US2989717A - Variable resistor - Google Patents

Description

June 20, 1961 w. F. o'sHl-:A ET AL VARIABLE RESISTOR Filed July 6, 1959 ATTORN EY United States Patent O 2,989,717 VARIABLE RESISTOR William F. OShea, Hathoro, and Kalman B. Litsou,

Abbiugton, Pa., assignors to Wirt Company, Philadelphia, Pa., a corporation of Pennsylvania Filed July 6, 1959, Ser. No. 825,315 '12 Claims. (Cl. SSS-166) This invention relates to variable resistors as used in the electronic and electrical arts. More particularly this invention relates to variable resistors of the type generally known as potentiometers, although the principles of the invention are just as readily applicable to the variable resistors of the rheostat type.

The potentiometer type of variable resistance is widely used in the electronic and electrical arts to generally provide the function of either a control element or that of a monitoring element. Most potentiometers are enclosed in a housing having a shaft extending outward therethrough, and which when rotated moves a contact point -along the resistance element contained within the housing. Known types of potentiometers include single units, that is, units containing a single resistance element and a single movable contact operated by the usual shaft. Other types of known potentiometers provide for the aggregation of a number of such single units which may either be all simultaneously and synchronously operated by a single shaft, or which may have concentric operating shafts so that one shaft operates one control element and a second shaft operates a second control element associated with a second resistance. Stacked units which are individually operable have been in the past usually limited in number to a stacked arrangement embodying merely two individual potentiometer units.

Yet another type of known potentiometer is the multiple turn type of unit which usually employs a helically wound resistance wire and a movable contact, again operated by a protruding shaft, which is rotatable through a plurality of successive turns in the same direction, as for example ten turns or 3600 degrees of rotation, but these multiple turn units all require that the operating shaft be counter-rotated in order to reset the potentiometer to a particular val-ue of resistance once that value has been passed by the forward rotation of the movable contact element. In other words, all of the known multiple turn types of potentiometer units have incorporated at some point a physical stop which prevents continued rotation of the operating shaft in a given direction and requires that the shaft be counter or reverse rotated to reestablish some particular desired setting of the movable contact along the resistance element.

Moreover because the foregoing described types of potentiometers generally are completely enclosed devices and shaft operated, it is possible to operate such potentiometers only by having access to the shaft. In some instances, this type of construction poses a serious design problem when it is necessary to incorporate such devices into operating equipment. Accordingly, it is a primary object of this invention to provide a novel potentiometer construction wherein the movable contact may be continuously rotated unidirectionally through any desired number of complete revolutions so that the movable contact may be shifted from a high resistance position to a low resistance position without reversing the direction of rotation of the contact.

It is another object of this invention to provide a novel potentiometer construction which allows for any number of units to be stacked one upon another and which yet allows each unit to be individually adjusted to diterent desired settings of the movable potentiometer contact.

lStill another object of this invention is to provide a Patented June 20, 1961 Pice novel potentiometer construction in which access to the movable contact may be had from opposite sides of the unit for purposes of adjustment thereof so that the physical location of the potentiometer in a piece of associated equipment is rendered much less critical.

Yet another object of this invention is to provide a novel potentiometer construction which is small in size, relatively inexpensive to manufacture and physically rugged so as to withstand adverse environmental conditions.

The foregoing and other objects of the invention will become apparent from a careful reading of the following specification in conjunction with an examination of the appended drawings, wherein:

FIGURE l is a front elevational view of one embodiment of the potentiometer according to the invention shown mounted to a supporting structure;

FIGURE 2 is a bottom view of the potentiometer illustrated in FIGURE l with a portion of the casing broken away to reveal certain details of the interior construction;

FIGURE 3 is an exploded View, in perspective, of the potentiometer illustrated in FIGURES l and 2 and illustrates the various elements which when assembled comprise the potentiometer;

FIGURE 4 is a cross-sectional view taken through the potentiometer of FIGURE 2 as indicated by the lines 4 4, the rotor element being repositioned in the showing of FIGURE 4 as compared to that of FIGURE 2 for the purpose of better illustrating the organization of the various parts;

FIGURE 5 is a top View of a second embodiment of the invention and differs from FIGURE 2 in that three terminal lugs are shown instead of the two seen in the illustration of FIGURE 2;

FIGURE 6 is a cross-sectional view through the potentiometer illustrated in FIGURE 5 as would be seen when viewed along the lines 6-6 of the latter figure;

FIGURE 7 is a plan sectional view such as would be seen when viewed along the lines '7-7 of FIGURE 6.

In the several figures like elements are denoted by like reference characters.

Turning now to an examination of the drawings consider rst the embodiment of the invention illustrated in FIGURES 1 through 4, directing attention rstly to the exploded View illustrated in FIGURE 3. In the showing of FIGURE 3, it will be observed that the potentiometer according to the invention consists essentially of `seven principal parts which when assembled together result in the iinished potentiometer construction as best seen in the showing of FIGURE 4. The basic parts of the potentiometer are a cover shell 10, an insulating ring 12 to which is secured a pair of terminal lugs 13y by the rivets 14, an annular insulating element 15 recessed to receive a cylindrical insulator 16 upon which is wound the resistance element 17, a rotor element 18 having integrally formed therewith the potentiometer movable contact 19, a potentiometer back cover plate 11, and a tab lock plate 20 for securing the rotor 18 to the back plate `11 and properly indexing the rotor relatively to the resistance element.

The cover shell l0 is lformed with a depressed top central region 25, the center region of which is circularly cut away as at 26 to provide a through hole. A plurality of locking tabs 27 are extended downward in longitudinal continuation of the cylindrical side `surface of the cover shell 10 and are so peripherally positioned that in the assembled potentiometer these locking tabs 27 it within the `slots 28 notched into the skirt 29 of the back plate 11. The back plate 11 is secured to the cover shell 10 by turning the tabs 27 inwardly into underlying contacting relation with the 'back plate, this tab securernent being best seen in the showing of FIGURE 2. Also extended downwardly in longitudinal continuation of the cover shell cylindrical side wall in the same manner as are the tabs 27, `are a pair of long tabs 3th, these longr tabs being positioned to fall within the notches 31 also seen to be punched out of the skirt 29 in the back plate 11. These long tabs 30 are provided for mounting the entire potentiometer assembly to a suitable support, as for example that illustrated as 31 in `FIGURE 1. The mounting is accomplished by projecting the tabs 30 downward through holes v32 formed in the support 31.

As will be subsequently seen, the embodiment of the invention illustrated in FIGURES 1 through 4 utilizes the cover shell itself as the point of electrical connection to the movable contact 19 of the rotor 18. Such arrangement is very convenient when the potentiometer is to be mounted to a phenolic board such as is used in printed circuitry. If for example lthe mounting member 31 illustrated in FIGURE 1 were in fact a phenolic board, the tabs 30 could be soldered to after being bent into locking position as illustrated, or in the alternative, if the through holes 32 in the board 31 were eyeletted then the long tabs 30 would not even need to be bent under as illustrated but could be merely projected downward through the eyelets and soldered directly thereinto.

As best seen in the showings of FIGURES 3 and 4, the insulator ring 12 to which are aftixed the terminal lugs 13 is formed so that its outside diameter is the same as the inside diameter of the cover shell 11i, so that the in sulation ring 12. may be slipped snugly within the shell 10 with the terminal lugs 13 projected outward through the rectangular aperture cut into the cylindrical side wall of the cover shell 10, the terminal lugs 13 being electrically isolated -from the metallic cover shell 18. Similarly, the recessed insulator is formed with its outer diameter the same as the inner diameter of the insulating ring 12 so that it may be nested within the latter and seated against the inside surface of the cover shell top wall as best seen in FIGURE 4.

As also best seen n FIGURE 4, the depressed central portion of the cover shell top wall is dimensioned so that the downwardly sloping portion 33 thereof is formed in the shape ot' an annulus of complemental configuration to a similarly formed annulus 34 cut or molded into the upper inside region of the insulator element 15. An annular recess 35 formed in the insulator 15 snugly receives and retains the insulating ring 16 upon which is wound the potentiometer resistance element 17. The resistance element 17 consists of a continuous length of resistance wire which is helically space-wound about the insulating ring 16 so that adjacent turns spaced about the periphery thereof do not contact one another. The ends 36 of the toroidally wound resistance element 17 are then electrically connected to the terminal lugs 13.

The rotor 18 is formed from a metallic disc which is centrally cross-punched as at 37, and punched semi-circumferentially to provide a yoke 38 including the contact 19 bent up out of the plane of the rotor 18. The back plate 11 is centrally apertured at 39 and of such size that the cross-punched area 37 in the rotor 18 is. circumscribable by the circular periphery of the aperture 39 in the back plate 11. Disposed below the back plate 11 is the tab locking plate which comprises a metallic disc crosspunched in its central regio-n and having four tabs 40 bent upward at substantially right angles to the plane of the disc 27.0. The spacing of the tabs 2li is such that in their opstanding position as shown in FIGURE 3, these tabs may be projected upwardly through the aperture 39 in the back plate 11 with all of the tabs lightly contactedly engaging the edge of the aperture 39 so that the tab locking plate 20 is not free to shift laterally relative to the back plate 11.

When now the rotor 18 is moved downward so that its undersurface is brought into engagement with the upper surface 41 of the back plate 11, each of the four tabs 4l) on the tab locking plate 20 will be projected upwardly through and immediately adjacent the end of each arm of the punched out cross 37 in the rotor 18. The tabs 40 may then be bent outward and downward upon the upper surface of the rotor 18 so that the rotor 18, the back plate 11, and the tab locking plate 20 are secured together as a unit and the rotor 18 and tab locking plate 2i) are locked together and free to rotate relative to the back plate 11. With the cover shell 10, insulating ring 12., insulator 15 and resistance element 17 all assembled together in the manner previously described, the back plate 11 may be seated against the under edge of the cover shell 10 with the tabs 27 projected through the slots 28. The tabs 27 may be then bent under the back plate as previously described to secure the back plate and rotor assembly and form the nished potentiometer.

As best seen in FIGURE 4, the movable contact 19 of the roto-r 18 engages the resistance element 17 when the back plate 11 is secured to the cover shell 10. The yoke 38 bent up out of the plane of the rotor disc 18 and carrying the movable Contact 19 is of course overbent when the rotor 18 is fabricated so that in the nished potentiometer the contact 19 is always in a spring biased condition against the resistance element 17 by virtue of the fact that the yoke 38 is forced downwardly toward the plane of the rotor when the back plate 11 is seated and locked against the bottom edge of the cover shell 10.

It should now be apparent that the rotor 18 may be caused to rotate by projecting a screw `driver or other tool into the cross-punch 37 either from the top of the potentiometer through the hole 26 in the cover shell 10 or from the bottom of the potentiometer through the tab locking plate 20. Also, it should be now clear that a number of such units may be stacked one upon the other with the apertures in the cases aligned so that an adjusting tool may be projected into the stack to selectively adjust a given potentiometer without disturbing the settings of the others. Moreover, it will be appreciated that the rotor may be continuously rotated in the same direction through as many complete turns as may be desired, and that during the course of each complete turn the moving contact 19 will provide a discontinuity of resistance as measured between the terminal lugs 13.

The discontinuity may be in the form either of a momentary short circuit or Zero resistance condition if the contact 19 bridges between the ends 36 of the resistance element 17, or, as measured between one terminal lug 13 and the cover shell 10, there may appear a momentary open circuit or innite resistance if the contact 19 breaks electrical connection with one end of lthe resistance `winding 17 prior to making connection with the other end. Obviously, either of these two conditions may be established by allowing the appropriate amount of spacing between the ends of the resistance element winding when taking into account the surface area of the movable contact 19. lIn some cases it may be found desirable to cement the mounted resistance element 17 into the insulator ring 15, and in turn cement the insulator rings 15 and 1'2 into the cover shell 10 in order to insure that rotation of the movable contact 19 does not tend to cause the resistance element 17 or the terminal lugs 13 to be carried along.

Turning now to an examination of FIGURES 5, 6 and 7, and as best illustrated by the comparative showings of FlGURES 4 and 6, it will be seen that the difference between these two embodiments resides in a difference in the back plate and rotor assembly. In the showing of FIGURE 6 it will be seen that the back plate, designated as 21, is formed from an insulating material and that interposed between the rotor 18 and the insulating back plate 21 is a metallic ring 22 having a third terminal lug 124 projecting outward therefrom. The metallic ring 22 is secured to the insulating back Vplate 21 by means of a plurality of spaced rivets 23, and the tab lock plate 20 is seen to now secure the rotor 18 into downward pressed contact with the metallic ring 22. Hence, the terminal lug 24 is electrically connected to the movable contact 19 of the rotor 18 and the cover shell 10 is electrically isolated therefrom. Thus, the embodiment of FIGURES 5, 6 and 7 provides the usual three terminal lug potentiometer arrangement while remaining substantially, structurally and functionally, the same as the potentiometer construction illustrated in FIGURES l through 4.

Having now described my invention in connection with particularly illustrated embodiments thereof, it will be appreciated that various changes and modiiications will occur from time to time to those persons normally skilled in the art without departing from the essential spirit or scope of the invention, and accordingly it is intended to claim the same broadly as well as specifically as indicated by the appended claims.

What is claimed as new and useful is:

1. A variable electrical unit comprising, an electrical resistance element formed in the shape of an incomplete circular ring, a resistance element enclosing housing comprising a cover shell and a cover back plate removably secured to the shell, an insulating element carried by and disposed within said cover shell and supporting said resistance element in spaced relation from said cover shell, a rotatable contact element and means rotatably securing the same to said cover back plate for rotation Within said housing in contacting engagement with said resistance element throughout the full incomplete circular extent of the latter, said contact element and back plate and contact element securing means being detachable as a unit from said cover shell.

2. The variable resistance unit according to claim 1 wherein said contact element securing means secures said rotatable contact element to said cover back plate in continuous electrical contact therewith and said cover back plate is an electrical conductor.

3. The variable resistance unit according to claim 1 wherein said cover back plate is an electrical insulator and has aixed thereto an electrically conductive collector ring which includes a terminal lug extending laterally beyond the back plate edge, said contact element securing means securing said rotatable contact element in continuous electrical contact with said collector ring.

4. The variable resistance unit according to claim v1 wherein said rotatable contact securing means is disposed partially externally to said back plate and extends therethrough for securement to said rotatable contact element, said rotatable element and securing means being rotatable as a unit relative to said back plate.

5. The variable resistance unit according to claim 1 wherein said rotatable contact element is continuously rotatable in a given sense through an unlimited number of complete turns, the ends of said incomplete ring resistance element being spaced apart a distance less than the length of contacting engagement between said resistance element and rotatable contact element, whereby said contact element bridges between the ends of said resistance element during one interval of each complete rotation to shortcircuit the same.

f6. The variable resistance unit according to claim 1 wherein said rotatable contact element is continuously rotatable in a given sense through an unlimited number of complete turns, the ends of said incomplete ring resistance element being spaced apart a distance in excess of the length of contacting engagement between said resistance element and rotatable contact element, whereby said contact element is electrically disconnected from said resistance element during one interval of each complete rotation thereof.

7. The variable resistance unit according to claim 2 wherein said cover shell is also an electrical conductor and said cover back plate is secured thereto in electrical contact therewith, whereby said housing is always at the electrical potential of said rotatable contact and constitutes an external terminal therefor.

8. The variable resistance unit according to claim 2 wherein said cover back plate is centrally circularly apertured, said rotatable contact element is formed from a rnetallic disc centrally cross-punched and semi-circumferentially punched to provide a contact carrying yoke bent up out of the plane of the disc, and said contact element securing means is a tab locleing plate formed from a disc centrally cross-punched to provide an upstanding locking tab `extending `from the end of each cross arm, the crosspunching of said contact element ydisc and tab locking plate being substantially congruent and inscribable within the cover back plate circular aperture, said contact element disc and tab locking plate being non-rotatably secured together and rotatably `secured to said back plate upon `opposite sides thereof by means of said tabs being extended through the back plate laperture and contact element vdisc and bent outward down upon the latter.

9. The variable resistance unit according to claim 3 wherein said cover back plate is centrally circularly apertured, said rotatable Contact element is formed from a metallic disc centrally cross-punched and semi-circumferentially punched to provide `a contact carrying yoke bent up out of the plane of the disc, and said contact element securing means is a tab locking plate formed from a disc centrally cross-punched to provide an upstanding locking tab extending from the end of each cross arm, the crosspunching of said contact element disc and tab locking plate being substantially congruent and inscribable within the cover back plate circular aperture, said contact element disc and tab locking plate being non-rotatably secured together and rotatably secured to said back plate upon opposite sides thereof by means of said tabs being extended through the back plate aperture and contact element disc and bent outward down upon the latter.

l0. A variable electr-ical resistance unit comprising, an electrical resistance element formed in the shape of an incomplete circular ring, an insulator element formed with an annular slot which extends only partially into the body of the insulator and within which slot the said ring resistance element is disposed with one `sicle of the ring exposed for contact with a rotatable contact element, an openbacked cover shell within which is disposed the said insulator element 'and resistance element with the exposed side of the resistance element facing the open back of the cover shell and the insulator element intervening the resistance element and the cover shell, a cover shell back plate removably secured to the cover shell, and a rotatable contact element and means rotatably securing the same to the inside face of the back plate for rotation within said cover shell in contacting engagement with said resistance element throughout the full incomplete circular extent of the latter.

11. The variable resistance unit according to claim 10 wherein said cover shell and cover back plate are electrical conductors and are secured together in electrical contact with one another, and wherein said rotatable contact element is maintained in continuous electrical contact with said cover back plate by said securing means.

12. The variable resistance unit 'according to claim 10 further including an electrical conductor ring secured to said cover back plate and having a terminal extending laterally therefrom, and wherein said rotatable contact element is maintained in continuous electrical connection with said electrical conductor ring by said securing means.

References Cited in the file of this patent UNITED STATES PATENTS 2,669,634 Daily etal Feb. 16, 1954 2,745,927 Daily et al May 15, 1956 2,866,055 Arisman et al Dec. 23, 1958 2,871,324 Budd Mar. 26, 1959 2,908,882 Gottschall et a'l Oct. 13, 1959

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