rotating sheet. A plurality of tracks of field video signals can be recorded concentrically on the sheet 1.

Next, a description will be given of the operation of re-coating the recording signal of an arbitrary track.

First, the magnetic head 2 is set by the head feeding mechanism so that it comes into contact with the rewriting trunk of the rotating magnetic sheet 1, and the changeover switch 9 is switched to the contact position. Next, when the starting switch 13 of the control voltage generator 11 is opened and opened, the control voltage generator 11 generates a gradually increasing control voltage as shown in FIG. 2a). This control voltage is applied to the power supply circuit 12 and the erase signal generator 10, and the power supply circuit 12 has a control voltage of Vs as shown in FIG.
It is configured to erase and supply power to the signal generator 10 only during the period from VB to VB. With these control voltages and power supply voltages applied, the erase signal generator 10 outputs a second signal.
During the period tS to iE as shown in Figure c) K, a sweep signal whose frequency is from f8 to fE is output. here,
The oscillation start frequency f8 is set near the recording frequency of the color signal (approximately IMHz in the embodiment), and the oscillation stop frequency fE is set to a frequency outside the band of the luminance signal (approximately tsMHz in the embodiment).

The above erase signal is applied as an erase current to the magnetic head 2 by the recording amplifier 8 through the changeover switch 9. Here, the head current amplitude is greater than or equal to the current during video signal recording (
Make sure to increase the sweep time (tg-1s)
is set to be a sufficiently long time (about 2 seconds in the embodiment) relative to the time for one rotation of the sheet (1/60 seconds).

By the above operation, the recorded signal is erased, and the frequency (outside the signal band) at the time when the erase signal stopped sweeping is recorded on the track of the magnetic sheet. However, since the recording wavelength of this erase signal is sufficiently short compared to the recording wavelength of the video signal, the erase signal can be sufficiently erased by recording the rewritten video signal q following the above-mentioned recording operation explanation. is,
There is almost no problem in practice, and it becomes possible to rewrite high-quality signals.

Next, a second embodiment will be explained with reference to FIG. This embodiment is almost the same as the first embodiment described in FIGS. 1 and 2 in terms of configuration and operation, but the differences are as follows.
As shown in Fig. 3b) and c)K, the power supply voltage Vcc supplied to the erase signal generator 10 is gradually attenuated after the oscillation frequency sweep is stopped (tie), so that the oscillation amplitude is gradually reduced to the frequency fE. This is a point made to attenuate. In this embodiment, the erasure signal amplitude is controlled in this way.
This makes it possible to eliminate residual erased signals on the magnetic sheet, making it possible to ensure high image quality when restoring signals more reliably than in the first embodiment. It has been made possible.

Next, a third embodiment will be explained with reference to FIG. 4. Fourth
In the figure, the same parts as those in FIG. 1 described above are given the same reference numerals and explanations are omitted, and the rotary seat and motor configuration are also the same as in FIG. 1, and illustration thereof is omitted. In this embodiment, the video signal recording operation is exactly the same as in the first embodiment. The difference from the first embodiment is that the voltage controlled oscillator 11 constituting the erase signal generator 10 is also used as the FM modulator 5 for recording video signals. In the embodiment, a changeover switch 14 is provided on the input side of the FM modulator 5, and is configured to switch between the modulation voltage from the video signal circuit system and the control voltage for erasing. Here, the FM modulator 5 used is one that can be varied from about IMH2 to 15 MHz or more depending on the input signal voltage. Since the FM modulator is used as the oscillator for the erasure signal as in this embodiment, the erasure,
For rewriting, it is only necessary to add a control voltage generator 11 whose voltage increases gradually, resulting in the great advantage that the configuration becomes very simple. However, the erasing operation is the same as in the previous embodiment, but during video recording, recording is performed once per sheet rotation, whereas during erasing, the output is output from the FM modulator 5 to the recording amplifier 8 for a period of 18 to iE as described in the previous embodiment. Since it is necessary to continue outputting the signals, it is natural that the recording signal circuit system 4 is equipped with the circuit configuration thereof, and detailed explanation thereof will be omitted.

[Effects of the Invention] According to the present invention, it becomes possible to erase a cursed image signal over a wide band, and it becomes possible to repeatedly use the magnetic sheet by changing its shape. Since the present invention utilizes the recording head for erasing, it is possible to selectively erase the magnetic disk without adding any new mechanism.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the configuration of the first embodiment, Fig. 2 is an explanatory diagram of signal operation in the first embodiment, Fig. 3 is an explanatory diagram of signal operation in the second embodiment, and Fig. 4 FIG. 2 is a configuration block diagram illustrating a third embodiment. l... Rotating magnetic sheet, 2... Magnetic head 5...
- FM modulator, 6... Video signal circuit system 8... Recording amplifier, 10... Erasing signal generator 11... Control voltage generator. No. 2 / Figure 2

Claims (1)

[Claims] 1. In a video signal erasing device for erasing a video signal from a magnetic disk having a plurality of concentric video signal recording tracks, the oscillation frequency is sequentially changed from a first oscillation frequency to a second oscillation frequency. An erasing device for a video signal, comprising an erasing signal generating means for increasing the number of erase signals, an amplifier circuit for amplifying the output of the erasing signal generating means, and a magnetic head for writing the output of the amplifier circuit on the magnetic disk.
. 2. Claim 1, characterized in that the first oscillation frequency is near the frequency of the color signal component of the video signal, and the second oscillation frequency is higher than the frequency of the luminance signal component of the video signal. A device for erasing video signals. 3. A video signal erasing device according to claims 1 or 2, wherein the amplifier gradually attenuates the output amplitude. 4. A video signal erasing device according to claims 1 or 2, wherein the erasing signal generating means gradually attenuates the output amplitude. 5. The video signal erasing device according to claim 3, wherein the amplifier gradually attenuates the output amplitude at the second oscillation frequency. 6. The video signal erasing device according to claim 4, wherein the erasing signal generating means gradually attenuates the output amplitude at the second oscillation frequency. 7. Frequency modulation means for frequency modulating the video signal, a recording amplifier for amplifying the output of the frequency modulation means, a magnetic head for writing the output of the recording amplifier onto a magnetic disk, and applying a gradually increasing control voltage to the frequency modulation means. A video signal erasing device having a control voltage generating means.