US2594493A - Circuit controlling device - Google Patents

Description

April 1952 G. o. PUERNER CIRCUIT CONTROLLING DEVICE Filed July 28, 1948 INVENTOR.

Patented Apr. 29, 1952 CIRCUIT CONTROLLING DEVICE George 0. Puerner, Indianapolis, Ind., assignor to P. R. Mallory & Co., Inc., Indianapolis, Ind., a corporation of Delaware Application July 28, 1948, Serial No. 41,133

21 Claims.

This invention relates to electrical control devices and, more particularly, to variable resistance devices, volume controls, and switches wherein balanced operation is attained with a minimum number of parts.

Volume controls incorporating switch means therein heretofore have required a comparatively large number of parts to build up the several known sub-assemblies such as the rotary control head containing the contactor and the subassemblies in turn were organized in an operative unit by using other elements. Such construction was relatively expensive because the cost ofzmaterial, fabrication of individual elements, andassembling of the latter was high. Further, the previous control devices utilizing switch elements were not dynamically balanced as well as it was desired because the function of electrical contacting in volume control work was carried out in two distinct levels or arcuate steps, one contact of the contactor being on one step and another contact opposite the first making contact on a lower resistive path or current transfer surface. In accordance with the present invention, the above difficulties in the construction and operation of an electrical control device of the volume control type have been completely overcome.

It is an object of the invention to improve the construction and operation of electrical control devices.

It is a further object of the invention to provide a novel volume control device having comparatively few parts.

It is another object of the invention to provide an electrical control device incorporating both a variable resistance and a switch which are easily assembled in a minimum period by relatively unskilled workers.

It is a still further object to provide a variable resistance device with switch means having a balanced mode of operation.

It is still another object of the invention to provide ,a balanced rotary combined switch and variable resistance which is reliable in operation even though it is manufactured at a low cost.

Other objects of the invention will be apparent from the following description and accompanying drawing taken in connection with the appended claims.

For a fuller understanding of the nature and objects of the invention as well as for specific fulfillment thereof, reference should be had to the following detailed description taken in connection with the accompanying drawing, in which:

Figure 1 is a partial longitudinal section having parts in elevation of an electrical control device embodying the present invention;

Figure 2 is a plan view taken on the lines 2-2 of Figure 1;

Figure 3 is a section on the lines 33 of Figure 1;

Figure 4 is a top view of the insulating body on which a contactor is held;

Figure 5 is a bottom view of a contactor for use with the structure of Figure 1;

Figure 6 is a side elevational view of the contactor;

Figure 7 is a bottom view of the base member showing an arcuate resistive path and a combined collector ring and terminal; and

Figure 8 is a perspective view of another embodiment of the present invention.

While a preferred embodiment of the invenvention is described herein, it is contemplated that considerable variation may be made in the method of procedure and the construction of parts without departing from the spirit of the invention. In the following description and in the claims, parts will be identified by specific names for convenience, but they are intended to be as generic in their application to similar parts as the art will permit.

Referring now to the drawings in detail and particularly to Figure l, the rotary electrical control device may comprise an open-ended shell IO mounted on a housing I I of a rotary switch I2 having a movable switch actuator I3 extending freely through an aperture I4 in a bottom portion I5 of the housing I0. The mounting for the housing I0, which is open at one end to receive a basemember I6, is conventional except for the fact that a central elongated element I'I within the switch I2 extends through an opening in the bottom portion I5 of the shell so as to act as a sort of rivet holding first the switch parts of switch I2 within the housing I I and then the switch I2 to the shell ID. The rivet I'Lhas an inner enlarged portion acting as a bearing I8 for a purpose to be described hereinafter.

The base member I6 has an arcuate resistive path 20 on the inner surface thereof and is secured in the open end portion of the shell ID by conventional logs.

The control device also includes an elongated rotatable element 22, preferably a flat member, extending through an opening I9 in the base member I6 and this rotatable element has a body 23 of insulating material such as a suitable plastic molded to the inner end thereof.

The plastic body 23 includes a cylindrical hearing portion 24 inserted through the opening I9 3 of the base member :8 and has a head portion generally indicated as 25 with two spaced surfaces BI and 62 within the shell iii. A transversely flexible and rotatable contactor is interposed between one of the surfaces 6! and 62 such as surface 6| of the head portion 25 and the resistive path 20 in sliding relation therewith upon.

being properly flexed by the confining head portion and surface 6|.

The contactor 2! is held on head portion 25 for joint rotation with the elongated element 22 by key means such as the diametrically opposite. protuberances 28 on the head portion 25 cooperating with complementary key means 2? on the contactor 2i. tactor 2! are provided with interengaging portions 26, 21 respectively locking them, together effectively only after the contactor is con pliantly positioned by flexing it downwardly against the retaining surface Bi which is prevented from moving inwardly by having the bottom. of the insulating molding 23 contact the bearing is within the shell to and/or the bottom of the shell It, whereby the head portion and contactor are prepared for joint rotation with the elongated element 22.

The head portion 25 and con- The base member IS, shown more clearly in central opening, I9 which is occupied by a portion 8 of the molded body 23 connecting the head 25 to the cylindrical bearing portion 24. The resistive path 28, which may comprise carbonaceous material adhered to an arcuate insulative strip, is placed on the underside of the base member it. The ends of the path 20 are stapled to the enlarged portion 33 of the base member IE through holes 32 by the ears 2?" of the terminals 25'. A contactor ring or electrical contactor surface 28 is concentric with. the arcuate and fiat resistive path and in the same plane. therewith. ihe contactor surface 28 and a connector 2:; are formed as one unit by stamping from flat sheets of metal and the unit is held to the base member [6 by depressing a reduced portion 35 substan tially-midway of the connector 29 through a hole 34 in the enlarged portion 33 of the base member 16 and then crimping over a part of the portion 35 on the outside surface ofthe base member 16.

The contactor 21 having a central opening 36 therein is held between the base member l 8 and the head portion of the molded body 23 only after the elongated element 22 is inserted through the aperture 19 in the base member I6 which is then rigidly fixed to the shell It in the manner described heretofore.

The contactor 21 is stamped or pressed from a sheet of resilient material such as Phosphor bronze to form oppositely extending. arcuate-shaped springcontacting arms 59. and ill having on the inner end thereof contacts 43 and 44 respectively on one side of the bearing 2a or elongated element 22 at. slightly different distancesfrom the longitudinal'axis thereof. Opposite to contacts'eiiand 44 on theother side of the bearing 2 there are found'brush contacts 31 and 58 on arc-like arms 45.and 48 respectivelyformed by arcuate slots 63. 64 terminating with ends within the main body of the. contactor 2|. The arms'lld and lfaiare continuous as contrasted with the arms M! and 4! which are separated at the region adjacent the contacts 43 and M. The contact arms 40, til, and so are bent into the position shown in Figure 6 at the same time that the contactor 21 is stamped from a thin sheet of metal. Since the contactor 2i is interposed between a retaining surface 8! on the head portion 25 and the combined arcuate resistive path 2E and the contact surface 23 which combination are in the same plane, and since the path 26 and surface 28 are concentric with each other, the distance between the center of, the contactor 2i and the contacts 43, dd is only slightly less than the distancebetween the same center and the contacts 3?, 53' so as to providev a substantially balanced thrust upon the bearing M for the elongated member 22 when it is rotated.

A feature of the present invention as'described above resides in the manner in which the contactor 2! is held in position on the rotatable element 22 for sliding contact with the resistive surface 28 and the brush collector surface 28. The construction of the volume control device is such that no rivets or similar fastening means are required to hold the contactor 2! in an operative position. Viewed in another light, this feature is accomplished by providing a one piece molded body 23 capable of having several functions on the inner end of the fiat element 22, the body 23 having a plate-shaped head portion 25 with at least one planar retaining surface 8! with protruding integral key means 28 cooperating with the slotted contactor 2| for mutual engagement when the base member i6 is assembled with the shell to after the contactor 2i is interposed, is properly aligned and is flexed between the head portion 25 and the respective contacted surfaces 26 and 23. Thus, the complexity of previouscontrol devices is entirely eliminated. The inward movement of the enlarged head portion 25 is .prevented by an inner central protruding bearing 49 therein engaging the complementary centralbe-aring it in the base of the housing It! and thereby avoiding other previously necessary parts. The latter structural feature serves not only as a hearing but as a means for biasing the flexible contactor 2! against the fixed contacted surfaces 20 and 28 in a well balanced manner.

The described rotatable assembly including the contactor 2! is further centralized for rotation by placing an externally-threaded. shaft-supporting bushing 53 around the cylindrical bearing 24. The bushing 58. has aninner enlarged generally hexagen-shaped portion 5| with an inwardly protruding tapered collar 5i seatedwithin the aperture it! of the base member I5, and is retained against the top or outside of the base member to by a spider-like metallic element 52. The spider 52 has three symmetrically arranged and radially extendin arms, 53, a l and, 55 struck out from an outwardly protruding and centrally bored portion 5a.

The arms 53, 5d and are held ,in place. by the lugs 57, 53 and 59 respectively which are integral with the open-end portion of the shell [0 in a manner similar to that described for the initial holding of the base member 15- to the open end of the shell ill by using the lugs-9- The spider 52 not. only retains theexternallythreaded bushing 5 3 againstthe base member [6. but'also holds the-base member it more firmly against the shell it than would otherwise be provided by the two lugs 93. However, it. is within the purview of this invention to omit both the spider 52 and bushing since a bushing cooperating with the bearing 24 of the shaft 22 may be formed integral with the base member Hi. It can also be seen that the lugs 9 can be used to prevent the electrical control device from turning as a whole by having holes in the chassis through which the lugs 9 are inserted when the device is mounted on the chassis in a conventional manner.

The bottom or innermost side of the enlarged plate-shaped head portion 25 is formed as a substantially flat surface 62 which carries switch operating means such as a single web-like or radially extending protuberance 65 which engages the movable switch actuator |3 during either clockwise or counterclockwise movement of the elongated element 22 holding the parts heretofore described because the protuberance 65 is originally placed between two spaced vertical sides 66 and 61 of the movable switch actuator |3 positioned within the eccentrically located sector-like aperture I4.

A peripherally located stop means such as the radial extension 8! integral with the head portion 25 engages an inwardly depressed and eccentrically located stop portion 88 on the inner circular wall side of the shell Hi so as to limit the rotational movement of the contacts 41 and 48 over the arcuate resistive path to an angle less than 360 after the switch i2 is turned on by the actuating element 65 moving the actuator l3 of the switch I2.

, A thin strip of insulating material 68 is inserted within the shell l5 for engaging with the uninterrupted major portion of the side walls thereof and the underside of the base member Iii to provide substantial sealing of the inner rotatable electrical contacts away from the atmosphere and to give more positive insulation between the shell and the parts which are touched by the operator. Under certain conditions this strip can be left out.

Referring again to the rotatable elongated element 22, it should be noted that it is an elongated flat metallic member having at an outer end thereof a protruding portion 60 stamped therefrom fixedly to retain a knob 69. Therefore, another feature of this invention is the use of a flat shaft extension which may be also stamped out or produced in a similar manner on a mass production basis so as to lower the cost thereof.

In order to accommodate another usage of the subject electrical control devices and/or to further simplify the above-mentioned rotatable assembly including the molded head portion and fiat metallic shaft-extension 22, the latter is omitted and a stub shaft 85 with a bearing portion 8| and knurled end 82 containing a transverse slot 83 is substituted as shown in Figure 8. This arrangement is particularly advantageous when the subject volume control shown in Figure 1 is used as a trimmer control in television receivers. The knurled end 82 may fit within a recess of a panel (not shown) for easy manipulation either by the fingers of an operator or by a screw driver engaging the outside of the knurled end 82 and/ or the slot 83. Thus, the shaft extension 22 is molded in a shorter form as an integral part of the molded head portion 25 so as to further reduce the cost of the subject rotatable assembly and to prevent unauthorized persons from misaligning a signal wave receiver in which the volume control is used.

Referring to Figure 3, the assembling of the contactor 2| with the protruding head portion 25 is further demonstrated for the purpose of showing how the number of parts of the previous In the operation of the electric control device the knob 53 is turned in a clockwise direction so as to first rotatably move the switch actuator |3 to a closed position through the sliding action of an enlarged curved portion or eccentric pin H of the radial lug 65 within a slot formed by the spaced sides 65 and 61 of the actuator I3. Thus, the resistive path 20 is placed in connection with an electrical circuit (not shown) and after the above operation the knob 69 may be turned in the same direction by degrees depending upon the percentage of the resistive path 20 it is desired to have in a controlled circuit (not shown also) through the electrical bridge contactor 2| as one versed in the art can realize.

The rotation of the knob 69 and shaft 22' with the retaining surface 6| and the coupled contactor 2| in a reverse or counterclockwise direction and ultimately to a switch-off position of the actuator i3 is limited to a predetermined small angle after the switch I2 is turned off.

The clockwise rotation of the head portion 25 and contactor 2| includes a relatively large angle because of the substantial arc distance between the side 16 of the stop 81 in the off-position of the switch actuator l3 shown in Figure 3 and the side of the inwardly protruding lug 88 of the shell l0. Since the contacts 43 and 44 are on slightly different radii proper contact will be made upon the inner contacted surface 28 and the same holds true of the contacts 47 and 48 making contact to the resistive path 28. It should be further noted that since the brush or contact surface 28 is in the same plane occupied by the resistive path 25, the rotation of the contactor 2| by moving the knob 69 will be very smooth.

From the above disclosure, it can be seen that a new and novel electric control device is presented having the features of a flat shaft 22 so as to minimize the cost thereof and of a simplified sub-assembly including an insulating multifunction molded body 23 having the contactor retaining surface SI of the head portion 25 and a contactor 2| without the use of rivets. Additional simplification is produced because the head portion 25 and the cylindrical bearing 24 connected thereto is molded on an inexpensive flat shaft extension. Since contactor 2| is interposed between the surface BI and the various contacted surfaces found on the underside of the base member l6 which is, in turn, held rigidly to the outer portion of the shell |El by means not requiring rivets, etc., and since the inward movement of the head portion 25 is prevented by the protruding bearing element 49 contacting the inside bottom of the shell H), a simplified electric control device is produced. It will be noted that the contactor 2|, after it is coupled to the outer side of the head portion 25 through the alignable means 25, 21, is really held in an operative position on the head portion 25 by the resilient action of the contacting arms 40, ll, 45 and 45 respectively responding to the opposing action of the fixed base member Hi and is associated contacted surfaces after the base member I6 is assembled with the shell H1 is a manner already discussed.

While the present invention, as to its objects and advantages, has been described herein as carried out in specific embodiments thereof, it is not desired to be limited thereby but it is in- 7, tended to cover: the invention broadly within the spirit and scope of: the appended claims.

What is claimed is:

- 1". Arotor for a circuit controlling device integrally molded. from: plastic insulating material, said rotor' comprising an. enlarged body portion. having a flat surface generally perpendicular to the-rotor axis, said surface having. aplurality of lugs formed thereon, a reduced bearing portion of ci'rcularc'ross section protruding. from one end of said body and. centrally coupled thereto, and a boss protruding from the other end of said body,- said boss: being. recessedxto form a. bearing support for the. other end of. said. rotor.

2 In a. circuit-controlling device having. a con-' tractor, and av bushing; a rotor integrally molded from plastic insulating material, said. rotor comprising an enlarged. body portion defining a pair of facing: semicircular segments of unequalarea having a flat surface. perpendicular to the rotor axis, said: surface. having a plurality of lugs formed. thereon. for supporting said contactor, astop projection eAtendi-n horizontally from the periphery of said larger segment of body, a reduced. bearing. portion of circular cross section protruding fromone end of saidbody and adapted to; fit withinz said bushing to support one end of the: rotor, said reduced. portion having? a slot at its. outer end. and a boss protruding from the other end of said. body, said. boss being recessed to form a bearingsupport for the other end of. said. rotor,

3.. Ina circuit controlling device having, a contactonand a bushing a rotor integrally molded from: plastic insulating: material, said rotor comprising an. enlarged body portion defining a pair of? facing semicircular segments of unequal area having, a flat surface. perpendicular to the rotor axis, said surface having a plurality of lugs formed thereon forsupporting a contactor, a stop projection extending outwardly from the periphcry of said larger segment of. said body, a reduced bearing portion of circular cross section protruding from one end ofv said body'and adapted to fit within abushing to support oneend of the rotor,

saidreduced: portion having aslot at its outer end, a bossprotruding from the other end of said body, said. boss being recessed to form a bearing support for the other. end of. said rotor, and a switch actuating member. projecting, outwardly from. the other end. of. said body, said member being. spaced from the rotor axis.

4, A variable. resistance comprising, in. combination, casing, having a bushing extending therefrom, a rotor formed from molded insulating. material having an enlarged body portion disposed within said casing, areduced bearing portion protruding from one end of said body portionandjournalled in said bushing to form a bearing for one end of said. rotor, a boss. protruding from the other end of said. body portion, said boss having a recess formed therein, a pin mounted: on said. casing and extending into said recess to forma bias adjustable bearing support for the other end of said rotor, said body portion having a fiat surface facing and closely spaced to onewallofsaid casing, anarcuate resistance element. mounted on said casing wall, a plurality of lugs.- formed on. said surface, and a contactor formed from spring material mounted. between said resistance element. and said surface, said contactor having. cut. out portions cooperating with saidllugst'o prevent rotation of the contactor with respect to said. rotor, and said contactor being maintained in engagement with said 5111- 8'. face solely by the resilience of said spring material, the thrust impartedto the rotor by said contactor being taken up by said bias adjustable bearing support.

5. A Variable resistance comprising, in combination, a casing having a bushing extending therefrom, a rotor formed from molded insulating material. having. an enlarged body portion disposed. within said casing, a reduced bearing portion protruding from one end of said body portion and journalled in said bushing to form a bearing for one end of. said rotor, a: boss pro) truding from the other end of said body portion, said. boss. having; a recess formed therein, a pin mounted on: said casing; and extending into said recess to form a: bias adjustable bearing support for the other end: of: said rotor, said body portion having. a: fiat surface facing and: closely spaced; to one wallof. said casing, an arcuate resistance element mounted on said casing: wall, an arcuate metal strip of smaller radiusthan' saidresistance element mounted. on said casing wall. inconcentrio relation with" said resistance element, whereby said strip and. said element lie in a common plane, a plurality of lugs'formed: on said surface, and. a resilient contactor having a portion. engaging. said surface and a plurality ofv contact arms.

engaging said strip and said resistance element,

said contactorhaving recessed portions cooperating with said lugs to prevent rotati'on oi the con.- tacto'r' relative: to the: rotor, said contactor: being maintained in engagement; with said surface solely by-the resilience of said contactor;

6.- A combined variable resistance: and switch comprising, in combination, acasing having. a bushing extending therefrom a switch uni-t secured to said casing, said switch unit having an.

actuating member projecting through: said casing, a rotor f'ormed from-molded insulating materialhaving an enlarged generally cylindrical body portion disposed within said casing, a-stop member projecting from the periphery of said body portion, a lug formed in aid casing cooperating with said stopmember to limit-the angular move-- ment of said rotor, apinprotruding from and integral with said rotor, said pin beingspaced' from the rotor axis and being engageable with said actuating member to operate said switch unit, areduced bearing portion formedintegrally with said body portion and journalled insaid bushing, said body portion having a flat surface facing and closely spaced to the casing- Wall' having said bushing, an arcuateresistanceelement mounted on said casing wall, and a contactor formed from spring material mounted between said surface and said resistance element, said contactor being'maintained inengagement with said surface solely by the resilience ofsaid' spring material.

7. A combined variable resistance and switch comprising, in combination, a casing having a bushing extending therefrom, a switch unit secured to said casing, said switch unit havingan actuating'mcmber projecting through said casing, a rotor formedfrom molded insulating material having an enlarged generally cylindrical body portion disposed within said casing, a-stop mem-- ber projecting from the periphery of said body portion; a hug formed in said casing cooperating with said stop member to limit the angular movement of said rotor, a pin protruding from and integral with said rotor, said pin being spaced from the rotor axisand being engageable with said actuating member to operate said switch unit, a reduced bearing portion formed integrally with said body portion and Journalled in said bushing to form a bearing for one end of said rotor, a boss protruding from the other end of said body portion, said boss having a recess formed therein, a pin mounted on said casing and extending into said recess to form a bias adjustable bearing support for the other end of said rotor, said body portion having a flat surface facing and closely spaced to one wall of said casing, an arouate resistance element mounted on said casing wall, a pluralty of lugs formed on said surface, and a contactor formed from spring material mounted between said resistance element and said surface, said contactor having out out portions cooperating with said lugs to prevent rotation of the contactor with respect to said rotor, and said contactor being maintained in engagement with'said surface solely by the resilience of said spring material, the thrust imparted to the rotor by said contactor being taken up by said bias adjustable bearingsupport.

8. In a circuit controlling device having a housing, a bushing, a contactor element and a resistance element; a rotor enclosed by said housing comprising a main body of insulating material, said body having a plurality of surfaces, a bearing portion integrally molded to one of said surfaces, and a boss oppositely placed with respect to said bearing portion on said other surface, said bearing portion insertable in said bushing and said boss engaging said housing of said circuit controlling device to provide a two point suspension for said rotor in the operation thereof.

9. In a circuit controlling device; a rotor as in claim 8 wherein said rotor includes projecting means substantialy medially placed on said surface opposite said surface including said boss, said projecting means connected to said bearing surface so as to retain said contactor element on said surface.

10. A circuit controlling device as in claim 8 wherein said resistance element is placed adjacent said contaotor element on said surface opposite said surface including said boss.

11. A rotor integrally molded from plastic insulating material comprising two facing semicircular segments having a plurality of longitudinally spaced surfaces, one of said segments having a diameter greater than its other segment, a plurality of ledges formed by the juxtaposition of the diameters of said segments, a stop projecting from the periphery of said larger segment, a bearing portion extending along an axis substantially vertical with respect to one of said spaced surfaces, said bearing portion having a plurality of lugs extending radially therefrom along said one surface toward its periphery, and a boss molded to the other of said spaced surfaces, said boss having a rib extending longitudinally along said other surface in a direction diametrically opposite said stop formed on said larger semi circular segment.

12. A rotor as in claim ll. wherein said boss has recess formed therein for holding a second bearing means.

13. A rotor as in claim 11 wherein said bearing portion is centrally positioned on said one of said surfaces and has a flat shaft molded thereto.

14. In an electrical control device having a base provided with a resistance element and a bushing, and having a cup-shaped cover attached to the base and coacting therewith to provide a housing: a shaft journaled in the bushing and projecting into the housing; a driver fixed to the shaft at the end thereof inside the housing, said 10 driver having an annular rearward projection concentric'to the shaft with the extreme rear edge of said projection lying in a plane normal to the shaft axis and beyond the adjacent end of the shaft so as to provide a smooth uninterrupted runner adapted to ride on and receive support from the bottom wall of the cup-shaped cover, whereby said runner and the bottom wall of the cup-shaped cover constitute a thrust bearing; and a contactor carried by the driver and interposed between the base and the driver, said contactor having spring contact fingers to resiliently bear against the resistance element and by the spring tension thereof hold the circular runner against the bottom of the cup-shaped cover.

115. In an electrical control, the combination with a base having a bearing and an annular resistance element concentric therewith and exposed on the inner face of the base, and a, cupshaped cover attached to the base and coacting therewith to provide a housing enclosing said resistance element, of: a shaft journaled in the bearing and projecting into the housing; a driver fixed to the shaft at the end thereof inside the housing; a contactor carried by the driver and having a spring contact finger to ride upon and resiliently bear against the resistance element; and an annular runner integral with the driver and extending rearwardly therefrom, said runner being concentric to the control shaft and its rearmost edge lying in a plane normal to the shaft axis and beyond the adjacent end of the shaft to ride upon and be supported by the inner face of the cup-shaped cover whereby said annular runner and the wall of the cover upon which it rides constitute a thrust bearing to hold the shaft and driver against inward displacement from a position maintaining the spring contact finger under tension.

16. An electrical control of the type having cooperating rotatable and stationary elements enclosed within a housing with the rotatable element movable by means of a shaft protruding from one wall of the housing, characterized by the provision of a thrust bearing comprising, the wall of the housing opposite that through which the shaft protrudes; and a part on the shaft bearing against said rear wall, the part on the shaft which engages the rear wall being a smooth annular runner concentric to the shaft axis with its rearmost edge lying in a plane perpendicular to said shaft axis and extending beyond the rearmost portion of the shaft so as to have a smooth running bearing upon the rear wall of the housing.

1'7. The electrical contra! set forth in claim 16 further characterized by the fact that said part on the shaft is a one piece molding of insulating material.

18. In an electrical resistance device: a base having a hole therethrough for the reception of a control shaft; a resistance element on the inner face of the base; a control shaft journaled in the hole in the base; a driver fixed to the shaft and overlying the inner face of the base; a spring contactor mounted on the driver and engaging the resistance element, the tension of the spring contactor imparting a rearward thrust to the driver and shaft; a cup-shaped cover positioned over the rear face of the base and coacting with the base to define a housing for the resistance element and contactor; and a thrust bearing to oppose the rearward thrust engendered upon the shaft and driver by the tension of the spring contactor, said thrust bearing comprising, a ring in- 111 v tegral with the driver and projecting :rearwardly therefrom "beyond the rearmost portion of the shaft, the rear edge of said ring lying on a plane normal to the shaft axi and having a smooth sliding engagement with the adjacent end wall of the cup-shaped cover.

19. The electrical resistance device of claim 18 further characterized by the provision of cooperating stop abutments on the driver and the cupshaped cover to define the limits of rotation of the'rotatable elements of the control.

20. :In a variable resistance device of the type in which a resistance element is traversed by a contactor driven by a rotatable control shaft passing through. a hole in a base of insulating material, and wherein the control shaft is biased endwise toward the rear of the device: a cover attached to "the "base over the rear face thereof, said cover coacting with the base't-o form a housing forthe device and having a wall substantially normal to the shaft axis and opposite the rear end of the shaft; a driver for the contaetor fixed to the shaft inside the' hous ng; and a circular runner .on the rear of the driver extending beyond the rearmost portion of the shaft and throughout its entire circumference bearing against said "wall of the cover toprovide a smooth running thrust bearing for supporting the shaft against the rearward end thrust thereon.

"21. The variable resistance device of claim 20 further characterized by the provision of co operating stop abutments on the driver and the cover for limiting rotation of the driver and consequently the contactor.

GEORGE O. JPUERNER.

REFERENCES orrEn Thefollowing references are of record in the file of this patent;

UNITED STATES 'PATENTS

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