US3107336A

US3107336A - Variable resistor

Info

Publication number: US3107336A
Application number: US809771A
Authority: US
Inventors: Richard E Caddock; Warren D Hulbert
Original assignee: Bourns Inc
Current assignee: Bourns Inc
Priority date: 1959-04-29
Filing date: 1959-04-29
Publication date: 1963-10-15
Anticipated expiration: 1980-10-15
Also published as: GB923607A

Description

Oct. l5, 1963 R. E. cADDocK ETAL VARIABLE REsIsToR Filed April 29, 1959 N@ iw,

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United States Patent 67,335 VARABLE RESESTQE Richard E. Caddocir, Ames, iowa, and Warren D.. Heibert, Riverside, Calif., assignors to Eourns, line., a ecrporation of @alitornia Filed Apr. 2%, i959, Ser. No. tlStJl Stalins. (Cl. 33h-lh) The present invention relates to variable resistors, and more particularly to precision potentiometers of the type wherein a wiper is moved along a resistance element by means of a rotatable leadscrew.- One of the primary objects of the invention is to provide a potentiometer of the class described, which is sealed against the entrance of humidity and dust, and which is so constructed as to permit its manufacture in extremely small sizes.

A further object of the invention is to provide a leadscrew actuated potentiometer having a high degree of reliability, exceptional stability of settings, and extreme accuracy of adjustment.

Another object is to provide a leadscrew actuated potentiometer which is extremely simple in cons-truction, and which can be quickly and easily assembled.

Still another object of the invention is to provide a leadscrew actuated potentiometer capable of operating at relatively high temperature.

These objects are achieved in the present invention by a construction embodying a housing or body of high temperature resistant plastic having a cavity formed in one side thereof, in which a leadscrew is journaled. Mounted on the said one side of the housing is a lid holding a resistance element having a ceramic mandrel. A slider is operatively associated with the leadscrew and has a contact wiping on the element, the said slider forming an electrical connection between the element and the leadscrew. Terminals are electrically connected to the leadscrew and to the resistance element, and a screw adjusting head is connected to one end of the leadscrew by a non-conductive coupling member.

The construction of the slider forms one `aspect of the invention and comprises a U-shaped sheet metal body which engages the leadscrew from below and tits snugly against opposite sides thereof. A generally U-shapcd spring wire Contact member has its ends anchored in the bottom of the slider body adjacent one end thereof, and the arms of the spring Wire contact member are bowed into an arc of approximately 180 degrees `and extend upward alongside the leadscrew adjacent the other end of the slider body. The center portion of the U- shaped contact member passes through vertical guide slots in the sides of the slider body, and extends across the top of the leadscrew, yieldingly engaging the thread of the leadscrew midway between the ends of .the slider body to provide a releasable driving connection between the slider and the leadscrew. Electrical connection is made between the resistance element and the leadscrew by the Contact member, and the leadscrew is electrically connected, in turn, to one of the terminals by means of a spring clip of novel construction, having `an aperture through which one end of the leadscrew passes, and a bowed spring linger which overlies the leadscrew and presses against the same with spring pressure.

rl`he foregoing and other objects and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of a preferred embodiment thereof, reference being had to the accompanying drawings, wherein:

FIGURE 1 is a longitudinal section, taken lat i-l in FlGURE 2, through a leadscrew actuated potentiometer embodying the principles of the invention;

FIGURE 2 is a transverse sectional view of the same taken at 2-2 of FlGURE l;

FIGURE 3 is a sectional view, URE l; and

FIGURE 4 is an exploded perspective view of the housing land lid of the instrument illustrated herein.

in the drawings, the instrument is designated in its entirety by the reference numeral l0, and is seen to comprise `a generally rectangular body il of electrically nonconductive, high temperature plastic or equivalent material, having a cavity l2 formed in one side thereof, and a lid .t3 mounted on said one side to enclose said cavity. The main `portion of the cavity l2 is relatively deep, and occupies approximately two-thirds of the length of the housing in the mid-portion thereof; there being a relatively shallow portion i4 of the cavity extending from one end of the main portion l2 to the adjacent end of the body il. The sides of the cavity are flat `and substantially parallel, except for narrow shoulders 1.5 and le, which extend lengthwise of the body along the sides thereof. At the end of the body opposite the shallow portie-n it, :the cavity is provided with a step 2t), which provides support for one end of the lid 13.

Rotat-abiy supported within the body il parallel to the longitudinal thereof, is a leadscrew 2i having a smooth unthreaded portion at one end thereof. The Smooth portion 22 of the leadscrew is inserted into and journaled within a smooth bearing hole 23. At its other end, the leadscrew 2l is enlarged in diameter to provide a smooth surfaced cylindrical portion 24, which is journaled within a bore 2.5 in the body il.. The enlarged cylindrical portion 2dof the leadscrew is provided with a circumferential groove 216, which is engaged by a U- shaped retainer 3b that is seated within the housing il, to hold the leadscrew against endwise movement.

The enlarged portion 24 of the leadscrew terminates within the bore Z5, and is provided with a socket 3l in its end, into which is inserted one end of a coupling member 32 of ceramic or other electrically non-conductive material. The other end of the coupling member 32 is inserted into a socket 33 in a head 34, which is disposed within a slightly enlarged counterbore 3S in the end of the body. The outer end of the head 3ft projects beyond the end of the body il and is slotted at 36 to receive a screwdriver blade. The coupling member 32 is an interference tit in both of the sockets 3l and 33, `and thus the head Tiltis fixedly connected to the leadscrew 2l so that the two rotate as one. The adjacent ends of the enlarged port-ion and head 34 are spaced apart slightly to form a circumferential groove, and disposed within this groove is an O-ring @il of elastomeric material, which eals the clearance between the leadscrew and the body il vagainst the entrance of moisture or dirt into the cavity.

The lid i3 is likewise formed of non-conductive material, and is provided with an outer surface 41, which is ilush with the outer surface of the body 11 when assembled in place. One end ofthe lid 13 is provided with a ledge 42 which seats on the step 2f?, while the other end d3 is relatively shallow to fit within the shallow groove i4, `and is provided with a shallow channel 44'- on its inner surface (see FIGURE 4) to forman aperture through which the terminal wires pass. Between the ledge d2 and end portion 43, the lid i3 has sides 46 and 4-7, which project down into the cavity l2 and seat on the shoulders i5. The

sides

46 and 47 are connected at one end by an end wall 4S, which ts against the end of the cavity l2 and abuts against the leadscrew retainer to hold the latter in place.

The inwardly projecting portion of the lid 13 has a narrow slot E@ provided therein, with slightly enlarged end portions 5l and 52. Seated within the slot 5t?, 5l, S2 is a resistance element 53, which may either be of the wirewound type, as shown, or it may be a composition eletaken at 3 3 in FIG- entrasse ment. In the illustrated embodiment, wire windings are wrapped around a ceramic mandrel dwhich is apertured centrally at 55 to receive a terminal strip 56. The terminal strip 56 extends through the mandrel from one end thereof to the other, and at its right-hand end (FlGURE l) the strip is bent around at 57 to overly the windings at the end of the element, where it is silver soldered or otherwise electrically connected to the resistance wire or cornposition. The left-hand end of the strip 56 projects beyond the end of the mandrel 54, and is soldered or spot welded to a terminal wire 649 lying within the channel i4 in the lid i3. The resistance wire windings at the left-hand end of the element are electrically connected by a tab oil to the upturned end of a terminal wire 62, which is likewise idsposed within the channel ll of the lid l. The terminal wires 60 and 62 are separated from one another by a triangularly shaped spacer 63 which projects upwardly from the bottom of the channel ed. Also, terminal wire 62 extends upwardly through a diagonal slot 641 in the end of the body Ill, so that the terminal wires are spaced apart where they leave the instrument body.

When the lid "i3 is assembled to the body ll, the resistance element 53 extends parallel to the leadscrew 2l and is spaced a short distance therefrom. Associated with the leadscrew 21 and operatively connected therewith is` a slider 65 having a contact member 66 which wipes on the top surface of the resistance element 53 to form an electrical connection between the element and the leadscrew. The slider 65 is preferably formed of sheet metal bent into a generally U-shaped configuration, and engages the leadscrew 2l from below. The slider 65 has a bottom 70 and upwardly projecting sides 7l at opposite sides thereof. The contact 66 includes a portion lying on top of the bottom '70, and is bent down over one end and back at an angle to provide a spring iinger having a rounded end portion i2 that wipes on the resistance element. The portion of the contact member 66 overlying the bottom 7@ is silver soldered or spot welded to the said bottom portion, and bears against the underneath side of the leadscrew, to make electrical contact therewith. The sides 7l of the slider t snugly against opposite sides of the leadscrew 2l, as shown in FIGURE 2, and formed in the top edges of the sides are vertical guide slots 73, the purpose of which will be explained presently.

The driving connection between the leadscrew 2l and slider 65 is effected by means of a spring wire member 'ld which is bent into a generally U-shaped conguration, with its ends projecting up into holes in the bottom 70 of the slider, where they are soldered or otherwise rigidly joined to the bottom 70. As best shown in FIG- URE l, the sides of the spring wire member extend downwardly and to the right from their point of attachment, and then extend upwardly and rearwardly in an arcuate bow along both sides of the leadscrew to the point where they join the center section 74' that extends transversely across the top of the leadscrew. This transverse center portion 74 of the spring wire extends through and is slidable vertically within the guide slots '73, so that its movement is restricted by the slots. The center portion 74 of the spring wire member yieldingly engages the thread of the leadscrew, so that as the leadscrew is turned, the slider 65 is moved lengthwise thereof.

Being free to move vertically within the guide slots 73, the center portion '74 of the spring wire member 74 is adapted to ride up over the crests of the leadscrew threads when the leadscrew is forcibly turned while the slider is restrained against free movement lengthwise of the leadscrew, as when the slider has reached either end of its travel. The long length of spring arm afforded by the bowed side portions of the spring member "/4 provides a considerable amount of resiliency, allowing the center portion 74 to ratchet over a turn of the leadscrew thread without unduly stressing the sides of the spring wire member. It will also be noted that the spring wire member '74 engages the leadscrew thread approximately half way between the ends of the slider 65. rlhis is an important feature, as it tends to stabilize the slider by holding both ends of the bottom 7d firmly against the bottom of the leadscrew. The slider is thus prevented from becoming cocked at an angle to the leadscrew, as might otherwise happen if the spring wire member engaged the leadscrew adjacent one end oi the slider. Tabs iii) are bent downwardly from opposite sides of the bottom '7d of the slider adjacent one end thereof, and these tabs Si) slidably engage the sides of the body lll, as shown in FIGURE 2, so as to restrain the slider against ttirningv'ith the leadscrew.

Those skilled in the art will recognize from the foregoing description that the leadscrew 2l serves as an electrical return from the contact 66. The leadscrew is adapted to be connected into the electrical circuit with which the potentiometer l@ is to be used, by means of a terminal wire 8l which extends through a hole 32 in the end of the body lll. The terminal wire 8l projects into the cavity l2 and through an aperture 83 in a leadscrew terminal clip 84, which bears against one end of the cavity l2. The terminal clip S4 is also provided with a circular aperture S5 through which the smooth bearing portion 22 of the leadscrew 2l passes. Flanges 86 are bent inwardly from the side edges of the clip 84, and these anges bear against the sides of the cavity 12 to hold the clip against lateral displacement. Bent downwardly from the top edge of the clip 8d is a bowed spring tnger 87, the free end of which yieldingly presses against the smooth bearing portion 22 of the leadscrew to make electrical contact therewith. The terminal wire 3l lies against one of the side flanges 86 and is silver soldered or otherwise suitably joined thereto.

The potentiometer 10 is adapted to be mounted upon a suitable supporting structure, and to this end the body 1l is provided with a pair of mounting holes 9i) adjacent the ends of the body. Mounting screws may be passed through the holes 9h to secure the body lll to the supporting structure. Y

In assembling the potentiometer 1l), the leadscrew 2l Vwith the head 34 and coupling member 32 assembled thereto is inserted through the bore 25, and the slider 65 is slipped over the inner end of the leadscrew so that the spring wire member 74 is operatively engaged with the threads of the leadscrew. The smooth bearing portion 22 of the leadscrew is then inserted through the hole in the terminal clip 34, and into the bearing hole 23. When the leadscrew 21 is fully seated in the body 1l, the retainer 3i) is slipped down into the cavity 12 so that it engages the circumferential groove 26 in the large bearing portion 24 at the head end of the leadscrew. The resistance element 53, with terminal wires 6l) and 62 attached thereto, is then inserted into the cavity 5t), 5l, 52 in the lid i3, and the lid is dropped into place in the open side of the body 11, so that it closes the cavity l2. The lid 13 is cemented to the body around its entire edge, and the apertures in the end of the body through which the terminal wires 60, 62 and S1 pass are then lled with a suitable potting agent, such as epoxy resin 95. The instrument is then ready for use.

While we have shown in considerable detail what We believe to be the preferred form of our invention, it will be understood by those skilled in the art that various changes may be made in the shape and arrangement of the several parts without departing from the scope of the following claims.

We claim:

1. A variable resistor comprising an elongated body having a cavity formed in one side thereof, a lid mounted on said one side of said body of enclose said` cavity, a resistance element mounted on the inner face of said lid and having a pair of terminal wires connected to the ends thereof, said lid having one end portion thereof projecting -to the end of said body, said projecting one end portion being received within a shallow groove in said one side of said body and cooperating therewith to form an aperture through which said terminal wires pass, a leadscrew rotatably supported on said body within said cavity parallel to said resistance element, a slider operatively engaged by said leadscrew lto be moved thereby, said slider having a contact wiping on said resistance element and Ielectrically connected to said leadscrew, and a third terrninal wire electrically connected to said leadscrew.

2. A variable resistor comprising a body, a resistance element mounted on said body, `a leadscrew of conductive material disposed parallel to said resistance element and rotatably supported at its ends by said body, said leadlscrew having fa smooth unthreaded portion adjacent one end thereof, Aa slider operatively engaged by said :leadscrew so as Ito be moved thereby when the Ileadscrew is turned, contact means yon said slider wiping on said resistance element and making electrical connection with said leadscrew, la lea-dscrew terminal clip of conductive sheet metal comprising a rst part perpendicular to the axis of said leadscrew and a second part perpendicular to said first part, said first part having an aperture provided therein through which said smooth portion `of said leadscrew extends, said second part having a lip at its outer end yieldingly engaging said smooth portion of said leadscrew to make electrical contact therewith, and terminal means connected to said clip.

3. A variable resistor comprising an elongated body having a cavity formed in one side thereof, an electrically conductive leadscrew extending through said cavity and journaled at its ends in the ends of said body, said leadscrew having a smooth Unthreaded portion adjacent one end thereof, a lid mounted on said one side of said body to enclose said cavity, a resistance element mounted on the inner face of said lid parallel to said leadscrew, a slider operatively engaged by said leadscrew so as to be moved thereby when the leadscrew is turned, Contact means on said slider wiping on said resistance element and making electrical connection with said leadscr'ew, a leadscrew terminal clip of conductive sheet metal, said clip havng la center porton disposed perpendicular to the longitudinal axis of said ieadscrew, and side portions bent at right angles yto said center portion so as to lie flat against the side walls of said cavity, said center portion having yan aperture provided therein through which said smooth portion of said leadscrew passes, a top portion bent at right angles to said center portion so` as to overlie said leadscrew, said top portion 'having -a lip yieldingly engaging said smooth portion of said leadscrew to make electrical contact therewith, and terminal means connected to said clip.

4. In a variable resistor having a housing, a leadscrew rotatably supported on said housing, and a resistance element mounted on said housing parallel to said leadscrew, the improvement comprising a slider consisting of a generally U-shaped sheet metal body, the bottom of said U-shaped slider body bearing against the bottom of said leadscrew and the sides -thereof extending upwardly along opposite sides of the leadscrew, said sides having generally vertical guide slots formed in the top edges thereof adjacent the midpoint of said body, `a spring wire member bent into a generally U-shaped configuration, the ends of said spring wire member being anchored in the bottom of said slider body adjacent one end thereof, the arms of said spring wire member being bowed and extending upwardly alongside said leadscrew adjacent the other end of said slider body, the center portion of said spring wire member extending transversely across the top of said leadscrew and yieldingly engaging the thread thereof, said center portion of said spring member being slidable vertically within said guide slots to allow the same to ride up `over .-the crests of the leadscrew thread when said leadscrew is forcibly turned while said slider is restrained against free movement lengthwise of the leadscrew, 'and a contact member attached #to the bottom of said slider body and wiping on said lresistance element.

5. The invention as deiined in claim 4, wherein said slider body has ltabs bent downwardly from the bottom thereof adjacent the sides, said tabs slidably engaging the sides of said housing so as to prevent said slider body from turning with said leadscrew.

References Cited in the file of this patent UNITED STATES PATENTS 2,745,054 Leyenberger May 8, 1956 2,860,216` Hubbard Nov. 1l, 1958 2,870,302 Bourns Jan. 20, 1959 2,870,304 OBrian Jan. 20, 1959 2,873,337 Bourns Feb. 10, 1959 2,873,338 Elliott Feb. 10, 1959 2,882,375 Bourns Apr. 14, 1959 2,886,681 Bourns May 12, 1959 2,895,116 Morrison July 14, 1959 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3, 1075336 October l59 1963,

Richard E. Caddock et al.,

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4', line 69, for "of enclose read to enclose column 5, line 39, for "porton" vread --M portion Signed and sealed this 21st day of April 1964a (SEAL) Attest: EDI/JARD J. BRENNER ERNEST W. SWIDER Attestng Officer Commissioner of Patents

Claims

1. A VARIABLE RESISTOR COMPRISING AN ELONGATED BODY HAVING A CAVITY FORMED IN ONE SIDE THEREOF, A LID MOUNTED ON SAID ONE SIDE OF SAID BODY OF ENCLOSE SAID CAVITY, A RESISTANCE ELEMENT MOUNTED ON THE INNER FACE OF SAID LID AND HAVING A PAIR OF TERMINAL WIRES CONNECTED TO THE ENDS THEREOF, SAID LID HAVING ONE END PORTION THEREOF PROJECTING THE END OF SAID BODY, AND PROJECTING ONE END PORTION BEING RECEIVED WITHIN A SHALLOW GROOVE IN SAID ONE SIDE OF SAID BODY AND COOPERATING THEREWITH TO FORM AN APERTURE THROUGH WHICH SAID TERMINAL WIRES PASS, A LEADSCREW ROTATABLY SUPPORTED ON SAID BODY WITHIN SAID CAVITY PARALLEL TO SAID RESISTANCE ELEMENT, A SLIDER OPERATIVELY ENGAGED BY SAID LEADSCREW TO BE MOVED THEREBY, SAID SLIDER HAVING A CONTACT WIPING ON SAID RESISTANCE ELEMENT AND ELECTRICALLY CONNECTED TO SAID LEADSCREW, AND A THIRD TERMINAL WIRE ELECTRICALLY CONNECTED TO SAID LEADSCREW.