JPS5839546Y2 - Magnetic head for erasing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an erasing magnetic head for erasing a recording magnetic field recorded on a magnetic recording medium.

The erasing magnetic head according to the present invention can be used as an erasing head in an audio or image magnetic tape recording/reproducing device.

As conventional erasing methods, a DC erasing method and an AC erasing method are known.

The former erases data by applying a strong DC magnetic field to the magnetic recording medium to magnetically saturate the medium, and the medium after erasing is magnetized to a so-called residual magnetic flux density Br.

This method can be used in two ways: a method that uses permanent magnets and a method that uses DC electromagnets, and has the feature of being able to apply a strong magnetic field, but both have the disadvantage that noise remains on the medium after erasing. have.

On the other hand, the latter AC erasure method uses 10 to 100 KH on the medium.
It applies an alternating current erasing magnetic field of about z, and takes advantage of the fact that the medium moves away from the head, gradually reducing the magnetic hysteresis loop at that time.The residual magnetic flux after erasing becomes zero, and no noise remains. It has characteristics.

By the way, in the case of AC erasing, ferrite with low high-frequency loss is used as the core of the erasing head, but ferrite has a low saturation magnetic flux density, so it is not suitable for erasing magnetic recording media with high coercivity such as recent alloy tapes. do not have.

In addition, as a compromise between the two methods, for example, a permanent magnet is used to generate a DC magnetic field that alternates N-8-N-8-... in the direction of movement of the medium and gradually becomes weaker. There is a method that provides the same effect as AC demagnetization at a low frequency.

Although this type of method is improved compared to the normal DC cancellation method, it produces more noise than the AC cancellation method and is not satisfactory.

Now, the coercive force He of the magnetic recording medium is the same as that of the conventional 7"-Fe
3000e for 203, 500-6 for CrO2
000e, and 10,000e or more for alloy magnetic powder.

Furthermore, due to the recent demand for high-density recording, there is a trend toward the use of media with higher coercive force.

On the other hand, magnetic materials for heads for erasing magnetic fields recorded on these media include up to CrO2 (Hc=500
6000e), it is possible to use conventional ferrite, but ferrite is insufficient for erasing media with a higher He content.

On the other hand, for erasing a medium having a large coercive force, an erasing head having a structure in which a sendust alloy is attached to the surface of ferrite has been proposed.

However, sendust has the disadvantage that it is a brittle material and is difficult to work with, and it cannot be used when the He content becomes even larger.

Therefore, the present invention aims to improve the above-mentioned drawbacks of the prior art, and its purpose is to provide an erasing head that erases magnetic recording media with a large coercive force at a low noise level.

The features of this invention to achieve this purpose are as follows: First, the medium is treated with a DC magnetic field, then the residual magnetic flux is brought to a value close to zero, and finally, the residual magnetic flux is reduced to zero by AC cancellation, and noise is removed. There is an erase head like this.

This will be explained in detail below with reference to the drawings.

First, the principle of the present invention will be explained with reference to FIG.

In the hysteresis loop of FIG. 1, it is assumed that the recording magnetic field of the magnetic recording medium is initially at point 1.

When a strong DC magnetic field is applied in the direction of the recording magnetic field, the magnetization moves from point 1 to point 2 and becomes saturated, and when the DC magnetic field is further removed, the magnetization moves to point 3.

In other words, the magnetization is aligned at point 3 regardless of the initial strength of the recording magnetic field, and this is the principle of conventional DC erasing.

In the present invention, next, a DC magnetic field H, which is larger than the coercive force He of the medium, is applied in the opposite direction to the DC magnetic field.

This moves the magnetization of the medium from point 3 to point 4, and then
By removing the DC magnetic field H, the magnetization moves to point 5 near zero.

Although the residual magnetic flux density at point 5 can be made very small by selecting the size of H, it is difficult to make it completely zero considering the variety of media and noise.

Next, perform AC cancellation using a normal ferrite.

The residual magnetization at point 5 is sufficiently small due to the pretreatment using a DC magnetic field, and can be sufficiently erased by ferrite, and since it is AC erased, noise characteristics are also excellent.

Note that the DC magnetic field used in the present invention is used to pre-process the medium in order to make the final AC erasure more effective, and therefore it is necessary to use a DC magnetic field to make the residual magnetization of the medium sufficiently small after that process. A DC magnetic field (preferably near zero) may be selected.

Further, based on the same principle, the effect can be increased by applying the DC magnetic field not only twice but also three or four times in opposite directions and gradually becoming smaller.

FIG. 2 shows a configuration example for explaining the principle of the erasing head according to the present invention, in which 10 is a first head that applies a DC magnetic field;
T is the traveling direction of the magnetic recording medium, 20 is a second head that applies an alternating magnetic field, the first head and the second head are arranged close to each other as shown in the figure, and both are housed in a single housing 30. .

The first head 10 has a permanent magnet 11 and yokes 12 and 13. One end of each yoke is connected to one pole S of the permanent magnet 11, and the other end is connected to the other pole N through spacers 12a and 13a.
to face.

The material of the permanent magnet 11 is, for example, a samarium-cobalt alloy, and the material of the yoke is a material with high magnetic permeability and high saturation magnetic flux density (for example, permalloy, amorphous magnetic material, soft iron, etc.).
use.

For example, beryllium copper is used as the spacers 12a and 13a, and the upstream spacer 13a is wide as shown in the figure.
A magnetic field of about 0,000e is applied to the medium, and the spacer 12a on the downstream side is narrow and applies a magnetic field of about 12,000e.

The second head 20 is made of ferrite material, a coil 21 is wound around a central core 25, and an alternating current of approximately 100 KHz is applied to the second head 20.

Yokes 26 and 27 face the central core via gaps 22 and 23.

The width of the gap 22.23 is 0.05 to 0.5 mm.

The second head 20 is the same as a conventional AC erasing head, and can also be used with other known AC erasing heads.

In the above configuration, when the magnetic recording medium moves in the direction of arrow T, the recording magnetic field that was initially at point l (FIG. 1) moves to point 2 through gap 13a, and after passing through the gap, it moves to point 2. 3, moves to point 4 at gap 12a, and moves to point 5 after passing through the gap.

The magnetization at point 5 becomes completely zero and is erased by AC erasing by the second magnetic head 20.

Figure 3 shows the configuration of the erasing head of the present invention that is optimal for implementing the principle of Figure 2, and the first head has a structure that is easier to manufacture than the embodiment shown in Figure 2. .

Note that the second head 20 and housing 30 in FIG. 3 are the same as in FIG. 2.

The first head 40 has a rod-shaped or plate-shaped permanent magnet 41 that is magnetized in the vertical direction as shown in the figure, and is made of a non-magnetic material that is provided on both sides of the permanent magnet and has the same height as the permanent magnet. It has a first spacer 42a and a second varnish spacer 42b, and a high magnetic permeability magnetic body 43 having a concave cross section that contacts the outer side of each spacer and the lower end of the first spacer, permanent magnet, and second varnish spacer. Convex portions 43a and 43b
The magnetic resistance can be changed by mutually changing the cross-sectional area.

The material of the permanent magnet has a high magnetic flux density, such as rare earth-cobalt alloy or alnico, but barium ferrite can also be used depending on the case.

The material of the spacer can be beryllium copper or glass.

In addition, the material of the high magnetic permeability material is ferrite, soft iron, Fe-
8i, amorphous alloy, sendust, etc. are possible.

The permanent magnet 41, the spacers 42a, 42b, and the upper ends 43a, 43b of the concave high permeability material 43 may be aligned horizontally,
If the surface is curved, the medium will run smoothly.

Furthermore, if the same curved surface is formed including the AC elements on the downstream side, the medium will run even more smoothly.

The upper end convex portion 43a of the concave high magnetic permeability material 43. Of 43b,
Since the cross-sectional area of 43a on the upstream side is made larger than 43b on the downstream side, and the magnetic resistance is lowered, a large amount of the magnetic flux emitted from the permanent magnet 41 enters 43a, and the magnetic flux is generated at the first spacer 42a. A sufficiently strong leakage magnetic field is applied to the medium, and a leakage magnetic field slightly stronger than the coercive force He is applied to the medium at the portion of the varnish spacer 42b.

Next, the test results of the present invention will be explained.

An alloy tape with a coercive force Hc of 10000e was used as the test tape, and a 333 Hz signal was recorded at +10 dB with a level of 250 nanowb/m as OdB.

When this was erased using the erasing head according to the present invention, the recording level could be reduced by 75 dB.

Note that 75 dB is close to the measurement limit of the measuring instrument used, and the actual erasure performance is thought to be even greater.

On the other hand, when a tape recorded under the same conditions was erased using a conventional AC erasing head, the recording level decreased by 60 dB.

Therefore, the erase head according to the present invention can improve the erase level by at least 15 dB compared to the conventional erase head.

As described above, the present invention can perform sufficient erasing even on alloy tapes having a large coercive force He by performing AC erasing with excellent noise characteristics after pretreatment with a strong DC magnetic field.

[Brief explanation of drawings]

FIG. 1 is a hysteresis curve for explaining the principle of the present invention, FIG. 2 is a principle diagram for explaining the erasing head according to the present invention, and FIG. 3 is a configuration example of the erasing head according to the present invention. 10.40: first head, 20: second head, 30: housing, 12a, 13a, 22, 23, 42a. 42b spacer, 11.41: Permanent magnet, 12゜1
3.43: Yoke, 25, 26, 27: Ferrite material,
21: Coil.

Claims (1)

[Scope of utility model registration request] first means for applying a DC magnetic field sufficient to substantially saturate a recording magnetic field to a magnetic recording medium, and then applying a weaker DC magnetic field to the magnetic recording medium in the opposite direction to the DC magnetic field;
and a second means disposed downstream of the first means for applying an alternating magnetic field to the magnetic recording medium, wherein the first means is rod-shaped or plate-shaped and magnetized in the vertical direction. A permanent magnet, a first spacer and a second varnish spacer made of a non-magnetic material provided on both sides of the permanent magnet and having the same height as the permanent magnet, and the outside of each spacer and the first spacer, permanent magnet, and second varnish spacer. It has a high magnetic permeability magnetic material having a concave cross section that contacts the lower end of the permanent magnet, and is characterized in that the magnetic resistances from the permanent magnet to both convex portions of the concave high permeability material are different from each other. A magnetic head for erasing.