Abstract:
A machine for bending sheet metal provides at least one sheet metal resting tool, at least one sheet metal pressing tool, and at least one sheet metal bending tool, parallel to one another; for moving the tools along a first and a second axis perpendicular to one another at least two electric motors are provided for moving the sheet metal pressing tool along the second axis, at least two electric motors for moving the sheet metal bending tool along the first axis and at least two electric motors for moving the sheet metal bending tool along the second axis; a command and control unit connected to the electric motors commands and controls the driving of the electric motors to maintain the parallelism between the tools in the operating step. In this manner, using hydraulic drives is avoided.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The object of the present invention is a machine for bending sheet metal. 
       PRIOR ART 
       [0002]    Machines for bending sheet metal are known, for example for making panels and other components of household appliances such as refrigerators, washing machines and dryers, dish-washing machines, ovens and others. 
         [0003]    Such machines comprise a sheet metal resting tool, a sheet metal pressing tool, and a sheet metal bending tool, parallel to one another, and each with a particular profile. The sheet metal resting tool normally moves according to a horizontal axis X, the sheet metal pressing tool normally moves according to a vertical axis Y that is perpendicular to the axis X, and the bending tool moves according to the two axes X and Y or, by interpolation, according to a rectilinear and/or curvilinear trajectory. 
         [0004]    The sheet metal that has to be bent, for example along a longitudinal edge, is tightened between the sheet metal resting tool and the sheet metal pressing tool with the edge to be bent protruding. The bending tool uses a preset bending movement to bend the edge of the sheet metal over an edge of one or the other of the two sheet metal resting and sheet metal pressing tools. The profile of the tools correspondingly determines the bending profile. 
         [0005]    Hydraulic drives are normally used for moving the tools. 
         [0006]    However, these hydraulic drives have the drawback that a variation in the temperature of the oil and in the type of oil used, or a loss of oil, can determine a variation in the bending parameters. 
         [0007]    Further, the hydraulic drive is rather a stiff system that does not enable parallelism errors between tools in the machine to be corrected. 
         [0008]    Lastly, the hydraulic drives require constant maintenance, which affects production costs. 
       OBJECT OF THE INVENTION 
       [0009]    The object of the present invention is to overcome the above drawbacks. 
       SHORT DESCRIPTION OF THE INVENTION 
       [0010]    This object is achieved by a machine for bending sheet metal according to claim  1 . 
     
    
     
       SHORT DESCRIPTION OF THE DRAWINGS 
         [0011]    In order to understand the invention better, an embodiment thereof is disclosed below by way of non-limiting example, illustrated in the attached drawings, in which: 
           [0012]      FIG. 1  is a side view of a machine for bending sheet metal according to the invention; 
           [0013]      FIG. 2  is a rear perspective view of the machine in  FIG. 1 ; 
           [0014]      FIG. 3  is another rear perspective view of the machine in  FIG. 1  with some components removed; 
           [0015]      FIG. 4  is a front perspective view of the machine in  FIG. 1 ; 
           [0016]      FIG. 5  is a perspective view of a detail of the machine in  FIG. 1 ; 
           [0017]      FIG. 6  is a side view of another detail of the machine in  FIG. 1 ; 
           [0018]      FIG. 7  is a simplified diagram of the command and control system of the machine in  FIG. 1 ; 
           [0019]      FIG. 8  is a perspective view of the machine in  FIG. 1 , also comprising a sheet metal positioning unit; 
           [0020]      FIG. 9  is a side view of the machine in  FIG. 8 ; 
           [0021]      FIG. 10  is a top view of the machine in  FIG. 8 ; 
           [0022]      FIG. 11  is a front view of the sheet metal positioning unit; 
           [0023]      FIG. 12  is a side view of the sheet metal positioning unit in  FIG. 11 ; 
           [0024]      FIG. 13  is a perspective view of a detail of the sheet metal positioning unit in  FIG. 11 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0025]    With reference to  FIGS. 1, 2, 5 , the illustrated machine for bending sheet metal, indicated generally with  10 , has a base  11  and a frame  12  that is mounted slidably on the base  11  through a series of horizontal rectilinear recirculating ball guides  13 . The frame  12  is moved along the guides  13  according to a horizontal axis X (indicated in  FIG. 1 ) by means of an electric motor M 1 . The motor M 1  is fixed to the base  11  and moves, via a reduction gear  14 , a threaded shaft  15  that is screw-coupled with a recirculating ball nut  16  that is integral with the frame  12 , so as to cause the frame  12  to move with respect to the base  11  along the axis X. 
         [0026]    With reference to  FIG. 1 , a longitudinal front wall  17  is integral with the frame  12 , a rectilinear sheet metal resting tool  18  being fixed on the longitudinal front wall  17 , the sheet metal resting tool  18  having a horizontal longitudinal extent that is perpendicular to the axis X, and having a preset section profile. 
         [0027]    With reference to  FIGS. 1, 2 , on the frame  12  a slide  19  is mounted that is arranged opposite and parallel to the wall  17 . The slide  19  is mounted slidably on the frame  12  through a series of rectilinear recirculating ball guides  20 . The slide  19  is moved along the guides  20  according to the horizontal axis X by two electric motors M 2 . Each motor M 2  is fixed to the frame  12  below and moves, via a reduction gear  21 , a threaded shaft  22  that is screw-coupled with a recirculating ball nut  23  that is integral with the slide  12 . The two motors M 2  thus determine movement of the slide  19  with respect to the frame  12  along the axis X. 
         [0028]    With reference to  FIGS. 1, 2 , on the slide  19 , at the wall  17 , a longitudinal plate  24  is mounted slidably on which is fixed a rectilinear sheet metal bending tool  25 , having a longitudinal horizontal extent, that is perpendicular to the axis X, and having a preset section profile. The plate  24  is slidable along a series of vertical recirculating ball nut guides  26 . The plate  24  is moved along the guides  26  according to a vertical axis Y, which is perpendicular to the axis X, by two electric motors M 3 . Each motor M 3  is fixed to the slide  19  above and moves, via a reduction gear  27 , a threaded shaft  28  that is screw-coupled with a recirculating ball nut  29  that is integral with the plate  24 . The two motors M 3  thus determine movement of the slide  19  with respect to the frame  12  along the axis Y. 
         [0029]    With reference to  FIGS. 1-4 , on the upper part of the frame  12  a longitudinal beam  30  is mounted. The beam  30  is slidable with respect to the frame  12  along a series of vertical recirculating ball nut guides  31  and is moved along the guides  31  according to the vertical axis Y by two electric motors M 4 . Each motor M 4  is fixed above to the frame  12  and moves, via a reduction gear  32 , a threaded shaft  33  that is screw-coupled with a recirculating ball nut  34  that is integral with the beam  30 . The two motors M 4  thus determine the movement of the beam  30  with respect to the frame  12  along the axis Y. 
         [0030]    Still with reference to  FIGS. 1-4 , on the beam  30  a longitudinal tool-holding bar  35  is mounted rotatably. The bar  35  has a square section and on each of the four faces a corresponding sheet metal pressing tool is fixed; the four sheet metal pressing tools, indicated specifically with  36 A, 36 B, 36 C, 36 D, have a horizontal longitudinal extent, which is perpendicular to the axis X, and each has a preset section profile that is different from the others. The bar  35  is rotated by an electric motor M 5  fixed to the beam  30  and connected via a reduction gear  37  and a belt transmission  38  to the tool-holding bar  35 . 
         [0031]    In  FIG. 6  there is shown the arrangement of the tools  18 ,  25 ,  36 A-D, which correspond to one another operationally and are parallel to one another. 
         [0032]    With reference to  FIG. 7 , with the motors M 1 , M 2 , M 3 , M 4 , and M 5  corresponding angular position transducers of the driving shaft are coupled, which are indicated respectively with T 1 , T 2 , T 3 , T 4 , and T 5 . The motors M and the transducers T are all connected to a command and control unit U. 
         [0033]    The operation of the disclosed and illustrated machine  10  for bending sheet metal is as follows. 
         [0034]    The sheet metal, indicated with L in  FIG. 1 , is conveyed by a suitable conveyor to at the machine  10  until it rests, along a side to be bent, on the tool  18 . 
         [0035]    The command and control unit U first drives the motor M 1  so as to move the frame  12  with respect to the base  11  along the axis X so as to position the tool  18  correctly with respect to the sheet metal L for bending the edge. 
         [0036]    Then the unit U drives the two motors M 4  so as to lower the beam  30  and with the beam  30  the tool-holding bar  35  along the axis Y until the tool of the preselected bar, for example the tool  36 A, presses the sheet metal L against the tool  18  so as to keep the sheet metal L blocked. 
         [0037]    At this point, the unit U suitably drives the motors M 2  and M 3  so as to move the bending tool  25  to bend the edge of the sheet metal L with a movement according to the two axes X and Y or, by interpolation, according to a rectilinear and/or curvilinear trajectory, in accordance with a well-known technique. The profile of the tools  18 ,  25 , 36 A-D and the movements of the bending tool  25  determine the type of bending of the edge of the sheet metal L. 
         [0038]    If it is desired to change the sheet metal pressing tool the unit U drives the motor M 5  that determines the rotation of the bar  35  until the preset sheet metal pressing tool  36 B, 36 C or  36  D is above the sheet metal resting tool  18 . 
         [0039]    The angular position transducers T 1 -T 5  enable the unit U to control with precision the rotation of the driving shafts and thus the movement of the tools  18 ,  25 , 36 A-D. 
         [0040]    The system with two electric motors that moves the single tool enables the tools to be kept perfectly parallel. Possible deformation that the tool may suffer can be also be corrected by acting in a suitable manner on the motors in a differentiated manner and counting on the mechanical clearance between screw shafts and ball nuts. Such advantages cannot be obtained when hydraulic drives are used for moving the tools. 
         [0041]    Further, unlike hydraulic drives, in the machine  10  there are no variations over time in bending parameters. 
         [0042]    Lastly, the machine  10  requires low maintenance and thus enables production costs to be lowered. 
         [0043]    A simplified machine embodiment can also be obtained that provides a sole sheet metal pressing tool and not a bar with several sheet metal pressing tools. 
         [0044]    It is clear that variants of and/or additions to what has been disclosed and illustrated above can be provided. 
         [0045]    Also more than two electric motors can be provided to drive a single tool, in function, for example, of the length of the tool. 
         [0046]    Also the system of transmission via threaded shaft and ball nut can be replaced by an equivalent transmission system, even if the disclosed and illustrated transmission system is particularly effective. 
         [0047]    Obviously, there can be variations in the number of tools and configuration versions and arrangement of the various parts of the disclosed and illustrated machines. 
         [0048]    In  FIGS. 8-13 , the machine  10  also includes a positioning unit  50  of the sheet metal to be bent. 
         [0049]    The positioning unit  50  comprises a supporting rack  51  on which a series of longitudinal belt-shaped brush surfaces  52  is mounted that are parallel to one another and have the function of supporting the sheet metal to be positioned. 
         [0050]    In the central part of the positioning unit  50 , between the belt-shaped surfaces  52 , a gap is obtained along which a rotating board  53  runs that is provided with suction cups  54  activated by a pneumatic system that is not illustrated. 
         [0051]    For the movement, with particular reference to  FIGS. 11, 12 , the rotating board  53  is mounted on a carriage  55  that is movable along longitudinal guides  56 . An electric motor M 6  is integral with the board  53 , which electric motor M 6  is connected, via a reduction gear  57 , to a pinion  58  that engages a longitudinal rack  59 . An angular position transducer of the shaft of the motor M 6  is provided that is not illustrated. 
         [0052]    For rotation, with reference to  FIG. 12 , a further electric motor M 7  is provided that is integral with the board  53  and connected via a reduction gear  60  to a known kinematic mechanism, for example a worm screw and helical ring gear, which is not illustrated, which transmits rotation of the shaft of the motor M 7  to the board  53 . In this case, there is also provided an angular position transducer of the shaft of the motor M 7 , which is not illustrated. 
         [0053]    The motors M 6  and M 7  and the respective angular transducers are connected to the command and control unit U of the machine  10 . 
         [0054]    On the front part of the positioning unit  50  a series of reference stakes is provided that enable the sheet metal to be placed initially in a correct manner on the unit  50 . 
         [0055]    With reference to  FIGS. 8, 10, 13 , a transverse row of reference stakes  61  is provided that are mounted on a fixed frame  62  and a pair of reference stakes  63  mounted on a movable frame  64  and arranged along an axis intersecting the axis along which the stakes  61  are arranged. 
         [0056]    The operation of the positioning unit  50  is as follows. 
         [0057]    The rotating board  53  is taken to the front part of the machine when the motor M 6  is driven. The sheet of sheet metal is rested on the rotating board  53  and on the belt-shaped surfaces  52 . The reference stakes  61  and  63  enable the sheet metal to be positioned correctly by placing the sheet metal at the reference stakes  61  and  63 . 
         [0058]    At this point the suction cups  54  are activated to hold the sheet metal on the rotating board  53  and the rotating board  53  is then moved to take the sheet metal to the rear part of the positioning unit  50  so that one side of the sheet metal is on the tool  18 . 
         [0059]    The machine  10  bends the side of the sheet metal in the manner seen above. 
         [0060]    If it is desired to bend another side of the sheet metal the motor M 7  is activated to rotate the rotating board  53  and take another side of the sheet metal to the tool  18 . 
         [0061]    After bending of the sides of the sheet metal has terminated, the rotating board  53  with the sheet metal is returned to the front part of the positioning unit  50  to remove the machined sheet metal. 
         [0062]    The angular transducers of the motors M 6  and M 7  provide to signal to the central unit U the position of the rotating board  53  for precision positioning of the sheet metal. 
         [0063]    A machine is thus obtained for sheet metal bending with a very simple and effective positioning unit. 
         [0064]    It is clear that also with regard to the positioning unit, variations and/or additions are possible, for example in the configuration and in the number of the elements.