US1781959A - Rheostat - Google Patents

Description

N0 18, 1930 N. c. scHELLENGER 1,781,959

BHEosTAT Filed Oct. 6, 1925 Inde/232377q Patented Nov. 18, 1930 UNITED STATES PATENT OFFICE NEWTON C. SCHELLENGER, 0F ELKHART, INDIANA, ASSIGNOR TO CHICAGO TELEPHONE SUPPLY COMPANY, OF ELKHART, INDIANA, A CORPORATION OF DELAWARE RHEOSTAT My invention 'relates to improvements in the electrical art and more particularly to control apparatus .such as rheostats and potentiometers.

I propose in general to provide a greatly improved rheostat which is not only substantially moisture proof but is adapted to withstand severe service and usage, such as is commonly experienced in radio apparatus.

In this rheostat of my invention, I employ an insulator strip rendered moisture proof by a preservative such as linseed oil. This strip is preferably treated in accordance with my novel process which includes impregnating the strip with linseed oil and subsequently tumbling the strip in a tumbler to remove surplus oil therefrom. The oil not only expels the moisture from each strip but in displacing the moisture. fills the pores of the strip. Also after the strip has been treated and dried, the oil on the surface of the strip oX idizes thus forming' a smooth moisture proof protective coating for the strip.

The insulator strip when vassembled in the rheostat is positioned between the metallic frame or base and the resistance strip which is preferably of the carbon type and is made in accordance with the features of my copending patent application, Serial No. 139,784, tiled October 6th, 1926.

Also I propose to provide novel arcuate shaped clamp plates associatedwith the ends of the resistance strip for clamping the resistance and insulator strips to the metallic frame. Each of the plates is provided -With a beveled edge for engagement with the contact roller of the contact arm and serves as a seat for the contact roller.

Now, in practice, I find that after an ordinary type of rheostat has been in service for a period of time, and especially if the usage of the same is severe, the contact arm will quite frequently fail to malte good contact with the resistance strip due either to wear or distortion of the parts. I propose to remedy this condition by providing a novel contact arm assembly having resilient means'for at all times insuring a good contact between the arm and the resistance.

Irl-accordance with the general features oi Serial No. 138,783.

my invention, I provide'a cup shaped metallic frame or base in which is disposed my novel contact arm assembly comprising a sliding arm having a. slotted portion for receiving a collar connected to the operative shaft of the rheostat and being provided with a bifurcated end for straddling a portion of the contact roller which has a rolling contact with the resistance strip. The sliding frame is resiliently connected to the collar on the shaft by the means of a screw and a spring surrounding the shank of the screw. This spring, as will be more fully described in the accompanying specification, permits of the sliding frame moving relative to the collar.

In accordance with other features of my invention, I furnish the cup shaped metallic frame or base with a transparent or Celluloid cover which is secured at its center by means of a screw to the end of the rheostat shaft. The outer or peripheral edge of this cover is adapted to engage the external edge of the resistance and insulating strips and the single screw at 'the center of the Celluloid cover serves to not only draw the center of the cover into tight engagement with the end of the shaft but serves tol also draw the peripheral edge of the cover into tight engagement With the said strip. The cover also supports the end of the .operating shaft thus holding it true with the axis of the frame. Obviously' the purpose of the cover is to prevent dust and other foreign matter from interfering with the proper operation of the contact roller. Also by substantially eliminating any dust from the interior of the rheostat, it is possible to prevent change in the resistance of the resistance strip.

Other objects and advantages of my invenn tion will more fully appear from the followin;r detail description taken in connection with the accompanying drawing, which illustrates one embodiment thereof and in which,

Figure 1 is a plan elevation of my no? rlieostat;

Fig. 2 is a perspective view ci the inswlat ing strip;

Fig. 3 is an enlarged sectional view of my rheostat taken on substantially the line 3 3 of F ig. 4; and

portion thimble is Fi 4 is a sectional view taken on substantially the line 4.--4 of Fig. 3.

Referring now to the drawing in detail, in which like reference numerals designate similar parts throughout the several views, denotes generally f a metallic frame or base which is preferably of cup shape. This frame may be made from sheet brass and is preferably a punch press product. Also if it is so desired, the frame may be buded and nickel-plated.

The cup-like frame or base 10 comprises a flat portion 11 and an annular rim 12. The port-ion 11 is provided with a central openingv 13 through which extends the reduced 14 of a thimble 15. The axis of the disposed parallel to the axis of the frame or base 10. l-Also the thimble 15 with the shoulder 16 sets tightly and squarely against'the frame portion 11. s

This thimble may be made on a screw .machine and is preferably made from brass rod. It also may be nickel-plated. In order to secure the thimble to the portion 11 of the frame '10, the reduced end 14 of the thimble 15 is riveted at 17 to the portion 11 inside of the cup 10.

lExtending through the bore 18 of the l thimble 15 is a shaft- 20 provided with a reduced portion .19 which projects into the interior of the cup-like frame 10. The shaft 20 `has an annular shoulder 21'which engages an annularshoulder 22 formed in the thimble 15. These two shoulders 21 and 22 cooperate to prevent movement of the shaft 20 in one direction. u

Also the thimble 15 is provided with an 1external. threaded portion 23 projecting through an annular opening 24 in a mounting anel 25. The frame 10 isftightly clamped to the panel 25 by means of a nut 26 threaded ont-o the portion 23 of the thimble 15 (Fig. 4). A thin washer 27 is preferably positioned between the nut 26 and the base of theI panel 25. Fastened to one end of the shaft 2O is a knob 28 which' includes a metallic thimble 29. The knob and thimble are se- .cured to the shaft by means of a set screw 30 extending through an aperture 31 formed in the knob 28. It will be observed from Fig. 4 that the knob 28 includes an annular `iange 33 for substantially enclosing the part used to fastenthe frame to the panel 25.V

AAlso the knob'33 may be made of any suitable insulation, such, .for example, as molded phenolic condensation matter.

Surrounding the reduced ortion 19 of A the shaft 20 is a collar 35, which has an exltension 36 telescoping a washer 37. The extension 36 istightly iitted into the washer orring-li-ke member 37 and has an annular lateral -liange 38 whichl serves to secure the 'member 37 to the collar 35. Both the collar H' and the member 37as well as the shaft 2O my bemade ffrorn'vsuitable brass rod. These parts may also be provided with a mechanical nickel-plate plating. The collar 35 is providedv with a pair of cut-awayportions 39 and 40 for receiving the legs 41 and 42 of a slidable frame 44. This frame 44, as will be more fully described hereinafter, is adapted to be moved relative to the collar 35.

Legs 41 and 42 of the frame 44 are connected at one end by means of a lateral extension piece 43. This extension piece 43 has an opening 45 through which the shank of a screw 46 extends. Disposed about the shank of the screw 46 is a coil spring 47 preferably of the compression type. One end of this spring abuts the head of the screw 46 and the other end abuts the extension piece 43. This screw 46 is threaded at 48 into the collar 35. Also it should be noted l i erably made of brass rod and in reality comprises two rolling portions 53 and 54 connected by the reduced ortion 51. Sliding frame 44 may be made rom relatively hard brass sheet. Both the frame and the roller are nickel-plated.

Located between the portion 11 of frame 10 and the flange 38 of the extension 36 and surroundin the reduced portion 19 is a spring was er 55. This washer serves to urge the contact arm assembly in a direction away from the panel 25. I have designated the contact arm assembly generally by the reference character 56. It will be evident that this assembly 56 which includes collar 35, sliding frame or arm 44 and roller 52, cancbe removed with facility from the shaft 20 by releasing the screw 46 from engage ment with the reduced portion 19. e

vPositioned. within the cup-like frame or base 10 and abutting theinner periphery of the side 12 is my novel insulating strip 601 I shall describe more in detail the process of making the strip hereinafter. This strip 60 is bent into an arcuate shape when it is mounted in the frame. A resistance strip 61 is also disposed-within the cup-like frame 10. This strip is bent into an arcuate shape and is contiguous with the insulating str1p 60 which serves to insulate the resistance strip 61 from the frame 1 0.

Resistance strip 61 is made in accordance with the features of my "copending patent application SerialNo. 139,784, filed October 6th, 1926. Briefly, this strip consists of a fibrous sheet of material having a coating of my novel resistance paint thereon. The resistance paint or coating consists of a Imixture of. graphite, lamp black and gum reference character 80.

shellac. In this mixture, I preferably employ 8 pennyweight of lamp black and 7 pennyweight of graphite. These carbons are mixed in a gum shellac solution of from 7 to 12 iiuid ounces .depending upon what resistance is desired. `The shellac is preferably diluted with alcohol until it gives a mixture which will read approximately 29 on a Baume ammonia hydrometer scale. The carbon paint may be applied to the sheet of fibrous material with a suitable varnish brush and then dried for agiven period of time at a temperature of 170O Fahrenheit. The advantages of this resistance are fully set out in my copending patent application.

The strip 6l is insulated from the flat portion 11 of the frame 10 by means of an annular gasket or washer 63. This gasket 63 ma be made of any suitable insulatin material such, for example, as press board. eferring to Fig. 3, it will be obvious that one end of the strip 60 and the corresponding en?. of the strip 61 are secured to the ange 12 of the frame 10 by means of a screw 65 and a pair of lock nuts 66 and 67. A washer 68 is disposed between the screw 67 and the outer peripher of the portion 12. An aperture 69 is provi ed in the frame 10 for accommodating the shank of screw 65. Also the screw 65 extends through suitable apertures or openings in the associated ends of the strips 60 and 61.

The other end of the strip 60 and the associated end of the resistance strip 61 are secured to the frame by means of a screw 70. This screw extends through an enlarged opening 71 in the annular flange 12 of the frame 10. A bushing 72 is disposed in the enlarged opening 71 and serves to insulate the shank of screw from the frame 10. Screw 70 is locked in place by means of a pair of lock nuts 73 and 74. A pair of wash-` ers 75 and 76 are disposed between nut 74 and the flange 12. Washer 75 is preferably made of metal and washer 76 must be made of insulating material so as to insulate the screw from the frame.

In Fig. 2, I have illustrated my novel insulating strip 60. This strip 60 has a pair of apertures or o enings 78 or receiving the screws 65 and 70 respectively, as previously described. The resistance strip 61 has a pair of similar lopenings adapted to be aligned with openings 78. I shall now proceed to describe in detail my novel clamping plates associated with the heads of the two screws 65 and 70.

I designate the clamping plates by the Since these two plates are identical as to structure, it is believed the description of lone will Ysuffice for both. Each -of the plates is arcuate in shape so as to accommodate itself to the arcuate shaped strips associated therewith. Also each plate has an aperture 81 through which sheets.

the shank of the associated screw extends. Each ofthe plates has a ground beveled ed e 82 adapted to be engaged by the roller 52. In order to insure a good electrical contact between the roller and each of the plates, I preferably make the plates from nickel silver These plates not only serve as clamps for securing the strips to the frame but also cooperate with the screw heads in limiting the travel of the cont'act roller. The heads of screws 65 and 70 actually serve as the stops for limiting the travel of the contact roller.

. The end of the portion 19 of shaft 20 is reduced at 85 so as to fit in opening 86 in a cover 87. The cover 87 is a circular plate of insulation, and is preferably made of transparent material such as lCelluloid. The pey ripheral edge of this cover is adapted to engage the outermost edges of the two strips 60 and 6l, as is obvious in Fi 4. Also the portion 1 9 of shaft 20 is provi ed with a threaded opening 88 for receiving the threaded shank of a screw 90. The screw 90 serves to draw the Celluloid cover 87 into tight engagement with the shoulder 91 on the shaft 20. Cover 87 not only protects the contact mechanism from dust and foreign matter but also protects the parts from moisture. n

I shall now describe in detail the process of manufacturing my novel insulating strips 60. Thestrips 60 are preferably punched press board and are each provided with the previously mentioned pair of perforations 78. Each strip is first boiled in a suitable oil such, for example, as linseed oil. This boiling operation results in themoisture being expelled from the strips and the oil in displacing the moisture fills the pores of the strips. After the strip has been tumbled and dried, itwill be found that the oil lhas oxidized thus providing a waterproof coating for the strip.

In order to remove the surplus oil from the strips, each strip is placed along with others immediately after boiling in a tumbling barrel and tumbled. This tumbling action not only removes the surplus oil from the strip, but also polishes its surface.

The roller 52 is adapted to exert substantially a one pound pressure on the resistance strip; this insuresa Vvery positive electrical connection between the roller and the resistance. By adjusting the screw 46, the tension of spring 47 can be varied thus enabling the pressure ofthe roller to be properly adjusted at all times.

The operation of my novel rheostat is believed to be obvious from the foregoing detail description of the same. By turning the knob onlshaft 20, the roller 52 can be made to roll along the surface of the resistance strip 61 to varyv the resistance. Any irregularities in the movement of the roller 52 are compensated for by the spring which permits the frame 44 to move relative to the collar 35.

I desire it understood that my invention is not to be limited by the above foregoing description but only insofar as defined by the scope and spirit of the appended claims.

I claim 1. In an electrical current control device, a cup shaped body, a resistance element disposed in said cup shaped body, movable contact means associated therewith and a clamping plate for securing the resistance element to the body, said plate having a beveled edge disposed in the path of movement of said lcontact means and having tracking cooperat'ion therewith.

'2. In an electrical current control device, an arcuate shaped cup constituting the frame ofthe device, a resistance disposed in the said cup, contact mechanism associated therewith including a contact roller adapted to cooperate with the said resistance, and an arcuate shaped clamping plate for fastening an end of the said resistance to the said cup, said plate having a beveled edge disposed in the path of movement of and cooperable with the roller. v

3. In an electrical current control device, a metallic frame comprising a cup shaped member,.a resistance strip disposedin the said member, an insulating strip for insulating the resistance from the frame, contact mechanism connected to the frame adapted to cooperate with the said resistance strip, said mechanism including a roller adapted to have a rolling engagement with the resistance strip, and means for clamping the ends of the Said strip to the frame, said means including a pair of *clamping plates, each of the said plates bein arcuate in shape and having a beveled edge isposed in the path of movement of and having tracking cooperation with the roller.

4. In an electrical current control device, a cup-like base, a resistance element disposed in the said base, contact mechanism positioned in the cup base adapted to cooperate with the said resistance element, said mechanism including a resiliently mounted roller adapted to have frictional enga ement with the said resistance element, 'an means for fastening the resistance element to the base comprising a stop for limiting the travel of the said roller and a beveled edged clamping plate drawn upon the resistance element by said stop and tracking the roller into cooperation with the sto 5. In an electrical current control device having an operating rod and a resistance element, the combination of a collar connected to the said rod, a slidable element associated with the said collar, an adjusting screw for connecting the said element to the collar, resilient means 4carried by the said screw for permitting the said slidable element to move Lvsnese relative to the collar, and a roller pivotally connected to the said slidable element adapted to have frictional engagement with the said resistance element.

6. In a device of the class described, the combination of a resistance element, a rotatable operating member having a splayed portion, a yoked member straddling the splayed portion of said operating member and having movement radially of the operating inember in a plane intersecting the axis thereof and contact means cooperable with said resistance element and associated with and operated by said yoked member.

7. In a device ofthe class described, the combination of a resistance element, a rotatable operating member having a splayed portion,a yoked member straddling the splayed portion of said operating member and having movement radially of the operating member in a plane intersecting the axis thereof, contact means cooperable with said resistance Velement and associated with and operated by said yoked member and means cooperating with said yoked member and yieldingly urging said contact means into contact with said resistance element.

8. In a device of the class described, the combination of a resistance element, a rotatable operating member having a splayed portion, a yoked member straddling the splayed portion of said operating member and having movement radially of the operating member in a plane intersecting the axis thereof, contact means cooperable with said resistance element and associated with and operated by said yoked member, an abutment and a spring interposed between said abutment and said yoked member and yieldingly urging said contact means into contact with said resistance element.

9. In an electric current control device having an operating rod anda resistance element, the combination of a collar, an arm movable with respect to the collar, a contact member carried by the arm, a screw rigidly securing the collar to the operating rod and a spring carried by the screw for yieldingly urging the contact member into contact with the resistance element.

10. In combination, an operating rod, a collar on the rod, an arm movable with respect to the collar, a headed screw rigidly securing the collar to the rod, a lug on the arm, and a spring disposed between the lug and the head of the screw.

v11. In combination, an operating rod, a

slotted collar on the rod, an army disposed in the slot in the collar and slidable therein, a headed screw rigidly securing the collar to the rod, a lug on the arm, and a spring disposed between the lug and the head of the screw for yieldingly urging the arm away from the head of the screw.

12. In combination, an operating rod, a col-

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