US3761672A

US3761672A - Apparatus and method for modifying wound wire devices

Info

Publication number: US3761672A
Application number: US00253282A
Authority: US
Inventors: H Baker; D Rathje; W Butek
Original assignee: SOLATRON ENTERPRISES
Current assignee: SOLATRON ENTERPRISES
Priority date: 1972-05-15
Filing date: 1972-05-15
Publication date: 1973-09-25
Anticipated expiration: 1990-09-25

Abstract

A method and apparatus for removing unwanted turns from wound wire segments first brazes foil strips to the unwanted turns at opposed points on the periphery and next passes a high energy electrical discharge between the foil strips. The electrical discharge is of a magnitude and duration sufficient to vaporize the turns of wire between the foil strips. Any unvaporized particles of wire are attached to the foil and can be easily removed. If two pairs of opposing electrodes are positioned adjacent each other, one of the electrodes of each pair can be used for the brazing step and both are used for the vaporizing step.

Description

United States Patent [191 Baker et al.

APPARATUS AND METHOD FOR MODIFYING WOUND WIRE DEVICES Sept. 25, 1973 3,573,422 4/1971 Langenbach 219/91 2,994,244 8/1961 Hay 219/68 X Primary ExaminerR. F. Staubly Assistant ExaminerL. A. Schutzman Att0rneyMarvin I-I. Kleinberg [5 7] ABSTRACT A method and apparatus for removing unwanted turns from wound wire segments first brazes foil strips to the unwanted turns at opposed points on the periphery and next passes a high energy electrical discharge between the foil strips. The electrical discharge is of a magnitude and duration sufficient to vaporize the turns of wire between the foil strips. Any unvaporized particles of wire are attached to the foil and can be easily removed. If two pairs of opposing electrodes are positioned adjacent each other, one of the electrodes of each pair can be used for the brazing step and both are used for the vaporizing step.

7 Claims, 8 Drawing Figures [75 l Inventors: Herbert Baker, Marina Del Rey;

David S. Rathje, Culver City; William T. Butek, Jr., Costa Mesa, .7 al QfQalL -W {73] Assignee: Solatron Enterprises, Inglewood,

Calif.

[22] Filed: May 15, 1972 [21] Appl. No.: 253,282

[52] U.S.Cl 2l9/68,2l9/9l,2l9/l17 [51] Int. Cl 823p 1/00 [58] Field of Search 219/68, 86', 89, 91, 219/1 17 [56] References Cited I UNITED STATES PATENTS 3,431,384 3/1969 Cooper 219/68 3,553,417 l/l971 Smith .l

POWER P0605? :appz V Pawn.

PATENTED 3.761.572

SHEET 10F 2 ,/',?0 Paws? SAZPPA) I F 7 xix?! 12 21 MN, P0405? N & 14 Sara? W l 48 J0 50 d f7! 7 APPARATUS AND METHOD FOR MODIFYING WOUND WIRE DEVICES The present invention relates to wound wire devices, and, more particularly, to a process and apparatus for removing unwanted turns of fine wire from a wound wire device.

Many uses are known for wound wire devices. For example, potentiometers are produced by winding a very fine, resistance wire about an appropriate mandrel and, through careful control of the winding operation, a desired resistance per unit length can be achieved. Apparatus for continuously winding potentiometer coils at high speed has been disclosed and claimed in US. Pat. No. 3,498,567 to H. Baker and D. Rathje. Other uses known for wound wire devices include musical instrument strings, cables and the like.

In the precision potentiometer field, however, many problems are encountered in preparing an individual wound wire element for incorporation into a potentiometer device. The wire wound mandrel is, as taught in the above patent, produced in a substantially continuous winding having predetermined resistance characteristics. This winding can then be cut into fixed lengths which are connected as a potentiometer device. In such an application, it is desirable to remove turns from the end of the mandrel or from between adjacent turns so as to provide fixed increments of resistance or appropriate terminations to which terminals may be attached.

In the prior art, the preparation of such wound wire segments for use as a potentiometer resistance element has been accomplished by having a worker with tweezers and a magnifying glass, laborously unwind the undesired turns of fine wire and cut or break the wire with the tweezers when the process is completed. It is then necessary to provide some means to prevent further unwrapping of the fine wire and to assure a good contact to a terminal.

The manual method described above has proved to be less than satisfactory although it is widely employed. Since human labor is relatively expensive, the costs of handling each element can be substantial and the process is a time-consuming one which, if not carefully done, can result in a high rejection rate of the finished devices.

According to the present invention, it has been found that undesired turns of the wound wire device can be removed by applying a high energy electrical discharge through the fine wires, which vaporizes or otherwise destroys the unwanted wire. This is accomplished by placing the wound wire device between opposing electrodes of a resistance type welder. When a high energy electrical discharge takes place between the electrodes, the unwanted turns conduct electrical current until the internal resistance becomes so great that the wires disintergrate or vaporize. Because the wire is relatively fine, virtually the entire span of wire between the electrodes is consumed. Whatever pieces of wire remain under theelectrodes can be easily removed.

It has also been discovered that the procedure can be improved upon by providing an intermediate foil strip between the electrodes and the winding. The foil strip may be a laminate of a less than optimum conductor of electricity such as stainless steel or Kovar or the like, to which has been laminated, plated or otherwise applied, a layer of gold solder or other low melting point i material. The low melting point metal is used to weld or braze the undesired turns to the strip.

When a high energy electrical discharge is applied between the electrodes, through the strips, the windings are vaporized as before but the remaining fragments of wire become embedded in the foil strip and therefore can be removed from the device. in addition,

the use of the intermediate strip tends to protect the welding electrodes, minimizing erosion and reducing the necessity for frequency dressing and cleaning of the electrode tips.

A preferred embodiment of the invention and method has been developed which employs two different welding techniques. A first and second pair of opposing electrodes are provided and are positioned closely adjacent each other. The foil strip underlies one electrode of each pair and a parallel gap welding technique is used to bond or braze the strip to the unwanted turns immediately underlying the strip. Because of the limited electrical energy employed in parallel gap welding, the strip is heated only enough to braze or solder the strip to the wires. This serves the two-fold function of attaching the strip to the wires and improving the electrical path from the electrode into the unwanted wire.

A similar arrangement is provided on the opposite side of the mandrel. The opposite electrodes of each pair are operated in a parallel gap welding step to bond a strip to the unwanted turns on the opposite side of the mandrel, as well. The electrodes of each pair are then connected to opposite terminals of a resistance welding power supply, which applies a high energy electrical impulse between the foil strips. As current is conducted through the unwanted windings, as above, the resistance of the fine wire is sufficient to cause rapid heating and evaporation or disintegration of the unwanted turns.

Any wire fragments remaining after the electrical discharge step are fixed to the foil strips which can then be easily removed, leaving a bare mandrel. The end of the wire remaining on the mandrel is also bonded to the strip but can be easily broken without damage to the winding.

Obviously, the invention can be practiced with individual segments of foil or with a continuous strip which can be moved to a fresh segment after each wound wire segment has been operated upon. Further, while the parallel gap welding step is not necessary, it has been found to be desirable and effective. It is therefore employed in the preferred embodiment of the present invention and is recommended when practicing the method.

Accordingly, it is an object of the present invention to provide an improved method for removing unwanted .tums from a wound wiredevice such as a potentiometer coil.

It is yet another object of the invention to provide an improved apparatus for removing unwanted turns from and advantages thereof will be better understood from the following description considered in connection with the accompanying drawings in which several preferred embodiments of the invention are illustrated by way of example. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the invention.

FIG. 1 is an idealized view of apparatus for practicing the present invention;

FIG. 2 including FIGS. 2a and 2b is a side view of a potentiometer coil with a partially broken away section enlarged to show detail;

FIG. 3 is an idealized end view, partly in block diagram, illustrating a preferred embodiment of the present invention employing both resistance and parallel gap welding techniques;

FIG. 4 is a side sectional view of the apparatus of FIG. 3 taken along the line 44 in the direction of the appended arrows;

FIG. 5 is an idealized end view illustrating an alternative embodiment of the present invention;

FIG. 6 is an end view of a wound wire device as an electrical discharge is passed through the undesired windings; and

FIG. 7 is a plan view of a segment of the ribbon of FIG. 3.

Turning first to FIG. 1 there is shown a wound wire device such as a potentiometer coil 10. The device includes a mandrel 12 which may be a ductile material such as copper. Helically wound around the mandrel 12 is a relatively fine resistance winding 14 which may be a varnished copper wire whose diameter is very small relative to the mandrel 12. A pair of electrodes l6, 18 are positioned adjacent the unwanted turns of resistance wire 14. The electrodes l6, 18 are connected across a power supply 20 which may be a conventional resistance welding power supply. A pushbutton 22 is shown as the means by which an electrical discharge can be initiated across the electrodes l6, 18.

In operation, the wound wire device 10 is placed with the unwanted fine wire 14 turns between the opposing

electrodes

16, 18. The power supply 20 is connected and the pushbutton 22 is actuated. A high energy, electrical discharge is conducted between

electrodes

16, 18 by the turns of wire 14 which are in contact with the electrodes. The electrical energy through the fine wire 14 is sufficiently great to vaporize or disintegrate substantially all of the wire 14 between the

electrodes

16, 18, leaving fragments or bits of the wire as indicated by the dotted segment lines. These fragments remain because the

electrodes

16, 18 also function as a limited heat sink, and the fragments are thus not evaporated by the discharge. Removal of the electrodes l6, l8 generally removes the wire fragments, as well.

In FIG. 2a there is shown a side view ofa typical segment of a potentiometer coil 10', illustrating a helical winding of a very fine resistance wire 14 on a mandrel 12'. Th encircled area is enlarged in FIG. 2b to show additional detail.

In FIG. 2b, the relative diameters of the mandrel l2 and the fine wire 14"can be appreciated. Generally,

the fine wire 14 is insulated with a varnish to afford electrical isolation between adjacent turns of the fine wire 14 and between the fine wire 14' and the mandrel 12'. An electrical potential is applied between the ends of the coil 10. An area extending in the axial direction is cleaned of insulation and a contact can pick off a potential that is related to the relative location of the contact.

Turning next to FIG. 3, there is shown a preferred embodiment of the present invention. As in FIG. 1, a wound wire device 30 includes a mandrel 32 and a fine wire 34 which is helically wrapped about the mandrel 32. In the preferred embodiment, two pairs of electrodes are employed. A first opposed electrode pair includes a first electrode 36 and a second electrode 38.

A third electrode 40 and a fourth electrode 42 form a second, opposed pair. A parallel gap welder power supply 44 is connected across the adjacent first and third electrodes 36, 40 of the different pairs. A second, similar parallel gap welding power supply 44' is connected across the second and fourth electrodes 38, 40 of the different pairs. It is, of course, possible that a single power supply 44 could be utilized and the adjacent electrodes would be connected in parallel.

A second, resistance welding power supply 46 is connected across at least one of the pairs of electrodes, here shown as the pair including the first and

second electrodes

36, 38. Between the wound wire device 30 and the electrodes, continuous foil strips 48, 48' are placed.

Each of the foil strips 48, 48' includes a base ofa fair conductor such as stainless steel, Kovar or the like. Bonded or laminated to the base layer is a thin coating ofa brazing material such as gold which has a relatively low melting point and which can be employed in a brazing operation. The ribbons 48, 48' are placed with the brazing metals adjacent the wound wire device 30.

This is best shown in FIG. 4 which is a side section of the apparatus of FIG. 3. As illustrated, the foil ribbons or strips 48, 48 are of a width substantially equal to the width of the wound portion which is to be removed. As shown, approximately four turns are to be removed.

In practicing the process of the present invention, and with reference particularly to FIGS. 3 and 4, initially the opposing pairs of electrodes are brought ad jacent the respective foil strips 48, 48' and slight pressure is applied, holding the foil 38, 38' against the fine wire 34. The parallel gap power supplies 44, 44' are energized and a current is passed between the first and third electrodes 36, 40, and the second and

fourth electrodes

38, 42.

This passage of electrical current causes local heating in the portion of the

foil

48, 48 that bridges between the adjacent electrodes and causes localized heating, melting the brazing material and effectively bonding the foil to the fine wire turns directly underlying the foil. The power supplies 44, 44' are then disconnected, and the resistance welding power supply 46 is connected and then energized. A high energy electrical discharge passes between the opposed electrodes, carried substantially by the turns of wire that have been bonded to the foil strips 48, 48'.

The resistance welding power supply 46 provides a short impulse of high current electrical energy which is sufficient to evaporate the complete turns of wire between the foil strips 48, 48'. However, because of the heat sink properties of foil strips 48, 48' and the electrodes with which they are in contact, fine wire fragments may be left which have been brazed to the foil strips 48, 48'. Further, one turn of the winding is bonded to only one of the foil strips and this one wire must be broken. However, the tensile strength of the fine wire 34 is such that the single turn can easily be broken without deleterious effect to the wound wire device 30.

The pressure on the pairs of electrodes may then be relaxed and the wound wire device 30 removed. The

foil 48, 48 can then be advanced slightly to a fresh position and the opposite end of the wound wire device 30 can be similarly dressed to remove the unwanted end turns.

In an alternative embodiment, indicated in FIG. 5, the continuous foil ribbons 48, .48 can be replaced with individual foil pieces of precisely determined width which can be placed under the electrodes before any pressure is applied. However, it has been found that the use of the continuous foil strips 48, 48' enables a faster, more repeatable process and avoids the need for the precise placement of the foil elements.

In FIG. 6, there is indicated the vaporizing process showing a fine wire turn to which a resistance welding discharge has been applied. Asis well known, the wire is rapidly heated to incandescence. Because of the magnitude of the discharge, substantially the entire wire is simultaneously heated to vaporization, leaving only fragments 50 at the electrodes. This is better illustrated in FIG. 7, which shows a segment of foil strip 48 having bonded thereto a plurality of fragments 50, remaining after the resistance welding discharge.

It has also been found that a ribbon strip intermediate the resistancev welding electrodes in a work piece has the added advantage of protecting the electrode from undue heating or burning during a discharge and eliminates the need for frequent cleaning and reshaping of the welding tip. In such an application, the foil need not include the lamination of brazing material. It is only necessary to provide a conductive strip, which, for this application, may be a good conductor such as copper or silver to assure that none of the electrical energy required for the resistance welding operation is lost in heating the interposed strips.

As has been noted above, the preferred embodiment utilizes a parallel gap welding step and a resistance welding step with an extra pair of opposed electrodes added for accomplishing this method. It is also noted that a satisfactory, but less desirable method could be performed with only the single pair of opposed electrodes employing foil strips, wherein the single, resistance welding electrical discharge accomplishes the vaporization of the unwanted fine wire turns and, at the same time, bonds the remaining fragments to the foil strips. It will therefore be apparent to those skilled in the art that modification and variations are possible without departing from the basic teaching of the present invention.

What is claimed as new is: 1. A method of removing turns of fine wire which have been wound on a mandrel comprising the steps of:

positioning electrodes on opposed sides of the mandrel with electrodes in contact with one or more turns of the winding of fine wire; applying a short duration electrical impulse between said electrodes sufficient for interrupting all turns intermediate said electrodes; and removing all interrupted turns.

2. The method of claim 1, above, further including the steps of:

positioning additional electrodes on opposed sides of the mandrel adjacent to electrodes already positioned;

placing a foil ribbon between electrodes and the turns to be removed; and

applying a first relatively low powered welding current between adjacent electrodes to weld said ribbon to the unwanted turns, prior to applying said short duration electrical impulse.

3. The method of claim 2, above, wherein said removing step includes the step of removing said foil with fragments of unwanted interrupted turns adherent thereto.

4. Apparatus for removing turns of fine wire wrapped on a mandrel comprising in combination:

a. electrode means including electrodes spaced apart and in contact with turns to be removed, and

b. power supply means coupled to said electrode means for applying electrical energy between said electrodes of power sufficient to interrupt all turns in contact with said electrodes, whereby unwanted turns on the mandrel are removed by an electrical discharge through the unwanted turns.

5. The apparatus of claim 4, above, further including contacting means including conductive foil segments adapted to be interposed between said electrodes and the turns to be removed, whereby electrical energy applied through said foil segments bonds the turns to said foil for easy removal thereof.

6. The apparatus of claim 5, above, wherein said electrode means include additional electrodes adjacent said spaced apart electrodes, said foil segments bridging adjacent electrodes, and wherein said power supply means include a secondary power supply connected across adjacent electrodes for applying parallel gap welding currents through said foil segments for bonding the turns to said segments.

7. Apparatus for removing a predetermined width of wire wrapped on a mandrel, comprising in combination:

a. a first pair of opposed electrodes adapted to receive the wire wound mandrel therebetween;

b. a second pair of opposed electrodes next adjacent the electrodes of said first pair and adapted to receive the wire wound mandrel therebetween;

c. conductive foil means including foil segments interposed between said electrodes and the wire wound mandrel;

d. first power supply means coupled to adjacent electrodes of said first and second pairs for applying a parallel gap welding current through said foil 'segments for bonding said foil segments to the wrapped wire; and

e. second power supply means coupled to at least one of each of said pairs of electrodes for applying a resistance welding current to a path including the wrapped wire between the opposed electrode of said pair,

whereby the resistance welding current interrupts the turns of wire between said opposed electrodes.

Claims

1. A method of removing turns of fine wire which have been wound on a mandrel comprising the steps of: positioning electrodes on opposed sides of the mandrel with electrodes in contact with one or more turns of the winding of fine wire; applying a short duration electrical impulse between said electrodes sufficient for interrupting all turns intermediate said electrodes; and removing all interrupted turns.

2. The method of claim 1, above, further including the steps of: positioning additional electrodes on opposed sides of the mandrel adjacent to electrodes already positioned; placing a foil ribbon between electrodes and the turns to be removed; and applying a first relatively low powered welding current between adjacent electrodes to weld said ribbon to the unwanted turns, prior to applying said short duration electrical impulse.

4. Apparatus for removing turns of fine wire wrapped on a mandrel comprising in combination: a. electrode means including electrodes spaced apart and in contact with turns to be removed, and b. power supply means coupled to said electrode means for applying electrical energy between said electrodes of power sufficient to interrupt all turns in contact with said electrodes, whereby unwanted turns on the mandrel are removed by an electrical discharge through the unwanted turns.

7. Apparatus for removing a predetermined width of wire wrapped on a mandrel, comprising in combination: a. a first pair of opposed electrodes adapted to receive the wire wound mandrel therebetween; b. a second pair of opposed electrodes next adjacent the electrodes of said first pair and adapted to receive the wire wound mandrel therebetween; c. conductive foil means including foil segments interposed between said electrodes and the wire wound mandrel; d. first power supply means coupled to adjacent electrodes of said first and second pairs for applying a parallel gap welding current through said foil segments for bonding said foil segments to the wrapped wire; and e. second power supply means coupled to at least one of each of said pairs of electrodes for applying a resistance welding current to a path including the wrapped wire between the opposed electrode of said pair, whereby the resistance welding current interrupts the turns of wire between said opposed electrodes.