US3042333A - Tension maintaining wind or unwind control - Google Patents

Description

July 3, 1962 s. WILDER, JR 3,042,333

TENSION MAINTAINING WIND OR UNWIND CONTROL Filed June 5, 1961 3 Sheets-Sheet 2 IN V EN TOR.

July 3, 1962 s. WILDER, JR

TENSION MAINTAINING WIND OR UNWIND CONTROL Filed June 5, 1961 3 Sheets-Sheet 3 NNNI! m 0el my WM 3 m 2% W M4 5% United States Patent ()1 3,042,333 TENSION MAINTAINING WIND OR UNWIND CONTROL Stuart Wilder, Jr., Columbus, Ind., assignor to The Reliance Electric and Engineering Company, Cleveland, Ohio, a corporation of Ohio Filed June 5, 1961, Ser. No. 115,002 9 Claims. (Cl. 242-755) The present invention relates to a control for maintaining desired tension in a strand, web or sheet of flexible material as that material is wound upon, or unwound from, a storage roll. In many operations in industry, such material is delivered to, or carried away from, such a roll at a controlled linear velocity; and it will be obvious that, because of the changing effective radius of material wound upon such a roll, the angular velocity of the roll must be continually reduced during a winding operation or continually increased during an unwinding operation.

In many applications of either winding or unwinding, it is desirable to maintain constant tension in the length of material which is travelling linearly relative to the roll; but in some applications, particularly in connection with winding operations, a so-called tapered tension is desired whereby the outer layers of the roll are more tightly wound than the inner layers, or vice versa. It is an object of the present invention to provide control means whereby constant tension may be maintained or whereby, alternatively, tapered tension of either type may be achieved.

In previously-available devices for controlling the tension in systems of the character here under consideration, a dance roll or a whip roll supported upon the material at a point removed from the effective peripheral surface of the material on the roll has been used, or, through one expedient or another, it has been attempted to sense torque and control tension without contact with the material. A dance or Whip roll has been found to be impractical for very wide webs or groups of serried strands, because of sagging or deflection which occurs in a whip roll shaft when it must cover a wide expanse. The devices which seek to sense tension without direct contact with the material are generally complex, expensive and diflicult to maintain.

A further object of the invention, then, is to provide a mechanically-simple control of the character under con sideration in which the element bearing upon the material to be wound or unwound senses merely the effective radius of the material currently on the roll and therefore is indifferent to the effective width of the material, since the information to which it is responsive may be taken from a very narrow portion of the material selected at any point in the width of the material.

A further object of the invention is to provide, in a control of the character under consideration, an element which is movable in response to the current torque required at the storage roll, which will always seek a position within its path of movement corresponding to the current torque required at the roll and which is resiliently restrained against movement beyond such a corresponding position by a force which is variable in accordance with the current value of the effective radius of the material on the storage roll.

A still further object of the invention is to provide, in a control of the character described, means whereby constant tension in the material may be maintained during an unwinding or winding operation or, by adjustment, tapering tension in the material may be achieved during a winding or unwinding cycle.

Further objects of the invention will appear as the description proceeds.

To the accomplishment of the above and related objects, my invention may be embodied in the forms illustrated in the accompanying drawings, attention being called to the fact, however, that the drawings are illustrative only, and that change may be made in the specific constructions illustrated and described, so long as the scope of the appended claims is not violated.

FIG. 1 is a somewhat diagrammatic end elevation of a control constructed in accordance with the present invention and illustrated in operative association with an unwinding storage roll;

FIG. 2 is a horizontal section through parts of the control, a fragment of the storage roll with material wound thereon being shown in plan;

FIG. 3 is an enlarged, fragmental elevation of parts of the control mechanism, with portions of the casingbroken away for clarity of illustration;

FIG. 4 is an elevation of one form of speed varying transmission which may advantageously be used in the control of the present disclosure; and I FIG. 5 is a view similar to FIG. 1 but illustrating a modified form of control associated with a winding storage roll and provided with adjusting means whereby tapering tension may be achieved.

Referring more particularly to FIGS. 1 to 4, it will be seen that I have illustrated a storage roll 10 upon which flexible material 11 is adapted to be wound. The reference numeral 12 indicates the minimum effective radius of material on the roll and the reference numeral 13 indicates the maximum effective radius of material on the roll. The reference numeral 14 indicates a length of material moving linearly away from the roll under the influence of forwarding means, such as the nip rolls 15, driven from an external source (not shown). Usually, but not necessarily, the forwarding means 15 will be so driven as .to move the length of material 14 at a constant linear velocity.

The external power source is suitably connected to drive a rotary means 16 at a constant ratio with respect to the forwarding means 15. In the illustrated embodiment of the invention, the rotary means 16 may be the input shaft of a speed varying transmission indicated generally by the reference numeral 17. One suitable form of speed varying transmission is illustrated in FIG. 4 and comprises a housing 18 in which the shaft 16 is journalled. An expansible V-pulley indicated generally by the reference numeral 19 comprises a coned disc 20 fixed to the shaft 16 and a mating coned disc 21 axially movable relative to the disc 20. A thrust bearing 22 is operatively connected to shift the disc 21 and has associated therewith a yoke 23 from which extends an axially shiftable operating member 24. A second expansible V-pulley indicated generally by the reference numeral 25 comprises a coned disc 26 fixed to the output shaft 29 of the transmission 17 and a mating coned disc 27 axially shiftable relative to the disc 26 and urged toward said disc 26 by a spring 28. A V-belt 30 provides a driving connection between the pulleys 19 and 25; and it will be clear that, as the disc 21 is moved toward the disc 20, the belt 30 will be crowded outwardly between said discs and will be pulled more deeply between the disc 26 and 27, thereby forcing the disc 27 away from the disc 26 against the tendency of the spring 28. Thus, the effective diameter of the pulley 19 will be increased and the effective diameter of the pulley 25 will be decreased to increase the speed of the shaft 29 relative to the speed of the shaft 16. Conversely, when the disc 21 is moved away from the disc 20, the belt 30 may move more deeply between the discs 20 and 21 as the spring 28 crowds the disc 27 toward the disc 26 to force the belt outwardly relative to said discs 26 and 27, thereby decreasing the speed of the shaft 29.

A worm 31 is mounted for rotation with the shaft 29,

Patented July 3', 1962 and for limited reciprocation relative thereto in suitable bearings in a housing 33, one end of said worm projecting from the housing and carrying, at its extremity, a head 32. Within the housing 33, the worm 31 meshes with a Worm wheel 34 fixed to a shaft 35 which carries, as well, a pinion 36 meshing with a bull gear 37 fixed to rotate with the storage roll 10.

A first lever 38 is pivoted at its lower end upon a fixed fulcrum 39 near the housing 33 and at its distal end, said lever carries a follower roller 40. A link 41 terminates at one end in a clevis 42 which is pivoted, as at 43, to the lever 38 intermediate the ends thereof. At its opposite end, the link 41 terminates in a toe 44 which straddles, and is guided upon, the shaft 29. A coiled spring 45 is sleeved on said shaft and is confined between the link toe 44 and the head 32 of the worm 31.

A second lever 46 has one end pivotally mounted on a fixed fulcrum 47 near the housing 33 and at its opposite end carries a pad 48 cooperatively engaging the distal end of the shiftable element 24. An intermediate portion of the lever 46 straddles the shaft 29 and is engaged by that end of the spring 45 which is adjacent the worm head 32.

When a loaded storage roll is mounted as shown, the lever 38 will be in its solid line position, the lever 46 will be in the position of FIG. 1 and the transmission 17 will be in the low-output-speed condition as shown. The free end of the material will be drawn off the roll and threaded between the nip rolls and will be led thence to a point of use (not shown). Now, when the external power source is energized, the forwarding means 15 and the rotary means 16 will be driven at a constant ratio.

As material is drawn off the storage roll by the forwarding means 15, force is applied thereby to tend to rotate the roll 10 in a clockwise direction. Through the gearing 37, 36, 34, that turning force is converted into a force tending to shift the worm 31 to the right, as viewed in FIG. 3. Such movement of the worm is resiliently resisted by the spring '45 to a degree dependent upon the current setting of the abutment toe 44; and it will be apparent that the current position of said toe is in turn dependent upon the position of the roller which measures the current efiective radius of the material 11 on the storage roll.

The parts are so proportioned and designed that the external power source drives the worm 31 in a direction corresponding to the counter-clockwise rotation of the worm wheel 34, but at a velocity such as to resist such worm wheel rotation. Thus, clockwise rotation of the roll 10 is resisted to a degree dependent upon the current force of the spring and upon the current speed of rotation of the worm 31. It follows that the tension in the run 14 of material is a function of current elfective radius of the material on the roll 10- and current spring resistance to axial movement of the worm. If tension in the run 14 should increase beyond a predetermined value, the tendency of the worm to move to the right will be correspondingly increased to compress the spring 45 and swing the lever 46 in a clockwise direction, thus shifting the element 24 and the disc 21 to the right to increase the speed of the shaft 29 to arrest rightward movement of the worm. Similarly, if tension in the run 14 should decrease below the predetermined value, the rightward tendency of the worm will be correspondingly decreased, the spring 45 will shift the worm to the left, the lever 46 Will be moved in a counter-clockwise direction and the speed of the shaft 29 will be correspondingly decreased.

As material is progressively drawn off the roll 10, the effective radius of material on the roll is correspondingly decreased and tension in the run 14 will tend to rise, but the reduction in elfective roll radius will tend to decrease the torque applied to the roll. The above-described tendency of the worm to compress the spring 45 will arise; but because of the above-described torque-reduction effeet, a proper balance would not be achieved if the abutment 44 were stationary or even if it moved at a rate equal to the rate of worm axial movement. To compensate for this difference, the current position of said abut- 5 ment 44 is placed under the control of the current effective radius of material on the roll 10.

It will be seen that the spring 45 acts on the toe 44 of the link 41 to hold the roller 40 yieldably in contact with the perimetral surface of material on the roll 10, thus measuring the current effective radius of such material. The parts are so proportioned and designed that, as the roller 40 follows progressive reduction of such effective radius, the rate of travel of the abutment 44 will exceed the rate of rightward movement of the worm 31 to such a degree as to compensate for the torque reduction resulting from reduction in effective radius, to maintain constant tension in the run 14 of material.

The necessary proportions may be defined as follows:

Where I is the distance from fulcrum 47 to the point 49 at which worm head 32 engages lever 46;

w is the total range of axial movement of worm 31;

l" is the distance from fulcrum 47 to pad '48; and

sis the total range of travel of shiftable element 24.

Where L is the distance from fulcrum 39 to point 43;

L" is the distance from fulcrum 39 to roller 40;

r is maximum roll eifective radius 13;

r" is minimum roll elfective radius 12; and

F is spring length change or the difierence between the axial force of the worm at the beginning of an unwind cycle and the axial force of the worm at the end of such a cycle, divided by the spring rate in pounds per 40 inch.

The axial force of the worm at the beginning of a cycle is Where T is desired tension in material run 14;

R is the pitch ratio of gear 37 to pinion 3,6; and

50 p is the pitch radius of worm Wheel 34.

The axial force of the worm at the end of a cycle is Now, if it be assumed that:

then

1250 inch-pounds Torque at worm wheel end of cycle Difference in necessary spring force from start to end of cycle=500-(l=400# Required length increase of spring Required spring force change 400 spring rate 409 Since w=4 (assumed), t must be 4"+l" =5", where t is total range of travel of abutment toe 44.

=1 inch Since ill 41/! ll! I l s 8 2 point 49 must be midway between fulcrum 47 and pad 48.

Since toe 44 must travel 5" while roller moves from r to r (12.5-2.5=l0"), point 43 must be midway between fulcrum 3 9 and roller 40.

Thus it will be seen that, as the unwinding cycle of the disclosed assembly progresses, the rate of travel of the abutment toe 44 exceeds the rate of axial movement of the worm 31 in the same direction by an amount which is constantly proportional to the rate at which the effective radius of the material wound on the storage roll 10 decreases. It will be seen, further, that the force with which the spring 45 resists axial movement of the worm 31 under the influence of the driving reaction of said worm upon the worm wheel 84, is progressively reduced at a rate equivalent to the rate of reduction of the effective radius of material wound on the roll 10.

In FIG. 5, I have illustrated a similar mechanism designed, however, for carrying out a winding cycle. I have shown a storage roll on which is to be wound a length of flexible material 51, and I have illustrated a run 54 of such material being advanced toward said roll by forwarding'means 55 driven from an external power source (not shown). Rotary means 56 is driven from said external power source at a constant ratio relative to the forwarding means 55 and as shown said rotary means may be the input shaft of a speed varying transmission 57 which may be structurally identical to the transmission 17 of FIGS. 1-4. A shiftable element 64 is movable oppositely to vary oppositely the speed of the output shaft 69 which is connected to drive the worm 71.

The worm 71, like the worm 31 above described, is mounted to rotate with the shaft 69, but is axially movable relative thereto and is provided at one end with an exposed head 72 for a purpose which will become apparent. The worm 71 meshes with a worm wheel 74 fixed to a shaft 75 which carries also a pinion 76 meshing with a bull gear 77 fixed relative to the storage roll 50.

A first lever 78 has one end mounted on a fixed fulcrum 79 near the Worm 71, and a follower roller 80, adapted to bear on the eifective peripheral surface of material wound on the roll 50, is carried at the opposite end of said lever 78. A link 81 carries at one end a clevis 8 2 which is pivotally connected to the lever 78 at a suitable point intermediate the ends of said lever; and at its opposite end the link is provided with an abutment toe 84 which straddles, and is guided on, the shaft 69 at a point spaced from the worm head 72. A coiled spring 85 is sleeved on the shaft 69 and is confined between the worm head 72 and said abutment toe 84. Ob-

viously, the spring 85 acts to press the follower roller resiliently against the effective periphery of the roll 51 of material wound on the storage roll 50', and yieldably to resist movement of the worm 71 axially to the right. As obviously, the degree of force with which said spring resists such worm movement will be a function of the current spacing between the worm head 72 and the abutment 84, and of the spring rate of such spring.

A second lever 86 is pivotally mounted at a suitable point intermediate its ends on a fixed fulcrum 87, and a yoke 88 at one end of said lever 86 engages a cross pin 92 to provide a twoway operative connection between said lever and the shiftable element 64 of the transmission 57, while the other end 89 of said lever is operatively engaged by said worm head 72 and is resiliently held thereagainst by the spring 85.

in this instance, the external power source acts affirmatively to drive the roll 50 instead of serving as a brake or drag. Thus, the rotary element 56 is driven at a velocity which is constantly proportional to the velocity of the forwarding means 55 and the ratio of the transmission 57 is set at such a value that the shaft 69 is driven at a speed to drive the roll 50, through the worm 71, worm wheel 74, pinion 76 and gear 77 at a velocity such as to exert upon the run 54 of advancing material a predetermined tension. The tension will be, in effect, measured by the spring-affected worm 71. That is, since the reaction effect upon the worm 71 of its effort to drive the worm wheel 74 in a clockwise direction tends to move the Worm toward the right, only so much torque can be exerted upon the worm wheel 74 as is proportionate to the force with which the spring currently resists rightward movement of the worm 71. As material is wound upon the roll 50, the effective radius of the roll increases, thereby tending to increase the tension in the material run 54 which is advancing at constant velocity, not only by reason of the increase in effective peripheral dimension of the roll but also by reason of the increase in the radial a-rm through which the rotating roll is acting on the run 54.

As tension in the run 54 tends to increase, however, the axial force acting on the worm 71 will overcome the current force of the spring 85 and the worm 71 will move toward the right to swing the lever 86 in a counter-clockwise direction whereby the shiftable element 64 will be affirmatively moved toward the left to reduce the speed of the transmission output shaft 69. At the same time, the increase in the effective radius of the material on the roll 59 will move the roller 80 to the left to shift the abutment 84 proportionately toward the left. Thus, worm movement and abutment movement additively compress the spring 85 to increase the force with which the spring 85 resists further worm movement toward the right.

"Ilhe factors which, in such a system, coact to determine the value of the tension in the run 54 may be selected to hold that value substantially constant throughout a Windup cycle.

Again, let

l'=distance from fulcrum 87 to point 89 l"=distance from fulcrum 87 to yoke 88 w=total range of axial movement of worm 71 s=total range of travel of shiftable element 64 L'=distance from fulcrum 79 to point 83 L"=distance from fulcrum 79 to roller 80 r'=maximum storage roll effective radius r"=rninimum storage roll effective radius F=spring length change or the difference between the axial force of the worm at the end of a windup cycle and the axial force of the Worm at the beginning of such a cycle, divided by the spring rate in pounds per inch T=the desired tension in material run 54 R=tl1e pitch ratio of gear 77 to pinion 76 p=the pitch radius of worm wheel 74 t=total range of travel of abutment toe 84 Then assume Torque at storage roll at end of windup cycle =12.5 2000:25000 inch-pounds Torque at worm Wheel at start of windup cycle Torque at worm Wheel at end of windup cycle 1250 inch-pounds 250 Axial force at worm at start of wrndup cycle 100# 1250 Anal force at worm at end of wmdup cycle: 2 5 =500# Difference in necessary spring force from start to end of cycle=500-100=400# Required length reduction of spring required spring force change 400 spring rate 50 Since it has been assumed above that W 4" and that s=4", l and I" must be equal.

Since 84 and 72 travel in opposite directions, w=4" and spring length reduction must be 8", t must be n n u Since follower roll must travel (rr")=",

and point 83 must be located 0.4 of the distance from follower 79 to roller 80 if constant tension is to be maintained in the material run 54.

If, however, it is desired to control the system in such a way as to provide tapered tension in which the tension in the run 54 decreases linearly from a value of, for instance, 2000 pounds at the start of a windup cycle to a value of, for instance, 1000 pounds at the end of the cycle, one way to accomplish that result is to select a spring 85 having a rate different from that assumed above. Thus =250 inch-pounds 2O =6251nch-pounds Axial force at worm at start of windup cycle 100# Axial force at worm at end of windup cycle=g ;=250# Ditference in necessary spring force from start to end of cycle=250-100=l50# Spring rate:

Length reduction of spring during cycle=8" Alternatively, such tapered tension may be achieved by shifting the point at which the link 81 is pivotally connected to the lever 78; and to that end, I have shown a series of spaced openings 90 above the point 83 and a series of spaced openings 91 below that point whereby adjustments may be selectively made in the point of connection between the link and the lever. Thus, if it is desired to use the spring 85 having a spring rate of 50#/inch and to achieve a linear reduction in tension from 2000 pounds to 1500 pounds during the cycle, a spring length reduction of 5.5 inches must occur during the cyle. Since w=4, 1 must be 5.54=l.5". Since roller 80 must move 10" as above, the ratio of L to L must be I and if L" is, for instance, 48", the link 81 must be pivoted to lever 73 at a point 7.2 from the fulcrum 79.

Or, if it is desired to increase the tension from, for instance, a starting value of 1000 pounds to a value of 2000 pounds at the end of the cycle, the reduction in spring length must be 9 inches, the travel of the abutment 84 must be 5" and the point of connection of link 81 to lever 78 must be midway between the fulcrum 79 and the roller 80. If a starting tension of 2000 pounds is to be increased to 2500 pounds at the end of the cycle, abutment 84 must travel 6.5" while worm 71 travels 4" in the opposite direction, and the point of pivotal connection between link 81 and lever 78 must be 0.65 of the length of the lever or 31.2 from the fulcrum if roller 80 is carried 48" from the fulcrum as above.

It will thus be seen that, in the windup system, the current tension in the run of material 54 is determined, when the control mechanism includes a spring having a predetermined spring rate, by the ratio between the rate of travel of the abutment 84 and the rate of axial movement of the worm 71; and that, for any selected rate of axial movement of the Worm, if the ratio between the force with which the spring resists axial movement of the worm and the product of tension by the eifective radius of material wound on the storage roll is held constant, the tension in the run 54' will remain constant.

It will also be seen that, if the rate of travel of the abutment 84 is so modified as to change the force with which the spring 85 resists such worm movement at a rate different from the rate of change of the eifective radius of material on the storage roll, tension in the run 54 will be progressively changed during a windup cycle to produce a tapered tension effect. Expressed otherwise, if the ratio between the force with which the spring resists axial movement of the worm and the product of tension by the current effective radius of material wound on the storage roll i progressively varied during the cycle, the tension in the run 54 will be correspondingly progressively varied.

The above calculations ignore the factors of frictional resistance to movement of the control parts and any net holding force which may be required to maintain a particular setting of any specific form of speed-varying transmission used in the system. These are factors which are familiar to those who are skilled in the art to which the present invention pertains, and compensation therefor may be achieved, in accordance with conventional practice, by suitable linkage changes and/or by interposing a servo-motor device between the shiftable element which controls the transmission ratio and the equivalent of the disc 21. Also it will be obvious to those skilled in the art that suitable dimensions for the 9 follower roller and its mounting lever, relative to the force of the spring and the character of the material being wound or unwound, will be selected so that the follower roller will not exert an undue crushing effect upon the material wound on the storage roll.

While the external power source for the system will ordinarily be operated at constant speed so that the material will be forwarded toward or away from the storage roll at constant linear velocity, it will be appreciated that, since the means 15 or 55 and the rotary element 16 or 56 are so connected to the power source as to be driven at a constant ratio, the disclosed control mechanisms will perform their intended functions without significant loss of effectiveness even if the power source is operated at varying speeds.

While a push-pull connection between the lever 36 and the shiftable element 64 has been shown in FIG. and is believed to be preferable in most windup systems, it will be clear that in some such installations a one-way connection like that shown in FIG. 1 may be used. It will also be understood that it may sometimes be desirable to use a two-way connection between the elements 46 and 24 in a system of the type shown in FIG. 1.

I claim as my invention:

1. Means for automatically controlling the rate of rotation of a storage roll for flexible material comprising, in combination with such a roll, a length of flexible mate rial wound on said roll, means for forwarding said material relative to said roll, rotary means driven at a constant ratio with respect to said forwarding means, a speed-varying transmission including an input shaft connected to be driven from said rotary means, an output shaft, and an element shiftable oppositely to vary oppositely the speed of said output shaft relative to the speed of said input shaft, a worm wheel having a constant-ratio driving connection with said roll, a worm having a constant-ratio driving connection with said out put shaft, mounted for axial reciprocation, and meshing with said worm wheel, spring means yieldably resisting axial movement of said Worm under the influence of the driving reaction of said worm on said worm wheel, means operatively connecting said worm to shift said shiftable element oppositely in response to opposite axial movement of said worm, a movable backing abutment for said spring means, and means variably positioned in accordance with variations in the effective radius of flexible material wound on said roll and operatively connected to move said abutment.

2. Means for automatically controlling the rate of rotation of a storage roll for flexible material comprising, in combination with such a roll, a length of flexible material wound on said roll, means for forwarding said material relative to said roll, rotary means driven at a constant ratio with respect to said forwarding means, a speed-varying transmission including an input shaft connected to be driven from said rotary means, an output shaft, and an element shiftable oppositely to vary oppositely the speed of said output shaft relative to the speed of said input shaft, a Worm wheel having a constant-ratio driving connection with said roll, a worm having a constant-ratio driving connection with said output shaft, mounted for axial reciprocation, and meshing with said worm wheel, follower means arranged to bear on the effective periphery of material on said roll, spring means cooperatively associated with said follower means and with said worm to urge said follower means yieldably toward the axis of said roll and yieldably to resist movement of said Worm axially in one direction, and means providing an operative connection between said worm and said shiftable element so constructed and arranged that axial movement of said worm results in corresponding movement of said shiftable element.

3. Means for automatically controlling the rate of rotation of a storage roll for flexible material comprising, in combination with such a roll, a length of flexible material wound on said roll, means for forwarding said material relative to said roll, rotary means driven at a constant ratio with respect to said forwarding means, a speed-varying transmission including an input shaft connected to be driven from said rotary means, an output shaft, and an element shiftable oppositely to vary oppositely the speed of said output shaft relative to the speed of said input shaft, a worm wheel having a constant ratio driving connection with said roll, a worm axially shiftably mounted on said output shaft but rotationally fixed thereto and meshing with said worm wheel, a lever fulcrumed adjacent said worm and carrying a follower arranged to bear on the effective periphery of material on said roll, abutment means spaced from one end of said worm and arranged for travel along the axis of said output shaft, a coiled spring sleeved on said output shaft and confined between said abutment means and said one end of said worm, link means providing an operative connection between said abutment means and said lever, said spring acting through said abutment means, said link means and said lever to urge said follower yieldably toward the axis of said roll, and means providing an operative connection between said worm and said shiftab-le element so constructed and arranged that axial movement of said worm results in corresponding movement of said shiftable element.

4. Means for automatically controlling the rate of rotation of a storage roll for flexible material comprising, in combination with such a roll, a length of flexible material wound on said roll, means for forwarding said material relative to said roll, rotary means driven at a constant ratio with respect to said forwarding means, a speed-varying transmission including an input shaft connected to be driven from said rotary means, an output shaft, and an element shifitable oppositely to vary oppositely the speed of said output shaft relative to the speed of said input shaft, a worm wheel having a constant-ratio driving connection with said roll, a worm axially-shiftably mounted on said output shaft but rotationally fixed thereto and meshing with said worm wheel, a first lever fulcrumed at one end near said worm and carrying a follower at its other end arranged to bear on the effective periphery of material on said roll, abutment means spaced from one end of said worm and ar ranged for travel along the axis of said output shaft, a coiled spring sleeved on said output shaft and confined between said abutment means and said one end of said worm, link means secured at one end to said abutment means and pivotally connected at its opposite end to said first lever between its fulcrum and said follower, said spring acting through said abutment means, said link means and said lever to urge said follower yieldably toward the axis of said roll, and a second lever fulcrumed at one end near said Worm and, at its opposite end, operatively engaging said shiftable element, said one end of said worm operatively engaging said second lever intermediate the ends thereof.

5. Means for automatically controlling the rate of rotation of a storage roll for flexible material comprising, in combination with such a roll, a length of flexible material wound on said roll, means for forwarding said material relative to said roll, rotary means driven at a constant ratio with respect to said forwarding means, a speed-varying transmission including an input shaft connected to be driven from said rotary means, an output shaft, and an element shiftable oppositely to vary oppositely the speed of said output shaft relative to the speed of said input shaft, a worm wheel having a constant-ratio driving connection with said roll, a worm axially-shiftably mounted on said output shaft but rotationally fixed thereto and meshing with said worm wheel, a first lever fulcrumed at one end near said worm and carrying a follower at its other end arranged to bear on the effective periphery of material on said roll, abutment means spaced from one end of said worm and arranged for travel along the axis of said output shaft, a coiled spring sleeved on said output shaft and confined between said abutment means and said one end of said worm, link means secured at one end to said abutment means and pivotally connected at its opposite end to said first lever between its fulcrum and said follower, said spring acting through said abutment means, said link means and said lever to urge said follower yieldably toward the axis of said roll, and a second lever fulcrumed intermediate its ends near said WOl'IIl, one end of said second lever operatively engaging said shiftable element and the other end of said second lever being operatively engaged by said one end of said worm.

6. A constant-tension unwind control according to claim 1 wherein the rate of travel of said abutment exceeds the rate of axial movement of said Worm in the same direction by an amount constantly proportional to the rate at which the effective radius of the material wound on said storage roll decreases.

7. A constant-tension unwind control according to claim 4 wherein the effective lengths of said levers and the points at which said link mean is pivotally connected to said first lever and said worm operatively ,oaaass engages said second lever are so chosen that the force with which said spring resists axial movement of said worm is reduced at a rate equivalent to the rate of reduction of the effective radius of material on said roll.

8. A constant-tension windup control according to claim 1 wherein the rate of travel of said abutment bears a predetermined ratio to the rate of axial movement of said Worm to maintain substantially constant the ratio between the force with which said spring means resists axial movement of said worm and the product of desired tension by the eifective radius of material on said roll.

9. A controlled-tension windup control according to claim 1 wherein the rate of travel of said abutment relative to the rate of axial movement of said worm modifies the force with which said spring means resists such worm movement at a rate different from the rate of change or" the effective radius of material on said roll.

References Cited in the file of this patent UNITED STATES PATENTS 2,775,263 Rush Dec. 25, 1956 2,775,415 Rush Dec. 25, 1956 2,916,227 Bowen Dec. 8, 1959

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