Method for winding an inner coil of a transformer

This method is for winding an inner coil of a transformer, the transformer including a ferrite core with an inner groove for receiving the winding, the ferrite core being provided with a radial inlet groove for feeding in and feeding out of the winding wire. The wire is fed through a winding mandrel with a transverse longitudinal bore. The ferrite core is pushed onto the winding mandrel and moved rotatably and axially, thereby forming the inner coil in the inner grove of the ferrite core.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to a device for winding an inner coil of a 
transformer, the transformer of the inner coil including a ferrite core 
with an inner groove for receiving the coil, the ferrite core being 
provided with a radial inlet groove for feeding in and feeding out of the 
winding wire. 
2. Description of the Prior Art 
It is known in the prior art to employ rotating head wheels with one or a 
plurality of heads in video recorders or recorder for digital recording 
and replay of signals to or from a magnetic tape. Thereby the signals are 
recorded by means of oblique tracks on the magnetic tape. It is further 
known to employ rotary transformers to communicate the signals between a 
head wheel and the stationary part of a head drum. These rotary 
transformers typically include a stationary part which is associated with 
the stationary head drum and a part associated with the rotating head 
wheel and rotating therewith. Both the stationary and the moving parts 
include a coil. A head drum arrangement must have as many transformers as 
there are heads on the head wheel. 
For example, the use of such transformers is disclosed in laid open patent 
DE-A1-38 10 037. The transformers disclosed therein include inner and 
outer ferrite cores, each of which include a coil. The signal 
transformation and communication is performed radially between the ferrite 
cores mounted in the outermost stationary part and the ones mounted in the 
inner rotating part. 
Due to the miniaturization of head drum units as well as the increased 
frequency range to be handled and due to the increased numbers of 
transformers, the size of the transformers must be reduced. This results 
in higher accuracy requirements for the transformers. This concerns the 
ferrite cores themselves to a certain extent, for example, the slot 
between the outer and inner core and, on the other hand, the coils. The 
coils of a very thin wire (for example, at a magnitude of 0.15 mm. 
diameter) must be wound very accurately in a very tight space. In order to 
mount a coil of a specific defined shape in a ferrite core, supporting 
auxiliary means may be used. 
A rotary transformer for a recorder is disclosed in DE-A1-38 31 721 which 
employs a radially acting transformer. In this case, a plastic core with 
grooves is employed for the accurate guiding of the wire winding, which 
can be easily made and which assures a high degree of accuracy of the 
winding of the coil. 
However, the use of such an auxiliary means is rather expensive. Moreover, 
the handling of a plastic core of such small dimension is also very 
difficult. 
The placement of coils directly into a winding groove of ferrite core of an 
axial transformer is disclosed in DE-A1-36 26 275. With this device, a 
wire coil is wound in an axial groove in the plane surface of a ferrite 
core. This is performed with the assistance of a rotating winding disk 
which is mounted concentrically to the ferrite core, into which the 
winding wire is introduced through a guide slot. The purpose of this 
device is to replace preassembled coils which cannot be inserted into the 
winding groove because of large tolerances. 
OBJECTS AND SUMMARY OF THE INVENTION 
It is an object of the invention to provide a device to make the coil of 
the outer core of a transformer with a high degree of accuracy in a very 
simple and economical manner. Thereby, the winding wire should be mounted 
into the inner groove of the outer core without any further additional 
parts. 
This object of the invention is solved by a device for winding an inner 
coil of a transformer, the transformer of the inner coil including a 
ferrite core with an inner groove for receiving the coil, the ferrite core 
being provided with a radial inlet groove for feeding in and feeding out 
of the winding wire. 
The device in accordance with the invention inserts a coil into the inner 
groove of a ferrite core of a radial transformer. This is necessary 
because the insertion of a prewound coil into an inner groove is very 
difficult, on the one hand, and that the accuracy of the inner diameter of 
the coil must be very high, on the other hand.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings in detail wherein like numerals indicate like 
elements throughout the several views, one sees that FIG. 1 illustrates 
the sectional view of an outer or ferrite core 2 of a transformer with an 
inner groove 3 and a coil 4 made in accordance with the present invention 
device. The head end 9 or beginning of coil 4 and the tail end 10 of coil 
4 are guided to the outside of the coil 4 through inlet groove 5. The 
coil, which includes one or a plurality of coils is, sealed into a unit by 
heating or baking of an adherence layer which is applied according to the 
prior art on the winding wire immediately after the winding is completed, 
whereby the winding mandrel 7 remains in place. Thus it is assured that 
the inner diameter of coil 4 conforms with the diameter of ferrite bore 
11. This requires a high degree of accuracy, since in the slot in the 
completed transformer there must be only 25 micrometers between the inner 
and outer core. 
FIG. 2 illustrates a sectional view of the outer core 2 with the coil 4. In 
this exemplified embodiment the coil includes three coils. More or fewer 
coils may be used. The coil head end or beginning 9 feeds through inlet 
groove 5 into the inner groove 3 of the ferrite core 2. After the winding 
wire 6 has formed the desired number of the windings, the coil tail end 10 
is fed through the inlet groove 5 and out of the ferrite core 2. The inlet 
groove 5 is so shaped that the coil head end or beginning 9 and the coil 
tail end 10 are positioned side by side and do not cross over each other. 
FIG. 3 illustrates an example of the present invention in a partial view. A 
ferrite core 2 is mounted onto a winding mandrel 7. The coil 4 has been 
already partially performed. The mode of operation of the device in 
accordance with the invention is as follows: The winding wire 6 is fed 
through a transverse longitudinal 8 bore of winding mandrel 7. Before the 
start of winding, the ferrite core 2 is pushed onto the winding mandrel 7 
in such a manner that the exit of the winding wire 6 from the transverse 
longitudinal bore 8 combines in the same position with inlet groove 5. The 
ferrite core 2 is then pushed until the winding wire 6 engages on a flank 
of inner groove 3. Thereby, the coil head end or beginning 9 extends from 
the ferrite core 2 through the inlet groove 5. The ferrite core 2 is then 
picked up by a part of the device (here not shown in detail) on its outer 
diameter and clamped and is rotated by this device part around the winding 
mandrel axis. The ferrite core thereby performs a continuous movement in 
the axial direction which corresponds to the winding wire diameter during 
each rotation of the ferrite core. In this manner the individual coils are 
wound in a tight engaging manner. 
In another type of embodiment, the axial movement can naturally also be 
performed by the winding mandrel 7. When the desired number of coils is 
achieved, the end of the wire is lifted and cut off to the desired length 
of the winding tail end 10. The diameter of the winding mandrel 7 is only 
slightly smaller (in the micrometer-range) than the diameter of the 
ferrite bore, so that the inner diameter of the coil 4 substantially 
conforms with the diameter of the ferrite bore. 
In FIG. 4, the device is illustrated in the direction of arrow A of FIG. 3. 
Thereby, the ferrite core 2 is shown in a sectional view. The coil head 
end 9 is already moved out of the ferrite core 2. The winding wire 6 moves 
through the transverse longitudinal bore 8. The ferrite core is moved into 
a rotational movement in the direction of the arrow and the individual 
coils are thereby made. Thereby, the winding wire 6 is fed thereafter 
through the transverse longitudinal bore 8. Naturally, the inventive 
device may be designed in such a manner that the ferrite core 2 is 
stationary and the winding mandrel 7 rotates. 
Thus the several aforementioned objects and advantages are most effectively 
attained. Although a single preferred embodiment of the invention has been 
disclosed and described in detail herein, it should be understood that 
this invention is in no sense limited thereby and its scope is to be 
determined by that of the appended claims.