Patent Publication Number: US-2007113613-A1

Title: Die cushion apparatus of press machine

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application is a continuation application of U.S. application Ser. No. 11/180,732, filed Jul. 14, 2006, which is based on Japanese Patent Application No. 2004-209699, filed on Jul. 16, 2004, and Japanese Patent Application No. 2005-118514, filed on Apr. 15, 2005, the disclosures of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a die cushion apparatus of a press machine, and more particularly to a die cushion apparatus suitable for a press machine of a production facility for manufacturing various types of products of different sizes.  
      2. Description of the Related Art  
      A press machine A for executing drawing work, as shown in  FIG. 16 , includes a lower die (punch) E mounted on a bed B and an upper die (die) U mounted to a slide S, and includes a blank holder H operated to rise or fall through a cushion rod R by a die cushion apparatus C installed in the bed B.  
      The die cushion apparatus C includes a cushion pad Cp provided to be vertically movable in the bed B, and an oil pressure servo cylinder Cs for rising and lowering the cushion pad Cp. The die cushion apparatus C, when drawing a work W by lowering the slide S, operates to prevent a “crack,” a “wrinkle,” etc. from occurring in the product by pressing the work W to the upper die U at a predetermined pressure through the blank holder H.  
      Also, the die cushion apparatus C is controlled to sequentially operate a preliminary acceleration stroke a, a drawing stroke b, an auxiliary lift c, locking d, etc., as shown by a solid line (die cushion motion) with a motion (broken line) of the slide S (upper die U) as shown in  FIG. 17  based on position information of the blank holder H and pressure information to the work W.  
      Incidentally, the die cushion apparatus of the press machine is not only used as a means for driving the blank holder, but also it is used, without saying, as a buffer device and a lifting device of the product with various type pressing, such as “drawing,” “bending,” “cutting,” etc.  
      Meantime, a body of an automobile is noted as a typical product manufactured by frequently using a pressing work, however, since types of panels that form one automobile are various, there has been a problem that the production facility becomes uselessly large in scale.  
      More particularly, the panels forming one automobile are largely classified, as shown in  FIGS. 18A  to  18 C, into three types of a class A panel (a large size product) Pa, such as a roof panel, a floor pan, etc., a class B panel (an intermediate size product) Pb, such as a door panel, a hood panel, etc, and a class C panel (a small size product) Pc, such as various types of pillars, a cross member, etc. The class A panel Pa is manufactured in a press working line (tandem press line) PLa in which a plurality of specialized press machines Aa are aligned in parallel through a work loader T, the class B panel Pb is manufactured in a press working line (tandem press line) PLb in which a plurality of specialized press machines Ab are aligned in parallel through the work loader T, and further the class C panel Pc is manufactured in a press working line (tandem press line) PLc in which a plurality of specialized press machines Ac are aligned in parallel through the work loader T.  
      Thus, in the conventional production facility, since the class A panel Pa, the class B panel Pb and the class C panel Pc are respectively manufactured by the specialized press machine Aa, press machine Ab and press machine Ac, a plurality of press working lines are required to manufacture all the panels forming one automobile, and an inconvenience of introducing a large scale of the production facility has not been avoided.  
      In view of the above-mentioned fact, an object of the present invention is to provide a die cushion apparatus of a press machine which can manufacture a plurality of types of products having different sizes by one press machine and which can also achieve minimization of the production facility.  
     SUMMARY OF THE INVENTION  
      A first aspect of the present invention provides a die cushion apparatus of a press machine, comprising a plurality of die cushion units each having a cushion pad and an elevating drive unit for vertically moving the cushion pad, aligned in a bed in a direction perpendicular to a work conveying direction.  
      According to the die cushion apparatus of the first aspect of the invention, the plurality of die cushion units are provided in parallel along a direction perpendicular to the work conveying direction, a plurality of types of products can be manufactured by one press machine.  
      Further, according to the die cushion apparatus of the first aspect of the invention, since the plurality of types of products having different sizes are manufactured by one press machine, a production facility for manufacturing a large variety of types of products can be minimized as much as possible.  
      A second aspect of the present invention provides the die cushion apparatus according to the first aspect of the invention, which further comprises a control unit capable of individually and independently controlling the plurality of die cushion units.  
      According to the die cushion apparatus of the press machine of the second aspect of the invention, since the die cushion apparatus comprises the control unit for individually and independently controlling the plurality of die cushion units, it is possible to operate individual die cushion units for separate works or to operate only a specific die cushion unit.  
      A third aspect of the present invention provides the die cushion apparatus of a press machine according to the second aspect of the invention, wherein the control unit controls a plurality of die cushion units in synchronism with each other that are operated for a work common to each other.  
      According to the die cushion apparatus of a press machine of the third aspect of the invention, since a plurality of die cushion units, which operate on a common work, can be controlled in synchronism with each other, it is possible to make a work of a size extending over the plurality of die cushion units. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a sectional front view schematically showing an embodiment of a die cushion apparatus of a press machine according to the present invention;  
       FIG. 2  is a plan view of an essential portion showing an embodiment of the die cushion apparatus according to the present invention;  
       FIG. 3  is a sectional view taken along a line III-III in  FIG. 2  showing one embodiment of the die cushion apparatus according to the present invention;  
       FIG. 4  is a structural view of a control system in the die cushion apparatus shown in  FIG. 1 ;  
       FIG. 5A ,  FIG. 5B  and  FIG. 5C  are schematic plan views respectively showing operation modes of the die cushion apparatus according to types of products;  
       FIG. 6  is a conceptual view showing a structure of the die cushion apparatus when a small size product is manufactured;  
       FIG. 7  is an appearance perspective view showing a structure of a general mold;  
       FIG. 8  is a conceptual view showing a structure of the die cushion apparatus when an intermediate size product is manufactured;  
       FIG. 9  is a conceptual view showing a structure of the die cushion apparatus when a large size product is manufactured;  
       FIG. 10A  and  FIG. 10B  are conceptual plan views showing operation modes of the die cushion apparatus according to types of products;  
       FIG. 11A  and  FIG. 11B  are conceptual plan views showing operation modes of the die cushion apparatus according to types of products;  
       FIG. 12  is a schematic view showing another embodiment of a die cushion unit in the die cushion apparatus of the present invention;  
       FIG. 13  is a schematic view showing another embodiment of a die cushion unit in the die cushion apparatus of the present invention;  
       FIG. 14  is a schematic view showing another embodiment of a die cushion unit in the die cushion apparatus of the present invention;  
       FIG. 15  is a schematic view showing another embodiment of a die cushion unit in the die cushion apparatus of the present invention;  
       FIG. 16  is an entire conceptual view showing a conventional press machine;  
       FIG. 17  is an operation diagram showing the state of a motion in the die cushion apparatus; and  
       FIG. 18A ,  FIG. 18B  and  FIG. 18C  are conceptual plan views showing a press working line built by using a conventional press machine.  
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Embodiments of the present invention will be described in detail based on the accompanied drawings.  
       FIG. 1  to  FIG. 4  show an example of the die cushion apparatus of the present invention which is applied to a press machine for processing a work (metal plate) into a panel of a desired shape in a production facility of, for example, an automobile. Incidentally, since the entire structure of the press machine is not fundamentally different from the conventional press machine A shown in  FIG. 16 , a detailed description concerning the entire structure of the press machine will be omitted.  
      As shown in  FIG. 1  to  FIG. 3 , a first unit (die cushion unit)  11 , a second unit (die cushion unit)  12 , a third unit (die cushion unit)  13  and a fourth unit (die cushion unit)  14  that constitute a die cushion apparatus  10  are provided in a base (bed)  2  of a press machine  1  installed on a floor.  
      The first unit  11  includes a cushion pad  11 P having a rectangular shape viewed from above (plane view), and a pair of oil pressure servo cylinders  11 S,  11 S which are raising and lowering drive means for vertically moving the cushion pad  11 P.  
      The cushion pad  11 P is contained in one of four sections obtained by partitioning a peripheral wall  2 A of the base  2  by partition walls  2 B, and installed to be vertically movable with respect to the base  2  by slidably contacting a base guide g with a pad liner  1 .  
      Furthermore, the pair of oil pressure servo cylinders  11 S,  11 S are fixed to a beam  2 C installed in the base  2 , and synchronously operated like one oil pressure servo cylinder, by connecting mutual oil paths by pipes  11   p.    
      Needless to say, the oil pressure servo cylinder  11 S has a structure which can suitably change a pressure of a blank holder (a wrinkle suppressing pressure), a stroke, a locking position, etc., similarly to the oil pressure servo cylinder in a conventional die cushion apparatus.  
      The second unit  12  also includes a cushion pad  12 P having a rectangular shape viewed from above (plane view), and a pair of oil pressure servo cylinders  12 S,  12 S, similarly to the first unit  11 . The cushion pad  12 P is installed and contained vertically movably in one section of the base  2 , and the pair of oil pressure servo cylinders  12 S,  12 S are constructed to operate like one oil pressure servo cylinder.  
      Also, the third unit  13  includes a cushion pad  13 P having a rectangular shape viewed from above (plane view), and a pair of oil pressure servo cylinders  13 S,  13 S, similarly to the first unit  11 , and the cushion pad  13 P is installed and contained vertically movably in one section of the base  2 , and the pair of oil pressure servo cylinders  13 S,  13 S are operated like one oil pressure servo cylinder.  
      Furthermore, the fourth unit  14  also includes a cushion pad  14 P having a rectangular shape viewed from above (plane view), and a pair of oil pressure servo cylinders  14 S,  14 S, similarly to the first unit  11 . The cushion pad  14 P is installed and contained vertically movably in one section of the base  2 , and the pair of oil pressure servo cylinders  14 S,  14 S are operated like one oil pressure servo cylinder.  
      Here, the first unit  11 , the second unit  12 , the third unit  13  and the fourth unit  14  are provided to be aligned in a direction perpendicular to a work conveying direction (a direction perpendicular to the surface of paper in  FIG. 1 ). Thus, the cushion pads  11 P,  12 P,  13 P and  14 P in the units  11  to  14  are arranged as if one large die cushion pad was divided into four in the direction perpendicular to the work conveying direction.  
      More particularly, the first unit  11 , the second unit  12 , the third unit  13  and the fourth unit  14  are laid out in a positional state for use simultaneously in one step of pressing, and further, laid out so that a work and a product are conveyed simultaneously by a work conveying unit such as a vacuum cup, etc. extended in the direction perpendicular to the work conveying direction.  
      On the other hand, the die cushion apparatus  10  has an operation controller  20  for controlling to operate the first unit  11 , the second unit  12 , the third unit  13  and the fourth unit  14  independently from each other or synchronously with each other, to be described later.  
      The operation controller  20  has a first controller  21  for independently controlling the first unit  11 , and this first controller  21  controls to operate the first unit  11  in a predetermined die cushion motion (refer to  FIG. 17 ) based on position information and pressure information, similarly to the conventional die cushion apparatus.  
      Furthermore, the operation controller  20  has a second controller  22  for independently controlling the second unit  12 , a third controller  23  for independently controlling the third unit  13 , and a fourth controller  24  for independently controlling the forth unit  14 . These second controller  22  to the fourth controller  24  control to operate the second unit  12  to the fourth unit  14  in a predetermined die cushion motion (refer to  FIG. 17 ) based on position information and pressure information, similarly to the first controller  21 .  
      The operation controller  20  has a supervising controller  25  together with the first controller  21  to the fourth controller  24 . This supervising controller  25  outputs a command signal to the first controller  21  to the fourth controller  24  to be described later based on a working state inputted from an operation panel  26 , etc. of the press machine  1  to thereby supervise the independent operation control of the first unit  11 , the second unit  12 , the third unit  13  and the fourth unit  14  and also control to operate synchronously with each other in an arbitrary combination of the first unit  11  to the fourth unit  14 .  
      Incidentally, in the press machine  1 , a class A panel, such as a roof panel, etc., of a large size product, a class B panel, such as a door panel, etc. of an intermediate size product, and a class C panel, such as a cross member, etc. of a small size product can be used as an object to be worked. As shown in  FIG. 5A , when an object to be worked is the class A panel Pa, all the first unit  11  to the fourth unit  14  are used for manufacturing a common one class A panel Pa.  
      Also, as shown in  FIG. 5B , when an object to be worked is the class B panel Pb, the first unit  11  and the second unit  12 , which are adjacent to each other, and the third unit  13  and the fourth unit  14 , which are adjacent to each other, are used for manufacturing a common one class B panel Pb, respectively, and totally two class B panels Pb, Pb are manufactured.  
      Furthermore, as shown in  FIG. 5C , an object to be worked is the class C panel Pc, all the first unit  11  to the fourth unit  14  are used for manufacturing the class C panels Pc, respectively, and totally four class C panels Pc, Pc, Pc, Pc are manufactured.  
      Here,  FIG. 1  and  FIG. 4  show an embodiment when the class C panel (small size product) Pc like  FIG. 5C  is an object to be worked, and in the base  2  of the press machine  1 , a lower die L 1 , a lower die L 2 , a lower die L 3  and a lower die L 4  are installed respectively in an upper area of the first unit  1 , the second unit  12 , the third unit  13  and the fourth unit  14 .  
      A blank holder H 1 , a blank holder H 2 , a blank holder H 3  and a blank holder H 4  are installed in the upper area of the first unit  1 , the second unit  12 , the third unit  13  and the fourth unit  14  through a cushion pin CP 1 , a cushion pin CP 2 , a cushion pin CP 3  and a cushion pin CP 4 .  
      On the other hand, in the slide of the press machine  1 , an upper die U 1 , an upper die U 2 , an upper die U 3  and an upper die U 4  are mounted at positions opposed to the lower die L 1 , the lower die L 2 , the lower die L 3  and the lower die L 4  through holders  5 , respectively.  
      In the following description, in the press machine  1  of the above-mentioned structure, one scope of controlling to operate to the first unit  11  to the fourth unit  14  when the class A panel Pa, the class B panel Pb, and the class C panel Pc shown in  FIG. 5A ,  FIG. 5B  and  FIG. 5C  are manufactured will be described with reference to  FIG. 1  and  FIG. 4  showing the entire structure of the die cushion apparatus  10 .  
      In the press machine  1  of the above-mentioned structure, when the four class C panel Pc (refer to  FIG. 5C ) of the same shape are manufactured at the same time, as shown in  FIG. 6 , the lower dies L 1  to L 4 , and blank holders H 1  to H 4  are installed in the upper area of the first unit  11  to the fourth unit  14  in the bed  2 , the upper dies U 1  to U 4  corresponding to the lower dies L 1  to L 4  are installed in the slide  4 , and works Wc of the class C panel Pc is supplied to the individual dies.  
      An operation controller  20  of the die cushion apparatus  10  controls to operate the first unit  11  to the fourth unit  14  in a predetermined die cushion motion (refer to  FIG. 17 ) corresponding to the specification of the class C panel Pc independently from each other by the first controller  21  to the fourth controller  24  based on the working state (“four class C panels are manufactured,” “specification of class C panel,” etc.) inputted from a control panel  26 .  
      Incidentally, as shown in  FIG. 7 , square-rod shape heel guides La and heel guides Ua are projected from four corners of the lower die L 1  and the upper die U 1 . The blank holder H 1  is vertically moved with respect to the lower die L 1  while the blank holder H 1  is guided by the heel guide Ua by slidably contacting guide recesses Ha at four comers of the blank holder H 1  with the heel guide Ua.  
      The oil pressure servo cylinders  11 S,  11 S of the first unit  11  for vertically moving the blank holder H 1  are installed in parallel along the work conveying direction as shown in  FIG. 3 , but are connected via pipings  11   p ,  11   p  as described above, to operate like one oil pressure servo cylinder. Incidentally, a structure may be provided so that one oil pressure servo cylinder is provided.  
      On the other hand, in the press machine  1  of the above-mentioned structure, when the two class B panels Pb (refer to  FIG. 5B ) are manufactured simultaneously, as shown in  FIG. 8 , the lower die L 11  and the lower die L 12 , and the blank holder H 11  and the blank holder H 12  are installed in the upper area of the first unit  11  and the second unit  12  and in the upper area of the third unit  13  and the fourth unit  14 , and the upper die U 11  and the upper die  12  corresponding to the lower die L 11  and the lower die  12  are installed in the slide  4 , and works Wb of the class B panel Pb are supplied to the individual dies.  
      The operation controller  20  of the die cushion apparatus  10  controls to operate the first unit  11 , the second unit  12 , the third unit  13  and the fourth unit  14  in a predetermined die cushion motion (refer to  FIG. 17 ) corresponding to the specification of the class B panel Pb based on the working states (“two class B panels are manufactured,” “a common work for the first unit  11  and the second unit  12  is an object to be worked,” “a common work for the third unit  13  and the fourth unit  14  is an object to be worked,” and “specification of class B panel,” etc.) inputted from the control panel  26 .  
      Here, in the operation controller  20 , the first unit  11  and the second unit  12  provided to manufacture the one class B panel Pb are controlled to be operated synchronously with each other, and the third unit  13  and the fourth unit  14  provided to manufacture the other class B panel Pb are controlled to be operated synchronously with each other.  
      More particularly, the first unit  11  and the second unit  12  are controlled to be operated synchronously with each other in such a manner that the first unit  11  is controlled to be operated based on a command signal from the first controller  21  and the second unit  12  is controlled to be operated based on a feedback signal with the operation of the first unit  11 , by a so-called master/slave type controlling method.  
      Similarly, the third unit  13  and the fourth unit  14  are controlled to be operated synchronously with each other in such a manner that the third unit  13  is controlled to be operated based on a command signal from the third controller  23  and the fourth unit  14  is controlled to be operated based on a feedback signal with the operation of the third unit  13 , by a so-called master/slave type controlling method.  
      In this manner, the first unit  11  and the second unit  12 , and the third unit  13  and the fourth unit  14  are controlled to be operated synchronously with each other, and the blank holder H 11  and the blank holder H 12  vertically move without inclining in a direction perpendicular to the work conveying direction, and hence a damage of a die unit due to an inclination of the blank holder is prevented.  
      Incidentally, whether any of the first unit  11  and the second unit  12  with the common work Wb as an object to be worked is used as a master of the operation control or whether any of the third unit  13  and the fourth unit  14  with the common work Wb as an object to be worked is used as a master of the operation control can be, of course, suitably set in view of various conditions.  
      On the other hand, in the press machine  1  of the above-mentioned structure, when one class A panel Pa (refer to  FIG. 5A ) is manufactured, as shown in  FIG. 9 , one lower die L 20  and one blank holder H 20  are installed in the upper area of the first unit  11  to the fourth unit  14  in the bed  2 , and the upper die U 20  corresponding to the lower die L 20  is installed in the slide  4 , and the work Wa of the class A panel Pa is supplied.  
      The operation controller  20  of the die cushion apparatus  10  controls to operate the first unit  11 , the second unit  12 , the third unit  13  and the fourth unit  14  in a predetermined die cushion motion (refer to  FIG. 17 ) corresponding to the specification of the class A panel Pa based on the working states (“one class A panel is manufactured,” “a common work in the first unit  11  to the fourth unit  14  is an object to be worked,” “specification of the class A panel,” etc.) inputted from the control panel  26 .  
      Here, in the operation controller  20 , the first unit  11 , the second unit  12 , the third unit  13  and the fourth unit  14  are controlled to be operated synchronously with each other.  
      More particularly, the first unit  11  is controlled to be operated based on the command signal from the first controller  21 , and the second unit  12 , the third unit  13  and the fourth unit  14  are controlled to be operated based on the feedback signal with the operation of this first unit  11 , synchronously with each other by a so-called master-slave type controlling method.  
      Thus, the first unit  11 , the second unit  12 , the third unit  13  and the fourth unit  14  are controlled to be operated synchronously with each other, and the blank holder H 20  is thereby vertically moved without any inclination in a direction perpendicular to the work conveying direction, and hence a damage of the die unit due to the inclination of the blank holder is prevented.  
      Incidentally, any of the first unit  11  to the fourth unit  14  with a common work Wa as an object to be worked can be suitably set as a master for operation control in view of various conditions.  
      Thus, according to the press machine  1  adopting the die cushion apparatus  10  concerning the present invention, by using a different work as an object to be worked for each of the individual die cushion units of the first unit  11  to the fourth unit  14 , or by using a common work as an object to be worked for the combination of die cushion units, products of a plurality of types having different sizes can be manufactured by one press machine  1 .  
      Further, according to the die cushion apparatus  10  of the above-mentioned structure, since products of a plurality of types having different sizes can be manufactured by one press machine  1 , a production facility for manufacturing a wide variety of types of products can be minimized as much as possible.  
      Incidentally, as shown in  FIG. 10A , when four class C panels Pc 1 , Pc 2 , Pc 3 , and Pc 4  having largely different shapes (specification) are manufactured, the lower dies L 1  to L 4 , the blank holders H 1  to H 4 , and the upper dies U 1  to U 4 , which are respectively for the class C panels Pc 1  to Pc 4 , are used, and works Wc, Wc, Wc, and Wc of the class C panels Pc 1  to Pc 4  are supplied to the individual dies.  
      The operation controller  20  of the die cushion apparatus  10  is controlled to be operated in a predetermined die cushion motion (refer to  FIG. 17 ) corresponding to the specification of the class C panel Pc independent from each other by the first controller  21  to the fourth controller  24  based on the working state inputted from the control panel  26 .  
      More particularly, the first unit  11  to the fourth unit  14  are controlled to be operated independently along with pressure of a blank holder, stroke, operating timing, etc. corresponding to the specifications of the class C panels Pc 1  to Pc 4 .  
      Particularly, rising speeds of the first unit  11  to the fourth unit  14  are controlled so that the timings of the respective blank holders H 1  to H 4  reaching a predetermined lift rising end responding to a shape of a product become the same irrespective of a difference of the stroke due to a depth of drawing, etc. by considering a removal of the product by a work conveying unit, such as a vacuum cup, etc.  
      Thus, in the press machine  1  adopting the die cushion apparatus  10  according to the present invention, a plurality of the products having the same types (class B panel, class C panel) and largely different shapes (specifications) can be manufactured simultaneously in the same step.  
      On the other hand, as shown in  FIG. 10B , when two class C panels Pc, Pc and one class B panel Pb are manufactured, as shown in  FIG. 6 , the lower dies L 1 , L 2 , the blank holders H 1 , H 2 , and the upper dies U 1 , U 2  are installed, as shown in  FIG. 8 , the lower dies L 12 , the blank holder H 12 , and the upper die U 12  are installed, works Wc, Wc of the class C panel Pc are supplied between the lower dies L 1 , L 112  and the upper dies U 1 , U 2 , and the work Wb of the class B panel Pb is supplied between the lower die L 12  and the upper die U 12 .  
      The operation controller  20  of the die cushion apparatus  10  controls to operate the first unit  11  and the second unit  12  by the first controller  21  and the second controller  22  in a predetermined die cushion (refer to  FIG. 17 ) corresponding to the specification of the class C panel Pc independently from each other based on the working state inputted from the control panel  26 , and controls to operate the third unit  13  and the fourth unit  14  used to manufacture the class B panel Pb in a predetermined die cushion motion (refer to  FIG. 17 ) corresponding to the specification of the class B panel Pb synchronously with each other.  
      Also, the operation controller  20  controls the rising speeds of the first unit  11  to the fourth unit  14  so that the respective blank holders H 1  to H 4  become the same timings to reach a predetermined lift rising end responding to the shape of the product irrespective of the difference of the stroke due to the depth of the drawing, etc. by considering the removal of the product by the work conveying unit, such as a vacuum cup, etc.  
      Thus, in the press machine  1  adopting the die cushion apparatus  10  according to the present invention, a plurality of types of the products (class B panel, class C panel) having different sizes can be manufactured simultaneously in the same step.  
      Also, as shown in  FIG. 11A , when one class B panel Pb is manufactured, as shown in  FIG. 8 , the lower die L 11 , the blank holder H 11 , and the upper side U 11  are installed, and the work Wb of the class B panel is supplied between the lower die L 11  and the upper die U 11 .  
      The operation controller  20  of the die cushion apparatus  10  controls to operate the second unit and the third unit used to manufacture the class B panel Pb based on the working state inputted from the control panel in a predetermined die cushion motion (refer to  FIG. 17 ) corresponding to the specification of the class B panel Pb synchronously with each other.  
      Further, as shown in  FIG. 11B , when the two class C panels Pc, Pc are manufactured, as shown in  FIG. 6 , the lower dies L 2 , L 3 , the blank holders H 2 , H 3 , and the upper dies U 2 , U 3  are installed, and the work Wc of the class C panel Pc is supplied between the lower dies L 2 , L 3  and the upper dies U 2 , U 3 .  
      The operation controller  20  of the die cushion apparatus  10  controls to operate the second unit and the third unit used to manufacture the class C panel Pc by the second controller  22  and the third controller  23  based on the working state inputted from the control panel in a predetermined die cushion motion (refer to  FIG. 17 ) corresponding to the specification of the class C panel Pc independently from each other.  
      Thus, in the press machine  1  adopting the die cushion apparatus  10  according to the present invention, the specific die cushion may not be used. Further, which die cushion is selected can be set freely. It is needless to say that a die cushion should be selected so that an eccentric load generated at the working time may become as small as possible.  
      Here, in the above-mentioned embodiment, a plurality of die cushion units in which common works to each other are used as objects to be worked are controlled to be operated synchronously with each other by a master/slave type controlling method. However, as a structure for embodying the master/slave type controlling method, various existing structures may be suitably adopted.  
      Also, as a method for controlling to operate a plurality of die cushion units synchronously with each other, not only the master/slave type controlling method exemplified in the embodiment, but also existing various type controlling method may be, of course, effectively applied.  
      Further, in the above-mentioned embodiment, a rise and fall drive unit of the die cushion unit in the die cushion apparatus is exemplified in the example constructed by the oil pressure servo cylinder. However, for example, the rise and fall drive unit of the die cushion unit can be constructed by a suitable drive means, such as, for example, a motor-driven servo motor, etc.  
       FIG. 12  is a schematic view showing another embodiment of the die cushion unit. In this die cushion unit  100 , a cushion pad  101  is interconnected to a motor-driven servo motor  107  through a ball screw  102 , a coupling member  103 , a large pulley  104 , a belt  105  and a small pulley  106  and a rise and fall drive unit  110  is configured by these ball screw  102 , the coupling member  103 , the large pulley  104 , the belt  105 , the small pulley  106 , and the motor-driven servo motor  107 .  
      Incidentally, pad liners  1 ,  1 , . . . which are slidably contacted with a base guide provided at a base (bed) of the press machine, not shown, are provided on each side face of the cushion pad  101 .  
      A nut portion  102   a  of the ball screw  102  is fixedly provided to a lower portion of the cushion pad  101 , a threaded portion  102   b  of the ball screw  102  is engaged with the nut portion  102   a , and the lower part of the threaded portion  102   b  is connected to the coupling member  103 . Further, the coupling member  103  is supported by a bearing, etc., to the beam  108  in the base, and the large pulley  104  is provided at the lower part of the coupling member  103 . The small pulley  106  is provided at a rotary shaft of the motor-driven servo motor  107 , and a belt  105  is wound on the large pulley  104  and the small pulley  106 .  
      When the rotary shaft of the motor-driven servo motor  107  is rotated, the small pulley  106 , the large pulley  104 , the coupling member  103  and the threaded portion  102   b  are operated to be rotated. When the threaded portion  102   b  is rotated, the threaded portion  102   a  is linearly moved in a vertical direction, that is, in a rising or falling direction along the threaded portion  102   b , and thereby the cushion pad  101  is raised or lowered together with the nut portion  102   a.    
      In the above-mentioned die cushion unit  100 , the operation (rotation of the rotary shaft) of the motor-driven servo motor  107  constituting the rise and fall drive unit  110  is current controlled, and thereby the operation (pressure of a blank holder, stroke, locking position, etc.) of the cushion pad  101  can be suitably controlled, similarly to the oil pressure servo cylinder in the conventional die cushion unit.  
       FIG. 13  is a schematic view showing another embodiment of the die cushion unit. In a die cushion unit  200 , a cushion pad  201  is interlocked to a motor-driven servo motor  207  through a ball screw  202 , a coupling member  203 , a large pulley  204 , a belt  205  and a small pulley  206 , and a rise and fall drive unit  210  is configured by these ball screw  202 , the coupling member  203 , the large pulley  204 , the belt  205 , the small pulley  206  and the motor-driven servo motor  207 .  
      Incidentally, pad liners  1 ,  1 , . . . slidably contacted with a base guide provided in a base (bed) of the press machine, not shown, are provided on each side face of the cushion pad  201 .  
      A threaded portion  202   b  of the ball screw  202  is fixed to a lower part of the cushion pad  201 , a nut portion  202   a  of the ball screw  202  is engaged with this threaded portion  202   b , and the coupling member  203  is connected to the lower part of the nut portion  202   a . Further, the coupling member  203  is supported by a bearing, etc., to the beam  208  in the base, a large pulley  204  is provided in the lower part of the coupling member  203 , a small pulley  206  is provided on a rotary shaft of the motor-driven servo motor  207 , and the belt  205  is wound on the large pulley  204  and the small pulley  206 .  
      When the rotary shaft of the motor-driven servo motor  207  is rotated, the small pulley  206 , the large pulley  204 , the coupling member  203 , and the nut portion  202   a  are operated to be rotated. When the nut portion  202   a  is operated to be rotated, the threaded portion  202   b  is linearly moved in a vertical direction, that is, the rising and falling direction along the nut portion  202   a , and thereby the cushion pad  201  is operated to be raised or lowered together with the threaded portion  202   b.    
      Even in the above-mentioned die cushion unit  200 , an operation of the motor-driven servo motor  207  constituting the rise and fall drive unit  210  is current-controlled to be rotated, an operation (pressure of a blank holder, locking position, etc.) of the cushion pad  201  can be controlled suitably, similarly to the oil pressure servo cylinder in a conventional die cushion apparatus.  
       FIG. 14  is a schematic view showing another embodiment of the die cushion unit. In this die cushion unit  300 , a cushion pad  301  is coupled to a rotary shaft of a motor-driven servo motor  307  through a plunger rod  311  and a piston  312  and further through a ball screw  302 , a coupling member  303 , a large pulley  304 , a belt  305 , and a small pulley  306 , and a rise and fall drive unit  310  is constructed by these plunger rod  311 , the piston  312 , the ball screw  302 , the coupling member  303 , the large pulley  304 , the belt  305 , the small pulley  306  and the motor-driven servo motor  307 .  
      A columnar plunger rod  311  is fixed to the lower portion of the cushion pad  301 , and this plunger rod  311  is slidably supported by a cylindrical plunger guide  313  fixed to a beam  308  in the base. The plunger rod  311  is operated to be raised or lowered while being supported, and the plunger guide  313  guides the plunger rod  311  and the cushion pad  301  coupled to the plunger rod  311  in the rising or falling direction.  
      A cylinder  311   a  having an opening in a downward direction is formed at a lower part of the plunger rod  311 , a piston  312  is slidably contained in the cylinder  311   a , an oil pressure chamber  314  is formed by the inner wall surface of the cylinder  311   a  and the upper surface of the piston  312 , and pressure oil is filed in this oil pressure chamber  314 .  
      The oil pressure chamber  314  has its axial center which is the same as those of the plunger rod  311  and the ball screw  302 , and further a pressure oil port of the oil pressure chamber  314  is connected to an oil pressure circuit, not shown, and the pressure oil communicates between the oil pressure chamber  314  and the oil pressure circuit. The pressure oil in the oil pressure chamber  314  alleviates an impact generated when the upper die is contacted with the work, and when an oil pressure becomes a predetermined value or more, the pressure oil is exhausted to a tank (not shown) to perform an overload protective function.  
      A lower end of the piston  312  is contacted with an upper end of the threaded portion  302   a  in the ball screw  302 . A spherical recess surface  312   a  is formed on the lower end of the piston  312 , and a spherical surface protrusion surface  302   c  is formed on an upper end of the threaded portion  302   b  opposed the recess surface  312   a . Incidentally, a protruding surface may be formed on the lower end of the piston  312 , and a recess surface may be formed on the upper end of the threaded portion  302   b.    
      Here, a bar-like member like the threaded portion  302   b  is strong against an axial force operating at an end part, but weak to a bending moment. When the upper end of the threaded portion  302   b  is a spherical shape, even if the cushion pad  301  is inclined so that a bending moment is generated at the upper end of the threaded portion  302   b , only the axial force is operated at the threaded portion  302   b  entirety, and a damage of the threaded portion  302   b  due to the eccentric load can be prevented.  
      The nut portion  302   a  is engaged with the threaded portion  302   b  of the ball screw  302 , and the lower portion of the nut portion  302   b  is connected to the coupling member  303 . Further, the coupling member  303  is supported to the beam  308  in the base by bearing, etc., and the large pulley  304  is provided at a lower portion of the coupling member  303 . The small pulley  306  is provided at a rotary shaft of the motor-driven servo motor  307 , and the belt  305  is wound on the large pulley  304  and the small pulley  306 .  
      When the rotary shaft of the motor-driven servo motor  307  is rotated, the small pulley  306 , the large pulley  304 , the coupling member  303  and the nut portion  302   a  are operated to be rotated. When the nut portion  302   a  is rotated, the threaded portion  302   b  is linearly moved in a vertical direction, that is, a raising or lowering direction along the nut portion  302   a , and the cushion pad  301  is operated to be raised or lowered together with the threaded portion  302   b , the piston  312 , and the plunger rod  311 .  
      In the above-mentioned die cushion unit  300 , the operation of the motor-driven servo motor  307  constituting the rise or fall drive unit  310  is current-controlled, and the operation (pressure of a blank holder, stroke, locking position, etc.) of the cushion pad  301  can be suitably controlled, similarly to the oil pressure servo cylinder in the conventional die cushion apparatus.  
       FIG. 15  is a schematic view showing another embodiment of the die cushion unit. In this die cushion unit  400 , a cushion pad  401  is coupled to a rotary shaft of a motor-driven servo motor  407  through a plunger rod  411  and a piston  412  and further through a ball screw  402 , a coupling member  403 , a coupling  421  and a reduction gear  422 , and a rise and fall drive unit  410  is constructed by these plunger rod  411 , the piston  412 , the ball screw  402 , the coupling member  403 , the coupling  421 , the reduction gear  422  and the motor-driven servo motor  407 .  
      The motor-driven servo motor  407  is installed on a lower region of the coupling member  403 , and the reduction gear  422  is connected to the rotary shaft of the motor-driven servo motor  407 . Incidentally, the motor-driven servo motor  407  may include a reduction gear.  
      An output shaft of the reduction gear  422  is connected to the lower portion of the coupling member  403  through the coupling  421 , and the ball screw  402 , the coupling member  403 , the coupling  421 , and the output shaft of the reduction gear  422  are coaxially disposed. Further, according to a structure of the reduction gear  422 , a rotary shaft of the motor-driven servo motor  407  is also disposed coaxially with the ball screw  402 , etc.  
      Here, the die cushion unit  400  is fundamentally the same in the structure as the die cushion unit  300  described above except a layout of the motor-driven servo motor  407  to the coupling member  403 , and a transmission mechanism of a power from the motor-driven servo motor  407  to the coupling member  403 , and, therefore, in the constituting elements of the die cushion unit  400 , having the same operation as the die cushion unit  300  are attached by numerals of  400  order adding 100 to the same numerals in  FIG. 14 , and a detailed description will be omitted.  
      In the die cushion unit  400 , when the rotary shaft of the motor-driven servo motor  407  is rotated, a gear, etc. in the reduction gear  422  are rotated, the output shaft of the reduction gear  422 , the coupling  421 , the coupling member  403 , and the nut portion  402   a  are operated to be rotated. When the nut portion  402   a  is rotated, the threaded portion  402   b  is linearly moved in a vertical direction, that is, in a raising and lowering direction along the nut portion  302   a , and thereby the cushion pad  401  is operated to be raised or lowered together with the threaded portion  402   b , the piston  412 , and the plunger rod  411 .  
      Even in the above-mentioned die cushion unit  400 , the operation of the motor-driven servo motor  407  constituting a rise and fall drive unit  410  (the rotation of the rotary shaft) is current-controlled, and the operation of the cushion pad  401  (pressure of a blank holder, stroke, locking position, etc.) of the cushion pad  401  can be suitably controlled, similarly to the oil pressure servo cylinder in the conventional die cushion apparatus.  
      Incidentally, in the above-mentioned embodiments, the example in which the present invention is applied to the press machine for building a production facility of an automobile has been described. However, the die cushion apparatus according to the present invention can be effectively applied not only to the production facility of the automobile, but also the press machine for building the production facility of various products.