US3569896A

US3569896A - Ultrathin miniature potentiometer with recessed drive wheel means

Info

Publication number: US3569896A
Application number: US791476*A
Authority: US
Inventors: William D Kirkendall
Original assignee: Weston Instruments Inc
Current assignee: CORNELL-DUBIILIER MARKETING Inc; CORNELL-DUBLILIER MARKETING Inc; Weston Instruments Inc
Priority date: 1969-01-15
Filing date: 1969-01-15
Publication date: 1971-03-09
Anticipated expiration: 1988-03-09

Abstract

Miniaturized variable resistors of the circular type having a drive wheel rotatable in a housing and an arcuate resistance element slidably engaged by a contact driven by the drive wheel. The drive wheel has a rim thicker than the web of the wheel and substantial portions of the resistance element are located within the rim to provide an ultrathin potentiometer.

Description

O United States Patent [1l]3,569,896

[72] Inventor William D. Kirkendall [56] References Cited Dalton, Pa. UNITED STATES PATENTS [21] P 1,424,515 8/1922 Parkin 338/252 [22] Filed Jan. 15, 1969 2,576,044 11/1951 Rrchman 338/170 [45 Patented Mar. 9, 1971 [73] Assignee wagon I I ts hm 3,099,810 7/1963 Habereder 338/148 Newark, NJ. 3,242,450 3/1966 Bourns 338/168 Primary Examiner-Laramie E. Askin Assistant Examiner-Gerald P. Tolin Att0meys-William R. Sherman, Stewart F. Moore, Jerry M. [54-] ULTRATHIN MINIATURE Presson and Roylance, Abrams, Kruger, Berdo and Kaul WITH RECESSED DRIVE WHEEL MEANS 6 ABSTRACT: Miniaturized variable resistors of the circular [52] US. Cl 338/162 type having a drive wheel rotatable in a housing and an arcu- [51] Int. Cl. 1101c 5/02, ate resistance element slidably engaged by a contact driven by HOlc 1/ 12 the drive wheel. The drive wheel has a rim thicker than the [50] Field of Search 338/(screw web of the wheel and substantial portions of the resistance eledigest), 143, 148, 149, 160-162, 166-168, 170, ment are located within the rim to provide an ultrathin poten- 174, 226, 252, 305, 317 tiometer.

5 5i"? 9 4 4 45 I 1 y re /5 6 I41 59 57 I6 0, 4 l3 a 24 ULTRATHIN MINIATURE POTENTIOMETER WITH RECESSED DRIVE WHEEL MEANS This invention relates to variable resistors of the miniature trimmer potential type in which a rotary contact slideable on a arcuate resistance element is driven in arcuate path by a rotatable drive wheel. More particularly, the invention relates to an improved potentiometer which may be termed ultranthin, since a potentiometer of particular operating characteristics constructed in accordance with this invention has a height, as measured in a direction along the axis of the drive wheel, which is substantially less than that of prior art potentiometers of like characteristics.

Presently known miniature potentiometers require housing sufficiently high to accommodate the drive wheel in a zone or plane above the resistance element and rotary contact. Although present miniature potentiometers of this type, which are usually housed in a square casing have transverse dimensions on the order of 0.35 inch and a height on the order of 0.187 inch it is desirable to reduce the height even more.

There is a continuing effort in the electronic industry toward reducing the size of electrical components to provide smaller circuit packages." Such packages may, for example, take the form of stacked printed circuit boards with miniature components on the circuit boards. At present, miniaturization has so highly developed that frequently the highest or thickest components on the printed circuit board are the potentiometers. To permit closer spacing of circuit boards in a stack, special mounting procedures are frequently resorted to, including recesses and. cutouts in the circuit boards to accommodate the potentiometers so that the boards may be more closely stacked. However, when such special mounting procedures are required, there is a corresponding increase in the number of operations required to be performed with attendant increase in manufacturing costs. With the ultrathin potentiometer of this invention, special mounting procedures are not necessary to obtain close stacking of the circuit boards, since this ultrathin potentiometer requires no more space than is usually provided for ventilation of the various components mounted on the circuit boards.

Present miniature potentiometers require a housing of sufficient height or depth to locate the drive wheel for the rotary contact in a zone or plane spaced from the zone or plane of the resistance element. Some of these prior potentiometers are disclosed, for example, in my copending application Ser. No. 598,4l6 filed Dec. 1, 1966, now patent number 3,478,294, and my U.S. Pat. No. 3,369,208 dated Feb.- 13, 1968.

in applicants ultrathin" potentiometer, the substantial reduction in height of the potentiometer results from a construction in which the elements of the potentiometer are so arranged that the drive wheel and resistance element have substantial portions thereof in a common plane or zone transverse to the axis of the drive wheel. Although the advantageous embodiment, which will be subsequently described, accomplish the ultrathin construction by using a hollow or recessed drive wheel, and locating the resistance element substantially within the side faces of the drive wheel, it is within the purview of the contemplated scope of this invention to locate the resistance element outside the drive wheel so long as substantial portions of the resistance element are in the region between the planes defined by the side faces of the drive wheel.

Accordingly, it is a general object of this invention to provide a miniature variable resistor or potentiometer which is ultrathin.

Another object is a miniature potentiometer of approxi mately one-half the height of the presently known miniature potentiometers.

Another object is a miniature potentiometer of ultrathin construction in which the drive wheel which drives the rotary contact is hollow or has a recess therein, and the arcuate resistance element on which the rotary contact slides is located primarily within the region defined by the side faces of the drive wheel.

faces of the housing containing them.

A further object is a miniature potentiometer having operating characteristics substantially the same as prior art potentiometers, and including a gear wheel and resistance element each of the same height as prior art potentiometers, but with an overall height of approximately one-half that of prior potentiometers.

A further object is a miniature potentiometer having a closed housing, a contact drive wheel and contact in the housing, a slip clutch connection between the contact and drive wheel, a resistance element-within the housing, and electrical leads electrically connected to the resistance element and contact and extending through a wall of the housing.

Numerous other features and advantages of the potentiometer of this invention will become apparent with reference to the drawings, which fonn a part of this specification and in which:

FIG. 1 is a plan view of a preferred embodiment of the potentiometer with portions of the upper casing, worm wheel, contact, and contact spring cut away to show additional details;

FIG. 2 is a sectional view taken along line 2-2 of FIG. 1;

FIG. 3 is a plan view of the base of the potentiometer housing with resistance element and leads mounted thereon;

FIG. 4 is an enlarged partial front elevational view in section of a prior art potentiometer; and

FIG. 5 is an enlarged partial front elevational view in section of the potentiometer of this invention.

Referring now to the drawings in detail and particularly to FIGS. l3, there is shown a potentiometer 1 constructed in accordance with this invention. Potentiometer 1 includes a sealed housing 2 having a cover 3 and a base 4 which extends into and is secured to the cover.

As shown at FIG. 1, cover 3 is generally square as viewed in plan and has opposed parallel sidewalls 5 and 6 which extend perpendicularly to opposed

parallel sidewalls

7 and 8. Extending across the upper ends of sidewalls 5--8 and integral therewith is a top wall 9. Sidewalls 58 and top wall 9 define a downwardly opening recess or cavity 10 within cover 3. Both cover 3 and base 4 are of molded plastic material having good electrical insulating characteristics.

Base 4 fits into and extends across the bottom of cover 3 to close the bottom of recess 10. The inside surfaces of sidewall 6-8, adjacent the bottom of cover 3, are provided with a step 11 which cooperates with upper surface 12 and flange surface 13 of the base to facilitate cementing base 4 to the cover. A step 11 is not provided along sidewall 5 of the cover, nor is there is flange along side edge 14 of thebase. Projecting upwardly from base 4 is a cylindrical post 15 which has its axis extending along the geometric center of the potentiometer. Post 15 projects upwardly from a generally cylindrical protuberance 16 having an arcuately curved side surface 17 and a flat top wall 18.

Mounted on base 4 are

electrical leads

19, 20, and 21 which extend through the base and have integral terminals 22-24, respectively, which project from bottom surface 25 of the base. Projecting upwardly from surface 12 of the base is a generally rectangular block 26 which functions as a stop for the movable contact of the potentiometer, and also serves to facilitate positioning the resistance element used in the potentiometer on the base.

Seated in recess 17 is an arcuately curved wire wound resistance element 27. Resistance element 27 is circular as viewed in cross section and this cross sectional curvature corresponds with the curvature of seat 17. Resistance element 27 is generally C-shaped as viewed in plane plan, at FIG. 3, and presents flat facing

ends

28 and 29 which engage the opposite side faces of block 26. Resistor 27 is secured to the base with a suitable cement. While resistance element 27 is shown as a wire wound element, resistance elements of cermet, or metal.

film can also be used.

Lead 19 is connected to resistance element 27 adjacent end 29 and lead 21 is connected to the resistance element 27 adjacent end 28. As shown at FIG. 5, the inner end of lead 19 is arcuately curved to conform with the curvature of resistance element 27, and is mechanically and electrically secured to the resistance element by welding. Similarly, lead 21 has its inner end arcuately curved and is also secured to resistance element 27 by welding. As shown at'FIG. 3, lead 21 has an intermediate portion 30 which curves arcuately in spaced relation to post 15 and is recessed into surface 18. Lead 21 then extends downwardly through the base to exit from the base as terminal 24. The inner end of lead 20 encircles post and sits on surface 18.

Mounted for rotation in cover 3, about an axis parallel to sidewall 5, is a lead screw 31. Lead screw 31 has a cylindrical tip 32, a helical worm thread 33, a retaining collar 34 and a slotted head 35 which facilitates rotating the lead screw with a screwdriver. Tip 32 of the lead screw extends into a cylindrical bore 36 formed within a block integral with and at a corner of cover 3. Cylindrical portion 37 of head 35 of the lead screw is positioned in a cylindrical bore 38 at the opposite side of the housing from bore 36. The axes of

bores

36 and 38 are aligned.

Collar 34 has an arcuately curved annular recess 39 to receive the rounded upper end of a lead screw retaining block 40. Block 40 projects upwardly from surface 12 of the base and has a height such that its curved upper end extends into recess 39 to prevent endwise movement of lead screw 31, when base 4 is inserted into and secured to cover 3. Disposed within bore 38 is an O-ring seal 41 which encircles the lead screw at a reduced diameter portion between collar 34 and cylindrical portion 37 of head 35.

Located within recess 10 is a gear wheel 45 having spur teeth 46 formed in its periphery. The gear wheel has a transverse web 47 provided with a centrally located opening 48 of a diameter to receive post 15. Post 15 functions as a journal and opening 48 provides a bearing surface for mounting gear wheel 45 for rotation about the axis of post 15, within the housing. Web 47 is spaced inwardly of end surface 49 of the gear wheel to provide a narrow annular surface which engages inside surface 50 of top wall 9. The narrow annular surface reduces friction between the wheel and inside surface 50 of the housing.

Slightly outwardly of opening 48, web 47 is provided with a circular array of equidistantly spaced recesses 51. Recesses 51 cooperate with an upwardly struck protuberance or projection 52 formed on movable contact 53, to provide the usual slip clutch connection. As shown at FIGS. 1, 2 and 5, contact 53 takes the form of a generally flat disc of circular outline having a resistance element engaging contact arm 54 which extends radially beyond the periphery of the disc portion of the contact. As shown at FIG. 5, contact arm 54 is bent slightly downwardly to engage the upper surface of resistance element 27. Contact 53 is formed from metal of good electrically conducting characteristics having sufficient springiness to maintain contact arm 54 in good electrical contact with the resistance element.

As previously described, lead has an inner end of arcuate configuration which encircles post 15 and lies flat against surface 18. With reference to FIGS. 1 and 2, it is seen that domeshaped metal spring 56 with a central opening is mounted on post 15 and extends between and engages the inner end of lead 20 and the lower surface of contact 53. Spring 56 is formed from a springy metal of good electrical conducting characteristics and provides the dual function of electrically connecting contact 53 to lead 20, and maintaining contact 53 in engagement with the web 47 of gear wheel 45.

Gear wheel 45 is molded from a material which is a good electrical insulator. Spur teeth 46 are formed on the exterior surface of an annular flange 57 integral with web 47. Flange 57 extends axially from web 47 and cooperates with the inside surface of the web to form a downwardly opening recess 53 within gear wheel 45. The lower edge 59 of flange 57 is spaced slightly from surface 12 of the base, as shown at FIG. 5. The

height of the space between surface 12 and edge 59 is exaggerated in FIG. 5 and it is to be understood that this space is merely sufficient to prevent engagement of edge 59 with surface 12 when gear wheel 45 is rotated. Hence, the height of gear wheel 45, as measured between surface 49 and edge 59, is only very slightly less than the height of recess 10, as measured between

surfaces

12 and 50.

With potentiometer l assembled, spur teeth 46 mesh with worm 33. Spring 56 electrically connects lead 20 with contact 53, and also urges the contact against the gear wheel so projection 52 is maintained in one of recesses 51. Rotating lead screw 31 causes gear wheel 45 to rotate and move contact arm 54 along resistance element 27. When the contact arm engages either side face of block 26, continued rotation of the gear wheel forces projection 52 out of one of recesses 51, and the projection then snaps into the next adjacent recess. Hence, damage to the potentiometer is avoided by this slip clutch action if the gear wheel is rotated beyond the range of movement of the contact.

As shown at FIG. 5, the maximum height within housing 2, between

surfaces

12 and 50, is the vertical distance h,. The height of resistance element 27 is h as measured along the axis of rotation of gear wheel 45. The axial height of gear wheel 45, between

surfaces

49 and 59, is h;,. As is evident with reference to FIG. 5, the height h is substantially less than the sum of the heights h and h By providing the recess 58 in gear wheel 45 and then arranging contact 53 and resistance element 27 so they are within the recess, a substantial height saving is obtained, as measured along the axis of rotation of the gear wheel. Hence, the overall height h, of potentiometer 1 of this invention is substantially less than the height of the prior art potentiometers.

With reference to FIG. 4, there is shown a prior art potentiometer having a resistance element of a height h and a gear wheel of a height h which heights are substantially the same respectively as the heights h and h of FIG. 5. However, because the gear wheel 45 of the prior art potentiometer is substantially solid and because resistance element 27' of the prior art potentiometer lies in a plane or zone substantially spaced from the gear wheel, so there is space 53 64 177 the overall height h of the cavity required to accommodate resistance element 27', contact 53, and f gear wheel 45 is substantially greater than the sum of hg and h It will also be observed with reference to FIGS. 4 and 5, that the thickness of top wall 9 and base 25 for potentiometer I of this invention are substantially the same respectively as the thickness of top wall 9 and base 25 of the prior art potentiometer of FIG. 4. Hence, potentiometer 1 of this invention, while having the same housing or casing wall thicknesses as the prior art potentiometer of FIGS. 4, has an overall height h. which is approximately one-half the height h, of the prior art potentiometer, while neither electrical insulating properties nor mechanical strength is sacrificed in the construction of potentiometer 1. However, a potentiometer which is ultrathin and has a height essentially one-half the height of the prior art potentiometer is provided.

In view of the above description, it is apparent that the potentiometer of FIGS. I3, and 5 has its various operating components, namely, lead screw 31, gear wheel 45, contact 53, spring 56, resistance element 27, and leads 19-21, in housing 2, that gear wheel 45 is mounted on post 15 for rotation upon rotation of lead screw 31, that contact 53 is driven by the gear wheel via recesses 51 and projection 52, that arm 54 slides along the resistance element, and that the contact is electrically connected to lead 20 via spring 56. It is also apparent that the upper or side surface 49 of the gear wheel lies in a plane normal to the axis of rotation of the gear wheel, that edge or side 59 lies in a second plane normal to the axis, that contact 53 is between these planes, and that resistance element 27 is substantially between these planes.

While a preferred embodiment of the potentiometer of this invention has been shown and described in detail, it is within the contemplated scope of this invention that numerous changes can be made in the construction shown and described herein without from the scope of this invention.

lclaim:

l. A miniature low profile variable potentiometer comprising a closed housing having a base, a top, and sidewall means connecting the base and the top anddefining a cavity therein; said top including an inside surface within said housing facing toward said base, and said base including a resistor mounting surface within said housing and facing toward said top; a drive wheel within said housing and mounted for rotation about an axis generally perpendicular to said base and top, said drive wheel having a flange defining a recess and presenting an outwardly facing peripheral surface; an arcuate resistance element seated on said resistor mounting surface and of a height to extend into said recess, a lead screw having a threaded portion in driving engagement with said peripheral surface of said drive wheel, said lead screw including means to manipulate same from outside the housing, whereby rotation of said lead screw causes rotation of said drive wheel; a contact coupled to said drive wheel for rotation therewith and engaging said resistor; said resistor, said flange, and said threaded portion of said lead screw each having portions thereof in a common zone defined by parallel planes generally perpendicular to the axis of rotation of the drive wheel and each passing through said resistance element, said flange, and said threaded portion of said lead screw; and a plurality of leads electrically connected respectively to said contact and said resistance element and accessible from outside said housing.

2. A low profile potentiometer according to claim 1 wherein the maximum height of said cavity equals the distance between said resistor mounting surface and said inner surface.

3. A potentiometer according to claim 2 wherein said threaded portion of said lead screw has a diameter greater than one-half theheight of the cavity but less than the height of the cavity.

4. A potentiometer according to. claim 2 wherein said flange has a height only slightly less than the maximum height of said cavity and terminates at an end face in a plane closely adl5 jacent said resistor mounting surface.

5. A potentiometer according to claim 1 wherein said housing is rectangular externally as viewed in plan; said sidewall means includes opposed pairs of parallel sidewalls, and said lead screw extends across said housing closely adjacent to one of said sidewalls and with its axis of rotation parallel with said one of said sidewalls.

6. A potentiometer according to claim 1 wherein said resistance element is a wire wound resistance element.

Claims

1. A miniature low profile variable potentiometer comprising a closed housing having a base, a top, and sidewall means connecting the base and the top and defining a cavity therein; said top including an inside surface within said housing facing toward said base, and said base including a resistor mounting surface within said housing and facing toward said top; a drive wheel within said housing and mounted for rotation about an axis generally perpendicular to said base and top, said drive wheel having a flange defining a recess and presenting an outwardly facing peripheral surface; an arcuate resistance element seated on said resistor mounting surface and of a height to extend into said recess, a lead screw having a threaded portion in driving engagement with said peripheral surface of said drive wheel, said lead screw including means to manipulate same from outside the housing, whereby rotation of said lead screw causes rotation of said drive wheel; a contact coupled to said drive wheel for rotation therewith and engaging said resistor; said resistor, said flange, and said threaded portion of said lead screw each having portions thereof in a common zone defined by parallel planes generally perpendicular to the axis of rotation of the drive wheel and each passing through said resistance element, said flange, and said threaded portion of said lead screw; and a plurality of leads electrically connected respectively to said contact and said resistance element and accessible from outside said housing.

3. A potentiometeR according to claim 2 wherein said threaded portion of said lead screw has a diameter greater than one-half the height of the cavity but less than the height of the cavity.

4. A potentiometer according to claim 2 wherein said flange has a height only slightly less than the maximum height of said cavity and terminates at an end face in a plane closely adjacent said resistor mounting surface.