Method for monitoring a folding process in a buckling folding machine

Abstract

A method according to the invention for monitoring a folding process in a pocket folding machine is a method comprising the following steps: providing a pocket folding machine (1) with a first pocket folding unit (3) and at least one further downstream folding unit (9); providing a stream (21) of sheets (20) to be folded, each with a printed first control mark (M1), which enter the first pocket folding unit (3) in an infeed direction (R1); folding the sheets (20) in the first pocket folding unit (3), whereby at least one first fold (25) is produced; transporting the sheets (20) as a stream on a first path (4) from the first pocket folding unit (3) in a first direction (R2) parallel to the infeed direction (R1) up to a transport stop (13) arranged substantially perpendicular to the first direction (R1); striking the sheets (20) against the transport stop (13) and thereby changing the transport direction;The invention transports the sheets (20) as a stream on a second path (6) in a second direction (R3) substantially parallel to the transport stop (13); and is characterized by the following steps: providing at least one optical sensor (30) arranged on the second path (6), which has an optical detection area (32) with a spatial extent at least in one direction perpendicular to the transport stop (13), and operating it such that, for each sheet (20) or for at least one selected sheet (20), a distance (A1) of at least the respective first control mark (M1) from a reference line (L1) is detected as it passes the detection area (32). The invention advantageously enables the production of folding machines to be increased while simultaneously improving their quality through sensor monitoring. The invention is used in industrial folding machines.

Description

invention

[0001] The invention relates to a method for monitoring a folding process in a pocket folding machine with the features of the preamble of claim 1. field of technology

[0002] The invention lies in the technical field of the graphic industry and there in particular in the area of ​​folding flexible, sheet-shaped printing materials or the industrial, i.e. high-quality and high-productivity production of folded products such as brochures, preferably made of paper, cardboard, corrugated board, plastic or composite material, in particular of printed paper. State of the art

[0003] Industrial folding machines with preferably several folding units (folding stations) for producing folded products from sheet-shaped printed material, for example paper, and with conveying units for moving the folded products are known in the prior art. The folding units can be, for example, pocket folding units and / or blade folding units for producing preferably multiple folds. The conveying units can be, for example, roller tables with inclined conveying rollers. Such folding machines also typically include a feeder for the sheets to be folded and a delivery unit for the folded products. The sheets to be folded can preferably be conveyed to the first folding unit as a stream and particularly preferably as a shingled stream.

[0004] Such folding machines also include a machine control system in the form of a digital computer with control software. The machine control system may include sensors that monitor the folding quality.

[0005] DE3234148 discloses a device and a method for determining folding deviations. Sheets entering a folding unit are guided by a lateral transport stop. Several control marks are printed on the sheets to be folded. Two control marks on each transported sheet are simultaneously detected by two sensors after folding and processed computationally to generate control signals for a control device. A change in the direction of the transported sheets is not provided for.

[0006] US10046939B2 discloses a method in which a sheet printed with several control marks in the form of QR codes enters a pocket folding unit and is folded. A camera is provided for capturing the control marks. Information stored in the QR code can be read from the control mark. The position and angle of the control mark can also be recorded. If the angle deviation is too large, the machine's production can be stopped. A change in the direction of the transported sheets is not provided for in this method.

[0007] EP3705429A1 discloses a folding machine with a pocket folding unit, two downstream blade folding units, and a device for carrying out a method for detecting misfolds. The sheet transport direction changes after each blade folding unit. Each blade folding unit is assigned a transport stop. The sheets are provided with several printed control marks. At each transport stop, a sensor for detecting the arrival of the sheet's leading edge and two cameras for simultaneously detecting two control marks each are arranged; thus, a total of three detection units are arranged at each stop. Detecting the control marks therefore appears to be complex and expensive.

[0008] Beyond the well-known sensor-based quality monitoring measures, industrial environments face increasing demands for ever-faster production while maintaining, and ideally even improving, quality. Therefore, sensor-based quality monitoring must be further refined. Technical task

[0009] It is therefore an object of the present invention to provide an improvement over the prior art, which in particular makes it possible to increase the production of folding machines and to improve their quality by means of sensor monitoring. Inventive solution to the problem

[0010] This problem is solved according to the invention by a method according to claim 1.

[0011] Advantageous and therefore preferred embodiments of the invention are evident from the dependent claims as well as from the description and the drawings.

[0012] A method according to the invention for monitoring a folding process in a pocket folding machine is a method comprising the following steps: providing a pocket folding machine with a first pocket folding unit and at least one further downstream folding unit; providing a stream of sheets to be folded, each with a printed first control mark, entering the first pocket folding unit in an infeed direction; folding the sheets in the first pocket folding unit, whereby at least one first fold is produced; transporting the sheets as a stream along a first path from the first pocket folding unit in a first direction parallel to the infeed direction up to a transport stop arranged substantially perpendicular to the first direction; striking the sheets against the transport stop and thereby changing the transport direction;Transporting the sheets as a stream on a second path in a second direction essentially parallel to the transport stop, and characterized by the following further steps: providing at least one optical sensor arranged on the second path, which has an optical detection area with a spatial extent at least in one direction perpendicular to the transport stop, and operating it in such a way that, for each sheet or for at least one selected sheet, a distance of at least the respective first control mark from a reference line is detected when passing the detection area. Advantageous forms and effects of the invention

[0013] The invention advantageously enables the production of folding machines to be increased while improving their quality through sensor monitoring.

[0014] The invention can be advantageously used in the context of sensor-based automatic quality monitoring and the adjustment / correction of a folding machine based thereon. Further developments of the invention

[0015] Preferred embodiments of the invention (hereinafter referred to as embodiments) are described below. These can also be combined with one another, unless technically precluded.

[0016] A further development can be characterized by the reference line being parallel to the longitudinal orientation of the transport stop. A further development can be characterized by the reference line being parallel to the (sheet) stop edge of the transport stop. A further development can be characterized by the reference line being parallel to an edge of the sheet. A further development can be characterized by the reference line being parallel to a folded edge of the sheet, for example, in the case that the sheet edge does not reliably rest against the stop edge of the transport stop. A further development can be characterized by the reference line being parallel to the first fold. It is particularly preferred that the reference line lies parallel to the stop edge if it is technically ensured that the sheets reliably rest against this edge; otherwise, it lies parallel to the fold.In this context, "parallel to" also means "identical to".

[0017] A further development can be characterized by the fact that each sheet has at least one additional printed control mark. A further development can be characterized by the fact that each sheet has two additional printed control marks. A further development can be characterized by the fact that each sheet has a second printed control mark and a third printed control mark as the additional control marks. Three control marks are particularly preferred.

[0018] A further training method can be characterized by recording the distance of the first control mark from the reference line. A further training method can be characterized by recording the distance of the second control mark from the reference line. A further training method can be characterized by recording the distance of the third control mark from the reference line.

[0019] A further development process can be characterized by the fact that the measured distance is mathematically compared to a predetermined target distance to determine any deviation, and that a correction is made if the deviation is not zero. A further development process can be characterized by the fact that the (at least once folded) sheet has a fold length and a fold angle, which are determined by the position and orientation of the fold. A further development process can be characterized by the fact that the fold length and / or the fold angle are calculated based on the measured distances. A further development process can be characterized by the fact that the correction changes the fold length and / or the fold angle. A further development process can be characterized by the fact that the first pocket folding unit has at least one folding pocket with an adjustable folding stop.A further development can be characterized by the presence of at least one adjusting device, preferably a motorized one. A further development can be characterized by the fact that the folding stop is adjusted by means of the adjusting device to correct the folding. The adjustment (linear and / or angular) is preferably carried out by means of two adjusting devices. A further development can be characterized by the fact that the transport stop or a feeder transport stop for the sheets entering the first pocket folding unit is adjusted by means of the adjusting device to correct the folding. A further development can be characterized by the fact that the sensor is arranged on the transport stop and is adjusted together with the transport stop.

[0020] Further training can be characterized by the fact that if a deviation exceeds a first predetermined maximum deviation, the sheet is rejected. Further training can be characterized by the fact that if a deviation exceeds a second predetermined maximum deviation, production on the pocket folding machine is stopped.

[0021] A further development process can be characterized by the fact that the first control mark has an optically detectable first edge and that the distance of the first edge from the reference line is recorded. A further development process can be characterized by the fact that the first control mark has an optically detectable second edge and that the distance of the second edge from the reference line is recorded.

[0022] Further training can be characterized by the fact that the sheet has printed fold marks and that the first control mark is different from the fold marks.

[0023] Further training can be characterized by the fact that the first control mark and at least one further control mark are different from each other.

[0024] A further development can be characterized by the fact that the second control mark has an optically detectable first edge and that the distance of the first edge from the reference line is recorded. A further development can be characterized by the fact that the second control mark has an optically detectable second edge and that the distance of the second edge from the reference line is recorded. A further development can be characterized by the fact that the third control mark has an optically detectable first edge and that the distance of the first edge from the reference line is recorded. A further development can be characterized by the fact that the third control mark has an optically detectable second edge and that the distance of the second edge from the reference line is recorded.

[0025] A further development can be characterized by the fact that the first control mark is printed in a first position on the sheet. A further development can be characterized by the fact that the second control mark is printed in a second position on the sheet, which differs from the first position. A further development can be characterized by the fact that – within the sensor's detection range – the position of the second control mark follows the position of the first control mark in the transport direction of the sheet. A further development can be characterized by the fact that the third control mark is printed in a third position on the sheet, which differs from the first and second positions. A further development can be characterized by the fact that – within the sensor's detection range – the position of the third control mark follows the position of the second control mark in the transport direction of the sheet.

[0026] Further training can be characterized by the fact that the control marks are printed on the sheet in such a way that the first edges of the control marks lie on a straight line.

[0027] A further development can be characterized by the fact that the first and second control marks have different shapes. A further development can be characterized by the fact that the first and second control marks are rectangles of different widths. A further development can be characterized by the fact that the first and third control marks are rectangles of different widths. A further development can be characterized by the fact that the second and third control marks are rectangles of the same width. A further development can be characterized by the fact that the first and second control marks are rectangles of the same length. A further development can be characterized by the fact that the first and third control marks are rectangles of the same length.A further development can be characterized by the fact that the length of the respective rectangle is greater than its width and is measured parallel to the respective leading edge of the incoming arcs. A further development can be characterized by the fact that the width of the respective rectangle is measured parallel to a respective side edge of the incoming arcs. It can be advantageous to choose the width of the first control mark to be different from the width of the second and / or third control marks, since the first control mark can then be identified by its width and distinguished from the second and / or third control marks. In this way, it is possible to monitor when a new arc in the shingle stream passes the sensor: The first control mark is placed near the leading edge of the arc.the beginning of the arc; with each new arc in the shingle stream, a new first control mark passes the sensor; at least the second control mark can then be used together with the first control mark when detecting / measuring and correcting the position and orientation of the arc, and if necessary - and improving the measurement - also the third control mark; however, the third control mark may be obscured in the shingle stream; if the third control mark is not obscured and is placed near the trailing edge of the arc, then the passage of the arc end can be detected by it.

[0028] Further training can be characterized by the fact that the first edge and the second edge of the first control mark are detected by the sensor, that a computational check is performed based on this to determine whether the first control mark has been recognized as such, and that the second control mark and / or the third control mark are only detected in this case, and that the comparison for a deviation is only carried out in this case.

[0029] Further training can be characterized by the fact that the respective control marks are located within a printed control strip. Further training can also be characterized by the fact that the respective control marks are integrated into the control strip.

[0030] Further training can be characterized by the fact that the first control mark and at least one further control mark are detected by the sensor one after the other.

[0031] A further development can be characterized by the fact that the flow of sheets on the first path is conveyed on a first transport device. A further development can be characterized by the fact that the first transport device includes a roller table. A further development can be characterized by the fact that the flow of sheets on the second path is conveyed on a second transport device. A further development can be characterized by the fact that the first transport device includes a roller table. A further development can be characterized by the fact that the roller table includes transport rollers angled in such a way that the sheets are pressed against the transport stop during transport in the second direction.

[0032] A further development can be characterized by the sensor being provided as a line sensor with a one-dimensional arrangement, i.e., with a row, of sensor cells. A further development can be characterized by the row of sensor cells being oriented perpendicular to the reference line. A further development can be characterized by the sensor being provided as an area sensor with a two-dimensional arrangement, i.e., with a field, of sensor cells. A further development can be characterized by the sensor being provided as a camera. A further development can be characterized by the sensor being provided as a sensor pair, with a first sensor arranged above the second transport device and a second sensor arranged below the second transport device.Further training can be characterized by the fact that the first sensor and the second sensor are arranged offset from each other in the transport direction of the bow.

[0033] A further development can be characterized by the fact that the sheets have at least two additional control marks per additional folding unit. A further development can be characterized by the fact that the pocket folding machine has at least one additional sensor or pair of sensors per additional folding unit, each of which is arranged and operated in such a way that the distance of the respective additional control mark from an additional reference line is detected.

[0034] Further training can be characterized by the provision of a computer. Further training can be characterized by the computer being part of the machine control system of the pocket folding machine. Further training can be characterized by the computer being operated and connected to the positioning device in such a way that the computer transmits control values ​​to the positioning device for the purpose of carrying out the correction.

[0035] Further training can be characterized by the provision of a shingled stream of sheets to be folded.

[0036] The features and combinations of features disclosed in the above sections Technical Field, Invention and Further Developments, as well as in the following section Exemplary Embodiments, represent – ​​in any combination with each other – further advantageous developments of the invention. Exemplary embodiments of the invention and figures

[0037] The Figures 1 to 3Figures show a preferred embodiment of the invention and its further developments. Corresponding features are identified in the figures by the same reference numerals.

[0038] Figure 1Figure 1 shows a schematic top view of a preferred embodiment of a pocket folding machine during the execution of a preferred embodiment of the method according to the invention. The illustrated pocket folding machine 1 comprises a feeder 2 and a first pocket folding unit 3 with at least one folding pocket 3a and at least one adjustable folding stop 3b. Sheets 20, for example made of paper, are fed as a stream 21 and preferably in a shingled pattern from the feeder 2 along a feeder transport stop 15, which guides the sheets 20, to the pocket folding unit 3 in an infeed direction R1 and are folded there or provided with at least one first fold 25. The folded sheets 20 are then guided by a first transport device 5 along a first path 4 in a first direction R2 until the sheets 20, with their leading sheet edge 24 or the fold 14, abut a transport stop 13 with a stop edge 14 and are deflected by it.Bounce-off of the sheets 20 at the transport stop 13 is preferably prevented, for example by hold-down devices. The folded sheets 20 are then conveyed by a second transport device 7 along a second path 6 in a second direction R3, which is oriented essentially perpendicular to the first direction R2. The second transport device 7 can include a roller table 8 with transport rollers 8a. Optionally, as shown, a further folding unit 9 can be provided, which produces at least one further fold; alternatively, the folded sheets 20 can be laid out directly. The sheets 20, optionally folded a second time, can be conveyed in a further direction R4 until they strike an additional transport stop 16 and are deflected by it into a further direction R5, which is oriented essentially perpendicular to the further direction R4.Afterwards, the sheets 20, which are optionally folded a second time, are preferably laid out or alternatively processed further, for example folded again and finally laid out.

[0039] The pocket folding machine 1 preferably comprises several positioning devices 10, for example linear motors, for automatically adjusting the transport stop 13, the feeder transport stop 15, and the optionally present at least one additional transport stop 16, as well as the folding stop 3b (or several folding stops 3b in the case of multiple folding pockets 3a). The positioning devices 10 are preferably controlled by a computer 11, which is preferably part of the machine control 12. The transport stops 13, 15, and 16 are preferably adjustable linearly and angularly, so that the guided sheets 20 to be folded can be changed linearly in their lateral positioning relative to the respective transport directions R1 / R2, R3 / R4, and R5, and also in their angular positioning and thus in their folding angle 27. The folding stop 3b is preferably adjustable relative to the folding pocket 3a, so that the sheets 20 to be folded can be changed in their folding length 26.

[0040] The pocket folding machine 1 comprises at least one optical sensor 30, which preferably has a series of sensor cells 31 and an optical detection area 32. The series of sensor cells 31 is preferably oriented substantially perpendicular to the direction R3. The sensor 30 can also be configured as a sensor pair 33 with a first sensor 34 and a second sensor 35, as shown; preferably one of the two sensors is arranged above the roller table 8 and the other sensor below it (in the illustration of the Figure 1 (The sensor 34 is shown below the roller table 8 as an example). If an additional folding unit 9 and an additional transport stop 16 are optionally provided, an additional sensor 36 or an additional sensor pair 37 may also be provided.

[0041] In Figure 1It is evident that the sheets 20 to be processed are each provided with, for example, at least three pre-printed control marks: a first control mark M1 at a first position P1, a second control mark M2 at a second position P2, and a third control mark M3 at a third position P3. The control marks are preferably positioned relative to each other and thus separable by image processing. The respective control marks are shown, for example, as rectangles, preferably as filled rectangles, each having the same length. The width of control mark M1 can, for example, be greater than the widths of the other two control marks. The control marks are arranged on the sheets 20 such that, after folding in the first pocket folding unit 3, the control marks are located close to the first fold 25 created.Furthermore, the three control marks are preferably arranged such that - after the sheet 20 has left the pocket folding unit 3 - the first control mark M1 is positioned at the beginning of the sheet, the second control mark M2 at the middle of the sheet and the third control mark M3 at the end of the sheet.

[0042] During their transport towards R3, the control marks M1, M2, and M3 enter the optical detection range 32 of the optical sensor 30. If, after the first fold, the control marks come to rest on the underside of the folded sheets 20, they are detected by a sensor on the underside of the roller table 8, and vice versa. Since the control marks can end up on either the top or bottom of the folded sheets depending on the type of fold, it is advantageous to provide a sensor pair 33 with an upper and a lower sensor 34, 35.

[0043] Figure 2Figure 1 shows an illustration of an exemplary sheet to be folded twice, including control marks. The sheet 20 is shown as an example, with several printed images 22 and a print control strip 23. Control marks M1, M2, and M3 are positioned near the first fold line to be created, while additional control marks M4, M5, and M6 are positioned near a second fold line to be created, which runs perpendicular to the first fold line. As shown, the additional control marks can be located within the print control strip. Fold marks M' can also be arranged on the sheet 20 in the usual manner; the control marks are different from the fold marks and are provided in addition to them.

[0044] In Figure 1It is evident that the sensor cells 31 of the optical sensor 30 are arranged such that the control marks M1, M2, and M3 conveyed by the optical detection area 32 can be detected as such and / or that their respective edges can be detected. The measured values ​​can be transmitted to the computer 11 and processed by it in such a way that control variables for the actuating means 10 can be derived from them. The position of the control marks and / or their edges are measured relative to a reference line L1. The reference line L1 is preferably parallel to the transport stop 13 or its stop edge 14; alternatively, preferably parallel to the fold line. The reference line L1 can particularly preferably be identical to the stop edge 14.Optionally, the additional sensor 36 can be used to measure relative to an additional reference line L2, which is preferably parallel to the optional additional transport stop 16.

[0045] Figure 3 Figure 1 shows a section of a folded sheet with control marks. It is evident that, as the sheet 20 is transported along the stop edge 14, the control marks M1, M2, and M3 pass through the optical detection area 32 in the direction of R3, and their edges K1 to K6 and / or their respective lengths L1, L2, and L3 and / or their respective widths B1, B2, and B3 can be detected. In the illustration, according to the preferred embodiment, the widths B1 and B2 are, by way of example, equal; the lengths L1, L2, and L3 are also, by way of example, equal. In the illustration, according to the preferred embodiment, the edges K1, K2, and K3 lie, by way of example, on a straight line G.

[0046] The following distances relative to the specified reference line L1 can be measured using the sensor 30 (which, in the illustration, is shown as being parallel or identical to the arc edge; alternatively, it could be shown as being parallel or identical to the stop edge 14): distance A1 of the first control mark M1 or its first edge K1, distance A1' of the first control mark M1 or its second edge K2, distance A2 of the second control mark M2 or its first edge K3, distance A2' of the second control mark M2 or its second edge K4, distance A3 of the third control mark M3 or its first edge K5, and distance A3' of the third control mark M3 or its second edge K6.

[0047] The following distances can also be measured using the sensor 30: distance A4 of the sheet 20 to the stop edge 14 or to the reference line L1, distance A5 of the first mark M1 or its first edge K1 to the sheet edge (parallel to the stop edge 14), distance A6 of the first mark M1 or its second edge K2 to the printed image 22 and distance A7 of the printed image 22 to the stop edge 14 or to the reference line L1.

[0048] The measured distances can be compared with specified distances. These specified distances may be known from the prepress stage.

[0049] The measured values ​​transmitted to computer 11 are processed computationally. Control parameters for at least one of the control devices 10 are calculated. For example, the measured distance can be compared to a specified target distance to determine any deviation, and a correction can be made if the deviation is not zero. For correction, one or more control devices 20 are actuated accordingly. The folding stop 3b can be adjusted linearly or angularly by means of the control device 10; and / or the transport stop 13 and / or a feeder transport stop 15 for the sheets 20 entering the first pocket folding unit can be adjusted linearly or angularly. In this way, the fold length 26 and the fold angle 27 of the first fold 25 can be monitored and corrected if necessary.It can also be provided that the first edge K1 and the second edge K2 of the first control mark M1 are detected by the sensor 30, that a computational check is performed on this basis to determine whether the first control mark M1 has been recognized as such, and that the second control mark M2 and / or the third control mark M3 are only detected in this case, and that the comparison for a deviation is only carried out in this case. Reference symbol list

[0050] 1 Pocket folding machine 2 Feeder 3 First pocket folding unit 3a Folding pocket 3b Folding stop 4 First path 5 First transport device 6 Second path 7 Second transport device 8 Roller table 8a Transport rollers 9 Additional folding unit 10 Positioning device 11 Computer 12 Machine control 13 Transport stop 14 Stop edge 15 Feeder transport stop 16 Additional transport stop 20 Sheet 21 Flow of sheets 22 Printed image 23 Print control strip 24 Sheet edge 25 First fold 26 Fold length 27 Fold angle 30 Optical sensor 31 Sensor cells 32 Optical detection range 33 Sensor pair 34 First sensor 35 Second sensor 36 Additional sensor 37 Additional sensor pair R1 Inlet direction R2 First direction R3 Second direction R4 Further direction R5 Further direction L1 Reference line L2 Additional reference line M1 First control mark P1 First position M2 Second control mark / further control mark P2 Second position M3 Third control mark / further control mark P3 Third position M4 Additional control marks M'Fold mark(s) K1 First edge of the first control mark K2 Second edge of the first control mark K3 First edge of the second control mark K4 Second edge of the second control mark K5 First edge of the third control mark K6 Second edge of the third control mark G Straight A1 Distance of the first control mark / its first edge to the reference line A1' Distance of the first control mark / its second edge to the reference line A2 Distance of the second control mark / its first edge to the reference line A2' Distance of the second control mark / its second edge to the reference line A3 Distance of the third control mark / its first edge to the reference line A3' Distance of the third control mark / its second edge to the reference line A4 Distance of sheet to stop edge / reference line A5 Distance of mark to sheet edge A6 Distance of mark to printed image A7 Distance of printed image to stop edge / reference line B1 Width of first control mark B2 Width of second control mark B3 Width of third control mark L1 Length of first control mark L2 Length of second control mark L3 Length of third control mark

Claims

1. A method of monitoring a folding operation in a buckle folding machine, comprising the steps of: Provision of a buckle folding machine (1) with a first buckle folding unit (3) and at least one downstream, further folding unit (9); Provision of a stream (21) of sheets (20) to be folded entering the first buckle folding unit (3) in an infeed direction (R1) and each having a printed first control mark (M1); Folding the sheets (20) in the first buckle plate folding unit (3), wherein at least one first fold break (25) is produced in each case; Transporting the sheets (20) as a stream on a first path (4) from the first buckle folding unit (3) in a first direction (R2) parallel to the infeed direction (R1) up to a transport stop (13) arranged substantially perpendicular to the first direction; Striking of the sheets (20) against the transport stop (13) and thus change of transport direction; Transporting the sheets (20) as a stream on a second path (6) in a second direction (R3) substantially parallel to the transport stop (13); characterized by the next step: Provision of at least one optical sensor (30) arranged on the second path (6), which has an optical detection area (32) with a spatial extension at least in a direction perpendicular to the transport stop (13), and operation of the same in such a way that for each sheet (20) or for at least one selected sheet (20), a distance (A1) of at least the respective first control mark (M1) from a reference line (L1) is detected as it passes the detection area (32).

2. Method according to claim 1, characterized in that the reference line (L1) is parallel to the stop edge (14) of the transport stop (13).

3. Method according to claim 1 or 2, characterized in that the reference line (L1) is parallel to the first fold break (25).

4. Method according to one of the preceding claims, characterized in that the sheets (20) have a printed second control mark (M2) and a printed third control mark (M3).

5. Method according to claim 4, characterized in that the distance (A1) of the first control mark (M1) from the reference line (L1) is detected and / or that the distance (A2) of the second control mark (M2) from the reference line (L1) is detected and / or that the distance (A3) of the third control mark (M3) from the reference line (L1) is detected.

6. Method according to one of the preceding claims, characterized in that the respective distance detected (A1, A2, A3) is compared computationally with a predetermined target distance as an actual distance to determine a deviation between them, and that a correction is made if the deviation is not zero.

7. Method according to claim 6, characterized in that an adjusting means (10) is provided and that, for correction, a fold stop (3b) is adjusted by means of the adjusting means (10) and / or that, for correction, the transport stop (13) or a feeder transport stop (15) is adjusted for the sheet (20) entering the first buckle folding unit (3) by means of the adjusting means (10).

8. Method according to one of the preceding claims, characterized in that the first control mark (M1) has an optically detectable first edge (K1) and that the distance (A1) of the first edge (K1) from the reference line (L1) is detected.

9. Method according to claim 8, characterized in that that the first control mark (M1) has an optically detectable second edge (K2) and that the distance (A1') of the second edge (K2) from the reference line (L1) is detected.

10. Method according to one of the preceding claims, characterized in that the sheet (20) has printed folding marks (M') and in that the first control mark (M1) is different from the folding marks (M').

11. Method according to claim 4, characterized in that the control marks (M1, M2, M3) are printed on the sheet (20) in such a way that their respective first edges (K1, K3, K5) lie on a straight line (G).

12. Method according to claims 4 and 9, characterized in that the first edge (K1) and the second edge (K2) of the first control mark (M1) are detected by the sensor (30), in that a computational check is carried out on the basis of this to determine whether the first control mark (M1) has been recognized as such, and in that the second control mark (M2) and / or the third control mark (M3) are only detected in this case and in that the comparison for a deviation is only carried out in this case.

13. Method according to one of the preceding claims, characterized in that the sensor (30) is provided as a line sensor with a one-dimensional arrangement, i.e. with a row, of sensor cells (31) and in that the row of sensor cells (31) is aligned perpendicular to the reference line (L1).

14. Method according to one of the preceding claims, characterized in that the sensor (30) is provided as a camera.

15. Method according to one of the preceding claims, characterized in that the sensor (30) is provided as a sensor pair (33), a first sensor (34) being arranged above the second transport device (7) and a second sensor (35) being arranged below the second transport device (7).

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