Paper making and fiber liberation – Processes and products – With measuring – inspecting and/or testing
Reexamination Certificate
2002-06-21
2004-03-16
Griffin, Steven P. (Department: 1731)
Paper making and fiber liberation
Processes and products
With measuring, inspecting and/or testing
C162S255000, C162S263000
Reexamination Certificate
active
06706149
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. §119 of German Patent Application No. 101 31 281.4, filed on Jun. 28, 2001, the disclosure of which is expressly incorporated by reference herein in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process to detect the presence of a paper, cardboard, tissue or other fibrous material web or a strip of the fibrous material web in machines for manufacturing and/or finishing the fibrous material web, whereby the fibrous material web is guided by at least one continuously circulating belt.
2. Discussion of Background Information
In order to be able to minimize the damage from a tear in the fibrous material web, it is important to detect the tear as early as possible. This makes it possible not just to reduce possible damage to the machine from a jam of the fibrous material web, but also to reduce the broke. In addition, it is also important for the control of the machine to detect the complete transfer of the fibrous material web when starting the machine.
In general, monitoring of the fibrous material web takes place on the basis of optical sensors or camera analysis systems. To this end, the belts are often designed in colors, which is intended to improve the recognizability of the fibrous material web. The reliability of the optical detection is impaired, however, by the contamination of the belts, the mostly warm, moist and contaminated air in the area of the machine as well as the contamination of the sensors or cameras. In addition to the high price of the measuring units, their reliability is unsatisfactory.
SUMMARY OF THE INVENTION
The invention therefore creates a process and a device to detect the presence of a fibrous material web or a strip thereof, which offer improved reliability with the use of a simple device.
According to the invention, in that the detection of the presence of a fibrous material web or a strip thereof takes place in an area of the machine in which the lack of the fibrous material web or a strip thereof or the successful transfer of the fibrous material web produces a change in the temperature of the belt, and detection takes place based on the measurement of the temperature of the side of the fibrous material web opposite the belt while it is being supported by the belt and/or the temperature of the side of the belt facing the fibrous material web after transfer of the fibrous material web to a following unit and/or the temperature of the side of the belt opposite the fibrous material web. This occurs on the basis of the knowledge that the temperature of the belt changes relatively quickly with the lack or addition of the fibrous material web or a strip thereof. In this process, at least one temperature sensor is allocated to the belt to measure the temperature of the side of the fibrous material web opposite the belt while it is being supported by the belt and/or the temperature of the side of the belt facing the fibrous material web after transfer of the fibrous material web to a following unit and/or the temperature of the side of the belt opposite the fibrous material web. Temperature sensors are substantially cheaper and more reliable than optical sensors.
The use of the process and the device is possible, in particular, where at least the temperature of the side of fibrous material web that is directed away from the belt deviates from the temperature of the belt. Above all, at least the temperature of the area of the belt touched by the fibrous material web should deviate from the temperature of the fibrous material web, at least, however, from the temperature of the side of the fibrous material web that is directed away from the belt.
This monitoring of the fibrous material web by use of temperature measurement can be realized inside the machine on several belts as well. A tear of the fibrous material web can thus be detected very early. Also advantageous is the use with the acceptance of the fibrous material web by the belt in order to establish that the leader strip is running across the width and that the fibrous material web has completely transferred when starting the machine.
In order to increase the reliability of the measuring arrangement, the temperature measurement can take place at several locations along the run of the belt and/or at several locations crosswise to the belt travel direction. The arrangement of several temperature measuring locations crosswise to the belt travel direction also permits monitoring of individual zones of the fibrous material web, so that the transfer of the strip of the fibrous material web that is getting wider can be relatively precisely detected when starting the machine.
The temperature measurement should be accomplished without contact so as not to impair the belt or the fibrous material web. Temperature sensors in the form of IR sensors or IR thermography cameras are particularly suitable for this. In this connection, a cleaning element, preferably in the form of an air jet, and/or a cooling element, can be allocated to the temperature sensors. Both substantially increase the reliability of the measurement. The temperature sensors should feature a measuring area with a diameter between about 20 and 200 mm, preferably between about 20 and 100 mm.
If several temperature sensors are present for temperature monitoring of a larger area, in particular, crosswise to the belt travel direction, the distance between two temperature sensors should be between about 100 and 1000 mm, preferably between about 200 and 600 mm. The sensors can also be arranged at several particularly interesting locations, for example in the edge areas of the fibrous material web shortly before and/or after an airborne web dryer or drying hood or the like. In addition, it can also be an advantage if at least one temperature sensor is embodied to be traversable crosswise to the fibrous material web. The temperature can thus be detected via this temperature sensor at least over a portion of the width of the belt or the fibrous material web.
In order to be able to improve the reliability even more, two temperature sensors instead of one can also be arranged very close together, whereby only the temperature changes that are detected by both temperature sensors are evaluated.
The use of temperature measurement is advantageous for fibrous material web detection in the area of the press section for dewatering the fibrous material web, whereby the belt is embodied as a press felt or a transfer belt. This applies in particular where the fibrous material web is heated before the temperature measurement by at least one heating element, preferably in the form of a heated press roll, a steam blower box or the like.
The use of the process and the device can also be accomplished advantageously in the area of a dryer section for drying the fibrous material web, whereby the belt is embodied as a drying screen. This provides a high degree of reliability of the process if before the temperature measurement the fibrous material web is heated by at least one heating element, preferably in the form of an IR radiator, a heated drying cylinder, hot-air jets or the like.
In general, but particularly in the described arrangements, in the press section and dryer section the temperature of the belt before contact with the fibrous material web is lower than that of the fibrous material web. It is thereby possible for the temperature of the belt to drop at least in the area touched by the fibrous material web when the fibrous material web or at least a part thereof is missing in the affected section. Depending upon the type of arrangement, it is also possible, however, that, due to the direct contact with the heating element, the temperature of the belt quickly increases at least in the area touched by the fibrous material web when the fibrous material web or at least a part thereof is missing in the affected section. If the fibrous material web is to be cooled, e.g., by a blower, the temperature conditions between th
Dick Wolfram
Mayer Roland
Prüssing Holger
Greenblum & Bernstein P.L.C.
Voith Paper Patent GmbH
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