US3803886A

US3803886A - System and method for controlling gauge and crown in a plate rolling mill

Info

Publication number: US3803886A
Application number: US00251963A
Authority: US
Inventors: J Sterrett; A Baeslack
Original assignee: Westinghouse Electric Corp
Current assignee: AEG Westinghouse Industrial Automation Corp
Priority date: 1972-05-10
Filing date: 1972-05-10
Publication date: 1974-04-16
Anticipated expiration: 1991-04-16
Also published as: FR2184002A1; FR2184002B1; ZA732642B; ES414583A1; DE2322315A1; JPS5819364B2; JPS5817684B2; JPS5477264A; JPS4948534A; BE799342A; IT987346B; CA995787A; AT323102B

Abstract

Plate gauge and crown are controlled in a rolling mill where conventional screwdown position is used to establish initial roll gap and the bending force reference used to control crown is employed to correct gauge deviations resulting therefrom. Hydraulic push-up cylinders are employed to maintain a roll gap which is held constant in one mode of operation with changes due to mill stretch and which is controllably varied in a second mode to provide proper output gauge.

Description

United States Patent [191 Sterrett et al.

[451 Apr. 16,1974

SYSTEM AND METHOD FOR [54] 3,531,960 l0/l970 Stone..'. 72/8 CONTROLLING GAUGE AND CROWN IN A Eff'i": 315 e PLATE ROLLING MILL 3,365,920 1/1968 Maekawa et al... 72/10 [75] Inventors: John D. Sterrett, Williamsville; 3,518,858 7/1970 Kamata 72/19 Alfred J. Baeslack, East Aurora, both of N.Y. Primary E xaminerMilton S. Mehr [73] Assignee: Westinghouse Electric Corporation, Attorney Agent or firm-R Brodahl Pittsburgh, Pa. [22] Filed: May 10, 1972 [57] ABSTRACT 11 d n H Plate gauge and crown are contro e in a to ing mi [211 App! 251,963 where conventional screwdown position is used to es- 1 1 tablish initial roll gap and the bending force reference 52 U.S. c1. 72/8, 72/245 used to control crown is p y to Correct gauge 51 lm. c1 B2lb 37/00 deviations resulting therefrom Hydraulic P p y 58 1V Field of Search 72/8, 19, 21, 11 inders are employed to maintain a roll p which is held constant in one mode of operation with changes 5 References C d due to mill stretch and which is controllably varied in UNITED STATES PATENTS a second mode to provide proper output gauge.

3,714,805 2/1973 Stone 72/8 12 Claims, 6 Drawing Figures SCREWDOWN A00 CONTROL SYSTEM 5-01 s-op TOP BACK- UP ROLL Hunt 1 ,110-011 TOP WORK ROLL =21 1 1 SERVO VALVE I 3 61 VALVE SPOOL BOTTOM WORK ROLL EAB Ui Q B 7-0 eorrom BACK-UP ROLL Bop B-Dr B-Op ,120-01 120-0 VE SIDE OPERATORSIDE HYDRAULIC SERVO HYDRALIC SERVO VALVE avALvE SPOOL VALVE 81 VALVE SPOOL POSITION REG. FOR POSITION REG, FOR PUSH- UP CYL. PUSH-UP CYL.

GEdr GEop 30o Qdr Qop GAUGE CORRECTION Pop Pdr CONTROL w LEvEL- SYSTEM Dbu I \T/ NCyl BEdr MGb Pi Bref B p 200 am BACK-UP ROLL Bopb BENDING FORCE Pdr CONTROL SYSTEM Pop ssrmarzo ig fg 1 ROLL DlAMETERtDbu) DESIRED ROLL PLATE CROWN CROWN (C) (Cr) WIDTH SCREWDOWN H00 CONTROL SYSTEM TOP BACK- UP RoLL DRIVE SIDE OPERATORSIDE HYDRAuLIc TOP WORK ROLL HYDRAULIC SERVO VALVE I SERVO VALVE gIVALVE SPOOL avALvEsPooL Q 'E' 'L BOTTOMWORK RoLL fi w Bdrb BOTTOMBACK-UPROLL B D B-Dr a-op I2 o-Dr I |20-Op DRIvE sIDE DPERATD'R SIDE HYDRAULIC SERVO HYDRALIC SERVO VALVE BIVALVESPOOL VALVEBI VALVESPOOL POSITION REG. FOR POSITION REG. FOR PUSHwUP CYL. PUSH-UP CYL.

GEdr GEop I 300 :Qdr Qop GAUGE I CORRECTION Pop Pdr. CONTROL w LEVEL SYSTEM -4---Dbu v i L m. b I f BEdr MG P Bre p 20o Bdrb BACK UP RoLL L Bopb BENDING FORCE Pdr CONTROL SYSTEM Pop ESTIMATED INITIAL RoLL. J L

FORCE) RoLL DlAMETER(Dbu) FIG. I.

SYSTEM AND METHOD FOR CONTROLLING GAUGE AND CROWN IN A PLATE ROLLING MILL CROSS-REFERENCES TO RELATED APPLICATIONS 1. Ser. No. 251,951, filed May 10, 1972 entitled Method and Apparatus for Controlling Crown in a Plate Rolling Mill by J. D. Sterrett and A. J. Baeslack and r 2. Ser. No. 273,896, filed July 21, 1972 entitled Method and Apparatus for Cold Rolling Mill Gauge Deviation Correction by B. N. Kitchell et al.

BACKGROUND OF THE INVENTION Prior art systems have been provided for both gauge and crown control with improvements in such systems being disclosed in copending application references (1 and (2) above. Heretofore, however, such controls have operated independently with the result that gauge changes due to crown control bending forces have not been directly compensated for in the gauge control system. Consequently, undesirable interactions between the roll bending and gauge control systems occur.

In general, the known gauge control systems use screwdown or wedge controls which operate upon signals representing gauge deviation, typically produced by X-ray apparatus or change IH'I'Oll force. Various methods of control are used to translate the gauge deviation signals into appropriate variations in the screwdown or wedge control in order to serve or regulate the roll gap to obtain the desired gauge. In copending application reference (2), provision is made to update the so-calledmill spring constant for improved screwdown regulation.

It has been found that, while the existing gauge control systems are satisfactory for establishing the desired- SUMMARY oF THE INVENTlON The precision and speed of gauge correction due to roll bending forces (crown control) and/or other factorssuch as mill spring constant changes or gap variations due to mill speed or temperature changes is improved in a system. where hydraulic push-up cylinders are used tocorrect for roll gap changes during rolling. The basiccontrol concept of the invention may be considered to be the maintaining of a constant roll gap for a constant desired gauge with automatic compensation for anticipated roll bending forces, mill spring changes, and other factors which affect the roll gap.

In order to anticipate gap changes due to roll bending forces, the bending force reference signal produced by the crown control system of copending application reference (1) is used, rather than a measure of the actual bending force developed through relatively slow acting hydraulic servo controls. Thus the roll bending force reference signal efiectively provides an anticipation of the actual bending forcewhich is later developed through the action-of the hydraulic servo system.

A spring constant signal relating the variation in roll gap to the anticipated roll bending force is generated or computed as a function of roll diameter and is then used with the roll bending force signal to develop a gauge change due to roll bending signal and provision is also made to provide compensation for gap changes due to bearing oil film thickness changes as a function of mill speed divided by rolling force.

The actual position of the push-up cylinders (for both the operator, and drive sides of the mill) is measured and compared (or combined through subtraction) with the gauge change due to roll bending signal and a first difference signal for gauge control is generated or computed. Gap changes, due to mill stretch changes are represented by a second difference signal which is generated or computed as a function of the change in gauge or gap which occurs after an initial or lock-on position has been set during the rolling of the head-end of a bar or plate. The second difference signal thus provides a measure of the gap change due to mill stretch. The gap changes are computed as a function of the product of measured rolling force or pressure times a roll pressure spring constant which itself is computed as a function of roll diameter and strip or plate width. The first and second difference signals corresponding to push-up cylinder position changes and mill stretch changes are combined to produce gauge error compensating drive signals for both the operator and drive sides of the mill. The drive signals may be considered to function as a vernier control for maintaining the roll gap constant, or may be referenced to a computed gap change signal to obtain a desired gauge.

The preferred embodiment herein is disclosed as an analog system with a combination of circuits, generators, integrators and the like performing various functions used according to the concept of the invention. Since the method of the invention may be practiced with either digital or analog hardware and since signal generators and computing circuits provide equivalent function, the terms generator or processor or computer are used throughout the specification as equivalents. Furthermore, all of the means shown, whether they are illustrated in an analog or digital form, or represented by equations, may be carried out by various types of means either analog or digital in form. Thus, the term signal is used herein to connote either an analog ordigital representation of an input, generated or computed internal function, oran output quantity and the term generator" is used to represent any means, whether analog or digital, for producing the desired representation. It should also be understood that special purpose analog devices such as limiters, integrators, dead-band circuits and function generators may all be replaced with equivalent digital devices which themselves may be developed as special-purpose wired computers or may be obtained through the use of a programmed digital computer.

The above andother 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 block diagram of a system incorporating the invention;

FIG. 2 is a schematic diagram showing suitable forms for bending force control system 200 and gauge correction control system 300 of FIG. 1;

FIG. 3 shows a specific arrangement for means 340 of FIG. 2 to produce drive and operator side mill stretch change signals DPdr and DPop;

FIG. 3A provides a summary of the basic control equations which are satisfied by the function of means 300 of FIG. 1;

FIG. 4 shows the relationship between mill deflection and rolling load which must be satisfied by the combination of 360 the roll force spring constant generator and the function generators 342 of FIG. 3; and

FIG. 5 is a schematic representation of the functions of generator 300 for producing the cylinder position change signals DQdr and DQop.

Reference is now made to FIG. 1 wherein a system employing the present invention is shown in block diagram form. The system includes a screwdown control 100 providing a means of positioning drive side and operator side bearings for the top back-up roll 1. The metal to be rolled is passed between a top work roll 2 and a bottom work roll 3, the position of which is controlled through a bottom back-up roll 4. Rolling pressures which are caused by working the metal are measured by conventional means such as load cells referenced as 5-Dr for the drive side and S-Op for the operators side producing signals Pdr and Pop, respectively. Roll bending forces for both top roll 1 and bottom roll 4 are developed through drive and operator side hydraulic servo valve and valve spool position regulators 110 which operate in a conventional manner to develop bending forces which are measured by top and

bottom load cells

6 and 7. The relationship between the load cells and bending forces measured is set forth in the following chart:

Force The height of bottom back-up roll 4 is controlled through conventional servo-valve and valve spool position regulators 120 which receive gauge error reference signals GEdr and GEop with the position of roll 4 on the drive and operator sides being represented by load cells 8-Dr and 8-Op, respectively. The drive side and operator side position signals are references as Qdr and Qop, respectively. It will be understood that while the actual signal produced by load cells 8 may be representative of force, such signals are readily translated into position representations as are employed herein. Controllers 1 l0-Dr and ll0-Op receive drive and operator side roll bending force error signals BEdr and BEop, respectively, which are produced by back-up roll bending force control system 200. l l0-Dr and l 10- Op respond to BEdr and BEop by allowing oil flow into or out of the bending cylinders until BEdr and BEop 0. System 200 receives the measured roll and bending force signals previously mentioned as well as representations of the following: desired crown (C); roll crown (Cr); plate width (Wp); roll diameter (Dbu); and estimated initial roll force (Pe). In addition to providing the drive and operator side oil flow reference signals for controllers 110, system 200 also provides certain signals utilized in gauge correction control system 300. In particular, a signal Bref (the required roll bending force) is produced which forms the basis for developing signals BEdr and BEop previously mentioned and signal MGb represents a factor which, when multiplied by Bref, enables system 300 to compensate for gauge changes caused by anticipated bending force. System 300 additionally receives a total bending force signal Pt corresponding to the summation of signals Pdr and Pop previously mentioned and signals V and NCyl defined below which are used in the gauge correction control. System 300 also receives signals Pdr and Pop directly as well as representations of plate width (WP) and roll diameter (Dbu). A signal represented as LEVEL is utilized to permit adjustment of roll 4 to a horizontal position. Gauge correction signals GEdr and GEop are applied to controllers I-Dr and l20-Op, respectively,

to cause positioning of roll 4 through suitable push-up cylinders.

Reference is now made to FIG. 2 for a more specific description of

control systems

200 and 300. Bending force control system 200 includes means 210 for generating a roll diameter adjustment factor MGb as a function of an input representation of roll diameter (Dbu). Signal MGb is applied to spring

constant generators

220 and 230 producing signals Mcb and Mcp as a function of signal MGb and a representation of plate width (Wp). Total rolling and bending signals Pt and Bt produced through summing

circuits

240P and 240B, respectively, are used in a crown error generator 250 to produce a crown error signal Ce. Generator 250 receives an initial estimated rolling force signal Pe through a switch SIS to simulate the presence of bending due to rolling load before metal enters the mill so as to permit establishment of initial bending forces before the actual rolling begins. Switch SIS then represents the fact that the metal is in the mill and so, when closed, presents signal Pt to generator 250 in place of the initial estimate Fe. The crown error signal Ce, generated in a manner more specifically described below, is applied to a deadband circuit 260 which drives a proportional integrator 270 providing output signal Bref. The dead band may be omitted in some cases depending on the mill characteristics. Signal Bref is limited by a bending force limiter 280 which receives a representation of maximum force and signal Pt. The components thus far described are those included in system 200. It will be understood that while terms generally considered to be analog have been used, the various functions of the components just described may be performed as well with a digital computer with wired logic or with a programmed computer.

Control system 200 also includes 290 the B- force control 290 (see FIG. 2) for the drive and operator sides, and-which has individual B- force controllers for the drive side and for the operator side. The drive side controller matches the average of the two roll bending force signals Bdrb and Bdrt to the roll bending force reference Bref. The difference is the bending force error BEdr for the drive side. BEdr is the oil flow or spool position reference for the drive side hydraulic servo valve spool position regulator, which is positioned proportional to BEdr to control oil flow into or out of the roll bending cylinder as determined by the polarity of BEdr. The resulting oil flow changes Bdrb and Bdrt until the average force equals Bref, and BEdr 0. The operation of the operating side is the same.

Rheostats permit trimming of Bref to shift the center of the roll crown as required to balance the mill.

Signal Bref is utilized in both reference generator 290 and in gauge correction for bending force generator 310 which forms part of system 300. Signal Gcb produced by generator 310 is combined with signals V and NCyl in a summing circuit 320 producing a signal referenced as Qo*Ms. Qo*Ms is the basic position reference for the bottom roll cylinders for an empty mill. The term Ms is a factor which is used to multiply a force representation to translate it into position units. Thus signals Qdr and Qop are also multiplied by the factor Ms to translate the force measurement into a position signal. It will be understood that if transducers are utilized for the function of 8-Dr and 8-Op of FIG. 1 where a direct representation of position is provided, the multiplication by factor Ms-is no longer required.

Signal NCyl represents nominal cylinder position at calibration and may be considered to be an initial reference position whereas signal V represents roll gap variation due to bearing oil film thickness changes caused by mill speed and rolling force. The gap variation occurs primarily because the bearing oil thickness increases as a function of speed increase and decreases as rolling force increases. Signals LEVEL AND Qo*Ms are utilized along with signals Qdr and Qop in genera tor 330 tov produce drive side and operator side difference signals DQdr and DQop. These difference signals represent the position change from the actual measured cylinder positions and the position to correct for the factors introduced into summing circuit 320. Gauge correction must also be made for mill stretch changes on both the drive and operator sides. Thus, generators 340dr and 3400p are provided both of which receive a signal MGp representing a roll force spring constant as produced by generator 360. The spring constant MGp is produced as a function of both strip width (Wp) and roll diameter (Dbu) and is used to permit translation of actual rolling force measured signals into gap changes. A change in mill stretch during rolling is represented by a difference signal (DPdr for the drive side and DPop for the operator side) which is combined with the corresponding position change signal produced by generator 330 in a suitable summing circuit 350. Thus, circuits 350dr and 3500p are the gauge error controllers and produce signals GEdr and GEop,

respectively, as will be noted also in FIG. 1.

Reference is now made to FIG. 3 wherein an analog representation of the mill stretch change function is set forth and to FIG. 3A where various equations are presented summarizing the function of the arrangement of FIG. 3. Considering first FIG. 3A, it will be noted that two modes of difference signal generating are provided, considered to be modes I and II. Referring again to FIG. 3, it will be noted that drive and operator side switches345 and 346 provide the inputs for summing amplifiers 347. 345 has switch positions corresponding to modes I and II. Switch 346 permits the choice of individual mill stretch signals (position NA), or an average signal in position A. The operation of means 340, which includes all of the elements shown in FIG. 3 except the MGp spring constant generator 360, will be considered first in terms of the mode I operation.

The representations of drive and operator side rolling forces (Pdr and Pop) are applied to respective scaling amplifiers 341 producing representations corresponding thereto which are then utilized in the operation of function generator 342 to produce function output signals F(Pdr) and -F(Pop) which will now be considered in terms of the chart of FIG. 4. Referring to FIG. 4, it will be noted that, for various widths of plate and diameters of rolls, a relationship may be established between mill deflection in inches and the rolling load. Thus, the function of generator 342 is to translate the rolling load representation which is applied to the generator into an output deflection signal corresponding thereto. However, since the function is a complex relationship involving not only the rolling load but the plate width and roll diameter, the translation is performed in two steps. Firstly, the function generator 342 produces a representation of the relationship between mill deflection and rolling load for a 90-inch wide plate and an -inch diameter roll and then this relationship is multiplied in multipliers 343 by function MGp to provide an output representation of the mill stretch change which occurs for the particular rolling force and plate width and roll diameter function. The proper relationship for generating signal MGp has been found through empirical analysis to provide the desired relationship as set forth in generator 360 of FIG. 3 as well as in the relationships shown in FIG. 4. Since the particular relationship may be varied for different applications, the important thing to note for the purpose of the present invention is that suitable compensation for variations in strip width and roll diameter must be provided in the general manner of the function of generator 360. Other variations for different mills and applications will be apparent to those skilled in the art. The particular form of means 360 is not shown since it will be apparent to those skilled in the art how either analog or digital computing means may be used to develop the desired signal MGp.

The output multipliers 343 may be considered to represent the function P*MGp where the drive side function is Pdr*MGp and the operator side is Pop MGp. When the head end of a strip to be rolled is first entered into the mill, switches AGCl and AGC2 coupled to the output of multipliers 343 are closed in order to provide input signals for drive and operator side mill stretch memories 344. This provides initial mill stretch representations where, on the drive side, the representation is PDo*MGp and on the operator side is POo*MGp. The basic mode I equations are:

DPopI Pop*MGp POo*MGp. These equations are obtained through summing amplifiers 347-DR and 347-0? while

switches

345 and 346 are in the mode I position. At this time, the memory initial output state of memories 344 are applied to switches 345-DR and 345-OP and then these initial mill stretch representations are subtracted from the current computation of mill stretch produced by multipliers 343 after switches AGCll and AGC2 have been opened. The multiplier outputs are applied through switches 346-DR and 346-0P to summing amplifiers 347-DR and 347-OP. The sign of the signals produced by memory 343 is opposite to that of multipliers 343 to provide the proper difference operation. The output of amplifiers, or summing devices 347, is suitably scaled by means of potentiometers 348 to provide the mill stretch difference signals DPdr and DPop. The potentiometer settings determine the percentage change in mill stretch to be compensated by movement of the bottom roll.

During mode II, all of the switches are moved to the II position and then the mill stretch memory signal is replaced by a signal represented as Pe*MGp corresponding to estimated mill stretch which may be provided through a computer, not shown. The mode II equations are:

DPdrII Pdr*Mgp Pe*MGp DPoplI Pop*Mgp Pe*MGp The bottom roll moves to roll the gauge for which Pe was calculated. Changing switches 346-dr and 346-op from position NA to A causes the drive and operator side mill stretch changes during rolling to be replaced with an averaged mill stretch change representation Pavg*MGp to provide a different mode II equation as follows:

- PDdrA DPopA Pavg*MGp Pe*MGp.

In FIG. 5, a combined analog schematic and computer equation representation of the various functions required for producing the position difference signal is presented. Force signals Qdr and Qop are applied to respective scaling amplifiers 33l-DR and 331-? where the multiplying factor Ms is introduced to translate these signals into corresponding position signals. These signals are combined with the position correction representation Qo*Ms generated by

means

310 and 320 of FIG. 2 to represent position changes in the bottom roll which are necessary to compensate for anticipated gap changes due to roll bending force, mill speed changes, and changes in the nominal cylinder position. Position signals Qo*Ms is defined as follows:

The representation of MGb is provided by means 210 producing the signal according to the equation:

The manner in which this bending spring constant is produced is more fully explained in copending application constituting reference (1) above. Basically, it is a function of the empirical relationship which relates the bending force reference (Bref) to the change in gap which occurs in response thereto. Thus, the product Bref*MGb in the equation for Qo*Ms provides a correction factor for the gap deviation due to the anticipated roll bending force. The factor MGb as developed by means 210 need not be referenced to the bending force, as is more fully explained in copending application constituting reference (1) above. Development of the MGb factor in this manner makes it possible to use it as an adjustment factor in the equations for developing spring constant signals MCp and MCb produced by

generators

220 and 230.

In FIG. 5, means 310 and 320 of FIG. 2 are shown as computing functions which may be developed with either an analog or digital computer to develop the representation of Qo*Ms. In FIG. 2, the product Bref*MGb is referenced as signal Gcb, produced by generator 310, which is then combined with the representations of nominal cylinder position (Ncyl) and the gap variation due to mill speed representation (V).

Signal Qo*Ms is then utilized in summing amplifiers 332-DR and 332-OP to produce difference signals DQdr and DQop defined as follows:

Representations of the drive side and operator side cylinder positions (Qdr and Qop) are applied to scaling amplifiers 331 which provide corresponding representations of Qdr*Ms and Qop*Ms. Signals L and L are obtained through a LEVEL input reference from potentiometer 333 and the inversion of this reference obtained through an amplifier 334.

Referring again to FIG. 2, it will be noted that the signals applied to hydraulic servo-valve and valve spool position regulators 120, referenced as GEdr and GEop, are obtained through summing amplifiers 3S0dr and 3500p, respectively. These signals may be defined as follows:

GEdr DPdr DQdr GEop DPop DQop.

GEdr and GEop are the oil flow or spool position references for Dr and 120-Op respectively. The servo-valve spools are positioned proportional to GE to control oil flow into or out of the bottom back up roll push-up cylinders as determined by the polarity. The resulting cylinder moves the bottom roll to change gauge until GE becomes zero.

From the foregoing description it should now be apparent that the invention provides a method and apparatus for controlling roll gap in a system where a constant gap may be maintained for variations in roll bending force required to obtain a desired crown as well as variations in screwdown forces which may establish an initial roll gap to be maintained.

We claim:

1. In apparatus for controlling the gauge and crown of a metal workpiece leaving a rolling mill, the combination of first means for controlling the setting of the roll opening in said rolling mill and for measuring the rolling forces resulting from the setting of the initial opening to produce rolling pressure signals; second means responsive to said rolling pressure signals and to representations of desired roll crown for controlling the roll bending forces in said mill by producing a bending force reference signal; and third means responsive to said bending force reference signal and to said rolling pressure signals for controlling the gauge of said metal workpiece rolled in said mill.

2. The combination of claim 1 wherein said third means includes means responsive to a representation of roll diameter for generating a bending force spring constant signal and means responsive to said spring constant signal and to said bending force reference signal for producing a gauge correction signal.

3. The combination of claim 1 wherein said third means produces a gauge correction signal used in the control of said gauge as a function of the product of said bending force reference signal and a roll diameter adjustment factor.

4. The combination of claim 3 wherein said third means further includes means responsive to a representation of roll position for producing a representation of roll gap variation due to changes in roll bending forces.

5. The combination of claim 4 wherein said third means is used to control the position of mill bottom back-up roll bearing supports to maintain constant roll gap.

6. The combination of claim 4 wherein said third means is used to control the position of mill bottom back-up roll bearing supports to control the gauge produced by the mill.

7. A method for operating a rolling mill system having gauge and crown controls, said method comprising: generating a bending force reference signal as a function of desired crown and roll crown and measured roll force and bending force; translating the bending force reference signal into corresponding bending forces to obtain the desired crown; and utilizing the bending force reference signal in the gauge control to correct for gauge deviation caused by said bending forces.

8. The method of claim 7 wherein said bending force reference signal is produced as a function of roll diameter and plate width as well as the desired and roll crown representations and further as a function of measured roll and bending force signals, and gauge deviation is corrected as a function of said bending force reference signal and a roll diameter adjustment factor.

9. The method of claim 8 wherein the gauge deviation correction for bending force is generated as a function of the product of said bending force reference signal and said roll diameter adjustment factor.

10. In a rolling mill system wherein roll gap is initially set by means of a roll gap position control and hydraulic push-up cylinders are employed to control roll gap during rolling, the combination comprising: first means responsive to signals representing the position of said push-up cylinders and to roll gap variation input signals for producing a position difference signal; second means responsive to signals representing rolling pressures and spring constants for gap variations due to rolling pressures for producing a mill stretch change signal; and third means responsive to said position difference signal and said mill stretch change signal for producing a gauge correction control signal for said push-up cylinders.

11. The combination of claim 10 wherein said first means receives a roll bending reference signal as one of said gap variation input signals and a representation of roll gap change due to bending force.

12. The combination of claim 11 wherein said position difference signal is produced as a function including the product of said roll bending reference signal and said representation of roll gap change due to roll bending force.