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Патент USA US2132594

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Oct. 11, 1938.
M. J. ARYIN
‘2,132,594
VARIABLE RES I STANCE DEVICE
Filed Oct. 31, 1936
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INVENTOR
UAR/0N
J ARV/N
BY
ATTORNEY
Patented Oct. 11, 1938
.
-
2,132,594
UNITED STATES PATENT OFFICE
, 2,132,594
VARIABLE RESISTANCE DEVICE
Marion J. Arvin, Indianapolis, Ind., assisnor to
P. R. Mallory & 00.. Inc., Indianapolis, Ind., a
corporation of Delaware
'
Application October 31, 1936, Serial No. 108,588
5 Claims.
This invention relates to resistance devices
and more particularly to variable devices com- '
prising an arcuate resistance element and a mov
ing contact therefor.
An object of the present invention is to improve
the construction of such devices.
Other objects of the invention will be apparent
from the following description and accompanying
ll)
drawing taken in connection with the appended
claims.
The invention comprises the features of con
struction, combination of elements, arrangement
of parts, and methods of manufacture and opera
tion referred to above or which will be brought
out and exempli?ed in the disclosure hereinafter
set forth, including the illustrations in the draw.
ing.
In the drawing:
Figure 1 is a face view of a variable resistance
device embodying one form of the present in
.vention;
.
Figure 2 is a section on the line 2-—2 of Figure
1, and .
Figure 3 is a perspective view of a spring wedge
for said device.
While a preferred embodiment of the inven
tion is described herein, it is contemplated that
considerable variation may be made in the meth
od of procedure and the construction of parts
without departing from the spirit of the inven
tion. In the following description and in the
claims, parts will be identi?ed by speci?c names
for convenience, but they are intended to be as
3
generic in their application to similar parts as
the art will permit.
In variable resistance devices, rheostats or po
tentiometers, particularly those comprising a
relatively costly and it is necessary to shape the
terminals so that they will clamp positively on
the ends of the resistance element. The use of
a solid wedge between the ends of the strip of in
sulating material is unsatisfactory because of Cl
loosening as a result of heating or drying out of
the insulating strip, with a resultant tendency
toward shrinkage.
{
In accordance with the present invention a
positive permanent anchoring means is provided 10
for the resistance element comprising a spring
member interposed between the ends of the ele
ment so as to hold the parts together under com
pression at all times.
Referring to the drawing, Figure 1 shows a 15
' face view of a variable resistance device in, with
the cover removed and Figure 2 shows a sec
tion through this device showing the details of
the improved spring wedge arrangement of the
present invention. The device ill comprises a
metal shell or cup I I having a cylindrical side
wall [2 and a ?at end wall I3. Disposed with
in.she1l l l and resting against the walls thereof
are lining members of sheet insulating material,
such as sheet Bakelite, one of said members com- 25
prising a disc I‘ disposed against end wall l3
and the other of said members comprising a cy
lindrical strip l5 disposed against the cylindrical
wall l2 of the cup.
The resistance element It, comprising a re- 3
sistance wire I‘! wound on a Bakelite strip I8, is
bent into generally cylindrical shape so as to ?t
within cup “with its outer surface against lin
ing member [5 and one of its edges against lining
member I‘. A pair of terminal lugs I9 and 20 35
pass through openings 2| and 22 in wall l2 of
the cup and through openings in lining member
I5, the inner ends of lugs l9 and 20 making elec
trical connection with the respective ends of the
resistance winding IT. A third terminal lug 23 40
passes through the wall of the cup and between
the ends 24 and 25 of strip I 8 and connects to
winding of resistance wire, such as are used for
volume controls in radio sets, the resistance ele
ment is commonly enclosed within a cylindrical
casing. It is a common practice, for example,
to wind the resistance wire on a strip of insulat
lng material, such as uncured Bakelite fibre, , rotatable contact member 26 in the center of the
which is then bent into a circular shape to con
cup. Member 26 carries a sliding contact por
45 form to the inside wall of a cup or housing. Since
tion 21 which slides along the free edge of re
_ the housing is usually formed of metal, it is nec
essary to provide a lining of insulating material
between the wall of the housing and the circular
Cl C
‘resistance element. It is also necessary to secure
the element within the housing in some positive
manner so that it will not become loose during
operation or after long periods of time. Various
methods have been used in the past for securing
the resistance element within the housing, such
These methods are
65 ‘as riveting and clamping.
sistance winding l‘! for varying the resistance
45
of the device.
In order to hold the resistance element securely
in place at- all times, spring wedge 28 (see Fig. 3)
is inserted between the ends 24 and 25 of strip I8. 50
Spring wedge 28 comprises a U-shaped piece of
spring metal, such as bronze or the like. The
wedge 28 is preferably formed with small pro
jections 29 and 30 on the outside edges of the
arms of the U, at the ends\thereof, which pro- 5;
2,132,594
2
jections become embedded in the ends of strip l8
when the spring wedge is forced into position.
Projections 29 and 30 may merely comprise the
burr, incident to shearing the metal used to form
the U-shaped spring element.
Since strip I8 is commonly formed of Bakelite
or some other synthetic resin material or resin
impregnated ?bres, it may have a tendency to
shrink upon heating or drying out. The spring
10 wedge 28 is inserted between the ends of the
element under compression so that it applies
a constant expanding force to the element l8,
thereby tending to hold the entire element se
curely against the wall of the well. Should the
element shrink at any time during its life, the
spring wedge will expand and remain pressed
?rmly against the ends so as to maintain the ele
ment securely wedged within the case at all
times.
With this arrangement, it may, in some in
20
stances, be unnecessary to form a special con
nection between terminals i9 and 20 and the
vwire of the resistance element since the pres
sure of the spring wedge will normally be suffi
cient to hold the ends of the resistance winding
?rmly against the terminal members.
While the present invention, as to its objects
and advantages, has been described herein as
carried out in speci?c embodiments thereof, it is
30 not desired to be limited thereby but it is intend
ed to cover the invention broadly within the
spirit and scope of the appended claims.
I claim:
1. A variable resistance device comprising a
35 cylindrical casing and a resistance element there
in, said element comprising a strip of material
bent to conform to the cylindrical wall of said
casing with the ends thereof spaced apart along
the wall of said casing and a U-shaped spring
wedge between said ends with the arms thereof
disposed in engagement with said ends and held
in compression by said ends.
.
2. The combination with an enclosing cup hav
ing'a circular wall; of a generally circular re
sistance unit surrounded by the circular wall of.
45
the cup and having adjacent end portions; and
a spreading device engaging said end portions
and exerting expanding action upon the resist
ance unit in a circular direction to press the re
sistance unit against the circular cup wall to
50 hold the resistance unit in assembly with the cup,
said spreading device comprising a U-shaped
spring wedge inserted between said end portions
with the arms thereof in engagement with the
55
end portions and held under compression solely
by engagement with said end portions.
3. A variable resistance device comprising an
enclosing cup having a cylindrical wall, a resist
ance unit surrounded by the cylindrical wall of
the cup and comprising a strip of sheet insulat
ing material and a winding of resistance wire
thereon, said unit being bent into generally cy
lindrical shape with the ends thereof adjacent
each other, and a spreading device engaging said
ends and exerting expanding action upon the
resistance unit in a circular direction to press 10
the resistance unit against the circular cup wall
to hold the resistance unit in assembly with the
cup, said spreading device comprising a U-shaped
spring wedge with the arms of said wedge dis
posed along said ends, said wedge being held un- '
der compression by engagement with said end
portions.
_4. A variable resistance device comprising an
enclosing cup having a cylindrical wall, a resist
ance unit surrounded by the cylindrical wall of 20
the cup and comprising a strip of sheet insulat
ing material and a winding of resistance wire
thereon, said unit being bent into generally cylin
drical shape with the ends thereof adjacent each
other, and a spreading device engaging said 25
ends and exerting expanding action upon the _
resistance unit in a circular direction to press
the resistance unit against the circular cup wall
to hold the resistance unit inassembly with the
cup, said spreading device comprising a U-shaped 30
spring wedge with the arms of said wedge dis
posed along said ends, said arms having pro
jections embedded in said ends, and said wedge
being held under compression by engagement
with said end portions.
5. The combination with an enclosing cup
having a circular wall, of a generally circular
resistance unit surrounded by the circular wall
of the cup and having adjacent end portions, said
resistance unit having a tendency to shrink with 40
age or change of condition, and a spreading de
vice engaging said end portions and exerting ex
panding action upon the resistance unit in a
circular direction to press the resistance unit
against the circular cup wall to hold the re
sistance unit in assembly with the cup, said
spreading device comprising a U-shaped spring
wedge inserted between said end portions with
the arms thereof in engagement with the end
portions and heldunder compression solely by E
engagement with said end portions, said spring
wedge being under su?cient initial compression
to maintain pressure against said ends after
shrinkage of said strip of material and without
subsequent adjustment.
'
MARION J. ARVIN.
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