EP1357539B1 - Method of manufacture and assembly of an acoustic panel comprising a double-resonator with a honeycomb core - Google Patents

Abstract

The acoustic panel is made with two honeycomb structures (30,50) separated by a septum (40). The septum is scanned by a digital camera and successive images transmitted to a computer, which monitors perforations of the septum, determining the rate of perforations by calculating the ratio of the number of holes to the number of pixels in the image.

Description

Technical field of the invention

The invention relates to acoustic panels with double resonator honeycomb core and more particularly to a method of assembly and control of such panels.

State of the art and problems to be solved

Acoustic panels with double resonator honeycomb core sandwich structures are well known for absorbing noise, especially on aircraft powertrains. These panels usually comprise the following successive layers in the direction of the thickness: a first skin called "acoustic" and multiperforated, that is to say comprising a plurality of holes, a first layer of honeycomb called "primary", a septum also multiperforated, a second layer of honeycomb called "secondary" and a second skin called "full" because not having holes. The honeycombs consist of a plurality of generally hexagonal cells, these cells being separated by thin partitions themselves having drainage notches to evacuate by gravity the water that would have penetrated into the acoustic panel during its operation. The acoustic skin and septum holes are regularly distributed and are each characterized by their perforation rate, that is to say by the ratio between the surface of the holes and the total surface of the layer considered. The acoustic skin and the solid skin are usually made of organic matrix composite material consisting of a variable number of layers of reinforcement fabric superimposed and embedded in a polymerized resin. Honeycomb layers are usually made of aluminum foil.
The acoustic properties of the panel, that is to say its rate of absorption of noise as a function of the frequency and the noise level of the noise, depend on the dimensioning of the components of the panel and in particular on the perforation rates of the full skin and the septum.

Each layer is made separately and methods for doing so are well known. The acoustic skin is usually pierced by the drill because the size of the holes allows it without difficulty. The septum may be drilled with the drill, but drilling with a laser beam is preferred because of the small size of the holes and their large number.
The acoustic panel is then assembled by arranging the different layers previously glued on a mold to the required shape and subjecting the assembly to a thermal cycle in an autoclave to tighten the layers against each other and to polymerize the glues. Note that the full skin can be made and glued in one operation on the panel.

The critical phase of the assembly process is the assembly by gluing the septum to the two layers of honeycomb. During the assembly indeed, a fraction of the septum holes is closed normally by the glue and it is taken into account to define the rate of perforation of the bare septum, that is to say before its assembly. This fraction easily reaches 50%. Too small or too large a fraction substantially changes the acoustic properties of the panel and renders it unsuitable for use. This fraction is minimal when the cells of each of the honeycomb layers are in phase, that is to say facing each other, because the adhesives used to assemble each of the honeycomb to the septum substantially close the same septum holes. This fraction becomes maximum when the cells of each of the honeycombs are in phase opposition, ie shifted to the maximum. The geometry of the honeycombs is unfortunately imprecise and the phenomenon which has just been described is consequently difficult to control.
This fraction also depends on the amount of glue used, but the bonding itself is well controllable.

The septum holes are usually very small, a diameter of about 0.3mm with about 50 holes per square centimeter. Such a septum is pierced before assembly with the drill but preferably by laser beam. The number and smallness of the holes make the drilling delicate. Thus, and although the piercing process is fairly well controlled, defects may occur.

• le raylomètre est un appareil pneumatique instable et il nécessite des ré-étalonnages fréquents ;
• le contrôle du septum nu est long car il faut appliquer le raylomètre successivement en différents endroits du panneau et attendre que la mesure soit stabilisée avant de la prendre en compte ;
• le contrôle de septum de grande taille nécessite des raylomètres spéciaux, donc coûteux, car ils doivent pouvoir atteindre le centre des septums.

It is known to measure the normalized resistance of the naked septum, that is to say before assembly, with a system of measurement of pressure loss called more simply "raylomètre". This method however has some disadvantages:

• the raylometer is an unstable pneumatic device and it requires frequent recalibrations;
• the control of the naked septum is long because it is necessary to apply the raylometer successively in different places of the panel and wait until the measurement is stabilized before taking it into account;
• the control of large septum requires special raylometers, so expensive, because they must be able to reach the center of the septa.

The inventors do not know satisfactory means for measuring in production the characteristics of a finished panel. Indeed.

A measurement made with the above-mentioned raylometer is tainted with very important errors caused by lateral leakage through the drainage slots in the partitions and also by the inevitable misalignment of the two honeycomb layers.

Another measuring instrument known as a "Kundt tube" is also known for directly measuring an acoustic impedance. Unfortunately, the measurements made with a Kundt tube on the panel described above are also tainted with very large errors from honeycomb cells straddling the edge of the Kundt tube when applied against it. the panel.

A first problem to be solved is to propose a method of assembly and control of acoustic panels to ensure the expected acoustic characteristics.

A second problem to be solved is to detect as soon as possible any defects likely to alter the characteristics of the panel, so as to interrupt the assembly process and therefore not to perform unnecessary assembly operations.

A third problem is to provide a reliable and inexpensive assembly and control method.

Presentation of the invention

• on assemble dans un premier temps par collage les deux nids d'abeilles avec le septum pour constituer un sous-ensemble, cet assemblage ayant malheureusement pour effet d'obstruer inévitablement une fraction des trous du septum ;
• postérieurement à l'assemblage des deux nids d'abeilles avec le septum et préalablement à l'assemblage de l'une au moins des deux peaux, l'un au moins des nids d'abeilles étant ainsi découvert, on contrôle du taux de perforation du septum en scannant le sous-ensemble avec une caméra numérique comportant un éclairage associé, la caméra étant disposée du coté d'un nid d'abeille découvert, la caméra prenant ainsi des prises de vue du septum au fond des alvéoles du nid d'abeille découvert, cet éclairage éclairant la zone du septum observée par la caméra, les images successives ainsi obtenues étant transmises à un ordinateur, l'ordinateur analysant les images et établissant le taux de perforation T du septum en appliquant la formule T = N1 / N dans laquelle N1 est le nombre de pixels correspondants aux trous dégagés et N le nombre de pixels de l'image.

According to claim 1, the invention proposes a method for assembling and controlling a double resonator honeycomb acoustic panel, the panel consisting of a plurality of layers to be assembled in the thickness direction. or: an acoustic skin, a primary honeycomb, a septum pierced with a plurality of holes, a secondary honeycomb and a solid skin, the method comprising preliminary operations for sizing the various layers to be assembled.
Such a panel is remarkable in that:

• The two honeycombs are first bonded together with the septum to form a subset, this assembly unfortunately having the effect of inevitably blocking a fraction of the septum holes;
• after the assembly of the two honeycombs with the septum and prior to the assembly of at least one of the two skins, at least one honeycomb being thus discovered, the rate of perforation is checked of the septum by scanning the subset with a digital camera with associated lighting, the camera being placed on the side of a honeycomb discovered, the camera thus taking shots of the septum at the bottom of the cells of the nest of bee discovered, this illumination illuminating the area of the septum observed by the camera, the successive images thus obtained being transmitted to a computer, the computer analyzing the images and establishing the perforation rate T of the septum by applying the formula T = N1 / N wherein N1 is the number of pixels corresponding to the cleared holes and N is the number of pixels of the image.

It is understood that the invention makes it possible to control the correct execution of the critical phase of the assembly process, namely the assembly of the septum with the two honeycombs. Thus, and since the other assembly operations are well controllable, the implementation of the invention makes it possible to ensure that acoustic panels are obtained as close as possible to the performances for which they have been designed, which provides a solution. to the first problem.

It is also understood that the invention makes it possible to control as soon as possible the proper execution of the critical phase of the assembly process since this control can be carried out immediately after this critical phase, which solves the second problem. When the control shows that the septum is defective, unnecessary assembly operations of the skins can be avoided.

It is also understood that the assembly and control process is inexpensive because it can be interrupted when the critical phase went wrong and because the control means themselves are inexpensive.

Finally, it is understood that the present invention has requested the selection and design of particular control means since the raylometer and the Kundt tube do not provide sufficient accuracy, in contrast to the proposed method of acquisition and image analysis.

Advantageously, and prior to the assembly of the septum with at least one of the honeycombs, a control of the perforation rate T of the naked septum is carried out by scanning the septum with a digital camera having associated lighting, this illuminating illumination the area of the septum observed by the camera, the successive images thus obtained being transmitted to a computer, this computer analyzing the images and establishing the perforation rate T of the septum by applying the formula T = N1 / N in which N1 is the number of pixels corresponding to the cleared holes and N the number of pixels of the image.

This cheap control operation makes it possible not to engage the assembly of acoustic panels from defective septa.

The invention will be better understood and the advantages it affords will become more clearly apparent from a detailed example of implementation of the method and the accompanying figures.

Description of figures

The figure 1 illustrates an acoustic panel on which the invention is applicable.

The figure 2 illustrates a naked septum.

The figure 3 illustrates an assembled septum.

The figure 4 illustrates the control of a naked septum.

The figure 5 illustrates the control of an assembled septum.

Description of a detailed example of implementation

We will refer first to the figure 1 . The acoustic panel 10 is a laminated structure constituted by the assembly of different layers in the direction of the thickness, that is successively: an acoustic skin 20, a "primary" honeycomb 30, a septum 40, a nest of 'bee says'secondary' 50 and finally a full skin 60.

The acoustic skin 20 is usually made of organic matrix composite material consisting of five to fifteen layers of unrepresented reinforcing fabric, which fabrics are embedded in a cured resin by polymerization, these fabrics usually being made of glass fiber, carbon fiber or Kevlar. The acoustic skin 20 is pierced with holes 22 following a regular mesh, their diameter being of the order of 1mm to 3mm, the perforation ratio, ie the ratio between the total surface of the holes 22 and the surface of the acoustic skin 20 being of the order of 15 to 25%.

The primary honeycomb 30 consists of adjacent cells 32 oriented in the direction of the thickness of the honeycomb 30, these cells 32 being separated by thin partitions 34, these partitions 34 having adjacent drainage notches 36 septum 40, these drainage notches 36 allowing the flow and evacuation of water that could have entered the panel 10 through the holes 22 of the acoustic skin 20. The cells 32 are usually hexagonal with a diameter inscribed, or width, usually between 3mm and 10mm, 1/8 ^th to 3/8 ^th of an inch. The partitions 34 may be made of aluminum strip.

The septum 40 is usually an organic matrix composite material consisting of one to five plies of unrepresented reinforcing fabric, which fabrics are embedded in a cured resin by polymerization, these fabrics usually being made of glass fiber, carbon fiber or carbon fiber. Kevlar. The septum 40 is also pierced with holes 42 following a regular mesh.

The secondary honeycomb 50 is similar to the primary honeycomb 30. However, its thickness or the width of its cells may be different. 52, 54 and 56 respectively refer to its alveoli, its partitions and its drainage notches which are adjacent to the full skin 60.

The full skin 60 is similar to the acoustic skin 20, the full skin 60 being however not perforated, the number and the composition of the fabric folds and the composition of the resin may be different.

The adhesive will be referenced 70 allowing the connection between the different layers of the panel 10.

We will now refer to the figure 2 . In this example corresponding to the most general shape, the holes 42 of the septum are arranged along straight or slightly curved parallel lines 75, the distance between two successive lines being denoted e, the pitch between two holes 42 on each line 75 being noted. p. The perforation rate T is then given by the formula: T = s / e * p.
The holes are laser drilled, the septum being arranged on a table having the same shape as it, the drilling apparatus being disposed at the end of a robot arm and running through the septum along the drilling lines 75.

We will now refer to the figure 3 . In this figure, the septum 40 is seen through the cells of one of the honeycomb 30, 50, for example through the cells of the secondary honeycomb 50. The primary honeycomb 30 is therefore not visible and its partitions 34 are shown dashed. The adhesive 70 is against the partitions 54 and extends a little on the septum to a bonding limit 77, this bonding limit 77 thus forming an approximately circular closed line. The holes 42 of the septum 40 appear within the bonding boundary 77, some holes 42a being obstructed by the adhesive holding the primary honeycomb 30 on the septum 40, these closed holes 42a being in the vicinity of the partitions 34 of the septum 40. primary honeycomb 30. The open holes will be referenced 42b.

We will refer again to the figure 1 .
The acquisition of the various layers 20, 30, 40, 50 and 60 is also performed, this acquisition comprising the drilling of the holes 22 of the acoustic skin 20 as well as the holes 42 of the septum 40 and pre-seeding of the layers. In a particular embodiment without affecting the present invention, the full skin 60 can be made and bonded to the secondary honeycomb in a single operation and therefore with a single thermal cycle.

We will now refer simultaneously to figures 2 and 4 .

The assembly of the panel is advantageously, but not necessarily, preceded by a control of the rate of perforation of the septum 40. This control can be exhaustive but it will preferably be performed by sampling to reduce the cost. The check can be done as follows.
Scanning the bare septum 40 with a digital camera 84 having a lens 86 88.96 associated lighting, 88.96 this lighting obviously illuminating the area of the septum observed by the camera 84, the septum 40 being in practice arranged on a support 82, the successive images 92 thus obtained being transmitted to a computer 94, the computer establishing the perforation ratio T by applying the formula T = N1 / N in which N1 is the number of pixels 100 corresponding to the holes 42 and N the number of pixels of image 92. The resolution of the camera and the magnification ratio of the image 92 are chosen so that each hole 42 covers at least 30 pixels in the image. In a preferred embodiment, this resolution is chosen so that each hole 42 covers 75 to 100 pixels in the image, the accuracy of the measurement being consequently improved by reducing the influence of the pixels straddling the edges. Holes.

In the case where episcopic illumination 88 is used, the pixels 100 corresponding to the holes 42 are those whose luminous level is below a predetermined threshold level. In the case where a diascopic light 90 is used, the pixels 100 corresponding to the holes 42 are those whose light level is greater than a predetermined threshold level. This threshold level is established by experimentation to give the most accurate measure, that is to say so that statistically half of the pixels straddling the edge of the hole have a level below this threshold and for the other half to have a level above this threshold.

In view of these results, the operator rejects the defective septa 40, that is to say the perforation rate is out of tolerance and possibly makes changes in the setting of the machine that made the drilling of the septum 40.

• la peau acoustique 20 est préencollée sur son coté qui sera au contact du nid d'abeille primaire 30 ;
• le nid d'abeille primaire 30 est préencollé aux extrémités des cloisons 34 qui seront au contact du septum 40 ;
• le septum 40 ne subit pas de pré encollage qui en obturerait les trous 42 car ceux-ci sont trop petits ;
• le nid d'abeille secondaire 50 est également préencollé aux extrémités des cloisons 54 qui seront au contact du septum 40 ;
• la peau pleine 60 est préencollée du coté qui sera au contact du nid d'abeille secondaire 50.

We will refer again to the figure 1 .
The assembly comprises preliminary pre-gluing operations of the different layers 20, 30, 40, 50 and 60 to be assembled, this pre-gluing preferably being carried out, but not necessarily, in the following manner:

• the acoustic skin 20 is pre-glued on its side which will be in contact with the primary honeycomb 30;
• the primary honeycomb 30 is pre-glued to the ends of the partitions 34 which will be in contact with the septum 40;
• the septum 40 does not undergo pre-gluing that would close the holes 42 because they are too small;
• the secondary honeycomb 50 is also pre-glued to the ends of the partitions 54 which will be in contact with the septum 40;
• the full skin 60 is pre-glued on the side that will be in contact with the secondary honeycomb 50.

After they are pre-sized, the two honeycomb layers 30, 50, and optionally one of the two skins 20, 60 are then assembled according to well-known methods, the subset thus obtained being referenced 12. The surface of at least one honeycomb 30, 50 remains uncovered and makes it possible to see the septum 40 at the bottom of the cells.

We will now refer to the figure 5 . The subset 12 is controlled, exhaustively or by sampling, as follows:
Scan the subassembly 12 with a digital camera 84 having a lens 86 88.96 associated lighting, the camera 84 thus taking shots of the septum 40 at the bottom of the cells of the honeycomb 30, 50 between the septum 40 and the objective 86, this illumination 88, 96 obviously illuminating the area of the septum observed by the camera 84 at the bottom of the cells of the honeycomb 30, 50, the subset 12 being in practice arranged on a support 82, the successive images 92 thus obtained being transmitted to a computer 94, the computer establishing the perforation rate T by applying the formula T = N1 / N in which N1 is the number of unrepresented pixels corresponding to the cleared holes 42b and N the number of pixels of the image 92. The resolution of the camera and the magnification ratio are chosen so that each hole 42 covers at least 30 pixels in the image 92. In a preferred embodiment, this resolution is chosen so that each hole 4 2 covers 80 to 100 pixels in the image, the accuracy of the measurement is therefore improved by reducing the influence of the pixels straddling the edges of the holes.
In the case where episcopic illumination 88 is used, the pixels corresponding to the holes 42 are those whose luminous level is below a preset threshold level, it sometimes happens that the adhesive 70 appears on the image with a luminous level also lower than this. threshold. In this case, the computer 94 delimits inside each cell the surface 76 of the septum 40 not covered by the glue 70, the computer 94 then seeking the pixels corresponding to the clear holes 42b only inside the surfaces 76 thus delimited. This delimitation implements a well-known image analysis function making it possible to define a closed line 77 approximately circular and of size greater than a given minimum, this closed line 77 then being a boundary between a first zone whose light level is below a predefined threshold and a second zone whose light level is greater than this same threshold, this closed line 77 corresponding to the limit of the spread of the glue 70 on the septum 40.

In the case where neither of the two skins 20, 60 is still assembled, it is possible to use diascopic lighting 90, the control method then being identical to the control method of the bare septum previously described.
The diascopic control mode allows a simpler image recognition because the clear holes 42b appear very bright and with excellent contrast on a dark background. It is however more difficult to implement with the large panels because the diascopic illumination 90 located behind the panel relative to the camera 84 must follow the movements of this camera 84.

In the case where episcopic illumination 88 is used, the pixels 100 corresponding to the holes 42 are those whose luminous level is below a predetermined threshold level. In the case where a diascopic light 90 is used, the pixels 100 corresponding to the holes 42 are those whose light level is greater than a predetermined threshold level. This threshold level is established by experimentation to give the most accurate measure, that is to say so that statistically half of the pixels straddling the edge of the hole have a level below this threshold and for the other half to have a level above this threshold.

The resolution of the camera and the magnification ratio of the image 92 are also chosen so that each hole 42 covers at least 30 pixels in the image. In a preferred embodiment, this resolution is chosen so that each hole 42 covers 75 to 100 pixels in the image, the accuracy of the measurement being consequently improved by reducing the influence of the pixels straddling the edges of the holes. The magnification ratio of the camera 84, however, must not be so high that the camera 84 has a field sufficient for each image 92 to completely cover at least one cell. In practice, this magnification ratio is of the order of 3 to 6.

In practice also, the perforation rate of the assembled septum must be equal to an average value of plus or minus 12%. In the case where the rate of perforation after assembly exceeds these limits, the assembled septum 40 is therefore defective, the process of assembly of the panel 10 is interrupted.

In a particular embodiment of the invention, the full skin 60 is made and bonded to the secondary honeycomb 50. This arrangement has the advantage of only imposing on the full skin 60 a single thermal cycle. simultaneously ensuring the polymerization of the resin matrix and glue.

1. 1. le contrôle du septum soit postérieur à son assemblage avec les deux nids d'abeilles qui lui sont adjacents,
2. 2. le septum à contrôler soit visible de l'extérieur à travers les alvéoles d'au moins un nid d'abeille. Dans le cas où l'éclairage est épiscopique, il suffit que le septum soit visible à travers l'un des nids d'abeilles et on peut donc effectuer le contrôle après l'assemblage de l'une des peau. Dans le cas où l'éclairage est diascopique, le septum doit être visible à travers les alvéoles de chacun des nids d'abeilles et il est alors nécessaire que le contrôle du septum soit effectué avant tout assemblage des peaux.

It is understood that the present invention can be implemented with different assembly sequences of the acoustic panel, the important thing being that:

1. 1. control of the septum is posterior to its assembly with the two honeycombs adjacent to it,
2. 2. the septum to be controlled is visible from the outside through the cells of at least one honeycomb. In the case where the illumination is episcopic, it suffices that the septum is visible through one of the honeycombs and can therefore be carried out after the assembly of one of the skin. In the case where the illumination is diascopic, the septum must be visible through the cells of each of the honeycombs and it is then necessary that the control of the septum is performed before assembling the skins.

• au contrôle d'un premier septum assemblé avec les deux nids d'abeilles qui lui sont adjacents, l'éclairage étant épiscopique ou diascopique,
• au contrôle du second septum après son assemblage pour constituer un sous-ensemble comportant les deux septums et les trois nids d'abeilles, le contrôle étant alors effectué avec un éclairage épiscopique,
• au contrôle des deux septums après leur assemblage avec les trois nids d'abeilles, le contrôle étant effectué avec un éclairage épiscopique, l'assemblage pouvant être effectué en un seul cycle thermique en autoclave, avec les trois nids d'abeilles.

Also known acoustic panels called "triple resonators" comprising successively in the direction of thickness: an acoustic skin, a first honeycomb, a first septum, a second honeycomb, a second septum, a third honeycomb and a full skin. The present invention is applicable:

• control of a first septum assembled with the two honeycombs adjacent thereto, the illumination being episcopic or diascopic,
• controlling the second septum after assembly to form a subset comprising the two septa and the three honeycombs, the control being then carried out with episcopic illumination,
• the control of the two septa after their assembly with the three honeycombs, the control being carried out with an episcopic lighting, the assembly being able to be carried out in a single thermal cycle in autoclave, with the three honeycombs.

Claims (12)

1. Method of assembling and monitoring a dual-resonator honeycomb acoustic panel, the panel (10) comprising a plurality of layers (20, 30, 40, 50 and 60) to be assembled in the direction of the thickness of the panel (10), namely: an acoustic skin (20), a primary honeycomb (30), a septum (40) pierced with a plurality of holes (42), a secondary honeycomb (50) and a full skin (60), the method comprising preliminary operations of gluing the various layers (20, 30, 40, 50 and 60) to be assembled,

   • then an initial assembly, by gluing, of the two honeycombs (30, 50) with the septum (40) previously pierced with holes (42), to form a subassembly, the holes (42) of the septum (40) still released after gluing being referenced (42b);

   characterized in that:

   • after the assembly of the two honeycombs (30, 50) with the septum (40) and prior to the assembly of at least one of the two skins (20, 60), at least one of the honeycombs (30, 50) thus being uncovered, the rate of perforation of the septum (40) is checked by scanning the subassembly (12) with a digital camera (84) comprising an associated lighting (88, 96), the camera (84) being positioned to the side of an uncovered honeycomb (30, 50), the camera (84) thus taking photos of the septum (40) at the bottom of the cells of the uncovered honeycomb (30, 50), this lighting (88, 96) illuminating the area of the septum (40) observed by the camera (84), the successive images (92) obtained in this way being transmitted to a computer (94), the computer (94) analysing the images (92) and establishing the rate of perforation T of the septum (40) by applying the formula T = N1/N, in which N1 is the number of pixels (100) corresponding to the released holes (42b) and N being the number of pixels of the image (92).
2. Method according to Claim 1, characterized in that the checking of the septum (40) is performed prior to the assembly of the two skins (20, 60) and in that the lighting (88, 96) is a diascopic lighting (96).
3. Method according to Claim 1, characterized in that the lighting (88, 96) is an episcopic lighting (88).
4. Method according to Claim 3, characterized in that, on the images (92), the computer (94) delimits, inside each cell, the surface (76) of the septum (40) not covered by the glue (70), this computer (94) looking for the pixels (100) that correspond to the released holes (42b) only inside these surfaces (76).
5. Method according to any one of Claims 1 to 4, characterized in that the resolution of the camera (84) and the enlargement ratio of the images (92) is appropriate for each hole (42à) of the septum (40) to cover at least 30 pixels (100).
6. Method according to any one of Claims 1 to 5, characterized in that the resolution of the camera (84) and the enlargement ratio of the images (92) is appropriate for each hole (42à) of the septum (40) to cover at least 75 pixels (100).
7. Method according to any one of Claims 1 to 6, characterized in that it is interrupted when the check of the assembled septum (40) shows that it is defective.
8. Method according to any one of Claims 1 to 7, characterized in that the full skin (60) is produced and glued onto the secondary honeycomb (50) in a single operation.
9. Method according to any one of Claims 1 to 8, characterized in that, prior to the assembly of the septum (40) with at least one of the honeycombs (30, 50), a check is carried out on the rate of perforation T of the bare septum (40) by scanning the septum (40) with a digital camera (84) comprising an associated lighting (88, 96), this lighting (88, 96) illuminating the area of the septum (40) observed by the camera (84), the successive images (92) obtained in this way being transmitted to a computer (94), the computer establishing the rate of perforation T by applying the formula T = N1/N in which N1 is the number of pixels (100) corresponding to the holes 42 and N being the number of pixels of the image (92).
10. Method according to Claim 9, characterized in that the assembly of the panel (10) is interrupted when the check of the bare septum (40) shows that this septum (40) is defective.
11. Method according to Claim 9 or 10, characterized in that the resolution of the camera (84) and the enlargement ratio of the images (92) is appropriate for each hole (42a) of the septum (40) to cover at least 30 pixels (100).
12. Method according to any one of Claims 9 to 11, characterized in that the resolution of the camera (84) and the enlargement ratio of the images (92) is appropriate for each hole (42à) of the septum (40) to cover at least 75 pixels (100).

Images