Abstract:
The invention relates to a press having a direct electric drive, without any motion transmitting apparatus, such as, for example, gears or gear drives wherein the electric direct drive is located between an eccentric  3  and a connecting rod  6  and brings about a relative movement between the eccentric  3  and the connecting rod  6.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This is a continuation-in-part application of pending international application PCT/EP2009/054624 filed Apr. 17, 2009 and claiming the priority of German Application No. 10 2008 028 652.4 filed Jun. 18, 2008. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention resides in a press with a press drive, for example, for the manufacture of metal sheet parts or for the deformation of massive metal components. 
     In the present state of the art, in the deformation of metal sheets for same time, mechanically driven presses with fly wheel drives have been used. In such presses, the travel-time curve of the plunger as generated by the kinematics of the drive which transmits the drive energy of the fly wheel to the plunger is predetermined. Changes in the travel-drive curve are only possible in connection with a stroke change. The striving for more productive manufacturing processes and the continually increasing requirements in the drawing processes resulted lately in the use of so-called servo presses in the shaping of sheet metal parts. 
     These servo presses are equipped with variable servo drives capable of generating different press forces. These presses are driven by one or several servomotors, which act directly on the drive train, without a fly wheel and without a clutch. In servo presses with relatively large press forces, high-moment torque motors are often used. With respect to speed and direction of rotation these motors can be controlled in a flexible manner so that they are programmable for different travel-time curves of the plunger. Curves from a sine-shaped course of an eccentric press, the curves of toggle joint lever drives or component design-specific curves may be established. The plunger can be independently positioned, it can be braked at any location or accelerated and it may even be operated in an oscillating back and forth movement by reversing the eccentric between two points. 
     Such a servo press is disclosed, for example, in DE 10 2004 009 256 B4. The press described herein includes several servomotors which jointly operate a plunger. The servomotors act on the plunger via a drive which has a mass moment of inertia. This mass moment of inertia may be increased by an additional fly wheel, if desired. However, altogether the resulting mass inertia moment is selected so as to be less than that of conventional presses in which the fly wheel stores sufficient energy to complete a working stroke. It is rather so small that the servomotors can accelerate the fly wheel from a stand still and again brake it to a stand still. With such a design, it is possible to operate the presses on one hand in a reversing operation with variable strokes wherein, on the other hand, high press forces can be obtained with the aid of the fly wheel. 
     It is, however, a disadvantage of this solution that in spite of drive simplifications, complicated and costly movement transmission means in the form of gears are still needed. DE 41 09 796 C2 discloses an arrangement for pressing, bending and punching of metal work pieces wherein a servomotor acts directly on an eccentric. With this arrangement the stroke length, as well as the press forces, are to be changed a simple manner. In addition, by an axial guiding of the plunger, it&#39;s surface of contact with the workpiece is to remain unchanged. A disadvantage of this solution however is surely a limitation to very small press forces. For large deformation presses with several pressure points, such an arrangement is not suitable. 
     Based on this state of the art, it is the object of the present invention to provide a press having a press drive which on one hand is capable to generate high press forces with a variable plunger movement and, on the other hand is of simple design and cost effective. 
     SUMMARY OF THE INVENTION 
     With reference to  FIGS. 1A and 1B , the invention relates to a press having a press drive, without any motion transmitting means, such as, for example, gears or gear drives wherein a direct electric drive  35  is located between an eccentric  3  and a connecting rod  6  and brings about a relative movement between the eccentric  3  and the connecting rod  6 . 
     The basic concept of the invention provides a press having a press drive with a direct electric drive without motion transmission means as, for example, gears or gear drives. This is achieved in that in a press drive having an eccentric is provided with a direct electric drive consisting of a rotor and a stator are used which act directly on the, one or several, connecting rods. The direct electric drive directly drives one eccentric or several eccentrics which are rotatably connected to the connecting rods. In principle, several variations of the press drive according to the invention are possible. In the preferred embodiment of the invention, the direct electric drive is disposed between an eccentric and a connecting rod rotatably supported on the eccentric. The eccentric is provided at its outer circumference with a number of permanent magnets corresponding to a desired press force. At the inner surface of the connecting rod eye facing the permanent magnets—coils are arranged. The operation of the direct electric drive of the press drive according to the invention corresponds essentially to the mode of operation of a permanent magnet synchronous motor. There is a difference in the mode of operation of the rotor and the stator in relation to the overall system. Which in a conventional permanent magnet synchronous motor the stator is stationary and the rotor rotates concentrically around the stator, in the direct electric drive according to the invention also the stator moves relative to the overall system of the press because of the eccentricity of the permanent magnet arrangement relative to the eccentric shaft. However, if the movement of the inner eye surface of the connecting rod relative to the outer surface of the eccentric is considered, the mode of operation corresponds to that of a rotor-stator structure of a permanent magnet synchronous motor. 
     The connecting rod is rotatably connected to the eccentric preferably via a friction bearing. In this way it is ensured, that between the permanent magnets which are arranged at the outer circumference of the eccentric and the windings which are arranged on the eye surface of the connecting rod, a gap of predetermined size is provided. Only two components of each press drive are connected with the surrounding structure. The eccentric shaft is rotatably supported at the head end. Common types of bearings known in the art may be used. The second connecting point is at the plunger. It is a design that is used in a conventional mechanical press. A bolt which is supported in the center of a connecting rod eye or bore, is rotatably supported at its outer end in the plunger or, respectively, in the pressure point of the plunger. In contrast to the conventional drives, the connecting point in the plunger serves the purposes for the press drive according to the invention, in addition to providing the motion on force transmission in the vertical direction, also, functions as a moment bearing. The drive moment is supported in the plunger bearing via plunger guide structures on the press frame. As a result, a separate moment support structure is not needed in connection with the press drive according to the invention. 
     Further advantages and particulars of the invention will become more readily apparent from the following description of advantageous embodiments with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a side view of the press drive according to the invention; 
         FIG. 1B  shows the press drive in an axial cross-sectional view; 
         FIG. 2  shows the press drive according to the invention in connection with a double toggle lever joint; and, 
         FIG. 3  shows two press drives according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1A  shows a direct press drive  1  according to the invention in a side view and  FIG. 1B  shows it in an axial cross-sectional view. Shown in the  FIGS. 1A and 1B  is an eccentric shaft  2  which is rotatably supported in a frame head piece  25  which is not shown in detail in the drawings. The eccentric shaft  2  is provided with an eccentric  3  and rotates it about the axis of the eccentric shaft  2 . At the outer circumference of the eccentric  3  numerous permanent magnets  4  are securely arranged. In a preferred embodiment the eccentric  3  consists of aluminum. The number of the permanent magnets  4  or, respectively, the poles together with the geometrical shape of components determines the size of the torque that can be generated and of the resulting press force. Opposite the permanent magnets  4  there are windings  5  which are mounted to the inner surface of the eye or opening of the connecting rod  6 . Between the outer surface of the permanent magnets  4  and the opposite surface of the windings  5  there is an air gap of generally a few millimeters. When the windings  5  are energized, a circumferentially directed force is generated via the permanent magnets  4  which cause rotation of the inner surface of the connecting rod eye relative to the eccentric  3 . 
     A detailed description of the direct electric drive  35  electromagnetic actions effective between the permanent magnets  4  and the winding  5  is not necessary here since they correspond exactly to the operational principle of permanent magnet synchronous motors which are well known in the art. 
     The connecting rod  6  and the eccentric  3  are interconnected rotatably by friction bearings  7  as shown in  FIG. 1B . At the end of the connecting rod  6  remote from the drive, the connecting rod  6  is provided with a bore  8  in which a bolt  9  is supported by means of a friction bearing  10 . This bolt  9  is rotatably connected at its outer ends to the plunger  11 . The plunger  11  is guided by the support frame  12  via a linear guide structure (not shown) in such as way that it is movable in vertical direction. When now, the eccentric  3  is isolated by the direct electric drive relative to the connecting rod  6 , the plunger  11  is moved vertically because the shaft  2  of the eccentric  3  is rotatably supported at its opposite ends on the frame head piece  25  and the bolt  9  is rotatably connected to the plunger  11 . 
       FIG. 2  shows another embodiment of the press drive  1  according to the invention. The drive arrangement for the connecting rod  13  corresponds to the drive arrangement as shown in  FIG. 1 . Between an eccentric  14  which is connected to a support shaft  15  and the connecting rod  13  the active elements of the direct electric drive, here the permanent magnets  16  and the windings  17 , are disposed. The permanent magnets  16  are operatively securely arranged on the outer surface of the eccentric  14  proximate the windings  17  mounted at the inner surface of the connecting rod eye. It is noted however, that vice versa, the permanent magnets could be arranged on the connecting rod  13  and the windings  17  on the eccentric. In the exemplary embodiment shown in  FIG. 2 , an enhanced press drive  1  is provided wherein the driven connecting rod  13  is not directly connected to the plunger  19 , but in this case, via a double toggle lever mechanism  18 . The double toggle joint lever mechanism  18  comprises a left hand toggle lever mechanism  20   a  and a right hand toggle lever mechanism  20   b . Each of the two toggle lever mechanisms  20   a ,  20   b  comprises an upper lever  21   a ,  21   b  and a lower lever  22   a ,  22   b . The upper levers  21   a  and  21   b  are connected to the lower levers  22   a ,  22   b  via connecting structures  23   a ,  23   b . The upper levers  21   a ,  21   b  are pivotally supported via the pivot joints  24   a ,  24   b  at the frame head piece  25 . The lower levers  22   a  and  22   b  are connected to the plunger  19  at the pivot points  26   a ,  26   b . The struts  29   a  and  29   b  are connected at their ends remote from the direct electric drive at the pivot points  27   a ,  28   a  to left hand (remote) toggle lever mechanism  20   a  and at the pivot points  27   b ,  28   b  to the right hand toggle mechanism  20   b  at the end of the connecting rod  13 . When now the connecting rod  13  is moved by the driven eccentric  14 ; that movement is transmitted via the double toggle lever mechanism  18  to the plunger  19  in such a way that it performs a vertical up and down movement. 
       FIG. 3  shows another exemplary embodiment of press according to the invention. In addition to the drive arrangement already shown in  FIG. 1  the two press drives  1  shown in  FIG. 3  include connecting rods  30  which are linked to the frame head piece  34  by way of links  32  by means of pivot joints  31  and  33  providing for a kinematics with much increased pressure focus near the bottom dead center position of the plunger structure similar to a toggle lever drive. With this kinematics relatively small press drives can be used which provide for relatively large pressure forces where they are needed that is near the bottom dead center position of the press drive. The two press drives  1  have no mechanical synchronization, for example, in the form of intermediate gears. Synchronization is provided electronically by the control of the direct electric drive. With such an electronic control, also a tilt movement of the plunger can be obtained by a predetermined unsynchronous drive control. If such a tilt control is used, provisions must be made for the plunger guide structure that parallelity deviations of the plunger can be accommodated. 
     The press drive  1  of the present invention can be used in connection with single-joint or multi-joint drives. Preferably the connecting rods  6 ,  13  of the present invention consist of a fiber-reinforced material. 
     The invention is not limited to the described exemplary embodiment. It encompasses also all variations within the frame of the inventive concept. 
     REFERENCE NUMERALS 
     
         
         
           
               1  press drive 
               2  eccentric shaft 
               3  eccentric 
               4  permanent magnets 
               5  windings 
               6  connecting rod 
               7  friction bearing 
               8  bore 
               9  bolt 
               10  friction bearing 
               11  plunger 
               12  machine frame 
               13  connecting rod 
               14  eccentric 
               15  support shaft 
               16  permanent magnets 
               17  windings 
               18  double toggle lever joint mechanism 
               19  plunger 
               20   a  left hand toggle lever mechanism 
               20   b  right hand toggle lever mechanism 
               21   a, b  upper lever 
               22   a, b  lower lever 
               23   a, b  connecting structure 
               24   a, b  pivot joints 
               25  frame head piece 
               26   a, b  pivot points 
               27   a, b  pivot points 
               28   a, b  pivot points 
               29   a, b  struts 
               30  connecting rod 
               31  pivot joints 
               32  links 
               33  pivot joints 
               34  frame head piece 
               35  direct electric drive