Calibration system and calibration method for a converting machine

Abstract

The invention relates to a calibration system (30) and a calibration method for a converting machine (20) having a die-cutting tool (18') and at least one transport unit (25) for conveying a web (1) through the converting machine in a transport direction (D) along a travel path. The calibration system comprises a first image sensor (33), a memory (36) and a control unit (34). The calibration system is configured to detect an actual position of a mark (42) on the web (1) and to compare it with a reference position of the mark (42) stored in the memory (36). When at least one of a longitudinal displacement (Δxi) and a transversal displacement (Δyi) of the mark exceeds a predetermined tolerance threshold (Txi, Tyi), a correction program stored in the memory is executed.

Description

Technical Field

[0001] This invention relates to a conversion machine suitable for producing folding boxes or flat packaging boxes. In particular, this invention relates to a calibration system for the conversion machine and a method for aligning printed images within the conversion machine. Background Technology

[0002] Folding boxes or flat packaging boxes can be produced in converting machines that include die-cutting machines. These types of machines print, fold, and cut sheet substrates of cardboard or paperboard. For sheet-feed machines, the sheet substrate initially enters the feeder module of the converting machine and then undergoes a series of operations at different workstations. Some types of converting machines are equipped with a rotary die-cutting machine with cutting edges for cutting the sheet.

[0003] However, sometimes it is possible to feed a sheet with a pre-printed image to the feeder module of the converter, instead of printing the sheet substrate in the converter.

[0004] Each sheet of material needs to be fed to ensure the image reaches the correct and constant position relative to the die-cutting machine. Variations in position result in the creases and cut lines not being placed at a consistent distance relative to the printed image, and the final box will not have the image in the same position.

[0005] In existing converters, the position of the sheet is controlled, not the position of the printed pattern. This control is called registration control. Registration is the alignment of the sheet within the converter and is related to the angular position of the rotating tools in different workstations. Registration control systems include optical detectors and use the leading edge of the sheet as a reference. When the converter itself performs the printing operation, this type of system typically provides acceptable cutting accuracy relative to the image.

[0006] For changeover machines that process pre-printed sheets, the position of the printed pattern on the sheet is unknown to the changeover machine because the registration control system has not yet determined the printing registration detection. This often results in inconsistent placement of the printed material on the finished box.

[0007] Registration can be set by adjusting the different workstations, for example, by adjusting the angular position of rotating tools such as printing cylinders and rotary dies. Document EP0615941 discloses an example of such an arrangement.

[0008] GB2491080 discloses a calibration device in which an image is taken from a reference mark, and in which calibration is performed directly on the processing tool to control the position of the tool on the substrate.

[0009] For other types of converters, such as those described in US2012 / 0194791, a continuous web substrate is supplied to the converter. As described in US2012 / 0194791, the timing angle position of the rotary tool is typically adjusted, rather than the position of the web.

[0010] Document EP3332927 discloses an apparatus suitable for detecting whether a reference mark is located on a crossbeam to determine the orientation of a sheet. Summary of the Invention

[0011] In view of the above problems, the object of the present invention is to ensure that the printed image is placed in substantially the same position on all boxes. This object is achieved by the converter according to claim 1 and the method according to claim 15.

[0012] According to a first aspect of the invention, a converter is provided, the converter including a rotary die-cutting tool and a plurality of individually controllable transfer drivers, each transfer driver being operatively connected to at least one transfer unit configured to transport sheet through the converter along a travel path in a transport direction, the converter further including a calibration system comprising:

[0013] An image sensor, configured to capture actual images of markings on a sheet passing through a converter.

[0014] The memory is configured to store the optimal location of a predetermined reference point in the storage markers, the optimal location including the x-coordinate and y-coordinate.

[0015] The control unit is configured to receive data from an image sensor and determine the abscissa and ordinate of a detected reference point in the marker, and to calculate the deviation of the position of the detected reference point relative to the position of a predetermined reference point, the deviation including longitudinal marker displacement and lateral marker displacement.

[0016] Furthermore, when at least one of the longitudinal mark displacement and the lateral mark displacement exceeds a predetermined tolerance threshold, the control unit is also configured to execute a correction program stored in the memory.

[0017] The converter's travel path extends from the feeder module to the rotary die-cutting tool. The longitudinal image displacement is in the sheet transport direction.

[0018] The detected reference point can correspond to the same position as a predetermined reference point in the markings. Both the detected and predetermined reference points have the same spatial longitudinal and lateral coordinates relative to the printed image on the sheet. However, the detected and predetermined reference points will not be in the same position relative to the converter and the predetermined coordinate system. The predetermined coordinate system can be defined by the image sensor.

[0019] The tolerance threshold can be a distance and can be defined in millimeters. In this embodiment, the longitudinal tolerance threshold can be set to "0". In this way, the correction procedure is set to the highest level of correction, since no longitudinal marker displacement is acceptable.

[0020] The predetermined reference point in the marker can be the theoretical centroid of the marker's two-dimensional shape. Therefore, the theoretical centroid can be the point located at the center of the two-dimensional marker.

[0021] The image sensor can be activated by detecting the leading edge using an optical detector, which may be separate from or integrated into the image sensor, and preferably located upstream of it. Alternatively, the trigger signal to activate the image sensor can be provided by a control unit. For example, the control unit can determine the activation time by obtaining the sheet position from the feeder module or by calculating the activation time based on operating parameters from the feeder module and / or the transfer unit.

[0022] An image sensor can be an optical sensor configured to measure the intensity of light reflected from a marker.

[0023] In one embodiment, if the lateral marker displacement exceeds a lateral tolerance threshold, the control unit is configured to issue an error signal. The error signal can be configured to activate the ejector module to eject the sheet.

[0024] In one embodiment, the operation of the feeder module is stopped when at least one sheet is detected to have a lateral mark displacement exceeding the lateral tolerance threshold.

[0025] In one embodiment, the calibration system further includes a feed sensor configured to detect the position of the leading edge of the sheet, and the control unit is further configured to calculate the feed alignment displacement by comparing the measured position of the leading edge with the optimal alignment position.

[0026] The control unit can be configured to calculate the feed alignment displacement by comparing the measured position of the leading edge with the optimal alignment position, and wherein the control unit is also configured to calculate an initial total longitudinal displacement corresponding to the sum of the longitudinal marking displacement and the feed alignment displacement.

[0027] In one embodiment, the calibration system includes a plurality of transmission sensors that are positioned along the transport direction on the travel path and configured to detect registration displacement.

[0028] The control unit can be configured to recalculate the total longitudinal displacement at each transmission sensor by adding additional registration displacement detected by the transmission sensors.

[0029] In an embodiment, if the initial total longitudinal displacement exceeds the longitudinal tolerance threshold, the operation of the transfer driver is adjusted, and the longitudinal position of the sheet is corrected by adjusting the speed of the transfer driver.

[0030] Each transfer driver is operatively connected to the first and second transfer units of the converter and is configured to uniformly control the operation of the first and second transfer units of the converter. The calibration system may also include a transfer sensor, which may be located at the second transfer unit in the transport direction. In this way, speed variations in the second transfer unit change the position of the sheet before it reaches the nearest downstream module (which may be a flexographic printing unit).

[0031] In one embodiment, if the initial total longitudinal displacement is below the maximum longitudinal correction limit, the control unit is configured to adjust only the operation of the transmission driver.

[0032] In an embodiment, if the initial total longitudinal displacement is higher than the maximum longitudinal correction limit, the correction procedure is configured to stop the feeder module and only restart the feeder module when the angular position of the rotary die-cutting tool is adjusted.

[0033] In one embodiment, the housing of the transmission unit includes a reference mark, preferably provided in the form of a line, extending along the transport direction of the converter, and the reference mark can be visually detected by an image sensor. In another embodiment, the reference mark may be located in a first transmission unit.

[0034] In one embodiment, the control unit is configured to calculate an initial correction, which is the sum of the longitudinal marker displacement and the feed fitting displacement, and wherein the control unit is further configured to calculate a plurality of fractional corrections such that the initial correction is equally distributed across the plurality of transmission units.

[0035] The calibration system is preferably connected to multiple individually controllable transmission drivers and is operatively connected to multiple transmission units.

[0036] In one embodiment, the calibration system includes a plurality of transmission sensors positioned along the transport direction on the travel path and configured to detect registration displacement, wherein each registration displacement detected by the transmission sensors is added to each subsequent fractional correction.

[0037] In an embodiment, the memory includes instructions for putting the control unit into a first operating mode and a second operating mode.

[0038] Furthermore, the control unit in the first operating mode is configured to deactivate the image sensor and provide correction only for each registration displacement detected by each transfer sensor, wherein each respective correction is performed only in each respective nearest downstream transfer located between the transfer sensor and the nearest downstream printing unit.

[0039] Furthermore, the control unit in the second operating mode is configured to activate the image sensor and provide multiple distributed fractional corrections.

[0040] The operating mode can be selected via the user interface. Fractional correction is not performed in the first operating mode. The control unit in the first operating mode is configured to provide instantaneous correction between registration displacement detection and the nearest downstream printing unit.

[0041] In an embodiment, the memory includes a transition memory and multiple data locations comprising multiple sheets present in the converter, and each data location includes location information of the sheet's location and a fractional correction required in the longitudinal direction.

[0042] According to a second aspect of the present invention, a method for calibrating a converter (20) is provided, the method comprising the following steps:

[0043] A) The sheet material is transported along the transport direction through the conversion machine.

[0044] B) Capture the actual image of the markings on the sheet.

[0045] C) Determine the x and y coordinates of the reference point being detected in the marker.

[0046] D) Obtain the x and y coordinates of the optimal position of the predetermined reference point from memory.

[0047] E) Calculate the deviation of the detected reference point's position from the optimal position of the predetermined reference point, including longitudinal and lateral mark displacements.

[0048] F) When at least one of the longitudinal mark displacement and the lateral mark displacement exceeds a predetermined tolerance threshold, the correction procedure is initiated.

[0049] In one embodiment, if the initial total longitudinal displacement exceeds the longitudinal tolerance threshold, the operation of the transmission driver is adjusted, and the position of the sheet is corrected by adjusting the speed of the transmission driver.

[0050] In an embodiment, the method further includes performing a step of selecting an operating mode between a first operating mode and a second operating mode before step A), wherein the method in the first operating mode does not include steps B) to F), and wherein the method includes the following steps:

[0051] -Printed sheets,

[0052] - The registration displacement is detected by multiple transmission sensors, and

[0053] - Correct each registration displacement between each individual transfer sensor and each nearest downstream printing unit.

[0054] Furthermore, the method in the second operating mode only includes all steps A) to F) defined in the method of the first aspect.

[0055] Therefore, in the first operating mode, each registration displacement is detected by a corresponding transfer sensor located a certain distance upstream of the printing unit, and the transfer unit located between the transfer sensor and the printing unit changes the position of the sheet by accelerating or decelerating the sheet's transport speed. The image sensor is preferably deactivated in the first mode. Attached Figure Description

[0056] Further advantages and features will become apparent from the following description and drawings of exemplary embodiments of the invention, wherein similar features are indicated by the same reference numerals, and wherein:

[0057] Figure 1a , 1b Figures 1c and 1d show plan and perspective views of the cardboard substrate and the box;

[0058] Figure 2 A cross-sectional schematic diagram of a rotary die-cutting machine according to the present invention is shown;

[0059] Figure 3 This is a schematic diagram of the calibration system according to the present invention:

[0060] Figure 4 A perspective schematic diagram of an exemplary rotary die-cutting machine apparatus is shown;

[0061] Figure 5 An example diagram of a transmission unit according to the present invention is shown;

[0062] Figure 6 A schematic diagram showing the displacement captured by this calibration system is presented; and

[0063] Figure 7a and 7b A schematic diagram of image capture for this calibration system is shown. Detailed Implementation

[0064] Figure 1a A sheet 1 made of cardboard or paperboard is shown, which is used to manufacture such as Figure 1d Box 1 is shown. Figure 1aAs shown, sheet 1 has a leading edge 6, a trailing edge 8, a first side edge 2, and a second side edge 4. Sheet 1 also includes a printed pattern or image 12.

[0065] Before the box 1” is assembled into a three-dimensional shape and has contents, it is usually provided as an intermediate blank 1', for example Figure 1b The flat packaging box 1' shown or as shown Figure 1c The folding box 1' shown is a flat packaging box 1', which is a sheet 1 that has been cut and folded, and is provided as a single layer. The folding box 1' is a flat box that is further folded and glued in a conversion machine.

[0066] In order to manufacture a flat packaging box 1' or a folding box 1', the sheet 1 undergoes a series of processing operations in a conversion machine, where the sheet 1 is cut and folded to form an intermediate blank 1'.

[0067] Figure 1b An example of an intermediate blank 1' obtainable from the conversion machine 20 according to the invention is shown. The intermediate blank 1' is typically provided with a first set of crease lines 13 and a second set of crease lines 14 transverse to the first set of crease lines 13. These crease lines 13, 14 may also be referred to as "fold lines" and allow the sheet 1 to be folded into a three-dimensional box 1". The intermediate blank 1' also has a cut 11 that forms the folded plate of the box 1".

[0068] For reference Figure 2 It shows a converter 20 according to the invention and its configuration for production. Figure 1b The intermediate blank 1'. As shown in the figure, the converter 20 includes a series of workstations in the form of a feeder module 23, a flexographic printing module 22 including one or more flexographic printing units 22a, 22b, 22c, 22d, and a rotary die-cutting module 26. The converter 20 may also include optional modules 27, such as a dryer module or an exhaust module.

[0069] like Figure 4 As shown, the rotary die-cutting module 26 includes a die-cutting roller 18 and an anvil 19, the anvil 19 being adapted to receive the sheet 1 in the gap therebetween. The rotary die-cutting module 26 is configured to cut and optionally fold the sheet 1.

[0070] The converter 20 also includes a main control unit (ECU) 21 and an operator interface or display 29. The main control unit (ECU) 21 is configured to control the overall operation of the converter 20, and the operator interface or display 29 is configured to display operable data and receive operator input.

[0071] The feeder module 23 is configured to receive a stack of cardboard sheets 1 and feed them one by one to the rotary die-cutting module 26 along the travel path P (extending in the transport direction D). The sheets 1 can be blank (i.e., unprinted) or have a pre-printed pattern 12.

[0072] The flexographic printing module 22 is arranged after the feeder module 23 and includes at least one flexographic printing unit 22a. Generally, multiple flexographic printing units 22a, 22b, 22c, 22d are provided to enable the printing process with inks of different colors.

[0073] The sheet 1 has a pre-printed image 12, such as decorations, patterns, branding, or company names related to the contents intended to be stored in the final box 1. The flexographic printing module 22 can be configured to print the sheet 1 at a preset position. However, if the sheet 1 has already been pre-printed when it is fed into the feeder module 23, the flexographic printing units 22a, 22b, 22c, and 22d in the converter 20 can be deactivated, leaving their printing cylinders idle and not in contact with the sheet 1. This can be achieved, for example, by deactivating and spacing the printing rolls and the opposing cylinders. In this way, the sheet 1 can pass through without contacting the printing cylinders.

[0074] When the converter 20 both prints the image 12 and cuts the sheet 1, the error is generally small. This is because the control system of the converter 20 is able to detect and calibrate the printing and cutting operations. The calibration and related settings between the printing and cutting operations can also be adjusted by the operator. Therefore, in this case, it may be easier to adjust the rotary die-cutting tool related to the printed image produced by the flexographic printing module 22 in the same machine, and it may be easier to ensure the alignment of the printed image 12 with respect to the rotary die-cutting tool.

[0075] The sheet 1 introduced into the feeder module 23 exhibits dimensional variations, and the sheet edges 2, 4; 6, 8 are not necessarily perpendicular to each other. These variations stem from the cutting process of the cardboard or paperboard sheet 1. In the standard process of producing cardboard sheet 1 in a corrugating machine, an outer pre-printed layer serves as an outer layer connection to form part of the cardboard. The continuous paper roll is then cut into individual sheets 1 in the corrugating machine. Consequently, deviations occur in the distance from the cut edge to the printed image, and the image 12 on the first sheet 1 is not necessarily located in the same position as the next sheet 1. Typically, the sheet 1 obtained in the corrugating machine has a longitudinal deviation of up to 4 mm or more.

[0076] In existing converters, the position where the rotary die-cutting tool should contact the sheet is defined by the position of the sheet's leading edge and is (if necessary) corrected by the converter's transfer driver. This is a typical method for calibrating alignment. Alignment is the alignment of the sheet within the converter and is related to the angular position of tools (e.g., rotary die-cutting tools) in different workstations of the converter.

[0077] Registration can be set by adjusting the positions of different workstations, such as adjusting the angle of rotating tools (printing cylinders and rotary die-cutting cylinders). Registration can be "correct / on target" or there can be registration displacement errors, which means misalignment between different operations.

[0078] Converters with rotary die-cutting modules operate at high speeds, sometimes with approximately 15 sheets moving simultaneously within the converter. In contrast, platen die-cutting machines carry only one sheet at a time. Therefore, the speed and number of sheets within a rotary die-cutting converter make it difficult to correct for registration errors for each sheet.

[0079] like Figure 2 and Figure 3 As shown, the converter 20 of the present invention has a calibration system 30. The calibration system 30 is configured to detect the position of the printed image 12 on each sheet 1 and enable the converter 20 to correct the position of each sheet 1 so that the image 12 on each sheet 1 reaches a constant position relative to the rotary die-cutting tool 18'. Therefore, the calibration system 30 is configured to detect the position of the pre-printed image 12, which exists on the sheet 1 already in the feeder module 26 of the converter 20.

[0080] like Figure 3 As shown, the calibration system 30 includes an optical sensing device 31, a calibration control unit or control unit 34, and a memory 36. The memory 36 includes at least one calibration program with instructions for adjusting the operation of the converter 20. The optical sensing device 31 includes a registration detection system 31a and an image detection system 31b.

[0081] like Figure 2 and Figure 5 As shown, the converter 20 has a transport system comprising a plurality of individually controllable transfer drives 24, each operatively connected to a transfer unit 25, the transfer unit 25 including a drive element 25', such as a roller 25' or a belt. The drive element 25' transports the sheet 1 forward along the travel path P in the transport direction D through the converter 20. Vacuum suction holes 25' are located around the rollers 25' and arranged to securely hold the sheet against the drive rollers 25'.

[0082] The transport unit 25 is a controllable conveying section that transports the sheet 1 in a controllable manner between different workstations, such as between the feeder module 23, flexographic printing units 22a, 22b, 22c, and 22d, and to the rotary die-cutting module 26. By adjusting the speed of the drive roller 25', the transport unit 25 can correct for displacement errors in the longitudinal direction, i.e., the primary transport direction D.

[0083] The conversion machine is typically used to produce a series of work batches of boxes 1” with different types in size and printed image 12. For a new work batch, if the size and configuration of the boxes change, the rotary die-cutting tooling needs to be changed. For each individual work batch, job specifications are provided that define the positions of the crease lines 13, 14 and the cut line 11 relative to the image or pattern 12. The specifications include theoretical distances defined from the edges 2, 4; 6, 8 of the ideal straight sheet, but are not typically defined relative to the edges of the actual sheet 1. Therefore, if the image 12 is not placed at a consistent distance from the edges 2, 4; 6, 8 of the sheet 1, the image 12 will not be placed in a consistent position on the finished flat package or folded box 1'.

[0084] After receiving the job specifications, the operator first changes the configuration of the die-cutting tool 18' on the die-cutting roller 18 to the converter 20, then adjusts the lateral position of the sheet 1 in the feeder module 23 and sets the longitudinal alignment.

[0085] like Figure 6 , 7a As shown in Figure 7b, the optical sensing device 31 is configured to determine the lateral image displacement Δyi and the longitudinal image displacement Δxi of the image 12 on the sheet 1 by detecting the displacement of the mark 42 on the sheet 1 in the lateral direction y and the longitudinal direction x. The lateral direction y and the longitudinal direction x are perpendicular to each other, and the longitudinal direction x overlaps with the transport direction D of the sheet 1.

[0086] Mark 42 is a reference mark positioned at a location with a predefined spatial relationship to the printed image 12. In other words, mark 42 is placed at a predefined distance from image 12 in both the lateral (y) and longitudinal (x) directions. Therefore, mark 42 is placed at predetermined coordinates from the printed image 12. For the pre-printed sheet 1, mark 42 is provided on the sheet 1, and preferably, mark 42 is printed together with and simultaneously with image 12. This ensures a fixed spatial correlation between mark 42 and image 12. Therefore, the determined lateral (Δyi) and longitudinal (Δxi) mark displacements of mark 42 are equal to the lateral (Δyi) and longitudinal (Δxi) displacements of the printed image 12.

[0087] Mark 42 is preferably placed in the edge of sheet 1 and outside the decorative pattern of image 12. Mark 42 can advantageously be located outside the outer edge of the box on sheet 1 so that it can be cut into pieces by rotating die-cutting module 26. Mark 42 is preferably placed near the leading edge 6 of sheet 1.

[0088] The total longitudinal displacement Δx of marker 42 overlaps with the transport direction D of sheet 1 via converter 20. Initially, the total longitudinal displacement Δx depends on the initial feed alignment displacement Δxr0 in feeder module 23 and the longitudinal marking displacement Δxi of marker 42 relative to the leading edge 6 of sheet 1. However, the longitudinal marking displacement Δxi of image 12 on the same sheet 1 is constant. However, as mentioned above, the longitudinal marking displacement Δxi varies between different sheets 1.

[0089] Therefore, the initial total longitudinal displacement Δx0 of the marker 42 in the feeder module 23 can be expressed as:

[0090] Δx0=Δxi+Δxr0

[0091] Then, the total longitudinal displacement Δx varies as the sheet 1 is transported along path P in the transport direction D. Therefore, each time the position of the leading edge 6 is detected by the transfer sensor 32, the subsequent total longitudinal displacement Δx can be obtained at each transfer sensor n. n The error detected by each transmission sensor 32 is different. This can be expressed by the following relationship:

[0092] Δx n =Δx0+Δxr n

[0093] Therefore, the total longitudinal displacement Δx at the nth transmission sensor 32 n It is the detected registration displacement Δxr n The sum of the initial total longitudinal displacement Δx0.

[0094] The lateral displacement Δy of the printed image 12 is an error, which is mainly due to the changes in the lateral sides 2 and 4 of the printed image 12 relative to the pre-printed sheet 1.

[0095] Lateral displacement Δy can also originate from incorrectly set side guides in the converter 20, but this is usually corrected by the machine operator. Therefore, it is primarily a static error, and not necessarily a dynamic error dependent on registration displacement error. When the lateral displacement Δy of the printed image 12 is caused solely by the displacement of the printed image 12 on the sheet 1, the following relationship applies:

[0096] Δy=Δyi

[0097] like Figure 2 and Figure 3As shown, the optical sensing device 31 includes a registration detection system 31a and an image detection system 31b. The image detection system 31b includes an image detection sensor 33 (also referred to herein as an image sensor) configured to capture an actual image Im1 of the mark 42 on the sheet 1 passing through the converter 20. The registration detection system 31a includes a feed sensor 32' and a series of downstream transfer sensors 32.

[0098] Information from sensors 32', 32, and 33 is integrated to continuously determine the total longitudinal displacement Δx and lateral displacement Δy of mark 42. Therefore, this optical sensing device 31 is configured to detect printing misalignment of the printed image 12 on the sheet 1 and registration displacement on the sheet 1 in the converter 20. Through the integration of these optical detection systems 31a and 31b, the position of mark 42 is continuously determinable as the sheet 1 passes through different workstations in the converter 20.

[0099] The image detection sensor 33 can be an optical sensor 33, such as a camera sensor 33. The image detection sensor 33 is configured to capture an actual image Im1 of the mark 42. The image detection sensor 33 is placed in a fixed position (i.e., at a reference position) and is preferably located at one end of the feeder transfer unit 25. This allows for early detection of mark displacements Δxi, Δyi. Therefore, corrections can be applied in the downstream transfer unit 25. This will be explained in more detail below. Optionally, the image detection sensor 33 is mounted on a guide rail and can be displaced to align with the mark 42. This is advantageous when the position of the mark 42 changes significantly, for example, between different sheet formats.

[0100] like Figure 6 As shown, the image detection sensor 33 is configured to capture an image Im1 of the portion of the sheet 1 where the mark 42 is located. The horizontal coordinate y1 and vertical coordinate x1 of the reference point P1 detected in the mark 42 can be determined from the image Im1 by the control unit 34, which is configured to receive data from the image sensor 33. Using the image recognition program stored in the memory 36, the control unit 34 can determine the horizontal coordinate y1 and vertical coordinate x1 of the reference point P1 detected in the mark 42.

[0101] The memory 36 is further configured to store the optimal position of a predetermined reference point P0 in the mark 42. The optimal position of the predetermined reference point P0 includes the horizontal coordinate y0 and the vertical coordinate x0. Reference points P0 and P1 are geometrically located at the same position in the mark 42, but will have different spatial coordinates. The optimal position of the predetermined reference point P0 can be determined from the reference image Im0. The reference image Im0 can be obtained through a machine learning process. For example, a first sheet 1 with mark 42 is typically input into the conversion machine 20. The image detection sensor 33 is activated and captures the image Im0 of the mark 42. The control unit 34 then calculates the optimal position of the reference point P0 in the mark 42, including the horizontal coordinate y0 and the vertical coordinate x0, and inputs the coordinates into the memory 36. This coordinate can be defined by the coordinate system of the image detection sensor 33. The angular position α of the rotary die-cutting tool 18' can then be selected based on the optimal position of the predetermined reference point P0. The reference image Im0 can be reset for different work batches or when the job specifications change. Therefore, the converter 20 is calibrated based on the optimal position of the reference image Im0 and the predetermined reference point P0.

[0102] An optical sensor (not shown) can be used to detect the passage of the leading edge 6 to activate the image detection sensor 33. Alternatively, the trigger signal to activate the image detection sensor 33 can be provided by the control unit 34. For example, the control unit 34 can determine the activation time by obtaining the sheet position from the feeder module 23 or by calculating the activation time based on operating parameters from the feeder module 23 and / or the transmission unit 25.

[0103] Through image processing, when the coordinates x1, y1 of the detected reference point P1 are compared with the coordinates x0, y0 of the predetermined reference point P0, the control unit 34 can determine the deviations, including the longitudinal marker displacement Δxi and the lateral marker displacement Δyi of the marker 42 on the captured image Im1. The advantage provided by the camera sensor 33 is that it does not require a specific geometry for the marker 42, because the system operates by comparing the coordinates x1, y1 of the actual reference point P1 in the image Im1 with the predefined reference ordinate x0 and lateral ordinate y0 of the reference position P0. Therefore, the following relationship applies:

[0104] Δxi=x1-x0

[0105] Δyi=y1-y0

[0106] Optionally, such as Figure 6As shown, the reference mark 35 can be disposed in the outer housing of the feeder transfer unit 25 and located within the field of view of the image detection sensor 33. The feeder transfer unit 25 is thus configured to firmly hold the sheet 1 while the reference mark 35 and the image Im1 are captured by the image detection sensor 33.

[0107] Reference marker 35 may be provided in the form of a line extending in the longitudinal direction (i.e., the transport direction D). Reference line 35 provides a physical and fixed reference for the captured image Im1. If displacement of the captured image Im1 occurs due to camera movement, reference marker 35 provides additional physical reference information to detect and correct camera capture / readout errors. For example, if the camera shifts due to vibration, it may cause capture errors.

[0108] like Figure 7a and 7b As shown, the reference point P1 and the predetermined reference point P0 detected in marker 42 can be the theoretical centroid of the shape. Therefore, the theoretical centroid can be the center point located in the two-dimensional marker 42.

[0109] The actual position of the marker 42 varies between different sheets 1. The control unit 34 is configured to calculate the longitudinal marker displacement Δxi and the lateral marker displacement Δyi between the actual position x1, y1 of the detected reference point P1 of each sheet 1 and the predetermined coordinates x0, y0 of the predetermined reference point P0.

[0110] Alternatively, a photodetector 33 can be used instead of the camera sensor 33. Such a photodetector 33 is configured to detect differences in the captured light. The photodetector 33 can emit light signals and capture return signals. In order for the optical sensing device 31 to be able to measure displacement in the lateral direction y and the longitudinal direction x, the sheet 1 can have two-dimensional optically readable markings 42.

[0111] To enable the photodetector to determine the lateral displacement Δy and the longitudinal displacement Δx, the mark 42 may include a body with a non-uniform shape having a varying longitudinal extension. Therefore, if the sheet 1 moves in the lateral direction, the thickness of the mark 42 changes. The thickness of the mark 42 is detectable by the photodetector 33, thus indicating the lateral position of the sheet 1.

[0112] Marker 42 may have an inclined trailing edge in the transport direction D. The trailing edge may have a constant slope k, which provides a functional relationship between the measured position in marker 42 and the lateral and longitudinal displacements.

[0113] like Figure 2 and Figure 6As shown, the registration detection system 31a includes a feed sensor 32', which is preferably an optical sensor and configured to detect the leading edge 6 of the sheet 1. Advantageously, the feed sensor 32' is placed at the transfer unit 25, close to the image detection sensor 33. In this way, the position of the detection mark 42 and the position of the leading edge 6 are used to determine the initial total longitudinal displacement Δx0 (which includes the feed registration displacement Δxr0 from the feeder module 23). The feed sensor 32' can be placed directly after the feeder module 23, for example, between the feeder module 23 and the first flexographic printing unit 22a.

[0114] However, for the undesirable registration displacement Δxr, registration error is frequent and depends not only on the initial settings on the converter 20 but also on any movement of the sheet 1 as it travels through the converter 20. Therefore, the registration displacement Δxr n The assessment is re-evaluated for each transmission sensor 32. For each detection from the transmission sensor 32, the registration displacement Δxrn can be re-estimated.

[0115] Therefore, the total longitudinal displacement Δxn reassessed (i.e. recalculated) at detection position n can be expressed as:

[0116] Δx n =(Δxr0+Δxi)+Δxr n

[0117] The detection position is the position of the transfer sensor 32. Therefore, it is advantageous to provide multiple n transfer sensors 32 for the registration detection system 31a, which are configured to detect the leading edge 6 of the sheet 1 at multiple positions. After the feed sensor 32', the multiple transfer sensors 32 are located downstream of the converter 20, close to the transfer unit 25, and are configured to detect the passage of the leading edge 6 in the transfer unit 25.

[0118] The feed sensor 32' can be located inside or behind the feeder module 23. The feed sensor 32' is preferably an optical detector, such as a photodetector (e.g., a high-speed unit), and is configured to detect the passage of the leading edge 6. The feed sensor 32' can be a sensor of the same type as the transfer sensor 32.

[0119] The feeder module 23 may advantageously include a general counter. The general counter may be included in the main control unit 21 or in the transfer driver 24 directly connected to the feeder module 23. The general counter is configured to calculate the theoretical transfer speed and determine which sheet 1 (multiple sheets are present simultaneously inside the machine) is detected each time the transfer sensor 32 detects the leading edge 6.

[0120] The memory 36 preferably includes a tolerance threshold Tyi for an acceptable lateral displacement Δyi of the marker 42. In this way, an acceptable displacement distance can be set for which the quality of "box 1" remains acceptable. Therefore, the threshold Tyi defines the acceptable lateral displacement Δyi that does not require correction.

[0121] The tolerance threshold Tyi can be selected by the operator on the operator interface 29. The required level of precision may vary depending on the type of box being produced. Typically, for high-end packages, higher precision is required than for some more basic boxes.

[0122] A threshold tolerance value Tyi can be set, for example, with an accuracy of 0.1 mm. If the actual marking displacement Δy is greater than the tolerance threshold value Tyi, the sheet 1 can be marked in the memory 36 for discarding or discharge. Optionally, the calibration procedure can be disabled for a specific sheet 1. In another embodiment, the calibration system 30 can automatically stop the feeder module 23 of the converter 20.

[0123] The initial total longitudinal displacement Δx0 can also have a threshold Txi. In some cases, the initial total longitudinal displacement Δx0 may exceed the maximum longitudinal correction limit Tx_max that the transmission driver 24 can correct. If the detected total longitudinal displacement Δx0 exceeds the maximum longitudinal correction limit Tx_max, the calibration system 30 can automatically stop the feeding of the machine 20.

[0124] When feeding is interrupted (and when the machine is empty), registration correction can be applied to the rotary die-cutting module 26. By adjusting the angular position α of the rotary die-cutting tool 18', the cutting edge of the rotary die-cutting tool 18' can be aligned with the image 12. Therefore, by adjusting the angular position α, a larger correction distance can be achieved in the longitudinal direction x. When the control unit 34 inputs the adjusted registration settings into the memory 36, feeding can be automatically restarted. Therefore, the calibration system 30 can automatically stop feeding, adjust the angle α of the rotary die-cutting roller, and resume feeding.

[0125] The control unit 34 is also configured to execute a correction program stored in the memory 36 when at least one of the longitudinal marker displacement Δxi and the lateral marker displacement Δyi exceeds a predetermined tolerance threshold Txi,Tyi. The program includes instructions for the transmission driver 24 so that the speed of at least one transmission unit 25 can be adjusted. Preferably, the speeds of multiple transmission units 25 are adjusted. The correction program can be initiated by the control unit 34 if the initial longitudinal displacement Δx0 is greater than the longitudinal tolerance threshold Txi and less than the maximum correction value Tx_max. The longitudinal tolerance threshold Txi can be set to "0", thereby setting the correction program to the highest level of correction.

[0126] Since multiple sheets 1 exist simultaneously in the converter 20, each sheet 1 is analyzed individually with respect to the longitudinal Δxi and lateral displacement Δyi of mark 42. Therefore, each transfer driver 24 is configured to implement different speeds by providing acceleration and deceleration to each sheet 1. The control unit 34 is also configured to determine which transfer unit 25 each corresponding sheet 1 contacts at a given time point. This is necessary to enable the provision of an appropriate displacement correction for each sheet 1, and this displacement correction is based on the specific displacement error Δx of each sheet 1.

[0127] The calibration system 30 is configured to correct the longitudinal mark displacement Δxi and the overlay displacement Δxr. Therefore, the initial correction Δc0 is provided by the calibration system 30 and is equal to the sum of the longitudinal mark displacement Δxi and the feed overlay displacement Δxr0. This can be expressed by the following relationship:

[0128] Δc0=Δxi+Δxr0

[0129] equals

[0130] Δc0=Δx0

[0131] Since the high speed of sheet 1 can be approximately 5 to 6 m / s, it is difficult to correct large displacement errors in a single step.

[0132] Because the converter 20 includes a series of independently controllable transfer drivers 24, a series of continuous longitudinal corrections can be performed via the transfer unit 25, located immediately preceding the first flexographic printing unit 22a or the second flexographic printing unit 22b, all the way to the rotary die-cutting module 26. This allows for distributed correction of each sheet 1, ensuring uniform transport of the sheet 1 through the converter 20 and avoiding sudden accelerations and decelerations. This allows for smooth transport of the sheet 1 throughout the converter 20.

[0133] Therefore, the calibration system 30 can calculate the fractional correction Δcf required for each transmission driver 24 by dividing the initial total longitudinal displacement Δx0 by the number N of transmission drivers 24 capable of being corrected. This can be expressed by the following relationship:

[0134]

[0135] Therefore, the initial feeder alignment displacement Δxr0 can be added to the marked displacement Δxi. This is advantageous because, in terms of the combination of the marked displacement Δxi and the alignment displacement Δxr, the maximum displacement typically occurs at feeder module 23.

[0136] Since there is a continuous registration displacement Δxr throughout the converter 20, each transmission sensor 32 can be configured to calculate the registration displacement Δxr. nThe new registration displacement Δxr n Preferably, it is added to the fractional correction Δcf and can be applied to the nearest downstream transmission unit 25. The actual correction applied to each transmission driver 24 can then be adapted to changes in the registration position that occur along the travel path P. This can be expressed by the following relationship:

[0137] Δcf1=Δcf+Δxr1

[0138] …

[0139] Δcf n =Δcf+Δxr n

[0140] The detection of the leading edge 6 can be sent to the transfer driver 24, which manages the speed of the transfer unit 25 in contact with the sheet 1. Alternatively, if the two transfer units 25 are configured as operably and mechanically connected portions, the same correction can be performed between them. The control unit 34 calculates the required correction Δcf for the sheet 1. n The required acceleration or deceleration of the transmission driver 24.

[0141] In order to correct the longitudinal position of the mark 42, the speed of at least one, preferably multiple, transmission drivers 24 is adjusted.

[0142] The presence of each sheet 1 can be determined by the registration detection system 31a. As previously mentioned, the registration detection system 31a, together with a general counter, can determine which transmission unit 25 is in contact with which sheet 1. This allows the calibration system 30 to apply specific corrections to each sheet 1.

[0143] The inventors also discovered that the calibration system 30 can have a first operating mode and a second operating mode. The operating mode selection can be entered on the operator interface 29.

[0144] The first operating mode can preferably correspond to a preset operating mode in which the flexographic printing module 22 of the converter 20 is activated and configured to print sheet 1. In the first operating mode, each registration displacement error Δxr detected by each transfer sensor 32 (and optionally also by the feed sensor 32') is corrected overall (or maximized) in each transfer unit 25 located between each corresponding transfer sensor 32, 32' and the nearest downstream printing unit. This results in the printed patterns from the flexographic printing units 22a to 22d being aligned with each other.

[0145] In the second operating mode, the flexographic printing module 22 is deactivated, and the calibration system 30 is therefore configured to use the entire distance through the flexographic printing module 22 as the correction distance. This allows for the correction of large longitudinal displacement errors that typically occur in the pre-printed sheet 1. As previously mentioned, these large longitudinal displacement errors correspond to the initial feed registration displacement Δxr0 and the longitudinal image displacement Δxi. In the second operating mode, the converter 20 can be configured only to cut the sheet 1.

[0146] Memory 36 may also include a rewritable transition memory 36, which includes a series of open locations for storing the longitudinal displacement Δxi, the lateral displacement Δyi, and the initial feeder alignment displacement Δxr0 for each sheet 1.

[0147] This allows the required fractional correction Δcf to be updated each time the position of the leading edge 6 is detected by the transmission sensor 32. n .

[0148] Lateral correction is required when the predetermined tolerance threshold Ty is exceeded. As mentioned earlier, the predetermined lateral tolerance threshold Ty can be set by the operator. A typical tolerance threshold Ty can be an error of 0.5–20 mm. When a lateral displacement Δy is detected to exceed the lateral threshold Ty, the control unit 34 can determine that sheet 1 is being discharged. The feeder module 23 is preferably stopped to avoid processing the erroneous sheet 1. Feeding can be stopped so that lateral correction can be applied to the die-cutting roller 18, preferably when the changeover 20 is empty. The feeder module 23 can automatically resume feeding after this correction.

[0149] Therefore, the calibration control unit 34 is configured to determine the lateral image displacement Δyi, the longitudinal image displacement Δxi, and the registration displacement Δxr, and further transmit the calculated corrections to the main control unit 21 to control the overall operation of the converter 20.

[0150] Using the current calibration system 30, the image detection system 31b only needs to determine the longitudinal displacement Δxi and lateral displacement Δyi of the mark 12 on the sheet 1 once. Afterward, the registration detection system 31a is able to identify the position of the mark 42 by continuously detecting the passage of the leading edge 6.

Claims

1. A converter (20) comprising a rotary die-cutting tool (18') and a plurality of individually controllable transfer drivers (24), each transfer driver being operatively connected to at least one transfer unit (25), the transfer unit (25) being configured to transport sheet (1) through the converter (20) along a travel path (P) in a transport direction (D), the converter (20) further comprising a calibration system (30) comprising: An image sensor (33) is configured to capture an actual image (Im1) of a mark (42) on a sheet passing through the converter (20). The memory (36) is configured to store the optimal position of a predetermined reference point (P0) in the marker (42), the optimal position including the horizontal coordinate (y0) and the vertical coordinate (x0). The control unit (34) is configured to receive data from the image sensor (33) and determine the abscissa (y1) and ordinate (x1) of the detected reference point (P1) in the marker (42), and calculate the deviation of the position of the detected reference point (P1) relative to the position of the predetermined reference point (P0), the deviation including longitudinal marker displacement (Δxi) and lateral marker displacement (Δyi). Wherein, when at least one of the longitudinal marker displacement (Δxi) and the lateral marker displacement (Δyi) exceeds a predetermined tolerance threshold (Txi, Tyi), the control unit (34) is further configured to execute a correction program stored in the memory (36). The calibration system (30) further includes a feed sensor (32') configured to detect the position of the leading edge (6) of the sheet (1), and the control unit (34) is further configured to calculate the feed alignment displacement (Δxr0) by comparing the measured position of the leading edge (6) with the optimal alignment position, and the control unit (34) is further configured to calculate an initial total longitudinal displacement (Δx0) corresponding to the sum of the longitudinal marking displacement (Δxi) and the feed alignment displacement (Δxr0). The control unit (34) is configured to calculate an initial correction (Δc0), which is the sum of the longitudinal marking displacement (Δxi) and the feed alignment displacement (Δxr0), and the control unit is further configured to calculate multiple fractional corrections (Δcf) such that the initial correction (Δc0) is equally distributed across the multiple transmission units (25). Wherein, the fractional correction (Δcf) corresponds to the initial total longitudinal displacement ( x0) divided by the number N of the transmission drivers (24) capable of performing the correction.

2. The converter according to the preceding claims, characterized in that, If the lateral marker displacement (Δyi) exceeds the lateral tolerance threshold (Tyi), the control unit (34) is configured to issue an error signal.

3. The converter according to claim 2, characterized in that, If the lateral marker displacement (Δyi) exceeds the lateral tolerance threshold (Tyi), the error signal is configured to activate the ejector module (27) to eject the sheet (1).

4. The converter according to claim 2 or 3, characterized in that, When at least one sheet (1) is detected to have a lateral marker displacement (Δyi) exceeding the lateral tolerance threshold (Tyi), the operation of the feeder module (23) is stopped.

5. The converter according to claim 1, characterized in that, The calibration system (30) also includes a plurality of (n) transmission sensors (32) which are set along the travel path (P) in the transport direction (D) and configured to detect registration displacement (Δxr).

6. The converter according to claim 5, characterized in that, If the initial total longitudinal displacement (Δx0) exceeds the longitudinal tolerance threshold (Txi), the operation of the transmission driver (24) is adjusted, and the longitudinal position of the sheet (1) is corrected by adjusting the speed of the transmission unit (25).

7. The converter according to claim 6, characterized in that, If the initial total longitudinal displacement (Δx0) is lower than the maximum longitudinal correction limit (Tx_max), the control unit (34) is configured to adjust only the operation of the transmission driver (24).

8. The converter according to claim 7, characterized in that, If the initial total longitudinal displacement (Δx0) is higher than the maximum longitudinal correction limit (Tx_max), the correction procedure is configured to abort the feeder module (23) and only restart the feeder module (23) when the angular position (α) of the rotary die-cutting tool (18') is adjusted.

9. The converter according to claim 2 or 3, characterized in that, The housing of the transmission unit (25) includes a reference mark (35), which can be visually detected by the image sensor (33).

10. The converter according to claim 9, characterized in that, The reference mark (35) is provided in the form of a line and extends along the transport direction (D) of the converter (20).

11. The converter (20) according to claim 1, characterized in that, The calibration system (30) includes a plurality of transmission sensors (32) which are set along the transport direction (D) on the travel path (P) and configured to detect registration displacement (Δxr), wherein each registration displacement (Δxr) detected by the transmission sensor (32) is added to each subsequent fractional correction (Δcf).

12. The converter (20) according to claim 11, characterized in that, The memory (36) includes instructions for putting the control unit (34) into a first operating mode and a second operating mode. And the control unit (34) in the first operating mode is configured to disable the image sensor (33) and only provide each registration displacement detected by each transmission sensor (32). The correction of xr), and wherein each respective correction is performed only in each of the nearest downstream transmission units (25) located between the transmission sensor and the nearest downstream printing unit. And the control unit in the second operating mode is configured to activate the image sensor (33) and provide multiple distributed fractional corrections (Δcf).

13. The converter (20) according to claim 12, characterized in that, The memory (36) includes a transition memory and a plurality of data locations including a plurality of sheets (1) present in the converter (20), wherein each data location includes position information of the location of the sheet (1) and a fractional correction (Δc0) required in the longitudinal direction.

14. A method for calibrating a converter (20), the method comprising the following steps: A) The sheet (1) is transported along the transport direction (D) through the converter (20). B) Capture the actual image (Im1) of the mark (42) on the sheet (1). C) Determine the abscissa (y1) and ordinate (x1) of the detected reference point (P1) in the marker (42). D) Obtain the x-coordinate (y0) and y-coordinate (x0) of the optimal position of the predetermined reference point (P0) from the memory (36). E) Calculate the deviation of the position of the detected reference point (P1) relative to the optimal position of the predetermined reference point (P0), the deviation including longitudinal marker displacement (Δxi) and lateral marker displacement (Δyi). F) Calculate the displacement corresponding to the longitudinal mark ( x i ) and feed sleeve displacement ( The initial total longitudinal displacement of the sum of xr0) x0), G) Calculate the initial correction ( c0), the initial correction ( c0) represents the longitudinal marking displacement (Δxi) and the feed fitting displacement ( The sum of xr0); and H) Calculate multiple fractional corrections (Δcf) to make the initial correction ( c0) is uniformly distributed across the plurality of transmission units (25), wherein the fractional correction (Δcf) corresponds to the initial total longitudinal displacement ( x0) divided by the number N of the transmission drivers (24) capable of performing the correction.

15. The method according to claim 14, characterized in that, If the initial total longitudinal displacement ( If x0 exceeds the longitudinal tolerance threshold (Txi), the operation of the transmission driver (24) is adjusted, and the position of the sheet (1) is corrected by adjusting the speed of the transmission driver (24).

16. The method according to claim 14 or 15, characterized in that, Before step A), the step of selecting an operating mode between a first operating mode and a second operating mode is performed, wherein the method in the first operating mode does not include steps B) to F), and wherein the method includes the following steps: - Print the sheet. - The registration displacement is detected by multiple transmission sensors (32). xr), and - Correct each registration displacement between each respective transmission sensor (32) and each nearest downstream printing unit (22a to 22d). xr), Furthermore, the method in the second operating mode contains only all steps A) to H).

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