US2873337A - Variable resistor - Google Patents

Description

Feb. 10, 1959 M. E. BouRNs ET AL 2,873,337

VARIABLE RESISTOR Filed Nov. 14, 1955 2 Sheets-Sheet l AGENT Feb- 10, 1959 M. E. BoURNs ET AL 2,873,337

VARIABLE RESISTOR Filed Nov. 14, 1955 2 Sheets-Sheet 2 /NVENTOQS BY raJJWm AGENT United States Patent() VARIABLE RESISTOR Marlan E. Bourns, Marvin E. Harrison, and Wilbur T. Hardison, Riverside, Calif.; said Harrison and said Hardison assignors to Bourns Laboratories, Inc.

Application November 14, 1955, Serial No. 546,634

4 Claims. (Cl. 20162) nearly to the degree which the present variable resistor design permits. In addition, the present variable resistors require the employment of either soldering or crimping techniques in order to mount suitable end terminals or lugs to the end terminations of the resistive element employed.

Therefore, it is an object of the present invention to provide a new and useful variable resistor.

It is a further object of the present invention to provide a new and useful variable resistor which will be extremely compact, easy to fabricate and assemble, and inexpensive to manufacture.

Another object of the present invention is to provide a novel variable resistor in which the shorting bar used is closely adjacent the periphery of the resistive element employed.

According to the present invention, an enclosure member or semi-enclosure member provides a suitable mount for a preferred resistive element with a substantially oval or elliptically-shaped cross-section characterized by a small ratio of minor axis to major axis. Novel, snap-on terminal clips are mounted at the extremities of the re.- sistive element. A shorting bar is employed having a configuration which permits a portion thereof to lie substantially adjacent the periphery of the resistive element. An appropriate electrical contact simultaneously engages the novel shorting bar and the exposed portion of the resistive element, and is linearly positioned by an appropriate lead screw.

The features of the present invention which are believed to be novel are set forth with particularity in the Vappended claims. The present invention, both as to its organization and manner of operation, together with further objects and advantages thereof, may best be understood by reference to the following description, taken in connection with the accompanying drawings, in which:

Figure 1 is a longitudinal sectional View taken through a variable resistor embodying the principles of the present invention;

Figure 2 is a top plan view of the same;` Figure 3 is a sectional view, taken along the line 3-3 in Figure l;

Figure 4 is a view similar to Figure 3, of another form of the invention, showing a different type of contact member;

Figure 5 is a transverse sectional view, taken through the plastic member which supports the resistance element and shorting bar, showing another form of resistance element and shorting bar;

Figure 6 is a perspective view of a terminal clip which is adapted to be snapped onto the ends of the resistance element of Figure 1;

Figure 7 is a perspective view of a slidable contact member of the type shown in Figure 1;

Figure 8 is a perspective view of the alternate form of slidable contact member shown in Figure 4;

Figure 9 is a perspective view of the sheet metal housing of Figure 1, with the bottom portion thereof being in n up direction, and in its extended condition;

Figure 10 is a view taken at 10-10 of the enclosure member of Figure 9, showing another form of bearing support for the lead screw;

Figure 11 is a perspective View of another modification of the contact member, showing a novel manner of engaging the lead screw;

Figure 12 is a perspective view of an additional embodiment of a variable resistor employing a semi-enclosure member;

Figure 13 is a transverse sectional view of the device of Figure 12. y

ln Figure l, variable resistor 10 is shown to consist of a sheet metal housing 11, having mounting tabs12 projecting from the ends thereof, a longitudinally extending lead screw 13, slidable contact member 14, insulating member 15, and resistance element 16. Resistance element 16 is provided with terminal clips 17, and with a conductive strip, or shorting bar member 18, having its own terminal lug projecting from the housing. The several configurations of slidable contact member 14, resistance element 16, terminal clips 17, and shorting bar member 18 shall be explained later.

Figure 2 is a top plan view of the device in Figure 1, showing with particularity how the terminal clips 17 and terminal lug of the shorting bar member 18 pass through suitable apertures in the insulating member 15, and also through enlarged apertures in the sheet metal housing 11. These apertures in the housing 11 are of sucient width and length to provide ample clearance for the terminal lugs, so that there is no electrical connection therewith.

Figure 3 is a sectional view taken along line 3--3 in Figure 1, showing with particularity that resistance element 16 has an oval or elliptical cross section. Cone ceivably, however, resistance element 16 may have other congurations, such as that of a rectangular bar having either or rounded corners.

The resistance element 16 comprises a central core 19, known as a card, upon which insulated resistance wire 20 is wound. Alternatively, the resistance element can take the form of a strip of composition material, such as bar 503 in Figure 5, which shall be shown and described later.

Figure 4 is a sectional view, similar to Figure 3, showing a modified form of the invention'. In this case, the contact member is generally U-shaped, and one leg of the U hears on one edge of the resistance element, while the other leg wipes on rounded portion of the shorting bar, where the latter is wrapped around the other edge of the resistance element. lThis arrangement permits an extremely compact organization, and is advantageous for extreme miniaturization.

As hereinbefore explained, the resistance element 16 of Figure l may simply comprise a resistive strip 503, manufactured from suitable resistance exhibiting composition, to which end terminals 18 may be mounted in tegrally therewith, during the molding process of lbar 503. The shorting bar is indicated at 502, and comprises Ya sheet metal strip which is bent to a ,U-shaped configura' 6,0410 accommodate the connection of an electrical lead or other electrical element. The bent side portions l601 :and 602 and base portion 603 are shaped to provide a socket that receives the extremities of resistance element .-16 of Figure 1. nwardly -directeddimples 605 areformed in portions 601, 602., and 603, `which press against `and make electrical 4Contact with windings of the wire 20. The slidable contact member of Figure 7 includes a block member 700, having .a threaded laperture 7.08 provided therein Yto receive the llead screw 12. The block ,member 700 also has a contact member 701, and means 702 to aix contact member 701 to block member 700. The securing means 702 may simply consist of a non- -round projection 702 molded in the top of the block 700, which passes through a correspondingly shaped hole 703 in the Contact 701. At the time the contact 701 is assembled on the block 700, the projection 702 is softened or melted and squashed down slightly to rivet the .contact to the block. Such a forming process for the slidable contact shown in Figure 7 indicates that a thermoplastic material will be most suitable for constituting block member '7 00. However, as is well known to the art, thermoplastics have appreciable coecients of expansion where changes lin ambient temperature occur, and without suitable corrective measures, the threaded aperture 70S wouid increase or decrease in diameter as .the plastic expands or contracts, causing the lead screw to tit loosely within the threaded aperture, or to bind. To avoid this condition, we have provided a slot '706 between base portion 707 of block member 700 and the screw-threaded aperture 708, so that the latter will remain substantially constant in diameter and therefore exhibit a uniform frictio-nal force on the lead screw, des pite a considerable range of expansion and contraction by the block member 700 due to temperature change.

T heslidable contact member, which is shown in Figure 8, is yan alternate form to that of Figure 7 and employs a block member 800, substantially equivalent to'block member 700 of Figure 7, but this time provided with a U-shaped contact member 301 which exhibits a wide separation between portions 802 and 803 thereof, as contrasted to the rather small separation between contact portions 709 and 710, of bifurcated contact member 709. The purpose of the wide .separation between portions 802 ,and .803 shall be hereinafter explained in detail.

Figure 9 shows and describes enclosure member 11 in Figure l, only this time in its upside down condition with bottom portion 900 open at, before being folded `down along the bend line 909. Enclosure 11 is shown provided with apertures 901, 902, and 903 provided in .top yportion 904 thereof. Apertures 901, 902, and 903 are of course provided to accommodate terminal clips 17 and the terminal portion of shorting Abar member 18, shown in Figure 1. Enclosure 11 is closed up by merely rfolding the bottom portion 900 down along the bend line 190,9 andsoldering the edges thereof .to the -adjoining edges 7of vthe side and end walls. Bottom portion 9,00 may be `provided with a contoured retaining tab 905 having a 4semi-circular recess in the end thereof which ts into .and cooperates with van annular `groove `906 of the lead screw 907, shown in dotted lines. The moved lend of @the lead screw Yis .dropped into .an v.opor-1 .notch 91.0 in :the end 9.11ct the enclosure., ,the bottom of which y,is .semi` .circular 1to receive the -greove 906 .of the `lead screw- 'Ihue .the notch 9.10am tab1905 cooperate .to form a com- 4pleteenclosure, with :a circularholein the endA 911 through which `.the .Slotted end .of the lead screw *907 projects tifnrzadiustmentzpurposes. aperture at the otherend endwise movement.

of the enclosure, through which the other end of the lead screw passes, may be sealed with an 0-ring (not shown).

Figure 10 is a view taken along the line 10-10 in Figure 9, showing that in lieu of the contoured retaining tab configuration of Figure 9, a keyhole slotted retaining tab 1000 may be provided at either end (or, if desired, both ends) of bottom portion 900 to receive an annular groove provided in the lead screw Asothat the lead screw need not pass through the ends of enclosure 11. The tab 1'000'is bent yback from the end of the bottom portion 900 `to provide clearance for the end of the lead screw. This tab 1000, when lused in conjunction with the enclosure construction of Figure -9, but without .the open notch 910 of the latter, makes it possible to hermetically seal the unit, inasmuch as 'the ends of the lead screw are rrr tatably supported solely by the tabs 1000 and are contained entirely within the connes of the enclosure 11. Thus, when the bottom portion 900 is soldered along its edges to the adjoining edges of the side and en dwalls, the enclosure 11 is sealed air tight.

With the above description of Figures 1 through 10, .it becomes possible at this time to describe fully the operation of the variable resistor in its various embodiments. One of the more important characteristics of the invention is ease o-f assembly. The several elements of the combination shown in Figure l are of course fabricated independently. Then resistance element 16, consisting either of a relatively at core and a plurality of insulated Vwindings wound thereupon or simply constituting a b ar of appropriate cross section manufactured from a resistance composition, is provided with terminal `clips 1 7 at the extremities thereof (Shown in detail in Figure 6). Next, shorting bar member 18 is disposed in proximity with resistance element 16. See vFigure 1 and Figure 3. In the case of a wire wound resistance element the sh0rting bar need only be disposed upon the insulation ofthe wires themselves to be insulated therefrom. Or, in the case of a resistance bar being employed, as shown in Figure 5, shorting bar 18 would need ybe vspaced from the resistance `bar member 500. As a secondary approach, there might conceivably be disposed an air gap between the shorting bar member and `the resistive bar. In either case, that is whether the resistance element 16 o f Figure 1 is employed or Whether the resistive member o f Figure 5 is used, the terminal projections are inserted through openings in the insulating member 15 and protrude through apertures 901 and 903 of Figure 9. The insulating member 15 itself `may be either glued to top portion 904 of enclosure 11 or may simply be press-fitted withinv 'the enclosure 11 so as to engage vand thereby rest upon top portion 904, or at least be in the proximity thereof. The terminal projection kof the shorting bar member 18 will likewise be inserted through an aperture provided therefor (aperture 902 in Figure 9) torprotrude from enclosure 11 (see Figure 1, Figure 2, and Figure 9). Lead screw 13 cooperating with slidable contact member 14 is next mounted in position yand may either be retained by the cooperation of either the contoured retaining `tab of Figure 9 or the contoured retaining tab of Figure 10 with the annular groove thereof. In either case, the lead screw is rotatably supported on the housing and is held against Bifurcated contact member 701 of slidable contact member 14 (see Figure A7) simultaneously engages shorting bar member 18 andan exposed winding of the resistance element 16, and this by means 0f portion 709 and 710 of the slidable contact member shown in Figure '7. The slidable contact member shown in 'Figure 7 may be used in conjunction with wire wound `resistance elements `and also'in conjunction with a'bar resistivernem- '-'ber such as that shown in Figure -5. This is also true of the slidable Contact member of Figure 8.

-The operation of the various embodiments shown and described in Figure '1 through Figure `10 and 'in the discussion relating thereto becomes apparent. 12012110.11 of `lead 'screw v13 causes -the progression in one of two oppostte directions of slidable contact member 14. The location of the slidable contact member 14 along the length of the resistance element determines the resistance between one of the terminal clips 17 and the terminal portion of shorting bar 18. Conceivably of course, the device of Figure 1 might include only one end terminal, together with the shorting bar member, for serving as a simple, two-terminal rheostat.

Figure ll describes a novel yet simplified contact member 1100 having a partially circular, internally threaded central member 1101 to engage and cooperate with lead screw 13. Upper end portions 1102 and 1103 are provided to accomplish the simultaneous engagement with the shorting bar and the resistance element. In the case of the utilization of contact member 1100 in Figure 11, lead screw 13 would of course have to be manufactured from an insulating material. The central member 1101 may consist of oppositely facing semi-circular straps struck out of the sheet metal ybase of the contact member 1100, which cooperate to form a threaded aperture for the lead screw.

Figures 12 Iand 13 show a variable resistor device incorporating a semi-enclosure member 1200, rather than the enclosure 11 of Figures 1 and 2. The configuration and assembly of the variable resistance unit of Figure 12 and Figure 13 is substantially the `same as that described in connection with Figures l through however, in the case of the embodiment shown in Figure 12 and Figure 13, insulating member 15 is held in place by the resilient cooperation therewith of L-shaped side portions 1201 and 1202. The embodiment shown in Figure 12 and Figure 13 may be used where hermetic sealing is not required.

While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from this invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modications as fall within the true spirit and scope of this invention.

We claim:

1. In a variable resistor, the combination of an elongated resistance element having one edge thereof rounded, a shorting bar of sheet metal cylindrically curved to conform to said one edge of said resistance element and overlying the same in close proximity thereto, said shorting bar being insulated from said resistance element, and a slidable contact wiping on an exposed portion of said resistance element and on said shorting bar.

2. A variable resistor comprising a box-like enclosure, one wall of said enclosure having a tab provided thereon adjacent one end of the enclosure, said tab being spaced from said one end and substantially parallel thereto, said tab having a keyhole slot formed therein, a resistance element mounted Within said enclosure, a lead screw disposed parallel to said resistance element, and a contact member mounted on said lead screw and wiping on said 6 resistance element, said contact member being movable lengthwise of said resistance element by rotation of said lead screw, said lead screw being rotatably supported at one end by said tab and having a circumferential groove engaged by said keyhold slot.

3. A variable resistor comprising a body, an elongated resistance element mounted thereon, a shorting bar of sheet metal curved to conform to one edge of said element and overlying the same in close proximity thereto, said shorting bar being insulated from said element, the other edge of said resistance element being exposed for electrical contact, and a contact member supported for movement along a path parallel to said resistance element and shorting bar, said contact member having two laterally spaced upstanding lingers which wipe on said exposed portion of said resistance element and the oppositely facing surface of said shorting bar.

4. In a variable resistor, an enclosure housing comprising four side walls and two end walls, three of said side walls and said end walls coacting to form a box open on one side, the fourth side wall being initially open and being adapted to be bent `down along one edge to enclose said housing, said fourth side wall having a tab bent down from one end thereof, said tab having a semi-circular recess in the end thereof, the adjacent end wall having an open notch formed therein with a semi-circular bottom, said notch and said tab being registered with one another when said fourth side wall is bent down to the closed position to form oppositely facing halves of a bearing aperture in said adjacent end wall, a lead screw having a circumferential groove formed therein which is received within said bearing aperture, a contact member disposed within said enclosure housing and movable lengthwise thereof by rotation of said lead screw, and a resistance element within said enclosure housing wiped by said contact member.

References Cited in the le of this vpatent UNITED STATES PATENTS 686,245 Bachman et al. Nov. 12, 1901 1,007,005 Lukaszewske Oct. 24, 1911 1,321,873 Ziegler Nov. 18, 1919 1,630,338 Gail May 31, 1927 1,880,239 Crouse Oct. 4, 1932 2,115,135 Benbow Apr. 26, 1938 2,357,433 Side Sept. 5, 1944 2,366,509 Francisco Jan. 2, 1945 2,486,931 Edwards et al. Nov. 1, 1949 2,506,482 Batcheller May 2, 1950 2,594,796 Olah Apr. 29, 1952 2,676,778 Pace et a1. Apr. 27, 1954 2,687,266 Cloedy et al Aug. 24, 1954 2,687,463 Riley Aug. 24, 1954 FOREIGN PATENTS 240,672 Switzerland May 16, 1946

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