US3394336A - Housing and terminal construction for variable resistance devices - Google Patents

Description

July 23. 1968 J. P. DOERING. JR

HC'USING AND TERMINAL CONSTRUCTION FOR VARIABLE RESISTANCE DEVICES 3 Sheets-Sheet 1 Filed June 14, 1966 FIG. 2

F's 3 INVENTOR.

JOHN P DOERING. Jr. BY

,fiidf z ATTORNEY y 1968 J. P. DOERING. JR 3,394,336

HOUSING AND TERMINAL CONSTRUCTION FOR VARIABLE RESISTANCE DEVICES Filed June 14, 1966 3 Sheets-Sheet 2 INVENTOR.

JOHN P DOERING Jr.

ATTORNEY July 23, 1968 J. P. DOERING, JR 3,394,336

aousme AND TERMINAL CONSTRUCTION FOR VARIABLE RESISTANCE DEVICES Filed June 14, 1966 3 Sheets-Sheet 5 FIG. 10

INVENTOR.

JOHN P. DOERING Jr.

ATTORNEY United States Patent 3,394,336 HOUSING AND TERMINAL CONSTRUCTION FOR VARIABLE RESISTANCE DEVICES John P. Doering, In, Santa Ana, Calif., assignor to Beckman Instruments, Inc., a corporation of California Filed June 14, 1966, Ser. No. 557,540 4 Claims. (Cl. 338-184) ABSTRACT OF THE DISCLGSURE A housing having side walls defining a cavity open at one end and having first and second slots formed in the side wall adjacent the opening, the slots being arranged and at an angle and communicating with each other. A terminal having portions thereof bent to fit the slots and retained in place by a cover lid having a protruding shoulder which extends into the first slot and abutting against the terminal thereby locking it in place within the respective slots.

The present invention relates to resistance devices and more particularly to the construction and mounting of terminal members in the housing of resistance devices.

The terminal and mounting arrangement of the present invention is particularly applicable to variable resistance devices such as potentiometers and rheostats and the term potentiometer as used hereinafter will be understood as pertaining to all types of variable resistance devices. In general, resistance devices and potentiometers comprise a resistance element or coil which is typically mounted within a housing through which are assembled one or more terminal members for electrically connecting the resistance element and the rotary wiper contact, in the case of variable resistance devices, into external circuitry. A terminal and the means for mounting it in the housing may be a significant part of the cost of a potentiometer because the mounting hole through the housing requires either machining or complicated sliding mold parts and because the terminal itself is frequently fabricated by a screw machine. In precision potentiometers of the type embodying a coiled resistance element wound upon a mandrel and inserted within the cavity of a housing, it is desirable to first position the resistance element and its associated wiper mechanism before inserting the terminal connectors and making connections thereto. In such a case it is necessary that the terminal member be positioned reasonably close to the portion of the resistance element to which it is to be attached and that openings be provided in the housing for making the proper electrical connections between the terminals and the respective portions of the coiled resistance wire.

The advantages of the present invention will become apparent as the following description proceeds and the features of novelty which characterize the invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

Briefly, the present invention is directed to a resistance device comprising a housing having side walls defining a cavity or recess in which is mounted a resistance element. The housing is open at one end and includes at least first and second slots formed in a side wall of the housing adjacent the opening with the second slot being disposed at an angle with respect to the first slot. A terminal member is provided having a first portion adapted to fit within the first slot and a second portion disposed at an angle therefrom and adapted to fit into the second slot. The terminal is retained in place within the end portion of the housing by means of a cover lid having a protruding shoulder which extends into the first "ice slot and abuts against the terminal thereby locking it into place against disengagement from the housing.

For a better understanding of the invention, reference may be had to the accompanying drawings in which:

FIGURE 1 is a perspective view of a multiturn variable resistance device employing a terminal mounted according to the present invention;

FIGURE 2 is a perspective view of a terminal employed in the vairable resistance device of FIGURE 1;

FIGURE 3 is an enlarged partial cross-sectional view showing the terminal mounted in the side wall of the housing and retained by the cover lid;

FIGURE 4 is a perspective view of a terminal construction for another embodiment of the invention;

FIGURE 5 is a partial cross-sectional view showing the terminal of FIG. 4 retained within the side wall by a cover lid;

FIGURE 6 is a partial perspective view of a single turn potentiometer disclosing the slot arrangement for retaining a terminal according to the invention;

FIGURE 7 is a perspective view showing the terminal member adapted to be mounted in the end wall of the housing disclosed in FIGURE 6;

FIGURE 8 is a partial cross-sectional view of the housing of FIG. 6 illustrating the terminal mounted thereon;

FIGURE 9 is a perspective view showing a variation of the embodiment illustrated in FIGS. 6-8; and

FIGURE 10 is a cross-sectional view of a multiturn variable resistance device employing a terminal and mounting arrangement according to a third embodiment of the invention.

Referring now to FIG. 1, there is shown an embodiment of the invention in the form of a multiturn potentiometer comprising a housing 10 including a side wall or walls 11 defining a cavity having mounted therein a resistance element 12. While in this embodiment, the side wall 11 of the housing is cylindrical in shape and the resistance element is annular, it should be understood that the side walls could form a rectangular or other shaped housing and the resistance need not be annular and mounted around the inner periphery of the cawty. The housing is preferably formed of an insulating material and may be molded from a plastic material, such as diallyl phthalate. In the present embodiment of the invention, the resistance element comprises a thin resistance wire 12 which is helically wound upon a coiled mandrel 12a. The coiled turns of resistance element are supported within the cavity within a spiral groove 13 formed or molded into the inner surface of the cylindrical wall 11.

As may best be seen in FIG. 3, there is rotatably mounted within the housing on a rotary shaft 25, adapted to extend through one of the end covers, a rotor, generally indicated by the reference numeral 16. The rotor 16 carries a block of insulating material, hereinafter termed a contact-guide assembly 17, which is slideably mounted within a longitudinal channel 16a formed in the rotor 16. The contact-guide assembly is adapted to follow the turns of the resistance element 12 as the rotor is rotated. More specifically, guide members 17a extend closely adjacent the turns of the resistance element and follow the resistance turns as the rotor is turned. The contact-guide assembly 17 also carries a contact means which comprises a resilient contact element 18 formed of a strip of spring bronze or the like and bent into a configuration so that it contacts the inner surface of the resistance wire during rotation of the rotor 16 and the carrier-guide assembly. The slider contact 18 is electircally connected to a suitable means for conducting electrical current. As shown in FIGURE 3, the wiper contact 18 is in contact through a conductive strip 19,

formedin the bottom of the guide channel 16, which in turn is electrically connected to a slider brush 20 engaging a bowed spring contact 21. Spring contact 21 is connected into the external electrical circuitry through means of a terminal attached to the spring contact and extending externally of the end cover, such as terminal 22 extending from end cover 23 in FIGURE 1.

In this embodiment of the invention, the housing is provided with a terminal block 14 extending outwardly from the surface of the housing and forming a mounting structure for the terminal members which are employed for connecting the device into an electrical circuit. As will be seen in FIGURES 1 and 3, the terminal block portion of the housing is provided with a first slot 24 which, in this embodiment of the invention is molded or otherwise cut into the wall of the housing and terminal block in a direction normal to the axis of the cylinder. A second slot 26 is formed in the housing at an angle with respect to the first slot 24. In the embodiment shown in FIGURE 1, slot 26 is formed in the upper surface of the terminal block 14 and is disposed at a right angle with respect to the slot 24 and communicates with the slot 24 at one end thereof. It will also be noted in FIGURE 3, that slot 24 extends across the thickness of the cylinder wall and exposes the upper surface of at least one turn or coil of the resistance element 12 mounted within the housing.

The terminal member 15 for this embodiment of the invention, as illustrated in FIGURES 2 and 3, is formed in a step-like configuration out of a strip of brass or other appropriate material. It comprises a first section 27 and a second section 28 arranged at an angle with respect to each other, the angle being the same as that between the respective slots 24 and 26. In this case the angle is a right angle. Section 27 is adapted to fit within the slot 24 and section 28 is adapted to fit within the slot 26. In this embodiment of the invention, the terminal is also provided with an upright section 29 adapted to extend outwardly from the housing. The upright section 29 may be provided with an opening 31 which is used for attaching the potentiometer into external electrical circuitry.

The dimensions of the sections 27 and 28 are preferably very close to the dimensions of the respective slots so that the terminal fits snugly therein. In order to more firmly hold the terminal member 15 within the slots, there maybe provided a pair of small protrusions, such as coins or tangs 32, extending outwardly from the opposite sides of the first section 27 of the terminal member. The outer surfaces of the tangs 32 are slightly wider apart then the width of the first slot 24 so that they dig into the sides of the slot and retain the terminal in place during the initial assembly operation.

*In the embodiment disclosed in FIGS. 1-3, the terminal member 15 is also provided with a pair of flanges 33 extending substantially normal to the plane of the first section 27 of the terminal. Flanges 33 extend generally parallel to the sides of the first slot 24 and serve to protect the electrical connector between the terminal with the resistance wire 12, which in this embodiment comprises a lead wire 34 welded to the surface of first section 27 of the terminal and tapped to the resistance wire 12. The flanges 33 prevent the retainer lid or cover lid 23, which is provided with an inwardly protruding shoulder 36 designed to fit within the first slot 24, from encountering the weld or the lead wire 34 and disrupting the electrical connection between the terminal and the resistance element. The shoulder 36 on the cover fits within the first slot 24 and the second slot 26 and is positioned in abutting relation against the surfaces 33a of the flanges thereby locking the terminal 15 firmly in place.

Because of the convenient access provided by the slot 24 to the exposed coil of the resistance element and to the surfaces of the terminal, the lead wire 34 is easily attached to make a strong and accurate electrical connection between these components. After the lid cover 23 is installed, the remaining exposed or open portion of the slot 24 may be sealed with a cement or other sealant, as desired. A cement, such as an epoxy material, also helps retain the terminal 15 in place. Alternatively, a projection (not shown) could be provided on the cover 23 whichwould fit within the second slot 26 and overlap the second section 28 of the terminal and'closethe opening above the first slot.

In FIGURES 4 and 5, anothe'r'embo'diment of the invention is disclosed. In this embodiment, the terminal is indicated by the reference numeral 40 and is provided with a first section 41 and a second section'42 adapted respectively to fit within slots 24 and 26 in the end of the housing 10. The terminal 40, in this embodiment, differs from that of FIGURE 2 in that there are no flanges extending outwardly from the first section and the protrusions or tangs 43 are formed on the end of the first section 41 rather than centrally thereon. 1

As in the embodiment of FIGURE 1, a pair of slots 24 and 26 serve as mounting seats for the first and second portions respectively of the terminal and the upright section 44 of the terminal extends outwardly from the housing. Also, in this embodiment the terminal is connected to the resistance wire 12 through a lead connection 34 welded to the first portion 41 of the terminal and tapped to the resistance wire 12. The cover lid 46 is provided with a protruding shoulder 47, adapted to abut against the upper portion of the first section 41 of the terminal. Shoulder 47 is not as thick as the housing wall and does not engage the first section 41 of the terminal in the region of the lead wire weld 48.

FIGURES 6-8 illustrate still another embodiment of the invention as applied to a single turn resistance element. This embodiment differs slightly from the previous embodiment in that the second slot or groove is not formed in the surface of the housing or terminal block. In this embodiment of the invention as may be seen in FIGURE 6, the first slot 51 is molded or otherwise formed in the housing wall adjacent the open end thereof in a direction substantially normal to the axis of the housing. The second slot 52 is formed at an angle to the first slot and molded or otherwise cut directly into the wall of the housing. In the embodiment shown, slot 52 is arranged substantially normal to the direction of slot 51 and extends through an annular mounting shoulder 54 adapted to serve as a mounting seat for the single turn resistance coil 53. Slot 52 also opens into the interior of the housing in a region closely adjacent the resistance coil 53. In this embodiment of the invention there is provided a terminal member generally designated by the reference numeral 56 having a first section 57 and a second section 58 disposed at an angle with respect to each other. First section57 also forms the upright portion of the terminal which extends outwardly from the housing. The terminal 56 may be stamped or otherwise constructed of a material. such as gold-plated brass or the like which is inexpensive, a good conductor, and easy to fabricate.

As may be seen in FIGURE 7, the second section 58 of the terminal may be provided with a plurality of protrusions or coins'59 or other surface interruptions which function as temporary holding means for retaining-the terminal member in the side wall of the housing during assembly. Coins 59 are disposed apart a distance greater than the width of the second slot 52 so that they cut into the side Walls of the slot 52 when the terminal isiinserted therein. In this embodiment of the invention, the second section 58 of the terminal member extends throughthe slot 52 and protrudes into the interior of the cavity formed within the housing so that the exposed end,thereof is positioned rather closely to the resistance element coil 53. A lead 61, attached to the resistance element 53,. may be spot welded or otherwise attached to the first-.section-58 of the terminal member. Tapping of the-lead is a simple operation in this construction because of the open construction of the potentiometer and the exposed spot welding surface available on the second section 58 of the terminal. Once the lead wire has been attached, an end cover 62 is attached to close the opening on this end of the housing. End cover 62 may be attached by any suitable means well known in the art, such as grooves, clamps or by means of a cement such as an epoxy glue. As in the previous embodiments, the cover lid 63, when positioned over the opening across one end of the housing, abuts against the first section 57 of the terminal member and securely retains the terminal member in place within the slot thereby locking it against disengagement from the housing.

FIGURE 9 illustrates a variation of the embodiment disclosed in FIGS. 6-8, in which the first slot 80 is formed in the cover lid or member 81. As in the illustration of the housing shown in FIG. 6, the second slot 82 in this variation is formed within the wall of the housing 83. The terminal member 84 is formed similarly as the terminal 58 shown in FIG. 7 with the second section 84 adapted to fit into the second slot 82 and the first section 85 extending outwardly in a direction substantially normal to the housing. When the cover is positioned over the opening to the housing cavity it fits over the cylindrical lip 86, formed on the wall thereof, and the slot 80 is designed to receive the first section 85 of the terminal. The cover lid, then, abuts against the first section 85 forcing it against the surface 87 of the wall of the housing thereby locking the terminal member in place within the slots formed respectively on the cover member and the housing member.

A similar embodiment of the invention is disclosed in FIGURE 10, in which the terminal members 66 are disposed in opposite ends of a terminal support block formed on the housing of a multiturn variable resistance device. A first slot 68 is formed in the opposite ends of the housing. A second slot 69, disposed at an angle with respect to the first slot 68, extends into the side wall of the housing. The terminal member 66 is provided with a first or upright section 71 and a second section 72 arranged respectively at the same angle as that between the respective slots 68 and 69; in this instance the angle being substantially a right angle. As in the embodiments shown in FIGURES 2 and 7, the terminal member 67 may be provided with coins or tangs (not shown) adapted to engage the sides or portions of the slot 69 as it is inserted therein.

It will be noted that this arrangement is somewhat similar to that shown in the first embodiment wherein the first slot 68 exposes the upper surface of at least one turn of the resistance element 73. This provides easy access to the resistance element and the surface of the terminal for attaching a connecting lead wire 74 therebetween. The cover lid 75 (only one of which is shown in FIG. 10) is provided with a shoulder 76 having a width designed to fit within the first slot 68 and is so designed and constructed that a portion thereof abuts against the surface of the first section 71 of the terminal and securely retains the terminal within the slots formed in the side wall of the housing. As will be seen in FIGURE 10, the end cover 75 is designed so that it engages the terminal member at a point above the region of the lead wire weld.

By the present invention there is provided a convenient terminal mounting arrangement for a resistance device which permits very low-cost stamped terminals to be employed and which may be mounted and securely retained in the resistor housing without the use of special tools. No drilling or tapping of the housing is required, thus the housing can be molded of diflicult-to-machine material. It is designed to make the attachment of the electrical conductor means between the terminal and the resistance element a simple operation with both the resistance and the connection portion of the terminal easily accessible through an opening or mounting slot formed in the housing.

While in accordance with the patent statutes there has been shown and describml what at present is considered to be the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, the intent of the appended claims to cover all such changes and modifications as fall with the true spirit and scope of the invention.

What is claimed is:

1. In a resistance device, the combination comprising:

a non-conductive housing having a side wall defining a cylindrical recess, said housing having an opening on at least one end thereof communicating with said recess;

a resistance element mounted in said recess, said resistance element being annular in shape and disposed around the inner surface of said recess;

a first slot in said side wall of said housing in said end thereof adjacent said opening to said recess;

a second slot in said side wall of said housing disposed at an angle to said first slot within said side wall of said housing and arranged substantially parallel to the axis of said annular resistance element, said second slot communicating with said first slot at one end thereof;

at least one of said slots being so arranged and so constructed as to expose the outer surface of a portion of said resistance element through said slot;

a terminal member including a first section fitting Within said first slot and a second section arranged at an angle to said first section and fitting within said second slot;

a terminal lead wire electrically connecting between said terminal member and said resistance element at said portion of said element exposed by one of said slots;

a retainer lid closing said opening to said recess, said lid having a portion abutting against said terminal thereby locking said terminal member into said slots and said side wall and preventing disengagement thereof from said housing.

2. The resistance element defined in claim 1 in which said terminal comprises a first section fitting into said first slot and a second section fitting into said second slot and a third section protruding upwardly from said second section and forming a terminal post extending substantially normal to said housing, and including a pair of flanges extending from said first section into abutting contact against said shoulder of said retainer lid to form an opening through said slot between said cover lid and said terminal through which an electrical connection can be made between said resistance element and said first section of said terminal member.

3. The resistance element as defined in claim 1 in which said second slot is disposed substantially parallel to the axis of said annular resistance element and so arranged and constructed as to expose the outer surface of a portion of said resistance element so that an electrical terminal lead wire may be connected between said resistance element and an exposed section of said terminal member.

4. A variable resistance device comprising a molded non-conductive housing having a cylindrical side wall defining a cylindrical recess, said housing having an opening on at least one end thereof communicating with said cylindrical recess;

a multiturn helically wound resistance element and its associated electrical wiper mechanism mounted in said recess, said helical resistance element being supported around the inner surface of said cylindrical recess;

a first slot in said side wall of said housing in said end thereof adjacent said opening to said recess, said slot exposing a portion of at least one turn of said resistance element;

a second slot formed in said side Wall of said housing disposed substantially normal to said first slot and communicating with said first slot at one end thereof;

an L-shaped terminal member including a first portion thereof fitting within said first slot and a second portion thereof fitting within said second'slot with said first portion abutting against the inner surface of said first slot;

a terminal wire electrically connected between said exposed portion of said resistance element and said L- shaped terminal member; and

a retainer lid closing said opening to said recess, said lid having a protruding shoulder fitting within said first slot and abutting against said first section of said terminal member thereby forcing said terminal A against said surface of said slot and locking-said terminal member against disengagement from said housing. .7

References Cited UNITED STATES PATENT S ROBERT K. SCHAEFER, Primary Examiner; H. J. HOHAUSER, Assistant Examiner.

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