US3725838A

US3725838A - Variable resistor having an improved wiper member

Info

Publication number: US3725838A
Application number: US00207753A
Authority: US
Inventors: G Hubert
Original assignee: Spectrol Electronics Corp
Current assignee: Spectrol Electronics Corp
Priority date: 1971-02-25
Filing date: 1971-12-14
Publication date: 1973-04-03
Anticipated expiration: 1990-04-03

Abstract

A variable resistor of the rotary type is illustrated having a rotatable wiper member, a substrate member carrying an arcuate resistance element and a collector element, all coaxially secured in a cylindrical housing. The wiper member comprises a relatively rigid carriage element having a screw driver slot therein for rotating the wiper member from the exterior of the housing. A resilient pad element is adhesively secured to the carriage element. A flexible contact element is secured to the face of the pad element facing the resistance and collector elements so that the contact element makes electrical contact between the collector and the desired location on the resistance element. The spacing between the substrate member and the carriage member within the housing is less than the uncompressed thickness of the pad element so that the pad urges the contact element into firm engagement with the resistance and collector elements. A portion of the pad element forms a peripheral seal with the substrate member to prevent the passage of contaminates to the resistance element.

Description

United States Patent [191 Hubert [54] VARIABLE RESISTOR HAVING AN IMPROVED WIPER MEMBER [75] Inventor: Gustav Hubert, Gabriel, Calif.

[73] Assignee: Spectrol Electronics Corporation,

City of Industry, Calif.

[ Notice: The portion of the term of this patent subsequent to Mar. 28, 1989, has been disclaimed.

[22] Filed: Dec. 14, 1971 [21] Appl. No.: 207,753

Related U.S. Application Data [63] Continuation-in-part of Ser. No. 118,750, Feb. 25,

1971, Pat. No. 3,652,970.

[52] U.S. Cl. ..338/174, 338/202 [51] Int. Cl. ..H0lc 1/12 [58] Field of Search ..338/160, 162, 164, 167, 114, 338/113, 111, 99, 71, 68, 93, 96,118,170,

[56] References Cited UNITED STATES PATENTS 3,652,970 3/1972 Hubert 338/183 [451 *Apr. 3, 1973 Primary Examiner-Richard B. Wilkinson Assistant Examiner-U. Weldon Attorney-Harry G. Martin, Jr. et a1.

[57] ABSTRACT A variable resistor of the rotary type is illustrated having a rotatable wiper member, a substrate member carrying an arcuate resistance element and a collector element, all coaxially secured in a cylindrical housing. The wiper member comprises a relatively rigid carriage element having a screw driver slot therein for rotating the wiper member from the exterior of the housing. A resilient pad element is adhesively secured to the carriage element. A flexible contact element is secured to the face of the pad element facing the resistance and collector elements so' that the contact element makes electrical contact between the collector and the desired location on the resistance element. The spacing between the substrate member and the carriage member within the housing is less than the uncompressed thickness of the pad element so that the pad urges the contact element into firm engagement with the resistance and collector elements. A portion of the pad, element forms a peripheral seal with the substrate member to prevent the passage of contaminates to the resistance element.

- 3 Claims, 4 Drawing Figures 2O \\l 3 INVENTOR.

GUSTAV HUBERT 5O FIIG.4 "M

ATTORNEY VARIABLE RESISTOR HAVING AN IMPROVED WIPER MEMBER CROSS REFERENCE TO RELATED APPLICATION Features of this invention are disclosed in my copending application, Ser. No. 118,750, filed Feb. 25,

BACKGROUND OF THE INVENTION This invention relates to variable resistors and more particularly to improved wiper elements suitable for rotary potentiometers.

Variable resistors, especially of the miniature, rotary trimming potentiometer type, have found wide acceptance because of their small size and low cost. Often they are used in an adverse environmental location where it is necessary to restrict the entrance of ambient gases or liquids into the interior of the potentiometer to prevent failure thereof. Also, the potentiometer may have to be sealed in the event it is to be installed on a printed circuit board which is washed with a solvent during the manufacturing process. In any event, it is highly desirable to prevent the entrance of moisture, dirt, abrasive matter and corrosive chemicals into the region occupied by the resistance and wiper elements toavoid failures or excessive electrical noise due to contact resistance variation and to prevent mechanical damage to the resistance element and the wiper contact by abrasion.

While conventional sealing arrangements, such as rings, often provide satisfactory seals, the small size sealing rings required in miniature potentiometers requires a tedious hand assembly operation which adds excessive cost to the unit in the event of good seal is not required for a particular application. Furthermore, prior sealing designs provide an air space within the potentiometer which, due to temperature or pressure variations to which it issubjected in manufacture or use, can give rise to a sufficient pressure difference across the seal to result in passage of ambient foreign material past the seal into the interior of the unit and eventually degrade or impair its operation.

Accordingly, it is a principal feature of this invention to provide a relatively simple trimmer potentiometer design having an effective, easily assembled and inexpensive sealing means to prevent the entrance of foreign material into the region of the resistance element and wiper element.

SUMMARY OF THE INVENTION An insulating substrate member is provided with an elongated resistance element and collector element thereon. A movable wiper member is provided with means for adjusting its movement. The wiper member comprises a relatively rigid carriage element having a relatively resilient pad element secured thereto. A wiper contact element is secured to the face of the pad element which faces the resistance and collector elements. The substrate member and the carriage element are secured so that the distance therebetween is less than the normal uncompressed thickness of the pad element so that the pad element urges the wiper contact into firm electrical engagement with the resistance element and the collector element. The pad element overlies the resistance element and forms a peripheral seal with the substrate which resists contamination of the resistor and collector elements with foreign material.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a central cross-sectional view through a variable resistor in accordance with this invention;

FIG. 2 is an isometric view of improved wiper member in accordance with this invention;

FIG. 3 is an isometric view of the substrate member showing the resistance and collector elements thereon; and

FIG. 4 is a cross-sectional view taken substantially on line IVIV of FIG. 1.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring to the drawings, there is shown a variable resistor 10 which in the preferred embodiment may be a trimmer potentiometer. Variable resistor 10 is provided with a housing member 1 1 having a hollow, cylindrical interior cavity which is preferably circular in cross-section. A rotatable wiper member 12 and a substrate member 13, which are also preferably circular in cross-section, are coaxially disposed within the circular cavity in the housing 1].

Terminal members

14, 15 and 16 are provided for making electrical connections with the resistance element.

One face 19 of substrate 13 is providedwith an elongated arcuate resistance element 20 having its ends deposited over and electrically contacting suitable

conductive terminations

21, 22. Resistance element 20 is preferably of the cermet type which comprises a plurality of metal or metallic alloy particles dispersed throughout a ceramic glass coating which may be deposited on face 19 of substrate member 13 by screen printing and subsequent firing. Substrate member 13 is preferably composed of a ceramic insulating material such as alumina.

Conductive terminations

21, 22 may also be deposited on face 19 of substrate 13 by screen printing and comprise a highly conductive metallic coating.

Terminal members

15 and 16 are inserted through appropriate holes in substrate 13 and soldered or brazed to make electrical contact with

terminations

21 and 22 which form the electrical ends of resistance element 20.

A suitable collector element 25 is formed in the center of substrate 13. Collector element 25 may comprise a conductive metal coating 26, similar to

terminations

21 and 22, formed around a central hole 27 through substrate 13. Terminal member 14 is bent to a desired shape to provide the desired final terminal pin configuration and one end thereof inserted through the hole formed by conductive coating 26. Solder or other conductive brazing material 25 is then applied to electrically and mechanically secure terminal 14 to conductive coating 26 and at the same to form a conductive surface region about the central area of substrate 13 as shown in the drawings. Alternatively, collector element 25 may be formed by depositing or securing a suitable conductive coating or element into surface 19 of substrate 13 to provide any desired shape for the collector element. Similarly, the resistance element may be, of any desired type such as a conductive resin or solid metal resistance material and may be arcuate or linear in shape if desired, and may be secured by any desired means to substrate 13.

Wiper member 12 is cylindrical in the embodiment illustrated, and is mounted coaxially within interior cavity 17 of housing 11. Wiper member 12 comprises a relatively rigid carriage element 30 which is provided I with means for adjusting its position from the exterior of housing 11. In the embodiment shown, carriage element 30 has a cylindrical, axial projection 31 which extends through a correspondingly shaped aperture in housing to allow rotational adjustment of the carriage element from the exterior of the housing by insertion of screw driver in screw driver slot 32. Alternatively, the carriage element may be provided with gear teeth so that it can be rotated by worm screw projecting externally from the housing.

Carriage element has one face 33 which faces toward substrate member 13 when the members are inserted in the housing. The other face 34 extends radially outwardly from cylindrical projection 31 and abuts against an opposing annular shoulder 35 on housing 1 1. If desired, an O-ring or other seal means (not shown) may be provided between

shoulders

34 and 35 to resist the entrance of dirt, moisture or other contaminates into the interior of housing 11.

Wiper member 12 also comprises a pad element which is made of a resilient material such as silicone rubber. Pad element 40 may be made of various resilient materials such as felt, poly-urethane foam or neoprene.- Preferably, the material selected for pad 40 is relatively impervious to moisture and is capable of withstanding whatever heat the variable resistor may be subjected to without losing resiliency. Resilient pad 40 is circular in cross-section and'is coaxially mounted within the interior of housing 11 with one surface 41 thereof facing substrate member 13. The other surface 42 of pad 40 is secured to carriage element 30 by adhesive 43, such as an epoxy glue, or other suitable means such as molding. v

A conductive wiper contact element 45 is disposed on one surface 41 of pad element Wiper contact element 45 preferably comprises a relatively deformable bar of finely divided electrically conducting metal particles which are flexibly bonded together by a suitable material such as a flexible or deformable resinous plastic binder. Contactelement 45 may comprise a flexible epoxy plastic filled with finely divided silver particles. Alternatively, wiper contact element 45 may comprise any electrical conductor such as metallic ink, flexible foil, wire woolor one or more metal wires disposed on face 41 of 'pad element 40. Wiper contact I element 45 is preferably sufficiently deformable or flexible, thick and electrically conductive sothat the contact element can follow the resilient deformation of pad 40 and makegood electrical contact between the resistance and collector elements. The wiper contact element is disposed in spaced relation with the edge of pad 40 so that an effective seal is formed radially outwardly of the wiper contact element. A silver filled epoxy plastic bar having a thickness of about 0.04 inches and a width of 0.05 inches has been found to produce very good electrical characteristics.

Substrate member 13 is coaxially secured in housing 11 by any desired means. It is preferred to secure substrate 13 in housing 11 by use of an insulating epoxy potting agent 50. Substrate member 13 is secured within the housing 1 1 so that the distance between face 33 of carriage element 30 and the upper surfaces of resistance element 20, collector element25 and face 19 of substrate member 13 is less than the uncompressed axial thickness of resilient pad element 40. Consequently, pad element 40 axially urges wiper contact element 45 into firm electrical and mechanical'engagement with resistance element 30 and collector element it is preferred to assemble the elements and members within housing 11 and to apply an axial force of about one pound on substrate member 13 by a suitable device to initially compress resilient pad element 40. As a small amount of the epoxy potting agent 50 is then poured into cavity 17 and cured sufficiently to secure substrate 13 in the desired position to hold pad 40. com-.

pressed. Thereafter the device exerting pressure on substrate 13 is removed and additional epoxy agent is poured into cavity 17 and finally cured to complete the assembly.

Pad element 40 extends radially outward from the axis of wiper member 12, an extent greater than resistance element 20 and wiper contact element 45 so that it completely overlies the resistanceand wiper elements. Consequently, an effective seal is formed adjacent the peripheral edges of pad element 40 and substrate member 13 at a location radially outwardly of the resistor and collector elements to effectively resist the entrance of foreign material between them. The seal completely surrounds both the resistor and collector elements to resist the passage of foreign material to them. The seal is also formed radially outwardly of the wiper contact element so" that passage of foreign material to the wiper contact element is resisted. A suitable lubricant, such as petroleum grease having a lithium anti-friction compound therein maybe provided between pad element 40,and substrate member 13. The lubricant not only serves the function of improving the setability of the wiper member by reducing its friction with thesubstrate, resistance and collector elements, but in addition, it serves to coat the surface of any foreign particles with a dielectric film to reduce noise.

It will be seen that a construction in accordance with this invention possesses the advantage of being simple and inexpensive to manufacture and easy to assembly in either a manual or automated production process.

The resilient pad serves to bias the wiper contact into engagement with the resistor and collector tracks and to form an effective sealing means, thereby eliminating the necessity of a separate seal and the attendant cost of assembling a separate seal. Further, there is no air space on the resistor side of the seal to create a pressure difference under varying temperature conditions.

While for purposes of illustration a preferred embodiment of this invention has been described, it will be apparent that the invention may be otherwise embodied within the scope of the following claims.

I claim:

1. A variable resistor comprising:

A. a substrate member comprising an electrically insulating material, one face of said substrate member being substantially flat, an arcuate resistance element disposed on said one face of said substrate member, and a collector element disposed on said one face of said substrate member;

B. a wiper member comprising:

C. a rotatable wiper member, said wiper member 1. arelatively rigid carriage element; 5 being disposed for rotation within said housing 2. a relatively resilient, pad element secured to member and having means associated therewith said carriage element in overlying relation with for adjusting the rotational position of said wiper the entire extent of said resistance element and member from the exterior of said housing member, said collector element; said wiper member comprising:

3. a wiper contact element disposed on said pad 10 l. a relatively rigid carriage element disposed for element, said contact element comprising an rotation in the cavity in said housing member; electrically conductive element overlying and 2. a relatively resilient, pad element secured to said contacting portions of both said resistance elecarriage element, said pad element having one ment and said collector element; substantially flat face compressed against said one 4. means for rotating said wiper member relative l5 face of said substrate member, said pad element to said substrate member so that the wiper conoverlying the entire extent of said resistance eletact can be moved across the arcuate resistance ment and said collector element to sealingly enelement to adesired location thereon; gage said one face of said substrate member at a 5. said carriage element being spaced from said relocation radially outward of said resistor and colsistance and collector elements by a fixed 2O lector elements to resist the passage of foreign distance less than the uncompressed thickness material to said resistance and collectorelements; of said resilient pad element so that said resilient a "P Contact n olsposed on Sald one o pad element is compressed to resiliently use of said pad element, sa d contact element compris- Said Contact element into firm electrical and mg a radially extending electrically conductive mechanical engagement with said resistor and Contact o f overlymg and oontactlng pornons collector elements, Said pad element being of both said resistance element and said collector pressed against and sealingly engaging the element, said pad element extending radially outstrate member at a location radially outwardly woroly beyond the n element; of and completely Surrounding the collector 4. sa d carriage element and said substrate member ment and the arcuate resistance element to rebemg spaced apart nouslng by a olstanoe sist the passage of contaminants to the resistor than the uncompressed of Sam and collector elements; and resilient pad element so that said resilient pad ele- C. terminal means for making electrical contact with ment P o between 5am suosn'ate said collector element and said resistance element. member 3 531d ge e ement to urge said one 2. A variable resistor as defined in claim 1 wherein o Said pad element Seanng engagement said resilient pad element extends radially outwardly n one face of solo suostrate menfber at a beyond Said wiper Contact element cation completely surrounding the resistance ele- A variable resistor comprising; ment, the collector element and the wiper contact A. a housing member, said housing member having n and to urge Solo Contact element P animerior cavity therein; 40 electrical and mechanical engagement with said B. a substrate member comprising an electrically inreslstor and collector elefnonts; n

Sulating material one face of Said substrate D. terminal means for making electrical contact with member being Substantially flat and facing the said collector element and sa d resistance element terior cavity of said housing member, an arcuately from the extenor of sold nouslng member' extending resistance element disposed on said one

Claims

1. A variable resistor comprising: A. a substrate member comprising an electrically insulating material, one face of said substrate member being substantially flat, an arcuate resistance element disposed on said one face of said substrate member, and a collector element disposed on said one face of said substrate member; B. a wiper member comprising: 1. a relatively rigid carriage element; 2. a relatively resilient, pad element secured to said carriage element in overlying relation with the entire extent of said resistance element and said collector element; 3. a wiper contact element disposed on said pad element, said contact element comprising an electrically conductive element overlying and contacting portions of both said resistance element and said collector element; 4. means for rotating said wiper member relative to said substrate member so that the wiper contact can be moved across the arcuate resistance element to a desired location thereon; 5. said carriage element being spaced from said resistance and collector elements by a fixed distance less than the uncompressed thickness of said resilient pad element so that said resilient pad element is compressed to resiliently urge said contact element into firm electrical and mechanical engagement with said resistor and collector elements, said pad element being compressed against and sealingly engaging the substrate member at a location radially outwardly of and completely surrounding the collector element and the arcuate resistance element to resist the passage of contaminants to the resistor and collector elements; and C. terminal means fOr making electrical contact with said collector element and said resistance element.

2. a relatively resilient, pad element secured to said carriage element in overlying relation with the entire extent of said resistance element and said collector element;

2. A variable resistor as defined in claim 1 wherein said resilient pad element extends radially outwardly beyond said wiper contact element.

2. a relatively resilient, pad element secured to said carriage element, said pad element having one substantially flat face compressed against said one face of said substrate member, said pad element overlying the entire extent of said resistance element and said collector element to sealingly engage said one face of said substrate member at a location radially outward of said resistor and collector elements to resist the passage of foreign material to said resistance and collector elements;

3. a wiper contact element disposed on said one face of said pad element, said contact element comprising a radially extending electrically conductive contact element overlying and contacting portions of both said resistance element and said collector element, said pad element extending radially outwardly beyond the wiper contact element;

3. A variable resistor comprising: A. a housing member, said housing member having an interior cavity therein; B. a substrate member comprising an electrically insulating material, one face of said substrate member being substantially flat and facing the interior cavity of said housing member, an arcuately extending resistance element disposed on said one face of said substrate member, and a collector element disposed on said one face of said substrate member; C. a rotatable wiper member, said wiper member being disposed for rotation within said housing member and having means associated therewith for adjusting the rotational position of said wiper member from the exterior of said housing member, said wiper member comprising:

3. a wiper contact element disposed on said pad element, said contact element comprising an electrically conductive element overlying and contacting portions of both said resistance element and said collector element;

4. means for rotating said wiper member relative to said substrate member so that the wiper contact can be moved across the arcuate resistance element to a desired location thereon;

4. said carriage element and said substrate member being spaced apart in said housing by a distance less than the uncompressed thickness of said resilient pad element so that said resilient pad element is compressed between said substrate member and said carriage element to urge said one face of said pad element into sealing engagement with said one face of said substrate member at a location completely surrounding the resistance element, the collector element and the wiper contact element, and to urge said contact element into electrical and mechanical engagement with said resistor and collector elements; and D. terminal means for making electrical contact with said collector element and said resistance element from the exterior of said housing member.

5. said carriage element being spaced from said resistance and collector elements by a fixed distance less than the uncompressed thickness of said resilient pad element so that said resilient pad element is compressed to resiliently urge said contact element into firm electrical and mechanical engagement with said resistor and collector elements, said pad element being compressed against and sealingly engaging the substrate member at a location radially outwardly of and completely surrounding the collector element and the arcuate resistance element to resist the passage of contaminants to the resistor and collector elements; and C. terminal means fOr making electrical contact with said collector element and said resistance element.