JP2023546245A - Method for operating hydraulic drives - Google Patents

Abstract

The present invention is a method for operating a hydraulic drive (100) comprising a hydraulic consumer (130) with a piston (134) positionable within a cylinder (132). 132) is connected at one connection (A) to the pressure medium accumulator (110) and at the other connection (B) to the pressure medium sink (120) via a proportional valve (140), where , the position (x) or velocity TIFF2023546245000006.tif6150 of the piston (134) is controlled in a closed loop using a model-based closed loop control in which the set position of the proportional valve (140) is preset.

Description

The invention relates to a method for operating a hydraulic drive comprising a hydraulic consumer with a piston positionable in a cylinder, as well as a calculation unit and a computer program for implementing the method.

BACKGROUND OF THE INVENTION Electrohydraulic shafts include pumps (usually operated using electric motors or drives) and hydraulic cylinders that allow electrical or electronic closed-loop control of the position of the cylinder piston, for example. It is a hydraulic drive device equipped with. Such electro-hydraulic shafts are used, for example, in so-called deep-drawing presses, injection molding machines, die-casting machines or machines of other forming technologies, as well as for example for moving heavy loads or machine parts. used. It is likewise possible to use, for example, a pressure medium accumulator instead of a pump or a combination of both. Furthermore, mention may also be made in this connection of hydraulic drives.

In such (electro)hydraulic shafts, a force release position control is usually provided, that is to say, for example, a force control or a position control, depending on the operating point. Alternatively, instead of a force control, an equivalent pressure control may be envisaged, for example on the basis of the relationship between the force and the pressure via the pressure acting surface in a hydraulic cylinder. Also, instead of position control, it is also possible to consider speed control.

In such closed loop control, the discharge volume and/or rotation speed of the pump (or drive motor) can be controlled in a closed loop. However, it is also possible, for example, to use a control valve arrangement for varying the volume flow of the working fluid at the inlet and/or outlet of the cylinder.

These components have usage limitations placed upon them, such as, for example, maximum pressure, dead time, and set speed limits. To this end, constraints and components can also be described in the model and intelligently incorporated into the rule design. Basically, the strong nonlinearities, dead times and limitations of such hydraulic systems present problems for closed-loop and open-loop control. To account for these systematic limitations in open-loop and closed-loop control, a continuous optimization problem can be solved in real time. In particular, model predictive control (MPC) and reinforcement learning (RL) approaches are used here, which require high computational power during runtime. In systems that should have a high bandwidth, this can no longer be resolved significantly and in any case becomes insignificant for high sampling rates.

DISCLOSURE OF THE INVENTION According to the invention, a method is proposed for operating a hydraulic drive, as well as a calculation unit and a computer program for implementing the method, with the features of the independent patent claims. Preferred embodiments are the subject of the dependent claims and the following description.

The present invention relates to a method for operating a hydraulic drive comprising a hydraulic consumer with a piston positionable in a cylinder. This hydraulic drive has two chambers, here designated for example by A and B, separated by a piston. Each chamber is then assigned to one of the plurality of connections (A, B). The hydraulic drive can in particular be a hydraulic shaft. In this case, the cylinder is connected at one connection (e.g. A) to a pressure medium accumulator (here, in particular, it can be a low-pressure accumulator) and/or to a pump, and at the other connection (e.g. B) to a control valve. It is connected via a device to a pressure medium sink. In particular, the tank is considered here as a pressure medium sink. However, it is also conceivable (via corresponding connections) to use the first side (ie chamber A) as a pressure medium sink (regeneration circuit).

The position or velocity of the piston is then controlled in a closed-loop manner using or within the framework of a model-based closed-loop control in which the set position of the control device is preset. The control device may include one or more continuously adjustable valves.

In this case, a reversing section model (or reversing system model) of the hydraulic drive is preferably used for setting and adjusting, in particular closed-loop control, the setpoint value for the (braking) force on the piston using a control device. is used. The control device, for example a proportional valve, is used here in particular in a closed-loop control circuit, i.e. in the (subordinate) closed-loop control circuit, the setting adjustment of the slider on the valve can also be carried out with feedback of the actual value of the position. can. In an inversion model, the actual output variables (eg, position) are used as model inputs, and the actual input variables (eg, volume flow or pressure) are used as model outputs.

By using such a position/speed control it is possible to react particularly well and quickly to different phases or to transitions between different phases, for example in the movement of a casting cylinder. . Furthermore, such a closed-loop control can be parameterized particularly easily and quickly.

In order to achieve the setpoint value for the force on the piston, the setpoint position of the proportional valve is preferably determined via planning of the setpoint pressure in the hydraulic drive and the resulting setpoint position of the proportional valve. A target progress curve is estimated. Planning the target pressure here includes, in particular, planning the differential pressure between two connections or measuring the pressure on one side and planning the pressure on the other side. This thus represents a type of pilot control or hybrid pilot control and closed loop control.

The variables whose actual values are required in this closed-loop control are here, in particular, the position of the piston and the two pressures on the two connections (A and B). These can be captured using suitable sensors, for example. Therefore, within the framework of model-based closed-loop control, the velocity and acceleration of the piston can also be determined from the position of the piston. From there, the desired flow rates (volume flow rates) can then also be determined on both sides and are therefore preset accordingly. In this context, in the case of model-based closed-loop control, on the basis of a model of the system (here, as mentioned above, in particular an inverted interval model is used), the trajectory, i.e. the variable (in this case the position) It should also be mentioned that the course curve can be calculated in advance and also online. Control variables are also referred to as state variables in the case of model-based closed-loop control and can take state constraints into account. For a more detailed description of the model, please also refer to the description of the drawings.

By connecting one of the connections (A side), for example via a switching valve, to a pressure medium accumulator, it can be derived there from a constant pressure, at least in a first approximation, or pre-determined depending on the stroke and speed. can be calculated, whereby only the pressure on the other side (B side) is relevant. Therefore, in trajectory planning, the underlying mechanical differential equations are taken into account, namely pressure, position and velocity, among others. In this case, the plan for the pressure target value can be limited to the plan for the B-side pressure. This is because the other side is directly connected to the pressure medium accumulator and thereby corresponds (at least approximately) to the accumulator pressure (the dynamic effect is here the A side pressure in the calculation at each timestamp). ).

When presetting the set position of the proportional valve, as mentioned above, in particular within the framework of the subordinate closed-loop control, a pilot control is preferably carried out as well, which pilot control can be used for selecting the proportional valve (directly in the open-loop control). (proportional valve controlled or pilot controlled proportional valve). In this case, the desired value for the position of the main stage of the proportional valve is expediently pilot-controlled. Here, the underlying system can for example describe a PT2 control system with dead time and state limits. The pilot control then uses the valve's main stage target value as an input. The dynamic characteristics of the proportional valve can be taken into account particularly well in this way.

In this regard, it should be noted that pilot control is effective as long as the internal conditions of the proportional valve are not saturated. However, an attempt is always made to open-loop control the proportional valve to saturation for as long as possible. Saturation here means, in particular, that the pilot stage is fully open for as long as possible. Using (normal) closed-loop control, this would only be achieved in a very short period of time. This is because position signals existing beyond the maximum opening value are lost. In contrast, with pilot control, the system acquires dynamic characteristics without becoming unstable. Thereby, the flow rate on the B side (or proportional valve side) can be set or preset with sufficient accuracy.

A particular advantage here is that even systems that are not themselves flat can be inverted (using the inverted interval model). Systems with hydraulic cylinders are essentially not considered flat. This is because the generation of the actuator force (which is introduced into the mechanical differential equation) is ambiguous, ie a given pressure difference on both sides is formed by a wide variety of combinations of pressures. However, especially in the case of die-cast circuits (or in general in the case of the interconnects mentioned in the introduction), inversion nevertheless works. This is because the pressure is biased in the cylinder and the chamber on the pressure medium accumulator side (A side) communicates directly with the accumulator pressure, for example via a switching valve. Therefore, in the state-space representation, it can be assumed that the pressure in this chamber of the cylinder is constant. The force increase therefore depends only on the pressure in the other chamber (B side). However, since the pressure medium accumulator has (somewhat) inherent dynamic properties, whereby the pressure is not constant in practice, further corrections can still be made in order to minimize errors in the pilot control. For example, if the pressure is measured or calculated in a chamber on the pressure medium accumulator side (side A), this pressure can additionally be used for the pressure planning in the other chamber or on the other side (side B). can. Therefore, the valve opening or set position of the proportional valve (on the B side) can be used as the only set variable (or actuator).

Thus, by using system and load models, highly dynamic processes, such as aluminum die casting, for example, can be handled even if the dynamics of the control loops of the system components involved are not optimal. can. Everything is no longer closed-loop controlled, but partially pilot-controlled (via the model), in particular taking into account known set-variable limits and dynamic characteristic limits. In a manner of speaking, a switchable planning filter algorithm is provided, which allows state trajectory planning in real time, in particular cylinder pressure bias, accumulator pressure, and actuator (i.e. proportional valve) dead time/setup dynamics. can be considered.

Additionally, pilot control rules based on flatness can be implemented by making the above assumptions and linearizing the underlying system model. This makes the residual error dynamics sufficiently small. This enables parameterization that can be retrofitted without using lookup tables or characteristic curves as much as possible. Additionally, this allows the development of large and small cylinder units to be significantly improved. This is because only the model parameters are variable, or only the model parameters need to be changed, while the underlying procedure (eg, mapped to software) remains essentially unchanged.

A further advantage is that the valves can be controlled in a much more dynamic open-loop manner than hitherto. As long as the valve is in a small signal range, the drive control time can be halved. Systems that are not flat can nevertheless be controlled by pilot control via the proposed method or adjustments made therein.

Additionally, within the framework of model-based monitoring of the hydraulic drive, it is also possible to compare predetermined values of variables with corresponding measured values. This can be done as "condition monitoring". Additionally, variable gear ratios can be used to increase efficiency and accuracy.

A computing unit according to the invention, for example a hydraulic axis control device, is configured to implement the method according to the invention, in particular with regard to programming techniques.

It is also advantageous to implement the method according to the invention in the form of a computer program or computer program product having a program code for implementing all method steps. This is because this incurs only a small outlay, especially if the implementing control device is anyway already existing because it is also used for further tasks. Suitable data carriers for providing computer programs are, in particular, magnetic, optical and electrical memories, such as, for example, hard drives, flash memories, EEPROMs, DVDs. Downloading the program via a computer network (Internet, intranet, etc.) is also possible.

Further advantages and embodiments of the invention will become apparent from the following description and the accompanying drawings.

The features mentioned above and those further explained below can be used not only in the combinations presented in each case, but also in other combinations or in a single context, without departing from the scope of the invention. Needless to say, it is.

The invention is schematically illustrated in the drawings on the basis of exemplary embodiments and will be explained in more detail below with reference to the drawings.

1 schematically shows a hydraulic drive suitable for carrying out the method according to the invention; FIG. 1 schematically illustrates the sequence of the method according to the invention in a preferred embodiment; FIG. 1 schematically shows a second embodiment of a hydraulic drive suitable for pressure induction of the method according to the invention; FIG. 1 schematically shows a third embodiment of a hydraulic drive suitable for pressure induction of the method according to the invention; FIG.

DETAILED DESCRIPTION OF THE DRAWINGS FIG. 1 schematically shows a hydraulic drive 100 with which the method according to the invention can be implemented, as will also be explained below. This hydraulic drive 100 comprises in this embodiment two pressure medium accumulators 110 and 112, in which case the pressure medium accumulator 110 is in particular (for example less than 300 bar, for example from 170 bar to 200 bar). The pressure medium accumulator 112 is in particular a high-pressure accumulator (for example with a pressure of more than 400 bar).

Furthermore, the pressure medium accumulators 110, 112 can be connected to a hydraulic consumer 130, which in the present case is a cylinder 132 with a positionable piston 134. The position of the piston or the position of the reference point thereon is indicated by x. By using a piston, for example, the load 136 can be moved. The cylinder 132 can be connected to the pressure medium accumulator 110 (low pressure accumulator) at the connection A via a valve 144 configured as a switching valve and to the pressure medium accumulator 112 (high pressure accumulator) via a proportional valve 146 It is. It goes without saying that during operation, preferably only one of the two pressure medium accumulators is connected, in which case in this embodiment in particular the connection to pressure medium accumulator 110 (low pressure accumulator) is In some cases, this is observed when the switching valve 144 is opened.

Furthermore, the cylinder 132 is connected to the working fluid tank 120 via a proportional valve 140 at the connection port B. The set position of the slider of the proportional valve 140 is indicated by y. Similarly, cylinder 132 can be connected to connection A via a proportional valve 142 at connection B. However, in the case of this embodiment, the illustrated situation in which the proportional valve 142 is closed should be observed in particular.

However, in principle it is possible to realize different interconnections for different operating phases of the hydraulic drive 100, e.g. by appropriate switching or switching of valves, as used e.g. in the framework of an aluminum die-casting. can do.

In the cylinder 132 or piston 134, the A-side piston surface is designated by _AA , and the annular B-side piston surface is designated by _AB . The A-side pressure (in the piston chamber) is _pA and the B-side pressure (in the annular chamber) is _pB . The discharge or flow rate to or from the cylinder 132 is indicated by Q _A on the A side and Q _B on the B side.

For example, valves 140, 142, 144 and 146 can be activated via calculation unit 150, which is configured as a control unit. The hydraulic drive device 100 can therefore be used as a hydraulic shaft.

（速度）並びに圧力ｐ_Ａ及び／又はｐ_Ｂも含まれる。これらは、状態制御部２１０及びパイロット制御部２２０に伝送される。次いで、ここでは、位置ｘについての目標値から比例弁１４０の設定位置ｙについての値が求められる。 FIG. 2 shows the sequence of the method according to the invention in a preferred embodiment. For closed-loop control of the position x of the piston, a state control 210 with a flatness-based pilot control 220 is used, which can be implemented, for example, on the calculation unit 150 and a hydraulic drive. 100 inversion models or interval models 200 are used. Here, target values (target trajectories) for state variables are determined. In particular, this includes not only the position x of the piston, but also its time derivative

(velocity) and pressure _pA and/or _pB . These are transmitted to the state control section 210 and the pilot control section 220. Then, here, a value for the set position y of the proportional valve 140 is determined from the desired value for the position x.

が属する。圧力ｐ（ここでは、既に述べたように、Ａ側における圧力は一定であるとみなすことができるため、Ｂ側における圧力のみが考慮される（ただし、両方の圧力でも可能である））は、速度及び加速度から決定することができる。フィルタパラメータは、好適には、（液圧式の駆動装置の）目標システムの動特性が（圧力媒体アキュムレータからの）既存の設定エネルギによって達成し得るように選択される。 Within the framework of the aforementioned trajectory planning, the setpoint value for the position x of the piston is subjected to, for example, an nth-order low-pass filtering, which then yields the nth-order derivative of the signal of the setpoint value. This includes, for example, speed

belongs to. The pressure p (here, as already mentioned, the pressure on the A side can be considered constant, so only the pressure on the B side is considered (although both pressures are also possible)) is: It can be determined from velocity and acceleration. The filter parameters are preferably selected such that the target system dynamics (of the hydraulic drive) can be achieved with the existing set energy (from the pressure medium accumulator).

As soon as it is possible to determine the correct setting variable (setting position of the proportional valve) y depending on the inverted model 200 of the system, based on the target pressure on the B side (using the volume flow equation), e.g. A setpoint value for the volumetric flow rate _QB can be determined, and from there a setpoint value for the set point y can also be determined. The system can be open-loop controlled so that position can be tracked with very small deviations. Phase shifts due to system dead time continue to be preserved.

についての実際値が生じる。この下位の閉ループ制御の枠内においては、同様にパイロット制御も行われ、詳細には、メインステージ１４０．２の設定位置又は位置において行われる。図３及び図４は、本発明に係る方法のシーケンスに関しては図１と異なるものではない。図３及び図４は、高圧アキュムレータ１１２に対する代替的な変形形態のみを示しているので、参照記号は、実質的に同一である。 This set position y is carried out within the framework of a subordinate closed-loop control in which the pilot stage 140.1 and the main stage 140.2 are taken into account, whereby the force F and the speed of the piston also represent the actual value x _ist of the position.

Actual values for . Within the framework of this subordinate closed-loop control, a pilot control also takes place, in particular in the set position or position of the main stage 140.2. 3 and 4 do not differ from FIG. 1 with respect to the sequence of the method according to the invention. Since FIGS. 3 and 4 only show alternative variations to the high pressure accumulator 112, the reference symbols are substantially the same.

The hydraulic drive shown schematically in FIGS. 3 and 4 differs from the hydraulic drive shown in FIG. The difference is that a pressure booster 152 is used, which pressure booster 152 is configured, for example, as a differential cylinder. The structure of this type of pressure intensifier 152 is well known and does not require further explanation. Here, a further low-pressure accumulator 111 is provided which can be connected to the intensifier pressure chamber via accumulator isolation valves 146 , 148 in order to tension the intensifier pressure chamber in the support direction of the cylinder 132 when connected to the low-pressure accumulator 110 . is necessary. Pressure intensifier 152 and cylinder 132 are assigned a control valve arrangement which can be operated independently of each other in that further proportional valves 146, 148 are arranged at the outlet of pressure intensifier 152. This differs from the control valve arrangement of FIG. 1 which is broken down into two possible proportional valves 140, 142. The check valve 143, which may be configured as a logic valve, for example, provides a rapid closing of the piston chamber 132 with respect to the low-pressure accumulator 110 upon pressure build-up in the piston chamber.

Closed-loop control of the pressure build-up is realized via a proportional valve 146 arranged in FIG. 3 at the outlet of the pressure intensifier and, in a further variant, in FIG. 4 at the inlet of the pressure intensifier 152. .

Claims (13)

A method for operating a hydraulic drive device (100) comprising a hydraulic consumer (130) with a piston (134) positionable within a cylinder (132), the method comprising:
Said cylinder (132) is connected at one connection port (A) to a pressure medium accumulator (110) and at the other connection port (B) to a pressure medium sink (120) via a proportional valve (140). ,
the position (x) or speed of the piston (134);

is closed-loop controlled using a model-based closed-loop control in which the set position (y) of said proportional valve (140) is preset. In order to set and adjust, in particular closed-loop control, the setpoint value for the force on the piston (134) using the proportional valve (140), a reversal section model (200) of the hydraulic drive (100) is provided. 2. The method according to claim 1, wherein the method is used. In order to achieve the target value for the force on the piston (134), the planning of the target pressure in the hydraulic drive (100) and the resulting set position of the proportional valve (140) ( 3. The method according to claim 1, wherein a setpoint curve of the setpoint position (y) of the proportional valve (140) is estimated via y). The planning of the target pressure includes planning a differential pressure between the two connections (A, B) or measuring pressure on one side and planning the pressure on the other side. , the method according to claim 3. 5. According to one of claims 1 to 4, a proportional valve having a main stage (140.2) and one or more pilot stages (140.1) is used as the proportional valve (140). the method of. 6. The method according to claim 1, wherein a pilot control is carried out when presetting the set position (y) of the proportional valve (140), in particular within the framework of a subordinate closed-loop control. . 7. The method according to claim 5 or 6, wherein in the pilot control for the proportional valve (140) a setpoint value for the position of the main stage (140.2) of the proportional valve is pilot controlled. 8. The cylinder (132) is connected to the pressure medium accumulator (110) at the connection port (A) via a valve (144), in particular a switching valve. the method of. 9. The method according to claim 1, wherein within the framework of model-based monitoring of the hydraulic drive (100), predetermined values of variables are compared with corresponding measured values. 10. The method according to any one of claims 1 to 9, wherein the hydraulic drive (100) is used for a hydraulic shaft. Computing unit (150) configured to implement the method according to any one of claims 1 to 10. Computer program, when executed on a computing unit (150), for causing said computing unit (150) to carry out the method according to any one of claims 1 to 10. A machine-readable storage medium on which a computer program according to claim 12 is stored.

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