JP2014210275A - Plate thickness control method and plate thickness control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plate thickness control method capable of improving plate thickness accuracy, by properly restraining hunting in an absolute value AGC.SOLUTION: A plate thickness control method of the present invention controls roll opening between a pair of work rolls for rolling a rolling material by a plate thickness control device based on the absolute value AGC which is provided with a limiter for setting a plate thickness deviation being a difference between a target value and an outlet side plate thickness by a calculation within a predetermined range. Such a plate thickness control method includes: a step of starting plate thickness control by the absolute value AGC when the rolling material bites in between the work rolls; a step of subtracting the plate thickness deviation in lock-on time from the plate thickness deviation inputted to the limiter thereafter by locking on the plate thickness deviation inputted to the limiter when the plate thickness control of a tip part of the rolling material finishes; and a step of inserting a roll opening correction quantity between the work rolls calculated based on the plate thickness deviation outputted from the limiter from a lock-on circuit by storing the quantity in the lock-om time.

Description

  The present invention relates to a sheet thickness control method and a sheet thickness control apparatus in hot rolling.

  When rolling a rolled material with a rolling mill, the distance between the pair of work rolls (roll gap amount) of the rolling mill that passes the steel plate is automatically adjusted so that the exit side plate thickness at the end in the plate width direction of the rolled material becomes the target plate thickness. Automatic thickness control (AGC: Automatic Gauge Control) is performed. For automatic plate thickness control, for example, when the plate is caught in the rolling mill, the rolling load is stored as the outgoing plate thickness based on the gauge meter type (lock-on), and thereafter the rolling amount is maintained so that the load is maintained. There is a BISRA-AGC that adjusts the absolute value, an absolute value AGC that adjusts the amount of reduction so that the predicted delivery side plate thickness is constant, and the like. With absolute value AGC, the plate thickness can be accurately controlled from the tip of the rolled material by obtaining lock-on information such as rolling load and roll gap amount at the time of lock-on, which is required when applying BISRA-AGC. it can.

As a sheet thickness control at the absolute value AGC, for example, in Patent Document 1, a rolling position S _{0 at} which the sheet thickness of the rolled material can be controlled to the target sheet thickness ha is set as the predicted rolling load F ₀ when the target sheet thickness ha is reduced. Is calculated by S ₀ = ha− (F ′ ₀ / M + δ ₀ + E) based on the value obtained by dividing the rolling constant by the elastic constant M1 of the rolling mill, the oil film thickness correction term δ ₀ , and the gauge meter type correction term E. A control method is disclosed. In this plate thickness control method, the converted plate thickness h ₀ ′ in the subsequent pass is estimated from the plate length L1 and the gauge meter plate thickness in the preceding pass and the plate length L1 + z in the subsequent pass by the mass flow constant law, and the conversion plate By correcting the gauge meter correction term E based on the deviation between the thickness (h ₀ = (L1 + Z) / L1 × h ₀ ′) and the gauge thickness (S ₀ + F ′ ₀ / M + δ ₀ ) in the subsequent pass The accuracy of the estimated delivery side plate thickness in the absolute value AGC is increased, and the plate thickness accuracy is improved.

  Further, in Patent Document 2, a gauge meter plate thickness is calculated using a rolling load detection value, a roll gap detection value, and a mill rigidity coefficient measured in advance, which are measured at a constant period. An automatic plate thickness control for controlling the plate thickness of a rolled material to a target plate thickness using the above is disclosed. In such automatic plate thickness control, the gauge meter plate thickness of the final stand is corrected by the difference between the signal of the plate thickness detector installed on the exit side of the finishing mill and the gauge meter plate thickness of the final stand, and the corrected gauge meter plate By controlling the roll gap of the final stand so that the thickness matches or approaches the target plate thickness on the exit side of the finish rolling mill, the accuracy of the tip end plate thickness is improved.

JP 58-212806 A JP-A-8-141614

  In the plate thickness control, if the amount of the tip portion outside the product required plate thickness range increases, the yield deteriorates accordingly. Therefore, it is desirable to start the plate thickness control immediately after the rolled material reaches the rolling mill. However, in the sheet thickness control method described in the above-mentioned patent document, if the absolute value AGC is started immediately after the rolled material reaches the rolling mill, hunting occurs due to a rapid roll opening correction, and the sheet thickness is controlled. It may not be possible. In order to suppress this hunting, usually, a countermeasure for providing a limiter is performed after calculating the thickness deviation. However, when the limiter is provided, the thickness deviation may be saturated at the middle portion where the rolling of the end portion of the rolled material is finished and the plate thickness is settled, and control may not be possible.

  Therefore, the present invention has been made in view of the above problems, and an object of the present invention is a novel and capable of appropriately suppressing hunting in the absolute value AGC and improving the thickness accuracy. An object of the present invention is to provide an improved plate thickness control method and plate thickness control apparatus.

  In order to solve the above-described problem, according to one aspect of the present invention, a plate thickness based on an absolute value AGC provided with a limiter that sets a plate thickness deviation that is a difference between a target value and a calculated output plate thickness within a predetermined range. The control device provides a plate thickness control method for controlling the roll opening degree between a pair of work rolls for rolling the rolled material. This sheet thickness control method is input to the limiter at the time when the sheet thickness control by the absolute value AGC is started when the rolled material is caught between the work rolls and the sheet thickness control of the leading end portion of the rolled material is completed. A step of subtracting the plate thickness deviation at the time of lock-on from the plate thickness deviation input to the limiter, and a roll between work rolls calculated based on the plate thickness deviation output from the limiter Adding the roll opening correction amount at the lock-on time to the opening correction amount.

  According to the present invention, in the thickness control by the absolute value AGC, when a limiter is provided that makes the thickness deviation correction amount within a predetermined range in order to prevent an excessive control output from being made, Since the thickness deviation is corrected excessively, the possibility that the limiter will function increases. Then, the roll opening is kept within a predetermined range by the function of the limiter, but the limiter saturation occurs during the thickness control of the middle portion where the thickness control of the tip of the rolled material is finished and the thickness is stable, The plate thickness deviation may not converge to the target value. Therefore, the thickness deviation input to the limiter is locked on when the thickness control of the leading end of the rolled material is finished, and then the thickness deviation at the lock-on time is subtracted from the thickness deviation inputted to the limiter. By adding the roll opening correction amount at the time of lock-on from another path to the roll opening correction amount between the work rolls calculated based on the plate thickness deviation output from the limiter, limiter saturation is avoided, and the rolled material This prevents the plate thickness control from becoming impossible.

  Here, the lock-on time may be determined in consideration of at least one of the size of the rolled material and the material.

  Moreover, in order to solve the said subject, according to another viewpoint of this invention, the plate | board thickness meter which measures the plate | board opening degree between a pair of work rolls which roll a rolling material, and the plate | board thickness after passing between work rolls Based on the measured value, a plate thickness control device is provided which is controlled by the absolute value AGC. Such a plate thickness control device includes an adjustment unit that calculates a roll opening degree correction amount between work rolls based on a plate thickness deviation that is a difference between a target value and a calculated delivery side plate thickness, and a roll opening calculated by the adjustment unit. Control target model for calculating the rolling load between the work rolls based on the degree of correction, a feedback unit for calculating the feedback value of the rolling load and roll opening calculated by the control target model, and a plate input to the adjustment unit Lock on the thickness deviation input to the limiter and the thickness deviation input to the limiter when the thickness deviation within the specified range and the thickness control of the tip of the rolled material are finished, and then lock on. The first lock-on circuit that subtracts the sheet thickness deviation at the time point, and the work roll that functions together with the first lock-on circuit and is calculated based on the sheet thickness deviation output from the limiter Characterized in that it comprises a second lock-on circuit for adding roll angle correction amount in the lock-on time on the roll opening correction amount.

  As described above, according to the present invention, it is possible to provide a plate thickness control method and a plate thickness control device capable of appropriately suppressing hunting at the absolute value AGC and improving the plate thickness accuracy.

It is explanatory drawing which shows the outline | summary of a hot rolling process. It is explanatory drawing which shows the positional relationship of the sheet thickness meter which measures the sheet thickness in the exit side of the said rolling mill, and the one rolling mill which comprises a finishing mill. It is a block diagram which shows the structure of the board thickness control apparatus which concerns on embodiment of this invention. It is a flowchart which shows the plate | board thickness control method which concerns on the same embodiment. It is explanatory drawing which shows transition of the plate | board thickness deviation at the time of performing plate | board thickness control by the conventional absolute value AGC, and a roll opening degree correction amount. It is explanatory drawing which shows transition of the plate | board thickness deviation at the time of performing plate | board thickness control which concerns on embodiment of this invention, and a roll opening degree correction amount. It is a graph which shows transition of the plate | board thickness deviation at the time of performing plate | board thickness control which concerns on embodiment of this invention with respect to a rolling mill actual machine, and a roll opening degree correction amount.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

<1. Overview of hot rolling process>
First, with reference to FIG. 1 and FIG. 2, the outline | summary of the hot rolling process which applies the plate | board thickness control apparatus which concerns on embodiment of this invention is demonstrated. In addition, FIG. 1 is explanatory drawing which shows the outline | summary of a hot rolling process. FIG. 2 is an explanatory view showing the positional relationship between one rolling mill 32 constituting the finishing rolling mill 30 and a thickness gauge 60 for measuring the thickness on the outlet side of the rolling mill 32.

  The hot rolling step is a step of continuously rolling the slab (rolled material 5) whose components have been adjusted and cast in the steel making step with a rolling mill to form a strip-shaped steel plate. As shown in FIG. 1, the rolled material 5 heated in the heating furnace 10 is rolled in the roughing mill 20, further rolled in the finish rolling mill 30, and up to a predetermined temperature in the steel plate cooling device 40. To be cooled. The rolled material 5 that has passed through the steel plate cooling device 40 is scraped in a coil shape by the scraper 50. In the hot rolling process, by controlling the temperature, roll surface, etc., a hot rolled steel sheet with less surface flaws and internal defects and good workability is built.

  The final plate thickness of the rolled material 5 formed by the hot rolling process, that is, the product required plate thickness is adjusted by the finishing mill 30. As shown in FIG. 1, the finish rolling mill 30 includes a plurality of rolling mills 32 having F1 to F7, for example. As shown in FIG. 2, each rolling mill 32 includes a pair of work rolls 34 and a pair of backup rolls 36. Each roll opening degree S (distance between the work rolls 34) is adjusted by the plate thickness control device 100 so that the exit side plate thickness of the final rolling mill 32 (F7) of the finish rolling mill 30 becomes the product required plate thickness. The outlet side plate thickness is controlled.

  The plate thickness control apparatus 100 according to the present embodiment adjusts the roll opening S of the rolling mill 32 based on the absolute value AGC based on the measurement result of the plate thickness meter 60. Conventionally, in the plate thickness control by the absolute value AGC, the roll opening degree is rapidly manipulated after the tip of the rolled material 5 is engaged with the rolling mill 32, so that excessive roll opening correction occurs and hunting occurs. May end up. When hunting occurs, the control becomes unstable and it becomes difficult to keep the plate thickness within the required plate thickness range. In order to suppress hunting, a countermeasure is usually provided to limit the roll opening correction amount after the thickness deviation is derived. However, when the limiter is provided, the limiter is saturated by the action of the absolute value AGC, and it may be impossible to control the plate thickness at the middle portion of the rolled material 5.

  Therefore, the plate thickness control apparatus 100 according to the present embodiment clears the plate thickness deviation at the time when the absolute value AGC absorbs the steep plate thickness deviation variation after the rolling mill 32 has caught the rolled material. A lock-on system that performs control to resume thickness control is adopted. Thereby, since the accumulated plate | board thickness deviation is reset to 0, the uncontrollable state by the limiter saturation in the middle part of the rolling material 5 can be avoided. Hereinafter, the configuration of the plate thickness control apparatus 100 according to the present embodiment and the plate thickness control method using the same will be described in detail.

<2. Thickness control>
[Configuration of plate thickness control device]
First, based on FIG. 3, the structure of the plate | board thickness control apparatus 100 which concerns on this embodiment is demonstrated. FIG. 3 is a block diagram showing the configuration of the plate thickness control apparatus 100 according to this embodiment. As shown in FIG. 3, the plate thickness control apparatus 100 includes a gauge meter error (GME) correction unit 110, an absolute value AGC unit 120, and a monitor AGC unit 130.

  The GME correction unit 110 performs setup correction of the roll opening degree. The GME correction unit 110 acquires the measurement value of the thickness gauge 60, and rolls based on the deviation from the initial roll opening (that is, the actual deviation) when the plate tip reaches the thickness gauge 60. The roll opening degree S of the machine 32 is corrected. Note that the initial roll opening is set based on the model calculation of the process computer.

  After the roll opening degree S is corrected by the GME correction unit 110, the absolute value AGC unit 120 controls the roll opening degree S so that the calculated plate thickness when the steady state is reached approaches the target value. The target value is the required product thickness. That is, in the absolute value AGC unit 120, the roll opening degree S is controlled so that the calculated plate thickness becomes the product required plate thickness. The absolute value AGC unit 120 includes an adjustment unit 121 that calculates a roll opening correction amount based on a plate thickness deviation that is a difference between the target value and the calculated delivery side plate thickness, and a roll opening correction amount that is calculated by the adjustment unit 121. A control target model 122 that calculates the rolling load P of the rolling mill 32 based on the above, and a feedback unit 123 that calculates a feedback value h (FB) from the rolling load P calculated by the control target model 122 and the roll opening S. Is provided. The adjustment unit 121, the control target model 122, and the feedback unit 123 perform feedback control that calculates the roll opening correction amount from the feedback value h and brings the roll opening S close to the target value.

  Further, the absolute value AGC unit 120 according to the present embodiment avoids an uncontrollable state caused by limiter saturation in the middle part of the rolling material 5 and a limiter 125 that limits and adjusts the thickness deviation input to the adjusting unit 121. For this purpose, a first lock-on circuit 126 and a second lock-on circuit 127 are provided.

  The limiter 125 limits the plate thickness deviation after deriving the plate thickness deviation in order to suppress hunting that may occur due to an abrupt roll opening operation performed after the end of the rolled material 5 is caught in the rolling mill. That is, the limiter 125 sets the plate thickness deviation correction amount to the upper limit value when the input plate thickness deviation exceeds the upper limit value of the predetermined range so that the roll opening operation of the work roll 34 is not excessive. If the value is below the lower limit value of the predetermined range, the thickness deviation correction amount is set to the lower limit value. Thereby, the roll opening operation amount of the work roll 34 is suppressed within a predetermined range, and the roll opening is not excessively operated. The plate thickness deviation correction amount limited by the limiter 125 is set to be larger as the product required plate thickness is larger. The plate thickness deviation correction amount set by the limiter 125 is output to the adjustment unit 121.

  The first lock-on circuit 126 and the second lock-on circuit 127 are provided to avoid limiter saturation in the middle portion of the rolled material 5. As described above, when the limiter 125 is provided in the absolute value AGC by the adjusting unit 121, the control target model 122, and the feedback unit 123, the limiter 125 may be saturated at the middle portion of the rolled material 5. Therefore, in the plate thickness control apparatus 100 according to this embodiment, the plate thickness deviation calculated before being input to the limiter 125 is operated by the first lock-on circuit 126, and the operation amount input to the control target model 122 is set. This is avoided by operating with the second lock-on circuit 127.

  The first lock-on circuit 126 is provided so as to function before the calculated plate thickness deviation is input to the limiter 125. When the first lock-on circuit 126 functions in response to the lock-on signal that causes the first lock-on circuit 126 to function, the first lock-on circuit 126 stores the plate thickness deviation at that time as the plate-on deviation at lock-on. The stored lock-on thickness deviation is converted into a roll opening correction amount and stored in the second lock-on circuit 127. At the same time, the first lock-on circuit 126 subtracts the lock-on thickness deviation from the subsequent thickness deviation. That is, when the first lock-on circuit 126 is functioning, the plate thickness deviation input to the limiter 125 is a value obtained by subtracting the plate thickness deviation at the time of lock-on.

  The plate thickness control device 100 outputs a lock-on signal after the plate thickness control at the tip of the rolled material 5 is completed and the plate thickness is stabilized. The output timing of this lock-on signal can also be set in advance based on, for example, at least one of the required product size, material, equipment conditions, rolling conditions, etc. For example, the rolling material 5 is caught in the rolling mill 32. This can be set according to time, such as after a predetermined time has elapsed since the time. Generally, when about 2 to 5 seconds have elapsed from when the rolling material 5 is caught in the rolling mill 32, the thickness control of the tip portion of the rolling material 5 is completed and the thickness is stabilized.

  When the thickness deviation is recorded by the first lock-on circuit 126, the roll opening degree correction amount between the work rolls calculated by the adjusting unit 121 based on the output value of the limiter 125 becomes zero. Therefore, the second lock-on circuit 127 locks on the roll opening correction amount before being locked on by the first lock-on circuit 126, and the feedback value of the roll opening S from the APC and the monitor AGC unit 130 Add the plate thickness deviation at lock-on to the input value. In other words, the second lock-on circuit 127 converts the value obtained by converting the thickness deviation, which is zeroed by the first lock-on circuit 126 when calculating the operation amount in the adjustment unit 121, into the roll opening correction amount to the APC of the control target model 122. At the time of input, the roll opening correction amount is returned to the lock-on state. Thereby, the controlled load model 122 can calculate the rolling load based on the actual thickness deviation.

  The monitor AGC unit 130 converts the plate thickness deviation into a roll opening correction amount so as to make the plate thickness deviation zero based on the measurement value by the plate thickness meter 60 and feeds it back to the absolute value AGC unit 120. The gentle thickness deviation is removed by the feedback of the monitor AGC unit 130. In the plate thickness control apparatus 100 according to the present embodiment, the monitor AGC unit 130 is not necessarily provided.

[Thickness control method]
Next, a plate thickness control method performed by the plate thickness control apparatus 100 according to the present embodiment will be described with reference to FIGS. FIG. 4 is a flowchart showing the plate thickness control method according to this embodiment. FIG. 5 is an explanatory diagram showing the time transition of the plate thickness deviation and the roll opening correction amount when the plate thickness control is performed by the conventional absolute value AGC. FIG. 6 is an explanatory diagram showing a time transition of the thickness deviation and the roll opening correction amount when the thickness control according to the present embodiment is performed.

  In the plate thickness control method according to the present embodiment, first, an initial roll opening is set (S100). The initial roll opening is set based on the model calculation of the process computer. Then, when the rolled material 5 bites into the rolling mill 32 (S110), sheet thickness control is started (S120, S130), and whether or not the sheet thickness control of the tip of the rolled material 5 is finished is confirmed. Is performed (S150). Whether or not the thickness control of the tip portion of the rolled material 5 has been completed can be determined, for example, based on whether or not a predetermined time has elapsed since the rolled material was caught in the rolling mill 32. The predetermined time is set to about 2 to 5 seconds, for example.

  The process of step S150 is repeatedly executed until it is determined that the tip end plate thickness control is completed. When it is determined that the tip thickness control is finished, the thickness control device 100 outputs a lock-on signal, and operates the first lock-on circuit 126 and the second lock-on circuit 127 of the absolute value AGC unit 120. (S160). The plate thickness deviation input to the limiter 125 by the operation of the first lock-on circuit 126 is a value obtained by subtracting the value at the time when the tip end plate thickness control is completed (that is, the plate thickness deviation at the time of lock-on). Limited. Further, when the second lock-on circuit 127 is operated, when the control target model 122 is input to the APC, the roll opening degree correction amount converted from the plate thickness deviation set to zero by the first lock-on circuit 126 is locked. The roll opening correction amount when on is added.

  By executing the process of step S160, the uncontrollable state that occurs when the limiter 125 is saturated in the middle portion of the rolled material 5 is avoided. For example, when the process of step S160 is not executed, as shown in FIG. 5, the thickness deviation varies sharply immediately after the rolling material 5 is caught. When the thickness deviation exceeds a certain value, the limiter 125 is saturated, and the roll opening correction amount is always set to the upper limit value. If it does so, roll opening will no longer be controllable and it will become difficult to converge plate thickness deviation to zero.

  On the other hand, when the process of step S160 is executed, as shown in FIG. 6, the first lock-on circuit 126 and the second lock-on circuit 127 are activated when the tip end plate thickness control is completed. As a result, the plate thickness deviation input to the limiter 125 becomes a value obtained by subtracting the plate thickness deviation at the time of lock-on, so that the absolute value of the output value of the limiter 125 becomes smaller than the actual value. The roll opening correction amount determined by the adjustment unit 121 to determine the roll opening correction amount based on the output value of the limiter 125 is small, but is locked to the roll opening correction amount by the second lock-on circuit 127. A value obtained by adding a value obtained by converting the plate thickness deviation at the time of turning on to the roll opening correction amount is input to the control target model 122. Therefore, as shown in the lower graph of FIG. 6, the roll opening correction amount input to the control target model 122 is not limited by the function of the limiter 125, and the value of the plate thickness deviation input to the adjustment unit 121 is determined. Even if it is zero, the value input to the controlled object model 122 is not changed.

  Accordingly, as shown in FIG. 6, the roll opening correction amount is controlled to vary in accordance with the thickness deviation, so that the rolling thickness 5 of the rolled material 5 is caught in the rolling mill 32. It is possible to maintain a stable state at the time when the later fluctuation of the steep thickness deviation is absorbed. Thus, even when the middle part of the rolled material 5 passes through the rolling mill 32, the limiter 125 is not saturated, and it is possible to avoid an uncontrollable state.

  Returning to the description of FIG. 4, even after the process of step S160 is executed, the thickness control of the rolled material 5 is performed by the processes of steps S120 and S130. At this time, the first lock-on circuit 126 and the second lock-on circuit 127 continue to operate. While the plate thickness control is being executed, it is determined whether or not to end the plate thickness control depending on whether or not the rolled material 5 has passed the final rolling mill 32 (F7 in FIG. 1) at a predetermined timing ( S140). Until the rolled material 5 passes through the final rolling mill 32, the processes of steps S120 and S130 are repeated. When the rolled material 5 passes through the final rolling mill 32, the plate thickness control process shown in FIG. And the plate | board thickness control process of FIG. 4 is newly performed at the timing at which the rolling of the following rolling material 5 is performed.

  The plate thickness control method by the plate thickness control apparatus 100 according to the present embodiment has been described above. According to the plate thickness control method, the plate thickness deviation is cleared by the first lock-on circuit 126 at the time when a steep plate thickness deviation variation after the rolling material biting by the rolling mill 32 is absorbed at the absolute value AGC. The plate thickness control is restarted. Further, the plate thickness deviation at the time of lock-on by the first lock-on circuit 126 is converted into a roll opening degree correction amount, and the second lock-on circuit 127 is influenced by the limiter 125 different from the first lock-on circuit 126. It is input to the controlled object model 122 from a route that does not exist. Thereby, since the accumulated plate | board thickness deviation is reset to 0, the uncontrollable state by the limiter saturation in the middle part of the rolling material 5 can be avoided.

[Example]
In FIG. 7, the time transition of the plate | board thickness deviation and the roll opening correction amount at the time of applying the plate | board thickness control method which concerns on this embodiment to the plate | board thickness control of the rolling mill 32 of the actual finishing mill 30 is shown. In the present example, plain steel having a width of 1193 mm and a thickness of 245 mm was used as the rolled material, and the plate thickness was controlled to a target plate thickness of 2.05 mm. At this time, the lock-on timing at the time when the thickness control of the front end portion of the rolled material was completed was 3.05 sec. As shown in FIG. 7, the thickness deviation is large immediately after the rolled material bites into the rolling mill 32, but after that, hunting does not occur and the thickness deviation has a value close to zero. At this time, it can be seen that the roll opening varies according to the plate thickness deviation without being limited by the limiter 125. From this, it was shown that the plate thickness control is appropriately performed by avoiding the limiter saturation by using the plate thickness control method according to the embodiment.

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

60 Plate Thickness Meter 100 Plate Thickness Control Device 110 GME Correction Unit 120 Absolute Value AGC Unit 121 Adjustment Unit 122 Model to be Controlled 123 Feedback Unit 124 Lock On Circuit 125 Limiter 126 First Lock On Circuit 127 Second Lock On Circuit 130 Monitor AGC Unit

Claims (3)

Roll opening between a pair of work rolls for rolling a rolled material by means of a plate thickness control device based on an absolute value AGC provided with a limiter with a plate thickness deviation that is the difference between the target value and the calculated delivery side plate thickness within a predetermined range. A thickness control method for controlling the degree,
Starting the thickness control by the absolute value AGC when the rolled material is caught between the work rolls;
The plate thickness deviation input to the limiter is locked on when the thickness control of the leading end of the rolled material is finished, and then the plate thickness deviation at the lock-on time is subtracted from the plate thickness deviation input to the limiter. Steps,
Adding a roll opening correction amount at the lock-on time to a roll opening correction amount between the work rolls calculated based on a plate thickness deviation output from the limiter;
A sheet thickness control method comprising:   The plate thickness control method according to claim 1, wherein the lock-on time is determined in consideration of at least one of a size and a material of the rolled material. It is a plate thickness control device that controls the roll opening degree between a pair of work rolls for rolling a rolled material by an absolute value AGC based on a measurement value of a plate thickness meter that measures a plate thickness after passing between the work rolls. And
An adjustment unit that calculates a roll opening correction amount between the work rolls based on a plate thickness deviation that is a difference between a target value and a calculated delivery side plate thickness;
A control target model that calculates a rolling load between the work rolls based on a roll opening correction amount calculated by the adjustment unit,
A feedback unit that calculates a feedback value of the roll opening based on the rolling load calculated by the control target model;
A limiter that makes the thickness deviation input to the adjustment unit within a predetermined range;
The plate thickness deviation input to the limiter is locked on when the thickness control of the leading end of the rolled material is finished, and then the plate thickness deviation at the lock-on time is subtracted from the plate thickness deviation input to the limiter. A first lock-on circuit;
A second function that functions together with the first lock-on circuit and adds a roll opening correction amount at the time of lock-on to a roll opening correction amount between the work rolls calculated based on a plate thickness deviation output from the limiter. A plate thickness control device comprising a lock-on circuit.

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