Patent Publication Number: US-11383279-B2

Title: Plate thickness control device and plate thickness control method

Description:
TECHNICAL FIELD 
     The present application relates to a plate thickness control device and a plate thickness control method. 
     BACKGROUND 
     For example, as described in Japanese Patent Application Laid-Open No. 2007-75850, there is known a plate thickness control device improved so as to suppress a plate thickness deviation due to a skid mark. In the art according to this publication, a component of the skid mark is extracted by filtering plate thickness data from a plate thickness meter. By using this extracted plate thickness change, control is performed to suppress the plate thickness deviation due to the skid mark. 
     CITATION LIST 
     Patent Literature 
     [PTL 1] JP 2007-75850 A 
     SUMMARY 
     Technical Problem 
     In hot-rolled finishing plate thickness control technique, it is considered that the plate thickness deviation due to the skid mark is suppressed by gauge meter AGC or feed forward AGC or the like. The gauge meter AGC is a method of detecting a change in a plate thickness on an entry side of a rolling mill as a change in a roll force, and adjusting a screw-down amount of rolls with respect to the detected change in the force. The feed forward AGC is a method of detecting a change in a plate thickness with a plate thickness meter provided on an entry side of a rolling mill, detecting that the change in plate thickness has reached a rolling mill position based on speed of a rolled material, and then adjusting a screw-down amount of the rolling mill. 
     In Japanese Patent Application Laid-Open No. 2007-75850, a plate thickness meter is used. The thickness mater is installed between a controlled rolling stand and a preceding rolling stand, and this installation position is severe environment for the plate thickness meter. When the plate thickness meter is installed in the severe environment, wear of the plate thickness meter tends to progress, and the plate thickness meter may abruptly fail. Because of such circumstances, there is a problem that reliability of the plate thickness meter is low from the viewpoint of use in the AGC. 
     In addition, the plate thickness meter is economically expensive and costly to maintain. Therefore, there may be a case where the plate thickness meter is not used and the feedforward AGC is not performed. In this case, the feedforward AGC using the plate thickness meter cannot be performed to suppress skid mark thickness variations. 
     On the other hand, in the gauge meter AGC, if a load feedback is unstable, a gain in the gauge meter AGC cannot be increased. In the gauge meter AGC, a screw-down amount of rolls is adjusted with respect to a force change. The reason why the load feedback becomes instability is, for example, a case in which a load cell for detecting force may include a lot of noise, or a case in which force is detected not by the load cell but by an oil pressure type PT (Pressure Transducer). In such a case, since a gain in the gauge meter AGC cannot be increased, there is a problem that the gauge meter AGC cannot reduce a plate thickness variation caused by the skid mark. 
     As described above, there are many practical problems in a conventional technique to suppress a plate thickness variation due to the skid mark, and there is still room for improvement. 
     The present application has been made to solve the above-mentioned problems, and an object thereof is to provide a novel plate thickness control device and a novel plate thickness control method capable of suppressing plate thickness variation due to a skid mark. 
     Solution to Problem 
     A first plate thickness control device according to the present application for controlling a plate thickness in a hot rolling mill including a rolling stand, the plate thickness control device includes: a pyrometer disposed on an entry side of the rolling stand; a difference calculation part for outputting a difference temperature between a lock-on temperature of a plate-to-be-rolled measured by the pyrometer and a measurement value other than a head end portion of the plate-to-be-rolled measured by the pyrometer; a tracking part for transferring the difference temperature from a position of the pyrometer to a position immediately below the rolling stand based on a plate speed of the plate-to-be-rolled; and a computation part for computing a screw-down amount of the rolling stand based on the difference temperature transmitted from the tracking part. 
     A second plate thickness control device according to the present application for controlling a plate thickness in a hot rolling mill including a rolling stand, the plate thickness control device includes: a skid mark detecting part for detecting temperature information representing a position of a skid mark included in a plate-to-be-rolled rolled by the rolling stand based on a measurement value of a pyrometer disposed on an entry side of the rolling stand; a tracking part for transferring the temperature information to a position immediately below the rolling stand based on a plate speed of the plate-to-be-rolled; and a computation part for computing a screw-down amount of the rolling stand so as to determine force applied to the skid mark by the rolling stand based on the temperature information transferred by the tracking part. 
     A plate thickness control method according to the present application includes: obtaining a measured value of a pyrometer provided on an entry side of a rolling stand of a hot rolling mill; outputting a difference temperature between a lock-on temperature of a plate-to-be-rolled measured by the pyrometer and a measured value other than a head end portion of the plate-to-be-rolled measured by the pyrometer; transferring the difference temperature from a position of the pyrometer to a position immediately below the rolling stand based on a plate speed of the plate-to-be-rolled; and calculating a screw-down amount of the rolling stand based on the transferred difference temperature. 
     A plate thickness control method according to the present application includes: detecting temperature information representing a position of a skid mark included in a plate-to-be-rolled rolled at a rolling stand of the hot rolling mill based on a measurement value of a pyrometer disposed on an entry side of the rolling stand; transferring the temperature information to a position immediately below the rolling stand based on a plate speed of the plate-to-be-rolled; and calculating a screw-down amount of the rolling stand so as to determine force applied to the skid mark by the rolling stand based on the transferred temperature information. 
     Advantageous Effects of Invention 
     The present application can perform feed forward control based on temperature deviation of the plate-to-be-rolled by tracking difference temperature information acquired by the pyrometer. Thereby, it is possible to suppress the plate thickness variation due to the skid mark. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram showing a configuration of a hot rolling mill on which a plate thickness control device according to an embodiment is mounted. 
         FIG. 2  is a control block diagram of a control calculation part included in the plate thickness control device according to the embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The present embodiment relates to a plate thickness control technique of a hot rolling mill  1  configured so that a plurality of rolling stands F 1  to F 7  are arranged in series and heated steel plates or the like are rolled in succession by these rolling stands F 1  to F 7 . 
       FIG. 1  is a diagram showing a configuration of the hot rolling mill  1  on which a plate thickness control device  20  according to the embodiment is mounted. The hot rolling mill  1  includes the plurality of rolling stands F 1  to F 7 , a plurality of screw-down devices  2 , a plurality of oil pressure regulating devices  2   a , a plurality of oil pressure PTs  3 , a plurality of electric motors  4 , and a plate thickness meter  11 . 
     The hot rolling mill  1  is a hot finishing rolling mill in which the plurality of rolling stands F 1  to F 7  are arranged in tandem. The plurality of rolling stands F 1  to F 7  include an initial rolling stand F 1 , intermediate rolling stands F 2  to F 6 , and a final rolling stand F 7 . The plate thickness control device  20  according to the embodiment performs plate thickness control at the final rolling stand F 7 . 
     The screw-down device  2  is an oil driven screw-down device provided in each rolling stand. The screw-down device  2  includes an oil cylinder and an oil tank (not shown). The oil pressure regulating device  2   a  includes a valve and the like for regulating an oil pressure of the screw-down device  2 . 
     The oil pressure PT  3  is a Pressure Transducer for measuring a load based on an oil pressure for driving the pressure screw-down device  2 . The oil pressure PT  3  is an oil pressure sensor, and is also a load detector for detecting roll force of respective rolling stands. 
     The electric motors  4  rotate rolls of each rolling stand. The plate thickness meter  11  is disposed on a delivery side of the hot rolling mill  1 . The plate thickness meter  11  can measure a plate thickness of a material-to-be-rolled which is rolled in the hot rolling mill  1 . 
     The plate thickness control device  20  includes a pyrometer  20   a , a screw-down control part  22 , and a control calculation part  30 . The plate thickness control device  20  can control a screw-down amount of the screw-down device  2  by controlling the oil pressure regulating device  2   a . It should be noted that the screw-down amount of the screw-down device  2  is assumed to correspond to a roll gap change amount ΔΔS, and is also referred to simply as a “screw-down amount ΔS” hereinafter. 
     The pyrometer  20   a  is one of components of the plate thickness control device  20 . The pyrometer  20   a  is disposed on the entry side of the final rolling stand F 7 , and more specifically, is disposed between the final rolling stand F 7  and the rolling stand F 6  which is a preceding stage thereof. 
     The screw-down control part  22  receives a plate thickness h which is an output signal from the plate thickness meter  11 , an output signal from the control calculation part  30 , and a load detecting signal from the oil pressure PT  3 . The screw-down control part  22  generates a control signal based on those received signals to control the oil pressure regulating device  2   a . The control calculation part  30  will be described later with reference to  FIG. 2 . 
     A front-stage plate thickness control device  19  is used as a control device for the initial rolling stand F 1  and the intermediate rolling stands F 2  to F 6 . A device in which the control calculation part  30  is omitted from the plate thickness control device  20  is the front-stage plate thickness control device  19 , and except for this point, the front-stage plate thickness control device  19  and the plate thickness control device  20  are assumed to have the same configuration. 
       FIG. 2  is a circuit block diagram of the control calculation part  30  included in the plate thickness control device  20  according to the embodiment. As shown in  FIG. 2 , the control calculation part  30  includes a first-order delay filter part  31 , a lock-on temperature acquisition part  32 , a difference calculation part  33 , a first gain part  34 , a tracking part  35 , and a computation part  41 . 
     The first-order delay filter part  31  performs on the output signal of the pyrometer  20   a  a first-order delay calculation which is set in advance. 
     The lock-on temperature acquisition part  32  acquires a lock-on temperature T LO  of the plate-to-be-rolled measured by the pyrometer  20   a  based on the output signals of the pyrometer  20   a . The “lock-on temperature T LO ” is a temperature of a portion in the vicinity of the head end of the material-to-be-rolled. This lock-on temperature T LO  can be used as a reference temperature for detecting skid marks. A temperature of the head end of the material-to-be-rolled may be the lock-on temperature T LO , or a temperature of a portion slightly inside from the head end of the material-to-be-rolled may be the lock-on temperature T LO . 
     The difference calculating part  33  receives an output signal from the first-order delay filter part  31  and the lock-on temperature T LO  from the lock-on temperature acquisition part  32 . The output signal of the first-order delay filter part  31  includes “a temperature measurement value for a portion other than the head end portion of the plate-to-be-rolled” measured by the pyrometer  20   a . The difference calculation part  33  outputs a difference temperature ΔT. The difference temperature ΔT is a difference between the lock-on temperature T LO  and the “temperature measurement value for the portion other than the end portion of the plate-to-be-rolled”. 
     The first gain part  34  receives an output from the difference calculation part  33 . The first gain part  34  multiplies the difference temperature ΔT outputted from the difference calculation part  33  by a predetermined first gain G 1 . In the following description, in order to simplify the description, the difference temperature ΔT multiplied by the first gain G 1  is also simply referred to as the “difference temperature ΔT” unless it is necessary to distinguish it. 
     The tracking part  35  receives an output from the first gain part  34 . The tracking part  35  transfers the difference temperature ΔT from a position of the pyrometer  20   a  to directly below the final rolling stand F 7  based on a plate speed of the plate-to-be-rolled. The method of detecting the plate speed may be achieved using any of various known techniques, and therefore description thereof will be omitted. For example, the plate speed may be detected by providing a plate speed meter (not shown), or the plate speed may be detected from a rotation speed or the like of the electric motors  4 . 
     The computation part  41  calculates a screw-down amount ΔS of the final rolling stand F 7  based on the difference temperature ΔT transmitted from the tracking part  35 . Specifically, the computation part  41  includes a proportional-differential control part  36 , a second gain part  37 , a third gain part  39 , an adding part  38 , and a screw-down amount calculation part  40 . 
     The proportional-differential control part  36  performs proportional differential control (PD control) on the difference temperature ΔT. According to the proportional-differential control part  36 , both the proportional control (P control) and the phase advance compensation (D control) can be performed on the temperature deviation (difference temperature ΔT) tracked up to directly below the rolling stand F 7  which is to be controlled. 
     The second gain part  37  multiplies an output of the proportional-differential control part  36  by a second gain G 2 . The third gain part  39  multiplies an output of the tracking part  35  by a third gain G 3 . The adding part  38  adds an output of the second gain part  37  and an output of the third gain part  39 . 
     The screw-down amount calculation part  40  calculates the screw-down amount ΔS based on the output value of the proportional-differential control part  36  and rolling parameters. The rolling parameters include a mill constant M and a plasticity coefficient Q. 
     As described above, according to the embodiment, by tracking the difference temperature ΔT acquired by the pyrometer  20   a , feed forward control based on the temperature deviation of the plate-to-be-rolled can be performed. As a result, it is possible to suppress plate thickness variation due to the skid mark. That is, the plate thickness control device  20  according to the embodiment can control the screw-down amount of the final rolling stand F 7 , which is a control target, with high accuracy by performing both the phase advance compensation (D control) and the proportional control (P control) on the difference temperature ΔT tracked by the tracking part  35  directly below the rolling stand F 7 . By using the screw-down amount ΔS calculated by the computation part  41  to accurately suppress the plate thickness variation due to the skid mark while adding other AGCs, it is possible to converge a delivery side plate thickness to a target plate thickness. 
     According to the embodiment, a preferable example is provided in which the screw-down control part  22  controls the screw-down device  2  based on the oil pressure measured by the oil pressure PT  3  and the screw-down amount ΔS calculated by the computation part  41 . There is a disadvantage that the screw-down amount ΔS calculated based on the oil pressure PT  3  is less accurate than a screw-down amount ΔS calculated by using a load cell. In this respect, the computation part  41  determines the screw-down amount ΔS based on the difference temperature ΔT tracked by the tracking part  35 , whereby the plate thickness control accuracy can be suppressed from decreasing. 
     In the embodiment, the hot rolling mill  1  does not include a load cell for detecting rolling force of the rolling stands F 1  to F 7 . Nevertheless, the computation of the screw-down amounts ΔS includes not only the load detecting signals of the oil pressure PT  3  but also the difference temperature ΔT tracked by the tracking part  35 , and thereby the plate thickness variation of the skid mark can be sufficiently suppressed. As a result, the plate thickness variation of the skid mark can be suppressed even if there is no load cell, and thus the load cell, which is an expensive device, may be omitted. Even when load cells are not provided as load detectors of each of the rolling stands F 1  to F 7  and the load detection of the oil pressure PT (Pressure Transducer) or the like is unstable, the plate thickness control device  20  can converge a plate thickness at the delivery side of the rolling stand to the target plate thickness. However, the plate thickness control device  20  according to the present embodiment may also be applied to the hot rolling mill  1  with a load cell. 
     According to an embodiment, a preferable example having the proportional-differential control part  36  is provided. This makes it possible to perform phase advance compensation by differential control (D control) as well as proportional control (P control), thereby suppressing plate thickness deviation caused by the skid mark with high accuracy. 
     The lock-on temperature acquisition part  32  and the difference calculation part  33  according to the embodiment correspond to a “skid mark detection part  42 ”. The skid mark detecting part  42  can detect temperature information (that is, the difference temperature ΔT) indicating the position of the skid mark included in the plate-to-be-rolled, based on the measurement value of the pyrometer  20   a . The computation part  41  can calculate the screw-down amount ΔS of the final rolling stand F 7  so as to determine force applied to the skid mark at the final rolling stand F 7  based on the temperature information (difference temperature ΔT) transferred by the tracking part  35 . 
     The pyrometer  20   a  acquires temperature information indicating the position of the skid mark, and on the basis of the tracking of the temperature information, it can be specified that the skid mark has reached immediately below the final rolling stand F 7 . As a result, the screw-down amount ΔS can be correctly calculated so that the final rolling stand F 7  applies an appropriate force to the skid mark. 
     It should be noted that the control calculation part  30  shown in  FIG. 2  may be configured of either an analog circuit or a digital circuit, may be configured in the form of a dedicated processing device, or may be constructed in the form of a general-purpose operation circuit including a CPU and a memory. The constituent elements of each of the above-mentioned “ . . . part(s)” may be provided as software function blocks by being replaced with “ . . . block(s)”. 
     It should be noted that, although the plate thickness control device  20  according to the embodiment is applied only to the final rolling stand F 7  in the embodiment, the plate thickness control device  20  may be applied to the rolling stands F 1  to F 6  while providing the pyrometer  20   a  on each entry side thereof, as a modification. 
     Although the hot rolling mill  1  having a plurality of rolling stands F 1  to F 7  has been described in the embodiment, the hot rolling mill  1  may be modified to have only one rolling stand F 7 . Also in this case, by using the temperature information of the pyrometer  20   a  in the case where load detection is unstable, it is possible to obtain an advantage that the plate thickness accuracy can be improved. 
     It should be noted that the plate thickness control device according to the embodiment may be provided as a “plate thickness control method of a hot rolling mill” by dividing each control process into steps. The plate thickness control method according to the embodiment is also implemented by adding each function of the plate thickness control device  20  (refer to  FIG. 2 ) to a plate thickness control device of an existing hot rolling mill, and the subsequent addition corresponds to an action of manufacturing the plate thickness control device  20  according to the embodiment. 
     REFERENCE SIGNS LIST 
     
         
           1  Hot rolling mill 
           2  Screw-down device 
           2   a  Oil pressure regulating device 
           3  Oil pressure PT (Pressure Transducer) 
           4  Electric motor 
           11  Plate thickness meter 
           19  Front-stage plate thickness control device 
           20  Plate thickness control device 
           20   a  Pyrometer 
           22  Screw-down control part 
           30  Control calculation part 
           31  First-order delay filter part 
           32  Lock-on temperature acquisition part 
           33  Difference calculation part 
           34  First gain part 
           35  Tracking part 
           36  Proportional-differential control part 
           37  Second gain part 
           38  Adding part 
           39  Third gain part 
           40  Screw-down amount calculation part 
           41  Computation part 
           42  Skid mark detecting part 
         F 1  Rolling stand (initial rolling stand) 
         F 2 -F 6  Rolling stand (intermediate rolling stand) 
         F 7  Rolling stand (final rolling stand) 
         T LO  Lock-on temperature 
         ΔS Screw-down amount (roll gap change amount) 
         ΔT Difference temperature