Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B30—PRESSES
  • B30B—PRESSES IN GENERAL
  • B30B15/00—Details of, or accessories for, presses; Auxiliary measures in connection with pressing
  • B30B15/0094—Press load monitoring means
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B30—PRESSES
  • B30B—PRESSES IN GENERAL
  • B30B15/00—Details of, or accessories for, presses; Auxiliary measures in connection with pressing
  • B30B15/14—Control arrangements for mechanically-driven presses

Definitions

• the present invention relates to a method for operating an electric press, the electrically operated press ram, at least one displacement sensor for detecting positions of the path of the press ram during its working stroke, at least one force transducer for detecting workpieces to be machined by the press ram during the working stroke applied pressing force, and includes a control, which controls the stroke in terms of distance and pressing force, with the steps:
• the known method is carried out on an electric press which comprises a spindle drive driven by an electric motor.
• the threaded spindle of the spindle drive is rotatably but axially immovable, while the spindle nut is non-rotatably but axially displaceably and is connected to the press ram.
• the electric press has displacement transducers and force transducers in order to record the course of the pressing force over the path of the press ram during its working stroke and to report it to a controller which controls the working stroke on the basis of this information.
• the press ram is moved into its starting position above the workpiece and then lowered onto the workpiece or workpieces to be machined. During this lowering, the pressing force is measured and it is recognized from an increase in this pressing force that the pressing process begins, whereupon the lowering speed of the press ram is reduced.
• the press ram is further lowered, the applied pressing force being monitored to determine whether it remains constant during the pressing process. Furthermore, the path of the press ram continues to be monitored in order to recognize the reaching of a joining position called the end position, in which the press ram does not substantially lower. When this end position has been reached, the press ram is moved back.
• the known method stops the pressing process because the end position is not reached and / or the pressing force is not constant, which is what can lead to unnecessary waste. Proceeding from this, it is an object of the present invention to further develop the method mentioned at the outset in such a way that gentle processing even of coarser tolerated parts is possible in order to avoid unnecessary rejects or to reduce the rejects.
• this object is achieved according to the invention in that, depending on the course of the pressing force, parameters are dynamically adapted via the path of the press ram, which indicate a successful course and / or completion of the pressing process.
• the inventors of the present application have recognized that the high rejection in the known method is due in particular to the fact that the start of the pressing process is detected dynamically, but not the completion of the pressing process.
• a fixed end position is specified here, the achievement or non-achievement of which determines the success of the pressing process.
• a constant pressing force is required during the pressing process, a deviation from this constant pressing force also being considered as a committee.
• the new method now enables intelligent assembly of workpieces that are more tolerant, since the parameters that are decisive for the result of the pressing process are dynamically derived and adapted from the course of the pressing force during the working stroke of the press ram. Based on these parameters, a statement can then be made after the completion of a pressing process as to whether the pressing process was successful and corresponds to predetermined test values.
• the end position is dynamically adjusted at the start of the press.
• the end position is shifted by the same amount by which the start of the press is shifted.
• a pattern curve is stored in the control, whereby a constant distance between the start of the press and the end position is always assumed and specified.
• the end position is dynamically adapted or recognized as a function of a strong increase in the pressing force in the region of the end position.
• the advantage here is that in addition to or instead of the rough adjustment of the end position depending on the start of the pressing, the direct joining point is recognized, for example when two workpieces have been pressed onto the block.
• the joining or end position can differ for different workpieces, so that the mere determination of the end position from the start of the pressing is not as reliable as the derivation of the joining position from the sharp increase in the pressing force.
• This can be done, for example, by permanently changing the pressing force over the distance or over time are monitored so that the joining point is recognized in real time by evaluating this slope.
• the pressing process is stopped in a dynamically adapted manner.
• the advantage here is that not only the joining position itself but also the pressing force to be applied in the joining position is dynamically adjusted depending on the tolerances of the workpieces.
• a relatively low pressing force was used, whereas a very high pressing force is already required for workpieces with different tolerances in order to press the workpieces onto the block in the joining position.
• a high pressing force that cannot be achieved is now specified, which is sufficient for all the tolerances that occur, but in many cases is much too high.
• the pressing process is ended dynamically as a function of the change in slope in the course of the pressing force as soon as the workpieces have reached the joining position.
• the parameter "joining or end position" is dynamically adjusted based on the position of the press ram at the start of the press, the sharp increase in the pressing force when the joining position is reached and, if appropriate, the current value of the pressing force when the joining position is reached, thereby reducing the effect of tolerances of the workpieces is significantly reduced, so that overall the reject rate drops sharply compared to the method known from the prior art.
• the course of the pressing force is monitored over the path of the press ram for compliance with certain parameter sets, the parameter sets being dynamically adapted as a function of the position of the press ram at the start of the press.
• the monitoring windows only have to be shifted depending on the start of the pressing so that differently tolerated parts can be detected. On the one hand, it is possible to close the windows along the path axis move, but on the other hand a displacement along the pressing force axis is possible.
• the parameter sets are determined by machining and measuring sample workpieces.
• the advantage here is that the processing and averaging of several workpieces can be used to define reliable parameter sets or windows which are important for the quality control of the pressing process. For example, in the parameter sets a permissible deviation with respect to the pressing force or path is specified, workpieces in which the windows are not traversed are rejected as rejects.
• the course of the pressing force is displayed on a screen in real time, at least during the processing of sample workpieces.
• the advantage here is that the course of the pressing force can already be observed in a simple manner during the so-called teach-in process, so that appropriate windows can already be specified which are then checked or still being processed during the processing of further sample workpieces can be changed.
• This as accurate as possible acquisition of the parameter sets or windows enables good control of the actual pressing process on workpieces intended for further processing, so that their rejects can be significantly reduced.
• the applied pressing force is changed using an electronic handwheel.
• the advantage here is that the required pressing force can be determined and specified in a simple and very precise manner, because not only the working stroke, that is the path of the press ram but also the pressing force applied in particular in the joining position can be adjusted by hand. In this way it can be prevented that an excessively high pressing force is predetermined, whereby despite the measures according to the invention described above, it would still be possible to destroy appropriately tolerated workpieces.
• optimal parameter sets can be determined with the help of sample workpieces, which are still gentle and reliable even with workpieces that are more tolerant or enable editing.
• the dynamic change of these parameter sets as a function of the current pressing force curve when machining workpieces enables, on the one hand, a reduction in rejects through optimally set pressing force and joining position, and, on the other hand, timely detection of failing pressing processes, as has already been described above.
• FIG. 1 shows a schematic block diagram of an electric press to be operated according to the invention.
• Fig. 2 shows an exemplary course of the pressing force over the path of the press ram, as was measured in the electric press from Fig. 1.
• Fig. 1 generally 10 denotes an electric press, which is operated via a control indicated at 11.
• a screen 12 a keyboard 14 and an electronic handwheel 15 are connected to the controller 11.
• an interface 16 of the electric press 10 is connected to the controller 11, which enables control and monitoring of the pressing processes, as will be described below.
• the electric press 10 has an electric motor 17 which is mounted on a housing 18.
• a schematically indicated press ram 19 protrudes from the housing 18 below and is actuated by the electric motor 17.
• the press ram 19 In the position shown in FIG. 1, the press ram 19 is in its initial position 27. If the press ram 19 is moved further down in FIG. 1, it comes into contact with the workpieces 21 and 22 at the start of the press 28, which it then presses on block during the further course of its working stroke 23, which is the case in its joining position 29. Then the press ram 19 is moved back into its starting position 27.
• Fig. 2 two curves 24, 24 'are shown as an example for the course of the pressing force over the path, the curve 24 is intended to be a comparison curve determined on the basis of sample workpieces.
• the press ram 19 In its position S B , the press ram 19 has reached the position in which the pressing process begins, so it must exert force in order to have the workpieces 21, 22 together.
• an increase in force is observed until after a camber 31, from adhesive friction when the pressing force decreases first again with further progression of the working stroke to finally come to rise again until upon reaching the joining position S F a force F F has reached.
• the pressing force F now rises steeply until the pressing process is interrupted and the ram 19 is retracted.
• the controller 11 continuously monitors the increase in the pressing force and now detects a strong change in the slope dF / ds or dF / dt at point F F , as a result of which the joining point is reached. Since the increase cannot be detected in any short time, there is a certain increase in the force ⁇ F to F m , which, however, does not cause any damage to the workpieces.
• the course of the curve 24 is also decisive for the result of the pressing process, so that the controller 11 monitors a whole series of parameters for compliance. These parameters include the joining position S F and the pressing force F. If, for example, the joining position S F is not reached, the pressing process was unsuccessful. However, since such a deviation does not necessarily have to indicate a failing pressing process, but rather can be attributed to the fact that the parts available are tolerated differently, the monitored parameters are now dynamically adjusted on the basis of the curve 24.
• the curve 24 ' has a lower pressing force when the joining point S F ' is reached, namely the pressing force F F '. If the control 11 would now stop the pressing process only when the force F m is reached , an unnecessarily high force would be applied, which is undesirable for reasons already mentioned. However, the control 11 recognizes the steep increase in the force and immediately stops the pressing process, so that the force can only increase to the value F m '.
• the curve can be any position in the window
• various such windows 32, 34 can be placed over the curve 24 in order to monitor different sections of the pressing process.
• the number and position of the windows depends on the workpieces 21, 22 available. However, this means that a new pattern curve 24 and new windows 32, 34 must be determined for different types of workpieces 21, 22.
• sample workpieces are available, for which purpose not only the working stroke 28 of the electric press 10 but in particular the pressing force F of the press ram 19 is set by means of the electronic handwheel 15.
• the current course of the pressing force is shown in real time on the screen 12, so that the installer, who is recording a new curve 24, can fine-tune the pressing force using the electronic handwheel 15 and check the result directly on the screen 12.
• Windows 32, 34 can then also be set on the screen 12.
• Now new sample workpieces are pressed, the current course of the pressing force being shown again on the screen 12 and at the same time the position of the windows 32, 34 can be checked.
• corresponding parameter sets are available, which include windows 32, 34 and the positions S B at the start of pressing 28 and S F at the end of the pressing process.

Landscapes

• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Control Of Presses (AREA)
• Manufacture Of Electron Tubes, Discharge Lamp Vessels, Lead-In Wires, And The Like (AREA)
• Apparatuses And Processes For Manufacturing Resistors (AREA)

Applications Claiming Priority (3)

Publications (2)

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ID=7820103

Family Applications (1)

Country Status (5)

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Family Cites Families (11)

• 1997
  • 1997-02-13 DE DE19705462A patent/DE19705462C2/de not_active Expired - Fee Related
• 1998
  • 1998-01-07 EP EP98907927A patent/EP0960017B1/fr not_active Expired - Lifetime
  • 1998-01-07 WO PCT/EP1998/000040 patent/WO1998035823A1/fr not_active Ceased
  • 1998-01-07 DE DE59803009T patent/DE59803009D1/de not_active Expired - Lifetime
  • 1998-01-07 AT AT98907927T patent/ATE212903T1/de active
• 1999
  • 1999-08-12 US US09/373,286 patent/US6293155B1/en not_active Expired - Lifetime

Non-Patent Citations (1)

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