EP2498982B1 - Machine press - Google Patents

Description

The present invention relates to a machine press having a machine structure, a lower tool carrier arranged in fixed spatial relation to the machine structure, an upper tool carrier which is linearly movable up and down by one operating stroke relative to the lower tool carrier, and an upper tool carrier acting on the upper tool carrier. the downward movement of the upper tool carrier causing hydraulic drive.

Machine presses of the type specified above are known in various designs. A typical example of such machine presses are press brakes, as they are used for bending of sheets. The relevant state of the art includes in particular the JP 05293548 A . JP 56165520 A . JP 05015928 A . JP 2000343126 A . JP 2001113317 A . AT 008633 U1 . EP 692327 B1 . EP 1564414 A1 . EP 103727 A1 . DE 1906317 . EP 1228822 B1 and EP 2036711 A1 , A machine press according to the preamble of claim 1 is from the AT 008633 U1 known.

The DE 9207905 U1 discloses a forming machine (eg hydraulic press or hydraulically driven forging machine) in which the drive comprises at least one pump cylinder which can be acted upon by a crank blowing apparatus and withdrawal cylinders which are constantly rechargeable accumulator pressure. The forming force applying cylinder is connected to the pump cylinder connected via a line which is connected via a controlled non-return valve to a low-pressure vessel. In a single-acting running retraction cylinder with a liquid accumulator or double action running retraction cylinder connecting line with the low pressure vessel, a second controlled check valve is arranged. By juxtaposing short crank strokes of the pump, longer total strokes of the working piston are achieved. A switching of the second check valve with the crank frequency prevents a return stroke during the reloading of the pump cylinder from the low pressure container via the first check valve.

On pressbrakes and other machine presses of the type specified in the introduction, various requirements are made in practice. Thus, the corresponding machines should be reliable, cost-effective, economical, space-saving, easy to maintain and user-friendly as well as long-lasting and process-efficient, ie fast, as well as with the highest precision and reproducibility work. There are also aspects of job security, energy efficiency and other environmental considerations such as the use of environmentally sound equipment.

It is an object of the present invention to provide a machine press as defined in the preamble of claim 1 which is distinguished by particular practicality in terms of the above-cited catalog, with particular emphasis on high reliability, ease of maintenance and ease of use, e.g. short process cycles, is laid.

• Der Hydraulikantrieb umfasst mindestens ein abgeschlossenes, autarkes hydraulisches Antriebssystem, welches seinerseits mindestens eine hydraulische Zylinder-Kolben-Einheit und mindestens ein diese beaufschlagendes, aus einem Vorratsbehälter versorgtes Hydraulikaggregat umfasst.
• Das mindestens eine hydraulische Antriebssystem ist zwischen einem Eilgang, in dem eine erste wirksame Kolbenfläche von dem mindestens einen Hydraulikaggregat beaufschlagt wird, und einem Pressgang, in dem das mindestens eine Hydraulikaggregat eine gegenüber der ersten wirksamen Kolbenfläche wesentlich größere zweite wirksame Kolbenfläche beaufschlagt, umschaltbar.

• Die Hydraulikflüssigkeit des mindestens einen hydraulischen Antriebssystems ist in einem den Vorratsbehälter bildenden Druckspeicher bevorratet, der dem gesamten betreffenden hydraulischen Antriebssystem ständig zumindest einen über dem Umgebungsdruck liegenden Basisdruck aufprägt.
• Zwischen dem kolbenstangenseitigen Arbeitsraum und dem kolbenseitigen Arbeitsraum mindestens einer hydraulischen Zylinder-Kolben-Einheit des mindestens einen hydraulischen Antriebssystems besteht keinerlei hydraulische Verbindung.
• Der obere Werkzeugträger ist mittels einer Federeinrichtung, die das Gewicht (die Gewichtskraft) des oberen Werkzeugträgers, des hieran angebauten Werkzeugs und der mit dem oberen Werkzeugträger verbundenen Komponenten des Hydraulikantriebs sowie die durch den in dem mindestens einen hydraulischen Antriebssystem herrschenden Basisdruck implizierte Schließkraft überkompensiert, in seine obere Endlage vorgespannt.

This object is achieved, as indicated in claim 1, by a machine press of the type described, which is characterized in a functional combination with each other further by the following features:

• The hydraulic drive comprises at least one self-contained hydraulic drive system, which in turn comprises at least one hydraulic cylinder-piston unit and at least one hydraulic unit acting on it and acting on a reservoir.
• The at least one hydraulic drive system is between a rapid traverse, in which a first effective piston surface is acted upon by the at least one hydraulic unit, and a press gear, in which the at least one hydraulic unit opposite the first effective piston area substantially larger second effective piston area acted upon, switchable.

• The hydraulic fluid of the at least one hydraulic drive system is stored in a pressure accumulator forming the reservoir, which constantly imposes at least one base pressure above the ambient pressure on the entire relevant hydraulic drive system.
• There is no hydraulic connection between the piston rod-side working space and the piston-side working space of at least one hydraulic cylinder-piston unit of the at least one hydraulic drive system.
• The upper tool carrier is overcompensated by means of a spring device which includes the weight (the weight) of the upper tool carrier, the tool attached thereto and the components of the hydraulic drive connected to the upper tool carrier, and the closing force implied by the base pressure prevailing in the at least one hydraulic drive system its upper end position biased.

A particularly pronounced advantage of the machine press according to the invention over the prior art is the achievable very high operating speed, ie the minimum cycle times. This is achieved by a possible in the application of the invention substantial shortening of the dead or Idle times, ie those times when the upper tool carrier of the machine press performs inefficient idle strokes. In that regard, the present invention uses, inter alia, the fact that in conventional Abkant- and other machine presses typically only a small proportion (eg 3mm) of the entire operating stroke (eg 40-50mm) forms the forming of the workpiece pressing, a much larger proportion of the operating stroke meanwhile represents an inefficient idle stroke. Although, as is also implemented in the machine press according to the invention, it is known that at least one hydraulic drive system of the hydraulic drive designed so that the idle stroke can be traversed in so-called. Rapid with comparatively high speed; however, as has now been recognized by the inventors of the present invention, there still remains a not inconsiderable potential for shortening the cycle time, without compromising or diminishing the achievement of the remaining practical requirements; On the contrary, various other requirements, as will be explained in detail below, can be achieved even further by machine presses according to the invention than in the prior art.

In functional interaction with the other, the machine press according to the invention distinguishing features is of particular importance that the at least one hydraulic drive system has a designed as a pressure accumulator reservoir for the hydraulic fluid, which is biased so that in the entire relevant hydraulic drive system always, ie at any place and at any time during the entire operating cycle ', a base pressure prevails, which is above the ambient pressure (standard conditions according to DIN). For this ensures a particularly rapid, complete and trouble-free filling of the at least one hydraulic cylinder-piston unit of the at least one hydraulic drive system at rapid speed, in which only a part of the total available piston area, namely only to achieve the high speed of the upper tool carrier the first effective piston surface, is acted upon by the hydraulic unit, which is supplied by the more than the remaining portion of the entire piston area limited working space (directly) from the reservoir (filled) is. In rapid traverse, the working space of the at least one hydraulic cylinder-piston unit which is not acted upon by the hydraulic unit is actively filled from the pressure accumulator in this way. This in turn allows both the increase in the speed of movement in rapid traverse and the use of relatively compact so-called "Nachsaugventilen", ie Nachsaugventilen with comparatively small flow cross-sections, without the risk of cavitation in the hydraulic fluid. The correspondingly compact dimensioning of the Nachsaugventile, which are typically switchable between a secured by a check valve Nachsaug- and working position and for the provision of the hydraulic drive (upward movement of the upper tool carrier) relevant passage position, affects accordingly low masses This in turn has a positive effect on the switching dynamics of the valve, which in turn benefits the machine dynamics. To that extent proves, again in functional interaction with the above-described technical aspects, as favorable that the upper tool carrier by means of a (permanently acting) spring means, the weight (weight) of the upper tool carrier, the attached thereto tool and the upper Tool carrier associated components of the hydraulic drive and overcompensated by the prevailing in the prevailing at least one hydraulic drive system base pressure closing force in the sense of opening the machine press, that is biased in its upper end position. For this causes immediately after completion of the application of the second effective piston area of the at least one hydraulic cylinder-piston unit of the at least one hydraulic drive system by the hydraulic unit, the opening of the machine press, which in turn advantageously (see below) shortest paths and thus the lowest Let accelerating masses be realized.

With regard to the generic AT 008633 U1 It is quite surprising that can achieve the desired benefits by the inventive design of the hydraulic drive. Because the fact that by the constant loading of the entire hydraulic drive system (or the entire hydraulic drive systems) by (each) an accumulator with a higher than the ambient pressure Pressure level in the drive system (or the drive systems) is always a force acting on the (respective) piston (closing force) is generated, makes a correspondingly larger or more dimensioned spring device required and initially suggests that the machine dynamics suffers that when lifting In addition to the weight of the moving parts, the spring device must also overcome or compensate for the said permanently acting force of the upper tool carrier. In that regard, the inventive design of the machine press is also by AT 008633 U1 just not suggested.

The above-described advantageous effects of the present invention set in typical applications already at a ambient pressure only moderately exceed the base pressure, for example, even if the base pressure in the relevant hydraulic drive system always, ie at any place and at any time during the entire operating cycle 'prevails, is about 1 bar above the ambient pressure. In such a design of the hydraulic drive system, the accumulator is designed so that it still imposes a positive pressure of about 1 bar above ambient pressure with minimal filling, ie with fully lowered piston of the associated cylinder-piston unit, the hydraulic system. A preferred base pressure is about 1 to 2 bar above ambient pressure. Preferably, the design of the pressure accumulator and its adaptation to the other components of the hydraulic drive system takes place in such a way that the maximum pressure in the pressure accumulator, which adjusts itself when the piston of the cylinder-piston unit is completely raised and thus the maximum filling of the pressure accumulator, is not more than about 5 bar, particularly preferably about 4 to 5 bar.

A first preferred embodiment of the invention is characterized in that the hydraulic drive comprises two hydraulic drive systems each having at least one cylinder-piston unit, wherein each of the two hydraulic drive systems comprises a separate hydraulic unit. Not only can shortest cable routes within the hydraulic drive be realized in this way, which in turn - due to the reduced masses to be moved and lower line losses - is favorable both for a high machine dynamics and for a high efficiency. Also from the point of view of ease of assembly, maintenance and service, this construction, as can be seen from the further explanations of the present invention, considerable advantages.

According to another preferred development of the present invention, the spring unit is integrated in at least one hydraulic cylinder-piston unit of the at least one hydraulic drive system. It is particularly preferably designed as a gas spring. In that regard, namely, the (filled with hydraulic fluid) piston rod working space of the relevant hydraulic cylinder-piston unit hydraulically with an external, correspondingly biased pressure accumulator - This has nothing to do with the pressure accumulator described above in the hydraulic drive system - be connected. Serving solely the opening of the machine press, in terms of pressure ratios, volumes and other design features specifically matched to the requirements existing so far pressure accumulator can be directly attached to the cylinder of the relevant hydraulic cylinder-piston unit, which in turn not only a laying of separate hydraulic lines superfluous but also - in terms of optimum efficiency - minimizes the masses to be moved and line losses.

It is even better if the piston rod working space of the relevant hydraulic cylinder-piston unit itself is filled with a spring gas which is compressed during the downward movement of the upper tool carrier. This reduces still further the moving masses in the piston rod working space, between this and the (external) pressure accumulator and in the latter needs to be moved, which further contributes to the possibility of further increasing the engine dynamics compared to the embodiment set forth above. The (gas-filled) piston rod working space can communicate with internal gas-filled compensation chambers provided inside the cylinder-piston unit, which can be arranged in particular in the piston and / or in the housing, in order to optimally adapt the spring characteristic of the gas spring to the respective application. Such internal compensation spaces in turn allow the Design of particularly compact and lightweight drive units with minimal moving masses, because the axial length of the piston rod working space does not need to exceed the stroke of the drive unit appreciably, only to provide the maximum compressed gas filling receiving residual space. The arrangement of the said compensation chamber in the piston at a suitable location can, moreover, contribute to a further reduction in weight.

In order to balance the hydraulic drive with a view to optimizing the conditions existing in rapid traverse and in press operation, it is particularly advantageous if the area ratio between the second effective working surface and the first effective working surface is at least 3.

In yet another preferred embodiment of the machine press according to the invention, a machine control is provided which is acted upon by a pressure sensor determining the working pressure in the at least one hydraulic drive system. The consideration of the existing in the respective individual pressing task in the hydraulic drive specific pressure conditions in the machine control allows a targeted individual influence on the hydraulic drive, not only to minimize the duration of each cycle ', but also with regard to the quality of the result of workpiece forming. This applies in a special way in the event that the hydraulic drive of machine press according to the invention has two or even more self-contained, self-contained hydraulic drive systems, which can be tuned to each other via an adjustment of the respective pressure conditions in the (common) machine control control technology. Thus, for example, the off-center feed of the machine press with a workpiece control technology compensate.

Yet another preferred embodiment of the machine press according to the invention is characterized in that in the at least one hydraulic drive system, the at least one hydraulic cylinder-piston unit and the associated hydraulic unit constitute a complete drive with a common control, valve and line block to the the assigned accumulator is directly connected, so that no free pipe or hose lines exist. As a result, optimal structural and functional conditions can be achieved in many respects, namely with regard to the required installation space, the achievable efficiency, the installation effort, the reliability, the maintenance and service friendliness. This meets the needs of the user and interests as far as possible, especially in the case of such a hydraulic complete drive with a - completely closed by the execution of the reservoir for the hydraulic fluid pressure accumulator - hydraulic system only electrical interfaces for machine control must exist.

The hydraulic unit is according to another preferred embodiment of the invention as Reversieraggregat, i. designed as an aggregate with reversible conveyor. More details are given below.

In the case of particular machine constellations, it may prove advantageous if the at least one hydraulic drive system comprises two (optionally differently configured) optionally switchable hydraulic pumps. In particular, in this case, the admission of the at least one hydraulic cylinder-piston unit in rapid traverse and in the press gear in a larger spectrum can be individually adapted to the specific pressing task, in particular by applying the first effective piston surface in rapid traverse with two parallel operated hydraulic pumps and loading the second effective piston area in the press gear with only one hydraulic pump.

Against a comparable background, it may be advantageous for particular machine constellations, if the at least one hydraulic drive system comprises two selectively switchable hydraulic cylinder-piston units, one of which can be connected in rapid traverse by hydraulic connection of the two working spaces with each other - as a differential cylinder. In particular, in this case in rapid traverse - in the interest of a quick movement of the upper tool carrier - only one of the hydraulic cylinder-piston units are acted upon, while in the press gear - to increase the pressing force - both hydraulic cylinder-piston units are acted upon.

Fig. 1

in perspektivischer, teilweise schematischer Ansicht ein Ausführungsbeispiel für eine als Abkantpresse ausgeführte, zwei hydraulische Antriebseinheiten aufweisende erfindungsgemäße Maschinenpresse,

Fig. 2

in perspektivischer Ansicht einen Komplettantrieb der bei der in Fig. 1 gezeigten Abkantpresse verwendeten Art,

Fig. 3

einen Hydraulikschaltplan der Antriebseinheiten der in Fig. 1 gezeigten Abkantpresse,

Fig. 4

eine Abwandlung des Hydraulikschaltplans nach Fig. 3,

Fig. 5

den Hydraulikschaltplan einer abgewandelten Antriebseinheit und

Fig. 6

eine Abwandlung des Hydraulikschaltplans nach Fig. 5; weiterhin zeigt

Fig. 7

den Hydraulikschaltplan sowie (schematisch) die konstruktive Gestaltung einer Zylinder-Kolben-Einheit einer wiederum anderen bevorzugten Ausführungsform der Erfindung.

In the following, the present invention will be explained in more detail with reference to preferred embodiments illustrated in the drawing. It shows

Fig. 1

in a perspective, partially schematic view of an embodiment of a machine designed as a press brake, two hydraulic drive units having machine press according to the invention,

Fig. 2

in perspective view a complete drive at the in Fig. 1 type press brake used,

Fig. 3

a hydraulic circuit diagram of the drive units of in Fig. 1 shown press brake,

Fig. 4

a modification of the hydraulic circuit diagram after Fig. 3 .

Fig. 5

the hydraulic circuit diagram of a modified drive unit and

Fig. 6

a modification of the hydraulic circuit diagram after Fig. 5 ; continues to show

Fig. 7

the hydraulic circuit diagram and (schematically) the structural design of a cylinder-piston unit of yet another preferred embodiment of the invention.

In the Fig. 1 machine press 1 shown as a press brake has a machine structure 3 comprising two C-frames 2. In a fixed spatial relationship to the machine structure 3, namely each fixed to the lower profile leg of the two C-frame 2, a lower tool carrier 4 with a lower bending tool 5 is arranged on this. An equipped with an upper bending tool 6, in Fig. 1 Upper tool carrier 7, which is shown in its uppermost position, can be moved linearly up and down relative to lower tool carrier 4 by one operating stroke H (double arrow A). Since the in Fig. 1 shown press brake to this extent corresponds to the well-known state of the art, further explanations are unnecessary in this respect. This also applies to constructive details known as such, not shown here, eg with regard to the connection of the bending tools with the respective associated tool carrier.

In order to effect the downward movement of the upper tool carrier, two hydraulic drive systems, namely a left hydraulic drive system 8 and a right hydraulic drive system 9 are provided, which together form a force acting on the upper tool carrier 7 hydraulic drive 10. The two hydraulic drive systems 8 and 9 are closed and self-sufficient, i. they have no hydraulic connection to each other. They are designed in the form of complete drives 11.

Each of the two complete drives 11 embodied in mirror image form comprises in particular (compare also the hydraulic circuit diagram according to FIG Fig. 3 ) a hydraulic cylinder-piston unit 12 with a cylinder 13 and a guided therein piston 14 whose piston rod is fixedly connected to the upper tool carrier 7, and a hydraulic cylinder-piston unit 12 acting hydraulic unit 15 with a driven by an electric motor 16 reversible hydraulic pump 17. The hydraulic pump 17 is a built-in pump in a common control -, Valve and line block 18 housed, which at the same time also forms a pump block and at the directly and the cylinder 13 and the electric motor 16 are flanged. Furthermore, a pressure accumulator 19 is flanged directly to the control, valve and line block 18, which forms a reservoir and expansion tank for the hydraulic fluid of the hydraulic drive system 8 and in particular the hydraulic unit 15 supplies. The hydraulic system is hermetically sealed. In him, the hydraulic fluid is clamped and prevails constantly and everywhere at least one lying above the ambient pressure base pressure, which is impressed him through the pressure accumulator 19. By the hydraulic cylinder-piston unit 12, the pressure accumulator 19 and required in Fig. 1 and 2 only schematically illustrated valves 20 and a filter 33 are flanged for the hydraulic oil directly to the control, valve and line block 18 and the hydraulic pump is housed in this, none of said hydraulic components interconnecting free, ie outside the control, valve - And line block 18 laid pipe or hose lines.

The upper tool carrier 7 is by means of a spring device 21, the weight of the upper tool carrier 7, the attached thereto tool 6 and connected to the upper tool carrier components of the hydraulic drive 10, that is, the piston 14 of the two hydraulic drive systems 8 and 9, and by The overriding of the base pressure in the two hydraulic drive systems implied closing force, in its upper end position ( Fig. 1 ). The spring device is integrated into the hydraulic cylinder-piston units 12 of the two hydraulic drive systems 8 and 9 such that in each case the piston rod working chamber 22 of the hydraulic cylinder-piston units 12 is hydraulically connected to an associated external pressure accumulator 23. The external pressure accumulator 23 is flanged directly to the associated cylinder 13, so that in turn no pressure accumulator 23 with the associated hydraulic cylinder-piston unit 12 connecting free pipe or hose exists. By appropriate gas bias in the pressure accumulators 23, the spring unit 21 is designed as a gas spring. Since the upward movement of the upper tool carrier 7 takes place solely by the spring means 21, ie by acting on the Kolbenstangenarbeitsräume 22 by the respectively associated pressure accumulator 23, the hydraulic system of the spring means 21 forms a closed system, in particular by none of the two cylinder-piston units '12 a hydraulic connection between the piston rod side working space 22 and the piston-side working space 24 is made.

The hydraulic drive 10 of the press brake is switchable between a rapid traverse and a press gear. In this case, after the upward force of the spring device 21 constantly acts on the upper tool carrier 7 at such a height that the weight of all the movable components of the press brake and the closing force implied by the base pressure prevailing in the two hydraulic drive systems are overcompensated and the upper tool carrier in FIG its uppermost position is biased, even at rapid traction active movement of the upper tool carrier 7 by the hydraulic drive 10, but not a free movement due to gravity. This is achieved by a respective auxiliary piston 26 dips into the piston 14 of the two hydraulic cylinder-piston units 12, namely in each case a bore 25 introduced therein. More about this is the AT 8633 U1 ( Fig. 3 and 4 including associated description) removable. As a result, a comparatively small first effective piston surface 27 is acted upon by the hydraulic unit at rapid speed, while a much larger second effective piston surface 48, which is composed of the first effective piston surface 27 of the auxiliary working space 28 and the annular surface 29 of the kobenseitigen working space, 24. To switch between the rapid traverse and the press gear, the valve 30, which closes the connection of the hydraulic unit 15 to the piston working space 24 in rapid traverse, opens in the press passage in contrast. In rapid traverse filling of the piston working chamber 24 via the secured via a check valve 31 path of the Nachsaugventils 32. The hydraulic unit 15 and the hydraulic cylinder-piston unit 12, in particular its auxiliary piston 26 and first effective piston surface 27, are coordinated so that at rapid traction - taking into account the weight of the movable components of the press brake and the closing force, the is adjusted by the provided via the pressure accumulator 19, prevailing in the piston working chamber 24 base pressure - the opposing force of the spring means 21 can be overcome.

For the pressing operation, the valve 30 is switched so that the hydraulic unit 15 acts in parallel on the piston working space 24 and the auxiliary working space 28. At the end of the closing movement, ie typically when the upper tool carrier 7 reaches a predetermined position, the delivery of the hydraulic unit 15 is shut down and stopped so that the upper tool carrier stops. The tool then stops for a short time before the so-called "decompression stroke" begins, ie the slow, controlled lifting of the upper tool and opening of the press over a small stroke (eg 2-3 mm) by reversal of the reversible hydraulic unit. At the end of the decompression stroke, that is, when the high pressure in the system is at least substantially reduced, the valve 30 and the Nachsaugventil 32 are reversed, so that adjusted in the piston working space 24 of the pressure accumulator 19 to the system impressed base pressure and the piston 14th retracts under the action of the spring means 21. The retraction of the piston 14 takes place in the Rapid traverse controlled (braked) by the auxiliary work space 28 is controlled and controlled in the pressure accumulator 19 via the still operated with respect to the closing of the press reverse flow direction hydraulic unit 15. In that regard, as is in Fig. 3 is shown in this hydraulic drive system, the flow rate of the hydraulic unit 15 and adjustable. The latter is associated with the fact that the capacity of the accumulator 19 is comparatively low, at least significantly smaller than the conventionally used ventilated tanks, so that only a reduced surface is available for heat dissipation. The machine control S communicates via corresponding control lines with the motor 16 of the hydraulic unit 15 and the valve 30 and the Nachsaugventil 32, namely the corresponding components of both hydraulic drive systems 8 and 9.

This in Fig. 4 illustrated modified hydraulic system differs from the one after Fig. 3 essentially by another embodiment of the hydraulic unit 15 '. This includes namely a fixed displacement pump 35, ie a continuously pumping pump. Accordingly, a pressure relief valve 36 is provided on the pressure side, which absteuert beyond the existing in the respective operating point requirement flow. Furthermore, a 3/3-Wegevantil 37 is disposed between the hydraulic unit 15 'and the hydraulic cylinder-piston unit 12.

This can take a closed position and an open position in addition to the zero position shown in which the three ports are locked against each other. In the closing position - depending on the position of the valve 30 - either only the auxiliary working space 28 (rapid traverse) or this and in addition also the piston working chamber 24 (press gear) is acted upon by the hydraulic unit 15 '. In the open position, the cylinder port 38 is connected to the pressure accumulator 19. The above statements apply similarly to the end of the press gear and the opening of the press. At the end of the closing movement, ie typically when the upper tool carrier 7 reaches a predetermined position, the directional control valve 37 is reversed to its zero position (blocking position), so that the upper tool carrier stops. To initiate the "decompression stroke", the directional control valve 37 is reversed to its open position, wherein the pressure reduction takes place both in the piston working space 24 and in the auxiliary working space 28 and the slow, controlled lifting of the upper tool and opening the press controlled via a discharge edge. At the end of the decompression stroke, the valve 30 and the Nachsaugventil 32 are reversed, so that in the piston working space 24 of the pressure accumulator 19 impressed on the system base pressure adjusts and the piston 14 retracts under the action of the spring means 21. The retraction of the piston 14 takes place in rapid traverse controlled (braked) by the auxiliary working space 28 via the directional control valve 37, namely controlled by the discharge edge and controlled in the pressure accumulator 19 is emptied.

Shown is in Fig. 4 Furthermore, a pressure in the hydraulic cylinder-piston unit 12 prevailing working pressure constantly receiving pressure sensor 39. The pressure signal is processed in the machine control S. It can be used in particular as auxiliary control variable in the sense that the signal of the independently operating displacement encoder is checked for its plausibility and possibly modified for further processing in the controller. The latter comes especially into consideration when the displacement measurement signal (eg in the case of a stuck component and / or excessive static friction) indicates no movement, but the pressure signal indicates such a working pressure within the hydraulic system that movement of the upper tool carrier would actually be expected. By taking into account or evaluating the pressure signal, such exceptional operating conditions can be detected and can be influenced on the machine control, for example, to prevent the safety at work threatening sudden breakage of the upper tool carrier with further pressure increase. Also, after the pressure sensor responds to changes in the hydraulic drive earlier than the distance measuring system, by adjusting the signals of the displacement measuring system and the pressure sensor, the control can be optimized in terms of the most accurate compliance with a given speed profile for the upper tool carrier, which can contribute to the cycle time - in particular by minimizing the transitional periods - to further shorten.

The hydraulic system according to the in Fig. 5 illustrated hydraulic circuit diagram differs from the after Fig. 4 in particular in that it has two structurally separate hydraulic cylinder-piston units 12'A and 12'B, whose pistons 14 ', however, are both connected to the upper tool carrier 7 and coupled to each other in this way. Of the two hydraulic cylinder-piston units 12'A and 12'B is optional, via the valve 30 'switchable, only one acted upon by the hydraulic unit 15', namely the hydraulic cylinder-piston unit 12 'shown on the right in the drawing. A, or both cylinder-piston units 12'A and 12'B simultaneously and in parallel. In rapid traverse alone, the hydraulic cylinder-piston unit 12'A is acted upon, so that the first effective piston surface 45 is identical to the end face of the piston 14'A. The piston working space 24'B of the other hydraulic cylinder-piston unit 12'B, which has no connection to the associated, in turn acted solely by the spring device 21 piston rod working chamber 22'B, fills via the Nachsaugventil 32. To avoid unnecessary hydraulic currents can in Rapid traverse the piston working space 24'A and the piston rod working space 22'A of the hydraulic cylinder-piston unit 12'A are short-circuited via the valve 40; In this switching position of the valve 40, the hydraulic cylinder-piston unit 12'A acts as a differential cylinder. In press case, if over one corresponding circuit of the valve 30 both hydraulic cylinder-piston units 12'A and 12'B piston side of the hydraulic unit 15 'are acted upon, ie the end face 45 of the piston 14'A and the end face 46 of the piston 14'B together the second effective Form piston surface 47, the piston rod working space 22'A the hydraulic cylinder-piston unit 12'A is connected by reversing the valve 40 to the pressure accumulator 19 to provide the maximum closing force.

Shown is in Fig. 5 Furthermore, a further on the pressure side of the hydraulic unit 15 'prevailing pump pressure continuously receiving further pressure sensor 41. The pressure signal of this pressure sensor is processed in a common for both hydraulic drive systems machine control.

This in Fig. 6 illustrated modified hydraulic system differs from the one after Fig. 5 While the pressure side of one pump 17 "A is constantly connected to the pressure port 42 of the directional control valve 37, the pressure side of the other pump 17" B can be connected to the pressure reservoir 19 via the valve 43 and Pump 17 "B thus be switched to circulation promotion. In rapid traverse of the hydraulic drive, due to the corresponding switching position of the valve 43, both pumps 17 "A and 17" B convey to the hydraulic cylinder-piston unit 12'A. In the press, however, promotes - due to a reversal of the valve 43 - only the pump 17 "A to both hydraulic cylinder-piston units 12'A and 12'B, while the pump 17" B promotes circulation. The check valve 44 secures the pressure side of the pump 17 "A against the valve 43.

The hydraulic system after Fig. 7 corresponds in essential aspects to those after Fig. 3 , For this reason, the explanations and explanations of the Fig. 3 in the same way, except as indicated below.

In the cylinder-piston unit 12 (shown schematically), the piston rod working chamber 22 is filled with a spring gas, wherein the gas filling is under a bias voltage via a corresponding filling pressure. The seals 51 which are illustrated schematically on the piston 14 and which bear sealingly on the inner surface 50 of the cylinder 13, are designed in a manner known to be suitable in view of the fact that they delimit a gas space from the piston-side hydraulic working space 24. With the piston rod working space 22 are via respective channels 52 and 53 two - each annular running - compensation spaces fluidly in communication, namely a cylinder-side first compensation chamber 54 and a piston-side second compensation chamber 55. By providing the corresponding compensation spaces for the gas filling of the gas spring unit 21 is the axial length of the piston rod working space 22 more or less completely for the stroke of the piston available, ie it is in the piston rod working space 22 only a small or no residual volume needed.

Merely to avoid misunderstandings, it should again be emphasized at this point that the illustration of the cylinder-piston unit 12 follows Fig. 7 is a schematic representation after it is particularly readily apparent that the cylinder 13 may not be constructed in one piece, but - in such a known manner - is assembled from several parts.

Claims (13)

1. A machine press (1), particularly a press brake, with a machine structure (3), a lower tool carrier (4) that is arranged in a fixed spatial relation to the machine structure, an upper tool carrier (7) that can be linearly displaced (A) upward and downward relative to the lower tool carrier by a working stroke (H), and a hydraulic drive (10) that acts upon the upper tool carrier and causes the downwardly directed motion of the upper tool carrier, wherein said hydraulic drive features at least one closed, autarkic hydraulic drive system (8; 9) that in turn comprises at least one hydraulic piston-cylinder unit (12; 12'A, 12'B) and at least one hydraulic power unit (15, 15', 15") that acts upon this piston-cylinder unit and is supplied from a storage tank, with said machine press having the following features:

   - the at least one hydraulic drive system (8; 9) can be switched between a rapid motion mode, in which a first effective piston area (27; 45) is acted upon by the at least one hydraulic power unit, and a pressing motion mode, in which the at least one hydraulic power unit acts upon a second effective piston area (48; 47) that is significantly larger than the first effective piston area;

   - no hydraulic connection whatsoever exists between the working chamber (22; 22'B) on the piston rod side and the working chamber (24; 24'B) on the piston side of at least one hydraulic piston-cylinder unit (12; 12'B) of the at least one hydraulic drive system;

   - the upper tool carrier (7) is prestressed into its upper end position by means of a spring unit (21) that overcompensates the weight of the upper tool carrier, the tool installed thereon and the components of the hydraulic drive connected to the upper tool carrier, as well as the closing force implied by the prevalent base pressure in the at least one hydraulic drive system;
   characterized in that

   - the hydraulic fluid of the at least one hydraulic drive system is stored in a pressure accumulator (19) that forms the storage tank and constantly subjects the entire associated hydraulic drive system to a base pressure that lies at least above the ambient pressure.
2. The machine press according to Claim 1, characterized in that the hydraulic drive (10) comprises two hydraulic drive systems (8, 9) that respectively feature at least one piston-cylinder unit (12; 12'A, 12'B), wherein each of the two hydraulic drive systems comprises a separate hydraulic power unit (15; 15', 15").
3. The machine press according to Claim 1 or Claim 2, characterized in that the spring unit (21) is integrated into at least one hydraulic piston-cylinder unit (12; 12'B) of the at least one hydraulic drive system (8, 9).
4. The machine press according to Claim 3, characterized in that the spring unit (21) is realized in the form of a pneumatic spring, wherein the piston rod working chamber (22) features a gas filling.
5. The machine press according to Claim 4, characterized in that a gas-filled compensation chamber (55) on the piston side and/or a gas-filled compensation chamber (54) on the cylinder side is fluidically connected to the piston rod working chamber (22).
6. The machine press according to Claim 3, characterized in that the spring unit (21) is realized in the form of a pneumatic spring, wherein the piston rod working chamber (22; 22'B) of the hydraulic piston-cylinder unit (12; 12'B) preferably is hydraulically connected to an external pressure accumulator (23).
7. The machine press according to one of Claims 1 to 6, characterized in that the area ratio between the second effective piston area (48) and the first effective piston area (27) amounts to at least 3.
8. The machine press according to one of Claims 1 to 7, characterized in that a machine control (S) is provided and acted upon by a pressure sensor (39, 41) that determines the working pressure in the at least one hydraulic drive system (8, 9).
9. The machine press according to one of Claims 1 to 8, characterized in that the at least one hydraulic piston-cylinder unit (12) and the associated hydraulic power unit (15) of the at least one hydraulic drive system (8, 9) represent a complete drive (11) with a common control, valve and conduit block (18), to which the associated pressure accumulator (19) is also directly connected such that no exposed tubing or piping exists.
10. The machine press according to one of Claims 1 to 9, characterized in that the at least one hydraulic drive system (8, 9) comprises two selectively connectable hydraulic pumps (17"A, 17"B) of preferably different design.
11. The machine press according to one of Claims 1 to 10, characterized in that the at least one hydraulic drive system (8, 9) comprises two selectively connectable hydraulic piston-cylinder units (12'A, 12'B), one of which (12'A) acts as a differential cylinder in the rapid motion mode.
12. The machine press according to one of Claims 1 to 11, characterized in that the cylinder (13) of the at least one hydraulic piston-cylinder unit (12; 12'A, 12'B) is arranged in a fixed spatial relation to the machine structure (3) and the piston rod of said piston-cylinder unit is connected to the upper tool carrier (7).
13. The machine press according to one of Claims 1 to 12, characterized in that the hydraulic power unit is realized in a reversible fashion.

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