JPH023288B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a rotary transformer, and in particular to a method for manufacturing a core thereof.

[Background of the invention]

2. Description of the Related Art Rotary transformers are widely used as means for transmitting electric signals between the rotating part and the stationary part in devices having an electric circuit for a rotating part and an electric circuit for a stationary part, for example, a rotating drum apparatus of a rotating head type VTR.

Figure 8 is a cross-sectional view of a rotary transformer called a flat type among this type of rotary transformer.
8 is a plan view of the stator side core of the rotary transformer shown in FIG. 8, and FIG. 10 is a plan view of the rotor side core of the rotary transformer shown in FIG. 8.

In these figures, 1 is the stator side core, 2
is the rotor side core, and both cores 1 and 2 are 40~
They face each other via a magnetic gap G of about 70 μm. A plurality of concentric coil grooves 1a and a plurality of coil extraction grooves 1b orthogonal to these coil grooves 1a are provided on the upper surface of the stator side core 1, and each coil groove 1a has a coil 3. is wound a predetermined number of turns, and each coil 3 is connected to a stationary part electric circuit (not shown) through each coil lead-out groove 1b.

On the other hand, the lower surface of the rotor side core 2 is also provided with a plurality of concentric coil grooves 2a and a plurality of coil extraction grooves 2b orthogonal to each coil groove 2a, similarly to the stator side core 1 described above. A coil 4 is wound in each coil groove 2a with a predetermined number of turns.
Each coil 4 is connected to a rotating part electric circuit (not shown) through each coil extraction groove 2b.

In the rotary transformer configured as described above, when an electric signal from the rotating part is applied to each coil 4 as a current waveform, a magnetic flux is generated, and a part of the magnetic flux is distributed to each coil 4 facing each other. The coils 3 are linked to each other, and a voltage is induced in each coil 3. The induced voltage of this coil 3 is
If the coupling coefficient K between coils 4 and 4 is constant, it will be proportional to the voltage applied to coil 4, so that signals can be transmitted between coils 3 and 4 that rotate relative to each other.

Conventionally, as a method for manufacturing the cores 1 and 2 of such a rotary transformer, a compression molding method is generally used in which soft ferrite magnetic powder is compressed in a uniaxial direction within a mold. A method for manufacturing a rotary transformer using this compression molding method will be described below.

First, the powdered raw material is granulated by mixing an appropriate amount of lubricant (powder) with soft ferrite magnetic powder.
This is placed in a mold and pressurized in a uniaxial direction using a mechanical press or a hydraulic press to form a core body having a coil groove and a coil extraction groove. next,
This core body is heated to a high temperature (1000 ~
(approximately 1,400°C), the powder is densified while proceeding with a solid phase chemical reaction between the powders, and a sintered body of cores 1 and 2 having desired magnetic properties and mechanical strength is obtained.

In the cores 1 and 2 obtained in this way, the pressure force during compression molding is not uniformly transmitted to the raw material filled in the mold due to friction between the raw material powders or between the raw material and the mold. Therefore, when the core body is fired, the shrinkage rate differs locally, causing deformation and warping. Therefore, the cores 1 and 2 after firing are subjected to mechanical processing such as surface polishing and grinding to achieve parallelism and flatness on both sides, and finally each coil groove 1a, 1
Coils 3 and 4 are wound and glued around b to obtain the rotary transformer shown in FIG.

However, in such conventional manufacturing methods for rotary transformers, a complex-shaped core body with coil grooves and coil extraction grooves is manufactured by compression molding, so the degree of filling of raw materials in the mold is uneven. As a result, as mentioned above, the cores 1 and 2 after firing are deformed and warped. Although these deformations and warps are slight, rotary transformers require high precision in the magnetic gap G between both cores 1 and 2, so the parallelism of the surfaces of cores 1 and 2 must be maintained at 10 μm or less. Not necessarily,
Therefore, it has been necessary to perform complicated machining such as surface polishing to improve the precision of the surfaces of the cores 1 and 2.

In addition, the heat shrinkage rate of raw materials during firing is 10~
20%, so if there is non-uniformity in the degree of filling of the raw material in the mold, the groove diameter accuracy and concentricity of the coil grooves 1a and 2a cannot be obtained due to the difference in local shrinkage rates, and the predetermined Another problem arises in that it becomes difficult to adhere and fix the shaped coils 3 and 4 into the respective coil grooves 1a and 2a.

Moreover, FIG. 11 is a cross-sectional view of a rotary transformer called a cylindrical type (coaxial type), and parts corresponding to those in FIG. 8 described above are given the same reference numerals.

The method for manufacturing the cores 1 and 2 of such a cylindrical rotary transformer is basically the same as the cores 1 and 2 of the flat rotary transformer, in which soft ferrite magnetic powder is mixed with an appropriate amount of lubricant (powder). The raw material is compression molded and then sintered. However, in this case, it is difficult to mold the complex-shaped core body with a mold, so first the cylindrical core body is compression molded. After that, insert coil grooves 1a and 2 into this.
A complicated process is employed in which a is formed by machining and then fired.

However, in a cylindrical rotary transformer, the dimensional accuracy of the magnetic gap G is determined by the inner diameter dimension of core 1 and the outer diameter dimension of core 2, so dimensional precision on the order of microns is required for the diameters of cores 1 and 2. Therefore, in the compression molding method, which tends to cause non-uniform filling of the raw material in the mold, the complicated process of polishing the peripheral surfaces of the cores 1 and 2 after firing is necessary.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide an inexpensive method for manufacturing a rotary transformer that eliminates the drawbacks of the prior art described above, omits surface polishing of the core.

[Summary of the invention]

In order to achieve this objective, the present invention heats and kneads 15 to 50% by volume of binder with soft ferrite magnetic powder to obtain a slurry-like raw material, and then injects this raw material into a mold to form coil grooves. After that, this core element is molded with 300 ~
The unique feature is that the core is manufactured by degreasing at a temperature of 500°C and then firing at a temperature of 1000 to 1400°C.

That is, the present invention molds the core body using an injection molding method known as a method for producing permanent magnets as disclosed in Japanese Patent Publication No. 55-33173.
This core body is degreased and fired to produce a core. This injection molding method requires a large amount of binder to improve the fluidity of the raw materials, and as a result, the core after firing becomes porous and the magnetic permeability μ of the core deteriorates. Therefore, it was conventionally considered to be unsuitable for the manufacturing method of rotary transformers, which require high magnetic permeability.

However, the present inventors have experimentally found that in a rotary transformer used through a magnetic gap between cores, the influence of the magnetic permeability μ of the core in the signal transmission path does not appear linearly.

That is, FIG. 12 shows that the magnetic gap G is approximately
Core magnetic permeability μ and coupling coefficient K when the diameter is 50 μm and the usage conditions of the rotary transformer are the same.
This is an explanatory diagram showing the relationship between the magnetic permeability μ and the horizontal axis.
, and the coupling coefficient K is plotted on the vertical axis.

As is clear from FIG. 12, the coupling coefficient K
deteriorates rapidly when the magnetic permeability μ becomes less than a certain value A, and changes proportionally while the magnetic permeability μ is within a predetermined range from point A to point B, and when the magnetic permeability μ exceeds point B, it deteriorates rapidly. It can be seen that it becomes saturated.

Therefore, the present inventors investigated the deterioration of the magnetic permeability μ due to the increase in the volume ratio of the binder in the raw material.
We investigated the relationship between increasing the volume ratio of binder and the fluidity of raw materials, and determined that the volume ratio of binder in raw materials was 15 to 50%.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a process diagram illustrating a method for manufacturing a rotary transformer according to the present invention.

As shown in FIG. 1, in order to improve the fluidity of the raw materials, a binder (binding material) is mixed with soft ferrite magnetic powder, and the mixture is heated and kneaded to form a slurry. The binder ratio at this time is
It varies somewhat depending on the particle size of the soft ferrite magnetic powder, but if it is too small, the fluidity of the raw material will decrease and injection will be difficult, and cracks will appear during the post-process firing, so we specified it as 15% by volume or more.

Next, this raw material is press-fitted into a mold to injection mold a core element having a coil groove and a coil extraction groove. Since this injection-molded core body contains a large amount of binder, it is heated to 300 to 500°C at a slow heating rate of 3 to 5°C/hr to degrease the binder.

FIG. 2 is an explanatory diagram showing the relationship between the blending ratio % of the binder and the magnetic permeability μ, in which the horizontal axis represents the volume ratio % of the binder in the raw material, and the vertical axis represents the magnetic permeability μ. From this figure 2, it can be seen that when the volume ratio of the binder in the raw material exceeds 50%, degreasing becomes insufficient, and a large number of non-magnetic pores are generated between the soft ferrite magnetic powders in the subsequent firing process.
Since it was found that the magnetic permeability μ deteriorated rapidly due to the influence of these demagnetizing fields, the volume ratio of the binder in the raw material was specified to be 50% or less.

Next, the core body after degreasing is fired at a high temperature of 1000 to 1400° C. for several hours (2 to 6 hours at peak temperature) to obtain a core (product) having coil grooves and coil extraction grooves. The stator side and rotor side cores obtained in this way are made by injecting slurry raw material with good fluidity into the mold, so the degree of filling of the raw material in the mold is uniform, and there is no deformation or warping during the subsequent process. does not occur. Therefore, it is possible to omit the surface polishing process after firing, which was indispensable in the conventional compression molding method, and the dimensions of the coil groove and coil pull-out groove can be precisely determined, making the coil installation work easier. will also be very easy.

FIG. 3 is a plan view showing an embodiment of the core manufactured by the above-described manufacturing method, and FIG. 4 is a sectional view taken along line A-A' in FIG. A recess 6 is provided on the surface of the core 1.
This is a gate portion formed inside, and portions corresponding to those in FIG. 8 described above are given the same reference numerals.

That is, according to the rotary transformer manufacturing method according to the present invention, since the core is manufactured by injection molding, the gate portion 6 always remains in the core 1 in a protruding state. Therefore, in order to eliminate the need for post-processing of the gate portion 6, in this embodiment, a recess 5 is provided on the surface of the core 1 opposite to the coil groove 1a, and the gate portion 6 is located within the recess 5. In this way, the gate part 6 is
It has been devised so that it does not cause any problems.

Note that the core 1 shown in FIGS. 3 and 4 above is an explanation of the stator side core,
Of course, such a core structure can also be applied to the core 2 on the rotor side. Further, the gate portion 6 may be formed at a position other than that shown in the above embodiment, for example, on the outer circumferential surface of a portion recessed from the maximum outer diameter of the core 1 (the portion indicated by arrow B in FIG. 3). In this case as well, if the gate portion 6 does not protrude beyond the maximum outer circumferential surface of the core 1, there is no need for post-processing by grinding the gate portion 6, so there is no substantial problem in using the rotary transformer.

FIG. 5 is a sectional view showing another embodiment of the cores 1 and 2 manufactured by the rotary transformer manufacturing method according to the present invention.

In this embodiment, a plurality of concave grooves 7 are provided concentrically on the surface of the cores 1 and 2 on the opposite side to the coil grooves 1a and 2a, and the grooves 7 form a portion of the cores 1 and 2 excluding the outermost periphery. The thickness of the cores 1 and 2 is made uniform, thereby making it more difficult for the cores 1 and 2 to be deformed or warped during firing.

FIG. 6 is a cross-sectional view showing still another embodiment of the core 2 manufactured by the rotary transformer manufacturing method according to the present invention, and FIG. 7 is an enlarged cross-sectional view taken along line C-C' in FIG. is a conductive paste that corresponds to a coil.

In these figures, the conductive paste 8 is applied to each coil groove 2a and the common coil extraction groove 2 before firing.
After being printed in each area b, they are simultaneously baked under the same conditions as firing. Therefore, compared to the conventional example in which a coil of a predetermined shape is adhesively fixed in the coil groove 2a and coil extraction groove 2b after firing, Productivity can be further improved. The method for forming a coil using the conductive paste 8 is such that the number of turns of the coil is 1.
It is suitable for the rotor side core 2 which requires only one turn, and in the case of the stator side core 1 which requires multiple turns, the coil 3 of a predetermined shape is inserted into the coil groove 1a and coil extraction groove 1b after firing, as in the conventional example. Needs to be fixed with adhesive. Furthermore, the method of forming a coil using the conductive paste 8 is extremely effective in the rotor-side core 2 according to the present invention, which has uniform heat shrinkage during firing, and is superior to the rotor-side core 2 formed by the conventional compression molding method. When applied, cracks are likely to occur due to uneven thermal contraction during firing, making it unsuitable.

In each of the above-mentioned embodiments, the manufacturing method according to the present invention was applied to a flat rotary transformer, but the manufacturing method according to the present invention was applied to a cylindrical (coaxial type) transformer as shown in FIG. Of course, it can be applied to rotary transformers. In the case of this cylindrical rotary transformer, the core shape is more complex than that of a flat rotary transformer, so conventionally the coil grooves were formed by machining after compression molding, and the surface was polished after firing. However, according to the present invention, the machining of these coil grooves and the surface polishing after firing can be omitted, so that a more remarkable effect is achieved in a cylindrical rotary transformer.

〔Effect of the invention〕

As explained above, according to the present invention, since the degree of filling of the raw material in the mold can be made uniform by the injection molding method, deformation or warpage does not occur in the core during subsequent firing, and therefore, The surface polishing process of the core after firing, which was conventionally indispensable, can be omitted, and an inexpensive rotary transformer can be provided.

[Brief explanation of drawings]

FIG. 1 is a process diagram showing an example of the method for manufacturing a rotary transformer according to the present invention, FIG. 3 is a plan view of a stator side core manufactured by the manufacturing method according to the present invention, FIG. 4 is a sectional view taken along line A-A' in FIG. 3, and FIG.
The figure is a sectional view showing another example of the core manufactured by the manufacturing method according to the present invention, and FIG. 6 is a further example of the rotor-side core manufactured by the manufacturing method according to the present invention. 7 is a sectional view taken along the line C-C', FIG. 8 is a sectional view of the flat rotary transformer to which the present invention is applied, and FIG. 9 is a plan view of the stator side core thereof. Fig. 10 is a plan view of the rotor side core, Fig. 11 is a sectional view of the cylindrical rotary transformer to which the present invention is applied, and Fig. 12 is the relationship between the magnetic permeability μ of the core and the coupling coefficient K in the rotary transformer. FIG. 1, 2...Core, 1a, 2a...Coil groove, 1
b, 2b... Coil extraction groove, 3, 4... Coil,
5... Concave portion, 6... Gate portion, 7... Concave groove, 8...
...Conductive paste.

Claims (1)

[Claims] 1. A method for manufacturing a rotary transformer comprising a stator-side core having a coil groove and a rotor-side core having a coil groove and facing the stator-side core via a predetermined magnetic gap, in which soft ferrite magnetic powder is After heating and kneading ~50% by volume of binder to obtain a slurry-like raw material, this raw material is injected into a mold to form a core body with coil grooves. ~500℃
A method for manufacturing a rotary transformer, characterized in that the core is manufactured by degreasing at a temperature of 1000 to 1400°C and further firing at a temperature of 1000 to 1400°C.