Method for calibrating a printhead position

Abstract

The invention relates to a method for calibrating the positioning of an inkjet printhead, the method comprising the following steps: a) printing a first motif at at least a first print position on a first web onto a substrate; b) positioning the printhead on a second web; c) printing a second motif at at least a second print position onto the substrate; d) optically detecting the first motif and the second motif by means of an optical sensor; e) determining the magnitude of a relative positional deviation between the first motif and the second motif; f) generating a control signal based on the magnitude of the relative positional deviation, wherein the control signal is used to compensate for the determined relative positional deviation.

Description

[0001] The invention relates to a method for calibrating a print head position.

[0002] In digital printing, especially with inkjet printers, the spacing between printed dot patterns and the spacing on a nozzle plate of a print head should be identical to create a uniform print image. However, it is possible that errors may occur during the positioning of the printed dot patterns, resulting in deviations in the print image that are already visible to the human eye. This is particularly the case in areas where printed dot patterns from different webs are located next to each other and / or at least partially overlapping within a certain print width specified by the design of the print head. The overlapping areas of different webs are referred to as the stitching area.

[0003] Errors in the positioning of printed dot patterns can be attributed to several sources of error, such as mechanical, environmental, design-related causes, or combinations thereof. Possible sources of error include, for example, mechanical inaccuracies in the printhead positioning, changes in the angle of the printhead relative to the substrate surface to be printed, inaccuracies in the arrangement of the nozzles on the printhead, droplet deviations, or a collection of various, rather minor errors and influencing factors. When printing on three-dimensional or 2.5-dimensional substrates, additional sources of error typically exist compared to two-dimensional substrates due to the additional third spatial dimension.

[0004] Typically, printhead calibration is performed using high-resolution measuring devices, such as laser sensors, to measure the printhead position as it moves along the substrate surface. This provides actual values ​​for the printhead position. The measured actual values ​​are compared by the controller with specified target values. If the actual and target values ​​differ, the printhead position is corrected.

[0005] However, this has the disadvantage that it only adjusts a single potential source of error, namely the print head position. Other errors, such as those mentioned above, cannot be corrected and / or compensated for.

[0006] A further disadvantage is that potential error sources can only be reduced by purchasing the most accurate device possible. However, this entails significantly higher costs. With each potential error source that is to be reduced and addressed individually, the costs increase further. However, only error sources known to the device operator can be addressed. A collection of many smaller, possibly unknown errors thus remains uncorrected.

[0007] It is now an object of the invention to provide an improved method for calibrating a print head position, whereby the positioning of the print head takes into account all sources of error in the generation of a dot pattern.

[0008] The object is achieved by a method for calibrating the positioning of an inkjet print head, in particular according to one of claims 1 to 15, wherein the method comprises the following steps, which are preferably carried out in the following order: a) printing a first motif at at least one first printing position on a first web onto a substrate, in particular with the print head, b) positioning the print head on a second web, c) printing a second motif at at least one second printing position onto the substrate, d) optically detecting the first motif and the second motif by means of an optical sensor, e) determining a size of a relative position deviation between the first motif and the second motif, f) generating a control signal based on the size of the relative position deviation, wherein the control signal is used to compensate for the determined relative position deviation.

[0009] The inventive method for calibrating a print head position makes it possible to account for all possible sources of error during digital printing without incurring higher costs, for example, by purchasing a device with lower manufacturing tolerances. Rather, the print head position is adjusted based on the analysis of a print image generated on a substrate.

[0010] It's not necessary to provide special calibration substrates or calibration inks. Instead, the substrate used in the printing process can be used. This offers the advantage that the substrate exhibits the typical tolerances and deviations, which are then taken into account during calibration. Since the same inks are used in the calibration process as in the printing process, their properties, such as drip and spreading properties, are also taken into account.

[0011] Furthermore, calibration takes place in print head positions that are also relevant to the printing process, for example, in stitching areas. This means that certain tolerances prevail in these print positions, particularly of a mechanical nature, such as the step accuracy of the print head position sensor drive, which are also relevant to the subsequent printing process.

[0012] A further advantage is that recalibration can be flexibly adapted to specific needs and requirements, as it can be performed inline within a manufacturing process. In one extreme case, calibration can be performed continuously during the printing process, particularly before each individual printing step, providing continuously updated correction values ​​and enabling the maximum possible print head position accuracy. In the other extreme case, calibration can be performed only once during machine setup and only recalibrated when insufficient deviations in the print image are detected to achieve the desired product quality.

[0013] Inline is understood here to mean that the steps of the method according to the invention are carried out in and / or during a particularly continuous manufacturing process, wherein the manufacturing process here comprises a printing process for printing a decorative print. This means that the calibration of the positioning of the print head and the printing of the decorative print take place one after the other essentially without interruption, in particular during a continuous manufacturing process. The calibration of the positioning of the print head can take place as an integral part of the manufacturing process. For example, if the calibration of the positioning of the print head has taken place, in particular after a feed and / or after a change of substrate, at least one step of the printing process for printing a decorative print follows without interruption of the manufacturing process.The individual steps of the method according to the invention and the method for printing a decorative print merge virtually seamlessly into one another. In particular, with an inline process, there is no intermediate storage and / or intermediate rolling or stacking of the substrate. The manufacturing process is thus preferably carried out continuously and without interruptions.

[0014] Further advantageous embodiments of the invention are described in the subclaims.

[0015] Preferably, the first lane corresponds to the first print head position and the second lane corresponds to the second print head position. It is possible for the print head to be arranged on one or more further lanes with a corresponding print head position. In particular, the relative positional deviation is determined between two motifs and / or the print head position is calibrated between two specific lanes. The motifs are therefore understood to be test motifs and in particular not decorative motifs. For example, the relative positional deviation between the first motif on the first lane and the second motif on the second lane is determined and preferably a further relative positional deviation of the second motif on the second lane relative to a further motif on a further lane is determined.

[0016] The printing positions preferably correspond to the positions of the nozzles in the print head, in particular a nozzle plate in the print head. The positions of the motifs thus correspond to one or more positions of the nozzles in the print head, in particular wherein a motif can comprise one or more printing positions. It is possible that the same or different nozzle(s), i.e. printing position(s), are used on the first web and on the second web to print the motifs. It is possible for a web to comprise one or more printing positions of the print head. The number of printing positions in a web thus corresponds to the maximum number of nozzles in the print head, and it is possible for a web to comprise a number of printing positions that corresponds entirely or partially to the maximum number of printing positions.If the number of printing positions of a web is less than the maximum possible number, the printing positions located at the outer edges of the respective web are used in particular for the process of calibrating the print head position.

[0017] In particular, the first and second webs are not arranged so as to overlap. In other words, the first and second webs are arranged side by side. There is no stitching area. This offers the advantage of ensuring that printed motifs are positioned on the material of the substrate surface and not on or overlapping with existing motifs. This achieves consistent surface properties in this printhead position for the printing process on the substrate.

[0018] Alternatively, it is possible for the first web and the second web to at least partially overlap in an overlapping area, preferably not completely overlapping, in particular with the first motif and the second motif being arranged in the overlapping area. Thus, a stitching area is present, which advantageously at least minimizes a transition area visually recognizable to a viewer between the first web and the second web.

[0019] It is possible that motifs, in particular the first motif and / or second motif, are formed from one or more reference elements, which are preferably selected from the group consisting of dot, line, cross, circle, ellipse or combinations thereof.

[0020] Preferably, the one or more reference elements have the same shape.

[0021] The minimum dimensions of a motif, preferably a reference element, depend on the droplet size of the nozzles. However, it is possible for the motifs to have a main extension along a spatial direction that corresponds to a multiple of the minimum dimensions. This main extension can be selected from a range of more than 0 mm to 10 mm, preferably 0.01 mm to 7 mm, more preferably 0.05 mm to 5 mm. This allows a sufficient amount of data to be analyzed for the method according to the invention without the speed of the printing and evaluation being negatively affected.

[0022] It is possible for the relative position deviation to be composed of a first and / or a second relative spatial direction deviation, in particular in an x-direction and / or a y-direction. In particular, the first spatial direction can be assigned to an x-direction, the second spatial direction to the y-axis, and a third spatial direction to the z-axis.

[0023] The relative position deviation may comprise a first relative spatial direction deviation that describes the relative spatial direction deviation along the x-axis, and the relative position deviation may comprise a second relative spatial direction deviation that describes the relative spatial direction deviation along the y-axis. The magnitude of the relative position deviation may preferably be determined from the magnitudes of the one or more relative spatial direction deviations.

[0024] The assignment refers to a three-dimensional coordinate system, with the nozzles arranged in a plane spanned by the x- and y-axes. In other words, the plane spanned by the x- and y-axes encompasses the surface of the nozzle plate facing the substrate. The z-axis is perpendicular to this plane, in the direction of the substrate surface to be printed.

[0025] The surface normal of the nozzle plate, which runs parallel to this z-axis, is preferably parallel to a surface normal of the substrate surface to be printed, which is located directly beneath the nozzle plate during the printing process. In particular, the substrate surface to be printed, which is located directly beneath the nozzle plate during the printing process, is understood to be the substrate surface associated with the respective path corresponding to the respective position of the print head.

[0026] This means that, in particular, the part of the substrate surface that is located directly beneath the nozzle plate during the printing process preferably runs largely parallel to the surface of the nozzle plate, or the surface normal of the nozzle plate and the surface normal of the part of the substrate surface that is located directly beneath the nozzle plate during the printing process preferably run largely parallel. In other words, printing takes place on the part of the substrate surface that runs largely parallel to the nozzle plate, or whose surface normal runs largely parallel to the surface normal of the nozzle plate.

[0027] Particularly when dealing with three-dimensional or 2.5-dimensional curved substrate surfaces, it is advantageous to adjust the distance along the z-axis between the nozzle plate and the part of the substrate surface that is located directly below the nozzle plate during the printing process, in particular to locally adapt the geometry that changes across the entire substrate surface, so that the highest possible local parallelism of the nozzle plate and the substrate surface is always achieved.

[0028] It is advantageous if, between adjacent printing paths on the substrate surface, the surface normal of the nozzle plate and / or the surface normal of the substrate surface needs to be adjusted as little as possible when adjusting the local parallelism of the nozzle plate and the substrate surface, in order to avoid strong angular differences between such adjacent paths. It is preferred if the surface normal of the nozzle plate of one path deviates from the surface normal of the nozzle plate of the respectively adjacent path by an angle of less than 30°, preferably by less than 20°, and / or if the surface normal of the substrate surface deviates from one path from the surface normal of the substrate surface of the respectively adjacent path by an angle of less than 30°, preferably by less than 20°.

[0029] It is advantageous if, in particular, all nozzles of the nozzle plate, in particular all nozzles of the nozzle plate that are assigned to the corresponding path, have a specified maximum distance along the z-axis to the part of the substrate surface that is located directly below the nozzle plate during the printing process.

[0030] It is preferred that all nozzles of the nozzle plate, in particular all nozzles of the nozzle plate assigned to the corresponding web, have a maximum distance of 15 mm along the z-axis, more preferably a maximum distance of 10 mm along the z-axis, even more preferably a maximum distance of 5 mm along the z-axis, from the part of the substrate surface that is located directly beneath the nozzle plate during the printing process. This allows for a largely consistent printing quality, in particular within a web and / or printhead position.

[0031] It is particularly preferred if the distance of the nozzle plate along the z-axis to the part of the substrate surface which is located directly below the nozzle plate during the printing process, between adjacent tracks, differs by no more than 10 mm along the z-axis, preferably by no more than 5 mm along the z-axis.

[0032] In order to adjust such a distance of all nozzles of the nozzle plate along the z-axis to the part of the substrate surface that is located directly below the nozzle plate during the printing process, the substrate or a support of the substrate can be readjusted accordingly before and / or during the printing process and / or the nozzle plate can be readjusted accordingly before and / or during the printing process.

[0033] It is preferred if the nozzle plate and / or the substrate and / or the holder are adjusted, preferably translationally, along the z-axis. Furthermore, it is possible for the substrate and / or the substrate holder to be adjusted by an angle relative to the nozzle plate. Alternatively or additionally, it is possible for the nozzle plate to be adjusted by an angle relative to the substrate and / or relative to the substrate holder.

[0034] The x-axis may run along the axis of a drive, particularly a linear drive, used to adjust the print head position.

[0035] In step d), the subjects are optically captured. It is possible that an image of an area encompassing the subjects is captured, which can be provided in step e). It is possible that the image is digitally stored and evaluated at least temporarily. Alternatively or additionally, it is possible that the optical capture takes place continuously on a film recording. In the following, an image is understood to mean a digital image or a frame of a film recording.

[0036] The image area is selected so that the first, second, third, and / or fourth subject is completely encompassed. The maximum dimensions of the subjects are thus defined by the image area. For example, at 280x magnification, the optical sensor produces an image area with dimensions of 0.9 mm x 1.7 mm.

[0037] It is possible to define subregions to detect the relative position deviation, particularly at the beginning of step d), with each subregion being assigned a motif, preferably a reference element. An image provided in step e) can comprise such a subregion of the optically detected area of ​​the optical sensor. The subregions are preferably rectangular in shape.

[0038] This advantageously ensures that the relative positional deviation between specific motifs is determined. Other distinctive markings, recesses, and / or patterns on the substrate surface that could otherwise be mistakenly identified as motifs are excluded from evaluation.

[0039] To further increase the accuracy of determining the relative position deviation, it is possible to process the subjects optically detected by the sensor, in particular photographs and / or film recordings of the subjects, with at least one filter. Preferably, the at least one filter is applied to a sub-area at a time.

[0040] For example, at least one color filter and / or at least one image filter may be used. At least one color filter may be used, selected from the group consisting of converting the image to a grayscale image, extracting a single color channel, and / or combinations thereof.

[0041] For example, the extracted color channel can be the red, green, or blue color channel if the image is in RGB format. Alternatively, the extracted color channel can be the cyan, magenta, yellow, or black color channel if the image is in CMYK format.

[0042] At least one image filter may be used, which is selected from the group consisting of highlighting edges, blurring edges, converting the image to a grayscale image with subsequent conversion to a binary image depending on a predetermined threshold, converting to a grayscale image with subsequent normalization of the gray levels between white and black, noise reduction, and / or combinations thereof.

[0043] A grayscale image is defined as an image whose pixels have no colors and vary in their blackness from black to white. The blackness is arranged on a scale with 256 values, where black has the value 0 and white has the value 255. A binary image is defined as an image that has only black and white pixels.

[0044] It is possible, preferably in step e), to determine the magnitude of the relative positional deviation by determining a first distance c1. The first distance c1 is determined in particular between the first and second motifs and preferably corresponds to an actual value of the distance between the first and second motifs.

[0045] Preferably, the first distance c1 is determined in at least one spatial direction, preferably for the first and / or second spatial direction. It is thus possible for the first distance c1 to have a value in the first spatial direction and a value in the second spatial direction.

[0046] It is possible that a second distance c2 is determined to determine the relative positional deviation, preferably spatial direction deviations. The second distance c2 corresponds to the target value of the distance and / or an integer multiple of the target value of the distance between the first and second motifs, more preferably between the first and second motifs, in particular in at least one spatial direction. In particular, the second distance c2 corresponds to the nozzle pitch or an integer multiple of the nozzle pitch, in particular in the nozzle plate of the print head. For example, the second distance c2 can have a size selected from a range of 6 nozzles to 24 nozzles, preferably 12 nozzles to 18 nozzles.

[0047] Preferably, particularly in step a), a third motif and a fourth motif are printed on the first web on the substrate. Preferably, the third motif is arranged at at least one third printing position, and the fourth motif is arranged at at least one fourth printing position. The third and fourth motifs can be optically detected by the optical sensor.

[0048] It is possible that the third and / or fourth motif is formed from one or more reference elements, preferably selected from the group consisting of dot, line, cross, circle, ellipse, or combinations thereof. It is possible that the one or more reference elements have the same shape.

[0049] It is possible for the third and / or fourth motif, preferably reference elements of the third and / or fourth motif, to correspond to the first motif, in particular the reference elements of the first motif, or to be at least partially encompassed by it. Preferably, the at least one first printing position encompasses the at least one third and / or fourth printing position. In particular, it is possible for at least one of the one or more reference elements of the first motif to be encompassed by the third motif and / or for at least one further of the one or more reference elements of the first motif to be encompassed by the fourth motif.

[0050] Preferably, the second distance c2 is determined between the third motif and the fourth motif in at least one spatial direction, preferably for the first and second spatial directions. It is thus possible for the second distance c2 to have a size in the first spatial direction and a size in the second spatial direction.

[0051] It is possible that the magnitude of the first and / or the second relative spatial direction deviation is determined from one of the one or more reference elements.

[0052] It is possible that the magnitude of the relative position deviation, preferably the relative spatial direction deviation, is measured several times on different reference elements.

[0053] It is possible for the magnitude of the first and second relative spatial direction deviations to be generated from the same reference element of the one or more reference elements. This is particularly possible for reference elements whose shape exhibits rotational symmetry. The reference elements are preferably arranged in the form of a point, a cross, and / or a circle.

[0054] Alternatively or additionally, it is possible that the magnitude of the first and second relative spatial direction deviations are determined from different reference elements.

[0055] It is possible that the reference element of the one or more reference elements used to determine the size of the first spatial direction deviation is arranged rotated by a defined angle, in particular by 90°, compared to the reference element of the one or more reference elements used to determine the size of the second spatial direction deviation.

[0056] For example, a first reference element can be arranged in the form of a line whose extension occurs in the first spatial direction, and a second reference element in the form of a line whose extension occurs in the second spatial direction.

[0057] It is possible that the magnitude of the relative position deviation is determined from the difference between the first distance c1 and the second distance c2, in particular for the first and / or second spatial direction.

[0058] In other words, the magnitude of the relative position deviation, in particular for the first and / or second spatial direction, can be represented by equation (1), where the magnitude of the relative position deviation is denoted by Li: Li = c 1 − c 2

[0059] If the size of the relative position deviation is specified as a function of the first and / or second spatial direction, i.e. as the size of the relative spatial direction deviation, the following equations (2) to (3) result: Li x = c 1 x − c 2 x Li y = c 1 y − c 2 y

[0060] In equations (2) and (3), the relative spatial direction deviation of the first spatial direction is denoted by Li x , and the relative spatial direction deviation of the second spatial direction is denoted by Li y . The relative spatial direction deviations can be determined by the values ​​of the first distance c1 and the second distance c2 in the respective spatial direction. The value in the first spatial direction of the first distance c1 is denoted by c1 x , and the values ​​in the second spatial direction of the first distance c1 are denoted by c1 y . The values ​​of the second distance c2 are denoted analogously.

[0061] The magnitude of the relative positional deviation, preferably the spatial direction deviation, is positive if the first distance c1 between the first and second motifs is too large. If the first distance c1 between the first and second motifs is too small, the magnitude of the relative positional deviation, preferably the spatial direction deviation, has a negative value. If the magnitude of the relative positional deviation, preferably the spatial direction deviation, is zero, the first distance c1 between the first and second motifs corresponds to the desired optimal distance.

[0062] In particular, the first distance c1, the second distance c2, the relative positional deviation, and / or the relative spatial direction deviations are determined as a number of pixels. Due to the constant distance of the optical sensor from the substrate surface and the known resolution of the optical sensor, the number of pixels can be converted. This can then be used to generate a control signal. For example, the number of pixels that form the distance between the third and fourth motif can be used. This is because the second distance c2, i.e. the distance between nozzles in the print head, is fixed and known. A factor can thus be created to convert the determined number of pixels into a metric system.

[0063] To determine the magnitude of the relative position deviation, preferably at least a relative spatial direction deviation, it is possible for the method, in particular step e), to comprise the following sub-steps, which are preferably carried out in the specified order: Providing an image of the optically recorded motifs, in particular of the first, second, third and / or fourth motif, summing up the color values ​​and / or gray values ​​of the pixels that are present in a pixel row in the image, wherein the pixel row runs along one or more main extensions of the respective motif, creating a histogram across the pixel rows on the basis of the summed color values ​​and / or gray values ​​and / or preferably brightness values, determining the extreme value, preferably maximum or minimum, of the histograms, determining the smallest distance between the extreme values ​​of the histograms of the optically recorded motifs, in particular between the first and second motifs and / or between the third and fourth motifs.

[0064] When creating the histogram, non-binary images, more preferably grayscale images, of the optically captured motifs are provided. It is possible to divide the sum of the accumulated color values ​​and / or gray values ​​of each pixel row by the number of pixels. The resulting mean value can be understood as the brightness value of the respective pixel row. The histograms can be created alternatively or additionally based on the brightness values ​​of the pixel rows.

[0065] The histogram is preferably created along the main extension of the motifs and / or the reference elements they encompass. Particularly preferably, the motif, preferably the reference element, is in the form of a line. The main extension of the motifs or reference elements is preferably in the first spatial direction or the second spatial direction. It is also possible for a motif and / or reference element to have two or more main extensions, for example, in the form of a cross.

[0066] If, for example, a motif is present that is darker than the substrate, a minimum can be determined as the extreme value from the summed color values, gray values ​​and / or brightness values. If the motif is brighter than the substrate, the extreme value is a maximum. The respective pixel row in which the extreme value is located can be understood as the center line of the motif, preferably the reference element, along the spatial direction of the pixel row. The smallest distance between the extreme values ​​of the motifs, preferably reference elements, can correspond to the distance between their center lines. The determined smallest distance between the extreme values ​​or center lines corresponds to the first distance c1 between the first and second motif and / or the second distance c2 between the third and fourth motif.

[0067] The above-described determination of the magnitude of the relative positional deviation using a histogram offers the advantage that the magnitude of the relative positional deviation, preferably the magnitude of the spatial direction deviations, is based on an average value across several pixels along the main extension of the reference element. This allows for particularly accurate values ​​to be obtained.

[0068] When determining the size of the relative position deviation by means of a histogram, motifs are preferably used which have at least two reference elements, wherein the size of the first and second relative spatial direction deviations are preferably determined using different reference elements.

[0069] Alternatively or additionally, it is possible that the method, in particular step e), comprises the following sub-steps: Determining the geometric centers of gravity of the optically detected motifs, in particular of the first and second motifs and / or the third and fourth motifs, preferably of at least one encompassed reference element in each case, determining the smallest distance between the geometric centers of gravity of the optically detected motifs, in particular between the first and second motifs and / or between the third and fourth motifs, preferably of at least one encompassed reference element in each case.

[0070] When determining the geometric center of gravity, the optically captured motif, preferably the first, second, third and / or fourth motif, is preferably present as a binary image.

[0071] The advantage of the procedure described above is that the first and second motifs each require only one reference element to enable the determination of the magnitude of the first and second relative spatial direction deviations. Preferably, the motif, preferably the reference element, is in a shape that exhibits rotational symmetry. For example, the reference elements are in the form of a point, a cross, and / or a circle.

[0072] When generating the control signal, the determined relative position deviation is preferably added to the original magnitude of the movement of the print head or substrate. It is possible for the control signal to be composed of a first and / or a second partial control signal, in particular in the first and / or second spatial direction.

[0073] In particular, a first partial control signal is generated from the size of the first relative spatial direction deviation and / or a second partial control signal is generated from the size of the second relative spatial direction deviation.

[0074] It may be that the control signal comprises the first partial control signal to compensate for the magnitude of the relative spatial direction deviation along the first spatial direction and the second partial control signal to compensate for the magnitude of the relative spatial direction deviation along the second spatial direction.

[0075] It is possible for the method according to the invention to be carried out inline during a manufacturing process in which the resulting product has a substrate printed with a decorative print. The manufacturing process thus comprises a process for printing the substrate. It is possible for the method steps to be carried out once or several times before, during and / or after a process for printing the substrate. In particular, the method steps of the method can be temporally adapted to process steps, in particular process cycles, of the process for printing the substrate. This offers the advantage that the calibration of the print head position can be carried out inline and / or continuously during the printing process. For example, it is possible for the calibration to be carried out after each printing step and / or after each substrate change and / or after a signal from quality control.

[0076] For example, it is possible to calibrate the print head position immediately before the printing process on the substrate to be printed. It is preferred if the motifs used to calibrate the print head position are covered by the subsequent printing with a decorative print and / or are positioned in the applied decorative print such that they are visually inconspicuous. This particularly means that the motifs are not perceptible within the decorative print, preferably with the naked eye. The decorative print is preferably printed in at least a partial area of ​​the first and second webs.

[0077] It is also possible to perform the calibration of the print head position on the substrate to be printed at a variety of print head positions distributed across the substrate surface to be printed. This allows different areas of the substrate surface to be printed to be captured during calibration, and in particular, different three-dimensional or 2.5-dimensional shaped areas of the substrate surface to be printed to be captured during calibration.

[0078] It is possible to calibrate the printhead positions for all lanes and then perform the steps of the process for printing on the substrate. Alternatively, it is possible to calibrate two lanes relative to each other and then print the substrate with a decorative print in the area of ​​both lanes. After printing, a further lane is calibrated relative to one of the already printed lanes, and then a decorative print is printed on the substrate in the area of ​​the further lane. This procedure can be repeated until all lanes have been calibrated relative to each other.

[0079] It is also possible that the calibration of the print head position on the substrate to be printed is carried out for substrates of different nature, in particular made of different materials and / or with different three-dimensional or 2.5-dimensional shaped geometries.

[0080] It is also possible to calibrate the print head position on the substrate to be printed on largely identical substrates, in particular those made of largely identical materials and / or with largely identical three-dimensional or 2.5-dimensional shaped geometries. This can, for example, be used to detect variations in quality between different batches or deliveries of the substrate with the calibration.

[0081] It is also possible that the calibration of the print head position on the substrate to be printed is carried out several times on one and the same substrate, in particular at different print head positions and / or at different times, for example before and / or after each process color to be printed.

[0082] The print head, whose position is calibrated by the method, is arranged in particular in a device. At least a first and second print head position can be set for the print head. The device can have further print heads, each of which has independent print head positions. The print head preferably has a plurality of nozzles whose positions in the print head are fixed relative to one another. The positions of the nozzles in the print head and thus the printing positions are typically predetermined by a nozzle plate. The print head is an inkjet print head, preferably a drop-on-demand print head, furthermore a piezoelectric inkjet print head and / or a thermoelectric inkjet (bubblejet) print head.

[0083] The print head is connected, in particular, to a first drive, in particular a linear drive. The first drive has a first position sensor. By means of the first drive, the print head position relative to the substrate can be adjusted, in particular controlled and / or regulated, in one or more spatial directions, in particular in the first and / or second spatial directions. In a preferred embodiment, it is possible for the print head to be rotatable, so that the angle of the print head relative to the substrate surface and / or relative to the substrate holder can be adjusted, in particular controlled and / or regulated.

[0084] The print head prints motifs onto a substrate. The substrate can be arranged on a holder, preferably a clamping device, plug-in device, axis and / or mandrel. The substrate, in particular the holder, is connected to a second drive, preferably a rotating drive. The second drive has a second position sensor. By means of the second drive, the substrate and / or the holder can be rotated along an axis during the process. It is possible for the second drive and / or the holder to make it possible for the position of the substrate relative to the print head, in particular in the first, second and / or third spatial direction, and / or the angle of the substrate relative to the print head to be adjusted, in particular controlled and / or regulated. For this purpose, it is possible for a third partial control signal to be generated for the second drive.

[0085] Typically, the magnitude of the relative positional deviation, particularly in at least one spatial direction, is smaller than the distance between two nozzles in the print head. The smallest step size of the first and / or second drive is typically smaller than the magnitude of the relative positional deviation, particularly in at least one spatial direction.

[0086] Furthermore, the device has an optical sensor by means of which the motifs, in particular the first, second, third and / or fourth motif, are optically detected.

[0087] It is possible that the optical sensor is a camera. Preferably, the optical sensor is an RGB camera, a grayscale camera, and / or a black and white camera.

[0088] Preferably, the position of the optical sensor, in particular relative to the substrate, can be adjusted, in particular controlled and / or regulated. The distance between the optical sensor and the substrate is kept constant. For example, the position of the optical sensor relative to the substrate can be adjusted, in particular controlled and / or regulated, by means of a drive comprising a position encoder. In this case, the optical sensor can have a third drive comprising a third position encoder. Alternatively or additionally, the position of the optical sensor relative to the substrate can be adjusted, preferably controlled and / or regulated, by means of the first and / or second drive.

[0089] Based on the determined magnitude of the relative position deviation between the motifs, in particular between the first and second motif, a control unit can generate and / or process a control signal and send it to the first and / or second drive.

[0090] The control signal can be used to compensate for the determined relative position deviation between the motifs, in particular by means of the first drive and / or by means of the second drive.

[0091] It is possible for the substrate to have a three-dimensional or 2.5-dimensionally shaped surface, at least in the region of the first and / or second track. In other words, the substrate has a surface that extends along the three spatial directions, at least in the region of the first and / or second track. The surface of the substrate can be composed of flat or curved surface pieces in the region of the first and / or second track. In the region of the first and / or second track, the substrate can have surface pieces that can be arranged at an angle to the plane spanned by the first spatial direction and the second spatial direction, and optionally surface pieces that are arranged in the plane spanned by the first spatial direction and the second spatial direction.

[0092] Furthermore, it is possible for the substrate to be rotated along a rotation axis during the process and / or for the angle of the substrate to be varied relative to the plane spanned by the first spatial direction and the second spatial direction, in particular the nozzle plate. It is possible for the first, second, and optionally further paths to be arranged along the direction of rotation of the substrate.

[0093] It is furthermore possible for the first, second, third and / or fourth motif to be arranged such that an angular dimension of greater than 0° to 180°, preferably 30° to 150°, more preferably 45° to 135°, is obtained between the motifs and the axis of rotation when viewed along the axis. It is possible for an imaginary connecting line between the first, second, third and / or fourth motif to run at least partially through the substrate volume and / or the surrounding volume. In other words, the imaginary connecting line does not run completely along the substrate surface. The substrate can be selected from the group consisting of tube, bottle, drinking vessel, can, packaging element or combinations thereof.

[0094] The invention is explained below using several exemplary embodiments with the aid of the accompanying drawings. The exemplary embodiments shown are therefore not to be understood as limiting. Fig. 1 shows a schematic representation of an inkjet printer. Figs. 2a, b, 3a, b show schematic representations of the relative alignment of the print head to the substrate. Figs. 4a, b show schematic representations of a first and second path. Figs. 5a, b show schematic representations of another first and second path, wherein the second path has a relative positional deviation from the first path.

[0095] In Fig. 1 a device is shown schematically which is suitable for carrying out the method according to the invention for calibrating the positioning of an inkjet print head 1, wherein the method according to the invention for calibrating the positioning of an inkjet print head 1 comprises at least the following steps: a) Printing a first motif at at least one first printing position on a first web 2 onto a substrate 4, in particular with the print head 1, b) Positioning the print head 1 on a second web 3, c) Printing a second motif at at least one second printing position onto the substrate 4, d) Optically detecting the first motif and the second motif by means of an optical sensor 6, e) Determining a size of a relative position deviation between the first motif and the second motif, f) Generating a control signal based on the size of the relative position deviation, wherein the control signal is used to compensate for the determined relative position deviation.

[0096] It is possible for the method according to the invention to be carried out inline during a manufacturing process in which the resulting product comprises a substrate 4 printed with a decorative print. The manufacturing process thus comprises a process for printing the substrate 4. It is possible for the method steps of the method according to the invention to be carried out once or several times before, during, and / or after a process for printing the substrate 4. In particular, the method steps of the method can be temporally adapted to process steps, in particular process cycles, of the process for printing the substrate 4.

[0097] For example, it is possible to calibrate the print head position immediately before the printing process on the substrate 4 to be printed. It is preferred if the motifs 5 used to calibrate the print head position are covered by the subsequent printing with a decorative print and / or are positioned in the applied decorative print such that they are visually inconspicuous. This means, in particular, that the motifs 5 are not perceptible within the decorative print, preferably with the naked human eye. The decorative print is preferably printed in at least a partial area of ​​the first and second webs 2, 3.

[0098] It is also possible for the calibration of the print head position on the substrate 4 to be printed to be carried out at a plurality of print head positions distributed over the substrate surface to be printed.

[0099] It is possible to calibrate the print head positions for all webs and then perform the steps of the method for printing the substrate. Alternatively, it is possible to calibrate two webs relative to each other, followed by printing the substrate with a decorative print in the area of ​​both webs. After printing, a further web is calibrated relative to one of the already printed webs, and then a decorative print is printed on the substrate 4 in the area of ​​the further web. This procedure can be repeated until all webs have been calibrated relative to each other.

[0100] It is further possible that the calibration of the print head position on the substrate 4 to be printed is carried out for substrates of different nature, in particular made of different materials and / or with different three-dimensional or 2.5-dimensional shaped geometries.

[0101] It is further possible that the calibration of the print head position on the substrate 4 to be printed is carried out for largely identical substrates 4, in particular made of largely identical materials and / or with largely identical three-dimensional or 2.5-dimensional shaped geometries.

[0102] It is further possible that the calibration of the print head position on the substrate 4 to be printed is carried out multiple times on one and the same substrate, in particular at different print head positions and / or at different times, for example before and / or after each process color to be printed.

[0103] As in Fig. 1 As shown, the device comprises the print head 1, which is calibrated by the method and which has at least a first and a second print head position. The device may comprise additional print heads (not shown), each of which has independent print head positions.

[0104] The print head 1 preferably has a plurality of nozzles whose positions in the print head 1 are fixed relative to one another. The positions of the nozzles in the print head 1, and thus the printing positions, are typically predetermined by a nozzle plate. Preferably, the printing positions correspond to the positions of the nozzles in the print head 1, in particular the nozzle plate. Thus, the positions of the motifs 5 correspond to one or more positions of the nozzles in the print head 1, in particular wherein a motif can comprise one or more printing positions. It is possible that the same or different nozzle(s), i.e. printing position(s), are used on the first web 2 and on the second web 3 to print the motifs 5. It is possible for a web to comprise one or more printing positions of the print head 1.The number of print positions in a web thus corresponds to the maximum number of nozzles in print head 1, and it is possible for a web to comprise a number of print positions that corresponds entirely or partially to the maximum number of print positions. If the number of print positions in a web is less than the maximum possible number, the print positions located at the outer edges of the respective web are used for the print head position calibration process.

[0105] For example, print head 1 is Fig. 1 an inkjet print head 1, preferably a drop-on-demand print head, further a piezoelectric inkjet print head and / or thermoelectric inkjet (bubblejet) print head.

[0106] The print head 1 is connected in particular to a first drive 8, which comprises a first position sensor 7. The device is in Fig. 1 with a linear drive that can adjust, in particular control and / or regulate, the print head position relative to the substrate 4 in the first spatial direction along the double arrow shown. In a preferred embodiment, it is possible for the print head 1 to be rotatable, so that the angle of the print head 1 relative to the substrate surface and / or relative to the holder of the substrate 4 can be adjusted, in particular controlled and / or regulated.

[0107] The print head 1 prints motifs onto a substrate 4. The substrate 4 can be Fig. 1 shown, be arranged on a holder 11. The holder 11 can be, for example, a clamping device, plug-in device, axis and / or mandrel. The substrate 4 is connected by the holder 11 to a second drive 10. The second drive 10 has a second position sensor 9. In Fig. 1 The second drive 10 is depicted as a rotating drive. This allows the substrate 4 arranged on the holder 11, represented by the curved arrow, to be rotated along an axis during the process. Furthermore, it is possible for the second drive 10 and / or the holder 11 to adjust, in particular control and / or regulate, the position of the substrate 4 relative to the print head 1, in particular in the first, second, and / or third spatial direction, and / or the angle of the substrate 4 relative to the print head 1.

[0108] The device according to Fig. 1 further comprises an optical sensor 6, by means of which the motifs 5, in particular the first, second and / or a third and / or fourth motif, are optically detected.

[0109] It is possible for the optical sensor 6 to be a camera. Preferably, the optical sensor 6 is an RGB camera, a grayscale camera, and / or a black-and-white camera.

[0110] Preferably, the position of the optical sensor 6, in particular relative to the substrate 4, can be adjusted, in particular controlled and / or regulated. In this case, the distance of the optical sensor 6 to the substrate 4 is kept constant. For example, the position of the optical sensor 6 relative to the substrate 4 can be adjusted by means of a Fig. 1 The optical sensor 6 can be adapted, in particular controlled and / or regulated, by means of the drive shown, comprising a position sensor. In this case, the optical sensor 6 can have a third drive comprising a third position sensor. Alternatively or additionally, the position of the optical sensor 6 relative to the substrate 4 can be adapted, preferably regulated and / or regulated, by means of the first and / or second drive 10.

[0111] The device further comprises a control unit 12. Based on the magnitude of the relative positional deviation between the motifs 5, in particular between the first and second motifs, determined by the method according to the invention, the control unit 12 can generate and / or process a control signal and send it to the first and / or second drive 8, 10. This is Fig. 1 represented by the arrows between the optical sensor 6 and the control unit 12 and the arrows between the control unit 12 and the first and second drives 8, 10. The control signal can be used, as described in step f) of the method according to the invention, to compensate for the determined relative position deviation between the motifs 5, in particular by means of the first drive 8 and / or by means of the second drive 10.

[0112] As in Fig. 1 As shown, a print image is printed on the substrate 4, which image comprises at least a first and a second web 3. The first web 2 and the second web 3 can be arranged next to one another, but not overlapping. Alternatively, it is possible for the first web 2 and the second web 3 to be arranged such that they at least partially overlap in an overlap region. The first motif and the second motif are preferably arranged in the overlap region.

[0113] Preferably, the first lane 2 corresponds to the first printhead position, and the second lane 3 corresponds to the second printhead position. It is possible for the printhead 1 to have one or more additional lanes with corresponding printhead positions.

[0114] It is possible for the substrate 4 to have a three-dimensional or 2.5-dimensionally shaped surface at least in the region of the first and / or second web 2, 3. In other words, the substrate 4 has a surface that extends along three spatial directions at least in the region of the first and / or second web 2, 3. The surface of the substrate 4 can be composed of flat or curved surface pieces in the region of the first and / or second web 2, 3. In the region of the first and / or second web 2, 3, the substrate 4 can have surface pieces that can be arranged at an angle to the plane spanned by the first spatial direction and the second spatial direction and optionally surface pieces that are arranged in the plane spanned by the first spatial direction and the second spatial direction.

[0115] Furthermore, it is possible for the substrate 4 to be rotated along a rotation axis during the process and / or for the angle of the substrate 4 to be varied relative to the plane spanned by the first spatial direction and the second spatial direction, in particular the nozzle plate. It is possible for the first and second paths 2, 3 and an optional further path to be arranged along the direction of rotation of the substrate 4.

[0116] It is further possible for the first, second, third and / or fourth motif to be arranged such that an angular dimension of greater than 0° to 180°, preferably 30° to 150°, more preferably 45° to 135°, is obtained between the motifs and the axis of rotation when viewed along the axis. It is possible for an imaginary connecting line between the first, second, third and / or fourth motif to run at least partially through the substrate volume and / or the surrounding volume. In other words, the imaginary connecting line does not run completely along the substrate surface. The substrate 4 can be selected from the group consisting of tube, bottle, drinking vessel, can, packaging element or combinations thereof.

[0117] The to Fig. 1 The relative adjustment of the print head to the substrate by adjusting the angle of the substrate 4 or the holder of the substrate relative to the print head 1 is shown schematically in the Fig. 2a und 2b shown. Fig. 2a und 2b show a three-dimensional substrate 4 with a rotation axis, for example in the form of a bottle, which is arranged below a print head 1. The angle between the rotation axis and the nozzle plate is Fig. 2a for example 19° and in Fig. 2b for example, 12°. The area of ​​the substrate 4 located directly below the nozzle plate of the print head 1 corresponds, for example, to the first web 2 or the substrate surface to be printed.

[0118] In Fig. 2a und Fig. 2b is the surface normal of the nozzle plate, which runs parallel to the z-axis, preferably parallel to a surface normal of the substrate surface to be printed, which is located directly below the nozzle plate during the printing process. The surface normal of the nozzle plate is in Fig. 2a und Fig. 2b shown as an arrow.

[0119] This means that, in particular, the part of the substrate surface that is located directly beneath the nozzle plate during the printing process preferably runs largely parallel to the surface of the nozzle plate, or the surface normal of the nozzle plate and the surface normal of the part of the substrate surface that is located directly beneath the nozzle plate during the printing process preferably run largely parallel. This is in Fig. 4a und 4b represented by a dot-dash line on the substrate surface

[0120] Particularly when dealing with three-dimensional or 2.5-dimensional curved substrate surfaces, it is advantageous to adjust the distance along the z-axis between the nozzle plate and the part of the substrate surface that is located directly below the nozzle plate during the printing process, in particular to locally adapt the geometry that changes across the entire substrate surface, so that the highest possible local parallelism of the nozzle plate and the substrate surface is always achieved.

[0121] It is advantageous if, between adjacent tracks, for example the first track 2 and another track not shown, the surface normal of the nozzle plate and / or the surface normal of the substrate surface needs to be adjusted with as little deviation as possible when adjusting the local parallelism of the nozzle plate and the substrate surface. In this case, it is preferred if the surface normal of the nozzle plate from one track deviates from the surface normal of the nozzle plate of the respectively adjacent track by an angle of less than 30°, preferably by less than 20°, and / or if the surface normal of the substrate surface deviates from one track and the surface normal of the substrate surface of the respectively adjacent track by an angle of less than 30°, preferably by less than 20°.

[0122] It is advantageous if, in particular, all nozzles of the nozzle plate, in particular all nozzles of the nozzle plate that are assigned to the corresponding path, have a specified maximum distance along the z-axis to the part of the substrate surface that is located directly below the nozzle plate during the printing process. Fig. 2a und Fig. 2b is the area of ​​the nozzles of the nozzle plate, which is represented by two dotted lines directly above the first web 2 to be printed.

[0123] It is preferred that all nozzles of the nozzle plate, in particular all nozzles of the nozzle plate that are assigned to the corresponding path, have a maximum distance of 15 mm along the z-axis, more preferably a maximum distance of 10 mm along the z-axis, even more preferably a maximum distance of 5 mm along the z-axis, to the part of the substrate surface that is located directly below the nozzle plate during the printing process.

[0124] It is particularly preferred if the distance of the nozzle plate along the z-axis to the part of the substrate surface which is located directly below the nozzle plate during the printing process, between adjacent tracks, differs by no more than 10 mm along the z-axis, preferably by no more than 5 mm along the z-axis.

[0125] It is preferred if the nozzle plate and / or the substrate 4 and / or the holder 11 are moved, preferably translationally, along the z-axis, for example by means of the Fig. 1 schematically illustrated second drive 10. Furthermore, it is possible that the substrate 4 and / or the holder 11 of the substrate 4 as shown in Fig. 2a und Fig. 2b shown is adjusted by an angle relative to the nozzle plate.

[0126] The Fig. 3a und Fig. 3b each show an alternative to the Fig. 2a und Fig. 2b in which the nozzle plate of the print head 1 can be adjusted relative to the substrate 4 and / or the holder 11 of the substrate 4 by an angle of 12° or 19°. In this case, the print head 1 is designed to be rotatable. The surface normal of the nozzle plate, represented by an arrow, is also preferably parallel to a surface normal of the substrate surface to be printed on a first web 2, which is located directly beneath the nozzle plate during the printing process.

[0127] To clarify the, for example, according to a device according to Fig. 1 and the method according to the invention, the printed image printed on the substrate 4 is shown in Fig. 4a A schematic representation of the first and second webs 2, 3 is shown. The representation is simplified so that the extension of the substrate 4 is visible only along the first and second spatial directions. As described in steps a) and b), a motif 5 is printed as the first motif on the first web 2, and a motif 5 is printed as the second motif on the second web 3.

[0128] The Fig. 4a The motifs 5 shown, preferably the first and second motifs, have a specific positional relationship to each other and are spaced apart from each other by a first distance c1. It is possible that the second web 3 and / or the second motif and after Fig. 4a has a relative position deviation to the first track 2 and / or the first motif.

[0129] The first distance c1 is determined during the method according to the invention, preferably in step e), in order to determine the magnitude of the relative position deviation. The first distance c1 preferably corresponds to an actual value of the distance between the first and second motifs.

[0130] Preferably, the first distance c1 is determined in at least one spatial direction, preferably for the first and / or second spatial direction. It is thus possible for the first distance c1 to have a size in the first spatial direction and a size in the second spatial direction.

[0131] The relative position deviation may comprise a first relative spatial direction deviation that describes the relative spatial direction deviation along the x-axis, and the relative position deviation may comprise a second relative spatial direction deviation that describes the relative spatial direction deviation along the y-axis. The magnitude of the relative position deviation can preferably be calculated from the magnitudes of the relative spatial direction deviations.

[0132] In Fig. 4b A schematic representation of a first web 2, for example, present in the method according to the invention, on which two motifs 5 are printed, which are referred to below as the third and fourth motifs. The third and fourth motifs have a second distance c2 from one another in at least one spatial direction. The second distance c2 corresponds to the nozzle spacing or an integer multiple of the nozzle spacing, in particular in the nozzle plate of the print head 1. For example, the second distance c2 can have a size selected from a range of 6 nozzles to 24 nozzles, preferably 12 nozzles to 18 nozzles.

[0133] Preferably, the third motif is arranged at at least one third printing position and the fourth motif at at least one fourth printing position. It is possible for the second distance c2 to correspond to the target value or an integer multiple of the target value of the first distance c1 or the distance between the first and second motifs of Fig. 4a corresponds.

[0134] In Fig. 4b It is shown that motifs 5, i.e. the first, second, third and / or fourth motif, can be formed from one or more reference elements.

[0135] The one or more reference elements are, as shown, preferably in the form of a dot or line. A reference element, for example in the form of a line, can have a main extension along a spatial direction that is preferably selected from a range of more than 0 mm to 10 mm, preferably 0.01 mm to 7 mm, more preferably 0.05 mm to 5 mm.

[0136] Alternatively, a cross, circle, ellipse, and / or combinations thereof are also possible. Preferably, the one or more reference elements have the same shape.

[0137] It is possible that the third and / or fourth motif, preferably reference elements of the third or fourth motif, corresponds to the first motif, in particular the reference elements of the first motif, or is at least partially encompassed by it.

[0138] As in Fig. 4b As shown using the example of two lines, it is possible for one of the one or more reference elements to be arranged at 90° relative to another of the one or more reference elements. The two lines can be used to determine the size of different spatial direction deviations. It is thus possible for the second distance c2 to have a size in the first spatial direction and a size in the second spatial direction.

[0139] In Fig. 5a und 5b A first and second track 2, 3 are shown schematically, each with a motif 5, which have a relative positional deviation from each other. The first distance c1 therefore does not correspond to the second distance c2. The relative positional deviation is denoted here by Li. The plus sign in front of the relative positional deviation in Fig. 5a or minus in Fig. 5b represents the sign of the relative position deviation. The position deviation according to Fig. 5a und 5b has a spatial direction deviation in the first spatial direction. In Fig. 5a und 5b Although not shown, it is possible that there is a second spatial direction deviation in the second spatial direction.

[0140] To determine the magnitude of the relative positional deviation, preferably the spatial direction deviation, the motifs 5 are optically detected. This occurs in step d) of the method according to the invention. It is possible for an image of an area in which the motifs 5 are arranged to be captured, which image can be provided in step e) of the method according to the invention. It is possible for the image to be at least temporarily stored and evaluated as a photograph. Alternatively or additionally, it is possible for the optical detection to occur continuously on a film recording.

[0141] Preferably, sub-areas are defined in the image to capture the relative position deviation, with each sub-area being assigned a motif 5, preferably a reference element. The sub-areas are preferably rectangular in shape.

[0142] To further increase the accuracy of determining the relative position deviation, it is possible to process the subjects 5 optically detected by the optical sensor 6, in particular photographs and / or film recordings of the subjects 5, with at least one filter. Preferably, the at least one filter is applied to a sub-area in each case.

[0143] For example, at least one color filter and / or at least one image filter may be used. At least one color filter may be used, selected from the group consisting of converting the image to a grayscale image, extracting a single color channel, and / or combinations thereof.

[0144] For example, the extracted color channel can be the red, green, or blue color channel if the image is in RGB format. Alternatively, the extracted color channel can be the cyan, magenta, yellow, or black color channel if the image is in CMYK format.

[0145] At least one image filter may be used, which is selected from the group consisting of highlighting edges, blurring edges, converting the image to a grayscale image with subsequent conversion to a binary image depending on a predetermined threshold, converting to a grayscale image with subsequent normalization of the gray levels between white and black, noise reduction, and / or combinations thereof.

[0146] It is possible that the magnitude of the relative position deviation is determined from the difference between the first distance c1 and the second distance c2, in particular for the first and / or second spatial direction.

[0147] As explained above, the magnitude of the relative positional deviation or relative spatial direction deviation can be determined by equations (1) to (3).

[0148] As in Fig. 5a As shown, if the first distance c1 between the first and second motif, and thus between the first and second track 2, 3, is too large, the relative positional deviation, preferably the spatial direction deviation, results in a value with a positive sign.

[0149] Is again, as in Fig. 5b shown, the first distance c1 between the first and second motif, i.e. the distance between the first and second track 2, 3, is too small, the size of the relative position deviation, preferably spatial direction deviation, has a negative value.

[0150] The determination of the second distance c2 between the third and fourth motif and the first distance c1 between the first and second motif can be carried out at least partially analogously to each other.

[0151] In particular, the first distance c1, the second distance c2, the relative positional deviation, and / or the relative spatial direction deviations are determined as a number of pixels. Due to the constant distance of the optical sensor 6 from the substrate surface and the known resolution of the optical sensor 6, a conversion factor for the number of pixels in a metric system can be created and applied from the second distance c2 of the third and fourth motifs. This can then be used to generate a control signal.

[0152] To determine the magnitude of the relative position deviation, preferably at least a relative spatial direction deviation, it is possible for the method according to the invention, in particular step e), to comprise the following sub-steps: Providing an image of the optically recorded motifs 5, in particular of the first, second, third and / or fourth motif, summing up the color values ​​and / or gray values ​​of the pixels that are present in a pixel row in the image, wherein the pixel row runs along the one or more main extensions of the respective motif 5, creating a histogram across the pixel rows on the basis of the summed color values ​​and / or gray values ​​and / or preferably brightness values, determining the extreme value, preferably maximum or minimum, of the histograms, determining the smallest distance between the extreme values ​​of the histograms of the optically recorded motifs 5, in particular between the first and second motifs and / or between the third and fourth motifs.

[0153] When creating the histogram, non-binary images, more preferably grayscale images, of the optically captured motifs 5 are provided. It is possible that the sum of the accumulated color values ​​and / or gray values ​​of each pixel row is divided by the number of pixels. Alternatively or additionally, the histograms can be created based on the brightness values ​​of the pixel rows.

[0154] The histogram is preferably created along the main extension of the motifs 5 and / or the reference elements encompassed by them. Particularly preferably, the motif 5, preferably the reference element, is in the form of a line. The main extension of the motifs 5 or reference elements is preferably in the direction of the first spatial direction or the second spatial direction. It is also possible for a motif 5 and / or reference element to have two or more main extensions, for example, in the form of a cross.

[0155] The determined smallest distance between the extreme values ​​corresponds to the first distance c1 between the first and second motif and / or the second distance c2 between the third and fourth motif.

[0156] When determining the size of the relative position deviation by means of a histogram, motifs 5 are preferably used which have at least two reference elements, wherein the size of the first and second relative spatial direction deviations are preferably determined by means of different reference elements.

[0157] Alternatively or additionally, it is possible that the process according to the invention, in particular step e), comprises the following sub-steps: Determining the geometric centers of gravity of the optically detected motifs 5, in particular of the first and second motifs and / or the third and fourth motifs, preferably of at least one encompassed reference element in each case, determining the smallest distance between the geometric centers of gravity of the optically detected motifs 5, in particular between the first and second motifs and / or between the third and fourth motifs, preferably of at least one encompassed reference element in each case.

[0158] When determining the geometric center of gravity, the optically detected motif 5, preferably the first, second, third and / or fourth motif, is preferably present as a binary image.

[0159] The image provided in step e) preferably has a partial area defined in step d). It may comprise such a partial area of ​​the optically detected area of ​​the optical sensor 6.

[0160] Preferably, the motif 5, preferably the reference element, is in a shape that exhibits rotational symmetry. For example, the motif, preferably the reference element, is in the form of a dot, a cross, and / or a circle.

[0161] Based on the magnitude of the determined relative position deviation, preferably relative spatial direction deviation, the control signal used to compensate for the determined relative position deviation, preferably relative spatial direction deviation, is generated in step f). It is possible for the control signal to be composed of a first and / or a second partial control signal, in particular in the first and / or second spatial direction. In particular, a first partial control signal is generated from the magnitude of the first relative spatial direction deviation and / or a second partial control signal is generated from the magnitude of the second relative spatial direction deviation. It may be that the control signal comprises the first partial control signal in order to compensate for the magnitude of the relative spatial direction deviation along the first spatial direction and the second partial control signal in order to compensate for the magnitude of the relative spatial direction deviation along the second spatial direction.

[0162] Of course, the listed versions can be combined with each other as desired and do not represent any limitations. Bezugszeichenliste

[0163] 1Print head 2First lane 3Second lane 4Substrate 5Motif 6Optical sensor 7First position sensor 8First drive 9Second position sensor 10Second drive 11Bracket 12Control unit

Claims

1. Method for calibrating the positioning of an inkjet print head (1) characterized by that the method comprises the following steps: a) printing a first motif at at least a first printing position on a first web (2) onto a substrate (4), b) positioning the print head (1) on a second web, c) printing a second motif at at least a second printing position onto the substrate (4), d) optically detecting the first motif and the second motif by means of an optical sensor (6), e) determining a magnitude of a relative positional deviation between the first motif and the second motif, f) generating a control signal based on the magnitude of the relative positional deviation, the control signal being used to compensate for the determined relative positional deviation.

2. Method according to claim 1 characterized by thata first distance c1 is determined between the first motif and the second motif in at least one spatial direction, in particular wherein the first distance c1 corresponds to the actual value of the distance between the first and second motif, and / or that to determine the relative position deviation, a second distance c2 is determined which corresponds to a target value of the distance or an integer multiple of the target value of the distance between the first and second motif.

3. Method according to one of the preceding claims characterized by thaton the first web (2) on the substrate (4), a third motif is printed at at least one third printing position and a fourth motif is printed at at least one fourth printing position, wherein the third and fourth motifs are optically detected by means of the optical sensor (6) and a second distance c2 between the third and fourth motifs is determined at least in one spatial direction, in particular wherein the third and / or fourth motif corresponds to the first motif or is at least partially encompassed by the first motif, and / or that the size of the relative position deviation is determined from the difference between the first distance c1 and the second distance c2.

4. Method according to one of the preceding claims characterized by thatthe first, second, third and / or fourth motif is formed from one or more reference elements, which are preferably selected from the group consisting of dot, line, cross, circle, ellipse or combinations thereof, in particular wherein the one or more reference elements have the same shape.

5. Method according to one of the preceding claims characterized by that the relative position deviation is composed of a first and / or a second relative spatial direction deviation.

6. Method according to one of the preceding claims characterized by that the magnitude of the first and / or second relative spatial direction deviation is determined from one of the one or more reference elements.

7. Method according to claim 6 characterized by that the magnitude of the first and second relative spatial direction deviation is determined from the same reference element of the one or more reference elements, or thatthe size of the first and second relative spatial direction deviation is determined from different reference elements of the one or more reference elements, and / or that the reference element of the one or more reference elements used to determine the size of the first spatial direction deviation is rotated by 90° compared to the reference element of the one or more reference elements used to determine the size of the second spatial direction deviation.

8. Method according to one of the preceding claims characterized by that the control signal is composed of a first and / or a second partial control signal, and / or that the partial control signal for the first spatial direction is generated from the size of the first relative spatial direction deviation and / or the partial control signal for the second spatial direction deviation is generated from the size of the second spatial direction deviation.

9. Method according to one of the preceding claims characterized by that the positions of the motifs (5), in particular the reference elements encompassed by the motifs, correspond to the positions of nozzles in the print head (1), and / or that the optical sensor (6) is a camera, and / or that the position of the optical sensor (6) is controlled, wherein a distance of the optical sensor (6) to the substrate (4) is kept constant.

10. Method according to one of the preceding claims characterized by that the first web (2) and the second web (3) are not arranged overlapping, or that the first web (2) and the second web (3) at least partially overlap in an overlapping region, in particular wherein the first and second motifs are arranged in the overlapping region.

11. Method according to one of the preceding claims characterized by thatthe method steps are carried out immediately before, during and / or immediately after a method for printing the substrate (4), each once or several times, in particular wherein the method steps of the method are adapted in time to method steps, in particular to process cycles, of the method for printing the substrate (4).

12. Method according to one of the preceding claims characterized by that to detect the relative position deviation, sub-areas are defined, each sub-area being assigned a motif (5), preferably a reference element, and / or that the first distance c1 and / or the second distance c2 is determined as a number of pixels, wherein the number of pixels is converted by means of the resolution of the optical sensor (6), in particular into a metric system.

13. Method according to one of the preceding claims characterized by thatthe method comprises the following substeps: - providing an image of the optically recorded motifs (5), in particular of the first, second, third and / or fourth motif, - summing the color values ​​and / or gray values ​​of the pixels that are present in a pixel row in the image, wherein the pixel row runs along one or more main extensions of the respective motif (5), - creating a histogram across the pixel rows based on the summed color values ​​and / or gray values, - determining the extreme values, preferably maxima or minima, of the histograms, - determining the smallest distance between the extreme values ​​of the histograms of the optically recorded motifs (5), in particular between the first and second motifs and / or between the third and fourth motifs, and / or thatthe method comprises the following sub-steps: - providing an image of the optically detected motifs (5), in particular of the first, second, third and / or fourth motif, - determining the geometric centers of gravity of the optically detected motifs (5), - determining the smallest distance between the geometric centers of gravity of the optically detected motifs (5), in particular between the first and second motif and / or between the third and fourth motif.

14. Method according to one of the preceding claims characterized by thatbased on the size of the relative position deviation between the first and second motifs, a control unit (12) generates and / or processes the control signal, and the print head position relative to the substrate (4) is adjusted by means of a first drive (8) comprising a first position sensor (7) and / or the position of the substrate (4) to the print head (1) is adjusted by means of a second drive (10) comprising a second position sensor (8), and wherein the print head position is adjusted by means of the first drive (8) and the position of the substrate (4) is adjusted by means of the second drive (10), in particular wherein the first drive (8) has a linear drive and / or the second drive (10) has a rotary drive.

15. Method according to one of the preceding claims characterized by that the substrate (4) has a three-dimensional or 2.5-dimensionally shaped surface at least in the region of the first and / or second web (2, 3), and / or thatthe substrate (4) is rotated along an axis during the process.

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