Method and system for aligning tools in a platen press

Abstract

Here is disclosed a method for aligning an upper tool with a lower tool in a platen press that makes creasing lines on a sheet of cardboard according to a creasing layout, the upper tool and the lower tool comprising creasing blades and creasing channels, the method including - measuring the shape of the crease in at least two points on any creasing line on the cardboard sheet, the shape being the difference between the actual surface of the sheet and a flat surface parallel to the cardboard, - calculating a value for the misalignment between the creasing knife and the creasing channel at each measurement point, - assigning each misalignment value to its corresponding measurement point, - calculating a correction that involves shifting the creasing blades in two different directions parallel to the flat surface to align them with the creasing channels, - converting the correction into a set of machine adjustments to align the upper and lower tools, - applying the machine adjustments to the platen press to align the upper and lower tools.

Description

[0001]METHOD FOR ALIGNING TOOLS IN A PLATEN PRESS TECHNICAL FIELD The present application generally relates to a method for aligning tools in a platen press, and more particularly to a technique for ensuring precise alignment of tools within the press for improved operational efficiency. Related domains include measuring length, thickness or similar linear dimensions, measuring angles, measuring areas, measuring irregularities of surfaces or contours, mechanical working or deformation of paper, cardboard or material worked in a manner analogous to paper and making containers of paper, cardboard or material worked in a manner analogous to paper. BACKGROUND ART A box of cardboard is produced from a sheet of cardboard by cutting and creasing the box on the sheet, separating the sheet into blanks followed by folding-gluing the blank. A die-cutting machine performs the cutting and creasing by creating cutting lines and creasing lines on the cardboard. Since the context of the invention is related to creasing, we will call it a creasing machine. The part of the machine that performs the creasing is called the platen press, where the sheet is sandwiched between an upper platen and a lower platen. The upper platen usually carries a set of cutting and creasing knives, while the lower platen is either flat or has some creasing grooves. In practice, since the platen press is used to produce different types of boxes, the knives and grooves are not on the platen itself but on a lower- and upper tool attached to the lower and upper platen, respectively. For producingproper creasing lines, the creasing grooves and the creasing knives must beperfectly aligned. Thus, the machine is equipped with an alignment mechanism that can move the tool with respect to the platen along the platen surface. The alignment mechanism moves either the tool carrying the knives or the tool carrying the grooves. Once the tools are aligned, they are kept in place during production. The patent document number EP3254840A1 discloses a creasing unit for creating fold lines in cardboard, comprising two crease rollers, each crease roller having a circumferential protrusion adapted for indenting cardboard to create a fold line, wherein the crease rollers are rotatably mounted next to each other such that each crease roller can rotate about its own centre axis and each crease roller is movable between at least a first position for creating a fold line and a second position for either allowing cardboard to pass the respective crease roller without being indented by the respective crease roller or for creating an additional indented line being less deep than the fold line.. This approach presents limitations. PROBLEM STATEMENT This application addresses the problem of aligning the upper and lower tools in a platen press used for creasing cardboard sheets. The application provides solutions for accurately measuring the shape of creases on the cardboard, calculating misalignment values, and applying machine adjustments to align the creasing blades and channels. The application also addresses the problem of geometrical correction and provides a method for identifying misaligned creasing lines and triggering warnings for corrective actions. The disclosed system further solves the problem of achieving alignment through an adjustment mechanism and a scanner unit for measuring the surface profile of the cardboard. SUMMARY Embodiments of the invention are associated with various advantages and / or technical effects. There is disclosed a method for aligning an upper tool with a lower tool in a platen press that makes creasing lines on a sheet of cardboard according to a creasing layout, the upper tool and the lower tool comprising creasing blades and creasing channels, the method including- measuring the shape of the crease in at least two points on any creasing line onthe cardboard sheet, the shape being the difference between the actual surface of the sheet and a flat surface parallel to the cardboard,- calculating a value for the misalignment between the creasing knife and thecreasing channel at each measurement point,- assigning each misalignment value to its corresponding measurement point,- calculating a correction that involves shifting the creasing blades or the creasingchannels (or both) in two different directions parallel to the flat surface to align the creasing blades with the creasing channels,- converting the correction into a set of machine adjustments to align the upperand lower tools,- applying the machine adjustments to the platen press to align the upper and lowertools.By measuring the shape of the crease in at least two points on any creasing line wemean that the shape is measured in (at least) two points located anywhere on thecardboard with the constraint that these points must be located on a creasing line. The disclosed method enhances the precision of creasing operations by enabling the detection and correction of misalignments between the creasing blades and channels, thereby improving the quality of the creased cardboard sheets. By measuring the shape of the crease at multiple points and calculating necessary adjustments, the method allows for a more comprehensive and accurate alignment process, reducing waste and increasing operational efficiency. The automatic conversion of calculated corrections into machine adjustments facilitates the practical application of the alignment process, making it easier to implement and integrate into existing workflows without the need for extensive manual intervention. The method provides the advantage of accurately measuring the shape of creases on a cardboard sheet, allowing for precise alignment of the creasing blades and channels. The method offers the advantage of calculating misalignment values at multiple measurement points, ensuring a comprehensive understanding of the alignment issues. The method offers the benefit of converting the calculated correction into machine adjustments, simplifying the alignment process and reducing manual intervention. The method offers the benefit of incorporating a geometrical correction, involving a rotation parameter, for further alignment of the creasing blades and channels. The method offers the benefit of identifying creasing lines with misalignment above a predetermined threshold and triggering a warning, facilitating prompt corrective action and minimizing production errors. The system provides the advantage of achieving precise alignment between the upper and lower tools of a platen press, ensuring accurate creasing of cardboard sheets. The system offers the advantage of utilizing a scanner unit to measure the surface profile of the cardboard sheet, allowing for the computation of adjustment machine parameters. The system offers the benefit of incorporating a third adjustment unit for inducing rotation of the tool, providing additional alignment capabilities. The system includes the advantage of connecting a separate machine to the platen press for transmitting adjustment machine parameters, allowing for remote alignment control. The system allows for the advantage of implementing a feedback loop with an in- line scanner unit, automatically adjusting the alignment of the upper and lower tools during the creasing process. In a development, the method further comprises a geometrical correction comprising a rotation parameter for further aligning the creasing blades and the creasing channels and wherein the creasing profile is measured in at least three points on any creasing line of the sheet of cardboard The inclusion of a rotation parameter in the geometrical correction allows for a more nuanced alignment that accounts for angular as well as translational misalignments, leading to a higher fidelity in the creasing process. The development enhances the adaptability of the method to a variety of creasing layouts and cardboard materials, as the additional rotation parameter can compensate for irregularities in the cardboard or variations in the creasing tool manufacturing.In a development, the method further comprises - the method measuring thesurface profile over at least part of the cardboard surface,- identifies the creasing lines from the surface profile or from a configuration file,- selects at least one point, preferably several points, on each of the creasing lines- computes a shape of the crease and a value of misalignment at the selected points- computes the geometrical correction for aligning the creasing blades and thecreasing channels by using a rigid translation model. Measuring the surface profile over at least part of the cardboard surface provides a comprehensive understanding of the cardboard's topography, which can be used to improve the precision of the creasing process. The ability to identify creasing lines from the surface profile or a configuration file streamlines the alignment process, allowing for automated selection of measurement points and reducing the potential for human error. Computing the shape of the crease and the value of misalignment at selected points on each creasing line ensures that the alignment is optimized across the entire sheet, which is critical for maintaining consistency in mass production. In a development, the method further comprises a geometrical correction being computed by using a rigid translation and rotation model. The use of a rigid translation and rotation model for computing the geometrical correction provides a more accurate representation of the actual misalignment conditions, leading to a more precise alignment of the creasing tools. This comprehensive model accounts for all degrees of freedom that can affect the alignment, ensuring that the resulting creases are sharp and accurately positioned, which is essential for high-quality packaging and folding applications. The enhanced accuracy of the alignment process reduces the likelihood of tool wear and damage, as well as the need for rework or adjustments during production runs, thereby improving the longevity of the tools and the efficiency of the press operation. In a development, the method further comprises a method is repeated until thecomputed geometrical correction has an amplitude below a predeterminedthreshold; the amplitude corresponding to the largest shift caused by applying the correction. Repeating the method until the computed geometrical correction falls below a predetermined threshold ensures that the alignment is within acceptable tolerances, leading to consistent and high-quality creasing results. The iterative approach allows for fine-tuning of the alignment, which is particularly beneficial for complex or high-precision creasing tasks where even minor misalignments can lead to significant quality issues. The method according to claim 5 identifies any creasing line with a value of misalignment above a predetermined threshold and, if at least one of the creasing lines exists, triggers a warning, which highlights the creasing line on a graphical representation of the creasing layout; the representation is displayed on a screen of the creasing machine or on a remote computer connected to the creasing machine. The method enhances quality control by automatically detecting misalignments in creasing lines, ensuring that the final product meets the desired specifications. By providing visual feedback on a graphical representation, the method facilitates quick identification and correction of errors, reducing downtime and improving operational efficiency. The ability to trigger warnings on both the creasing machine and a remote computer provides flexibility and convenience, allowing for monitoring and adjustments to be made from different locations. There is disclosed a system for aligning the upper tool or the lower tool of a platen press in a creasing machine configured to crease a sheet of cardboard according to a creasing layout, the system comprising- A platen press with- An upper tool- A lower tool- The upper tool carries a set of creasing blades and the lower tool carries a set ofcreasing channels, or vice-versa,- An adjustment mechanism configured to achieve alignment between the lowertool and the upper tool, comprising a first adjustment unit and a second adjustment unit that connect one of the tools to the upper or the lower platen, the mechanismis configured to displace the tool with respect to the platen according to a set ofadjustment machine parameters,- A scanner unit configured to measure the surface profile of a sheet of cardboardprocessed by the machine in at least two points of the creasing layout,- A computing unit for computing the adjustment machine parameters from thesurface profile according to the method of any to 6 The system's adjustment mechanism with dual adjustment units allows for precise alignment of the tools, leading to improved accuracy in the creasing process and higher-quality finished products. Integration of a scanner unit to measure the surface profile of processed cardboard enables real-time adjustments, in the sense that the adjustment may be performedwhile the machine is running at (very) low speed during a calibration phase. Thelow speed is needed so that the adjustments are made while the platen is open in-between two pressing operations. The computing unit's capability to compute adjustment parameters from the surface profile data ensures that the machine can self-correct without manual intervention, enhancing productivity and reducing the likelihood of human error. The system, according to claim 7, wherein the adjustment mechanism further comprises a third adjustment unit that connects one of the tools to the upper or the lower platen, the mechanism is configured to displace the tool with respect to the platen so as to induce a rotation of the tool with respect to the platen,- the scanner unit configured to measure the surface profile of the sheet ofcardboard in at least three points of the creasing layout,- the computing unit being configured for computing the adjustment machineparameters from the surface profile according to the method of any of claims 2 to 6 The inclusion of a third adjustment unit in the mechanism allows for rotational adjustments, providing an additional degree of control for fine-tuning the alignment of the tools. The ability to measure the surface profile at three points increases the precision of the alignment, ensuring a more uniform crease across the entire sheet of cardboard. The computing unit's advanced configuration for processing surface profile data from multiple points allows for a comprehensive analysis of the creasing layout, leading to more accurate machine adjustments. In a development, the system further comprises a scanner unit located in a machine separated from the platen press and wherein the machine is connected to the platen press for transmitting the adjustment machine parameters to the platen press and aligning the upper tool with the lower tool. The connectivity between the separate scanner unit and the platen press enables seamless transmission of adjustment parameters, streamlining the workflow and maintaining consistent quality. This configuration allows for the scanner unit to be used with multiple platen presses, providing a cost-effective solution for facilities with several creasing machines. It also allows the upgrade of existing machines with the method. In a development, the system further comprises a scanner unit being positioned in- line after the platen press along the path of transportation of the sheet of cardboard and wherein the scanner unit is connected to the platen press for building a feedback loop that automatically adjusts the alignment of the upper tool with respect to the lower tool, or vice versa. Positioning the scanner unit in-line after the platen press enables immediatequality assessment post-creasing, allowing for direct feedback and continuousprocess improvement. The establishment of an automatic feedback loop for alignment adjustments minimizes the need for operator intervention, leading to a more autonomous and efficient creasing process. The in-line scanner unit's ability to adjust the alignment of the tools based on post- press measurements ensures that any deviations are promptly corrected, maintaining high-quality output and reducing the risk of subsequent production issues. In a development, the system further comprises a scanner unit projecting at least one laser line on the sheet of cardboard for measuring the surface profile from the sheet of cardboard. The integration of a scanner unit that projects at least one laser line onto the sheet of cardboard enables the system to accurately determine the topography of the creasing lines. In a development, the system further comprises a scanner unit projecting at least two non-parallel lines on the sheet of cardboard for measuring the surface profile from the sheet of cardboard. The use of at least two non-parallel laser lines for scanning enables the system to capture a more detailed and accurate three-dimensional representation of the cardboard's surface profile. The use of at least two non-parallel laser lines also allows the recording of thesurface profile of creasing lines without having tight control of the advancement ofthe sheet under the scanner, which is required when using a single laser line for creasing lines that happen to be parallel to the laser line. BRIEF DESCRIPTION OF DRAWINGS The present disclosure is illustrated by way of example and not limited in the accompanying figures in which like reference numerals indicate similar elements. Embodiments of the application will now be described with reference to the attached drawings: Figure 1 shows a creasing machine with a scanner and a remote computer according to the invention Figure 2 shows an example of cardboard box with cutting and creasing lines Figure 3 shows a top view of the box of Figure 3 with the location of the creasing knives and creasing channels when the upper and lower tools are poorly aligned Figure 4 shows a perspective representation of the upper and lower tools that carry the creasing knives and creasing channels to produce the box of Figure 2 Figure 5 shows the example of Figure 3 along with the value of misalignment represented at selected points Figure 6 shows the shape of the crease for different misalignment valuesFigure 7 shows the basis functions used to represent the shapes of the creaseshown in Figure 6 Figure 8 shows an example of features extracted from the shape of the crease to compute the value of the misalignmentFigure 9 shows a typical creasing layout to produce several cardboard boxes froma single sheet of cardboardFigure 10 shows the example of Figure 8 with misaligned tool and show themisalignment details at selected pointsFigure 11 shows the example of Figure 9 with the different entities used for thecomputation according to the claimed methodFigure 12 shows an example of an adjustment mechanism used to adjust the lowertool on the lower platenFigure 13 shows an example of a scannerFigure 14 shows an example of a claimed methodFigure 15 shows another example of a claimed methodDETAILED DESCRIPTION The disclosed method aligns an upper tool 2 with a lower tool 1 in a platen press 3 that makes creasing lines on a sheet 5 of cardboard according to a creasing layout 8. The creasing layout 8 is defined in advance and depends on the job to be performed. The upper tool 2 comprises creasing blades 6 and the lower tool 1 comprises creasing channels. When the cardboard is creased, the blades are pushing the cardboard into the channels. Thus, the channels must be well aligned with the blades to create a proper crease 10. Creasing lines are used as guides forfolding the cardboard and are piecewise straight lines. When the upper and lowertools are misaligned, the blade does not push the cardboard in the channel properly, resulting in a deformed creasing line 4. In general, this operation is performed along with cutting the cardboard along cutting lines 38, which cut the cardboard by pinching it against the lower platen surface directly, thus not requiring alignment.The alignment method is based on the measurement of the shape 9 of the creaseto determine if the blade and channels are aligned, and if not, how to re-align them. For the sake of the explanation, let’s zoom in on a single point along the crease 10. We measure how much the channels and the knife are not perfectly aligned; in other words, we measure the value of the misalignment 15. For example, we measure by how many millimeters we need to shift the channels to align them withthe knife. By shifting the channel, we mean shifting it along the perpendicular tothe channel, since shifting the channel and the knives along the creasing line 4 doesnot affect the shape 9 of the resulting crease 10. When the tool can be shifted in one direction, X, then a single value of the misalignment 15 suffices in theory, i.e.,analyzing the crease in one single point suffices. When the tool can be shifted intwo directions (X and Y) along its surface, then we need at least two measurementsto align the tools properly. In other words, we need to analyze the crease in twodistinct points 11. Each point is on a distinct creasing line 4, said creasing lines being non-colinear. If the tool can be shifted and rotated, then we need to analyze thecrease in at least three points 11. The creasing lines on which the three points(P1,P2,...,P8) are chosen should not be colinear. If the points are colinear, it is notideal: the method can still work, but we may miss the alignment in one of thedirections by choosing to set it to zero. The analysis of the crease is performed usinga 3D measurement sensor, which measures the shape 9 of the crease by measuringthe surface of the cardboard perpendicular to the creasing line 4. In particular, it measures the deviation of the cardboard surface from a hypothetical perfectly flat surface 13. Then, from the value of the misalignment 15 and its associated point on the tool surface, we can compute the (geometrical) correction 18 to be appliedto either the upper tool 2 or the lower tool 1 for properly aligning the tools. Finally,this correction 18 has to be converted into a set of machine adjustments 21 that the operator or the machine automation can use to properly align the tool. For example, it may be converted into two values that the operator can apply to twoscrews for shifting the lower tool 1.Computing the value of the misalignmentThe value of misalignment 15 is computed from the shape 9 of the crease S(p),measured along a coordinate p perpendicular to the creasing line 4. In a preliminary training phase, we produce a set of cardboards where we misalign the upper tool 2 and the lower tool 1 by a controlled distance to create training samples. On these samples, we know the misalignment 15 at every location of the plane, thus, we also know the misalignment 15 Mp along the perpendicular of the creasing line 4 L. Thus, we can construct a function F:S(p) -> Mp using data collection and machine learning. In practice, according to an exemplary embodiment, to reduce the need for data, we can express the shape 9 of the crease S(p) as a sum of a set of basis functions Si(p), so that S(p) = a1*S1(p) + a2*S2(p) + a3*S3(p) + … + an*Sn(p). These basis functions can be easily computed using a singular value decomposition from the set of all the collected creasing shapes. We keep the singular vectors associated with the n largest singular values. For example, we may take n equal to 5; thus, we keep five singular vectors associated with the five largest singular values, which are shown in Figure 6. Thus, from the shape 9 of the crease 10, we obtain the set of parameters ai. Thus, in our example, we can replace each shape 9 of thecrease by a set of parameters ai for the rest of the computation. Thus, in ourexample, the estimation of the value of misalignment 15 reduces to constructing a function F:[a1, a2, … an] -> Mp, from the (known) parameters ai associated with each crease 10. The construction consists of choosing a parametric function F() a-priori, and estimating its parameters. Estimating the parameters of a function from a set of examples where the answer is known is a standard problem in the domain of machine learning called supervised learning. As a very crude estimation, this function F may be chosen to be a linear function and can be computed using a linear estimationtechnique: Thus, in this crude estimation, we need to find the parametersp1,p2,…,pn that minimize a loss function, for example p1,p2,…,pn = argmin[(a1*p1+a2*p2+….+an*pn)-Mp]^x, where x is chosen a priori. When x=2, the loss function is the L2 norm and can be solved using the least squares technique. We may also use x=1, or x=0.5 to emphasize the importance of small misalignments in the computation. Once this function F is built, we have a recipe for computing the the misalignment 15 value Mp from the shape 9 of the crease 10, which we can use to align the upper tool 2 with the lower tool 1 during production. An alternative approach for computing the value of the misalignment As an alternative method for computing the value of misalignment 15, we may use a neural network, for example, a multi-layer perceptron, as the function F and estimate the parameters using supervised learning given a set of known misalignment 15 values Mp. This leads to a more precise computation of the value of misalignment 15 but requires substantially more training data. An alternative approach for computing the value of the misalignment As another alternative method for computing the value of misalignment 15, wemay detect the value of the maximum gradient 40, the value of the minimumgradient 41. The ratio of these two values may be correlated to the value of themisalignment 15 in a calibration phase, in a similar manner than for the above- described method. As another alternative, we may detect the maximum value of the shape of thecrease 42, draw a line 46 at the middle height of the shape of the crease (the “level0” being the level of the uncreased cardboard). From there, we measure the area44 under the curve representing the shape of the crease and above said line 46 tothe left of the maximum 43 and the area 45 to the right of the maximum 43. Theratio of said areas 44,45 may be correlated to the value of the misalignment 15 ina calibration phase, in a similar manner than for the above-described method.Aligning the tool from the values of misalignment Computing a parametric alignment from a set of misalignment values is a fairly standard problem in computer vision or photogrammetry. It is reproduced here asan example to ensure the completeness of the disclosure.In this example, we compute an alignment correction consisting of a translation and a rotation to apply to the upper or lower tool from at least 3 values of misalignment. We apply a rigid rotation and translation model: The misalignmentcan be expressed as a rotation matrix R plus a translation T. This defines acoordinate transform.^^ = ^^ + ^where X is a coordinate in the plane parallel to the cardboard. In other words ^^′1^ ^^^^ α − sin α ^ ^^1^ ^^1 ^ With 3 unknown parameters, which are t1, t2, and the angle α. These parameters can be computed by non-linear optimization: Let Pi be a point on a creasing line, and Ni the perpendicular to this line. By applying the transformation above (rotation+translation), we can compute the point Qi after transformation: ^^ = RP^ + TTo align the creasing knives with the creasing channels, the distance between Qi and Pi should correspond to the value of misalignment computed from the shape of the crease. In other words, the distance Mi: Qi---Pi, projected on the perpendicular Ni to the creasing line should be equal to the value of misalignment Mp estimated from the shape of the crease. In mathematical terms, it translates into: ^Q^ − P^^ ⋅ N^ = Mp^Where ⋅ is the dot product (also called the inner product). We call the vector^Q^ − P^^ the shift.In practice, we may minimize a loss function L given by L^^^^ − P^^ ⋅ N^ − Mp^^over the chosen points. Thus, the transformation parameters t1, t2, and α are found by solvingarg min L ^^^^ − P^^ ⋅ N^ − Mp^^ Using any standard (iterative) non-linear optimization technique. L can be any loss function, for example, the mean squared error or L2 norm(L2(x) = x2). In practice, the L2 norm is not optimal, since it overemphasizes largevalues. Here, small errors are more important to be estimated correctly, since once aligned, the creasing knives and creasing channels should exhibit a value of misalignment equal to 0. If some knives are broken or badly aligned, they shouldbe regarded as outliers and should not impact the global alignment between theupper tool and the lower tool in a too important manner. Thus, a preferred choiceis the L1 norm or “Lasso loss” (L1(x) = absolute value of x). Another choice is theL0.5 norm, thus L(x) = sqrt(abs(x)). Please note that the loss function used here tocompute the tool alignment may differ from the loss function used to compute the value of misalignment from the shape of the crease. When applying a rigid translation model instead of a rigid translation and rotation model, the method is the same except that it needs only at least two points Pi, and the angle α is set to 0 instead of being computed. Toward machine parameters A creasing machine 28 has a platen press 3 with a lower platen 37 carrying a lower tool 1 and an upper platen carrying an upper tool 2. The platen press 3 can process the cardboard with a pressure value in the order of 500 tons, and thus control of the exact position of the platens is nearly impossible. Consequently, at least one of the platen has an adjustment mechanism 30 to adjust the position tool on the platen. One of the tools carries the creasing blades 6, and the other tools carry the creasing channels. The adjustment typically comprises two mechanisms: A first mechanism that shifts the tool along the X coordinate, and a second mechanism that shifts the tool along the Y coordinate. The X and Y coordinates are within the cardboard processing plane. Many platen presses have a third mechanism that shifts the tool along the X or Y coordinate and thus causes a rotation of the tool when properly combined with the two other mechanisms, as shown in Figure 11. To get a good precision, these mechanisms are usually equipped with screws and the adjustment consists in turning the screw. Computing the adequate set of adjustment parameters is like computing shift values from the rigid transformation model. It involves the inverse of said computation and is well-known from the man skilled in the art. The computing unit 33 that computes the value of misalignment 15 from the shape 9 of the crease 10, and the rigid transformation parameters may be located in the scanner unit 32, in the remote computer 29 or in the automation of the creasing machine 28. The further computing of the adjustment parameters may be computed by the same unit or by a separate one. Preferably, thecomputation of the value of misalignment 15 from the shape 9 of the crease andthe rigid transformation parameters are computed in the scanner unit 32, while the computation of the adjustment parameters are computed either in the remote computer 29 or by the automation of the creasing machine 28. Scanning the cardboard surfaceThe shape 9 of the crease can be scanned with an ad-hoc crease measuring devicethat can be found on the market. Several creases must be scanned, and then for each crease 10, the coordinate of the point must be entered in the control device,or the control device must indicate the location where the crease must bemeasured. In both cases, the method requires a step where the location of thecrease must be associated to the shape 9 of the crease to implement the alignmentmethod. A preferred solution comprises measuring the surface profile 22 of the cardboard over an area. Then identifying the creasing lines in said area, either by analyzing the surface profile 22 or by extracting the information from a configuration file that contains the creasing layout 8. Then, selecting several points (P1,P2,...,P8) on the creasing lines in said area (i.e., at least two or three points (P1,P2,...,P8) in total, depending on the number of degrees of freedom of the tool alignment). At each point, computing the shape 9 of the crease. The shape 9 of thecrease is computed by sampling the surface profile 22 along a perpendicular to thecreasing line 4 around the selected point. Then, we compute the geometrical correction 18 for aligning the creasing blades 6 and the creasing channels. This is done using numerical optimization, for example by minimizing a loss functioncomputed at each of the selected points (P1,P2,...,P8) by using the rigid translationor translation & rotation model. When applying said model, point P1,P2,...,P8 become points Q1,Q2,…Q8, respectively. Numerical optimization is preferably an iterative method. These iterations are stopped when the correction 18 to be applied is small enough. In other words, the method is stopped and the tool is considered to be aligned when all the (amplitude of the) shifts caused by the correction 18 are smaller than a predetermined threshold 24, for example, a threshold of 0.1 mm. The shift for a given point is defined as the displacement of said point caused by the rigid transformation model. Measuring the surface profile 22 of the cardboard over an area can be performed with a scanner unit 32. The scanner unit 32 may be located on a device separated from the creasing machine28 but connected to the machine. In this case, the adjustment parameters aretransmitted to the creasing machine 28 and displayed on the machine to help the operator align the tools or are directly applied for aligning the tools by the machine automation. The scanner unit 32 may be located inline in the creasing machine 28 downstream from the platen press 3 when following the path of the cardboard, for example, at the machine's exit. In this way, quality control and tool alignment can be performed in a closed loop during production without interrupting production, provided that the scanner unit 32 is connected to the machine control unit. The scanner unit 32 projects a laser line on the cardboard for scanning the cardboard surface. The laser line may be projected at an angle on the surface, for example at45°, and recorded by a camera 102. Alternatively, it might use the laser as a LIDARto recover surface information. The laser line might swipe the surface or may be fixed while moving the cardboard under the scanner, in which case, if there is a single laser line, the motion of the cardboard must be carefully controlled.Preferably, the scanner uses several laser lines at different angles on the cardboardsurface. In other words, the image of the laser line on the cardboard surface is not parallel. In this way, the motion of the cardboard under the scanner can be much less precise since the cardboard's local 3D surface information only depends on the analysis of the laser lines recorded by the camera (and not by how much the cardboard moved under the laser line). When using a single laser line, then the laser line orientation is chosen such that it is unlikely parallel to the creasing lines.More often than not, the creasing lines are oriented at Ω = 0°, 45°, and 90°. Thus asuitable orientation of the laser line would be between Ω = 20° and 30° with respectto the transversal orientation of the sheet of cardboard. When there are several laser lines, we might also choose said orientations (for example 20° and 110° for two lines), even if the advantage of this configuration is less important. A usualorientation for the laser line with respect to the surface of the sheet is β = 45°, butin some cases, lower angles, for example β = 10°, 20° or 30° may increase theprecision of the creasing profile. Detecting defective creases Once the upper tool 2 is aligned with the lower tool 1, the analysis of the shape 9of the crease may be used to detect defective creasing lines, or, equivalently,defective knives. A creasing line 4 is defective, if the value of misalignment 15computed from the shape 9 of the crease is above a predetermined threshold 24.If a defective creasing line 4 is detected, then a warning can be generated on themachine interface or on a connected remote computer 29. For example, a graphicalrepresentation of the creasing layout 8 can be displayed where the defectivecreasing line(s) 4 are highlighted.

Claims

CLAIMS 1. A method for aligning an upper tool (2) with a lower tool (1) in a platen press (3) that creates creasing lines on a sheet (5) of cardboard according to a creasing layout (8), the upper tool (2) and the lower tool (1) comprising creasing blades (6) andcreasing channels, the method including- measuring the shape (9) of the crease (10) in at least two points (11) on anycreasing line (4) on the cardboard sheet (5), the shape (9) being the difference between the actual surface (12) of the sheet (5) and a flat surface (13) parallel to the cardboard, -calculating (14) a value for the misalignment (15) between the creasing knife(16) and the creasing channel (19) at each measurement point (17), -assigning each misalignment (15) value to its corresponding measurementpoint (17), -calculating (14) a correction (18) that involves shifting (20) the creasing blades(6) or the creasing channels in two different directions (34) parallel to the flat surface (13) to align the creasing blades (6) with the creasing channels,- converting the correction (18) into a set of machine adjustments (21) to alignthe upper and lower tools, -applying the machine adjustments (21) to the platen press (3) to align theupper tool (2) with the lower tool (1).

2. The method according to claim 1, wherein the geometrical correction (18) comprises a rotation parameter for further aligning the creasing blades (6) and the creasing channels and wherein the creasing profile is measured in at least three points (11) on any creasing line (4) of the sheet (5) of cardboard 3. The method according to claim 1, wherein -the method measures the surface profile (22) over at least part of thecardboard surface,- identifies the creasing lines from the surface profile (22) or from aconfiguration file, -selects at least one point, preferably several points (11), on each of thecreasing lines -computes a shape (9) of the crease (10) and a value of misalignment (15) atthe selected points (11) -computes the geometrical correction (18) for aligning the creasing blades (6)and the creasing channels by using a rigid translation model.

4. The method according to claims 2 and 3, wherein the geometrical correction (18) is computed by using a rigid translation and rotation model.

5. The method according to any claims 1-4, wherein the method is repeated until the computed geometrical correction (18) has a maximum amplitude (23) below a predetermined threshold (24); said amplitude corresponds to the largest shift caused by applying the correction (18).

6. The method according to claim 5 identifies any creasing line (4) with a value of misalignment (15) above a predetermined threshold (24) and, if at least one of said creasing lines exists, triggers a warning (25), which highlights said creasing line (4) on a graphical representation (26) of the creasing layout (8); said representation is displayed on a screen (27) of the creasing machine (28) or on a remote computer (29) connected to the creasing machine (28).

7. A system for aligning the upper tool (2) or the lower tool (1) of a platen press (3) in a creasing machine (28) configured to crease (10) a sheet (5) of cardboard according to a creasing layout (8), the system comprising -A platen press (3) with- An upper tool (2)- A lower tool (1)- The upper tool (2) carries a set of creasing blades (6) and the lower tool (1)carries a set of creasing channels, or vice-versa, -An adjustment mechanism (30) configured to achieve alignment between thelower tool (1) and the upper tool (2), comprising a first adjustment unit and a second adjustment unit that connect one of the tools to the upper or the lower platen, the mechanism is configured to displace said tool with respect to the platen according to a set of adjustment machine parameters (31), -A scanner unit (32) configured to measure the surface profile (22) of a sheet(5) of cardboard processed by the machine in at least two points (11) of the creasing layout (8), -A computing unit (33) for computing the adjustment machine parameters (31)from the surface profile (22) according to the method of any of claims 1 to 6 8. The system, according to claim 7, wherein the adjustment mechanism (30) further comprises a third adjustment unit (36) that connects one of the tools to the upper or the lower platen, -the mechanism is configured to displace said tool with respect to the platenso as to induce a rotation of the tool with respect to the platen, -the scanner unit (32) is configured to measure the surface profile (22) of thesheet (5) of cardboard in at least three points (11) of the creasing layout (8), -the computing unit (33) being configured for computing the adjustmentmachine parameters (31) from the surface profile (22) according to the method of any of claims 2 to 6 9. The system, according to any one of claims 7-8, wherein the scanner unit (32) is located in a machine separated from the platen press (3) and wherein said machine is connected to the platen press (3) for transmitting the adjustment machine parameters (31) to the platen press (3) and aligning the upper tool (2) with the lower tool (1).

10. The system according to any one of claims 7-8, wherein the scanner unit (32) is positioned in-line after the platen press (3) along the path of transportation of the sheet (5) of cardboard and wherein the scanner unit (32) is connected to the platen press (3) for building a feedback loop that automatically adjusts the alignment of the upper tool (2) with respect to the lower tool (1), or vice versa.

11. The system according to any one of claims 7-10, wherein the scanner unit (32) projects at least one laser line on the sheet (5) of cardboard for measuring the surface profile (22) from the sheet (5) of cardboard.

12. The system according to any one of claims 7-11, wherein the scanner unit (32) projects at least two non-parallel laser lines on the sheet (5) of cardboard for measuring the surface profile (22) from the sheet (5) of cardboard.

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