US3533043A

US3533043A - Adjustable electronic component

Info

Publication number: US3533043A
Application number: US777780A
Authority: US
Inventors: Robert W Spaude
Original assignee: Allen Bradley Co LLC
Current assignee: Allen Bradley Co LLC
Priority date: 1968-11-21
Filing date: 1968-11-21
Publication date: 1970-10-06
Anticipated expiration: 1987-10-06

Description

R. w, SPAUDE ADJUSTABLE ELECTRONIC COMPONENT Oct. 6, 1970 Filed Nov. 21, 1968 INVENTOR" ROBERTWSPAUDE B aw w,

ATTORNEY United States Patent O 3,533,043 ADJUSTABLE ELECTRONIC COMPONENT Robert W. Spaude, Milwaukee, Wis., assignor to Allen- Bradley Company, Milwaukee, Wis., a corporation of Wisconsin Filed Nov. 21, 1968, Ser. No. 777,780 Int. Cl. H01c 5/02 US. Cl. 338167 6 Claims ABSTRACT OF THE DISCLOSURE An adjustable electronic component which may take the form of a resistor comprising a base having a fiat arcuately disposed contact-engaging resistance track and an annular conducting ring substantially concentric with and axially spaced from the resistance track. There is a contact element interposed between and in electrical engagement with both the resistance track and the annular ring, and which may take the form of a spheroid molded of a low resistance carbon composition. The contact is retained, along with a biasing spring, in the cavity of a cup-shaped rotatable contact carrier for retaining and positioning the contact into rotational engagement with both the resistance track and the conducting ring.

BACKGROUND OF THE INVENTION Field This invention pertains to an adjustable, variable resistance device useful in a variety of modified forms as a variable resistor, a variable potentiometer, a combination variable resistor or potentiometer and switch unti, and a type commonly called trimmer resistors or potentiometers.

Prior art A variety of variable resistance devices are known. In particular, Pat. No. 3,350,673 issued to the present inventor, discloses a device capable of providing a function similar to that of the present invention. However, it will be apparent that the patented device is of a more complicated configuration and includes additional moving parts, each dependent upon one another for tolerances and other factors than that of the present invention. The present invention also serves the purposes of providing a miniaturized device for the ever increasing demand towards miniaturization. Obviously, the lesser number of component parts in a device permit a more compact construction. The present device also permits the use of a novel sandwich arrangement for positioning terminals relative to the track, not found in previous construction.

SUMMARY OF THE INVENTION This invention contemplates the provision of a variable resistance device having a spring biased contact brush member, preferably including a spheroidal surface, and which may be in the form of a spheroid, which contact member is retained in the cavity of a cup-shaped, rotatable rotor element, and which is spring biased concurrently towards a relatively flat circular resistance track, and an outwardly flared surface of an annular conducting ring axially spaced from the resistance track. The usual terminal connections are made to the conducting ring and to the resistance track. In the case of a potentiometer, terminal pads are provided at opposite ends of the open-ended circular resistance track.

Terminal leads for the resistance track are provided as elements of a unitized subassembly and are connected to the track terminal pads. The leads are formed to bend rearwardly of the insulating support for the track and are sandwiched between the support and closure element. The elements of the terminal subassembly are cemented together with an epoxy resin or the like. The sandwich subassembly further provides a closure for a molded, open-ended casing housing the various components. The casing is arranged to receive the conducting or collector ring, which may be integrally molded therein as an insert, the rotatable rotor, or contact carrier, concentric with the axis of the ring, the spheroidal surfaced contact, or brush, member, a spring biasing the contact, and the terminal sandwiched acting as a closure for one end of the casing. At the opposite end of the casing there extends a portion of the rotor arranged for engagement with an adjusting tool, such as a screwdriver. At the said opposite end there is also positioned an O-ring which bears against the rotor and the inside of the casing wall to act as a seal for the casing. An annular insulating ring is then fastened by means of an adhesive, or by sonic welding, to the casing to mechanically retain the O-ring. It is contemplated that the rotor, itself, may be formed at its exposed end, replacing the annular insulating ring, to provide an adjusting thumbwheel which permits finger adjustment, if so desired, rather than by the use of a separate adjusting tool.

BRIEF DESCRIPTION OF THE DRAWINGS The attached drawing, which comprises a part hereof, and illustrating a preferred embodiment of the invention, is as follows:

FIG. 1 is a perspective view of an assembled potentiometer according to the principles of the present invention.

FIG. 2 is a cross-sectional view taken along the line 22 of FIG. 1.

FIG. 3 is a fragmentary perspective view of a resistance element of the potentiometer, and specifically illustrating the arrangement of positioning the terminals between the resistance element and an insulating closure plate retaining the terminals in place.

FIG. 4 is an illustrated exploded view in perspective of the component parts of a potentiometer made in accordance with this invention.

FIG. 5 is a front end view of the rotor, or contact carrier, for the device of FIGS. 1-4, inclusive, illustrating a stop member integrally molded therewith.

DESCRIPTION OF THE PREFERRED EMBODIMENT The illustrated embodiment of FIGS. 1-5, inclusive, is in a form suitable for use as a miniature potentiometer of the type commonly employed in communication and control circuits. It is shown in the form of a cube constructed of side or edge dimensions in the order of 4 inch. The variable resistance device is designated by the general reference character 1 and includes a molded housing, or casing 2. As stated previously, the housing 2 is preferably cube shaped, as shown, but may be of any other desired exterior configuration. The internal chamber 3 is of a general cylindrical configuration in order to provide for rotational operation of the movable contact elements contained therein. The chamber 3 is open at both ends, and at one end to the left, as viewed in FIG. 1 provides a recessed surface 4 defining a shoulder 5 for receiving an aperture, annular closure member 6 which may be secured in place by means of an epoxy cement, or by sonic welding, upon completion of the insertion of the various operating components, as will hereinafter be described. Seated within the hollow chamber 3 of the housing 2 is an annular, stationary, conducting or collector ring 7, which may be provided as an insert during the molding formation of the housing 2.

A substantially cylindrical rotor component, designated generally by the reference character 10, is arranged to be received within the chamber 3 of the housing 2 and includes a surface 16 conforming to the exposed, outwardly tapered, surface 22 of the conducting ring 7, which surface 22 also acts as a bearing surface for the surface 16 of the rotor 10. The rotor surface 16 is relieved at 17 along an arcuate path (not shown) for purposes hereinafter described. One end of the rotor extends through the housing 2 and the aperture 11 of the closure member 6 to provide access to a screwdriver slot 12, serving to permit rotation of the rotor, as desired. Obviously, other means for rotating the rotor may be provided, such as an opening for an Allen wrench or by means of a thumbwheel (not shown), which may be fastened to the protruding portion of the rotor 10' after assembly of the rotor in the casing.

Upon insertion of the rotor 10, and its various components, a pliant O-ring 13 is inserted between the surface of the chamber 3 of the housing 2 and the surface of the rotor 10 to provide a moisture seal, while permitting rotational movement of the rotor. The O-ring 13 may be comprised of silicone, neoprene or other rubber-like material.

With reference to both FIGS. 2 and 5, it will be observed that there are cooperating rotational stop members comprising an integrally molded stop 14 in the housing 2 and another integrally molded stop member 15 on the rotor 10 (see FIG. for purposes hereinafter described.

The cup-shaped rotor includes a re-entrant cavity 18, which is open at its bottom surface, as viewed in FIG. 4. The cavity 18 (see FIG. 4) is arranged to receive a biasing coil spring 19 resting against an angular wall 20 at one end thereof and against a conducting spheroidal contact member 21 at its opposite end. The spheroidal contact 21 may take the form of a molded carbon composition, low resistance material, or any other conducting material suitable for the purposes of practicing the present invention. Contact between the spheroidal contact 21 and the flared surface 22 of the conducting ring 7 provides electrical engagement with the conducting ring 7. The relieved surface portion 17 of the rotor 10 permits an unrestricted electrically conductive arcuate contact path for the contact 21. The conducting ring 7 is mechanically and electrically joined to a terminal lead 23 by means of percussive or other types of welding, or by means of soldermg.

An oppositely disposed portion of the conducting spheroidal contact 21 rests against a resistance track 26 (see FIG. 3) disposed on a stationary base 27. The base 27 comprises a square-shaped, supporting substrate 28 preferably consisting of insulating ceramic material. The substrate 28 supports a first contact surface in the form of a fired-on, arcuate, printed resistance track 26 comprised of a material having a designated resistance according to the desired design and material makeup. For instance, the track 26 may take the form of a printed and fired cermet of known composition. Opposite ends of the resistance track 26 terminate at termination pads 29. (Only one being shown in FIG. 3.) The termination pads 29 are preferably of a material, e.g. gold or silver, which can readily withstand the high temperatures and accommodate soldering or welding. As shown in FIGS. 3 and 4 the base 27 is angularly contoured at the corners 30 to receive terminal leads 31 and 32, respectively. This construction permits the

leads

31 and 32 to have access to the respective termination pads 29 without interfering with the end closure of the housing 2 as will later be described. The

termination wires

31 and 32 are preferably formed in an L-shape, or with a full reverse bend (not shown) around the base 27 to permit a sandwich-like subassembly construction together with the insulating closure member 33. As shown in FIG. 4, the casing 2 is provided with slots 34 for receiving the

terminals

31 and 32. The subassembly may be secured to the housing 2 by means of an epoxy resin or the like, to join and seal the closure member 33 to the edges of the housing.

The sandwich subassembly including the base 27, the terminal leads 31, 32 and the closure element 33 is preassembled as a unit with the components of subassembly being held together by means of an adhesive, such as epoxy resin, spread between the

members

27 and 33 before the terminals are welded to the resistance track 26 at the termination pads 29.

With reference to the exploded view of FIG. 4, it will be apparent that the device comprises a minimum number of parts, each of which is in coaxial alignment with its cooperating element. That is, the stationary collector, or conducting ring '7 is positioned, preferably as a molding insert in the casing 2, and the rotor extends through the opening of the ring-like element 7 and receives the spring 19 and the spheroid 21 within its cavity 18. The rotor 10 is provided with protrusions 35 arranged to contact the inwardly facing surface of the resistive element 27, radially spaced from the resistance track 26, in order to prevent the face of the rotor 10 from rubbing against the resistance track 26 during rotation due to any additional axial forces which may be introduced during rotative adjustment of the rotor 10. The subassembly comprising the base 27 and the closure 33 is then inserted and sealed in place relative to the housing 2, as before described. The O-ring 13 and the enclosure 6 are inserted to complete the entire assembly. Laterally spaced legs 36 on the bottom of the casing 2 provide a stand-off support for the housing 2 with cleanout clearance when mounted on a printed circuit board, or the like, and also provide a spacer for the

terminals

23, 31 and 32 to be bent backwardly (not shown), if so desired.

Once assembled, as the rotor 10 is rotated, for example by means of a screwdriver or other tool inserted within the slot 12, the conducting spheroid or brush contact 21, bridging the resistance track 26 and the conducting or collector ring 7, will be rotated therewith to vary the resistance between the collector ring lead 23 and one or both of the track leads 31, 32. Rotation is realized in either rotational direction and continues until the stop 15 on the rotor 10 engages the stop 14 integrally molded with the housing 2.

It will be observed that the bridging electrical contact between the surface 22 of the conducting ring 7, the spheroid 21, and the track 26 also presents a stable mechanical arrangement due to a wedging relationship between the spheroid and its concurrent engagement with the said surface and track. This permits excellent set tability characteristics which are obviously highly desirable for variable resistors and capacitors used for circuit trimming" purposes. So-called trimmers are adjusted to desired position and are rarely changed from this setting. It obviously follows that one of the paramount requirements of such devices is the ability to retain the setting until next adjusted. The present device has been found to be superior to conventional construction in this respect.

It will be appreciated that the present invention also provides a structure diminutive in size, while providing a device that is facilely assembled.

It should be fully appreciated, that although the preceding detailed discussion has been limited primarily to a potentiometer, the invention is by no means so limited. For example, the switch may be realized by making a portion of the contact engaging surface, or track of highly conductive material and the other of insulating material. Thus, the brush 21 can rotate between the collector ring 7 and the conductive arcuate portion of the track for on position, and bridge the ring 7 and the insulating portion of the track to off position. Furthermore, a capacitive element may be realized by varying the dielectric value between the terminals as the rotor is operated.

Iclaim:

1. An adjustable electronic component comprising, in

combination:

a casing having an open-ended, hollow chamber;

an annular, stationary conducting ring positioned in said chamber and having an outwardly flared, uninterrupted, circumferential marginal end portion;

a rotatable cylindrical rotor coaxial with said ring and contained in said chamber, said rotor defining a reentrant cavity at one end and having a portion at its opposite end protruding through said hollow chamber, said portion including means for providing rotational adjustment of said rotor, and said cavity being disposed angularly relative to the rotational axis of said rotor;

a stationary base positioned in said chamber spaced axially from and facing the flared end portion of said conducting ring, an arcuate, contact-engaging, planar surface disposed on the inner surface of said base, and at least one terminal lead supported by said base and in electrical engagement with the armate, contact-engaging surface;

an electrically conductive contact member retained in the cavity of said cylindrical rotor and arranged to simultaneously electrically and mechanically engage the outwardly flared surface of said conducting ring and the contact-engaging planar surface of said stationary base;

a compressible resilient member positioned within the cavity of said rotor and biasing said contact member angularly relative to said planar surface and into said simultaneous electrical engagement with said ring and the contact-engaging, planar surface of said base.

2. The adjustable electronic component of claim 1, in

which the contact member includes a spheroidal surface portion, said portion simultaneously electrically engaging the flared surface of said ring and the contact-engaging, planar surface of said base.

3. The adjustable electronic component of claim 1, in which the contact member is a spheroid.

4. The adjustable electronic component of claim 1, in which the conductive contact member is of a molded carbon composition.

5. The adjustable electronic component of claim 1, in which the contact-engaging surface of said base defines a resistance track.

6. The adjustable electronic component of claim 1, in which the stationary base comprises a sandwich construction including an insulating substrate member supporting said contact-engaging surface on one side thereof, a closure member substantially parallel with and spaced from said substrate member, at least one terminal lead disposed between said members and being formed at one end to electrically and mechanically engage the contactengaging surface on the other side of said substrate member, and means for retaining the said members and terminal of said construction in clamping relationship.

References Cited UNITED STATES PATENTS 2,492,727 12/ 1949 Ballard 338-202 XR 2,817,722 12/1957 Johnson 200- XR 3,294,929 12/1966 Johnson. 3,350,673 12/1967 Spaude 338l XR FOREIGN PATENTS 385,325 3/ 1965 Switzerland.

THOMAS J. KOZMA, IR., Primary Examiner U.S. Cl. X.R.