Patent Publication Number: US-2022219221-A1

Title: Bending system and tool transport method

Description:
TECHNICAL FIELD 
     The present invention relates to a bending system for bending a plate-shaped workpiece by using an automatically exchangeable tool, and a tool transport method for transporting the tool along a tool holder of a press brake or a selected stocker. 
     BACKGROUND ART 
     Patent Literature 1 proposes a bending system placed on a lateral side of a press brake and provided with a tool storage for storing a plurality of tools. The tool storage includes a plurality of stockers for retaining the plurality of tools. Each stocker extends in a left-right direction. Any selected stocker is configured to be able to be positioned at an exchange position for performing exchange (automatic exchange) of the tool. 
     The above bending system includes a tool exchange unit for exchanging tools with respect to a tool holder of the press brake and the stocker positioned at the exchange position. The tool exchange unit is disposed on the back side of a table of the press brake table so as to be movable in the left-right direction. The tool exchange unit includes a tool retention member for retaining the tools. The tool retention member is engageable-with and disengageable-from an engagement holes of the tools. The bending system includes a servo motor as a left-right moving unit configured to move the tool exchange unit in the left-right direction. 
     Patent Literature 2 proposes an upper holder for retaining upper tools of a press brake in an exchangeable manner. Patent Literature 3 proposes a tool installing and removing method and a tool storage of a press brake. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature 1: Japanese Patent No. 4672868 
         Patent Literature 2: Japanese Patent No. 5841800 
         Patent Literature 3: Japanese Patent No. 5947861 
       
    
     SUMMARY 
     Oil or the like often adheres to a side surface of the tool retained by the tool holder or the tool stocker. When a predetermined tool to be exchanged (to be transported) is in contact with another adjacent tool, the predetermined tool and the other tool may be bonded by oil or the like. If an attempt is made to transport the predetermined tool in this state in the left-right direction by the tool exchange unit, the other tool may be dragged by the predetermined tool and the position of the other tool may be shifted. As a result, the bending system may not be able to grasp the position at which the other tool is placed, and may not be able to stably perform an operation related to automatic tool exchange, which include an operation to transport the tools. If escape processing or taper processing is applied to a side surface of the tool as post-processing in order to prevent bonding between the adjacent tools, which causes the position of the other tool to be shifted, manufacturing cost (processing cost) of the tool is increased. 
     In other words, there is a problem that it is not easy to stably perform an operation related to automatic exchange of tools by a bending system while suppressing an increase in manufacturing cost of the tools. 
     The present invention aims at providing a bending system and a tool transport method capable of transporting only a predetermined tool to be exchanged in the left-right direction by a tool exchange unit without performing post-processing on a side surface of the tool. 
     A bending system according to an embodiment of the present invention includes a tool storage placed in a vicinity of a press brake and including a plurality of stockers extending in a left-right direction so as to be able to retain a plurality of tools, a first tool exchange unit and a second tool exchange unit each disposed on a back side or a front side of a table of the press brake so as to be movable in the left-right direction and configured to exchange a tool with respect to a tool holder of the press brake and a stocker selected from among the plurality of stockers, a left-right moving unit configured to move the first tool exchange unit and the second tool exchange unit in the left-right direction, respectively, and a control unit configured to control the first tool exchange unit, the second tool exchange unit, and the left-right moving unit. The first tool exchange unit includes a first tool retention member engageable-with and disengageable-from an engagement hole of a tool, the first tool retention member being able to retain the tool and configured to move in the left-right direction together with the first tool exchange unit. The second tool exchange unit includes a second tool retention member engageable-with and disengageable-from an engagement hole of a tool, the second tool retention member being able to retain the tool and configured to move in the left-right direction together with the second tool exchange unit. The control unit, when a first tool to be exchanged is in contact with an adjacent second tool not to be exchanged in the tool holder or the selected stocker, controls the first tool exchange unit, the second tool exchange unit, and the left-right moving unit such that the first tool retention member retains the first tool in a state of being engaged in an engagement hole of the first tool, the second tool retention member retains the second tool in a state of being engaged in an engagement hole of the second tool, and the first tool exchange unit subsequently moves in the left-right direction in a state in which a movement of the second tool exchange unit in the left-right direction is stopped. 
     A tool transport method according to an embodiment of the present invention is a tool transport method using a first tool exchange unit and a second tool exchange unit disposed 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. The tool transport method includes, when a first tool to be exchanged is in contact with an adjacent second tool not to be exchanged in a tool holder of the press brake or in a selected stocker in a tool storage placed in a vicinity of the press brake, retaining, by a first tool retention member of the first tool exchange unit, the first tool in a state in which the first tool retention member is engaged in an engagement hole of the first tool, retaining, by a second tool retention member of the second tool exchange unit, the second tool in a state in which the second tool retention member is engaged in an engagement hole of the second tool, and subsequently moving the first tool exchange unit in the left-right direction in a state in which a movement of the second tool exchange unit in the left-right direction is stopped. 
     According to the above configuration, since the second tool not to be exchanged is not dragged by the first tool to be exchanged, the position of the second tool is not shifted. As a result, only the first tool to be exchanged can be transported in the left-right direction by the first and second tool exchange units without performing post-processing on a side surface of the tool. 
     Therefore, it is possible to stably perform an operation related to automatic exchange of tools while suppressing an increase in manufacturing cost of the tools. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic front view illustrating a bending system according to an embodiment of the present invention. 
         FIG. 2  is a schematic front view illustrating a vicinity of stockers (upper stocker and lower stocker) positioned at the tool exchange positions. 
         FIG. 3  is an enlarged cross-sectional view taken along the line in  FIG. 1 . 
         FIG. 4  is a control block diagram of the bending system according to the embodiment of the present invention. 
         FIG. 5A  is a diagram illustrating a state in which a predetermined punch tool is in contact with an adjacent another punch tool in a plurality of upper tool holders. 
         FIG. 5B  is a diagram illustrating a state in which the predetermined punch tool is transported along the plurality of upper tool holders. 
         FIG. 5C  is a diagram illustrating a state in which the predetermined punch tool is transported along the plurality of upper tool holders. 
         FIG. 6A  is a diagram illustrating a state in which a plurality of predetermined punch tools are in contact with an adjacent another punch tool in the plurality of upper tool holders. 
         FIG. 6B  is a diagram illustrating an operation for transporting the plurality of predetermined punch tools along the plurality of upper tool holders. 
         FIG. 6C  is a diagram illustrating the operation for transporting the plurality of predetermined punch tools along the plurality of upper tool holders. 
         FIG. 6D  is a diagram illustrating the operation for transporting the plurality of predetermined punch tools along the plurality of upper tool holders. 
         FIG. 6E  is a diagram illustrating the operation for transporting the plurality of predetermined punch tools along the plurality of upper tool holders. 
         FIG. 7A  is a diagram illustrating an operation for transporting the plurality of predetermined punch tools along a plurality of upper tool holders. 
         FIG. 7B  is a diagram illustrating the operation for transporting the plurality of predetermined punch tools along the plurality of upper tool holders. 
         FIG. 7C  is a diagram illustrating the operation for transporting the plurality of predetermined punch tools along the plurality of upper tool holders. 
     
    
    
     DESCRIPTION OF EMBODIMENT 
     Embodiments of the present invention will be described with reference to  FIGS. 1 to 7C . 
     It should be noted that the “left-right direction” is one of the horizontal directions, which is the width direction of a press brake  16  or a tool storage  56 . The “front-back direction” is the depth direction of the press brake  16  or the tool storage  56 . The “tool” includes an upper tool and a lower tool. The “last tool” is the tool at the end when viewed from the tool transport direction. The “leading tool” is the tool at the foremost position when viewed from the tool transport method. In the drawings, “FF” indicates the forward direction, “FR” indicates the backward direction, “L” indicates the left direction, “R” indicates the right direction, “U” indicates the upward direction, and “D” indicates the downward direction. For convenience of explanation, in  FIGS. 5A to 7C , of the engagement holes of the plurality of punch tools, only an engagement hole  12   h  that is in a state of being engaged with an upper tool retention member  78  is illustrated. 
     As illustrated in  FIGS. 1 to 3 , a bending system  10  according to the present embodiment is a system for bending a plate-shaped workpiece (sheet metal) W by using a punch tool  12  as an upper tool and a die tool  14  as a lower tool that are automatically exchangeable. The engagement hole  12   h  in a circular hole shape or in an elongated hole shape is formed in the central portion of the punch tool  12  in the width direction so as to penetrate in the front-back direction. On a shank  12   s  as the base portion of the punch tool  12 , an engagement groove  12   g  for preventing the punch tool  12  from dropping is formed (see  FIG. 3 ). An engagement hole  14   h  in a circular hole shape or in an elongated hole shape is formed in the central portion of the die tool  14  in the width direction so as to penetrate in the front-back direction (see  FIG. 3 ). 
     The bending system  10  includes a press brake  16  for bending a work W by the cooperation of the punch tool  12  and the die tool  14 . 
     A configuration of the press brake  16  will be specifically described. The press brake  16  includes a main frame  18 . The main frame  18  includes a pair of side plates  20  that are separated from each other in the left-right direction and face each other, and a plurality of connecting members  22  that connect the pair of side plates  20  to each other. A lower table  24  extending in the left-right direction is disposed at the lower part of the main frame  18 . An upper table  26  extending in the left-right direction is disposed at the upper part of the main frame  18  so as to be vertically movable. A hydraulic cylinder  28  is disposed at the upper part of each side plate  20  as a vertical moving unit for vertically moving the upper table  26 . It should be noted that, instead of configuring the upper table  26  so as to be vertically movable, the lower table  24  may be configured to be vertically movable. Instead of the hydraulic cylinder  28 , a servo motor (not illustrated) may be used as the vertical moving unit. 
     At a lower end portion of the upper table  26 , a plurality of upper tool holders  30  are disposed at intervals in the left-right direction via fixture plates (fastening plates)  32 . Each upper tool holder  30  retains the punch tool  12  in an installable and removable manner. Each upper tool holder  30  has a known configuration, for example, shown in Patent Literature 2 and includes a holder main body  34 . A front clamp plate  36  for pressing the shank  12   s  of the punch tool  12  in a rearward direction is disposed on a front side of each holder main body  34  so as to be swingable. Each front clamp plate  36  includes, on a lower end side thereof, a pawl  36   c  that can be engaged in an engagement groove  12   g  of the punch tool  12 . A rear clamp plate  38  for pressing, in a forward direction, the shank  12   s  of the punch tool  12  in a state in which the front and back sides are inverted (in the front-back direction) is disposed on a rear side of each holder main body  34  so as to be swingable. Each rear clamp plate  38  includes, on a lower end side thereof, a pawl  38   c  that can be engaged in the engagement groove  12   g  of the punch tool  12  in the state in which the front and back sides are inverted. 
     A lower tool holder  40  extending in the left-right direction is disposed on the upper side of the lower table  24 . The lower tool holder  40  retains the die tool in an installable and removable manner. A holder groove  40   g  having a known configuration, for example, shown in Patent Literatures 2 and 3, for allowing a shank  14   s  of the die tool  14  to be inserted into is formed on the lower tool holder  40  along the left-right direction. The lower tool holder  40  includes a clamper  42  for securing (pressing) the die tool  14 . 
     An upper joint block  44  extending in the left-right direction is disposed on the right side portion of the upper table  26 . A joint groove  44   g  for allowing the shank  12   s  of the punch tool  12  to be inserted into is formed on the upper joint block  44  along the left-right direction. The joint grooves  44   g  of the upper joint blocks  44  are placed in series along the left-right direction in respective gaps between the holder main bodies  34  and the front clamp plates  36  in the plurality of upper tool holders  30 . 
     A lower joint block  46  extending in the left-right direction is disposed on the right side portion of the lower table  24 . A joint groove  46   g  for allowing the shank  14   s  of the die tool  14  to be inserted into is formed on the lower joint block  46  along the left-right direction. The joint groove  46   g  of the lower joint block is connected to the holder groove  40   g  of the lower tool holder  40 . 
     An upper support beam  48  extending in the left-right direction is disposed on the back side (rear side) of the upper table  26  via a plurality of brackets  50  (only one is illustrated). The upper support beam  48  projects to the right of the upper joint block  44 . A lower support beam  52  extending in the left-right direction is disposed on the back side of the lower table  24  via a plurality of brackets  54  (only one is illustrated). The lower support beam  52  projects to the right of the lower joint block  46 . 
     As illustrated in  FIGS. 1 and 2 , the tool storage  56  for storing the plurality of punch tools  12  and the plurality of die tools  14  is placed on the lateral side of the press brake  16  in the left-right direction (an example of the vicinity of the press brake  16 ). The tool storage  56  has, for example, the same configuration as the known configurations shown in Patent Literatures 1 and 3. 
     The configuration of the tool storage  56  will be briefly described. The tool storage  56  includes a plurality of upper stockers  58  (only one is illustrated) for retaining the plurality of punch tools  12 . Although only the upper stocker  58  positioned at an upper exchange position for exchanging the punch tool  12  is illustrated, the plurality of upper stockers  58  are placed along the front-back direction. Each upper stocker  58  extends in the left-right direction. A stocker groove  58   g  for allowing the shank  12   s  of the punch tool  12  to be inserted into is formed along the left-right direction on each upper stocker  58 . Each upper stocker  58  includes an engagement plate  60  that can be engaged in an engagement groove  12   g  of the punch tool  12 . Any selected upper stocker  58  is configured to be able to be positioned at the upper exchange position by an upper stocker moving mechanism (not illustrated). The upper stocker  58  positioned at the upper exchange position is supported by a pair of upper receiving members  62  disposed on the right end side of the front surface of the upper support beam  48 . 
     The tool storage  56  includes a plurality of lower stockers  64  (only one is illustrated) for retaining the plurality of die tools  14 . Although only the lower stocker  64  positioned at a lower exchange position for exchanging the die tool  14  is illustrated, the plurality of lower stockers  64  are placed along the front-back direction. Each lower stocker  64  extends in the left-right direction. A stocker groove  64   g  for allowing the shank  14   s  of the die tool  14  is inserted into is formed along the left-right direction on each lower stocker  64 . Any selected lower stocker  64  is configured to be able to be positioned at the lower exchange position by a lower stocker moving mechanism (not illustrated). The lower stocker  64  positioned at the lower exchange position is supported by a pair of lower receiving members  66  disposed on the right end side of the front surface of the lower support beam  52 . 
     As illustrated in  FIG. 3 , an upper guide rail  68  extending in the left-right direction is disposed on the back surface (rear surface) of the upper support beam  48 . On the upper guide rail  68 , a pair of upper tool exchange units  70  for exchanging the punch tool  12  for the plurality of upper tool holders  30  and the upper stocker  58  positioned at the upper exchange position are disposed so as to be movable in the left-right direction. In other words, the pair of upper tool exchange units  70  are disposed on the back side of the upper table  26  via the upper support beam  48  and the upper guide rail  68  so as to be movable in the left-right direction. Each upper tool exchange unit  70  transports the punch tool  12  between the upper tool holder  30  and the upper stocker  58  positioned at the upper exchange position. The pair of upper tool exchange units  70  includes a first upper tool exchange unit  70  and a second upper tool exchange unit  70 . 
     Each upper tool exchange unit  70  has the same configuration as the known configuration shown in Patent Literature 1. Each upper tool exchange unit  70  includes an upper unit main body  72  and an upper support member  74 . Each upper unit main body  72  is disposed on the upper guide rail  68  so as to be movable in the left-right direction. Each upper support member  74  is disposed on the upper unit main body.  72  so as to be movable in the front-back direction. Each upper support member  74  moves in the front-back direction with respect to each upper unit main body  72  by a drive of an air cylinder  76  as a front-back moving unit disposed at an appropriate position of each upper unit main body  72 . It should be noted that the upper support member  74  may be configured to be vertically movable with respect to the upper unit main body  72 . 
     Each upper tool exchange unit  70  includes an upper tool retention member  78  that is disposed on each upper support member  74  so as to be movable in the front-back direction and retains the punch tool  12 . The distal end side of each upper tool retention member  78  is formed in a round-bar shape or a hook shape. Each upper tool retention member  78  is engageable-with and disengageable-from an engagement hole  12   h  of the punch tool  12 . Each upper tool retention member  78  moves in the front-back direction with respect to each upper support member  74  by a drive of an air cylinder  80  as another front-back moving unit disposed at an appropriate position of each upper support member  74 . 
     A servo motor  82  as a left-right moving unit configured to move each upper tool exchange unit  70  in the left-right direction is disposed at an appropriate position of each upper unit main body  72 . Each servo motor  82  includes an encoder  84  as a position detector for detecting the position of each upper tool exchange unit  70  (each upper tool retention member  78 ) in the left-right direction. Each servo motor  82  includes a first servo motor  82  and a second servo motor  82 . Each encoder  84  includes a first encoder  84  and a second encoder  84 . 
     As illustrated in  FIG. 3 , a lower guide rail  86  extending in the left-right direction is disposed on the back surface of the lower support beam  52 . On the lower guide rail  86 , a pair of lower tool exchange units  88  for exchanging the die tool  14  for the plurality of lower tool holders  40  and the lower stocker  64  positioned at the lower exchange position are disposed so as to be movable in the left-right direction. In other words, the pair of lower tool exchange units  88  are disposed on the back side of the lower table  24  via the lower support beam  52  and the lower guide rail  86  so as to be movable in the left-right direction. Each lower tool exchange unit  88  transports the die tool  14  between the lower tool holder  40  and the lower stocker  64  positioned at the lower exchange position. The pair of lower tool exchange units  88  includes a first lower tool exchange unit  88  and a second lower tool exchange unit  88 . 
     Each lower tool exchange unit  88  has the same configuration as the known configuration shown in Patent Literature 1. Each lower tool exchange unit  88  includes a lower unit main body  90  and a lower support member  92 . The lower unit main body  90  is disposed on the lower guide rail  86  so as to be movable in the left-right direction. The lower support member  92  is disposed on the lower unit main body  90  so as to be movable in the front-back direction and vertically. Each lower support member  92  moves in the front-back direction with respect to each lower unit main body  90  by a drive of an air cylinder  94  as a front-back moving unit disposed at an appropriate position of each lower unit main body  90 . Each lower support member  92  moves vertically with respect to each lower unit main body  90  by a drive of an air cylinder  96  as a vertical moving unit disposed at an appropriate position of each lower unit main body  90 . 
     Each lower tool exchange unit  88  includes a lower tool retention member  98  that is disposed on each lower support member  92  so as to be movable in the front-back direction and retains the die tool  14 . The distal end side of each lower tool retention member  98  is formed in a round-bar shape or a hook shape. Each lower tool retention member  98  is engageable-with and disengageable-from an engagement hole  14   h  of the die tool  14 . Each lower tool retention member  98  moves in the front-back direction with respect to each lower support member  92  by a drive of an air cylinder  100  as another front-back moving unit disposed at an appropriate position of each lower support member  92 . 
     A servo motor  102  as a left-right moving unit configured to move each lower tool exchange unit  88  in the left-right direction is disposed at an appropriate position of each lower unit main body  90 . Each servo motor  102  includes an encoder  104  as a position detector for detecting the position of each lower tool exchange unit  88  (each lower tool retention member  98 ) in the left-right direction. Each servo motor  102  includes a first servo motor  102  and a second servo motor  102 . Each encoder  104  includes a first encoder  104  and a second encoder  104 . 
     As illustrated in  FIG. 4 , the bending system  10  includes a control device (an NC device)  106  as a control unit. The control device  106  controls the hydraulic cylinder  28  and the like on the basis of a processing program, and controls the tool storage  56 , the upper tool exchange unit  70 , and the like on the basis of a tool exchange program. The control device  106  is configured with a computer. The encoders  84 ,  104 , and the like are connected to the control device  106 . The control device  106  includes a memory (not illustrated) for storing the processing program, the tool exchange program, and the like, and a CPU (not illustrated) for executing the processing program and the tool exchange program. 
     In the plurality of upper tool holders  30 , when the predetermined punch tool  12  to be exchanged (to be transported) is in contact with an adjacent another punch tool  12 ′ not to be exchanged (see  FIG. 5A ), the control device  106  controls the first upper tool exchange unit  70  and the first servo motor  82  so that the upper tool retention member  78  of the first upper tool exchange unit  70  retains the predetermined punch tool  12  in a state of being engaged in the engagement hole  12   h  of the predetermined punch tool  12 . Further, the control device  106  controls the second upper tool exchange unit  70  and the second servo motor  82  so that the upper tool retention member  78  of the second upper tool exchange unit  70  retains the other punch tool  12 ′ in a state of being engaged in an engagement hole  12   h ′ of the other punch tool  12 ′ (see  FIG. 5B ). Subsequently, the control device  106  controls each servo motor  82  so that the first upper tool exchange unit  70  moves in the left-right direction until a target position is reached while acquiring the detection result from the first encoder  84  in a state in which a movement of the second upper tool exchange unit  70  in the left-right direction is stopped (see  FIG. 5C ). 
     Here, the control device  106  can grasp that the predetermined punch tool  12  is in contact with the adjacent other punch tools  12 ′ in the plurality of upper tool holders  30  on the basis of the tool exchange program. 
     In the above case and when there are a plurality of the predetermined punch tools  12  (see  FIG. 6A ), the control device  106  controls the first upper tool exchange unit  70  and the first servo motor  82  so that the upper tool retention member  78  of the first upper tool exchange unit  70  retains the last punch tool  12  (the punch tool  12  on the left side in  FIGS. 6A to 6E ) from among the plurality of predetermined punch tools  12  in a state of being engaged in the engagement hole  12   h  of the last punch tool  12 . Further, the control device  106  controls the second upper tool exchange unit  70  and the second servo motor  82  so that the upper tool retention member  78  of the second upper tool exchange unit  70  retains the other punch tool  12 ′ in a state of being engaged in the engagement hole  12   h ′ of the other punch tool  12 ′ (see  FIG. 6B ). Subsequently, the control device  106  controls each servo motor  82  so that the first upper tool exchange unit  70  moves in the left-right direction by a predetermined amount while acquiring the detection result from the first encoder  84  in a state in which the movement of the second upper tool exchange unit  70  in the left-right direction is stopped (see  FIG. 6C ). Here, the predetermined amount is a movement amount set in advance for separating the last punch tool  12  from the other punch tool  12 ′. 
     Thereafter, the control device  106  controls the first upper tool exchange unit  70  and the first servo motor  82  so that the upper tool retention member  78  of the first upper tool exchange unit  70  retains a leading punch tool  12  (the punch tool  12  on the right side in  FIGS. 6A to 6E ) from among the plurality of predetermined punch tools in a state of being engaged in the engagement hole  12   h  of the leading punch tool  12 . Further, the control device  106  controls the second upper tool exchange unit  70  and the second servo motor  82  so that the upper tool retention member  78  of the second upper tool exchange unit  70  retains the last punch tool  12  in a state of being engaged in the engagement hole  12   h  of the last punch tool  12  (see  FIG. 6D ). Subsequently, the control device  106  controls each servo motor  82  so that each upper tool exchange unit  70  moves in the left-right direction synchronously (or asynchronously) until a target position is reached while acquiring the detection result from each encoder  84  (see  FIG. 6E ). 
     It should be noted that the plurality of predetermined punch tools  12  may include an intermediate punch tool (not illustrated) that is between the leading punch tool  12  and the last punch tool  12 . In other words, the number of predetermined punch tools  12  may be three or more. Further, instead of moving the first upper tool exchange unit  70  in the left-right direction by a predetermined amount from the state illustrated in  FIG. 6B , each servo motor  82  may be controlled to be moved in the left-right direction until the target position is reached. 
     In the above case and when there are a plurality of the predetermined punch tools  12 , before the upper tool retention member  78  of the first upper tool exchange unit  70  retains the last punch tool  12  (see  FIG. 7C ), the control device  106  may control each upper tool exchange unit  70  and each servo motor  82  as follows. 
     In other words, the control device  106  control the first upper tool exchange unit  70  and the first servo motor  82  so that the upper tool retention member  78  of the first upper tool exchange unit  70  retains the leading punch tool  12  in a state of being engaged in the engagement hole  12   h  of the leading punch tool  12 . Further, the control device  106  control the second upper tool exchange unit  70  and the second servo motor  82  so that the upper tool retention member  78  of the second upper tool exchange unit  70  retains the last punch tool  12  in a state of being engaged in the engagement hole  12   h  of the last punch tool  12  (see  FIG. 7A ). Subsequently, the control device  106  controls each servo motor  82  so that the first upper tool exchange unit  70  moves in the left-right direction by a predetermined amount while acquiring the detection result from the first encoder  84  in a state in which the movement of the second upper tool exchange unit  70  in the left-right direction is stopped (see  FIG. 7B ). Here, the predetermined amount is a movement amount set in advance for separating the leading punch tool  12  from the last punch tool  12 . 
     When the predetermined punch tool  12  to be exchanged (to be transported) is in contact with the adjacent other punch tool  12 ′ not to be exchanged not only in the plurality of upper tool holders  30  but also in the upper stocker  58  positioned at the upper exchange position, the control device  106  also controls each upper tool exchange unit  70  and each servo motor  82  in the same manner as described above. Further, when the predetermined die tool  14  to be exchanged (to be transported) is in contact with the adjacent other die tool not to be exchanged (not illustrated) on the lower tool holder  40  and in the lower stocker  64  positioned at the lower exchange position, the control device  106  also controls each lower tool exchange unit  88  and each servo motor  102  in the same manner as described above. 
     The operation related to automatic exchange of the tools  12  and  14  by the bending system  10  will be described. 
     A control when the punch tool  12  is transported from the upper tool holder  30  to the upper stocker  58  positioned at the upper exchange position will be described. The control device  106  controls the servo motor  82  to move the upper tool exchange unit  70  in the left-right direction so that the upper tool retention member  78  is opposed to the engagement hole  12   h  of the punch tool  12  installed in the upper tool holder  30 . Next, the control device  106  causes the upper tool retention member  78  to retain the punch tool  12  while engaging the upper tool retention member  78  in the engagement hole  12   h  of the punch tool  12 . Then, the control device  106  controls the servo motor  82  to move the upper tool exchange unit  70  to the right so that the punch tool  12  is transported to the right and removed from the upper tool holder  30 . Furthermore, the control device  106  controls the servo motor  82  to move the upper tool exchange unit  70  to the right so that the punch tool  12  is transported to the right and installed in the upper stocker  58 . Thereafter, the control device  106  causes the upper tool retention member  78  to be removed from the engagement hole  12   h  of the punch tool  12  so that the punch tool  12  is released from a state in which the punch tool  12  is retained by the upper tool retention member  78 . 
     It should be noted that the punch tool  12  may be moved to the back side (rear side) of the upper table  26  by the upper tool exchange unit  70  after the punch tool  12  is removed from the upper tool holder  30 . 
     When the punch tool  12  is transported from the upper stocker  58  positioned at the upper exchange position to the upper tool holder  30 , the operation opposite to the above operation is performed. As a result, the punch tool  12  installed in the upper tool holder  30  and the punch tool  12  installed in the upper stocker  58  can be automatically exchanged. 
     When the die tool  14  is transported between the lower tool holder  40  and the lower stocker  64  positioned at the lower exchange position, the operation similar to the above is performed. As a result, the die tool  14  installed in the lower tool holder  40  and the die tool  14  installed in the lower stocker  64  can be automatically exchanged. 
     It should be noted that when the die tool  14  is installed in and removed from the lower tool holder  40  or the lower stocker  64 , the die tool  14  may be moved vertically by the lower tool exchange unit  88 . 
     Subsequently, the operation and effect of the embodiment of the present invention will be described, including the details of the tool transport method according to the embodiment of the present invention. The tool transport method according to the present embodiment is a method of transporting the tools  12  and  14  along the tool holders  30  and  40  or the stockers  58  and  64  positioned at the exchange positions. 
     As illustrated in  FIGS. 5A to 5C , when the predetermined punch tool  12  to be exchanged is in contact with the adjacent other punch tool  12 ′ to be exchanged in the plurality of upper tool holders  30  (see  FIG. 5A ), the control device  106  controls each upper tool exchange unit  70  and each servo motor  82  so as to operate as follows. 
     The predetermined punch tool  12  is retained in a state in which the upper tool retention member  78  of the first upper tool exchange unit  70  is engaged in the engagement hole  12   h  of the predetermined punch tool  12 . Further, the other punch tool  12 ′ is retained in a state in which the upper tool retention member  78  of the second upper tool exchange unit  70  is engaged in the engagement hole  12   h ′ of the other punch tool  12 ′ (see  FIG. 5B ). Subsequently, the first upper tool exchange unit  70  moves in the left-right direction until a target position is reached while acquiring the detection result from the first encoder  84  in a state in which the movement of the second upper tool exchange unit  70  in the left-right direction is stopped (see  FIG. 5C ). As a result, the position of the other punch tool  12 ′ is not shifted because the other punch tool  12 ′ is not dragged by the predetermined punch tools  12 . Therefore, without performing post-processing on a side surface of the punch tool  12 , only the predetermined punch tool  12  to be exchanged can be transported in the left-right direction by the upper tool exchange unit  70 . 
     As illustrated in  FIGS. 6A to 6E , in the above case and when there are a plurality of the predetermined punch tools  12  (see  FIG. 6A ), the control device  106  controls each upper tool exchange unit  70  and each servo motor  82  so as to operate as follows. 
     The last punch tool  12  is retained in a state in which the upper tool retention member  78  of the first upper tool exchange unit  70  is engaged in the engagement hole  12   h  of the last punch tool  12  from among the plurality of predetermined punch tools  12 . Further, the other punch tool  12 ′ is retained in a state in which the upper tool retention member  78  of the second upper tool exchange unit  70  is engaged in the engagement hole  12   h ′ of the other punch tool  12 ′ (see  FIG. 6B ). Subsequently, the first upper tool exchange unit  70  moves in the left-right direction by a predetermined amount in a state in which the movement of the second upper tool exchange unit  70  in the left-right direction is stopped (see  FIG. 6C ). As a result, the plurality of predetermined punch tools  12  can be separated from the other punch tools  12 ′. 
     Thereafter, the upper tool retention member  78  of the first upper tool exchange unit  70  retains the leading punch tool  12  in a state of being engaged in the engagement hole  12   h  of the leading punch tool  12  from among the plurality of predetermined punch tools  12 . Further, the upper tool retention member  78  of the second upper tool exchange unit  70  retains the last punch tool  12  in a state of being engaged in the engagement hole  12   h  of the last punch tool  12  (see  FIG. 6D ). Subsequently, each upper tool exchange unit  70  moves in the left-right direction synchronously (or asynchronously) until a target position is reached (see  FIG. 6E ). As a result, the position of the other punch tool  12 ′ is not shifted because the other punch tool  12 ′ is not dragged by the plurality of predetermined punch tools  12 . Therefore, without performing post-processing on a side surface of the punch tool  12 , only the plurality of predetermined punch tools  12  to be exchanged can be transported by the upper tool exchange unit  70  in the left-right direction along the plurality of upper tool holders  30 . 
     As illustrated in  FIGS. 7A to 7C , before the upper tool retention member  78  of the first upper tool exchange unit  70  retains the last punch tool  12 , the control device  106  may control each upper tool exchange unit  70  and each servo motor  82  so as to operate as follows. 
     The leading punch tool  12  is retained in a state in which the upper tool retention member  78  of the first upper tool exchange unit  70  is engaged in the engagement hole  12   h  of the leading punch tool  12 . Further, the last punch tool  12  is retained in a state in which the upper tool retention member  78  of the second upper tool exchange unit  70  is engaged in the engagement hole  12   h  of the last punch tool  12  (see  FIG. 7A ). Subsequently, the upper tool exchange unit  70  moves in the left-right direction by a predetermined amount in a state in which the movement of the second upper tool exchange unit  70  in the left-right direction is stopped. As a result, the leading punch tool  12  can be separated from the last punch tool  12 . 
     Here, in  FIGS. 5A to 7C , the transport direction of the predetermined punch tool  12  is illustrated as the right direction, the upper tool exchange unit  70  on the right side is the first upper tool exchange unit  70 , and the upper tool exchange unit  70  on the left side is the second upper tool exchange unit  70 . When the transport direction of the predetermined punch tool  12  is changed to the left, the upper tool exchange unit  70  on the left side is the first upper tool exchange unit  70  and the upper tool exchange unit  70  on the right side is the second upper tool exchange unit  70 . In other words, when the transport direction of the predetermined punch tool  12  is inverted, the first upper tool exchange unit  70  and the second upper tool exchange unit  70  are switched. 
     It should be noted that the control device  106  controls each upper tool exchange unit  70  and each servo motor  82  so as to operate in the same manner as described above when the predetermined punch tool  12  to be exchanged (to be transported) is in contact with the adjacent other punch tool  12 ′ not to be exchanged not only in the plurality of the upper tool holder  30  but also in the upper stocker  58  positioned at the upper exchange position. 
     When the predetermined die tool  14  (or the plurality of predetermined die tools  14 ) to be exchanged (to be transported) is/are in contact with the adjacent other die tool not to be exchanged (not illustrated) in the lower tool holder  40  and the lower stocker  64  positioned at the lower exchange position, the control device  106  also controls each lower tool exchange unit  88  and each servo motor  102  so as to operate in the same manner as described above. As a result, the position of the other die tool is not shifted because the other die tool is not dragged by the predetermined die tool  14  (or the plurality of predetermined die tools  14 ). Therefore, without performing post-processing on a side surface of the die tool  14 , only the predetermined die tool  14  (or the plurality of predetermined die tools  14 ) can be transported by the lower tool exchange unit  88  in the left-right direction along the lower tool holder  40 . 
     Therefore, according to the embodiment of the present invention, it is possible to stably perform the operation related to automatic exchange of the tools  12  and  14  by the bending system  10  while suppressing an increase in manufacturing cost of the tools  12  and  14 . 
     Instead of disposing the tool exchange units  70  and  88  on the back sides of the tables  26  and  24  so as to be movable in the left-right direction, the tool exchange units  70  and  88  may be disposed on the front sides of the tables  26  and  24  so as to be movable in the left-right direction. The location at which the tool storage  56  is placed may be other than the lateral side of the press brake  16  in the left-right direction as long as the location is in the vicinity of the press brake  16 . 
     Although the embodiments have been described above, the embodiments are merely examples described for facilitating the understanding of the present disclosure. The technical scope of the present disclosure is not limited to the specific technical matters disclosed in the above-described embodiments, but also includes various modifications, changes, alternative technologies, and the like that can be easily derived therefrom. 
     The present invention has, for example, the following configurations. 
     A bending system includes a tool storage placed in a vicinity of a press brake and including a plurality of stockers extending in a left-right direction so as to be able to retain a plurality of tools, a first tool exchange unit and a second tool exchange unit each disposed on a back side or a front side of a table of the press brake so as to be movable in the left-right direction and configured to exchange a tool with respect to a tool holder of the press brake and a stocker selected from among the plurality of stockers, a left-right moving unit configured to move the first tool exchange unit and the second tool exchange unit in the left-right direction, respectively, and a control unit configured to control the first tool exchange unit, the second tool exchange unit, and the left-right moving unit. The first tool exchange unit includes a first tool retention member engageable-with and disengageable-from an engagement hole of a tool, the first tool retention member being able to retain the tool and configured to move in the left-right direction together with the first tool exchange unit. The second tool exchange unit includes a second tool retention member engageable-with and disengageable-from an engagement hole of a tool, the second tool retention member being able to retain the tool and configured to move in the left-right direction together with the second tool exchange unit. The control unit, when a first tool to be exchanged is in contact with an adjacent second tool not to be exchanged in the tool holder or the selected stocker, controls the first tool exchange unit, the second tool exchange unit, and the left-right moving unit such that the first tool retention member retains the first tool in a state of being engaged in an engagement hole of the first tool, the second tool retention member retains the second tool in a state of being engaged in an engagement hole of the second tool, and the first tool exchange unit subsequently moves in the left-right direction in a state in which a movement of the second tool exchange unit in the left-right direction is stopped. 
     According to the above configuration, since the second tool not to be exchanged is not dragged by the first tool to be exchanged, the position of the second tool is not shifted. As a result, only the first tool to be exchanged can be transported in the left-right direction by the first and second tool exchange units without performing post-processing on a side surface of the tool. Therefore, it is possible to stably perform an operation related to automatic exchange of tools while suppressing an increase in manufacturing cost of the tools. 
     In the bending system, when the first tool includes a plurality of first tools, the control unit may control the first tool exchange unit, the second tool exchange unit, and the left-right moving unit such that the first tool retention member retains a last tool from among the plurality of first tools in a state of being engaged in an engagement hole of the last tool, the last tool being in contact with the second tool, the second tool retention member retains the second tool in a state of being engaged in the engagement hole of the second tool, the first tool exchange unit subsequently moves in the left-right direction by a predetermined amount in a state in which the movement of the second tool exchange unit in the left-right direction is stopped, the first tool retention member thereafter retains a leading tool from among the plurality of first tools in a state of being engaged in an engagement hole of the leading tool, the second tool retention member retains the last tool in a state of being engaged in the engagement hole of the last tool, and the first tool exchange unit and the second tool exchange unit then move in the left-right direction. 
     In the bending system, before the first tool retention member retains the last tool, the control unit may control the first tool exchange unit, the second tool exchange unit, and the left-right moving unit such that the first tool retention member retains the leading tool in a state of being engaged in the engagement hole of the leading tool, the second tool retention member retains the last tool in a state of being engaged in the engagement hole of the last tool, and the first tool exchange unit subsequently moves in the left-right direction by a predetermined amount in a state in which the movement of the second tool exchange unit in the left-right direction is stopped. 
     A tool transport method uses a first tool exchange unit and a second tool exchange unit each disposed 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. The tool transport method includes, when a first tool to be exchanged is in contact with an adjacent second tool not to be exchanged in a tool holder of the press brake or in a selected stocker in a tool storage placed in a vicinity of the press brake, retaining, by a first tool retention member of the first tool exchange unit, the first tool in a state in which the first tool retention member is engaged in an engagement hole of the first tool, retaining, by a second tool retention member of the second tool exchange unit, the second tool in a state in which the second tool retention member is engaged in an engagement hole of the second tool, and subsequently moving the first tool exchange unit in the left-right direction in a state in which a movement of the second tool exchange unit in the left-right direction is stopped. 
     According to the above configuration, since the second tool not to be exchanged is not dragged by the first tool to be exchanged, the position of the second tool is not shifted. As a result, only the first tool to be exchanged can be transported in the left-right direction by the first and second tool exchange units without performing post-processing on a side surface of the tool. Therefore, it is possible to stably perform an operation related to automatic exchange of tools while suppressing an increase in manufacturing cost of the tools. 
     The tool transport method described above may include, when the first tool includes a plurality of first tools, retaining, by the first tool retention member, a last tool from among the plurality of first tools in a state in which the first tool retention member is engaged in an engagement hole of the last tool, the last tool being in contact with the second tool, retaining, by the second tool retention member, the second tool in a state in which the second tool retention member is engaged in the engagement hole of the second tool, subsequently moving the first tool exchange unit in the left-right direction by a predetermined amount in a state in which the movement of the second tool exchange unit in the left-right direction is stopped, thereafter retaining, by the first tool retention member, a leading tool from among the plurality of first tools in a state in which the first tool retention member is engaged in an engagement hole of the leading tool, retaining, by the second tool retention member, the last tool in a state in which the second tool retention member is engaged in the engagement hole of the last tool, and then moving the first tool exchange unit and the second tool exchange unit in the left-right direction. 
     The tool transport method described above may include, before retaining the last tool by the first tool retention member, retaining, by the first tool retention member, the leading tool in a state in which the first tool retention member is engaged in the engagement hole of the leading tool, retaining, by the second tool retention member, the last tool in a state in which the second tool retention member is engaged in the engagement hole of the last tool, and subsequently moving the first tool exchange unit in the left-right direction by a predetermined amount in a state in which the movement of the second tool exchange unit in the left-right direction is stopped. 
     The entire contents of Japanese Patent Application No. 2019-092890 (application date: May 16, 2019) are incorporated herein.