WO1984002121A1

WO1984002121A1 - A device for measuring variations in web tension

Info

Publication number: WO1984002121A1
Application number: PCT/SE1983/000418
Authority: WO
Inventors: Yngve Lindstrand
Original assignee: Yngve Lindstrand
Priority date: 1982-12-03
Filing date: 1983-12-01
Publication date: 1984-06-07
Also published as: SE453487B; SE8206911D0; SE8206911L

Abstract

A device for measuring variations in the web tension occurring transversely across continuously advancing webs, such as paper webs (1). The device comprises a conducting roller (2) mounted at one side of the web (1) in parallel with the web plane and perpendicularly to the direction of travel of the web. The conducting roller (2) is provided with a number of leaf elements (4) of a thin film having piezoelectric properties, said leaf elements being disposed transversely along the roller envelope face (3). Each leaf element (4) has direct or indirect contact with at least one transmitter/receiver means (7) positioned adjacent the conducting roller (2), said transmitter/receiver means (7) arranged, during the advancement of the web (1), to register electric pulses emitted from each one of said leaf elements (4) in response to the web being pressed against said elements. The pulses thus received are transmitted for amplification and processing in order to estimate the variations in the web tension transversely across the web (1).

Description

A Device for Measuring Variations in Web Tension

The subject invention concerns a device for measuring variations in the web tension occurring transversely across continuously advancing webs, such as paper webs, said device comprising a conducting roller mounted to one side of the web in parallel with the web plane and perpendicularly to the direction of travel of the web, said web exerting a predetermined average pressure against the conducting roller. In continuously advanced paper webs, found for instance in the papermaking industry and in printing works, it is important from an economical viewpoint that the paper web is advanced at the highest possible speed. A critical factor of the web advancement speed is the tensile stress that occurs in the paper and the maximum speed is therefore limited by the tensile strength of the paper.

A common method of establishing the paper web tension is to allow the web to pass over a conducting roller and measure the forces involved at the roll mounting points. However, this measuring method provides but a crude image of the overall web tension. The tension may vary considerably across the width of the paper web, and many factors may cause these variations, for example variations in the humidity across the web width, variation in the surface weight and imperfect roundness of the rollers. All these factors contribute to the difficulty in obtaining optimum control of the speed of advancement and often are the causes of web ruptures at apparently low web tension. Consequently there is a need for means to measure and register in a reliable manner the variations in the web tension that occurs transversely across continuously advanced paper webs.

Recent experiments have shown that owing to certain physical relationships measurements of indirect quantities can be used to obtain indications of tension variations across the width of the web. For instance, there are various ways in which the paper web may be made to oscillate and the resonance may then be measured at different points across the width of the web. One advantage found in using measuring methods of this kind is that the measuring process may be effected without any means actually touching the web itself. However, these kinds of methods are very sensitive to external disturbances, which commonly occur in machinery halls in the form of noise and vibration. Hitherto it has therefore proved impossible to use these measuring methods practically under the conditions prevailing in the paper-manufacturing industry or in printing works where the web advancement speed is extremely high.

The purpose of the subject invention is to make it possible to obtain reliable measurements of the web tension at a number of points across the width of the web, allowing actions to be taken rapidly to lower the speed of advancement or to make other adjustments to the installation and equipment and thus avoid paper web ruptures. As a rule, ruptures of this kind involve prolonged standstills and therefore considerable productional losses. The device in accordance with the invention is characterised in that the conducting roller is provided with a number of leaf elements positioned transversely along the roller envelope face, said leaf elements consisting of a thin film,preferably between 5-55 μm, having piezoelectric properties, each one of said leaf elements having direct or indirect electric contact with at least one transmitter/receiver disposed adjacent the conducting roller, said transmitter/receiver arranged to register, during the advancement of the web, any electric pulses emitted from each one of said leaf elements in response to the web being pressed against said elements, and to transmit these pulses for amplification and processing to estimate the variations in the web tension occurring transversely across the web.

The invention will be described in closer detail in the following with reference to the accompanying drawing which illustrates schematically one embodiment of the device in accordance with the invention.

A paper web 1, for example in a printing press, is arranged during its advancement to pass over a conducting roller 2 which is mounted in parallel with the plane of the web and at right angles to its direction of travel. The pressure exerted by the paper web 1 against the conducting roller 2 is proportional to the tensile stress in the paper. Along its envelope face 3 the conducting roller 2 is provided with a number of leaf elements 4 of a very thin film possessing piezoelectric properties. The leaf elements 4 are positioned along a helical line across the envelope face 3 so that each leaf element covers one section of tne entire web width and so that only one or a few leaf elements at a time will be contacted by the paper web as the latter runs about the conducting roller 2. Via a line 5 which extends along the interior of the conducting roller to one of the roller ends, each leaf element 4 is connected to an analog signal output 6 arranged at said roller end. These outputs 6 are arranged at the end wall of the roller spaced equidistantly apart along a circular line about the roller mounting shaft. A transmitter/receiver 7 is mounted on a support arm 8 laterally of the end wall of the roller and opposite the circle of outputs 6. The outputs 6 could be in the form of faces arranged for contact with a contacting arm on the transmitter/receiver 7 or could be inductive means arranged for non-touch transmission of the generated signals to the contacting arm. The transmitter/receiver 7 is connected via a line 9 to an amplifier 10 which amplifies the signals transmitted by the transmitter/ receiver 7. The amplifier 10 is in turn connected via a line 11 to a digital converter 12 for conversion of the analog signals to digital data. These data are transferred via a line 13 to a computor 14. Each piezoelectric leaf element 4 emits an electric signal when, one by one in succession, they are exposed to pressure from the web. The signal is proportional to the pressure generating when the leaf element 4 is clamped against the paper web. Provided sufficiently sensitive registering means are used the film need have a thickness of merely 6 μm.

The computor 14 controls the regulation of the speed of advancement of the web, allowing the web to be run at optimum speed in relation to the thickness and tensile strength of the paper. Alternatively, the computer 14 may be used in machines for the manufacture of paper to control the process so that a paper web having an even profile of tension may be obtained and the plant be run at optimum speed. The invention is not limited to the embodiment described in the aforegoing but some variations and alternatives are possible within the scope of the appended claims. For instance, the leaf elements 4 may be disposed on a straight line along the envelope face of the conducting roller and be arranged to provide a simultaneous image of the variations in tension in a cross-section of the web. Other means for registration of the measurement values than those shown in the example may be used and the transmission of the registered values could be effected in a different way. For instance, it is possible to provide the conducting roller 2 with means for conversion of the analog electric signals obtained from the leaf elements 4 into digital pulses. The latter may be transmitted by means of a light-emitting diode (preferably positioned adjacent the centre of the shaft of the roller), said diode being arranged to emit pulse trains of infraredlight signals to a receiver. The latter converts the light pulse train into corresponding electric pulses and delivers them further directly to the computor 14.

It should be understood that the invention may be used to measure the tension in other webs than paper webs.

Claims

C l a i m s

1. A device for measuring variations in the web tension occurring transversely across continuously advancing webs, such as paper webs (1), said device comprising a conducting roller (2) which is mounted at one side of the web in parallel with the web plane and perpendicularly to the direction of travel of the web, said web (1) exerting a predetermined average pressure against said conducting roller, c ha r a c t e r i s e d i n t h a t the conducting roller (2) is provided with a number of leaf elements (4) positioned transversely along the envelope face (3) of the roller, said leaf elements (4) consisting of a thin film, preferably between 5 and 55 μm, having piezoelectric properties, each one of said leaf elements (4) having direct or indirect electric contact with at least one transmitter/receiver (7) disposed adjacent the conducting roller (2), said transmitter/receiver (7) arranged to register, during the advancement of said web, any electric pulses emitted from each one of said leaf elements (4) in response to said web being pressed against said elements, and to transmit said pulses for amplification and processing to estimate the variations in the web tension occurring transversely across the web.

2. A device as claimed in claim 1, c ha r a ct e r i s e d i n t h a t said leaf elements (4) are disposed along a helical path about the envelope face of the conducting roller (1).