MXPA96004123A - Magnetic head drum for a magnetic recording apparatus, and method to produce the same - Google Patents

Abstract

The present invention refers to a magnetic head drum for a magnetic recording apparatus, comprising a metallic ring having a predetermined thickness, and a supporting body made of plastic material which is formed in the metallic ring via an external aggregate formation process. The plastic material supporting body includes a peripheral ring-shaped portion, a central embossment portion for receiving a rotary shaft, and a lay portion which connects the ring-shaped portion with the embossment portion. A plurality of embossment magnetic heads is provided. A plurality of magnetic heads is provided in a periphery of the drum for spinning as a unit with the metallic ring. The present invention further discloses a method for the manufacture of a magnetic head drum through a plastic material injection-molding process, using a metallic ring having a predetermined thickness.

Description

MAGNETIC HEAD DRUM FOR A MAGNETIC RECORDING DEVICE AND A METHOD TO PRODUCE THE SAME BACKGROUND Pg I? INVENTION FIELD OF THE INVENTION The present invention relates to a magnetic head drum for a magnetic recording apparatus such as a video tape recorder. More particularly, the present invention relates to a magnetic head drum that carries one or more magnetic heads and adapted to rotate with the magnetic heads that are kept in contact with a magnetic recording tape. DESCRIPTION OF PREVIOUS TECHNIQUE The current video tape recorders, generally adopt a so-called azimuth exploration system, wherein a magnetic head drum carrying one or more magnetic heads is mounted with its axis of rotation inclined with respect to a direction of feeding a magnetic recording tape, such that the magnetic tape is fed on a plane inclined with respect to the axis of rotation of the drum, while being kept in contact with the peripheral surface of the drum. The magnetic head drum is rotated with a peripheral speed that is higher than the feed speed of the recording tape. As a result, the magnetic head in the drum moves in the REF: 23110 tape on sequential parallel scanning paths that are inclined with respect to the length of the tape. In general, the magnetic head drum is supported for rotation by an arrow in a stationary drum, of a diameter that is the same as that of the magnetic head drum. In order to increase the number of scanning paths, the magnetic head drum is generally provided with two or more magnetic heads located in diametrically opposed positions. In this type of mechanism, a substantially high frictional force is produced between the magnetic head drum and the magnetic recording tape since the peripheral speed of the head drum is higher than the speed of the belt. It should also be noted that the drum must have a certain extension of rotational inertia, so that the fluctuation in rotational speed of the drum can be suppressed. In view of the foregoing, it has been common practice to provide a magnetic head drum for a video tape recorder with a metallic material. In general, a drum of a desired shape is produced by molding an aluminum alloy and then machining on its peripheral surface. An inherent problem with this conventional magnetic head drum is that it is excessively heavy, since it is entirely made of a metallic material. Furthermore, it should be noted that the aluminum alloy molded part has to be subjected to desired machining, so that an amount of time and labor is required and the resulting product becomes expensive. BRIEF DESCRIPTION OF THE INVENTION The present invention is directed to solving the aforementioned problems encountered in the conventional magnetic head drum and has an aim in providing a magnetic head drum which is light in total weight, but which possesses a high inertia. rotational due to a mass concentrated in a peripheral portion. Another object of the present invention is to provide a magnetic head drum that is less expensive in manufacturing, but which can satisfactorily suppress fluctuation in the rotation speed. A further object of the present invention is to provide a magnetic head drum that is substantially free of electrostatic charge, which can be caused by sliding movements, between the magnetic recording tape and the surface of the drum. According to the present invention, the above and other objectives can be achieved by a magnetic head drum comprising a metal ring having a predetermined thickness, and a support body of plastic material that is provided within the metal ring by an external aggregate formation. The plastic support body is constituted by a peripheral ring portion connected to the metal ring, for supporting the metal ring and a central relief portion for receiving a rotary arrow. The magnetic head drum is further provided with at least one magnetic head for rotation with the magnetic head drum as a unit. In a preferred aspect of the present invention, the magnetic head drum is formed on an outer periphery of the peripheral ring portion of the plastic support body and an inner periphery of the metal ring with projections and recesses formed in a complementary manner, which they couple to hold them together, in such a way that a relative displacement between the support body and the metal ring is avoided. According to another aspect of the present invention, the metal ring is formed in a radially inner peripheral portion of an axial end with an inclined surface that slopes axially inwardly, toward a radially inward direction, to provide an increased contact area between the plastic support body and the metal ring, in order to avoid a relative displacement between the support body and the metal ring. Furthermore, in another aspect of the present invention, the plastic support body has an axial length that is larger than the axial length of the metal ring, and the metal ring and the support body are coplanar in a radial plane at the end above, while at the other end of the metal ring, the support body extends axially beyond the metal ring and radially beyond the inner periphery of the metal ring, to cover the other end mentioned above of the metal ring, for this way increasing the contact area between the plastic support body and the metal ring, to avoid a relative displacement between the support body and the metal ring. Preferably, the plastic support body is of a configuration including a ring portion, adapted to be connected to the inner periphery of the metal ring and a weft portion for connecting the ring portion with the enhancement portion. In this case, the ring portion can be partially cut, such that the inner periphery of the metal ring is partially exposed. The portion or portions of cut formed in this way can serve as an opening or relief openings, to pass one or more support members to hold the metal ring in a forming mold during a molding process, to constitute the support body of plastic. Further, in accordance with the present invention, it is preferable that the plastic support body is made of an electrically conductive plastic material to avoid electrostatic charges that may otherwise occur due to sliding movements between the magnetic recording tape and the magnetic head drum. The present invention further provides a method for manufacturing a magnetic head drum for a magnetic recording apparatus. The method uses a forming mold comprising a transverse sliding core divided into a plurality of core pieces and defining in a closed position, a recess which is adapted to be placed in intimate contact with the outer periphery of a metal ring, a male matrix having a cylindrical flat part of a smaller diameter than the inner diameter of the metal ring, the flat part is formed of an outer periphery with one or more projections for contact with the inner surface of the metal ring, the flat part is further formed in a end surface with a recess to form a support enhancement portion for the support body, and a female die having an inner surface adapted to be positioned opposite the end surface of the male die with a spacing. The method comprises steps for locating the metal ring, such that the metal ring is maintained between the sliding core and the projection on the flat part of the male die, closing the mold to provide a forming cavity between the inner surface of the die. metal ring and the flat part of the male die, between the end surface of the flat part of the male die and the inner surface of the female die, the enhancement portion for support, form recess on the end surface of the part flat of the male die, and inject molten plastic material into the forming cavity and solidify the material to produce a magnetic head drum of a structure having a metal ring with an integrally connected support body. In accordance with a preferred aspect of the present invention, the method for producing a magnetic head drum further comprises subjecting the outer surface of the metal ring having an integrally formed plastic support body through the process of external aggregate to a process of grinding to provide additional improved precision, particularly improved concentricity. The rectification process in this case can be carried out with reference to the rotating shaft of the support body. It is also preferable to form a plurality of shallow circumferential grooves in the metal ring to provide air slots that can be effective to prevent the tape from adhering to the drum. The circumferential grooves can be formed simultaneously when the rectification process is carried out.

The magnetic head drum according to the present invention has a metal ring in a peripheral portion, while the support body is made of plastic material. It is therefore possible to supply portions such as assemblies for connection to a drum supporting mechanism that require complicated molding of plastic material, such that it is possible to decrease the need for subsequent work such as machining at a later stage. In this way, the costs for machining can be reduced in general. It can further be noted that although the support body is made of a lightweight plastic material, substantial mass is concentrated in the peripheral portion due to the peripheral portion formed by the ring of a metallic material, so that a high level can be maintained. rotating inertia. The magnetic head drum has a peripheral portion for sliding contact with the magnetic tape, however, the peripheral portion is made of the metal ring, so that sufficient frictional resistance can be ensured. It may be possible that electrostatic charges may occur due to sliding movements between the magnetic recording tape and the surface of the magnetic head drum, however it is possible to cause the charge to dissipate through the metal ring. If it is not sufficient for the metal ring to discharge the electrostatic charge, the plastic support body can be formed from an electrically conductive plastic material. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a perspective view of a mechanism for moving tape, for a video tape recorder having a magnetic head drum, to which the present invention can be applied; Figure 2 is a perspective view showing a magnetic head drum and a stationary drum; Figure 3 is a perspective view of a magnetic head drum, according to an embodiment of the present invention; Figure 4 (a) is a sectional view of a magnetic head drum illustrated in Figure 3; Figure 4 (b) is a side elevation view of the drum; Figure 5 is a fragmentary sectional view of an amplified scale of the magnetic head drum; Figur-a 6 is a perspective view showing a section on line VI-VI in Figure 4 (b); Figure 7 is a bottom view of the magnetic head drum; Figure 8 (a) is a horizontal sectional view of a mold for producing the magnetic head drum, the mold is illustrated in an open position; Figure 8 (b) is a vertical sectional view of the mold in the open position; Figure 9 (a) is a horizontal sectional view of the mold in a closed position; and Figure 9 (b) is a vertical sectional view of the mold in the closed position. DESCRIPTION OF THE PREFERRED MODALITY With reference to the drawings, particularly in the Figure 1, an example of a magnetic head drum to which the present invention can be applied is illustrated in an operating condition. A magnetic recording tape 1 is illustrated as it passes between a supply spool 2, and the collection spool 3, which is located in a cartridge. The tape 1 is directed from the cartridge by a plurality of guide posts 4 and passes around a magnetic head drum assembly 5. In Figure 1, the number 6 designates a full-width erasing head, 7 a head of sound and 8 a control head. The magnetic recording tape 1 is displaced in the direction illustrated by an arrow which is held between a clamping roll 9 and a winch 10. The magnetic head drum assembly 5 includes a lower stationary drum 5a, which is held stationary, and an upper rotating drum or magnetic head drum 5b, which is rotatably held in the lower stationary drum 5a. The upper rotating drum or magnetic head drum 5b, has an outer periphery in which a plurality of magnetic heads 11 are transported in circumferentially spaced positions. As is well known in the specialty of video tape recording technology, the magnetic head drum assembly 5 has a rotating shaft 5c, which is inclined with respect to a plane on which the magnetic recording tape 1 is advanced. The magnetic recording tape 1 is forced by a guide post 4 towards the drum assembly 5, such that it is placed in a slanted contact with the surface of the drum 5. The upper rotating drum 5b, is rotated in the direction of the tape at a peripheral speed higher than the forward speed of the tape 1. As a result, inclined strips of recording bands are produced on the magnetic recording tape 1. In the magnetic recording apparatus as illustrated, the present invention it is applied to the magnetic head drum O liable upper 5b. With reference to Figure 2, it will be noted that the lower stationary drum 5a, comprises a planar bottom portion 5d, a ring-shaped flange 5e, extending upwards from the periphery of the bottom portion 5d, and an enhancement of support 5f extending upwards from the center of the bottom portion 5d. The magnetic head drum 5b is mounted on the upper end portion of a support shaft 12, which has a rod portion 12a, which is rotatably received by an axial bore 5g formed in the center of the support hoop 5f of the stationary drum lower 5a. Figures 3 to 7 illustrate structures of the magnetic head drum 5b. As illustrated in Figure 3, the magnetic head drum 5b comprises a metal ring 14 which is made of a suitable metallic material such as an aluminum alloy, and a support body 15 formed inside the metal ring 14 by molding of injection of a plastic material. As illustrated in Figures 4 (a) and 5, the metal ring 14 has an axial length 1 that is smaller than the axial length L of the support body 15 and the upper end surface of the metal ring 14 is coplanar with the upper end surface of the support body 15. The other end of the support body 15 extends axially beyond the other end of the metal ring 14 to provide an axial extension 15a that also extends radially outward to cover the lower end surface of the metal ring 14. The support body 15 made of a plastic material includes a peripheral ring-shaped portion or a vertical flange portion 15b, which connects to the inner surface of the metal ring 14, and a hollow cylindrical relief portion. 15c, adapted to connect with the upper end portion of the support shaft 12, a frame portion 15d that is formed to connect the overall flange portion 15b and the central relief portion 15c. With reference to Figure 5, it will be noted that the metal ring 14 is formed in an inner peripheral portion of the upper end surface with an inwardly inclined surface 14a, which is covered by the plastic support body 15. Furthermore, as is illustrated in Figure 6, the metal ring 14 is formed through the inner peripheral surface with serrated pattern 14b. Similarly, the flange portion 15b of the support body 15 is formed on the outer surface with a toothed pattern 15e of a configuration complementary to the toothed pattern 14b in the metal ring 14. The toothed patterns 14b and 15e are coupled together. The connection between the metal ring 14 and the support body 15 is ensured by the contact between the inclined surface 14a at the upper end of the metal ring 14 and the plastic material of the support body 15, the coupling between the aforementioned toothed patterns 14b and 15e and the contact between the end surface of the metal ring 14 and the radially external extension 15a of the support body 15., in such a way that it is possible to eliminate any possibility of relative displacement between the metal ring 14 and the support body 15 under a frictional force that may occur during operation. It may be possible to omit one or both of the inclined surfaces 14a and the upper end of the metal ring 14 and the coupling in the toothed patterns 14b and 15e, depending on the contact pressure under which the magnetic recording tape is maintained eh contact with the magnetic head drum 5b. The radially outward extension 15a formed in the lower portion of the support body 15 provides an additional advantage as will be described later. With reference to Figure 3, it will be noted that the vertical flange 15b of the plastic support body 15 is formed in peripherally spaced positions with cuts 16. The material of the root portion of the vertical flange 15b, is completely removed in the locations of the cuts 16 to provide cutting recesses 16a as illustrated in Figure 6. The inner surface of the metal ring 14 is exposed at the locations of the cutting recesses 16a. The central enhancement portion 15c of the support body 15 is formed on the upper end surface with a plurality of bolt holes 17 which are adapted to be used to connect the motor or its parts for rotary movement with the magnetic head drum 5b. The central enhancement portion 15c of the support body 15 is formed at its center with a bore 18 for adapting the rod portion 12a of the support shaft 12.

Figure 7 shows the lower surface of the magnetic head drum 5b. With simultaneous reference to Figure 4 (a), the extension 15a of the support body 15 has a peripheral annular portion projecting downwardly and the weft portion 15d has a planar bottom surface slightly offset upwardly from the projecting portion towards down. The bottom surface of the weft portion 15d is received by an annular flange 12b formed in the support shaft 12. The central relief portion 15c of the support body 15 has an internal cylindrical cavity to which the cylindrical flat portion 12c of the support arrow 12 is adapted. The weft portion 15d of the support body 15 is formed in circumferentially spaced positions with a plurality of threaded holes 19, for receiving screws for connecting the support body 15 to the annular flange 12b. The plastic support body 15 is formed with magnetic head mounting recesses 20, which extend from the bottom surface of the weft portion 15d to the bottom surface of the extended portion 15a. The recesses 20 open to the outer periphery of the extended portion 15a. It will be noted in Figure 5 that the outer periphery of the extended portion 15a has an upper end that is in the same radial position as the outer periphery of the metal ring 14 and is slightly inclined downwardly toward the radially inward direction. The outer periphery of the stationary drum 5a which is located below the magnetic head drum 5b, is in the same radial position as the outer periphery of the metal ring 14 of the magnetic head drum 5b. Therefore, it will be understood that the outer periphery of the extended portion 15a of the plastic support body 15 is displaced radially inward with respect to the outer periphery of the metal ring 14 of the magnetic head drum 5b and the outer periphery of the drum stationary 5a. The arrangement is effective to maintain the extended portion 15a of the plastic support body 15 out of contact with the magnetic recording tape 1. The magnetic head is mounted on the support body 15, such that the magnetic space is located at the downward extension 21 of the outer periphery of the metal ring 14. In Figure 5, the recess 20 for mounting the magnetic head is illustrated by a dotted line. As illustrated in Figure 4 (a), the support body 15 is formed in the weft portion 15d, with the threaded holes for mounting the magnetic head 22 extending to the magnetic head mounting recesses 20. As described, the support body has a complicated configuration and also has to be provided with various recesses and openings. Conventionally, a magnetic head drum has been manufactured from an aluminum alloy block through machining processes such as cutting.

In accordance with the aforementioned embodiment of the present invention, portions that are complicated in configuration and require various openings are all provided by injection molding a plastic material. Therefore it will be appreciated that the need to machine is reduced and the manufacturing cost can be substantially decreased. In general, a magnetic head is formed at its periphery with a plurality of shallow peripheral grooves 14c, to provide an air layer that can prevent the magnetic recording tape from adhering to the head. It will be noted that according to the present invention, these grooves can easily be formed in the metal ring. The grooves may be formed in the metal ring before it is mounted in the plastic support body 15, but may alternatively be formed after the external aggregation process has been carried out. The outer peripheral portion of the metal ring can be machined after it has been integrally assembled by the external aggregate forming process which the supporting shaft takes as a reference. This will provide increased accuracy, particularly with respect to concentricity. Figures 8 and 9 show an example of the method for manufacturing a magnetic head drum according to the present invention. In Figures 8 (a) and (b), a mold in an open portion is illustrated in horizontal and vertical sections. The mold comprises a lower male die 30, a female upper die 31 and a transversely slidable sliding core 32. In the illustrated embodiment, the sliding core is divided into two core pieces 32a. The male core 30 includes a centrally located cylindrical core 30a, which is formed with projections 30b formed at circumferential distances of 90 ° to project in a radially outward direction. The projections 30b are of configurations complementary to the configurations of the cuts 16 and 16a in the support body 15 of the magnetic head drum 5b. The male die 30 has a recess 30c which is of a configuration complementary to the outer configuration of the central relief portion 15c of the support body 15 of the magnetic head drum 5b. The female die 31 includes a bottom surface 31 a, complementary in configuration with the bottom surface of the magnetic head drum 5 b and a core 31 b which is adapted to be inserted in the recess 30 c, formed in the core 30 a of the male die 30. The core 31b of the female matrix 31 cooperates with the recess 30c formed in the core 30a of the male die 30, to provide a mold cavity for forming the enhancement portion 15c of the magnetic head drum 5b.

The metal ring 14 for forming the magnetic head drum 5a is adapted to the core 30a of the male die 30 as illustrated in Figure 8 (a). In this case, the projections 30b of the core 30a are kept in contact with the inner periphery of the metal ring 14 to thereby hold the metal ring 14. In this position, the metal ring 14 and the core 30a define a cavity therebetween. forming the vertical flange 15b of the support body 15. The mold is then closed as illustrated in Figures 9 (a) and (b) and molten plastic is injected into the mold cavity formed in the mold. After the injected plastic material solidifies, the molded product is removed from the mold to obtain a desired magnetic head drum. In order to increase the accuracy, particularly the concentricity of the outer periphery of the magnetic head drum, the metal ring 14 which becomes integral with the support body 15, through the process of external aggregate formation, is subjected to the outside peripheral to a grinding operation. In the grinding operation, the arrow coupling portion for adapting the support shaft 12, that is, the inner diameter DI of the coupling hole 18 in the support body 15, and the inner diameter D2 of the cylindrical recess of the portion of central highlight 15c, is taken as reference. The amount of grinding can preferably be 0.1 to 0.05 mm.

Conventionally, a magnetic head drum of this type is formed on the outer peripheral surface with air slots to provide an air layer between the outer surface of the drum and the magnetic recording tape, to prevent the tape from adhering to the surface of the drum. In accordance with the present invention, it is preferable that these air slots are formed by providing the outer periphery of the metal ring with a plurality of shallow peripheral grooves 14c. The peripheral grooves can be formed simultaneously with the grinding process on the outer peripheral surface of the metal ring. According to the present invention, the magnetic head drum for use with a magnetic recording apparatus is constituted by an elaborated peripheral portion of a metal ring and an inner support body made of plastic material, in such a way that it is possible to reduce the need for machining operation and decrease the manufacturing cost. It should also be noted that since the peripheral portion is made of a metal ring, it is possible to eliminate the problem of wear due to contact with the tape. Since the rotational inertia can be provided sufficiently, there will be no risk of rotational fluctuations caused by the use of a plastic material.

The invention in this way has been illustrated and described with reference to a specific structure, however it should be noted that the invention is in no way limited to the details of the structures illustrated since changes and modifications may be practiced within the scope of the claims. annexes. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention. Having described the invention as above, property is claimed as contained in the following:

Claims (12)

1. CLAIMS 1. A magnetic head drum for a magnetic recording apparatus, characterized in that it comprises a metal ring of a predetermined thickness, and a support body of plastic material formed in the metal ring through an external aggregate forming process, the support body of the plastic material includes a peripheral ring-shaped portion and a central enhancement portion for receiving a rotary arrow, at least one magnetic head that is provided at a periphery of the drum to rotate as a unit with the metal ring. A magnetic head drum according to claim 1, characterized in that the peripheral ring-shaped portion of the support body of the plastic material is formed on an outer periphery with a toothed pattern and the metal ring is formed on a periphery interior with a toothed pattern that is complementary to the toothed pattern on the outer periphery of the supporting body, the toothed pattern on the supporting body and the toothed pattern on the metallic ring are coupled together, to avoid a relative displacement between the body of support and the metallic ring. A magnetic head drum according to any one of claims 1 or 2, characterized in that the metal ring is formed in an inner peripheral portion of an axial end with an inclined surface, which inclines inward radially and inwardly axially, to increase the contact area between the plastic material support body and the metal ring, in order to avoid relative displacement between the support body and the metal ring. A magnetic head drum according to claim 3, characterized in that the support body of plastic material has an axial length that is larger than that of the metal ring, the metal ring is coplanar at an axial end with the body of The support body has an extended portion, which projects at the other end of the metal ring axially beyond the metal ring, and radially beyond the inner peripheral surface of the metal ring, to cover the other end of the metal ring. A magnetic head drum according to claim 3, characterized in that at least one magnetic head is mounted with a magnetic space located on an outer periphery of the extended portion of the support body. A magnetic head drum according to any of claims 1 to 5, characterized in that the support body of plastic material is connected in the ring-shaped portion with an inner periphery of the metal ring, a frame portion is provided to connect the ring-shaped portion with the enhancement portion, the ring-shaped portion is partially cut to form at least one cut wherein the metal ring is partially exposed. A magnetic head drum according to any of claims 1 to 3, characterized in that the support body of plastic material has an axial length that is larger than the metal ring, to provide at least one axial end with an extension which projects axially beyond the metal ring and covers an adjacent end of the metal ring, the extension has an outer periphery located on one side adjacent to the end of the metal ring, in a radial position which is the same as that of the outer periphery of the metal ring. metallic ring, the extension is inclined radially inward towards an axial external direction. 8. A magnetic head drum according to claim 7, characterized in that at least one magnetic head is mounted in the extension. 9. A magnetic head drum according to any of claims 1 to 8, characterized in that the support body of plastic material is formed of an electrically conductive plastic material. 10, A method for manufacturing a magnetic head drum, characterized in that it comprises the steps of: providing a forming mold including a sliding, transversely slidable core, divided into a plurality of core pieces and adapted to define in a closed position, a cavity for intimate contact with an outer periphery of a metal ring, a male die having a cylindrical flat part, is smaller in diameter than the inner periphery of the metal ring and at least one projection formed on an outer surface of the flat part for contact with the inner periphery of the metal ring, the flat part has an end surface formed with a recess to form a support enhancing portion, and a female matrix having an inner surface that is adapted to be held against the end surface of the flat part of the male matrix; holding the metal ring between the sliding core and the projection of the flat part of the male die, closing the female die to form a mold cavity between the inner periphery and the projection on the flat part of the male die, the end surface of the projection of the male matrix and the inner surface of the female matrix, and by the recess to form the support enhancement portion, injecting molten plastic material into the cavity, and solidifying the plastic material to obtain a magnetic head drum, having a support body of plastic material, integrally connected with the metal ring. A method for manufacturing a magnetic head drum according to claim 10, characterized in that it also includes a step to rectify the outer periphery of the metal ring, after the metal ring integrally connects with the support body, take the Rotary axis of the support body as a reference to obtain an improved concentricity of the outer periphery of the metal ring. A method for manufacturing a magnetic head drum according to claim 10, characterized in that it further includes a step of forming shallow peripheral grooves, after the metal ring integrally connects with the support body to provide air slots. to avoid adherence of a magnetic tape.