EP1443219B1 - 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 with at least one piston which is movable in a housing between two end positions and limits two working spaces, wherein the working spaces are connectable to a pressure supply system, which is under a system pressure, wherein at least one position of the piston in the housing is detected. The invention also relates to a diagnostic device with a pneumatic actuator with at least one piston which is movable in a housing between two end positions and limits two working spaces, which are connectable to a pressure supply system, which is under a system pressure, wherein at least one position of the piston in the Housing by means of the diagnostic device can be displayed.

Such diagnostic methods and devices use, for example, a pneumatic actuator with a piston which is movable in a housing between two end positions and limits a first working space, which is connectable to a pressure supply system, which is under system pressure and with a position sensor, by means of which at least one Position of the piston is visible in the housing.

Such pneumatic actuators belong to the order of the pressure medium transmission and transmitted by means of a claimable only on pressure medium movement from the drive to the output. A gas (in particular air) acts as a medium under pressure on a drive member embodied as a piston and displaces it in a cylindrical housing in the axial direction or rotates it - in the case of a rotary-leaf drive - around a rigid axle. The output member is, for example, a rotatable shaft, wherein each axial displacement of the piston in the housing directly causes rotation of the output shaft.

The described pneumatic actuators with position sensors for the piston position are known, 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. Thus, a malfunction of the known actuators, z. B. reflected in deviations from a desired position, are determined. The on the known actuators Based on this, diagnostics allow a quick localization of a faulty actuator in a plant, significantly facilitating and speeding up troubleshooting and reducing downtime caused by malfunction.

In systems with a large number of actuators - and purely statistically correspondingly higher probability of error - and in systems that are intended for continuous operation apart from scheduled maintenance intervals, the remaining downtimes must be avoided if possible to increase the availability. However, the known actuators offer - except for statistical considerations - virtually no way to determine their specific individual life and the life of the drive and actuator (eg armature) formed unit, so that here only the possibility of greatly reduced replacement intervals or (multiple ) redundant design of the relevant system parts remains.

Both variants are inevitably associated with a reduced use of the capital invested and should therefore be avoided as far as possible for economic reasons.

European Patent Specification EP 0 947 901 A2 discloses a maintenance monitoring system for valves of steam turbines. In this case, a valve is equipped with a long shaft, which is provided on the opposite side with a piston. This piston sits in a pressure chamber, which is acted upon by an inlet with hydraulic pressure. By means of a pressure transducer, the pressure in the chamber is continuously measured and compared with a target value, whereby conclusions can be made on whether the stroke of the valve, or the valve itself, is in tact.

US Pat. No. 5,251,148 discloses a process control valve in which side walls in the area of the liquid flow are arranged with different sensors and thus the flow through the valve can be controlled and at the same time different parameters of the liquid, for example the temperature, are recorded. Again, the valve has a shaft which is equipped at its end opposite the valve with a piston, which in turn housed in a cylinder is. The cylinder has two openings for receiving compressed air and two pressure sensors, which measure the air pressure in the area above the piston and in the area below the piston. The signals from all the sensors are routed to a control system that allows the current measured values to be compared with readings recorded at a previous point in time. If deviations occur, possible errors in the process flow can be detected and corrective measures initiated.

task

The invention has for its object to propose an alternative diagnostic method and corresponding devices and actuators that allow the prediction of the individual life of an actuator.

solution

Based on the known diagnostic method, the object is achieved according to the invention in that the difference between a characteristic pressure, which is the static pressure component of the applied pressure in a working space, and a reference pressure, which is the static pressure component of the pressure applied in a second working space, when the second working space is not connected to the pressure supply system, determined by means of a Differenzdruckmesselements and compared with a setpoint.

Typically, the first working space before the start of a switching operation - ie the movement of the piston from one end position to the other - unpressurized. If the first working space is connected to the pressure supply system, the pressure applied 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 set against the movement, the piston is accelerated in the direction of the other end position. Starting from this "breakaway point", only lower amounts of sliding friction force counteract the compressive force.

Depending on a variety of variables - the system pressure and the viscosity of the pressure medium, the inflow of the working space and the effective piston area, the sliding friction forces between the piston and the housing and If necessary, further mechanical or compressive forces acting on the piston, in particular of forces for the actuation of a valve to be switched with the actuator (eg valve or the like), establish a characteristic state profile of the actuator. As a rule, after an intake phase, an "equilibrium" is achieved, which is characterized by a substantially constant speed of the piston at a substantially 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 working space continuously increases to the level of the system pressure (unless the working space has excessive leakage losses), thereby providing a backup of the piston in this position against inadvertent resetting, in addition to the now re-acting static friction forces becomes.

Any wear of the contact surfaces between the piston and the housing, any pollution-induced reduction in inlet or outlet areas of the first working space, any leakage in the pneumatic system, as well as any change in operating parameters on the respective actuator-driven element, such as a ball valve, will cause changes Condition profiles reflected in characteristic changes in static pressure in a work space. The measurement of the static pressure component of the applied pressure in a working space as characteristic pressure of the actuator thus represents - in conjunction with the known position determination of the piston - the ideal basis for the diagnosis of the current state of an actuator and the valve operated therewith.

The diagnostic method according to the invention is applicable not only to actuators which can be coupled with an element to be actuated (eg armature) in the form of a separate component, but also to those actuators which form a structural unit with the element to be actuated and like them for example, in WO 00/04311 are disclosed.

The difference between the characteristic pressure and a reference pressure is compared with the desired value, wherein the reference pressure is the static pressure component of the applied pressure in a second working chamber and wherein the second working chamber is not connected to the pressure supply system. Such a configuration is particularly useful in Connection with actuators, which have a two-sided effective piston between two alternately acted working spaces. Depending on the working direction of the actuator, the static pressure in the respectively pressurized working space alternately sets the characteristic pressure, the static pressure in the other working chamber represents the reference pressure.

The difference between the respective characteristic and reference pressures in the work spaces can be determined with minimal structural complexity in a usable for both directions of actuation differential pressure measuring element. Such measuring elements are well known and available for a variety of applications and sizes as inexpensive mass product on the market. The miniaturization of this measuring element allows - with appropriate dimensions of the component in question - its integration in the housing or even in the piston of the actuator according to the invention.

As part of a diagnosis according to the invention, a profile of the pressure difference between two operating points of the actuator is preferably compared with a course of the desired value. Depending on the requirements of the diagnosis, the pressure curves from the beginning of the application to breakaway, from breakaway to striking in the other end position and from this point to reach the system pressure in the diagnosis and, if appropriate, with the movement profile of the piston between the End positions are correlated. Any deviation from the relevant setpoint, for example, can be used as a trigger of an immediate visual inspection during operation, as a prerequisite for replacement at the next scheduled downtime or prophylactically for automatic switching to a redundant system path.

A diagnostic method according to the invention preferably determines a pressure reserve for a switching operation, wherein the pressure reserve is the difference between a maximum value of the pressure difference before breakage of the piston and the system pressure. This pressure reserve corresponds indirectly - via the pressurized piston surface in a cylindrical housing of a linearly acting actuator - a power reserve or - on the pressurized piston surface and the effective lever arm in a rotary drive - a torque reserve as a measure of the adjustable in principle from the rest position load: exceeds the static friction the load the force or torque reserve of the actuator, so the setting process is blocked. Particularly preferably, a warning signal is generated when falling below a minimum limit pressure reserve.

Furthermore, in the context of a diagnostic method according to the invention, an actuating pressure is advantageously determined for a setting process, wherein the setting pressure is the value of the pressure difference when an end position of the piston is reached. The set pressure defined in this way corresponds to the pressure required to complete the setting process - for example, to completely open or close a valve. An increase in the control pressure can indicate, on the one hand, wear of sealing and sliding surfaces of the actuator or of the set element and an increase in the sliding friction forces caused thereby. On the other hand, deposits on the actuator or on the provided element, which hinder the reaching of the end position - for example, in a fluid-technical system, a solids deposit of the fluid deposited on the valve seat - also result in an increase in the setting pressure. Again, it is particularly helpful if a warning signal is generated when a maximum limit pressure is exceeded.

If, instead of continuous monitoring of the pressure difference, only individual discrete values are to be measured for the diagnosis of an actuator, the measurement of the pressure reserve and the pressure difference or one of the two values is advisable. The measurement can then be triggered particularly simply by an electric pulse generator, for example each registers the beginning or the end of an (electrically conductive) contact between the pistons or between a piston and the housing end.

Both limits - limit pressure reserve and limit pressure - are typically largely freely selectable depending on the particular use of the actuator, but should always be selected with a surcharge to the adhesive or Gleitreibungskräften of the load to be placed, which absorbs fluctuations in these forces on the one hand, on the other hand wear Increasing the pressure difference during operation allows replacement of the actuator at plannable intervals.

Particularly in the case of large quantities, the pre-assembly of actuators lends itself to fixed set limit values. For special applications can also actuators be provided, which allow adjustment of a limit value directly on the actuator. Limit values can also be stored in the form of fixed numerical values in an external diagnostic device. The diagnostic device is then connected to the actuator via a pressure line or - necessarily, especially at longer distances between the actuator and the diagnostic device - via a data line for transmitting the current value of the pressure difference or even the pressure reserve and / or the control pressure.

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

The object is also achieved according to the invention starting from the known diagnostic device in that a differential pressure measuring element is provided with which the difference between a characteristic pressure, which is the static pressure component of a voltage applied in a working space, and a reference pressure, the static pressure component of the second working space applied pressure is when the second working space is not connected to the pressure supply system, can be measured and evaluated by means of the diagnostic device. Such a diagnostic device is used to carry out the above-described diagnostic method according to the invention. Also, the diagnostic device according to the invention can be used in conjunction with actuators, which are merged with the valve to be operated to form a structural unit.

The object is thus already achieved, starting from the known actuator according to the invention by two pressure measuring connections, where by means of a Differenzdruckmesselements a pressure difference can be measured.

A diagnostic device according to the invention preferably has a digital computing unit in which the comparison of the two characteristic pressures is carried out. Suitable electronic Computing units are well known and available in various designs as mass-produced inexpensively on the market. Basically, the use of analog pneumatic comparators is possible. However, apart from special cases, for example, exclude the use of electronic components, this variant is not preferred for cost reasons. On the one hand, the use of programmable electronic computing units makes it possible to use commercially available standard components; on the other hand, the diagnostic device according to the invention can be used for other purposes in a particularly favorable manner, namely by reprogramming instead of exchanging components. As a diagnostic device in the context of the invention, in particular, a commercial digital computer is to be considered, which is programmed for use in the aforementioned type.

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 with reference to schematic sketches of an 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 integrated with a diagnostic device according to the invention

Figure 1 shows a pneumatic actuator 1 according to the invention with rack-pinion principle and a closed cylindrical housing 2, two in this axially mounted and self-centering guided, counter-movable piston 3 and a radially emerging from the housing 2 rotatable output shaft 4. The rotation of the output shaft 4 is by two connected to the piston 3 racks 5, which are arranged axially in the housing 2 and engage in a not shown, arranged on the circumference of the output shaft 4 teeth, fixedly coupled to the axial movement of the piston 3. The two pistons 3 close in the housing 2, the inner working space 6, in which the racks 5 and the output shaft 4 extend. With the housing 2, the pistons 3 close the outer working spaces 7. In the outer working spaces 7 compression springs 8 are arranged, which push the pistons 3 at non-pressurized working spaces 6, 7 to each other.

The housing 2, the piston 3 and the racks 5 are made of an aluminum alloy by die casting. The outer surfaces are anodized and additionally coated with epoxy resin. The output shaft 4 is made of stainless steel and is provided for connection to the element to be set with a 2-flat, not shown. The working chambers 6, 7 are sealed to the piston 3 with not shown Nitrilkautschukdichtungen against each other.

The illustrated actuator 1 according to the invention has a nominal pivot angle of 120 °. The actuator 1 brings on the element to be positioned at a system pressure 9 of 10 bar a torque of up to 8000 Nm. The working medium is filtered air (PNEUROP / ISO Class 4).

The actuator 1 has two pressure ports 10, 11, which can be acted upon by means of a switching element 12 mutually with the working fluid or vented.

About the first pressure port 10, the inner working space 6, via the second pressure port 11, the outer working spaces 7 are acted upon. In the illustrated position, the inner working space 6 is acted upon by the first pressure port 10 with the working fluid, the outer working spaces 7 are connected via the second pressure port 11 with the environment and have ambient pressure. The compression springs 8 are block and thus define the end position of the piston. 3

As can be seen from FIG. 2, lower diagram, the pistons 3 are at the beginning 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 chambers 7 are acted upon by the working fluid and the inner working chamber 6 vented. The static pressure component of the pressure present in the outer working chambers 7 is applied to the pressure measuring connection 15 as the characteristic pressure, the static pressure component of the pressure present in the inner working chamber 6 is present at the reference pressure measuring connection 16 as a reference pressure. In a positioning process from 120 ° position 14 in the 0 ° position 13, the functions of pressure and reference pressure measuring port 16 are reversed, but the operation of the diagnosis described below is identical.

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

Figure 2 shows the course of the differential pressure 19 and the path 23 at this actuator 1 according to the invention during the adjustment process: At the beginning of the differential pressure corresponds to the amount 19 of the system pressure 8. In the normal position, the differential pressure 19 is defined negative. First, the amount of the differential pressure 19 drops to 0 (equal pressures on both sides of the piston 3) and then rises to a maximum pressure 24 below the system pressure 8 at. When concerns this maximum pressure 24, the force acting between the piston 3 and the housing 2 and in the connected element static friction is overcome, the piston 3 break loose. The difference between the maximum pressure 24 and the system pressure 8 is referred to as pressure reserve 25. The pistons 3 now move towards each other at a substantially constant speed. In this case, the differential pressure 19 drops to a lower, also substantially constant amount.

In the end position, the racks 5 are in contact with the respectively opposite piston 3. The movement of the piston 3 ends, the differential pressure 19 increases up to the system pressure 8 at. The pressure level when reaching the end position is referred to as control pressure 26.

Figure 3 shows the actuator 1 according to the invention integrated with a diagnostic device according to the invention 20. The diagnostic device 20 has a position indicator 27, which indicates the position of the output shaft 4. At the diagnostic device 20, not shown central electrical connections - a terminal block, an actuator-sensor connector and a bus connection - arranged. The position sensor 21 is arranged on the output shaft 4 electronic angle sensor, which also acts as a limit switch. In addition, the diagnostic device 20 has a non-illustrated self-adjusting inductive limit switch. By means of the diagnostic device 20, the differential pressure 19 and the swivel angle is monitored in the sense of a "Condition Monitoring" and, if appropriate, an alarm signal is generated on an alarm output 28 to a superordinate 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 workspace

7

Outer 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 (8)

1. A method for testing a pneumatic actuator (1), comprising at least one piston (3) which is movable in a housing (2) between two end positions and delimits two working chambers (6, 7), with the working chambers (6, 7) being connectable to a pressure supply system which is under a system pressure (8), with at least one position of the piston (3) in the housing (2) being recognized, characterized in that the difference between a characteristic pressure which is the static pressure share of the pressure applied in a working chamber (6, 7) and a reference pressure which is the static pressure share of the pressure applied in a second working chamber (6, 7) when the second working chamber (6, 7) is not connected to the pressure supply system is determined by means of a differential pressure measuring instrument and is compared with a setpoint value.
2. A method for testing according to the preceding claim, characterized in that a development of the pressure difference between two operating points of the actuator (1) is compared with a development of the setpoint value.
3. A method for testing according to one of the preceding claims, characterized in that a pressure reserve (25) is determined for a switching process, with the pressure reserve (25) being the difference between a maximum value of the pressure difference before breakaway of the piston (3) and the system pressure (8).
4. A method for testing according to the preceding claim, characterized in that a warning signal is generated when a minimum limit pressure reserve is fallen below.
5. A method for testing according to one of the preceding claims, characterized in that a set pressure (26) is determined for an actuating process, with the set pressure (26) being the value of the pressure difference upon reaching an end position of the piston (3).
6. A method for testing according to one of the preceding claims, characterized in that a warning signal is generated upon exceeding a maximum limit set pressure.
7. An apparatus (20) for testing, comprising a pneumatic actuator (1) having at least one piston (3) which is movable in a housing (2) between two end positions and delimits two working chambers (6, 7) which are connectable to a pressure supply system which is under a system pressure (8, with at least one position of the piston (3) in the housing (2) being representable by means of the apparatus (20) for testing, characterized in that a differential pressure measuring element is provided with which the difference is measurable between a characteristic pressure which is the static pressure share of a pressure applied in a working chamber (6, 7) and a reference pressure which is the static pressure share of the pressure applied in the second working chamber when the second working chamber is not connected with the pressure supply system, and can be evaluated by means of the apparatus (20) for testing.
8. An apparatus (20) for testing according to the preceding claim, characterized in that the apparatus (20) for testing comprises a digital computing unit.

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