Abstract:
Provided is a bending apparatus for a plate-shaped metal workpiece, including: a suction device (suction pad) configured to suck a surface of a plate-shaped metal workpiece in a removable manner; a plurality of expansion and contraction devices (servo screw jacks) each including the suction device mounted on a distal end thereof and being capable of expanding and contracting a length ranging from a proximal end thereof to the suction device; and an apparatus base (bed) on which the proximal end of each of the expansion and contraction devices is mounted. The bending apparatus is configured to form the plate-shaped metal workpiece under bending deformation by expanding and contracting the expansion and contraction devices under a state in which the suction device sucks the surface of the plate-shaped metal workpiece.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a technology of bending a metal plate, such as a plate-shaped metal workpiece (plate-shaped workpiece) used as an outer-plate (or a skin) of an aircraft, into an arc shape (cylindrical shape) at a predetermined curvature. 
         [0003]    2. Description of the Related Art 
         [0004]    Hitherto, an outer shell of an aircraft (having a substantially cylindrical shape in horizontal cross-section) is obtained by coupling together several outer-plates (skins) of the aircraft each bent at a predetermined curvature (for example, each having approximately a size of a thickness of from 2 mm to 10 mm×a width of 2.5 m×a length of from 6 m to 10 m) so as to be formed into a cylindrical shape. Accordingly, outer-plate (or skin) workpieces (plate-shaped workpieces) each cut into a predetermined size are subjected to tip forming by a large-sized press brake (forming machine) one by one (three-point bending (see  FIG. 8 ) is performed repeatedly at intervals of approximately 20 mm about one hundred and twenty five times, or three-point bending is performed more times when adjustment of a curvature is necessary), thereby forming each of the outer-plate workpieces (by cylindrical bending or constant curvature bending) into a single contour having a curvature radius R of approximately 3,000 mm. Then, the plurality of outer-plate workpieces (plate-shaped workpieces) each formed to have the predetermined curvature are coupled together, thereby obtaining the outer shell of the aircraft. 
         [0005]    In this case, in order to reduce a weight of the aircraft, a plurality of pocket grooves (dents) are formed on an inner side (side to be punched) of the outer-plate of the aircraft, which is to be subjected to cylindrical bending. There are actually a variety of shape patterns of the pocket grooves (dents) (see reference symbol  3 A in  FIG. 1B , and  FIG. 8 ). 
         [0006]    When a region having the pocket grooves (dents) formed therein is subjected to cylindrical bending, as illustrated in  FIG. 8 , a board (such as a cardboard (filler having a hardness nearly equal to a hardness of a plate)), which conforms to a size and a shape of each of the pocket grooves, is placed in advance (embedded or fitted) in each of the pocket grooves (for example, see Japanese Patent Application Laid-open No. 2012-213792 and Japanese Patent Application Laid-open No. 2011-194426), and forming is performed under a state in which concaves and convexes are eliminated (a thickness of an entire region of the outer-plate workpiece is equalized). In this manner, a product formed into a uniform contour (product bent into a cylindrical shape with a predetermined curvature) is obtained. 
         [0007]    In this case, in order to obtain a predetermined contour (curvature or profile), every time pressing operation is performed several times, an operator needs to measure the contour, and to minutely adjust a pushing amount of a punch. 
         [0008]    It is necessary to minutely adjust a thickness of the cardboard (filler) in order to minutely adjust the pushing amount of the punch. Operation itself of embedding the cardboard into each of the pocket grooves is complicated and requires a long period of time. In addition, even a skilled worker spends a long period of time to minutely adjust the thickness of the cardboard (minutely adjust a height thereof). Accordingly, in actuality, it takes, for example, four hours to form and complete one outer-plate. 
         [0009]    In addition, the outer-plate workpiece (plate-shaped workpiece) of the aircraft is a significantly large component having a width dimension of approximately 2.5 m and a length dimension (longitudinal dimension) of approximately from 6 m to 10 m, despite of a small thickness of approximately from 2 mm to 10 mm. Therefore, the outer-plate workpiece deflects due to a self-weight after forming. Accordingly, when the contour is measured in the deflecting state, in actuality, it is difficult to conduct with good accuracy an inspection of whether or not the predetermined curvature is obtained, and a skill is required. 
         [0010]    Further, in order to prevent damage to the outer-plate workpiece at the time of forming, rubber is wound around the punch, and a cover plate (which is a member softer than the outer-plate workpiece) is laid on a die. Accordingly, forming accuracy changes due to aged deterioration of the rubber and the cover plate. Thus, in actuality, it is difficult to perform forming at fixed accuracy for a long period of time. Further, in a tip forming method, a distance between front and rear bearing points of the die (see  FIG. 8 ) is small. As a result, a load applied to deform the workpiece is increased, and a press is required to have high capacity. 
         [0011]    Further, hitherto, the outer-plate (or skin) has been formed by the tip forming method using the press brake (forming machine). Accordingly, in order to receive the outer-plate workpiece having the length dimension (longitudinal dimension) of approximately from 6 m to 10 m, a large-sized press brake having a frontage (column interval) of 10 m or more has been needed. 
         [0012]    Accordingly, as illustrated in  FIG. 7A  and  FIG. 7B , a slide (punch) of the press brake deflects, and hence has an immense size in order to ensure rigidity (to suppress longitudinal deflection), which leads to increase of mass and increase of operation energy. In addition, a long period of time is needed to store the operation energy, and a long operation cycle is needed. Thus, in actuality, production efficiency of the press brake is low. 
         [0013]    Adoption of a three-point press forming method ( FIG. 8 ) employing the tip forming method when bending the outer-plate of the aircraft into a cylindrical shape is considered as a cause of the following: work that has hitherto required a long period of working hours (work of embedding cardboards into the pocket grooves (dents) and work of forming the outer-plate in while minutely adjusting thicknesses of the cardboards); and the press brake (forming machine) having an immense size and a wide frontage for receiving a large workpiece. 
         [0014]    In this context, it is desired to create a new forming method that needs no work of filling the pocket grooves even when any patterns of pocket grooves are formed, is capable of obtaining a product shape in several forming steps, and needs no large-sized forming machine. 
       SUMMARY OF THE INVENTION 
       [0015]    According to one embodiment of the present invention, there is provided a bending apparatus for a plate-shaped metal workpiece, including: 
         [0016]    a suction device configured to suck a surface of a plate-shaped metal workpiece in a removable manner; 
         [0017]    a plurality of expansion and contraction devices each including the suction device mounted on a distal end thereof, each of the plurality of expansion and contraction devices being capable of expanding and contracting a length ranging from a proximal end thereof to the suction device; and 
         [0018]    an apparatus base on which the proximal end of each of the plurality of expansion and contraction devices is mounted, 
         [0019]    the bending apparatus being configured to form the plate-shaped metal workpiece under bending deformation by expanding and contracting the plurality of expansion and contraction devices under a state in which the suction device sucks the surface of the plate-shaped metal workpiece. 
         [0020]    In the one embodiment of the present invention, the proximal end may be pivotable with respect to the apparatus base. 
         [0021]    In the one embodiment of the present invention, the bending apparatus for a plate-shaped metal workpiece may further include a clamping device configured to clamp an end portion of the plate-shaped metal workpiece in a thickness direction of the plate-shaped metal workpiece in a releasable manner, and the plate-shaped metal workpiece may be formed under bending deformation in such a manner that the clamping device is pivoted with respect to the apparatus base while clamping the end portion of the plate-shaped metal workpiece in the thickness direction. 
         [0022]    In the one embodiment of the present invention, the clamping device may be movable in a width direction of the plate-shaped metal workpiece. 
         [0023]    In the one embodiment of the present invention, expansion and contraction amounts of the plurality of expansion and contraction devices may be controllable. 
         [0024]    In the one embodiment of the present invention, after forming the plate-shaped metal workpiece under bending deformation by expanding or contracting the plurality of expansion and contraction devices in the same direction, the bending apparatus may form the plate-shaped metal workpiece under bending deformation by expanding or contracting the plurality of expansion and contraction devices in a direction opposite to the same direction in sequential order from an innermost expansion and contraction device toward an outermost expansion and contraction device. 
         [0025]    According to one embodiment of the present invention, there is provided a bending method for a plate-shaped metal workpiece, including, by using a bending apparatus for a plate-shaped metal workpiece including: 
         [0026]    a suction device configured to suck a surface of a plate-shaped metal workpiece in a removable manner; 
         [0027]    a plurality of expansion and contraction devices each including the suction device mounted on a distal end thereof, each of the plurality of expansion and contraction devices being capable of expanding and contracting a length ranging from a proximal end thereof to the suction device; and 
         [0028]    an apparatus base on which the proximal end of each of the plurality of expansion and contraction devices is mounted, 
         [0029]    forming the plate-shaped metal workpiece under bending deformation by expanding and contracting the plurality of expansion and contraction devices under a state in which the suction device sucks the surface of the plate-shaped metal workpiece. 
         [0030]    In the one embodiment of the present invention, the bending method for a plate-shaped metal workpiece further includes, after forming the plate-shaped metal workpiece under bending deformation by expanding or contracting the plurality of expansion and contraction devices in the same direction, forming the plate-shaped metal workpiece under bending deformation by expanding or contracting the plurality of expansion and contraction devices in a direction opposite to the same direction in sequential order from an innermost expansion and contraction device toward an outermost expansion and contraction device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]      FIG. 1A  is a plan view (top view) of a bending apparatus for a plate-shaped metal workpiece according to an embodiment of the present invention. 
           [0032]      FIG. 1B  is a partial plan view (top view) of a plate-shaped metal workpiece to be formed by the bending apparatus for a plate-shaped metal workpiece. 
           [0033]      FIG. 1C  to  FIG. 1E  are side views of the bending apparatus for a plate-shaped metal workpiece when viewed from a width direction of the bending apparatus. 
           [0034]      FIG. 2A  to  FIG. 2F  are side views for respectively illustrating Step  1  to Step  6  of forming steps of the bending apparatus (method) for a plate-shaped metal workpiece according to the embodiment of the present invention. 
           [0035]      FIG. 3A  to  FIG. 3E  are side views for illustrating Step  7  to Step  11  of the forming steps of the bending apparatus (method) for a plate-shaped metal workpiece according to the embodiment of the present invention. 
           [0036]      FIG. 4A  is a side view for illustrating a state in which pivotal movement (rocking angles) of servo screw jacks is controlled by servomotors with respect to a bed of the bending apparatus for a plate-shaped metal workpiece according to the embodiment of the present invention. 
           [0037]      FIG. 4B  is a side view for illustrating a state in which the pivotal movement (rocking angles) of the servo screw jacks is automatically controlled by springs with respect to the bed. 
           [0038]      FIG. 5A  is an enlarged side view for illustrating a configuration example of one of bender-cum-clamp members of the bending apparatus for a plate-shaped metal workpiece according to the embodiment of the present invention. 
           [0039]      FIG. 5B  is a partial plan view (top view) of the one of bender-cum-clamp members. 
           [0040]      FIG. 6A  is a side view for illustrating a forming method in a case of simultaneously bending both ends of the plate-shaped metal workpiece at a predetermined curvature by the servo screw jacks and the bender-cum-clamp members of the bending apparatus for a plate-shaped metal workpiece according to the embodiment of the present invention. 
           [0041]      FIG. 6B  is a side view for illustrating a forming method in a case of bending one end of the plate-shaped metal workpiece at a predetermined curvature. 
           [0042]      FIG. 7A  is a view of a related-art press brake when viewed from a feeding direction (length direction) of a plate-shaped metal workpiece (view for illustrating a wide frontage of the press brake). 
           [0043]      FIG. 7B  is a side view of  FIG. 7A . 
           [0044]      FIG. 8  is a side view for illustrating a related-art cylindrical bending method employing three-point bending. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0045]    The present invention has been made in view of the above-mentioned circumstances, and has an object to provide a bending apparatus and a bending method for a plate-shaped metal workpiece, which are capable of forming (bending into a cylindrical shape) a plate-shaped metal workpiece for an outer-plate (or a skin) of an aircraft and the like at a predetermined curvature efficiently with high accuracy and a relatively simple and low-cost configuration. 
         [0046]    Now, a bending apparatus and a bending method for a plate-shaped metal workpiece according to an embodiment of the present invention are described with reference to the attached drawings. Note that, the present invention is not limited to the embodiment described below. 
         [0047]    The inventors of the present invention have focused on the fact that a plurality of pocket grooves (dents) having various shapes are formed in an inner surface (on a side of a center of a curvature radius) of an outer-plate (or a skin) of an aircraft to be formed into a cylindrical shape, but an outer surface (opposite surface) of the outer-plate is flat and has no pocket. Thus, the inventors of the present invention have created a method of bending an outer-plate workpiece (plate-shaped workpiece) into a cylindrical shape (at a predetermined curvature) by sucking and pulling the outer surface (on a side opposite to the center of the curvature radius) of the outer-plate of the aircraft to be formed into a cylindrical shape, thereby forcibly deforming the outer-plate workpiece (plate-shaped workpiece) through the pulling. 
         [0048]    The suction is performed using a suction pad (such as vacuum suction and magnetic attraction), and a position of the suction pad in a height direction (position thereof in an up-and-down direction in  FIG. 2A  to  FIG. 2F ) can be controlled by a servo screw jack (actuator capable of performing position control) or the like. 
         [0049]    Specifically, as illustrated in  FIG. 1C  to  FIG. 1E ,  FIG. 2A  to  FIG. 2F ,  FIG. 3A  to  FIG. 3E ,  FIG. 4A , and  FIG. 4B , in a bending apparatus  1  for a plate-shaped workpiece according to this embodiment, a plurality of servo screw jacks  20 A to  20 G each having a suction pad  10  (suction cup in a case of vacuum suction) mounted to a distal end thereof are mounted to a bed  2  through pivots  21   a  to  21   g.    
         [0050]    Note that, the suction pad  10  corresponds to an example of a suction device according to the present invention, and the servo screw jacks  20 A to  20 G correspond to an example of expansion and contraction devices according to the present invention. Further, the bed  2  corresponds to an apparatus base according to the present invention. 
         [0051]    In this embodiment, as the plate-shaped workpiece (plate-shaped metal workpiece)  3  being a workpiece for an outer-plate of an aircraft and the like, a metal material such as extra-super duralumin (2524 T3) is exemplified. As illustrated in  FIG. 1A  and  FIG. 1B , for example, the plate-shaped workpiece  3  has approximately a size of a thickness of from 2 mm to 10 mm×a width of 2.5 m×a length of from 6 m to 10 m. Further, as illustrated in  FIG. 1B , a plurality of pocket grooves (dents)  3 A having various shapes are formed (carved) in an upper surface of the plate-shaped workpiece  3 . 
         [0052]    As illustrated in  FIG. 1C ,  FIG. 2A  to  FIG. 2F ,  FIG. 4A , and  FIG. 4B , the servo screw jacks  20 A to  20 G are arranged in line along a circumferential direction of a cylindrical shape of the plate-shaped workpiece  3  to be bent into the cylindrical shape (arc shape) (along a width direction of the plate-shaped workpiece  3 ). Further, the servo screw jacks  20 A to  20 G are supported by the pivots  21   a  to  21   g  in a pivotable manner, respectively, and the servo screw jacks  20 A to  20 G are pivoted so that a center axis of each of the servo screw jacks  20 A to  20 G in a longitudinal direction (a center axis thereof in an expansion-and-contraction direction) is moved toward a center of a curvature radius of the plate-shaped workpiece  3  to be bent into the cylindrical shape at a predetermined curvature (along a direction of a normal line of the cylindrical shape). 
         [0053]    Further, as illustrated in  FIG. 1A , the servo screw jacks  20 A to  20 G are arranged in a plurality of rows along a length direction of the plate-shaped workpiece  3 . In this embodiment, in the length direction, servo screw jacks  20 H to  20 M are arranged between a row of the servo screw jacks  20 A to  20 G and another row of the servo screw jacks  20 A to  20 G adjacent thereto. Further, the servo screw jacks are arranged in a staggered pattern so that center positions of the suction pads  10  can be as close to each other as possible in the length direction, specifically, the servo screw jacks are arranged in a staggered pattern so that, in the width direction, the servo screw jack  20 H is arranged between the servo screw jacks  20 A and  20 B, and the servo screw jack  20 I is arranged between the servo screw jacks  20 B and  20 C. 
         [0054]    In the following, the servo screw jacks  20 A to  20 G are described as a representation of the plurality of servo screw jacks. 
         [0055]    The bending apparatus  1  for a plate-shaped workpiece configured as described above bends the plate-shaped workpiece  3  into a cylindrical shape (arc shape) at a predetermined curvature in the following steps. 
         [0056]    In Step  1  (represented by S 1  in  FIG. 2A , the same holds true for the following description), as illustrated in  FIG. 2A  and  FIG. 1C , height positions of the suction pads  10  of the respective servo screw jacks  20 A to  20 G (expansion and contraction amount of the respective servo screw jacks  20 A to  20 G) are adjusted so that the suction pads  10  are brought into a flat form. This form is a standby form (or standby state). In this standby form, the plate-shaped workpiece  3  is carried and set onto the suction pads  10 . 
         [0057]    In Step  2  (S 2 ), as illustrated in  FIG. 2B , the suction pads  10  suck a lower surface (surface having no pocket groove) of the plate-shaped workpiece  3 . 
         [0058]    In Step  3  (S 3 ), as illustrated in  FIG. 2C  and  FIG. 1D , bender-cum-clamp members  30 A and  30 B support vicinities of both widthwise ends of the plate-shaped workpiece  3  from below. Further, under a state in which the suction pads  10  suck the plate-shaped workpiece  3 , through position control (control of expansion and contraction amounts of the respective servo screw jacks  20 A to  20 G), rods  20   a  to  20   g  of the respective servo screw jacks  20 A to  20 G are lowered (contracted) to predetermined positions where the predetermined curvature is obtained, thereby lowering the suction pads  10 . In this manner, a vicinity of a widthwise center of the plate-shaped workpiece  3  is subjected to plastic working (bent into a cylindrical shape) at a predetermined curvature (with a curvature radius R of approximately 1,000 mm). 
         [0059]    Note that, springback of extra-super duralumin is significant. Thus, when the extra-super duralumin is deformed at a curvature with a curvature radius R of approximately 1,000 mm, the extra-super duralumin having a curvature with a curvature radius R of approximately 3,000 mm is obtained after being released (see  FIG. 1D ). 
         [0060]    In this case, positions of both widthwise end portions of the plate-shaped workpiece  3  are shifted inward in accordance with bending deformation of the plate-shaped workpiece  3 . Accordingly, the bender-cum-clamp members  30 A and  30 B, which support the vicinities of the both widthwise ends of the plate-shaped workpiece  3  from below, are movable inward in accordance with the inward shifting of the plate-shaped workpiece  3 . 
         [0061]    Specifically, the bender-cum-clamp member  30 A ( 30 B) is constructed as illustrated in  FIG. 5A  and  FIG. 5B . Horizontal movement of the bender-cum-clamp member  30 A ( 30 B) in the width direction can be achieved using a linear guide mechanism or the like capable of controlling a position of a body base  302  of the bender-cum-clamp member  30 A, which is threadingly engaged with a rotary screw  301 , relatively to the bed  2  in such a manner that the rotary screw  301  is rotated by a servomotor  303 . 
         [0062]    In Step  4  (S 4 ), as illustrated in  FIG. 2D , the both widthwise ends of the plate-shaped workpiece  3  are nipped by the bender-cum-clamp members  30 A and  30 B, respectively. Further, the bender-cum-clamp member  30 B illustrated on the left side in  FIG. 2D  is pivoted (or rotated) clockwise by a predetermined angle, and the bender-cum-clamp member  30 A illustrated on the right side in  FIG. 2D  is pivoted (or rotated) counterclockwise by a predetermined amount (predetermined rotation angle) (rotation angle position control is performed). Thus, the vicinities of the both widthwise ends are subjected to plastic working (bent into a cylindrical shape) at the predetermined curvature (with the curvature radius R of approximately 1,000 mm). At this time, in order to obtain the predetermined curvature (with the curvature radius R of approximately 1,000 mm) at the vicinities of the both widthwise ends, positions of the servo screw jacks  20 A to  20 G are controlled by preset control amounts, and positions of the corresponding suction pads  10  are controlled to appropriate positions. 
         [0063]    In this case, the bender-cum-clamp members  30 A and  30 B correspond to an example of a clamping device according to the present invention. 
         [0064]    As illustrated in  FIG. 2D ,  FIG. 5A , and  FIG. 5B , the bender-cum-clamp members  30 A and  30 B nip the widthwise end portions of the plate-shaped workpiece  3  between a claw portion (nipper portion)  30   a  and a base portion  30   c  and between a claw portion (nipper portion)  30   b  and a base portion  30   d  by pivoting the claw portions  30   a  and  30   b  that are respectively pivoted about pivot shafts  31 A and  31 B by a servomotor  304  or the like. In this nipping state, the bender-cum-clamp members  30 A and  30 B further pivot the claw portions  30   a  and  30   b  and the base portions  30   c  and  30   d  about the pivot shafts  31 A and  31 B by a predetermined amount (predetermined rotation angle) (rotation angle position control is performed), thereby being capable of subjecting (bending into a cylindrical shape) the vicinities of the both widthwise ends to plastic working at the predetermined curvature (with the curvature radius R of approximately 1,000 mm). 
         [0065]    Note that, as illustrated in  FIG. 5A , opposing surfaces of the claw portion (nipper portion)  30   a  and the base portion  30   c  and opposing surfaces of the claw portion (nipper portion)  30   b  and the base portion  30   d  are each formed to have a curvature with a curvature radius R of approximately 1,000 mm. 
         [0066]    In Step  5  (S 5 ), as illustrated in  FIG. 2E , the suction pad  10  of the servo screw jack  20 D, which is positioned at a widthwise center portion among the servo screw jacks  20 A to  20 G, is lifted through position control, and a region to be bent at the predetermined curvature (with the curvature radius R of approximately 1,000 mm) is enlarged toward the widthwise end portions. 
         [0067]    At this time, in order to achieve enlargement of the region to be bent at the predetermined curvature (with the curvature radius R of approximately 1,000 mm) toward the widthwise end portions, rotation angle positions of the bender-cum-clamp members  30 A and  30 B are controlled by preset control amounts, and positions of the other servo screw jacks  20 A to  20 C and  20 E to  20 G are also controlled by preset control amounts. Thus, positions of the corresponding suction pads  10  are controlled to appropriate positions. 
         [0068]    In Step  6  (S 6 ), as illustrated in  FIG. 2F , the suction pads  10  of the servo screw jacks  20 C and  20 E, which are adjacent to the servo screw jack  20 D positioned at the widthwise center portion among the servo screw jacks  20 A to  20 G, are lifted up through position control, and the region to be bent at the predetermined curvature (with the curvature radius R of approximately 1,000 mm) is further enlarged toward the widthwise end portions. 
         [0069]    At this time, in order to achieve enlargement of the region to be bent at the predetermined curvature (with the curvature radius R of approximately 1,000 mm) toward the widthwise end portions, the rotation angle positions of the bender-cum-clamp members  30 A and  30 B are controlled by preset control amounts, and positions of the other servo screw jacks  20 A,  20 B,  20 F, and  20 G are also controlled by preset control amounts. Thus, positions of the corresponding suction pads  10  are controlled to appropriate positions. 
         [0070]    In Step  7  (S 7 ), as illustrated in  FIG. 3A , similarly, the suction pads  10  of the servo screw jacks  20 B,  20 C,  20 D,  20 E, and  20 F among the servo screw jacks  20 A to  20 G are lifted up through position control, and the region to be bent at the predetermined curvature (with the curvature radius R of approximately 1,000 mm) is further enlarged toward the widthwise end portions. The bender-cum-clamp members  30 A and  30 B, and the other servo screw jacks  20 A and  20 G are controlled in the same manner as that of Step  6 . 
         [0071]    In Step  8  (S 8 ), as illustrated in  FIG. 3B  and  FIG. 1E , the suction pads  10  of all of the servo screw jacks  20 A to  20 G are lifted up through position control, and the region to be bent at the predetermined curvature (with the curvature radius R of approximately 1,000 mm) is enlarged up to the widthwise end portions. 
         [0072]    As described above, after the servo screw jacks  20 A to  20 G (plurality of expansion and contraction devices) are expanded or contracted in the same direction (in a downward direction in  FIG. 2A  to  FIG. 2F  and  FIG. 3A  to  FIG. 3E ) to form the plate-shaped workpiece  3  under bending deformation (Steps  3  and  4 ), the servo screw jacks  20 A to  20 G are sequentially (gradually) expanded or contracted in a direction opposite to the same direction (in an upward direction in  FIG. 2A  to  FIG. 2F  and  FIG. 3A  to  FIG. 3E ) from the innermost servo screw jack  20 D (from two servo screw jacks ( 20 J and  20 K) when two servo screw jacks are positioned at a vicinity of a center among the servo screw jacks as in a case of the servo screw jacks  20 H to  20 M) toward the outermost servo screw jacks  20 A and  20 G, thereby forming the plate-shaped workpiece  3  under bending deformation (Steps  5 ,  6 ,  7 , and  8 ). In this manner, bending deformation at the predetermined curvature can be gradually enlarged from the inner side toward the outer side of the plate-shaped workpiece  3 . Accordingly, forming can be performed uniformly on an entire widthwise region of the plate-shaped workpiece  3  at a relatively small curvature with good accuracy. 
         [0073]    In Step  9  (S 9 ), as illustrated in  FIG. 3C , the region to be bent at the predetermined curvature (with the curvature radius R of approximately 1,000 mm) reaches the widthwise end portions in Step  8  so that the forming is finished. Accordingly, the bender-cum-clamp members  30 A and  30 B are released. 
         [0074]    In Step  10  (S 10 ), as illustrated in  FIG. 3D , loads applied to the respective rods  20   a  to  20   g  of the servo screw jacks  20 A to  20 G are detected by a load sensor or the like, and positions of the rods (lengths of the rods) of the servo screw jacks  20 A to  20 G are controlled so as to equalize the loads applied to the respective rods  20   a  to  20   g.  In this manner, in a state without deflection due to a self-weight, a contour (curvature or profile) of the plate-shaped workpiece  3  can be measured, and whether or not a predetermined contour (curvature or profile) is obtained can be inspected. 
         [0075]    Accordingly, as compared to a case of performing measurement under a state in which the plate-shaped workpiece  3  deflects due to the self-weight as in the related art, an actual contour (curvature or profile) can be obtained with good accuracy. 
         [0076]    Note that, unlike a press brake (forming machine), the bending apparatus  1  for a plate-shaped workpiece according to this embodiment does not include a component such as a punch (slide) arranged above the plate-shaped workpiece  3 . Accordingly, after the forming is performed, on the forming spot (under a state in which the plate-shaped workpiece  3  is placed on the suction pads  10  of the servo screw jacks  20 A to  20 G), the contour (curvature or profile) of the plate-shaped workpiece  3  can be measured using a three-dimensional shape measuring device  50  employing a laser. Thus, as compared to the related-art case where the plate-shaped workpiece  3  is temporarily moved from the press brake (forming machine) to a wide space in order to measure the contour (curvature or profile) of the plate-shaped workpiece  3 , the bending apparatus  1  can contribute to simplification of work of measuring the contour, reduction of working hours, and the like, and also can increase production efficiency. 
         [0077]    Whether or not the predetermined contour (curvature or profile) is obtained is determined based on the measurement result obtained in Step  10  (S 10 ). When the predetermined contour (curvature or profile) is not obtained, Step  3  to Step  10  are repeated. In consideration of a difference between a target value and a measurement value, position control is performed on the suction pads  10  of the servo screw jacks  20 A to  20 G so as to obtain the predetermined contour (curvature or profile). 
         [0078]    On the other hand, when the predetermined contour (curvature or profile) is obtained in Step  10 , bending steps proceed to Step  11  (S 11 ). As illustrated in  FIG. 3E , sucking of the suction pads  10  of the servo screw jacks  20 A to  20 G is cancelled. Thus, the plate-shaped workpiece  3  is released, and then carried to an outside. 
         [0079]    In this case, as illustrated in  FIG. 2A  to  FIG. 2F ,  FIG. 4A ,  FIG. 4B , and the like, the servo screw jacks  20 A to  20 G according to this embodiment are constructed so that the rods  20   a  to  20   g  thereof serving as output portions are expanded and contracted (moved upward and downward) with respect to bodies of the servo screw jacks  20 A to  20 G. 
         [0080]    Specifically, each of the servo screw jacks  20 A to  20 G can control an expansion and contraction amount of each of the rods  20   a  to  20   g  by rotating a built-in screw by an electric motor while controlling a rotation amount of the built-in screw. Further, the suction pad  10  is mounted in a rockable manner to a tip of each of the rods  20   a  to  20   g  through a spherical joint, a universal joint, or the like. 
         [0081]    Further, as illustrated in  FIG. 4A , the servo screw jacks  20 A to  20 G are mounted to the bed  2  so as to be pivotable about the pivots  21   a  to  21   g,  respectively. However, for example, pivotal movement amounts (rotation amounts) of the servo screw jacks  20 A to  20 G can be controlled by servomotors  22   a  to  22   g,  respectively. 
         [0082]    With this configuration, when bending is performed by sucking the plate-shaped workpiece  3  using the suction pads  10 , the expansion-and-contraction direction of each of the rods  20   a  to  20   g  (the center axis thereof in the longitudinal direction) can be always conformed to a direction of a normal to a bend of the plate-shaped workpiece  3 . Accordingly, the plate-shaped workpiece  3  can be bent at the predetermined curvature efficiently and precisely. 
         [0083]    Further, as illustrated in  FIG. 4B , instead of the servomotors  22   a  to  22   g,  springs  23   a  to  23   g  may support the servo screw jacks  20 A to  20 G to enable the servo screw jacks  20 A to  20 G to pivot about the pivots  21   a  to  21   g,  respectively. 
         [0084]    When the springs  23   a  to  23   g  are each set to have a relatively low (weak) elastic force (restoring force), the expansion-and-contraction direction of each of the rods  20   a  to  20   g  (the center axis thereof in the longitudinal direction) can be automatically conformed to the direction of the normal to the bend along with the bend of the plate-shaped workpiece  3  when performing bending by sucking the plate-shaped workpiece  3  using the suction pads  10 . Accordingly, the plate-shaped workpiece  3  can be bent at the predetermined curvature efficiently and precisely with a simple configuration. 
         [0085]    As described above, according to the bending apparatus  1  for a plate-shaped workpiece of this embodiment, without performing cylindrical bending employing three-point bending as in the case of the related-art press brake, the suction pads  10  are moved while sucking one surface side of the plate-shaped workpiece  3 , to thereby deform the plate-shaped workpiece  3 . With this method, the plate-shaped workpiece  3  is bent into a cylindrical shape. Accordingly, even with a simple and low-cost configuration, the plate-shaped workpiece for an outer-plate of an aircraft and the like can be formed (bent into a cylindrical shape) at a predetermined curvature efficiently with high accuracy. 
         [0086]    Further, unlike the related art, the bending apparatus  1  for a plate-shaped workpiece according to this embodiment does not use a press brake significantly increased in size in order to ensure rigidity (to suppress deflection in the longitudinal direction). Accordingly, operation energy can be reduced, and also an operation cycle can be reduced. Consequently, production efficiency can be increased. 
         [0087]    Further, in a tip forming method, a distance between front and rear bearing points of a die (see  FIG. 8 ) is small. As a result, a load applied to deform a workpiece is increased, and a press is required to have high capacity. However, according to the bending apparatus  1  for a plate-shaped workpiece of this embodiment, a distance between bearing points for a load (distance between the bender-cum-clamp members  30 A and  30 B) is large. Accordingly, the plate-shaped workpiece can be deformed with a relatively small load. 
         [0088]    That is, according to this embodiment, it is possible to provide the bending apparatus and the bending method for a plate-shaped metal workpiece, which are capable of forming (bending into a cylindrical shape) the plate-shaped metal workpiece for an outer-plate of an aircraft and the like at the predetermined curvature efficiently with high accuracy and the relatively simple and low-cost configuration. 
         [0089]    Note that, an example of operation of the bender-cum-clamp members  30 A and  30 B is as follows. As illustrated in  FIG. 6A  ( FIG. 2D  and the like), under a state in which the bender-cum-clamp members  30 A and  30 B respectively nip the both widthwise end portions of the plate-shaped workpiece  3 , the right bender-cum-clamp member  30 A is pivoted (rotated) counterclockwise, and the left bender-cum-clamp member  30 B is pivoted (rotated) clockwise, thereby being capable of bending and deforming the plate-shaped workpiece  3  at the predetermined curvature. 
         [0090]    In addition, as illustrated in  FIG. 6B , under a state in which the bender-cum-clamp member  30 A nips a widthwise end portion of the plate-shaped workpiece  3 , the right bender-cum-clamp member  30 A is pivoted counterclockwise, whereas the left bender-cum-clamp member  30 B is released, thereby bending and deforming a right end side of the plate-shaped workpiece  3  at a relatively small curvature. This operation method is assumable as the operation of the bender-cum-clamp members  30 A and  30 B. 
         [0091]    Note that, in this embodiment, vacuum suction using the suction pads  10  can be employed. In addition, magnetic attraction using an electromagnet or the like may be employed depending on a material of the plate-shaped workpiece  3 . 
         [0092]    Further, in this embodiment, the workpiece for an outer-plate of an aircraft is described as an example of the plate-shaped workpiece  3 , but the present invention is not limited thereto. As long as the plate-shaped workpiece can be bent and deformed while being sucked by the suction pads  10 , the plate-shaped workpiece is not particularly limited thereto irrespective of whether or not the plate-shaped workpiece has pocket grooves (dents) formed therein. 
         [0093]    Further, in this embodiment, description is made of the case where the plate-shaped workpiece  3  set in a substantially horizontal posture as illustrated in  FIG. 1A  to  FIG. 1E ,  FIG. 2A  to  FIG. 2F ,  FIG. 3A  to  FIG. 3E ,  FIG. 6A , and  FIG. 6B  is deformed at a convex downward (concave upward) curvature, but the present invention is not limited thereto. The present invention is also applicable to a case where the plate-shaped workpiece  3  is deformed at a convex upward (concave downward) curvature. 
         [0094]    Further, in this embodiment, the contour (curvature or profile) of the plate-shaped workpiece  3  after the forming is measured using the three-dimensional shape measuring device  50  employing a laser, and the forming is performed once or a plurality of times until the predetermined contour (curvature or profile) is obtained. However, the contour (curvature or profile) may be measured by another method (for example, a method of using a dial gauge or the like). 
         [0095]    Further, in this embodiment, description is made of the configuration in which the bender-cum-clamp members  30 A and  30 B being the clamping device are arranged at the both widthwise ends of the plate-shaped workpiece  3 , respectively. However, depending on a required curvature, both of the bender-cum-clamp members  30 A and  30 B may be omitted, or at least one of the bender-cum-clamp members  30 A and  30 B may be omitted. 
         [0096]    Further, pivoting functions of the bender-cum-clamp members  30 A and  30 B may be omitted. 
         [0097]    The embodiment described above is merely an example for describing the present invention. It goes without saying that various modifications may be made without departing from the gist of the present invention.