Corrugated board installation and method for checking planar position of sheet of corrugated board

Abstract

The invention relates to a corrugated cardboard installation (2) and to a method for monitoring such a corrugated cardboard installation (2), in which sheets (6) are partially placed one above the other on a conveyor belt (10) extending in a longitudinal direction (8) such that a front edge (26) of a preceding sheet (6) rests on a following sheet (6). A defined area of a conveying device (4) of the corrugated board installation (2) is predetermined as a test area (12), and an image (I) of the test area (12) is recorded with a camera (22). When viewed in the longitudinal direction (8), the camera (22) is oriented obliquely forward in the direction of the test region (12) so as to be oriented obliquely on a front edge (26) of the sheet (6) located in the test region (12). On the basis of at least one of the recorded images (I), the deviation of the contour of the leading edge (26) from the planar position of the sheet (6) is analyzed by means of an automatic image evaluation.

Description

Technical Field

[0001] The invention relates to a corrugated board machine and a method for checking the planar position of sheets of corrugated board. Background Art

[0002] Corrugated board plants are generally known for the production of individual sheets of corrugated board. In the production of the sheets, the best possible planar position of the individual sheets is sought, since this is a decisive criterion for quality and further processing. In this context, planar position is understood to mean that the respective sheet is planar and has no curvature. Deviations from this planar position in the form of curvature are also referred to as "warping".

[0003] In EP 1 473 147 A1, an undesired curvature of a sheet is detected by means of a camera-based system. In this case, the height of different points on the sheet is detected and evaluated. Checking whether a sheet deviates from a planar position is also referred to below as "warp detection".

[0004] Camera-based systems for monitoring corrugated board plants or for controlling manufactured corrugated board are known. Markings are applied to the corrugated board. For example, DE 10 2015 204 407 A1 describes a luminous marking system.

[0005] In such camera-based monitoring systems, detecting deviations from a planar position requires high precision in order to obtain reliable statements about such deviations. Summary of the invention

[0006] The object of the present invention is therefore to ensure a reliable and automatic check of the planar position of sheets produced in a corrugated board plant at low cost.

[0007] According to the invention, this object is achieved by a method for monitoring the planar position of a sheet of corrugated board, wherein:

[0008] a) the sheets are partially placed one above the other on a conveyor belt extending in the longitudinal direction and are conveyed in the longitudinal direction so that the leading edge of the preceding sheet rests on the succeeding sheet,

[0009] b) a limited area of ​​the conveying device of the corrugated board machine is predetermined as the test area,

[0010] c) providing at least one camera, using the camera to record images from the test area, wherein:

[0011] d) when viewed in the longitudinal direction, the camera is positioned in front of the test area and is oriented obliquely in the direction of the test area and thus obliquely over the front edge of the sheet material located in the test area,

[0012] e) Analyzing the contour of the front edge, in particular with regard to deviations of the respective sheet from the planar position of the sheet, by means of automatic image evaluation, based on at least one of the recorded images.

[0013] According to the invention, this object is also achieved by a corrugated board machine, wherein:

[0014] at least one conveying device extending in the longitudinal direction is arranged to convey sheets of corrugated cardboard, wherein, during operation, the sheets are partially placed one above the other on the conveyor belt so that the leading edge of the preceding sheet rests on the succeeding sheet,

[0015] - a defined area of ​​the conveying device is predetermined as a test area,

[0016] - at least one camera is configured to record images of the test area, wherein

[0017] - when viewed in the longitudinal direction, the camera is positioned in front of the test area and is oriented obliquely in the direction of the test area and thus obliquely on the front edge of the sheet material located in the test area,

[0018] The evaluation unit is arranged to analyze, based on at least one of the recorded images, deviations of the contour of the leading edge from the planar position of the sheet by means of automatic image evaluation.

[0019] The advantages and preferred embodiments mentioned below with respect to the method will also be transferred to the corrugated board plant accordingly, and vice versa.

[0020] In the corrugated board plant and method, it is particularly important that, on the one hand, the camera position is arranged obliquely in front of the test area so that the viewing direction of the camera points from the front to the corresponding overlapping front edge of the corresponding sheet. Preferably, the conveying device is provided with lighting so that the front edge or the corresponding shadow projection makes the front edge clearly visible in the image. This makes a reliable, automatic image evaluation of the contour and thus of the front edge profile possible. Based on the profile of the front edge in the transverse direction, i.e. perpendicular to the longitudinal direction, curvatures and bulges formed on the front edge of the corresponding sheet can be directly detected and can be accurately evaluated as characteristic values ​​that deviate from the plane position.

[0021] For warpage detection, preferably only the evaluation of the profile of the leading edge described in detail below is used.

[0022] The evaluation unit is designed and configured accordingly and has in particular a processor, generally a data memory and in particular one or more suitable algorithms, with the aid of which an automatic image evaluation is carried out.

[0023] In contrast to the height measurements known from the prior art, in which the respective sheet is observed from above and a distance measurement to a reference height is performed, this edge evaluation can be achieved with a simple method and with high reliability with regard to the desired "warp" detection. Therefore, in particular the height measurement is omitted.

[0024] Another significant advantage of the described method and the described corrugated board plant is that a large amount of additional information can be obtained simultaneously with the aid of the camera, so that the camera can and preferably is used for further automatic and manual monitoring tasks. Overall, this edge evaluation measure thus keeps the overall monitoring and system complexity for controlling the corrugated board plant in the corrugated board production process low.

[0025] Thus, for example, by directly identifying the corresponding front edge, even the individual identification of the corresponding sheet, in particular the sheet end, is implicitly allowed and given. In the case of pure height detection, the identification of the corresponding sheet must also be provided in order to be able to reliably associate the measured distance profile with the corresponding sheet.

[0026] According to a first embodiment, the camera records a single image, and according to a second embodiment, a sequence of images is generated in a stream and further processed.

[0027] The conveying device is in particular part of a corrugated board plant in the so-called dry end region. In particular, the conveying device is part of a depositing system which is arranged downstream of a transverse cutter which separates the produced continuous corrugated board into individual sheets. In the depositing system, the sheets are deposited on one or more conveyor belts, also referred to as depositing belts, and are further conveyed, for example, to a stacking device. In this case, the individual sheets are deposited and conveyed in such a way that they overlap relative to one another. They therefore overlap one another in a stacking manner. This is also referred to hereinafter as a stacking arrangement.

[0028] Typically, a plurality of conveyor belts are provided, which are adjacent to one another, in particular one above the other. In this case, at least one camera is mounted on each conveyor belt. In this case, at least one camera is directed to a specific sub-area of ​​the conveyor device, in particular a specific sub-area of ​​the conveyor belt, which forms a test area of ​​the conveyor device. This means that the camera images the sub-area of ​​the conveyor device in the corresponding recorded image. In this case, the camera is adjusted in such a way that at least a part of the recorded image images the test area.

[0029] According to a preferred design, in order to identify the front edge, edge extraction is performed and the extracted front edge is obtained. Therefore, a suitable executable program / algorithm is installed in the evaluation unit, with the help of which the edge extraction is automatically performed. Such algorithms for detecting and extracting edges in recorded images are basically known and are also referred to as edge detection filters. In this case, for example, points with a predetermined brightness change in the recorded image, in particular the gray value image, are determined. Such algorithms allow the contour of the front edge to be reliably identified.

[0030] In a next step, the extracted front edge is preferably evaluated according to the deviation from the plane position. To this end, the profile of the front edge is evaluated, in particular with regard to maximum values, minimum values, deviations from the average value, curvature behavior, etc.

[0031] For this purpose, the extracted front edge is conveniently approximated by a mathematical function by curve fitting. The deviation of the mathematical function from the plane position is then evaluated. Specifically, the aforementioned parameters, at least some of them, are analyzed by function analysis, for example by forming derivatives or the like.

[0032] The curve fitting is, for example, a high-order polynomial fit. Preferably, a so-called spline interpolation is performed. This is suitable to a large extent for warp detection, since very strong curvatures can occur in the sheet, for example through grooves, which can be well approximated by spline interpolation.

[0033] According to a preferred design, the sheet is further analyzed for distortion, preferably based on the identified and extracted front edge. The sheet is usually oriented parallel to the longitudinal direction and has edges and structures extending along the longitudinal direction, such as outer edges, grooves or longitudinal cutting edges. The front edge is usually configured as a transverse edge, which extends transversely to this longitudinal edge of the sheet and, therefore, when correctly deposited on the conveyor belt, is also transverse to the longitudinal orientation of the conveyor belt. When analyzing whether the sheet is distorted, the image evaluation is now used to automatically check whether the front edge extends transversely to the longitudinal direction. For this purpose, for example, the length of the front edge, i.e. its extent in the transverse direction, is measured by means of automatic image evaluation and compared with a set value. The set value is generated by the (known) width of the corresponding sheet and the imaging geometry of the camera. In this case, the width of the sheet is preferably used for evaluation and read out from the device control. In the case of distortion, the measured edge length is less than the set value. Based on the difference with the set value, it is also preferred to draw conclusions about the degree of distortion. If a distortion is detected, in particular a distortion exceeding a limit value, a warning message is issued in particular. According to a preferred improvement, when a distortion is detected, the degree of distortion is also determined.

[0034] Finally, in a preferred embodiment, previously identified rotations are automatically taken into account during the warp detection. Thus, after the rotation has been identified, for example, an image correction is first performed to compensate for the rotation. For this purpose, for example, the image is rotated so that the previously measured distortion of the sheet is compensated and reversed to this extent. This measure allows a reliable assessment of the extracted front edge.

[0035] In order to achieve the simplest possible design for detecting deviations in the plane position, the height measurement is omitted. In the height measurement, the distance from a reference level to several surface areas, in particular of the sheet material, is usually measured. This omission reduces the cost of the device.

[0036] In a preferred embodiment, a plurality of markers are fixedly attached to the conveyor belt in the region, which markers are associated with the test region, in particular limit the test region. In particular, the camera also detects the markers so that they are included in the recorded image. The markers can be passive or active markers. Active markers have active light-emitting elements, such as (LED) light sources. Passive markers lack such light-emitting elements. Passive markers are, for example, colored markers or reflective elements. These passive markers are attached to the edge of the conveyor belt, for example, in the form of foil.

[0037] As an alternative or in addition to marking, the test scope is defined by defined settings and configurations, for example during commissioning of the system. This includes, for example, a defined alignment of the camera relative to the conveyor.

[0038] Furthermore, based on the markings, it is preferably likewise checked by means of automatic image evaluation whether the test area recorded in the recorded image is oriented according to a predetermined set orientation. This measure is used in particular to check the technical adjustment of the system, in particular the adjustment of the camera relative to the conveyor belt. Thus, changes in the camera position during operation, for example due to vibrations etc. and the accompanying misalignments are detected. Preferably, an automatic correction is performed when such deviations of the imaged test area from the set orientation are detected. For example, if it is detected that the imaged test area is twisted or distorted relative to its set orientation, a corresponding image transformation is performed, which reverses this twist / distortion. This is preferably done before edge extraction and its analysis is performed.

[0039] By arranging the camera obliquely in front of the test area, the recorded image usually has a perspective, in particular a so-called vanishing point perspective. This is understood to mean that parallel structures extending in the longitudinal direction taper to each other in the direction of the imaginary escape point. In a preferred refinement, it is now provided that - before checking the recorded image for deviations from a planar position - a correction of this vanishing point perspective is automatically performed. This is understood to mean that the recorded image is automatically processed by a suitable image transformation so that the edges that actually extend in parallel also extend parallel to each other in the recorded image. This also means, in particular, that the recorded perspective image is converted into a top view image. This correction is particularly important when the sheet deposited on the conveyor belt extends only over a portion of the width of the conveyor belt and is arranged at the edge. The camera is usually preferably arranged in the center of the conveyor belt. Due to the arrangement of the camera in front of the test area, the eccentric arrangement of the sheet leads to distortions in a certain way, which can lead to errors in edge detection and edge evaluation if no appropriate correction for the vanishing point perspective is performed.

[0040] In corrugated board plants, several individual sheets are often arranged side by side on a conveyor belt. These individual sheets are also called plates. They are produced, for example, by dividing the sheet into different individual sheets in the longitudinal direction. In a preferred development, it is now provided that an automatic detection of these individual sheets occurs and is performed. For this purpose, an automatic image evaluation is used to evaluate longitudinal structures in the recorded images, such as cutting edges or grooves extending in the longitudinal direction. Here, in a preferred design, an automatic edge extraction is again performed.

[0041] In this case, the brightness contrast is usually less pronounced than at the front edge, so that edge detection is more difficult. In a preferred refinement, therefore, information from the device control is used, which is taken into account for the automatic image evaluation. This information is in particular information about where the grooving or cutting is to be carried out. In particular, the position of the cutting blade is extracted from the device control and taken into account in the image evaluation. In this way, the image area of ​​the longitudinal structure to be checked can be clearly limited. Another information is, for example, the width of the respective single sheet, which is known and stored in the device control.

[0042] If a plurality of such individual sheets are arranged side by side on the conveyor belt, then, as described above, it is preferably analyzed whether each of these individual sheets arranged side by side deviates from a planar position.

[0043] In an advantageous embodiment, the camera is simultaneously used for an optical monitoring system, which is configured for optical manual monitoring of the corrugated board machine by an operator. For this purpose, the image recorded by the camera is displayed in particular on a monitoring monitor of the monitoring system monitored by the operator. This enables optical manual control of the corrugated board machine, in particular of the conveyor, in particular in real time. Due to the perspective arrangement of the camera, which is tilted relative to the conveyor belt, the conveyor and the conveyed sheets can be observed well overall.

[0044] In order to check whether the sheet material deviates from the flat position, the camera has a high total triggering, which is in the millimeter range. This is understood to mean that adjacent image points shown in the image image and resolve two real points of the conveyor device, which are only a few millimeters apart, in particular in the range of 1-5 mm.

[0045] The test area imaged in the figure usually extends over the entire width of the conveyor belt. This is usually in the range between 100 cm and 400 cm, in particular in the range between 250 cm and 350 cm. Furthermore, the depth of the test area in the longitudinal direction is preferably less than 1 m, in particular in the range between 40 cm and 75 cm. Depending on the arrangement of the camera, the depth can also be greater.

[0046] According to the invention, a corrugated board machine is also provided having the features of claim 15. This combination of features represents an independent invention. The right to file a divisional application is reserved. The aspects described below in conjunction with the invention also represent preferred developments of the above-described corrugated board machine and the above-described method.

[0047] According to this aspect, a housing is attached in the region of the test area, which housing at least partially covers the conveyor device, at least the conveyor belt, and spans the longitudinal direction in the transverse direction. By means of the housing, the test area is shielded in a targeted manner with respect to the surroundings, so that the test area is at least partially protected and shielded from light incident from the sides or from above. Furthermore, an illumination element is provided, which illuminates the test area, in particular the front edge, in a defined manner. This measure improves the visibility of the test area, in particular the visibility of the front edge, making the automatic image evaluation more reliable and accurate.

[0048] A further advantage of the housing is that, in addition to the optical shielding, further protection of the test area is achieved, for example against contamination.

[0049] In a preferred design, the lighting element is dimmable so that the light intensity can be adjusted. This enables the light intensity to be adapted to the ambient light conditions and also during operation.

[0050] Alternatively or additionally, the color of the light is adjustable. In this way, the recognizability of structures in the test area of ​​the camera can be particularly improved. Thus, in particular when using passive markers, the recognizability of the marker can be increased by selecting the color of the light.

[0051] The lighting element is preferably attached to the housing, in particular to the inside. In a preferred design, the housing generally has at least one side wall, preferably two side walls and a top wall. The top wall preferably spans the entire width of the conveyor belt. It particularly connects the two side walls. It is fixed to the conveyor device, for example, at the edge side. In general, in a longitudinal view, the housing is L-shaped, preferably U-shaped. By arranging on the inside, in particular on the inside of the top wall, a targeted illumination of the area shaded by the housing is achieved.

[0052] In a preferred embodiment, the lighting element is attached and / or shielded in such a way that the lighting element is not visible to the camera and / or the light emitted by the ventilation element is not radiated into the camera. In this case, "invisible" is understood to mean that the lighting element is not visible in the image recorded by the camera. At least the lighting element, in particular the light cone emitted by the lighting element, is aligned in such a way that it does not radiate into the camera. This ensures good recognizability of the illuminated test area, in particular no over-radiation (high brightness) of partial areas in the image recorded by the camera occurs. In order to achieve such shielding of the lighting element in the direction of the camera, a membrane is arranged, for example.

[0053] In order to shield the test area as well as possible, the housing consists of an optically opaque material.

[0054] The housing is preferably formed only in the region of the test area, so that it extends only over a portion of the conveying device. In particular, it is adapted in the longitudinal direction to the length of the test area and has a length corresponding, for example, to between 0.5 and twice the length of the test area. The length preferably corresponds, for example, to 0.7-1.5 times the length of the test area.

[0055] The height of the housing relative to the height of the conveyor belt is preferably in the range of 0.2 m to, for example, a maximum of 1 m, and preferably in the range of less than 0.7 m or even less than 0.5 m. Overall, a relatively narrow area of ​​the conveyor is thus shaded and thus protected as well as possible from ambient light.

[0056] In a preferred embodiment, the lighting element extends transversely to the longitudinal direction and has a plurality of individually controllable areas. Thus, specifically defined transverse areas can be illuminated by the individually controllable areas. This is particularly useful when the entire width of the conveyor is not utilized, i.e. when the deposited sheets do not cover the entire width.

[0057] Specifically, the lighting element has a plurality of light emitting elements. Preferably, a single LED is provided as the light emitting element. The light emitting elements can be controlled individually or in groups to form a controllable area.

[0058] The different possibilities mentioned above, such as dimmability for setting a suitable illumination, setting of the light color, in particular by using RGB light sources, are preferably also implemented during operation of the device, ie during performance of the method, and individually or in any desired combination. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Embodiments of the invention are explained in more detail below with reference to the accompanying drawings. These are shown in a partially highly simplified representation:

[0060] Figure 1 A conveying device as part of a corrugated board machine is shown in transverse cross section;

[0061] Figure 2 shows a perspective view of the conveyor belt in the viewing direction of the camera;

[0062] Figure 3 A schematic block diagram showing components of a corrugated board machine is shown;

[0063] Figure 4 shows a recorded image of the test area with the extracted leading edge, and

[0064] Figure 5 The result of the curve fitting is shown, which reproduces the profile of the extracted front edge. DETAILED DESCRIPTION

[0065] Figure 1 and Figure 2 A highly simplified illustration shows a partial area of ​​a conveyor device 4 as a detail of a corrugated board plant 2, by means of which individual sheets 6 of corrugated board are conveyed and transported in a conveying direction. The conveying direction simultaneously defines the longitudinal direction 8 of the conveyor device 4. The conveyor device 4 has a conveyor belt 10 guided by a belt carriage 11.

[0066] The individual sheets 6 rest on the conveyor belt 10, i.e., they each overlap a portion in the longitudinal direction 8. Therefore, they overlap each other in a stacked manner. This overlapping arrangement is also referred to as a stacked arrangement hereinafter. In operation, the conveyor belt 10 runs continuously so that the sheets 6 are continuously conveyed in the longitudinal direction 8. The width of the conveyor belt 10 transverse to the longitudinal direction 8 is generally in the range between 100 cm and 400 cm, in particular in the range between 250 cm and 350 cm. This width defines the maximum corrugated board width that the corrugated board machine 2 can produce. In an embodiment, the width of the sheet 6 is significantly smaller than the width of the conveyor belt 10.

[0067] A predetermined sub-area is assigned to the conveying device 4 as a test area 12. Figure 2 1. It is indicated by dashed lines in the figure. It is preferably a rectangular partial area of ​​the conveyor device 4, in particular of the conveyor belt 10. In the exemplary embodiment, the markings 14 are arranged at the corners of the test area 12, i.e. at the edge of the conveyor belt 10. For example, they are integrated in the edge flange 16. They are essentially fixedly mounted on the conveyor device 4. As an alternative, the test area 12 is defined by a defined configuration and alignment of, for example, a camera 22.

[0068] Furthermore, the conveying device 4 generally has a support frame 18 (see Figure 1 ), by which the conveying device 4 is fixed, for example, to the floor, and the supporting frame 18 is also configured to mechanically hold the conveyor belt 10. In the embodiment, only one conveyor belt 10 is shown. However, the conveying device 4 usually has a plurality of conveyor belts 10, which are arranged, for example, one above the other or even adjacent to each other. Typically, the respective conveyor belts 10 are arranged obliquely and convey the sheet 6 to a higher level. A stacking device for stacking individual sheets 6 is usually arranged after the conveyor belt 10.

[0069] Furthermore, a camera system 20 is assigned to the respective conveyor belt 10, which has at least one camera 22 and is formed in the exemplary embodiment by the camera 22. The camera 22 is positioned in front of the test area 12 and slightly above the conveyor belt 10 opposite to the longitudinal direction 8. The camera 22 is oriented toward the test area 12, i.e., the detection area of ​​the camera 22 is oriented toward the test area 12.

[0070] The camera 22 is typically preferably a CCD camera with a suitable CCD sensor with a suitable pixel density. The resolution of the camera 22 is sufficiently high. In particular, the resolution is in the millimeter range, i.e., two adjacent pixels in the recorded image I represent a real distance (of the test area 12) in the range of several millimeters, in particular in the range of 1-5 mm.

[0071] Typically, the transport device 4 has an illumination device 24 with at least one illumination element, by means of which at least one partial region, in particular the test region 12, is suitably illuminated. Figure 1 In the embodiment of FIG. 1 , several lighting elements are shown. The lighting of the test area 12 ensures that the image I recorded by the camera 22 (see, for example, Figure 4 ) is of sufficient quality for the provided image evaluation. Depending on the design of the marking 14, in particular when it is configured as a reflective element or a light-emitting element, the illumination also ensures good recognizability of the marking 14 in the recorded image I. For example, the illumination element is located in the region of the camera 22 and illuminates the marking 14 from there. However, it is preferred to use an active marking 14 with a light-emitting element, such as an LED, as the marking 14.

[0072] Due to the overlapping arrangement of the individual sheets 6 and the illumination, the front edge 26 of the individual sheets 6 can be well detected by the high light-dark contrast (in this respect, see in particular Figure 2 and Figure 4 ). Figure 2 It is also shown that the sheet 6 is grooved and / or cut in the longitudinal direction 8. In each case, this is indicated by two cutting lines 28 in the case of a single sheet 6. If a respective sheet 6 is completely cut, there are several individual sheets 6A, 6B, 6C, which are also generally referred to as plates. Unless otherwise stated, the following embodiments relate to a variant in which the respective sheet 6 has only grooves and is not subdivided into individual sheets 6A, 6B, 6C.

[0073] In the normal case, the sheet 6 is oriented in the longitudinal direction 8 , ie usually the cut line 28 and / or its edges are oriented parallel to the longitudinal direction 8 .

[0074] However, it may also happen that the individual sheets 6 are rotated from this set position when they are deposited on the conveyor belt 10 , as is shown in a simplified manner with the aid of one of the sheets 6 .

[0075] The corrugated board machine 2 usually consists of several parts. With the help of the corrugated board machine 2, a continuous corrugated board is first produced from a paper web, which is then cut to produce individual sheets 6. The structure and method of operation of such a corrugated board machine 2 are basically known and are usually as follows:

[0076] The paper web is unwound from the unwinding machine and fed to other downstream components of the corrugated board machine 2. For uninterrupted operation, for example, a so-called splicing machine is provided, with the help of which uninterrupted operation is possible even when the paper rolls are replaced.

[0077] Single-faced corrugated board webs are initially produced with the help of single-face machines (single-facers). One of the webs is corrugated with the help of corrugating rollers and then glued to a first cover web on one side. This is usually supplied to other machines for further processing via a so-called bridge, and a second cover web opposite the first cover web is usually glued to the fluting layer of the single-faced corrugated board web. For this purpose, it is usually first supplied to a so-called preheater. For gluing, a gluing unit is provided. In addition, heating devices, traction devices and other belt guides for guiding the webs and / or the produced corrugated board web are preferably provided in order to make quality and trouble-free operation possible. The part of the corrugated board plant up to the production of double-faced corrugated board is called the so-called wet end.

[0078] The dry end follows immediately. In this case, the previously produced continuous web of corrugated board is processed and cut. Usually, first a so-called short transverse cutter is provided, with the help of which, for example in the case of a format change, the so-called starter waste is removed. In addition, the dry end, in particular after the short transverse cutter, has an automatic cutting and slotting machine, which cuts or at least slots the corrugated board web in the longitudinal direction, thereby inserting a defined click area.

[0079] Finally, a so-called transverse cutter is arranged downstream, which cuts the corrugated board web in the transverse direction to produce individual sheets 6. Furthermore, a depositing system with the above-mentioned conveying device 4 is arranged downstream of the transverse cutter. A stacking device for stacking individual sheets 6 is usually arranged downstream of the conveying device 4.

[0080] The following special combination Figure 3 , Figure 4 and Figure 5 The special design of the corrugated board machine 2 and the method for monitoring the corrugated board machine are explained in more detail, in particular with regard to monitoring whether there are deviations from the planar position of the individual sheets 6:

[0081] according to Figure 3 , the camera 22 is connected to an evaluation unit 30, which in an embodiment is also connected to an equipment controller 32. The latter is arranged, for example, in a monitoring room 34, which is equipped with a plurality of monitors 36, which are part of a manual optical monitoring system 38. The image recorded by the camera 22 is displayed on one of the monitors 36, in particular as a real-time stream, so that an operator can visually monitor the equipment.

[0082] The machine controller 32 , which can also be divided into several control units, controls the operation of the corrugated board machine 2 , in particular also the operation of the conveying device 4 . Figure 3 The evaluation unit 30 shown separately in FIG. 1 can be part of the device controller.

[0083] In order to detect the warping, i.e. to assess whether the sheet 6 deviates from a flat position, the image I is continuously recorded by the camera 22 (see Figure 4 ). These are, for example, single images or streams.

[0084] The camera 22 records images at a suitable recording rate (refresh rate). For example, the recording rate is in the range of 30 to 60 frames per second (30 Hz-60 Hz). In principle, cameras with higher or lower recording rates can also be used.

[0085] The recorded image I, ie the corresponding electronic image data, is transmitted to an evaluation unit 30. The evaluation unit 30 is suitably arranged to perform automatic image evaluation and image processing. To this end, the evaluation unit 30 has at least one suitable processor and one or more suitable algorithms and a memory.

[0086] The process of image processing and image evaluation comprises in particular the following steps:

[0087] For example, in step a, a first image correction is performed, wherein the distortion caused by the camera lens is corrected.

[0088] In step b, the marking 14 is detected in the recorded image I and the test area 12 is determined.

[0089] In a further step c, a first evaluation is performed. For example, it is checked whether the test area 12 shown in the recorded image I is oriented according to a set orientation. If this is not the case, an image correction, such as a rotation or distortion of the recorded image I, is preferably performed.

[0090] Furthermore, the identified test area 12 is preferably extracted, for example by cutting the image I into the test area 12 identified in the image I.

[0091] Finally, in this step c, a correction of the vanishing point perspective is preferably performed. In this case, an image transformation is particularly performed such that the perspective view caused by the camera position is transformed into a top view.

[0092] The above steps a to c are preparatory steps for preparing images before the actual warpage inspection, which is performed in the following steps:

[0093] For example, in step d, the corresponding sheet 6 is usually first detected and identified. This is achieved, for example, by detecting the front edge 26 shown.

[0094] In a subsequent step e, edge detection is performed with the aid of a suitable algorithm, so that the contour of the front edge 26 in the recorded image I is identified and extracted. As an example, this is done in Figure 4 This is shown in FIG. 2 by means of a line in which the lower front edge 26 is represented by boldface, which line thus depicts the identified contour of the front edge 26 , thereby forming an extracted front edge 26 ′.

[0095] Figure 4 An image I processed according to steps a to c is generally shown, wherein also the extracted front edge 26 ′ is shown.

[0096] In a subsequent step f, an analysis and evaluation of the identified contour of the front edge 26 is performed again with the support of a suitable algorithm. To this end, in a first step, a mathematical approximation of the extracted front edge 26' is performed so that the contour of the front edge 26 is described by a mathematical function. The result of this mathematical approximation is Figure 5 The curve obtained by mathematical approximation is plotted on the y-axis around the zero position. The x-axis represents the extent of the front edge 26 in the transverse direction.

[0097] Based on this mathematical function, a function analysis is then performed to derive characteristic values ​​of the profile of the front edge 26. These characteristic values ​​are particularly maximum values, minimum values, distances between these maximum values ​​and minimum values, curvature values, (e.g., sliding) average values, and preferably also statistical characteristic values, such as (standard) deviations from the average value. One or more of these characteristic values ​​are used for analysis. For different characteristic values, set values ​​are predetermined. If these values ​​are exceeded, an inadmissible deviation from the plane position is detected, and a corresponding error message is output. Additionally or alternatively, the characteristic values ​​of the characterizing curve are output and / or stored, particularly also associated with the basic image I recorded respectively.

[0098] In addition to this recognition and evaluation of the plane position, during the automatic image evaluation, the sheet material 6 is preferably also simultaneously monitored for further features or errors based on the image I recorded with the camera 22:

[0099] For example, it is monitored whether the sheet 6 is oriented in its respective set orientation, i.e., generally parallel to the longitudinal direction 8. In each case, the front edge 26 generally extends perpendicularly to the longitudinal direction 8. To analyze the set orientation, the length of the front edge 26 in the image I is measured, for example by means of image evaluation. If this length is less than the set length, this indicates that the sheet 6 is twisted.

[0100] In the case where a plurality of individual sheets 6A, 6B, 6C are arranged adjacent to each other, automatic identification of the individual sheets 6A, 6B, 6C is preferably also provided. In addition, as described above in connection with the sheet 6, an analysis and evaluation of the profile of the leading edge 26 is performed individually for each individual sheet 6A, 6B, 6C to detect deviations from the planar position.

[0101] In order to identify the individual sheets 6A, 6B, 6C, the image evaluation preferably evaluates the recorded image I with respect to the cutting line 28 oriented in the longitudinal direction 8. This is again achieved by edge detection. Preferably, additional information is additionally used by the device controller 32, for example about the position of the cutting knife introduced into the cutting line 28 and / or about the width of the respective sheet 6 or individual sheets 6A, 6B, 6C. Based on this additional information, the evaluation is focused only on a limited image area, thereby reducing the computing effort and at the same time improving the quality of the evaluation.

[0102] Combination Figure 2 As a preferred improvement, but also as an independent invention, a housing 40 is formed in the region of the test area 12. In an embodiment, the housing 40 is U-shaped and has two side walls 42 and a top wall 44 connecting the two side walls 42 to each other. The housing 40 spans the entire width of the conveyor device 4 in the test area 12. In an embodiment, the length of the housing 40 in the longitudinal direction 8 corresponds to the length of the test area 12. On the inner side of the top wall 44, a lighting element 46 is arranged, which extends transversely through the conveyor belt 10. The lighting element 46 has, in particular, individual LEDs as individual light-emitting elements, which are arranged adjacent to each other in the transverse direction. Therefore, the lighting element 46 is an LED strip. The lighting element 46 is dimmable and is preferably also dimmed during operation according to the current lighting situation. In addition, in a preferred improvement, there is also the possibility of setting a color, which is preferably also appropriately selected during operation, so that the recognizability of the desired structure in the test area 12 is clearly displayed in the image of the camera. In particular, this improves the visibility of the front edge 26 and / or the marking 14. The lighting element 46 has individually controllable regions or segments, which are preferably arranged adjacent to each other in the lateral direction. In each case, these regions are in particular groups of individual LEDs.

[0103] By means of this design, the test area 12 is appropriately illuminated according to the current requirements and lighting conditions, wherein the intensity and / or color are appropriately set for this purpose. In the desired edge detection, this particularly achieves a better highlighting of the shadow projection of the front edge 26. The housing 40 protects the test area 12 from scattered light and other sources of interference incident from the outside and from contamination. The light cone emitted by the lighting element 46 is preferably directed obliquely in the downward direction, in particular, overall preferably in such a way that the shadow projection of the front edge 26 is highlighted as strongly as possible.

[0104] Reference numerals list

[0105]

Claims

1. A method for monitoring the planar position of a sheet (6) of corrugated cardboard in a corrugated cardboard machine (2), wherein: a) the sheets (6) are partially placed one above the other on a conveyor belt (10) extending in the longitudinal direction (8) so that the front edge (26) of the preceding sheet (6) rests on the succeeding sheet (6), b) a defined area of ​​the conveying device (4) of the corrugated board machine (2) is predetermined as a test area (12), c) providing at least one camera (22) with which an image (I) is recorded from the test area (12), characterized in that: d) when viewed in the longitudinal direction (8), the camera (22) is positioned in front of the test area (12) and is oriented obliquely in the direction of the test area (12) and thus obliquely on the front edge (26) of the sheet (6) located in the test area (12), e) analyzing, based on at least one of the recorded images (I), deviations of the contour of the front edge (26) from the planar position of the sheet (6) by means of automatic image evaluation.

2. The method according to the preceding claim, characterized in that In order to identify the front edge (26), edge extraction is performed and an extracted front edge (26') is obtained.

3. The method according to the preceding claim, characterized in that The profile of the extracted front edge (26') is evaluated based on the deviation from the planar position.

4. The method according to the preceding claim, characterized in that For evaluation, the extracted front edge (26') is approximated by curve fitting and the mathematical function contained therein is evaluated based on the deviation from the planar position.

5. The method according to any one of the preceding claims, characterized in that In particular, based on the evaluation of the front edge (26), the sheet (6) is checked for distortion.

6. The method according to any one of the preceding claims, characterized in that There is no need to measure the distance of the surface area of ​​the respective sheet (6) relative to the reference height.

7. The method according to any one of the preceding claims, characterized in that A marking (14) associated with the test area (12) is fixedly attached in the area of ​​the conveyor belt (10), wherein the marking (14) is also detected by the camera (22) so that it is included in the recorded image (I).

8. Method according to the preceding claim, characterized in that The position of the marking (14) in the recorded image (I) is evaluated and a check is made as to whether the test area (12) imaged in the recorded image (I) is oriented according to a predetermined set orientation.

9. The method according to any one of the preceding claims, characterized in that Since the camera (22) is arranged obliquely in front of the test area (12), the recorded image (I) has a vanishing point perspective, and a correction of the vanishing point perspective is automatically performed.

10. The method according to any one of the preceding claims, characterized in that A plurality of individual sheets (6A, 6B, 6C) are arranged side by side on the conveyor belt (10) and an automatic detection of the individual sheets is carried out, wherein for this purpose the longitudinal structure is preferably evaluated and in particular information from the device controller (32) is also used.

11. The method according to any one of the preceding claims, characterized in that A plurality of single sheets (6A, 6B, 6C) are arranged side by side on the conveyor belt (10), and each single sheet (6A, 6B, 6C) is checked for deviation from a planar position.

12. The method according to any one of the preceding claims, characterized in that The camera (22) is simultaneously used in an optical monitoring system (38) for optical manual monitoring by an operator.

13. The method according to any one of the preceding claims, characterized in that The camera (22) has a resolution in the millimeter range.

14. A corrugated board equipment (2), wherein - at least one conveying device (4) extending in the longitudinal direction (8) is arranged to convey a sheet (6) of corrugated board, wherein: During operation, the sheets (6) are partially placed one above the other on the conveyor belt (10) so that the leading edge (26) of the preceding sheet (6) rests on the succeeding sheet (6), - a defined area of ​​the conveying device (4) is predetermined as a test area (12), - at least one camera (22) is configured to record an image (I1) of the test area (12), characterized in that - when viewed in the longitudinal direction (8), the camera (22) is positioned in front of the test area (12) and is oriented obliquely in the direction of the test area (12) and thus obliquely on the front edge (26) of the sheet (6) located in the test area (12), The evaluation unit (26) is arranged to analyze the deviation of the contour of the front edge (26) from the planar position of the sheet (6) by means of automatic image evaluation based on at least one of the recorded images (I).

15. A corrugated board machine (2), in particular a corrugated board machine according to the preceding claim, wherein: - at least one conveying device (4) extending in the longitudinal direction (8) is arranged for conveying sheets (6) of corrugated cardboard, - a defined area of ​​the conveying device (4) is predetermined as a test area (12), - at least one camera (22) is configured to record an image (I1) of the test area (12), characterized in that - the camera (22) is aligned with the test area (12) for recording an image showing the test area, - wherein a housing (40) covering the transport device (4) is attached in the region of the test area (12), wherein a lighting element (46) is arranged which illuminates at least a part of the test area (12).

16. Corrugated board machine (2) according to the preceding claim, wherein one or more of the following features are realized a) the lighting element (46) is dimmable and / or the color of the light is adjustable, b) the light cone emitted by the lighting element (46) is oriented obliquely in the direction of the test area (12), c) the lighting element (46) is attached to the 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 attached and / or shielded such that the lighting element (46) is not visible to the camera (22) and / or the light emitted by the lighting element (46) is not radiated 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 region (12) and its length in the longitudinal direction (8) is particularly adapted to the length of the test region (12), for example in the range of 0.5 to 2 times the length of the test region (12), h) The lighting element (46) extends transversely to the longitudinal direction (8) and has a plurality of individually controllable areas, in particular a plurality of individual LEDs, which are preferably controllable individually or in groups.

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