WO2024184063A1 - Method for actuating a fluid actuator, and device for carrying out the method - Google Patents

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

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

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

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, consisting essentially of 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 servo motor which can be electrically controlled, regulated and/or switched by means on the low-pressure side and/or high-pressure side. The advantage of this solution is that there is essentially no pulsation when a high-pressure medium is introduced into a filler or no flaking of brittle materials during water jet cutting. Furthermore, pressure fluctuations, particularly when switching a cutting valve on and off, are kept to a minimum by using the hydraulic drive, which largely prevents overloading of components. In the specific embodiment, the low- and/or high-pressure side means referred to are pressure sensors which, when inserted into assignable fluid lines, detect the pressure prevailing there and transmit it as an electrical output variable to an electrical control system for operating the pump's servo motor.

Based on this prior art, the invention is based on the object of creating an improved solution. This object is achieved by a method with the features of patent claim 1 and a device with the features of patent claim 8.

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

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

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

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

- Reversing the actuator in the opposite direction of movement.

This prevents the actuator from hitting the respective end position at maximum speed, which is usually formed by the front sides of the associated actuator housing, but rather a predeterminable virtual braking point is approached by means of a position control, preferably at maximum speed, and when the braking point is reached, the actuator speed is then decelerated in such a way that it reaches the end position at a significantly decelerated speed, without causing damage to the actuator and its housing. Since the actuator is in the context of a pressure transmission in If the two opposing actuation directions are intended to ensure the delivery of fluid under high pressure to a consumer, after reaching one end position the actuator is redirected to 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 delivery 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.

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 at least by the following initialization steps:

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

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

- Referencing one end position as zero or starting point,

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

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

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

- Saving the current position value in the respective end position.

Due to the fact that after switching on the device or system there is no information about the current position of the actuator, it is moved to one of the two positions at a defined setup speed. End positions initially driven. The end position is detected by means of an assignable proximity switch, which is preferably arranged stationary on the actuator housing. Proximity switches of this type, also known as proximity initiators, are sensors that react to approach, i.e. without direct contact, for example with the moving parts of the actuator or with the fluid used, without contact.

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 in order to detect the second end point or the second end position. During the movement process, a theoretical position and speed actual value is calculated using the hydraulic transmission ratio between the pump and actuator and the knowledge of 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.

In this case, position control is used as an adaptive position control, which is characterized by at least the following steps:

- Adoption of the current position value saved from the initialization,

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

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

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

- Calculate the braking point for the opposite direction of movement.

If, as explained, the initialization routine has been successfully completed, the cyclic operation of the application begins with the storage of the current position of the actuator and the calculation of the braking point in order to reach the end point in the shortest possible time. This significantly improves efficiency. The calculated distance to initiate the braking process depends on several factors: deceleration of the drive, maximum speed, distance between the end points and a freely selectable factor to make manual adjustments to the process. The system then moves at a specified maximum speed. As soon as the virtual braking point is reached, the drive unit decelerates to a second specified target speed until the hydraulic actuator has reached the end point. The drive then switches off and again stores the current position and calculates the braking point for the opposite direction of movement. A movement 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 also taken into account. Examples of this include: temperature, pump wear and oil condition. Overall, an adaptive position control for a closed hydraulic axis is created, in the form of the actuator, without a position measuring system.

The invention further relates to a device for carrying out the method described above, wherein the actuator has a hydraulic working cylinder, preferably in the form of a synchronous cylinder. Furthermore, a proximity switch on the housing side sets the end position of the Piston-rod unit of the hydraulic working cylinder in question. In contrast to the known displacement measuring devices, the proximity switch responds directly to the end position of the actuator without hysteresis processes occurring that could affect the timely transmission of the sensor measurement. A proximity switch also operates essentially wear-free compared to displacement measuring systems with their assignable moving components.

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, the hydraulic pump and the actuator together forming a closed hydraulic supply circuit so that any leakage losses that may occur are avoided.

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

In the following, the method according to the invention and the device are explained in more detail using an embodiment according to the drawing. In this case, the basic and not to scale representation shows the

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 chart of Fig. 2; and

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, which is 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 hydraulic oil flowing in and out is therefore always the same and the piston-rod unit 16 therefore also moves in and out at the same speed in both directions. The piston-rod unit 16 in the initial 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.

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 part 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 in the same way. The respective gas compressor 24 extracts gas, for example hydrogen gas, from the inlet side from a low-pressure line 26 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 opened for the delivery to the high-pressure side 30. A compressor cycle can now proceed as follows. If the piston 12 of the actuator 10 moves to the right (as viewed in Fig. 1) into the first or front end position x, it takes the two compressor pistons 22 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 pushes the highly compressed gas quantity via the additional right check valve 32 into the high-pressure line 30 when the right check valve 28 is closed.

After the right end position for the piston 12 of the piston-rod unit 16 is 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 left additional check valve 32 with the left check valve 28 closed. The right check valve 28 also opens and gas flows noticeably from the low-pressure line 26 into the expanding gas space of the right gas compressor 24, since its compressor piston 22 is moved from right to left. The right additional check valve 32 is therefore closed. After the left end position for the piston 12 is reached, the direction is reversed and the loading and unloading cycle for the two gas compressors 24 is repeated as described above.

The two cylinder chambers 20 of the actuator 10 are each connected to a supply line 34, 36, which can be supplied with fluid of a predetermined pressure by a hydraulic pump 38 in the form of a reversing pump. In particular, the reversing pump 38 is able to alternately push fluid back and forth between the two supply lines 34, 36 in order to move the piston-rod unit 16 of the actuator 10 back and forth alternately. Since the amount of fluid 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 manages with a constant amount of fluid. 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.

The hydraulic or reversing pump 38 is driven by an electric motor M which can be controlled by a controller 42 and which is symbolically shown with an arrow in Fig. 1 to indicate its controllability. The controller 42 receives the sensor data from two proximity switches 44 on the input side, which in this case are each arranged at the end of the actuator housing 18 and thus monitor the position of the piston 12 as soon as it hits the adjacent front end 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 pass it on 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.

Two valves 46, 48 are used to empty the hydraulic supply circuit 40, which, when switched accordingly, create a fluid-carrying connection between the respective supply line 36, 38 and a storage tank T The two valves 46 and 48 serve as discharge valves in order to regulate the thermal balance of the hydraulic oil in combination with the additional supply device 50. In this way, a defined amount of oil is discharged when the cylinder is extended and retracted, and fresh oil from the supply device 50 is fed back into the closed circuit. Valve 48 is opened when extending, valve 46 is opened when retracting. 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 secured to the tank side with the storage tank T via a pressure relief valve 54. Downstream in the flow direction there is a spring-loaded check valve 56 which opens in the direction of 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 prevent an unwanted backflow of fluid from the supply lines 34, 36 in the direction of the filter 58.

All of the essential fluid components mentioned are accommodated in a dashed frame 66 as shown in Fig. 1. The device mentioned does not require any low- and/or high-pressure detection means, such as pressure sensors inserted into 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 situation of the actuator 10 without contact, there are no measurement transmission errors due to the use of Transmission media, such as a fluid. It is also possible to dispense with position measuring systems that are susceptible to hysteresis during transmission, which are also subject to wear, which is not the case with the proximity switches 44.

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.

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

v(t)_zyi = Geschwindigkeit des Kolbens 12 des Aktors 10, The control 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 control 42. The rear, second end position y can therefore also be saved as the zero reference point. If referencing to zero has been successfully completed, the relevant 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 in the opposite direction takes place in order to detect the second end point or end position y. If the rear, second end position y is reached, the retraction routine does not need to be continued and a stop is made again by switching off the motor M. When the second end position y is reached, the drive in the form of the motor M is switched off and the calculated, current position is saved as the maximum end position position. Furthermore, during the movement process from the first end position x to the second end position y, a theoretical position and speed actual value is calculated as follows via the hydraulic transmission ratio between pump 38 and actuator 10 and the knowledge of the current speed values

v(t) _zyi = speed of piston 12 of actuator 10,

Vpumpe = delivery volume of the reversing pump 38, n(t)Motor = speed of the motor M, .voi = volumetric efficiency of the pump 38,

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

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 at the second end position proximity switch 44 for the initialization routine according to the above formula.

If all steps of the initialization are completed successfully, the initialization is considered finished and "End Init" is displayed. 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 a storage of the current position, as shown in Fig. 2. In particular, when the current position is stored as part of the cyclic process, 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 and a freely selectable factor c to make manual adjustments to the process. The calculation is carried out according to the following formula: with

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

Vmax = maximum speed for piston 12,

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

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

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 the 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 end position x, y with a low impact speed on the actuator housing 18. Then the motor M switches off and again stores the current position and calculates the braking point for the opposite direction of movement, which can be seen from the process flow diagram in Fig. 2. If the respective end position x, y is then reached, the cycle is repeated, whereby the initialization routine must be completed. Due to the recurring storage of the end positions x, y using the two proximity switches 44 and the respective calculation of the virtual braking point, system and environmental factors are taken into account, such as temperature, pump wear and oil condition. Overall, the process flow control provides an 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), - Decelerating 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 a 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 predeterminable 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 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 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.