Patent Publication Number: US-9889621-B2

Title: Press and method for pressing workpieces

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a 35 U.S.C. § 371 U.S. National Stage of PCT/EP2012/051789, filed Feb. 2, 2012, which claims priority to German Patent Application No. DE 10 2011 000 473.4, dated Feb. 2, 2011. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a press for pressing workpieces and a method for pressing workpieces. 
     2. Background and Relevant Art 
     Various forming machines (presses) (see, for example, VDI-Lexikon Band Produktionstechnik Verfahrenstechnik [Production Engineering Process Engineering], Publisher: Hiersig, VDI-Verlag, 1995, pages 1107 to 1113) are known for pressing workpieces in the case of cold forming, in particular in the case of sheet metal forming, or warm forming, in particular in the case of forging of metallic forgeable materials. At least one slide with a first pressing tool of the press is driven by a drive and moved relative to a second pressing tool of the press so that the workpiece can be formed by pressing forces between the pressing tools. 
     The mechanical presses which generally operate in a travel-dependent manner use mechanical drives, for example, servomotor drives, with a very wide range of transmission mechanisms, for example, eccentric drive mechanisms (eccentric presses) or toggle drive mechanisms (toggle presses). The forming force or slide force is dependent on the travel or the position of the slide. 
     The mechanical components of mechanical presses are subject to significant strain as a result of the high forces which occur during pressing operations, as a result of which their performance is limited. Weight compensation of the slide is furthermore generally required. 
     The hydraulic presses which generally operate in a force-dependent manner use a hydraulic drive by means of a hydraulic medium such as oil or water, the pressure energy of which is converted by pistons running in hydraulic cylinders into mechanic forming work. The slide force corresponds to the product of hydraulic pressure and piston surface and is largely independent of the position of the slide. The hydraulic drive of the piston can be a direct pump drive with a motor-driven controllable pump (see e.g. DE 196 80 008 C1) or also a hydraulic accumulator drive with a pressure accumulator and motor-driven pump for producing the pressure in the pressure accumulator. The technical and energy outlay for output-regulated hydraulic pumps is nevertheless relatively high. 
     BRIEF SUMMARY OF THE INVENTION 
     The object of the invention thus lies in making available a new press and a new pressing method. 
     This object is achieved according to the invention by a press with the features of claim  1  and a method according to claim  7 . Advantageous configurations and further developments of the inventions will become apparent from the dependent claims. 
     A movement profile refers in particular to a travel/time profile or speed/time profile or speed/travel profile or force/time profile or force/travel profile. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is explained in greater detail below on the basis of exemplary embodiments. Reference is also made to the drawings, in which: 
         FIG. 1  shows a hydraulic press with an eccentric drive mechanism, in the case of which the working piston is in an upper position, in a circuit diagram, 
         FIG. 2  shows the press according to  FIG. 1 , in the case of which the working piston is in a lower position, 
         FIG. 3  shows a hydraulic press with a pump drive mechanism for the working piston, wherein the working piston is in an upper position, in a circuit diagram, and 
         FIG. 4  shows the press according to  FIG. 3 , in the case of which the working piston is in a lower position, in each case schematically. Corresponding parts and variables are provided with the same reference numbers in  FIGS. 1 to 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In all the exemplary embodiments of hydraulic press  1  according to  FIGS. 1 to 4 , said press  1  comprises a slide  10  and a hydraulic slide drive unit  1  with a hydraulic working piston  2  which is hydraulically movable axially with respect to working axis A in an associated hydraulic or working cylinder  3  filled with hydraulic medium M. A first piston region  21  of working piston  2  adjusted in terms of its outer diameter to the inner diameter of working cylinder  3  and sealed off from the inner surface of working cylinder  3  separates in this case a lower cylinder space  32  of working cylinder  3  from an upper cylinder space  31  in a pressure-tight manner—at least within leakage tolerances. A second piston region  22  of working piston  2  configured to be smaller in terms of outer diameter than first piston region  21  and formed here as a piston rod runs through lower cylinder space  32  so that only the annular or hollow-cylindrical region of lower cylinder space  32  surrounding second piston region  22  is filled with hydraulic medium M. 
     Working piston  2  moves slide  10 , coupled or fastened thereon, of press  1  on which a pressing tool  15  is located. As a result, pressing tool  15  can be moved in individual working steps in a pressing movement or in a pressing direction P towards a workpiece, not shown, to be pressed, which is located on a second pressing tool  16  and, in a subsequent return movement, back away from there or opposite to the pressing direction. 
     In the case of a forward movement of working piston  2  along working axis A, which is carried out in pressing direction P, volume V 1  of upper cylinder space  31  increases and volume V 2  of lower cylinder space  32  decreases and, in the case of the return movement of working piston  2  opposite to pressing direction P, volume V 1  of upper cylinder space  31  increases and volume V 2  of lower cylinder space  32  increases again. 
       FIG. 1  shows an upper position of working piston  2 , in the case of which first piston region  21  has a distance x 1  from the upper wall of working cylinder  3 , and  FIG. 2  shows a lower position of working piston  2 , in the case of which first piston region  21  has a distance x 2  from the upper wall of cylinder  3 , wherein difference Δx=x 2 −x 1  represents the maximum working stroke or maximum travel of working piston  2  along working axis A. The corresponding volume difference in the case of maximum working stroke Δx is ΔV 1 =Δx A 1  in upper cylinder space  31 , wherein A 1  is the surface area of the upper active cross-sectional surface of piston region  21  of working piston  2 , and ΔV 2 =Δx A 2  in lower cylinder space  32 , wherein A 2  is the surface area of the lower active cross-sectional surface, which annularly surrounds piston region  22 , of piston region  21  of working piston  2 . Slide  10  coupled to working piston  2  correspondingly travels an axial distance or vertical stroke between an upper position z 1  (in the case of distance x 1  of the working piston) and a lower position z 2  (in the case of distance x 2  of working piston  2 ), which corresponds to a maximum vertical working stroke Δz=z 2 −z 1  of slide  10 . 
     In general terms, slide drive unit  1  comprises a working body which is guided hydraulically in a working chamber, which is formed in the exemplary embodiment as working cylinder  3 , and is formed in the exemplary embodiment as drive piston  2  which separates the working chamber into a first, preferably upper, sub-chamber and a second, preferably lower, sub-chamber. The invention is not restricted to the formation and arrangement indicated in the exemplary embodiment of the working chamber and its sub-chambers and of the working piston. For example, a cross-section which deviates from a cylinder, a horizontal arrangement of movement or also a different form of the working body or an arrangement which is, for example, star-shaped or intersected at 90°, of several working bodies and working chambers with respective slides for joint machining of a workpiece are also possible. 
     A controllable valve  4  is connected hydraulically to upper cylinder space  31 , which controllable valve  4  is connected between upper cylinder space  31  and a medium reservoir  5  for hydraulic medium M. Control connections for opening and closing valve  4  are designated by S 1  and S 2 . In the open state of valve  4 , medium M can flow from or into medium reservoir  5  as a function of the present pressure difference, but cannot in the closed state of valve  4 . 
     A delivery unit  60  of a servo pump  6  is furthermore connected hydraulically between medium reservoir  5  and upper cylinder space  31 . Hydraulic connection line between servo pump  6  and upper cylinder space  31  is designated by  36 . Delivery unit  60 , for example, a screw conveyor or a delivery pump wheel or an internal gearwheel of an internal gearwheel pump, can be driven by means of an output shaft  62  of a servomotor  61  and indeed in both delivery directions by reversal of the direction of rotation of output shaft  62  of servomotor  61  as shown. Servomotor  61  is connected via an electric line  56  to an electric converter  55  which is in turn connected via an electric line  53  to control device  50   
     A further servo pump  7  is connected via a hydraulic connection line  37  to lower cylinder space  32  of working cylinder  3 . Delivery unit  70  of second servo pump  7  is connected between connection line  37  and medium reservoir  5 , which delivery unit  70  is again driven in the direction of delivery via an output shaft  62  by a servomotor  71  so as to be switchable, wherein in particular the direction of rotation of servomotor  71  can be reversed. Servomotor  71  is connected via an electric line  57  to converter  55 . 
     A pressure transducer  14  assigned to front cylinder space  32  is connected into connection line  37 , which pressure transducer  14  is connected via a line  54  to control device  50 . 
     Unless indicated otherwise, electric lines are marked by dashed lines in  FIGS. 1 to 4  and hydraulic lines are marked by continuous lines and mechanical connections are likewise marked by continuous lines. The term line or control line comprises both wire-connected and wireless, e.g. optical or radio-supported, transmission or connection passages 
     A check valve  44  is furthermore connected in each case into hydraulic connection lines  36 ,  37  and  39 , which check valve  44  is connected to medium reservoir  5  and respective servo pump  6 ,  7  and  17  is protected from idling. 
     Finally, upper cylinder space  31  and lower cylinder space  32  are assigned in each case an overload safety device  13  which is connected to medium reservoir  5  and limits the hydraulic pressure for protection of the components exposed to hydraulic pressure from overloading. 
     In the exemplary embodiment according to  FIGS. 1 and 2 , upper cylinder space  31  of working cylinder  3  is in hydraulic connection via a connection channel  38  to a drive cylinder space  82  of a drive cylinder  80  of a drive unit  8  for working piston  2 . Drive cylinder space  82  and connection channel  38  are likewise filled with hydraulic medium M. 
     Volume V 3  of drive cylinder space  82  can be changed by a drive piston  81  which is axially movable in drive cylinder  80  and can be driven via a connecting rod, in particular a main rod,  98  of an eccentric unit  9 . Connecting rod  98  mechanically connects drive piston  81  to an eccentric  92  on an eccentric disk  91 . Eccentric axis E of eccentric  92  runs eccentrically in a radius r about an axis of rotation D of eccentric disk  91  in the case of its rotation about an angle of rotation φ. A drive motor  18 , in particular a torque motor with a high torque, is provided as the rotational drive for eccentric disk  91 , which drive motor  18 , preferably via a transmission  19 , drives eccentric disk  91  in the case of a reversible direction of rotation of drive motor  18  or of transmission  19  and which is connected via an electric line  58  to converter  55 . 
     In the position according to  FIG. 1 , eccentric axis E lies on a horizontal H through axis of rotation D and connecting rod  98  runs substantially vertically between eccentric  92  and drive piston  81 . In the position according to  FIG. 2 , eccentric disc  91  is further rotated with eccentric  92  about an angle of rotation φ=90° and eccentric axis E now lies on a vertical V, which runs through axis of rotation D, and indeed below axis of rotation D so that connecting rod  98  now runs obliquely between eccentric  92  and drive piston  81 . Axis of rotation D can, however, also lie precisely perpendicularly above the center of drive piston  81 . 
     An axial movement of drive piston  81  results from this eccentric movement of eccentric unit  9 . The distance of drive piston  81  from the lower wall of drive cylinder  80  is designated by y 1  in  FIG. 1  and by y 2  in  FIG. 2 , wherein y 1 &gt;y 2 . Difference Δy=y 1 −y 2  between the positions in  FIG. 1  and  FIG. 2  is the maximum working stroke of drive piston  81  and corresponds on the drive side to the eccentric rotation of eccentric  92  about angle of rotation φ=90° on one hand and on the output side to maximum working stroke Δx of working piston  2  and correspondingly to maximum working stroke Δz of slide  10  on the other hand. 
     Maximum working stroke Δy and also the pressing or forming force which can be achieved are dependent on radius r of eccentric  92 , on the selected or set maximum angle of rotation φ and on the length of connecting rod  98 , which are all referred to below as eccentric parameters. The volumetric difference of volume V 3  of drive cylinder space  82  which corresponds to this maximum working stroke Δy is ΔV 3 =Δy A 3 , wherein A 3  is the surface area of the lower active cross-sectional surface of drive piston  81 . 
     As a result, the pressure in medium M changes and/or, in the case of a reduction in volume V 3  by movement of drive piston  81  downwards in  FIGS. 1 and 2 , medium M flows from drive cylinder space  82  via connection channel  38  into lower cylinder space  31  of working cylinder  3  or vice versa. 
     Surface A 3  of drive piston  81  is generally selected to be smaller than upper surface A 1  of working piston  2 , wherein the ratio is determined according to the desired transmission of force which is proportional to the respective surfaces across the substantially equal pressure. 
     Drive unit  8  and eccentric unit  9  with drive motor  18  jointly form a first hydraulic delivery device which is connected hydraulically on one hand to the first sub-chamber of the working chamber and on the other hand to the medium reservoir and can be reversed in terms of its direction of delivery and represents a mechanical-hydraulic hybrid drive. This design provides high forming forces even or precisely at the end of the pressing travel (as a result of the variable transmission of the sinusoidal kinematics) in the case of increasing forming forces and is also particularly suitable for compression or for cold forming or for holding the slide in specific force-loaded positions, e.g. in the case of heat treatment (annealing) or for flowing operations in the workpiece. Servo pump  7  is one exemplary embodiment of a second hydraulic delivery device which is connected hydraulically on one hand to the second sub-chamber of the working chamber and on the other hand to the medium reservoir and can be reversed in terms of the direction of delivery. 
     Servo pump  6  however forms a third hydraulic conveying device which is connected hydraulically on one hand to the second sub-chamber of the working chamber and on the other hand to the medium reservoir and can be reversed in terms of the direction of delivery. This third hydraulic delivery device formed by servo pump  6  primarily serves to equalize leaks in the hydraulic system which can only be equalized to a limited extent by the eccentric drive due to the restricted stroke, but can additionally also be called on for assistance or as part of the first delivery device during pressing. 
     In the exemplary embodiment according to  FIG. 3  and  FIG. 4 , instead of eccentric drive  9  and drive unit  8  as the first conveying device, a servo pump  17  is provided with a delivery unit  170 , which is again driven via an output shaft  172  by a servomotor  171 , which is connected via a line  57  to converter  55 , and can be operated in both directions of delivery. Servo pump  17  is connected on one side via a hydraulic connection line  39  to rear cylinder chamber  31  of working cylinder  3  and on the other side to medium reservoir  5 . A pressure transducer  12  is provided in connection line  39  for measuring the pressure in connection line  39  and thus also of rear cylinder space  31 , wherein pressure transducer  12  is again connected via line  52  to control device  50 . The second delivery device is furthermore formed with servo pump  7 . 
     The third hydraulic delivery device formed with servo pump  6  thus serves in this embodiment according to  FIGS. 3 and 4  for assistance of the purely hydraulic first delivery device and operates in a parallel connection to this during pressing so that the delivery volumes are added together. 
     The axial position of slide  10  (or also of working piston  2 ) along the working stroke is measured by means of an associated position measurement device or by means of a travel measurement pick-up  11  which is connected via a line  51  to a control device  50 . 
     Control device  50  is also connected to a control connection  51  of controllable valve  4  via a line  59  in order to move the valve from the open into the closed or a less wide open state or vice versa. 
     Control device  50  is provided for control, in particular for open-loop control and/or closed-loop control and/or monitoring, of the working processes and individual components of the forming machine. 
     Control device  50  controls (or: performs open-loop or closed-loop control) via converter  55  drive motor  18  of the first hydraulic delivery device ( 8 ,  9 ) and servomotor  71  of the second hydraulic delivery device or servo pump  7  and via control connection S 1  controllable hydraulic valve  4  for automatic open-loop or closed-loop control of the volumetric flows and pressures as well as the direction of flow of the hydraulic medium between medium reservoir  5  and the first sub-chamber ( 31 ) of the working chamber ( 3 ) and between medium reservoir  5  and the second sub-chamber ( 32 ) of the working chamber. This control of the volumetric flows, pressures and direction of flow of the hydraulic medium by control device  50  is carried out as a function of the slide position of slide  10  measured by means of slide position measurement device  11  and of stored or desired movement profiles of the slide and/or possibly of input information from users. Control device  50  thus operates in a hydraulically open open-loop or closed-loop control circuit and must actuate the two delivery devices so that that they are precisely coordinated with one another. 
     Converter  55  preferably comprises a temporary energy reservoir, not shown in greater detail, with which electrical energy of at least one of the delivery motors generated by generation in one process phase is temporarily stored and used in a subsequent or later process phase for motor operation of at least one of the delivery motors, preferably of the respective other delivery motor of the respective other delivery device. In particular, at least one capacitor in an intermediate circuit of the converter or in a capacitor module or kinetic energy reservoir coupled to the intermediate circuit can be used as the temporary energy reservoir of the converter. 
     A SINAMICS energy management system used by Siemens in the SIMOTION control units for servo presses with direct driving of the slide via servo torque motors (cf. SIMOTION brochure E20001-A660-P620 from 2008, which can be obtained at www.siemens.de/umformtechnik) can be used as temporary energy storage systems, which SINAMICS energy management system is correspondingly adapted for the servo drives ( 60 ,  70 ,  18 ,  170 ) of the present hydraulic press. 
     A method for pressing a workpiece using the press according to the invention, in particular according to  FIGS. 1 and 2  or  FIGS. 3 and 4 , comprises the following method steps or sub-phases of each operational step or operating cycle which are checked by means of control device  50 : 
     1. overrunning (or: idle stroke) 
     2. pressing stroke 
     3. relief of pressure (or: decompression operation) 
     4. controlled return stroke. 
     In the case of the overrunning or idle stroke mentioned under Point  1  of working piston  2  and thus of slide  10 , working piston  2  moves or sinks downwards in cylinder  3  under the action of gravity, with valve  4  being at least partially opened by control device  50  in order to allow a comparatively large volumetric flow of hydraulic medium M to flow out of medium reservoir  5  into upper cylinder space  31 , and the second conveying device actuated by control device  50 , servo pump  7 , pumps medium M out of lower cylinder space  32  into medium reservoir  5 . Alternatively or additionally, servo pump  6  can also pump hydraulic medium M into upper cylinder space  31 . 
     Control device  50  preferably controls by means of converter  55  the delivery volumetric flow or delivery pressure of the second delivery device, servo pump  7 , so that the movement of working piston  2  is braked or also accelerated according to a defined movement profile, in particular travel/time profile or speed/time profile or speed/travel profile or force/time profile or force/travel profile, wherein working piston  2  moves at a defined starting point in the defined movement profile within a time provided in the movement profile or resulting therefrom. The starting point is fundamentally any desired point between the two end points of maximum working stroke Δx corresponding to a starting point of slide  10  between the two end points of maximum working stroke Δz of slide  10 . 
     In the embodiment according to  FIG. 3  and  FIG. 4  without an eccentric unit, the idle stroke can also be omitted, i.e. the starting point for the working stroke can be located at the very top or the total stroke can be equal to the working stroke. 
     The movement of working piston  2  and thus of slide  10  during overrunning or the idle stroke is compared with the position values of position measurement device  11  by control device  50  and correspondingly adjusted or regulated by controlling valve  4  and servo pump  7  and, where applicable, also servo pump  6 . 
     The starting point for the working stroke is preferably a point at which pressing tool  15  comes into contact with the workpiece and is thus braked which is detected or monitored by control device  50  by travel measurement by means of position measurement device  11 . 
     During overrunning or the idle stroke, torque motor  18  ( FIG. 1  and  FIG. 2 ) or servomotor  171  ( FIG. 3  and  FIG. 4 ) is stationary, valve  4  is open and servo pump  7  is in operation. By placing pressing tool  15  on the workpiece and stopping servo pump  7 , the overrunning or idle stroke movement of working piston  2  is stopped at the starting point of the working stroke. 
     Control device  50  begins with the pressing stroke mentioned under Point  2  which represents the actual pressing operation and during which the hydraulic pressure and thus the pressing forces are reduced. The pressing stroke is once again based on a stored, defined movement or force profile which is passed through from the starting point. 
     For the pressing stroke via converter  55 , control device  50  puts into operation torque motor  18  of eccentric drive mechanism  9  ( FIG. 1  and  FIG. 2 ) or servomotor  171  ( FIG. 3  and  FIG. 4 ) and closes valve  4 . Via eccentric drive mechanism  9  and drive unit  8  ( FIG. 1  and  FIG. 2 ) or servomotor  171  ( FIG. 3  and  FIG. 4 ), a working pressure is built up in rear cylinder space  31  of working cylinder  3 , which working pressure pushes slide  10  and pressing tool  15  fastened thereon for the pressing operation downwards into or against the workpiece and presses the workpiece into the second tool. The torque of torque motor  18  and the eccentric parameters as well as the transmission of force via drive unit  8  ( FIG. 1  and  FIG. 2 ) or the torque of servomotor  171  ( FIG. 3  and  FIG. 4 ) determine the pressing force during the pressing stroke. The working stroke or pressing travel of slide  10  during the pressing stroke can be set by setting angle of rotation φ (stroke adjustment) ( FIG. 1  and  FIG. 2 ) or via the angle of rotation of servomotor  171  ( FIG. 3  and  FIG. 4 ). 
     The pressing movement of working piston  2  or slide  10  again follows a movement profile defined in control device  50 , wherein the travel measurement again supplies via position measurement device  11  information about the location of slide  10 , which information is used via control device  50  and converter  55  for control of torque motor  18  ( FIG. 1  and  FIG. 2 ) or of servomotor  171  ( FIG. 3  and  FIG. 4 ) so that slide  10  can be driven in a travel-controlled manner. It is, however, alternatively also possible to provide pressure-dependent control or travel control with an upper pressure limit. An upper limit can be set for the torque of the respective drive motor (upper pressure limit) or a torque profile can be specified in a travel-dependent manner (pressure-dependent control). In the case of torque motor  18 , the torque is preferably specified dynamically so that the eccentric kinematics are taken into account. In the case of angles φ close to 90°, i.e. at the lower point, a higher hydraulic pressure can be generated with the same torque at torque motor  18 . 
     Servo pump  7  is shifted into a low torque mode during the pressing stroke or servomotor  71  is not energized, rather generates a generator current regeneratively as a result of the medium flowing through delivery unit  70  and displaced out of lower cylinder space  32 , the charge or energy of which generator current is temporarily stored by converter  55 . 
     If e.g. slide  10  must remain in a certain position at the working pressure during the pressing stroke, e.g. for flowing operations in the workpiece, servo pump  6  can be/remain activated in order to equalize leaks by refilling hydraulic medium M from medium reservoir  5  into upper cylinder space  31  (leakage pump). 
     The pressing stroke is terminated if, according to  FIG. 2 , slide  10  reaches its lower end position (bottom dead center). 
     Once slide  10  has reached its lower end point, control device  50  immediately begins the return movement. This initially begins with a passive operation, the pressure relief or decompression operation stated under Point  3 , in the case of which hydraulic medium M is again relieved of pressure by the compression volume which is dependent on the compressibility of medium M. Valve  4  remains closed. Torque motor  18  ( FIG. 1  and  FIG. 2 ) or servomotor  171  ( FIG. 3  and  FIG. 4 ) is shifted into a low torque mode, i.e. it can be easily rotated, the decompression of hydraulic medium M moves drive piston  81  upwards and, via eccentric disk  9 , torque motor  18  is moved in the opposite direction ( FIG. 1  and  FIG. 2 ) or servo pump  170  is rotated in the opposite direction together with servomotor  171  ( FIG. 3  and  FIG. 4 ) and feeds generator energy into converter  55  and its temporary energy reservoir. 
     Finally the controlled return stroke stated under  4  is carried out as the fourth and last step, in the case of which controlled return stroke servo pump  7  is once again put into operation by control device  50  via converter  55 , but in the opposite direction of delivery to overrunning, wherein the temporarily stored energy is reused by converter  55 . Servo pump  7  pumps hydraulic medium M via line  37  out of medium reservoir  5  into lower cylinder space  32  and increases the pressure there. Valve  4  is furthermore opened again. Working piston  2  and slide  10  is as a result lifted back into the starting position or also into a different starting position by means of servo pump  7 . As a result, displaced hydraulic medium M flows through open valve  4  out of rear cylinder space  31  into medium reservoir  5 . 
     In all the exemplary embodiments according to  FIG. 1  to  FIG. 4 , lower cylinder space  31  is assigned a pressure transducer  12  for monitoring and measuring the pressure. The signals of pressure transducer  12  are transmitted via a line  52  to control device  50 . In  FIGS. 1 and 2 , the pressure transducer is assigned a connection line  38  between a drive cylinder space of servo pump  17  and rear cylinder space  31 , while in  FIGS. 3 and 4  it is assigned hydraulic line  37  between servo pump  17  and rear cylinder space  31 . 
     Pressure transducer  12  measures the pressure for open-loop or closed-loop control of the pressure in particular for the working stroke. Pressure transducer  14  measures the pressure at front cylinder space  32  in particular also for a monitoring function, e.g. as to whether the workpiece is in contact with the pressing tool or is not even held against it which would be demonstrated in the differentiation of the threshold value for the pressure. 
     It is furthermore also possible to omit the idle stroke or overrunning in Step  1 , for example, only for a simple stroke as a working stroke, in the case of which only the eccentric operates, which occurs e.g. in the case of stretching. 
     One advantage of the press and the pressing method according to the invention lies in it being possible to set the working stroke or the upper working point the lower working point of the working stroke as desired within the total stroke or maximum working stroke and the overloading can be managed safely by the pressure relief valves at any point in the stroke. Moreover, no weight compensation of the slide is required as in the case of mechanical eccentric presses. Driving via eccentric unit delivers at the lower dead center or lower working point large torques along with smaller drive output than in the case of hydraulic presses. No output-regulated hydraulic pump is required. Moreover, no flywheel is required and the eccentric can also only operate in a partial angle range. 
     Servo pump  6  serves in particular to equalize leaks in the hydraulic system and can pump additional hydraulic medium out of medium reservoir  5  into the hydraulic system. 
     Servo pumps  6 ,  7  and  17  are in particular hydraulic servo pumps, for example, axial piston pumps, driven with position-regulated servomotors  61 ,  71  and  171 , which fix the pump rotors or pistons, and fitted with a hydraulic equalization reservoir, in particular medium reservoir  5 . 
     In principle, instead of pistons and cylinders, a different configuration for the hydraulic elements can be selected so that it is then possible to talk more generally about chambers instead of cylinders and sub-chambers instead of cylinder regions or bodies instead of pistons. 
     Instead of the servo pumps represented and drive unit  8 , other hydraulic delivery devices are furthermore also possible. 
     Hydraulic medium M can be an oil or also water or a mixture thereof or also a so-called HFA emulsion. The compression volume is generally higher in the case of oil than in the case of water and can, for example, be around 2 percent by volume at 300 bar. 
     LIST OF REFERENCE SIGNS 
     
         
         
           
               1  Slide drive unit 
               2  Working piston 
               3  Working cylinder 
               4  Return valve 
               5  Medium reservoir 
               6 ,  7  Servo pump 
               8  Drive unit 
               9  Eccentric unit 
               10  Slide 
               11  Distance meter 
               12  Pressure transducer (pressing) 
               13  Overload safety device 
               14  Pressure transducer (lifting) 
               15  Pressing tool 
               18  Drive motor (torque motor) 
               19  Transmission 
               21 ,  22  Piston region 
               31 ,  32  Cylinder space 
               36 ,  37  Connection line 
               38  Connection channel 
               39  Connection line 
               44  Pressure relief valve 
               50  Control device 
               51 ,  52  Line 
               53 ,  54  Line 
               55  Converter with intermediate circuit 
               56 ,  57  Line 
               58 ,  59  Line 
               60 ,  70  Delivery unit 
               61 ,  71  Servomotor 
               62 ,  72  Output shaft 
               80  Drive cylinder 
               81  Drive piston 
               82  Drive cylinder space 
               91  Eccentric disc 
               92  Eccentric 
               98  Connecting rod 
             A Working axis 
             M Hydraulic medium 
             H Horizontal 
             V Vertical 
             D Axis of rotation 
             E Eccentric axis 
             r Radius 
             φ Angle of rotation 
             x 1 , x 2  Height 
             Δx Stroke