US3744287A

US3744287A - Hydraulic interstand tension regulating and automatic gauge control system for multi-stand rolling mills

Info

Publication number: US3744287A
Application number: US00180374A
Authority: US
Inventors: A Silva; G Gaines
Original assignee: Westinghouse Electric Corp
Current assignee: AEG Westinghouse Industrial Automation Corp
Priority date: 1971-09-14
Filing date: 1971-09-14
Publication date: 1973-07-10
Anticipated expiration: 1990-07-10
Also published as: RO64389A; AR196885A1; FR2152969B1; FR2152969A1; IT967408B; BR7206367D0; AT318527B; ZA725693B; BE788725A; PL74675B1

Abstract

A system for controlling the delivery gauge and the interstand tensions of a tandem rolling mill by means of hydraulic cylinders located at each stand of the mill. The hydraulic cylinders, in turn, are controlled by the electrical circuitry of this invention. Gauge is controlled at the first and last stands only, while interstand tension is controlled by tensiometer feedback signals which are compared with tension reference signals to generate error signals for controlling the pressure exerted by the hydraulic cylinders and, thus, the roll gap at each stand. The speeds of all stands except the last are maintained constant. The system incorporates a deadband feature to avoid excessive operation of the hydraulic cylinders in response to noise signals.

Description

United States Patent 1 1 Silva et al.

[ HYDRAULIC INTERSTAND TENSION REGULATING AND AUTOMATIC GAUGE CONTROL SYSTEM FOR MULTI-STAND ROLLING MILLS [111 3,744,287 1451 July 10, 1973 3,355,918 12/1967 Wallace 72/8 3,531,961 10/1970 Dunn 72/8 3,170,344 2/1965 Marrs 72/11 3,169,421 2/ 1965 Bloodworth 72/11 [75] Inventors: Antonio V. Silva, San Paulo, Brazil; Primary Examiner-Milton Mehy George P. Gaines, Williamsville, Attorney-F. H. Henson, .1. J. Wood and R. G. N.Y. Brodahl [73] Assignee: Westinghouse Electric Corporation, ABSTRACT Pittsburgh, A system for controlling the delivery gauge and the in- 22 F1 d: Se L 14 1971 terstand tensions of a tandem rolling mill by means of 1 16 p hydraulic cylinders located at each stand of the mill. PP 180,374 The hydraulic cylinders, in turn, are controlled by the electrical circuitry of this invention. Gauge is con- [52] Us CL D 72/8 trolled at the first and last stands only, while interstand 51 1m. (:1 B211 37/12 tehsih is hY tehsimhete feedback Signals [58] Field of seal-11 72/s-11 which ale h1Pared with reference signals 72/16 generate error signals for controlling the pressure exerted by the hydraulic cylinders and, thus, the rOll gap [56] References Cited at each stand. The speeds of all stands except the last are maintained constant. The system incorporates a UNITED T T PATENTS deadband feature to avoid excessive operation of the g hydraulic cylinders in response to noise signals. 315071134 4/1970 Silva 72/8 12 Claims, 4 Drawing Figures TERSION REFERENCE fl TO TENSION REGULATORS r TENSION STANDS TENSION REGULATOR REGULATOR TO STAND a 2 TENSION I REGULATOR s5 2 I I0 l6 l2 0 1'; en T g 3224 L 531F361 wear 81%? 48 46 0| 0 DEL-IVERY GI 62 SH SPEED 38 SPEED RE ufi rsiiis SPEED REGULATOR REGULATOR STA D 3&4 REGULATOR 1L 1 ll '1 sPEEO 46 REFERENCE HYDRAULIC INTERSTAND TENSION REGULATING AND AUTOMATIC GAUGE CONTROL SYSTEM FOR MULTI-STAND ROLLING MILLS BACKGROUND OF THE INVENTION In the rolling of metal strip material in a tandem rolling mill, the various stands of the mill are set up so that each reduces the strip by a given increment to produce the desired final gauge at the output of the mill. For this purpose, it is desirable to maintain the interstand tensions constant since the reduction effected in any one stand depends not only on the roll setting of that stand, but also on the tensions on the strip at each side of the stand.

in the past, tandem rolling mills have been provided wherein the roll gap spacing of the first stand is controlled by an automatic gauge control system to compensate for changes in the thickness in the strip entering the mill. The change in the screwdown on the first mill results in an alteration in the reduction of the strip at that stand and, hence, a change in speed of the strip leaving the first stand and entering the second stand. This, in turn, alters the tension between the first and second stands; whereas it is desired to maintain interstand tension constant. Accordingly, in tandem rolling mills of this type, means are provided for maintaining the interstand tensions constant so as to prevent variations in tension from affecting output gauge. Usually, a gauge measuring device, such as an X-ray gauge, measures the thickness of the material leaving the last stand; and if it should deviate from a desired value, the speed of the last stand is varied to compensate for any changes in gauge.

In the past, variations in roll gap spacing to vary tension and/or gauge have been made by means of a mechanical screwdown device. Such mechanical devices, however, have a certain inherent delay time which must be taken into account in any control system. It has been found that instead of using a mechanical screwdown to effect changes in the roll gap, better results can be obtained by using hydraulic cylinders beneath the lower roll chocks, usually the chocks for the lower backup rolls. There are two cylinders, one on each side of the mill, which exert an upward pressure on the chocks and, hence, on the lower backup and work rolls. The hydraulic cylinders are actuated by a source of hydraulic fluid under constant pressure; and means are provided for delivering the fluid to the hydraulic cylinders whereby the rolls are urged together under constant pressure. Flow control means are provided to assure substantially identical volumes of hydraulic fluid to each cylinder such that both ends of the roll will be forced upwardly or downwardly in equal amounts, thereby insuring substantially constant pressure across the width of the roll gap.

SUMMARY OF THEINVENTION In accordance with the present invention, a system is provided for regulating the tension between at least two stands in a tandem rolling mill of the type wherein a pair of hydraulic cylinders are used to exert pressure on the opposite ends of a roll in each stand to vary the pressure exerted by the roll and the roll gap spacing of the stand. This is achieved by deriving electrical error signals proportional to the difference between the actual and measured values of tension between each pair of stands and using these error signals to vary the horizontal positions of the pistons in the cylinders engaging the ends of a roll in each stand until the error signal for that stand is reduced below a predetermined magnitude.

Corrective action is taken only after the error signal exceeds a certain magnitude; and the error correction is terminated when the error signal falls below a predetermined magnitude to avoid excessive operation of the pistons in response to noise signals. Servo systems are provided for controlling the positions of the pistons within the cylinders; and these servo systems are simultaneously actuated when the aforesaid error signal rises above a predetermined magnitude to change the position of both cylinders simultaneously, thereby insuring that the forces at opposite ends of the rolls will always be the same.

Specifically, there is provided in accordance with the invention means for measuring the tension between at least two stands of a tandem rolling milland for producing a first electrical signal proportional thereto, means for producing a second electrical signal proportional to desired tension between said two stands, means for comparing said first and second electrical signals to produce an error signal, means for producing a third electrical signal proportional to the actual horizontal position of the piston in one of said cylinders, and means for producing a fourth electrical signal proportional to the actual horizontal position of the piston in the other of the cylinders. The third and fourth electrical signals are stored and used in servo systems which control the positions of the pistons as a function of the third and fourth signals, respectively. When the aforesaid error signal rises above a predetermined magnitude, the magnitude of the third and fourth electrical signals stored in the respective servo systems are varied to thereby vary the positions of the pistons through the servo means until the error signal is at least partially reduced in magnitude.

In the preferred embodiment of the invention, the actual horizontal positions of the pistons in the respective cylinders on each side of a stand in a mill are measured by means of force transducers (load cells) coupled to the piston through spring means whereby the load cell output will represent cylinder position. The output of the load cells is then applied to an integrating operational amplifier which stores the value of cylinder position and compares this with a value proportional to actual cylinder position to vary actual cylinder position if the two values are not the same.

When the error signal derived from a comparison of actual and desired interstand tension rises above a predetermined value as detected by a deadband detector, the error signal is applied to integrating operational amplifiers in the servo systems for the respective cylinders to thereby change the stored value of cylinder position. This, when compared with actual cylinder position, will actuate the cylinders to vary the horizontal position of the pistons therein, thereby varying roll gap spacing to compensate for the variation in tension.

Further, in accordance with the invention, a tandem rolling mill is provided employing hydraulic roll actuation of the type described above and wherein automatic gauge control of the first stand is provided as well as the last stand. Preferably, the gauge control for the first stand is based upon a consideration of mill housing stretch; while the gauge control at the last stand is based upon a variation in delivery strip speed. The roll gap spacings of the intermediate stands are varied to maintain tension constant as explained above.

The above and other objects and features of the invention will become apparent from the following detailed description taken in connection with the accompanying drawings which form a part of this specification, and in which:

FIG. 1 is a schematic diagram of the overall control system of the invention;

FIG. 2 is an elevational plan view of a set of rolls for one of the stands shown in FIG. 1 and illustrating the manner in which hydraulic cylinders are utilized to produce forces at the opposite ends of the rolls in the stand;

FIG. 3 is a detailed schematic circuit diagram of the tension control system of the invention as applied to two hydraulic cylinders for one stand of the mill; and

FIG. 4 is a plot of tension versus time showing the operation of the deadband detector of the invention.

With reference now to the drawings, and particularly to FIG. 1, the tandem rolling mill shown includes five stands, only three of which are shown and designated as S1, S2 and S5. It will be understood, of course, that stands S3 and S4, not shown, are intermediate stands S2 and S5. Each stand, such as stand Sl, includes an outer housing which carries

work rolls

12 and 14 backed up by

backup rolls

16 and 18, respectively. The

rolls

12 and 14 are carried, at their opposite ends, in suitable chocks, not shown. Similarly, the upper backup roll 16 is carried in a movable chock 20 connected to a screwdown mechanism, schematically illustrated at 22, the arrangement being such that the position of the backup roll 16 can be varied upwardly or downwardly by actuation of the screwdown mechanism 22. In most rolling mills, the screwdown mechanism 22 is utilized to vary the roll gap spacing between the

work rolls

12 and 14; however in the mill of the present invention, it is ordinarily utilized only to establish a nominal or preset roll gap spacing which is then varied by hydraulic means, hereinafter described, to compensate for variations in gauge of the strip material passing through the mill.

The ends of the lower backup roll 18 are carried in vertically movable chocks 24, only one of which is shown in FIG. 1. Each chock 24 rests, at its lower end, on a cantilever beam 26 which, in turn, engages a vertically reciprocable piston 28 disposed within a cylinder 30. Between the ends of the cantilever beam 26 and a shoulder at the underside of the housing 10 are load cells or

strain gauges

32 and 34 which will produce electrical signals proportional to the force between the ends of the cantilever beam 26 and the housing 10. These forces, in turn, are proportional to the displacement of the piston 28 within the cylinder 30. When the piston 28 moves up, for example, the ends of the cantilever beam 26, which acts as a spring, are compressed against the

load cells

32 and 34. If the cantilever beam 26 is carefully manufactured to present a linear relationship between the force applied and the resulting compression then the following equation applies:

F=k,'d

where:

F force applied to the springs,

d distance moved by the springs, and

k, the sping constant of the springs.

This means that there will be a proportionality between the cylinder position d and the output of the load cell. Hence, the load cell outputs, which are summed, represent cylinder position and can be used as a feedback signal for the cylinder position regulator, hereinafter described.

As shown in FIG. 2, there are two cylinders 30A and 308 on each side of the mill housing, as well as two pistons 28A and 288 within the respective cylinders. The pistons 28A and 288, in turn, are connected through chocks 24 (FIG. 1) to the opposite ends of the lower backup roll 18. Assuming that the positions of the ends of the upper backup roll 16 are maintained constant by the screwdown mechanism 22, variation in the horizontal positions of the pistons 28A and 2813 will vary the rolling forces applied at the roll gap as well as the opening of the roll gap which is that gap defined between the working rolls l2 and 14 and through which metal strip material, identified by the reference numeral 36 in FIG. 1, passes. As will be seen, it is necessary that the forces exerted by the two pistons 28A and 28B'be equal at all times. Consequently, the pressure of the hydraulic fluid introduced into the cylinders 30A and 303 must likewise be equal.

The rolls in each of the stands 81-55 are driven by drive motors DI-DS coupled to generators Gl-GS. The generators and motors, in turn, are regulated by speed regulator circuits 38-1, 33-2, 38-5, etc. These circuits are controlled by a speed reference signal on lead 40 which establishes the speeds at each of the stands. As will be understood, the speed of each succeeding stand must be greater than the speed of the preceding stand since the gauge of material in each stand is less than that at the preceding stand.

In accordance with the present invention, all of the stands except the last stand are driven at constant, fixed speeds. The speed of the last stand is controlled in a manner hereinafter described in order to compensate for gauge variations at the output of the mill.

The tension between each of the stands in the mill must be maintained constant. At the same time, it is axiomatic that the volume of material entering one side of the roll bite of any stand during a time interval At must be equal to the volume of the material leaving the roll bite during the same time interval. This can be expressed as:

where:

G, and G are the entrance and exit gauges, respectively, and

V, and V are the speeds of the strip at the entrance and exit sides of the mill, respectively. Assuming that the roll gap spacing, which determines G is fixed, an increase in gauge G, at the entrance side of the mill will result in a decrease in the entrance speed V,, since the speed V, at the exit side of the mill is fixed by the fixed speed drive for the mill rolls. As the speed V, at the entrance to stand S2 decreases, for example, the tension in the strip 36 between stands S1 and S2 will increase. This increase in tension, however, can be compensated for by increasing the roll gap spacing (i.e., G in Equation 2 given above). Similarly, if the input gauge G, should decrease, the tension will decrease and the quantity V will increase. This can be compensated for by decreasing the roll gap spacing (i.e., quantity G in Equation 1). All of this can be summarized by stating that when the gauge at the input to a stand increases, the roll gap spacing must be increased to maintain constant tension between it and the preceding stand; whereas when the gauge at the input decreases, then the roll gap spacing must likewise be decreased.

In accordance with the present invention, interstand tension between the respective stands is measured by tensiometers T2, T3, T5, etc. The signal from tensiometer T2 on lead 40 is compared with tension reference signal on lead 42 by a tension regulator 44. If the two are not the same, an error signal is generated; and if this error signal exceeds a maximum amplitude of i 3 percent, the tension regulator 44 actuates a hydraulic control circuit 46 to vary the pressure beneath the piston 28 for that stand and, hence, move the piston upwardly or downwardly to vary the roll gap spacing, depending upon the polarity of the error signal. The roll gap spacing, however, is varied in this manner only on stands S2-S5. The first stand S1 does not incorporate a tension regulating feature. Rather, the hydraulic control system 48 for the first stand is controlled by means of an entry automatic gauge control system 50 connected 1 to an X-ray thickness gauge 52 at the output of the first stand S1 as well as to strain

gauges

32 and 34. Additionally, the entry automatic gauge control system 50 is connected to a strain gauge 54 between the screwdown mechanism 22 and the chock 20. Strain gauge 54 produces a signal proportional to the total roll force.

While various types of automatic gauge control systems for the first stand can be used in accordance with the invention, it is preferred to use an automatic gauge control system based upon the equation:

(A m) Q/ s) where:

P total roll force as measured by load cell 54,

Q the force reading of

load cells

32 and 34,

M the spring constant of the mill, and

M, the spring constant of the cantilever beam 26. The X-ray gauge 52 measures the actual gauge of the strip material leaving the stand S1, and if it is not the same as the desired gauge, then an error signal is generated which changes the roll spacing to the hydraulic control circuit 48 until the error signal is zero and the gauge is constant.

As mentioned above, the speeds of all of the stands except the last stand S5 are maintained constant. At the output of stand S5, the thickness of the issuing strip material is measured by X-ray gauge 56. From gauge 56, the material passes over billy roll 58 and thence to a take-up reel 60. 1f the thickness as measured by the X-ray gauge 56 is not equal to the desired delivery gauge, then a delivery automatic guage control system 62 alters the speed of the motor D5 until the gauge assumes the desired gauge. Remembering, again, that (7 V must equal G V a variation in G, from a desired gauge can be compensated for by a corresponding change in V Of course, at the output ,of stand S5, tension is not a controlling factor.

With reference now to FIG. 3, the details of the electrical circuitry for controlling the hydraulic force applied to the cylinders of a single one of the stands are shown. The tension feedback signal on lead 40 from tensiometer T2, for example, is applied through resistor 64 to a summing point 66. Also applied to the summing point 66 through resistor 68 is the tension reference signal on lead 42. The summing point 66, in turn, is connected to the input of a proportional operational amplifier 70 having a feedback path including a resistor 72. Should the tension feedback signal and the tension reference signal be the same, the difference signal at point 66 will be zero. However, if the tension feedback and the tension reference signals are not the same, then an error signal will appear at the summing point 66 as well as at the output 74 of the operational amplifier 70.

The error signal at point 74 is adapted to be applied through resistor 76 and normally open contacts 78 of relay 80 to the inputs of two operational amplifiers 82A and 823. Operational amplifies 82A, for example, is provided with a feedback path including capacitor 84A and a second feedback path including resistor 86A. Normally, the feedback path which includes resistor 86A is connected to the input of the amplifier 82A through normally closed contacts 88 of relay 80. Similarly, the operational amplifier 82B is provided with a feedback path including capacitor 84B and a second feedback path including resistor 863, this second feedback path normally being connected to the input of the amplifier 823 through closed contacts 90 of relay 80. The outputs of the two

load cells

32A and 34A on one side of the stand are summed at point 92 and applied through resistor 94 and contacts 88 to the input of amplifier 82A. Similarly, the outputs of the two

load cells

32B and 34B. are summed at point 96 and applied through resistor 98 and contacts 90 to the input of amplifier 82B. The output of amplifier 82A is applied through resistor 100 to the input of proportional operational amplifier 102A. Likewise, the summed strain gauge signal at point 92 is applied through resistor 104A to the input of amplifier 102A. These signals are of opposite polarity such that when they are equal, the input to amplifier 102A is zero, as is its output. Amplifier 102A is provided with a feedback path including resistor 106A.

The output of amplifier 82B is connected to a similar operational amplifier 1028 having its input connected through resistors 100B and 1048 to the output of amplifier 82B and point 96, respectively. Amplifier 1023 is provided with a feedback path including resistor 106B.

The output of amplifier 102A is adapted to be applied through normally open contacts 108 of relay 109 and resistor 1 10A to the input of an operational amplifier 112A having a first feedback path including a resistor 114A. The output of operational amplifier ll2A is connected to the coil of a flow servo valve 116A, the other end of the coil 116A being connected to ground through resistor 118A. The other end of coil 116A is also connected through a current feedback path including resistor 120A to the input of amplifier 112A. The flow servo control valve coil 116A, in turn, controls the hydraulic control circuit 46A which controls the position of the piston 28A in cylinder 30A. When piston 28A moves upwardly or downwardly, so also will the signal at point 92 produced by the

load cells

32A and 34A, as will be understood.

flow servo valve coil 1168 with the other end of the coil being connected to ground through ressitor 118B and back to the input of amplifier 1123 to resistor 1208. The coil 1168, in turn, controls the hydraulic control circuit 468 which controls the position of piston 288 in cylinder 388 on the other side of the stand.

Reverting to the operational amplifier 70, its output is also applied to a deadband detector 124 which is essentially a voltage detector. The deadband detector, for example, may incorporate a Zener diode which will break down when the error signal exceeds a certain value. Whenever the deadband detector detects an error signal of i 3 percent, a signal on lead 126 will energize

relays

80 and 109. As the error signal falls, the signal on lead 126 will fall to zero, deenergizing relays 80 and 109 whenever the error falls back to i 1. 5 percent. This isshown, for example, in FIG. 4. When the actual tension error signal exceeds 3 percent of the desired tension signal, the deadband detector 124 will energize relays 80 and l09 .'Then, as the actual tension error signal falls to, 1.5 percent, the

relays

80 and 109 will be deenergized.

If it is assumed, for example, that the error signal at the output of operational amplifier 70 is :3 percent, then relays 80 and 109 are energized: Energization of relay 80 closes contacts 78 and opens

contacts

88 and 90. During this time,

andsince contacts

88 and 90 are open, the

operational amplifiers

82A and 82B become integrators by virtue of the feedback path through

capacitors

84A and 84B. The error signal from amplifier 70, in effect, changes the value of the signal stored at the output of the operational amplifiers 82A and 828. However, as soon as the error drops below i 1.5 percent and relay 80 becomes'deenergized, the tension error signal is removed from the inputs of amplifiers 82A and 828. At the same time, closing of

contacts

88 and 90 transforms amplifiers 82A and 823 into proportional amplifiers. The output of amplifiers 82A and 828 will then remain equal to the value they had just before the cylinders were stopped.

When the outputs of the

operational amplifiers

82A and 82B are changed in this manner, the plus and minus signals from amplifier 82A and summing point 92, for example, will cause a proportional error output from amplifier 102A which is applied through contacts 108, which are now closed, to the input of amplifier 112A. Amplifier 112A will now actuate coil 116A to vary the hydraulic control circuit 46A, causing the cylinder 28 to move upwardly or downwardly. This change in piston position is now sensed by the

load cells

32A and 34A, causing the signal at point 92 to vary until it is equal to that at the output of operational amplifier 82A, whereupon the corrective action ceases. The circuitry for cylinder 30B operates in the same manner. I

Summarizing the operation of the system, the outputs of the operational amplifiers 82A and 828 will remain constant, just so long as the error signal at point 74 does not exceed 3 percent. When it does exceed 2 3 percent, contacts 78 close and

contacts

88 and 90 open causing a correction to be initiated; whereupon the

capacitors

84A and 84B are charged to the correct initial value, and the pistons 28A and 288 will smoothly start moving from their present to the new position as commanded by amplifiers 102A and 1023. There is, of course, a similar system for stands S3, S4 and S5, all of which maintain the interstand tensions for the tandem mill constant.

Although the invention has been shown in connection with a certain specific embodiment, it will be readily apparent to those skilled in the art that various changes in form and arrangement of parts may be made to suit requirements without departing from the spirit and scope of the invention. A

We claim as our invention:

1. in a rolling mill stand of the type wherein a pair of hydraulic cylinders having pistons therein operatively connected to roll chocks are used to exert pressure on the opposite ends of a roll to vary the pressure exerted by the roll and the roll gap spacing of the stand, the

combination of means for controlling the tension of strip material passing into the roll gap of the mill stand comprising:

means for measuring the tension of strip material entering said rolling mill stand and for producing a first electrical signal proportional thereto, means for producing a second electrical signal proportional to the desired tension of strip material entering said mill stand, means for comparing said first and second electrical signals to produce an error signal,

hydraulic control means for said hydraulic cylinders,

means responsive to said error signal for actuating said hydraulic control means to vary the pressure exerted by said hydraulic cylinders until said error signal is at least partially reduced, I

switch means for applying said error signal to said means responsive to the error signal, said switch means being normally open, and

means for closing said normally open switch means to apply said error signal to the means responsive thereto only when the error signal exceeds a predetermined magnitude.

2. The combination of claim 1 including means for again opening said switch means when said error signal falls below a predetermined magnitude.

' 3. The combination of claim 2 wherein said switch means is closed when the error signal is equal to about i 3 percent of said first signal and said switch device is again opened when said error signal is less that about i 1.5percent of said first signal.

4. Thecombination of claim 1 wherein said means responsive to said error signal includes an integrating operational amplifier responsive to both said error signal and a third signal porportional to the positions of said pistons within the hydraulic cylinders, and proportional operational amplifier means connected to the output of said integrating amplifier means and connecting said integrating amplifier means to said hydraulic control means.

5. The combination of claim 4 including spring means connected to said pistons within the hydraulic cylinders, and load cell means interposed between said spring means and a stationary point, said load cell means producing said third signal proportional to the horizontal position of the pistons within said cylinders.

6. The combination of claim wherein there are load cell means for both hydraulic cylinders on opposite sides of the mill, and including separate operational amplifier means and hydraulic control means for opposite sides of the mill, said error signal being simultaneously applied to both of said operational amplifier means.

7. In a gauge control system for a tandem rolling mill of the type wherein a pair of hydraulic cylinders having pistons therein are used to exert pressure on the opposite ends of a roll in each stand of the mill to vary the pressure exerted by the roll and the roll gap spacing of the stand, the combination of means for controlling the interstand tension of strip material passing between at least two stands of the mill comprising:

means for measuring the tension between said two stands of the mill and for producing a first electrical signal proportional thereto,

means for producing a second electrical signal proportional to desired tension between said two stands,

means for comparing said first and second electrical signals to produce an error signal,

means for producing a third electrical signal proportional to the position of the piston in one of said cylinders,

means for producing a fourth electrical signal porportional to the position of the piston in the other of said cylinders,

means for storing said third and fourth electrical signals,

servo means for controlling the position of said pistons as a function of said third and fourth signals respectively, and

means operable when said error signal rises above a predetermined magnitude for simultaneously varying the magnitudes of said third and fourth signals to thereby vary the positions of said pistons through said servo means until said error signal is at least partially reduced in magnitude.

8. The combination of claim 7 wherein said' means operable when said error signal rises above a predetermined magnitude comprises a deadband detector, and means operatively connected to said deadbeand detector for applying said error signal to said servo means.

9. The combination of claim 7 including means for measuring the gauge of strip material at the output of the first stand in said tandemgmill and for actuating the hydraulic cylinders of said firststand to change its roll gap spacing when the measured gauge departs from a desired value.

10. The combination of claim 9 including means for measuring the gauge of strip material issuing from the last stand of said tandem mill, and means coupled to said last-mentioned measuring means for varying the speed of said last stand when the measured gauge of strip material issuing from the last stand departs from a desired value. I

11. The combination of claim 10 including means for maintaining the speed at all stands in the mill constant with the exception of said last stand.

12. In a tandem rolling mill for strip material of the type wherein gage is controlled by manipulating at least the first or last stand in the mill while tension is maintained essentially constant at the input and output sides of at least one intermediate stand of the mill and wherein a pair of hydraulic cylinders having pistons. therein operatively connected to roll chocks are used to exert pressure on the opposite ends of a roll in said intermedaite stand to thereby vary the pressure exerted by the roll and the roll gap spacing of the stand, the combination of means for controlling the tension of strip material passing into the roll gap of said intermediate stand comprising:

means for measuring the tension of strip material entering said intermediate stand and for producing a first electrical signal proportional thereto,

means for producing a second electrical signal proportional to the desired tension of strip material entering said intermediate stand,

hydraulic control means for said hydraulic cylinders,

and

means responsive to said error signal for actuating said hydraulic control means to vary the pressure exerted by said hydraulic cylinders until said error signal is at least partially reduced.

Claims

1. In a rolling mill stand of the type wherein a pair of hydraulic cylinders having pistons therein operatively connected to roll chocks are used to exert pressure on the opposite ends of a roll to vary the pressure exerted by the roll and the roll gap spacing of the stand, the combination of means for controlling the tension of strip material passing into the roll gap of the mill stand comprising: means for measuring the tension of strip material entering said rolling mill stand and for producing a first electrical signal proportional thereto, means for producing a second electrical signal proportional to the desired tension of strip material entering said mill stand, means for comparing said first and second electrical signals to produce an error signal, hydraulic control means for said hydraulic cylinders, means responsive to said error signal for actuating said hydraulic control means to vary the pressure exerted by said hydraulic cylinders until said error signal is at least partially reduced, switch means for applying said error signal to said means responsive to the error signal, said switch means being normally open, and means for closing said normally open switch means to apply said error signal to the means responsive thereto only when the error signal exceeds a predetermined magnitude.

3. The combination of claim 2 Wherein said switch means is closed when the error signal is equal to about + or - 3 percent of said first signal and said switch device is again opened when said error signal is less that about + or - 1.5 percent of said first signal.

4. The combination of claim 1 wherein said means responsive to said error signal includes an integrating operational amplifier responsive to both said error signal and a third signal proportional to the positions of said pistons within the hydraulic cylinders, and proportional operational amplifier means connected to the output of said integrating amplifier means and connecting said integrating amplifier means to said hydraulic control means.

6. The combination of claim 5 wherein there are load cell means for both hydraulic cylinders on opposite sides of the mill, and including separate operational amplifier means and hydraulic control means for opposite sides of the mill, said error signal being simultaneously applied to both of said operational amplifier means.

7. In a gauge control system for a tandem rolling mill of the type wherein a pair of hydraulic cylinders having pistons therein are used to exert pressure on the opposite ends of a roll in each stand of the mill to vary the pressure exerted by the roll and the roll gap spacing of the stand, the combination of means for controlling the interstand tension of strip material passing between at least two stands of the mill comprising: means for measuring the tension between said two stands of the mill and for producing a first electrical signal proportional thereto, means for producing a second electrical signal proportional to desired tension between said two stands, means for comparing said first and second electrical signals to produce an error signal, means for producing a third electrical signal proportional to the position of the piston in one of said cylinders, means for producing a fourth electrical signal proportional to the position of the piston in the other of said cylinders, means for storing said third and fourth electrical signals, servo means for controlling the position of said pistons as a function of said third and fourth signals respectively, and means operable when said error signal rises above a predetermined magnitude for simultaneously varying the magnitudes of said third and fourth signals to thereby vary the positions of said pistons through said servo means until said error signal is at least partially reduced in magnitude.

8. The combination of claim 7 wherein said means operable when said error signal rises above a predetermined magnitude comprises a deadband detector, and means operatively connected to said deadbeand detector for applying said error signal to said servo means.

9. The combination of claim 7 including means for measuring the gauge of strip material at the output of the first stand in said tandem mill and for actuating the hydraulic cylinders of said first stand to change its roll gap spacing when the measured gauge departs from a desired value.

10. The combination of claim 9 including means for measuring the gauge of strip material issuing from the last stand of said tandem mill, and means coupled to said last-mentioned measuring means for varying the speed of said last stand when the measured gauge of strip material issuing from the last stand departs from a desired value.

12. In a tandem rolling mill for strip material of the type wherein gage is controlled by manipulating at least the first or last stand in the miLl while tension is maintained essentially constant at the input and output sides of at least one intermediate stand of the mill and wherein a pair of hydraulic cylinders having pistons therein operatively connected to roll chocks are used to exert pressure on the opposite ends of a roll in said intermediate stand to thereby vary the pressure exerted by the roll and the roll gap spacing of the stand, the combination of means for controlling the tension of strip material passing into the roll gap of said intermediate stand comprising: means for measuring the tension of strip material entering said intermediate stand and for producing a first electrical signal proportional thereto, means for producing a second electrical signal proportional to the desired tension of strip material entering said intermediate stand, means for comparing said first and second electrical signals to produce an error signal, hydraulic control means for said hydraulic cylinders, and means responsive to said error signal for actuating said hydraulic control means to vary the pressure exerted by said hydraulic cylinders until said error signal is at least partially reduced.