EP3031541B1

EP3031541B1 - Control system of tandem rolling mill and control method of tandem rolling mill

Info

Publication number: EP3031541B1
Application number: EP15196195.0A
Authority: EP
Inventors: Masahiro Kayama; Shigetoshi KURIHARA; Masayoshi Tachibana
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 2014-12-05
Filing date: 2015-11-25
Publication date: 2018-02-28
Anticipated expiration: 2035-11-25
Also published as: CN105665449B; JP6438753B2; JP2016107297A; EP3031541A1; CN105665449A

Description

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a control system of a tandem rolling mill and control method of a tandem rolling mill and, more particularly, to a control system of a tandem rolling mill and control method of a tandem rolling mill which are suitable for stabilization of rolling and securing good quality of a strip by, upon calculating a roll position of work rolls of each stand for rolling the strip to a desired thickness prior to full-scale rolling of the strip, adjusting a calculated value of the roll position to an optimized value which allows a target strip thickness to be obtained.

Description of Prior Art

In tandem rolling, a processing procedure is employed in which prior to rolling, the rolling condition of a concerned strip is predicted, a roll position (corresponding to a gap between upper and lower work rolls) and a roll speed are determined, a head end of the strip is controlled and, thereafter, the roll position and the roll speed are gradually corrected to proper values using a strip thickness and a strip tension which are obtained from a detector. Therefore, it is necessary to determine proper values for reference values for the roll position of each rolling stand and the roll speed by prediction calculation. In particular, in hot strip rolling in which strips are batch-rolled one by one, it is required that a head end thickness of the strip is accurately controlled to a target and, in order to stabilize rolling at the time when the head end of the strip is bit into each rolling stand of a finish mill, proper values for reference values for the roll position of the each rolling stand and the roll speed are determined by prediction calculation. The most important aspect is the roll position for obtaining the target strip thickness at a delivery side of a final stand, and the roll position is required to be properly determined. Hereinafter, the roll position indicates a roll position of work rolls.
As related methods of determining a proper value for the roll position, there are following methods. In Japanese Unexamined Patent Application Publication No. 2013-198920 , a method is disclosed in which head end portion thickness charts of rolling results are classified by steel grades and strip thicknesses and memorized, and adjustment of the roll position is performed in such a manner that a length of deviation of thickness from the head end is shortened, from a head end portion thickness chart and a thickness grade, corresponding to a strip to be next rolled, and a strip thickness of this strip.
Moreover, in Japanese Unexamined Patent Application Publication No. 2004-42058 , a method is disclosed in which an inter-stand thickness gauge is provided between stands, and a roll position of a downstream stand (stand after the inter-stand thickness gauge) is corrected according to a target inter-stand strip thickness and a deviation of the inter-stand thickness gauge.
However, the related art has the following problems.
In the method disclosed in Japanese Unexamined Patent Application Publication No. 2013-198920 , actually, the strip thickness charts of the concerned classes are not always similar every time, so that when behavior of the head end of the strip to be next rolled is consequently different from the memorized strip thickness chart, the proper adjustment of the roll position may not be performed. Moreover, there is a problem that processing for storing and collating data will increase a calculation amount.
In the method disclosed in Japanese Unexamined Patent Application Publication No. 2004-42058 , the correction of the roll position requires the inter-stand thickness gauge which is not provided in general hot strip rolling, so that there is a problem that the cost of the system will become expensive and labor for maintenance of the system will be increased.
JP 2004042058 A relates to an intermediate plate thickness gauge that is arranged between a final rolling stand and a first stand in a continuous hot rolling equipment and a finishing plate thickness gauge that is arranged at the outlet side of the final rolling stand.
US 3186200 A relates to an automatic thickness regulator for strip rolling mills.
JP S61 129218 A discloses rolling down devices 9-12, rolling down control devices 23-26, sheet thickness control devices 27-30 and sheet thickness deviation detectors 35-38 are respectively disposed to rolling rolls 1-4 of the respective stands.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a control system of a tandem rolling mill and method, by which it is possible to perform an arithmetic operation of a proper roll position without the provision of any special detector, by means of simple arithmetic operation, and obtain a target strip thickness.
To attain the object, according to the present invention, roll force of each stand is predicted from information about a target strip thickness and a chemical composition of a coil to be next rolled that is obtained from a host computer, a roll position of each stand is predicted using an inter-stand strip thickness calculation section predicting a strip thickness between stands and rolling results captured from a controlled object in addition to a control reference setup section calculating control references for a roll position and a roll speed, a roll position deviation calculation section calculating a deviation between the predicted roll position and an actual roll position, a strip thickness deviation calculation section calculating a deviation between a target strip thickness, at a finish mill delivery side that is fetched from the control reference setup section, and an actual strip thickness obtained as a rolling result, and a roll position compensation amount calculation section calculating a roll position compensation amount from a roll position deviation and a strip thickness deviation are provided, and the control reference setup section is configured to calculate the roll position using the calculated roll position compensation amount.
More particularly, the roll position compensation amount calculation section calculates a deviation between a calculation result obtained by assigned the rolling result to a roll position calculation formula, as a roll position prediction error. By addition and subtraction of the roll position prediction error with respect to next roll position calculating result, a roll position of a few error can be calculated with respect to the next coil. The strip thickness deviation calculation section calculates an error from a target strip thickness for a strip thickness at a finish mill final stand delivery side which is obtained as a result of the strip thickness control. When the strip thickness error is large, in next rolling, the roll position is compensated in the direction that the error is reduced, whereby a strip thickness error of the next coil can be reduced. In the roll position compensation amount calculation section, by addition of the roll position deviation and the strip thickness deviation with suitable significance, an error of the roll position calculation formula can be reduced while considering the reduction in the strip thickness deviation. The control reference setup section compensates the roll position of each stand, that is calculated on the basis of a rolling theory, by the roll position compensation amount that is fetched from the roll position compensation amount calculation section, and calculates a final roll position reference, whereby strip thickness accuracy at the finish mill delivery side is enhanced.
According to the present invention, it is possible to perform an arithmetic operation of a proper roll position without the provision of any special detector, by means of simple arithmetic operation, and enhance strip thickness accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is an explanation view showing a configuration of a control system of a tandem rolling mill according to the present invention;
Fig. 2 is a view showing a processing procedure in a control reference setup section 101;
Fig. 3 is a view showing a configuration of a draft schedule memory section 102;
Fig. 4 is a view showing a configuration of a speed pattern memory section 103;
Fig. 5 is a view showing a processing procedure in an inter-stand strip thickness calculation section 111;
Fig. 6 is a view showing a processing procedure in a roll position deviation calculation section 112;
Fig. 7 is a view showing a processing procedure in a strip thickness deviation calculation section 113;
Fig. 8 is a view showing a processing procedure in a roll position compensation amount calculation section 115;
Fig. 9 is a view showing a configuration of a roll position compensation amount calculation gain memory section 114;
Fig. 10 is a view showing a configuration of a roll position compensation amount memory section 116;
Fig. 11 is an explanation view showing a configuration of a control system of a tandem rolling mill according to a second embodiment of the present invention;
Fig. 12 is a view showing a processing procedure in a strip similarity calculation section 1102; and
Fig. 13 is a view showing a processing procedure in a strip class memory section 1101.

DETAILED DESCRIPTION OF THE INVENTION

When a roll position of each stand for rolling a strip into a desired thickness prior to regular rolling of the strip is calculated in a finish stand of a hot rolling mill and a cold tandem mill, it is possible to calculate the roll positon, that enhances strip thickness accuracy, with a simple operation. As a result, a strip whose head end thickness has high accuracy can be obtained and tandem rolling can be stabilized. Moreover, in the finish stand of the hot rolling mill, head end passing (roll biting processing of the strip with respect to each stand) becomes smooth and quality failure can be reduced.
Fig. 1 shows an embodiment of the present invention. In this embodiment, an example in a case where a control system of a tandem rolling mill is a control system of a hot strip tandem rolling mill is shown. Operations of respective calculation sections of this embodiment and processing shown in flow charts can be executed specifically by a computer. The control system 100 of the tandem rolling mill receives various signals from a control object 150 and outputs a control signal to the control object 150. First of all, a configuration of the control object 150 is explained. The control object 150 in this embodiment is a hot strip tandem rolling mill that is provided with a finish mill 160. The finish mill 160 in the illustrated embodiment is composed of a plurality of rolling stands. In this embodiment, a configuration in which seven rolling stands 161 are continuously arranged is employed. In Fig. 1, a strip 163 is moved from the left to the right, and a roughing bar 165 whose thickness is approximately 30 mm is rolled by a roughing mill that is a previous station, whereby a thin strip 163 is produced. In some cases, the roughing bar 165 is called an incoming bar, a transfer bar, etc. In the finish mill 160, the roughing bar 165 is sequentially processed thin by rolling in the respective rolling stands 161 and finally discharged as a strip 163, having a thickness of approximately 1 mm to 15 mm, at a delivery side of F7 that is a final rolling stand. In the finish mill 160, work rolls 162 with which the respective rolling stands 161 are provided directly roll the roughing bar 165 and the strip 163. According to the present invention, a roll speed means a peripheral speed of the work roll 162. In this embodiment, a multi-gauge 164 that measures the thickness, width and temperature of the strip 163 is provided at the delivery side of the final rolling stand (F7) of the finish mill 160. Though omitted in this embodiment, in fact, various detectors that includes a thermometer, a shapemeter measuring the flatness of the strip, a crop profile gauge measuring images of head and tail end shapes of the roughing bar 165, surface inspection equipment detecting a surface flaw of the strip 163, etc. are provided at respective sections as detectors for detecting states of the roughing bar 165 and strip 163, as needed.
Next, a configuration of the control system 100 of the tandem rolling mill is explained. The control system 100 of the tandem rolling mill includes a control reference setup section 101 that receives, from a host computer 50, information including a steel grade, a target strip thickness, a target width, etc. that are required for rolling of each strip to be rolled, and refers to a draft schedule memory section 102 and a speed pattern memory section 103 to calculate a roll force, a roll position of the work roll 162, a roll speed of the work roll 162, etc. with respect to each rolling stand 161, a result collection section 110 that collects a rolling result from the control object 150, a control reference value which the control system 100 of the rolling mill actually outputs to the control object, an inter-stand strip thickness calculation section 111 that predicts strip thicknesses among the stands (hereinafter referred to as inter-stand (strip) thicknesses) using data which the result collection section 110 collects, a roll position deviation calculation section 112 that calculates a deviation between an predicted value of the roll position, that is calculated using entry and delivery thicknesses predicted in the inter-stand strip thickness calculation section 111 and the roll force of each rolling stand 161 that is captured from the result collection section 110, and a roll position actual-value of each rolling stand 161 that is captured from the result collection section 110, a strip thickness deviation calculation section 113 that calculates an incremental difference between a target strip thickness of the F7 delivery, that is captured from the control reference setup section 101, and an actual strip thickness of the F7 delivery that is captured from the result collection section 110, and a roll position compensation amount calculation section 115 that calculates a compensation amount of the roll position of each rolling stand 161 by calculation using the deviation of the roll position of each rolling stand 161, that is captured from the roll position deviation calculation section, and the strip thickness deviation that is captured from the strip thickness deviation calculation section 113, and outputs the compensation amount to the control reference setup section 101.
Hereinafter, the operation of each section will be explained in detail. In Fig. 2, a processing procedure which the control reference setup section 101 performs is shown. The control reference setup section 101 receives information, including the steel grade, the target strip thickness, the target strip width, etc. that are required for rolling, from the host computer 50 and, thereafter, calculates a control reference including the roll position, the roll speed, etc. with respect to the strip to be rolled, from the information. When the strip 163 is rolled in the finish mill 160, the head end of the strip 163 is rolled according to the control reference which the control reference setup section 101 outputs, so that in order to obtain a desired strip thickness from the head end, the roll force in each stand and the roll position of the work roll 162 are required to be suitable and, in order to stabilize behavior when the strip roll-bites into a downstream stand, the roll speed of each stand is required to be a reference that is balanced without any disturbance of a mass flow of the strip 163 (the product of the strip thickness and a strip speed).
First of all, in S2-1, a draft schedule that is information corresponding to how thin the roughing bar 165 and the strip 163 should be formed is captured from a corresponding item of the draft schedule memory section 102.
In Fig. 3, a configuration example of the draft schedule memory section 102 is shown. In the illustrative example, the draft schedule memory section 102 stores a difference in percent between the strip thicknesses of the entry and delivery relative to the entry strip thickness in rolling in each rolling stand 161. Respective draft schedules are classified by the steel grades, strip thicknesses and strip widths of strip to be rolled. The difference between the strip thicknesses of the entry and delivery relative to the entry strip thickness is called a draft. For example, a 35 mm roughing bar 165 whose steel grade is SS400, whose target strip thickness is 2.5 mm, and whose target strip width is 900 mm is considered. A class in which the target strip thickness is 2.0 to 3.0 mm, and the target strip width is equal to or less than 1000 mm corresponds to this. Fig. 3 shows that the 35 mm roughing bar 165 is rolled by 14 mm corresponding to 40% on an F1 entry side to obtain an F1 delivery strip thickness of 21 mm. In F2, an entry strip thickness of 21 mm that is rolled at a draft of 35% to obtain an F2 delivery strip thickness of 13.65 mm is shown. A deviation which is produced between the F7 delivery strip thickness obtained in this way and the target strip thickness of 2.5 mm can be eliminated by compensating the draft of each stand according to the draft. In this way, in S2-1, the control reference setup section 101 searches a corresponding class portion of the draft schedule memory section 102 from the steel grade, strip thickness, and strip width of the strip to be next rolled that it receives from the host computer 50, and calculates the draft of each stand in order that the final stand (F7 in this embodiment) delivery strip thickness is also obtained. Next, a speed pattern is fetched from the speed pattern memory section 103, and the roll speed of each rolling stand is calculated in S2-2.
In Fig. 4, a configuration of the speed pattern memory section 103 is shown. A strip speed (initial speed), at the time when the head end of the strip 163 is discharged from the F7 (final rolling stand), with respect to the steel grade, target strip thickness, and target strip width of the strip 163, a subsequent first acceleration rate, a subsequent second acceleration rate, a subsequent regular speed, a deceleration rate at the time when the strip speed is reduced to a final speed at the time when the tail end of the strip 163 is rolled from the regular speed, and the final speed are stored with respect to each class. The control reference setup section 101 determines the steel grade, strip thickness and strip width of the strip 163 and extracts a corresponding speed pattern from the speed pattern memory section 103. This indicates that, for example, when the steel grade is SS400, the strip thickness is 1.2 to 1.4 mm, and the strip width is equal to or less than 1000 mm, an initial speed of 650 mpm, a first acceleration rate of 2 mpm/s, a second acceleration rate of 12 mpm/s, a regular speed of 1100 mpm, a deceleration rate of 6 mpm/s, and a final speed of 700 mpm are set. The initial speed is a speed of the strip 163 at the time when the head end of the strip 163 is discharged from the final rolling stand 161 (F7), the first acceleration rate is an acceleration rate at the time when the strip 163 subsequently increase its speed, the second acceleration rate is an acceleration rate during the strip speed reaches the regular speed after the strip 163 is roll-bit into a down coiler that is post-stage facility, and the deceleration rate is a deceleration rate at the time when the strip reduces its speed to the final speed in order to stably passes through respective stands. Next, a rolling temperature of each stand is calculated in S2-3. The temperatures of the roughing bar 165 and strip 163 are predicted by combining temperature prediction calculations in which a value, detected by a thermometer installed to each section of the control object 150, heat transfer by radiation, heat transfer, heat generation by plastic deformation of the strip due to rolling, roll conduction between rolls, etc. are taken into consideration. Many temperature prediction methods are introduced in thermodynamics literature and, moreover, temperature change in rolling is described in detail in Chapter 6 (Temperature Change in Rolling) of "Theory and Practice of Strip Rolling" (Iron and Steel Institute of Japan), for example, so that detailed explanation of them is omitted. In S2-4, a deformation resistance that is a value corresponding to hardness of the strip to be rolled in each stand is calculated. Methods for finding the deformation resistance are described in various literatures. The method is described in detail in Chapter 7 "Deformation Resistance" of "Theory and Practice of Strip Rolling" (Iron and Steel Institute of Japan ), for example. As a typical calculation formula for the deformation resistance, there may be employed the following formula in which a predicted strip temperature T of the strip at the time of rolling is used. $kf = K ε^{n} {(d ε / dt)}^{m} \exp (A / T),$
where ∈ is defined as a strain, (de/dt) is defined as a strain speed, and K, n, m, and A are defined as constants determined for each of the steel grades ("Theory and Practice of Strip Rolling", 7.54 Formula).
Next, the roll speed of each rolling stand is calculated in S2-5. Since the speed pattern which is captured in S2-2 is the F7 delivery strip speed, a delivery strip speed in each rolling stand is calculated, based on this, as follows. First of all, the delivery strip speed in each rolling stand is calculated (Formula 2). ${Vs}_{i} = {Vs}_{7} \times h_{i} / h_{7},$
where Vsi is a delivery strip speed in the stand, hi is a delivery strip thickness in an i-th stand, and h₇ is a delivery strip thickness in the F7 stand (final rolling stand). Next, using a forward slip, the roll speed of each rolling stand is calculated from the delivery strip speed in each rolling stand. Here, the forward slip is a value that corresponds to a ratio of the peripheral speed of the work roll to the delivery strip speed of the strip to be rolled in the work roll. For example, the forward slip is known to be expressed as follows. $f = F (H, h, R', Kp, tb, tf),$
where H is an entry strip thickness, h is a delivery strip thickness, R' is a deformed roll diameter, Kp is a deformation resistance, tb is an entry tension, and tf is a delivery tension. The details of the forward slip are described in "Theory and Practice of Strip Rolling" (Iron and Steel Institute of Japan) and the like. If the forward slip is used, there is a relationship between the roll speed and the delivery strip thickness (Formula 4). ${Vr}_{i} = {Vs}_{i} / f_{i},$
where Vr_i is a roll speed of the i-th stand, and f_i is a forward slip of the i-th stand. The forward slip is calculated for each rolling stand and the roll speed of each rolling stand is found in S2-6. The details of a roll force prediction formula are described in "Theory and Practice of Strip Rolling" (Iron and Steel Institute of Japan) and the like and expressed as follows (Formula 5), for example. $P = G (w, Kp, Qp, tf, tb, R', H, h, μ),$
where w is a strip width, Kp is the deformation resistance, Qp is a roll pressure function, and µ is a friction coefficient. In general, there is a discrepancy between roll force obtained by the roll force prediction formula and roll force obtained in actual rolling, so that in order to reduce the discrepancy and enhance roll force prediction accuracy, the roll force is actually predicted by multiplying a suitable compensation coefficient with P. The detail of the compensation coefficient will be hereinafter described in connection with a roll position compensation amount memory section 116. Finally, in S2-7, the roll position (roll gap) of the work rolls is calculated. Though a basic portion of the roll position calculation is represented by a relational expression [Formula 6], practically, in order to enhance calculation accuracy, various compensation terms including vender pressure controlling deflection of the roll are added. $S = h - P / K,$
where S is a roll position, P is a roll force, and K is a mill spring constant.
The control reference setup section 101 outputs the roll position and the roll speed, which are calculated as described above, as control references with respect to a strip to be next rolled. A roll position control section 130 performs roll position control in such a manner that the roll position of the work rolls 162 becomes a value as per the control reference, with respect to the control reference of the roll position that is outputted by the control reference setup section 101. Similarly, a speed control section 140 performs speed control in such a manner that the speed of the work rolls 162 becomes a value as per the control reference, with respect to the speed control reference outputted by the control reference setup section 101.
The control reference regarding to a coil to be next rolled is calculated by the control reference setup section 101 prior to rolling, whereas a series of arithmetic operations which are to be performed by the inter-stand strip thickness calculation section 111, the roll position deviation calculation section 112, the strip thickness deviation calculation section 113, and the roll position compensation amount calculation section 115 which are described hereinafter are performed at the time when the rolling is finished, using the rolling result of the rolled strip 163. The rolling that is subjected to the operations is called "concerned rolling", and the strip 163 that is produced by the concerned rolling is called "concerned strip".
In Fig. 5, processing procedures which the inter-stand strip thickness calculation section 111 performs are shown. The inter-stand strip thickness calculation section 111 predicts delivery strip thicknesses t₁ to t₇ in F1 to F7 at the time when the strip 163 is rolled, on the basis of the rolling results. These strip thicknesses are hereinafter referred to as "inter-stand strip thicknesses". Moreover, when a detector that measures the strip thickness of the roughing bar 165 is not provided, estimation of a thickness to of the roughing bar 165 is also performed. In S5-1, the value t₇ of the strip thickness that is measured by the multi-gauge 164 on the delivery side of the final stand (F7) is fetched. On the entry and delivery sides of F7, a so-called constant mass-flow law in which the product of the strip thickness and the strip speed becomes constant is established. In S5-2, an F7 entry strip thickness (=an F6 delivery strip thickness) is predicted according to the constant mass-flow law. That is, t₆ is calculated according to [Formula 7]. $T_{6} = t_{7} \times V_{7} \times (1 + f_{7}) / \{V_{6} x (1 + f_{6})\},$
where t₇ is a measured F7 delivery strip thickness, V₇ is a peripheral speed of an F7 work roll, f₇ is a forward slip of F7, V₆ is a peripheral speed of an F6 work roll, and f₆ is a forward slip of F6. As the forward slips f₆ and f₇, there is used the value which is calculated by the control reference setup section 101 using the value that is calculated by using [Formula 3] prior to rolling of the concerned strip. The forward slip is calculated by estimation using the Formula, so that it is a value including a certain error. On the inter-stand strip thickness predicted using this, an error is also superposed. In S5-3 to S5-8, the same processing as the processing using [Formula 7] is repeated, whereby the entry strip thickness is predicted in the order of F6, F5, F4, F3, F2, and F1. That is, an arithmetic operation in which the strip thickness on the stand entry side is found from each forward slip and the strip thickness on the stand delivery side is performed in order from the downstream rolling stand. Though the example where the delivery strip thicknesses in respective stands are found in order from the downstream rolling stand has been discussed in connection with this embodiment, they may be simultaneously found from a relationship among the delivery strip thickness in F7, the F7 forward slip, the forward slip of each stand, and the roll speed.
In Fig. 6, processing procedures of the roll position deviation calculation section 112 are shown. In S6-1, the entry and delivery strip thicknesses in the concerned stand according to the concerned rolling are fetched from the inter-stand strip thickness calculation section 111. Next, in S6-2, actual values of the roll force and the roll position which are related to the concerned stand with respect to the concerned strip are fetched from the result collection section 110, and the roll position is predicted by [Formula 6], using the actual result of the roll force. The actual values of the roll force and roll position are generally captured at the same position of the head end of the concerned strip. For example, values after the strip is bit into each stand and approximately 2 to 3 mm of the strip is discharged may be collected as the actual results. In S6-3, a roll position deviation (DsO_c)i that is a difference between the actual value of the roll position, that is captured in S6-2, and the roll position calculated in S6-2 is calculated according to [Formula 8]. $(DsO_c) i = (Dsa) i - (Dse) i,$
where (Dsa)i is an actual roll position of i stand with respect to the concerned strip, and (Dse)i is a predicted roll position of i stand with respect to the concerned strip. In S6-4, whether processing for calculating the roll position deviation with respect to all stands is completed is determined and, unless they are finished, the processing in S6-1 to S6-3 is repeated. If the processing for calculating a roll position deviation value with respect to all stands is completed, the processing by the roll position deviation calculation section 112 is ended.
In Fig. 7, processing procedures of the strip thickness deviation calculation section 113 are shown. In S7-1, a target strip thickness is fetched from the control reference setup section 101. In S7-2, the actual strip thickness that is measured by the multi-gauge 164 on the F7 delivery side is fetched from the result collection section 110. In S7-3, a strip thickness deviation (hd)7 is calculated according to [Formula 9]. $(hd) 7 = htarget - ha 7,$
where (hd)7 is a strip thickness deviation on the F7 delivery side, (ha)7 is an actual strip thickness, and htarget is a target strip thickness. As indicated by [Formula 9], the strip thickness deviation is calculated by the difference (hd)7 between the F7 delivery strip thickness detected by the multi-gauge 164 and the target strip thickness.
In Fig. 8, a processing procedure of the roll position compensation amount calculation section 115 is shown. In S8-1, the strip thickness deviation is fetched from the strip thickness deviation calculation section 113. In S8-2, the roll position deviation of the concerned stand is fetched from the roll position deviation calculation section 112. In S8-3, a roll position compensation amount calculation gain is fetched from the roll position compensation amount calculation memory section 114.
In Fig. 9, a configuration of the roll position compensation amount calculation memory section 114 is shown. The roll position compensation amount calculation memory section 114 is composed of a roll position deviation gain and a strip thickness deviation gain. In the example of Fig. 9, they are classified by the steel grade, the strip thickness, and the strip width. For example, Fig. 9 shows that if the steel grade is SS400, the strip thickness 2.0 to 3.0 mm, and the strip width is equal to or less than 1000 mm, 0.5 is stored as the roll position deviation gain and 0.45 is stored as the strip thickness deviation gain. Moreover, Fig. 9 shows that if the steel grade is SS400, the strip thickness is equal to or more than 12.0 mm, and the strip width is equal to or more than 1400 mm, 0.5 is stored as the roll position deviation gain and 0.55 is stored as the strip thickness deviation gain.
In S8-4, the value (Ds0_c)i of the roll position compensation amount that is memorized as the result of the latest rolling is fetched from the roll position compensation amount memory section 116. In Fig. 10, a configuration of the roll position compensation amount memory section 116 is shown. In this embodiment, the roll position compensation amount that is memorized in the roll position compensation amount memory section 116 is classified by the steel grade and the strip thickness, and the roll position compensation amount of the concerned class of each stand that has been outputted in response to the past rolling is memorized. Values (Zp_p)i of the roll force compensation amounts regarding the respective stands (F1 to F7) are stored every classes. In Fig. 10, an example in which if the steel grade is SS400, and the strip thickness is equal to or less than 1.6 mm, 0.21, -0.03, 0.14, 0.03, -0.1, 0.18 and 0.31 are stored in order from F1 is illustrated. In S8-5, the roll position compensation amount (Ds0)i is calculated according to [Formula 10], using the values and the gain which are fetched in S8-1 to S8-4, and outputted to the control reference setup section 101. $(Ds 0) i = α \cdot (Ds 0_c) i + (1 - α) \cdot (Ds 0_p) i + β \cdot (hd) i,$
where α is the roll position deviation gain, β is the strip thickness deviation gain, and (Ds0_c)i is a roll position compensation amount of an ith stand that is fetched from the roll position compensation amount memory section 116. α is a coefficient that determines a distribution ratio between the roll position compensation amount, based on the past rolling result stored in the roll position compensation amount memory section 116, and the roll position compensation amount calculated by the rolling result of the strip 163 that is subjected to immediate rolling, and takes the value of 0 to 1. When α is 0, the roll position compensation amount that is calculated by the rolling result of the concerned strip 163 is ignored, and the roll positon compensation amount (Ds0)i of the concerned stand is determined by calculation using the roll position compensation amount based on the past rolling result that is stored in the roll position compensation amount memory section 116. Conversely, when α is 1, the roll positon compensation amount (Ds0)i is calculated using the rolling result of the strip 163 subjected to the immediate rolling, and the roll position compensation amount based on the past rolling result that is stored in the roll position compensation amount memory section 116 is ignored. When 0<a<1.0, they are proportionally divided by a ratio according, to α. For example, when α is 0.5, the roll position compensation amount stored in the roll position compensation amount memory section 116 and the roll position compensation amount calculated by the immediate rolling result are proportionally divided by the same ratio. On the other hand, β is a coefficient corresponding to consideration of the strip thickness deviation at the F7 delivery side to what extent and generally takes the value of 0 to 1. When β is 0, it is indicated that the roll position compensation amount (Ds0)i is calculated without consideration of the strip thickness deviation. Conversely, when β is 1, it is indicated that the value corresponding to the strip thickness deviation is directly added to the roll position compensation amount (Ds0) of each stand. When O<β<1.0, it is indicated that, under the consideration of the strip thickness deviation at a ratio according to β, the roll position of each stand is compensated in the direction that the strip thickness deviation is reduced. Moreover, a third item on the right side becomes a small value when the strip thickness deviation is small. Therefore, when the strip thickness deviation is small, the third item does not affect the calculation result of (Ds0)i, so that the strip thickness can be maintained small and in a proper condition. In S8-6, the roll position compensation amount (Ds0)i of the concerned stand which is calculated by [Formula 10] is stored in the roll position compensation memory section 116. In S8-7, whether the processing with respect to all stands is completed is confirmed and, unless the processing is not completed, the processing S8-2 to S8-6 is repeated. When the processing with respect to all stands is finished, the processing of the roll position compensation amount calculation section 115 in the concerned rolling is finished.
The roll position compensation amount (Ds0)i that has been calculated is used in the control reference setup section 101 as follows. Though in S2-7 of Fig. 2, the roll position is calculated according to the calculation [Formula 6], the calculation of the roll position after the roll position compensation amount is fetched from the roll position compensation calculation section 115 is performed as follows. That is, the roll position in which the target strip thickness is obtained at the F7 delivery side is set in each stand, so that a roll position set value (S)i is calculated by adding the roll position compensation amount (Ds0)i as indicated by [Formula 11]. $(S) i = (h) i - (P) i / (K) i + (Ds 0) i,$
where (S)i is the roll position, (h)i is a strip thickness that becomes a target, (P)i is the roll force, (K)i is the mill spring constant, and "i" is a value corresponding to an i-th stand.
Practically, in order to calculate the roll position with high accuracy, various items that include vender pressure of each stand, a compensation item at the time when the roll force is low roll force, an item corresponding a zero point of the roll position, an item of an oil film thickness only, etc. are added.
In this embodiment, the hot strip tandem rolling finishing mill is employed as the controlled object 150, and the control system of the hot strip tandem rolling mill is employed as the control system 100 of the tandem rolling mill. However, even if the controlled object 150 may be a cold strip tandem rolling mill, the present invention can be directly applied to. Moreover, in this embodiment, the finish mill 160 is composed of seven rolling stands 161. However, in some cases, the tandem mill may be composed of four to six stands. Even in these cases, the present invention can be directly applied to. Moreover, in some cases, the finish mill 160 may be composed of one stand or two stands, and the strip 163 may be produced by reciprocating rolling. Even in these cases, the present invention can be directly applied to by detecting or predicting the strip thicknesses on the entry side and the delivery side.
Fig. 11 illustrates a second embodiment of the present invention in which a function of making the distribution coefficient α, used in [Formula 11], variable according to similarity between strips which are rolled one after another is added. A strip similarity calculation section 1102 fetches similarity numbers regarding the steel grade of the strip, that was subjected to the latest rolling, and the steel grade of the strip, that is next rolled, from a strip class memory section 1101, and outputs them to a distribution coefficient calculation section 1103. The distribution coefficient calculation section 1103 calculates a proper value for the distribution coefficient α, based on the similarity, between the strips rolled one after another, which it receives from the strip similarity calculation section 1102, and outputs the proper value to the roll position compensation amount calculation section 115. In S8-5 processing, the roll position compensation amount calculation section 115 performs the calculation of [Formula 10] using α which it receives from the distribution coefficient calculation section 1103.
In Fig. 12, a processing procedure of the strip similarity calculation section 1102 is illustrated. In S12-1, the strip similarity calculation section 1102 fetches the similarity number regarding the steel grade of the strip subjected to the latest rolling and the similarity number regarding the steel grade of the strip next rolled, from the strip class memory section 1101.
In Fig. 13, a configuration of the strip class memory section 1101 is illustrated. The similarity numbers are defined correspondingly to the respective steel grades.
This means that the closer the similarity numbers are, the further similar properties (deformation resistance and the like) of their steel grades are, and the further away the similarity numbers are, the properties of the steel grades are different. For example, from the strip class memory section 1101, it can be seen that the similarity of SS400 and the similarity of SS490 are 4 and 5, respectively, and they are different from each other in steel grade but they are steel grades having large similarity therebetween. On the other hand, it can be seen that the similarity number of SPHC is 2 and the similarity between SS400 and SPHC is larger than the relation between SS400 and SS490. Moreover, it can be seen that the similarity number of SS400 and the similarity number of DP are considerably different from each other, and they are heterogeneous steel grades. Next, in S12-2, from a difference between similarity numbers Vni, Vnj of two strips, similarity between these strips V is calculated according [Formula 12]. $V = | Vni - Vnj | .$
From [Formula 12], it can be seen that the smaller V is, the larger the similarity is, and the larger V is, the smaller the similarity is. Finally, in S12-3, the similarity V is outputted to the distribution coefficient calculation section 1103. In the distribution coefficient calculation section 1103, the distribution coefficient α is calculated by [Formula 13], for example. $α = 1 - (V / Vc) .$
Incidentally, when Vc < V, V = Vc, and Vc is similarity corresponding to α =0. By [Formula 13], when the similarity is large (when V is small), α becomes a value close to 1 and, when the similarity is small (when V is large), α becomes a value close to 0. Moreover, when V is larger than Vc, α becomes 0. The roll position compensation amount calculation section 115 calculates [Formula 10] using α.
As described above, the present invention can be effectively applied to the setup control of the tandem rolling mill.
Features, components and specific details of the structures of the above-described embodiments may be exchanged or combined to form further embodiments optimized for the respective application. As far as those modifications are apparent for an expert skilled in the art they shall be disclosed implicitly by the above description without specifying explicitly every possible combination.

Claims

A control system (100) of a tandem rolling mill which takes a tandem rolling mill, provided with a plurality of rolling stands (161), as a controlled object, and controls a strip thickness of a strip (163), which is continuously rolled by work rolls (162) provided at each of the rolling stands (161), to a desired value, the control system (100) comprising:
a roll position deviation calculation section (112) predicting a roll position of the work rolls (162) provided at each rolling stand, using a rolling actual value obtained in each of the plurality of rolling stands (161), when the strip is rolled, and calculating a roll position deviation of the work rolls (162) in the each rolling stand, on the basis of the predicted roll position, and the roll position actual value of the work rolls (162) in the each rolling stand that is obtained by the rolling;

a strip thickness deviation calculation section (113) calculating a deviation between a target strip thickness and a strip thickness of the strip detected by a strip thickness measuring section provided at a delivery side of a rolling stand at a final stage of the tandem rolling mill;

a roll position compensation amount calculation section (115) calculating a roll position compensation amount in the each rolling stand from each roll position deviation calculated in the roll position compensation amount calculation section (115), and the strip thickness of the strip that is calculated in the strip thickness deviation calculation section (113); and

a control reference setup section calculating roll positions of the work rolls (162) in the each rolling stand with respect to a strip to be next rolled, compensating the calculated roll positions with the roll position compensation amounts, and calculating roll positions to be set in the each rolling stand.
The control system (100) of the tandem rolling mill according to claim 1, further comprising a roll position compensation amount calculation gain memory section (114) memorizing a roll position deviation gain, that is a constant equal to or more than 0, or equal to or less than 1, that indicates significance of the roll position deviations, a strip thickness deviation gain, that is a constant equal to or more than 0, or equal or less than 1, that indicates significance of the strip thickness deviations of the strip, correspondingly to at least one of a steel grade, a target strip thickness, and a target strip width; wherein
the roll position compensation amount calculation section (115) obtains the roll position deviation gain and the strip thickness deviation gain that correspond to the steel grade, target strip thickness, and target strip width of the rolled strip, from the roll position compensation amount calculation section (115), and calculates the roll position compensation amounts by addition of a value, in which the roll position deviation and the obtained roll position deviation gain are multiplied, and a value in which the strip thickness deviation of the strip and the obtained strip thickness deviation gain are multiplied.
The control system (100) of the tandem rolling mill according to claim 1 or 2, further comprising a roll position compensation amount memory section (116) memorizing the roll position compensation amount, calculated in previous rolling results, for each rolling stand, correspondingly to a steel grade, a target thickness, and a target width of the strip, wherein
the roll position compensation amount calculation section (116) calculates the roll position compensation amount, to be outputted to the control reference setup section (101), from the roll position deviation calculated by the roll position deviation calculation section (112), the strip thickness deviation calculated by the strip thickness deviation calculation section (113), and the roll position compensation amount calculated in the previous rolling.
The control system (100) of the tandem rolling mill according to at least one of the claims 1 - 3, further comprising an inter-stand strip thickness calculation section (111) in order calculating an inter-stand strip thickness, that is a thickness at an entry side of each of the plurality of rolling stands, toward an upstream from at the rolling stand at the final stage the tandem rolling mill, on the basis of the strip thickness detected by the strip thickness gauge provided at the delivery side of the rolling stand at the final stage of the tandem rolling mill, and a roll speed that is a peripheral speed of the work roll of each of the plurality of rolling stands; wherein
upon calculating the roll position of the work roll in the rolling on the basis of rolling results of the rolled strip, the roll position deviation calculation section (112) predicts the roll position of the work roll of each of the plurality of work rolls using the inter-stand strip thickness calculated by the inter-stand strip thickness calculation section (111).
The control system (100) of the tandem rolling mill according to at least one of claims 1-4, further comprising a similarity number memory section memorizing a similarity number, that become similar values according to a level of similarity of a property of the strip, correspondingly to a steel grade of the strip;
a strip similarity calculation section (1102) obtaining a similarity number of the rolled strip and a similarity number of a strip to be next rolled, from the similarity number memory section, and calculating a difference between the obtained two similarity numbers as a similarity; and
a distribution coefficient calculation section (1103) calculating a distribution coefficient that is a constant equal to or more than 0, or equal to or less than 1, on the basis of the calculated similarity; wherein
the roll position compensation amount calculation section calculates the roll position compensation amount from a value, in which the calculated roll position compensation amount and the roll position compensation amount that is obtained from the roll position compensation amount memory section (116) and calculated in the previous rolling, are divided by the calculated distribution coefficient and added, and the strip thickness deviation calculated by the strip thickness deviation calculation section.
The control system (100) of the tandem rolling mill according to claim 5, wherein the distribution coefficient calculation section (1103) calculates the distribution coefficient in such a manner that the smaller the similarity is, the larger the distribution coefficient becomes, and the larger the similarity is, the smaller the distribution coefficient becomes.
A control method of a tandem rolling mill, comprising:
a roll position deviation calculating step in which a computer, that controls a tandem rolling mill that continuously rolls a strip (163) with a plurality of rolling stands (161), predicts a roll position of a work roll (162) of each rolling stand using a rolling actual value obtained in each of the plurality of rolling stands (161) when the strip is rolled, and calculates a roll position deviation in each rolling stand on the basis of a rolling actual value in each rolling stand that is obtained in the rolling;

a strip thickness deviation calculating step which calculates a deviation between a target strip thickness of the strip (163) and the strip thickness measured at a delivery side of a final rolling stand of the tandem rolling mill;

a roll position compensation amount calculating step which calculates a roll position compensation amount in each rolling stand (161), from the roll position deviation in each rolling stand, that is calculated in the roll position deviation calculating step, and the strip thickness deviation that is calculated in the strip thickness deviation calculating step; and

a control reference setup step which calculates the roll position of the work roll (162) in the each rolling stand (161) with respect to a strip to be next rolled, compensates the roll position of the work roll (162) in the each rolling stand (161), which is calculated, by the roll position compensation amount in the each rolling stand that is calculated in the roll position compensation amount calculating step, and calculates a roll position to be set in the each rolling stand (161), using the compensated roll position.