Paper making and fiber liberation – Processes and products – With measuring – inspecting and/or testing
Reexamination Certificate
2000-08-25
2001-07-24
Fortuna, Jose (Department: 1731)
Paper making and fiber liberation
Processes and products
With measuring, inspecting and/or testing
C073S037700, C073S159000, C324S229000, C702S097000, C356S389000, C356S370000
Reexamination Certificate
active
06264793
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method of measuring the caliper of paper, the method comprising measuring the caliper of paper substantially continuously during papermaking by a sensor being arranged above and/or under the paper, the sensor measuring the caliper of the paper at least on one side of the paper mainly without contacting the surface of the paper.
The invention also relates to an apparatus for measuring the caliper of paper, the apparatus comprising means above and/or below the paper for measuring the caliper of the paper substantially continuously during papermaking by a sensor being arranged on at least one side of the paper to measure the caliper of the paper mainly without contacting the surface of the paper.
BACKGROUND OF THE INVENTION
In a paper machine, the caliper and other properties of paper and paperboard are typically continuously monitored as the paper is moving. Gauges are usually fastened to what is known as a measuring beam, in which the gauges continuously move in a reciprocating manner in the transverse direction of the paper and continuously measure the paper as it moves forward. Sensors are arranged as close to the surface of the paper as possible to improve measuring accuracy. This causes a plurality of problems, e.g. if the measuring sensors for some reason come into contact with the surface of the paper, the sensors may leave tracks on the paper. Furthermore, the contact may cause fouling of measuring heads, resulting in impaired measuring accuracy in the long run. Sensors contacting the irregularities of the surface of the paper may also cause holes to be formed in the paper. Consequently it is known to use what is known as an air bearing, the sensors being provided with a bored hole or holes through which air is blown in between the sensor and the paper web. Owing to the air bearing, the sensor is able to stay clear of the web, and hence e.g. the irregularities on the surface of the paper do not come into contact with the measuring head. This avoids formation of holes in the paper. Formation of traces on the surface of the paper is also avoided and fouling of the sensors diminishes. Such an air bearing solution is disclosed in e.g. German Offenlegungsschrift 40 11 646 and in WO 95/30877. However, in an air bearing, the thickness of the air layer between the paper and the sensor is about 50 micrometers. When both sides of the paper comprise sensors which are subjected to an air bearing, the total thickness of the air layer is about 100 micrometers. The thickness of the air layer is considerable with respect to the desired measuring accuracy, which is about 1 micrometers. The effect of a thick air layer on the measuring results is usually compensated for by mathematical proceedings. A sample is taken from each produced paper roll and its caliper is analyzed at a laboratory, whereby the effect of the air layer can be determined. However, this is a dissatisfactory manner since it only reveals a momentary actual caliper of the paper. Furthermore, during the time the sample is being analyzed at the laboratory, and before the result is ready, a large quantity of paper has been produced, the caliper of which can no longer be influenced. Hence this is not a flexible manner to adjust the caliper of a web.
U.S. Pat. No. 5,132,619 discloses an apparatus for measuring the caliper of paper, wherein an air bearing is used to keep the apparatus out of contact with the paper to be measured. The sensor, in turn, is arranged to move against the paper by pressurized air. Consequently, the sensor leaves a mark in papers of a more sensitive quality in particular. The sensor also very easily gets fouled. Furthermore, the structure of the equipment is complex and laborious.
It is the object of the present invention to provide a method and an apparatus which avoid the above drawbacks.
SUMMARY OF THE INVENTION
The method of the invention is characterized by bringing the sensor measuring mainly without contact at given intervals into momentary contact with the surface of the paper.
The apparatus of the invention is characterized by comprising a control unit for controlling the sensor measuring mainly without contact to momentarily contact the surface of the paper.
It is an essential idea of the invention to measure the caliper of paper by a sensor mainly without the sensor contacting the paper, but bringing the sensor at given intervals into momentary contact with the paper. The sensor is preferably brought into contact with the paper at the edge of the paper web.
It is an advantage of the invention that occasional removal of the non-contacting feature allows accurate measurement of the caliper of paper at given intervals and thereby accurate determination of the effect of the thickness of the air layer on the measurement. The measuring result is also immediately available, whereby the whole run can be controlled when required and the caliper of the paper can be changed during the run. Contact of the sensor with the paper can be arranged to take place at the edge of the paper web, where the sensors stop anyhow in order to change moving directions. In this case the sensors do not have to be separately stopped for the measurement.
In addition to paper, the term paper refers in this context also to paperboard.
REFERENCES:
patent: 3582002 (1971-06-01), Langstroth et al.
patent: 4031752 (1977-06-01), Sanders
patent: 4292838 (1981-10-01), Larsen
patent: 4903528 (1990-02-01), Balakrishnan et al.
patent: 4929895 (1990-05-01), Typpo
patent: 4970895 (1990-11-01), Houghton et al.
patent: 5074050 (1991-12-01), Williams
patent: 5113358 (1992-05-01), Reber
patent: 5132619 (1992-07-01), Typpo
patent: 5575078 (1996-11-01), Moulton, III
patent: 5770949 (1998-06-01), Sgro
patent: 40 11 646 (1991-10-01), None
patent: WO 95/30877 (1995-11-01), None
Moisio Hannu
Ojala Mauri
Alston & Bird LLP
Fortuna Jose
Metso Paper Automation Oy
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