US2141908A - Combined volume control and switch unit - Google Patents

Description

Dec. 27, 1938.

COMBINED VOLUME CONTROL AND SWITCH UNIT Original Filed Dec. 11, 1933 3 Sheets-Sheet 1 NUI I INVENTOR BY W c. J. HATHORN 2,141,908 Y Dec. 27, 1938. c. J. HATHORN COMBINED VOLUME CONTROL AND SWITCH UNIT Original Filed Dec. 11, 1933 5 Sheets-Sheet 2 BY mvzmon 117% 1938- c. J. HATHORN 2,141,908

COMBINED VOLUME CONTROL AND SWITCH UNIT Original Filed Dec. 11, 1953 3 Sheets-Sheet 3 INVENTOR ATTORNEY Patented Dec. 27, 1938 UNITED STATES 2,141,908 PATENT OFF 1C Clarence J. Hathorn, St. Marys, Pa... assignor to The Staelrpole Carbon Company, a corporation of Pennsylvania Original application December 11, 1933, Serial No.

701,802. Divided and this application February 27, 1936, Serial No. 66,050

16 Claims.

My invention relates to an adjustable resistance device combined with an electric circuitmaker or breaker unit operated by a single control, and is particularly adapted for use in radio circuits and public addressing systems.

This is a divisional application of my prior patent application Serial No. 701,802, filed December 11, 1933.

Adjustable resistance devices are employed in radio circuits or public addressing systems to control the volume of sound emitted by the loud speaker; and the circuit-maker or breaker, in the form of a snap-switch, is employed to open or close the electrical power circuit. As the combined volume control and power switch unit must be compact it is necessary to position the various elements constituting the instrumentalities in such manner as to reduce the space occupied to a minimum value.

It is an object of my invention to provide in a rheostat or volume control a movable contact shoe or current collector which will adjust itsell to any irregularities appearing on the surface of the resistance element and still not cause any abrasion between the contact shoe and the resistance element.

Another object of my invention is to provide a novel spring pressure arm for engaging a resistance element contact shoe wherein the turning torque will be applied substantially along the entire length of the pressure arm.

Another object of my invention is to combine a power switch together with a volume control so that the switch during assembly will be placed on the volume control in a predetermined position.

Another object of my invention is to provide a power switch which will simultaneously close or open the electrical circuit at two places in order to quickly extinguish the arc.

A further object of my invention is to provide a power switch wherein the same spring which closes or opens the circuit also maintains the contact between the bridging terminal and the terminals connected to the outside circuit.

A still further object of my invention is to provide a simple, eflicient snap-switch trigger mechanism.

A still further object of my invention is to provide a resistance element that may be held so that the holding means will not obstruct the resistance element contact shoe nor will the contact shoe harm the resistance element adjacent the holding means.

Other objects of my invention are to provide an improved device of the character described. which is easily and economically produced, that is sturdy in construction, and which has a maximum efllciency and accuracy in operation.

with the above and related objects in view,

my invention consists in the following described details of construction and combination of parts, which will be more fully understood from the following description, when read in conjunction with the accompanying drawings, in which:

Figure l is a perspective view of the assembled volume control and switch unit embodying my invention.

Figure 2 is a sectional view taken through the volume control unit and its casing.

Figure 3 is a side view of the snap switch circuit terminal.

Figure 4 is a plan view of the terminal shown in Figure 3.

Figure 5 is a plan view of the volume control.

Figure 6 is a plan view of the assembled snap switch.

Figure 'l is a sectional view of the snap switch casing alone.

Figures 8 and 9 are plan and side elevational views respectively, of the snap-switch torsional spring.

Figures 10 and 11 are plan and side eleva; tionai views respectively, of the snap-switch trigger.

Figures 12 and 13 are plan and side elevational views respectively, 01' the contact throw arm for the snap switch.

Figure 14 is a plan view of the assembled volume control pressure arm, its contact shoe holding member, and the contact shoe.

Figure 15 is a sectional view taken on the line Iii-i5 0! Figure 14.

Figure 16 is a perspective view of a modified contact shoe embodying my invention.

Figures 17 and 18 are plan and side elevational views respectively, of the snap switch contact bar and its pivotal holding support.

Figure 19 is a sectional view of the contact shoe and its holding member as taken on the line i9--l9 01' Figure 5.

Figure 20 is a perspectiveview of the contact shoe as shown in Figures 2 and 5.

Figures 21 and 22 are perspective views oi the holding nut and bolt respectively, for holding the volume control resistance element, the base and the terminal in operative relationship.

Figure 23 is a plan view, looking from the top of the pressure arm, wherein another modifled contact shoe and holder is shown.

Figure 24 is a sectional view taken on the line 24-24 of Figure 23.

Figure 25 is a perspective view of the modified contact shoe as shown in Figures 23 and 24.

Figures 26 and 27 are plan and side views respectively, of a modified type of holding-nut having therein a nest for the contact shoe.

Figures 28 and 29 are plan and side views respectively, of another modification of a holding nut having therein an extension to contact one edge of the resistance element.

Figure 30 is a fragmentary sectional view of another modification of a rheostat.

Figure 31 is an assembled perspective view of the cylindrical contact shoe and its movable and pressure members.

Figure 32 is an exploded view of Fig. 31.

Figure 33 is an exploded view of the modified resistance element and its "tap-off" connections.

Figure 34 is a fragmentary plan view of another modification of the resistance tap-off.

Figure 35 is a sectional view taken on the line 35-45 of Figure 34.

Figure 36 is a fragmentary sectional view taken through another modification of a volume control.

Figure 3'? is an exploded view of the insulated rotatable member, the contact shoe, the pressure spring, and the pressure spring holding member.

Referring now in detail to the drawings I show in Fig. l a combined volume control and switch unit embodying my invention and in Fig. 2 is shown the volume control as it is when used alone. A rheostat or volume control base. generally designated as A, is formed of an insulating material upon which a resistance element, generally designated as B, is arcuately mounted.

The base A has an arcuate edge 20 forming the major peripheral portion of the base and, an extending edge 22 forming the minor peripheral portion of the base, both edges extending in the same plane but the minor peripheral arcuate edge 22 extends a greater distance from a central aperture than the edge 20.

A plurality of recesses 24 extend on the outside face 26 of the base but within the radial limits of the peripheral edge 22. Each recess has therein a conducting strip of metal or terminal 28 which connects the outside circuit to the resistance element, as hereinafter explained in greater detail. Each terminal is of a width substantially equal to that of the recess in order to prevent any laterally displacement of the terminal.

The extension serves the following purposes: (1) it spaces and insulates each of the terminals from the metallic cover in order to prevent any short circuit occurring between the terminals and the metallic cover; (2) the single extension aligns the cover withrespect to the base in a predetermined position; hence, the snap switch which is mounted on the cover will always be in its correct position; and (3) the single extension interfits with a suitable notch in the cover in order to form a substantially closed housing.

The central terminal member 30 is adapted to connect a movable contactor or contact shoe 3|, which forms one side of the derived electrical circult, to an external circuit, whereas the other terminal members 28 and 32 are connected to the minimum and maximum resistance extremities of the resistance element. It is to be noted that the groove or recess 24 is sufficiently deep in the outer surface of the base so that the rivet or grommet for retaining and electrically connecting the terminal will be removed from engaging the panel upon which the rheostat control is mounted. Such arrangement of the grooves prevents short-circuits between the panel and the rheostat.

Mounted exteriorly upon the base A is a stud 35 which may be a separate piece securely held on the base or it may be molded integrally with the base. The stud fits into a complementary opening on the panel to which the unit is attached in order to prevent any relative turning movement of the unit about the axis of the shaft when the control shaft is rotated.

A journal bushing, generally designated as C. is mounted centrally through the aperture in the base A. The bushing. of the single-hole mounting type, is exteriorly threaded as at I and is held in position by its flange ll engaging one face of the base, and also, a retaining nut 4|! threaded on the bushing and engaging the other face of the base. The above mentioned arrangement of the flange and nut prevents any relative movement between the bushing and the base either in a rectilinear direction along the longitudinal axis of the bushing or in a rotary direction about the bushing.

Journaled for rotary movement within the bushing C is an elongated control shaft 2 substantially of cylindrical formation. An annular groove 44, suitably positioned from the outer end of the shaft, receives a lock-washer or split-clip 46 for preventing the shaft from moving inwardly since the lock-washer 46 may engage the end of the journal bushing. The serrated inner end portion 48 of the shaft, carrying a rotatable insulating member 50, fits into a complementary opening 52 of the aforesaid member. The rotatable member, at assembly, is forced upon the shaft so the serrations therein bite into the wall forming the opening 52 to secure the rotatable member rigidly in operative position. The rotatable member in addition to turning in unison with the shaft also prevents the shaft from moving outwardly from the journal bushing.

The rheostat may be regulated in any desired manner as by means of a knob which is positioned on the outer end of the control shaft. The knob is held to the control shaft by means of a set screw which engages a suitable flattened portion of the shaft.

The film-type of resistance element B, is concentrically positioned upon the base A close to its outer edge and the ends of the resistance film are suitably connected to the outside terminals as by rivets. belts, or screws of electrical conducting material.

For details of construction of a specific resistance element reference is made to the copending application of Henry B. Arnold and Ernest G. Jacobs, Serial Number 663,538, filed March 30, 1933.

However, I provide a novel means of connecting the resistance element, the base and the terminal together. A bolt 54 of good electrical conducting material, having a screw-threaded shank is passed through one end of the terminal, through the base and through oneend of the resistance element with the head of the bolt against the terminal. An internally threaded nut 56, having a cylindrical outer surface 51 and a radial extending flange 58, is screwed onto the bolt. However, the bolt may be screwed on the nut without any change in function. The circular flange 5B of the bolt makes a good electrical contact with the resistance element as a considerable contact area is established between the flange and the resistance element thus, minimizing the contact resistance. The outer surface 51 of the nut extends upwardly and provides a stop for the contact shoe as the nut is impinged upon by the pressure arm at the limit of its stroke. The flange of the bolt may have a crescent shaped cutout portion ill to form a nest for the contact shoe, as well shown in Figs. 26 and 27. Hie

diameter of the recess or nest is slightly larger than the diameter of the contacting shoe together with its holder so that the contact shoes periphry is separated from the concentric edge of the terminal by only a few thousandths of an inch. or the flange, of high conductivity material, may are shaped to have an elongated extension Bl. ee Figs. 28 and 29, along one edge of the resistance element which edge will be in close proximity to the contact shoe as the shoe approaches the end of the resistance element. Such extension provides a low resistance between the shoe and the terminal to enable a low resistance hop-oil to be made.

By using a low resistance extension at one terminal it may be necessary to widen the resistance element adjacent that particular terminal, but such widening does not affect the function of the device. Thus, there are two resistances of different resistivities in overlapping, parallel, electrical contacting relationship at one end of the resistance element. In a combined switch and rheostat unit the control shaft must move a predetermined distance away from the low resistance terminal before the switch is opened; and, if no provision for a low resistance hop oil' were made the initial minimum resistance would be of a very high resistance value instead of a low resistance value.

A flexible pressure arm 62 is comprised of a thin slightly bowed substantially rectangular metallic member. An opening, through which a fastening rivet or bolt may pass, is formed at one end of the pressure arm 62 and the other end of the pressure arm carries a contact-shoe holding member 64 which functions both for moving the contact shoe 3| over the resistance element upon movement of the pressure arm and, also, for permitting the contact shoe to adjust itself on the resistance element.

The pressure arm is fastened, at the end with the opening therein, within a groove 68 which extends across the rotatable insulating member. The point of attachment of the pressure arm on the rotatable insulating member is at a greater distance from the contact shoe than the radial distance from the control shaft to the resistance element. This arrangement provides flexibility to the arm which otherwise would not be obtained since the pressure arm would be too rigid due to the relative short distance between the control shaft and the resistance element.

The pressure arm holding rivet Ill, eccentrically mounted with respect to the control shaft, is of sufllclent length to engage and provide the driving torque for the snap-switch trigger mechanism, as hereinafter further described.

The pressure arm as commonly used and com posed of two arms which converge together has a tendency to twist a very small amount about the fulcrum of each arm due to the lack of transverse rigidity at the free end of the arms. The hereinabove related twisting or torsional movement produces a slight noise in the loud speaker of the circuit when the contact shoe is moved by the pressure arm. In my novel arrangement no twisting of the pressure arm will occur when movement of the contact shoe takes place because of the transverse stiffness of the pressure arm 62, which is of one piece, and the engagement of the arm with the side walls forming the groove 88. It should be observed that a turning couple actuates the rotary movement of the pressure arm irrespective of the direction of movement, for each of the sides H and 13 of the pressure arm are engaged by each of the side walls of the groove.

As illustrated in Figure 2 of the drawings a resilient washer 12 of electrical conducting material is mounted on the base and has a tongue which is connected to the mid-terminal 30. In sliding contact engagement with the washer I2 is another complementary spring washer ll fastened directly on the rotatable insulating member by the pressure ann holding rivet or bolt 10. The washer N has the tendency to spring away from the lower surface of the rotatable insulating member ill, but rotates with that member. Thus, it is seen that an electrical connection is made between the resistance element and the terminal 30 irrespective of the position of the contact shoe; the circuit being completed through the contact shoe 66, the spring arm 62, the sliding washer H, and its stationary complementary washer I2 and the terminal Sll. As the washers l2 and H are concentrically positioned away from the control shaft an insulated control shaft is provided.

The rigid flat self-adjusting contact shoe 3!, of the wiping type, engages the resistance element B. The shoe, also of suitable electrical conducting material, may be constructed of a disk or circular formation, see Figs. 2, 19 and '20, and due to its construction it presents a large contact area on the resistance element thus effecting a low contact resistance; or in order to approximate a line contact the shoe 16, see Figs. 23, 24 and 25, has two of its diametrical arcuate edges removed so that it is wide, in order to extend across the resistance element, and relatively short in length as compared with its width and it is.

also, short in length as compared with the linear length of the resistance element.

The disk-shaped contact shoe 3| has its periphery engaged by a flange or rim 78 of the complementary cup-shaped holding member 64; the holding member being mounted on the end of the pressure arm. The cup-shaped member 64 is comprised of a flat base 80 and the downturned flange 78 which forms the cup or receptacle for the contact shoe, see Figs. 19 and 20. A round- "headed rivet 84 pierces both the pressure arm and the base of the cupshaped member and holds them rigidly together after the rivets outer end is expanded.

The modified contact shoe 16, as shown in Figs. 24 and 25, is held within a complementaryshaped holding member 85 which is mounted on the end of the pressure arm.. A round-headed rivet 81 functions on the shoe l6 similarly as the rivet 84 functions on the contact shoe 3|.

The central upper surface of the contact shoe 3| is engaged by the rivet head 86 of the rivet 84, as is well shown in Figs. 2 and 19, when the contact shoe is positioned on the resistance element and within the cup-shaped member. The shoe will seat or adjust itself properly on the resistance element and travel over any irregularities or imperfections therein, as a slight loss motion exists between 'the periphery of the shoe and its complementary surrounding flange, and in addition to the loss-motion arrangement the rounded rivet head substantially engages the upper central portion of the shoe at a point. Thus, a low resistance contact is practically assured at all times between the resistance element and the contact shoe.

It is to be noted, at this time, that the pressure arm is electrically connected t the resistance element by virtue of the connect ons or electrical path through the contact shoe, the holding bolt and, also, the cup-shaped shoe moving member.

In Figs. 14, 15 and 16 is shown another embodiment of a contact shoe, wherein a cup-shaped contact shoe BI is comprised of a flat surface III for engaging the resistance element and a peripheral flange 22 extends from the flat contact surface. The peripheral flange of the shoe cooperates with a complementary disk 94 mounted on the end of the pressure arm so that movement of the pressure arm moves the contact shoe member; The rounded head of a rivet 88, which holds the disk to the pressure arm, engages the upper portionof the flat surface OII oi the contact shoe and permits the contact shoe to pivotally move about the head. By the hereinabove described arrangement the contact shoe, in view of its universal connection with the shoe holding disk and the rivet. will travel over any irregularities or imperfections which may appear on the resistance element and thus insures substantially a uniform contact resistance.

The rheostat shell or housing 92 is comprised of a circular planar metallic base whose peripheral edge or flange is bent to project substantially perpendicular to the base. During the stamping operation a plurality of cars I00, I02, I04 and I06 and also a short recess are formed on the extremity of the flange by removing the surrounding metal. The short peripheral recess is formed in the flange to fit over the base extension 22.

The cars I00, I02 are so positionedrthat they engage the sides "II, II oi the minor peripheral edge 22 and when all the cars I00, I02, III4 and I are downturned orclinched over the outside face 0! the base A no relative movement may occur between the base and its casing in either a rotary direction about the axis of the shaft or in a longitudinal direction along the axis of the shaft.

Interiorly mounted abutting the inner periphery oi the casing flange is a circular disposed strip of insulation II2 of uniform width. The strip of insulation is disposed between the resistance element and the flange of the casing and serves to extrude dirt, dust, moisture and other foreign substances trom entering the casing, it serves to prevent any short-circuits between the rheostat elements and the casing, and it further serves as a positioning means so that the base of the casing will remain at a predetermined distance from the insulating base.

A snap switch, generally designated as 8, shown assembled with the volume control in Fig. 1, and shown in greater detail in Fig. 6, may be mounted on the base of the casing or shell 98 by any suitable means. An aperture is provided through the shell so a trigger operating mechanism 4 on the switch may protrude therethrough. The

aperture on the shell for the trigger is suiiiciently large so that the trigger does not, at any time, contact the shell.

The switch S is securely mounted on the back of the metallic casing, and the casing 88 when grounded acts as an electromagnetic and an electrostatic shield to prevent any feedback noises from the power circuit when the contact shoe is moved.

The switch mechanism is mounted within an insulating base, preferably comprised of a molded phenol condensation product. A pivot II. is located in the lower portion of the switch-base H8 and upon the pivot is loosely mounted a contact carrying arm III of insulating material which is wide at its free end portion. A contact or short-circuiting blade member I22 comprising a substantially rectangular low-resistance metallic bar is pivotally mounted as at I24 in the same plane as the contact carrying arm.

A contact spring support I26, see Figs. 1'7 and 18, carries at one end thepivot I24 about which the contact member I22 is mounted. The other end I28 of the contact spring support is securely attached to the contact arm by a suitable holding means as, ior example, an eyelet or a rivet.

Likewise loosely mounted on the same pivot. as shown in Fig. 6 is the switch-throw trigger I I4 which has laterally extending wings Ill and I22 for limiting the movement of the trigger by engaging the flange I34 of the switch base. Extending perpendicular to but in the same plane as the wings I and I32 is a member I", to which one leg of the torsional spring is attached. A pair of arms I28 and I40 are integrally formed at one end of the member I36 by a stamping operation with the trigger member. The arm projects perpendicular to the body or member I of the trigger and are adapted to be transiently engaged by the bolt III on the rotatable member for moving the trigger from one side to the other side.

A torsional spring I42 has one of its legs I44 connected to the switch-throw trigger and its other leg I46 connected to the contact carrying arm. 7

Movement of the trigger does not actuate the contact carrying memer until the medial axis of the closed end of the spring passes slightly beyond dead center as the trigger compresses the springarms of the torsional spring together. The energy stored in the spring rapidly turns the contactcarryingmember, either closing the electrical circuit when the terminals are bridged or breaking the circuit when the bridging contact is moved away from the terminals. However, as the rheostat control shaft also actuates the snap switch it is essential that the control shaft be rotated through a small fraction of the entire angle that it may be rotated before the switch is actuated. as such arrangement allows the major movement of the control shaft to control the position of the contact shoe on the resistance element.

The torsion spring I42 not only throws the contact carrying member with great velocity but also presses the carrying member I inwardly against the switch base H8, so that in circuit closing position the side wall I 43 of the contact member I22 engages a terminal flange I54, and the front wall I45 of the contact member I22 engages the shank I56.

The snap switch circuit terminals I 48 and ISO, see Figs. 3, 4, and 6, suitably spaced apart, are adapted to be contacted by the bridging member I22 for closing the circuit and also are positioned to limit the movement of the contact carrying member I2II at the circuit closing end of its osclllation.

To the outside end oi each snap switch terminal is connected an electrical conducting strip of metal, having an eye or opening therein. Lead wires from the main circuit pass through the eye and are soldered to the conducting strip in order to make a low resistance connection.

Each of the snap-switch terminals is comprised of a hollow cylindrical base I52 which passes through and holds itself to the base and the outside circuit terminal in rigid relationship after its end is peened over. From the other end of the terminal extends the flange I54 which tapers until 15 mac the cylindrical shank I56 is reached. The contact bar electrically contacts the cylindrical shank and also the flange to bridge the terminals and thus close the circuit.

It is to be recalled, at this time, that the breaking of an electrical circuit creates an are which tends to pit and destroy the contacts. By the above arrangement of the power circuit contacts a double break in the circuit is simultaneously efiected by a snap switch which is a decided advantage as the arc is quickly extinguished with very little burning of the contacts.

As the torsional spring tends to press or urge the contact carrying arm against the base, the side I43 of the bridging bar I22 and the flange I54 of each terminal are the first and the last portions to make an electrical contact. Thus a wiping action, which tends to keep the contacts clean, and a bump-type of contact is employed, maintaining a low contact resistance in operation. It is seen that the arcing will primarily take place between the flange and the side of the short clrcuiting bar. parts which ordinarily perform no function in the device nor do they affect the main contacts. Therefore, since arcing does not occur at the main contacts, the main conducting surfaces remain relatively clean so that the life of the switch will be prolonged.

An internal extending ridge portion I 50, see Fig. 6, of the switch base adjacent the upper portion of the contact carrying member I20 limits the backward movement of the contact carrying member. An arcuate formed groove I in the base formed in the path of the swing of the arm I20 permits the pivotal member I28 to slide freely therein; and another arcuate groove I62 in the path of the movement of the end of the torsional spring prevents any frictional engagement between the end I46 of the spring and the base.

The resistance gradient curve of the res stance element is 'made non-uniform or irregular, s nce the resistance variation of the resistance element is other than a linear function of the movement of the contact shoe thereon. The nonuniform resistance element is used in order that the volume of sound emitted by the loud speaker in a radio circuit shall be directly proportional to the movement of the resistance control arm. In order to practically obtain in a derived electrical circuit the predetermined resistance gradient of the resistance element it is theoretically necessary to have a contact solely on a line, for otherwise a wide contact current collector obliterates. at all times, a definite proportion of the resistance element causing the resistance to jump considerably from one value to another instead of varying in infinitesimal steps to give a smooth progression curve. It is, also, essential that the contact shoe be clean, otherwise oxidation of the metal, or dirt, will cause the contact resistance to be so high that no current will be taken from the resistance element. To more nearly approximate the above mentioned ideal conditions I provide a cylindrical contact member of electrical conducting material wherein the curved bounding sur-" face frictionally engages the resistance element approximately on a line. i

Referring now, more particularly to Figs. 30, 31, 32 and 33, I show another modification of a volume control or rheostat wherein a resistance element 200 coated on one side with a carbonaceous film is suitably mounted upon a non-conducting base 202. Intermediate the minimum and the maximum resistance terminals is a tapoil' 202. At this tap-oi! I coat the under-side of the resistance element with a conducting film of a length substantially equal to that of the width of a tap-01f terminal 204. The short under-side film coating is but a continuation of the main film coating and is placed on the resistance element to reduce the resistance value of the tap-ofl' to a minimum value.

A rivet 206 passes through the insulating base 202, through an end of a strip of metal electrical conducting material 204 and through one end of an outside tap-off terminal 208. The head of the rivet 206 is constructed so that it will be flush with the surface of the insulating base after its shank end is expanded or peened over to hold the strip of conducting material 204 and one end of the outside tap-oil terminal 200 in position. The narrow conducting strip 204, however, has one end 2I0 engage the resistance element at its outer edge but the end 2I0 is positioned so that a cylindrical contact shoe 2I2 will not be obstructed in its movement over the resistance element. The strip 204 abuts the outer peripheral edge of the insulating base and is sufllciently bent inwardly from the peripheral edge to have the rivet 206 pass therethrough to hold it in engagement with the tap-off terminal 208. This strip 204 and the rivet 206 renders a low contact resistance from the resistance element to the terminal 208. The cylindrical contact shoe 2I2 is positioned on the resistance element so its longitudinal axis will extend substantially parallel to the longitudinal axis of the movable arm and its cylindrical bounding surface engages the resistance element in order to obtain substantially-a line contact. The shoe 2I2, constructed of high electrical conductivity material, is held within, a complementary opening 226 of a movable member, generally designated as 2I6, and so accommodates itself on the resistance element.

The movable member 2IB has an opening 2Il in its main portion 220, and from the main portion is a bend 22I which passes partially around the movable insulating member 222 and then has an offset portion 224 within which is located an opening 220 for the contact shoe 2I2.

When the shoe is within the opening 220 movement of the insulating member 222 pushes the shoe as one of the walls 225 or 221, which partially define the opening 220, engages the curved bounding surface 220 of the contact shoe. However, the member 2I,6 only applies the moving force to the cylindrical contact shoe. A separate pressure arm 220 having an opening 220 in one end and a downturned portion 222 at the other end provides a suitable pressure for urging the contact shoe into engagement with the resistance element. Abolt 234 passes through a rotary contactor member 230, through the insulating member 222, through the openings 2I0 and 220 of the movable member 2I6 and the pressure arm 228 respectively, and holds the above elements together alter its end is expanded or peened over.

Although the pressure arm and the movable arm are disclosed as being constructed of separate elements a single movable element having an extending ear to serve as a pressure member may be employed. The contact shoe may either roll or it may slide on the resistance element depending on the tightness of the contact shoe in its complementary opening in the movable arm and, also, the pressure exerted by the pressure arm.

Assembling and constructing the elements,

shown in Figs. 30, 31 and 32, so that a beneflcial wiping or burnishing action will take place between the resistance element and the contact shoe, it is to be observed that the same area of the contact shoe does not always engage or wipe the resistance element when the direction of rotation of the contact shoe is changed. Or in other words when the contact shoe moves counterclockwise a definite .contact surface or area of the shoe engages the resistance element; however, when the direction is reversed to a clockwise direction, the contact shoe shifts or rolls slightly to another or second contact area. Further movement of the contact shoe in the clockwise direction only brings the second area or surface in engagement with the resistance element. As the general effect of the movement of the contact shoe on the resistance element is that of a burnishing or wiping contact the contact surface will generally be kept clean from any corrosive effects and of particles of dust, and the contact shoe will also slide over any projections or irregularities on the surface of the resistance element without scoring the resistance element.

The resistance element may be widened as at 226 to have an extending conducting edge which may, if desired, readily be engaged by the end 2i! of the conducting strip 264.

' It is oftentimes difllcult to make the required tap on the volume control which tap is used in a tone correction or automatic .tone compensation circuit. This difficulty may be overcome by using another modification of a tap-oi! embodied within a volume control, as shown in Figs. 34 and 35. The periphery of the resistance element 246 is extended or widened as at 242 at the tap-oil: such construction being similar to the radially extending portion designated as 238 in Fig. 33.

A rivet 244, for holding a tap-off terminal 246, has a head which is flush with the inside face of the insulating base 246. The head of the rivet is engaged by the abutting face of the resistance element which may be coated by a low resistance conducting film only at the abutting portion in order to aid in reducing the contact resistance. The conducting film on the tap-oil 242, of course, is electrically connected to the main conducting material or film of the resistance element. A second rivet 250 pierces and retains, after its ends are expanded, the outside tap-ofl terminal 246, the base 246 and the widened portion 242 of the resistance element.

In Fig. 33 the upper surface of the resistance element and upper surface of the widened portion 236 is coated with a conducting material and in Fig. 35 I show a rivet 256 passing through extension 233, the base, and the terminal 246, so that when the ends of the rivet 266 are peened over the resistance element the base and the terminal are held together mechanically, and the resistance element and the terminal are electrically joined.

By making the rivet 26 of suflicient strength the holding rivet 244, Fig. 35, may be dispensed with. This structure may be used at other places on the resistance element since the contact shoe may pass the holding bolt without passing over the holding bolt. The resistance element may also be widened near its ends so that the arcuate movement of the contact shoe may be increased.

The tone compensation projection, extension, or tap-oi! on either of the arcuate resistance a,141,aos

elements 2lli| and 246 usually is located to one side of the main conducting surface of the resistance element and usually is located between the terminals or ends of the resistance element.

Referring now to Figs. 36 and 3'? wherein is shown an insulating base, generally designated as D, for holding and moving a cylindrical contact shoe 262.

The insulating base D has a disc portion 264, and centrally extending from one face of the insulating base is a cylindrical portion 265 having a bore 256 within which bore a control shaft 256 may be operabiy retained. Upon the periphery of the disc portion 254 is an extension 266 which need be of no greater thickness than the thickness of the disc portion 264. The extension 266 protrudes over the arcuately mounted resistance element and is sufficiently wide to have its walls 262 and 264 which define its width. engage each of the projecting terminal connectors 266 of the resistance element at the limit of its movement in either direction, thus the extension limits the movement of the insulating base. The

linear distance between the walls 262 and 264 must be such that the full length of the resistance element is utilized when the control shaft rotates the contact shoe from the stop position at one end ofthe resistance element to the stop position at the opposite end of the resistance element.

The cylindrical contact shoe 252, of the same type as that designated as 2l2 in Figs. 30, 31 and 32, is mounted within an oblong bore 266 through the extension 268, so that the longitudinal axis of the contact shoe will remain substantially parallel to the surface of the resistance element as the contact shoe 262 is pushed by either of the walls 210, 212. The particular wall which may engage the curved bounding surface of the contact shoe depends, of course, upon the direction of movement of the control shaft. Extending from the oblong bore in the extension is a circular I bore 214 which completes an aperture through the extension. A helical pressure spring 216 of electrical conducting material and of predetermined elasticity is freely compressible within the circular bore'214 and urges the contact shoe 262 into electrical engagement with the resistance element.

Since the resistance element is of the film conducting type and the contact shoe presents substantially a line contact the resistance gradient curve as obtained will have a smooth progression instead of a noticeable step-by-step resistance value progression.

A metal strip 216 of electrical conducting material has an opening at one end and is of substantially rectangular formation. The strip 212 retains the helical spring 216 in position by covering or partially covering the circular bore 214 wherein the helical spring is encased. The apertured end of the metal strip is rigidly retained on the insulating member D by an electrical conducting rivet 286 which also retains the sliding electrical collector member 262 on the insulating member D. The electrical circuit from the adiustable contact shoe 252 to the outside terminal is completed through the helical spring 216, the strip 218, the rivet 266, the sliding collector member 282 and a stationary collector member over which the sliding member 262 moves. The outside terminal member. of course. is electrically connected to the stationary collector member.

Within an aperture 264 adjacent the periphery of the movable insulating base D is an extending cam stud 2" securely mounted in the aperture I84 which stud is adapted for operating a snapswitch throw trigger mechanism, after a suitable snap-switch is attached in operative relationship on the volume control in order that both the snap-switch and the volume control may be operated by a single control shaft.

From the above defined structure and arrangement of parts it is seen that a rigid insulated movable arm or base of unitary construction may readily be employed within a volume control. Of course, the resiliency provided by the spring 216 reacting against the cylindrical contact shoe 252 permits the shoe to adjust itself on the resistance element irrespective of any irregularities thereon, and it also maintains a proper electrical contact pressure between the resistance element and the contact shoe without causing any scoring of the resistance element when movement of the contact shoe occurs. The pressure of the spring in addition to performing the functions as above stated also determines whether a rolling or a sliding movement is to occur between the cylindrical contact shoe and the resistance element. If the pressure of the spring on the contact shoe is suiilciently large then the frictional component is such as to prevent the curved surface of the contact shoe from rolling on the resistance element when the contact shoe is pushed so that corrosion of the contact shoe does not occur because of the sliding action between the shoe and the resistance element, and if the pressure of the spring on the contact shoe becomes or is predeterminedly low then the cylindrical contact shoe will roll over the resistance element when the shoe is pushed, but the spring eliminates any corrosive coating from the shoe.

Although the above embodiments of the invention have been described in considerable detail, such description is intended as illustrative rather than limiting, as the invention may be variously embodied. My invention, therefore, is not to be restricted except as it is made necessary by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. In an adjustable resistance device, a resistance element, an electrical conducting contact shoe adapted to move over said resistance element, a pressure arm for moving said contact shoe, means between said shoe and said pressure arm including an interfltting cup-shaped member complementary to said contact shoe for moving said shoe. and a convex shaped member on said pressure arm engaging the upper surface of said contact shoe for pressing the contact shoe on said resistance element whereby the contact shoe may adjust itself on the resistance element.

2. In an adjustable resistance device comprising a resistance element, an electrical conducting contact disk shoe adapted to move over said resistance element, a pressure arm for moving said contact shoe, means between said resistance element and said pressure arm including an interfltting cup-shaped member and the complementary disk shoe whereby the contact shoe may adjust itself on"the resistance element to make a good electrical connection, and a convex member attached to said pressure arm and abutting the central portion of the contact shoe whereby there may be relative motion of one member with respect to the other member about the central projecting element as .the pivot.

3. In a rheostat comprising a resistance element completely coated with conducting material on one side, and partially coated with conducting material on its opposite side intermediate its terminals, both of said coatings continuously united, a holding bolt engaged by said partial coating, said bolt attached to the base of the rheostat, and a clip connected to one edge of the completely coated side and held in position by said holding bolt.

4. A volume control of the adjustable resistance type having an automatic tone compensating tap on the resistance element and an insulating base, comprising an extension on the edge of the resistance element, said resistance element having a complete coating of conducting film on its outer surface and a partial coating on its under surface contiguous of its upper surface coating, a tap-off terminal, a rivet through the insulating base electrically ccnnect ing the tap-oil terminal and the under side of the resistance element, and a second rivet electrically connecting the resistance-element extension and the tap-oil terminal.

5. An adjustable resistance device comprising a resistance element, and means for selectively electrically engaging said resistance element along its length, said means comprising a cupshaped member and a disk-like member interfitting with and complementary to said cupa resistance element, a pressure arm, a cupshaped member attached to one end of said pressure arm by a rivet passing through said pressure arm and centrally through said cup-shaped member, said rivet having its ends upset to hold the cup-shaped member and the pressure arm together, the upset end of the rivet with n said cup-shaped member being convex, a disk contact member complementary to said cup-shaped memher and having one surface abutting said convex rivet head, said disk contact member adapted to be moved in selective electrical engagement with the resistance element and along the length of the resistance element.

'7. In an adjustable resistance device, a resistance element, a cup-shaped member, a disk-like member inter-fitting with and complementary to said cup-shaped member, both of said members being adapted to be moved over said resistance element, and a centrally projecting convex member interposed between the cup-shaped member and said disklike member whereby there may be relative motion of one member with respect to the other member about the central projecting member as the pivot;

8. In an adjustable resistance device; a resistance element; a cup-shaped member; a disk-l ke member interfitting with and complementary to said cup-shaped member; said disk-like member in engagement with, and adapted to move over and adjust itself in selective electrical connection with the resistance element along the length of the resistance element, and a centrally projecting convex member interposed between the cup-shaped member and said disk-like member whereby there may be relative motion of one member with respect to the other member about the central projecting member as the pivot.

9. In an adjustable resistance device, a resist- I'll ance element, a cup-shaped member having a list base, a disk-like member interfltting with and complementary to said cup-shaped member whereby the cup-shaped member may seat itself properly on the resistance element, said flat base of said cup-shaped member beingin engagement with and adapted to be moved over said resistance element, and a centrally projecting convex member interposed between the cup-shaped member and said disk-like member whereby there may be relative motion of one member with respect to the other member about the central project'ng member as the pivot.

10. A volume control of the adjustable resistance type comprising a substantially flat base; an arcuate film-type of resistance element adapted to lie flat on one face of said base, said resistance element of substantially a constant width; a tone compensating extension radially extending from and integrally formed with an edge of said resistance element; a terminal mounted upon the opposite face of said base; a rivet of electrical conducting material passing through said extension, through said base. and through said termias]; means on the ends of said rivet whereby the extension, the base, and the terminal will be mechanically held together, and said resistance element and said terminal will be electrically joined together; a rotatable shaft, and a contact member engaging said resistance element and movable in selective engagement with said resistance element upon movement of said rotatable shaft, said contact member being movable along side of said extension, said tone compensating extension being located intermediate the ends of the resistance element. a

11. A volume control of the adjustable resistance type having an automatic tone compensating tap on the resistance element, said volume control comprising a base having a flat portion; an arcuate film type of resistance element adapted to lie flat on said base, said resistance element of substantially a constant width; an electrically conducting illm coated tone compensating extension radially extending from and integrally formed with an edge of said resistance element; a terminal; a rivet of electrical conducting material passing through said extension; through said base, and through said terminal; means on the ends of said rivet whereby the extension. the base, and the terminal will be mechanically held together, and said resistance element and said terminal will be electrically joined together; a rotatable shaft: and a contact member engaging said resistance element'and movable in selective engagement with said resistance element upon movement of said rotatable shaft; said contact member being movable upon said resistance element alongside of said extension, said tone compensating extension being located intermediate the ends of the resistance element.

12. A volume control of the adjustable resistance type, a base, a carbonaceous film type of resistance element for said base, a tone compensating tap integrally formed with said resistance element a conductive film coating on said tap, means of an electrical conducting type connecting the carbonaceous film on the main body of the resistance element with the coating on the tap, and a contact element adapted to selectively engage a portion of the resistance element andbeingadaptedtopasssaldtapwhileengaging said carbonaceous him. said tone compensating tap located intermediate the ends of the resistance element.

13. A rheostat comprising a resistance element having a base of insulating material, an electrical conducting film on the surface of said base, an extension integrally formed with said insulatlng material and lying in the same plane as the major portion of the insulating base. an electrical film type of coating on the surface of said extension and joined to said electrical conducting film. said extension being located intermediate the ends of the resistance element, and an electrical conducting shoe adapted to selectively engage a portion of the conducting dim and being adapted to pass beside said extension while engaging said film.

14. In a rheostat a film-like carbonaceous resistance element: a cylindrical electrical conducting contact shoe having its curved bounding surwill be pushed along the surface of said resistance element, said am extending across the central portion of said insulating member; a flexible pressure member having its free end engage the upper portion of said surface of said contact member whereby the contact member is pressed into engagement with the resistance element; an electrical conducting member mounted on the lower surface of said insulating member; a holding electrical conducting member passing through the insulated member and an end of the contact shoe arm and the pressure member and the first-mentioned conductor member, whereby all of said members will be held together, said holding member being located substantially diametrically opposite the contact shoe.

15. An adjustable resistance device comprising a resistance element of the conducting film type, a film of conducting material of arcuate formation and of substantially constant width for the major portion of its linear length, a tap of filmllke conducting material integrally united with the main film of the resistance element, said tap located between the ends of the resistance element, and an electrical contact shoe selectively engaging a portion of the resistance element and being adapted to pass said tap while engaging sa'd film of conducting material.

16. A rheostat comprising an arcuate resistance element having a base and a carbonaceous coat: ing thereon, a projection extending from and integrally formed with said resistance element, said projection having a conducting film thereon, and said coating and said film being electrically joined together, an electric terminal, means whereby said terminal may be connected to said film, and a contact shoe adapted to selectively CERTIFICATE OF CORRECTION.

Patent No. 2,11 .1,908. December 27, 1958.

' CLARENCE J. HATHORN.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 8, second column, lines 51 and 52, claim 11+, strike out the words and semicolon "said arm extending across the central portion of said insulating member;"; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this "('th day of March, A. D. 1939.

Henry Van Arsdale.

(Seal) Acting Commissioner of Patents.

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