Patent Publication Number: US-2021187951-A1

Title: Spittoon cartridge for a printing device

Description:
BACKGROUND 
     Printing devices like ink-jet printers may have to be cleaned regularly to maintain image quality and e.g. prevent partial or complete clogging of print head nozzles. To this end, printing devices can comprise a maintenance subsystem to perform cleaning operations on a print head of the printing device. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       In the following, a detailed description of various examples is given with reference to the figures. The figures show schematic illustrations of 
         FIG. 1 a   : a spittoon cartridge in accordance with an example in side view; 
         FIG. 1 b   : the spittoon cartridge of  FIG. 1 a    in top view; 
         FIG. 2 : a spittoon cartridge with a floater that is to mechanically block a spit roller according to an example in side view; 
         FIG. 3 : a spittoon cartridge with a floater that is to mechanically block a gear drive in accordance with an example in a perspective view; 
         FIG. 4 : the floater of the spittoon cartridge of  FIG. 3  in a perspective view; 
         FIG. 5 a   : the floater and the gear drive of the spittoon cartridge of  FIG. 3  in a disengaged state; 
         FIG. 5 b   : the floater and the gear drive of the spittoon cartridge of  FIG. 3  in an engaged state; 
         FIG. 6 : a printing device with a spittoon cartridge in accordance with an example in top view; and 
         FIG. 7 : a flow chart for an example of a method of controlling a spittoon cartridge. 
     
    
    
     DETAILED DESCRIPTION 
     To clean a print head, a printing device can comprise a spittoon cartridge, into which material can be ejected from the print head nozzles, e.g. to remove material from the nozzles to prevent clogging. The spittoon cartridge can comprise a waste tank to store the ejected material. Over time, the waste tank can fill up and the material may spill, contaminating other parts of the printing device. To prevent this, the filling level of the waste tank can be monitored by estimating the amount of material in the waste tank, e.g. by recording the number of ejection processes or determining the number of drops ejected into the spittoon cartridge. The resulting estimates, however, have a large uncertainty, in particular due to unknown evaporation rates during the ejection and from the waste tank. 
       FIGS. 1 a  and 1 b    depict an example of a spittoon cartridge  100  in side view and top view, respectively. The spittoon cartridge  100  may for example be employed in a printing device (not shown in  FIG. 1 a   ) as detailed below with reference to  FIG. 6 . A longitudinal direction of the spittoon cartridge  100  is denoted as the X direction in the following, which may e.g. be aligned with a media advance direction in the printing device. A transverse direction of the spittoon cartridge  100  is denoted as the Y direction in the following, which may e.g. be aligned with a scanning direction of a print head of the printing device. The direction perpendicular to the X direction and the Y direction is denoted as the Z direction in the following, which may e.g. be a vertical direction in the printing device, i.e. aligned with the direction of gravity. 
     The spittoon cartridge  100  comprises a waste tank  102  to store material  104  ejected from a print head. The waste tank  102  may for example have a volume between 5 cm 3  and 1000 cm 3  or more and may have an opening, e.g. in a top wall or an upper portion of a side wall, to receive the material  104 . The waste material  104  may e.g. comprise a printing fluid such as ink or 3D printing material. The spittoon cartridge  100  may further comprise a transfer unit  106  to transfer material ejected from the print head into the waste tank  102 . The transfer unit  106  can comprise movable parts and may e.g. comprise a conveyor belt or a rotatable spit roller as detailed below. The transfer unit  106  can for example be arranged above the waste tank  102  in the Z direction such that the print head may be positioned adjacent to the transfer unit  106  to minimize a spit distance between the print head and the transfer unit, e.g. to avoid that aerosol which might be generated when ejecting material from the print head leaks out. The transfer unit  106  may e.g. be arranged adjacent to or in an opening in a top face or cover of the spittoon cartridge  100 . 
     The spittoon cartridge  100  also comprises a floater  108 , which is movably arranged in the spittoon cartridge  100 . The floater may for example comprise plastic, metal or a combination thereof. A position of the floater  108  depends on a filling level  110  of the waste tank  102 . The position of the floater  108  may e.g. be defined as the center of mass of the floater  108  or the position of a predefined point of the floater  108 , e.g. a geometric center of the floater  108  or a point on a side, bottom or top surface of the floater  108 . The filling level  110  may e.g. be an average height along the Z direction up to which the waste tank  102  is filled with the material  104 . In one example, a position of the floater  108  along the X direction depends on the filling level  110 , e.g. such that the floater  108  moves to the right along the X direction when the filling level  110  increases as illustrated by the respective arrows m 1  and m 2  in  FIG. 1 a   . Additionally or alternatively, a position of the floater  108  along the Y direction or the Z direction may depend on the filling level  110 . In the example shown in  FIG. 1 a   , the floater  108  is arranged in a cavity  102 A extending outwards from a main body of the waste tank  102  along the X direction. The cavity  102 A may be filled at least partially with the material  104 . An increase in the filling level  110  may lead to an increase of the pressure in the material  104  in the cavity  102  A and may thus press the floater  108  outwards along the X direction, e.g. against a flexible element  112  like a spring. In one example, the floater  108  may extend to the outside of the spittoon cartridge  100  at least partially, e.g. such that a change in the position of the floater  108  is visible or can be detected from the outside. 
     The floater  108  is to impede transfer of material by the transfer unit  106  if the floater  108  reaches a predefined warning position. The floater  108  may further prevent transfer of material by the transfer unit  106  if the floater reaches  108  a predefined threshold position. The predefined threshold position can for example be a position of the floater  108  that corresponds to a threshold filling level  114  of the waste tank  102 . The threshold filling level  114  may e.g. be a filling level of the waste tank  102  below which there is no risk of spilling material from the waste tank  102  under normal or close to normal operating conditions. The predefined warning level may for example be the position of the floater  108  corresponding to a warning filling level of the waste tank  102 , e.g. to indicate that the spittoon cartridge may have to be replaced or emptied soon. The warning filling level may be lower than the threshold filling level  114 , for example a certain fraction of the threshold filling, e.g. 90% of the threshold filling level  114 . Preventing transfer of material by the transfer unit  106  refers to preventing operation of the transfer unit  106  such that there is no active transfer of material into the waste tank  102  by the transfer unit  106 . In some examples, there may still be passive transfer of material, e.g. printing fluid ejected onto the transfer unit  106  that passes into the waste tank  102  by itself without operation of the transfer unit  106 . 
     The transfer unit  106  may be coupled to an actuator  116 , e.g. an electric motor, to move moveable parts of the transfer unit  106 . The floater  108  reaching the predefined warning position may for example impede transfer of material by the transfer unit  106  by changing an electric drive signal for the actuator  116  or by triggering a warning signal for the actuator  116  if the floater  108  reaches the predefined warning position, e.g. by opening or closing an electric circuit. Accordingly, the floater  108  reaching the predefined threshold position may for example prevent transfer of material by the transfer unit  106  by interrupting an electric drive signal for the actuator  116  or by triggering an interrupt signal for the actuator  116  if the floater  108  reaches the predefined threshold position, e.g. by opening or closing an electric circuit. The spittoon cartridge  100  may also comprise a sensor  118  to detect whether the floater  108  has reached the predefined warning or threshold position, e.g. a contact sensor or a proximity sensor like a capacitive sensor, a magnetic field sensor or a photoelectric sensor. The sensor  118  may e.g. change or interrupt the electric drive signal for the actuator  116  or trigger the warning or interrupt signal for the actuator  116 . 
     In other examples, the floater  108  may mechanically engage an element of the transfer unit  106  or of the actuator  116  or a coupling element coupling the transfer unit  106  to the actuator  116 , e.g. a gear drive or drive belt, to impede or prevent transfer of material by the transfer unit  106 . The floater  108  can for example impede the transfer of material by the transfer unit  106  by increasing a load of the actuator  116 , e.g. by generating a friction force. The floater  108  may e.g. mechanically impede or block the movement of the respective element as detailed below with reference to  FIGS. 2, 3, 4   a  and  4   b . In this example, the floater  108  reaching the predefined warning or threshold position and impeding or preventing transfer of material by the transfer unit  106  may be based entirely on mechanical interaction. 
       FIG. 2  illustrates another example of a spittoon cartridge  200  in side view. Similar to the spittoon cartridge  100 , the spittoon cartridge  200  also comprises a waste tank  102  to store material  104 , a transfer unit  106  to transfer material into the waste tank  102  and a floater  108 . The transfer unit  106  comprises a spit roller  202 . The spit roller  202  may for example be a rotatably mounted rod or cylinder and may be coupled to an actuator to rotate the spit roller  202 . The spit roller  202  may e.g. be arranged in an opening in a top face or cover of the spittoon cartridge  200  to receive material ejected from a print head placed adjacent to the spit roller  202 . By rotating the spit roller  202 , material ejected onto the spit roller  202  may be transferred to the waste tank  102 , which may e.g. be arranged underneath the spit roller  202 . 
     In the spittoon cartridge  200 , the floater  108  is movably arranged in the waste tank  102  to float on the material  104  contained in the waste tank. The floater  108  may e.g. comprise a material with a lower density than the material  104  or may comprise a recess or a cavity such that an average density of the floater  108  is lower than the density of the material  104 . The floater  108  is to mechanically impede or block the rotation of the spit roller  202  if the floater reaches a predefined warning or threshold level corresponding to a predefined warning or threshold position. 
     The floater  108  may for example comprise a blocking element  204 , e.g. a protrusion or an arm, that enters a gap  206  between the spit roller  202  and a wall of the waste tank  102  or spittoon cartridge  200  as the filling level of the waste tank  102  increases as illustrated by the respective arrows m 1  and m 2  in  FIG. 2 . The blocking element  204  may come in contact with the spit roller  202  when the floater  108  reaches the predefined warning level. This may lead to an increased friction that impedes the rotation of the spit roller  202  without completely blocking the rotation. The friction may increase gradually as the floater  108  approaches the predefined threshold level and may e.g. exceed a driving force generated by an actuator when the floater  108  reaches the predefined threshold level, thereby blocking the rotation of the spit roller  202 . A shape of the blocking element  204  may be adapted to a shape of the gap  206  such that blocking element  204  mechanically blocks the rotation of the spit roller  202  if the floater reaches the predefined threshold level, e.g. by coming in contact with both the spit roller  202  and the wall. To ensure that the blocking element  204  is aligned with the opening  206 , the movement of the floater  108  may be constrained along the X direction, e.g. using a guiding groove in a side wall of the waste tank  102 . 
     In  FIG. 3 , another example of a spittoon cartridge  300  is shown in a perspective view. The spittoon cartridge  300  comprises a waste tank  102  to store material  104  (not shown in  FIG. 3 ), a transfer unit  106  having a spit roller  202  and a floater  108 . The spittoon cartridge  300  further comprises an actuator  116 , which is coupled to the transfer unit  106  via a gear drive  302 , wherein the gear drive  302  may comprise a plurality of cog wheels. 
       FIG. 4  shows a perspective view of the floater  108  of the spittoon cartridge  300  according to an example. The floater  108  comprises a main body  304 , which is movably arranged in the waste tank  102  to float on the material  104  contained in the waste tank  102 . The main body  304  may e.g. have a cuboid or approximately cuboid shape. The main body  304  may e.g. comprise a material with a lower density than the material  104  or may comprise a cavity or a recess  306  such that an average density of the floater  108  is lower than the density of the material  104 . The floater  108  further comprises an arm having a front portion  308 , a center portion  310  and an end portion  312 , wherein the front portion  308  is connected to the main body  308 . The arm may be attached to the main body  304  or may be integrally formed with the main body  304 . The front portion  308  may for example have a rectangular or approximately rectangular shape and may e.g. be an extension of a top face of the main body  304 . 
     The center portion  310  of the arm is pivotally connected to a bearing point  314  of the spittoon cartridge such that the floater  108  can pivot or rotate around a rotation axis through the bearing point  314 . The center portion  310  may e.g. have a cylindrical shape extending along a direction perpendicular or approximately perpendicular to the vector connecting the center portion  310  to the main body  304 . A longitudinal axis of the center portion  310  may e.g. be the rotation axis of the floater  108 . The bearing point  314  may for example be a groove or recess on top of a side wall of the waste tank  102 , in which the center portion is arranged. In another example, the bearing point  314  may be a hole or cut-out in a side wall of the waste tank  102 , which encloses the center portion  310  as illustrated in  FIG. 3 . 
     The end portion  312  of the arm is arranged such that the end portion  312  mechanically impedes the gear drive  302  coupled to the transfer unit  106  if the main body  304  reaches the predefined warning level. This is illustrated in  FIGS. 5 a  and 5 b    and explained in more detail below. The end portion  312  may further mechanically block the gear drive  302  if the main body  304  reaches the predefined threshold level. The end portion  312  may for example be a protrusion, e.g. a rectangular or approximately rectangular protrusion, extending from the center portion  310  in a direction away from the main body  304 , e.g. such that the front portion  308  and the end portion  312  enclose an angle between 90° and 270° as seen in side view. The end portion  312  may for example be arranged such that the end portion  312  and the main body  304  move in opposite or approximately opposite directions when the floater  108  rotates around the rotation axis through the bearing point  314 . In one example, the end portion  312  may be connected to a side part of the center portion  310  that is located on the other side of the bearing point  314  as a part of the center portion  310  connected to the front part  308 . 
       FIGS. 5 a  and 5 b    show a side view of the floater  108  and the gear drive  302  of the spittoon cartridge  300 .  FIG. 5 a    depicts a situation, in which the floater  108  has not reached the predefined warning level, e.g. because the filling level of the waste tank  102  is lower than a warning filling level.  FIG. 5 b    depicts a situation, in which the floater has reached the predefined warning level, e.g. because the filling level of the waste tank  102  is at or above the warning filling level. Since the main body  304  of the floater  108  in the spittoon cartridge  300  floats on the material  104  in the waste tank  102 , the position of the main body  304  along the Z direction rises with a rising filling level of the waste tank  102 . As the material  104  presses the main body  304  upwards, the floater  108  rotates around the rotation axis through the bearing point  314  as illustrated by the respective arrows m 2  and r 2  in  FIG. 5 b   . Accordingly, the end portion  312  is lowered and moves closer to the gear drive  302 . When the main body  304  reaches the predefined warning level, the end portion  312  mechanically engages the gear drive  302 , e.g. a cog wheel of the gear drive  302 , and impedes the gear drive  302 , e.g. by impeding the rotation of the cog wheel. Thereby, the transfer of material by the transfer unit  106  is impeded. When the main body  304  rises further and reaches the predefined threshold level, the end portion  312  may mechanically block the gear drive  302 , e.g. by preventing the cog wheel from rotating. Thereby, the transfer of material by the transfer unit  106  is prevented as the actuator  116  can no longer drive the transfer unit  106 . Blocking the gear drive  302  may block the actuator  116  as well. In some examples, the floater  108  may not rotate continuously, but may exhibit a discrete number of stable configurations or orientations, wherein each transition between configurations may require a certain torque, e.g. a certain buoyancy acting on the main body  304 , in order for the floater  108  to go from a given configuration to the next. The floater  108  may for example have two stable configurations, a disengaged state in which the floater  108  does not engage the gear drive  302  and an engaged state in which the floater  108  engages the gear drive  302 . The floater  108  may remain in the disengaged state until the torque generated by the buoyancy of the main body  304  in the waste material  104  exceeds a certain threshold when the filling level  110  reaches the warning filling level. At this point, the floater  108  may transition to the engaged state. 
     In other examples, the configuration may differ from the one shown in  FIGS. 5 a  and 5 b   . For example, the point at which the end portion  312  mechanically engages the gear drive  302  may be different. Alternatively, the end portion  312  may directly engage the actuator  116  or the spit roller  202 . The end portion  312  may comprise a rotary damper, wherein the rotary damper engages the gear drive  302 , the actuator  116  or the spit roller  202  to create an additional resistance. The rotary damper may for example comprise a rotatable cog wheel to engage the respective element and the cog wheel may be coupled to a static element through a layer of a viscous fluid that generates a brake force when the cog wheel rotates. In one example, the gear drive  302  may be arranged above the floater  108  and the floater  108  may comprise a blocking element  204 , e.g. arranged on the main body  304 , instead of the end portion  312 , wherein the blocking element  204  engages the gear drive  302  as the floater  108  rotates around the rotation axis. Alternatively, the floater  108  may be similar to the one shown in  FIG. 2  and may e.g. be arranged in a guiding groove in a side wall of the waste tank  102  to move along the Z direction instead of rotating around the bearing point  314 . In yet another example, the end portion  312  may be connected to a center part of the center portion  310  that is located on the same side of the bearing point  314  as a part of the center portion  310  connected to the front part  308 . Furthermore, a different coupling element between the actuator  116  and the spit roller  202  may be used, e.g. a drive belt, wherein the floater  108  engages the drive belt to mechanically block the drive belt. 
       FIG. 6  depicts a printing device  600  in accordance with an example in top view. The printing device  600  comprises a print head  602 , e.g. an ink-jet print head having a reservoir for a printing fluid such as ink and a nozzle plate for depositing the printing fluid on a print medium. The print head  602  can be movable along a print head path  604  in a scanning direction, which may e.g. be aligned with the Y direction and is illustrated by the arrow labeled “Y” in  FIG. 6 . The scanning direction may e.g. be perpendicular to a direction of movement of the print medium, also referred to as media advance direction. The media advance direction may be aligned with the X direction. In other examples, the printing device  600  may be a 3D printer and the print head  602  may be moveable in multiple directions. The printing device  600  may comprise an actuator for moving the print head  602  along the print head path  604 , for example an electric motor coupled to a carriage carrying the print head  602  via a drive belt or a gear drive such as a worm drive. 
     The printing device  600  comprises a spittoon cartridge  606 , which can e.g. be similar to one of the spittoon cartridges  100 ,  200  or  300  and comprises a waste tank  102 , a rotatable spit roller  202  and a floater  108 . The position of the floater  108  depends on a filling level of the waste tank  102  and the floater  108  impedes rotation of the spit roller  202  if the floater  108  reaches a predefined warning level or position, e.g. as described above with reference to  FIGS. 1, 2, 5   a  and  5   b . The floater  108  may further prevent rotation of the spit roller  202  if the floater  108  reaches a predefined threshold level or position. The spittoon cartridge  606  can be arranged in a maintenance zone of the printing device  600 , which may e.g. be adjacent to an end point of the print head path  604 . The spittoon cartridge  606  may be arranged such that a nozzle plate of the print heat  604  is located above the spit roller  202  of the spittoon cartridge  606  as seen in the direction of view in  FIG. 6  when the print head  602  is moved to the maintenance zone. In one example, the spittoon cartridge  606  may be at a fixed position in the printing device  600 , whereas in other examples, the spittoon cartridge  606  may be moveable within the printing device  600 . To move the spittoon cartridge  606 , the printing device  600  may further comprise an actuator, e.g. an electric motor coupled to the spittoon cartridge  606  via a drive belt or a gear drive such as a worm drive. In some examples, the spittoon cartridge  606  may be a subsystem of a maintenance cartridge that also comprises other subsystems for cleaning the print head  602 , e.g. a wiping subsystem for wiping the print head  602  and a capping subsystem for covering a nozzle plate of the print head  602 . 
     The printing device  600  further comprises a blockage detector  608  to detect if the rotation of the spit roller  202  is impeded. The blockage detector  608  may also detect if the rotation of the spit roller  202  is prevented. In one example, the blockage detector  608  may be connected to a sensor to detect if the rotation of the spit roller  202  is impeded or prevented, e.g. an inductive or magnetic sensor or a rotary encoder that detects how fast or whether the spit roller  202  rotates. The blockage detector  608  may for example determine a revolution speed of the spit roller  202  and compare the determined revolution speed to an expected revolution speed. Alternatively, the blockage detector  608  may be connected to a sensor, e.g. the sensor  118 , to detect whether the floater  108  has reached the predefined warning or threshold level and thus impedes or prevents the rotation of the spit roller  202 . 
     In the example shown in  FIG. 6 , the blockage detector  608  is connected to an actuator  116  that is coupled to the spit roller  202 , e.g. via the gear drive  302 , to monitor an electric signal of the actuator  116 , e.g. a motor current, a motor voltage or an electric sensor signal of a sensor in the actuator  116 , e.g. an inductive or magnetic sensor or an encoder. The blockage detector  608  may detect if the rotation of the spit roller  202  is impeded or prevented by detecting from the electric signal whether movement of the actuator  116  is impeded or blocked. The blockage detector  608  may e.g. detect a change of a load of the actuator  116  by monitoring the electric signal of the actuator. For example, the blockage detector  608  may detect that there is an unexpected rise in motor current or voltage or change in sensor or encoder signal which may be an indication of an impeded or blocked actuator. This may e.g. be the case when the floater  108  mechanically impedes or blocks the rotation of the spit roller  202  or the gear drive  302 . Alternatively, the blockage detector  608  may detect whether an electric drive signal for the actuator  116  is changed or interrupted or a warning or interrupt signal for the actuator  116  is triggered. The blockage detector  608  may further determine quantitatively how strongly the rotation of the spit roller  202  is impeded, e.g. by determining the load of the actuator  116  from the electric signal. 
     The blockage detector  608  may be part of a controller that controls the actuator  116 , e.g. by sending drive commands to the actuator  406  or by providing a suitable electric drive signal, e.g. a pulse-width modulated drive voltage. The actuator  116  may be part of the spittoon cartridge  606 , e.g. as in the spittoon cartridge  300 . In other examples, the actuator  116  may be outside of the spittoon cartridge  606 , e.g. attached to a chassis or frame of the printing device  600 , and may e.g. be coupled to the spit roller  202  or the gear drive  302  via a drive belt. The actuator  116  may also be used for moving the spittoon cartridge  606  or a maintenance cartridge comprising the spittoon cartridge  606 . 
     When the blockage detector  608  detects that the rotation of the spit roller  202  is impeded or blocked, the printing device  600  can enter an error state. The printing device  600  may remain in the error state as long as the rotation of the spit roller  202  is impeded or blocked, e.g. until the spittoon cartridge  606  has been replaced or emptied. In the error state, the printing device  600  may refrain from ejecting additional material into the spittoon cartridge  606 , e.g. to avoid spilling of material from the waste tank  102 . If the spittoon cartridge  606  is movable, the printing device  600  may move the spittoon cartridge  606  to a servicing position, e.g. a position, in which the spittoon cartridge  606  can be accessed by a user. The printing device  600  may further interrupt a current printing job, when the printing device  600  enters the error state, or may delay future printing jobs until the rotation of the spit roller  202  is no longer impeded or prevented, e.g. after the spittoon cartridge  606  has been replaced or emptied. In one example, the printing device  600  may comprise a second spittoon cartridge, e.g. adjacent to an opposing end of the print head path  604 . In the error state, the printing device  600  may eject material into the second spittoon cartridge instead of the spittoon cartridge  606 . 
     The printing device  600  may further generate an error signal if the printing device is in the error state. The error signal may e.g. comprise switching on an indicator light on the printing device  600 , e.g. a light-emitting diode with a corresponding label, displaying an error message on a display of the printing device  600 , generating an audio warning and/or sending an error message to a control device of the printing device  600 , e.g. a computer connected to the printing device  600 . 
       FIG. 7  shows a flow chart of a method  700  of controlling a spittoon cartridge according to an example. The method  700  may for example be performed with the printing device  600  and will be described in the following with reference to  FIG. 6 . This is, however, not intended to be limiting in any way. The method  700  may be executed with any suitable printing device or spittoon cartridge comprising a waste tank, a transfer unit and a floater, such as the spittoon cartridges  100 ,  200 , and  300 . The method  700  may for example be executed as part of a startup process or a cleaning routine of the printing device  600 . In one example, the method  700  may be executed each time material is ejected into the spittoon cartridge  606  or each time the filling level  110  of the waste tank  102  changes. 
     In  702 , a position of the floater  108  is adjusted to the filling level  110  of the waste tank  102 . The position of the floater  108  may for example be adjusted based on a predefined correspondence between the position of the floater  108  and the filling level  110 , i.e. the floater  108  may be moved to the position that is associated with the current filling level  110 . The position of the floater  108  may e.g. be the center of mass of the floater  108  or the position of a predefined point of the floater  108 , e.g. a geometric center of the floater  108  or a point on a bottom or top surface of the floater  108 . In one example, a position of the floater  108  along the X direction may be adjusted to the filling level  110 , e.g. as illustrated in  FIG. 1 a   . The position of the floater  108  may e.g. be adjusted such that the position along the X direction depends linearly on the filling level. Additionally or alternatively, a position of the floater  108  along the Y direction or the Z direction may be adjusted to the filling level  110 . For example, if the floater  108  is movably arranged in the waste tank  102  to float on the material  104  as for the spittoon cartridges  200  and  300 , the position of the floater  108  along the Z direction may be adjusted such that the position is equal to or approximately equal to the filling level. 
     The method  700  may further comprise determining, in  704 , whether the floater  108  has reached a predefined threshold level, i.e. whether the position of the floater  108  is equal to or exceeds the predefined threshold level. For this, a sensor like the sensor  118  may be used. In some examples, this may comprise determining the position of the floater  108 . 
     If the floater  108  has reached the predefined threshold level, the operation of the transfer unit  106  may be prevented in  706 , e.g. by preventing active transfer of material into the waste tank  102  by the transfer unit  106 . This may for example comprise mechanically blocking, e.g. with the floater  108 , the transfer unit  106 , a component thereof like the spit roller  202  or an element coupled to the transfer unit  106 , e.g. the gear drive  302 . In other examples, this may comprise generating an interrupt command or interrupt trigger signal for an actuator coupled to the transfer unit  106 , e.g. the actuator  116 , or interrupting an electric drive signal of the actuator. 
     The method  700  may further comprise determining, in  708 , whether the floater  108  has reached a predefined warning level, e.g. in case the floater  108  has not reached the predefined threshold level. The floater  108  has reached the predefined warning level when the position of the floater  108  is equal to or exceeds the predefined warning level. As in  704 , a sensor like the sensor  118  may be used for this and in some examples  708  may comprise determining the position of the floater  108  or using a position of the floater  108  determined previously, e.g. in  704 . 
     If the floater  108  has reached the predefined warning level, the operation of the transfer unit  106  is impeded in  706 , for example by increasing a load of an actuator coupled to the transfer unit  106 . For this, the floater  108  may be brought in contact with the transfer unit  106 , a component thereof like the spit roller  202  or an element coupled to the transfer unit  106 , e.g. the gear drive  302 , in order to generate a friction force. Alternatively, this may comprise generating a warning command or warning trigger signal for an actuator coupled to the transfer unit  106 , e.g. the actuator  116 , or changing an electric drive signal of the actuator. In one example, the load of the actuator may be increased gradually the further the position of the floater  108  exceeds the predefined warning level or the closer the position of the floater  108  is to the predefined threshold level. If the floater  108  has not reached the predefined warning level, the method  700  may proceed to  712 . 
     The method  700  may comprise, in  712 , detecting whether operation of the transfer unit  106  is impeded or prevented. As described above with reference to  FIG. 6 , this may comprise reading out an electric signal of an actuator coupled to the transfer unit  106 , e.g. the actuator  116 , wherein the electric signal may e.g. be a motor current, a motor voltage or an electric sensor signal of a sensor in the actuator  116 , e.g. an inductive or magnetic sensor or a rotary encoder. The electric signal may be used to detect whether operation of the transfer unit  106  is impeded or prevented, e.g. by detecting an increase, decrease or change in the shape of the electric signal that is associated with an increased load or a mechanical blockade of the actuator. In one example,  712  may comprise quantifying how strongly operation of the transfer unit  106  is impeded, e.g. by determining a load of the actuator  116 . In other examples,  712  may comprise determining whether a moveable element of the transfer unit  106 , e.g. the spit roller  202 , moves or whether the floater  108  has reached the predefined warning or threshold level. 
     If operation of the transfer unit  106  is impeded or prevented, the spittoon cartridge  606  may be moved to a servicing position in  706  and/or  710 , e.g. a position, in which the spittoon cartridge  606  can be accessed by a user.  706  and/or  710  may further comprise setting the printing device  600  to an error state and/or generating an error signal, e.g. as described above. 
     The method  700  may be executed and modified in various ways. As far as technically feasible, the method  700  may be performed in any order and different parts may be performed simultaneously at least in part. For example, the position of the floater  108  may be adjusted continuously in  702  throughout execution of the entire method  700 , e.g. by using a floater  108  that is movably arranged to float on the material  104  in the waste tank. Furthermore, impeding or preventing operation of the transfer unit  106  in  706  and  710 , respectively, may be performed simultaneously at least in part with the adjustment of the position of the floater  108  in  702 , e.g. with the spittoon cartridge  200  or  300 , for which an adjustment of the position of the floater  108  may cause the blocking element  204  or the end portion  312  of the arm of the floater  108  to mechanically engage the spit roller  202  and the gear drive  302 , respectively, thereby impeding or preventing operation of the transfer unit  106 . 
     This description is not intended to be exhaustive or limiting to any of the examples described above. The print head maintenance assembly, printing device and method disclosed herein can be implemented in various ways and with many modifications without altering the underlying basic properties.