Method for positioning an actuator

Abstract

The invention relates to a method for positioning an actuator (12), in particular in the form of a hydraulic cylinder (14), which is connected to a hydraulic supply circuit (10) having a pressure-supply device (32) in the form of a motor-pump group (34), characterized in that, during the movement process of the actuator (12), by means of the hydraulic transmission ratio between the pump (36) and the actuator (12), taking into account the current rotational speed n of the motor (M), a theoretical actual position value s (t)zyl and actual speed value v (t)zyl is calculated, and in that at least this theoretical actual position value is used as an actual value for a position controller for a motor controller (FU) of the motor-pump group (34).

Description

[0001]HYDAC KINESYS GMBH Industriestraße, 66280 Sulzbach / Saar, Germany Method for positioning an actuator The invention relates to a method for positioning an actuator, in particular in the form of a hydraulic working cylinder, which is connected to a hydraulic supply circuit with a pressure supply device in the form of a motor-pump group.DE 102018001303 A1 discloses a valve device comprising: - an inlet connection on an inlet side for supplying a hydraulic consumer, in particular in the form of a hydraulic working cylinder, with pressure fluid; - an outlet connection on an outlet side for discharging pressure fluid from the connectable consumer, wherein, depending on the control direction of this consumer, the inlet side changes to the outlet side and the outlet side to the inlet side; - a pressure supply connection; and - a return connection, wherein a pressure control device acts on the respective inlet side and a volume flow control device acts on the respective outlet side.In this way, a type of decentralized valve control is created with so-called separate control edges, which offer the possibility of separate control of valve elements on the inlet and outlet sides of a hydraulic consumer, such as a hydraulic working cylinder, that can be connected to the valve device. DE 102020002960 A1 discloses a system for braking a displacement-controlled drive system, which can be driven for movement by means of an inlet and an outlet pressure on an inlet and outlet side, respectively, wherein, by means of an electro-proportional adjustment of at least one valve element, an outlet volume flow of the drive system is controlled in such a way that the outlet pressure is decoupled from the movement of the drive system and can be freely preset, and is coupled with the inlet pressure, which can thus be reduced to the level necessary for the movement of the drive system.Because the inlet and outlet pressures can be adjusted independently of each other electro-proportionally, it is possible to set the pressure at the working port belonging to the outlet path independently of the pressure at the working port belonging to the inlet path. DE 102021003236 A1 discloses a method for adapting the control of a proportional valve to its functional operation as part of a fluid system, comprising the following steps: - Determining measured values ​​of the proportional valve during its operation outside the fluid system; - Creating a characteristic curve field based on the measured values; - Integrating the proportional valve into the fluid system; and - Adapting the control of the proportional valve to the fluid system, based on the characteristic curve field, by means of a control device.The aforementioned process steps eliminate the need for costly and time-consuming active adaptation of the proportional valve's control to the fluid system, which includes a hydraulic consumer such as a working cylinder and into which the proportional valve is integrated, in the sense of a learning process by the fluid system manufacturer or user. Based on this prior art, the invention aims to further improve known solutions. A method with the features of claim 1 in its entirety achieves this objective.According to the characterizing part of claim 1, during the actuator's movement process, a theoretical actual position and speed value ( ) is calculated using the hydraulic transmission ratio between the pump and the actuator, taking into account the current rotational speed of the motor, and at least this theoretical actual position value serves as the actual value of a position controller for a motor control system of the motor-pump group. This theoretically determined position value can then be used as the actual value of the position controller. The theoretical position value ( ) is determined according to the following formulas. with = pump delivery volume ( ) = motor speed = volumetric efficiency = piston area on a piston or rod side of the actuator. In a further preferred embodiment of the method according to the invention, it is provided that during initialization, the actuator is moved to at least one of its two end positions by means of a defined setup speed, the detection of which is carried out by means of an evaluation of the increase of an attributable load pressure, and that if a predefinable threshold value is exceeded with regard to the load pressure, the motor-pump group is stopped as a drive for the actuator in order to subsequently relieve an associated pressure chamber of the actuator, and / or that if the predefinable threshold value is undershot with regard to the load pressure, the motor-pump group stops again and the current position of the actuator associated with this is defined as the zero point or starting position.This enables the precise positioning of an actuator during operation. Preferably, it is further provided that continuous referencing takes place during operation in order to include system- and environment-related factors such as temperature, pump wear, oil condition, etc., and to minimize any associated tracking error concerning the actuator's actual position. Preferably, it is further provided that a process step similar to "clamping the workpiece," comparable to performing an initialization routine, serves as the reference point during referencing.After completion of the function or process step "clamping the workpiece," in which the pressure control has generated a desired clamping pressure, the actuator is actively relieved by the motor-pump group according to a preferred embodiment of the inventive method. When the pressure falls below a predefinable value, the motor-pump group stops, and the resulting current position is stored as a new reference or starting point in the motor control unit, so that any function can subsequently be called up again via the actuator. In this way, the respective cylinder chamber of the actuator is actively relieved by the drive, and when a defined pressure value is reached, the drive stops, and the current position is stored as a new reference point. Subsequently, any function can be called up again.In this way, the positioning of an actuator-supported clamping system is enabled by means of a displacement-controlled hydraulic system without a translational absolute encoder. Initially, during initialization, and because no information about the actuator's current position is available after the system is switched on, the actuator is moved to one of its two cylinder end positions at a defined setup speed. The respective end position is then detected by evaluating the load increase. If the load rises above a defined threshold, the drive is stopped, and the system then actively relieves the pressure chamber to a defined setpoint. If the desired pressure is undershot, the drive stops, and the current position is defined as the zero point relative to the actuator's position.The solution according to the invention also includes a device for carrying out the method described above, with the features specified in claim 7. Further embodiments of the device according to the invention are the subject of the dependent claims. The method according to the invention is explained in more detail below with reference to a device as shown in the drawing. Figures 1 and 2, in the manner of hydraulic circuit diagrams, show a hydraulic supply device for an actuator, such as a hydraulic working cylinder, in a schematic and not-to-scale representation; and Figures 3 and 4, in the manner of a flowchart, show the execution of an initialization and a working cycle using a device according to Figures 1 and 2, wherein the path branching off to the right in Figure 3 at "Initialized yes" leads in the direction of the arrow to the left input side "Ready for operation" in Figure 4.Figure 1 shows a fluidic or hydraulic supply circuit 10 with a hydraulic consumer in the form of an actuator 12, which is designed as a hydraulic differential piston cylinder 14. The differential piston cylinder 14 has a conventional piston-rod unit 16 that separates a piston chamber 18 from a rod chamber 20. Furthermore, the piston-rod unit 16 is guided longitudinally within an actuator housing 22. When the piston-rod unit 16 extends to the right (as viewed in Figure 1), the volume of the piston chamber 18 increases, and the volume of the rod chamber 20 decreases accordingly. When the unit 16 retracts, the corresponding volume ratios for the piston chamber 18 and the rod chamber 20 are reversed.An electromagnetically actuated 4 / 2-way valve 24, shown in Figure 1 in its spring-loaded home position, controls the opposing movements of the actuator 12. In this position, the piston chamber 18 is connected to a reservoir 28 via fluid lines 26, and the rod chamber 20 is connected to a central fluid supply or pressure supply unit 32 via further fluid lines 30. When the valve 24 is switched, the positions of the piston chamber 18 and rod chamber 20 are relieved of pressure towards the reservoir 28. Thus, the piston-rod unit 16 moves in and out of the actuator housing 22 in opposite directions. These processes are well-known and will not be discussed in further detail here.The central pressure supply unit 32 comprises a conventional motor-pump assembly 34 with a hydraulic pump 36, designed as a constant-displacement pump, which draws fluid from the storage tank 28 on the input side and feeds fluid of a predetermined quantity and pressure into the supply circuit 10 via a supply line 38 on the output side. The valve 24 is connected to this supply line via a corresponding fluid-carrying inlet. Furthermore, the motor-pump assembly 34 includes a variable-speed electric motor M, which is coupled to the input side of the hydraulic pump 36 via a shaft connection 40. A frequency converter (FC) is used to control the motor M. The FC receives input sensor data from a pressure sensor 42 and a speed sensor 44.For pressure measurement, the pressure sensor 42 is connected in the supply line 38 of the working circuit 10, and for speed measurement, the speed sensor 44 measures the rotational speeds at the shaft connection 40. Other motor control concepts are conceivable here. A pilot-operated pressure relief valve 46 with spring space relief serves to protect the hydraulic supply or working circuit 10. This relief is connected to the discharge side of the valve 46 in the return line towards the reservoir 28. For this function, the pressure relief valve 46 is connected in the supply circuit 10 between a junction 48 and the reservoir 28. The discharge side of the hydraulic pump 36, as well as one of the other fluid lines 30 along with its associated supply line 38, connect to the junction 48.For the sake of completeness, it should also be mentioned that the pressure sensor 42, with its pressure-measuring input side, is connected to the supply line 38 via a further junction 50. The device shown in Figure 1 enables a method for positioning the actuator 12, in particular in the form of the hydraulic working cylinder 14, which is connected to the hydraulic supply circuit 10 with the central pressure supply device 32 in the form of the motor-pump group 34, whereby during the movement of the actuator 12, a theoretical position is determined by means of the hydraulic transmission ratio between the pump or hydraulic pump 36 and the actuator 12, taking into account the respective current speed of the motor M. sitions and the actual speed value ( ) is calculated, whereby at least this theoretical actual position value serves as the actual value of a position controller for the motor control FU of the motor-pump group 34. After the theoretical position value ( ) can be determined according to the formulas given at the beginning, the actuator 12 is moved to at least one of its two end positions 52, 54 by means of a defined setup speed as part of an initialization for the position procedure. One end position 52 is formed by housing parts of the actuator housing 22, against which the piston of the piston-rod unit 16 abuts with its free end face, whereas the other or further end position 54 is formed by further housing parts of the actuator housing 22, against which the piston abuts on the rod side in its maximum deflected position.The inventive method does not necessarily require that the end positions 52, 54 are actually reached by the piston-rod unit 16; rather, it suffices to approach these positions, the detection of which is achieved by evaluating the increase of an attributable load pressure. If a predefinable threshold value for the load pressure is exceeded, the motor-pump group 34, which drives the actuator 12, is stopped in order to subsequently relieve the pressure in an associated pressure chamber 18 or 20 of the actuator 12. If the predefinable threshold value for the load pressure is undershot, the motor-pump group 34 is stopped again, and the corresponding current position of the actuator 12 is defined or referenced as the zero point or initial position.The individual initialization steps associated with this, as well as the resulting sequence of events, are illustrated in Figure 3 using flowcharts, so that the individual steps will not be discussed in detail here. It is understood that the evaluation steps mentioned, as well as the sensor data acquisition, are performed by at least one processing unit (CPU), which is an integral part of the motor control unit (VFD). A further device for implementing the method according to the invention is shown in Figure 2, and this solution will only be explained insofar as it differs significantly from the embodiment shown in Figure 1.In the embodiment according to Figure 2, the 4 / 2-way valve 24 is omitted, and the alternating supply of the piston chamber 18 and rod chamber 20 of the actuator 12 is achieved via a fluid pump 36, which, in reversing mode, can feed fluid at a predetermined pressure in both directions into associated supply lines 38 connected to the piston chamber 18 and the rod chamber 20. To implement a closed-loop system, a hydraulic accumulator 56 is integrated into the supply circuit 10. This accumulator compensates for any missing volume during the oscillating operation of the actuator 12 and, when activated, is supplied with fluid at a predetermined pressure from the lines 38 via the pressure relief valve 46. To detect the pressure value situation at the actuator 12, two pressure sensors 42, each pointing towards the piston chamber 18 and the rod chamber 20, are now connected in the supply circuit 10.On the output side, the two pressure sensors 42 supply the motor control unit (FU) of the motor-pump group 34 with their sensor data in the form of pressure values. Furthermore, the hydraulic accumulator 56 can be supplied with fluid at a predefined pressure if a controllable check valve 58 opens and then, viewed in the direction of Figure 2, supplies fluid from the hydraulic pump 36 via the left supply line 38 to the fluid supply line 60 of the accumulator 56, whereby the hydraulic pump 36 is directly supplied with circulating fluid without the storage tank 28. A control line 62, connected to the right supply line 38, which leads to the rod chamber 20 of the actuator 12, serves to control the check valve 58.If the fluid pressure in the right supply line 38, as viewed in Figure 2, is higher than in the left, the check valve 58 opens and establishes a fluid-carrying connection between the left fluid supply line 38 and the fluid feed line 60. Spring-loaded check valves 64, additionally connected in the supply circuit 10, prevent unwanted backflow of fluid in the opposite direction to the actual supply direction. Thus, as viewed in Figure 2, the pressure relief valve 46 is protected against backflow on its inlet side by the two upper spring-loaded check valves 64, so that the pressure relief valve 46 receives its fluid on the inlet side exclusively via the respective supply line 38, provided that the corresponding response pressure is above the preset actuation pressure of the respective check valve 64 of the upper pair.The further spring-loaded check valve 64 opens towards the right supply line 38 with one outlet of the fluid or hydraulic pump 36 as soon as the pressure in the fluid supply line 60 is greater than in the aforementioned right supply line 38. Instead of a differential cylinder as actuator 12, a synchronous cylinder (not shown) or a correspondingly designed hydraulic motor (also not shown) can also be used.

Claims

Patent claims 1. Method for positioning an actuator (12), in particular in the form of a hydraulic working cylinder (14) connected to a hydraulic supply circuit (10) with a pressure supply device (32) in the form of a motor-pump group (34), characterized in that during the movement of the actuator (12), a theoretical position ( ) and actual speed value ( ) is calculated using the hydraulic transmission ratio between the pump (36) and the actuator (12), taking into account the respective current rotational speed of the motor (M), and that at least this theoretical actual position value serves as the actual value of a position controller for a motor control unit (VFD) of the motor-pump group (34).

2. Method according to claim 1, characterized in that the theoretical position value ( determined according to the following formulas wird with = delivery volume of the pump ( ) = speed of the motor = volumetric efficiency = piston area on a piston or rod side of the actuator.

3. Method according to claim 1 or 2, characterized in that, during initialization, the actuator (12) is defined by means of a defined- The actuator (12) is moved at a set speed to at least one of its two end positions (52, 54), the detection of which is carried out by means of an evaluation of the increase of an attributable load pressure, and that if a predefinable threshold value is exceeded with respect to the load pressure, the motor-pump group (34) is stopped as the drive for the actuator (12) in order to subsequently relieve an associated pressure chamber (18, 20) of the actuator (12) and / or that if the predefinable threshold value with respect to the load pressure is undershot, the motor-pump group (34) stops again and the associated current position of the actuator (12) is defined as the zero point or starting position. 4.A method according to one of the preceding claims, characterized in that, in order to include system- and environment-related factors and to minimize any associated tracking error concerning the actual position value of the actuator (12), continuous referencing is performed during operation.

5. A method according to one of the preceding claims, characterized in that, within the framework of referencing, a process step "clamping the workpiece" is used as a reference or starting point within the method. 6.Method according to one of the preceding claims, characterized in that after the completion of the process step "clamping the workpiece", in which the pressure control has generated a desired clamping pressure, the actuator (12) is actively relieved by the motor-pump group (34) and that if a predefinable pressure value is undershot, the motor-pump group (34) stops and the associated current position is stored as a new reference or starting point in the motor control (VFD) such that. Subsequently, any function can again be called via the actuator (12).

7. Device for carrying out a method according to one of the preceding claims, characterized in that at least one actuator (12) is provided which is connected to a hydraulic supply circuit (10) with a motor-pump group (34) and with at least one pressure sensor (42) at least on an actuation side (18, 20) of the actuator (12), which transmits its measured value data to a motor controller (VFD), which specifies the pump output for the hydraulic supply circuit (10) via the speed of the motor (M).

8. Device according to claim 7, characterized in that the actuator (12) is formed from a differential piston cylinder (14) or a synchronous cylinder. 9.Device according to claim 7 or 8, characterized in that the motor-pump group (34) has at least one constant-speed pump which feeds fluid into the associated supply circuit (10) in one pumping direction (Figure 1) or in reverse operation (Figure 2) in both counter-rotating pumping directions.

10. Device according to any one of claims 7 to 9, characterized in that the hydraulic supply circuit (10) has a valve control device (24) for reversing the actuator (12) when using a pump (36) with only one delivery direction.

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