Electrical coil with tap transferring to end-layer position

Disclosed is a coil including winding support means for supporting a base layer of wire including a first predetermined number of turns wound in a precision pattern about the support means. A wire tap layer is wound about the support means at an average pitch ratio substantially equal to a second predetermined number of turns for the tap layer divided into the first predetermined number of turns. A tap of wire is then taken from an end of said wire tap layer. Finally, a subsequent wire layer is wound over and in an opposite direction to the tap layer, wound at an average pitch ratio substantially equal to the first predetermined number of turns in the tap layer divided by the difference between the first predetermined number of turns and the second predetermined number of turns. The present invention is also directed to a method of winding a coil.

FIELD OF THE INVENTION 
The present invention relates to electrical coils. More particularly, the 
invention is directed to coils having taps made at an end-layer position, 
and a method for making such coils. 
BACKGROUND OF THE INVENTION 
Winding of coils for transformers is a well known art and many different 
transformer configurations have been used in the past and are available 
today. Typically, a transformer coil includes a bobbin having a number of 
layers of wound wire, each layer of wound wire applied over a prior layer 
of wound wire. 
In the manufacture of coils, it sometimes becomes necessary to tap a lead 
from an intermediate layer of wound wire, i.e., a layer wound about the 
bobbin, onto which an additional layer or layers are to be wound. The 
previously available process for tapping such a lead from the coil during 
manufacture is rather cumbersome. For example, if a tap is to be made at a 
point midway across a layer of wound wire, the winding process must be 
halted in order that a certain amount of wire can be unwound from the wire 
feed spool and from the transformer coil bobbin itself. The two wire ends 
are then secured by twisting and anchoring them outside of the winding 
area of the coil bobbin. 
The winding process is then resumed at the point on the layer where the tap 
was made. The winding for that layer proceeds until the end of the layer 
is reached. Winding then stops again, so that spacers may be attached to 
the bobbin in such a manner that the difference in height between the 
pre-tap portion of the wound coil and the post-tap portion can be 
eliminated. The subsequent layer is then wound over the tapped layer and 
the spacers. The winding process at this stage is slow and often results 
in a misalignment of layers on wound over the tapped layer. In the 
situation where a precision winding pattern is required, the tapping 
process described above often adversely effects the precision of the 
pattern, resulting in a high reject rate. As used herein, the term 
"precision winding" means that the wire in each layer makes the same 
number of turns, and the turns of successive layers are not randomly 
placed but are neatly stacked or nested one on top of another. Each turn 
of wire is wound immediately adjacent the wire of the previous turn, in a 
generally spiral pattern about the bobbin core or other winding axis. The 
winding pattern is not strictly spiral. Rather, the wire is would normal 
to the winding axis about most of the winding axis; the wire advances to 
the next position at a crossover point. In the case of a rectangular 
bobbin, the wire is wound normal to the axis for three of the four sides 
of the bobbin. Between the third and fourth corners of the rectangle the 
wire is angled to rest adjacent the wire from the previous turn at corner 
4. This pattern is repeated throughout the winding of the layer, such that 
the turns are parallel to one another for three of the four sides of the 
bobbin; the crossover point is consistently on one side of the bobbin. 
OBJECTS OF THE INVENTION 
It is an object of the present invention to provide an inductance coil in 
which taps can be made at any layer of the coil, and all subsequently 
would layers maintain any desired precise winding pattern. 
An additional object is provide an inductance coil having intermediate taps 
taken at the end of a predetermined layer by changing the winding pitch of 
the wound layer on which the taps are taken. 
An additional object is to provide a coil for an inductor or transformer 
having an intermediate tap at the end of the layer in which all layers are 
of equal thickness. 
SUMMARY OF THE INVENTION 
These and other objects are met by the present invention directed to a coil 
including winding support means for supporting a base layer of wire 
including a first predetermined number of turns wound in a precision 
pattern about the support means. A wire tap layer is wound about the 
support means at an average pitch ratio substantially equal to a second 
predetermined number of turns for the tap layer divided into the first 
predetermined number of turns. A tap of wire is then taken from an end of 
said wire tap layer. Finally, a subsequent wire layer is wound over and in 
an opposite direction to the tap layer, wound at an average pitch ratio 
substantially equal to the first predetermined number of turns in the tap 
layer divided by the difference between the first predetermined number of 
turns and the second predetermined number of turns. 
The present invention is also directed to a method of winding a coil.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to the drawings, and in particular, FIG. 1, there is shown a 
conventional rectangular-shaped bobbin 10 for a coil which is to be used 
in the inductor, transformer or other similar device. The bobbin 10 is 
made of any suitable insulating material, e.g. plastic, and has a center 
core 12 with a through opening 14 into which the arbor of the winding 
machine (not shown) is inserted. Flanges 16 and 17 are provided at each 
end of core 12. 
Electrically conductive wire 20 is wound about the predefined winding axis 
of core 12. FIG. 1 shows such a winding which is made in a precision 
pattern. As seen, the wire 20 is spirally wound about the core 12. The 
winding is typically started at one end of the core, e.g., adjacent flange 
16. The wire is then wound in a continuous spiral pattern with each turn 
of the wire lying adjacent to the previous turn. For a rectangular-shaped 
bobbin, the wire is spirally wound by winding wire 20 normal to the 
predefined winding axis for three sides of the rectangle. Between two 
successive corners, e.g. the third and fourth corners, wire 20 skips from 
a parallel path at the third corner to a position adjacent the wire 
previously laid down at the fourth corner. The wire is then wound normal 
to the predefined winding axis for the succeeding three corners. 
The winding continues until the opposite end of the core is reached (e.g., 
at flange 17), thereby defining a layer. Wire 20 is generally of circular 
cross-section and uniform diameter, but wire of other geometric shapes can 
be used. Thus, when the first layer is wound about core 12, a surface 
consisting of a series of alternating convex ridges and concave grooves is 
created. A second layer is then started by continuing winding of wire 20 
into the first groove adjacent the last turn of wire in the underlying 
layer. The turns of the second layer are laid in the series of grooves 
defined by the spirally wound wire of the underlying layer. The process 
continues for each subsequent layer until the desired number of turns have 
been wound about the core. Similarly, on the next layer, the turns are 
laid in the space between each two turns of the next layer. 
As shown in FIG. 1, often times a tap 23 is made in one of the intermediate 
layers, sometimes at the mid-point of such a layer, in order to impart 
desired electrical characteristics to the coil. Often a coil must have a 
specific number of turns, at which point a tap must be made. Depending on 
the length of core 12 and the thickness of wire 20, this tap point may 
occur anywhere along a layer, at which point, the wire is conventionally 
pulled against the direction of winding, generally perpendicular to the 
winding towards the outside of the coil to allow any electrical 
connections to be made. The wire is then drawn back (as wire 22) to the 
point of winding where the tap was made, and winding continues. Thus, a 
tap includes interrupting the winding of a coil after a predetermined 
number of turns have been wound, extending the winding wire towards the 
end of the core and outside of the coil, extending the same or a different 
length of wire from the outside of the coil towards the point of winding 
where the tap was taken, and resuming winding layers until the next tap 
point, if any, is reached. Depending on the specifications for a 
particular coil, one or more additional layers may be laid on top of the 
layer in which the tap was made. As can be easily understood and seen in 
FIGS. 1, 2 and 2a, the tap causes an unevenness in the layer having the 
tap, because the turns wound into the core after the tap is made must wind 
over the lengths of wire drawn perpendicular to the windings to and from 
the outside the coil for the tap. Additional layers wound over the tap 
layer cannot be smoothly wound onto the core because the series of 
alternating grooves and ridges formed by a wound layer, and relied on to 
guide the winding of subsequent layers, are disrupted when a tap is made. 
As shown in FIG. 2a, the unevenness caused by making a tap is smoothed 
somewhat by providing a spacer arch 19 to rest over the wires 22 and 23. 
However, even with a spacer arch the winding of wire is irregular, and 
precision winding is not possible. 
FIGS. 3-4, and 5-6 show a transformer coil which is wound in accordance 
with the present invention. Here, a number of layers are wound in the 
manner shown in FIG. 1 up to the point where the tap is to be made. 
If it is determined, for example, that the desired number of turns will 
occur at the mid-point of the next layer, (and a tap made at that point) 
then the winding of the layer to be tapped is altered according to the 
present invention. 
If the tap is to be made at the mid-point, i.e., at half the number of 
turns available for the layer, then the pitch of the winding is increased 
two-fold. Referring to FIG. 3, the wire 24 being wound is laid into 
alternating grooves, crossing over alternating ridges once per revolution 
about the core 12 (i.e., once per turn), generally between the third and 
fourth corners of the rectangular bobbin. In this manner, when the entire 
layer is wound, it will contain only half the number of turns it would 
have had if the pitch had not been increased two-fold. Thus, at the end of 
this tap layer, the tap 26 can be made at the end of the layer, such that 
no wire traverses the coil perpendicular to the windings. 
The wire at the end of the tap layer can be drawn through an opening 28, 
such as an aperture or slot, in the wall of flange 16 or 17 to enable the 
tap to be made. 
Thereafter, the wire drawn back to the core, optionally through opening 28, 
or another opening, and a subsequent layer is laid down in the opposite 
direction as the tap layer. The pitch of the wire 25 in this subsequent 
layer is the same as the pitch of the preceding layer, i.e. double the 
pitch of a non-tap layer. As shown in FIG. 3, this layer is wound into the 
grooves of the first layer not filled by the tap layer, and the windings 
of the tap layer are crossed, once per turn. From a groove at the third 
corner, two ridges are skipped and the wire settles into the groove at the 
fourth corner. When this subsequent layer reaches the end of the core at 
the opposite flange of the bobbin from whence the tap was taken, the 
original series of alternating ridges and grooves is created and any 
number of additional layers can be wound at normal pitch. If any 
additional taps are desired, the procedure described above can be used as 
many times as is practical. 
From a numerical point of view, for example, assume that there are to be 66 
turns of wire on a layer and the tap is to be taken at the mid-point. On 
the first layer of double pitch, there would be about 33 turns and the tap 
would be taken at the end of the layer. On the next layer, there would be 
33 turns going in the opposite direction from the tap layer. Thereafter, 
the winding is resumed back to 66 turns per layer. 
If the layer included an odd number of turns, e.g. 65 turns of wire per 
layer, a tap can still be taken at the mid-point. Here, the tap layer 
might have 32 turns would at double pitch and the subsequent layer would 
have 33 turns would in the opposite direction at double pitch. Conversely, 
the tap layer could be wound with 33 wires and the subsequent layer would 
have 32 turns. 
If an additional tap is to be pulled, at a subsequent layer, the same 
procedure would be followed as described previously. 
The invention as previously described assumes that the tap is to be made at 
the mid-point. However, the invention is not limited to this particular 
tapping procedure or location. For example, if it is determined that the 
tap is to be made at a point one-third the way through a normal layer, 
then those one-third turns would be wound onto the core, but at triple the 
pitch. The tap would then be taken. Thereafter, on the next layer going 
back in the opposite direction, the remaining number of turns which were 
not taken off during the tap layer would be laid down. Thus, if 22 turns 
were laid down for the tap layer, then the next layer would contain 44 
turns. Thereafter, the layers continue with the standard number of turns 
(66) in the example being described. 
The same situation would obtain in the opposite case. For example, if the 
tap is to be taken at two-thirds of a normal layer, instead of either 
one-half or one-third of the layer. Using the example of 66 turns per 
normal layer, the tap would be taken after a layer having a pitch such 
that 44 turns would fill the space between the two flanges on the bobbin. 
On the next layer in the opposite direction, the remainder of a full layer 
would be laid down, e.g. 22 turns in the above example. Thereafter the 
winding process would continue in the normal manner. 
It can be seen that as a general rule the average winding pitch ratio of 
the tap layer and the subsequent layer can be easily calculated as 
follows: 
##EQU1## 
where, n=number of turns of normal, base layer, and 
Y=number of turns in tap layer. 
This formula can be used to calculate the average pitch ratio for any 
number of turns in a tap layer. Thus, referring to FIG. 5, for example, 
the base layer has 9 turns, i.e., n=9 wound at a pitch of 1. If a tap is 
to be taken after a one third of the number of turns of a normal, or base 
layer, then the tap layer would contain only 3 turns of wire 24. Thus, 
according to the formula above, Y=3. To ensure that tap layer is evenly 
wound about the core, ending at the opposite end from the starting point, 
the average pitch ratio is calculated according to the formula above: 
##EQU2## 
As shown in FIG. 5 the tap layer 24 is wound at an average pitch ratio of 
3; the wire is laid into every third groove, once per turn. The subsequent 
layer 26 is calculated as: 
##EQU3## 
Thus, as shown in FIG. 5, the subsequent layer 26 is wound with a average 
pitch ratio of 1.5. However, it is not feasible to wind the layer with any 
non-integer pitch ratio because a non-integer pitch ratio involves winding 
angles which would not deposit wire directly into grooves of the preceding 
layer. This occurs because non-integer pitch ratios involve moving the 
wire at fractional (non-whole number) wire diameters. For this reason, the 
term "average pitch ratio" is used. Thus, where a average pitch ratio of 
1.5 is required, the wire is wound by an alternating pitch ratio of 1 and 
2, throughout the layer. The average of 1 and 2 is 1.5. In this manner, 6 
turns of layer 26 will be made. 
The winding of the coils of the present invention can be carried out by a 
winding machine, particularly one which is computer controlled and which 
can be programmed in the appropriate manner. That is, the program 
basically would be one which would wind the number of turns up until the 
layer of the tap is to be taken. Thereafter, the winding pitch would be 
increased so that the required number of turns, fewer than the full number 
for a layer, would be wound between the two flanges of the bobbin. The 
machine would then stop, or would be manually stopped by the operator, and 
the tap made. Thereafter, the machine would resume going back in the 
opposite direction to lay down the subsequent layer with the required 
number of turns to make up the total of the normal layer and thereafter 
continuing with the winding of the normal layer and the standard number of 
turns in such a layer. 
The coil and process for winding the same as described above has 
substantial advantages over the prior art. First of all, substantial 
saving of labor are realized since the operator does not have to stop the 
machine at a mid-position on a layer, perform anchoring and spacing steps 
and thereafter start the winding again. Also, the intermediate tapping 
point on a layer is eliminated since all taps can be made to occur at the 
end of a wound layer, at the flange of the bobbin. This results in a coil 
which has no enlarged, uneven projections on any given layer. 
Consequently, the winding pattern is not disturbed and better electrical 
characteristics are achieved with fewer rejected coils. 
The description above teaches the inclusion of a tap layer over a normal 
layer. Depending on the type of bobbin employed it is possible to include 
a tap layer as the first layer, i.e., before a normal layer has been wound 
onto the bobbin. This can be done where a "pre-grooved" bobbin is 
employed. Bobbins often include scoring or grooves, equally spaced and of 
the same diameter as the wire to be wound, located at each corner of the 
rectangular bobbin. Conventionally, the scoring is included to help guide 
the wire about the bobbin for winding the first layer for precision 
winding of a coil. This scoring can also be used for winding a tap layer 
as the first layer in a coil constructed according to the present 
invention. The scoring will retain the wire wound at a pitch ratio other 
than 1. 
The above description of the invention relates to winding a coil about a 
bobbin. The invention can also be used in applications where no bobbin is 
used: i.e., self-supporting coils. A self-supporting coil is 
conventionally constructed by winding wire about a collapsible, 
rectangular mandrel. Usually the mandrel is scored with grooves as 
described above. In use, the mandrel is provided in a normal, 
non-collapsed condition during winding. After the coil has been wound and 
any taps according to the present invention have been taken, collapsing 
means of the mandrel are activated to enable the wound coil to be 
withdrawn from the mandrel without disturbing the coil structure. The 
result is a self-supporting, bobbinless coil. 
As can be seen, in accordance with the invention, an arrangement is 
provided for winding the tap so that it occurs at the end of the layer. 
The winding quality is consistently good. In addition, the coil can be 
wound using a computer controlled winding machine. The rejects resulting 
from this winding process are practically eliminated.