EP2712688A1 - Die cushion drive and method for operating a die cushion drive - Google Patents

Abstract

The die cushion drive (1) has electric machine (5) for driving pump (8), and hydraulic cylinders (3,4) having chambers (21-24). The pump feeds chambers of the hydraulic cylinders. The hydraulic cylinders are mechanically connected to die cushion (2). An independent claim is included for method for driving die cushion drive.

Description

The invention relates to a die cushion drive. In a hydraulic press, a movable die cushion may be provided. The movement of the die cushion is achieved by means of a die cushion drive. In hydraulic presses, the pressure in the hydraulic medium is generated in particular by means of a pump driven by an electric motor.

An object of the invention is to provide an effective die cushion drive, or specify an effective method for operating a die cushion drive.

A solution of the problem results in a die cushion drive with the features of claim 1 or in a method of operating a die cushion drive according to claim 6. Further embodiments of the claimed device or the claimed method will become apparent according to claims 2 to 5 or 7 to 13th

In a hydraulic die cushion, a defined controlled counterforce is applied in the forming area. This is done for example by one or a plurality of hydraulic cylinders, wherein a plurality means at least two. The hydraulic fluid (particularly oil) displaced by movement of a hydraulic cylinder in a chamber of the cylinder is e.g. drained into a tank.

In the control of the force exerted by the die cushion or in the control of the force exerted by the die cushion movement, high accuracy is advantageously required from a process engineering point of view. This means that sensors and / or regulators as well as actuators in particular have a sampling time of "1 ms in order to achieve a fast response of an actuator. Examples of sensors are: pressure sensor, Speed sensor, position sensor, etc. Examples of actuators are: hydraulic valve (in particular a proportional valve or a servo valve), a hydraulic pump (in particular a servo pump), an electric machine (in particular a synchronous machine or an asynchronous machine).

In a pressure control only via hydraulic pumps, it is difficult to achieve fast rise times, which can be used in one embodiment of the die cushion drive for system pressure hydraulic pressure accumulator, which are loaded via pump technology.

In one embodiment of the die cushion drive, a hydraulic accumulator and fast proportional valves are used in hydraulic drawing cushion. However, it is difficult to recover energy from a movement of the die cushion. In one embodiment, however, a pneumatic accumulator is filled, for example via a receding hydraulic cylinder, with which then an upward movement of the die cushion is realized. When using an electrically driven die cushion energy recovery is possible by a generator operation of an electrical machine used there.

In a further embodiment of the die cushion drive, a pump is used per piston side of the hydraulic cylinder, which is driven by electric machines, the electric machines are regeneratively operable to recover energy. Then, a generator operation is advantageous for each direction of movement of the hydraulic cylinder possible.

In one embodiment of a die cushion drive, this has a first pump, a first electric machine for driving the first pump and a hydraulic cylinder or a plurality of hydraulic cylinders. The hydraulic cylinder or cylinders each have a first chamber and a second chamber for hydraulic fluid, wherein the first pump is provided for supplying the first chamber, or the first chambers of the hydraulic cylinder, wherein the hydraulic cylinder or the hydraulic cylinders are mechanically connected to a die cushion. To enable energy recovery, the electric machine can be operated as a generator. If hydraulic fluid is pressed by the pump, the pump serves as a drive for the electrical machine, which generates electrical energy in regenerative operation and feeds it back into a power network and / or into a capacitor and / or into a DC link of a drive network.

In one embodiment of the die cushion drive, a pump (in particular a servo pump) supplies a multiplicity of first chambers (in particular upper chambers of the respective hydraulic cylinder) together. This reduces the number of electrical and mechanical components if it is not necessary to provide a pump driven by an electrical machine for each first chamber of a plurality of hydraulic cylinders.

In one embodiment of the die cushion drive, a pressure sensor is provided for measuring the hydraulic pressure in a first pressure line between the first pump and the hydraulic cylinder or the plurality of hydraulic cylinders. The pressure sensor serves as an aid for adjusting a pressure at the first chamber of one of the hydraulic cylinders by means of the first pump. The sensor measures an actual value that can be used for pressure regulation or pressure control.

The hydraulic cylinder or the hydraulic cylinders each have, in addition to the first chamber, a second chamber, wherein the second chamber is in particular a lower chamber. Each die cushion is one or a plurality of hydraulic cylinders present, being provided in a configuration for the second chambers separate pressure sensors. In particular, for a plurality of hydraulic cylinders with respect to the second chambers of these cylinders, at least one respective pressure sensor and / or a steady hydraulic valve and / or a servo pump. The servo pumps are each mechanically coupled with an electric machine that can be operated both mechanically and generically. The pressure sensors may also be attached to pressure lines which are directly connected to the respective second chamber of the cylinder to measure the pressure in the second chamber.

In one embodiment of the die cushion drive, a first hydraulic cylinder of the plurality of hydraulic cylinders is connected to its second chamber via a second pressure line to a second pump, wherein a second hydraulic cylinder of the plurality of hydraulic cylinders connected to its second chamber via a third pressure line to a third pump is. In this way, the respective first chamber of the hydraulic cylinder can be fed via only one pump, and the respective second chambers of these cylinders can be fed or emptied separately from one another via different pumps which are separate from one another. This allows flexible control of different hydraulic cylinders.

In one embodiment of the die cushion drive, the second pressure line is connected to a first valve and the third pressure line is connected to the second valve, wherein in particular a first pressure sensor for measuring the pressure in the second pressure line and a second pressure sensor for measuring the pressure in the third pressure line is available. Via the valves, it is possible to discharge hydraulic fluid from the respective second chamber in addition to the pumps connected to the second chambers of the hydraulic cylinders. The valves may be a proportional valve or a servo valve. The valves, like the electric machines for driving the pumps (in particular the servo pumps) are actuators of a control of the die cushion drive.

In one embodiment of the die cushion drive, the valve is used as an actuator for a pilot control when Hydraulikflüssikeit from the second chamber of the respective cylinder is dismissed. The second chambers associated pumps can be used as an actuator for pressure control.

In order to be able to control the die cushion even better or to operate the die cushion drive more energy efficient, the valve is used as an actuator for the pressure control and the respective electrically driven pump, which is assigned to the second chamber of the respective cylinder, as an actuator for the pilot control , The valves have a fast response and are therefore very well suited as an actuator for a fast control. Due to the coupling of electrical machine and pump, this actuator has a lower rigidity with respect to the control, so that it is advantageous not to use this for the pressure control but as an actuator for the pressure precontrol. This can also have the advantage that energy can be fed back into a power grid by the generator operation of the electric machine. Since a smaller volumetric flow of hydraulic fluid is also necessary for the regulation by the valve as a manipulated variable, if this is compared with a valve which serves as an actuator for a pressure regulator, it results that comparatively more hydraulic fluid is passed through the pump in a displacement phase can, which is directly coupled to the second chamber.

In one embodiment of the die-cushion drive, the first electric machine is controllable by means of a first drive control, wherein the second electric machine is controllable by means of a second drive control, wherein the third electric machine is controllable by means of a third drive control, wherein a data bus data-technically interconnects the drive controls. Advantageously, the pressure control of the die cushion is integrated with the valve as a manipulated variable in a control device, which also has the drive control or a plurality of drive controls. By integrating the regulations The signal propagation times improve and a faster, improved control of the die cushion is achieved.

In a method of operating a die cushion drive, pressure control and pilot control are active during controlled movement of the die cushion. For pilot control, a pump is used, which is also referred to below as the second pump with respect to the following figure designation. The second pump is coupled to a second electric machine. The electric machine drives the pump so or is driven by this particular in generator operation of this. Advantageously, the electric machine is operated as a generator during a period in which the feedforward control is active. In particular, this period is a period in which a plunger of the press exerts a force on the die cushion and plungers as well as die cushions move in the same direction. As an actuator of the pressure control, the first valve is used. The valve is, for example, a proportional valve or a servo valve. Due to the generator operation of the electric machine of the pump, which hangs with the pressure line of the valve, the energy efficiency of the press can be increased.

In one embodiment of the method for operating a die cushion drive, a die cushion drive is used, which has one of the embodiments already described. Also in the following description of the figures further embodiments of the die cushion drive will be described.

In one embodiment of the method, when the ram of the press of the press on the die cushion is switched to the pressure control. The switching takes place, for example, from a position control or speed control to the position control. For the regulation of position, speed or pressure, controller types known from control engineering can be used.

In one embodiment of the method, the die cushion is pre-accelerated before the impact of the plunger on the die cushion. This allows a reduction of disturbances for the control of the die cushion when ram and die cushion meet.

In one embodiment of the method, a pilot control of the die cushion is performed, so that the pilot control by means of the second pump or in particular by means of a third pump or further pump takes place as an actuator for this pilot control. The second, third or further pump are connected to chambers of hydraulic cylinders in such a way that hydraulic fluid is displaced from these chambers during a pressure (displacement phase).

In one embodiment of the method, these chambers are also each connected to a valve. In a variation of the method, the valves are closed when the second and the third pump serve as a drive for the respective generator-operated electric machine. In another variation, these valves are active as an actuator (open or closed) and serve to control the pressure of the die cushion. In one embodiment of the method, a discharge is performed at the end of the drawing area. This additionally improves the system behavior.

In one embodiment of the method for operating a die cushion drive pressure control and feedforward control are both active in a displacement phase, in particular, a weighting factor for the feedforward control is variable. This weighting factor can be changed (reduced or increased) before the control and / or during control. This can be used to set the influence of the feedforward control on the behavior of the die cushion.

In one embodiment of the method for operating a die cushion drive, the first pump is inactive in the displacement phase. The first pump is the pump, which is a variety supplied by similar chambers of different hydraulic cylinders with Hydraulikflüssgkeit. The first pump is advantageously connected to the second or third or further pump such that hydraulic fluid is exchangeable. For example, hydraulic fluid from the valves or the second or third or further pump Hydraulikflüssikgeit be pressed by the passive first pump. Thus, in this passive operating state of the first pump, these serve as a drive for the associated first electric machine, which can also be operated as a generator and can thus regenerate electrical energy.

In one embodiment of the method for operating a die cushion drive, the first pump is activated in a phase of an upward movement of the die cushion. Both the first pump and all other pumps can advantageously be operated in four quadrants. This also applies accordingly to the electrical machines which are coupled to the pumps.

FIG 1

eine erste Phase eines Pressvorgangs einer Presse mit einem Ziehkissen;

FIG 2

eine zweite Phase eines Pressvorgangs einer Presse mit einem Ziehkissen;

FIG 3

eine dritte Phase eines Pressvorgangs einer Presse mit einem Ziehkissen.

FIG 4

einen Ziehkissenantrieb ohne Steuerventile;

FIG 5

einen Ziehkissenantrieb mit einem Drucktank;

FIG 6

einen Ziehkissenantrieb mit je zwei Pumpen pro Zylinder; und

FIG 7

einen Ziehkissenantrieb mit nur einer Gemeinschaftspumpe.

The invention will be described by way of example with reference to figures. Showing:

FIG. 1

a first phase of a pressing operation of a press with a die cushion;

FIG. 2

a second phase of a pressing operation of a press with a die cushion;

FIG. 3

a third phase of pressing a press with a die cushion.

FIG. 4

a die cushion drive without control valves;

FIG. 5

a die cushion drive with a pressure tank;

FIG. 6

a die cushion drive with two pumps per cylinder; and

FIG. 7

a die cushion drive with only one community pump.

1. 1. Eine Abwärtsbewegung des Stößels und ggf. eine Vorbeschleunigung des Ziehkissens vor dem Auftreffpunkt;
2. 2. Eine Verdrängungsphase: Beim Auftreffen des Stößels auf das Ziehkissen wird in Druckregelung umgeschaltet und am Ende des Ziehbereichs wird gegebenenfalls entlastet;
3. 3. Eine Aufwärtsbewegung des Stößels und anheben des Ziehkissens in eine Ausgangsstellung.

A sequence of a pressing operation of a press with die cushion can be broken down by way of example into the following steps (phases):

1. 1. A downward movement of the plunger and possibly a pre-acceleration of the die cushion before the impact point;
2. 2. A displacement phase: Upon impact of the plunger on the die cushion is switched to pressure control and at the end of the drawing area is optionally relieved;
3. 3. An upward movement of the plunger and lifting the die cushion in a starting position.

In order to better describe these steps is exemplified in the following FIGS. 1 to 3 directed. It will FIG. 1 used to describe the first step, FIG. 2 to describe the second step and FIG. 3 to describe the third step. In the description of the figures, the same reference numerals are used for similar elements.

The representation according to FIG. 1 schematically shows a section of a press 40 with a plunger 32 and a die cushion 2. With arrows, the potential directions of movement 33 of the plunger 32 and the potential directions of movement 34 of the die cushion 2 are shown. For the movement of the die cushion 2, a die cushion drive 1 is provided. This die cushion drive 1 has the die cushion 2 and a first 3 and second 4 hydraulic cylinders 3, 4 connected thereto. A die cushion can also be beweget with a hydraulic cylinder number of one or more two, which, however, in the FIGS. 1 to 3 not shown. The first hydraulic cylinder 3 has a first chamber 21 (upper chamber) and a second chamber 23 (lower chamber). The second hydraulic cylinder 4 also has a first chamber 22 (upper chamber) and a second chamber 24 (lower chamber). The first chambers 21 and 22 of the hydraulic cylinders 3 and 4 are fed or emptied via a first pressure line by means of a first pump 8. The second chamber 23 of the hydraulic cylinder 3rd is fed or emptied via a second pressure line 26 by means of a second pump 9. The second chamber 24 of the hydraulic cylinder 4 is fed or emptied via a third pressure line 27 by means of a third pump 10. The first pump 8 is coupled to a first electric machine 5. The second pump 9 is coupled to a second electric machine 9. The third pump 10 is coupled to a third electric machine 7. The electrical machines 5, 6 and 7 can be operated by a motor or by a generator, wherein for controlling the electrical machines 5, 6, 7 drive controllers 28, 29 and 30 are provided. Although not every part of a drive is shown, it is not shown, for example, the converter itself, it can be seen that a first drive control 28 controls the first electric machine 5, that a second drive control 29 controls the second electric machine and that a third drive control 30 the third electric machine regulates. The drive controls 28, 29 and 30 are connected to each other via a data bus 31 in terms of data technology. On the data bus and a parent Ziehkissenregelung 35 is connected. By means of the parent die cushion control 35, for example, valves 15 and 16 can also be actuated. In one embodiment of the die cushion drive 1, various controllers can also be integrated in a control device, which is not shown. The valves 15 and 16 can be divided into a first valve 15 and a second valve 16. The first valve 15 is connected to the second pressure line. The second valve 16 is connected to the third pressure line 27. Via a manifold 36, the first, second and third pump 8, 9, and 10 and the first and second valves 15 and 16 are connected together. The manifold 36 is emptied into a tank 20 and can receive hydraulic fluid from the tank. For measuring hydraulic pressures, a first pressure sensor 11 is provided for the second pressure line 26, a second pressure sensor 12 is provided for the third pressure line 27, and a third pressure sensor 13 is provided for the first pressure line. The pressure sensors 11, 12 and 13 detect in particular for a Pressure control Pressure actual values. The data connection of the pressure sensors 11, 12 and 13 to the pressure control is not shown in the figures to maintain clarity.

In the FIGS. 1 to 3 Movement directions 14 of the die cushion 2 and flow direction 17, 18 and 19 of the hydraulic fluid are shown by arrows.

The FIG. 1 is intended to represent a first phase of a pressing operation, wherein the first phase may precede other phases not shown. In one embodiment of the die cushion drive 1 in the first phase (downward movement), a common servo pump 8 (first pump) for the oil supply (oil is a hydraulic fluid) of all die cushion cylinder (first hydraulic cylinder 3 and second hydraulic cylinder 4) provide, with a pilot control for the die cushion cylinder 3 and 4 via individual pumps (second pump 9 and third pump 10) per cylinder 3 and 4 is controlled. Advantageously, the first and second valves 15 and 16, which are required in particular in the second phase as hydraulic valves; closed in this first phase. In the second phase (displacement phase), which is closer to the FIG. 2 is described with the impact of the plunger 32 on the die cushion 2 (between plunger and die cushion is not shown to be pressed part), the pressure control via the hydraulic valves 15 and 16 started and on the other hand, via the respective servo pump 9 and 10, the movement the die cushion piloted.

The representation according to FIG. 2 shows how FIG. 1 a die cushion drive 1, wherein the plunger 32 rests on the die cushion 2. An intermediate material to be pressed is not shown. With the FIG. 2 is the phase two shown in the converted to the pressure control of the die cushion 2. Now, the second pump 9 and the third pump 10 are used as actuators for a pilot control and the first valve 15 and the second valve 16 as Used actuators for pressure control, so this combination results in an advantage of rapid control of valves and in addition the regenerative capacity of pumps with particular servomotors (second electric machine 6 and third electric machine 7). Advantageously, in one embodiment, the pressure control can also be used in addition to the precontrol via the servo pumps 9 and 10. Also, a common servo pump 8 (first pump) can be switched off or it can be built with this a common system pressure.

In the illustration after FIG. 3 is a third phase, an upward movement of the die cushion 2, shown, wherein in Figure three, the plunger is no longer shown. The upward movement is illustrated by the arrow 14. The upward movement is controlled or regulated by means of the respective servo pump (second and third pumps 9 and 10) of the die cushion cylinders 3 and 4. For a better movement control, a counterpressure can be built up via the common system pressure pump (first pump 8). The flow directions 17, 18 and 19 for the hydraulic fluid rotate in comparison to the steps 1 and 2, as also in FIG. 3 is shown.

Through the combination of servo pump and hydraulic valve in the displacement phase, can be achieved via the valve, a fast pressure control and fed back via the servo pump, the main oil flow (this is the hydraulic fluid) regenerative. If the valve and pump both regulate the pressure regulation in the displacement phase, you may work against each other. To avoid this, the main oil stream is e.g. via the pump two and three dissipated and fed back by the pressure regenerative energy. About the valves 15 and 16 fast reaction times can be achieved in the scheme.

The figures described below focus on the hydraulic concept of the die cushion drive.

The representation according to FIG. 4 shows a variation of the die cushion drive 1, wherein in the illustrated variation of the die cushion drive 1 for the second chambers 23 and 24 of the hydraulic cylinders 3 and 4, only the pumps 9 and 10 and provides no valves, as in the FIGS. 1 to 3 shown. This embodiment without control valves has the advantage that less mechanics is used, which can fail. By the use of the pumps 9 and 10, which are driven by the electric machines 6 and 7, further, a pressure control, as well as a pilot control can be performed. The pumps 9 and 10 serve as an actuator for the pilot control and for pressure control. The electric machines 6 and 7 can continue to be operated as a generator when the second chambers 23 and 24 are reduced in size, wherein advantageously the pump 8 is used as an actuator for the pressure control.

The representation according to FIG. 5 shows a die cushion drive 1, wherein the supply of the first chambers 21 and 22 takes place with hydraulic fluid via a pressure tank 47. The pressure tank 47 forms a kind of battery pump. This differs from the version in FIG. 4 shown. This also allows complex mechanics to be reduced, which increases the reliability.

The representation according to FIG. 6 shows a die cushion drive 1, in which the first chambers 21 and 22 of the hydraulic cylinders 3 and 4 are operated by separate pumps 8 and 42. The first chamber 21 of the hydraulic cylinder 3 is connected via a fourth pressure line 43 to the first pump 8, wherein the pressure in the pressure line 43 via a fourth pressure sensor 45 is measurable. The first chamber 22 of the hydraulic cylinder 4 is connected via a fifth pressure line 44 to the fourth pump 42, wherein the pressure in the pressure line 44 via a fifth pressure sensor 45 is measurable. The use of four pumps, two for each cylinder, has the advantage that the hydraulic cylinders 3 and 4 are more independent of each other are controllable. Each hydraulic cylinder 3, 4 has an additional actuator for pressure control and / or pilot control, which does not directly affect the behavior of other cylinders, as in a shared pump for the first chambers FIG. 4 the case is. The pump 42 is connected to the electric machine 41. Since two cylinders are assigned to each cylinder and thus also two electrical machines, at least one of the electric machines per cylinder can be operated as a generator, if the further motor is operated. Both electric machines can also be operated by a motor, which, if appropriate, helps to improve the quality of control in the case of pressure regulation.

The representation according to FIG. 7 shows a further variation of a die cushion drive 1. In the illustrated system, the first pump 8 is used to build up a hydraulic pressure for the whole hydraulic system. The first hydraulic cylinder 3 is connected to the first and second chambers 21, 23 to a first 3/4-way valve 48. The connection is made via the second pressure line 26 and the fourth pressure line 43. The first pressure sensor 11 is used for pressure measurement in the second chamber 23. The fourth pressure sensor 45 is used for pressure measurement in the first chamber 21. The second hydraulic cylinder 4 is connected to the first and second Chamber 22, 24 connected to a second 3/4-way valve 49. The connection is made via the third pressure line 27 and the fifth pressure line 44. The second pressure sensor 12 is used for pressure measurement in the second chamber 24. The fifth pressure sensor 46 is used to measure pressure in the first chamber 22. There is only one pump 8, the with the electric machine 5 is coupled, wherein the electric machine 5 is motorized as well as generically operable.

Claims (13)

A die cushion drive (1) which has a first pump (8), a first electric machine (5) for driving the first pump (8) and one or a plurality of hydraulic cylinders (3, 4), wherein the hydraulic cylinder or cylinders (3, 4 ) have a first chamber (21, 22) and a second chamber (23, 24), wherein the first pump (8) for feeding the first chambers (21, 22, 23, 24) of the hydraulic cylinder or cylinders (3, 4) is provided, wherein the hydraulic cylinders (3, 4) with a die cushion (2) are mechanically connected. The die-cushion drive (1) according to claim 1, wherein a pressure sensor (13) for measuring the hydraulic pressure is provided in a first pressure line (25) between the first pump (8) and the hydraulic cylinders (3, 4). Die cushion drive (1) according to claim 1 or 2, wherein a first hydraulic cylinder (3) of the plurality of hydraulic cylinders (3, 4) with its second chamber (23) via a second pressure line (26) with a second pump (9) is connected in that a second hydraulic cylinder (4) of the plurality of hydraulic cylinders (3, 4) is connected to its second chamber (23) via a third pressure line (27) to a third pump (9). The die cushion drive (1) according to one of claims 1 to 3, wherein the second pressure line (26) is connected to a first valve (15) and wherein the third pressure line (27) is connected to the second valve (16), wherein in particular a first Pressure sensor (11) for measuring the pressure in the second pressure line (26) and a second pressure sensor (12) for measuring the pressure in the third pressure line (27) is present. Die cushion drive (1) according to one of claims 1 to 4, wherein the first electric machine (5) by means of a first drive control (28) is controllable, wherein the second electrical Machine (6) by means of a second drive control (29) is controllable, wherein the third electric machine (7) by means of a third drive control (30) is controllable, wherein a data bus (31) connects the drive controls (28, 29, 30) data technology. A method for operating a die cushion drive (1), wherein during a controlled movement of the die cushion (2) a pressure control and a pilot control are active, wherein for pilot control a second pump (9) is used, wherein the second pump (9) with a second electrical Machine (6) is coupled, wherein during the feedforward control, the electric machine (6) is operated as a generator, wherein a first valve (15) is used as an actuator of the pressure control. A method for operating a die cushion drive (1) according to claim 6, wherein a die cushion drive (1) is used according to one of claims 1 to 5, wherein upon impact of a plunger (32) on the die cushion (2) is switched to the pressure control. A method of operating a die cushion drive (1) according to claim 6 or 7, wherein the die cushion (2) is pre-accelerated prior to impact of the plunger (32) on the die cushion (2). Method for operating a die-cushion drive (1) according to one of claims 6 to 8, wherein a pilot control of the die cushion (2) is carried out, wherein the pilot control takes place in particular by means of the second pump (9) and the third pump (10), wherein in particular the first valve (15) and the second valve (16) are closed. A method of operating a die cushion drive (1) according to claim 6 or 9, wherein a discharge is performed at the end of the drawing area. Method for operating a die cushion drive (1) according to one of claims 6 to 10, wherein in a displacement phase pressure control and feedforward control are both active, wherein in particular a weighting factor for the pilot control is variable. A method of operating a die cushion drive (1) according to any one of claims 6 to 11, wherein in the displacement phase, the first pump is inactive. A method of operating a die cushion drive (1) according to any one of claims 6 to 12, wherein in a phase of upward movement of the die cushion (2), the first pump (8) is active.

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