Patent Publication Number: US-2022234088-A1

Title: Bending system

Description:
TECHNICAL FIELD 
     The present disclosure relates to a bending system for performing bending for a plate-shaped workpiece (a sheet metal). 
     BACKGROUND ART 
     A bending system includes a press brake to perform bending for a workpiece, and the press brake includes upper and lower tables and tool holders provided on the respective tables and configured to retain tools. Further, the bending system includes a tool rack arranged on the side of the press brake and configured to store a plurality of tools. The tool rack has a plurality of stockers for retaining tools in which selected arbitrary stockers are configured such that the stockers can be positioned at exchange positions for performing tool exchange. Furthermore, the bending system includes tool exchange units for transporting tools between the tool holders and stockers positioned at the exchange positions, and each tool exchange unit has a tool retention member that is engageable with and disengageable from an engagement hole of a tool (see Patent Literature 1). 
     As prior-art techniques related to the present disclosure, techniques shown in Patent Literatures 2 to 4 exist in addition to the technique of Patent Literature 1. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature 1: Japanese Patent No. 5947861 
         Patent Literature 2: Japanese Patent No. 4672868 
         Patent Literature 3: Japanese Patent No. 4558852 
         Patent Literature 4: Japanese Patent Application Laid-Open Publication No. 2003-71519 
       
    
     SUMMARY 
     A conventional bending system does not recognize actual positions of tools in a left-right direction on tool holders. Therefore, the conventional bending system has the following problem. 
     For example, if a tool is fitted to a position deviated from a regular arrangement position on a tool holder corresponding to tool layout information, and engagement or disengagement of a tool retention member with an engagement hole of a tool (a retention operation) fails, an alarm occurs, and an operation related to tool transportation by a tool exchange unit stops. Further, for example, if a clamp plate or a clamper of a tool holder is accidentally released after tools are fitted to the tool holder, there is a possibility that the tools slightly move and are displaced from regular arrangement positions on the tool holder, and, therefore, it is not possible to perform the operation related to tool transportation by a tool exchange unit. Furthermore, for example, tools are randomly laid out on a tool holder by manual work or the like, it is not possible to lay out again the tools at the regular arrangement positions on the tool holder by a tool exchange unit. That is, in the former case, there is a problem that it becomes difficult to stabilize automatic operation of the bending system. Here, the operation related to tool transportation is assumed to include an operation of exchanging tools fitted to a tool holder with tools fitted to a stocker, an operation of retaining a tool by a tool retention member and an operation of laying out tools on a tool holder or a stocker. 
     In a case where tools are randomly laid out on a tool holder by manual work or the like in a general-purpose bending system without tool exchange units, problems similar to the above also occur. 
     Therefore, an object of the present disclosure is to provide a bending system capable of accurately recognizing actual positions of tools in a left-right direction on a tool holder or on a stocker. 
     A bending system according to a first aspect of one or more embodiments includes: a moving body provided on a back side or a front side of a table of a press brake so as to be movable in a left-right direction; a moving actuator configured to cause the moving body to move in the left-right direction relative to the table; and a position detector configured to detect a position of the moving body in the left-right direction. The bending system according to a first embodiment includes: a hole detector provided on the moving body and configured to detect an engagement hole for causing a tool retention member of a tool exchange unit to be engaged and disengaged, the engagement hole being a part of a tool fitted to a tool holder provided on the table; and a hole position acquisition unit configured to acquire a position of the engagement hole of the tool in the left-right direction, based on the position of the moving body in the left-right direction at the time of the engagement hole of the tool being detected. 
     The bending system according to the first aspect may further include an information reader provided on the moving body and configured to read, from a storage medium provided to the tool, tool information including a width dimension of the tool in the left-right direction and a relative position of the engagement hole in the tool. 
     According to the first aspect, the moving body is moved in the left-right direction relative to the table by driving of the moving actuator while the position of the moving body in the left-right direction is being detected by the position detector. Further, during the movement of the moving body, the engagement hole of the tool is detected by the tool detector. Then, the hole position acquisition unit acquires the position of the engagement hole of the tool in the left-right direction, based on the position of the moving body in the left-right direction at the time of the engagement hole of the tool being detected. Thereby, the bending system can recognize an actual position of the engagement hole of the tool in the left-right direction on the tool holder. 
     A bending system according to a second aspect of one or more embodiments further includes: a moving body provided on a back side or a front side of a table of a press brake so as to be movable in a left-right direction; a moving actuator configured to cause the moving body to move in the left-right direction relative to the table; and a position detector configured to detect a position of the moving body in the left-right direction. The bending system according to the second aspect includes: an end face detector provided on the moving body and configured to detect an end face of a tool fitted to a tool holder provided on the table; and an information reader provided on the moving body and configured to read, from a storage medium provided to the tool, tool information including a width dimension of the tool in the left-right direction and a relative position of an engagement hole in the tool, the engagement hole being a part of the tool and being for causing a tool retention member of a tool exchange unit to be engaged and disengaged. The bending system according to the second aspect further includes: a hole position acquisition unit configured to acquire a position of the engagement hole of the tool in the left-right direction, based on the position of the moving body in the left-right direction at the time of the end face of the tool being detected, and the read tool information about the tool. 
     According to the second aspect, the moving body is moved in the left-right direction by driving of the moving actuator while the position of the moving body in the left-right direction is being detected by the position detector. During the movement of the moving body, the end face of the tool is detected by the tool detector, and the tool information about the tool is read by the information reader. Then, the hole position acquisition unit acquires the position of the engagement hole of the tool in the left-right direction, based on the position of the moving body in the left-right direction at the time of the end face of the tool being detected, and the read tool information about the tool. Thereby, the bending system can recognize an actual position of the engagement hole of the tool in the left-right direction on the tool holder. 
     A bending system according to a third aspect of one or more embodiments includes: a moving body provided on a back side or a front side of a table of a press brake so as to be movable in a left-right direction; a moving actuator configured to cause the moving body to move in the left-right direction relative to the table; and a position detector configured to detect a position of the moving body in the left-right direction. The bending system according to the third aspect further includes: an end face detector provided on the moving body and configured to detect an end face of a tool fitted to a tool holder provided on the table; and an information reader provided on the moving body and configured to read, from a storage medium provided to the tool, tool information including a width dimension of the tool in the left-right direction. The bending system according to the third aspect further includes a tool position acquisition unit configured to acquire a position of the tool in the left-right direction (a position of the end face of the tool in the left-right direction or a position of the center of the tool in the left-right direction), based on the position of the moving body in the left-right direction at the time of the end face of the tool being detected, and the read tool information about the tool. 
     The bending system according to the third aspect may further include an information reader provided on the moving body and configured to read, from a storage medium provided to the tool, tool information including a width dimension of the tool in the left-right direction. 
     According to the third aspect, the moving body is moved in the left-right direction by driving of the moving actuator while the position of the moving body in the left-right direction is being detected by the position detector. During the movement of the moving body, the engagement hole of the tool is detected by the hole detector, and the tool information about the tool is read by the information reader. Then, the tool position acquisition unit acquires the position of the tool in the left-right direction, based on the position of the moving body in the left-right direction at the time of the engagement hole of the tool being detected, and the read tool information about the tool. Thereby, the bending system can recognize an actual position of the tool in the right direction on the tool holder. 
     According to the present disclosure, it is possible to accurately recognize an actual positions of a tool in a left-right direction on a tool holder or stocker. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic front view of a bending system according to first and second embodiments. 
         FIG. 2  is a schematic right side view of the bending system according to the first embodiment, and shows that die tools are retained by a lower tool retention member, and punch tools are retained by an upper tool retention member. In  FIG. 2 , a lower joint block and an upper joint block are omitted. 
         FIG. 3  is an enlarged diagram of a part III in  FIG. 2 . 
         FIG. 4( a )  is a schematic diagram showing that an engagement hole of a die tool is being detected, and that identification information about the die tool is being read in the first embodiment.  FIG. 4( b )  is a schematic diagram showing that a monitoring beam moves in a left-right direction in the first embodiment. 
         FIG. 5( a )  is a schematic diagram showing that an engagement hole of a punch tool is being detected, and that identification information about the punch tool is being read in the first embodiment.  FIG. 5( b )  is a schematic diagram showing that a monitoring beam moves in the left-right direction in the first embodiment. 
         FIG. 6  is a control block diagram of the bending system according to the first and second embodiments. 
         FIGS. 7A (a) and  7 A(b) are schematic diagrams illustrating a retry process of a lower tool exchange unit and the like according to the first embodiment. 
         FIGS. 7B (a) and  7 B(b) are schematic diagrams illustrating a retry process of the lower tool exchange unit and the like according to the first embodiment. 
         FIGS. 8A (a) and  8 A(b) are schematic diagrams illustrating a layout process of the lower tool exchange unit and the like. 
         FIGS. 8B (a) and  8 B(b) are schematic diagrams illustrating a layout process of the lower tool exchange unit and the like. 
         FIG. 9( a )  is a schematic diagram showing that an end face of a die tool is being detected, and that identification information about the die tool is being read in a second embodiment.  FIG. 9( b )  is a schematic diagram showing that a monitoring beam moves in the left-right direction in the second embodiment. 
         FIG. 10( a )  is a schematic diagram showing that an end face of a punch tool is being detected, and that identification information about the punch tool is being read in the second embodiment.  FIG. 10( b )  is a schematic diagram showing that the monitoring beam moves in the left-right direction in the second embodiment. 
         FIGS. 11A (a) and  11 A(b) are schematic diagrams illustrating a retry process of a lower tool exchange unit and the like according to the second embodiment. 
         FIGS. 11B (a) and  11 B(b) are schematic diagrams illustrating a retry process of the lower tool exchange unit and the like according to the second embodiment. 
         FIGS. 12A (a) and  12 A(b) are schematic diagrams illustrating a layout process of the lower tool exchange unit and the like according to the second embodiment. 
         FIGS. 12B (a) and  12 B(b) are schematic diagrams illustrating a layout process of the lower tool exchange unit and the like according to the second embodiment. 
         FIG. 13  is a control block diagram of a bending system according to a third embodiment. 
         FIGS. 14( a ) and 14( b )  are schematic diagrams illustrating a process of detecting an end face of a die tool in the third embodiment. 
         FIG. 15  is a control block diagram of a bending system according to a fourth embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First to fourth embodiments will be explained below with reference to  FIGS. 1 to 15 . 
     In the specification and Claims of the present application, “being provided” is assumed to include being indirectly provided via another member in addition to being directly provided. “A left-right direction” is one of horizontal directions and is synonymous with a lateral direction of a press brake, a tool rack, a tool holder or a tool. “A front-back direction” refers to a horizontal direction orthogonal to the left-right direction and is synonymous with a depth direction of the press brake or the tool rack. “Read tool information about a tool” is assumed to include reading identification information about a tool corresponding to tool information about the tool. In the drawings, “FF”, “FR”, “L”, “R”, “U” and “D” refer to a front direction, a back direction, a left direction, a right direction, an up direction and a down direction, respectively. 
     First Embodiment 
     As shown in  FIGS. 1 to 3 , a bending system  10  according to a first embodiment is a system for performing bending for a plate-shaped workpiece (a sheet metal) W using punch tools  12  as automatically exchangeable upper tools and die tools  14  as lower tools. Further, the bending system  10  includes a press brake  16  to perform bending for the workpiece W in cooperation with the punch tools  12  and the die tools  14 . First, a configuration of the press brake  16  will be specifically explained. 
     The press brake  16  includes a main frame  18 , and the main frame  18  has a pair of side plates  20  separated in the left-right direction and facing each other, and a plurality of coupling members  22  to couple the pair of side plates  20 . Further, at a lower part of the main frame  18 , a lower table  24  extending in the left-right direction is provided. At an upper part of the main frame  18 , an upper table  26  extending in the left-right direction is provided being movable in a vertical direction. At an upper part of each side plate  20 , a hydraulic cylinder  28  is provided as a vertically moving actuator to cause the upper table  26  to move in the vertical direction relative to the main frame  18 . 
     The lower table  24  may be configured to be movable in the vertical direction instead of configuring the upper table  26  to be movable in the vertical direction. As vertically moving actuators, servo motors (not shown) may be used instead of the hydraulic cylinders  28 . 
     On the upper side of the lower table  24 , a lower tool holder  30  to removably retain die tools  14  is provided, and the lower tool holder  30  extends in the left-right direction. On the lower tool holder  30 , a holder groove  30   g  into which shanks (bases)  14   s  of the die tools  14  are to be inserted is formed along the left-right direction, the holder groove  30   g  being in a publicly known configuration as shown in Patent Literatures 2 and 3. The lower tool holder  30  has a hydraulic clamper  32  to fix the die tools  14  to the lower table  24 . 
     Here, as shown in  FIG. 4 , in the center of each die tool  14  in the left-right direction (the lateral direction), an engagement hole  14   h  as a part of the die tool  14  is penetratingly formed. At positions corresponding to the engagement hole  14   h  (for example, on the lower side of the engagement hole  14   h ) on both faces (the front face and back face) of the die tool  14 , identification marks  14   m  as storage media storing identification information about the die tool  14  are provided by engraving, and each identification mark  14   m  is configured with a two-dimensional code. The identification information about the die tool  14  corresponds to tool information about the die tool  14 , and the tool information about the die tool  14  includes a type, shape, width dimension in the left-right direction and height dimension of the die tool  14 , a relative position of the center of the engagement hole  14   h  in the die tool  14  and the like. The width dimension of the die tool  14  in the left-right direction is assumed to include a dimension from an end face  14   e  of the die tool  14  to the center of the die tool  14  in the left-right direction. The relative position of the center of the engagement hole  14   h  in the die tool  14  is assumed to include a dimension from the end face  14   e  of the die tool  14  to the center of the engagement hole  14   h  in the left-right direction and an amount of deviation of the center of the engagement hole  14   h  relative to the center of the die tool  14 . 
     As shown in  FIGS. 1 to 3 , an upper tool holder  34  to removably retain the punch tools  12  is provided on the lower side of the upper table  26 , and the upper tool holder  34  extends in the left-right direction. On the upper tool holder  34 , a holder groove  34   g  into which shanks (bases)  12   s  of punch tools  12  are to be inserted is formed along the left-right direction, the holder groove  34   g  being in a publicly known configuration as shown in Patent Literatures 2 and 3. The upper tool holder  34  has a hydraulic clamp plate  36  to fix the punch tools  12  to the upper table  26 . 
     Here, as shown in  FIG. 5 , in the center of each punch tool  12  in the left-right direction, an engagement hole  12   h  as a part of the punch tool  12  is penetratingly formed. At positions corresponding to the engagement hole  12   h  (for example, on the lower side of the engagement hole  12   h ) on both faces of the punch tool  12 , identification marks  12   m  as storage media storing identification information about the punch tool  12  are provided by engraving, and each identification mark  12   m  is configured with a two-dimensional code. The identification information about the punch tool  12  corresponds to tool information about the punch tool  12 , and the tool information about the punch tool  12  includes a type, shape, width dimension in the left-right direction and height dimension of the punch tool  12 , a relative position of the center of the engagement hole  12   h  in the punch tool  12  and the like. The width dimension of the punch tool  12  in the left-right direction is assumed to include a dimension from an end face  12   e  of the punch tool  12  to the center in the left-right direction. The relative position of the center of the engagement hole  12   h  in the punch tool  12  is assumed to include a dimension from the end face  12   e  of the punch tool  12  to the center of the engagement hole  12   h  in the left-right direction and an amount of deviation of the center of the engagement hole  12   h  relative to the center of the punch tool  12 . 
     As shown in  FIG. 1 , on one side (the right side) of the lower tool holder  30  in the left-right direction, a lower joint block  38  extending in the left-right direction is provided. On the lower joint block  38 , a joint groove (not shown) into which the shank  14   s  of a die tool  14  is to be inserted is formed along the left-right direction. The joint groove of the lower joint block  38  is connected to the holder groove  30   g  (see  FIG. 3 ) of the lower tool holder  30 . Further, on one side of the upper tool holder  34  in the left-right direction, an upper joint block  40  extending in the left-right direction is provided. On the upper joint block  40 , a joint groove (not shown) into which the shank  12   s  of a punch tool  12  are to be inserted is formed along the left-right direction. The joint groove  40   g  of the upper joint block  40  is connected to the holder groove  34   g  (see  FIG. 3 ) of the upper tool holder  34 . 
     As shown in  FIGS. 1 and 2 , the bending system  10  includes a tool rack  42  arranged on the side (the right side) of the press brake in the left-right direction and storing a plurality of die tools  14  and a plurality of punch tools  12 . The tool rack  42  is, for example, in a publicly known configuration as shown in Patent Literatures 1 and 4. The configuration of the tool rack  42  will be simply explained. 
     The tool rack  42  has a plurality of lower stockers  44  for retaining one or more die tools  14 , and the plurality of lower stockers  44  are arranged in the front-back direction. Each lower stocker  44  extends in the left-right direction, and, on each lower stocker  44 , a stocker groove  44   g  into which the shanks  14   s  of die tools  14  are to be inserted is formed along the left-right direction. 
     A configuration is made so that a selected arbitrary lower stocker  44  is movable in the front-back direction by such a lower stocker movement mechanism (not shown) as shown in Patent Literature 1. Alternatively, the plurality of lower stockers  44  are configured to be synchronously movable in the front-back direction by such a lower stocker movement mechanism (not shown) as shown in Patent Literature 4. A configuration is made so that the selected arbitrary lower stocker  44  is positioned at a lower tool exchange position contiguous to the lower joint block  38  in the left-right direction, by its movement in the front-back direction. When the arbitrary lower stocker  44  is positioned at the lower tool exchange position, the stocker groove  44   g  of the lower stocker  44  is connected to the joint groove of the lower joint block  38 . 
     The tool rack  42  has a plurality of upper stockers  46  for retaining one or more punch tools  12 , and the plurality of upper stockers  46  are arranged along the front-back direction. Each upper stocker  46  extends in the left-right direction, and, on each upper stocker  46 , a stocker groove  46   g  into which the shanks  12   s  of punch tools  12  are to be inserted is formed along the left-right direction. 
     A configuration is made so that a selected arbitrary upper stocker  46  is movable in the front-back direction by such an upper stocker movement mechanism (not shown) as shown in Patent Literature 1. Alternatively, the plurality of upper stockers  46  are configured to be synchronously movable in the front-back direction by such an upper stocker movement mechanism (not shown) as shown in Patent Literature 4. A configuration is made so that the selected arbitrary upper stocker  46  is positioned at an upper tool exchange position contiguous to the upper joint block  40  in the left-right direction, by its movement in the front-back direction. When the arbitrary upper stocker  46  is positioned at the upper tool exchange position, the stocker groove  46   g  of the upper stocker  46  is connected to the joint groove of the upper joint block  40 . 
     As shown in  FIGS. 1 to 3 , a lower guide  48  extending in the left-right direction is provided on the back side (the rear side) of the lower tool holder  30 , and the lower guide  48  projects to the right of the lower joint block  38 . On the back side of the lower table  24 , a pair of lower tool exchange units  50  as lower moving bodies are provided being movable in the left-right direction via the lower guide  48 . The lower tool exchange units  50  transport die tools  14  between the lower tool holder  30  and a lower stocker  44  positioned at the lower tool exchange position. Each lower tool exchange unit  50  moves in the left-right direction relative to the lower table  24  by driving of a servo motor  52  as a left-right moving actuator provided at an appropriate position on the lower tool exchange unit  50 . The servo motor  52  has an encoder  54  as a position detector to detect a position of the lower tool exchange unit  50  in the left-right direction. 
     Each lower tool exchange unit  50  is in a publicly known configuration as shown in Patent Literatures 2 and 3, and has a lower unit body  56  provided on the lower guide  48  being movable in the left-right direction and a lower support member  58  provided on the lower unit body  56  being movable in the front-back direction and in the vertical direction. The lower support member  58  moves in the front-back direction relative to the lower unit body  56  by driving of an air cylinder  60  as a front-back moving actuator provided at an appropriate position on the lower unit body  56 . The lower support member  58  moves in the vertical direction relative to the lower unit body  56  by driving of an air cylinder  62  as a vertically moving actuator provided at an appropriate position on the lower unit body  56 . 
     Each lower tool exchange unit  50  has a lower tool retention member (a lower hook member)  64  provided on the lower support member  58  being movable in the front-back direction, and the lower tool retention member  64  is engageable with and disengageable from the engagement hole  14   h  of a die tool  14 . The lower tool retention member  64  moves in the front-back direction relative to the lower support member  58  by driving of an air cylinder  66  as another front-back moving actuator provided at an appropriate position on the lower support member  58 . 
     Since an operation of retaining a die tool  14  by the lower tool retention member  64  is commonly known as shown in Patent Literatures 2 and 3, details thereof will be omitted. 
     As shown in  FIGS. 3 and 4 , at an appropriate position on each lower support member  58 , a photoelectric sensor  68  is provided as a hole detector to detect the engagement hole  14   h  of a die tool  14  fitted to the lower tool holder  30 . The photoelectric sensor  68  is configured to emit an inspection beam B and detect the engagement hole  14   h  of the die tool  14  from a result of receiving a reflected beam of the inspection beam B, in a state of being located at the same height as the engagement hole  14   h  of the die tool  14 . 
     On the lower side of the photoelectric sensor  68  on each lower support member  58 , a two-dimensional code reader  70  as an information reader is provided, and the two-dimensional code reader  70  reads tool identification information about a die tool  14  from an identification mark  14   m  in a state of being located at the same height as the identification mark  14   m . In other words, on the lower side of the photoelectric sensor  68  on the lower support member  58 , the two-dimensional code reader  70  to read tool information about the die tool  14  via the tool identification information about the die tool  14  is provided. 
     The photoelectric sensor  68  and the two-dimensional code reader  70  may be provided on the lower unit body  56  instead of being provided on the lower support member  58 . 
     As shown in  FIGS. 1 to 3 , an upper guide  72  extending in the left-right direction is provided on the back side of the upper tool holder  34 , and the upper guide  72  projects to the right of the upper joint block  40 . On the back side of the upper table  26 , a pair of upper tool exchange units  74  as upper moving bodies are provided being movable in the left-right direction via the upper guide  72 . The upper tool exchange units  74  transport punch tools  12  between the upper tool holder  34  and an upper stocker  46  positioned at the upper tool exchange position. Each upper tool exchange unit  74  moves in the left-right direction relative to the upper table  26  by driving of a servo motor  76  as a left-right moving actuator provided at an appropriate position on the upper tool exchange unit  74 . The servo motor  76  has an encoder  78  as a position detector to detect a position of the upper tool exchange unit  74  in the left-right direction. 
     Each upper tool exchange unit  74  is in a publicly known configuration as shown in Patent Literatures 2 and 3, and has an upper unit body  80  provided on the upper guide  72  being movable in the left-right direction and an upper support member  82  provided on the upper unit body  80  being movable in the front-back direction and in the vertical direction. The upper support member  82  moves in the front-back direction relative to the upper unit body  80  by driving of an air cylinder  84  as a front-back moving actuator provided at an appropriate position on the upper unit body  80 . The upper support member  82  moves in the vertical direction relative to the upper unit body  80  by driving of an air cylinder  86  as a vertically moving actuator provided at an appropriate position on the upper unit body  80 . 
     Each upper tool exchange unit  74  has an upper tool retention member (an upper hook member)  88  provided on the upper support member  82  being movable in the front-back direction, and the upper tool retention member  88  is engageable with and disengageable from the engagement hole  12   h  of a punch tool  12 . The upper tool retention member  88  moves in the front-back direction relative to the upper support member  82  by driving of an air cylinder  90  as another front-back moving actuator provided at an appropriate position on the upper support member  82 . 
     Since an operation of retaining a punch tool  12  by the upper tool retention member  88  is commonly known as shown in Patent Literatures 2 and 3, details thereof will be omitted. 
     As shown in  FIGS. 3 and 5 , at an appropriate position on each upper support member  82 , a photoelectric sensor  92  is provided as a hole detector to detect the engagement hole  12   h  of a punch tool  12  fitted to the upper tool holder  34 . The photoelectric sensor  92  is configured to emit an inspection beam B and detect the engagement hole  12   h  of the punch tool  12  from a result of receiving a reflected beam of the inspection beam B, in a state of being located at the same height as the engagement hole  12   h  of the punch tool  12 . 
     On the upper side of the photoelectric sensor  92  on each upper support member  82 , a two-dimensional code reader  94  as an information reader is provided, and the two-dimensional code reader  94  reads identification information about a punch tool  12  from an identification mark  12   m  in a state of being located at the same height as the identification mark  12   m . In other words, on the upper side of the photoelectric sensor  92  on the upper support member  82 , the two-dimensional code reader  94  to read tool information about the punch tool  12  via the identification information about the punch tool  12  is provided. 
     The photoelectric sensor  92  and the two-dimensional code reader  94  may be provided on the upper unit body  80  instead of being provided on the upper support member  82 . 
     As shown in  FIGS. 1 and 6 , the bending system  10  includes a database  96  storing tool information about the plurality of die tools  14  and tool information about the plurality of punch tools  12 . The tool information about the plurality of die tools  14  is associated with identification information about the plurality of die tools  14  in the database  96 . The tool information about the plurality of punch tools  12  is associated with identification information about the plurality of punch tools  12  in the database  96 . 
     The bending system  10  includes a control device  98  to control the hydraulic cylinders  28  and the like based on a processing program and controls the lower tool exchange units  50  and the like based on a tool exchange program. The control device  98  is configured with a computer, and the encoders  54 , the photoelectric sensors  68 , the two-dimensional code readers  70 , the encoders  78 , the photoelectric sensors  92 , the two-dimensional code readers  94 , the database  96  and the like are connected to the control device  98 . The control device  98  has a memory (not shown) storing the processing program, the tool exchange program and the like, and a CPU (not shown) that executes the processing program and the tool exchange program. 
     The processing program and the tool exchange program include layout information showing a layout state of die tools  14  and layout information showing a layout state of die tools  14  on each lower stocker  44 . The processing program and the tool exchange program include layout information showing a layout state of the punch tools  12  and layout information showing a layout state of the punch tools  12  on each upper stocker  46 . 
     By executing the tool exchange program, the CPU of the control device  98  demonstrates functions as a hole position acquisition unit  100 , a tool information acquisition unit  102 , a retry control unit  104  and a layout control unit  106 . Specific content of functions of the hole position acquisition unit  100 , the tool information acquisition unit  102 , the retry control unit  104  and the layout control unit  106  are as below. 
     As shown in  FIGS. 4 to 6 , based on positions of the lower tool exchange units  50  in the left-right direction at the time of engagement holes  14   h  of die tools  14  being detected by the photoelectric sensors  68 , the hole position acquisition unit  100  acquires positions of centers of the engagement holes  14   h  of the die tools  14  in the left-right direction by calculation. The hole position acquisition unit  100  acquires the positions of the centers of the engagement holes  14   h  of the die tools  14  in the left-right direction in consideration of relative positions of the photoelectric sensors  68  relative to the lower unit bodies  56 . Similarly, based on positions of the upper tool exchange units  74  in the left-right direction at the time of engagement holes  12   h  of punch tools  12  being detected by the photoelectric sensors  92 , the hole position acquisition unit  100  acquires positions of centers of the engagement holes  12   h  of the punch tools  12  in the left-right direction by calculation. The hole position acquisition unit  100  acquires the positions of the centers of the engagement holes  12   h  of the punch tools  12  in the left-right direction in consideration of a relative positions of the photoelectric sensors  92  relative to the upper unit bodies  80 . 
     Referring to the database  96 , the tool information acquisition unit  102  acquires tool information about the die tools  14 , including width dimensions of the die tools  14  in the left-right direction and relative positions of the centers of the engagement holes  14   h , based on identification information about the die tools  14  from the two-dimensional code readers  70 . Similarly, referring to the database  96 , the tool information acquisition unit  102  acquires tool information about the punch tools.  12 , including width dimensions of the punch tools  12  in the left-right direction and relative positions of the centers of the engagement holes  12   h , based on identification information about the punch tools  12  from the two-dimensional code readers  94 . 
     As shown in  FIGS. 3, 4, 6, 7A and 7B , if the operation of retaining a die tool  14  by one of the lower tool retention members  64  fails (see  7 ( a )), the retry control unit  104  executes a retry process of the lower tool exchange unit  50  and the like as below. Here, the failure in the operation of retaining the die tool  14  by the lower tool retention member  64  is judged by the fact that the air cylinder  60  or  66  has not reached a stroke end. If the operation of retaining the die tool  14  by the lower tool retention member  64  fails, an alarm occurs. 
     The retry control unit  104  controls the servo motor  52  so that the lower tool exchange unit  50  moves in the left-right direction (for example, in the left direction) relative to the lower table  24  by an amount corresponding to a relative position of the engagement hole  14   h  of the die tool  14 , which is tool information about the die tool  14  acquired immediately after the alarm occurs (see  FIG. 7A (a)). Next, the retry control unit  104  controls the servo motor  52  so that the lower tool exchange unit  50  moves in the left-right direction (for example, in the right direction) relative to the lower table  24  near a position where the alarm occurred (see  FIGS. 7A (b) and  7 B(a)). After that, based on a position of the center of the engagement hole  14   h  of the die tool  14  in the left-right direction acquired during movement of the lower tool exchange unit  50 , the retry control unit  104  controls the lower tool exchange unit  50  to retry the operation of retaining the die tool  14  by the lower tool retention member  64  (see  FIG. 7B (b)). 
     If the operation of retaining a punch tool  12  by one of the upper tool retention members  88  fails, the retry control unit  104  also executes the retry process of the upper tool exchange unit  74  and the like similarly to the above. 
     As shown in  FIGS. 3, 4, 6, 8A and 8B , if the clamper  32  is accidentally released after a plurality of die tools  14  are fitted to the lower tool holder  30 , the layout control unit  106  executes a layout process of the lower tool exchange units  50  and the like as below. Similarly, if a plurality of die tools  14  are randomly fitted to the lower tool holder  30  by manual work of a worker, the layout control unit  106  also executes the layout process of the lower tool exchange units  50  and the like as necessary. 
     The layout control unit  106  controls the servo motors  52  so that the lower tool exchange units  50  move in the left-right direction (for example, in the right direction) relative to the lower table  24  from the side of the lower table  24  (see  FIGS. 8A (a) and  8 A(b) and  FIG. 8B (a)). After that, based on acquired positions of the centers of the engagement holes  14   h  of the plurality of die tools  14  in the left-right direction and tool layout information about the plurality of die tools  14 , the layout control unit  106  controls the lower tool exchange units  50  to lay out again the plurality of die tools  14  at regular arrangement positions on the lower tool holder  30  (see  FIG. 8B (b)). Alternatively, based on the positions of the centers of the engagement holes  14   h  of the plurality of die tools  14  in the left-right direction and tool layout information about the plurality of die tools  14  on a lower stocker  44 , the layout control unit  106  controls the lower tool exchange units  50  to remove the plurality of die tools  14  from the lower tool holder  30  and lay out them at regular arrangement positions on the lower stocker  44  as necessary. 
     The operation of laying out die tools  14  by the lower tool exchange units  50  is commonly known as shown in Patent Literatures 2 and 3, details thereof will be omitted. 
     If the clamp plate  36  is accidentally released after a plurality of punch tools  12  are fitted to the upper tool holder  34 , the layout control unit  106  also executes a layout process of the upper tool exchange units  74  and the like similarly to the above. 
     Next, operation and effects of the first embodiment will be explained. 
     In the case of transporting die tools  14  from the lower tool holder  30  to a lower stocker  44  positioned at the lower tool exchange position, the control device  98  controls the servo motor  52  to cause the lower tool exchange units  50  to move in the left-right direction and causes the lower tool retention members  64  to face the engagement holes  14   h  of the die tools  14  fitted to the lower tool holder  30 . Then, while causing the lower tool retention members  64  to be engaged with the engagement holes  14   h  of the die tools  14 , the control device  98  causes the lower tool retention members  64  to retain the die tools  14 . Furthermore, the control device  98  controls the lower tool exchange units  50  to remove the die tools  14  from the lower tool holder  30 . The die tools  14  may be removed from the lower tool holder  30  by being caused to slide in the right direction on the lower tool holder  30 . 
     Next, the control device  98  controls the servo motors  52  to cause the lower tool exchange units  50  to move in the right direction and cause the lower tool retention members  64  to be located at positions corresponding to the lower stocker  44  positioned at the lower tool exchange position. Then, the control device  98  controls the lower tool exchange units  50  to fit the die tools  14  to the lower stocker  44 . After that, the control device  98  causes the lower tool retention members  64  to be disengaged from the engagement holes  14   h  of the die tools  14  and releases the state of retaining the die tools  14  by the lower tool retention members  64 . The die tool  14  may be fitted to the lower stocker  44  by being caused to slide in the right direction on the lower joint block  38 . 
     In the case of transporting die tools  14  from a lower stocker  44  positioned at the lower tool exchange position to the lower tool holder  30 , an operation opposite to the operation described above is performed. Thereby, it is possible to perform automatic exchange of die tools  14  fitted to the lower tool holder  30  with die tools  14  fitted to the lower stocker  44 . 
     In the case of transporting punch tools  12  between the upper tool holder  34  and an upper stocker  46  positioned at the upper tool exchange position, an operation similar to the above is also performed. Thereby, it is possible to perform automatic exchange of punch tools  12  fitted to the upper tool holder  34  with punch tools  12  fitted to an upper stocker  46 . 
     If the operation of retaining a die tool  14  by one of the lower tool retention members  64  fails in the case of transporting die tools  14  from the lower tool holder  30  to a lower stocker  44  positioned at the lower tool exchange position (see  FIG. 7A (a)), the following operation is performed. 
     Immediately after an alarm occurs, while referring to the database  96 , the tool information acquisition unit  102  acquires tool information about the die tool  14  including a relative position of the engagement hole  14   h  of the die tool  14 , based on identification information about the die tool  14  from the two-dimensional code reader  70 . Then, the retry control unit  104  controls the servo motor  52  to cause the lower tool exchange unit  50  to move in the left-right direction (for example, in the left direction) relative to the lower table  24  by an amount corresponding to the relative position of the engagement hole  14   h  of the die tool  14  (see  FIG. 7A (a)). The tool information acquisition unit  102  may acquire tool information about the die tool  14  based on a detection result from the encoder  54  at the time of the occurrence of the alarm and layout information about the die tool  14 . 
     Next, the retry control unit  104  controls the servo motor  52  to cause the lower tool exchange unit  50  to move in the left-right direction near the alarm occurrence position while monitoring detection results from the encoder  54  (see  FIG. 7A (b)). Further, during the movement of the lower tool exchange unit  50 , the photoelectric sensor  68  emits an inspection beam B and detects the engagement hole  14   h  of the die tool  14  from a result of receiving a reflected beam of the inspection beam B (see  FIG. 7B (a)). Then, based on a position of the lower tool exchange unit  50  in the left-right direction at the time of the engagement hole  14   h  of the die tool  14  being detected and the like, the hole position acquisition unit  100  acquires a position of the center of the engagement hole  14   h  of the die tool  14  in the left-right direction. 
     After that, based on the acquired position of the center of the engagement hole  14   h  of the die tool  14  in the left-right direction, the retry control unit  104  controls the lower tool exchange unit  50  to retry the operation of retaining the die tool  14  by the lower tool retention member  64  (see  FIG. 7B  (b)). Thereby, it is possible to continue the operation related to the transportation of the die tools  14  by the lower tool exchange units  50 . 
     If the operation of retaining a punch tool  12  by one of the upper tool retention members  88  fails in the case of transporting punch tools  12  from the upper tool holder  34  to an upper stocker  46  positioned at the upper tool exchange position, an operation similar to the above is also performed. Thereby, it is possible to continue the operation related to the transportation of the punch tools  12  by the upper tool exchange units  74 . 
     In a case where the clamper  32  is accidentally released after a plurality of die tools  14  are fitted to the lower tool holder  30 , a case where a plurality of die tools  14  are randomly fitted to the lower tool holder  30 , or the like, the following operation is performed. 
     The layout control unit  106  controls the servo motors  52  to cause the lower tool exchange units  50  to move in the left-right direction (for example, in the right direction) relative to the lower table  24  from the side of the lower table  24  while monitoring detection results from the encoders  54  (see  FIGS. 8A (a) and  8 A(b) and  FIG. 8B (a)). During the movements of the lower tool exchange units  50 , the photoelectric sensors  68  emit inspection beams B and detect the engagement holes  14   h  of the plurality of die tools  14  from results of receiving reflected beams of the inspection beams B. Then, based on positions of the lower tool exchange units  50  in the left-right direction at the time of the engagement holes  14   h  of the plurality of die tools  14  being detected and the like, the hole position acquisition unit  100  acquires positions of the centers of the engagement holes  14   h  of the plurality of die tools  14  in the left-right direction (see  FIG. 8A (b)). Thereby, the bending system  10  can recognize an actual layout state of the plurality of die tools  14  on the lower tool holder  30 . During the movements of the lower tool exchange units  50 , the tool information acquisition unit  102  may acquire tool information about the plurality of die tools  14 . 
     After that, based on the acquired positions of the centers of the engagement holes  14   h  of the plurality of die tools  14  in the left-right direction and tool layout information about the plurality of die tools  14 , the layout control unit  106  controls the lower tool exchange units  50  to lay out again the plurality of die tools  14  at regular arrangement positions on the lower tool holder  30  (see  FIG. 8B (b)). Alternatively, based on the acquired positions of the centers of the engagement holes  14   h  of the plurality of die tools  14  in the left-right direction and tool layout information about the plurality of die tools  14  on a lower stocker  44 , the layout control unit  106  controls the lower tool exchange units  50  to remove the plurality of die tools  14  from the lower tool holder  30  and lay out them at regular arrangement positions on the lower stocker  44 . Thereby, it is possible to continue the operation related to the transportation of the die tools  14  by the lower tool exchange units  50 . 
     In a case where the clamp plate  36  is accidentally released after a plurality of punch tools  12  are fitted to the upper tool holder  34 , a case where a plurality of punch tools  12  are randomly fitted to the upper tool holder  34 , or the like, an operation similar to the above is also performed. Thereby, it is possible to continue the operation related to the transportation of the punch tools  12  by the upper tool exchange units  74 . 
     If there are gaps among a plurality of die tools  14  during movement of the lower tool exchange units  50 , the photoelectric sensors  68  detect the end faces  14   e  of die tools  14  on the middle side. The bending system  10  can determine whether there are gaps among the plurality of die tools  14 , based on tool layout information about the plurality of die tools  14 . 
     In short, according to the first embodiment, based on positions of the lower tool exchange units  50  in the left-right direction at the time of the engagement holes  14   h  of die tools  14  being detected by the photoelectric sensors  68 , and the like, the hole position acquisition unit  100  acquires positions of the centers of the engagement holes  14   h  of the die tools  14  in the left-right direction by calculation, as mentioned above. Based on positions of the upper tool exchange units  74  in the left-right direction at the time of the engagement holes  12   h  of punch tools  12  being detected by the photoelectric sensors  92  and the like, the hole position acquisition unit  100  acquires positions of the centers of the engagement holes  12   h  of the punch tools  12  in the left-right direction. Further, the tool information acquisition unit  102  acquires tool information about die tools  14  based on identification information about the die tools  14  from the two-dimensional code readers  70 . The tool information acquisition unit  102  acquires tool information about punch tools  12  based on identification information about the punch tools  12  from the two-dimensional code readers  94 . Thereby, the bending system  10  can accurately recognize actual positions of the engagement holes  14   h  of a plurality of die tools  14  in the left-right direction on the lower tool holder  30  and actual positions of the engagement holes  12   h  of a plurality of punch tools  12  in the left-right direction on the upper tool holder  34 . 
     Therefore, according to the first embodiment, it is possible to stabilize automatic operation of the bending system  10  without the operation related to transportation of die tools  14  by the lower tool exchange units  50  and the like being interrupted in the middle of the operation and the like. 
     Second Embodiment 
     As shown in  FIG. 1 , a bending system  108  according to a second embodiment has a configuration similar to that of the bending system  10  according to the first embodiment except for a part thereof. Among components of the bending system  108 , components different from those of the bending system  10  will be explained. Among the plurality of components of the bending system  108 , components corresponding to components of the bending system  10  are given the same reference signs in drawings. 
     As shown in  FIGS. 6 and 9 , at an appropriate position on each lower support member  58 , a photoelectric sensor  110  is provided as an end face detector to detect the end face  14   e  of a die tool  14  fitted to the lower tool holder  30  instead of the photoelectric sensor  68  (see  FIG. 4 ). The photoelectric sensor  110  is configured to emit an inspection beam B and detect the end face  14   e  of the die tool  14  from a result of receiving a reflected beam of the inspection beam B, in a state of being located at the same height as a part higher than the engagement hole  14   h  on the die tool  14 . 
     The photoelectric sensor  110  may detect the end face  14   e  of the die tool  14  in a state of being located at the same height as the engagement hole  14   h  of the die tool  14 . In this case, the control device  98  judges which of the end face  14   e  and engagement hole  14   h  of the die tool  14  the detection target of the photoelectric sensor  110  is, based on tool layout information and the like about a plurality of die tools  14 . 
     As shown in  FIG. 10 , at an appropriate position on each upper support member  82 , a photoelectric sensor  112  is provided as an end face detector to detect the end face  12   e  of a punch tool  12  fitted to the upper tool holder  34  instead of the photoelectric sensor  92  (see  FIG. 5 ). The photoelectric sensor  112  is configured to emit an inspection beam B and detect the end face  12   e  of the punch tool  12  from a result of receiving a reflected beam of the inspection beam B, in a state of being located at the same height as a part lower than the engagement hole  12   h  on the punch tool  12 . 
     The photoelectric sensor  112  may detect the end face  12   e  of the punch tool  12  in a state of being located at the same height as the engagement hole  12   h  of the punch tool  12 . In this case, the control device  98  judges which of the end face  12   e  and engagement hole  12   h  of the punch tool  12  the detection target of the photoelectric sensor  110  is, based on tool layout information and the like about a plurality of punch tools  12 . 
     As shown in  FIG. 6 , in the second embodiment, the control device  98  has a hole position acquisition unit  114 , a retry control unit  116  and a layout control unit  118  instead of the hole position acquisition unit  100 , the retry control unit  104  and the layout control unit  106 . Specific content of functions of the hole position acquisition unit  114 , the retry control unit  116  and the layout control unit  118  are as below. 
     As shown in  FIGS. 6, 9 and 10 , based on positions of the lower tool exchange units  50  in the left-right direction at the time of end faces  14   e  of die tools  14  being detected, and acquired tool information about the die tools  14  (relative positions of the engagement holes  14   h  of the die tools  14 ), the hole position acquisition unit  114  acquires positions of the centers of the engagement holes  14   h  of the die tools  14  in the left-right direction by calculation. The hole position acquisition unit  114  acquires the positions of the centers of the engagement holes  14   h  of the die tools  14  in the left-right direction in consideration of relative positions of the photoelectric sensors  110  relative to the lower unit bodies  56 . Similarly, based on positions of the upper tool exchange units  74  in the left-right direction at the time of end faces  12   e  of punch tools  12  being detected, and acquired tool information about the punch tools  12  (relative positions of the engagement holes  12   h  of the punch tools  12 ), the hole position acquisition unit  114  acquires positions of the centers of the engagement holes  12   h  of the punch tools  12  in the left-right direction by calculation. The hole position acquisition unit  114  acquires the positions of the centers of the engagement holes  12   h  of the punch tools  12  in the left-right direction in consideration of relative positions of the photoelectric sensors  112  relative to the upper unit bodies  80 . 
     As shown in  FIGS. 3, 6, 9, 11A and 11B , if the operation of retaining a die tool  14  by one of the lower tool retention members  64  fails (see  11 A(a)), the retry control unit  116  executes a retry process of the lower tool exchange unit  50  and the like as below. 
     The retry control unit  116  controls the servo motor  52  so that the lower tool exchange unit  50  moves in the left-right direction (for example, in the left direction) relative to the lower table  24  by an amount corresponding to a relative position of the engagement hole  14   h  of the die tool  14 , which is tool information about the die tool  14  acquired immediately after an alarm occurs (see  FIG. 11A (a)). Next, the retry control unit  116  controls the servo motor  52  so that the lower tool exchange unit  50  moves in the left-right direction (for example, in the right direction) relative to the lower table  24  from the side of the die tool  14  (see  FIGS. 11A (b) and  11 B(a)). After that, based on an acquired position of the center of the engagement hole  14   h  of the die tool  14  in the left-right direction, the retry control unit  116  controls the lower tool exchange unit  50  to retry the operation of retaining the die tool  14  by the lower tool retention member  64  (see  FIG. 11B  (b)). 
     If the operation of retaining a punch tool  12  by one of the upper tool retention members  88  fails, the retry control unit  116  also executes the retry process of the upper tool exchange unit  74  and the like similarly to the above. 
     As shown in  FIGS. 3, 6, 9, 12A and 12B , if the clamper  32  is accidentally released after a plurality of die tools  14  are fitted to the lower tool holder  30 , the layout control unit  118  executes a layout process of the lower tool exchange units  50  and the like as below. Similarly, if a plurality of die tools  14  are randomly fitted to the lower tool holder  30  by manual work of a worker, the layout control unit  118  also executes the layout process of the lower tool exchange units  50  and the like as necessary. 
     The layout control unit  118  controls the servo motors  52  so that the lower tool exchange units  50  move in the left-right direction (for example, in the right direction) relative to the lower table  24  from the side of the lower table  24  (see  FIGS. 12A (a) and  12 A(b) and  FIG. 12B (a)). After that, based on acquired positions of the centers of the engagement holes  14   h  of the plurality of die tools  14  in the left-right direction and tool layout information about the plurality of die tools  14 , the layout control unit  106  controls the lower tool exchange units  50  to lay out again the plurality of die tools  14  at regular arrangement positions on the lower tool holder  30  (see  FIG. 12B (b)). Alternatively, based on the positions of centers of the engagement holes  14   h  of the plurality of die tools  14  in the left-right direction and tool layout information about the plurality of die tools  14  on a lower stocker  44 , the layout control unit  118  controls the lower tool exchange units  50  to remove the plurality of die tools  14  from the lower tool holder  30  and lay out them at regular arrangement positions on the lower stocker  44  as necessary. 
     If the clamp plate  36  is accidentally released after a plurality of punch tools  12  are fitted to the upper tool holder  34 , the layout control unit  118  also executes a layout process of the upper tool exchange units  74  and the like similarly to the above. 
     Next, operation and effects of the second embodiment will be explained. 
     If the operation of retaining a die tool  14  by one of the lower tool retention members  64  fails in the case of transporting the die tools  14  from the lower tool holder  30  to a lower stocker  44  positioned at the lower tool exchange position (see  FIG. 11A (a)), the following operation is performed. 
     Immediately after an alarm occurs, while referring to the database  96 , the tool information acquisition unit  102  acquires tool information about the die tool  14  including a relative position of the engagement hole  14   h  of the die tool  14 , based on identification information about the die tool  14  from the two-dimensional code reader  70 . Then, the retry control unit  116  controls the servo motor  52  to cause the lower tool exchange unit  50  to move in the left-right direction (for example, in the left direction) relative to the lower table  24  by an amount corresponding to the relative position of the engagement hole  14   h  of the die tool  14  (see  FIG. 11A (a)). The tool information acquisition unit  102  may acquire tool information about the die tool  14  based on a detection result from the encoder  54  at the time of the occurrence of the alarm and layout information about the die tool  14 . 
     Next, the retry control unit  116  controls the servo motor  52  to cause the lower tool exchange unit  50  to move in the left-right direction (for example, in the right direction) from the side of the die tool  14  while monitoring detection results from the encoder  54  (see  FIG. 11A (b)). Further, during the movement of the lower tool exchange unit  50 , the photoelectric sensor  110  emits an inspection beam B and detects the end face  14   e  of the die tool  14  from a result of receiving a reflected beam of the inspection beam B (see  FIG. 11B (a)). Then, based on a position of the lower tool exchange unit  50  in the left-right direction at the time of the end face  14   e  of the die tool  14  being detected, acquired tool information about the die tool  14  and the like, the hole position acquisition unit  114  acquires a position of the center of the engagement hole  14   h  of the die tool  14  in the left-right direction. 
     After that, based on the acquired position of the center of the engagement hole  14   h  of the die tool  14  in the left-right direction, the retry control unit  116  controls the lower tool exchange unit  50  to retry the operation of retaining the die tool  14  by the lower tool retention member  64  (see  FIG. 11B  (b)). Thereby, it is possible to continue the operation related to the transportation of the die tools  14  by the lower tool exchange units  50 . 
     If the operation of retaining a punch tool  12  by one of the upper tool retention members  88  fails in the case of transporting punch tools  12  from the upper tool holder  34  to an upper stocker  46  positioned at the upper tool exchange position, an operation similar to the above is also performed. Thereby, it is possible to continue the operation related to the transportation of the punch tools  12  by the upper tool exchange units  74 . 
     In a case where the clamper  32  is accidentally released after a plurality of die tools  14  are fitted to the lower tool holder  30 , a case where a plurality of die tools  14  are randomly fitted to the lower tool holder  30 , or the like, the following operation is performed. 
     The layout control unit  118  controls the servo motors  52  to cause the lower tool exchange units  50  to move in the left-right direction (for example, in the right direction) relative to the lower table  24  from the side of the lower table  24  (see  FIGS. 12A (a) and  12 A(b) and  FIG. 12B (a)). During the movements of the lower tool exchange units  50 , the photoelectric sensors  110  emit inspection beams B and detect the end face  14   e  of a die tool  14  on the left end side from results of receiving reflected beams of the inspection beams B. The tool information acquisition unit  102  acquires tool information about the plurality of die tools  14  (width dimensions of the die tools  14  in the left-right direction and relative positions of the centers of the engagement holes  14   h ). Further, based on positions of the lower tool exchange units  50  in the left-right direction at the time of the end face  14   e  of the die tool  14  on the left end side being detected, the acquired tool information about the plurality of die tools  14  and the like, the hole position acquisition unit  114  acquires positions of the centers of the engagement holes  14   h  of the plurality of die tools  14  in the left-right direction (see  FIG. 12A (b)). Thereby, the bending system  10  can recognize an actual layout state of the plurality of die tools  14  on the lower tool holder  30 . 
     After that, based on the acquired positions of the centers of the engagement holes  14   h  of the plurality of die tools  14  in the left-right direction and tool layout information about the plurality of die tools  14 , the layout control unit  118  controls the lower tool exchange units  50  to lay out again the plurality of die tools  14  at regular arrangement positions on the lower tool holder  30  (see  FIG. 12B (b)). Alternatively, based on the acquired positions of the centers of the engagement holes  14   h  of the plurality of die tools  14  in the left-right direction and tool layout information about the plurality of die tools  14  on a lower stocker  44 , the layout control unit  118  controls the lower tool exchange units  50  to remove the plurality of die tools  14  from the lower tool holder  30  and lay out them at regular arrangement positions on the lower stocker  44 . Thereby, it is possible to continue the operation related to the transportation of the die tools  14  by the lower tool exchange units  50 . 
     If there are gaps among the plurality of die tools  14  during the movements of the lower tool exchange units  50 , the photoelectric sensors  110  detect the end faces  14   e  of die tool  14  on the middle side. The bending system  10  can determine whether there are gaps among the plurality of die tools  14 , based on tool layout information about the plurality of die tools  14 . 
     In a case where the clamp plate  36  is accidentally released after a plurality of punch tools  12  are fitted to the upper tool holder  34 , a case where a plurality of punch tools  12  are randomly fitted to the upper tool holder  34 , or the like, an operation similar to the above is also performed. Thereby, it is possible to continue the operation related to the transportation of the punch tools  12  by the upper tool exchange units  74 . 
     In short, according to the second embodiment, based on positions of the lower tool exchange units  50  in the left-right direction at the time of the engagement holes  14   h  of die tools  14  being detected by the photoelectric sensors  68 , and the like, the hole position acquisition unit  100  acquires positions of the centers of the engagement holes  14   h  of the die tools  14  in the left-right direction by calculation, as mentioned above. Based on positions of the upper tool exchange units  74  in the left-right direction at the time of the engagement holes  12   h  of punch tools  12  being detected by the photoelectric sensors  92  and the like, the hole position acquisition unit  100  acquires positions of the centers of the engagement holes  12   h  of the punch tools  12  in the left-right direction. Further, the tool information acquisition unit  102  acquires tool information about die tools  14  based on identification information about the die tools  14  from the two-dimensional code readers  70 . The tool information acquisition unit  102  acquires tool information about punch tools  12  based on identification information about the punch tools  12  from the two-dimensional code readers  94 . Thereby, the bending system  10  can accurately recognize actual positions of the engagement holes  14   h  of a plurality of die tools  14  in the left-right direction on the lower tool holder  30  and actual positions of the engagement holes  12   h  of a plurality of punch tools  12  in the left-right direction on the upper tool holder  34 . 
     Therefore, according to the second embodiment, it is possible to stabilize automatic operation of the bending system  10  without the operation related to transportation of die tools  14  by the lower tool exchange units  50  and the like being interrupted in the middle of the operation and the like. 
     Third Embodiment 
     As shown in  FIG. 13 , a bending system  120  according to a third embodiment uses torque sensors  122  to detect torques of the servo motors  52  as end face detectors to detect the end faces  14   e  of die tools  14 , instead of the photoelectric sensors  110  (see  FIG. 6 ). Each torque sensors  122  is configured to detect the end face  14   e  of a die tool  14  when a detected torque of its corresponding servo motor  52  (a detection result) exceeds a predetermined threshold. Similarly, the bending system  120  uses torque sensors  124  to detect torques of servo motors  75  as end face detectors to detect the end faces  12   e  of punch tools  12 , instead of the photoelectric sensors  112  (see  FIG. 6 ). Each torque sensor  124  is configured to detect the end face  12   e  of a punch tool  12  when a detected torque of the servo motor  75  exceeds a predetermined threshold. 
     In the third embodiment, the control device  98  has an end face detection control unit  126  and has a hole position acquisition unit  128  instead of the hole position acquisition unit  100  (see  FIG. 6 ). Specific content of functions of the end face detection control unit  126  is as below. 
     As shown in  FIGS. 13 and 14 , before detecting the end faces  14   e  of die tools  14 , the end face detection control unit  126  controls one lower tool exchange unit  50  so that one lower tool retention member  64  faces an end face  14   e  on one side of the die tools  14  (for example, an end face on the left side) in the left-right direction (see  FIG. 14( a ) ). Further, before detecting the end face  14   e  on the one side of the die tools  14 , the end face detection control unit  126  controls the other lower tool exchange unit  50  so that the other lower tool retention member  64  retains an engagement hole  14   h  on the other side of the die tools  14 , or the retention state is continued (see  FIGS. 14( a ) and ( b ) ). Alternatively, before detecting the end face  14   e  on the one side of the die tools  14 , the end face detection control unit  126  controls the other lower tool exchange unit  50  so that the other lower tool retention member  64  is in contact with or close to the end face  14   e  on the other side (for example, an end face on the right side) of the die tools  14 . 
     Similarly, before detecting the end faces  12   e  of punch tools  12 , the end face detection control unit  126  controls one upper tool exchange unit  74  so that one upper tool retention member  88  faces an end face  12   e  on one side of the punch tools  12  (for example, an end face on the left side) in the left-right direction. Further, before detecting the end face  12   e  on the one side of the punch tools  12 , the end face detection control unit  126  controls the other upper tool exchange unit  74  so that the other upper tool retention member  88  retains the engagement hole  12   h  of a punch tool  12 , or the retention state is maintained. Alternatively, before detecting the end face  12   e  on the one side of the punch tools  12 , the end face detection control unit  126  controls the other upper tool exchange unit  74  so that the other upper tool retention member  88  is in contact with or close to an end face  12   e  on the other side (for example, an end face on the right side) of the punch tools  12 . 
     Based on a position of the one lower tool exchange unit  50  in the left-right direction at the time of the end face  14   e  on the one side of the die tools  14  being detected, and acquired tool information about the die tool  14  (a relative position of the engagement hole  14   h  of the die tool  14 ), the hole position acquisition unit  128  acquires a position of the center of the engagement hole  14   h  of the die tool  14  in the left-right direction by calculation. The hole position acquisition unit  128  acquires the position of the center of the engagement hole  14   h  of the die tool  14  in the left-right direction in consideration of a relative position of the one lower tool retention member  64  relative to the lower unit body  56 . Similarly, based on a position of the one upper tool exchange unit  74  in the left-right direction at the time of the end face  12   e  on the one side of the punch tools  12  being detected, and acquired tool information about the punch tool  12  (a relative position of the engagement hole  12   h  of the punch tool  12 ), the hole position acquisition unit  128  acquires a position of the center of the engagement hole  12   h  of the punch tool  12  in the left-right direction by calculation. The hole position acquisition unit  128  acquires the position of the center of the engagement hole  12   h  of the punch tool  12  in the left-right direction in consideration of a relative position of the one upper tool retention member  88  relative to the upper unit body  80 . 
     The bending system  120  performs an operation related to detection of the end faces  14   e  of the die tools  14  as below. 
     The end face detection control unit  126  controls one lower tool exchange unit  50  so that one lower tool retention member  64  faces one end face  14   e  of a die tool  14  on the left end side in the left-right direction. Further, the end face detection control unit  126  controls the other lower tool exchange unit  50  so that the other lower tool retention member  64  retains the engagement hole  14   h  of a die tool  14  on the right end side, or the retention state is continued (see  FIG. 14( a ) ). Alternatively, the end face detection control unit  126  controls the other lower tool exchange unit  50  so that the other lower tool retention member  64  is in contact with or close to the other end face  14   e  of the die tool  14  on the right end side. Then, the retry control unit  116  or a layout control unit  119  controls the servo motors  52  to cause the lower tool exchange units  50  to move in the left-right direction (for example, in the right direction) from the side of the die tools  14  while monitoring detection results from the encoders  54 . 
     Then, the one lower tool retention member  64  comes into contact with the one end face  14   e  of the die tool  14  on the left end side; a detection torque of one servo motor  52  exceeds the predetermined threshold; and one torque sensor  122  detects the one end face  14   e  of the die tool  14  on the left end side (see  FIG. 14( b ) ). Based on a position of the one lower tool exchange unit  50  in the left-right direction at the time of the one end face  14   e  of the die tool  14  on the left end side being detected, the hole position acquisition unit  114  acquires a position of the center of the engagement hole  14   h  of the die tool  14  on the left end side in the left-right direction by calculation. Further, in a state of the other lower tool retention member  64  being in contact with the other end face  14   e  of the die tool  14  on the right end side, a detection torque of the other servo motor  52  exceeds the predetermined threshold, and the other torque sensor  122  detects the other end face  14   e  of the die tool  14  on the right end side. Based on a position of the other lower tool exchange unit  50  in the left-right direction at the time of the other end face  14   e  of the die tool  14  on the right end side being detected and the like, the hole position acquisition unit  114  acquires a position of the center of the engagement hole  14   h  of the die tool  14  on the right end side in the left-right direction by calculation. 
     The bending system  120  performs an operation related to detection of the end face  12   e  of a punch tool  12  similarly to the above. 
     According to the third embodiment, operation and effects similar to those of the second embodiment described above can be obtained. 
     Fourth Embodiment 
     As shown in  FIG. 15 , a part of the technical items described in the second embodiment may be applied to a general-purpose bending system  130 . The bending system  130  according to a fourth embodiment does not include the tool exchange units  50  or  74  (see  FIG. 6 ), the tool rack  42  (see  FIG. 6 ), the servo motors  52  or  76  (see  FIG. 6 ) or the like. The photoelectric sensors  110  and the two-dimensional code readers  70  are provided at appropriate positions on sliders  132  with back gauge mechanisms as moving bodies, respectively. Servo motors  134  as left-right moving actuators to cause the sliders  132  to move in the left-right direction are connected to the control device  98  of the bending system  130 . Encoders  136  as position detectors to detect positions of the sliders  132  in the left-right direction are connected to the control device  98  of the bending system  130 . 
     The control device  98  of the bending system  120  includes a tool position acquisition unit  138  instead of the hole position acquisition unit  114  (see  FIG. 6 ). Based on positions of the sliders  132  in the left-right direction at the time of the end faces  14   e  (see  FIG. 9 ) of die tools  14  being detected, and acquired tool information (width dimensions of the die tools  14  in the left-right direction) about the die tools  14  (see  FIG. 1 ), the tool position acquisition unit  138  acquires positions of the end faces  14   e  of the die tools  14  in the left-right direction by calculation. Similarly, based on positions of the other slider  132  in the left-right direction at the time of the end faces  12   e  (see  FIG. 9 ) of punch tools  12  being detected, and acquired tool information (width dimensions of the punch tools  12  in the left-right direction) about the punch tools  12 , the tool position acquisition unit  138  acquires positions of the end faces  12   e  of the punch tools  12  in the left-right direction by calculation. Thereby, the bending system  130  can accurately recognize actual positions of end faces  14   e  of a plurality of die tools  14  in the left-right direction on the lower tool holder  30  (see  FIG. 1 ) and actual positions of end faces  12   e  of a plurality of punch tools  12  in the left-right direction on the upper tool holder  34  (see  FIG. 1 ). 
     In the fourth embodiment, a die tool  14  does not need to have an engagement hole  14   h , and a punch tool  12  does not need to have an engagement hole  12   h.    
     The present disclosure is not limited to the explanations of the first to fourth embodiment described above. For example, the present disclosure can be implemented in various aspects as below. 
     As hole detectors to detect the engagement holes  14   h  of die tools  14 , cameras to pick up images of the engagement holes  14   h  of the die tools  14  may be used instead of using the photoelectric sensors  68 . In this case, using a reference image for the engagement holes  14   h  of the die tools  14 , the hole position acquisition unit  100  judges whether a picked-up image corresponds to the reference image or not by pattern matching. Similarly, as hole detectors to detect the engagement hole  12   h  of punch tools  12 , cameras to pick up images of the engagement holes  12   h  of the punch tools  12  may be used instead of using the photoelectric sensors  92 . 
     Instead of providing the identification marks  14   m  to a die tool  14 , an IC chip storing tool information about the die tool  14  may be attached. Similarly, instead of providing the identification marks  12   m  to a punch tool  12 , an IC chip storing tool information about the punch tool  12  may be attached. In this case, an IC chip reader as an information reader reads the tool information about the die tool  14  and the tool information about the punch tool  12 . 
     The photoelectric sensors  68  (or  108 ) and the two-dimensional code readers  70  may be provided on sliders (see  FIG. 13 ) with back gauge mechanisms as moving bodies provided on the back side of the lower table  24  being movable in the left-right direction, instead of being provided on the lower tool exchange units  50 . Alternatively, the photoelectric sensors  68  (or  108 ) and the two-dimensional code readers  70  may be provided on bending indicators (not shown) as moving bodies provided on the front side of the lower table  24  being movable in the left-right direction. 
     The operation related to tool exchange may be performed by a tool change robot (not shown) instead of performing the operation related to tool exchange by the lower tool exchange units  50  and the upper tool exchange units  74 . 
     The scope of rights included in the present invention is not limited to the first to fourth embodiments described above. 
     The present disclosure is related to the subjects described in Japanese Patent Application 2019-107126 filed on Jun. 7, 2019 and Japanese Patent Application 2020-093079 filed on May 28, 2020, the disclosed content of which is incorporated herein by reference in its entirety.