US3704993A

US3704993A - Drive system for strip material

Info

Publication number: US3704993A
Application number: US58332A
Authority: US
Inventors: Gaetano Monaco
Original assignee: Steel Company of Canada Ltd
Current assignee: Steel Company of Canada Ltd
Priority date: 1970-07-27
Filing date: 1970-07-27
Publication date: 1972-12-05
Anticipated expiration: 1989-12-05
Also published as: CA960716A

Abstract

The specification and drawings disclose a regenerative drive system for transferring and conserving energy in a process line of a strip steel mill. Coiled steel is unwound from a pay-off reel with the aid of helper rollers and proceeds through different treatments. A pay-off pump is operatively connected to, is driven by, and acts as a drag on the pay-off reel thus creating tension in the strip. A metering motor is driven by the pay-off pump and is directly connected to an electric motor by means of a shaft in order to aid the electric motor in driving a hydraulic helper roller pump. The hydraulic helper drive pump is in fluid communication with and ordinarily drives one or more hydraulic motors in parallel which motivate the helper rollers. The metering motor and the hydraulic pump are mechanically connected to each other through the electric motor. In this manner energy can be redistributed between the pay-off reel and the helper rollers. One way in which the energy can be redistributed is by having at least some of the pumps convert to motors and vise versa in order to aid in driving the other elements.

Description

United States Patent Monaco [s4] DRIVE SYSTEM FOR STRIP MATERIAL [72] Inventor: Gaetano Monaco, Hamilton, On-

tario, Canada [73] Assignee: The Steel Company of Canada Limited [22] Filed: July 27, 1970 [21] Appl. No.: 58,332

[52] US. Cl. ..242/75.53, 60/53 WW [451 Dec. 5, 1972 Primary Examiner-Stanley N. Gilreath Assistant Examiner-Milton S. Gerstein Attorney-Fay, Sharpe and Mulholland [5 7] ABSTRACT The specification and drawings: disclose a regenerative drive system for transferring and conserving energy in a process line of a strip steel mill. Coiled steel is unwound from a pay-off reel with the aid of helper rollers and proceeds through different treatments. A payoff pump is operatively connected to, is driven by, and acts as a drag on the pay-off reel thus creating tension in the strip. A metering motor is driven by the pay-off pump and is directly connected to an electric motor by means of a shaft in order to aid the electric motor in driving a hydraulic helper roller pump. The hydraulic helper drive pump is in fluid communication with and ordinarily drives one or more hydraulic motors in parallel which motivate the helper rollers. The metering motor and the hydraulic pump are mechanically connected to each other through the electric motor. In this manner energy can be redistributed between the pay-off reel and the helper rollers. One way in which the energy can be redistributed is by having at least some of the pumps convert to motors and vise versa in order to aid in driving the other elements.

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8 or 8 INVENTOR. GAETANO MONACO ATTORNEYS DRIVE SYSTEM FOR STRIP MATERIAL Feedback systems vary the displacement of the different hydraulic motors and pumps in order to maintain the desired tension and speed of the line.

A similar regenerative system is used in the tension reel and bridle rolls in order to maintain a given speed and tension. That is, a dual shafted electric motor drives hydraulic pumps which in turn drive hydraulic motors connected to the bridle rolls and the tension reel. Energy available from the dragging action of the bridle is utilized in the bridle pump (now operating as a motor) aiding in turning the electric motor. With such aid a reduced amount of electric power is drawn by the electric motor.

. BACKGROUND OF THE INVENTION It is extremely important in a strip steel process line to maintain a precise speed. The various liquids and other processes through which the strip steel passes havea specific time in which to act. Therefore, any variation of the time of one of the processes in the line could result in defective material which would have to be scrapped.

Maintenance of a specific tension is also important. Any significant variation of the tension in the strip at high temperatures would cause it to stretch out resulting in an uneven strip width. Excess width variation of the strip make it unsuitable for its intended use. Good tension regulation is also very important to insure strip tracking in the process line.

In strip steel processing mills it is common to start with the steel in coils or rolls. The coiled steel is generally loaded on what is commonly known as a payoff reel. The steel is unrolled from the pay-off reel by having it pass through deflector rollers and helper rollers which act to motivate the strip. The strip continues through the various processes and eventually interweaves between two rollers known as bridle rolls. After the line passes through the bridle rolls it coils on a reel known as a tension reel. Tension is created in the initial section of the strip by placing a drag on the pay-off reel.

-Existing drives forsteel process lines are to a great extent of an electrical nature. They utilize a direct current drive system and electrical regeneration for the power developed by a drag generator which is motivated by the pay-off reel. This power is fed back into the electrical network in an effort to conserve some energy. However, it has been found that the high inertia of the electric motor armature makes the system sluggish. That is the system has a high response time in order to correct any variation from the desired tension or speed.

Some hydraulic drives are used on process lines. These hydraulic drives usually attempt to maintain a proper tension in the strip by relieving the pressure through a relief valve. Also, in some cases the power developed in the pay-off pump has been partially utilized in a metering motor which is hydraulically connected to the pay-off pump and mechanically connected to a helper roll. This type of drive has no ability to reverse its function from pump to motor, and auxiliary equipment is required to establish the initial back tension in the strip. Another method of developing strip back tension is by the use of a slipping clutch. In effect a slipping clutch, or a relief valve dissipates energy in the form of heat.

The instant invention makesuse of the supplementary energy in the system by channeling it through hydraulic and mechanical means to another part of the system to which power must normally be added. In effect this allows the conversation of some of the energy which would otherwise simply be dissipated.

This drive system includes an electro-hydraulic servo control to correct the parameters such as speed and tension of the process line. It makes use of the versatility of electronic controls and the compactness and more positive nature of hydraulic power to achieve a better degree of control and shorter time responses for corrections than purely electrical means. A unique feature of this system is that the main drive sections are connected to each other through the primary power source, an electric motor. In this respect the system is said to'be hydromechanicalregenerative.

In most instances thepower developed in the pay-off reel during the process of developing strip back tension is utilized in driving the helper drives. Similarly, the power developed in the bridle rolls while dragging is utilized in the tensionreel system. In some situations,

system can be transferred as the need arises.

SUMMARY OF THE INVENTION .This invention relates to a regenerative system for motivating a strip or strand of material 'and has a first rotating member and a second rotating member to aid in motivating a common strip of material. A first hydraulic pump is operatively connected to the first rotating member. A first hydraulic motor is in fluid communications with thefirst hydraulic pump and driven by it. An electric motor is mechanically connected to the first hydraulic motor and a second hydraulic pump is also mechanically connected to the electric motor. A second hydraulic motor is in fluid communication with anddriven by a second hydraulic pump. The second hydraulic motor is operatively connected to the second rotating member whereby energy may be redistributed between thefirst rotating member and the second rotating member.

In one embodiment of this invention, an electric motor drives hydraulic pumps through dual shafts. The pumps in turn drive hydraulic motors which turn rotating members. Again, available energy in one section of the system may be redistributed to the other section through the electric motor.

Servo controls for the hydraulic motors and pumps may change their displacement in order to compensate for changes in speed or tension of the strip of material. In the drawings:

FIG. 1 is a schematic showing a path through which strip steel passes in a rolling mill.

FIG. 2 shows a schematic of a variable displacement axial piston pump and the angular relationship between its swashplate and the pumping piston block.

FIG. 3 is a schematic representation of an axial piston pump. 7

FIG. 4 shows a combination hydraulic pump and motor.

FIG. 5 illustrates a schematic diagram of a pay-off reel system.

FIG. 6 is a schematic of the hydraulic pump-motor combination and controls for the pay-off reel system.

FIG. 7 shows the hydraulic pump-motor combination and controls for the helper drive system.

FIG. 8 is a schematic representation of the bridle roll system.

FIG. 9 is a schematic diagram of the tension reel drive used in this invention.

FIG. l'is a schematic hydraulic circuit diagram of this regenerative system utilized with pay-off and helper rolls and tension reel.

FIG. 11 is a schematic hydraulic circuit diagram of this regenerative system utilized with the take-up or tension roll. I

In some process lines it is of the utmost importance to maintain constant speed and constant tension with a minimum power input-to the system. In such situations, the regeneration or transfer of energy from one location having excess energy to another having a deficiency is a practical solution. The type of process line where regenerative system of this invention may be used is illustrated in FIG. 1.

Basically, strip steel 1 is unrolled from a pay-off reel 2 and proceeds through a relatively large number of steps illustrated schematically by the group of helper rollers shown generally as 3. This system may include heating, cooling, baths and the like. Helper rollers 4 are spaced along the line to aid in moving the strip and. to keep the tension level gradient through the line to a minimum. A take-up or tension reel 5 receives the treated steel strip from bridle rolls 6 and 6(a) and rolls it up.

The regenerative system of this invention has two subsystems. Subsystem I refers to an electro-hydraulic interconnection between the pay-off reel 2 and helper rollers 4. Subsystem II refers to the tension reel 5 and bridle rolls 6 and 6(a) which are hydromechanically interconnected to transfer energy to each other. The exchange of power or energy in both systems generally takes place by virtue of the hydromechanical connections in its components, by monotoring' the control variables such as speed or tension, and feeding back these signals to the controller.

This relatively complex hydraulic system uses basic hydraulic equipment such as hydraulic motors and pumps. This hydraulic pump-motor system basically utilizes a servo controlled hydraulic pump supplying hydraulic fluid under pressure to a hydraulic motor, also referred to interchangeably in the art as a fluid motor. The fluid motor rotates at a speed that is a function of the output of hydraulic fluid from the hydraulic pump, thus the turning speed of the fluid motor is said to be proportional to flow of hydraulic fluid supplied by the pump.

The hydraulic pumps and the hydraulic motors in this system are essentially identical units. They are axial piston type units. A typical piston pump and similarly a fluid motor is generally illustrated in FIG. 2 and shown in schematic in FIG. 3.

The pump comprises a cylinder block 7 having a plurality of axially disposed cylindrical bores 7(a) for receiving therein close fitting pistons 7(b). A circular, disc-like swashplate 8 is connected to a drive shaft 8(a) and the two are in a perpendicular relationship to each other. The centerline 8(b) of the circular swashplate and that of the drive shaft coincide.

The pistons 7(b) of the pump are connected to the swashplate 8 by means of connecting rods or piston rods 9. The ends of the piston rods 9 are attached to the pistons and swash-plate through suitable means such as a ball-and-socket.

FIG; 3 shows that variable angular relationship can be created between the centerline 9(a) of the cylinder block and the centerline 8(b) of the swashplate and drive shaft. Such an angular relationship is designated by a which can be any angle between zero and the maximum allowed by the structure of the pump.

The pumping action is a function of and controlled by the angular axial differential a between the centerline 9(a) of the cylinder block 7 and the centerline 8(b) of the drive shaft 8(a). The displacement of the pump is by definition, the volume of hydraulic fluid the pump will supply for each complete single revolution of the pump. This volume can be calculated. Knowing the diameter of each bore 7(a) and .stroke 9(b) of each piston 7(b) and the total number of pistons in the pump, the displacement of the pump will equal piston area it stroke x number of pistons. In fixed displacement pumps, pump output is constant. However, in variable displacement pumps, as used in this design, output can be and is in fact varied infinitely between zero and maximum by changing the angular relationship 0: between the centerline 9(a) of the cylinder block 7 and the centerline 8(b) of the drive shaft 8(a). It can, in fact, be shown that when angle a is zero, pump displacement is zero and therefore pump output is zero. Conversely, when angle a is maximum, displacement is maximum and pump output is maximum at any given rotating speed.

The pump action is a result of the continuous reciprocal motion of each piston within the pump block. As the block rotates each piston within the block moves from its most forward position, 7(c), to its foremost rearward position, 7 (d). This is done in a rotary motion of degrees during which the piston draws in fluid through an intake port into the bore. As the piston reverses its linear direction, it begins to expel the oil under pressure. This portion of the cycle is completed in the remaining 180' of travel of the piston. The continuous reciprocating action of a plurality of pistons continuously draws in and expels fluid from each bore in quick succession creating the pump action of the unit.

The action of a hydraulic motor is analogous to that described for the pump. The major difference is that hydraulic fluid enters the hydraulic motor at high pressure and leaves the motor at low pressure. This, of course, is exactly opposite the action of the pump where hydraulic fluid enters the pump at low pressure (usually atmospheric) and leaves the pump at high pressure (system operating pressure).

A basic premise of the system of this invention is that the power in a fluid system is related to torque. The parameters that govern torque in a fluid pump are piston stroke and hydraulic pressure. The action of piston stroke can be explained with the aid of FIG. 3, which is a schematic diagram of a variable displacement pump showing only two of the pistons at varying positions of their respective strokes.

When the centerline 9(a) of the cylinder block 7 is in perfect alignment with the centerline 8(b) of the drive shaft 8(a) angle a equals zero. This results in zero piston stroke, zero displacement of the pistons and zero displacement of oil. No flow means no hydraulic power output, therefore zero torque.

The cylinder block centerline can be moved infinitely to any angular relationship a with respect to the centerline 8(b) of the drive shaft 8(a) between zero and full output. Assuming arbitrarily that FIG. 3 represents -a condition wherein the piston stroke oil displacement within the pump is assumed to be 50% of maximum, the torque developed by the pump will be 50% of maximum torque. This is a result of an increased angle a which causes a component of force tangent to the swashplate. Thus, the torque can be varied by simply adjusting the angle a between the cylinder block and the drive shaft which thereby varies the displacement.

If accurate changes in torque are desired, it is important to know not only that torque varies with displacement of the pistons, but that it is directly proportional thereto. This proposition stems from the fact that, in an ideal situation, the power is constant and is the product of torque and the number of revolutions. Symbolically, this may be expressed as P=TN where P is power, T is torque and N is the number of revolutions. The number of revolutions N of a pump or motor is dependent on its displacement. FIG. 4 is helpful in understanding the interrelation between torque, number of revolutions an displacement. t

The hydraulic pump 11 and fluid motor 12 are assumed to be identical units with an efficiency of 100%. inefficiencies will, of course, occur but the basic relations will not be significantly altered by these assumptions. If the angle B between the centerlines of the drive shaft and the cylinder block in the hydraulic motor equaled the angle a in the pump 11, the displacements of the pump and motor would be equal. Moreover, since the power input from thepump would equal the output from the motor in an ideal system and since equal displacements will give equal rotational speed, then relation P=TN will result in equal torque in both the pump 11 and motor 12.

FIG. 41 illustrates a situation where the hydraulic motor 12 is stroked so its displacement is 50% of maximum while pump displacement is kept at 100%.The hydraulic motor 12 will be able to accept, during each revolution, only 511% of the oil being supplied to it through high pressure line 11(a) by the pump 11 which is still supplying the maximum flow. But since all of the oil supplied by the hydraulic pump 11 must somehow be accepted by the hydraulic motor 12, the hydraulic pump 11 must somehow be accepted by the hydraulic motor 12, the hydraulic motor must make two revolutions for every one revolution of the pump. Since the hydraulic power P supply by the pump remains constant and equals the product of torque and number of revolutions (TN), it follows that by doubling the speed of the hydraulic motor 12, the output torque of the hydraulic motor 12 is halved. Thus output torque is a direct function of the displacement which governs the rotational speed of the fluid motor. Or stated more generally, pump torque is directly proportional to its displacement.

PAY-OFF REEL SYSTEM A schematic of the pump and fluid motor drive of the pay-off reel system is illustrated in FIG. 5 and utilizes the principles and structures discussed above. As noted in FlG. 1 the pay-off reel is the source of strip steel to be treated. For purpose of consistent treatment of the steel it is imperative that the steel unrolls from the payoff reel at a constant tension and speed. Particular problems are involved in maintaining these conditions, however, since the reduction in diameter of the unwinding coil causes the pay-off reel to increase its angular speed. In general the tension and speedcompensations occur by varying the angle between drive shafts and cylinder blocks of the hydraulic pumps and motors and therefore their displacement and torque. Strip tension-can also be varied byregulating the hydraulic pressure since it also is related to the torque.

In the pay-off controls of FIGS a metering motor 126 is forced to turn at a constant speed because it is connected to a constant speed electric motor 130. A hydraulic pay-off pump 1211 acts as a drag on and is motivated by the pay-off reel which is unrolled by the moving strip of steel. The pay-off reel is continuously reducing in diameter and thus continuously speeding up. The pay-off pump therefore has a tendency to accelerate and pump fluid faster to the metering motor 126 than it can accept. The metering motor 126 being connected to an AC motor (within the limitation of induction motor slippage, 3 per cent from zero to full load) will not speed up. This impllies that for a given line speed the volume received by the metering motor is practically constant. The increase in pay-off pump angular speed, due to the decrease in coil diameter, is compensated by a decrease in pay-off pump displacement to maintain a constant pump flow and hor sepower. The displacement of the metering motor 126 is directly dependent only on the steel speed. 7 V g The steel strip tension is dependent on the hydraulic pressure in the system. Higher pressures result in higher torques in the pumps and motors which therefore pull the strip together. The -strip tension can therefore be controlled by regulating the pressure.

In the pay-011' reel system of FIG. 5, the variable displacement pump 1211 delivers fluid through a high pressure power line 126m) to the variable displacement metering motor 126 which returns it through a low pressure return line 120(a). An actuator 1122 governs the angular movement of the pump 120 in response to a fluid signal from a servo valve 121.. A torque motor 13 in combination with control amplifier 5d and appropriate feedback from a pressure transducer 157 control the servo valve 121.

in F116. 5 the pay-oft pump 126 is set at maximum displacement which corresponds to the maximum positional torque setting. This is the initial pay-off pump setting when the diameter of the steel coil is the largest. As the coil pays off the coil diameter decreases, and for a given line speed the angular speed of the mandrel holding the pay-off reel will increase. As pump speed increases, for a given displacement, the pump tends to supply more oil than the metering motor can accept. The net result is a tendency for hydraulic pressure to rise.

strip linear This tendency for system pressure to rise is quickly detected by the strain gauge type pressure transducer 157. The pressure transducer 157 generates a feedback signal which is compared with the reference signal resulting in an error signal. The error signal is amplified and the current output from the amplifier is used to deflect a torque motor 13. I

The torque motor 13 comprises a permanent magnet stator 17, a permanent magnet 18, a coil winding 19, and a rotor 20 connected pivotally to a member 21 which reciprocates' the spool 22 within the servo valve 121.

Assuming that the current output from the amplifier causes the rotor 20 of the torque motor 13 to rotate counterclockwise, the member 21 will move the spool 22 to the right, away from the torque motor 13.

The servo valve 121 has four fluid ports. One port 23 is for incoming, supply pressure fluid, and the other port 24 is for return, low pressure fluid. As the spool 22 moves to the right, a spool land 25 uncovers the valve port 27 and the spool land 26 uncovers the valve port 28. Supply oil flowing into the servo valve 121 through the supply port 23 flows through the now open port 28 through the fluid line 16 into the rod end 29 of the actuator 122. Simultaneously, fluid escapes from the head end 29(a) of actuator through line and port 24. The piston 31 and rod 32 in the actuator 122 retract upwardly. The rotating pump drive shaft 117 and the swashplate 30 are stationary (in a linear plane) and act as a type of hinge for the pump 120 which swings slightly upward, together with the piston block 32. This action reduces the angle a and therefore reduces pump output displacement. T

Since the diameter of the steel coil on the pay-off reel is reduced continuously the pump displacement decreases continuously, and very gradually, to maintain the present hydraulic pressure and strip tension.

In addition to developing a constant strip back tension, the pay-off system performs other functions. More specifically, after the coil is loaded on the pay-off reel mandrel, the pay-off reel is jogged forward to allow the head end of the coil to be welded to the tail end of the strip in the line.

After welding, the pay-off reel is jogged into reverse to take out slack and establish strip back tension. How the drive performs these functions is illustrated in FIG. 6.

Item 53 is the feedback positional transducer for the yoke. The yoke position potentiometer applies a reference signal to the linear amplifier. With the coil on the pay-off reel mandrel, the operator turns the positional transducer 53 to a position on a graduated scale corresponding to the coil diameter. This reference voltage to the linear amplifier 56 ultimately causes the payoff pump yoke to assume an angle consistent with the diameter of the coil.

The yoke is now locked in position. By using the jog forward button, a reference signal is applied to the linear amplifier 54 of the metering motor 126, causing the metering motor 126 to assume a predetermined position. Since the pay-off reel 116 is stationary and the metering motor 126 is connected to a rotating A.C. electric motor 130, the piston displacement resulting from the angle of the swashplate 152 of the metering motor causes the metering motor to become a servo controlled pump and the pay-off pump now momentarily operates as a motor.

After welding the ends of the strips together a jog reverse situation is created. This causes the yoke of the metering motor 126 to cross the center position and assume a preset angle. Here again, the hydraulic metering motor 126 momentarily becomes a pump, and the payoff pump 120 becomes a motor. Since the yoke position of the hydraulic metering motor 126 is now over center, the flow is reversed, the pay-off reel 116 (which can be seen in FIG. 10) jogs in the opposite direction.

The next step, FIG. 6 is to set strip back tension, which is done by applying a reference signal to the integrating amplifier 55. By using relays, the integrating preamplifier 55 is connected with the metering motor linear amplifier 54. At this point, the preamplifier is disconnected with the pay-off pump linear amplifier 56. The tension setting reference signal produces an output from the metering motor 126 until the required hydraulic pressure is developed.

Hydraulic pressure in the line is sensed by a pressure transducer 57, whose output signal is fed back into the integrating preamplifier 55. When hydraulic pressure reaches the required level, the feedback signal from the pressure transducer 57 is equal but opposite in polarity to the tension reference signal.

These offsetting signals create a zero voltage and an output from the preamplifier consistent with the requirements of leakage flow. It should be noted that the flow required for the jogging operation is considerably larger than leakage fiow. When the slack is taken up and the mandrel stops, the entire output from the metering motor 126 being available to increase system pressure and make up for leakage, causes hydraulic pressure in the system to reach immediately the preset value with a tendency to overshoot. However, the pressure transducer 57 detects this tendency and its output signal tends to be higher. than the reference signal. The error voltage resulting from the summation of the two signals decreases the output hydraulic flow from the metering motor 126.

After all transients have decayed to zero the output from the preamplifier assumes a value consistent with the leakage make up requirements of the system. As soon as the line starts to run, a comparator relay switches the connection of the integrating preamplifier 55 from the metering motor linear amplifier 54 to the pay-off pump linear amplifier 56.

The reference signal to the metering motor is now line speed and the reference signal to the pay-off pump 120 is strip tension. The metering motor 126 now assumes a yoke angle position that produces a fluid displacement consistent with line speed and the pay-off pump 120 is servo controlled to maintain a constant preset hydraulic pressure and strip tension.

HELPER DRIVE SYSTEM Helper rollers located down the line from the pay-off reel are powered by fluid motors. The helper rollers aid in moving the strip steel through the various processes while maintaining a constant tension in the strip. The helper drive control system shown in FIG. 7 illustrates a control amplifier 35 signaling a torque motor 36 which governs the fluid flow in a servo valve 176. An actuator 194 reacts to the fluid in the servo valve 176 and adjusts the angular position of a variable displacement pump 161i which is connected to one or more fixed dis placement hydraulic helper motors one of which is shown at 168. Such helper motors are usually connected in parallel. A pressure transducer 157(a) senses the pressure and feeds back a signal to the control amplifier 35. A positional transducer (not shownlis also used in this system. The electrical components used are known in the art and will not be described in detail.

In the helper system the hydraulic pressure is controlled in order to control the tension in the strip line. As shown above, the output torque of a hydraulic motor is directelyproportional to applied pressure; therefore, controlling pressure controls and output torque of the hydraulic motor.

The helper drive'control system operates by transmitting a reference signal to a control amplifier 35, which represents a certain torque or tension. The control 35 emits an output current which is a function of the error voltage applied to the control amplifier 35. The torque motor comprises a permanent magnet stator 38, a permanent magnet 39, a coil 40, and a rotor 37 connected pivotally to a member 41 which reciprocates a spool 45 within the servo valve 176.

Assuming that the output current from the amplifier causes the rotor 37 of the torque motor 36 to rotate clockwise, the member 41 will move the spool 45 toward the left, in the direction of the torque motor 36. A servo valve176 has an inlet port 42 for the supply pressure fluid, and an outlet port 43 for return, low

pressure fluid. As the spool 41 moves to the left, the spool land 4d uncovers the valve port 46 and the spool land 47 will uncover the valve port 48. Supply oil flowing into the servo valve 176 through the supply port 42 flows through the now open port 46 through the fluid line 49 into the head end 197 of the actuator 19.4 causing the piston 195 and the rod 198 in the actuator 194 to extend. Since the rotating shaft 199 and the swashplate 50 are essentially stationary (in a linear plane) the swashplate acts as a type of hinge for the pump 161 which swings slightly downward, increasing pump displacement in proportion to the reference signal.

As system pressure reaches a preset value, the feedback signal fromthe pressure transducer 157(a) equals the reference signal, but with opposite polarity. The net result is a zero error signal, and the pump yoke is locked in that position.

I Should system pressure tend to exceed the preset pressure, the signal from the pressure transducer 157 (a) will exceed the reference signal resulting in an error with re versed polarity, providing an amplifier output current to deflect the torque motor 36 counterclockwise. As the servo valve spool 45 shifts to the right, oil flow is directed into the rod end 196 of the actuator 1958, thereby pivoting upwardly the cylinder block of the variable displacement pump 16]. and reducing the angle with the swashplate. As explained earlier, the reduced angle reduces the displacement of the pump and gives an output flow to the motor 168 consistent with that required to maintain the preset hydraulic pressure. it should be emphasized that regardless of line speed, a preset hydraulic pressure is maintained and the torque and line tension is thereby controlled. The pump flowis automatically adjusted to compensate for the load and internal leakage.

l9. BRIDLE SYSTEM The bridle system includes apair of rollers 6 and 6(a) (FIG. 1) about which the strip interweaves and appropriate apparatus (FIG. 8) which is used to control and maintain the line speed. Broadly the bridle control system includes a variable displacement pump 204 motivating two parallel fixed

displacement fluid motors

205 and 206 and their connected. rollers 6 and 6(a). A positional transducer 53 in conjunction with a linear amplifier 51,- integrating preamplifier 54 and a tachometer 234 act in combination to signal a torque motor 52, servo valve 228 and anactuator 227. i

in operation, a reference voltage is applied to the integrating preamplifier which corresponds to a desired line speed for the strip steel. The linear amplifier 51 receives the signal from the integrating preamplifier-54.

, Output current from the linear amplifier 51 is'received in the servo valve 228 toward the left, in the direction of the torque motor 52. The servo valve 228 has an inlet port 61 for the supply of high pressure fluid, and an outlet port 62 for return low pressure fluid. As the spool moves to the left, a spool land 63 uncovers a valve port 64 and a spool land 65 uncovers a valve port 66.

Supply oil flowing into the servo valve 228 through the supply inlet port 61 flows through the now open port 64 through the fluid line 67 into the head end 250 of the actuator 227 causing the piston 231 and the'rod 260 to extend. Since the rotating shaft.255 and the swashplate 261 are-essentially stationary, (ile., in the plane of the paper) a pump 204 rotatably connected to the rod 260 swings slightly downward increasing pump.

displacement until it reaches a setting proportional to the reference-signal. I i

' The pump 204 delivers a volume of oil as a function of pump displacement and angular speed. A large percentage of this volume'is used to drive the

hydraulic motors

205 and 206 through lines 68 and 68(a).The balance of the fluid is wasted as internal leakage.

The amount of leakage is affected by the temperature of the hydraulic fluid (fluid viscosity) and by the clearances in the cylinders. Furthermore, the pump 204 is driven by an A.. electric motor having speed droop characteristics. Since the quantitative effect of these factors is difficult to predict, a positional control system for the yoke does not give accurate speed reguthe right, directing oil to the rod end 249 of the actuator 227, decreasing the angle of the swashplate and thus decreasing the delivery of the pump 204. After transients caused by reference change and load disturbances have died out, steady state conditions prevail.

When the feedback signal from the tachometer 234 is equal to the reference signal, the actuator assumes a position which produces a pump delivery consistent with line speed and leakage make-up requirements.

TENSION REEL SYSTEM The take-up on tension reel rewinds the strip steel after it has been processed. Because the take-up coil has a continuously increasing diameter compensation must be made to'keep the line tension constant. The compensation includes a variable torque which allows the force on the strip to remainconstant.

The torque during coil build-up is adjusted by varying the tension reel motor displacement. The pump displacement is a function of line speed only. The absolute strip tension is a function of hydraulic pressure in the system.

The tension reel control system is illustrated in FIG. 9 and has generally a linear amplifier 70 which transmits signals to a torque motor 71 and receives a feedback signal from a positional transducer 270.

The torque motor 71 governs fluid flow-through a servo valve 246 to an actuator 248. A variable displacement pump 236 is motivated by the actuator 248 and supplies fluid to a variable displacement fluid motor 238. A pressure compensator 271 and a fluid motor actuator 272 control the angular movement of the fluid motor 238.

More specifically, a referencevoltage is applied to the linear amplifier 70. Assuming that the current output from the linear amplifier causes the rotor 72 of the torque motor 71 to rotate clockwise, the servo valve spool shifts toward the torque motor.

This movement admits control fluid to the head end 74 of the actuator 248, extending the piston 75 and rod 77. The pivotably attached pump 236 swings slowly downwardly increasing pump displacement until it reaches a value which is consistent with the line speed. When this position is reached, the output voltage from the pump yoke positional transducer 270 is equal but opposite in polarity to the reference voltage, resulting in zero error signal. The output current from the linear amplifier 70 is zero. The torque motor returns to zero deflection, shifting the servo valve spool 73 to null position, blocking all ports. The actuator 248 is now locked hydraulically in that position, maintaining the preset pump displacement and a constant pump output as a function of line speed.

The actuator 272 controlling the fluid motor 238 is single acting, that is, it is extended by hydraulic pressure and retracted by the mechanical action of a spring, 84. In the absence of hydraulic pressure fluid in the line 273(3) the spring action will stroke the fluid motor to the position of minimum displacement. System pressure is set by the setting of a spring 85 in the pressure compensator 271.

In operation, the fluid motor remains at minimum displacement until hydraulic pressure fluid acting on the circular area 86 exceeds the force executed by the spring.

At the start of the rewind operation for any given line speed the coil diameter and torque are at minimum and the mandrel angular velocity at maximum. During each revolution of the mandrel, the radius of the coil increases an amount equal to the thickness of the strip.

For a given angular velocity, the linear speed of the strip would increase. However, an increase in strip speed is not possible because speed of the bridle holding the strip steel is controlled, and the bridle will therefore maintain a preset speed regardless of load. The net result is that the hydraulic motor 238 must slow down. However, since the hydraulic motor is receiving a constant flow of fluid from the pump 236, any slow down tendency increases hydraulic pressure in the line 273.

As soon as pressure rises, the equilibrium in the pressure compensator is disrupted. When the force exerted on the compensator spool area 86 by the hydraulic fluid exceeds the force exerted by the spring 85, the spool 87 shifts to the left, admitting control pressure fluid to the head end 80 of the actuator 272 controlling the fluid motor 238.

The fluid motor 238 swings downward, pivoting about swashplate 88, increasing the angle of the motor swashplate 88, and thus increasing the displacement of the fluid 'motor. The hydraulic motor 238 can now receive a large volume of. fluid per'revolution and can accommodate the constant pump flow output at a lesser angular speed, thus retaining a constant hydraulic pressure.

During coil build-up, the action of the compensator is continuous. The compensator spool 87 shifts to the left, establishing a minute, but continuous flow of oil to the motor actuator 27 2.

The. displacement of the fluid motor increases gradually, and angular speed similarly decreases. Since torque is a function of the motor displacement, it gradually increases in proportion to coil-diameter, and a constant strip tension is maintained. As hydraulic flow and pressure are kept constant the power also remains constant, producing a constant horsepower, variable torque.drive.

SUBSYSTEM I The control units illustrated in FIGS. 5 and 7 comprise an important part of subsystem I shown in FIG. 10. Equally important, however, is the drive means by which power or energy can be redistributed within the system to insure maximum efficiency. While the previously described controls in FIGS. 5 and 7 make the necessary changes to bring the speed and tension to the desired values, power can be transferred in either direction between the pay-off reel for the coiled steel and the helper rollers which assist in conveying the strip steel. FIG. 10 is a schematic representation of the system governing the action of the pay-ofi reel 116 and sion to the strip. The pu nip assembly 119 comprises pumping member 120 which is a'variable displacement bi-directional piston type hydraulic pump controlled by an electro-hydraulic servo control 121. The servo control121 varies the displacement or hydraulic output from the hydraulic pump 120 by means of an actuator 122. The pump assembly is also equipped with a yoke brake 123 controlled by a solenoid operated directional valve 124.

The pay-off pump 120 supplies hydraulic fluid through appropriate conduits to drive a hydraulic metering'motor assembly shown generally at 125. This hydraulic motor assembly comprises a hydraulic motor member 126 which is a variable displacement, bidirectional, piston type hydraulic motor controlled by an electro-hydraulic servo control 127. The servo con- 120(b), and 12d(c), the hydraulic pressure acting on the topside of the check valve 141 exerts a force that is substantially greater than the force exerted on the bottom side of check valve 141 by virtue of the hydraulic pressure in the hydraulic line 133(a).

However, since pump section 13 is of a fixed displacement type, the oil being pumped by pump section 133 must find an escape path. This it does through an unloading relief valve 139 which is set to open at 100 psi. Thus, relief valve 139 will open at a considerably lower pressure than main system relief valve 142 which is set to open at 2500 psi. After passingthrough valve trol 127 varies the displacement or hydraulic input into the hydraulic motor 126 by means of an actuator 128. A rotary output shaft 129 is coupled to an electric motor 130.

In normal operation, it can be assumed that the payoff reel 116 is rotating clockwise in such a manner that the pump 120 also rotates clockwise. Hydraulic oil flows from the pump 120 through port 120(d) hydraulic line 120(a), past a high pressure relief valve 142, then through hydraulic lines 120(b).and 120(c) entering the hydraulic motor 126 through port 126(a). The purpose of the pressure relief valve 142 is to allow the oil to bypass the metering motor thus allowing free wheeling of the pay-off reel pump. it also relieves line 120(b) from excessive pressure due to abnormal operation' of the system. The hydraulic motor also rotates clockwise, driving the output shaft 129 as shown by the arrow 131, coupled to the electric motor 130. The hydraulic oil leaves the hydraulic motor 126 through port 126(b), flowing through lines 126(c) and 126(d) reentering the hydraulic pump 120 through port 120(e). This path is known in the art as a closed circuit because oil from the hydraulic motor does not return to the tank, instead, it flows to the intake side of the hydraulic pump.

As is the case in most hydraulic systems, a minimal amount of hydraulic fluid leakage may occur which, while not detrimental, if small, may nevertheless affect the proper functioning of the hydraulic system. in order to remedy this situation, the hydraulic system is equipped with auxiliary components which have a manifold purpose.

These components include a double vane pump 132, having two

pump sections

133 and 134. Both pump sections have a fixed displacement and are driven simultaneously by an electric motor 135 through a drive shaft 136. Each section of the double vane pump 132 performs specific and independent functions in the pay-off circuit.

Hydraulic oil is drawn into pump 132 from a hydraulic'reservoir 137 through a suction strainer 138. Oil flow into the pump 132 is then divided, a Portion of the incoming oil flows into the pump section 133, the balance of the oil flowing into the pump section 134. Output oil from pump section 133 flows through hydraulic line 133(a) past a low pressure relief valve 139 through a pressure filter 140, to a check valve 141.

If, as it was assumed, the output oil from the hydraulic pump 1211 is through high pressure lines 120(a),

139, the oil returns to the hydraulic reservoir, 137 (a).

1t bears noting that generally most hydraulic systems have but one hydraulic reservoir. Such, in fact, is the case in subsystem I, where the reservoir was first designated by numeral 137. However, the complexity of many sophisticated hydraulic system requiresthat many lines be connected to the same reservoir from a plurality of locations within the hydraulic system. In

drawing schematic diagrams of hydraulic systems, it would be totally impracticable to show all lines returning to the reservoin'lt has thus become a customary procedure in the art to draw small reservoir symbols in the proximity of a hydraulic component which is in fact connected to the reservoir. Such is the case with low pressure relief valve 139. It is shown connected to reservoir 137(a) which in fact represents the reservoir 137. It will be understood that all small reservoir symbols in the circuit diagram drawn similar to 137(a), do in fact represent the reservoir 137.

Output oil from pump section 134 flows through a hydraulic line 134(a) and through a pressure filter 143, until it reaches a tee connection in the hydraulic line at point 144, where the output flow from pump section 134 splits: part of the hydraulic oil flows into line 134(b) and part into line- 134(c).

' The portion of oil flowing through line 134(c) flows past a relief valve, 146, set'to open at 400 psi until the oil reaches a point in the circuit designated by numeral 145. 1

Since it was assumed that the hydraulic motor 126 is rotating clockwise and that its, intake port is item 126(a) and its output port 126(b), hydraulic line 126( b) becomes a return line, and therefore of necessity a low pressure line.

At point 145, output oil from the pump section 134 joins with the return oil flowing from port 126(b) and the combined flows flow through line 126(c) to supply the intake port (e) of the hydraulic pump 12h.

. It was noted earlier that even in the best designed hydraulic system, a small amount of oil leakage was likely, and is almost unavoidable. It thus becomes evident that as small quantities of fluid leak out of the hydraulic system, regardless of how slow the leaks might be, that eventually the hydraulic system will become partly or totally devoid of oil and there will not be enough fluid to supply the intake port 120(e) of the pump 120. This phenomenon is known as pump starvation or cavitation. One way of preventing cavitation is by providing the intake side of a pump with a constant The other function of section 134 is to supply pressure fluid to the electro-

hydraulic servo valves

121 and 127 to actuate their respective actuators 122 and Line 120(b) will become the low pressure line only if it desired to drive the pay-off pump (which now acts as a motor) and it is independent from the direction of pay-off reel rotation. The make-up fluid flows from the pump section 133 through line 120(b) into metering motor 126 through port 126(a).

The helper roller circuit is supplied by a double section pump, shown generally at 160. One of the sections 161 has a variable delivery output, while the other section 162 has a fixed delivery output. Separate hydraulic lines supply each pump section. Oil flows to the intake port of pump section 161 from the reservoir through a suction filter 163. Oil flowing to the intake port of pump section 162 flows through a suction filter 164. Output oil from pump section 161 flows through a pressure filter 165, past a solenoid-controlled relief valve 166, set to open when system pressure reaches 2,500 psi through a solenoid-controlled, 4-way, 2-position, directional control valve 167, to supply fluid in parallel to four, bi-directional, fixed displacement

hydraulic motors

168, 169, 170 and 171 through four, solenoidcontrolled, polot actuated, 4-way, 3-position, spring centered

directional control valves

172, 173, 174 and 175.

Note that unlike the center positions of the

servo valves

121, 127 and 176,

directional control valves

172, 173, 174 and 175- do not have a blocked center or neutral position. instead, when

valves

172, 173, 174 and 175 are in center or neutral position, they allow the oil in the hydraulic lines of both sides of the

fluid motors

168, 169, 170 and 171 to become interconnected to each other and to the return lines leading back to reservoir.

Each

fluid motor

168, 169 170 and 171 drives a

helper roller

176, 177, 178 and 179 respectively, through a

respective gear box

180, 181, 182-and 183.

Return fluid flows back toreservoir 137 through check valve 184 and through heat exchanger 185. The water cooled heat exchanger 185 is controlled by a temperature responsive flow control valve 186 which is sensitive to temperature signals from a probe 187 through an electrical connection 188. Should all returning fluid be unable to pass through the heat exchanger 185, the excess fluid returns to the reservoir 137 through a by-pass check valve 189.

The purpose of pump section 162 is to provide pressure fluid to vary the output of the variable displacement pump section 161. Oil from pump section 162 flows to a point 191 where the flow is split in two directions simultaneously. Part of the oil flows through pressure filter 192 to a servo valve 176 where oil flow is blocked. At the same time, oil flows to the rod end of 196 a small hydraulic cylinder 194 which is connected mechanically to the swashplate of the pump section 161.

Note that the output from pump section 162 flows directly to the rod end 196 of cylinder 194, thus maintaining the stroked position of pump section 161 and preventing any inadvertent counterstroking. As mentioned, the balance of the oil passing through pressure filter 192 flows to the electrohydraulic servo valve 176 where flow is blocked. When the servo valve 176 reacts in response to a command signal, it shifts to position (a) allowing control fluid to flow to the head end 197 of the stroking cylinder 194 extending it and stroking the variable displacement pump 161, thus altering its output.

Note that the pressure of the fluid on both sides of the piston 195 of the cylinder 194 is the same. The reason the cylinder extends is because the pressurized fluid is acting on differential areas. The area of the piston on the head end 197 of the cylinder is larger than the annular area on the rod end 196 because of the area occupied on the cylinder by the end of the rod.

Should the servo valve 176 be commanded to shift to position (b), the pressure passage will be blocked, but oil in the head end of the cylinder is allowed to flow back to reservoir at low pressure. Since the rod end 196 of the cylinder is constantly pressurized, the cylinder will retract stroking the pump accordingly.

When the pay-off reel and helper system are in equilibrium the speed of the strip between the helper rollers and the pay-off reel equals the speed of the strip downstream of the helper rollers. The strip tension at the exit side of the helper roll is lower than the entry tension by an amount consistent with the power supplied on the helper roll. in this normal mode of operation, strip steel causes the rotation of pay-off reel 116 which drives the pay-off pump 120. Metering motor 26 is driven by and is a drag on t he pump 120. The metering motor 126 assists the electric motor 130-in'supplying energy to the hydraulic motor 161. The electrical power supplied to the electric motor 130 can thereby be reduced by an amount approaching the power supplied by the metering motor 126.

As the strip steel comes off the pay-off reel 116, it decreases in diameter. Since the line speed of the strip remains effectively constant, the angular speed of the pay-off reel 116 must increase. As the pay-off reel 116 increases, the speed of the pump increases for given displacement and the pump tends to supply more oil than the metering motor is set to receive. There is then at least a temporary increase in pressure and speed of the metering motor 126. The increase in metering motor speed is due to electric motor slippage and it is only3 per cent from zero load to full load. The compensation system described above will quickly correct any deviation.

SUBSYSTEM Il The bridle rolls hydraulic circuit is also known in the art as a closed loop circuit. A fixed displacement vane pump 200 driven by an electric motor 201 supplies make-up or supercharge fluid to two circuits supplied by two separate variable displacement piston pumps shown generally at 202 and 203.

Pumps

202 and 203 are driven by the same electric motor 235 which is equipped with double end drive shafts, 255 and 256 respectively. Each pump has two sections: one variable 204 and one fixed displacement 225.

Fluid flows into the supercharge pump 200 from a hydraulic reservoir 211 and through a suction filter 212. As the hydraulic fluid flows out of the pump 200, it passes through pressure filter 213, then flows past a relief valve 214 which is set to open at 250 psi, and reaches the point designated at 215. At this junction point, flow splits: part flowing through a check valve 2116, part flowing in parallel through a check valve 217. The fluid flowing through check valve 216 flows into a cross-over check valve-and-relief valve shown generally at 210, always flowing to the low pressure side of the circuit, to make up any deficiency in fluid flow.

Since the pump section 204 is undirectional and since the system is not equipped with a directional control valve, the two

fluid motors

205 and 206 supplied by the pump section 204 rotate in the same direction.

Directional control is provided however, by shifting the yoke across the center null position. Make-up, supercharge fluid from pump 200, when it reaches the junction point 224 will flow normally through line (b),

check valve 221, lines and (d) to the inlet side of the pump to provide make-up fluid to the pump 204 if any is needed The supercharge fluid flows-to the low pressure line. Either line can be a low pressure line depending on whether the bridle is motoring or dragging. Depending on where system over-pressurization is taking place, cross relief flow will be through check valve 220, relief valve 210 and check valve 223, or through check valve 222, relief valve 219 and check valve 221 depending on the direction of rotation of the fluid motors.

The purpose of the pump section 225 is to provide pressure fluid to vary the output of variable displacement pump section 204 by stroking its swashplate. This is accomplished by controlling the position of the servo valve 220. Oil flow from pump section 225 passes through a filter 226, then flows to a point 230 where flow splits and flows in two directions simultaneously. Part of the oil flows to the blocked port in servo valve 223 and part of the oil flows to the rod end 249 of the actuator 227 which is connected mechanically to the swashplate of pump 204 to control the output of that pump. This system is protected by a relief 229.

The output from the pump section 225 flows directly to the rod end 249 of cylinder 227 thus maintaining pump section 204 in its stroked position and preventing any inadvertent counterstroking.

Then the servo valve 220 responds to a command signal, the servo valve 220 shifts to position (a) allow ing control fluid to flow to the head end 250 of the stroking control cylinder'227, extending it and stroking the variable displacement pump 204 to alter its output. Note that the pressure of the fluid on both sides of the piston 2311 of the cylinder 227 is the same. The reason the cylinder extends when the servo valve 220 shifts to the (a) position is because the pressurized fluid is acting on differential areas. The area of the head end 250 of the piston being larger than the annular area of the rod end 240 of the piston, the cylinder extends. Should the servo valve 227 be commanded to shift to the (b) position, the pressure passage in the valve would be blocked. However, oil in the head end of the control cylinder 227 is allowed to flow back to reservoir 21131 at atmospheric pressure. Since the rod end 249 of the cylinder 227 is constantly pressurized, the control cylinder 227 will retract slightly, stroking the pump and altering output flow accordingly.

Should system pressure rise above the spring setting of relief valve 224, the relief valve 2T4 would open, allowing fluid to return to reservoir 211 directly through a heat exchanger 232 which is controlled by thermostat control valve 233. A temperature probe 234 signals and controls the setting of thermostat control valve 233. A bypass valve 251 allows excess fluid to return to reservoir 211 bypassing the heat exchanger 232.

Signal for the servo valve originates in the line speed potentiometer (not shown) and the feedback tachometer. The purpose of pressure transducer 234 is to indicate only the pressure differential in the lines with no control functions.

The bridle system 204 is the master speed controller for the line and will run at a speed which is a function of a reference signal. If the strip tension at the entry side of the bridle is greater than the tension at the exit side, the bridle supplies power to the strip, causing the bridle to motor. The servo controlled hydraulic pump 204 is driven by the same A.C. electric motor 235 which also drives pump section 236 which supplies the tension reel circuit. A tachometer 237 monitors and controls the speed of the bridle rolls. The tachometer 237 generates a feedback signal which keeps the

fluid motors

205 and 206 rotating at a constant, preset speed regardless of load fluctuations.

in the tension reel circuit, the servo controlled, variable displacement hydraulic pump 236, driven by the A.C. motor 235, supplies pressure fluid to a variable displacement, pressure compensated, bi-directional fluid motor 230.

A vented, relief valve shown generally at 239, is part of a cross connected circuit which includes

check valves

240, 241, 242, and 243, the relief valve 244 and the solenoid controlled, spring returned normally closed directional control valve 245.

A servo control 246 controls the stroking of the pump 236 in a manner similar to the action of the servo control valve 220 and pump 204. Similarly, the smaller, fixed displacement pump 247 supplies control fluid to the cylinder 240 as does pump 225 to cylinder 227.

if the tension of the stripat the tension reel is set higher than the tension of the strip at the entry side of the bridle, the. strip is in effect powering the bridle which is said to be dragging.

During dragging conditions, the two

bridle fluid motors

205 and 206 in effect act like hydraulic pumps and the servo controlled pump 204 acts like a servo controlled fluid motor. The power developed by the dragging action of the bridle is used to assist the A.C. motor in driving the servo controlled, variable displacement tension reel hydraulic pump 236.

As the additional power from the hydraulic pump 204, which is acting like a motor, is applied to the AC. motor 235, less electrical power is required. This reduction of electrical power input into the system will increase its efficiency. While there may be a temporary increase in pressure and/or tension in the bridle system as power is transferred to it, the compensation systems described above will quickly bring them back to their correct levels.

if the strip tension setting in the tension reel is lower than the back tension in the lines, the

bridle rollers

207 and 200 in effect exert a pull on the entry side of the strip and the

bridle rollers

207 and 200 are said to be motoring. When the

bridle rollers

207 and 200 are motoring they are driven by the

fluid motors

205 and 206 which are driven by the pump 204. The A.C. motor drives the pump 204.

Since the power is transmitted hydraulically from one section to another through a mechanical connection to a common A.C.motor the system is said to be hydro-mechanical regenerative.

lclaim:

l. A regenerative system for motivating a strand of material comprising:

a first rotatable means in-contact with the strand of material;

a second rotatable means to aid motivating the strand of material, the strand of material extending between the first and second rotatable means;

a first hydraulic pump convertible to a hydraulic motor operatively connected to the first rotatable means;

a first hydraulic motor convertible to a hydraulic pump operatively connected to the first hydraulic pump and capable of being driven by it;

an electric motor operatively connected to the first hydraulic motor;

a second hydraulic'pump convertible to a hydraulic motor operatively connected to the electric motor;

a second hydraulic motor convertible to a hydraulic pump operatively connected and capable of being driven by a second hydraulic pump;

the second hydraulic motor convertible to a hydraulic pump operatively connected to the second rotatable means whereby power may be redistributed between the first rotatable means and the second rotatable means by interchanging the functions of at least some of the hydraulic pumps and motors.

2. The regenerative system of claim 1 whereinthe first hydraulic pump has a variable displacement in order to compensate for changes in tension of the strand. 4

3. The regenerative system of claim 2 which further comprises a servo control which governs the displacement of the first hydraulic pump, said servo control acting in response to a signal from a pressure transducer which senses system hydraulic pressure.

4. The regenerative system of claim 3 which further includes a torque motor and fluid valve wherein the servo control includes a control amplifier which receives the feedback from the pressure transducer and transmits it to the torque motor which activates the fluid valve to vary the displacement of the first hydraulic pump.

5. The regenerative system of claim 2 wherein the second hydraulic pump has a variable displacement in order to compensate for changes in tension of the strand.

6. The regenerative system of claim 2 which further includes a second servo control wherein the displacement of the second hydraulic pump is governed by the second servo control.

7. The regenerative system of claim 6 wherein the second servo control includes a pressure transducer which senses the line pressure, means for comparing the line pressure with a reference signal and means for changing the displacement of the second hydraulic pump in response to a signal from the means for comparing.

8. The regenerative system of claim 7 wherein the means for comparing a control amplifier and the means for changing the displacement of the hydraulic pump comprises a torque motor which actuates a fluid valve and fluid actuator in fluid communication therewith in response to a signal from the control amplifier.

9. The regenerative system of claim 2 wherein the first rotatable means is a pay-off reel which uncoils the strand of material, the second rotatable means is a helper roller which aids in motivating the strand, the first hydraulic pump is the pay-off pump and acting as a drag on and normally motivated by the pay-off reel; and,

the first hydraulic motor is a metering motor.

10. The regenerative system of claim 9 wherein the electric motor has dual shafts respectively connected to the metering motor and the second hydraulic pump so that if the pay-off reel is being motivated by the strand then the pay-off reel drives the pay-off pump thereby driving the metering motor which aids in the driving of the second hydraulic pump through the electric motor; and,

if the helper roller is being driven by the strand the second hydraulic motor converts to a hydraulic pump and the second hydraulic pump changes to a hydraulic motor which aids in turning the metering motor through the electric motor.

1. The regenerative system of claim 10 which further comprises a servo control mechanism and wherein the pay-off pump is the variable displacement type which is controlled by the servo control mechanism.

12. The regenerative system of claim 11 which further comprises a second servo control mechanism wherein the metering motor is the variable displacement type which is regulated by the second servo control mechanism.

13. Theregenerative system of claim 11 wherein the servo controls for the pay-off pump are responsive to a pressure in the system and the metering motor is responsive to line speed.

14. A regenerative system for motivating a strand of material comprising:

at least one first rotatable means;

a second rotatable means;

the strand of material extending between the first and second rotatable means;

at least one first hydraulic motor convertible to a hydraulic pump operatively connected to the first rotatable means;

a first hydraulic pump convertible to a hydraulic motor in fluid communication with and capable of being driven by the first hydraulic motor;

an electric motor operatively connected to the first hydraulic pump;

a second hydraulic pump convertible to a hydraulic motor operatively connected to the electric motor;

a second hydraulic motor convertible to a hydraulic pump in fluid communication with and capable of being driven by the second hydraulic pump;

the second rotatable means operatively connected to the second hydraulic motor whereby power may be redistributed between the first and second rotatable means by interchanging the functions of at least some of the hydraulic pumps and motors.

15. The regenerative system of claim 14 wherein the first hydraulic pump has a variable displacement to adjust the speed of the first rotatable means and therefore the speed of the line.

16. The regenerative system of claim which further includes a servo control mechanism wherein the displacement of the first hydraulic pump is governed by the servo control mechanism.

17. The regenerative system of claim 16 wherein the servo control mechanism includes a tachometer which records line speed, a feedback means to transmit the signal from the tachometer,a control means for comparing the tachometer signal to a reference signal and transmitting a signal to a torque motor which is in fluid communication with and command of a fluid valve and an actuator which varies the displacement of the first hydraulic pump.

18. The regenerative system of claim 17 wherein the second hydraulic pump has a variable displacement.

19. The regenerative system of claim 18 which further comprises a second servo control mechanism wherein the displacement of the second hydraulic pump is governed by the second servo control mechanism.

20. The regenerative system of claim 19 wherein the second servo control mechanism includes a positional transducer, a means for comparing a reference signal and a signal from the positional transducer and a means for changing the displacement of the second hydraulic pump.

21. The regenerative system of claim 20 wherein the means for comparing includes a linear amplifier and the means for changing the displacement includes a torque motor and a fluid valve and an actuator governed by the action of the torque motor.

22. The regenerative system of claim 18 wherein the second hydraulic motor has a variable displacement.

23. The regenerative system of claim 22 which further includes a pressure sensitive fluid actuator wherein the displacement of the second hydraulic motor is governed by the pressure sensitive fluid actuator.

2d. The regenerative system of claim 14 wherein at least one first rotatable means are bridle rolls for governing the speed of the strand of material; and

the second rotatable means is a tension reel which rewinds the strand of material.

25. The regenerative system of claim 24 wherein the electric motor has dual shafts respectively connected to the first hydraulic pump and the second hydraulic pump whereby if either pump has an excess of energy it can be transferred through the electric motor to the other hydraulic pump since the first hydraulic motor is convertible to a hydraulic pump and the first hydraulic pump is convertible to a hydraulic motor which will aid the electric motor in motivating the second hydraulic pump.

26. The regenerative system of claim 25 which further includes a servo control mechanism wherein the first hydraulic pump is the variable displacement type which is regulated by the servo control mechanism.

27. The regenerative system of claim 26 wherein the servo control mechanism includes a tachometer which measures the speed of the strand and gives a signal.

23. The regenerative system of claim 27 wherein the servo control mechanism further includes a means for comparing the tachometer signal with a reference signal; a means for transmitting a tachometer signal to the means for comparing and means for varying the displacement of the first hydraulic pump in response to a signal for the means for comparing in order to maintain a desired speed of the strand of material.

29. The regenerative system of claim 28 wherein the second hydraulic pump is the variable displacement type in order that it may be set for a given strand speed.

30. The regenerative system of claim 29 wherein the second hydraulic motor is the .variable displacement type in order to compensate for the increase in angular velocity of the tension reel as the strand rewinds.

31. The regenerative system of claim 31 which further includes a pressure compensator wherein the displacement of the second hydraulic motor is governed by the pressure compensator which is sensitive to the system pressure in order to decrease the angular velocity of the tension reel as the strand of material rewinds.

32. A regenerative system for motivating a strand of material comprising:

a first rotatable means in contact with the strand of material; v

a second rotatable means to aid'in motivating the strand of material, the strand of material extending between the first and second rotatable means;

a first hydraulic pump operatively connected to the first rotatable means; e

a first hydraulic motor in fluid communication with the hydraulic pump and capable of being driven by it;

a first electric motor mechanically connected to the first hydraulic motor;

a second hydraulic pump mechanically connected to the electric motor;

a second hydraulic motor in fluid communication with and capable of being driven by the second hydraulic pump;

the second hydraulic motor operativelyconnected to the second rotatable means whereby energy may be redistributed betweenthe first rotatable means and the second rotatable means;

at least one third rotatable means;

at least one third hydraulic motor convertible to a hydraulic pump operatively connected to the third rotatable means;

a third hydraulic pump convertible to a hydraulic motor in fluid communication with and capable of being driven by the third hydraulic motor;

a second electric motor mechanically connected to the third hydraulic pump;

a fourth hydraulic pump convertible to a hydraulic motor mechanically connected to the second electric motor;

a fourth hydraulic motor convertible to a hydraulic pump in'fluid communication with and capable of being driven by the fourth hydraulic pump;

a fourth rotatable means operativelyconnected to the fourth hydraulic motor, the third and fourth rotatable means being in contact with the strand of material whereby energy may be redistributed between the third and fourth rotatable means.

33. The regenerative system of claim 32 wherein the first rotatable means is a pay-off reel for uncoiling the

Claims

1. A regenerative system for motivating a strand of material comprising: a first rotatable means in contact with the strand of material; a second rotatable means to aid motivating the strand of material, the strand of material extending between the first and second rotatable means; a first hydraulic pump convertible to a hydraulic motor operatively connected to the first rotatable means; a first hydraulic motor convertible to a hydraulic pump operatively connected to the first hydraulic pump and capable of being driven by it; an electric motor operatively connected to the first hydraulic motor; a second hydraulic pump convertible to a hydraulic motor operatively connected to the electric motor; a second hydraulic motor convertible to a hydraulic pump operatively connected and capable of being driven by a second hydraulic pump; the second hydraulic motor convertible to a hydraulic pump operatively connected to the second rotatable means whereby power may be redistributed between the first rotatable means and the second rotatable means by interchanging the functions of at least some of the hydraulic pumps and motors.

2. The regenerative system of claim 1 wherein the first hydraulic pump has a variable displacement in order to compensate for changes in tension of the strand.

9. The regenerative system of claim 2 wherein the first rotatable means is a pay-off reel which uncoils the strand of material, the second rotatable means is a helper roller which aids in motivating the strand, the first hydraulic pump is the pay-off pump and acting as a drag on and normally motivated by the pay-off reel; and, the first hydraulic motor is a metering motor.

10. The regenerative system of claim 9 wherein the electric motor has dual shafts respectively connected to the metering motor and the second hydraulic pump so that if the pay-off reel is being motivated by the strand then the pay-off reel drives the pay-off pump thereby driving the metering motor which aids in the driving of the second hydraulic pump through the electric motor; and, if the helper roller is being driven by the strand the second hydraulic motor converts to a hydraulic pump and the second hydraulic pump changes to a hydraulic motor which aids in turning the metering motor through the electric motor.

11. The regenerative system of claim 10 which further comprises a servo control mechanism and wherein the pay-off pump is the variable displacement type which is controlled by the servo control mechanism.

13. The regenerative system of claim 11 wherein the servo controls for the pay-off pump are responsive to a pressure in the system and the metering motor is responsive to line speed.

14. A regenerative system for motivating a strand of material comprising: at least one first rotatable means; a second rotatable means; the strand of material extending between the first and second rotatable means; at least one first hydraulic motor convertible to a hydraulic pump operatively connected to the first rotatable means; a first hydraulic pump convertible to a hydraulic motor in fluid communication with and capable of being driven by the first hydraulic motor; an electric motor operatively connected to the first hydraulic pump; a second hydraulic pump convertible to a hydraulic motor operatively connected to the electric motor; a second hydraulic motor convertible to a hydraulic pump in fluid communication with and capable of being driven by the second hydraulic pump; the second rotatable means operatively connected to the second hydraulic motor whereby power may be redistributed between the first and second rotatable means by interchanging the functions of at least some of the hydraulic pumps and motors.

16. The regenerative system of claim 15 which further includes a servo control mechanism wherein the displacement of the first hydraulic pump is governed by the servo control mechanism.

17. The regenerative system of claim 16 wherein the servo control mechanism includes a tachometer which records line speed, a feedback means to transmit the signal from the tachometer, a control means for comparing the tachometer signal to a reference signal and transmitting a signal to a torque motor which is in fluid communication with and command of a fluid valve and an actuator which varies the displacement of the first hydraulic pump.

24. The regenerative system of claim 14 wherein at least one first rotatable means are bridle rolls for governing the speed of the strand of material; and the second rotatable means is a tension reel which rewinds the strand of material.

28. The regenerative system of claim 27 wherein the servo control mechanism further includes a means for comparing the tachometer signal with a reference signal, a means for transmitting a tachometer signal to the means for comparing and means for varying the displacement of the first hydraulic pump in response to a signal for the means for comparing in order to maintain a desired speed of the strand of material.

30. The regenerative system of claim 29 wherein the second hydraulic motor is the variable displacement type in order to compensate for the increase in angular velocity of the tension reel as the strand rewinds.

32. A regenerative system for motivating a strand of material comprising: a first rotatable means in contact with the strand of material; a second rotatable means to aid in motivating the strand of material, the strand of material extending between the first and second rotatable means; a first hydraulic pump operatively connected to the first rotatable means; a first hydraulic motor in fluid communication with the hydraulic pump and capable of being driven by it; a first electric motor mechanically connected to the first hydraulic motor; a second hydraulic Pump mechanically connected to the electric motor; a second hydraulic motor in fluid communication with and capable of being driven by the second hydraulic pump; the second hydraulic motor operatively connected to the second rotatable means whereby energy may be redistributed between the first rotatable means and the second rotatable means; at least one third rotatable means; at least one third hydraulic motor convertible to a hydraulic pump operatively connected to the third rotatable means; a third hydraulic pump convertible to a hydraulic motor in fluid communication with and capable of being driven by the third hydraulic motor; a second electric motor mechanically connected to the third hydraulic pump; a fourth hydraulic pump convertible to a hydraulic motor mechanically connected to the second electric motor; a fourth hydraulic motor convertible to a hydraulic pump in fluid communication with and capable of being driven by the fourth hydraulic pump; a fourth rotatable means operatively connected to the fourth hydraulic motor, the third and fourth rotatable means being in contact with the strand of material whereby energy may be redistributed between the third and fourth rotatable means.

33. The regenerative system of claim 32 wherein the first rotatable means is a pay-off reel for uncoiling the material, the second rotatable means is a helper roller, the third rotatable means are bridle rolls and the fourth rotatable means is a tension reel for rewinding the strand of material.

34. The regenerative system of claim 33 wherein the first hydraulic pump is a pay-off pump operatively connected to the pay-off reel and acting as a drag on the pay-off reel thereby creating tension in the line between the pay-off reel and the helper roller.

35. The regenerative system of claim 34 wherein the first hydraulic motor is actuated by the pay-off pump and normally aids in turning the first electric motor which drives the second hydraulic pump.

36. The regenerative system of claim 36 wherein the first electric motor has dual shafts respectively connected to the first hydraulic motor and the second hydraulic pump whereby excess energy in either the first hydraulic motor or the second hydraulic pump may be transferred between them through the first electric motor thereby conserving electric energy.

37. The regenerative system of claim 36 wherein the second electric motor has dual shafts respectively connected to the third hydraulic pump and the fourth hydraulic pump whereby excess energy in either pump can be transferred to the other through the second electric motor since the third hydraulic motor is convertible to a hydraulic pump and the third hydraulic pump is convertible to a hydraulic motor if the bridle roll is dragging, thus enabling the third hydraulic pump acting as a motor to aid in motivating the fourth hydraulic pump through the second electric motor, and since the fourth hydraulic motor is convertible to a hydraulic pump and the fourth hydraulic pump is convertible to a hydraulic motor if the tension reel is dragging thus enabling the fourth hydraulic pump acting as a motor to aid in motivating the third hydraulic pump through the second electric motor.

38. The regenerative system of claim 37 which further comprises servo controls wherein the pay-off reel pump and the metering motor have variable displacements which are servo controlled to maintain a preset line pressure and line tension.

39. The regenerative system of claim 37 wherein the second hydraulic pump has a variable displacement which is servo controlled by one of the servo controls and sensitive to the pressure in the system.

40. The regenerative system of claim 34 wherein the displacement of the third hydraulic pump is variable and governed by one of the servo controls which includes a tachometer to sense the line speed, a feedback means to transmit signals from the tachometer, control means for comparing the tachometer''s signal to a reference signal and transmitting a signal to a torque motor which is in fluid communication with and in command of a fluid valve which varies the displacement of the third hydraulic pump.

41. The regenerative system of claim 40 wherein the displacement of the fourth hydraulic pump is variable and controlled by one of the servo controls.

42. The process of motivating a strand of material while conserving energy comprising: motivating a pay-off reel means in contact with the strand; motivating a helper roller contact with the strand; creating a tension in the strand; driving a pay-off pump by means of the pay-off reel at least a portion of the time thereby creating a drag on the pay-off reel; driving a first hydraulic motor with the pay-off pump which transfers energy to said helper roller at least some of the time; driving the helper roller by means of a second hydraulic motor at least some of the time; driving the second hydraulic motor by means of a second hydraulic pump at least some of the time; driving the second hydraulic pump at least partially by means of the first hydraulic motor through a first electric motor which is operatively connected to the first hydraulic motor and the second hydraulic pump.

43. The process of claim 42 which further includes: passing the strand of material through a third rotatable means; coiling the strand on a fourth rotatable means; transferring excess power from one of the rotatable means to the other through a hydro-mechanical system.

44. The process of claim 43 wherein the third rotatable means is at least one bridle roll, the fourth rotatable means is a tension reel and further comprises: passing the strand of material in contact with the bridle roll; recoiling the strand of material on the bridle roll; and driving the tension reel and bridle roll by means of an electric motor operatively connected to a bridle roll pump and a tension reel pump which drive a bridle roll hydraulic motor and a tension reel hydraulic motor respectively whereby excess energy in either the bridle roll or tension reel may be transferred to the other components through the second electric motor.

45. The process of claim 44 further comprising: governing the speed of the bridle rolls and therefore the linear speed of the strand of material.

46. The process of claim 45 further comprising: varying the angular speed of the tension reel as the strand of material is coiled on it.

47. The process of claim 46 further comprising: varying the displacement of the pay-off pump and first hydraulic motor in order to maintain a constant tension of the strand of material.

48. The process of claim 47 further comprising: varying the displacement of the bridle roll hydraulic pump in order to govern the linear speed of the strand material.

49. The process of claim 48 further comprising: varying the displacement of the tension reel hydraulic pump and motor to control the tension in the strand of material.