Patent Publication Number: US-2018029360-A1

Title: Method and controller to stabilize an ink meniscus in an inkjet printing system

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This patent application claims priority to German Patent Application No. 102016113929.7, filed Jul. 28, 2016, which is incorporated herein by reference in its entirety. 
     BACKGROUND 
     The present disclosure relates to a method and a corresponding controller configured to stabilize the ink meniscus of a nozzle of an inkjet printing system. 
     An inkjet printing system typically comprises one or more print heads respectively having a plurality of nozzles, wherein each nozzle is configured to fire or eject ink droplets onto a recording medium. A nozzle thereby typically comprises a pressure chamber in which pressure is built up in order to generate an ink droplet. The pressure chambers of the individual nozzles of a print head may be connected with a common ink reservoir via one or more ink supply channels. Such a printing system is described in US2010/0053252A1, for example. 
     A print head having a relatively high density of nozzles, as presented in US2010/0053252A1, may lead to interactions between adjacent nozzles of a print head. The print quality of an inkjet printing system may thereby be negatively affected. In particular, failures of individual nozzles may occur due to the interactions. 
     BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES 
     The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate the embodiments of the present disclosure and, together with the description, further serve to explain the principles of the embodiments and to enable a person skilled in the pertinent art to make and use the embodiments. 
       FIG. 1  illustrates a block diagram of an inkjet printing system according to an exemplary embodiment of the present disclosure; 
       FIG. 2  illustrates a nozzle according to an exemplary embodiment of the present disclosure; 
       FIGS. 3 a , 3 b , and 3 c    illustrate examples of activation situations of a series of adjacent nozzles according to exemplary embodiments of the present disclosure; 
       FIG. 3 d    illustrates print data for the activation of a series of adjacent nozzles according to an exemplary embodiment of the present disclosure; 
       FIG. 4  illustrates a workflow diagram of a method for stabilizing the ink meniscus of a nozzle of a print head according to an exemplary embodiment of the present disclosure. 
    
    
     The exemplary embodiments of the present disclosure will be described with reference to the accompanying drawings. 
     DETAILED DESCRIPTION 
     In the following description, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the present disclosure. However, it will be apparent to those skilled in the art that the embodiments, including structures, systems, and methods, may be practiced without these specific details. The description and representation herein are the common means used by those experienced or skilled in the art to most effectively convey the substance of their work to others skilled in the art. In other instances, well-known methods, procedures, components, and circuitry have not been described in detail to avoid unnecessarily obscuring embodiments of the disclosure. 
     An object of the present disclosure is to reduce the influence of adjacent nozzles on a nozzle in a print head in order to prevent failures of the nozzle, and thus to increase the print quality of an inkjet printing system. 
     According to one aspect, a method is described for stabilizing the ink meniscus at a nozzle opening of a first nozzle of a print head. The pressure chamber of the first nozzle is thereby connected via an ink supply channel with pressure chambers of one or more adjacent nozzles of the print head, wherein the one or more adjacent nozzles are activated simultaneously with the first nozzle at one or more activation points in time to print image points of a print image onto a recording medium. 
     In an exemplary embodiment, the method can include the determination of whether at least a portion of the one or more adjacent nozzles should eject ink at an activation point in time at which the first nozzle should eject no ink. For example, this may be determined on the basis of the print data of a print image to be printed. In an exemplary embodiment, depending on the determination, the method can include the activation of the first nozzle at the activation point in time with a negative pressure reduction pulse via which a negative pressure in the pressure chamber of the first nozzle is reduced (e.g. at least temporarily) without thereby producing an ink ejection. Air entrapment or air intake into an ink supply channel of the print head, and therefore nozzle failures, may be avoided via the selective insertion of negative pressure reduction pulses in one or more nozzles that should produce no ink ejection at an activation point in time. 
     According to a further aspect, the inkjet printing system can include a controller. The controller can be for a print head of the inkjet printing system. The controller can be configured to execute one or more methods according to exemplary embodiments of the present disclosure. 
       FIG. 1  shows a block diagram of an inkjet printing system  100  according to an exemplary embodiment of the present disclosure. The printing system  100  presented in  FIG. 1  is configured for printing to a web-shaped recording medium  120  (also designated as a “continuous feed”). However, the aspects of the present disclosure are also applicable to printing systems  100  that are configured to print to a sheet-shaped or page-shaped recording medium  120 . A web-shaped recording medium  120  is typically taken off from a roll (the take-off) and then supplied to the print group of the printing system  100 . A print image is applied onto the recording medium  120  by the print head, and the printed recording medium  120  is taken up again onto an additional roll (the take-up) after fixing/drying, or is cut into sheets. 
     In  FIG. 1 , the transport direction of the recording medium  120  is represented by an arrow. The printing system  100  thereby typically has only a single transport direction, such that each point of the recording medium  120  is only directed one time past a specific nozzle of the printing system  100 . The nozzles may thereby be installed fixed (e.g. immobile) in the printing system  100 . The recording medium  120  may be produced from paper, paperboard, cardboard, metal, plastic, textiles, and/or other suitable and printable materials. 
     In the exemplary embodiment illustrated in  FIG. 1 , the print group of the printing system  100  comprises four print head arrangements  102  (that are respectively also designated as print bars), but is not limited thereto. The different print head arrangements  102  may be used for printing with inks of different colors (e.g. black, cyan, magenta and/or yellow). The print group may one or more additional print head arrangements  102  for printing additional colors or additional inks (e.g. Magnetic Ink Character Recognition (MICR) ink). 
     In an exemplary embodiment, a print head arrangement  102  comprises one or more print heads  103 . As illustrated in  FIG. 1 , a print head arrangement  102  can include five respective print heads  103 , but is not limited thereto. One or more of the print heads  103  may in turn be subdivided into a plurality of print head segments, wherein each print head segment can include a plurality of nozzles (or one or more nozzles). 
     In an exemplary embodiment, the installation position/orientation of a print head  103  within a print head arrangement  102  may depend on the type of print head  103 . In an exemplary embodiment, one or more (e.g. each) print head  103  comprises multiple nozzles, wherein each nozzle is configured to fire or eject ink droplets onto the recording medium  120 . For example, a print head  103  may comprise  2558  effectively used nozzles that are arranged along one or more rows transversal to the transport direction of the recording medium  120 , but is not limited thereto. In an exemplary embodiment, the nozzles in the individual rows may be arranged offset from one another. In an exemplary embodiment, a respective line on the recording medium  120  may be printed transversal to the transport direction by means of the nozzles of a print head  103 . Via the use of L rows with (transversally offset) nozzles (L&gt;1), an increased resolution may be provided. In total, for example, K=12790 droplets along a transversal line may be fired onto the recording medium  120  via a print head arrangement  102  depicted in  FIG. 1  (for example for a print head of approximately 21.25 inches with 600 dpi (dots per inch)). In other words, a print head arrangement  102  may comprise K (for example K=12790) nozzles for printing a line (or transversal line) of a print image, wherein the K nozzles may be arranged in L rows so that each row of nozzles has (on average) K/L nozzles. In an exemplary embodiment, one or more (e.g. each) print head arrangement  102  may be configured to print a transversal line of a specific color onto the recording medium  120  with the K nozzles as needed. The nozzles in the L different rows may thereby be activated with a time offset relative to one another in order to ensure that a transversal line (also designated as a line) is printed by the nozzles. 
     In an exemplary embodiment, the printing system  100  includes a controller  101  that is configured to activate one or more actuators of the individual nozzles of the individual print heads  103  to apply a print image onto the recording medium  120 . The controller  101  can be configured to activate the actuator(s) based on print data. The controller  101  includes activation hardware in an exemplary embodiment. In an exemplary embodiment, the controller  101  includes processor circuitry that is configured to perform one or more operations and/or functions of the controller  101 , such as activating one or more actuators. 
     In an exemplary embodiment, the printing system  100  includes K nozzles that may be activated with a specific activation frequency to print a line (e.g. transversal to the transport direction of the recording medium  120 ) with K pixels or K columns onto the recording medium  120 . In an exemplary embodiment, the nozzles are immobile or installed fixed in the printing system  100 , and the recording medium  120  is directed past the stationary nozzles with a defined transport velocity. A defined nozzle thus prints a corresponding defined column (in the transport direction) onto the recording medium  120  (in a one-to-one association). A maximum of one ink ejection thus takes place via a defined nozzle per line of a print image. 
       FIG. 2  shows a nozzle  200  of a print head  103  according to an exemplary embodiment. In an exemplary embodiment, the nozzle  200  includes walls  202  which, together with an actuator  220 , form a container or a pressure chamber  212  to accommodate ink. An ink droplet may be fired onto the recording medium  120  via a nozzle opening  201  of the nozzle  200 . The ink forms what is known as a meniscus  210  at the nozzle opening  201 . Furthermore, the nozzle  200  includes an actuator  220  (e.g. a piezoelectric element) that is configured to vary the volume of the pressure chamber  212  for accommodating ink or to vary the pressure in the pressure chamber  212  of the nozzle  200 . In particular, the volume of the pressure chamber  212  may be reduced, and the pressure in the pressure chamber  212  may be increased, by the actuator  220  as a result of a deflection  222 . An ink droplet is thus ejected from the nozzle  200  via the nozzle opening  201 .  FIG. 2  shows a corresponding deflection  222  of the actuator  220  (dotted lines). Moreover, the volume of the pressure chamber  212  may be increased by the actuator  220  (see deflection  221 ) in order to draw new ink into the pressure chamber  212  via an ink supply channel  230 . 
     The ink within the nozzle  200  may thus be moved via a deflection  221 ,  222  of the actuator  220 , and the chamber  212  may be placed under pressure. A defined movement of the actuator  220  thereby produces a corresponding defined movement of the ink. The defined movement of the actuator  220  is typically produced via a corresponding defined waveform or a corresponding defined pulse of an activation signal of the actuator  220 . In particular, via a fire pulse (also designated as an ejection pulse) to activate the actuator  220  it may be brought about that the nozzle  200  ejects an ink droplet via the nozzle opening  201 . Different ink droplets may be ejected via different activation signals to the actuator  220 . In particular, ink droplets having different droplet size (for example 5 pl, 7 pl or 12 pl) may thus be ejected. Furthermore, via a pre-fire pulse to activate the actuator  220  it may be produced that, although the nozzle  200  produces a movement of the ink and an oscillation of the meniscus  210 , no ink droplet is thereby ejected via the nozzle opening  201 . 
     The different nozzles  200  of a print head  103  or of a print head segment are partially connected with one another, and with an ink reservoir, via one or more ink supply channels  230 . Ink may be drawn into the pressure chamber  212  of a nozzle  200  via the ink supply channels  230  (e.g. if the actuator  220  is located in the deflection  221 ). The nozzles  200  of a print head  103  (or of a print head segment) may thereby mutually influence one another indirectly via the one or more ink supply channels  230 . 
     As presented above, at least a portion of the K nozzles  200  for printing a line of a print image are arranged in parallel in a print head  103  (relative to the transport direction of the recording medium  120 ). For example, K/L nozzles  200  of a print head  103  may be arranged in a row (transversal to the transport direction). These K/L nozzles  200  may be activated simultaneously to print a line of a print image, and may thereby mutually affect one another due to the connection via the one or more ink supply channels  230 . 
       FIG. 3 a    shows an exemplary arrangement of three nozzles  301 ,  302 ,  303  that may be activated simultaneously. In the example presented in  FIG. 3 a   , the first nozzle  301  and the third nozzle  303  should thereby eject no ink at an activation point in time, whereas the second nozzle  302  should eject an ink droplet  311  at the activation point in time (which is illustrated by the dashed deflection  222  of the actuator  220 , which is shown relatively large). Within the scope of the ejection of an ink droplet  311 , the second nozzle  302  draws ink via the one or more ink supply channels  230  (depicted by the arrows in  FIG. 3 a   ). 
       FIG. 3 b    shows an example in which the second nozzle  302  and the third nozzle  303  should eject an ink droplet  311 ,  313  simultaneously at an activation point in time, and for this should draw ink from the one or more ink supply channels  230  (see arrows in  FIG. 3 b   ). The first nozzle  301  adjacent to the second and third nozzle  302 ,  303  should not eject ink droplets at this activation point in time, such that the actuator  220  of the first nozzle  301  is typically not activated with a pulse in order to deflect the actuator  220 . The suction of ink by the adjacent second and third nozzle  302 ,  303  may lead to the situation that ink is drawn from the chamber  212  of the first nozzle  301  via the one or more ink supply channels  230 , such that a negative pressure in the chamber  212  of the first nozzle  301  is generated and the meniscus  210  at the nozzle opening  201  of the first nozzle arrangement  301  is thereby drawn inward. Due to the negative pressure in the chamber  212  of the first nozzle  301 , air may be drawn into the chamber  212  of the first nozzle  301  via the nozzle opening  201 , whereby the ink ejection of the first nozzle  301  in a following print line (meaning at a subsequent activation point in time) may be negatively affected. The ink ejection in one or more adjacent nozzles  302 ,  303  may thus negatively affect the droplet formation of the first nozzle  301 . 
     In other words, during printing multiple nozzles  301 ,  302 ,  303  (for example the nozzles  301 ,  302 ,  303  of a row of the print head  103 ) are often activated simultaneously in said inkjet print head  103 . These nozzles  301 ,  302 ,  303  may thereby be connected with one another via ink supply channels  230 . Especially given print heads  103  with a relatively high image dot density (for example of 1200 dpi), the phenomenon may then result that individual nozzles  301  fail after adjacent nozzles  302 ,  303  that draw ink from the same print head-internal supply channel  230  have been activated in order to eject ink droplets. This phenomenon is therefore due to the fact that air above the nozzle opening  201  of the unactivated nozzle  301  is drawn inside the nozzle chamber  212 , since ink is not sufficiently quickly replenished from the ink supply or from the ink reservoir via the ink supply channel  230  (as illustrated in  FIG. 3 b   ). Due to the negative pressure being applied at the print head  103  or at the nozzles  301 ,  302 ,  303 , these air bubbles may then be drawn further inside the print head  103  within a short time. As a result, multiple nozzles  301 ,  302 ,  303  or entire rows of nozzles  301 ,  302 ,  303  may fail due to this air inclusion. In particular, this effect may occur when relatively many nozzles  302 ,  303  are activated at an activation point in time (in order to eject ink droplets) and only individual nozzles  301  are not activated (and thus eject no ink droplets). In particular, the individual unactivated nozzles  301  may then fail due to air inclusions. 
     The mutual negative effect of nozzles  301 ,  302 ,  303  that draw ink from a common ink supply channel  230  typically increases with the increasing number of nozzles  301 ,  302 ,  303  that are activated at an activation point in time in order to eject ink droplets. In particular, the pressure fluctuations, and therefore the negative effects, increase with the increasing number of activated nozzles  301 ,  302 ,  303  (or with an increasing proportion of activated nozzles  301 ,  302 ,  303  to the total number of nozzles  301 ,  302 ,  303  of an ink supply channel  230 ). 
     In an exemplary embodiment, the failure of nozzles  301  may be counteracted via dedicated purge &amp; wipe intervals for the cleaning and regeneration of nozzles  301 ,  302 ,  303 . However, this leads to a reduction of the printing speeds and to an increase of the required printing resources (in particular ink). 
     In an exemplary embodiment, in order to prevent or reduce a negative effect on a first nozzle  301  that should eject no ink at an activation point, the first nozzle  301  may be activated with the activation signal at the activation point in time via which the actuator  220  of the first nozzle  301  is deflected (see deflection  322  in  FIG. 3 c   ), such that the negative pressure (produced by the adjacent one or more nozzles  302 ,  303 ) is reduced in the pressure chamber  212  of the first nozzle  301  but no ink ejection from the first nozzle  301  is thereby produced. In an exemplary embodiment, in particular, the first nozzle  301  may be activated with pre-fire pulse at the activation point in time in order to reduce the negative pressure in the pressure chamber  212  of the first nozzle  301 . The pulse for activation of the first nozzle  301  may generally be designated as a negative pressure reduction pulse. 
     In an exemplary embodiment, the negative pressure reduction pulse may be generated depending on how the one or more adjacent nozzles  302 ,  303  of the first nozzle  301  are activated at the activation point in time. The print data  330  for the (simultaneously activated) nozzles  301 ,  302 ,  303  may be analyzed for this purpose (see  FIG. 3 d   ). Via corresponding activation signals  331 ,  332 ,  333 , the print data  330  specify whether, at an activation point in time  334 , a nozzle  301 ,  302 ,  303 
         should print a “white” pixel, and thus typically is not activated [sic] a pulse (activation signal  333 ); or   should print a “non-white” pixel, and thus is activated with a fire pulse (activation signal  331 ).       

     In an exemplary embodiment, based on the print data  330 , it may be determined whether, at a defined activation point in time  334 , the (possibly directly) adjacent nozzles  302 ,  303  of the first nozzle  301  should print a “non-white” pixel while the first nozzle  301  should print a “white” pixel. If this is the case, the print data  330  may be adapted in order to have the effect that the first nozzle  301  is activated with a negative pressure reduction pulse (activation signal  332 ) at the defined activation point in time  334 . Nozzle failures in a print head  103  may thus be avoided reliably and without overheating of the actuators  220  of the individual nozzles  301 ,  302 ,  303 . 
     In other words, individual nozzles  301  which do not print at a specific point in time  334  while other nozzles  302 ,  303  print simultaneously may be activated with a negative pressure reduction pulse (in particular with a pre-fire pulse) (as shown in  FIG. 3 c   ) in order to prevent the failure of nozzles  301 ,  302 ,  303  of a print head  103 . While the nozzles  302 ,  303  print, ink is resupplied into the pressure chambers  212  of the nozzles  302 ,  303  via the ink supply channel  230 , which may lead to a negative pressure in the print chambers  212  of the one or more non-printing nozzles  301 . In the one or more non-printing nozzles  301 , the negative pressure reduction pulse may then have the effect that the one or more non-printing nozzles  301  achieve a certain resistance or counter-pressure against the applied negative pressure, and as a result of this no air is drawn into the respective pressure chambers  212  via the nozzle openings  201  of the one or more non-printing nozzles  301 . Nozzle failures may thus be prevented. 
     In an exemplary embodiment, in order to select the one or more nozzles  301  that must be stabilized with a negative pressure reduction pulse at an activation point in time  334 , which nozzles  301 ,  302 ,  303  are activated at which point in time  334  with which activation signals  331 ,  333  (as shown in  FIG. 3 d   , for example) may be identified with the aid of a modified pixel preview function (for example on the basis of print data  330 ). If a certain number of nozzles  302 ,  303  in a nozzle row are activated with a fire pulse at a defined point in time  334 , a decision may be made as to whether one or more unactivated adjacent nozzles  301  should be activated with a negative pressure reduction pulse at the defined point in time  334 . Given a non-printing nozzle  301  at an activation point in time  334 , a negative pressure reduction pulse may thereby be inserted if the number of (possibly directly adjacent) nozzles  302 ,  303  that should print a “non-white” pixel at the activation point in time  334  is greater than or equal to a predefined numerical threshold. On the other hand, the insertion of a negative pressure reduction pulse may be omitted. 
     The probability of the drawing of air into a nozzle  301  typically increases with the increasing number of printing nozzles  302 ,  303 . The numerical threshold may be selected such that the probability of the suction of air is at or below a defined probability threshold. 
       FIG. 4  shows a workflow diagram a method  400  to stabilize the ink meniscus  210  at a nozzle opening  201  of a first nozzle  301  of a print head  103 . The pressure chamber  212  of the first nozzle  301  is thereby connected via (at least) one ink supply channel  230  with pressure chambers  212  of one or more adjacent nozzles  302 ,  303  of the print head  103 . The first nozzle  301  and the one or more adjacent nozzles  302 ,  303  are moreover typically connected via the (at least one) ink supply channel  230  with an ink reservoir from which ink may be conveyed into the pressure chambers  212  of the nozzles  301 ,  302 ,  303 . 
     The nozzles  301 ,  302 ,  303  designated as adjacent nozzles  301 ,  302 ,  303  in this document may be nozzles that are connected with one another via a common ink supply channel  230 . In other words, all nozzles  301 ,  302 ,  303  of an inkjet printing system  100  that access a common ink supply channel  230  may be designated as nozzles  301 ,  302 ,  303  adjacent to one another. 
     Moreover, there may be gradations in the degree of adjacency between nozzles  301 ,  302 ,  303  that attach to a common ink supply channel  230 . For example, nozzles  301 ,  302 ,  303  may be arranged next to one another (transversal to the transport direction) and be connected to an ink supply channel  230  running transversal to the transport direction. In such an instance, a first nozzle  301  (that is not situated at the edge) has two directly or immediately adjacent nozzles  302 ,  303  (as shown in  FIG. 3 a   , for example). Moreover, a first nozzle  301  may have still more adjacent nozzles to the left of the second nozzle  302  and/or to the right of the third nozzle  303 , which nozzles have a decreasing degree of adjacency with increasing distance from the first nozzle  301 , however. In other words: the degree of adjacency of a defined, adjacent nozzle relative to the first nozzle  301  may decrease with the number of nozzles that are situated between the defined adjacent nozzle and the first nozzle  301 . 
     The one or more adjacent nozzles  302 ,  303  are typically activated simultaneously with the first nozzle  301  at an activation point in time  334 , or at a sequence of activation points in time  334 , in order to print image points of a print image (or corresponding sequences of image points) on a recording medium  120 . For example, the print head  103  may have L rows (arranged transversal to the transport direction) of nozzles  301 ,  302 ,  303 . The first nozzle  301  and the one or more adjacent nozzles  302 ,  303  may be part of a row of nozzles  301 ,  302 ,  303 , or correspond to a row of nozzles  301 ,  302 ,  303  of a print head  103 . 
     At the activation point in time, image points may be printed onto a line of the print image by the first nozzle  301  and the one or more adjacent nozzles  302 ,  303 , wherein the image points lie in different columns. A line thereby travels transversal to the transport direction, and a column travels longitudinal to the transport direction. At a sequence of activation points in time  334 , the first nozzle  301  and the one or more adjacent nozzles  302 ,  303  may respectively print a sequence of image points in different columns of the print image. 
     In an exemplary embodiment, the method  400  includes the determination  401  of whether at least a portion of the one or more adjacent nozzles  302 ,  303  should eject ink at an activation point in time  334  at which the first nozzle  301  should eject no ink. In other words, it may be determined whether at least a portion of the simultaneously activated one or more adjacent nozzles  302 ,  303  prints a “non-white” image point (with ink ejection) onto the recording medium  120  at an activation point in time  334  at which the first nozzle  301  prints a “white” image point (without ink ejection) onto the recording medium  120 . In such a situation, it may occur that air is drawn into the pressure chamber  212  of the first nozzle  301  via the nozzle opening  210  of the first nozzle  301 , which might lead to nozzle failures. The suction of air into the pressure chamber  212  of the first nozzle  301  may in particular take place when the one or more nozzles  302 ,  303  directly adjacent to the first nozzle  301  eject ink at the activation point in time  334 . 
     In an exemplary embodiment, based on the determination  401 , the method  400  additionally includes the activation  402  of the first nozzle  301  at the activation point in time  334  with a negative pressure reduction pulse via which a negative pressure in the pressure chamber  212  of the first nozzle  301  is reduced at least temporarily without, however, thereby producing an ink ejection by the first nozzle  301 . For this purpose, an actuator  220  of the first nozzle  301  may in particular be activated with the negative pressure reduction pulse at the activation point in time  334  in order to at least temporarily reduce the volume of the pressure chamber  212  of the first nozzle  301  so that the negative pressure in the pressure chamber  212  of the first nozzle  301  is reduced. It may thus be avoided that, during a printing pause of the first nozzle  301 , air is suctioned via the nozzle opening  310  of the first nozzle  301  due to the activation of the one or more adjacent nozzles  302 ,  303 , which might lead to nozzle failures. 
     The first nozzle  301  and the one or more adjacent nozzles  302 ,  303  may typically be activated simultaneously at a sequence of activation points in time  334  in order to respectively print a corresponding sequence of image points of the print image on the recording medium  120 . The activation points in time  334  of the sequence of activation points in time  334  may thereby follow in series with an activation frequency (or with a line clock) in order to print image points of different lines onto the recording medium  120  with the activation frequency. The time interval between two successive activation points in time  334  of the sequence of activation points in time  334  thereby corresponds to the time period that is provided to a nozzle  301 ,  302 ,  303  in order to print the image point of a line of a print image. 
     The actuator  220  of a nozzle  301 ,  302 ,  303  may be activated or excited with an ejection pulse (or fire pulse), wherein the ejection of ink from the nozzle opening  210  of the nozzle  301 ,  302 ,  303  is produced by the ejection pulse. Within the time interval between two successive activation points in time  334 , an ejection pulse thereby typically includes a first phase in which the volume of the pressure chamber  212  of the nozzle  301 ,  302 ,  303  is increased and a second phase in which the volume of the pressure chamber  212  of the nozzle  301 ,  302 ,  303  is reduced. A negative pressure in the pressure chamber  212  of a different nozzle  301  may be caused via the ink supply channel  230  due to the increase of the volume in the pressure chamber  212  of a nozzle  302 . 
     In other words, to eject ink the volume of the pressure chamber  212  of a nozzle  301 ,  302 ,  303  may be increased at least temporarily, during the time interval between two successive activation points in time  334 , in order to draw ink into the pressure chamber  212  of the nozzle  301 ,  302 ,  303  via the ink supply channel  230 . A negative pressure may thereby be generated in the pressure chamber  212  of a different nozzle, in particular in the pressure chamber  212  of the first nozzle  301 . 
     The negative pressure reduction pulse may be designed such that, via the negative pressure reduction pulse, the negative pressure in the pressure chamber  212  of a nozzle  301 ,  302 ,  303  is at least temporarily reduced during the time interval between two successive activation points in time  334  of the sequence of activation points in time  334 . In particular, the negative pressure reduction pulse may be designed such that the negative pressure in the pressure chamber  212  of a nozzle  301 ,  302 ,  303  is reduced in the first phase of an ejection pulse. The intake of air via the nozzle opening  201  of a non-printing nozzle  301 ,  302 ,  303  may thus be particularly effectively avoided. 
     The first nozzle  301  and the one or more adjacent nozzles  302 ,  303  respectively comprise a pressure chamber  212  and an actuator  220  via which the volumes of the respective pressure chambers  212  may be varied. The actuators  220  of the first nozzle  301  and of the one or more adjacent nozzles  302 ,  303  may respectively be activated at an activation point in time  334  with one activation signal  331 ,  333  from a plurality of different activation signals  331 ,  333  (for example M different activation signals, for example with M=4 or 8). For example, the number of different activation signals  331 ,  333  may be established by a maximum number of bits (for example 2 or 3 bits) for the activation signals  331 ,  333 . With which activation signal  331 ,  333  the nozzle  301 ,  302 ,  303  is activated may then be communicated to a nozzle  301 ,  302 ,  303  via a bit sequence. In particular, the pulse or the waveform for the actuator  220  of a nozzle  301 ,  302 ,  303  may be indicated by the activation signal  331 ,  333 . 
     In an exemplary embodiment, the plurality of activation signals  331 ,  333  may include: a first activation signal  331  (for an ejection pulse) via which the volume of the pressure chamber  212  of a nozzle  301 ,  302 ,  303  is varied (during the time interval between two successive activation points in time  334 ) such that an ink droplet is ejected through the nozzle opening  201  of the nozzle  301 ,  302 ,  303 ; a second activation signal  333  via which the volume of the pressure chamber  212  of a nozzle  301 ,  302 ,  303  remains unchanged (during the time interval between two successive activation points in time  334 ); and a third activation signal (for a pre-ejection pulse, for example) via which the volume of the pressure chamber  212  of a nozzle  301 ,  302 ,  303  is varied (during the time interval between two successive activation points in time  334 ) such that, although the ink meniscus  210  moves, no ink droplet is ejected through the opening  201  of the nozzle  301 ,  302 ,  303 . 
     In an exemplary embodiment, the third activation signal may thereby correspond to a pre-fire pulse via which the ink meniscus  210  at the nozzle opening  201  of a nozzle  301 ,  302 ,  303  is moved in order to reduce the viscosity of the ink within the pressure chamber  212  of the nozzle  301 ,  302 ,  303 . In other words, the ink meniscus  210  at the nozzle opening  201  of a nozzle  301 ,  302 ,  303  may be vibrated by the pre-fire pulse in order to mix ink in the pressure chamber  212  or in a region of the ink meniscus  210  of the nozzle  301 ,  302 ,  303  so that the viscosity of the ink within the pressure chamber  212  or in the region of the ink meniscus  210  of the nozzle  301 ,  302 ,  303  increases more slowly. Furthermore, the third activation signal  332  may correspond to the negative pressure reduction pulse. The use of the pre-fire pulse to reduce the negative pressure in the pressure chamber  212  of the first nozzle  301  is advantageous since nozzle failures may thus be avoided in a more data/bit-efficient manner (without needing to define an additional specific activation signal with a separate data code for a negative pressure reduction pulse). 
     In an exemplary embodiment, the determination  401  may include the analysis of print data  330  that indicate the activation signals  331 ,  333  for the one or more adjacent nozzles  302 ,  303 . The print data  330  for the first nozzle  301  for the activation point in time  334  may thereby indicate the second activation signal  333 . In particular, on the basis of the print data  330  it may be determined that the first nozzle  301  should be activated with the second activation signal  333  at the activation point in time  334 . 
     In an exemplary embodiment, the method  400  may include the changing of print data  330  so that the print data  330  for the first nozzle  301  indicate the third activation signal  332  for the activation point in time  334  if it has been determined that the first nozzle  301  should be activated with a negative pressure reduction pulse at the activation point in time  334 . Nozzle failures may thus be efficiently avoided by changing the print data  330 . 
     In an exemplary embodiment, the method  400  may include the determination of a number of the one or more adjacent nozzles  302 ,  303  that should eject ink at the activation point in time  334 . The first nozzle  301  may be activated with a negative pressure reduction pulse at the activation point in time  334  (possibly only) when the determined number is greater than or equal to a numerical threshold. The numerical threshold may thereby correspond to a proportion of 50% or more of the one or more adjacent nozzles  302 ,  303 . A selective activation of the first nozzle  301  with a negative pressure reduction pulse may thus take place so that an overheating of the actuators  220  of the nozzles  301 ,  302 ,  303  may be avoided (while simultaneously avoiding nozzle failures). 
     In an exemplary embodiment, alternatively or additionally, the method  400  may include the determination of a degree of adjacency of the one or more adjacent nozzles  302 ,  303  that should eject ink at the activation point in time  334 . In particular, a degree of adjacency may be determined for each of the one or more ejecting adjacent nozzles  302 ,  303 . Furthermore, a (possibly weighted) mean degree of the adjacency of the one or more ejecting nozzles  302 ,  303  may possibly be determined. The first nozzle  301  may then be activated with a negative pressure reduction pulse at the activation point in time  334  depending on the (possibly mean) degree of adjacency of the one or more ejecting adjacent nozzles  302 ,  303 . For example, an activation with a negative pressure reduction pulse may possibly take place only when the determined (possibly mean) degree of adjacency reaches or exceeds a predefined adjacency threshold. For example, the first nozzle  301  may possibly be activated with a negative pressure reduction pulse only when at least one or at least both of the directly adjacent nozzles  302 ,  303  should eject ink. In an exemplary embodiment, alternatively or additionally, a property (e.g. a shape) of the negative pressure reduction pulse may be adapted based on the determined (e.g. mean) degree of adjacency. The negative pressure produced in the first nozzle  301  typically decreases with decreasing (possibly mean) degree of adjacency. The pressure produced by the negative pressure reduction pulse in the pressure chamber  212  of the first nozzle  301  may correspondingly decrease with decreasing (possibly mean) degree of adjacency. The print quality and the droplet formation may thus be further improved. 
     In an exemplary embodiment, the controller  101  and/or  105  of a print head  103  of an inkjet printing system  100  may be configured to execute the method  400 . In particular, the controller  101  and/or  105  may be configured to determine whether at least a portion of the one or more adjacent nozzles  302 ,  303  should eject ink at an activation point in time  334  at which the first nozzle  301  should not eject ink. Depending on this, the controller  101 ,  105  may then activate the first nozzle  301  at the activation point in time  334  with a negative pressure reduction pulse via which a negative pressure in the pressure chamber  212  of the first nozzle  301  is reduced without producing an ink ejection. In particular, depending on the determination  401  it may be determined whether the first nozzle  301  should be activated or not with a negative pressure reduction pulse at the activation point in time  334 . The insertion of a negative pressure reduction pulse may thereby depend
         on the number of adjacent nozzles  302 ,  303  that should eject ink at the activation point in time  334 ; and/or   on the arrangement of the adjacent nozzles  302 ,  303  relative to the first nozzle  301 .       

     A method  400  and a corresponding controller  101 ,  105  are thus described in which one or more non-printing first nozzles  301  are induced to generate a negative pressure reduction pulse—in particular a pre-fire pulse—at an activation point in time  334  depending on the number and/or position of adjacent nozzles  302 ,  303  that eject ink at the activation point in time  334 . 
     The method according to an exemplary embodiment enables nozzle failures during the printing operation to be prevented or reduced, and thus enables the print quality of a printing system  100  to be increased. Furthermore, load fluctuations within a print head  103  may be compensated for, and crosstalk between the nozzles  301 ,  302 ,  303  of a print head  103  may be reduced. Moreover, the productivity of a printing system  100  may be increased and the resource consumption (in particular of ink) may be reduced, since refresh measures may be reduced or entirely avoided. 
     In an exemplary embodiment, a computer readable medium (e.g. memory, hard drive, disc, etc.) is provided that stores computer code and/or instructions, that when executed by a processor, controls the processor to perform one or more methods of the present disclosure. 
     Conclusion 
     The aforementioned description of the specific embodiments will so fully reveal the general nature of the disclosure that others can, by applying knowledge within the skill of the art, readily modify and/or adapt for various applications such specific embodiments, without undue experimentation, and without departing from the general concept of the present disclosure. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein. It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by the skilled artisan in light of the teachings and guidance. 
     References in the specification to “one embodiment,” “an embodiment,” “an exemplary embodiment,” etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. 
     The exemplary embodiments described herein are provided for illustrative purposes, and are not limiting. Other exemplary embodiments are possible, and modifications may be made to the exemplary embodiments. Therefore, the specification is not meant to limit the disclosure. Rather, the scope of the disclosure is defined only in accordance with the following claims and their equivalents. 
     Embodiments may be implemented in hardware (e.g., circuits), firmware, software, or any combination thereof. Embodiments may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may include read only memory (ROM); random access memory (RAM); magnetic disk storage media; optical storage media; flash memory devices; electrical, optical, acoustical or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Further, firmware, software, routines, instructions may be described herein as performing certain actions. However, it should be appreciated that such descriptions are merely for convenience and that such actions in fact results from computing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc. Further, any of the implementation variations may be carried out by a general purpose computer. 
     For the purposes of this discussion, “processor circuitry” can include one or more circuits, one or more processors, logic, or a combination thereof. For example, a circuit can include an analog circuit, a digital circuit, state machine logic, other structural electronic hardware, or a combination thereof. A processor can include a microprocessor, a digital signal processor (DSP), or other hardware processor. In one or more exemplary embodiments, the processor can include a memory, and the processor can be “hard-coded” with instructions to perform corresponding function(s) according to embodiments described herein. In these examples, the hard-coded instructions can be stored on the memory. Alternatively or additionally, the processor can access an internal and/or external memory to retrieve instructions stored in the internal and/or external memory, which when executed by the processor, perform the corresponding function(s) associated with the processor, and/or one or more functions and/or operations related to the operation of a component having the processor included therein. 
     In one or more of the exemplary embodiments described herein, the memory can be any well-known volatile and/or non-volatile memory, including, for example, read-only memory (ROM), random access memory (RAM), flash memory, a magnetic storage media, an optical disc, erasable programmable read only memory (EPROM), and programmable read only memory (PROM). The memory can be non-removable, removable, or a combination of both. 
     REFERENCE LIST 
       100  printing system 
       101  controller of the printing system  100   
       102  print head arrangement/print bar 
       103  print head 
       105  controller of the print head arrangement 
       120  recording medium 
       200 ,  301 ,  302 ,  303  nozzle 
       201  nozzle opening 
       202  wall 
       210  meniscus 
       212  chamber 
       220  actuator (piezoelectric element) 
       221 ,  222 ,  322  deflection of the actuator 
       230  ink supply channel 
       330  print data 
       331  activation signal for the printing of a “non-white” pixel 
       332  activation signal for a negative pressure reduction pulse 
       333  activation signal for the printing of a “white” pixel 
       334  activation point in time 
       400  method for stabilizing the ink meniscus of a nozzle 
       401 ,  402  method steps