AU427996B2 - Variable resistor and method of making same - Google Patents

Description

23, 144/70 This invention relates generally to varibale resistors

and, more particularly, to a sealed variable resistor hav-

ing an in-situ molded housing and the method of making the

same, Variable resistors of all types and particularly

miniature potentiometers are well known in the prior art

and have been used for long periods of time. These devices

and particularly the miniature potentiometers must be

sealed from the ambient atmosphere to preclude the entry

of foreign contaminants which might interfere with the

mechanical or electrical functioning of such devices. The

housings of such prior art devices have traditionally been

made of several parts, preferably of plastic, which are

brought together and bonded. by the use of various well-

known adhesives. The use of such adhesives necessitated much

hand assembly operation which not only increased the cost of

manufacture of-such devices but also in many instances

lowered the quality thereof. As is also well known in the

prior art, the use of adhesives for such bonding purposes

presented low-voltage breakdown areas which for many operat-

ions are not desirable.

In order to further accomplish the desired seal, part-

icularly between the rotating portions extending externally

of the housing of the device for adjustment purpdses and the

housing, an 0 ring is normally utilized. As is well known,

such 0 rings are inserted into a groove formed within a

portion of the housing and are then compressed by being

brought into contact with a section of the housing. Such

operations require hand assembly thus again increasing the

cost of the device. Furthermore, as is well known, such 0 427996

23 144 no rings are subject to inherent material flaws, to ageing which causes the seal of the 0 ring to become defective, and to misalignment of the 0 ring with the grooves provided for .it. Such prior art devices also by necessity were manu- factured utilizing a multitude of parts in order to accomp- lish desired electrical and mechanical functioning thereof. Such multitude of parts not only increased the cost of manufacture but at the same time inherently decreases the reliability of the device. It is an object of the present invention to provide a variable resistor which accomplishes a seal between the internal parts of the variable resistor and the outside ambient atmosphere while obviating the prior art sealing', problems. It is another object of the present invention to provide a variable resistor which includes a housing that is sealed from the ambient atmosphere without the use of adhesives. It is another object of the present invention to provide a method of manufacturing a variable resistor which: is simple, efficient and inexpensive and results in a superior, more reliable variable resistor than those pre- sently in existence in the prior art. With the above stated objectives in view there is provided according to the invention:- A variable resistor comprising a base member of electrically non-conductive material carrying a resistance element and electrically conductive leads connected to said resistance element; a rotor of electrically non-conductive 4 7996

23, 14 4 no material carrying an electrically conductive contact element

and having adjusting means; shroud means engaging said base

member and said rotor and urging said contact element into

contact with said resistance element, said rotor means in

eluding a resiliently deformable means extending outwardly

therefrom into engagement with said aligning means. A practical arrangement of the invention both as to

its organization and method of operation will become appar-

ent from a consideration of the following description taken

in conjunction with the accompanying drawing which is pre-

sented by way of example only and is not intended as a

limitation upon the scope of the present invention and in

which: Figure I is a perspective view of a completed vari-

able resistor constructed in accordance with the present

invent ion;

Figure 2 is an exploded view, partly in cross-section,

of some portions of a variable resistor constructed in

accordance with the present invention;

Figure 3 is a cross-sectional view of the elements

of a variable resistor as illustrated in Fig. 2 brought

together in aligned relationship within the cavity of a

mold prior to the formation of the in-situ molded housing;

and Figure 4 is a perspective view, partly in cross-sect- with the ion, of a completed variable resistor in accordance

structure and method of the present invention.

Referring now to the drawing and more particularly to a completed variable resistor in accordance Figure 1 thereof, shown generally at 10. The with the present invention is t 79 6

23,1444no variable resistor 10 is shown as a trimmer potentiometer

and includes a body or housing portion 11 having electric-

ally conductive pin members or leads 12, 13 and 14 extend-

ing therefrom. A rotatable adjusting means 15 is access-

ible from the exterior of the body portion 11 of the hous-

ing as is illustrated for purposes of adjusting the

electrical resistance of the potentiometer 10 in accordance

with that which is desired for any given application.

Referring now more particualarly to Fig. 2, the

internal construction of the potentiometer 10 is ilustrated

more in detail. As is shown in Fig. 2, a resistance element

21 is disposed on the upper surface 22 of a base member such

as sub-strate 23. In the presently preferred embodiment of

the present invention, the sub-strate 23 is constructed of

a ceramic material such, for example, as steatite. As is

illustrated in Fig. 2, the resistance element 21 may be

constructed of a partially conductive material applied as

a very thin layer by means well known to the art, to the

surface of the ceramic sub-strate 23. It should, however,

be expressly understood that the resistance element 21 may

be of any type desired for a particular application. For

example, a wire wound resistance element may be utilized in

which case the sub-strate or base 23 would be changed

sufficiently to receive that particular resistance element. The base 23 defines a centrally disposed bore 24

which receives an electrically conductivecenter post

As is illustrated in Fig. 2 the center post 25 is a cont-

inuation of electrical lead 26 which extends externally in

the finished product as one of the pin members 12, 13 or 14

as shown in Fig. 1. An additional lead 27 extends through 799 6 an opening (not shown in Fig.' 2) defined by the base nember 23 and makes electrical connecti on to one terminal portion 28 of the electrical resistance element 21. Similar elect- rical connection is made by a third electrical lead (not shown) to'the opposite terminal portion of the resistance element 21 as Is well known in the prior art. The base member 23 defines a notch or recess 29 which is utilized for alignment purposes as will become more fully apparent herein below. An electrical contact element 31 is provided for mak- ing movable electrical contact to the resistance element 21 and to the electrically conductive center post 25. The con- tact element 31 defines a centrally disposed aperture 32 which receives the center post 25. A tongue 33 is struck from the contact 31 and turned under and back and also defines an opening (not shown in Fig. which is aligned with the opening 32 and also receives the center post (This structure is more clearly seen in Fig. A plurality of openings 34~ are equally distributed about the contact 31 and are disposed to receive a like number of protrusions extending downwardly from the rotor as will'be more fully described hereinbelow. A stiffening rib 35 is -provided in the contact element to strengthen; the arm forming the fingers 36. The opening formed by striking the tongue 33 receives a protrusion extending down- wardly from the rotor, which protrusion is heat-deformed to rigidly secure the contact element to the rotor. Extend- ing also downwardly, from the general plane described by the contact member 31, are two contact fingers 36 ivhich make the movable electrical contact with the resistance element .427996

23,144no 21. The two contact fingers 36 are provided to assure

electrical interconnection between the center post 25 and

the resistance element 21 at all times.

The rotor shown generally at 41 includes'a body

member 42 having an upper surface 43 defining a slot or

kerf 44 adapted to receive an adjusting tool as is well

known in the prior art. The upper surface 43 and kerf 44 is illustrated at 15 in Fig. 1 as it relates to the overall

structure of the potentiometer 10. The body 42 of the rotor defines a stop means such as tongue 45 extending out-

wardly therefrom. As is well known in the prior art, the stop means may be eliminated if a continuously rotatable

potentiometer is desired. The body 42 of the rotor 41 def- ines a central bore 46 which is adapted to receive the

center post 25. Extending downwardly from the lower surface of the body member 42 is a protrusion 47 which extends

through the opening 35 and which is heat-deformed to secure

the contact member 31 to the rotor 41. A plurality of protrusions 48 also extend downwardly from the lower surface

of the body portion 42 of the rotor 41 and extend through

the openings 34 in thecontact member. The bottom surface of these protrusions 48 engage that portion of the top sur- face 22 inwardly of the resistance element 21 as shown at

22a when the potentiometer is in its fully assembled form. The purpose of such engagement is to stabilize the rotor and thus the contact fingers 36 upon the resistance element

21 to preclude accidental relative movement between the con-

tact fingers and the resistance element when an adjusting

tool is inserted into the kerf 44 or the potentiometer is

otherwise contacted. Thus the protrusions 48 function as

427996

44 /c a thrust bearing for the rotor 41. Extending radially outwardly from the body 4+2 of the rotor 41 is a flange 51 which terminates in an upwardly turned lip 52 having a curved upper surface 53. The flange 51 is resiliently deforsable and in its non-stressed state (as shown in Fig. 2) is angularly disposed in an upward dir- ection, as viewed in Fig. 2 clearly shown in dashed lines in Fig. 3) for purposes which will be more fully explained hereinbelow. Preferably the rotor is formed in such manner that the body 42 and flange 51 are integrally molded as a single unitary structure and preferably are made of a fiberglass filled plastic material which thus provides spring or resiliency to the rotor assembly and particularly to the flange 51. An aligning means or shroud member shown generally at 61 includes a body 62 which is octagonal in configurat- ion. It should, however, be understood that the body can have any geometric configuration desired without departing form the spirit or scope of the present invention. The body 62 defines at its upper end a collar 63 which in turn defines an opening 64 adapted to receive the upper portion of the body 4+2 of the rotor 41. The collar 63 is displaced inwardly from the outer surface of the shroud body 62 for a purpose to be more fully described hereinbelow. Internally of the

body 62 there is provided a stop lug 65 which cooperates with the stop tongue 4+5 on the rotor 4+1 to preduide the contact fingers 36 leaving the resistance element 21.* As was above pointed out, however, the stop lub 65 may be dispensed with. A plurality Of shoulders 66 and 67 are provided on the int- ernal surface of the body 62. Projecting downwardly from

4[2799

J, 14 4 no the shoulder 66 is a key 68 which mates with the recess

or notch 29 in the base 23 to thereby properly align the

resistance element 21 and the stop lug 65. A recess 69 is provided in the lower edge of the body 62 through which

one of the leads 26 -27 passes. Additional recesses similar to that illustrated at 69 are also provided for

the remaining leads.

The particular relationship of each of the parts des-

cribed above in detail with respect to Pig. 2 can be

better understood by viewing Fig. 3 to which reference is

hereby made.. As is illustrated in Fig. 3, the three major sub-assemblies of the potentiometer have been brought

together; the rotor is positioned upon the base by inserting the center post 25 into the bore 46 in such a

manner that the thrust bearings 48 rest upon the surface

22a of the base 23. The shroud 61 is then positioned

over the rotor 41 in such a manner that the upper portion

of the body 42 extends through the opening 64 therein. In so doing the shoulder 67 formed internally on the body 62

contacts the upper curved surface 53 of the flange 51. When the shoulder 67 first contacts the surface 53 of the flange

51, the flange is in the non stressed position shown in

dotted lines in Fig. 3. Thereafter the shroud 61 is forced

downwardly, as viewed in Fig. 3, to the position illustrated

in solid lines, in such a manner that the shoulder 66 rests

upon the outer edge of the surface 22 of the base 23 as

illustrated. In this manner the shroud 61 properly aligns

each of the operating parts of the potentiometer in their

proper dimensional and spatial relationship.

Referring again to the flange 51, it should be

42799

23.14 4 o expressly noted that a continuous dynamic seal is provided

between the upper surface of the lip 52 and the shoulder 67

on the internal portion of the body 62. By providing the flange 51 in a resiliently deformable form through the

utilization of the fiberglass filled nylon, a continuous

upward stress is provided to assure an effective seal.

After alignment of the three major sub-assemblies in

the manner above described, the combination is placed within

a mold. The mold is schematically illustrated at 71 in

Pig. 3. It will be noted that the shroud 61 is spaced in- wardly from all surfaces of the mold except the upper sur-

face as viewed in Fig. 3. This spacing is accomplished by

spacer members 72 provided on the face of the mold. The

desired spacing is provided for reception of the final outer

housing for the potentiometer. It should be noted that the

mold is provided with an aligning and receiving means (not

shown) for receiving the leads 26-27 of the potentiometer.

After the sub-assemblies have thus been properly

aligned and placed within the mold, in such a manner that

the upper surface as viewed in Fig. 3 thereof makes intimate

contact with the top surface of the shoulder 63 and the

upper surface 43 of the body 42 of the rotor, as is illust-

rated in Fig. 3, the mold is closed into the position illust-

rated in Fig. 3. Thereafter a flowable plastic material

is injected into the space 73 provided entirely about the

thus assembled sub-combination.of the potentiometer. The

plastic material thus injected is caused to set, after which

the mold 71 is parted and the finalized potentiometer is

removed therefrom.

By reference to Fig. 4 the completed potentiometer

10- 427.996

23144/70 is illustrated in its final form. As can therein be seen, the outer housing 81 appears as a shell which has adhered to or fused with the surface of the shroud and in any event has completely surrounded the entire sub-assembly as placed within the mold and above described, with the exception of the upper surface of the collar and the upper surface of the rotor which were in contact with the surface of the mold and were thus "coined off." Thus a complete seal or bond of the housing by In-situ molding thereof has been accomplished. This In-situ mdoing retains the sub-assemblies in proper aligned position as above described and retains thusly the flange 51 in its stressed position, as illustrated in Pig. 3. It can thus be now more fully appreciated that the flange 51 with the upturned lip 52 thereof by being stressed against the shoulder 67 operates as a sealing gland to seal the internal electrical portions of the potentio- meter from the ambient atmosphere and contaminants which may be present therein. It should also be noted that the leads 26-27 shown leaving the housing of the potentiometer at 900 displaced from the longitudinal axis of the rotor may leave parallel thereto if such is desired. It should also be noted that any pin configuration desired for any particular application may readily be obtained with the construction of the potent- iometer of the present invention. There has thus been disclosed a simple, rugged, vari- able resistor having a minimum number of parts and which is externally sealed by an in-situ molded outer housing that accomplishes a bond or seal of the housing without the use of adhesives. Although a specific form of a potentiometer

4279 96

2 4 4 no in accordance with the present invention has been illustrated and described in detail, such is not to be taken as a limit-

ation upon the scope of the present invention but merely as

illustrative thereof.

Claims (1)

1. 23.14 4e The claims defining the invention are as follows:-

   A variable resistor comprising a..base member

   of electrically non-conductive material carrying a resistance

   element and electrically conductive leads connected to said

   resistance element, a rotor of electrically non-conductive

   material carryihg an electrically conductive contact

   element, shroud means engaging said base member and said

   rotor and urging said contact element into contact with

   said resistance element, said rotor being rotatably adjust-

   able about its axis, said rotor having a resiliently deformable flange extending outwardly therefrom and forming a continuous dynamic seal when engaged with a shoulder formed internally in said shroud means, a housing member molded in situ about the base, the rotor and the shroud means, thereby retaining the parts in assembled position.

   2. A variable resistor as defined in claim 1 in

   which said resiliently deformable flange is formed integrally

   with said rotor and serves upon engagement with the shoulder in said shroud means to yieldingly urge said contact element into contact with said resistance element.

   3. A variable resistor as defined in claim 2

   in which said rotor further includes thrust bearing means

   extending axially therefrom into engagement with the

   surface of said base member.

   4. A variable resistor as defined in claim 2

   in which said rotor is molded of plastic material and said

   flange is of fiberglass filled plastic.

   18 427996

   2o, 144 A A variable resistor as def ne in claim

   4 in which said flange in its non-assembled state is angularly disposed with respect to the longitudinal axis

   of said rotor in a direction such that said flange in its

   assembled state applie6 a continuous force against said

   shoulder.

   6. A variable resistor as defined in claim

   in which said shroud means is a molded plastic member

   defining a second shoulder engaging said base member.

   7. A variable resistor as defined in claim 6 which further includes a plurality of protrusions extending from said rotor, and formed integrally therewith, into

   contact with the same surface of said base member upon which

   said resistance element is disposed.

   DATED this 11th day of August. 1972. SPECTROL ELECTRONICS CORPORATION

   EDWD.WATERS SONS Russell Street MELBOURNE. VIC. 4 7.9 6

   2,i 144/Y

   IX

   42 igs