US3725755A

US3725755A - Systems for driving reels at controlled speed and power and improved apparatus for effecting such driving

Info

Publication number: US3725755A
Application number: US00092576A
Authority: US
Inventors: L Stabile
Original assignee: Vanguard SpA
Current assignee: Vanguard SpA
Priority date: 1969-11-27
Filing date: 1970-11-25
Publication date: 1973-04-03
Anticipated expiration: 1990-04-03
Also published as: CA961570A

Abstract

A system for winding and unwinding material on a reel which can act as a regulated system ''''with constant power'''', when confronted with variations in the angular speed W of the reel, due to variations of diameter, and as a purely ''''velocity'''' regulated system, when confronted with variations in linear velocity V of the material, in transient phases of strong acceleration, by taking advantage of the combination of the availability of the full feeding of the motor field, and of the direct control of values and amounts involved, thereby eliminating the need for recourse to means for approximate simulation of these values.

Description

United Stat 6S Patent 1 91 11 3,725,755 Stabile 1 Apr. 3, 1973 s41 SYSTEMS FOR DRIVING REELS AT 3,543,270 12 1970 CONTROLLED SPEED AND POWER 3,448,357 1969 AND IMPROVED APPARATUS FOR 3 2 5 332 EFFECT ING SUCH DRIVING [75] Inventor: Lucio Stabile,Milan, Italy Primary Examiner-George Harris Assistant ExaminerW. E. Duncanson, Jr. [73] Assignee. Vanguard U.S., Millbrae, Calif. Attorney Youm and Tarom [22] Filed: Nov. 25, 1970 R 57 ABST ACT [21] Appl. No.: 92,576 1 I A system for winding and unwinding material on a reel which can act as a regulated system with constant Fm'elgn Apphcatlon Dam power", when confronted with variations in the angu- Nov. 27, 1969 Italy ..2s01s A/69 speed w of the reel, due th variations of diameter, and as a purely velocity" regulated system, when 52 us. c1 ..318/6 with variations in linear velocity V of the 51 Int. Cl. ..B65h 25/28 material in transient Phttses 0f Stmtg accelettttitm, by h u 7 taking advantage of the combination of the availability [58] Field seam 318/6 of the full feeding of the motor field, and of the direct [56] References Cited control of values and amounts involved, thereby eliminating the need for recourse to means for approx- UNiTED STATES PATENTS imate simulation of these values.

3,519,903 7/1970 Carter ..3l8/6 10 Claims, 5 Drawing Figures SYSTEMS FOR DRIVING REELS AT CONTROLLED SPEED AND POWER AND IMPROVED APPARATUS FOR EFFECTING SUCH DRIVING This invention relates to improvements in systems for the driving of rotating bodies, such as winding and unwinding reels, wherein the tension or pull, which must be applied and maintained on the material during the winding or unwinding must be maintained constant under variable conditions of angular speed and/or acceleration and any kind of resistance to rotary movement.

Drives of the character with which this invention is concerned are mainly, but not exclusively, intended for causing the desired movement, by exerting a pulling force on the material during the winding (or unwinding) around reels, the material generally consisting of a continuous ribbon or sheet of, for example, paper, plastic materials, fabrics, rubber, laminates of various kinds, as well as metals, such as steel, aluminum or the like. The pulling force must remain constant with the different diameters which may be present at the moment by the roll or spool during the winding or unwinding operation. In general, such winding and unwinding must be carried out at constant tangential speed, but the condition of constancy of tension or counter-tension, applied to the material in a continuous ribbon or sheet, must be observed even under different conditions of speed (which may be modified at will during the tending of the reel) and during acceleration or deceleration.

Because of the variability of these conditions, in which the only constant parameter is, in practice, that represented by the pull or tension applied to the material, the problems inherent in assuring the constancy of this parameter are many and complex. These problems are especially difficult to solve when, to guarantee the quality and uniformity of the work, the pull must be kept strictly constant, or varied according to a predetermined rule, as a function of the requirements of the process.

Considering, typically, that the conditions of constant pull and constant linear speed of the material must be observed rigorously during winding and unwinding (and thus constant peripheral speed of the outer winding of the'spool), and assuming that the friction losses are also constant, it is evident that the reel or mandrel must be driven with constant power, thus applying to the reel a torque which is inversely proportional to its angular speed. More precisely, the product of the torque and the angular speed must be a constant, considering that the power occurring is applied to the ribbon material, the linear speed and tension of which must both be constant, independently of the variations of the diameter of the roll or spool during the winding or unwinding around the reel.

If the pull is kept constant, the torque to be applied to the reel must undergo considerable variation when other factors intervene which change the resistance to movement, especially when rotational inertia resistances come into play during acceleration and deceleration. These inertia resistances may reach values which are very high, because of the mass of the components in rotation. Moreover, the mass may vary widely since acceleration and deceleration may occur either at the beginning or at the end of the winding or unwinding operation. The importance of this variability will be evident when it is considered that, in modern plants with continuous processes, reels are commonly used for winding and unwinding which may have a ratio of diameters (diameter of the empty reel to the wound material) on the order of 1:10. The initial mass of a roll or spool of quite heavy material may be many times greater than the total of all the other components in rotation.

Considering then that the variations of the peripheral speed, for example, at the beginning and at the end of the winding, and also during same, are effected with constant acceleration, the power to be applied to the reel shaft must be such as to compensate not only the resistance due to the constant pull, but also that resulting from the acceleration, imposed on a mass of which the values may be very different during different phases of operation.

Many means and systems have been proposed for the driving of reels at variable angular speed and with constant pull, at least within certain limits of approximation. Generally, these drives include, as sources of mechanical energy, direct current electric motors, fed

and controlled by devices and circuits which are controlled, in turn, by signals representing the linear speed of the material and of the tension or pull applied to same. At most, it may be considered that these drives are controlled in speed, in the sense that every time a signal is introduced showing a change from a predetermined linear speed of the system, the drive intervenes.

These known means, at most, produce satisfactory results for the purposes of observing constancy of linear speed and pull. However, insufficient or irregular results, for the purposesof pull and/or promptness of response, are experienced during acceleration and deceleration. The inadequacy of the prior art approaches is particularly apparent where the acceleration and deceleration is quite rapid, for example, in the case of driving reels of reversible rollers, paper calenders or rotary stamping machines, in which the torque required for accelerating or decelerating in the required short time, may be enormously greater (even on the order of 10021) than the torque necessary to keep the desired constant pull on the material once the roll or machine has been brought up to speed.

It is the principal object of this invention to provide an improved system for driving rotating reels, rolls or the like.

It is an important object of this invention to provide a system for winding or unwinding material on a reel and wherein the motor is always operated at full field and the full torque of the motor is always available.

It is a further object of this invention to provide a system for winding or unwinding material on a reel and wherein a constant force is applied to the material under differing conditions of speed and acceleration.

It is a more specific object of the invention to provide a system for winding and unwinding a ribbon or sheet of material on a reel wherein the control for the motor driving the reel is controlled by signals which are representative of the diameter of the material wound around the reel at any given moment, the linear speed of the material at that same moment and the product of the angular velocity of the reel and the torque applied at any instant whereby the drive for the reel is controlled both in velocity and in power.

Other objects, features and advantages of the invention will become more apparent from the following description which, when taken with the attached drawings, discloses but a preferred form of the invention.

Referring now to the drawings:

FIG. 1 is a schematic diagram of a conventional control circuit for winding and unwinding reels.

FIG. 2 is a graphical plot of kinetic energy versus roll diameter.

FIG. 3 is a graphical presentation of a group of curves representing the power required as various parameters are varied.

FIG. 4 is a schematic diagram of a control circuit embodying the principles of this invention.

FIG. 4A is a modified embodiment of the circuit of FIG. 4.

Referring now more in detail to the drawings, there is illustrated a reel driven by a motor M with direct current, from which is unwound material in a ribbon 12, under a counter-tension measured by a mechanical system 14, for example of the so-called dancer type, and at a linear speed, measured in turn, for example, by a friction pulley 16. The mechanical means of measurement of the tension and the speed are associated with transducer means 18 and 20 which introduce to the

circuits

22 and 24, respectively, signals which are proportional to the pull and linear speed, respectively. Both of these signals are applied to one connection, the summing point 26.

The armature of the motor M is fed through a current regulator 28, which can control the current which is supplied from the feed line, or the current supplied to the line from the armature itself, when the motor acts as braking means. This system of feeding the armature may be represented by a known motor-generator arrangement of the so-called Ward-Leonard type, or by a system with silicon controlled rectifiers (SCRs) one example of which has been described in Italian Pat. No. 687,000.

The field of the same motor is, in turn, fed through a current regulator 30. In the conventional system of FIG. 1, by means of a potentiometer 32, it is possible to apply a reference current to the regulator 28 and thus preset the value of the current that is to circulate in the armature itself. Such current will remain constant independently of the speed of the motor.

The field regulator 30, on the other hand, receives a reference signal of the field current, from a potentiometer 34, the position of which is determined by a servo motor 36 which, through an operational amplifier 38, fed from the point 26, displaces the potentiometer 34 as a function of the error between the signal of the linear velocity of the material, given by the tachometer generator 20 through the circuit 24, and the voltage of the motor armature which is applied to the summing point 26 through a circuit 40.

With decrease of the diameter of the material present on the reel 10, the angular speed W of the reel and the motor tends to increase, because of the progressive reduction of the radius, and the constancy of the linear speed V of the material which is unwound and thus the voltage generated by the armature increases also, applied at 26 through the circuit 40. Because of the constancy of the linear speed V and the consequent constancy of the signal produced by the tachometer generator 20 and applied at 26 through the circuit 24, at the point 26 there is an error signal which causes the servo motor 36 to move in the direction of decreasing the reference of the field of the motor, thus reducing the excitation of the motor itself so that the same voltage generated corresponds to the increased angular speed W.

Thus, it may be seen that the system operates to keep constant the voltage generated by the motor.

Since the armature current is kept constant by the armature regulator 28, the product of the voltage generated by the motor and the armature current will remain constant despite variations in the radius of the winding around the reel 10. In other words, the power delivered by the motor is constant, which is identified with the constancy of pull on the material 12 and the linear speed V of same, if the losses of the system are negligible. However, since these losses are not negligible, as a rule, the transducer 18, connects to the summing point 26 so as to calibrate the error signal and correct the voltage generated by the motor M, to take into account the losses of the system.

When, on the other hand, a variation of the linear speed V of the material occurs, the tachometer generator 20 will produce at 26 a reference signal of the voltage generated by the motor M, proportional to such increased velocity V. In other words, by increasing the signal in the circuit 24, the level of the constant voltage generated by the motor, will increase and thus the level of the power generated.

The known devices include a branch circuit 42 which, branching from the velocity signal (the signal given by the tachometer generator 20 at the circuit 24 from the output of which is a connection 44 applied to the branch circuit), produces at its output a signal proportional to the acceleration, and which, through a potentiometer 46 is applied to the armature regulator 28, in the form of an additional current signal, proportional to the acceleration.

The potentiometer 46 is driven, together with the potentiometer 34, by the servo motor 36. Since, as indicated above, the potentiometer 34 is'displaced as a function of the variation of the diameter during the unwinding of the reel 10, the correction signal of the torque, which is thus applied to the point 48, also results between certain limits of approximation, proportional to the mass of the reel at the moment of the acceleration.

Obviously, these known devices and drive assemblies may, and in practice are, embodied in various constructions and with different circuit equivalents. However, the ideas used up to now for the type and for the uses considered, are, in practice, the following:

a. The current of the motor armature is adjusted by a potentiometer 32 proportional to the pull, or to the tension or counter-tension which it is desired to exert on the material during the winding on, or unwinding from, the reel.

b. The change in angular velocity W necessary to compensate for variations in the instantaneous diameter of the winding, or the roll or spool, is obtained through variations of the field current of the motor.

c. The variation of torque necessary to follow the variations of the linear speed V of the material, or to fulfill the transient torque requirements presented in acceleration or deceleration, is obtained indirectly by means of a compensation system.

d. The exact regulation of the value of the pull is obtained through a transducer 18, which applied at 26 a signal to correct the value of the field current of the motor (through the servo system 36,38).

From paragraph (c) it will be seen immediately that the signal determining the variations in power which are necessary to meet transient energy requirements, in the phases of acceleration, is obtained through a simulator system of the values operative during the variations. In fact, the branch circuit 42 simulates the signal of acceleration, while the position of the potentiometer 46 simulates the moment of inertia of the reel, while its instantaneous position is proportional to the instantaneous diameter of the roll.

Since these signals can be produced by adopting suitable connections, it is not possible to obtain an exact representation of the actual values in play. In fact, the inertia resistances, due to acceleration, vary according to the mass of all the rotating components and the square of their velocity. One part of these components (the axle of the reel, the rotors of the motor, the transmissions, etc.), has a constant moment of inertia which does not vary, and is thus fixed, while the roll has a variable moment of inertia as its diameter varies, this moment of inertia being proportional to the cube of the diameter. All the rotating masses, fixed and variable, have, however, an angular speed which varies in linear fashion as a function of the variation in diameter, with linear speed V constant.

Therefore, the kinetic energy possessed by the total of the rotating masses varies according to a very complicated function with the diameter of the roll. Such a variation may be represented by the curve C in the graph of FIG. 2, in which the total kinetic energy E of the rotating mass is indicated on the ordinate, while the diameter D of the roll is indicated on the abscissa. This curve is the resultant of the sum of the energy possessed by the fixed masses (energy prevailing particularly at high angular speeds, and, thus, with small roll diameters), and of the roll of material, respectively,

which mass increases, but angular speed decreases with increase of diameter.

Moreover, the drive devices may also be adjusted (by acting on the potentiometer 32), to adapt the machine to different materials, more or less thin, or more or less heavy. These variations of adjustments affect, in a very complex way, the variations of kinetic energy possessed at every instant by the totality of the rotating masses.

In conclusion, and as a result of long experience, it has been found practically impossible to reproduce, by simulator systems, the actual variations incurred during operation, especially in the transient phases of acceleration. The practical use of the systems is limited by the efficiency of the means of correction and of the servomechanisms controlling same, the sensitivity of which and the speed of response of which are subject to well-known limitations. Therefore, the most desirable performance cannot be achieved, nor even closely approached using the known technology, considering the quite narrow limits of linear speed, angular speed, acceleration, constancy of pull and ratio between maximum and minimum diameter of the roll.

Considering the prior art from another aspect, since the variation in speed is obtained by varying the field current, it is evident that the maximum ratio between diameters (reel full reel empty) is related to the inherent limitations of DC motors, with separate excitation, operating with wide ratios of speed by variation of the field current. By using special motors, it is possible to reach ratios up to 1:6, but it is well-known that great difficulties are encountered in the case of motors in which the power is on the order of several hundred kilowatts.

Moreover, the variation of speed of a DC motor, by variation of the field current, is a variation with constant power, and thus the torque which the motor can give decreases with increase of speed. In other words, the faster the motor turns, the less torque is available for achieving acceleration. This limitation is particularly serious in the initial or final phases of acceleration or deceleration. In other words, using the known means and systems, there is available in many cases only a fraction, and sometimes a very small fraction, of the torque which the motor could supply if it operated at full field".

The principles of this invention may be better understood by considering first the graph of FIG. 3. That graph depicts a group of curves each point of which corresponds to a constant product of the respective parameters on the abscissa and on the ordinate. For example, indicated on the abscissa is torque C and on the ordinate the angular speed W. Each curve corresponds to a given power P, P and P", identifiable, in this case, with the value of the pull and a given linear speed V of the material 12 during winding on or unwinding from the reel 10.

Suppose, for example, that it is desired to operate at constant speed and pull. The power occurring in the drive will be constant and represented, for example, by the curve P, for given values of speed V and pull. Obviously, if the tension or pull is doubled or tripled from that determining the curve P, the constant power to be given would be represented by the curve P or the curve P", respectively, and so on.

The above applies also, assuming that the values of the ordinate represent the armature voltage T, and those of the abscissa the intensity I of the field current. In this case, and assuming, according to the known method, that only the field current is varied to meet a change in load torque, the variation of the power can be obtained only by proportional variation of this current, naturally within the limits of availability, as indicated above.

However, the need for varying the power may depend not only on that of varying the torque, to adapt the machine to a change in pull, but also, in the transient intervals of acceleration. To meet the added torque required during acceleration, the power required changes and these changes also correspond to a passage between different curves of the group of curves of FIG. 3.

Variations in the power in the transient phases of acceleration (when the acceleration loads are added algebraically to those due to pull, having values much greater than those of these latter loads) is effected, according to the invention, in response to a signal, in the determination of which there cooperates a function of the momentary power delivered by the motor. This function, which in turn is a real, true power signal is combined with a speed signal derived, for example, through a conventional tachometer generator. The resultant signal is thus, subject to suitable manipulations, used for the regulation of the motor, either in power or in velocity. During the normal operation of the reel, at constant power, the control of the drive is generally based on the power portion of the combined signal (i.e., the portion which prevents changes which would otherwise occur due to variation of the diameter of the roll) while in the transient phases the velocity portion of the same combined signal is controlling.

In other words, the improvement consists, in one essential characteristic, of the substitution for the conventional compensation systems, (which are a system operating indirectly on the basis of a simulating system of the variations of actual values), of a direct system, through which the drive reacts to the actual changes in these actual values, with evident improvement in fidelity of control and immediacy of response.

According to another important characteristic of the invention, the system of driving and control of the driving of the motor is such as to give this system the capacity to act as a system regulated to constant power when confronted with changes in angular speed of the reel (due to variations in the diameter'of the wound material) and as a system regulated purely in velocity when confronted with variations in linear speed of the material, especially in the transient phases of strong acceleration, positive or negative.

Such a system permits the use of a transducer as a corrector of pull, both during changes in diameter and in transient acceleration phases, and under conditions of diameter and speed, in which the motor is required to reverse the direction of the torque, for example, to compensate for mechanical loading, when the latter might influence the torque due to pull, especially during the unwinding operation, during which the countertension to be applied to the material may be insufficient to absorb the mechanical loads.

More specifically, these advantageous characteristics resulting from the application of the invention, are obtained by effecting the control of the motor not only on the field but also on the armature with the control on the armature permitting the motor to give its maximum torque at any speed between a state of rest and the maximum operating speed.

In other words, and again referring to the graph of FIG. 3, in which each curve represents a constant product of field intensity and armature voltage, the passage from one curve to another, to meet transient inertia loads, is obtained, at least for the most part, by modifying the voltage" factor in the amount necessary to give the greater power required, with full field.

For the control of the armature it is necessary to have available much more powerful armature drive circuits, and therefore more costly ones than those to be used in drives of which the motors are controlled exclusively by control of the excitation. This condition might, under some circumstances, be considered a limitation of the invention; however, such apparently harmful limitation is in practice, only applicable where feed systems of the rotary type (such as Ward- Leonard groups and the like) are used, while this limitation, has negligible importance when more modern feed systems such as thyratrons or SCRs and the like, are used with the increased cost being largely compensated by the performance of the improved system.

FIG. 4 represents a typical circuit diagram of an improved device according to the invention. In this diagram, the components are not described individually, since they are well known in the art: neither are the return conductors indicated, nor the accessories not necessary for an understanding of the invention, and which correspond to those of the conventional device of FIG. 1, and are given the same numerical references.

As in the preceding case, an armature current regulator 28 imposes on the motor armature M the value of current determined by its reference at the point 48'. Similarly, a regulator 30 of the field current of the motor, imposes on the field 50 a value of the field current, depending on the references it receives at point 52.

The operational amplifier 38 receives, as input signals of reference and reaction, respectively, an error signal resulting from a signal emitted by the tachometer generator 20, through the circuit 24', proportional to the linear speed V of the material 12, and a signal emitted by a tachometer generator 54, applied through the circuit 56, these two signals being applied at the point 26'. The field 58 of the tachometer generator 54 is fed by a field current regulator 60, which will be discussed hereinafter.

Assuming that the field current in field 58 of the generator 54, has a fixed and constant value, this generator behaves as a conventional tachometer generator. This tachometer is connected through a conventional mechanical connection 62 to the motor M and thus to the reel 10. Consequently, its signal is proportional to and indicative of the angular speed W of the reel. In this case it may be assumed that the system acts as a drive regulated in speed, in which the operational amplifier 38 is an amplifier for the regulation of speed, since it amplifies the difference between the reference of linear velocity applied through the circuit 24' and the reference (which constitutes the reaction) applied through the circuit 56, the error of speed, so amplified, being applied at the summing point 64 so as to impose an armature current value in the motor such as will generate a driving torque equal to the load torque applied to the shaft of the motor itself.

The same signal arrives at the point 52 through another amplifier 66, with high gain and sharp saturation characteristics. The task of this amplifier is to assure that with very slight values of the error signal resulting from the output of amplifier 38, the full field of the motor will be retained constantly. This is to be distinguished from those conventional systems of speed regulation, in which suitable values of armature current and of field are imposed at the same time, in order to generate the necessary torque, and, thus, in which both the field and the armature vary at the same time according to the error signal.

The same error signal amplified in 38' is applied then through a circuit 68 to a servo motor 36' which acts on a potentiometer 46' regulating a value which is applied, through a circuit 70 to the regulator 60 of the field current of the tachometer generator 54 and through an attenuating potentiometer 32' to the same point or connection 64.

The value of the signal at the output of the potentiometer 46', being proportional to the momentary diameter of the spool or roll, is a true diameter signal.

Considering the system of FIG. 4 in its operation, confronted with variations in linear speed V of the material, not due to variations in diameter of the roll, and for the purpose of discussion momentarily holding the pull constant, the variation of the peripheral or tangential speed of the material wound must follow strictly the speed V, since the linear and tangential velocities are the same. This situation is perfectly met, since the system acts as a regulator of the angular speed W of the reel 10.

In the transient phases of acceleration and deceleration, there is found a small, but sometimes not negligible variation in winding or roll diameter, especially if these transient phases have a certain time duration. This last variation is compensated in the known way be the tension transducer 18, of which the output circuit 22 applies to the same point or connection 64 a corrective signal, which suitably corrects the error signal amplified and applied by 38'.

The operation of the same system will now be considered in the presence of variations of the diameter of the roll wound at each instant around the reel 10.

The output of the operational amplifier 38' reaches the servo motor 36, which, displacing the potentiometer 46' causes it to take a position such that the diameter signal, coming from the potentiometer, affects the value of the armature current of the motor M, and the value of the field current of excitation in field 58 of the tachometer generator 54. When the motor is operated with full field, as indicated above, with the amplifier 66, the result is that the current signal which arrives at 48 depends upon the torque produced at the moment by the motor. Since the signal from potentiometer 46' also controls the field current of the tachometer generator 54, the signal generated by the latter and applied, through the output circuit 56, at the point 26', is a power signal, since it is proportional to the power, as will be explained below. In fact, the electromotive force (schematically indicated by the arrow 72) corresponds to the product of the angular velocity and the flux generated by the field 58 of the generator, this angular velocity being representative of that of the reel.

Since it is a fundamental characteristic of this tachometer generator, with separate adjustable excitation, that the flux generated by the field is strictly proportional to the field current, the electromotive force 72 is proportional to the product of thislatter current and the angular velocity of the motor, and the field current is proportional to the torque of the motor itself, thus providing proportionality between the electromotive force and the power given by the motor at the moment, and justifying the designation of the signal applied through the circuit 56 as a power signal.

Consequently, any time that the diameter of the roll wound around the reel 10 tends to grow, for example, there will be a tendency to decrease the angular velocity of the motor M by which is generated a difference between the voltage given by the

tachometer generators

20 and 54, both applied at 26, and thus there will be an error signal which, amplified by the operational amplifier 38', will cause the displacement of the servo motor 36', which in turn will cause the potentiometer 46' to take a new position, such as to cause an increase of the armature current of the motor M and of the current in the field 58 of the tachometer generator 54, so that the voltage generated by this latter tachometer generator 54 will again equal the voltage generated by the first tachometer generator 20, bringing into balance again the output of the operational amplifier 38'.

Thus, it may be seen that, faced with infinitesimally small variations of the diameter of the winding around the reel 10, compatible with the precision of the system, the output of the operational amplifier 38' is zero, and the torque signal, corresponding to the momentary diameter of said winding, is maintained by the position of the potentiometer 36. The potentiometer 32', in turn, permits varying the ratio between the signal applied to the point 74 and that applied to the point 64, according to the amount of pull that is necessary, depending on the material to be wound on or unwound from the reel 10.

Since the drive system feeding the motor M is reversible in direction, this system can function perfectly under all conditions required for the driving of a reel of machines of practically any kind, especially for the driving of reversible rollers, in which the reels must accelerate and decelerate in very short times, and alternately wind and unwind.

The above-described system is also advantageous to use for the driving of plants for the production of paper and the like, the reels of which must operate on rolls of which the maximum and minimum diameters are in a very high ratio to each other, even above 10:1, and where it is also desirable that the acceleration and deceleration of the rotating masses, which have very high and greatly variable moments of inertia, take place in the shortest possible times.

Moreover, the system is also especially adapted to handling conditions of operation in which the pull must be varied as a function of a predetermined rule based on the variation of the diameter. Since in this device, the position of the potentiometer 46' represents at every moment the diameter of the winding present around the reel 10, the available signal permits a simple variation of pull under the desired conditions, for example, by making the setting of the potentiometer 32' subject, according to the functions desired, to the potentiometer 46 Finally, since the signal applied through the circuit 56 may be considered either as a speed signal, when it depends, with power constant, on the angular velocity W, or as a power signal, under the conditions considered and analyzed above, a signal constant in velocity (given by the tachometer generator 20 and applied through the circuit 24), or a power signal are present at point 26' and in amplifier 38'. Thus, a device according to this invention can act as a regulated system with constant power", when confronted with variations in the angular speed W of the reel, due to variations of diameter, and as a purely velocity" regulated system, when confronted with variations in linear velocity V of the material, in transient phases of strong acceleration, by taking advantage of the combination of the availability of the full feeding of the motor field, and of the direct control of values and amounts involved, thereby eliminating the need for recourse to means for approximate simulation of these values.

Referring now to FIG. 4A, a modified embodiment of the circuit of FIG. 4 is illustrated. According to this modified embodiment, the

components

58, 60, 70 and 74 are omitted, and tachometer 54' is connected by lead 56 to a further potentiometer 46". This potentiometer has a movable contact arm driven by motor 36', concurrently with potentiometer 46'.

In the modified embodiment of FIG. 4A, lead 56 applies to junction 26 the output of tachometer 54 which, in this case, is a conventional permanent excited tachometer, designed to provide an output purely representative of the speed of motor M. This uninfluenced output speed signal is applied to the lead 56, and then modified by the variable resistance provided by the second potentiometer 46", the contact arm of which is actuated by motor 36', concurrently with potentiometer 46. Therefore, lead 56' applies to junction 26 a signal basically representative of the speed of the motor and influenced by the output of that junction, which through amplifier 38', controls the motor 36'.

From another point of view,'it might be said that in the original embodiment of FIG. 4, the motor 36 influences the output of tachometer 54, as such output is generated by varying the field 58 of the tachometer 54, while in the modified embodiment of FIG. 4A the motor 36' modifies the output after it has been provided, acting on potentiometer 46.

The present system and the means for carrying it out have been described and represented solely by way of example, and not for limitation, it being understood that these means may be modified and the principles of the invention carried out with individually different components, known per se in the art, without departing from the spirit and scope of the invention as defined by the appended claims.

Having described specific preferred embodiments of the invention, the following is claimed:

1. In an apparatus having a reel and a web which is to be wound onto or from the reel and a motor for controlling the lineal speed of the web at the reel to maintain the speed at the reel substantially the same as that at a station spaced from the reel along the web to control the tension in the web between the reel and said station, means for signaling the relative speeds of said web at said reel and said station comprising circuit means monitoring conditions indicative of the lineal speeds of the web at said reel and at said station and providing first and second signals having a characteristic which varies in accordance with said linear speeds and a first circuit for comparing said first and second signals and providing an error signal which varies with the difference of said speeds, control means for energizing said motor in accordance with the values of a characteristic of a control signal, said control means having input means to which said control signal is applied, and control signal means for applying a control signal having a plurality of components which vary with different conditions to said input means comprising circuitry connecting said first circuit to said input means-to immediately establish a first component of said control signal having a value which is in accordance with the instantaneous difference in speeds of said web at said reel and at said station, said control means further including additional means for providing a second component of said control signal in addition to the component from said first circuit which signal component varies in accordance with the diameter of said reel.

2. An apparatus as defined in claim 1 wherein said additional means for providing a signal component comprises signal integrating means having an input connected to receive said error signal and an output connected to said input means.

3. An apparatus as defined in claim 2 wherein one of said first and second signals is responsive to detection circuit means connected to said motor for tracking said lineal speed at said reel, said first circuit comprises combining circuit means for subtracting either of said first and second signals from the other of said first and second signals, said control means comprises amplifying means, said circuitry'comprises algebraic adding means for additively combining more than first and second components.

4. An apparatus as defined in claim 1 further comprising web deflection means intermediate said reel and said station deflecting the path of travel of said web to provide a web storage loop and tensioning said web, and tension transducer means operably connected to said web deflection means providing a tension signal dependent upon tension of said web at said deflection means, said tension signal being connected to said input means of said control means for establishing still another component of said control signal for energizing said motor.

5. A method for maintaining substantially constant tension in a web between a reel and a station at which web speed is determined by a factor different from reel speed comprising the steps of providing a signal which varies with reel diameter, providing a second signal which varies with the instantaneous difference in lineal speeds at said reel and at said station, and combining said signals to vary angular speed of said reel in accordance with both signals to maintain the lineal speed at said reel substantially the same as at said station.

6. An improved system for driving apparatus for winding and unwinding continuous ribbons of material at a controlled lineal speed and power, said ribbons of material passing a station spaced apart from said apparatus, comprising a motor having an armature and a field and operatively connected to said apparatus, and I a control circuit for said motor, said control circuit comprising: first means for producing a signal dependent upon the instantaneous diameter of the wound material, second means for producing a signal as a function of the lineal speed of the material at said station spaced apart from said apparatus, third means for producing a signal as a function of the instantaneous lineal speed of the material at the apparatus, 1 fourth means for comparatively combining said lineal speed signals from said second and third means to produce an error signal, and

means for combining said signals from said first and fourth means to produce an operating signal to said motor which is operative to control said system both in lineal speed and in power, wherein said motor is fed with direct current and has independent excitation on the field and the armature,

said operating signal being operative to control both the field and the armature.

7. The improved system of claim 6 and further including amplifier means having high gain and sharp saturation characteristics, 7

said amplifier means being operative to apply said operating signal to the field of said motor, whereby any error signal introduced to the circuit maintains the motor at full field.

8. The improved system of claim 6 and further including attenuation means acting on said signal produced by said first means whereby said apparatus can be adapted to various materials and pull values.

9. An improved system for driving apparatus for winding and unwinding continuous ribbons of material at a controlled lineal speed and power, said ribbons of material passing a station spaced apart from said apparatus, comprising a motor having an armature and a field and operatively connected to said apparatus, and

a control circuit for said motor, said control circuit including:

first means for producing a signal representing the instantaneous diameter of the wound material,

second means for producing a signal as a function of the lineal speed of the material at said station spaced apart from said apparatus,

third means for producing a signal as a function of the instantaneous lineal speed of the material at the apparatus,

fourth means for comparatively combining said signals from said second and third means to produce an error signal, and

means for combining said signals from said first and fourth means to produce an operating signal to said motor which is operative to control said system both in lineal speed and in power,

wherein said signal produced by said third means comprises a voltage proportional to said instantaneous lineal speed and is generated by tachometric means operating in dependence upon both the instantaneous angular velocity of said apparatus and the signal from said first means.

10. The improved system of claim 9 wherein said tachometric means comprises a tachometer generator with controllable excitation, said controllable excitation being controlled by the signal produced by said first means.

Claims

1. In an apparatus having a reel and a web which is to be wound onto or from the reel and a motor for controlling the lineal speed of the web at the reel to maintain the speed at the reel substantially the same as that at a station spaced from the reel along the web to control the tension in the web between the reel and said station, means for signaling the relative speeds of said web at said reel and said station comprising circuit means monitoring conditions indicative of the lineal speeds of the web at said reel and at said station and providing first and second signals having a characteristic which varies in accordance with said linear speeds and a first circuit for comparing said first and second signals and providing an error signal which varies with the difference of said speeds, control means for energizing said motor in accordance with the values of a characteristic of a control signal, said control means having input means to which said control signal is applied, and control signal means for applying a control signal having a plurality of components which vary with different conditions to said input means comprising circuitry connecting said first circuit to said input means to immediately establish a first component of said control signal having a value which is in accordance with the instantaneous difference in speeds of said web at said reel and at said station, said control means further including additional means for providing a second component of said control signal in addition to the component from said first circuit which signal component varies in accordance with the diameter of said reel.

3. An apparatus as defined in claim 2 wherein one of said first and second signals is responsive to detection circuit means connected to said motor for tracking said lineal speed at said reel, said first circuit comprises combining circuit means for subtracting either of said first and second signals from the other of said first and second signals, said control means comprises amplifying means, said circuitry comprises algebraic adding means for additively combining more than first and second components.

6. An improved system for driving apparatus for winding and unwinding continuous ribbons of material at a controlled lineal speed and power, said ribbons of material passing a station spaced apart from said apparatus, comprising a motor having an armature and a field and operatively connected to said apparatus, and a control circuit for said motor, said control circuit comprising: first means for producing a signal dependent upon the instantaneous diameter of the wound material, second means for producing a signal as a function of the lineal speed of the material at said station spaced apart from said apparatus, third means for producing a signal as a function of the instantaneous lineal speed of the material at the apparatus, fourth means for comparatively combining said lineal speed signals from said second and third means to produce an error signal, and means for combining said signals from said first and fourth means to produce an operating signal to said motor which is operative to control said system both in lineal speed and in power, wherein said motor is fed with direct current and has independent excitation on the field and the armature, said operating signal being operative to control both the field and the armature.

7. The improved system of claim 6 and further including amplifier means having high gain and sharp saturation characteristics, said amplifier means being operative to apply said operating signal to the field of said motor, whereby any error signal introduced to the circuit maintains the motor at full field.

9. An improved system for driving apparatus for winding and unwinding continuous ribbons of material at a controlled lineal speed and power, said ribbons of material passing a station spaced apart from said apparatus, comprising a motor having an armature and a field and operatively connected to said apparatus, and a control circuit for said motor, said control circuit including: first means for producing a signal representing the instantaneous diameter of the wound material, second means for producing a signal as a function of the lineal speed of the material at said station spaced apart from said apparatus, third means for producing a signal as a function of the instantaneous lineal speed of the material at the apparatus, fourth means for comparatively combining said signals from said second and third means to produce an error signal, and means for combining said signals from said first and fourth means to produce an operating signal to said motor which is operative to control said system both in lineal speed and in power, wherein said signal produced by said third means comprises a voltage proportional to said instantaneous lineal speed and is generated by tachometric means operating in dependence upon both the instantaneous angular velocity of said apparatus and the signal from said first means.