US2909753A - Resistance elements and method of making same - Google Patents

Description

Oct. 20, 1959 J. c. PERRY, JR 2,90 ,7

RESISTANCE ELEMENTS AND METHOD OF MAKING SAME Filed Aug. 30. 1955 Fla]. FIG. 2. 1716.5. 1 16.6.

iiiiiiimlili lllrii INVENTOR. JOHN CHARLES PaaQnd/a BY HIS ATTORNEYS. HARE/s, K/ECH, FosnzR & Heme/s llnited States Patent 2,909,753 RESISTANCE ELEMENTS AND METHOD OF MAKING SAME ilolni Charles Perry, In, San Gabriel, Califi, assignor, by

mesne assignments, to Beckman Instruments, Inc., F ulle'rton, Califl, a corporation of California Application August 30, 1955, Serial No. 531,368

9 Claims. (Cl. 338-298) This invention relates to resistance elements and to a method of making same. More particularly, the invention relates to resistance elements suitable for use in potentiometer-s or the like. While applicable both to resistors of the deposited-film type and of the wire-wound type, the latter will be herein illustrated by way of example.

In the potentiometer industry two types of Wound resistor elementsare common, one having a round cross section and the other having essentially a rectangular cross section. The latter are wound on flat, straight mandrels or cards made of insulating material, the resistance wire being wound about the card while the latter is being turned in a lathe or winding machine. Later, the cards are bent around and clamped to or within a circular member of the potentiometer so as to dispose the card in a circle with its edge exposed for contact by a rotating wiper arm. One reason for utilizing cards instead of round mandrels is to provide added lengths of resistance wire in the finished potentiometer within the same radial space factor, permitting the design of potentiometers of added resistance value. The speed at which a resistance wire can be wound around a card is strictly limited because of the flapping action or unequal winding rate of the resistance wire as the flat mandrel or card is turned.

It is an object of the present invention to windthe wire initially on a round mandrel, thus permitting winding with much higher speed and accuracy, and then to -deform or flatten the resulting wound structure to change fitS cross-sectional shape, the core and its winding being thus simultaneously changed in shape. It is another object of the invention to produce resistance elements in a t'less expensive way while still providing a greater accuracy in the finished product.

In the preferred practice of the invention, a tubular core of deformable material, usually a soft metal such as copper, is surrounded by a resistance member separated therefrom by suitable insulating material, opposed sides of the resulting tubular structure being then pressed toward each other to produce an elongated cross section. It is an object of the invention to produce resistance elements in this way.

While the resistance member may be'a deposited layer of resistance material applied to or surrounding the hollow core, it is usually a helically wound resistance wire. If the wire is coated with a sheath of insulating material, it can be wound directly upon a metal mandrel, the insulating material being later removed in a longitudinal zone to be traversed by the rotary wiper or contact of the potentiometer. Alternatively or in addition to this manner of insulating the resistance member from the core, I may initially encompass the tubular core with a sheath of insulating material, as by wrapping the core -with a pressure-sensitive tape formed of insulating material and applied either longitudinally or helically. This ---assures a higher breakdown voltage rating between the core and the resistance member. It is an object of the invention to apply such a sheath of pressure-sensitive tape to a tubular core before placing the resistance memher in position.

The use of a sheath of deformable insulating material immediately around the tubular core is particularly desirable with wire-wound resistances because the resistance wire can embed itself slightly in the sheath material and thus more firmly hold its position during subsequent processing, including the deforming step. Irrespective of whether a pressure-sensitive tape is used and irrespective of whether it is applied helically or longitudinally to the core, it is an object of the invention to apply a sheath of tape-like insulating material to the core before winding the bare or insulated resistance wire helically therearound whereby the winding operation will cause the wire to embed itself slightly in the sheath material.

A further object of the invention is to provide a re sistance element and a method of making same in which the tubular core is initially cylindrical and in which this core is sidewardly compressed after the resistance member has been applied, the sideward compression serving to flatten the structure either to a point where the opposed sides of the tubular core are in contact or to a point where such opposed sides are closer together than initially to produce a hollow-core resistance element. In the latter instance, the unit will provide a flow path within the core through which a cooling fluid or the like may 'be circulated if desired. The pressing or sideward compression will be hereinafter referred to as flattening, irrespective of whether the opposed side walls are brought into engagement with each other, the term being inclusive of any operation wherein the opposed side walls are brought closer to each other to elongate the cross section of the unit.

A further object of the invention is to provide a re.- sistance element and a method of making same in which the flattened unit is subsequently deformed into circular or helical shape with either a flat side or an edge dis.- posed outwardly. It is an important advantage of the invention that this operation shapes the unit to a permanent form. This is in contradistinction to prior attempts to deform units in which the resistance wire is wound around a flexible card and wherein the ends of the flexible card tend to spring back into straight form. Even if such a flexible unit is tightly clamped in place, it does not usually form a true circle. On the other hand, the permanently deformable core of the present invention permits bending of the unit into a permanent circular or helical form. The result is a more accurate location of the resistance wire so that a potentiometer of greater linearity or accuracy can be produced.

It is an object of the invention to provide a continuous method of making a wire-wound resistance element from a spool of resistance wire and a reel of tubular core material in which the tubular core material is passed by the winding station in a continuous piece and the resistance wire is continuously wound on the core as it passes the winding station, the wound unit being flattened and then being bent into a coil prior to being cut into indi vidual resistance elements.

A further object of the invention is to provide a resistance element of controlled resistance per unit of length and a novel method of making same in which a tubular core is varied in cross section or in peripheral dimension while still in tubular form, the resistance member being then applied and the unit then flattened in the manner referred to. above. It is thus possible to produce resist ance elements of tapered or nonlinear resistance.

The invention alsovcomprises novel details of construction and novel combinations and arrangements of parts which will more fully appear in the course of the following description. The drawing merely shows and the description merely describes preferred embodiments of the present invention which are given by way of illustration or example.

In the drawing:

Fig. 1 is a view of a tubular core in the process of being wound with tape and a resistance wire;

Fig. 2 is a cross-sectional view of the structure of Pi 1;

Fig. 3 is a view similar to Fig. 1 showing an alternative way of sheathing the core with an insulating material before winding the resistance wire in place;

Fig. 4 is a cross-sectional view of the structure of Fig. 3;

Fig. 5 is a view of the wound unit of Fig. 1 after the flattening operation;

Fig. 6 is a cross-sectional View of the structure of Pi 5;

7 is a side view of a single-turn resistance element made according to the teachings of the invention;

Fig. 8 is an end view of a resistance element of Fig. 7;

Fig. 9 is a side view of a multiple-turn flat-wound resistance element formed according to the teachings of the invention;

Fig. 10 is a side view of a multiple-turn edge-wound resistance element of the invention;

Fig. 11 is a side view of a resistance wire wound on a tubular core having a varying cross section;

Fig. 12 is a cross-sectional view of the structure of Fig. 11 taken along the line 1212 thereof;

Fig. 13 is a side view of the wound core of Fig. 11 after the flattening operation; and

Fig. 14 is a cross-sectional view of the structure of Fig. 13 taken along the line 14-14 thereof. 7

Referring particularly to Figs. 14, the preferred practice of the invention starts with a tubular core 10 made of a malleable material, typically copper, aluminum, or the like, which may be subsequently flattened without rupture and without materially affecting its mechanical properties. In a continuous operation, this tubular core moves longitudinally past a winding station while in cylindrical form. A thin-walled copper tubing is a typical tubular core 10. i

If desired, the tubular core 10 may be coated with an insulating material prior to being wound with resistance wire. The preferred way of accomplishing this result is shown in Fig. 1 which suggests the progressive winding of a tape 11 of insulating material helically about the core 14 in edge-to-edge manner immediately ahead of the winding station. Preferably this tape is a pressuresensitive adhesive tape made of insulating material. This material should preferably be sufficiently soft to permit the later-wound resistance wire to embed slightly therein. Instead of applying the tape 11 helically, as suggested in Fig. 1, a wider tape 11 may be applied longitudinally in encircling relationship with the core 10, the edges of the tape either abutting or, as shown in Fig. 3, overlapping slightly. In either instance, the tape can be applied progressively as the core moves longitudinally relative to the winding station. It should be clear, however, that it is not always necessary to apply such a sheath of insulating material about the core It) before it is wound.

At the winding station, a resistance wire 14 is wound helically about the core 10. This wire is preferably coated with an insulating material, although a bare wire can be used if the tape 11 or 11' is provided and if the "wire is space-wound on the tubular core.

The wound unit of Fig. 1 or Fig. 3 is next flattened by being sidewardly deformed or pressed to bring opposed side walls 15 and 16 closer together. This may be done by pressing the wound unit between the flat jaws of a press or by continuously passing the unit between suitable rollers. The degree of deformation or flattening 'will depend upon the desired cross-sectional shape of the resistance element and may vary from a slight deforma- 'tion of the core to an oval shape to the shape of Fig. 6, in which the opposed side walls 15 and 16 are parallel but still spaced to provide an internal channel 17 which may be used as a flow path for a coolant fluid, or even to a form in which the opposed side walls 15 and 16 are brought into face-to-face contact as shown in section in Figs. 10 and 14. The resulting flattened resistance element can be cut into lengths for use in straight form or for bending into the circular form of Figs. 7 and 8.

Desirably, however, the flattened unit is continuously formed into the flat-wound helix of Fig. 9 or the edge wound helix of Fig. 10, being used in such helical shapes for multiturn potentiometers or being cut into sections which can be subsequently deformed into a single plane to form resistance elements of any desired arcuate length up to a full circle. The flattened unit can be wound into the helical forms of Figs. 9 and 10 by use of suitable forming equipment or by being wound about a mandrel. While the single-turn unit of Figs. 7 and 8 is shown as being flat-wound, it should be understood that such single-turn units may also be edge-wound in which event they may represent segments of an edge-wound helix such as in Fig. 10. 5

An important advantage of this method of making resistance elements lies in the fact that high speed and accuracy can be achieved, along with economy, particularly in a continuous winding operation. Thus, a reel containing many feet of the tubular core 10 may be used, the tubing being continuously fed past a winding station where the resistance wire 14 and near which, if desired, the tape 11 or 11' is applied. The wound unit may be flattened in sections between the jaws of a press or may be continuously passed between suitable rollers. The wound and flattened unit may then be cut into short sections, if straight resistance elements are desired. -If circular resistance elements are desired, the flattened, wound unit may be continuously formed into a flat-wound or edgewound helix which can be used as such or from which one or more single-turn units may be cut.

The invention may also be used to produce resistance elements having varying or nonlinear resistance characteristics, as suggested in Figs. 11-14 which illustrate a rather extreme situation where the resistance per unit of length increases and decreases in a localized zone. In producing such resistance elements, the tubular core 10 is first upset or swaged while still in tubular form to produce a cross section varying in peripheral length at positions progressively along the length of the tubular core. In Fig. 11, a tubular core 30 has been internally expanded to produce a locally expanded zone 32 of larger diameter. A resistance wire 34 is then wound about the periphery of the expanded and normal-size zones of the core, the entire unit being then flattened to any desired extent. Fig. 14 suggests an extreme flattening in which opposite side walls 35 and 36 of the tubular core 30 are brought into contact with each other. Any flattening deforms the zone 32 as well as the remaining length of the core 30. The resistance per unit of length in the flattened zone 32 will be different, as compared with the remaining length of the wound unit, because of the greater length of the resistance wire 34 wound in this zone. By controlling the degree of initial peripheral deviation, resistance elements of any desired nonlinear function can be produced. Alternatively, resistance elements of extremely accurate linearity can be produced by correlating the cross-sectional peripheral length of the core with the diameter of the resistance wire. It should be understood also that while Fig. 11 suggest a localized internal expansion'of the tubular core to obtain a localized increase in resistance per unit of length, compression of a localized portion of the tubular core will produce a section'of decreased periphery and thus a section of decreased resistance per unit of length.

If an insulated resistance wire is used and the resistance element is to be a part of a potentiometer having a movable contact arm or wiper, a zone of the insulation is later removed in the area swept by the contact. This can be done either before or after the unit is formed into the circular or helical shapes of Figs. 7-10.

Although several exemplary embodiments of the invention have been disclosed and discussed, it will be understood that other applications of the invention are possible and that the embodiments disclosed are subject to various changes, modifications and substitutions without necessarily departing from the spirit of the invention.

1 claim as my invention:

1. In a resistance element, the combination of: a flattened tubular core of malleable metal; and a plurality of turns of resistance wire encircling said core.

2. In a resistance element, the combination of: a core comprising a length of flattened tubing of malleable metal with said length of tubing bent into a self-supported ring to form a ring-shaped core; and a plurality of turns of resistance wire encircling said ring-shaped core and insulated therefrom.

3. In a resistance element, the combination of: a helical core comprising a length of flattened tubing of malleable metal with said length of tubing bent into a self-supported flat-wound first helix; and a resistance wire wound about such helical core as a second helix having said first helix as an axis.

4. In a resistance element, the combination of a helical core comprising a length of flattened tubing of malleable metal with said length of tubing bent into a self supported edge-wound first helix; and a resistance wire wound about such helical core as a second helix having said first helix as an axis.

5. In a resistance element, the combination of: a flattened tubular core having a cross-sectional shape much wider measured along a major axis than along a transverse minor axis, the width of the flattened core measured in the direction of said major axis varying in different portions spaced lengthwise of said core; and a plurality of turns of resistance wire encircling said portions.

6. In a nonlinear wire-wound resistance element, the combination of: a flattened tubular core differing in peripheral dimension at different portions spaced along the length of the core; and a plurality of turns of resistance wire encircling and insulated from said portions.

7. In a resistance element, the combination of: a hollow metal core having a cross-sectional shape much wider measured along a major axis than along a transverse minor axis, said core having a fluid passage therethrough from end to end thereof; and a plurality of turns of resistance wire encircling said core.

8. In a resistance element, the combination of: a tubular core having a cross-sectional shape much wider measured along a major axis than along a transverse minor axis, with said tubular core flattened to bring the inner surface of opposing sides of said core into contact, the width of the flattened core measured in the direction of said major axis varying in different portions spaced lengthwise of said core; and a layer of resistance material carried on the outer surface of said portions.

9. In a resistance element, the combination of: a flattened tubular core having a cross-sectional shape much Wider measured along a major axis than along a transverse minor axis, said core having a fluid passage therethrough from end to end thereof, the width of the flattened core measured in the direction of said major axis varying in different portions spaced lengthwise of said core; and a layer of resistance material carried on the outer surface of said portions.

References Cited in the file of this patent UNITED STATES PATENTS 1,026,377 Barringer May 14, 1912 1,093,792 Madsen Apr. 21, 1914 1,755,314 Carter Apr. 22, 1930 1,767,716 Stoekle June 24, 1930 1,957,188 Wiggins May 1, 1934 2,247,869 Beers July 1, 1941 2,466,227 Gilman et al Apr. 5, 1949 2,542,806 Ford et al. Feb. 20, 1951 2,754,569 Kornei July 17, 1956 FOREIGN PATENTS 1,491 Great Britain July 22, 1908 12,886 Australia May 31, 1933 of 1933

Claims (1)

1. IN A RESISTANCE ELEMENT, THE COMBINATION OF: A FLATTENED TUBULAR CORE OF MALLEABLE METAL; A PLURALITY OF TURNS OF RESISTANCE WIRE ENCIRCLING SAID CORE.

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