DE19524042A1 - Drive for hydraulic presses with high stroke rate - Google Patents

Abstract

The drive of a hydraulic press has at least one double-acting piston-cylinder unit (2,3) with a drive piston (5) for displacement of a press ram (1). During an initial phase of operation of the press, with the unloaded ram (1) moving downwards, the upper and lower cylinder spaces (7,8) of the piston-cylinder unit (2,3) are connected via a valve system (10), while a motor/pump system (12-16) with a vol.-controlled hydromotor/pump unit (14) is foreseen for the subsequent forming phase. The unit (14) is driven by at least one chargeable accumulator system (19), and its controllable torque is transmitted to a controllable pump (12) communicating with the top cylinder space (7) of piston/cylinder unit.

Description

The invention relates to a control of the drive Hydraulic press according to the preamble of claim 1.

For hydraulic presses, the press ram has a or several piston-cylinder units connected. Essentials Characteristics of the hydraulic drive are the pressure and represents the flow rate of the pressure medium Pumps and control devices (power, pressure and Stroke controller) can both parameters on the respective Work process to be adjusted.

Depending on the type of drive, a distinction is made between hydraulic Presses with direct pump drive and hydraulic Presses with accumulator drive (see e.g. Manfred Weck: Machine Tools Vol. 1, pp. 103 to 105). With the immediate or direct drive is one of an electric motor driven constant or variable displacement pump (hydraulic pump) the main working cylinder, which is used to generate the pressing force the large cylindrical piston surface and for lifting the Tappet on the smaller ring surface of the piston of the piston Pressure medium is applied to the cylinder unit.  

The pump and the drive motor must always be on the greatest power requirement of the press. The High pressure pump can be used as a variable displacement pump or adjustable Hydraulic pump can be designed for continuous adjustment the flow rate and thus the ram speed guarantee.

At low pressure, there is a large amount of liquid promoted and thereby the ram with the upper part of the tool conveyed a great speed while at the actual forming process at a lower speed high pressure is required. This is for a quick one Stroke as rapid traverse and for a high power application at Forming process expedient.

The disadvantage, however, is that the drive energy of the pump keeps changing between zero and a maximum. This results in considerable loads on the power grid. A disadvantage of Direct drive is also that the position energy of the ram as well as the downward moving masses of the system stay as that from the ring cylinder during the downward movement pressure medium flowing out of the piston only via a Directional control valve is drained into a tank or oil tank.

Another form of drive for hydraulic presses is Combination of the pump drive with a storage drive according to DE 27 47 548. To reduce the energy requirement the excess retraction force that occurs when the Drive piston charges a storage system.

A double-acting drive piston is used here. This arrangement offers the possibility of one Working cycle the rapid traverse initially only by loading of the drive piston in a first cylinder-piston system to raise and later at a  desired increase in compression force a second cylinder-piston Apply pressure to the unit.

In addition to the actual cylinder-piston system at least a second cylinder-piston system required to bring the pressing force to the required value increase. This requires a considerable structural Effort of the cylinder-piston units. In addition, for the separate regulation also corresponding regulation and Control components required.

Another disadvantage is that from the storage system total pressure potential consumed and partly unused on Control valve is converted into heat.

The overall energy balance is very high in storage operation unfavorable and brings none with the solution listed decisive improvement.

The invention has for its object a novel Method of driving a hydraulic press to propose the one to those described above Systems addressed disadvantages can be avoided. In particular, a press drive using a Hydraulic accumulator can be proposed, the high Efficiency with optimal mode of operation enabled.

This task is based on the drive one hydraulic press of the type listed, according to the invention solved by the characterizing features of claim 1.

In the subclaims are useful and advantageous Developments and improvements to the hydraulic drive specified according to the main claim.  

Advantages of the invention

The invention is based on the idea using Hydraulic energy is stored in a hydraulic motor Convert drive power or torque.

Using the so-called "secondary control", a consistently high pressure level from a storage system a control pump or a controllable hydraulic motor supplied.

This creates a torque on the hydraulic motor, which is the size of the memory pressure and the Volume flow is determined. Because with a control pump Volume flow is adjustable in its amount, can also a required torque can be regulated precisely. This adjustable torque is used to cover peak loads specifically used as an additional pump drive.

By increasing the torque can be driven with the Pump system reached a significantly higher pressure potential will.

As this higher pressure, as described below, only at the forming process and thus only a small way of Drive cylinder is required is an excellent one Guaranteed energy balance.

This method, contrary to the prior art, only the required power from the pressure storage system removed and the power loss kept absolutely low.

The performance of the required drive motors must be in accordance with proposed invention no longer for peak performance the press can be dimensioned, but by Distribution of the individual press functions by up to 50% be interpreted lower.  

The individual steps are:

• 1st step:
  Downward stroke of the working cylinder through the well-known pump drive at high speed and low pressure.
• 2nd step:
  Forming process at reduced speed and high pressure. The required higher drive torque is taken from the storage system in the form of an additional drive power, in which an almost constant pressure acts on a controllable hydraulic motor.
  At constant pressure, the torque generated on the hydraulic motor in addition to the drive motor is a function of the hydraulic motor swivel angle, which regulates the oil volume flow.
• 3rd step:
  Upward stroke of the working cylinders by the pump drive at high speed and low pressure.
• 4th step:
  During the removal of the finished part and the feeding of a new circuit board, charging of the storage system when the pumps for the drive of the working cylinders are installed empty.

This combined drive thus ensures that the Base load of the press applied by an electric motor will while covering a peak load additional torque from a storage system in Connection with an adjustable hydraulic motor available stands.  

Further details and advantages of the invention are described in more detail by way of example with reference to the three figures. Figs. 1 to 3 schematically show the ram of a press with 2 cylinders and various drive systems.

Description of exemplary embodiments

In Fig. 1, a press ram 1 is shown for a hydraulic press, not shown, on the underside of which an upper part of a forming tool, not shown, is attached.

The up and down movement of the press ram 1 takes place via two hydraulic cylinders or piston-cylinder units ( 2 , 3 ) acting on the press ram, which serve as lifting and working cylinders for carrying out the forming process or the punching operation on the workpiece.

Instead of two hydraulic cylinders 2 , 3 , a centrally arranged hydraulic cylinder or four hydraulic cylinders arranged in the corner regions of the press ram 1 can also be provided as the press cylinder. The two hydraulic cylinders or piston-cylinder units 2 , 3 are arranged symmetrically on the press ram 1 and equipped with a symmetrical arrangement of the drive and control elements. The structure and the mode of operation are therefore described using the left hydraulic drive shown in the figure.

Accordingly, the hydraulic cylinder 2 consists of a cylinder 4 , a piston 5 and a piston rod 6 , which is connected to the press ram 1 .

Above the working piston 5 there is a cylinder chamber 7 which is circular in cross section, and below the working piston 5 is a cylinder chamber 8 which is annular in cross section. The effective circular upper pressure surface A 1 on the working piston 5 is consequently determined by the diameter d 1 of the working piston 5 . The effective lower annular pressure surface A₂ is formed by the area difference with respect to the diameter d₁ of the working piston 5 minus the diameter d₂ of the piston rod 6 .

The upper cylinder chamber 7 is connected to the lower cylinder chamber 8 via a hydraulic line 9 , 9 '. The press valve 10 is interposed in this hydraulic line. Via the line 11 , a volume flow controllable hydraulic pump 12 and a pump 13 , which can also be operated as a hydraulic motor, are connected to the press valve 10 .

14 designates a hydraulic device which can also be operated as a pump or hydraulic motor, this device has a controllability of the volume flow. A power sensor 16 is located on the electric motor 15 .

A clutch 27 connects the pump / motor 13 to the pump / motor 14 .

Pump / motor 14 is connected to the storage system 19 via line 17 and storage valve 18 .

Line 20 connects the identical drive system 21 for the hydraulic cylinder 3 to the common storage unit 19 , but a separate storage unit for each hydraulic cylinder 2 , 3 is also possible.

The upper cylinder space 7 of the piston-cylinder unit 2 is provided with an additional pre-filling device 22 which serves to compensate for the different filling volume of the two cylinder spaces 7 , 8 when the working piston 5 is moving. Since there is no piston rod 6 in the upper cylinder chamber 7 , there is a volume difference in the hydraulic medium displaced in the two cylinder chambers 7 , 8 . For this purpose, the pre-filling device 22 has a controllable check valve 23 and a hydraulic line 24 to an oil container 25 . The arrow 26 shows a flow direction of the check valve 23 .

Also with an oil tank 25 ', the control pump 12 and control pump / hydraulic motor 14 is connected.

According to alternative embodiments of the invention according to FIG. 2, the drive for the hydraulic press can also be equipped with a direct connection of the controllable pump / hydraulic motor 14 via the coupling 27 to the volume-controllable hydraulic pump 12 , that is to say the hydraulic motor 14 drives the pump 12 directly. Compared to the exemplary embodiment according to FIG. 1, one unit is therefore less required. According to the embodiment of FIG. 2, the hydraulic pump 12 and the hydraulic pump or hydraulic motor 14 accordingly directly on a shaft via clutches to the electric motor 15 is connected. Furthermore, Pos. 14, according to Fig. 2 can also be operated both as a pump and as a motor. Volume or pressure control can be carried out very precisely by regulating elements (not shown) on the units 12 and 14 , which enables a very high efficiency of the system. This significantly improves the system compared to the state of the art.

In the embodiment according to FIG. 3, the pump / hydraulic motor arrangement 13 according to FIG. 1 is equipped with a volume flow control.

The drive system 21 is of identical design in the alternative solutions according to FIGS. 2 and 3, as described above.

The press drive according to the invention works as follows:

Phase 1

As a prerequisite for the working cycle of the press, the storage unit 19 is first charged to the desired pressure or preload. For this purpose, motor 15 drives the hydraulic device 14 to the pump in this operating state as a pump from oil reservoir 25 'via line 17 and storage valve 18 in the storage unit 19 .

Coupling 27 can decouple the pump 12 and pump / motor 13 during this phase, or 12 , 13 is operated in a so-called "closed circuit".

When the closed circuit is switched on, the hydraulic medium is simply supplied ineffectively via pump 12 to pump / motor 13 and from there it is sucked in again by pump 12 , 13 operating as a hydraulic motor in this operating state.

As for the press operating as a start condition, the upper tool and hence also the plunger 1 must be located in the uppermost position, may, as a further switching position during charging press valve 10 pump 12 or pump / motor 13 connected to the cylinder chamber 8, which is then acted upon with hydraulic medium . The pressure buildup in the cylinder chamber 8 causes a vertical movement of the piston 5 and thus of the connected via the piston rod 6 with piston 5 to slide 1 to its upper reversing position.

When the plunger 1 moves downward in the direction of the workpiece, only a small hydraulic pressure is required in the first movement sequence, since the weight of the plunger 1 and the upper tool support the downward movement. However, the cylinder chamber 7 requires a large volume of oil per unit of time if a rapid movement is desired. This is achieved through 3 measures:

• 1. Suction of the oil from the pre-filling device 22 . In this case, check valve 23 is opened or controlled by the resulting negative pressure and the hydraulic medium is sucked in via line 24 from container 25 .
• 2. The hydraulic medium displaced from the cylinder chamber 8 is conveyed via the line 9 'through a corresponding switching position of the press valve 10 and via line 9 into the cylinder chamber 7 .
• 3. Motor 15 drives the regulating pump 12 and the device 13 working as a pump, which promotes via line 11 , the hydraulic medium drawn in from the container 25 'via the press valve 10 and line 9 to the cylinder chamber 7 .

The downward speed can be regulated via the volume flow control of the regulating pump 12 .

Since the downward movement is supported by the released position energy of the downward weights of tappet 1 , upper tool, piston 5 and piston rod 6 , the drive torque to be applied by the drive motor 15 is low.

Furthermore, the pump / motor unit 14 is in the so-called zero position and runs around free of funding or works as a pump and delivers from container 25 'via line 17 and charging valve 18 into the storage system 19th

Phase 2

The second work phase concerns the actual forming process or cutting process on the workpiece, ie the actual working stroke, in which a high pressing force is required. In this phase, the press ram 1 is moved further downward at a greatly reduced working speed, an additional pressurization in the cylinder space 7 above the working piston 5 being necessary to carry out the forming process.

In phase 1, the electric motor 15 was used to cover the base load. At the beginning of phase 2, an increase in the power requirement is measured by the power sensor 16 and a control signal is sent to the pump / motor device 14 . This causes a volume control on the hydraulic motor 14 , which is now regulated from the zero position to a position precisely defined by the size of the adjustable swivel angle. The storage valve 18 is opened and the storage pressure, in conjunction with the regulated volume flow, generates the required torque on the hydraulic motor 14 . This torque is added to the torque of the drive motor 15 to form a total drive torque for the pumps 12 and 13 .

The pumps 12 and 13 are thus able to generate the required pressure for the forming process in the cylinder space. 7 Depending on the force profile specific to the workpiece, the required pressure profile in the cylinder space 7 can also be process-controlled.

Phase 3

In the third working phase, after the shaping process on the workpiece has been carried out, the press ram 1 is moved back into its upper starting position. For this purpose, the pressure medium must be displaced from the upper cylinder space 7 into the oil container 25 via the prefilling device 22 .

For this purpose, the check valve 23 is opened and the pressure medium can flow into the oil container 25 via line 24 .

Furthermore, to achieve the vertical stroke of the cylinder chamber 8 by the pumps 12 , 13 , via the line 11 , the press valve 10 and the line 9 'with pressure medium.

Here, the pump / hydraulic motor 14 is switched to zero position and is therefore ineffective. The pumps 12 , 13 are only driven by the electric motor 15 .

After reaching the upper turning point, the Tappet initially in the rest position. In this phase the finished Workpiece removed and a new board to be machined fed.

Since no energy is required for the movement sequence of the press, this point in time is used to charge the storage system 19 . For this cycle, pumps 12 , 13 are first switched to a closed circuit in the form already described in phase 1 .

The device 14 is operated as a pump and driven by the electric motor 15 . From container 25 'then the pump 14 promotes via line 17 in the storage system 19th This charging process is ended until the desired pressure level in the storage system 19 has been reached.

The press can then start a working cycle again.

The parallelism of the tappet position and the synchronism of the cylinders can be achieved by a displacement measuring system 28 , which gives control signals to the control pump 12 , which is decisive for the speed control.

With the press control according to the invention that is too installing electric drive power significantly below of those at normal, directly driven and before all memory operated presses is required.

The invention is not based on that shown and described Embodiment limited. Rather, it includes everyone professional training within the scope of Property rights claims.

Claims (10)

1. A method for controlling the drive, in particular a hydraulic press and in particular for forming and / or cutting sheet metal, plastics or the like, with at least one piston-cylinder unit ( 2 , 3 ) which can be acted on from both sides for driving a press ram ( 1 ), the drive piston ( 5 ) by means of a hydraulic medium in the sense of a displacement of the press ram ( 1 ), characterized in that in a first working phase of the press during the downward movement of the unloaded press ram ( 1 ) the upper ( 7 ) and the lower ( 8 ) cylinder space of the pistons Cylinder unit ( 2 , 3 ) is connected via a valve device ( 10 ) and that a motor / pump device ( 12 to 16 ) with a volume-controllable hydraulic motor / pump device ( 14 ) is provided for the subsequent forming phase of the press, which at least via a rechargeable storage system ( 19 ) is driven and its adjustable torque ei ner controllable pump device ( 12 ) can be supplied, which acts on the upper cylinder chamber ( 7 ) of the piston-cylinder unit ( 2 , 3 ) via the valve device ( 10 ) with hydraulic medium. 2. The method according to claim 1, characterized in that the hydraulic motor ( 14 ) by an electric motor ( 15 ) preferably with a power sensor ( 16 ) can be driven, the hydraulic motor ( 14 ) to increase the drive torque of the electric motor ( 15 ) in the Forming phase serves. 3. The method of claim 1 or 2, characterized in that the hydraulic motor (14) can be driven by an electric motor (15), wherein the hydraulic motor (14) serves as a pump for charging the storage system (19). 4. The method according to any one of the preceding claims 1 to 3, characterized in that the motor / pump device (12 to 16) comprises an electric motor (15) preferably with a power output ports (16), the torque adjustable to a hydraulic motor / pump device (14) with Volume flow is transferable, the hydraulic motor / pump device ( 14 ) on the one hand for charging a storage system ( 19 ) from a hydraulic medium container ( 25 ') and on the other hand for volume-controlled torque transmission by means of the drive energy of the storage system ( 19 ) to one of the hydraulic motor / pump devices ( 14 ) downstream further, optionally controllable hydraulic motor / pump device ( 12 , 13 ) is used for the tappet drive. 5. The method according to claim 1 or 4, characterized in that the motor / pump device ( 12 to 15 ) comprises a hydraulic motor ( 14 ), which is preferably connected via a coupling device ( 27 ) with a first, optionally controllable hydraulic motor / pump device ( 13 ) is, which in turn interacts with a volume flow controllable hydraulic pump ( 12 ), the controllable volume flow from a hydraulic medium reservoir ( 25 ') via a press valve ( 10 ) to the upper ( 7 ) or lower ( 8 ) cylinder space of the piston-cylinder unit ( 2 , 3 ) is. 6. The method according to any one of the preceding claims 1 to 5, characterized in that for a volume compensation between the upper ( 7 ) and lower ( 8 ) cylinder space, the upper cylinder space ( 7 ) of the piston-cylinder unit ( 2 , 3 ) by means of a prefilling device ( 22nd ) with controllable check valve ( 23 ) can be acted upon with hydraulic medium or hydraulic medium can be discharged. 7. The method according to any one of the preceding claims 1 to 6, characterized in that in a third working phase after the shaping process on the workpiece, the electric motor ( 15 ) via a hydraulic pump ( 14 ) located in the "O position", the hydraulic motor acting as a pump / Pump device ( 13 ) or the volume flow-controllable hydraulic pump ( 12 ) drives, hydraulic medium being conveyed from a container ( 25 ') via a press valve ( 10 ) into the lower cylinder chamber ( 8 ) and a prefilling device ( 22 ) balancing the volume between the upper ( 7 ) and lower ( 8 ) cylinder space of the piston-cylinder unit ( 2 , 3 ). 8. The method according to any one of the preceding claims, characterized in that on the press ram (1) has two or four piston-cylinder units (2, 3) are provided which are adjustable operated by a measuring system (28) on the press ram (1) independently. 9. The method according to claim 1, 4 or 5, characterized in that the volume flow controllable hydraulic motor / pump arrangement ( 14 ) is connected via a coupling device ( 27 ) with a possibly volume flow controllable hydraulic motor / pump device ( 12 , 13 ) and serves as a drive means. 10. The method according to claim 1 or 9, characterized in that on the hydraulic pump ( 12 ) and / or the hydraulic motor / pump arrangement ( 14 ) control members are provided, by means of which a volume or pressure control takes place.