US2863030A

US2863030A - Variable resistors and potentiometers

Info

Publication number: US2863030A
Application number: US655456A
Authority: US
Inventors: Page Victor Arthur William
Original assignee: Plessey Co Ltd
Current assignee: Plessey Co Ltd
Priority date: 1956-02-16
Filing date: 1957-02-04
Publication date: 1958-12-02
Anticipated expiration: 1975-12-02
Also published as: GB842607A; DE1097532B; FR1166233A

Description

Dec. 2, 1958 v. A. w. PAGE 2,863,030

VARIABLE RESISTORS AND POTENTIOMETERS Filed Feb. 4, 1957 2 Sheets-Sheet l 5 I 4 I Fla.

Dec. 2, 1958 v. A. w. PAGE 2,863,030

VARIABLE RESISTORS AND POTENTIOMETERS Filed Feb. 4, 1957 2 SheetsSheet 2 United States Patent VARIABLE RESISTORS AND POTENTIOMETERS Victor Arthur William Page, Rockley, Marlborough, England, assignor to The Plessey Company Limited, Ilford, England, a British company Application February 4, 1957, Serial No. 655,456

Claims priority, application Great Britain February 16, 1956 Claims. (Cl. 20155) This invention relates to variable resistors and potentiometers and provides an improved construction in which the electrically operative elements are combined in a self-contained sub-assembly ready for the insertion of an actuating spindle.

According to one aspect of the invention the resistor or potentiometer comprises a base or stator element, in one face of which a circular or part-circular resistance track and a circular or part-circular contact ring or ring segment are arranged substantially concentrically around a central guide bore extending through the base. A movable contact element, adapted to connect selected point of the resistance track with the contact ring or segment, is rotatable by a bush member extending through and journalled in the guide bore of the base, and is secured against axial movement out of said bore by a self-locking clip device or other locking member at the back of the base, and preloaded resilient means acting axially between the face of the resistance track and contact ring or segment and the bush member are provided for maintaining the bush member in the axial position determined by the locking member. These resilient means maintain a predetermined contact pressure between the contact element and the resistance track and contact ring or segment. The bush member has an axial bore for the insertion of an operating shaft or other operating member and means for coupling the hush with said shaft, or the like, for common rotation. These coupling means are preferably so constructed that they freely allow axial movement of the spindle relative to the bush.

It is a particular advantage of this construction that the contact pressure is determined before the operating spindle is inserted and will not be affected by the assembly with the spindle thus eliminating a hitherto unavoidable factor of uncertainty in the electrical characteristics. Inaccuracy in the length of the actuating spindle will therefore not effect the electrical characteristics of a resistor or potentiometer according to the invention.

The accompanying drawings illustrate the invention Fig. 1 is an elevation, partly in section, of the subassembly containing the electrically operative elements,

Fig. 2 is an underneath plan view,

Fig. 3 is a sectional elevation showing a complete resistor or potentiometer,

Fig. 4 similarly shows two resistors or potentiometers actuated by a common shaft for ganged control,

Fig. 5 shows two resistors or potentiometers arranged similarly for individual adjustment by coaxial shafts, and

Fig. 6 shows a simplified complete resistor or potentiometer suitable for use in preset circuits.

Referring now first to Figs. 1 to 3, a base or stator element 1 made of insulating material, for example of a phenol-formaldehyde plastic, carries on one of its faces a part-annular resistance track 2 and, concentric therewith a contact ring 3, both accommodated in suitable groove-like recesses. A movable contact element for co-operation with the track 2 and contact ring 3 is constituted by a resilient contact carrier 4, which is equipped with contact brushes 5 and 6 respectively engaging the tracks 2 and 3. A hub member or bush 7 extending through and guided in a central cylindrical aperture 8 of the base 1 is provided with a flange 9 which faces the tracks 2 and 3 in spaced relation. The contact carrier 4'is located relative to the bush 7, so as to maintain the brushes 5 and 6 in respective engagement with the tracks 2 and 3, by an eccentric portion 19 of the bush and by being formed at diametrically opposite .points with upwardly (with reference to Fig. 1) decesses 11 of the flange 9, thus coupling the contact carrier with the hub for common rotation; the curved back of the contact carrier is supported against the flange 9, so that its resilience in conjunction with the spacing between this flange and the base 1 determines the contact pressure by which the brushes 5 and 6 are applied to the tracks 2 and 3. This spacing is determined by a stop in the form of washer 12 of resilient metal provided with internally projecting tongues 13 which are deflected or, since preferably a washer having pre-bent teeth is employed, further deflected as the washer is forced onto the bush 7. This sliding-on movement is limited by the abutment of the end face 20 of eccentric bush portion 19 against the face of the base 1 or contact ring 3. A plain metal washer 14 is preferably inter posed between the washer 12 and the back of the base 1 An axially projecting lug 15 suitable for the operation of an on/off switch and a radially projecting stop lug 16 may be provided at the back of the flange 9 as shown.

The base 1 is provided with electric terminal strips 21 and 22 respectively connected to the two ends of the resistance track 2 and a further terminal strip 23 connected to contact track 3.

The bore 17 of the bush 7 is preferably a through bore as shown in Fig. 3, provided with internally projecting axially extending coupling ribs, for example in form of serrations 18 extending from the back surface of the flange 9 through about half the length of the bush 7.

The sub-assembly just described comprises all those elements which affect the electrical characteristics of a complete variable resistor or potentiometer. It has the advantage over known devices that it can be combined with an actuating shaft in such manner that the application pressure of the contact members 5, 6 is not affected by movement of the shaft relative to the base, and that therefore considerable tolerances in the length of the shaft are permissible.

Fig. 3 shows a complete resistor suitable for singlehole fixing in a radio chassis, incorporating this subassembly. A shaft 24, which has a fluted end portion 25 slidably fitting into the serrated part 18 of the bore 17, is journalled in the mounting bush 26 of a housing base 27, two spring rings 28 being provided for locating it axially. The circular rear portion 29 of the base 1 fits into a recessed step 30 of the housing base 27, and a housing cap 31, having two clip arms 32 extending longitudinally and accommodated in suitable notches 33 (Fig. 2) in the circumference of base 1 and housing base 27, complete the assembly.

Fig. 4 shows a similar arrangement, in which however two sub-assemblies, each as shown in Figs. 1 and 2, are mounted on a common shaft 24a. As shown, each unit may be enclosed in a separate housing, the cap 31a of the housing for the inner unit having a hole through which the shaft can pass, and carrying a light housing base 27a for the outer unit. The shaft 24:; has a fluted portion 25a which extends from the serrated part of the bush of the inner unit through the Whole length of the bush 7 of the outer unit.

In the embodiment of Fig; 5 the two units are similarly arranged and housed,.but the shaft 24b of the inner unit is bored longitudinally to accommodate rotatably a reduced-diameter'spindle part 124a of a second shaft 112 for the actuation of the outer unit.

Fig. 6 illustrates a very simple embodiment, it particularly intended for use as. a pre-set resistor o k I tentiometer. The shaft is constituted by a plug integral with a moulded-plastic setting knob which extends through a hole in the housing cap 310. if the knob is made-of reasonably soft plastic, for example polythene, and the bush member of hard plastic, for example a phenolic-resin composition, it is not necessary for the plug 34 to be'fluted in manufacture, since the serrations 18 will bite into the surface of the plug when the same is forced into the bore of the bush. The knob 35 may be provided With a flange or car 36 which is held captive between the housing cap 31c and the flange Z of the bush '7. The housing cap 31c has screw-threaded bosses 37, by which it can be attached to the back of a panel or like wall.

What is claimed is:

1. A variable resistor device, comprising a base member of insulating material having two parallel surfaces, a guide bore extending therethrough to interconnect said surfaces, and a resistor track and a contact track both arranged at one of' said surfaces, substantially concentrically with said bore, a bush of insulating material extending through said here and having an end projecting from the surface containing said tracks, said end being formed with a circumferential shoulder in contact with said surface and with an abutment flange spaced from said surface and extending radially yond said shoulder, a movable contact element rotatably guided on said bush between said shoulder and said abutment flange and having two contact points and a support point, said contact points respectively resting on said contact track and on said resistance track, and said support point resting against said abutment flange and being resiliently movable axially of the bush towards and away from said contact points, and a thrust collar co-operating with the other said surface of the base member and having resilient locking legs extending from said collar into resilient self-locking engagement with said bush outside the base member adjacent said other surface thereof.

2. A device as claimed in claims 1, wherein a metal washer is interposed between the thrust collar and the base member.

3. A device as claimed in claim 1, further comprising a housing member, located on the circumference of the base member.

4. A device as claimed in claim 3, wherein said housing member includes an inwardly projecting stop and the abutment flange of the insulating bush is provided with a projection co-operating with said stop for limiting the rotation of said bush in the guide bore.

5. A device as claimed in claim 1, further comprising a bearing member having locating means co-operating with the circumference of the base member for ensuring alignment of saidbearing member with the bore of the base member.

References (Jilted in the file of this patent UNITED STATES PATENTS 1,356,634 Koch Oct. 26, 1920 1,624,038 Carter Apr. 12, 1927 1,773,609 Yoshiyasu Aug. 19, 1930 2,145,953 Schellenger Feb. 7, 1939 2,401,037 Arvin May 28, 1946