Device for detecting a temperature and method for estimating a temperature and for detecting an evenness of an applied adhesive layer

Abstract

The present invention relates to a device (1) for determining the temperature of an adhesive layer (3) applied on a surface (2), comprising a first temperature measuring unit (7, 7a) for detecting, in a non-contact manner, a first temperature (Ta) or temperature distribution (T), a first deflection means (6, 6a) which is configured to deflect heat radiation from the applied adhesive layer (3) to the first temperature measuring unit (7, 7a), and a control unit (8) which is configured to process the detected first temperature (Ta) or temperature distribution (T). The present invention also relates to a method for estimating a temperature (Tf) of an adhesive layer (3) applied on a surface (2) in a joining point, comprising the following steps: producing a relative movement with a relative speed (v) in an advancing direction (X) between the surface (2) and an application unit (12), which applies the adhesive (3) to the surface (2) with an application temperature (T0), and a temperature measuring unit (7, 7a, 7b) which is arranged downstream of the application unit (12) and upstream of the joining point in the advancing direction, determining a first temperature (Ta) of a point on the adhesive layer (3) at a first measuring time (ta) and a second temperature (Tb) of the same point on the adhesive layer (3) at a second measuring time (tb), calculating a temperature difference (ΔT) on the basis of the first temperature (Ta) and the second temperature (Tb), calculating an estimated cooling function on the basis of the temperature difference (ΔT) and a time difference (Δt) between the first measuring time (ta) and the second measuring time (tb), and extrapolating an estimated temperature (Tf) in the joining point. The present invention also relates to a method for detecting the evenness of an adhesive layer (3) applied on a surface (2), comprising the following steps: producing a relative movement with a relative speed (v) in an advancing direction (X) between the surface (2) and an application unit (12), which applies the adhesive (3) to the surface (2) with an application temperature (T0), and a temperature measuring unit (7, 7a, 7b) which is arranged downstream of the application unit (12) in the advancing direction (X) and has a measuring frequency and a flat measuring region, determining a first temperature distribution in a portion (A1-A6) of the adhesive layer (3) at a first measuring time, and identifying defective points in the adhesive layer (3) on the basis of deviations in the temperature distribution.

Description

[0001] HOMAG GmbH

[0002] Homagstraße 3 - 5

[0003] 72296 Schopfloch

[0004] Device for detecting a temperature and method for estimating a temperature and for detecting a uniformity of an applied adhesive layer

[0005] Technical area

[0006] The invention relates to a device for detecting a temperature and to a method for estimating a temperature at a joining point and for detecting a uniformity of an applied adhesive layer, in particular for fastening an edge band to a narrow surface of a plate-shaped workpiece consisting at least partially of a wood, wood material, plastic or the like.

[0007] State of the art

[0008] Panel-shaped workpieces made of wood or wood-like materials are typically provided with an edge band, which is bonded to the narrow surface of the workpiece using an adhesive. Thermoplastic hotmelt adhesives such as EVA and PO, as well as PUR hotmelt, are predominantly used for this purpose. In addition to the thickness of the applied adhesive layer and the contact pressure at the contact point, significant factors influencing the quality of an adhesive bond are the temperature and uniformity of the applied adhesive layer at the contact point.

[0009] Determining the temperature of an adhesive layer at the contact point is difficult in practice. Due to the inaccessibility of the adhesive layer at the contact point, the temperature can neither be measured directly nor calculated with sufficient accuracy. It is hardly possible to determine all influencing factors (e.g. type and application temperature of the adhesive, type and surface temperature of the substrates, temperature and humidity of the ambient air, etc.) and to take them into account in the calculation. In order to ensure a high-quality adhesive bond, there is a need for a solution to determine the temperature of an applied adhesive layer at the contact point simply and with sufficient accuracy.

[0010] To determine the thickness of an adhesive layer, the difference in weight between an adhesive-coated test workpiece and an uncoated workpiece is currently measured by manually weighing it, and the resulting layer thickness is then calculated. Since no edgeband is applied, the test workpiece is rejected. Furthermore, continuous monitoring of the production process is not possible.

[0011] In practice, determining the layer thickness by weighing proves to be very complex and inaccurate, as the applied adhesive mass is relatively small compared to the workpiece mass, and the required mechanical components complicate the design. Due to discontinuous adhesive removal and the high viscosity of the adhesive, volume flow monitoring is also impractical.

[0012] Wood and wood-like materials are also inhomogeneous and, due to the low adhesive layer thicknesses, do not allow for the measurement methods established in the metalworking industry. Other measurement methods, such as terahertz measurement technology, optical coherence tomography, or radar technology, are too uneconomical and / or too inaccurate for determining adhesive layer thickness.

[0013] Furthermore, determining the layer thickness (at random or average) alone is not sufficient to make reliable statements about the quality of an adhesive bond. The layer thickness can vary greatly across the application area, meaning that in places where the adhesive is applied locally, sufficient bond strength cannot be achieved, while in places where the adhesive is applied locally, excess adhesive can contaminate the workpiece. To ensure a high-quality adhesive bond, there is therefore a need for a solution for determining the uniformity of an applied adhesive layer.

[0014] To achieve the above-mentioned objects, temperature measuring units can be used according to the invention which must be aligned and spaced apart perpendicular to the surface of the adhesive layer in order to deliver meaningful measurement results and to be able to cover the largest possible measuring range. In order to record the temperature of an adhesive layer applied to a side surface of a workpiece, conventional temperature recording devices must therefore be aligned horizontally, which can make installation in a machine difficult or even impossible. In order to ensure a high-quality adhesive bond, there is therefore a further need for a temperature recording device which can overcome this disadvantage and at the same time fulfill the above-mentioned objects.

[0015] DE 10 2016 213216 A1 describes a method for controlling the temperature of an application roller, wherein the temperature of the applied hot melt adhesive is detected by means of a measuring device.

[0016] DE 10 2017 122701 A1 discloses a coating device for coating a narrow side of a workpiece, which device controls a detection device for detecting a surface property on the surface of the workpiece to be coated and, based thereon, a device for acting on the adhesive.

[0017] DE 10 2020 129553 A1 further discloses a device for applying adhesive to the narrow side of a plate-shaped workpiece made of wood or wood substitute materials or to edge bands with a device for detecting the amount of adhesive present or consumed in the application device or its change over time.

[0018] EP 3 042743 A1 describes a method for machining workpieces, in particular edgebands provided with a functional layer, which are heated by a heat source, and the reflected heat is recorded using imaging techniques. Based on an evaluation of the recorded data, the energy emitted by the heat source is adjusted to a predetermined target value for control or regulation.

[0019] EP 3 771537 A1 describes a camera processing method which records the edge joint of free-form parts using a camera which follows the pressure roller.

[0020] There is a need for a simple and economical solution for in-process monitoring of the adhesive application, for determining the adhesive temperature at the joining point, for determining the uniformity of the adhesive application, for detecting contamination of the application unit, as well as for documentation and assignment to an individual workpiece.

[0021] Description of the invention

[0022] A device according to the invention for temperature detection is defined in claim 1. A method according to the invention for estimating a temperature at a joining point is defined in claim 4. A method according to the invention for detecting the uniformity of an applied adhesive layer is defined in claim 9. Subclaims relate to specific embodiments. The device according to the invention and the methods according to the invention all contribute, as described above, to solving the technical problem of ensuring a high-quality adhesive bond.A device according to the invention for determining the temperature of an adhesive layer applied to a surface, in particular for fastening an edge band to a narrow surface of a plate-shaped workpiece made at least partially of wood, wood-based material, plastic or the like, comprises a first temperature measuring unit for contactless detection of a first temperature or temperature distribution, a first deflection means which is designed to deflect heat radiation from the applied adhesive layer to the first temperature measuring unit and a control unit which is designed to process the detected first temperature or temperature distribution.

[0023] Temperature detection devices must be positioned as perpendicular to the measuring surface as possible and at a sufficient distance from it in order to deliver meaningful measurement results and to cover the largest possible measuring range. Conventional temperature detection devices are unsuitable for detecting the temperature of an adhesive layer applied to the side of a workpiece and thus ensuring a high-quality adhesive bond because they take up a lot of space perpendicular to the measuring surface, i.e. in the horizontal direction, which makes their installation in a compact machine for applying an adhesive layer to the side of a workpiece difficult or even impossible.Due to its small extent perpendicular to the measuring surface and due to its small minimum distance to the measuring surface, the device according to the invention can be easily installed or retrofitted even in confined spaces such as in the present application. The deflection angle is preferably between 85° and 95°. By adjusting the deflection angle, the device according to the invention can also be individually adapted to the respective conditions. Depending on the application, the deflection angles can be, for example, between 45° and 135° or preferably between 60° and 120°. Mirrors, prisms or optical fibers can be used as deflection means, for example. These can be mirrors, prisms or optical fibers that are able to conduct thermal radiation, in particular infrared light with wavelengths between 8pm and 14pm, and which can be made of glass or plastic.

[0024] In one embodiment, the device according to the invention further comprises a second temperature measuring unit for contactless detection of a second temperature or temperature distribution and a second deflection means which is configured to deflect heat radiation from the applied adhesive layer to the second temperature measuring unit, wherein the control unit is further configured to process the detected second temperature or temperature distribution.

[0025] The provision of a second temperature measurement unit enables the detection of temperature differences even with simple point sensors (pyrometers). This allows the cooling rate of an adhesive layer to be determined easily and inexpensively, allowing the temperature of the adhesive layer at the joining point to be estimated.

[0026] In one embodiment, the device according to the invention further comprises a display unit which is configured to communicate with the control unit and to display the detected first and / or second temperature or temperature distribution, in particular graphically, and which is preferably provided in the vicinity of the application site of the adhesive layer.

[0027] The provision of a display unit for graphically displaying the recorded temperatures has the advantage that an operator can easily recognize when a temperature deviates from a predetermined setpoint or when areas of the adhesive layer have different temperatures due to uneven adhesive application.

[0028] In addition to or alternatively to a display unit, an output unit can also be provided which is designed to output a visual, acoustic, haptic or electronic signal and / or to interrupt an automated process, in particular if an inadmissible deviation is detected. The output unit can be designed as a warning light, siren and / or vibration unit and / or send an electronic message (e.g. to a mobile phone) and / or interrupt the power supply to a machine. This makes it easy to inform an operator if, for example, a temperature deviates from a predetermined target value or if areas of an applied adhesive layer have large temperature differences due to uneven adhesive application.

[0029] A method according to the invention for estimating a temperature of an adhesive layer applied to a surface at a joining point, in particular for attaching an edge band to a narrow surface of a plate-shaped workpiece made at least partially of wood, wood-based material, plastic or the like, in particular using a device according to the invention, comprises producing a relative movement with a relative speed in a feed direction between the surface and an application unit which applies the adhesive layer to the surface at an application temperature, as well as a temperature measuring unit which is arranged behind the application unit and in front of the joining point in the feed direction,determining a first temperature of a point on the adhesive layer at a first measurement time and a second temperature of the same point on the adhesive layer at a second measurement time, calculating a temperature difference based on the first temperature and the second temperature, calculating an estimated cooling function based on the temperature difference and a time difference between the first measurement time and the second measurement time, and extrapolating an estimated temperature at the joining point.

[0030] A point that is further away in the feed direction from the application point of the adhesive layer will have already experienced a longer cooling time than a point that is closer to the application point in the feed direction, if no further heat is added after the adhesive has been applied to the workpiece, e.g. to keep it warm or reheat it. When evaluating an imaginary measuring line in the feed direction (based on at least two measuring points), a temperature gradient results which depends, among other things, on the type of adhesive, the adhesive temperature at the time of application, the amount of adhesive, the type of material, the workpiece temperature and the ambient temperature. All parameters are assumed to be constant since the process only lasts a short time. A mathematical function is approximated to the determined temperature gradient and extrapolated so that the temperature at the joining point can be estimated.Based on this temperature, the application temperature of the application unit or the feed speed of the feed unit can be controlled to a setpoint.

[0031] In one embodiment of the method according to the invention, the first temperature and the second temperature are averaged over a region perpendicular to the feed direction.

[0032] Depending on the height of the adhesive layer at which the individual measurements are taken perpendicular to the feed direction, the measured temperatures or temperature differences can vary considerably, as, for example, a point at the edge of the adhesive layer cools faster than a point in the center of the adhesive layer. By using average values, these differences can be compensated for, thus improving the temperature estimate at the joining point.

[0033] In one embodiment, the method according to the invention further comprises controlling the application temperature and / or the relative speed on the basis of the estimated temperature and a predetermined temperature at the joining point.

[0034] By appropriately controlling the application temperature and / or the relative speed, the temperature at the joining point can be adjusted so that it assumes a predetermined target value, which is necessary to ensure an optimal adhesive bond.

[0035] In one embodiment of the method according to the invention, the temperature measuring unit has a measuring frequency and a linear or planar measuring range, wherein a point on the adhesive layer is detected by the temperature measuring unit at least twice while it moves along the temperature measuring unit.

[0036] A temperature measurement unit with a spatial measurement range (e.g., a thermal camera) has the advantage that virtually any number of measurements can be performed simultaneously at different locations on the adhesive layer using the same measuring unit. This allows the cooling behavior of the adhesive layer to be determined more accurately without additional hardware, thus improving the temperature estimate at the joining point.

[0037] In one embodiment of the method according to the invention, the temperature measuring unit has at least two sensors arranged one behind the other in the feed direction, wherein a point on the adhesive layer is detected successively by both sensors as it moves along the temperature measuring unit. Compared to a temperature measuring unit with a spatial measuring range (e.g., a thermal camera), two temperature sensors arranged one behind the other in the feed direction (e.g., pyrometers) have the advantage that they are significantly less expensive and that no complex software solution is required to determine the temperature difference.

[0038] A method according to the invention for detecting the uniformity of an adhesive layer applied to a surface, in particular for fastening an edge band to a narrow surface of a plate-shaped workpiece made at least partially of wood, wood-based material, plastic or the like, in particular using a device according to the invention, comprises producing a relative movement with a relative speed in a feed direction between the surface and an application unit which applies the adhesive layer to the surface at an application temperature, as well as a temperature measuring unit which is arranged behind the application unit in the feed direction and has a measuring frequency and a flat measuring range, determining a first temperature distribution in a section of the adhesive layer at a first measuring time,the detection of defects in the adhesive layer based on deviations in the temperature distribution, and preferably the graphical representation of the temperature distribution and / or the defects in the adhesive layer by a display unit.

[0039] When evaluating the thermal image, the edge areas of a workpiece are examined for a closed adhesive joint. The dimensions of the workpiece are known or are recorded by a recording device and forwarded to the image processing unit. The time-controlled image recording shows which image area the workpiece is located in. If adhesive has been applied to this narrow surface area, this can be detected by the thermal camera as an increased temperature value. If no temperature increase is detectable in the edge area, then no or insufficient adhesive has been applied. If there are gaps in the adhesive application in the edge area, the bond is of insufficient quality. Similar to the edge area, the adhesive distribution in the interior of the narrow surface can also be detected.This is particularly interesting when using pressboard or high MDE boards with convex jointing cutters, when it comes to determining whether the adhesive is sufficiently wetted. Due to the loose filling in the center of the chipboard, only partial wetting with the adhesive occurs. These areas can be identified by evaluating the temperature values ​​after application. If a defect is detected, the corresponding workpiece is rejected.

[0040] In one embodiment, the method according to the invention further comprises calculating an average temperature of the adhesive layer based on the first temperature distribution, calculating a temperature deviation of a point on the adhesive layer from the average temperature, and detecting a defect if the temperature deviation exceeds a predetermined temperature deviation.

[0041] By determining the deviations from the average temperature of a measurement, the uniformity of an adhesive layer at varying average temperatures can be easily determined based on the deviations from this temperature, without the need to know or consider additional parameters (such as the application temperature or the adhesive layer thickness). This is particularly advantageous when defects are detected automatically.In one embodiment, the method according to the invention further comprises determining a second temperature distribution in the section of the adhesive layer at a second measurement time, calculating a temperature difference distribution in the section of the adhesive layer on the basis of the first temperature distribution and the second temperature distribution, and detecting a defect if the temperature difference at a point on the adhesive layer exceeds a predetermined maximum temperature difference or falls below a predetermined minimum temperature difference.

[0042] Since the applied adhesive layer continuously cools while the surrounding temperature remains at a substantially constant temperature, the surroundings can be easily filtered out from the images. Furthermore, artifacts caused by relative movement, which are almost identical in two consecutive images, can also be filtered out, significantly improving the sharpness of the images. If the measured temperature difference exceeds a predetermined maximum temperature difference, the adhesive is cooling too quickly, indicating that the layer is too thin. If the measured temperature difference falls below a predetermined minimum temperature difference, the adhesive is cooling too slowly, indicating that the layer is too thick.

[0043] In one embodiment, the method according to the invention further comprises determining a second temperature distribution in the section of the adhesive layer at a second measurement time, calculating a temperature difference distribution in the section of the adhesive layer based on the first temperature distribution and the second temperature distribution, calculating an average temperature difference of the adhesive layer based on the temperature difference distribution, calculating a temperature difference deviation of a point on the adhesive layer from the average temperature difference, and detecting a defect if the temperature difference deviation exceeds a predetermined temperature difference deviation.

[0044] By determining the deviations from the average temperature difference between two measurements (i.e., the average cooling rate), the uniformity of an adhesive layer at varying cooling rates can be easily determined based on the deviations from this value, without requiring the knowledge or consideration of additional parameters (such as the adhesive layer thickness). This is particularly advantageous when defects are detected automatically.

[0045] In one embodiment, the method according to the invention further comprises detecting contamination of the application unit when the defects are horizontal and / or have periodically recurring patterns.

[0046] The condition of the application roller can also be determined from the temperature distribution or temperature difference distribution of an applied adhesive layer. For example, if a pronounced horizontal surface is detected, it is likely a chip between the dosing unit and the application roller, preventing the adhesive from being applied to the corresponding area. If a chip is detected, a warning is issued or automatic cleaning is performed.

[0047] In one embodiment, the method according to the invention further comprises manual or automated cleaning and / or manual or automated replacement of the application unit when contamination has been detected.

[0048] The automated cleaning of the application unit has the advantage of relieving the operator and avoiding defects in the adhesive layer caused by a contaminated application unit, thus always ensuring an optimal bond. Automated cleaning can be achieved, for example, by the dosing unit briefly increasing the adhesive flow between the processing of two workpieces in order to rinse contaminants such as adhering chips from the application unit. An automated change can be achieved, for example, by a contaminated application unit being automatically replaced with a clean application unit when contamination is detected. This means that the processing of several workpieces in a throughput process does not have to be interrupted.

[0049] In one embodiment, the method according to the invention further comprises the creation of an error log based on the detected defects, the creation of a data record based on the error log and an identification number of the workpiece, and the storage of the data record in a database.

[0050] Storing the detected errors and assigning them to a workpiece ID makes it possible to remove the affected workpieces and store them for further processing. Furthermore, the quality of the adhesive application on a workpiece can be documented, allowing for better tracking of any future complaints.

[0051] Preferably, individual or all steps of the method according to the invention are carried out automatically or computer-assisted.

[0052] Short description of the drawings

[0053] Further features and advantages of a device, a use and / or a method will become apparent from the following description of embodiments with reference to the accompanying drawings. These drawings show:

[0054] Fig. 1a is a schematic perspective view of a first embodiment of the inventive

[0055] Device for determining the temperature of an applied adhesive layer;

[0056] Fig. 1b is a schematic perspective view of a second embodiment of the device according to the invention for determining the temperature of an applied adhesive layer;

[0057] Fig. 2 is a schematic perspective view of a

[0058] Pressing unit at the joining point of an edge band

[0059] Fig . 3a is a schematic perspective view of a

[0060] Machine for applying an adhesive layer and a first device for determining the temperature of the applied adhesive layer;

[0061] Fig. 3b is a schematic plan view of the machine for applying an adhesive layer and the first device for determining the temperature of the applied adhesive layer;

[0062] Fig. 4a is a schematic perspective view of a machine for applying an adhesive layer and a second device for determining the temperature of the applied adhesive layer;

[0063] Fig. 4b is a schematic plan view of the machine for applying an adhesive layer and the second device for determining the temperature of the applied adhesive layer; Fig. 5 is a cooling function of an applied

[0064] adhesive layer;

[0065] Fig. 6a shows a measuring range of a thermal camera at a first measuring time;

[0066] Fig. 6b shows a measuring range of a thermal camera at a second measuring time;

[0067] Fig. 7a Temperature distributions of a deposited

[0068] Adhesive layer at nine consecutive measurement times

[0069] Fig. 7b a temperature difference distribution of an applied adhesive layer

[0070] Fig. 8a a temperature or temperature difference

[0071] Distribution of an applied adhesive layer with highlighted defects

[0072] Fig. 8b a temperature or temperature difference distribution of an applied adhesive layer with a characteristic pattern

[0073] Fig. 9 a process for capturing, processing and

[0074] Evaluation of thermal images of an applied adhesive layer

[0075] Description of embodiments

[0076] The same reference numerals appearing in different figures indicate identical, corresponding, or functionally similar elements.

[0077] Fig. 1a shows a schematic perspective view of a first embodiment of the device (1) according to the invention for determining the temperature of an applied adhesive layer. In this embodiment, the device (1) comprises a temperature measuring unit (7) which communicates with a control unit (8), as well as a deflection means (6) which deflects heat radiation in the direction of the temperature measuring unit (7). In the example shown, an adhesive layer applied laterally to a workpiece emits heat radiation in a horizontal direction. The heat radiation strikes a deflection mirror (6) and is reflected vertically by it in the direction of a temperature measuring unit (7) arranged above it. The signal detected by the temperature measuring unit (7) is forwarded to a control unit (8), which detects and processes the signal. Due to this structure, the extension of the device (1) perpendicular to the measuring surface, i.e.in the horizontal direction, can be significantly reduced.

[0078] Fig. 1b shows a schematic perspective view of a second embodiment of the device (1) according to the invention for determining the temperature of an applied adhesive layer. In this embodiment, the device (1) comprises two temperature measuring units (7a, 7b) which communicate with a common control unit (8), as well as two deflection means (6a, 6b) which deflect heat radiation in the direction of the respective temperature measuring units (7a, 7b). The mode of operation of the second embodiment essentially corresponds to the mode of operation of the first embodiment described above. By providing two temperature measuring units (7a, 7b) and deflection means (6a, 6b) each, the temperature can also be recorded at two measuring points or in two measuring areas simultaneously.

[0079] Fig. 2 shows a schematic perspective view of a pressing unit (14) at the joining point of an edge band (5). The workpiece (4), on whose lateral narrow surface (2) an adhesive layer (3) is applied, moves at a relative speed (v) along the pressing unit (14), which presses the edge band (5) with a defined contact force against the applied adhesive layer (3) and thus

[0080] creates an adhesive bond.

[0081] Fig. 3a to 4b each show schematically a machine (10) for applying an adhesive layer (3) to a narrow surface (2) of a plate-shaped workpiece (4) and a device (1) for determining the temperature of the applied adhesive layer (3) with a display unit (9) which is provided near the application unit (12).

[0082] The machine (10) comprises a dosing unit (11) for dosing a stream of adhesive to be applied and an application unit (12) for applying the adhesive to the narrow surface (2) of the workpiece (4). The machine (10) further comprises a movement unit (not shown) for moving the workpiece (4) at a relative speed (v) in a horizontal feed direction (X) and a pressing unit (not shown) for pressing an edge band (5) against the applied adhesive layer (3).

[0083] The dosing unit (11) withdraws a defined amount of adhesive per unit of time from a reservoir and passes it on to the application unit (12), which applies the adhesive to the narrow surface (2) of the workpiece (4). Before being applied to the workpiece (4), the adhesive is heated to a defined application temperature (T0) by the dosing unit (11) or by the application unit (12). The dosing unit (11) can be designed as a valve, pump, or wiper unit and can also be integrated into the application unit (12). The application unit (12) can have a slot-shaped outlet whose width can be adjustable and whose height extends essentially over the entire height of the narrow surface (2) of the workpiece (4).

[0084] While the workpiece (4) is moved along the application unit (12), the adhesive is continuously applied by the application unit (12) to the narrow surface (2) of the workpiece (4), so that an adhesive layer (3) that is as uniform as possible is formed thereon. The thickness of the adhesive layer (3) can be adjusted by varying the adhesive flow provided by the dosing unit (11) and / or by varying the relative speed (v) generated by the movement unit.

[0085] Fig. 3a and 3b each show a machine (10) with a first embodiment of a device (1) for determining the temperature of an applied adhesive layer (3). This embodiment comprises a temperature measuring unit (7) with a linear or planar measuring range, which detects the temperature distribution (T) in a region of the applied adhesive layer (3) that extends at least in the feed direction (X) without contact (e.g. with the aid of a thermal camera), so that the temperatures (Ta, Tb) can be determined at two points on the adhesive layer (3) at a defined distance (x) in the feed direction (X).

[0086] Fig. 4a and 4b each show a machine (10) with a second embodiment of a device (1) for determining the temperature of an applied adhesive layer (3). This embodiment comprises two temperature measuring units (7a, 7b) which are arranged at a defined distance (x) in the feed direction (X) and each record the temperature (Ta, Tb) at a point or in a region of the applied adhesive layer (3) without contact (e.g. with the aid of a pyrometer), so that the temperatures (Ta, Tb) can be determined at two points on the adhesive layer (3) at a defined distance (x) in the feed direction (X).

[0087] The determined temperatures (Ta, Tb) can either be recorded directly at two measuring points spaced apart in the feed direction (X) or averaged over two measuring areas spaced apart in the feed direction (X) which extend in a direction (Z) perpendicular to the feed direction (X). Fig. 5 shows a cooling function of an applied adhesive layer (3). As described above, the temperatures (Ta, Tb) are first determined at two points on the adhesive layer (3) spaced apart in the feed direction (X). The relative speed (v) of the workpiece (4) and the distance (x) between the measuring points or measuring areas result in a time difference (tb-ta) that a point on the adhesive layer (3) needs to get from the first to the second measuring point or measuring area. Together with the determined temperatures (Ta, Tb), the cooling rate of the adhesive layer (3) can be determined and a cooling function can be estimated.The estimation of the cooling function can be improved by additionally considering the application temperature (T0). Finally, by extrapolation, the temperature (Tf) of the adhesive layer (3) at the joining time (tf), i.e., at the joining point, can be estimated.

[0088] The use of a thermal camera with a line or area sensor has the advantage that each pixel value represents the temperature at a point on the adhesive layer (3), i.e., at multiple points in time after adhesive application, taking the relative velocity (v) into account. Thus, a large number of temperature values ​​can be recorded to more accurately determine the cooling function using multiple reference values ​​and further improve the estimate of the temperature (Tf) of the adhesive layer (3) at the joining point.

[0089] The advantage of the method according to the invention is that it is not necessary to determine and take into account all factors influencing the temperature (Tf) of the adhesive layer (3) at the joining point, such as the type and application temperature (T0) of the adhesive, the type and surface temperature of the substrates, or the temperature and humidity of the ambient air, which enables a much simpler and more accurate temperature estimation. Fig. 6a and 6b show the measuring range of a thermal camera (7) at different measuring times. The measuring range is divided into a plurality of sections (S1-Sn) in the feed direction (X). The adhesive layer (3), which moves past the thermal camera (7) at a relative speed (v), is divided into a plurality of sections (A1-A6) in the feed direction (X).

[0090] Fig. 6a shows the measuring range at a first measuring time, in which there is a first section (A1) in the first section (S1), a second section (A2) in the second section (S2), a third section (A3) in the third section (S3), etc.

[0091] Fig. 6b shows the measurement area at a second measurement time, after the adhesive layer (3) has moved a short distance past the thermal camera (7). The first section (A1) is no longer in the measurement area. The second section (A2) is now located in the first section (S1), the third section (A3) in the second section (S2), and so on.

[0092] Fig. 7a shows temperature distributions of an applied adhesive layer at multiple measurement times as it passes through the individual sections of a thermal camera. The sections, the measurement frequency of the thermal camera, and the relative speed of the workpiece are coordinated so that the workpiece moves by the width of one section with each measurement.

[0093] The determined temperature distribution is displayed, for example, on an electronic display unit, allowing an operator to continuously monitor the adhesive application. Based on local temperature differences, the operator can then identify irregularities, particularly in the edge area or in the center of the adhesive layer, and initiate appropriate countermeasures if necessary, such as adjusting the volume flow or relative speed or cleaning the application unit. With the help of automatic image recognition, the appropriate countermeasures can also be initiated automatically.

[0094] Due to the absolute temperature measurement, the area surrounding the adhesive layer, which also emits thermal radiation, is also visible in the measured temperature distribution. Furthermore, the measured temperature distribution exhibits a relatively high degree of blur due to the continuous relative speed of the adhesive layer compared to the thermal camera.

[0095] Fig. 7b shows a temperature difference distribution of an applied adhesive layer that overcomes the aforementioned problems. Based on two images of a section of the adhesive layer taken at different times (cf. Fig. 6a / b), a temperature difference between the first and second measurement is determined for each point of a section of the adhesive layer, resulting in a temperature difference distribution.

[0096] Because the applied adhesive layer cools continuously while the surrounding temperature remains essentially constant, the area surrounding the adhesive layer can be easily filtered out of the images. Furthermore, artifacts caused by relative motion, which are virtually identical in two consecutive images, can also be filtered out, significantly improving the sharpness of the images.

[0097] Fig. 8a shows a temperature or temperature difference distribution of an applied adhesive layer with highlighted defects. Based on the (absolute) temperature distribution or temperature difference distribution described above, defects can be automatically detected and identified if the measured temperature or the measured temperature difference at a point on the adhesive layer exceeds or falls below a specified temperature or temperature difference. By appropriately highlighting the affected areas (shown in white in Fig. 8a) or a corresponding message on an electronic display, the operator can be made aware of this so that appropriate countermeasures can be initiated. Alternatively, the countermeasures can also be initiated automatically.

[0098] Fig. 8b shows a temperature or temperature difference distribution of an applied adhesive layer with a characteristic pattern. The temperature or temperature difference distribution of an applied adhesive layer shown in Fig. 8a and described above can exhibit characteristic patterns that may indicate wear or contamination of the application unit, such as, in particular, horizontally pronounced or periodically recurring defects, which are outlined in dashed lines in Fig. 8b. By highlighting the affected areas or providing a corresponding message on an electronic display, the operator can be alerted so that appropriate countermeasures can be initiated. Alternatively, the countermeasures can also be initiated automatically.

[0099] The following describes the process of applying adhesive to a workpiece's narrow side using a continuous process and measuring the uniformity of the applied adhesive layer in more detail using a specific application example (see Fig. 10). The process can be used equally well for applying adhesive to strip-shaped edge sealing material and on CNC-controlled machines.

[0100] Melted hot melt adhesive (temperature approx. 130-220 °C) is applied to the narrow side of a workpiece via a roller, with the workpiece being guided past the application roller using a transport device. Immediately after application, a specific area of ​​the workpiece is scanned in the feed direction by an IR camera to detect thermal radiation (wavelength range 8-14 pm). Within the image area, no additional heat is introduced into the adhesive, so it cools due to the temperature difference from the ambient temperature.

[0101] The camera's frame rate is selected such that each point on the adhesive layer is captured multiple times by the camera as it moves through the image area, which is divided into several sections. While the camera's frame rate can remain constant, the feed speed can be variably selected, whereby the number and spatial width of the sections vary. Overall, the image area has a spatial extent in the feed direction of approximately 100 mm, but can also be higher or lower. For further processing of the data, it is advantageous if the sections each have the same spatial width.

[0102] While the adhesive layer cools continuously, images are captured discretely. Using an image stitching algorithm, images of the entire adhesive layer are generated for each section. Each image represents the adhesive layer at points in time that differ by the inverse of the frame rate.

[0103] Due to the high feed rate and the duration of the image acquisition, the images captured by the camera exhibit technical blurring. By subtracting two images from each other, a type of unsharp masking can be achieved, giving the resulting image a higher contrast and a sharper appearance, which has a beneficial effect on subsequent image processing.

[0104] If adhesive has been applied, there must be a positive temperature difference in this area because the applied adhesive cools down continuously. If no adhesive has been applied, the temperature difference is zero or negative if workpiece areas without adhesive were heated by neighboring areas with adhesive. For reliable defect detection, the positive temperature difference in an image area must be above a threshold value (e.g. >10 K). An image area can be a single pixel, for example. The image data is recorded as long as the workpiece is in the image area. The evaluation of the image data and a reaction to it takes place after the workpiece has left the image area.

[0105] It will be apparent to those skilled in the art that individual features described in different embodiments may also be implemented in a single embodiment, provided they are not structurally incompatible. Likewise, various features described in a single embodiment may also be provided in multiple embodiments individually or in any suitable subcombination.

[0106] Reference sign

[0107] 1 device for temperature detection

[0108] 2 Surface (narrow surface of a workpiece)

[0109] 3 adhesive layers

[0110] 4 Workpiece

[0111] 5 edge band

[0112] 6(a / b) Deflection means

[0113] 7 (a / b) Temperature measuring unit

[0114] 8 Control unit

[0115] 9 Display unit

[0116] 10 machines

[0117] 11 Dosing unit

[0118] 12 order units

[0119] 14 Pressing unit

[0120] X Feed direction x Distance in feed direction V Relative speed

[0121] T (a / b) recorded temperature ( -distribution)

[0122] TO Application temperature of the adhesive

[0123] Tf estimated temperature at the joining point t(a / b) measuring time to order time tf joining time

[0124] A1-A6 sections of the adhesive layer

[0125] Sl-Sn sections of the measuring range

Claims

CLAIMS 1. Device (1) for determining the temperature of an adhesive layer (3) applied to a surface (2), in particular for fastening an edge band (5) to a narrow surface of a plate-shaped workpiece (4) made at least partially of wood, wood-based material, plastic or the like, comprising a first temperature measuring unit (7, 7a) for the contactless detection of a first temperature (Ta) or temperature distribution (T), a first deflection means (6, 6a) which is designed to deflect heat radiation from the applied adhesive layer (3) to the first temperature measuring unit (7, 7a) and a control unit (8) which is designed to process the detected first temperature (Ta) or temperature distribution (T).

2. Device (1) according to claim 1, further comprising a second temperature measuring unit (7b) for contactless detection of a second temperature (Tb) or temperature distribution and a second deflection means (6b) which is designed to deflect heat radiation from the applied adhesive layer (3) to the second temperature measuring unit (7b), wherein the control unit (8) is further designed to process the detected second temperature (Tb) or temperature distribution.

3. Device (1) according to claim 1 or 2, further comprising a display unit (9) which is arranged to communicate with the control unit (8) and to represent the detected first and / or second temperature (Ta, Tb) or temperature distribution (T) in particular graphically and which is preferably provided near the application site of the adhesive layer (3).

4. A method for estimating a temperature (Tf) of an adhesive layer (3) applied to a surface (2) at a joining point, in particular for attaching an edge band (5) to a narrow surface of a plate-shaped workpiece (4) consisting at least partially of wood, wood material, plastic or the like, in particular using a device (1) according to one of claims 1 to 3, comprising the steps: Producing a relative movement with a relative speed (v) in a feed direction (X) between the surface (2) and an application unit (12) which applies the adhesive layer (3) to the surface (2) at an application temperature (T0), as well as a temperature measuring unit (7, 7a, 7b) which is arranged behind the application unit (12) and in front of the joining point in the feed direction, Determining a first temperature (Ta) of a point on the adhesive layer (3) at a first measuring time (ta) and a second temperature (Tb) of the same point on the adhesive layer (3) at a second measuring time (tb), Calculation of a temperature difference (AT) based on the first temperature (Ta) and the second temperature (Tb), Calculation of an estimated cooling function based on the temperature difference (AT) and a time difference (At) between the first measurement time (ta) and the second measurement time (tb) and Extrapolation of an estimated temperature (Tf) at the joining point.

5. The method according to claim 4, wherein the first temperature (ta) and the second temperature (tb) are averaged over a range perpendicular to the feed direction (X).

6. The method according to claim 4 or 5, further comprising the step: Control of the application temperature (TO) and / or the relative speed (v) based on the estimated temperature (Tf) and a predetermined temperature at the joining point.

7. The method according to any one of claims 4 to 6, wherein the temperature measuring unit (7, 7a, 7b) has a measuring frequency and a linear or planar measuring range, wherein a point on the adhesive layer (3) is detected by the temperature measuring unit (7, 7a, 7b) at least twice while moving along the temperature measuring unit (7, 7a, 7b).

8. Method according to one of claims 4 to 6, wherein the temperature measuring unit (7, 7a, 7b) has at least two sensors (7a, 7b) arranged one behind the other in the feed direction (X), wherein a point on the adhesive layer (3) is detected by both sensors (7a, 7b) one after the other as it moves along the temperature measuring unit (7, 7a, 7b).

9. Method for detecting the uniformity of an adhesive layer (3) applied to a surface (2), in particular to detect the uniformity of an adhesive layer (3) applied to a narrow surface of a plate-shaped and to attach an edge band (5) to a workpiece (4) consisting at least partially of wood, wood material, plastic or the like, in particular using a device (1) according to one of claims 1 to 3, comprising the steps: Producing a relative movement with a relative speed (v) in a feed direction (X) between the surface (2) and an application unit (12) which applies the adhesive layer (3) to the surface (2) at an application temperature (T0), as well as a temperature measuring unit (7, 7a, 7b) which is arranged behind the application unit (12) in the feed direction (X) and has a measuring frequency and a flat measuring range, Determining a first temperature distribution in a section (A1-A6) of the adhesive layer (3) at a first measuring time and Detection of defects in the adhesive layer (3) on the basis of deviations in the temperature distribution and preferably a graphical representation of the temperature distribution and / or the defects in the adhesive layer (3) by a display unit (9).

10. The method of claim 9, further comprising the steps: Calculation of an average temperature of the adhesive layer (3) based on the first temperature distribution, Calculation of a temperature deviation of a point on the adhesive layer (3) from the average temperature, Detect a defect when the temperature deviation exceeds a specified temperature deviation.

11. Method according to claim 9, further comprising the steps: Determining a second temperature distribution in the section (A1-A6) of the adhesive layer (3) at a second measuring time, Calculating a temperature difference distribution in the section (A1-A6) of the adhesive layer (3) based on the first temperature distribution and the second temperature distribution, Detection of a defect when the temperature difference at a point on the adhesive layer (3) exceeds a predetermined maximum temperature difference or falls below a predetermined minimum temperature difference.

12. The method of claim 9, further comprising the steps: Determining a second temperature distribution in the section (A1-A6) of the adhesive layer (3) at a second measuring time, Calculating a temperature difference distribution in the section (A1-A6) of the adhesive layer (3) based on the first temperature distribution and the second temperature distribution, Calculation of an average temperature difference of the adhesive layer (3) based on the temperature difference distribution, Calculation of a temperature difference deviation of a point on the adhesive layer (3) from the average temperature difference, Detection of a defect when the temperature difference deviation exceeds a specified temperature difference deviation.

13. The method according to any one of claims 9 to 12, further comprising the step: Detection of contamination of the application unit (12) if the defects are horizontal and / or have periodically recurring patterns.

14. The method according to claim 13, further comprising the step of: manual or automated cleaning and / or changing of the application unit (12) when contamination has been detected.

15. The method according to any one of claims 9 to 14, further comprising the steps: Creation of an error log based on the detected defects, Creation of a data record based on the error log and an identification number of the workpiece ( 4 ), Storing the data record in a database.

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