US3076615A - Warp beam control for textile machines - Google Patents

Description

Feb. 5, 1963 R. L. couuon 33761615 mum comer. FOR TEZTIlE mmmms Filed March 17, 1961 Shawn-Sheet 1 INVEN TOR. /POBERTL Co/v/vo/es,

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Feb. 5, 1963 R. CONNORS 3,076,515

WARP BEAM con'mor. FOR TEXTILE MACHINES Filed March 17, 1961 3 Sheets-Sheet 3 flgggerl. Comm/Q5 Ari-claws vs 3,076,615 WARP BEAM CQNTROL FOR TEXTILE MACHXNES Robert L. Connors, Tonawanda, N.Y., assignor to Van Raalte Company, Inc, North 'lonawanda, NJY. Filed Mar. 17, 1961, Ser. No. 96,572 8 Claims. (Cl. 242-455) This invention relates to motion control means and particularly to combined tensioning and feed control means for continuous strands or strips of material such as in feeding warp threads to a textile machine.

The principles of the present invention will be discussed herein as the same may be embodied in driving and controlling the rotation of warp beams or Warp spools of tricot knitting machines to control the tension of the numerous warp threads passing from a warp beam or spool to the knitting mechanism, such threads being sometimes referred to collectively as the yarn sheet. As will appear from the following discussion of this particular adaptation of the principles of the present invention, the conditions under which warp thread feeding operations are accomplished present peculiar control problems which may be present to a greater or lesser extent in other textile machines and in other industrial filament, strand, strip or sheet feeding.

A primary consideration in warp knitting machines is the constant feeding of yarn from the warp beam to the knitting mechanism at a uniform speed and under constant tension despite the constantly changing beam diameter, as the yarn unwinds therefrom; the intermittent and uneven manner in which the knitting mechanism takes up the yarn in the knitting cycle; and other factors which tend to vary the relative speed of the warp beam and the tension of the yarn passing to the knitting mechanism.

In knitting machines generally and in tricot warp knitting machines particularly the knitting elements pull the yarn from the warp in an intermittent and somewhat erratic fashion. Considering a single stitch, the knitting motion involves pulling the yarn from the warp in about live or six intermittent increments during each stitch, and even these increments are not uniform so that the resultant oscillations are not of uniform amplitude.

A tension bar normally bears yieldably against the yarn sheet as it passes between the warp beam and the knitting mechanism and this tension bar, or its equivalent, thus oscillates rapidly since the yarn comes from the warp beam at a substantially continuous rate and is thus con sumed at the knitting mechanism by intermittent increments and at an irregular rate.

This oscillation, while it is of quite small amplitude, is of considerable frequency since it is perhaps five or six times the rpm. of the knitting machine which varies from about 400 to 1,000 r.-p.m. so that the tension bar may oscillate as fast as 6,000 times per minute. In Simplex machines there are two stitches per rotation of the cam shaft so that this frequency is perhaps twelve times cam shaft speed in such machines. Under ordinary circumstances this oscillation or vibration substantially complicates the problem of maintaining constant tension and uniform feeding speed but the system of the present invention utilizes the oscillation of the tension means to effect accurate speed control of the warp beam or spool.

Among other things, the manner in which the tension means oscillation is employed in the present system for controlling tension and producing a uniform warp feed speed is such as to substantially eliminate hunting and overshooting in the control adjustment means, which is a particularly vexatious problem in prior art warp beam speed control arrangements.

In warp knitting even more than in most other textile producing processes, tension control is of prime importance. Variations in yarn tension manifest themselves by Patented Feb. 5, 1963 variations in the kind and quality of cloth which is produced. These variations may appear as visible shade marks in the fabric and in any event manifest themselves in variations in runner length. This latter characteristic is well understood in the knitting industry and measures the number of inches of yarn consumed in making a given number of stitches.

Variations in runner length are so prevalent under present conditions in the knitting industry as to be accepted as a necessary evil. The accuracy and uniformity of yarn tension in employing the apparatus and methods of the present invention are such that runner length may be held so accurately as to require no attention from beginning to end of a warp beam. Furthermore, this constancy may be held to at various tension adjustments so that runner length may be initially selected by a predetermined tension adjustment and continuously uniform results will follow automatically.

Besides producing fabric of better quality, the present invention avoids wastage due to production of imperfect fabric and effects substantial savings in laborbecause of the considerable reduction in attention required with knitting machines employing the present warp beam and ension control. Also, maintenance costs are reduced which effects savings in labor costs.

Several embodiments of the principles of the present invention are illustrated in the accompanying drawings and described in detail in the following specification. However, it is to be understood that such embodiments are set forth by way of example and to illustrate the principles of the invention. The spirit and scope of the invention is not limited to the exemplary embodiments thus shown nor otherwise than as defined in the appended claims.

In the drawings:

FIG. 1 is a fragmentary side elevational view of portrons of a tricot knitting machine, illustrating one form of the waip feed and tensioning regulating means of the present invention in somewhat schematic form;

FIG. 2 is a fragmentary view of a portion of the structure of FIG. 1 on an enlarged scale, illustrating the contact adjusting means thereof:

FIG. 3 is a diagrammatic view of a modified form of the electrical portion of the control means of the present invention; and

FIG. 4 is a diagrammatic view .of a further modified form of such electrical portion.

PEG. 1 illustrates an embodiment of the present inventionin a simple rudimentary form which is satisfactory Within certain limitations or under certain conditions and aptly illustrates the basic principles of the invention. However, it is difficult and not entirely practical under all conditions to make and break circuits carrying large currents very rapidly, and accordingly the systems illustrated in FIGS. 2 and 3 are hi hly advantageous and may be successfully employed throughout a widely varying range of the various operating conditions and requirements.

eferring to FIG. 1, the numeral 10 designates a warp beam or warp spool of a tricot knitting machine. It will be understood by those skilled in the knitting machine art that two such warp beams are normally employed but an illustration of the manner in which the control means of the present invention operates in conjunction with one such Warp beam will sufiice, it being understood that the entire tensioning and speed control arrangement may be duplicated in connection with the other warp beam. Actually certain power supply components may be common to two warp beam control setups merely in the interests of economy and simplification.

The warp beam ll) is mounted upon a warp shaft 5.1 which is mechanically driven at a variable rate from the knitting machine proper, as for instance from the cam shaft 12 thereof. The latter carries a sprocket 13 which is connected to a sprocket 14 on a countershaft 15 by a driving chain 16. In FIG. 1 a variable speed transmission is designated 20 and its. input and output shafts are designated 21 and 22, respectively.

Output shaft 22 connects with a worm shaft 23 by means of a coupling 24 and a worm 25 on worm shaft 23 drives a worm wheel 26 on warp shaft 11. Thus the Warp beam is rotated from and with the cam shaft of the knitting machine but at a variable ratio determined by the speed setting of variable transmission 20. The worm drive to the warp shaft is inherently irreversible so that rotative moments of the warp shaft cannot be transmitted to the driving means.

In passing from warp beam 10 .to knitting mechanism indicated schematically at 30 in FIG. 1 the Warp threads or Warp sheet indicated at 31 pass beneath a snub rod 32 and then over a tension rod 33. As is known in the art, the knitting mechanism 30 draws yarn from the warp beam intermittently and this intermittent pull of the knitting mechanism against the warp yarn applies an intermittent tension to the warp yarn. Tension rod 33 may be resiliently mounted in various ways to apply a yieldable resilient tensioning force against the warp threads. In the illustrated instance the tension rod 33 is carried at one end of laterally spaced tension arms 35 which are fixed to a transversely extending tension arm pivot shaft 36.

The tension arms 35 are biased in a warp thread tensioning direction by compression coil springs 37 which act between extensions 38 of the tension arms and adjustable abutment means 39 on spring rods 40. As indicated above the tension arms 35 and pivot shaft 36 oscillate under the periodic intermittent yarn pulling action of the knitting mechanism. If the mean position of the arms and shaft can be maintained constant with a given, tension setting of abutment means 39, then uniform warp tension is. assured and this in turn reflects a warp beam drive which is delivering yarn at a speed synchronized with the speed of the knitting mechanism so that warp tension is rendered constant.

In the embodiment of FIG. 1 this synchronization and uniform tension are attained in the following manner. A contact arm 42 is fixed to tension arm pivot shaft 36 for oscillation therewith between a pair of resiliently mounted contacts 44 and 45. A small universal geared motor 46 has an output shaft 47 which drives the speed,

adjustment shaft of the variable transmission unit 20 in one direction or the other to adjust the speed setting of the latter.

The series windings of the motor 46 are indicated schematically in FIG. 1 wherein the armature thereof is designated 50 and the forward and reverse field'windings are designated 51 and 52. Winding 51 connects with contact 44 by means of a conductor 54 and winding 52 connects with contact 45 by means of a conductor 55. When a contact is closed, the circuit is from a supply conductor 56 to the contact arm 42, through one of the conductors 54 or 55 and its associated field winding 51 or 52, through armature-50 and back to a second supply conductor 57.

When the'warp beam drive is on speed and the yarn tension is correct for the particular setting of adjustable abutment 39 the contact arm will oscillate between the resilient contacts 44 and 45 and engage them for equal time periods, thus energizing the field coils 51 and 52 of adjusting motor 46 equally in opposite directions during each short cycle of oscillation of tension shaft 36. These rapidly successive opposing impulses cancel each other and motor 46 remains stationary.

If the mean position of tension arms 35 moves toward the tight side, that is, if the tension tends to increase, thus calling for an increase, in speed of rotation of the warp beam; to maintain the desired constant warp feed and constant tension, then the oscillation of the contact arm will be displaced so that it contacts the tight contact 45 for a longer period than it contacts the loose contact, during each oscillation.

The preponderance of contact engagement will be accurately proportionate to the degree of deviation of the tension rod 33 and this preponderance will produce greater torque impulses in field coil 52 than in field coil 51. This produces a relatively slow rotation of motor 46, output shaft 47, and the speed adjusting shaft of the variable speed transmission 26, to regulate the latter and step up the speed of the warp beam to compensate for the aforesaid deviation, whatever the reason for such deviation may be.

Means are preferably provided for adjusting the distance between the contacts 44 and 45 to suit various amplitudes of normal oscillation of the tension shaft 36 as may be encountered under different knitting conditions. Such means may be as illustrated on a slightly enlarged scale in FIG. 2 wherein the contacts 44 and 45 are pivoted as at 60 and 61 and have spring biasing arms 62 and 63 bearing against abutments 64- and 65 to bias the contactstoward each other but permit yieldable outward movement when the contacts of contact arm 42 bear thereagainst. An adjusting screw 67 has a cam or wedgev formation 68 which projects between the contacts 44 and 45 and determines their minimum spacing to suit a given set of operating conditions.

Reference will now be had to the embodiment shown schematically in FIG. 3 and it is to be understood that this embodiment varies from that of FIG. 1 only in the electrical means extending from the spaced contacts which are engaged by the contact arm designated 42 in FIG. 1 which lead ultimately to the field coils of the variable transmission adjusting motor 46. In the two embodiments illustrated in FIGS. 3 and 4 separate transducer means are utilized between the alternating contacts and the adjusting motor. In FIG. 3 the transducing means comprises a thyratron trigger circuit and in FIG. 4 the transducing means comprises a switching reactor control circuit.

In the embodiment of FIG. 3 the conductors from the contacts corresponding to the contacts 44 and 45 of FIG. 1, instead of leading directly to the adjusting motor field windings, trigger an opposed pair of thyratron tubes to produce the desired opposing energization of the adjusting motor field windings in the manner illustrated schematically in FIG. 3.

As is well known in the electronic art, in a thyratron tube the formation of an arc and hence the conduction of current from anode to cathode is prevented by the shielding action of the grid when a suflicient negative voltage is impressed on the grid. However, if the grid voltage is increased from such negative voltage to a less negative value or a low positive value, a critical grid'voltage is reached at which conduction will start (i. e. anode current starts) and the tube is said to fire, provided that the anode is positive.

The critical grid voltage at which trigger action begins depends on various factors such as the electrode geometry, anode voltage, and sometimes the temperature of the gas in the tube. However, once conduction starts the grid loses further control and output continues. However, with alternating current voltages conduction ceases during the negative half of the cycle so that the grid regains control of tube output once during each alternating current cycle.

In FIG. 3 the numerals 144 and 145 designate contacts corresponding to the loose and tight contacts 44 and 45 of the embodiment of FIG. 1 and are alternately closed in an identical manner to that described in the case of FIG. 1. The general circuitry of FIG. 3 will be understood by those skilled in the electronic arts and need not be described in detail.

In this embodiment the adjusting motor armature is designated and the field windings 151 and 152. The

. gized.

' Contacts 144- and 145 are connected to the grids of thyspcctivcly.

When a given contact 144 or 145 is open the negative grid voltage is greater than the critical grid voltage and the thyratron is thus prevented from firing. That is, the grid voltage is greater in a negative direct-ion. When one of the contacts closes, the resistors in series therewith at opposite sides of the grid connection act as voltage dividers and the grid voltage moves instantaneously in a positive direction and the thyratron fires.

A variable resistor 166 in series with the armature 15% of the correction motor serves as a motor speed control to set the rate of control thereof.

The remaining circuit elements shown in FIG. 3 are largely conventional in thyr-atron tube circuitry and are briefly as follows:

The resistors 170 through 173 are voltage dividers Whose values are selected so that when the contacts 144 'or 145 close the respective grid bias is such that the thyratron tube fires. The resistors 174 and 175 are merely protective grid resistors which limit the grid bias.

The numeral 180 designates a filament supply transformer for the thyratron tubes. The condensers 181 and 182 comprise bypass capacitors between the grids and cathodes of the thyratron tubes to protect against transient or surge voltages. The resistors 183 and 190 are isolation resistors and comprise part of the conventional grid bias voltage level circuit. Switch 184 is controlled by the main machine driving motor to energize the control circuitry of FIG. 3 when the machine is started up. The numeral 185 designates a grid bias supply transformer and the numerals 186 and 187 designate grid bias supply rectifiers. The numeral 183 designates a conventional filter capacitor. The numeral 1S9 designates a supply voltage transformer.

A still further control arrangement is shown schematieally in FIG. 4 and this embodiment involves a switching reactor control circuit. FIG. 4 shows contacts 244 and 245 which correspond, respectively, to the loose and tight contacts of the preceding embodiments, and forward and reverse field coils 251 and 252 of an adjustment motor likewise corresponding to that of the preceding embodiment, the armature thereof being designated 25s in FIG. 4. It is to be understood that in this as in the preceding embodiments the entire control circuit will be duplicated to control the other warp beam of a conventional knitting machine.

Referring to the field winding 25?. of H6. 4 and the manner in which the same is energized by closure of the contacts 244, a bridge arrangement 27d supplies direct current to two control windings 27d and 277, the arrangement being such that the windings are of opposite polarity. Winding 277 is in series with the tension arm contacts 244. Output windings 2% and 281 are arranged to provide full wave rectification and consequent full wave current to the The reverse field winding 252 is alternately energized and deenergized in a similar manner under the control of contacts 245 throu h a duplicate switching reactor control arrangement. Control windings 286 and 23-7 correspond, respectively, to control windings 27d and 277, and output windings 29h andiel correspond to the output windings 3% and 281, respectively. As in the preceding embodiment, a variable resistor 266 in series with the motor circuit 2%, 251, 252 serves as a speed control for the adjustment motor.

in FIG. 4 the numerals 2%? and 29d designate adiustable current limiting or control resistors and the numerals 7 97 through 3% designate rectifiers which convert the A.C. output of the magnetic amplifier gate windings to direct current for the motor field coils 251 and 252.

This switching reactor arrangement is particularly advanta eous since it involves no moving parts and is virtually impervious to vibration and shock. These features are important from the standpoint of minimum maintenance, long life, and the ability to mount the control directly on the knitting machine without concern due to the vibration of. the machine.

in certain modern knitting machines the conventional tension arms and pivot shaft arrangements are being replaced by spring plates which extend the full width of the machine. These plates are secured along one edge and have a curved surface at the opposite edge for engagement against the warp. Thus the flexure of this entire plate provides the spring tension against the warp threads. The control means of the present invention in its various forms is equally adaptable to warp tension members of this type.

Contacts corresponding to the contact arm 32 may be mounted at opposite faces of such a spring plate at a point outwardly of its fixed edge to cooperate with spaced tight and loose contacts in the same manner as decribed above.

I claim:

1. Control apparatus for continuous material being un wound from a reel and passing to intermittent take-up means including resilient means bearing against said material between said reel and said take-up means to maintain tension in said material and adapted to oscillate under the intermittent action of said take-up means, a pair of spaced electrical contacts, and means disposed between said contacts and movable with said tensioning means, the spacing of said contacts being substantially less than the normal amplitude of oscillation 013 said last mentioned means whereby the latter engages both of said contacts successively and alternately during each cycle of oscillation of said tensioning means, variable drive means for said reel and a reversible electric motor engaging the same to vary the ratio of said drive means in response to rotation of the motor in either direction, said contacts having opposed electrical connection with said motor whereby the direction and magnitude of energization of said motor is a substantially continuous resultant of the relative time periods of closure of said pair of contacts during each cycle of oscillation of said tensioning means.

2. Control apparatus for continuous material being unwound from a reel and passing to intermittent take-up means including means bearing against said material between said reel and said take-up means and adapted to oscillate under the intermittent action or" said take-up means, a pair of. spaced electrical contacts, and means disposed between said contacts and movable with said oscillating means, the spacing of said contacts being substantially less than the normal amplitude of oscillation of said last mentioned means whereby the latter engages both of said contacts successively and alternately during each cycle of oscillation of said oscillating means, variable drive means for said reel and a reversible electric motor engaging the same to vary the ratio of said drive means in response to rotation of the motor in either direction, said contacts having opposed electrical connection with said motor whereby the direction and magnitude of energization of said motor is a substantially continuous resultant of the relative time periods of closure of said pair of contacts during each cycle of oscillation of said oscillating means.

3. Control apparatus for continuous material being unwound from a reel and passing to intermittent take-up means including variable drive means for substantially continuously rotating said reel, resilient means bearing against said material between said reel and said take-up means to maintain tension in said material and adapted to oscillate under the intermittent action of said take-up means, a reversible electric motor engaging said variable drive means to vary the ratio thereof in response to rotation of the motor in either direction, a pair of normally open circuits for reversely energizing said motor, means comprising a pair of spaced abutments and means comprising an abutment disposed between the spaced abutments, one of said abutment means being movable with said tensioning means, the spacing of said spaced abutments being substantially less than the amplitude of oscillation of the movable abutment means whereby the abutment between the spaced abutments engages both of said spaced abutments successively and alternately during each cycle of oscillation of said tensioning means, said pair of normally open circuits being adapted to be closed successively and alternately by engagement of each of said spaced abutments with the abutment therebetween, at least one of said abutment means being resiliently yieldable whereby variations in tension of said material which displaces the center of oscillation of said tensioning means produces unequal abutment time periods with respect to said spaced abutments, said oscillations being relatively rapid whereby the direction and magnitude of energization of said motor is a resultant of the relative time periods of closure of said two pair of reverse circuits during each cycle of oscillation of said tensioning means.

4. Control apparatus for continuous material being unwound from a reel and passing to intermittent take-up means including variable drive means for substantially continuously rotating said reel, means bearing against said material between said reel and said take-up means and adapted to oscillate under the intermittent action of said take-up means, a reversible electric motor engaging said variable drive means to vary the ratio thereof in response to rotation of the motor in either direction, a pair of normally open circuits for reversely energizing said motor, means comprising a pair of spaced abutments and means comprising an abutment disposed between the spaced abutments, one of said abutment means being movable with said oscillating means, the spacing of said spaced abutments being substantially less than the amplitude of oscillation of the movable abutment means whereby the abutment between the spaced abutments engages both of said spaced abutments successively and alternately during each cycle of oscillation of said oscillating means, said pair of normally open circuits being adapted to be closed successively and alternately by engagement of each of said spaced abutments with the abutment therebetween, at least one of said abutment means being resiliently yieldable whereby variations in tension of said material which displaces the center of oscillation of said oscillating means produces unequal abutment time periods with respect to said spaced abutments, said oscillations being relatively rapid whereby the direction and magnitude of energization of said motor is a resultant of the relative time periods of closure of said pair of reverse circuits during each cycle of oscillation of said oscillating means.

5. In combination, reel means and intermittently operating material engaging means spaced therefrom, said material passing from one of said means to the other, yieldable means bearing against said material between said reel and said engaging means and adapted to oscillate under the intermittent action of said engaging means, a pair of spaced electrical contacts, and means disposed between said contacts and movable with said yieldable oscillating means, the spacing of said contacts being substantially less than the normal amplitude of oscillation of said last mentioned means whereby the latter engages both of said contacts successively and alternately during each cycle of oscillation of said yieldable oscillating means, variable drive means for said reel and a reversible electric motor engaging the same to vary the ratio of vsaid drive means in response to rotation of the motor variable drive means for substantially continuously rotating said reel, control apparatus comprising yieldable means bearing against said material between said reel and said engaging means and adapted to oscillate under the intermittent action of said engaging means, a reversible electric motor engaging said variable drive means to vary the ratio thereof in response to rotation of the motor in either direction, a pair of normally open circuits for reversely energizing said motor, means comprising a pair of spaced abutments and means comprising an abutment disposed between the spaced abutments, one of said abutment means being movable with said oscillating means, the spacing of. said spaced abutments being substantially less than the amplitude of oscillation of the movable-abutment means whereby the abutment between the spaced abutments engages both of said spaced abutments successively and alternately during each cycle of oscillation of said yieldabl oscillating means, said pair of normally open circuits being adapted to be closed successively and alternately by engagement of each of said spaced abutments with the abutment therebetween, at least one of said abutment means being resiliently yieldable whereby variations in tension of said material which displaces the center of oscillation of said yieldable oscillating means produces unequal abutment time periods with respect to said spaced abutments, said oscillations being relatively rapid whereby the direction and magnitude of, energization of said motor is a substantially continuous resultant of the relative time periods of closure of said two pair of reverse circuits during each cycle of oscillation of said yieldable oscillating means.

7. Control apparatus for continuous material being unwound from a reel and passing to intermittent take-up means including means bearing against said material between said reel and said take-up means and adapted to oscillate under the intermittent action of said take-up means, a pair of spaced electrical contacts, and means disposed between said contacts and movable with said oscillating means, the spacing of said contacts being substantially less than the normal amplitude of oscillation of said last mentioned means whereby the latter engages both of said contacts successively and alternately during each cycle of oscillation of said oscillating means, variable drive means for said reel and a reversible electric motor engaging the same to vary the ratio of said drive means in response to rotation of the motor in either direction, and transducer means acting between said contacts and said motor whereby the direction and magnitude of energization of said motor is a substantially continuous resultant of the relative time periods of closure of said pair of contacts during each cycle of oscillation of said oscillating means.

8. Control apparatus for continuous material being unwound from a reel and passing to intermittent take-up means including variable drive means for substantially continuously rotating said reel, means bearing against said material between said reel and said take-up-means and adapted to oscillate under the intermittent action of said take-up means, a reversible electric motor engaging said variable drive means to vary the ratio thereof in response to rotation of the motor in either direction, means comprisingta pair of spaced abutments and means comprising an abutment disposed between the spaced abutment-s, one of said abutment means being movable with said oscillating means, the spacing of said spaced abutments being substantially less than the amplitude of oscillation of the movable abutment means whereby the abutment between the spaced abutments engages both of said spaced abutments successively and alternately during each cycle of oscillation of said oscillating means, a pair of normally open circuits adapted to be closed successively and alternately by engagement of each of said spaced abutments with the abutment therebetween, at least one of said abutment means being resiliently yieldable whereby variations in tension of said material which displaces the center of oscillation of said oscillating means produces unequal abutment time periods with respect to said spaced abutments and consequent unequal time periods of energization of said pair of circuits, and

10 transducer means acting between said circuits and said motor whereby the direction and magnitude of energization of said motor is a resultant of the relative time periods of closure of said pair of circuits during each cycle of oscillation of said oscillating means.

References Cited in the file of this patent UNITED STATES PATENTS 2,664,724 Lambach et a1 Jan. 5, 1954 2,719,419 Fleckenstein Oct. 4, 1955 2,720,093 Lambach et al Oct. 11, 1955 2,734,253 Suggs Feb. 14, 1956 FOREIGN PATENTS 844,453 Great Britain Aug. 10, 1960

Claims (1)

1. CONTROL APPARATUS FOR CONTINUOUS MATERIAL BEING UNWOUND FROM A REEL AND PASSING TO INTERMITTENT TAKE-UP MEANS INCLUDING RESILIENT MEANS BEARING AGAINST SAID MATERIAL BETWEEN SAID REEL AND SAID TAKE-UP MEANS TO MAINTAIN TENSION IN SAID MATERIAL AND ADAPTED TO OSCILLATE UNDER THE INTERMITTENT ACTION OF SAID TAKE-UP MEANS, A PAIR OF SPACED ELECTRICAL CONTACTS, AND MEANS DISPOSED BETWEEN SAID CONTACTS AND MOVABLE WITH SAID TENSIONING MEANS, THE SPACING OF SAID CONTACTS BEING SUBSTANTIALLY LESS THAN THE NORMAL AMPLITUDE OF OSCILLATION OF SAID LAST MENTIONED MEANS WHEREBY THE LATTER ENGAGES BOTH OF SAID CONTACTS SUCCESSIVELY AND ALTERNATELY DURING EACH CYCLE OF OSCILLATION OF SAID TENSIONING MEANS, VARIABLE DRIVE MEANS FOR SAID REEL AND A REVERSIBLE ELECTRIC MOTOR ENGAGING THE SAME TO VARY THE RATIO OF SAID DRIVE MEANS IN RESPONSE TO ROTA-

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