US3329920A

US3329920A - Variable resistance potentiometer

Info

Publication number: US3329920A
Application number: US582327A
Authority: US
Inventors: Americo A Vercesi; Roy R Segerdahl
Original assignee: Fairchild Camera and Instrument Corp
Current assignee: Fairchild Semiconductor Corp
Priority date: 1966-09-27
Filing date: 1966-09-27
Publication date: 1967-07-04
Anticipated expiration: 1984-07-04

Description

y 1967 A. A. VERCESI ETAL. 3,329,920

VARIABIJE RESISTANCE POTENTIOMETER 2 Sheets-Sheet 1 Filed Sept. 2'7, 1966' INVENTOR.

AMER/C0 n. l/EACES/ R0) R- SEGERDfll/L W I l W, WQQMW,

ly 1967 A. A. VERCESI ETAL. 3,329,920

VARIABLE RESISTANCE POTENTIOMETBR Filed Sept. 27, 1966 2 Sheets-Sheet 2 ATTORNEY United States Patent 3,329,920 VARIABLE RESISTANCE POTENTIOMETER Americo A. Vercesi, Woodbury, and Roy R. Segerdahl,

Bellmore, N.Y., assignors t0 Fairchild Camera & In-

strumcnt Corporation, Syosset, N.Y., a corporation of New York Filed Sept. 27, 1966, Ser. No. 582,327 6 Claims. (Cl. 338--300) This application is a continuation-in-part of our copending application Ser. No. 504,459, filed Oct. 24, 1965, now Patent Number 3,299,389, issued Jan. 17, 1967, which, in turn, is a continuation of our application Ser. No. 264,130, filed Mar. 11, 1963, now abandoned.

This invention is concerned with potentiometers, and with methods and apparatus for making potentiometers. More particularly, it is concerned with variable resistance potentiometers and with methods and apparatus for making such potentiometers of the class in which a track of conductive plastic is deposited on a base of insulating material and a movable wiper or contact arm or brush rides on the surface of the track to provide a variable resistance or voltage.

It is known that variable resistance potentiometers may be prepared by depositing a track of conductive plastic material on an insulating base as a viscous solution or suspension in a volatile solvent. The conductive plastic material is usually a thermosetting resin such las a phenolformaldehyde or a urea-formaldehyde resin having finely divided carbon or other conductive material suspended therein. Other resins including vinyl and polyester resins, such as polystyrene or condensation products of dibasic acids and dibasic alcohols such as phthalic acid and ethylene glycol can be employed. After the track has been thus deposited, the resulting. product is compression molded with the application of heat to produce the final potentiometer.

In any case, such potentiometers are frequently of the crowned type in which the track projects upwardly from the base in crowned configuration, or of the projected track type in which a flat track also projects above the base. Each of these types is inherently disadvantageous in that the projecting portion adds to the space occupied by the instruments, and additionally the tracks are readily damaged because of their exposed positions. Both types of potentiometers also lend themselves to manufacturing difiiculties.

Heretofore, it has been the practice in the art to adjust the resistance characteristics of the potentiometer along its length by trimming the width of the conductive track. However, this procedure is not entirely satisfactory since the range of resistance characteristics which can be built into a potentiometer by trimming the width of the conductive track is limited, such as by the minimum width of the contact arm or brush, available space, etc.

In arranging a known potentiometer of the aforementioned class for operation, a wiper arm or contact forms a movable junction with the track, and various leads appropriate to the electrical circuit in which the potentiometer is to be employed are connected to the conductive track and the arm.

It will be appreciated by those persons skilled in the art that the resistance of a particular unit length of the track depends upon the resistivity of the conductive pl-ae tie and the width, depth and length of the track; i.e. the greater the volume, the smaller the resistance because as the volume increases, the number of paths for the flow of current through the plastic increases. Additionally, to reproduce a non-linear function, it is necessary for the resistance to vary in a non-linear manner throughout the length of the track. In other words, the volume of the track must vary from unit length to unit length. This can be achieved by varying either the depth or the width and it has been the practice to produce such variation in resistance by trimming the width of the track. It is known that for efiicient operation, the track should be at least as wide as the contacting portion of the wiper arm, and the minimum of the arm is set by various factors such as mechanical requirements, contact resistance, current carrying capacity, etc. Space and size considerations usually limit the maximum permissible width of the track.

To illustrate this by practical example, one may consider a known potentiometer as having a track of uniform depth and a maximum Width of 0.125 inch forming a junc tion with a contact arm whose width is 0.025 inch. Minimum resistance will be observed in a unit length where the width of the track is at its maximum, i.e. 0.125 inch. Maximum resistance will be observed in a unit length where the width of the track is at its practical minimum, i.e. 0.025 inch. The resistance can be varied, therefore, only in the ratio of 0.125 inch to 0.025 inch, or 5 to 1.

However, the resistance per unit length of the track can also be varied without varying the width of tht track by varying the depth of the track, and this introduces another parameter which makes it possible to markedly increase the aforesaid ratio. For example, if the depth is varied from a value ten times as great in one'unit length as in another, the resistance can be varied in the ratio of 10 to 1 for a given width.. If both width and depth can be varied, the range of resistance variability is the product of the aforesaid ratios, i.e. 50 to 1.

Heretofore a practical method and apparatus for varying the depth of the potentiometer track has not been available.

Accordingly, the present invention contributes a practical potentiometer which is free of the aforementioned difficulties and disadvantages, as well as a method and apparatus for varying the depth of the potentiometer track, thus to produce potentiometers having considerably wider ranges of resistance characteristics for predetermined operating conditions than has been obtainable heretofore.

Briefly, the present invention includes a potentiometer of the class described integrally co-m'olded and comprising a base, and a thin spray coating of particles deposited on the outside surface of the base forming a variable resistance conductive plastic track varying in its depth dimension in proportion to the resistance characteristics at given points on the track. The track is flush with the surface of the base and the particles of the coating are pressed into co-mingling attitude with respect to thesurface particles of the base for receiving a movable wiper thereon, and conductive terminals are deposited in electrical connection with the underside of the track and flush with the surface of the base outside of the track width.

An important feature of the present invention resides in the provision of potentiometers having tracks of wide range resistance characteristics and in which the track itself is flush with the base surface thus to reduce the space occupied by the instrument and to eliminate track damage.

As a particular feature of the present invention, we provide an apparatus in which a conductive plastic spray of substantially constant density is directed through an orifice in a masking plate and adheres to a potentiometer base which is rotated by suitable means, such as a motor. Actually, a pressure gun utilizing substantially constant air pressure, for example, may be employed for directing the plastic spray. In any case, a conductive plastic track is deposited on the base, and with repeated application of the plastic, the track depth will increase.

'Since the spray density is substantially constant and the motor rotates at substantially constant speed, a particle area of the surface of the track is exposed to spray of substantially uniform density for a substantially constant period of time during each revolution of the motor. The depth of spray deposited on the base is proportional to the size of the masking plate orifice, and the size thereof is varied by means, such as a cam, driven in the desired relation to the rotation of the base.

Thus, as .a further feature of the invent-ion, we provide a spray-throttling cam which is positioned behind the orifice in the masking plate, and which is driven in a manner to vary the size of the masking plate orifice. This cam can be designed, as will be described hereinafter, so that varying amounts of spray will be depoisted on different areas of the track during each revolution of the base. The result is that the resistance increments per unit of annular movement of the base can be varied over a wide range and in such a manner that potentiometers having wide variations of resistance characteristics can be produced.

There has thus been outlined rather broadly the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject of the claims appended hereto. Those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures for carrying out the several purposes of the invention. It is important, therefore, that the claims be regarded as including such equivalent constructions as do not depart from the spirit and scope of the invention.

A specific embodiment of the invention has been chosen for purposes of illustration and description, and is shown in the accompanying drawings, forming a part of the specification, wherein:

FIG. 1 is a plan view, partly in section, of one form of the apparatus of this invention;

FIG. 2 is a sectional view taken along the lines 22 of FIG. 1;

FIG. 3 is a front view of a portion of the apparatus taken along the lines 3-3 of FIG. 1;

FIG. 4 is an enlarged detail view of the orifice of the apparatus of FIG. 1;

FIG. 5 is an enlarged perspective view of a potentiometer constructed according to the concept of this invention;

FIG. 6 is a perspective view of one form of apparatus for molding the potentiometer of FIG. 5;

FIG. 7 is an enlarged transverse sectional view of the apparatus of FIG. 6;

FIG. 8 is a side elevational view, partially in section, of another form of apparatus for molding the potentiometer;

FIG. 9 is a plan view of still another form of apparatus for molding the potentiometer; and

FIG. 10 is an enlarged sectional view taken along the line 1010 of FIG. 5.

In the embodiment of the invention illustrated in FIG. 5, there is shown a potentiometer indicated generally at 10 having a substantially cylindrical base 12 and a thin spray coating of particles deposited on the outside surface of the base forming a variable resistance conductive plastic track 14 which varies in its. depth dimension in proportion to the resistance characteristics at given points on the track. It is noted that the track is of generally spiral configuration. Conductive plastic terminals 16 are electrically connected with the underside of the track 14 and flush with the surface of the base outside of the track width as shown in FIG. 10. Normally a terminal is provided at each end of the track, one being shown in FIG. 10.

Still referring to FIG. 5, a slip ring 18 is provided at each end of the track, the slip ring being connected to the terminals. A wiper arm or contact 20 forms a movable junction with the track. Also, wiper arms or contacts 22 form movable junctions with the slip rings 18, respectively.

FIGS. 14 illustrate apparatus adapted to the manufacture of the multi-turn potentiometer 1%). As shown in FIGS. 14, the apparatus comprises a movable plate 23 reciprocably mounted on a base member 29. A spray gun assembly generally designated by reference numeral 30, a threaded nut 31, a gear train generally designated by reference numeral 32 and various other parts to be more fully described hereinafter are attached to the plate 28. The spray gun assembly 3d includes the spray gun 33 and the support plate 34 which is secured to the movable plate 28 by

bolts

35 and 36. An air line 37 is connected to a compressed air source (not shown) for example, for actuating the spray gun. The gear train 32 comprises an elongated gear 38 mounted on a shaft 39 extending to a gear box 40. A shaft 41 extends from the gear box and a bevel gear 42 is mounted at the end thereof.

The apparatus also includes a constant speed or synchronous motor 43 having a shaft 44 with a first beveled gear 45 intermediate its ends and a second beveled gear 46 at its end. The shaft 44 is journaled at 47. A second shaft 48 extends substantially at right angles to the shaft 44 and carries a bevel gear 49 meshing with bevel gear 46 so that the motion of the shaft 44 is transmitted to shaft 48. The gear ratio between these two

gears

46, 49 may be 1 to 1. Shaft 48 is supported by journals 50 and 51 respectively.

A mandrel 52 is removably mounted between

plates

53 and 54 on shaft 48 by nuts 56, and the potentiometer 10 is mounted on the mandrel 52 (FIGS. 1-3). A spur gear 57 is carried on shaft 48 and meshes with gear 38 in a 1 to 1 gear ratio, wherefore the constant speed motor 43 drives the gear train 32 and the potentiometer 10 rotates at substantially constant speed about a fixed axis.

Bevel gear 42 of gear train 32 meshes with bevel gear 58 on an end of shaft 59 which, as shown, passes behind the potentiometer 10 and is supported by journals 59a and 59b respectively. At the opposite end of shaft 59 a spray throttling cam 60 is mounted which, therefore, is rotatable by motor 43. Again, this cam 60 has the desired dimensions and contour.

A masking plate 61 formed with an interiorly located throughbore generally designated by reference numeral 62, consisting of two communicating preferably

square orifices

63 and 64 is positioned between the spray gun 30 and cam 60. The orifice 63 faces the spray gun and is of greater cross sectional area than the orifice 64. The purpose of the spray throttling cam 60 is this embodiment is the same as the corresponding cam 22 in the previously described embodiment. As shown in FIG. 4, a marginal zone of the cam is aligned between the orifice 64 and the potentiometer 10 so that as it rotates, it effectively changes the dimensions of the throughbore 62 with the result that greater or lesser amounts of spray are deposited on particular areas of the potentiometer base 12.

A further bevel 45 carried by shaft 44 meshes with a bevel gear 65 mounted on the upper end of a shaft 66 at a 1 to 1 ratio. This shaft 66 extends into a gear box 67. Shaft 68 extending from the gear box 67 transmits the motion of shaft 65 as modified by the gear train (not shown) in the gear box 67, and is coupled to screw member 70 journaled in two support members 71 and 73. The traveling nut 31 threadably engages the threaded portion 74 of screw member 70' and is secured to movable plate 28 by a brace 75 (FIG. 4).

Microswitches

77, 78 are connected to a reversing control apparatus 79 by wires 80' and 81 respectively. The reversing control apparatus 79 is connected to a power source (not shown) and to the constant speed motor 43. The purpose of this arrangement will be explained more fully hereinafter.

In operation of the apparatus shown in FIGS. 1-4 for the production of a multi-turn potentiometer, the potentiometer is rotatable with the shaft 48 but does not undergo any vertical movement as viewed in FIG. 1. Reicprocating plate 28 does undergo vertical movement controlled by the movement of traveling nut 31 activated by the turning of the screw member 70. Screw member 70 is in turn rotated by the motor 43 through shaft 44 and

bevel gears

45 and 65. Movement of the plate 28 is modified by the gear train in gear box 67 to control the number of turns of the resistance track 14 on the potentiometer base 12 as will be explained more fully hereinafter. The reciprocal motion of moving plate 28 is of course imparted to all of the parts which are attached to it. Thus, spray gun assembly 30, gear train 32, masking plate 61, spray throttling cam 60, shaft 59 and bevel gear 58 all undergo reciprocating up and down motion. As gear 57 rotates, it remains in operative engagement with gear 38 while the latter reciprocates vertically. The constant density spray from the spray gun 33 passes through the orifice 64 onto the potentiometer base 12. Since the potentiometer base 12 is rotating, the spray is deposited as a helical track 14 on the base 12. The thickness or depth of the track is controlled by the spray throttling cam 60 whose marginal zone is contoured effectively to vary the width of the orifice 64.

As shown in FIGS. 1-4, the cam 60 changes the effective width of the orifice 64. This, in turn, affects the thickness of the conductive track 14. Since the same particle area of the potentiometer base 12 is exposed to the same amount of spray with each complete upward and downward movement of the reciprocable plate 28, the result is that a potentiometer having a conductive track 14 of variable depth is produced.

It will be seen that the number of turns of the helical track 14 on the potentiometer base 12 will depend upon the number of complete revolutions made by the base 12 during each upward or downward movement of the plate 28. This reciprocal motion in turn is controlled by the rotation of the screw member 70 which is controlled through the gear box 67 the latter being actuated 'by the constant speed motor 43'. The rotation of the motor 43 is transmitted to the potentiometer base 12 by the

shafts

44 and 48 and by the bevel bears 46 and 49. Since both the potentiometer base 12 and the screw member 70 are rotated by the constant speed motor 43, it is apparent that by proper selection of the gear ratio in gear box 67 and the lead of threaded portion 74, potentiometer 10 could undergo any number of complete revolutions for each upward and downward movement of the reciprocating plate 28. Thus, potentiometers with any number of turns per fixed length of base 12, say for example, 5, l0, g

20, etc. can be prepared. If the pitch of the threaded portion 74 is such that at a gear ratio of 1 to 1 in gear box 67 screw member 70 makes twice as many turns as potentiometer base 12 during a fixed length of movement of traveling nut 31 and it is desired to make a potentiometer having 10 turns in the fixed length, it is necessary to change the gear box ratio from 1 to 1 to 2 to 1 so that screw member 70 will make 10 turns instead of 20 turns during the fixed length of travel of the nut 31. The length of travel of the nut 31 is equal to the lateral distance between the top and the bottom of the helical track 14.

It is important to the apparatus illustrated in FIGS. 'l4 that the same particle area on the surface of the potentiometer base 12 be exposed to a substantially uniform spray density for a substantially constant period with each upward and downward motion of the reciprocating plate 29. This result is achieved by controlling the degree of rotation of the spray throttling cam and its dimensions and contour and also by adapting synchronous motor 43 to be reversible. In the manufacture of a 10 turn potentiometer, the gear ratio in the gear box 40 is 10 to '1 so that for each complete revolution of the gear 57, the cam 60 will rotate 36, i.e., one-tenth of a complete revolution. At the end of 10 complete revolutions of the gear 57 and the potentiometer base 12 the movable plate 28 will have made one complete upward or downward movement and will reverse its direction in a manner to be described. At the same time, the direction of rotation of the cam 60 and the potentiometer base 12 will be reversedso that the last particle area on the potentiometer track to be exposed to spray during the movement in one direction will be the first particle area to be exposed to spray during the movement in the opposite direction. Furthermore, since the spray throttling cam 60 is reversed at the same time, the last effective width of the orifice 64 during one vertical movement of the plate 28 will be the first effective width during vertical movement of the plate 28 in the opposite direction. Therefore each particle area on the poteniometer base is exposed for exactly the same period of time to spray of constant density through an orifice of the same dimensions during each upward and downward movement of the movable plate 28.

For the manufacture of a 20 turn potentiometer the gear ratio in the gear box 40' would be 20 to 1 and the cam would make one-twentieth of a complete revolution with each complete revolution of the potentiometer base 12. For a 5 turn potentiometer the corresponding angular rotation of the cam would be one-fifth of 360 for each complete revolution of the potentiometer base 12. In these instances, the potentiometer base 12 would make 20 and 5 complete revolutions respectively for each complete vertical movement of the reciprocating plate 28. The angular velocity of the cam is equal to the reciprocal of the number of turns of the conductive plastic track 14 multiplied by the angular velocity of the potentiometer base.

The reciprocating motion of the plate 28 is controlled by means of the reversible synchronous motor 43, the reversing control appraatus 79 and the

switches

77 and 78. The reversing control apparatus 79 is well known in the art and is controlled by stable switching means operated in response to application of voltages upon either of the two leads 80 and 81 to switch the power supply leads to the motor 43 in a manner such that the synchronous motor is driven in a direction corresponding to the

lead

80 or 81 last receiving a finite voltage. It will be readily understood by one skilled in the art that such a reversing means may take any of a variety of known forms.

Switches

77 and 78 are located on the support members 71 and 73 and are oriented so that their movable contact member is closed whenever the traveling nut 31 reaches either extreme of its operating movement. Upon closure of the switch contacts, a finite voltage is supplied to lead 80 or 81 of the reversing control apparatus 79 to cause it to switch the input supply leads to the synchronous motor 43 so that the motor drives the shaft 44 in the opposite direction. This in turn reverses the direction of rotation of the potentiometer 10 and the spray throttling cam 60.

It will be apparent from the foregoing and from a study of the figures that effective operation of the embodiment of FIGS. 1-4 requires that the height of gear 38 and of the threaded portion 74 of screw member be at least equal to the height of the potentiometer base .12, or at least that portion of the potentiomeer base 12 on which the potentiometer track is to be deposited.

In practice it is expedient to make both gears 38 and threaded portion 74 long enough to accommodate the longest potentiometer base 12 and to provide control means to permit the manufacture of shorter potentiometers.

Such control means may take a variety of forms but a simple form thereof is illustrated in FIGS. 1 and 2. As shown, the control means comprises a horizontal base portion 83 attached to the support for the traveling nut 31. An adjustable rod 84 is secured to the base portion 83 by wing nut 85. The rod is in the plane of the controls of the

microswitches

77 and 78 and activates them by striking the controls at the end of each vertical motion of the traveling nut 31. A number of rods 84 of different lengths may be provided for the manufacture of variable length potentiometers.

Potentiomters having resistance characteristics of any practical desired value can be prepared utilizing the apparatus of this invention. Most potentiometers are prepared by rotating the cam and the potentiometer base at from about 30 to about 100 rpm. for from about onehalf to about one and one-half minutes, utilizing a spray gun pressure of from about 30 to 40 lbs. per square inch. Once the spray has been deposited, the potentiometer blank is compressed and molded to produce the finished product.

The basic concept on which this invention is based is the concept of spraying the conductive plastic on the insulator base while controlling the amount which is permitted to accumulate on a selected particle area. It makes possible the production of a new class of flush track potentiometers in which the conductive track is flush with the insulator base surface. Moreover, these new potentiometers, by the use of the methods and apparatus of this invention, can be prepared with hitherto unattainable efliciencies.

Heretofore potentiometers have been prepared by first preparing molds with track indents. The terminations were then placed in the mold cavity and the conductive plastic either sprayed into the indents or loaded therein as a dry powder. The bridges were then installed and the cavity filled with insulator powder. The potentiometer blank was then molded with the application of heat and pressure. It will be apparent that each time a potentiometer of different performance characteristics was required a new mold had to be manufactured.

However, in the practice of this invention only molds having flat surfaces are necessary. The contours of the conductive plastic track are controlled by the spraying techniques. Any number of insulator bases may be prepared by simply compressing the insulator plastic into any desired shape, e.g., a circular disc or a cylinder. As best seen in FIG. 10, the leads or terminals 16 are scribed onto the surface of the base 12, for example with a lettering pen, and then the conductive plastic is sprayed onto the base forming the track. Any breaks in the track can be attained by the use of masking tape. The base with the deposited track is then compressed in a mold having a flush surface until the track surface is flush with the surface of the base. It will be seen that it is not necessary to prepare special molds each time a new potentiometer design is required. As is clearly shown in FIG. 10, the conductive plastic terminals 16 are in electrical connection with the underside of the track and flush with the surface of the base outside of the track Width.

Referring to FIGS. 6 and 7, there is shown one form of mold, indicated generally at 86, for compressing and molding the potentiometer blank to produce the finished product. The mold 86 is hollow and has a rigid outside wall 88 and a flexible inside wall 90 fabricated from an elastomeric material such as rubber, for example. In operation the potentiometer blank 10 is inserted inside the mold and the mold is inflated with air, or the like, through a connection 92. Then the assembly is subjected to heat. In this way the potentiometer blank is compressed until the track 14 and the terminals 16 are flush with the base as seen in FIG. 10. Then the air pressure is released and the finished potentiometer blank 10 is removed from the mold.

Referring next to FIG. 8, there is shown another form of mold 94. This mold is rigid and is provided with an inside wall 96 having a very small taper 98. This mold is used with a silghtly modified potentiometer blank 10a which is formed with substantially the same taper 98. In operation the potentiometer blank is inserted in the mold until the outside wall thereof engages the inside wall of the mold and thereby compresses the track 14 and the terminal so that they become flush with the surface of the base. Normally heat is applied simultaneously with the pressure. It is noted that in this embodiment the track width or thickness will have to be adjusted to compensate for the difference in diameter along the length thereof. Normally, the wiper or contact is spring loaded so that it can readily compensate for the diameter difference along the length of the potentiometer base.

Referring next to FIG. 9, there is shown still another form of mold which comprises three (3)

rollers

1100, 102 and 104 mounted on

spindles

106, 108 and 110, respectively, for rotation. The rollers are mounted in spaced relationship one with respect to the others and with at least one of the rollers being resiliently movable so that the potentiometer blank can be positioned therebetween with the other surfaces pressing against the opposite side of the potentiometer blank to cause the track and terminals to become flush with the base as described hereinbefore. Normally heat is applied simultaneously with the pressure.

The compression temperature and pressure depend on a variety of factors well known to those skilled in the art and are in no way critical to the operation of this invention. Some of the factors which enter into the selection of a particular molding temperature and pressure include the identity of the conductive plastic, the amount of conductive materials suspended in the plastic, the shape and size of the particles of conductive material, and the resistance decrease desired during the molding operation. Many potentiometers are prepared at a temperature of from about 250 F. to about 350 F. and at a pressure of from about 500 to about 4,000 lbs. per square inch. In any case, it will be appreciated that potentiometers produced according to the present concept have tracks of wide range resistance characteristic which are flush wtih the base surface to which they are applied.

While the description of the invention has been given in terms of what are presently considered to be the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope of the invention. It is the intention, therefore, that the appended claims cover all such changes and modifications as fall within the spirit and scope of the invention.

What is claimed and desired to be secured by Letters Patent is:

l. A potentiometer of the class described integrally comolded and comprising non-flexible plastic electrically insulating base having an uninterrupted continuous outside surface mountable for rotation about an axis which is angularly disposed with respect to the surface, a wafer thin spray coating of particles deposited on said surface of the base forming a variable resistance conductive plastic track varying in its depth dimension in proportion to the resistance characteristic at given points on said track, said track being flush with said surface of the base and the particles of said coating being pressed into co-rningling associations with respect to the surface particles of said surface of the base for receiving a movable Wiper thereon, and conductive plastic terminals in electrical contact with the underside of said track and flush with said surface of the base outside of the track width.

2. A potentiometer according to claim 1 wherein said base is substantially cylindrical.

3. A potentiometer according to claim 2 wherein said conductive plastic track is of spiral configuration.

4. A potentiometer according to claim 3 wherein said terminals are slip rings one being disposed towards each end of said cylinder, said slip rings being connected to the ends of said conductive terminals respectively.

5. A potentiometer according to claim 1 wherein said conductive plastic track is a thermosetting resin having finely divided carbon suspended therein.

6. A potentiometer according to claim 1 wherein said base is conical and has a slightly tapered outside surface.

Schellenger 338-314 Tellkamp 338-172 Kohring 338--300 X Planer et a1. 338300X Lanning 338300 RICHARD M. WOOD, Primary Examiner.

V. Y. MAYEWSKY, Assistant Examiner.

Notice of Adverse Decisions in Interferences In Interference No. 97,035 involvin Patent No. 3,329,920, A. A. Veroesi and R. R. Segerdahl, VARIABLE R SIS'IANOE POTENTIOMETER, final judgment adverse to the patentees was rendered June 27, 1971, as to claim 3.

[Ofiicial Gazette M arch 6, 1.973.]

Claims

1. A POTENTIOMETER OF THE CLASS DESCRIBED INTEGRALLY COMOLDED AND COMPRISING NON-FLEXIBLE PLASTIC ELECTRICALLY INSULATING BASE HAVING AN UNINTERRUPTED CONTINUOUS OUTSIDE SURFACE MOUNTABLE FOR ROTATION ABOUT AN AXIS WHICH IS ANGULARLY DISPOSED WITH RESPECT TO THE SURFACE, A WAFER THIN SPARY COATING OF PARTICLES DEPOSITED ON SAID SURFACE OF THE BASE FORMING A VARIABLE RESISTANCE CONDUCTIVE PLASTIC TRACK VARYING IN ITS DEPTH DIMENSION IN PROPORTION TO THE RESISTANCE CHARACTERISTIC AT GIVEN POINTS ON SAID TRACK, SAID TRACK BEING FLUSH WITH SAID SURFACE OF THE BASE AND THE PARTICLES OF SAID COATING BEING PRESSED INTO CO-MINGLING ASSOCIATIONS WITH RESPECT TO THE SURFACE PARTICLES OF SAID SURFACE OF THE BASE FOR RECEIVING A MOVABLE WIPER THEREON, AND CONDUCTIVE PLASTIC TERMINALS IN ELECTRICAL CONTACT WITH THE UNDERSIDE OF SAID TRACK AND FLUSH WITH SAID SURFACE OF THE BASE OUTSIDE OF THE TRACK WIDTH.