Method for generating a line clock for a printing device and a corresponding printing device

Abstract

Method for generating an output clock (303) for controlling pixel generation units of a printing device (100) for printing pixels of a sequence of lines of a print image on a recording medium (120); the method (400) performing the following steps: - determining (401) a basic clock (301) with a sequence of basic clock signals (302) by means of a transmitter unit (110) for detecting an extent of a relative movement between the pixel generation units and the recording medium (120) in the transport direction (1); and - determining (402) a sequence of output clock signals (304) of the output clock (303) on the basis of the sequence of basic clock signals (302); wherein the determining (402) of an output clock signal (304) at least partially comprises the temporal delay of a basic clock signal (302); wherein the sequence of output clock signals (304) is determined such that -- when printing a line with each Q ten Output clock signal (304) is used to achieve a target pixel resolution of the print image in the transport direction (1) on average over a reference period, where Q is an integer with Q ≥ 1; and -- a period of Q output clock signals (304) is not less than a minimum time required by the pixel generation units to print the pixels of a line, characterized in that -- v indicates a number of basic clock signals (302) which, in order to enable the target pixel resolution, lie on average over the reference period between two directly consecutive output clock signals (304); -- a time period T g between two directly consecutive basic clock signals (302); -- a basic clock signal (302) by a delay time (305) of h k · T g is delayed to a k testo determine the output clock signal (304) of the output clock (303), with 0≤h_k≤1; -- to determine the k ten Output clock signal (304) a k tes Reference clock signal by the delay time (305) h k · T g is delayed; -- the k te Reference clock signal corresponds to a basic clock signal (302) from the basic clock (301); wherein -- h k is calculated according to the following relationship: hk = v + hk − 1 − ⌊ v + hk − 1 ⌋ ; and -- ⌊ ⌋ is the rounding operator for rounding to an integer.

Description

[0001] The invention relates to a method for generating a line clock for controlling pixel generation units of a printing device, in particular for controlling nozzles of an inkjet printer.

[0002] Inkjet printers can be used to print on recording media (such as paper). An inkjet printer can comprise one or more printing bars, each with one or more print heads. Each printing bar can be used to print a specific color. The recording medium can be transported past the one or more printing bars in one transport direction to print a print image line by line onto the recording medium.

[0003] The control of the nozzles for printing a line of a print image typically occurs in accordance with a line clock, which depends on the advance of the recording medium, in particular on the distance traveled by the recording medium in the transport direction. The line clock typically comprises a sequence of line clock signals, with each line clock signal causing the printing of a line of a print image.

[0004] A slip-free encoder roller with a rotary encoder can be used to record the feed or the distance traveled by the recording medium. The encoder roller is driven by the recording medium so that the encoder roller has an angular velocity corresponding to the transport speed of the recording medium. The feed or the distance traveled by the recording medium is thus indicated by a change in the angular position of the encoder roller. The angular position can then be provided by a rotary encoder arranged on the encoder roller. In particular, the rotary encoder can output a sequence of basic clock signals, whereby the time interval between two clock signals corresponds to a specific change in the angular position and thus a specific feed of the recording medium. The sequence of basic clock signals forms a basic clock.

[0005] The line clock for controlling the nozzles of an inkjet printer is typically determined based on the base clock. However, depending on the pixel resolution in the transport direction and / or the thickness of the recording medium, the base clock may not have the required resolution for the line clock to be determined. The lack of resolution of the base clock can lead to inaccuracies and, in particular, to irregularities in the sequence of line clock signals of the line clock. This can cause print image distortions, particularly at relatively high transport speeds and / or relatively high pixel resolutions in the transport direction.

[0006] Document EP 2 581 230A1 discloses an inkjet recording apparatus comprising an inkjet head having a nozzle and an ejection energy generating element configured to enable the ejection of droplets from an ejection opening of the nozzle. The inkjet recording apparatus further includes a head moving device configured to reciprocate the inkjet head to scan a recording medium onto which the droplets ejected from the nozzle are applied. The apparatus has a linear encoder configured to output signals for determining a position of the inkjet head and an ejection trigger signal generating device configured to generate ejection trigger signals in accordance with the output signals of the linear encoder.

[0007] Document DE 10 2011 000 220A1 discloses that for printing line-by-line grouped image information onto a recording medium, wherein the recording medium is moved past a print head at a variable speed, a measuring device regularly determines the position and / or a speed value of the recording medium in its direction of movement, and measurement signals are generated intermittently. In an electronic divider circuit, a firing signal is generated from each nth measurement signal, where n is a divider value that is dynamically changed across multiple image lines during printing.

[0008] Document US 2013 / 0 176 577A1 discloses a variable-resolution printing system. The system includes a variable-resolution printer coupled to a position encoder and a configuration module. The position encoder provides a pulse train to a printer controller, the pulse train indicating the movement of a target relative to the printer.

[0009] The present invention is based on the object of presenting a method for generating a clock for controlling the pixel generation units of a printing device and a corresponding printing device so that lines of a print image can be printed without errors.

[0010] The object is achieved by a method having the features of independent claim 1. Advantageous embodiments are described, inter alia, in the dependent claims.

[0011] The method according to claim 1 serves to generate an output clock for controlling pixel generation units of a printing device for printing pixels of a sequence of lines of a print image on a recording medium, wherein a line preferably runs transversely to the transport direction. The method comprises determining a basic clock with a sequence of basic clock signals by means of a transmitter unit which is configured to detect an extent or a distance of a relative movement between the pixel generation units and the recording medium. Furthermore, the method comprises determining a sequence of output clock signals of the output clock on the basis of the sequence of basic clock signals, wherein determining an output clock signal at least partially (i.e. at least for one or more of the output clock signals) comprises delaying a basic clock signal in time.In other words, at least one output clock signal can be determined by temporally delaying at least one basic clock signal. The sequence of output clock signals can be determined such that when printing a line with each Q. ten Output clock signal (in particular on average over a reference period) a target pixel resolution of the print image in the transport direction is achieved, where Q is an integer with Q ≥ 1. In addition, the sequence of output clock signals can be determined such that a period of Q output clock signals is not less than a minimum time that the pixel generation units require to print the pixels of a line.

[0012] In the following, embodiments of the invention are described in more detail with reference to a schematic drawing. Fig. 1 is a block diagram of an exemplary inkjet printer; Fig. 2a and Fig. 2b an exemplary embodiment of a sensor unit from different perspectives; Fig. 3a, Fig. 3b, Fig. 3c exemplary basic measures, starting measures and line measures; and Fig. 4 a flowchart of an exemplary method for determining an output clock.

[0013] This document deals with the precise and efficient determination of a line clock for a printing device, in particular for an inkjet printer, based on a path-based basic clock.

[0014] Fig. 1 shows a block diagram of an exemplary inkjet printer 100. The Fig. The printing device 100 shown in Figure 1 is designed for continuous printing, i.e., for printing on an "endless" or web-shaped recording medium 120 (also referred to as "continuous feed"). The marking medium 120 is typically unwound from a roll (the unwinder) and then fed to the printing unit of the printing device 100. The printing unit applies a print image to the recording medium 120, and the printed recording medium 120 is wound up again on another roll (the rewinder) (possibly after fixing / drying the print image). Alternatively, the printed recording medium 120 can be cut into sheets or pages by a cutting device. Fig. In Figure 1, the transport direction 1 of the recording medium 120 is represented by an arrow. The statements in this document are also applicable to a printing device for printing sheet-shaped or page-shaped recording media 120. Furthermore, the statements are applicable to other printing devices (e.g., also toner-based printing devices).

[0015] In the illustrated example, the printing unit of the printing device 100 comprises four separate printing bars 102 spaced apart from one another in the transport direction 1. The different printing bars 102 can be used for printing with inks of different colors (e.g., black, cyan, magenta, and / or yellow). The printing unit can also comprise additional printing bars 102 for printing with other colors.

[0016] Each print head 103 comprises a plurality of nozzles 104, each nozzle 104 being configured to fire or eject ink drops onto the recording medium 120. In Fig. 1 shows exemplary nozzles 104 for a print head 103. For example, a print head 103 can comprise, for example, 2558 or 5312 effectively used nozzles 104, which are arranged along one or more rows transversely to the transport direction 1 of the recording medium 120. The nozzles 104 in the individual rows can be arranged offset from one another. By means of the nozzles 104 of a print head 103, one line at a time can be printed on the recording medium 120 transversely to the transport direction 1. By using several rows with typically transversely offset nozzles 104, an increased pixel resolution transversely to the transport direction 1 can be provided. In total, Fig. 1, for example, K=12790 or K=26560 drops are fired along a line onto the recording medium 120 (e.g. for a print width of approximately 56cm with 600 dpi (dots per inch).

[0017] The printing device 100 further comprises a control unit 101 (e.g., a control hardware and / or a controller) which is configured to control the actuators of the individual nozzles of the individual print heads 103 in order to apply a print image to the recording medium 120 as a function of print data.

[0018] The printing device 100 thus comprises at least one printing bar 102 with K nozzles, which can be controlled with a specific line clock to print a line (transverse to the transport direction 1 of the recording medium 120) with K pixels or K columns onto the recording medium 120. Due to the arrangement in multiple rows, the nozzles of a print head 103 are typically controlled with a (fixed) time offset from one another to print a line. In the example shown, the nozzles are immobile or fixedly installed in the printing device 100, and the recording medium 120 is guided past the stationary nozzles at a specific transport speed. A specific nozzle 104 can print the pixels of a corresponding column running in the transport direction 1 onto the recording medium 120. This configuration is referred to as a 1:1 assignment, since each column is assigned a nozzle 104.Thus, a maximum of one ink ejection per line of a print image occurs through a specific nozzle 104.

[0019] The printing device 100 further comprises a rotary encoder unit 110, which is configured to provide a basic clock for determining the line clock for controlling the nozzles of the printing device 100. As shown in the Fig. 2a and Fig. 2b from different perspectives, the rotary encoder unit 110 comprises a encoder roller 201, which is driven by the recording medium 120 moving in the transport direction 1 and which moves (slip-free) with the recording medium 120. One revolution of the encoder roller 201 thus corresponds to a specific path d of the recording medium (e.g., d=200mm).

[0020] The rotary encoder unit 110, in particular an incremental encoder, can also comprise at least one rotary encoder 200, which, for example, has a disk 202 provided with slots 205, which is located between at least one light-emitting diode 204 and at least one photodetector 203. Preferably, two slightly offset photodetectors 203 are provided, which, upon rotation of the disk 202, emit two electrically phase-shifted, preferably rectangular, signals A and B, preferably by 90°. An AB counter can determine the direction of rotation of the disk 202 from these two signals and count the edge changes of the electrical signals. In total, up to four clock signals can be generated per slot 205, which are referred to in this document as basic clock signals. A sequence of basic clock signals can thus be provided by one rotary encoder unit 110.The distance between two adjacent basic clock signals corresponds to a certain basic clock path d. g of the recording medium (e.g. d g = 200mm / 262,144 ≈ 763 nm, where the circumference of the disk 202 is, for example, 200mm and the disk 202 has, for example, 65,536 slots 205, and four basic clock signals are generated per slot 205. Consequently, the exemplary encoder unit 100 can generate a sequence of 262,144 basic clock signals per revolution of the encoder roller 201.

[0021] The number of lines printed on a specific path of the recording medium 120 in transport direction 1 depends on the pixel resolution in transport direction 1. At a resolution of 1200 dpi, one line of a print image corresponds to a path of the recording medium 120 of approximately 21.2 µm. Therefore, a line clock with a sequence of line clock signals should be provided so that the interval between two line clock signals corresponds to a path d z of the recording medium 120 of d z ≈21.2µm. The line clock should be determined based on the basic clock provided by the encoder unit 110. Based on the basic clock, an output clock can first be determined with a sequence of output clock signals. The line clock can then be determined by down-clocking the output clock by the factor Q, where Q is an integer with Q ≥ 1 (e.g., Q = 6). Thus, with each Q tenOutput clock signal one line of a print image can be printed.

[0022] Typically, the basic clock path is d g not an integer multiple of the required line path d z This is due, among other things, to the fact that a pixel resolution in transport direction 1 can be flexibly adjusted if necessary and thus the line path d z Alternatively or additionally, the basic clock path d g depend on the thickness of the recording medium 120 when the recording medium 120 is at least partially wound around the donor roller 201. Thus, path ratios v=d2Q⋅dg which are not integers. Since the basic clock pulse is proportional to the basic clock pulse path d g and since the output clock to be determined is proportional to d z / Q, this results in clock ratios that are not integers.

[0023] One possibility to still determine an output clock based on the basic clock, which on average represents the desired line path d z / Q is to vary the number of basic clock signals between two output clock signals for the sequence of output clock signals in such a way that the desired line spacing d z / Q. In particular, the number of base clock signals between two output clock signals can be ⌊v⌋ and ⌊v⌋+1 be varied so that the time average is v (where ⌊⌋ the rounding operator).

[0024] However, this means that depending on the resolution of the base clock, there may be more or less large fluctuations in the line spacing d zFurthermore, the nozzles 104 of an inkjet printer 100 typically have a limitation with respect to a maximum possible line clock. In particular, a nozzle 104 typically has a minimum time duration T min which the nozzle 104 requires to process a waveform for ejecting an ink droplet. With a relatively high pixel resolution B and / or with a relatively high transport speed of the recording medium 120, it may be that the minimum time period T min with a line spacing of Q · v · d g is maintained, but with a line spacing of Q⋅⌊v⌋⋅d2 The available time between Q output clock signals is insufficient to fully process the waveform required to eject an ink droplet. This can result in print image defects (particularly missing pixels).

[0025] Fig. 3a shows an exemplary basic clock 301 with a sequence of basic clock signals 302. In the example shown, some directly consecutive basic clock signals 302 are identified as "a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "1", "m", "n", "o". As explained above, an exemplary encoder unit 110 supplies 262144 basic clock signals 302 per revolution of the encoder roller 201. For a pixel resolution of 1200 dpi, it may be necessary to generate 56086 output clock signals 304 of the output clock 303 per revolution. This results in a clock ratio of v ≈ 4.6. This clock ratio can be realized on average by randomly selecting the number of basic clock signals 302 between two output clock signals 304 between ⌊v⌋=4 and ⌊v⌋+1=5 is varied.

[0026] In the example of Fig. 3a, an output clock signal 304 is generated for each of the basic clock signals “q”, “e”, “j”, “o”, etc. Between two output clock signals 304 there are thus 4, 5, 5, 4, 5, 5, etc. basic clock signals 302. From the output clock 303, the line clock 309 can then be generated by down-clocking or sub-sampling by the factor Q (e.g. Q = 6 in the Fig. 3a shown example) so that for each Q te Output clock signal 304 generates a line clock signal 310.

[0027] The print heads 103 of a printing device 100 typically have only a limited printing frequency (e.g., 64 kHz). At a relatively high transport speed of the recording medium 120, for example, 80 m / min, it can happen that, in a sequence of relatively closely spaced output clock signals 304, the time between two line clock signals 310 is so short that the maximum possible printing frequency of a print head 103 is exceeded. For example, the minimum time period specified by the print head 103 in the above example can correspond to a minimum permissible distance between two line clock signals 310 of 6 x 4.56 = 27.36 basic clock signals 302. This minimum permissible distance would be undershot, for example, if, in the Fig. 3a, the intervals between the output clock signals 304 would not be 4, 5, 5, 4, 5, 5 basic clock signals, but 4, 4, 5, 4, 5, 5 basic clock signals.

[0028] The random fluctuations in the generation of the output clock signals 304 and thus in the generation of the line clock signals 310 can thus lead to impairments in the control of the print heads 103 of a printing device 100 and thus to the impairment of the print quality.

[0029] The above-mentioned fluctuations in determining the line clock can be reduced in particular by increasing the resolution of basic clock signals 302. The resolution of basic clock signals 302 can be increased, for example, by arranging two or more rotary encoders 200 (e.g., two or more disks 202 with sensors 203) on a encoder roller 201, each of which is phase-shifted from one another. Alternatively or additionally, the number of encoder rollers 201 can be increased with one or more rotary encoders 200 per encoder roller 201 (which have a phase shift from one another). However, these measures require additional installation space and additional costs. Furthermore, these measures can only reduce the inaccuracies or fluctuations, but not completely eliminate them.

[0030] The following describes a method for determining the line clock 309 based on a path-based basic clock 301, which allows a line clock 309 to be determined efficiently and precisely. In addition to the path-based basic clock 301, the method uses a time-based interpolation between two basic clock signals 302 to determine an output clock signal 304.

[0031] Fig. 3b shows an exemplary basic clock 301 with a sequence of basic clock signals 302. In the example shown, an output clock 303 is to be determined with a sequence of output clock signals 304, each comprising v = 4.6 basic clock signals 302. The first output clock signal 304 is generated simultaneously with the basic clock signal "a". A delay time factor h is also initialized with the first output clock signal 304 (h = 0). After the first output clock signal 304, ⌊v+h⌋=4 Basic clock signals 302 are waited for. The then reached basic clock signal “e” can be used as

[0032] Reference clock signal for the next output clock signal 304 to be generated. To place the output clock signal 304, a time-based interpolation between the reference clock signal ⌊v+h⌋ (ie the basic clock signal “e”) and the following basic clock signal ⌊v+h⌋+1 (ie the base clock signal “f”). In particular, when the reference clock signal is reached ⌊v+h⌋ (ie the basic clock signal “e”) a timer is started to delay the output clock signal 304 by a delay time t 305, wherein the delay time t corresponds to a fraction of the period T g between two directly consecutive basic clock signals. The delay time factor h = t / T g the remaining part of the clock ratio v, ie r=v+h−⌊v+h⌋, ⌊v+h⌋=⌊4.6+0.6⌋=5 which is still required to achieve the desired clock ratio v between the output clock signals 304. In the example shown, the remainder corresponds to r = 0.6 and the delay time t = 0.6 · T g .

[0033] Starting from the reference clock signal (ie the basic clock signal “e”), r=v+h−⌊v+h⌋ Basic clock signals 302 are waited for in order to determine a new reference clock signal. In the example shown, the new reference clock signal is the basic clock signal "j". The new reference clock signal is then in turn increased by the remaining r=v+h−⌊v+h⌋ delayed, where r = 5.2 - 5 = 0.2. The new delay time factor is therefore h = 2. Starting from the basic clock signal “j”, the next reference clock signal is thus ⌊v+h⌋=⌊4.6+0.2⌋=4 Basic clock signals 302, with a new delay time factor h=r=v+h−⌊v+h⌋=4.8−4=0.8. This process can be continued continuously to determine an output clock 303 based on the basic clock 301, wherein the distance between two output clock signals 304 corresponds exactly to the distance between v basic clock signals 302, even if v is not an integer.

[0034] To generate a k ten Output clock signal 304 can thus be a reference clock signal by hk=v+hk−1−⌊v+hk−1⌋ be delayed, where h k-1 corresponds to the delay time factor with which the (k - 1) te Output clock signal 304 was delayed, and where h k the delay time factor of k ten Output clock signal 304. To determine the reference clock signal for the (k + 1) ten Output clock signal 304 can be based on the reference clock signal for the k ten Output clock signal 304 ⌊v+hk⌋ Basic clock signals 302 must be waited for. ⌊v+hk⌋te Basic clock signal 302 after the reference clock signal for the k te Output clock signal 304 then corresponds to the reference clock signal for the (k + 1) te Output clock signal 304.

[0035] The timer for delaying a specific reference clock signal can be set based on the basic clock 301. For example, the time period T g between two directly consecutive base clock signals 302 based on one or more base clock signals 302 that are located directly before the specific reference clock signal. For example, the time periods T g for a plurality of pairs of basic clock signals 302. The time period T g can then be determined as a (moving) average. This allows an output clock 303 to be determined precisely (even with a changing transport speed).

[0036] To determine the output clock 303, it may be advantageous to determine an intermediate clock 307 (with a sequence of intermediate clock signals 308) on the basis of the basic clock 301 (see Fig. 3c). The intermediate clock 307 can be determined such that an intermediate clock signal 308 coincides in time with a basic clock signal 302 and that directly successive intermediate clock signals 308 of the sequence of intermediate clock signals 308 have, on average, a distance of v basic clock signals 302 from each other, where v is a real number with v ≥ 1. The intermediate clock 307 thus already (on average) ensures the desired pixel resolution B in transport direction 1. The intermediate clock 307 can thus Fig. 3a shown output clock 303.

[0037] On the other hand, it can happen (as already mentioned in connection with Fig. 3a), the time interval between (Q + 1) directly consecutive intermediate clock signals 308 is not sufficient to execute the waveform for ejecting an ink droplet. This can lead to a loss of print quality for such lines. It can therefore be advantageous to delay at least some of the intermediate clock signals 308 in order to determine corresponding output clock signals 304. The k te Intermediate clock signal 308 can be used as a reference clock signal for a k tes Output clock signal 304 can be considered, where the k te Output clock signal 304 compared to the k ten Intermediate clock signal 308 at h k = v̂ - (n k - h k-1 ) is delayed. Where h k-1 the delay time factor of (k - 1) ten Output clock signal 304 (as a fraction of the time interval T g between two basic clock signals 302) and n kthe number of basic clock signals 302 between the (k - 1) ten Intermediate clock signal 308 and the k ten Intermediate clock signal 308. v̂ ∈ [v min ,v], where V min is the minimum time interval between two output clock signals 304 required for the complete processing of a waveform by the nozzles 104 of a print head 103 (v min is a real number, with V min ≥ 1). By such a time delay of at least some of the intermediate clock signals 308, an output clock 303 can be provided, wherein the output clock signals 304 have, on average over time, a distance of v basic clock signals 302 from each other (and thus the requirements with regard to the pixel resolution B are met) and wherein the distance between two directly consecutive output clock signals 304 is never less than the minimum distance of V min Basic clock signals 302.

[0038] Fig. Figure 3c illustrates the generation of an output clock 303 based on an intermediate clock 307. In particular, Fig. 3c shows an exemplary basic clock 301 with a sequence of basic clock signals 302. In the example shown, an intermediate clock 307 is generated with a sequence of intermediate clock signals 308, which on average have a distance of v = 4.6 basic clock signals 302 from each other. A first intermediate clock signal 308 is generated simultaneously with the first basic clock signal "a". Furthermore, a first output clock signal 304 is generated simultaneously with this first intermediate clock signal 308. After the first intermediate clock signal 308, ⌊v⌋ or ⌊v⌋+1 Basic clock signals 302 are waited for before the next intermediate clock signal 307 is generated. In the example shown, ⌊v⌋=4 and ⌊v⌋+1=5 Specifically, in the example shown, the second intermediate clock signal 308 is ⌊v⌋=4 Basic clock signals 302 are generated (ie for the basic clock signal "e"). As already explained above, the second intermediate clock signal 308 should be delayed to a minimum in order to avoid disturbances in the printing operation. In particular, it should be ensured that v min = 4.56 is not undershot. In the example shown, the second intermediate clock signal 308 is therefore shortened by 0.56 of the basic clock length T g shifted to be output as the second output clock signal 304. This local delay of 0.56 is stored as the delay time factor h. Upon reaching the basic clock signal "j", the third intermediate clock signal 304 is generated (in the example shown after ⌊v⌋+1=5 basic clock signals 302). When generating the third output clock signal 304, the stored delay can be reduced, taking into account the delay of the second output clock signal 304. For the third output clock signal 304, it should also be ensured that the minimum distance between two output clock signals 304 V min = 4.56 is not undershot. For this purpose, the third intermediate clock signal 308 only needs to be increased by 0.12 of the basic clock length T g to be output as the third output clock signal 304. This local delay of only 0.12 is stored as the delay time factor h.

[0039] When the basic clock signal “o” is reached, after ⌊v⌋+1=5 Basic clock signals 302, the fourth intermediate clock signal 308 is generated. When generating the fourth output clock signal 304, the stored delay can now be completely eliminated, taking into account the delay of the third output clock signal 304. For the fourth output clock signal 304, it should also be ensured that the minimum distance between two output clock signals 304 of v min = 4.56 is maintained. To achieve this, no delay of the fourth intermediate clock signal 308 is required to be output as the fourth output clock signal 304. The local delay is therefore zero and is stored as the delay time factor h.

[0040] By reducing the delay time, it can be ensured that the output clock 303 and thus also the line clock 309 are synchronized with the base clock 301 at regular intervals. This should occur at least once per revolution of the encoder roller 201.

[0041] The control unit 101 of a printing device 100 can thus generate an output clock 303 for a minimum time T min per print line so that the waveform can be executed by the nozzles of the printing device 100 in each print line. If the minimum time T min If the delay time has not yet been reached after the number of clock signals 302, 304, the controller can delay the print line (i.e., the output clock signal 304) (if necessary, until the next base clock signal 302). The delay 305 can be stored as an overhang (e.g., from a base clock signal 302). The overhang can then be reduced again in subsequent output clock signals 304.

[0042] Thus, rotary encoder units 110 with a fixed (path-based) resolution can be used to flexibly generate line clocks 309 for a printing device 100. The use of rotary encoder units 110 with a fixed resolution typically enables a relatively high frequency of the basic clock signals 302 and thus a relatively high pixel resolution in transport direction 1.

[0043] The control unit 101 can be configured to communicate with each Q ten Output clock signal 304 is used to initiate the printing of a line of a print image. Q can be, for example, Q=6 or Q=12.

[0044] Fig.4 shows a flowchart of an exemplary method 400 for generating an output clock 303 for controlling pixel generation units of a printing device 100 for printing pixels of a sequence of lines of a print image on a recording medium 120 (in particular on a web-shaped recording medium 120). The method 400 can be executed by a control unit 101 of the printing device 100. The printing device 100 can in particular be an inkjet printer, and the pixel generation units can be nozzles 104, each configured to eject an ink droplet for printing a pixel.

[0045] The pixel generation units (e.g., the nozzles 104 of a print head 103) and the recording medium 120 exhibit a relative movement in a transport direction 1. In particular, the recording medium 120 can be guided past the (stationary) pixel generation units in the transport direction 1. A print image can then be printed line by line onto the recording medium 120, with one line running transversely to the transport direction 1.

[0046] The method 400 comprises determining 401 a basic clock 301 with a sequence of basic clock signals 302. The basic clock 301 can be generated or determined by means of a sensor unit 110 (in particular by means of a rotary sensor unit), wherein the sensor unit 110 is configured to detect an extent of a relative movement between the pixel generation units and the recording medium 120 in the transport direction 1. In this case, the basic clock 301 can be determined such that the distance between two directly adjacent basic clock signals 302 has a specific extent or a specific distance d g of the relative movement between the pixel generation units and the recording medium 120. Thus, a path-based basic clock 301 can be determined or generated. The extent of the gThe relative movement is typically independent of the transport speed. This means that with increasing transport speed, the time interval between two basic clock signals 302 typically decreases. On the other hand, the path of the relative movement indicated by the basic clock signals 301 typically remains unchanged.

[0047] In addition, the method 400 comprises determining 402 a sequence of output clock signals 304 of the output clock 303 based on the sequence of basic clock signals 302. In this case, determining 402 an output clock signal 304 comprises at least partially (ie at least for one or more output clock signals 304 of the output clock 303) delaying a basic clock signal 302. In other words, a time-based delay of one or more (path-based) basic clock signals 302 can be carried out in order to determine the sequence of output clock signals 304 of the output clock 303.

[0048] The sequence of output clock signals 304 can be determined in such a way that when printing a line with each Q ten Output clock signal 304 (at least on average over a reference period) achieves a target pixel resolution B of the print image in transport direction 1, where Q is an integer with Q ≥ 1. In other words, the output clock 303 enables the pixel generation units to be controlled in accordance with the target pixel resolution B (where B indicates the number of pixels per unit of travel).

[0049] Furthermore, the sequence of output clock signals 304 can be determined such that a period Q of (directly consecutive) output clock signals 304 is not less than a minimum time T minwhich the pixel generation units need to print the pixels of a line. In other words, the output clock 303 can ensure that a maximum possible control frequency or printing frequency (ie the inverse of the minimum time, ie 1Tmin) the pixel generation units is not exceeded.

[0050] A method 400 is thus described with which an output clock 303 for controlling pixel generation units of a printing device 100 is generated based on a (rotary) encoder-generated basic clock 301. The output clock 303 is generated by temporally delaying at least some of the basic clock signals 302 of the basic clock 301, so that a requirement regarding the pixel resolution and a requirement regarding the maximum control frequency of the pixel generation units are met. Thus, a high-quality print image can be printed even at a high pixel resolution and / or at a high transport speed.

[0051] The method 400 may include determining a time period T g between two directly consecutive basic clock signals 302. The time period T g depends on the (current) transport speed or printing speed. To determine the time period Tg for the generation of a k ten Output clock signal 304 of the output clock 303, the time interval between basic clock signals 302 can be determined, which are in time directly before the k ten Output clock signal 304. Thus, the time period T g for the generation of the k ten Output clock signal 304 can be determined with high accuracy.

[0052] A basic clock signal 302 can then be delayed by a delay time 305 of h k · T g be delayed to a k tes Output clock signal 304 of output clock 303 to be determined, with 0 ≤ h k ≤ 1 (typically h k < 1). In particular, the k te Output clock signal 304 can then be delayed in time with respect to the basic clock signal 302 if it is determined that a time interval between the k ten Output clock signal 304 and the directly preceding (k - 1) tenOutput clock signal 304 is not sufficient (e.g. less than T min / Q The delay time 305 for the individual output clock signals 304 can be determined in such a way that (if necessary for all output clock signals 304 of the output clock 303) the time interval between the k ten Output clock signal 304 and the directly preceding (k - 1) ten Output clock signal 304 a minimum time interval (e.g. T min / Q). This way (while maintaining the target pixel resolution B) the loss of individual pixels can be avoided.

[0053] The delay time 305 of the k ten Output clock signal (especially the delay time factor h k ) is preferred when determining a subsequent output clock signal 304, in particular when determining a directly subsequent (k + 1) tenOutput clock signal 304. In this way, the target pixel resolution B and the minimum time T min between print lines.

[0054] The method 400 may include determining a sequence of intermediate clock signals 308 of an intermediate clock 307 based on the sequence of basic clock signals 302. The intermediate clock 307 may be generated or determined such that a (path-based) distance d zw between two directly consecutive intermediate clock signals 308 (in particular on average over the reference period) Q times the target pixel resolution B of the print image in transport direction 1. In particular (on average over the reference period) B=1Q⋅dzw be.

[0055] Furthermore, the sequence of intermediate clock signals 308 can be determined such that the sequence of intermediate clock signals 308 corresponds to a subset of the sequence of basic clock signals 302. In other words, each intermediate clock signal 308 of the intermediate clock 307 can correspond exactly to one basic clock signal 302 of the basic clock 301. The intermediate clock 307 can thus also be a purely path-based clock, so that the distance d zw between two directly successive intermediate clock signals 308 corresponds (exactly) to an extent (in particular a path) of the relative movement between the pixel generation units and the recording medium 120.

[0056] The intermediate clock 307 can thus already ensure that the output clock 303 generated from the intermediate clock 307 enables the target pixel resolution B. The output clock signals 304 of the output clock 303 can then be determined at least partially by delaying the corresponding intermediate clock signals 308. By delaying the time, it can be achieved that the minimum time T min between print image lines. Determining an intermediate clock 307 thus enables robust and reliable generation of the output clock 303.

[0057] In particular, for each intermediate clock signal 308 of the intermediate clock 307, an output clock signal 304 of the output clock 303 can be determined (in a one-to-one relationship). The k te Output clock signal 304 can then be delayed by the delay time 305 h k · T g opposite the k tenIntermediate clock signal 308 can be delayed (for k = 0, ..., Z, where Z corresponds to the end of a printing process).

[0058] The delay time carry or delay time factor h k can be determined recursively, as h k = v̂ - (n k - h k-1 ), where n k the number of basic clock signals 302 between the (k - 1) ten Intermediate clock signal 308 and the k ten Intermediate clock signal 308. n k fluctuate (in order to achieve the target pixel resolution B on average over time). v̂ is a real number, with v^≥TminQ⋅Tg⋅vmin=TminQ⋅Tg indicates the number of basic clock signals 302 that (at the current transport speed) must be at least between two output clock signals 304 in order to achieve the minimum time T (typically specified by a print head 103) minbetween two print lines. The above-mentioned recursive formula for determining the delay time factor can thus reliably ensure that the minimum time T min is adhered to.

[0059] Furthermore, v̂ ≤ v, where v is a real number such that v=1Q⋅dg⋅B. v indicates the number of basic clock signals 302 that must be present on average over time between two output clock signals 304 in order to achieve the target pixel resolution B. In other words, v indicates the number of basic clock signals 302 that must be present on average over the reference period between two directly consecutive output clock signals 304 in order to provide the target pixel resolution B. Thus, the above-mentioned recursive formula for determining the delay time factor can reliably ensure that the specified target pixel resolution B is achieved.

[0060] As an alternative to determining an intermediate clock 307, the output clock 303 can be determined directly from the base clock 302. To determine the k ten Output clock signal 304 can be a k tes Reference clock signal by the delay time 305 h k · T g be delayed, whereby the k te Reference clock signal corresponds to a basic clock signal 302 from the basic clock 301. In particular, the reference clock signal for the k te Output clock signal 304 to the ⌊v+hk−1⌋th Basic clock signal 302 after the reference clock signal for the (k - 1) te Output clock signal 304, where ⌊⌋ is the rounding operator for rounding down to an integer. The delay time carry or factor h k can be determined recursively, as hk=v+hk−1−⌊v+hk−1⌋. By using this formula, a uniform output clock 303 can be determined, wherein the output clock signals 304 have a uniform spacing of v basic clock signals 302 from each other.

[0061] This document also describes a printing device 100 that includes pixel generation units for printing pixels of a sequence of lines of a print image on a recording medium 120. The printing device further includes movement means configured to move the recording medium 120 and the pixel generation units relative to one another in the transport direction 1. Furthermore, the printing device 100 includes a transmitter unit 110 configured to generate a basic clock 301 with a sequence of basic clock signals 302, wherein a distance between two basic clock signals 302 indicates an extent or a path or a distance of the relative movement between the pixel generation units and the recording medium 120.

[0062] The printing device 100 further comprises a control unit 101, which is configured to determine, on the basis of the sequence of basic clock signals 302, a sequence of output clock signals 304 of an output clock 303 for controlling the pixel generation units, wherein the output clock signals 304 are determined at least partially by temporally delaying basic clock signals 302. The sequence of output clock signals 304 can in particular be determined such that when printing a line with each Q ten Output clock signal 304 achieves a target pixel resolution of the print image in transport direction 1 on average over a reference period, where Q is an integer with Q ≥ 1. In addition, the sequence of output clock signals 304 can be determined such that a period of time required by Q output clock signals 304 is not less than a minimum time required by the pixel generation units to print the pixels of a line.

[0063] The control unit 101 may be further configured to operate with each Q ten Output clock signal 304 of output clock 303 to cause the printing of one line of the sequence of lines.

[0064] The encoder unit 110 can comprise one or more encoder rollers 201, which are driven by the recording medium 120 moving past the pixel generation units in the transport direction 1. By using multiple encoder rollers 201 (with multiple rotary encoders 200), the resolution of the basic clock 301 can be increased. On one (in particular, on each) encoder roller 201, multiple rotary encoders 202 can be arranged, each generating a sequence of clock signals, wherein the sequence of clock signals from two rotary encoders 200 are phase-shifted from one another and wherein the sequence of basic clock signals 302 is generated based on the sequence of clock signals from multiple rotary encoders 200. By using multiple rotary encoders 200, the resolution of the basic clock 301 can be further increased. This, in turn, enables a reduction in print image artifacts (at high pixel resolution and / or high transport speed).

[0065] The measures described in this document enable precise print image positioning, especially precise positioning of lines within a print image. Furthermore, print image artifacts (such as missing pixels and / or streaks or irregularities in the transport direction) can be avoided. List of reference symbols 1 transport direction 100 printing device 101 Control unit of the printing device 100 102 pressure bars 103 Printhead 104 nozzle 110 encoder unit 200 encoders 201 donor roller 202 disc 203 Photodetector 204 LED 205 slot 301 basic beat 302 basic clock signal 303 Output clock 304 Output clock signal 305 time delay 307 Intermediate bar 308 Intermediate clock signal 309 line pitch 310 Line clock signal 400 methods for determining a line clock. 401, 402 Procedural steps

Claims

[1] Method for generating an output clock (303) for controlling pixel generation units of a printing device (100) for printing pixels of a sequence of lines of a print image on a recording medium (120); the method (400) performing the following steps: - determining (401) a basic clock (301) with a sequence of basic clock signals (302) by means of a transmitter unit (110) for detecting an extent of a relative movement between the pixel generation units and the recording medium (120) in the transport direction (1); and - determining (402) a sequence of output clock signals (304) of the output clock (303) on the basis of the sequence of basic clock signals (302); wherein the determining (402) of an output clock signal (304) at least partially comprises the temporal delay of a basic clock signal (302); wherein the sequence of output clock signals (304) is determined such that -- when printing a line with each Q ten Output clock signal (304) is used to achieve a target pixel resolution of the print image in the transport direction (1) on average over a reference period, where Q is an integer with Q ≥ 1; and -- a period of Q output clock signals (304) is not less than a minimum time required by the pixel generation units to print the pixels of a line characterized by , that -- v indicates a number of basic clock signals (302) which, in order to enable the target pixel resolution, lie on average over the reference period between two directly consecutive output clock signals (304); -- a time period T g between two directly consecutive basic clock signals (302); -- a basic clock signal (302) by a delay time (305) of h k · T g is delayed to a k testo determine the output clock signal (304) of the output clock (303), with 0≤h_k≤1; -- to determine the k ten Output clock signal (304) a k tes Reference clock signal by the delay time (305) h k · T g is delayed; -- the k te Reference clock signal corresponds to a basic clock signal (302) from the basic clock (301); wherein -- h k is calculated according to the following relationship: hk=v+hk−1−⌊v+hk−1⌋; and -- ⌊⌋ is the rounding operator for rounding to an integer. [2] Method according to claim 1, wherein the delay time (305) of the k ten Output clock signal (304) in determining a subsequent output clock signal (304), in particular in determining a directly subsequent (k + 1) ten output clock signal (304). [3] Method according to claim 1, wherein the reference clock signal for the (k + 1) te Output clock signal (304) to the ⌊v+hk⌋ten Basic clock signal (302) after the reference clock signal for the k te Output clock signal 304.

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