Measuring and testing – Dynamometers – Responsive to multiple loads or load components
Patent
1986-05-09
1987-12-08
Levy, Stewart J.
Measuring and testing
Dynamometers
Responsive to multiple loads or load components
7386245, G01L 508
Patent
active
047111330
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a meter for measuring the tension in moving webs.
PRIOR ART
The non-contact measurement of moving webs is known in the art and has been employed, for example, for regulating tension when winding paper onto reels and unwinding paper therefrom. Examples of this technique are found in U.S. Pat. No. 2,945,637. In accordance there with, the web is drawn in a curved path over a perforated curved plate through the holes of which air is blown so as to produce a kind of air-cushion bearing between the plate and the paper. The greater the tension in the paper, the less air is consumed, so that the air pressure increases inwardly of the perforated plate. A similar arrangement is known from the Swedish Pat. No. 207 513, although in this case the pressure is measured via one or more measuring apertures located in the wall in which the air-exhaust orifices are seated, so that it is possible to measure the web tension at a number of positions across the width of the web.
These known non-contact web-tension measuring apparatus, however, have the disadvantage that it is necessary to change the direction of the web, by drawing the same over a plate or like element, admittedly while supporting the same on an air cushion and therewith in a manner which is contactless at least in principle, but not reliably so in practice. Although, as far as the arrangement disclosed in the aforesaid Swedish patent is concerned, it is possible to measure web tension at mutually different locations across the width of the web, these measurements can only be taken at fixed locations determined by the construction.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a non-contact web tension meter which can be placed against a web without needing to change the direction of the web, and the position of which, can be freely moved to any part of the web whatsoever across the breadth of the web, and which is therewith suitable for incorporation in a transversable measuring head, for co-action with other measuring devices operative in measuring thickness, moisture content and other variables of interest with regard to process controls and quality controls. The measuring process shall preferably provide a linear or substantially linear result.
In explanation of this object, it may be mentioned that during his work with thickness gauges for measuring the thickness of moving paper webs, the present inventor discovered that the thickness of a paper web, at least when measured in a contactless manner or with low surface pressure, surprisingly changes when a change in web tension occurs. One might presume that an increase in tension would result in a thinner paper, due to transverse contraction. What was found during experimentation, however, was something far more complicated, a matter which, moreover, is contingent on the kind of thickness gauge or meter used. When a non-contact meter of the kind disclosed in Swedish Published Application No. 434 997 is used, stretching of the web will initially result, in the case of newsprint, in the measured thickness increasing by 3-4 micron (force 0-0.2 N/m) and then increasing more gradually by some further microns (force 0.2-1.0 N/m), and only when this point is reached, decreasing when tension is increased. This effect is apparently due to the "pile" of the paper rising as the paper is placed under tension. Consequently, in order to obtain a true value in respect of the thickness of the paper, it is necessary to know the tension therein, in order to make a suitable correction. Newsprint can have a standard thickness of 80 microns, and it is desirable to be able to maintain control of this thickness to within about one or two microns, or better. In addition, it should be noted that contacting thickness meters have an even greater dependency on web tension than do present day non-contacting thickness meters.
Measurements of the web tension, correlated with other measurements, is desirable in continuous manufacture control processes, for control
REFERENCES:
patent: 3201985 (1965-08-01), Williams
patent: 3779074 (1973-12-01), Breyer
patent: 3850024 (1974-11-01), Ando et al.
patent: 3861207 (1975-01-01), Barbee
patent: 3868851 (1975-03-01), Breyer
patent: 3884076 (1975-05-01), Studer
patent: 4070902 (1978-01-01), Knobel
patent: 4106330 (1978-08-01), Hinrichs
Levy Stewart J.
Williams Hezron E.
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