Patent Publication Number: US-10786845-B2

Title: Actuator device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is the United States national phase of International Application No. PCT/EP2016/075798 filed Oct. 26, 2016, and claims priority to Switzerland Patent Application No. 1582/15 filed Oct. 29, 2015, the disclosures of which are hereby incorporated in their entirety by reference. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to an actuator device for linear movement of an actuator output element along a movement axis. The invention relates also to a use of the actuator device. 
     Description of Related Art 
     During the process of shaping a deformable material in a forming device it is often necessary, on the one hand, to support the deformable material against movement or to brake a process-related displacement of the deformable material in a controlled way and, on the other hand, to eject the finished shaped material from a forming die. In some cases relatively large supporting and ejecting forces are required for that purpose. On the other hand, at least the ejection of the deformable material should take place at high speed so as to ensure a high machine cycle rate of the forming device. 
     WO 2010/118799 A1 describes a device for ejecting shaped parts from a forming die of a forming device. The ejecting device comprises two coupled drive units, of which one applies the relatively large release force required for releasing the shaped parts from the forming die, while the other performs the actual ejecting movement with a smaller ejection force but at a considerably higher speed. In one arrangement the drive unit responsible for applying the release force comprises a hydraulic cylinder in which a piston having a narrowly defined stroke length is displaceably mounted. The piston acts upon a rod-shaped ejector pin which breaks the shaped part away from the forming die. The drive unit for the actual ejecting movement comprises an electric motor drive which effects further movement of the ejector pin, the shaped part then being fully ejected from the forming die. The stroke length of that drive unit is substantially greater than the piston stroke length of the hydraulic drive unit. The electric motor drive can be a linear motor direct drive or a servo motor which is connected to the ejector pin, for example, by means of a rack and pinion connection. 
     That known ejecting device is not suitable for supporting a shaped part in the forming die during the forming operation or for braking the process-related displacement of the shaped part in a controlled way during the forming operation. 
     A problem underlying the present invention is therefore to provide an actuator device of the generic kind which is suitable both for moving an object and for supporting an object against undesirable deflected movements when acted upon by an external force, and also for controlled braking of an object in the event of its being displaced as a result of the action of an external force. 
     SUMMARY OF THE INVENTION 
     That problem is solved by the actuator device according to the present invention. Preferred uses of the actuator device are described herein. 
     The essence of the invention lies in the following: an actuator device for linear movement of an actuator output element along a movement axis comprises a first drive unit and a second drive unit. The first drive unit has a first piston chamber and a first piston mounted so as to be linearly displaceable therein and also first hydraulic means for displacing the first piston in the first piston chamber. The second drive unit has the actuator output element which is linearly movable along the movement axis and which can be coupled to the first piston of the first drive unit for thrust, so that by movement of the first piston in an outward direction the actuator output element is likewise moved in the outward direction. The second drive unit has a second piston chamber joined to the first piston chamber for conjoint movement therewith and a second piston mounted so as to be linearly displaceable in the second piston chamber and also second hydraulic or pneumatic means for displacing the second piston in the second piston chamber. The second piston is joined to the actuator output element for conjoint movement therewith, so that by movement of the second piston in the outward direction the actuator output element is movable out of the second piston chamber and by movement of the second piston in an inward direction opposite to the outward direction the actuator output element is movable into the second piston chamber. The actuator device has a position-measuring device for detecting the positions of the first piston and the second piston relative to a reference position that is fixed with respect to the device for a position-controlled movement of the actuator output element. 
     Because the second drive unit is in the form of a hydraulic or pneumatic piston drive, the actuator device is suitable not only for moving an object but also for supporting and braking an object. The position-measuring device for detecting the positions of the first piston and the second piston relative to a reference position that is fixed with respect to the device makes it possible to effect position-controlled movement of the actuator output element. 
     Advantageously the first drive unit is configured to generate a larger thrust force than the second drive unit. Conversely, it is advantageous if the second drive unit is configured to accelerate and move the second piston more quickly than the first drive unit accelerates and moves the first piston. In that way it is possible to combine a large thrust force and a rapid advance movement in an optimum way. 
     Advantageously the actuator device has pressure sensors for detecting the pressures in the first piston chamber and the second piston chamber of hydraulic or pneumatic medium located in the first piston chamber and the second piston chamber. This makes it possible to effect pressure- or force-controlled movement of the actuator output element. 
     Advantageously the actuator device comprises a control device which co-operates with the position-measuring device and the pressure sensors for the purpose of position- and force-controlled movement of the first piston and the second piston. 
     Preferably the actuator device has servo valves, which are arranged to be actuated by the control device and are advantageously configured for continuous operation, for supplying and discharging hydraulic or pneumatic medium to and from the first and second piston chambers. By means of the servo valves, the movement of the actuator output element can be controlled precisely and continuously. 
     Alternatively the actuator device has speed-controlled pumps, which are arranged to be actuated by the control device, for supplying and discharging hydraulic or pneumatic medium to and from the first and second piston chambers. 
     Advantageously the first drive unit comprises a bladder or diaphragm accumulator for resetting the first piston in the inward direction. In an advantageous alternative arrangement the first drive unit comprises a gas accumulator for resetting the first piston in the inward direction. This makes it possible to return the first piston with very little effort. 
     Advantageously an impact element is joined to the second piston for conjoint movement therewith, via which impact element the second piston is displaceable in the outward direction by the first piston. 
     According to a further aspect of the invention, the actuator device is used for applying a directed force to a deformable material in a forming device. 
     In an advantageous use, the deformable material is ejected from a forming die by the actuator device. In another advantageous use, during a forming process the deformable material is supported by the actuator device against the action of an external force. In a further advantageous use, displacement of the deformable material brought about by the action of an external force is braked in a controlled way by the actuator device. 
     The actuator device according to the invention is described in greater detail below on the basis of exemplary embodiments and examples of use and referring to the accompanying drawings, wherein: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1 —is a diagrammatic view of an exemplary embodiment of the actuator device according to the invention; 
         FIG. 2 —is a block diagram of a control device of the actuator device of  FIG. 1 ; 
         FIG. 3 —is a diagrammatic view of the actuator device of  FIG. 1  in the context of a forming device; 
         FIGS. 4-9 —show the actuator device of  FIG. 1  in various phases in a first application, and an associated force-path-time diagram; 
         FIGS. 10-17 —show in diagrammatic form the process sequence of a second application during the piercing/separating of a shaped part in a forming device; 
         FIGS. 18-22 —show the actuator device of  FIG. 1  in various phases in the second application during the piercing/separating of a shaped part, and an associated force-path-time diagram; 
         FIGS. 23-28 —show in diagrammatic form the process sequence of a third application during the descaling and shaping of a shaped part in a forming device; 
         FIGS. 29-34 —show the actuator device of  FIG. 1  in various phases in the third application during the descaling and shaping of a shaped part, and an associated force-path-time diagram; and 
         FIGS. 35-36 —each show in diagrammatic form a variant of a detail of the actuator device. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     The following observations apply in respect of the description which follows: where, for the purpose of clarity of the drawings, reference symbols are included in a Figure but are not mentioned in the directly associated part of the description, reference should be made to the explanation of those reference symbols in the preceding or subsequent parts of the description. Conversely, to avoid overcomplication of the drawings, reference symbols that are less relevant for immediate understanding are not included in all Figures. In that case, reference should be made to the other Figures. 
     The exemplary embodiment of the actuator device according to the invention shown with its functionally most important parts in  FIGS. 1-3  comprises a first drive unit  10  and a second drive unit  20 . The first drive unit  10  comprises a piston chamber  11 , for example a cylindrical piston chamber, having a first piston  12  which is mounted so as to be linearly displaceable therein. The second drive unit  20  comprises a piston chamber  21 , for example a cylindrical piston chamber, having a second piston  22  mounted so as to be linearly displaceable therein. The two piston chambers  11  and  21  are arranged in alignment one behind the other with respect to a movement axis A and are fixedly joined to one another. 
     The first piston chamber  11  is connected by way of two lines  15   a  and  15   b  to first hydraulic means which comprise a hydraulic source, which is only symbolised by a line  16 , two hydraulic accumulators  17   a  and  17   b , a first 4-port servo valve  18  configured for continuous operation, and a collecting tank  19 . As explained further below, only three of the four ports of the servo valve  18  are used, so that the first servo valve  18  can also be in the form of a 3-port valve. The two lines  15   a  and  15   b  open into the first piston chamber  11  in the region of the two longitudinal ends thereof. The line  15   a  leads to the first servo valve  18 . Via the line  15   b  the hydraulic accumulator (bladder or diaphragm accumulator)  17   b  is connected to the first piston chamber  11 . On the side of the line  15   a  the operating pressure of the first hydraulic means is up to about 350 bar (high-pressure circuit). On the side of the line  15   b  the operating pressure is substantially lower. The hydraulic accumulator  17   b  is therefore in the form of a low-pressure accumulator. On the side of the line  15   b  it is also possible to use a pneumatic pressure medium instead of a hydraulic medium, in which case a gas accumulator would be provided instead of the hydraulic accumulator  17   b . This is of advantage if a hydraulic bladder or diaphragm accumulator does not have sufficiently short reaction times for the particular use of the actuator device. 
     A rod-shaped impact element  23  is joined to the second piston  22  for conjoint movement therewith, which impact element passes, with sealing, through an end wall  21   a  of the second piston chamber  21  and through an adjoining end wall  11   a  of the first piston chamber  11  and projects into the first piston chamber  11 . On the side of the second piston  22  opposite the impact element  23  there is mounted for conjoint movement therewith a rod-shaped actuator output element  24 . The actuator output element  24  passes, with sealing, through an end wall  21   b  of the second piston chamber  21 , which end wall is located opposite the end wall  21   a , and (in the retracted state shown) projects slightly out of the second piston chamber  21 . The two pistons  12  and  22  and the impact element  23  and the actuator output element  24  are oriented in alignment (coaxially) with respect to the movement axis A. 
     The second piston chamber  21  is connected via two lines  25   a  and  25   b  to second hydraulic means which comprise a hydraulic source, which is only symbolised by a line  26 , a hydraulic accumulator  27 , a second 4-port servo valve  28  configured for continuous operation, and a collecting tank  29 . The two lines  25   a  and  25   b  open into the second piston chamber  21  in the region of the two longitudinal ends thereof. The operating pressure of the second hydraulic means is up to about 150 bar (low-pressure circuit). Instead of the second hydraulic means it would also be possible to provide pneumatic means, in which case analogously a pneumatic source would then be used instead of the hydraulic source and a gas accumulator instead of the hydraulic accumulator. 
     Connected to the first piston chamber  11  are two pressure sensors  31  and  32  which detect the pressures of a hydraulic medium located in the first piston chamber  11  on each side of the first piston  12 . Likewise, two pressure sensors  33  and  34  are connected to the second piston chamber  21 , which pressure sensors detect the pressures of a hydraulic or pneumatic medium located in the second piston chamber  21  on each side of the second piston  22 . 
     The actuator device also has a position-measuring device  40  which detects the positions of the first piston  12  and the second piston  22  relative to a reference position that is fixed with respect to the device. The magnetically operating position-measuring device  40  comprises a sensor bar  41 , position magnets  42  and  43  and an electronic measuring unit  44 . The position magnets  42  are fixedly arranged in the first piston  12 . The position magnets  43  are arranged in the free end of the impact element  23  and are fixedly joined thereto. Since the impact element  23  is in turn joined to the second piston  22  for conjoint movement therewith, the position of the second piston  22  is obtained directly from the position of the impact element  23 . The fixed sensor bar  41  is arranged axially and projects through the first piston  12  into the free end of the impact element  23 . In the event of a movement of the first or second piston  12 ,  22 , respectively, the position magnets  42 ,  43 , respectively, generate corresponding signals in the sensor bar  41  from which the electronic measuring unit  44  forms position or travel distance information. 
     The second piston  22  of the second drive unit  20  can be moved along the movement axis A in the direction of arrow P 1  (outward direction) as a result of being acted upon by pressurised hydraulic medium via the line  25   a  and in the direction of arrow P 2  (inward direction) as a result of being acted upon by pressurised hydraulic medium via the line  25   b . The impact element  23  is accordingly moved therewith and the actuator output element  24  is moved respectively out of and back into second piston chamber  21 . 
     The first piston  12  of the first drive unit  10  can be moved along the movement axis A in the direction of arrow P 1  (outward direction) as a result of being acted upon by pressurised hydraulic medium via the line  15   a . The return movement of the first piston  12  in the direction of arrow P 2  (inward direction) is effected as a result of the first piston  12  being acted upon by hydraulic medium from the hydraulic accumulator  17   b  via the line  15   b . The second piston  22  is coupled to the first piston  12  via the impact element  23  solely for thrust. That is to say, the first piston  12  is able to carry along the second piston  22  and therewith the actuator output element  24  in the outward direction only during its movement in the outward direction. The coupling of the two pistons  12  and  22  for thrust is of course active only when the two pistons are located in those positions in which the impact element  23  is in contact with the first piston  12 , as shown in  FIG. 1 . As a result of the described coupling of the two drive units  10  and  20 , or the pistons  12  and  22  thereof, the actuator output element  24  can (depending upon the position of the two pistons) be moved in the direction of arrow P 1 , that is to say moved outwards, by both drive units  10  and  20 . More details in this connection are given hereinbelow with reference to typical examples of use. 
     The movement or travel of the first piston  12  and the second piston  22  along the movement axis A can be pressure- or force-controlled by corresponding regulation of the servo valves  18  and  28  with the aid of the pressure sensors  31 - 34  (pressure and force are proportional over the effective piston surface areas) and position-controlled with the aid of the position-measuring device  40 . As shown in block diagram form in  FIG. 2 , the actuator device has for that purpose a control device  50  which co-operates with the position-measuring device  40  and the pressure sensors  31 - 34  and, by appropriate actuation of the two servo valves  18  and  28 , is configured to effect position- and force-controlled movement of the first piston  12  and the second piston  22  and therewith the actuator output element  24 . The control device  50  also comprises an operator interface  51 , via which it is possible to set the required forces and pressures and piston positions or piston stroke lengths during practical use of the actuator device. Instead of or in addition to the pressure sensors  31 - 34 , a force sensor can also be mounted on the actuator output element  24 , the force signal of which can be used for controlling the movement of the pistons. 
     The two drive units  10  and  20  have different layouts. The first piston  12  of the first drive unit  10  has an effective piston surface area that is substantially greater than that of the second piston  22  and is also acted upon by higher operating pressure. As a result, the first drive unit  10  can generate substantially greater thrust/holding forces or braking forces than the second drive unit  20 . Conversely, however, the movement of the first piston requires a substantially greater volume flow rate and is therefore slower. The second piston  22  of the second drive unit  20  has a relatively small effective piston (annular) surface area. As a result, the second drive unit  20  is able to generate only relatively small thrust/holding forces or braking forces. On the other hand, however, the second piston  22  can be accelerated and moved relatively quickly with a small volume flow rate. The combination of the two drive units  10  and  20  allows a certain degree of separation of force and movement. It enables very large thrust forces to be generated at relatively low speed and for smaller thrust forces to be generated via a relatively large piston stroke length at relatively high speed. The combination of the two drive units  10  and  20  provides optimum flexibility in respect of the use conditions or the usability of the actuator device. 
     In practice the first and second piston chambers  11  and  21  are preferably hollow-cylindrical and the first and second pistons  12 ,  22 , respectively, are correspondingly cylindrical. The internal diameter of the first piston chamber  11  is, for example, about 80 mm, that of the second piston chamber  21  about 50 mm. The diameter of the impact element  23  and the diameter of the actuator output element  24  are in each case about 40 mm. With those dimensions the effective piston surface area of the first piston  12  is Π*40 2 mm 2  on each side and the effective piston (annular) surface area of the second piston  22  is Π*(25 2 −20 2 ) mm 2  on each side. 
     The actuator device according to the invention is suitable for applications in which an object needs to be acted upon with a directed force. The application of force can be used, for example, to effect controlled movement of the object over a certain distance along a movement axis and in so doing overcome a resistance opposing the movement of the object (thrust force). An example thereof is the ejection of a shaped workpiece from a forming die of a forming device. The application of force can also be used to support or hold an object in place during the action of an opposing external force (holding force). An example thereof is the support of a blank to be shaped in a forming die while the blank is being acted upon by a punch. Furthermore, the actuator device is suitable for effecting controlled braking of the movement of the object brought about by the opposing action of an external force (braking force). An example thereof is the introduction, with controlled braking, of a blank into the forming die of a forming device. Movement, support and braking of an object can also be combined by means of the actuator device according to the invention and implemented in any desired order. The actuator device according to the invention is very especially suitable for use in forming devices for moving, supporting and braking shaped parts. 
     The basic functions of the actuator device (movement, support, braking), which will be apparent from the following description of typical applications, are individually adjustable and adaptable to the application in question. The fundamental advantages of the actuator device according to the invention are low wear to mechanical components; smooth movement sequence when used in a high-speed forming process; safe, central application of force; scope for very flexible realisation of the positions in the process; and a high degree of safety as a result of overload protection of the hydraulic system. 
       FIG. 3  shows the actuator device in a practical application, the actuator device being flange-mounted as a unit on a machine body  110  of a forming device  100 . In the drawing the first and second hydraulic means are here combined in a hydraulic block  60 , with only the hydraulic accumulator  17   b , the two servo valves  18  and  28  and the two lines  25   a  and  25   b  being indicated separately. 
     The machine body  110  of the forming device has a through-opening  111  into which the actuator output element  24  of the actuator device projects. On the side of the machine body  110  opposite the actuator device there is mounted a forming die  120  which likewise has a through-opening  121  and in which deformable material (shaped workpiece) W is located. Between the deformable material W and the actuator output element  24  there is located an ejector ram  122 . On movement of the second piston  22  in the direction towards the machine body  110 , the actuator output element  24 , via the ejector ram  122 , ejects the deformable material or the shaped workpiece W out of the die  120 . 
       FIGS. 4-9  show the actuator device in various operating phases when used as an ejecting device for a deformable material that has been shaped in a forming device. As shown in  FIG. 3 , the actuator output element  24  drives an ejector ram  122  which in turn ejects the deformable material W out of a forming die  120 . The forming device with the forming die and the deformable material and also the ejector ram are not shown in  FIGS. 4-9 . 
     For the ejection of a deformable material that has been shaped in a die, first of all a relatively large release force is required in order to break the deformable material away from the die, the deformable material being moved only a negligible amount in the die at relatively low speed. For the subsequent actual ejecting movement, then only a considerably smaller ejection force is required, but the deformable material (depending upon its dimensions) is displaced over a relatively large travel distance out of the die until it passes over the front edge thereof. In the interests of a high machine cycle rate, i.e. a short machine cycle, of the forming device, the ejection of the deformable material must be effected with the highest possible acceleration and speed. 
       FIG. 4  shows the actuator device in the starting position, wherein the two pistons  12  and  22  and therewith the actuator output element  24  have traveled into a predetermined position which depends upon the height of the deformable material (in the ejection direction) and the position thereof in the die (distance from the front edge of the die). The configuration corresponds to that of  FIG. 3 . 
       FIG. 5  shows the actuator device in a release phase. Both pistons  12  and  22  are moved outwards in a position-controlled manner, the release force being applied by the first drive unit  10  or the piston  12  thereof. The impact element  23  is still in contact with the first piston  12 . During the outward movement of the first piston  12 , the hydraulic medium in front of the first piston  12  is pushed into the hydraulic accumulator  17   b . The release of the deformable material from the die is effected in a position-controlled manner with limitation of the maximum pressure or maximum force. 
       FIG. 6  shows the actuator device in a thrusting phase. Once the deformable material has been released from the die, which can be recognised by a drop in pressure or by a force signal if a corresponding force sensor is mounted on the actuator output element  24 , the second piston  22  moves outwards in a position-controlled manner, the actuator output element  24  ejecting the deformable material from the forming die (moving it into a position in front of the front edge of the die). That is the actual ejecting movement, which can be carried out very quickly by means of the second drive unit  20 . The first piston  12  is in the meantime returned to its starting position in a position-controlled manner by the pressure of the hydraulic accumulator  17   b . The servo valve  18  opens in a controlled manner to the collecting tank  19 . Alternatively the first piston  21  can also be reset during the subsequent return movement (inward direction) of the second piston  22  by the latter via the impact element  23 . 
       FIG. 7  shows the actuator device in a holding phase. The first piston  12  is located in its starting position, the second piston  22  and the actuator output element  24  have moved outwards to an extent such that the deformable material is located in front of the front edge of the forming die, from where it can be transported away by the transport system of the forming device. 
     In the next machine cycle of the forming device, fresh deformable material (blank to be shaped) is positioned in front of the forming die and introduced into the forming die, for example, by means of an appropriately force-actuated punch. As a result, the actuator output element  24  is pushed in the inward direction P 2  by the blank (via the ejector ram). The actuator device is then located in a braking phase shown in  FIG. 8  in which the control of the movement of the second piston  22  changes from position-control to force-control with position-monitoring and the introduction movement of the blank is opposed by, that is to say braked by, a controlled braking force. During the introduction of the blank the second piston  22  is moved inwards in a force-controlled manner, with position-monitoring, until it reaches its starting position according to  FIG. 4 . The braking force is relatively small and is in any case set to be small enough not to bring about any deformation of the blank. 
     The blank is then formed into the desired shape in the forming die by the punch of the forming device. 
       FIG. 9  shows the thrust force that arises during an ejection cycle of the actuator device and that is to be applied by the device via the actuator output element  24  thereof and also the travel path (stroke length from the starting position) of the actuator output element  24  as a function of the cycle time t. The dashed line shows the travel path s, the solid line shows the force F. During the release phase ( FIG. 5 ) the actuator output element  24  moves only a relatively short distance. The release force to be applied is (briefly) relatively high. In the subsequent thrusting phase ( FIG. 6 ) the actuator output element  24  is greatly accelerated with application of a relatively small force and is rapidly moved outwards to its full extent. A brief stationary period is followed by the holding phase ( FIG. 7 ) and then the braking phase ( FIG. 8 ), the actuator output element  24  being moved inwards into its starting position according to  FIG. 4  again in a force-controlled manner with a constant braking force. 
       FIGS. 10-17  show a typical process sequence during piercing and separation of a shaped part in a forming device. 
     Of the forming device only a separating die  220 , a stamping punch  230 , a separating sleeve  240  and a spacer sleeve  250  are shown. A blank to be pierced and separated (deformable material) is denoted by U. Analogously to  FIG. 3  the spacer sleeve  250  is joined to the actuator output element  24  of the actuator device via an impact element (not shown) and is force-actuated by the latter during operation.  FIGS. 18-21  show the corresponding positions of the actuator output element  24  and the two pistons  12  and  22  during the individual steps of the process sequence. 
     The forces described below as “strong force” and “weak force” are to be understood as being the thrust, holding and braking forces applied by the first drive unit  10  and the second drive unit  20 . 
     At the beginning of the piercing and separating process the two pistons  12  and  22 , starting from a starting position ( FIG. 21 ), move outwards in a position-controlled manner into the position shown in  FIG. 18  (thrusting phase) and  FIG. 19  (holding phase). The spacer sleeve  250 , which is driven or force-actuated by the actuator output element  24 , is located just in front of the front edge of the separating die  220 . The deformable material U has been positioned in front of the separating die  220  by a transport device of the forming device ( FIG. 10 ). 
     In the next step the stamping punch  230  and the separating sleeve  240  move towards the separating die  220  and press the deformable material U a short way into the latter ( FIG. 11 ). This movement is braked by the actuator device with a small force, the second piston  22  being moved inwards until it assumes the position shown in  FIG. 20 . 
     In the next step ( FIG. 12 ), the stamping punch  230  thrusts a core portion UK of the deformable material U into the spacer sleeve  250 , the actuator device supporting the spacer sleeve  250  with a large force. 
     In the next step ( FIG. 13 ), the separating operation begins. The separating sleeve  240  moves towards the separating die  220  and thrusts the deformable material U into the forming die. At the same time the two pistons  12  and  22  of the actuator device return to their starting positions ( FIG. 21 ) in a position- and force-controlled manner and during this inward movement brake the displacement of the spacer sleeve  250  with a small force. In this step the portion of the deformable material that remains after the stamping-out of the core portion UK is divided into an annular centre portion UM and an annular rim portion UR, as shown in  FIG. 14 . 
     Then the stamping punch  230  and the separating sleeve  240  move back again ( FIG. 15 ). 
     Simultaneously or subsequently the actuator output element  24  moves outwards again in a position-controlled manner ( FIG. 18 ) and begins the operation of ejecting the centre portion UM ( FIG. 16 ). Once the actuator output element has reached the holding position shown in  FIG. 19 , the centre portion UM is located in front of the separating die  220 , where it can be transported away by the transport device of the forming device ( FIG. 17 ). A new piercing and separating cycle can then begin. 
       FIG. 22  shows the thrust force that arises during a piercing and separating cycle of the actuator device and that is to be applied by the device via the actuator output element  24  thereof and also the travel path (stroke length from the starting position) of the actuator output element  24  as a function of the cycle time t. The dashed line shows the travel path s, the solid line shows the force F. 
       FIGS. 23-28  show a typical process sequence for descaling and shaping a shaped part in a forming device. 
     Of the forming device only a forming die  320 , a punch  330  and an ejector ram  350  are shown. A blank (deformable material) to be descaled and shaped is denoted by U. Analogously to  FIG. 3  the ejector ram  320  is joined to the actuator output element  24  of the actuator device directly or via an impact element (not shown) and is force-actuated by the latter during operation.  FIGS. 29-33  show the corresponding positions of the actuator output element  24  and the two pistons  12  and  22  during the individual steps of the process sequence. 
     The process cycle is shown starting from deformable material U that has already been shaped in the forming die  320  ( FIG. 23 ). The punch  330  has already returned. The actuator output element  24  and the pistons  12  and  22  are located in the starting position shown in  FIG. 29 , the ejector ram  350  assuming the position shown in  FIG. 23 . 
     Next the release and ejection of the deformable material U from the forming die  320  takes place.  FIG. 30  shows the actuator device in the release phase.  FIG. 31  shows the actuator device in the ejection phase and  FIG. 32  shows the positions of the two pistons  12  and  22 , which have moved outwards together, in the fully extended state (holding phase), the deformable material then being located in front of the forming die  320  ( FIG. 24 ) and can be transported away. The release and ejection of the deformable material is effected in the same way as described in connection with  FIGS. 4-8 . The release is effected with a large force, the further ejection with a small force. 
     In the next step, the finished shaped deformable material is transported away and a new blank U to be shaped is positioned in front of the forming die  320  by the transport device of the forming device ( FIG. 25 ). The actuator output element  24  is still in the holding position according to  FIG. 32 . 
     Before the actual forming operation, the blank U is descaled. For that purpose the blank is compressed slightly by means of the punch  330 , the required large counter-force (holding force) being applied by the actuator device, or the actuator output element  24  thereof, which is located in the holding position ( FIG. 32 ). 
     Next the forming process begins, wherein the punch  330  presses the blank U into the forming die  320  ( FIG. 27 ), while the actuator output element moves into its starting position shown in  FIG. 29  in a force- and position-controlled manner. While the blank U is being pressed into the forming die  320 , the actuator output element  24  brakes the introduction movement of the blank in a force-controlled manner.  FIG. 33  shows the actuator device in this braking phase. 
     As soon as the actuator output element  24  and the two pistons  12  and  22  have reached their starting position, the actuator output element  24  opposes the inward movement of the blank with a large force, the blank then undergoing final shaping in the forming die by the punch ( FIG. 28 ). 
     The forming device is then ready for a new process cycle. 
       FIG. 34  shows the thrust force that arises during a descaling and forming cycle of the actuator device and that is to be applied by the device via the actuator output element  24  thereof and also the travel path (stroke length from the starting position) of the actuator output element  24  as a function of the cycle time t. The dashed line shows the travel path s, the solid line shows the force F. 
     In the exemplary embodiments described above, the supply and discharge of hydraulic medium is effected by means of servo valves  18  and  28 .  FIGS. 35 and 36  show a variant of the first and second drive units in which speed-controlled pumps are used instead of servo valves. 
     In addition to the components already described, the drive unit  10 ′ comprises a hydraulic tank  119  and a speed-controlled pump  118   a  driven by an electric servo motor  118   b . The pump  118   a  is connected to the first piston chamber  11  via the line  15   a.    
     In addition to the components already described, the second drive unit  20 ′ comprises a speed-controlled pump  128   a  driven by an electric servo motor  128   b . The pump  128   a  is connected to the second piston chamber  21  via the lines  25   a  and  25   b . An additionally present diaphragm or bladder accumulator  127  is connected to the two lines  25   a  and  25   b  via a respective non-return valve  127   a  and  127   b , respectively. 
     The two servo motors  118   b  and  128   b  (instead of the servo valves  18  and  28 ) are actuated by the controller  50 . 
     The mode of operation of the two drive units is clear to the person skilled in the art and requires no further explanation.