JPH03225901A - Rotary transformer and manufacture thereof - Google Patents

Abstract

PURPOSE:To manufacture a high performance rotary transformer with high dimensional accuracy through reduced number of machining process by forming a resin layer of thickness less than 1mm on the peripheral face of a cylindrical ferrite core opposing to the peripheral face onto which a winding is applied and on at least one axial end face thereof. CONSTITUTION:Material ferrite powder is compression molded to produce a cylindrical core which is then baked and a resin layer 5 is integrally formed, through injection molding, on one axial end face and one peripheral face of cylindrical cores 1, 2. The resin layer 5 is formed thinner than 1mm with remarkably high dimensional accuracy. Axial end face and peripheral face, on which the resin layer 5 is not formed, are then polished with the surface of the resin layer 5 as a reference while furthermore coil grooves 3, 4 are made through grinding thus producing a core for a coaxial rotary transformer. Dimensional accuracy of thus injection molded resin layer is such that the dimensional allowance is less than + or -0.003mm and the geometric allowance of circularity, flatness and cylindricity is less than 0.003mm.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a rotary transformer used in video tape recorders and the like.

(Prior art) This rotary transformer is used in video tape recorders (V
TR), used in a rotating head cylinder,
It plays the role of transmitting signals between the rotating magnetic head and the stationary main body circuit. This rotary transformer is available in flat plate type and coaxial type, but both require high dimensional accuracy.

A cross-sectional view of this conventional coaxial rotary transformer is shown in the second figure.
As shown in the figure. This conventional example has an inner core 21 with four coil grooves 22 formed on the outer periphery, and four coil grooves 24 on the inner periphery.
The outer core 23 having the outer core 23 formed therein is opposed to each other. The cylindrical core for this coaxial rotary transformer is made by compressing ferrite raw powder into a cylindrical shape and firing it.
The end faces, outer and inner circumferential surfaces, and coil grooves were ground to give a predetermined core shape.

Further, FIG. 4 shows a cross-sectional view of a conventional flat plate type rotary transformer. In this conventional example, four coil grooves 42 are formed on one surface of a disk-shaped ferrite core 41 having a through hole 43 in the center, and windings (not shown) are attached to the coil grooves 42, and the surface is They are made to face each other. The coil grooves in the disk-shaped ferrite 3-core may be formed using a mold during compression molding or by grinding after firing, but the core may be deformed due to shrinkage during firing. In order to improve the dimensional accuracy of each part, it was necessary to form coil grooves by machining.

(Problems to be Solved by the Invention) In recent years, there has been a strong trend toward higher image quality, multifunctionality, and miniaturization of VTRs, and rotary transformers are required to have higher performance and smaller size. In order to achieve high performance in a rotary transformer, it is necessary to improve the dimensional accuracy and assembly accuracy of each part, and to increase the number of channels. It is necessary to form many coil grooves, and it is necessary to improve processing accuracy.

However, ferrite cores undergo deformation due to shrinkage during firing and are hard and brittle, making it difficult to improve machining accuracy and increasing machining time and low dripping, resulting in high costs. .

4- In view of the above, an object of the present invention is to provide a rotary transformer that can achieve high dimensional accuracy.

(Means for Solving the Problems) The present invention provides a rotary transformer in which windings are attached to opposing surfaces of a plurality of cylindrical ferrite cores.
a thickness of 1 on a circumferential surface opposite to the circumferential surface to which the winding of the cylindrical ferrite core is attached, and on at least one end surface in the axial direction;
A resin layer is formed within the plane.

Further, in a rotary transformer in which windings are attached to opposing planes of a plurality of disk-shaped ferrite cores, at least the surface of the disk-shaped ferrite cores opposite to the surface to which the windings are attached has a thickness of 1 mm. The resin layer is formed within the following.

Further, a resin layer is formed by injection molding, and the winding groove is formed with high dimensional accuracy using the resin layer portion as a reference plane.

(Example) A sectional view of a first example according to the present invention is shown in FIG. In this example, after firing a cylindrical core made by compression molding ferrite raw material powder, a resin layer 5 was integrally formed by injection molding on one end surface in the axial direction and one circumferential surface of one cylindrical core 1°2. .

The resin layer 5 formed by injection molding has a thickness of III[lI or less, and is formed with extremely high dimensional accuracy. Using the surface of this resin layer 5 as a reference, the axial end surface and peripheral surface on which the resin layer 5 is not formed are ground, and the coil grooves 3 and 4 are further formed by grinding to form a core for a coaxial rotary transformer. did.

At this time, the dimensional accuracy of the resin layer formed by injection molding was within dimensional tolerance ±0.003 nm, and the geometric tolerances such as roundness, flatness, cylindricity, etc. were 0.003 nwn or less.

In addition, the dimensional accuracy of the cylindrical core after firing is ±
It was about 0.1■, which was much worse than the resin layer of the present invention. In addition, by grinding based on this resin layer, the dimensional accuracy of other parts can be adjusted to ± dimensional tolerance.
Geometric tolerances such as roundness, coaxiality, and surface angle were within 0.005 mm, and accuracy equivalent to or higher than that of the conventional technology was obtained.

Further, a second embodiment according to the present invention is shown in FIG.

In this embodiment, a resin layer 32 was integrally formed on one surface of the disk-shaped core 31 by injection molding after firing a disk-shaped core 31 obtained by compression-molding ferrite raw material powder. Using the surface of the resin layer 31 of this disc-shaped core 31 as a reference, the opposing surface was polished, and the coil groove 33 was further ground to form a core for a flat plate type rotary transformer.

Further, a sectional view of a third embodiment according to the present invention is shown in FIG. This embodiment is a coaxial type rotary transformer, in which a resin layer 53 is integrally formed by injection molding on the surface of a cylindrical core 51 other than the peripheral surface where the coil groove 52 to which the winding is attached is formed. It is.

Further, a sectional view of a fourth embodiment according to the present invention is shown in FIG. This embodiment is a flat plate type rotary transformer, in which a resin layer 63 is integrally formed by injection molding on the outer surface of a disk-shaped core 61 other than the surface where the coil groove 62 to which the winding wire is attached is formed. It is.

According to the present invention, since the opposing surface and the coil groove are ground by injection molding based on the resin layer formed on the rotary transformer core, the step of forming the reference surface by grinding is not necessary, and Since a highly accurate reference surface can be used, each grinding process can easily achieve high dimensional accuracy.

(Effects of the Invention) According to the present invention, a rotary transformer with high dimensional accuracy can be obtained in a process with a small number of processing steps, and a high-performance rotary transformer can be obtained.

As a result, it is possible to easily cope with the high image quality and multifunctionalization of VTRs.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a first embodiment according to the present invention, FIG. 2 is a cross-sectional view of a conventional example, and FIG. 3 is a cross-sectional view of a second embodiment according to the present invention. , FIG. 4 is a cross-sectional view of another conventional example, FIG. 5 is a cross-sectional view of a third embodiment according to the present invention, and FIG. 6 is a cross-sectional view of a fourth embodiment according to the present invention. Fig. 1.2.51...Cylindrical core, 3.4.3
3.52.62...Coil groove, 5, 32.53.6
3...Resin layer.

Claims (4)

[Claims] 1. In a rotary transformer in which windings are attached to opposing circumferential surfaces of a plurality of cylindrical ferrite cores, at least one of the circumferential surfaces of the cylindrical ferrite cores opposite to the circumferential surfaces to which the windings are attached, and at least one of the cylindrical ferrite cores in the axial direction. A rotary transformer characterized by having a resin layer with a thickness of 1 mm or less on an end face. 2. In a rotary transformer in which windings are attached to opposing planes of a plurality of disk-shaped ferrite cores, a resin having a thickness of 1 mm or less is applied to at least the plane opposite to the plane to which the windings are attached of the disk-shaped ferrite cores. A rotary transformer characterized by having a layer. 3. In a method for manufacturing a cylindrical ferrite core for a rotary transformer in which windings are attached to opposing circumferential surfaces of a plurality of cylindrical ferrite cores, the cylindrical ferrite core is molded and fired, and then the cylindrical ferrite core is A resin layer is injection molded on a peripheral surface opposite to the peripheral surface to which the winding is attached and at least one end surface in the axial direction, and the winding groove is ground using the resin layer as a reference surface. Manufacturing method of rotary transformer. 4. In a method for manufacturing a disc-shaped ferrite core for a rotary transformer, in which windings are attached to opposing planes of a plurality of disc-shaped ferrite cores, after the disc-shaped ferrite core is molded and fired, at least the disc-shaped ferrite core is 1. A method for manufacturing a rotary transformer, comprising injection molding a resin layer on one plane of a shaped ferrite core, and grinding a winding groove using the resin layer as a reference surface.