US2485895A

US2485895A - Tension controlling apparatus

Info

Publication number: US2485895A
Application number: US731210A
Authority: US
Inventors: Elmer J Larsen; Oscar G Nelson
Original assignee: Western Electric Co Inc
Current assignee: AT&T Corp
Priority date: 1947-02-27
Filing date: 1947-02-27
Publication date: 1949-10-25
Anticipated expiration: 1966-10-25

Description

Oct. 25, 1949. E. J. LARSEN EI'AL TENSION CONTROLLING APPARATUS 5 Sheets-Sheet 1 Filed Feb. 2?. 1947' INVENTORS EJ LARSE N 06 NELSON ATTORNEY ,Oct. 25, 1949. E. J. LARSEN ETAL TENSION CONTROLLING APPARATUS 3 Sheets-Sheet 2 Filed Feb. 2'7, 194? Oct. 25, 1949. LARsEN r 2,485,895

TENSION CONTROLLING APPARATUS Filed Feb. 27, 1947 3 Sheets-Sheet 3 lNl/ENTORS EJ LARSEN 0.6. NELSON A T TORNEV Patented Oct. 25, 1949 TENSION CONTROLLING APPARATUS Elmer J. Larsen and Oscar G. Nelson, Baltimore Md., assignors to Western Electric Company, Incorporated, New York, N. Y., a corporation of New York Application February 27, 1947, Serial No. 731,210

Claims. (01. 242-45) This invention relates to tension controlling apparatus, and more particularly to tension'controlling apparatus for strand rewinding machines and the like.

In general, strand rewinding machines consist of a supply reel rotatably mounted so that the strand material contained thereon may be withdrawn therefrom, and a takeup reel rotated by suitable driving means to rewind thereon the strand from the supply reel. When it is necessary to maintain the linear speed of the strand constant during the rewinding operation a constant speed capstan is disposed intermediate the supply reel and takeup reel for withdrawing the strand from the supply reel at a uniform speed. Usually the takeup reel is coupled to an induction type torque motor in order that the speed of the takeup reel may be constantly reduced as the radius of application of the strand to the reel increases. To maintain a predetermined tension on the strand between the supply reel and the constant speed capstan during the rewinding operation, the supply reel is usually coupled to a suitable breaking mechanism capable of applying a predetermined braking force on the supply reel being rotated by the unwinding of the strand therefrom. The braking force applied to the supply reel must be constantly reduced in proportion to the constantly decreasing radius of withdrawal of the strand from the supply reel in order to maintain a substantially constant tension on the strand as it is being unwound from the supply reel. To accomplish this result, the braking mechanism is usually adjusted manually or automatically by means responsive to the variations in the tension of the strand which occur during the rewinding operation.

The necessity of maintaining" constant tension on the strand during a rewinding operation depends largely on the structure of the strand itself. Where the nature of the strand is such that any stretching effect produced thereon by variations in the tension seriously affect the original quality of the strand, such stretching be controlled within very close limits. One type of strand requiring very accurate control of the tension applied thereon during a rewinding operation is a coaxial unit which consists of a solid central conductor centrally disposed within an outer tubular conductor.

An object of the invention is to provide new and improved tension controlling appartus.

Another object of the invention is to provide tension controlling apparatus for strand rewinding machines, wherein the linear speed of the 2 strand actuates electrical control mechanisms for simultaneously decreasing the speed of the takeup reel and the braking force applied on the supply reel as the rewinding operation proceeds from an empty to a full takeup reel.

In accordance with a preferred embodiment of the invention, there is provided a coaxial conductor rewinding machine comprising a supply reel containing a length of coaxial unit, a takeup reel on which the coaxial unit is to be rewound, an A. C. motor coupled to the supply reel, a D. C. motor for driving the takeup reel, motor control apparatus for supplying D. C. potential to the said motors to cause the D. C. motor to drive the takeup reel and the A. C. motor to act as a breaking generator driven by the supply reel as the coaxial unit is unwound therefrom, and a tachometer generator driven by the advancing coaxial unit as it travels from the supp y reel to the takeup reel, the output of said generator being applied to decrease the D. C. potential supplied to the braking motor and driving motor in direct proportion to the constantly changing unwinding radius and takeup radius of the supply reel and takeup reel, respectively, whereby constant speed and tension is maintained on the coaxial unit during the entire rewinding operation.

A clear understanding of the invention may be had from the following detailed description of a specific embodiment thereof, when read in conjunction with the appended drawings, in which:

Fig. 1 is a plan view of a rewinding apparatus forming a preferred embodiment of the invention;

Fig. 2 is a front elevation of the rewinding apparatus shown in Fig. 1;

Fig. 3 is an enlarged front view of a portion of the apparatus shown in Figs. 1 and 2;

Fig. 4 is a horizontal, sectional view taken along line 4-4 of Fig. 3;

Fig. 5 is a sectional view taken along line 55 of Fig. 3;

Fig. 6 is a sectional view taken along line 66 of Fig. 5;

Fig. 7 is a sectional view taken along line 'l'! of Fig. 5; and

Fig. 8 is a schematic wiring diagram of the electrical circuit forming a part of the apparatus shown in Fig. 1.

Referring now in detail to the drawings, and particularly to Figs. 1 and 2, it will be noted that a reel l0 containing a predetermined length of a coaxial unit II is rotatably supported in a supply stand I2 and coupled to a conventional A. C. gear type induction motor. IS. The coaxial unit il mate position of the fault from the outer end of the cable is located by the testing apparatus, after which the reel of defective coaxial unit is positioned in the stand l2 in order that a required length of the coaxial unit may be unwound from the cable in order to make the faulty portion of the cable accessible for repair purposes.

The outer 'end of the coaxial unit contained on the reel l (Fig. 1) is fed through an electric testing apparatus indicated generally at I5, then betweena pair of pulleys i6 and I1 mechanically coupled to a tachometer generator l8 through a gear unit 20. The end of the coaxial unit then is secured to the winding drum of a takeup reel 2| rotatably supported in a conventional type of a traversing takeup stand 22, which stand and reel are driven by a D. C. gear motor 23. Suitable electrical control apparatus, indicated generally at 24, is mounted in a housing 25 and arranged to supply D. C. potential to the primary windings of the A. C. motor 13 and to the D. C. motor 23. A table 26 is positioned adjacent to the housing 25 to provide a working surface on which the coaxial unit ll may be supported during repair operations thereon.

.The tachometer generator is and the D. C. motor control apparatus 24 may be of any suitable design. However, the tachometer generator used in the present apparatus is manufactured by the Westinghouse Electric Manufacturing Company and known commercially as a type BC-46 rated at 100 watts at 250 R. P. M. The control apparatus 24 consists of a unit manufactured by the Westinghouse Electric .Manufacturing Company, known commercially as a type 11 Mot-otrol having a plurality of rectifier tubes provided with control grids for converting a suitable A. C.

potential to D. C. potential and electronic apparatus connectedto the control grids for regulating the D. C. output of the rectifier tubes. The tachometer generator I8 and the gear unit 20 are mounted on a common base 21 .(Fig. 2) -posi tioned in front of the housing 25 so that the pulleys I6 and I! are laterally and horizontally aligned with the coaxial unit I l as it passes from the supply reel ID to the takeup reel 22. The housing 25 is provided with a suitable control panel 28 on which are mounted the various operating buttons and control instruments by means of which the operator may control the operation of the rewinding apparatus.

In order to repair a faulty coaxial unit, it is necessary to expose the faulty portion of the unit, and to do this a predetermined amount of coaxial unit must be withdrawn from the supply reel l0 and the withdrawn portion must be taken up by the takeup reel 2|. When the faulty portion of the coaxial unit passes through the testing apparatus I5, an indicator will indicate this fact and the operator will render th entire rewinding apparatus inoperative so that the faulty portion 01 the cable may be repaired on the table 26. After the necessary repairs have been made, the rewinding operation is continued until the entire length of coaxial unit originally contained on the1 szupply reel i0 is taken up by the .takeup ree 2.

Since great care is exercised in the manufacture of such coaxial units in order to produce a unit having certain required electrical characteristics, it is obviously necessary that during the rewinding operation on the coaxial unit ll, constant tension must be maintained on the unit in order that the original quality of the unit be preserved. It is diflicult to maintain uniform tension on the coaxial unit during such a rewinding operation because the radius of application of the coaxial unit to the takeup reel 22 is constantly increasing, which tends to cause an increased linear speed of the coaxial unit -I I. Furthermore, the efiect of the constant decrease in the withdrawal radius of the unit leaving the supply reel constantly decreasing is to gradually increase the tension on the coaxial unit being withdrawn therefrom. Consequently, some means must be provided for correspondingly decreasing the speed of the takeup reel as its radius of application increases and to decrease the braking effect of the motor l3 as the unwinding radius of the supply reel decreases.

In order to effect a constant decrease in the operating speed of the motor 23 and a constant decrease in the braking effect exerted on the supply reel by the motor l3, the tachometer generator I8 is driven by the coaxial unit II at its normal operating speed so as to generate a predetermined output voltage, which is supplied to .the control apparatus 24 to effect a corresponding decrease in thte D. C. potential supplied to the A. C. braking motor l3 and the D. C. driving motor 23. The linear speed at which the coaxial unit ll may travel during the rewinding operation is relatively slow, that is, in the neighborhood of 50 feet per minute, due to the fact that the purpose of the rewinding operation is to be able to detect when the faulty portion of the unit passes through the electricaltesting apparatus I5. Since it is necessary to run the coaxial unit II at a linear speed commensurate with the detecting ability of the electrical apparatus 15, it is necessary to interpose a suitable driving means, such as the gear unit 20, between the pulleys l6 and I1 and the generator H3 in order that the generator may be driven at its normal operating speed.

Each of the pulleys l6 and I1 is provided with a rubber ring 30 positioned in a peripheral groove provided in the respective pulley, which rubber ring serves to provide a non-slip drive between the coaxial unit and the pulleys I6 and i1. Guides 3l3l, having bores 33-33 therein, are positioned on the front face of a box-like housing 32 of the gear unit 20 so that the axes thereof intersect a vertical line passing through the axes of the pulleys I6 and I! at a point equidistant from the center of rotation of each pulley. In this manner the bores 33-33 provided in the guides 3l3| serve to maintain that portion of the coaxial unit ll engaged by the pulleys in a substantially horizontal position with respect thereto regardless of the angle at which the coaxial unit is being withdrawn from the supply reel or the angle at which it is being taken up by the takeup reel.

The pulley I6 (Figs. 3 and 4) is secured on the end of a shaft 34, which projects through an elongated aperture 35 provided in the front of the housing 32. The shaft. 34 is rotatably mounted in a yoke 36 pivotally mounted on a shaft 31 extending into oppositely disposed bores provided in the housing 32 and mounted in bearings 38-48 fitted in opposite sides of the yoke 36. A spring 8 40 is positioned between a bracket 4i internally mounted on the right hand wall of the housing 32 (Fig. 3) and another bracket .42 secured on the free end of the yoke 38 and is maintained in position therebetween by a post 42 threadedly positioned in the bracket 4! and extending therefrom downwardly through an aperture 44 pro vided in the bracket 42. The spring 40, being arranged in this manner, urges the yoke 38 downwardly and, consequently, urges the shaft 34 and the pulley l8 downwardly, whereby the pulley exerts a predetermined pressure against the surface of the coaxial unit engaged thereby.

The pulley i1 (Figs. 3 and is secured on the end of a shaft 45, which projects through an elongated aperture 46 provided in the housing 32 and vertically aligned with the aperture 35 through which the end or the shaft 34 extends. The shaft 45 is rotatably mounted in a yoke 41 pivotaliy mounted on a shaft 50 extending into oppositely disposed bores provided in the housing 32 and into bearings 5i5i fitted in opposite sides of the yoke 41. A spring 52 (Fig. 3) is positioned between a pad 53 provided on a base 54 of the housing 32 and a bracket 55 secured on the free end of the yoke 41 and is maintained in an upright position therebetween by a pin 56 threadedly positioned in the pad 53 in an upright position so that its free end extends through an aperture 51 provided in the bracket 55. The spring 52 urges the free end of the yoke 41 upwardly and, consequently, urges the pulley l'l upwardly, whereby the pulley is urged against the periphery of the coaxial unit H A gear 60 (Figs. 4 and 6) is secured on the shaft 34 and engages a pinion 6| secured on one end of a bushing 52 rotatably mounted on the shaft 31 by means of bearings 63-63 fitted in the extremities of the central bore of the bushing 62 and having a gear 84 secured on the opposite end thereof. A gear 65 (Figs. 5 and 6) is secured on the shaft 45 and engages a pinion 66 secured on one end of a bushing III rotatably mounted on the shaft 50 by means of bearings ii-Ii fitted in the ends of the bushing and having a gear 12 keyed on the other end thereof. The gear 12 meshes'with the gear 64 (Figs. 4 and 7) secured on the'bushing 62 and driven by the gear 60 through the pinion GI and also a. pinion I3 secured on the end of the armature shaft I4 of the tachometer generator it.

It is believed to be apparent from the abovedescribed arrangement of the gears and their respective'pinions within the gear unit 20 that,

when the coaxial unit is advancing in the direction of the arrow (Fig. .3), the upper pulley I6 is driven in a counterclockwise direction, the lower pulley I1 is driven in a clockwise direction, and the gear unit 28 combines the driving force of the two pulleys at the gears 64 and I2, which in turn drive the tachometer generator through the pinion 13 mounted on the armature shaft 14 of the tachometer generator.

A bracket 80 (Figs. 3 and 4) is mounted on the right side of the housing 32 and has one leg of a hinge 8i secured on the end thereof, the other leg of the hinge 8i being secured to a base 82 on which a conventional counter 83 is mounted. The counter 83 is provided with a drive wheel 84 having its periphery 85 k/nurled and in engagement with the upper surface of the coaxial unit ll being advanced through the guides 3l3i and between the drive pulleys i6 and i1. Having the counter 83 mounted in this manner,

the drive wheel 84 is maintained against the up- 23 through

wires

94 and 95.

per surface of the coaxial unit by its own weight. A support 88 is secured to the bracket II and has a pair of sensitive electric switches "-81 mounted thereon in such a manner that their respective operating buttons 90-" are directly under the base 82 on which the counter 83 is mounted. As long as the coaxial unit is being advanced from the supply reel to the takeup reel. it serves to maintain the counter 83 in a substantially horizontal position, in which position the base 82 is disengaged from the buttons of their respective switches. However, when the inner end of the coaxial unit is advanced beyond the counter 83 and its driving wheel 84, the counter 83 and the base 82 fall downwardly about the hinge 8i, whereupon the base 82 strikes the buttons -30 of the switches 81-81 and'actuates their respective switching mechanisms. The switches 81-81 may be any type of switch having a normally closed contact which is opened upon the actuation of its operating button. The switches are electrically connected to the control apparatus 24 in such a manner that when they are actuated by the droppin of the counter 83 the takeup motor 23 is disconnected from the apparatus 24.

Referring to the schematic wiring diagram shown in Fig. 8, a motor control apparatus indicated genera'ly at 24 is connected to terminals 9l9l, which represent any suitable source of A. C. potential. The A. C. potential supplied to the control apparatus is converted by A. C. rectiflcr tubes provided therein to a D. C. potential, which is supplied to one phase of the induction motor l3 through

wires

92 and 93, and to a D. C. potential, which is supplied to the D. C. motor The tachometer generator I8 is connected to the control apparatus 24 so that the D. C. potential generated thereby is applied to the control grids of the rectifler tubes to control the D. C. potential supplied to the motors I3 and 23. The continuity of the D. C. circuit from the control apparatus 24 to the D. C. motor 23 is controlled byeontacts 96-96 connected to the

wires

94 and 85 The contacts 95-96 are arranged to be actuated by an operating coil 91, which is connected across the A. C. supply terminals 8i-9i in series with the normally closed switches 81-81 which are positioned to be actuated by the base 82 (Fig. 3) when the base drops downwardly as the end of the coaxial unit Ii is advanced beyond the righthand guide 3| Operation The above-described apparatus operates in the following manner:

A reel Ili containing a length of coaxial unit H, which has been tested and found to be defective, is positioned in the supply stand i2 so as to be mechanically coupled to the output shaft of the A. C. gear type induction motor II. The outer end of the coaxial unit II isthreaded through the fault detector test set l5, and then is passed between the pulleys l6 and i1, under the drive wheel 84 of the counter 83 and to the winding drum of the takeup reel 2i rotatabiy positioned in the takeup stand 22 and mechanically coupled to the D. C. gear motor 23. The operator of the rewinding apparatus then'actuates the start button on the control panel 28' of the housing 25 causing the control apparatus 24 to supply D. C. potential to the D. C. gear motor 23'and to one of the primary windings of the A. C gear motor i3 The D. C. motor 23 rotates the takeup reel 2i coupled thereto, whereby the coaxial unit II is withdrawn from the supply reel III, is advanced through the several members mentioned previously and is rewound'on the takeup reel. The supply reel I is rotated by the withdrawal of the coaxial unit therefrom. which reel in turn rotates the A. C. motor I3. The motor l3, by having D. C. supplied to one of its primary windings, acts as a brakin generator and exerts a predetermined braking force on the reel l0, thereby causing a given tension to be applied to the coaxial unit. The motor control apparatus 24 is adjusted, in this particular case, so that the initial linear speed of the coaxial unit H is approximately 50 feet per minute. The movement of the coaxial unit ll rotates the pulleys l6 and I I (Fig. 3) in the direction indicated by the arrows, which pulleys drive the tachometer generator l8 through the gear unit 20 at its rated speed of approximately 250 R. P. M.

The D. C. output potential of the tachometer generator I8 is directed to the control apparatus 24, which is supplying the D. C. operating potential to the takeup reel motor 23 and the D. C. braking potential to the A. C. motor l3. The D. C. potential generated by the tachometer generator being driven by the coaxial unit is directed to the grids of the rectifier tubes forming part of the control apparatus 24 and thereby controls the D. C. potential supplied by the apparatus 24 to the motors 23 and I3.

As the wind-ing'diameter of the takeup reel increases, that is, as the quantity of coaxial unit positioned on the takeup reel increases from layer to layer, the linear speed of the coaxial unit tends to increase which in turn tends to increase the tension on the coaxial unit. This increase in the linear speed of the coaxial unit drives the tachometer generator at a greater speed, which results in a greater output potential from the tachometer generator. This increased potential is directed to the grids of the rectifier tubes of the control apparatus 24 and serves to decrease the D. C. output of the rectifler tubes. This results in a decreased D. C. potential being supplied to the takeup motor 23 and thereby causes the speed of the motor to be reduced until the peripheral speed of the reel is reduced to its original operating speed, which in turn maintains the linear speed of the coaxial unit substantially constant. In other words, as the winding diameter of the takeup reel, 2| continues to increase, as layer after layer of the coaxial unit is woundv thereon, the output potential of the tachometer generator maintains a very sensitive control over the D. C. potential being supplied to the takeup motor 23, whereupon the linear speed of the coaxial unit H, as the rewinding operation continues from an empty takeup reel to a full takeup reel, is maintained substantially constant.

Obviously, as the winding diameter of the takeup reel is constantly increasing, the unwinding diameter of the supply reel III is constantly decreasing in which case the braking eflect exerted on the reel by the motor I 3 must be decreased correspondingly in order to maintain a uniform tension on the coaxial unit ll throughout the rewinding operation. Since the decreased D. C. potential is also being supplied to the A. C. motor l3, which is acting as a braking generator driven by the supply reel I0 due to the withdrawal of the coaxial unit therefrom, a decreased braking force is exerted thereby on the supply reel l0. Therefore, the speed at which the operator the number of feet of the coaxial unit which has been advanced through the testing apparatus l5. Since the coaxial unit ll contained on the supply reel I0 is known to be defective at a point approximately a predetermined distance from the outer end thereof, it is believed to be obvious that the counter serves to put the operator on the alert for the passage of the faulty portion of the coaxial unit through the testing apparatus [5. When the testing apparatus I5 indicates that the faulty portion of the coaxial unit has passed therethrough, the operator immediately stops the rewinding apparatus in order that the faulty portion may be repaired before being rewound on the takeup reel.

Since the speed of the takeup gear motor 23 is controlled solely by the speed of the coaxial unit II as it drives the tachometer generator l8, 9. safety device is provided on the rewinding machine to prevent the motor 23 from running away when the inner end of the coaxial unit is advanced past the pulleys l6 and I! which drives the tachometer generator. This device consists of the pair of sensitive electrical switches 8'l--8I having the normally closed contacts operated by their respective operating buttons -90. When the end of the coaxial unit is advanced beyond the wheel 84 of the counter 83, the hingedly mounted counter falls downwardly and the base 82 engages and depresses the operating buttons 90-90, thereby opening the normally closed contacts of the switches 81-81. The opening of the switches 81-81 deenergizes the coil 9'! and the contacts 9696 drop open, thereby disconnecting motor 23 from the control apparatus 24. In this way the motor 23 is prevented from running away as soon as the control exerted thereon by the tachometer generator l8 ceases.

While the above-described apparatus is particularly well adapted to control the speed and tension of a coaxial unit being rewound from a supply reel to a takeup reel, it may be modified in many ways to control the tension of various types and kinds of materials which may require rewinding in order to carry out some process or to perform some related operation thereon.

What is claimed is:

1. Tension controlling apparatus for coaxial unit rewinding machines, which comprises in combination a rotatably mounted supply reel containing a coaxial conductor supply to be unwound therefrom, a rotatably mounted takeup reel to receive the coaxial conductor from the supply reel, an A. C. motor mechanically coupled to the supply reel, a variable speed D. C. motor mechanically coupled to the takeup reel, means for supplying a variable D. C. potential to the said motors to cause the D. C. motor to rotate the takeup reel and withdraw the coaxial conductor from the supply reel and the A. C. motor to act as a braking generator driven by the supply reel, a tachometer generator electrically connected to the D. C. potential supplying means, a gear unit having its output shaft arranged to drive the tachometer generator, a pair of pulleys arranged to engage opposite sides of the advancing coaxial conductor and drive the gear unit, said gear unit and its driving pulleys being arranged to convert the relatively low speed of the pulleys to a substantially higher rated speed of the tachometer generator, and resilient means for urgingthe periphery of the pulleys against the surface of the advancing coaxial conductor, whereby a substantially positive drive between the conductor and drive pulleys is obtained.

2. Tension controlling apparatus for strand rewinding machines, which comprises in combination a rotatably mounted supply reel containing a strand supply to be unwound therefrom, a rotatably mounted takeup reel to receive the stand from the supply reel, an A. C. motor mechanically coupled to the supply reel, a variable speed D. C. motor mechanically coupled to the takeup reel, means for supplying a D. C. potential to the said motors to cause the D. C. motor to rotate the takeup reel and withdraw the strand from the supply reel and the A. C. motor to act as a braking generator driven by the supply reel, means for varying the D. C. potential applied to said motors, a tachometer generator electrically connected to the D. C. potential controlling means for regulating the D. C. potential supplied to the motors by the said D. C. potential supplying means, and means driven by the advancing strand for driving the tachometer generator, whereby when the linear speed of the strand tends to increase due to the increased winding diameter of the takeup reel the increased speed imparted to the tachometer generator reduces the D. C. potential supplied to the D. C. motors thereby maintaining the strand at substantially uniform tension and speed.

3. Tension controlling apparatus for strand rewinding machines, which comprises in combination a rotatably mounted supply reel containing a strand supply to be unwound therefrom, a rotatably mounted takeup reel to receive the strand from the supply reel, an induction motor mechanically coupled to be driven by the supply reel, a variable speed D. C. motor mechanically coupled to drive the takeup reel, means for supplying a variable D. C. potential to the said motors .to cause the D. C. motor to rotate the takeup reel and withdraw the strand from the supply reel and the A. C. motor to act as a braking generator when driven by -the withdrawal of the strand from the supply reel, a tachometer generator electrically connected to the D. C. supply means for varying the D. C. potential supplied to the D. C. driving motor and the A. C. motor, a gear unit mechanically coupled to the tachometer generator, and a pair of juxtaposed pulleys mechanically coupled to the gear unit and arranged to be driven by the strand being advanced from the supply reel by the takeup reel, whereby the tachometer generator is driven by the advancing strand by said pulleys and gear unit and serves to constantly reduce the D. C. potential supplied to the motors and consequently the speed of the D. C. driving motor and the braking effect of the A. C. brake motor as the winding diameter of the takeup reel constantly increases during the winding operation.

4. Tension controlling apparatus for coaxial unit rewinding machines, which comprises in combination a rotatably mounted supply reel containing a coaxial unit to be unwound therefrom, a rotatably mounted takeup reel to take up the coaxial unit from the supply reel, an A. C. motor mechanically coupled to the supply reel. a variable speed D. C. motor mechanically coupled D. C. motor to rotate the takeup reel and withdraw the coaxial unit from the supply reel and the A. C. motor to act as a braking generator when driven by the withdrawal of the strand from the supply reel, a tachometer generator electrically connected to the D. C. potential supplying means for varying the D. C. potential supplied to the motors, a gear unit having its output shaft arranged to drive the tachometer generator, a pair of juxtaposed pulleys provided on the input shafts of the gear unit and positioned so as to be driven by the advancing coaxial unit and drive the tachometer generator through the gear unit, resilient means for urging the periphery of the pulleys against the surface of the advancing coaxial unit, and means engaged by the advancing coaxial unit for rendering the takeup motor inoperative when the coaxial unit is disengaged from the gear unit driving pulleys, whereby as the coaxial unit is withdrawn from the supply reel by the takeup reel it drives the tachometer generator which in turn varies the D. C. potential supplied to the motors in accordance with the linear speed of the coaxial unit and thereby maintains a uniform speed and tension of the coaxial unit throughout the unwinding operation.

5. Tension controlling apparatus for coaxial unit rewinding machines, which comprises in combination a rotatably mounted supply reel containing a supply of coaxial units to be unwound therefrom, a rotatably mounted takeup reel to take up the coaxial unit from the supply reel, an A. C. motor mechanically coupled to the supply reel, a variable speed D. C. motor mechanically coupled to rotate the takeup reel, electronic means for supplying a D. C. potential to the said motors to cause the D. C. motor to rotate the takeup reel and withdraw the strand from a supply reel and the A. C. motor to act as a brake when driven bythe withdrawal of the coaxial unit from the supply reel, a tachometer generator electrically connected to the D. C. potential supply means for varying the D. C. potential being supplied to the said motors, a gear unit arranged to drive the tachometer generator, a pair of pulleys rotatably positioned on the gear unit so that the strand passes between the peripheries of said pulleys and connected to drive the gear unit and the generator coupled thereto, resilient means for urging the pulleys against the surface of the strand being advanced therebetween, and means provided on the gear unit adjacent to the drive pulleys for guiding the advancing strand so that it passes between the peripheries of the drive pulleys in a straight path regardless of the angle at which the strand is being withdrawn from the supply reel or taken up by the takeup reel. ELMER J. LARSEN. OSCAR G. NELSON.

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

UNITED STATES PATENTS