US2877328A - Variable resistors - Google Patents

Description

March 10, 1959 M. BOURNS VARIABLE RESISTORS Filed July 5, 1955 3 Sheets-Sheet l 7 March 10, 1959 M. E. BOURNS 2,877,328

VARIABLE RESISTORS Filed July 5, 1955 3 Sheets-Sheet 2 INVENTOR.

22 ZZZ M1 March 1959 M. E. BOURNS 2,877,328

VARIABLE RESISTORS Filed July 5, 1955 5 Sheets-Sheet 3 IN VEN TOR.

2,877,328 Ice Patented Mar. 10, 1959 VARIABLE RESISTORS Marlan E. Bourns, Riverside, Calif. Application July 5, 1955, Serial No. 519,846 Claims. (Cl. 201-55) The present invention relates to new and improved variable resistors.

During recent years there has been a constant demand for variable resistors which are exceedingly light and small, and which are very rugged in construction so as to be capable of withstanding a great deal of physical abuse. An object of this invention is to provide new and improved variable resistors, and in particular potentiometers, having these characteristics.

A more detailed object of the invention is, however, to provide a new class of variable resistors which can be easily assembled by automatic machines and techniques with a minimum of labor. Those skilled in the art will realize that this is exceedingly important inasmuch as electrical devices such as resistors are generally very small devices having a large number of individual parts. Formerly, such instruments were completely assembled by hand. Obviously, this is a very expensive and time-consuming procedure.

Another objective of this disclosure is to teach the construction of variable resistors which can be satisfactorily utilized as component parts of larger assemblies with a minimum of difiiculty. In particular it is an object of this invention to provide variable resistors such as potentiometers which can be readily mounted within a wire cage type of construction by machine. Those skilled in the art will realize that such a wire cage type of construction is the type of construction covered by the so-called Tinker Toy project. For this Tinker Toy type of assembly, twelve wires are arranged parallel to one another in a square configuration with three of the wires being disposed on each side of the square. Various electrical elements such as, for example, capacitors, fixed resistors and the like are positioned within this cage parallel to one another at right angles to the individual wires.

The features of the instant invention will be best more fully explained with reference to the accompanying drawings, in which:

Fig. 1 is a side view of a vention;

Fig. 2 is a cross sectional view taken at line 22 of Fig. 1;

Fig. 3 is a cross sectional view taken at line 3--3 of potentiometer of the in- .Fig. 1;

taken at line 7-7 of Fig. 9 is a cross sectional view taken at line 9-9 of Fig. 8;

Fig. 10 is a side view similar to Fig. l of a second modified potentiometer of the invention;

Fig. 11 is a cross sectional view taken at line 11-41 of Fig. 10;

Fig. 12 is a cross sectional view taken at line 12-12 of Fig. 10; and

Fig. 13 is a cross sectional view taken at line 13-43 of Fig. 11.

It is to be understood that the accompanying drawings are made so as to clearly illustrate the essential features of the invention; hence, in certain cases they do notrepresent commercial units drawn to scale. It is possible to modify the various dimensions of the parts shown to produce any number of different constructions embodying the essential features of they present invention. Where convenient for purposes of explanation and illustration like numerals have been used to designate like parts.

These essential features are set forth in detail in the appended claims. If desired, however, the invention may be explained by summarizing it as being concerned with electrical instruments such as potentiometers or variable resistors which include: a non-conductive base having an upper surface; a non-conductive top rotatably mounted upon said base so as to be spaced from the base, said top having a lower surface positioned parallel to said upper surface; an arcuate resistance strip or element mounted upon said lower surface about the center of rotation of said top; a conductive strip or element electrically connected to said resistance strip, said conductive strip being mounted on said lower surface of said top, and including an arcuate portion formed concentrically with said resistance strip; terminal means located on the upper surface of said base; and resilient contact means secured to said terminal means so as to engage said resistance strip and said arcuate portion of said conductive strip.

The actual details of the invention as well as the meaning of the various terms utilized in the above brief summary are best explained by direct reference to the accompanying drawings. In Figs. 1 through 4 of the drawings there is shown a potentiometer 10 having a non-conductive base 12 formed of ceramic or other material. This base 12 is preferably in the shape of a small square wafer having formed along the sides 14 thereof a plurality of notches 16 which are designed to hold individual wires such as are employed in the aforenoted Tinker Toy type of construction. Within the center of the base 12 there is formed an opening 18 through which there projects a hollow rivet 20 in such a manner that this rivet extends beyond an upper surface 22 of the base 12 in order to hold upon this base a non-conductive top 24. This top is preferably of a circular form and is of a smaller diameter than the length of the sides 14 of the base 12, so as to fit entirely within the confines of the edges of this base.

Around the top 24 there is formed a spacing ring 26 having a knurled outer surface 28. This knurled outer surface is arranged so that it may be engaged by an appropriate tool or the hand of an individual in order to rotate the top 24 about the rivet 20. Thus, with the construction shown the rivet 20 serves essentially as a pivot means serving to mount the top 24 with respect to the base 12. The top 24 and the spacing ring 26 may be formed out of any appropriate non-conductive material such as, for example, a phenolic composition. They may be attached to one another by any convenient means such as, for example, an adhesive or the like.

The top 24 includes a lower surface 30 which is positioned parallel to the upper surface 22 of the base 12 so as to be spaced above this upper surface. Formed upon the lower surface is an arcuate resistance strip 32 having ends 34 and 36 located soas to be centered aboutthe n'vet 20. Also upon the lower surface 30 there is posi- I terminal portion 40 3 tinned a first electrically conductive strip 38 having a overlying the end 34 of the resistance strip. This first electrically conductive strip also includes an arcuate portion 35 concentrically located within the resistance strip 32. A second electrically conductive strip 44 is also mounted upon the lower surface 30 so that a terminal portion of 46 of it overlies the end 36 of the resistance strip 32; this second electrieally conductive strip also includes a second arcuate portion 48 located concentrically to the resistance strip a 32 and the arcuate portion 42. The resistance strip 32 and the electrically conductive strips 38 and 44 are preferably formed out of known materials, such as inks loaded with resistance particles and silver inks, by conventional printed circuit techniques. It is hardly considered necessary to describe in detail such procedures and materials inasmuch as they are well known to the art at the present time.

Terminal means 50, 52, and 54 formed out of a conductive printed circuit compositions such as silver inks are located upon the upper surface 22 of the base 12 so as to project to the sides 14 of this base beyond the spacing ring 26. Attached to these terminals 50, 52, and 54 are small resilient metal contacts 56, 58, and 60, the construction of which are best seen in Fig. of the drawings. These contacts are formed identically so as to each include a bottom 62 adapted to be attached by solder or the like to one of the terminals 50, 52, or 54, a resilient center arm 64 and an upper end section 66. The upper end sections 66 of the contacts 56, 58 and 60 are designed to bear against resistance strip 32 and the first and second electrically conductive strips 38 and 44, so that as the top 24 is turned about the rivet 20, these contacts engage different portions of resilient strip 32 and the arcuate portions 42 and 48. From a detailed consideration of the drawings, it will be realized that with this construction the resistance between the contacts 56, 58, and 60 and the corresponding terminals will be varied as the top 24 is turned.

In Figs. 6, 7, 8 and 9 of the drawings, a modified potentiometer 68 of the invention is shown which includes a base 12' of the category previously described. For convenience of explanation, the individual parts of this base will not be renumerated in detail. The individual parts of this base and the parts of various other elements which are the same as in the potentiometer 18 are not enumerated in this portion of the description. Such parts are merely designated by the same numerals as used in the preceding discussion in the same manner in which the base 12' is designated.

The potentiometer 68 differs from the potentiometer in that the terminals 50', 52' and 54' employed are of slightly different shape than the terminals previously described. However, if desired, these terminals may be of substantially the same shape as those indicated in Fig. 2 of the drawings. Conversely, the terminals shown in Fig. 2 of the drawings may be of substantially the same shape as the terminals shown in Fig. 7.

Attached to each of these terminals 50', 52, and 54 are contact elements 56, 58', and 60 as previously described. The contact 56 is designed to electrically connect an arcuate resistance strip 32' positioned about the rivet to the appropriate terminal 50'.

Upon the lower surface of the top 24 only one electrically conductive strip 70 similar to the strip 38, is employed. This electrically conductive strip includes a terminal portion 72 overlying the center of the resistance strip 32 so as to engage this strip. It also includes an arcuate portion 74 positioned concentrically with the resistance strip 32' about the rivet 20. The contact 58 previously described is also designed to engage the arcuate resister strip 32'. With this construction the two contacts 56' and 58' are intended to engage the resistance strip 32 on opposite sides of the terminal portion 72. The third contact 60' is so located as to normally engage the arcuate portion 74 of the electrically conductive strip 70. It is readily seen from a consideration of the foregoing description of the modified potentiometer 68 that the resistance between the terminal portion 72 or the contact 60 and either of the contacts 56' and 58' varies as the top 24' is rotated about the rivet 20' during the use of this potentiometer.

In Figs. 10 through 13 of the drawings a second modified potentiometer of the invention is shown which differs from either potentiometer 1 and/or the potentiometer 68 in that what in efiect is a double resistance strip is utilized so that the entire potentiometer may be turned thereon an arc of slightly less than 360'. It will be noted by those skilled in the art that various stop means (not shown) may obviously be employed so as to limit the amount the top 24 may be turned in order to prevent the contact elements shown in all of the potentiometers indicated from moving off of the strips they respectively engage.

Since practically all of the parts shown in the potentiometer 80 are identical with the various parts of the potentiometers 10 and 68, like numerals are used to designate the same parts as previously indicated. Such numerals are, in the Figs. 10 through 13, designated by a double prime symbol for convenience.

The potentiometer 8G differs primarily from the potentiometers 18 and 68 in that two arcuate resistance strips 82 and 84 are employed together with a center electrically conductive strip 70". This center strip includes a terminal portion 72 which overlies the resistance strip 84 at approximately the same point where this resistance strip is joined through a small electrically conductive segment 86 to the resistance strip 82. With the construction shown the top 24" may be turned so as to place the contact elements 56", 58" and 60" in engagement with the resistance strips 82, 84 and the conductive strip 76 respectively.

In order that the potentiometer 88 may operate satisfactorily, it is preferable to form both the resistance strip 82 and the resistance strip 84 in such a manner that the change in resistance in each of these strips along an arc of the same number of degrees is the same. This may be accomplished in several ways. One procedure is to use difierent resistance inks for the two different resistance strips. Another procedure is to vary their widths as shown so that the width of the resistance strip 84 is less than the resistance strip 82. In other words, when the two arcuate resistance strips in the potentiomcter 80 are manufactured of a material having the same resistivity the effective width of this material or cross sectional area of this material is altered so that the cross sectional area or efiective width of the inner strip is less than that of the outer strip. If desired, the strips may be described as having the same resistance per unit angle.

in order to utilize the potentiometers 16, 68 and 80 for the purposes intended, it is necessary to attach various wires or other like means to the terminals. With the constructions shown part of the upper surfaces of the various bases are always exposed so that wires or the like may be readily soldered to these terminals. If it is desired to utilize either the potentiometers illustrated as variable resistors, it is only necessary to connect two different wires to these units in the obvious manner.

Those skilled in the art will realize from the foregoing that the potentiometers shown are very efiicient units for the purposes intended and that these potentiometers may be readily assembled with a minimum of difiiculty by a machine or by hand. They will further realize that these potentiometers are very light weight, reliable units, and that they employ a different principle of op eration from what has been seen in the prior related units. Because of this, this present invention is to be afiorded wide latitude and is to be considered as being base; resilient electrical contact means secured to said limited only by the appended claims. terminal means so as to project therefrom and engage I claim: said resistance element and said arcuate portion of said 1. A new and improved potentiometer which comelectrically conductive element as said top is rotated prises: a non-conductive base having an upper surface; 5 with respect to said base. a non-conductive top rotatably mounted on said base, 3. An electrical instrument as defined in claim 2 said top being spaced from said base, and having a lower wherein: said resistance element is arcuate in shape; and surface spaced from said base; an arcuate resistance wherein said conductive element comprises a first arcuate element mounted on said lower surface about the center strip and a second arcuate strip, said arcuate strips of of rotation of said top; a first conductive element m0untsaid conductive element being electrically connected to ed on said lower surface so as to be electrically conthe ends of said resistance strip. nected to an end of said resistance element, said first 4. A variable resistor which comprises: a base; a top; conductive element including an arcuate portion formed a hollow rivet securing said top to said base, so that concentrically with said arcuate resistance element; a said top can be rotated with respect to said base; a resecond conductive element mounted on said lower sursistance element located on said top adjacent to said face so as to be electrically connected to the other end base; an electrically conductive element located on said of said resistance element, said second conductive eletop adjacent to said base, said conductive element being ment including an arcuate portion formed concentrically connected to said resistance element; contact means on with said arcuate resistance element; terminal means said base engaging said resistance element and said elecloeated on said upper surface of said non-conductive base; trically conductive element; and terminal means conelectrically conductive resilient contact means attached nected to said contact means.

to said terminal means so as to engage said resistance 5. An electrical instrument of the class described which element and said first arcuate portions of said first and comprises: a square base formed of a non-conductive second conductive elements as said top is rotated with material, said base having a plurality of notches formed respect to said base. 2 in the sides thereof to engage parallel mounting rods; 2. A potentiometer which comprises: a. square non circular top formed of a non-conductive material, said conductive base having a fiat upper surface; means detop being of smaller dimension than the length of a side fining a centrally located hole within said base; pivot of said square base; a hollow rivet securing said top to means located within the said hole so as to project from said base, so that said top can be rotated with respect said base past said upper surface; a non-conductive cir- 3 to said base, said hollow rivet extending all the way cular top of smaller diameter than the length of a side through said base and said top; a resistance element of said square base having a centrally formed aperture located on said top adjacent to said base; an electrically located therein, positioned with said pivot means proconductive element located on said top adjacent to said jecting through said aperture, said non-conductive top base, said conductive element being connected to said being spaced from said base and including a flat lower 3 resistance element; contact means on said base engaging surface located parallel to said upper surface; means said resistance element and said electrically conductive formed on said top whereby said top may be engaged element; and terminal means connected to said contact and rotated about said pivot means; an arcuate resistance means. element located on said lower surface so as to have its center coincident with the center of said pivot means; References Cited in the file of this patent an electrically conductive element located on said lower surface, said electrically conductive element being elec- UNITED STATES PATENTS trically connected with said resistance element and in- ,6 3,009 Warner Nov. 27, 1928 eluding an arcuate portion formed concentrically with 1,241 Roscntretcr Oct. 12, 1948 said arcuate resistance element; electrically conductive ,682 Tellkamp July 11, 1950 terminal means located on said upper surface of said 7 44 R n eta! 1951

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