US2850608A - Adjustable electrical resistors - Google Patents

Description

"sqm-2,Y 195s 2,850,608v

ADJUSTABLE ELECTRICAL RESISTORS M. EfguRNs ETA.

` Filed Nov. '7, 1955 MIT uw@ A@ ADJUSTABLE ELECTRICAL RESISTRS Mai-lan E. Booms, Edward ll. Goeppinger, and Wilbur T. Hardison, Riverside, and Handley M. Cornish, ir., Arlington, Calif.; said Goeppinger, Hardison, and Cornish assignors to Booms Laboratories, inc.

Application November 7, 1955, Serial No. 545,464

7 Ciaims. (Cl. 2011-1-62) This invention reiates to new and improved adjustable electrical resistors, and, in particular, to a species of adjustable electricai resistors commonly termed potenti? ometers.

There is considerable competition amongst manufacturers of potentiometers and like electrical instruments at the present time. A broad aim of this invention is 'to provide new potentiometers which will serve to give the manufacturers of these new units a competitive advantage over the other instruments presently being manufactured.

A potentiometer, in order to benefit a manufacturer in the present competitive market, must possess a number of distinct advantages over known units. The new potentiometers herein described may be distinguished from known units in a number of dierent ways, alliof which are believed to relate to -the commercial utility. of these new units.

The new adjustable electrical resistors herein described employ comparatively light weight housings having reinforcing ribs fomied on the interior thereof so as to prevent collapse of the walls of the housings. With this type of structure the individual housings utilized may be manufactured out of metals such as aluminum, stainless steel or out of various plastics such as, for example, a high molecular weight nylon composition by extrusion techniques. These housings, once manufactured, may be cut to any desired length by a manufacturer so as to eliminate the necessity of keeping on hand a number of separate different housings of different sizes for different sized units. i

Another major advantage of the new units of this invention lies in the fact that a number of different types of end closures may be kept in stock, and these end closures may be used with any size of potentiometer manufactured in accordance with this invention with a standard housing cut from an extrusion. These end closures with the invention may, if desired, be stocked so as to be formed with any type male or female connections, screw type terminals, solder lugs, or the like.

Alsotend type closures used with the invention can be manufactured so as to provide for virtually any desired type of shaft actuation desired. Thus, rigidly secured shafts can be used with the units herein described byappropriate formation of end closures with the center openings serving as bearings. Also, end closures capable of being yused with any of a number ofdiiferent size units can be developed utilizing screw actuation, iexible shaft type actuation, or the like.

The above discussion will indicate to those skilled in the art certain broad objectives of the invention. It is to be emphasized, however, that the invention is not limited to units having these broad objectives, inasmuch as various different details of construction, as will hereinafter be set forth, arey considered to be of independent significance. These details, as well as other objects and advantages of the invention, will be more fully explained by the remainder of this specification including the apyes Patented Sept.. 2, 195% pended claims, and by the accompanying drawings, in which:

Fig. l is an isometric View of a potentiometer manufactured in accordance with this disclosure;

Fig. 2 is a cross sectional view taken at line 2-2 of Fig. l;

Fig. 3 is a cross-sectional View taken at line 3--3 of Fig. 2;

Fig. 4 is a detailed cross sectional view taken at line 4-4 of Fig. 2;

Fig. 5 is a detailed cross sectional view similar to part of Fig. 2, showing the use of screw type terminals;

Fig. 6 is an isometric View of a modified slider which may be employed with the invention;

Fig. 7 is an isometric view of a second modified slider which can be employed with the invention; and

Fig. 8 is a side view of the slider illustrated in Fig. 7 showing the manner in which this slider is employed.

in all figures of the drawings, like numerals are used to designate like parts whenever convenient for purposes of illustration and explanation. lt is to be understood that the invention is not limited to units having the precise shape and dimensions shown in the drawings, inasmuch as considerable modification is possible without departing from the essential nature of this invention as explained in this specification.

The appended claims effectively summarize the novel features of this invention which are considered important. For purposes of explaining the invention, it is pos'- sible to briefly state that it is concerned with adjustable electrical resistors, each of which comprises: an elongated housing of rectangular cross section, said housing including parallel top and bottom walls, and parallel side walls; a pair of upper reinforcing ribs located in a plane parallel to said top wall, each of said upper ribs being located on the interior of one of said side walls, said upper ribs being spaced from said top wall and serving to reinforce said side walls; a pair of lower reinforcing ribs located in a plane parallel to said bottom walls, each of said lower ribs being located on the interior of one of said side walls, said lower ribs being spaced from said bottom wall and said upper ribs, and serving to reinforce said side walls; a support member located within said housing so as to extend from adjacent one end thereof to adjacent the other end thereof, said support member being supported by said lower ribs, and being spaced from said bottom; a resistance element carried by said support member so as to have a surface exposed on the side of said support member adjacent to said top; a slider carried by said upper ribs, said slider including resilient Contact means projecting therefrom so as to engage said exposed surface of said resistance element so as to establish electrical communication therewith; a closure located within one end of said housing; means projecting through said closure operatively connected to said slider whereby said slider may be moved within said housing causing said resilient contact means to engage different parts of said exposed surface of said resistance element; a closure positioned within the other end of said housing; electrical terminal means attached to said second closure; electrical wires connecting the ends of said resistance element and said terminal means, said electrical wires extending through the space between said bottom and said support member.

Unfortunately, a summary of this category is not considered to be sufficiently explanatory in nature to fully appraise even those skilled in the art to which this invention pertains of the precise nature of the invention. In Figs. l, 2 and 3 of the drawings there is shown a potentiometer it) having a housing l2 including top and bottom walls 141. and 16 respectively, and side walls l. lt will be realized from consideration 0f Fig. 3 that th L housing is of essentially rectangular cross sectional shape, and is formed with comparatively thin wall sections. On the side walls 18 adjacent to the top 14 there are formed upper reinforcing ribs 28 which project into the interior of the housing 12. These ribs are located in a plane parallel to the top 14, and are spaced therefrom. A pair of lower reinforcing ribs 22 similar to the upper ribs are also provided on the side walls 18 adjacent to the bottom 16'. These lower ribs are in a plane parallel to the bottom 16, and are spaced from both the bottom wall 16 and the upper ribs 20. The housing 12 is preferably formed so as to have two axes of bilateral symmetry located at -right angles-to one ranother. Thus,

with this construction, the ribs 2t) and 22 are spaced from.

oneanother along the side walls 18 so as to provide effective reinforcement to these side walls.

Upon the lower ribs 22 there is held a support member 24 extending from adjacent to one end of the housing 12to adjacent tothe other end of this housing so that elongated notches 26 in it fit against the ribs 22. This support member 24 is held in this position by means of resilient metal retaining clips 28 which are secured to the ends of the support 24 by means of screws 3th'. These clips, as is best seen in Fig. 3 of the drawings, are shaped so as to have curved ends 32 which engage the lower ribs 22 tending to center the support member 24 between the side walls 18.

Within the side of the support member 24 adjacent to the top V14 there are provided two elongated grooves 34 and 36'. The groove 34 is adapted so as to carry a conventional wound resistance element 38 so that a surface of this element is exposed. The other groove 36 is provided with an electrical return 40 consisting of an elongated sheet of metal bent in the shape of a U. This electrical return includes a projecting end or tongue 42 which extends through an opening 44 in the support member 24so as to, in effect, lie within the space between the support member 24 and the bottom wall i6. Through other openings 46 wires 43am attached to the ends of the resistance element 38 as by solder or like means so that these ends may be connected to prong type male plugs 50 mounted upon the end closure 52. A wire 48 is also used to connect the end 42 to one of the plugs 50. This closure 52 is held within an end of the housing 12 by means of screws 54. These plugs 50 may be formed so as to include serrations 56 facing the exterior of the housing 12 .so that they may be merely driven within the end Vclosure 52 during manufacture so as to be securely mounted. The end closure 52 is preferably formed of any convenient non-conductive material suchas, for example, a iilled phenolic resin or the like so as to include a peripheral groove 58 enabling the closure 52 to be positioned partially within the housingY 12 so that it may not be readily dislodged. The position of the screws 54 is quite important with the invention inasmuch as these screws extend through the ribs and22. The walls of the housing 12 are preferably so thin so as not to provide a sufficient thickness for the screws S4 to engage. However, the ribs 2t) and 22 are sufficiently thick so as to provide sufficient contact area to enable the screws 54' to be securely mounted or carried by the housing 12.

Within the end of the housingi12 remote from the closure 52 there is located anotherend closure 6@ which is essentially the same as the closure 52 except that no plugs are provided in this closure 68, and instead an opening 62 is provided therein so as to serve as a bearing support for a shaft 64 which is used to adjust the'po tentiometer 10. An end 66 of the shaft 64 iits closely against a slider 68 which is carried upon the upper ribs 20 as will be explained. This end 66. of the shaft 6a is secured to a small wire 7E) which projects througna generally conical opening 72 in a non-'conductive block Y 74 of a phenolic resin or tl e like forming a part-of the slider 68. The endof the wire 70 remote Hom the shaft d 64 is bent over into a hook shape within a notch 76 in the block 74.

This construction of the slider is considered to be particularly advantageous inasmuch as when the shaft 64 is moved towards the end closure 52 this shaft hits against the block 74 pushing the slider 68. This eliminates the problem of the Wire linkage used from being ever used under compression where buckling of the wire is likely. When the shaft 64 is moved towards the end closure 68 the wire is under tension and it will be realized that there is substantially no danger of buckling under these conditions. The shape of the conical opening 76 and the wire 7l) permits a good deal of misalignment of the slider 68 and the shaft 64 without interfering with the operation of the potentiometer 10.

The block 74 is provided with edge notches 78 which engage the upper ribs 2i!I in much the same manner in which the notches 26 engage the lower ribs 22. This block 74 is held in position against the ribs 20 by means of a top plate 80 secured to the upper surface of the block 74 by means of what, in effect, are the equivalent to rivets 82 formed by melting over projections of the thermoplastic such as nylon material forming the block 74. This top plate 80 is provided with sides 84 of approximately the same basic contiguration as the ends 32 previously described, and is preferably formed out of a resilient metal.

Attached to the surface of the block` 74 adjacent to the support member 24 is a resilient contact member 86 which may be formed out of a single sheet of resilient metal; this contact member may be secured to the block` 74 in .any desired manner. One preferred means for accomplishing this purpose is to metalize part of the surface of the block 74 and then to solder the contact member 86 directly to this metalized surface.

With the preferred construction of the invention, the contact member 86 includes three resilient lingers 88 of different length engaging the resistance element 381y This contact member also preferably includes three resilient fingers 90 engaging the electrical return 40. As willl be apparent from the close examination of Fig. 3 of the drawings, the center finger of each of these `sets is shorter` than the outer fingers of each of Vthese sets ofiingers so that the fingers effectively engage different areasor paths on the resistance element 38 andthe electrical return 40 as the slider 68 is moved. The feature of using a plurality of iingersin thismanner is quite desirable as it tends to lower the noise obtained during the use of the potentiometer 10, and also in that the various fingers located in the manner shown serve to engage different parts of the resistance element 38 and their electrical return 40 in such a manner as to Ytend to prevent any twisting which might occur through maloperation of the slider 68.

In Fig. 5 of the drawings there is shown a portion of a modified end closure 52 of the invention employing instead ofthe plug connections 50 previously described a small metal sleeve V92 provided with a tapped interior surface so that a screw 94 may be secured to it in order to connect the potentiometer 10 into a circuit. Wires 48 as previously described, are with this modification soldered directly to the sleeve 92. It will be understood by those skilled in the art that other types of end connections can be substituted with end closures such as a closure 52 in the same manner in which the construction shown in Fig. 5 was created.

In Fig. 6 of the drawings a modified slider 96 of the invention' is shown which consists'of a block 98 such as the block 74 previously described having secured to the top thereof by means of screws a top plate 102 similar to the top plate 80 previously indicated. This top plate differs from the top plate 80, however, in that on it four projecting-ends 104 such as the ends 32 are provided to engage the vupper ribs 20. In addition, side projecting ends V106 are provided so as to resiliently engage the opposed ends of the upper ribs 20 providing spring tension against these upper ribs. This latter feature is considered desirable inasmuch as it tends to prevent misalignment or binding of the slider 96 during movement thereof. Also, it is considered desirable because it provides a unifoim amount of friction opposing the motion of the slider 96. The top plate 80 acting in conjunction with the block 74 also provides a certain measure of this friction but the friction in this case is not as carefully controlled as in the construction shown in Fig. 6 of the drawings.

This construction in Fig. 6 is also advantageous inasmuch as a shaft 64 may be attached directly to a strip S projecting from the top plate 102. This strip is bent so as to include two segments 110 and 112 located at an angle to one another so that as the two segments 110 and 112 are bent toward one another the shaft 64 may be inserted through generally oval shaped openings 114 formed therein. When the segments are released after having been so bent, the strip 108 will tend to straighten out effectively engaging the shaft 64 and holding the end of this shaft. Because of the inherent exibility of the strip 108 a slight amount of misalignment of the shaft 64' is permissible when the slider 96 is utilized. A contact member such as the contact member 86 may be secured directly to the block 74 as previously indicated.

In Fig. 7 of the drawings a second modified slider 116 of the instant invention is shown which is preferably formed out of a single sheet of sheet metal such as, for example, spring steel, so as to include projecting tongues or ends 118 which are designed so that when this modified slider is used, these tongues 118 engage with the upper and lower surfaces of the ribs 2d effectively holding this slider to these ribs. In order to center the slider 116 when it is used in this manner, stabilizing tongues 12d are preferably formed so as to project therefrom so as to present surfaces remote from the central part of the slider 116 which are designed to bear directly against the ends of the ribs 20.

Formed within the center portion of the slider 116 are projecting resilient contact arms 122 which are designed to engage the electrical return and resistance element 38 previously described. From one end of the slider 116 there projects a strip 124 having a iirst wall 126 located at an angle to the main or center portion of the slider 116 and a second wall 128 located at an angle to this first wall. Within wall 128 there is formed a relatively narrow passage 13) leading to an enlarged circular opening 132. This arrangement is provided so that the slider 116 may be used with a shaft 64 having secured to the end thereof a smaller shaft 134 leading to an end ball 136. Thus, with this construction, the shaft 134 may be inserted through the passage 130 and the ball 136 will be held between the walls 126 and 128 much in the manner of a common ball and socket joint. This type of joint is quite desirable in that it prevents misalignment.

It is preferable with this modification of the invention to coat all of the slider 116 except for the contact arms 122 with a non-conductive plastic as by dipping the slider in a hot melt of polyethylene or the like or in an organosol type of suspension containing a vinyl resin. A plastic coating of this category when applied to all except the contact arms 122 effectively insulates slider 116 so as to prevent any danger of shorting. If desired, this expedient can be dispensed with and small blocks of a non-conductive resin secured to the ends 118 and the stabilizing tongues 124i so as to etectively insulate the slider 116 from the housing 12. Similar insulation means can be applied to the strip 124'. if the shaft 64 is made out of a conductive material. Such means, of course, can be dispensed with if the shaft 64 is formed of a nonconductive material. Such means, of course, can be dispensed with if the shaft 64 is formed of a non-conductive material.

Those skilled in the art to which this invention pertains will realize a large number of other modications can be made in the inventive concept present in this specification without departing from the essential nature of this inventive concept. As an example of such modiiication in a number of different types of enclosures besides those shown ycan be employed, including enclosures embodying dust shields or other structures.

We claim:

l. An adjustable electrical resistor which comprises: an elongated housing of rectangular cross section, said housing including parallel top and bottom walls, and parallel side walls; a pair of upper reinforcing ribs located in a plane parallel to said top wall, each of said upper ribs being located on the interior of one of said side walls, said upper ribs being spaced from said top wall and serving to reinforce said side walls; a pair of lower reinforcing ribs located in a plane parallel to said bottom Wall, each of said lower ribs being located on the interior of one of said side walls, said lower ribs being spaced from said bottom wall and said upper ribs, and serving to reinforce said side walls; a support member located within saidhousing so as to extend from adjacent one end thereof to adjacent the other end thereof, said support member being supported by said lower ribs, and being spaced from said bottom; a resistance element carried by said support member so as to have a surface exposed on the side of said support member adjacent to said top; a slider carried by said upper ribs, said slider including resilient contact means projecting therefrom so as to engage said exposed surface of said resistance element so as to establish electrical communication therewith; a closure located within one end of said housing; means projecting through said closure operatively connected to said slider whereby said slider may be moved within said housing causing said resilient contact means to engage different parts of said exposed surface of said resistance element; a second closure positioned within the other end of said housing; electrical terminal means attached to said second closure; and electrical wires connecting the ends of said resistance element and said terminal means, said electrical wires extending through the space between said bottom and said support member.

2. A resistor as defined in claim 1 wherein said means projecting from said closure comprises: a shaft having an end to which there is secured a projecting wire; and wherein said slider includes a block of a non-conductive resin having a conical opening formed therein facing said shaft and wherein said end of said shaft is positioned adjacent to said block with said wire projecting into and through said conical opening so as to be secured to said block at the end of said opening remote from said shaft, and wherein said end of said shaft is positioned adjacent to said block so as to hit against said block when said shaft is moved toward said block.

3. A resistor as defined in claim l wherein: said means projecting through said closure comprises a shaft having an end `and wherein said slider comprises a single sheet of sheet metal having a center portion, said sheet being formed so as to include tongues adapted to engage 'the upper and lower surfaces of said upper ribs and tongues having surfaces designed to bear directly against the ends of said ribs and means adapted to hold the end of said shaft, said means holding the end of said shaft.

4. A resistor as defined in claim 3 wherein: said means adapted to hold the end of said shaft comprises: a strip having a first wall located at an angle to the center portion of said slider and a second wall located at an angle to said first wall, said second wall including means dening a narrow passage leading to means deiining circular opening, and wherein a small shaft having a ball end is secured to said end of said shaft and said shaft is held by said with said ball end being positioned between said Walls and said small shaft projecting through said.ropening. i

, 5. A variable resistorcomprisingan elongatedhousf ing khaving acavityformed therein, the inner surfacesrof said housinghave two spacedpairs of longitudinally extending parallel ribs formed thereon, a support member containedwithin. said Acavityand supported on one of said pairs of .ribs, arresistance element mounted on the side of said support member adjacent said other pair of ribs, a contact member slidably supported on said other pair of ribs and =wiping on said resistance element, means projecting through a.wall of said housing for shifting said contact member along the length otsaid resistance element, and. terminal means .connected to said-resistance element and electrically ,connected to said `contact, men1` ber.

6. A variablerresistor comprising a housing, a resistancevelement mounted on` said housing, a Contact mem* ber slidably Supported for movement parallel to said resistance element and wiping thereon, said contact memn ber including a main body portion, means at one end of said Contact member defining a pair of opposed Walls spaced apart along the direction of travel o'said contact member, the outer of said walls being notched and havingr an enlarged opening at the bottom of the notch, and a push rod extendingy through one end of said housing and operatively connected to said contact member, said push rod having a slender shaft portion passing through said notch insaid outer wall of said-contact member, and a .ballat the..end.o'f.said1slender-shaftdportion contined ...between -said .opposed.walls, said .ball and said opposedend walls .forming aball and socket joint betweensaidzpush. rodnand said contact member so as-to accommodate,misalignment between them.

`7. A Lvariable resistor as denedin .claim 5, wherein said contact member includes means at one end-thereof defining a socket, and a push rod projecting-through one end of said housing, said push `rod having a ball formed on the rend thereof, said'ball being confined within said seclietto form a flexible jointbetween said push Yrod and said, contactmember, .so as to acccommodatemisalignment4 between them.

References Cited in the le of this .patient UNITED STATES PATENTS 1,122,289 Loveland Dec. 279, 1914 1,282,797 Fonts Oct. 2 9, 1918 1,341,431 Morrow May 25, y1920 2,448,968 Franck Sept. 7, 1948 2,668,218 Searle Feb,` 2, 1954 2,706,230 Bourns et al. Apr. l2, 19,55

yFOREIGN PATENTS 182,686 Germany Sept. `14,- 1905

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