Press drive with energy recovery

Abstract

An electro-hydrostatic actuator system for a press drive, having an upper piston with a press surface, which acts from a first direction, wherein the press surface of the upper piston is actuated by means of a piston rod in a hydraulic cylinder of the upper piston and traverses a first distance in a press run, and a first electro-hydrostatic actuator for driving the upper piston, comprising a first pump and a first motor generators which is controlled by a first controller. The system furthermore comprises at least one auxiliary piston with a press surface, which acts from a second direction opposite the first direction, wherein the press surface of the auxiliary piston is actuated by means of a piston rod in a hydraulic cylinder of the auxiliary piston and traverses a second distance in the press run, and a second electro-hydrostatic actuator for driving the at least one auxiliary piston, comprising a second pump and a second motor generator which is controlled by a second controller. The second motor generator is operated as a generator in the press run, thereby generating energy which is provided to the first motor generator or auxiliary piston, which are operated as motors, via the common DC bus.

Claims

1. An electro-hydrostatic actuator system for a press drive, comprising: an upper piston having a press surface acting from a first direction, wherein the press surface of the upper piston is actuated via a piston rod in a hydraulic cylinder of the upper piston and traverses a first distance in a press run, at least two auxiliary pistons, each auxiliary piston having a press surface acting from a second direction opposite the first direction, wherein the press surface of each auxiliary piston is actuated via a piston rod in a hydraulic cylinder of the auxiliary piston and traverses a second distance in the press run, a first electro-hydrostatic actuator operable to drive the upper piston, comprising a first pump and a first motor generator which is controlled by a first controller, and a second electro-hydrostatic actuator operable to drive at least one of the at least two auxiliary pistons, comprising a second pump and a second motor generator which is controlled by a second controller, wherein in the press run, the second motor generator of the second electro-hydrostatic actuator is operated as a generator, and wherein at least one of the press surfaces of the auxiliary pistons has a different thickness than another press surface of the auxiliary pistons.

2. The actuator system according to claim 1, wherein the second distance of the second press surface is a function of the first distance of the first press surface and the second distance in the first direction is shorter than the first distance.

3. The actuator system according to claim 1, wherein at least one of the press surfaces has a different resting distance than another press surface of the auxiliary pistons.

4. The actuator system according to claim 1, wherein the system comprises a plurality of upper pistons.

5. The actuator system according to claim 4, wherein each of the plurality of upper pistons comprises an electro-hydrostatic actuator.

6. The actuator system according to claim 1, wherein the first controller, which is assigned to the first motor generator, has a first control characteristic, and the second controller, which is assigned to the second motor generator, has a second control characteristic.

7. The actuator system according to claim 6, wherein the first control characteristic and/or the second control characteristic is described linearly, polynomially or by supporting points.

8. The actuator system according to claim 6, wherein the first control characteristic and/or the second control characteristic is determined by a central control unit.

9. The actuator system according to claim 1, further comprising an electrical supply line connected to the first controller and the second controller, wherein the second controller feeds current into the supply line in the press run.

10. The actuator system according to claim 1, wherein the system includes a rapid traverse, wherein the second motor generator of the second electro-hydrostatic actuator is operated as a motor.

11. An electro-hydrostatic actuator system for a press drive, comprising: an upper piston having a press surface acting from a first direction, wherein the press surface of the upper piston is actuated via a piston rod in a hydraulic cylinder of the upper piston and traverses a first distance in a press run, at least two auxiliary pistons, each auxiliary piston having a press surface acting from a second direction opposite the first direction, wherein the press surface of each auxiliary piston is actuated via a piston rod in a hydraulic cylinder of the auxiliary piston and traverses a second distance in the press run, a first electro-hydrostatic actuator operable to drive the upper piston, comprising a first pump and a first motor generator which is controlled by a first controller, and a second electro-hydrostatic actuator operable to drive at least one of the at least two auxiliary pistons, comprising a second pump and a second motor generator which is controlled by a second controller, wherein in the press run, the second motor generator of the second electro-hydrostatic actuator is operated as a generator, and wherein at least one of the press surfaces has a different resting distance than another press surface of the auxiliary pistons.

12. The actuator system according to claim 11, wherein the second distance of the second press surface is a function of the first distance of the first press surface and the second distance in the first direction is shorter than the first distance.

13. The actuator system according to claim 11, wherein at least one of the press surfaces of the auxiliary pistons has a different thickness than another press surface.

14. The actuator system according to claim 11, wherein the system comprises a plurality of upper pistons.

15. The actuator system according to claim 14, wherein each of the plurality of upper pistons comprises an electro-hydrostatic actuator.

16. The actuator system according to claim 11, wherein the first controller, which is assigned to the first motor generator, has a first control characteristic, and the second controller, which is assigned to the second motor generator, has a second control characteristic.

17. The actuator system according to claim 16, wherein the first control characteristic and/or the second control characteristic is described linearly, polynomially or by supporting points.

18. The actuator system according to claim 16, wherein the first control characteristic and/or the second control characteristic is determined by a central control unit.

19. The actuator system according to claim 11, further comprising an electrical supply line connected to the first controller and the second controller, wherein the second controller feeds current into the supply line in the press run.

20. The actuator system according to claim 11, wherein the system includes a rapid traverse, wherein the second motor generator of the second electro-hydrostatic actuator is operated as a motor.

Description

(1) The following are shown:

(2) FIG. 1: A schematic drawing of an exemplary embodiment of a system according to the invention.

(3) FIG. 1 shows an example embodiment of an electro-hydrostatic actuator system 10 according to the invention. In particular, the auxiliary pistons 200 and the press surface 120 of the upper piston 100 are shown only partially. The parts not shown are substantially symmetrical with respect to the line of symmetry 50. As shown in FIG. 2, in some embodiments, the system 10 has a plurality of upper pistons 100.

(4) FIG. 2: A schematic drawing of another exemplary embodiment of a system according to the invention.

(5) The powder press drive shown has an upper piston 100 and a plurality of auxiliary pistons 200a, 200b, 200c. Since the auxiliary pistons shown are constructed substantially identically, with the exception of the press surfaces 220, auxiliary pistons and their subcomponents are designated in the following with the same reference signs (e.g., 200a, 200b, 200c, 212, 216). Arranged between the upper piston 100 and the auxiliary pistons 200a, 200b, 200c is a mold 400 which contains a pressed material 410, e.g., powder. The upper piston 100 has a cylinder 110 comprising a first piston chamber 112 and a second piston chamber 114. The cylinder 110 is subjected to hydraulic pressure by a first electro-hydrostatic actuator 130 comprising a pump 132 and a motor generator 134. In the exemplary embodiment shown, the pump volume is variable; however, it is also possible to use a motor generator 134 having a variable speed or else a combination of both. The motor generator 134 is connected via the controller 140 of the upper piston to the electrical supply line 320 which, as shown here, may be designed as a DC bus. The DC bus 320 is supplied with energy via the power supply 310.

(6) In the press run, the motor generator 134 acts, in motor function, on the first piston chamber 112. As a result, the piston 116 comprising the piston rod 118 is pressed downward and thus actuates the press surface 120 of the upper piston 100, which thus acts on the one hand on the pressed material 410 in the mold 400 and on the other hand displaces the press surfaces 220 of the auxiliary pistons 200a, 200b, 200c. The press surfaces 220 are connected to the piston rods 218 of the auxiliary pistons 200a, 200b, 200c. The pistons 216 in the cylinders 210 of the auxiliary pistons 200a, 200b, 200c thereby pressurize the second piston chambers 214 of the auxiliary pistons 200a, 200b, 200c so that the hydraulic fluid of the cylinders 210 actuates the pumps 232 of the second electro-hydrostatic actuators 230. The pumps 232 are connected to the motor generators 234. These motor generators 234 are operated as generators in the press run. The motor generators 234 can thus feed power to the DC bus 320 via the controllers 240 so that the current draw of the motor generator 134 of the upper piston 100 from the power supply 310 is reduced in the press run. The press surfaces 220 of the auxiliary pistons 200a, 200b, 200c have a different thickness 222 in order to be optimally adapted to the regions of the powder blank to be produced. However, as shown in the auxiliary piston 200b, the press surfaces 220 may also be spaced apart from a base line by a resting distance or offset 224 in the starting position. This can at least partially replace the different thickness 222 and thus enables further flexibilization in the use of the auxiliary pistons 200a, 200b, 200c.

(7) In the embodiment described here, the press run (and also the rapid traverse) is controlled via the central control unit 350. These contain the control characteristics for the upper piston 100 and the auxiliary pistons 200a, 200b, 200c and thus control the controllers 140 and 240 via the control bus 360. This control bus 360 can be implemented, for example, as a field bus or also as a wireless connection.

(8) In the rapid traverse, the motor generators 234 of the auxiliary pistons 200a, 200b, 200c are operated as motors. The second piston chamber 214 of the auxiliary pistons are thus pressurized so that the press surfaces 220 of the auxiliary pistons 200a, 200b, 200c are pushed upward. In cases where the press surfaces 120 of the upper piston 100 are thereby also pressed upward, the motor generator 134 of the upper piston can be operated as a generator and current can be fed into the DC bus 320 via the controller 140.

LIST OF REFERENCE SIGNS

(9) 10 Electro-hydrostatic actuator system 50 Line of symmetry 100 Upper piston 110 Cylinder of the upper piston 112 First piston chamber of the upper piston 114 Second piston chamber of the upper piston 116 Piston of the upper piston 118 Piston rod of the upper piston 120 Press surface of the upper piston 130 First electro-hydrostatic actuator 132 Hydraulic pump/motor unit of the upper piston 134 (Servo) motor generator of the upper piston 140 Controller of the upper piston 200a, 200b, 200c Auxiliary piston 210 Cylinder of the auxiliary piston 212 First piston chamber of the auxiliary piston 214 Second piston chamber of the auxiliary piston 216 Piston of the auxiliary piston 218 Piston rod of the auxiliary piston 220 Press surface of the auxiliary piston 222 Thickness of the press surface 224 Resting distance (offset) of the press surface 230 Second electro-hydrostatic actuator 232 Hydraulic pump/motor unit of the auxiliary piston 234 (Servo) motor generator of the auxiliary piston 240 Controller of the auxiliary piston 310 Central power supply 320 Electrical supply line, DC bus 350 Central control unit 360 Control bus (also wireless) 400 Mold 410 Pressed material, powder