Abstract:
The invention relates to hydraulic control in a hydraulic system for the operation of a machine tool such as a press for processing material of a certain type, especially for the operation of the scrap cutters. Said control allows for impact attenuation and combined rapid motion switching with load compensation and transfer of a hydraulic medium of a hydraulic cylinder for the movement of the other. According to the invention, said control comprises hydraulic media of a hydraulic cylinder for pre-control of a first main valve element ( 2.4.0 ), a second main valve element ( 2.7.0 ) and a third main valve element ( 3.7.0 ) which are functionally combined and a fourth valve ( 2.5 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a 371 national phase application of International Application No. PCT/DE03/01022 having an international filing date of Mar. 27, 2003, and which claims priority to German Application No. DE 102 23 267.9 filed May 24, 2002.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The invention relates to a hydraulic control in a hydraulic system for the operation of a machine tool such as a press for processing material of any desired type, such as presses and/or shears, in particular for shears for cutting metal scrap, as “scrap shears”.  
         [0004]     2. Prior Art  
         [0005]     Machine tools such as presses essentially comprise 
        a column having at least one hydraulic cylinder guided and fastened therein for driving a tamper, pressing or holding down the material, toward a table and at least one hydraulic cylinder guided and fastened therein for driving a tool, finally processing and cutting the material, toward a fixed tool in said table, and     a “hydraulic control” with tank, pumps, control blocks, valve elements and nozzles and also the hydraulic medium for the cyclic operation of the first and second cylinders.        
 
         [0008]     It is known to provide means in the hydraulic control which generate a damping pressure for damping a “(cutting) impact” at least in one of the hydraulic cylinders at the end of its working stroke, such as, for example, after the severing of metal scrap.  
         [0009]     The general problematic nature of these (cutting) impacts has been known for a long time and has already been described in detail in publications DE 28 08 091 A1, DE 28 24 176 A1, DE 29 09 118 A1, DE 35 34 487 A1, DE 22 21 290 C3, 29 DE 28 777 C2, DE 31 12 393 C2 and DE 195 29 134 A1.  
         [0010]     A useful and already known solution to the problem can be gathered from the preamble of the main claim of EP 0 765 203 B1, in which case this embodiment is to be advantageously augmented by the characterizing features such as 
        the control pressure corresponding to the damping pressure can be built up by inflow of control oil from the piston-side cylinder space of the working cylinder via a bypass line into the control space, and     a check valve which shuts off flow toward the piston-side cylinder space is arranged in the bypass line.        
 
         [0013]     The previously known hydraulic control can be effectively presented in the following steps with regard to the outflow relevant to the damping of the (cutting) impact (with reference to EP 0765203, also published as U.S. Pat. No. 5,832,807): 
    1. The cylinder descends with the cutter. A counterpressure is generated in the rod space  12  of the cylinder by means of a pressure valve  54 . The valve  54  interacts with the valve  31  as a two-stage pressure-limiting valve, the valve  31  constituting the main stage. The valve  38  is held by the spring in the position with throughflow P-A, since the control pressure in  40  at this instant is still low. The counterpressure in the rod space during the downward travel is necessary in order to hold the load attached to the cylinder. Without this counterpressure, the cylinder, due to the weight of the piston rod and the attached load G, would travel faster than predetermined by the pump quantity due to gravitational effects. This would result in a vacuum in the piston space  10 , and this vacuum can cause problems with the seals of the cylinder.     2. The cylinder, or the cutter, comes down on the material. The pressure in the piston space  10  increases, since the cylinder is no longer moved for the time being. The pump continues to deliver oil, which leads to a pressure increase in the piston space  10 . This pressure increase continues via the control line  62 , the valve  58  and the line  40  and leads to shifting of the valve  38  into position A-T. Accordingly, the control space of the valve  31  is connected via the nozzle  21  and the valve  38  to the tank; the valve  31  opens against the spring. As a result, the previously required counterpressure in the annular space  12  of the cylinder collapses. The cylinder can now apply the full desired force, defined by pressure times piston area, for cutting the material. The cutter cuts the material when the cutting force is reached.     3. The cutter is accelerated by the oil volume, acting as a spring, in the piston space. Immediately after the cutting, the pressure in the piston spaces  10  collapses through expansion. At the same time, the valve  38 , in the absence of control pressure, shifts back into basic position P-A. The oil flow produced by the accelerated cylinder is partly directed via the nozzle  36  and the valve  38  to the control space of the valve  31 . The top pressure on the annular-space side is limited, as in section  3 . 1 , via the two-stage pressure-limiting valve ( 54 / 31 ). This counterpressure already constitutes a (cutting) impact damping.     4. As can be seen under 2, before the cutting instant, the pressure in the piston space  10  is high and the pressure in the annular space  12  is relieved toward the tank. Since the pressure in the piston space  10  is now higher than in the annular space  12 , oil flows via the line  68  and the nozzles  70  and  36  and the check valve  72  from the piston space to the annular space and thus via the valve  31  to the tank. This oil flow multiplied by the applied pressure can adversely produce an unintentional power loss. 
        During the severing (as described in 3), the pressure in the piston space  10  collapses, at least partly. Since the pressure in the piston space  10  has decreased and pressure has been generated in the annular space by the accelerated cylinder, there is the risk that no oil can flow via the line  68 . The pressure gradient then becomes opposed to the check valve.     The line  68  will therefore also lead to a mutual effect instead of the assisting damping. Furthermore, it is to be emphasized that the valve  38  must first of all shift into the basic position for the desired (cutting) impact damping to come into effect. The precondition for this is that the pressure in the line  40  (thus previously in the piston space  10 ) must have collapsed. Thus, in particular cases, no oil can flow via the line  68  and accordingly via the valve  38 , since this at best requires additional means on account of the circuit logic and the oil required is fed via the nozzle  36  of the pilot control.    
       
 
         [0020]     In addition, the (cutting) impact damping present per se is accordingly to be assisted with simple means by the 4th step, which, however, does not appear possible without further means or may lead to further complications.  
         [0021]     The hydraulic controls already realized in industrial practice with the features (in accordance with the steps  1  to  3  described above) defined in the preamble of abovementioned EP 0 765 203 B1, in particular in scrap shears, have proved to be functional with regard to (cutting) impact damping; however, they are in need of improvement in the context of a complex hydraulic problem. With regard to the effectiveness of the technical means of the function described in step  4 , this would only be partly realizable and only if additional means were to be used. This means at least a considerable cost outlay.  
         [0022]     According to DE 43 12 283 A1, the search for solution approaches, such as, for example, in large, but continuously working channel baling presses, shows a control for a hydraulic heavy-duty actuator which is to be controlled under load from an extended working position into a return movement, a hydraulically pressurized working space of the actuator being connected to a return line of low pressure via a directional control valve, the valve position of which is set hydraulically via a control line which has at least one choke orifice.  
         [0023]     In this case, a pressure-stabilizing delay element is connected in between the directional control valve and the choke orifice.  
         [0024]     If the mode of operation of this control is analyzed with regard to the machine of the design mentioned at the beginning, valve operation for reducing relief impacts is certainly presented and a bracketed pressure from a system is reduced as smoothly as possible in order to reduce impacts extending into the tank line. However, the rapid buildup of a counterpressure in a cylinder and then also the limiting of this counterpressure by this measure is not possible.  
         [0025]     An approach to the solution of the present problem does not follow from this disclosure.  
         [0026]     The aim of building up a counterpressure as rapidly as possible and of limiting it in a cylinder of the machines of the generic type, taking into account their specific mode of operation, also cannot be achieved by the solution according to EP 1 186 783 A1. According to this, only the oil flowing off from the one cylinder is used for generally applying pressure to and driving a second cylinder. This effect is assumed to be known in order to actually fulfill the basic function of the hydraulic control in these machines.  
         [0027]     It can therefore be stated that the problem of the (cutting) impact damping by means of hydraulic control for presses defined at the beginning, in particular shears for cutting metal scrap, has hitherto not been solved comprehensively within the scope of the entire hydraulic system.  
         [0028]     Thus, the volume of the hydraulic medium provided by the pumps in hydraulic controls for machine tools such as presses, in particular shears for cutting metal scrap, constitutes a limit to the speed of the sequences of hydraulic cylinders, since the hydraulic medium flowing to the tank remains unused as a rule. There is also that fact that perpendicularly working hydraulic cylinders, such as in said presses or shears, with attached masses of, for example, tools impose special demands on the hydraulic control. If the annular space of the cylinder is simply relieved toward the tank during the downward travel of this cylinder, the extension being effected downward, the piston of the cylinder could descend due to the dead mass and the attached load and could possibly run in advance of the action of the pumps. This has an adverse effect at least on the service life of the cylinder seals and may also be disadvantageous for the entire hydraulic system.  
         [0029]     Finally, in conventional hydraulic controls for uses described above, with the simultaneous upward movement of two cylinders, the cycle time of the processing operation, such as after the shearing for example, is considerably restricted.  
       BRIEF SUMMARY OF THE INVENTION  
       [0030]     These problems, in their entirety, associated per se with the corresponding hydraulic system, such as 
        (cutting) impact damping with simple means and/or     rapid-motion control with load compensation and/or     oil transfer with increase in output 
 
 as a complex hydraulic control of the application described at the beginning, give rise to the definition of the object according to the invention. 
       
 
         [0034]     The object of the invention is to provide such a hydraulic control in a hydraulic system for the operation of a machine tool such as a press for processing material of any desired type, in particular for scrap shears, which, in a functional combination of partly known features, 
        produces (cutting) impact damping with little constructional outlay in terms of hydraulic means, with which (cutting) impact damping the maximum counterpressure on the annular-space side of the cylinder can be set at a higher level than in conventional solutions for generating a counterpressure,     links rapid-motion control with load compensation and uses the hydraulic medium flowing off in a conventional manner to the tank, and/or     for the purpose of reducing the cycle time and increasing the output of the machine, during the simultaneous upward movement of two cylinders, uses the outflowing hydraulic medium of one of the cylinders for driving or moving the other cylinder at the same pump delivery quantity.        
 
         [0038]     In effect, a complex hydraulic control in the hydraulic system for the operation of machine tools, such as presses, in particular scrap shears, is provided which, in addition to the solved problem of functionally simple but functionally fully effective impact damping, increases the output rates of the material to be processed without increasing the installed capacity and the construction cost, whereby the operator can also be provided with a machine having a higher energy service value.  
         [0039]     The invention is explained with reference to an exemplary embodiment according to the scheme of the hydraulic circuit for the operation of scrap shears with the aid of the drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0040]     The circuit corresponding to the hydraulic system according to the invention is schematically shown in the drawing. In the drawing, the line ______.______. outlines the actual control. A first hydraulic cylinder for the drive of a tool, such as a cutter slide with the cutter  1 . 1 . 3  which cuts the material, is shown in a simplified manner by  1 . 1 , and a second hydraulic cylinder for the drive of a further tool, such as a tamper  1 . 2 . 3  for holding down the material to be cut, is shown in a simplified manner by  1 . 2 .  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0041]     The hydraulic inlets or outlets for the hydraulic medium of the bottom space  1 . 1 . 2 ,  1 . 2 . 2  in both cylinders  1 . 1  and  1 . 2  are designated by A and those of the annular space  1 . 1 . 1 ,  1 . 2 . 1  are designated by B. T symbolizes the line to the tank (not shown), and P 1  and P 2  explain the connections to the pressure lines and the pumps (not shown).  
         [0042]     The basic circuit of the hydraulic control for the operation according to the invention of the scrap shears is first of all preset with a second valve  2 . 2  between the bottom space  1 . 1 . 2  of the first hydraulic cylinder  1 . 1  and the tank T and with a third valve  2 . 3  between the annular space  1 . 1 . 1  and the connection to the pressure supply P 1 .  
         [0043]     Furthermore, a fifth valve  3 . 3  is provided between the bottom space  1 . 1 . 2  of the second hydraulic cylinder  1 . 2  and the connection to the pressure supply P 2  and a sixth valve  3 . 2  between the bottom space  1 . 2 . 2  and the tank T.  
         [0044]     Finally, a seventh valve  3 . 3  is to be arranged between the annular space  1 . 2 . 1  and the connection to the pressure supply P 2  and an eighth valve  3 . 4  is to be arranged between the annular space and the tank T.  
         [0045]     The function essential to the invention of the hydraulic control, which acts in the hydraulic system in accordance with the definition of the object, is explained in more detail in subsections I, II and III below.  
         [0000]     I. Functional Part—(Cutting) Impact Damping  
         [0046]     In scrap shears, the cutter slide  1 . 1 . 3  with the connected piston of the cylinder is accelerated after the shearing of the material. The cause is a high pressure in the bottom space  1 . 1 . 2  of the cylinder  1 . 1  up to just before the cut. The compressed volume of the hydraulic medium acts as an energy store. The latter accelerates the cylinder  1 . 1  with cutter slide  1 . 1 . 3 . Before the cutting or shearing, the annular space  1 . 1 . 1  of the cylinder  1 . 1  is relieved. In order to counteract the acceleration of the cutter slide  1 . 1 . 3  and a resulting hydraulic impact, a counterpressure is generated in the annular space  1 . 1 . 1  of the cylinder  1 . 1 , this counterpressure being suitable for damping the hydraulic impact.  
         [0047]     At the instant directly before the material is cut through, a first valve  2 . 1  (not mentioned hitherto) between the bottom space  1 . 1 . 2  and tank T and also a pilot-control valve  2 . 4 . 3  (not mentioned), as further elements according to the invention, are in the operated position. As a result, the bottom space  1 . 1 . 2  is connected via the first valve  2 . 1  to the connection to the pressure supply P 1 , which is fed by the hydraulic pumps (not shown). The annular space  1 . 1 . 1  of the first hydraulic cylinder  1 . 1  is relieved toward the tank (not shown) via a first main valve element  2 . 4 . 0  with cap  2 . 4 . 1 .  
         [0048]     The drive motors (not shown) of the hydraulic pumps are protected against overload by a suitable output limit of the pumps. This output limit sets a lower delivery flow of the hydraulic medium at high pressures, so that the product of pressure and volumetric flow, which product corresponds to the hydraulic power, remains virtually constant. Accordingly, the volumetric flow of the hydraulic medium is low at high pressures compared with the volumetric flow at low pressures. The speed of the first hydraulic cylinder  1 . 1  is therefore also lower at high pressures compared with that at low pressures.  
         [0049]     The opening stroke of the first main valve element  2 . 4 . 0  is adapted by an integrated spring (not designated) to the volumetric flow via the relevant valve.  
         [0050]     During an abrupt rapid movement of the piston of the first hydraulic cylinder  1 . 1  (as described above), the first main valve  2 . 4 . 0  is now delayed in its opening movement by a nozzle  2 . 4 . 1 . 1  essential to the invention. At the same time, the pressure in the annular space  1 . 1 . 1  of the cylinder  1 . 1  is set by the pressure valve  2 . 4 . 2 , as pilot control of the first main valve element  2 . 4 . 0 , to the pressure set at the pressure valve  2 . 4 . 2 . The delay in the opening of the second main valve element  2 . 4 . 0  is surprisingly sufficient for generating a limited counterpressure and thus for (cutting) impact damping.  
         [0051]     Consequently, with simple means and in an advantageous manner, the maximum counterpressure on the annular space side  1 . 1 . 1  of the first hydraulic cylinder  1 . 1  can be set higher than in the previously known solutions for generating a counterpressure, whereby this partial solution can also be realized with less outlay in terms of construction.  
         [0000]     II. Functional Part—Rapid-Motion Control Linked with Load Compensation  
         [0052]     The delivery volume made available by the pumps has hitherto constituted a limit in the cylinder speed in hydraulic scrap shears, in which case the hydraulic medium flowing in a conventional manner to the tank is now to be utilized. Furthermore, perpendicularly working hydraulic cylinders  1 . 1  and  1 . 2  with attached loads due to the weight of the tools, such as cutter slide  1 . 1 . 3  and tamper  1 . 2 . 3 , are to be controlled in a special manner.  
         [0053]     If the annular spaces  1 . 1 . 1  and  1 . 2 . 1  were simply to be relieved toward the tank T during the downward travel of the cylinders  1 . 1  and  1 . 2 , in the course of which the extension is effected downward, the respective piston of the hydraulic cylinders  1 . 1  and  1 . 2  could descend due to the dead weight and the attached load of said tools and adversely move in advance of the action of the hydraulic pumps. This would have in particular adverse effects on the service life of the cylinder seals.  
         [0054]     As a countermeasure, in accordance with the object, during the downward travel in the respective annular space  1 . 1 . 1 ,  1 . 2 . 1 , a pressure is to be generated which is large enough to compensate for the attached load, such as the tools for example. It has been determined in pilot tests that a pressure difference between annular and bottom space  1 . 1 . 1 ,  1 . 1 . 2  and  1 . 2 . 1 ,  1 . 2 . 2  of the hydraulic cylinders  1 . 1 ,  1 . 2  is suitable for compensating for the load due to weight. At the same time, the hydraulic medium flowing off at B on the annular-space side is to be used for the purposes of a conventional rapid-motion control.  
         [0055]     By means of the circuit according to the drawing, both requirements are realized in a combined manner by virtue of the fact that a second main valve element  2 . 7 . 0  with cap  2 . 7 . 1 , intermediate plate  2 . 7 . 2 , pressure valve or choke (nozzle)  2 . 7 . 3  and directional control valve  2 . 7 . 4  and, similarly, a third valve element  3 . 7 . 0  with cap  3 . 7 . 1 , intermediate plate  3 . 7 . 2 , pressure valve or choke (nozzle)  3 . 7 . 3  and directional control valve  3 . 7 . 4  are arranged according to the invention.  
         [0056]     These circuits are especially advantageous for downward movements with a low counterforce on the hydraulic cylinders  1 . 1 ,  1 . 2 .  
         [0057]     The respective valve combination, from the second and third main valve element  2 . 7 . 0 ,  3 . 7 . 0 , interacts with a pilot-control arrangement which is formed by the cap  2 . 7 . 1 ,  3 . 7 . 1 , intermediate plates  2 . 7 . 2 ,  3 . 7 . 2 , pressure valves or chokes (nozzles)  2 . 7 . 3 ,  3 . 7 . 3  and the directional control valves  2 . 7 . 4 ,  3 . 7 . 4 .  
         [0058]     This pilot-control arrangement, in the linking according to the drawing, in combination with the respective main valve element  2 . 7 . 0 ,  3 . 7 . 0 , constitutes a controllable pressure valve having a check function, in which case the pressure on the annular-space side can be set relative to the pressure on the piston side so as to be matched to the hydraulic cylinders  1 . 1 ,  1 . 2 .  
         [0059]     An alternative combination of a separate rapid-motion valve with load-compensation function could constitute an optimum solution from the energy point of view.  
         [0000]     III. Functional Part—Transfer of the Hydraulic Medium  
         [0060]     During the simultaneous upward movement of two cylinders  1 . 1 ,  1 . 2  as described above, the outflowing hydraulic medium of one of the cylinders  1 . 1 ,  1 . 2  is to be used for moving the other cylinder  1 . 1 ,  1 . 2 . The quantity of hydraulic medium which is thus obtained compared with conventional concepts considerably reduces the cycle time of the press, in particular of scrap shears, at the same pump delivery quantity.  
         [0061]     The circuit according to the invention produces an increase in output compared with conventional concepts. The circuit for such use of the outflowing hydraulic medium is realized according to the invention by a fourth valve  2 . 5  between the bottom space  1 . 2 . 2  and the annular space  1 . 1 . 1 . In the circuit shown, the cylinder  1 . 1 ,  1 . 2  driven via the outflowing medium can be additionally driven with further pumps.  
       INDUSTRIAL APPLICABILITY  
       [0062]     Although the invention is specifically explained with regard to the hydraulic system of scrap shears, it can be applied to the operation of machine tools such as presses of the generic type mentioned at the beginning in which, to all intents and purposes, the complex problem of impact damping, rapid-motion control with load compensation, and/or transfer of the hydraulic medium between at least two hydraulic cylinders is to be solved.  
       LIST OF DESIGNATIONS  
       [0000]    
       
         
           
               1 . 1  First hydraulic cylinder for driving a tool such as  1 . 1 . 3   
               1 . 1 . 1  Annular space  
               1 . 1 . 2  Bottom space  
               1 . 1 . 3  Cutter slide with cutter  
               1 . 2  Second hydraulic cylinder for driving a tool such as  1 . 2 . 3   
               1 . 2 . 1  Annular space  
               1 . 2 . 2  Bottom space  
               1 . 2 . 3  Tamper for holding down the material  
               2 . 1  First valve between bottom space  1 . 1 . 2  and P 1   
               2 . 2  Second valve between bottom space  1 . 1 . 2  and tank T  
               2 . 3  Third valve between annular space  1 . 1 . 1  and P 1   
               2 . 4 . 0  First main valve element  
               2 . 4 . 1  Cap  
               2 . 4 . 1 . 1  Nozzle  
               2 . 4 . 2  Pressure valve  
               2 . 4 . 3  Pilot-control valve  
               2 . 5  Fourth valve between bottom space  1 . 2 . 2  and annular space  1 . 1 . 1   
               2 . 7 . 0  Second main valve element  
               2 . 7 . 1  Cap  
               2 . 7 . 2  Intermediate plate  
               2 . 7 . 3  Pressure valve or choke (nozzle)  
               2 . 7 . 4  Directional control valve  
               3 . 1  Fifth valve between bottom space  1 . 2 . 2  and P 2   
               3 . 2  Sixth valve between bottom space  1 . 2 . 2  and tank T  
               3 . 3  Seventh valve between annular space  1 . 2 . 1  and P 2   
               3 . 4  Eighth valve between annular space  1 . 2 . 1  and tank T  
               3 . 7 . 0  Third main valve element  
               3 . 7 . 1  Cap  
               3 . 7 . 2  Intermediate plate  
               3 . 7 . 3  Pressure valve or choke (nozzle)  
               3 . 7 . 4  Directional control valve  
              A Inlet/outlet, bottom space  
              B Inlet/outlet, annular space  
              Connection to the pressure supply  
              Connection to the pressure supply  
              T Connection to the tank