Patent Publication Number: US-10766249-B2

Title: Method and controller to prevent ink leakage from a print head

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This patent application claims priority to German Patent Application No. 102017118443.0, filed Aug. 14, 2017, which is incorporated herein by reference in its entirety. 
     BACKGROUND 
     The disclosure relates to a method and a corresponding controller that are designed to prevent the leaking of ink from a print head of an inkjet printing device. 
     An inkjet printing device for printing to a recording medium comprises one or more print heads having respectively one more nozzles. The nozzles are respectively set up to eject ink droplets in order to print dots of a print image onto the recording medium. The printing process of an inkjet printing device may be interrupted, in particular in order to clean the one or more print heads. The one or more print heads may be driven out of a printing position into a cleaning position for cleaning of the print heads. 
     In particular given the movement of the one or more print heads between the cleaning position and the printing position, it may occur that ink leaks from the one or more nozzles of a print head. The leaked ink may dry on a nozzle plate of the print head, and thus lead to a negative effect on the one or more nozzles of the print head. The print quality of the inkjet printing device is thereby in turn negatively affected. 
    
    
     
       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 a    illustrates a block diagram of an inkjet printing device according to an exemplary embodiment of the present disclosure; 
         FIG. 1 b    illustrates a cleaner of an inkjet printing device according to an exemplary embodiment of the present disclosure; 
         FIG. 2  illustrates an ink supply for a print head according to an exemplary embodiment of the present disclosure; 
         FIG. 3 a    illustrates a pressure curve of the physical pressure of ink in a print head given a cleaning process according to an exemplary embodiment of the present disclosure; 
         FIG. 3 b    illustrates a pressure curve of the physical pressure of ink in a print head given a printing pause according to an exemplary embodiment of the present disclosure; and 
         FIG. 4  illustrates a flowchart of a method for avoiding the leaking of ink from 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. Elements, features and components that are identical, functionally identical and have the same effect are—insofar as is not stated otherwise—respectively provided with the same reference character. 
     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 prevent the leaking of ink from a print head of an inkjet printing device in a reliable and efficient manner, in order to increase the print quality of the inkjet printing device. 
     According to one aspect of the disclosure, a method is described for preventing the leaking of ink from a print head of an inkjet printing device, wherein the print head comprises at least one nozzle. The method includes the determination that a printing interruption phase or that a previous print preparation phase was carried out (e.g. printing—head cleaning) of the print head is present/or was present. Moreover, the method includes, in reaction to this, the reduction of a physical rest pressure of the ink in the nozzle to a printing interruption level that is lower than a printing operation level which is used as a rest pressure during a printing phase of the print head. 
     According to a further aspect of the disclosure, a controller for an inkjet printing device is described that comprises a print head having at least one nozzle. The controller is configured to determine that a printing interruption phase of the print head is present. Moreover, the controller is configured to induce, in reaction to this, a reduction of a physical rest pressure of the ink in the nozzle to a printing interruption level that is lower than a printing operation level which is used as a rest pressure during a printing phase of the print head. 
       FIG. 1 a    illustrates an inkjet printing device  100  according to an exemplary embodiment. The inkjet printing device  100  can be configured to print to a recording medium  120  in the form of a web (also referred to as a “continuous feed”, since the recording medium  120  is supplied to the printing device  100  continuously, for example from a roll), but is not limited thereto. The recording medium  120  may be produced from, for example, paper, paperboard, cardboard, metal, plastic, textiles, a combination thereof, and/or other materials that are suitable and can be printed to. In a continuous feed application, the recording medium  120  is typically taken off a roll (take-off) and then supplied to the print group  140  of the printing system  100 . A print image is applied onto the recording medium  120  by the print group  140 , and the recording medium  120  that is printed to is taken up again (possibly after fixing/drying of the print image) onto an additional roll (the take-up). Alternatively, the recording medium  120  that is printed to may be cut into sheets or individual pages by a cutting device. In  FIG. 1 a   , the transport direction  1  of the recording medium  120  is represented by an arrow. The exemplary embodiments of the present disclosure are also applicable to a printing device  100  for printing to recording media  120  in the form of webs or pages. 
     In an exemplary embodiment, the print group  140  of the printing device  100  comprises multiple print bars  102  that may respectively be used for printing with ink of different colors (for example black, cyan, magenta, and/or yellow, and possibly Magnetic Ink Character Recognition (MICR) ink and/or orange, violet and green (OVG) ink. A primer is thereby also conceivable. 
     A print bar  102  may comprise one or more print heads  103  that are, if applicable, arranged next to one another in multiple rows in order to print dots of different columns  31 ,  32  of a print image onto the recording medium  120 . In the example depicted in  FIG. 1 a   , a print bar  102  comprises five print heads  103 , for example, wherein each print head  103  prints the dots of a group of columns  31 ,  32  of a print image onto the recording medium  120 . 
     In the embodiment depicted in  FIG. 1 a   , each print head  103  of the print group  140  comprises multiple nozzles  21 ,  22 , wherein each nozzle  21 ,  22  is configured to fire or eject ink droplets onto the recording medium  120 . For example, a print head  103  of the print group  140  may comprise 2558, 5116 or more effectively utilized nozzles  21 ,  22  that are arranged along one or more rows transversal to the transport direction  1  of the recording medium  120 . The nozzles  21 ,  22  in the individual rows may be arranged offset to one another. By means of the nozzles  21 ,  22  of a print head  103  of the print group  140 , dots of a portion of a line of a print image may be printed onto the recording medium  120  transversal to the transport direction  1 , meaning along the width of the recording medium  120 . 
     In an exemplary embodiment, the printing device  100  additionally comprises a controller  101  (for example, an activation hardware, control circuit, and/or processor) that is configured to activate actuators of the individual nozzles  21 ,  22  of the individual print heads  103  of the print group  140  in order to apply the print image onto the recording medium  120  depending on print data. In an exemplary embodiment, the controller  101  includes processor circuitry that is configured to activate the actuators based on the print data. 
     The print group  140  of the printing device  100  thus comprises at least one print bar  102  having K nozzles  21 ,  22  that may be activated with a defined line clock signal in order to print a line (transversal to the transport direction  1  of the recording medium  120 ) with K pixels or K columns  31 ,  32  of a print image onto the recording medium  120 . The nozzles  21 ,  22  may be distributed among one or more print heads  103 . In the presented example, the nozzles  21 ,  22  are installed stationary or fixed in the printing device  100 , and the recording medium  120  is directed past the stationary nozzles  21 ,  22  with a defined transport velocity in the transport direction  1 . Alternatively or additionally, the one or more print heads  103  may be moved across the recording medium  120  (for example transversal to the transport direction  1  of the recording medium  120 ). 
     In the example depicted in  FIG. 1 a   , a specific nozzle  21 ,  22  prints a corresponding specific column  31 ,  32  (in the transport direction  1 ) of a print image onto the recording medium  120 . In other words, a one-to-one association between nozzles  21 ,  22  and columns  31 ,  32  may exist so that the dots of a first column  31  of the print image may be printed exclusively by a first nozzle  21 , and the dots of a second column  32  of the print image may be printed exclusively by a different, second nozzle  22 . Each nozzle  21 ,  22  of a print head  103  of the print group  140  may thus be associated with precisely one column  31 ,  32 , and each column  31 ,  32  may be associated with precisely one nozzle  21 ,  22  of a print head  103 . A maximum of one ink ejection (wherein multiple partial droplets are possibly ejected in one ink ejection that combine into one dot or pixel, at the latest on the recording medium  120 ) thus takes place via a specific nozzle  21 ,  22  per line of a print image. With this it is sought to generate a dot on the recording medium. 
     In an exemplary embodiment, the printing device  100  comprises one or more cleaners  150 . A print bar  102  may be transferred from a printing position at which the print bar  102  is arranged above the recording medium  120  into a cleaning position within a cleaner  150 . For this purpose, the print bar  102  may be moved in the movement direction  2  indicated by an arrow. The printing device  100  may have a cleaner  150  for each print bar  102  or print head  103 . 
       FIG. 1 b    shows the underside or the nozzle plate of a print head  103  of a print bar  102  within a cleaner  150 . Arranged on the underside or the nozzle plate of the print head  103  are the outputs of the one or more nozzles  21 ,  22  of the print head  103 . In the cleaner  150 , the nozzle plate of a print head  103  may initially be sprayed with a cleaning agent. Furthermore, the one or more nozzles  21 ,  22  of the print head  103  may be induced to eject ink, for example by increasing the (rest) pressure within the one or more nozzles  21 ,  22 . This step may be referred to as “purging.” The underside of the print head  103  may subsequently be cleaned with a wiper  151 . The wiper  151  may be moved across the nozzle plate in the direction indicated by the double arrow in order to clean said nozzle plate. This step may be referred to as “wiping”. 
     Movement of a print bar  102  or print head  103  between the cleaning position and the printing position may lead to ink leaking from the one or more nozzles  21 ,  22  of a print head  103 . This may be disadvantageous, in particular, on the way from the cleaning position to the printing position, since the nozzle plate of the print head  103  is soiled again due to the leaking of the ink. The leaked ink may dry and thus lead to a negative effect on a nozzle  21 ,  22 . For example, it may lead to nozzle failures and/or to deviations of the flight path of ink droplets. The print quality of an inkjet printing device  100  may thus be negatively affected as a result. 
     Upon movement of a print bar  102  or of the print head from the cleaning position into the printing position, ink may thus (e.g. depending on the ink temperature, the surface tension of the ink, the surface energy of the print head surface  212 , etc.) leak from a nozzle  21 ,  22  and dry out. Upon the start of printing, due to the leaked and dried ink, the nozzle  21 ,  22  may possibly not clearly fire (i.e. “fire clear”). In particular, it may also possibly occur that not all nozzles  21 ,  22  of a print head  103  or of a print bar  102  are completely regenerated by refresh measures, meaning by the printing of refresh print images before the actual printing of print data-dependent print images. Nozzle failures and print image disruptions may thus occur. 
       FIG. 2  shows the ink supply of an example of a print head  103 . The individual nozzles  21 ,  22  of a print head  103  may be supplied via an ink channel  201 . The ink channel  201  may thereby refer to the ink from a negative pressure tank  203  or ink storage tank. The negative pressure tank  203  may in turn be supplied with ink from an ink reservoir via a supply channel  202 . The negative pressure tank  203  may be used to set a specific physical negative pressure within the individual nozzles  21 ,  22  of the print head  103 . Via this negative pressure, it may be ensured that an ink meniscus forms at the output of a nozzle  21 ,  22 . In operation, the ink meniscus may be set into motion by an actuator of the nozzle  21 ,  22  (for example by a piezoelectric actuator) in order to eject an ink droplet from the nozzle  21 ,  22 . In an exemplary embodiment, the physical (negative) pressure in the nozzles  21 ,  22  of a print head may be set to a printing operation level in a printing phase. The printing operation level may thereby be set mechanically via the height difference  213  between the nozzle plate  212  of the print head  103  and the fill level  211  of the negative pressure tank  203 . A typically fixed (negative) pressure at the printing operation level results from the typically fixed height difference  213 . 
     The use of a physical pressure at the printing operation level is typically optimized for the generation of ink droplets in printing operation. On the other hand, it has been shown that a physical pressure at the printing operation level cannot reliably prevent a leaking of ink in a printing interruption phase of a print head  103 . In particular, it may lead to a leaking of ink if the physical pressure is also maintained at the printing operation level during the transport of a print head  103  between the printing position and the cleaning position. For example, vibrations of the print head  103  during the transport may lead to a leaking of ink. Furthermore, a leaking of ink may also occur in printing pauses in which, although a print head  103  remains at the printing position, no ejection of ink droplets takes place. The extent to which ink leaks from a print head  103  may thereby depend on the operating age of the print head  103 . It has been shown that the extent of leaked ink also typically increases with increasing operating age, and/or with a degradation of the state of the nozzle plate  212  of a print head  103 . 
     In an exemplary embodiment, the printing device  100  includes a pressure adjuster  205  that is configured to vary the physical pressure in a nozzle  21 ,  22  of a print head  103 . In particular, a physical rest pressure in a rest state of the nozzle  21 ,  22  may be adapted by the pressure adjuster  205 . The physical rest pressure is thereby typically negative, meaning that the physical rest pressure is typically a negative pressure. The actuator of the nozzle  21 ,  22  may then vary the physical pressure within the nozzle  21 ,  22 , starting from this physical rest pressure, in order to set the ink meniscus of the nozzle  21 ,  22  into motion. In an exemplary embodiment, the pressure adjuster  205  includes processor circuitry that is configured to adjust the pressure in the nozzle(s)  21 ,  22  of the print head  103 . 
     In an exemplary embodiment, the pressure adjuster  205  is configured to vary the fill level  211  in the negative pressure tank  203  via an ink channel  204  to vary the level of the physical pressure within the one or more nozzles  21 ,  22  of a print head  103 . For example, air may be pumped into the negative pressure tank  203  or be drawn from the negative pressure tank by means of a compressed air source, in order to adapt the rest pressure within the one or more nozzles  21 ,  22 . At the negative pressure tank  203 , a sensor  206  may be arranged that indicates sensor data with regard to the rest pressure. The sensor  206  may, for example, comprise a pressure sensor and/or a preferably analog fill level height sensor. The controller  101  of the printing device  100  may be configured to control or regulate the pressure adjuster  205  depending on the sensor data of the sensor  206 . The rest pressure within the one or more nozzles  21 ,  22  of a print head  103  may thus be regulated to a specific level. 
     In an exemplary embodiment, the pressure adjuster  205  is configured to adapt the rest pressure depending on the operating state of a print head  103 . For example, the rest pressure may be set to the printing operation level in a printing operation, or during a printing phase of the print head  103 . In an exemplary embodiment, the printing operation level is adapted depending on the operating age of the print head  103  and/or depending on the state of the nozzle plate  212  of the print head  103 . In particular, the printing operation level may be decreased with increasing operating age, meaning that the absolute value of the negative pressure of the ink in a nozzle  21 ,  22  may be improved with increasing operating age, or with degradation and/or variation of the state of the nozzle plate  212 . 
     On the other hand, in an exemplary embodiment, given a printing operation or in a printing pause of the print head  103 , the physical rest pressure may be decreased to a printing interruption level, meaning that the negative pressure may be further increased in magnitude relative to the printing operation level. In an exemplary embodiment, the printing interruption level thereby depends on the operating age of the print head  103  and/or on the state of the nozzle plate  212 , and typically decrease—i.e. increase in magnitude—with increasing operating age, or with degradation of the state of the nozzle plate  212 . Furthermore, the printing interruption level of the physical rest pressure may be adjusted such that, although the ink meniscus of the one or more nozzles  21 ,  22  are drawn further into the respective nozzle chambers, the ink meniscus does not tear off and thereby does not cause an air inclusion within the respective nozzle chambers. In an exemplary embodiment, the printing interruption level is determined experimentally for a specific type of print head  103 . 
       FIG. 3 a    shows a chronological pressure curve  310 , according to an exemplary embodiment, of the physical rest pressure in a printing interruption during which a print head  103  is cleaned. To “purge” the one or more nozzles  21 ,  22  of the print head  103 , the physical pressure within the nozzles  21 ,  22  is increased to a positive value in a purge phase  311  so that ink is driven out of the nozzles  21 ,  22 . In a transport phase  312 , the physical pressure is reduce to a negative printing interruption level  302  for the transport of the print head  103  from the cleaning position to the printing position. In a printing phase  313 , the physical negative pressure is then increased thereby decreasing the absolute value of pressure to the respective negative printing operation level  301  so that the print head  103  may be used for the printing of a print image on a recording medium  120 . 
       FIG. 3 b    shows a chronological pressure curve  320 , according to an exemplary embodiment, of the physical rest pressure in a printing interruption during which, although the print head  103  remains at the printing position, no print image is printed onto a recording medium  120 . During the printing phases  321  of the printing operation, the physical rest pressure in the nozzles  21 ,  22  is set to the printing operation level  301 . On the other hand, the printing interruption level  302  of the physical rest pressure is set during a printing pause  322 . 
     The transition from the purge phase  311  to the transport phase  312  and the transition from the transport phase  312  to the printing phase  313  have been depicted as a step functions in  FIG. 3 a   . These transitions can also have a certain finite slope to it. The transition from the printing phase  321  to the printing pause  322  and the transition from the printing pause  322  to the printing phase  321  have been depicted as a step function in  FIG. 3 b   . These transitions can also have a certain finite slope to it. 
     If applicable, in an exemplary embodiment, a regulated negative pressure may thus be set in the negative pressure tank  203  after a purge/wipe process, possibly independently of the age of the print head  103  (e.g., depending on the wear due to cleaning and/or the wear due to the printing operation). The leaking of ink during the travel time from the cleaning position into the printing position may thus be prevented. 
     In an exemplary embodiment, the pressure adjuster  205  is configured to adjust the negative pressure, for example, via a valve. This process may take a certain amount of time. Alternatively or additionally, the negative pressure may be regulated depending on the measured pressure in the negative pressure tank  203 . In an exemplary embodiment, a regulated negative pressure is adjusted and/or regulated as needed, for example depending on the wear of the nozzle plate, the viscosity of the ink, and/or the temperature of the ink. The regulated negative pressure in the negative pressure tank  203  may then prevent the leaking of the ink from a nozzle  21 ,  22  given a printing interruption. In particular, it may have the effect that ink only leaks—if at all—shortly before the beginning of the printing operation, and thus cannot dry and therefore clog the nozzle  21 ,  22 . 
     As a result of this, a reliable regeneration of the nozzles  21 ,  22  of a print head  103  may be produced via refresh measures after the end of a printing interruption. Nozzle failures may thus be avoided, and the print quality of a printing device  100  may be increased. 
     During the print head service life, a surface coating on the nozzle plate  212  may be damaged, for example by mechanical friction of the wiper  151  upon cleaning and/or by manual cleaning of the nozzle plate  212  or by inadvertent contact with recording medium. The valve effect of a nozzle  21 ,  22  may therefore decrease in the course of the print head service life. In an exemplary embodiment, to maintain the valve function of the nozzles  21 ,  22 , the negative pressure at the negative pressure tank  203  is increased in magnitude corresponding to the print head service life, or corresponding to the state of the nozzle plate  212 . The adjustment of the negative pressure may take place individually for each print head  103  or jointly for the print heads  103  of a print bar  102 . 
     Via the adaptation of the negative pressure in a print head  103 , a high print quality may be enabled, in particular at the start of printing and possibly also during the printing operation with an old print head  103 . Via the adaptation of the negative pressure, a leaking of ink during a printing interruption may be avoided. At the same time, via a precise adjustment of the negative pressure and/or of the fill level of the nozzles  21 ,  22  it may be achieved that no air may enter into the nozzle channel of a print head  103 . Moreover, a necessary amount of refresh measures, in particular the number of refresh print images that are to be printed, may be reduced via the measures described in this document. 
       FIG. 4  shows a workflow diagram of a method  400  according to an exemplary embodiment for preventing the leaking of ink from a print head  103  of an inkjet printing device  100 . The inkjet printing device  100  may be designed as described in according to the exemplary embodiments of the present disclosure, for example, as described in connection with  FIG. 1 a   . The print head  103  of the printing device  100  comprises at least one nozzle  21 ,  22 . The print head  103  typically comprises a plurality of nozzles  21 ,  22 , but is not limited thereto. 
     In an exemplary embodiment, the method  400  includes the determination  401  that a printing interruption phase  312 ,  322  of the print head  103  is present. In a printing interruption phase  312 ,  322 , typically no activation of the actuators of the one or more nozzles  21 ,  22  of a print head  103  takes place. 
     In an exemplary embodiment, the print head  103  is configured to be moved from a printing position into a cleaning position for a cleaning of the print head  103 . For example, the printing position may be arranged directly above a recording medium  120 . On the other hand, the cleaning position may be arranged laterally offset, in a cleaner  150  of the printing device  100 . For example, the print head  103 —in particular as part of a print bar  102  having multiple print heads  103 , as depicted in  FIG. 1 a   —may be moved along the movement direction  2  to the cleaning position. A cleaning of the nozzle plate  212  of the print head  103  may then take place at the cleaning position. The printing interruption phase  312 ,  322  may correspond to a transport phase  312  during which the print head  103  is moved from the cleaning position back to the printing position, in particular following a cleaning. 
     In an exemplary embodiment, alternatively or additionally, the printing interruption phase correspond to a printing pause  322  between two printing phases  321 . In a printing phase  321 , an activation of the actuators of the one or more nozzles  21 ,  22  of a print head  103  thus takes place. On the other hand, typically no activation and/or deflection of the actuators of the one or more nozzles  21 ,  22  of the print head  103  takes place during a printing pause  322 . The print head  103  nevertheless typically remains at the printing position, in particular above the recording medium  120 , in a printing pause  322 . 
     In an exemplary embodiment, in reaction to the determination  401  that the print head  103  is located in a printing interruption phase  312 ,  322 , the method  400  also includes the reduction  402  of a physical rest pressure of the ink in the nozzle  21 ,  22  to a printing interruption level  302 . The physical rest pressure is thereby typically negative, meaning a negative pressure. The printing interruption level  302  is lower than the printing operation level  301  which is used during a printing phase  313 ,  321  of the print head  103  as a typically negative physical rest pressure. In other words, in a printing interruption phase  321 ,  322 , the physical rest pressure of the ink in the nozzle  21 ,  22  of the print head  103  may be reduced in phase  322 , in particular in comparison to the physical rest pressure that is used for the printing operation of the nozzle  21 ,  22 . 
     A method  400  is thus described in which, in a printing interruption phase  312 ,  322 , in particular upon transport of the print head  103  from a cleaning position to a printing position, the negative pressure in the ink chamber of a nozzle  21 ,  22  of a print head  103  is reduced relative to the negative pressure in a printing phase  313 ,  321  of the print head  103 . The leaking of ink during the printing interruption phase  312 ,  322  may thus be reliably avoided, and in particular the initial print quality of an inkjet printing device  100  may be increased. 
     In an exemplary embodiment, the physical rest pressure corresponds to a physical pressure in an ink chamber of the nozzle  21 ,  22  that is present if the actuator of the nozzle  21 ,  22  is located in a rest state and/or is not activated and/or is not supplied with current. The physical rest pressure may, for example, correspond to the pressure in the ink chamber of the nozzle  21 ,  22  that is present if the actuator of the nozzle  21 ,  22  does not exhibit any deflection from a rest position. The set physical rest pressure may thereby correspond to the possible pump capacity of, for example, the piezoelectric actuators. 
     In an exemplary embodiment, the printing interruption level  302  is such that substantially no air is drawn via the nozzle  21 ,  22  into the ink chamber and/or into an ink channel  201  of the nozzle  21 ,  22 . In an exemplary embodiment, the printing interruption level  302  may be experimentally determined for this purpose. A leaking of ink may typically be reliably avoided if the physical rest pressure in the ink chamber is low, i.e. if a high (in terms of magnitude) negative pressure is present in the ink chamber. In an exemplary embodiment, the printing interruption level  302  is therefore as close as possible to a limit level as of which air is drawn via the nozzle  21 ,  22  into the ink chamber and/or into the ink channel  201  of the nozzle  21 ,  22 . 
     The physical rest pressure of the ink in the nozzle  21 ,  22  may be regulated at the printing interruption level  302 . The leaking of ink may thus be especially reliably avoided. 
     In an exemplary embodiment, the method  400  includes the determination of state information with regard to a state of the nozzle plate  212  of the print head  103 . In particular, the state information may indicate the state of a protective layer on the nozzle plate  212 . For example, the state information may include or indicate: a number of operating hours of the print head  103 ; an age of the print head  103 ; and/or a number of cleaning processes (e.g. wiping processes) that have been performed on the nozzle plate  212  of the print head  103 . In an exemplary embodiment, an optical refresh print image evaluation is likewise possible immediately after the start of printing. In an exemplary embodiment, this take place using a camera, such as a charge coupled device (CCD) camera or the like. The set pressure  302  may thereby be monitored and corrected as necessary. In an exemplary embodiment, the printing interruption level  302 , and possibly the print operating level  301 , is then adapted depending on the state information. In particular, the printing interruption level  302 , and possibly the print operating level  301 , may be reduced—meaning that the respective physical negative pressure may be increased in terms of magnitude—if the state information indicates that the state of the nozzle plate  212  has degraded or been altered, or that the nozzle plate  212  has aged. A high initial print quality may thus be achieved even given an advanced age of a print head  103 . 
     In an exemplary embodiment, the method  400  is executed separately for each print head  103  of a print bar  102 . In particular, the rest pressure for each print head  103  may be adapted individually and/or independently of the other print heads  103  of a print bar  102 . The leaking of ink may thus be prevented in a particularly reliable manner. On the other hand, the rest pressure for multiple print heads  103  of a print bar  102 , in particular for all print heads  103  of a print bar  102 , may be adapted jointly in a way that is especially efficient in terms of cost and installation space. A common negative pressure tank  203  and/or a common pressure adjuster  205  may then be provided for multiple print heads  103 . In a printing device  100  with multiple print bars  102  for different inks, the method  400  may respectively be executed for the individual print bars  102 . 
     Furthermore, a controller  101  for an inkjet printing device  100  is described in this document. The printing device  100  thereby comprises a print head  103  having at least one nozzle  21 ,  22 . In an exemplary embodiment, the controller  101  is configured to determine that a printing interruption phase  312 ,  322  of the print head  103  is present. Typically, no activation of the actuators of the one or more nozzles  21 ,  22  of the print head  103  thereby takes place in a printing interruption phase  312 ,  322 . 
     The controller  101  is also configured to induce the physical rest pressure of the ink in the nozzle  21 ,  22  to be reduced to a printing interruption level  302  that is lower than a printing operation level  301  which is used as a physical rest pressure during a printing phase  313 ,  321  of the print head  103 , possibly only when it has been determined that a printing interruption phase  312 ,  322  of the print head  103  is present. In an exemplary embodiment, the controller  101  includes processor circuitry that is configured to determine phases of the print head  103 , and/or induce or otherwise control an adjustment of pressure of the tank  203 . For example, the controller  101  can control the pressure adjuster  205  to adjust the pressure. 
     In an exemplary embodiment, the inkjet printing device  100  includes a negative pressure tank  203  with ink, wherein the negative pressure tank  203  is connected with the print head  103  via an ink channel  201 . Ink for the printing operation of the print head  103  may thus be provided via the ink channel  201 . The negative pressure tank  203  may be arranged with a defined height difference  213  below the nozzle plate  212  of the print head  103 . In particular, a height difference  213  may exist between the fill level  211  of the ink in the negative pressure tank  203  and the nozzle plate  212 . The physical rest pressure in the nozzle  21 ,  22  of the print head  103  may be adjusted to the printing operation level  301  via the (possibly hard-set) height difference  213 . In particular, the physical rest pressure of the ink in the nozzle  21 ,  22  may be set at the printing operation level  301  solely by the height difference  213 . 
     Moreover, in an exemplary embodiment, the inkjet printing device  100  includes a pressure adjuster  205  that is configured to vary a physical pressure and/or an ink fill level  211  in the negative pressure tank  203 . The physical rest pressure of the ink in the nozzle  21 ,  22  of the print head  103  may thus be indirectly varied. In an exemplary embodiment, the pressure adjuster  205  includes, for example, a valve and/or a pump and/or a compressed air source (in particular a Venturi nozzle). In an exemplary embodiment, alternatively or additionally, the pressure adjuster  205  is configured to vary the height difference  213  between the negative pressure tank  203  and the nozzle plate  212  in order to vary the physical rest pressure of the ink in the nozzle  21 ,  22 . In an exemplary embodiment, the controller  101  is configured to induce the pressure adjuster  205  to reduce the physical rest pressure of the ink in the nozzle  21 ,  22  to the printing interruption level  302 . 
     In an exemplary embodiment, the inkjet printing device  100  includes a sensor  206  that is configured to acquire sensor data with regard to the physical rest pressure of the ink in the nozzle  21 ,  22 . For example, a pressure sensor and/or a fill level sensor may be arranged at the pressure adjuster  205  in order to acquire the sensor data with regard to the physical rest pressure of the ink in the nozzle  21 ,  22 . In an exemplary embodiment, the controller  101  is configured to reduce (or otherwise adjust), in particular to regulate, the physical rest pressure of the ink in the nozzle  21 ,  22  to the printing interruption level  302  depending on the sensor data. 
     In an exemplary embodiment, the inkjet printing device  100  includes the controller  101  described herein. 
     In an exemplary embodiment, the printing device  100  includes a print head  103  having at least one nozzle  21 ,  22 , wherein the nozzle  21 ,  22  is configured to eject ink droplets onto a recording medium  120  in a printing phase  313 ,  321  in order to print a print image onto the recording medium  120 . Moreover, in an exemplary embodiment, the printing device  100  includes a negative pressure tank  203 , wherein the negative pressure tank  203  is connected with the print head  103  via an ink channel  201  in order to provide ink for the printing of a print image. 
     Furthermore, in an exemplary embodiment, the printing device includes a pressure adjuster  205  that is configured to vary a physical negative or positive pressure in the tank  203  in order to vary a physical rest pressure of the ink in the nozzle  21 ,  22 . In an exemplary embodiment, the controller  101  of the printing device  100  is configured to induce the pressure adjuster  205  to vary the physical rest pressure of the ink in the nozzle  21 ,  22 . 
     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 computer). 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, the term “processor circuitry” shall be understood to be circuit(s), processor(s), logic, or a combination thereof. A circuit includes an analog circuit, a digital circuit, state machine logic, other structural electronic hardware, or a combination thereof. A processor includes a microprocessor, a digital signal processor (DSP), central processing unit (CPU), application-specific instruction set processor (ASIP), graphics and/or image processor, multi-core processor, or other hardware processor. The processor may be “hard-coded” with instructions to perform corresponding function(s) according to aspects described herein. Alternatively, the processor may access an internal and/or external memory to retrieve instructions stored in the 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 is 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 
     
         
           1  transport direction (of the recording medium) 
           2  movement direction (of a print bar) 
           21 ,  22  nozzle 
           31 ,  32  column (of the print image) 
           100  printing device 
           101  controller 
           102  print bar 
           103  print head 
           120  recording medium 
           150  cleaner 
           151  wiper 
           201  ink channel 
           202  supply channel 
           203  negative pressure tank 
           204  ink channel 
           205  pressure adjuster 
           206  sensor 
           211  fill level 
           212  nozzle plate 
           213  height difference 
           301  printing operation level 
           302  printing interruption level 
           310  pressure curve of the physical rest pressure 
           311  purge phase 
           312  transport phase 
           313  printing phase 
           320  pressure curve of the physical rest pressure 
           321  printing phase 
           322  printing pause 
           400  method for preventing the leaking of ink 
           401 - 402  method steps