Method and apparatus for determining print data for an inkjet printing device

Abstract

Device for determining print data for a print image (300) to be printed by a print bar (102) of an inkjet printing device (100); wherein the print bar (102) comprises one or more nozzles (21, 22); wherein the print data for a plurality of pixels of the print image (300) each indicate an amount of ink to be ejected by each nozzle (21, 22) of the print bar (102); wherein the device (101) is configured - to determine, based on the print data, a time course (400) of an ink flow rate (402) of ink (202) that flows into the print bar (102) and / or is ejected from the one or more nozzles (21, 22) of the print bar (102) during the printing of the print image (300); - to determine, based on the temporal profile (400) of the ink flow rate (402), whether, during the printing of the printed image (300), an ink ejection error will be caused by at least one nozzle (21, 22) due to changes in the ink flow rate (402); - to determine an amplitude spectrum (410) based on the temporal profile (400) of the ink flow rate (402), which for a multitude of change frequencies (311) of the ink flow rate (402) indicates an amplitude (412) of a frequency component of the temporal profile (400) of the ink flow rate (402) for the respective change frequency (311); - to determine, based on the amplitude spectrum (410), whether an ink ejection error will occur during the printing of the print image (300) due to changes in the ink flow rate (402); and - to adjust the print data for the print image to be printed (300) depending on whether it is determined that an ink ejection error will be caused or not.

Description

[0001] The invention relates to a method and a corresponding device that make it possible to determine print data for a print image that can be printed without ink ejection errors by a print bar of an inkjet printing device.

[0002] An inkjet printing device for printing onto a recording medium can comprise a print bar with one or more printheads, each with one or more nozzles. The nozzles are each configured to eject ink droplets to print pixels of a printed image onto the recording medium.

[0003] To supply the individual printheads with ink, ink can be fed to each printhead of a print bar via supply lines from an ink reservoir. Due to the design of the ink supply system of a print bar, individual nozzle failures, i.e., ink ejection errors, may occur during printing, which impairs the print quality.

[0004] This document addresses the technical problem of preventing ink ejection errors, particularly those caused by the ink supply, during the printing of a printed image, in order to improve the print quality. This problem is solved by the features of independent device claim 1 and independent method claim 9.

[0005] According to one aspect of the invention, a device for determining print data for a print image to be printed by a print bar of an inkjet printing device is described, wherein the print bar comprises one or more nozzles. The print data indicates, for a plurality of pixels of the print image, the amount of ink to be ejected by each nozzle of the print bar.

[0006] The device is configured to determine and / or predict, based on the print data, the ink flow rate over time. This ink flows into the print bar and / or is ejected from the one or more nozzles of the print bar during printing. The device is further configured, based on the ink flow rate over time, to determine and / or predict whether, during printing, changes in the ink flow rate will cause an ink ejection error, in particular a nozzle failure, from at least one nozzle. Finally, the device is configured to adjust the print data for the image to be printed depending on whether or not an ink ejection error is determined or predicted.

[0007] According to a further aspect of the invention, a method for determining print data for a print image to be printed by a printhead of an inkjet printing device is described. The method comprises determining, based on the print data, the time-dependent profile of the ink flow rate that flows into the printhead and / or is ejected from one or more nozzles of the printhead during the printing of the image. Furthermore, the method comprises determining or predicting, based on the time-dependent profile of the ink flow rate, whether an ink ejection error will occur from at least one nozzle during the printing of the image. The method also includes adjusting the print data for the image to be printed depending on whether or not an ink ejection error is determined or predicted.

[0008] Exemplary embodiments of the invention will now be described in more detail with reference to the schematic drawing. These show: Fig. 1 a block diagram of an exemplary inkjet printing device; Fig. 2 an exemplary ink supply to the one or more printheads of a print bar of an inkjet printing device; Fig. 3a-3c are exemplary printed images with different frequencies of change in ink flow quantity, i.e., with different frequencies of ink flow rate; Fig. 3d an exemplary number of nozzle defects as a function of the change frequency of the ink flow rate; Fig. 4a an exemplary time course of the ink flow rate; Fig. 4b an exemplary amplitude spectrum of the temporal course of the ink flow rate; and Fig. 5 A flowchart of an exemplary procedure for determining print data for a print image to be printed.

[0009] The in Fig. The printing device 100 shown in Figure 1 is designed for printing onto a sheet-shaped, flat, disc-shaped, or tape-shaped recording medium 120. The recording medium 120 can be made of paper, cardboard, carton, metal, plastic, textiles, a combination thereof, and / or other suitable and printable materials. The recording medium 120 is guided through the printing unit 140 of the printing device 100 along the transport direction 1, indicated by an arrow.

[0010] In the illustrated example, the printing unit 140 of the printing device 100 comprises two printing bars 102, each printing bar 102 being usable for printing with ink of a specific color, e.g., black, cyan, magenta, and / or yellow, and optionally MICR ink. Different printing bars 102 can be used for printing with different inks. Furthermore, the printing device 100 typically includes at least one fuser or drying unit, which is not integrated into Fig. 1 is shown and is set up to fix a printed image printed on the recording medium 120.

[0011] A print bar 102 can comprise one or more print heads 103, which may be arranged side by side in several rows to print the pixels of different columns 31, 32 of a print image onto the recording medium 120. In the Fig. In the example shown, a print bar 102 comprises five print heads 103, each print head 103 printing the pixels of a group of columns 31, 32 of a print image onto the recording medium 120. The number of print heads 103 of a print bar 102 can be, for example, 5, 10 or more.

[0012] Each printhead 103 of the printing unit 140 comprises in the Fig. In the embodiment shown in Figure 1, several nozzles 21, 22 are provided, each nozzle 21, 22 being configured to fire or propel ink droplets onto the recording medium 120. For example, a printhead 103 of the printing unit 140 can comprise several thousand effectively used nozzles 21, 22 arranged along several rows transverse to the transport direction 1 of the recording medium 120. By means of the nozzles 21, 22 of a printhead 103 of the printing unit 140, pixels of a line of a printed image can be printed onto the recording medium 120 transverse to the transport direction 1, i.e., along the width of the recording medium 120.

[0013] The printing device 100 further comprises a control device 101, e.g. a control hardware and / or a controller, which is configured to control the actuators of the individual nozzles 21, 22 of the individual printheads 103 of the printing unit 140 in order to apply the printed image to the recording medium 120 depending on print data.

[0014] The printing unit 140 of the printing device 100 thus comprises at least one printing bar 102 with K nozzles 21, 22, which can be arranged in one or more printheads 103 and which can be controlled with a specific line rate to print one line at a time, running transversely to the transport direction 1 of the recording medium 120, with K pixels or K columns 31, 32 of a printed image onto the recording medium 120, e.g. with K>1000. In the illustrated example, the nozzles 21, 22 are fixed in the printing device 100, and the recording medium 120 is moved past the stationary nozzles 21, 22 at a specific transport speed.

[0015] Fig. Figure 2 shows the ink supply of an example printhead 103. With the in Fig. The ink supply shown in Figure 2 can supply one or more printheads 103 of a print bar 102 with ink 202 of a specific ink type, e.g., a specific color. The in Fig. The ink supply shown in 2 can be provided for each print bar 102 and / or for each type of ink used in a printing device 100.

[0016] Ink 202 can be supplied to the individual nozzles 21, 22 of a printhead 103 via an ink supply channel 206. The ink supply channel 206 can draw the ink 202 from a vacuum or backpressure reservoir 201. The vacuum reservoir 201, in turn, can be supplied with ink 202 from a supply reservoir 204 via an ink supply channel 208. The ink 202 can be conveyed from the supply reservoir 204 into the vacuum reservoir 201 by means of a supply and delivery module 205, in particular by means of a pump. The vacuum reservoir 201 can be used to set a specific physical vacuum within the individual nozzles 21, 22 of the printheads 103. This physical vacuum ensures that no ink 202 leaks from nozzles 21, 22 during the printing operation of the printing device 100.Furthermore, the physical vacuum can cause an ink meniscus to form at the outlet of a nozzle 21, 22, which can be set in motion by an actuator of the nozzle 21, 22, e.g. by a piezoelectric actuator, in order to eject an ink droplet from the nozzle 21, 22.

[0017] The physical vacuum can be mechanically adjusted via the height difference between the nozzle plate of the printheads 103 and the fill level of the vacuum reservoir 201. To adjust the vacuum in the nozzles 21, 22, the fill level of the vacuum reservoir 201 can thus be set, and in particular regulated, to a specific fill level value. Alternatively or additionally, the vacuum in the vacuum reservoir 201 can be adjusted by a pressure module 214, e.g., by a pump.

[0018] During relatively high load changes, i.e., relatively large changes in the ink application on a recording medium 120, such as in a coloring process that repeatedly alternates between 0% and 100%, nozzle failures can occur during printing. This can happen particularly when all printheads 103 of a print bar 102 start printing simultaneously with a relatively high load, i.e., with a relatively high ink application.

[0019] By generally defining a reduction in the maximum achievable color gamut, i.e., by reducing the maximum possible ink application or the maximum possible amount of ink on the recording medium 120, such disruptions to the printing process, in particular such nozzle failures or ink ejection errors, can be avoided. The maximum achievable color gamut, which prevents ink flow-related disruptions to the printing process, can be experimentally determined and defined during the development of a printing device 100.

[0020] However, a blanket reduction of the maximum achievable color gamut of printed images leads to a limitation in print quality. This document describes measures that can reliably prevent ink flow-related disruptions in printing operations, possibly even without a blanket reduction of the maximum achievable color gamut.

[0021] As explained above, a printing device 100, and in particular its ink supply, can be susceptible to changes in printing load, especially fluctuations in ink flow rate, when printing an image. The susceptibility of a printing device 100 to changes in ink flow rate during printing can be determined experimentally. This is exemplified in the Fig. 3a to 3d representation. Fig. Figure 3a shows a printed image 300 with a colored image area 301 and with a non-colored image area 302. The colored image area 301 includes, for example, several colored lines, while the non-colored image area 302 has several non-colored lines. Fig. 3a shows only one period of the printed image 300, i.e. the printed image 300 can alternately show a colored image area 301 and a non-colored image area 302 over several periods.

[0022] At the transition between the two image areas 301 and 302, there is an abrupt change in the ink flow rate, in particular an abrupt increase in the ink flow rate at a transition from an uncolored image area 302 to a colored image area 301, and an abrupt decrease in the ink flow rate at a transition from a colored image area 301 to an uncolored image area 302. During the periodic sequencing of the in Fig. In the printed image section shown in 3a, the ink flow rate changes with a specific frequency. This frequency depends on the number of lines per image area 301, 302 and / or the transport speed of the recording medium 120. In the Fig. In the example shown in 3a, the rate of change of the ink flow rate is 1Hz.

[0023] It can, as in the Fig. 3b and Fig. 3c is shown, further print images 300 with different change frequencies of the ink flow rate are considered, for example 2Hz in Fig. 3b and Fig. 4Hz in Fig. 3c. Thus, a large number of print images (300) with a corresponding number of change frequencies of the ink flow rate can be viewed and / or printed.

[0024] For each change frequency, the number of ink ejection defects, particularly nozzle failures, that occur when printing the respective print image 300 can be determined. Thus, by using or printing the multitude of different print images 300 for the corresponding multitude of change frequencies, a number of ink ejection defects can be determined that result from changes in the ink flow rate, i.e., ink flow rates, at the respective change frequency. From this, as exemplified in Fig. A sensitivity characteristic curve 310 for the printing device 100, in particular for a print bar 102 or for a print head 103, is shown in 3D. The sensitivity characteristic curve 310 indicates the number 312 of ink ejection errors as a function of the change frequency 311 of the ink flow rate. The sensitivity characteristic curve 310 thus indicates at which one or more change frequencies 311 of the ink flow rate the printing device 100, in particular the print bar 102, exhibits a particularly high or a particularly low susceptibility to ink ejection errors.

[0025] The evaluation and / or control device 101 of the printing device 100 can be configured to analyze the print data for a print image 300 to be printed. The print data may have been determined within the framework of a rasterization process for an original image to be printed. The original image may be, for example, a computer image or a PDF file that displays a color value in a specific color space, e.g., an RGB color space, for each pixel in a matrix. In the rasterization process, a data record can be determined for each nozzle 21, 22 and for each line based on the original image, whereby the data record indicates • whether or not ink should be ejected; and • the amount of ink to be ejected as part of the ink ejection process.

[0026] The print data thus includes, for a large number of lines, data sets for the individual nozzles 21, 22 of the print bar 102.

[0027] As exemplified in Fig. As shown in Figure 4a, the device 101 can be configured to determine a time profile 400 of the ink flow rate 402 based on the print data. In particular, the ink flow rate 402 per unit of time or per line cycle 401 can be determined, which must be supplied by the ink supply in a print bar 102 or in a printhead 103 of the printing device 100 during the printing of the print image 300 in order to print the print image 300. Furthermore, the device 101 can be configured to check or predict, based on the determined time profile 400 of the ink flow rate 402 and, if applicable, based on the sensitivity characteristics or characteristic curve 310 of the print bar 102, whether one or more ink flow-related ink ejection errors occur during the printing of the print image 300.

[0028] For this purpose, the device 101 can be configured to perform a spectral analysis of the time course 400 of the ink flow rate 402. In particular, as exemplified in Fig. Figure 4b shows that an amplitude spectrum 410 of the time course 400 of the ink flow rate 402 can be determined. The amplitude spectrum 410 can be determined, for example, using a Fast Fourier Transform. Within the framework of frequency analysis, the time course 400 of the ink flow rate 402 can be decomposed into a multitude of different frequency components for a corresponding multitude of change frequencies 311 of the ink flow rate 402. The amplitude spectrum 410 can indicate an energy value or an amplitude 412 of the respective frequency component within the time course 400 of the ink flow rate 402 for each frequency component.

[0029] Based on the amplitude spectrum 410, one or more frequency components for one or more change frequencies 311 can be identified that could cause, or are causing, an ink ejection error. In particular, the amplitude 412 of the frequency component for a specific change frequency 414 can be compared with an amplitude threshold 415, where the amplitude threshold 415 indicates the amplitude 412 at which one or more ink ejection errors are expected to occur. Thus, one or more frequency components of the time course 400 of the ink flow rate 402 can be determined that have such a high amplitude 412 that one or more ink ejection errors are expected to occur when printing the print image 300.

[0030] The amplitude threshold 415 used to identify a critical frequency component can depend on the change frequency 311. In other words, the amplitude thresholds 415 can be different for different change frequencies 311. The amplitude thresholds 415 can be determined based on the sensitivity characteristics 310, in particular such that the amplitude threshold 415 decreases with increasing sensitivity and increases with decreasing sensitivity. Fig. Figure 4b shows an exemplary progression 420 of the amplitude threshold values ​​415 for different change frequencies 311.

[0031] If it is detected that the time course 400 of the ink flow rate 402 exhibits one or more frequency components that could or will cause an ink ejection error when printing the print image 300, the print data can be modified. In particular, the rasterization of the original image can be adjusted to determine modified print data that results in a time course 400 of the ink flow rate 402 that does not exhibit any frequency component that could cause an ink ejection error, especially one that does not exhibit any frequency component with an amplitude 412 that exceeds the amplitude threshold 415 for the respective change frequency 311.

[0032] The device 101 can thus be configured to specifically examine the data to be printed, i.e., the print data, for certain change frequencies 311. In particular, one or more change frequencies 311 can be considered at which the print bar 102 exhibits a particularly high sensitivity with respect to fluctuations in the ink flow rate 402. For these one or more change frequencies 311, the amplitude threshold 415 is typically relatively low. These one or more critical change frequencies 311 can result from the design of the ink supply and / or the print bar 102, in particular from the arrangement, e.g., offset from one another and / or at a certain distance, of the one or more printheads 103 and / or from the arrangement of the ink supply channels 206 and / or from the design of the ink supply system, e.g., with respect to resistance and / or damping.

[0033] The analysis of pressure load changes can be performed via a Fourier transform of the print data, in particular a Fourier transform of the time course 400 of the ink flow rate 402, so that an amplitude spectrum 410 is provided which, for each frequency 311 of the change in the flow rate, indicates the value or amplitude 412 of the ink flow rate at that change frequency 311. If, at a specific frequency 414, such as 2 Hz, the amplitude 412 of the flow rate exceeds the experimentally determined amplitude threshold 415, the ink quantity can be reduced and / or adjusted by re-rasterizing the print data to ensure stable operation of the printing device 100. Conversely, if no critical change frequency 311 is identified, the ink quantity can be increased and / or adjusted by re-rasterizing the print data to expand the color space used for the printed image 300.

[0034] Fig. Figure 5 shows a flowchart of an exemplary, optionally computer-implemented, method 500 for determining print data for a print image 300 to be printed by a print bar 102 of an inkjet printing device 100. The print bar 102 comprises at least one print head 103 with one or more nozzles 21, 22. The print image 300 and the print data may have been derived from an original image by rasterization. The print data may indicate, for a plurality of pixels of the print image 300, the amount of ink to be ejected by each nozzle 21, 22 of the print bar 102.

[0035] Method 500 comprises determining, based on the print data, the time course 400 of the ink flow rate or the amount of ink 202 that flows into the print bar 102 during the printing of the print image 300 and / or that is ejected from the one or more nozzles 21, 22 of the print bar 102 during the printing of the print image 300. The time course 400 can display the ink flow rate or the cumulative ink amount for a multitude of time points or for a multitude of line cycles 401 or for a multitude of lines of the print image 300. In other words, the time course 400 can display a value for the cumulative ink amount for a multitude of line cycles 401. It is thus possible to determine how the ink flow will change over time during the printing of the print image 300.The temporal profile 400 of the ink flow quantity 402 can be determined without the print image 300 actually being printed by the print bar 102.

[0036] Method 500 further comprises determining or predicting 502, based on the temporal profile 400 of the ink flow rate 402, whether, during the printing of the print image 300, changes in the ink flow rate 402 will cause an ink ejection error from at least one nozzle 21, 22. For this purpose, a frequency analysis of the temporal profile 400 of the ink flow rate 402 can be performed, as described in this document. The determination 502 can be carried out without the print image 300 actually being printed by the print bar 102.

[0037] Furthermore, the procedure 500 includes adjusting the print data 503 for the print image 300 to be printed, depending on whether or not it is determined that an ink ejection error will occur. The print data can be determined by expanding or reducing the color gamut of the print image 300, particularly by re-rasterizing the original image. The procedure 500 can be repeated iteratively, if necessary, to achieve an optimized compromise between the largest possible color gamut and the avoidance of ink ejection errors, especially the avoidance of nozzle failures caused by changes in the ink flow rate.

[0038] A method 500 is thus described by which print data for a print image 300 can be adapted and / or determined in such a way that the temporal profile 400 of the ink flow rate 402 caused by the print data does not exhibit any changes in quantity or flow rates that could cause ink ejection errors, in particular nozzle failures. Furthermore, the print data can be determined or adapted in such a way that the print image 300 has the largest possible color gamut.

[0039] Furthermore, this document describes a device 101 for determining print data for a print image 300 to be printed by a print bar 102 of an inkjet printing device 100. The print bar 102 comprises at least one print head 103 with one or more nozzles 21, 22. The print data indicates, for a plurality of pixels of the print image 300, the amount of ink or the droplet size to be ejected by each nozzle 21, 22 of the print bar 102.

[0040] The device 101 can be configured to determine, based on the print data, the time course 400 of the ink flow rate 402 of ink 202 that flows into the printing bar 102 during the printing of the print image 300 and / or that is ejected from the one or more nozzles 21, 22 of the printing bar 102 during the printing of the print image 300.

[0041] The time course 400 of the ink flow rate 402 can indicate a quantity of ink 202 for each sequence of line cycles 401. A line cycle 401 can correspond to the time required to print one line of the print image 300. The printhead 103 typically comprises a plurality of nozzles 21, 22, which are configured to print a corresponding plurality of pixels in a corresponding plurality of columns 31, 32 of the print image 300 at a specific line cycle. The print data can indicate the quantity of ink to be ejected at the specific line cycle for each of the plurality of nozzles 21, 22.

[0042] The device 101 can be configured to sum the ink quantity from the plurality of nozzles 21, 22, as indicated by the print data, for a specific line cycle 401 in order to determine a quantity value of the time-dependent profile 400 of the ink flow rate, or the ink quantity 402, for that specific line cycle. Similarly, the quantity values ​​for different line cycles 401 can be determined to ascertain the time-dependent profile 400 of the ink flow rate 402. The time-dependent profile 400 of the ink flow rate 402 can thus indicate how the ink flow rate, or in short, the ink quantity 402, changes when printing different lines of the print image 300. The time-dependent profile 400 of the ink flow rate 402 can optionally be determined solely based on the print data. In particular, the time-dependent profile 400 of the ink flow rate 402 can be determined before the print image 300 is printed onto a recording medium 120.

[0043] The device 101 can further be configured to determine and / or predict, based on the time course 400 of the ink flow rate 402, whether, during the printing of the printed image 300, changes in the ink flow rate 402 will cause an ink ejection error, in particular a nozzle failure, of at least one nozzle 21, 22. In particular, it can be determined whether the time course 400 of the ink flow rate 402 exhibits one or more ink flow rates, e.g., as one or more frequency components of an amplitude spectrum 410 of the time course 400 of the ink flow rate 402, by which an ink ejection error will be caused.

[0044] The device 101 can be configured to determine an amplitude spectrum 410 based on the time course 400 of the ink flow rate 402. This spectrum indicates, for a multitude of change frequencies 311 of the ink flow rate 402, the amplitude 412 of a frequency component of the time course 400 of the ink flow rate 402 for each change frequency 311. In other words, it can be determined which ink flow rates or change frequencies 311 of the ink flow rate 402, with what intensity or energy, are contained in the time course 400 of the ink flow rate 402. The amplitude spectrum 410 can be determined, for example, by means of a Fourier transform.

[0045] It can then be precisely determined or predicted, based on the amplitude spectrum 410, whether an ink ejection error will occur during the printing of the print image 300 due to changes in the ink flow rate 402. For this purpose, the device 101 can be configured to compare the amplitude 412 of a frequency component for a specific change frequency 414 with an amplitude threshold value 415 for the specific change frequency 414. This comparison can be performed for each of the plurality of change frequencies 414. It can then be determined or predicted with particular precision, depending on the comparison, whether an ink ejection error will occur. If necessary, it can also be determined or predicted which frequency component of the time course 400 of the ink flow rate 402, and thus which change frequency 311, will cause an ink ejection error.

[0046] The amplitude thresholds 415 can differ for different change frequencies 311. This allows for precise consideration of the frequency-dependent sensitivity of the pressure bar 102 to changes in the ink flow rate 402. The amplitude thresholds 415 for the different change frequencies 311 may have been determined experimentally beforehand, e.g., using test print images 300, as exemplified in the Fig. 3a to 3c are shown.

[0047] The device 101 can further be configured to adjust the print data for the print image 300 to be printed, depending on whether or not an ink ejection error is expected. In particular, the device 101 can be configured to re-rasterize the original image corresponding to the print image 300, depending on whether or not an ink ejection error is expected. This allows the print quality of the printing device 100 to be increased efficiently and reliably. In particular, ink ejection errors, especially nozzle failures, can be reliably avoided.

[0048] The device 101 can be configured, if it is determined or predicted that the print data will cause an ink ejection error, to adjust the print data in such a way that the adjusted print data will not cause an ink ejection error. This can be achieved, in particular, by reducing the color gamut of the print image 300. By reducing the color gamut, the intensity of color changes in the print image 300, and thus the amplitude 412 of frequency components of the amplitude spectrum 410, can be reduced. Alternatively or additionally, print data for different halftone screens of the original image can be determined, and it can be checked or predicted, using the described method 500, which of the print data will not cause an ink ejection error.

[0049] Alternatively or additionally, if it is determined that no ink ejection error will occur with the print data, the print data can be adapted by extending the color space of the print image 300 such that it is also determined that no ink ejection error will occur with the adapted print data. For example, the color space can be extended to such an extent that the resulting amplitudes 412 of the frequency components of the amplitude spectrum 410 remain below the respective amplitude threshold 415, but are at least partially closer to the amplitude threshold 415 than for the original print data.

[0050] The device 101 thus enables an improved compromise between providing the largest possible color gamut and avoiding ink ejection errors.

[0051] The device 101 can be configured to identify, based on the amplitude spectrum 410, at least one first frequency component for a first change frequency 311 that has an amplitude 412 exceeding the predefined amplitude threshold 415 for the first change frequency 311. If necessary, all frequency components for which this is the case can be identified.

[0052] The print data can be adjusted so that the amplitude 412 of the first frequency component of the amplitude spectrum 410 determined based on the adjusted print data is equal to or less than the predefined amplitude threshold 415. In particular, the print data can be adjusted so that this condition is met for all frequency components. This reliably prevents ink ejection errors.

[0053] The device 101 can be configured to determine, based on the amplitude spectrum 410, that the amplitudes 412 of the plurality of frequency components are each below a respective predefined amplitude threshold 415. It can thus be determined that no ink ejection errors are caused.

[0054] The print data can nevertheless be adjusted such that the amplitudes of the multitude of frequency components of the amplitude spectrum determined on the basis of the adjusted print data are each below the respective predefined amplitude threshold value and thus continue to prevent ink ejection errors. Furthermore, the print data can be adjusted such that the amplitudes of the multitude of frequency components of the amplitude spectrum determined on the basis of the adjusted print data are at least partially closer to the respective predefined amplitude threshold value than the amplitudes of the multitude of frequency components of the amplitude spectrum determined on the basis of the unadjusted print data. In this way, a reliable expansion of the color gamut of the print image to be printed can be achieved.

[0055] The measures described in this document can increase the stability and / or print quality of a printer 100. Furthermore, maintenance costs resulting from ink dispensing problems, particularly due to nozzle failures, can be reduced. Finally, the productivity of a printer 100 can be increased. Reference symbol list 1. Transport direction (of the recording medium) 21, 22 nozzle Columns 31 and 32 (of the printed image) 100 printing device 101 (Control) device 102 pressure bars 103 Printhead 120 recording media 140 printed works 201 (vacuum) containers 202 ink 204 (storage) containers 205 Conveyor module (pump) 206, 208 Ink supply channel 214 Pressure module (pump) 300 print images 301, 302 area (print image) 310 Sensitivity characteristic 311 Change frequency (ink flow rate) 312 Sensitivity 400 Time course of the ink flow rate 401 Time / Line measure 402 Ink flow rate / Quantity value 410 Amplitude spectrum of ink flow rate 412 Amplitude (ink flow rate or frequency component) 414 critical change frequency 415 Energy or flux rate threshold 420 Threshold frequency function 500 methods for determining print data 501-503 Procedure steps

Claims

[1] Device for determining print data for a print image (300) to be printed by a print bar (102) of an inkjet printing device (100); wherein the print bar (102) comprises one or more nozzles (21, 22); wherein the print data for a plurality of pixels of the print image (300) indicate a quantity of ink to be ejected by each nozzle (21, 22) of the print bar (102); wherein the device (101) is configured, - to determine, based on the print data, a time course (400) of an ink flow rate (402) of ink (202) that flows into the print bar (102) and / or is ejected from the one or more nozzles (21, 22) of the print bar (102) during the printing of the print image (300); - to determine, based on the temporal profile (400) of the ink flow rate (402), whether, during the printing of the printed image (300), an ink ejection error will be caused by at least one nozzle (21, 22) due to changes in the ink flow rate (402); - to determine an amplitude spectrum (410) based on the temporal profile (400) of the ink flow rate (402), which for a multitude of change frequencies (311) of the ink flow rate (402) indicates an amplitude (412) of a frequency component of the temporal profile (400) of the ink flow rate (402) for the respective change frequency (311); - to determine, based on the amplitude spectrum (410), whether an ink ejection error will occur during the printing of the print image (300) due to changes in the ink flow rate (402); and - to adjust the print data for the print image to be printed (300) depending on whether it is determined that an ink ejection error will be caused or not. [2] Device according to claim 1, wherein the device (101) is configured, - to compare an amplitude (412) of a frequency component for a given change frequency (414) with an amplitude threshold (415); and - depending on the comparison, to determine whether an ink ejection error will occur due to a change in the ink flow rate (402) with the specified change frequency (414). [3] Device according to claim 2, wherein - Amplitude thresholds (415) for different change frequencies (311) are different; and / or - the amplitude thresholds (415) for different change frequencies (311) were determined experimentally in advance. [4] Device according to any one of claims 1 to 3, wherein the device (101) is configured, - to identify, on the basis of the amplitude spectrum (410), at least a first frequency component for a first change frequency (311) that has an amplitude (412) exceeding a predefined amplitude threshold (415); and - to adjust the pressure data such that the amplitude (412) of the first frequency component of an amplitude spectrum (410) determined on the basis of the adjusted pressure data is equal to or less than the predefined amplitude threshold (415). [5] Device according to any one of claims 1 to 4, wherein the device (101) is configured, - to determine, based on the amplitude spectrum (410), that the amplitudes (412) of the multitude of frequency components are each below a respective predefined amplitude threshold (415); and - to adjust the pressure data such that the amplitudes (412) of the multitude of frequency components of an amplitude spectrum (410) determined on the basis of the adjusted pressure data -- each below the respective predefined amplitude threshold (415); and -- at least partially closer to the respective predefined amplitude threshold (415) than the amplitudes (412) of the multitude of frequency components of the amplitude spectrum (410) determined on the basis of the unadjusted pressure data. [6] Device according to one of the preceding claims, wherein - the temporal progression (400) of the ink flow quantity (402) for a sequence of line cycles (401) indicates a quantity value of ink (202) for each cycle; - the printhead (103) comprises a plurality of nozzles (21, 22) which are configured to print a corresponding plurality of pixels of a corresponding plurality of columns (31, 32) of the printed image (300) at a given line cycle; - the print data for each of the multiple nozzles (21, 22) indicate an amount of ink to be ejected at the specific line cycle; - the device (101) is set up to sum the ink quantity of the plurality of nozzles (21, 22) indicated by the print data for the specified line cycle in order to determine a quantity value of the time course (400) of the ink flow quantity (402) for the specified line cycle. [7] Device according to one of the preceding claims, wherein the device (101) is configured to re-rasterize an original image corresponding to the print image (300) depending on whether it is determined that an ink ejection error will be caused or not. [8] Device according to one of the preceding claims, wherein the device (101) is configured, - if it is determined that the print data will cause an ink ejection error, to adjust the print data, in particular by reducing a color space of the print image (300), such that the adjusted print data is determined to prevent an ink ejection error; and / or - if it is determined for the print data that no ink ejection error will be caused, to adapt the print data by extending the color space of the print image (300) so that it is also determined for the adapted print data that no ink ejection error will be caused. [9] Method for determining print data for a print image (300) to be printed by a print bar (102) of an inkjet printing device (100); wherein the print bar (102) comprises one or more nozzles (21, 22); wherein the print data for a plurality of pixels of the print image (300) indicate an amount of ink to be ejected by each nozzle (21, 22) of the print bar (102); wherein the method (500) comprises, - Determine (501), based on the print data, a time course (400) of an ink flow quantity (402) of ink (202) that flows into the print bar (102) and / or is ejected from the one or more nozzles (21, 22) of the print bar (102) during the printing of the print image (300); - Determine (502), based on the temporal profile (400) of the ink flow rate (402), whether during the printing of the print image (300) an ink ejection error will be caused by changes in the ink flow rate (402) from at least one nozzle (21, 22); - to determine an amplitude spectrum (410) based on the temporal profile (400) of the ink flow rate (402), which for a multitude of change frequencies (311) of the ink flow rate (402) indicates an amplitude (412) of a frequency component of the temporal profile (400) of the ink flow rate (402) for the respective change frequency (311); - to determine, based on the amplitude spectrum (410), whether an ink ejection error will occur during the printing of the print image (300) due to changes in the ink flow rate (402); and - Adjusting (503) the print data for the print image to be printed (300) depending on whether it is determined that an ink ejection error will be caused or not.

Images