Method for operating a hydraulic system of an industrial machine

Abstract

The invention relates to a method (46) for operating a hydraulic system (16) of an industrial machine (2), which hydraulic system comprises an actuator (14) and a hydraulic pump (26) which are connected fluidically by means of a hydraulic line (22) which is assigned a pressure sensor (34). The hydraulic pump (26) comprises an electric motor (32) and a pump head (24) driven by the latter. According to the method (46), a pressure within the hydraulic line (22) is measured by means of the pressure sensor (34), and a first pressure value (54) is generated therefrom. A second pressure value (58) is determined on the basis of operating data (55) of the electric motor (32) and a theoretical model (60). A fault (64) is detected if the first pressure value (54) differs from the second pressure value (58) by more than a tolerance value (62). The invention further relates to an industrial machine (2).

Description

[0001] Description

[0002] Method for operating a hydraulic system of an industrial machine

[0003] The invention relates to a method for operating a hydraulic system of an industrial machine and to an industrial machine having a hydraulic system. The hydraulic system comprises an actuator and a hydraulic pump, which are fluidly connected via a hydraulic line.

[0004] Industrial machines are used to create or at least process workpieces. In some cases, a relatively large force is applied to a component of the industrial machine, and thus to the workpiece being created. To provide such forces, a hydraulic system is typically used. This system includes an actuator, which exerts the force on the workpiece or on another part of the industrial machine that acts on the workpiece. The actuator is typically connected to a hydraulic pump via a hydraulic line, with hydraulic fluid being carried through the hydraulic line. The hydraulic pump provides the desired operating pressure so that the actuator can be moved as needed.

[0005] In order for the actuator to move in a predetermined manner, the operating pressure must be adjusted appropriately. To increase the accuracy of machining the workpiece, the operating pressure is regulated to a specific setpoint using the hydraulic pump. Therefore, it is necessary to measure the actual operating pressure in the hydraulic line, for which purpose a pressure sensor associated with the hydraulic line is used.

[0006] During operation, it is possible that an electrical cable connecting the hydraulic sensor to the hydraulic pump control system may become damaged, or that the hydraulic sensor itself may become damaged, resulting in no measurement data being provided. To prevent an operating pressure of 0 bar from being incorrectly assumed, which could cause the hydraulic pump to operate and damage the industrial machine, a pressure sensor is typically used. This sensor provides a sensor signal as an offset even at a pressure of 0 bar. This makes it possible to distinguish whether the pressure sensor is correctly connected to the control system or whether there is no operating pressure in the hydraulic line. However, this increases manufacturing costs.

[0007] Furthermore, it is possible that the electrical cable connecting the pressure sensor to the control system is exposed to electrical and / or magnetic fields that induce an electrical voltage within it. This distorts the transmitted measured values, and consequently, the actuator does not operate as desired. To remedy this, shielding the electrical cable is required, which further increases manufacturing costs.

[0008] The invention is based on the object of specifying a particularly suitable method for operating a hydraulic system of an industrial machine and a particularly suitable industrial machine, wherein manufacturing costs are advantageously reduced and reliability is increased.

[0009] With regard to the method, this object is achieved according to the invention by the features of claim 1 and with regard to the industrial machine by the features of claim 8. Advantageous further developments and refinements are the subject of the respective subclaims.

[0010] The method serves to operate a hydraulic system of an industrial machine. During operation, the industrial machine is used, in particular, to create or machine a workpiece. The industrial machine is suitable, expediently provided, and configured for this purpose. For example, the industrial machine is a roller, a press, or a cutting tool. The industrial machine is particularly preferably a casting machine, and preferably an injection molding machine. The hydraulic system has an actuator, by means of which a component of the industrial machine is moved during operation. For example, the actuator is operatively connected to a punch, a slide, a wheel, or a cutting edge of the industrial machine, or the actuator itself forms the punch / cutting edge / wheel or the like.At least the actuator is provided and configured to act on the workpiece to be created / machined, for example, directly or via another component of the industrial machine, wherein, in particular, a mechanical coupling is present between the workpiece and the actuator. In particular, the actuator is mechanically attached to the other component, in particular rigidly. Preferably, the industrial machine is an injection molding machine, and, for example, a slide, a tool, a valve, and / or a screw is moved by means of the actuator, or the actuator at least partially forms each of these.

[0011] The hydraulic system further comprises a hydraulic pump which is fluidly connected to the actuator via a hydraulic line. During operation, a hydraulic fluid, in particular an oil, is carried via the hydraulic line, with pressure being created in the hydraulic fluid by the hydraulic pump. In particular, an operating pressure is set in the hydraulic line by means of the hydraulic pump, which operating pressure is also referred to simply as pressure below and by means of which the actuator is acted upon. Preferably, the fluid connection is such that the actuator is moved in the desired manner due to the operating pressure provided by the hydraulic pump. For example, a valve or other actuating unit is introduced into the hydraulic line and is additionally actuated accordingly for this purpose.

[0012] For example, the hydraulic system is formed solely by the actuator, the hydraulic pump, and the hydraulic line. Alternatively, further hydraulic lines are provided, by means of which the hydraulic pump is connected to the actuator, so that the actuator can be moved in different directions and / or in different ways. Particularly preferably, the hydraulic system also comprises a reservoir for the hydraulic fluid and / or a compensating pressure vessel, so that the buildup of overpressure, excessive pressure splashes, or the like in the hydraulic system is prevented. Alternatively, or in combination with this, a pressure relief valve is provided, which opens, for example, when the operating pressure exceeds a limit pressure, so that the overpressure is reduced. This prevents damage.The industrial machine or at least the hydraulic system is expediently suitable, in particular designed and configured, for the maximum or nominal pressure during normal operation to be between 100 bar and 400 bar. In particular, any pressure relief valve is adapted to this. For example, the hydraulic system also has one or more additional actuators that are fluidly connected to the hydraulic pump via the hydraulic line or at least one hydraulic line. Thus, it is possible to operate several such actuators using the hydraulic pump.

[0013] The hydraulic pump comprises an electric motor and a pump head driven by it. The electric motor is expediently designed to be brushless, for example, a brushless direct current (BLDC) motor or at least a synchronous motor. In particular, the electrical power of the electric motor is between 200 W and 500 kW. In particular, the hydraulic pump comprises an inverter or servo drive, which supplies current to the electric motor. The inverter / servo drive expediently comprises a bridge circuit, for example, a B6 circuit.

[0014] During operation, a portion of the hydraulic fluid is conveniently located in the pump head, which is used, for example, to pump the hydraulic fluid when the electric motor is operating. For example, the pump head comprises an impeller or gear drive for this purpose. Alternatively, the pump head comprises, for example, an axial piston or plunger / slider that is moved in a longitudinal direction when the electric motor is operating, resulting in intermittent pumping of the hydraulic fluid. In particular, the pump head has an inlet and an outlet, at least one of which is fluidly connected to the hydraulic line.

[0015] The hydraulic system further comprises a pressure sensor assigned to the hydraulic line. The pressure sensor is suitable, in particular provided and configured, to measure a pressure prevailing within the hydraulic line, in particular the pressure of the hydraulic fluid. The measured pressure is, for example, the static pressure, the dynamic pressure or the total pressure. Preferably, the pressure sensor is located on the high-pressure side of the hydraulic pump so that the operating pressure provided by the hydraulic pump can be measured by means of the pressure sensor. For example, the pressure sensor is arranged at a distance from the hydraulic pump or, for example, partially inserted into it, in particular the pump head. This enables assembly as a module. Alternatively, for example, the pressure sensor is arranged in the region of the actuator so that essentially the pressure by means of which the actuator is operated can be determined.

[0016] The method provides that the pressure sensor measures the pressure within the hydraulic line and uses this to create a first pressure value. The pressure sensor thus measures the operating pressure prevailing in the hydraulic line and / or the hydraulic fluid. In particular, the measured value created by the pressure sensor is used as the first pressure value. Alternatively, a value derived from this value or at least a corresponding value, such as an electrical voltage provided by the pressure sensor, is used.

[0017] Furthermore, a second pressure value is determined based on operating data of the electric motor and a theoretical model. For this purpose, the operating data of the electric motor are first recorded and preferably measured. Examples of corresponding operating data include a speed of the electric motor, a power output by the electric motor, an electric current conducted by the electric motor, and / or an electrical voltage applied to the electric motor. The operating data are, in particular, already available and are used, for example, to control the hydraulic pump, preferably the electric motor, and / or to determine its respective state.

[0018] The theoretical model is, in particular, a so-called digital twin of the industrial machine or at least of the hydraulic system. At least, however, the second pressure value can be determined based on the theoretical model, which is, in particular, static, and the dynamically changing operating data, and is determined according to the method. The second pressure value corresponds to the assumed pressure within the hydraulic line that results when the electric motor is operating with the corresponding operating data. In other words, the second pressure value is the theoretical pressure that results from the operation of the electric motor. The second pressure value is not a setpoint, but changes depending on the operating data, which are, in particular, measured.The theoretical model preferably takes into account the inertia or friction of the hydraulic fluid or other components of the hydraulic system and / or, for example, the efficiency of the electric motor and / or the pump head. In particular, the theoretical model includes one or more differential equations of motion of the industrial machine.

[0019] An error is detected if the first pressure value deviates from the second pressure value by more than one tolerance value. For this purpose, the difference between the two pressure values ​​is determined and compared with the tolerance value. In particular, the absolute value of the difference is used, so that the comparison is not signed. The tolerance value is in particular greater than 1 bar and preferably less than 20 bar. In particular, the tolerance value is 10 bar. This makes it possible to use a simplified theoretical model in which minor fluctuations in the first pressure value, for example due to manufacturing tolerances, are not taken into account without the error being falsely detected.

[0020] The method therefore particularly performs a plausibility check of the first pressure value generated by the pressure sensor. This makes it possible to detect a failure of the pressure sensor, for example due to a broken electrical cable, even without the pressure sensor providing a measured value at non-existent pressure. This makes it possible to use a comparatively inexpensive or already existing pressure sensor, which is also used in particular in the hydraulic system and which, at a pressure of 0 bar, delivers a measured value of 0 A or 0 V. This also makes it possible to detect disturbed measurement signals provided by the pressure sensor. The disturbance occurs, for example, due to damage to any electrical cable and / or due to the coupling of interference signals, in particular due to an induced electrical voltage.In other words, a malfunction of the hydraulic system and thus of the industrial machine can be detected using the process, namely when the error, in particular an implausible sensor value, is detected. As a result, it is possible to react to this and take appropriate action, for example, preventing damage to the industrial machine and / or reducing scrap of the tools processed / produced with it and / or reducing downtime.

[0021] For example, the error is always detected as soon as the first pressure value deviates from the second pressure value by more than the tolerance value. However, the error is particularly preferably only detected if the two pressure values ​​deviate from each other by more than the tolerance value for a predetermined period of time. In this case, it is particularly irrelevant how the deviation changes within the time period, as long as the deviation is greater than the tolerance value. The predetermined time period is preferably constant or, for example, dependent on a current operating point of the hydraulic system. In particular, the time period is greater than 0.1 seconds and less than 10 seconds. Advantageously, the time period is 1 second or 2 seconds. This ensures that comparatively short-term fluctuations in the pressure, i.e. a short-term change in the first pressure value, do not lead to the detection of an error.Such changes are triggered, for example, by a desired change in the actuator's operation, such as when the actuator starts or stops moving. As a result, it is not necessary to incorporate this behavior into the theoretical model, which is why the theoretical model is simplified. This also accelerates the determination of the second pressure value and makes it comparatively robust.

[0022] The hydraulic pump is expediently controlled to a setpoint if no error is detected. When the hydraulic pump is controlled to the setpoint, the first pressure value is used as the actual value. The control thus minimizes the deviation between the first pressure value and the setpoint. The setpoint is specified in particular using a higher-level control or regulation system, by means of which the actuator is operated. Parameters are preferably derived from the setpoint, namely a specific pressure, by means of which the electric motor is operated, such as an electric current carried by the electric motor and / or a speed. A lower-level control system is expediently present, by means of which the electric motor is controlled to the corresponding parameters.The subordinate control system advantageously uses the operating data of the electric motor, or part of it, which is used to determine the second pressure value. Due to the control of the hydraulic pump, the actuator is moved in the desired manner, so that the activities performed by the industrial machine are essentially as desired.

[0023] For example, after the error is detected, the hydraulic pump is essentially stopped immediately. Thus, the pressure in the hydraulic system is not increased any further. However, it is particularly preferred for the hydraulic pump to continue operating after the error is detected, so that pressure continues to prevail in the hydraulic system and this pressure is increased if necessary. In this case, the hydraulic pump continues to operate until the actuator has a predetermined state. In other words, due to the operation of the hydraulic pump, the actuator is moved and brought into the predetermined state even after the error is detected. If the actuator is in the predetermined state, the operation of the hydraulic pump is terminated, thus leaving the actuator in the predetermined state.

[0024] The predetermined state is a state from which, in particular, restarting the industrial machine is possible or facilitated. For example, the actuator is moved to a park position for this purpose. This simplifies restarting the industrial machine after the fault has been rectified, e.g., after replacing or repairing the pressure sensor, without requiring any further extensive work in addition to repairing / replacing the pressure sensor. If the industrial machine is an injection molding machine, for example, to achieve the predetermined state, essentially all of the remaining molten plastic is ejected and / or any plastic present in a mold is removed, thus eliminating the need for subsequent, comparatively time-consuming cleaning.

[0025] In particular, the end of an operating cycle is used as the predetermined state. Following this, the actuator is expediently located in a starting or reference position. In other words, the current work step(s) on the respective workpiece during whose processing / production the error was detected are completed, thus ending the operating cycle. Although this workpiece is most likely defective and cannot be used any further, the actuator is subsequently at the beginning of a new operating cycle, so that after the error has been rectified, the industrial machinery can essentially be used immediately to process / produce a new workpiece. It is also not necessary to specify a separate predetermined state that is only approached in the event of an error, for example, which reduces overhead.

[0026] For example, after the fault is detected, the hydraulic pump is operated in a controlled mode. However, it is particularly preferred that the hydraulic pump is controlled to a further setpoint, with the second pressure value being used as the actual value. This ensures that, despite the hydraulic pump continuing to operate after the fault is detected, excessive pressure does not build up in the hydraulic system and / or undesirable behavior of the actuator does not occur. It is also not necessary for the settings for the hydraulic pump to be known in advance for an operating cycle, for example in order to move the actuator into the predetermined state, but rather this is done by means of (dynamic) control to the further setpoint, for which the actual value created from the second pressure value is used in particular. In particular, it is not necessary for the operating variables for a machine cycle to be known in advance.This means that (continued) operation is possible even without an additional setpoint. Furthermore, it may be possible to continue using the industrial machine after the error has been detected, for example if a reduced quality of the workpieces produced / machined with it is permissible. In this case, for example, the hydraulic pump is controlled using the second pressure value until the pressure sensor or, if applicable, a line assigned to the pressure sensor has been replaced / repaired. This can happen, for example, while the industrial machine continues to operate, or it is temporarily shut down for this purpose. Following this, control is continued using the first pressure value, which was determined using the replaced pressure sensor. This means, for example, that shutting down the entire industrial machine is not necessary. For example, the additional setpoint corresponds to the setpoint.However, the additional setpoint is particularly preferably different from the first setpoint and is, for example, derived from the second setpoint and expediently corresponds to a slower operation of the industrial machine, thus reducing the load on it. In particular, the additional setpoint is such that the accuracy of determining the second pressure value is increased.

[0027] Particularly preferably, when the hydraulic system is in operation, the hydraulic pump is always operated in a controlled manner to a respective setpoint, with the first pressure value being used as the actual value if there is no error, and the second pressure value being used as the actual value if the error has been detected.

[0028] For example, the required pressure is maintained after the error is detected. Preferably, however, the pressure is reduced after the error is detected. If the industrial machine, in particular the hydraulic system, continues to operate, this occurs in particular with a reduced pressure. For this purpose, in particular a valve is actuated so that at least a slight pressure reduction occurs initially. Alternatively, the pressure is reduced via the hydraulic pump. For example, the pressure is reduced to a value between 90% and 50% of the pressure prevailing before the error was detected. As a result, the danger to objects in the vicinity of the industrial machine or at least the hydraulic system is reduced if the damage to the pressure sensor occurred, for example, due to overload and / or a leak. In particular, any further setpoint is adjusted to the reduced pressure.In particular, the reduced pressure causes the actuator to move more slowly.

[0029] The industrial machine comprises a hydraulic system having an actuator and a hydraulic pump, which are fluidly connected by a hydraulic line to which a pressure sensor is assigned. For example, the hydraulic line is made at least partially of rubber and is thus flexible. Alternatively, or in combination with this, the hydraulic line is made at least partially of a tube, which is made, for example, of a plastic or metal. The hydraulic pump comprises an electric motor and a pump head driven by it. In particular, the hydraulic pump comprises a servo drive / converter, by means of which the electric motor is operated.

[0030] The hydraulic system operates according to a method in which the pressure sensor measures the pressure within the hydraulic line and uses this to determine a first pressure value. A second pressure value is determined based on operating data from the electric motor and a theoretical model. A fault is detected if the first pressure value deviates from the second pressure value by more than a tolerance value.

[0031] The hydraulic system, for example the possible servo drive / converter, expediently has a control unit that is suitable, in particular provided and configured, for carrying out the method. The control unit comprises, for example, an application-specific integrated circuit (ASIC) or, particularly preferably, a computer that is suitably programmable. In particular, the control unit comprises a storage medium on which a computer program product, also referred to as a computer program, is stored. Upon execution of this computer program product, i.e., the program, the computer is prompted to carry out the method. The invention also relates to such a hydraulic system. The industrial machine is expediently a component of an industrial plant that, for example, comprises several such industrial machines or other industrial machines.The industrial machine is used, for example, to create and / or process a workpiece and is, for example, a (hydraulic) press. In this case, a punch / slider is expediently formed or at least driven by the actuator. Alternatively, the industrial machine is, for example, a cutting machine, and a cutting edge is driven by the actuator. Particularly preferably, the industrial machine is a plastic injection molding machine, and the actuator drives, for example, a conveyor screw and / or a punch / slider, by means of which a liquefied plastic is injected into a mold. Alternatively, or in combination with this, the actuator is assigned, for example, to the mold and is used to open the mold or move it in some other way.In particular, the hydraulic system comprises several corresponding actuators, preferably assigned to the same industrial machine, with only a single hydraulic pump being present. This reduces manufacturing costs.

[0032] The invention also relates to a computer program product. The computer program product comprises a number of instructions which, when the program (computer program product) is executed by a computer, cause the computer to carry out a method for operating a hydraulic system of an industrial machine. The hydraulic system has an actuator and a hydraulic pump which are fluidly connected by means of a hydraulic line to which a pressure sensor is assigned. The hydraulic pump comprises an electric motor and a pump head driven thereby. In the method, a pressure within the hydraulic line is measured by means of the pressure sensor, and a first pressure value is created from this. Based on operating data of the electric motor and a theoretical model, a second pressure value is determined, and an error is detected if the first pressure value deviates from the second pressure value by more than a tolerance value.The computer is expediently a component of a control unit and is formed, for example, by means of the control unit. The computer preferably comprises a microprocessor or is formed by means of the microprocessor. The computer program product is, for example, a file or a data carrier containing an executable program that, when installed on a computer, automatically executes the method.

[0033] The invention further relates to a storage medium on which the computer program product is stored. Such a storage medium is, for example, a CD-ROM, a DVD, or a Blu-ray disc. Alternatively, the storage medium is a USB stick, an SD card, or another storage device that is, for example, rewritable or only writable once. Such a storage device is, for example, a flash memory, a RAM, or a ROM.

[0034] The further developments and advantages explained in connection with the method are also to be transferred analogously to the industrial machine / the hydraulic system / the control unit / the computer program product / the storage medium as well as to each other and vice versa.

[0035] An embodiment of the invention is explained in more detail below with reference to a drawing. In the drawings:

[0036] Fig. 1 schematically shows an industrial machine with a hydraulic system, and Fig. 2 shows a method for operating the hydraulic system.

[0037] Corresponding parts are provided with the same reference numerals in all figures.

[0038] Figure 1 shows a simplified schematic representation of an industrial machine 2 in the form of an injection molding machine. The industrial machine 2 has a cavity 6 provided by a housing 4, into which a filling funnel 8 opens. The cavity 6 opens into a nozzle 10, at the end of which, during operation, a mold (not shown in detail) is located. On the side opposite the nozzle 10, the cavity 6 is delimited by a movable slide 12.

[0039] The slide 12 is a component of an actuator 14 of a hydraulic system 16. On the side of the slide 12 opposite the cavity 6, a piston 17 of the actuator 14 is attached to the slide. The piston 17 partially defines a working volume 18 of the actuator 14, which is located in a further housing 19 of the actuator 14. The piston 17 is mounted for longitudinal movement by means of the further housing 19, so that the size of the working volume 18, which is filled with a hydraulic fluid 20 of the hydraulic system 16, can be changed. When hydraulic fluid 20 is pumped into the working volume 18, its size increases, and the piston 17 and therefore also the slide 12 are moved. As a result, the volume of the cavity 6 is reduced, so that plastic (not shown in detail) located in the cavity 6 is pressed through the nozzle 10.

[0040] The hydraulic system 16 has a hydraulic line 22, by means of which the working volume 18 and a pump head 24 of a hydraulic pump 26 of the hydraulic system 16 are fluidly connected. The hydraulic line 22 is connected to the high-pressure side of the pump head 24. On the low-pressure side, a further hydraulic line 28 is fluidly connected to the pump head 24, by means of which the pump head 24 is connected to a reservoir 30, which also contains the hydraulic fluid 20. When the pump head 24 is operated, the hydraulic fluid 20 is pumped from the reservoir 30 into the working volume 18, so that the piston 17 is moved. The pressure of the hydraulic fluid 20 prevailing in the hydraulic line 22 is increased to 200 bar. To drive the pump head 24, the hydraulic pump 26 has an electric motor 32, which is a brushless DC motor.The electric motor 32 is energized by means of a servo drive 33 or inverter of the hydraulic pump 26.

[0041] A pressure sensor 34 is assigned to the hydraulic line 26, by means of which the pressure prevailing in the hydraulic line 22 can be measured. For this purpose, the pressure sensor 34 is connected fluidically or at least pressure-wise to the hydraulic line 22. The pressure sensor 34 is signal-connected to a control unit 36, by means of which the hydraulic system 16 is operated. For this purpose, the control unit 36 ​​is connected to the servo drive 33, and the servo drive 33 is adjusted accordingly by means of the control unit 36, so that the electric motor 32 is energized according to certain specifications. A valve 38 is also assigned to the hydraulic line 22, which is also signal-connected to the control unit 36, so that the valve 38 can be switched by means of the control unit 36.In this case, it is possible to drain the hydraulic fluid 20 located in the working volume 18 via the valve 38, thereby reducing the pressure therein. It is also possible, with a corresponding adjustment of the valve 38, to pump the hydraulic fluid 20 to the side of the piston 17 opposite the working volume 18, so that the piston and consequently also the slide 12 are moved away from the nozzle 10.

[0042] The control unit 36 ​​has a computer 40 in the form of a programmable microprocessor. The control unit 36 ​​also includes a storage medium in the form of a memory 42, on which a computer program product 44 is stored. The computer program product 44 has a number of instructions which, when the program is executed by the computer 40, cause the computer 40 to perform a method 46, shown in Figure 2, for operating the hydraulic system 16. Thus, the hydraulic system 16 is operated according to the method 46, and the control unit 36 ​​is provided and configured to at least partially perform the method 46.

[0043] The process 46 begins in a first work step 48. At the start of the first work step 48, the slide 12 is at the position furthest from the nozzle 10 that the slide 12 can assume, so that the working volume 18 is minimal. There is also no plastic in the cavity 6. When the process 46 is initiated, a plastic is poured in via the filling funnel 8, and in a subsequent second work step 50, the hydraulic pump 26 is regulated to a setpoint 52 by means of the control unit 36, so that pressure is built up in the hydraulic line 22, which leads to a movement of the piston 17 and thus also of the slide 12 in the housing 4. Consequently, the plastic located in the cavity 6 is pressed out through the nozzle 10. The setpoint 52 is stored in the memory 42 and varies depending on the position of the slide 12 in the housing 4.The setpoint 52 is also adapted to the plastic used and the mold used, which is connected to the nozzle 10.

[0044] The pressure within the hydraulic line 22 is measured by means of the pressure sensor 34, and a first pressure value 54 is created from this. The first pressure value 54 corresponds to the pressure prevailing in the hydraulic line 22 and is used as the actual value for the control. In other words, by changing the operating setting of the electric motor 32, the pressure in the hydraulic line 22 and therefore also the newly created first pressure value 54 are changed until it corresponds to the then applicable setpoint 52. For this purpose, the current supply to the electric motor 32 is adjusted, for which a lower-level control system is used. Based on the difference between the setpoint 52 and the first pressure value 54, a power to be generated by the electric motor 32 and a required electrical current to be supplied by the electric motor 32 are determined. Based on this, an electrical voltage to be applied to the electric motor 32 is determined.For the subordinate control of the power / electrical current / electrical voltage to be applied, operating data 55 are used as the respective actual values, which are measured by sensors not shown in detail. The operating data 55 used here are a current speed of the electric motor 32 as well as an electric current currently being conducted by the electric motor 32 and / or the currently applied electric voltage.

[0045] In a third work step 56, which is performed essentially simultaneously with the second work step 50, the first pressure value 54 is compared with a second pressure value 58. This is determined, namely calculated, based on the operating data 55 and a theoretical model 60 stored in the memory 42. In summary, the second pressure value 58 is determined based on the operating data 55 of the electric motor 32 and the theoretical model 60. The second pressure value 58 is thus a theoretical value and corresponds to the pressure within the hydraulic line 22 that would result due to the operation of the hydraulic pump 26, assuming no malfunction or the like.

[0046] The deviation between the second pressure value 58 and the first pressure value 54 is created. For this purpose, the absolute value of the difference between the two pressure values ​​54, 58 is created. The deviation is compared with a tolerance value 62. An error 64 is detected if the first pressure value 54 deviates from the second pressure value 58 by more than the tolerance value 62. The tolerance value 62 is 10 bar. The error 64 is only detected if the deviation exceeds the tolerance value 62 for a predetermined period of time. The predetermined period of time is 1 second. Thus, if the deviation is only greater than the tolerance value 62 for 0.1 second, the error 64 is not detected. In summary, the error 64 is only detected if the first pressure value 54 deviates from the second pressure value 58 by more than the tolerance value 62 for the predetermined period of time.

[0047] If error 64 is not present, the second work step 50 and the third work step 56 are carried out again, namely until the slide 12 strikes the nozzle 10 or an end position located there. Following this, the hydraulic pump 26 reduces the hydraulic fluid 20 from the working volume 18 until it is minimal. For this purpose, the valve 38 is switched and the hydraulic fluid 20 present in the working volume 18 is drained into the reservoir 30. In addition, the hydraulic fluid 20 is pumped into the space opposite the working volume 18 in the further housing 19, so that the piston 17 is moved. Following this, the slide 12 is again in the position furthest away from the nozzle 10. Then a work cycle / operating cycle 66 is ended. Following this, the first to third work steps 48, 50, 56 are carried out again.Alternatively, the industrial machine 2 is shut down and the operating cycle 66 is only carried out again when necessary. Due to the completion of the operating cycle 66 and the position of the slide 12, there is no longer any plastic in the cavity 6 after the completion of each operating cycle 66, so that a new operating cycle 66 can be started essentially immediately.

[0048] If error 64 is detected, the pressure sensor 34 is malfunctioning, so the measurement data generated by it, and therefore also the first pressure value 54, are incorrect. Thus, the control of the hydraulic pump is also faulty, and the injection-molded parts produced with industrial machine 2 are rejected.

[0049] After error 64 has been detected, a fourth work step 68 is performed. In this step, the hydraulic pump 26 continues to operate and is regulated to a further setpoint 70. The further setpoint 70 deviates from the setpoint 52, but is derived from it. The further setpoint 70 corresponds to a reduced movement speed of the spool 12, although the spool 12 still moves. As a result, the further setpoint 70 is lower than the setpoint 52. Therefore, the valve 38 is first actuated, and the pressure of the hydraulic fluid in the hydraulic line 22 is reduced. Alternatively, the pressure can be reduced via the hydraulic pump 26.

[0050] When controlling to the further setpoint 70, the second pressure value 58 is used. The second pressure value 58 is used as the actual value for the control, and the current supply to the electric motor 32 is adjusted based on the difference between the second pressure value 58 and the further setpoint 70. The electrical current used for this purpose continues to be controlled. The fourth work step 68 is carried out until the slide 12 has also been moved to the stop on the nozzle 10, which is stored in the further setpoint 70. Consequently, the plastic located in the cavity 6 is pressed out through the nozzle 10. The time window until the slide 12 rests there is increased compared to when the setpoint 52 is used and in the case where no error 64 is present.Subsequently, the slide 12 is spaced from the nozzle 10 until the working volume 18 is minimal, for which purpose the valve 38 is switched so that the hydraulic fluid 20 located in the working volume 18 is pumped back into the reservoir 30 by the hydraulic pump 26. Consequently, the operating cycle 66 during which the error 64 occurred is terminated.

[0051] Following this, a fifth work step 72 is performed, shutting down the hydraulic pump 26, and ending the process 46. In other words, after detecting the error 64, the hydraulic pump 26 continues to operate until the actuator 14 reaches a predetermined state. The predetermined state corresponds to the end of the operating cycle 66. Since the industrial machine 2 is subsequently in the same state, with the exception of the damaged pressure sensor 34, as at the start of the process 46, after replacing or repairing the pressure sensor 34, it is essentially possible to restart the industrial machine 2 immediately, eliminating the need for a time-consuming and costly cleaning of the cavity 6 of any remaining plastic residues.

[0052] The invention is not limited to the exemplary embodiment described above. Rather, other variants of the invention can also be derived therefrom by those skilled in the art without departing from the scope of the invention. In particular, all individual features described in connection with the exemplary embodiment can also be combined with one another in other ways without departing from the scope of the invention.

[0053] List of reference symbols

[0054] 2 industrial machines

[0055] 4 housings

[0056] 6 cavity

[0057] 8 filling funnels

[0058] 10 nozzle

[0059] 12 sliders

[0060] 14 Actuator

[0061] 16 Hydraulic system

[0062] 17 pistons

[0063] 18 working volume

[0064] 19 additional housing

[0065] 20 Hydraulic fluid

[0066] 22 Hydraulic line

[0067] 24 Pump head

[0068] 26 Hydraulic pump

[0069] 28 additional hydraulic lines

[0070] 30 reservoirs

[0071] 32 electric motor

[0072] 33 Servo drive

[0073] 34 Pressure sensor

[0074] 36 Control unit

[0075] 38 Valve

[0076] 40 computers

[0077] 42 storage

[0078] 44 Computer program product

[0079] 46 procedures

[0080] 48 first step

[0081] 50 second step

[0082] 52 Setpoint

[0083] 54 first pressure value

[0084] 55 Operating data 56 third work step

[0085] 58 second pressure value

[0086] 60 theoretical model

[0087] 62 Tolerance value 64 Error

[0088] 66 operating cycle

[0089] 68 fourth step

[0090] 70 additional setpoint

[0091] 72 fifth step

Claims

Claims 1. Method (46) for operating a hydraulic system (16) of an industrial machine (2), which has an actuator (14) and a hydraulic pump (26) which are fluidically connected by means of a hydraulic line (22) to which a pressure sensor (34) is assigned, wherein the hydraulic pump (26) comprises an electric motor (32) and a pump head (24) driven thereby, in which - a pressure within the hydraulic line (22) is measured by means of the pressure sensor (34) and a first pressure value (54) is created therefrom, - a second pressure value (58) is determined based on operating data (55) of the electric motor (32) and a theoretical model (60), and - an error (64) is detected if the first pressure value (54) deviates from the second pressure value (58) by more than a tolerance value (62).

2. Method (46) according to claim 1, characterized in that the error (64) is only detected if the first pressure value (54) deviates from the second pressure value (58) by more than the tolerance value (62) for a predetermined period of time.

3. Method (46) according to claim 1 or 2, characterized in that the hydraulic pump (26) is controlled to a desired value (52), the first pressure value (54) being used as the actual value if no error (64) is detected.

4. Method (46) according to one of claims 1 to 3, characterized in that after detection of the error (64), the hydraulic pump (26) continues to operate until the actuator (14) has a predetermined state.

5. Method (46) according to claim 4, characterized in that an end of an operating cycle (66) is used as the predetermined state.

6. Method (46) according to claim 4 or 5, characterized in that the hydraulic pump (26) is controlled to a further desired value (70), the second pressure value (58) being used as the actual value.

7. Method (46) according to one of claims 1 to 6, characterized in that after detection of the error (64) a pressure is reduced.

8. Industrial machine (2), in particular an injection molding machine, comprising a hydraulic system (16) having an actuator (14) and a hydraulic pump (26) which are fluidly connected by means of a hydraulic line (22) to which a pressure sensor (34) is assigned, wherein the hydraulic pump (26) comprises an electric motor (32) and a pump head (24) driven thereby, and wherein the hydraulic system (16) is operated according to a method (46) according to one of claims 1 to 7.

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