WO2010136271A2

WO2010136271A2 - Control method of a digital hydraulic controller

Info

Publication number: WO2010136271A2
Application number: PCT/EP2010/055280
Authority: WO
Inventors: Ville Hopponen
Original assignee: Metso Paper, Inc.
Priority date: 2009-05-29
Filing date: 2010-04-21
Publication date: 2010-12-02
Also published as: WO2010136271A3; DE102009026609A1

Abstract

A digital hydraulic controller has valves that can be switched individually and in different combinations thereof. Each of these valve switch combinations corresponds to a flow rate. A currently required flow rate (D_new) is selected from a limited number of flow rates which are smaller than the entire number of flow rates. The limited number of flow rates lies in a range close to the previous current flow rate (D_old).

Description

CONTROL METHOD OF A DIGITAL HYDRAULIC REGULATOR

description

The invention relates to a control method of a digital hydraulic controller.

Hydraulics is widely used as actuation and control means; In particular, actuators are hydraulically driven, with which large forces can be set and exercised with high accuracy.

Typically, a working fluid, e.g. Hydraulic oil, water, a water emulsion, a gas or a gas emulsion used, which is pressurized by a pump.

The introduction of the pressurized hydraulic oil into a hydraulic actuator, e.g. one

Hydraulic cylinder or a hydraulic motor is typically controlled by a proportional control valve or

Proportional valve controlled, which can be electrically, hydraulically or pneumatically driven.

Such a control valve has a displaceable or displaceable spool or spool, which in

In response to its location in an associated valve body, it can set a target pressure at the outlet by controlling the pressure of hydraulic oil supplied by the pump. The mobility of the control piston in the valve housing necessarily requires a certain clearance or gap between the control piston and valve housing, so that an internal leakage of the control valve is unavoidable. The gap size must not be too narrow, otherwise the valve would be too susceptible to contamination in the hydraulic oil. Recently, alternative pressure regulators have been developed, which in this application are to be referred to throughout as digital hydraulic pressure regulators. If such digital hydraulic pressure regulator used as a pressure reducer, they are referred to throughout the present application as a digital hydraulic pressure reducer.

The operation of the digital hydraulic pressure regulator, for example, in the journal fluid no. 7-8, 2008 p. 12, 13 described in more detail. The improved readability of this application, the method of operation of digital hydraulic pressure regulator is again summarized very briefly:

In the simple case, a digital hydraulic pressure regulator consists of a series of valves connected in parallel, which have only ON / OFF functions; So simple ON / OFF switching valves are that allow or interrupt a flow and can be consistently referred to in this application as valves. The valves are all connected to a common supply line on the one hand and to a common output line on the other. The valves themselves may be conventional solenoid valves, i. Be valves with electromagnetic drive. Of course, other forms of drive can be chosen.

By connecting or installing throttle elements or by the valves themselves, it is ensured that the valves have different flows when they are open. If, for example, four valves are provided, then the flow rates Q in the individual, in each case by the associated valve selectively releasable passages in the ratio of 1: 2: 4: 8 to each other; at a larger number of valves will continue this series accordingly.

By opening and closing individual valves or valve combinations, which are determined and selected on the basis of mathematical models by a computer, a rapid and precise pressure adjustment in the output line or in the actuator connected thereto can now be achieved. This is achieved by replacing the analogue control curve of the initially described proportional control valve with a digitally generated (approximate) control curve. Due to the omission of non-linearities and / or hysteresis of the analogue proportional valve, this curve can be a step-like approximated straight line which allows a control point to approach a control point quickly and (virtually) free of overshoot.

Another advantage of the digital hydraulic control is that the valves are either open or closed, i. To maintain a desired pressure in a closed (and unchanged) system, the valves are simply closed and there are no internal leakage flows. This is a clear difference to the conventional proportional valve, which is always flowed through by a hydraulic oil flow. This constantly costs energy for the hydraulic pumps, e.g. in the paper machine.

Thus, it can be seen that the use of digital hydraulic pressure regulators permits

To operate hydraulic pumps less often or shorter, which saves energy.

A digital hydraulic actuator is normally assigned four valve banks, each having a same Number of valves and / or restrictors have. A schematic representation of such a hydraulic system, which can be used for example on a paper machine, is shown in FIG. 1. The valve banks are also referred to as a digital flow control unit and are therefore provided in FIG. 1 with the abbreviation DFCU.

The hydraulic system of Fig. 1 consists of a by means of two actuators 1, 5 displaceable cylinder 3, which is to be guided against a fixed cylinder 7. The actuators 1, 5 have a first chamber A and a second chamber B. If the pressure in the respective chamber A is increased in relation to the pressure in the respective chamber B, there is an advancing movement of the movable cylinder 3 against the fixed cylinder 7. In contrast, there is a return movement when the pressure in the respective chamber B is increased. Each actuator 1, 5 is a digital hydraulic controller 2, 4 assigned, which have the same structure.

In order to achieve the feed movement, the valves of the valve banks PA in the two digital hydraulic controllers 2, 4 are switched so that a connection between a pump P for generating a hydraulic pressure in a working fluid and the chamber A in the actuators 1, 5 is made , At the same time, the valves of the valve banks B-T in the digital hydraulic controllers are switched to establish communication between the respective chambers B and a tank T for the hydraulic fluid. The switching of the valves creates a certain flow for the hydraulic fluid.

For a reset movement, accordingly, the valve banks PB and AT in the two digital hydraulic Controllers 2, 4 switched so that a connection between the pump P and the chamber B is made in the actuators.

In addition, an accumulator may be provided between the pump and the valve banks which is supplied with hydraulic fluid as needed via the pump so that a minimum hydraulic pressure is always available in the hydraulic system. In this case, the pressure accumulator can be supplied with the hydraulic fluid from the tank T.

Since the hydraulic fluid can flow in both directions through the valve banks AT, PA, PB, BT, it is possible in certain operating states to switch the valve banks so that the hydraulic fluid from the tank into one of the chambers A or B (TA, TB) is sucked. Also, in certain operating conditions, it may be possible to let the hydraulic fluid flow from one of the chambers A or B to the pressure accumulator or pump (A-P, B-P).

Since each valve bank has a plurality of valves and throttles of the same, there is a very large number of different valve switching combinations or these corresponding respective flows. For example, with six valves per valve bank, there are a number of 2 ¹² = 4096 different valve switch combinations or flow rates alone for the feed motion, as well as a further 4096 flow rates for the return movement.

Since an excessively high computing power is required to determine the flows just required in the operation of such a hydraulic system, an approach has been taken in which only the flows most likely to be required to produce a desired pressure in the actuator 1 are checked. FIG. 4 shows the reduction of the flows to be checked on the basis of a coordinate system in which each point corresponds to a possible valve switching combination or a possible flow. However, not all 4096 possible flows are shown for reasons of space.

The hatched area in Fig. 4 indicates a sector containing the most likely flows to be considered for review. In the prior art, the out-of-sector flows are ignored in the review. In the case of the mentioned six valves per valve bank, the number of flows to be checked is reduced to approximately 400 to 800 in this way.

Although this reduction leads to a lower requirement for the computing power used, the required computer power to check these 400 to 800 flows is still too high or requires too much time to verify. This, in turn, adversely affects the control of the hydraulic system.

In addition, by limiting to the 400 to 800 most likely valve switching combinations, it is not possible to have others outside this range

To produce valve switching combinations. Therefore, it is not possible to react appropriately in particular situations deviating from the most common standard situations.

Thus, it is the object of the invention to provide a control method of a digital hydraulic controller provide that requires a reduced computer power.

The object of the invention is achieved by a control method of a digital hydraulic controller according to claim 1. Advantageous embodiments are set forth in the dependent claims.

According to the invention, a digital hydraulic controller has valves that can be switched on one another individually and in different combinations. Each of these

Valve switch combinations corresponds to a flow. A currently required flow will be limited

Number of flows selected that is less than the total number of flows. In addition, the limited number of flows is in a range around the previous current flow.

As a result, the control can advantageously approach the valve combination in all directions, the corresponding flow of which creates the pressure ratio required in the actuator. In addition, the control is not limited to a limited number of flows.

Advantageously, the valves are divided into two valve banks or digital flow control units, so that the flows can be transferred into a two-dimensional coordinate system. The axes of the coordinate system correspond to the valve switching combinations or flows of the individual valve banks.

It can be particularly advantageous for the area from which the selection of the currently required flow takes place to be the flow field in the coordinate system define. In this case, the center of the flow field can advantageously be formed by the previously current flow.

In addition, the flow field in the ordinate as well as in the abscissa direction can be defined by the same number of flows.

It can be particularly advantageous if the valve banks each have six valves, that the flow field has a square shape, which can be defined by 7 x 7 flow rates or by 4 x 4 flow rates.

Alternatively, the flow field may include other shapes such as e.g. have a cross shape, a circular shape or an ellipse shape.

According to the invention, the selection of the currently required flow can be carried out by means of a mathematical algorithm from the limited number of flow rates or from the flow field. A penalty function can be used particularly advantageously as a mathematical algorithm.

Particularly advantageous corresponds to the currently required flow that valve switching combination that leads to a pressure that is closest to a target pressure. In this case, the target pressure may correspond to the pressure which is to be present in a pressure chamber of an actuator to achieve a specific state.

A digital hydraulic controller, which is operated according to the above-described control method, can be used in a hydraulic system for a machine with a be used hydraulic actuator. Further, in the hydraulic system, a high-pressure accumulator for storing a hydraulic working fluid under pressure and a pump for feeding the high-pressure working fluid into and charging the high-pressure accumulator may be provided.

Further advantages of the invention will become apparent from the following description taken in conjunction with the figures.

In the figures shows:

1 shows a hydraulic system for a machine to which the control method according to the invention can be applied;

FIG. 2 is a schematic view of an exemplary construction of digital flow control units of a digital hydraulic controller; FIG.

3 is a schematic representation of a method for selecting a currently required flow according to an embodiment of the invention;

Fig. 4 is a schematic representation of a method for reducing selectable flow rates according to the prior art.

A control method of a digital hydraulic controller according to the embodiment may be carried out on a hydraulic system according to FIG. 1, which has already been dealt with in the introduction to the description. 2 shows a schematic arrangement of the individual digital flow control units (DFCU) or valve banks AT, PA, PB, BT, each with five valves. The valves are solenoid valves. The valves are followed by a throttle, whereby different flow rates of the individual valves can be achieved.

2, the valve banks of the digital hydraulic controller 2 are shown, which is assigned to the actuator 1. In this case, the valve banks P-A and B-T are combined for one feed movement, while the valve banks P-B and A-T are combined for a return movement.

Although not shown in FIGS. 1 and 2, an accumulator is provided between the pump and the valve banks, which is supplied with hydraulic fluid as needed by the pump so that a minimum hydraulic pressure is available at all times. In this case, the pressure accumulator can be supplied with the hydraulic fluid from the tank T.

In the following explanations for explaining the control method according to the invention of a digital hydraulic controller, a reset movement is treated using the example of the digital hydraulic controller. In this case, the hydraulic fluid from the pump or the accumulator via the valve bank P-B is passed into the chamber B of the actuator 1, while the hydraulic fluid from the chamber A of the actuator 1 is passed through the valve bank A-t in the tank.

Fig. 3 shows a coordinate system which represents a part of the possible valve switching combinations of the valve banks PB and AT. In brackets, the possible reversal of the flow direction (B-P and TA) is indicated under certain operating conditions. Each point in the coordinate system corresponds to a possible flow through a Valve switching combination of the valve banks PB and AT is brought about. Since the valve banks PB and AT each have five valves, there are a total of 2 ¹⁰ = 1024 possible valve switching combinations or flow rates.

To perform the reset movement, starting from a previously current flow D _a i _t by means of a penalty function, a currently required flow D _new determined whose valve switching combination in the actuator provides the pressure which is closest to the required pressure for the reset movement.

According to the method of the embodiment, before the determination by means of the penalty function, a flow field in the form of a square is formed around the previously current one

Flow D _a i _t defined. The square field has 7 x 7 = 49 flows and is shown in FIG. 3 by dashed lines.

Because of this, instead of the 1024 possible

Flows only 49 flows including the previous current flow D _a i _{t t} be checked by means of Penalty function. This leads to an advantageous reduction of the required computer power or computing time of about 1/20.

In the next step, a new flow field whose size is again 7 x 7 flows is defined in order to determine the currently required flow rate D _new . In Fig. 3, this new flow field is drawn with solid lines and hatching. Thereafter, the currently required flow D _{new is defined} as the previous current flow and the determination of the next currently required flow is made one of the channels in the hatched square.

In an experiment conducted by the inventors, six valves were provided per valve bank in a hydraulic system according to that shown in Fig. 1, resulting in 2 ¹² = 4096 different valve switching combinations. Carrying out the method according to the invention with a quadratic flow field of 7 × 7 = 49 flows, compared to the method shown in the prior art in FIG. 4, led to an improvement of 4.29 ms to 0.23 ms in the feed motion and to an improvement of 3.065 ms to 0.41 ms in the return movement.

In a further experiment, the method was also carried out at a pressure adjustment in a state in which the cylinder 3 was fully delivered to the fixed cylinder 7. The pressure adjustment is at an operation of e.g. a paper machine in this state required to ensure at all times compliance with the required distance and pressure between the cylinders, on the one hand to obtain an excellent product and on the other hand to prevent damage or failure of the cylinder.

In the pressure adjustment, the flow field was reduced from 126 points according to the prior art to 16 points, resulting in a time reduction from 2.1 ms to 0.31 ms.

A further advantage achieved by the method according to the invention is that, due to the reduction of the necessary computer power, it is used on a commercial PC instead of a specially designed one Research PC can be operated with excessive computer power.

Thus, it is possible by means of the control method according to the invention for a digital hydraulic controller to significantly reduce the computing time or the required computing time, which on the one hand enables a faster execution of the control and on the other hand leads to a significant cost reduction, since commercial industrial computers can be used.

Claims

claims

1. A control method of a digital hydraulic controller with valves that are individually and in different combinations with each other, each of these valve switching combinations corresponds to a flow, characterized in that a currently required flow (D _new ) is selected from a limited number of flows, the smaller is the total number of flows and is in a range around the previous current flow (D _a i _t ).

2. Control method of a digital hydraulic controller according to claim 1, wherein the valves on two valve banks (A-

T, P-B; P-A, B-T), and the flows are transferred into a two-dimensional coordinate system whose axes correspond to the valve switching combinations or the flows of the individual valve banks (A-T, P-B, P-A, B-T).

3. Control method of a digital hydraulic controller according to claim 2, wherein the area from which the selection of the currently required flow rate (D _new ) takes place, is defined as a flow field in the coordinate system.

4. A control method of a digital hydraulic controller according to claim 3, wherein the midpoint of the flow field is formed by the previous actual flow rate (D _a i _t ).

5. A control method of a digital hydraulic controller according to claim 3 or 4, wherein the flow field is defined by the same number of flows in the ordinate and in the abscissa direction.

6. A control method of a digital hydraulic controller according to any one of claims 3 to 5, wherein the flow field has a square shape.

7. Control method of a digital hydraulic controller according to claim 6, wherein six valves are provided per valve bank, and the field is defined by 7 x 7 = 49 flows or by 4 x 4 = 16 flows.

8. A control method of a digital hydraulic controller according to claim 5, wherein the flow field has a cross shape.

9. Control method of a digital hydraulic controller according to one of the preceding claims, wherein the selection of the currently required flow rate (D _new ) from the limited number of flow rates or from the flow field is performed by means of a mathematical algorithm.

10. Control method of a digital hydraulic controller according to claim 9, wherein a penalty function is used as the mathematical algorithm.

11. Control method of a digital hydraulic controller according to one of the preceding claims, wherein the currently required flow rate (D _new ) leads to a pressure which is closest to a target pressure.

12. Hydraulic system for a machine having a hydraulic actuator, a high-pressure accumulator for storing a hydraulic working fluid under pressure, a pump for feeding and charging the working fluid at high pressure into the high-pressure accumulator, and a digital hydraulic pressure regulator associated with the hydraulic actuator and having control means according to the control method according to the preceding claims.