EP0652100B1 - Method of simulating the load dependent tilt of the slide of mechanical presses, on a hydraulic work-in press - Google Patents

Description

The invention relates to a method for simulating the load-dependent ram tilting of mechanical presses on a hydraulic incorporation press according to the preamble of patent claim 1.

Forces acting off-center on the press ram cause the ram to tilt. The dimension of the ram tilt is an important factor for assessing the quality of presses, since the shape accuracy of the machined workpiece or sheet metal part also depends on this.
In hydraulic presses, in particular SMC presses (DD-PS 289 970, DE-OS 37 26 578), it is known to arrange the position of the ram to measure the parallel operation at the corner points of the press table and to position at least four counter-cylinders which can be pressurized with pressure oil which, at least in the working area of the press, exert a force which counteracts the deviations in parallelism of the ram movement. The counter cylinders are pressurized by means of servo valves, which in turn can be controlled by an electronic comparator and evaluation circuit as a function of the parallelism deviations detected by the respectively associated displacement measuring system.

und ${\text{M}}_{\text{y}}{\text{= f}}_{\text{2}}{\text{(k}}_{\text{y}}\text{)}$

oder ${\text{C}}_{\text{x}}{\text{= f}}_{\text{3}}{\text{(k}}_{\text{x}}\text{)}$

und ${\text{C}}_{\text{y}}{\text{= f}}_{\text{4}}{\text{(k}}_{\text{y}}\text{)}$

der zu simulierenden Produktionspresse angeben.
Zu diesem Zweck wird die von den z. B. SMC-Pressen bekannte Kurzhubtechnik eingesetzt. Sie besteht aus vier an den Eckpunkten des Pressentisches angeordneten Hydraulikzylindern, die jeweils mittels eines Servoventils und einer Regeleinrichtung steuer- bzw. regelbar sind. Die vier Hydraulikzylinder sind mit Druckaufnehmern ausgestattet, die eine kontinuierliche Druckmessung in den Zylinderräumen zulassen. Der Stößel setzt bei seiner Abwärtsbewegung kurz vor Beginn des Arbeitsbereiches auf die ausgefahrenen Kolben der Arbeitszylinder auf und verdrängt bei seiner Weiterbewegung das Druckmedium aus den Zylinderräumen.In the case of mechanical presses, which generally do not contain any additional devices for regulating the parallel operation, the faulty behavior of the respective press is taken into account when the tool is incorporated. In the possibly lengthy familiarization process, the press is not available for production tasks.
The incorporation of tools is therefore often not carried out on highly productive mechanical production presses, but on hydraulic incorporation presses. If the incorporated tools are used in the production presses, Corrective work is often still required, which reduces production reliability and thus productivity. The main cause is the load-dependent ram tilting of the production press, which cannot be simulated and simulated on the hydraulic incorporation press.
The invention has for its object to provide a method according to which the tilting behavior of production presses with different spring stiffness can be simulated on a hydraulic incorporation press with simple means.
According to the invention this is achieved by the features described in the characterizing part of patent claim 1. Further detailed embodiments of the invention are described in claims 2 and 3.
For the simulation of the tilting behavior of production presses on hydraulic presses, experimentally determined function profiles of the tilting of the ram (k _{x, y} ) depending on the tilting moment (M _{kx, ky} ) are available for both axes (x, y).
In the case of the tilting simulation, the objective is now, depending on the actually acting tilting moment (in relation to the respective axis), to have the plunger tilted only as far as the function profiles stored in a control system ${\text{M}}_{\text{x}}{\text{= f}}_{\text{1}}{\text{(k}}_{\text{x}}\text{)}$

and ${\text{M}}_{\text{y}}{\text{= f}}_{\text{2nd}}{\text{(k}}_{\text{y}}\text{)}$

or ${\text{C.}}_{\text{x}}{\text{= f}}_{\text{3rd}}{\text{(k}}_{\text{x}}\text{)}$

and ${\text{C.}}_{\text{y}}{\text{= f}}_{\text{4th}}{\text{(k}}_{\text{y}}\text{)}$

of the production press to be simulated.
For this purpose, the z. B. SMC presses known short stroke technology used. It consists of four hydraulic cylinders arranged at the corner points of the press table, each of which can be controlled or regulated by means of a servo valve and a regulating device. The four hydraulic cylinders are equipped with pressure transducers that allow continuous pressure measurement in the cylinder rooms. When the plunger moves downwards just before the start of the working area, it is placed on the extended pistons of the working cylinders and, as it moves on, displaces the pressure medium from the cylinder chambers.

Fig. 1:

eine schematische Darstellung der auf die Stößelfläche der Presse wirkenden Kippmomente bei außermittiger Belastung,

Fig. 2:

eine Regeleinrichtung für die Stößelkippung als Blockschaltbild,

Fig.3:

die Schaltungsanordnung zu Fig. 2,

Fig. 4:

eine zweite Ausführung der Regeleinrichtung als Blockschaltbild und

Fig. 5:

die Schaltungsanordnung zu Fig. 4.

Within the working area of the press ram, it is braced on both sides by its drive (press cylinder) and by the short-stroke cylinders. The unloaded tappet (to which no process force acts) can be deliberately tilted into a certain position by generating different pressures between two pairs of cylinders (front - back, left - right).
In order to hold an eccentrically loaded ram in its ideal parallel position to the press table, pressures of different sizes must also be set between the cylinder pairs (front - back, left - right), which restore the state of equilibrium to the eccentric force. The pressure differences occurring in the equilibrium state represent the size of the actually acting tilting moments.
A tilting moment that changes with respect to direction and time cannot, however, be determined directly without feedback without the aid of additional sensors.
Furthermore, a distance measuring system is attached to each ram corner, which records the distance between the press ram and the press table with a high resolution. The ram tilt can be determined by comparing the four distance dimensions.
The invention now makes it possible to tilt the tappet in a defined manner for each axis from the predetermined assignment of tilting to tilting moment and to react quickly to changes in the tilting moment.
The effect, ie the tilting, is first recorded and then the cause, the tilting moment, is compensated by a counter-torque by regulating different pressures in the counter-cylinders until an equilibrium state is reached on the basis of the stored tilting function. It is characteristic of the state of equilibrium that the set counter torque allows exactly the tappet tilt, which corresponds to the tilting moment according to the stored tilt function. If the tilting moment changes, the counter moment is readjusted based on the resulting tappet tilt. With the help of the counter moment, it will ensured that the tappet does not tilt further than agreed when the load is off-center and returns to its initial position when the tilting moment decreases.
The invention is explained in more detail below using two exemplary embodiments. The associated drawings show:

Fig. 1:

1 shows a schematic illustration of the tilting moments acting on the ram surface of the press when the load is off-center,

Fig. 2:

a control device for tappet tilting as a block diagram,

Fig. 3:

2 shows the circuit arrangement for FIG. 2,

Fig. 4:

a second embodiment of the control device as a block diagram and

Fig. 5:

the circuit arrangement of Fig. 4th

The device arrangement for load-dependent tilt control (FIGS. 1, 3, 5) consists of the four stop spindles 2, each arranged in a corner point of the plunger 1, the associated counter-cylinders 3, including displacement measuring systems 4, pressure measuring systems 5 and control valves 6, and an electronic control device 7.

• vier Kraftreglern 11 mit Korrektureinrichtung,
• der Einrichtung zur Ermittlung der Stößelkippungen 12,
• der Einrichtung zur Ermittlung der Sollwerte für die Gegenhaltemomente in x- und y-Richtung 13 und
• der Einrichtung zur Verteilung der Sollwerte für die Gegenhaltekräfte 14,14a auf die vier Gegenhaltezylinder 3.

The stop spindles 2 connected to the press ram 1 are used to set the working area of the device and are set depending on the tool dimensions so that they actuate the counter-cylinders 3 connected to the press table and the displacement measuring systems 4 during the forming process. The control valves 6 serve to influence the pressures or forces in the counter-cylinders 3, which are reported to the control device 7 via the pressure measuring systems 5. The control device 7 uses the signals from the pressure and displacement measuring systems 4, 5 and the control parameters entered to generate the control signals for the control valves 6.
The control device 7 (FIGS. 2 and 3) consists of the following components:

• four force controllers 11 with correction device,
• the device for determining the ram tilts 12,
• the device for determining the setpoints for the counter moments in the x and y directions 13 and
• the device for distributing the target values for the counter-holding forces 14, 14 a to the four counter-holding cylinders 3.

und ${\text{M}}_{\text{ky}}{\text{= g(k}}_{\text{y}}\text{)}$

die Gegenhaltemomente ermittelt bzw. die dazu proportionalen Signale (M_x1, M_x2, M_y1, M_y2) erzeugt. Die Kippungskennlinien können an realen Pressen gemessen und als Parameter in die Regeleinrichtung 7 eingegeben werden.
Die Zuordnung dieser Momentensignale auf die vier Gegenhaltezylinder 3 und somit die Bildung der Kraft- bzw. Drucksollwerte erfolgt durch eine Summiereinrichtung 14, deren Summierpunkte den vier Kraftreglern 11 zugeordnet sind. Hierbei werden für jeden Kraftregler 11 die ihm zugeordneten Komponenten der Gegenhaltemomente in x- und y-Richtung aufsummiert.
Die Ausregelung der so ermittelten Sollwerte erfolgt durch die schon beschriebenen Kraftregler 11. Dadurch wird erreicht, daß nach Auftreten eines Kippmomentes der Stößel 1 so weit kippen kann, bis in Abhängigkeit vom Kippweg ein zum Kippmoment gleichgroßes Gegenhaltemoment aufgebaut ist.The force regulators 11 are each assigned to a counter-holding cylinder 3 and influence the counter-holding forces to limit the tappet tilting via control valves 6. They are designed, for example, as PID controllers, the control parameters (P, I, D components) being able to be adapted to the behavior of the controlled system by means of correction devices. This makes it possible, for example, to eliminate disruptive influences from the behavior of the control valves 6 and from the variable volume of the oil columns in the counter-cylinders 3. The feedback of the actual value takes place via pressure measuring systems 5, whereby when using differential cylinders, two pressure measuring systems 5, each assigned to the upper and lower cylinder chamber, and devices for forming an area-weighted difference 15, actual value signals proportional to the respective counterforce are generated. These signals are fed back to summing points 16, via which an additional offset signal (F _min ) can also be used to specify the minimum counterforce.
In a further system component (device 13), the counter moments that are required to limit the ram tilting to the desired value are determined separately according to the x and y directions of the ram 1. For this purpose, signals k _x and k _y proportional to the ram tilt in the x and y directions are first generated from the actual path values of the four ram corner points by two summing devices 12. Depending on the direction (sign) of the determined tilts, the signals are assigned to two signal paths, which in turn are assigned to specific groups of counter-cylinders 3 (distributor 14a). These signals (k _x1 , k _x2 , k _y1 , k _y2 ) are then used with the aid of the tilting characteristic curves ${\text{M}}_{\text{kx}}{\text{= f (k}}_{\text{x}}\text{)}$

and ${\text{M}}_{\text{ky}}{\text{= g (k}}_{\text{y}}\text{)}$

the counter torque is determined or the proportional torque Signals (M _x1 , M _x2 , M _y1 , M _y2 ) generated. The tilt characteristics can be measured on real presses and entered as parameters in the control device 7.
The assignment of these torque signals to the four counter-cylinders 3 and thus the formation of the force or pressure setpoints is carried out by a summing device 14, the summing points of which are assigned to the four force regulators 11. For each force regulator 11, the components of the counter-holding moments assigned to it are added up in the x and y directions.
The setpoint values determined in this way are regulated by the force controllers 11 already described. This ensures that after the occurrence of a tilting moment, the tappet 1 can tilt until a counter torque equal to the tilting moment is built up, depending on the tilting moment.

) für jeden Eckpunkt des Stößels 1 steuer- bzw. regelbar ist.In a further embodiment (FIGS. 4 and 5) it is assumed that a conscious tilting of the ram by a defined amount is possible if a defined stiffness ( ${\text{c}}_{\text{i}}{\text{= F}}_{\text{i}}{\text{/ Δ s}}_{\text{i}}$

) can be controlled or regulated for each corner point of the ram 1.

kann direkt in die Steuerung eingegeben oder aus der Funktion $\text{M = f(k)}$

steuerungsintern ermittelt werden.
Für den Fall einer nicht zu vernachlässigenden Steifigkeit der Simulationspresse stehen Korrekturfunktionen 23a zur Verfügung.
Nachdem die Soll-Steifigkeiten für die x- und die y-Achse mit Hilfe der gespeicherten Funktionen 23 und ggf. 23a ermittelt sind, erfolgt in dem Sollwertverteiler 24 die Zuordnung der Sollwerte zu den einzelnen Gegenhaltezylindern 3 durch Überlagerung der jeweils ermittelten Steifigkeitswerte der x- und y- Achse.
In den Summierpunkten 26 werden die Soll-Steifigkeitswerte mit den zugehörigen Ist-Steifigkeitswerten verglichen und den Steifereglern 21 zugeführt.
Jeder der vier Steiferegler 21 beeinflußt über ein Servoventil 6 den Druck im Gegenhaltezylinder 3, bis die Abweichung der Ist-Steifigkeit von der Soll-Steifigkeit ausgeglichen ist.In the simplest case, the tilting behavior of production presses has a linear relationship between tilting and tilting moment. Then the rigidity that must be simulated with each counter-holding cylinder 3 is constant. This means that, for example, a higher-level controller 23 first calculates the stiffnesses for each axis (x, y) and then assigns a stiffness setpoint value to each of the four counter-holding cylinders 3 by superimposing them in a setpoint distribution 24. The control device 7 of each counter cylinder 3 has the task of keeping the flexibility of the counter cylinder 3 constant.
The force exerted on the tappet 1 by the respective cylinders 3 is determined from the areas and pressure values of the counter-holding cylinder 3. The instantaneous tilting values of the ram 1 are converted from the measured distance values between the ram 1 and the table in a device 22 calculated. For each counter-cylinder 3, the momentary stiffness c _{i is} determined from the determined force F _i and the calculated tilt Δ s _i in a device for calculating the stiffness 27 and compared with the setpoint in a summing point 26. The difference resulting from this comparison is transmitted to the stiffness controller 21. This changes the pressure ratio in the counter-cylinder 3 by means of a servo valve 6 in such a way that the resulting rigidity corresponds to the target value.
If there is no linear relationship between the ram tilt and the tilting moment in production presses, the setpoint is determined as a function of the measured ram tilt, as shown in FIGS. 4 and 5. The stiffness-tilt functions 23 and 23a stored in a control serve this purpose. These functions represent the dependence of the tipping stiffness c _x and c _{y of} the ram (of the production press to be simulated) on the tipping k _x and k _y about the x and y axes. The function $\text{c = f (k)}$

can be entered directly into the control or from the function $\text{M = f (k)}$

be determined internally by the control system.
Correction functions 23a are available in the event of a rigidity of the simulation press that should not be neglected.
After the target stiffnesses for the x and y axes have been determined with the aid of the stored functions 23 and possibly 23a, the target values distributor 24 assigns the target values to the individual counter-cylinders 3 by superimposing the respectively determined stiffness values of the x- and y axis.
In the summing points 26, the target stiffness values are compared with the associated actual stiffness values and fed to the stiffness controllers 21.
Each of the four stiffness regulators 21 influences the pressure in the counter cylinder 3 via a servo valve 6 until the deviation of the actual stiffness from the desired stiffness is compensated.

Claims (3)

1. Method of simulating the load-dependent ram tilting of mechanical presses on a hydraulic cavity press having at least one pressure cylinder connected to the press ram for developing a working pressure which acts upon the workpiece, having at least four holding-up cylinders acting upon the ram in the opposite direction to the working motion, having displacement measuring systems for detecting the ram position at any one time and having a control device for individual pressurization of the holding-up cylinders,
   characterized in
   that the oil pressure in the holding-up cylinders is controlled in such a way that at least in the working region - on the basis of the determined ram tilt - in each case sufficient force is opposed to the ram to limit the load-dependent ram tilts in the x- and y-axis to values which are preselected by means of parameterizable tilting characteristics ${\text{M}}_{\text{x}}{\text{= f}}_{\text{1}}{\text{(k}}_{\text{x}}\text{)}$

   

   and ${\text{M}}_{\text{y}}{\text{= f}}_{\text{2}}{\text{(k}}_{\text{y}}\text{)}$

   

   or ${\text{c}}_{\text{x}}{\text{= f}}_{\text{3}}{\text{(k}}_{\text{x}}\text{)}$

   

   and ${\text{c}}_{\text{y}}{\text{= f}}_{\text{4}}{\text{(k}}_{\text{y}}\text{)}$

   

   .
2. Method of simulating the load-dependent ram tilting according to claim 1,
   characterized by the cyclic execution of the following steps in the working region of the press:

   1. detection of the pressure or the pressure difference and calculation of the effective piston force for each holding-up cylinder,

   2. detection of the distance between press bed and ram by means of displacement measuring systems at each ram corner and calculation of the ram tilts k_x and k_y for the x- and the y-axis from the distance differences,

   3. determination of the setpoint holding-up moments for the x- and y-axis with the aid of preselected function characteristics and the actual ram tilts,

   4. determination of the setpoint forces for the holding-up cylinders by superimposition of the tilting moments while taking the geometric proportions of the press into account,

   5. comparison between setpoint and actual forces and input of the force differences into the force control units,

   6. influencing of the control valves by means of the actuating signals of the force control units in such a way that the pressures in the holding-up cylinders are varied until a conformance of setpoint and actual forces is achieved,

   it being possible within the cycle for steps to be executed either in parallel or in a different sequence.
3. Method of simulating the load-dependent ram tilting according to claim 1,
   characterized by the cyclic execution of the following steps in the working region of the press:

   1. detection of the pressure or the pressure difference and calculation of the effective piston force for each holding-up cylinder,

   2. detection of the distance between press bed and ram by means of displacement measuring systems at each ram corner and calculation of the ram tilts k_x and k_y for the x- and the y-axis from the distance differences and the dimensions of the ram surface,

   3. calculation of the actual stiffness value c for each holding-up cylinder from the piston force and the calculated ram tilt k_x or k_y,

   4. determination of the setpoint stiffness values for the x- and y-axis with the aid of preselected function characteristics and the actual ram tilts,

   5. determination of the setpoint stiffness values for the holding-up cylinders by superimposition of the setpoint stiffness values for the x- and y-axis while taking the geometric proportions of the press into account,

   6. comparison between setpoint and actual stiffness value and input of the stiffness difference into the stiffness control unit,

   7. influencing of the control valves by means of the actuating signals of the control units in such a way that the pressures in the holding-up cylinders are varied until a conformance of setpoint and actual stiffness value has been achieved,

   it being possible within the cycle for steps to be executed either in parallel or in a different sequence.

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