Device and method for detecting foreign bodies in a scattered mat

Abstract

The invention relates to a device (21) and a method for detecting foreign bodies in a mat (5) scattered on a conveying device (4) during the production of a material sheet, wherein the mat (5) consists at least partially of fibers or chips and binders which are pressed under increased temperature, wherein at least one first sensor device (6) operating with electromagnetic or ultrasonic waves or with magnetic fields or with radiometry is provided, which is directed at one or more spatial measuring areas (22) of the mat in order to detect foreign bodies (10).To better estimate when a foreign body can damage the steel strip (18a, 18b) of a continuous press (2) and thus raise the threshold for triggering a foreign body rejection (11), at least a second sensor device (7) is provided, which is also aligned with the measuring ranges (22), wherein the first sensor device (6) is suitable for material detection of the foreign body (10), and the second sensor device (7) is suitable for determining the foreign body dimensions. Furthermore, the invention relates to a production plant for material sheets equipped with the device (21) or the method for detecting foreign bodies.

Description

[0001] The invention relates to a device for detecting foreign bodies in a mat scattered on a conveyor system during the production of a material sheet, wherein the mat consists at least partially of fibers or chips and binders which are pressed together under increased temperature, and wherein at least one first sensor device operating with electromagnetic or ultrasonic waves or with magnetic fields or with radiometry is provided, which is directed at one or more spatial measuring areas of the mat in order to detect foreign bodies.

[0002] The invention further relates to a method for detecting foreign bodies in a mat scattered on a conveying device during the production of a material sheet, wherein the mat consists at least partially of fibers or chips and binders which are pressed together under increased temperature, wherein at least one first sensor device operating with electromagnetic or ultrasonic waves or with magnetic fields or with radiometry is used, which is directed at one or more spatial measuring areas of the mat in order to detect foreign bodies.

[0003] The invention further relates to a production plant for manufacturing material panels with a spreading station for spreading a mat onto a conveyor device, wherein the mat consists at least partially of fibers or chips and binders, and a press for compacting the mat, which includes the inventive device for detecting foreign bodies, as well as a manufacturing method for material panels with a spreading station in which a mat is spread onto a conveyor device, wherein the mat consists at least partially of fibers or chips and binders and is compacted in a press which uses the inventive method for detecting foreign bodies.

[0004] The term "material panels" primarily refers to wood-based panels that have already been manufactured in a preferably continuous press. Examples include particleboard, MDF, or OSB panels, where the particles containing the mat are essentially wood fibers or wood chips bonded with a binder. More recently, other lignocellulosic materials, such as fibers from annual plants (e.g., rice straw), have also been used for pressing material panels. However, material panels, as defined in the invention, can also be insulation boards, gypsum boards, plastic boards, or other material panels whose particles have been pressed in a continuous press with heat application using rotating belts. The applicant markets such a press under the name ContiRoll.In this process, binders are usually added to the particles before continuous pressing to ensure that the material sheets have high stability.

[0005] The fibers or chips are spread in a spreading station onto a conveying device, usually a conveyor belt (also called a forming belt), where they form a mat that is conveyed towards the press. In the continuous press, hydraulic components apply high pressure via mostly heated pressure plates and rollers to the upper and / or lower steel press belt, between which the mat is compacted at the same feed rate as the press belts. These press belts are typically only 0.5 to 4 mm thick and very sensitive to excessive point pressure. Excessive dents or damage can cause the entire system to produce only rejects. Replacing the press belts is costly and labor-intensive and understandably undesirable.Considering the high levels of compaction and thus thickness changes (from mat to material sheet) in continuous pressing, it becomes clear that even relatively small, hard foreign particles inside the mat can penetrate the surface and damage the press belts. Typical compaction values ​​are given in kg / m. 3 are at product Density after dispersion Density according to press MDF 18 - 35 600 - 900 Span 140 - 150 550 - 750 OSB 60 - 70 500 - 700

[0006] Especially with MDF boards, the thickness of the mat to the material board is reduced so much that even smaller embedded foreign bodies can easily penetrate the surface.

[0007] However, before spreading, shavings or fibers undergo various processes, such as shredding, washing, or spraying with binding agents, until they are stored in large bunkers in front of or above the spreading station. During these numerous upstream processes, unwanted foreign matter often becomes embedded in the spreading mat. Depending on the size and hardness of the foreign matter, it can protrude from the surface during the compaction process of the press and damage the press belts.

[0008] Therefore, it is standard practice to inspect the mat before it enters the press. A metal detector is frequently used for this purpose. However, there are also systems where the conveyor belt is x-rayed. If a foreign object is found, the production process is stopped by removing the affected part of the mat using a foreign object removal device. This can be a type of drop chute that opens when the conveyor belt is pulled back slightly. However, there are also systems where the contaminated mat section is vacuumed or brushed off the conveyor belt.

[0009] For example, German patent DE 10 2004 048 275 B3 describes the possible use of a metal detector. Such metal detectors operate inductively with a transmitter coil through which an alternating current flows, generating an alternating magnetic field. If this alternating field passes through a conductive material beneath the probe, eddy currents are induced, which in turn generate a measurable magnetic field. Metal objects pose the greatest risk due to their density, and metal detectors are relatively inexpensive. The detector can detect individual metal objects with sufficient accuracy. However, non-ferrous metals such as copper or aluminum are not included.

[0010] Metal parts are also significantly reduced in size during the production process (shavings, dust). A metal detector integrates the metal mass into its field of view and cannot distinguish between a single larger object and many smaller ones. This means that the metal detector will also detect a harmless layer of metal dust as a foreign object, thus unnecessarily interrupting production.

[0011] On the other hand, the metal detector cannot detect larger, equally harmful clumps of glue or, for example, a plastic nut.

[0012] Other foreign object detection systems have similar problems. An X-ray-based sensor with sufficient area resolution can detect the silhouette of an object with correspondingly higher densities. However, the scanner cannot determine the object's height, and therefore its volume and mass. Thus, while not only metallic foreign objects are detectable, those made of other materials with a correspondingly high density are also identified.

[0013] However, since the foreign body scanner can only detect the surface of the foreign body, a correspondingly flat body that is harmless to the press belt would result in a false triggering of the foreign body ejection device.

[0014] Besides the inductive metal detector and the X-ray scanner, there are many other theoretical sensor devices for detecting foreign objects in a mat. These include a) Image sensors with visible and invisible light b) Ultrasonic transmitters and sensors c) Sensors based on the magneto-optical Kerr effect d) Radioactive or radiometric sensors e) Magnetic sensors (MRI)

[0015] All these possible sensors and measuring methods can be part of the invention and be present in the first sensor device or procedurally represent its operation. However, they all share the characteristic that they cannot detect the foreign object completely and would frequently cause unnecessary production interruptions in order to protect the press belt.

[0016] Therefore, the purpose of the invention is to better estimate, in the manufacturing process of material plates, when a foreign body can damage the steel belt of a continuous press, thereby raising the threshold for triggering foreign body rejection and consequently interrupting production less frequently.

[0017] The problem is solved by means of an apparatus with the features of claim 1 and in particular by providing at least one second sensor device in a multimodal manner, which is also aligned to the measuring ranges, and wherein the first sensor device is suitable for performing material detection of the foreign body, and the second sensor device is suitable for determining at least one foreign body dimension.

[0018] The problem is solved methodically with the features of claim 13 and in particular by using at least a second sensor device in a multimodal manner, which is also aligned to the measuring ranges, optionally with a time delay, wherein the first sensor device performs material detection of the foreign body and the second sensor device determines at least one dimension of the foreign body.

[0019] By combining a first sensor device suitable for at least approximately identifying the material of the foreign body, and a second sensor device suitable for determining the dimensions of the foreign body, a harmful foreign body can be identified much better than before.

[0020] In some systems, the first sensor is used for detection in the direction the mat passes through, followed by the second sensor. In other systems, the reverse order may be more efficient. This depends on the material being spread and the thickness or density of the mat. In one case, it might be preferable to first determine the material and then the dimensions of the foreign object; in another, it might be more efficient to determine the dimensions of the foreign object first and then the material. The terms "first" and "second" sensor simply indicate that there are two different sensor units that can be used in any order.

[0021] The term measuring range refers to the area, whether flat or spatially limited, that the respective sensor device can detect. Such a measuring range can extend across the entire width and / or thickness of the mat.

[0022] Preferably, the first sensor device includes a sensor for detecting the metal content of a foreign object. With such a sensor, for example, an inductively supported detector using electromagnetic coils, it is immediately apparent if a ferrous metal part is present in the mat. In combination with a second, also preferred, sensor device suitable for detecting the dimensions of the foreign object material, preferably three-dimensionally (for example, sensors supported by X-rays or radiometry are suitable), the hazard posed by the foreign object to the press belt can be determined. Thus, the operator of the production plant knows immediately, for example, that production of material sheets does not need to be interrupted if the metal detector has been triggered, but the second sensor device indicates that it is only scattered, minute metal particles.

[0023] Claims 4 to 7 specify particularly useful sensor devices. These sensor devices are already used in other technical fields, such as medicine or food technology, and have proven their worth.

[0024] A particularly advantageous feature is the provision of an evaluation unit capable of performing a sensor fusion of at least one first sensor unit and at least one second sensor unit.

[0025] Sensor fusion algorithmically combines the measurement results from at least one initial sensor and at least one secondary sensor to create a complete and precise assessment of the foreign object's condition. Based on a predefined damage matrix, it then determines whether the foreign object is harmful to the press belt. This matrix provides a clear classification based on factors such as the foreign object's material and dimensions. Similarly, dependency algorithms can be implemented, containing formulas that define a critical state for the foreign object when a calculated threshold is exceeded.

[0026] Preferably, in a case of estimated potential harm to the press belt, i.e. depending on the result of the sensor fusion in the evaluation unit, a foreign body ejection device can be activated.

[0027] The opening of an discharge chute or the activation of a suction device by this inventive device for detecting foreign objects is therefore completely automatic. The operator of the production plant can also be certain that production will only be interrupted if a foreign object potentially damaging the press belt is detected, or at least if such damage is highly probable. For example, according to the evaluation unit, if a large but very flat foreign object is hidden in the mat, which would already trigger a production stoppage with a conventional foreign object scanner, it would be possible to continue running the production plant and, if necessary, cut out the area containing the foreign object from the resulting material sheet. Therefore, the production plant does not need to be stopped for foreign objects that are detected but pose no risk to the press belt.

[0028] The trend in the production of material sheets is towards ever thinner and lighter sheets. These are particularly affected by the problem, and the device according to the invention is especially suitable for mat thicknesses of less than 8 mm. Therefore, it is advantageous if, in addition to at least one first sensor device and at least one second sensor device, a thickness, density, or basis weight measuring device for the mat is provided.

[0029] Such thickness, density, or basis weight measuring devices are common in the production of coated mats that are pressed into material sheets and are familiar to experts. However, they are typically used only to measure the uniformity across the coating height and / or across the width and length of the conveyor belt.

[0030] In the device according to the invention, the determined thickness, density, or basis weight measurement can also be transmitted to the evaluation unit. This measurement can then be taken into account in the evaluation matrix for foreign body material and dimensions. Even small foreign bodies can endanger the press belt, especially in the case of thin mats.

[0031] It is particularly advantageous that a displacement / time detection device is provided for synchronizing the sensor signals of at least one first sensor device and at least one second sensor device.

[0032] Especially when at least one first sensor and at least one second sensor are positioned some distance apart along the mat's transport path, it must be ensured that the measured values ​​from the first sensor and the second sensor are correctly correlated with the same measuring point. Therefore, depending on the mat's transport speed, the measured values ​​from the downstream measuring point will arrive at the evaluation unit later. This time lag must be taken into account. The distance / time measurement device can detect this time difference and transmit it to the evaluation unit. Often, the distance between the sensor devices is fixed, so the distance / time measurement device only transmits the speed of the conveying device, such as the conveyor belt.The evaluation unit can then calculate the time offset of the measurement signals and take this into account when analyzing the foreign bodies.

[0033] Alternatively, it can also be provided that at least one first sensor device and at least one second sensor device simultaneously detect the same measuring point on or in the mat. In this case, they could even be housed in a single casing.

[0034] The procedural advantages are analogous to those described for the device. The method claims essentially correspond to the device claims for detecting foreign bodies in a mat spread onto a conveyor system.

[0035] Crucially, the process also offers significant advantages over the prior art. For example, assuming a metal detector as the first sensor device and a second sensor device that captures the dimensions of the foreign material three-dimensionally, the following three examples demonstrate how effective sensor fusion can be: - The second sensor detects a corresponding surface area or dimension of an object. The first sensor then detects the metal mass corresponding to the object's surface area. This confirms the presence of a hazardous metal object, and a foreign object removal system is activated. - The second sensor does not detect any suspicious area or dimensions, but the metal detector reports a corresponding mass of metal. This indicates a larger field of distributed metal dust and not a hazardous foreign object. Foreign object removal is therefore unnecessary. - The second sensor detects a corresponding surface area or dimension of a body. If the first sensor does not detect any metal, then it is certainly a non-metallic body (e.g., a lump of glue) which would be treated accordingly if it lay above a separate threshold. Above a certain dimension, whose

[0036] Since the value also depends on the thickness of the mat and the press gap height, a foreign body removal system is activated.

[0037] Claims 22 and 23 state that it is advantageous to use both the device according to the invention and the analogous and corresponding method according to the invention for detecting foreign bodies in a production plant between the spreading station and the continuous presses.

[0038] The invention will now be explained in more detail with reference to two exemplary embodiments illustrated in the drawings. These show... Fig. 1. A system for producing a material plate according to the invention, comprising a device according to the invention for detecting foreign bodies in a schematic side view. Fig. 2 an alternative arrangement of the sensor devices

[0039] In Fig.Figure 1 schematically depicts a section of a plant 1 for the production of a material panel. On the left side, the end of a spreading station 3 is indicated, with which chips or fibers, wetted with binders, are spread onto a long conveying device 4, in this embodiment a conveyor belt running over a support structure 17, towards a mat 5. The mat 5 can have several different layers with chips or fibers of varying sizes, which may also be oriented in different directions. In the Fig. Figure 1 shows only a short section of mat 5 schematically for the sake of clarity.

[0040] At the right edge, i.e., at the end of the conveying section, is the inlet to a continuous press 2. This press has an upper press belt 18a and a lower press belt 18b, which run continuously around various deflection rollers 16 and can apply pressure to the mat 5 from both sides. The press belts 18a and 18b are thin metal belts that can be damaged by localized pressure from sharp or hard foreign objects, such that the damage is transferred to the pressed mat 5 and is visible on the material sheet upon exiting the press 2 (not shown).

[0041] This means that a foreign body 10 endangering the press belt 18a, 18b is in the mat 5 (in Fig.(2 shown in more detail) must be removed by a foreign object removal device 11 before entering the continuous press 2. In this embodiment, the foreign object removal device 11 is a type of drop chute that can be opened by retracting a cover and / or a movable conveyor belt section 12 via adjustment motors 20. After removing the mat section containing a foreign object 10 that could potentially endanger the press belts 18a, 18b, the mat 5 no longer has a straight edge. Therefore, the system 1 for producing a material panel has a diagonal saw 9 that can cut a new straight edge into the mat 5 at right angles to the feed direction. This edge can then easily enter the continuous press 2.

[0042] The novel aspect of this system according to the invention is the device 21 and the method for detecting foreign bodies in a mat 5 scattered on the conveyor 4. Crucially, a first sensor device 6 and a second sensor device 7 are used. The first sensor device 6 is suitable for material identification of the foreign body, and the second sensor device 7 is suitable for determining the foreign body's dimensions. In this embodiment, sensor device 7 is pre-configured with sensor device 6. In other cases, the two sensor devices 6 and 7 operate in reverse order, as can also be seen schematically in... Fig. 2 is indicated.

[0043] But back to Fig.1. The physical measuring system of the sensor device 7 is equipped to determine the dimensions of a foreign body, optionally even three-dimensionally. In this embodiment, it can, for example, be a sensor device (7) that uses X-rays. As the mat moves forward, the same spatial measuring area 22 is covered, in which a foreign body 10 (see also Fig. 2) was detected on a larger scale and examined by the sensor device 6. This sensor device 6 can determine the material of the foreign body 10 or at least its density, so that a statement can be made from the dimensions and material properties as to whether the foreign body 10 is harmful to the press belts 18a, 18b in the continuous press 2. It may be sufficient to determine the metal content of the foreign body 10, which is possible with an inductive metal detector.

[0044] To expedite decision-making, an evaluation unit 15 is provided, equipped with signal lines S1 to S5. It receives measured values ​​from the first sensor unit 6 via signal line S1 and from the second sensor unit 7 via signal line S2. Since the foreign object limit values ​​stored in the evaluation unit 15 are highly dependent on the current mat thickness or density, corresponding data is supplemented via signal line S3 from an additionally installed thickness, density, or basis weight measuring device 8. To account for the time interval between a measuring area 22 from the second sensor unit 7 and the first sensor unit 6 during measurements, the evaluation unit 15 is also informed by a conveyor belt speed sensor 19 with signal line S4 via a displacement / time recording device 13.

[0045] If the evaluation unit 15 detects a foreign body threatening the press belts 18a and 18b of the continuous press 2, it activates the foreign body ejection device 11.

[0046] In Fig. 2 are the two sensor devices 6, 7 in reverse order as we are in Fig. 1. However, the two sensor devices 6, 7 are housed in a single casing 14 and are therefore arranged so close together that the measuring ranges 22 of the sensor devices 6, 7 at least partially overlap and both can perform their measurements simultaneously. A large foreign object 10 is contained in the mat 5, which is transported on the conveyor belt 4. If one considers the same sensor types as in the exemplary embodiment of the Fig.If sensor 1 remains, sensor 6 detects the material, for example metal, and sensor 7 identifies the dimensions, possibly even three-dimensionally, so that the connected evaluation unit can immediately decide, based on the measured values ​​and stored limit values, whether a foreign object rejection device needs to be activated. However, the invention is also intended to encompass other measurement methods for sensor 6 and 7. These include sensor assemblies operating with electromagnetic or ultrasonic waves, magnetic fields, or radiometry. Reference symbol list 1 Plant for the production of a material plate 2 (Entry into) continuous press 3 (End of) Spreading Station 4 Conveyor device, conveyor belt 5 Mat (excerpt only) 6 First sensor setup 7 Second sensor device 8 Thickness, density or basis weight measuring device 9 Diagonal saw 10 foreign bodies 11 Foreign object removal device 12 Movable cover or conveyor belt section 13 Distance / Time Recording Device 14 Housings of the sensor devices 15 Evaluation unit 16 Deflection roller 17 Support structure of the conveyor system 18a Upper press belt 18b Lower press belt 19 tape speed meters 20 Adjustment motor 21 Device for detecting foreign bodies 22 Measuring range S1 signal line first sensor device S2 signal line second sensor device S3 signal line thickness gauge S4 signal line conveyor belt speed S5 signal line to foreign object ejection device

Claims

[1] Device for detecting foreign bodies (21) in a mat (5) scattered on a conveyor device (4) during the production of material plates, wherein the mat (5) consists at least partially of fibers or chips and binding agents which are pressed under increased temperature, wherein at least one first sensor device (6) operating with electromagnetic or ultrasonic waves or with magnetic fields or with radiometry is provided, which is directed towards one or more spatial measuring areas (22) of the mat in order to detect foreign bodies (10), characterized by that at least one second sensor device (7) is provided, which is also aligned with the measuring areas (22), and wherein the first sensor device (6) is suitable for detecting the material of the foreign body (10), and the second sensor device (7) is suitable for determining at least one foreign body dimension. [2] Device according to claim 1, characterized bythat the at least one first sensor device (6) is suitable for detecting the metal content of the foreign body material. [3] Device according to claim 1, characterized by that the at least one second sensor device (7) is suitable for detecting the dimensions of the foreign body material three-dimensionally. [4] Device according to one of claims 1 to 3, characterized by that the at least one first sensor device (6) comprises a preferably inductively acting metal detector. [5] Device according to one of claims 1 to 4, characterized by that the at least one second sensor device (7) comprises an X-ray-based sensor. [6] Device according to one of claims 1 to 5, characterized by that the at least one first sensor device (6) or the at least one second sensor device (7) comprises a sensor based on thermography. [7] Device according to one of claims 1 to 6, characterized by that the at least one first sensor device (6) or the at least one second sensor device (7) comprises a sensor based on ultrasonic waves with a sound reflection receiver. [8] Device according to one of claims 1 to 7, characterized by that an evaluation device (15) is provided which is capable of carrying out a sensor fusion of the at least one first sensor device (6) and the at least one second sensor device (7). [9] Device according to claim 8, characterized by that a foreign body ejection device (11) can be activated in the evaluation device (15) depending on the result of the sensor fusion. [10] Device according to one of claims 1 to 9, characterized bythat in addition to the at least one first sensor device (6) and the at least one second sensor device (7), a thickness, density or basis weight measuring device (8) is provided for the mat (5). [11] Device according to one of claims 1 to 10, characterized by that a path / time detection device (13) is provided for synchronizing the sensor signals of the at least one first sensor device (6) and the at least one second sensor device (7). [12] Device according to one of claims 1 to 10, characterized by that the at least one first sensor device (6) and the at least one second sensor device (7) are accommodated in a housing (14). [13] Method for detecting foreign bodies (10) in a mat (5) scattered on a conveyor device (4) during the production of material plates, wherein the mat (5) consists at least partially of fibers or chips and binding agents which are pressed in a continuous press (2) with an increase in temperature, wherein at least one first sensor device (6) operating with electromagnetic or ultrasonic waves or with magnetic fields or with radiometry is used, which is directed towards one or more spatial measuring areas (22) of the mat (5) in order to detect foreign bodies (10), characterized by , that at least one second sensor device (7) is used, which is also aligned, optionally with a time delay, with the measuring areas (22), wherein the first sensor device (6) is used to detect the material of the foreign body (10) and the second sensor device (7) is used to determine at least one foreign body dimension. [14] Method according to claim 13, characterized by that the at least one first sensor device (6) detects the metal portion of the foreign body material. [15] Method according to claim 13 or 14, characterized by that the at least one second sensor device (7) detects the dimensions of the foreign body material three-dimensionally. [16] Method according to one of claims 13 to 15, characterized by that a sensor fusion of the signals of the at least one first sensor device (6) and the at least one second sensor device (7) is carried out via an evaluation device (15). [17] Method according to claim 16, characterized by that depending on the result of the sensor fusion in the evaluation device (15) a decision is made as to whether a foreign body ejection device (11) is activated. [18] Method according to claim 16 or 17, characterized by that the evaluation unit (15) alarms about harmful foreign bodies (10) depending on the mat thickness or mat density or activates the foreign body ejection device (11). [19] Method according to one of claims 13 to 18, characterized by that the at least one first sensor device (6) and the at least one second sensor device (7) use different physical working methods. [20] Method according to one of claims 13 to 19, characterized by that a distance / time detection device (13) is used to synchronize the signals for the same measuring range (22). [21] Method according to one of claims 13 to 19, characterized bythat the at least one first sensor device (6) and the at least one second sensor device (7) simultaneously detect the same measuring range (22). [22] Production plant for the production of material boards with a spreading station (3) for spreading a mat (5) onto a conveyor device (4), the mat (5) consisting at least partially of fibres or chips and binding agents, and a continuous press (2) for compacting the mat (5), characterized by that a device for detecting foreign bodies (21) according to one of claims 1 to 12 is present between the scattering station (3) and the continuous press (2). [23] Manufacturing method for material boards with a spreading station (3) in which a mat (5) is spread onto a conveyor device (4), wherein the mat (5) consists at least partially of fibres or chips and binding agents and is compacted in a continuous press (2), characterized bythat a method for detecting foreign bodies according to one of claims 13 to 21 is used between the scattering station (3) and the continuous press (2).

Images