Method for regulating the output pressure of a hydraulic drive system, use of the method and hydraulic drive system

Abstract

A method for regulating output pressure of a hydraulic drive system by using a rotational speed as the actuating variable. The method includes determining a setpoint rotational speed main component of motor drive as a pilot control signal, determining an error rotational speed as a regulating deviation from a comparison of an actual pressure value of the hydraulic drive system and a setpoint pressure value of the hydraulic drive system and adjoining regulating amplifier, adding the determined setpoint rotational speed main component to the determined error rotational speed to create the setpoint rotational speed as the actuating variable, and converting the created setpoint rotational speed into an input rotational speed of the motor drive to drive the hydraulic drive system at the converted rotational speed in order to generate regulated output pressure of the hydraulic drive system which represents actual pressure value.

Claims

1. A method for regulating output pressure of a hydraulic drive system by using a rotational speed as an actuating variable, wherein the hydraulic drive system has a hydraulic pump and a motor drive which drives the hydraulic pump, the method comprising: determining a setpoint rotational speed main component of the motor drive as a pilot control signal; determining an error rotational speed as a regulating deviation from a comparison of an actual pressure value of the hydraulic drive system and a setpoint pressure value of the hydraulic drive system and an adjoining regulating amplifier; adding the determined setpoint rotational speed main component to the determined error rotational speed to create a setpoint rotational speed as the actuating variable; and converting the created setpoint rotational speed into an input rotational speed of the motor drive to drive the hydraulic drive system at the converted rotational speed in order to generate regulated output pressure of the hydraulic drive system which represents an actual pressure value, wherein the determined setpoint rotational speed main component comprises a first setpoint rotational speed component and a second setpoint rotational speed component, and wherein the second setpoint rotational speed component is calculated from a volume flow setpoint and a conveyed volume flow parameter of the hydraulic drive system.

2. The method according to claim 1, wherein the first setpoint rotational speed component is calculated from the setpoint pressure value, a maximum pressure of the hydraulic pump, and a rotational speed parameter of the motor drive to produce the maximum pressure.

3. The method according to claim 2, wherein the volume flow setpoint of the hydraulic drive system is determined from at least one parameter of an actuator coupled to and driven by the hydraulic drive system and/or a first element which is driven by the hydraulic drive system or a second element which influences the hydraulic drive system.

4. The method according to claim 3, wherein the second element comprises a die and a plunger.

5. The method according to claim 1, further comprising a sensor element configured for sensing at least one parameter, wherein the volume flow setpoint of the hydraulic drive system is determined from the at least one parameter.

6. The method according to claim 1, wherein an algebraic sign of the first setpoint rotational speed component contrasts with an algebraic sign of the second setpoint rotational speed component.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:

(2) FIG. 1 illustrates a regulating system for the output pressure according to a known method;

(3) FIG. 2 illustrates a first schematic diagram for determining hydraulic pump parameters;

(4) FIG. 3 illustrates a second schematic diagram for determining hydraulic pump parameters;

(5) FIG. 4 illustrates a flow chart of an embodiment of a method according to the present invention;

(6) FIG. 4a illustrates an exemplary single line equivalent circuit diagram of a first motor drive for the method according to the present invention;

(7) FIG. 4b illustrates an exemplary single line equivalent circuit diagram of a second motor drive for the method according to the present invention;

(8) FIG. 5 illustrates a first design example of a block diagram of regulating the output pressure according to the present invention;

(9) FIG. 6 illustrates a second embodiment of a block diagram of regulating the output pressure according to the present invention;

(10) FIG. 7 illustrates a possible embodiment of a deep drawing device according to the current state of the art; and

(11) FIG. 8 illustrates exemplary signal progressions for regulating the output pressure according to the present invention by use of actuator parameters.

(12) Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate embodiments of the invention and such exemplifications are not to be construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION OF THE INVENTION

(13) FIG. 1 shows a regulating system for output pressure P.sub.OUT of a hydraulic drive system 10 according to a known method, as described for example in U.S. Pat. No. 6,379,119 B1. Hydraulic drive system 10 consists of a power amplifier 3, an electromotive drive 4 and a hydraulic pump 5. Hydraulic pump 5 provides an output pressure P.sub.OUT at its outlet, with which for example a pull-push device as illustrated for example in FIG. 7 in the embodiment of a deep draw device 8 is driven.

(14) According to FIG. 1, regulating of output pressure P.sub.OUT occurs on the basis of an idealized linear relationship between the physical dimensions of pressure P, conveying volume Q.sub.P of hydraulic pump 5 determined by its size and a torque M by determining of set and actual values of a motor current I.sub.MOT as a control variable.

(15) The following hydrostatic load torque applies for an ideal displacement pump as an example for a hydraulic pump 5 which is to be viewed without friction and losses at the sealing gap:
M.sub.POUT=Q.sub.P/(2*π)*P.sub.OUT  (1)
with: M.sub.POUT=torque at the hydraulic pump

(16) Q.sub.P=conveying volume of hydraulic pump per rotation

(17) P.sub.OUT=output pressure at the hydraulic pump.

(18) According to FIG. 1, a setpoint pressure value P.sub.SET is compared in a comparator 1 with a pressure actual value P.sub.FBK. The comparison result is an error pressure P.sub.ERR which is supplied to a regulating amplifier 2. Regulating amplifier 2 is designed as a PID-regulator. According to FIG. 1, a current setpoint value 1.sub.SET is set as the control variable. This current setpoint value 1.sub.SET is supplied to amplifier 3. Amplifier 3 produces motor current I.sub.MOT from current setpoint value I.sub.SET. Motor 4 transfers torque M.sub.MOT resulting from I.sub.MOT to pump 5. Output pressure P.sub.OUT is detected by way of a sensor element and by way of an analog digital converter 6 is returned to comparator 1 as pressure actual value P.sub.FBK. Amplifier 3 is generally suitable for synchronous or asynchronous motors. Motor current I.sub.MOT is a three-phase system.

(19) The regulating system according to FIG. 1 is based on the following system considerations. Driving torque M.sub.MOT is opposed by hydrostatic load torque M.sub.POUT according to equation (1), a friction component of pump 5 and a rotor inertia of motor 4 as well as pump 5.

(20) The following applies:
M.sub.MOT=MPOUT+M.sub.FRICT+J.sub.TOTAL*α)  (2) with: α=angular acceleration M.sub.FRICT=mechanical friction of pump due to size and type J.sub.TOTAL=J.sub.MOTOR J.sub.PUMP as rotor inertia pump and motor

(21) For angular acceleration a of pump 5, the following arises from changing equation (2):
α=(M.sub.MOT−M.sub.POUT−M.sub.FRICT)/(J.sub.MOT+J.sub.PUMP)  (3)

(22) The following applies for rotational speed ω of pump 5:
ω(t)=∫.sub.0.sup.∞α(t)*dt  (4)

(23) For a user having a significant and variable volume flow Q.sub.(t) this arrangement is disadvantageous, since the necessary rotational speed w of pump 5 depends also on the actual required volume flow Q.sub.(t), for example for a stroke movement of the cylinder in order to support the draw cushion.

(24) FIG. 2 and FIG. 3 are schematic diagrams used to determine hydraulic pump parameters which are used for regulating output pressure P.sub.OUT according to the invention.

(25) FIG. 2 shows a characteristic curve of conveying volume Q in dependence of the rotational speed w of a fixed displacement pump 5 during pressureless operation. In a very good approximation volume flow Q is proportional to rotational speed w during pressureless operation. Typical maximum rotational speeds ω.sub.MAX are 314 rad/s, in other words 3000 rotations per minute. Conveying volume Q.sub.OUT in pressureless operation is calculated as follows:
Q.sub.OUT(ω)=ω.sub.IN*Q.sub.P  (5)

(26) with: Q.sub.P=conveying volume of pump 5 per rotation.

(27) FIG. 3 shows a second schematic diagram used to determine hydraulic pump parameters. It illustrates a characteristics curve of pump 5, for example of a fixed displacement pump operating against blocked pressure output. Output pressure P.sub.OUT is calculated as follows:
P.sub.OUT(w)=P.sub.MAX*ω.sub.IN/ω.sub.PMAX  (6)
with: P.sub.MAX=maximum pressure ω.sub.IN=input rotational speed ω.sub.PMAX=rotational speed at maximum pressure with blocked pressure output.

(28) Used pumps 5, in particular piston or geared pumps are highly effective even under high pressure P. Thus, typically only a low rotational speed is ω.sub.PMAX is necessary to produce maximum pressure P.sub.MAX. For example, rotational speed ω.sub.PMAX of a comparatively good pump 5 can be 12 rad/s (=120 rpm) at maximum pressure P.sub.MAX, whereas rotational speed ω.sub.PMAX of a comparatively inferior pump can be 31 rad/s (=300 rpm) at maximum pressure P.sub.MAX.

(29) As already mentioned, the pressure regulating system according to FIG. 1 considers only the pump characteristics according to FIG. 3. This results disadvantageously only in stable regulating of the pressure as long as no significant volume flow Q is removed. With a rotational speed value ω greater than a few hundred revolutions per minute the regulating system fails.

(30) When using the inventive regulating system in a deep draw device 8 according to FIG. 7 attention must be paid that an element, for example the draw cushion moves as intended. Pump 5 must thereby be able to accept the displaced fluid volume and to remove volume flow Q. Pump 5 is designed such that the expected maximum volume flow Q.sub.MAX results in a maximum rotational speed of ω.sub.PMAX (for example approx. 3000 rpm). The rotational speed regulating range which is to be controlled may be between very few revolutions per minute, resulting from the low rotational speed ω.sub.PMAX at maximum pressure P.sub.MAX and several thousand revolutions per minute, resulting from the expected high volume flow Q.sub.MAX.

(31) In conventional control methods the control circuit can only be reliably parameterized for a fraction of this rotational speed control range, for example to a rotational speed range of 0 to a few hundred revolutions per minute. To illustrate the actual rotational speed range to several thousand revolutions per minute, sufficiently great control separations must be dealt with. This is not possible with the PID controls due to the time constants which have to be considered.

(32) FIG. 4 illustrates a flow chart of an embodiment of the method according to the present invention. Method 100 comprises process steps 101 to 104 as explained below. In step 101 a setpoint rotational speed main component ω.sub.SET1+2 of electromotive drive 4 is determined as pilot control signal. In step 102 an error rotational speed ω.sub.ERR is determined as a control deviation from a comparison of an actual pressure value P.sub.FBK of hydraulic drive system 10 and a setpoint pressure value P.sub.SET of hydraulic drive system 10 and adjoining regulating amplifier 2. In step 103, adding of the determined setpoint rotational speed main component ω.sub.SET1+2 to the determined error rotational speed ω.sub.ERR occurs in order to form a setpoint rotational speed ω.sub.SET as the actuating variable in the inventive regulating system. In step 104 the created setpoint rotational speed ω.sub.SET is converted into a rotational speed ω.sub.IN of motor drive 4 for driving of hydraulic drive system 10 with the converted rotational speed to produce the regulated output pressure P.sub.OUT of hydraulic drive system 10 as the pressure actual value P.sub.FBK.

(33) Regulating method 100 according to the invention can be easily parameterized, is stable during operation and has substantial lower regulating deviation than the regulating method according to FIG. 1. In FIG. 4 the pressure control does not occur via torque M.sub.MOT of the driving motor, but via setpoint rotational speed ω.sub.SET (or frequency f of the motor drive arising therefrom) as the actuating variable.

(34) FIG. 4a illustrates an exemplary equivalent circuit diagram of one phase of a three-phase motor drive 4 (three-phase a.c. motor) for the method according to the invention with which inventive conversion step 104 and the therefrom resulting rotational speed regulation can be clarified. As mentioned, drive 4 is for example an asynchronous three-phase a.c. motor. For better understanding of the operation in a rotary speed regulating system of motor drive 4, consideration of the equivalent circuit diagram of the asynchronous motor is useful. This equivalent circuit diagram illustrates an electric circuit equivalent to that of motor drive 4 as is also seen for amplifier 3 with frequency converter 7.

(35) On the left side of FIG. 4a the equivalent circuit diagram of the stator winding is illustrated. This consists of the ohmic resistor Rs, in particular a copper resistor and equivalent series resistance of the hysteresis losses and a reactance Xs of the stator winding-inductivity during asynchronous operation. On the right side of FIG. 4a, the equivalent circuit diagram of the rotor winding is illustrated. This consists of a reactance Xr of the rotor winding-inductivity and ohmic resistor Rr. Reactance Xr represents the resulting inductivity of an immobile motor. Effective resistor Rr of the rotor consists of the equivalent value of the effective power emitted by motor drive 4 and the ohmic resistance of the short circuit cage which is stepped up according to the square of the stator's number of turns. The equivalent value of the effective power changes with the change in torque M or respectively the load on motor drive 4.

(36) In idle operation, that is in no-load operation of hydraulic drive system 10 the equivalent circuit diagram of motor drive 4 consists essentially of resistors Rs and Xs. The current I.sub.MOT consumption during idle operation is almost equivalent to the rated current. With increasing load, in other words with the buildup in output pressure P.sub.MAX in hydraulic drive system 10 the active current increases because of resistance Rr. The phase angle between current I.sub.MOT and voltage U.sub.MOT reduces by almost ϕ=90° to lesser values.

(37) The load dependent active current produces a drop in voltage at resistor Rr, but only an insignificantly greater drop in voltage at resistor Rs. Consequently, the losses increase quicker with increasing load in the rotor than in the stator. Resistors Rs and Rr cause increasing losses with the square of the current consumption. Therefore, the efficiency of motor drive 4 decreases with increasing load.

(38) In inverter operation, reactance Xs becomes increasingly less with decreasing frequency f.sub.MOT. When adhering to the rated current the voltage delivered by frequency converter 7 must therefore drop. With this, the ratio of voltage divider Rs relative to Xs becomes less favorable and leads to increasing losses relative to the available motor power. Frequency converter 7 can possibly detect the voltage divider ratio Rs/Rr on its own.

(39) A (non-illustrated) frequency converter 7 now enables rotational speed w to be adjusted infinitely from almost zero to the rated speed without torque M.sub.MOT dropping in doing so (basic adjustment range). Motor drive 4 can also be operated via rated rotational frequency. However, the delivered torque M.sub.MOT then drops, since the operating voltage can no longer be adapted to the increased frequency.

(40) FIG. 4a shows the application of torque control for asynchronous motors, however the invention is not limited to same. The regulating system can also be used with synchronous motors, for example three phase synchronous motors.

(41) FIG. 4b illustrates an exemplary equivalent circuit diagram of one phase of a three-phase motor drive 4 (three phase a.c. current motor) for the inventive method with which inventive conversion step 104 and the therefrom resulting torque control can be clarified. According to FIG. 4b, motor drive 4 is for example a synchronous three phase a.c. current motor. The equivalent circuit diagram according to FIG. 4b illustrates an electrical circuit, equivalent to motor drive 4 as is also seen for amplifier 3 with frequency converter 7.

(42) For the synchronous motor to be able to operate as an electromotive drive 4—in other words as a three phase a.c. synchronous motor—an energizing field is necessary in the rotor circuit so that due to a direct current energized rotor winding (field winding) or a permanent magnet a magnetic field (energizing field) is produced which in the individual branches of the stator winding induces a stator voltage Us. Moreover, electric energy must be supplied via the stator winding, so that the three phase a.c. synchronous motor can deliver torque M.sub.MOT (see equation 2).

(43) Below is a brief description of the function of the synchronous motor illustrated in FIG. 4b in motor operation. The synchronous motor idles in the fixed network. Due to pump 5 a load occurs on the motor shaft. Motor 4 would reduce its rotational speed ω, however motor 4 now consumes electric power and stator current, Is, illustrated in FIG. 4 increases. Now, a motor torque M.sub.MOT becomes effective which counteracts load torque M.sub.LOAD. Stator current Is causes a differential voltage Ud at the synchronous reactance Xd. The inductive reactance of the stator winding and its ohmic resistance can herein be neglected. Due to voltage drop Xd, a stator current Id dependent rotor displacement angle forms which acts against the rotational direction in the motor operation. Thus, rotor voltage Up shifts toward line voltage US with the rotor angle against the rotational direction. The motor continues to run with synchronous rotational speed ω. No slippage—as is the case with the asynchronous motor—occurs.

(44) FIG. 5 illustrates a first embodiment of a block diagram of regulating an output pressure P.sub.OUT system according to the present invention. Herein, the conveying volume setpoint Q.sub.SET is fed into a computing unit 9. Computing unit 9 therefrom calculates a setpoint rotational speed main component ω.sub.SET1+2 as pilot control signal. Setpoint rotational speed main component ω.sub.SET1+2 of setpoint rotational speed ω.sub.SET is generated herein advantageously without influence of disturbances. The interactions already discussed in FIG. 2 and FIG. 3 are advantageously used for this purpose, which will be discussed in more detail in regard to FIG. 6. In addition, an actual pressure value P.sub.FBK is obtained from a pressure sensor 113 and converted by way of an AD-converter 6 into a digitized sensor output value for determination of output pressure P.sub.OUT; compared in comparator 1c with setpoint pressure value P.sub.SET and the error rotational speed ω.sub.ERR supplied to a PID regulating amplifier 2.

(45) Setpoint rotational speed main component ω.sub.SET1+2 is added in adder 1b to error rotational speed ω.sub.ERR thus obtaining a setpoint rotational speed ω.sub.SET as the actuating variable. Thus, actuating variable for the motor is no longer motor current I.sub.MOT but motor rotational speed ω.sub.SET. In an actuator movement this corrective signal ω.sub.ERR has a small part in the rotational speed control. The part is considerably less than 50%, preferably less than 20%. This permits regulating of the hydraulic drive system in a robust and at the same time accurate manner.

(46) With the inventive regulating method, the lossy and non-linear characteristics of hydraulic drive system 10 as well as its compression and decompression effects are considered. The therefore necessary corrective value—error rotational speed ω.sub.ERR—has a small component compared to the total rotational speed range of pump 5. This error rotational speed (DERR can now be easily and robustly determined with an additional component from a simple PID-regulator. The following applies:
ω.sub.ERR=PID(P.sub.SET−P.sub.FBK)  (7)

(47) With: PID=function of a PID regulator 2 P.sub.SET=setpoint pressure P.sub.FBK=actual pressure value

(48) Corrective signal ω.sub.ERR does not have to cover the entire rotational speed range of pump 5, since it is added to setpoint rotational speed main component ω.sub.SET1+2. Therefore, only the deviation between the simplified linear model and the actual system has to be regulated.

(49) Hydraulic drive system 10 according to FIG. 5 includes a power amplifier 3 and a frequency converter 7 in order to produce an input rotational speed ω.sub.IN for motor drive 4 from setpoint rotational speed ω.sub.SET with which motor drive 4 is driven in order to drive hydraulic pump 5 and in order generate output pressure P.sub.OUT.

(50) FIG. 6 illustrates a second design example of a block diagram for regulating output pressure P.sub.OUT according to the present invention. In contrast to the first design example according to FIG. 5, computing unit 9 is shown in more detail and in addition a consuming device 8 (for example a cylinder) is indicated. The following description is based on the previous description of FIG. 5 which will not be repeated here.

(51) According to FIG. 6, a first setpoint rotational speed component ω.sub.SET1 is formed from setpoint pressure P.sub.SET. For this, the relationship illustrated in equation (6) and FIG. 3 is applied in a computing unit 9a. The following applies:
ω.sub.SET=P.sub.SET/P.sub.MAX*ωP.sub.MAX  (8)

(52) The algebraic sign of first setpoint rotational speed component ω.sub.SET1 is positive, in order to build up output pressure P.sub.OUT.

(53) A second setpoint rotational speed component ω.sub.SET2 is formed from volume flow Q.sub.SET. For this, the relationship illustrated in equation (5) and FIG. 2 is applied in a computing unit 9a. The following applies:
ω.sub.SET2=Q.sub.SET/Q.sub.P  (9)

(54) Second setpoint rotational speed component ω.sub.SET2 is necessary in order to accept volume flow Q caused by pump 5 due to the movement of the actuator. The algebraic sign of second setpoint rotational speed component ω.sub.SET2 can be positive or negative, depending on the direction of movement in actuator 8. For example during the draw process (see FIG. 8, time span from t.sub.CP to t.sub.BDC) the algebraic sign is negative. In this time span pump 5 operates as a hydrometer and must accept fluid from the cylinder of the actuator. If the pump were to be driven only with this second setpoint rotational speed component ω.sub.SET2 then no output pressure P.sub.OUT would be generated.

(55) Both setpoint rotational speed component ω.sub.SET1 and ω.sub.SET2 are added in adder 1a.

(56) As already described in FIG. 5, corrective rotational speed ω.sub.ERR is formed from the difference between setpoint pressure value P.sub.SET and pressure actual value P.sub.FBK—determined via pressure sensor 113 (not show in FIG. 6)—by way of comparator 1c and PID regulator 2. Setpoint rotational speed ω.sub.SET is then obtained at the output of adder 1b as follows:
ω.sub.SET1=ω.sub.SET2+ω.sub.ERR  (10) ω.sub.SET1=component for volume flow ω.sub.SET2=component for pressure build-up ω.sub.ERR=component for compensating of non-linear malfunctions

(57) The now obtained setpoint rotational speed ω.sub.SET is transferred to amplifier 3 as actuating variable, as descried in FIG. 5.

(58) In FIG. 6 it is already indicated that a device 8 as a consuming device is connected to pump 5. This device 8 comprises an actuator which is driven by hydraulic drive system 10. The actuator is for example a cylinder, supporting a draw cushion as an element in a deep draw device, as illustrated for example in FIG. 7. A sensor element (not illustrated) on or in the actuator detects pressure actual value P.sub.FBK, which is provided by way of a first AD converter 6a to comparator 1c.

(59) In addition it is indicated in FIG. 6 that volume flow Q.sub.SET is removed from device 8. The relevant value is provided by way of a second AD converter 6b to computing unit 9b in order to determine second setpoint rotational speed component ω.sub.SET2. This volume flow Q.sub.SET is detected by a sensor element (not illustrated) that is mounted on an additional element, for example on the upper or lower tool of the deep draw device in FIG. 7, wherein the additional element influences hydraulic drive system 10.

(60) Setpoint volume flow Q.sub.SET can for example be determined simply from an actuator speed and an effective actuator surface or an element speed and an effective element surface. The speed signal can for example be determined by way of a differentiation of a path detected by a sensor element. From the first derivation of the position of the actuator or of the element the speed of the additional actuator may for example be deduced. The following applies:
V.sub.ACTUATOR=d/dt POS.sub.ACTUATOR  (11) With: V.sub.ACTUATOR=speed of actuator/element POS.sub.ACTUATOR=position of actuator/element

(61) Volume flow Q.sub.SET then is calculated:
Q.sub.SET=V.sub.ACTUATOR*A.sub.Wirk  (12) With: A.sub.Wirk=effective surface of actuator/element

(62) With determined volume flow Q.sub.SET, second setpoint rotational speed component ω.sub.SET2 can then be determined according to equation (9).

(63) In an additional embodiment, volume flow Q.sub.SET can also result directly from the distance/time specification of a primary movement control. For example, the speed of an element in device 8, for example the upper tool and/or the draw cushion is known to a primary CNC control. With a crank mechanism for the upper tool the speed can be calculated for example from the angle position and angle speed of the crank drive. This CNC can thus deliver operand V.sub.ACTUATOR or the calculated result Q.sub.SET directly to computing unit 9.

(64) FIG. 7 illustrates one design example of a device 8 in FIG. 6 according to the current state of the art. Device 8 is for example a deep draw device which is connected with hydraulic drive system 10 and is driven at least partially by same.

(65) A support 105 is provided in device 8 shown in FIG. 7. A draw cushion table 107 is provided as an element in order to arrange a material 108 on its surface. Arranged material 108 is formed by way of device 8, for example in a drawing process in order to produce a component therefrom. For this purpose, material 108 is clamped in a material retainer 109. Draw cushion table 107 is moved by way of a hydraulic cylinder 106, causing a drawing punch 112 to move in vertical direction. A position sensor element 114 is provided to sense position POS.sub.ACTUATOR of draw cushion table 107. Hydraulic cylinder 106 is moved in vertical direction by way of hydraulic drive system 10 consisting of amplifier 3, motor 4 and pump 5, and thus moves draw cushion table 107 and thereby also drawing punch 112. An additional position sensor element 114 is provided to detect position POS.sub.ACTUATOR of hydraulic cylinder 106. A pressure produced by pump 5 is detected by pressure sensor 113 in order to detect the actual pressure value P.sub.PFK.

(66) An additional element 110—in this case an upper tool—is moved in upward and downward direction in FIG. 7 by way of a crank mechanism and by way of a non-illustrated drive device. Additional element 110 includes for example a die 111 and a plunger 115. An additional position sensing element 114 is provided in order to detect position POS.sub.ACTUATOR of additional element 110, for example die 111.

(67) The mode of operation of the device is explained in the description of FIG. 8. In regard to the deep drawing process and relevant technical arrangements and dynamic effects we refer you to reference book (“Handbuch der Umformtechnik”, especially chapter 4. (Handbook for forming technology), Springer Publishing, edition 1, edited by Schuler GmbH.).

(68) FIG. 8 shows exemplary signal curves for regulating output pressure P.sub.OUT according to the invention by using actuators and their sensory data.

(69) FIG. 8 illustrates a distance/time progression of additional element 110—also referred to as upper tool or slide—and the distance/time progression of element 107—also referred to as draw cushion or die cushion, abbreviated as DC.

(70) Additional element 110 can for example be moved up and down by way of the crank mechanism. In the case of a crank mechanism additional element 110 follows the progression of a hyperbolic function. With alternative servo-electric or servo-hydraulic drives additional element 110 can be any desired distance/time relationship.

(71) From the curve in FIG. 8 it can be easily seen at the top that element 107 is waiting on a collision position CP and that this position initially does not change. As soon as additional element 110 impacts element 107 in collision position CP at time point t.sub.CP due to the crank mechanism, additional element 110 determines the distance/time behavior of element 107 to the point of a lower dead center BDC to an additional time point t.sub.BDC. In the time span between the two points in time t.sub.CP and t.sub.BDC the drawing process of material 108 occurs. After additional element 110 is moved upward by the crank mechanism and thereby lifts off element 107 the controlled non-critical reverse movement of element 107 back to collision point CP occurs, so that after interim removal of the manufactured/formed component a new material 108 can be positioned.

(72) In the lower signal curve in FIG. 8, setpoint pressure value P.sub.SET for regulating output pressure P.sub.OUT according to the invention is also shown for the drawing process. According to first progression a, this can be a constant pressure or any other desired progression b, for example according to a look-up table LUT. This is compared with actual pressure value P.sub.PFK that is captured by way of pressure sensor 113. It should be appreciated that the volume flow setpoint Q.sub.SET of the hydraulic drive system 10 may be determined by use of at least one parameter of an actuator and/or element 128 or an element 110 which is driven by the hydraulic drive system 10 or an element 110 which influences the hydraulic drive system 10.

(73) Within the scope of the invention, all described and/or drawing and/or claimed elements can be combined with each other as desired.

(74) While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.

COMPONENT IDENTIFICATION LIST AND ABBREVIATIONS

(75) 1a, b adder 1c Comparator 2 PID regulator 3 Amplifier 4 motor/motoric drive 5 pump 6a, b analog digital converter 7 frequency converter 8 device for deep drawing with hydraulic actuator 9a, b computing unit 9 10 hydraulic drive system 100 method 101-104 process steps 105 support 106 cylinder 107 draw cushion table 108 material, blank 109 material retainer 110 additional element—upper tool 111 die 112 drawing punch 113 pressure sensor 114 sensor element for position detection 115 plunger A.sub.WIRK effective surface of actuating cylinder a constant setpoint pressure during drawing process b optional setpoint pressure during drawing process BDC lower dead center of upper tool CP collision point between upper tool and draw cushion DC draw cushion I.sub.MOT motor current I.sub.S stator current I.sub.SET current setpoint value J.sub.MOTOR rotor inertia motor J.sub.PUMP rotor inertia pump J.sub.TOTAL total rotor inertia M.sub.FRICT mechanical friction of pump M.sub.MOT motor torque M.sub.POUT torque of pump, hydrostatic load torque P.sub.ERR error pressure P.sub.FBK actual pressure value P.sub.MAX maximum pressure P.sub.OUT output pressure P.sub.SET, P.sub.CMD setpoint pressure value Q.sub.OUT output conveying volume of pump during operation Q.sub.P conveying volume of pump per revolution Q.sub.SET setpoint conveying volume QSET Rs stator winding—effective resistance Rr rotor winding—effective resistance s travel path of additional actuator t time t.sub.BDC time point below dead center t.sub.CP time point collision point Ud differential voltage Us stator voltage Up rotor voltage A.sub.ACTUATOR speed of additional actuator Xs stator winding—reactance X.sub.r rotor winding—reactance X.sub.d reactance synchronous motor—synchronous reactance α angular acceleration ω.sub.ERR error rotational speed of pump to compensate for non-linear, malfunctions ω.sub.IN input rotational speed ω.sub.MAX maximum rotational speed of pump ωP.sub.MAX rotational speed of pump to produce maximum pressure against blocked pressure output ω.sub.SET setpoint rotational speed of pump ω.sub.SET1 first setpoint rotational speed component for pressure build-up of pump ω.sub.SET2 second setpoint rotational speed component for volume flow of pump ω.sub.SET1+2 setpoint rotational speed main component as pilot control signal