SK181299A3 - Method for determining the orientation of fibre structure in a mineral wool mat - Google Patents

Abstract

The invention concerns a method for determining the orientation of fibre structure in a mineral wool mat, and in particular in a crimped mineral wool mats, which consists in recording on a video camera at least one image of a mineral wool mat predetermined zone and in evaluating said image luminous density profile using digital image processing. The vertical fibre proportion and the crimping fineness are computed from the luminous density profile and are digitally and/or graphically represented and evaluated.

Description

Technical field

The invention relates to a method for determining the orientation of the fiber structure in a mineral wool mat and in particular the so-called "creped" mineral wool mats. The invention will be described in particular for a creped mat (the term "mat" as used herein refers to a slab or mat of mineral wool without limitation in terms of thickness or flexibility, i.e., in the narrower sense or slab) of mineral wool.

BACKGROUND OF THE INVENTION "Creped" mineral fiber mats, e.g. in which the orientation of the fibers, rather than being parallel to one plane, is "quasi-random", is intended for a variety of applications, especially when pressure is to be applied without causing too much compression or tension perpendicular to their surface , without delamination of the mat.

Traditionally, the mineral wool mats are layered, being formed continuously by depositing fibers conveyed by air streams onto a conveyor. Prior to being deposited on the conveyor, the fibers are coated with a bituminous substance to be bonded to each other, thereby rendering the mat formed cohesive. The bituminous material which is applied in liquid form is crosslinked by a heat treatment carried out on the mat before being brought to the desired thickness and bulk density.

Traditional methods of mat formation result in products whose properties do not perfectly meet all the requirements posed by certain special applications. In addition to the insulating properties generally required, it is sometimes necessary that the products used have very specific mechanical properties. This is the case, for example, with products

31365 / H supporting, for example, structural elements of the building and which therefore have to withstand severe compressions, such as products serving as insulation for roof terraces accessible to the operation. Similarly, in the case of products used for external insulation, they must in particular be able to withstand tearing forces.

In order to obtain products having these special properties, it is necessary to change the traditional methods of manufacturing the mat.

In a traditional method, the formation of a mat by depositing fibers on a receiving conveyor or an analogous device leads to intertwining with felting, which is not homogeneous in all directions.

It can be experimentally stated that the fibers tend to deposit parallel to the receiving surface. This tendency is the more pronounced the longer the fibers are. This mat structure is favorable in terms of their insulating properties and also in terms of tensile strength in the longitudinal direction.

Thus, for many uses such a structure is advantageous. However, it is understood that such a structure is not most suitable when the product is to resist compression or tearing in the direction of its thickness.

Methods for obtaining "quasi-random" fiber orientation are known. Thus, for example, European patent application EP-A-0 133 083 proposes that fiber mats taken at the receiving device be continuously compressed in the longitudinal direction after passing through a pair of rollers driven at a certain speed to a pair of conveyors at a lower speed. than the previous speed. Higher compression rates can be achieved when the compression is performed in a plurality of successive stages, particularly with mats where compression is more difficult to achieve without the formation of creases. If the compression is performed in several phases, the properties of the product obtained can be improved to the same degree of final compression.

It is generally believed that the thermomechanical properties of these products are closely related to the arrangement of the fibers in the mat. Until now, however, creping has been evaluated qualitatively; based on visual observation, and the creping rate, or better the compression rate in terms of speed change between

31365 / H conveyors is not representative of the general characteristics of the products obtained. Visual assessment does not permit a systematic expression of the relationship between the geometrical characteristics of the product and its thermomechanical characteristics in a reproducible manner. Moreover, such a quality control is not at all applicable on a production line, for example for production control.

It therefore appears necessary to be able to control the arrangement of the fibers in the mats and thus to control the quality of the products produced, in particular their thermal and mechanical properties. In particular, this would ensure the constant quality of the end products in detecting those which go beyond the standard conditions and would allow the 'history' of production of each of the products for ex-post control to be maintained. In addition, this would allow, on the basis of these data, the possibility of regulating production.

It is essential that these measurements be non-contact, that the geometric structure of the products to be measured is not damaged and that the results are known in real time and that they are equally storable for processing.

The present inventors have focused on the extraction of the predominant fiber directions in a mineral wool mat present at various scales.

For this purpose, an arbitrary vertical reference base was established in order to determine the 'vertical fiber fraction' corresponding to the overall erection of the fibers on a macroscopic scale. The microscopic scale determines the isotropic nature of the fiber arrangement, hereinafter referred to as the "crepe softness". The authors have shown that it is not necessary to individually visualize the threads, but that the visualization of more or less large 'packages' is sufficiently representative.

It is therefore an object of the present invention to provide a method for determining the fiber structure orientation of a mineral fiber mat, and in particular a " creped " mineral fiber mat, which makes it possible to determine the proportion of vertical fibers and creep fineness.

SUMMARY OF THE INVENTION

The invention provides a method for determining the orientation of a fiber mat structure

31365 / H of mineral wool, in particular creped mineral wool mats, in which a specified area of the mineral wool mat is illuminated at an oblique angle of incidence of light by means of a video camera mounted on an axis substantially perpendicular to the plane of that area Each digit of the image is assigned a digital signal corresponding to its light density (luminance), which digitization takes place directly in the camcorder or in the digitization stage downstream of it, and by means of an image processing system from digital light density signals (luminance) ) determines the proportion of vertical fibers and the fineness of creping.

The invention thus provides a method by which a quantitative determination of the fiber arrangement in a mineral wool mat can be carried out in a simple manner without the need for expensive optical devices. The equipment required for the leanness of the mineral wool mat to be investigated comprises only the lighting equipment and the video camera and can be stored without difficulty directly at the level of the mineral wool mat production line.

Advantageously, before the image is recorded, dust is removed from said area, which dust removal can be effected, for example, by intense air flow or by suction under high pressure.

Preferably, the camcorder is connected to an input card for image acquisition and processing, allowing the image to be digitized at 512 x 512 pixels to 256 gray levels. The card also has two parameters, gain and offset, which should be carefully aligned for good quantification of the video signal. Preferably, a CCD camera (chargé coupled device) is used whose CD reader comprises 768 x 512 square photosensitive elements with a size of 10x10 pm ² .

According to a preferred embodiment of the invention, the vertical fiber fraction and the crepe fineness are determined from digital signals using the MORLET 2D wavelet transform algorithm. The authors have found that among a number of functions that verify the admissibility conditions in terms of wavelet transforms, the MORLET wavelet transform is advantageously adapted for its ability to select

31365 / H orientation and its oscillating progression, which is close to the structure of the images to be analyzed.

According to a particularly efficient embodiment of the invention, the determination of the orientation of the fiber structure of the mineral wool mat is carried out by recording, in particular, four images of said area taken by a CCD camera at different locations, then processing each of the recorded images and averaging the values before final calculation the proportion of vertical fibers and the fineness of the fibers.

The authors found that the values obtained from the image are reproducible from multiple images recorded at different locations in the same product. In this way, when averaging multiple images of the same control area sensed at different locations, representative mean values are generated.

It is also preferred that said region is distinguished into at least two parts and the fiber structure orientation for each of these parts is determined.

In this way, which is advantageous for a mineral wool mat having a large thickness, it is possible, for example, to determine the fiber structure for the upper half of the mat and for the lower half of the mat. The fiber arrangement is thus quantified in the thickness of the mat in a different way, which makes it possible to control the quality of the products in an in-depth manner.

It goes without saying that the method of the invention is applicable to a static article or to a mineral fiber production line on which a mat is placed on a moving conveyor.

The invention also relates to an apparatus for carrying out the method according to the invention. Preferably, the device comprises an illumination device that illuminates a designated area of the mineral wool mat at an oblique angle of incidence of light, a CCD camera mounted on an axis substantially perpendicular to the plane of said area, and an image processing system.

Preferably, the device also comprises a dust removal device which will preferably be a device that blows intensively air or which sucks under strong pressure.

According to a preferred embodiment of the invention, the image processing system comprises a filter stage implemented by means of a filter,

31365 / H leading to an image region of a two-dimensional linear transformation, such as a MORLET 2D wavelet transformation.

Preferably, the above-described method of the invention is used to obtain correlation data between the mechanical properties and / or thermal properties of the mineral wool mat and the obtained values of the vertical fiber fraction and crepe fineness.

It is likewise advantageous if the above method is used to automate production lines for producing creped mineral wool mats, allowing automatic control of the longitudinal compression rate of the creping machine depending on the data obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

BRIEF DESCRIPTION OF THE DRAWINGS The invention is explained in more detail below with reference to the accompanying drawings, in which: FIG. 1 is a schematic diagram of the apparatus necessary for carrying out the method; FIG. 2 is a block diagram of the essential components required for digital image processing; FIG. Fig. 3 is a block diagram of a calculator for calculating the proportion of vertical fibers and creep fineness based on digitized signals; 4 shows a printed representation of the measured crepe fineness profile; and FIG. 5 is a printed representation of a measured vertical fiber fraction profile.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIG. 1, a mineral wool web 1 of about 40 mm thickness, made continuously, and shown here in the form of a mineral wool slab section, is moved at a speed of about 20 meters per minute according to the slab thickness in the direction of arrow F to a cutting station (not shown). At a suitable location of the production line, a sufficiently wide area on one planar side of the mineral wool web 1 is stripped of the intense air stream 2 of the dust.

At the level of this region, two halogen lamps 3 and 4 are located on the side of the mineral wool strip 1. The light emitted by the halogen lamps 3, 4,

31365 / H extends the planar side of the mineral wool web 1 at an incidence angle of from 30 ^° to 60 ° and preferably at an incidence angle of 45 °. Inclined illumination at the highest possible angle of incidence is advantageous to obtain good sharpness of the obtained image. Conversely, the incidence angle must not be too large, since the mineral fiber bands then reflect an increasing proportion of light, leading to overexposure of the camera.

Between the two lamps 3 and 4 a CCD camera 5 is arranged substantially perpendicular to the side of the mineral wool web 1. The images recorded by the CCD camera 5 are transmitted by a line 6 to an image processing system 7 in which digital image processing is performed.

The image processing system 7 comprises, as shown in the schematic representation of FIG. 2, the processor 9, the calculator 10, and the mass memory 11. The calculator 12 is connected to a control keyboard 12 as well as a data visualization device 13 and a printer 14. In addition, the digital image processing device may include a display display 15 connected to the processor 9 and a drawing device. images 16.

The CCD camera comprises an analog-to-digital converter 8. In this converter 8, there are signals for each point of the image, which define its position and its brightness or gray value, i.e. the signal. its luminous density, transmitted to the corresponding digital signals. In order to describe the light density with sufficient accuracy by means of digital signals, the total area of luminance to be covered must be divided into a sufficiently large number of gray levels. The number of gray levels must be at least 128, and good results are obtained when 256 gray levels are available.

The processor 9 serves inter alia to operate, using known methods of processing video images, the original video image into a video image having a better contrast than the original image. Known image processing cards, as commercially available, may be used for this image processor 9.

The processor 9 includes an image memory in which the video image is stored, the contrast of which has been improved. The video image transformed by the processor 9 and having improved image contrast forms the basis for subsequent processing

31365 / H image, performed by calculator 10. Calculator 10 calculates, using the algorithm developed for this purpose, the luminous density information stored in the memory of the processor images 9, the proportion of vertical fibers and the fineness of creping. A mass storage device 11 is attached to the calculator 10 for storing programs and for archiving video images with improved contrast and / or images calculated therefrom, as well as associated values of vertical fiber fraction and creep fineness.

The development of the algorithm according to which the calculation of the vertical fiber fraction and the creep fineness is performed in the calculator 10 based on the image information present in the image memory of the processor 9, using a wavelet transform algorithm of the two-dimensional function.

The wavelet transformation of a two-dimensional function is expressed in a four-dimensional space (a, b, Θ), where a is a coefficient of dilation scale, b is a translation parameter, and Θ is an orientation parameter.

A preferred method of analysis is to perform a wavelet transformation of MORILLET 2D images, passing, for example, all dilation scales to 0.05 <a <0.6 (scaling equivalent to scaling [0.36: 4.27 mm] to enlarge the image by 7.5 pixels / mm, this magnification being variable according to the field of view) and all orientations for 0 <Θ <180 °, where θ = 0 ° for the reference vertical direction, at each point of the image. For each pair (a, Θ) a two-dimensional graph is obtained corresponding to the wavelet transform coefficient MORLET C! (a, b, Θ). This analysis is performed with an angle step θ = 10 ° and a step a = 0.05 for the dilation scale.

Only the average of the MORLET wavelet transformation coefficient modules (a, b, Θ) of the MCTO (a, na) to obtain cumulators C (Θ) is retained. From cumulants C (Θ), the proportion of vertical fibers at a scale of 0,3 <a <0,6 and the creep fineness at a dilation scale of 0,05 <a <0,3 are calculated, which of course are modulated according to the nature of the mineral wool product and the criterion studied. It is then possible to graphically express the vertical fiber fraction profile as well as the creep fineness profile. These calculations can be performed using the formulas:

31365 / H tidid 1

TfV = ^ cos (2.0,) .l C (0, β, = 0 ’\ Π. = U where means

TfV = vertical fiber fraction cos (2,0j) = weighting factor n = 18 fineness

n where σ = standard deviation n = 18

Thus, to calculate the proportion of vertical fibers and the crepe fineness, it is sufficient to know the course of luminance or the effective light density (luminance) on the region of the mineral wool strip 1 in the form of numerical values for different image points. . Preferably, the evaluation will be performed on the basis of a plurality of successive images taken on the same side of the mineral wool web 1, but at different locations from which the cumulative calculation results are averaged to obtain the final values.

Even more preferably, the mineral wool slab has a thickness of greater than 40 mm, such that the evaluation is performed in the upper half and lower half of the thickness of the mineral wool strip 1, distinguishing the values obtained for each of the halves to obtain better accuracy of the overall fiber structure orientation. mineral fiber mats.

Fig. 3 shows, in block diagram form, how the calculator 10 performs processing of various image points, for example, during evaluation

31365 / H single video image. The digitized measured luminance value L of each point of the image is transmitted via line 17 to the Gaussian filter 18 in the frequency space. At the output 19 of this Gaussian filter 18, a signal corresponding to the MORLET 2D wavelet transform coefficient modules for a a Θ 0, (a, b, Θ) appears. This signal C, (a, b, Θ) is transmitted to summation stage 20, which is the average of the MORLET MCTO wavelet transformation modules (a, Θ), which is now transmitted to summation stage 21, where the cumulative coefficients are formed. MCTO (a, Θ) on the dilatation scale 0.05 <a <0.3 C [o, o5: o, 3] (θ)> and to the next summation stage 22, where the cumulative of MCTO coefficients (a, Θ) is formed ) on a dilation scale of 0.3 <a <0.6 0 (0.3.0,61 (0) The cumulant C signal (0, 5o, 3] (9) is transmitted to the countdown stage 23 where the standard deviations of the cumulants are formed; and the cumulant signal C [o.3: o, 6] (0) j is transmitted to the countdown stage 24, in which the weighted vertical fiber fraction calculation is performed The lines 25 and 26 at the respective outputs of the countdown stages 23 and 24 now carry each corresponding signal which directly corresponds to the fineness of the fibers and the proportion of vertical fibers at the location relative to the measured image. and transferred to the individual units shown in Figure 2 for re-evaluation and / or storage.

Further details on the wavelet transforms of the two-dimensional function, and in particular the MORLET 2D wavelet transform, are described in "Waves and Waves, the Saga of a Mathematical Instrument" by Barbara Búrke Hubbard, published by Belin pour la Science.

The result of the signal processing performed in the described manner can be displayed and archived in any way. The illustration, which can be realized both by image and by printing, is shown in the form of printed images in FIG. 4. and 5.

Fig. 4 shows in polar coordinates the cumulative profile of MCTO coefficients (a, Θ) on a dilatation scale of 0.05 <a <0.3. The standard deviations of the cumulants are visually depicted by plots of circles indicating maximum and minimum. Fig. 5 shows the profile in polar coordinates

31365 / H cumulators of MCTO coefficients (a, Θ) on a dilation scale of 0.3 < a < 0.6, wherein the predominant fiber orientation is visually illustrated by plotting a line joining the maxima.

The position and values of the fiber orientation deficiencies, particularly in the case of creped mineral fiber boards, can thus be automatically detected and archived. Alternatively, the data can be transmitted via the interface to an automatic system in which the cutting of the mineral wool web and the sorting of the mineral wool boards can be performed based on these data according to different quality requirements or where the longitudinal compression speed of the creping device can now be controlled based of this data.

Such a method of determination may also be performed on a static product at a location other than the production line. Advantageously, such determination of the fiber structure orientation of the article allows to accurately correlate the properties of the article, such as mechanical or thermal properties, with the calculated values of vertical fiber fraction and crepe fineness. Thus, such correlation analyzes provide better knowledge and control of the properties of mineral fiber products.

The invention is not limited to this embodiment, is not intended to be limited to interpretation, and encompasses all types of processes for determining the fiber structure of a mineral wool mat in which an illuminated area of a mineral fiber mat at an oblique angle is illuminated. a measuring field arranged substantially perpendicular to the plane of the area, each digital image being associated with a digital signal corresponding to its light density (luminance), the digitizing being carried out directly in the video camera or in a digitizing stage located at its output, and In the image processing system, the proportion of vertically oriented fibers and the fineness of creping are determined from the digital light density (luminance) signals.

Claims (10)

PATENT CLAIMS 1. A method of determining the orientation of the fiber structure of the mineral wool web, particularly crepe mineral wool mats, in which illuminates the intended area of mineral wool web oblique incidence of light ^R, a video camera supported on a shaft substantially perpendicular to the plane of the Also, at least one image of said area is recorded to each area, a digital signal corresponding to its light density is assigned to each point of the image, and this digitization takes place directly in the camcorder or in a digitization stage downstream of it, and they determine the proportion of vertical fibers and the fineness of creping from the digital light density signals. Method according to claim 1, characterized in that the proportion of the vertical fibers and the fineness of the fibers are calculated from the digital light density signals using a wavelet transform algorithm of the two-dimensional function. Method according to claim 2, characterized in that the wavelet transform MORLET 2D is used. Method according to any one of claims 1 to 3, characterized in that at least four images of said area are recorded by a CCD camera, taken at different locations, processing each of the recorded images, and the obtained values averaged before the final calculation the proportion of vertical fibers and the fineness of the fibers. Method according to any one of claims 1 to 4, characterized in that said region is distinguished into at least two parts and the orientation of the fiber structure is determined for each of these parts. 31365 / H Method according to any one of claims 1 to 5, characterized in that the mineral fiber mat lies on a moving conveyor. The apparatus for carrying out the method according to claim 1, characterized in that it comprises an illumination device that illuminates a designated region of the mineral wool mat at an oblique angle of incidence of light, a CCD camera mounted on an axis substantially perpendicular to the plane of said region, and image processing system. The apparatus of claim 7, wherein the image processing system comprises a filter stage implemented by means of a filter leading to an image region of a two-dimensional linear transformation, such as a MORLET 2D wavelet transformation. Use of the method according to any one of claims 1 to 6 to obtain correlation data between the mechanical properties and / or thermal properties of the mineral wool mat and the obtained values of the vertical fiber fraction and the crepe fineness. Use of a method according to any one of claims 1 to 6 for automating production lines for producing creped mineral wool mats, allowing automatic control of the longitudinal compression rate of the creping machine depending on the data obtained.