Device and method for controlling or regulating the movement of a drawing cushion of a drawing cushion press and drawing cushion press

Abstract

In summary, the invention relates to a device and a method for controlling or regulating the movement of a drawing cushion in a drawing cushion press. The device comprises a position encoder (11), a speed controller (12), a current controller (13), and a motor control unit (14) for providing a rated current for an electric drive (15) of a fluid-hydraulic motor pump unit (20) for moving a drawing cushion in a drawing cushion press. The position encoder (11) is designed to calculate a target speed based on a drawing cushion position command and drawing cushion information. The speed controller (12) calculates a target current based on the target speed. The current controller (13) calculates a control signal based on the target current, and the motor control unit (14) calculates the rated current based on the control current. In this respect, the dynamics of the control of the electric machine can be improved.

Description

[0001] The present invention relates to a device for controlling or regulating a movement of a drawing cushion of a drawing cushion press and a method for controlling or regulating a movement of a drawing cushion of a drawing cushion press as well as a drawing cushion press. State of the art

[0002] Drawing cushion presses are known in the prior art. For example, EP 1 882 534 A1 describes a drawing cushion press based on a direct pump drive, with which it is possible to recover process energy.

[0003] A characteristic feature of the drawing cushion press based on a direct pump drive is that the control device regulates the torque of the electric motor of the direct pump drive based on the drawing cushion pressure command and the detected pressure, such that the drawing cushion pressure corresponds to the pressure command. In this respect, the drawing cushion press described in EP 1 882 534 A1 includes a pressure control system that outputs a motor torque as a control signal for the electric motor.

[0004] In addition to the load pressure at the pump, which is directly proportional to the motor torque, the torque setpoint at the electric motor also requires control inputs for the acceleration and deceleration of the inertia within the pump's direct drive. Furthermore, control inputs are needed within the motor torque itself to compensate for friction and motor losses, for example. Neither acceleration nor loss components are commanded to the electric motor by the described control system. Consequently, the motor torque or current to be commanded is subject to very strong fluctuations depending on the motor, pump, and cylinder losses. This, however, has the disadvantageous effect that the quality and dynamics of the state-of-the-art electric motor control do not meet the requirements of modern forming processes that utilize drawing cushions.

[0005] Against this background, it is an object of the present invention to at least partially overcome the disadvantages of the prior art, or to improve the prior art.

[0006] This problem is solved according to a first aspect of the present invention by a device with the features specified in claim 1. The problem is also solved by a method with the features of claim 8 and a drawing cushion press with the features of claim 13. The invention thus provides a device for controlling or regulating the movement of a drawing cushion of a drawing cushion press, comprising a position encoder, a speed controller, a current controller, and a motor control unit for providing a rated current for an electric drive of a fluid-hydraulic motor pump unit for moving a drawing cushion of a drawing cushion press. The position encoder is provided for calculating a target speed based on a drawing cushion position command and drawing cushion information. The current controller is provided for calculating a control signal based on the target current.The motor control unit is designed to calculate the rated current based on the control signal.

[0007] The rated current comprises the electrical current provided for the operation of the electric drive based on the target current.

[0008] It has been advantageously recognized that improved control behavior can be achieved when the input variable to a motor or the manipulated value from a position, speed, or force controller is proportional to the rate of force or pressure increase. If a motor speed is provided to drive the motor-pump unit, a significant improvement in dynamic control performance is achieved. Dynamic control performance is a prerequisite for being able to replicate the desired pressure or force profiles during the pulling process. The acceleration and loss components in the electric drive are automatically compensated for and do not need to be considered further.

[0009] Advantageously, specifying a motor speed allows for very simple controller switching between position and force control of the pulling cylinder. Since the controller's output signal is the motor speed in both modes, the transition can be correspondingly smooth and jerk-free. This functionality is required for a pulling cushion during the transition from the pre-acceleration phase (position-controlled) to the pulling process (force-controlled). The same applies to the transition from the pulling process (force-controlled) to the return movement (position-controlled).

[0010] During the drawing process (force-controlled), the speed of the drawing cushion represents the disturbance variable for the force control. This speed is measured at the drawing cushion or is determined by the speed of the ram during this phase and is therefore known. If the output signal of the force control is a rotational speed, the known value of the drawing cushion speed can advantageously be introduced into the control loop as a disturbance variable, thus further improving the force control.

[0011] Further advantageous embodiments of the invention are the subject of the dependent claims and the exemplary embodiments described below.

[0012] In an advantageous embodiment of the device according to the first aspect of the present invention, a calculation of the target rotational speed is provided based on drawing die information that is detected by a drawing die detector.

[0013] The drawing punch information includes, for example, the pressure in the cylinder chamber or the position of the drawing cushion. The drawing punch detector is, for example, a pressure sensor for detecting the pressure in a first and a second chamber of the hydraulic cylinder. The drawing punch detector measures the pressure. An appropriate force, in particular the actual force, is determined from the measured pressure and the area of ​​the corresponding chamber of the hydraulic cylinder. Advantageously, the already installed and cost-effective pressure sensors in the system can be used.

[0014] In an alternative embodiment, the drawing die detector can be designed as a force measuring cell that is installed on the piston rod of the hydraulic cylinder between the piston rod and the workpiece.

[0015] In an alternative embodiment, the drawing die detector includes acceleration sensors.

[0016] In an advantageous embodiment of the device according to the first aspect of the present invention, the actuator comprises a position controller, a speed controller or a force controller.

[0017] Advantageously, force controllers can be used to determine a target speed during the drawing process, depending on the drawing process. For example, position controllers and speed controllers can be used to determine a target speed during the movement of the tool and cylinder towards and away from the workpiece.

[0018] In a further advantageous embodiment of the device according to the first aspect of the present invention, the device comprises a current detector for detecting the control signals of the electric drive. The current controller uses a setpoint current which is the difference between the setpoint current and the feedback of the rated current of the electric drive detected by the current detector.

[0019] The electric drive comprises three phases, and the motor torque is derived from the electric currents of these three phases. The currents in the three phases of the electric drive are measured using a current detector. In an alternative embodiment, only the electric currents in two phases of the electric drive need to be measured, and the current in the third phase can then be determined.

[0020] This has the advantage that existing current detectors on the electric drive can be used to determine the current. Feedback of the actual current of the electric drive helps to derive the actual rotational speed, thus making the control system and the system being controlled more dynamic. Furthermore, the control bandwidth of the system is increased.

[0021] In a further advantageous embodiment of the device according to the first aspect of the present invention, the device comprises a speed sensor for detecting the instantaneous speed of the electric drive. The speed controller uses a target speed that is the difference between the target speed and the feedback of the instantaneous speed of the electric drive detected by the speed sensor.

[0022] This has the advantage that existing sensors on the electric drive can be used, providing information about the actual rotational speed of the motor.

[0023] In a further advantageous embodiment of the device according to the first aspect of the present invention, the speed controller uses a target speed which includes a disturbance variable.

[0024] This has the advantage that, for example, during the drawing process in power mode, the speed can be introduced as a disturbance variable. This improves the quality of the force control. Advantageously, during the movement of the hydraulic cylinder, for example towards the workpiece, where the force is controlled by the force controller in addition to the movement, a rotational speed can be provided to the motor-pump unit so that it corresponds to the rotational speed of the tool. Thus, with previously provided information about the speed, overshoots in the system, such as pressure maxima or minima of the motor-pump unit, can be avoided, and the system operates more dynamically, reducing the load on the actuator.

[0025] In a further advantageous embodiment of the device according to the first aspect of the present invention, the setpoint rotational speed of the actuator is proportional to the increase in force or pressure within the drawing cushion press.

[0026] This has the advantage that, regardless of any disturbances occurring at the draw cushion press, the values ​​of which are unknown (e.g., friction in the cylinder, friction in the motor-pump unit, losses in the electric drive), a speed is set via a speed controller, and disturbances and thus losses are compensated for. For example, stick-slip behavior of the motor-pump unit can be reduced by setting the speed. The speed controller provides current for the set speed, from which the torque for the motor is generated.

[0027] The above embodiments and further developments can be combined with one another as appropriate. Further possible embodiments, further developments, and implementations of the invention also include combinations of features of the invention described previously or subsequently with regard to the exemplary embodiments, even if not explicitly mentioned. In particular, those skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the present invention.

[0028] Furthermore, according to a second aspect of the present invention, the invention provides a method for controlling or regulating a movement of a drawing cushion of a drawing cushion press with the features specified in claim 8.

[0029] The invention therefore provides a method for controlling or regulating the movement of a drawing cushion of a drawing cushion press comprising the following steps: Receiving a draw cushion position command and draw cushion information by the position transmitter, calculating a target speed by the position transmitter based on the received draw cushion position command and the draw cushion information, calculating a target current by the speed controller based on the calculated target speed, calculating a control signal by the current controller based on the calculated target current, and calculating a rated current by a motor control unit based on the calculated control signal, to provide a rated current for an electric drive of a fluid hydraulic motor pump unit for moving a draw cushion of a draw cushion press.

[0030] In an advantageous embodiment of the method according to the second aspect of the present invention, the target rotational speed is calculated based on information from the drawing die. This information is acquired by a drawing die detector.

[0031] In a further advantageous embodiment of the method according to the second aspect of the present invention, the current controller uses a setpoint current. The setpoint current is the difference between the setpoint current and the feedback of the rated current of the electric drive detected by a current detector.

[0032] In a further advantageous embodiment of the method according to the second aspect of the present invention, the target rotational speed is calculated based on information from the drawing die. This information is acquired by a drawing die detector.

[0033] In a further advantageous embodiment of the method according to the second aspect of the present invention, the current controller uses a setpoint current which is a difference between the setpoint current and the feedback of the nominal current of the electric drive detected by a current detector.

[0034] In a further advantageous embodiment of the method according to the second aspect of the present invention, the speed controller uses a target speed. The target speed is the difference between the target speed and the feedback of the instantaneous speed of the electric drive detected by a speed sensor.

[0035] In a further advantageous embodiment of the method according to the second aspect of the present invention, the speed controller uses a target speed which includes a disturbance variable.

[0036] Furthermore, according to a third aspect of the present invention, the invention provides a drawing cushion press comprising a device according to claims 1 to 7.

[0037] The present invention will be explained in more detail below with reference to the exemplary embodiments shown in the schematic figures of the drawings.

[0038] This shows: Fig. 1 a schematic block diagram to illustrate an embodiment of a device according to the invention for controlling or regulating the movement of a drawing cushion of a drawing cushion press; Fig. 2 a schematic flowchart to illustrate a possible embodiment of a method according to the invention for controlling or regulating a movement of a drawing cushion of a drawing cushion press; Fig. 3a-3d a diagram to illustrate the force control during a deep drawing process including disturbance variable feedforward in a possible embodiment of a device according to the invention for controlling or regulating a movement of a drawing cushion of a drawing cushion press.

[0039] The accompanying drawings are intended to provide a further understanding of the embodiments of the invention. They illustrate embodiments and, in conjunction with the description, serve to explain the principles and concepts of the invention. Other embodiments and many of the advantages mentioned will become apparent with reference to the drawings. The elements of the drawings are not necessarily shown to scale.

[0040] In the figures of the drawing, identical, functionally equivalent and similarly acting elements, features and components - unless otherwise stated - are each provided with the same reference symbols.

[0041] Fig. Figure 1 shows a block diagram illustrating an embodiment of a device according to the invention for controlling or regulating the movement of a drawing cushion of a drawing cushion press.

[0042] In Fig. Figure 1 shows the device 10 comprising a control loop for controlling a drawing cushion press with a cascade circuit of a position encoder 11, a speed controller 12, a current controller 13 and a motor control unit 14. The position encoder 11 can be configured as a position controller, speed controller or force controller.

[0043] In an advantageous embodiment, the actuator 11, for example a force controller, receives as a control variable a difference from a drawing cushion information, for example the target force F, in the force operation or the actual drawing process of the drawing cushion press. S and an actual force F I The target force F S is the reference variable (setpoint). The actual force F IThis includes information about the drawing die and results from the difference in forces, which corresponds to the pressure in the two chambers of the hydraulic cylinder. The force is calculated using the measured pressure and the area of ​​the corresponding chamber of the hydraulic cylinder. The actual force F I This results from the difference, since both chambers of the hydraulic cylinder have a mutual effect. The pressure in each chamber is determined via a draw-punch detector 16 and 19.

[0044] The draw ram detector 16, 19 is, for example, a pressure sensor. Pressure sensors provided in the hydraulic cylinder can be used, for example.

[0045] In an alternative embodiment, the drawing die detector 16, 19 is designed as a force measuring cell.

[0046] In another alternative embodiment, the drawing die detector 16, 19 is designed as a position sensor, for example an acceleration sensor.

[0047] The manipulated variable provided to the actuator 11 results from the difference between the setpoint force F S and the actual force F I The actuator 11 sets a target rotational speed n S The control variable supplied to the speed controller 12 is a difference between the target speed n supplied by the actuator 11 and the speed controller 12. S , the instantaneous speed (actual speed) n I and the disturbance variable 30. As a result, the speed controller 12 sets a target current I. S ready for the current regulator 13.

[0048] The reference variable supplied to the current controller 13 is a difference between the set current I supplied by the speed controller 12 and the set current I. S and the actual current I SThe current controller 13 provides a control signal for controlling the motor control unit 14 based on the reference variable provided by the speed controller 12.

[0049] The control signal can, for example, comprise a pulse-width modulated voltage. The motor control unit 14, for example a frequency converter, converts the pulse-width modulated voltage into a rated current for operating the electric machine 15 to drive the motor pump unit 20. The rated current is the electrical current drawn by the electric drive 15 during operation of the motor pump unit 20 and the drawing cushion press, based on the control signal provided to the motor control unit 14. The electric drive 15 is, for example, a three-phase AC motor. The motor pump unit 20 provides the hydraulic energy for operating the drawing cushion press.

[0050] A current detector 17 is connected to the output of the motor control unit 14. The current detector 17 determines the electric current in the three phases of the electric drive 15 and provides the determined electric current via feedback to the current controller 13 for calculating a control signal. The current value in the three phases of the electric drive 15 is determined via the current detector 17. For this purpose, existing current detectors 17 on the electric drive 15 can be used to determine the actual current I. S to determine and feed back to the current controller 13 for further processing. This simplifies the derivation of the actual speed of the electric drive 15 and thus makes the control system and the system to be controlled more dynamic. In addition, the control bandwidth in the system is increased.

[0051] In an alternative embodiment, the control signal for the electric drive can be provided by a control via a controlled current at the current controller 13.

[0052] A speed sensor 18 is connected to the electric drive 15 of the motor pump unit 20. The speed sensor 18 determines the instantaneous speed n. I of the electric drive 15 and represents the determined instantaneous speed n I via feedback to the speed controller 12 for calculating a target current I S ready. Conventional speed sensors 12, for example those already provided on the electric drive 15, can be used to determine the rotational speed of the electric drive 15. Additional speed control can advantageously increase the dynamics of the current control in the inner loop of the overall control system of the electric drive 15.

[0053] In an alternative embodiment, the electric drive 15 can be controlled via a controlled rotating field by means of the speed encoders already provided on the electric drive 15.

[0054] To calculate the manipulated variable for the rotary controller 12, the disturbance variable 30 is taken into account. The velocity is used as the disturbance variable 30. In particular, the velocity of the drawing cushion can be used as a disturbance variable for force control during the drawing process. This velocity is measured at the drawing cushion or is determined by the velocity of the ram during this phase and is therefore known. If the output signal of the force control is a rotational speed, the known value of the drawing cushion velocity can advantageously be introduced into the control loop as a disturbance variable, thus further improving the force control.

[0055] Fig. Figure 2 shows a schematic flowchart illustrating a possible embodiment of a method according to the invention for controlling or regulating the movement of a drawing cushion of a drawing cushion press.

[0056] In the illustrated embodiment, the process comprises several steps. In a first step S1, the actuator 11 receives a draw cushion control command and draw cushion information. The draw cushion information includes, for example, the target force F. S .

[0057] In a further step S2, a target rotational speed n is set. S The target speed n is calculated by the actuator 11 based on the received draw cushion actuator command and the draw cushion information. S This results from the difference in the target force F S and the actual force I S The actual force I SThe pressure in the chambers of the hydraulic cylinder is the difference between the product of the current pressure in the chambers and the area of ​​the hydraulic cylinder. The pressure in the chambers can be determined via the draw-punch detectors 16, 19, for example, pressure sensors.

[0058] In one embodiment, the target rotational speed comprises n S a difference from the instantaneous rotational speed n fed back from the drive machine 15 I and an applied disturbance variable, for example the speed of the draw cushion. The instantaneous rotational speed n I The speed of the electric drive motor 15 is determined by a speed sensor 18.

[0059] In a further step S3, a target current I is set. S by the speed controller 12 based on the calculated target speed n S calculated. In one possible embodiment, the target current I comprises S the difference between the set current I provided by the actuator 12 Sand the actual current I supplied by the motor control unit 14 to the electric drive 15 I The actual current I I is provided by a feedback loop. The electrical current of the actual current I I is determined, for example, by a current detector.

[0060] In a further step S4, a control signal is generated by the current controller 13 based on the target current I provided by the speed controller 12. S calculated. The control signal can, for example, comprise a pulse-width modulated voltage. The motor control unit 14, for example a frequency converter, converts the pulse-width modulated voltage in a further step S5 into a rated current for operating the electric machine 15 for driving the fluid-hydraulic motor pump unit 20 to move a drawing cushion of a drawing cushion press.

[0061] Fig. Figures 3a to 3d show a diagram to illustrate the force control during a deep drawing operation, including disturbance variable feedforward, in a possible embodiment of a device according to the invention for controlling or regulating the movement of a drawing cushion of a drawing cushion press.

[0062] In the Fig. Figures 3a to 3d depict a deep-drawing process with the pre-acceleration of the drawing cushion activated. The measurement was performed using a simulation tool to prevent any damage caused by commissioning errors. The in Fig. Figures 3a to 3d show that the test demonstrates stable force control throughout the entire deep-drawing stroke. The force build-up occurs without any significant overshoot.

[0063] In Fig. Figure 3a shows the ram and cylinder positions 1 to 4 of the draw cushion. The curves are sequential, and the cylinders move in parallel. The draw cushion is actively pre-accelerated in the time range of 0s to 1s. At time 1s, the ram strikes the draw cushion and displaces it. The forming process takes place in the time range of 1s to 7s. At time 7s, the ram moves upwards while the draw cushion remains in the pressing position. The formed part can be removed (see time range 7s to 10s). In the time range of 10s to 13s, the draw cushion cylinders return to their starting position. The new formed part can be inserted.

[0064] In Fig. Figure 3b shows the velocity of the draw cushion cylinders 1-4 and the velocity of the plunger. In the time range from 0s to 1s, the draw cylinders are pre-accelerated. During this time range, there is a relative velocity between the plunger and the draw cushion cylinder. At time 1s, the plunger and draw cushion make contact. From 1s to 7s, the plunger displaces the draw cushion, therefore the velocities of the plunger and draw cushion are identical.

[0065] Fig. Figure 3c shows the force on the drawing cylinders calculated from the chamber pressures. This force represents the controlled variable during the drawing process in the time range of 1 s to 7 s. Fig. Figure 3c shows the control quality of the force control at a constant setpoint of 250 kN per cylinder. The actual force follows the setpoint profile almost perfectly, even though the draw cushion cylinder is moving (see Figure 3c). Fig. 3b) This force control quality is only achievable due to force control by means of speed specification according to the present invention, since only in this way can the control disturbance variable (speed of the cylinder) be implemented. In addition, any hydraulic-mechanical losses that occur, for example friction, are compensated for by the speed specification of the force controller.

[0066] Fig. Figure 3D shows the pressures on side A and side B of the drawing cushion cylinder. From the respective pressures, the respective output force of the drawing cylinders can be calculated using the area of ​​the drawing cylinder (see figure). Fig. 3c).

[0067] In summary, the invention relates to a device and a method for controlling or regulating the movement of a drawing cushion in a drawing cushion press. The device comprises a position encoder (11), a speed controller (12), a current controller (13), and a motor control unit (14) for providing a rated current for an electric drive (15) of a fluid-hydraulic motor pump unit (20) for moving a drawing cushion in a drawing cushion press. The position encoder (11) is designed to calculate a target speed based on a drawing cushion position command and drawing cushion information. The speed controller (12) calculates a target current based on the target speed. The current controller (13) calculates a control signal based on the target current, and the motor control unit (14) calculates the rated current based on the control current.

[0068] In this respect, the dynamics of the control of the electric machine can be improved. Reference symbol list 10 device 11 Position transmitters 12 speed controllers 13 current regulators 14 Engine control unit 15 electric drive 16 Draw die detector 17 Current detector 18 Speed ​​sensors 19 Draw die detector 20 Motor pump unit 30 Disturbance variable 100 procedures S1-S4 process steps

Claims

[1] Device (10) for controlling or regulating a movement of a drawing cushion of a drawing cushion press comprising a position encoder (11), a speed controller (12), a current regulator (13) and an engine control unit (14) for providing a rated current for an electric drive (15) of a fluid hydraulic motor pump unit (20) for moving a drawing cushion of a drawing cushion press, wherein the actuator (11) is provided for calculating a target rotational speed based on a draw cushion actuator command and draw cushion information, the speed controller (12) is designed to calculate a target current based on the target rotational speed, the current controller (13) is provided for calculating a control signal based on the target current, and the motor control unit (14) is provided for calculating the rated current based on the control current. [2] Device (10) according to claim 1, wherein the calculation of the target rotational speed is based on drawing die information acquired by a drawing die detector (16, 19). [3] Device (10) according to one of the preceding claims 1 and 2, wherein the actuator (11) comprises a position controller, a speed controller or a force controller. [4] Device (10) according to any one of the preceding claims 1 to 3, comprising a current detector for detecting the control signals of the electric drive (15), wherein the current controller (13) uses a setpoint current which is a difference between the setpoint current and the feedback of the nominal current of the electric drive (15) detected by the current detector (17). [5] Device (10) according to any one of the preceding claims 1 to 4, comprising a speed sensor for detecting an instantaneous speed of the electric drive (15), wherein the speed controller (12) uses a target speed which is a difference between the target speed and the feedback of the instantaneous speed of the electric drive (15) detected by the speed sensor (18). [6] Device (10) according to any one of the preceding claims 1 to 5, wherein the speed controller (12) uses a target speed comprising a disturbance variable (30). [7] Device (10) according to any one of the preceding claims 1 to 6, wherein the set speed of the actuator (11) is proportional to the force or pressure increase within the drawing cushion press. [8] Method (100) for controlling or regulating the movement of a drawing cushion of a drawing cushion press comprising the steps: Receiving (S1) a draw cushion position command and draw cushion information by the position transmitter (11); Calculating (S2) a target rotational speed by the actuator (11) based on the received draw cushion actuator command and the draw cushion information; Calculating (S3) a target current through the speed controller (12) based on the calculated target speed; Calculating (S4) a control signal by the current controller (13) based on the calculated target current; and Calculating (S5) a rated current by a motor control unit (14) based on the calculated control signal, for providing a rated current for an electric drive (15) of a fluid hydraulic motor pump unit (20) for moving a drawing cushion of a drawing cushion press. [9] Method (100) according to claim 8, wherein the target rotational speed is calculated on the basis of drawing die information acquired by a drawing die detector (16, 19). [10] Method (100) according to one of the preceding claims 8 and 9, wherein the current controller uses a setpoint current which is a difference between the setpoint current and the feedback of the nominal current of the electric drive (15) detected by a current detector (17). [11] Method (100) according to any one of the preceding claims 8 to 10, wherein the speed controller (12) uses a target speed which is a difference between the target speed and the feedback of the instantaneous speed of the electric drive (15) detected by a speed sensor (18). [12] Method (100) according to any one of the preceding claims 8 to 11, wherein the speed controller (12) uses a target speed comprising a disturbance variable (30). [13] Draw cushion press comprising a device (10) according to claims 1 to 7.

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