EP2435714B1 - Method for monitoring the function of a hydraulic system of a paper or cardbord machine, the hydraulic system comprising a hydraulic accumulator - Google Patents

Description

The invention relates to a method for monitoring the operation of a hydraulic system

Paper machines have hydraulic actuators that are actuated by a pressurized working fluid whose pressure and / or flow is regulated by regulators.

In paper machines, the hydraulic is widely used as actuation and control means when large forces are to be adjusted and applied with high accuracy.

The working fluid, e.g. Hydraulic oil is pressurized by a pump and the introduction of the pressurized hydraulic oil into a hydraulic actuator, such as a hydraulic actuator. a hydraulic cylinder or hydraulic motor is typically controlled by a proportional control valve or proportional valve, which may be electrically, hydraulically, or pneumatically driven.

Such a control valve has a slidable or displaceable spool or spool which, in response to its location in an associated valve housing, can adjust a desired pressure at the outlet by controlling the pressure of hydraulic oil delivered by the pump becomes. 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 or Pressure reducer, for example, in the journal fluid no. 7-8, 2008 pages 12, 13th described. The mode of operation of digital hydraulic pressure regulators can be briefly summarized as follows:
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 are simple ON / OFF switching valves 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, ie 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; for a larger number of valves this series will continue 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 very 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.

In the digital hydraulic control, the valves are usually closed after setting the target pressure, i. to maintain a desired pressure in a closed (and unchanged) system, neither working fluid is withdrawn nor supplied to this system. However, in practice, this steady-state condition may require or permit individual control interventions, particularly in response to changes elsewhere in the machine / control system.

However, after the quantities of working fluid displaced during these individual control interventions are relatively small, It has been found that the usual hydraulic power supply can be replaced by a supply unit which has a pump and at least one pressure accumulator from which working fluid is made available to the regulator.

To replenish the accumulator, the pump is occasionally turned on and builds up the pressure in the memory again.

Such systems are from the DE 32 27 264 A1 . DE 32 27 265 A1 and the DE 33 03 549 C1 known.

In complex hydraulic systems, leaks or internal leakages may occur which, however, may go unnoticed in an automatic control by means of digital hydraulic controllers because leakages are compensated, i. the pressure measurement alone does not indicate any leakage.

The invention has for its object to provide a simple and reliable method for monitoring the leakage of a hydraulic system of a machine for producing a fibrous web, with which this leakage can be reliably detected. The object is achieved in terms of the method with a method according to claim 1.

Advantageous developments of the invention are set forth in the subclaims.

In the method according to the invention for monitoring the operation of a hydraulic system of a paper machine, the hydraulic system for controlling working fluid pressures uses at least one digital hydraulic controller which draws working fluid stored under pressure from at least one pressure accumulator. The hydraulic system is provided with a supply unit which is switched on as needed to fill the pressure accumulator. In the method according to the invention, the actual switch-on frequency and / or switch-on duration of the supply unit is compared with an expected switch-on frequency and / or switch-on duration, the actual switch-on frequency and / or switch-on duration starting with each restart of the machine and after reaching a stable operating state in which a setpoint pressure in a hydraulic Actuator is closed and the valves of the digital hydraulic controller are normally closed, is detected again, it being concluded from the comparison of the actual Einschalthäufigkeit with the expected Einschalthäufigkeit on a leak in the hydraulic system, when the actual Einschalthäufigkeit exceeds the expected Einschalthtenäufigkeit, and / or wherein it is concluded from the comparison of the actual duty cycle with the expected duty cycle on a leak in the hydraulic system, when the actual duty cycle exceeds the expected duty cycle.

From the actual Einschalthäufigkeit the supply unit can be closed directly to the working fluid consumption. If this working fluid consumption exceeds the expected value, it can be concluded that there may be a leak. The expected value for the switch-on frequency is not necessarily a fixed value, but can change in the operation of the machine by changing boundary conditions in a comprehensible manner, so that the expected value can be adjusted accordingly.

The supply unit can be switched on to different needs, for example, the supply unit can be turned on before an adjustment or setting process is initiated in the machine. Preferably, the supply unit is then switched on as needed when the pressure in the accumulator falls below a predetermined value.

It is possible to estimate the expected turn-on frequency from observations or to determine it empirically. The expected switch-on frequency is preferably calculated by calculating an expected withdrawal quantity of working fluid from the pressure accumulator per unit of time and relating it to the storage volume of the pressure accumulator or the pressure accumulator.

In paper machines sometimes it comes to web breaks. After such a web break, the machine must be restarted.

In detail, it can be provided in the method that a counter is used which counts the number of switch-on operations of the supply unit. A memory can be used which stores the counted number. A computing device with a timer may be used which proportates the counted number at the time to obtain the actual turn-on frequency.

Preferably, the computing device compares the value for the actual power-on frequency with a predetermined value and displays a message when that value is exceeded. The message may be particularly conspicuous, e.g. If necessary, an optical and / or acoustic alarm can be output if the specified switch-on frequency is exceeded.

The method is also applicable to a hydraulic system having a plurality of supply units, wherein preferably the individual supply units are each monitored with regard to the switch-on frequency.

The inventive method also includes an additional or alternative detection of the duty cycle of the supply unit. From the actual duty cycle of the supply unit can be closed directly to the working fluid consumption. This working fluid consumption exceeds the expected Value, it can be concluded that there may be a leak. The expected value for the duty cycle is not necessarily a fixed value, but can change in the operation of the machine by changing boundary conditions in a comprehensible manner, so that the expected value can be adjusted accordingly.

The supply unit can be switched on to different needs, for example, the supply unit can be turned on before an adjustment or setting process is initiated in the machine. Preferably, the supply unit is then switched on as needed when the pressure in the accumulator falls below a predetermined value.

It is possible to estimate the expected duty cycle from observations or to determine empirically. The expected switch-on duration is preferably calculated by calculating an expected removal quantity of working fluid from the pressure accumulator and relating it to the delivery rate of the supply unit. The duty cycle monitored here is the accumulated duty cycle of the utility.

With this procedure, therefore, the actual flow rate of the supply unit with the expected flow rate of the supply unit is compared, so that an excessive flow rate can be closed to a fault in the hydraulic system.

Specifically, it may be provided in the method that a counter is used which detects the duration of the switch-on operations of the supply unit. A memory can be used which stores the detected power-on events and adds their durations. A computing device compares the sum to a predetermined value or expectation value and displays a message if that value is exceeded. The message may be particularly conspicuous, e.g. If necessary, an optical and / or acoustic alarm can be output if the preset duty cycle is exceeded.

The method is also applicable to a hydraulic system having a plurality of supply units, wherein preferably the individual supply units are each monitored with respect to the duty cycle.

Hereinafter, applications of the invention in a paper machine will be described.

• Fig. 1 zeigt ein Anwendung des erfindungsgemäßen Verfahrens; und
• Fig. 2 zeigt eine Anwendung der digitalhydraulischen Regelungstechnik.
• Fig. 3 zeigt eine weitere Anwendung der digitalhydraulischen Regelungstechnik.

The invention and will be explained again with reference to the following drawings.

• Fig. 1 shows an application of the method according to the invention; and
• Fig. 2 shows an application of digital hydraulic control technology.
• Fig. 3 shows another application of digital hydraulic control technology.

In one application of the method according to the invention is according to Fig. 1 a pair of differential cylinders 1 are provided. Each pressure chamber; So piston-side pressure chamber and rod-side pressure chamber of each differential cylinder 1 is provided with its own digital hydraulic pressure regulator 2.

A supply unit 3 bottom left in Fig. 1 has a pump 31 with a motor, a tank 32 and a pressure accumulator 33, which can be filled with the help of the pump 31 under pressure, that can be charged.

A monitoring device 4, which is here shown for the sake of clarity as a separate unit, but in practice may also be provided in the control unit of the pressure regulator, is able to detect switching on and off of the pump 33. In the monitoring device 4, a counting device (not shown) is realized, which can detect the switching-on frequency and / or the duration of the pump operation. This detected or actual value can be compared with a predetermined expected value in a comparison device (not shown) provided in the monitoring device 4. If the comparison shows that the supply unit has to be operated more often or longer than is to be expected by the operation, then an error in the hydraulic system, e.g. be closed on a leak.

The monitoring device 4 is designed to issue a display or a visible or audible alarm by means of a display device and / or an alarm device (not shown) if it can be concluded that a fault has occurred in the hydraulic system.

Fig. 2 shows a cooling device that is applicable, for example, to a hydraulic system that can use the invention.

In the Fig. 2 a hydraulic circuit 5 is shown, which includes a tank 51, a pump 52, an optional pressure accumulator 54, a filter 7 and a heat exchanger 53. The branch to a hydraulic load is in Fig. 2 Not shown. A cooling water circuit with the heat exchanger 53 and the supply line 62 and the drain line 63 includes a controller 6, which is constructed as a digital hydraulic controller, as previously described in detail. The controller 6 is used in the present case for flow control in the cooling water flow. By opening one or more valves simultaneously in the controller 6, the volume flow of the cooling water through the controller 6 can be set well. As a reference variable for the controller 6 can serve the temperature of the hydraulic oil in the tank 51, which is detected by a sensor 61. In the heat exchanger 53, the hydraulic oil releases its heat to the cooling water, wherein with the cooling water flow, the amount of heat dissipated is adjustable.

In Fig. 2 is shown in the hydraulic circuit 5, a pressure accumulator 54, which can also be omitted. The hydraulic circuit 5 may also be a lubricant circuit which serves to supply to be lubricated points in the machine.

There are also other uses and applications of digital hydraulic controllers as a pressure regulator or as a flow regulator, especially in paper machines conceivable. Such digital hydraulic controllers are described in this description previously in connection with liquids as a pressure regulator and as a flow regulator. With the same construction and functionality However, these regulators can also be used as flow regulators or as pressure regulators for gases.

In the former case, the use of a digital hydraulic controller to control the flow of compressed air into an eddy current generator (also called a vortex generator or vortex tube) is proposed. These eddy current generators are used to generate cold air and are operated with compressed air. However, the air consumption of these generators is relatively high and the flow rate is usually manually adjusted by a handwheel until the cold air is obtained at the desired temperature and in the desired amount at the output of the eddy current generator. Once selected settings remain unchanged despite changes in the temperature in the environment of the machine, as long as sufficient cold air is present. Fluctuations in pressure in the supply line are not taken into account. In existing systems, two-point controllers controlled by the cold air temperature are used together with the handwheel to interrupt or release the compressed air supply by means of a simple, electrically closable valve. However, this procedure is very inaccurate, so that expensive air generated in this way remains unused.

It is now proposed to use a digital hydraulic controller for adjusting the air flow in the eddy current generator instead of the handwheel with a two-point controller. As a control variable, the temperature of the cold air, the flow or other suitable parameters can then be selected, according to which the air supply to the vortex generator is controlled by means of the flow controller. This with little effort considerably refined control allows significant Savings in compressed air without sacrificing performance on the paper machine. The mode of action of the controller corresponds to that of a digital hydraulic controller in the regulation of flow rates of liquids.

A possible use of the digital hydraulic controller as a pressure regulator for controlling the pressure of gases is given, for example, in the control of adjusting hoses. Valve hoses are used, for example, to set a squeegee, or to keep in an operating position. The force with which the doctor acts on, for example, a paper web must be controlled very precisely. For this purpose, a regulator should already be sufficient, which has three to six parallel switching valves.

These control hoses are often pneumatically operated, ie operated with compressed air. The regulation of the pressure in such a control tube has hitherto usually been done by manually adjustable throttles, combined with ejectors and electromagnetic switching valves. However, it was difficult to always ensure accurate control of the pressure force of the adjusting tube on the doctor blade.

Now, if a digital hydraulic controller with six or twelve parallel switching valves is used, a very accurate pressure control of the air in the adjusting tube can be achieved. The mode of action of the controller corresponds to that of a digital hydraulic controller in the regulation of pressures in liquids.

In Fig. 3 Another application of the digital hydraulic control is shown. This application concerns the cooling of rotary joints with digital hydraulic technology.

In Fig. 3 an arrangement with two metal band calenders 7 is shown, to which, as described herein, the digital hydraulic control technique is applied.

The metal belt calenders 7 are operated at high temperatures, so that cooling of the rotary joints is required. The refrigeration points are 71 in Fig. 3 indicated.

In particular, with the usual control valves, which are considered in view of the high oil temperatures at all in practice difficult to flush the cooling lines of the rotary joints sufficiently, as always dirt leads to problems with the flow measurement. Purging the lines with the flow regulators to avoid damaging the expensive control valves may cause the flow control valves to quickly become blocked or blocked again.

A metal belt calender 7 of Fig. 3 shown distributed by the assignee under the product name ValZone, has up to nine refrigeration points 71, each of which is supplied by a digital hydraulic flow regulator 2. According to calculations, a series with four switching valves is sufficient for each cooling point 71, so that a digital hydraulic regulator with nine times four (9x4) switching valves is sufficient to ensure the cooling of the cooling points 71. These switching valves are inexpensive and reliable because of the low flow and low pressure levels.

The digital hydraulic control requires only a pressure measurement and a temperature measurement of the oil flowing into the supply unit 3. The switching valves can be embedded in a system simulation "Simulink" and run only as control valves without feedback. The typical flow rate is 6 to 9 l / min at oil temperatures of 70 to 75 ° C. The oil is thin at these temperatures anyway, so that the temperature dependence is small. Temperature switches as safety devices can also be present on the rotary joints.

The digital hydraulic controller, which has been explained in this application corresponds in its operation to the previously described in detail regulators. In particular, the insensitivity to dirt and the flushability by the simple robust construction also form an advantage for the digital hydraulic controller in this application. It is e.g. In addition, it is possible to compensate for partial or complete blockage of individual valves by means of the other valves by means of calibration procedures or error detection methods, by selecting suitable other valve combinations. In this way, a possible, slightly limited, continued until the next business interruption safer operation of the cooling can be ensured.

Claims (10)

1. Method for monitoring the function of a hydraulic system of a machine for producing a fibrous web, such as a paper or board machine, wherein

   the hydraulic system uses at least one digital-hydraulic controller for controlling operating fluid pressures, which takes operating fluid stored under pressure from at least one pressure accumulator,

   the hydraulic system is provided with a supply unit, which is switched on as necessary in order to fill the pressure accumulator, and

   the actual switch-on frequency and/or switch-on duration of the supply unit is compared with an expected switch-on frequency and/or switch-on duration, wherein the actual switch-on frequency and/or the actual switch-on duration is/are detected again, beginning with each new start of the machine and after reaching the stable operating state, in which a target pressure in a hydraulic accumulator is maintained and the valves of the digital-hydraulic controller are as a rule closed, wherein, from the comparison of the actual switch-on frequency with the expected switch-on frequency, it is concluded that there is a leak in the hydraulic system if the actual switch-frequency exceeds the expected switch-on frequency, and/or wherein, from the comparison of the actual switch-on duration with the expected switch-on duration, it is concluded that there is a leak in the hydraulic system if the actual switch-on duration exceeds the expected switch-on duration.
2. Method according to Claim 1, characterized in that the supply unit is switched on as necessary when the pressure in the pressure accumulator falls below a predefined value.
3. Method according to Claim 1, characterized in that the actual switch-on duration is a cumulative switch-on duration from successive operating phases of the supply unit.
4. Method according to Claim 1, characterized in that the expected switch-on frequency is calculated in that an expected removal quantity of operating fluid from the pressure accumulator per unit time is calculated and related to the storage volume of the pressure accumulator or the pressure accumulators.
5. Method according to Claim 1 or 3, characterized in that the expected switch-on duration is calculated in that an expected removal quantity of operating fluid from the pressure accumulator is calculated and related to the delivery output from the supply unit.
6. Method according to one or more of the preceding Claims 1 or 4, characterized in that use is made of a counter which counts the number of switch-on operations of the supply unit, in that use is made of a memory which stores the number counted, and in that use is made of a computing device with a timer, which relates the number counted to the time in order to obtain the actual switch-on frequency.
7. Method according to one or more of the preceding Claims 1 or 5, characterized in that use is made of a counter which detects the duration of the operating phases of the supply unit, and in that use is made of a memory with an addition function, which stores the acquired durations of the operating phases and adds them up to form an actual switch-on duration.
8. Method according to Claim 6 or 7, characterized in that a comparison device compares the value for the actual switch-on frequency or the actual switch-on duration with a predefined value and displays a message if this value is exceeded.
9. Method according to Claim 8, characterized in that an optical and/or acoustic alarm is output if the predefined value is exceeded.
10. Method according to one or more of the preceding claims, characterized in that the hydraulic system has a plurality of supply units, wherein the individual supply units are each monitored with regard to the switch-on frequency and/or switch-on duration.

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