US2620990A

US2620990A - Method and apparatus for winding resistance elements

Info

Publication number: US2620990A
Application number: US695606A
Authority: US
Inventors: Henry H Cary; Roland C Hawes; Michael E Stickney; Kenyon P George
Original assignee: Beckman Instruments Inc
Current assignee: Beckman Coulter Inc
Priority date: 1946-09-09
Filing date: 1946-09-09
Publication date: 1952-12-09
Anticipated expiration: 1969-12-09

Description

Dec. 9, 1952 H. H. CARY E'I'AL METHOD AND APPARATUS FOR WINDING RESISTANCE ELEMENTS Filed Sept. 9, 1946 1 lZZ A 0 q i m a W 5 n1 0 m 5N u o a: C 6 a R m M i m Mb 8LT 110M M m M II. a

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AND POWER SUPPLY //v ve/v-rofis. HENRY H. CARY Roma/v0 C. HA was MICHAEL E. STICKNEY KENYON P. GEORGE B Y THE/R A TTORNE Y5. HARE/5, K/acmFosrlska Hnm/s Patented Dec. 9, 19152 UNITED STATES PATENT OFFICE METHOD AND APPARATUS FOR WINDING RESISTANCE ELEMENTS California Application September 9, 1946, Serial No. 695,606

16 Claims. 1

Our invention relates to the winding of resistance elements or other wound structures in which a filamentary member, such as a wire, is wound around a core member.

The patent to Marlow, No. 2,334,880, discloses a winding machine by which a resistance wire can be wound about a core member in compact helical turns to produce a resistance element which can then be coiled into helical form for use in a multi-turn variable resistor or potentiometer. The present invention is an improvement over the structure disclosed therein, and has among itsobjects the control of the winding operation to produce an electrical resistance element which has a carefully controlled or substantially uniform resistance per unit of length of the resistance element, irrespective of variations in resistance of the filamentary member or resistance wire wound around the core member to produce the resistance element.

In the prior machine, the resistance per unit of length of the finished resistance element would vary slightly with the diameter and composition of the resistance wire and with the eiiective diameter of the core member. Except when using resistance wire of almost prohibitive cost, variations in diameter or composition tend to prevent the winding of resistance elements of uniform resistance per unit of length, such as are required in certain circuits or devices where extreme accuracy or linearity is necessary. For example, in a spool of ordinary resistance wire, it is not uncommon to rind progressive change in diameter of 5% from one end of the wire to the other, due to wearing or the die usedfor drawing the wire. Variations in composition from point to point and variations in effective diameter of the core member are also troublesome in manufacturing precision-type resistance elements.

It is an object of the present invention to provide a novel method and apparatus for making precision-type resistance elements in which the resistance per unit of length can be held to within 0.1% or less of that desired.

Another important object is to change the pitch or spacing of the turns of resistance wire wound around the core member, this change being in response to variations in resistance of th wire.

Another object is to measure progressively the electrical resistance of the resistance wire, whether before winding, after winding, or both before and after winding, the resulting measurement being used to change the pitch or spacing of the turns being wound on a core member to produce a resistance element of accurately controlled resistance per unit of length.

A further object is to develop an electrical potential or current which varies with the resistanc of already-wound turns and employ this in the control of the winding operation to compensate for slow variations in size of the core member or slow variations in composition or size of the resistance wire.

The angle of feed of the resistanc wire to the advancing core member determines the pitch or spacing of the turns of the wire on the core. Any attempt to change this angle of feed in response to measurement of resistance between two closely-spaced contacts engaged by the resistance wire advancing to be wound becomes difficult, both because of the rapidity of feed and the small resistance involved. We prefer to dispose one contact (herein termed the initial contact) in such engagement with the advancing wire, and another contact in engagement with a wound portion of the resistance element. It is an object to accomplish this and also to reduce the efiect of contact resistance on the control desired.

By operating in the above way, the system :becomes responsive, partially to the incremental resistance of the advancing Wire and partially to the resistance of an already-wound portion of the wire, e. g., the angle of feed changes with an average resistance or the resistance of a section of the wire partly wound and partially unwound. It is preferable, however, in most exacting practice, to change the angle of feed in response to a weighted average. Thus, additional contacts can be spaced along the advancing, already-wound, resistance element and the resistance between each contact and the initial contact can be used to influence the control of the feed angle. In fact, the efiects of such resistances can be combined to produce a weighted average resistance or net resistance varying with the weighted average, and this can be connected in a suitable bridge circuit connected to control the feed angle. It is an object of the present invention to provide such an arrangement.

Still another object is to provide a novel method and apparatus for selectively coating a resistance element to adhere the resistance wire and the core member at a selected zone, while leaving exposed for contact another zone of the resistance element.

Referring to the drawing, illustrating one embodiment of the invention:

Fi 1 is a side elevational viewof a Winding A machine, the elements being shown diagrammatically;

Fig. 2 is a horizontal sectional view of the winding machine at one of the coating stations, being taken as indicated by the line 22 of Fig. 1 and Figs. 3a and 3b represent a disjoined wirin diagram, the line of disjoining being indicated at A-A in each view.

Referring particularly to Fig. 1, the winding machine of the invention is indicated generally by the numeral II] and is shown as including a vertical frame II mounted on a wall or suitable support, not shown. Mounted on the vertical frame II are various components, shown diagrammatically in Fig. 1 for purpose of clarity.

Generally speaking, the winding machine I0.

winds a filamentary member or resistance wire I2 in spaced helical turns about a core member I3. This core member I3- is preferably a wire, typically a copper wire, coated with enamel or other insulating material, the wire having a relatively large diameter as compared with the resistance wire I2. The core member I3 is slowly unwound from a spool I5 carrying a shaft I6 journalled in uprights I! supported by the vertical frame II or a suitable foundation. The innermost end of the core member I3 is indicated by the dotted line I8 and is preferably connected to a slip ring I9 carried by the spool I5 to be engaged by a brush contact 26 carried by one of the uprights II, this brush contact being grounded for purposes to be later mentioned.

The core member I3 rises first through a winding station, indicated generally by the numeral 22, where the resistance wire I2 is wound helically therearound in spaced turns. Essentially, the winding equipment (shown in greater detail in the patent supra) includes a winding frame 23 carried by a hollow spindle 24 journalled in brackets 25 and 26 attached to the vertical frame I I and carrying a pulley 21 connected to a driving motor 28 by a belt 29. The resistance wire I2 is drawn from a spool 36 freely journalled on the spindle 24. The withdrawn wire is threaded around two feed pulleys 3| and 32 carried by the winding frame 23. The motor 28 rotates the frame 23 rapidly, and the resistance wire from the pulley 32 is fed to the core member I3 to be wound helically therearound' as the core member moves upwardly, thus forming a resistance element 33, previously mentioned;

The frame 23 provides a lower member 34 carrying an insulating member 35 which supports upper and lower contacts 36 and 31, respectively engaging and making electrical contact with the bare resistance wire I2 asit is fed to the core member I3. One of these contacts 36, 3'! (e. g., the contact 36) corresponds to the aforesaid initial contact. The contacts 36 and 31 are respectively connected to

slip rings

38 and 39 carried by the frame 23 and respectively. engaged by brush contacts 46 andAI carried by a block of insulating material 42 secured to the bracket 26. Electrical currents can thus be supplied to the contacts 36 and 31.

Mounted immediately above the bracket 25 is a diiferential 45 which may be of any well known type, such as that illustrated in detail in the patent, supra. For example, the upper end of the hollow spindle 24 may carry one or more planet gears, each rotating about, and meshed with, two sun gears. One of these sun gears may be driven by a worm gear 48 meshed with a worm 49 driven by a differential motor 50.

The other sun gear is integral with a gear 5I. The rotation of the differential motor 50 is added algebraically to the rotation of the main motor 28 by the action of the differential 45. In other words, the rotation of the gear 5I will represent the algebraic sum of the rotations of the

motors

28 and 50. In the preferred arrangement, the motor 28 turns at substantially constant speed and the speed of the differential motor 50 is changed, by means to be later described, to vary with the measured resistance of the resistance element and/or the resistance of the resistance wire I2. With this arrangement, the differential motor 56 need not be reversible but merely a variable-speed drive, and the rotation of the gear 51 will be the arithmetic sum of the two motor rotations.

Means is provided for translating the rotation of the gear 5| into an advancing movement of the core member I3. This means is shown as an advancing means 52, which may serve also as a forming mechanism. The advancing means 52 may be constructed identically with that shown in the patent supra. As diagrammatically shown, it includes a forming roll 53 having a shallow peripheral groove into which the rising resistance element 33 is pressed by rolls 54 carried by a yoke 55. This yoke is resiliently pressed toward the roll 53 by a follower 56 engaging a cam 51, which can be moved by an operating handle 58. Preferably, the roll 53 carries a gear 59 rotating therewith about a shaft 60 carried in a frame 6I connected to the vertical frame II. The rolls 54 respectively carry gears meshing with the gear 59. The gear 59 and its attached roll 53 is driven by a gear 62 which, in turn, is driven by a shaft 63 operatively associated with the gear 5I, as through any intermediate gearing. This gearing is shown diagrammatically in Fig. 1 as including

meshed gears

64 and 65, the latter being driven by a shaft 66 carrying a gear 61 meshing with the gear 5|. The arrangement is such that the roll 53 turns proportionally to the gear 5I, the resistance element 33 being pressed into the groove of the roll 53 by the rolls 54.

In this way, the resistance element 33 can be coiled helically, as described in the patent supra, the resistance element progressively moving from the groove of the roll 53 so that continued operation will produce any desired number of helical turns. In this instance, the final coiled product is a helix having a plurality of major turns. Each major turn is composed of a length of the resistance element 33 and includes a length of the core member I3 about which is helically wound, in minor turns, the resistance wire I2. Such an ultimate product is particularly useful as a winding of a multiturn helical potentiometer or variable resistor of the type shown, for example, in the patent to Cary et al., No. 2,361,010. When thus used, it is desirable that the inner face of each major turn present bare resistance wire for engagement with a rotary contact. At the same time, it is often desirable that some or all of the remaining portions of each major turn be coated with insulating material. In the patent to Marlow, supra, a coated resistance wire was employed and means was provided for abrading the coating from the resistance element in an inwardly facing zone contacted by the rotary contact of the variable resistor or potentiometer. The present invention represents an improvement in eliminating this abrading action and in coating the resistance element 33 only on opposite sides with a suitable enamel, the enamel serving the dual purpose of bonding the minor turns of the resistance wire l2 to the core member l3 and, if desired, separating the major turns of the ultimate product.

Referring again to Fig. l, the resistance element 33 moves upwardly, as rapidly as it is wound and at a speed determined by the roll 53, through the hollow spindle 24 and through central passages of the differential 45 and the gear 5|. It then moves through a contact station It where the wound bare resistance wire is contacted by sequential auxiliary contacts 1| to 16, inclusive, shown diagrammatically in Fig. 1 and functioning to aid in the desired resistance measurement which controls the speed of the differential motor 5i) and thus the driving speed of the roll 53.

If desired, the resistance element 33 may then move through a heating station H where it is heated by an electric oven 78 in a manner preliminary to soften the coating of insulating material on the core member I3.

The rising resistance element 33 then moves through a varnish application station 83 of the type suggested in Fig. 2. For example, the resistance element 33 may move upward through a housing 3| mounting nozzles 33 connected to a supply pipe 84 and serving to flow insulating material on opposite sides of the resistance element 33 to form

coatings

85 and 83, shown greatly enlarged in Fig. 2, and leave exposed or uncoated faces 81 and 88 of the resistance element 33, one of these faces serving ultimately a the zone of contact for the aforesaid rotary contact of the variable resistor Or potentiometer. In practice, we prefer to flow onto the sides of the rising resistance element an insulating varnish of the type which polymerizes or sets when heated. Products known as Formex or Formvar are suitable, as well as other insulating enamels which set by drying and/or application of heat.

The resistance element 33, thus coated on its sides, may then move upward through a heating station 90 where it is heated by an oven 9! to harden the previously-applied

coatings

85, 83. In some instances, a second coating of insulating enamel or varnish may desirably be applied to the sides and, if so, the resistance element 33 moves upward successively through an application station 93, similar to the station 80, and through a heating station 9 similar to the heating station 93 previously described. If this equipment is used, a second coating will be applied to the sides of the resistance element 33. Any such coatings will serve the very desirable function of maintaining the minor turns of the resistance wire 12 permanently separated or spaced as originally wound. Such coatings will also bond the minor turns to the coating of the core member 13.

The present invention contemplates a control of the winding operation in response to the actual resistance of a length of the resistance Wire l2 to produce a resistance element 33 having a predetermined or carefully controlled resistance per unit of length, e. g., a substantially constant resistance per unit of length, irrespective of minor variations in diameter or composition of the resistance wire 12 and irrespective of minor changes in size of the core member l3. In the preferred arrangement, this is accomplished by changing the rate of feed of the core member E3 to change, in effect, the angle of feed of the resistance wire 12 and to change the spacing or pitch of the minor turns of the resistance wire i2 to wind the resistance element 33 to have a substantially constant resistance per unit of length. The present invention is capable of holding the resistance variations to 0.1% or less.

Such a mode of operation requires measuring the resistance of the resistance wire either before or after it is wound on the core member l3. Incremental measurements of resistance of the incoming resistance wire at the winding station are difficult to make due to the relatively low resistances involved and the extreme rapidity with which the differential motor 53 must respond. Also, such incremental measurement would not compensate for changes in size of the core member l3. For these and other reasons, we prefer to measure primarily the resistance of the resistance wire [2 after it is wound and use this measurement to control the speed of the differential motor 56. In the present specification and claims, the words measurement" or measuring are used in a broad sense and quite irrespective of whether the measurement is translated into visible means or recorded. Rather, in the preferred operation, the measurement is transitory and i made by a suitable bridge circuit.

In some instances, the bridge circuit can be a simple Wheatstone bridge of the A. C. type, one arm of the bridge being a length of the resistance wire I2, preferably after it is wound on the core member 13. Such a simple system might involve two contacts, e. g., the contacts 35 and ii. However, difficulties are encountered with such a simple system because, first, irregularities in the resistance will tend to be reproduced cyclically in the ultimate winding and, second, because the control resistance will vary with variations in contact resistance. In this latter respect, particles of dust, etc., might lodge between one of the contacts and th resistance wire, thus destroying the desired control.

Any trouble with variations in contact resistance is minimized in the present invention by use of a circuit related to a Kelvin double bridge 95, shown in Fig. 3a as a part of a bridge circuit 93. In addition, however, we prefer to control the differential motor 59 in response to a weighted average of resistance. This can be accomplished by using the series of contacts H to 16, inclusive,

although the invention is not limited to the particular number of such contacts illustrated. In practice, even a larger number can be employed. The effect of the system to be described is to measure the resistance of the resistance wire [2 between contacts 36 and H, between contacts 36 and E2, the contacts 36 and 13, etc., these resistances being weighted to be of progressively less importance in controlling the diiferential motor 53. Thus, a minor change in size of the incoming resistance wire I2 will be immediately detected between contacts 36 and H. However, this defect will have progressively less effect on the resistances between

contacts

36 and 12, 36 and 73, 36 and M, etc. The use of multiple contacts H to it in the circuit arrangement to be described also eliminates contact resistance effects at these contacts. Further, if a particle of dust lodges between one of the contacts and the resistance element 33, it will not substantially interfere with the accuracy of the control as the first later contact will make good contact with the resistance Wire and maintain the control.

Referring now to the bridge circuit 96 of Fig. 3a, the Kelvin-bridge arrangement includes a resistor 91 connected to the initial contact 36 and also to a potentiometer winding 98 and a fixed resistor 99 connected in series, the resistor 99 being connected by a conductor 99a to the contact 31. The potentiometer winding 98 has an ad justable arm I connected to the primary winding of an output transformer I M. The resistance of the resistor 91 and that portion of the potentiometer winding to the left of the-arm I00 is designated as R1. Similarly, the resistance of the resistor 99- and that portion of the potentiometer winding to theright of the arm I00 is designated as R2.

The contact 31 is connected, through fixed and variable resistors I02 and I03 (total resistance being indicated by Rs), to-a secondary winding I04 of an input or power transformer through a conductor I05. The primary winding of this transformer may be connected to a 110 volt A. C. supply circuit. The remaining terminal of the secondary winding I04 is grounded as indicated at I06 and electrically connected to the auxiliary contact 16. Acros the auxiliary contacts 11 andresistor IIO is-connected across contacts 13 and 14; a resistor III- across the contacts 14 and 15; and a resistor II2' across contacts 15 and 16-.

If the auxiliary contacts 1| to 16' are equally spaced along the resistance element 33, the resistors I01, I69, IIO, III, and H2 are of equal value and, if appropriately valued with respect to the resistance I08, no current will flow through the leads connected with the respective contacts, in case the resistance per unit length of element 33 is uniform, thereby eliminating contact resistance effects; If d is the distance between each pair of auxiliary contacts 1! to 16 and e is the distance between contacts 36 and H and R108 is the electrical resistance of resistance I09, the resistance of each of the resistors I01, I09, etc., should equal a resistor II8 having a value designated as R4- and connected between the primary of the output transformer IN and the conductor I05. Roughly speaking, the entire bridge circuit 96 may be visualized a having one leg consisting of the resistors I01I I2- (total resistance R) a second leg, joined with the first and comprising a resistance Rs, representing the total resistance of the resistance element 33 between contacts 36 and 16; a third leg including the resistor H3 having a resistance R4 and a fourth leg including the Kelvin-bridge arrangement 95. (including R1 and R2), together with R3; The bridge is in balance if the following equation i fulfilled:

any source of voltage canbe interposed in conductor 99a. and the bridge will stay in balance. The Kelvin-bridge arrangement thus compensates for the IR drop or contact resistance at contact 31 so that this contact resistance has no effect on thebridge, particularly if R5 is large relative to such contact resistance.

As the bridge circuit 96 is energized by alternating current, there may be capacity effects betweenthe resistance wire I2 and the core member I3 which may be troublesome by' reason of production of out-of-phase currents. Also, if the coated resistance element 33 is heated, thecoating becomes somewhat conducting and it is desirable to. eliminate any potential difference between the core member I3 andthe resistance wire I2. To eliminate any troublesome effects from such sources, We prefer, first, to ground the slip ring I9 connected to the core member I3, as suggested at H9 in Fig. 3a and, second, to connect a variable condenser I20 across serially-connected resistors I02, I03. This condenser can beused to correct any out-of-phase condition. serves to-prevent overloading of the amplifier. to be later described, by maintaining the bridge in approximate reactive balance in addition to the self-maintained resistive balance.

Any unbalance in the bridge circuit 96 is. represented by an alternating potential across the output transformer II. can be employed for. translating the electrical output variations into appropriate speed. variations of the difierential motor 50. As shown, the secondary winding of the outputtransformer' IN.

is connected by leads IM and I22 to the input.

of an amplifier I23, which may be of conventional design employing two electron tubes I25. and I26, respectively of the triple-grid and triode types. The circuit connections shown will. be found suitable but are not. described in detail as they will be apparent to those skilled in the art and asother voltage amplifiers can be employed.

The output from the amplifier I23 is fed to an input transformer I29 of a synchronous rectifier I 3:) of well-known design energized by a transformer I31 connected to. a l10-volt A. C. source. This synchronous rectifier is shown as employing two twin diode tubes I32 and I33'connected in" a bridge rectifier circuit to the secondary It func-- windings of transformers I29 and- I3I. tions'to convert the A. C. output from the amplifier intoa pulsating D. C. potential having a polarity determined by the phase relationship between the amplifier output (which changes with unbalance of the bridge circuit 96 and propor tional to the degree of unbalance.

The-output from the'filter I35 is shown as fed to the input of a motor control circuit I40, not

perse a part of the present invention, and shown It also.

Any suitable means.

If desired, this directional pulsating as including a D. C'. amplifier section MI employing a triple-grid tube I43 and a power amplifier tube I44 connected as a two-stage amplifier substantially as shown. A variable resistor M6 provides an adjustable bias control for the tube I43. Power transformer I55, rectifier tubes l52 and IE3, condensers l! and I53 and inductance I59 constitute a conventional power supply for the entire amplifier. The diiferential motor 56 is of the D. C. type and is connected between the center tap of one of the secondary windings of the transformer I55 and the cathode of the tube With such a system, it is desirable that the difierential motor 58 run at a normal speed (e. g., about 300 R. P. M.) if the bridge circuit 56 is in balance and there is no signal to the synchronous rectifier I38. An unbalance of the bridge circuit in one direction will then increase the speed of the differential motor 5:? to change the rate of advancement of the resistance element 33, while an unbalance in the other direction will decrease the motor speed. The preferred arrangement is such that the motor speed is never reduced to zero during the normal control. In fact, it is usually desirable to adjust the system so that accidental stoppage of the differential motor 59 will cause the resistance wire to be wound in compact turns on the core member 53, thus preventing any overlap or pi ing up of turns should stoppage of the motor 56 occur. The bias control, effected by the variable resistor M6, is adjusted to give the normal speed of the motor 59 when no signal is being impressed on filter 135. Thereafter, the incoming signal, as determined by the unbalance of the bridge, will further vary the bias of the tube I43 and thus the speed of the difierential motor 50.

It should be clear that quite dissimilar control circuits can be used for varying the speed of the differential motor 50 in response to bridge unbalance. It should be clear also that other types of differentials 45 may be used, and that the motor 5!! may be made reversible to efiect the desired control. Also, even with substan tially the same system as illustrated, it should be clear that, instead of operating normally with the bridge circuit 95 balanced, this bridge circuit could be set in an unbalanced condition and that the system could be used. to develop a D. C. bias applied to the motor 50 for desired speed control thereof.

Various changes and modifications can be made without departing from the spirit of the invention as defined in the appended claims.

We claim as our invention:

1. A method of winding a resistance wire about a core member to form a resistance element of accurately controlled resistance per unit of length, which method includes the steps of: winding said resistance wire in turns around said core member to produce the resistance element; continuously measuring the resistance of a section of said resistance wire of fixed and constant length during the winding thereof; and smoothly and continuously varying the spacing of said turns with changes in said measured resistance to produce said resistance element of accurately controlled resistance per unit of length.

2. A method of winding a resistance wire about a core member to form a resistance element of constant resistance per unit of length, which method includes the steps of winding said resistance wire in turns around said core member to produce the resistance element; measuring the resistance of an already-wound section of said resistance element of fixed and constant length, said section having one terminus near the position where said resistance wire is first wound around said core member and another terminus at a fixed position along the already-wound resistance element; and smoothly and continuously varying the spacing of said turns with changes in said measured resistance to produce said resistance element of constant resistance per unit of length.

3. A method of winding a resistance wire about a core member to form a resistance element of accurately controlled resistance per unit of length, which method includes the steps of: winding said resistance wire in turns around said core member at a winding station to produce the resistance element; sending an electric current through a section of said resistance wire of constant length, said section having one terminus near the winding station and another terminus at a fixed position along an already wound portion of said resistance element to produce a voltage drop across said section; and varying the angle of feed of said resistance wire to said core member at said winding station in relation to changes in said voltage drop to produce said resistance element of accurately controlled resistance per unit of length.

4. A method of winding a resistance wire about a core member to form a resistance element of accurately controlled resistance per unit of length, which method includes the steps of: longitudinally and non-rotatably advancing said core member through a winding station; winding said resistance wire around the advancing core member at said winding station to produce turns having a pitch determined by the rate of advancement of said core member; measuring the electrical resistance of a constantlychanging section of the resistance wire, said section being of constant length; and varying the rate of longitudinal advancement of said core member in relation to changes in said measured resistance of said resistance wire to produce a resistance element having an accurately controlled resistance per unit of length.

5. In a machine for winding a resistance wire in turns around a core member to form a resistance element of accurately controlled resistance per unit of length, the combination of: means for longitudinally advancing said core member relative to a winding station; means at said winding station for winding said resistance wire about said advancing core member in spaced turns to produce the resistance element; means for measuring the resistance of a constant-length section of said resistance wire, a portion of said constant-length section being a wound wire portion and another portion of said section being an unwound wire portion; operating means connected to said longitudinally advancing means for changing the rate of advancement of said core member relative to the rate of winding of said resistance wire therearound; and means for controlling said operating means in response to changes in resistance of said section to produce said resistance element of accurately controlled resistance per unit of length.

6. In a machine for winding a resistance wire in spaced turns about a core member advancing relative to a winding station to form aresistance element of accurately controlled resistance per 11 :unit of length, the combination of operating means forchanging the rate of advancement of said core member relative to said winding station to change thespacing of said turns; a pair of contacts; means for mounting said contacts at spaced positions for relative movement between said resistance wire and each contact during electrical contact between said resistance wire and each of the contacts, one of said contacts engaging a relatively moving and yet-unwound portion of said wire adjacent said winding station and the other of said contacts engaging a relatively moving and already-wound portion of said wire, the contacts being bridged by a constantly-changing predetermined-length section of the resistance wire; a bridge circuit connected to said contacts and responsive to a change in electrical resistance of the contact-bridging section of resistance wire to produce an electrical output varying with changes in such resistance of said contact-bridging section; and means receiving the output of said bridge circuit and operatively connected to said operating means to control same'in response to changes in such resistance to produce said resistance element of accurately controlled resistance per unit of length.

7. In a machine for winding a resistance Wire in spaced turns about a core member advancing through a winding station to form a resistance element of accurately controlled resistance per unit of length, the combination of operating means including means for changing the rate of advancement of said core member relative to said Winding station to change the spacing of said turns; a first contact engaging said resistance wire adjacent said Winding station; a second contact and means for mounting same to progressively engage sequential sections of alreadywound resistance wire of the resistance element at a position beyond said winding station and while said operating means is advancing said resistance element past said second contact; means for establishing a potential difference between said contacts to send current through the intervening section of resistance wire to produce a voltage drop between said contacts determined by the resistance of said intervening section; and electrical means operatively connecting said lastnamed means and said means for changing the rate of advancement of said core member to control the latter in response to changes in said voltage drop to vary the spacing of said turns and produce said resistance element of accurately controlled resistance per unit of length.

8. In a machine for winding a resistance wire in spaced turns about a core member advancing through a winding station to form a resistance element of accurately controlled resistance per unit of length, the combination of a difierential and means for connecting same to change the rate of advancement of said core member relative to said winding station to change the spacing of said turns; a first contact engaging said resistance wire adjacent said winding station; a second contact engaging the already-wound resistance wire of the resistance element at a position beyond said winding station as the resistance element moves past said second contact; a bridge circuit connected to said contacts to send an electrical current through the section of resistance wire that is transiently between said contacts in bridging relationship therewith, said bridge circuit including means for producing an electrical output varying with the electrical resistance of said intervening section; and means receiving the trical output to produce a resistance element electrical output of saidbridge circuit and operatively connected to said differential for varying the spacing of said turns to produce a resistance element of accurately controlled resistance per unit of length, said bridge circuit including means for compensating for contact resistance between at least one of said contacts and said resistance Wire.

9. In a machine .for winding a resistance wire in spaced turns about a core member to form a resistance element of accurately controlled resistance per unit of length, the combination of: advancing means for relatively moving said core member and a winding station; means at said winding station for winding said resistance wire about said advancing core member in spaced turns; means for measuring the electrical resistance of a section of said resistance wire of fixed length, said measuring means including a first contact slidably engaging said resistance wire at a position adjacent said winding station and a second contact slidably engaging said resistance wire at a position removed from said winding station and means for mounting said first andsecond contacts a fixed distance from each other; a differential controlling said advancing means; and means operatively connecting said differential and said measuring means to change the spacing of said turns and produce a resistance element of accurately controlled resistance per unit of length.

10. In a machine for winding a resistance wire in spaced turns about a core member advancing relative to a winding station to form a resistance element of accurately controlled resistance per unit of length, the combination of: operating means for changing the rate of advancement of said core member relative to said winding station to change the spacing of said turns; an initial contact engaging said resistance wire adjacent said winding station; a plurality of auxiliary contacts engaging the resistance wire of said resistance element at spaced positions beyond said winding station; a plurality of resistors respectively connected across adjacent pairs of said auxiliary contacts and connected in series with each other; a bridge circuit including as one leg the serially connected resistors and as another leg that section of said resistance wire between said initial contact and the auxiliary contact farthest removed from said winding station, said bridge producing an electrical output varying with changes in resistance of said resistance wire; and means receiving said electrical output and operatively connected to said operating means for controlling the spacing of said turns in response to changes in said elecof accurately controlled resistance per unit of length.

11. A combination as defined in claim 6 in which said core member provides a surface of insulating material and said resistance wire is bare when wound thereon, including means for selectively coating a side portion of the resistance element with an adhesive liquid to secure the spaced turns to the core member and to leave uncoated a face of said resistance element.

12. A combination as defined in claim 6, including means for applying selectively to opposite sides of said resistance element a coating of adhesive to secure the turns to the core member and leave exposed and uncoated a face of said resistance element, and including means for bending the resulting resistance element to form 13 a Winding having inner and outer peripheries, the exposed face of said resistance element being disposed at one of said peripheries.

13. In a potentiometer winder having a winding form rotator and a wire traverser, a differential for varying the speed relationship between the winding form rotator and the wire traverser, and means responsive to resistance error for overdriving the differential, said lastnamed means including resistance-measuring means for measuring the resistance of a constant-length section of said wire to determine such resistance error, said resistance-measuring means including first and second contacts engaging said wire at constantly-spaced positions therealong, there being continual relative advancement of said wire past each of said contacts, said first contact being at a position to engage said wire adjacent the position of winding thereof, said second contact being at a position to engage an already-wound portion of said wire, the position of said second contact being removed from the position of winding.

14. In a potentiometer winder having a winding form support, Wire feeding means, mechanism for relatively rotating the winding form support with respect to the wire feeding means, and means for traversing one of said elements with respect to the other, a diiierential for varying the speed relationship between the rotating means and the traversing means, and means responsive to resistance error for cverdriving the diiferential, said last-named means including a first contact engaging the wire adjacent the position it is wound, such last-named means including also a second contact and means for mounting said second contact to sequentially engage already-wound portions of said wire as they move past the second contact.

15. In a machine for winding a resistance wire in spaced turns about an electrically-conductive core member advancing relative to a winding station to form a resistance element of accurately controlled resistance per unit of length, said resistance element being insulated from the core member, the combination of: operating means for changing the rate of advancement of said core member relative to said winding station to change the spacing of said turns; a pair of contacts electrically contacting said resistance wire at spaced positions; means electrically connected to said core member for maintaining same at the potential of one of said contacts; a bridge circuit connected to said contacts and responsive to a change in electrical resistance of the intervening section of resistance wire to produce an electrical output varying with changes in such resistance; and means receiving the output of said bridge circuit and operatively connecting to said operating means to control same in response to changes in such resistance to produce said resistance element of accurately controlled resistance per unit of length.

16. In a machine for winding a resistance wire from a wire-feeding means at a winding station to a core member during relative rotation between said core member and said wire-feeding means and during relative longitudinal movement between said core member and said winding station to wind said wire on said core in spaced turns and form a resistance element of accurately controlled resistance in difierent sections thereof, the combination of operating means for relatively changing such rotation and such longitudinal movement to change the spacings of the turns of resistance wire as the latter is wound on said core member from said wire-feeding means; first and second contact means respectively electrically connected to wound. and yetunwound portions of said resistance wire to provide a section of the resistance wire electrically between said contact means, one of said contact means comprising a plurality of spaced contacts engaging said resistance wire at spaced positions during relative movement between such resistance wire and each of said spaced contacts, the other of said contact means being a main contact; a plurality of impedances respectively connected across adjacent pairs of said spaced contacts and in series with each other; a bridge circuit including as one leg the seriallyconnected impedances and as another leg that test section of said resistance wire between said main contact and that one of said spaced contacts farthest removed from said winding station, said bridge producing an electrical output varying with changes in a weighted average of the resistance of the resistance wire comprising said test section; and a control device receiving said electrical output and operatively connected to said operating means for controlling the spacing of said turns in response to changes in said electrical output.

HENRY H. CARY. ROLAND C. HAWES. MICHAEL E. STICKNEY. KENYON P. GEORGE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,627,188 Lightfoot May 3, 1927 1,627,213 Stone May 3, 1927 1,782,397 Adams Nov. 25, 1930 2,334,880 Marlow Nov. 23, 1943 2,466,227 Gilman et a1 Apr. 5, 1949 2,468,144 Van Alen Apr. 26, 1949