Method for actuating a fluid actuator, and device for carrying out the method

Abstract

A method for actuating a fluid actuator (10), comprising at least the following steps: - carrying out an initialization in order to determine at least one defined end position (x, y) in a movement direction of the actuator (10), and subsequently - carrying out position control on the basis of a virtual brake point, belonging to the end position (x, y), for the actuator (10), - retarding the speed of the actuator (10) at the brake point until the following end position (x, y) in the movement direction is reached, and - reversing the actuator (10) into the opposite movement direction.

Description

[0001] Method for controlling a fluidic actuator and device for carrying out the method

[0002] The invention relates to a method for controlling a fluidic actuator and a device for carrying out the method.

[0003] EP 2 610 490 B 1 discloses a hydraulic drive with a quantity and / or pressure control for a pressure intensifier of a high-pressure device, essentially comprising a motor drive with a pump for a pressure medium and a control system, wherein a constant-flow pump or a pump which delivers a constant volume per revolution is used as the hydraulic drive. The hydraulic drive is driven by a servomotor which can be electrically controlled, regulated and / or switched by means on the low-pressure side and / or high-pressure side. The stated advantage of this solution is that there is essentially no pulsation when a high-pressure medium is introduced into a filler material or there is no chipping of brittle materials during waterjet cutting.Furthermore, pressure fluctuations, especially when switching a cutting valve on and off, are minimized by the use of the hydraulic drive, thus largely preventing component overload. The low- and / or high-pressure side devices mentioned are, in their specific form, pressure sensors that, when inserted into assigned fluid lines, detect the prevailing pressure there and transmit it as an electrical output variable to an electrical controller for operating the pump's servo motor.

[0004] Based on this prior art, the invention seeks to provide an improved solution. This object is achieved by a method having the features of patent claim 1 and a device having the features of patent claim 8.

[0005] The method according to the invention for controlling a fluidic actuator is characterized by at least the following method steps:

[0006] - Performing an initialization to determine at least one defined end position in a direction of movement of the actuator, and then

[0007] - Carrying out a position control based on a virtual braking point for the actuator associated with the end position,

[0008] - Deceleration of the speed of the actuator at the braking point until the end position following in the direction of movement is reached; and

[0009] - Reversing the actuator in the opposite direction of movement.

[0010] This prevents the actuator from hitting the respective end position, which is usually formed by the end faces of the associated actuator housing, at maximum speed. Instead, a position control system is used to approach a predefined virtual braking point, preferably at maximum speed. Once the braking point is reached, the actuator speed is then slowed down so that it reaches the end position at a significantly slower speed without causing damage to the actuator or its housing. Since the actuator is intended to ensure the delivery of fluid under high pressure to a consumer in both opposing actuation directions as part of a pressure transmission, once one end position is reached, the actuator is reversed in the opposite direction of movement in order to reach the opposite end position.If the process and the associated device are used in the area of ​​hydrogen dispensing points, such as hydrogen filling stations, the hydrogen is compressed to a high pressure of 700 to 900 bar before being delivered to the vehicle to be refueled.

[0011] Before carrying out the actual cyclic process sequence using position control within the framework of high-pressure compression, an initialization routine is necessary, which is characterized by at least the following initialization steps:

[0012] - Controlling the actuator by means of a drive in one direction of movement until one of its two possible end positions is reached,

[0013] - Detection of the respective end position by means of a sensor device,

[0014] - Referencing one end position as zero or starting point,

[0015] - Controlling the actuator in the opposite direction of movement to detect the further end position,

[0016] - Determination of theoretical position and speed actual values ​​during the movement of the actuator between the two end positions,

[0017] - Switching off the drive when the further end position is reached, and

[0018] - Saving the current position value in the respective end position.

[0019] Due to the fact that no information about the actuator's current position is available after the device or system is switched on, it is initially moved to one of the two end positions at a defined setup speed. The end position is detected by an assignable proximity switch, which is preferably mounted stationary on the actuator housing. Proximity switches, also known as proximity initiators, are sensors that respond to approach without direct contact, for example, with the moving parts of the actuator or with the fluid used.

[0020] If one of the two end positions is reached by the actuator, this reference point is defined as the zero point. This is followed by a movement in the opposite direction to detect the second end point or the second end position. During the movement process, a theoretical actual position and speed value is calculated using the hydraulic transmission ratio between the pump and actuator and the current speed values. When the end position is reached, the drive is switched off, and the calculated current position is saved as the maximum end position. This completes the initialization routine and a cyclical movement sequence can be started.

[0021] In this case, a position control is used as adaptive position control, which is characterized by at least the following steps:

[0022] - Adoption of the current position value saved during initialization,

[0023] - Calculation of a virtual braking point in order to reach the corresponding end position in the shortest possible time,

[0024] - Movement of the actuator, preferably with a preset maximum speed, until

[0025] - Reaching the virtual braking point with subsequent reduction to a preset target speed until the actuator has finally reached the corresponding end position, - Switching off the drive and preferably saving the current position, and

[0026] - Calculate the braking point for the opposite direction of movement.

[0027] Once the initialization routine has been successfully completed, as described above, the application begins cyclic operation by saving the current position of the actuator and calculating the braking point to reach the end point as quickly as possible. This significantly improves efficiency. The calculated distance to initiate the braking process depends on several factors: drive deceleration, maximum speed, distance between the end points, and a freely selectable factor for manual process adjustments. The system then travels at a specified maximum speed. Once the virtual braking point is reached, the drive unit decelerates to a second specified target speed until the hydraulic actuator reaches the end point. The drive then switches off, saves the current position, and calculates the braking point for the opposite direction of movement.A motion profile follows as described above. This cycle can be repeated as often as required. Due to the recurring storage of the end positions and the respective calculation of the braking point, system- and environmental factors are taken into account. Examples include temperature, pump wear, and oil condition. Overall, this creates an adaptive position control system for a closed hydraulic axis, in the form of an actuator, without a position measuring system.

[0028] The invention further relates to a device for carrying out the method described above, wherein the actuator comprises a hydraulic working cylinder, preferably in the form of a synchronous cylinder. Furthermore, a proximity switch on the housing side detects the end position of the piston-rod unit of the respective hydraulic working cylinder. Unlike known displacement measuring devices, the proximity switch responds directly to the end position of the actuator without hysteresis processes that could impair the timely transmission of the sensor measurement. Furthermore, a proximity switch operates essentially wear-free compared to displacement measuring systems with their associated movable components.

[0029] Particularly preferably, a hydraulic pump is used to drive the actuator, preferably in the form of a reversible pump which drives the piston-rod unit in both opposite directions of movement, wherein the hydraulic pump and the actuator together form a closed hydraulic supply circuit so that any leakage losses that may occur are avoided.

[0030] Preferably, the piston-rod unit, with its two rods, each drives an independent gas compressor, which alternately draws in gas in the low-pressure range and delivers it to a consumer in a highly compressed state. Alternatively, it is also possible to initiate gas compression directly via the actuator.

[0031] In the following, the method according to the invention and the device are explained in more detail using an exemplary embodiment according to the drawing. In this diagram, not to scale, the

[0032] Fig. 1 shows, in the form of a hydraulic circuit diagram, the essential components of a device for carrying out a method according to the flow diagram of Fig. 2; and

[0033] Fig. 2 shows the essential process steps of the method according to the invention in the form of a flow chart. Fig. 1 shows the essential components of the device according to the invention in the form of a conventional hydraulic circuit diagram. The device has an actuator 10 in the form of a hydraulic working cylinder, which is designed as a so-called synchronous cylinder. A synchronous cylinder, also called a synchronous cylinder, has a piston rod 14 on each side of a centrally arranged piston 12, so that a total of one piston-rod unit 16 of the actuator 10 is formed with two piston rods 14. The volume of the incoming and outgoing hydraulic oil is therefore always the same, and thus the piston-rod unit 16 also moves in and out at the same speed in both directions. The piston-rod unit 16 in the starting position of the actuator 10, as shown in Fig.1, divides two equally sized cylinder chambers 20 within an actuator housing 18. Depending on the application, however, it is certainly possible to change the volume of the cylinder chambers 20 in the initial position by selecting different rod and / or piston cross sections, for example, to design one cylinder chamber with a larger volume than the other cylinder chamber.

[0034] The two free ends of the respective piston rod 14 lead out of the associated actuator housing 18 and are each operatively connected to an associated compressor piston 22, which is a component of a gas compressor 24. The two compressor pistons 22 correspond in terms of their geometric design to the piston 12 of the actuator 10. The two gas compressors 24 are also constructed identically. The respective gas compressor 24 draws gas, for example hydrogen gas, from a low-pressure line 26 on the inlet side, with the check valve 28 then open. Furthermore, the respective gas compressor 24 is connected on the outlet side to a high-pressure line 30, which leads to a consumer, for example in the form of a (motor) vehicle to be refueled with hydrogen. The respective additional check valve 32 is then open for the corresponding delivery to the high-pressure side 30. A compressor cycle can now proceed as follows. Moving in the direction of view in Fig.1, the piston 12 of the actuator 10 moves to the right, into the first or front end position x, driving the two compressor pistons 22 along with it in the same direction via the respective piston rod 14. This increases the inflow volume on the inflow side of the left gas compressor 24, and the gas is fed accordingly via the open left check valve 28. On the other side, the compressor piston 22 simultaneously compresses the gas taken up in the right gas compressor 24 in the previous cycle and, with the right check valve 28 closed, pushes the highly compressed gas quantity out into the high-pressure line 30 via the additional right check valve 32.

[0035] After the right end position for the piston 12 of the piston-rod unit 16 has been reached, the actuator 10 is switched and the piston 12 moves from its right end position in the opposite direction, and thus into the left, rear or second end position y. The gas previously taken in during the inflow process is now compressed in the left gas compressor 24 and delivered to the high-pressure line 30 via the additional left check valve 32 with the left check valve 28 closed. Furthermore, the right check valve 28 opens and gas flows visibly from the low-pressure line 26 into the expanding gas chamber of the right gas compressor 24, since its compressor piston 22 is moved from right to left. The additional right check valve 32 is therefore closed. After reaching the left end position for the piston 12, the control is reversed and the loading and unloading cycle for the two gas compressors 24 is repeated as described above.

[0036] The two cylinder chambers 20 of the actuator 10 are each connected to a supply line 34, 36, which can be supplied with fluid at a predefined pressure by a hydraulic pump 38 in the form of a reversing pump. In particular, the reversing pump 38 is capable of alternately pushing fluid back and forth between the two supply lines 34, 36 in order to alternately move the piston-rod unit 16 of the actuator 10 back and forth. Since the fluid quantity is alternately pushed from one cylinder chamber 20 via the supply lines 34, 36 into the other cylinder chamber 20 at a constant rate, depending on the direction of rotation of the reversing pump 38, the corresponding drive for the actuator 10 essentially requires a constant fluid quantity. In this respect, the hydraulic pump in the form of the reversing pump 38 together with the actuator 10 and the supply lines 34, 36 forms a closed hydraulic supply circuit 40.

[0037] The hydraulic or reversing pump 38 is driven by an electric motor M controlled by a controller 42, which is symbolically indicated by an arrow in Fig. 1 to indicate its controllability. The controller 42 receives sensor data from two proximity switches 44 on its input side. In this case, these are each arranged at the end of the actuator housing 18 and thus monitor the position of the piston 12 as soon as it touches the adjacent end face in the actuator housing 18. In addition to proximity switches, conventional limit switches can also be used, which can detect the end position of the piston 12 in the actuator housing 18 and transmit it to the controller 42.As soon as a limit or proximity switch 44 detects an end position of the piston 12, it informs the controller 42, which then controls the electric motor M in such a way that the reversing pump 38 pumps fluid in the other direction, so that the piston 12 can assume an opposite direction of movement until it reaches its opposite end position within the actuator housing 18.

[0038] Two valves 46, 48 are used to drain the hydraulic supply circuit 40. When switched accordingly, they establish a fluid-carrying connection between the respective supply lines 36, 38 and a storage tank T. The two valves 46 and 48 serve as discharge valves, in combination with the additional supply device 50, to regulate the thermal balance of the hydraulic oil. Thus, a defined amount of oil is discharged when the cylinder is extended and retracted, and fresh oil from the supply device 50 is pumped back into the closed circuit. Valve 48 is opened during extension, valve 46 is opened during retraction. The opposite side is closed accordingly.Furthermore, an additional supply device 50 is optionally provided, consisting of a conventional motor-pump unit 52, wherein the output side of the associated hydraulic pump is protected via a pressure relief valve 54 to the tank side with the storage tank T. A spring-loaded check valve 56 is provided downstream in the flow direction, which opens toward a fluid filter 58 and closes in the opposite direction.The fluid or hydraulic filter 58 is connected on the output side to a branch point 60 which opens into a connecting line 62 between the two supply lines 34, 36 on the output side of the reversing pump 38, wherein further spring-loaded check valves 64 are arranged towards both supply lines 34, 36, which open in the direction of the respective supply line 34, 36 and close in the opposite direction in order to accordingly prevent an unwanted backflow of fluid from the supply lines 34, 36 in the direction of the filter 58.

[0039] All of the essential fluid components mentioned are housed in a dashed-line frame 66, as shown in Fig. 1. The device in question does not require any low- and / or high-pressure side detection means, such as pressure sensors installed in the fluid lines. Rather, the use of proximity switches 44 allows for trouble-free monitoring of the actuator piston 12. Since the proximity switches 44 detect the operating status of the actuator 10 without contact, no measurement transmission errors occur due to the use of transmission media, such as a fluid. Hysteresis-prone position measuring systems can also be dispensed with during transmission, as they are also subject to wear, which is not the case with the proximity switches 44.

[0040] In the following, the operation of a device according to Fig. 1 is explained in more detail using the flow chart according to Fig. 2.

[0041] After commissioning or starting the device by switching it on, a check is carried out to determine whether initialization has already taken place or not. If the system is not initialized, an initialization routine is called up. This is shown in Fig. 2 (Continued). The actuator is moved to one of its two end positions x, y, for example to a front, first end position x, at a defined setup speed. If the front end position x has not yet been reached, which can be checked using one of the two proximity switches 44, the routine is repeated, i.e. the piston-rod unit 16 of the actuator 10 is extended further until the front end position x is reached, which the assignable proximity switch 44 detects and forwards to the controller 42.

[0042] The controller 42 then stops the electric motor M, which in turn stops the hydraulic or reversing pump 38. If one of the two end positions, front end position x or rear end position y, is reached, this reference point is defined as the zero point by the controller 42. Thus, the rear, second end position y can also be saved as the zero reference point. If referencing to zero is successfully completed, the corresponding routine does not need to be repeated; instead, the piston-rod unit 16 is retracted with respect to the stationary actuator housing 18 at a predeterminable setup speed, and a movement occurs in the opposite direction to detect the second end point or end position y. Once the rear, second end position y is reached, the retraction routine does not need to be continued, and a stop occurs again by switching off the motor M.When the second end position y is reached, the drive in the form of motor M is switched off, and the calculated current position is saved as the maximum end position. Furthermore, during the movement from the first end position x to the second end position y, a theoretical actual position and speed value is calculated as follows using the hydraulic transmission ratio between pump 38 and actuator 10, as well as the knowledge of the current speed values. v(t) zyi = speed of the piston 12 of the actuator 10,

[0043] Vpumpe = Displacement of the reversing pump 38, n(t)Motor = Speed ​​of the motor M, .voi = Volumetric efficiency of the pump 38,

[0044] Azyi = effective ring-piston area of ​​the piston 12 (without rod portion) and s(t)zyi = travel distance of the piston 12

[0045] During the initialization, the travel of the piston 12 is fixed at the first end position proximity switch 44 with Smin = 0 mm and Smax is stored according to the above formula at the second end position proximity switch 44 for the initialization routine.

[0046] If all initialization steps have been successfully completed, the initialization is considered complete and "End Init" is output. As soon as the initialization routine has been successfully completed according to the flow chart on the Continued page in Fig. 2, the cyclic operation of the application begins with saving the current position, as shown in Fig. 2. In particular, with the saving of the current position as part of the cyclic process flow, a virtual braking point is calculated in order to reach one of the two end positions x, y in the shortest possible time. The calculated distance Sbrake to initiate the braking process depends on several factors: deceleration of the drive, maximum speed, distance of the end points or end positions x, y from each other, as well as a freely selectable factor c to make manual adjustments to the process. The calculation is carried out according to the following formula: with

[0047] Smin = 0 mm as value for the first end position proximity switch 44, c = freely selectable factor,

[0048] Vmax = maximum speed for piston 12,

[0049] Vbrake = Target or braking speed after reaching the virtual braking point up to the respective end position x, y and

[0050] Smax = maximum distance to the second end position proximity switch 44

[0051] As explained, the movement is carried out at a specified maximum speed, and as soon as the virtual braking point is reached, the drive unit in the form of motor M decelerates to the second specified target speed, which is significantly lower than the maximum speed, until the piston 12 of the actuator 10 reaches the respective end point as the end position x, y with a low impact speed on the actuator housing 18. The motor M then switches off and again stores the current position and calculates the braking point for the opposite direction of movement, which results from the process flow diagram in Fig. 2. Once the respective end position x, y is reached, the cycle is repeated, whereby the initialization routine must have been completed.Due to the recurring storage of the end positions x and y using the two proximity switches 44 and the respective calculation of the virtual braking point, system- and environmental factors such as temperature, pump wear, and oil condition are also taken into account. Overall, the process control system provides adaptive position control of a closed hydraulic axis without a position measuring system. This has no equivalent in the state of the art.

Claims

Patent claims 1 . Method for controlling a fluidic actuator (10) with at least the following steps: - Carrying out an initialization to determine at least one defined end position (x, y) in a direction of movement of the actuator (10), and then - performing a position control based on a virtual braking point for the actuator (10) associated with the end position (x, y), - Deceleration of the speed of the actuator (10) at the braking point until the end position (x, y) following in the direction of movement is reached, and - Reversing the actuator (10) in the opposite direction of movement.

2. Method for controlling a hydraulic actuator (10) according to Claim 1 with at least the following initialization steps: - controlling the actuator (10) by means of a drive (M) in one direction of movement until one of its two possible end positions (x, y) is reached, - detecting the respective end position (x, y) by means of a sensor device (44), - Referencing one end position (x; y) as zero or starting point, - controlling the actuator (10) in the opposite direction of movement in order to detect the further end position (y; x), - Determination of theoretical position and speed actual values ​​during the movement of the actuator (10) between the two end positions (x, y), - Switching off the drive (M) when the further end position (x, y) is reached, and - Saving the current position value in the respective end position (x, y).

3. Method according to claim 1 or 2, characterized in that the position control is implemented as an adaptive position control and comprises at least the following steps: - Adoption of the current position value saved during initialization, - Calculation of a virtual braking point in order to reach the corresponding end position (x, y) in the shortest possible time, - moving the actuator (10), preferably with a predeterminable maximum speed, until - reaching the virtual braking point with subsequent reduction to a preset target speed until the actuator (10) has finally reached the corresponding end position (x, y), - Switching off the drive (M) and preferably saving the current position, and - Calculate the braking point for the opposite direction of movement.

4. Method according to one of the preceding claims, characterized in that during the initialization during a movement process of the actuator (10) between the two end positions (x, y) to determine the theoretical actual position and speed values, the hydraulic transmission ratio between a hydraulic pump (38) driven by the drive (M) and the actuator (10) is used, taking into account the associated speed values ​​of the drive (M).

5. Method according to one of the preceding claims, characterized in that the position of the two end positions (x, y) is used to calculate the respective braking point, as well as the maximum speed of the actuator (10) during the initialization until the respective end position (x, y) is reached and a braking speed of the actuator (10) at the respective braking point.

6. Method according to one of the preceding claims, characterized in that the end positions (x, y) of the actuator (10) are repeatedly stored and the respective braking point is repeatedly calculated.

7. Method according to one of the preceding claims, characterized in that at least one proximity switch (44) is used to determine the respective end position (x, y) of the actuator (10) without a position measuring system.

8. Device for carrying out a method according to one of the preceding claims, characterized in that the actuator (10) has a hydraulic working cylinder, preferably in the form of a synchronous cylinder, and that a respective proximity switch (44) on the housing side determines the end positions (x, y) of the piston-rod unit (16) of the working cylinder.

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

10. Device according to claim 8 or 9, characterized in that the piston-rod unit (16) with its two piston rods (14) each drives a gas compressor (24) which alternately sucks in gas in the low-pressure range and releases it in a highly compressed state.

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