Method and device for operating an electropneumatic valve

The disclosure relates to a method and device for operating an electropneumatic valve for driving a pneumatic actuator drive to activate fittings in automation systems. The valve has at least one electropneumatic transducer and a pneumatic booster. The pneumatic booster has at least one 3/3 way valve with a blocking center position for optionally connecting an air inflow duct or an air outflow duct to a connecting duct, which connects to the actuator drive. The ducts are activated as a function of an electrical actuation signal by the electropneumatic transducer. At least one position of the 3/3 way valve with a blocking center position is measured and a correction value of a variable of the actuation signal is determined based on the measured value and the electrical actuation signal.

RELATED APPLICATION

This application claims priority under 35 U.S.C. §119 to German Patent Application No. 10 2008 028 190.5 filed in Germany on Jun. 12, 2008, the entire content of which is hereby incorporated by reference in its entirety.

FIELD

The present disclosure relates to a method and device for operating an electropneumatic valve for driving pneumatic actuator drives to activate fittings in automation systems.

BACKGROUND INFORMATION

Electropneumatic valves are used to drive and control the position of actuator drives or control drives, including both single-acting and double-acting designs, as well as for blocking and venting designs.

Valves of this type are known in principle. See, for example, EP 1758 007 A1. According to this document, the valve is composed of at least a control pressure regulator, a pneumatic booster, an electropneumatic transducer, an air inflow duct, an air outflow duct, and a connecting duct which connects to the actuator drive.

A pneumatic booster is understood within the scope of this description to be a technical device which controls a pneumatic output signal using a pneumatic input signal.

The electropneumatic transducer can be supplied here with an operating medium from the air inflow duct. This operating medium is typically a compressed gas, but any other fluid medium can be utilized. The operating medium which is fed to the electropneumatic transducer usually has a pneumatic pressure which is required to position the drive. In order to perform internal control of the pneumatic booster, a significantly lower control pressure of the same operating medium, which is as constant as possible, is extracted from the air inflow duct. For this purpose, the operating medium is fed to a control pressure regulator which reduces the pressure of the operating medium to the desired control pressure and regulates it to a constant value. The pneumatic booster is controlled with the operating medium which is reduced to the control pressure. Possible impurities are kept away from the pneumatic system by means of filters.

The electropneumatic valve is activated by feeding in electrical energy after the electropneumatic valve has been supplied with the operating medium as a pneumatic energy carrier. For this purpose, the electropneumatic valve is equipped with an electropneumatic transducer, which is driven electrically and manipulates the control pressure to perform pneumatic driving of the pneumatic booster.

The electropneumatic transducer is a converter which, on the basis of an electrical input signal, influences the control pressure circuit of the pneumatic booster in a selective fashion. By means of this electropneumatic transducer it is possible to control the pneumatic booster in such a way that, in a first operating mode, the operating medium is fed in a selective fashion from the air inflow duct into the connecting duct which connects to the pneumatic actuator drive, or, in a second operating mode, the operating medium is fed in a selective fashion from the pneumatic actuator drive into the atmosphere via the air outflow duct, or, in a third operating mode, the operating medium is enclosed in a selective fashion in the actuator drive maintain the instantaneous position of the actuator drive. For this purpose, the pneumatic booster has a first pneumatic valve for connecting the air inflow duct to the connecting duct which connects to the actuator drive, and a second pneumatic valve for connecting the air outflow duct to the connecting duct which connects to the actuator drive. Such an arrangement is referred to according to the standards as a 3/3 way valve with a blocking center position.

EP 1758 007 A1 also discloses equipping the electropneumatic transducer with piezoelectric bender actuators which can be driven with a small amount of electrical energy. The low energy demand is a core requirement for use in two-conductor devices in automation equipment which draw their energy from a 4.20 mA current loop via their driving signal.

A transmission characteristic curve can describe the assignment of the electrical input signal in an electrical unit at the electropneumatic transducer to the output signal at the connecting duct which connects to the actuator drive as a set opening cross section or as a through-flow unit. The transmission characteristic curve can be defined, for example, by three characteristic ranges which, starting from the venting range, extends via the sealing-tight range to the ventilation range.

The sealing-tight range describes the range of electrical driving in which the electropneumatic valve seals tight the side located on the connecting duct which connects to the actuator drive with respect to all possible ventilation and venting paths. In the ventilation range, the output of air through the connecting duct which connects to the actuator drive is essentially proportional to the electrical driving signal with a very largely constant gradient up to the full air output signal. In the venting range, the air output signal at the air outflow side follows the electrical driving signal essentially proportionally, with a very largely constant gradient up to the full air outflow rate.

The transition from the sealing-tight range into the venting range is the opening point for venting, and the transition from the sealing-tight range into the ventilation range is the opening point for ventilation. The opening points for ventilation and venting are highly significant for the use of the electropneumatic valve in an electropneumatic position regulator for high regulating quality with respect to the connected actuator drive.

A high regulating quality is impeded in an electropneumatic valve of this type by the hysteresis between the forward characteristic curve and return characteristic curve and the drift of the opening points. In the case of electropneumatic transducers with piezo technology, these effects are due in particular to the piezo ceramic and are dependent on ambient influences such as the temperature of the piezo ceramic and/or moisture/soiling on its surface and resulting leakage currents. In particular, valves with piezo bender actuators can be provided with a corresponding surface. These effects occur in a similar form with magneto-inductive driving means.

However, other influences such as extension of the length of the materials used, friction in the overall structure and adjustment devices, and the mechanical setting behavior of the electropneumatic transducer, which can be caused, in particular, by temperature cycles over the permissible temperature range, also cause these effects.

Since the opening points drift over such influencing variables, an opening point cannot be reliably assigned to a previously determined electrical actuation variable for the pilot control valve. Alternatively, a through-flow quantity at the output which is sufficiently small for a regulating process cannot be reliably assigned to a constant value which is applicable at any time and has been determined by calibration when the system was activated.

The compensation of hysteresis can also be significant for the regulating quality. Since there is an offset between a forward characteristic curve and a return characteristic curve, the pneumatic booster does not follow the electrical actuation variable directly. Since the magnitude of the hysteresis is also subject to such ambient influences, it is not known, at the operating time, how much the actuation variable has to be changed in order to control the opening cross section or the quantity of air in the pneumatic booster with the desired order of magnitude in the opposite direction.

SUMMARY

An exemplary method is provided for operating an electropneumatic valve to drive a pneumatic actuator drive. The electrompneumatic valve has at least one electropneumatic transducer and at least one pneumatic booster. The pneumatic booster has at least one 3/3 way valve with a blocking center position for optionally connecting a connecting duct, which is connectable to the actuator drive, to at least one of an air inflow duct and an air outflow duct, which ducts can be activated by means of the electropneumatic transducer as a function of an electrical actuation signal. According to an exemplary embodiment, at least one position of the 3/3 way valve with a blocking center position can be measured, and a correction value of a variable of the electrical activation signal can be determined based on the measured value and the electrical actuation signal.

An exemplary device provided herein is configured to operate an electropneumatic valve. The electropneumatic valve can be configured to drive a pneumatic actuator drive, and can include at least one electropneumatic transducer and at least one pneumatic booster, which can have at least one 3/3 way valve with a blocking center position configured to optionally connect a connecting duct, which can be connectable to the actuator drive, to at least one of an air inflow duct and an air outflow duct. The at least one electropneumatic transducer can be configured to activate the at least one of the air inflow duct and the air outflow duct in accordance with an electrical actuation signal.

According to an exemplary configuration, the device can include an adjustment means for measuring at least one position of the 3/3 way valve with the blocking center, determining a correction value of a variable of the electrical actuation signal based on the measured position and the electrical actuation signal, and adjusting the electrical actuation signal in accordance with the determined correction value.

DETAILED DESCRIPTION

A method for operating an electropneumatic valve is disclosed which permits the quantity of air at the connecting duct which connects to the actuator drive to be specified and set in accordance with the electrical actuation signal, independent of drift and/or hysteresis.

The disclosure is based on an electropneumatic valve for driving pneumatic actuator drives. The electropneumatic valve can have at least one electropneumatic transducer and a pneumatic booster. The pneumatic booster can have at least a first pneumatic valve for connecting an air inflow duct to a connecting duct which connects to the actuator drive, and a second pneumatic valve for connecting an air outflow duct to the connecting duct which connects to the actuator drive. The actuator drive and values can be which are activated by means of the electropneumatic transducer as a function of an electrical actuation signal.

Exemplary embodiments of the present disclosure are based, in part, on the realization that high regulating quality can be achieved in all the areas of use of the respective end application, in particular in an electropneumatic position regulator, only if the desired cross sections of the valve and therefore the quantities of the operating medium can be set or metered reliably. Knowledge of the actual opening points facilitates this. The gradient of the characteristic curve is largely unaffected in this context.

According to an exemplary embodiment, at least one position of the 3/3 way valve with a blocking center position is measured, and a correction value of the actuation variable is determined from the measured value from the electrical actuation signal.

Acquiring the actual position of the observed pneumatic valve allows both the influences of the drift of the opening point and the hysteresis on the setting of the quantity of air at the connecting duct which connects to the actuator drive to be eliminated.

According to another exemplary embodiment of the present disclosure, the position of the 3/3 way valve with the blocking center position is measured during a calibration phase. As a result, correct quantities of air can advantageously be set at the very start of the current operation.

According to another exemplary embodiment of the present disclosure, the calibration is adapted during the current operation. This ensures that the influences of the drift of the opening point are compensated.

FIG. 1illustrates an exemplary electropneumatic valve10for driving a pneumatic actuator drive30which has at least one electropneumatic transducer16and at least one pneumatic booster which has a 3/3 way valve with a blocking center position11. The 3/3 way valve with a blocking center position11is designed to optionally connect a connecting duct18, which connects to the actuator drive30, to an air inflow duct12or to an air outflow duct13. The correct activation of the 3/3 way valve with a blocking center position11is carried out by means of an electropneumatic transducer16as a function of an electrical actuation signal22. For this purpose, the electropneumatic transducer16is connected, via a pressure regulator14and a throttle device15, to the air inflow duct12, and is therefore supplied with a low and constant pressure.

The actuator drive30is connected via a lifting rod31to a fitting32which is suitable for controlling the flow of a process medium through a pipeline.

The electrical actuation signal22for activating the electropneumatic transducer16is derived from a setpoint valve21using a signal processing device20. In this context, the transmission characteristic curve of the electropneumatic valve10as illustrated inFIG. 2, should be taken into account. As illustrated in the example ofFIG. 2, the profile of the air flow L as a measure of the air through-flow rate per time unit in the direction of through-flow plotted against the control voltage S of the electrical actuation signal22exhibits, for example, three significant ranges.

In a first range, between 0% control voltage S and an opening point which is denoted by P1, the air flow L is negative, which means that the actuator drive30is being vented. In this context, the 3/3 way valve with the blocking center position11is set in such a way that the connecting duct18, which connects to the actuator drive30, is connected to the air outflow duct13. Consequently, the air which is stored in the actuator drive30passes through the air outflow duct13into the surrounding environment.

In a subsequent second range of the control voltage S between the opening points P1and P2, the air flow L is equal to zero, which means that the connecting duct18, which connects to the actuator drive30, is sealed tight with respect to all possible ventilation and venting paths. In this context, the 3/3 way valve with a blocking center position11is in its blocking center position. Consequently, the air is stored in the actuator drive30. The sealing tight range extends virtually symmetrically around approximately 50% of the control voltage S.

Finally, in a subsequent third range of the control voltage S between the opening point P2and 100% control voltage S, the air flow L is positive, which means that the actuator drive30is being ventilated. In this context, the 3/3 way valve with a blocking center position11is set in such a way that the connecting duct18, which connects to the actuator drive30, is connected to the air inflow duct12. Consequently, the actuator drive30is filled with air.

Furthermore, the behavior of the electropneumatic valve10is subject to hysteresis. This means that a change in direction of the control voltage S is transformed into an equivalent change in the air flow L only after a certain delay. This behavior, which is referred to as hysteresis, is illustrated inFIG. 2by hatched surfaces at the respective characteristic curve sections.

According toFIG. 1, the pneumatic booster which is formed by the 3/3 way valve with a blocking center position11has at least one sensor17for sensing the position of the 3/3 way valve with a blocking center position11. In an exemplary configuration of the electropneumatic valve10, the sensor17is of a type which senses in a contactless fashion. In this context, it is possible for the sensor17to be of the magneto-inductive sensing type, for example. In particular, the sensor17can be formed by an air-core coil.

The sensor17can be connected to the signal processing device20. The signal processing device20determines a correction value of a variable of the actuation signal based on the electrical actuation signal22and the measured value of the position of the 3/3 way valve with a blocking center position11. For this purpose, at least one position of the 3/3 way valve with a blocking center position11can be measured when there is a predefinable electrical signal to which a manipulated control pressure corresponds, and a correction value of the actuation variable can be determined from the measured value, in acordance with the electrical actuation signal22. In an exemplary embodiment, the position of the 3/3 way valve with the blocking center position11can be measured, for example, during a calibration phase.

The signal processing device20can be configured to determine a correction value, which yields the associated electrical actuation signal22as an offset with respect to the setpoint value21. The correction value can be determined from the actuation signal22and the measured actual position of the 3/3 way valve with a blocking center position11. Thus, the signal processing device20can, for example, adjust the electrical actuation signal22in accordance with the determined correction value. Accordingly, the signal processing device can be a control unit and/or an adjustment means of a device configured to operate the electropneumatic value10. According to an exemplary embodiment, the position of the 3/3 way valve with the blocking center position11can be measured when the 3/3 way valve with the blocking center position11is in the fully ventilated position, for example.

Alternatively, it is possible for the position of the 3/3 way valve with the blocking center position11to be measured when the 3/3 way valve with the blocking center position11is in the fully vented position, for example.

According to another exemplary embodiment of the present disclosure, it is possible for the position of the 3/3 way valve with the blocking center position11to be measured when the 3/3 way valve with the blocking center position11is in the tightly sealing position, for example.

In another exemplary configuration of the present disclosure, the calibration can be adapted during the current operation. This can counteract the drift of the opening points.

In yet another exemplary configuration of the present disclosure, the calibration of the electropneumatic valve10can be carried out during the calibration of the controlled pneumatic actuator drive30.

Advantageously, the aforementioned exemplary embodiments have such a low energy demand that use in two-conductor devices in automation equipment, which draw their energy from a 4.20 mA current loop by means of their driving signal, is possible.

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