JPH0740330B2 - Magnetic eraser - Google Patents

Description

The present invention relates to an erasing device in magnetic recording. In particular, the present invention relates to erasing information recorded in concentric tracks on a magnetic recording medium for each track by using a recording or reproducing magnetic head, for example, a wide band, such as an FM-modulated video signal. A high-frequency recording signal can be satisfactorily erased, and a relay for switching the magnetic head between recording or reproducing and erasing is eliminated.

<Prior Art> As a method of erasing information recorded on a magnetic recording medium such as a magnetic tape or a magnetic disk, an AC erasing method is well known. This is a magnetic recording medium, as shown in FIG.
This is a method of applying an alternating magnetic field so that it gradually decreases from the saturation level. Due to this gradually decreasing AC magnetic field, the hysteresis loop of the magnetization of the magnetic recording medium becomes gradually smaller, and finally the magnetization becomes zero. That is, after the magnetic flux is once saturated, a loop is drawn up to the magnetic neutral point and converged to eliminate residual magnetism. In FIG. 7, 100 is an alternating magnetic field, 101
Indicates a hysteresis loop, and 102 indicates a change in magnetic flux.

For AC erase, (1) a method using a bulk eraser and (2) a method using an erase-only magnetic head are common. In the method using the bulk eraser, the amplitude of the AC magnetic field generated by the bulk eraser itself is usually gradually attenuated. On the other hand, in the method using the magnetic head dedicated to erasing, the amplitude of the magnetic head does not need to be changed, but the magnetic field generated by the magnetic head within the time when any point on the magnetic recording medium passes over the gear head of the magnetic head. It is necessary to alternate the polarities of. Therefore, the erase-only magnetic head has a very wide gap, for example, about several tens of μm. That is, as shown in FIG. 8, the magnetic head 10
The component H _x of the magnetic field H received by the magnetic recording medium 104 from 3 in the medium longitudinal direction is maximum in the central portion of the gear 105, and gradually attenuates as the distance from the central portion of the gear 105 increases. Therefore,
If the polarity of the magnetic field is changed a number of times within the time that any one point on the magnetic recording medium 104 passes over the gear 105, the magnetic field received by that point gradually decreases like the waveform shown by reference numeral 100 in FIG. An alternating magnetic field is generated, and the magnetic flux is once saturated in the vicinity of the center of the gear, and as it moves away from the center of the gear, a loop is drawn up to a magnetic neutral point to converge and the residual magnetism disappears.
As a result, AC erase is performed.

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

On the other hand, according to the method (2) using the magnetic head dedicated to erasing, erasing can be performed for each track. However, since the magnetic head different from the recording or reproducing head is required, the cost of the magnetic recording or reproducing apparatus is increased and the miniaturization of the apparatus is prevented. Especially recently developed,
Electronic still cameras and recording devices that record video signals on concentric tracks using a small magnetic disk of about 47 mmφ are not practical because it is difficult to secure a space for installing the magnetic head for erasing.

<Problems to be Solved by the Invention> Therefore, it is convenient if the erasing as described in (2) above can be performed using the recording or reproducing magnetic head.
However, in an apparatus that records or reproduces a signal in a relatively low frequency band such as an audio tape recorder, there is no problem, but in an apparatus that records or reproduces a signal in a high frequency band such as a magnetic disk type electronic still camera. , The magnetic head for recording or reproduction has a gear head of 0.1 μm
Since it is on the order of, it is virtually impossible to erase AC. For example, rotate a 47mmφ magnetic disk 60 times per second,
In an electronic still camera system that records a video signal on a concentric track using the low carrier FM method and one field on a track, the recording or reproducing video head has a 0.25-gear tape so that a high-frequency signal of about 10 MHz can be recorded. Is about 0.35 μm. Therefore, in order to perform erasure as described in (2) above using a video head with such a narrow gear, the video head has a recording or playback frequency exceeding the upper limit of 50 to 100 MHz. A magnetic field with a high frequency and a sufficiently large amplitude must be generated. However, with the current technology, it is not easy and extremely expensive to make a recording or reproducing video head capable of generating such an ultra-high frequency magnetic field. Moreover, even if an ultra-high frequency magnetic field is generated, the magnetic field can reach only an extremely shallow surface layer in the magnetic recording medium because of the ultra-high frequency, and a low-frequency signal of about 1 MHz or less recorded even in the deep layer. Remains without being erased. For the above-mentioned reason, AC erase using a video head has not been put into practical use.

As a method of erasing each track by using the magnetic head, there is a method of recording a signal having a relatively high single frequency within a recording or reproducing frequency band by superimposing it on the track to be erased. Even with this method, the previously recorded signal is erased to some extent, but the signal recorded after being overlapped afterwards naturally remains large, so it cannot be said that the erasure is essentially performed. Further, when the frequency band of a previously recorded signal such as a video signal is wide, there is a disadvantage that a low frequency component remains considerably large.

In order to solve various drawbacks and restrictions which occur in the method of applying the high frequency magnetic field to the magnetic recording medium by the recording or reproducing magnetic head for erasing, the same track is recorded in one magnetic head like a recording apparatus using a magnetic disk. Therefore, it is known that a method of applying a DC current pulse to perform erasing is effective in a system capable of repeating scanning many times. For example, Japanese Patent Publication Nos. 47-19378 and 5
See 1-1409 and JP-A-48-66414. In each of the erasing methods disclosed in the respective publications, the erasing current is formed by connecting a plurality of rectangular current pulses by changing the current direction and gradually decreasing the level. The polarity of the rectangular current pulse changes at every time required for one rotation of the magnetic disk. According to these erasing methods, the low frequency component of the previously recorded signal is not erased and remains at the normal rotation speed of the magnetic disk as described above. The same effect as AC erasing can be expected in erasing a single track.

However, in the erasing method using the DC current pulse, in principle, it is necessary to apply a DC current whose polarity is reversed to the coil of the magnetic head. The terminal, for example, the secondary side (amplifier side) of the step-up transformer cannot switch between the erase signal circuit and the recording or reproduction signal circuit, and the primary side of the step-up transformer, that is, a place where a weak signal is handled, is erased. It becomes necessary to switch between recording and reproduction. Adopting a relay circuit or the like for this switching is not appropriate because it complicates the circuit for mounting while demanding a compact device. Therefore, it has not been possible to obtain a practical erasing device having a switching circuit for erasing and recording or reproducing with high reliability of operation.

In view of the above-mentioned problems of the prior art, the present invention is intended to realize a novel magnetic erasing apparatus which solves various drawbacks and restrictions.

That is, an object of the present invention is to basically guarantee an erasing effect similar to that of a bulk eraser when erasing for each concentric recording track is performed using a recording or reproducing magnetic head.
Another object of the present invention is to provide a magnetic erasing device which has a simple switching mechanism between the erasing mode and the recording or reproducing mode and is highly reliable and suitable for downsizing.

<Means for Solving the Problems> The structure of the present invention that achieves the above-mentioned object is a gradual voltage generation circuit that generates a DC voltage that gradually decreases during erasure and that the generated voltage becomes zero during recording / reproduction, and this gradual decrease voltage A voltage / current conversion circuit that generates a DC current that gradually decreases by converting the output voltage of the generation circuit into a current, a reference transistor that is diode-connected and that allows the DC current that gradually decreases to flow, and a base that is the base of the reference transistor. A first transistor connected to form a first current mirror circuit with the reference transistor; a second transistor having a base connected to the base of the reference transistor to form a second current mirror circuit with the reference transistor; The first switch which is interposed between the output terminal of the first transistor and the ground to perform switching. A switching circuit having a switching transistor and a second switching transistor which is interposed between the output terminal of the second transistor and the ground and performs switching, and a magnetic circuit between the output terminals of the first and second transistors. A recording / reproducing head coil for scanning concentric tracks on the recording medium, and a series circuit in which a secondary coil is connected in series with a primary coil of a transformer connected to a recording / reproducing amplifier. At times, both the first and second switching transistors are kept on, and at the time of erasing, the first and second switching transistors are alternately turned on / off every period equal to or longer than the scanning period of one track. And a switch control circuit for controlling.

<Operation> Now, let us consider a recording apparatus in which the magnetic disk 1 is rotated by the motor 2 as shown in FIGS. 2 and 3 and the magnetic head 3 is brought into contact with the magnetic disk 1 for recording or reproduction. In FIG. 2, reference numeral 4 is a coil of the magnetic head 3. Also the third
The figure is a plan view of FIG. 2, 5 is a concentric track,
Reference numeral 6 is the disk rotation direction. Here, the period during which the magnetic head 3 scans the track 5 once is set to T _s (for example, T _s = 1/60).
sec). It is assumed that an erasing current 7 is alternately applied to the coil 4 of the magnetic head 3 every period when the polarity is T _p and the amplitude is gradually reduced exponentially as shown in FIG. However, T _p ≧ T _s . Then, since T _p ≧ T _s , at any point on the track 5, a magnetic field 8 whose polarity alternates and whose amplitude gradually decreases for each T _p as shown in FIG. To work. In this case, the minimum value I ₁ of the erase current 7 in the first constant polarity period is a value that can generate a magnetic field that magnetizes the magnetic disk 1 to a saturation level. As a result, at any point on the track 5, the magnetic flux is once saturated and then a loop is drawn up to the magnetic neutral point to converge, so that the residual magnetism disappears. It is desirable that the amplitude of the erase current 7 be attenuated as slowly as possible in a region close to zero.

In the present invention, the two semiconductor switches between the output terminals of the two DC constant current sources and their return paths are alternately turned on / off, so that T _p is set at an arbitrary point on the track as shown in FIG. An erasing current having a waveform as illustrated in FIG. 5 flows in the magnetic head between the output terminals of the two DC constant current sources so that the magnetic field 8 having alternating polarity and gradually decreasing amplitude acts on each magnetic field. T _p is determined by the switch control circuit, and the change in amplitude is determined by the current control circuit. In this case, the load of the DC power supply changes depending on whether the semiconductor switch is turned on or off, but since the load is a constant current source, the output current of the DC power supply has a value determined by the current control circuit regardless of load fluctuations.

The transformer galvanically isolates the recording or reproducing amplifier from the magnetic head. When all the semiconductor switches are turned on, the magnetic head coil and the primary coil of the transformer form a closed loop via the two semiconductor switches of the circuit connected in series, and the recording current can be passed to the coil of the magnetic head through the transformer. Further, the reproduction signal generated in the coil of the magnetic head can be taken out from the transformer. In recording or reproduction, by setting the current values of all the DC constant current sources to zero, the DC noise on the recording current or reproduction signal is reduced.

<Example> Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

The magnetic eraser of the present embodiment comprises a gradually decreasing voltage generating circuit I, a voltage / current converting circuit II, a switching circuit III, a series circuit IV and a switch control circuit V. These circuits will be sequentially described.

The gradually decreasing voltage generating circuit I has a transistor Tr ₁ , voltage dividing resistors R ₁ and R ₂ for determining a voltage value, a time constant circuit formed by a capacitor C and a resistor R ₃ , and a buffer amplifier Am. . Further, the terminal A receives an erasing command 10 which is a high level (H) signal during erasing, and a recording / reproducing command 11 which is a low level (L) signal during recording / reproducing. Therefore, at the time of erasing, the transistor Tr
₁ becomes conductive, and a gradually decreasing DC voltage V _R is generated across the resistor R ₃ , and this voltage V _R is output via the buffer amplifier Am. Gradually decreasing the DC voltage V _R is constant by exponentially decaying when it is determined by the resistor R ₃ and capacitor C. on the other hand,
At the time of recording / reproducing, the transistor Tr ₁ becomes non-conductive by the recording / reproducing command 11 of L, and the output voltage of the gradually decreasing voltage generating circuit I becomes zero.

The voltage / current conversion circuit II is composed of a transistor Tr ₂ and a resistor R _4, and converts the gradually decreasing direct current voltage V _R supplied to the base of the transistor Tr ₂ into a reference current I ₀ which is a gradually decreasing direct current. (See FIG. 4 (b)).

The switching circuit III includes a reference transistor Tr ₃ and a transistor.
It is composed of Tr ₄ and Tr ₅ , switching transistors Tr ₆ and Tr ₇ , and resistors R ₅ , R ₆ and R ₇ . Resistance that acts as a feedback
The resistance values of R ₅ , R ₆ , and R ₇ are equal to each other. The reference transistor Tr ₃ is diode-connected. The bases of the transistors Tr ₃ and Tr ₄ are connected to each other to form a first current mirror circuit, and a reference current I ₀ passed through the reference transistor Tr ₃ and a collector current I ₁ passed through the transistor Tr ₄ are Are equal. The bases of the transistors Tr ₃ and Tr ₅ are connected to each other to form a second current mirror circuit, and the reference current I ₀ and the collector current I ₂ flowing through the transistor Tr ₅ have the same value.
The switching transistors Tr ₆ and Tr ₇ are alternately turned on / off by the switch control circuit V (Fig. 4 (c),
(See (d)). This polarity switching interval T _p is the track scanning cycle
It is set equal to or longer than T _s .

Series circuit IV is composed of a primary coil 12a to coil 4 and the transformer 12 of the recording and reproducing head 3 are connected in series, is connected to the collector of the transistor Tr _4, Tr _5. The secondary coil 12b of the transformer 12 is connected to the recording / reproducing amplifier 13.

The switch control circuit V includes transistors Tr ₈ , Tr ₉ , Tr ₁₀ ,
It has a Tr ₁₁ and a flip-flop FF. Transistor
The base of Tr ₉ is connected to the Q terminal of flip-flop FF, and the base of transistor Tr ₁₁ is connected to the terminal of flip-flop FF. The base of the transistor Tr ₁₀ is connected to the collector of the transistor Tr _8, the base of the transistor Tr ₈ is One connected to the terminal A. Further, the emitter of the transistor Tr ₉ is connected to the base of the switching transistor Tr ₆ of the switching circuit III, and the emitters of the transistors Tr ₁₀ and Tr ₁₁ are connected to the base of the switching transistor Tr ₇ of the switching circuit III. At this time, the pulse 14 is always input to the terminal B connected to the CP terminal of the flip-flop FF at every polarity switching interval T _p . When T _p = T _s, a PG pulse or VD pulse is used as the pulse 14, and when T _p > T _s , a signal obtained by dividing the pulse signal of the frequency generator is used as the pulse 14. Therefore, at the time of erasing, since the transistor Tr ₈ becomes conductive by the erasing command 10 of H, the PR terminal of the flip-flop FF becomes L, the flip-flop FF is preset, and the base of the transistor Tr ₁₀ becomes L, so that the transistor Tr ₁₀ becomes non-conductive. It becomes conductive. At this time, pulse 14 changes polarity switching interval T _p
Since it is input every time, the flip-flop FF terminal Q,
Become H and L alternately and the transistor T
r _9, Tr ₁₁ is turned on / off alternately. Therefore, the switching transformer Tr ₆ , connected to the transistors Tr ₉ and Tr ₁₁ ,
Tr ₇ turns on and off alternately. On the other hand, at the time of recording / reproducing, since the transistor Tr ₈ becomes non-conductive by the recording / reproducing command of L, the PR terminal of the flip-flop FF becomes H, the flip-flop FF is not preset, and the transistor Tr ₁₀ becomes conductive. Therefore, since the transistor Tr ₉ is conductive while the Q terminal remains H, the switching transistor Tr ₆ is turned on, and since the transistor Tr ₁₀ is conductive, the switching transistor Tr ₇ is turned on.

Here, the overall operation of this embodiment will be described.

At the time of erasing, the erasing command 10 is input to the terminal A, and the reference current I ₀ which is a gradually decreasing direct current is generated in the voltage / current conversion circuit II. This reference current I ₀ (FIG. 4 (b)) also flows through the reference transistor Tr ₃ of the switching circuit III. At this time, the switch control circuit V alternately turns on / off the switching transistors Tr ₆ and Tr _{7 in} every polarity switching period T _p (FIGS. 4 (c) and 4 (d)). Therefore, due to the current mirror effect, collector currents I ₁ and I ₂ whose current values are equal to the reference current I ₀ flow alternately. Therefore, the erasing current 7 as shown in FIG. 4 (e) flows through the coil 4 of the magnetic head 3 for erasing.

At the time of recording / reproducing, the recording / reproducing command 11 is input to the terminal A, and the currents I ₀ , I ₁ , and I ₂ are not generated. Further, the switching transistors Tr ₆ and Tr ₇ are both turned on by the switch control command V (FIGS. 4 (c) and 4 (d)). Therefore, recording / reproducing signals can be transmitted / received via the recording / reproducing amplifier 13 and the transformer 12 for recording / reproducing.

<Effects of the Invention> According to the present invention, since the magnetic head is switched between recording or reproducing and erasing by turning on / off the semiconductor switch and controlling the direct current constant current source by the current mirror circuit, the circuit configuration is simple. Easy miniaturization and high reliability. That is, the constant current source may be a very simple one, and the current control is easy.

Further, according to the present invention, the magnetic head for recording or reproduction can be used to perform erasing for each concentric track at a residual erasing level similar to that of a bulk eraser.

Further, according to the present invention, the polarity of the erase current may be inverted every period in which the scanning period of one track of the track coincides, or may be inverted every period longer than the scanning period of one track of the track. Even in the case of, it is possible to perform high-performance erasing similar to a bulk eraser for each concentric track.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit configuration diagram of an embodiment of a magnetic erasing device of the present invention, FIG. 2 is a side view showing the relationship between a magnetic disk and a magnetic head, and FIG. 3 is FIG. FIG. 4 is an enlarged plan view of FIG. 4, FIG. 4 is an operation explanatory diagram of the apparatus of FIG. 1, FIG. 5 is a diagram showing an example of waveform of erase current, FIG. 6 is an explanatory diagram of erase principle, and FIG. 7 is an AC erase principle. FIG. 8 is an explanatory diagram of a magnetic field exerted on the magnetic recording medium by the magnetic head. In the drawings, I is a gradually decreasing voltage generation circuit, II is a voltage / current conversion circuit, and III
Is a switching circuit, IV is a series circuit, V is a switch control circuit, 1
Is a magnetic disk, 3 is a magnetic head, 4 is a coil, 7 is an erasing current, 12 is a transformer, 13 is a recording / reproducing amplifier, and Tr ₃
Is a reference transistor, Tr ₄ and Tr ₅ are transistors, Tr ₆ and T
r ₇ is a switching transistor.

Claims (1)

[Claims] 1. A gradually decreasing voltage generating circuit that generates a gradually decreasing direct current voltage during erasing and a zero generating voltage during recording / reproducing, and a direct current that gradually decreases by converting the output voltage of the gradually decreasing voltage generating circuit into a current. A voltage / current conversion circuit for generating a current, a reference transistor that is diode-connected and through which the gradually decreasing direct current flows, and a base that is connected to the base of the reference transistor and forms a first current mirror circuit together with the reference transistor. A first transistor, a second transistor whose base is connected to the base of the reference transistor to form a second current mirror circuit together with the reference transistor, and a second transistor which is interposed between the output terminal of the first transistor and the ground to perform switching. Output terminals of the first switching transistor and the second transistor to be performed A switching circuit having a second switching transistor interposed between grounds for performing switching, and recording / reproducing for scanning a concentric track of a magnetic recording medium between output terminals of the first and second transistors and A series circuit in which the erasing head coil and secondary coil are connected in series with the primary coil of the transformer connected to the recording / reproducing amplifier, and both the first and second switching transistors during recording / reproducing. A switch control circuit that keeps on and alternately controls the first and second switching transistors during erase every predetermined period equal to or longer than the scanning period of one cycle of the track. Characteristic magnetic erasing device.