Method for operating a fluid system and fluid system

Abstract

In a method for operating a fluid system (11) comprising a control device (19) having a control functionality and a piezo valve arrangement (20) controllable by the control device (19), the method comprises the following steps: - Providing a target working pressure at the working connection (28a, 28b), - measuring the actual working pressure at the working connection (28a, b) by the pressure sensor (43a, 43b), transmitting the measured data to the control device (19) and applying the algorithm to compare the actual working pressure with the target working pressure, - Activation of at least one integrator (48) for integrating the control deviation of the control voltage (= offset voltage) after the actual working pressure is constant over a certain period of time. - Change of the control voltage depending on the determined target / actual deviation taking into account the integrator operation,

Description

[0001] The invention relates to a method for operating a fluid system and to a fluid system. The fluid system comprises a control device having a control function and a piezo valve arrangement controllable by the control device, wherein the piezo valve arrangement has a ventilation connection connected to a pressure source and a vent connection connected to a pressure sink. The piezo valve arrangement has at least one ventilation valve designed as a piezo valve connected to the ventilation connection and at least one vent valve designed as a piezo valve connected to the vent connection. The ventilation and vent valves are each connected to at least one working connection connected to a working chamber of the fluid consumer, and the ventilation and vent valves each have at least one piezo bending transducer.which, in a closed position, rests against a valve seat of the associated valve and closes a through opening in a fluid-tight manner and which, depending on an applied control voltage, can be moved into open positions at different distances from the valve seat.

[0002] Such fluid systems have been known for a long time.

[0003] DE 11 2004 000 574 T5 discloses a multi-valve positioning system for fluid-operated cylinders, which has at least one electrically operated, proportional flow control valve, wherein at least one pressure sensor for measuring the chamber pressures and a position sensor for determining the position of the piston are also provided.

[0004] WO 2017 / 045 701 A1 discloses a valve control and a method for operating a valve control. The valve control serves to electrically control at least one valve actuator, comprising a control circuit configured to influence an electrical energy flow between an electrical source and the actuator, a bus interface for communication with a higher-level control arrangement, and a sensor means configured to determine a physical variable of the energy flow that changes due to electrical control of the valve actuator, and to provide a sensor signal dependent on the determined physical variable.It is provided that the control circuit is designed to determine a state value for the valve drive based on the sensor signal and at least one characteristic value of a physical quantity from the group: energy flow duration, energy flow voltage, energy flow current, filling pressure and to provide the state value at the bus interface.

[0005] DE 10 2010 035 263 B4 discloses a piezo valve comprising a valve housing and a control unit movably arranged therein. The control unit has a control body with a base section and two control fingers, each protruding through a solid-state joint, which cooperate with a valve seat. Each control finger is actuated by a piezo actuator designed as a stack translator. Activation of a piezo actuator causes the control body to bend, and one of the control fingers to lift off the associated valve seat.

[0006] The use of piezo valves in fluid systems has the advantage of low power consumption and proportional behavior depending on the applied voltage, making them ideal for use as proportional valves. Furthermore, such piezo valves have a long service life, short switching times, and essentially no switching noise.

[0007] Furthermore, piezo valves often have a soft sealing seat, whereby the soft sealing seat is characterized by the fact that the tightness can be easily ensured without placing high design and manufacturing requirements and whereby tightness can be guaranteed over the entire working range (e.g. even in the event of temperature changes).

[0008] However, these aforementioned advantages of the piezo valve and the soft sealing seat are also coupled with control engineering challenges. For example, a piezo valve, and especially the associated piezo bending transducer, is subject to aging, which significantly alters the properties of the piezo bending transducer. Furthermore, such piezo valves are sensitive to temperature changes and changing differential pressures at the bender or bending transducer. The soft sealing seat is also subject to the aforementioned effects.

[0009] This results in the problem that, among other things, a drift of the offset voltage can occur; in particular, the opening point of the piezo valve depends on the aforementioned effects.

[0010] Due to the physical properties of the piezo valve, the opening point shifts significantly over the course of its life cycle, even after storage with short operating times, which affects the performance of the application and therefore cannot be neglected.

[0011] The object of the invention is therefore to provide a method for operating a fluid system and a fluid system that prevents the above-described negative effects from having an impact on the performance of the associated application.

[0012] This object is achieved by a method for operating a fluid system having the features of independent claim 1 and by a fluid system having the features of independent claim 8. Further developments of the invention are presented in the subclaims.

[0013] The method according to the invention for operating a fluid system comprising a control device having a control functionality and a piezo valve arrangement controllable by the control device, wherein the piezo valve arrangement has a ventilation connection connected to a pressure source and a ventilation connection connected to a pressure sink, wherein the ventilation connection and the working connection are each connected to a pressure sensor coupled to the control device, and wherein the control device has a control algorithm with at least one implemented integrator, the method proceeds according to the following steps: - Providing a target working pressure at the working connection, - Measuring the actual working pressure at the working connection by the pressure sensor, transmitting the measured data to the control device and applying the algorithm to compare the actual working pressure with the target working pressure, - Activation of at least one integrator for integrating the control deviation of the control voltage after the actual working pressure has been constant over a certain period of time, - Change of the control voltage depending on the determined target / actual deviation taking into account the integrator operation,

[0014] This makes it possible to identify and compensate the offset voltage of the aeration and vent valve during operation. In particular, the offset voltage required for the opening point of the aeration and vent valve can be determined during operation. This allows the application to continue running as required while the offset voltage shift is identified. Therefore, stopping the application is not necessary.

[0015] A further advantage is that the process only requires pressure sensors. It is not necessary to measure the actual mass flow. Furthermore, no position sensors are required. This results in a relatively simple and cost-effective design of the fluid system and operation of the process.

[0016] Another important aspect is that the implemented integrators are only active under defined conditions. This means that the integrators can be switched on and off, or activated and deactivated. One such defined condition is the presence of a constant actual working pressure over a specific period of time. If the target working pressure changes to a different value due to the application, the integrators are deactivated. The algorithm makes it possible for the manipulated variable to be integrated and added to the output of the control device with the control functionality, which could also be referred to as a controller, until the control device output reaches zero. The remaining control deviation is thus eliminated by the integrators, so that the control error is zero. If the control device output is zero, the entire offset voltage is mapped by the integrators.

[0017] In a further development of the invention, at least two independently activatable integrators are implemented in the control algorithm, of which at least one is effective during ventilation through the ventilation valve and at least one other is effective during ventilation through the ventilation valve.

[0018] In a further development of the invention, as already mentioned, at least one integrator of the control algorithm is deactivated if the target working pressure is changed or the measured actual working pressure changes over a certain period of time.

[0019] It is possible that the application requires that the pressure in a working chamber remains constant over a certain period of time. In this case, it is possible to "lock in" the pressure in the working chamber by closing the vent valve and the vent valve, but the pressure could drop due to disturbances. To remedy this problem, both the vent valve and the vent valve are activated so that the pressure is then regulated back to the required constant target working pressure. However, with this type of operation of the vent valve and vent valve, fluid could overflow from the pressure source via the vent valve and from there to the pressure sink, which would lead to internal air consumption, which is what we want to prevent.

[0020] In order to remedy this problem, a further development of the invention provides that the at least one integrator of the vent valve is slowly driven towards a lower limit value during operation, the speed being lower than the integration of the control deviation of the control voltage.

[0021] Another approach is to activate the at least one integrator of the ventilation valve or the at least one integrator of the vent valve, and integrate the offset voltage of the flexural transducer of the ventilation valve or the offset voltage of the flexural transducer of the vent valve, while the other flexural transducer is placed in a defined state. For example, a defined state is the closed position of the vent valve's flexural transducer.

[0022] In a further development of the invention, the fluid consumer has two separate, in particular independently ventilated or vented working chambers, of which a first venting valve and a first venting valve with a first working connection and a first pressure sensor are assigned to a first working chamber and a second venting valve and a second venting valve with a second working connection and a second pressure sensor are assigned to a second working chamber.

[0023] Particularly preferably, the fluid consumer is a single- or double-acting working cylinder. In this case, the working spaces are fluid-loaded working chambers. However, other fluid consumers are also conceivable, for example, single- or double-acting diaphragm drives, fluidic, particularly pneumatic, grippers, or a pressure-controlled volume unit.

[0024] It is possible for the control device to have at least one pressure regulator, for example two independent pressure regulators.

[0025] The invention further relates to a fluid system for operating a fluid consumer, wherein the fluid consumer has a control device having a control functionality and a piezo valve arrangement controllable by the control device, wherein the piezo valve arrangement has a ventilation connection connected to a pressure source and a venting connection connected to a pressure sink, wherein the piezo valve arrangement has at least one ventilation valve designed as a piezo valve connected to the ventilation connection and at least one venting valve designed as a piezo valve connected to the venting connection, wherein the ventilation and the venting valve are each connected to at least one working connection connected to a working chamber of the fluid consumer, and wherein the ventilation and the venting valve each have at least one piezo bending transducer,which, in a closed position, rests against a valve seat of the associated valve and closes a through-opening in a fluid-tight manner and which, depending on an applied control voltage, is movable into open positions raised to different distances from the valve seat, wherein the ventilation connection and the working connection are each connected to a pressure sensor coupled to the control device, and wherein the control device has a control algorithm with at least one implemented integrator, and wherein the control device is designed to compare the actual working pressure with the desired working pressure from a provided desired control voltage, which corresponds to a desired desired working pressure at the working connection, and from a measurement of the actual working pressure at the working connection by the pressure sensor, wherein the at least one integrator can be activated to integrate the control deviation of the control voltage,after the actual working pressure is constant over a certain period of time and the control voltage can be changed depending on the determined target / actual deviation, taking into account the integrator operation.

[0026] In a further development of the invention, the control device is designed to carry out the method according to one of claims 1 to 7.

[0027] In a further development of the invention, the piezo valves each have two independently controllable piezo bending transducers or bending transducers.

[0028] In a further development of the invention, the fluid system comprises four piezo valves connected together in a bridge circuit. Such an arrangement is particularly suitable for controlling and regulating the pressures of fluid consumers with two working chambers. With this configuration, both working ports and thus both working chambers can be vented and vented independently of one another. In this case, one working chamber is assigned a vent and a vent valve, and the other working chamber is also assigned a vent and a vent valve.

[0029] In a further development of the invention, the pressure sensor assigned to the ventilation connection for determining the ventilation or supply pressure is designed as an absolute pressure sensor.

[0030] In a further development of the invention, a pressure sensor for determining the vent or exhaust air pressure is assigned to the vent connection. This can also be an absolute pressure sensor.

[0031] The invention further comprises a computer program product for use in a computer device comprising instructions which, when executed in a control device of a fluid system, carry out the method according to one of claims 1 to 7.

[0032] A preferred embodiment of the invention is illustrated in the drawing and explained in more detail below. The drawing shows: Fig. 1 a schematic representation of a preferred embodiment of the fluid system according to the invention with which the method according to the invention can be carried out, Fig. 2 a schematic representation of the drift of the offset voltage in a diagram with dimensionless parameters, Fig. 3 an enlarged view of a piezo valve of the fluid system from Fig. 1, Fig. 4- a flowchart (block diagram) of the method according to the invention and Fig. 5 a flow diagram according to a first approach to minimizing / eliminating the internal air consumption.

[0033] The Fig. 1 shows a preferred embodiment of the fluid system 11 according to the invention. The illustrated fluid system 11 is purely exemplary and, in the example shown, has a fluid consumer 12 in the form of a double-acting working cylinder. The purely schematically illustrated, double-acting working cylinder has a cylinder housing 13 in which a piston 14 is mounted for linear displacement by means of fluid pressure. The piston 14 divides an interior space 15 of the cylinder housing 13 into a first working chamber 16 and a second working chamber 17. The piston 14 is connected to a piston rod 18, which extends out of the cylinder housing 13 and can be connected at its free end to an output member (not shown).

[0034] The fluid system 11 further comprises a control device 19 having a control functionality and a piezo valve arrangement 20 that can be controlled by the control device 19.

[0035] As further stated in Fig. 1, the piezo valve arrangement has a vent port 22 connected to a pressure source 21 and a vent port 24 connected to a pressure sink 23.

[0036] In the example shown, the piezo valve arrangement 20 comprises a piezo bridge circuit 25 with a plurality of piezo valves. At least one vent valve 26a, 26b, designed as piezo valves, is provided in the example shown for the bridge circuit 25 and connected to the vent port 22. At least one vent valve 27a, 27b, designed as piezo valves, is provided in the example shown for the bridge circuit 25 and connected to the vent port 24. The vent and vent valves 26a, 26b; 27a, 27b are each connected to at least one working port 28a, 28b connected to a working chamber 16, 17 of the fluid consumer 12.

[0037] In the example shown, a first valve pair consisting of a first vent valve 26a and a first vent valve 27a is connected to a first working port 28a, which is connected to the first working chamber 16. Accordingly, a second valve pair consisting of a second vent valve 26b and a second vent valve 27b is connected to the second working chamber 17 of the double-acting working cylinder via a second working port 28b.

[0038] With this valve connection it is possible to ventilate or vent both working chambers 16, 17 simultaneously or to ventilate one of the working chambers and vent the other.

[0039] The Fig. Figure 3 shows a schematic representation of a piezo valve used in the piezo bridge circuit. In the example shown, the piezo valve is designed as a so-called piezo cartridge 29, which has a cartridge housing 30 with two opposing housing end faces 31a, 31b. The first housing end face 31a is penetrated by several channels, one of which is an inflow channel 32a, through which pressurized fluid originating from the pressure source 21 can flow into the interior of the cartridge housing 30. Furthermore, the first housing end face 31a is penetrated by two working channels 32b, 32c, which are fluidically connected to the first or second working connection or, alternatively, to a vent connection. The opposite housing end face 31b is penetrated by schematically indicated electrical contact means 34.

[0040] The piezo valve also has a generally two-part valve housing 33 located within the cartridge housing 30. The valve housing defines an elongated valve chamber 35 inside, which is connected to the interior of the cartridge housing via valve housing inlet openings 60. A strip-shaped bending transducer 36 having a longitudinal configuration is located in the chamber.

[0041] As particularly in Fig. 3, the bending transducer 36 has an elongated bearing section 37, which is mounted on two only schematically indicated bearing sections 38a, 38b of the valve housing 35. On the underside of the bending transducer 36 opposite the bearing sections 38a, 38b, the bearing section 37 is acted upon by a spring element 39 in the direction of the bearing sections 38a, 38b. Starting from the front bearing point 38a, the bending transducer protrudes towards a free end in the form of a working section 40. At the free end of the working section 40 is a control section 41, which can be, for example, a pad made of rubber material, fixed to the bending transducer 36. A controllable valve opening 42 is assigned to the control section 41 on the bending transducer 36, which merges into one of the previously mentioned working channels 32b, 32c. The respective working channel 32a, 32b is - as mentioned - assigned to the first or second working chamber 16, 17.

[0042] A pad made of a soft material, such as rubber, is expediently used as the control section 41. This so-called "soft sealing seat" ensures that tightness can be easily ensured when the control section 41 rests against the valve opening 42 to be controlled, without placing high design and manufacturing demands. Furthermore, tightness is ensured throughout the entire operating range, even during temperature changes, for example, because the soft pad partially digs into the valve seat section on the housing side, and therefore a temperature change alone does not pose a risk of leakage.

[0043] The bending transducer advantageously has a trimorphic design with elongated piezoelectric bodies attached to one another lengthwise with an interposed inner electrode. Each piezoelectric body is provided with an outer electrode on the outer side opposite the inner electrode. A control voltage can be selectively applied to the electrodes via electrical contact means 34, which extend from the valve housing and are only indicated schematically. This voltage induces a deflection force in the working section 40 due to the reverse piezoelectric effect.

[0044] As particularly in Fig. As shown in Figure 3, the piezo valve in the example shown has two bending transducers 36 arranged in a mirror image of each other. Accordingly, a second control section 41b and a second controllable valve opening 42b associated with the control section 41b are provided.

[0045] Both bending transducers of the piezo valve have a 2 / 2 function, ie the corresponding control section 41a, 41b is either fluid-tight against the associated controllable valve opening 42a, 42b or is lifted more or less far from the valve seat section on the housing side when the control voltage is applied, depending on the applied control voltage.

[0046] The two bending transducers 36 of a respective piezo valve can be controlled independently of each other, so that either only one of the two controllable valve openings 42a, 42b is opened, or alternatively, both valve openings 42a, b are open or closed simultaneously. Opening both valve openings 42a, b ensures increased flow and faster pressure buildup in the associated working chamber compared to only one valve opening being open, for example, if the piston 14 of the double-acting working cylinder needs to be moved quickly from one position to another.

[0047] An important aspect is that the bending transducers have a proportional function, meaning that the associated valve opening opens more or less depending on the applied control voltage. An important effect here is that such piezo valves require a minimum control voltage for the associated valve opening to open at all. This required minimum control voltage also defines the opening point of the piezo valve.

[0048] This is in Fig. 2 illustrates where a dimensionless value of the voltage is plotted as the abscissa and the dimensionless degree of opening of the valve between 0 and 1 is plotted as the ordinate.

[0049] In the diagram of the Fig. 2 two characteristic curves can be seen, of which the left characteristic curve represents the ideal characteristic curve 70 of the piezo valve, i.e. in a state in which the influencing factors described in more detail below are not present.

[0050] It can be seen that a certain minimum control voltage is required for the bending transducer to be lifted from the associated valve opening. Increasing the applied control voltage also increases the degree of opening of the valve opening, i.e., the bending transducer with the pad lifts further away from the associated valve opening until, at a certain control voltage, the valve opening 42a, 42b is completely open.

[0051] The performance of a proportional application depends heavily on the correct identification of the opening point. If this is unknown, or if the actual opening point shifts relative to an opening point assumed in the control system, this can lead to steady-state inaccuracies in the best case and, in the worst case, to instabilities in the application. In either case, the required performance cannot be achieved or maintained.

[0052] Due to the physical properties of the piezo valve, the opening point shifts so significantly over the course of its life cycle, even after storage and short periods of operation, that this impacts the performance of the application and therefore cannot be ignored. The causes include aging, temperature changes, the differential pressure at the bender, the piezo effect, and the mechanical design of the 2 / 2-way valve.

[0053] To remedy the problem described above, the fluid system according to the invention is equipped with a control device 19 with a closed-loop control functionality. Furthermore, the fluid system 11 has a pressure sensor 43a, 43b coupled to the working port 28a, 28b. In the example shown, a first pressure sensor 43a is assigned to the first working port 28a, and a second pressure sensor 43b is assigned to the second working port. The pressure sensors 43a, 43b are each coupled to the control device. The pressure sensors 43a, 43b can be designed as differential pressure sensors.

[0054] The pressure sensors are capable of measuring the actual working pressure at the associated working connection 28a, 28b and transmitting the values of the measured actual working pressure in the form of control signals to the control device 19.

[0055] In the example shown, a pressure sensor 44 is also assigned to the pressure source 21, although this pressure sensor is not absolutely necessary. The pressure sensor 44 assigned to the pressure source can be designed as an absolute pressure sensor. Furthermore, it is also possible to assign a pressure sensor 45 to the pressure sink 23, although this pressure sensor 45 is also not absolutely necessary. The pressure sensor of the pressure sink 23 can also be designed as an absolute pressure sensor.

[0056] The Fig. Figure 4 shows, by way of example, the design of a control device 19 equipped with a control function and used in the fluid system 11 according to the invention. The control device, designated overall by reference numeral 19, has a comparator 46 capable of comparing the measured actual working pressure with the target working pressure. A controller 47 is connected downstream of the comparison, which executes a control function according to an algorithm if the actual working pressure deviates from the target working pressure. The controller 47 is expediently designed as a P controller or PD controller. Associated with the controller 47 is at least one integrator 48, which integrates the manipulated variable and adds it to the controller output until the controller output reaches zero. A further comparator 49 is provided for this purpose.The control device 19 further comprises a path 50 which comprises signal generation and control of the corresponding bending transducers of the piezo valves.

[0057] During operation of the piezo valve, the factors described above may cause a shift in the offset voltage and thus also a shift in the opening point of the piezo valve. Such a drift in the offset voltage is Fig. 2. In comparison to the ideal characteristic curve, it is clearly visible here with the operating characteristic curve 71 shifted to the right that a larger control voltage is necessary for the piezo valve to open.

[0058] In order to counteract the above-described problem of the drift of the offset voltage and thus also the drift of the opening point of the piezo valves, the method according to the invention for operating the fluid system 11 is carried out in the fluid system 11 according to the invention.

[0059] First, the target working pressure is provided at the associated working port 28a, 28b. For example, it is possible to control and open both bending transducers of the first venting valve 26a, thus venting the first working chamber 16. At the same time, it is possible to energize both bending transducers of the second venting valve 27b, causing them to open and vent the second working chamber. This causes the piston to move to the right.

[0060] Next, the actual working pressure is measured at the working connection, the measurement data are transmitted to the control device 19 and, using the algorithm, the actual working pressure is compared with the target working pressure.

[0061] In the specific example, the actual working pressure at the first working port 28a is measured by the first pressure sensor 43a, and simultaneously the actual working pressure at the second working port 28b is measured by the second pressure sensor 43b. The actual working pressure at the first working port 43a and the actual working pressure at the second port initially change, since pressure builds up in the first working chamber 16 while pressure is reduced in the second working chamber 17. If the second working chamber 17 is not completely vented, the piston will come to a standstill after a certain period of time and then, after a certain subsequent pressure build-up and pressure reduction phase, constant pressures will occur in the first working chamber 16 and the second working chamber 17.

[0062] After the actual working pressure is constant over a certain period of time, if the actual working pressure deviates from the target working pressure, at least one integrator 48 is activated, whereby the control deviation of the control voltage is integrated and added to the output of the controller until the output of the controller becomes zero.

[0063] If the output of regulator 47 is zero, the entire offset voltage is mapped by the integrators. Since it can be assumed that the change in the offset voltage is slow compared to the change in state, the integrators 48 can be operated slowly.

[0064] However, the above-described property of system 50 (measured value = setpoint due to the integrating behavior) is only valid for steady-state conditions. Therefore, both the setpoint working pressure and the actual working pressure must be constant. Consequently, the integrators 48 may only be active when steady-state setpoint and measured values are present. In the dynamic case, when the setpoint or measured values are changing, the integrators 48 are not active.

[0065] In addition, further measures are necessary to ensure the correct adaptation of the offset voltage.

[0066] For this purpose, it is provided that each ventilation and vent valve 26a, 26b; 27a, 27b is assigned its own integrator 48.

[0067] Furthermore, it must be ensured that the integration does not lead to any internal air consumption, i.e. it must be prevented that there is an overflow from the ventilation valve to the vent valve.

[0068] Such a situation can occur, for example, if both working chambers 16, 17 are to be kept at a certain, constant pressure. While it would then be possible to close both vent valves, it is quite possible that disturbances (e.g., damaged seals) could cause pressure fluctuations that would then need to be compensated for, in which case both the vent valve and the vent valve 27a, b would be active.

[0069] The Fig.Figure 5 shows a flowchart illustrating a first approach to solving the aforementioned problem. According to the first approach, both integrators—that is, the integrators of the ventilation valve and the vent valve—are slowly moved toward a lower limit during operation, with the speed being significantly lower than the integration of the offset voltage. The integrators are thus essentially run "empty," but at a slower speed than the offset voltage compensation, so that the internal air consumption is slowly reduced. According to the flowchart of the first approach, the integrators 48 are slowly moved toward a lower limit during operation according to the "slow reduction 55" process step.If a stationary setpoint and actual value 56 is present, the previously described adaptation of the offset voltage is carried out, whereby either a control error-dependent increase 57 of the control voltage of the ventilation valve 26a, 26b or a control error-dependent increase 58 of the control voltage of the vent valve 27a, 27b takes place.

[0070] In a second, not shown, approach to reducing internal air consumption, the offset voltage of a bending transducer of a piezo valve, for example, one of the ventilation valves 26a, 26b, is integrated, while the corresponding other piezo valve, for example, the vent valve 27a, 27b, is placed in a defined state, for example, with the associated bending transducer in the closed position. This allows the effect of ventilation on the one hand and ventilation on the other to be separated.

Claims

[1] Method for operating a fluid system (11) comprising a control device (19) having a control functionality and a piezo valve arrangement (20) controllable by the control device (19), wherein the piezo valve arrangement (20) comprises a ventilation connection (22) connected to a pressure source (21) and a venting connection (24) connected to a pressure sink (23), wherein the piezo valve arrangement (20) comprises at least one ventilation valve (26a, 26b) designed as a piezo valve and connected to the ventilation connection (22) and at least one venting valve (27a, 27b) designed as a piezo valve and connected to the venting connection (24), wherein the ventilation and venting valves (26a, 26b; 27a, 27b) are each connected to at least one working connection connected to a working chamber (16, 17) of the fluid consumer (12) (28a, 28b) are connected, and wherein the supply and exhaust valves (26a, b;27a, b) each have at least one piezo bending transducer (36) which, in a closed position, rests against a valve seat of the associated valve (26a, 26b; 27a, 27b) and closes a valve opening (42a, 42b) in a fluid-tight manner and which, depending on an applied control voltage, can be moved into open positions lifted to different distances from the valve seat, wherein the ventilation connection (22) and the working connection (28a, 28b) are each connected to a pressure sensor (43a, 43b) coupled to the control device (19), and wherein the control device (19) has an algorithm with at least one implemented integrator (48), the method comprising the following steps:; - Providing a target working pressure at the working connection (28a, 28b), - measuring the actual working pressure at the working connection (28a, 28b) by the pressure sensor (43a, 43b), transmitting the measured data to the control device (19) and applying the algorithm to compare the actual working pressure with the target working pressure, - Activation of at least one integrator (48) for integrating the control deviation of the control voltage after the actual working pressure has been constant over a certain period of time, - Change of the control voltage depending on the determined target / actual deviation taking into account the integrator operation, [2] Method according to claim 1, characterized by that at least two independently activatable integrators (48) are implemented in the algorithm, of which at least one is effective during venting through the venting valve (26a, 26b) and at least one other is effective during venting through the venting valve (27a, 27b). [3] Method according to claim 1 or 2, characterized bythat the at least one integrator (48) of the algorithm is deactivated when the target working pressure is changed or the measured actual working pressure changes over a certain period of time. [4] Method according to one of the preceding claims, characterized by that the at least one integrator (48) of the ventilation valve (26a, 26b) and the at least one integrator of the vent valve (27a, 27b) are slowly moved towards a lower limit value during operation, the speed being lower than the integration of the control deviation of the control voltage. [5] Method according to one of the preceding claims, characterized bythat the at least one integrator (48) of the ventilation valve (26a, 26b) or the at least one integrator (48) of the venting valve (27a, 27b) is activated and the offset voltage of the piezo bending transducer (36) of the ventilation valve (26a, 26b) or the offset voltage of the piezo bending transducer (36) of the venting valve (27a, 27b) is determined, while the respective other piezo bending transducer (36) is placed in a defined state. [6] Method according to one of the preceding claims, characterized byin that the fluid consumer (12) has two working chambers (16, 17) which can be ventilated or vented separately, in particular independently of one another, of which a first venting valve (26a) and a first venting valve (27a) with a first working connection (28a) and a first pressure sensor (43a) are assigned to a first working chamber (16), and a second venting valve (26b) and a second venting valve (27b) with a second working connection (28b) and a second pressure sensor (43b) are assigned to a second working chamber (17). [7] Method according to one of the preceding claims, characterized by that the fluid consumer (12) is a single- or double-acting working cylinder, fluidic, in particular pneumatic gripper or a pressure-controlled volume unit. [8] Fluid system for operating a fluid consumer (12), with a control device (19) having a control functionality and a piezo valve arrangement (20) which can be controlled by the control device (19), wherein the piezo valve arrangement (20) has a ventilation connection (22) connected to a pressure source (21) and a venting connection (24) connected to a pressure sink (23), wherein the piezo valve arrangement (20) has at least one ventilation valve (26a, 26b) designed as a piezo valve and connected to the ventilation connection (22) and at least one venting valve (27a, 27b) designed as a piezo valve and connected to the venting connection (24), wherein the ventilation and venting valves (26a, 26b; 27a, 27b) are each connected to at least one working connection connected to a working chamber (16, 17) of the fluid consumer (12) (28a, 28b), and wherein the supply and venting valves (26a, 26b; 27a,27b) each have at least one piezoelectric bending transducer (36) which, in a closed position, rests against a valve seat of the associated valve (26a, 26b; 27a, 27b) and closes a valve opening (42a, 42b) in a fluid-tight manner and which, depending on an applied control voltage, can be moved into open positions raised to different distances from the valve seat, wherein the ventilation connection (22) and the working connection (28a, 28b) are each connected to a pressure sensor (43a, 43b) coupled to the control device (19), and wherein the control device (19) has an algorithm with at least one implemented integrator (48), and wherein the control device (19) is designed to determine from a provided target working pressure at the working connection (28a, 28b) and from a measurement of the actual working pressure at the working connection (28a, 28b) by the pressure sensor (43a, 43b) to compare the actual working pressure with the target working pressure,wherein the at least one integrator (48) is activatable for integrating the control deviation of the control voltage after the actual working pressure has been constant over a certain period of time, and wherein the control voltage is variable as a function of the determined target / actual deviation, taking into account the integrator operation. [9] Fluid system according to claim 8, characterized by that the control device (19) is designed to carry out the method according to one of claims 1 to 7. [10] Fluid system according to claim 8 or 9, characterized by that the piezo valves each have two independently controllable bending transducers (36). [11] Fluid system according to one of claims 8 to 10, characterized by that a pressure sensor (44) assigned to the ventilation connection (22) is designed as an absolute pressure sensor for determining the ventilation or supply pressure. [12] Fluid system according to one of claims 8 to 11, characterized by that a pressure sensor (45) for determining the venting or exhaust air pressure is assigned to the venting connection (24). [13] Computer program product for use in a computer device comprising instructions which, when executed in a control device (19) of a fluid system (11), carry out the method according to one of claims 1 to 7.

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