US2859314A

US2859314A - Variable resistors and potentiometers

Info

Publication number: US2859314A
Application number: US619076A
Authority: US
Inventors: Quint Bernard Henry John
Original assignee: Plessey Co Ltd
Current assignee: Plessey Co Ltd
Priority date: 1955-11-04
Filing date: 1956-10-29
Publication date: 1958-11-04
Anticipated expiration: 1975-11-04

Description

NOV. 4, 1958 J, QUlNT 2,859,314

VARIABLE RESISTORS AND POTENTIOMETERS Filed Oct. 29, 1956 2 Sheets-Sheet 1 Nov. 4, 1958 B. H. J. QUINT 2,859,314

VARIABLE RESISTORS AND POTENTIOMETERS Filed Oct. 29, 1956 2 Sheets-Sheet 2 mus/V702 5. m emf United States Patent VARIABLE RESISTORS AND POTENTIOMETERS Bernard Henry John Quint, Swindon, England, assignor to The Plessey Company Limited, Ilford, England, a British company Application October 29, 1956, Serial No. 619,076

Claims priority, application Great Britain November 4, 1955 8 Claims. (Cl. 201-55) This invention relates to variable resistors and potentiometers, hereinafter jointly referred to as variable resistor devices, of the kind in which a contact or wiper arm has two contact points adapted to wipe respectively along two tracks arranged concentrically about a spindle on which the arm is mounted. In a well-known construction of such resistor or potentiometer the arm comprises three parts. A stop or driving plate is secured on the spindle and is provided with an abutment co-operating with fixed stop means for limiting the rotation of the shaft, and in many cases a further abutment means for actuation of an on-and-off switch; an insulating plate is secured to the stop plate; and the arm is completed by a spring attached to the insulating plate. In many cases this spring is shaped with suitable contact parts for sliding co-operation with two concentric tracks, of which generally the inner one is a collector ring, whereas the outer one is the resistance track; in other cases the spring is provided with a carbon brush at one or both contact points.

The present invention has for an object to provide a simplified construction of the arm. According to the invention the wiper arm comprises a resilient plate of flexible material mounted on the spindle with its plane perpendicular to the spindle axis, a floating contact brush for co-operation with the two tracks, and a bridge member of insulating material which connects the brush member to, and transmits pressure thereto from, the resilient plate. Preferably the plate of spring steel or other resilient material is sub-divided by slots or apertures into a central part which is adapted to be secured on the control shaft and is extended to one side of the shaft to form an abutment for co-operation with fixed stop means to limit the movement of the arm, and an outer part which is located at the opposite side of the shaft and is connected with the remainder of the plate by narrow and therefore more readily flexible strips substantially parallel to the centre line of the arm. These flexible strips allow the outer part to yield resiliently longitudinally of the shaft. The sliding contacts proper are provided in suitable spatial relation on a floating brush, which is connected to the arm by a bridge member. The latter is secured to the outer part of the plate in such manner as to be resiliently applied by the resilient action of the plate on the bridge member to the two contact tracks and move around the shaft jointly with the spring plate While being pivotally movable relative thereto about an axis which extends tangentially to such rotary movement. The bridge member or pivot means includes an insulating body, by which the contact parts are electrically insulated from the shaft. An abutment for operating an on-and-oif switch may be formed on the spring plate by bending upwardly a tongue extending longitudinally of the arm, which is blanked out of the abutment part of the plate and bent up about its edge adjacent to the shaft. For greater rigidity the bent-up portion is preferable curved about an axis parallel to the shaft, and in order to compensate for the loss of rigidity of the abutment part of the plate due to the blanking out of the tongue, an embossed ridge may be provided on the plate along the two lateral edges of the cut-out portion, said ridge being continued if desired by a further ridge extending along one or both of the other edges of the cutout portion. The pivot axis about which the bridge member can moverelative to the spring plate, is preferably arranged nearer to the resistance track than to the collector ring, so that due to the different leverage, greater contact pressure is applied at the point of contact with the former than at the point of contact with the latter.

The pivotal connection between the bridge member and spring plate is preferably effected by a yoke plate of insulating material which is provided at one side with a tongue or tongues engaging a slot, or a line of slots or notches, provided in the spring plate, and the other end of which is adapted to engage grooves or notches in the brush member so as to pivot jointly with the latter in the said slot or slots or notches of the spring plate. The brush member may consist of a substantially rectangular block of carbon provided at one surface with two rounded humps serving as contact points, the block being provided on two opposite sides with parallel grooves for engagement by the sides of a U-shaped cut-out provided in the yoke member. According to a modification, the brush member may consist of sheet metal bent in U- shape to provide a bottom surface and two side walls extending longitudinally of the arm. The contact points are constituted by dimpling out parts of the bottom. The bent-up side walls are provided at their free edges opposite to the base with notches into which the yoke member is adapted to engage with the bottom edge of its U-shaped cut-out. The spring plate may be secured to the control shaft by being spun over a reduced diameter extension at one end thereof, and while hitherto it was generally necessary to use a high-grade material having high corrosion resistance and low electrical resistance, for example beryllium copper, nickel silver, or Phosphor bronze, the spring plate according to the present invention may be made from ordinary spring steel.

The accompanying drawing illustrates an embodiment of the invention;

Fig. l is a sectional elevation of the variable resistor,

Fig. 2 is an end elevation,

Fig. 3 is an exploded view showing one end of the spring plate with the yoke plate and brush, and

Fig. 4 is a perspective view showing another form of brush.

Referring now to the drawing, the potentiometer has a part-circular resistance track 6 and a contact ring 5 concentrically embedded in an insulating base 10.

Mounted rotatably in a bush 11 secured to the base is a spindle 4, and a blade 1 of spring steel or other resilient material is secured on the spindle 4 by means of a reduced-diameter end portion 4a of the spindle, which extends through a corresponding hole in the plate 1 and is spun over at its outer end so that the plate 1 will rotate jointly with the shaft.

A carbon brush 3 having two projecting contact humps c is secured to the plate 1 by a bridge or yoke 2 of insulating material in such manner as to be able to pivot about a fulcrum which is tangential to the arm movement about the spindle 4 to distribute the resilient pressure of the plate 1 to the two contact humps c. The two humps c are respectively in contact with the resistance track 6 and the contact ring 5. The potentiometer is enclosed in a housing 12, which in a well known manner carries an on-off switch 13 which is automatically operated by an abutment member g carried by the arm plate 1 when the latter moves to and from one end of its movement. The housing also carries end stop means 12a which co-operate with an abutment f an arm 1 for limiting thejrotary movement of the arm about the spindle axis.

Referring now more particularly to the construction of the wiper arm, the spring plate it is provided with a slot a into which a reduced-width centre part in at one end of the yoke member 2 engages, while the U- shaped cut-out 2b at the opposite end of the yoke member engages grooves b at the two Sides of the carbon brush 3.

A cut-out e separates the contact-carrying part lb of the spring plate 1 from an abutment-carrying part to. The latter is provided with the abutment f. A curved tongue g is cut out of an aperture 5 and bent up as shown to operate the on-and oif switch 13, and a reinforcing ridge h is pressed out around the aperture i. The yoke 2 engages the bridge member 3 at a point nearer to the hump c which cooperates with the resistance track 6 than to the other hump, so that greater contact pressure is applied on the resistance track 6 than on the contact ring 5.

Fig. 4 shows a metal brush 3a which may be used in place of the carbon brush 3 of Fig. 3, and which is formed of bent sheet metal. Notches a are provided for engagement by the yoke 2.

What I claim is:

1. A variable resistor including; a body member; a spindle rotatably mounted on said body member; a resilient plate carried by said spindle and constrained to rotate therewith, the plate extending transversely of the spindle; first and second concentric tracks supported by the body member, the tracks being concentrically arranged around the axis of rotation of said spindle; a floating brush member for wiping co-operation with each of the tracks, a member of insulating material which connects the brush member to, and which transmits pressure thereto from, the resilient plate; a stop member on the resilient plate limiting the range of rotation of the spindle; and an abutment on the resilient plate for operating an on and olf switch means.

2. A variable resistor including a body member; first and second tracks supported by the body member the tracks being concentric; a rotatable spindle located at the centre of the tracks; a resilient plate carried by the spindle and constrained to rotate therewith, the plate extending transversely of the spindle to overlie at least a part of said body that is intersected by said tracks, said plate being sub-divided by an aperture to provide a first part which is connected to the spindle, and which first part is extended to one side of the spindle to form a stop means for limiting the angular range of the rotary movement of the arm, and a second part, which is located at the opposite side of the spindle to the first part, which second part is connected with the remainder of the plate by narrow, and therefore more flexible, strips extending substantially parallel to the centre line of the plate; a floating brush member for wiping co-operation with each of the tracks; a member of electrically insulating material connecting the brush member to the second part of the plate, in such manner that the resiliency of the plate acts always to maintain the said wiping cooperation; and an abutment on the resilient plate for operating an on and off switch means.

3. A variable resistor including; a body member, a spindle rotatably mounted on said body member; a re silient plate carried by said spindle and constrained to rotate therewith, the plate extending transversely of the spindle; first and second concentric tracks supported by the body member, the tracks being concentrically arranged around the axis of rotation of said spindle; constact members for wiping co-operation With each of the tracks, a member of insulating material which floatingly connects the contact member to the resilient plate; and which transmits pressure to the contact member from the resilient plate; a stop member on the resilient plate limiting the amount of angular rotation of the spindle; and an abutment on the resilient plate for operating an on-off switch means, the abutment being formed by bending upwardly a tongue extending longitudinally of the resilient plate, which tongue is blanked out of the plate, at a location between the stop member and the spindle, and which is deformed about its edge adjacent to the shaft.

4. A variable resistor including; a body member; first and second concentric annular tracks supported by the body member; a rotatable spindle located at the centre of the tracks; a resilient plate carried by the spindle and constrained to rotate therewith, the plate extending transversely of the spindle to overlie at least a part of said body, that is intersected by said tracks, said plate being sub-divided by at least one aperture, into a first part which is connected to the spindle, and which is extended to one side of the spindle to form stop means for limiting the angular range of the rotary movement of the arm, and a second part, which is located at the opposite side of.the spindle to the first part which second part is connected with the remainder of the plate by narrow, and therefore more flexible, strips extending substantially parallel to the centre line of the plate; a floating brush contact member for wiping co-operation with each of the tracks; a member of electrically insulating material connecting the brush contact member to the second part of the plate, in such manner that the resiliency of the plate acts always to maintain the said wiping cooperation; and an abutment for operating an on and otf switch located, that abutment being located between the stop means and the spindle, and consisting of a tongue which has been produced by a blanking operation, and which is integrally connected with the plate at a location adjacent the spindle.

5. A variable resistor as claimed in claim 4, in which said tongue has a curved cross-section in a plane taken transverse to the axis of rotation of the spindle.

6. A variable resistor as claimed in claim 4, wherein a strengthening ridge is provided in the resilient plate, the ridge being located in said first part and adjacent two lateral edges of the aperture left by the blanking out of the tongue.

7. A variable resistor including; a body member; a first track of resistor material; a second track serving as a collecting track concentrically arranged relative to the first track; a rotatable spindle located at the centre of the tracks; .a resilient plate carried by the spindle and constrained to rotate therewith, the plate extending transversely of the-spindle to overlie at least a part of said body, that is intersected by said tracks, said plate being sub-divided by an aperture to provide a first part which is connected to the spindle, and which first part is extended to one side of the spindle to form stop means for limiting the angular range of the rotary movement of the arm and second part, which is located at the opposite side of the spindle to the first part which second part is connected with the remainder of the plate by narrow, and therefore more flexible, strips extending substantially parallel to the centre line of the plate; a contact member for wiping co-operation with the first and second tracks; a member of electrically insulating material floatingly connecting the brush contact member to the outer part of the plate, the fulcrum axis about which the brush contact member can pivot relative to the plate being nearer to the first track than to the second track whereby, owing to the different leverage, greater contact pressure is applied by the resilient plate at the point of contact of the brush contact member with the first track than with the second track; and an abutment on the resilient plate for operating an on and off switch means.

8. A variable resistor as claimed in claim 2, wherein the brush contact member is shaped as a substantially rectangular block having in two opposite side walls slots for engagement by the sides of the member of electrically insulating material.

References Cited in the file of this patent UNITED STATES PATENTS