US2396970A - Variable resistance - Google Patents

Description

March 19, 1946. F. E. RILING VARIABLE RESISTANCE Filed Feb. 2. 1944 w 2 @.0 U f. @29ml M m 1mm. ov \\\\\\\\S IN m O o u mw v w 5 f 3 F 7 l o 4 i d Patented Mar. 19, 1946 UNITED STATESI PATENT ori-'ICE VARIABLE RESISTANCE Floyd E. Riling, Anderson, Ind., assignor to P. It.

Mallory & Co., Inc., Indianapolis, Ind., a corporation of Delaware Application February 2, 1944, Serial No. 520,726 solsims. (creol-s) slider adapted to make electrical connectionto E any desired point of the element.

Heretofore, considerable difficulty 'was expe-z rienced in providing electrical connection of constant and negligible resistance to the sliding element. It was customary to provide a double slider element one sliding surface of which was resiliently applied to the resistance element, the

other sliding surface being applied to a fixed at This type ofV contact ring, or its equivalent. structure, however, although employed on a substantial scale, was farfrom being satisfactory,V as two slidingcontacts were introduced into the circuit and their resistance was appreciable and valso subject to variations due to oxidation of the The result was i cooperating contact surfaces. that noise was produced particularly when the control was already in use for some time and such circuit noise necessitated frequent replace-l ment of the otherwise but slightly used control. Some relief was made possiblerby providing a coil spring wire for electrical connection of the rotative slider and the stationary soldering lug therefor. This type of structure, however, has introduced other complications. As it is considered desirable'to insulate the main shaft vof the variable resistance from the slider, provision had to be made for positive insulation ofthe shaft from factory and successful when carried into-practice on a practical and commercial scale.

It is an object of the present invention to eliminate the foregoing difficulties experienced in the construction'and operation of conventional variable esistances. j

It is another object of the present invention to provide a variable resistance of novel and improved character in which a positive electrical connection of negligible resistance is established and maintained between the sliding contact and its binding post or terminal, and such connection is maintained insulated from the main shaft without the provision of insulating materials interposed between the metallic conductor and the shaft.

It is a further object of the invention to provide a conductor in the form of a conically wound re- 1 silient metallic memberhaving such shape and the coil spring and this could be obtained only by surrounding the corresponding portions of the shaft with a member or sleeve of insulating material. Also the individual turns of the coil spring would frictionally .engagethe surface of the insulatlve sleeve provided between the same and the shaft and become entangled with each other. The .result was either early destruction of the cylindrical coil spring or increased binding and tension thereof which tended to'return the slider todesign that during rotation of one of the flxed points .of such member the several turns will be automatically forced away from the center so that both binding of the turns and their accidental.' contact with the4 shaft are positively avoided. I

The invention also contemplates a novel and improved variable resistance of the rotary type which is simple in character and construction,

provides positive and at all times reliable electrical connection of the sliding contact with its ilxed terminal and which may be readily manufactured and sold on a practical and commercial y scale at a low cost.

Other and further objects and advantages of the invention will become apparentifrom the following description taken in conjunction with the accompanying drawing; in which Fig. 1 illustrates a vertical sectional view of a variable resistance embodying the principles of the present invention; 'y

Fig. 2 depicts a top elevational View of the vari- "able reslstanceshown in Fig. 1;

Fig. 3ls `a perspective enlarged view of a con- I ically wound resilient; metallic conductor forming part of the variable resistance structure shown in Figs. 1 and 2;

Fig. 4 is a similar view of a modified. resilient l connecting member; and

ward its normal position of rest so that the slider did not positively maintain its adjustment. Al-

though various suggestions and proposals 'were made to eliminate this diillculty, nonel of these suggestions and-proposals wascompletely satis- Fig. 5 is a vertical sectional embodiment of the invention.

Referring now more particularly to Figs. 1 and 2 of the drawing, reference character I0 denotes view of a modiiied a base member made of insulating material having an upwardly extending cylindrical wall H. About-this wall is curved a strip of insulating materlal I2 around which are wound closely spaced turns of resistance wire I3 forming the resistance element of the unit. The ends of strip I2 are similarly held together by means of an eyem let I8 clamping a soldering lug I'I.

Base member I is provided with a central opening I8 having such dimensions that a shaft I9 may readily pass therethrough. A metal plate is resting against the bottom surface of the base 15 member and has a bearing member 2I rigidly connected to a center opening therein. This bearing member is provided witha shouldered portion 22 upon which the center portions of plate 2n .may

rest and a. threaded sleeve portion 23 adapted to 2 cooperate with a. corresponding threaded nut (not shown) for the purpose of one-hole mounting of the complete unit. Bearing member 2| is provided with a longitudinally extending opening 2Ia of circular cross section forming a slidingt with 25 shaft I9 in which the shaft may be readily rotated. 'I'he shaft is also provided with a circumferential groove 24 at the end of threaded sleeve 23 in which there is inserted a conventional clinch ring 25. Y

To the upper end of shaft I9 is rigidly connected an insulativ'e disc 26. This rigid connection may be obtained, for example, by tight t of the shaft into a central opening 21 in the disc and by crimping the weakened upper terminal portions of the shaft upon the disc. This insulative disc 26 has the object of carrying the moving contact structure in the form of a circular plate 29 made of resilient metal from which radially extends a slider or contact arm 30. major or body portion of circular contact plate 29 is disconnected from the portion bearing the slidver by means of a curved incision 3| of the shape illustrated whereby great flexibility of contact arm 30 with respect to plate 29 is obtained and read- 45 ily yielding resilient pressure of the contact arm upon the resistance element is assured. Against the lower surface of insulative plate l29 is resting ange 32 of a downwardly depending metallic sleeve 33. Contact arm plate 29, insulating plate 50 28 and metal sleeve 33 are held together by means of a pair of rivets or eyelets 34. It will be noted that both contact arm plate 29 and sleeve 33 end at a distance from shaft I9 sufficient to prevent their direct metallic contact whereby the shaft is insulated from the slider contact under all operating conditions. y

Electrical connection between the contact arm and the xed terminal or soldering lug I'I is proflexible wire 35 wound in the form' of a conicallyshaped spiral. One end 36 of this wire is extended for rotary displacement to a negligible value and also to indefinitely extend the life of the connecting member. The dimensions of the spiral and its winding directions are so correlated to the direction of adjustment of the contact arm that in the initial position the several windings of the spiral vided by means of a relatively thin'and resiliently 60 are widely spaced from the center or axial line of the unit so that any additional rotation of the contact arm will tend to unwind the spiral and to force its turns away from shaft I9 and sleeve 33. This form of construction in addition to the oonical shape of the spiral, which provides each successive turn with a slightly greater diameter than the preceding one, positively prevents binding of the connecting spiral and thus provides an electrical connection which will function satisfactorily and free from 'operating diiculties practically indenitely.

Fig. 3 illustrates an enlarged perspective view of the connecting member wound in a conical spiral form which is preferred for the purposes of the invention. However, equal or similar re-l sults may be obtained by providing the connecting member in the form of a at spiral 40, as this is illustrated in Fig. 4. In this case the turns of the spiral are originally formed in one plane and the ultimate conically-wound spiral structure is automatically obtained when ends 4I and 42 of the spiral are connected to the contact-arm and to the corresponding fixed terminal, respectively, whereby the turns of the spiral are slightly pulled apart in the axial direction.

Fig. 5 illustrates a vertical sectional view of a modified embodiment of the present invention. As this embodiment is practically identical with the one described in the foregoing-and similar reference characters havebeen used to denote corresponding parts, its structure and operation will 'be readily understood without any further description. The difference between the two embodiments resides in the omission of metallic sleeve member 33. Even though in this case there is no mechanical element interposed between the turns of the connecting spiral 35 and the shaft, accidental contact between the spiral member and The 40 the shaft is prevented by the shape and the mechanical characteristics of the spiral connecting member, as this has been fully explained in the foregoing. In the absence of sleeve 33, which also has the object of preventing displacements of the shaft in the'axial direction, it is desirable to provide a shoulder or small protuberance 43 of appropriateshape in shaft I9 in order to nx sha! I9 in the axial direction.

While the present invention; as to its objects and advantages, hasbeen described herein as carried out in specific embodiments thereof, itis not desired to be limited thereby but it is intended to cover the invention broadly within the spirit and scope of the appended claims.

What is claimed is:

1. A variable resistance comprising in combination a base, an annular resistance element mounted on said base, a shaft rotatably mounted in said base,a vmetallic contact arm insulatedly -secured to said shaft and adapted to make sliding contact with progressive portions of said resistance element during rotary displacement of said shaft, a fixed terminal, and a conically wound spiral spring having its end closest to its axis connected to said contact arm and its end most distant from its axis connected to said terminal, the winding direction of said spiral being so determined with respect to the direction of rotation of said shaft that in the initial position of said shaft the turns of said wire are spaced from said shaft and that during rotation of said shaft said turns will be :forced away from said shaft and will positively prevent electrical contact therewith.

2. A variable resistance comprising in combination a base, an annularv resistance element vsaid shaft adapted to make contact with portions of said resistance element during rotary displacement of said shaft, a pair of fixed terminals respectively connected tothe ends of said resistance element, a third fixed terminal for said contact arm, and a metallic conductor extending from said contact arm to said third fixed terminal and having the form of a conically wound spiral having its successiveturns spaced at increasing distances from the shaft in the initial position of the shaft and being so constructed and arranged that upon rotation of the shaft the spiral will be unwound and its turns will be forced further away from the shaft.

3. A variable resistance comprising in combination a base of insulating material, an annular resistance element mounted on said base, a shaft mounted in said base for rotation within an angle less than 360 degrees, an arm constituted of insulating material secured to said shaft, a resilient contactorextending from said arm into sliding contact-making position with exposed portions of said resistance element, a terminal for said contactor, and an electrical connection between said contacter and said terminal in the form of spring wire wound to a conically tapering spiral, said spiral being wound counter-clockwise from said terminal and having its turns spaced from the shaft whereby said turns will be slightly unwound and forced further away from the shaft during a clockwise rotation of the shaft not exceeding 360 degrees.

4. A variable resistance comprising in combination a base, an annular resistance element mounted on said base, a shaft rotatably mounted in said base, an insulative plate secured to said shaft and rotatable therewith, a resilient contact arm extending from said plate and adapted to slidably engage said resistance element, a metallic spacer sleeve depending from said plate and spacedly surrounding the terminal portion of said shaft extending into said base, a fixed terminal,

and an electrical conductor in the form of a conlcally wound spiral spring wire having its ends respectively connected to said contact arm and to said terminal, the winding direction of said spiral wire being so determined with respect to the direction of rotation of said shaft that in the initial yposition of said shaft the turns of said wire are slidably engageable with said resistance element,

a flanged metallic sleeve member depending from the bottom surface of said disc and spacedly surrounding the terminal portions of said shaft, said contact plate and said flanged sleeve being electrically and mechanically connected to each other through said insulative disc, a fixed terminal, and

an electrical conductor in the form of a conically wound spiral spring wire having its ends respectively connected to said contact plate and to said terminal, said metallic sleeve acting as a stop member against axial displacements of said shaft, the winding direction of said spiral wire being so determined with respect to the direction of rotation of said shaft that in the initial position of said shaft the turns of said wire are spaced from said sleeve and that during rotation of said shaft said turns will be forced away from said sleeve. FLOYD E. RJLING.

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