Method and device for detecting the position of a piston

Abstract

The invention relates to a method and a device for detecting an undesired position of a piston (12) adjustable in an interior (10) of a housing, which divides the interior into a fluid-filled first pressure chamber (18) and a fluid-filled second pressure chamber (20), wherein the first pressure chamber is connected to a fluid-carrying first line (22) and the second pressure chamber is connected to a fluid-carrying second line (24). The first pressure chamber (18) is connected to the second pressure chamber (20) via a bypass (30) in which a valve (32) is arranged.

Description

[0001] The invention relates to a device for detecting an undesired position of a piston adjustable in the interior of a housing, which divides the interior into a fluid-filled first pressure chamber and a fluid-filled second pressure chamber, wherein the first pressure chamber is connected to a fluid-carrying first line and the second pressure chamber is connected to a fluid-carrying second line, wherein, to adjust the piston, fluid can be supplied to the pressure chamber connected to it via one of the lines and fluid can flow out of the other pressure chamber via the line connected to it.

[0002] In particular, the device relates to a pressure cylinder or a clamping device, preferably a swivel clamp, with a piston to detect the position of the piston, from which a piston rod with a clamping element such as a clamping iron extends. The piston is actuated by a pressure medium and is displaceable within a working cylinder of the clamping device. The axial movement of the drive piston can be converted into a swivel and axial movement, for example, by a cam mechanism.

[0003] The invention also relates to a method for detecting an undesired position of a piston adjustable in the interior of a housing, which divides the interior into a first pressure chamber connected to a first line and filled with fluid and a second pressure chamber connected to a second line and filled with fluid, wherein, in order to adjust the piston to a desired position, the first pressure chamber is pressurized with fluid flowing through the first line while fluid simultaneously flows out of the second pressure chamber through the second line.

[0004] In clamping devices, position sensing is usually pneumatic. For example, according to EP 2 764 953 A1, pneumatic valves can be provided in a swivel clamp, which are mechanically actuated by a piston rod or by a piston in a drive cylinder. This requires additional installation space for the pneumatic valves, thus increasing the axial length.

[0005] From DE 10 2022 115 370 A1, a clamping device is known in which the position of the piston is also pneumatically monitored. For this purpose, control elements are actuated which, depending on the position of a piston rod, open or close a flow connection from an air supply duct to an exhaust duct. This can be detected by means of a pressure sensor or a flow sensor, so that the position of the piston or piston rod is recognized.

[0006] According to the current state of the art, this requires design modifications to the piston or piston rod, whereby the piston must lie flush against the inner surface of the cylinder to such an extent that the test air cannot escape uncontrollably. Furthermore, in addition to the fluid required to actuate the piston, oil or compressed air must be provided for operating the pneumatic control elements.

[0007] WO 2021 / 013295 A1 discloses a pneumatic or hydraulic piston rod cylinder with a first and a second pressure chamber connected to each other via a bypass.

[0008] The present invention is based on the objective of further developing a device and a method of the type mentioned at the outset in such a way that it is possible to reliably detect when the piston has reached a desired position using structurally simple measures.

[0009] Another aspect is the ability to determine, in the event of a malfunction, whether the piston is incorrectly positioned.

[0010] To solve at least one of the problems, the system essentially provides for the first pressure chamber to be connected to the second pressure chamber via a bypass. This bypass allows a connection between the two chambers to be established when the pressure in the chamber used to adjust the piston exceeds a defined pressure value, and when fluid flowing through the bypass can be detected. The defined pressure value is typically the pressure required for trouble-free piston adjustment.

[0011] A connection between the first and second pressure chambers does not necessarily mean that there must be a direct connection between them. Rather, the connection can also be made via the pipe leading to one of the pressure chambers, as well as the other pressure chamber or a pipe leading to it.

[0012] In particular, it is provided that the bypass originates from the line through which the fluid flows to adjust the piston and is directly connected to the pressure chamber from which fluid flows when the piston is adjusted.

[0013] Preferably, the first pressure chamber is connected to the second pressure chamber indirectly or directly via a bypass, wherein a device is arranged in or associated with the bypass, the device being designed such that the flow of fluid via the bypass is prevented when the pressure in the pressure chamber used to adjust the piston is below a predetermined pressure value Pv, and that fluid flows via the bypass when the pressure in the pressure chamber used to adjust the piston is above the predetermined pressure value Pv, and that the undesired position can be detected by means of fluid flowing through the bypass.

[0014] To enable trouble-free opening and closing of the bypass, a device such as a valve, in particular a pressure relief check valve or a similarly acting element, should be arranged within or associated with the bypass. The valve opens and allows fluid flow from the first line or pressure chamber to the second pressure chamber or line when the fluid pressure in the first line or pressure chamber reaches a predetermined pressure value of, for example, at least 40 bar, preferably at least 50 bar. The valve is closed and prevents fluid flow from the first line or pressure chamber to the second pressure chamber or line when the fluid pressure in the first line or pressure chamber is less than the predetermined pressure value of, for example, at least 40 bar, preferably at least 50 bar. Fluid flow from the second pressure chamber to the first line or pressure chamber is then prevented.The first pressure chamber is blocked by the valve, regardless of the pressure prevailing in the second pressure chamber.

[0015] To detect the fluid flowing when the bypass is open, a flow-detecting sensor should be assigned to the line through which the fluid flowing from the pressure chamber drains.

[0016] The sensor and / or an additional detection element, such as a timer, can be used to measure the duration of the fluid flow through the line. Under normal operating conditions, the piston reaches its end position within a predefined target time T_target, e.g., T_target = 5 seconds. If the piston is blocked in an undesired position without reaching the desired position, for example, during a crash, the pressure at the valve rises above the predefined pressure value, causing the valve to open. In this case, fluid continues to flow through the bypass into the second pressure chamber and the second line. The flow rate and its duration are measured by the sensor. As soon as the flow rate exceeds the target time T_target, the undesired position, e.g., a blocked piston, is detected.

[0017] Alternatively, the sensor or another sensing element can be used to measure the volume of fluid flowing through the line per unit of time. The volume of fluid flowing during normal operation—that is, the fluid flowing through the line when the adjustment is made—should be greater than the volume of fluid flowing through the bypass per unit of time. In this case, if the piston is no longer adjusted without reaching the desired position (e.g., during a crash), the volume of fluid flowing through the line carrying the outflowing fluid will differ from the volume of fluid flowing out of the pressure chamber per unit of time during normal operation.

[0018] Upon reaching the desired position—typically the open position in a clamping device—a pressure would normally build up in the pressure chamber used to adjust the piston. This pressure would be higher than that corresponding to the piston's proper movement, potentially allowing fluid to flow through the bypass. However, this is prevented by a primary seal on the piston, which blocks the bypass connection to the pressure chamber from which the fluid would flow. Therefore, the sensor no longer detects fluid flow after the set time T_set has elapsed. Consequently, it becomes clear that the piston is in the desired position—for example, in the fully open position in a clamping device, or in the locked position if the locking position is to be detected.

[0019] The invention can be characterized in that the sensor is assigned to the line through which fluid flows out of the pressure chamber connected to it, and that when the desired position of the piston is reached, a connection between the bypass and the line is blocked.

[0020] In particular, it is provided that, in order to adjust the piston to the desired position, the first pressure chamber is connected to the first line carrying the pressurized fluid, that before reaching the desired position the bypass is connected to the second pressure chamber, that the sensor is assigned to the second line, and that the piston has a first seal by which, when reaching the desired position, the bypass is shut off from the second pressure chamber.

[0021] In particular, the invention is also characterized in that the piston has a second seal spaced apart from the first seal and extending offset in the direction of the first pressure chamber, wherein the first seal has a distance to the second seal such that, when the desired position is reached, the connection between the bypass and the interior runs between the first and the second seal.

[0022] Furthermore, the sensor or another device should make it possible to detect the quantity or duration of the flow of fluid through the second line over time.

[0023] The sensor or device can be a flow meter, particularly one with a timer. The flow meter can measure mechanically or optically. Generally, various technical methods are used to measure flow.

[0024] As mentioned, the device is preferably a clamping device, in particular a swivel clamp, with a piston rod extending from the piston and passing through the housing.

[0025] The fluid in question is, in particular, a hydraulic fluid.

[0026] A method for detecting an undesired position of an adjustable piston within the interior of a housing, which divides the interior into a first pressure chamber connected to a first line and filled with fluid, and a second pressure chamber connected to a second line and filled with fluid, is characterized in that the first pressure chamber is connected to the second pressure chamber via a bypass, to which a device is assigned or in which a device is arranged, through which fluid flows from the first pressure chamber or the first line into the second pressure chamber when the pressure in the first pressure chamber exceeds a predetermined value, and that, in the event of an undesired positioning of the piston and the associated pressure build-up exceeding the predetermined value, the fluid flowing into the second pressure chamber via the bypass is detected by a sensor.and that, upon reaching the desired position, the bypass to the second pressure chamber is closed. After the bypass is closed, no fluid flows from the second pressure chamber when the piston is stationary, thus detecting that the piston is in the desired position.

[0027] In particular, the first pressure chamber is connected directly or indirectly to the second pressure chamber via a bypass, wherein a device is arranged in or associated with the bypass which determines a flow direction for the fluid, wherein, in the event of an undesired positioning of the piston and the associated pressure build-up in the first pressure chamber above a predetermined pressure value Pv, the device is opened and fluid flows into the second pressure chamber, wherein the undesired positioning is detected by means of fluid flowing through the bypass.

[0028] In particular, a valve, such as a pressure relief check valve, is used as the device that blocks or releases the flow of fluid from the first pressure chamber to the second pressure chamber, through which fluid cannot flow when there is a pressure in the first pressure chamber or the first line leading to it that corresponds to a proper or faultless function of the piston movement.

[0029] When the piston is properly adjusted, fluid cannot flow from the second pressure chamber to the first pressure chamber via the valve, as the valve operates as a check valve in the closed direction. This does not negatively affect the function of the device.

[0030] If the piston becomes blocked in an undesired position, the pressure in the first line or pressure chamber rises above a predetermined pressure value. The valve then operates as a pressure relief valve and opens.

[0031] The duration T of the fluid flow is measured. If the duration T exceeds the predetermined target time T_target, an undesired position is detected. If the measured duration T is less than or equal to the previously determined target time T_target, normal operation is occurring.

[0032] To open the bypass, it is provided that the bypass is released in the flow direction via the device or valve, such as a pressure relief check valve, when a pressure P1 is present at the device or bypass, e.g. of at least 40 bar, preferably at least 50 bar, which is at least 30%, preferably at least 50%, preferably at least 80% higher than the pressure P2 that prevails during proper operation and thus when adjusting the piston, e.g. preferably 10 bar to 30 bar.

[0033] Furthermore, the invention relates to a clamping device, in particular a swivel clamp, with a piston adjustable in an interior of a housing and a piston rod extending from the piston and passing through the housing, wherein the piston divides the interior into a fluid-filled first pressure chamber and a fluid-filled second pressure chamber, wherein the first pressure chamber is connected to a fluid-carrying first line and the second pressure chamber to a fluid-carrying second line, wherein, for adjusting the piston, the fluid can be supplied to the pressure chamber connected to it via one of the lines and fluid can flow out of the other pressure chamber via the line connected to it.

[0034] The clamping device is characterized in that the first pressure chamber is connected to the second pressure chamber indirectly or directly via a bypass, and that a device is arranged in or associated with the bypass, wherein the device is designed such that a flow of fluid is prevented via the bypass when the pressure in the pressure chamber used to adjust the piston is below a predetermined pressure value Pv, and that a fluid flows via the bypass when the pressure in the pressure chamber used to adjust the piston is above the predetermined pressure value Pv.

[0035] Preferably, the device is a valve, in particular a pressure relief check valve, which in a first direction operates as a pressure relief valve and opens at a pressure P2 that is greater than the predetermined pressure value Pv, with Pv preferably in the range of 40 bar < Pv < 50 bar, and closes at a pressure P1, with P1 < Pv, and in a second direction operates as a check valve and closes independently of the applied pressure.

[0036] Preferably, the first pressure chamber is connected to the first line carrying pressurized fluid, wherein the piston has a first seal by which the bypass is shut off from the second pressure chamber when the desired position is reached.

[0037] The piston can have a second seal spaced apart from the first seal and extending in the direction of the first pressure chamber, wherein the first seal has a distance to the second seal such that, when the desired position is reached, a connection between the bypass and the interior space runs between the first and second seals.

[0038] Further details, advantages and features of the invention will become apparent not only from the claims and the features to be derived therefrom - individually and / or in combination - but also from the following description of a preferred embodiment.

[0039] They show: Fig. 1. A schematic representation of an adjusting device, such as a clamping device, in which a piston is in a first end position. Fig. 2 the device according to Fig. 1 with the piston in an intermediate position and Fig. 3 the device according to Fig. 1 and Fig. 2 with the piston in a second end position.

[0040] The invention is particularly intended for clamping devices, such as swivel clamps, without this constituting any limitations. The figures also represent schematic diagrams intended to clarify the invention.

[0041] The device comprises a housing (not shown) containing a cylindrical interior 10, in the longitudinal direction of which a piston 12 is adjustable. A piston rod 14 extends from the piston rod, passing through the cylindrical interior at an end face 16 and the housing containing the cylindrical interior. A clamping iron can then extend from the piston rod 14 to fix a workpiece.

[0042] In the Fig. Figure 1 shows the piston 12 in a first basic position, in which a workpiece is fixed if the device is designed as a clamping device. The clamping device, such as a swivel clamp, is properly released when the piston 12 moves to the second end position according to Fig. 3 is located, i.e., in a desired position.

[0043] The piston 12 divides the interior space 10 into a first pressure chamber 18 and a second pressure chamber 20. The first pressure chamber 18 is connected via a first line 22 and the second pressure chamber 20 via a line 24 to a reservoir of fluid, such as hydraulic fluid. The fluid is supplied to the lines 22 and 24 to the desired extent by means of a pump, depending on whether the piston 12 is to be moved to the left or to the right in the drawings. Furthermore, valves (not shown) are provided to enable switching. Reference is made to the well-known prior art in this respect.

[0044] To move piston 12 from the first end position ( Fig. 1) into the second end position ( Fig. 3) To adjust the position, the fluid – hereinafter referred to as hydraulic fluid – is supplied to the first pressure chamber 18 via line 22, so that the piston 12 is moved to the right by the pressurization of the piston base 26. At the same time, fluid located in the second pressure chamber 20 flows out via the second line 24.

[0045] To determine whether the piston 12 is in its second end position, a sensor 28 is assigned to the second line 24, which detects or measures the hydraulic fluid flowing from the second pressure chamber 20. Hydraulic fluid does not flow through the second line 24 if the piston 12 is in the second position according to the... Fig. 3 is located.

[0046] In the event of a malfunction, for example, if the piston 12 is located within the interior 10 in a position that deviates from the second end position—or, if the first end position is to be monitored, from the first end position—the sensor 28 would no longer detect the flowing hydraulic fluid. Consequently, despite the piston 12's incorrect position, an erroneous signal would be given that the piston 12 is in its second end position, a desired position, i.e., in the exemplary embodiment, in the relaxed position of the swivel clamp. To prevent this, the invention provides that a connection exists between the first line 22 and the second pressure chamber 20 via a bypass line 30, which is blocked when the piston 12 is correctly adjusted to the second end position.

[0047] Preferably, a valve 32, such as a pressure relief check valve, is used to shut off the bypass 30. Other suitable devices are also possible, which ensure that the bypass 30 only allows a flow connection between the first line 22 and thus the first pressure chamber 18 in the direction of the second pressure chamber 20 in the event of a malfunction.

[0048] The corresponding device, hereinafter always referred to as valve 32, opens in the flow direction when, due to the piston 12 being held in an undesired position, the supply of fluid via the first line 22 causes a pressure to build up that exceeds a predetermined pressure value. In this case, the valve 32 opens in the form of a pressure relief valve, so that hydraulic fluid flows into the second pressure chamber 20 via the bypass 30, displacing hydraulic fluid from it and flowing out via the second line 24. This is detected by the sensor 28, thus signaling that the second end position has been reached. Fig. 3 has not yet been reached.

[0049] To ensure that no hydraulic fluid can flow through the second line 24 in the second end position, since in the second end position 12 the pressure in the first pressure chamber 18 and thus in the first line 22 also exceeds the permissible pressure required for the trouble-free movement of the piston 12 and therefore the bypass 30 is open, it is further provided that fluid flowing through the bypass line 30 in the flow direction of the check valve 32 cannot enter the first and second pressure chambers 18, 20. For this purpose, the piston 12 has two seals 34, 36 running parallel to each other, of which seal 34 closes off the bypass line 30 from the second pressure chamber 20 and seal 36 closes off the bypass line 30 from the first pressure chamber 18 when the piston 12 is in the desired position, i.e., in the exemplary embodiment in the second end position. Fig. 3).

[0050] The seals 34 and 36 are therefore spaced such that, in the desired position of the piston 12, the bypass line 30 is sealed off from both the first pressure chamber 18 and the second pressure chamber 20, preventing hydraulic fluid from entering the bypass line 30. In this case, no fluid flows through the second line 24, so that the sensor 28 signals that the piston 12 is in the second end position, i.e., in the desired position.

[0051] Accordingly, the teaching of the invention can also be used to monitor the Fig. 1. The first end position to be removed can be used.

[0052] To distinguish whether the fluid flowing through the second line 24 is normally displaced by the correct adjustment of the piston 12, or the amount of hydraulic fluid displaced via the bypass line 30 when the piston is incorrectly positioned, the flow time is measured. This takes advantage of the fact that, under normal operating conditions, the piston moves from its compressed position within a target time T_target, e.g., 5 seconds ( Fig. 1) into the relaxed position ( Fig. 3) The procedure is as follows. If the piston is blocked, fluid flows through the bypass as described previously. This fluid flow continues to be detected despite the blocked piston. If the flow time exceeds the target time T-target, a blockage of the piston is detected.

[0053] Under normal operating conditions, the pressure in the first pressure chamber 18 is between 10 and 30 bar, in order to move the piston 12 from the left to the right position in the cylindrical interior 10. If the piston 12 stops outside the second end position, for example due to a crash, the pressure builds up in the first pressure chamber 18 and thus in the line 22.

[0054] Valve 32 should be opened at a pressure of at least 40 bar, preferably at least 50 bar.

Claims

[1] Device for detecting an undesired position of a piston (12) adjustable in an interior (10) of a housing, which divides the interior into a fluid-filled first pressure chamber (18) and a fluid-filled second pressure chamber (20), wherein the first pressure chamber is connected to a fluid-carrying first line (22) and the second pressure chamber is connected to a fluid-carrying second line (24), wherein, for adjusting the piston, fluid can be supplied into the pressure chamber connected to it via one of the lines and fluid can flow out of the other pressure chamber via the line connected to it, characterized by, that the first pressure chamber (18) is connected directly or indirectly to the second pressure chamber (20) via a bypass (30), that a device (32) is arranged in or associated with the bypass, wherein the device (32) is designed such that the flow of fluid via the bypass (30) is prevented when the pressure in the pressure chamber (18) pressurized for adjusting the piston (12) is below a predetermined pressure value Pv, and that fluid flows via the bypass (30) when the pressure in the pressure chamber (18) pressurized for adjusting the piston (12) is above the predetermined pressure value Pv, and that the undesired position can be detected by means of fluid flowing through the bypass. [2] Device according to claim 1, characterized by , that the fluid flowing through the bypass (30) can be detected by means of a sensor (28) or another device. [3] Device according to claim 1 or 2, characterized by , that the sensor (28) is assigned to the line (24) through which fluid flows from the pressure chamber (20) connected to it, and that when the desired position of the piston (12) is reached, a connection between the bypass (30) and the pressure chamber (20) is blocked. [4] Device according to at least one of the preceding claims, characterized by , that to adjust the piston (12) to a desired position, such as the end position of the piston (12), the first pressure chamber (18) is connected to the first line (22) carrying pressurized fluid, that the sensor (28) is assigned to the second line (24), and that the piston (12) has a first seal (34) by which, when the desired position is reached, the bypass (30) is closed off from the second pressure chamber (20). [5] Device according to at least one of the preceding claims, characterized by, that the piston (12) has a second seal (36) spaced apart from the first seal (34) and extending offset towards the first pressure chamber (18), wherein the first seal has a distance to the second seal such that when the desired position is reached, a connection between the bypass (30) and the interior (10) runs between the first and the second seal. [6] Device according to at least one of the preceding claims, characterized by , that the amount or duration of the flow of the fluid flowing through the second line (24) can be detected by means of the sensor (28) or another device, depending on time and / or volume. [7] Device according to at least one of the preceding claims, characterized by that the device is a pressure cylinder or a clamping device, in particular a swivel clamp, with a piston rod (14) extending from the piston (12) and passing through the housing. [8] Device according to at least one of the preceding claims, characterized by that the fluid is a hydraulic fluid. [9] Method for detecting an undesired position of a piston (12) adjustable in an interior (10) of a housing, the piston dividing the interior into a first pressure chamber (18) connected to a first line (22) and filled with fluid and a second pressure chamber (20) connected to a second line (24) and filled with fluid, wherein, in order to adjust the piston to a desired position, the first pressure chamber is pressurized with fluid flowing through the first line while fluid simultaneously flows out of the second pressure chamber through the second line, characterized by, that the first pressure chamber is connected to the second pressure chamber indirectly or directly via a bypass (30), that a device is arranged in or associated with the bypass which determines a flow direction for the fluid, that if the piston (12) is positioned in an undesired position and the associated pressure build-up in the first pressure chamber exceeds a predetermined pressure value Pv, the device is opened and fluid flows into the second pressure chamber, whereby the undesired positioning is detected by means of fluid flowing through the bypass. [10] Method according to claim 9, characterized by , that fluid flowing into the second pressure chamber via the bypass is detected by a sensor (28), and that when the desired position is reached the bypass is closed off from the second pressure chamber. [11] Method according to claim 9 or 10, characterized by, that in order to adjust the piston (12) in the absence of obstruction the pressure in the first pressure chamber is P1, with P1 in the range of at least 10 bar, preferably 30 bar, and that in the event of incorrect positioning of the piston in the first pressure chamber a pressure P2 prevails, with P2 of at least 40 bar, preferably at least 50 bar. [12] Device, such as a pressure cylinder or clamping device, in particular a swivel clamp, with a piston (12) adjustable in an interior (10) of a housing and a piston rod (14) extending from the piston (12) and passing through the housing, wherein the piston (12) divides the interior into a fluid-filled first pressure chamber (18) and a fluid-filled second pressure chamber (20), wherein the first pressure chamber is connected to a fluid-carrying first line (22) and the second pressure chamber is connected to a fluid-carrying second line (24), wherein, for adjusting the piston, fluid can be supplied to the pressure chamber connected to it via one of the lines and fluid can flow out of the other pressure chamber via the line connected to it, characterized by, that the first pressure chamber (18) is connected directly or indirectly to the second pressure chamber (24) via a bypass (30), that a device (32) is arranged in or associated with the bypass, wherein the device (32) is designed such that a flow of fluid is prevented via the bypass (30) when the pressure in the pressure chamber pressurized for adjusting the piston (12) is below a predetermined pressure value Pv, and that a fluid flows via the bypass (30) when the pressure in the pressure chamber pressurized for adjusting the piston (12) is above the predetermined pressure value Pv. [13] Device according to claim 12, characterized by , that the device (32) is a valve, in particular a pressure relief check valve, which opens at a pressure P2 that is greater than the specified pressure value Pv, with Pv preferably in the range of 40 bar < Pv < 50 bar, and closes at a pressure P1, with P1 < Pv. [14] Device according to claim 12 or 13, characterized by , that the first pressure chamber (18) is connected to the first line (22) carrying pressurized fluid, and that the piston (12) has a first seal (34) by which, when the desired position is reached, the bypass (30) is shut off from the second pressure chamber (20). [15] Device according to at least one of the preceding claims 12 to 14, characterized by , that the piston (12) has a second seal (36) spaced apart from the first seal (34) and extending offset towards the first pressure chamber (18), wherein the first seal has a distance to the second seal such that when the desired position is reached, a connection between the bypass (30) and the interior (10) runs between the first and the second seal.

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