FI62419B - MAETARE FOER ATT MAETA SPAENNINGEN AV MEMBRANER ELLER PAPPERSBAND UTAN KONTAKT - Google Patents

Description

rBl CUMULATION PUBLICATION, oyMQ

JHf lBJ (11) UTLÄGGININOSSKRIFT 62419 c Paten tti raytnno tty 10 12 1922

Patent aj c ri d el at ^ T ^ (51) K ».ik? / I« ta.3 G 01 L 5/10 SUOMI — FINLAND pi) 790371 (22) H «k # mi« pilvt - An * 6knlng «Dif 05.02.79 * * (23) AlkupUvt - Glkl | h * t $ dag 05.02.79 (11) Tttlhit | external * k * l - Bllvlt offantllg 06.08.80

Patents are registered .. »___________. . .....

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Pitait · och refittarityrelaan AmMcan uttajd och uti.ikrlftvn publksrsd 31.08.82 (32) (33) (31) Pyr ^ «« r «tu ^ Kauf — Bvfird priorltst (71) (72) Mauri Veikko Luukkala, Haukilahdenranta 23B 5> 02170 Espoo 17, Suomi-Finland (FI) (5 * 0 Contactless tension meter for membrane, membrane tax paper web -Matare för att mät spänningen av membraner eller pappersband utan kontakt

In printing or paper machines, measuring the tension of the paper web is quite important in adjusting the operation of the machine. Web breaks are one of the most important uncertainties in the operation of a printing press. Due to the interruptions in the web, it is not possible to give the exact time when the printing is completed, for example when printing newspapers or the like, but only the probable production time with rather large tolerances. If the operation of the printing press could be improved in this respect, the tolerances could also be substantially eliminated. Anyway, the rupture of the web is understandably accompanied by financial losses in many forms. This is also the case with paper and coating machines.

Today, web tension is measured mainly by two methods. Another method is to measure the tensile force between the rollers with different force sensors (e.g. strain gauge strips) and another is to blow a small pit into the paper web with compressed air and to measure the depth of the pit pneumatically. The depth of slag is a measure of tension. The method of measuring the attraction between two rollers is a previously known method, but it has certain drawbacks.

2,624 9 mm. its sensitivity is not good enough. in addition, its installation is cumbersome, as part of the roller system has to be dismantled and new types of axle supports with sensors have to be installed. As a material blowing method, which has also been used in some contexts as a measure of tension, it is inaccurate and its sensor touches the raised lift, which is not desirable.

In the present invention, the tension of the paper is measured without mechanical contact from both the moving and the tossed paper wave electronically using sound pulses. A membrane wave ouls is generated externally in the paper, which travels in opposite directions in the direction of the maximum stress. The travel time of this membrane wave over a given distance is directly a function of the tension, if the surface area of the paper is known.

The principle of the method is illustrated by thinking of the language of the violin; the tighter the tongue of the violin, the higher the frequency at which it vibrates. The tighter the paper web, the more the membrane wave pulse travels in it. It should be noted that there is an essential difference from a violin tongue or the like: when studying the vibration of a violin tongue or a drum diaphragm, a particular standing wave and standing wave mode structure is considered, which is often quite complex, depending on the boundary conditions, the violin tongue or the drum diaphragm , the method of attachment, etc., while the edge points or the length of the web are of no importance in the present method. You also don't have to touch the web, but the whole measurement is from the air.

1-yt The present device is based on the equation of motion of a film or the like under tension known per se, x.

In this equation, y is the deviation perpendicular to the film, x is the coordinate axis along the stress, T is the stress (Newton / m), f is the floating weight, and t is the time. From this wave equation, the rate of propagation of the "disturbance" or deviation in the x-coordinate direction v = »^? 5,62419

Strictly speaking, this equation holds true only in a vacuum, since the air surrounding the membrane loads the film slightly, changing the speed of the wave propagation, making it cycle-dependent (dispersive). In practice, however, the dispersion is o-called small in the frequency ranges that will be used in this context. Experiments have further shown that the noneus paper of the membrane wave is smaller than the speed of sound in air (i.e. 340 m / s). This is due to the fact that the propagating membrane wave does not radiate into the air, i.e. it cannot be heard, even if the period number of the membrane wave is, for example, 400 Hz, i.e. in the hearing range of the ear. However, a membrane wave, when its speed is less than the speed of sound in the air, generates a rapidly attenuating pressure pulse in the vicinity, which can be detected, for example, by microphones. In other words, membrane waves do not have so-called remote field, but a mere near field that can be detected by microphones placed close enough.

In practical factory tests, it has been found that for the paper thicknesses and stresses in question, the most common speed of the membrane wave is about 100 m / s and the usable frequency is about 4 ^ 0 Fz. This implies some important points for the operation of the device. First, the wavelength will be about 25 cm, which means that the method of mounting a loudspeaker near paper or the like already disclosed in already known patent applications will not work, because the loudspeaker is round, so the phase of the wave generated in the paper or the like is indeterminate. often about 20-25 cm, in which case even complete phase reversal may occur. The phase of the membrane wave pulse to be generated should be well defined only in such a way that the wave fronts leave in the same phase, which is only possible by generating a pressure line in paper or the like by means of a narrow gap. If the sound beam generated by the loudspeaker is not limited to a plate with a narrow gap, no membrane wave is generated in the membrane, as can be easily demonstrated in experiments by removing that plate. When the gap is further oriented so that it is perpendicular to the direction of movement of the web, a membrane wave front is created in which all the particles of the wave propagate at the same speed in the same direction and the detection of the wave by the microphone becomes easy. The in-wave wavefront is not generated by a loudspeaker with a circular circumference. The width of this gap in the direction of stress shall not exceed one quarter of the wavelength; the length of the gap perpendicular to the stress must be at least one wavelength in order to generate a well-defined membrane waveform in phase.

In slitters and similar machines, the web speed can often increase up to 20 m / s. On the other hand, when the speed of the membrane wave is about 100 m / s, this can lead to an error of up to 20¼, when, for example, the speed of the slitter is accelerated from zero to the maximum speed, unless the web speed is compensated in a certain way. An error of 10-20% in the tension may mean that, for example, the tension peaks break the web, unless the error caused by the speed has been compensated as described above.

U.S. Patent No. 3,854,329 discloses an invention in which tension is measured by generating a transverse vibration in a film by means of an electromagnetic loudspeaker and by measuring the flow rate of the resulting vibration with two microphones located on the same side of the loudspeaker relative to the paper. This American patent does not elaborate on the structure or velocity compensation of the above-mentioned electromagnetic loudspeaker. If the loudspeaker is circular, it generates membrane waves in all directions and at the same time phase reversal can occur because a clear phase front has not been defined geometrically.

As shown above, speed compensation must be made for the device to operate in an industrial environment. The American application does not disclose any compensation arrangement and cannot be implemented with the two microphone arrangement described. Speed compensation can only be performed with two microphones located on the opposite side to the loudspeaker and with a suitable olefinical arrangement, as disclosed in the present application.

The present invention is characterized by the features of the claim.

5,62419

Figure 1 illustrates the propagation of the membrane wave in the direction of stress.

Figure 2 schematically shows a membrane wave generation arrangement.

Figure 3 schematically shows an arrangement according to the present invention.

As can be seen from Figure 1, the membrane wave should have a well-defined wavelength and phase angle. Furthermore, it can be seen that the wave propagates in the direction of the tension, which in practical situations is the same as the direction of propagation of the web. Tension measurement measures the travel speed of a membrane wave; when v and is known, the stress is given by the formula T «.

A momentary deflection 2 is intentionally created in the membrane, e.g. with a loudspeaker 1, so that the loudspeaker 1 (or the like) is brought close enough to the paper. In front of the loudspeaker 1 there is still a plate 3 with a narrow slot or hole through which the sound pulse o-mouths into the paper, causing the paper to vibrate at the opening. This externally generated vibration 4 travels in opposite directions in the direction of the tension according to the membrane wave equation at a speed v = «| y Twenty centimeters away from the loudspeaker (transmitter) 1 a microphone 5 (or equivalent) is mounted The microphone 5, in turn, is connected to an electronic microphone amplifier 6, which amplifies the signal generated by the membrane wave. When the distance from the microphone 5 to the loudspeaker 1 is known, the velocity of the membrane wave is obtained from the electronically detected travel time, and the velocity (tension) is obtained from the velocity, because the basis weight is known. The loudspeaker can be electrically controlled by an electronic signal generator 7, with which signals of different lengths can be generated at the desired frequency, whereby the frequency of the membrane wave can also be targeted in the desired manner. Several methods such as phase detection, autocorrelation or digital calculation can be used in the electronic measurement of the membrane wave travel time. Since speed is obtained from each of the above methods, it is irrelevant which electronic measurement method is used. In principle, the flow can be measured with a single microphone, but with the help of two microphones, for example, the effect of the paper web's own speed can be reversed.

Figure 3 shows the measurement arrangement used in practice because it shows the self-speed compensation arrangement of the paper web. Since practical tests have shown that the tension can be measured with an accuracy of about 1-3%, it is necessary that speed compensation be performed, as the error caused by speed can be 5-20%; moreover, it is difficult to measure the actual speed of the paper web itself separately.

Let the distance of each microphone 8 from the loudspeaker 9 S and let the web move in the other direction at the speed C. Then the speed of the membrane wave 4 in the direction of the web speed increases by C and in the opposite direction decreases by C. Then the travel time s in the web speed direction is and in the opposite direction „'/ r * c -ja. . When the web speed C is eliminated, the tension / “j ^ ^ 2 its expression Tm is obtained, in which the web speed thus does not occur.

In practice, it is possible to measure t1 and tg, from which the corrected T can be measured electronically, because ^ and S are otherwise known.

A further advantage of the present method is that it is specifically a traveling wave pulse and not a standing wave. Namely, the standing wave is very sensitive to attachment, paper length, etc .; when looking at a traveling wave pulse, the reflections from the edges are not affected and the paper behaves as if it were infinitely long. Another advantage is that the measuring devices do not touch the membrane, which can thus move freely in its own plane.

The present method is also suitable for plastic films and other membranes to which the above equation (1) applies.

Claims (4)

7 6241 9 1. An altar of a paper web, plastic film, non-membrane or similar tension or tension under moving or hired tension, in which aenbrane waves are generated on the said membrane by a separate electromagnetic loudspeaker, characterized in that the sound beam of the electromagnetic loudspeaker plate (1) ), in which the gap is perpendicular to the motion of the web and in which the width of the gap is less than a quarter of the wavelength of the menbran wave, , that the signal generated by the membrane wave can be detected as an electrical signal in an amplifier connected to the microphone. Tension gauge for a stressed membrane, paper web or the like according to claim 1, characterized in that the effect of the own velocity of the diaphragm or nasal diaphragm on the diaphragm pulse travel is compensated by two microphones (8) located at a certain distance from the loudspeaker (9) that in the opposite direction, in which case the signals received from the microphone of the municipality can be combined in such a way that the ralna's own speed does not affect the measurement result. A tension meter for a non-membrane, paper web or the like according to claims 1 and 2, characterized in that said menbran, paper web or the like is a paper web in a printing machine, paper machine or slitter whose tension is to be measured. A non-membrane tension meter according to claims 1, 2 and 3, characterized in that said membrane is a plastic film in a machine for producing a plastic film.