JP3014664B2 - Magnetic head drum for magnetic recording device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic head drum for supporting a magnetic head in a magnetic recording apparatus such as a video tape recorder and rotating while contacting the magnetic head with the tape.

[0002]

2. Description of the Related Art A video tape recorder generally employs a so-called azimuth scanning method, in which a magnetic head drum for supporting a magnetic head is mounted with a rotating shaft inclined with respect to a magnetic tape feeding direction. The magnetic tape contacts the surface of the magnetic head drum while being sent along a plane inclined with respect to the rotation axis of the magnetic head drum. The magnetic head drum is rotated at a peripheral speed higher than the feeding speed of the magnetic tape, and as a result, the magnetic head on the magnetic head drum repeatedly scans on the magnetic tape obliquely. Usually, the magnetic head drum is rotatably supported by a rotating shaft on a fixed drum having the same diameter as the magnetic head drum. In order to increase the number of scanning lines for recording, two or more magnetic heads are provided on diametrically opposed positions on the magnetic head drum.

[0003] Since the peripheral speed of rotation of the magnetic head drum is higher than the tape feeding speed, a strong frictional force acts between the magnetic head drum and the magnetic tape. Further, in order to suppress the rotational unevenness of the magnetic head drum, it is necessary to maintain the rotational inertia of the drum at a certain level.

[0004] From such a viewpoint, a conventional magnetic head drum for a video tape recorder is formed of a metal material. Usually, a drum having a desired shape is obtained by finishing a molded product of an aluminum alloy by machining.

A conventional magnetic head drum of this type has a problem that it is heavy because it is entirely made of metal. Further, since it is necessary to perform a required machining process on the cast product of the aluminum alloy, the process requires time and labor, and the obtained product becomes expensive. In order to solve this problem, a magnetic head drum composed of a metal ring having a predetermined thickness and a plastic material support formed inside the metal ring by outsert molding has been disclosed in Japanese Patent Application Laid-Open No. Hei 9-473329. No. proposed. In the magnetic head drum described in this publication, a support made of a plastic material includes a peripheral ring-shaped portion joined to a metal ring and supporting the metal ring, a central boss portion receiving a rotation shaft, and a peripheral ring. And a flat web portion connecting the shape portion to the central boss portion. The magnetic head drum is provided with a magnetic head at a peripheral portion so as to rotate integrally with the drum.

The magnetic head drum having such a configuration has a metal ring in the peripheral portion and the support is made of a plastic material. Therefore, a portion requiring complicated processing such as an attachment portion of the drum to the support mechanism is required. All can be formed by molding plastic materials, reducing the need for post-processing machining. Therefore, the processing cost is reduced as a whole. Further, the support is formed of a lightweight plastic material, but the peripheral portion is formed of a ring made of a metal material, so that the mass is concentrated on the peripheral portion, and the rotational inertia can be maintained high. Further, since the peripheral portion of the magnetic head drum that is in sliding contact with the magnetic tape is formed of a metal ring, the frictional force can be sufficiently maintained. The sliding between the magnetic tape and the surface of the magnetic head drum generates static electricity, and the metal ring can dissipate the static electricity. Some magnetic head cases and other parts attached to the magnetic head drum require grounding, so that the support must be provided with conductivity. For this purpose, the support made of a plastic material may be formed of a conductive plastic material.

However, since a conductive plastic material is very expensive, it is not preferable to form the entire support with a conductive plastic material because the manufacturing cost of the magnetic head drum itself increases.

[0008]

SUMMARY OF THE INVENTION Accordingly, the present invention relates to a magnetic head drum of the type described in the above-mentioned Japanese Patent Application Laid-Open No. Hei 9-147329 comprising a metal ring and a support made of a plastic material. The problem to be solved is to provide an inexpensive structure for imparting at least the necessary degree of conductivity to the support.

[0009]

In order to solve the above-mentioned problems, the present invention provides a magnetic head drum comprising a metal ring having a predetermined thickness, and a plastic material formed inside the metal ring by outsert molding. A supporting member made of a plastic material, the supporting member made of a plastic material includes a peripheral ring-shaped portion joined to the metal ring and supporting the metal ring, a central boss portion for receiving a rotating shaft, and a peripheral ring-shaped portion. A flat web portion extending between the boss portion and a magnetic head provided on the peripheral portion so as to rotate integrally with the ring, and the support is made of a substantially electrically insulating plastic material. Once formed, a plate of conductive material is attached along at least one surface of the aforementioned web portion of the plastics material support.

[0010] In a preferred aspect of the present invention, the plate of the conductive material attached to the web portion of the support is formed of a metal plate. In another preferred aspect of the present invention, the metal ring is attached so as to surround the outer periphery of the peripheral ring-shaped portion of the support, and the plate of the conductive material has an outer peripheral edge inside the peripheral ring-shaped portion of the support. Arrange almost along the circumference. The conductive material plate may be electrically connected to the metal ring at the peripheral portion, but static electricity generated by sliding between the magnetic tape and the magnetic head drum can be dissipated by the metal ring. This electrical connection is not necessarily required. The magnetic head drum is supported by a metal rotating support shaft at a central boss portion of the support, and a web portion of the support is fixed to a flange provided on the rotary support shaft by a mounting screw. In the magnetic head drum according to the present invention, the conductive plate disposed along the surface of the web portion of the support is grounded to the support shaft via the mounting screw when the magnetic head drum is mounted. The magnetic head mounted on the magnetic head drum is also mounted on the web portion of the support with mounting screws. Therefore, the case of the magnetic head is also grounded to the support shaft by the conductive plate.

[0011]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. FIG. 1 is a perspective view showing an example of a magnetic head drum to which the present invention is applied in a used state. The magnetic tape 1 is stretched between a supply reel 2 and a take-up reel 3 arranged in a cassette, pulled out of the cassette by a plurality of guide posts 4, and passed around a magnetic head drum assembly 5. . In the figure, reference numeral 6 denotes a full-width erasing head, 7 denotes an audio head, and 8 denotes a control head. The magnetic tape 1 is sandwiched between the pinch roller 9 and the capstan 10 and driven to be fed in the direction indicated by the arrow. The magnetic head drum assembly 5 includes a lower fixed drum 5a held in a fixed state, and an upper rotating drum rotatably supported by the lower fixed drum 5a, that is, a magnetic head drum 5b. A plurality of magnetic heads 11 are supported on the outer periphery of the upper rotating drum, that is, the magnetic head drum 5b, at circumferentially spaced positions. As is well known in the art of video tape recorders, the magnetic head drum assembly 5 has a rotation shaft 5c that is inclined with respect to the feed plane of the magnetic tape 1, and the magnetic tape 1 is positioned with respect to the surface of the drum 5. Guide post 4 so that it contacts
Is attracted toward the drum assembly 5. The upper rotating drum 5b is driven to rotate in the direction of the arrow so that the rotational peripheral speed is higher than the feed speed of the magnetic tape 1. As a result, a recording band is formed on the magnetic tape 1 in an oblique stripe shape.

The present invention is applied to the upper rotating drum, ie, the magnetic head drum 5b in the magnetic recording apparatus exemplified above. Referring to FIG. 2, the lower fixed drum 5a is made of metal and includes a flat bottom 5d, a ring-shaped flange 5e standing upright from the periphery of the bottom 5d, and a bearing boss 5f standing upright from the center of the bottom 5d. . The magnetic head drum 5b is attached to the upper end of a metal support shaft 12 having conductivity, and the shaft portion 12a of the support shaft 12 is rotatable in the center shaft hole 5g of the bearing boss 5f of the lower fixed drum 5a. Can be received. 3 to 7 show the structure of the magnetic head drum 5b. As shown in FIG. 3, the magnetic head drum 5b has a metal ring 1 made of a suitable metal material such as an aluminum alloy.
4 and a support 15 made of an electrically insulating plastic material formed by injection molding inside the metal ring 14. As shown in FIGS. 4A and 5, the metal ring 14 has an axial length 1 smaller than the axial length L of the support 15, and the upper end face of the metal ring 14 and the upper end face of the support 15. Are located on the same plane. The other end of the support 15 protrudes in the axial direction from the other end of the metal ring, and the protruding portion in the axial direction protrudes radially outward to form a radial protruding portion 15 a that covers the lower end surface of the metal ring 14. Has formed.

A support 15 made of a plastic material includes a peripheral ring-shaped portion or upright flange portion 15b joined to the inner periphery of the metal ring 14, and a hollow cylindrical central boss portion connected to the upper end of the support shaft 12. 15c, and a flat web portion 15d is formed to connect the flange portion 15b and the lower end portion of the central boss portion 15c. As shown in FIG. 5, an inclined surface 14a that is inclined inward is formed on the upper end surface of the metal ring 14 at a position close to the inner periphery, and a support 15 made of a plastic material covers the inclined surface 14a. ing. Further, as shown in FIG. 6, on the inner peripheral surface of the metal ring 14, serrated irregularities 14b are formed over the entire circumference. Similarly, on the outer peripheral surface of the flange portion 15b of the support 15, irregularities 15e having a shape corresponding to the saw-tooth irregularities 14b of the metal ring 14 are formed.
b and 15e engage with each other.

The contact between the inclined surface 14a at the upper end of the metal ring 14 and the plastic material of the support 15,
b, 15e and the contact between the lower end surface of the metal ring 14 and the radially extending portion 15a of the support body 15 ensure the coupling force between the metal ring 14 and the support body 15 and the friction applied during operation. The possibility of relative displacement between the metal ring 14 and the support 15 due to the influence of the force is eliminated. Depending on the contact pressure at which the magnetic tape 1 contacts the magnetic head drum 5b, one or both of the inclined surface 14a at the upper end of the metal ring 14 and the engagement of the irregularities 14b and 15e may be omitted. Alternatively, as another configuration, the saw-tooth
Instead of b and 15e, recesses are formed at intervals in the circumferential direction on either the inner peripheral surface of the metal ring 14 or the outer peripheral surface of the flange portion 15b of the support body 15, and the other engages with this concave portion. By forming the convex portion, the relative displacement between the metal ring 14 and the support 15 can be spun. The radial extension 15a formed at the lower portion of the support 15 has another advantage of facilitating the molding of the magnetic head mounting portion, as described later.

As shown in FIG. 3, the magnetic head drum 5b
Upright flange 15b of the support 15 made of plastic material
Are formed with notches 16 at positions spaced apart in the circumferential direction. At the position of the notch 16, the root of the upright flange 15b is completely cut away to form a notch hole 16a as shown in FIG. At the position of the notch 16a, the inner peripheral surface of the metal ring 14 is exposed. A plurality of bolt holes 17 for mounting motor components for rotating and driving the magnetic head drum 5b are formed in the upper end surface of the center boss 15c of the support 15. A hole 18 is formed in the center of the center boss 15c of the support 15 so as to fit with the upper end of the shaft 12a of the support shaft 12. FIG. 7 shows a magnetic head drum 5
It is a figure which shows the lower surface of b. Referring also to FIG. 4 (a), the projecting portion 15a of the support 15 has a peripheral portion projecting downward annularly, and is slightly retracted upward from the downward projecting portion to form a flat web portion 15d. A bottom surface is formed. The bottom surface of the web portion 15d is
Is received by the annular flange 12b formed at the bottom. Support 1
The central boss 15c has a cylindrical cavity inside, and the cylindrical platform 12c of the support shaft 12 fits into the cylindrical cavity. The web portion 15d of the support 15 has the web portion 1
A plurality of screw holes 19 for inserting screws for screwing 5d to the annular flange 12b of the support shaft 12 are formed at intervals in the circumferential direction.

The support 15 made of a plastic material has a recess 20 for attaching a magnetic head from the bottom of the web 15d to the bottom of the overhang 15a.
The recess 20 is open at the outer periphery of the overhang 15 a of the support 15. Referring to FIG.
The outer periphery of “a” has the upper end on the same radius as the outer periphery of the metal ring 14 and is slightly inclined inward in the radial direction downward. The outer periphery of the fixed drum 5a disposed below the magnetic head drum 5b is formed on the metal ring 1 of the magnetic head drum 5b.
4 and on the same radius. Therefore, the outer periphery of the protruding portion 15a of the support 15 made of plastic material is located at a position which is recessed radially inward from the outer periphery of the metal ring 14 of the magnetic head drum 5b and the outer periphery of the fixed drum 5a. With this arrangement, the overhanging portion 15a of the support 15 made of plastic material does not contact the magnetic tape 1.

The magnetic head is mounted on the support 15 such that the magnetic gap is located on a lower extension 21 of the outer periphery of the metal ring 14. FIG. 5 shows the concave portion 20 for attaching the magnetic head by an imaginary line. As shown in FIG. 4A, a magnetic head mounting screw hole 22 communicating with the magnetic head mounting recess 20 is formed in the web portion 15d of the support 15. Some magnetic head cases and other parts attached to the magnetic head drum require grounding. Therefore, it is necessary to impart conductivity to the magnetic head drum. For this purpose, it is conceivable to form the support 15 from a conductive plastic material. However, since the conductive plastic material is very expensive, its use is not preferable because the manufacturing cost of the magnetic head drum is greatly increased. Therefore, in this embodiment of the present invention, the support 15 is formed of a substantially electrically insulating plastic material, and along one surface of the web portion 15d of the support 15, such as an aluminum alloy plate. A plate 23 made of a conductive material is disposed. The plate 23 has a radially outer peripheral portion located along the peripheral ring-shaped portion, that is, the flange portion 15b of the support body 15, and a radially inner peripheral portion located along the outer periphery of the central boss portion 15c. A screw insertion hole 19a is formed in the plate 23 at a position overlapping the screw insertion hole 19 formed in the web portion 15d of the support 15, and a notch 22a is formed at a position corresponding to the magnetic head mounting screw hole 22. Are formed. This conductive plate 23
Is grounded to the support shaft 12 by a set screw for screwing the support 15 to the annular flange 12b of the support shaft 12,
The magnetic head is attached to the magnetic head mounting recess 20 of the support 15.
The magnetic head is electrically connected to a case of the magnetic head via a mounting screw for mounting the magnetic head.

As described above, the shape of the support 15 is complicated, and it is necessary to provide various recesses and holes. Conventionally, a magnetic head drum has been formed by machining such as cutting from an aluminum alloy block. In the above embodiment of the present invention, all parts having a complicated shape and requiring various holes are formed by injection molding of a plastic material. Thus, the need for machining is reduced, and manufacturing costs can be significantly reduced. In the magnetic head drum, a plurality of shallow circumferential grooves 14c are generally formed in the periphery in order to form an air layer that prevents sticking of the magnetic tape, but the groove for this purpose is easily formed in the metal ring. Can be formed. This groove may be formed in the metal ring alone, but may be formed after outsert molding as described in JP-A-9-147329.

Further, when the outer peripheral portion of the metal ring is integrated with the support after the outsert molding and is polished with the support shaft as a reference, the accuracy (particularly the roundness) is further improved. This magnetic head drum can be manufactured by the method described in JP-A-9-147329.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an example of a tape drive mechanism of a video tape recorder using a magnetic head drum to which the present invention is applied.

FIG. 2 is a perspective view showing a magnetic head drum and a fixed drum.

FIG. 3 is an exploded perspective view of a magnetic head drum according to one embodiment of the present invention.

4A is a sectional view of the magnetic head drum shown in FIG. 3,
(b) is a side view of the magnetic head drum.

FIG. 5 is an enlarged sectional view of a part of the magnetic head drum.

FIG. 6 is a perspective view showing a cross section taken along line VI-VI of FIG. 4 (b).

FIG. 7 is a bottom view of the magnetic head drum.

[Explanation of symbols]

1 magnetic tape, 2 supply reel, 3 take-up reel,
5 Drum assembly, 5a fixed drum, 5b magnetic head drum, 11 magnetic head, 14 metal ring, 15
Support

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-9-147329 (JP, A) JP-A-1-162221 (JP, A) JP-A-3-194717 (JP, A) JP-A-61-147 271611 (JP, A) JP-A-4-353612 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B 5/52 G11B 5/53 G11B 15/61

Claims (3)

(57) [Claims] 1. A metal ring having a predetermined thickness and a support made of a plastic material formed by outsert molding inside the metal ring, wherein the support made of a plastic material is formed of a metal ring. A peripheral ring-shaped portion joined to the metal ring and supporting the metal ring, a central boss portion for receiving a rotation axis, and a flat web portion extending between the peripheral ring-shaped portion and the central boss portion. Is a magnetic head drum for a magnetic recording device provided with a magnetic head so as to rotate integrally with the ring, wherein the support is substantially formed of an electrically insulating plastic material, and the support is formed of the plastic material. A magnetic head drum for a magnetic recording device, wherein a plate made of a conductive material is attached along at least one surface of the web portion of the support. 2. The magnetic head drum according to claim 1, wherein the plate of the conductive material is a metal plate. 3. The magnetic head drum according to claim 1, wherein the metal ring is attached so as to surround an outer periphery of a peripheral ring-shaped portion of the support, and the plate of the conductive material is formed of an external material. A magnetic head drum having a peripheral edge arranged substantially along an inner periphery of a peripheral ring-shaped portion of the support.