FR2529340A1 - Quantitative measurement of aq. surface film on substrate - by comparison of transmitted or reflected strengths of polarised microwave beams - Google Patents

Abstract

In the mfr. of corrugated cardboard, a water-based paste is applied to the semi-finished board in a series of parallel bands (111). Two microwave beams of equal strength, with a wavelength of at least 3-5 times the distance between the paste bands, and which are respectively polarised in planes running parallel to, and at right angles to, the bands, are directed towards the pasted surface. Receivers (31,32) on the same side, or on the far side, of the surface monitor the reflected or transmitted waves, and the difference in the power, or in the phases, of the two waves is converted to a control signal, which is proportional to the mass of paste per unit area of the surface. The process gives an immediate result which can be used to apply automatic corrections to the applicator unit.

Description

Method and device for measuring the quantity
glue deposited during the production of corrugated cardboard
The present invention relates to a method and a device for measuring the quantity of water per square meter contained in parallel strips of an aqueous product deposited on a substrate, and in particular: for measuring the quantity of glue per square meter deposited on the groove paper during the production of corrugated cardboard.

 The manufacture of single-sided corrugated cardboard as well as double-sided, or more, involves depositing strips of glue on the top of corrugations of the corrugated paper. In order to optimize manufacturing and avoid defects in corrugated cardboard, regular monitoring of the amount of glue deposited per square meter on the corrugated paper is essential.

 In the current state of the technique, the control of this deposit t glue is carried out by weighing a sample of cardboard just glued, ax and after drying of this sample, which allows to estimate the weight of c deposited on the sample, the adhesive used being an aqueous product of determined composition. Such a measurement by treatment of samples is very long, and therefore does not allow immediate intervention in the event of co tation of bad sizing.

 The object of the present invention is to allow an instantaneous measurement of the quantity of adhesive deposited per square meter on the top of the corrugations of the corrugated paper, the measurement appearing in the form of an electrical sign, which makes it possible to envisage its easy use. in an electronic device for automatic adjustment of the gluing machine. The invention also applies, more generally, to the measurement of the quantity of water contained in parallel strips of an aqueous product deposited on a substrate.

 The method of the invention is characterized in that it consists in measuring the difference between the characteristics of the waves reflected or transmitted by the material covered with the strips of glue, or other aqu product from two electromagnetic waves emitted towards the material with polarizations. rectilinear and orthogonal, or substantially orthogonal, one of them being substantially parallel to the adhesive strips, and the common length of the joint is at least equal to the sum of the intervals ending three to five successive strips.

 The invention also includes a device for implementing this process, characterized in that it comprises - a hyper-frequency generator, - a microwave circuit connected to said generator and allowing transmission, towards the material , of two waves of the same frequency and polarized rectilinearly at right angles, or substantially at right angles, one of these two waves being substantially parallel to the bands of aqueous product.

a device for detecting one and the same electrical characteristic of each of the two waves reflected or transmitted by said material from said emitted waves, as well as for subtracting these two characteristics.

 The invention will be better understood with the aid of the following description of a few exemplary embodiments, with reference to the appended drawings in which - FIG. 1 is a schematic overview of a sizing installation for double corrugated cardboard. face using the method of Itinvention, - Figure 2 is an explanatory diagram helping to understand the method of the invention, - Figure 3 shows schematically a first measuring device according to the invention, - Figure 4 shows schematically a second device of measurement according to the invention, - Figure 5 is a schematic representation of a variant of the arrangement.

tif of Figure 4, - Figure 6 is a perspective view of a T-five arms usable for devices according to the invention shown schematically in Figures 7 and 8 - Figure 7 is a schematic view of another example of a measuring device according to the invention, - Figure 8 schematically shows a last example of measuring device according to the invention.

Referring first to Figure 1, there is designated by reference 1 a strip of single-sided cardboard scrolling in the direction of the arrow around a drive roller 2. In a very conventional manner, glue is deposited on the top of the undulations of the strip 1 by means of a rotary cylinder 3, the lower part of which dips in the
e glue tank 4. Also very conventionally, the thickness / of the film of glue deposited by the cylinder 3 is adjusted by an auxiliary cylinder 5, called "doctor cylinder", the center distance of which with the cylinder 3 is adjustable by by means of a conventional eccentric device, not shown, and controlled remotely for example by an electric motor 6.

 At the exit of the cylinder 2, the cover paper 7 is pressed against the glued corrugations of the strip 1 via the cylinder 8. The double-sided cardboard strip 9 thus formed is then passed through a non-drying device. visible in the drawing.

 In accordance with the measurement method of the invention, for the understanding of which reference will also be made to FIG. 2, a first microwave applicator 10 emits a first electromagnetic wave with rectilinear polarization and whose electric field El is parallel to the lines d humidity 11 due to the deposit of glue 111, and a second microwave applicator 12 emits a second wave with rectilinear polarization, of the same frequency as the first, but whose electric field E2 is perpendicular to the humidity lines 11. The waves reflected by the glued cardboard strip 9 are picked up by the applicators 10 and 12 and subtracted in an electronic detector and comparator unit 13 which, for example, realizes the difference in the reflected electrical powers.

The electrical power reflected by the cardboard 9 from
Inonde El emitted by the applicator 10 is linked to the humidity lines l1 due to the deposition of glue, parallel to the field El, as well as to the inherent humidity of the substrate constituted by the corrugated cardboard 9 by disregarding the glue. On the other hand, the power reflected from the wave E2 perpendicular to the humidity lines 11, is practically independent of the latter, but is linked to the substrate in the same way as for the El wave. The difference in the reflected powers performed in the electronic unit 13 then gives the value of the power reflected by the glue lines 111 alone.

 The wavelength emitted by the applicators 10 and 12 is chosen so that the strips 111 form a grid tight enough to be sufficient to pass the waves through the strip 9. In the case of common corrugated cardboard, the glue lines are spaced 3 to 9 millimeters apart and have a width of 1 or 2 hillimeters. So that the wavelength J emitted includes at least three to five lines of glue 11, a value of J will be chosen for a few centimeters, as the case may be. Advantageously, the wavelength of three centimeters will be chosen, that is to say a frequency close to 1000 MHz for which one easily finds all the components necessary on the market.

 Instead of operating, in the electronic unit 13, the difference of the powers reflected or transmitted from the waves E1 and E2, it is possible to operate the difference of other electrical characteristics of these. In particular, in the most common case where the two waves E1 and E2 are transmitted in phase concordance, generally from the same microwave generator, it will be possible to measure the phase difference between the waves reflected or transmitted which generally gives a more precise measurement.

 The electrical signal supplied at 14 by the electronic unit 13 is therefore dependent on the quantity of water contained in the glue lines 111, and as a result of the quantity of glue deposited, the percentage of dry product in the aqueous mixture constituting the glue being assumed to be invariable and known in advance.

 An electronic control and calculation block 15 receives information 14 from block 13, as well as information 16 from a data entry 17 indicating the percentage of water in the glue, information 18 from a data entry 19 indicating the width of the cardboard strip 9, and information 20 providing, from a speed sensor 22 and an associated electronic block 21, the running speed of the cardboard strip 9.

 The computer 15 deduces from this information the weight of glue deposited per square meter on the cardboard and, for example, consequently supplies the motor 6 by its output 23 with a space correction signal e, which makes it possible to decrease or increase the amount of glue deposited per square meter.

 We will now describe some nonlimiting examples of microwave devices allowing the implementation of the invention.

 FIG. 3 represents a device operating, as is the case for the installation of FIG. 1, by reflection of the transmitted waves.

 I1 comprises a microwave generator 24, emitting a wave of wavelength equal to three centimeters, and supplying, by means of a power divider by two 25, of rectangular waveguides 26 operating on the fundamental world H10 and d 'a twist 27 operating a 90 degree rotation, two emitting horns 28 and 29, the horn 28 emitting an electric field wave El parallel to the glue lines 111, and the horn 29 emitting an electric field wave E2 perpendicular to these lines glue. Optionally, it is possible, in order to avoid an excessive loss of information by transmission through the strip 9, to interpose behind the latter a reflective metal sheet 30, or any other wave reflector.

 The reflected waves are picked up via directional couplers (31, 32) and applied to detector diodes (33, 34) which supply the comparator electronic unit 35 with signals proportional to the electric power of the reflected waves. The comparison block 35 realizes the difference of the signals coming from the diodes 33 and 34 respectively, which allows, as explained previously, to develop an electrical signal representative of the quantity of water contained in the car meter in the glue lines 11.

 FIG. 4 represents a device similar to that of FIG. 3, but operating by transmission of the waves through the band of tone, instead of operating by reflection of these. This device is therefore composed of the same elements (24 to 29) as the previous device, pounding function in the same way, but here it is picked up using the horns (36, 37 and detected using the diodes (38, 39) the waves transmitted, by firing from the waves emitted, by the glued strip 9. The electrical powers thus detected are, as before, subtracted in an electronic comparison block 40, similar to the previous block 35. the same reasons as those explained above, an electrical signal representative of the quantity of water contained per square meter in the lines of glue 111 is thus obtained.

 FIG. 5 represents a device practically identical to that of FIG. 4, but using a phase bridge 41 measuring the phase shift between the two transmitted waves, instead of measuring their powers. This phase bridge comprises, in a very conventional manner, a magic tee 42, two detector diodes (43, 44), and an electronic comparison unit 64 effecting the difference of the signals from diodes 43 and 44. As previously, the electrical signal supplied by the comparator 64 is representative of the quantity of water contained per square meter in the lines of glue 111.

All the previous embodiments use two separate horns to transmit and receive the two polarized waves rectilinear and at right angles. It is possible to simplify the assembly by using only one horn for this purpose, thus transmitting and receiving the two waves:
In addition to the advantage of simplification, this working method has the advantage of making reflection or transmission measurements on the same strips of glue for each of the waves emitted E1 and E2.

 A convenient device, known but not widely used, allowing to hold two polarized waves rectilinearly and at right angles in the same guide, is the Tee with five arms, represented in FIG. 6. As can be seen in the drawing, this Tee with five arms consists of a Greek cross 45 in standard rectangular guide, coupled to a circular guide 46 of diameter equal to the width of the four guides making up the cross, and whose axis is parallel to the short sides of these guides. If we send waves at A and B, they emerge through the circular guide 46 with rectilinear and crossed polarizations at right angles as indicated, and according to the mode corresponding to the fundamental mode.

 FIG. 7 very schematically shows an example of assembly, in accordance with the invention, operating by reflection and using only a single horn 47, cone in ltespèce, to transmit and receive the two waves of electric fields El and E2. One uses, coupled to the generator 24, a Tee with five arms 49 such as that of FIG. 6 and the two non-excited arms of which are closed on suitable impedances 48. The cross-polarized waves coming from the Tee 49 are applied to the horn 47 by means of a circular guide 50. The two reflected waves are picked up separately by two couplers (51, 52), produced in a circular guide according to the conventional technique, and are detected by diodes (33, 34) as in all previous cases. The detected signals are then subtracted in the associated electronic unit, which has not been shown in the drawing.

 In particular in the case of weak deposits, it will often be advantageous to carry out the measurement on the transmitted waves and not on those reflected, the measurements by transmission being generally more precise. FIG. 8 very schematically represents an assembly that can be produced for this purpose, always by using a transmitter horn 47, common to the two orthogonal waves, and in this case by using another receiver horn 53 for the two waves transmitted.

 As can be seen in the drawing, the receiving part is completely symmetrical with the transmitting part. It uses in particular a Tee with five arms 54 identical to Tee 49. In this example, the waves from Tee 54 are applied to a phase bridge similar to that of FIG. 5, and therefore composed of a magic Tee 42, detector diodes 43 and 44, and a subtractor 64. Obviously, such a phase bridge could very well be used in the assembly with couplers and detector diodes of FIG. 7, and vice versa.

 In these last two embodiments, it is obvious that we can replace the guides (50), couplers (51, 52) and horns (47, 53), all of circular type, by similar elements, but of square type it suffices for this to add to the T-arms with five arms used transitions "circular guide-square guide", these devices being in the current domain of the skilled person. The measurement would then be a little more precise, because the electric fields are rigorously crossed at all points of the square guide, which is true only for two planes in the case of the circular guide.

Claims (10)

 1.- Method for measuring the quantity of water per square meter contained in parallel strips of an aqueous product deposited on a substrate, in particular for measuring the quantity of glue per square meter deposited on the corrugated paper during of the manufacture of corrugated cardboard, characterized in that it consists in measuring the difference between the characteristics of the electromagnetic waves reflected or transmitted by the material (9) lined with strips of glue (111), or other aqueous product, from two electromagnetic waves (E1, E2) emitted towards said material with rectilinear and substantially orthogonal polarizations, one of which (El) is substantially parallel to the bands (111) of common aqueous product, and whose wavelength - (n) is at least equal to the sum of the intervals separating three to five successive bands.  2. A measurement method according to claim 1, characterized in that the difference in the electrical powers of the two waves reflected or transmitted by said material is measured.  3. A measurement method according to claim 1, applied in the case where the two waves are transmitted in phase concordance, characterized in that the phase difference between the two waves reflected or transmitted by said material is measured.  4.- Method for measuring, according to any one of claims 1 to 3, of the quantity of glue per square meter deposited on the corrugated paper during the manufacture of corrugated cardboard, characterized in that the common wavelength used is three hundred meters.  5.- Device for implementing the method according to any one of claims 1 to 4 characterized in that it comprises - at least one microwave generator (24) - at least one microwave circuit (25 to 29) connected to said generator, or said generators, and allowing the emission, towards the material (9), of two electromagnetic waves (E1, E2) of the same frequency and polarized rectilinearly at right angles, or substantially at right angles, the one of the two waves (El) being emitted substantially parallel to the strips of aqueous product, - at least one device (31 to 35) for detecting one and the same electrical characteristic of each of the two waves reflected or transmitted by said material to from said transmitted waves, as well as from subtraction of these two electrical characteristics.  6.- Device according to claim 5, applied to the gluing of corrugated cardboard, characterized in that it is coupled to an electronic device (15) for automatic adjustment of the quantity of adhesive deposited.  7.- Device according to claim 5, characterized in that it uses a device (31, 33, 32, 34, 35 or 38, 39, 40) for detecting and subtracting the electric powers of the two waves reflected or transmitted,  8.- Device according to claim 5, applied in the case of the use of a device (24, 25) for transmitting the two waves (E1, E2) in phase concordance characterized in that it uses a device ( 41, 43, 44, 64) for measuring the phase difference between the two reflected or transmitted waves.  9.- Device according to any one of claims 1 to 8, characterized in that it uses one and the same transmitter and / or receiver (47, 53) for the two crossed waves.  10.- Device according to any one of claims 5 to 9, of the type comprising at least one device for detecting reflected waves, characterized in that it further comprises a wave reflector (30) placed behind said material (9).