Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41F—PRINTING MACHINES OR PRESSES
  • B41F31/00—Inking arrangements or devices
  • B41F31/02—Ducts, containers, supply or metering devices
  • B41F31/04—Ducts, containers, supply or metering devices with duct-blades or like metering devices
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21G—CALENDERS; ACCESSORIES FOR PAPER-MAKING MACHINES
  • D21G3/00—Doctors
  • D21G3/005—Doctor knifes
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41F—PRINTING MACHINES OR PRESSES
  • B41F33/00—Indicating, counting, warning, control or safety devices
  • B41F33/0009—Central control units

Definitions

• the invention relates to a scraper device assigned to a contact surface, in particular a rotating roll, with a scraper intended to be placed against the roll for pressing the scraper against the roll by means of a pressurized fluid and with at least one sensor arranged on the scraper according to the generic term of Claim 1.
• scrapers are used in many places. These have a thin blade made of metal or plastic or a fiber composite material, which is pressed against a roller in order to clean it or to ensure that the still moist paper web separates from the roller.
• the blade is a consumable item that needs to be replaced regularly.
• Blades mounted in a doctor holder are known from the prior art.
• the doctor holder remains permanently in the machine. According to the prior art, the doctor holder is connected to a pneumatic system, by means of which the holder or the blade itself is applied to the roller by the action of the compressed air.
• a scraping device is known with at least one strain gauge sensor arranged on the scraper, with which the contact pressure of the scraper can be measured when it is in contact with the roller.
• a plurality of strain gauge sensors can be distributed over the length of the scraper.
• WO 2014/176590 A1 discloses systems and methods for measuring the load and vibration of doctor blades and for reducing the vibration.
• a piezoelectric dynamic strain gauge is attached to a support element that supports the doctor blade.
• the static component corresponds to the blade pressure that is to be determined, ie the pressure with which the blade of the scraper rests on the roller surface.
• the dynamic component arises from the fact that the air pressure in the pneumatic system requires a certain amount of time to build up completely or, if the roller is rotating, from vibrations of the rotating parts. This dynamic component is of no interest when measuring the blade pressure.
• the air pressure for the application pneumatics is often set by opening or closing the corresponding valves, or the air pressure is controlled at a central switchgear cabinet, from which there are, for example, hose connections to the scraper holders.
• the hose connections can have a length of up to 100 m. This means that the distance between the doctor and the pressure source depends on the installation position of the doctor. This means that it takes a different amount of time before the full contact pressure is applied to the scraper. Time spans between 1 s and 30 s were observed on paper machines until the full contact pressure was applied.
• Piezoelectric measurement technology can be used to measure numerous physical quantities such as pressure and acceleration.
• pressure sensors a thin membrane of known dimensions and a solid base is used to ensure that the pressure loads the components in a desired direction.
• acceleration sensors a so-called seismic mass, ie a mass subject to vibrations, is connected to piezoelectric crystal elements.
• F Newton's second law of motion
• the disadvantage of this measurement setup is that the sensor responds to more than a single physical quantity, namely pressure and acceleration, the sensor not distinguishing between these two quantities.
• the sensor acts similar to a capacitor and only generates an electrical voltage when there is a change in state.
• a voltage is generated. If the applied pressure is constant, the sensor only emits a voltage for a certain time. If the voltage has discharged, no further measurands can be determined until the point in time at which the pressure changes again. The speed or acceleration of the pressure change has an influence on the voltage generated. This fact can be compensated by calibration or a complex sensor design with several elements in different spatial levels.
• the scraping device comprises in particular a scraper and feed lines for a fluid for applying the scraper.
• the invention enables measurements to be made on different scraping devices without having to carry out a separate calibration each time or without a sensor design consisting of several components is required. A measuring system equipped with sensors only needs to go through a single basic calibration.
• control unit that controls the speed at which the scraper can be applied to the contact surface, in particular the roller.
• the speed at which the scraper can be applied to the contact surface can be controlled in particular by applying the scraper in a definable or defined and also reproducible manner by the application of the pressurized fluid Wise.
• the doctor blade When the pressure builds up in the hose connection, the doctor blade is already moving and the application process starts, but not in a defined manner, but strongly dependent on the situation on the system such as the hose lengths etc.
• control unit By providing the control unit, defined conditions are now created.
• the connections in front of the control unit can now be filled with fluid before the measurement or the application process, so that defined pressure conditions prevail at the start of application at the input of the control unit - how long this takes and with which dynamic the pressure is built up is irrelevant .
• the control unit can then, for example, control the application process and thus the application speed of the scraper via the opening and closing of valves and the corresponding time specifications. Since the pressure of the fluid at the inlet of the control unit is known, as is the situation in the control unit itself (Hose lengths, valve dynamics, etc.) are known and fixed, this process can also be reproduced, regardless of how far the respective scraper is from the compressed air source. Advantageous developments result from the subclaims.
• the doctor preferably comprises a doctor blade for pressing against the roller and a doctor holder for receiving the doctor blade.
• doctor blade does not necessarily have to be manufactured in one piece.
• the doctor blade consists of several - separately transportable - segments that can be mechanically and electrically connected to one another according to the width of the paper machine before use.
• the scraper is advantageously connected to at least one switch, by means of which the scraper can be placed against the contact surface or in particular the roller or can be swiveled away from it.
• the invention also relates to a method for determining the contact pressure of a scraper according to the preamble of patent claim 5.
• this object is achieved in that a scraper that can be pressed onto a contact surface is connected to a control unit that controls the inflow of a pressurized fluid and that the fluid is connected to the scraper for a predeterminable application time is initiated, during which the pressure is increased up to a desired pressure maximum.
• the application time is preferably chosen so that it is matched to the pressure rise time used during the calibration.
• control unit comprises a switching means, in particular an adjustable time switching relay, by means of which the desired application time is selected.
• a throttle valve is provided between the switch and a connection of the scraper, by means of which the supply pressure of the fluids when flowing into the control unit is reduced to a contact pressure of the scraper.
• the control unit can have one or more connections through which it can be supplied with fluid.
• the fluid can be compressed air.
• Contact pressures of the fluid, with which the doctor is applied to the roller can be between 1 and 3 bar, in particular between 1.5 and 2 bar.
• Supply pressures of the fluid can be at different levels.
• supply pressures of 8 bar - 12 bar can be provided if, for example, the fluid is supplied via the factory's compressed air network.
• the supply pressures can also be lower, e.g. 4 - 5 bar. These can be achieved, among other things, by mobile compressed air sources.
• the throttle valve By interposing the throttle valve, it can be ensured that the application pressure is always at the same level, regardless of the supply pressure, as long as the supply pressure is at least as high or higher than the application pressure.
• the application pressure is the pressure level with which the application of the doctor is operated, i.e. the pressure with which the doctor holder is to be applied, and not the contact pressure with which the applied doctor presses on the roller.
• a measuring system determines the contact pressure of the scraper during the application process.
• the measuring system preferably determines the contact pressure of the scraper, in particular on the surface of the roller, by specifying the duration and a pressure of the fluid during the application process. Due to the specified time, individual calibration can be dispensed with, since the unit enables any pneumatic doctor holder of a machine for processing a printing material, in particular a paper machine, in a defined time at a defined pressure of the fluid, i.e. That is, to apply compressed air or a hydraulic medium to the contact surface, in particular a roller.
• the sources of error in the sensor acceleration, as occurs in the prior art, and the speed of the change in state can be eliminated using the control or monitoring unit according to the invention via a basic calibration.
• FIG. 1 shows a schematic representation of a doctor attached in a doctor holder, which lies against a roller, and
• FIG. 2 shows a control unit for controlling the contact pressure of the scraper on a contact surface.
• a doctor blade 11 can be placed against the outer surface of a roller 12 (FIG. 1) by means of a doctor blade holder 15. Whether the hose 20 is acted upon and with which contact pressure the blade 11 presses against the roller 12 is detected by means of a sensor 13, which is for example a piezo sensor or a strain gauge, wherein the strain gauge can also be designed as a piezo sensor.
• the scraper blade 11 is mounted in a scraper holder 15 and is pressed against the restoring force e.g. of a spring 14 or a pneumatic hose by means of a lay-on or pneumatic hose 20 against the outer surface of the roller 12 or pulled off it, the hose 20 being provided with a connection 2 through which the compressed air is supplied
• connection 2 (Fig. 2) is connected to a pneumatic control or monitoring unit 1.
• the connection hose 20 is connected to the compressed air supply via the control unit 1 via connection 2. With increasing pressure, the hose 20 expands and presses the doctor blade 11 in the direction of the surface of the roller 12. The contact pressure of the blade 11 is determined by means of the sensor 13. To determine the profile of the blade 11 across the width of the roller, i.e. H. In their longitudinal direction, many sensors 13 are usually provided.
• the compressed air is made available, for example, by the compressed air supply of a paper mill and has a pressure of 8 bar or 12 bar, for example.
• the control unit 1 comprises a valve or a switch 8 for applying the compressed air to the connection 2 and thus to the scraper 10 as well as a valve or a switch 9 for lifting the scraper 10 from the roller 12.
• the above-mentioned air pressure is on the switch 8 at.
• the pressure with which the doctor holder 15 is to be acted upon can be set manually or automatically at a throttle 5.
• This application pressure is well below the pressure level of the compressed air supply. Typical values for this application pressure are between 1 and 3 bar, in particular between 1.5 and 2 bar. Accordingly, a connection 3 is provided for a pressure supply at the pressure level of the factory system, namely for up to 12 bar, and / or a connection 4 for a pressure of up to 4.5 bar.
• a pressure gauge 6 can optionally be provided. If the switch 8 is opened, the application process of the doctor blade 11 starts. The measuring process of the sensors or the single sensor 13 on the doctor blade 11 also starts. Since the control unit 1 is connected directly to the connection 2 of the scraper 10, the application process starts almost without delay by pressing the switch 8.
• control unit 1 comprises a time switching relay 7 as a switch.
• a fixed application time can be set on this. The times for this are, for example, in a range between 0.5 s and 20 s, preferably between 1 s and 5 s.
• the number of variants is preferably determined to be less than 10, since a calibration is carried out in advance for each variant must to correct the dynamic error.
• the application time begins with the actuation of the switch 7. After a predetermined time has elapsed, the pressure supply to the scraper 10 is interrupted. This takes place via the valve 9. Alternatively, the valve 8 could also be closed.
• a drain is preferably provided on the valve 9, with which the compressed air can be drained from the application hose 20 of the scraper 10. This makes it possible to lift the scraper 10 or the blade 11 from the roller 12 again and to carry out a defined measurement again during this lifting process.
• the value measured by the sensor 13 will increase from the time it is switched on until the end of the measurement period.
• a display unit (not shown here) has a pressure peak which then slowly falls again, usually over a period of seconds.
• the actual application force of the scraper 10 on the roller 12 can be deduced from the curve progression from switching on until the peak is reached. For this step from the curve progression to the current force value, calibrations are carried out in advance.
• a very small distance between the outlet 2 of the control system 1 and the inlet to the attachment hose 20 is preferably maintained. In any case, the same length must be present during operation as during the calibration measurements. A length of less than 2 m, in particular less than 1 m, is advantageous.
• the sources of error “sensor acceleration” and “speed of the change in state” are eliminated using the control unit 1 via the basic calibration.
• the compressed air in the attachment hose 20 can be released by actuating the switch 9.
• a measurement can be carried out again with a system based on piezo sensors. If the measurement is made using other sensors such as B. Strain gauges, the measurement can also be carried out between the application and the lifting process. The pressure in the hose 20 of the doctor holder 15 remains between the application and the lift-off.
• the invention can be implemented with a compressed air buffer. This applies in particular to a system for producing or processing a printing substrate web in which access to an independent compressed air system is difficult or impossible. Furthermore, a low or high frequency change between putting on and taking off can be implemented in a sinusoidal shape.
• the execution can be carried out with an output signal on the measuring system independently of the sensors used.
• the setting of the throttle 5 can be carried out automatically.
• the control or monitoring unit 1 can also be used independently of the sensors used, in which case only the advantage that the pressure can be set is used. It is also possible to use measuring systems that are motion-independent and not based on the piezo principle.
• the control unit 1 thus represents an electropneumatic control unit which can serve as a power source for peripheral devices, for example for peripheral devices such as light bars or a measuring system for measuring the load profile of the Scraper 10. It is also possible to measure the tightness of the scraper 10.

Landscapes

• Inking, Control Or Cleaning Of Printing Machines (AREA)
• Paper (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=71527747

Family Applications (1)

Country Status (5)

Families Citing this family (2)

Family Cites Families (8)

• 2019
  • 2019-07-03 DE DE102019117901.7A patent/DE102019117901A1/de not_active Withdrawn
• 2020
  • 2020-06-24 CN CN202080047935.9A patent/CN114051455B/zh active Active
  • 2020-06-24 EP EP20737368.9A patent/EP3994308A1/de active Pending
  • 2020-06-24 US US17/624,402 patent/US20220356647A1/en active Pending
  • 2020-06-24 WO PCT/EP2020/067616 patent/WO2021001226A1/de unknown

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