Corrugated cardboard production unit and method for monitoring a corrugated cardboard production unit

Abstract

The invention relates to a corrugated cardboard production unit (2) and to a method for monitoring such a corrugated cardboard production unit (2). A defined region of a conveyor device (4) of the corrugated cardboard production unit (2) is specified as a test region (12), and a camera system (20) comprising at least one camera (22) is provided, by means of which images (I1) are captured. The camera (22) is oriented in the direction of the test region (12) such that the test region (12) is imaged in the captured image (I1), the position of the markers (14) is detected using the camera system (20), and the test region (12) is determined in the captured image (I1) on the basis of the detected position. If a deviation of the imaged test region (12) from a target orientation (27) is identified, an automatic image correction is preferably carried out. In this manner, an inspection of the adjustment of the camera (22) is facilitated and a reliable image analysis is ensured for a subsequent analysis, for example in order to automatically inspect the flatness of the sheets (6).

Description

[0001] Description

[0002] Corrugated board plant and method for monitoring a corrugated board plant

[0003] The invention relates to a corrugated board plant and a method for monitoring a corrugated board plant.

[0004] Corrugated board lines are well known and are used to produce individual sheets of corrugated board. During sheet production, the goal is to achieve the best possible flatness of each sheet, as this is a crucial criterion for quality and further processing. Flatness refers to a sheet being flat and without any warping. A deviation from this flatness in the form of a curve is also referred to as "warp."

[0005] EP 1 473 147 A1 describes the detection of undesired curvature of arches using a camera-based system. The height levels of various points on an arch are recorded and evaluated. The inspection of the arches for deviations from flatness is also referred to below as "warp detection."

[0006] Camera-based systems for monitoring a corrugated board line or for inspecting the corrugated boards produced are also well known. These involve applying markers to the corrugated board. For example, a luminescent marker system is described in DE 10 2015 204 407 A1. Detecting a deviation from the flatness requires a high degree of accuracy in order to obtain reliable information about such a deviation with such a camera-based monitoring system.

[0007] Based on this, the invention is based on the object of ensuring reliable monitoring of a corrugated board plant, in particular reliable monitoring of the sheets produced, especially with regard to a deviation from the flatness.

[0008] According to the invention, the object is achieved by a corrugated board plant in which

[0009] - at least one conveyor device extending in a longitudinal direction and provided with at least one conveyor belt is arranged for conveying sheets of corrugated cardboard,

[0010] - a defined area of ​​the conveyor system, especially the conveyor belt, is specified as the test area (region of interest),

[0011] - several markers are fixed to the conveyor system and correlated to the test area,

[0012] - a camera system with at least one camera is arranged, wherein preferably exactly one camera is arranged per conveyor belt, which camera is designed to record images and which is aligned in the direction of the inspection area and also set up in such a way that the inspection area is depicted in the respectively recorded image,

[0013] - wherein the camera system is further designed to optically detect the position of the markers,

[0014] - an evaluation unit is arranged which is designed to determine the test area in the displayed image on the basis of the detected position of the markers.

[0015] The object is further achieved according to the invention by a method for monitoring a corrugated board plant, in which

[0016] - a defined area of ​​a conveyor system of the corrugated board plant is specified as the inspection area, - a camera system with at least one camera is arranged, with which images are taken and which is aligned towards the inspection area in such a way that the inspection area is depicted in the recorded image,

[0017] - whereby the position of the markers is recorded using the camera system and the test area in the recorded image is determined based on the recorded position.

[0018] The advantages and preferred design variants listed below for the corrugated board plant also apply to the process and vice versa.

[0019] The embodiments according to the invention are based on the consideration that for the reliable and precise evaluation of the images recorded with the camera system, particularly with regard to monitoring the flatness, a highly precise adjustment of the respective camera in relation to the inspection area, i.e. to the "region of interest" (ROI), is necessary. Furthermore, the invention is based on the knowledge that during operation of the system, even after an initially highly precise adjustment of the camera system, misalignment can occur, so that, for example, the recorded image contains errors such as distortion or twisting, compared to a correct adjustment of the camera. Such misalignment and the resulting image artifacts are disadvantageous for the downstream image analysis, especially with regard to identifying the flatness of the respective sheets.

[0020] By determining the position of the markers in the displayed image, the actual representation and orientation of the inspection area in the captured image (imaged inspection area) is captured. This inspection area depicted in the image is taken into account for further image analysis, especially for warp detection.

[0021] In the method described here, in particular, an automatic image evaluation is used to determine and identify the actual test area in the recorded image on the basis of the identified positions of the markers and preferably to check whether this area is correctly displayed in the image.

[0022] The inspection area preferably has a width corresponding to the width of the conveyor belt. Furthermore, the inspection area has a longitudinal depth that is preferably less than 1 m and in particular in the range between 40 cm and 75 cm. Depending on the camera arrangement, the depth can also be greater.

[0023] For testing and evaluation, the evaluation unit features a suitable processing unit with processor, memory, etc. Algorithms or computer programs are stored for evaluation, which perform the corresponding evaluations and tests fully automatically based on the recorded image data and, if necessary, additional sensor data. Known or adapted image evaluation algorithms can be used for this purpose.

[0024] The system according to the invention therefore also checks, in particular, the correct alignment of the at least one camera with respect to the inspection area based on the detected position of the stationary markers. If an incorrect alignment (misalignment) is detected, suitable measures are preferably taken to at least compensate for such a misalignment. This is done, in particular, by automatically correcting the recorded image. The corrected image is then used for subsequent, further automatic (image) processing, in particular for warp detection.

[0025] This check is performed continuously during operation of the corrugator. This means that the camera system continuously captures images, which are then continuously evaluated. Specifically, an image evaluation, particularly a warp detection, is performed for each individual sheet. For this purpose, the correct alignment check described here is performed in advance. According to a first embodiment, the camera captures individual images, and according to a second embodiment, image sequences are created and further processed in the manner of a stream.

[0026] It's important to note that the markers are fixed to the conveyor system, for example, at the edge of the conveyor belt. Therefore, they are not attached to the corrugated board. For example, the markers define the corner points of the inspection area.

[0027] The conveyor system is a section of the corrugated board line in the so-called dry end area. Specifically, the conveyor system is part of a stacking system, which is located downstream of a cross cutter that cuts the produced continuous corrugated board into individual sheets. The sheets are deposited in the stacking system onto one or more conveyor belts, also known as delivery belts, and then conveyed further, for example, to a stacking device. The individual sheets are deposited and conveyed overlapping one another. They therefore rest on top of one another like shingles. This is also referred to below as a shingled arrangement.

[0028] Frequently, several conveyor belts are provided, arranged side by side and, in particular, one above the other. In such a case, such a camera system is installed on each conveyor belt. At least one camera is aimed at a specific section of the conveyor system, and specifically at the conveyor belt, which forms the inspection area of ​​the conveyor system. This means that the camera images a section of the conveyor system in each captured image. The camera is adjusted such that at least part of the captured image depicts the inspection area.

[0029] If, in this case, the camera system is designed to detect the position of the markers, this refers to optical detection of the position of the individual markers. This is preferably done with the camera that also images the inspection area. Alternatively or additionally, it is also possible to provide separate additional optical sensors, for example additional cameras, whose positions are fixedly correlated to the position of the at least one camera that images the inspection area, so that a correlation can be established between the position of the markers detected by these additional optical sensors and the image recorded by the camera.

[0030] Preferably, a predetermined target orientation is specified for the imaged test area, wherein the evaluation unit is configured to check the recorded images based on the detected position of the markers to determine whether the target orientation corresponds to the orientation of the imaged test area.

[0031] In particular, it is checked whether one or more edges of the test area are depicted in the desired orientation in the image. The markers are generally arranged in pairs, opposite each other, along a connecting line perpendicular to the longitudinal direction. The connecting line therefore defines a predefined orientation of the test area, which—if correctly adjusted—is horizontally oriented in the captured image.

[0032] If a deviation from the target orientation is identified, in a preferred embodiment, the recorded image is subjected to an image transformation using the evaluation device in such a way that the imaged inspection area assumes the specified target orientation. For this purpose, the image is subjected to a suitable image transformation. If, for example, it is detected that the imaged inspection area is rotated or distorted relative to the target orientation, the image is rotated and / or rectified so that the imaged inspection area is brought into line with the target orientation. This measure therefore makes the image prepared in this way available for subsequent further image analysis, in particular with regard to the evaluation of the flatness (warp detection).In a preferred embodiment, a recording area of ​​the at least one camera is selected such that both the inspection area and the markers are simultaneously included in a respective recorded image. This enables particularly simple evaluation and verification, since the position of the markers is already directly included in the recorded image. Automatic image analysis detects the position of the markers in the image, thus determining the actual inspection area depicted in the image. This area is then compared, in particular, with the specified target orientation.

[0033] The optical markers have generally defined optical properties. Such optical properties include, for example, color, light intensity, a defined geometry of the markers, or, when using active light pulses as markers, a predefined pulse frequency. Furthermore, a filter is provided that is sensitive to the respective optical property. This filter can be an optical filter for the camera. This is, for example, temporarily moved in front of the camera and thus alternately positioned, or alternatively, it is permanently attached.

[0034] The filter is preferably an electronic filter integrated into the evaluation unit, specifically within the automatic image evaluation. "Sensitive to the respective optical property" means that the filter is designed with respect to the optical property and, for example, has a certain bandwidth, so that (only or primarily) the respective optical property (e.g., color) is transmitted. With an electronic filter, the respective property is preferably emphasized, and other image information that does not correspond to the optical property is at least partially suppressed.

[0035] This measure makes the individual markers clearly identifiable and, in particular, clearly distinguishable from the rest of the image content, thus increasing the reliability of automatic image analysis. Overall, this type of filtering ensures a clear assignment of the markers with regard to their position and thus a reliable identification of the inspection area in the captured image.

[0036] In a useful development, the various markers differ in their optical properties, as mentioned above, and the evaluation unit is designed to identify these different optical properties, particularly with the help of automatic image analysis. This ensures that the position of the markers is recorded precisely and that, for example, the positions of two markers are not accidentally swapped and incorrectly assigned.

[0037] According to a preferred, first embodiment, the markers are reflective elements, also referred to as reflectors, or luminescent elements. Specifically, they are, for example, adhesively bonded foils, which are particularly designed as reflective foils or are luminescent. Reflective elements are generally understood to have a reflectance greater than 0.8 or 0.9. Reflectance is the ratio between incident and reflected light.

[0038] In a preferred further development, the embodiment variant with the reflection elements provides for active illumination of the markers so that, due to their high degree of reflection, they appear as luminous image elements in the recorded image and are thus clearly identifiable.

[0039] If reflection films are mentioned here, this particularly refers to so-called retroreflective films, in which the incoming light is reflected back in the direction of the irradiating light source and thus in particular to the camera, at least largely independently of the angle of incidence.

[0040] Such reflective elements, or luminescent elements, are also referred to as passive markers because they do not have their own light source. The advantage of these special passive markers compared to other passive markers, such as simple color markings, is their improved visibility, which reduces the risk of evaluation errors during automatic image analysis.

[0041] In a preferred embodiment, the markers are active markers with at least one (active) light-emitting element. These are therefore also referred to as light-active markers. The light-emitting element forms an active, particularly controllable, light source and is designed, for example, as one or more LEDs. The use of active markers increases their visibility and identification in the captured image, ensuring reliable image analysis.

[0042] In a suitable embodiment, the light elements are designed to emit light pulses, i.e., a pulsating light signal is emitted by the active marker. A constant, predetermined pulse frequency is preferably set.

[0043] In the embodiment with the different optical properties of the various markers, in a preferred further development, different markers have different pulse frequencies.

[0044] Especially when using variable markers, such as light pulses, a video or stream is recorded and evaluated with the camera so that the temporal changes, especially the pulsing / flashing and especially the pulse frequency(ies), are recorded and evaluated.

[0045] When using active markers, the light element is preferably oriented toward the camera. This ensures reliable detection of the marker's position.

[0046] In a preferred embodiment, the active marker is provided with an adjusting element for aligning the luminous element and / or a diaphragm. This serves, in particular, to align the luminous element toward the camera or, in the case of aligning a diaphragm, to align the light emitted by the luminous element.

[0047] In a preferred embodiment, the active marker has a diffuser or an optical filter arranged in front of the light element. Studies have shown that in certain situations, overexposure can occur in the captured image due to the active light element, which is detrimental to further image analysis. The diffuser therefore reduces the resulting light intensity. As an alternative to the diffuser, a suitable filter can be used, for example, to reduce the light intensity.

[0048] The markers are preferably placed at the edge of the conveyor belt of the conveyor device and, in particular, mark the corners of the inspection area. Alternatively, they have a fixed spatial relationship to the corners of the edge area.

[0049] The test area is preferably a rectangular area. Preferably, at least four markers are provided, i.e., two on each edge. Each marker is preferably assigned to a corner point of the test area.

[0050] The camera is preferably positioned opposite a conveyor system and thus opposite the longitudinal direction of the conveyor system, at a distance from the inspection area. The camera is positioned, for example, between 1 m and 4 m from the inspection area. Furthermore, the camera is preferably positioned above the conveyor belt, so that it is directed at an oblique angle toward the inspection area.

[0051] In a preferred embodiment, the at least one camera is arranged centrally with respect to the conveyor belt, ie at half the width of the conveyor belt.

[0052] In a preferred embodiment, the evaluation unit is further configured to make statements about a property of the sheets, particularly about their flatness, based on the captured images. Automatic image recognition methods are used for this purpose. Preferably, the contour of an edge of the sheet is evaluated with regard to curvature. The edge of the sheet is positioned in the specified image area and thus in the inspection area.

[0053] According to the invention, a corrugated board system is further configured with the features of claim 15. This combination of features constitutes an independent invention. The right to file a divisional application for this invention remains reserved. The aspects described below in connection with this further invention also represent preferred developments of the previously described corrugated board system and the previously described method.

[0054] According to this aspect, an enclosure is installed in the area of ​​the inspection zone, which at least partially covers the conveyor device, at least the conveyor belt, and spans the transverse direction transversely to the longitudinal direction. This enclosure provides targeted shading of the inspection zone from the surroundings, so that the inspection zone is at least partially protected and shaded from light incidence, especially from the side or from above. Furthermore, a lighting element is arranged, which illuminates the inspection zone and specifically the front edge in a defined manner. This measure improves the visibility of the inspection zone and in particular of the markers or front edges of the arches of the front edge, making automated image analysis more reliable and accurate.

[0055] Thanks to the improved and dedicated illumination, markers for identifying the test area can be omitted, for example. However, these are still preferably used as described above. The targeted illumination makes the markers easier to recognize, especially when using passive markers. Another advantage of the enclosure is that, in addition to providing visual shading, it also provides other protection for the test area, for example, from contamination.

[0056] In a preferred embodiment, the lighting element is dimmable, allowing the brightness to be adjusted. This allows the brightness to be adjusted to the ambient lighting conditions and also allows it to be adjusted during operation.

[0057] Alternatively or additionally, the light color can be adjusted. This allows the camera to specifically improve the visibility of structures in the inspection area. Especially when using passive markers, the light color can be adjusted to improve the visibility of the markers.

[0058] The lighting element is preferably attached to the housing, in particular on an inner side. In a preferred embodiment, the housing generally has at least one side wall and preferably two side walls as well as a top wall. The top wall preferably spans the conveyor belt across its entire width. In particular, it connects the two side walls. These are fastened to the conveyor device at the edges, for example. Overall, the housing - viewed in the longitudinal direction - is L-shaped and preferably U-shaped. By arranging it on an inner side and in particular on the inside of the top wall, targeted illumination of the area shaded by the housing is achieved.

[0059] In a preferred embodiment, the lighting element is mounted and / or shaded in such a way that the lighting element is not visible to the camera and / or that the light emitted by the ventilation element does not shine into the camera. Invisible here means that the lighting element is not recognizable in the image recorded by the camera. At the very least, the lighting element, specifically a cone of light emitted by the lighting element, is aligned in such a way that it does not shine into the camera. This ensures good recognizability of the illuminated inspection area, in particular without overexposure (high brightness) of partial areas in the image recorded by the camera. In order to achieve this shading of the lighting element in the direction of the camera, an aperture, for example, is arranged.

[0060] In order to provide the best possible shading of the test area, the enclosure is made of an optically non-transparent, opaque material.

[0061] The enclosure is preferably formed only in the area of ​​the test area, thus extending over only a portion of the conveyor system. Specifically, it is longitudinally adapted to the length of the test area and has a length that corresponds, for example, to between 0.5 and twice the length of the test area. Preferably, the length corresponds, for example, to 0.7 to 1.5 times the length of the test area.

[0062] The height of the enclosure is preferably between 0.2 m and, for example, a maximum of 1 m, and preferably less than 0.7 m or even less than 0.5 m – relative to the height of the conveyor belt. Overall, this shades a relatively narrow area of ​​the conveyor system and thus provides the best possible protection from ambient light.

[0063] In a preferred embodiment, the lighting element extends transversely to the longitudinal direction and has several individually controllable areas. The individually controllable areas therefore allow for the targeted illumination of defined transverse areas. This is particularly useful when the entire width of the conveyor system is not utilized, i.e., when the sheets on it do not cover the entire width.

[0064] Specifically, the lighting element comprises multiple lighting elements. Individual LEDs are preferably used as lighting elements. The lighting elements can be controlled either individually or in groups to form the controllable areas. The various options described above, such as dimming to adjust a suitable illuminance and adjusting the light color (especially through the use of RGB lamps), are preferably implemented during system operation, i.e., during the implementation of the method, and are implemented individually or in any combination.

[0065] An embodiment of the invention is explained in more detail below in conjunction with the figures, which show, in some cases highly simplified representations,

[0066] FIG 1 shows a conveyor device as part of a corrugated board plant in a lateral cross-sectional view,

[0067] FIG 2 a perspective view of a conveyor belt in the direction of a camera,

[0068] FIG 3 shows a schematic block diagram of a camera, an evaluation unit and markers,

[0069] FIG 4A, 4B are illustrations explaining the correction of a recorded image and

[0070] FIG 5 shows an exemplary, highly simplified representation of a light-active marker with camera.

[0071] FIGS. 1 and 2 show, in highly simplified representations, a section of a corrugated board plant 2, a portion of a conveyor device 4, by means of which individual sheets 6 of corrugated board are conveyed and transported in a conveying direction. The conveying direction simultaneously defines a longitudinal direction 8 of the conveyor device 4. The conveyor device 4 has a conveyor belt 10, which is guided by a belt carrier 11.

[0072] The individual sheets 6 rest on the conveyor belt 10, overlapping each other by a portion in the longitudinal direction 8. During operation, the conveyor belt 10 runs continuously, so that the sheets 6 are continuously conveyed in the longitudinal direction 8. The conveyor belt 10 has a width transverse to the longitudinal direction 8 that is typically in the range between 100 cm and 400 cm, and in particular in the range between 250 cm and 350 cm. This width defines the maximum corrugated board width that can be produced with the corrugator 2. In the exemplary embodiment, the width of the sheets 6 is significantly less than the width of the conveyor belt 10.

[0073] A predetermined sub-area is assigned to the conveyor system 4 as the test area 12. This is represented by dashed lines in Figure 2. This is preferably a rectangular sub-area of ​​the conveyor system 4, specifically of the conveyor belt 10. In the exemplary embodiment, markers 14 are arranged at the corners of the test area 12, specifically at the edge of the conveyor belt 10. For example, they are integrated into an edge-side flange 16. They are generally mounted in a fixed location on the conveyor system 4.

[0074] The conveyor device 4 further generally comprises a support frame 18 (see FIG. 1 ), by means of which the conveyor device 4 is fastened, for example, to a floor and which is also designed to mechanically hold the conveyor belt 10. In the exemplary embodiment, only one conveyor belt 10 is shown. However, conveyor devices 4 frequently comprise several conveyor belts 10, which are arranged, for example, one above the other or next to one another. Typically, each conveyor belt 10 is arranged at an angle and conveys the sheets 6 to a higher level. A stacking device for stacking the individual sheets 6 is usually arranged downstream of the conveyor belt 10.

[0075] A camera system 20 is also assigned to each conveyor belt 10, which has at least one camera 22 and is formed by the latter in the exemplary embodiment. The camera 22 is positioned opposite the longitudinal direction 8 in front of the inspection area 12 and slightly above the conveyor belt 10. The camera 22 is oriented toward the inspection area 12, i.e., a detection range of the camera 22 is aligned with the inspection area 12.

[0076] Typically, the conveyor device 4 has a lighting device 24 with at least one lighting element, with the aid of which at least a partial area and in particular the inspection area 12 is suitably illuminated. In the embodiment of Figure 1, several lighting elements are shown. The illumination of the inspection area 12 ensures that the images 11 recorded by the camera 22 (see, for example, Figure 4A) have a quality sufficient for the intended image analysis. Depending on the design of the markers 14, especially if they are designed as reflective elements or as luminescent elements, the lighting also ensures good recognizability of the markers 14 in the recorded image 11. In a preferred embodiment, it is specifically provided that a lighting element is positioned in the area of ​​the camera 22 and irradiates the markers 14 from there.

[0077] A corrugated board machine 2 generally consists of several components. Using the corrugated board machine 2, continuous corrugated board is first produced from paper webs, which are then cut to produce the individual sheets 6. The structure and operation of such a corrugated board machine 2 are generally known and typically as follows:

[0078] The paper webs are unwound from a dispenser and fed to the other downstream components of corrugator 2. For uninterrupted operation, so-called splicers are provided, for example, which enable uninterrupted operation even when changing paper rolls.

[0079] Using a so-called single-facer machine, a single-sided corrugated board web is first produced. One of the paper webs is corrugated using a corrugated roller and then glued on one side to a first cover web. This is usually fed to further machines via a so-called bridge for further processing, and a second cover web is usually glued onto the corrugated layer of the single-sided corrugated board web, opposite the first cover web. For this purpose, the web is typically first fed to a so-called preheater. A gluing unit is provided for gluing. To ensure quality and trouble-free operation, heating devices, pulling devices and other belt guides for guiding the paper webs and / or the produced corrugated board web are also preferably provided.The section of a corrugated board plant up to the production of double-sided corrugated board is called the wet end.

[0080] This is followed by the dry end. This is where the previously produced continuous corrugated board web is processed and cut to size. Typically, a so-called short cross cutter is provided first, which is used to remove the so-called start-up waste, for example, during a format change. Furthermore, the dry end, particularly downstream of the short cross cutter, features a cutting and creasing machine that cuts or at least creasing the corrugated board web lengthwise, thus inserting defined click areas.

[0081] Finally, a so-called cross cutter is arranged downstream, which cuts the corrugated cardboard web in the transverse direction to produce the individual sheets 6. Further downstream of the cross cutter is the storage system, which includes the previously described conveyor device 4. The stacking device for stacking the individual sheets 6 is typically arranged downstream of the conveyor device 4.

[0082] The special design of the corrugator 2 and the method for determining the test area 12 in images 11 recorded by the camera 22 are explained in more detail below, particularly in connection with FIGS. 3, 4A and 4B:

[0083] According to FIG. 3, the camera 22 is connected to an evaluation unit 26. The exemplary embodiment further shows that the evaluation unit 26 is connected to the markers 14, for example, to control them. This is particularly provided in the case of so-called active markers 14, which have an active light element 28 (see FIG. 5).

[0084] During operation of the corrugated board machine 2, the camera 22 continuously captures images and transmits the captured images 11, i.e., the corresponding electronic image data, to the evaluation unit 26. The evaluation unit 26 is suitably configured to perform automatic image evaluation and image processing. For this purpose, the evaluation unit 26 has at least one suitable processor and one or more suitable algorithms, as well as a memory.

[0085] The evaluation unit 26 carries out the following steps in particular, which are also explained in more detail in connection with FIG 4A and FIG 4B:

[0086] First, the markers 14 shown in the recorded image 11 are identified using automatic image recognition and thus the test area 12 shown in the recorded image 11 is also determined.

[0087] In the next step, it is automatically checked whether the displayed test area 12 assumes a specified target orientation 27. This is shown in FIGS. 4A and 4B by a thick dashed line and as a rectangle. Typically, with correct adjustment, the camera 22 is oriented such that a horizontal line in the displayed image 11 runs parallel to a connecting line between two opposing markers 14. A deviation of the connecting line from the horizontal indicates a rotation of the camera 22. The connecting line is automatically determined during image analysis based on the determined positions of two opposing markers 14.

[0088] Additionally or alternatively, it is also checked whether the angular position of the individual markers 14 relative to each other corresponds to an expected target angle. Due to the positioning of the camera 22 above the conveyor belt 10 and in front of the inspection area 12, a vanishing point perspective results, which leads to a trapezoidal representation of a rectangular inspection area 12 in the image 11 shown. A deviation from the expected target angles indicates, for example, distortion.

[0089] If a deviation of the test area 12 shown in the recorded image 11 from the target orientation 27 is identified during this check, an image correction is preferably carried out automatically, in which an image transformation is carried out so that the test area 12 shown in the image assumes its specified target orientation.

[0090] Figure 4A illustrates, by way of example, a deviation from the target orientation 27 due to a rotation. During image transformation, the displayed test area 12 is rotated and brought into the desired target orientation. The result of this image processing is a corrected image I2, which is preferably output and / or saved. The corrected image I2 is illustrated by way of example in Figure 4B.

[0091] The result of this image processing, specifically the corrected image I2, forms the basic template for further automatic image evaluation, in particular for checking the flatness of the individual sheets 6. Due to the previous check and, if necessary, correction of the orientation of the test area 12 shown in the image, a reliable automatic, camera-based check of the flatness of the individual sheets 6 is possible.

[0092] FIG. 5 shows an exemplary embodiment of a marker 14 as an active marker 14. This marker has the aforementioned light element 28, specifically an LED, which emits light toward the camera 22. The active marker 14 is preferably configured and / or positioned such that the emitted light is oriented toward the camera 22. The emitted light is represented in FIG. 5 by a light beam 30.

[0093] In the exemplary embodiment, the active marker 14 has a lens 32 arranged upstream of the luminous element 28 and a diffuser 34. These elements are used to specifically adjust the desired focusing or widening of the emitted light.

[0094] Figure 5 also shows a diaphragm 36, which in the exemplary embodiment is designed as a circular ring segment that surrounds the lighting element 28 and has a defined opening area. Furthermore, in a preferred embodiment, an adjusting element 38, shown only in a highly simplified manner, is provided, with the aid of which the diaphragm 36 can be adjusted and, in particular, rotated. This defines the orientation and / or expansion of the light beam 30.

[0095] In a preferred embodiment, the light element 28 emits light pulses at a defined frequency. A respective active marker 14 therefore flashes at a predetermined flashing frequency.

[0096] Preferably, 14 different frequencies are set and provided for the different markers so that the markers can be differentiated based on the blinking frequencies.

[0097] The evaluation unit 26 is suitably configured to detect and evaluate these flashing frequencies. For this purpose, in particular, several recorded images 11 are compared with each other. Furthermore, the image recording frequency of the camera 22 is sufficiently high to identify and, in particular, evaluate the sequence of light pulses.

[0098] The camera captures a total of 22 images at a suitable frame rate (refresh rate). The frame rate is, for example, in the range of 30 to 60 frames per second (30 Hz - 60 Hz). In principle, cameras with higher or lower frame rates can also be used.

[0099] The frequency of the light pulses is preferably matched to the camera's capture rate and, in particular, coupled with it. For example, it is possible to determine the frequency of the light pulses based on the number of images between two light pulses. The frequency of the light pulses is therefore generally preferably lower than the camera's capture rate.

[0100] The camera 22 is preferably a CCD camera with a suitable CCD sensor and a suitable pixel density. The resolution of the camera 22 is sufficiently high. Specifically, the resolution is in the millimeter range, i.e., two adjacent pixels in the captured image 11 represent a real distance (of the inspection area 12) in the range of a few millimeters, in particular in the range of 1-5 mm.

[0101] In connection with Figure 2, as a preferred further development but also as an independent invention, a housing 40 is formed in the region of the testing area 12. In the exemplary embodiment, this housing 40 is U-shaped and has two side walls 42 and a top wall 44 which connects the two side walls 42 to one another. The housing 40 spans the entire width of the conveyor device 4 in the testing area 12. In the exemplary embodiment, the housing 40 has a length in the longitudinal direction 8 that corresponds to the length of the testing area 12. On the inside of the top wall 44, a lighting element 46 is arranged which extends transversely across the conveyor belt 10. The lighting element 46 has, as individual lighting elements, in particular individual LEDs which are lined up next to one another in the transverse direction. The lighting element 46 is therefore a type of LED bar.The lighting element 46 is dimmable and is preferably dimmed during operation depending on the current lighting situation. Furthermore, in a preferred development, there is also the possibility of adjusting the color, which is preferably also selected appropriately during operation to clearly distinguish the desired structures within the inspection area 12 in the camera image. In particular, this improves the visibility of the front edges of the sheets 6 and / or the markers 14. The lighting element 46 has individually controllable areas or segments, which are preferably arranged next to one another in the transverse direction. These areas are in particular groups of individual LEDs.

[0102] This design ensures that the inspection area 12 is appropriately illuminated depending on the current requirements and lighting situation, with the intensity and / or color being adjusted accordingly. The enclosure 40 with its defined illumination of the inspection area 12 improves, for example, the visibility of the markers 14 or the front edges of the individual sheets 6, which are preferably used for WARP detection. The enclosure 40 protects the inspection area 12 from externally incident scattered light and other sources of interference, as well as from contamination.

[0103] A light cone emitted by the lighting element 46 is preferably oriented obliquely downwards, and overall preferably in such a way that a shadow cast by the front edge 26 is as prominent as possible.

[0104] List of reference symbols

[0105] 2 corrugated board lines

[0106] 4 Conveyor system

[0107] 6 sheets

[0108] 8 Longitudinal direction

[0109] 10 Conveyor belt

[0110] 11 band carriers

[0111] 12 Test area

[0112] 14 markers

[0113] 16 flange

[0114] 18 Support structure

[0115] 20 camera system

[0116] 22 Camera

[0117] 24 Lighting device

[0118] 26 Evaluation unit

[0119] 27 Target orientation

[0120] 28 light elements

[0121] 30 light beams

[0122] 32 lens

[0123] 34 Diffuser

[0124] 36 aperture

[0125] 38 Control element

[0126] 40 Enclosure

[0127] 42 side wall

[0128] 44 upper wall

[0129] 46 lighting element

[0130] 11 captured image

[0131] I2 corrected image

Claims

Claims Corrugator (2), in which - at least one conveyor device (4) extending in a longitudinal direction (8) is arranged for conveying sheets (6) of corrugated cardboard, - a defined area of ​​the conveyor (4) is specified as the test area (12), - several markers (14) are fixedly attached to the conveyor (4) and are correlated to the test area (12), - a camera system (20) with at least one camera (22) is arranged, which is designed to record images (11) and which is aligned in the direction of the test area (12) in such a way that the test area (12) is depicted in the respectively recorded image, - wherein the camera system (20) is further designed to detect the position of the markers (14), - an evaluation unit (26) is arranged which is set up to determine the test area (12) in the recorded image (11) on the basis of the detected position of the markers (14). Corrugated cardboard plant (2) according to the preceding claim, characterized in that a predetermined target orientation (27) is predetermined for the imaged test area (12), wherein the evaluation unit (26) is set up to check the recorded images (11) on the basis of the detected position of the markers (14) to determine whether the target orientation (27) corresponds to the orientation of the imaged test area (12).Corrugated cardboard plant (2) according to the preceding claim, characterized in that the evaluation device is designed in such a way that, in the event of a lack of agreement between the target orientation (27) and the orientation of the imaged test area (12), the recorded image (11) is subjected to an image transformation in such a way that the imaged test area (12) assumes the predetermined target orientation (27). Corrugated cardboard plant (2) according to one of the preceding claims, characterized in that a recording area of ​​the at least one camera (22) is selected such that both the inspection area (12) and the markers (14) are contained simultaneously in a respective recorded image (11). Corrugated cardboard plant (2) according to one of the preceding claims, characterized in that the markers (14) have defined optical properties and that a filter is provided which is sensitive with regard to these optical properties. Corrugated cardboard plant (2) according to one of the preceding claims, characterized in that the various markers (14) differ in terms of their optical properties and the evaluation unit (26) is designed to distinguish between the markers (14) based on the different optical properties.Corrugated cardboard system (2) according to one of the preceding claims, characterized in that the markers (14) are reflective elements and / or luminescent elements. Corrugated cardboard system (2) according to one of claims 1 to 6, characterized in that the markers (14) are active markers (14) with at least one luminous element (28). Corrugated cardboard system (2) according to the preceding claim, characterized in that the luminous elements (28) are designed to emit light pulses. Corrugated cardboard system (2) according to the preceding claim, characterized in that the luminous elements (28) of different markers (14) differ in terms of frequency. Corrugated cardboard plant (2) according to one of claims 8 to 10, characterized in that the active marker (14) has one or more of the following properties, - the light element (28) is directed towards the camera (22), - an adjusting element (38) is provided for aligning the lighting element (28) and / or a diaphragm (36), - a diffuser (34) or a filter is assigned to the lighting element (28). Corrugated cardboard plant (2) according to one of the preceding claims, characterized in that the markers (14) are each placed at the edge next to a conveyor belt (10) of the conveyor device (4) and, in particular, mark corner points of the inspection area (12). Corrugated cardboard plant (2) according to one of the preceding claims, characterized in that the at least one camera (22) is arranged above the conveyor belt (10) and, counter to the longitudinal direction (8), at a distance from the inspection area (12). Corrugated cardboard plant (2) according to one of the preceding claims, characterized in that the evaluation unit (26) is configured to make statements about a property of the sheets (6), in particular about a flatness of the sheets (6), based on the recorded images (11). Corrugated cardboard plant (2), in particular according to one of the preceding claims, in which - at least one conveyor device (4) extending in a longitudinal direction (8) is arranged for conveying sheets (6) of corrugated cardboard, - a defined area of ​​the conveyor (4) is specified as the test area (12), - preferably several markers (14) are fixedly attached to the conveyor device (4) and are correlated to the test area (12), - a camera system (20) with at least one camera (22) is arranged, which is designed to record images (11) and which is directed towards Test area (12) is aligned in such a way that the test area (12) is depicted in the respective recorded image, - wherein the camera system (20) is preferably designed to detect the position of the markers (14), wherein - in the region of the inspection area (12), a housing (40) covering the conveyor device (4) is mounted, wherein a lighting element (46) is arranged that illuminates at least part of the inspection area (12). Corrugated cardboard system (2) according to the preceding claim, in which one or more of the following features is / are realized: a) the lighting element (46) is dimmable and / or the light color is adjustable, b) a light cone emanating from the lighting element (46) is oriented obliquely toward the inspection area (12), c) the lighting element (46) is mounted on an inner side of the housing (40), d) the housing (40) has at least one side wall (42), preferably two side walls (42) and a top wall (44), e) the lighting element (46) is mounted and / or shaded in such a way,that the lighting element (46) is not visible to the camera (22) and / or the light emitted by the lighting element (46) does not shine into the camera (22), f) the housing (40) is made of an opaque material, g) the housing (40) is formed only in the region of the test area (12) and has a length in the longitudinal direction (8) that is particularly adapted to the length of the test area (12), for example in the range from 0.5 times to 2 times the length of the test area (12), h) the lighting element (46) extends transversely to the longitudinal direction (8) and has several individually controllable areas, in particular a plurality of individual LEDs, which can preferably be controlled individually or in groups. Method for monitoring a corrugated cardboard plant (2), in particular according to one of the preceding claims, in which - a defined area of ​​a conveyor device (4) of the corrugated board plant (2) is specified as the inspection area (12), - a camera system (20) with at least one camera (22) is arranged, with which images (11) are recorded and which is aligned towards the inspection area (12) in such a way that the inspection area (12) is depicted in the recorded image (11), - wherein the position of the markers (14) is detected with the aid of the camera system (20) and the test area (12) in the recorded image (11) is determined on the basis of the detected position.

Images