Patent Publication Number: US-2011061431-A1

Title: Plate bending method and bending angle detection device

Description:
TECHNICAL FIELD 
     The present invention relates to a method of bending a plate and a bending angle detection apparatus, and more particularly to a method of bending a plate and bending angle detection apparatus in which labor required for a work of bending a plate can be reduced. 
     BACKGROUND ART 
     Patent Literature 1 discloses an apparatus for bending a strip material. The apparatus comprises a stationary die having a slit, and a movable die which is rotatably fitted onto a shaft body of the stationary die. 
     According to the invention disclosed in Patent Literature 1, the parallelism of a pair of opposing pressing die portions of the movable die is not impaired during a bending process, and only the shaft body can be easily replaced without disassembling gears of a rotation transmission mechanism, and the movable die. 
     Patent Literature 2 discloses a method of bending a plate. In the method, a plate is fed out from an outlet, and, during when the feeding of the plate is stopped, the plate is pressed against an end portion of the outlet side, thereby bending the plate. 
     According to the invention disclosed in Patent Literature 2, even an unskilled person can bend easily and rapidly a plate into a desired shape in a similar manner as a skilled person. 
     Patent Literature 3 discloses a method of bending a plate. In the method, the below-described two steps are repeated. In the first step, a feed bearing is contacted with a plate. In the second step, while the plate is intermittently fed out through a slit formed in a stationary die, each time when the feeding of the plate is stopped by a stop of operation of a servomotor, the plate is pressed by a pressing member against an outlet corner portion of the slit, thereby being a plate. 
     According to the invention disclosed in Patent Literature 3, when a plurality of places of a plate such as a blade member are automatically bent in a sequential manner, the plurality of bent places can be accurately determined. 
     Patent Literature 4 discloses an apparatus for processing a plate. The apparatus comprises a bending process shape inputting unit, a characteristic data inputting unit, and a calculating unit. The bending process shape inputting unit receives an input of a geometric bending process shape of a long plate. The characteristic data inputting unit receives characteristic data related to a process of bending the plate. The calculating unit calculates bending data of the plate based on the geometric bending process shape which is received by the bending process shape inputting unit, and the characteristic data which are received by the characteristic data inputting unit. 
     According to the invention disclosed in Patent Literature 4, characteristics related to the process of bending the plate are considered, whereby the plate can be accurately processed.
     Patent Literature 1: Pamphlet of International Publication No. 95/00266   Patent Literature 2: Japanese Patent Application Laid-Open No. 2001-353528   Patent Literature 3: Japanese Patent Application Laid-Open No. 8-215761   Patent Literature 4: Japanese Patent Application Laid-Open No. 6-304685   

     DISCLOSURE OF THE INVENTION 
     Problem to be Solved by the Invention 
     In the inventions disclosed in Patent Literatures 1 to 3, however, there is a problem in that it is difficult to bent a plate to an angle desired by the user, because, when a force is applied in order to bend a plate and thereafter the force is cancelled, springback occurs and the angle of the bent portion is varied. The term “springback” means a phenomenon that, when a force is applied to a plate at a degree by which plastic deformation occurs and thereafter the force is removed from the plate, deformation due to elastic deformation is eliminated from deformation of the plate. It is difficult to estimate the degree by which the angle of the bent plate is varied by springback. 
     In the invention disclosed in Patent Literature 4, a long plate can be accurately processed, but there is a problem in that it is difficult to obtain characteristic data required in the process. Usually, characteristic data are produced from data of the degree by which a plate is bent in a bending process, and a result of a measurement of the angle of a portion which is bent by the bending process. When the characteristic data are produced in this way, it is necessary to process the data after the bending process and the measurement of a sample produced by the process are repeated. The work requires a prolonged time period and much labor. The work increases the labor and required time period of the whole bending process. 
     The invention has been conducted in order to solve the above-discussed problems. It is an object of the invention to provide a method of bending a plate and bending angle detection apparatus in which labor required for a work of bending a plate can be reduced. 
     Means for Solving the Problem 
     In order to attain the object, according to a certain aspect of the invention, the method of bending a plate is a method of bending a plate by a bending machine. In the method of bending a plate, a work of bending the plate is repeated a plurality of times until it is detected that an angle of a bent portion of the plate reaches a predetermined angle, in a state where the plate is attached to the bending machine and springback is completed. 
     The work of bending the plate is repeated a plurality of times until it is detected that the angle of the bent portion of the plate reaches the predetermined angle, in a state where the plate is attached to the bending machine and springback is completed. Therefore, it is not necessary to remove the plate and measure the angle of the bent portion. It is not necessary also to consider springback. As a result, labor required for the work of bending the plate can be reduced. 
     Furthermore, preferably, the above-described method of bending a plate is a method in which the plate is further bent until a bending angle detection apparatus connected to the bending machine detects it. 
     Furthermore, preferably, the above-described bending angle detection apparatus is contacted with the plate to measure a direction of the plate before the bending machine bends the plate, and a direction of the plate after the bending machine bends the plate. 
     According to another aspect of the invention, the bending angle detection apparatus detects an angle. The bending angle detection apparatus is an apparatus which is connected to a bending machine. The angle is an angle of a bent portion of a plate which is bent by the bending machine. The bending angle detection apparatus comprises a signal production device, a connecting portion, a drive device, and a rotation angle detection device. The signal production device produces a signal corresponding to whether the apparatus is contacted with the plate or not. The connecting portion rotatably connects the signal production device to the bending machine. The drive device drives the signal production device so that the signal production device is rotated. The rotation angle detection device detects a rotation angle of the signal production device. The connecting portion has a holder which is fixed to the bending machine, and bearings which are connected to the holder. The bearing rotatably positions the signal production device so that, when the bending machine bends the plate, the rotation axis of the plate coincides with that of the signal production device. 
     By the connecting portion, the signal production device is rotatably connected to the bending machine so that a rotation axis of the plate in the case where the bending machine bends the plate coincides with that of a rotation member. Furthermore, the signal production device is driven by the drive device so that the signal production device is rotated. The rotation angle of the signal production device is detected by the rotation angle detection device. Therefore, the rotation angle of the signal production device coincides with that of the plate which is bent by the bending machine. The signal production device produces the signal corresponding to whether the apparatus is contacted with the plate or not. When the rotation angle detection device detects the rotation angle of the signal production device at the time when the signal is produced, therefore, it is possible to detect the rotation angle of the plate which is bent by the bending machine, without detaching the plate from the bending machine. When the rotation angle of the plate is measured in a state where springback is completed, it is not required to consider an error due to springback. As a result, labor required for the work of bending the plate can be reduced. 
     Effects of the Invention 
     In the method of bending a plate and bending angle detection apparatus of the invention, labor required for a work of bending a plate can be reduced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an external view of a bending angle detection apparatus of an embodiment of the invention. 
         FIG. 2  is a stereoscopic exploded view of the bending angle detection apparatus of the embodiment of the invention. 
         FIG. 3  is an external view of a servomotor in the embodiment of the invention. 
         FIG. 4  is a sectional view of a part of the servomotor in the embodiment of the invention. 
         FIG. 5  is an external view of a spring joint in the embodiment of the invention 
         FIG. 6  is a stereoscopic exploded view of the spring joint in the embodiment of the invention. 
         FIG. 7  is a sectional view of the spring joint in the embodiment of the invention. 
         FIG. 8  is a first view showing the operation of the spring joint in the embodiment of the invention, in the case where a torque is applied. 
         FIG. 9  is a second view showing the operation of the spring joint in the embodiment of the invention, in the case where a torque is applied. 
         FIG. 10  is an external view of a holder in the embodiment of the invention. 
         FIG. 11  is an external view and sectional view of a sensor ring L in the embodiment of the invention. 
         FIG. 12  is a perspective view of the sensor ring L in the embodiment of the invention. 
         FIG. 13  is an external view and sectional view of a sensor ring R in the embodiment of the invention. 
         FIG. 14  is a perspective view of the sensor ring R in the embodiment of the invention. 
         FIG. 15  is an arrow viewing view of the bending angle detection apparatus of the embodiment of the invention. 
         FIG. 16  is an arrow viewing view of the bending angle detection apparatus of the embodiment of the invention in a situation where the sensor ring L is removed. 
         FIG. 17  is a first sectional view of the bending angle detection apparatus of the embodiment of the invention in a state where the servomotor is removed. 
         FIG. 18  is a second sectional view of the bending angle detection apparatus of the embodiment of the invention in a state where the servomotor is removed. 
         FIG. 19  is a perspective view of a bending machine. 
         FIG. 20  is a perspective view showing a situation where the bending angle detection apparatus of the embodiment of the invention is attached to the bending machine. 
         FIG. 21  is a control block diagram of the bending machine. 
         FIG. 22  is a conceptual diagram showing a situation where a blade member plate is passed through a slit of a bending shaft. 
         FIG. 23  is a conceptual diagram showing a situation where a claw of a rotary cylinder is contacted with the blade member plate. 
         FIG. 24  is a conceptual diagram showing a situation where a microswitch R in the embodiment of the invention is contacted with the blade member plate for preparation. 
         FIG. 25  is a conceptual diagram showing a situation at a timing when the blade member plate is bent by the claw of the rotary cylinder. 
         FIG. 26  is a conceptual diagram showing a situation where the microswitch R in the embodiment of the invention is contacted with the blade member plate in order to measure an angle. 
         FIG. 27  is a conceptual diagram showing a situation where the microswitch R in the embodiment of the invention is reversely rotated. 
         FIG. 28  is a flowchart showing a control procedure of a process of bending the blade member plate in the embodiment of the invention. 
     
    
    
     DESCRIPTION OF REFERENCE NUMERALS 
     
         
           50  bending angle detection apparatus 
           60  servomotor 
           62  holder 
           64  sensor ring L 
           66  sensor ring R 
           68  spacer 
           70  bearing 
           72  bolt 
           80  bending machine 
           90  rotary cylinder 
           91  touch panel 
           92  bending shaft 
           93  cylinder rotation motor 
           94 ,  95  top plate 
           96 ,  97  gear case 
           98  controlling portion 
           100  motor body 
           102  rotation angle sensor 
           104  spring joint 
           106  first gear 
           108  second gear 
           110  upper rotary cylinder 
           112  first spring 
           114  middle rotary cylinder 
           116  second spring 
           118  lower rotary cylinder 
           130 ,  132 ,  134  projection 
           140 ,  142 ,  144  hole 
           150 ,  160  body 
           152  microswitch L 
           154 ,  164  gear 
           156  sector plate 
           158 ,  168  groove 
           162  microswitch R 
           166  protrusion 
           170 ,  172  rotation axis 
           180  cylinder rotation motor I/O 
           182  first external I/O 
           184  second external I/O 
           186  third external I/O 
           188  touch panel I/O 
           190  flash memory reading device 
           300  blade member plate 
           350  flash memory 
       
    
     MODE FOR CARRYING OUT THE INVENTION 
     Hereinafter, an embodiment of the invention will be described with reference to the drawings. The foregoing summary of the invention and the following detailed description of the preferred embodiment of the invention are better understood when read in conjunction with the accompanying drawings. For the purpose of illustrating the invention, the drawings depict the present preferred embodiment. In the following description, the identical components are denoted by the same reference numerals, and also their names and functions are identical. Therefore, they will not be described repeatedly in detail. 
       FIG. 1  is an external view of a bending angle detection apparatus  50  of the embodiment.  FIG. 2  is a stereoscopic exploded view of the bending angle detection apparatus  50  of the embodiment.  FIG. 3  is an external view of a servomotor  60 .  FIG. 4  is a sectional view of a part of the servomotor  60 .  FIG. 5  is an external view of a spring joint  104 .  FIG. 6  is a stereoscopic exploded view of the spring joint  104 .  FIG. 7  is a sectional view of the spring joint  104 .  FIGS. 8 and 9  are views showing the operation of the spring joint  104  in the case where a torque is applied.  FIG. 10  is an external view of a holder  62 .  FIG. 11  is an external view and sectional view of a sensor ring L  64 .  FIG. 12  is a perspective view of the sensor ring L  64 .  FIG. 13  is an external view and sectional view of a sensor ring R  66 .  FIG. 14  is a perspective view of the sensor ring R  66 .  FIG. 15  is a view looking in the direction of the arrow A in  FIG. 1 . FIG.  16  is a view showing a situation where the sensor ring L  64  is removed in  FIG. 15 .  FIG. 17  is a sectional view of the bending angle detection apparatus  50  in a state where the servomotor  60  is removed.  FIG. 18  is a sectional view of the bending angle detection apparatus  50  as viewing in a direction perpendicular to  FIG. 17 .  FIG. 19  is a perspective view of a bending machine  80  to which the bending angle detection apparatus  50  of the embodiment is to be attached.  FIG. 20  is a perspective view showing a situation where the bending angle detection apparatus  50  is attached to the bending machine  80 .  FIG. 21  is a control block diagram of the bending machine  80 .  FIG. 22  is a conceptual diagram showing a situation where a blade member plate  300  is passed through a slit (not shown) of a bending shaft  92  in order to be bent by a claw of a rotary cylinder  90 .  FIG. 23  is a conceptual diagram showing a situation where the claw of the rotary cylinder  90  is contacted with the blade member plate  300  in order to start the bending of the blade member plate  300 .  FIG. 24  is a conceptual diagram showing a situation where a microswitch R  162  is contacted with the blade member plate  300  for preparation of measurement of the angle of the bent blade member plate  300 .  FIG. 25  is a conceptual diagram showing a situation at a timing when the blade member plate  300  is bent by the claw of the rotary cylinder  90 .  FIG. 26  is a conceptual diagram showing a situation where, after the blade member plate  300  is bent, the microswitch R  162  is contacted with the blade member plate in order to measure the angle.  FIG. 27  is a conceptual diagram showing a situation where, after the angle of the blade member plate  300  is measured, the microswitch R  162  is reversely rotated.  FIG. 28  is a flowchart showing a control procedure of a process of accurately bending the blade member plate  300  without previously measuring springback. 
     The bending angle detection apparatus  50  of the embodiment is attached to the bending machine  80 . The bending angle detection apparatus  50  is connected to the bending machine  80 , and measures the angle of a plate which is bent by the bending machine  80 . The bending machine  80  will be described later. 
     The bending angle detection apparatus  50  of the embodiment comprises the servomotor  60 , the holder  62 , the sensor ring L  64 , the sensor ring R  66 , spacers  68 , and bearings  70 . 
     The servomotor  60  is controlled by a controlling portion  98  of the bending machine  80  which will be described later. The servomotor  60  drives the sensor ring L  64  and the sensor ring R  66 . The servomotor  60 , the sensor ring L  64 , and the sensor ring R  66  are attached to the holder  62 . The tip end of the bending shaft  92  of the bending machine  80  is fitted into the holder  62 . The bending shaft  92  is passed through the rotary cylinder  90  which is similarly a component of the bending machine  80 , and then fitted into the holder  62 . The sensor ring L  64  measures the angle of the bent portion of the blade member plate  300 , from one side face of the blade member plate  300 . The sensor ring R  66  measures the angle of the bent portion of the blade member plate  300 , from the side face opposite to the sensor ring L  64 . The spacers  68  are members for maintaining the bearings  70  to adequate positions. The bearings  70  are members for rotatably positioning the sensor ring L  64  and the sensor ring R  66  so that, when the blade member plate  300  is bent by the bending machine  80 , the rotation axis of the blade member plate  300  coincides with the rotation axes of the sensor ring L  64  and the sensor ring R  66 . The spacers  68  and the bearings  70  are connected to the holder  62  by bolts  72 . 
     The servomotor  60  will be described with reference to  FIGS. 3 and 4 . The servomotor  60  comprises the motor body  100 , a rotation angle sensor  102 , a spring joint  104 , a first gear  106 , and a second gear  108 . The motor body  100  produces a torque for rotating the first gear  106  and the second gear  108 . The sensor ring L  64  and the sensor ring R  66  are driven by the torque. The rotation angle sensor  102  detects the rotation angle of the rotor of the motor body  100 . The spring joint  104  is attached to the rotor of the motor body  100 , and the rotation shafts of the first gear  106  and the second gear  108 , to transmit the torque produced by the motor body  100  to the first gear  106  and the second gear  108 . The first gear  106  meshes with a gear  154  of the sensor ring L  64  to transmit the torque to the sensor ring L  64 . The second gear  108  meshes with a gear  164  of the sensor ring R  66  to transmit the torque to the sensor ring R  66 . 
     The structure of the spring joint  104  will be described with reference to  FIGS. 5 to 7 . The spring joint  104  comprises an upper rotary cylinder  110 , a first spring  112 , a middle rotary cylinder  114 , a second spring  116 , and a lower rotary cylinder  118 . 
     The rotor of the motor body  100  is fitted into the upper rotary cylinder  110 . The upper rotary cylinder  110  transmits the torque produced by the motor body  100  to the middle rotary cylinder  114 . A projection  130  is disposed on the lower end of the upper rotary cylinder  110 . The first spring  112  is fitted to the upper rotary cylinder  110  and the middle rotary cylinder  114 , and, when the upper rotary cylinder  110  cannot directly transmit the torque to the middle rotary cylinder  114 , transmits the torque produced by the motor body  100  to the middle rotary cylinder  114 . The middle rotary cylinder  114  is fitted into the upper rotary cylinder  110  and the lower rotary cylinder  118  while being passed through the first spring  112  and the second spring  116 . The middle rotary cylinder  114  transmits the torque which is transmitted by the upper rotary cylinder  110  or the first spring  112 , to the second spring  116 . A projection  132  is disposed on a middle portion of the middle rotary cylinder  114 . The second spring  116  is fitted to the middle rotary cylinder  114  and the lower rotary cylinder  118 , and, when the middle rotary cylinder  114  cannot directly transmit the torque to the lower rotary cylinder  118 , transmits the torque produced by the motor body  100  to the lower rotary cylinder  118 . The rotation shafts of the first gear  106  and the second gear  108  are fitted into the lower rotary cylinder  118 . The lower rotary cylinder  118  transmits the torque produced by the motor body  100  to the rotation shafts of the first gear  106  and the second gear  108 . A projection  134  is disposed on the upper end of the lower rotary cylinder  118 . 
     The operation of the spring joint  104  will be described with reference to  FIGS. 8 and 9 . It is assumed that a torque which is clockwise as viewed from the motor body  100  is transmitted to the spring joint  104 . At this time, the upper rotary cylinder  110  is rotated in the same direction as the rotor of the motor body  100 . When the upper rotary cylinder  110  is rotated, the projection  130  of the upper rotary cylinder  110  pushes the projection  132  of the middle rotary cylinder  114 . When the projection  132  is pushed, also the middle rotary cylinder  114  is rotated in the same direction as the rotor of the motor body  100 . When the middle rotary cylinder  114  is rotated, the torque produced by the motor body  100  is transmitted through the second spring  116  to the lower rotary cylinder  118 . In this case, however, the second spring  116  is deformed, and hence the torque transmitted to the lower rotary cylinder  118  is not so large. When a resistance is applied to the lower rotary cylinder  118  for any reason, the lower rotary cylinder  118  is not rotated. 
     By contrast, it is assumed that a torque which is counterclockwise as viewed from the motor body  100  is transmitted to the spring joint  104 . At this time, the upper rotary cylinder  110  is rotated in the same direction as the rotor of the motor body  100 . However, the projection  130  of the upper rotary cylinder  110  does not push the projection  132  of the middle rotary cylinder  114 . The torque produced by the motor body  100  is transmitted to the middle rotary cylinder  114  by the first spring  112 . In this case, however, the first spring  112  is deformed, and hence the torque transmitted to the middle rotary cylinder  114  is not so large. When a resistance is applied to the lower rotary cylinder  118  for any reason, the resistance is applied also to the middle rotary cylinder  114  through the projection  132  and the projection  134 , and hence the middle rotary cylinder  114  is not rotated. 
     The structure of the holder  62  will be described with reference to  FIG. 10 . The holder  62  comprises a hole  140 , a hole  142 , and a hole  144 . The rotation shafts of the first gear  106  and the second gear  108  are passed through the hole  140 . The tip end of the bending shaft  92  of the bending machine  80  is fitted into the hole  142 . A bolt for fixing the holder  62  to the bending machine  80  is passed through the hole  144 . The sensor ring L  64  and the sensor ring R  66  are connected to the holder  62  in a state where the rings are rotatable, by the bearings  70 . 
     The configuration of the sensor ring L  64  will be described with reference to  FIGS. 11 and 12 . In the sensor ring L  64 , the body  150  comprises a microswitch L  152  and a gear  154 . The body  150  has a shape similar to an article in which the sidewall is cylindrical and a circular hole is opened in the bottom, and which is turned upside down. A sector plate  156  is attached to the upper end of the sidewall, i.e., the portion which is formed as the bottom of the body  150  in  FIG. 11 , and the microswitch L  152  is fixed to the sector plate  156  and the upper end of the sidewall. The microswitch L  152  comprises a switch box which incorporates a push button type switch, and a contact plate which is attached to the switch box via a hinge. When the contact plate is contacted with the blade member plate  300  which is to be bent by the bending machine  80 , the contact plate pushes the switch in the switch box. This causes the sensor ring L  64  to function as a device which produces a signal corresponding to whether the apparatus is contacted with the blade member plate  300  or not. The gear  154  is disposed on the edge of the hole in the portion which is formed as the top plate of the body  150  in  FIG. 11 . However, the gear  154  is not disposed over the whole circumference of the edge. In the edge, there is a portion where the gear  154  is not disposed. A groove  158  into which flanges of the bearings  70  are to be fitted is disposed slightly below the gear  154 . 
     The configuration of the sensor ring R  66  will be described with reference to  FIGS. 13 and 14 . In the sensor ring R  66 , the body  160  comprises a microswitch R  162  and a gear  164 . The body  160  has a cylindrical shape. A protrusion  166  is disposed on the lower end of the sidewall of the body  160 . The microswitch R  162  is attached to the protrusion. The microswitch R  162  is structured in a similar manner as the microswitch L  152 . Similarly with the sensor ring L  64 , therefore, the sensor ring R  66  produces a signal corresponding to whether the apparatus is contacted with the blade member plate  300  or not. The gear  164  is disposed on the edge of the upper end of the body  160  in  FIG. 13 . However, the gear  164  is not disposed over the whole circumference of the edge. In the edge, there is a portion where the gear  164  is not disposed. A groove  168  into which flanges of the bearings  70  are to be fitted is disposed slightly below the gear  164 . 
     The placement of the sensor ring L  64  and other components will be described with reference to  FIGS. 15 to 18 . As described above, the sensor ring L  64  and the sensor ring R  66  are connected to the holder  62 . The sensor ring L  64  and the sensor ring R  66  are not directly connected to the holder  62 . Members which are directly connected to the holder are the spacers  68 . The bearings  70  are connected to the holder  62  through the spacers  68 . The flanges of the bearings  70  are fitted into the groove  158  of the sensor ring L  64  and the groove  168  of the sensor ring R  66 , whereby the sensor ring L  64  and the sensor ring R  66  are indirectly connected to the holder  62 . 
     At this time, the gear  154  of the sensor ring L  64  meshes with the first gear  106 , and the gear  164  of the sensor ring R  66  meshes with the second gear  108 . According to the configuration, the torque produced by the motor body  100  of the servomotor  60  is transmitted to the sensor ring L  64  and the sensor ring R  66 . 
     The position where the sensor ring L  64  is fixed is different from that where the sensor ring R  66  is fixed. Since they are different from each other, the rotation axis  170  of the sensor ring L  64  is different from the rotation axis  172  of the sensor ring R  66 . The rotation axis  170  and the rotation axis  172  are located in the vicinity of an edge of the blade member plate  300  which is bent by the rotary cylinder  90 . More specifically, the rotation axis  170  is placed so as to coincide with the rotation axis when the blade member plate  300  is bent toward one side by the rotary cylinder  90 , and the rotation axis  172  is placed so as to coincide with the rotation axis when the blade member plate  300  is bent toward the other side. Since the rotation axis  170  and the rotation axis  172  coincide with the rotation axis when the blade member plate  300  is bent, the rotation angle of the sensor ring L  64  or the sensor ring R  66  coincides with the bending angle of the plate. In many cases, the rotation axis when the blade member plate  300  is bent is located at a distance which is equal to one half of the thickness of the blade member plate  300 , from the tip end of the claw of the rotary cylinder  90 , and at a distance which is equal to one half of the thickness of the blade member plate  300 , from the side face thereof. 
     The manner of the attachment of the bending angle detection apparatus  50  will be described with reference to  FIGS. 19 and 20 . The bending machine  80  comprises a top plate  94  and a gear case  96 . The bending shaft  92  is fitted into a hole of the top plate  94 . The gear case  96  houses gears which are not shown. The gears transmit a torque to a feed bearing which is used for feeding the blade member plate  300 , and which is not shown. In order to attach the bending angle detection apparatus  50 , the top plate  94  and the gear case  96  are replaced with another top plate  95  and another gear case  97 . No hole into which the bending shaft  92  is to be fitted is formed in the top plate  95 , and a screw hole into which the bolt that is passed through the holder  62  is to be screwed is disposed in the gear case  97 . Namely, the bending angle detection apparatus  50  is connected to the bending machine  80  by screwing the holder  62  to the gear case  97 . 
     The bending machine  80  further comprises a touch panel  91  and a cylinder rotation motor  93 . The touch panel  91  is a device which displays information, and through which the user inputs information. The cylinder rotation motor  93  drives the rotary cylinder  90 . 
     The controlling portion  98  of the bending machine  80  will be described with reference to  FIG. 21 . The bending machine  80  further comprises the controlling portion  98  in addition to the touch panel  91  and the cylinder rotation motor  93 . When the bending angle detection apparatus  50  is not connected, the controlling portion  98  controls the bending process on the blade member plate  300 . When the bending angle detection apparatus  50  is connected, the controlling portion  98  controls also the angle measurement by the bending angle detection apparatus  50 , in addition to the bending process on the blade member plate  300 . The controlling portion  98  comprises a cylinder rotation motor I/O (input/output)  180 , a first external I/O  182 , a second external I/O  184 , a third external I/O  186 , a touch panel I/O  188 , a flash memory reading device  190 , a ROM (Read Only Memory)  192 , a RAM (Random Access Memory)  194 , and a CPU (Central Processing Unit)  196 . 
     The cylinder rotation motor I/O  180  outputs a control signal to the cylinder rotation motor  93 . The first external I/O  182  is connected to the servomotor  60 , receives an input of information indicative of the rotation angle from the rotation angle sensor  102 , and outputs a control signal to the motor body  100 . The second external I/O  184  receives a signal input by the microswitch L  152 . The third external I/O  186  receives a signal input by the microswitch R  162 . The touch panel I/O  188  outputs an image signal to the touch panel  91 , and receives an input of information by the user through the touch panel  91 . The flash memory reading device  190  reads control programs which are to be executed by the CPU  196 , from a flash memory  350 . The control programs are used for performing not only the process of bending the blade member plate  300  but also the control on the bending angle detection apparatus  50 . The ROM  192  stores programs for reading the control programs from the flash memory  350 , and executing them. The RAM  194  temporarily stores the control programs read from the flash memory  350 . Furthermore, the RAM  194  temporarily stores data for enabling the CPU  196  to process information. The CPU  196  sequentially executes the control programs stored in the RAM  194 , thereby controlling the process of bending the blade member plate  300  and the angle measurement by the bending angle detection apparatus  50 . 
     The procedure of measuring the angle of the blade member plate  300  in the bending angle detection apparatus  50  of the embodiment will be described with reference to  FIGS. 22 to 27 . 
     It is assumed that the sector plate  156  and the protrusion  166  are placed in a state where they contact with each other, at a position which is opposite to the servomotor  60  with respect to the bending shaft  92 . In the embodiment, the positions of the sensor ring L  64  and the sensor ring R  66  at this time are referred to as “reference position”. In this state, feed rollers (not shown) of the bending machine  80  feed the blade member plate  300  through the slit of the bending shaft  92 .  FIG. 22  shows this situation. 
     When the blade member plate  300  is fed, the controlling portion  98  outputs the control signal to the cylinder rotation motor  93  through the cylinder rotation motor I/O  180 , thereby driving the cylinder rotation motor  93 . Therefore, the rotary cylinder  90  is rotated, and the tip end of the claw reaches the bending start position.  FIG. 23  shows this situation. 
     When the tip end of the claw of the rotary cylinder  90  reaches the bending start position, the servomotor  60  produces a torque in accordance with the control of the controlling portion  98 . The torque is transmitted to the sensor ring L  64  and the sensor ring R  66  through the first gear  106  and the second gear  108 . Therefore, the sensor ring R  66  is rotated. The sensor ring L  64  is rotated at first, but the rotation is stopped in mid-course because, as shown in  FIG. 11 , the gear  154  is not disposed over the whole circumference of the edge of the body  150 , and, as a result, the first gear  106  does not mesh with the gear  154 . On the basis of the rotation angle data which are input by the rotation angle sensor  102 , the controlling portion  98  knows the rotation angle of the second gear  108 . As a result, the controlling portion  98  indirectly knows also the rotation angle of the microswitch R  162 . When contacted with the blade member plate  300 , the microswitch R  162  inputs a signal into the third external I/O  186 . The CPU  196  detects the rotation angle of the microswitch R  162  based on the rotation angle of the second gear  108  at the timing when the microswitch R  162  inputs the signal.  FIG. 24  shows this situation. 
     When the rotation angle of the microswitch R  162  is detected, the controlling portion  98  causes the cylinder rotation motor  93  to drive. Therefore, the rotary cylinder  90  is rotated, and the tip end of the claw of the rotary cylinder  90  bends the blade member plate  300 .  FIG. 25  shows this situation. 
     When the blade member plate  300  is bent, the servomotor  60  produces a torque in accordance with the control of the controlling portion  98 . The torque is transmitted to the sensor ring R  66  through the second gear  108 . Therefore, the microswitch R  162  is again rotated. When again contacted with the blade member plate  300 , the microswitch R  162  again inputs the signal into the third external I/O  186 .  FIG. 26  shows this situation. The CPU  196  detects the rotation angle of the microswitch R  162  based on the rotation angle of the second gear  108  at the timing when the microswitch R  162  again inputs the signal. When the rotation angle of the microswitch R  162  is detected, the CPU  196  calculates the angle difference between the rotation angle and that of the microswitch R  162  which is initially detected. As described above, the rotation axis of the microswitch R  162  or i.e., the sensor ring R  66  exists on the rotation axis when the blade member plate  300  is bent. Therefore, the calculated angle difference is equal to the rotation angle of the bent portion of the blade member plate  300 . The angle difference is enabled to be calculated by previously storing the tooth number of the second gear  108  and that of the gear  164  in the RAM  194 . The tooth numbers can be stored in the RAM  194  by reading them from the flash memory  350  as a part of the control programs, or a data file which is independent from the control programs. 
     When the angle difference is calculated, the servomotor  60  produces a torque in accordance with the control of the controlling portion  98 . The torque is transmitted to the sensor ring R  66  through the second gear  108 . Therefore, the microswitch R  162  is again rotated. As a result of the rotation, the microswitch R  162  is returned to the reference position. When returned to the reference position, the protrusion  166  pushes the sector plate  156 . Therefore, the gear  154  again meshes with the first gear  106 .  FIG. 27  shows this situation. 
     The control procedure for accurately bending the blade member plate  300  without previously measuring springback will be described with reference to  FIG. 28 . The control procedure performed when the blade member plate  300  is rightward bent is not particularly described, but is similar to that performed when the blade member plate  300  is leftward bent, except that the direction of the blade member plate  300  is measured by the microswitch L  152 . 
     In step S 250 , the CPU  196  of the bending machine  80  causes the feed rollers which are not shown, to drive to feed the blade member plate  300  by a predetermined length. 
     In step S 252 , the CPU  196  outputs a control signal for producing a torque, to the servomotor  60 . The servomotor  60  produces a torque in accordance with the control signal. When the torque produced by the servomotor  60  is transmitted, the sensor ring R  66  is rotated. In this case, one of the sensor ring L  64  is rotated at first, and then does not mesh with the first gear  106 , so that the sensor ring is not rotated finally. 
     In step S 254 , the CPU  196  determines whether the sensor ring R  66  detects the blade member plate  300  or not, based on the signal which is input to the third external I/O  186  by the microswitch R  162 . If it is determined that the blade member plate  300  is detected (YES in step S 254 ), the process is transferred to step S 256 . If not (NO in step S 254 ), the process is transferred to step S 252 . 
     In step S 256 , the CPU  196  outputs a control signal for stopping the production of a torque, to the servomotor  60 . Therefore, the rotations of the first gear  106  and the second gear  108  are stopped. 
     In step  5258 , the CPU  196  calculates the rotation angle of the sensor ring R  66  based on the rotation angle data which are input by the rotation angle sensor  102 . When the rotation angle of the sensor ring R  66  is calculated, the CPU  196  stores the rotation angle in the RAM  194 . The rotation angle indicates the starting point of the process of bending the blade member plate  300 . 
     In step  5260 , the CPU  196  the CPU  196  outputs a control signal for producing a torque, to the servomotor  60 . When the control signal is input, the rotor of the motor body  100  rotates. In the embodiment, the rotation angle at this time is an angle satisfying the following requirement. The requirement is that the angle of the bent portion of the blade member plate  300  equal to an angle which is designated by the user through the touch panel  91 . In accordance with the rotation of the rotor, the sensor ring R  66  tries to rotate. However, the sensor ring is blocked by the blade member plate  300 , and hence the sensor ring R  66  does not rotate. Therefore, the upper rotary cylinder  110  of the spring joint  104  is relatively rotated with respect to the lower rotary cylinder  118 . 
     In step S 262 , the CPU  196  causes the cylinder rotation motor  93  to drive. Therefore, the rotary cylinder  90  is rotated, and the blade member plate  300  is bent in the direction in which it is separated from the microswitch R  162 . At this time, the first spring  112  and second spring  116  of the spring joint  104  are returned from the state where the springs are elastically deformed, to that where the springs are not elastically deformed. Therefore, the microswitch R  162  tracks the blade member plate  300 . 
     In step S 264 , based on the signal which is input by the microswitch R  162 , the CPU  196  determines whether the microswitch R  162  becomes not to detect the blade member plate  300  or not. If it is determined that the microswitch becomes not to detect the blade member plate  300  (YES in step S 264 ), the process is transferred step to S 266 . If not (NO in step S 264 ), the process is transferred to step S 262 . 
     In step  5266 , the CPU  196  again causes the cylinder rotation motor  93  to drive. This causes the rotary cylinder  90  to be further rotated, and the blade member plate  300  is further bent. Namely, the blade member plate  300  is further pressed. The rotation angle of the rotary cylinder  90  is an angle at which the elastic deformation of the blade member plate  300  slightly advances. Thereafter, the CPU  196  causes the cylinder rotation motor  93  to reversely rotate. Because of the reverse rotation of the cylinder rotation motor  93 , the rotation angle of the rotary cylinder  90  is returned to the angle at the timing when the microswitch R  162  becomes not to detect the blade member plate  300  as a result of the rotation of the rotary cylinder  90  in step S 262 . At this time, the direction of the blade member plate  300  is slightly returned by springback, but is not returned in the direction before the further pressing because of advancement of the elastic deformation. As a result, the angle of the blade member plate  300  when the claw of the rotary cylinder  90  is separated approaches the angle which is designated by the user. 
     In step  5268 , based on the signal which is input by the microswitch R  162 , the CPU  196  determines whether the microswitch R  162  becomes not to detect the blade member plate  300  or not. If it is determined that the microswitch becomes not to detect the blade member plate  300  (YES in step S 268 ), the process is transferred to step S 270 . If not (NO in step S 288 ), the process is transferred to step  5266 . 
     In step  5270 , the CPU  196  causes the servomotor  60  to drive so that the microswitch R  162  is returned to the reference position. 
     In step  5272 , the controlling portion  98  updates information in order to perform the next bending process. 
     As described above, the bending machine  80  in the embodiment accurately bends the blade member plate  300  based on the direction of the blade member plate  300  which is detected by the bending angle detection apparatus  50  as a result of the angle measurement. Springback is not measured. Therefore, the user of the bending machine  80  is not required to manually measure springback each time. To begin with, it becomes unnecessary to know in detail what extent of rotating of the rotary cylinder  90  corresponds to accurate bending of the blade member plate  300 . Therefore, labor required for the work of bending the blade member plate  300  can be correspondingly reduced. 
     All points of the disclosed embodiment are exemplifications. The scope of the invention is not limited based on the above-described embodiment. It is a matter of course that various design changes may be made without departing the spirit of the invention. 
     For example, the spring joint  104  is not limited to the above-described configuration. In place of the above-described spring joint  104 , a plate spring or a rubber-made cylinder may be used which transmits the torque supplied by the motor body  100  of the servomotor  60  to the signal production device, and which is elastically deformed by the torque. In place of the spring joint  104 , another buffer member may be used. In the case where a buffer member is used, the buffer member is requested to transmit the torque supplied by the motor body  100  to the sensor ring L  64  or the sensor ring R  66 , and to be elastically deformed by the torque supplied by the motor body  100 . The spring joint  104  may be omitted. 
     In place of the configuration in which the rotation angles of the sensor ring L  64  and the sensor ring R  66  are indirectly measured by the rotation angle sensor  102 , the rotation angles may be directly measured. A specific measure for directly measuring the rotation angles, a method may be employed in which a spur gear meshes with the gear  154  of the sensor ring L  64  and the gear  164  of the sensor ring R  66 , and an angle sensor is connected to its shaft. 
     In place of the servomotor  60 , another drive device may drive the sensor ring L  64  and the sensor ring R  66 . The mechanism for the driving is particularly limited. 
     In place of the sensor ring L  64  and the sensor ring R  66 , a signal production device which produces a signal corresponding to whether the apparatus is contacted with the blade member plate  300  or not, in a mechanism that is different from the rings may be disposed in the bending angle detection apparatus  50 . As an example of such a signal production device, there is a device in which a microswitch is caused to linearly run, and its rotation angle is calculated based on the positional relationship between the position where the microswitch is contacted with the blade member plate  300 , and the position of the rotation axis of the blade member plate  300  that is bent. 
     The bending angle detection apparatus  50  may comprise a controlling portion. In this case, the controlling portion may be configured in a similar manner as the controlling portion  98 . According to the configuration, the bending angle detection apparatus  50  can measure the angle of the bent portion of the blade member plate  300  without depending on the controlling portion  98  of the bending machine  80 . In the case where springback is to be measured, the controlling portion of the bending angle detection apparatus  50  may cooperate with the controlling portion  98  of the bending machine  80 . 
     The program recording medium from which the controlling portion  98  reads control programs is not limited to the flash memory  350 . For example, the medium may be a USB memory. Alternatively, control programs may be received via the Internet.