Methods for operating hydraulic drives

Abstract

The present invention relates to a method for operating a hydraulic actuator (100a), the hydraulic actuator comprising a hydraulic pump (120) driven by a variable-speed electric motor (110) and a hydraulic load (130) connected to the hydraulic pump (120), the hydraulic load having a positionable element (132), wherein the method is based on a model (200) of the hydraulic actuator (100a) and the speed (n) of the hydraulic pump (120). ist The position (x) or velocity estimate (x) of the positionable element (132) for the hydraulic load (130) is obtained by determining the number of rotations or rotations. ist And based on position and / or velocity estimates (x) ist ) The hydraulically operated drive (100a).

Description

Technical Field

[0001] The present invention relates to a method for operating a hydraulic actuator, the hydraulic actuator comprising a hydraulic pump driven by a variable-speed electric motor and a hydraulic load connected to the hydraulic pump, wherein the hydraulic load has positionable elements; furthermore, the present invention relates to a computing unit and a computer program for implementing the method. Background Technology

[0002] An electro-hydraulic shaft relates to a hydraulic actuator having a motor, a hydraulic pump, and a hydraulic cylinder, wherein electrical or electronic adjustment of the position of, for example, the cylinder or its piston is possible. Such electro-hydraulic shafts are used, for example, in so-called deep-drawing presses, injection molding machines, or other molding technology machines, as well as for the movement of heavy loads or machine parts.

[0003] In most cases, such electro-hydraulic shafts have separate force-position adjustments, meaning that force or position adjustment occurs, for example, based on the operating point. Instead of force adjustment, pressure adjustment can also be provided, based on the premise that the relationship between force and pressure, for example, the pressure acting on the surface of a hydraulic cylinder, is equivalent.

[0004] In such adjustments, for example, a valve can be used to change the volumetric flow rate of the hydraulic fluid in the cylinder. Adjustment of the rotational speed of the motor driving the hydraulic pump can also be achieved. The hydraulic pump can be configured, in particular, as a fixed-displacement pump with a fixed delivery rate per working cycle or as a variable-displacement pump with a variable delivery rate. Summary of the Invention

[0005] According to the present invention, a method for operating a hydraulic actuator, a computing unit, and a computer program for implementing the method are proposed.

[0006] This invention relates to a method for operating a hydraulic actuator, the hydraulic actuator comprising a hydraulic pump, particularly a fixed displacement pump, driven by a variable-speed electric motor, and a hydraulic load connected to the hydraulic pump, the hydraulic load having a positionable element. The hydraulic load with the positionable element is preferably a hydraulic cylinder having a piston as the positionable element.

[0007] The operation of such hydraulic actuators typically involves regulating, or if necessary, controlling only the position of a positionable element, or if necessary, the speed, and on the other hand, controlling the pressure applied to the positionable element of the hydraulic load, or if necessary, the force applied through the positionable element of the hydraulic load. Furthermore, for completeness, it should be mentioned that pressure regulation and force regulation are equivalent in hydraulic loads, since pressure through the working surface is associated with force. As explained at the beginning, separate force-position regulation can be provided here, i.e., force or pressure regulation or position or speed regulation (or each, if necessary, only controlled) occurs based on the operating point. Similarly, as already explained, valves for varying the volumetric flow of the hydraulic medium in a hydraulic load can be used, for example, in such regulation. And, alternatively, regulation, particularly of the secondary speed of the motor driving the hydraulic pump, can be achieved, the motor speed being associated with, and particularly even identical to, the pump speed.

[0008] For such a hydraulic actuator to operate properly, it is necessary to obtain the relevant parameters, namely, in particular the position or velocity of the positionable element and the actual values ​​of pressure or force. This can be detected or measured using appropriate sensors (arranged at suitable locations on the hydraulic load).

[0009] However, this is disadvantageous due to the high cost of such sensor mechanisms and their integration into hydraulic actuators. This high cost is often undesirable, especially in simple applications using hydraulic actuators.

[0010] In this context, it is proposed that: based on the model of the hydraulic drive and the number of revolutions or rotations of the hydraulic pump (which, as explained, is related to the number of revolutions or rotations of the electric motor and can also be applied synonymously), position and / or velocity estimates of the position or velocity of the positionable element for the hydraulic load are obtained, thereby or based on which the hydraulic drive is subsequently operated, or more precisely, its method is to use the position and / or velocity estimates as actual values ​​for the positionable element used to regulate the hydraulic load.

[0011] This is achieved by adjusting, in particular, the pressure applied to or the force applied by the positionable element of the hydraulic load. Conversely, it is preferable to control the position and / or speed of the positionable element of the hydraulic load, although it can also be adjusted within the scope of this invention.

[0012] The model can be, for example, a physical model of a hydraulic actuator, taking into account all relevant geometric dimensions of the specific hydraulic actuator. From this, for example, it is possible to calculate: how much hydraulic medium is delivered to the hydraulic load during pump rotation and how much displacement the positionable element thereby moves. Dynamic effects can also be considered in particular. This thus provides a type of model-based sensor mechanism that is sufficient to meet requirements without the need for physical sensors. An observer is also mentioned, by means of which estimates are obtained. In a simple implementation, the quantity change is produced as the product of pump rotation and the delivery quantity, and the position change is produced as the quotient of the quantity change and the cylinder cross-sectional area.

[0013] This approach provides a particularly simple, cost-effective, and robust solution for hydraulic drives, such as electro-hydraulic actuators or shafts, as illustrated above. Furthermore, it is plug-and-play, meaning it is more or less easy to create and apply, and also easy to handle in service situations, thus enabling a wide range of applications. The proposed model-based approach is particularly accurate for simple applications with, if necessary, limited dynamics and precision, such as lifting shafts (Hubachsen), clamping shafts (Klemmachsen), or accessories.

[0014] When using estimated values ​​(i.e., position and / or velocity estimates) for position and / or velocity, the values ​​or actual values ​​of the pressure applied to or the force applied through the positionable element can be obtained using sensors. For example, one could consider using a pressure sensor on each side of a hydraulically loaded differential cylinder.

[0015] However, it is also preferable to obtain pressure or force estimates based on the model of the hydraulic actuator, especially when using or based on the actual value of the torque of the electric motor (or, if necessary, the corresponding current), wherein the hydraulic actuator operates based on the pressure or force estimate, i.e., the pressure or force estimate can be used, for example, as the actual value for the aforementioned adjustment. A pressure or force sensor is not necessary, at least in the location involved. This can provide a simpler and more advantageous solution, as is sufficient, for example, in applications such as adjusting actuators, lifting shafts, or lifting tables.

[0016] Preferably, leakage of the hydraulic medium is also considered in the model of the hydraulic actuator, as this may occur, for example, in the hydraulic load, pump, and hydraulic lines. The amount of leakage here is also related to the displacement through which the positionable element passes, and, if necessary, its velocity. This makes the operation or regulation of the hydraulic actuator more accurate even in the absence of sensors. As already emphasized, different types of operation can be distinguished here in particular. Thus, for example, leakage of the hydraulic medium can be considered individually (i.e., with different factors if necessary) for the removal and / or insertion and / or recovery of the positionable element. Recovery here refers to the operation of the differential cylinder, in which the two cylinder chambers are hydraulically connected and filled with hydraulic medium by an additionally supplied volumetric flow. The cylinder is removed here because, at approximately the same pressure, the removal force through the (larger) piston face exceeds the insertion force through the (smaller) annular face. In the case of removal, the oil pushed from the annular chamber is guided into the piston chamber. This volumetric flow no longer needs to be delivered by the "normal" (or conventional) volumetric flow source (pump / valve). Effectively, a "normal" volumetric flow source must also deliver hydraulic fluid to the rod face (= piston face - annular face), thus requiring a significantly smaller volumetric flow from the "normal" source, or achieving a significantly higher evacuation speed using the maximum volumetric flow of the "normal" source. The so-called "rapid evacuation line" is also mentioned here.

[0017] Furthermore, it is preferable to repeatedly (e.g., at periodic time intervals or based on the total displacement traversed by the locatable element) correct the position and / or velocity estimates by moving the locatable element, under hydraulic load, toward a reference position. In such a reference position, such as an end position or end stop (i.e., when the locatable element is fully moved in or out, or reaches a mechanical stop, or a position that can be accurately detected by other means), the position of the locatable element is based on, for example, its geometry being known in itself. Reaching the end stop can be identified, for example, by motor torque and optionally by a pressure sensor (if present). Any reference position can be identified, for example, by a simple detector (switch contact). It is suitable to set such a position to a state that is reached as frequently as possible, for example, in each cycle.

[0018] If, at such a reference location, the estimated value differs from the actual value—a drift that is often unavoidable even for accurate models in practice—then correction can be implemented, meaning the estimate can be reset. Such correction is particularly effective at compensating for drift in estimates caused by leakage.

[0019] The arithmetic unit according to the present invention, such as the control unit of an electro-hydraulic shaft, is specifically configured by programming techniques to implement the method according to the present invention.

[0020] It is also advantageous to implement the method according to the invention in the form of a computer program or computer program product with program code for implementing all method steps, because this results in particularly low costs, especially if the control device used for execution is also used for other tasks and therefore exists anyway. Suitable data carriers for providing the computer program are particularly magnetic, optical, and electrical memories, such as hard disks, flash memory, EEPROM, DVDs, and others. Moreover, it is also possible to download the program via computer networks (Internet, intranet, etc.).

[0021] Further advantages and design solutions of the present invention are derived from the specification and drawings.

[0022] It goes without saying that the features described above and below can be applied not only in the combinations described herein, but also in other combinations or individually, without departing from the scope of protection of this invention. Attached Figure Description

[0023] The present invention is schematically illustrated with reference to the embodiments in the accompanying drawings and will be described in detail below with reference to the drawings.

[0024] Figure 1a and 1b A hydraulic actuator is schematically shown, which is suitable for implementing the method according to the invention.

[0025] Figure 2 A model of a hydraulic actuator is schematically shown, as it may be used in the method according to the invention in a preferred embodiment. Detailed Implementation

[0026] exist Figure 1a The diagram schematically illustrates a hydraulic actuator 100a, in which the method according to the invention can be implemented, as will also be explained below. The hydraulic actuator 100a here has a variable-speed electric motor or actuator 110, which is connected, for example, to a hydraulic pump 120 via a coupling 115. The hydraulic pump 120 is, for example, an axial piston pump implemented as a fixed-displacement pump with a fixed delivery volume per working cycle. The hydraulic pump 120 can be driven at variable speeds by means of the electric motor 110.

[0027] Furthermore, the hydraulic pump 120 is connected to the hydraulic load 130, which is here a cylinder 131 with a positionable element 132 configured as a piston. The hydraulic pump 120 is connected to the cylinder 131 at both ends, thus allowing movement of the piston 132 in both directions—depending on the direction of rotation of the hydraulic pump 120. The electric motor 110 can be controlled by an arithmetic unit 150 configured as a control unit, or, if necessary, by additional components such as a converter or frequency converter. The hydraulic drive 100a can therefore be used as an electro-hydraulic shaft.

[0028] To operate the hydraulic actuator 100a, the position x of the piston or positionable element 132 can be controlled or, if necessary, adjusted according to the method of the invention in a preferred embodiment. For this purpose, a rated value x for position x can be predetermined for the control unit 150, for example. soll .

[0029] To adjust the position x, the current actual value x ist For example, it is necessary. The actual value x ist However, instead of detecting or measuring with the aid of sensors or displacement sensors, the actual value x is estimated by observer 155. ist This is a position estimate. Here, the model is based on a hydraulic actuator (as referenced below). Figure 2 (As will be further explained) and the current speed n of the hydraulic pump 120 or the electric motor 110 in the same sense. ist Find the actual value x ist For example, it can be calculated or estimated that a certain number of revolutions is necessary for a certain duration—or a certain number of revolutions—in order to move the piston by a certain displacement. Accordingly, the electric motor can be controlled using, for example, a current I as a regulating parameter for secondary adjustment of the number of revolutions.

[0030] As explained at the beginning, the pressure applied to piston 132 can also be adjusted. For this purpose, the actual pressure value p... ist It is necessary that the actual pressure value in the hydraulic actuator 100a—as in the position—is not obtained by means of a sensor or pressure gauge, but rather, for example, by means of an observer 155, i.e., based on a model and the torque M of the electric motor 110. ist (This torque is obtained from the current that generates the torque, if necessary).

[0031] To correct, for example, the position estimate, the piston can be moved to a reference position x. R Here, the piston, for example, mechanically reaches a stop (here: fully engaged). The reference position x R For example, it can be stored in the control unit, so that if the position estimate obtained for this purpose according to the model is compared with the reference position x... R If the location value is different, then the location estimate can be corrected.

[0032] This method allows for particularly simple and robust control or regulation of hydraulic drives without the need for costly sensors, which is accurate enough, at least for simple applications.

[0033] exist Figure 1b The diagram schematically illustrates a hydraulic actuator 100b, in which the method according to the invention can also be implemented. This differs from the method according to... Figure 1a The hydraulic actuator 100a is equipped with two pressure sensors 140 and 141, which can measure the pressure p in the pressure medium on side A of cylinder 131. A Or the pressure p on side B of cylinder 131 B These pressure values ​​are then supplied to the control unit 150 and used there as actual values ​​in control or regulation. Compared to a reference... Figure 1a The method described here therefore only estimates the location, but not the pressures. Furthermore, see the section on... Figure 1a The description.

[0034] This approach also allows for simple and robust control or regulation of hydraulic actuators, at least partially, without the need for cost-intensive sensors, which is advantageous compared to... Figure 1a The slightly more complex variations are also accurate enough.

[0035] exist Figure 2 The diagram schematically illustrates a hydraulic actuator model 200, as it can be used or is used in a preferred embodiment of the method according to the invention, and this model particularly takes into account leakage. The rotational speed n of the electric motor 110 and the delivery flow V of the pump are considered. g The hydraulic medium volume flow Q that causes the hydraulic pump P .

[0036] Volumetric flow Q reaching the cylinder Z In principle, it corresponds to the volumetric flow Q of the hydraulic pump. P However, subtracting the leakage volume flow Q leak The leakage volumetric flow is based on the loss due to a leak, such as in a pump or pipeline. This leakage volumetric flow Q leak It is now related to the leakage coefficient k and the speed n of the electric motor (or pump).

[0037] As has already been explained, it has been shown that: leakage or leakage volume flow Q leak The leakage coefficient can vary depending on the cylinder's movement, which is taken into account in Model 200. Specifically, the leakage coefficient is selected based on the specific circumstances, and the revolutions per minute (RPM) is multiplied by the leakage coefficient to obtain the actual leakage volumetric flow rate Q. leak Therefore, for example, when removing a cylinder, a coefficient k is used. out For the shift-in coefficient k in And for the recycling of the removal using the coefficient k recu These coefficients can be determined for specific applications, such as on a test bench. To better illustrate this, an example of such coefficients is: k out = 0.7% * V g k in= 3.5% * Vg, and k recu = 2.4% * Vg. In practice, these coefficients are typically related to the specific pump, and if necessary, to the valves, hydraulic medium, operating pressure, cylinder seals, etc. This allows for further improvement of the hydraulic actuator's operation.

Claims

1. Method for operating a hydraulic drive (100a, 100b), which comprises a hydraulic pump (120) driven by an electric motor (110) with variable number of revolutions and a hydraulic load (130) connected to the hydraulic pump (120) with a positionable element (132), wherein calculating a position and / or speed estimate for the position or speed of the positionable element (132) of the hydraulic load (130) on the basis of a model (200) of the hydraulic drive (100a, 100b) and the number of revolutions or rotations of the hydraulic pump (120), and wherein the position and / or speed estimate is corrected in that the positionable element (132) of the hydraulic load (130) is moved towards a reference position, wherein a pressure and / or force estimate for the pressure exerted on the positionable element (132) of the hydraulic load (130) or the force exerted by the positionable element (132) of the hydraulic load (130) is calculated on the basis of the model (200) of the hydraulic drive (100a) in addition, wherein the hydraulic drive (100a, 100b) is operated on the basis of the position and / or speed estimate and / or pressure and / or force estimate.

2. The method of claim 1, wherein, The position and / or speed estimate is used as an actual value for the regulation of the positionable element (132) of the hydraulic load (130).

3. The method of claim 2, wherein, The position and / or speed of the positionable element (132) of the hydraulic load (130) and / or the pressure exerted on the positionable element (132) of the hydraulic load (130) and / or the force exerted by the positionable element (132) of the hydraulic load (130) is regulated by means of the regulation.

4. The method of claim 2 or 3, wherein, The position and / or speed of the positionable element (132) of the hydraulic load (130) is controlled.

5. The method of claim 1, wherein, A secondary regulation of the number of revolutions of the hydraulic pump (120) is carried out.

6. The method of claim 1, wherein, Leakage of the hydraulic medium is taken into account in the model (200) of the hydraulic drive (100a, 100b).

7. The method of claim 6, wherein, The leakage of the hydraulic medium is taken into account individually for the movement out and / or movement in and / or recovery movement out of the positionable element (132) of the hydraulic load (130).

8. The method of claim 1, wherein, The position and / or speed estimate is repeatedly corrected in that the positionable element (132) of the hydraulic load (130) is moved towards a reference position.

9. The method of claim 1, wherein, A fixed-displacement pump or a variable-displacement pump is used as hydraulic pump (120).

10. The method of claim 1, wherein, The hydraulic drive (100a, 100b) is used for an electric hydraulic axle.

11. Computing unit (150), which is set up to carry out the method according to any one of the preceding claims 1 to 10.

12. Computer program product, which, when executed on a computing unit (150), causes the computing unit (150) to carry out the method according to any one of claims 1 to 10.

13. Machine-readable storage medium having stored thereon a computer program, which, when executed on an operating unit (150), causes the operating unit (150) to carry out the method according to any one of claims 1 to 10.

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