Sheet processing machine

Abstract

The sheet converting machine (10) has an apparatus (44) for monitoring the sheets (12) and a transport mechanism (26) for moving the sheets (12) along a handle direction through the sheet converting machine (10). The apparatus (44) includes a light emitting element that forms a light barrier in the sheet path between the light emitting element and the light receiving element. A control unit (46) is connected to the light receiving element and is adapted to record each sheet (12) passing through the sheet path.

Description

[Technical field]

[0001] The present invention relates to a sheet processing machine having an apparatus for monitoring a sheet. [Background technology]

[0002] Sheet converters, also known as converters, are used in the packaging industry to convert raw materials, such as cardboard, paper, or foil, typically in the form of sheets, into intermediate or final products. The converting steps may include, for example, printing, cutting, folding, die-cutting, stamping, and / or fold-gluing. Typically, the individual steps are performed at successive stations of the sheet converter, with the sheets being transported from one station to the next by a transport mechanism. The sheets may be collected in a vertical stack after conversion in a designated stacking area of ​​the sheet converter.

[0003] Modern sheet converting machines allow a high throughput of sheets. However, not only the processing speed but also the quality of the processing process are relevant parameters in the packaging industry. For example, the punching process involves cutting incisions in the sheet by means of a punching tool, the incisions being formed in a previous processing step. If the punching tool is not aligned well and / or the incisions are not formed in a sufficiently accurate manner, the blank extruded from the sheet may have a distorted shape. Moreover, it is possible that the blank is not extruded from the sheet at all. Therefore, there is a need for a means to check the status of the process of the sheet converting machine.

[0004] WO 2018 / 175644 discloses a method for measuring sheet characteristics, such as dimensions, position or orientation, by means of a number of sheet sensors.

[0005] EP 2886498 A1 shows a sheet processing device with an inspection section for inspecting the sheets and a cutting section for cutting the sheets according to the result of the inspection of the sheets in the inspection section. The device may include a number of optical sensors and an array-shaped optical sensor. If the number of sheets detected in the detection section does not match the number of cut sheets, any obtained count value is assumed to be "abnormal" and processing is stopped.

[0006] In US2019 / 0144224, a sheet converting converter is configured to measure the forward position of a registration mark printed on a sheet, which is used to detect the alignment of the leading lateral edge. Furthermore, an additional "pre-correction sensor" is used to detect the passage of the leading lateral edge. The alignment information is then used to control an actuator module that moves the gripping elements of a gripping bar to find an optimal gripping position so that the placement error is corrected. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2018 / 175644 [Patent Document 2] European Patent Application Publication No. 2886498 [Patent Document 3] US Patent Application Publication No. 2019 / 0144224 Summary of the Invention [Problem to be solved by the invention]

[0008] SUMMARY OF THE PRESENT EMBODIMENT It is an object of the present invention to provide a means for monitoring sheets in a sheet converting machine. [Means for solving the problem]

[0009] The object of the present invention is solved by a sheet processing machine having an apparatus for monitoring sheets and a transport mechanism for conveying the sheets along a handling direction in the sheet processing machine. The apparatus comprises a light emitting element, which forms a light barrier in the sheet path between the light emitting element and the light receiving element. A control unit is connected to the light receiving element and is configured to record each sheet passing through the sheet path.

[0010] The invention is based on the idea that a sheet passing through the sheet path blocks or at least attenuates the light emitted by the light-emitting element, i.e. the sheet blocks or attenuates a barrier of light. This blocking or attenuation can be detected by the light-receiving element so that a control unit can record each sheet passing through the sheet path, making it possible to draw conclusions about the process of the sheet processing machine.

[0011] Preferably, the light barrier formed in the sheet path by the light emitting element and the light receiving element is a light curtain. For example, the light emitting element may comprise a plurality of individual light emitting sources and the light receiving element may comprise a plurality of light receiving sensors, each light receiving sensor being associated with one of the light emitting sources.

[0012] Depending on the number of light emitting sources and the number of light receiving sensors, the dimensions of the sheet path and the spacing between associated sets of light emitting sources and light receiving sensors, the light curtain may essentially become a continuous light curtain.

[0013] To increase the reliability of the device for monitoring the sheets, the light curtain may span at least 80% of the width of the sheet path, in particular at least 90% of the width of the sheet path. Preferably, the light curtain spans essentially the full width of the sheet path to ensure that a sheet cannot pass through the sheet path without being registered by the control unit. Furthermore, these variations allow using similar devices to monitor a wider size range of processed sheets.

[0014] In one variation, the light receiving element may be configured to measure light intensity.

[0015] In other words, the light receiving element can detect any attenuation of the light emitted by the light emitting element, i.e., the light receiving element can provide more nuanced information than just a YES / NO detection.

[0016] This variation is particularly useful where the sheet is at least partially transparent, for example based on the thickness of the sheet and / or the type of material of the sheet, such that light can pass through the sheet but is attenuated based on the transparency of the sheet.

[0017] In one variation, the light receiving and light emitting elements are mounted on a first rail and a second rail, respectively, which may define a path for the sheets, and which may further include at least one mounting point for incorporating a device for monitoring the sheets into an existing sheet processing machine.

[0018] The first and second rails may be parallel to one another to provide a simple configuration for aligning the light emitting and receiving elements, which is particularly advantageous when multiple light emitting sources and light receiving sensors must be carefully aligned.

[0019] The control unit in particular comprises a storage module for storing information about the sheet and / or the sheet processing machine.

[0020] For example, the expected number of sheets can be stored in a memory module of the control unit, the expected number being determined based on the number of sheets provided to and / or taken from a filling station of the sheet converting machine, In this variant, the control unit is adapted to compare the current number of sheets that have passed through the sheet path with the expected number of sheets.

[0021] In other words, a control unit may be provided at the filling station and adapted to verify that all sheets already taken from the filling station have respectively passed a device for monitoring the sheets.

[0022] The expected number of sheets can be an absolute number of sheets and / or per unit time, e.g., sheets per second. Hence, the value of the expected number of sheets can be selected to be the most appropriate for the type of sheet converting operation currently being performed by the sheet converting machine.

[0023] Additionally, the transparency of the sheet may be stored as information about the sheet in a storage module of the control unit.

[0024] If the light receiving element is capable of measuring light intensity, the transparency of the sheet can be used to determine if the light barrier is blocked or not based on a threshold. In other words, if the light intensity detected by the light receiving element is below the threshold but not zero, the control unit can still count this measurement as a blocked light transmission.

[0025] The threshold value may also be stored in a memory module of the control unit.

[0026] Furthermore, the target shape of the seat may be stored in a memory module of the control unit.

[0027] The target shape can be determined based on a reference sheet passing through the sheet path, which can be passed through the sheet path by an operator of the sheet processing machine before the actual sheet is processed, such that the signal sequence received by the control unit corresponds to the shape of the reference sheet, from which the target shape can be calculated by the control unit and stored in the storage module.

[0028] Similarly, the reference sheet may be automatically determined to be the last sheet scanned during setup of the sheet converting machine before starting each converting operation, and therefore, in this variant, it is not necessary for the reference sheet to be manually passed by the operator through the sheet path.

[0029] In a further variant, the information of the reference sheet may be provided in the form of a file, such as a PDF file, which is stored in a storage module of the control device. The file may be transmitted to the machine through a remote computer connected to the machine, such as a cloud computer. To perform the analysis from the shapes contained in the file, the control unit may determine for each reading of the light receiving element whether the light is completely blocked, partially blocked or not blocked by a sheet having the expected shape. By blocked it is meant that the sheet completely covers the sensor when the reading is performed, regardless of the transparency of the sheet.

[0030] In other words, as long as the necessary information to compare the target shape to the sheet is available to the control unit, there is no need to actually pass a reference sheet through the sheet path and take separate measurements to determine the target shape, again allowing the target shape to be essentially designed in advance without the need to actually produce a reference sheet.

[0031] The target shape may in particular include the target dimensions of the sheet and / or the target contour of the sheet. The target dimensions may in particular include the overall length, width and height of the sheet, while the target contour may in particular indicate the transition of the edges of the sheet. Furthermore, the contour may include surface information of the sheet, such as, for example, cutouts, incisions, perforations and / or creases.

[0032] Additionally, the target shape may include the transparency of the reference sheet, which allows setting a threshold based on the transparency of the reference sheet.

[0033] In order to provide the operator of the sheet processing machine with information about the current status of the sheet processing machine, the sheet processing machine may be equipped with a human-machine-interface connected to the control unit, such as, for example, a touch-sensitive display.

[0034] The control unit may be adapted to send a warning message to the human-machine interface of the sheet processing machine if the current number of sheets is lower than the expected number of sheets. Such a problem may occur if a sheet gets jammed in any processing station of the sheet processing machine and / or if the sheet processing machine does not operate at the intended processing speed. Thus, an operator may be informed by a warning message being displayed on the human-machine interface, so that the operator can intervene if necessary.

[0035] In particular, if there are no sheets in the filling station of the sheet processing machine, a warning message is sent to the human-machine interface. In this case, the warning message can also be an error message, which is displayed more prominently in the human-machine interface than the warning message. For example, the error message can block further operation of the sheet processing machine until it is clearly acknowledged by an operator of the sheet processing machine, for example by operator confirmation.

[0036] Similarly, the control unit may be adapted to send a warning message to the human-machine interface if the target shape of the at least one sheet does not correspond to the target shape. Thus, an operator may be informed by a warning message displayed on the human-machine interface that the at least one sheet was not obtained in the target shape, e.g. the sheet was damaged and / or at least one blank was not properly extruded from the sheet.

[0037] Further, the control unit can store a count of at least one sheet that does not match the target shape and can transmit this count to a human-machine interface to enable an operator to identify the at least one sheet that may be in error.

[0038] Furthermore, if a predetermined number of sheets are found not to conform to the target shape, an error message can be sent to the human-machine interface. The predetermined number can be set to indicate a faulty processing station of the sheet processing machine. An operator receiving the respective error message can therefore decide to stop operation of the sheet processing machine in order to minimize waste resulting from postponed use of the incorrectly operating sheet processing machine.

[0039] Operation of the sheet converting machine can also be automatically stopped when a stop criterion is detected by the control unit.

[0040] The stopping criterion may be a predetermined large deviation from the target shape, for example a deviation indicating that a blank that should not have been removed is no longer present in a predetermined position of the device for monitoring the sheet.

[0041] In such cases, the lost part is likely to be stuck inside the sheet converting machine, increasing the risk of damaging the sheet converting machine and leading to unwanted downtime. By stopping the machine based on the stop criteria, the risk of damage to the sheet converting machine is at least mitigated.

[0042] In other words, a device for monitoring sheets can serve not only as a security device, but also as a quality control device.

[0043] A device for monitoring the sheet may be disposed between the waste removal station and the blank separation station of the sheet processing machine, making it possible to verify whether the preformed blanks in the sheet have been properly prepared for obtaining the blanks in the blank separation station, e.g., whether any waste parts have been properly removed and whether the blanks are of the correct shape and / or position in the sheet.

[0044] The sheets are preferably made of paper, cardboard, foil or a composite thereof.

[0045] Further advantages and features will become apparent from the following description of the invention and from the accompanying drawings which show non-limiting exemplary embodiments of the invention. [Brief description of the drawings]

[0046] [Figure 1] 1 shows diagrammatically a sheet processing machine according to the invention; [Diagram 2] 2 is a schematic plan view of a sheet to be processed by the sheet processing machine of FIG. 1; [Diagram 3] 2 shows a perspective view of an apparatus for monitoring sheets in the sheet processing machine of FIG. 1; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0047] Figure 1 shows diagrammatically a sheet processing machine 10 making it possible to cut blanks 11 (see Figure 2) from a series of sheets 12. These blanks are usually intended to be subsequently folded and glued to form packaging boxes. However, the sheets 12 may also be made generally of, for example, paper, cardboard, foil, composites thereof or other materials routinely used in the packaging industry.

[0048] The sheet converting machine 10 comprises a series of processing stations juxtaposed but independent of one another to form a single assembly. The machine 10 comprises a filling station 14 followed by a cutting station 16 (also commonly referred to as a stamping station) including, for example, a die or platen press 18 where the sheet 12 is deformed by cutting, a waste removal station 20 where most of the waste material is removed, a blank separation station 22 (also commonly referred to as a receiving station) for separating (or stamping) the blanks 11 using a stamping tool 23, and a rejection station 24 for removing residual waste material 25 (see FIG. 2) of the stamped sheet 12.

[0049] The number and nature of the converting stations may vary depending on the nature and complexity of the converting process being performed on sheet 12 .

[0050] The sheet converting machine 10 also has a transport mechanism 26 , which in the embodiment shown is a conveyor, enabling each sheet 12 to be moved individually from the exit of the filling station 14 to a rejection station 24 .

[0051] The conveyor employs a series of gripper bars 28 movably mounted by two loops of chain 30, one located laterally on either side of the sheet converting machine 10. Each loop of chain 30 moves around a loop that allows the gripper bars 28 to follow a trajectory that passes successively through the cutting station 16, the waste removal station 20, the blank separation station 22 and the rejection station 24.

[0052] Each gripper bar 28 travels an outward path in the substantially horizontal plane of the path between the drive wheels 32 and the idler wheels 34, and then travels a return path over the top of the sheet converting machine 10. Upon returning to the drive wheels 32, each gripper bar 28 can then grasp a new sheet 12 at the leading edge of the sheet 12.

[0053] In FIG. 1, each processing station is shown in the form of two rectangles respectively representing the top and bottom of a processing machine located on either side of the plane of movement of sheet 12.

[0054] In FIG. 1, the lateral (or left-right), longitudinal and vertical directions are shown in an orthogonal spatial system (T,L,V).

[0055] The terms "upstream" and "downstream" are defined relative to the direction of movement of sheet 12 in the handle direction, as indicated by arrow D in FIG.

[0056] In FIG. 2, the current state and shape of a sheet 12 being processed by sheet converter 10 (see FIG. 1) is shown, with a plan view of sheet 12 arranged according to the successive stations of sheet converter 10 of FIG.

[0057] At the filling station 14, the sheet 12 is provided as a flat sheet having a rectangular or square surface.

[0058] At cutting station 16, the contour of blank 11 is prepared by forming lines of weakness 38 in sheet 12, such as by a series of cuts and / or perforations.

[0059] At waste removal station 20, selected portions of sheet 12 are cut out and ejected from sheet 12, as shown by the shaded areas in FIG.

[0060] Finally, the blanks 11 are separated from the sheet 12 at a blank separation station 22 and, in the embodiment shown, two cross-shaped blanks 11 with a central opening 42 are obtained from the sheet 12 .

[0061] The remainder of the sheet 12, ie, the residual waste sheet 25, is removed at a reject station 24.

[0062] Of course, the sequence shown in Figure 2 is merely exemplary in nature. Different shapes and sizes of sheets 12 and / or blanks 11 may be used and formed by the sheet converting machine 10, depending on the type of use of the sheets 12 and the converting stations provided by the sheet converting machine 10, respectively.

[0063] Returning to FIG. 1, the sheet converting machine 10 further includes an apparatus 44 for monitoring the sheet 12 being transported downstream by the transport mechanism 26 from the waste removal station 20 to the blank separation station 22 .

[0064] In principle, the device 44 can be placed between any two processing stations of the sheet processing machine 10, depending on which current condition of the sheet 12 is most important and / or most suitable for monitoring the correct operation of the sheet processing machine 10.

[0065] The devices 44 are connected to the control unit 46, for example by an Ethernet connection. However, the devices 44 can also be connected to the control unit 46 by any means that provides a sufficiently fast exchange of signals between the devices 44 and the control unit 46. For example, the connection can be established wirelessly, such as by Wi-Fi.

[0066] The control unit 46 comprises a memory module 48 in which the number of sheets 12 presented at the filling station 14 and the processing speed, i.e. the number of sheets 12 processed by the sheet processing machine 10 per second, are stored.

[0067] The control unit 46 is further connected to a human-machine interface 50, which in the embodiment shown is a touch-sensitive display. The human-machine interface 50 allows an operator (not shown) of the sheet converting machine 10 to be informed of the current status of the sheet converting machine 10 and also allows the operator to control the operation of the sheet converting machine 10.

[0068] In FIG. 3, a device 44 for monitoring the seat 12 is shown in a perspective view.

[0069] The device 44 comprises a first rail 52 and a second rail 54, the first rail 52 having integrated (i.e., not explicitly shown) light emitting elements and the second rail 54 having integrated (i.e., not explicitly shown) light receiving elements. The light emitting elements have multiple light emitting sources, in particular multiple laser emitting spots, while the light receiving elements have multiple light receiving sensors, each associated with one light emitting source. This configuration leads to an essentially continuous light curtain 56 between the first rail 52 and the second rail 54.

[0070] The first rail 52 is attached to a frame 58 of the blank separating station 22 by a number of attachment points 60 - only one of which is shown in FIG. 3 - such that the light curtain 56 is positioned within a sheet path 62 .

[0071] 3, the light curtain 56 spans most of the width of the sheet path 62 along the lateral direction T. The light curtain 56 in particular spans at least 80% or at least 90% of the width of the sheet path 62. In principle, the light curtain 56 could also span the entire width of the sheet path 62.

[0072] In the following, the mode of operation of the sheet converting machine 10 with respect to the apparatus 44 will be explained in more detail.

[0073] As explained above, the sheet converter 10 is used to convert a stack of sheets 12. More specifically, the sheet converter 10 is used to cut blanks 11 from the sheets 12.

[0074] The device 44 for monitoring the sheets 12 is used to provide feedback to determine whether the sheet converting machine 10 is operating correctly, i.e., whether all of the sheets 12 presented to the filling station 14 are converted and all of the produced blanks 11 are of the correct shape.

[0075] For this purpose, the filling station 14 is connected to the control unit 46, and is adapted to transmit to the control unit 46 the total number of sheets 12 provided in the filling station 14. The total number of sheets 12 can also be provided by an operator of the sheet processing machine 10 via a human-machine interface 50. The control unit 46 stores the total number of sheets 12 in a memory module 48.

[0076] Furthermore, before processing the sheet 12, the operator provides a reference sheet which passes through the sheet path 62. The reference sheet corresponds to the desired configuration of the sheet 12 after passing the waste removal station 20 and before entering the blank separation station 22 (see FIG. 3). In order to provide the reference sheet, the sheet processing machine 10 may have an additional (not shown) operator access in a processing station upstream of the device 44 for monitoring the sheet, i.e. in the waste removal station 20 in the embodiment shown.

[0077] The control unit 46 records the signal sequence received from the light receiving elements of the device 44 as the reference sheet passes through the sheet path 62 and stores the signal sequence in the memory module 48 for reference. Based on the signal sequence, the control unit 46 calculates the target dimensions and / or target contour of the sheet 12.

[0078] Additionally, the control unit 46 can store machine information for the sheet converting machine 10 in a memory module 48, such as the target processing speed for the sheet converting machine 10 in sheets per second. The machine information can also be set by an operator via a human-machine interface 50.

[0079] As soon as a processing operation for converting a sheet 12 begins, the control unit 46 records each sheet 12 passing through the apparatus 44, more specifically, through the sheet path 62. The recording involves counting the sheets 12 passing through the apparatus 44 to obtain a current number of sheets 12, and comparing the signal sequence provided by the photoreceptor elements of each passing sheet 12, which corresponds to the shape of each sheet 12, with a signal sequence stored in the memory module 48, i.e. a target shape.

[0080] Alternatively, the control unit 46 may use the reference file to calculate a reference signal sequence received from the light receiving elements of the device 44 as the sheet 12 passes through the sheet path 62. To do so, based on the target shape of the sheet 12, the control unit determines for each reading of the light receiving elements whether the light is completely blocked, partially blocked or not blocked at all by the sheet 12 having the correct shape. The transparency level, i.e., the light intensity detected by the light receiving elements when the light is completely blocked by the sheet, may be calculated from the average, median or any suitable statistical value of a set of readings that are completely blocked from the first sheet or from the first several sheets of a converting run.

[0081] Preferably, during the analysis with the reference file, the control unit may ignore the readings that are partially blocked by the sheet and use only the readings that are either completely blocked or not blocked at all. As an alternative, the control unit may decide to assign a target value for each reading of the individual light receiving element that depends on the proportion of light blocked by the sheet at its position and time. This target value may then be compared with the actual reading during the evaluation. This last alternative may preferably be used when the field of view of the light receiving element is larger than the waste (i.e. the part of the sheet that is rejected by the machine), thereby making it possible to control the quality despite a coarse arrangement of the light receiving elements.

[0082] The control unit 46 is adapted to calculate an expected number of sheets 12 based on the number of sheets 12 initially provided to the filling station 14 and the number of sheets 12 already taken from the filling station 14. To this end, the filling station 14 transmits to the control unit 46 the number of sheets 12 already taken from the filling station 14.

[0083] The control unit 46 essentially continuously compares the expected number of sheets 12 with the current number of sheets 12. If the current number of sheets 12 is less than the expected number of sheets 12, the control unit 46 sends a warning message to the human-machine interface 50 to inform the operator of the sheet converting machine 10 that there may be a problem with the operation of the sheet converting machine 10. For example, one of the sheets 12 may be stuck inside the waste removal station 20 instead of being delivered to the blank separation station 22.

[0084] If there are no more sheets 12 in the filling station 14 and the number of sheets 12 is still less than the expected number of sheets 12 , the control unit 46 can send an error message to the human-machine interface 50 .

[0085] The error message may be made more visually prominent than the warning message to ensure that the operator cannot ignore the discrepancy in the number of sheets 12.

[0086] Furthermore, if the control unit 46 asserts that the shape of at least one sheet 12 does not match the target shape stored in the memory module 48, the control unit 46 sends a warning message to the human-machine interface 50 to inform the operator that the blank 11 coming from the sheet 12 does not have the desired shape or has not been successfully extruded from the sheet 12 at all.

[0087] The control unit 46 is also capable of transmitting the current number of sheets 12, in this case, so that the operator can easily identify the blanks 11 in the resulting pile of blanks 11 produced by the sheet processing machine 10 and collected in the blank separation station 22.

[0088] Thus, the sheet converting machine 10 according to the present invention provides a simple and reliable device for monitoring the correct processing of the sheets 12 in the sheet converting machine 10. In this way, any unforeseen situation during the production of the blanks 11, such as damage to the blanks 11 or loss of the sheets 12, can be identified in order to ensure a high quality of the blanks 11 and to minimize the waste produced by the sheet converting machine 10 and its downtime.

Claims

1. 1. A sheet processing machine having a device (44) for monitoring a sheet (12) and a transport mechanism (26) for moving the sheet (12) within the sheet processing machine (10) along a handling direction, comprising: The device (44) a light emitting element and a light receiving element, the light receiving element being assigned to the light emitting element, the light emitting element and the light receiving element forming a light barrier in the sheet path (62) between the light emitting element and the light receiving element; a control unit (46) connected to the light receiving element and adapted to register each sheet (12) passing through the sheet path (62); the control unit (46) comprises a storage module (48) for storing information about the seat (12); the information includes a predetermined target shape of the sheet (12); The registration of each sheet includes comparing a signal sequence provided by the light receiving elements of each passing sheet (12) with the target shape of the sheet (12). A sheet processing machine characterized by:

2. 2. The sheet processing machine of claim 1, wherein the light barrier formed in the sheet path by the light emitting element and the light receiving element is a light curtain.

3. 3. The sheet processing machine of claim 1, wherein the light curtain (56) spans at least 80% of the width of the sheet path (62).

4. 2. The sheet processing machine of claim 1, wherein the light receiving element and the light emitting element are mounted on a first rail (52) and a second rail (54), respectively.

5. 5. The sheet converting machine of claim 4, wherein the first rail (52) and the second rail (54) are parallel to each other.

6. 2. The sheet processing machine of claim 1, wherein an expected number of sheets is stored in the memory module of the control unit, the expected number being determined based on the number of sheets provided in and / or taken from a filling station of the sheet processing machine, and the control unit is adapted to compare a current number of sheets that have passed through the sheet path with the expected number of sheets.

7. The sheet processing machine according to claim 1, wherein the target shape of the sheet (12) is determined based on a reference sheet that has passed through the sheet passage (62).

8. 2. The sheet converting machine of claim 1, wherein the target shape of the sheet is determined by the control unit based on a reference file transmitted to the sheet converting machine from a remote computer.

9. The sheet processing machine according to claim 7 or 8, wherein the target shape includes a target dimension of the sheet (12) and / or a target outer shape of the sheet (12).

10. 2. The sheet processing machine of claim 1, wherein the sheet processing machine (10) comprises a human-machine-interface (50) connected to the control unit (46).

11. 11. The sheet processing machine of claim 10, wherein the control unit is adapted to send a warning message to the human-machine interface of the sheet processing machine if the current number of sheets is less than the expected number of sheets or if there are no more sheets in the filling station.

12. 12. The sheet processing machine according to claim 10 or 11, wherein the control unit (46) is adapted to send a warning message to the human-machine-interface (50) if the target shape of at least one sheet (12) does not match the target shape.

13. 2. The sheet processing machine of claim 1, wherein the device for monitoring the sheet (12) is located between a waste removal station (20) and a blank separation station (22) of the sheet processing machine (10).

14. 2. A sheet converting machine according to claim 1, wherein the sheet (12) is made of paper, cardboard, foil or a composite thereof.

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