JP2005116091A - Magnetic head device, magnetic tape recording and reproducing device, and method for shielding external induction field to magnetic head device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic head device which excludes influence of noise caused by external induction field, and also to provide a magnetic tape recording and reproducing device, and a method for shielding an external induction field. <P>SOLUTION: The magnetic head device M is provided with a magnetic head A provided with magnetic cores 7, 8 on the surfaces 6 facing the media of shield cases 3, 4a, and a shield cover 5. The magnetic head device is provided with: a top face plate 5a; and a shielding part 5d formed by making a part of the top face plate 5a project to the front side of the medium facing surface 6 and also bending the tip thereof toward the medium facing surface 6. The width of the shielding part 5d along the sliding contact direction of the magnetic recording medium is formed narrower than that of the medium facing surface 6, and also a notched part 5f is arranged on one side of the shielding part 5d in the sliding contact direction of the magnetic recording medium. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a magnetic head device, a magnetic tape recording / reproducing device, and a method for shielding an externally induced magnetic field with respect to the magnetic head device, and more particularly to a magnetic head device, a magnetic tape recording / reproducing device, and a magnetic head device provided with a shield cover. The present invention relates to a method for shielding an external induction magnetic field.

  FIGS. 13 and 14 are a plan view and a perspective view of a magnetic head device used for recording and reproducing sound in a conventional magnetic tape magnetic recording apparatus such as a VTR described in Patent Document 1 below. 13 and 14, reference numeral 10 denotes a magnetic head device. The magnetic head device 10 is formed by integrating a recording / reproducing head 11 and an erasing head 12 adjacent to each other at the side thereof. A shield cover 30 is attached to the apparatus 10.

  The recording / reproducing head 11 includes a shield case 13 and magnetic cores 14 and 15 fixed inside the shield case 13 and exposed to the tape sliding contact surface 13 a on the front surface of the shield case 13. The erasing head 12 includes a case 16 and a magnetic core 17 that is fixed to the inside of the case 16 and exposed to the tape sliding contact surface 16 a on the front surface of the case 16.

  The shield cover 30 is extended forward and laterally from the tape sliding contact surfaces 13a and 16a of the recording / reproducing head 11 and the erasing head 12 and from the side edge of the recording / reproducing head 11 opposite to the erasing head 12 respectively. An extension 31 is provided. Bending portions 31a and 31b that are bent downward are provided on the front and sides of the extension portion 31, respectively. Note that the shield cover 30 is not extended obliquely forward of the erasing head 12.

  The magnetic head device 10 configured as described above erases an audio signal by the magnetic core 17 of the erasing head 12 when the magnetic tape is slid in contact with the tape sliding contact surfaces 13a and 16a on the front surfaces of the heads 11 and 12, respectively. The control signal is recorded and reproduced by the magnetic cores 14 and 15 of the recording / reproducing head 11.

  According to the magnetic head device 10 described above, even if the noise source N that generates an external induction magnetic field as shown in FIG. The external induction magnetic field can be absorbed, and the external induction magnetic field with respect to the magnetic head device 10 can be shielded.

  FIG. 15 is a schematic plan view of a magnetic tape recording / reproducing apparatus 110 such as a VTR equipped with the above composite head. In FIG. 15, reference numeral 111 denotes a rotating drum that is driven to rotate by a motor, reference numeral 112 denotes an image head mounted on the rotating drum 111, reference numeral 113 denotes a delivery-side tape reel, reference numeral 114 denotes a magnetic tape, and reference numerals 115a and 115b denote A guide post, 116 is a capstan, 117 is a pinch roller, 118 is a take-up tape reel, and 121 is a full-width erasing head.

When a tape cassette including the reels 113 and 118 and the magnetic tape 114 is inserted into the magnetic tape recording / reproducing apparatus 110, guide posts 115a disposed at a standby position between the sending-side tape reel 113 and the take-up tape reel 118, The magnetic tape 114 is wound around the rotating drum 111 by moving 115b along the direction of the dashed line in FIG. In the magnetic head device 10 described above, the extension 31 is not formed on a part of the shield cover 30, so that the shield cover 30 does not overlap the track of the guide post 115 b.
Japanese Utility Model Publication No. 62-35403

By the way, when the magnetic head device 10 is incorporated in the magnetic tape magnetic recording device 110, there are cases where the externally induced magnetic field from a specific direction cannot be sufficiently shielded. That is, in the magnetic tape recording / reproducing apparatus 110 shown in FIG. 15, when the noise source N ₁ such as a transformer is disposed obliquely in front of the recording / reproducing head 11, an external induction magnetic field generated by the noise source N ₁ is shielded by the shield cover 30. of can be sufficiently shielded by the extension 31, when the noise source N ₂ is disposed obliquely forward toward erasing head 12, the shielding effect against the external induction field noise sources N ₂ is not sufficient, the external induction field In some cases, it was affected. To enhance the direction of the shielding effect of the noise source N ₂ it is necessary to provide an extension of the shield cover to the noise source N ₂ side, but there is the trajectory of the guide post 15b is a noise source N ₂ side as described above For this reason, the extension portion cannot be provided, and the shielding of the external induction magnetic field is insufficient.

  The present invention has been made in view of the above circumstances, and is a magnetic head device capable of eliminating the influence of noise caused by an externally induced magnetic field, a magnetic tape recording / reproducing apparatus including the magnetic head device, and an externally induced magnetic field for the magnetic head device. An object is to provide a shielding method.

In order to achieve the above object, the present invention employs the following configuration.
A magnetic head device according to the present invention includes a magnetic head having a magnetic core on a medium facing surface of a shield case, the magnetic recording medium being slidably contacted with the magnetic core, and a shield that is attached to the magnetic head and shields an external induction magnetic field. The shield cover is provided with an upper surface plate that is attached to one side surface that intersects the medium facing surface of the shield case, and the upper surface plate includes a part of the upper surface plate. A shielding portion is provided that protrudes forward of the facing surface and has its tip bent toward the medium facing surface. The width of the shielding portion along the sliding direction of the magnetic recording medium is the width of the medium facing surface. It is formed narrower than the width, and a notch portion is provided on one side of the shielding portion in the sliding contact direction of the magnetic recording medium.

  As described above, the orientation of the bulging portion of the directivity curve of the externally induced magnetic field can be changed by providing the cutout portion in the shielding portion. Therefore, the external induction magnetic field can be shielded regardless of the position of the generation source of the external induction magnetic field with respect to the magnetic head device. In addition, since the width of the shielding portion of the shield cover is narrowed, the magnetic head device can be reduced in size.

  The magnetic head device of the present invention is the magnetic head device described above, wherein the source of the external induction magnetic field is provided outside the magnetic head device, and the notch portion of the shield cover is formed of the shield cover. The bulging portion of the directivity curve of the externally induced magnetic field is set to a position where the direction is directed away from the generation source.

With the above configuration, it is possible to shield the external induction magnetic field with respect to the magnetic head device.
The directivity curve indicates the directivity for attenuating the external induction magnetic field jumping from the outside with respect to the magnetic head device. When the shield cover is viewed in plan, it has an 8-character shape centering on the shield cover. It is a curve. Further, the bulging portion of the directivity curve is a portion indicating a direction in which the shielding effect against the external induction magnetic field is lowest.

  The magnetic head device of the present invention is the magnetic head device described above, wherein the notch is on one side of the shielding portion in the sliding direction of the magnetic recording medium and away from the generation source. It is provided.

  According to said structure, by providing a notch part, while reducing the volume of the shielding part on the side away from the generation source, it is possible to relatively increase the volume of the shielding part on the side near the generation source. The shielding effect against the external induction magnetic field can be enhanced.

  Next, a magnetic tape recording / reproducing apparatus according to the present invention includes the magnetic head device according to any one of the above and a rotating drum having a video head, and the magnetic tape drawn from the tape reel is the rotating drum. And a tape loading path configured to be in sliding contact with the magnetic head device.

  According to the above configuration, since the magnetic recording head device having the above-described shielding ability against the external induction magnetic field is provided, it is not necessary to limit the position of the external induction magnetic field generation source, and the magnetic tape has a high degree of freedom in design. A recording / reproducing apparatus can be provided. Further, as the magnetic head device can be reduced in size, the magnetic tape recording / reproducing device can also be reduced in size.

  An externally induced magnetic field shielding method for a magnetic head device according to the present invention is a method for shielding an externally induced magnetic field for any one of the foregoing magnetic head devices, wherein the notched portion is in a sliding direction of the magnetic recording medium. By adjusting the width along the direction, the direction of the bulging portion of the directivity curve of the externally induced magnetic field of the shield cover is set to a position that makes the direction away from the generation source.

  According to said structure, by adjusting the width | variety of a notch part, the direction of the bulging part of a directivity curve can be finely adjusted, and the bulging part can be faced in the direction which remove | deviates from a generation source.

As described above, according to the magnetic head device of the present invention, the direction of the bulging portion of the directivity curve of the external induction magnetic field can be easily changed, and the external induction magnetic field can be shielded. Further, it is possible to reduce the size of the magnetic head device.
Further, according to the method for shielding an externally induced magnetic field with respect to the magnetic head device of the present invention, the bulge portion of the directivity curve can be directed away from the generation source only by adjusting the width of the notch. It is possible to easily design the magnetic shield of the device.

(First embodiment)
A first embodiment of the present invention will be described below with reference to the drawings. 1 is an exploded perspective view of the magnetic head device according to the present embodiment, FIG. 2 is a front view of the magnetic head device shown in FIG. 1, and FIG. 3 is a partial sectional plan view of the magnetic head device shown in FIG. is there.

  As shown in FIGS. 1 and 2, the magnetic head device M of this embodiment includes a magnetic head part A and a shield cover 5 attached to the magnetic head part A. The magnetic head portion A includes a recording / reproducing magnetic head (hereinafter abbreviated as a recording / reproducing magnetic head) 1 and a voice erasing magnetic head 2. The recording / reproducing magnetic head 1 is configured in a shield case 3 and the voice erasing magnetic head 2 is configured in a resin case 4 in which a core and a coil are stored. The erasing magnetic head 2 may be a dummy head having no degaussing function.

  As shown in FIGS. 1 and 2, the shield case 3 is made of, for example, a NiFe alloy or the like and formed by drawing or the like. The shield case 3 has a circular shape in the sliding direction of the magnetic recording medium. An arc-curved medium facing surface 3d, a pair of side surfaces 3c and 3e adjacent to the medium facing surface 3d, and an upper surface (one side surface) 3b and a lower surface 3f adjacent to the medium facing surface 3d are formed. The resin case 4 is formed by molding or the like. The resin case 4 includes a medium facing surface 4d curved in the sliding contact direction of the magnetic recording medium and a pair of side surfaces adjacent to the medium facing surface. 4c and 4e, and an upper surface 4b and a lower surface 4f adjacent to the medium facing surface 4d are formed.

  The recording / reproducing magnetic head 1 and the erasing magnetic head 2 are bonded and bonded to each other by interposing a resin adhesive (not shown) between the side surfaces 3e and 4c of the shield case 3 and the resin case 4. The magnetic head portion is configured. Accordingly, in the magnetic head portion A, the medium facing surfaces 6 of the magnetic head portion A are formed by integrating the medium facing surfaces 3d and 4d of the heads 1 and 2 together.

  The recording / reproducing magnetic head 1 has a medium facing surface 3d formed with two cores 7 at the top and bottom, and a medium facing surface 4d of the erasing magnetic head 2 with one core 8 formed on the top. . The upper core 7a is for audio signals and the lower core 7b is for control signals, and the magnetic gap 7c is exposed on the medium facing surface 3d.

  Next, as shown in FIGS. 1 to 3, the shield cover 5 is formed by, for example, pressing a plate material such as a NiFe alloy, tinplate, or galvanized steel plate, and the upper surface 3 b of the magnetic head portion A or 4b, a pair of sandwiching portions 5b and 5c that extend from both ends of the top plate 5a toward the magnetic head portion A and elastically sandwich the side surfaces 3c and 4e of the magnetic head portion A, and the top plate 5a. Is mainly configured by a shielding portion 5d formed by projecting a part of the front end of the medium to the front side of the medium facing surface 6 and bending the tip thereof in parallel with the medium facing surface 6. On the rear side of the shield cover 5, a back surface portion 5 e that extends from the rear end of the upper surface plate 5 a to the magnetic head portion A side and positions the front and rear direction of the shield cover 5 is formed. These clamping parts 5b and 5c, the shielding part 5d, and the back surface part 5e are formed by being bent into a box shape by pressing or the like. The upper surface plate 5a is provided with a circular adhesive resin injection hole 5g, and this adhesive resin injection hole 5g is filled with an adhesive resin (not shown) for joining the shield case 3 and the resin case 4 to the shield cover 5. . Further, the shield cover 5 may be welded to the magnetic head portion A.

As shown in FIG. 3, the width X ₁ along the sliding direction of the magnetic recording medium of the shielding portion 5d is formed to be narrower than the width X ₂ of the bearing surface 6. Moreover, as shown in FIGS. 1-3, the notch part 5f is provided in the one side of the sliding direction of the magnetic recording medium of the shielding part 5d. The notch 5f is provided on the side away from the source of the external induction magnetic field such as a transformer. Thus, by providing a cutout portion 5f by cutting out a part of the shielding portion 5d, the volume of the shielding portion 5d on the side away from the generation source is reduced, and at the same time the volume of the shielding portion 5d on the side closer to the generation source. Will be relatively increased. As a result, the magnetic shielding effect of the shield cover 5 is affected, and the directivity of the externally induced magnetic field changes, thereby changing the magnetic shielding directivity.

  Here, a graph of the directivity curve of the magnetic head device M is shown in FIG. 4, and a graph of the directivity curve of the magnetic head device without the notch is shown in FIG. 5. The directivity curves shown in FIGS. 4 and 5 represent the level of externally induced noise when the shield cover is viewed in plan. As shown in FIGS. 4 and 5, the noise directivity curve of the shield cover basically draws an 8-shaped curve in which two substantially circular bulged portions are connected. The direction of the arrow shown between the two bulging portions is the direction in which the noise level is low and the direction of the magnetic shielding property of the shield cover. This directivity direction shows the highest magnetic shielding property against the external induction magnetic field. On the other hand, the direction with the highest noise level in the bulging portion shows a low magnetic shielding property against the external induction magnetic field.

Comparing FIG. 4 with FIG. 5, the directivity curve of FIG. 4 has a shape rotated clockwise by a predetermined angle α with respect to the directivity curve of FIG. Thus, by providing the notch portion 5f, the volume balance of the shielding portion 5d is lost, and the directivity of externally induced noise can be changed. When the source of the external induction magnetic field exists outside the magnetic head device M, the direction of the bulging portion of the directivity curve of the shield cover 5 is set in a direction away from the source by providing the notch 5f. The external induction magnetic field with respect to the magnetic head device M can be shielded. In addition, according to the magnetic head device of the present embodiment, the orientation of the bulging portion of the directivity curve can be changed simply by changing the position of the notch portion 5f in the shielding portion 5d. Can be increased.
Note that the angle α is an angle in a direction of an arrow with a low directivity curve maintenance level when the forward direction of the shield cover is 0 °.

FIG. 6 shows a magnetic tape recording / reproducing apparatus 210 equipped with the above magnetic head device. In FIG. 6, reference numeral 111 denotes a rotating drum that is driven to rotate by a motor, reference numeral 112 denotes a video head mounted on the rotating drum 111, reference numeral 113 denotes a delivery-side tape reel, reference numeral 114 denotes a magnetic tape, and reference numerals 115a and 115b denote Reference numeral 116 denotes a capstan 16, reference numeral 117 denotes a pinch roller, reference numeral 118 denotes a take-up tape reel, and reference numeral 121 denotes a full width erasing head.
In this magnetic tape recording and reproducing apparatus 210, source N ₃ of the external induction noises is provided diagonally in front of the erase head 2, cut-out portions 5f are formed in the shielding portion 5d of the side away from the source N ₃ It has become a relationship.
According to the magnetic tape recording / reproducing apparatus 210, since the magnetic head apparatus M is provided, it is not necessary to limit the position of the source of the external induction magnetic field, and the magnetic tape recording / reproducing apparatus 210 having a high degree of design freedom is provided. Can be provided. Further, as the magnetic head device M can be reduced in size, the magnetic tape recording / reproducing device 210 can also be reduced in size. Further, by reducing the width of the shielding portion 5d, there is no possibility that the shield cover 5 overlaps the track of the guide post 115b.

(Second Embodiment)
Next, a second embodiment of the present invention will be described with reference to the drawings. FIG. 7 is an exploded perspective view of the magnetic head device according to the present embodiment, and FIG. 8 is a front view of the magnetic head device shown in FIG. Of the components shown in FIGS. 7 and 8, the same components as those described in the first embodiment are designated by the same reference numerals, and the description thereof is omitted.

As shown in FIGS. 7 and 8, the magnetic head device K of the present embodiment includes a magnetic head portion B and a shield cover 25 attached to the magnetic head portion B. The magnetic head portion B is composed of only a recording / reproducing magnetic head (hereinafter abbreviated as a recording / reproducing magnetic head) 1. The recording / re-use magnetic head 1 is configured by storing a core, a coil and the like in a shield case 3.
The shield case 3 includes a medium facing surface 3d curved in an arc shape in the sliding direction of the magnetic recording medium, a pair of side surfaces 3c and 3e adjacent to the medium facing surface 3d, and an upper surface adjacent to the medium facing surface 3d. (One side) 3b and the lower surface 3f are formed.

  The recording / reproducing magnetic head 1 has a medium facing surface 3d formed with two cores 7 at the top and bottom, and a medium facing surface 4d of the erasing magnetic head 2 with one core 8 formed on the top. . The upper core 7a is for audio signals and the lower core 7b is for control signals, and the magnetic gap 7c is exposed on the medium facing surface 3d.

The shield cover 25 is formed by, for example, pressing a plate material such as a NiFe alloy, tin plate, or galvanized steel plate. The upper surface plate 25a and the upper surface plate 25a are attached to the upper surface 3b of the magnetic head portion A. Is mainly composed of a shielding portion 25d formed by projecting a part thereof toward the front side of the medium facing surface 2d and bending the tip thereof in parallel with the medium facing surface 3d.
Further, on the rear side of the shield cover 25, a back surface portion 25e that extends from the rear end of the upper surface plate 25a to the magnetic head portion A side and positions the shield cover 25 in the front-rear direction is formed. Further, the shield cover 25 is formed with a pair of clamping portions 25b and 25c. The sandwiching portions 25b and 25c extend from both ends of the back surface portion 25e to the magnetic head portion A side and elastically sandwich the side surfaces 3c and 3e of the magnetic head portion A.
The shield cover 25 is formed by bending the sandwiching portions 25b and 25c, the shielding portion 25d, and the back surface portion 25e into a box shape by pressing or the like. The upper surface plate 25a is provided with a circular adhesive resin injection portion 25g, and this adhesive resin injection portion 25g is filled with an adhesive resin (not shown) for joining the shield case 3 and the shield cover 25 together. The shield cover 25 may be welded to the magnetic head part B.

  As shown in FIGS. 7 and 8, the width of the shielding portion 25 d along the sliding direction of the magnetic recording medium is narrower than the width of the medium facing surface 6. Further, a notch portion 25f is provided on one side of the shielding portion 25d in the sliding direction of the magnetic recording medium. The notch 25f is provided on the side away from the source of the external induction magnetic field such as a transformer. Thus, by providing a cutout portion 25f by cutting out a part of the shielding portion 25d, the volume of the shielding portion 25d on the side away from the generation source is reduced, and at the same time the volume of the shielding portion 25d on the side closer to the generation source. Will be relatively increased. Thereby, the magnetic shielding effect of the shield cover 25 is affected, and the directivity of the externally induced magnetic field is changed, whereby the magnetic shielding directivity can be changed.

  According to the magnetic head device K of the present embodiment, the same effect as that of the magnetic head device M of the first embodiment can be obtained.

Hereinafter, the present invention will be described in more detail with reference to examples. In the present embodiment, an externally induced noise measuring apparatus and test results performed using the measuring apparatus will be described.
FIG. 9 shows an example of a device for measuring externally induced noise. This device is formed by connecting an oscillator 41 and a variable resistor 42 to Helmholtz coils 40, 40, and a first device between the Helmholtz coils. And the power source 43 and the recorder 44 are connected to the magnetic head device via BPF (band pass filter: a filter that passes only a signal having a frequency of 50 Hz or 60 Hz). It is configured as follows. In the measurement apparatus having this configuration, an equal magnetic field is generated between the Helmholtz coils, and the noise directivity is measured by rotating the magnetic head device to obtain a noise directivity curve.

  In the magnetic head device having the shield cover of Experimental Examples 1 to 4 shown in FIGS. 10A to 10D, using the external induction noise measuring device shown in FIG. 9, the level and directivity of the external induction noise depending on the width of the notch portion. The rate at which changes are measured. The shield case used in this example is made of permalloy, the shield cover is made of permalloy, and the width of the shielding portion is 4.58 to 7.3 mm (2.72 to 0 mm in terms of the width of the notch). ) Were prepared and measured. The results are shown in FIGS.

  The shield cover shown in FIG. 10A has a shielding portion width of 7.3 mm (0 mm in terms of the notch width), and the shield cover shown in FIG. 10B has a shielding portion width of 6.5 mm (notch portion). 10C), and the shield cover shown in FIG. 10C has a shielding portion width of 5.63 mm (represented by a notch width of 1.67 mm). In the shield cover shown, the width of the shielding portion is 4.58 mm (2.72 mm in terms of the width of the notch portion).

FIG. 11 is a graph showing the relationship between the width of the shielding part and the level of the external induction magnetic field of the magnetic head devices of Experimental Examples 1 to 4. As shown in FIG. 11, it can be seen that the level of the externally induced magnetic field increases as the width of the shielding portion decreases. The relationship between the width of the shielding portion and the level of the external induction magnetic field is approximately linearly proportional, and when the width of the shielding portion is x and the level of the external induction magnetic field is y ₁ , y ₁ = −1. It can be seen that the relationship is 014x-78.364.

FIG. 12 is a graph showing the relationship between the width of the shielding part and the directivity (angle) of the magnetic head devices of Experimental Examples 1 to 4. The directivity angle in FIG. 12 corresponds to the angle α in the graphs showing the directivity curves in FIGS. 4 and 5. As shown in FIG. 12, when the width of the shielding portion is shortened (when the width of the notch portion is increased), it can be seen that the directivity curve rotates clockwise. Relationship width and directivity α of the shield portion is proportional to nearly linear, the width of the shielding section and x, directional α when a _{y 2,} the _{y 2} = _-8.6288x + 62.794 It turns out that it becomes a relationship.

  As shown in FIG. 12, the directivity can be changed by changing the width of the shielding part (the width of the notch part). Therefore, the directivity of externally induced noise can be finely adjusted with respect to the externally induced noise source by changing the width of the shielding portion. Thereby, the bulging part of the directivity curve with a low shielding effect can be directed in a direction away from the generation source.

FIG. 1 is an exploded perspective view of a magnetic head device according to a first embodiment of the present invention. FIG. 2 is a front view of the magnetic head device shown in FIG. FIG. 3 is a partial sectional plan view of the magnetic head device shown in FIG. FIG. 4 is a graph showing a directivity curve of the magnetic head device shown in FIG. FIG. 5 is a graph showing the directivity curve of the magnetic head device when no cutout is provided. FIG. 6 is a plan view showing a magnetic tape recording / reproducing apparatus including the magnetic head device shown in FIG. FIG. 7 is an exploded perspective view of the magnetic head device according to the second embodiment of the present invention. 8 is a front view of the magnetic head device shown in FIG. FIG. 9 is a schematic diagram illustrating an example of an external induction noise measuring device. FIG. 10 is a schematic view showing a shield cover of the magnetic head device of Experimental Examples 1 to 4. FIG. 11 is a graph showing the relationship between the width of the shielding part and the level of the external induction magnetic field of the magnetic head devices of Experimental Examples 1 to 4. 12 is a graph showing the relationship between the width of the shielding portion and the directivity direction of the magnetic head devices of Experimental Examples 1 to 4. FIG. FIG. 13 is a plan view showing a conventional magnetic head device. FIG. 14 is an exploded perspective view showing a conventional magnetic head device. FIG. 15 is a schematic plan view showing a magnetic tape recording / reproducing apparatus equipped with a conventional magnetic head device.

Explanation of symbols

3, 4 ... shield case, 3b, 4b ... upper surface (one side surface), 3d, 4d, 6 ... medium facing surface, 5, 25 ... shield cover, 5a, 25a ... upper surface plate, 5d, 25d ... shielding part, 5f, 25f ... notches, 7, 8 ... core (magnetic core), 14 ... magnetic tape (magnetic recording medium), 112 ... video head, 111 ... rotating drum, 113 ... tape reel, 210 ... magnetic tape recording / reproducing apparatus, A , B: Magnetic head part (magnetic head), M, K: Magnetic head device, N ₃ ... Source of externally induced magnetic field, X ₁ ... Width of shielding part, X ₂ ... Width of medium facing surface

Claims (5)

A magnetic head having a magnetic core on the medium facing surface of the shield case and having a magnetic recording medium slidably contacted with the magnetic core, and a shield cover attached to the magnetic head and shielding an externally induced magnetic field,
The shield cover includes an upper surface plate that is attached to one side surface that intersects the medium facing surface of the shield case, and the upper surface plate projects a part of the upper surface plate to the front side of the medium facing surface. And a shielding portion formed by bending the tip thereof toward the medium facing surface, and the width of the shielding portion along the sliding contact direction of the magnetic recording medium is narrower than the width of the medium facing surface, 2. A magnetic head device according to claim 1, wherein a notch portion is provided on one side of the shield portion in the sliding contact direction of the magnetic recording medium.   A direction in which the external induction magnetic field generation source is provided outside the magnetic head device, and the cutout portion of the shield cover deviates from the generation direction of the bulging portion of the directivity curve of the external induction magnetic field of the shield cover. The magnetic head device according to claim 1, wherein the magnetic head device is set at a position facing the head.   3. The magnetic head device according to claim 2, wherein the cutout portion is provided on one side of the shielding portion in the sliding contact direction of the magnetic recording medium and on a side away from the generation source.   A magnetic head device according to any one of claims 1 to 3 and a rotating drum provided with a video head, wherein a magnetic tape drawn from a tape reel is wound around the rotating drum and A magnetic tape recording / reproducing apparatus comprising a tape loading path configured to be in sliding contact with a magnetic head device. 4. A method for shielding an externally induced magnetic field with respect to a magnetic head device according to claim 1, wherein a shield cover is formed by adjusting a width of the cutout portion along a sliding direction of the magnetic recording medium. A method for shielding an externally induced magnetic field with respect to a magnetic head device, characterized in that the direction of the bulging portion of the directivity curve of the externally induced magnetic field is set to a position that is directed away from the generation source.

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