EP2182221B1 - Electro-pneumatic system for controlling a double-acting pneumatic actuator - Google Patents

Description

The invention relates to an electro-pneumatic system for controlling a double-acting pneumatic actuator having a first pneumatic working chamber and a second pneumatic, independent controllable working chamber.

Usually, an electro-pneumatic system has a pneumatic pilot control stage for generating a pneumatic pilot control signal, in particular an I / P converter, which pilot signal is delivered to a main pneumatic control stage, such as an air pressure booster, which is connected to a supply pressure source of, for example, 6 bar air pressure. For this exemplary case, the air pressure booster can produce a maximum control pressure of 6 bar.

Double-acting pneumatic drives are widely used in the process engineering industry, especially in power plant technology. Typical applications of double-acting pneumatic actuators are directed, for example, to demanding control tasks in which, for example, a valve flap in a fluid-carrying pipeline is to be set quickly and reliably. A double-acting pneumatic actuator requires no internal springs, which should drive an actuator of the drive in a specific emergency position when the pneumatic drive is vented. The double-acting pneumatic actuator may have a control piston separating two pneumatic working chambers, which is coupled to the valve flap and is displaced between the working chambers at a defined differential pressure. Double-acting actuators have the general advantage of being particularly robust and durable, at the same time a structurally simple and cost-effective design is guaranteed.

Usually, the double-acting pneumatic actuator is controlled by a so-called electro-pneumatic positioner, which generates an electrical control signal based on an actual electrical variable, such as the position of the control valve of the process plant, and an electrical setpoint signal from the parent control room and it by means of an I / P Converts converter in a pneumatic pilot signal, which is supplied to a reversing amplifier, which directs opposing main pneumatic control signals to the working chambers of the double-acting pneumatic actuator. The pneumatic working chambers of the double-acting pneumatic actuator are pressurized in opposite directions by a constant pressure medium value.

An example of a double acting pneumatic actuator is in DE 100 21 744 A1 specified, in which the pressure difference between the two working chambers of the actuator is defined as a controlled variable. To adjust the pressure differential, the pneumatic reversing amplifier receives the control pressure generated by the I / P converter, based on which the desired control pressure differential is created in the working chambers of the double-acting pneumatic actuator. At the first output of the inverting amplifier is the control pressure of the I / P converter, wherein at the second output a corresponding counter-pressure is built up, which complements with control pressure at the first output to the constant supply air pressure, for example, 6 bar.

An electronic control or regulating device for a double-acting cylinder is off DE 20 2004 002 504 U1 known.

This results in a functional requirement of the inverting amplifier that the decrease of the first control pressure in the first working chamber causes a corresponding increase of the second control pressure in the second working chamber, wherein the mean pressure value is fixed.

Usually, a double-acting, pneumatic actuator operates by means of a supply pressure of about 6 bar, with a constant pressure average value of 3.5 bar is set between the first and second working chamber. The double-acting pneumatic actuator can realize fast control cycles, but has the disadvantage, due to the compressibility of the operating medium air at 3.5 bar not to be sufficiently load-resistant. Requires the field of application of the actuator higher load stiffness, it is known that often hydraulic hydraulic actuators are used, which are expensive to purchase and especially for lack of environmental compatibility of the hydraulic oil can not be considered for all applications.

It is an object of the invention to overcome the disadvantages of the prior art, in particular to provide a positioner which is to control a double-acting, pneumatic universally applicable actuator and is also operational when control cycles combined with a high and in particular selectable load rigidity by the actuator can be reached.

This object is solved by the features of claim 1. Thereafter, the electro-pneumatic system according to the invention is improved in that the pneumatic pilot stage upstream of a separation electronics for oppositely dividing an electrical control signal received by the electro-pneumatic system or generated by a control electronics of the electro-pneumatic system by an electrical control mean value in two electrical mirror image signals is. According to the invention, the separation electronics are designed to set the control mean value, wherein the precontrol stage generates, based on the control mean value and the mirror image signals, two pilot control signals set in opposite directions about a pneumatic mean value. The pneumatic pilot control signals are each supplied to a main control stage to pressurize the respective working chambers of the double-acting actuator with the set pressure medium value and the respective pressure difference.

With the inventive measure the upstream connection of a separation electronics, a pneumatic reversing amplifier is dispensable. In this way, the electro-pneumatic system is much simpler and cheaper to build. Above all, the fixed assignment of the outlet pressures and thus an unchangeable pressure mean value is overcome, because according to the invention the generation of the pressure difference is shifted by means of common signals from the pneumatic side towards the electronics side. According to the invention, the mean pressure value between the pneumatic output signals can now be varied as desired between the atmosphere and the maximum supply pressure (for example 6 bar). In this way, for example, a positioner for a double-acting pneumatic actuator can be provided, the last-load for fast control and very stable in certain operating situations.

In a preferred embodiment of the invention, the pneumatic pilot stage has two mutually independently electrically controllable I / P converters, of which one I / P converter receives a first electrical mirror image signal from the separation electronics, while the other I / P converter receives the second electrical mirror image signal which is opposite to the first electric mirror image signal with respect to a variable average.

It is clear that the mirror image signals of the separation electronics can also be adjusted so that both pneumatic working chambers can be acted upon with the maximum supply pressure of the respective main stage in order to form the double-acting pneumatic actuator as rigid as possible. However, the sum, ie the mean pressure, of the pressures prevailing in the working chambers can be well below 3 bar, for example 1 or 2 bar, in order to be able to realize rapidly variable control cycles.

In a preferred embodiment of the invention, the separation electronics have a voltage divider which receives the control signal and generates two voltage control signals set in opposite directions by a variable voltage average.

In this case, the voltage divider may be connected to two voltage / current converters, of which one voltage / current converter receives the first voltage control signal, while the other voltage / current converter receives the second thereto opposing voltage control signal.

In one embodiment of the invention, an output of the respective voltage / current converter is connected to a respective I / P converter.

In a further development of the invention, the electro-pneumatic system is designed as a positioner and has a microprocessor for receiving a position setpoint and a position feedback from a position sensor, based on which the electrical control signal is generated.

In a preferred embodiment of the invention, a device for adjusting the control mean value is connected to the separation electronics. The adjustment means may preferably comprise an operating knob or switch operable from the outside of the system. For example, the setting means may receive a setting value via a communication means such as HART, BUS, radio, Bluetooth, Zigbie WLAN, etc.

Furthermore, the invention relates to an arrangement with an inventive electro-pneumatic system and with a pneumatic pilot stage downstream main control stage, which are formed of two independently controllable, pneumatic amplifiers. The pneumatic amplifiers are each connected to a supply pressure source, for example, 6 bar.

Preferably, one pneumatic amplifier is connected to the output of an I / P converter of the pneumatic pilot stage, while the other pneumatic amplifier is connected to the input of the other I / P converter of the pilot pneumatic stage.

In a further development of the invention, a first I / P converter of the pneumatic pilot stage and an associated pneumatic amplifier in a closed, in particular intrinsically safe housing, while the second I / P converter of the pilot stage and the associated pneumatic amplifier of the main control stage in a second, separated from the first housing, closed, in particular intrinsically safe housing are housed, which is in particular attached to the first housing.

Preferably, the pneumatic pilot stage and the main pneumatic control stage are housed in a common housing.

Furthermore, the invention relates to a method for expanding or upgrading an existing electro-pneumatic system for controlling a double-acting pneumatic actuator having a first pneumatic working chamber and a second independently controllable working chamber, wherein the electro-pneumatic system, a power / pressure Transducer or I / P converter and a pneumatic amplifier connected thereto.

According to the invention, a second I / P converter and a second with the second I / P converter connected pneumatic amplifier provided. Two electrical control signals divided inversely by a variable average are generated and an electrical control signal is applied to each of the I / P converters to generate counter-rotating pneumatic pilot signals for delivery to the respective pneumatic booster.

The inventive electro-pneumatic system, the arrangement according to the invention and the upgrade method according to the invention, the double-acting pneumatic drive can be adjusted not only in view of the variable air pressure difference in the working chambers, which results from the opposing working chamber pressures, but also the pressure average between the adjustable working chamber pressures can be adjusted to adjust the stiffness of the double acting pneumatic actuator. The height of the working chamber pressure average value is already set at the electronic level of the electro-pneumatic system by setting the mean value by adjusting the control mean value in addition to the opposing control signals. This means that when connected to a supply pressure source of 6 bar, pneumatic main amplifiers, the pressure average of atmospheres up to 6 bar is adjustable. It is clear that the largest pressure difference in the working chambers is reached when the pressure mean value is about 3.5 bar. At a pressure average of 4 bar, a pressure difference of up to 4 bar is available. With a pressure mean value of 5 bar, a maximum pressure difference of 2 bar is available.

The pressure difference causes the relative displacement of the actuator piston of the pneumatic, double-acting actuator, while the set pressure value determines the stiffness of the double-acting pneumatic actuator.

Figur 1

ein Schaubild eines elektro-pneumatischen Systems gemäß dem Stand der Technik zum Steuern eines doppelt wirkenden pneumatischen Stellantriebs;

Figur 2

ein Schaubild eines erfindungsgemäßen elektro-pneumatischen Systems;

Figur 3

ein Schaubild eines erfindungsgemäßen Feldgeräts mit einem erfindungsgemäßen doppelt wirkenden Stellantrieb;

Figur 4

ein Schaubild eines erfindungsgemäßen Feldgeräts in einer weiteren Ausführung mit einem doppelt wirkenden pneumatischen Stellantrieb;

Figur 5

ein Schaubild eines erfindungsgemäßen Feldgeräts in einer weiteren Ausführung mit einem doppelt wirkenden pneumatischen Stellantrieb; und

Figuren 6a bis 6c

Diagramme, welche den Verlauf elektrischer Spannungs-Steuersignale U_y+, U_y- und dessen veränderlichen Mittelwert cp (16 %, 76 %, 50 %).

Further advantages, characteristics and features of the invention will become apparent from the present description of preferred embodiments of the invention with reference to the accompanying drawings, in which:

FIG. 1

a diagram of an electro-pneumatic system according to the prior art for controlling a double-acting pneumatic actuator;

FIG. 2

a diagram of an electro-pneumatic system according to the invention;

FIG. 3

a diagram of a field device according to the invention with a double-acting actuator according to the invention;

FIG. 4

a diagram of a field device according to the invention in a further embodiment with a double-acting pneumatic actuator;

FIG. 5

a diagram of a field device according to the invention in a further embodiment with a double-acting pneumatic actuator; and

FIGS. 6a to 6c

Charts showing the course of electrical voltage control signals U _y +, U _y - and its variable mean cp (16%, 76%, 50%).

In general, a conventional positioner for a double-acting pneumatic actuator comprises a known electro-pneumatic system a, as used in e.g. FIG. 1 is shown. The electro-pneumatic system has an electronic controller b, which receives an electrical position setpoint U _W from a non-illustrated, higher-level control room of the process plant and an electronic position actual value U _X from a position sensor, not shown, and processes the position of a detected to be set process valve member.

The electronic controller b calculates an electrical control signal U _Y and outputs this via its output to the input of a U / I converter c, which generates a corresponding electrical control current signal and forwards to an I / P converter d. Based on the control current signal, the I / P converter generates a pilot pneumatic signal which is passed to a main control stage in the form of an air power amplifier e connected to a supply air pressure (not shown in the drawing) of 6 bar.

The subsequent to the air power amplifier e pneumatic reversing amplifier f is used to set two by a constant pressure mean value of about 3.5 bar in opposite directions, main hydraulic control signals H ₊ , H _- to be generated, which are then acted upon by the respective working chamber of the double-acting pneumatic actuator. The venting of the pneumatic drive is done via the vent port g. The mean pressure of the inverting amplifier f can not be adjusted, so that the double-acting pneumatic actuator has a constant load rigidity. The mechanism of the inverse amplifier f allows only a very inaccurate adjustment of the main pneumatic control signals, which is why readjustments of the actuating piston of the double-acting actuator are necessary.

The electro-pneumatic system according to the invention is in the embodiment according to FIG. 2 generally designated by the reference numeral 1 and is designed as a positioner. The electro-pneumatic system 1 comprises an electronic controller 3, which receives a position setpoint U _W from a plant control room (not shown) and a position actual value U _X from a position sensor (not shown). The electronic controller 3 calculates an electrical control signal U _y , which is supplied to a separation electronics 5 according to the invention. The separation electronics 5 comprises a voltage divider 7 which divides the electrical voltage control signal U _Y into a first voltage control signal U _y + and into a second voltage control signal Uy-. The voltage signals U _y +, U _y - have an antisense to a control mean value cp, which is intended to ultimately cause the desired pressure difference in the working chambers of the double-acting pneumatic actuator, which pressure difference corresponds to a specific displacement of the actuating piston of the double-acting pneumatic actuator , The mean value generated by the separation electronics 5 is variable and corresponds to the pressure mean value by which the control pressures should behave in opposite directions. Each generated average corresponds to a certain control pressure average.

The voltage divider 7 is connected to an operable from the outside 8 of the electro-pneumatic system 1 Arbeitsdruckmittelwerteinstellrichtung 9, for example in the form of a knob over which the electrical control mean cp is adjustable by the opposite voltage / control signals U _y +, U _y - variable are.

Both the first voltage control signal U _Y + and the second voltage control signal Uy- are fed to a first U / I converter 11 and a second U / I converter 13, respectively from the electrical voltage control signals U _y +, U _y - generates a first and second current control signal which are supplied to the input of a first I / P converter 15 and a second I / P converter 17. In the first and second I / P converter opposite sense pneumatic pilot signals are supplied, namely a first pilot signal P ₊ and a second pilot signal P _- . The first and the second pneumatic pilot signal P ₊ , P _- have the desired ingenuity by a set pneumatic pilot control average. The pilot signals P ₊ , P- are independent pressure signals with an absolute signal level. The pneumatic precontrol average results from the mean value of the absolute precontrol signals P ₊ , P _- . The two pneumatic precontrol signals P ₊ , P- are fed to a first air power amplifier 19 and a second air power amplifier 21, respectively. Both air power amplifiers 19, 21 are connected to its own supply pressure source 23, 25 of 6 bar. The main pneumatic control signals H ₊ , H- are supplied to the respective pneumatic working chambers of the pneumatically acting actuator.

With the electro-pneumatic system 1 according to the invention, a reversing amplifier (f) is dispensable. In addition, the main pneumatic control value can be easily adjusted to continuously adjust the stiffness of the double-acting actuator.

In FIG. 3 an embodiment of a field device 31 according to the invention with an inventive, designed as a positioner electro-pneumatic system 1 is shown, which is housed in a common intrinsically safe housing 33. For ease of reading the figure description, the same reference numerals for the same components of the electro-pneumatic system as in FIG. 2 also in FIG. 3 used.

The electronic controller 3 receives an electrical position setpoint U _W from a parent, not shown control room of a process plant. The electrical actual position value U _X is fed from a position sensor 35 to the input 37 of the electronic controller 3 through the housing 33 of the positioner.

The opposite, main pneumatic control signals H ₊ , H- the main control stage are transmitted via pneumatic lines 39, 41 a first working chamber 27 and a second working chamber 29 of a double-acting pneumatic actuator 43. The double acting pneumatic actuator 43 has a displaceable separating piston 45 which separates the first working chamber 27 from a second working chamber 29, so that the working chamber 27, 29 are independently pneumatically controlled.

The separating piston 45 is connected to a control valve 47 of the process plant via a control rod 49, detects the position of the position sensor 35. The control valve 47 serves to regulate a fluid flow within a fluid line of the process plant.

As in FIG. 3 can be seen, the separation electronics 5, the second I / P converter, the second air power amplifier 21 and an electronic part of the Arbeitsdruckkammermittelwerteinstelleinrichtung 9 may be disposed within a separate inner housing 51 which is housed within the positioner housing 33. The adjusting device 9 can be actuated from the outside, which is indicated by the arrow 53. In this way, the operation of an electro-pneumatic system 1 according to the invention can also be transferred to existing electro-pneumatic systems by system components are installed in the additional inner housing 51 in the positioner housing 33 and connected to the controller. In addition, the inner housing 51 has two outputs, an electrical output for the first I / P converter and a pneumatic outlet for connection of the second pneumatic line 41.

A field device execution according to FIG. 4 differs from the according to FIG. 3 in that access to the pneumatic lines 39, 41 for the main control signals H ₊ , H- pressure sensors 61, 63. The detected electrical pressure signals H ₊ , H- are supplied to the electronic controller 3 in order to readjust the main control signals H ₊ , H- as well as their absolute values with regard to the working fluid pressure value cp on the basis of the actual position value U _X.

The field device version according to FIG. 5 differs from the design according to FIG. 4 in that the positioner housing 33 are separated from an additional outer housing 69 for the separation electronics 5, an electronic part of the adjusting device 9, the second I / P converter and the second air power amplifier 21. The additional outer housing 69 is an input for receiving the electrical control signal U _Y , a pneumatic output for transmitting the first current control signal to the first I / P converter 15 and a pneumatic output for transmitting the second main control signal H _- to the second working chamber 29 of the double-acting pneumatic drive 43 flanged to the positioner housing 33. The positioner housing 33 has corresponding outputs or inputs, which are positioned mirror-symmetrically to the input / output of the outer housing 69.

In the diagrams 6a to 6c, the different Druckbeaufschlagbarkeit the working chambers 27, 29 of the double-acting pneumatic actuator 43 is indicated, wherein in the respective diagrams 6a to 6c each have a different pressure average cp and the possible curves of the absolute voltage control signals U _y + and U _y - are shown, which lead to the absolute main control mean H ₊ , H-.

In FIG. 6a is the working pressure mean cp set at 50%, ie 50% (3.5 bar) of a maximum pressure of 6 bar is set as the pressure mean value of the working pressures in the working chambers. In order to move the separating piston 45 of the double-acting actuator, now, starting from the working pressure mean value cp, a pressure difference is generated by generating the opposing control signals U _y + and U _y -. The complete range from 0 to 100% can be used for the control signals. For example, for the first control signal U _y + 100% value signal (ie 6 bar) can be set, which may be due to the antisense, the control signal Uy- at 0%, ie at atmospheric pressure. In this case, a maximum displacement of the separating piston 45 can be achieved.

On the other hand, if the working pressure average cp is set to 76%, as in FIG. 6b is shown, there is a working pressure average of about 4.6 bar. In this way, the load stiffness of the double-acting, pneumatic actuator against the operating condition according to FIG. 6a elevated. With a working pressure mean value of cp = 76%, the maximum pressure difference between the working chambers is limited to 48% (2x24%). If a 6 bar pressure value is set for the first control signal U _y +, the opposite control signal value U _y - is set to a corresponding 52% (76% - 24%).

In FIG. 6c is an operating situation with a reduced working pressure average cp of 16% shown. In this way, the double-acting, pneumatic actuator is low-load. The actual working pressure mean value is 2 bar, with a maximum mean pressure difference in the working chambers 27, 29 of 32%, ie 3 bar, is allowed. In this case, the working pressure in the first working chamber could be set to 2 bar maximum while the pressure in the second working chamber is 1.0 bar.

With the change of the working pressure mean cp of 50% in order to increase or decrease the rigidity, the maximum adjustable pressure difference in the working chambers 27, 29 decreases accordingly.

The features disclosed in the foregoing description, the figures and the claims may be of importance both individually and in any combination for the realization of the invention in the various embodiments.

LIST OF REFERENCE NUMBERS

1

electro-pneumatic system

3

electronic regulator

5

Auftrennelektronik

7

voltage conductor

8th

outside

9

Arbeitsdruckmittelwerteinstelleinrichtung

11, 13

U / I converter

15, 17

I / P transducer

19, 21

Air capacity booster

23, 25

Supply pressure source

27, 29

working chamber

31

field device

33

casing

35

position sensor

37

entrance

39, 41

pneumatic lines

43

pneumatic actuator

45

separating piston

47

Control valve

49

control rod

51

inner housing

33

Positioner housing

53

arrow

61, 63

pressure sensor

69

outer casing

a

electro-pneumatic system

b

electronic regulator

c

U / I converter

d

I / P transducer

e

Air capacity booster

f

inverting amplifier

G

exhaust port

H ₊ , H-

main pneumatic control signals

P ₊ , P _-

pneumatic pilot signals

U _W

electrical position setpoint

U _X

electrical position actual value

_UY

electrical control signal

U _y +, U _y -

electrical voltage control signals

cp

electrical control mean value

Claims (14)

1. An electropneumatic system (1) for controlling a double action pneumatic actuator (43), which has a first pneumatic working chamber (27) and a second pneumatic working chamber (29), which is controllable independently of the first pneumatic working chamber (27), comprising a pneumatic precontrol stage for generating a pneumatic precontrol signal for forwarding to a pneumatic main control stage, characterised in that dividing electronics (5) for oppositely dividing an electrical control signal U_Y, received by the electropneumatic system (1) or generated by regulating electronics (3) of the electropneumatic system (1), around an electrical control average cp into two electrical mirror image signals are connected upstream of the pneumatic precontrol stage and in that the dividing electronics (5) are designed for setting the control average cp, wherein the precontrol stage is designed to generate two precontrol signals, on the basis of the control average cp and the mirror image signals, which can be set oppositely around a pneumatic average.
2. The electropneumatic system (1) according to claim 1, characterised in that the pneumatic precontrol stage has two I/P converters (15, 17) that can be controlled independently of one another, of which one I/P converter (15) receives the one electrical mirror image signal, whilst the other I/P converter (17) receives the other electrical mirror image signal.
3. The electropneumatic system (1) according to claim 1 or 2, characterised in that the dividing electronics (5) have a voltage divider (7), which receives the control signal U_Y and generates two voltage control signals U_Y+, U_Y- set oppositely around a voltage average.
4. The electropneumatic system (1) according to claim 3, characterised in that the voltage divider (7) is connected to two voltage/current converters (11, 13), of which one voltage/current converter (11) receives the one voltage control signal U_Y+, whilst the other voltage/current converter (13) receives the other opposite voltage control signal U_Y-.
5. The electropneumatic system (1) according to claim 4, characterised in that one output of the respective voltage/current converter (11, 13) is connected to one I/P converter (15, 17) in each case.
6. The electropneumatic system (1) according to one of the preceding claims, characterised in that it is realised as a position controller and has a microprocessor for receiving a desired position value (U_W) and an actual position value (U_X) from a position sensor (35), on the basis of which the electrical control signal U_Y is generated.
7. The electropneumatic system (1) according to one of the preceding claims, characterised in that an electrical apparatus (9) for setting the control average cp is connected to the dividing electronics (5).
8. The electropneumatic system (1) according to claim 7, characterised in that the setting apparatus (9) comprises a control knob (9) that can be operated from the outside of the system.
9. The electropneumatic system (1) according to claim 7 or 8, characterised in that the setting apparatus (9) receives a setting value via communication means, such as HART, BUS, radio, Bluetooth, ZigbieWLAN, etc.
10. An arrangement with an electropneumatic system (1) according to one of claims 1 to 9 and with a main control stage connected downstream of the pneumatic precontrol stage, which are formed from two pneumatic amplifiers (19, 21) that can be controlled independently of one another.
11. The arrangement according to claim 10, characterised in that one pneumatic amplifier (19) is connected to the output of an I/P converter (15), whilst the other pneumatic amplifier (19) is connected to the input of the other I/P converter (17) of the precontrol stage.
12. The arrangement according to claim 10 or 11, characterised in that a first I/P converter (15) of the pneumatic precontrol stage and a pneumatic amplifier (19) connected thereto are contained in a closed first housing (33), whilst the second I/P converter (17) of the precontrol stage and the pneumatic amplifier (21) of the main control stage connected thereto are accommodated in a second closed housing (51, 69), which in particular is fastened in or on the first housing (33).
13. The arrangement according to one of claims 10 to 12, characterised in that the pneumatic precontrol stage and the pneumatic main control stage are accommodated in a common position controller housing (33, 51).
14. A method for expanding an existing electropneumatic system (1) for controlling a double action pneumatic actuator (43), which has a first pneumatic working chamber (27) and a second pneumatic working chamber (29) that can be controlled independently of the first pneumatic working chamber (27), wherein the electropneumatic system (1) comprises a first I/P converter (15) and a first pneumatic amplifier (19) connected thereto, characterised in that a second I/P converter (17) and a second pneumatic amplifier (21) connected to the second I/P converter (17) are provided and two electrical control signals divided oppositely around a changeable average are generated and one electrical control signal is supplied to each of the I/P converters (15, 17), in order to generate a first and a second opposite pneumatic precontrol signal on the basis of the average and the electrical control signals.

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