US2999993A

US2999993A - Potentiometer

Info

Publication number: US2999993A
Application number: US778522A
Authority: US
Inventors: Walter A Sherwood
Original assignee: Chandler Evans Inc
Current assignee: Chandler Evans Inc
Priority date: 1958-12-05
Filing date: 1958-12-05
Publication date: 1961-09-12
Anticipated expiration: 1978-09-12

Description

Sept. 12, 1961 w. A. SHERWOOD POTENTIOMETER Filed Dec. 5, 1958 2 Sheets-Sheet l INVENTOR h ATTORNEY Sept. 12, 1961 W. A. SHERWOOD POTENTIOMETER 2 Sheets-:Sheet 2 Filed Dec. 5, 1958 INVENTOR W6? 0. M

MTTORNEYS United States Patent 2,999,993 POTENTIOIVIETER Walter A. Sherwood, Hempstead, N.Y., assignor, by mesne assignments, to Chandler Evans Corporation, West Hartford, Conn., a corporation of Delaware Filed Dec. 5, 1958, Ser. No. 778,522 8 Claims. (Cl. 338-176) This invention relates to a potentiometer and method of making same.

It is an object of the invention to provide a potentiometer of great durability in which the resistance element is isolated from the contact region so that wear resulting from movement across said region of a slider or other movable contact will have little or no effect upon the resistance value, even when the contact pressure is substantial.

Another object is to provide a multiplicity of connecting elements between the resistance element and the contact region, all being continually in electric and thermal communication with the resistance element and thus aiding in the dissipation of heat therefrom.

A further object is to provide a composite resistance element in which the components may have, for example, opposite temperature coefiicients, and may be so disposed as to constitute a resistance element having a zero temperature coeflicient over a given range.

A still further object is to provide a potentiometer in which the resistance element may be profiled or otherwise shaped and correlated with the shape or path of movement of the adjustable contact to obtain an output representing almost any desired function, linear or otherwise.

Another object is to provide a method of making potentiometers of the character described in which only very simple apparatus is used effectively to make simultaneously a plurality of potentiometer units having identical or differing sizes or shapes, as desired.

A further object is to provide certain improvements in the form, construction, arrangement and materials of the potentiometers, and in the steps of the method, whereby the above named and other objects may effectively be attained.

Practical embodiments of the invention are represented in the accompanying drawings, wherein:

FIG. 1 represents a perspective view of a potentiometer;

FIG.- 2 represents a detail section on the line II,II of FIG. 1, on an enlarged scale, parts being broken away;

FIG. 3 represents a more or less diagrammatic elevation of apparatus suitable for carrying out themethod,

parts being in section;

FIG. 4 represents a perspective view of the product of the apparatus of FIG. 3, on an enlarged scale and with parts broken away, said product being a plurality of potentiometers in an intermediate stage of manufacture;

FIG. 5 represents in section a detail of an alternative form of potentiometer construction;

ice

and those adjoining it (4, 5) being covered with a resinous insulating coating 6. The laminated body may conveniently be provided also with end blocks 7, 8, and a suitable binding post 9 or other desired terminal is normally connected to the resistance material 3 at each end thereof, either directly on the end blocks or through conductive clips or other mounting means. The face 10 of the laminated body is left wholly or partially exposed for the passage thereover of a slider or other movable contact (not shown) of any well-known or approved type.

The performance characteristics of such a potentiometer depend on the proportions of the several elements and the materials from which they are made. The laminated body of FIGS. 1 and 2. may, for instance, have a vertical thickness of /8" to A, a length from end to end of 1" to 4" (depending on the range to be covered) and a width from A3 to an inch or two. Each foil conductor bar 1 may have a thickness of .00025 to .0005" and each lamina of insulation may have a thickness of .0005" to .001, all said dimensions being given as examples and not as limitations. The layer of resistance material 3 is in electrical contact with the entire bottom edge of each conductor bar 1, said material being graphite or lamp 'black for the higher resistances or a vacuum deposited film of metal such as Nichrome, nickel, silver or other appropriate material for lower resistances. By judicious selection of materials on the basis of their known coeflicients of resistance, potentiometers having resistances covering desired ranges within the over-all limits of about 10 ohms to about 50 megohms can be provided; a convenient and commonly required unit is that having a range from 50 to ohms. The resistance 3 may also be composite, i.e., a carbon film having a negative temperature coefficient combined with a metallic film having a positive temperature coeflicient, to produce a resistance having a zero temperature coefficient over a given range.

The foil conductor bars 1 can suitably be made from such materials as aluminum, silver, Phosphor bronze and nickel. The wear resistance of the softer materials can be improved by plating the upper edges (at the face 10 of the laminated body) with chromium.

The laminations of insulating material 2 are conveniently made of paper impregnated with an insulating adhesive, such as one of the epoxy compounds, or a Mylar (polyethylene 'terephthlate resin) film; such materials are suitable for use up to temperatures of 250 F. to 300 F. but for higher temperatures glass or other inorganic materials may be needed. Teflon (polytetrafluoroethylene) can withstand temperatures up to about 400 F. but has limited dielectric properties.

A simple form of apparatus for making potentiometers 'of the character described is shown, somewhat diagrammatically, in FIG. 3, Where supply rolls of foil 11 and paper 12 are supported on a stand 13 with their axes horizontal and parallel. The winder comprises a pair of pins 14, spaced apart, lying parallel with the supply roll axes and suitably supported so that at least one pin can be revolved around the winder axis 15. As shown in FIG. 3 the pins 14 are equidistant from the axis 15 and both revolve as indicated by the arrow 16.

The foil 11 runs straight from its supply roll to the winder, while the paper 12 passes into a tank 17 containing liquid adhesive, under a guide roll 18 (shown as being secured resiliently to the bottom of the tank by a spring 19), then up between wipers 20 and on upward to the winder. It will be evident that, as the winder pins 14 are revolved around the axis 15, the paper and foil looped around the pins at each end and having parallel straight sidesspaced apartby approximately the diameter of thepins. Whena sufiicient number of laminations have been built up, the elongated body is slipped off the pins and its sides pressed firmly together, as by clamping jaws 21 (FIG. 4), the pressure being continued until the adhesive has been" set, with or without the use of heat. The'laminated t body is then-removed from the clamps and is'cut transversely ('e.g., sawed-n lines-22 of FIG. 4) into blocks of approximately the desired size, the lamination-edge faces of which-may then be milled or ground to the proper exact'size. To'rem'ove burrs which might'produce short circuits between laminations the blocks may be dipped into a caustic soda'b'ath (for aluminum foil) then washed in nitric acid to'neutralize the soda and rinsed in water toremove the'acid and soda. By careful control of the timing, this treatment can remove all burrs and smeared edges andwill give a clean fresh surface on which the applied'resistance film will make excellent electrical contact with the foil edges. After the resistance layer 3 has been applied to a selected surface all surfaces except the working surface (normally opposite-the layer 3) are coated witha resinousinsulating compound 6.

If increased wear resistance and local hardness are required under any special circumstances the edges" of the foil at the working face may be plated with chromium or the like.

According to the alternative procedure illustrated in FIGS. 5, 6 and 7, a body of insulating material 22, such as glass, has fine parallel grooves 23- cut in one of its surfaces. A deposit of metal, such as silver, is then a'pplied'to the grooved surface, filling the grooves and covering the lands between the grooves at least to some extent, as shown at 24-inFIG. 5. The coated surface is then ground off (FIG. 6) to a depth suflicient'to remove the coating and some of the glass, leavinga'smoothly ground surface 25 (FIG. 7) traversed by bars of conducting material 26. A layer of resistance material 27 is applied to an adjacent surface of the insulating. body 22, making good electric contact with theexposed ends of the conductive bars 26. An insulating and protective covering (like the coating 6, BIG. 1) may then be applied to all surfaces except the ground working surface 25.

In each form shown and described above, the resistance material is completely enclosed by a protective coating, is never touched directly-by the slider or other movable contact, but is brought into electrical connection therewith through conductive strips touching the'resistancematerial at a multiplicity of' spaced points. The movable contact travels along a smooth working. surface; where it bears on the conductive strips one by one or, preferably, with a span of about- 2 to 2 /2 of such strips. The foil layers (FIGS. 1 and 2) or metal bars '(FIG: 7) are as numerous and closely spaced as possible so as to minimize the resistance difference'between adjacent layers orbars and thus-improvethe resolution. Thus, a one inch block may be made up of foil and paper layers each having a 'tliickness of .0005, or .001" per double layer,- so that there will be" 1000 doublelayers per inch. Such ablock can be made by operating the apparatus of FIG. 3 through 500 revolutions of the jig:.bearing;.the pins 14. Thealternative-form of FIG. 7 is particularly. suited to use with: heavier loads but'can'be' made to give ultra fine resolution bythe use of adiffraction grating (20,000 or more grooves per inch) for the-body 22.

By. varying. the size, shape and/orcompositionof the layers of resistance material 3 or 27 the responses maybe varied as desired with straight lineartravel of the: slider or other movable contact. Also, by varying the rate and/ or path of travel of the pick-upmeans other variations'in the response can be obtained. For example,-ifthe pick-up is caused to follow a circular path on the working .

surface

10 or 25 it will give a continuous sine wave output. If the pick-up traverse is an arc, the dispositionof the resistance material can be--such that equal-angles of traverse will give equal resistance increl ments. If the laminated unit of FIGS. 1 to 4 is mounted in, and held together by, a frame (particularly one capable of compressing the laminations) the adhesive may be omitted.

It will be understood that various changes may be made in the form, construction, arrangement and material of the several parts and in the steps of the method without departing from the'spirit and scope of the invention. v

What I'claim is:

l. A potentiometer comprising thin parallel strips of conductive material, insulating material so disposed as to separate said conductive strips, a body of continuously conductive material lying in contact with each of said strips, parts of said strips and said insulating. material spaced from the resistance material lying exposed in a common plane to constitute a smooth working-surface for the passage of suitable pick-up means, and a protective insulating coating covering the resistance material and'adjacent surfaces of the conductive strips and insulating material.

2. A potentiometer according to claim 1 in which the conductive material is metal foil and the insulatingmaterial is in the form of thin sheets laminated with the foil to form a multi-laminar block with the edges of the foil exposed on at least two faces thereof, the resistance material beingv applied to one of said faces in contact with each foil lamina and another of said faces constituting the working surface.

3. A potentiometer according. to claim 1 in which the insulating material separating the conductive material is paper impregnated with an insulating adhesive.

4. A potentiometer according to claim 1 in which the insulatingmaterial' separating the conductive material is a fusible inorganic vitreous material.

5. A potentiometer according to claim 1 in which the body of resistance material is a vacuum deposited film of metal.

6. A potentiometer comprising thin parallel strips of conductive material, insulating material so disposed as to separate said conductive strips, and a body of continuously conductive resistance material lying in contact with each of said strips, parts of said strips and said insulating material spaced from the resistance material lying exposed in a common plane to constitute a smooth working surface for passage of suitable pick-up. means, and a protective insulating coating coveringthe resistance material and adjacent surfaces of the conductive strips and insulating material, the strips of conductive material being'provided, at their parts along the path of travel of the pick-up means, with a conductive plating of higher wear-resistant material.

7. In a potentiometer of the character described, an elongated composite body of continuously conductive re sistance material constituted by a layer of material havingv a negativetemperatu're coefficient and a layer of material having a positive temperature coeflicient, so associated that'the effective temperature coefiicient of the composite body is, throughout a desired range, a function of the'sum of -the' coefficients of said layers.

8; A' potentiometer of the character described comprising, an elongated body of continuously conductive resistance material, a plurality of strips of conductive material each having one end in contact with the resistance material and the points of contact being'spaced along said elongated body, insulating-means separating said strips of conductive material, and a Working surface spaced from the resistance material and comprising exposed parts of the conductive strips separated bysaid insulating means, the body of resistance material being constituted by a layer of materialhaving a negative temperature coefficient and a layer of material having a positive temperature coefficient, so associated that the "effectivetemperature coeflicient' of-the composite body is, throughout a desired range, a function of the sum of the coeflicients of said layers.

References Cited in the file of this patent UNITED STATES PATENTS Re. 10,944 Weston ..1...... July 17, 1888 6 Rothschild Dec. 24, 1907 Ribbe Apr. 20, 1909 Ruger Sept. 16, 1913 Stoekle June 24, 1930 McCreary Nov. 21, 1933 Brown Aug. 14, 1956 [Moore et a1 Mar. 18, 1958