AU2007249130B2

AU2007249130B2 - Gauge control system

Info

Publication number: AU2007249130B2
Application number: AU2007249130A
Authority: AU
Inventors: Hiroyuki Imanari
Original assignee: Toshiba Mitsubishi Electric Industrial Systems Corp
Current assignee: Toshiba Mitsubishi Electric Industrial Systems Corp
Priority date: 2007-01-22
Filing date: 2007-01-22
Publication date: 2010-01-28
Anticipated expiration: 2027-01-22
Also published as: AU2007249130A1

Description

DESCRIPTION GAUGE CONTROL SYSTEM Technical Field [0001] The present invention relates to a gauge control system that is provided on a rolling mill for rolling a metallic material to control the fluctuations in thickness of the metallic material being rolled (rolled material). Background Art [0002] As one of quality control methods for rolling sheets and plates, automatic gauge control (AGC) that controls the thickness of the central portion in the width direction of the rolled material is carried out. As specific gauge control methods for carrying out this automatic gauge control, for example, monitor AGC that feeds back the measurement value of a gauge meter provided on the rolling mill exit side, gauge meter AGC (GM AGC) using a gauge meter thickness estimated from a roll force or a roll gap (a gap between the top and bottom mill rolls), and mill modulus control (MMC) utilizing a roll force, are cited. [0003] In the above-described automatic gauge control, as the disturbance that hinders the improvement in thickness accuracy, in hot rolling, for example, the fluctuations in temperature of the rolled material is cited. Also, as the disturbance common to hot -2 rolling and cold rolling, for example, the fluctuations in tension generated by the deterioration in tension control, the change of speed or roll gap made by the manual operation of an operator, the roll eccentricity caused in relation to the roll rotation position by the poor accuracy of roll construction or roll grinding, and the like are cited. [0004] Of these disturbances, the roll eccentricity is caused by an axial runout occurring mainly when a key groove for pouring oil to an oil bearing of a support roll is subjected to a high roll force of several hundred tons to two to three thousand tons. If the axial runout is produced by the roll eccentricity, the fluctuations in roll gap are also generated in association with the rotation of roll. Even in the case of a roll having no key groove, the fluctuations in roll gap are generated in association with the roll rotation by the asymmetry at the time of roll grinding or the deviation of thermal expansion. [0005] The device for controlling the roll gap feeds back the detection value of a roll gap detector so that the roll gap approaches a set value to control a reduction device and the like. However, the disturbance caused by the axial runout of roll such as roll eccentricity cannot be detected by the roll gap detector. In other words, the axial runout of roll does not appear in the detection value of roll gap detector. Therefore, even if the roll gap detector is used, the disturbance caused by the axial runout of roll cannot be controlled. However, the disturbance caused by the axial runout of roll actually changes the roll gap, so that this disturbance appears in the roll force. Therefore, the disturbance caused by the axial runout of roll is a major cause of hindering the improvement in thickness accuracy in the above-described MMC, GM-AGC, and the like that utilize the roll force to control the thickness.

-3 [0006] To reduce the disturbance caused by roll eccentricity such as the axial runout, roll eccentricity control has so far been carried out. As this roll eccentricity control, three control methods described below are mainly known. In the description below, it can be thought that the same holds true in the case of what is called a 2Hi mill that is formed by two top and bottom mill rolls only, in the case of what is called a 4Hi mill that is formed by four rolls of two top and bottom mill rolls and two top and bottom support rolls, in the case of what is called a 6Hi mill that is formed by six rolls of two top and bottom mill rolls, two top and bottom intermediate rolls, and two top and bottom support rolls, and in other cases. Therefore, the mill roll is expressed as a work roll (WR), and the roll other than the mill roll, such as the support roll, is expressed by a back-up roll (BUR). [0007] (A) Roll eccentricity control 1 Before a rolled material is rolled, the top and bottom work rolls are rotated in a state in which the rolls are brought into contact with each other and a fixed force is applied (kiss-roll state), and a kiss-roll force is detected. The detected kiss-roll force is, for example, Fourier transformed at a high speed to analyze the roll eccentricity frequency. Assuming that roll eccentricity of the analyzed frequency occurs during the rolling, the feedback control utilizing the roll force is not carried out, and a roll gap manipulated variable is outputted so as to reduce the influence exerted by the assumed roll eccentricity (for example, refer to Patent Documents 1 and 2). (B) Roll eccentricity control 2 -4 The fluctuations in thickness are measured by using a gauge meter provided on the rolling mill exit side. A thickness deviation is computed by correlating the thickness fluctuations measured by the gauge meter with the roll rotation position, and, based on the computed thickness deviation, the roll gap is controlled so as to reduce the thickness fluctuations caused by the roll eccentricity (for example, refer to Patent Document 3). (C) Roll eccentricity control 3 The roll force is taken in during the rolling of a rolled material, and a roll eccentricity component is extracted from the taken-in roll force. The extracted roll eccentricity component is converted into a roll gap signal, and the roll gap is controlled so as to restrain the roll force fluctuations caused by the roll eccentricity (for example, refer to Patent Document 4). [0008] Patent Document 1: Japanese Patent Laid-Open No.60-141321 Patent Document 2: Japanese Patent Laid-Open No.62-254915 Patent Document 3: Japanese Patent Laid-Open No.11-77128 Patent Document 4: Japanese Patent Laid-Open No.2002-282917 Disclosure of the Invention Problems to be Solved by the Invention [0009] In the method shown in the roll eccentricity control 1 described in Patent Documents 1 and 2, the roll eccentricity frequency is analyzed based on the kiss-roll force, and the roll gap manipulated variable during the rolling is controlled based on the analysis result. Therefore, this method has a problem in that gauge control of high accuracy -5 cannot be realized. Specifically, in the method shown in the roll eccentricity control 1, the fluctuation component of force occurring in relation to the roll rotation position is assumed to be a sinusoidal wave. However, in the fluctuation component of the actual force, not only a frequency component of a lowest-order frequency, what is called a basic frequency, but also a frequency component two times, three times, or more of the basic frequency sometimes appears. Therefore, this method has a problem in that in the case of combined disturbance, it is difficult to specify the disturbance having any frequency to be reduced. Further, in general, the back-up roll is often a cause of roll eccentricity. However, since the roll eccentricity may be caused by the grinding condition, the thermal expansion, and the like of work roll, the cause of roll eccentricity sometimes changes during the rolling. Also, the amplitude of fluctuations of the kiss-roll force is often a cause of the hardness and the like of the rolled material being rolled and differs from the amplitude of fluctuations of the roll force. Therefore, it is difficult to exactly analyze the roll eccentricity frequency. [0010] In the method shown in the roll eccentricity control 2 described in Patent Document 3, the rolling mill to which the gauge control can be applied is limited to a rolling mill provided with the gauge meter on the exit side thereof. Also, for example, in the case of a hot-rolled sheet tandem rolling mill formed by seven stands, as the fluctuations in product thickness, the thickness fluctuations generated by the roll eccentricity of the fifth, sixth and seventh stands of the later stage are prone to appear. However, the gauge meter is generally provided on the seventh stand exit side. In this case, the thickness fluctuations caused by the roll eccentricity of the fifth and sixth stands -6 cannot be controlled, which presents a problem in that the gauge control of high accuracy cannot be realized. Further, in order to exactly perform the tracking of rolled material from the rolling stand to the gauge meter arranged on the exit side thereof, it is necessary to exactly acquire the speed of rolled material. The speed of rolled material can be calculated based on the circumferential speed and forward slip of roll. While the circumferential speed of roll can be measured actually, the forward slip thereof is a predicted value. Therefore, there also arises a problem in that the speed of rolled material has an error, so that exact tracking cannot be realized. [0011] In the method shown in the roll eccentricity control 3 described in Patent Document 4, the actually occurring fluctuations of roll force are used to control the roll gap. Therefore, comparing with the methods shown in the roll eccentricity control 1 and 2, the fluctuation component that greatly affects the sheet thickness can be controlled directly, and the roll condition that is changed by the progress of rolling can be reflected properly. Also, since the transfer of rolled material need not be considered, no tracking error is produced unlike the roll eccentricity control 2. However, it is necessary to collect the actually measured values of roll force to extract the roll eccentricity component. Therefore, there arises a problem in that gauge control of high accuracy cannot be carried out during the time when the back-up roll rotates one turn after the start of rolling. Also, in the case where the back-up rolls arranged on the upside and downside have a different diameter, there arises a problem in that the gauge control of high accuracy is difficult to carry out as compared with the case where back-up rolls having the same diameter are arranged on the upside and downside.

-7 [0012] Hereunder is explained the reason why the gauge control of high accuracy is difficult to carry out in the case where the back-up rolls arranged on the upside and downside have a different diameter. In most of the rolling mills for rolling metallic materials, the work rolls are generally driven. In this case, the power of one motor or motors connected in series is transmitted to the work rolls via a pinion gear or the like, and the top and bottom work rolls are driven by the transmitted power. To equalize the circumferential speeds of the top and bottom work rolls, the diameter of the driven work roll is controlled with an accuracy within about 0.5 mm. On the other hand, for the undriven back-up rolls, the control of diameter is not so strict, and the diameter is sometimes 10% or more different. In the case where a diameter difference is produced between the top and bottom back-up rolls, in addition to the fluctuations in roll force of a short period, which is generated by the roll eccentricity, fluctuations in roll force of a long period, which is called beat or waviness, are generated. [0013] Figure 8 is graphs showing influences of the diameter difference and roll eccentricity of the top and bottom back-up rolls on the roll force and the roll gap. Figure 8(a) shows the simulation result of roll force fluctuations, and Figure 8(b) shows the simulation result of roll gap fluctuations. Both of Figures 8(a) and 8(b) show computation results at the time when the diameter of the top back-up roll is 1170 mm and that of the bottom back-up roll is 1260 mm. Also, in Figure 8(b), the broken line indicates the gap fluctuations generated by the rotation of the top back-up roll, the chain line indicates the gap fluctuations generated by the rotation of the bottom back-up roll, -8 and the solid line indicates the total gap fluctuations generated by the rotation of the top and bottom back-up rolls. [0014] In Figure 8, in the case where a diameter difference is produced between the top and bottom back-up rolls, the gap fluctuations generated by the rotation of each of the top and bottom back-up rolls are expressed as a sinusoidal wave having a different period. The total gap fluctuations obtained by lapping the above-described gap fluctuations and the roll force fluctuations have a wave component having a short period of about 0.5 second, which is produced by the rotation (roll eccentricity) of the top and bottom back up rolls, and a waviness component having a long period of about 4.5 seconds, which is produced by the diameter difference between the top and bottom back-up rolls. [0015] Since Figure 8 shows a simulation result, the gap fluctuations can easily be shown in a form of being divided into the top and bottom back-up rolls. Actually, however, for both of the roll force and the roll gap, only one value can be detected in the up and down direction. On the rolling mill, in many cases, a force detector is provided in at least two locations in the width direction of rolled material, namely, on the work side (WS) and on the drive side (DS), and the roll force can be measured independently on WS and DS. However, in the principle of measurement, the roll forces of the top and bottom work rolls cannot be detected independently. Also, in the case where there is a diameter difference between the top and bottom back-up rolls, a difference in rotational speed between the top and bottom back-up rolls also arises. Therefore, in the case where the rotational speed of either one of the top and bottom back-up rolls is used as a reference, -9 the rotational speed of the other back-up roll is not considered. For this reason, the fluctuations in roll force caused by the roll eccentricity cannot be restrained sufficiently. [0016] In order to solve the above-described problems, it is necessary to take 5 consideration by separating the top and bottom back-up rolls as in the method shown in the roll eccentricity control 3. Specifically, the fluctuations in roll force generated by the rotation of the top back-up roll and the fluctuations in roll force generated by the rotation of the bottom back-up roll are properly separated from the total roll force fluctuations, and control must be carried out based on the fluctuations in separated 10 upper and lower roll forces. However, Patent Document 4 does not disclose a concrete method therefor. [0017] Means for Solving the Problems 15 [0018] Therefore, according to one aspect of the present invention there is provided a gauge control system which is provided on a rolling mill for rolling a metallic material to control fluctuations in thickness caused by roll eccentricity of top and bottom work rolls and top and bottom back-up rolls of a rolling stand, comprising: 20 a force detector for detecting a kiss-roll force and a roll force; a kiss-roll force fluctuation extracting means which separately extracts, based on the kiss-roll force detected by the force detector at a plurality of rotation positions of the top and bottom work rolls and the top and bottom back-up rolls, a fluctuation component caused by the roll eccentricity of the top work roll and the top 21298321 (GHMatters) 26/11/09 -10 back-up roll at each of the rotation positions and a fluctuation component caused by the roll eccentricity of the bottom work roll and the bottom back-up roll at each of the rotation positions of the kiss-roll force; a roll force fluctuation extracting means which separately extracts, based 5 on the roll force detected by the force detector at each of the rotation positions, a fluctuation component caused by the roll eccentricity of the top work roll and the top back-up roll at each of the rotation positions and a fluctuation component caused by the roll eccentricity of the bottom work roll and the bottom back-up roll at each of the rotation positions of the roll force; 10 a manipulated variable computing means which computes, based on the fluctuation components of kiss-roll force extracted separately by the kiss-roll force fluctuation extracting means and the fluctuation components of roll force extracted separately by the roll force fluctuation extracting means, a roll gap command value corresponding to each of the rotation positions for a predetermined period of time after 15 the start of rolling of the metallic material so as to reduce the fluctuations in thickness of the metallic material being rolled; and a roll gap controlling means which controls a roll gap according to each of the rotation positions based on the roll gap command value computed by the manipulated variable computing means. 20 Effect of the Invention [0019] According to an embodiment the present invention, the fluctuations in roll force generated by the rotation of the top back-up roll and the fluctuations in roll 21298321 (GHMatters) 26/11/09 - 11 force generated by the rotation of the bottom back-up roll are properly separated from each other, and the roll gap is controlled according to the separated fluctuations in roll force, by which gauge control can be carried out with high accuracy. 5 Brief Description of the Drawings [0020] Figure 1 is a general configuration view of a gauge control system in accordance with an embodiment of the present invention. Figure 2 is a graph showing the concept of measured roll force. 10 Figure 3 is an explanatory view for explaining the positional relationship of the work roll and the back-up roll. Figure 4 is a graph showing the fluctuations of roll force caused by a change in rotation angle of the back-up roll. Figure 5 is an explanatory view for explaining the operation of the kiss-roll force 15 fluctuation extracting means in the embodiment of the present invention. Figure 6 is a configuration diagram showing an essential portion of the gauge control system in accordance with the embodiment of the present invention. Figure 7 is a general configuration view of a gauge control system in accordance with an embodiment of the present invention. 20 Figure 8 is graphs showing influences of the diameter difference and roll eccentricity of the top and bottom back-up rolls on the roll force and the roll gap. Description of Symbols [0021] 21298321 (GHMatters) 26/11/09 - 12 1 rolled material, 2 housing, 3 work roll, 3a top work roll, 3b bottom work roll, 4 back-up roll, 4a top back-up roll, 4b bottom back-up roll, 4c reference position, 5 reduction device, 6 force detector, 7 roll rotational speed detector, 8 roll reference position detector, 9 roll gap detector, 10 kiss-roll force fluctuation extracting means, 11 roll force fluctuation extracting means, 12 manipulated variable computing means, 13 roll gap controlling means, 14 position scale, 14a reference position, 15 force distributing means, 16 upper force fluctuation extracting section, 17 lower force fluctuation extracting section, 18a roll force recording means, 18b roll force recording means, 19a average value computing means, 19b average value computing means, 20a difference computing means, 20b difference computing means, 21a upper adding means, 21b lower adding means, 22a upper switch, 22b lower switch, 23 roll gap correction amount computing means, 24a limit, 24b limit, 25a switch, 25b switch, 26a adder, 26b adder Best Mode for Carrying Out the Invention [0022] The present invention will now be described in more detail with reference to the accompanying drawings. In the drawings, the same symbols are applied to the same or - 13 equivalent elements, and the duplicated explanation thereof is simplified or omitted as necessary. [0023] Embodiment 1 Figure 1 is a general configuration view of a gauge control system in accordance with an embodiment 1 of the present invention. In Figure 1, symbol 1 denotes a rolled material consisting of a metallic material rolled by a rolling mill, 2 denotes a housing of the rolling mill, 3 denotes a work roll formed by a top work roll 3a and a bottom work roll 3b, 4 denotes a back-up roll formed by a top back-up roll 4a and a bottom back-up roll 4b, 5 denotes a reduction device for applying a roll force to the rolled material 1, 6 denotes a force detector for detecting a kiss-roll force and a roll force, 7 denotes a roll rotational speed detector for detecting the number of revolutions of roll, 8 denotes a roll reference position detector for detecting a predetermined reference position each time the back-up roll 4 rotates one turn, and 9 denotes a roll gap detector for detecting a gap between the top and bottom work rolls 3a and 3b, namely, a roll gap. [0024] Symbol 10 denotes a kiss-roll force fluctuation extracting means, and 11 denotes a roll force fluctuation extracting means. The kiss-roll force fluctuation extracting means 10 separately extracts, based on a kiss-roll force detected by the force detector 6 at a plurality of rotation positions of the top and bottom work rolls 3a and 3b and the top and bottom back-up rolls 4a and 4b, a fluctuation component caused by the roll eccentricity of the top work roll 3a and the top back-up roll 4a at each of the rotation positions of the kiss-roll force and a fluctuation component caused by the roll eccentricity of the bottom work roll 3b and the bottom back-up roll 4b at each of the rotation positions of the kiss- - 14 roll force. The roll force fluctuation extracting means 11 separately extracts, based on the upper and lower fluctuation components of the kiss-roll force extracted separately by the kiss-roll force fluctuation extracting means 10, a fluctuation component caused by the roll eccentricity of the top work roll 3a and the top back-up roll 4a at each of the rotation positions and a fluctuation component caused by the roll eccentricity of the bottom work roll 3b and the bottom back-up roll 4b at each of the rotation positions of the detected roll force of the roll force detected by the force detector 6 at each of the rotation positions. [0025] Symbol 12 denotes a manipulated variable computing means, and 13 denotes a roll gap controlling means. The manipulated variable computing means 12 computes, based on the upper and lower fluctuation components of the roll force extracted separately by the roll force fluctuation extracting means 11, a roll gap command value corresponding to each of the rotation positions so as to reduce the thickness fluctuations in the rolled material 1 being rolled. The roll gap controlling means 13 controls the roll gap according to each of the rotation positions based on the roll gap command value computed by the manipulated variable computing means 12. Also, the roll gap controlling means 13 controls the reduction device 5 with a value obtained by adding a roll gap correction amount computed by the manipulated variable computing means 12 to a roll gap amount obtained by, for example, MMC or GM-AGC being a set value of roll gap. In the following explanation of the embodiment 1, explanation is given of the case of a 4Hi mill formed by four rolls of two top and bottom work rolls 3 and two top and bottom back-up rolls 4 as one example. [0026] - 15 The gauge control system is configured as described above, and the rolled material 1 is rolled by the work roll 3, in which the roll gap and speed are adjusted properly, so as to provide a desired sheet thickness on the exit side. The work roll 3 is configured so that the deflection in the roll width direction is small because the top work roll 3a is supported from the upside by the top back-up roll 4a and the bottom work roll 3b is supported from the downside by the bottom back-up roll 4b. Also, the back-up roll 4 is supported turnably with respect to the housing 2, and has a construction capable of sufficiently withstanding the roll force applied to the rolled material 1. [0027] Two types of the reduction devices 5 are available: an electrically controlled reduction device (called electrical reduction) and a hydraulically controlled reduction device (called hydraulic reduction). The hydraulic reduction provides higher-speed response. Therefore, in order to carry out roll force control corresponding to the wave component having a short period such as the disturbance caused by roll eccentricity, the hydraulic reduction capable of providing high-speed response is generally employed. Also, the gap between the top and bottom work rolls 3a and 3b, namely, the roll gap is adjusted by the reduction device 5. The force detector 6 detects a kiss-roll force or a roll force by a method in which a roll force is directly measured by a load cell embedded between the housing 2 and the reduction device 5, a method in which a roll force is calculated from the pressure detected by a hydraulic reduction device, or the like method. [0028] The roll rotational speed detector 7 is provided on the work roll 3 or the shaft (not shown) of a motor for driving the work roll 3 to detect the number of revolutions of the -16 work roll 3 or the like. The roll rotational speed detector 7 is configured so as to be capable of detecting the number of revolutions of the work roll 3 and also detecting more detailed rotation angle by being provided with a pulse output section that generates pulses according to the rotation angle of the work roll 3 and an angle computing section that detects the pulse generated from the pulse output section and computes the rotation angle of the work roll 3. In the case where the ratio of diameter between the work roll 3 and the back-up roll 4 is known, based on the number of revolutions and rotation angle of the work roll 3 detected by roll rotational speed detector 7, the number of revolutions and rotation angle of the back-up roll 4 in the case where no slip occurs between the work roll 3 and the back-up roll 4 can be computed easily. [0029] The roll reference position detector 8 detects a reference position, for example, by detecting an object to be detected which is provided on the back-up roll 4 by using a sensor such as a proximity switch, each time the back-up roll 4 rotates one turn. Also, the roll reference position detector 8 detects the reference position by taking out pulses relating to the rotation angle of the back-up roll 4, for example, by utilizing a pulse generator and thereby detecting the rotation angle of the back-up roll 4. Although Figure 1 shows the case where the roll reference position detector 8 is mounted on the top back-up roll 4a only, the configuration may be such that the roll reference position detector 8 is mounted on the top and bottom back-up rolls 4a and 4b so that the reference positions of the top and bottom back-up rolls 4a and 4b may be detected. Figure 7, which is a general configuration view of another gauge control system, shows a gauge control system corresponding to the system shown in Figure 1, in which the roll reference position detector 8 is not mounted. In the gauge control system shown in Figure 7, the - 17 signal sent from the roll reference position detector 8 is not used. The details of this gauge control system are described later. The roll gap detector 9 is provided, for example, between the back-up roll 4 and the reduction device 5 to indirectly detect a roll gap formed between the top and bottom work rolls 3a and 3b. [0030] Next, referring to Figures 2 to 6, the configurations and operations of the kiss-roll force fluctuation extracting means 10, the roll force fluctuation extracting means 11, and the manipulated variable computing means 12 are explained specifically. Figure 2 is a graph showing the concept of measured roll force. As shown in Figure 2, even in the case where roll eccentricity does not occur on the back-up roll 4 etc., the roll force fluctuates with time, namely, the rotation of roll due to the temperature change, thickness change, or the like of the rolled material 1. On the other hand, in the case where roll eccentricity occurs on the back-up roll 4 etc., the roll force is expressed as a force obtained by lapping the fluctuation component of roll force caused by the roll eccentricity on the fluctuation component of roll force caused by anything other than the roll eccentricity. The basic concept of the specific control of this gauge control system explained below is that the fluctuations in roll force caused by the roll eccentricity is properly separated from the fluctuations in roll force caused by anything other than the roll eccentricity, and the fluctuations in roll force caused by the roll eccentricity is controlled by this gauge control system and the fluctuations in roll force caused by anything other than the roll eccentricity is controlled by the MMC or GM-AGC. [0031] - 18 Next, referring to Figure 3, explanation is given of the matters that are necessary when the configurations and operations of the roll force fluctuation extracting means 11 and the like are explained. Figure 3 is an explanatory view for explaining the positional relationship of the work roll and the back-up roll. In Figure 3, symbol 14 denotes a position scale for detecting the rotation position of the back-up roll 4, which is fixed on the housing 2 etc. of the rolling mill, and 4c denotes a reference position that is preset in a part of the back-up roll 4 and rotates in association with the rotation of the back-up roll 4. The position scale 14 is provided on the outside just close to the back-up roll 4, for example, so as to surround the periphery of the back-up roll 4, and the scale is provided so that the entire periphery of the back-up roll 4 is divided into n equal parts, that is, at each predetermined angle (360/n degrees) with the rotating shaft of the back-up roll 4 being the center. The position scale 14 is numbered to (n-1)-th taking a reference position 14a (fixed reference position) of the position scale 14 as 0. As the number n, values of 30 to 40 are set. The position scale 14 is provided to explain the roll force fluctuation extracting means 11 and the like, and the scale itself need not be marked on the actual equipment. [0032] In Figure 3, Owmo is the rotation angle of the work roll 3 at the time when the reference position 4c of the back-up roll 4 coincides with the fixed reference position 14a, and Owr is the rotation angle of the work roll 3 after the back-up roll 4 has rotated through OBT. The symbol 0 represents an angle. The left suffixes W and B represent the work roll 3 and the back-up roll 4, respectively, and the right suffixes T and B represent the top side and the bottom side, respectively. In the description below, the rotation angle of the back-up roll 4 means an angle through which the reference position 4c of the back-up roll - 19 4 moves from the fixed reference position 14a in association with the rotation of the back-up roll 4. For example, a phrase "the rotation angle of the back-up roll 4 is 90 degrees" indicates that the reference position 4c of the back-up roll 4 is located at a position at which the reference position 4c has rotated through 90 degrees in the rotation direction of the back-up roll 4 from the fixed reference position 14a. Also, the state in which the rotation angle of the back-up roll 4 is on the closest scale of the position scale 14 (for example, the j-th scale of the position scale 14) is explained as "the number of rotation angle of the back-up roll 4 is j". [0033] At the reference position 4c of the back-up roll 4 and the fixed reference position 14a, a sensor such as a proximity sensor and an object to be detected by the sensor are embedded, respectively, by which the roll reference position detector 8 may be formed by the sensor and object to be detected. In such a case, for example, when the proximity sensor provided at the reference position 4c of the back-up roll 4 rotates together with the back-up roll 4 and reaches the fixed reference position 14a, the object to be detected, which is embedded at the reference position 14a, is detected by the proximity sensor. That is to say, the reference position 4c of the back-up roll 4 is recognized as having passed through the fixed reference position 14a. [0034] Next, referring to Figure 4, a method for extracting the fluctuation component caused by roll eccentricity of the roll force is explained. Figure 4 is a graph showing the fluctuations of roll force caused by a change in rotation angle of the back-up roll. In Figure 4, in the case where the reference position 4c of the back-up roll 4 is located at the reference position 14a, that is, in the case where the number of rotation angle of the back- - 20 up roll 4 is 0, the roll force is P 1 0 . As the number of rotation angle of the back-up roll 4 proceeds to 1, 2, 3 ..., the roll force changes to P 11 , P 12 , P 13 ... The back-up roll 4 rotates one turn, and the number of rotation angle again becomes 0 from (n-1), where the roll force P 20 is sampled. If the roll forces Plo and P 2 0 are connected to each other by a straight line at this time, this straight line can be regarded as a roll force excluding the fluctuations in roll force caused by the roll eccentricity. Therefore, the fluctuations in roll force caused by the roll eccentricity can be determined from the difference between the roll force P 11 , P 12 , P 1 3 ... P 20 measured at each number of rotation angles and the straight line. [0035] The actually measured value of the roll force Pij often contains a noise component in addition to the fluctuations in roll force caused by temperature fluctuations, thickness fluctuations, tension fluctuations, and the like and the fluctuations in roll force caused by roll eccentricity. Therefore, the actually measured values of the actual roll forces Pij are not distributed on a gentle curve as shown in Figure 4, and in some cases, it is difficult to identify the roll force Pio at the start point and the roll force P(i+1)o at the end point, which are to be connected to each other to determine the straight line. If it is assumed that the change of the roll force P(i+1)o from the roll force Pio is not so large, a difference APj between each measured roll force Pio, P, 1 , Pi 2 , Pi 3 ... P(i+1)o and the average value of n number of roll forces Pio, Pu, Pi 2 , Pi 3 ... Pi(nl) can be regarded as a fluctuation component caused by the roll eccentricity of roll force. The advantage of this method is that the sampling of actually measured values of roll forces can be reduced to the (n-1)-th, and the method is invulnerable to the fluctuations in roll force caused by noise etc. A method in - 21 which the actually measured value of the roll force is subjected to filtering to reduce the noise component is also effective. [0036] Next, referring to Figure 5, the kiss-roll force fluctuation extracting means 10 is explained. Figure 5 is an explanatory view for explaining the operation of the kiss-roll force fluctuation extracting means in the embodiment 1 of the present invention. [0037] A method for extracting the fluctuation component caused by roll eccentricity of a kiss-roll force by using the kiss-roll force fluctuation extracting means 10 is equivalent to the method shown in Figures 3 to 5 of Patent Document 1. In the method described in Patent Document 1, the fluctuation of force at the kiss-roll time is converted into a roll eccentricity amount, namely, a gap amount. The conversion is accomplished, for example, in the blocks 103 and 113 shown in Figure 3. However, since it can be considered that at the kiss-roll time, there are no force fluctuations other than the force fluctuations caused by roll eccentricity, the force, not the gap, may be used as it is. Also, in the method described in Patent Document 1, a device for generating sampling pulses is needed. However, if the rotation position of the back-up roll is found, the device is not necessarily needed. Also, the mark pulse generator in Patent Document 1 corresponds to the roll reference position detector 8 of this application. However, the mark pulse generator is not necessarily needed if the rotation position of the back-up roll is found. [0038] In the operation in this application, in Figure 5, first, the top and bottom back-up rolls 4a and 4b are rotated with the top and bottom work rolls 3a and 3b being in a kiss roll state, and the kiss-roll force and the rotation angles of the top and bottom back-up - 22 rolls 4a and 4b are measured and recorded in succession from the reference position 4c of the back-up roll 4. At this time, the reference position 4c of the back-up roll 4 need not necessarily be caused to coincide with the fixed reference position 14a. Figure 5 shows a case where the kiss-roll force is measured and recorded every five degrees of rotation angle of the back-up roll 4. The upper table in Figure 5 gives one example of data of one turn with the top back-up roll 4a being a reference. In the state given in the upper table in Figure 5, a difference in rotation angle of 15 degrees is produced between the top and bottom back-up rolls 4a and 4b. In such a case, if the difference in diameter between the top and bottom back-up rolls 4a and 4b is zero, even if the top back-up roll 4a is rotated any turns, the difference in rotation angle between the top and bottom back up rolls 4a and 4b keeps the state of 15 degrees. However, in the case where a difference in diameter between the top and bottom back-up rolls 4a and 4b is produced, as the rotation of the top back-up roll 4a proceeds from one turn to two turns and so on, the difference in rotation angle between the top and bottom back-up rolls 4a and 4b increases. After predetermined rotations according to the diameter difference, the difference in rotation angle between the top and bottom back-up rolls 4a and 4b becomes (15+360) degrees, and returns to the initial state. The lower table in Figure 5 gives one example of one turn with the bottom back-up roll 4b being a reference, showing a case where a difference in rotation angle of 20 degrees is produced between the top and bottom back up rolls 4a and 4b. Patent Document 1 describes that a force is read for every sampling pulse in the blocks 102, 112, 203 and 213 shown in Figure 3. The example shown in Figure 5 of this application corresponds to the case where sampling pulses are generated every five degrees in the method described in Patent Document 1. Also, since the above-described measurement must be made in a kiss-roll state, the measurement can be - 23 made utilizing the time before the start of rolling, for example, when the back-up roll 4 or the work roll 3 is exchanged. [0039] By measuring the fluctuations in force at the kiss-roll time by the method equivalent to the method described in Patent Document 1 in this manner, the fluctuation components of force at the kiss-roll time in accordance with the rotation angles of the top and bottom back-up rolls 4a and 4b can be determined by the following formula. [0040] [Formula 1] PTOP = PTOPo sin(OTOP +TOP [0041] [Formula 2] PBOT PBO sin(OBOT + OBOT) in which, pTop is the fluctuation component of force at the kiss-roll time for the top back up roll 4a, PBOT is the fluctuation component of force at the kiss-roll time for the bottom back-up roll 4b, pTropo is the amplitude of fluctuation component of force at the kiss-roll time for the top back-up roll 4a, PBon is the amplitude of fluctuation component of force at the kiss-roll time for the bottom back-up roll 4b, 6 Top is the rotation angle of the top back-up roll 4a from the fixed reference position 14a, OBOT is the rotation angle of the bottom back-up roll 4b from the fixed reference position 14a, #rop is the phase difference of the top back-up roll 4a from the fixed reference position 14a, and PBOT is the phase difference of the bottom back-up roll 4b from the fixed reference position 14a. [0042] - 24 Next, referring to Figure 6, the specific configurations and operations of the roll force fluctuation extracting means 11 and the manipulated variable computing means 12 are explained. Figure 6 is a configuration diagram showing an essential portion of the gauge control system in accordance with the embodiment 1 of the present invention. In Figure 6, symbol 15 denotes a force distributing means, 16 denotes an upper force fluctuation extracting section, and 17 denotes a lower force fluctuation extracting section. The force distributing means 15 separates a roll force P detected by the force detector 6 into a roll force PT generated on the top back-up roll 4a and a roll force PB generated on the bottom back-up roll 4b assuming that the roll force P is generated individually on the top back-up roll 4a and the bottom back-up roll 4b. The upper force fluctuation extracting section 16 extracts, based on the roll force PT separated by the force distributing means 15, the fluctuation component caused by roll eccentricity of the roll force PTj at a plurality of rotation positions of the top back-up roll 4a. The lower force fluctuation extracting section 17 extracts, based on the roll force PB separated by the force distributing means 15, the fluctuation component caused by roll eccentricity of the roll force PBj at a plurality of rotation positions of the bottom back-up roll 4b. The roll force fluctuation extracting means 11 is made up of the force distributing means 15, the upper force fluctuation extracting section 16, and the lower force fluctuation extracting section 17. [0043] Also, symbol 18a denotes n number of roll force recording means provided so as to correspond to the rotation angle numbers of the back-up roll 4. In each of the roll force recording means 18a, the roll force PTj at the time when the back-up roll 4 reaches the corresponding rotation angle number is recorded for a predetermined period of time.

- 25 Symbol 19a denotes an average value computing means that computes, based on the roll force PTj recorded in the roll force recording means 18a, the average value of n number of roll forces PTj detected during one turn of the back-up roll 4, and 20a denotes a difference computing means provided corresponding to each of the roll force recording means 18a. The difference computing means 20a computes and outputs a difference APTj between the roll force PTj recorded in the roll force recording means 18a and the average value each time the back-up roll 4 rotates one turn. [0044] The upper force fluctuation extracting section 16 is made up of the roll force recording means 18a, the average value computing means 19a, and the difference computing means 20a. On the other hand, the lower force fluctuation extracting section 17 has the same configuration as that of the upper force fluctuation extracting section 16, and includes roll force recording means 18b, an average value computing means 19b, and difference computing means 20b. [0045] Also, in Figure 6, symbol 21a denotes an upper adding means, 21b denotes a lower adding means, 22a denotes an upper switch, 22b denotes a lower switch, and 23 denotes a roll gap correction amount computing means. The upper adding means 21a adds the fluctuation component caused by roll eccentricity of the roll force PTj sent from the upper force fluctuation extracting section 16 for each rotation angle number. The lower adding means 21b adds the fluctuation component caused by roll eccentricity of the roll force PBj sent from the lower force fluctuation extracting section 17 for each rotation angle number. The upper switch 22a outputs the fluctuation component caused by roll eccentricity of the roll force PTj, which is added for each rotation angle number by the upper adding means - 26 21a, according to the rotation angle number of the back-up roll 4. The lower switch 22b outputs the fluctuation component caused by roll eccentricity of the roll force PBj, which is added for each rotation angle number by the lower adding means 21b, according to the rotation angle number of the back-up roll 4. The roll gap correction amount computing means 23 computes the correction amount of roll gap corresponding to the rotation angle number of the back-up roll 4 based on the output value of the upper switch 22a and the output value of the lower switch 22b. [0046] The manipulated variable computing means 12 is made up of the upper adding means 21a, the lower adding means 21b, the upper switch 22a, the lower switch 22b, and the roll gap correction amount computing means 23. The upper adding means 21a and the lower adding means 21b have the same configuration, and also the upper switch 22a and the lower switch 22b have the same configuration. For example, the upper adding means 21a includes a limit 24a, a switch 25a, and adders 26a. The limit 24a checks the upper and lower limits of the difference APTj sent from the difference computing means 20a. The switch 25a is turned on each time the back-up roll 4 rotates on turn, that is, each time the computation of average value in the average value computing means 19a is finished, and simultaneously delivers the difference APTj sent from the limit 24a. Each of the adders 26a is provided corresponding to each rotation angle number of the back-up roll 4 to add the difference sent from the switch 25a for each rotation angle number. [0047] Next, the operations of the roll force fluctuation extracting means 11 and the manipulated variable computing means 12 are explained.

- 27 In the force detector 6, only one value can be sampled as a roll force for one stand. Therefore, the force distributing means 15 separates the roll force P detected by the force detector 6 into the roll force PT generated on the top back-up roll 4a and the roll force PB generated on the bottom back-up roll 4b, for example, by the following formulas. [0048] [Formula 3] PT =aP -k, -PBOT [0049] [Formula 4] P, =(1 - a)P - k 2 PTOP in which, P is the actually measured value of roll force (a value detected by the force detector 6), a is a weighting factor (generally, 0 s a s 1), and ki and k 2 are adjustment factors (generally, 0 ski s 1, 0 s k2 s 1). The weighting factor a may be a fixed value of, for example, 0.5 or may be determined by the following formula. [0050] [Formula 5] _ PTOP PTOP + PBOT [0051] In the case where the difference in diameter between the top and bottom back-up rolls 4a and 4b is small, the configuration may be such that only either one of the upper force fluctuation extracting section 16 and the lower force fluctuation extracting section 17 is used, or the configuration may be such that the roll force P detected by the force detector 6 is separated in a predetermined ratio. For example, the configuration is made - 28 so that in the case where the ratio r calculated by the following formula is smaller than a certain threshold value, it is judged that the difference in diameter between the top and bottom back-up rolls 4a and 4b is small. [0052] [Formula 6] r = | DTOP - DO I X100[%] (DTOp - DBOT ) / 2 in which, DTop is the diameter of the top back-up roll 4a, and DBOT is the diameter of the bottom back-up roll 4b. As the threshold value, a value of, for example, about 2 to 3% is used. In the case where the ratio r is smaller than the predetermined threshold value, and only the upper force fluctuation extracting section 16 is used, the factors have only to be such that a =1, k, = 0, and k 2 = 0, or the functions of the lower force fluctuation extracting section 17 have only to be made inoperative. [0053] In the upper force fluctuation extracting section 16, the roll force PmU that is detected by the force detector 6 in the case where the rotation angle number of the back up roll 4 is 0 and is separated by the force distributing means 15, the roll force PT in the case where the rotation angle number is 1, and the roll force Pr 2 in the case where the rotation angle number is 2 are recorded in the corresponding roll force recording means 18a in succession with the rotation of the back-up roll 4. In each of the roll force recording means 18a, the inputted roll force PTj is held during one turn of the back-up roll 4, that is, until the rotation angle number of the back-up roll 4 becomes 0 again. The average value computing means 19a computes the average value based on n number of roll forces P-m to PT(n.1) when the rotation angle number of the back-up roll 4 reaches (n-1).

- 29 The difference computing means 20a outputs the difference APTj between the roll force Prj and the average value computed by the average value computing means 19a as the fluctuation component caused by roll eccentricity of the roll force. The upper force fluctuation extracting section 16 performs the above-described operation for each rotation of the back-up roll 4 to output the difference APTj, namely, the fluctuation component caused by roll eccentricity of the roll force for each rotation angle number. [0054] The above-described method is a computation method in the case where the roll force excluding the fluctuation component caused by roll eccentricity is regarded as the average value of n number of roll forces Pr to PT(n.1). However, as described with reference to Figure 4, the straight line connecting the roll forces PM and PTn in the case where the rotation angle number of the back-up roll 4 is zero may be regarded as the roll force excluding the fluctuation component caused by roll eccentricity of the roll force PTj. In such a case, the difference between the roll force PTj and the straight line is the difference APTj, namely, the fluctuation component caused by roll eccentricity of the roll force PTj. [0055] In the upper adding means 21a, after the upper and lower limits of the output value of the difference computing means 20a have been checked, by the adder 26a, the processing shown in the following formula is carried out based on the output of the switch 25a, and the difference APTj is added. [0056] [Formula 7] Zj [k +1]= Z [k]+ APri - 30 in which, Zj is the value of the adder 2j, k is the number of adding operations (generally, coincides with the number of revolutions of the back-up roll 4), and j is 0 to n-1. The adder 26a is cleared to zero before the rolled material 1 is rolled, and each time the back up roll 4 rotates one turn and the computation of average value performed by the average value computing means 19a is finished, the difference APTj is added one time. [0057] Also, in the processing carried out in the adder 26a, it is also effective that the influence of the value added in the past is reduced, and the influence of the fluctuation component of a roll force close to the present time is highly rated. In such a case, the processing shown by the following formula is carried out in place of Formula 7. [0058] [Formula 8] Zj [k +1]=bZj [k]+ APrj in which, b is an oblivion factor. The adding of the difference APTj for each rotation angle number can be explained easily from the general control rule. In the case where an object to be controlled has no integrating system like the object to be controlled in this embodiment, the removal of steady-state deviation accomplished by putting an integrator on the control device side is reasonable from the viewpoint of the control rule as well. In the present invention, the object to be controlled is not a continuous value system but a discrete value system, so that an adder, not an integrator, is used. [0059] The upper switch 22a sends a difference APATj added by the adder 26a to the roll gap correction amount computing means 23 according to the rotation position of the back-up roll 4. For example, when the reference position 4c of the back-up roll 4 passes - 31 through the reference position 14a of the position scale 14, namely, the scale 0, only SWo of the upper switches 22a is turned on, and APA-y is taken out of X 0 of the adders 26a. Also, when the reference position 4c of the back-up roll 4 reaches the scale 1 of the position scale 14, only SW 1 is turned on, and only APATI is taken out of 11. The above described operation is repeatedly performed for each rotation position of the back-up roll 4. [0060] The above-described operation is an operation for taking out the fluctuation component generated by the rotation of the top back-up roll 4a from the total fluctuation components caused by roll eccentricity of the roll force. On the other hand, the fluctuation component generated by the rotation of the bottom back-up roll 4b can also be taken out of the total fluctuation components by the same method as described above. That is to say, the fluctuation component caused by roll eccentricity of the roll force is outputted from the lower force fluctuation extracting section 17 for each rotation angle number based on the roll force PB generated on the bottom back-up roll 4b. Based on this output value, a difference APAB in accordance with the rotation position of the back up roll 4 is outputted to the roll gap correction amount computing means 23 via the lower adding means 21b and the lower switch 22b. [0061] The roll gap correction amount computing means 23 computes, based on the differences APAT and APAB sent from the upper switch 22a and the lower switch 22b, a roll gap correction amount AS (mm), which compensates the fluctuation component caused by roll eccentricity of the roll force, by the following formulas. [0062] - 32 [Formula 9] -S (M + Q).A MQ [0063] [Formula 10] AS, - (M + Q) *AB MQ Also, the upper and lower roll gaps cannot be controlled separately, so that the upper and lower roll gaps must be outputted by being added. [0064] [Formula 11] AS = KTNE (AST +ASB in which, M is a mill constant, Q is the plasticity factor of the rolled material 1, KTUNE is an adjustment factor, AST is the roll gap correction amount for the top back-up roll 4a, ASB is the roll gap correction amount for the bottom back-up roll 4b, APAT is the difference in roll force produced by the top back-up roll 4a (output of the upper switch 22a), and APAB is the difference in roll force produced by the bottom back-up roll 4b (output of the lower switch 22b). The roll gap controlling means 13 adds the roll gap correction amount AS computed by the manipulated variable computing means 12 to the roll gap amount obtained by MMC or GM-AGC, and gives the added roll gap amount to the reduction device 5. [0065] In the case where the reduction device 5 is controlled by the above-described configuration, time lag cannot sometimes be neglected depending on the response of the - 33 reduction device 5. For example, in the case where the response of hydraulic reduction is 60 rad/sec of cut-off frequency, if the response finish is set at 100%, the time for reaching 95% is 0.05 sec. Also, a computation time lag etc. may be added to this lag. Assuming that the time required for one turn of the back-up roll 4 is about 0.5 to 1 second, the above-described time lag of 0.05 sec corresponds to 1/10 to 1/20 of the time required for one turn of the back-up roll 4, so that highly accurate gauge control may become difficult to carry out. [0066] In such a case, by moving forward the timing of outputting the roll gap correction amount AS of the manipulated variable computing means 12, the above-described problem can be solved. In Figure 3, if the division number n equals 40, and the time required for one turn of the back-up roll 4 is 0.8 second, the time during which the back up roll 4 advances one scale of the position scale 14 is 0.02 second. Therefore, if the time lag of 0.05 second has occurred, the roll gap correction amount AS has only to be given to the roll gap controlling means 13 ahead of 2.5 scales of the position scale 14. [0067] In the above explanation, various measuring operations and computing operations have been performed with the rotation of the back-up roll 4 being used as a reference. However, the same control can be carried out with the rotation of the work roll 3 being used as a reference. [0068] Also, in Figure 6, if the adders 26a and 26b are cleared to zero at the time of the start of rolling, during the time when the back-up roll 4 rotates one turn after the start of rolling, the actually measured values of roll force must be sampled, so that the above- - 34 described control cannot be carried out. Therefore, APAT and APAB are calculated by performing the calculation given by the following formula. Hereunder, only the method for calculating APAT in the case where the upper switch 22a and the lower switch 22b are closed in Figure 6 is described, and the description of the method for calculating APAB is omitted because this method is the same as the method for calculating APAT. [0069] [Formula 12] AP, = pZ [k ]+ (1 - 8)Z j [n : previous] or [0070] [Formula 13] APr = BZj k ]+(1 -6)TOPj in which, Zj[k] is the value of the adder 26a for controlling that material, k is the number of adding operations (generally, coincides with the number of revolutions of the back-up roll 4), Zj[n: previous] is the final value of the adder 26a for the material having been rolled just before that material, PTOPj is the value at the rotation angle position j of the back-up roll 4 of the force fluctuation at the kiss-roll time caused by the top back-up roll 4a, and P is a weighting factor (0 :s s r 1). [0071] It is when the difference in diameter between the top and bottom back-up rolls 4a and 4b is small that Formula 12 is applied. Also, it is assumed that the weighting factor P is changed depending on the time from the start of rolling or the number of revolutions of the back-up roll 4 from the start of rolling, and, generally, the initial value thereof is 0 and weighting factor P approaches 1 as the rolling operation proceeds. = 1 means that - 35 the roll force of that material is used a hundred percent. Therefore, the timing of p = 1 is the point of time when the accuracy of fluctuation in roll force caused by the roll force fluctuation extracting means 11 becomes sufficiently high. Also, the minimum value of timing of P = 1 is timing when the top back-up roll 4a or the bottom back-up roll 4b has rotated one turn. [0072] According to the embodiment 1 of the present invention, in the case where the fluctuations in roll force caused by roll eccentricity exist, the fluctuations in roll force can be restrained, and therefore the fluctuations in sheet thickness caused the fluctuations in roll force can be restrained. Also, the control method of the embodiment 1 can also be applied to the case where the difference in diameter between the top and bottom back-up rolls 4a and 4b is large, so that the degree of freedom of roll control is improved. Also, a fluctuation component that cannot be analyzed by a method in which the fluctuations in roll force caused by roll eccentricity is restrained by frequency analysis, which method has been used conventionally, can also be extracted and controlled. Further, for the reason of equipment construction, a gauge meter is not needed, and a decrease in accuracy caused by tracking error does not occur. [0073] Embodiment 2 Figure 7 is a general configuration view of a gauge control system in accordance with an embodiment 2 of the present invention. In the gauge control system shown in Figure 7, the roll reference position detector 8 in the embodiment 1 is not provided. In the explanation of the kiss-roll force fluctuation extracting means 10 in the embodiment 1, -36 the gauge control system in accordance with the embodiment 2 corresponds to the case where the mark pulse generator is absent in Patent Document 1. [0074] The roll reference position detector 8 is often formed by a proximity switch, and must be mounted on each of the back-up rolls 4, which results in a high cost. Also, after the roll reference position detector 8 has been assembled to the rolling mill, a wiring for taking out a signal from the sensor is needed, which poses a problem in that much time and labor are required for maintenance work. Therefore, from the viewpoint of equipment maintenance, it is better that the roll reference position detector 8 is absent. [0075] In general, for the work roll 3, a roll must be interposed at the time of exchange of the work roll 3. Therefore, to exactly know the rotation angle, a sensor is mounted. Since the diameters of the work roll 3 and the back-up roll 4 are known, the rotation angle of the back-up roll 4 can be learned from the rotation angle of the work roll 3. Therefore, according to the above-described method, the roll reference position detector 8 is not necessarily needed. [0076] However, it is also thought that a slip occurs between the work roll 3 and the back up roll 4, and therefore the positional relationship between both the rolls shifts. To deal with this case, some consideration is needed. For example, the influence of the past information is reduced with the elapse of time by introducing the oblivion factor in Formula 8, identification of kiss-roll force fluctuations using Formulas 1 and 2 is performed frequently not only at the time of roll exchange but also during the time when rolling is not performed, or the values of the adjustment factors k, and k 2 in Formulas 3 -37 and 4 are decreased. By taking such consideration, measures can be taken against the positional shift of the back-up roll 4. Industrial Applicability 5 [0077] As described above, according to the gauge control system in accordance with the present invention, a fluctuation component that cannot be analyzed by frequency analysis can also be extracted and controlled, and therefore the gauge control can be carried out with higher accuracy. Also, for the reason of equipment 10 construction, a gauge meter is not needed, and a decrease in accuracy caused by tracking error does not occur. In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or 15 necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention. 20 It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country. 21298321 (GHMatters) 26/11/09

Claims

1. A gauge control system which is provided on a rolling mill for rolling a metallic material to control fluctuations in thickness caused by roll eccentricity of top and bottom work rolls and top and bottom back-up rolls of a rolling stand, comprising: 5 a force detector for detecting a kiss-roll force and a roll force; a kiss-roll force fluctuation extracting means which separately extracts, based on the kiss-roll force detected by the force detector at a plurality of rotation positions of the top and bottom work rolls and the top and bottom back-up rolls, a fluctuation component caused by the roll eccentricity of the top work roll and the top 10 back-up roll at each of the rotation positions and a fluctuation component caused by the roll eccentricity of the bottom work roll and the bottom back-up roll at each of the rotation positions of the kiss-roll force; a roll force fluctuation extracting means which separately extracts, based on the roll force detected by the force detector at each of the rotation positions, a 15 fluctuation component caused by the roll eccentricity of the top work roll and the top back-up roll at each of the rotation positions and a fluctuation component caused by the roll eccentricity of the bottom work roll and the bottom back-up roll at each of the rotation positions of the roll force; a manipulated variable computing means which computes, based on the 20 fluctuation components of kiss-roll force extracted separately by the kiss-roll force fluctuation extracting means and the fluctuation components of roll force extracted separately by the roll force fluctuation extracting means, a roll gap command value corresponding to each of the rotation positions for a predetermined period of time after the start of rolling of the metallic material so as to reduce the fluctuations in thickness 21298321 (GHMatters) 26/11/09 -39 of the metallic material being rolled; and a roll gap controlling means which controls a roll gap according to each of the rotation positions based on the roll gap command value computed by the manipulated variable computing means. 5

2. The gauge control system according to claim 1, wherein where the difference in diameter between the top and bottom back-up rolls is smaller than a predetermined threshold value, by separating the roll force detected by the force detector in a predetermined ratio, the roll force fluctuation extracting means extracts the 10 fluctuation component caused by the roll eccentricity of the top work roll and the top back-up roll and the fluctuation component caused by the roll eccentricity of the bottom work roll and the bottom back-up roll of the roll force.

3. The gauge control system according to claim 1, wherein 15 for a predetermined period of time after the start of rolling of the metallic material, the manipulated variable computing means computes the roll gap command value based on a predetermined weighted added value of the fluctuation component of roll force extracted separately by the roll force fluctuation extracting means at the time of rolling of the metallic material; and 20 the fluctuation component of the kiss-roll force extracted separately by the kiss-roll force fluctuation extracting means.

4. The gauge control system according to any one of claims I to 3, and substantially as herein described with reference to the accompanying drawings. 21298321 (GHMatters) 26111M9