US3008111A

US3008111A - figure

Info

Publication number: US3008111A
Authority: US
Publication date: 1961-11-07
Anticipated expiration: 1978-11-07

Description

Nov. 7, 1961 JULIE 3,008,111

INFINITE RESOLUTION POTENTIOMETER Filed Oct. 15, 1958 INVENTOR. LOE BE JU LIE BY BLAIR, SPENCER s BUCKLES ATTORNEYS.

United States Patent Dfifice 3,008,111 Patented Nov. 7, 1961 3,008,111 INFINITE RESOLUTION POTENTIOMETER Loebe Julie, Julie Research Labs. Inc., 603 W. 130th St., New York 27, NY. Filed Oct. 13, 1958, Ser. No. 766,947 11 Claims. (Cl. 338-202) This invention relates to improvements in variable resistance devices, and more particularly to means for providing finer gradations of resistance variation over any desired range. The invention is particularly useful in the manufacture of precision potentiometers for use in modern electronic devices or systems, as for example in precision control systems or analogue computers.

In the precision electrical arts, variable potential dividers are employed for many purposes, as for example to derive a voltage which varies in accordance with the angular rotation of a shaft, or to generate a voltage of a preselected wave form, or corresponding to a particular mathematical function, in response to mechanical shaft motion. The demand for greater precision in elec-" trical computers or control devices has required the manufacture of potentiometers to precise tolerances. For many practical considerations which are recognized in the art, the most uniform precision production of potentiometers has been of the wire-wound type in which a precisely drawn resistance wire is wound in uniformly spaced turns on a suitable insulating support and an electrical contactor is provided for movement over successive turns to select the desired amount of resistance included in an electrical circuit (or more frequently to tap a desired potential proportional to the contactor movement).

A long recognized problem in this art has been that of making a suitable moving contact to the resistance coil, and of effecting smooth or uniform changes in resistance as the contactor is moved over the coil turns. This problem is particularly acute in very high resistance otentiometers where the resistance of each turn of wire may be quite substantial, thus giving rise to abrupt changes or jumps in resistance value as the sliding contact advances from one turn to thenext. Such abrupt changes give rise to undesirable noise when the potentiometers of the prior art are employed as variable voltage means in communication or computer circuitry. To cope with this problem various ingenious schemes have been devised, including means for moving a sliding contactor through a helical path in constant engagement with but a single turn of helically wound resistance wire. Another proposal has been to employ two or more rotatable drums in combination with a gear drive and means for unwinding a strand of resistance wire from one drum simultaneously with winding it upon another, and making electrical contact to the strand as it is being wound. All such prior art devices have been costly and cumbersome, in addition to posing maintenance problems due to their susceptibility to mechanical failure.

Accordingly, a principal object of the present invention is to overcome the disadvantages of the prior art by providing a potentiometer having substantially infinite resolution of resistance variation over any desired range of resistance. A further object is to provide a substantially noise-free variable potential device. Another ob ject is ot provide such improved resolution and noisefree operation in a more compact physical form of construction for potentiometers. Another object is to provide a more economical form of construction for high precision potentiometers. An additional object is to provide all of the advantages above mentioned in a simple but rugged potentiometer device capable of long life and reliable operation. Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the features of construction, combinations of elements, and arrangements of parts, which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention reference should be had to the following description taken in connection with the accompanying drawing in which like references designate corresponding parts in the several figures.

FIGURE 1 is a perspective view of a a cylindrical wire-wound potentiometer employing a rotatable wiper arm in accordance with the invention;

FIGURE 2 is an enlarged view of the contacting portion of the wiper arm of FIGURE 1 and showing the resistance element in the contactor portion thereof;

FIGURE 3 illustrates an alternative embodiment of the invention as adapted to a linear potentiometer construction;

FIGURE 4 is an enlarged structural schematic view showing in greater detail the manner in which the distributive resistance wiper element of the movable contactor engages a plurality of fixed turns of resistance Wire in the potentiometer construction according to the invention; and

FIGURE 5 is an electrical schematic diagram useful in illustrating the operation of the invention.

The invention may be employed in any type of variable resistance or tapped potential device which employs a movable contactor. The precision benefits of the invention derive from my use of a distributive contact of relatively high electrical resistivity. Thus the contactor of my invention serves as a homogeneous interpolating device between the turns of the main potentiometer winding. According to one embodiment the resistive contact material may extend along the exposed turns of the main winding with negligible depth, while in another embodiment the resistive material of the contacting surface may have appreciable depth. In both of these embodiments the electrical connection to the resistive slider is made to the center of the contact material, on the contactor face opposite the main winding engaging surface. By virtue of the homogeneous resistance of the contactor, the resistance or voltage contribution of the main winding points to the tapped potential at the slider connection point are averaged. Thus the invention provides a variable potential divider capable of producing a monotonic function of voltage variation with physical movement of the variable member.

Referring now to FIGURE 1 of the drawings, a cylindrical potentiometer indicated generally at 10 includes a wire-wound resistance element 12 comprising a strand of resistance wire 14 wound upon an insulating card 16 and enclosed within an insulated casing 18. Opposite ends of resistance wire 14 are secured to

external terminals

20 and 22 in a conventional manner. A rotatable shaft 24 extends normally through the casing 18, through a conventional bushing. Affixed to the inner end 26 of shaft 24 is a rotatable wiper arm 28 which in this embodiment is formed of insulating material. The radiallydisposed end 30 of rotatable arm 28 carries on its under surface, in conductive engagement with the exposed surfaces of resistance wire 14, a resistance element 32 which may either be formed of a separate winding upon the insulated arm 28 or may be composed of a substantially homogeneous resistance material as will be described more fully in reference to FIGURE 2. At a central point 34 on Wiper resistance element 32, electrical connection is made by conductor 36, the opposite end of which may be connected to the shaft end 26 and/or to a metallic wiper arm 38 in conductive engagement with the flat surface of metallic collar 40. Collar 40 is connected by a conductive strap 42 to an external center tap terminal 44. Thus a continuous conductive path through

conductors

36, 38, and 42 serves to maintain terminal 44 constantly at the potential of mid-point 34- on the resistive wiper element 32. The manner in which this structure operates to provide monotonic voltage functions will be described more fully hereinafter with reference to FIGURE 4 and FIGURE 5.

Referring now to FIGURE 2, the details of the resistive Wiper contact may be more clearly seen as follows: The resistive portion of the wiper contact element 32 may be formed of a helically wound resistance wire embedded in a suitable insulating material 33, as for example an epoxy resin, with the surface portions of each turn lying in a common plane being bared for engagement with the main potentiometer winding; or the resistance portion 32 of the wiper arm may be formed of a film type resistance material as for example rhodium, beryllium, titanium, chromium, or of an alloy including any desired combination of these elements. Alternatively, resistive portion 3 2 may be formed of selected carbon compounds, as for example boron-carbon, or pyrolytic-carbon. It is preferable that the total distributive resistance of the wiper resistive element 32 should bear a predetermined relation to the resistance of the main wiper turns with which the surface of resistive element 32 is normally in conductive engagement. Preferably the total distributed resistance of element '32 should be at least twice the resist-ance of the corresponding winding turns with which element 32 is in engagement when the wiper arm is assembled in the structure shown in FIGURE 1.

Reference is now made to FIGURE 3 of the drawings which discloses an alternative structural embodiment wherein the main body of the resistance comprises a helically wound resistance coil 50, mounted upon an insulating rod or drum 52 which may be mounted upon a suitable 'base 53 by means of

brackets

54 and 55.

Opposite ends

56 and 58 of the resistance coil may be secured to drum 52 by means of

clamps

60 and 62 by which connections may be made to an external potential source.

Vertical supports

64 and 65 secured to base 53 may hold a longitudinal slider carrying rod 66 substantially parallel to the axis of resistance drum 62. Rod 66 supports and guides a movable slider member generally indicated at 68 which comprises an insulated slider handle 70 to which is afiixed by means of compression springs 72-72 a resistive contact member 74 having a substantially homogeneous, uniformly distributed resistance. A slider tap connection made by conductor 76 to the central point '78 of resistive slider element 74 completes the electrical connections for this embodiment of the invention. It will be apparent, of course, that slider connection.- 76 may be brought out loosely as shown in FIGURE 3 or that suitable means, as for example, a Phosphor-bronze spring slider arrangement may be employed to establish this connection with slider guiding rod 66 if desired. The distributive resistance element 74 in the embodiment of FIGURE 3 may be formed of any of the materials discussed above in reference to the construction of resistive element 32 as described in FIGURE 2, or resistive sliding contactor 74 may be formed of a suitable carbon compound.

Referring now to FIGURE 4 which is a structural schematic diagram, it will be seen that the resistive wiper element 32 conductively engages a plurality (as shown 3) of resistance turns on the main potentiometer winding 14. For effective operation the wiper contactor must always engage at least two turns of the main potentiometer winding 14, and preferably the movable resistance Wiper element should engage three or more turns of winding 14. Ideally the total distributed resistance of wiper element 32 should at least equal or substantially exceed the total resistance of the maximum number of potentiometer winding turns engaged. A minimum resistance ratio of 2:1 has been found satisfactory for most purposes.

4; Referring now to FIGURE 5, which is an electrical schematic diagram of a potential divider according to the invention, the manner in which the invention operates to achieve noise free uniform monotonic functions will be readily understood. As seen in FIGURE 5, the slider contactor 32 always engages at least two contacts on the potentiometer winding 14. For purposes of illustration in this fimlre the engaging points on the resistance winding are designated as separate taps (which in effect they are on a wire-wound potentiometer) and three taps (here designated l, 2, and 3) are shown in engagement with the contacting surface of resistance wiper element 32. As the slider 32 is advanced along the winding in the direction show-n by the arrow in FIGURE 5 the resistance between either end of the potentiometer winding 14 and the slider connection 36 does not vary abruptly by an amount equal to the total resistance between each tap (or turn of the winding) but the resistance changes gradually and uniformly with each incremental motion of the resistance slider 32, thus producing monotonic voltage functions.

The total resistance between opposite ends of the slider element 32 should preferably exceed the total resistance between two adjacent turns or tapped points of the potentiometer winding by a substantial amount (of the order of 2 to 1 or more). As the slider moves from left to right as indicated by the arrow in FIGURE 5, the slider resistance portion a between the center tap c and contact point 1 increases simultaneously with decreasing resistance of portion b between center tap c and contact point 2, until 0 is in direct engagement with 2. As motion of slider 32 continues in the same left-to-right direction, the resistance portion a becomes disengaged from contact point 1 while increasing portions of resistance a are inserted between center tarp c and contact point 2. Simultaneously, decreasing resistance of portion b appears between center tap c and contact point 3. Thus, a uniform transition of resistance values is obtained as the resistive slider element 32 moves along successive increments of the main potentiometer winding 14.

It will be readily apparent to those skilled in the art that the utility of the invention is not limited to resistance type voltage dividers, as disclosed in the preferred embodiment, but that the resistive contactor of the invention may be employed to derive smoothly changing monotonic voltage variations, as a function of relative motion, from a multiple tap electrical transformer, or from any other source of multiple potential values. Thus, for example, the coil 14 shown schematically in FIGURE 4 and FIGURE 5 of the drawing may be a transformer winding, or the separate taps such as l, 2 and 3 in. FIGURE 5 may be connected to different cells of a multicell battery potential source, if desired.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efiiciently attained and, since certain changes may be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention which, as a matter of language, might be said to fall therebetween.

Having described my invention, what -I claim as new and desire to secure by Letters Patent is:

1. Variable electrical resistance apparatus comprising, in combination, a first resistive element of predetermined fixed resistance value and having the resistance thereof distributed over an exposed surface area, a second resistive element of a different predetermined resistance value and having the resistance thereof distributed over a lesser substantially contiguous surface area, means establishing electrical conductivity between the exposed surface area of said second element and at least a portion of the exposed surface area of said first element, means establishing an external electrical connection to a central portion of said second resistive element, and further means enabling relative motion between said first and second elements whereby the exposed distributed resistive portion of said second element may be brought into conductive engagement with successive portions of the exposed resistive surface area of said first element.

2. The combination of claim 1 in which the total distributed resistance of said second element is of a value at least twice the resistance of the corresponding portion of said first element in conductive engagement with said second element at any given time, regardless of relative motion between said first and second elements.

3. The combination of claim 1 in which said first resistive element is adapted for stationary mounting and said second resistive element is move-ably mounted with respect thereto for conductive engagement with successive portions thereof.

4. The combination of claim 1 in which said first resistive element comprises a toroid of resistance wire wound upon a substantially cylindrical member of insulating material with an annularly disposed substantially plane surface of said toroid being exposed for conductive engagement with the distributed resistive portion of a rotatable second resistive element.

5. Monotonic voltage dividing means comprising, in combination, a substantially unifomly distributed fixed resistance element formed of substantially homogeneous resistance material, an uninterrupted surface portion of said resistance material being exposed for conductive engagement with a plurality of voltage taps, means establishing simultaneous conductive engagement between different portions of said exposed surface and a plurality of different potential taps, further means establishing electrical connection to a center portion of said resistance material, and means for imparting relative motion between said resistance element and the engaging potential taps whereby the voltage potential appearing at said further connection means represents a continuous average of the potential appearing at adjoining voltage taps in conductive engagement with said resistance element.

6. A slidably moveable wiper contact member for variable potential dividing devices comprising, an element of constant resistance material having a substantially uniformly distributed electrical resistance value throughout, a substantially uninterrupted surface portion of said material exposed for electrically conductive engagement with a plurality of adjacent potential conducting members, and means establishing an external electrical connection to a centrally disposed portion of said resistance element.

7. A noise free linear potentiometer, substantially as described, comprising in combination, a first resistance element adapted for the application of a differential voltage thereacross, said first resistance element having an elongated exposed surface area, the resistance per unit length in the direction of said elongation of said first resistance element being substantially constant over said exposed surface area whereby a linear voltage continuum is established over said exposed surface area when a differential voltage is applied across said first resistance element, a second resistance element adapted for slidable engagement with a relatively small area of said elongated exposed surface area of said first resistance element, the resistance per unit length of the contacted surface area of said second resistance element in the direction of said elongation being more than twice that of the resistance per unit length of said exposed surface area of said first resistance element, a low resistance tap to a point in said second resistance element, said point being spaced from said contacted surface area along a line perpendicular to a plane tangent to said contacted surface area at the center of gravity of said contacted surface area, whereby when a differential voltage is applied across said first resistance element and said second element is slidably moved along said elongated exposed surface area of said first resistance element in the direction of said elongation the voltage produced at said tap is a linear function of the position of said second resistance element with respect to said first resistance element and is relatively unaffected when small areas of said surfaces are separated by impurities and surface discontinuities.

8. Variable electrical resistance apparatus comprising, in combination, a toroid of resistance wire wound upon a member of insulating material forming a first resistive element of predetermined fixed resistance value and having the resistance thereof distributed over an exposed surface area, a substantially uniformly distributed helical winding of resistance wire mounted upon a rotatable arm of insulating material forming a second resistive element of a different predetermined resistance value and having the resistance thereof distributed over a lesser surface area, an annularly disposed substantially plane surface of said toroid being exposed for conductive engagement with the distributed resistive portion of said second resistive element, means establishing electrical conductivity between the exposed surface area of said second element and at least a portion of the exposed surface area of said first element, means establishing an external electrical connection to a central portion of said second resistive element, and said arm being rotatably mounted in the axis of said toroid whereby said wire-wound second resistive element may be progressively rotated into successive engagement with substantially all portions of the exposed plane surface area of said first resistive element.

9. Variable electrical resistance apparatus comprising, in combination, a first resistive element of predetermined fixed resistance value and having the resistance thereof distributed over an exposed surface area, a second resistive element of a different predetermined resistance value, said second resistive element being a substantially homogeneous member formed of resistance material selected from the group including rhodium, beryllium, titanium, chromium, and alloy mixtures thereof, the resistance of said second resistive element being distributed over a lesser surface area, means establishing electrical conductivity between the exposed surface area of said second element and at least a portion of the exposed surface area of said first element, means establishing an external electrical connection to a central portion of said second resistive element and further means enabling relative motion between said first and second elements whereby the exposed distributed resistive portion of said second element may be brought into conductive engagement with successive portions of the exposed resistive surface area of said first element.

10. Variable electrical resistance apparatus comprising, in combination, a first resistive element of predetermined fixed resistance value and having the resistance thereof distributed over an exposed surface area, a second resistive element of a different predetermined resistance value, said second resistive element being a substantially homogeneous member formed of a compound in which carbon is the principal ingredient, the resistance of said second resistive element being distributed over a lesser surface area, means establishing electrical conductivity between the exposed surface area of said second element and at least a portion of the exposed surface area of said first element, means establishing an external electrical connection to a central portion of said second resistive element, and further means enabling relative motion between said first and second elements whereby the exposed distributed resistive portion of said second element may be brought into conductive engagement with successive portions of the exposed resistive surface area of said first element.

11. An infinite resolution potentiometer, comprising in combination, a first resistive element of predetermined fixed resistance value and having anexposed surface area substantially extending from one electrical end thereof to the other, said first resistive element adapted to be connected across a source of electrical potential, a second resistive element of a diiferent predetermined resistance value and having a substantially contiguous surface area thereof exposed for electrically conductive engagement with at least a portion of the exposed surface area of said first element, means establishing an external electrical tap near the electrical center of said exposed area of said second resistive element, and means for establishing electrical conductive engagement between the exposed surface areas of said first and second resistive elements and for enabling relative motion between said first and second resistive elements, whereby when said first resistive element is connected to a source of electrical potential and said second resistive element is moved relative to and in electrical conductive engagement with said first resistive element a substantially smoothly varying potential is produced at said external electrical tap.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Zeitschrift fiir instrumentenkunde, vol. 34, 1914, page 149.