Method for operating a fluid actuator and device for carrying out this method

Abstract

The method for operating the fluid actuator (10) includes at least the steps of: performing initialization to determine at least one defined end position (x, y) in one movement direction of the actuator (10); subsequently, performing position control based on a virtual braking point for the actuator (10) belonging to the end position (x, y); slowing down the velocity of the actuator (10) at the braking point until it reaches the next end position (x, y) in the movement direction; and reversing the actuator (10) in the opposite movement direction.

Description

[Technical Field]

[0001] The present invention relates to a method for operating a fluid actuator and to a device for carrying out this method. [Background technology]

[0002] Patent Document 1 discloses a hydraulic drive system with a flow rate and / or pressure regulation device for a pressure booster of a high-pressure device, essentially consisting of a motor drive with a pump for the pressure medium and a control device. The hydraulic drive system uses a fixed displacement pump or a pump that pumps a constant volume per revolution. The hydraulic drive system is driven by a servomotor that is electrically controllable, adjustable, and / or switchable by means on the low-pressure side and / or the high-pressure side. The advantages of this solution include the fact that almost no pulsation occurs when the high-pressure medium is introduced into the filler material, preventing the flakes of fragile material during waterjet cutting. Furthermore, pressure fluctuations, especially when switching the cutoff valve on and off, are minimized by the use of a hydraulic drive system, thereby significantly avoiding overloading of components.

[0003] In a practical embodiment, the aforementioned low-pressure side and high-pressure side means are pressure sensors that are inserted into the allocable fluid lines to detect the pressure in the lines and transmit the pressure as an electrical output variable to an electrical control device for operating the pump servo motor. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] European Patent No. 2610490 Summary of the Invention [Problem to be solved by the invention]

[0005] The object of the present invention is to provide an improved solution based on this prior art, which is achieved by a method having the features set forth in claim 1 and a device having the features set forth in claim 8. [Means for solving the problem]

[0006] The method for controlling a fluid actuator according to the present invention comprises at least the following steps: - performing an initialization to determine at least one defined end position in one direction of movement of the actuator; Following this, - implementing a position control based on virtual braking points for the actuators, which belong to end positions; - slowing down the speed of the actuator at the braking point until it reaches a next end position in the direction of movement; - reversing the actuator in the opposite direction of travel; It is characterized by: [Effects of the Invention]

[0007] In this way, the actuator is prevented from colliding at maximum speed with its respective end position, which is usually defined by the end face of the corresponding actuator housing, but instead approaches a predefinable virtual braking point by position control, preferably at maximum speed, and upon reaching the braking point, the actuator speed is reduced so that the actuator moves to its end position at a significantly reduced speed without damaging the actuator and its housing during this process. As the actuator is intended to ensure that high-pressure fluid is discharged to the consumer in both opposing directions of actuation as part of the actuation for pressure boosting, once the actuator reaches one end position, it is reversed in the opposite direction of movement to reach the opposite end position. When this method and corresponding device are used in the area of ​​a hydrogen discharge point, such as a hydrogen filling station, hydrogen is compressed to a high pressure of 700 to 900 bar before being discharged to each vehicle to be refueled.

[0008] As part of the high pressure compression, an initialization routine is required before the actual cycle process sequence can be performed by the position control. The initialization routine includes at least the following initialization steps: - actuating the actuator by means of a drive device in one direction of movement until it reaches one of said two possible end positions; - detecting each end position by means of a sensor device; - referencing one end position as the zero or starting point; - actuating the actuator in the opposite direction of movement to detect the other end position; - determining the actual values ​​of the theoretical position and velocity of the actuator as it moves between two end positions; - stopping the drive when the other end position is reached; - storing the current position value at each end position; It is characterized by:

[0009] After switching on the device or system, as there is no information available about the current position of the actuator, the actuator is first moved at a defined, set speed to one of two end positions. The end positions are detected by means of a configurable proximity switch, which is preferably arranged fixedly in the actuator housing. Such proximity switches, also known as proximity initiators, are sensors that react on proximity without contact, without direct contact with the moving parts of the actuator or the fluid used.

[0010] When the actuator reaches one of the two end positions, this reference point is defined as the zero point. Then, movement continues in the opposite direction to find the second end point or second end position. During the movement, the theoretical position and actual speed values ​​are calculated based on the hydraulic transmission ratio between the pump and the actuator and the current speed value. When the end position is reached, the drive is stopped and the calculated current position is stored as the maximum end position. This completes the initialization routine, and the cycle movement sequence can begin.

[0011] In this step, the position control is implemented as an adaptive position control, which includes at least the following steps: - accepting the value of each said current position stored at initialization; - calculating a virtual braking point so as to reach the relevant end position in the shortest possible time; - moving the actuator, preferably at a predefinable maximum speed; - after reaching the virtual braking point, decelerating to a predefinable target speed until the actuator finally reaches the associated end position; - stopping the drive and preferably storing its current position; - Calculating braking points for movement in the opposite direction; It is characterized by:

[0012] As described above, once the initialization routine is successfully completed, the application's periodic operation begins with storing the current position of the actuator and calculating a virtual braking point to reach the corresponding end position in the shortest time. This significantly improves efficiency. The calculated distance for initiating brake application depends on several factors, such as the drive's deceleration, maximum speed, the distance between the end positions, and a freely selectable coefficient for manually adapting the process. The process is then carried out at the maximum possible speed. As soon as the virtual braking point is reached, the drive unit is decelerated to a specified second target speed until the hydraulic actuator reaches the end position. The drive is then stopped, and the current position is again stored and a braking point for the opposite direction of movement is calculated. The movement profile described above is then executed. This cycle can be repeated any number of times. By repeatedly storing the end positions and calculating the braking point each time, both system and environmental factors are considered. Examples include temperature, pump wear, and oil condition. These provide adaptive position control for closed hydraulic shafts in the form of actuators without the use of distance measurement systems.

[0013] The present invention also relates to an apparatus for carrying out the aforementioned method, in which the actuator has a hydraulic working cylinder, preferably in the form of a synchronous cylinder. Furthermore, a proximity switch on the housing determines the end positions of the piston rod unit of the corresponding hydraulic working cylinder. In contrast to known distance measuring devices, the proximity switch responds directly to the end positions of the actuator and does not result in hysteresis behavior that could adversely affect the timely transmission of the sensor measurement values. Furthermore, the proximity switch operates virtually wear-free, compared to distance measuring systems with associated moving parts.

[0014] More preferably, a hydraulic pump in the form of a reversible pump is used to drive the actuator, which drives the piston rod unit in both opposite directions of movement of the piston rod unit, the hydraulic pump and the actuator together forming a closed hydraulic supply circuit, as a result of which potential leakage losses are avoided.

[0015] Preferably, the two rods of the piston rod unit each drive an independent gas compressor, which alternately draws in gas in the low pressure range and discharges it in a compressed state at high pressure to the consumer. Alternatively, gas compression can be performed directly via an actuator.

[0016] The method and device according to the invention are explained in more detail below on the basis of examples shown in the drawings, which are schematic and not to scale. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a hydraulic circuit diagram showing the main components of an apparatus for carrying out the method illustrated in the flow charts of FIGS. [Figure 2] FIG. 2 is a flow chart showing the main method steps of the method according to the invention. [Figure 3] FIG. 3 is a flow chart showing the main method steps of the method according to the present invention, and is a continuation of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0018] FIG. 1 shows the main components of the device according to the invention in the form of a general hydraulic circuit diagram. The device includes an actuator 10 in the form of a hydraulic working cylinder, which is configured as a so-called synchronous cylinder. A synchronous cylinder, also known as a double-piston cylinder, has one piston rod 14 on each side of a centrally located piston 12, so that the piston rod unit 16 of the actuator 10 as a whole is configured with two piston rods 14. Therefore, the amount of hydraulic fluid flowing in and out is always the same, and the piston rod unit 16 extends and retracts in both directions at the same speed. As shown in FIG. 1, the piston rod unit 16 at the start of the actuator 10 divides the interior of the actuator housing 18 into two cylinder chambers 20 of equal size. However, depending on the application, it is also possible to change the volume of the initial cylinder chambers 20 by selecting different rod and / or piston cross-sectional areas, e.g., to configure one cylinder chamber with a larger volume than the other.

[0019] The two free ends of each piston rod 14 extend outward from the corresponding actuator housing 18 and are operatively connected to a corresponding compressor piston 22. The compressor pistons form part of a gas compressor 24. In this process, the two compressor pistons 22 correspond in geometric configuration to the pistons 12 of the actuator 10. The two gas compressors 24 are also similarly configured. In this process, each gas compressor 24 extracts gas, for example, hydrogen gas, from a low-pressure conduit 26 on the inlet side, and a check valve 28 is opened accordingly. Furthermore, each gas compressor 24 is connected on the outlet side to a high-pressure conduit 30. The high-pressure conduit leads to a consumer, for example, a vehicle (automobile), from which hydrogen is to be supplied to a tank. For this discharge to the high-pressure side 30, a respective check valve 32 is opened.

[0020] The compressor cycle proceeds as follows: When the piston 12 of the actuator 10 moves to a first position on the right, i.e., the front end position x, as viewed in Fig. 1, the actuator moves the two compressor pistons 22 in the same direction via their respective piston rods 14. This causes an inlet volume to expand on the inlet side of the left gas compressor 24, and gas is directed through the open left check valve 28. Meanwhile, the compressor pistons 22 simultaneously compress the gas contained in the right gas compressor 24 during the previous cycle, and with the right check valve 28 closed, push the highly compressed gas volume through another right check valve 32 into the high-pressure conduit 30 with the other left check valve 32 closed.

[0021] After reaching the right end position for the piston 12 of the piston rod unit 16, the actuator 10 is reversed, and the piston 12 moves from its right end position in the opposite direction to a left rear end position, i.e., a second end position y. As part of the inlet process, the previously accommodated gas is now compressed in the left gas compressor 24 and, with the left check valve 28 closed, is discharged to the high-pressure conduit 30 through the other left check valve 32. Furthermore, as the right check valve 28 opens and the compressor piston 22 of the right gas compressor 24 moves from right to left, increasing gas flow from the low-pressure conduit 26 into the expanding gas chamber of the right gas compressor 24. Therefore, the other right check valve 32 is closed. After reaching the left end position for the piston 12, the operation is reversed again, and the load and unload cycles for the two gas compressors 24 are repeated as described above.

[0022] The two cylinder chambers 20 of the actuator 10 are connected to respective supply conduits 34, 36, which can be supplied with fluid at a predetermined pressure by a hydraulic pump 38 in the form of a reverse pump. In particular, the reverse pump 38 moves fluid alternately back and forth between the two supply conduits 34, 36, thereby causing the piston rod unit 16 of the actuator 10 to move back and forth alternately. Depending on the direction of rotation of the reverse pump 38, fluid is alternately pumped from one cylinder chamber 20 through the supply conduits 34, 36 into the other cylinder chamber 20, so that actuation of the actuator 10 is achieved with a substantially constant fluid volume. The hydraulic pump in the form of the reverse pump 38, together with the actuator 10 and the supply conduits 34, 36, thus form a closed hydraulic supply circuit 40.

[0023] An electric motor M, controllable by a control device 42, serves as a drive for the hydraulic pump or reverse pump 38. The electric motor M is symbolically indicated by an arrow in FIG. 1 to illustrate its control capabilities. The control device 42 receives sensor data from two proximity switches 44 on the inlet side. In this embodiment, these proximity switches are located at the ends of the actuator housing 18, respectively, and monitor the position of the piston 12 as it approaches the adjacent end face within the actuator housing 18. In addition to the proximity switches, conventional limit switches may also be used in this process. The limit switches can detect the end positions of the piston 12 within the actuator housing 18 and transmit this information to the control device 42. As soon as the limit switch or proximity switch 44 detects the end positions of the piston 12, it notifies the control device 42. The control device then controls the reverse pump 38 to pump fluid in the opposite direction, allowing the piston 12 to move in the opposite direction until it approaches the opposite end position within the actuator housing 18.

[0024] To drain oil from the hydraulic supply circuit 40, two valves 46, 48 are connected, each forming a fluid-transporting connection between the supply lines 36, 38 and the storage tank T. In combination with an additional supply device 50, the two valves 46, 48 serve as drain valves for regulating the thermal balance of the hydraulic oil. This allows a defined amount of oil to be drained when the cylinder extends or retracts, and fresh oil from the supply device 50 is re-supplied into the closed circuit. Valve 48 opens during extension, valve 46 opens during retraction, with the opposite sides correspondingly closed. Optionally, an additional supply device 50 consisting of a conventional motor-pump unit 52 can also be provided. The outlet side of the corresponding hydraulic pump is protected from the tank side of the storage tank T via a pressure limiting valve 54. A spring-loaded check valve 56 is then provided in the flow direction, opening toward a fluid filter 58 and closing in the opposite direction. The outlet side of the fluid or hydraulic filter 58 is connected to a branch point 60 which leads into a connecting conduit 62 between the two supply conduits 34, 36 at the outlet side of the reverse pump 38. Further, towards the two supply conduits 34, 36, further spring-loaded check valves 64 are arranged. These check valves open when viewed from the direction of the respective supply conduits 34, 36 and close when viewed in the opposite direction, thereby preventing undesired backflow of fluid from the supply conduits 34, 36 towards the filter 58.

[0025] All of the major fluid components described above are housed within the area 66 shown by the dashed line in FIG. 1. The device described above operates without inserting low- and / or high-pressure detection means, such as pressure sensors, into the fluid conduits. Instead, the proximity switch 44 is used to monitor the operation of the actuator piston 12 without interruption. The proximity switch 44 detects the operating status of the actuator 10 in a non-contact manner, eliminating measurement transmission errors caused by transmission media such as fluids. It also eliminates the need for a distance measurement system, which is prone to hysteresis and wear during transmission and does not suffer from such problems as those encountered with the proximity switch 4.

[0026] The operation of the device shown in FIG. 1 will now be described in detail based on the flow charts shown in FIGS.

[0027] After commissioning the device or after starting up after power-on, it is checked whether initialization has already taken place. If the system has not been initialized, an initialization routine is carried out. This initialization routine is shown in FIG. 3 (a continuation of FIG. 2). In this step, the actuator moves at a defined set speed to one of two end positions x, y, for example to the first end position x on the front side. If the front end position x has not yet been reached (this can be determined by one of the two proximity switches 44), the routine is repeated. That is, the piston rod unit 16 of the actuator 10 is extended until it reaches the front end position x, which is detected by the assignable proximity switch 44 and transmitted to the control device 42.

[0028] The control device 42 then stops the electric motor M, which in turn stops the hydraulic pump or reverse pump 38. When one of the two end positions, i.e., the forward end position x or the rearward end position y, is reached, the control device 42 defines such reference point as the zero point. The rearward second end position y can therefore also be stored as the reference point zero. Once the zero reference is successfully completed, the associated routine does not need to be repeated. Instead, the piston rod unit 16 is retracted at a predefinable set speed relative to the actuator housing 18, which is kept stationary, causing a movement in the opposite direction, and the second end point or second end position y is detected.

[0029] When the second rearward end position y is reached, there is no need to proceed further with the reversing routine and the motor M is again stopped or switched off. When the second end position y is reached, the drive in the form of the motor M is stopped and the calculated actual position is stored as the maximum end position. Furthermore, during the process of moving from the first end position x to the second end position y, based on the hydraulic transmission ratio between the pump 38 and the actuator 10 and the current speed values, the actual values ​​of the theoretical position and speed are calculated as follows:

number

[0030] As part of the initialization, in each case, the distance of the piston 12 at the proximity switch 44 on the first end position side is set to S min = 0 mm, and S at the second end position of the proximity switch 44 is determined based on the following formula: max is stored for the initialization routine.

[0031] If all initialization steps are completed successfully, the initialization is considered complete and "Init completed" is output.

[0032] Upon successful completion of the initialization routine shown in the flow chart of Figure 3, which is a continuation of Figure 2, the current position is stored and the cyclic operation of the application is initiated as shown in Figure 2. In particular, as part of the cyclic process sequence, the current position is stored and a virtual braking point is calculated in order to reach one of two end positions x, y in the shortest possible time. The calculated distance S to initiate braking brems depends on several factors, namely the reduction in speed of the drive, the maximum speed, the distance between the end or terminal positions x, y and a freely selectable factor c for manually adapting the process. The calculation is carried out according to the following formula:

number

[0033] As explained, moving at a defined maximum speed, upon reaching a virtual braking point, the drive unit in the form of motor M decelerates to a defined second target speed, significantly lower than the maximum speed, until the piston 12 of the actuator 10 reaches the respective end point, designated as end position x, y, at a slower approach speed in the actuator housing 18. Then, as shown in the process flow diagrams of FIGS. 2 and 3, motor M stops, again stores the current position, and calculates the corresponding braking point for the opposite direction of movement. Upon reaching each end position x, y, the cycle is repeated, but the initialization routine must be completed beforehand. The repeated storage of end positions x, y by the two proximity switches 44 and the respective calculation of the virtual braking point take into account both system and environmental factors, such as temperature, pump wear, and oil condition. Overall, the process sequence control ensures adaptive position control for a closed hydraulic shaft without a distance measurement system, something not found in the prior art.

Claims

1. A method of operating a fluid actuator (10), comprising: - carrying out an initialization to determine at least one defined end position (x, y) in one direction of movement of said actuator (10); Following this, - implementing a position control based on a virtual braking point for said actuator (10) belonging to said end position (x, y); - slowing down the speed of the actuator (10) at the braking point until the next end position (x, y) in the direction of movement is reached; - reversing said actuator (10) in the direction opposite to said direction of movement; The method includes at least

2. at least, - actuating said actuator (10) by means of a drive (M) in one of said directions of movement until it reaches one of its two possible end positions (x, y); - detecting each of said end positions (x, y) using a sensor device (44); - referencing one of said end positions (x; y) as the zero or starting point; - actuating said actuator (10) in the direction opposite to said direction of movement in order to detect the other of said end positions (y; x); - determining the actual values ​​of the theoretical position and velocity of the actuator (10) as it moves between the two end positions (x, y); - stopping said drive (M) when the other end position (x, y) is reached; storing the value of the current position at each of said end positions (x, y); An initialization step including: The method of claim 1.

3. The position control is implemented as adaptive position control and includes at least: - accepting the value of each said current position stored at initialization; - calculating the virtual braking point so as to reach the relevant end position (x, y) in the shortest possible time; - moving said actuator (10), preferably with a predefinable maximum speed; - after reaching the virtual braking point, decelerating the actuator (10) to a predefinable target speed until it finally reaches the associated end position (x, y); - stopping said drive (M) and preferably storing said current position; - calculating said braking points for movements in the opposite direction; characterized in that it comprises The method according to claim 1 or claim 2.

4. 4. The method according to claim 1, wherein the hydraulic transmission ratio between the hydraulic pump (38) drivable by the drive (M) and the actuator (10) is used as part of the initialization during the movement of the actuator (10) between the two end positions (x, y), incorporating the associated speed value of the drive (M) to determine the actual values ​​of the theoretical position and speed.

5. 5. The method according to claim 1, wherein the positions of the two end positions (x, y) are used together with the maximum velocity of the actuator (10) and each braking point is calculated as part of initialization until a braking velocity of the actuator (10) at each end position (x, y) and each braking point is reached.

6. 6. A method according to any one of claims 1 to 5, characterized in that the end positions (x, y) of the actuator (10) are repeatedly stored and each braking point is repeatedly calculated.

7. 7. The method according to claim 1, further comprising determining each of the end positions (x, y) of the actuator (10) without using a distance measurement system, using at least one proximity switch (44).

8. 8. A device for carrying out the method according to claim 1, wherein the actuator (10) comprises a hydraulic working cylinder, preferably in the form of a synchronous cylinder, and housing-side proximity switches (44) respectively define the end positions (x, y) of a piston rod unit (16) of the working cylinder.

9. 9. The device according to claim 8, characterized in that the pump for the hydraulic pressure is a reversible pump (38), which drives the piston rod unit (16) in both opposite directions of movement of the piston rod unit (16), and the pump (38) and the actuator (10) form a closed hydraulic supply circuit (40).

10. 10. The device according to claim 8 or claim 9, characterized in that the two piston rods (14) of the piston rod unit (16) each drive one gas compressor (24), which alternately draws in gas in a low pressure range and discharges it in a compressed state at high pressure.

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