US2883122A

US2883122A - Constant tension unwinding control

Info

Publication number: US2883122A
Application number: US327003A
Authority: US
Inventors: Jr Richard Le Baron Bowen
Original assignee: Individual
Current assignee: Individual
Priority date: 1952-12-19
Filing date: 1952-12-19
Publication date: 1959-04-21
Anticipated expiration: 1976-04-21

Description

April 21, 1959 R. LE BARON BOWEN, JR 2,383,122

CONSTANT TENSION UNWINDING CONTROL I Filed Dec. 19, 1952 2 Sheets-Sheet 1 IN V EN TOR.

Richug LeBorpn Bowendr.

$11M, M Jam r.

ATTORNEY A ril 21, 1959 R. LE BARON BOWEN, JR 2,883,122

I CONSTANT TENSION UNWINDING CONTROL Filed Dec. 19, 1952 2 Sheets-Sheet 2 'IN V EN TOR.

Richard l eBoron Bowen,Jr.

Jami)? ATTORN EY United States Patent CONSTANT TENSION UNWINDING CONTROL Richard Le Baron Bowen, Jr., Pawtucket, RI.

Application December 19, 1952, Serial No. 327,003

17 Claims. (Cl. 24275.5)

This invention relates to constant tension unwinding and/ or winding control and more particularly to a mechameans for driving winding and unwinding rolls simultaneously in such manner that the linear speed and the tension of the material between the rolls will be maintained substantially constant without regard to the changing diameters of the two rolls.

A further object of the invention is the provision of apparatus of this character which may be reversed for operation in either direction at will,

And still another object of the persent invention is to provide a velocity control on the rewind shaft and compensate for the increasing linear speed of the web as the roll increases in diameter.

Other objects of the present invention will be pointed out in part and become apparent in part in the following specification and claims.

Uniform tension is a prerequisite to uniformity of product in many strip processing machines such as textiles, paper, imitation leather, aluminum foil, printing and the like. Especially is this true in coating machinery where the tension on the web or strip effects the nature of the application of the coating being applied to the cloth.

In the past constant tension control mechanisms have been of the so-called on-off type. This type of control mechanism inherently produces hunting, that is, the tension would build up gradually to some predetermined value above an arbitrary average, when the control mechanism would correct the tension to some predetermined value below the arbitrary average. A graph representa: tion of this type of control would produce a zig-zag curve of tension against time. s

The present invention overcomes this irregularity of tension control by correcting any deviation in the tension instantaneously. The rate of correction is in direct proportion to the error of tension. A graph of the present control mechanism would tend to produce a straight line for tension against time.

of reference indicate corresponding parts in the figures:

Figure 1 shows an embodiment of the present invention in diagrammatic form, for the sake of clarity and simplicity and presents the mechanism for either winding or unwinding the strip.

Figure 2 is a diagrammatic form of a combination wind, unwind mechanism and to that end is a modification of Figure 1.

Figure '3 is a diagrammatic form of a gear pump.

2,883,122 Patented Apr. 21, 1959 wherein a strip or web of material 11 is being fed from a drum 9 at a constant linear velocity to a beam 12. The mechanism driving drum 9, also drives shaft 30 so that the speeds of both drum 9 and shaft 30 are constant at all times. Inasmuch as the problem is to maintain the tension of web 11 constant, it follows that the power input to shaft 70 must be maintained constant. To that end, shaft 30 transmits its power to shaft 23 through a pair of bevel gears 27 and 28. Mounted on shaft 23 and fixed to rotate with it, are two sprockets 26 and 31.

Four separate units of mechanism are provided to accomplish the desired result. They are a variable speed transmission, generally indicated at 17; a differential gear train generally indicated at 21; a second differential gear train generally indicated at 34 and brake mechanism generally indicated at 58.

These

mechanisms

17, 21, 34 and 58 are interconnected by any well known power transmission means such as belts and pulleys, gear trains and the like, but are illustrated as comprising chain and sprocket drives.

The variable speed transmission 17 comprises a pair of

parallel shafts

70 and 71 rotatably mounted in housing 72. Each

shaft

70, 71 carries a pair of

coned disks

73 and 74, respectively, forming expansive V-pulleys, which are splined to said shafts. Coned

disks

73, 74 are operatively connected by edge-active belt 75 and may be simultaneously and oppositely adjusted to provide variable speed by the simultaneous adjustment of

levers

76 and 77 which are operatively connected to coned

disks

73, 74

r and movably separated by link 78. The ends of

levers

76, 77 are fixed to threaded shaft 80 by means of threaded

bearings

81, 82. The rotation of threaded shaft 80 simultaneously and oppositely moves

cone disks

73, 74 on

shafts

70, 71, thereby varying the speed of rotation of shaft 70 relative to shaft 71.

The differential gear train 21 comprises three

shafts

90, 91 and 92 rotatively mounted in housing 93. A shaft 94 centrally fixed to shaft 92 has rotatively mounted thereon

bevel gears

95 and 96 which are operatively connected to bevel.

gears

97 and 98 rotatably mounted on shaft 92. A spur gear 100 fixed to bevel gear 97 meshes with spur gear 101 fixed to shaft 90. Sprocket 102 fixed to bevel gear 98 is operatively connected by means of a chain 103 to sprocket 104 fixed to shaft 91. It becomes evident, that

shafts

90, 91 when rotated in the same direction and at the same speed cause shaft 92 to remain idle. However, any difference in the speed of

shafts

90, 91 when turning in the same direction, will cause shaft 92 to rotate, the speed of this rotation being proportional to the difference in the speeds of

shafts

90 and 91.

description of the entire mechanism.

The brake mechanism 58 consists of a brake drum 54 secured to a shaft 53. A pair of brake shoes 55 pivotally mounted as at 57 embrace brake drum 54 with a gripping action determined by screw 56 adjustably mounted in Referring to the drawing in which similar characters the end opposite the pivot 57 of brake shoes 55. A bevel gear 52 mounted on shaft 53 operatively engages with bevel gear 51 mounted on shaft 46. This brake mechanism is well known in the art.

A sprocket 33 secured to shaft 106 is operatively connected to sprocket 31 by means of a chain 32. A sprocket 36 fixed to shaft 105 is operatively connected to sprocket 38 fixed to shaft 71 by means of chain 37. A sprocket 42 fixed to shaft 107 is operatively connected to sprocket 44 secured to shaft by means of chain 43. A sprocket Referring to the drawings and particularly to Figure 1,

24 secured to shaft 91 is operatively conn'ected'to sprocket 26 by means of chain 25. A sprocket 50 secured to shaft 46 is operatively connected to sprocket 47 fixed to shaft 92 by means of chain 48. Shaft 90 is united with shaft 71 by means of a coupling 108 well known in the art.

In operation, let it be assumed that beam 12 is just beginning to take up strip or web 11. In this condition axle 13 will travel at its maximum revolutions per minute. Drum 9 supplies web 11 at a constant and predetermined linear speed to beam 12. Shaft 30 and drum 9 are in harmony. Shaft 30 drives axle 13 through bevel gears 27, 28, shaft 23, sprocket 26, chain 25, sprocket 24, shaft 91, differential gear train 21,

shafts

90, 71,

cone disks

74, 73, belt 75, shaft 70,

bevel gears

15 and 14. Axle 1.3 will be driven at the maximum speed at which the diameter of beam 12 will allow itself to be driven. Thus, if the diameter of beam 12 doubles during the winding, the speed of axle 13 will be reduced to one half. It may be said that the speed of axle 13 varies inversely with the diameter of the beam. As the speed of axle 13 decreases, a decrease in speed is transmitted through

bevel gears

14, 15, shaft 70, cone disk 73, belt 75, cone disk 74, shaft '71 to shaft 90 of differential gear train 21, causing shaft 92 and brake 58 to increase in speed, thereby decreasing the power transmitted from intake shaft 30 to axle 13, since the torque applied to each shaft of differential gear train 21 remains constant. This decrease in power is reflected directly by a decrease in tension, since constant power is a prerequisite for constant tension.

Control differential 34 is so designed, that when

shafts

105 and 106 turn at similar speeds, shaft 107 remains motionless.

When shaft 71 decreases in speed, shaft 105 of difierential 34 also decreases in speed since it is connected to shaft 71 by

sprockets

38, 36 and chain 37. This decrease in speed of shaft 105 causes rotation of shaft 107 and threaded shaft 88 through

sprockets

42, 44 and chain 43. This changes the relative speeds of

cone disks

73 and 74 through

levers

76 and 77 thereby maintaining the speed of shaft 71 constant at all times. Since the speeds of

shafts

90 and 91 of differential 21 remain constant, the speed of shaft 92 and thus brake 58 likewise remain constant, so that constant power is applied to shaft 71 and thus to beam 12 at all times, thereby maintaining constant tension on web 11.

At the start of the winding, brake 58 will be adjusted to a predetermined setting which will cause a predetermined tension.

The purpose of the control mechanism is to maintain the power input to axle 13 constant, thereby maintaining the tension constant. If web 11 broke, shaft 70 would assume its maximum speed as soon as possible.

A gear pump generally indicated at 110 may be substituted for brake 58 (see Figure 4). Shaft 46 would be operatively connected to pump 110 and sprocket 50 would be fixed to shaft 46 as previously described for brake 58. Gear. pump- 110 comprises a pump 111 operatively connected to a reservoir 112 by means of suction line 113 on one side and discharge line 114 on its opposite side. A discharge valve 115 controls the torque exerted by the pump.

Figure 2 represents an additional application of the mechanism shown in Figure 1 and described above. To that end, it is a modification of Figure 1.

Two

variable speed transmissions

17 and 17A are employed in place of one and two

differential gear trains

21 and 34 are employed as in Figure l with brake 58 or gear pump 110 functioning as described.

The modified form encompasses control of two beams on either side of a dye jig, for example, instead .of controlling one'beam. To that end, a second variable speed transmission 17A is employed to control the second beam axle 184 in the same manner as the first beam axle '13 is controlled. Two motors 161 and 178 are substituted in the modified form for the machine drive employed in Figure 1. 1

There are two driving connections between

shafts

91 and 165. One consists of sprockets 24, 68 and chain 67. The other consists of sprockets 24A, 68A and chain 67A. Only one drive is necessary if the web is Wound upon the same beam at all times, but if the web is reversed, first from one beam to the other and then back again; two drives become necessary. When beam 12 is winding, this compound drive between

shafts

165 and 91 provides that shaft 91 of differential 21 revolves faster than shaft 90. When beam 185 is winding, the drive makes shaft 90 revolve faster than shaft 91.

To accomplish this result, sprockets 24 and 24A are provided with conventional manually controlled slip clutches with the releasing mechanisms connected to a single lever between the clutches, so that when one is engaged, the other is disengaged, and vice versa. These clutches are of the friction disk type and are well known in the art. Since sprockets 68 and 68A are made fast to shaft 165, it is obvious that chains 67 and 67A both are in motion at all times.

The modified form provides winding on either beam and therefore is termed a wind and/ or an unwind constant tension control because the beams are under constant tension control while winding or unwinding.

In one direction of Wind, motor 161 is the drive means. In the other direction of wind, motor 170 is the drive means. It is obvious that the motors cause the shafts to rotate in opposite directions and that the

variable speed transmissions

17 and 17A rotate in opposite directions.

In operation, web 11 is being unwound from beam 185, past an idler roller 86, which is schematic for some processing machines, such as a dye jig, and onto beam 12 where it is wound up. Axles '13 and 184 are suitably supported in the machine frame, not shown, and are provided with

bevel gears

14 and 183, respectively.

Shafts

70 and 181 provided with

cone disks

73 and 73A which are connected by means of

belts

75 and 75A respectively to

cone disks

74 and 74A, mounted on

shafts

71 and 165, have fixed thereto

bevel gears

15 and 182 which operatively engage

bevel gears

14 and 183, respectively.

Shaft 71 provided with sprocket 38 is operatively connected to sprocket 36 through chain 37. Sprocket 36 is fixed to shaft 105. Shaft 165 provided with sprocket 174 is operatively connected to sprocket 33 through chain 175. Sprocket 33 is fixed to shaft 106.

Shafts

105 and 106 of differential gear train 34 operate the mechanism as previously described, terminating in control of shaft 107 which has sprockets 42 and 180 fixed to it.

Threaded shaft provided with sprocket 44 is operatively connected to sprocket 42 through chain 43. Threaded shaft 176 provided with sprocket 177 is operatively connected to sprocket 180 through chain 178. Shaft 71 provided with sprocket 62 is operatively connected to motor 161 through chain 63 and sprocket 64 fixed 10 motor shaft 161A. Shaft 165 provided with sprocket 171 is operatively connected to motor 170 through chain 172 and sprocket 173 fixed to motor shaft 170A. Shaft 165 is also provided with sprocket 68 which is operatively engaged with shaft 91 of differential gear train 21 through chain 67 and sprocket 24 fixed to shaft 91. Shaft of differential gear train 21 is connected to shaft 71 by means of coupling 108. Shaft 92 of differential gear train 21 provided with sprocket 47 is operatively connected to 'brake mechanism 58 or gear pump through sprocket 5.0 and chain 48.

Motor 161 through variable speed transmission 17 is driving axle 13 and supplying the power to wind up beam 12. Motor is off but the motor shaft is idly running. Motor 161 applies a drag on web 11 which causes beam .to turn, thereby turning variable speed transmission 17A, and the connecting shafts. Tension is applied to web 11 by putting a drag on axle 1841 through brake 58. Axl v184 t rns at What ver pe d th d ameter of bea 185 allows it to turn. Thus, shaft 184 actually does turn at a predetermined speed, which, however, isdetermined by the diameter of the roll, and not by anything the mechanism does.

As beam 185 decreases in diameter due to unwinding, axle 184 turns at an increasing speed, even if the linear speed of the web remained constant. However, as beam 12 increases in diameter, the linear speed of web 11 will tend to increase. Thus, the increase in the, speed of axle 184 due to the decreasing diameter of beam 185 is further increased by the increase in the linear speed of web 11.

As shaft 181 increases in speed through

bevel gears

182, 183 it will cause shaft 165 to speed up through

cone disks

73A, 74A, and belt 75A. Shaft 106 will speed up running faster than shaft 105 being driven from motor 161; therefore shaft 107 will revolve to compensate for the difference in speed between

shafts

105, 106. Shaft 107 through sprockets 180, 177 and chain 178 will cause threaded shaft 176 to change the relation between

cone disks

74A, and 73A thereby decreasing the speed of shaft 165 relative to shaft 181. It is evident that the speed of shaft 165 is thus maintained constant at all times. At the same time shaft 107 through

sprockets

42, 44 and chain 43 will cause threaded shaft 80 to change the relation between

cone disks

74, 73 thereby reducing the speed of shaft 70, hence axle 13 and beam 12 and thus maintaining the linear speed of web 11 essentially constant.

1 There must be a slip factor between

shafts

71 and 165 or else web 11 would break because of the non-linearity of the two

transmissions

17, 17A. To that end brake 58 is caused to produce a drag on shaft 92. Shaft 91 is secured to shaft 165, causing the drag to influence shaft 181. This brake allows a slip factor creating a degree of freedom between

axles

13 and 184. Without this freedom,

shafts

165 and 71 would be united as if by a chain drive, binding the mechanism and eventually causing a breaking strain on web 11.

As axle 184 tends to increase in speed, shaft 181 and shaft 165through belt 75A will also increase, increasing the speed of shaft 106 of controlling differential 34. Since this brings

shafts

105 and 106 out of hamony, shaft 107 will turn, shifting transmission 17A to compensate for the decrease in diameter of the beam 185, and likewise shifting transmission 17 to compensate for the increase in the web speed due to the increased diameter of beam 12. These changes maintain the linear speed of the web and the tension on the web essentially constant.

Assume that the device is operating as shown in Figure 2 and in the direction indicated by the arrows. Beam 12 is winding and beam 185 is unwinding. Assume that beam 185 is four feet in diameter and beam 12 is one foot in diameter at the start of the winding operation and that at the end of winding operation, beam 185 is one foot in diameter and beam 12 is four feet in diameter. Assume for the purposes of explanation that at the start of the winding operation,

shafts

71 and 165 both turnat 200 rpm. Shaft 71 is driven by motor 161, so its speed remains constant; the speed of shaft 165 is maintained constant by the control differential 34 as previously described. Thus at the end of the winding operation the speed of both these

shafts

71, 165 is still 200 rpm.

At the start of the winding operation the

transmissions

17 and 17A are both shifted to one extreme, so that shaft 181 turns at 100 r.p.m. and shaft 70 at 400 r.p.m. At the end of the winding operation, shaft 181 must turn four times the speed of shaft 70 since beam 12 is now four times the diameter of beam 185. Thus the speed of shaft 181must be, 400 rpm. and the speed of shaft 70 must be 100 r.p.m., since both transmissions are shifted the same amount by differential 34.

Thus the linear velocity of the web is maintained exact- -ly constant.

If idler roller. 86eis a dye jig, it may become desirable to transfer web 11 from beam 12 to beam 185, in which event motor 161'would be shut off and motor started up, with the mechanism functioning as just described but the operational impulse would come from shaft 181 instead of shaft 70.

. Having shown and described a preferredembodiment of the present invention, by way of example, it should be realized that structural changes could be made and other examples given without departing from either the spirit or scope of this invention.

What I claim is:

1. A winding and unwinding mechanism comprising in combination a drive shaft, a variable speed transmission having an input and output, adjusting means for varying the setting of said transmission, said output connected to a load means, a pair of differential gear units, each having a first shaft, a second shaft, and a third shaft, means connecting the said first shafts to said drive shaft, means connecting said second shafts to the input side of said variable speed transmission, means connected, to the third shaft of one of said differential gear units for providing a torque differential between the first and second shafts thereof, and means connecting the third shaft of the other of said differential gear units to the adjusting means of the variable speed transmission for varying the setting thereof to maintain the said torque differential constant so as to maintain the torque transmitted from said drive shaft to said input shaft constant.

2. A winding and unwinding mechanism comprising in combination a drive shaft, 2. variable speed transmission having an input and output, adjusting means for varying the setting of said transmission, said output connected to a load means, a pair of differential gear units, each having a first shaft, a second shaft, and a third shaft, means connecting the said first shafts to said drive shaft, means connecting said second shafts to the input side of said variable speed transmission, a brake connected to the third shaft of one of said differential gear units for providing a torque differential between the first and second shafts thereof, and means connecting the third shaft of the other of said differential gear units to the adjusting means of the variable speed transmission for varying the setting thereof to maintain the said torque differential constant so as to maintain the torque transmitted from said drive shaft to said input shaft constant.

3. A winding and unwinding mechanism comprising in combination a drive shaft, a variable speed transmission having an input shaft and an output shaft, said output shaft connected to a load means, an adjusting shaft for varying the setting of said variable speed device, a differential unit connecting said drive shaft to said input shaft and through which torque is transmitted from said drive shaft to said input shaft, means connected to said unit for providing a predetermined torque differential between said drive shaft and said input shaft, a second differential unit, a shaft for said second differential unit connected to said drive shaft, a second shaft for said second differential unit connected to said input shaft, a third shaft for said second differential unit connected to said adjusting shaft for varying the setting of the variable speed device to maintain the said torque differential constant so as to maintain the torque transmitted from said drive shaft to said input shaft constant.

4. A winding and unwinding mechanism comprising in combination a drive shaft, a variable speed transmission having an input shaft, an output shaft, and an adjusting shaft for varying the setting of the variable speed transmission, said output shaft connected to a load means, a first differential, a first shaft for the differential connected to said drive shaft, a second shaft for the differential connected to said input shaft, means connected to said differential for providing a predetermined torque differential between the said first and second shafts, a second ditferentiaha shaft for said second differential connected to said drive shaft, a second; shaft for said second differential connected to said input shaft, and a third shaft "7 for :said second differential connected to said adjusting shaft for varying the sett g of the variable speed transmission to maintain the said torque differential constant so as to maintain the torque transmitted from said drive shaft to said input shaft constant.

5. A winding and unwinding mechanism comprising :in combination a drive shaft, a variable speed transmission ,having an input shaft an output shaft, and, an adjusting shaft for varying the setting of the variable speed transmission, said output shaft connected to a load means, a first differential, a first shaft for said differential connected to said drive shaft, a second shaft for .said differential connected to said input shaft, a third shaft for said differential, means connected to said third shaft for providing ,a predetermined torque differential between the said first and second shafts, .a second differential, a shaft for said second differential connected to saiddrive shaft, a second shaft for said second differential connected to said input shaft, and .a third shaft for said second differential connected to said adjusting shaft for varying the setting of the variable speed transmission to maintain the said torque differential constant so as to maintain the torque transmitted through said first differential constant.

:6. A winding and unwinding mechanism comprising in combination a drive shaft, a variable speed transmission having an input shaft, an output shaft, and an adjusting shaft for varying the setting of the variable speed transmission, a differential gear unit, a shaft for said gear unit connected to said drive shaft, a second shaft for said gear unit connected to said input shaft, a third shaft for said gear unit, means connected to said third shaft providing a predetermined torque differential between the said first .and second shafts, a second differential gear unit, a shaft for said second differential gear unit connected to said drive shaft, ,a second shaft for said second differential gear unit connected to said input shaft, and a third shaft for said second differential gear unit connected to said adjusting shaft for varying the setting of the variable speed transmission to maintain the said torque differential between said first and second shafts of the first said differ- .ential gear unit constant so as to maintain the torque transmitted through said first differential constant.

7. A winding and unwinding mechanism comprising in combination a take-up beam, .a drive shaft, a variable speed transmission, adjusting means for varying the speed of said transmission, means connecting the output side of said variable speed transmission to said take-up beam, a ,pair of differential units each having a first shaft, a second shaft, and a third shaft, means connecting the said first shafts to said drive shaft, means connecting the said second shafts to the input side of said variable speed transmission, means connected .to the third shaft of one of said differential units .providing a predetermined torque differential between the first and second shafts thereof, and means connecting the third shaft of the other of said differential units to the adjusting means of the variable speed transmission for varying the setting thereof to maintain the said torque differential constant so as to maintain the torque transmitted from said drive shaft to said beam Constant.

8. A winding and unwinding mechanism comprising in combination a take-up beam, a drive shaft, a variable speed transmission having an input shaft, an output shaft, and an adjusting shaft for varying the setting of the variable speed transmission, means connecting said beam to said output shaft, a differential unit connecting said drive shaft to said input shaft and through which torque is transmitted from said drive shaft to said input shaft, means connected to said differential unit providing a predetermined torque differential between said drive shaft and input shaft, a second differential unit, a first shaft for said second differential unit connected to said drive shaft, a second shaft for said second differential unit connected to said input shaft, and a third shaft for said second differential zunit connected to said adjusting shaft and operable upon va predetermined load placed .onsaid output shaft for varying the setting .ofzthe variable speed device to maintain the said torque differential between :the said drive shaft and input shaft constant so as to maintain the torque transmitted atosaid take=up beam constant.

9. A winding and unwinding mechanism-comprising in -,combination a drive shaft, .apair of variable speed transmissions, adjusting means for varying the setting of said transmission, means connecting said drive shaft to the input side of zone of said transmissions, a pair of .differential units each having a first shaft, a second shaft, .and a third shaft, means connecting the said first shafts to the input side of one of said transmissions, means connecting the said second shafts to the input side of the other of said transmissions, means connected to the third shaft of one of said differential units providing a predetermined torque differential between the first and second shafts thereof, and means connecting the third shaft of the other of said differential units to the adjusting means of said transmissions for varying the setting thereof so as to maintain said torque differential constant so as to maintain the velocity of the input side :of said transmission constant.

10. A winding and unwinding mechanism comprising in combination a drive shaft, a pair of variable speed transmissions, each having an input shaft and an adjusting shaft for varying the setting of said transmission, :meaus connecting the input shaft of one of said transmissions to said drive shaft, a first differential, a shaft for said first differential connected to said drive shaft, a second shaft for said first differential connected to the input shaft of the other of said transmissions, means connected to said first differential providing a predetermined torque differential between said drive shaft and the input shaft of the said other of said transmissions, a second differential, a shaft for said second differential connected to the input shaft of one of said transmissions, a second shaft for said second differential connected to the input shaft of the other of said transmissions, and a third shaft for said second differential connected to the adjusting shafts of said transmission for varying the setting thereof so as to maintain the said torque differential constant and the velocity of the said input shafts constant.

11. A winding and unwinding mechanism comprising in combination a pair of variable speed transmissions, each having an input shaft, an output shaft, and an adjusting shaft for varying the setting of said transmissions, said input shafts being connected to load means, a pair of differentials, each having a first shaft, a second shaft, and a third shaft, means connecting said first shafts to the input shaft of one of said transmissions, means for connecting the second shafts to the input shaft of the other of said transmissions, means connected to the third shaft of one of said differentials providing a predetermined torque differential between the first and second shafts thereof, means connecting the other of said third shafts to the said adjusting shaft to vary the setting of said transmission so as to maintain said torque differential constant, a separate drive connected to each of said input shafts, and means for actuating either one of said drives.

12. A winding and unwinding mechanism according to claim 11 wherein said separate drives are electric motors.

13. A winding and unwinding mechanism according to claim 11 wherein said separate drives are electric motors and each provides a drag on said input shafts when in the rest condition.

14. A mechanism as in claim 7 wherein the means providing the torque differential is a brake.

.15. A mechanism as in claim 7 wherein the means providing the torque differential is a pump.

16. A mechanism as in claim 9 wherein the means providing the torque differential is a brake.

' 17. A mechanism as in claim 9 wherein the means 2,358,112 Smith Sept. 12, 1944 providing the torque differential is a pump. 2,392,226 Butterworth et a1. Ian. 1, 1946 2,496,977 Bechle Feb. 7, 1950 References Cited in the file of this patent 2,584,454 H rd Feb, 5, 1952 U T D STATES PATENTS 5 2,599,795 White n 1952 1,706,109 Dodge Mar. 19 1929 2,608,741 Reeves p 1952 2,168,071 Perry Aug. 1, 1939 FOREIGN PATENTS 2,346,903 Cafirey Apr. 18, 1944 60,926 Denmark May 17, 1943