DE102016200924B4 - Method and control device for determining a wear condition - Google Patents

Abstract

Method for determining a wear state of a fluidically driven working device (2) with two pressure chambers (4, 5) and a working member (6) which can be moved between a first and a second position by applying pressure to the pressure chambers (4, 5), comprising the steps : increasing (S2, S6) a pressure difference between the two pressure chambers (4, 5), detecting (S4, S8) a pressure value of one of the pressure chambers (4, 5) and/or a value derived therefrom when a change in position of the working member (6 ) is detected, and determining a wear state of the working device (2) according to the detected pressure value and/or the value derived therefrom, characterized in that increasing (S2, S6) the pressure difference and detecting (S4, S8) a pressure value and/or derived value is carried out at least twice in succession, at least one of the pressure chambers (4, 5) being pressurized the second time with a different pressure than the first time, so that two different pressure values and / or derived values are obtained and these pressure values and / or derived values are used as a basis for determining the state of wear.

Description

The invention relates to a method for determining a wear state of a fluidically driven working device with two pressure chambers and a working member which can be moved between a first and a second position by pressurizing the pressure chambers. The method includes the steps of: increasing a pressure difference between the two pressure chambers, detecting a pressure value of one of the pressure chambers and/or a value derived therefrom when a change in position of the working member is detected, and determining a wear state of the working device according to the detected pressure value and/or the value derived from it.

The invention further relates to a control device for a system comprising a fluid supply device with at least two working ports, at each of which a predetermined pressure can be set, a pressure sensor device for detecting the pressures present at the working ports, and a fluidically driven working device with two pressure chambers, each with are fluidly connected to the working connections, and a working member which can be moved between a first and a second position by pressurizing the pressure chambers, and a sensor device for detecting a change in position of the working member. The control device is designed to issue control commands to the fluid supply device, so that an increase in a pressure difference between the two pressure chambers is caused, and to detect a pressure signal from the pressure sensor device when a change in position of the working member is detected from a received sensor signal from the sensor device.

In the case of the working device mentioned, wear usually occurs after a certain period of use or after a certain number of position changes of the working member, which can impair the functionality of the working device.

In a working device designed as a pneumatic cylinder, wear can occur, for example, on a piston seal. As is known, a pneumatic cylinder includes a working chamber, often referred to as a cylinder bore, in which a piston with an associated piston seal is movably mounted. The piston seal is located between the piston and the inner wall of the working chamber and serves to divide the working chamber into two mutually sealed pressure chambers.

Friction occurs between the seal and the inner wall of the working chamber during operation. Over time, the seal and/or the inner wall of the working chamber wears out and abrasion occurs. The friction of the seal against the inner wall typically increases as seal wear progresses. At the end of the wear process, a leak ultimately occurs between the two pressure chambers.

According to the method mentioned at the beginning, a state of wear is determined depending on which pressure in a pressure chamber or which pressure difference between the pressure chambers is required in order to allow the working member to change position. For this determination of the state of wear, it is assumed in particular that the change in position of the working member occurs from a rest position or that the working member is set in motion from a rest position. The pressure at which the position of the working member changes is also referred to below as the breakaway pressure.

From the breakaway pressure or the corresponding pressure difference between the pressure chambers, it can be concluded how large the frictional force is that must be overcome in order to set the working member in motion. The greater the friction force to be overcome, the higher the required pressure or the required pressure difference at which a change in position takes place.

The size of the friction force is in turn an indication of whether wear is present. Thus, a state of wear can be determined simply by determining the frictional force or by determining a variable that is dependent on the frictional force or correlates with it. In particular, the determination of the frictional force or the breakaway pressure or the pressure difference already represents the determination of the state of wear.

Based on the determined friction force, the control of the working device can then be adjusted, for example, in order to compensate for the determined friction force or the increase in friction force caused by wear.

In particular, if the friction force or the aforementioned size exceeds a certain threshold value, it can be assumed that a certain state of wear has been reached. Preferably, the wear condition is determined based on a comparison of the detected pressure value and/or the value derived therefrom with a reference value.

For example, the pressure value or the pressure difference at which the position change occurred, or a value derived therefrom, is compared with a reference value. Based on the comparison, the wear condition can finally be determined.

This makes it easy and efficient to determine early on whether there is wear or not.

It is known from the prior art to determine the leakage of a working device. That's how it describes DE 103 55 250 A1 a leakage determination in a working device, wherein a leakage is determined by means of a detected pressure, a detected volume flow and an equation adapted to proper operation.

The DE 42 18 320 A1 describes how to test a valve during a switching process by measuring the pressure progression over time, deriving a function-specific quantity from the progression and comparing the function-specific quantity with a stored basic quantity. A pressure value can be used as a function-specific variable.

The DE 10 2010 060 550 A1 describes how to detect times at which a piston passes certain switching points in order to detect wear. Movement information is derived from the times, from which a degree of wear is determined.

The US 4,029,122 A describes a device and a method for indicating whether frictional forces in a position modulation valve are approaching a predetermined coefficient of friction. The pressure forces required to move a valve actuator predetermined distances to an open and a closed position are monitored.

The EP 1 812 718 B1 describes a diagnostic module for detecting changes in load and friction. Pressure values and force values are determined in a pressure build-up phase, a travel phase, and a travel phase in the opposite direction. The force values are compared with reference values for diagnosis.

It is an object of the invention to provide a method and a control device in order to be able to reliably determine a wear condition at an early stage in a working device of the type mentioned at the outset.

This task is solved using the features defined in the characterizing part of claim 1.

According to the invention, increasing the pressure difference and detecting a pressure value and/or derived value is carried out at least twice in succession, with at least one of the pressure chambers being subjected to a different pressure, in particular a different counterpressure, the second time than the first time, so that two different pressure values and/or derived values are obtained and these pressure values and/or derived values are used as the basis for determining the state of wear.

For example, one of the pressure chambers is first set to a first pressure and the pressure difference between the pressure chambers is increased until movement of the working member is detected. The pressure value of the other pressure chamber at which the movement of the working member occurred is recorded as the first pressure value.

Subsequently, a pressure chamber, preferably the same pressure chamber that was previously set to the first pressure, is set to a second pressure that is different from the first pressure, and the pressure difference between the pressure chambers is increased again until movement of the working member is detected. This time too, it is recorded at which pressure value in the other pressure chamber the working member begins to move. This pressure value is then recorded as a second pressure value.

By now using the first and second pressure values and/or values derived therefrom to determine the state of wear, the reliability of the determination can be increased.

The method described is particularly simple and efficient because the sensors required to carry out this method are already present in many fluidically driven systems. This means that the method according to the invention can be used in these systems without additional sensors having to be provided for this purpose.

A further advantage of the method according to the invention is that the state of wear can be detected at an early stage, in particular before leakage occurs. A lot of abrasion is usually generated before the leak occurs and it is possible that the functionality of the system is already impaired at this point. The abrasion can, for example, contaminate a valve associated with the working device and lead to increased wear there. Furthermore, the abrasion can lead to contamination of the environment. With the method according to the invention, the state of wear can be detected at an early stage. This makes it possible to prevent the contamination mentioned by taking appropriate action, such as maintenance or replacement of the working device.

The working device for which the state of wear is determined is, in particular, a working device which has a working chamber in which the working member is movably mounted. Preferably, a seal is provided between the working member and an inner wall of the working chamber, which divides the working chamber into the two pressure chambers. The friction force described then arises in particular from friction between the seal and the inner wall of the working chamber. The seal is designed, for example, as a sealing lip.

In particular, the working device is a pneumatic device, such as a double-acting pneumatic cylinder.

The pressure difference between the two pressure chambers can be increased in various ways. For example, the pressure of one of the two pressure chambers can be set to a fixed value, and the pressure in the other pressure chamber can be increased from a pressure below the fixed value or decreased from a pressure above the fixed value. The increase or decrease can take place continuously or gradually.

In the simplest variant, one of the pressure chambers is not pressurized or is switched to a venting state, so that, for example, an ambient pressure is present there. Subsequently, the pressure in the other pressure chamber is increased from a venting state.

The mentioned derived value, which is derived from the detected pressure value, is, for example, the pressure difference that exists between the two pressure chambers when a position change occurs. The wear condition can be determined based on the pressure value and/or the pressure difference.

The reference value is, for example, a value determined and stored in advance. The reference value can in particular represent a threshold value. If the pressure value and/or the derived value exceeds this threshold value, it can be assumed that wear is present.

Advantageous developments of the invention are the subject of the subclaims.

When increasing the pressure difference, one of the pressure chambers is preferably subjected to a predeterminable pressure and the pressure of the other pressure chamber is increased or decreased.

The predeterminable pressure is preferably a constant pressure. Alternatively, it can be provided that the predeterminable pressure is variable over time, with a rate of change for a change in this pressure expediently being smaller than a rate of change of the pressure increase or decrease in the other pressure chamber. The predeterminable pressure is expediently provided by means of a fluid supply device, for example a valve arrangement, with which pressure control and/or regulation can be implemented.

This means that when the pressure difference increases, both pressure chambers are pressurized. In particular, both pressure chambers are subjected to pressures that are higher than an ambient pressure that prevails in an environment of the working device, in particular higher than atmospheric pressure. The predeterminable pressure that is present in one pressure chamber and against which the position change should take place is also referred to below as counterpressure.

The procedure described achieves the particular advantage that a higher pressure is required to set the working member in motion, since not only the frictional force but also the force resulting from the counterpressure must be overcome. This means that larger pressures can be used to determine the state of wear, which may be advantageous if the system is not able to provide or accurately detect smaller pressures.

The procedure described is also advantageous for another reason. The working device mentioned can be designed in such a way that an existing counterpressure also increases the frictional force to be overcome. This can be due, for example, to the fact that the pressure in the pressure chambers acts on an element that causes the frictional force, such as a seal, and presses it against a corresponding running surface, such as the inner wall of a working chamber. Due to this effect, the frictional force, which acts as an indication of wear, increases as the counterpressure increases. Accordingly, the pressure or pressure required to change the position is also determined Pressure difference is larger and can therefore be recorded better.

The described increase in the pressure difference when both pressure chambers are pressurized can be done in various ways.

For example, a first pressure chamber can be pressurized with a fixed pressure p1 and the pressure p2 can be increased in a second pressure chamber. In this way, the pressure difference p2-p1 can be increased in order to ultimately achieve a pressure difference at which the position of the working member changes in the direction of the first pressure chamber.

Alternatively, the second pressure chamber can be pressurized with a fixed pressure p2 and the pressure p1 in the first pressure chamber can be reduced. In this case too, the pressure difference p2-p1 is increased so that a change in position can ultimately be effected.

In particular, a pressure relationship is obtained from the two pressure values and this pressure relationship is used as the basis for determining the state of wear.

With this measure, forces that additionally act on the working member but are not caused by wear on a seal can be effectively eliminated.

For example, these forces can be weight forces from work loads coupled to the working member. By forming a pressure relationship, these forces can be eliminated so that they do not influence the determination of the wear condition.

As a rule, the strength of the frictional force depends on the pressures applied to the pressure chambers. In contrast, the additional forces mentioned are independent of the pressures applied. Therefore, it is possible to relate the two pressure values to one another in such a way that the components attributable to the pressure-independent forces cancel each other out.

The steps of the method are expediently carried out in an installed and preferably loaded state of the working device.

As described above, when determining two pressure values, the friction force - and thus the state of wear - can be determined independently of the other forces acting on the working member. This makes it possible in particular to carry out the described determination of the state of wear even if the working device to be tested is installed in an operating environment in which the working member is possibly coupled to a work load and can be loaded with weight forces, for example.

The working device is preferably a double-acting cylinder, in particular a pneumatic cylinder.

The cylinder expediently comprises a working chamber in which the working member is guided in a linearly movable manner. The working member divides the working chamber into the two pressure chambers. In order to seal the two pressure chambers from one another, there is a seal, in particular arranged on the piston, between the working member, which in this case is also referred to as a piston, and the inner wall of the working chamber. The described determination of the state of wear relates in particular to the condition of this seal and the condition of the inner wall of the working chamber. Alternatively or additionally, the described determination of the state of wear can also relate to other sealing or friction points, such as a cylinder seal which is provided between a piston rod and an outlet opening for the piston rod and which serves to seal the working chamber of the cylinder to the outside.

Preferably, the working member is a piston which has a piston rod on one side.

In this case, the pressure chambers can in particular be pressurized in such a way that when the position changes, the piston moves in a direction in which the piston rod retracts.

Due to the piston rod, there is less surface area on one side of the piston on which the pressure of the respective pressure chamber can act than on the other side of the piston. This means that only the area not occupied by the piston rod effectively acts on the piston rod side. Accordingly, a higher pressure or a larger pressure difference must be applied in order to cause a change in the position of the piston. This makes the measurement more sensitive.

According to a preferred embodiment, when a change in position is detected, the pressurization of the pressure chambers is switched and/or switched off, so that the working member comes to a standstill and/or is moved to a predetermined position, preferably a previous position.

In this way, the working member is only moved minimally when determining the state of wear, that is, the determination of the state of wear takes place quasi-statically and can, under certain circumstances, also be carried out while the working device is in operation.

The predetermined or previous position can be a position that the working member held before the determination of the state of wear was carried out. For example, this is an end position.

The above-mentioned task is also achieved for a control device of the type mentioned at the outset by means of the features defined in the characterizing part of claim 10. According to the invention, the control device is designed to issue control commands to the fluid supply device, so that an increase in a pressure difference between the two pressure chambers is caused, to detect a pressure signal from the pressure sensor device when a change in position of the working member is detected from a received sensor signal by the sensor device, and one Determine the state of wear of the working device according to the detected pressure signal and/or a value derived therefrom.

According to advantageous developments, the control device is designed to implement one or more of the above-described embodiments of the method according to the invention.

According to one embodiment, the control device is designed to determine a frictional force when determining the state of wear and to adapt a control of the working device according to the determined frictional force. In particular, the control device is designed to adapt the control of the working device in such a way that an increased frictional force that acts on the working member of the working device due to a state of wear is compensated for by the adapted control.

The above-mentioned task is also achieved for a method of the type mentioned at the outset by means of the features defined in the characterizing part of claim 12. According to the invention, the method comprises the steps: setting a pressure difference between the two pressure chambers, detecting a time period that the working member requires to move from a first position to a second position and/or a value derived therefrom, and determining a wear state of the working device according to the time period recorded and/or the value derived therefrom.

From the recorded time period it can be concluded how great the frictional force is that must be overcome in order to move the working member from the first position to the second position. The greater the friction force to be overcome, the longer the time period recorded.

The size of the friction force is in turn an indication of whether wear is present. By determining the friction force or the time period, a state of wear can be determined. In particular, the determination of the friction force or the time period already represents the determination of the state of wear.

The first and second positions are preferably the two end positions of the working member. The working member is moved to the first position, for example, before the pressure difference is set. The two pressure chambers are then subjected to the pressure difference at least until the working member has moved into the second position.

According to one embodiment, when setting the pressure difference, both pressure chambers are subjected to predeterminable pressures.

In particular, both pressure chambers are subjected to pressures that are higher than an ambient pressure that prevails in an environment of the working device, in particular higher than atmospheric pressure.

The procedure described is particularly advantageous for the reason explained below. The working device mentioned can be designed in such a way that the pressures present in the pressure chambers increase the frictional force to be overcome. This can be due, for example, to the fact that the pressures in the pressure chambers act on an element that causes the frictional force, such as a seal, and press it against a corresponding running surface, such as the inner wall of a working chamber. Due to this effect, the friction force, which acts as an indication of wear, increases as pressure increases. Accordingly, the time period required to move the working member from the first position to the second position also increases and can therefore be better recorded.

According to a further embodiment, the setting of the pressure difference and detection of a time period and/or a derived value is carried out at least twice in succession, with at least a first pressure chamber being pressurized the second time with a different pressure than the first time, so that several time periods and/or derived values are obtained and the time periods and/or derived values are used as a basis for determining the state of wear.

For example, the working member is first moved into a first position, preferably a first end position. A first pressure chamber is subjected to a first pressure. The pressure difference is then adjusted by applying a second pressure to a second pressure chamber, preferably a pressure that is greater than the first pressure. The working member then moves into the second position, preferably a second end position. The time period required for the working member to move from the first position to the second position is recorded. The working member is then moved back to the first position. The first pressure chamber is pressurized with a third pressure that differs from the first pressure. A pressure difference is set by applying a fourth pressure to the second pressure chamber. The fourth print is preferably different from the second print. The working member moves again to the second position and the time period that the working member needs to do this is recorded. A wear condition is determined based on the two time periods. A frictional force, for example, can be determined as a state of wear.

According to a further embodiment, setting the pressure difference and detecting a time period is repeated until a detected time period equals the time period that was detected the first time, with the pressure with which the second pressure chamber is applied every time from the second time onwards is varied.

For example, the working member is first moved into a first position, preferably a first end position. A first pressure chamber is subjected to a first pressure. The pressure difference is then adjusted by applying a second pressure to a second pressure chamber, preferably a pressure that is greater than the first pressure. The working member then moves into the second position, preferably a second end position. The time period required for the working member to move from the first position to the second position is recorded as the first time period. The working member is then moved back to the first position. The first pressure chamber is pressurized with a third pressure that differs from the first pressure. A pressure difference is set by applying a fourth pressure to the second pressure chamber. The fourth print is preferably different from the second print. The working member moves again to the second position and the time period that the working member needs to do this is recorded as the second time period.

Now a comparison is made between the first and second time periods. If the two time periods are essentially the same, the fourth pressure is used as an indicator of the state of wear.

If the two time periods differ, the pressure in the second pressure chamber is varied until a time period is recorded that is equal to the first time period. For this purpose, the working member is moved again into the first position, the first pressure chamber is subjected to the third pressure and a pressure difference is set between the two pressure chambers, this time the second pressure chamber being subjected to a different pressure than the previous time. The time period is recorded again and compared with the first time period. Varying the pressure of the second pressure chamber and detecting a time period is repeated until a detected time period equals the first time period. The pressure of the second pressure chamber at which this time period was achieved is then used as an indicator of the wear condition.

• 1 ein Flussdiagramm eines Verfahrens zur Bestimmung eines Verschleißzustandes gemäß einem technischen Beispiel;
• 2 ein Flussdiagramm eines Verfahrens zur Bestimmung eines Verschleißzustandes gemäß einer Ausführungsform;
• 3 eine schematische Darstellung eines Systems umfassend eine Steuerungseinrichtung, eine Fluidversorgungseinrichtung und eine Arbeitsvorrichtung;
• 4 ein schematisches Schaubild, in dem verschiedene Losbrechdrücke und Gegendrücke zueinander in Beziehung gesetzt sind;

Exemplary embodiments of the invention are explained below with reference to the drawing. This shows

• 1 a flowchart of a method for determining a wear condition according to a technical example;
• 2 a flowchart of a method for determining a wear condition according to an embodiment;
• 3 a schematic representation of a system comprising a control device, a fluid supply device and a working device;
• 4 a schematic diagram in which various breakaway pressures and counterpressures are related to one another;

In the following description of the figures, the same designations are used for functionally identical components, with no multiple description of functionally identical components.

The 1 shows a technical example of a method for determining a wear condition. The 2 shows an embodiment of a method according to the invention for determining a wear condition. The 3 shows an exemplary system in which the in the 1 and 2 The procedures shown can be carried out.

For a better understanding, the following should first be explained in the 3 system shown can be purified.

That in the 3 The system shown includes a control device 1, a working device 2 and a fluid supply device 3.

The control device 1 is communicatively connected to both the fluid supply device 3 and the working device 2. In particular, the control device 1 is connected to a communication interface 18 of the fluid supply device 3 via a communication interface 17 and a communication connection 15. The control device 1 can send control commands to the fluid supply device 3 via the communication connection 15.

The control device 1 is further connected to the working device 2 via a communication interface 17 and a communication connection 16. In particular, the control device 1 is communicatively connected to a sensor device 14 of the working device. The control device 1 can, for example, receive sensor signals from the sensor device 14 via the communication connection 16.

The control device 1 can, as shown, be designed as an independent unit. Alternatively, the control device 1 can be designed as an additional hardware module of another control unit. The control device does not necessarily have to be physically separate from the fluid supply device 3 or the working device 2, as shown, but can instead be arranged in the same housing as the fluid supply device 3 or the working device 2.

The fluid supply device 3 is designed in particular as a valve arrangement and is connected to a fluid supply line 11 and a fluid discharge line 12 via fluid connections 25. In a pneumatic configuration of the system shown, the supply line 11 is a ventilation line and the discharge line 12 is a ventilation line.

The fluid supply device 3 is designed to provide certain pressures at its working ports 21 and 22 in response to one or more control commands from the control device 1. For this purpose, the fluid supply device 3 is designed, for example, to carry out pressure control and/or regulation.

The fluid supply device 3 includes a pressure sensor device 13 with which the pressures present at the working ports 21 and 22 can be detected. The fluid supply device 3 is designed to transmit the detected pressures and/or values derived therefrom to the control device 1.

The working connections 21 and 22 are connected to respective consumer connections 23 and 24 of the working device 2 via fluid connections 19 and 20.

In the example shown, the working device 2 is designed as a double-acting piston rod cylinder. The working device 2 includes a cylindrical working chamber 26, in which a working member 6 designed as a piston 8 is movably guided. The piston 8 has a piston rod 7 on one side, which passes through the working chamber at the end and can be coupled to a system component, not shown, which is to be set in motion by the working device 2. On the piston 8 there is a seal 9 which seals and slides against the inner wall 27 of the working chamber 26 and divides the working chamber 26 into a first pressure chamber 4 and a second pressure chamber 5. By way of example, it is provided that the working chamber 26, the piston 8 and the piston rod 7 are made of metallic materials and that the seal 9 is made of a plastic material, in particular a rubber-elastic material.

The first pressure chamber 4 can be subjected to a certain pressure by the fluid supply device 3 via the consumer connection 21, the fluid connection 19 and the working connection 23. Furthermore, the second pressure chamber 5 can be subjected to a certain pressure by the fluid supply device 3 via the consumer connection 22, the fluid connection 20 and the working connection 24.

Depending on the pressures present in the pressure chambers 4 and 5, the working member 6 moves within the working chamber 26. The arrow provided with the reference number 10 points in the 3 a possible movement path of the working member 6.

The sensor devices 14 are in particular designed as limit switches and can thus detect whether the working member 6 is in one of its two end positions in the working chamber 26. The sensor devices designed as limit switches are preferably set up to detect at least a certain range of movement, for example a few millimeters of the movement path , of the working member. Alternatively or additionally, the sensor device 14 can also be designed as a position sensor system in order to for example, to be able to detect any positions of the working member 6 along the entire movement path 10. The sensor device 14 expediently outputs or provides sensor signals from which a change in position of the working member 6 can be concluded.

Alternatively or additionally, it is possible for a sensor device to be used to detect a change in position of the working member 6, which is based on the pressure sensor device 13 described above. As a rule, when the position of the working member changes, there is an at least temporary change in pressure in one or both pressure chambers 4 and 5. By means of appropriate signal processing of pressure values that are detected by the pressure sensor device 13, it is possible to detect this pressure change and to respond to it Change in position of the working member 6 to close. The pressure sensor device 13 with corresponding signal processing can therefore also be used as a sensor device for detecting the change in position. When using the pressure sensor device 13 as a sensor device for detecting the change in position, the sensor device 14 described above can be dispensed with.

According to the invention, the control device 1 is designed to determine a wear condition of the working device 2. For this purpose, the control device 1 is designed to issue control commands to the fluid supply device 3, so that an increase in a pressure difference between the two pressure chambers 4, 5 is caused. Furthermore, the control device 1 is designed to detect a pressure signal from the pressure sensor device 13 when a change in position of the working member 6 is detected from a received sensor signal from the sensor device 14. As already described above, the pressure sensor device 13 can serve as the sensor device for detecting the change in position, so that the change in position is detected by the pressure sensor device 13 on the basis of pressure values. The control device 1 can accordingly be designed to detect or record a specific pressure value if the pressure values indicate that a change in position has occurred. Finally, the control device 1 is designed to determine a wear state of the working device 2 according to the detected pressure signal and/or a value derived therefrom.

Preferably, the control device is designed to determine the state of wear based on a comparison of the detected pressure signal and/or a value derived therefrom with a stored reference value.

In this way, in particular, a wear condition can be determined that influences how much pressure is required to set the working member 6 in motion. In particular, this involves wear of the friction points between the seal 9 and the inner wall 27 of the working chamber 26 of the working device 2. When worn, the frictional forces increase, so that a correspondingly higher force and thus also a correspondingly higher pressure are required to actuate the working member 6 is needed.

In particular, the control unit 1 is designed to adapt the control of the working device based on the determined state of wear or the determined frictional force in order to compensate for the determined frictional force or the increase in the frictional force caused by the wear.

The following are with reference to the 1 and 2 exemplary methods are described with which a wear condition of a working device can be determined.

These procedures can be used in particular in the 3 System 30 shown and explained above can be used. In particular, the control device 1 can be designed to carry out one or both of these methods.

Although the methods described below are described in the context of the system 30, they are not limited thereto. The methods described below can also be used in other systems that enable pressure control and/or regulation of the pressure chambers as well as detection, in particular direct or indirect detection, of a change in position of the working member.

That in the 1 The method shown begins with step S2, in which a pressure difference between the two pressure chambers 4 and 5 is increased.

In the system of 3 This can be done, for example, by the control device 1 giving a corresponding command to the fluid supply device 3. The fluid supply device 3 then increases, for example, the pressure of its working connection 23, while the working connection 24 is vented or is subjected to a constant pressure.

It is preferably ensured beforehand that the working member 6 is in a position in which a movement of the working member 6 is possible by means of an increase in the pressure difference, which can be detected by the sensor device 14. Special It is preferably provided that the working member 6 is positioned in one of the two end positions. By way of example, it is assumed that the working member 6 stands still before the pressure difference increases.

In the example shown the 3 the working member 6 is, for example, in a first end position in which the piston rod 7 is retracted and the piston 8 rests on the sensor device 14 designed as a limit switch. In this end position, the volume of the first pressure chamber 4 is minimal and the volume of the second pressure chamber 5 is maximum. The pressure difference is now increased, for example by setting the pressure of the second pressure chamber 5 to a fixed value and increasing the pressure of the first pressure chamber 4. The second pressure chamber 5 can expediently be switched to a venting state and the first pressure chamber 4 can be subjected to an increasing pressure starting from a venting state.

In step S3 it is checked whether a change in position of the working member 6 is detected.

In the system 30 the 3 the control device 1 is designed to detect sensor signals from the working device 2 and to determine on the basis of the received sensor signals that a change in position of the working member 6 has occurred.

If the piston 6, as in the 3 shown, is in the first end position before the increase in the pressure difference or is moved into this, the change in position is detected when the control device 1 receives the signal that the working member 6 is no longer in the first end position.

As long as there is no change in position, step S2 - i.e. increasing the pressure difference between the two pressure chambers 4 and 5 - continues.

If a change in position is finally detected in step S3, a pressure value and/or a derived value is detected in step S4.

In the system 30 of 3 the control device 1 is designed to receive pressure values from the fluid supply device 3 and to detect a current pressure value and/or a value derived therefrom when detecting a change in position. Preferably, the pressure of the first pressure chamber 4 at which or to which the position change of the working member 6 took place is recorded. Alternatively or in addition, a value derived from this can also be recorded. The derived value can be, for example, the pressure difference between the pressures of the two working connections 23 and 24 at which the change in position of the working member 6 took place.

Finally, in step S4, the state of wear of the working device 2 is determined. For this purpose, the control device 1 is designed, for example, to compare the recorded pressure value and/or the value derived therefrom with a stored reference value. The stored reference value can in particular be based on a pressure value or a value derived therefrom, which was determined in a proper state - that is, in a state in which there is no wear. The reference value can be determined, for example, by carrying out steps S2, S3 and S4 when the working device 2 is in a proper state. Alternatively, the reference value can also be determined empirically or analytically and stored in advance in the control device 1.

The reference value can in particular be a threshold value. The threshold value can be formed by forming a multiple of a value representing a normal state or by adding an offset value to such a value.

If the determined pressure value or the value derived therefrom exceeds the reference value or the threshold value, it can be concluded that a state of wear is present. Corresponding information can be stored in the control device 1 and/or reported to a higher-level controller.

According to a variation of the 1 In the method shown, both pressure chambers 4 and 5 are pressurized when the pressure difference is increased. In particular, both pressure chambers 4 and 5 are subjected to pressures that are higher than atmospheric pressure.

For example, the second pressure chamber 5 is first subjected to a fixed pressure and then, subsequently, the pressure in the first pressure chamber 4 is increased. Preferably, the first pressure chamber 4 starts with a pressure that is below or above the pressure of the second pressure chamber 5 or equal to it.

Alternatively, it is also possible to apply a fixed pressure to the first pressure chamber 4 and, starting from a pressure that is preferably greater, in the second pressure chamber 5. is less than or equal to the pressure of the first pressure chamber 4 to lower the pressure of the second pressure chamber 5.

In both ways, the pressure difference is increased, which results from subtracting the pressure of the second pressure chamber 5 from the pressure of the first pressure chamber 4.

The control device 1 is in particular designed to send corresponding control commands to the fluid supply device 3 in order to bring about the described increase in the pressure difference.

In the methods described above, the working member 6 is extended. Alternatively, it is also possible to carry out the method in such a way that the working member 6 is retracted. The control device 1 can be designed to send control commands to the fluid supply device 3 in order to cause the pressure chambers 4 and 5 to be subjected to a pressure difference which causes a change in the position of the working member 6 in the retraction direction.

In the 2 A second method is shown with which a state of wear of the working device 2 can be determined. As in the variation of the method described above 1 are also used in the process 2 both pressure chambers are pressurized.

The method begins with step S1, in which a pressure chamber, for example the second pressure chamber 5 3 , is applied with a first pressure. This pressure is also referred to below as the first counterpressure pg1.

Subsequently, as already explained above, the pressure difference between the two pressure chambers 4 and 5 is increased in step S2.

Steps S3 and S4 are, as already mentioned above in connection with 1 explained, carried out. In step S4, in particular a pressure of the first pressure chamber 4 is recorded as a pressure value, at which a change in the position of the working member 6 takes place. This pressure is also referred to below as the first breakaway pressure pl11.

Following step S4, step S5 is carried out, in which one of the pressure chambers is subjected to a second pressure. Preferably, the second pressure chamber 5 is pressurized again, namely a second pressure that differs from the first pressure. This second pressure is also referred to below as the second counterpressure pg2.

In steps S6 and S7, the pressure difference between the two pressure chambers 4 and 5 is then increased again until a change in position of the working member 6 is detected.

In particular, the control device 1 is designed to issue corresponding control commands to the fluid supply device 3.

In step S8, a second pressure value and/or second derived value is recorded. Preferably, the pressure in the first pressure chamber 4 or the pressure difference at which the position change takes place is recorded as a second pressure value or second derived value. This is preferably done by the control device 1. The second pressure value is also referred to below as the second breakaway pressure pl12.

In step S9, the state of wear of the working device 2 is finally determined taking into account the two pressure values or the two derived values. For this purpose, a pressure relationship is first determined from the two pressure values or derived values.

wobei Δpl die Differenz der bei zwei verschiedenen Gegendrücken aufgenommenen Losbrechdrücke bezeichnet und Δpg die Differenz der beiden Gegendrücke bezeichnet.For example, the following size DB is determined as the pressure relationship: $$\text{DB}=\left(\Delta \text{pl}-\Delta \text{pg}\right)/\Delta \text{pg}$$

where Δpl denotes the difference between the breakaway pressures recorded at two different counterpressures and Δpg denotes the difference between the two counterpressures.

Applied to the case described above, in which the breakaway pressures pl11 and pl12 were determined at the counter pressures pg1 and pg2, the following pressure relationship results: $$\text{DB}=\left(\left(\text{pl12}-\text{pl11}\right)-\left(\text{<figure-callout id="2" label="pg" filenames="DE102016200924B4\_0005.png" state="{{state}}">pg</figure-callout>}2-\text{pg1}\right)\right)/\left(\text{pg2-pg1}\right)$$

This variable can now be used as a basis for determining the state of wear, for example by comparing it with a corresponding reference value or a reference pressure relationship.

The advantage of this approach will be discussed below with reference to 4 be explained.

The 4 shows a diagram in which various breakaway pressures pl11, p112, p121, p122, p131 and pl32 are recorded as examples in each of which a change in the position of a working member 6 has taken place.

The counter pressure mentioned above is recorded on the x-axis of the diagram. This counterpressure represents, in particular, the pressure that is set in the second pressure chamber 5 when determining the state of wear.

The breakaway pressure is recorded on the y-axis of the diagram - that is, the pressure in a first pressure chamber 4 at which a change in position of a working member 6 occurs.

The breakaway pressures pl11 and pl12 illustrate a first case in which there is no wear and the working member 6 is not loaded. In this first case, a change in position of the working member 6 is essentially only opposed by normal frictional forces and the counterpressure of the second pressure chamber 5.

The breakaway pressures pl21 and pl22 illustrate a second case in which there is also no wear. In contrast to the first case, however, the working link 6 is loaded here. For example, a work load is coupled to the working member 6 and the weight of the work load acts on the working member 6, so that higher breakaway pressures are required to change the position than in the first case discussed above.

The breakaway pressures pl31 and pl32 illustrate a third case. In this case, the working member 6 is unloaded, but there is now wear. Accordingly, the breakaway pressures are also increased compared to the first case.

As can be seen from the case studies described and the 4 As can be seen, an increase in the breakaway pressures can result from both a load on the working member 6 and wear. If the load on the working member is not known, only one breakaway pressure can be recorded with only one counterpressure (as is the case, for example, according to the method of 1 can be done) it cannot be distinguished whether an increased breakaway pressure is due to an increased work load or to wear.

For this reason, it is advantageous to record two breakaway pressures at two different counterpressures and to use these two breakaway pressures as the basis for determining the state of wear.

Again 4 can be easily removed, recording two different breakaway pressures makes it possible to distinguish wear from pure workload. While under a pure work load the breakaway pressures increase by almost the same amount regardless of the counterpressure, in the case of wear the increase in the breakaway pressures depends on the counterpressure.

In the 4 This can be seen from the fact that the vertical distances between pl21 and pl11 or pl22 and pl12 are the same, while the vertical distance between pl32 and pl12 is greater than the vertical distance between pl31 and pl11. You put it like in the 4 indicated by the dotted lines, respective straight lines through the measuring points of the different cases, the difference between wear and a pure work load can also be recognized by the fact that in the former there is a change in the slope of the line, while in the latter the slope of the line remains essentially constant.

This different behavior is due to the fact that an applied counter pressure usually increases the wear-dependent friction of the working member. In the working device 2 the 3 The counterpressure applied acts, for example, on the seal 9 and thus increases the wear-dependent frictional force acting on the working member 6. The wear-dependent friction force is therefore dependent on the counterpressure applied.

In contrast, the work load acting on the working member 6 is independent of the counterpressure applied.

The breakaway pressures recorded therefore essentially consist of a backpressure-dependent component and a backpressure-independent component, whereby wear can usually only be determined from the former.

By now recording two breakaway pressures at two different counterpressures, the counterpressure-independent component can be calculated out. As already explained above, this can be done in particular by determining the pressure relationship DB.

In this way, disruptive influences of a work load acting on the working member 6 can be effectively and efficiently compensated for, so that the accuracy of the wear determination can be increased.

The control device 1 is expediently designed to calculate a corresponding pressure relationship and to use this as a basis for determining the state of wear.

According to a variation of the methods described above, the working member 6 is moved to a second end position after a change in position is detected and the time period required for this is recorded. This time period is also dependent on the wear of the working device 2 and can therefore be used as a basis for determining the state of wear in addition to or as an alternative to the pressure values described above. Preferably, two different time periods at two different counterpressures are recorded and used as a basis for determining the state of wear.

Claims (13)

Method for determining a wear state of a fluidically driven working device (2) with two pressure chambers (4, 5) and a working member (6) which can be moved between a first and a second position by applying pressure to the pressure chambers (4, 5), comprising the steps : increasing (S2, S6) a pressure difference between the two pressure chambers (4, 5), detecting (S4, S8) a pressure value of one of the pressure chambers (4, 5) and/or a value derived therefrom when a change in position of the working member (6 ) is detected, and determining a wear state of the working device (2) according to the detected pressure value and / or the value derived therefrom, characterized in that increasing (S2, S6) the pressure difference and detecting (S4, S8) a pressure value and / or derived value is carried out at least twice in succession, at least one of the pressure chambers (4, 5) being pressurized the second time with a different pressure than the first time, so that two different pressure values and / or derived values are obtained and these pressure values and / or derived values are used as a basis for determining the state of wear. Procedure according to Claim 1 , characterized in that when increasing (S2, S6) the pressure difference, one of the pressure chambers (4, 5) is subjected to a predeterminable pressure and the pressure of the other pressure chamber (4, 5) is increased or decreased. Procedure according to Claim 1 or 2 , characterized in that a pressure relationship is obtained from the two pressure values and this pressure relationship is used as the basis for determining the state of wear. Method according to one of the preceding claims, characterized in that the steps of the method take place in an installed and preferably loaded state of the working device (2). Method according to one of the preceding claims, characterized in that the working device (2) is a double-acting cylinder. Method according to one of the preceding claims, characterized in that the working member (6) is a piston (8) and preferably has a piston rod (7) on one side of the piston (8). Procedure according to Claim 6 , characterized in that the chambers (4, 5) are pressurized in such a way that when the position changes, the piston (8) moves in a direction in which the piston rod (7) retracts. Method according to one of the preceding claims, characterized in that when a change in position is detected (S4, S8), the pressurization of the pressure chambers (4, 5) is switched and/or switched off, so that the working member (6) comes to a standstill and/or is moved to a predetermined position, preferably a previous position. Control device (1) for a system (30) comprising a fluid supply device (3) with at least two working ports (23, 24), at each of which a predetermined pressure can be set, a pressure sensor device (13) for detecting the pressure at the working ports (23, 24) applied pressures, and a fluidically driven working device (2) with two pressure chambers (4, 5), which are each fluidly connected to the working connections (23, 24), and a working member (6) which is activated by pressurizing the pressure chambers (4 , 5) can be moved between a first and a second position, and a sensor device (14) for detecting a change in position of the working member (6), the control device (1) being designed to issue control commands to the fluid supply device (3), so that a Increasing a pressure difference between the two pressure chambers (4, 5) and detecting a pressure signal from the pressure sensor device when a change in position of the working member (6) is detected from a received sensor signal from the sensor device (14), wherein increasing the pressure difference and Detecting the pressure signal is carried out at least twice in succession, with at least one of the pressure chambers (4, 5) being subjected to a different pressure the second time than the first time, so that two different pressure signals are obtained, and a state of wear of the working device (2) according to the recorded pressure signals and/or values derived therefrom. Control device (11). Claim 9 , characterized in that the control device (11) is designed to determine a frictional force when determining the state of wear and to adapt a control of the working device (2) according to the determined frictional force. Method for determining a wear state of a fluidically driven working device (2) with two pressure chambers (4, 5) and a working member (6) which can be moved between a first and a second position by applying pressure to the pressure chambers (4, 5), comprising the steps : Setting a pressure difference between the two pressure chambers, detecting a time period that the working member (6) requires to move from a first position to a second position and/or a value derived therefrom, and determining a wear condition of the working device (2) according to the detected time period and/or the value derived therefrom, characterized in that the setting of the pressure difference and detection of a time period and/or a derived value is carried out at least twice in succession, with at least a first pressure chamber being pressurized the second time with a different pressure than the first time, so that multiple time periods and/or derived values are obtained and the time periods and/or derived values are used as the basis for determining the state of wear. Procedure according to Claim 11 , characterized in that when setting the pressure difference, both pressure chambers (4, 5) are subjected to predeterminable pressures. Procedure according to Claim 11 or 12 , characterized in that the setting of the pressure difference and detection of a time period is repeated until a detected time period equals the time period that was detected the first time, from the second time onwards the pressure with which the second pressure chamber is applied each time Sometimes it varies.

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