MULTI-HEAD TRANSDUCER ASSEMBLY FOR HELICAL SCAN VIDEO TAPE RECORDERS

Abstract: An electromagnetic transducer assembly for used in a helical-scan type video tape recorder includes a pair of mag­ netic heads secured to a nonmagnetic base and successively arranged in spaced relationship with each other in the direc­ tion of transport of a magnetic medium, each of the heads comprising a generally U-shaped core having a pair of limb portions and a web portion therebetween, a generally I-­ shaped core connected to the limb portions to form a closed magnetic circuit having a magnetic gap therein, and a coil wound on the closed magnetic circuit, the I-shaped cores of the heads respectively having confronting edges extending unparallel to the magnetic gaps.

Description: The present invention relates generally to electromagnetic transducers, and more particularly to a multi-head video transducer assembly for helical scan type video tape recorders. Multi-head magnetic transducer assemblies are currently employed in helical scan video tape recorders to effect still-picture or slow-motion playback. Such a multi-head transducer assembly comprises a pair of magnetic heads secured to a base and arranged successively in spaced relationship in the direction of transport of a magnetic tape. Each head has a generally U-shaped core and an I-shaped core connected to the limb portions of the U-shaped core to form a closed magnetic circuit with a magnetic gap therein. The heads are arranged so that the I-shaped core of each head is located in opposition to the I-shaped core of the other head. The opposite portions of the I-shaped cores adjacent the magnetic gaps respectively have right-angled edges which run parallel to the magnetic tape. However, it has been difficult to obtain satisfactory image quality on such special mode playback. The present invention is based on the discovery that the image quality is subject to degradation from crosstalk between the paired transducer heads due to the creation of false magnetic gaps at the sharp edge portions of the I-shaped cores which are held in intimate sliding contact with a magnetic tape as it runs along the transducer heads. JP-A-60-13312 shows a magnetic head device having two heads each comprising a U-shaped core and I-shaped core connected to its limbs to form a magnetic gap. The gaps may be non-parallel to the confronting edges of the two I-shaped cores. Reference is also made to EP-A-0157498 which is not a prior publication of this case. According to the present invention, there is provided an electromagnetic transducer assembly for used in a helical-scan type video tape recorder, comprising: a nonmagnetic base; and a pair of magnetic heads secured to said base and successively arranged in spaced relationship with each other in the scanning direction with respect to a magnetic medium, each of the heads comprising a generally U-shaped core having a pair of limb portions and a web portion therebetween, a generally I-shaped core connected to said limb portions to form a closed magnetic circuit having a magnetic gap therein, and a coil wound on said closed magnetic circuit, the magnetic gaps converging in a cross-sectional plane parallel to the sliding surfaces of said I-shaped cores and the I-shaped cores of said heads respectively having confronting edges extending unparallel to the magnetic gaps, characterised in that said confronting edges extend along straight lines in a cross-sectional plane parallel to sliding surfaces of said I-shaped cores for sliding contact with the magnetic medium, and are flat and converge in a direction opposite to that in which the magnetic gaps converge. The present invention will be described in further detail with reference to the accompanying drawings, in which: Fig. 1 is a front elevational view of a video transducer assembly according to an embodiment of the present invention; Fig. 2 is a plan view of the video transducer assembly shown in Fig. 1. Like or corresponding parts are denoted by like or corresponding reference numerals throughout the views. Figs. 1 and 2 illustrate a video transducer assembly according to an embodiment of the present invention. The video transducer, generally indicated by the reference numeral 20, is adapted to be mounted in the rotary cylinder of a helical scan type video tape recorder between upper and lower drum halves thereof. The video transducer 20 comprises a pair of ring-shaped electromagnetic transducer heads 11a, 11b securely mounted on a mount of head base 19. The transducer heads 11a, 11b comprises generally U-shaped ferromagnetic cores 12a, 12b, respectively, and I-shaped ferromagnetic cores 13a, 13b, respectively, secured to the front and rear limb portions of the U-shaped cores 12a, 12b, respectively. The distal end of the front limb of each of the U-shaped cores 12a, 12b, which faces the I-shaped core 13a, 13b, is tapered, and likewise the surface of each of the I-shaped cores 13a, 13b, which faces the tapered distal end of the front limb of the U-shaped core 12a, 12b, is complementarily tapered, thus forming a magnetic gap 15a, 15b. The opposite sides of the front limbs of the U-shaped cores 12a, 12b and the associated I-shaped cores 13a, 13b are recessed across the magnetic gaps 15a, 15b. The reason for this is to provide a con-centration of magnetic flux lines across the magnetic gaps 15a, 15b. As shown in FIG. 1, the magnetic gap 15a is inclined to the vertical in a direction opposite to the inclination of the magnetic gap 15b to the vertical. The recessed portions are filled with molded masses of glass 16a, 16b to precisely define the gap length. The magnetic heads 12a and 12b are laterally spaced apart so that the distance L between the magnetic gaps 15a and 15b is preferably equal to 1 millimeter or less. To ensure this amount of spacing, the transverse dimension of each I-shaped core is smaller than the transverse dimension of the web portion of each U-shaped core. A coil 14a is wound on the web portion of the U-shaped core 12a and further wound on the I-shaped core 13a. Likewise, a coil 14b is wound on the web portion of the U-shaped core 12b and further wound on the I-shaped core 13b. During recording, a specified one of the heads is used to record a video program and the same head is used on playback. During a special mode of operation such as still-picture and slow-motion, the other head is additionally brought into play. The I-shaped cores 13a, 13b have confronting edges 17a, 17b which are unparallel to the magnetic gaps 15a, 15b and which extend along straight lines, respectively, in a cross-sectional plane parallel to surfaces of the I-shaped cores 13a, 13b which slidingly contacts the magnetic tape. In each of the embodiment shown in FIGS. 1 and 2, the confronting edges 17a, 17b that extend unparallel to the magnetic gaps 15a, 15b are effective in the elimination of a magnetic gap effect which would otherwise be produced by confronting edges parallel to the magnetic gaps, and hence in reproducing images of good quality. The flat confronting edges 17a, 17b shown in FIGS. 1 and 2 can easily be formed, with the result that the I-shaped cores 13a, 13b can easily be manufactured and the magnetic heads 11a, 11b can be produced inexpensively. The flat confronting edges 17a, 17b have azimuths oppposite to those of the magnetic gaps 15a, 15b for effective reduction of crosstalk, i.e. the edges converge in the opposite direction from that in which the gaps converge. Each of the windings 14a and 14b has N1 turns on the U-shaped core and N2 turns on the I-shaped core. To avoid radio interference, the turn ratio N1/N2 is preferably proportional to the ratio S2/S1, where S1 and S2 represent respectively the cross-sectional area of the magnetic circuit on the web portion of each U-shaped core (which corresponds to the area of contact of the U-shaped core with the magnetic tape) and the cross-sectional area of the magnetic circuit on the I-shaped core (which corresponds to the area of contact of the I-shaped core with the magnetic tape). Since the strength of radio interference noise produced is proportional to the core's cross-sectional area, radio interference noise introduced to the U-shaped core is cancelled by that introduced to the I-shaped core. The provision of the windings on both cores also raises the output level of the head without substantially increasing thermal noise due to the resistive component of the coils. Since the coils 14a, 14b are wound on both of the U-shaped cores 12a, 12b and the I-shaped cores 13a, 13b, they have a greater number of turns with respect to the same impedance than would coils wound on only the U-shaped cores 12a, 12b. Therefore, the video transducers of the present invention can produce an increased output signal without increasing the impedance noise of the magnetic heads. Experiments showed that crosstalk between the heads 11a and 11b was improved by approximately a range of from 9 to 12 dB for the transducers shown in FIGS. 1 and 2

Claims: An electromagnetic transducer assembly for used in a helical-scan type video tape recorder, comprising: a nonmagnetic base (19); and a pair of magnetic heads secured to said base and successively arranged in spaced relationship with each other in the scanning direction with respect to a magnetic medium, each of the heads comprising a generally U-shaped core (11a, 11b) having a pair of limb portions and a web portion therebetween, a generally I-shaped core (13a, 13b) connected to said limb portions to form a closed magnetic circuit having a magnetic gap (15a, 15b) therein, and a coil (14a, 14b) wound on said closed magnetic circuit, the magnetic gaps (15a, 15b) converging in a cross-sectional plane parallel to the sliding surfaces of said I-shaped cores and the I-shaped cores of said heads respectively having confronting edges (17a, 17b) extending unparallel to the magnetic gaps, characterised in that said confronting edges extend along straight lines in a cross-sectional plane parallel to sliding surfaces of said I-shaped cores for sliding contact with the magnetic medium, and are flat and converge in a direction opposite to that in which the magnetic gaps converge.

Inventors: KUDO, MASAHIRO, MICHIWAKI, SHIGERU MITSUWASA KAZOKU APAATO, NIWA, KAZUHIRO
Applicants: VICTOR COMPANY OF JAPAN, LIMITED
Application year: 1986
Main classification: G11B5
IPC codes: G11B5