JPS5928496Y2 - magnetic recording device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording device that has a DC erasing magnetic head and a recording magnetic head, and is configured to supply an AC bias current to the recording magnetic head together with a recording signal.

Methods for erasing residual magnetism caused by recording on a magnetic recording medium such as a magnetic tape include a direct current erasing method and an alternating current erasing method.

In the AC erasing method, an alternating current is passed through the coil of the erasing magnetic head, and as the recording medium passes through the air gap of the erasing magnetic head, it is magnetized to a saturated state, and then as it moves away from the air gap, it is repeatedly reversed by the AC magnetic field. magnetized, and the strength of the magnetization gradually decreases,
Finally, it reaches a state of zero remanence with respect to the magnetic neutral point,
This is a method to completely demagnetize a magnetic recording medium.

This AC erasing method reliably erases the residual magnetism of the magnetic recording medium, and is therefore widely used in current magnetic recording devices.

However, this AC elimination method is not without drawbacks.

In other words, when the coercive force Hc of the magnetic material of the magnetic recording medium is large, the erasing power supplied to the erasing magnetic head increases accordingly, and when the coercive force Hc is too large, the recording signal on the magnetic recording medium cannot be sufficiently processed. In order to erase data, it is necessary to supply a very large erasing current, but in this case, the erasing head generates heat due to eddy current loss, and in extreme cases, it may be damaged due to the heat.

Therefore, in reality, it may not be possible to flow an erasing current that is sufficient to erase recorded signals on the magnetic recording medium.

The simplest direct current erasing method is a method in which a strong direct current magnetic field is applied to a magnetic recording medium using a permanent magnet or an electromagnet, and all residual magnetism caused by recording on the magnetic recording medium is converted to saturation rectilinear magnetization and erased.

If a permanent magnet is used, this method does not require a large amount of erasure power as in the AC erasure method described above, and therefore can be applied to battery-powered tape recorders, and can also be applied to cassette tape recorders with radio receivers. This is preferable because there is no risk that the beat between the high-frequency signal in the radio receiver and the erased AC signal that occurs with the AC cancellation method will be recorded on the magnetic tape as a harmful signal. A fatal drawback is that when a signal is recorded on a magnetic recording medium and then reproduced, the reproduced signal is distorted.

In view of these points, the present invention provides a magnetic recording device for use in a magnetic recording device that has a DC erasing magnetic head and a recording magnetic head, and supplies an AC bias current to the recording magnetic head together with a recording signal. This invention proposes a system that can reduce the distortion of reproduced signals caused by using a DC erase magnetic head for different AC bias currents supplied depending on the medium.

The present invention will be described in detail below with reference to several embodiments with reference to the drawings.

First, a first embodiment of the present invention will be described with reference to FIG.

In FIG. 1, T is a magnetic tape as a magnetic recording medium.

He is a DC erasing magnetic head, which in this example is a permanent magnet made of ferrite, for example.

The portion facing the tape T is magnetized to either a north pole or a south pole.

In this case, the strength of magnetization is determined by this DC erase magnetic head He.
The strength of the magnetic field is set so as to provide a magnetic field sufficient to magnetically saturate the magnetic tape T.

Hr is a recording magnetic head.

This recording magnetic head Hr has a core made of a laminated metal magnetic material such as permalloy and a coil wound around it.

Then, an AC bias current is supplied to the recording magnetic head H'r together with a recording signal.

Q is a transistor constituting a recording amplification circuit, and a recording signal is supplied to its base.

The emitter of transistor Q is grounded, and its collector is connected to power supply 1B through load resistor R1.

M is a bias trap circuit consisting of a parallel circuit of a capacitor C2 and a coil L, and the collector of the transistor Q is connected to one end of the coil of the recording magnetic head Hr through the capacitor C1 and further through this bias trap circuit M. The end is grounded.

Further, the OSC is a bias oscillator, and the AC bias current from the OSC is supplied to one end of the coil of the recording magnetic head Hr through a capacitor C3 for adjusting the bias current i.

Note that the AC bias current is varied by adjusting the capacitance of the capacitor C3 according to the coercive force of the magnetic recording medium used.

The above configuration is similar to that of a conventional magnetic recording device.

In the present invention, a direct current is supplied to the recording magnetic head Hr.

and a DC erasing magnetic head He and a recording magnetic head Hr.
This recording magnetic head Hr is set so that the running direction components of the respective partial magnetic fields on the escape side of the magnetic tape as a magnetic recording medium of each DC magnetic field reflected on the magnetic recording medium, that is, the magnetic tape T, are on the opposite side. Select the direction of the direct current to be applied to the

In this case, the partial magnetic field on the escape side refers to the magnetic field applied to the magnetic tape T by the magnetic heads He and Hr at the moment when the magnetic tape T leaves the tape contact portion of the magnetic heads He and Hr.

For this reason, in the example of FIG.
2 is connected to supply direct current to the recording magnetic head Hr.

Furthermore, the current value ID of the DC current supplied to the recording magnetic head Hr is calculated as follows: fB: frequency of AC bias current, IB (fB) : Peak current value of AC bias current of frequency t'H, Z(lO
3) Impedance of the recording magnetic head to an alternating current with a double layer wave number of 103 Hz, Z (fB): when the frequency is f
The impedance of the recording magnetic head with respect to the alternating current bias current B) is selected.

The reason why the DC current flowing through the magnetic recording head Hr is limited as described above is that the core of the magnetic recording head Hr is made of a metal magnetic material and that it depends on the current value of the AC bias current. The above-mentioned limit values were obtained experimentally.

IDO was defined as above because this value was determined by the fact that the core of the recording magnetic head Hr was made of a metal magnetic material, and a coefficient was provided to compensate for changes in magnetic resistance due to frequency. .

In Figure 2, the horizontal axis represents the DC current flowing through the recording magnetic head Hr, and the vertical axis represents the distortion rate of the reproduction signal recorded on the magnetic tape by this magnetic recording device, and the change in distortion rate with respect to the DC current was measured. It is something.

In Figure 2, 1 is the AC bias current (peak value) IB
is 2.9 mA, and 2 is the characteristic curve for IB-3 and 7 mA.

Incidentally, the value of the AC bias current is generally set to these values, that is, 2.
It is common to use between 9 mA and 3.7 mA.

0.1 in each of these curves (1) and (2)
3 IDO and the location of the IDO are illustrated.

The magnetic tape used in the measurements shown in Figure 2 was C-
6OCR tape speed 4.8 cm/s, AC bias current frequency 100 KHz, recording signal frequency IK
It is Hz.

According to the graph of FIG. 2, the limitation of the direct current flowing through the above-mentioned magnetic recording head is clarified.

That is, it can be seen that if the DC current IDO value is selected in this way, the distortion rate of the reproduced output will be low enough to be usable.

Next, with reference to FIG. 3, the reason why the distortion rate of the reproduced output is reduced by the above-described configuration even though a DC erasing magnetic head is used will be described.

Figure 3 is a graph in which the horizontal axis represents the recording magnetic field applied to the magnetic tape and the vertical axis represents the residual magnetization of the magnetic tape. This is a curve obtained when AC bias recording is performed after erasing, and this curve is point symmetrical at the origin O, and has an inflection point at the origin 0.

Curve 3 shows a curve obtained when AC bias recording is performed after erasing using a DC erasing magnetic head; in this case, the inflection point P is not at the origin O, and is
It is located at a point shifted by D in the horizontal axis direction indicating the recording magnetic field.

Note that this shifted polarity is located on the left or right side of the vertical axis indicating residual magnetization depending on the polarity of magnetization of the DC erasing magnetic head.

When recording is performed by simply supplying a recording signal to a recording magnetic head as in the past, the recording signal is supplied so as to swing around the vertical axis indicating residual magnetization. Since the curve 3 intersects with the vertical axis indicating the residual magnetization, the residual magnetization obtained is extremely distorted, and this is why in the conventional DC erasing method, the reproduced output is This means that it is distorted.

Therefore, in the present invention, the point of inflection of curve 3, that is,
A point where the characteristic of residual magnetization with respect to the recording magnetic field is almost a straight line, that is, as shown in FIG. 3, the operating point of the recording magnetic head Hr is shifted by HD in this figure, that is, a DC current is applied to correspond to that inflection point. If the recording signal is made to oscillate around the position, residual magnetization will be formed without distortion in the recording signal.

Therefore, the distortion of the reproduced output is significantly reduced.

Further, it is natural that the distortion of the reproduced output increases as the distance from the inflection point P of the curve 3 increases, and the closer to this inflection point, the smaller the distortion of the reproduced output.

Of course, even at this inflection point P, the curve of residual magnetization with respect to the recording magnetic field is not a perfect straight line, so the distortion rate of the reproduced output will not be O, but the distortion of the reproduced output will be sufficient for practical use. becomes smaller.

Generally, when an alternating current bias current is supplied to the recording magnetic head Hr, in order to prevent the core of the recording magnetic head from being magnetized, the alternating current bias current is adjusted to the level shown in FIG. 4A when the recording operation is stopped. , recording operation stop time t
Normally, the current value is gradually decreased from 0 to avoid magnetization.

Therefore, in the present invention, since DC current is supplied to the recording magnetic head Hr, in order to avoid magnetizing the core of the recording magnetic head Hr, an AC bias current is supplied as shown in FIG. 4B. It is desirable to stop supplying the DC current at a time point t1 when the level of the DC current is lower than the level of the DC current after the time to.

Note that means for this purpose are not shown in the embodiment shown in FIG.

Next, other mutually different embodiments of the present invention will be explained with reference to FIGS. 5, 6, and 7, but parts corresponding to those in FIG. omitted.

In the embodiment shown in FIG. 5, a resistor R2 for supplying direct current to the recording magnetic head Hr is connected between the collector of the transistor Q2 and the connection midpoint between the capacitor C1 and the bias trap circuit M. The other configurations are the same as in FIG. 1.

The example shown in FIG. 5 has a slight drawback, compared to the embodiment shown in FIG. 1, that when the operating point of the recording amplification circuit changes due to changes in temperature, etc., the direct current changes.

In the embodiment shown in FIG. 6, the bias oscillator osc is connected to the primary coil of the oscillation transformer TR, one end of the secondary coil is connected to one end of the recording magnetic head Hr, and the other end is connected to the capacitor C4.
This is a case in which a resistor R2 for supplying direct current to the recording magnetic head Hr is connected between the connection point between the oscillation transformer TR and the capacitor C4 and the power supply 1B.

The other configurations are the same as in FIG. 1. As described above, when the coercive force of the magnetic tape changes, the optimum AC bias current also changes accordingly, and therefore the value of the DC current supplied to the recording magnetic head Hr must also be changed.

In this case, in the case of a magnetic recording device that can use magnetic tapes with greatly different coercive forces, as shown in FIG. 7, in place of the resistor R2 in FIG. Resistor R,! A, R, , b and c are provided, and these resistors can be switched by a changeover switch SW.

The resistance values of these resistors R2a, R2b, and R2c are set in accordance with the coercive force of the magnetic tape used, and are changed simultaneously with the switching of the alternating current bias current.

Although switching of the AC bias current is not shown in FIG. 7, for example, the switching of the capacitor C
3 may be replaced by a changeover switch using different capacitors.

According to the magnetic recording device of the present invention described above, it has a DC erasing magnetic head and a recording magnetic head using a core of a metal magnetic material, and an AC bias current is supplied to the recording magnetic head together with a recording signal. In a magnetic recording device, a DC current is supplied to a recording magnetic head, and each part of the magnetic recording medium on the escape side of each DC magnetic field applied to the magnetic recording medium by the DC erasing magnetic head and the recording magnetic head is The direction of the direct current is selected so that the directions of the strike direction components of the magnetic field are opposite, and the current value I of this direct current is
D, for different AC bias currents supplied depending on the magnetic recording medium used, fB: frequency of AC bias current, IB (fB) peak current value of AC bias current of double layer wave number fB, Z (103): Frequency is 10”H
The impedance of the recording magnetic head with respect to an alternating current of z, Z (fB): the impedance of the recording magnetic head with respect to an exchange bias current with a frequency of fB). Despite the use of a DC erasing magnetic head, distortion of the reproduced output can be made small for different AC bias currents supplied accordingly.

In addition, even though a DC erasing magnetic head is used in this way, the distortion rate of the playback output can be reduced, so unlike the AC erasing method, significant erasing power is not required, making it suitable for battery-powered tape recorders. It is suitable for application, and when applied to a cassette tape recorder with a radio receiver, the beat between the high frequency signal in the radio receiver and the erased AC signal, which occurs in the AC cancellation method, becomes a harmful signal and is recorded on the magnetic tape. There is no risk of this occurring and is therefore suitable.

Furthermore, when the DC erasing magnetic head is constructed of a permanent magnet, the erasing power is further reduced.

Furthermore, as can be seen from the graph in FIG. 2 above, the curve of the distortion rate of the reproduction output with respect to the DC current flowing through the recording magnet has a relatively broad range of allowable distortion rate.
There is no need to finely adjust the resistance value of a resistor for supplying direct current.

In addition, when alternating current bias currents are switched depending on the coercive force of the magnetic tape used, if there is a portion that overlaps the range of direct currents selected by these switched alternating current bias currents, that direct current A fixed resistor can be used to set the current value, and there is no need to prepare a plurality of resistors and switch the DC current value at the same time as the AC bias current, as in the embodiment shown in FIG. 7 described above.

Furthermore, the optimum value of the DC current supplied to the recording magnetic head does not depend on the recording level of the recording signal or the recording frequency.

Furthermore, since the direct current is about 1/10 of the alternating current bias current, there is no risk of adversely affecting the linearity of input/output characteristics, saturated output, etc.

Incidentally, the direct current supplied to the recording magnetic head needs to be set so that the coercive force of the magnetic medium is small.

The above-mentioned DC erasing magnetic head may be of a so-called head type in which a coil is wound around a core and a DC current is supplied to the core, in addition to the above-mentioned permanent magnet.

Furthermore, an electromagnet configuration in which a coil is simply wound around a bar magnet may be used.

Further, the shape of the magnet or core of the erasing magnetic head is arbitrary.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an example of the magnetic recording device of the present invention, FIG. 2 is a characteristic curve diagram for explaining the present invention, FIG. 3 is a characteristic curve diagram for explaining the present invention, and FIG. 4 is a diagram for explaining the present invention. The waveform diagrams shown in FIGS. 5, 6, and 7 are circuit diagrams showing other different embodiments of the present invention. He is an erasing magnetic head, Hr is a recording magnetic head, and T is a magnetic tape as a magnetic medium.

Claims (1)

[Claims for Utility Model Registration] A DC erasing magnetic head that applies a saturation magnetic field to a magnetic recording medium, and a recording signal and an AC bias current that are supplied to the magnetic recording medium to form a magnetic field on the magnetic recording medium by the DC erasing magnetic head. In a magnetic recording device having a recording magnetic head to which a direct current is supplied for applying a magnetic field in the opposite direction to residual magnetization, the recording magnetic head is configured using a core of a metallic magnetic material, and the recording magnetic head is The DC current value IB supplied to the head is expressed as follows: fB: Frequency fB of AC bias current (fB) AC bias current with two frequencies fB Peak value Z(103): Impedance Z(fB) of the recording magnetic head using the core of the metal magnetic material in response to an AC bias current with a frequency of 103H2: A magnetic recording device characterized in that the impedance is selected within the range of the recording magnetic head used.