Patent Publication Number: US-2023142679-A1

Title: Edge crack detection device, rolling mill facility and edge crack detection method

Description:
TECHNICAL FIELD 
     The present disclosure relates to an edge crack detection device, a rolling mill facility and an edge crack detection method. 
     BACKGROUND ART 
     In the process of producing a metal plate, an edge crack may be formed at an end portion of the metal plate in the plate-width direction. It is important to detect an edge crack appropriately since growth of an edge rack may lead to breakage of the metal plate. 
     Patent Document 1 discloses a technique to detect an edge crack of a steel plate on the basis of an abrupt decrease of the plate thickness in the longitudinal direction of the steel plate at a plate edge portion using an edge profile meter disposed on the output side of the rolling process line. The edge profile meter disclosed in Patent Document 1 includes an X-ray generator and an X-ray detector disposed so as to face one another at the plate edge portion. The X-ray detector includes a plurality of sensors arranged in the plate-width direction, and is configured to measure the distribution of the plate thickness by detecting X-rays generated by the X-ray generator and attenuated by the steel plate. 
     Citation List 
     Patent Literature 
     Patent Document 1: JPH9-89809A 
     SUMMARY 
     Problems to be Solved 
     Meanwhile, in a case where an edge crack of a metal plate being conveyed on a rolling line or the like is detected by using a plurality of sensors (elements) arranged in the plate-width direction, a calculator needs to receive and process a large number of detection signals continuously sent from the plurality of sensors at short intervals. Thus, to appropriately detect a small edge of a metal plate being conveyed at a high speed, it is desired to detect an edge crack efficiently. 
     In view of the above, an object of at least one embodiment of the present invention is to provide an edge crack detection device, a rolling mill facility, and an edge crack detection method capable of detecting an edge crack of a metal plate efficiently. 
     Solution to the Problems 
     According to at least one embodiment of the present invention, an edge crack detection apparatus for detecting an edge crack of a metal plate being conveyed includes: a detection part including a plurality of elements arranged along a plate width direction of the metal plate, each of the plurality of elements being configured to be capable of detecting presence or absence of the metal plate at a position of the element in the plate width direction; a plate edge position determination part configured to determine a plate edge position of the metal plate in the plate width direction on the basis of a detection result of each of a plurality of first elements positioned within a first region in the plate width direction, from among the plurality of elements; and an edge crack detection part configured to detect an edge crack of the metal plate on the basis of a detection result of each of a plurality of second elements selected on the basis of the plate edge position and positioned within a second region which is narrower than the first region in the plate width direction, from among the plurality of elements. 
     Furthermore, according to at least one embodiment of the present invention, a rolling mill facility includes: a rolling mill apparatus for rolling a metal plate; and the above described edge crack detection apparatus configured to detect an edge crack at an end portion, in the plate width direction, of the metal plate during rolling by the rolling mill apparatus. 
     Furthermore, according to at least one embodiment of the present invention, a method of detecting an edge crack of a metal plate being conveyed, using a detection part including a plurality of elements arranged along a plate width direction of the metal plate, each of the plurality of elements being configured to be capable of detecting presence or absence of the metal plate at a position of the element in the plate width direction, includes: a step of determining a plate edge position of the metal plate in the plate width direction on the basis of a detection result of each of a plurality of first elements positioned within a first region in the plate width direction, from among the plurality of elements; a step of selecting, on the basis of the determined plate edge position, a plurality of second elements positioned within a second region which is narrower than the first region in the plate width direction, from among the plurality of elements; and a step of detecting an edge crack of the metal plate on the basis of a detection result by each of the plurality of the selected second elements. 
     Advantageous Effects 
     According to at least one embodiment of the present invention, it is possible to provide an edge crack detection device, a rolling mill facility, and an edge crack detection method capable of detecting an edge crack of a metal plate efficiently. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a schematic configuration diagram of a rolling mill facility according to an embodiment. 
         FIG.  2    is a schematic configuration diagram of an edge crack detection apparatus according to an embodiment. 
         FIG.  3    is a schematic configuration diagram of an edge crack detection apparatus according to an embodiment. 
         FIG.  4    is a flowchart showing a flow of the process of detecting an edge crack according to an embodiment. 
         FIG.  5    is a schematic diagram of an edge crack formed on a metal plate. 
         FIG.  6    is a diagram for describing the process of detecting an edge crack according to an embodiment. 
         FIG.  7    is an enlarged view of the schematic diagram of  FIG.  6   , showing a plate edge portion of a metal plate. 
         FIG.  8    is a schematic configuration diagram of an edge crack detection apparatus according to an embodiment. 
         FIG.  9    is a schematic configuration diagram of an edge crack detection apparatus according to an embodiment. 
         FIG.  10    is a flowchart showing an example of the determination process by the first determination part. 
         FIG.  11    is a schematic configuration diagram of an edge crack detection apparatus according to an embodiment. 
         FIG.  12    is a schematic configuration diagram of an edge crack detection apparatus according to an embodiment. 
         FIG.  13    is a flowchart showing an example of the determination process of the second determination part. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It is intended, however, that unless particularly identified, dimensions, materials, shapes, relative positions and the like of components described in the embodiments shall be interpreted as illustrative only and not intended to limit the scope of the present invention. 
     (Configuration of rolling mill facility) 
     The following description describes a rolling mill facility for rolling a metal plate as an example of application of an edge crack detection apparatus according to some embodiments. Nevertheless, the edge crack detection apparatus according to some embodiments may be applied to a metal plate processing apparatus other than the rolling mill facility. 
       FIG.  1    is a schematic configuration diagram of a rolling mill facility to which an edge crack detection apparatus according to an embodiment is applied. As depicted in  FIG.  1   , a rolling mill facility  1  includes a rolling mill apparatus  2  configured to roll a metal plate S, and an edge crack detection apparatus  100  for detecting an edge crack of the metal plate S. 
     The rolling mill apparatus  2  includes at least one rolling mill stand  10  for rolling the metal plate S. In the illustrative embodiment depicted in  FIG.  1   , the rolling mill apparatus  2  includes a single rolling mill stand  10 . In another embodiment, the rolling mill apparatus  2  may include two or more rolling mill stands  10 . 
     The rolling mill apparatus  2  includes an unwinder  4  for unwinding a coil of the metal plate S toward the rolling mill stand  10 , and a rewinder  14  for rewinding the metal plate S from the rolling mill stand  10 . Furthermore, an input-side pinch roll  6  and an output-side pinch roll  12  for guiding the metal plate S may be disposed between the rolling mill stand  10  and the unwinder  4 , and between the rolling mill stand  10  and the rewinder  14 . 
     The rolling mill stand  10  depicted in  FIG.  1    includes a pair of work rolls  15 ,  16  disposed so as to pinch the metal plate S being a rolling material, and a pair of intermediate rolls  17 ,  18  and a pair of backup rolls  19 ,  20  disposed opposite to the metal plate S across the pair of work rolls  15 ,  16 , respectively. The intermediate rolls  17 ,  18  and the backup rolls  19 ,  20  are configured to support the work rolls  15 ,  16 . Furthermore, the rolling mill stand  10  includes a rolling reduction device (not depicted) for rolling down the metal plate S by applying a load to the pair of work rolls  15 ,  16 . 
     A motor (not depicted) is connected to the work rolls  15 ,  16  via a spindle (not depicted) or the like, such that the work rolls  15 ,  16  are rotary driven by the motor. When the metal plate S is rolled, the motor rotates the work rolls  15 ,  16  while the rolling reduction device rolls down the metal plate S and thereby a friction force is generated between the work rolls  15 ,  16  and the metal plate S. The metal plate S is conveyed to the output side of the work rolls  15 ,  16  by the friction force. 
     (Configuration of edge crack detection apparatus) 
       FIGS.  2  and  3    are each a schematic configuration diagram of an edge crack detection apparatus according to an embodiment. 
     As depicted in  FIGS.  1  to  3   , the edge crack detection apparatus  100  includes a detection part  30  disposed in the vicinity of an end portion, in the plate-width direction, of the metal plate S to be conveyed, and a processing part  50  for processing the signals from the detection part  30 . 
     The processing part  50  includes a plate edge position determination part  52  for determining the plate edge position of the metal plate S in the plate width direction on the basis of the signals from the detection part  30 , and an edge crack detection part  54  for detecting an edge crack of an end portion of the metal plate S in the plate width direction (hereinafter, also referred to as merely an edge portion) on the basis of the signals from the detection part  30 . 
     The processing part  50  includes a calculator including a processor (CPU), a storage device (memory device; RAM and the like), an auxiliary storage part, and an interface, for instance. The processing part  50  is configured to receive signals from the detection part  30  via an interface. The processor is configured to process the accordingly received signals. Furthermore, the processor is configured to process the program expanded in the storage device. Accordingly, the respective functions of the above described functional parts (the plate edge position determination part  52  and the edge crack detection part  54 ) are realized. 
     The content of process at the processing part  50  is implemented as a program to be executed by the processor. The program may be stored in the auxiliary storage part. When the program is executed, the program is expanded in the storage part. The processor is configured to read out the program from the storage device, and execute the commands contained in the programs. 
     As depicted in  FIG.  3   , the detection part  30  includes a plurality of elements  36  arranged along the plate width direction of the metal plate S. Each of the plurality of elements  36  is configured to be capable of detecting presence or absence of the metal plate S at the position of the element  36  in the plate width direction. The signal indicating the detection result of presence or absence of the metal plate S is sent to the processing part  50 . 
     In some embodiments, the detection part  30  is configured to detect an edge crack using radiation (e.g., X-rays). In the illustrative embodiment depicted in  FIG.  3   , the detection part  30  includes a radiation receiving part  34  including the plurality of elements  36 , and a radiation generation part  32  disposed opposite to the radiation receiving part  34  across the metal plate S. The radiation generation part  32  is configured to generate radiation  101  (X-rays of the like) which radiates towards the plurality of elements  36  of the radiation receiving part  34 . 
     In an embodiment, the plurality of elements  36  are semiconductor elements that output signals upon receiving the radiation  101 . Each of the plurality of elements  36  is configured to detect absence of the metal plate S at the position of the element  36  in the plate width direction upon receiving the radiation  101 , and detect presence of the metal plate S at the position of the element  36  in the plate width direction when not receiving the radiation  101 . 
     That is, in the region where the metal plate S exists in the plate width direction, the radiation  101  from the radiation generation part  32  is blocked by the metal plate S. Thus, each of the elements  36  positioned in this region does not receive the radiation  101 , and thus does not output signals that indicate reception of the radiation  101 . Conversely, in the region where the metal plate S does not exist in the plate width direction, the radiation  101  from the radiation generation part  32  is not blocked by the metal plate S. Thus, each of the elements  36  positioned in this region receives the radiation  101 , and outputs signals that indicate reception of the radiation  101 . 
     The above described semiconductor elements may be cadmium telluride (CdTe) semiconductor elements. CdTe semiconductor have a high resolution, and thus is likely to appropriately detect the plate edge position and an edge crack of the metal plate S being conveyed at a high speed. 
     The arrangement pitch of the plurality of elements  36  in the plate width direction is not particularly limited, and may be not smaller than 0.05 mm and not greater than 1 mm, for instance. 
     (Process flow of edge crack detection) 
     The following description describes the flow of the process of detecting an edge crack by an edge crack detection apparatus  100  according to some embodiments (method of detecting an edge crack).  FIG.  4    is a flowchart showing a flow of the process of detecting an edge crack by an edge crack detection apparatus  100  according to some embodiments. 
     As depicted in  FIG.  4   , in an embodiment, firstly, the position of the plate edge E of the metal plate S in the plate width direction is determined on the basis of the detection result by each of the plurality of first elements  36 A positioned within the first region R 1  (see  FIG.  3   ) in the plate width direction, from among the plurality of elements  36  (S 2 ). 
     With regard to the step  2 , a case illustrated in  FIG.  3    will be described. In the example illustrated in  FIG.  3   , of the plurality of first elements  36 A, the first element  36 A′ and the first elements  36 A positioned at the inner side of the first element  36 A′ in the plate width direction (closer to the side of the center line of the metal plate S) each detect presence of the metal plate S at the position of the respective first elements  36 A. Meanwhile, of the plurality of first elements  36 A, the first elements  36 A positioned at the outer side of the first element  36 A′ in the plate width direction (at the side opposite to the center line of the metal plate S) detect absence of the metal plate S at the position of the respective first elements  36 A. Thus, in such a case, it is determined that the plate edge E is positioned at the position of the first element  36 A′ in the plate width direction. 
     The length of the first region R 1  in the plate width direction is set such that the plate edge E falls within the range of the first region R 1  even in a case where the metal plate S meanders to some extent during conveyance. The length of the first region R 1  in the plate width direction may be ¼of the plate width of the metal plate S or longer. 
     Next, the edge crack detection part  54  selects a plurality of second elements  36 B to be used in detection of an edge crack in the subsequent step S 6 , from among the plurality of elements  36 , on the basis of the position of the plate edge E determined in step S 2  (S 4 ). The plurality of second elements  36 B are positioned within a second region R 2  which is narrower than the first region R 1  in the plate width direction. 
     The above described second region R 2  may be a region including the position of the plate edge E (that is, the position of the first element  36 A′). In an embodiment, as depicted in  FIG.  3    for instance, the second region R 2  may be a region between the position of the plate edge E and a position offset inward from the position of the plate edge E in the plate width direction. Alternatively, in an embodiment, the second region R 2  may be a region between a position offset inward from the position of the plate edge E in the plate width direction and a position offset outward from the position of the plate edge E in the plate width direction. 
     Furthermore, it is sufficient if the edge crack detection part  54  selects a plurality of second elements to be used in detection of an edge crack on the basis of the position of the plate edge E. The edge crack detection part  54  may always detect all the way up to the most inner element in the plate width direction as the elements at the inner end in the plate width direction belonging to the second region R 2 . Also in this case, the first region is narrower than the second region. 
     In the example detected in  FIG.  3   , of the plurality of elements  36 , each of the elements  36  selected as the second element  36 B also functions as the first element  36 A. That is, in some embodiments, each of the plurality of elements  36  may be configured to be capable of functioning as both of the first element  36 A and the second element  36 B. 
     The length of the above described second region R 2  in the plate width direction may be set on the basis of the length, in the plate width direction, of an edge crack which may be formed on the metal plate S. For instance, the length of the second region R 2  in the plate width direction may be twice the maximum length, in the plate width direction, of an edge crack which is expected to form on the metal plate S, or longer. 
     Furthermore, the number of the plurality of first elements  36 A may be not smaller than 20 times and not greater than 200 times the number of the plurality of second elements  36 B. 
     Next, the edge crack detection part  54  detects an edge crack of the metal plate S on the basis of the detection result by each of the plurality of second elements  36 B selected in step S 4  (S 6 ). 
     Herein,  FIG.  5    is a schematic diagram of an edge crack (shaded area in  FIG.  5   ) formed on the metal plate S. As depicted in  FIG.  5   , the edge crack  90  is a defect that forms on an end portion of the metal plate S in the plate width direction. The edge crack  90  normally has a shape recessed inward in the plate width direction from the plate edge E of the metal plate S. The edge crack  90  in  FIG.  5    has a width W in the plate width direction of the metal plate S, and a length L in the longitudinal direction of the metal plate S. 
     In a case where the edge crack  90  (an absent part of the metal plate S) exists on the metal plate S, each of the second elements  36 B at a position where the edge crack  90  exists in the plate width direction detects absence of the metal plate at the position. Furthermore, each of the second elements  36 B at a position where the edge crack  90  does not exist in the plate width direction detects presence of the metal plate S at the position. Accordingly, it is possible to detect presence or absence of an edge crack at the metal plate S on the basis of the detection results by the plurality of second elements  36 B. 
     According to the above described embodiment, it is possible to detect an edge crack using a small number of second elements  36 B selected on the basis of the position of the plate edge E determined from the detection results obtained by the plurality of first elements  36 A. Thus, it is possible to reduce the calculation process load compared to a case where a large number of elements are used to detect an edge crack, and it is possible to detect an edge crack efficiently. Furthermore, in the above described embodiment, a relatively small number of second elements  36 B are used to detect an edge crack, and thus it is easier to detect an edge crack in a short cycle compared to a case where a large number of elements are used. Thus, it is possible to appropriately detect a small edge crack of the metal plate S being conveyed at a high speed. 
     In some embodiments, in step S 2 , the plate edge position determination part  52  obtains the detection result by each of the plurality of first elements  36 A and determines the position of the plate edge E on the basis of the detection results, at intervals of a first cycle time T 1 . Then, in step S 6 , the edge crack detection part  54  obtains the detection result by each of the plurality of second elements  36 B at intervals of a second cycle time T 2  which is shorter than the first cycle time T 1 . 
       FIG.  6    is a diagram for describing the edge crack detection process according to an embodiment, schematically showing the detection position of each of the plurality of elements  36  in the plate width direction and the longitudinal direction of the metal plate S as the detection position moves in the advance direction in accordance with advance of the metal plate S. In  FIG.  6   , the detection positions by the plurality of first elements  36 A are shown in dotted line  102 , and the detection positions by the plurality of second elements  36 B are shown in dotted line  104 . A premise here is that the metal plate S is conveyed at a constant speed V. The metal plate S advances by distance L 1  (=V×T 1 ) during the first cycle time T 1  and advances by distance L 2  (=V×T 2 ) during the second cycle time T 2 . 
     In  FIG.  6   , the plurality of first elements  36 A are each configured to detect, in sequence from the first element  36 A positioned at the most outer side in the plate width direction, presence or absence of the metal plate S at the position of the first element  36 A in the plate width direction. Furthermore, the plurality of second elements  36 B are each configured to detect, in sequence from the second element  36 B positioned at the most outer side in the plate width direction, presence or absence of the metal plate S at the position of the second element  36 B in the plate width direction. In  FIG.  6   , the second region R 2  is the region at the inner side, in the plate width direction, of the position (P 1 , P 2 , or the like) at the plate edge E determined by the plurality of first elements  36 A. 
     In a case where the detection result by each of the plurality of first elements  36 A is obtained (i.e., the state of each of the plurality of first elements  36 A is read in) once every first cycle time T 1 , as depicted in  FIG.  6   , the metal plate S advances by distance L 1  during the first cycle time T, and thus the plurality of first elements  36 A detect presence or absence of the metal plate S at the respective positions within the first region R 1  in the plate width direction in the range of the longitudinal direction length L 1  of the metal plate S. In the above range of the length L 1 , normally, a single position of the plate edge (P 1 , P 2  in the drawing) is detected. 
     Furthermore, in a case where the detection result by each of the plurality of second elements  36 B is obtained (i.e., the state of each of the plurality of second elements  36 B is read in) once every second cycle time T 2 , as depicted in  FIG.  6   , the metal plate S advances by distance L 2  during the second cycle time T, and thus the plurality of second elements  36 B detect presence or absence of the metal plate S at the respective positions within the second region R 2  in the plate width direction in the range of the longitudinal direction length L 2  of the metal plate S. 
     The change of the position of the plate edge E during conveyance of the metal plate S is relatively slow compared to the conveyance speed of the metal plate S. For instance, in a case of a typical rolling mill apparatus, the plate edge position may change only a few millimeters while the metal plate S advances a few meters. In this case, the position of the plate edge E changes gradually, and thus it is possible to detect the change of the position of the plate edge E without shortening the detection cycle considerably. Meanwhile, the size of an edge crack of the metal plate S is considerably small relative to the conveyance speed of the metal plate S. For instance, while a typical conveyance speed in a rolling mill apparatus is several hundred mpm (or several thousand mm/s), the length of an edge crack in the longitudinal direction of the metal plate S is about 0.5 to several mm. Thus, to detect an edge crack without an oversight, it is necessary to shorten the detection cycle to some extent. 
     In this regard, according to the above described embodiment, the detection result by each of the plurality of first elements  36 A is obtained at intervals of the first cycle time that is relatively long, and thus it is possible to suppress an increase in the load of calculation process to determine the position of the plate edge E. Also, the detection result by each of the plurality of second elements  36 B is obtained at intervals of the second cycle time that is relatively short, and thus it is possible to detect a small edge crack of the metal plate S being conveyed at a high speed more reliably. 
     In some embodiments, the second cycle time T 2  is not longer than 1/10of the first cycle time T 1 . That is, the advance distance L 2  of the metal plate S in the second cycle time T 2  depicted in  FIG.  6    is not longer than 1/10of the advance distance L 1  of the metal plate S in the first cycle time T 1 . 
     In this case, the detection result by each of the plurality of first elements  36 A is obtained at intervals of the first cycle time T 1  that is relatively long, or specifically, ten times or more compared to the second cycle time T 2 , and thus it is possible to suppress an increase in the load of calculation process to determine the position of the plate edge E. Also, the detection result by each of the plurality of second elements  36 B is obtained at intervals of the second cycle time T 2  that is relatively short, or specifically, 1/10or less compared to the first cycle time T 1 , and thus it is possible to detect a small edge crack of the metal plate S being conveyed at a high speed more reliably. 
     In some embodiments, in step S 2 , the plate edge position determination part  52  is configured to obtain the detection results by the plurality of first elements  36 A in the first cycle time T 1  by reading in the state of the plurality of first elements  36 A in sequence along the plate width direction every first cycle time T 1 . Furthermore, in a case where the state of the plurality of first elements  36 A is read in in sequence along the plate width direction from the outer side toward the inner side in the plate width direction every first cycle time T 1 , the detection position of presence or absence of the metal plate S by the plurality of first elements  36 A is as indicated by the dotted line  102  in  FIG.  6   . 
     According to the above described embodiment, the detection results by the plurality of first elements  36 A are obtained by reading in the state of the plurality of first elements  36 A in sequence along the plate width direction at intervals of the first cycle time T 1 , and thus it is possible to determine the position of the plate edge E of the metal plate S with a relatively simple configuration. For instance, the plate edge position determination part  52  may be implemented as a program of a relatively simple configuration. 
     In  FIG.  6   , the detection speed indicated by the dotted line  104  is higher than the detection speed indicated by the dotted line  102 . Such a high detection speed is more preferable for detection of an edge crack. The detection speed is not limited to the above. The detection speed of the dotted line  104  may be the same as, or smaller than that of the dotted line  102 . Herein, the detection speed refers to “the travel distance (number of elements to be detected)/sampling time”. 
     In some embodiments, in step S 6 , the edge crack detection part  54  is configured to obtain the detection results by the plurality of second elements  36 B in the second cycle time T 2  by reading in the state of the plurality of second elements  36 B in sequence along the plate width direction at intervals of the second cycle time T 1 . Furthermore, in a case where the state of the plurality of second elements  36 B is read in in sequence along the plate width direction from the outer side toward the inner side in the plate width direction at intervals of the second cycle time T 2 , the detection position of presence or absence of the metal plate S by the plurality of second elements  36 B is as indicated by the dotted line  104  in  FIG.  6   . 
     According to the above described embodiment, the detection results by the plurality of second elements  36 B are obtained by reading in the state of the plurality of second elements  36 B in sequence along the plate width direction at intervals of the second cycle time T 2 , and thus it is possible to detect an edge crack of the metal plate S with a relatively simple configuration. For instance, it is possible to implement the edge crack detection part  54  as a program of a relatively simple configuration. 
       FIG.  7    is an enlarged view of the schematic diagram of  FIG.  6   , showing a plate edge portion of the metal plate S. The dots in the drawings (solid circles and empty circles) each indicate a detection result by corresponding one of the second elements  36 B. A solid circle indicates detection of absence of the metal plate S at the position of the corresponding second element  36 B in the plate width direction, and an empty circle indicates detection of presence of the metal plate S at the position of the corresponding second element  36 B in the plate width direction. 
     In some embodiments, in step S 6 , the edge crack detection part  54  is configured to detect an edge crack on the basis of the number of the second elements  36 B having detected absence of the metal plate S at the position of the second element  36 B in the plate width direction (that is, the number of the solid circles in  FIG.  7   ), from among the plurality of second elements  36 B. 
     The edge crack detection part  54  may be configured to obtain the number of the second elements  36 B having detected absence of the metal plate S at the position of the second element  36 B in the plate width direction from among the plurality of second elements  36 B at intervals of the second cycle time T 2 , and detect an edge crack on the basis of the number at intervals of the second cycle time T 2 . 
     When an edge crack of the metal plate S exists, the second elements  36 B corresponding to the position of the edge crack in the plate width direction detect absence of the metal plate S at the position, and the other second elements  36 B detect presence of the metal plate S at positions corresponding to the respective other second elements  36 B. According to the above described embodiment, it is possible to detect an edge crack of the metal plate S appropriately on the basis of the number of the second elements  36 B having detected absence of the metal plate S at the position of the second element  36 B in the plate width direction, from among the plurality of second elements  36 B. 
     In some embodiments, in step S 6 , the edge crack detection part  54  is configured to determine that the metal plate S has an edge crack if each of a predetermined number or more of the second elements  36 B arranged continuously detect absence of the metal plate S, from among the plurality of second elements  36 B. 
     For instance, the edge crack detection part  54  may determine that the metal plate S has an edge crack when L or more continuously arranged second elements  36 B detect absence of the metal plate S in a case where the total number of the second elements is M. 
     More specifically, as depicted in  FIG.  7    for instance, the edge crack detection part  54  may determine that the metal plate S has an edge crack if five or more second elements  36 B detect absence of the metal plate S continuously in a case where the total number of the second elements  36 B is ten. In the example illustrated in  FIG.  7   , in the cycles C 1  to C 4  of the second cycle time T 2 , the number of second elements  36 B that detect absence of the metal plate S continuously is 1, 3, 6, and 4, respectively. That is, in cycle C 3 , five or more (specifically, six) second elements  36 B detect absence of the metal plate S continuously, and thus it can be determined that the metal plate S has an edge crack at the position corresponding to the cycle C 3  in the longitudinal direction. 
     In some embodiments, in step S 6 , the edge crack detection part  54  is configured to determine that the metal plate S has an edge crack if a ratio N/M of the number N of the second elements  36 B detecting absence of the metal plate S to the number (total) M of the plurality of second elements is not smaller than a predetermined value. 
     For instance, the edge crack detection part  54  may determine that the metal plate S has an edge crack when the above ratio N/M is not smaller than ½. For instance, in the example depicted in  FIG.  7   , the total number (M) of the second elements  36 B is ten. Furthermore, in the cycles C 1  to C 4  of the second cycle time T 2 , the number (N) of the second elements  36 B that detect absence of the metal plate S continuously is 1, 6, 6, and 4, respectively. Thus, in the cycles C 2  and C 3 , N/M is not smaller than 1/2, and thereby it is possible to determine that the metal plate S has an edge crack at the positions corresponding to the cycles C 2  and C 3  in the longitudinal direction. 
       FIGS.  8  and  9    are each a schematic configuration diagram of an edge crack detection apparatus  100  according to an embodiment.  FIG.  8    is a planar view of the vicinity of the rolling mill stand  10  of the rolling mill facility  1 . 
     As depicted in  FIG.  8   , in an embodiment, at the side of the first end E 1  of the metal plate S in the plate width direction, a plurality of detection parts  30  (the upstream side detection part  30 A and the downstream side detection part  30 B) are disposed at different positions in the advance direction of the metal plate S. Furthermore, as depicted in  FIG.  9   , the processing part  50  includes a plurality of plate edge position determination parts  52  and a plurality of edge crack detection parts  54  disposed corresponding to the respective detection parts  30 . Specifically, an upstream side plate edge position determination part  52 A and an upstream side edge crack detection part  54 A are provided corresponding to the upstream side detection part  30 A, and a downstream side plate edge position determination part  52 B and a downstream side edge crack detection part  54 B are provided corresponding to the downstream side detection part  30 B. 
     The upstream side edge crack detection part  54 A is configured to determine possibility of existence of an edge crack on the metal plate S on the basis of whether the second element  36 B positioned at the inner side of the plate edge E 1  determined by the upstream side plate edge position determination part  52 A detects absence of the metal plate S, from among the plurality of second elements  36 B of the upstream side detection part  30 A. The downstream side edge crack detection part  54 B is configured to determine possibility of existence of an edge crack on the metal plate S on the basis of whether the second element  36 B positioned at the inner side of the plate edge E 1  determined by the downstream side plate edge position determination part  52 B detects absence of the metal plate S, from among the plurality of second elements  36 B of the downstream side detection part  30 B. 
     The processing part  50  includes a first determination part  56  configured to determine whether the metal plate S has an edge crack on the basis of the determination results by the upstream side edge crack detection part  54 A and the downstream side edge crack detection part  54 B. The first determination part  56  is configured to determine that the metal plate S has an edge crack when only one of the upstream side edge crack detection part  54 A or the downstream side edge crack detection part  54 B determines that there is a possibility of an edge crack at the same time. 
       FIG.  10    is a flowchart showing an example of the determination process by the first determination part  56 . Firstly, as described above, each of the upstream side edge crack detection part  54 A and the downstream side edge crack detection part  54 B detects the possibility of existence of an edge crack on the metal plate S (S 102 ). As a result, if the upstream side edge crack detection part  54 A determines that there is a possibility of an edge crack of the metal plate S (S 104  in YES), the first determination part  56  determines whether the downstream side edge crack detection part  54 B has determined that there is a possibility of an edge crack of the metal plate S at the same time as the determination by the upstream side edge crack detection part  54 A in step S 104  (S 106 ). 
     In a case where the downstream side edge crack detection part  54 B has not determined that there is a possibility of an edge crack on the metal plate S at the same time (No in S 106 ), it is determined that the metal plate S has an edge crack (S 108 ), and the flow is completed. Conversely, in a case where the downstream side edge crack detection part  54 B has determined that there is a possibility of an edge crack of the metal plate S (Yes in S 106 ), it is determined that the metal plate S may not have an edge crack (S 110 ), and the flow is completed. 
     The first determination part  56  may be configured to determine that meandering (oscillation in the plate width direction) has occurred on the metal plate S instead of an edge crack when both of the upstream side edge crack detection part  54 A and the downstream side edge crack detection part  54 B determine that there is a possibility of an edge crack at the same time (Yes in S 106 ). 
     Alternatively, the first determination part  56  may be configured to determine that meandering (oscillation in the plate width direction) has occurred on the metal plate S instead of an edge crack when both of the upstream side edge crack detection part  54 A and the downstream side edge crack detection part  54 B determine that there is a possibility of an edge crack of the same size in the plate width direction or the longitudinal direction of the metal plate S in step S 106  at the same time. 
     In the above steps S 102  to S 110 , the same description is still applicable when the upstream side edge crack detection part  54 A and the downstream side edge crack detection part  54 B are switched. 
     According to the above described embodiment, it is determined that the metal plate S has an edge crack when only one of the upstream side edge crack detection part  54 A or the downstream side edge crack detection part  54 B determines that there is a possibility of an edge crack at the same time, and thus it is possible to suppress erroneous determination regarding presence and absence of an edge crack. For instance, it is possible to suppress wrongly determining existence of an edge crack when meandering is actually occurring on the metal plate S. 
       FIGS.  11  and  12    are each a schematic configuration diagram of an edge crack detection apparatus  100  according to an embodiment.  FIG.  11    is a planar view of the vicinity of the rolling mill stand  10  of the rolling mill facility  1 . 
     As depicted in  FIG.  11   , in an embodiment, at the side of the first end E 1  and the side of the second end E 2  of the metal plate S in the plate width direction, detection parts  30  (the first-end side detection part  30 C and the second-end side detection part  30 D) are disposed, respectively. Furthermore, as depicted in  FIG.  12   , the processing part  50  includes a plurality of plate edge position determination parts  52  and a plurality of edge crack detection parts  54  disposed corresponding to the respective detection parts  30 . Specifically, a first-end side plate edge position determination part  52 C and a first-end side edge crack detection part  54 C are provided corresponding to the first-end side detection part  30 C, and a second-end side plate edge position determination part  52 D and a second-end side edge crack detection part  54 D are provided corresponding to the second-end side detection part  30 D. 
     The first-end side edge crack detection part  54 C is configured to determine possibility of existence of an edge crack on the metal plate S on the basis of whether the second element  36 B positioned at the inner side of the plate edge E 1  determined by the first-end-side plate edge position determination part  52 C detects absence of the metal plate S, from among the plurality of second elements  36 B of the first-end side detection part  30 C. The second-end side edge crack detection part  54 D is configured to determine possibility of existence of an edge crack on the metal plate S on the basis of whether the second element  36 B positioned at the inner side of the plate edge E 2  determined by the second-end side plate edge position determination part  52 D detects absence of the metal plate S, from among the plurality of second elements  36 B of the second-end side detection part  30 D. 
     The processing part  50  includes a second determination part  58  configured to determine whether the metal plate S has an edge crack on the basis of the determination results by the first-end side edge crack detection part  54 C and the second-end side edge crack detection part  54 D. The second determination part  58  is configured to determine that the metal plate S has an edge crack if the first-end side edge crack detection part  54 C determines that there is a possibility of an edge crack and the second element  36 B of the second-end side edge crack detection part  54 D positioned at the outer side of the position of the plate edge E 2  in the plate width direction does not detect presence of the metal plate S at the same time. 
       FIG.  13    is a flow chart showing an example of the determination process of the second determination part  58 . Firstly, as described above, each of the first-end side edge crack detection part  54 C and the second-end side edge crack detection part  54 D detects the possibility of existence of an edge crack on the metal plate S (S 202 ). As a result, if the first-end side edge crack detection part  54 C determines that there is a possibility of an edge crack of the metal plate S (S 204  in YES), the second determination part  58  determines whether, at the second-end side edge crack detection part  54 D, the second element  36 B positioned at the outer side of the position of the plate edge E 2  in the plate width direction has detected presence of the metal plate S at the same time as the determination by the first-end side edge crack detection part  54 C in step S 204  (S 206 ). 
     If the second-end side edge crack detection part  54 D determines that the second element  36 B positioned at the outer side of the position of the plate edge E 2  in the plate width direction does not detect presence of the metal plate S at the same time (No in S 206 ), it is determined that the metal plate S has an edge crack (S 208 ), and the flow is completed. Conversely, if the second-end side edge crack detection part  54 D determines that the second element  36 B positioned at the outer side of the position of the plate edge E 2  in the plate width direction has detected presence of the metal plate at the same time (Yes in S 206 ), it is determined that there is a possibility that the metal plate S does not have an edge crack (S 210 ), and the flow is completed. 
     The second determination part  58  may be configured to determine that meandering (oscillation in the plate width direction) has occurred on the metal plate S instead of an edge crack if the first-end side edge crack detection part  54 C determines that there is a possibility of an edge crack and the second-end side edge crack detection part  54 D determines that the second element  36 B positioned at the outer side of the position of the plate edge E 2  in the plate width direction detects presence of the metal plate S at the same time (Yes in S 206 ). 
     Alternatively, the second determination part  58  may be configured to determine that meandering (oscillation in the plate width direction) has occurred on the metal plate S instead of an edge crack when both of the first-end side edge crack detection part  54 C and the second-end side edge crack detection part  54 D determine offset of the plate edge E 1  and the plate edge E 2  toward the same direction at the same time in step S 206 . 
     In the above steps S 202  to S 210 , the same description is still applicable when the first-end side edge crack detection part  54 C and the second-end side edge crack detection part  54 D are switched. 
     According to the above described embodiment, it is determined that the metal plate S has an edge crack when only one of the upstream side edge crack detection part  54 A or the downstream side edge crack detection part  54 B determines that there is a possibility of an edge crack at the same time, and thus it is possible to suppress erroneous determination regarding presence or absence of an edge crack. For instance, it is possible to suppress wrongly determining existence of an edge crack when meandering is actually occurring on the metal plate S. 
     According to the above described embodiment, it is determined that the metal plate S has an edge crack if the first-end side edge crack detection part  54 C determines that there is a possibility of an edge crack and the second-end side edge crack detection part  54 D determines that the second element  36 B positioned at the outer side of the position of the plate edge E 2  in the plate width direction does not detect presence of the metal plate S at the same time, and thus it is possible to suppress erroneous determination regarding presence or absence of an edge crack. For instance, it is possible to suppress wrongly determining existence of an edge crack when meandering is actually occurring on the metal plate S. 
     The overview of an edge crack detection apparatus, a rolling mill facility, and an edge crack detection method according to some embodiments will be described below. 
     (1) According to at least one embodiment of the present invention, an edge crack detection apparatus for detecting an edge crack of a metal plate being conveyed includes: a detection part including a plurality of elements arranged along a plate width direction of the metal plate, each of the plurality of elements being configured to be capable of detecting presence or absence of the metal plate at a position of the element in the plate width direction; a plate edge position determination part configured to determine a plate edge position of the metal plate in the plate width direction on the basis of a detection result of each of a plurality of first elements positioned within a first region in the plate width direction, from among the plurality of elements; and an edge crack detection part configured to detect an edge crack of the metal plate on the basis of a detection result of each of a plurality of second elements selected on the basis of the plate edge position and positioned within a second region which is narrower than the first region in the plate width direction, from among the plurality of elements. 
     With the above configuration (1), it is possible to detect an edge crack using a small number of elements (fewer second elements than first elements) selected on the basis of the plate edge position determined from the detection results by the plurality of first elements. Thus, it is possible to reduce the calculation process load compared to a case where a large number of first elements are used to detect an edge crack, and it is possible to detect an edge crack efficiently. Furthermore, with the above configuration (1), a relatively small number of second elements are used to detect an edge crack, and thus it is easier to detect an edge crack in a short cycle compared to a case where a large number of elements are used. Thus, it is possible to appropriately detect a small edge crack of a metal plate being conveyed at a high speed. 
     (2) In some embodiments, in the above configuration (1), the plate edge position determination part is configured to obtain the detection result by each of the plurality of first elements at intervals of a first cycle time and determine the plate edge position on the basis of the detection result, and the edge crack detection part is configured to obtain the detection result by each of the plurality of second elements at intervals of a second cycle time which is shorter than the first cycle time. 
     While the change of the position of the plate edge during conveyance of the metal plate is relatively slow compared to the conveyance speed of the metal plate, the size of an edge crack is small relative to the conveyance speed of the metal plate. In this regard, with the above configuration (2), the detection result by each of the plurality of first elements is obtained at intervals of the first cycle time that is relatively long, and thus it is possible to suppress an increase in the load of calculation process for determining the position of the plate edge. Also, the detection result by each of the plurality of second elements is obtained at intervals of the second cycle time that is relatively short, and thus it is possible to detect a small edge crack of the metal plate being conveyed at a high speed, more reliably. 
     (3) In some embodiments, in the above configuration (2), the second cycle time is not longer than 1/10of the first cycle time. 
     With the above configuration (3), the detection result by each of the plurality of first elements is obtained at intervals of the first cycle time that is relatively long, or specifically, that is ten times or more compared to the second cycle time, and thus it is possible to suppress an increase in the load of calculation process for determining the position of the plate edge. Also, the detection result by each of the plurality of second elements is obtained at intervals of the second cycle time that is relatively short, or specifically, that is 1/10or less compared to the first cycle time, and thus it is possible to detect a small edge crack of the metal plate being conveyed at a high speed more reliably. 
     (4) In some embodiments, in the above configuration (2) or (3), the plate edge position determination part is configured to read in a state of the plurality of first elements in sequence along the plate width direction at intervals of the first cycle time to obtain the detection result by the plurality of first elements in the first cycle time. 
     With the above configuration (4), the detection results by the plurality of first elements are obtained by reading in the state of the plurality of first elements in sequence along the plate width direction at intervals of the first cycle time, and thus it is possible to determine the position of the plate edge of the metal plate with a relatively simple configuration. 
     (5) In some embodiments, in any one of the above configurations (2) to (4), the edge crack detection part is configured to read in a state of the plurality of second elements in sequence along the plate width direction at intervals of the second cycle time to obtain the detection result by the plurality of second elements in the second cycle time. 
     With the above configuration (5), the detection results by the plurality of second elements are obtained by reading in the state of the plurality of second elements in sequence along the plate width direction at intervals of the second cycle time, and thus it is possible to detect an edge crack of the metal plate with a relatively simple configuration. 
     (6) In some embodiments, in any one of the above configurations (1) to (5), the edge crack detection part is configured to detect the edge crack on the basis of the number of the second element detecting absence of the metal plate at a position of the second element in the plate width direction, from among the plurality of second elements. 
     When an edge crack of the metal plate exists, the second elements corresponding to the position of the edge crack in the plate width direction detect absence of the metal plate at the position, and the other second elements detect presence of the metal plate at positions corresponding to the respective other second elements. With the above configuration (6), it is possible to detect an edge crack of the metal plate appropriately on the basis of the number of the second elements having detected absence of the metal plate at the position of the second element in the plate width direction, from among the plurality of second elements. 
     (7) In some embodiments, in the above configuration (6), the edge crack detection part is configured to determine that the metal plate has the edge crack if each of a predetermined number or more second elements which are arranged continuously detect absence of the metal plate, from among the plurality of second elements. 
     With the above configuration (7), it is possible to detect an edge crack of the metal plate appropriately on the basis of detection of absence of the metal plate at a position in the plate width direction corresponding to the second element by each of a predetermined number or more second elements continuously arranged, from among the plurality of second elements. 
     (8) In some embodiments, in the above configuration (6) or (7), the edge crack detection part is configured to determine that the metal plate has the edge crack if a ratio of the number of the second elements detecting absence of the metal plate to the number of the plurality of second elements is not smaller than a predetermined value. 
     With the above configuration (8), it is possible to detect an edge crack of the metal plate appropriately on the basis of that a ratio of the number of the second elements detecting absence of the metal plate to the number of the plurality of second elements is not smaller than a predetermined value. 
     (9) In some embodiments, in any one of the above configurations (1) to (8), the second region is a region between the plate edge position and a position offset inward in the plate width direction from the plate edge position. 
     An edge crack of a metal plate forms within a positional range at the inner side from the plate edge of the metal plate. With the above configuration (9), it is possible to detect an edge crack of the metal plate appropriately on the basis of the detection results by the plurality of second elements within the second region being a region at the inner side of the plate edge position. 
     (10) In some embodiments, in any one of the above configurations (1) to (9), the edge crack detection part is configured to determine a possibility of existence of the edge crack of the metal plate on the basis of whether the second element positioned at an inner side of the plate edge position detects absence of the metal plate, from among the plurality of second elements. The edge crack detection apparatus includes: an upstream side edge crack detection part being the edge crack detection part; a downstream side edge crack detection part being the edge crack detection part and being disposed at a position different from that of the upstream side edge crack detection part in a conveyance direction of the metal plate; and a first determination part configured to determine that the metal plate has the edge crack if, at the same time, only one of the upstream side edge crack detection part or the downstream side edge crack detection part determines that there is a possibility of the edge crack. 
     With the above configuration (10), it is determined that the metal plate has an edge crack when only one of the upstream side edge crack detection part or the downstream side edge crack detection part positioned at different positions in the conveyance direction of the metal plate determines that there is a possibility of an edge crack at the same time, and thus it is possible to suppress erroneous determination regarding presence or absence of an edge crack. 
     (11) In some embodiments, in any one of the above configurations (1) to (8), the edge crack detection part is configured to determine a possibility of existence of the edge crack of the metal plate on the basis of whether the second element positioned at an inner side of the plate edge position detects absence of the metal plate, from among the plurality of second elements. The edge crack detection apparatus includes: a first-end side edge crack detection part being the edge crack detection part; a second-end side edge crack detection part being the edge crack detection part and being disposed at an opposite side to the first-end side edge crack detection part across the metal plate in the plate width direction; and a second determination part configured to determine that the metal plate has the edge crack if, at the same time, the first-end side edge crack detection part determines that there is a possibility of the edge crack and the second element of the second-end side edge crack detection part positioned at an outer side of the plate edge position in the plate width direction does not detect presence of the metal plate. 
     With the above configuration (11), it is determined that the metal plate has an edge crack if the first-end side edge crack detection part determines that there is a possibility of an edge crack and the second element of the second-end side edge crack detection part positioned at the outer side of the position of the plate edge in the plate width direction does not detect presence of the metal plate at the same time, and thus it is possible to suppress erroneous determination regarding presence or absence of an edge crack. 
     (12) In some embodiments, in any one of the above configurations (1) to (11), the detection part includes: a radiation receiving part including the plurality of elements; and a radiation generation part disposed at an opposite side to the radiation receiving part across the metal plate and configured to generate radiation which radiates toward the radiation receiving part. Each of the plurality of elements is configured to detect absence of the metal plate at a position of the element in the plate width direction when receiving the radiation, and detect presence of the metal plate at the position of the element in the plate width direction when not receiving the radiation. 
     The vicinity of the processing apparatus (e.g., rolling mill apparatus) for a metal plate is often a harsh environment where rolling mill oil and fume scatter in large quantity, the apparatuses vibrate, and the place is dark, for instance. In this regard, with the above configuration (12), an edge crack sensor which detects an edge crack by using radiation is used, and thus it is possible to detect an edge crack in the vicinity of a processing apparatus under a harsh environment. 
     (13) According to at least one embodiment of the present invention, a rolling mill facility includes: a rolling mill apparatus for rolling a metal plate; and the edge crack detection apparatus according to any one of the above (1) to (12) configured to detect an edge crack at an end portion, in the plate width direction, of the metal plate during rolling by the rolling mill apparatus. 
     With the above configuration (13), it is possible to detect an edge crack using a small number of second elements (fewer second elements than first elements) selected on the basis of the plate edge position determined from the detection results by the plurality of first elements. Thus, it is possible to reduce the calculation process load compared to a case where a large number of first elements are used to detect an edge crack, and it is possible to detect an edge crack efficiently. Furthermore, with the above configuration (13), a relatively small number of second elements are used to detect an edge crack, and thus it is easier to detect an edge crack in a short cycle compared to a case where a large number of elements are used. Thus, it is possible to appropriately detect a small edge crack of a metal plate being conveyed at a high speed. 
     (14) According to at least one embodiment of the present invention, a method of detecting an edge crack of a metal plate being conveyed, using a detection part including a plurality of elements arranged along a plate width direction of the metal plate, each of the plurality of elements being configured to be capable of detecting presence or absence of the metal plate at a position of the element in the plate width direction, includes: a step of determining a plate edge position of the metal plate in the plate width direction on the basis of a detection result of each of a plurality of first elements positioned within a first region in the plate width direction, from among the plurality of elements; a step of selecting, on the basis of the determined plate edge position, a plurality of second elements positioned within a second region which is narrower than the first region in the plate width direction, from among the plurality of elements; and a step of detecting an edge crack of the metal plate on the basis of a detection result by each of the plurality of the selected second elements. 
     According to the above method (14), it is possible to detect an edge crack using a small number of second elements (fewer second elements than first elements) selected on the basis of the plate edge position determined from the detection results by the plurality of first elements. Thus, it is possible to reduce the calculation process load compared to a case where a large number of first elements are used to detect an edge crack, and it is possible to detect an edge crack efficiently. Furthermore, according to the above method (14), a relatively small number of second elements are used to detect an edge crack, and thus it is easier to detect an edge crack in a short cycle compared to a case where a large number of elements are used. Thus, it is possible to appropriately detect a small edge crack of a metal plate being conveyed at a high speed. 
     Embodiments of the present invention were described in detail above, but the present invention is not limited thereto, and various amendments and modifications may be implemented. 
     Further, in the present specification, an expression of relative or absolute arrangement such as “in a direction”, “along a direction”, “parallel”, “orthogonal”, “centered”, “concentric” and “coaxial” shall not be construed as indicating only the arrangement in a strict literal sense, but also includes a state where the arrangement is relatively displaced by a tolerance, or by an angle or a distance whereby it is possible to achieve the same function. 
     For instance, an expression of an equal state such as “same” “equal” and “uniform” shall not be construed as indicating only the state in which the feature is strictly equal, but also includes a state in which there is a tolerance or a difference that can still achieve the same function. 
     Further, for instance, an expression of a shape such as a rectangular shape or a cylindrical shape shall not be construed as only the geometrically strict shape, but also includes a shape with unevenness or chamfered corners within the range in which the same effect can be achieved. 
     On the other hand, an expression such as “comprise”, “include”, “have”, “contain” and “constitute” are not intended to be exclusive of other components. 
     Reference Signs List
           1  Rolling mill facility     2  Rolling mill apparatus     4  Unwinder     6  Input-side pinch roll     10  Rolling mill stand     12  Output-side pinch roll     14  Rewinder     15  Work roll     16  Work roll     17  Intermediate roll     18  Intermediate roll     19  Backup roll     20  Backup roll     30  Detection part     30 A Upstream side detection part     30 B Downstream side detection part     30 C First-end side detection part     30 D Second-end side detection part     32  Radiation generation part     34  Radiation receiving part     36  Element     36 A,  36 A′ First element     36 B Second element     50  Processing part     52  Plate edge position determination part     52 A Upstream side plate edge position determination part     52 B Downstream side plate edge position determination part     52 C First-end side plate edge position determination part     52 D Second-end side plate edge position determination part     54  Edge crack detection part     54 A Upstream side edge crack detection part     54 B Downstream side edge crack detection part     54 C First-end side edge crack detection part     54 D Second-end side edge crack detection part     56  First determination part     58  Second determination part     100  Edge crack detection apparatus     101  Radiation   E Plate edge   E 1  First end   E 2  Second end   R 1  First region   R 2  Second region   S Metal plate