US3572596A

US3572596A - Cable stressing and winding apparatus

Info

Publication number: US3572596A
Application number: US718138A
Authority: US
Inventors: Maximiliaan J Dykmans
Original assignee: Individual
Current assignee: DYK PRESTRESSED TANKS Inc
Priority date: 1968-04-02
Filing date: 1968-04-02
Publication date: 1971-03-30
Anticipated expiration: 1988-03-30

Abstract

In wrapping wire around a concrete tank to prestress the same a motor-driven carriage travels around the tank with a sprocket wheel engaging a chain that extends around the tank. Simultaneously, the wire is fed from a supply spool onto a wire gripping drum and is then laid on the outer tank wall with a wire tension established by monitoring deviations in stress with respect to a nominal value of stress and using such deviations to produce changes in the difference in peripheral lineal speed between the sprocket wheel (carriage speed) and the gripping drum such that such stress is maintained substantially constant at said nominal value whereby the wire is uniformly and accurately stressed when and as it is being wrapped around the tank wall. The carriage is supported on a tower having wheels engaging both the ground and the tank wall so that wire may be supplied from a point on the machine within or outside the tank. In one form a differential gear system is used. In another form a pair of hydraulic motors is used with one of such motors operating as a pump for the other motor. In another form a variable gear drive is provided between the sprocket wheel and gripping drum. In another form a force is applied to a stressing block acting on the wire in accordance with the stress in the wire. In another form the effective diameter of a gripping drum is changed in accordance with stress in the wire.

Description

United States Patent [72] Inventor Maximiliaan J. Dykmans 4434 Mayapan Dr., La Mesa, Calif. 92041 [21] Appl. No. 718,138 [22] Filed Apr. 2, 1968 [45] Patented Mar. 30, 1971 [54] CABLE STRESSING AND WINDING APPARATUS 20 Claims, 10 Drawing Figs.

[52] US. Cl 242/721 [51] Int. Cl B21f 17/00 [50] Field of Search 242/7 (PS),

11 (PS), 7; 242/7.2l, 7.22, 7.23, 7.02

[56] References Cited UNITED STATES PATENTS 2,520,402 8/1950 l-lirsh 242/722 2,749,054 6/1956 Crom,Jr... 242/722 3,229,924 l/l966 Vogt 242/702 3,338,527 8/1967 Citidzey 242/722 2,415,500 l 2/1947 Kennisonm' 242/722 2,589,366 3/1952 Gauthier 242/722 3,379,385 4/1968 Osweiler 242/722 Primary ExaminerBilly S. Taylor Attorney-Lyon & Lyon ABSTRACT: In wrapping wire around a concrete tank to prestress the same a motor-driven carriage travels around the tank with a sprocket wheel engaging a chain that extends around the tank. Simultaneously, the wire is fed from a supply spool onto a wire gripping drum and is then laid on the outer tank wall with a wire tension established by monitoring deviations in stress with respect to a nominal value of stress and using such deviations to produce changes in the difference in peripheral lineal speed between the sprocket wheel (carriage speed) and the gripping drum such that such stress is maintained substantially constant at said nominal value whereby the wire is uniformly and accurately stressed when and as it is being wrapped around the tank wall. The carriage is supported on a tower having wheels engaging both the ground and the tank wall so that wire may be supplied from a point on the machine within or outside the tank. In one form a differential gear system is used. In another form a pair of hydraulic motors is used with one of such motors operating as a pump for the other motor. In another form a variable gear drive is provided between the sprocket wheel and gripping drum. In another form a force is applied to a stressing block acting on the wire in accordance with the stress in the wire. In another form the effective diameter of a gripping drum is changed in accordance with stress in the wire.

/ rizu [E Bil k a Patented March 30, 1971 3,512,596

4 Sheets-Sheet 3 (IABLE STRESSING AND WINDING APPARATUS The present invention relates to improved means and techniques which are particularly useful in the prestressing of concrete structures such as, for example, reservoirs, nuclear reactor housings, pipe and pressure vessels in general although it will be appreciated that the invention in its broader aspects is useful for other purposes such as, for example, laying cables under controlled tension.

A specific object of the present invention is to provide means and techniques whereby a more uniform and accurate stressing of wire is obtained in the process of wrapping of the same around cylindrical structures.

Another specific object of the present invention is to provide a system of this character in which the wire tension is automatically adjusted so as to make such wire tension substantially constant in intensity.

Another specific object of the present invention is to provide a system of this character in which stresses are monitored to derive information as to the condition of stresses in the wire and using such information in such a manner as to change relative speeds between carriage travel and rate at which the wire is wrapped to thereby obtain a substantially constant tension in the wire during the wrapping process.

Another specific object of the present invention is to provide a system of this character in which a differential mechanism is controlled in accordance with changes in stress so as to minimize variations in such stress.

Another specific object of the present invention is to provide a system of this character in which a pair of hydraulic motors is used with one of such motors being used as a pump for the other motor in controlling and maintaining substantially constant a stress condition in the system.

The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. This invention itself, both as to its organization and manner of operation, together with further objects and advantages thereof, may be best understood by reference to the following. description taken in connection with the accompanying drawings in which:

FIG. I illustrates relationship of apparatus with respect to a concrete wall of a tank around which a carriage effectively pulls itself while laying wire on the tank in a stressed condition.

FIG. 2 illustrates a system incorporating apparatus shown in FIG. ll.

FIG. 3 is a modified system also embodying features of the present invention.

FIG. 4 is another modification embodying features of the present invention.

FIG. 5 illustrates another modification.

FIG. 6 illustrates still another modification.

FIGS. 7, 8 and 9 illustrate details of the ground-based carriage which carries the equipment illustrated in FIG. 1.

FIG. 7 is in general a top plan view.

FIG. 8 is a view in side elevation.

FIG. 9 is also a top plan view and illustrates one method of wire feeding.

FIG. 10 illustrates details of an alternate control system.

In FIG. I a sprocket chain C encircles the outer wall W of the concrete structure T. The chain C may be considered stationary particularly since the major length of the same is in nonsliding contact with wall W. The chain C is used to propel the wheeled carriage 7 having wheels 8 around the wall and it will be seen that as illustrated in FIG. 1 such chain C passes in turn in this order over: guide sprockets 2 and 3, spring-loaded tensioning sprocket 4 urged by spring 4A, drive sprocket 22 on shaft I0 and sprocket wheel 20. The drive sprocket 22 is on shaft It which also mounts a larger sprocket wheel 33. A drive chain 32 extends over wheel 33 and sprocket wheel 31 on the output shaft of hydraulic drive motor 30.

The The wire, strand, cable or the like S which is wrapped around the wall W with tension uniformly and accurately being applied to such cable during such wrapping extends from a supply reel G on turntable H in FIGS. 8 and 9. The wire S extends to and around a wire gripping drum 21 (which is coaxially mounted with the previously mentioned sprocket wheel 20 but which may rotate independently of the same on

different shafts

20A, 21A as illustrated in FIG. 2) and then to the structure wall W for prestressing of the same. At the point where the wire S first engages the drum 21 the wire is springurged against such drum by device 6 for purposes of assuring a nonslip condition between the wire and its gripping drum 2i.

For some purposes the wire gripping drum has a sprocket wheel 218 secured thereto as illustrated in FIG. 2 with a chain 41 extending over such wheel 21B and a sprocket wheel 42 on shaft 40.

The wire S is tensioned and thus stretched as a result of the lineal speed of the carriage 7 being somewhat greater than the rate at which the wire S is laid on the wall, i.e. assuming that the effective diameters of sprocket wheel 20 and wire drum M are the same, as they may be in practice, the sprocket wheel 20 rotates somewhat faster than the wire gripping drum 2] to cause the wire to be stretched and hence tensioned.

It is of importance that such tensioning be uniformly and accurately established during the wire wrapping operation and for that purpose the systems described herein are of particular usefulness.

In FIG. 2 the shaft 10 also drives an axle gear of a differential system 82. The other axle gear 84 and a sprocket wheel 15 are on the shaft 11. A chain 16 passes over sprocket l5 and a sprocket 16 on shaft 40 so that the wire drum sprocket 21B and connected wire drum 21 rotate together.

A plurality of spider gears 86, each joumaled for rotation in the differential housing 87, are in mesh with the

axle gears

80, 84. A ring gear 89 on housing 87 is in mesh with a gear 98 on the output shaft 96 of a control motor 92.

The control motor 92 is controlled by the output of a servosystem 97 having two inputs which are compared in system 97 and functioning to control motor 92 in accordance with such comparison. One of such inputs is a current or voltage derived from a torque transducer 100 associated with shaft 40 in such a manner as to produce such current or voltage that changes in intensity with the torque being applied to shaft 40. The other input is a manually adjustable input derived from the tap 102 on potentiometer resistor I03 having its outside terminals'connected to opposite terminals of voltage source I04. As a result of any change in torque in shaft 40, from a nominal value, there is a change in the output of servosystem 93 to cause the motor 92 to rotate at a different speed which in turn causes the shaft 40 to rotate at a different speed until the torque sensed by transducer Mill is restored to such nominal value. In other words a self-balancing system is provided such that the tension of wire S, related to the torque in shaft 40 is maintained substantially constant during the operation of the system.

In the modification shown in FIG. 3 the chain sprocket 20 is, as previously described, driven by the hydraulic motor 30. In this instance a motor 60 has its output shaft 62 coupled to shaft 10 upon which the sprocketwheel 22 is mounted for purposes described later. The wire drum sprocket wheel 215 has its sprocket chain 41 extending over the sprocket wheel 42 of shaft 40 which in this instance is coupled to the output shaft of a hydraulic motor 61 acting as a hydraulic pump. The

motors

60 and 61 may be of the so-called high torque low r.p.m. type and are preferably of identical construction. Each of

such motors

60 and 61 has its fluid inlet openings connected to the pump 70 via a check valve 71.

The inlet line 60A to motor 60 which is connected to pump outlet line 61A may have a pressure of, for example, 2000 p.s.i. and its outlet line 6013 which is connected to pump inlet line 613 may have a pressure of, for example, 50 p.s.i. These lines 60B, 61B are connected to the reservoir or sump 60C through a check valve 60D, the inlet line 70A of pump 70 being in communication with sump 60C.

. A torque transducer 72 for monitoring the intensity of torque developed in shaft 40 has its current or voltage output applied as one input to the servosystem 74. A second input for system 74 is derived from the manually adjustable tap 75 on potentiometer resistance 76 having its outside terminals connected to voltage source 77. A comparison is made between these two inputs and in accordance with such comparison a voltage is developed on the output lead 78 for controlling the pressure delivered by the pump 70.

Inasmuch as the

motors

60 and 61 are of identical construction and inasmuch as the effective diameters of sprocket wheel 20 and wire gripping drum 21 are the same diameter, the motor 61, while nominally a motor, acts as a pump, pumping fluid to the other motor 60 to tend to increase its speed. The motor 61 thus functioning as a pump effectively serves as a brake and the effectiveness of such braking action is established by torque conditions in shaft 40. Motor 61 acting as a pump and motor 60 maintain a balance in forces. Thus, should, for example, the torque in shaft 40 exceed a nominal value, a corresponding output is developed on output lead 78 so as to reduce the outlet pressure of pump 70 and cause a reduction in the differential speed between drive sprocket 20 and wire drum 21 to restore the torque in shaft 40 to its nominal value.

The other hydraulic motor 30 is supplied with substantially constant pressure from pump 30A and rotates the chain sprocket 20 which causes the carriage to be driven forward. During the travel of the carriage 7 the motor 61 is driven by the drum with the motor 61 acting as a pump to supply energy to the motor 60.

Here again instead of using a torque transducer 72 the servosystem 74 may be controlled by a transducer 50.

In the system shown in FIG. 4 a variable gear transmission system 90 incorporating a differential speed meter 90A and handwheel 90B is used to control the relative speeds of

shafts

21A and 20A upon which chain sprocket wheel 20 and wire drum 21 are mounted respectively. In this case chain C driven by the drive motor 95 through the transmission system 90 passes over a sprocket wheel 91 on shaft 90C of transmission 90 which has its related shaft 90D mounting sprocket wheel 93 and chain 99 extends around

sprocket wheels

93 and 218.

The gear ratio between shafts 90C and 90D of transmission 90 may be adjusted manually using handwheel 908 in accordance with speed information being monitored on speed meter 90A. Such handwheel 908 may also be controlled automatically in accordance with the functioning of servosystem, the handwheel 908 being then automatically adjusted via a mechanical connection represented by dotted line 94A extending from servosystem 94 to handwheel 908 to change the gear ratio such that the tension in wire S, sensed by transducer 50, is maintained substantially constant during the wire wrapping operation. A torque transducer 95 sensing the torque in shaft 90D may be used for this latter purpose of mounting substantially constant wire tension.

Other means may be used to automatically adjust the difference in lineal speed between on the one hand the lineal speed of carriage 7 (FIG. 1) as it travels around the wall W and on' the other hand the lineal speed at which the wire is being supplied. The systems previously described involve a wire gripping drum 21 of constant effective diameter but in accordance with the modification shown in FIG. the effective diameter of the gripping drum 121 is automatically controlled in accordance with changes in stress conditions to change this previously mentioned difference in lineal speed such that the wire tension is maintained substantially constant during the wire wrapping operation.

For this latter purpose, in FIG. 5, the wire drum 121 may generally comprise a plurality of

wire engaging blocks

122, 123, 124, 126, 127, etc. each with an outer generally V- shaped groove within which the wire S is wedged. These blocks 122, etc. are slidably mounted in a circular frame 130 and are held in adjusted position by a corresponding

hydraulic ram

122A, 123A, 124A, 125A, 126A, etc. each having a piston controlling the radial positioning of the corresponding be supplied with fluid under pressure through a corresponding conduit l2lCl26C from a common conduit which may include the hollow shaft 121A of frame 130. In operation of the modification in FIG. 5 when the stress sensed by transducer 50 changes, the pressure supplied to the rams l22A-I27A etc. is changed so as to change the effective diameter of wire gripping drum 121 such that the wire tension is maintained substantially constant. Thus, for example, when the wire tension tends to increase the effective diameter of wire drum 121 is increased by raising the pressure applied jointly to the rams. In such case the wire drum 121 is connected directly to the carriage drive sprocket 20 so as to rotate at the same speed. The transducer 50 may, for example, involve a potentiometer type resistance having its tap adjusted directly in accordance with the position of a movable roller and hence in accordance with the tension in wire S passing over the pair of fixed rollers 52 and 53 and movable intermediate roller 51. These rollers provide a substantially constant deflection of the wire. End portion 54A of rod 50 conforms with roller 51 and follows its movement when and as there is slight change in wire tension to adjust the tap on such potentiometer which in turn causes the servosystem 97 in FIG. 10 to function to restore and maintain the wire tension at a substantially constant value. The voltages on

resistances

50 and 103 in FIG. 10 are compared in servosystem 97 whose output control motor 92 may be used to control the pressure applied to rams l22A-I27, etc. for purposes mentioned above. Other structures may he used for changing the effective diameter of the wire feed out means and in that regard, for example, the wire gripping drum may be in the form of a conical drum around which a plurality of turns of the wire is wound and in such case a segmented ring or tapered member cooperating with such conical drum is raised or lowered in accordance with a condition monitored in the system such that the wire feed out point on the conical drum is correspondingly changed, such segmented ring or tapered member contacting the last convolution of the wire, i.e. the turn of smallest effective diameter and being raised or lowered in accordance with, for example, hydraulic pressures developed in response to such condition being monitored such that such condition is automatically maintained at a nominal value.

It will also be appreciated that while for illustrative purposes the drawings show a separate chain C (FIG. I) to provide the traction for the carriage other means may be used for that purpose. For example, the wire itself may be used, in which case, the wire supplied from its supply reel first extends around the concrete structure W (one or more turns of the same contact and bind around the structure wall) and after leaving such wall the wire may be wound around a wire gripping drum (for example, corresponding to sprocket wheel 20) which when rotated causes the carriage to travel around the structure; and after leaving such drum the wire may pass around a second gripping drum (for example, corresponding to drum 21) prior to being laid on the wall under tension.

The present invention in its broader aspects may also be applied to machines of the character described in the US. Pat. No. 3,229,924 issued Jan. 18, I966 to Vogt as now described in relation to FIG. 6 herein which is a modification of the structure shown in FIG. 5 of such Vogt patent. For ease of comparison corresponding parts in these two FIGS. under comparison have the same reference numerals raised, however, by in FIG. 6 herein.

In FIG. 6 the strength of coil compression spring 133 is adjusted by adjustment of the pressure supplied to ram 170 having its plunger 171 serving as a movable abutment for one end of spring 133, the other end of spring bearing on angle lever 161 is pivoted on shaft 166 and which has its arm 161b bearing against the wire clamping means or segment 131 to press such segment with a force dependent upon the pressure applied to ram 170. The pivot shaft 166 of each clamping segment 131 is supported by a fork member 167 each of which is arranged upon one of the stop members 134. The wire is clamped wire engaging block in the frame 130. Each of these rams may 75 between the clamping jaws I35 and 136. When the force acting upon the wire 130 in the direction of the arrow 162 becomes greater than the force acting upon the clamp segment 131 then the clamp segment is moved in the direction of rotation denoted by arrow 162. The force acting upon the clamp segment 131 through the agency of the angle lever 161 is automatically changed by changing the pressure applied to ram 170 in accordance with wire tension sensed by transducer 50 using a servosystem as previously described such that the tension in the wire is maintained substantially constant during the wire wrapping operation.

The carriage 7 of FIG. 1 may be supported for vertical adjustment in a movable framework involving as shown in FIGS. 7, 8 and 9 two trussed

end sections

201, 203 and an open center section 202 in the form of an elevator shaft within which the carriage 7 may move vertically while being guided by engagement of rollers 205 with one or more vertical guide tracks 206. The carriage 7 is supported on cable 210 which is driven by a winch (not shown) which may be mountedon one of the

end sections

201, 203 or on the carriage 7 itself.

The

end sections

201, 203 at their lower ends each mounts a pair of wheels 212 engaging an extension of the base B of the concrete structure and also a pair of wheels 213 engaging the outer surface of circular concrete wall W. Wheels 213(FlG. 8) engage the lower portion of the wall and various means may be used to assure their continued contact with the wall as, for example, by providing wheels 220. engaging the inner surface of wall W, or by cables 222 extending from

end sections

201, 203 to a center post P which as illustrated in FIG. 8 may be located on the-roof R- or on the floor F of the concrete structure, the cables in each instance being attached to a structure T in the form of a rotatable tumet or cylinder which may turn on post P when and as the

carriage structure

201, 202, 203 moves around the tank or concrete structure. This arrangement also has the advantage that the wire supply reel G (F IG. 9) may be rotatably supported on a turntable H which turns when and as the structure 201, 202,203 moves around the tank and the wire is being wound around-the tank.

The term wire as used herein may. be considered in its broadest meaning to include'cable, strand, wireand the like, either metallic or nonmetallic.

While the particular'embodiments of the present invention have been shown and described, itwill be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the this invention.

lclaim:

l. in a system of the character described wherein a carriage moves around a stationary circular structure to lay and tension wire on the same, a carriage for movement around said stationary circular structure; means for supporting said carriage adjacent to the outer wall of said circular structure for circumferential movement around said circular structure; a wire supply; means on said carriage for gripping wire supplied thereto from said wire supply; said gripping means including at least one movable element; means for moving said carriage around said circular structure; means for producing movement of said movable element such that a tension is developed in said wire; means operating concurrently with said movement producing means-for sensinga condition representative of the tension in said wire and developinga first signal; means developing a second signal independently of said first signal but representative ofa desired tension in said wire; a ser vosystem responsive to and controlled inaccordance with said first and second signals and functioning to produce a control signal representative of the difference in said first signal and said second signal; and means responsive to said control signal and controlling said movement producing means to restore said first signal to a value commensurate with said second signal.

2. A system as set forth in claim 1 wherein said means for sensing a condition representative of the tension in said wire is a torque transducer in a shaft which is part of said movement producing means.

3. A system as set forth in claim 1 in which said movement producing means includes a differential system having two axle gears coaxially disposed with a plurality of spider gears coupling said axle gears and being rotatably supported on a housing and with said housing having an external gear, one of said axle gears being coupled to said carriage moving means, the other of said axle gears being coupled to movable element, a motor, means controlling said motor in accordance with torque developed in the couplingbetween said movable ele ment and said other axle gear and means coupling the output of said motor to said external gear.

4. A system as set forth in claim 3 wherein said housing completely encloses said axle gears and said spider gears.

5. A system-asset forth in claim 1 wherein said means for supporting said carriage includes a frame structure having ground engaging wheels upon which such frame structure rests.

6. A system as set forth in claim 1 in which said wire supply includes a wire reel rotatably supported within said circular structure.

7. A system as set forth in claim 1 wherein said gripping wire means includes a drum around which the wire is gripped without substantial slippage between the wire and drum.

8. A system as set forth in claim 1 in which said carriage moving means includes a chain extending around the circular structure and a motor driven sprocket on said carriage engaging said chain.

9. A system as set forth in claim 1 in which said means for developing said first signal includes a torque transducer and said means for developing a second signal includes an adjustable potentiometer type resistance.

10. A system as set forth in claim 1 in which said servosystem is a self-balancing system.

11. A system as set forth in claim 1 in which said servosystem controls a bidirectional motor having an output shaft, a differential system having a one axle gear and a second axle gear and a ring gear, means coupling said output shaft to said ring gear, means coupling said one axle gear to said carriage moving means, and means coupling said second axle gear to said wire gripping means.

l2.- A system as set forth in claim 1 including a first hydraulic motor driven by said'carriage moving means, a second hydraulic motor having its operating shaft coupled to said wire gripping means and a hydraulic pump having its outlet hydraulically coupled to each of said hydraulic motors, said pump being controlled by said servosystem.

13. A system as set forth in claim 1 wherein said carriage movingmeans includes a motor and a chain engaging sprocket driven through a first coupling system, said motor having an output coupled to said wire gripping means through a second coupling system, an adjustable gear system in one of said coupling systems and controlled by said servosystem.

14. A system as set forth in claim 1 in which said movable element is a part of the wire gripping means which is in the form of a drum around which the wire extends, the effective diameter of said drum'being changed in accordance with the position of said movable element, and means for positioning said movable element in accordance with stress being developed in said wire.

15. A system as set forth in claim 1 in which said movable element is a spring-urged slidable element engaging said wire and controlled in accordance with tension being developed in said wire.

116. A system as set forth in claim 1 in which said movement producing means includes a first motor means coupled to said carriage moving means; second motor means coupled to said wire gripping means; said second motor means being capable of functioning as a source of energy; a first coupling connecting the input of said first motor means to the output of saidsecond motor means functioning as a source of energy; a second coupling connecting the output of said first motor means to the input of said second motor means; a source of energy having its output connected to said first coupling; the output of the last-mentioned source of energy being controlled by said servosystem.

17. A system as set forth in claim 16 in which said first motor means is a hydraulic motor; said second motor means being a hydraulic motor capable of functioning as a hydraulic pump.

18. A system as set forth in claim 1 in which said movement producing means includes a first hydraulic motor coupled to said carriage moving means, a second hydraulic motor coupled to said wire gripping means, said second hydraulic motor capable of functioning as a hydraulic pump, a first hydraulic coupling connecting the inlet of said first hydraulic motor to the outlet of said second hydraulic motor functioning as a hydraulic pump, a second hydraulic coupling with a pressure relieve valve draining to tank and connecting the outlet of said first hydraulic motor to the inlet of said second hydraulic motor, a hydraulic pump having its outlet connected to said first hydraulic coupling, the output of said hydraulic pump being controlled by said servosystem.

19. A system as set forth in claim I wherein said wire gripping means permit bidirectional movement of said movable element without affecting the effectiveness of said wire gripping means on said wire.

20. A system as set forth in claim 1 in which said movement producing means includes a variable gear with the input coupled to said carriage moving means and the output coupled to said wire gripping means, adjusting means on said variable

Claims

1. In a system of the character described wherein a carriage moves around a stationary circular structure to lay and tension wire on the same, a carriage for movement around said stationary circular structure; means for supporting said carriage adjacent to the outer wall of said circular structure for circumferential movement around said circular structure; a wire supply; means on said carriage for gripping wire supplied thereto from said wire supply; said gripping means including at least one movable element; means for moving said carriage around said circular structure; means for producing movement of said movable element such that a tension is developed in said wire; means operating concurrently with said movement producing means for sensing a condition representative of the tension in said wire and developing a first signal; means developing a second signal independently of said first signal but representative of a desired tension in said wire; a servosystem responsive to and controlled in accordance with said first and second signals and functioning to produce a control signal representative of the difference in said first signal and said second signal; and means responsive to said control signal and controlling said movement producing means to restore said first signal to a value commensurate with said second signal.

3. A system as set forth in claim 1 in which said movement producing means includes a differential system having two axle gears coaxially disposed with a plurality of spider gears coupling said axle gears and being rotatably supported on a housing and with said housing having an external gear, one of said axle gears being coupled to said carriage moving means, the other of said axle gears being coupled to movable element, a motor, means controlling said motor in accordance with torque developed in the coupling between said movable element and said other axle gear and means coupling the output of said motor to said external gear.

5. A system as set forth in claim 1 wherein said meAns for supporting said carriage includes a frame structure having ground engaging wheels upon which such frame structure rests.

12. A system as set forth in claim 1 including a first hydraulic motor driven by said carriage moving means, a second hydraulic motor having its operating shaft coupled to said wire gripping means and a hydraulic pump having its outlet hydraulically coupled to each of said hydraulic motors, said pump being controlled by said servosystem.

13. A system as set forth in claim 1 wherein said carriage moving means includes a motor and a chain engaging sprocket driven through a first coupling system, said motor having an output coupled to said wire gripping means through a second coupling system, an adjustable gear system in one of said coupling systems and controlled by said servosystem.

14. A system as set forth in claim 1 in which said movable element is a part of the wire gripping means which is in the form of a drum around which the wire extends, the effective diameter of said drum being changed in accordance with the position of said movable element, and means for positioning said movable element in accordance with stress being developed in said wire.

16. A system as set forth in claim 1 in which said movement producing means includes a first motor means coupled to said carriage moving means; second motor means coupled to said wire gripping means; said second motor means being capable of functioning as a source of energy; a first coupling connecting the input of said first motor means to the output of said second motor means functioning as a source of energy; a second coupling connecting the output of said first motor means to the input of said second motor means; a source of energy having its output connected to said first coupling; the output of the last-mentioned source of energy being controlled by said servosystem.

19. A system as set forth in claim 1 wherein said wire gripping means permit bidirectional movement of said movable element without affecting the effectiveness of said wire gripping means on said wire.

20. A system as set forth in claim 1 in which said movement producing means includes a variable gear with the input coupled to said carriage moving means and the output coupled to said wire gripping means, adjusting means on said variable gear to control the output speed in relation to the input speed, a motor coupled to said adjusting means and said motor being controlled by said servosystem commensurate with said tension in said wire.