1. An apparatus (100) for controlling hot rolling tandem mill, a control object (150) of the apparatus being a hot rolling mill (151) having a plurality of rolling stands (152), values of the control object such as a strip thickness of a steel plate rolled continuously by work rolls provided in the rolling stands and a tension of the steel plate between rolling stands being controlled to become desired values by the apparatus, the apparatus (100) for controlling hot rolling tandem mill comprising: a setup unit (101) which calculates and outputs at least a command value of a rolling load of each rolling stand, a command values of a roll gap of each of the work rolls, and a command value of a roll speed of the work roll, as a control command for a strip to be rolled in a predetermined pass; and a speed command compensation unit (109) which compensates the command value of the roll speed output by the setup unit by using a rolling load, a roll gap, and a roll speed at time when a top end part of a strip rolled in a preceding pass which is some pass preceding the predetermined pass was rolled by a predetermined rolling stand, a rolling load, a roll gap, and a roll speed at time when the strip rolled in the preceding pass was rolled at a part other than the top end part by the predetermined stand, or a result of a computation using the rolling load, the roll gap, and the roll speed.

2. The apparatus (100) for controlling hot rolling tandem mill according to claim 1, wherein the speed command compensation unit (109) converts a roll speed of the predetermined stand at time when the strip rolled in a preceding pass which is some pass preceding the predetermined pass was tandem-rolled stably at a part other than the top end part by the stand to a roll speed of the stand at time when the top end is being rolled by the stand, by a computation utilizing that a mass-flow which is a product of a strip speed and a strip thickness is constant, and compensates the command value of the roll speed which is output by the setup unit, by using the converted roll speed.

3. The apparatus (100) for controlling hot rolling tandem mill according to claim 1, wherein the speed command compensation unit (109) converts a roll speed of the stand at time when the strip rolled in a preceding pass which is some pass preceding the predetermined pass was rolled stably by the stand to a roll speed of the stand at time when the top end part was rolled by the stand, by a computation using a rolling load and a load gap at this time and a rolling load and a load gap at time when the front end part was rolled by the stand and utilizing that a mass-flow which is a product of a strip speed and a strip thickness is constant, and compensates the command value of the roll speed which is output by the setup unit, by using the converted roll speed.

4. An apparatus (100) for controlling hot rolling tandem mill, a control object (150) of the apparatus being a hot rolling mill (151) having a plurality of rolling stands (152), values of the control object such as a strip thickness of a steel plate rolled continuously by work rolls provided in the rolling stands and a tension of the steel plate between rolling stands being controlled to become desired values by the apparatus, the apparatus (100) for controlling hot rolling tandem mill comprising: a setup unit (101) which calculates and outputs at least a command value of a rolling load of each rolling stand, a command value of a roll gap of each of the work rolls, and a command value of a roll speed of the work roll, as a control command for a strip to be rolled in a predetermined pass; and a speed command compensation unit (109) which compensates the command value of the roll speed output by the setup unit by using a rolling load, a roll gap, and a roll speed at time when a top end part of a strip rolled in a preceding pass which is some pass preceding the predetermined pass was rolled by a predetermined rolling stand, a rolling load, a roll gap, and a roll speed at time when the strip rolled in the preceding pass was rolled at a part other than the top end part by the predetermined stand, a rolling load, a roll gap, and a roll speed at time when a top end part of a strip rolled in the preceding pass was rolled by a final delivery stand (F7), a rolling load, a roll gap, and a roll speed at time when the strip rolled in the preceding pass was rolled at a part other than the top end part by the final delivery stand, or a result of a computation using the rolling load, the roll gap, and the roll speed.

5. The apparatus (100) which controls hot rolling tandem mill according to claim 1, further comprising: an actual result collection unit (104) which collects control command values which are output by the apparatus (100) for controlling hot rolling tandem mill and detected values sent from the control object; a top end value extraction unit (105) which extracts a rolling load, a roll gap, and a roll speed at time when a determinate length of the strip was rolled by each rolling stand, as values of the top end part; a top end value storage unit (107) which stores the rolling load, the roll gap, and the roll speed of each rolling stand (152) extracted by the top end value extraction unit (105) a stabilized value extraction unit (106) which extracts a rolling load, a roll gap, and a roll speed of each rolling stand (152) at time when a final delivery stand rolled a determinate length of the strip, as values of a stabilized part of the strip; and a stabilized value storage unit (108) which stores the rolling load, the roll gap, and the roll speed of each rolling stand (152) extracted by the stabilized value extraction unit (106), wherein the speed command compensation unit (109) compensates the command value of the roll speed which is output by the setup unit (101), in accordance with a result of computation using the rolling loads, roll gaps and roll speeds stored in the top end value storage unit (107) and the stabilized value storage unit (108) in association with the strip rolled in the preceding pass.

6. The apparatus (100) for controlling hot rolling tandem mill according to claim 1, further comprising a speed command balance unit (110), wherein when some of compensation values of roll speeds of respective stands which are output by the speed command compensation unit (109) exceeds an upper limit value or a lower limit value, the speed command balance unit (110) limits a compensation value 1 of the pertinent stand to the upper limit value or the lower limit value, calculates a compensation value 2, and modifies the compensation values of the respective stands to minimize changes of relative relations among the compensation values of the respective stands.

7. The apparatus (100) for controlling hot rolling tandem mill according to claim 1, further comprising a speed command balance unit (110), wherein when some of compensation values of roll speeds of respective stands which are output by the speed command compensation unit (109) exceeds an upper limit value or a lower limit value, the speed command balance unit (110) limits a compensation value 1 of the pertinent stand to the upper limit value or the lower limit value, calculates a compensation value 2, and minimizes relative changes of the compensation values of the respective stands by dividing the compensation value 2 by the compensation value 1 and multiplying the compensation values of the respective stands by a resultant quotient.

8. A method for controlling hot rolling tandem mill, a control object (150) of the method being a hot rolling mill (151) having a plurality of rolling stands (152), values of the control object such as a strip thickness of a steel plate rolled continuously by work rolls provided in the rolling stands and a tension of the steel plate between rolling stands being controlled to become desired values by the method, the method for controlling hot rolling tandem mill comprising the steps of: calculating at least a command value of a rolling load of each rolling stand, a command value of a roll gap of each of the work rolls, and a command value of a roll speed of the work roll, as a control command for a strip to be rolled in a predetermined pass; and compensating the command value of the roll speed by using a rolling load, a roll gap, and a roll speed at time when a top end part of a strip rolled by a predetermined rolling stand in a preceding pass which is some pass preceding the predetermined pass was rolled, a rolling load, a roll gap, and a roll speed at time when the strip rolled in the preceding pass was rolled at a part other than the top end part by the predetermined stand, or a result of a computation using the rolling load, the roll gap, and the roll speed, and thereby calculating a new command value of the roll speed.

9. The method for controlling hot rolling tandem mill according to claim 8, comprising the steps of: converting a roll speed of each stand at time when the strip rolled in a preceding pass which is some pass preceding the predetermined pass was tandem-rolled stably at a part other than the top end part by the stand to a roll speed of the stand at time when the top end is being rolled by the stand, by a computation utilizing that a mass-flow which is a product of a strip speed and a strip thickness is constant; and compensating the command value of the roll speed calculated for the strip to be rolled in the pass or subsequent passes on the basis of the converted roll speed and the command value of the roll speed for the strip rolled in the preceding pass, and thereby calculating a new command value of the roll speed.

10. The method for controlling hot rolling tandem mill according to claim 8, comprising the steps of: calculating at least a command value of a rolling load of each rolling stand, a command value of a roll gap of the work roll, and a command value of a roll speed of the work roll, as a control command for a strip to be rolled in the predetermined pass; converting a roll speed of each stand at time when the strip rolled in a preceding pass which is some pass preceding the predetermined pass was tandem-rolled stably by the stand to a roll speed of the stand at time when the top end was rolled by the stand, by a computation using a rolling load and a load gap at this time and a rolling load and a load gap at time when the front end part of the strip was rolled by the stand and utilizing that a mass-flow is constant; and compensating the command value of the roll speed calculated for the predetermined steel plate to be rolled, by using the converted roll speed and the command value of the roll speed for the steel plate rolled in the preceding pass, and thereby calculating a new command value of the roll speed.

11. The method for controlling hot rolling tandem mill according to claim 8, comprising the steps of: calculating at least a command value of a rolling load of each rolling stand, a command value of a roll gap of the work roll, and a command value of a roll speed of the work roll, as a control command for a strip to be rolled in the predetermined pass; taking in a rolling load, a roll gap, and a roll speed at time when a top end part of a strip rolled in a preceding pass was rolled by the rolling stand, a rolling load, a roll gap, and a roll speed at time when the strip rolled in the preceding pass was rolled stably by the stand, a rolling load, a roll gap, and a roll speed at time when a top end part of a strip rolled in the preceding pass was rolled by a final delivery stand (F7), a rolling load, a roll gap, and a roll speed at time when the strip rolled in the preceding pass was tandem-rolled stably by the final delivery stand; and compensating the command value of the roll speed calculated for the steel plate to be rolled in the predetermined pass, by using a result of computation using the rolling loads, the roll gaps, and the roll speeds taken in, and thereby calculating a new command value of the roll speed.

BACKGROUND OF THE INVENTION
The present invention relates to an apparatus and a method for controlling a hot rolling tandem mill. In particular, the present invention relates to an apparatus and a technique for controlling a hot rolling tandem mill suitable for stabilizing rolling immediately after the top end of a strip is bitten into a stand and obtaining a fine strip quality by controlling a mass-flow (a product of a strip thickness and a strip speed) between rolling stands with high precision.
In the technique field of hot rolling, the so-called rolling tandem mill in which a plurality of rolling stands are provided and high temperature strips are worked in order by the plurality of rolling stands is used.
If the strip speed is fast as compared with the roll speed of a downstream stand when the top end of the strip is bitten into the stand, then the strip slackens and the rolling becomes unstable. To the contrary, if the strip speed is slow, then the strip is pulled between the stands and generated excessive tension contracts the strip width and the strip thickness and aggravates the strip quality. Therefore, it is necessary to control the roll speeds of respective stands to suitable values and control the strip speed between the stands to make a mass-flow (the product of the strip thickness and the strip speed) constant.
As for a conventional technique for conducting this smoothly, a method of calculating a loop quantity of the strip between the stands on the basis of a signal from a strip thickness gauge attached between the stands, a looper angle, rolling loads, roll gaps, and roll speeds of upstream and downstream stands and compensating a roll speed of the downstream stand on the basis of the calculated loop quantity is described in, for example, JP-A-2007-185703.
Furthermore, for example, in JP-A-6-335719, a method of actually measuring or predicting a delivery strip thickness of a downstream stand and compensating a main machine speed (work roll speed) of an upstream stand before the strip is bitten into a downstream stand, in order to improve a response of compensation is described.

SUMMARY OF THE INVENTION
However, theses conventional techniques have problems described below. In the hot rolling mill, the strip thickness gauge is typically provided only in the delivery side of a final stand. In the technique according to JP-A-2007-185703, it is necessary, in addition, to install a strip thickness gauge, and interconnections and a gauge panel required for the strip thickness gauge, between the stands, resulting in a problem that the system becomes expensive and maintenance and periodical calibration of the strip thickness gauge are needed. Furthermore, this technique is effective to only between stands having a strip thickness gauge, and consequently there is a former problem that the mass-flow crumbles between stands having no strip thickness gauge. It is not realistic from the viewpoint of the cost and maintenance to provide strip thickness gauges between a larger number of stands, resulting in a problem.
In the technique in JP-A-6-335719, there is a problem that installation of a strip thickness gauge is needed in the same way in the case where a delivery strip thickness of a downstream stand is actually measured. Furthermore, in the case where prediction is conducted, there is a problem that the precision of control is aggravated depending upon a prediction error.
Therefore, an object of the present invention is to provide an apparatus and a method for controlling a hot rolling tandem mill capable of stabilizing rolling immediately after the top end of the strip is bitten into a stand without largely depending upon a strip thickness prediction precision between stands even if a strip thickness gauge is not installed between stands, and providing a steel plate of good quality.
In order to achieve the object, the present invention provides an apparatus for controlling hot rolling tandem mill, a control object of the apparatus being a hot rolling mill having a plurality of rolling stands, values of the control object such as a strip thickness of a steel plate rolled continuously by work rolls provided in the rolling stands and a tension of the steel plate between rolling stands being controlled to become desired values by the apparatus, the apparatus for controlling hot rolling tandem mill including a setup unit for calculating and outputting at least a command value of a rolling load of each rolling stand, a command values of a roll gap of each of the work rolls, and a command value of a roll speed of the work roll, as a control command for a strip to be rolled in a predetermined pass, and a speed command compensation unit for compensating the command value of the roll speed output by the setup unit by using a rolling load, a roll gap, and a roll speed at time when a top end part of a strip rolled in a preceding pass which is some pass preceding the predetermined pass was rolled by a predetermined rolling stand, a rolling load, a roll gap, and a roll speed at time when the strip rolled in the preceding pass was rolled at a part other than the top end part by the predetermined stand, or a result of a computation using the rolling load, the roll gap, and the roll speed.
Or the present invention provides an apparatus for controlling hot rolling tandem mill, a control object of the apparatus being a hot rolling mill having a plurality of rolling stands, values of the control object such as a strip thickness of a steel plate rolled continuously by work rolls provided in the rolling stands and a tension of the steel plate between rolling stands being controlled to become desired values by the apparatus, the apparatus for controlling hot rolling tandem mill including a setup unit for calculating and outputting at least a command value of a rolling load of each rolling stand, a command value of a roll gap of each of the work rolls, and a command value of a roll speed of the work roll, as a control command for a strip to be rolled in a predetermined pass, and a speed command compensation unit for compensating the command value of the roll speed output by the setup unit by using a rolling load, a roll gap, and a roll speed at time when a top end part of a strip rolled in a preceding pass which is some pass preceding the predetermined pass was rolled by a predetermined rolling stand, a rolling load, a roll gap, and a roll speed at time when the strip rolled in the preceding pass was rolled at a part other than the top end part by the predetermined stand, a rolling load, a roll gap, and a roll speed at time when a top end part of a strip rolled in the preceding pass was rolled by a final delivery stand, a rolling load, a roll gap, and a roll speed at time when the strip rolled in the preceding pass was rolled at a part other than the top end part by the final delivery stand, or a result of a computation using the rolling load, the roll gap, and the roll speed.
Or the present invention provides a method for controlling hot rolling tandem mill, a control object of the method being a hot rolling mill having a plurality of rolling stands, values of the control object such as a strip thickness of a steel plate rolled continuously by work rolls provided in the rolling stands and a tension of the steel plate between rolling stands being controlled to become desired values by the method, the method for controlling hot rolling tandem mill including the steps of calculating at least a command value of a rolling load of each rolling stand, a command value of a roll gap of each of the work rolls, and a command value of a roll speed of the work roll, as a control command for a strip to be rolled in a predetermined pass, and compensating the command value of the roll speed by using a rolling load, a roll gap, and a roll speed at time when a top end part of a strip rolled by a predetermined rolling stand in a preceding pass which is some pass preceding the predetermined pass was rolled, a rolling load, a roll gap, and a roll speed at time when the strip rolled in the preceding pass was rolled at a part other than the top end part by the predetermined stand, or a result of a computation using the rolling load, the roll gap, and the roll speed, and thereby calculating a new command value of the roll speed.
(Technical Effect)
According to the present invention, roll speeds of respective stands are controlled in a hot rolling tandem mill to keep the mass-flow between stands constant with reference to, for example, a stabilization state of a strip rolled the last time, and as a result, rolling of the top end of the strip can be stabilized and a strip of a high quality can be produced.

BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an explanation diagram showing a configuration of a control apparatus for a hot rolling tandem mill according to the present invention;
FIG. 2 shows processing executed by a setup unit 101;
FIG. 3 shows a configuration of a draft schedule table 102;
FIG. 4 shows a configuration of a speed pattern table 103;
FIG. 5 shows processing conducted by a top end value extraction unit 105;
FIG. 6 shows processing conducted by a stabilized value extraction unit 106;
FIG. 7 shows configurations of a top end value storage unit 107 and a stabilized value storage unit 108;
FIG. 8 shows processing conducted by a speed command compensation unit 109;
FIG. 9 is a schematic diagram for explaining the processing conducted by the speed command compensation unit 109;
FIG. 10 shows processing conducted by a speed command balance unit 110; and
FIG. 11 is a schematic diagram for explaining the processing conducted by the speed command balance unit 110.

DESCRIPTION OF THE EMBODIMENTS
Hereafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows an embodiment of the present invention. A control apparatus 100 for hot rolling tandem mill includes, for example, a single or a plurality of computers and their input/output devices. The control apparatus 100 receives various signals from a control object 150 and outputs control signals to the control object 150. First, a configuration of the control object 150 will be described. A function of “--- unit” is mounted as software or an input/output circuit in the single computer or the plurality of distributed computers. In the present embodiment, the control object 150 is a hot rolling tandem mill including a plurality of stands. In the example shown in FIG. 1, a mill 151 has a configuration in which seven rolling stands 152 are disposed consecutively. In FIG. 1, a steel plate moves from the left to the right. A roughing bar 161 having a thickness of approximately 30 mm produced by a roughing-down mill in a preceding process is worked to become thinner successively by rolling in respective rolling stands 152 in the mill 151, and finally threaded as a steel plate 160 having a thickness in the range of 1 to 10 mm on a delivery side of F7. A device which directly rolls the roughing bar 161 and the steel plate 160 is a work roll 153. In the present invention, a term “roll speed” means a circumference speed of the work roll 153. In the present embodiment, a strip thickness gauge 154 is provided on a delivery side of the final rolling stand (F7) in the mill 151 to measure the strip thickness of the steel plate 160.
A configuration of the control apparatus 100 for the hot rolling tandem mill will now be described. The control apparatus 100 for the hot rolling tandem mill includes a setup unit 101 for receiving information, such as a steel grade, a target strip thickness, and a target strip width, required for rolling from a higher rank computer 50 with respect to each of steel plates to be rolled and calculating a roll gap of the work roll 153, a roll circumference speed (roll speed) of the work roll 153, and a rolling load with respect to each of the rolling stands 152 with reference to a draft schedule table 102 and a speed pattern table 103, an actual result collection unit 104 for collecting actual results of rolling and control command values which are actually output to the control object, a top end value extraction unit 105 for extracting rolling data of a top end part of the steel plate 160 rolled the last time from data collected by the actual result collection unit 104, a top end value storage unit 107 for storing values extracted by the top end value extraction unit 105, a stabilized value extraction unit 106 for extracting a roll speed, a rolling load, and a roll gap of each rolling stand 152 after rolling of the steel plate 160 has reached a stabilized state, a stabilized value storage unit 108 for storing values extracted by the stabilized value extraction unit 106, a speed command compensation unit 109 for taking in contents of the top end value storage unit 107 and the stabilized value storage unit 108 and compensating the roll speed calculated by the setup unit 101 with respect to a steel plate to be rolled next time, a speed command balance unit 110 for taking in an output of the speed command compensation unit 109 and limiting speed compensation quantities for respective rolling stands 152 to a range between upper and lower limits with due regard to balances between rolling stands, a speed control unit 111 for exercising speed control in response to a final roll speed command, and a roll gap control unit 112 for controlling an actual roll gap by using a signal such as a difference (strip thickness deviation) between an actual strip thickness and the target strip thickness measured by the strip thickness gauge 154, in response to a roll gap command which is output by the setup unit 101.
Hereafter, operations of the respective units will be described. FIG. 2 shows processing executed by the setup unit 101. The setup unit 101 receives information, such as a steel grade, a target strip thickness, and a target strip width, required for rolling from the higher rank computer 50, and then calculates a control command for a steel plate to be rolled thereafter. The top end of the strip is rolled in accordance with the control command which is output by the setup unit 101. For stabilizing the behavior taken when the strip is bitten into a downstream stand, therefore, a well-balanced command is needed to prevent roll speeds of respective stands from disturbing the mass-flow of the steel plate 160. First, at S2-1, a draft schedule which is information corresponding to how thin the roughing bar 161 and the steel plate 160 are to be made in each of the rolling stands 152 is taken in from an corresponding item in the draft schedule table 102.
FIG. 3 shows a configuration example of the draft schedule table 102. In the example shown in FIG. 3, the draft schedule stores a value rolled by each rolling stand 152 with respect to a thickness difference between the roughing bar 161 and the steel plate 160, by using a percentage to the thickness difference. Respective draft schedules are classified according to the steel grade, the strip thickness, and the strip width of a steel plate to be rolled. For example, it is supposed that a roughing bar 161 of 35 mm is SS400 in steel grade, 2.5 mm in target strip thickness, and 900 mm in target strip width. The roughing bar 161 corresponds to a class which is in the range of 2.0 to 3.0 mm in target strip thickness and 1,000 mm or below in target strip width. The roughing bar 161 of 35 mm is rolled to become a steel plate 160 of 2.5 mm. With respect to a strip thickness difference of 32.5 mm, it is shown in FIG. 3 that its 24% is rolled at F1 and its 16% is rolled at F2. In other words, at F1,
[Expression 1]
32.5 mm * 24/100 = 7.8 mm,
and consequently it is shown that the roughing bar of 35 mm should be rolled to 27.2 mm (= 35 mm – 7.8 mm). In the same way,
[Expression 2]
32.5 mm * 16/100 = 5.2 mm,
and consequently it is shown that the strip of 27.2 mm should be rolled to 22.0 mm (= 27.2 mm – 5.2 mm) at F2. With respect to a certain class, the total sum of numerical values of the rolling stands in the draft schedule is 100. By repeating similar calculation procedures, the strip thickness on the delivery side of F7 (the final stand) becomes 2.5 mm which is the target strip thickness. In this way, the setup unit 101 retrieves a pertinent class place in the draft schedule table 102 on the basis of the steel grade, strip thickness, and strip width of a steel plate to be rolled next time received from the higher rank computer 50, and takes in rolling quantities of respective rolling stands, at S2-1. Then, the setup unit 101 takes in a speed pattern from the speed pattern table 103 and calculates roll speeds of respective rolling stands, at S2-2.
FIG. 4 shows a configuration of the speed pattern table 103. With respect to the steel grade, target strip thickness, and target strip width of the steel plate 160, a speed (initial speed) at the time when the top end of the strip 160 is threaded from the F (the final rolling stand), then a first acceleration, a second acceleration, a maximum speed, a deceleration at the time when conducting deceleration from the maximum speed to a final speed at the time when rolling the tail end of the steel plate 160, and the final speed are stored for each class. The setup unit 101 judges the steel grade, strip thickness, and strip width of the steel plate 160, and extracts a corresponding speed pattern from the speed pattern table 103. For example, it is shown that an initial speed of 650 mpm, a first acceleration of 2 mpm/s, a second acceleration of 12 mpm/s, a maximum speed of 1,100 mpm, a deceleration of 6 mpm/s, and a final speed of 900 mpm are set, when the steel grade is SS400, the strip thickness is in the range of 2.0 to 3.0 mm, and the strip width is 1,000 mm or less. Then, at S2-3, the setup unit 101 presumes the rolling temperature. Temperatures of the roughing bar 161 and the steel plate 160 are presumed by combining values detected by a pyrometer with a temperature prediction calculation with due regard to heat radiation and heat transfer. A large number of temperature presumption methods are introduced in documents of thermodynamics. In addition, the temperature change in rolling is described in detail in, for example, the sixth chapter “Temperature change in rolling” in “Theory and practice of plate rolling (The Iron and Steel Institute of Japan). Therefore, detailed description of the temperature change in rolling will be omitted. At S2-4, the setup unit 101 calculates deformation resistance which is a value corresponding to hardness of a strip rolled at each rolling stand. The deformation resistance is described in various documents. For example, the deformation resistance is described in detail in the seventh chapter “Deformation resistance” in “Theory and practice of plate rolling (The Iron and Steel Institute of Japan).” Using a presumed strip plate temperature T at the time of rolling, a representative calculation formula of the deformation resistance is given by
[Expression 3]
kf = Ken(de/dt)mexp(A/T)
e: strain
(de/dt): a strain speed
K, n, m and A: constants depending upon every steel grade
(formula 7.54 in “Theory and practice of plate rolling.”)
Then, at S2-5, the setup unit 101 calculates a roll speed of each rolling stand. Since the speed pattern taken in at S2-2 is a delivery strip speed of F7, a roll speed of each rolling stand is calculated from this as described hereafter. First, the delivery strip speed of each rolling stand is calculated according to [Expression 4].
[Expression 4]
Vsi = Vs7 * hi/h7
Vsi: a delivery strip speed of the i th stand
hi: a delivery strip thickness of the i th stand
h7: a delivery strip thickness of the seventh stand (final rolling stand)
Then, the roll speed of each rolling stand is calculated from the delivery strip speed of each rolling stand by using a forward slip. The forward slip is a ratio of the delivery strip speed to the roll speed, and there is a relation represented by [Expression 5] among them.
[Expression 5]
Vri = Vsi / fi
Vri: a roll speed of the i th stand
fi: a forward slip of the i th stand
The forward slip is described in the same way in the second chapter “Two-dimensional rolling theory” in “Theory and practice of plate rolling.” And it is widely known that the forward slip is represented by a relational expression as represented by, for example, [Expression 6].
[Expression 6]
f = g1 (H, h, R’, tb, tf, kf)
f: a forward slip
H: an entry strip thickness of a rolling stand
h: a delivery strip thickness of the rolling stand
R’: a deformed roll diameter
tb: a backward tension of a steel plate
tf: a forward tension of the steel plate
kf: deformation resistance
[Expression 5] is calculated every rolling stand, and the roll speed of each rolling stand is found.
In addition, the rolling load is calculated at S2-6. The rolling load is also described in the same way in the second chapter “Two-dimensional rolling theory” in “Theory and practice of plate rolling.” The rolling load increases in value as the deformation resistance increases, as the entry strip thickness increases, and as the delivery strip thickness decreases. The rolling load is represented by the following relational expression.
[Expression 7]
p = g2 (H, h, R’, tb, tf, kf, Qp, Qs)
p: a rolling load
Qp: a peening function
Qs: a roll force function
In addition, the roll gap of the work roll 153 is calculated at S2-7. A basic part of the roll gap calculation is represented by a relation expression [Expression 8]. As a matter of fact, various compensation items are added to improve the calculation precision.
[Expression 8]
S = h – p/K
S: the roll gap
p: the rolling load
K: a mill modulus constant
The setup unit 101 outputs the roll speed and the roll gap calculated as described above with respect to a steel plate to be rolled next time.
FIG. 5 shows processing conducted by the top end value extraction unit 105. The actual result collection unit 104 collects actual result data, such as rolling information and a steel plate temperature sent from the control object 150 and command values which are output to the control object 150 by the hot rolling tandem mill control apparatus 100, periodically or in association with a constant length of the steel plate. The top end value extraction unit 105 takes in values of the roll gap, rolling load, and roll speed at the time when the top end of the strip 160 was rolled, from among such outputs of the actual result collection unit 104 every rolling stand. In the present embodiment, actual result values are taken in as for the roll gap and rolling load, and set values which are output by the speed control unit 111 are taken in as for the roll speed. At S5-1, a decision is made whether a delivery thickness (rolling length) of the steel plate 160 in each rolling stand has reached a determinate length. The rolling length is typically contained in a signal taken in from the control object 150, and calculated by integrating the speed of the steel plate 160 which is presumed from the roll speed of each rolling stand by using the forward slip according to the relation in [Expression 5]. In the present embodiment, extraction of data of a top end part is conducted by paying attention to the rolling length. If it is judged at S5-1 that the delivery thickness of the steel plate 160 has not reached the determinate length, the processing at S5-1 is repeated. If it is judged at S5-1 that the delivery thickness has reached the determinate length, the roll speed, the roll gap and the rolling load of the pertinent rolling stand are taken in from the actual result collection unit 104 at S5-2. A decision is made at S5-3 whether the processing is finished for all rolling stands. If not finished, the processing at S5-1 to S5-2 is repeated for rolling stands which are not finished in processing. At time when taking in the roll speed, of the top end of the strip is finished for all rolling stands, the processing for the steel plate 160 conducted by the top end value extraction unit 105 is finished.
FIG. 6 shows processing conducted by the stabilized value extraction unit 106. The stabilized value extraction unit 106 takes in values of the roll gap, the rolling load and the roll speed of the respective rolling stands at the same time point when the rolling has reached the stabilized state, from among the outputs of the actual result collection unit 104. At S6-1, a decision is made whether the delivery thickness (rolling length) at F7 of the steel plate 160 has reached a determinate length. The rolling length is typically contained in the signal taken in from the control object 150, and calculated by integrating the speed of the steel plate 160 which is presumed from the roll speed of F7 by using the forward slip according to the relation in [Expression 5]. When the rolling length of F7 is small, the rolling is in a transient state immediately after biting the steel plate 160. If the rolling length becomes large, the rolling is stabilized. In view of this, the stability of the rolling is judged by paying attention to the rolling length and stabilized data is extracted, in the present embodiment. If it is judged at S6-1 that the delivery thickness at F7 of the steel plate 160 has not reached a determinate length, the processing at S6-1 is repeated. If it is judged at S6-1 that the delivery thickness at F7 of the steel plate 160 has reached the determinate length, the roll speeds, the roll gaps and the rolling loads of the respective rolling stands are taken in simultaneously from the actual result collection unit 104 at S6-2.
FIG. 7 shows configurations of the top end value storage unit 107 and the stabilized value storage unit 108. The top end value storage unit 107 stores values of the roll gap, the rolling load, and the roll speed which are extracted and output by the end value extraction unit 105 to correspond to the time when each rolling stand has rolled the top end of the strip. For example, it is stored that the roll gap of F1 was 30.40 mm, the rolling load of F1 was 2,364 tons, and the roll speed of F1 was 27 mpm. The stabilized value storage unit 108 stores values of the roll gap, the rolling load, and the roll speed of respective rolling stands which are output by the stabilized value extraction unit 106 to correspond to the time when rolling has reached the stabilized state. For example, it is stored that the roll gap of F1 was 29.78 mm, the rolling load of F1 was 2,380 tons, and the roll speed of F1 was 26.4 mpm.
FIG. 8 shows processing executed by the speed command compensation unit 109. First, at S8-1, the speed command compensation unit 109 takes in the roll gap, the rolling load, and the roll speed of a preceding coil top end part corresponding to each rolling stand from the top end value storage unit 107. Then, at S8-2, the speed command compensation unit 109 takes in the roll gap, the rolling load, and the roll speed of a preceding coil stabilized part corresponding to each rolling stand from the stabilized value storage unit 108. At S8-3, the speed command compensation unit 109 calculates a compensation quantity of a speed command every rolling stand. A method for the calculation will now be described in detail with reference to FIG. 9. FIG. 9 shows behaviors of the top end of the strip and the rolling stand in the stabilized state by taking the j th stand (Fj) as an example. FIG. 9(a) shows a behavior of the top end of the strip. It is shown that the rolling load, the roll gap, and the roll speed immediately after a top end 903 of the strip is rolled are Pact-top, Sact-top and Vset, respectively and the delivery strip thickness of the Fj stand is h. On the other hand, FIG. 9(b) shows a behavior after the rolling has reached a stabilized state. The top end 904 of the strip is located on the delivery side of F7 (final rolling stand), and all rolling stands are conducting the rolling and are in a balanced state. It is shown that the rolling load, the roll gap, and the roll speed at this time are Pact-stab, Sact-stab and Vstab, respectively and the delivery strip thickness of the Fj stand is h. Since the product (mass-flow) of the strip thickness and the strip speed is constant at this time, a proper roll speed of the top end is derived on the basis of the balanced state as in [Expression 9]
[Expression 9]
Vtop_est * (1 + ftop) * (Stop + Ptop/M) = Vstab * (1 + fstab) * (Sstab + Pstab/M)
Vtop_est: a proper roll speed at the time when the top end part of the strip is rolled
ftop: a forward slip at the time when the top end part of the strip is rolled
Stop: a roll gap at the time when the top end part of the strip is rolled
Ptop: a rolling load at the time when the top end part of the strip is rolled
M: a mill constant
Vstab: a roll speed at the time when the stabilized part of the strip is rolled
fstab: a forward slip at the time when the stabilized part of the strip is rolled
Sstab: a roll gap at the time when the stabilized part of the strip is rolled
Pstab: a rolling load at the time when the stabilized part of the strip is rolled
V * (1 + f) corresponds to the strip speed, and (S + P/M) corresponds to the strip thickness.
Supposing that 1 + ftop ˜ 1 + fstab,
[Expression 10]
Vtop_est * (Stop + Ptop/M) = Vstab * (Sstab + Pstab/M)
is obtained. Therefore,
[Expression 11]
Vtop_est = Vstab * (Sstab + Pstab/M) / (Sstab + Pstab/M + Stop - Sstab + (Ptop - Pstab) / M)
= Vstab * h / (h + Stop - Sstab + (Ptop - Pstab) / M)
where Sstab + Pstab/M = h
In the same way, as for F7 (final rolling stand),
[Expression 12]
V7top_est = V7stab * h7 / (h7 + S7top - S7stab + (P7top - P7stab) / M)
is obtained. Furthermore, the final rolling stand is a start point of speed control and the roll speed does not change during the rolling. Therefore,
[Expression 13]
V7stab = V7set
It is also possible to set another stand as the start point of the speed control. A speed compensation coefficient ai of each rolling stand is a ratio of a proper speed command calculated from a roll speed in a balanced rolling state to a speed command which was set for the strip 160 rolled the last time. The proper speed command is found by converting the roll speed in the balanced rolling state to a roll speed at the top end of the strip in accordance with a law that the mass-flow is constant, by using the strip thickness in the balanced rolling state and the strip thickness at the time when the top end of the strip is rolled, every stand. In other words, the proper speed command can be calculated using [Expression 14].
[Expression 14]
ai = (Vi_top_est / Vi_set) * (V7_set / V7_top_est)
= (Vi_act_stab / Vi_set) * hi / {(hi + Si_act_top - Si_act_stab + Pi_act_top - Pi_act_stab) / Mi} * {(h7 + S7_act_top - S7_act_stab + P7_act_top - P7_act_stab) / M7} / h7
Vi_act_stab: a roll speed at the time when the i th stand rolled the stabilized part of the strip
Vi_set: a roll speed set quantity at the time when the i th stand rolled the top end part of the strip
hi: a delivery strip thickness of the i th stand
Si_act_top: a roll gap at the time when the i th stand rolled the top end part of the strip
Si_act_stab: a roll gap at the time when the i th stand rolled the stabilized part of the strip
Pi_act_top: a rolling load at the time when the i th stand rolled the top end part of the strip
Pi_act_stab: a rolling load at the time when the i th stand rolled the stabilized part of the strip
Mi: mill constant of the i th stand
V7_act_stab: a roll speed at the time when the seventh stand rolled the stabilized part of the strip
V7_set: a roll speed set quantity at the time when the seventh stand rolled the top end part of the strip
h7: a delivery strip thickness of the seventh stand
S7_act_top: a roll gap at the time when the seventh stand rolled the top end part of the strip
S7_act_stab: a roll gap at the time when the seventh stand rolled the stabilized part of the strip
P7_act_top: a rolling load at the time when the seventh stand rolled the top end part of the strip
P7_act_stab: a rolling load at the time when the seventh stand rolled the stabilized part of the strip
M7: mill constant of the seventh stand
In other words, a compensation quantity for compensating a roll speed calculated by the setup unit can be calculated from the roll speed, the rolling load and the roll gap at the time when the top end of the strip rolled the last time was rolled and the roll speed, the rolling load and the roll gap after the rolling of the strip reached the stabilized state. Or for simplifying the calculation, it is conceivable to conduct a calculation as follows:
[Expression 15]
ai = (Vi_top_est / Vi_set) * (V7_set / V7_top_est)
= (Vi_act_stab / Vi_set) * hi / {(hi + Si_act_top - Si_act_stab + Pi_act_top - Pi_act_stab) / Mi}
At S8-3, a compensation quantity of the speed command is calculated by such a calculation every rolling stand. By the way, since F7 is a rolling stand which becomes a start point of the speed command, the speed command compensation quantity a7 of F7 (final rolling stand) is 0. At S8-4, a decision is made whether the calculation of the speed compensation quantity has been finished for all rolling stands. Unless finished, the processing at S8-1 to S8-4 is repeated. If the calculation of the speed compensation quantity is finished for all rolling stands, the processing is finished.
FIG. 10 shows processing conducted by the speed command balance unit 110. The speed command balance unit 110 takes in speed command compensation quantities of respective rolling stands which are output by the speed command compensation unit 109. If there is a rolling stand for which a compensation quantity exceeding an upper/lower limit restriction is calculated, then the speed command balance unit 110 limits the compensation quantity to the range between the upper and lower limits and conducts processing of balancing compensation quantities of other rolling stands. At S10-1, a decision is made whether there is a rolling stand for which the speed command compensation quantity has exceeded an upper/lower limit. If there isn’t a rolling stand for which a compensation quantity has exceeded an upper/lower limit, the processing is finished. If there is a rolling stand for which a compensation quantity has exceeded an upper/lower limit, then processing of limiting the speed command compensation quantity of the rolling stand between the upper and lower limits is conducted at S10-2 and subsequent steps. At S10-2, the speed command balance unit 110 identifies a rolling stand for which the absolute value of the speed command compensation quantity is maximum, and calculates a speed compensation balance quantity a0 by dividing the upper/lower limit value aL of the speed command compensation quantity by a maximum value of the absolute value of the speed command compensation quantity.
[Expression 16]
a0 = aL / |amax|
a0: a speed compensation balance quantity
aL: an upper/lower limit value of the speed compensation quantity
amax: a maximum value of absolute value of speed compensation quantity
At S10-3, the speed command balance unit 110 calculates a compensation quantity after the balancing by multiplying the compensation quantity of each rolling stand by a0.
[Expression 17]
ai-b = a0 * ai
ai-b: a speed compensation quantity after being balanced
FIG. 11 schematically shows contents of processing conducted by the speed command balance unit 110. In FIG. 11, owing to a compensation quantity 1101 before balancing, a speed command compensation quantity for the first stand (F1) is maximized and the speed command compensation quantity for the first stand (F1) exceeds an upper limit value together with the speed command compensation quantity for the second stand (F2).
The speed compensation balance quantity a0 is obtained by dividing the upper/lower limit value aL by amax. And a compensation quantity after balancing (a black circle in FIG. 11) is obtained by dividing each speed compensation quantity before balancing (a white circle in FIG. 11) by the speed compensation balance quantity a0.
The roll gap control unit 112 compensates the roll gap command received from the setup unit 101 by reflecting a change of an actual result of the rolling load and a difference between the strip thickness of the actual result detected by the strip thickness gauge 154 and a target strip thickness, and outputs a value obtained after the compensation to the control object 150. The control of the roll gap is called AGC (Automatic Gauge Control), and various techniques such as Bisra AGC, Monitor AGC, and Gauge meter AGC are known. A change of the roll gap causes changes of mass-flow values of the entry strip and the delivery strip. For compensating this, roll speeds of a stand having a changed roll gap and its upstream stands are changed.
The speed control unit 111 uses a value obtained by adding the speed compensation quantity which is output by the roll gap control unit 112 to the speed command which is output by the speed command balance unit 110, as a command value, and exercises speed control of each of the work rolls 153. A speed control system is typically composed of a control system of proportional integration called ASR (Automatic Speed Control).
In the present embodiment, the absolute value of the upper limit of the speed command compensation quantity is set equal to the absolute value of the lower limit of the speed command compensation quantity. Even if the absolute values are different from each other, however, processing can be conducted in a way of similar thinking by defining amax as a ratio of ai to the upper/lower limit value. Furthermore, a configuration in which the speed command balance unit 110 is removed and the speed control unit 111 operates in accordance with a speed command which is output by the speed command compensation unit 109 is also conceivable.
In the present embodiment, stabilized part data is extracted by paying attention to the rolling length. Alternatively, the values of the roll gap, the rolling load, and the roll speed may be directly used. In this case, the stability of the rolling is judged according to whether they do not change in excess of a determinate value, and it is used as a condition for stabilized data extraction.
In FIG. 2, the setup unit 101 starts the calculation from the draft schedule and calculates the rolling load, the roll gap and the roll speed. However, a technique of starting the calculation from the load balance is also known. The present invention can be applied to this case as well in the same way.
In the present invention, the circumference speed of the work roll 153 is set to be the compensation object of the speed command. Even if the rotation speed motor of the main machine motor which drives the work roll or the speed command of the main machine drive is set to be the compensation object, however, equivalent processing can be implemented.
As described heretofore, the top end value storage unit stores values of the roll speed, the rolling load, and the roll gap of each stand at the time when the stand rolled the top end part of a strip rolled the last time. The stabilized value storage unit stores the roll speed, the rolling load, and the roll gap of each stand at the time when rolling for the strip rolled the last time reached a stabilized state. The speed command compensation unit executes computation on a roll speed in a stabilized state in which the mass-flow of each stand becomes nearly constant and the rolling is balanced, to compensate changes in a roll gap from the top end of the strip and the rolling load. In this way, the speed command compensation unit calculates a roll speed which should be calculated with respect to the top end of the strip rolled the last time. And the speed command compensation unit outputs a ratio of this roll speed to the roll speed actually output by the setup unit, as the speed command compensation quantity. The speed command balance unit checks the upper/lower limit of the speed compensation quantity for each stand. When the speed compensation quantity for a certain stand departs from the upper/lower limit, the speed command balance unit conducts processing of limiting the speed compensation quantity to a range between the upper and lower limits while paying attention to compensation balances among the stands.
In setup of a strip to be rolled next time, it is possible to calculate and output a speed command which makes the mass-flow of each stand approximately constant by compensating the roll speed command value calculated by the setup unit, by use of the speed compensation quantity.
The present invention can be applied effectively to setup control of a hot rolling tandem mill.

CLAIMS:CLAIMS:
1. An apparatus (100) for controlling hot rolling tandem mill, a control object (150) of the apparatus being a hot rolling mill (151) having a plurality of rolling stands (152), values of the control object such as a strip thickness of a steel plate rolled continuously by work rolls provided in the rolling stands and a tension of the steel plate between rolling stands being controlled to become desired values by the apparatus, the apparatus (100) for controlling hot rolling tandem mill comprising:
a setup unit (101) which calculates and outputs at least a command value of a rolling load of each rolling stand, a command values of a roll gap of each of the work rolls, and a command value of a roll speed of the work roll, as a control command for a strip to be rolled in a predetermined pass; and
a speed command compensation unit (109) which compensates the command value of the roll speed output by the setup unit by using a rolling load, a roll gap, and a roll speed at time when a top end part of a strip rolled in a preceding pass which is some pass preceding the predetermined pass was rolled by a predetermined rolling stand, a rolling load, a roll gap, and a roll speed at time when the strip rolled in the preceding pass was rolled at a part other than the top end part by the predetermined stand, or a result of a computation using the rolling load, the roll gap, and the roll speed.
2. The apparatus (100) for controlling hot rolling tandem mill according to claim 1, wherein the speed command compensation unit (109) converts a roll speed of the predetermined stand at time when the strip rolled in a preceding pass which is some pass preceding the predetermined pass was tandem-rolled stably at a part other than the top end part by the stand to a roll speed of the stand at time when the top end is being rolled by the stand, by a computation utilizing that a mass-flow which is a product of a strip speed and a strip thickness is constant, and compensates the command value of the roll speed which is output by the setup unit, by using the converted roll speed.
3. The apparatus (100) for controlling hot rolling tandem mill according to claim 1, wherein the speed command compensation unit (109) converts a roll speed of the stand at time when the strip rolled in a preceding pass which is some pass preceding the predetermined pass was rolled stably by the stand to a roll speed of the stand at time when the top end part was rolled by the stand, by a computation using a rolling load and a load gap at this time and a rolling load and a load gap at time when the front end part was rolled by the stand and utilizing that a mass-flow which is a product of a strip speed and a strip thickness is constant, and compensates the command value of the roll speed which is output by the setup unit, by using the converted roll speed.
4. An apparatus (100) for controlling hot rolling tandem mill, a control object (150) of the apparatus being a hot rolling mill (151) having a plurality of rolling stands (152), values of the control object such as a strip thickness of a steel plate rolled continuously by work rolls provided in the rolling stands and a tension of the steel plate between rolling stands being controlled to become desired values by the apparatus, the apparatus (100) for controlling hot rolling tandem mill comprising:
a setup unit (101) which calculates and outputs at least a command value of a rolling load of each rolling stand, a command value of a roll gap of each of the work rolls, and a command value of a roll speed of the work roll, as a control command for a strip to be rolled in a predetermined pass; and
a speed command compensation unit (109) which compensates the command value of the roll speed output by the setup unit by using a rolling load, a roll gap, and a roll speed at time when a top end part of a strip rolled in a preceding pass which is some pass preceding the predetermined pass was rolled by a predetermined rolling stand, a rolling load, a roll gap, and a roll speed at time when the strip rolled in the preceding pass was rolled at a part other than the top end part by the predetermined stand, a rolling load, a roll gap, and a roll speed at time when a top end part of a strip rolled in the preceding pass was rolled by a final delivery stand (F7), a rolling load, a roll gap, and a roll speed at time when the strip rolled in the preceding pass was rolled at a part other than the top end part by the final delivery stand, or a result of a computation using the rolling load, the roll gap, and the roll speed.
5. The apparatus (100) which controls hot rolling tandem mill according to claim 1, further comprising:
an actual result collection unit (104) which collects control command values which are output by the apparatus (100) for controlling hot rolling tandem mill and detected values sent from the control object;
a top end value extraction unit (105) which extracts a rolling load, a roll gap, and a roll speed at time when a determinate length of the strip was rolled by each rolling stand, as values of the top end part;
a top end value storage unit (107) which stores the rolling load, the roll gap, and the roll speed of each rolling stand (152) extracted by the top end value extraction unit (105)
a stabilized value extraction unit (106) which extracts a rolling load, a roll gap, and a roll speed of each rolling stand (152) at time when a final delivery stand rolled a determinate length of the strip, as values of a stabilized part of the strip; and
a stabilized value storage unit (108) which stores the rolling load, the roll gap, and the roll speed of each rolling stand (152) extracted by the stabilized value extraction unit (106),
wherein the speed command compensation unit (109) compensates the command value of the roll speed which is output by the setup unit (101), in accordance with a result of computation using the rolling loads, roll gaps and roll speeds stored in the top end value storage unit (107) and the stabilized value storage unit (108) in association with the strip rolled in the preceding pass.
6. The apparatus (100) for controlling hot rolling tandem mill according to claim 1, further comprising a speed command balance unit (110),
wherein when some of compensation values of roll speeds of respective stands which are output by the speed command compensation unit (109) exceeds an upper limit value or a lower limit value, the speed command balance unit (110) limits a compensation value 1 of the pertinent stand to the upper limit value or the lower limit value, calculates a compensation value 2, and modifies the compensation values of the respective stands to minimize changes of relative relations among the compensation values of the respective stands.
7. The apparatus (100) for controlling hot rolling tandem mill according to claim 1, further comprising a speed command balance unit (110),
wherein when some of compensation values of roll speeds of respective stands which are output by the speed command compensation unit (109) exceeds an upper limit value or a lower limit value, the speed command balance unit (110) limits a compensation value 1 of the pertinent stand to the upper limit value or the lower limit value, calculates a compensation value 2, and minimizes relative changes of the compensation values of the respective stands by dividing the compensation value 2 by the compensation value 1 and multiplying the compensation values of the respective stands by a resultant quotient.
8. A method for controlling hot rolling tandem mill, a control object (150) of the method being a hot rolling mill (151) having a plurality of rolling stands (152), values of the control object such as a strip thickness of a steel plate rolled continuously by work rolls provided in the rolling stands and a tension of the steel plate between rolling stands being controlled to become desired values by the method, the method for controlling hot rolling tandem mill comprising the steps of:
calculating at least a command value of a rolling load of each rolling stand, a command value of a roll gap of each of the work rolls, and a command value of a roll speed of the work roll, as a control command for a strip to be rolled in a predetermined pass; and
compensating the command value of the roll speed by using a rolling load, a roll gap, and a roll speed at time when a top end part of a strip rolled by a predetermined rolling stand in a preceding pass which is some pass preceding the predetermined pass was rolled, a rolling load, a roll gap, and a roll speed at time when the strip rolled in the preceding pass was rolled at a part other than the top end part by the predetermined stand, or a result of a computation using the rolling load, the roll gap, and the roll speed, and thereby calculating a new command value of the roll speed.
9. The method for controlling hot rolling tandem mill according to claim 8, comprising the steps of:
converting a roll speed of each stand at time when the strip rolled in a preceding pass which is some pass preceding the predetermined pass was tandem-rolled stably at a part other than the top end part by the stand to a roll speed of the stand at time when the top end is being rolled by the stand, by a computation utilizing that a mass-flow which is a product of a strip speed and a strip thickness is constant; and
compensating the command value of the roll speed calculated for the strip to be rolled in the pass or subsequent passes on the basis of the converted roll speed and the command value of the roll speed for the strip rolled in the preceding pass, and thereby calculating a new command value of the roll speed.
10. The method for controlling hot rolling tandem mill according to claim 8, comprising the steps of:
calculating at least a command value of a rolling load of each rolling stand, a command value of a roll gap of the work roll, and a command value of a roll speed of the work roll, as a control command for a strip to be rolled in the predetermined pass;
converting a roll speed of each stand at time when the strip rolled in a preceding pass which is some pass preceding the predetermined pass was tandem-rolled stably by the stand to a roll speed of the stand at time when the top end was rolled by the stand, by a computation using a rolling load and a load gap at this time and a rolling load and a load gap at time when the front end part of the strip was rolled by the stand and utilizing that a mass-flow is constant; and
compensating the command value of the roll speed calculated for the predetermined steel plate to be rolled, by using the converted roll speed and the command value of the roll speed for the steel plate rolled in the preceding pass, and thereby calculating a new command value of the roll speed.
11. The method for controlling hot rolling tandem mill according to claim 8, comprising the steps of:
calculating at least a command value of a rolling load of each rolling stand, a command value of a roll gap of the work roll, and a command value of a roll speed of the work roll, as a control command for a strip to be rolled in the predetermined pass;
taking in a rolling load, a roll gap, and a roll speed at time when a top end part of a strip rolled in a preceding pass was rolled by the rolling stand, a rolling load, a roll gap, and a roll speed at time when the strip rolled in the preceding pass was rolled stably by the stand, a rolling load, a roll gap, and a roll speed at time when a top end part of a strip rolled in the preceding pass was rolled by a final delivery stand (F7), a rolling load, a roll gap, and a roll speed at time when the strip rolled in the preceding pass was tandem-rolled stably by the final delivery stand; and
compensating the command value of the roll speed calculated for the steel plate to be rolled in the predetermined pass, by using a result of computation using the rolling loads, the roll gaps, and the roll speeds taken in, and thereby calculating a new command value of the roll speed.