EP1443219A1 - Method and device for testing a pneumatic actuator - Google Patents

Abstract

The diagnosis method has a working space (6,7) of the setting drive (1) coupled to a pressure supply system which is below the system pressure (8), the position of the setting drive piston (3) within the setting drive housing (2) being detected. The static pressure component of the pressure in the working space is measured between 2 operating points of the setting drive and compared with a required pressure characteristic. Also included are Independent claims for the following: (a) a diagnosis device for a pneumatic setting drive; (b) a pneumatic setting drive.

Description

The invention relates to a diagnostic method for a pneumatic actuator at least one piston which is movable in a housing between two end positions and delimits a first work space, the work space having a pressure supply system is connectable, which is under a system pressure, and at least one position of the piston in the housing is recognized. The invention also relates to a diagnostic device for a pneumatic actuator with at least one piston, which in a housing is movable between two end positions and delimits a first working space, which can be connected to a pressure supply system which is under a system pressure stands, with at least one position of the piston in the housing by means of the diagnostic device can be represented.

Diagnostic methods and devices of this type use, for example, a pneumatic one Actuator with a piston that moves in a housing between two end positions is and delimits a first work space with a pressure supply system is connectable, which is under a system pressure and with a position transmitter, by means of whose at least one position of the piston can be seen in the housing.

Such pneumatic actuators belong to the order of the pressure medium gear and transmit a movement from the surface using a medium that can only be subjected to pressure Drive for output. A gas (especially air) acts as a medium under pressure designed as a piston drive member and moves it in a cylindrical Housing in the axial direction or it rotates - in the case of a rotary leaf drive - around a rigid one Axis .. The output member is, for example, a rotatable shaft, with each axial displacement of the piston in the housing immediately causes rotation of the output shaft.

The pneumatic actuators described are known with position sensors for the Piston position, for example from DE 101 52 178 A1, DE 100 26 082 C1, EP 0 894 983 A2, WO 91/10070 A1, WO 91/19907 A1 and DE 42 41 189 A1. The Known actuators allow monitoring of the piston position during operation. A malfunction of the known actuators, which can occur, for. B. in deviations from a target position. On the well-known actuators based diagnostic procedures allow a quick localization of a faulty one Actuators in a system, significantly facilitate and accelerate in this way troubleshooting and reduce downtime caused by malfunction.

In systems with a large number of actuators - and statistically correspondingly higher Error probability - and in systems that apart from scheduled maintenance intervals intended for continuous operation must increase availability the remaining downtimes should also be avoided as far as possible. The well-known actuators offer - except for statistical considerations - practically no possibility to determine their specific individual lifespan and the lifespan of the Actuator and actuator (e.g. armature) formed unit, so that here only the possibility greatly shortened replacement intervals or (multiple) redundant design of the relevant plant parts remains.

Both variants are inevitably associated with a reduced use of the capital employed connected and should therefore be avoided if possible for economic reasons become.

task

The invention has for its object a diagnostic method and corresponding Propose devices and actuators that predict individual life enable an actuator.

solution

Based on the known diagnostic method, the object of the invention solved in that a characteristic pressure is measured and evaluated, the characteristic pressure is the static pressure component of the pressure present in the first work space.

Typically, the first working area is depressurized before the start of a switching operation - that is, the movement of the piston from one end position to the other. If the first working space is connected to the pressure supply system, the pressure in the first working space initially rises continuously without the piston being set in motion. Only when the pressure force acting on the piston from the pressure medium exceeds the static friction forces opposing the movement, is the piston accelerated in the direction of the other end position. Starting from this _" breakaway point", only small amounts of sliding friction forces counteract the compressive force.

Depending on a large number of variables - the level of the system pressure and the viscosity of the pressure medium, the inflow cross-section of the working area and the effective piston area, the sliding friction forces between the piston and the housing and, if necessary, other (external) mechanical or pressure forces, In particular, forces for actuating a valve to be switched with the actuator (e.g. valve or the like) result in a characteristic status profile of the actuator. As a rule, an _" equilibrium" is reached after a running-in phase, which is characterized by an essentially constant speed of the piston at an essentially constant static pressure in the first working space.

The movement of the piston ends (normally) with the stop in the other end position. From this point on, the static pressure in the first work area increases continuously up to the level of the system pressure (provided the work area is not excessive Leakage losses), which - in addition to the now again static friction forces - Secure the piston in this position against accidental Reset is effected.

Any wear on the contact surfaces between the piston and the housing, each due to contamination caused reduction of inflow or outflow cross sections of the first Workspace, every leak in the pneumatic system and every change of operating parameters on the element driven by the actuator in each case - for example a ball valve - causes changes in this status profile, which are reflected in reflect characteristic changes in the static pressure in the first work space. The measurement of the static pressure component in the first working area Pressure as the characteristic pressure of the actuator thus provides - in connection with the known Positioning the piston - the ideal basis for diagnosing the current Status of an actuator and the valve operated with it.

The diagnostic method according to the invention is not only applicable to actuators that can be coupled with an element to be actuated (e.g. fitting) in the form of a separate component are, but also in such actuators that with the element to be actuated form a structural unit and as disclosed for example in WO 00/04311.

A course of the characteristic pressure is preferred in the context of a diagnosis according to the invention between two operating points of the actuator with a course of the setpoint compared. Depending on the requirements of the diagnosis, the pressure profiles from Start of loading up to the breakaway point, from the breakaway point to the stop in the other end position and from this point in time until the system pressure is reached flow into the diagnosis and, if necessary, with the movement profile of the piston be correlated between the end positions. Any deviation from that in question Setpoint can, for example, trigger an immediate visual inspection in progress Operation, as a reservation for the exchange in the next scheduled shutdown or prophylactically for automatic switchover to a redundant system path be used.

The difference between the characteristic pressure and a reference pressure is preferably measured with compared to the nominal value, the reference pressure being the static pressure component of the in one second working space is present and the second working space is not included is connected to the pressure supply system. Such a configuration is available especially in connection with actuators that have a double-acting piston between two alternately loaded work rooms. Depending on The working direction of the actuator then alternately sets the static pressure in the each pressurized work space the characteristic pressure, the static pressure in the other workspace represents the reference pressure.

The difference between the respective identification and reference pressures in the work rooms can be used for both directions of operation with minimal construction effort Differential pressure measuring element can be determined. Such measuring elements are general known and for a variety of uses and sizes as inexpensive Mass product available on the market. The miniaturization of this measuring element allows - with the appropriate dimensions of the component in question - its integration into the housing or even in the piston of the actuator according to the invention.

Alternatively, in particular in connection with an actuator that only has one side the pressurized piston and a - for example - spring-loaded Resetting option can be within the scope of a diagnostic method according to the invention also the characteristic pressure can be compared with a constant pressure. Generally measuring elements are known, for example, which have an absolute pressure (against a vacuum) determine. However, the differential pressure measuring element already mentioned can also be used in this sense be used if the connection for the reference pressure, for example with the external environment of the actuator is connected. Integration is also an option here of the measuring element in the piston.

A diagnostic method according to the invention preferably determines for a switching operation a pressure reserve, the pressure reserve being the difference between a maximum value the pressure before the piston breaks loose and the system pressure. This pressure reserve corresponds indirectly - via the pressurized piston surface in a cylindrical Housing of a linear actuator - a power reserve or - via the pressurized piston surface and the effective lever arm in a rotary actuator - a torque reserve as a measure of the load that can generally be set from the rest position: If the static friction of the load exceeds the force or torque reserve of the actuator, then the adjustment process is blocked. It is particularly preferred if the value falls below a minimum Limit pressure reserve generates a warning signal.

Furthermore, it becomes more advantageous in the context of a diagnostic method according to the invention A control pressure is determined for a control process, the control pressure being the value of the Pressure when reaching a final position of the piston. The characteristic pressure defined in this way corresponds to the pressure required to complete the setting process - for example, to completely opening or closing a valve - is required. An increase in Characteristic pressure can, on the one hand, lead to wear on the sealing and sliding surfaces of the actuator or the posed element and a resulting increase in Point out sliding friction forces. On the other hand, deposits also act on the actuator or on the element that hinder the reaching of the end position - for example In a fluid power plant, a solid load deposited at the valve seat of the fluid - in an increase in the characteristic pressure. Again, it’s especially helpful if a warning signal is generated when a maximum limit signal pressure is exceeded.

Instead of continuously monitoring the characteristic pressure, only individual discrete ones should be used Values for diagnosing an actuator are measured, so measuring the Pressure reserve and the characteristic pressure or one of the two values: The measurement can then triggered particularly easily, for example, by an electrical pulse generator the beginning or the end of an (electrically conductive) contact between registered the piston or between a piston and the housing end.

Both limit values - limit pressure reserve and limit signal pressure - are typically in Depending on the respective application of the actuator largely freely selectable, should but basically with a surcharge against the static or sliding friction forces of the load to be selected, on the one hand fluctuations of this Absorbs forces, on the other hand with wear-related increase in the characteristic pressure during operation enables the actuator to be replaced at predictable intervals.

The prefabrication of actuators is particularly useful for large quantities fixed limit values. Actuators can also be used for special purposes be provided which allow a limit value to be set directly on the actuator. Limit values can also be in the form of fixed numerical values in an external diagnostic device be filed. The diagnostic device is then over with the actuator a pressure line or - in particular with larger distances between the actuator and the diagnostic device - via a data line for transmission the current value of the characteristic pressure or only the pressure reserve and / or the Signal pressure connected.

A warning signal in the context of such a diagnostic method according to the invention can for example in the form of simple - and generally known - optical or acoustic Signal elements are output, which are arranged directly on the actuator. However, a warning signal can - alternatively or additionally - take the form of an electrical one or have an electromagnetic signal that is arranged on the actuator Diagnostic device on a further away display element, for example on a central scoreboard or transmitted to a control computer for a larger system becomes.

The task is also inventively based on the known diagnostic device solved in that a characteristic pressure can be measured by means of the diagnostic device and can be evaluated, the characteristic pressure being the static pressure component of one in the first Working space is present pressure. Such a diagnostic device is used for execution of the diagnostic method according to the invention described above. Even the invention Diagnostic device can be used with actuators that work with the actuating valve are fused into a structural unit.

A diagnostic device according to the invention preferably has a digital computing unit in which the comparison of the characteristic pressure with the setpoint is carried out. suitable Electronic computing units are generally known and in different designs Cost-effectively available on the market as mass products. The use is also fundamental analog pneumatic comparators possible. Aside from special cases, This excludes the use of electronic components, for example but not preferred for cost reasons. The use of programmable electronic On the one hand, computing units enable the use of standard components available on the market, on the other hand, the diagnostic device according to the invention can be so special cheap - namely by reprogramming instead of replacing components - for other purposes are used. As a diagnostic device in the sense of the invention in particular also to look at a commercially available digital computer for use is programmed in the manner mentioned.

A diagnostic device according to the invention can have a comparison element by means of whose characteristic pressure is comparable to a reference pressure. The characteristic pressure and the reference pressure then becomes the reference element based on the actuator supplied via pressure lines. The actuator itself then requires - except for connection options for these pressure lines - no other special equipment. In particular in applications that are due to high wear and therefore short life of the Actuator are marked with a diagnostic device according to the invention The actuator used is then manufactured in a particularly simple and cost-effective manner Tobe offered.

The task is therefore already based on the known actuator according to the invention solved by a pressure measuring connection, on which by means of a pressure measuring element a characteristic pressure is measurable, the characteristic pressure being the static pressure component of one in the first working space is present pressure. An actuator according to the invention preferably has a reference measuring connection on which by means of a reference pressure measuring element a reference pressure is measurable, the reference pressure being the static pressure component of a pressure present at a second work space and wherein the second work space is decoupled from the pressure supply system. Such an actuator only enables the diagnostic procedure described to be carried out.

An actuator according to the invention can have an integrated diagnostic device such as that described above. When using miniaturized components, the Actuator according to the invention then with the same dimensions as for the respective requirements commercially available actuators manufactured and therefore used in exchange for them become.

embodiment

Fig. 1

einen erfindungsgemäßen Stellantrieb,

Fig. 2

der Druckdifferenz- und Wegverlauf über der Zeit an diesem Stellantrieb,

Fig. 3

dieser Stellantrieb integriert mit einer erfindungsgemäßen Diagnosevorrichtung

The invention is explained below using schematic sketches of an exemplary embodiment. Show it

Fig. 1

an actuator according to the invention,

Fig. 2

the pressure difference and path over time on this actuator,

Fig. 3

this actuator integrates with a diagnostic device according to the invention

Figure 1 shows a pneumatic actuator 1 according to the invention with rack and pinion principle and a closed cylindrical housing 2, two axially mounted in this and self-centering, counter-rotating piston 3 and a radial rotating output shaft 4 emerging from the housing 2. The rotation of the output shaft 4 is by two racks 5 connected to the pistons 3, which are axially in the housing 2 are arranged and in a, not shown, on the circumference of the output shaft 4th engage arranged teeth, firmly coupled to the axial movement of the piston 3. The two pistons 3 enclose the inner working space 6 in the housing 2, in which also the racks 5 and the output shaft 4 extend. With the housing 2 the pistons 3 enclose the outer working spaces 7. In the outer work rooms 7 compression springs 8 are arranged, the pistons 3 on top of one another in unpressurized working spaces 6, 7 to push.

The housing 2, the pistons 3 and the racks 5 are made of an aluminum alloy manufactured in the die casting process. The outer surfaces are anodized and additional coated with epoxy resin. The output shaft 4 is made of stainless steel and is for connection on the element to be provided with a 2-flat, not shown. The Working spaces 6, 7 are on the piston 3 with nitrile rubber seals, not shown sealed against each other.

The actuator 1 according to the invention shown has a nominal swivel angle of 120 ° on. The actuator 1 brings the element to be set at a system pressure 9 a torque of up to 8000 Nm from 10 bar. Filtered is used as the working medium Air (PNEUROP / ISO class 4).

The actuator 1 has two pressure connections 10, 11, which are by means of a switching element 12 can be alternately pressurized or vented with the working medium.

The inner working space 6 is connected via the first pressure connection 10, and via the second Pressure connection 11, the outer working spaces 7 are acted upon. In the illustrated Position is the inner working space 6 via the first pressure connection 10 with the working medium pressurized, the outer working spaces 7 are via the second pressure connection 11 connected to the environment and have ambient pressure. The compression springs 8 lie on a block and thus define the end position of the pistons 3.

As can be seen from FIG. 2, lower diagram, the pistons 3 are at the start of the setting process in the basic position (or _“ 0 ° position”) 13 of the actuator 1 according to the invention, at the end of the setting process in the other end position, here the _“ 120 ° position "14. By switching the switching element 12, the outer working spaces 7 are acted upon by the working medium and the inner working space 6 is vented. The static pressure component of the pressure present in the outer work spaces 7 is present as the characteristic pressure at the pressure measurement connection 15, and the static pressure component of the pressure present in the inner work space 6 is present as the reference pressure at the reference pressure measurement connection 16. In an actuating process from the 120 ° position 14 to the 0 ° position 13, the functions of the pressure and reference pressure measurement connection 16 are interchanged, but the method of operation of the diagnosis described below is identical.

The pressure measuring connection 15 and the reference pressure measuring connection 16 have a differential pressure measuring element 17 connected, the measured via a pressure signal line 18 Differential pressure 19 reports to the diagnostic device 20. In addition, is on the actuator 1, a position sensor 21 is arranged, which via a position signal line 22 reports the measured position of the pistons 3 to the diagnostic device 20.

Figure 2 shows the course of the differential pressure 19 and the path 23 on this invention Actuator 1 during the actuating process: At the beginning, the differential pressure corresponds 19 in terms of the amount of the system pressure 8. In the basic position, the differential pressure is 19 defined negatively. First, the amount of differential pressure 19 drops to 0 (same pressures on both sides of the piston 3) and then rises to one below the system pressure 8 lying maximum pressure 24. When this maximum pressure 24 is concerned, the acting between the piston 3 and the housing 2 and in the connected element Overcoming static friction, the pistons 3 break loose. The difference between that Maximum pressure 24 and the system pressure 8 is referred to as the pressure reserve 25. The pistons 3 now move towards each other at a substantially constant speed. Here, the differential pressure 19 drops to a lower, also essentially constant amount.

In the end position, the racks 5 are in contact with the opposite one Piston 3. The movement of the piston 3 ends, the differential pressure 19 increases to System pressure 8 on. The pressure level when the end position is reached is set signal 26 designated.

FIG. 3 shows the actuator 1 according to the invention integrated with a diagnostic device 20 according to the invention. The diagnostic device 20 has a position indicator 27 which indicates the position of the output shaft 4. Central electrical connections (not shown) —a terminal strip, an actuator sensor connector and a bus connection — are arranged on the diagnostic device 20. The position transmitter 21 is an electronic angle transmitter arranged on the output shaft 4, which also functions as an end position detector. In addition, the diagnostic device 20 has a self-adjusting inductive limit switch (not shown). By means of the diagnostic device 20, the differential pressure 19 and the swivel angle are monitored in the sense of _" condition monitoring" and, if necessary, a warning signal is generated at an alarm output 28 to a higher-level control unit.

1

Stellantrieb

2

Gehäuse

3

Kolben

4

Abtriebswelle

5

Zahnstange

6

Innerer Arbeitsraum

7

Äußerer Arbeitsraum

8

Druckfeder

9

Systemdruck

10

Erster Druckanschluss

11

Zweiter Druckanschluss

12

Schaltelement

13

0°-Stellung

14

120°-Stellung

15

Druckmessanschluss

16

Referenzdruckmessanschluss

17

Differenzdruckmesselement

18

Drucksignalleitung

19

Differenzdruck

20

Diagnosevorrichtung

21

Positionsgeber

22

Positionssignalleitung

23

Weg

24

Maximaldruck

25

Druckreserve

26

Stelldruck

27

Stellungsanzeiger

28

Alarmausgang

In the figures are

1

actuator

2

casing

3

piston

4

output shaft

5

rack

6

Inner work space

7

Outside work space

8th

compression spring

9

system pressure

10

First pressure connection

11

Second pressure connection

12

switching element

13

0 ° position

14

120 ° position,

15

Pressure sensing port

16

Reference pressure measuring connection

17

Differential pressure measuring element

18

Pressure signal line

19

differential pressure

20

diagnostic device

21

locator

22

Position signal line

23

path

24

maximum pressure

25

pressure reserve

26

actuating pressure

27

position indicator

28

alarm output

Claims (14)

Diagnostic method for a pneumatic actuator (1) with at least one piston (3), which is movable in a housing (2) between two end positions and delimits a first working space (6, 7), the working space (6, 7) having a pressure supply system is connectable, which is under a system pressure (8), and at least one position of the piston (3) in the housing (2) is identified, characterized in that a characteristic pressure is measured and evaluated, the characteristic pressure being the static pressure component of the first working space (6, 7) is present pressure. Diagnostic method according to the preceding claim, characterized in that a curve of the characteristic pressure between two operating points of the actuator (1) is compared with a curve of the setpoint. Diagnostic method according to one of the preceding claims, characterized in that the difference between the characteristic pressure and a reference pressure is compared with the target value, the reference pressure being the static pressure component of the pressure present in a second working space (6, 7) and the second working space ( 6, 7) is not connected to the pressure supply system. Diagnostic method according to claim 1, characterized in that the characteristic pressure is compared with a constant pressure. Diagnostic method according to one of the preceding claims, characterized in that a pressure reserve (25) is determined for a switching operation, the pressure reserve (25) being the difference between a maximum value of the characteristic pressure before the piston (3) breaks loose and the system pressure (8). Diagnostic method according to the preceding claim, characterized in that a warning signal is generated when the pressure falls below a minimum limit pressure reserve. Diagnostic method according to one of the preceding claims, characterized in that an actuating pressure (26) is determined for an actuating process, the actuating pressure (26) being the value of the characteristic pressure when an end position of the piston (3) is reached. Diagnostic method according to one of the preceding claims, characterized in that a warning signal is generated when a maximum limit signal pressure is exceeded. Diagnostic device (20) for a pneumatic actuator (1) with at least one piston (3) which is movable between two end positions in a housing (2) and delimits a first working space (6, 7) which can be connected to a pressure supply system which is under a system pressure (8), wherein at least one position of the piston (3) in the housing (2) can be represented by the diagnostic device (20), characterized in that a characteristic pressure can be measured and evaluated by means of the diagnostic device (20), whereby the characteristic pressure is the static pressure component of a pressure present in the first working space (6, 7). Diagnostic device (20) according to the preceding claim, characterized in that the diagnostic device (20) has a digital computing unit. Diagnostic device (20) according to one of claims 9 to 10, characterized by a comparison element, by means of which the characteristic pressure is comparable to a reference pressure. Pneumatic actuator (1) with at least one piston (3), which is movable in a housing (2) between two end positions and delimits a first working space (6, 7) that can be connected to a pressure supply system that is under a system pressure (8) stands and with a position transmitter (21), by means of which at least one position of the piston (3) in the housing (2) can be identified, characterized by a pressure measuring connection (15), at which a characteristic pressure can be measured by means of a pressure measuring element, the characteristic pressure being the static pressure component of a pressure present in the first working space (6, 7). Pneumatic actuator (1) according to the preceding claim, characterized by a reference measuring connection at which a reference pressure can be measured by means of a reference pressure measuring element, the reference pressure being the static pressure component of a pressure applied to a second working space (6, 7) and the second working space ( 6, 7) is decoupled from the pressure supply system. Pneumatic actuator (1) according to one of claims 12 to 13, characterized by an integrated diagnostic device (20) according to one of claims 9 to 11.

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