Method for checking the adhesion between layers of a construction panel, and corresponding device

Abstract

The present invention relates to a device (40) for checking a bond between two layers of materials of a construction panel (9) formed by cutting, on a production line, a flow of layers of materials that are stacked and bonded together, so as to produce construction panels provided with edge surfaces, the checking device (40) comprising means for detecting a bonding defect between the two layers of materials, and being characterised in that the detection means comprise at least: - means (13) for capturing an image of an edge surface of the construction panel (9), and - means (7) for analysing the image thus captured.

Description

[0001] DESCRIPTION

[0002] Title of the invention: Method for controlling adhesion between layers of a construction panel and corresponding device

[0003] The present invention relates to the field of the construction industry and in particular to the manufacture of construction panels based on plaster or another material such as cement. The invention relates more specifically to:

[0004] - a method of controlling a bond between a layer of a material such as plaster and external layers of material which grip this layer of material in pincers, these different layers constituting such a construction panel,

[0005] - an associated control device and

[0006] - a process for manufacturing such panels.

[0007] Gypsum-based building panels in particular are manufactured on a production line by spreading an inner layer of plaster mixed with water on an outer layer of paper or glass fiber material, this inner layer then being covered with another outer layer of paper or glass fiber material. These inner and outer layers are then dried and cut into building panels. Adhesion between the outer layers and the inner layer is achieved by entanglement of plaster crystals around the paper or glass fibers of the outer layers, this entanglement being promoted by the hydration of the materials which allows the formation of crystals and pores between these crystals. Poor adhesion between these layers leads to detachment of the outer layers, which is detrimental in particular for the drying of the panels or for their packaging.

[0008] Currently, in order to check the quality of the bond between the internal plaster layer and the external paper layers of a construction panel, an operator makes crosses on the surface of the panel taken from the production line, and attempts to peel off the paper on this surface, or attempts to peel off the paper directly from the edge of the panel. If the operator manages to completely peel off the paper, without leaving any underthickness of paper stuck to the plaster, it means that the bond between the internal plaster layer and the paper layers of the construction panel is not satisfactory. Otherwise, the quality of this bond is considered satisfactory. These manual checks are therefore time-consuming and cannot be repeated identically, as the force and speed of peeling depend in particular on the operator.

[0009] Furthermore, this type of verification takes place on a wet construction panel, often before the construction panel has dried, and therefore before the bonds between the plaster and paper crystals have completely formed. This is due in particular to the fact that it is desired to avoid blocking the dryers by the paper peeling off during the drying of the panel. These prior art verifications are carried out randomly on a few construction panels, at different locations on the production line, the frequency of these checks being a function of the variability of the materials used and the stability of the production process on this production line. The bond between the materials of the different panels being checked is therefore not at the same stage of formation during these verifications. The time taken by an operator to check a panel alone influences the quality of the bond, which he will evaluate manually.Similar checks take place during the manufacture of plasterboard covered with glass fibers.

[0010] These prior art checks therefore do not allow the quality of the bond between the different materials of a construction panel to be quantified, and even less so a reliable quantification carried out identically for all the construction panels on a production line.

[0011] The present invention aims to remedy at least in part the drawbacks of the prior art, by providing a method for controlling a connection between the layers of a construction panel, an associated device and a method for manufacturing a construction panel integrating such a control method, which make it possible to make the quantification of the quality of the connection between the layers of the construction panel more reliable.

[0012] To this end, the invention proposes a method for controlling a bond between at least two layers of materials of a construction panel formed by cutting on a production line a flow of layers of materials superimposed and bonded together, so as to produce construction panels provided with edges, the control method comprising a step of detecting a bond defect between the two layers of materials, the control method being characterized in that the detection step comprises sub-steps:

[0013] - image capture of a slice of the construction panel, and

[0014] - analysis of the image thus captured.

[0015] Thanks to the invention, the control of the good adhesion between a layer of plaster or cement of the construction panel, and an external layer of the construction panel made of paper or glass fiber material, is carried out in the same way on the panels of the production line, without manually tearing off an external layer of a construction panel. Indeed, image capture is used to detect a natural detachment of the layers of materials from each other, due to insufficient formation of the bond between these layers of materials. Preferably, the detection step takes place at the same point of the production line for all the construction panels controlled. More preferably, each panel of the production line is controlled by the control method according to the invention.

[0016] It should be noted that the construction panel may include layers of materials other than plaster and paper or a glass fiber-based material, the invention being applicable to any type of construction panel whose manufacture may lead to problems of detachment between the layers of materials. For example, the construction material includes an internal layer of cement covered with external layers of paper or glass fibers.

[0017] According to an advantageous characteristic of the method for controlling a bond according to the invention, the image capture sub-step is preceded by a sub-step of sending a gas onto the edge of the construction panel. This gas is, for example, air or water vapor. Sending water vapor can prevent overheating of the panel during a subsequent drying step. This sub-step of sending a gas makes it possible to promote the detachment of the layers of materials when they do not have a sufficiently strong bond between them to prevent this detachment, and therefore makes it possible to quantify the quality of this bond. It should be noted that this detachment takes place naturally between the layers of different materials, and not between two sub-thicknesses of paper as can happen with manual tearing of the paper on a construction panel in the prior art.

[0018] According to another advantageous characteristic of the method for controlling a connection according to the invention, during the gas sending sub-step, the gas is sent at a predetermined pressure of between 1 and 6 bars. This relative pressure (i.e. added to atmospheric pressure) is for example maintained at the same value throughout the detection step, or is modulated according to the arrival of the construction panel facing a camera implementing the image capture sub-step. For example, this pressure changes according to a pressure ramp. A construction panel position sensor on the production line preferably makes it possible to interrupt the sending of the pressurized gas between two detection steps.

[0019] According to another advantageous characteristic of the method for controlling a bond according to the invention, the analysis sub-step provides a value representative of a level of detachment between the two layers of materials on at least part of the wafer, and is followed by a sub-step of comparison between the value representative of a level of detachment and a predetermined detachment threshold. This representative value is for example a measurement of maximum detachment between two layers of materials as visible on the captured image, or an average detachment between these two layers, calculated following the analysis of this captured image.

[0020] Preferably, when the construction panel comprises more than two layers of materials and thus at least two interfaces between two layers, the analysis sub-step provides a representative value of a detachment level for a single interface between two layers or for the two interfaces between the layers of materials among the layers of materials of the construction panel, each representative value being compared to the detachment threshold predetermined during the comparison sub-step.

[0021] Preferably again, the comparison sub-step is followed by a diagnostic sub-step concluding that there is a bonding fault as soon as at least one representative value provided by the analysis sub-step is greater than the detachment threshold, or that there is no bonding fault in the opposite case. This diagnosis is for example displayed on a screen, which allows an operator to eject the panel from the production line in the event of a fault and / or to quickly adjust a parameter of the production line.

[0022] The invention also relates to a manufacturing method on a manufacturing line of construction panels comprising at least two layers of materials, the manufacturing method comprising steps:

[0023] - superposition of layers of materials, producing a flow of superimposed layers of materials,

[0024] - formation of a bond between the layers of materials thus superimposed, and

[0025] - cutting the flow of layers of materials superimposed and linked together so as to form construction panels, the manufacturing method being characterized in that it implements the control method according to the invention.

[0026] In one embodiment of the invention, said superimposed layers of materials are layers of plaster and paper.

[0027] The bond formation step begins at the layering step, since the plaster mixed with water and deposited on a layer of paper can begin to bond with the paper. This formation step, which uses the hydration of the materials, may include the addition of an additive, during a pre-mixing step of the plaster and water. The cutting step possibly takes place during this bond formation step. Preferably, the bond formation step is followed by a step of drying the layers of materials, and the detection step takes place between the cutting step and the drying step. Thus, a defective panel can be detected before moving on to the drying step.

[0028] According to an advantageous characteristic of the method for manufacturing construction panels according to the invention, the detection step is followed by a step of ejecting the construction panel from the production line when at least one value representative of a level of detachment provided by the analysis sub-step is greater than a high threshold. This high threshold corresponds for example to a dimension of an inlet mouth of a dryer used during the drying step. Thus when the detachment is too significant, the construction panel is not sent directly into a dryer, which it risks blocking.

[0029] According to another advantageous characteristic of the method for manufacturing construction panels according to the invention, the detection step is followed by a step of adjusting at least one parameter of the manufacturing line as a function of at least one value representative of a level of detachment provided by the analysis sub-step, or as a function of the conclusion of the diagnostic sub-step. This parameter is, for example, when the layers of materials comprise a layer of plaster and layers of paper, a quantity of water used per quantity of dry plaster, during a step of mixing these quantities to form the layer of plaster, prior to the step of superimposing the layers of materials. This water / dry plaster ratio is adjusted so as to promote the formation of the bond between the layer of plaster and the layers of paper.When the diagnosis corresponds to an absence of bonding defect, this quantity of water used per quantity of dry plaster is for example reduced during this adjustment step. The quantity of water per quantity of dry plaster adjusted here concerns the entire plaster layer or only one or more interface sub-layers of this plaster layer, at the interface between the plaster layer and one or more layers of materials external to this plaster layer. In this case the mixing step may comprise different mixtures, for example an initial mixture of water, wet plaster and other possible compounds, intended to form a main internal layer of plaster, this initial mixture then being modified to produce the interface sub-layers. The term "mixture" is used here in the broad sense and can be understood as a "preparation of a mixture".

[0030] According to an advantageous characteristic of the method for manufacturing construction panels according to the invention, said superimposed layers of materials comprise a layer of plaster, and the manufacturing method comprises several steps of detection at a point of the manufacturing line on different construction panels arriving successively at this point, and an analysis sub-step providing a value representative of a zero detachment level for each interface between two of the superimposed layers of materials is followed by an adjustment step consisting of reducing a quantity of water used per quantity of dry plaster to form, prior to the step of superimposing the layers of materials, a mixture intended to form the layer of plaster or an interface sub-layer of the layer of plaster with another of the superimposed layers of materials,said adjustment step being repeated after each subsequent analysis sub-step until a subsequent analysis sub-step provides a value representative of a non-zero detachment level but lower than the predetermined detachment threshold. This reduction in water therefore affects the entire plaster layer or only one or more interface sub-layers of this plaster layer, at the interface between the plaster layer and one or more layers of materials external to this plaster layer.,

[0031] In one embodiment of the invention, said superimposed layers of materials comprise a layer of plaster, and said at least one parameter is chosen from a list comprising:

[0032] - a ratio between on the one hand a quantity of accelerator of a chemical reaction between water and the plaster of the plaster layer, and on the other hand a quantity of retarder of a chemical reaction between water and the plaster of the plaster layer, the quantities of accelerator and retarder being injected into a mixture intended to form the plaster layer during a mixing step prior to the superposition step, - a quantity of foaming agent injected into the mixture,

[0033] - a quantity of fluidifier injected into the mixture,

[0034] - a quantity of water used per quantity of dry plaster to form the mixture,

[0035] - a target density of the plaster layer of the building panel, and

[0036] - a target weight of the construction panel.

[0037] Several parameters can be adjusted simultaneously during this adjustment step. The above list is of course not exhaustive. The target density is adjusted for example by changing the amount of foaming agent injected during the mixing step, or the amount of water used per amount of dry plaster during the mixing step, which affects the entire plaster layer or only one or more interface sub-layers of this plaster layer, at the interface between the plaster layer and one or more layers of materials external to this plaster layer.

[0038] For example, said superimposed layers of materials comprise at least one layer of plaster and one layer superimposed on the layer of plaster, the layer of plaster comprising an interface sub-layer with the layer superimposed on the layer of plaster, and said at least one parameter is chosen from a list comprising:

[0039] - a ratio between, on the one hand, a quantity of accelerator of a chemical reaction between water and the plaster of the interface sub-layer, and on the other hand, a quantity of retarder of a chemical reaction between water and the plaster of the interface sub-layer, the quantities of accelerator and retarder being injected into a mixture intended to form the interface sub-layer prior to the superposition step,

[0040] - a quantity of foaming agent injected into the mixture,

[0041] - a quantity of water used per quantity of dry plaster to form the mixture,

[0042] - a target density of the building panel interface sub-layer, and

[0043] - a target weight of the interface sub-layer.

[0044] In one embodiment of the invention, the method for manufacturing construction panels according to the invention comprises several steps of detection at a point of the production line on different construction panels arriving successively at this point, and each detection step is followed by a step of adjustment of said at least one parameter, the adjustment step using a regulator receiving as input the difference between a current setpoint value of said at least one parameter on the production line, and an estimated value of said at least one parameter from at least one value representative of a level of detachment resulting from the detection step. In other words, in this embodiment of the invention, the adjustment step is carried out according to a regulation loop. This of course uses a model making it possible to estimate a value of the parameter corresponding to a given level of detachment.When several parameters are modified during these adjustment steps, the model has as many variables as parameters.

[0045] The invention finally relates to a device for monitoring a connection between two layers of materials of a construction panel formed by cutting on a production line a flow of layers of materials superimposed and linked together, so as to produce construction panels provided with edges, the monitoring device comprising means for detecting a connection defect between the two layers of materials, and being characterized in that the detection means comprise at least:

[0046] - means for capturing an image of a slice of the construction panel, and

[0047] - means of analyzing the image thus captured.

[0048] The control device advantageously further comprises at least one nozzle for sending gas onto the edge of the construction panel, at a predetermined pressure.

[0049] The control device advantageously comprises a means for detecting the position of a construction panel on the production line, and means for sending gas according to the position detected by said detection means. These gas sending means are for example the nozzle(s) mentioned above.

[0050] Finally, in the control device according to the invention, a main direction of projection of the gas by the nozzle is preferably oriented facing the edge of the construction panel and / or parallel to a longitudinal direction of movement of the construction panel. The control device according to the invention has advantages similar to those of the control method according to the invention and the manufacturing method according to the invention.

[0051] Other characteristics and advantages of the invention will become apparent from the following description on the one hand, and from several examples of embodiment given for informational and non-limiting purposes with reference to the attached schematic drawings on the other hand, in which:

[0052] [fig 1] represents steps of a method of manufacturing construction panels according to the invention, in one embodiment of the invention,

[0053] [fig 2] represents a line for manufacturing construction panels according to the invention, in this embodiment of the invention,

[0054] [fig 3] represents a device for controlling a connection between two layers of materials of a construction panel according to the invention, before a detection step implemented by this control device, in this embodiment of the invention,

[0055] [fig 4] represents the control device of figure 3, during a detection step implemented by this control device, in this embodiment of the invention,

[0056] [fig 5] represents an image taken by the control device of figures 3 and 4, during a detection step implemented by this control device, in this embodiment of the invention,

[0057] [fig 6] represents an embodiment of a step of adjusting a parameter of the manufacturing process according to the invention, in a context of the embodiment of the invention, and

[0058] [fig 7] represents another embodiment of a step of adjusting a parameter of the manufacturing method according to the invention, in another context of the embodiment of the invention.

[0059] According to one embodiment of the invention, a manufacturing method 1 of construction panels according to the invention is described in relation to figures 1 and 2. More specifically, in this embodiment of the invention, the manufacturing method 1 makes it possible to manufacture plasterboard panels covered with layers of paper and is implemented by the manufacturing line 3 illustrated in figure 2. These construction panels are rectangular plates of small thickness which comprise an internal layer 901 of plaster (shown in figure 5), and external layers 900, 902 of paper on the surfaces of these plates, each external layer 900, 902 of paper in fact comprising several thicknesses of paper, for example two or three thicknesses of paper.

[0060] Returning to Figures 1 and 2, a first step of the manufacturing method according to the invention is the firing 80 of the gypsum, which forms plaster. This first step is followed by a mixing step 90 of the plaster thus obtained, water, and other possible compounds detailed later. This mixing step 90 provides a mixture of wet plaster. A portion of this mixture is optionally taken to modify its properties, for example using specific additives, and is intended to form plaster undercoats as explained later.

[0061] A next step of the manufacturing method according to the invention is the superposition 100 of the layers of materials 900, 901, 902 on the manufacturing line 3. For this, the wet plaster mixture obtained in the mixing step 90 is spread on a first layer 900 of paper whose edges are folded so as to contain the mixture, then covered with a second layer 902 of paper, the whole being compressed as these materials advance on the manufacturing line 3, by an extruder formed of a pair of rollers making it possible to rectify the thickness of the superposition of layers.

[0062] In the case where the mixing step 90 comprises a sampling of mixture, intended to form in the plaster layer 901 interface sub-layers with the paper layer 900, 902 of compositions or densities different from the rest of the plaster layer 901, the production line 3 comprises one or more specific rollers. These specific rollers are used to spread the sampling of mixture, of composition or density different from the rest of the mixture, on the paper layer 900, 902, which forms on each paper layer 900, 902, an interface sub-layer of wet plaster. Then, in the superposition step 100, the rest of the mixture is spread on the first paper layer 900 covered with one of the interface sub-layers formed previously. The rest of the mixture thus spread forms the internal part of the plaster layer 901.This inner portion is then covered with the second layer of paper 902, the other of the previously formed interface sub-layers being disposed between the inner portion and the second layer of paper 902.

[0063] In this superposition step 100, a superposition of a first layer 900 of paper, a layer 901 of plaster and a second layer 902 of paper is obtained in the following order, this superposition of layers being continuous for the duration of the manufacturing method 1. The superposition of layers of materials 900, 901, 902 at the output of step 100 therefore produces a flow of elongated layers of materials 900, 901 and 902.

[0064] The deposition of the wet plaster mixture between the layers of paper 900 and 902 contributes to forming a bond between the layers of paper 900, 902 and the layer of plaster 901. The superposition step 100 is therefore part of a step 200 of forming a bond between the layers of materials 900, 901, 902. This step 200 of forming a bond is promoted by the hydration of the plaster and the layers of paper by the water resulting from the mixing step 90. Indeed, at the interface between the layer 901 of plaster and the layers 900, 902 of paper, this hydration promotes the formation of plaster crystals which surround, by hardening, the fibers of the first thickness of paper of the layers 900, 902 of paper, and which thus allow the formation of a bond between the layers 900, 902 of paper and the layer 901 of plaster. This bond allows good adhesion between layers 900, 902 of paper and layer 901 of plaster.An additive or accelerator is optionally added to the water of the plaster mixture during the mixing step 90 prior to the layering step 100, to respectively promote or accelerate this bond formation. This bond formation step 200 therefore includes the formation of plaster crystals which become entangled around the fibers of the paper, this formation being completed before the building panels 9 enter a drying step 500, during which hot air is blown onto the building panels 9. This drying step 500 makes it possible to evacuate the excess water added during the mixing step 90 to improve the fluidity of the wet plaster mixture. The superposition step 100 is followed by a cutting step 300 of the flow of layers of materials 900, 901, 902 into rectangular construction panels 9 (shown in Figures 3 and 4) which move along the production line on rotating rollers 8.For information purposes, these construction panels 9 are approximately two and a half metres long.

[0065] In this embodiment of the invention, the cutting step 300 takes place after the superposition step 100, when the plaster is hard enough, and before the drying step 500.

[0066] According to the invention, the manufacturing method 1 further comprises a step 400 of detecting a bonding defect between the layers of materials 900, 901, 902, for example between the plaster layer 901 and the first layer of paper 900 and / or between the plaster layer 901 and the second layer of paper 902. This detection is carried out on a slice of a construction panel 9, therefore after the cutting step 300.

[0067] In this embodiment of the invention, the detection step 400 takes place between the cutting step 300 and the drying step 500, therefore during the bond formation step 200. This is in fact a “wet” detection. This “wet” detection step 400 is advantageously carried out as close as possible to the cutting device used during the cutting step 300, in order on the one hand to have a weaker adhesion, therefore easier to characterize, between the plaster layer 901 and the paper layers 900, 902 and on the other hand to allow rapid ejection of a bad plate, and rapid activation of a feedback loop making it possible to adjust the manufacturing method 1 according to the invention when a defect is detected, as described later.

[0068] In an alternative embodiment of the invention, the detection step 400 takes place after the drying step 500, in this case it is a “dry” detection. The two detections can of course be combined.

[0069] This detection step 400 is preferably carried out on all the construction panels 9 moving on the production line 3 during the implementation of the manufacturing method 1 according to the invention. Alternatively, the detection step 400 is carried out only on a sample of construction panels 9, for example only on one construction panel 9 among ten construction panels moving on the production line 3.

[0070] The detection step 400 is the main step of a method 4 for controlling a connection between two layers of materials of a construction panel 9, implemented in hardware and software by a control device 40 shown in Figures 2 and 3.

[0071] The control device 40 comprises at least one camera 13 fixed to a beam and interfaced with a computer 7, by a wireless link 14, for example a Wi-Fi connection using the IEEE 802.11 standard. Preferably several cameras are used in order to control the entire edge of the construction panel 9. Preferably also the control device 40 comprises a lighting system capable of illuminating the edge of the panel 9 so that a detachment of a layer of paper 900 or 902 from the layer of plaster 901 forms a shadow between this layer of paper 900 or 902 and the layer of plaster 901, thus promoting a contour detection carried out during an image analysis sub-step described later.

[0072] The control device 40 also comprises at least one nozzle 11 for sending gas, here pressurized air 12, against the construction panels 9 arriving on the production line 3. On this production line 3, the construction panels move in a longitudinal direction L in a direction 10 of movement, thanks to the rollers 8. The construction panels 9 have been cut in the cutting step 300, in the direction of their width in a transverse direction T orthogonal to the longitudinal direction L and to a vertical direction V.

[0073] One or more nozzles 11 are preferably arranged between the rollers 8 of the same section of the manufacturing line 3 in the transverse direction T, and are preferably arranged in such a way that their air jets have directions substantially parallel to the longitudinal direction, that is to say parallel to the longitudinal direction L to within a few degrees (for example to within 10 degrees). In this way their air jets are oriented substantially orthogonally to the slices of the construction panels 9 produced in the cutting step 300. The nozzles 11 are arranged vertically under the camera 13 and longitudinally in the vicinity of the longitudinal position of the camera 13.

[0074] In this embodiment of the invention, a single nozzle 11 is preferably used, placed vertically under the vertical position of the construction panel 9, its air jet forming an angle of, for example, between 5° and 15° with the longitudinal direction L. This makes it possible to test both the adhesion between the plaster layer 901 and the first paper layer 900, and the adhesion between the plaster layer 901 and the second paper layer 902. This main embodiment is preferred for reasons of cost and simplicity, since a single nozzle is used and the nozzle position 11 does not need to be adjusted according to the thickness of the manufacturing panel 9. However, alternative embodiments are possible, in which this angle is, for example, between 5° and 20°, between 5° and 30°, or between 5° and 45°. Furthermore, as a variant, the nozzle 11 only allows the adhesion to be tested between the plaster layer 901 and a single layer of paper 900 or 902.

[0075] In another embodiment, a nozzle 11 is used, placed vertically above the vertical direction of the building panel 9, the air jet from this nozzle forming with the longitudinal direction L an angle of between 5° and 15°, between 5° and 20°, between 5° and 30°, or between 5° and 45°. The vertical position of the nozzle 11 is adjusted according to the thickness of the building panel 9. In this other embodiment variant, the nozzle 11 tests the adhesion between the plaster layer 901 and each of the paper layers 900, 902, or between the plaster layer 901 and a single paper layer 900, 902. Finally, combinations of these variants are conceivable, in which two nozzles are used, one placed vertically below the vertical position of the building panel 9, and the other placed vertically above the vertical position of the building panel 9.

[0076] Thus, in Figure 3, the construction panel 9 is moistened and has just passed the cutting step 300, the air 12 sent by the nozzles 11 reaches under the surface of the construction panel 9. In Figure 4 on the other hand, the nozzles 11 blow the air 12 facing a slice of the construction panel 9 moving in the direction of movement 10. This air 12 is preferably sent under pressure slightly higher than atmospheric pressure, for example at two bars. This relative pressure of the air 12 (that is to say added to the atmospheric pressure) at the outlet of the nozzles 11 is predetermined and between 1 and 6 bars.

[0077] The air 12 at the outlet of the nozzles 11 is for example sent continuously at the same pressure during the passage of the construction panels 9.

[0078] Alternatively, the pressure of the air 12 at the outlet of the nozzles 11 evolves according to an upward pressure ramp, when the control method is configured to associate a pressure threshold with a detachment of one of the layers of paper 900, 902 from the layer of plaster 901. This pressure threshold makes it possible to quantify the level of adhesion between this layer of paper 900 or 902 and the layer of plaster 901. This configuration is for example activated by an operator, the control device comprising a human-machine interface, in particular a screen making it possible to visualize, using the camera 13, the detachment of one of the layers of paper 900 or 902 from the layer of plaster 901. This screen also makes it possible to visualize, in particular, measurements and diagnostics resulting from the detection step 400 as described later.These measurements and diagnostics are displayed for each building panel 9 controlled by the control method according to the invention, one diagnosis and one measurement being preferably displayed for the connection between the first layer of paper 900 and the layer of plaster 901, and another diagnosis and another measurement being displayed for the connection between the second layer of paper 902 and the layer of plaster 901.

[0079] Also preferably, the nozzles 11 only send air 12 when the edge of a construction panel 9 is facing the nozzles 11. For this purpose, a position sensor of the panel 9 on the production line 3 interacts with the nozzles 11 via the computer 7.

[0080] Returning to Figure 1, the detection step 400 comprises a first sub-step 410 of sending air 12 by the nozzles 11, onto the edge of a construction panel 9 facing the nozzles 11. The following sub-step is the capture 420 of an image of the edge of the construction panel 9 by the camera 13. The air 12 blown onto the edge of the construction panel 9, makes it possible to detach one of the layers of paper 900 or 902 from the layer of plaster 901 when the bond between the layers of paper 900 and plaster 901, or between the layers of paper 902 and plaster 901, is not sufficient to allow good adhesion of the paper to the plaster.

[0081] The capture sub-step 420 therefore provides an image 130 shown in FIG. 5, in which a detachment 921 between the plaster layer 901 and the paper layer 902 is potentially the sign of poor adhesion between the paper layer 902 and the plaster layer 901. The image 130 is displayed on the screen of the control device 40. It is noted in this example of use of the control method according to the invention that the paper layer 900 is not detached from the plaster layer 901, a sign of good adhesion between these two layers 900 and 901.

[0082] The next sub-step is the analysis 430 of the image 130 obtained during the previous capture sub-step 420. This image analysis uses contour detection to locate the different layers of the construction panel 9, and the detachment 921 between the paper layer 902 and the plaster layer 901. This contour detection is followed, in this analysis sub-step 430, by a measurement Dmes of the maximum detachment visible on the image 130, between the material layers 901 and 902 of the construction panel 9. This measurement is a value representative of a level of detachment between the material layers 901 and 902 of the construction panel 9. In this analysis sub-step 430, another contour measurement between the material layers 900 and 901 gives a zero value of maximum detachment between these material layers 900 and 901.

[0083] Given that in this embodiment of the invention, only the second layer of paper 902 is detached from the plaster layer 901, the following description of the control method and the manufacturing method according to the invention will only detail the steps and sub-steps of these methods relating to this detachment 921, these steps and sub-steps being transposable to the case where the plaster layer 901 and the first layer of paper 900 are also detached from each other, or even to the case where both the first layer of paper 900 and the second layer of paper 902 are both detached from the plaster layer 901.

[0084] In an alternative embodiment of the invention, this analysis sub-step 430 provides an average value of a detachment between the paper layer 902 and the plaster layer 901 on at least part of the edge of the construction panel 9. This average value is also a value representative of a level of detachment between the layers of materials 901 and 902 of the construction panel 9. In another alternative embodiment, the analysis sub-step 430 provides a value of a detachment surface between the layers of materials 901 and 902 of the construction panel 9, this surface value also being able to be considered as a value representative of a level of detachment between the layers of materials 901 and 902 of the construction panel 9.

[0085] The next sub-step is the comparison 440 between a value of the maximum detachment measurement Dmes and a predetermined detachment threshold S 1. This predetermined detachment threshold SI is for example set at 2 mm (millimeters). Preferably this predetermined detachment threshold SI is between 1 mm and 4 mm. Alternatively, the detachment threshold SI is for example 1 mm, 3 mm or 4 mm.

[0086] In the variant embodiment of the invention using an average value of a detachment between the paper layer 902 and the plaster layer 901, the comparison sub-step 440 compares this average value to a predetermined detachment threshold SI set for example at 1 mm.

[0087] The following sub-step is a diagnosis 450 concluding that there is a bonding defect or an absence of bonding defect between the layers of materials for which detachment has been measured in the analysis sub-step 430. In this diagnosis sub-step 450, if in step 440 the value representative of a maximum detachment level (therefore the maximum detachment measurement Dmes or the average detachment value in the corresponding embodiment variant) is greater than the predetermined detachment threshold S 1 (branch Y at the output of step 440 in FIG. 1), then the diagnosis sub-step 450 concludes that there is a bonding defect between the plaster layer 901 and the paper layer 902, otherwise (branch N at the output of step 440 in FIG. 1) the diagnosis sub-step 450 concludes that there is an absence of bonding defect between the plaster layer 901 and the paper layer 902. In the latter case the next step is the drying step 500.The diagnosis resulting from the diagnosis sub-step 450 is displayed on the screen of the control device according to the invention.

[0088] In this embodiment of the invention, when the diagnostic sub-step 450 concludes that there is a bonding defect between the plaster layer 901 and the paper layer 902, the detection step 400 is followed by a step 550 of comparing the value representative of a maximum detachment level with a high threshold S2 corresponding to a maximum acceptable detachment value for allowing the construction panel 9 to pass into a dryer. This high threshold S2 may be equal to the predetermined detachment threshold S1 (in which case step 550 is not necessary, the diagnostic sub-step 450 then being followed by a step 600 of ejecting the construction panel 9 from the manufacturing line 3 as soon as a bonding defect is detected), but is preferably strictly greater than the predetermined detachment threshold S1. In this embodiment of the invention, this high threshold S2 is set at 6mm.Alternatively, it is set at 3, 4 or 5 mm, always remaining higher than the predetermined SI detachment threshold, which is, for example, 1, 3 or 4 millimeters in these variants.

[0089] If step 550 of comparing the representative value of a maximum detachment level with a high threshold S2 determines that this representative value is greater than the high threshold S2, then (branch N at the output of step 550) the following step is a step 600 of ejecting the construction panel 9 from the manufacturing line 3. Thus the defective construction panel 9 does not go to the drying step 500, which it risks blocking, due to the narrowness of the mouths of the dryers used during this drying step 500.

[0090] If, on the contrary, step 550 of comparing the representative value of a maximum detachment level with a high threshold S2 determines that this representative value is lower than the high threshold S2, then (branch Y at the output of step 550) the following step is the drying step 500.

[0091] Furthermore, in this embodiment of the invention, the detection step 400 is optionally followed by a step 700 of adjusting a parameter of the manufacturing line 3. This adjustment step is conditioned on the value representative of a detachment level obtained during the analysis sub-step 430, or on the conclusion of the diagnosis sub-step 450. The adjustment step 700 is for example activated as soon as a connection fault is diagnosed during the diagnosis sub-step 450. In particular, in order to keep the value representative of a detachment level below the predetermined threshold SI, or another threshold lower than this predetermined threshold SI, this other threshold then corresponding to a target detachment threshold, one or more of the following parameters are modified during this adjustment step 700, which are listed here in order of preference:

[0092] - a quantity of plaster crystal formation accelerator in the plaster layer 901, added during the mixing step 90. Such an accelerator makes it possible to accelerate the formation of hydrated calcium sulfate from, on the one hand, the hemihydrated calcium sulfate present in the plaster and, on the other hand, the water during the mixing step 90. This accelerator is, for example, a heat-resistant accelerator (or HRA) such as small gypsum crystals;

[0093] - a quantity of plaster crystal formation retarder in the plaster layer 901, added during the mixing step 90. Such a retarder, well known to those skilled in the art, makes it possible to delay the formation of hydrated calcium sulfate during the mixing step 90, and is used on the one hand to prevent lumps from forming in the mixing apparatus used during this mixing step 90, which would require stopping the production line, and on the other hand so that the mixture resulting from this step is not too viscous to be able to spread it on the paper layer 900;

[0094] - a quantity of foaming agent injected during the mixing step 90, this foaming agent forming a stable or unstable foam; the more this quantity increases, the more the adhesion between the paper and the plaster is potentially reduced. Preferably, a foaming agent producing an unstable foam, or a mixture of unstable foam and stable foam, is used;

[0095] - a target density of the plaster layer 901 of the construction panel 9. The higher this density, the better the adhesion between the paper layers 900 or 902 and the plaster layer 901. The density of the plaster layer is for example increased or decreased by increasing or respectively decreasing the amount of water used per amount of dry plaster during the mixing step 90. However, increasing this amount of water then requires increasing the energy used during the drying step 500 of the construction panels. Therefore, preferably, rather than the density of the plaster layer, the density of the plaster sub-layers at the interface of the plaster layer 901 with the paper layers 900 and 902, mentioned previously in relation to the mixing 90 and superposition 100 steps, is modified by modifying in these plaster sub-layers the amount of water per amount of dry plaster in these sub-layers.Another way of modifying the density of the plaster layer 901 of the building panel 9 is to inject more or less air into this plaster layer, using a foaming agent as previously mentioned. Preferably, when this latter solution is chosen, only the densities of the plaster sub-layers at the interface of the plaster layer 901 with the paper layers 900 and 902 are modified, which makes it possible not to significantly change the density of a building panel 9 in its entirety;

[0096] - a quantity of water used per quantity of dry plaster during the mixing step 90; in fact, below a critical value of this water / dry plaster ratio, the adhesion between the layers of paper 900 or 902 and the layer of plaster 901 is not satisfactory. A water / dry plaster ratio that is too high, on the other hand, deteriorates the strength of the paper and therefore the interface between the layers of paper 900 or 902 and the layer of plaster 901. Preferably, this quantity of water is used as a parameter during the adjustment step 700 only when the manufacturing line 3 includes the specific rollers mentioned above, in order to modify only the quantity of water used in the portion of mixture taken at the mixing step 90 and forming the plaster sub-layers at the interface of the layer of plaster 901 with the layers of paper 900 and 902;

[0097] - a quantity of additive promoting the bond between the layers of paper 900 or 902 and the layer of plaster 901, injected during the mixing step 90. This quantity of additive possibly only concerns interface sub-layers between the layer of plaster 901 and the layers of paper 900, 902;

[0098] - a duration of the bond formation step 200, itself modifiable by adjusting the speed of the production line 3;

[0099] - a target weight of the construction panel 9, achieved by modifying in particular a flow rate of air injected into the plaster mixture during the mixing step 90; the greater the air injected, the poorer the adhesion between the layers of paper 900 or 902 and the layer of plaster 901. Preferably, this target weight is used as a parameter during the adjustment step 700, only when the production line 3 includes the specific rollers mentioned above, in order to modify only the quantity of air injected into the plaster sub-layers at the interface of the layer of plaster 901 with the layers of paper 900 and 902;

[0100] - a quantity of fluidizer injected into the mixture. This fluidizer is an additive optionally added to the mixture formed at mixing step 90 to make the mixture more fluid and therefore easier to spread on the layers of paper 900, 902 without adding more water to this wet plaster mixture.

[0101] It should be noted that the mixture of plaster and water produced in step 90 also advantageously includes starch, which is an additive promoting the bond between the layers of paper 900 or 902 and the layer of plaster 901, but only during drying. Indeed, the starch contained in the mixture migrates to the interface between the layers of plaster and paper and gels during the drying step 500. In the variant embodiment where the detection step 400 takes place after the drying step 500, the quantity of starch in the mixture in step 90 can therefore be adjusted in this step 700.

[0102] Furthermore, since it is the right balance between the amount of accelerator and retarder that improves the adhesion of the plaster layer 901 to the paper layers 900, 902 without impairing the fluidity of the wet plaster mixture made in step 90, the parameters of the amount of accelerator and retarder are alternatively replaced by a parameter that is a ratio between an amount of accelerator and retarder, used during the mixing step 90.

[0103] In this embodiment of the invention, when the representative value of a detachment level obtained during the analysis sub-step 430 is greater than the predetermined detachment threshold S 1, or the target detachment threshold, several adjustment steps 700 are implemented after as many detection steps carried out successively on different construction panels 9. These adjustment steps 700 are repeated until the representative value of a detachment level obtained during a last analysis sub-step 430 becomes less than or equal to the predetermined detachment threshold SI or the target detachment threshold.These adjustment steps 700 modify a Peons setpoint value of one of the parameters mentioned above making it possible to improve the adhesion between the layers of materials 901 and 902, for example a quantity of water per quantity of dry plaster during the mixing step 90, using a regulator 15 shown in FIG. 6, this regulator being for example of the Proportional, Integral, Derivative (also called PID) type. This quantity of water per quantity of dry plaster corresponds to that used to form the plaster layer 901 or plaster sub-layers at the interface between the plaster layer 901 and the paper layers 900, 902.

[0104] During an adjustment step 700, the PID regulator receives as input a difference between a current setpoint value Peons of the parameter on the production line 3, and an estimated value Pest of the parameter from the representative value of a detachment level resulting from the detection step 400 preceding the adjustment step 700. This estimation Pest of the value of the parameter, here a quantity of water per quantity of dry plaster, uses a model 16, giving the quantity of water per quantity of dry plaster used during the mixing step 90 as a function of the representative value of a detachment level. This model is for example obtained empirically.In this embodiment of the invention, when the value representative of a detachment level obtained during the analysis sub-step 430 is zero, that is to say that the layers of materials 901 and 902 are not detached from each other on the edge of the panel 9 checked during the detection step 400, one or more adjustment steps 700 are carried out to reduce the quantity of water per quantity of dry plaster used during the mixing step 90.

[0105] In this case, as shown in FIG. 7, the adjustment steps 700 are repeated until the value representative of a detachment level obtained during a last analysis sub-step 430 becomes non-zero but less than or equal to the predetermined detachment threshold SI or to the target detachment threshold.

[0106] More precisely, after an analysis sub-step 430 of the manufacturing method 1, during a first comparison sub-step 441, it is verified whether the representative value of a detachment level obtained during the analysis sub-step 430 is zero.

[0107] If this is the case (branch Y in Figure 7), the amount of water per amount of dry plaster used during the mixing step 90 is decreased, and this first comparison sub-step 441 is repeated in a following analysis sub-step 430.

[0108] If, on the contrary, the representative value of a detachment level obtained during the analysis sub-step 430 is non-zero (branch N in FIG. 7), it is checked during a second comparison sub-step 442 whether the representative value of a detachment level obtained during the analysis sub-step 430 is less than or equal to the predetermined detachment threshold SI or to the target threshold. If this is the case (branch Y in FIG. 7), the adjustment step 700 is no longer repeated at least until a subsequent detection step 400 issues a diagnosis of a bonding defect between the layers of materials 900, 901 and 902, or provides a value representative of a zero detachment level. If this is not the case (branch N in Figure 7), the amount of water per amount of dry plaster used during the mixing step 90 is increased using the control loop of Figure 6.Of course, the invention is not limited to the examples which have just been described and numerous adjustments can be made to these examples without departing from the scope of the invention.

Claims

CLAIMS 1- Method for controlling (4) a bond between at least two layers (900, 901, 902) of materials of a construction panel (9) formed by cutting on a production line a flow of layers of materials (900, 901, 902) superimposed and bonded together, so as to produce construction panels provided with edges, the control method (4) comprising a step of detecting (400) a bond defect between the two layers (900, 901, 902) of materials, the control method (4) being characterized in that the detection step (400) comprises sub-steps: - capturing (420) an image (130) of a slice of the construction panel (9), and - analysis (430) of the image (130) thus captured. 2- Method for controlling (4) a connection according to the preceding claim, characterized in that the sub-step of capturing (420) an image (130) is preceded by a sub-step of sending (410) a gas (12) onto the edge of the construction panel (9). 3- Method for controlling (4) a connection according to the preceding claim, characterized in that during the sub-step of sending (410) the gas (12), the gas (12) is sent at a predetermined pressure of between 1 and 6 bars. 4- Method for controlling (4) a connection according to any one of the preceding claims, characterized in that the analysis sub-step (430) provides a value representative of a level of detachment (Dmes) between the two layers of materials (900, 901, 902) on at least part of the slice, and is followed by a comparison sub-step (440) between the value representative of a level of detachment (Dmes) and a predetermined detachment threshold (SI). 5- Method for controlling (4) a connection according to the preceding claim, in which the construction panel (9) comprises more than two layers of materials (900, 901, 902) and in which the analysis sub-step (430) provides a value representative of a detachment level (Dmes) for each interface between two layers of materials (900, 901, 902) among the layers of materials of the construction panel (9), each representative value being compared to the detachment threshold (SI) predetermined during the comparison sub-step (440). Tl 6- Method for controlling (4) a connection according to claim 4 or 5, characterized in that the comparison sub-step (440) is followed by a diagnostic sub-step (450) concluding that there is a connection fault as soon as at least one representative value (Dmes) provided by the analysis sub-step (430) is greater than the detachment threshold (SI), or that there is no connection fault, in the opposite case. 7- Manufacturing method (1) on a construction panel manufacturing line (9) comprising at least two layers (900, 901, 902) of materials, the manufacturing method (1) comprising steps: - superimposing (100) the layers of materials (900, 901, 902), producing a flow of superimposed layers of materials, - forming a bond (200) between the layers of materials (900, 901, 902) thus superimposed, and - cutting (300) the flow of layers of materials superimposed and linked together so as to form construction panels (9), the manufacturing method (1) being characterized in that it implements the control method (4) according to any one of claims 1 to 6. 8- Manufacturing method (1) of construction panels (9) according to claim 7, wherein the step of forming a bond (200) being followed by a step of drying (500) the layers of materials (900, 901, 902), the detection step (400) takes place between the cutting step (300) and the drying step (500). 9- Method of manufacturing (1) construction panels (9) according to claim 7 or 8, wherein said superimposed layers of materials (900, 901, 902) are layers of plaster and paper. 10- Manufacturing method (1) of construction panels (9) according to any one of claims 7 to 9 taken in combination with claim 4 or 5, wherein the detection step (400) is followed by a step of ejection (600) of the construction panel (9) from the manufacturing line when at least one value representative of a detachment level (Dmes) provided by the analysis sub-step (430) is greater than a high threshold (S2). 11- Manufacturing method (1) of construction panels (9) according to any one of claims 7 to 10 taken in combination with claim 4, 5 or 6, in which the detection step (400) is followed by a step of adjustment (700) of at least one parameter of the manufacturing line as a function of at least one value representative of a level of detachment (Dmes) provided by the analysis sub-step (430), or as a function of the conclusion of the diagnostic sub-step (450). 12- Manufacturing method (1) of construction panels (9) according to claim 11, in which said superimposed layers of materials (900, 901, 902) comprise a layer of plaster (901), and in which said at least one parameter is chosen from a list comprising: - a ratio between on the one hand a quantity of accelerator of a chemical reaction between water and the plaster of the plaster layer (901), and on the other hand a quantity of retarder of a chemical reaction between water and the plaster of the plaster layer (901), the quantities of accelerator and retarder being injected into a mixture intended to form the plaster layer (901) during a mixing step (90) prior to the superposition step (100), - a quantity of foaming agent injected into the mixture, - a quantity of fluidifier injected into the mixture, - a quantity of water used per quantity of dry plaster to form the mixture, - a target density of the plaster layer (901) of the building panel (9), and - a target weight of the construction panel (9). 13- Manufacturing method (1) of construction panels (9) according to claim 11, wherein said superimposed layers of materials (900, 901, 902) comprise at least one layer of plaster (901) and one layer superimposed (900, 902) on the layer of plaster (901), the layer of plaster (901) comprising an interface sub-layer with the layer superimposed (900, 902) on the layer of plaster (901), and wherein said at least one parameter is chosen from a list comprising: - a ratio between on the one hand a quantity of accelerator of a chemical reaction between water and the plaster of the interface undercoat, and on the other hand a quantity of retarder of a chemical reaction between water and the plaster of the interface sub-layer, the quantities of accelerator and retarder being injected into a mixture intended to form the interface sub-layer prior to the superposition step (100), - a quantity of foaming agent injected into the mixture, - a quantity of water used per quantity of dry plaster to form the mixture, - a target density of the interface sub-layer of the building panel (9), and - a target weight of the interface sub-layer. 14- Manufacturing method (1) of construction panels (9) according to claim 11 taken in the dependency of claim 5, in which said superimposed layers of materials (900, 901, 902) comprise a layer of plaster (901), the manufacturing method (1) comprising several detection steps (400) at a point of the manufacturing line on different construction panels (9) arriving successively at this point, and in which an analysis sub-step (430) providing a value representative of a zero detachment level (Dmes) for each interface between two of the superimposed layers of materials (900, 901, 902) is followed by an adjustment step (700) consisting of reducing a quantity of water used per quantity of dry plaster to form, prior to the superposition step (100) of the layers of materials,a mixture intended to form the plaster layer (901) or an interface sub-layer of the plaster layer (901) with another of the superimposed layers of materials (900, 902), said adjustment step (700) being repeated after each subsequent analysis sub-step (430) until a subsequent analysis sub-step (430) provides a value representative of a detachment level (Dmes) not zero but lower than the predetermined detachment threshold (SI)., 15- Device (40) for controlling a connection between two layers of materials (901, 902) of a construction panel (9) formed by cutting on a production line a flow of layers of materials (900, 901, 902) superimposed and linked together, so as to produce construction panels provided with edges, the control device (40) comprising means for detecting a defect in the connection between the two layers of materials (901, 902), and being characterized in that the detection means include at least: - means for capturing (13) an image (130) of a slice of the construction panel (9), and - means (7) for analyzing the image (130) thus captured. 16- Device (40) for controlling a connection according to the preceding claim, characterized in that it further comprises at least one nozzle (11) for sending gas (12) onto the edge of the construction panel (9), at a predetermined pressure. 17- Control device (40) of a connection according to the preceding claim, comprising a means for detecting the position of a construction panel (9) on the production line, and means for sending gas (12) as a function of the position detected by said detection means. 18- Control device (40) of a connection in the direction 15 or 16 in which a main direction of projection of the gas (12) by the nozzle (11) is oriented facing the edge of the construction panel (9) and / or parallel to a longitudinal direction of movement of the construction panel (9).

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