SCRAPER DEVICE AND METHOD FOR DETERMINING THE CONTACT PRESSURE OF A SCRAPER

Abstract

The invention relates to a doctor device, associated with a contact surface, in particular a rotating roller. The doctor device has a doctor blade, provided for placement against the roller, for bringing the doctor blade into contact with the roller by way of a pressurized fluid. At least one sensor is provided on the doctor blade, for generating a measured value for the contact pressure of the doctor when it is placed against the roller. There is a control unit which controls the speed at which the doctor can be placed against the contact surface, in particular the roller.

Claims

1-11. (canceled)

12. A doctor device, comprising: a doctor to be applied to a contact surface by pressure from a fluid under pressure; at least one sensor arranged on said doctor, said sensor being configured to generate a measured value for a contact pressure when said doctor is disposed to press against the roll; and a control unit configured to control a speed with which said doctor is applied to the contact surface.

13. The doctor device according to claim 12, wherein the contact surface is a surface on a rotating roll and said doctor is configured to be applied to the contact surface of the rotating roll.

14. The doctor device according to claim 13, wherein said doctor comprises a doctor blade for pressing onto the roll and a doctor holder for holding said doctor blade.

15. The doctor device according to claim 12, which comprises at least one switch connected to said doctor and configured to selectively apply said doctor to the contact surface or pivot said doctor away from the contact surface.

16. The doctor device according to claim 15, wherein the contact surface is a surface on a rotating roll and said at least one switch is configured to cause the doctor to approach, or pivot away from, the contact surface of the rotating roll.

17. The doctor device according to claim 12, wherein said sensor comprises a piezoelectric sensor or a strain gauge.

18. A method of determining a contact pressure of a doctor, the method comprising: connecting the doctor to a control unit that is configured to control an inflow of a fluid under pressure; pressing the doctor onto a contact surface under control of the control unit while controlling the inflow of the fluid under pressure and leading the fluid up to the doctor for a predefinable application time to thereby increase the pressure up to a desired pressure maximum.

19. The method according to claim 18, which comprises choosing the application time to match a pressure rise time used during a calibration.

20. The method according to claim 18, wherein the control unit comprises a switching means configured to choose the desired application time.

21. The method according to claim 20, wherein the switching means is a timer relay.

22. The method according to claim 18, which comprises providing a throttle valve between the switch and a connector of the doctor, and lowering a supply pressure of the fluid at an inflow to the control unit by way of the throttle valve to an application pressure of the doctor.

23. The method according to claim 18, which comprises using a measuring system to determine the contact pressure of the doctor during an application process.

24. The method according to claim 23, which comprises using the measuring system to determine the contact pressure of the doctor by predefining a time period and a pressure of the fluid during the application process.

25. The method according to claim 23, wherein the measuring system uses at least one piezoelectric sensor or a strain gauge.

Description

[0038] The invention will be explained in more detail below in an exemplary embodiment and with reference to the following drawings, in which:

[0039] FIG. 1 shows a schematic illustration of a doctor which is fixed in a doctor holder and rests on a roll,

[0040] FIG. 2 shows a control unit for controlling the contact pressure of the doctor on a contact surface.

[0041] A doctor blade 11 can be applied to the lateral surface of a roll 12 (FIG. 1) by means of a doctor blade holder 15. Whether the hose 20 is pressurized, and with which contact pressure presses the blade 11 against the roll 12 is detected by means of a sensor 13 which, for example, is a piezoelectric sensor or a strain gauge, wherein the strain gauge can simultaneously be formed as a piezoelectric sensor.

[0042] The doctor blade 11 is mounted in a doctor holder 15 and is pressed by means of an application or pneumatic hose 20 against the lateral surface of the roll 12 or withdrawn from the latter counter to the restoring force, for example of a spring 14 or of a pneumatic hose, wherein the hose 20 is provided with a connector 2 via which the compressed air is supplied.

[0043] The connector 2 (FIG. 2) is connected to a pneumatic control unit 1. Via the connector 2, the application hose 20 is connected to the compressed air supply via the control unit 1. As the pressure rises, the hose 20 expands and presses the doctor blade 11 in the direction of the surface of the roll 12. The contact pressure of the blade 11 is determined by means of the sensor 13. To determine the profile of the blade 11 over the width of the roll, i.e. in the longitudinal direction of the latter, many sensors 13 are usually provided. The compressed air is provided, for example, by the compressed air supply of a paper mill and has, for example, a pressure of 8 bar or else of 12 bar.

[0044] The control unit 1 comprises a valve or a switch 8 for applying the compressed air to the connector 2 and therefore to the doctor 10, and also a valve or a switch 9 for lifting the doctor 10 off the roll 12. The compressed air designated above is applied to the switch 8. The pressure which is to be applied to the doctor holder 15 can be adjusted manually or automatically at a throttle 5. This application pressure lies considerably below the pressure level of the compressed air supply. Typical values for this application pressure lie between 1 and 3 bar, in particular between 1.5 and 2 bar. Accordingly, a connector 3 for a pressure supply at the pressure level of the factory system is provided, namely for up to 12 bar, and/or a connector 4 for a pressure of up to 4.5 bar. A manometer 6 can optionally be provided downstream of the throttle 5.

[0045] If the switch 8 is opened, the application process of the doctor blade 11 is started. The measuring operation of the sensors or of the single sensor 13 on the doctor blade 11 is also likewise started. Since the control unit 1 is connected directly to the connector 2 of the doctor 10, the application process starts virtually immediately with the actuation of the switch 8.

[0046] In addition, the control unit 1 comprises a timer relay 7 as a switch. A defined application time can be adjusted on this relay. The times for this lie, 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 the order of magnitude of 10, since for each variant a calibration has to be carried out in advance, in order to correct the dynamic error.

[0047] The application time begins with the actuation of the switch 7. Following the expiry of a predefined time, the pressure supply to the doctor 10 is interrupted. This is done via the valve 9. Alternatively, the valve 8 could also be closed.

[0048] An outlet, with which the compressed air from the application hose 20 of the doctor 10 can be discharged, is preferably provided on the valve 9. As a result, it is possible to lift the doctor 10 or the blade 11 off the roll 12 again and, during this lifting process, to carry out a defined measurement once more. The value measured by the sensor 13 will rise from the time it is switched on until the end of the measuring time period. When the valve 9 (or else the valve 8) is closed, a display unit (not illustrated here) has a pressure peak, which then falls again ii slowly, as a rule over a time period of seconds. From the course of the curve from the time of switching on until the peak is reached, it is possible to draw conclusions about the real application force of the doctor 10 on the roll 12. For this step from the course of the curve to the current force value, calibrations are carried out in advance. Since only a relatively low number of measuring time periods is stored, for example a maximum of ten, and all the remaining adjustments remain the same, this is possible with little outlay.

[0049] Preferably, a very small distance is maintained between the outlet 2 of the control system 1 and the inlet to the application hose 20. In every case, the same length must be present during operation as during the calibration measurements. A length of less than 2 m, in particular of less than 1 m, is advantageous.

[0050] According to the invention, the error sources “sensor acceleration” and “speed of the state change” are eliminated via the control unit 1 by using the basic calibration. After the measuring process, the compressed air in the application hose 20 can be discharged by actuating the switch 9. During the process of lifting the doctor 10, a measurement can be carried out again by using a system based on piezoelectric sensors. If the measurement is carried out by using other sensors such as, for example, strain gauges, the measurement can also be carried out between the application process and the lifting process. Between the application and the lifting, the pressure in the hose 20 of the doctor holder 15 is maintained.

[0051] The invention can be implemented with a compressed air buffer. This applies in particular to a system for producing or processing a printing material web, in which the access to an independent compressed air system is not accessible or accessible only with difficulty. It is additionally possible for a low-frequency or high-frequency change between application and lifting in sinusoidal form to be implemented. The performance can be completed with an output signal to the measuring system, irrespective of the sensors used. The throttle 5 can be adjusted automatically. The control unit 1 can also be used independently of the sensors used, only the advantage of the adjustability of the pressure then being used. It is also possible to use measuring systems which are movement-dependent and not ii based on the piezoelectric principle. Therefore, the control unit 1 constitutes an electro-pneumatic control unit, which can be used as a power source for peripheral devices, for example for peripheral devices such as light beams, for example, or a measuring system for measuring the load profile of the doctor 10. Likewise, tightness measurements can also be carried out on the doctor 10.

LIST OF DESIGNATIONS

[0052] 1 Pneumatic control unit [0053] 2 Doctor holder/application hose connector [0054] 3, 4 Compressed air supply connector [0055] 5 Throttle valve [0056] 6 Manometer (analog or digital) [0057] 7 Timer relay [0058] 8, 9 Switch/valve [0059] 10 Doctor [0060] 11 Doctor blade [0061] 12 Roll [0062] 13 (Piezoelectric) sensor [0063] 14 Restoring element [0064] 15 Doctor holder [0065] 20 Application hose/pneumatic hose (with connector 2)