JPS6315655B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic erasing head used in a magnetic recording/reproducing device.

In general, as methods for erasing signals from recording media such as magnetic tapes, there are known alternating current erasure methods (AC erasure methods), methods that use permanent magnets, and methods that use a combination of these methods. Also, among the devices that use permanent magnets, there are those of the saturation erasing type that apply a saturation magnetic field to the recording medium to erase the signal, and the gradually decreasing alternating magnetic field type that applies a reverse and gradually decreasing magnetic field to the recording medium running on the head surface. AC erasure type) is known.

As shown in FIG. 1, a conventional magnetic erasing head of the gradually decreasing alternating magnetic field type has a tape sliding surface 1 of the magnetic head.
A magnetic material 2 is arranged on the magnetic material 2, and this magnetic material 2 is magnetized so that the magnetic field strength gradually decreases to form multiple poles of N and S poles, and when the magnetic tape passes over the magnetic material 2, This erases magnetic tape in a pseudo-AC manner. Conventional magnetic erase heads like this are pseudo-AC, so they have a lower S/R than saturation erase type.
N has the advantage of being superior. However, in the case of the above-mentioned pseudo AC type, there is a limit to the number of alternating poles that can be taken due to dimensions and magnetization technology, and the limit is about 10 poles at most. Therefore, if the magnetic properties of the magnetic tape to be erased are different, or if the contact with the magnetic tape becomes uneven, the magnetic tape becomes magnetically neutral 4 as shown in Figure 2. It is not erased, and only m DC residual magnetization remains. However, the second
In the figure, numeral 3 shows the BH curve of the magnetic tape, and numeral 5 shows the magnetic field strength distribution of the erase head applied to the magnetic tape. Therefore, the magnetic tape draws a minor loop as indicated by the arrow, and finally reaches the point of DC residual magnetization m. In order for the magnetic tape after erasing to be at the magnetic neutral point, that is, for the DC residual magnetization m to be zero, it is very difficult to set the magnetic field distribution 5 of the erase head in an erase head with a small number of alternating poles. The strength of the magnetic field applied to the tape varies even due to slight variations in the state of contact with the tape, and normally DC residual magnetization m remains. When recording and reproducing are performed using a tape in which such direct current residual magnetization remains, a large amount of even-order distortion occurs, which is a major drawback.

The present invention eliminates such conventional drawbacks, and has a working surface for the magnetic tape formed of a permanent magnet material and a high magnetic permeability material, and has the high magnetic permeability material on the tape exit side of the working surface. The permanent magnet material is made smaller than the length of the permanent magnet material in the tape sliding direction so that a predetermined length of the permanent magnet material remains on the tape entrance side, and the track width of the magnetic tape to be erased. The permanent magnet is buried in the center of the permanent magnet material so as to have a thickness that is approximately half that of the permanent magnet material, and the operating surface is configured so that the magnetic field gradually decreases from the tape inlet side to the tape outlet side, so as to reduce even-order distortion. It is composed of

DESCRIPTION OF THE PREFERRED EMBODIMENTS The magnetic erasing head of the present invention will be described below with reference to drawings of embodiments. FIG. 3 shows an embodiment of the magnetic erasing head of the present invention. In FIG. have. A magnet material 10 having a width slightly larger than the track width T of the magnetic tape is disposed on this tape sliding surface 1, and a high magnetic permeability material 11 is embedded in this magnet material 10. The high magnetic permeability material 11 has a length k smaller than the length l of the magnet material 10 in the tape running direction in contact with the magnetic tape, and has a length k smaller than the length l of the magnet material 10 in the tape running direction, and It is located at the center of the track width T of the magnetic tape and on the tape exit side 13 of the magnetic tape 10 in the tape running direction. Further, the width t of the high magnetic permeability material 11 is approximately 1/2 of the track width T to be erased on the magnetic tape. and,
The erasing head element having the above structure has its magnet material 1
It is magnetized with an alternating magnetic field that gradually decreases from zero. When magnetized in this manner, magnetic poles as shown in FIG. 3 appear on the sliding surface of the erasing head. That is, a magnetic field appears that gradually decreases from the tape inlet side 12 toward the tape outlet side 13, and in the part where only the magnet material 10 is made (the part with width W), the magnetic field becomes N, S, N, S, N, while in the part made of high magnetic permeability material In the part where 11 is (the part with width t), N, S, S,
N, S. This is because the high magnetic permeability material 11 forms a magnetic pole opposite to the surrounding magnetic pole.

Next, the operating state when a magnetic tape is erased using such a magnetic erasing head will be explained with reference to FIG. In FIG. 4, 20 indicates the magnetic field distribution curve of the magnetic erasing head of this example, and as mentioned above, in the width W portion of the magnet material 10, 21, 22,
23, 24, 25 gradually decreasing alternating magnetic fields, while in the width t part 21, 22, 23', 24', 2
5' becomes a gradually decreasing alternating magnetic field. However, 23′,
24' and 25' have polarities opposite to those of 23, 24, and 25, respectively, and their amplitudes are approximately equal to each other. On the other hand, 26 is the B-H of the magnetic tape to be erased.
It shows a curve. By the alternating magnetic field of the magnetic erase head, i.e. 21, 22, 23, 2
Due to the magnetic fields 4 and 25, the magnetic tape moves from the major loop to the minor loop 27→
It follows the paths 28→29, 30→31→32 and reaches the point of residual magnetization n. On the other hand, 21,2
2, 23', 24', and 25' near the center of the track of the magnetic tape (width t part), 27→28→33→34→35→36→37
It follows this path and reaches the point of residual magnetization p. The polarities of the residual magnetizations n and p are opposite to each other, and their absolute values are approximately equal. By the way, if recording and reproducing are performed using a magnetic tape in which residual magnetization of only m or p remains uniformly, a phenomenon in which even-order distortion increases occurs, but in the method of this embodiment, one track The residual magnetization has regions with mutually opposite polarities (n and p), and each region (width t portion and width S portions on both sides)
Since the ratio is approximately 1:1, the even-order distortions cancel each other out and are significantly reduced.

In the above embodiment, the case where the magnetic erasing head has five alternating poles has been described, but it is not necessarily limited to five poles. In addition, high magnetic permeability material 1
1 is 3 counting from 12 on the tape entrance side of the erase head.
Although the magnetic tape is inserted from the end to the tape exit side 13, the insertion position is determined appropriately depending on the type of magnetic tape to be erased and the magnetic pole strength of each magnetic pole of the erasing head, so that the even-order distortion is minimized. Just set it.

As described above in detail, in the magnetic erasing head of the present invention, a permanent magnet material and a high magnetic permeability material form the operating surface for the magnetic tape, and a high magnetic permeability material is permanently attached to the tape exit side of the operating surface. The length of the magnetic material in the tape sliding direction is made small so that a predetermined length of permanent magnetic material remains on the tape entrance side, and the length of the magnetic tape is approximately half the width of the track to be erased. The magnetic tape to be erased is embedded almost in the center of the permanent magnet material so that it has a certain thickness, and the magnetic field gradually decreases from the tape inlet side to the tape outlet side, so that the magnetic tape to be erased is buried in the center of the permanent magnet material. Depending on the position, the tape receives different alternating attenuation magnetic fields, and the polarity of the magnetic field applied to the tape is reversed from the position where the high magnetic permeability material is placed, and the thickness of the high magnetic permeability material embedded in the permanent magnet is reversed. Approximately one-half of the track width is finally magnetized to the opposite polarity, resulting in a magnetic erasing head with less distortion, and has the advantage of less noise as it is magnetized in a gradually decreasing magnetic field. Furthermore, by inserting a high magnetic permeability material, it is possible to form a region of opposite polarity in the track width direction, which has the advantage that magnetization can be easily performed.

[Brief explanation of the drawing]

FIG. 1 is a front view of a conventional gradually decreasing alternating magnetic field type magnetic erasing head, and FIG. 2 is a diagram showing the erasing process when erasing a magnetic tape with the same head. FIG. 3 is a front view of a magnetic erasing head according to an embodiment of the present invention, and FIG. 4 is a diagram for explaining the process of erasing a magnetic tape by the same head. 10... Magnet material, 11... High magnetic permeability material.

Claims (1)

[Claims] 1. It has a working surface for the magnetic tape formed of a permanent magnetic material and a high magnetic permeability material, and the high magnetic permeability material is applied to the tape exit side of the working surface along the length of the permanent magnetic material in the tape sliding direction. A predetermined length of the permanent magnet material remains on the tape entrance side, and the thickness of the permanent magnet material is approximately half the width of the track to be erased on the magnetic tape. A magnetic erasing head embedded in the center and configured such that the operating surface has a magnetic field that gradually decreases from the tape inlet side to the tape outlet side.