Patent Publication Number: US-7721584-B2

Title: Work conveyance device, press machine and bar removal method

Description:
This application is a U.S. National Phase Application under 35 USC 371 of International Application PCT/JP2006/307553 filed Apr. 10, 2006. 
   TECHNICAL FIELD 
   The present invention relates to: a workpiece transfer device that transfers a workpiece to a subsequent step in a plurality of steps in press-processing; a press machine including the workpiece transfer device; and a bar-detaching method for detaching a bar of the workpiece transfer device. 
   BACKGROUND ART 
   A press machines such as a transfer press that conducts a plurality of steps in press-processing is provided with a workpiece transfer device that sequentially transfers a workpiece to a subsequent step. The workpiece transfer device includes a pair of bars disposed along a workpiece transfer direction, the pair of bars each having a workpiece holder for holding the workpiece. The pair of bars are moved in feed, lift and clamp directions to transfer the workpiece. 
   In the press machines, when a die is changed, the workpiece holder and the bars need to be replaced. Accordingly, each of the bars of a related-art workpiece transfer device is constituted by a portion fixed to the press machine and a portion for holding the workpiece holder, the two portions being separable from each other (see, for instance, Patent Document 1). In the workpiece transfer device disclosed in Patent Document 1, a first bar and a second bar of the bars are connected to each other and separated from each other by a connecting device. 
   The connecting device includes: a wedge-shaped member provided on the first bar; and an engaging claw provided on the second bar and engageable with the wedge-shaped member. The wedge-shaped member is provided on an end of a piston. When the piston is moved by air pressure, the wedge-shaped member protrudes toward the second bar to engage with the engaging claw, so that the first bar is connected with the second bar. To release the connection, a disconnecting device that is provided as a separate component from the connecting device opens the engaging claw to release the engagement of the wedge-shaped member. 
   [Patent Document 1] Japanese Utility Model Registration No. 2583175 (Pages 5 to 7, FIG. 1) 
   DISCLOSURE OF THE INVENTION 
   Problems to be Solved by the Invention 
   Recently, a workpiece transfer device that is provided with a feed carrier movable on a bar in a feed direction has been suggested. In such a workpiece transfer device, the plurality of feed carriers connected with each other by connecting members are disposed on each of the bars. The workpiece transfer carriers have a structure in which the plurality of feed carriers are moved on the bar in the feed direction in accordance with movement of the connecting members by a driver such as a liner motor. 
   In the workpiece transfer devices, when a die is replaced, the bar and the connecting members on which the feed carriers are connected need to be separated and detached. However, a structure that enables the separation and connection of the connecting members has not been developed. Granted that a conventional connecting device disclosed in the afore-mentioned Patent Document 1 is applied to the connecting members, the structure will be complicated. Further, the number of components will be increased, which causes difficulty in control, maintenance and the like and inefficiency in operation. 
   An object of the present invention is to provide a workpiece transfer device from which a bar can be easily detached with a simple structure, a press machine equipped with the workpiece transfer device and a bar-detaching method of the workpiece transfer device. 
   Means for Solving the Problems 
   A workpiece transfer device of a press machine according to an aspect of the invention includes: a pair of bars that are disposed substantially in parallel to a workpiece transfer direction; a workpiece holder that holds a workpiece; a feed driving mechanism that moves the workpiece holder in the workpiece transfer direction relative to the pair of bars; and a bar driving mechanism that drives the pair of bars at least either in a lift direction or in a clamp direction. The pair of bars each include a fixed bar that is fixed on the bar driving mechanism, a movable bar that is separable from the fixed bar and a bar connecting device that connects the fixed bar and the movable bar. The feed driving mechanism includes a slide member that is supported by the movable bar and slidable, a movable member that is supported by the fixed bar and slidable, a connecting portion that connects the slide member and the movable member and a feed driving source that is provided on the fixed bar and moves the movable member in the workpiece transfer direction. The connecting portion includes an engaging portion that is provided one of the slide member and the movable member and an engaged portion that is provided the other of the slide member and the movable member and engageable with the engaging portion. The engaging portion can engage with the engaged portion in a direction substantially orthogonal to a longitudinal direction of the pair of bars. 
   According to the aspect of the invention, since the connecting portion is provided between the slide member and the movable member, the slide member and the movable member can be separated from each other. Accordingly, when a die is exchanged, the bar is divided into the fixed bar and the movable bar and the slide member is separated from the movable member. Hence, it is possible to carry-out (carry-in) the slide member and the bar from (to) the press machine in the die replacement, which facilitates the die replacement. 
   The connecting portion includes the engaging portion and the engaged portion. The engaging portion can engage with the engaged portion in the direction substantially orthogonal to the longitudinal direction of the bar. Accordingly, by moving the fixed bar in the direction substantially orthogonal to the longitudinal direction of the bar relative to the movable bar, the engaging portion can engage with the engaged portion. Since the slide member and the movable member move in the longitudinal direction of the bar in a general workpiece transfer, the engagement between the engaging member and the engaged member will not be released. Thus, since the arrangement where the engaging portion engages with the engaged portion in the direction substantially orthogonal the longitudinal direction of the bar is employed, no conventional connecting device having an actuator, a disconnecting device or the like is required to separate the slide member from the movable member and to connect the slide member to the movable member. Hence, the structure of the workpiece transfer device can be simplified and the workpiece transfer device can be lighter in weight and smaller in size. Further, since the structure of the connecting portion can be also simplified, the number of components will be reduced, which decrease the costs of the workpiece transfer device while improving efficiency in maintenance. 
   In the workpiece transfer device of the press machine, the engaging portion may engage with the engaged portion in a vertical direction. 
   According to the aspect of the invention, since the engaging portion engages with the engaged portion in the vertical direction, the engaging portion can engage with the engaged portion by moving the fixed bar in the vertical direction relative to the movable bar. Also in a case where the bar driving mechanism of the workpiece transfer device of the press machine is equipped with a mechanism to move the bar in a lift direction, the bar driving mechanism can be used as it is to connect the slide member with the movable member and to separate the slide member from the movable member, so that the structure of the workpiece transfer device can be simplified and the connection and separation can be easily conducted. 
   In the workpiece transfer device of the press machine, the engaging portion may be formed in a substantially T-shape in plan view, and the engaged portion may be formed in a substantially C-shape in plan view. 
   According to the aspect of the invention, since the engaging portion is formed in the substantially T-shape in plan view and the engaged portion is formed in the substantially C-shape in plan view, the engaging portion can easily engage with the engaged portion and the engagement therebetween can be properly maintained without being released even when the slide member and the movable member are moved in a feed direction. 
   Note that the planes of the engaging portion and the engaged portion in plan view are orthogonal to a direction in which the engaging portion engages with the engaged portion. For example, when the engaging portion engages with the engaged portion in the vertical direction, the shapes of the planes parallel to the horizontal plane of the engaging portion and the engaged portion are the substantially T-shape and the substantially C-shape. 
   In the workpiece transfer device of the press machine, the fixed bars may be provided on ends of the movable bar, and the feed driving source may be provided to at least one of the fixed bars. 
   According to the aspect of the invention, since the fixed bar is provided on both ends of the movable bar, this structure in which the movable bar is supported at both ends achieves a stable transfer of the workpiece. When the feed driving source is provided on both of the fixed bars, output capacity per feed driving source may be small. On the other hand, when the feed driving source is provided either one of the fixed bars, the entire structure of the device can be simplified. 
   In the workpiece transfer device of the press machine, the bar connecting device may include: a fixed-side connecting portion that protrudes from an end of the fixed bar toward the movable bar; a movable-side connecting portion that protrudes from an end of the movable bar toward the fixed bar to overlap with the fixed-side connecting portion; and a holding means that is disposed in the fixed bar to hold the movable-side connecting portion against the fixed-side connecting portion by a holding member being advanced and retracted in a longitudinal direction of the fixed bar by air pressure. 
   According to the aspect of the invention, when the holding member is protruded in the longitudinal direction from the end of the bar by air pressure with the fixed-side connecting portion and the movable-side connecting portion overlapped, the movable-side connecting portion is held between the fixed-side connecting portion and the holding member. Accordingly, the fixed bar is connected with the movable bar. In order to detach the movable bar from the fixed bar, the holding member is evacuated by controlling the air pressure. Since the holding member protrudes and evacuates in the longitudinal direction of the fixed bar, the holding member will not be overlapped on the movable-side connecting portion when the holding member is evacuated. Hence, by moving the fixed bar relative to the movable bar, the movable-side connecting portion will be spaced from the fixed-side connecting portion, thereby releasing the connection between the fixed bar and the movable bar. 
   Since the holding member is advanceable and retractable by air pressure, the responsiveness will be excellent, so that the holding member can be moved in a speedy manner, thereby shortening die replacement time. Additionally, unlike the conventional control using hydraulic pressure, a complicate connecting device will not be required, so that the arrangement of the holding member can be simplified, thereby facilitating the control, operation and maintenance of the holding member. 
   Since the holding means is accommodated in the fixed bar, space efficiency of the workpiece transfer device can be enhanced, thereby promoting downsizing of the workpiece transfer device. Further, since the holding member protrudes and evacuates in the longitudinal direction of the fixed bar, the holding member will not be overlapped on the movable-side connecting portion when the holding member is evacuated. Hence, the movable-side connecting portion can be easily detached from the fixed-side connecting portion, which facilitates the detachment. 
   In the workpiece transfer device of the press machine, one of the fixed-side connecting portion and the movable-side connecting portion may be provided with a guide pin projecting toward the other of the fixed-side connecting portion and the movable-side connecting portion, and the other of the fixed-side connecting portion and the movable-side connecting portion may be provided with a guide hole in which the guide pin is inserted. 
   According to the aspect of the invention, since the guide pin projects toward either of the fixed-side connecting portion or the movable-side connecting portion, the guide pin can be inserted into the guide hole at the same time when the fixed-side connecting portion is moved to be overlapped on the movable-side connecting portion. Hence, the fixed-side connecting portion and the movable-side connecting portion can be easily positioned. 
   In the workpiece transfer device of the press machine, the bar driving mechanism may move the fixed bar in the direction substantially orthogonal to the longitudinal direction of the pair of bars relative to the movable bar such that the fixed-side connecting portion and the movable-side connecting portion are overlapped with each other or spaced from each other while the connecting portion engages with or disengages from the connecting portion. 
   According to the aspect of the invention, since the connecting portion is connected or released at the same time when the fixed-side connecting portion and the movable-side connecting portion are overlapped or spaced, no conventional connecting device having an actuator, a disconnecting device or the like is required to separate the slide member from the movable member and to connect the slide member to the movable member. Hence, the structure of the workpiece transfer device can be simplified and the workpiece transfer device can be lighter in weight and smaller in size. Further, since the structure of the connecting portion can be also simplified, the number of components will be reduced, which decreases the costs of the workpiece transfer device while improving the efficiency in maintenance. 
   A press machine according to an aspect of the invention is provided with the above-described workpiece transfer device of the press machine. 
   According to the aspect of the invention, since the press machine is provided with the above-described workpiece transfer device of the press machine, the advantages same as those of the above-described workpiece transfer device of the press machine can be achieved, whereby the weight and size thereof can be reduced and the efficiency in maintenance can be improved. In addition, since the bar can be easily detached, the die replacement will be easy, so that the die replacement time can be shortened. 
   A bar detaching method of the above-described workpiece transfer device of the press machine according to an aspect of the invention includes: a positioning process in which the feed driving mechanism moves the connecting portion to a position corresponding to that of the bar connecting device; and a connection-releasing process in which the bar driving mechanism moves the fixed bar in the direction substantially orthogonal to the longitudinal direction of the pair of bars relative to the movable bar to release a connection of the bar connecting device and a connection of the connecting portion. 
   According to the aspect of the invention, the bar connecting device and the connecting portion are positioned in the positioning process. When the fixed bar is moved relative to the movable bar in the connection-releasing process, the connection of the bar connecting device is released and the engagement of the engaging portion with the engaged portion is released. In other words, a single movement can detach both of the bar connecting device and the connecting portion, which facilitates the bar detachment. Further, since the slide member and the movable member are connected by the engagement between the engaging portion and the engaged portion, an actuator used in a conventional connecting device will not be required. Hence, when the slide member and the movable member are connected with each other in the die replacement, operation checking of the actuator or the like will be unnecessary, thereby further simplifying the die replacement. Therefore, the die replacement time can be shorter. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is an overall view of a press machine of an embodiment of to the invention; 
       FIG. 2  is a perspective view showing a workpiece transfer device of the aforesaid embodiment of the invention; 
       FIG. 3  is a side view showing a bar connecting device of the aforesaid embodiment of the invention; 
       FIG. 4  is a partially-enlarged plan view of the bar connecting device of aforesaid embodiment of the invention; 
       FIG. 5  is a side cross-sectional view of a holding means of the aforesaid embodiment of the invention; 
       FIG. 6  is a plan view showing a connecting portion of the aforesaid embodiment of the invention; 
       FIG. 7  is an illustration showing how a bar of the workpiece transfer device is detached in the aforesaid embodiment of the invention; 
       FIG. 8  is an illustration showing how the bar of the workpiece transfer device is detached in the aforesaid embodiment of the invention; 
       FIG. 9  is an illustration showing how the bar of the workpiece transfer device is detached in the aforesaid embodiment of the invention; and 
       FIG. 10  is an illustration showing how the bar of the workpiece transfer device is detached in the aforesaid embodiment of the invention. 
   

   EXPLANATION OF CODES 
     1 : transfer press (press machine) 
     2 : workpiece 
     14 : bar 
     15 : bar connecting device 
     16 : air clamp (holding means) 
     41 : transfer feeder (workpiece transfer device) 
     52 : workpiece holder 
     70 : feed driving mechanism 
     71 : slide plate (slide member) 
     72 : movable plate (movable member) 
     73 : plate connecting portion (connecting portion) 
     75 : feeding linear motor (feed driving source) 
     141 : fixed bar 
     142 : movable bar 
     151 : fixed-side connecting portion 
     152 : movable-side connecting portion 
     153 A: guide pin 
     153 B: guide hole 
     165 : clamp member (holding member) 
     731 : engaging portion 
     732 : engaged portion 
   BEST MODE FOR CARRYING OUT THE INVENTION 
   An embodiment of the present invention will be described below with reference to the drawings. 
     FIG. 1  is an overall view of a transfer press (a press machine)  1  of the present embodiment of the invention. In  FIG. 1 , the transfer press  1  includes: a press main body  1 A having a bed  23 , an upright  21 , a crown  20  and a slide  22 ; a die  11  having an upper die  12  and a lower die  13 ; a moving bolster  30 ; and a transfer feeder (a workpiece transfer device)  41 . 
   The bed  23  (a foundation) of the transfer press  1  is provided under a floor (FL). On a top surface of the bed  23 , a plurality of uprights  21  (four in total in the embodiment, only two of the uprights are shown in  FIG. 1 ) stand so as to face each other in a feed direction F (a direction parallel to a transfer direction T of a workpiece  2 ) and in a clamp direction (a direction horizontally orthogonal to the feed direction F i.e. a direction orthogonal to the sheet surface of  FIG. 1 ). On the uprights  21 , the crown  20  in which a slide driver (not shown) is provided is supported. Below the crown  20 , the slide  22  that can be raised and lowered by the slide driver is suspended. On a bottom surface of the slide  22 , a plurality of upper dies  12  usable in a plurality of steps in press-molding are aligned along the feed direction in a detachable manner. On the top surface of the bed  23 , the moving bolster  30  is provided. On a top surface of the moving bolster  30 , a plurality of lower dies  13  (which are respectively paired with to the upper dies  21 ) are provided in a detachable manner so as to face the respective upper dies  12 . 
   The moving bolster  30  will be described in detail below. 
   The moving bolster  30  can be transferred to and from the top surface of the bed  23  to replace a used die  11  (the upper die  12 , the lower die  13 ) with a new die  11 . 
   A rail (not shown) is provided on the floor and the bed  23 . The moving bolster  30  includes a driver to self-travel on the rail. When the moving bolster  30  self-travels owing to the driver, the moving bolster  30  moves in the clamp direction while passing between the pair of uprights  21  standing in parallel in the workpiece transfer direction T, thus being transferred into (or out of) the transfer press  1 . 
   Note that the moving bolster  30  is generally prepared in two sets. A first set of the moving bolster  30  carrying the used die  11  is automatically exchanged with a second set of the moving bolster  30  carrying a to-be-next-used die  11  that is mounted thereon in advance outside the transfer press  1 , thereby speedily exchange the dies  11  in accordance with a workpiece type. 
   Next, the transfer feeder  41  will be described in detail below. 
     FIG. 2  shows a perspective view of the transfer feeder  41 . In  FIG. 2 , the transfer feeder  41  includes: a pair of bars  14  respectively disposed on the right and left of the workpiece transfer direction T (also referred to herein as bar assemblies); a workpiece holder  52  provided on each of the pair of bars  14  to hold the workpiece  2 ; a feed driving mechanism  70  that moves the workpiece holder  52  in the feed direction F; and a lift/clamp device (a bar driving mechanism)  80  that moves the pair of bars  14  in the clamp direction and an up-and-down direction (a direction orthogonal to the feed direction F and the clamp direction, i.e., a lift direction L, see  FIG. 1 ). 
   The pair of bars  14  are positioned in parallel to the feed direction F with a predetermined distance from each other. 
   Frames  33 A are respectively provided on the bed  23  at positions between the pairs of uprights  21  on both sides (upstream and downstream sides) of the workpiece transfer direction T in which the moving bolster  30  transfers the workpiece. The frames  33 A each have the lift/clamp device  80 . 
   The bars  14  each include: fixed bars  141  fixed on ends of the lift/clamp device  80 ; a movable bar  142  provided between the fixed bars  141  and detachable from the fixed bars  141  during the die exchange; and bar connecting devices  15  for connecting the fixed bars  141  and the movable bar  142 . 
     FIGS. 3 and 4  show the bar connecting device  15 .  FIG. 3  is a side view of the bar connecting device  15 .  FIG. 14  is a plan view of the bar connecting device.  FIG. 4  shows the bar  14  with the feed driving mechanism  70  removed when seen from an upper side. 
   The bar connecting devices  15  each include: a fixed-side connecting portion  151  provided on a side of the fixed bar  141 ; a movable-side connecting portion  152  provided on a side of the movable bar  142 ; a positioning mechanism  153  that positions the movable-side connecting portion  152  and the fixed-side connecting portion  151 ; an air clamp (a holding means)  16  that fixes the movable-side connecting portion  152  to the fixed-side connecting portion  151 ; and an air supplier (not shown) that supplies air to the air clamp  16 . 
   The fixed-side connecting portion  151  projects from an end of the fixed bar  141  toward the movable bar  142  in a longitudinal direction of the bar  14 . The fixed-side connecting portion  151  is formed in a plate-like shape and provided such that a plane thereof lies in a substantially horizontal direction. On a bottom surface of the fixed-side connecting portion  151 , a fixed-side rib  151 A is provided to reinforce the fixed-side connecting portion  151 . The fixed-side ribs  151 A are provided at a plurality of positions (two positions in this embodiment), each fixed-side rib  151 A extending along the longitudinal direction of the bar  14  from the end of the fixed bar  141  to a position adjacent to an end of the fixed-side connecting portion  151 . These fixed-side ribs  151 A enhance the strength of the fixed-side connecting portion  151  in the lift direction L. 
   The movable-side connecting portion  152  projects from an end of the movable bar  142  toward the fixed bar  141  in the longitudinal direction of the bar  14 . The movable-side connecting portion  152  is formed in a plate-like shape and provided such that a plane thereof lies in a substantially horizontal direction. On a top surface of the movable-side connecting portion  152 , a movable-side rib  152 A is provided to reinforce the movable-side connecting portion  152 . The movable-side ribs  152 A are provided at a plurality of positions (two positions in this embodiment), each movable-side rib  152 A extending along the longitudinal direction of the bar  14  from the end of the movable bar  142  to a position adjacent to an end of the movable-side connecting portion  152 . These movable-side ribs  152 A enhance the strength of the movable-side connecting portion  152  in the lift direction L. 
   The positioning mechanism  153  includes a guide pin  153 A provided on the fixed-side connecting portion  151  and a guide hole  153 B formed in the movable-side connecting portion  152 . The guide pins  153 A are provided at two positions on outer sides of the fixed-side ribs  151 A so as to be aligned in a direction orthogonal to the longitudinal direction of the bar  14 , each guide pin  153 A projecting from the fixed-side connecting portion  151  upward (i.e. toward the movable-side connecting portion  152 ). The guide holes  153 B are formed in the movable-side connecting portion  152  at two positions corresponding to the positions of the guide pins  153 A. The guide holes  153 B are disposed on outer sides of the movable-side ribs  152 A so as to be aligned in a direction orthogonal to the longitudinal direction of the bar  14 . 
   In the thus-arranged positioning mechanism  153 , by inserting the guide pins  153 A in the guide holes  153 B, the fixed-side connecting portion  151  and the movable-side connecting portion  152  are positioned in the feed direction F and the clamp direction. The positioning mechanism  153  (the guide pins  153 A and the guide holes  153 B) also functions to receive load in the clamp direction which is applied on the positioning mechanism  153  while the bar  14  is being moved in the clamp direction. 
     FIG. 5  shows a side cross-sectional view of the air clamp  16 . As shown in  FIG. 5 , the air clamp  16  may be driven by the air pressure to hold the movable-side connecting portion  152  against the fixed-side connecting portion  151 . For example, an air-driven clamp Model TLA manufactured by Pascal Corporation is used in this embodiment. The air clamp  16  includes a case  161  accommodated in the fixed bar  141 ; an air supply chamber  162  provided in the case  161 ; a piston  163  disposed in the air supply chamber  162 ; a piston rod  164  advanceable and retractable in accordance with movement of the piston  163 ; and a clamp member (a holding member)  165  that clamps the movable-side connecting portion  152  in accordance with the advancement and retraction of the piston rod  164 . 
   When seen in a cross-sectional direction of the fixed bar  141 , the entire case  161  is accommodated in the fixed bar  141 . In a longitudinal direction of the fixed bar  141 , almost the entire case  161  is accommodated in the fixed bar  141  except for a part of the case  161  protruding from an end of the fixed bar  141 . The thus-arranged case  161  is fixed to the fixed bar  141  using screws and the like. In the case  161 , the air supply chamber  162  is provided on a side apart from the end of the fixed bar  141 . 
   As described above, since the case  161  is accommodated in the fixed bar  141 , the air clamp  16  does not greatly protrude from the end of the fixed bar  141 . Hence, dimensions of the fixed-side connecting portion  151  and the movable-side connecting portion  152  in the longitudinal direction of the bar  14  can be short, thereby preventing reduction in strength of a connecting portion of the bar  14 . 
   The air supply chamber  162  is partitioned into two divisions by the piston  163 . In one division i.e. an air supply chamber  162 A, a compression spring  163 A is provided between the piston  163  and an inner wall of the case  161 . The piston  163  can be biased by the compression spring  163 A toward an air supply chamber  162 B. The two air supply chambers  162  ( 162 A,  162 B) are connected with the air supplier, so that predetermined-pressure air can be supplied to the air supply chambers  162  ( 162 A,  162 B). 
   An end of the piston rod  164  is fixed to the piston  163 . The piston rod  164  penetrates through the air supply chamber  162 . A wedge-shaped member  164 A is fixed to the other end of the piston rod  164  outside the air supply chamber  162 . A hooked member  164 B is provided on the other end of the piston rod  164  on a further distal side than the wedge-shaped member  164 A. 
   A bottom surface of the wedge-shaped member  164 A is slidable in an axial direction of the piston rod  164  relative to the case  161 . A top surface of the wedge-shaped member  164 A is a slant surface inclined toward the distal side of the piston rod  164  so as to reduce its dimension from the top surface to the lower surface, whereby the wedge-shaped member  164 A is tapered as a whole toward the distal side. The hooked member  164 B protrudes upward in a hook-like shape. 
   The clamp member  165  includes a clamp portion  165 A that holds the movable-side connecting portion  152 , an operating portion  165 B that transfers the advancement and retraction of the piston rod  164  to the clamp member  165 , a spring mounting portion  165 C on which a spring  167  for biasing the clamp member  165  to the piston rod  164  is mounted. The clamp member  165  includes a rotary shaft  165 D extending in a direction orthogonal to the advancement and retraction direction (the longitudinal direction of the bar  14 ), the rotary shaft  165 D being inserted in an elongated hole  161 A formed in the case  161  (as shown in the dotted line in  FIG. 6 ). Note that since the major axis of the elongated hole  161 A is aligned in the longitudinal direction of the fixed bar  141 , the clamp member  165  is supported so as to be rotatable relative to the case  161  and slidable in the longitudinal direction of the bar  14 . 
   The clamp portion  165 A can protrude from the case  161 . A bottom surface on the distal side of the clamp portion  165 A can abut on the top surface of the movable-side connecting portion  152 . The bottom surface of the clamp portion  165 A may be flat to stably abut on the top surface of the movable-side connecting portion  152 . When the clamp portion  165 A abuts on the top surface of the movable-side connecting portion  152 , the movable-side connecting portion  152  is sandwiched between the clamp portion  165 A and the fixed-side connecting portion  151 . Accordingly, the movable-side connecting portion  152  is fixed against the fixed-side connecting portion  151  in the lift direction L. Hence, the fixed-side connecting portion  151  and the clamp portion  165 A function to receive load in the lift direction L which is applied thereon while the bar  14  is being moved in the lift direction L. 
   The operating portion  165 B is provided with a follower  168  that abuts on the wedge-shaped member  164 A and is rotatable relative to the operation portion  165 B. 
   A step  169  is provided on the operation portion  165 B at a position more adjacent to a distal end of the fixed bar  141  than the follower  168  and is engageable with the hooked member  164 B of the piston rod  164 . 
   The spring mounting portion  165 C extends downward below the rotary shaft  165 D in a direction substantially orthogonal to an extending direction of the operating portion  165 B with the rotary shaft  165 D as an intersection. On a surface of the spring mounting portion  165 C on the opposite side of the end of the fixed bar  141 , the spring  167  is mounted to be disposed between the surface and the case  161 . The spring  167  biases the clamp member  165  in a rotational direction around the rotary shaft  165 D, thereby pressing the follower  168  of the operating portion  165 B to the wedge-shaped member  164 A at a predetermined biasing force. The biasing force makes the follower  168  suitably follow the wedge-shaped member  164 A in accordance with the movement of the piston rod  164 , so that the clamp member  165  can be reliably moved. 
   The air clamp  16  is provided with a limit switch  161 B for detecting excess movement of the clamp member  165 . 
   In the air clamp  16 , when air is supplied to the air supply chamber  162 A, the air pressure as well as the biasing force from the compression spring  163 A are applied on the piston  163 , so that the piston  163  is moved to the air supply chamber  162 B. The piston rod  164  is also moved in accordance with the movement of the piston  163  and the wedge-shaped member  164 A is moved toward the distal side of the fixed bar  141 . At this time, the follower  168  of the clamp member  165  rotates on the top surface of the wedge-shaped member  164 A. However, since the thickness in the up-and-down direction of the wedge-shaped member  164 A gradually increased, the clamp member  165  rotates around the rotary shaft  165 D against the biasing force of the spring  167 . The slant top surface of the wedge-shaped member  164 A generates force that presses the clamp member  165  to the distal side in the longitudinal direction of the fixed bar  141  on the follower  168 . The force slides the rotary shaft  165 D relative to the elongated hole  161 A of the case  161 , thereby moving the clamp member  165 . In other words, the clamp portion  165 A is protruded from the case  161  and simultaneously rotated to move toward the fixed-side connecting portion  151 . 
   By the rotation and the advancement and retraction, the clamp member  165  rotates downward while moving in the longitudinal direction of the bar  14  Accordingly, the clamp portion  165 A abuts on the movable-side connecting portion  152  with a predetermined force to hold the movable-side connecting portion  152  against the fixed-side connecting portion  151 . 
   Since the piston  163  is biased in advance at a predetermined biasing force by the compression spring  163 A, a predetermined clamp force by the clamp member  165  can be obtained with small air pressure, thereby promoting power saving. In addition, since such an arrangement can realize a predetermined clamp force with small air pressure, an air-pressure clamp can be employed in place of a high-pressure hydraulic clamp of the related art, thereby simplifying the structure, control and operation of the bar connecting device  15 . 
   Even when the air supply is stopped in failure, the movable-side connecting portion  152  can be held with the biasing force of the compression spring  163 A, thereby reliably preventing a problem such as a release of the connection. 
   Further, since the clamp force is obtained by moving the piston  163  by the air pressure, the piston  163  can be moved more quickly as compared with an arrangement where the piston  163  is moved by hydraulic pressure, thereby reducing time required to exchange the die. 
   On the other hand, in order to release the movable-side connecting portion  152  from holding the air clamp  16 , the air is supplied to the other air supply chamber  162 B. 
   When the air is supplied to the air supply chamber  162 B, the piston  163  is moved against the biasing force from the compression spring  163 A toward the air supply chamber  162 A. The piston rod  164  is moved in accordance with the movement of the piston  163 , so that the wedge-shaped member  164 A is evacuated. Accordingly, the clamp member  165  evacuates in accordance with the movement of the piston rod  164  while rotating around the rotary shaft  165 D, so that the clamp portion  165 A is accommodated in the case  161  (see the double-dotted line of the clamp member  165  in  FIG. 5 ). 
   Returning to  FIGS. 2 and 3 , the feed driving mechanism  70  includes: a slide plate (a slide member)  71  on which a plurality of workpiece holders  52  are detachably provided; a movable plate  72  connected with the slide plate  71 ; a plate connecting portion (a connecting portion)  73  that connects the slide plate  71  to the movable plate  72  and separates the slide plate  71  from the movable plate  72 ; and a feeding linear motor (a feed driving source)  75  that is attached on the movable plate  72  to move the movable plate  72  and the slide plate  71  in the feed direction F. 
   The slide plate  71  is formed by a plurality of plate-like members connected to each other and covers a top surface of the movable bar  142 . The plurality of workpiece holders  52  are attached on the slide plate  71  at substantially regular intervals such that each pair of workpiece holders  52  can hold the workpiece  2 . 
   The movable plate  72  can be guided on the fixed bar  141  in the feed direction F by the guide rails  74  provided on lateral surfaces of the fixed bar  141 . 
     FIG. 6  shows an enlarged plan view of the plate connecting portion  73 . As shown in  FIG. 6 , the plate connecting portion  73  includes: an engaging portion  731  provided on an end of the movable plate  72 ; and an engaged portion  732  that is provided on an end of the slide plate  71  and engaged with the engaging portion  731 . 
   Several engaging portions  731  are provided (two in this embodiment) on the end of the movable plate  72 , each of the engaging portions  731  projecting toward the slide plate  71 . The engaging portions  731  each have a substantially T-shape in plan view. The engaged portion  732  is engaged with a distal end  731 A of the engaging portion  731 . Slant portions  731 B are respectively provided on an upper side in a thickness direction on a distal side and on a base side of the distal end  731 A. The slant portions  731 B guide the distal end  731 A in the engaged portion  732  when the distal end  731 A is moved upward to engage with the engaged portion  732 , whereby the distal end  731 A can easily engage with the engaged portion  732 . 
   The engaged portions  732  are provided on the end of the slide plate  71  at positions corresponding to those of the engaging portions  731  and each have a substantially C-shape in plan view dented toward the movable plate  72 . The distal end  731 A of the engaging portion  731  is inserted in the up-and-down direction (the vertical direction) into the concave of the engaged portion  732 , so that the engaging portion  731  engages with the engaged portion  732 . 
   Note that between the engaging portion  731  and the engaged portion  732 , a predetermined gap (play) may be provided so as to facilitate the engagement. The gap may be set within a range where displacement in relative positions of the pair of workpiece holders  52  will not affect on holding performance of the workpiece  2 . 
   Owing to the thus-arranged plate connecting portion  73 , when the movable plate  72  and the slide plate  71  are relatively moved in the up-and-down direction (the thickness direction, the vertical direction), the engaging portion  731  engages with or disengages from the engaged portion  732 . 
   Since the slide plate  71  and the movable plate  72  are slidable on the top surface of the movable bar  142  and an top surface of the fixed bar  141  respectively, when the movable plate  72  is driven by the feed linear motor  75  with the plate connecting portion  73  connected, the slide plate  71  and the movable plate  72  slide on the bar  14  in the feed direction F. Note that since the positions in the up-and-down direction of the slide plate  71  and the movable plate  72  are determined and guided by the top surface of the bar  14 , the positions in the up-and-down direction of the engaging portion  731  and the engaged portion  732  of the plate connecting portion  73  will not be misaligned, thereby preventing disengagement of the slide plate  71  and the movable plate  72 . 
   Since the plate connecting portion  73  includes the engaging portion  731  and the engaged portion  732 ; and the slide plate  71  and the movable plate  72  can be connected only by engaging the engaging portion  731  with the engaged portion  732 , it is unnecessary to use an actuator or the like as the plate connecting portion  73 , thereby simplifying the structure of the plate connecting portion  73  and preventing operation failure of the actuator. In addition, since the structure of the plate connecting portion  73  can be simplified, the total number of components of the plate connecting portion  73  can be reduced, thereby promoting downsizing and weight-reducing of the plate connecting portion  73 . Further, since the actuator or the like is not required, operation checking of the actuator or the like can be omitted, whereby die exchange time can be shortened and maintenance efficiency can be improved. 
   The feed linear motor  75  includes: a magnet plate  76  (a fixing portion) laid on the top surface of the fixing bar  141  in the feed direction F; and a coil plate  77  (a movable portion) provided so as to face the magnet plate  76  and fixed on a bottom surface of the movable plate  72 . When a current is given to the coil plate  77  such that shifting magnetic field is generated on the coil plate  77 , the coil plate  77  is moved by attraction and repulsion of the magnet plate  76 . When the movable plate  72  is moved together with the coil plate  77 , the slide plate  71  is moved in accordance with the movement of the movable plate  72  on the movable bar  142  in the feed direction F. Accordingly, the plurality of workpiece holders  52  attached on the slide plate  71  are concurrently moved in the feed direction F while the distances between the workpiece holders  52  are maintained. 
   As described above, since the plurality of workpiece holders  52  are detachably provided on the slide plate  71  and the slide plate  71  is driven by the feed linear motor  75 , the plurality of workpiece holders  52  can be moved by the feed linear motor  75  (or two feed linear motors  75 ) per one bar  14 . Hence, the number of the feed linear motors  75  can be decreased, thereby reducing the costs of the transfer feeder  41 . 
   Note that when two feed linear motors  75  are provided, the feed linear motors  75  are respectively provided on both fixed bars  141  on both sides of the movable bars  142 . Note that when a single feed linear motor  75  is provided, the feed linear motor  75  is provided on either one of the fixed bars  141  on both sides of the movable bars  142 . 
   Note that the position of the magnet plate  76  relative to the fixed bar  141  may not be on the top surface of the fixed bar  141  but may be laid along a lateral surface or a bottom surface of the fixed bar  141 . 
   Further, in the description above, the magnet plate and the coil plate of the linear motor are respectively provided on a fixed side and a movable side. However, the magnet plate may be provided on the movable side and the coil plate may be provided on the fixed side. 
   Although not shown in detail in the figures, the lift/clamp device  80  includes a lift device that moves the bars  14  in the lift direction L and a clamp device that moves the bars  14  in the clamp direction. 
   The lift device moves (lifts) the bar  14  up and down by rotating a screw with a lift driving motor. The clamp device moves the bars  14  in the clamp direction by rotating a screw with a clamp driving motor. Note that in the movement in the clamp direction, the pair of bars  14  moves in opposite directions. Specifically, the pair of bars  14  moves in a direction toward each other or apart from each other. 
   Next, operations of the thus-arranged transfer press  1  will be described below. 
   In order to transfer the workpiece  2 , the transfer feeder  41  performs a three-dimensional movement including: a feed/return movement in which the workpiece holder  52  is reciprocated by the feed linear motor  75  in the workpiece transfer direction T on the bar  14 ; a raising/lowering movement (a lifting up/down movement) in which the bar  14  is raised/lowered (lifted up/down) by the lift/clamp device  80 ; and a clamp/unclamp movement in which the bar  14  is reciprocated by the lift/clamp device  80  in a direction vertically-orthogonal to the workpiece transfer direction T. By properly reciprocating the workpiece holder  52  in the feed direction F, the lift direction L and the clamp direction, the workpiece  2  is sequentially transferred from a lower die  13  on the upstream (the left side in  FIG. 1 ) to a lower die  13  on the downstream (the right side in  FIG. 1 ). 
   Since the workpiece holder  52  needs to be replaced with a new workpiece holder  52  suitable for the new die when the die  11  is replaced with a new die, the workpiece holder  52  and the bar  14  are placed on the moving bolster  30  to be transferred from a workpiece transfer region to the outside. Note that the bar  14  is supported by the lift/clamp device  80  provided on the frame  33 A, which hinders carrying-out of the bar  14 . 
   Hence, the movable bar  142  of the bar  14  is separated and detached from the fixed bar  141  and the movable bar  142  is placed on the bar receiving table  31  of the moving bolster  30 . At this time, since the slide plate  71  needs to be detached as well as the movable bar  142 , the slide plate  71  is detached from the movable plate  72 . 
   How to detach the bar  14  will be described below. 
   Detaching of the bar  14  includes: a positioning process for positioning the plate connecting portion  73  above the bar connecting device  15 ; a holding-releasing process for releasing the holding of the movable bar  142  by the fixed bar  141 ; an engagement-releasing process for releasing engagement between the fixed bar  141  and the movable bar  142  and engagement between the slide plate  71  and the movable plate  72  by moving the fixed bar  141  downward relative to the movable bar  142 ; and a movable-plate-evacuating process for evacuating the movable plate  72  in a direction apart from the slide plate  71 . 
     FIGS. 7 and 8  show the positioning process. In the positioning process, as shown in  FIG. 7 , the lift/clamp device  80  places the bar  14  on the bar receiving table  31 . In this state, since the workpiece holder  52  has been used to transfer the workpiece  2 , the movable plate  72  and the slide plate  71  are located at predetermined positions and the plate connecting portion  73  is displaced from the bar connecting device  15 . Accordingly, the movable plate  72  and the slide plate  71  are slid by the feed linear motor  75  in the feed direction F, whereby moving the plate connecting portion  73  is moved from a position shown in  FIG. 7  to a position shown in  FIG. 8  which coincides with the position of the bar connecting device  15 . By the positioning process, the plate connecting portion  73  is disposed above the bar connecting device  15 . 
   Next in the holding-releasing process, air is supplied to the air supply chamber  162 B of the air clamp  16  to rotate and evacuate the clamp member  165 . At this time, the clamp member  165  is accommodated in the case  161 , so that the clamp member  165  will not protrude above the movable-side connecting portion  152 . By the holding-releasing process, the movable-side connecting portion  152  is released from holding by the fixed-side connecting portion  151  and by the clamp member  165 , so that the bar connecting device  15  is free in the up-and-down direction. 
   In the connection-releasing process, as shown in  FIG. 9 , the lift/clamp device  80  moves the bar  141  downward. Accordingly, the guide pin  153 A disengages from the guide hole  153 B, so that the connection of the bar connecting device  15  is released, thereby disengaging the movable bar  142  from the fixed bar  141 . Simultaneously, since the engaging portion  731  is moved downward, the engagement of the engaging portion  731  and the engaged portion  732  is released, thereby releasing the connection between the slide plate  71  and the movable plate  72 . Note that the holding-releasing process and the connection-releasing process are included in a connection-releasing process according to the invention. 
   Thus, by the positioning process and the connection-releasing process, the bar connecting device  15  and the plate connecting portion  73  can be simultaneously detached. Specifically, since both of the projecting direction of the guide pin  153 A and the engaging direction of the engaging direction of the engaging portion  731  are vertical, when the guide pin is moved downward relative to the movable bar  142  in order to disengage the guide pin  153 A from the guide hole  153 B, this movement makes the engaging portion  731  move downward relative to the engaged portion  732 , thereby releasing the engagement of the engaging portion  731 . Hence, the bar  14  can be easily detached by a single operation, thereby simplifying the detachment of the bar  14 . 
   In the movable-plate-evacuating process, as shown in  FIG. 10 , the feed linear motor  75  is driven to further move the movable plate  72  in the feed direction F such that the movable plate  72  is spaced from the slide plate  71 . Accordingly, the engaging portion  731  is evacuated to a position so as not to interfere with the engaged portion  732  or the movable bar  142 . 
   Then, the moving bolster  30  is moved in a right and left direction (a direction orthogonal to the workpiece transfer direction T) of the transfer press  1  such that the movable bar  142  and with the moving bolster  30  are carried to the outside of the transfer press  1  (carrying-out process). In order to attach the bar  14  on which a to-be-next-used workpiece holder  52  is attached to the transfer feeder  41 , reverse procedure to the above-described detaching process of the bar  14  is conducted. The attaching process of the bar  14  includes: a movable-bar-moving process, an engaging process and a movable-bar-holding process. In the movable-bar-moving process, the movable bar  142  to be used in the next pressing is placed on the bar receiving table  31  outside the transfer press  1  and then the moving bolster  30  is moved to carry the movable bar  142  into the transfer press  1 . Subsequently, the moving bolster  30  is placed at a predetermined position on the bed  23  such that: the fixed-side connecting portion  151  is positioned below the movable-side connecting portion  152 ; the guide pin  153 A is positioned below the guide hole  153 B; and the engaging portion  731  is positioned below the engaged portion  732 . 
   In the engaging process, the lift/clamp device  80  moves the fixed bar  141  upward such that the guide pin  153 A is inserted in the guide hole  153 B, thereby engaging the bar connecting device  15 . Simultaneously with this engagement, the engaging portion  731  engages with the engaged portion  732 , thereby establishing a connection of the plate connecting portion  73 . Note that the positions in the up-and-down direction of the fixed bar  141  and the movable bar  142  are determined by abutting of the fixed-side connecting portion  151  on the movable-side connecting portion  152 . Hence, the positions in the up-and-down direction of the engaging portion  731  and the engaged portion  732  are also accordingly determined, so that the slide plate  71  and the movable plate  72  are suitably positioned in the up-and-down direction. 
   Herein, when the guide pin  153 A is inserted in the guide hole  153 B, the bottom surface of the movable-side connecting portion  152  contacts the top surface of the fixed-side connecting portion  151 . Thus, the movable-side connecting portion  152  is disposed on the fixed-side connecting portion  151 . Hence, for example, even when the fixed bar  141  is excessively moved upward, the movable bar  142  will receive no load although the movable bar  142  is located above the bar receiving table, thereby preventing the bar  14  from being damaged. Accordingly, since it is unnecessary to ensure high accuracy in movement amount of the fixed bar  141 , the position control of the fixed bar  141  can be simplified while the top surface of the fixed-side connecting portion  151  can be reliably brought into contact with the bottom surface of the movable-side connecting portion  152 , whereby positioning of the fixed bar  141  and the movable bar  142  in the lift direction L can be facilitated. 
   In the movable-bar-holding process, air is supplied to the air supply chamber  162 A of the air clamp  16  to move the piston  163  toward the end of the fixed bar  141 . Then, the clamp member  165  protrudes from the case  161  and rotates around the rotary shaft  165 D to move the clamp portion  165 A downward, whereby the movable-side connecting portion  152  is held between the clamp portion  165 A and the fixed-side connecting portion  151 . 
   Note that the engaging process and the movable-bar-holding process are included in a connection process. 
   By an attaching process described above, the movable bar  142  is attached to the fixed bar  141  and the slide plate  71  is connected with the movable plate  72 . 
   Note that the bar receiving table  31  may be provided with a lifting device or a means for moving the movable bar  142  in the clamp direction. In such an arrangement, when the die  11  is placed on the moving bolster  30  in the die exchange conducted outside the main body of the transfer press  1 , the distance between the bars  14  can be widened, thereby facilitating the exchange of the die  11 . 
   Note that the present invention is not limited to the aforesaid embodiment but also includes modifications, improvements and the like as long as an object of the invention can be achieved. 
   The engagement direction of the engaging portion and the engaged portion is not limited to the vertical direction but may be any direction such as a horizontal direction. For instance, when the engaging portion and the engaged portion are engaged in a horizontal direction, the engagement therebetween can be released by moving the fixed bar in the horizontal direction (the clamp direction) relative to the movable bar. 
   In the aforesaid embodiment, the engaging portion is attached on the movable member and the engaged portion is attached on the slide member. However, the arrangement is not limited thereto and the engaging portion may be attached on the slide member while the engaged portion may be attached on the movable member. In other words, it is only necessary that either of the slide member or the movable member is provided with the engaging portion and the other is provided with the engaged portion. The number of the engaging portion and the engaged portion and the positions thereof are not limited to two and the above-described positions but any number of the engaging portion and the engaged portion may be provided at any positions. 
   The shapes of the engaging portion and the engaged portion are not limited to the substantially T- and C-shapes but may be any shape as long as the engagement therebetween can be achieved. For example, the engaging portion and the engaged portion may have hook-like shapes engageable with each other. Alternatively, the engaging potion may be a pin and the engaged portion may be a hole into which the engaging portion is inserted. 
   The bar driving mechanism is not limited to the one that drives the bar in the lift direction and the clamp direction but the bar driving mechanism may drive the bar only in either of the lift direction L or the clamp direction. 
   The feed driving source is not limited to the linear motor but may be any type such as an electric motor. 
   The best arrangement, implementation and the like for embodying the present invention have been disclosed above, but the invention is not limited thereto. In other words, although the present invention is illustrated and described by exemplifying the particular embodiment, a person skilled in the art can add various modifications in shape, material, quantity and other detail arrangements to the aforesaid embodiment without departing from the technical idea and the scope of the invention. 
   Hence, in the above disclosure, the description limiting the shapes, materials and the like is intended to facilitate the understanding of the invention but is not for restricting the scope of the invention. Therefore, description using the names of the components without a part of or all of the limitation in the shapes, materials and the like is also included in the invention. 
   INDUSTRIAL APPLICABILITY 
   The present invention is applicable to a transfer press that performs a plurality of press processes with a single machine and sequentially transfers a workpiece to a subsequent process and to a series-connected tandem press.