CA1046610A - Automatic gauge control method - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

The present invention provides a new and improved method of automatically controlling gauge adapted to eliminate the formation of off-gauge portions in the rolled material during accelerating or decelerating conditions in the rolling speeds.
According to the invention, the thickness of a rolled strip, sheet and foil is detected by a thickness gauge provided at the exit of the rolling mill. The detected result is converted into control functions in dependence on an independent function of deviation value in thickness and the rate of thickness variation. These control functions are multiplied by one another thereby producing a first compensating control input.
In addition, the rolling speed of the mill is detected to obtain an absolute value of the rate of changes in the rolling speed, which is multiplied by the control function in dependence on an independent function of deviation value in thickness so that a second compensating control input is obtained. The first and second compensating control inputs are added to an input indica-tive of the thickness deviation value to produce a control input by which the thickness of the strip, sheet and foil is accurately controlled.

Description

10466~0 In recent rolling mills, there ha~ been a continually increasing demand for metal strip, sheet and foil produced to close tolerances in thickness, and it has been a common practice to have modern rolling mills equipped with automatic gauge control systems. At present, the usual method of controlling gauge is to measure the thickness of the strip as it leaves the mill by means of a suitable strip thickness gauge such as an X-ray thick-ness gauge the output of which, after suitable modification, 10 continuously adjust the position of the rolls or the tension applied to the strip, so that a substantially constant thickness is maintained in the rolled material. In another method of controlling gauge, an eIectric compensating circuit is proposed which positively compensates the causes of thickness variations of the rolled material. With these prior rolling expedients, the performance efficiencies of the rolling mills have been increased with a result that the rolling speeds of the mills are con- -siderably increased. Various methods of controlling gauge pro-posed in the prior art are usually dependent on a control input 20 based on only the thickness variations by which a substantially constant thickness is maintained in the rolled material provided that the rolling speeds of the mills are maintained at a constant value. These expedients, however, suffer from the drawbacks in that the control input merely based on the thickness variations is not suited for controlling gauge especially in the so-called transition periods such as accelerating or decelerating operations of the mill and, thus, a considerable time is required before the thicknes~ variations are approximately reach d within an allowable range of a predetermined thickness. In this instance, 30 there exists an off-gauge portions on leading and trailing ends of - 1 - ~ ' , . . -- - ,.
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10'~;610 1 the rolled material. These off-gauge portions may be caused of a high production of scrap material and in some cases may stop the plant entirely. It will thus be necessary to eliminate the formation of off-gauge portions in the transition periods of rolling operations with a view to improve the productivity o~
the mill.

SUMMARY OF THE INVENTION
It is, therefore, an lmportant o~ject of the present invention to provide a new and improved method of automatically controlling gauge adapted to eliminate t~e formation of off-gauge portions in the rolled material during accelerating or decelerating conditions in the rolling speeds. To achieve this object, the present invention features to measure the thickness of the strip, sheet and foil by a thickness gauge provided at the exit of the mill. The measured result ls conve~ted into control functions in terms of independent function of deviation value in thickness and the rate of thickness variation, res-pectively. These control functions are multiplied by one another thereby producing a first compensating control input. In addition, the rolling speed of the mill is detected to obtain ` an absolute value of the rate of rolling speed, which is multiplied by the control function as the independent function of the deviation value in thickness so that a second compensating control input is obtained. The first and second compensating ~
control inputs are added to an input representing the thickness ~-variations to produce a control input by which the thickness of the strip, sheet and foil is accurately controlled.
More specifically, a principal concept of the present invention i5 based on the fact that the gauge variations in accelerating and decelerating conditions of the mill are caused ' . ' 104661 o 1 mainly by varying coef~icient of friction ~etween rolls and stock and varying thickness of oil film in the bearing, and that the thickness variations of the strip, sheet and foil is dependent on changes in rolling speeds during acceleration and deceleration due to the varying coefficient of friction between the rolls and stock and closely related to positive or negative quantities of the accelerations.
A detail description will now be made with reference to the acceleration of the mill. If a gauge control system is 10 actuated to correct the thickness of the sheet to a given value in dependence on the thickness deviations measured by a thickness gauge,the gauge control system tends to be responsive to an absolute deviation in thickness at measuring or sampling time of the thickness and try to adjust the rolls so that a predetermined thickness is obtained in the rolled material. Since, however, the rolling speeds continuously vary during acceleration, the gauge control system is adversely affected by the acceleration at the sampling time. Thus, the measured result of the thickness - is insufficient for preventing under corrections, so that a sub-20 stantial length of sheet may have passed through the mill before the correct thickness is restored. In other words, even when the -. .
thickne~s deviations are accurately measured with a view to correcting the absolute thickness deviations at the sampling time, the gauge control system can not be precisely controlled merely by the measured data due to another factor affected by the acceleration. It will thus be seen that it is necessary to take the acceleration into consideration for accurately controlling the gauge control system. Since this acceleration is regarded as a directivity of the thic~ness deviations, the acceleration should be duly considered in controlling gauge~

, , '' ' - .' " ' . ' . ' ~'': '' ' ' ' ''' ' ' 10~;610 1 While the thickness deviations of the stock at exit o~
the mill remain within a range which can be corrected by the automatic gauge control syste~, it should be noted that the thickness deviations are reflected as sudden changes during the accelerating and decelerating conditions. Thus, the rate of variations in thickness at the acceleration or deceleration is quite effective for accurately controlling gauge.
BRIEF DESCRIPTION OF THE DRAWINGS
--Fig. 1 is a schematic diagram illustrating a method ~0 of controlling gauge at acceleration or deceleration in accordance with the present invention;
Fig. 2 is a view illustrating the relationship between the rolling speed and the thickness deviation attained by the method of the present invention;
Fig. 3 is a view illustrating the result of gauge con-trol performed in accordance with a conventional method; and Fig. 4 is a view illustrating the result of gauge i control performed in accordance with the method of the present invention.
; 20 DESCRIPTION OF PREFERRED EMBODIMENTS
A method of the present invention will be described in ~ -detail hereinafter with reference to a preferred embodiment.
Referring now to Fig. 1, there is schematically shown a rolling mill 1 including a pair of mill work rolls la, a pair -of backing rolls lb engaging with the mill work rolls la, respectively, and a roll-adjusting device 2 adapted to adjust the roll gap so that strip, sheet and foil is maintained at a giv~n setting thickness. One of the mill work rolls la is 30 connected to and driven by an electric motor 3, to which a pilot generator 4 serving as a speed sensor to detect the rolling speed ;`

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' ~ ' ~ ' ' ' 10466~.0 1 is also connected. A differentiator 5 is connected to the pilot generator 4 and functions to convert a signal representative of the rolling speed detected by the pilot generator 4 into a signal indicative of acceleration or deceleration. This signal is applied to a convertor 6, by whi¢h the acceleration or deceleration indicating signal is converted into a signal indicative of an absolute value. Designated as 7 is a thickness gauge provided at the exit of the rolling mill 1 and detects the thickness deviation values of the sheet leaving the rolls to produce signals 10 representative thereof. These signals are applied to function generators 8 and 9, which compute control functions in dependence on the thickness deviations. It should be noted in this instance that the control functions are determined by the material of the stock and the rolling conditions, and that the positive or negative qualities of the control functions correspond to the - positive or negative qual;ties of the thickness deviations. The thickness deviation indlcating signal is also applied to a differentiator 10 by which the varying rate of thickness deviations is obtained. Indicated by reference numeral 11 is a multiplier 20 which serves to multiply the control ~unction generated by the function generator 8 and the varying rate of the thickness deviations by one another for thereby producing a ~irst compensa-ting control input. A multiplier 12 is connected to the con-vertor 6 and the function generator 9 and serves to multiply the absolute value of the acceleration or deceleration and the control function by one another for thereby producing a second compensat-; ing control input. The first ~nd second compensating control inputs are applied to an adding device 13, by which the first and second compensating control inputs are added. An automatic 30 gauge control system 14 is connected to the thickness gauge 7and the adding device 13 to receive the input indicative of the .

104~610 1 thickness deviation as well as first and second compensating control inputs for thereby controlling the roll-adjusting device

2 in dependence thereon so that a given thickness is maintained in the rolled material. It is to be understood that the automatic gauge control system may be of any known construction and arrangement and, therefore, a detail description of the same is herein omitted for the sake of simplicity o~ description.
With the rolling mill thus arranged, the stock is passed through the rolling mill 1 and the rolling is initiated.
10 The rolled sheet is then passed through the thickness gauge 7, which detects the thickness deviation ~H relative to a setting - thickness during an arbitrarily determined sampling time period.
Assuming now that the rolling speeds vary from accelerating time to constant speed time and thereafter to decelerating time, and that the thickness deviation aH has a value as shown in Fig. 2. First of all, with regard to the point A, the input signal representative of thickness deviation aH >0 is applied to the function generators 8 and 9, di~ferentiator 10 and automatic gauge control system 14. The thickness deivation ~H applied to 20 the differentiator 10 is defined as the rate of variations indicating the tendency of variations of the thickness deviations ; at sampling ti~e by the minute sampling time dt and the minute thickness deviation daH. It will thus be seen that the rate ~ -of changes daH/dt>0 in thickness deviation at the point A indicates ~;
that the thickness deviation at the point A increases as shown in Fig. 2. If the gauge control is made merely in accordance with the thickness deviation aH at ~he point A, the roll-adjusting device 2 is actuated with a fixed control irrespective of whether the thickness deviation ~H increases or decreases and whether 30 the rate of changes in thickness deviation is constant or varying. ``
Consequent1y, a difficulty is encountered in accurately controlling ` ` 10~610 1 gauge to the setting value with a result that off-gauge portions are produced in a larger amount and,therefore, a desirable end result can not be obtained. In this respect, the rate of thickness deviations should be duly considered. The rate d~H/dt of the thickness deviation ~H is added with a control function ftQH) în the adding device 11, the control function being produced by the function generator 8 in which the function is selected to be a predetermined value in dependence on the material of the stock and the rolling conditions. Thus, the adding device 11 produces a first compensating input f(~H) dQH/dt>O. On the other hand, the pilot generator 4 generates a signal indicative of the rolling speed V, which is applied to and differentiated in the differentiator 5 so that the rate - of changes dV/dt>O in the rolling speed is obtained. This rate of changes in the rolling speed is converted into an absolute value of ¦dV/dt¦>O by the convertor 6. The acceleration indicated by ¦dV/dt¦~O of the rolling speed V is then multiplied in the multiplier 12 by the control function F(aH) produced by the function generator-9 in which the function is selected to be a predetermined value in dependence on the material of the stock and the rolling conditions as in the function generator 8. The multiplier 12 thus produces a second compen-~ sating input indicated by F(~H) ¦dV/dt¦>O. It will thus be ;~ seen that the first compensating input f~H) d~H/dt>O is based .. .
~ on the rate of variations in the thickness deviation ~H and ::
-~ the second compensating input F(~H)¦dV/dt¦>O is based on the acceler~tion of the rolling speed V. The first and second compensating inputs are then added to each other in the addin~
device 13, the product being f(QH)-d~H/dt + F(~H) ¦dV/dt¦~O

which will oe utilized as a compensating control input relative . :, ' ,:' :-.,; '; :~

104~6~0 1 to the thickness deviation at the point A. This control input is applied to the automat;c gauge control system 14, to which the input ~H is also applied from the thickness gauge 7. ~hus, the automatic gauge control system 14 is responsive to the sum of the control input from the adding device 13 and the input from the thickness gauge 7, viz., the sum of ~H + f~H)-daH/dt + F(AH)- t dV/dt¦, and generates an output in dependence thereon.
This output is applied to the roll-adjusting de~ice 2, by which the gap between the rolls la is reduced so that the thickness of the rolled sheet is immediately corrected to the setting value.
Turning now to the point B in Fig. 2, the input in- -dicative of the thickness deviation ~H is applied to the function generators 8 and 9, differentiator 10 and automatic gauge control system 14 in a manner as previously mentioned.
The thickness deviation ~H at the point B is equal to that at the point A. However, the rate of changes is d~H/dt>O as ;
seen in Fig. 2 so that the first compensating input is expressed as f(~H) d~H/dt>O. From this it may be apparent that the quality and the value of the first compensating input for the point B are different from those of the first compensating input for the point A. On the other hand, the rolling speed detected by the pilot generator 4 is at a value different from that at the point A but the varying rate of rolling speed differentiated by the differentiator 5, viz., the acceleration dV/dt>O is - equal to that obtained at the point A so that the second com-pensating input represented by F~H) ¦dV.dt¦>O of the point B is equal to that of the point A. It will thus be noted that the value of inputs applied to the automatic gauge control system 14 at the point B is smaller than that of the inputs applied . ~

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10~ 0 thereto at the point A by an amount equal to 2¦f(AH) daH/dt¦ .
Namely, the thickness deviation ~H has a tendency to increase at the poi~t A and, therefore, the thickness of the sheet exceeds beyond the setting value. For this reason, the automatic gauge control system 14 applied with the inputs ~H + ¦ f (~H) daH/dtl + ¦F (AH) dV/dt¦, the sum of which is larger in value than the thickness deviation ~H so that the thickness deviation is immediately corrected to the setting value. At the point B, however, the thickness deviation ~H has a tendency to decrease and approach the setting value and, accordingly, the automatic gauge control system is applied with the control inputs AH- If (~H) dQH/dtl + ¦F tQH) dV~dt¦ so that the thickness of the sheet is corrected to the setting value in an immediate manner.
The thickness deviation QH and the rolling speed V are computed at the points C, D and E in a manner similar to that as previously mentioned hereinabove. The automatic gauge control system is applied with control inputs -¦AH¦ + ¦f(~H)-dQH/dt¦ -¦F(~H)~dV/dt¦ at the point C, control inputs ~H - ¦f(AH)-d~H/dt¦
+ ¦F(~H)-dV/dt¦ at the point D, and control inputs - ¦ ~H ¦ - : :
20 If (~H~ daH/dt~ H) dV/dt¦ at the point E, respectively, so that the thickness of the sheet is immediately corrected to the setting value.
It should be born in mind that the value of dV/dt is zero at the constant rolling speed and, in this instance, the automatic gauge control system is applied with control inputs f(~H)-dAH/dt.
Fig. 3 shows the result of the gauge control attained in accordance with the prior art method, and Fig. ~ shows the result of the gauge control performed in accordance with the method of the present invention.

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, , 10~661 1 Figs. 3 and 4 illustrate the thickness profiles of the sheet having the thickness of 0,23 mm rolled from the aluminum - strip having the thickness of 0.5 mm by a single-stand rolling mill. In Fig. 3, the thickness deviation ~H, the value of output of the automatic gauge control system and the rolling load (operator sideJ are plotted in terms of the rolling speed varying from Vl = 10 m/min to V2 = 330 m/min. In Fig. 4, the thickness deviation ~H, the value of output of the automatic gauge control system and the rolling load are plotted in terms of ~he rolling speed which is accelerated from Vl = 10 m/min to V2 = 470 m/min. In Figs. 3 and 4, the rolling speeds are accelerated at degrees approximately equal to each other.
However, the level of the constant rolling speed V2 in Fig. 3 is lower than that of Fig. 4. This is due to the fact that since the rolling speed is not considered as a factor for the control input, the thickness of the strip is decreased below the setting thickness as the acceleration increases and, thus, the acceleration time is limited. In order to increase the level of the constant rolling speed V2, it has hexetofore been proposed to accelerate the rolling spe~d in a stepwise manner.
In this prior expedient, the speed of response and the relative stability as well as operativity of the rolling mill are lower than those of the result o~ the gauge control attained by the method of the present invention.
Turning now again to Figs. 3 and 4, the rise time in which the rolling speed is accelerated to a point at which the setting thickness is obtained takes 17 seconds in the method of Fig. 3, whereas the rise time in the method of Fig. 4 takes only 6.5 seconds which show that the method of controlling gauge according to the present invention is advantageous over the prior .
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104~610 1 art method. Further, the settling time before the tolerance reaches within a range + 2~ takes 55 seconds in th~ method of Fig. 3, whereas, in Fig. 4, the settling time takes only 22 seconds so that off-gauge is considerably reduced.
Furthermore, the off-gauge portions are produced in a larger amount in the prior art method before the rolling speed decelerate to the threading speed even when the allowable thickness deviation is in a range of + 3~ during deceleration, whereas, in the method of the present invention, it is almost - 10 possible to eliminate the off-gauge portions while decelerating the rolling speed to the threading speed and maintaining the ~:
allowable tolerance within + 2%, though not shown in the drawings.
It will now be appreciated from the foregoing des-cription that a method of the present invention will provide a remarkable effect especially during accelerating condition in which the rolling speed is accelerated to the constant rolling : speed and decelerating condition in which the rolling speed is decreased from the constant rolling speed to the threading speed whereby the formation of off-gauge portions that would ;~ 20 otherwise be produced at leading and trailing ends of the rolled strip in the prior art expedient can be satisfactorily ~ eliminated and.the constant rolling speed is significantly ~.
- ; increased thereby providing high productivity of the rolling mill :.

~;~ and increasing:commercial value. .
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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of automatically controlling gauge in a rolling mill comprising the steps of:
detecting the thickness of a rolled strip, sheet and foil by a thickness gauge provided at the exit of the rolling mill;
computing control functions in dependence on an independent function of deviation value in thickness and the rate of thickness variation based on a detected result; producing a first compensating control input by multiplying said control functions by one another;
detecting the rolling speed of said rolling mill; producing an absolute value of the rate of changes in the rolling speed;
multiplying the control function in dependence on an independent function of deviation value in thickness by said absolute value of the rate of changes in the rolling speed thereby producing a second compensating control input;
adding said first and second compensating control inputs to an input indicative of the thickness deviation value thereby producing a control input;
and controlling gauge in dependence on said control input.