Patent Publication Number: US-2022234349-A1

Title: Controller and method for operating a printing device given the presence of a recording medium elevation

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This patent application claims priority to German Patent Application No. 102021101892.7, filed Jan. 28, 2021, which is incorporated herein by reference in its entirety. 
     BACKGROUND 
     Field 
     The disclosure relates to a method and a corresponding controller for operating a printing device, in particular an inkjet printing device, given detection of an elevation of the recording medium to be printed to. 
     Related Art 
     An inkjet printing device for printing to a recording medium has at least one print bar having one or more print heads, wherein each print head typically has a plurality of nozzles. The nozzles are respectively configured to eject ink droplets in order to print dots of a print image onto the recording medium. 
     During the printing operation, the print bar with the one or more print heads is typically arranged relatively closely, for example 2 mm or less, above the surface of the recording medium to be printed to, in order to enable an optimally high print quality. Therefore, there is the risk that an elevation of the recording medium, for example a local adhesive area of the recording medium, causes a contact between the surface of the recording medium and the nozzle plate of a print head of the printing device, which may lead to a negative effect on the print head. 
    
    
     
       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 block diagram of an inkjet printing device according to an exemplary embodiment. 
         FIGS. 2 a  to 2 c    different states of a print bar upon traversing an elevation of a recording medium, according to exemplary embodiments. 
         FIG. 3  plots of time diagrams for the operation of a printing device given a detected recording medium elevation according to an exemplary embodiment. 
         FIG. 4  a flowchart of a method for operating a printing device in reaction to a detected recording medium elevation according to an exemplary embodiment. 
     
    
    
     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. The connections shown in the figures between functional units or other elements can also be implemented as indirect connections, wherein a connection can be wireless or wired. Functional units can be implemented as hardware, software or a combination of hardware and software. 
     An object of the present disclosure is to efficiently and reliably protect a printing device, in particular an inkjet printing device, from a negative effect of an elevation of a recording medium to be printed to. 
     According to one aspect of the disclosure, a controller for controlling a printing device is described that has at least one printing unit having at least one print bar. The printing device is designed to produce a relative movement between the printing unit and a recording medium to be printed to by the printing unit, in order to print sequential lines of a usable print image onto the recording medium during the printing operation. 
     The controller is configured to detect an elevation of the print image to be printed to and, in reaction thereto, to produce a printing pause of the printing operation upon continuation of the relative movement between the printing unit and the recording medium. The controller is also configured to induce the effect that, during the printing pause, the printing gap between the printing unit and the recording medium is enlarged, for example by raising the printing unit, so that the detected elevation of the recording medium may be directed past the printing unit within the scope of the continued relative movement. Moreover, the controller is configured to induce the effect that the printing gap between the printing unit and the recording medium is reduced again after the detected elevation of the recording medium has been directed past the printing unit, and to resume the printing operation after the printing gap between the printing unit and the recording medium has been reduced. 
     According to a further aspect of the disclosure, a method is described for controlling a printing device that has at least one printing unit having at least one print bar. The printing device is designed to produce a relative movement between the printing unit and a recording medium to be printed to by the printing unit, in order to print sequential lines of a usable print image onto the recording medium during the printing operation. 
     The method includes the detection of an elevation of the recording medium to be printed to and, in reaction thereto, the production of a printing pause of the printing operation of the printing unit given simultaneous continuation of the relative movement between the printing unit and the recording medium. Furthermore, the method includes having the effect that, during the printing pause, the printing gap between the printing unit and the recording medium is enlarged so that the detected elevation of the recording medium may be directed past the printing unit within the scope of the continued relative movement, in particular without the elevation thereby contacting the printing unit. Moreover, the method includes having the effect that the printing gap between the printing unit and the recording medium is reduced again after the detected elevation has been directed past the printing unit. The method also includes the resumption of the printing operation of the printing unit after the printing gap between the printing unit and the recording medium has been reduced. 
     The printing device  100  depicted in  FIG. 1  is designed for printing to a recording medium  120  in the form of a belt or web or page or sheet. The printing device  100  may, if applicable, be designed to take the recording medium  120  in the form of a web off of a roll. The recording medium  120  may be manufactured from paper, paperboard, cardboard, metal, plastic, textiles, a combination thereof, and/or other materials that are suitable and can be printed to. The recording medium  120  is transported along the transport direction  1 , represented by an arrow, through at least one printing unit  141 ,  142  of the printing device  100 . 
     In the depicted example, a printing unit  141 ,  142  of the printing device  100  comprises two print bars  102 , wherein each print bar  102  may be used for printing with ink of a defined color, for example black, cyan, magenta, and/or yellow, and if applicable MICR ink. Furthermore, the printing device  100  typically comprises at least one fixing or drying unit (not shown) that is configured to fix a print image printed onto the recording medium  120 . 
     A print bar  102  may comprise one or more print heads  103  that are possibly arranged side by side in a plurality of rows in order to print the dots of different columns  31 ,  32  of a print image onto the recording medium  120 . In the example depicted in  FIG. 1 , a print bar  102  comprises five print heads  103 , 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 , each print head  103  of a printing unit  141 ,  142  comprises a plurality of nozzles  21 ,  22 , wherein each nozzle  21 ,  22  is configured to fire or eject ink droplets onto the recording medium  120 . A print head  103  of a printing unit  141 ,  142  may, for example, comprise multiple thousands of effectively utilized nozzles  21 ,  22  that are arranged along a plurality of rows transverse to the transport direction  1  of the recording medium  120 . By means of the nozzles  21 ,  22  of a print head  103  of a printing unit  141 ,  142 , dots of a line of a print image may be printed onto the recording medium  120  transverse to the transport direction  1 , meaning along the width of the recording medium  120 . 
     In an exemplary embodiment, the printing device (printer)  100  also includes a controller  101 , for example an activation hardware and/or a processor, that is configured to activate the actuators of the individual nozzles  21 ,  22  of the individual print heads  103  of the printing units  141 ,  142  in order to apply the print image onto the recording medium  120  depending on print data. In an exemplary embodiment, the controller  101  includes processing circuitry  122  that is configured to perform one or more functions and/or operations of the controller  101 , including activating the actuators of the individual nozzles  21 ,  22  of the individual print heads  103  of the print group  140  to apply the print image onto the recording medium  120  based on print data, processing print and/or other data, controller one or more modes of the printer device  100  and/or controlling one or more operations of the printing device  100 . In an exemplary embodiment, the controller  101  includes one or more interfaces  124  (e.g. a wired and/or wireless input and/or output interface, transceiver, or the like) that is configured to receive or output data or information. For example, the controller  101  may receive signals generated by one or more components of the printing device  100  (e.g. from a user interface of the printer device  100 ) and/or output control signals to one or more components of the printing device  100 . In an exemplary embodiment, the controller  101  includes a memory configured to store data/information, and/or store executable code that is executable by the processing circuitry  122  to cause the processing circuitry to perform the operation(s) of the controller  101 . 
     A printing unit  141 ,  142  of the printing device  100  thus comprises at least one print bar  102  with K nozzles  21 ,  22  that may be activated with a defined line timing in order to print a line with K pixels or K columns  31 ,  32 —for example with K&gt;1000—of a print image onto the recording medium  120 , the line traveling transverse to the transport direction  1  of the recording medium  120 . In the depicted example, the nozzles  21 ,  22  are installed immobile 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. 
     Furthermore, the printing device  100  may comprise one or more regenerators  150  for the corresponding one or more print bars  102  of the one or more printing units  141 ,  142 . A print bar  102  may be transitioned from a printing position, at which the print bar  102  is arranged above the recording medium  120 , into a cleaning or service position. For this purpose, the print bar  102  may be moved in the movement direction  2 , indicated by an arrow. In the cleaning or service position, the nozzle plates of the one or more print heads  103  of a print bar  102  may then be cleaned, for example wiped off, using a regenerator  150 . A purging of the one or more print heads  103  with ink may also take place in the regenerator  150 . The printing device  100  may have at least or precisely one regenerator  150  for each print bar  102 . 
     In the example depicted in  FIG. 1 , the printing device  100  has two, possibly structurally identical, printing units  141 ,  142  that, for example, may be used for printing to the front side and back side of the recording medium  120 . A turning unit (turner)  160  may be arranged between the two printing units  141 ,  142 , which turning unit  160  is designed to turn the recording medium  120  so that the front side of the recording medium may be printed to by the first printing unit  141  and the back side of the recording medium  120  may be printed to by the printing unit  142 . 
     As explained above, recording media  120  may exhibit disturbances, for example adhesive areas, joints, dog-ears, or other deformations. The printing gap between the surface of the recording medium  120  that is to be printed to and the nozzle plates of the one or more print heads  103  of the printing device  100  is typically relatively small, for example less than 2 mm, in order to achieve an optimally high print quality. Therefore, there is the risk that a damaged spot or disturbance of the recording medium  120  contacts, and possibly damages, the nozzle plate of a print head  103 . 
     The printing device  100  may comprise a sensor  110  that is configured to detect an elevation of the recording medium  120  to be printed to. The sensor  110  may be arranged before the first printing unit  141 , relative to the transport direction  1  of the recording medium  120 . The controller  101  of the printing device  100  may be configured to interrupt a running printing process as soon as an elevation of the recording medium  120  is detected on the basis of the sensor data of the sensor  110 . The detected elevation of the recording medium  120  may then be directed through the first printing unit  141  and through the optional second printing unit  142  without the recording medium  120  being printed to. A user of the printing device  100  may also be enabled to manually restart the printing process as soon as the detected elevation of the recording medium  120  has passed the one or more printing units  141 ,  142  of the printing device  100 . 
     The aforementioned reaction of the printing device  100  to a detected elevation of the recording medium  120  leads to a relatively high expenditure for the user of the printing device  10 , and/or to a relatively large amount of spoilage that must be rejected and discarded. Given a restart of the printing process, a cleaning of the one or more print heads  103 , in particular a purging of the one or more print heads  103 , within the one or more regenerators  150  is also typically necessary, which is linked with a relatively high ink consumption and with an additional time cost. 
     The one or more print bars  102 , in particular the one or more print heads  103 , may be designed such that the individual print bars  102  may be moved orthogonal to the surface of the recording medium  120  in order to increase the distance or the printing gap between the respective print bar  102  and the surface of the recording medium  120 . This is depicted by arrows in  FIGS. 2 a  through 2 c   , by way of example. 
     The controller  101  of the printing device  100  may be configured to have the effect, in reaction to a detected elevation  210  of the recording medium  120  to be printed to, that the individual print bars  102  of a printing unit  141 ,  142  are raised. The print bar  102  closest to the elevation  210  may thereby be set into motion first, and the following print bars  102  may then be raised gradually, as depicted by way of example in  FIG. 2   b.    
     After the elevation  210  has passed a print bar  102 , this print bar  102  may be lowered again so that the print bars  102  of a printing unit  141 ,  142  are gradually lowered again, as depicted by way of example in  FIG. 2 c   . The raising and the lowering of the print bars  102  may be effected in an especially energy-efficient and prompt manner via the sequential raising and/or lowering of the print bars  102 . This enables the duration of the printing pause to be reduced. 
       FIG. 3  shows examples of time diagrams for the operation of the printing device  100  in reaction to a detected elevation  210 . The elevation  210  is detected at a detection point in time  311 . In reaction thereto, a printing pause signal  303  may be set by the controller  101 . The printing pause signal  303  has a defined time length  333  that indicates the duration for which the printing operation of a printing unit  141 ,  142  should be paused due to the detected elevation  210 . 
       FIG. 3  also shows the transport velocity  304  of the recording medium  120  as a result of the elevation  210  detected at the detection point in time  311 . The transport velocity  304  is not reduced (at least in a first step). In other words, the recording medium  120  is invariably moved further within the printing device  100  even after detection of an elevation  210 . 
     As emerges from  FIG. 1 , the first printing unit  141  exhibits a first spatial distance  131  from the sensor  110  for detection of elevations  210 , and the optional second printing unit  142  exhibits a second spatial distance  132  from the sensor  110  for detection of elevations  210 . The spatial distances  131 ,  132  correspond, depending on the transport velocity  304  of the recording medium  120 , to time intervals  331 ,  332  between the sensor  110  and the respective printing unit  141 ,  142 . In particular, the time intervals  331 ,  332  may be proportional to the spatial distances  131 ,  132 , wherein the proportionality factor depends on the transport velocity  304 , in particular corresponds to the transport velocity  304 . 
       FIG. 3  shows a first control signal  301  for the first printing unit  141  and a second control signal  302  for the optional second printing unit  142 . The first control signal  301  may be chronologically offset by the first time interval  331  relative to the printing pause signal  303 , and may indicate the time period in which the first printing unit  141  implements a printing pause. The second control signal  302  may accordingly be chronologically offset by the second time interval  332  relative to the printing pause signal  303 , and may indicate the time period in which the second printing unit  142  implements a printing pause. 
       FIG. 3  shows the beginning point in time  312  for the beginning of the printing pause for the first printing unit  141 , and the end point in time  313  for the end of the printing pause for the first printing unit  141 . Furthermore,  FIG. 3  shows the beginning point in time  314  for the beginning of the printing pause of the second printing unit  142 , and the end point in time  315  for the end of the printing pause of the second printing unit  142 . 
     During the respective printing pause, the one or more print bars  102  of the respective printing unit  141 ,  142  may, as depicted in  FIGS. 2 a  to 2 c   , initially be moved away from the surface of the recording medium  120  and, after traversal of the elevation  210 , toward the surface of the recording medium  120  again, in order to reliably prevent a contact between the elevation  210  of the recording medium  120  and the nozzle plates of the respective print heads  103  in the one or more print bars  102 . 
     As emerges from  FIG. 3 , the printing pauses of the individual printing units  141 ,  142  are time-limited. Following a printing pause, the printing operation may be resumed, in particular at the point at which the printing operation was interrupted. For example, a printing pause may have been begun following the printing of a defined page x of the usable print image to be printed. After ending the printing pause, the printing may be resumed with the printing of the directly following page x+1 of the usable print image. 
     The lower portion of  FIG. 3  shows a time diagram in which the printing pause has a chronological duration  333  that enables the detected elevation  210  to be entirely guided through the first printing unit  141  and through the second printing unit  142  before the printing pause is ended again. This control of the printing device  100  may be efficiently realized via a controller  101  of the printing device  100 . 
     The upper portion of  FIG. 3  shows a time diagram in which the printing pause has a chronological duration  333  that enables the detected elevation  210  to be guided through precisely one printing unit  141 ,  142  before the printing pause is ended again. The printing pause for the respective printing unit  141 ,  142  may thereby be ended again as soon as the elevation  210  has traversed the respective printing unit  141 ,  142 . The printing pause for a printing unit  141 ,  142  may thus be limited to the duration that the elevation  210  requires in order to traverse the respective printing unit  141 ,  142 . An especially short printing pause may thus be enabled, whereby the effects of a detected elevation  210  of the recording medium may be further reduced, in particular with respect to spoilage and/or printing efficiency. 
     A usable print image to be printed by the printing device  100  may be subdivided into a sequence of pages. The individual pages may be identified via an index x, for example. The controller  101  may be configured to place the printing pause for a printing unit  141 ,  142 —meaning the control signal  301 ,  302  for a printing unit  141 ,  142 —in time, depending on the printing pause signal  303 , such that the printing pause begins directly following the printing of a complete page x, so that the printing of the directly following page x+1 may be begun after the ending of the printing pause. In other words, the printing pause may be chronologically placed such that no incompletely printed page is printed on the recording medium  120  directly before the printing pause, and/or only completely printed pages are printed on the recording medium  120 . A printing pause for a detected elevation  210  may thus be enabled in an especially resource-efficient manner. 
     The time interval  331 ,  332  and/or the duration of a printing pause, or of the corresponding control signal  301 ,  302 , may thus be determined depending on
         the transport velocity  304  of the recording medium  120 ;   the spatial distance  131 ,  132  between the sensor  110  and the respective printing unit  141 ,  142 ; and/or   the arrangement of the individual pages x in the usable print image to be printed.       

     For example, the time interval  331 ,  332  T may be determined on the basis of the formula 
     
       
      
       T=D/v−Δ 
      
     
     wherein D is the spatial distance  131 ,  132 , and wherein v is the transport velocity  304 . Δ is a time offset that results from the fact that the printing pause is already begun after the ending of a completely printed page x, and not only at the most recent possible point in time at which a completely printed page x+1 is, however, present. 
     Accordingly, the duration Q of the printing pause or of the control signal  301 ,  302  may be determined on the basis of the following formula 
     
       
      
       Q=R+Δ 
      
     
     wherein R is the duration that the elevation  210  requires in order to traverse precisely one printing unit  141 ,  142  (for the instance depicted in the upper portion of  FIG. 3 ), or in order to traverse both printing units  141 ,  142  (for the instance depicted in the lower portion of  FIG. 3 ). 
     The controller  101  may be configured to induce a printing unit  141 ,  142  to print a trailer print image having one or more trailer pages after the ending of the printing of the page x of the print image and before the beginning of the printing pause. Alternatively or additionally, the controller  101  may be configured to induce a printing unit  141 ,  142  to print a leader print image having one or more leading pages after the ending of the printing pause and before the printing of the page x+1 of the print image. The one or more trailer pages and/or the one or more leader pages may be used by a post-processing unit of the printing device  100 , for example by a cutter configured to cut out the individually printed pages of the usable print image, to synchronize with the printing device  100  and the inserted printing pause. For this purpose, the one or more trailer pages and/or the one or more leader pages may include a pattern that can be precisely and reliably detected by the post-processing unit. The insertion of one or more trailer pages and/or of one or more leader pages enables effects of a detected elevation  210  on the process for producing print products to be further reduced. 
     The ending and/or the beginning of the printing of a page of the usable print image may take place earlier or later by the duration that is required to print the one or more trailer pages or the one or more leader pages. 
     The printing device  100  may thus be configured to process a disturbance  210  of the recording medium  120  not as an error, with a printing stop following thereon, but rather as a status change that leads to a printing pause, in particular to a temporary and/or time-limited printing pause. One or more trailer pages may be inserted as needed, in particular before the beginning of the printing pause, so that a print good post-processing machine may more easily process the printing interruption and a synchronization to the print pages of the usable print image may subsequently take place. 
     The printing process in a printing unit  141 ,  142  is paused before the damaged spot  210  of the recording medium  120  reaches the first print bar  102  of the printing unit  141 ,  142 . Given a printing device  100  having a plurality of printing units  141 ,  142 , in particular for two-sided printing, the one or more following printing units  142  may continue to print without pause during the printing pause of the first printing unit  141 . The recording medium  120  thereby continues to run at the full transport velocity  304 . 
     The one or the plurality of print bar(s)  102 , meaning the one of more print bars  102 , of the first printing unit  141  are moved away from the surface of the recording medium  120  during the printing pause before the damaged spot  210  of the recording medium  120  has reached the respective print bar  102 . The damaged spot  210  is then transported past the individual print bars  102 . The individual print bars  102  may subsequently be moved toward the surface of the recording medium  120  again, and the printing process may be automatically continued again. The controller  101  may insert one or more leading pages as needed so that the post-processing may synchronize to the following pages of the usable print image. 
     In the further proceeding, given a printing device  100  having a plurality of printing units  141 ,  142 , the damaged spot  210  of the recording medium  120  is transported to the second printing unit  142 . Here as well, it proceeds as before in the first printing unit  141 : the printing process is paused before the disturbance  210  arrives at a print bar  102  of the second printing unit  142 . The respective print bar  102  is moved away from the surface of the recording medium  120 , the recording medium  120  is transported by the respective print bar  102 , and the respective print bar  102  is subsequently brought into printing position again. The printing process is continued at the correct page, matching the already printed usable print image of the first printing unit  141 . The first printing unit  141  continues to print during the printing pause of the second printing unit  142 . 
     If applicable, a simplified realization may be used, in particular for a duplex printing device  100 , in which a damaged spot  210  is driven completely through the duplex printing device  100  until the second printing unit  142  has been traversed. 
     Upon detection of a disturbance  210  of the recording medium  120 , the printing process may be paused. The print bars  102  of the one or more printing unit(s)  141 ,  142  are then moved away from the recording medium  120 , and the disturbance  210  is driven at full transport velocity  304  through the complete printing device  100 , in particular through all printing units  141 ,  142  of the printing device  100 . 
     If applicable, the recording medium  120  may be stopped automatically along a stop ramp after the detected disturbance  210  has traversed the complete printing device  100 . A relatively brief standstill of the recording medium  120  my then be produced. The printing process may subsequently be restarted automatically. The described measures may thus be particularly efficiently implemented. A user of the printing device  100  may thus also be made aware of the presence of a disturbance  210  of the recording medium  120 . 
     The printing pause of a printing unit  141 ,  142  that has been produced due to a detected disturbance or elevation  210  may be brief, such that no purging of the one or more print heads  103  is required following the printing pause. The controller  101  may be configured to determine the duration of the printing pause of a printing unit  141 ,  142  or of a print head  103 . For example, this may take place using the aforementioned formula. On the basis of the determined duration, a decision may then be made as to whether a purging of the print head  103  within the regenerator  150  is implemented following the printing pause, before resuming the printing operation, or whether no purging of the print head  103  is implemented. The effects of a detected elevation  210  on the productivity and/or on the efficiency of the printing device  100  may be further reduced by avoiding a purging of the print head  103 . 
       FIG. 4  shows a workflow diagram of an example of a, possibly computer-implemented, method  400  for controlling a printing device  100 , in particular an inkjet printing device  100 , that has at least one printing unit  141 ,  142  having at least one print bar  102 . The print bar  102  may have one print head  103  or a plurality of print heads  103 , for example. The method  400  can be executed by a controller  101  of the printing device  100 . 
     The printing device  100  is designed to produce a relative movement between the print bar  102  and/or the print head  103  and a recording medium  120  to be printed to by the print head  103 , in order to print sequential lines of a usable print image onto the recording medium  120  during the printing operation. The relative movement may take place along a defined transport direction  1 , wherein the transport direction  1  may travel orthogonal to the arrangement of the individual line of the usable print image. Within the scope of the relative movement, the recording medium  120  may be directed past a stationary print bar  102  and/or stationary print head  103 . The recording medium  120  may be a recording medium  120  in the form of a web, a page, or a sheet. 
     The method  400  includes the detection  401  of an elevation  210  of the recording medium  120  to be printed to, in particular an elevation  210  that is larger or higher than the printing gap between the print bar  102  and/or the print head  103  and the recording medium  120 . The elevation  210  may be detected on the basis of the sensor data of a sensor  110 , wherein the sensor  110  is arranged before the printing unit  141 ,  142 , in particular before the print bar  102  and/or the print head  103  of the printing unit  141 ,  142 , relative to the transport direction  1 . 
     Furthermore, in reaction to the detection  401  of an elevation  210 , the method  400  includes effecting, in particular automatically effecting  402 , a printing pause of the printing operation of the print bar  102  and/or of the print head  103  given continuation of the relative movement between the print bar  102  (and/or the print head  103 ) and the recording medium  120 . In particular, the transport velocity  304  of the relative movement may thereby be maintained. On the other hand, the printing operation for printing of the usable print image is interrupted in the printing pause. The interruption thereby takes place at a defined point of the usable print image, in particular after ending the printing of a defined page of the usable print image. 
     The method  400  also includes effecting  403 , in particular automatically effecting  403 , that the printing gap between the print bar  102  (and/or the print head  103 ) and the recording medium  120  is enlarged during the printing pause so that the detected elevation  210  of the recording medium  120  may be directed past the print bar  102  (and/or the print head  103 ) within the scope of the continued relative movement. The enlargement of the printing gap may be produced by raising the print bar  102  (and/or the print head  103 ). 
     Furthermore, the method  400  includes effecting  404 , in particular automatically effecting  404 , that the printing gap between the print bar  102  (and/or the print head  103 ) and the recording medium  120  is reduced again after the detected elevation  210  of the recording medium  120  has been directed past the print bar  102  (and/or the print head  103 ). The reduction of the printing gap may be produced by lowering the print bar  102  (and/or the print head  103 ). 
     Moreover, the method  400  includes the resumption  405 , in particular the automatic resumption  405 , of the printing operation of the print bar  102  (and/or of the print head  103 ) to print the usable print image, and thus the ending of the printing pause, after the printing gap between the print bar  102  (and/or of the print head  103 ) and the recording medium  120  has been reduced. The printing of the usable print image may thereby be resumed directly following the defined point, in particular the defined page, of the usable print image at which the interruption of the printing of the usable print image previously took place. 
     Furthermore, in this document a controller  101  is described for controlling a printing device  100 , in particular an inkjet printing device  100 . The printing device  100  comprises at least one printing unit  141 ,  142  having at least one print head  103 , and/or having at least one print bar  102  having one or more print heads  103 . During the printing operation, a defined printing gap, for example with a gap width of 2 mm or less, may be present between the print bar  102  (and/or the print head  103 ) and a recording medium  120  to be printed to. 
     The printing device  100  may be designed to produce a relative movement between the print bar  102  (and/or the print head  103 ) and the recording medium  120  to be printed to by the print bar  102  (and/or the print head  103 ), in order to print sequential lines of a usable print image on the recording medium  120  during the printing operation. The usable print image may thereby comprise a sequence of pages that are printed sequentially, line by line, onto the recording medium  120  during the printing operation. 
     The controller  101  may be configured to detect an elevation  210  of the recording medium  120  to be printed to. In particular, an elevation  210  may thereby be detected that is larger or higher than the gap width of the printing gap between the print bar  102  (and/or the print head  103 ) and the recording medium  120 . The printing device  100  may comprise a sensor  110 , for example a camera, that is configured to capture sensor data with respect to the surface of the recording medium  120  that is to be printed to. The controller  101  may be configured to detect the elevation  210  of the recording medium  120  on the basis of the sensor data of the sensor  110 . Relative to the transport direction  1  of the relative movement, the sensor  110  may be arranged at a defined spatial distance  331 ,  332  before the printing unit  141 ,  142 , in particular before the print bar  102  (and/or the print head  103 ) of the printing unit  141 ,  142 . 
     The controller  101  may also be configured to produce a printing pause of the printing operation in reaction to the detection of an elevation  210  of the recording medium  120 . The relative movement between the print bar  102  (and/or the print head  103 ) and the recording medium  120  may thereby be continued, in particular during the entire printing pause. The printing operation of the print bar  102  (and/or the print head  103 ), in particular for printing of the usable print image, may also be interrupted during the printing pause. 
     Furthermore, the controller  101  may be configured to induce, during the printing pause, that the printing gap between the print bar  102  (and/or the print head  103 ) and the recording medium  120  is enlarged, in particular relative to the printing gap that is used during the printing operation. The enlargement of the printing gap may take place such that the detected elevation of the recording medium  120  may be directed past the print bar  102  (and/or the print head  103 ) within the scope of the continued relative movement without the print bar  102  (and/or the print head  103 ) thereby being contacted. For this purpose, the enlargement of the printing gap may be effected depending on the height of the elevation  210  as determined on the basis of the sensor data of the sensor  110 . A negative effect on the print bar  102  (and/or the print head  103 ) due to the detected elevation  210  of the recording medium  120  may thus be prevented in an especially reliable and time-efficient manner. 
     The controller  101  may also be configured to induce that the print group between the printing unit  141 ,  142  and the recording medium  120  is reduced again after the detected elevation  210  of the recording medium  120  has been directed past the printing unit  141 ,  142  within the scope of the continued relative movement. The printing gap may thereby be reduced to the gap width provided for the printing operation. 
     In general, the printing unit  141  or  142  may have at least one print head. A plurality of print heads  103  for printing a single color may be arranged in a print bar  103 . 
     Furthermore, the controller  101  may be configured to end the printing pause and resume the printing operation after the printing gap between the printing unit  141 ,  142  and the recording medium  120  has been reduced. 
     A controller  101  is thus described that is designed to detect an elevation  210  of a recording medium  120  to be printed to, by which elevation  210  the printing unit  141 ,  142  of a printing device  100  might be negatively affected. The controller  101  is also configured to automatically produce a time-limited printing pause of the printing unit  141 ,  142  in which the printing gap between the printing unit  141 ,  142  and the recording medium  120  is temporarily enlarged in order to direct the detected elevation  120  past the printing unit  141 ,  142 . A negative effect on the printing device  100  given the presence of a damaged recording medium  120  may thus be efficiently and reliably avoided. 
     The controller  101  may be configured to determine the beginning point in time  312 ,  312  for beginning, or for the beginning of, the printing pause, and/or the end point in time  313 ,  314  for ending, or for the end of, the printing pause, depending on the spatial distance  331 ,  332  between the sensor  110  and the printing unit  141 ,  142 , in particular the print bar  102  and/or the print head  103  of the printing unit  141 ,  142 . The beginning point in time  312 ,  314  may thereby be determined such that the printing pause is begun before the detected elevation  210  of the recording medium  120  reaches the printing unit  141 ,  142 , in particular the print bar  102  and/or the print head  103  of the printing unit  141 ,  142 . Alternatively or additionally, the end point in time  313 ,  314  may be determined such that the printing pause is ended after the detected elevation  210  of the recording medium  120  has been directed past the printing unit  141 ,  142 , in particular past the print bar  102  and/or the print head  103  of the printing unit  141 ,  142 . A negative effect on the print bar  102  and/or the print head  103  of the printing unit  141 ,  142  may thus be reliably and efficiently prevented. 
     During the printing pause, the relative movement between the printing unit  141 ,  142  and the recording medium  120  has a defined transport velocity  304 . The transport velocity  304  during the printing pause may thereby correspond to the transport velocity  304  during the printing operation, in particular without modification. The controller  101  may be configured to determine the beginning point in time and/or the end point in time of the printing pause especially precisely depending on the transport velocity  304  during the printing pause. 
     The controller  101  may be configured to induce the printing unit  141 ,  142  to print a trailer print image onto the recording medium  120  before the beginning of the printing pause and after interruption of the printing of the usable print image. Alternatively or additionally, the controller  101  may be configured to print a leader print image onto the recording medium  120  after ending the printing pause and before resuming the printing of the usable print image. The trailer print image and/or the leader print image may thereby respectively comprise a (possibly predefined) pattern that enables a post-processing device, for example a cutter, to identify the usable print image and/or locate the usable print image on the recording medium following the printing device  100 . A reliable post-processing of a printed recording medium  120  may thus be enabled even given the presence of a defective recording medium  120 . 
     The controller  101  may be configured to effect that the printing pause is begun only after conclusion of a completely printed page of the usable print image. This may in particular take place such that the printing of a page of the usable print image within the sequence of pages directly following the completely printed page may be begun after ending the printing pause, possibly directly after printing the optional leader print image. The printing pause may thus be inserted precisely with respect to the page within the sequence of pages of the usable print image. The effects of a defective recording medium  120  on the printing process may thus be further reduced. 
     The printing unit  141 ,  142  may have a plurality of successive print bars  102 , for example for different colors and/or for different ink types. The printing device  100  may be designed such that, within the scope of the relative movement, the detected elevation  210  of the recording medium  120  is successively directed in a defined order, in particular along the transport direction  1 , past the successive print bars  102  and/or the print heads  103  of the printing unit  141 ,  142 . 
     The controller  101  may be configured to induce that, during the printing pause, the printing gaps between the successive print bars  102  and/or the successive print heads  103  and the recording medium  120  are respectively enlarged with a time offset relative to one another according to the defined order. The enlargement of the printing gaps may thereby in particular respectively take place “just in time” as the elevation  210  reaches the respective printing unit  141 ,  142 . The enlargement of the printing gaps of the successive printing units  141 ,  142  may thus take place similar to a wave motion. 
     Alternatively or additionally, the controller  101  may be configured to induce that the printing gaps between the successive printing units  141 ,  142  and the recording medium  120  are respectively reduced, with a time offset relative to one another according to the defined order, as soon as the elevation  210  of the recording medium  120  has been directed past the respective printing unit  141 ,  142 . The reduction of the gap width of the printing gaps may thereby respectively begin as soon as the elevation  210  has passed the respective printing unit  141 ,  142 . The reduction of the printing gaps may thus take place in the reverse direction corresponding to the enlargement of the printing gaps, similar to a wave motion. 
     The sequential increase and/or decrease of the printing gap enables the duration of the printing pause to be further reduced, so that the effects of a defective recording medium  120  may be further reduced. Furthermore, the power requirement of the printing device  100  for the increase and/or decrease of the printing gap may thus be reduced. 
     The printing device  100  may comprise a first printing unit  141  having at least one first print bar  102 , for example for printing to a front side of the recording medium  120 . Furthermore, the printing device  100  may comprise a second printing unit  142  having at least one second print bar  102 , for example for printing to the back side of the recording medium  120 . The printing device  100  may be designed such that, within the scope of the relative movement, the detected elevation  210  of the recording medium  120  is first directed past the first print head  141  and subsequently past the second printing unit  142 . 
     The controller  101  may be configured to produce a printing pause of the first printing unit  141 , and to continue the printing operation in the second printing unit  142  while the detected elevation  210  of the recording medium  120  is being directed past the first printing unit  141 . Alternatively or additionally, the controller  101  may be configured to produce a printing pause of the second printing unit  142 , and to continue the printing operation in the first printing unit  141  while the detected elevation  210  of the recording medium  120  is being directed past the second printing unit  142 . Time-limited printing pauses may thus be selectively produced for every single printing unit  141 ,  142 . The effects of a defective recording medium  120  on the printing process may thus be reduced to a particular degree. 
     Alternatively, the controller  101  may be configured to produce a chronologically contiguous printing pause of the first printing unit  141  and of the second printing unit  142  that is sufficiently long in order to direct the detected elevation  210  of the recording medium  120  past the first printing unit  141  and past the second printing unit  142 . A contiguous printing pause for a plurality of printing units  141 ,  142  may thus be produced which may be implemented in a printing device in an especially efficient and reliable manner. 
     The controller  101  may be configured to determine a duration of the printing pause before resuming the printing operation following the printing pause. In particular, the contiguous duration may be determined during which the printing unit  141 ,  142  was not used for printing a print image. Before resuming the printing operation, a regeneration measure of the printing unit  141 ,  142  may then be produced or suppressed depending on the determined duration of the printing pause. A high print quality of the printing device  100  may thus be efficiently ensured. 
     Furthermore, in this document a printing device  100  is described that comprises the controller  101  described in this document. 
     The duration of a printing interruption, i.e. a printing pause, due to a detected elevation  210  may be reduced via the measures described in this document, whereby the resource consumption and/or the spoilage may be reduced and/or the productivity of the printing device  100  may be increased. If applicable, a purging of the one or more print heads  103  of the printing device  100  following the printing pause may also be avoided via a time-reduced interruption of the printing operation, whereby the ink consumption may be reduced and the productivity of the printing device  100  may be further increased. Furthermore, manual interventions by a user of the printing device  100  may be avoided via the automatic insertion of a printing pause and via the automatic resumption of the printing operation, whereby the efficiency of the printing device  100  is further increased. 
     To enable those skilled in the art to better understand the solution of the present disclosure, the technical solution in the embodiments of the present disclosure is described clearly and completely below in conjunction with the drawings in the embodiments of the present disclosure. Obviously, the embodiments described are only some, not all, of the embodiments of the present disclosure. All other embodiments obtained by those skilled in the art on the basis of the embodiments in the present disclosure without any creative effort should fall within the scope of protection of the present disclosure. 
     It should be noted that the terms “first”, “second”, etc. in the description, claims and abovementioned drawings of the present disclosure are used to distinguish between similar objects, but not necessarily used to describe a specific order or sequence. It should be understood that data used in this way can be interchanged as appropriate so that the embodiments of the present disclosure described here can be implemented in an order other than those shown or described here. In addition, the terms “comprise” and “have” and any variants thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or equipment comprising a series of steps or modules or units is not necessarily limited to those steps or modules or units which are clearly listed, but may comprise other steps or modules or units which are not clearly listed or are intrinsic to such processes, methods, products or equipment. 
     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 “processing circuitry” shall be understood to be circuit(s) or processor(s), or a combination thereof. A circuit includes an analog circuit, a digital circuit, data processing circuit, other structural electronic hardware, or a combination thereof. A processor includes a microprocessor, a digital signal processor (DSP), central processor (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 (printer) 
               101  controller 
               102  print bar 
               103  print head 
               110  sensor 
               131 ,  132  spatial distance 
               120  recording medium 
               122  processing circuitry 
               124  interface (input/output) 
               141 ,  142  printing unit 
               150  regeneration unit (regenerator) 
               160  turning unit (turner) 
               210  elevation (recording medium) 
               301  control signal for the first printing unit 
               302  control signal for the second printing unit 
               303  printing pause signal 
               304  transport velocity 
               311 - 315  points in time 
               331 ,  332  time interval 
               333  duration of the printing pause 
               400  method for operating a printing device given a detected recording medium elevation 
               401 - 405  method operations