US3224691A

US3224691A - Method and apparatus for winding spiral resistance elements

Info

Publication number: US3224691A
Application number: US105353A
Authority: US
Inventors: Oram John Anderson
Original assignee: RELIANCE Manufacturing Co SOUTHWARK
Current assignee: RELIANCE MANUFACTURING Co (SOUTHWARK) Ltd; RELIANCE Manufacturing Co SOUTHWARK
Priority date: 1960-05-03
Filing date: 1961-04-25
Publication date: 1965-12-21
Anticipated expiration: 1982-12-21
Also published as: FR1288482A; GB975132A; DE1188178B

Description

J- A. ORAM Dec. 21, 1965 METHOD AND APPARATUS FOR WINDING SPIRAL RESISTANCE ELEMENTS 6 Sheets-Sheet 1 Filed April 25, 1961 A Trek/v55" J. A. ORAM Dec.21, 1965 METHOD AND APPARATUS FOR WINDING SPIRAL RESISTANCE ELEMENTS 6 Sheets-Sheet 2 Filed April 25, 1961 R 9 S SQStiIEEZI Dec. 21, 1965 J. A. ORAM 3,224,691

METHOD AND APPARATUS FOR WINDING SPIRAL RESISTANCE ELEMENTS Filed April 25, 1961 6 Sheets-Sheet 5 //V VE/V TOR Dec. 21, 1965 QRAM 3,224,691

METHOD AND APPARATUS FOR WINDING SPIRAL RESISTANCE ELEMENTS Filed April 25. 1961 6 Sheets-Sheet 4:

ATTORNEY) Dec. 21, 1965 J. A. ORAM 3,224,691

METHOD AND APPARATUS FOR WINDING SPIRAL RESISTANCE ELEMENTS Filed April 25. 1961 6 Sheets-Sheet 5 v //\/l ENTOR 5 y /7 mm, m c ,ZZEJV A TTORNEYS J. A. ORAM Dec. 21, 1965 METHOD AND APPARATUS FOR WINDING SPIRAL RESISTANCE ELEMENTS Filed April 25, 1961 6 Sheets-Sheet 6 lNl ENTOR ATTORNEYS United States Patent 3,224,691 METHOD AND APPARATUS FOR WINDENG SPIRAL RESISTANCE ELEMENTS .llohn Anderson Dram, Leighton Buzzard, England, assignor to Reliance Manufacturing Company (Southwarlt) Limited, London, England, a British company Filed Apr. 25, 1961, Ser. No. 105,353 Claims priority, application Great Britain, May 3, 1960, 15,654/60 17 (Ilaims. (Cl. 242-9) The present invention relates to machine-s for winding spiral resistance elements, that is resistance elements which have an elongated core of insulating material which carries a winding of resistance wire and is itself wound into a spiral.

Such resistance elements can be used in variable resistance devices such as otentiometers. For example, a spiral resistance element can be formed in which an elongated, fiexible member of insulating material has resistance wire wound around it along its length and the flexible member carrying the winding of resistance wire is in turn wound into a flat spiral of say ten convolutions. In using such an element to manufacture, for example, a potentiometer, connections are made to the two ends of the resistance wire and a wiper is caused to follow a track along the spiral while making contact with the resistance wire.

For some purposes, such as in analogue computers, the law relating angular movement of the spindle which causes the wiper to traverse the spiral, and change of resistance between the wiper and one end of the resistance element is required to be rectilinear to a high degree of accuracy, and it is one object of the present invention to provide an improved machine for winding a spiral resistance element whereby the attainment of such a law is facilitated.

According to the present invention, a machine for winding a spiral resistance element comprises a coiling head for coiling an elongated flexible, insulating core into a spiral, a guide adapted to guide the elongated core through a winding head to the coiling head and having an outlet mouth adjacent the coiling head, the winding head being adapted to wind wire about the core as it passes from the outlet mouth of the guide to the coiling head, and means for moving the guide and winding head in dependence upon the progressive increase in the diameter of the spiral in such a manner that the mouth of the guide moves substantially along a line radial of the centre of the spiral and that the length of core tangential to the spiral and extending to the mouth of the guide subtends a substantially constant angle at the centre of the spiral. Thus if it is arranged that the coiling head and the Winding head rotate at constant speeds, as the diameter of the spiral progressively increases the linear speed of the elongated core passing through the mouth of the guide also increases. In this way the pitch of the turns in the wire winding automatically increases in such a way that the resistance of the wire per unit of are around the spiral is constant throughout all convolutions of the spiral. On the other hand the relative speeds of the coiling head and winding head can be varied to give any desired law relating change of resistance around the convolutions of the spiral. By means of a machine according to the invention it has been found possible automatically to manufactur a spiral resistance element for a potentiometer having a linear law which is accurate to within 0.1 percent.

The invention will now be described by way of example with reference to the accompanying drawings, in which:

FIG. 1 is a front elevation of a machine for winding a spiral resistance element,

FIG. 2 is a plan, partly cut away, of the machine shown in FIG. 1,

FIG. 3 is a rear elevation of the machine shown in FIG. 1,

FIG. 4 shows a part of FIG. 1 to an enlarged scale,

FIG. 5 is a cross-section taken along the line '55 of FIG. 4,

FIG. 5a shows a detail of FIG. 1 to an enlarged scale, and

FIG. 6 shows a part of FIG. 4 to a further enlarged scale at the end of a winding operation.

In the drawings a machine for winding a spiral resistance element comprises a main frame 10 which carries a driving motor 11 coupled by a driving belt 12 to a pulley 13.

The pulley 13 is directly-coupled to an infinitely-variable speed gear followed by a reduction gear of fixed ratio all shown within a housing 14.

The output shaft of the reduction gear is shown at 15 and has a helical groove 16 formed therein. A helical gear wheel 17 has a peg 18 which engages in the groove 16 whereby the gear wheel 17 can be driven by the shaft 15.

The helical gear wheel 17 engages with the teeth of a large gear wheel 19 carried by a shaft 20 journalled in the main frame 10.

At the end of the shaft 20 remote from the large gear wheel 19 there is a coiling head 21 consisting of an eX- tension of the shaft 20 of a size suitable to receive the insulating boss 22 (shown clearly in FIGS. 4, 5 and 6) on to which a spiral resistance element is to be wound.

Mounted at the top of the main frame 10 is a spool 23 of insulating ribbon from which the ribbon 24 passes over a pressure roller 25, a magnetic clutch 26, and

idler rollers

27, 28 and 29 on to the boss 22. The

rollers

28 and 29 are mounted on spindles supported between two

parallel arms

30 and 31 which are pivoted on the main frame 10 at their ends remote from the coiling head 21.

A rail device 32 fixed to the front of the main frame supports a carriage 33 carrying a subsidiary frame 34. The carriage 33 can slide horizontally along the rail device as indicated by the arrow 35 and is urged to the left in FIG. 1 by a tension spring 36.

The subsidiary frame 34 consists of two plates 37 and 3S suitably braced at 39, and separated by the member 40 so as to be held rigidly parallel to one another.

A tubular guide 41 is mounted on the member 4d at an angle of to the vertical as shown and its upper end of frusto-conical shape adjacent the coiling head 21 has a mouth 42 (FIG. 4) formed therein. A further reel 43 of insulating ribbon 44 is mounted on the front of the main frame and the ribbon 44- passes through the guide 41 and the mouth 42 of the guide on to the coiling head 21.

Mounted for rotation about the guide 41 is a Winding head 45 which has a spool 46 of resistance wire 47 and a guide pulley 48 supported on a supporting arm 49.

The winding head 45 is rotated by a driving shaft 50 through gear wheels 51 and 52 and the shaft 50 which is provided with universal joints at 53 and 54 is also telescopic whereby movement of the subsidiary frame in the horizontal direction can be accommodated.

The upper end of the shaft 50 is coupled through

bevel gears

55 and 56 to a clutch (not shown) inside the pulley 13. The clutch is controlled by a lever 57 and solenoid 58 as will be described later.

A revolution counter 59 is coupled to the lower end of the shaft 5t through universal joints 60 and 61 whereby the number of revolutions of the winding head can be counted.

The left-hand ends (in FIG. 1) of the upper arms of the

plates

37 and 38 of the subsidiary frame 34 are inclined at an angle of as shown and form abutment surfaces for a roller 62 carried by the

pivoted arms

30 and 31. Pivoting of the

arms

30 and 31 in the direction of the arrow 63 causes the subsidiary frame 34 to move horizontally to the right as indicate-d by the arrow 35.

As shown in FIGS. 2 and 3 the helical gear wheel 17 is coupled to a vertical arm 64 which is pivotally mounted at its upper end to two

further arms

65 and 66. These in turn are pivotally mounted on the main frame.

The coupling between the gear wheel 17 and the arm 64 is of any suitable kind which will permit the gear wheel 17 to rotate whilst permitting the arm 64 to move the gear wheel axially by rotation of the arm about the pivots at is upper end.

The lower end of the arm 64 carries a small pulley 67 which is urged by means of a spring (not shown) into engagement with the edge 68 of a cam 69 mounted for horizontal sliding movement to the left and right as viewed in FIG. 2. A slide 70 supports the cam 69 and is pivotally mounted at 71 to enable a rack 72 for moving the cam 69 to be engaged with a pinion 73 at will, the pinion 73 being driven by a chain and

sprocket drive

74, 75 and 76 from the shaft 20. In order to move the slide 70 and hence engage or disengage the pinion 73 and rack 72 a vertical lever 77 is provided. When the lever is down the rack and pinion are in engagement and when the lever 77 is up the rack and pinion are out of engagement. A spring 78 urges the upper end of the lever 77 (FIG. 3) to the left and a latch 79 engages with a top plate 80 (FIG. 2) to hold the rack and pinion out of engagement.

In operation for winding a spiral resistance element the machine functions as follows:

Referring to FIG. 4 this shows in the full-line position of the elements the start of a winding operation.

The ribbon 24 is fed around the

rollers

28 and 29 and affixed to the boss 22 on which the resistance element is to be wound. With the clutch in the pulley 13 disengaged so that the shaft 50 is stationary the motor 11 is switched on to rotate the coiling head 21 through a single revolution whereby one turn (360) of the ribbon 24 is wound on the core 22. At this stage the ribbon 44 is fed through the guide 41 and the mouth 42 and into the spiral where it becomes trapped between the layers of ribbon 24. When 180 of ribbon 44 is on the spiral the motor is stopped. The free end of the resistance wire 47 on the reel 46 is fed over the guide pulley 48 and anchored to the coiling head 21 by means of a clip 82 (FIG. 5) carried by the coiling head. The clutch in the pulley 13 is then engaged by energization of the solenoid 58 and the machine is ready to start winding.

It will be assumed initially that the rack 72 and pinion 73 are disengaged. The motor 11 is switched on whereby the ceiling head is rotated and progressively winds a double spiral of the two

ribbons

24 and 44. At the same time the winding head 45 is rotated by the shaft 50 and the wire 47 is wound around the ribbon 44 in a single layer winding, the conical end of the ribbonguide 41 providing a smooth surface over which the wire 47 can slide. Thus winding takes place around the ribbon 44 immediately after it leaves the mouth 42.

As the diameter of the spiral progressively increases the roller 29 bearing on the spiral causes the

arms

34 and 31 to be pivoted in the direction of the arrow 63. The roller 62 hearing against the 45 abutments on the

plates

37 and 38 of the subsidiary frame causes the sub sidiary frame to move horizontally in the direction of the arrow 35 as shown by the dotted line position in FIG. 4. The mouth 42 of the guide 41 lies in a horizontal plane containing the axis of the coiling head and hence of the spiral and, as the subsidiary frame 34 carrying the guide 41 moves horizontally, the mouth 42 likewise moves horizontally and hence it moves along a line radial of the centre of the spiral.

As the angle through which the

arms

30 and 31 rotate is small the movement of the roller 29 and hence the roller 63 can be regarded as rectilinear from a practical point of view and the direction of this movement is at 45 to the horizontal. In this way the angle of the ribbon 44 extending from the mouth 42 to the spiral being wound is always at 45 to the horizontal whereby the angle subtended by this length of ribbon at the axis of the spiral is always 45 likewise.

Thus as the diameter of the spiral increases and hence its peripheral speed increases, the linear speed of the ribbon passing through the mouth 42 of the guide 41 likewise increases and the spacing of the turns of wire 47 wound around the ribbon 44 also increases. With the arrangement shown and described the increase in spacing of the turns of resistance wire is such that the resistance per unit are taken around the axis of the spiral is constant throughout all convolutions of the spiral to a high degree of accuracy. It is assumed that the resistance per unit length of the wire 47 is constant.

FIG. 4 shows in full-lines the starting conditions for winding and in broken lines the conditions when winding is completed. The section shown in FIG. 5 corresponds to the condition when winding is completed. FIG. 1 shows the conditions when the spiral is half-wound and FIG. 6 shows to an enlarged scale a fully wound spiral of ten convolutions. The variation in the spacing of the turns of wire 47 to maintain a constant resistance per unit are can be seen in FIG. 6 from the variation in the spacing of the generally radially-extending lines 47 in the different convolutions.

Referring now to a number of details of construction, it is preferred to supply adhesive to both sides of the ribbon 24 which serves to insulate the convolutions of the spiral from one another. This is effected by providing a flow of adhesive through two

fine tubes

83 and 84, the former providing adhesive on the top of the ribbon 24 as it passes towards the roller 28 and the tube 84 providing adhesive on the other surface of the ribbon 24 as it passes around the boss 22 towards the ribbon 44. The adhesive also prevents movement of the turns 01 wire relative to one another and hence ensures insulation between the turns of wire.

The adhesive is contained in a container 85 and the tubes extend to near the bottom of the container. Air under pressure is supplied from a suitable source (not shown) into the container to cause flow of adhesive out through the

tubes

83 and 84. When winding is completed the flow of adhesive is arrested by opening the container to the atmosphere.

The function of the magnetic clutch 26 is to provide a progressively reducing tension in the ribbon 24 as the spiral grows. The clutch is of the iron dust type with an energising electromagnet. The pull of the clutch and hence the tension in the ribbon can be varied by varying the current through the electromagnet. Any suitable means (not shown) can be used to effect this as the spiral grows. For example a variable resistor in series with the energising electromagnet can be varied by the subsidiary frame 34 as it moves.

The cam 69 is brought into use when it is desired to vary the law relating resistance per unit length of are around the spiral. Axial movement of the helical gear wheel 17 causes rotation of the gear wheel 19. By use of the helical groove 16 and the peg 18 movement of the gear wheel 17 axially is accompanied by a rotational movement of the gear wheel 17 whereby the rotation of the gear wheel 19 is increased.

Thus as the cam 69 is driven horizontally during winding the arm 64 is moved through a small angle about its upper end causing the gear wheel 19 to be given an additional rotation which modifies the law relating resistance per unit are in the finished spiral element.

One application of this is to a potentiometer using the spiral resistance element, in which a wiper arm does not track exactly along a radius. By means of the cam 69 a correction can be made whereby despite the nonr-adial tracking of the wiper arm the relationship between change of resistance with angular rotation of the wiper spindle is constant.

To ensure that an exact whole number of convolutions are wound on the spiral a switch 86 (FIG. 3) is used to disengage the clutch in the pulley 13 and to switch off the motor 11. The motor and clutch are switched off when the switch 86 is opened by a cam 87 aifixed to the large gear wheel 19. It will be appreciated that as the cam 87 opens the switch 86 exactly at the end of each revolution of the gear wheel 19 and hence the coiling head 21 it is necessary to connect a further switch (not shown) in parallel with the switch 86 and to ensure that the further switch is not opened until the last convolution of the spiral has commenced and the cam 87 is clear of the switch contacts of the switch 86.

The further switch can be manually operable or it can be operated by the cam 69 or rack 72. The cam 87 is adjustable and has a scale 88 whereby the cam can be accurately set to zero before winding starts.

For some purposes it may be desired to wind a spiral resistance element identical with a master potentiometer. To achieve this the master potentiometer is so mounted at the rear of the machine as to have its wiper driven from the shaft 20. In addition connections are made to the wire at the inner end of the spiral to be wound and a contact is made with the wire as it leaves the reel 46. Thus a comparison can be made continually between the resistance of the master potentiometer and the spiral being wound.

. It is arranged that whenever a difference between the two appears a correction is applied to the spiral being wound. The correction can be achieved in any suitable manner to vary the relative speeds of the coiling head and the winding head.

For example, the infinitely-variable speed gear can be varied manually or by a servo. This is particularly useful if the wire 47 should prove to be constantly different from its rated resistance per unit length. For short term corrections it is preferred to modify the pivoting arrangement for the vertical arm 64 controlling the axial movement of the gear wheel 17. The

arms

65 and 66 instead of being pivoted on the main frame can be pivoted on a slide (not shown) which can slide parallel to the axis of the gear wheel 17. A servo following the comparison between the master potentiometer and the spiral being wound can actuate the slide for making short term corrections.

To control the motor 11, the solenoid 58, the adhesive supply, and the machine generally, a switchboard is provided with switches 89 (FIG. 2).

The reel 46 is provided with a brake to ensure that the reel cannot overrun during winding causing tangling of the wire 47. The brake (seen best in FIGS. 1 and 5(a)) comprises a brake shoe 9t) normally held in contact with the reel 46 by means of a spring 91. When win-ding commences the pull of the wire 47 on the pulley 48 is transmitted through the support 49 which has an arm 92. The arm 92 engages with a rod 93 carrying the brake shoe 90 and lifts off the brake shoe 90. The rod 93 is kept in engagement with the arm 92 by means of a further spring 94 tending to apply the brake. Any tendency for the reel 46 to overrun is counteracted by the release of pull on the support 48 allowing the spring 94 to apply the brake.

It is preferred to arrange that the ribbon 24 is wider than the ribbon 44 whereby in the finished resistance element the ribbon 24 interleaving the convolutions of the spirally-wound ribbon 44 stands proud and defines a channel which can act as a guide for a wiper as described in copen'ding patent application Serial No. 105,433, filed April 25, 1961, now Patent No. 3,156,890.

I claim:

1. A machine for winding a spiral resistance element,

comprising a coiling head for coiling an elongated flexible, insulating core into a spiral, a winding head, a guide adapted to guide the elongated core through the winding head to the coiling head and having an outlet mouth adjacent the coiling head, the winding head being adapted to wind wire about the core as it passes from the outlet mouth of the guide to the coiling head, and means for moving the guide and winding head in dependence upon the progressive increase in the diameter of the spiral in such a manner that the mouth of the guide moves substantially along a line radial of the centre of the spiral and that the portion of the core extending from the mouth of the guide to the spiral essentially tangential thereto subtends a substantially constant angle at the centre of the spiral.

2. A machine according to claim 1, wherein the means for moving the said guide and winding head in dependence upon the increase in the diameter of the spiral comprise a follower device coupled to the guide and winding head and bearing upon the peripheral surface of the spiral so as to be moved as the diameter of the spiral increases.

3. A machine according to claim 1, wherein said means for moving the guide and winding head includes a carriage mounted on a slide, and wherein the guide and the winding head are mounted upon the carriage, the carriage being capable of sliding on said slide along a straight path such that the mouth of the guide follows a line radial to the centre of the spiral.

4. A machine according to claim 3, wherein the carriage carries an abutment surface disposed at right-angles to the direction of movement of the means for moving the guide andwinding head and at right-angles to the axis of the spiral, and the arrangement is such that the direction of movement of the carriage on the slide is at 45 to the abutment surface and that the direction of the elongated insulating core extending from the mouth of the guide to the spiral is parallel to the abutment surface.

5. A machine according to claim 4, wherein means are provided for coiling a second insulating ribbon between the convolutions of the spiral.

6. A method of winding a spiral resistance element, comprising the steps of passing an elongated, flexible, insulating core through a guide coiling the core into a spiral of progressively increasing diameter after it has passed through the guide, and winding wire about the core as it passes from the guide to the spiral at a distance from the axis of the spiral fixedly proportional to the increasing diameter of the spiral at any instant during winding.

7. A method according to claim 6, wherein an insulating ribbon is coiled between the convolutions of the spiral.

8. A machine for winding a spiral resistance element, comprising a guide, a coiling head to draw an elongated, flexible, insulating core through the guide and to coil the core into a spiral, a winding head spaced from the coiling head to wind wire about the core as the core passes from the guide to the coiling head, a movable carriage, and means including a spacing device coupled to the winding head through said carriage to move the winding head so that winding takes place at a distance from the axis of the spiral fixedly proportional to the increasing diameter of the spiral at any instant during winding, the winding head being mounted on the carriage for transverse movement relative to said coiling head by means of said spacing device.

9. A machine according to claim 8 wherein said guide is mounted on the carriage and further comprising a slide upon which said carriage is mounted, the guide being hollow and having an outlet mouth from which the core passes to the coiling head, and the carriage being capable of sliding on said slide along a straight path such that the outlet mouth of the guide follows a line radial of the center of the spiral.

18. A machine according to claim 8, wherein the core is in the form of a ribbon.

11. A machine according to claim 10, wherein means are provided for coiling a second insulating ribbon between the convolutions of the spiral.

12. A machine according to claim 8, wherein the spacing device comprises a follower device coupled to the winding head and bearing upon the peripheral surface of the spiral so as to be moved as the diameter of the spiral increases.

13. A machine according to claim 12, wherein the follower device is a roller.

14. A machine according to claim 13, wherein the roller is mounted at one end of an arm which is pivotally mounted at its other end.

15. A machine according to claim 13, wherein said means to move the winding head includes a carriage on which the guide and the winding head are mounted and a slide upon which said carriage is mounted, the guide being hollow and having an outlet mouth from which the core passes to the coiling head, the carriage being capable of sliding on said slide along a straight path such that the outlet mouth of the guide moves along a line radial of the center of the spiral, an abutment surface on the carriage disposed at right angles to the direction of movement of the roller and parallel to the axis of the spiral, the direction of movement of the carriage being 45 to the abutment surface, and the core extending from the outlet mouth of the guide to the spiral in a direction parallel to the abutment surface.

16. A method of making a spiral-resistance element comprising simultaneously coiling both an elongated flexible insulating core and a flexible insulating ribbon into a double spiral by means of a rotatable coiling head, the convolutions of the ribbon interleaving the convolutions of the core and winding wire about the core as the core passes to the coiling head at a distance from the axis of the spiral formed by the core having a predetermined relation to the increasing diameter of the spiral formed by the core at any instant during winding and substantially along a rectilinear line radial of the center of the spiral formed by the core.

17. A machine for winding a spiral-resistance element comprising a coiling head capable of simultaneously coiling both an elongated flexible insulating core and a fiexible insulating ribbon into a spiral in a manner such that the convolutions of the core interleave the convolutions of the ribbon, a winding head capable of rotating about said core to wind wire about the core upon its passage to the coiling head, a movable carriage, and spacing means coupled to the winding head for moving the winding head as winding takes place at a distance from the axis of the spiral formed by the core having a predetermined relation to the increasing diameter of the spiral formed by the core at any instant during winding and substantially along a rectilinear line radial of the center of the spiral formed by the core, the winding head being mounted on the carriage for transverse movement relative to the coiling head by means of said spacing means.

References Cited by the Examiner UNITED STATES PATENTS 807,133 12/1905 Scott 242-9 1,674,527 6/1928 Shepherd 57-18 1,723,261 8/1929 Varley 242-10 1,855,876 4/1932 Barker 57-18 2,123,238 7/1938 Franz 242-10 2,462,191 2/1949 Hodnette 242-10 2,688,450 9/1954 Bell 242-10 2,936,516 5/1960 Adair 29-15568 MERVIN STEIN, Primary Examiner.

HARRISON R. MOSELEY, RUSSELL C. MADER,

Examiners.

Claims

6. A METHOD OF WINDING A SPIRAL RESISTANCE ELEMENT, COMPRISING THE STEPS OF PASSING AN ELONGATED, FLEXIBLE, INSULATING CORE THROUGH A GUIDE COILING THE CORE INTO A SPIRAL OF PROGRESSIVELY INCREASING DIAMETER AFTER IT HAS PASSED THROUGH THE GUIDE, AND WINDING WIRE ABOUT THE CORE AS IT PASSES FROM THE GUIDE TO THE SPIRAL AT A DISTANCE FROM THE AXIS OF THE SPIRAL FIXEDLY PROPORTIONAL TO THE INCREASING DIAMETER OF THE SPIRAL AT ANY INSTANT DURING WINDING.
8. A MACHINE FOR WINDING A SPIRAL RESISTANCE ELEMENT, COMPRISING A GUIDE, A COILING HEAD TO DRAW AN ELONGATED, FLEXIBLE, INSULATING CORE THROUGH THE GUIDE AND TO COIL THE CORE INTO A SPIRAL, A WINDING HEAD SPACED FROM THE COILING HEAD TO WIND WIRE ABOUT THE CORE AS THE CORE PASSES FROM THE GUIDE TO THE COILING HEAD, A MOVABLE CARRIAGE, AND MEANS INCLUDING A SPACING DEVICE COUPLED TO THE WINDING HEAD THROUGH SAID CARRIAGE TO MOVE THE WINDING HEAD SO THAT WINDING TAKES PLACE AT A DISTANCE FROM THE AXIS OF THE SPIRAL FIXEDLY PROPORTIONAL TO THE INCREASING DIAMETER OF THE SPIRAL AT ANY STANT DURING WINDING, THE WINDING HEAD BEING MOUNTED ON THE CARRIAGE FOR TRANSVERSE MOVEMENT RELATIVE TO SAID COILING HEAD BY MEANS OF SAID SPACING DEVICE.