Fluidic system, process and control device

Abstract

Fluidic system (10) for use in a potentially explosive atmosphere, comprising: - a pneumatic actuator (3) with a pressure chamber (14) and an actuator element (15) which can be set in motion by applying compressed air to the pressure chamber (14), - a valve arrangement (1) configured to connect the pressure chamber (14) to a compressed air source (6) to supply compressed air to the pressure chamber (14), and / or to fluidically connect the pressure chamber (14) to a pressure fluid sink (7) to release the compressed air from the pressure chamber (14), - a control unit (2) configured to control the valve arrangement (1), and - a system volume that can be pressurized with compressed air, comprising a pressure chamber internal volume (44) of the pressure chamber (14), a valve arrangement internal volume (45) of the valve arrangement (1) and / or a connection internal volume (46) of a fluidic connection (5), wherein the control unit (2) is designed, in addition to a normal operating mode in which the pressure chamber (14) is pressurized with compressed air to set the actuator element (15) in motion, to provide a purging mode and in the purging mode to actuate the valve arrangement (1) such that compressed air is repeatedly supplied to the system volume and system fluid present in the system volume is drained, so that the system fluid is diluted with the compressed air and at least partially removed from the system volume, wherein the valve arrangement (1) comprises at least one valve unit (11, 12) for fluidically connecting the system volume to the compressed air source (6) and / or the pressure fluid sink (7), wherein the fluidic system (10) is configured to operate at least one element of the valve unit (11, 12) with a reduced voltage (V2, V3) compared to the normal operating mode in the purging mode.

Description

[0001] The invention relates to a fluidic system for use in a potentially explosive atmosphere, comprising: a pneumatic actuator with a pressure chamber and an actuator element that can be set in motion by pressurizing the pressure chamber, a valve arrangement configured to connect the pressure chamber to a compressed air source in order to supply compressed air to the pressure chamber, and / or to fluidically connect the pressure chamber to a pressure fluid sink in order to discharge compressed air from the pressure chamber, a control unit configured to actuate the valve arrangement, and a system volume that can be pressurized with compressed air, comprising the internal volume of the pressure chamber and / or the internal volume of the valve arrangement and / or the internal volume of a connection of a fluidic connection of the fluidic system.

[0002] For example, the fluidic system is designed to operate in an environment containing a potentially explosive atmosphere; that is, in an environment where an ambient fluid, such as ambient air, contains flammable substances, for example, flammable gases, liquids, vapors, aerosols, and / or dusts. In particular, if the pressure within the system volume is not greater than the ambient pressure, for example, atmospheric pressure, the potentially explosive atmosphere can penetrate the system volume. Under certain circumstances, the operation of the fluidic system can then lead to ignition of the potentially explosive atmosphere. For example, a component of the fluidic system, such as the valve assembly, may be electrically operated, and an electrical discharge could ignite the potentially explosive atmosphere. The valve assembly, for example, includes a piezoelectric actuator.In this case, ignition can be caused by a voltage drop across the piezo actuator.

[0003] Particularly before switching on, commissioning, after a power failure, and / or after a pressure loss in the fluidic system, the composition of the system fluid present in the system volume at that time may be unknown. It cannot be ruled out that the system fluid contains flammable substances. Commissioning the fluidic system in this condition may pose a risk of ignition of flammable substances.

[0004] DE 10 2014 217 181 A1 describes a pressure control circuit with a switching valve for controlling pressure in a consumer. The switching valve has a valve element that is ballistically actuated, whereby the switching time of the switching valve is so short that it performs an opening stroke from the closed position, but without reaching its fully switched open position, falls back into the closed position.

[0005] DE 10 2015 213 936 A1 describes a flushing device for a hydrostatic device. The flushing device creates an intentional fluid leakage from the low-pressure side of the hydrostatic device to a low-pressure area.

[0006] German patent DE 103 13 176 A1 describes an agricultural tillage implement with a pressure or level compensation system using hydraulic cylinders. Hydraulic fluid is introduced into the system via one line and flows back out via another. This process flushes air out of the system.

[0007] One objective of the invention is to increase the operational reliability of the fluidic system.

[0008] The problem is solved by a fluidic system according to claim 1. In addition to a normal operating mode in which the pressure chamber is pressurized with the pressure fluid to set the actuator in motion, the control unit is configured to provide a purging mode and, in the purging mode, to control the valve arrangement such that compressed air is repeatedly supplied to the system volume and system fluid present in the system volume is drained, so that any system fluid contained in the system volume is diluted with the compressed air and at least partially removed from the system volume. The valve arrangement comprises at least one valve unit for fluidically connecting the system volume to the compressed air source and / or the pressure fluid sink, wherein the fluidic system is configured to operate at least one element of the valve unit with a reduced voltage compared to the normal operating mode in the purging mode.

[0009] In this way, the system fluid present in the system volume at the start of the purge cycle can be gradually replaced by compressed air. The system fluid is defined as the mixture of all fluids and substances present in the system volume at the start of the purge cycle. The composition of the system fluid is generally unknown – it is possible that the system fluid contains substances that could be ignited by the normal operation of the fluidic system. In particular, it cannot be ruled out before the purge cycle that at least some proportion of the system fluid originates from a potentially explosive atmosphere and contains flammable substances.

[0010] The compressed air used to replace the system fluid is supplied by the compressed air source. This compressed air should ideally be a fluid that does not contain any substances that could be ignited by the fluidic system. By reducing the proportion of system fluid and increasing the proportion of compressed air within the system volume, the risk of explosive system fluid reaching and igniting an electrically operated component of the fluidic system, such as the valve assembly, during normal operation can be reduced. Consequently, operational safety can be improved.

[0011] According to a preferred embodiment, the control unit is configured to automatically initiate the purge mode. In particular, the control unit is configured to automatically switch from the normal operating mode to the purge mode. Furthermore, the control unit is preferably configured to actuate the valve arrangement in purge mode such that the actuator retains its current position, thus expediently preventing any movement of the actuator during purge mode. Additionally, the valve arrangement is operated at a lower voltage in purge mode than in the normal operating mode. Advantageously, the compressed air supply and system fluid drainage are repeated in purge mode until at least 95%, and in particular at least 99%, of the system fluid has been replaced by the pressurized fluid. Advantageously, the valve arrangement comprises one or more piezo actuators.

[0012] Advantageous further training is the subject of the sub-claims.

[0013] The invention further relates to a fluidic system according to claim 6.

[0014] The invention further relates to a method according to claim 14 and a method according to claim 15.

[0015] Preferably, the method is carried out using the fluidic system described herein. Advantageously, the method is designed in accordance with a further development of the fluidic system described herein.

[0016] Exemplary embodiments are explained below with reference to the figures. This shows Fig. 1 a schematic representation of a fluidic system, Fig. 2. A diagram of the pressure profile over time during a rinsing procedure. Fig. 3 a schematic representation of a control device, Fig. 4 a flowchart of a process for operating a fluidic system, Fig. 5 a piezo actuator with an initial circuit, and Fig. 6 a piezo actuator with a second circuit.

[0017] The Fig. Figure 1 shows an exemplary design of a fluidic system 10. The fluidic system 10 is particularly suitable for use in an explosive atmosphere.

[0018] The fluidic system 10 comprises a fluidic actuator 3 with a pressure chamber 14 and an actuator element 15, which can be set in motion by pressurizing the pressure chamber 14 with a pressure fluid.

[0019] The fluidic system 10 further comprises a valve arrangement 1 configured to connect the pressure chamber 14 to a pressure fluid source 6 in order to supply the pressure fluid to the pressure chamber 14, and / or to fluidically connect the pressure chamber 14 to a pressure fluid sink 7 in order to drain the pressure fluid from the pressure chamber 14.

[0020] The fluidic system 10 further comprises a fluidic connection 5, via which the valve arrangement 1 is fluidically connected to the pressure chamber 14.

[0021] The fluidic system 10 comprises a system volume that can be pressurized with the pressure fluid, which includes a pressure chamber internal volume 44 of the pressure chamber 14 and / or a connection internal volume 46 of the fluidic connection 5 and / or a valve arrangement internal volume 45 of the valve arrangement 1.

[0022] The fluidic system 10 further comprises a control unit 2 configured to actuate the valve arrangement 1. The control unit 2 is configured to provide a normal operating mode and, in the normal operating mode, actuates the valve arrangement 1 such that the pressure chamber 14 is pressurized with the pressurized fluid, thereby setting the actuator element 15 in motion. In addition to the normal operating mode, the control unit 2 is configured to provide a purge mode and, in the purge mode, actuates the valve arrangement 1 such that the system volume is repeatedly pressurized and vented with pressurized fluid, thus diluting any system fluid contained in the system volume with the pressurized fluid and at least partially removing it from the system volume.

[0023] Further exemplary details will be explained below.

[0024] The system volume comprises all those volumes that are exposed to the pressurized fluid, particularly during normal operation, and that are fluidically connected to one another. Preferably, the system volume comprises the internal volume of the pressure chamber 44, the internal volume of the connection 46, and / or the internal volume of the valve assembly 45.

[0025] The fluidic system 10 comprises, by way of example, the pressure fluid source 6 and / or the pressure fluid sink 7. The pressure fluid source 6 is in particular a compressed air source. The pressure fluid sink 7 is expediently a fluidic connection to the atmosphere. Preferably, a check valve (not shown in the figures) is provided at the pressure fluid sink 7.

[0026] The valve arrangement 1 comprises, by way of example, a first valve unit 11 and a second valve unit 12. The first valve unit 11 is located in a first fluidic path from the pressure fluid source 6 to the pressure chamber 14. Opening the first valve unit 11 establishes a fluidic connection between the pressure chamber 14 and the pressure fluid source 6, and closing the first valve unit 11 interrupts this connection. The second valve unit 12 is located in a second fluidic path from the pressure fluid sink 7 to the pressure chamber 14. Opening the second valve unit 12 establishes a fluidic connection between the pressure chamber 14 and the pressure fluid sink 7, and closing the second valve unit 12 interrupts this connection.

[0027] The valve assembly 1, in particular the two valve units 11, 12, are fluidically connected to the pressure chamber 14 via the fluidic connection 5. The fluidic connection 5 is, for example, a pipe assembly. The fluidic connection 5 comprises one or more hoses and / or one or more fluidic channels. Advantageously, the fluidic connection 5 includes a fluidic connection section integrated into the fluidic actuator 3 and / or in the valve assembly 1.

[0028] The fluidic connection 5 comprises, by way of example, two valve assembly branches 41, 42, which are fluidically connected to the valve units 11, 12, and an actuator branch 43, which is fluidically connected to the fluidic actuator 3. The two valve assembly branches 41, 42 and the actuator branch 43 converge at a connection point and together form a Y-structure. The aforementioned first fluidic path runs via the first valve assembly branch 41 and the actuator branch 43. The aforementioned second fluidic path runs via the second valve assembly branch 42 and the actuator branch 43. Consequently, both fluidic paths to the pressure chamber 14 run via the same connection section of the fluidic connection 5 – namely, via the actuator branch 43.

[0029] The fluidic actuator 3 is, in particular, a pneumatic actuator. The fluidic actuator 3 is advantageously designed as a fluidic drive, in particular as a pneumatic drive. The fluidic actuator 3 is, in particular, a valve drive. By way of example, the fluidic actuator 3 is designed as a drive cylinder, in particular as a pneumatic drive cylinder. The fluidic actuator 3 advantageously comprises a cylindrical actuator body.

[0030] By pressurizing the pressure chamber 14 with the pressure fluid, the position of the actuator element 15 can be changed. In particular, the position of the actuator element 15 changes when the pressure prevailing in the pressure chamber 14 exceeds a breakaway pressure. Preferably, the fluidic actuator 3 is designed to actuate a valve element of a valve (not shown in the figures), in particular a process valve, by changing the position of its actuator element 15.

[0031] The actuator element 15 expediently comprises a piston 16 and optionally a piston rod 17.

[0032] The fluidic actuator 3 is expediently designed as a single-acting actuator. By way of example, the fluidic actuator 3 comprises a spring element 18. The spring element 18 provides a restoring force that pushes the actuator element 15 into a first position. By pressurizing the pressure chamber 14 with the pressure fluid, a fluidic actuating force can be provided that acts against the restoring force and pushes the actuator element 15 into a second position.

[0033] According to an alternative embodiment not shown in the figures, the fluidic actuator can also be designed as a double-acting actuator. In this case, the spring element 18 can be omitted. Advantageously, the fluidic actuator has a second pressure chamber. By pressurizing the second pressure chamber with the pressure fluid, a fluidic actuating force can be provided that forces the actuator element into the first position.

[0034] The fluidic system 10 further comprises, by way of example, a sensor arrangement 4. The sensor arrangement 4 comprises, by way of example, a pressure sensor unit 8 and / or a position sensor unit 9. The pressure sensor unit 8 is configured to detect a pressure value Pw related to the system volume. For example, the pressure sensor unit 8 is configured to detect a differential pressure between the pressure prevailing in the system volume, in particular in the fluidic connection 5 and / or the pressure chamber 14, and an ambient pressure, in particular atmospheric pressure. The pressure sensor unit 8 provides the detected pressure value Pw to the control unit 2. The position sensor unit 9 is advantageously configured to detect the position of the actuator element 15 and to provide the control unit 2 with a corresponding position signal.

[0035] The control unit 2 is configured to provide a control command and, in accordance with the control command, to actuate the valve arrangement 1 in order to move the actuator element 15 into a position specified, in particular, by the control command. The control command is transmitted, for example, from a higher-level control system (not shown in the figures), such as a programmable logic controller (PLC), to the control unit 2. Advantageously, the control unit 2 is configured to perform position control of the actuator element 15 and / or pressure control of the pressure value Pw using the sensor arrangement 4.

[0036] Preferably, the control unit 2 is designed to keep the pressure in the system volume above the ambient pressure at all times during normal operating mode, in particular by means of a pressure control, which is carried out, for example, by controlling the valve arrangement 1 and taking into account the pressure value Pw detected by the pressure sensor unit 8.

[0037] In addition to its normal operating mode, the control unit 2 has a purge mode. Advantageously, the control unit 2 is configured to operate in either the normal operating mode or the purge mode. Advantageously, in the normal operating mode, the control unit 2 is configured to perform the aforementioned actuation of the valve arrangement 1 according to a control command in order to move the actuator element 15 to a predetermined position. Furthermore, the control unit 2 is preferably configured not to perform the aforementioned actuation of the valve arrangement 1, in which the actuator element 15 is moved to a predetermined position according to the control command, in the purge mode. For example, in the purge mode, the control unit 2 is configured to ignore control commands that specify a position and / or change of position of the actuator element.

[0038] Advantageously, the control unit 2 is designed to provide mode information indicating which mode - i.e., the normal operating mode or the rinsing mode - the control unit 2 is currently in.

[0039] According to a preferred embodiment, the control unit 2 is configured to automatically enter purge mode, in particular to automatically switch from normal operating mode to purge mode. Advantageously, the control unit 2 is configured to enter purge mode based on a detected event. The detected event is, for example, the switching on of the control unit 2. The detected event can also be a power loss and / or the commissioning of the fluidic system 10. Furthermore, the detected event can be a pressure loss in the system volume, in particular the detection of a pressure value Pw indicating that the pressure in the system volume is neither greater nor less than the ambient pressure, in particular atmospheric pressure.

[0040] According to an embodiment not shown, the fluidic system comprises a process valve assembly. The process valve assembly includes, in particular, a control device 20 designed as a control head and / or positioner head, which is schematically represented in Fig. Figure 3 shows the process valve assembly. The process valve assembly further comprises the fluidic actuator 3, which in this embodiment is configured as a valve drive. The process valve assembly also includes a process valve. The control device 20 comprises the control unit 2, the valve arrangement 1, and optionally a connecting section of the fluidic connection 5. The control device 20 expediently includes a mechanical interface with which the control device 20 can be attached to a housing of the fluidic actuator 3. By way of example, the control device 20 has a housing 19 in which, in particular, the control unit 2 and / or the valve arrangement 1 are arranged. The mechanical interface is, in particular, arranged on the outside of the housing 19. Expediently, the control device 20 is attached to the fluidic actuator 3, and the fluidic actuator 3 is attached to the process valve.The actuator element 15 is mechanically coupled to a valve element of the process valve and serves to actuate the valve element.

[0041] The rinsing mode will be discussed in more detail below.

[0042] As mentioned above, in flushing mode, the system volume is repeatedly aerated and vented with pressurized fluid by actuating the valve arrangement 1, so that the system fluid present in the system volume before the flushing mode is diluted with the pressurized fluid and at least partially removed from the system volume. In particular, the control unit 2 is configured to execute a flushing procedure in flushing mode, which specifies the actuating of the valve arrangement 1 as described above.

[0043] The Fig. Figure 2 shows a graph of the pressure value Pw over time during purge mode. The pressure value Pw alternates between a lower limit Pmin and an upper limit Pmax. When the upper limit Pmax is reached, the pressure value Pw is reduced to the lower limit Pmin. When the lower limit Pmin is reached, the pressure value Pw is increased to the upper limit Pmax. The pressure value Pw over time has an exemplary triangular waveform.

[0044] Advantageously, the control unit 2 is configured to actuate the valve arrangement 1 in flushing mode such that the pressure value Pw repeatedly reaches the upper limit Pmax and the lower limit Pmin alternately. In particular, the control unit 2 is configured to actuate the valve arrangement 1 in flushing mode such that the pressure value Pw in the Fig. The temporal profile of the pressure value Pw shown in section 2 is achieved.

[0045] The control unit 2 is preferably configured to control the valve arrangement 1 in flushing mode such that the valve arrangement 1 performs a plurality of flushing cycles in succession, wherein in each flushing cycle the system volume is fluidically connected to the pressure fluid source 6 in a first flushing phase and subsequently fluidically connected to the pressure fluid sink 7 in a second flushing phase. By fluidically connecting the system volume to the pressure fluid source 6, the pressure value Pw is increased from Pmin to Pmax in the first flushing phase. By fluidically connecting the system volume to the pressure fluid sink 7, the pressure value Pw is reduced from Pmax to Pmin in the second flushing phase. Advantageously, there is no fluidic connection between the system volume and the pressure fluid sink 7 in the first flushing phase. Advantageously, there is no fluidic connection between the system volume and the pressure fluid source 6 in the second flushing phase.

[0046] In the first flushing phase, the pressure fluid is added to the system volume without draining the system fluid already contained within it. The system fluid mixes with the pressure fluid. The pressure Pw increases.

[0047] In the second purge phase, the fluidic connection to the compressed air sink 7 is established. The fluid present in the system volume – i.e., the mixture of pressure fluid and system fluid – is at least partially drained from the system volume. The pressure Pw decreases.

[0048] By repeatedly performing the flushing cycle, which comprises the first and second flushing phases, the initially present system fluid in the system volume is gradually replaced by the pressurized fluid. The flushing cycle is expediently performed 5, 6, 7, 8, 9, or 10 times, or more than 10 times. Alternatively or additionally, the control unit 2 is configured to perform the flushing mode for a predetermined duration, continuously repeating the flushing cycle during this time.

[0049] The lower limit Pmin is expediently chosen to be greater than the ambient pressure, thus preventing the ingress of ambient fluid into the system volume. The upper limit Pmax, as explained below, is expediently chosen to prevent the actuator element 15 from being set in motion.

[0050] Advantageously, the control unit 2 is designed to control the valve arrangement 1 in normal operating mode in such a way that the pressure value Pw exceeds the upper limit value Pmax.

[0051] As mentioned above, the fluidic connection 5 between the valve assembly 1 and the pressure chamber 14 includes a connecting section – the actuator branch 43 – through which both the compressed air supply and the system fluid discharge occur. The two valve assembly branches 41, 42 are directly connected to each other. If both valve units 11, 12 were opened simultaneously, the pressurized fluid supplied from the pressurized fluid source 6 could flow directly out via the compressed air sink 7 and would not need to flow through the actuator branch 43 and / or into the pressure chamber 14. In this case, dilution and / or removal of the system fluid present in the actuator branch 43 and / or the pressure chamber 14 would not occur or would only occur to a very limited extent.By opening the valve units 11, 12 sequentially, improved mixing of the system fluid present in the actuator branch 43 and / or the pressure chamber 14 with the pressure fluid can be achieved, so that the system fluid can be removed from the system volume faster or with fewer flushing cycles.

[0052] The fluidic system 10 is advantageously configured to limit the pressurized fluid supply and / or the system fluid discharge in purging mode so that the actuator element 15 remains in its current position. Advantageously, the control unit 2 is configured to always actuate the valve arrangement 1 in purging mode such that no movement of the actuator element 15 occurs. Preferably, the control unit 2 is configured to carry out the compressed air supply and / or the system fluid discharge in purging mode taking into account a sensor signal provided by the sensor arrangement 4, and in this way advantageously ensures that the actuator element 15 remains in its current position.

[0053] For example, the control unit 2 is configured to actuate the valve arrangement 1, taking into account the pressure value Pw, such that the pressure value Pw does not exceed the upper limit Pmax and / or does not fall below the lower limit Pmin. For example, the control unit 2 is configured to compare the pressure value Pw with the upper limit Pmax and to close the first valve unit 11 and / or open the second valve unit 12 when the pressure value Pw reaches the upper limit Pmax. Advantageously, the control unit 2 is further configured to compare the pressure value Pw with the lower limit Pmin and to close the second valve unit 12 and / or open the first valve unit 11 when the pressure value Pw reaches the lower limit Pmin.The upper limit Pmax is preferably chosen such that it is smaller than a pressure value Pw at which the actuator element 15 is set in motion, i.e. in particular smaller than a pressure value Pw at which the breakaway pressure required for the movement of the actuator element 15 is reached.

[0054] Alternatively or additionally, the control unit 2 is configured to limit the pressure fluid supply and / or the pressure fluid discharge in flushing mode, taking into account the position of the actuator 15 detected by the position sensor unit 9, so that the actuator 15 remains in its current position. If, for example, the control unit 2 determines, based on the detected position, that the actuator 15 begins to move, this movement can be stopped and / or reversed by appropriately controlling the valve units 11, 12, so that the actuator 15 remains in its position.

[0055] The fluidic system 10 is advantageously configured to operate at least one element of the valve unit 11, 12 – for example, the ceramic layer 31 described below – with a reduced voltage compared to the normal operating mode during the purging mode. The fluidic system 10 is particularly configured to operate at least this element with a non-reduced voltage after the purging mode in the normal operating mode.

[0056] With reference to the Fig. 5 and Fig. Section 6 below will describe in more detail the construction and operation of the valve units 11, 12.

[0057] The valve units 11, 12 are expediently designed as piezo valve units. Each valve unit 11, 12 comprises a respective piezo actuator 30, which serves to open and / or close the respective valve unit 11, 12.

[0058] The piezo actuators 30 are expediently designed as piezo benders. For example, a sealing rubber (not shown in the figures) on the piezo bender is pressed against a fluidic passage by a metal spring (not shown in the figures) in a de-energized state, thus closing the valve unit. When voltage is applied to one or more ceramic layers of the piezo bender, the piezo bender bends in the opposite direction to the metal spring, and the valve unit opens.

[0059] The piezo actuator 30 expediently comprises a first ceramic layer 31, a second ceramic layer 32, and an intermediate layer 33 arranged between the first ceramic layer 31 and the second ceramic layer 32. The intermediate layer 33 is, for example, a carbon fiber reinforced plastic and can therefore also be referred to as a CFRP layer. A separate voltage V2, V3 can be applied to each ceramic layer 31, 32 to actuate the piezo actuator 30. The first ceramic layer 31 has a polarization with a first polarization direction PR1. The first polarization direction PR1 is, for example, directed towards the intermediate layer 33. The second ceramic layer 32 has a polarization with a second polarization direction PR2. The second polarization direction PR2 differs from the first polarization direction PR1 and is, in particular, antiparallel to it.The second polarization direction PR2 runs, for example, in the direction towards the intermediate layer 33.

[0060] Each Piezo Actuator 30 can conveniently be operated in two different modes. In the Fig. Figure 5 shows the operation of the piezo actuator 30 in the first mode and in the Fig. Figure 6 shows the operation of the piezo actuator 30 in the second mode. The two modes differ in how the two ceramic layers 31, 32 are controlled. The circuits of the piezo actuator 30 shown in the Fig. 5 and Fig. Figure 6 should be understood in particular as equivalent circuit diagrams.

[0061] In the first mode, voltage V2 is applied to the first ceramic layer 31 and voltage V3 is applied to the second ceramic layer 32. Both ceramic layers 31 and 32 are used to actuate the piezoelectric actuator. For example, a voltage V1 is divided into the two voltages V2 and V3 by a voltage divider, such as the two resistors R1 and R2. Voltage V2 has the same polarization direction as PR1, and voltage V3 has the opposite polarization direction to PR2. The voltages V2 and V3 across the first ceramic layer 31 and the second ceramic layer 32 in the first mode are advantageously each lower than the voltage V2 across the first ceramic layer in the second mode.

[0062] In the second mode, a voltage – voltage V2 – is applied only to the first ceramic layer 31. Here, voltage V2 is, for example, equal to voltage V1. Voltage V2 has the same orientation as the polarization direction PR1. No voltage is applied to the second ceramic layer 32. For example, the second ceramic layer 32 is short-circuited.

[0063] The control unit 2 is advantageously configured to operate the valve arrangement 1 in the first mode during flushing mode, preferably exclusively in the first mode. The control unit 2 is further advantageously configured to operate the valve arrangement in the second mode during normal operating mode.

[0064] Consequently, in the rinsing mode, the first ceramic layer 31 is operated with a reduced voltage V2 compared to the normal operating mode. After the rinsing mode, in the normal operating mode, the first ceramic layer 31 is operated with the full, unreduced voltage V2. In the rinsing mode, both ceramic layers 31 and 32 are used to actuate the piezo actuator 30. In the normal operating mode, only one ceramic layer 31 is used to actuate the piezo actuator 30.

[0065] The described procedure allows the piezo actuator 30, and preferably the piezo actuator 30 of each valve unit 11, 12, to be operated with lower voltages V2, V3 in purge mode. The voltages V2, V3 are advantageously chosen to be so low that even if flammable substances contained in the system fluid flow through the internal volume 45 of the valve assembly 1 in purge mode, ignition of these substances by actuating the piezo actuator 30 is not possible. Furthermore, in normal operating mode, the piezo actuator 30 can be operated with a non-reduced voltage V2 and preferably without actuating the second ceramic layer 32. Such operation can lead to a longer service life of the piezo actuator 30.In normal operating mode, the system fluid is replaced to such an extent by the pressure fluid that there are no flammable substances in the system volume, or only such a small amount of flammable substances that ignition is not possible even with the unreduced voltage V2.

[0066] Advantageously, the voltage V2 in the second mode is more than twice as high as in the first mode. Preferably, the voltage V2 is less than 100 volts in the first mode and more than 200 volts in the second mode.

[0067] The following is intended with reference to the Fig. 4 a procedure for operating the fluidic system 10 will be explained.

[0068] At the start of the process, the system fluid, whose composition is unknown and therefore undefined in this state, is located in the system volume, in particular in the internal volume 46 of the connection and / or the internal volume 45 of the valve assembly. Advantageously, the process begins at a time when the fluidic system 10 is not yet switched on and / or has experienced a pressure loss in the system volume, allowing the ambient atmosphere to enter the system volume.

[0069] The drive element 15 is in an exemplary zero position; the volume of the pressure chamber 14 can be zero in this state.

[0070] The first valve unit 11 is closed, for example, and the second valve unit 12 is open. Advantageously, both valve units 11 and 12 are not energized.

[0071] In a first step, control unit 2 (S1) starts the SM flushing mode, specifically automatically. The flushing procedure described below is then carried out in SM flushing mode. It is advantageous to operate valve units 11 and 12 at a reduced voltage in SM flushing mode, for example, in the first mode described above.

[0072] In step S2, the first flushing phase of a flushing cycle, as described above, is performed. The first valve unit 11 opens and the second valve unit 12 closes. The system volume (which can also be referred to as the "drive train") is pressurized. The system fluid is mixed with the incoming pressurized fluid, for example, air. For example, in step S2, the pressure increases by > 1 bar. For example, the control unit 2 measures the "flushing volume" via the pressure sensor unit 8.

[0073] When the pressure value Pw reaches the upper limit Pmax, the control unit 2 continues with step S3.

[0074] In step S3, the second flushing phase of a flushing cycle, as described above, is carried out. The first valve unit 11 is closed and the second valve unit 12 is opened.

[0075] The system volume is vented down to the lower limit Pmin. As a result, parts of the system volume are already filled with the "safe" pressure fluid and / or dilution has occurred.

[0076] When the pressure value Pw reaches the lower limit Pmin, the control unit 2 continues with step S4.

[0077] In step S4, it is checked, for example, whether a termination condition for the rinsing mode exists, such as whether a predetermined number of rinsing cycles has been reached and / or whether the rinsing mode has already lasted for a predetermined time.

[0078] If the termination condition is met, control unit 2 ends the rinsing mode. Control unit 2 then expeditiously continues in step S5 with the normal operating mode BM.

[0079] If the termination condition is not met, control unit 2 returns to step S2.

[0080] In the event of a detected compressed air or power failure, the system returns to step S1.

[0081] Further exemplary aspects will be discussed below.

[0082] Before the purging mode is executed, the atmosphere inside the valve units 11, 12, which are designed as piezoelectric valves, is undefined. This condition is assumed to exist when the control device 20, for example, a pneumatic actuator in which the valve units 11, 12 are used, has just been switched on, or when a pressure drop has occurred in the supply pressure, for example, in the pressure provided by the pressure fluid source 6. In this state, the valve units are operated in the first mode. In this way, the required explosion protection can be achieved using the "low power apparatus" protection type.

[0083] In the subsequent flushing mode, the system volume, i.e., for example, the free volumes of the fluidic actuator 3 (e.g., a working cylinder), the valve arrangement 1 (e.g., a valve block), the fluidic connection 5 (e.g., lines), and the valve units 11, 12 (e.g., piezo valves), is “flushed” with a volume that is expediently at least 5 times the relevant housing volume in accordance with IEC / EN 60079-2.

[0084] After "flushing" in flushing mode, a non-explosive, safe atmosphere exists within the piezo valves. The valve units 11 and 12 can therefore be operated in the second mode, particularly as long as no pressure loss within the fluidic actuator 3 is detected by the pressure sensor unit 8. The fluidic system 10 is now operated in normal operating mode.

[0085] The system volume, in particular the pressure chamber 14, is expediently flushed by filling and emptying the entire circuit via cyclic pressure changes within the actuator. During this process, the valve units 11, 12 are in the first mode, meaning that an explosive atmosphere may be present on the ceramic layers 31, 32 of the valve units 31, 32.

[0086] First, the pressure in the system volume is increased by opening the first valve unit 11. The first valve unit 11 can also be referred to as a vent valve. Advantageously, the pressure in the system volume remains below the value at which the actuator element 15 can be moved.

[0087] In a subsequent phase, the pressure in the system volume is reduced again via the second valve unit 12. The second valve unit 12 can also be referred to as the vent valve. In this process, a portion of the gas that was located in the pressure chamber 14 is expelled and replaced by compressed air.

[0088] This purging process is repeated several times until there is no longer any explosive atmosphere in the drive train.

[0089] This pumping method allows the drive to be flushed in a controlled manner at startup before the control unit 20 - for example a positioner - begins its actual work.

[0090] Consequently, it is possible to purge pneumatic drives (e.g., the fluidic actuator 3) of actuators (e.g., a process valve) with piezoelectric valves by varying the pressure in order to remove explosive atmospheres from the drive train (e.g., the system volume) without the drive (e.g., the actuator element 15) having to move. After this purging, normal operation is possible without risk, as the existing overpressure prevents any explosive atmosphere from reaching hazardous potentials. Thus, a purging process takes place by varying the pressure; the drive does not need to move during this process. Advantageously, the piezoelectric valves are operated in the first mode during the purging process, which makes them temporarily explosion-proof.

Claims

[1] Fluidic system (10) for use in a potentially explosive atmosphere, comprising: - a pneumatic actuator (3) with a pressure chamber (14) and an actuator element (15) which can be set in motion by applying compressed air to the pressure chamber (14), - a valve arrangement (1) configured to connect the pressure chamber (14) to a compressed air source (6) to supply compressed air to the pressure chamber (14), and / or to fluidically connect the pressure chamber (14) to a pressure fluid sink (7) to release the compressed air from the pressure chamber (14), - a control unit (2) configured to control the valve arrangement (1), and - a system volume that can be pressurized with compressed air, comprising a pressure chamber internal volume (44) of the pressure chamber (14), a valve arrangement internal volume (45) of the valve arrangement (1) and / or a connection internal volume (46) of a fluidic connection (5), wherein the control unit (2) is designed, in addition to a normal operating mode in which the pressure chamber (14) is pressurized with compressed air to set the actuator element (15) in motion, to provide a purging mode and in the purging mode to actuate the valve arrangement (1) such that compressed air is repeatedly supplied to the system volume and system fluid present in the system volume is drained, so that the system fluid is diluted with the compressed air and at least partially removed from the system volume, wherein the valve arrangement (1) comprises at least one valve unit (11, 12) for fluidically connecting the system volume to the compressed air source (6) and / or the pressure fluid sink (7), wherein the fluidic system (10) is configured to operate at least one element of the valve unit (11, 12) with a reduced voltage (V2, V3) compared to the normal operating mode in the purging mode. [2] Fluidic system (10) according to claim 1, wherein the fluidic system (10) is configured to operate at least the element of the valve unit (11, 12) with a non-reduced voltage (V2, V3) after the purging mode in normal operating mode. [3] Fluidic system (10) according to claim 1 or 2, wherein the valve unit (11, 12) comprises a piezo actuator (30) and the element is a ceramic layer (31) of the piezo actuator (30). [4] Fluidic system (10) according to claim 3, wherein the piezo actuator (30) has two ceramic layers (31, 32) and the fluidic system (10) is configured to use both ceramic layers (31, 32) for actuating the piezo actuator (30) in rinsing mode and / or to use only one ceramic layer (31) for actuating the piezo actuator (30) in normal operating mode. [5] Fluidic system according to one of the preceding claims, wherein the fluidic system (10) is configured to limit the compressed air supply and / or the system fluid drain in flushing mode so that the actuator element (15) remains in its current position. [6] Fluidic system (10) for use in a potentially explosive atmosphere, comprising: - a pneumatic actuator (3) with a pressure chamber (14) and an actuator element (15) which can be set in motion by applying compressed air to the pressure chamber (14), - a valve arrangement (1) configured to connect the pressure chamber (14) to a compressed air source (6) to supply compressed air to the pressure chamber (14), and / or to fluidically connect the pressure chamber (14) to a pressure fluid sink (7) to release the compressed air from the pressure chamber (14), - a control unit (2) configured to control the valve arrangement (1), and - a system volume that can be pressurized with compressed air, comprising a pressure chamber internal volume (44) of the pressure chamber (14), a valve arrangement internal volume (45) of the valve arrangement (1), and / or a connection internal volume (46) of a fluidic connection (5), wherein the control unit (2) is configured, in addition to a normal operating mode in which the pressure chamber (14) is pressurized with compressed air to set the actuator element (15) in motion, to provide a purging mode and, in the purging mode, to actuate the valve arrangement (1) such that compressed air is repeatedly supplied to the system volume and system fluid present in the system volume is drained, so that the system fluid is diluted with the compressed air and at least partially removed from the system volume, wherein the fluidic system (10) is configured, in the purging mode, to limit the compressed air supply and / or the system fluid draining such that the actuator element (15) in remains in his current position. [7] Fluidic system (10) according to a preceding claim, wherein the fluidic system (10) comprises a sensor arrangement (4) and is configured to perform the compressed air supply and / or the system fluid draining in purging mode taking into account a sensor signal provided by the sensor arrangement (4). [8] Fluidic system (10) according to claim 7, wherein the sensor arrangement (4) comprises a pressure sensor (8) for detecting a pressure value (Pw) related to the system volume, and the control unit (2) is configured to control the valve arrangement (1) taking into account the pressure value (Pw) such that the pressure value (Pw) does not exceed an upper limit (Pmax) and / or does not fall below a lower limit (Pmin). [9] Fluidic system (10) according to claim 8, wherein the control unit (2) is configured to control the valve arrangement (1) in flushing mode such that the pressure value (Pw) repeatedly reaches the upper limit (Pmax) and the lower limit (Pmin) alternately. [10] Fluidic system (10) according to a preceding claim, wherein the control unit (2) is configured to control the valve arrangement (1) in flushing mode such that the valve arrangement (1) performs a plurality of flushing cycles in succession, wherein in each flushing cycle the system volume is first fluidically connected to the compressed air source (6) and subsequently fluidically connected to the pressure fluid sink (7). [11] Fluidic system (10) according to one of the preceding claims, wherein the control unit (2) is configured to automatically enter the rinsing mode. [12] Fluidic system (10) according to claim 11, wherein the control unit (2) is configured to enter the flushing mode based on a detected event, a detection of a power loss, a switch-on, a commissioning and / or a pressure loss. [13] Fluidic system (10) according to one of the preceding claims, comprising the fluidic connection (5) which has a connecting section between the valve arrangement (1) and the pressure chamber (4) through which both the compressed air supply and the system fluid drain take place. [14] Method for operating a fluidic system (10) for use in a potentially explosive atmosphere, wherein the fluidic system (10) comprises: a pneumatic actuator (3) with a pressure chamber (14) and an actuator element (15) which can be set in motion by pressurizing the pressure chamber (14), a valve arrangement (1) configured to connect the pressure chamber (14) to a compressed air source (6) in order to supply the compressed air to the pressure chamber (14), and / or to fluidically connect the pressure chamber (14) to a pressure fluid sink (7) in order to discharge the compressed air from the pressure chamber (14), wherein the valve arrangement (1) comprises at least one valve unit (11, 12) for fluidically connecting the system volume to the compressed air source (6) and / or the pressure fluid sink (7), a control unit (2) configured to control the valve arrangement (1) and a system volume capable of being pressurized with compressed air, comprising a pressure chamber internal volume (44) of the pressure chamber (14), a valve arrangement internal volume (45) of the valve arrangement (1) and / or a connection internal volume (46) of a fluidic connection (5), wherein the method comprises the steps: - Putting the control unit (2) into a purging mode, wherein the purging mode is in addition to a normal operating mode in which the pressure chamber (14) is pressurized with compressed air to set the actuator element (15) in motion, - in the purging mode: Controlling the valve arrangement (1) such that compressed air is repeatedly supplied to the system volume and system fluid present in the system volume is drained, so that the system fluid is diluted with the compressed air and at least partially removed from the system volume, wherein in the purging mode at least one element of the valve unit (11, 12) is operated with a voltage (V2, V3) reduced compared to the normal operating mode. [15] Method for operating a fluidic system (10) for use in a potentially explosive atmosphere, wherein the fluidic system (10) comprises: a pneumatic actuator (3) with a pressure chamber (14) and an actuator element (15) which can be set in motion by pressurizing the pressure chamber (14), a valve arrangement (1) configured to connect the pressure chamber (14) to a compressed air source (6) to supply compressed air to the pressure chamber (14), and / or to fluidically connect the pressure chamber (14) to a pressure fluid sink (7) to discharge compressed air from the pressure chamber (14), a control unit (2) configured to actuate the valve arrangement (1), and a system volume that can be pressurized with compressed air, comprising a pressure chamber internal volume (44) of the pressure chamber (14), a valve arrangement internal volume (45) of the valve arrangement (1), and / or a The internal volume (46) of a fluidic connection (5) comprisesthe procedure includes the following steps:, - Putting the control unit (2) into a purging mode, wherein the purging mode is in addition to a normal operating mode in which the pressure chamber (14) is pressurized with compressed air to set the actuator element (15) in motion, - in the purging mode: Controlling the valve arrangement (1) such that compressed air is repeatedly supplied to the system volume and system fluid present in the system volume is drained, so that the system fluid is diluted with the compressed air and at least partially removed from the system volume, wherein in the purging mode the compressed air supply and / or the system fluid draining is limited so that the actuator element (15) remains in its current position.

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