Method for operating a corrugator, method for printing on a web, corrugator

Abstract

The invention relates to a method for operating a corrugator (2), wherein a corrugated cardboard web (4) is conveyed through the corrugator (2) in a conveying direction (F), wherein a first format (28) and a second format (30) following after the first format are printed on the corrugated cardboard web (4) one behind the other in the conveying direction (F), wherein each format (28, 30) has a plurality of printed images (34, 36, 38, 40, 42) of the same type which are located on the corrugated cardboard web (4) one behind the other in the conveying direction (F), wherein, for each printed image (34, 36, 38, 40, 42), there is a register mark (44, 46) on the corrugated cardboard web (4), wherein the register marks (44, 46) are detected by means of a sensor unit (48), wherein, on the basis of the register marks (44, 46), a cutting unit (18) is controlled such that the corrugated cardboard web (4) is divided into a plurality of pieces having one printed image (34, 36, 38, 40, 42) each, wherein the first format (28) has a normal portion (50) and an advance-warning portion (52) adjoining the normal portion (50), wherein a beginning of the advance-warning portion (52) is indicated by a variation of the register marks (44, 46), wherein, if a variation of the register marks (44, 46) is recognized, a format change is triggered after the advance-warning portion (52) of the first format (28) has passed, by means of which format change the corrugator (2) is set to process the second format (30). The invention also relates to a method for printing on a web (4, 6) and to a corrugator (2).

Description

[0001] Description

[0002] Method for operating a corrugated board plant, method for printing a web, corrugated board plant

[0003] The invention relates to a method for operating a corrugated board plant, a method for printing a web for use in such a process and a corrugated board plant.

[0004] A corrugator is used to produce corrugated board. Several paper webs, i.e., webs of paper, are fed into the corrugator. These paper webs are suitably processed and joined together to form a corrugated board web; each paper web then forms a layer of the corrugated board web. Depending on its design, the corrugated board web has one or more fluted layers, each of which is sandwiched between two non-fluted layers. The paper webs are joined to form the corrugated board web in the so-called wet end of the corrugator. The wet end is followed by the dry end of the corrugator, where the corrugated board web is cut lengthwise and crosswise and thus separated into individual sheets.

[0005] In principle, it is possible for at least one of the paper webs to already be printed or to be printed in the corrugator, before or after the paper webs are joined to form the corrugated board web. Such a paper web is also referred to as a pre-print because, unlike printing on the individual sheets after separation, printing takes place in advance, i.e. before any division. The printing covers, for example, a single format with a print image that repeats in the conveying direction (i.e. in the longitudinal direction of the paper web) and the corrugated board web is then divided so that each sheet contains one or more print images. Of particular interest are pre-prints that contain multiple formats, i.e. paper webs each with a different print image.Each format contains several similar print images, but now several formats with different print images arranged longitudinally one after the other are arranged together on a single paper web and thus also on the resulting corrugated board web. Such multi-formats typically arise when using a digital printer, which is not tied to a single printing form and thus a single print image, but can be easily and quickly converted to different print images, allowing a single paper web to be printed successively with a wide variety of formats as needed.

[0006] Each format corresponds to a separate print job, with its own processing requirements and, in particular, its cutting requirements in the corrugator. For such webs, a so-called format change is required at the beginning of a new format, i.e., a conversion of the corrugator from the previous format to the new one. The format change specifically concerns adjusting the cutting to the new format, as the sheets may now have different dimensions and require different cuts.

[0007] Reference is made to US 2019 / 0 193 368 A1 , EP 3 800 041 A1 , EP 3 352 981 B1 , EP 3 305 486 B1 and EP 3 800 041 A1 .

[0008] For example, EP 3 352 981 B1 describes that printed information markings in the form of QR codes contain information which can be used to identify which products are to be produced via a data lookup table. The required cutting settings for a cutting device can then be identified in advance so that it can be controlled appropriately. The QR codes are each unique for unambiguous identification, and a special visual inspection unit is used to detect and evaluate the QR codes. Against this background, one object of the invention is to improve a format change during operation of a corrugated board plant. In particular, an automatic format change should be possible without using a separately printed mark, e.g. a QR code. For this purpose, a correspondingly improved method for operating a corrugated board plant is to be specified.Furthermore, a method for printing a web for use in such a process and a corresponding corrugated board plant are to be specified.

[0009] The object is achieved according to the invention by a first method having the features according to claim 1, by a second method having the features according to claim 15 and by a corrugated cardboard plant having the features according to claim 16. The object is also achieved in particular by a web (paper web or corrugated cardboard web) which is printed according to the method according to claim 15. Advantageous embodiments, further developments and variants are the subject of the dependent claims. The statements regarding the first method also apply analogously to the second method, the corrugated cardboard plant and the web and vice versa. If steps for one of the methods are stated implicitly or explicitly below, advantageous embodiments for the corrugated cardboard plant result from the fact that it is designed to carry out one or more of these steps. For this purpose, the corrugated cardboard plant has in particular a correspondingly designed control unit.

[0010] The first method is used to operate a corrugated board plant. Within the process, a corrugated board web is conveyed through the corrugated board plant in a conveying direction. The conveying direction corresponds, in particular, to the longitudinal direction of the corrugated board web. The corrugated board web is assembled from several paper webs by the corrugated board plant. However, the details of this assembly are of secondary importance here. Each paper web is typically fed to the corrugated board plant as a paper roll.

[0011] A first (leading) format and a second, subsequent format are printed on the corrugated board web in the conveying direction. The formats are either printed within the corrugator using an integrated printer onto one of the paper webs before or after joining to form the corrugated board web, or pre-printed outside the corrugator using a separate printer, so that the paper roll fed into the corrugator is already printed. In either case, the formats are printed before the corrugated board web is cut in the dry end of the corrugator (pre-print).

[0012] Without limiting generality, the following assumes two formats, with the first format preceding and being processed before the second, and the second format following and being processed after the first. However, the explanations apply analogously to any number of formats arranged one after the other and processed sequentially on the corrugator. The explanations for the first format also apply analogously to all other formats.

[0013] A particular format comprises several similar print images arranged one after the other on the corrugated cardboard web in the conveying direction, in particular, printed on it. In particular, the format comprises no further print images apart from these similar print images. A particular format is therefore characterized by a print image that repeats in the longitudinal direction. The print images of the first format differ in particular from the print images of the second format (so-called "multi-order"), so that a format change is required to process the corrugated cardboard web, with which the processing is adapted to each new format.

[0014] A particular format corresponds in particular to a specific print job, according to which a specific print image is to be printed in a specific number. In this case, several different print jobs are carried out on a single corrugated board web, paper web or paper roll. This is also referred to as “multi order”, in contrast to “single order”, in which only a single print image is used. If necessary, several, optionally even different print images for different sheets are arranged next to one another, i.e. in the transverse direction perpendicular to the conveying direction. The corrugated board web is then additionally divided into individual blanks by a longitudinal cut along the conveying direction, which are then each further divided into individual sheets. If the print images arranged next to one another are of the same type, this is referred to as a “single lane”, if they are different, this is referred to as a “multiple lane”.

[0015] A registration mark is arranged on the corrugated cardboard web for each printed image, in particular printed, preferably at the beginning or end of a respective printed image or integrated into it. Each format thus has several registration marks, in particular exactly one registration mark for each printed image. The registration marks are detected by a sensor unit of the corrugator. The corrugated cardboard web is guided past the sensor unit and the sensor unit monitors the corrugated cardboard web at least in a predetermined partial area in which the registration marks are repeatedly arranged. In particular, the registration marks are always arranged at the same position in the transverse direction perpendicular to the conveying direction. The registration marks are arranged in the conveying direction within a respective format, in particular equidistant, namely at a distance which corresponds to a length of the printed image of the format.However, the distance typically varies from format to format due to the different print images. In addition to the registration marks, the corrugated board web optionally features a side strip for position control.

[0016] Based on the registration marks, a cutting unit of the corrugator is preferably controlled in such a way that the corrugated board web is cut into several pieces, each with a printed image, i.e. the corrugated board web is separated. This is also referred to as “cut-to-mark”, or CMC for short. The cutting unit is in particular a cross cutter which makes a cross-section, i.e. one perpendicular to the conveying direction. If necessary, the corrugated board web has already been cut into several blanks (also: partial webs) along the conveying direction using a longitudinal cutter. The cutting unit is controlled in such a way that as soon as a registration mark is detected by the sensor unit, the cutting unit is synchronized with the registration mark and is then activated accordingly to make a cut at the correct position. The registration marks therefore serve as triggers for the cutting unit.By using the registration marks, the cut is synchronized with the actual travel of the corrugated board web and is performed with particularly high precision and dimensional accuracy. In principle, the registration marks can also be used alternatively or additionally for a function other than the aforementioned control of the cutting unit, e.g., to control another part of the corrugated board line. Generally, the registration mark serves to implement a first function. In the following, without limiting the generality, it is assumed that the registration marks are used to control a cutting unit.

[0017] An important advantage of the invention is now in particular that the aforementioned registration marks can also be used to provide advance warning of an impending format change (second function), in order to be able to prepare for such a change in good time and then initiate it correctly. The registration marks therefore fulfil two functions: according to a first function, the registration marks are used to control the cutting unit in order to actually cut the corrugated cardboard web, and according to a second function, the registration marks are additionally used to indicate a format change and to initiate the necessary adjustments to the corrugator in good time. In connection with the first function, the registration marks are also referred to as cutting marks. This advantageously makes it possible to dispense with additional, separate marks such as QR codes for indicating a format change, and for this reason such codes are preferably not used here.

[0018] In particular to implement the second function mentioned, the first format has a normal section and a pre-warning section which adjoins the normal section, wherein the start of the pre-warning section (and in principle also the end of the normal section) is indicated by a variation in the registration marks. In principle, it is sufficient if only one registration mark is designed differently than the other registration marks. The differently designed registration mark then indicates the start of the pre-warning section. Another important aspect of the invention is in particular the use of the pre-warning section to indicate a format change in advance. If a variation in the registration marks is detected, a format change is initiated after the end of the pre-warning section of the first format, with which the corrugator is set to process the second format.By varying the registration marks, it is therefore known when a format change is due while the first format is being changed. As the expiration of the pre-warning section can be waited for, there is enough time to prepare for the format change; the length of the pre-warning section is suitably selected for this purpose. Accordingly, any idle length between two successive formats is drastically minimized or even eliminated entirely. The length of the pre-warning section, in particular, is known in advance, so that when the variation is detected, i.e. when the varied registration mark is detected, it is automatically known how much of the first format is still left (remaining run length) before the second format begins. The length of the pre-warning section is, for example, transferred to a control unit of the corrugator as a job parameter for the respective format or entered by an operator.Optionally, a print sample is taken at the beginning of printing a web with the formats, and the length of the pre-warning section is determined empirically based on this and then used subsequently. In combination with the web speed at which the corrugated board web is being conveyed, the remaining run length can also be represented as a remaining time. Similarly, in combination with the regularly known length of an individual print image, the remaining run length can also be represented as a remaining number of print images.

[0019] An advantage of the invention described here is that no additional mark is required to correctly initiate a format change; instead, an existing mark, namely the registration mark, is used. In a suitable embodiment, the same sensor unit then detects the presence of the registration marks for controlling the separating unit and also detects the variation of the registration marks to initiate the format change. The registration marks are detected in particular at only a single position along the conveying direction. Accordingly, advantageously, no additional sensor unit is required; instead, the registration marks themselves, i.e. their presence (for the first function) and their variation (for the second function) can be detected with one and the same sensor unit. In combination, this makes existing corrugated board lines particularly easy to convert because no additional hardware is required.To convert an existing corrugated board plant, it is only necessary to vary the registration marks within a format, in particular by suitable printing, in order to realize the described division into normal section and pre-warning section, and to adapt the operating software of the corrugated board plant in such a way that the variation is also recognized.

[0020] In general, the registration marks of the normal section are suitably designed according to a first registration mark type and at least the first registration mark of the pre-warning section is designed according to a second registration mark type. The first and second registration mark types differ from one another accordingly, so that a variation is formed. In the present case, it is not necessary for each printed image to be individually identified; rather, it is sufficient that a distinction can be made between two sections of the format, namely the normal section which runs first and the pre-warning section which runs next to it and is also an end section of the format. Accordingly, in a suitable embodiment, the individual printed images are not individualized using unique marks such as QR codes or barcodes.

[0021] A particularly preferred embodiment is one in which several and preferably all of the registration marks of the pre-warning section are designed according to the second registration mark type, i.e. the pre-warning section is not indicated merely by a single, varied registration mark, but generally by registration marks which differ from those of the normal section. In a suitable embodiment, all of the registration marks of the pre-warning section are designed in the same way and differ in particular from the registration marks of the normal section. This redundancy of variation ensures that the pre-warning section is recognized even if the detection of an individual registration mark fails, e.g. if the relevant section of the corrugated cardboard web was previously ejected. In this way, it is still possible to initiate the format change at least approximately in good time.

[0022] The variation of the registration marks is preferably a variation of at least one geometric feature of the registration marks. However, the variation is preferably not a variation of the color of the registration marks. The variation of a geometric feature has the advantage, particularly over the color variation, that the variation can be implemented using the existing sensor unit for detecting the registration marks.

[0023] Each registration mark is expediently designed as a so-called bar mark, which can be easily detected even with a simple contrast sensor. Accordingly, each registration mark then has several bars arranged one behind the other in the conveying direction. The bars can be of the same or different types. A bar mark is also much simpler in design than a QR mark or a barcode. The bars each have a width measured in the conveying direction and are - also measured in the conveying direction - spaced from each other by a distance (also referred to as a gap). The geometric feature that is now varied for the second function is suitably the width, the distance, a number of bars, an interchange (inversion) of bars and distances (i.e. position of bars and distances). A combination of several geometric features for the variation is also possible.

[0024] Preferably, the variation of the registration marks lies outside a tolerance for the implementation of the first function, so that the deviation due to the variation is measurable. However, despite the variation, the registration mark expediently retains a space requirement on the paper web. For example, the registration marks along the normal section have three bars, each with a width of 5 mm and a distance from each other of also 5 mm (abbreviated to [5] 5 [5] 5 [5]), and the tolerance for the implementation of the first function is 1 mm in the longitudinal direction. A suitable variation is then that one of the bars is changed by more than 1 mm. The registration marks on the pre-warning section, on the other hand, are now varied, for example, in that each registration mark now has only two bars, or in that the width of the two outermost of the three bars is now

[0025] 4 mm and the width of the middle bar is 7 mm, although the distances remain unchanged (short [4] 5 [7] 5 [4]). This means that one of the bars is varied by more than the tolerance. At the same time, a total space requirement of 25 mm results for both registration marks. If the tolerance is less than 1 mm, the width of the two outermost of the three bars can also be varied to 6 mm and the distances are reduced accordingly to 4 mm. The above values ​​and variations are only examples and in principle many different variants are possible and suitable.

[0026] In general, the variation of the registration marks is advantageously within an existing specification for use as crop marks. Furthermore, the registration marks are advantageously arranged in the same position as such crop marks, i.e., the position of the registration marks relative to the printed image is not varied.

[0027] Preferably, the registration marks have at least the same overall width despite the variation. The overall width is measured in the conveying direction. This simplifies the conversion of existing corrugated board systems, since a potentially restricted detection range of the sensor unit is not exceeded, and thus the existing sensor unit can continue to be used to implement the invention described here.

[0028] The length of the pre-warning section is selected to suit the specific order and the specific corrugator. In a suitable design, the pre-warning section contains several, at least 10 or at least 100, register marks, or is at least 150 m long. Longer pre-warning section lengths, e.g. 300 m or more, are also suitable. Depending on the specific design of the corrugator, the pre-warning section can, however, also have a completely different length. By detecting the variation, i.e. by detecting the first register mark which differs from the previous register marks of the format, the subsequent web run is advantageously compared with the previously known length of the pre-warning section in order to then initiate the format change at the right time.Instead of simply measuring the web path from the beginning of the format or counting the number of print images that have passed through, synchronization and, if necessary, correction are performed in this case, either alternatively or additionally, in order to initiate the format change as precisely as possible at the actual transition from the first to the second format. This synchronization and / or correction is therefore a preparation for the format change. Alternatively or additionally, the format change is prepared during the pre-warning phase by appropriately initializing one or more processing units, particularly separating units, of the corrugator.

[0029] As already described, the pre-warning section has a predetermined length. Preferably, upon detection of the variation, i.e., ideally at the beginning of the pre-warning section, a web sensor on the corrugator measures the length of the corrugated board web (i.e., web length). Upon reaching the predetermined length, the format change is initiated. The web sensor, e.g., an encoder, measures the length of the web from the detection of the first varied registration mark, thus counting down the known length of the pre-warning section. In this way, the format change is synchronized with the actual web path.

[0030] As already described, the length of the advance warning section and the web length can be measured as the actual length, e.g., in meters, in the number of print images, or as time. Accordingly, the specified length is specified in a suitable configuration as a number of print images (i.e., as the target number of pieces) or as a web length (i.e., as the remaining running meter, e.g., in meters).

[0031] Preferably, a format length is specified for each format, from which, in conjunction with a completed length of the corrugated cardboard web, a remaining running length of the format is determined. The completed length is measured, in particular, using the aforementioned web guide sensor. The completed length is preferably measured repeatedly or continuously. Upon detection of the variation, the remaining running length is then corrected based on the specified length of the pre-warning section, and the format change is initiated when the remaining running length expires. In short: the remaining running length is synchronized with the actual web run.

[0032] Preferably, the sensor unit is arranged directly upstream (i.e., upstream along the conveying direction) of the separating unit. Alternatively or additionally, the sensor unit is expediently arranged directly downstream of a paddle station for dividing the (already longitudinally divided) corrugated cardboard web into several different conveying paths. "Directly" is understood in particular to mean that no processing or dividing of the corrugated cardboard web takes place between the sensor unit and the separating unit or the paddle station. The sensor unit can, in principle, also be arranged at any other position, e.g., upstream of the paddle station or upstream of a gluing unit of the corrugating machine.

[0033] A particularly preferred embodiment is one in which the sensor unit for detecting the registration marks has a contrast sensor. A contrast sensor is particularly simple in terms of design and also with regard to detecting the registration marks, especially in comparison to image recognition, a camera-based vision system, a visual inspection unit, or the like. A contrast sensor has a measuring field in which only the brightness of the passing web is measured. Depending on the brightness, a corresponding sensor signal is then output. When there is a light / dark change or vice versa, a corresponding edge (ascending or descending) is generated in the sensor signal. By detecting the edges and determining their distance from one another, the width and distance of the bars of a bar mark and, in general, certain characteristic patterns in the sensor signal are determined based on the respective design of the registration marks.By comparing the determined patterns with the previously known, expected patterns of the registration marks, the presence and variation of the registration marks are then detected.

[0034] The second method is used to print a web (paper web or corrugated cardboard web) for use in the first method described above. In the second method, a first format and a subsequent second format are printed onto the web one after the other in the conveying direction, with each format having a plurality of identical print images arranged one after the other on the web in the conveying direction. In addition, a registration mark is arranged, in particular printed, on the web for each print image. The first format has a normal section and a pre-warning section which adjoins the normal section, with the start of the pre-warning section being indicated by a variation of the registration marks.

[0035] A corrugated board plant according to the invention is designed to carry out the first method as described above and preferably also to carry out the second method as described above. To carry out the second method, the corrugated board plant optionally has a printer with which the corrugated board web or a paper web is printed accordingly for this purpose. The corrugated board plant furthermore has a plurality of unwinders, optionally with an integrated splice unit, for receiving and unwinding the individual paper webs. Furthermore, the corrugated board plant has one or more single-facers and / or double-facers for corrugating one or more of the paper webs, and one or more gluing units for applying glue to one or more of the paper webs in order to subsequently join them together to form the corrugated board web.Furthermore, the corrugated board web comprises the aforementioned separation unit, in particular a cross cutter, as well as optionally further separation units, in particular a short cross cutter for removing rejects, a longitudinal cutter, and / or a cutting and creasing machine. For example, the corrugated board web is first passed through a short cross cutter, then through a cutting and creasing machine, and finally through a cross cutter. In particular, the corrugated board system also comprises a stacker for receiving the individual sheets. The stacker forms, in particular, one end of the corrugated board system.

[0036] In the following, exemplary embodiments of the invention are explained in more detail with reference to a drawing. In each case, the following schematically show:

[0037] Fig. 1 a corrugated board plant,

[0038] Fig. 2 a track,

[0039] Fig. 3 a variant of the track from Fig. 2,

[0040] Fig. 4 is a detailed view of a section of the track from Fig. 2,

[0041] Fig. 5 shows a registration mark of a first registration mark type,

[0042] Fig. 6 a registration mark of a second registration mark type,

[0043] Fig. 7 shows a variant of the second type of registration mark from Fig. 6.

[0044] Fig. 1 shows an exemplary embodiment of a corrugated board plant 2. During operation of the corrugated board plant 2, a corrugated board web 4 is conveyed through the corrugated board plant 2 in a conveying direction F. The conveying direction F corresponds to a longitudinal direction of the corrugated board web 4. The corrugated board web 4 is assembled from several paper webs 6 by the corrugated board plant 2. Each paper web 6 is fed to the corrugated board plant 2 as a paper roll. The corrugated board plant 2 optionally has a printer 8 with which the corrugated board web 4 or a paper web 6 is printed.

[0045] The corrugated board system 2 further comprises a plurality of unwinders 10, optionally with an integrated splice unit, for receiving and unwinding the individual paper webs 6. Furthermore, the corrugated board system 2 comprises one or more single facers 12 and / or double facers 14 for corrugating one or more of the paper webs 6, and one or more gluing units 16 for applying glue to one or more of the paper webs 6 in order to subsequently join them together to form the corrugated board web 4. Furthermore, the corrugated board web 2 shown here as an example comprises a separating unit, more precisely a cross cutter 18, as well as further separating units, namely a short cross cutter 20 for removing rejects, and a cutting and creasing machine 22. At the end, the corrugated board system 2 comprises a stacker 24 for receiving individual sheets 26.

[0046] Various embodiments of paper webs 6 are shown in Figs. 2 and 3. On such a paper web 6 and correspondingly on a corrugated board web 4 produced therefrom, a first (leading) format 28 and a second format 30 following this are printed one after the other in the conveying direction F. The formats 28, 30 are either printed within the corrugated board system 2 using a printer 8 integrated therein onto one of the paper webs 6 before or after joining to form the corrugated board web 4, or pre-printed outside the corrugated board system 2 using a separate printer, so that the paper roll 6, which is fed to the corrugated board system 2, is then already printed. In any case, printing with the formats 28, 30 takes place before the corrugated board web 4 is cut in the dry end 32 of the corrugated board system 2 (pre-print).

[0047] A respective format 28, 30 has a plurality of similar print images 34, 36, 38, 40, 42, which are printed one after the other on the corrugated cardboard web 4 in the conveying direction F. In the embodiment of Fig. 2, the respective format 28, 30 has no further print images apart from similar print images 34, 36, 38, in Fig.

[0048] 3, however, does. In each case, a respective format 28, 30 is characterized by a print image 34, 36, 38, 40, 42 recurring in the longitudinal direction, as can be seen in Figs. 2 and 3. As can also be seen in Figs. 2 and 3, the print images 34, 36, 38, 40, 42 of the first format 28 regularly differ from the print images 34, 36, 38, 40, 42 of the second format 30 (so-called "multi-order"), so that a format change is necessary for processing the corrugated cardboard web 4, with which the processing is adapted to a new format 28, 30. A respective format 28, 30 corresponds to a specific print order, according to which a specific print image 34, 36, 38, 40, 42 is to be printed in a specific number. Accordingly, several different print jobs are realized on a single corrugated board web 4, paper web 6, or paper roll. If necessary, as shown in Fig. 2 and 3, several, optionally even different, print images (see Fig.3), for different sheets also arranged next to each other, ie in the transverse direction Q perpendicular to the conveying direction F. The corrugated cardboard web 4 is then additionally divided into individual blanks by a longitudinal cut along the conveying direction F, which are then subsequently divided further into individual sheets 26. If the printed images 34, 36, 38, 40, 42 arranged next to each other are of the same type (Fig. 2), this is referred to as a "single lane"; if they are different (Fig. 3), this is referred to as a "multiple lane".

[0049] A registration mark 44, 46 is printed on the corrugated cardboard web 4 for each printed image 34, 36, 38, 40, 42. Fig. 4 shows a section of a first format 28 with registration marks 44 at the beginning or end of a respective printed image 34, 36, 38, 40, 42. Thus, each format 28, 30 has several registration marks 44, 46, in this case precisely one registration mark 44, 46 for each printed image 34, 36, 38, 40, 42. The registration marks 44, 46 are detected by a sensor unit 48 of the corrugator 2. The corrugated cardboard web 4 is guided past the sensor unit 48 and monitored by it. The registration marks 44, 46 are always arranged at the same position in the transverse direction Q. Embodiments of the registration marks 44, 46 are shown in Figs. 5, 6 and 7.

[0050] Based on the registration marks 44, 46, the cross cutter 18 is controlled in such a way that the corrugated cardboard web 4 is divided into several pieces, each with a printed image 34, 36, 38, 40, 42, i.e., the corrugated cardboard web 4 is separated. In this case, the corrugated cardboard web 4 has already been divided into several blanks (also: partial webs) along the conveying direction F by the cutting and creasing machine 22. The control of the cross cutter 18 is such that as soon as a registration mark 44, 46 is detected by the sensor unit 48, the cross cutter 18 is activated, if necessary with a predefined delay, to perform a cut. The registration marks 44, 46 therefore serve as triggers for the cross cutter 18.

[0051] In this case, the sensor unit 48 is arranged directly upstream of the cross cutter 18. No processing of the corrugated cardboard web 2 takes place between the sensor unit 48 and the cross cutter 18. The sensor unit 48 shown here has a contrast sensor (not explicitly shown) for detecting the registration marks 44, 46.

[0052] The aforementioned registration marks 44, 46 are also used here to provide advance warning of an impending format change in order to prepare for such a change in a timely manner and then initiate it correctly. The registration marks 44, 46 thus fulfill two functions: according to a first function, the registration marks 44, 46 control the cross cutter 18 to actually cut the corrugated board web 4. According to a second function, the registration marks 44, 46 are additionally used to indicate a format change and to initiate the necessary adjustments of the corrugator 2 in a timely manner. In connection with the first function, the registration marks 44, 46 are also referred to as cutting marks.

[0053] To implement the second function mentioned, the formats 28, 30 each have a normal section 50 and a pre-warning section 52 which adjoins the normal section 50, wherein the beginning of the pre-warning section 52 is indicated by a variation of the registration marks 44, 46. In this case, it is generally sufficient if only one registration mark 46 is designed differently than the other registration marks 44. The differently designed registration mark 46 then indicates the beginning of the pre-warning section 52. In general, the registration marks 44 of the normal section 50 are designed according to a first registration mark type, e.g. as shown in Fig. 5, and at least the first registration mark 46 of the pre-warning section 52 is designed according to a second registration mark type, e.g. as shown in Figs. 6 and 7. The first and second registration mark types 44, 46 differ from one another, so that a variation is formed.If a variation of the registration marks 44, 46 is detected, a format change is initiated after the pre-warning section 52 of the first format 28 has elapsed, with which the corrugator 2 is set to process the second format 30. By varying the registration marks 44, 46, it is thus known when a format change is to take place during the first format 28. The length X1 of the pre-warning section 52 is known in advance, so that upon detection of the variation, i.e. upon detection of the varied registration mark 46, it is automatically known how much length of the first format 28 still remains (remaining run length) before the second format 30 begins.

[0054] In this case, the same sensor unit 48 detects both the presence of the registration marks 44, 46 for controlling the cross cutter 18 and the variation of the registration marks 44, 46 for initiating the format change. The registration marks are detected at only a single position along the conveying direction F.

[0055] In one possible embodiment, several or all of the registration marks 46 of the pre-warning section 52 are designed according to the second registration mark type, i.e., the pre-warning section 52 is not merely indicated by a single, varied registration mark 46, but generally by registration marks 46 that differ from those of the normal section 44. In one possible embodiment, all of the registration marks 46 of the pre-warning section 52 are designed identically. This creates a redundancy of variation.

[0056] The variation of the registration marks 44, 46 in this case is a variation of at least one geometric feature of the registration marks 44, 46. The registration marks 44, 46 shown in Figs. 5, 6, and 7 are each designed as so-called bar marks, which can be easily detected with a contrast sensor. Each registration mark 44, 46 has several bars 54 arranged one behind the other in the conveying direction F, which bars can be of the same or different design. The bars 54 each have a width X2 measured in the conveying direction F and are each spaced apart from one another by a distance X3, also measured in the conveying direction F. The geometric feature that is now varied for the second function is, for example, the width X2, the distance X3, or a number of bars 54.

[0057] The variation of the registration marks 44, 46 lies outside a tolerance for the implementation of the first function, so that the deviation due to the variation is measurable. For example, the registration marks 44 along the normal section 50, as shown in Fig. 5, have three bars 54, each with a width X2 of 5 mm and a distance X3 from each other of also 5 mm. The registration marks 46 on the advance warning section 52, in contrast, are now varied in that, for example, as shown in Fig. 6, a respective registration mark 46 now has only two bars 54, or that, as shown in Fig. 7, the width X2 of the two outermost of the three bars 54 is now 6 mm and the distance X3 is correspondingly reduced to 4 mm. In general, the variation of the registration marks 44, 46 lies within an existing specification for use as cutting marks. In addition, the registration marks 44, 46 are arranged in the same position as such cutting marks, i.e.The position of the registration marks 44, 46 relative to the printed image 34, 36, 38, 40, 42 is not varied. In Figs. 5 and 7, the registration marks 44, 46 still have the same overall width X4 despite the variation. The overall width X4 is measured in the conveying direction F.

[0058] The length X1 of the pre-warning section 52 is selected depending on the specific order and the specific corrugator 2. For example, the pre-warning section 52 contains several, e.g., at least 10, registration marks 46 or is at least 150 m long.

[0059] With the detection of the variation, i.e., with the detection of the first registration mark 46, which differs from the preceding registration marks 44 of formats 28, 30, the subsequent web path is now compared with the previously known length X1 of the pre-warning section 52 in order to then initiate the format change at the correct time. Therefore, instead of simply measuring the web path from the beginning of format 28, 30 or counting the number of print images 34, 36, 38, 40, 42 that have passed through, synchronization and, if necessary, correction are carried out in this case as an alternative or in addition in order to initiate the format change precisely at the actual transition from the first format 28 to the second format 30.

[0060] In addition, upon detection of the variation, a web guide sensor 56 of the corrugator 2 measures the length of the corrugated board web 2 (i.e., web length), and upon reaching the specified length X1, the format change is initiated. Thus, with the web guide sensor 56, e.g., an encoder, the running web length is measured from the detection of the first varied registration mark 46, thus counting down the previously known length X1 of the prewarning section 52. In this way, the format change is synchronized with the actual web path.

[0061] The length X1 of the advance warning section 52 and the track length can be measured as actual length, e.g. in meters, in number of print images 34, 36, 38, 40, 42 or as time.

[0062] For each format 28, 30, a format length X5 is also specified, from which, in conjunction with a completed length of the corrugated cardboard web 2, a remaining run length of the format 28, 30 is determined. The completed length is measured using the aforementioned web guide sensor 56. Upon detection of the variation, the remaining run length is then corrected based on the specified length X1 of the pre-warning section 52, and the format change is initiated when the remaining run length expires. In short: the remaining run length is synchronized with the actual web run.

[0063] The variation of the registration marks 44, 46 is realized here in a method for printing the paper web 6 or the corrugated cardboard web 4. Accordingly, a first format 28 and a subsequent second format 30 are printed one after the other on the web 4, 6 in the conveying direction F, wherein a respective format 28, 30 has a plurality of identical printed images 34, 36, 38, 40, 42, which are arranged one after the other on the web 4, 6 in the conveying direction F, e.g. as shown in Figs. 2 and 3. In addition, a registration mark 44, 46 is printed on the web 4, 6 for each printed image 34, 36, 38, 40, 42. The first format 28 has a normal section 50 and a pre-warning section 52 which adjoins the normal section 50, wherein a beginning of the pre-warning section 52 is indicated by a variation of the registration marks 44, 46.

[0064] List of reference symbols

[0065] 2 corrugated board lines

[0066] 4 corrugated cardboard web

[0067] 6 Paper web

[0068] 8 printers

[0069] 10 dispensers

[0070] 12 single facers

[0071] 14 Double Facers

[0072] 16 Glue plant

[0073] 18 cross cutters (separating unit)

[0074] 20 short cross cutters

[0075] 22 Cutting and creasing machine

[0076] 24 filing

[0077] 26 sheets

[0078] 28 first format

[0079] 30 second format

[0080] 32 Dry End

[0081] 34 Print image

[0082] 36 Print image

[0083] 38 Print image

[0084] 40 Print image

[0085] 42 Print image

[0086] 44 Registration stamp (first registration stamp type, for standard section)

[0087] 46 Pass mark (second pass mark type, for advance warning section)

[0088] 48 Sensor unit

[0089] 50 normal section

[0090] 52 early warning section

[0091] 54 bars

[0092] 56 Web guide sensor

[0093] F Conveying direction

[0094] Q transverse direction

[0095] X1 Length (of the warning section) X2 Width (of a bar)

[0096] X3 Distance (between two bars)

[0097] X4 total width

[0098] X5 format length

Claims

Claims 1. Method for operating a corrugated cardboard plant (2), a. wherein a corrugated cardboard web (4) is conveyed through the corrugated cardboard plant (2) in a conveying direction (F), b. wherein a first format (28) and a subsequent, second format (30) are printed one after the other on the corrugated cardboard web (4) in the conveying direction (F), c. wherein a respective format (28, 30) has a plurality of identical printed images (34, 36, 38, 40, 42) which are arranged one after the other on the corrugated cardboard web (4) in the conveying direction (F), d. wherein a registration mark (44, 46) is arranged on the corrugated cardboard web (4) for each printed image (34, 36, 38, 40, 42), e. wherein the registration marks (44, 46) are detected with a sensor unit (48), f. wherein the first format (28) has a normal section (50) and a pre-warning section (52) which adjoins the normal section (50), g. wherein a start of the pre-warning section (52) is indicated by a variation of the registration marks (44, 46), h.wherein, if a variation of the registration marks (44, 46) is detected, after the expiration of the pre-warning section (52) of the first format (28), a format change is initiated, with which the corrugated board system (2) is set to process the second format (30).

2. The method according to claim 1, wherein the variation of the registration marks (44, 46) is a variation of at least one geometric feature of the registration marks (44, 46).

3. Method according to claim 2, wherein a respective registration mark (44, 46) has a plurality of bars (54) arranged one behind the other, which, measured in the conveying direction (F), each have a width (X2) and which are spaced apart from one another by a distance (X3) measured in the conveying direction (F), wherein the geometric feature is the width (X2) or the distance (X3) or a number of bars (54).

4. Method according to one of claims 1 to 3, wherein the registration marks (44) of the normal section (50) are formed according to a first registration mark type, wherein at least the first registration mark (46) of the pre-warning section (52) is formed according to a second registration mark type.

5. Method according to one of claims 1 to 4, wherein all registration marks (46) of the pre-warning section (52) are of the same design.

6. Method according to one of claims 1 to 5, wherein the registration marks (44, 46) despite the variation have at least the same total width (X4) measured in the conveying direction (F).

7. The method according to any one of claims 1 to 6, wherein the pre-warning section (52) contains a plurality of registration marks (44, 46).

8. Method according to one of claims 1 to 7, wherein the pre-warning section (52) has a predetermined length (X1), wherein upon detection of the variation with a web travel sensor (56) a length of the corrugated cardboard web (4) that has passed through is measured and upon reaching the predetermined length (X1), the format change is initiated.

9. The method according to claim 8, wherein the predetermined length (X1) is specified as a number of print images (34, 36, 38, 40, 42) or as a web length.

10. Method according to one of claims 1 to 9, wherein for each format (28, 30) a format length (X5) is predetermined, from which in conjunction with a run-through length of the corrugated cardboard web (4) a remaining running length of the format (28, 30) is determined, wherein upon detection of the variation the remaining running length is corrected on the basis of the predetermined length (X1) of the pre-warning section (52) and then the format change is initiated upon expiry of the remaining running length.

11. Method according to one of claims 1 to 10, wherein the same sensor unit (48) detects both a presence of the registration marks (44, 46) for controlling the separating unit (18) and detects the variation of the registration marks (44, 46) for initiating the format change.

12. Method according to one of claims 1 to 11, wherein a separating unit (18) is controlled by means of the registration marks (44, 46) in such a way that the corrugated cardboard web (4) is divided into several pieces, each with a printed image (34, 36, 38, 40, 42), 13. The method according to claim 12, wherein the sensor unit (48) is arranged immediately upstream of the separation unit (18).

14. Method according to one of claims 1 to 13, wherein the sensor unit (48) for detecting the registration marks (44, 46) has a contrast sensor.

15. A method for printing a web (4, 6) for use in a method according to one of claims 1 to 13, a. wherein a first format (28) and a subsequent second format (30) are printed one after the other on the web (4, 6) in the conveying direction (F), b. wherein a respective format (28, 30) has a plurality of identical printed images (34, 36, 38, 40, 42) which are arranged one behind the other on the web (4, 6) in the conveying direction (F), c. wherein a registration mark (44, 46) is arranged on the web (4, 6) for each printed image (34, 36, 38, 40, 42), d. wherein the first format (28, 30) has a normal section (50) and a pre-warning section (52) which adjoins the normal section (50), e. wherein a start of the pre-warning section (52) is indicated by a variation of the registration marks (44, 46).

16. Corrugated cardboard plant (2) which is designed to carry out a method according to one of claims 1 to 15.

Images