Plant and method for commanding and controlling a ram of a servo press

Abstract

Plant (10, 10') for commanding and controlling a ram (11) of a servo press (12), comprising: - a pumping unit (22) which is intended to pump a feed fluid; an actuator unit (16, 16') of said ram (11) which is alternately mobile at least with an active working stroke or with a passive return stroke; a hydraulic connection and transport circuit (13) which connects said pumping unit (22) and said actuator unit (16) and transports a feed fluid of said actuator unit (16, 16'); wherein said pumping unit (22) comprises at least one servo pump (23) fluidically connected to at least one cartridge valve (21) fluidically connected to said actuator unit (16, 16').

Description

[0001] "PLANT AND METHOD FOR COMMANDING AND CONTROLLING A RAM OF A SERVO PRESS"

[0002] D E S C R I P T I O N

[0003] Field of application

[0004] The present invention relates to a plant and a method for commanding and controlling the ram of a servo press , to make the working cycle and the structure of the press more economical , simple, effective and safe. Said servo press may be applied for example for bending or punchi ng / deformi ng sheet metal , or other operations on other workpieces .

[0005] State of the Art

[0006] A known hydraulic circuit installed on a press for actuating its ram comprises a series of components that allow it to perform, for carrying out operations on workpieces such as punching or bending, a rapid approach stroke toward the workpiece, followed by a slower extra-stroke to perform the operation, and a final return stroke to the rest position raised from the workpiece.

[0007] Typically, according to the known art, presses are divided into two types , precisely presses that have a ram with a significant weight of its own that affects the general operation and presses that have rams with a weight considered light and that have little influence on the general operation .

[0008] In both types of servo presses , to move the ram, servo pumps are used, composed of a brushless motor combined with an internal gear pump or piston pump, which, in addition to controlling the speed and direction of the actuator that moves the ram, with the use of a measuring system determines its position and with the use of a pressure transducer can limit the load.

[0009] In all the cases mentioned, to reverse the direction ofmotion of the ram and perform the required operations , the pumps must be able to reverse their direction of rotation as quickly as possible, typically in a few tens of milliseconds , to allow the workpiece processing cycles to be carried out.

[0010] The circuits described above have a high number of components , are expensive, complex to manufacture and can be improved in terms of operating efficiency. There is therefore a need to develop a plant for commanding and controlling a ram of a servo press that can overcome at least one of the drawbacks of the art.

[0011] Summary of Invention

[0012] One purpose of the invention is to improve the known state of the art.

[0013] In particular, one purpose of the present invention is to provide a plant for controlling and commanding a ram of a servo press that is compact, with a limited number of components compared to current solutions , simple to manufacture, efficient and safe.

[0014] According to one aspect of the invention, a plant for commanding and controlling a ram of a servo press is provided in accordance with the features of claim 1.

[0015] Further features are specified in the dependent claims . The invention allows the following advantages to be obtained:

[0016] - the plant is made with a significantly reduced number of components compared to plants known in the field with consequent reduction in costs and manufacturing complexity;

[0017] - increase of more than 50% in the rapid movement speed of the ram with very short times to reach maximum speed, with consequent increase in plant performance by exploiting the acceleration of the servo pump;

[0018] - as mentioned above, current plants exploit the kinetic energy represented by the weight of the ram, with limitationsin the acceleration phase, because the pump will have to, before starting, pressurize the line present between the sustaining valve and the pump, to avoid the consequent fall of the ram. In this case only the acceleration of gravity is available, while the present plant can bring the ram to maximum speed in less than 100 msec;

[0019] - the rapid movement speed of the ram can significantly increase because in case of emergency the certified "STO" function is activated, with the interruption of the driver power supply, which responds in a time of less than 10 msec. In traditional plants , the anti-fall of the ram is entrusted to a pair of two monitored solenoid valves placed on the line connecting the rod side of the cylinder, however having a response time close to 25 msec;

[0020] - possibility of moving the ram in both directions at very low speed and with extreme positioning precision (current plants control at reduced speed and precision only the descent, the ascent is entrusted to a metering device) ;

[0021] - reduction of the quantity of hydraulic oil having provided a sealed tank, pressurized at about a couple of bar, containing a hydraulic compensator, which completely isolates the oil from the atmosphere, allowing the replacement of the same oil at doubled intervals , practically 20 , 000 hours of servo pump operation;

[0022] - the supply of the hydraulic compensator at a value close to a couple of bar, charged when the ram is at the T.D .C. (Top Dead Center) favors the operation and duration of the servo pump itself ;

[0023] - by guaranteeing said pressure in the tank, the intake valve will be sized to operate with oil speed close to 6 instead of 3 m / sec, consequently reducing the size and cost of the same ;

[0024] - the presence of the accumulator on the rod side ofthe cylinder, replacing the balancing valve, significantly improves the repeatability of the B.D .C. (Bottom Dead Center) ;

[0025] the presence of the hydraulic compensator placed inside the sealed tank, in addition to reducing the quantity of oil necessary for the correct operation of the plant and extending the replacement deadline, will keep the oil isolated from the atmosphere. With this arrangement, the compressibility value of the oil can be neglected, allowing to obtain a regulation rigidity, with maximum repeatability close to one micron in the positioning of the working cylinder, during the working process in fact, the servo pump functions as a pressure regulator in combination with the ram position measuring system.

[0026] Brief Description of the Drawings

[0027] Further features and advantages of the invention will become more evident from the detailed description of a preferred, but not exclusive, embodiment of a plant for commanding and controlling the ram of a servo press , illustrated by way of non-limiting example in the attached drawing tables in which:

[0028] - figures 1 to 7 are schematic views of a plant for controlling and commanding a ram of a servo press in various operating conditions ;

[0029] - figure 8 illustrates the control plant with some variants , which can be variously combined with the plant of figures 1 to 7 .

[0030] Detailed Description of a Preferred Embodiment

[0031] With reference to the cited figures , see in particular fig. 1 , a plant 10 for controlling and commanding a ram 11 , or plunger, of a servo press 12 comprises a hydraulic circuit 13.

[0032] Said plant 10 comprises a tank 14 for containing a feedfluid, in particular oil , adapted to flow through the various branches of the hydraulic circuit 13.

[0033] Said ram 11 is connected to at least one piston 15 of an actuator unit 16 provided with a cylinder 17 where said piston 15 is housed. Said piston 15 comprises a rod associated with the ram 11. In the figures only one actuator unit 16 is shown placed at one end of the ram 11 , but a further actuator unit may be provided at the other end of the ram 11 not illustrated in the figure. Alternatively, the servo press 12 may also be provided with only one actuator unit, therefore only one cylinder 17. In the case of pistons 25 of plunger cylinders , two are provided to balance the thrust during the rapid approach phase. By means of said actuator unit 16, said ram 11 is alternately mobile at least with an active working stroke or with a passive return stroke .

[0034] Said cylinder 17 comprises two chambers 18 and 19 respectively above and below the piston 15. Upstream of the cylinder 17 a unidirectional intake valve 20 is provided for the supply of the fluid.

[0035] In fluidic connection with the chamber 18 a cartridge valve 21 is positioned, in turn fluidically connected to a pumping unit 22. Said pumping unit 22 comprises a servo pump 23 associated with a brushless motor 24 . Said cartridge valve 21 is sized based on the flow rate of the servo pump 23 and regulates the quantity of oil that flows between the cylinder 17 , in particular the chamber 18 , and the servo pump 23. Said servo pump is in particular with two-quadrant operation, in the relative Cartesian diagram of rotation speed (or flow rate) and torque (or pressure) .

[0036] Said actuator unit 16 comprises a further piston 25 mobile inside a chamber 26 fluidically connected to said pumping unit 22. Said chamber 26 is advantageously integratedin the wall of said cylinder 17.

[0037] In said tank 14 a hydraulic compensator 27 is provided, which can be filled with air at the desired pressure and which can be used to keep the hydraulic circuit 13 isolated, that is , which completely isolates the oil from the atmosphere, allowing the replacement of the same oil at doubled intervals . The charging of the hydraulic compensator 27 occurs when the piston 15 is at the T.D .C. (Top Dead Center) .

[0038] To said tank 14 another pumping unit 28 is connected, which provides a pump 29 associated with an electric motor 30. Said pumping unit 28 feeds an accumulator 31. Said accumulator 31 is in fluidic communication with the chamber 19 of the cylinder 17. Said pumping unit 28 also feeds a further accumulator 32 .

[0039] In the plant 10 a series of solenoid valves El , E2 , E3, E4 , E5 and E6 are also provided in suitable positions .

[0040] An operating sequence of the present plant 10 is described below.

[0041] In fig. 1 the plant 10 is in a rest situation. The servo pump 23 is stopped, all solenoid valves E1-E6 are deenergized. The ram 11 remains in position finding the intake valve 20 closed. The motor pump 23 sends the oil to discharge filtering it.

[0042] In fig. 2 the plant 10 is in a rapid descent phase of the piston 25 and therefore of the ram 11. The servo pump 23 rotates in the right direction (RH) reaching maximum speed in a few tens of milliseconds , the intake valve 20 is open by depression.

[0043] In fig. 3 the plant 10 is in a transition phase between the rapid descent and a working condition, that is , a situation in which the servo press 12 operates on a sheet metal , for example bending it, punching it, or other. Uponreaching the slowdown point and start of work, the coil of the solenoid valve El (+) is first energized, maintaining in the chamber 26 the pressure relative to the setting of a maximum pressure valve 33, set at a value such as to avoid the rise of the ram 11.

[0044] After about a hundred milliseconds , when the intake valve 20 is closed, fig. 4 , the coil of the solenoid valve E2 is energized by de-energizing El , the servo pump 23 thus feeds both the chamber 26 and the main cylinder 17 performing the working phase illustrated in the diagram of fig. 4. The servo pump 23 rotates in the RH direction at a set speed, allowing the piston 15 to reach the desired B.D .C. (Bottom Dead Center) . The presence of the sustaining accumulator 31 , instead of the balancing valve, significantly improves the repeatability of the position at B.D .C. , therefore improves and refines the positioning of the ram 11 during the operation .

[0045] In fig. 5 there is a "floating" situation of the ram 11 , represented by the double arrow and the dashed lines . If verification of the achieved tolerance of the obtained operation is required, for example the bending of a sheet metal , the servo pump 23 can rotate slowly in the LH direction, to release the sheet metal from the bending tool , the angle measuring system, normally a laser system mounted on a slide, will verify the obtained value, with the possibility of intervening to correct it. The "floating" phase is obtained by energizing the coil E2 and commanding the rotation direction of the servo pump in both directions . Alternatively, leaving the coil E2 de-energized and energizing E6 instead for the opening of the intake valve, the command in both directions of the servo pump would achieve a floating phase also during the rapid movement phase .In fig. 6 there is a decompression phase. Once the working phase is completed, with possible verification of the obtained bending value, the servo pump 23 will rotate in the LH direction to carry out the decompression phase. The choice to use the servo pump 23 in this phase, without providing for the use of a specific cartridge, is due to the fact that the oil used is free of air. In the event that the hydraulic compensator 27 is not provided in the tank 14 , it will be useful , also based on the size of the cylinder, to use a specific cartridge adjustable in the opening time and in the extent of the opening itself to carry out said phase quickly. In this phase the servo pump 23 would remain stationary with the brushless motor 24 in torque, controlled to discharge the oil contained in the cylinder of the piston 25 due to the effect of the return of the piston 15 of the cylinder 17 in the decompression phase. In the illustrated diagram, in this phase the coil E6 of the two-position solenoid valve is energized for the command of the intake valve, when the pressure in the main cylinder 17 reaches about a quarter of the pilot pressure present in the accumulator 32 , automatically the intake valve 20 will open allowing the rapid rise phase.

[0046] In fig. 7 there is the rapid rise phase of the ram 11 , in which the servo pump 23 will rotate in the LH direction controlling the quantity of oil that exits from the chamber 26 to determine the rapid rise speed and the stop position of the piston 15 at the T.D .C.

[0047] The pump 29 can be sized for example for a flow rate of 2 1 / min, sufficient to pilot the intake valve (s) , on the delivery branch the presence of a filter 34 for example of 6 micron, a safety valve 35 and the three-position solenoid valve E4 / E5 is provided. At each first start-up, before starting the pump 29, the coil E5 is energized to verify,with the reading of the transducer 36, if the retention cartridge 37 is perfectly sealed. The accumulator 31 will have in addition to the transducer also a safety pressure switch, a PED maximum pressure valve to protect the accumulator. To discharge said accumulator 32 , the presence of a metering device 38 and a sealed solenoid valve is provided. The metering device will be sized so that, once the accumulator 32 is discharged, it limits the descent speed of the ram to less than 10 mm / sec (safety speed) . By energizing the solenoid valve E4 with pump 29 in motion, the accumulator 32 will be charged, equipped with a pressure transducer to keep it charged in the pressure range, for example, 40 - 70 bar. By energizing the coil of the solenoid valve E6 in the decompression phase, the intake valve 20 will open when, as already mentioned, in the working cylinder 17 the pressure value linked to the pressure of the accumulator 32 is reached.

[0048] If the plant required a higher source for extra services , the same would also provide for charging the accumulators .

[0049] To equip a servo press , for example for shearing, the operation would undergo the modification described below: instead of programming the slowdown / start of work point, the ram would be brought to the rapid approach speed in contact with the material to be processed. When the ram position transducer undergoes a speed containment variation (the ram pushed by the piston 25 cannot advance because it has encountered an obstacle that requires a higher force and stops) , the coil of the solenoid valve El is energized and after 100 msec the coil of the solenoid valve E2 , deenergizing El . At this point, the coil of the solenoid valve E6 is energized, for the opening command of the intake valve 20 and the ram 11 advances fed by the servo pump 23 whichsends oil both to the chamber 26 and to the working cylinder 17. When the ram reaches the programmed height (or the transducer reads a sudden pressure drop, because the tools have completed the shearing) , the servo pump 23 rotates in the LH direction to start a rapid return of the ram. When the pressure in the chamber 18 of the main cylinder 17 drops to a pressure value equal to 40% of the pilot pressure, that is , the pressure contained in the accumulator 31 , the intake valve opens favoring the return of the ram to the T.D .C. As regards the accumulator 31 , which essentially acts as a cushion, we point out that even assuming the complete emptying of the nitrogen, the ram cannot descend uncontrolled, but is pushed by the servo pump 23. The oil contained in the chamber 19 of the cylinder 17 will go to discharge through the "PED" safety valve and as a consequence of the absence of nitrogen, the ram will not perform the rapid rise stroke.

[0050] In the event that a thrust greater than that available from the accumulator / cushion is required in the initial phase of the ram rise, as for example in forging servo press plants , a pair of plunger cylinders with mechanical stop may be provided, which in the final forming phase, pushed by the main ram, charge an accumulator, which in the initial rise phase will help the ram itself to rise.

[0051] In fig. 8 the plant 10 ’ is illustrated with some variants compared to the plant of figures 1 to 7 . The plant 10 ’ of fig. 8 can be used as an alternative to the plant 10 of fig. 1 , or one or more variants provided therein can be adopted for the plant 10 of said figures 1 to 7 .

[0052] One variant concerns a circuit simplification in which the solenoid valve El and the maximum pressure valve 33 are eliminated. The command of the servo pump 23 at the beginning of the slowdown phase reduces its rotation speed in about 30msec and when the ram 11 approaches the working speed. With the intake valve close to closing, the coil E2 is energized, simultaneously and abruptly increasing the rotation speed of the servo pump to perform the working phase, feeding both cylinders . In particular applications , such as for servo presses for hot deformation, the original scheme of the plant 10 of fig. 1 can be activated.

[0053] It is also advisable to replace part of the oil contained in the accumulator 31 , when the plant 10 ’ is switched off .

[0054] With the machine off , with the ram at the T.D .C. , the coil E3 is energized which provides for discharging the accumulator 31 , passing the oil through the metering device 38 , sized to contain the descent speed of the ram at a value lower than about 10 mm / sec, in case of malfunction of the same solenoid valve, for a time such as to guarantee the discharge of about 40% of the oil contained.

[0055] Consequently, when the plant is switched on again, the pressure of the accumulator 31 will be brought back to the rated value .

[0056] A further variant is the possibility of providing an actuator device 16 ’ with a triple-effect cylinder 17 ’ . In this case the chamber 26 of fig. 1 fluidically connected to the pumping unit 22 is substantially integrated inside said cylinder 17 ’ .

[0057] As regards the tank 14 , at the choice of the end customer and depending on the size of the plant, it will be possible to :

[0058] - Use the pressurized tank complete with hydraulic compensator 27 , with all the advantages listed in the text. The hydraulic compensator 27 can for example be sized according to the quantity of oil that it will have to supply and receive when the ram 11 of the servo press is moved fromthe B.D .C. to the upper one and the internal chamber of the compensator will be fed by a compressed air source;

[0059] - Provide as an alternative to the tank described above, an expansion vessel equipped with an anti-oil membrane;

[0060] - Opt for a tank complete with hydraulic compensator 27 immersed in the tank, with the internal chamber connected to the atmosphere, a choice that does not allow the reduction of the size of the intake valve, requiring maximum care of the intake lines of the servo pump, to guarantee a long duration ;

[0061] - Or use a normal tank with an increase in the quantity of oil necessary for good operation of the plant, with reduction of the time between one replacement and the next of the oil , reducing the rigidity of the transmission with consequent reduction of the position repeatability of the ram at the B.D .C.

[0062] It has been practically verified that the invention achieves the intended purposes . The invention as conceived is susceptible to modifications and variations , all falling within the inventive concept. Furthermore, all details can be replaced with other technically equivalent elements .

[0063] In practical implementation, the materials used as well as the shapes and dimensions may be any, according to requirements , without thereby departing from the scope of protection of the following claims .

Claims

C L A I M S1 . Plant ( 10 , 10 ’ ) for commanding and controlling a ram ( 11 ) of a servo press ( 12 ) , comprising :- a pumping unit (22 ) which is intended to pump a feed fluid; - an actuator unit ( 16 , 16 ’ ) of said ram ( 11 ) which is alternately mobile at least with an active working stroke or with a passive return stroke ;- a hydraulic connection and transport circuit ( 13) which connects said pumping unit (22 ) and said actuator unit ( 16 , 16 ’ ) and transports said feed fluid of said actuator unit ( 16) , wherein said pumping unit (22 ) comprises at least one servo pump (23) fluidically connected to at least one cartridge valve (21 ) fluidically connected to said actuator unit ( 16 , 16 ’ ) .2 . Plant ( 10 , 10 ’ ) as in claim 1 , characterized in that it comprises a hydraulic compensator (27 ) associated with a tank ( 14 ) of said feed fluid .

3. Plant ( 10 , 10 ’ ) as in claim 2 , characterized in that said hydraulic compensator (27 ) is housed inside said tank ( 14 ) .4 . Plant ( 10 , 10 ’ ) as in any claim hereinbefore , characterized in that said actuator unit ( 16) comprises at least a first piston ( 15) and at least a second piston (25) which are associated with said ram ( 11 ) and mobile inside respective chambers ( 18 , 19 , 26) in fluidic communication with said hydraulic circuit ( 13) .5 . Plant ( 10 , 10 ’ ) as in claim 4 , characterized in that the chamber (26) of said second piston is integrated in a cylinder ( 17 ) of said first piston ( 15) .

6. Plant ( 10 , 10 ’ ) as in claim 4 or 5 , characterized in that said chamber (26) is created on the side of said cylinder ( 17 ) .7 . Plant ( 10 , 10 ’ ) as in any claim 1 to 3 hereinbefore , characterized in that said actuator unit ( 16 ’ ) comprises atriple-effect cylinder (17 ’ ) .

8. Plant (10 , 10 ’ ) as in any claim hereinbefore, characterized in that said servo pump (23) is associated with a brushless motor (24) .

9. Plant (10 , 10 ’ ) as in any claim hereinbefore, characterized in that it comprises another pumping unit (28) for drawing the feed fluid from said tank (14) in order to fill one or more accumulators (31 , 32) .

10. Plant (10 , 10 ’ ) as in any claim hereinbefore, characterized in that said servo pump (23) is configured for two-quadrant operation.

11. Method for controlling and commanding a ram (11) of a servo press (12) by means of a plant (10 , 10 ’ ) as in any claim hereinbefore, comprising:- activating a pumping unit (22) which is fluid-dynamically connected to an actuator unit (16, 16 ’ ) by means of a hydraulic circuit (13) , and which has an active rotation and a passive counter-rotation;- alternately driving said actuator unit (16, 16 ’ ) between an active working stroke during said active rotation and a return stroke during said counter-rotation; wherein in at least one of either said active rotation and / or said counterrotation said actuator unit (16, 16 ’ ) cooperates with at least one servo pump (23) of said pumping unit (22) , the servo pump (23) being fluidically connected to at least one cartridge valve (21) fluidically connected to said actuator unit (16 , 16 ’ ) .

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