Patent Document

CROSS REFERENCE TO RELATED APPLICATIONS 
     This is application is a continuation of commonly assigned patent application U.S. Ser. No. 09/906,486, filed Jul. 26, 2001, now abandoned entitled “A Continuous Ink-Jet Printing Apparatus With Integral Cleaning” in the name of David L. Jeanmaire. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to the field of ink jet printing devices, and in particular to a continuous ink jet printer in which a gas-flow type droplet deflector is used both to deflect non-printing droplets from printing droplets and to implement a printhead cleaning operation. 
     BACKGROUND OF THE INVENTION 
     Digitally controlled color ink jet printing capability is accomplished by one of two technologies referred to as “drop-on-demand” and “continuous stream,” respectively. Both require independent ink supplies for each of the colors of ink provided. Ink is fed through channels formed in the printhead. Each channel includes a nozzle from which droplets of ink are selectively extruded and deposited upon a medium. Typically, each technology requires separate ink delivery systems for each ink color used in printing. Ordinarily, the three primary subtractive colors, i.e. cyan, yellow and magenta, are used because these colors can produce, in general, up to several million perceived color combinations. 
     Drop-on-demand ink jet printing, provides ink droplets for impact upon a print medium using a pressurization actuator (thermal, piezoelectric, etc.). Selective activation of the actuator causes the formation and ejection of a flying ink droplet that crosses the space between the printhead and the print medium and strikes the print medium. The formation of printed images is achieved by controlling the individual formation of ink droplets, as is required to create the desired image. Typically, a slight negative pressure within each channel keeps the ink from inadvertently escaping through the nozzle, and also forms a slightly concave meniscus at the nozzle thus helping to keep the nozzle clean. Conventional drop-on-demand ink jet printers utilize a pressurization actuator to produce the ink jet droplet at orifices of a print head. Typically, one of two types of actuators are used including heat actuators and piezoelectric actuators. With heat actuators, a heater, placed at a convenient location, heats the ink. This causes a quantity of ink to phase change into a gaseous steam bubble that raises the internal ink pressure sufficiently for an ink droplet to be expelled. With piezoelectric actuators, an electric field is applied to a piezoelectric material possessing properties that create a mechanical stress in the material, thereby causing an ink droplet to be expelled. The most commonly produced piezoelectric materials are ceramics, such as lead zirconate titanate, barium titanate, lead titanate, and lead metaniobate. 
     By contrast, continuous stream ink jet printing, uses a pressurized ink source which produces a continuous stream of ink droplets. Electrostatic charging devices are placed close to the point where a filament of working fluid breaks into individual ink droplets. The ink droplets are electrically charged and then directed to an appropriate location by deflection electrodes having a large potential difference. When no print is desired, the ink droplets are deflected into an ink capturing mechanism (catcher, interceptor, gutter, etc.) and either recycled or discarded. When printing is desired, the ink droplets are not deflected and allowed to strike a print medium. Alternatively, deflected ink droplets may be allowed to strike the print medium, while non-deflected ink droplets are collected in the ink capturing mechanism. Continuous ink jet printing devices are faster than drop on demand devices and produce higher quality printed images and graphics. However, each color printed requires an individual droplet formation, deflection, and capturing system. 
     One of the problems associated with both types of ink jet technologies is that of printhead reliability. For continuous ink jet printers a common problem is initial stream instability that occurs when the printheads are turned on during start-up. Initial stream instability is often due to dynamics associated with surface wetting near the nozzles as well as any differential wetting that results from surface contamination. Initial aberrations of the ink stream may also originate from the presence of air bubbles in the printhead. Low ink pressures during the start-up and shut-down transitions is another common source of stream instability in the form of temporary jet misdirection. Prior art methods of coping with such instabilities require the use of a cap or nozzle that move over the printhead nozzles at shut-down and/or start-up time and effectively contain the ink streams and/or ink droplets emanating from the print head at start-up and/or shutdown time. 
     In addition to stream instabilities that occur during start-up and shut-down, ink jet printheads develop problems from ink which has dried around nozzles after a period of operation. A combination of dried ink, paper fibers and dust can result in partial or complete blocking of nozzle apertures. Periodic maintenance is normally performed to remove dried ink and these other contaminates from the nozzle plate and ink collecting structures. It is well known in the art to rinse the head with water and blow air across it to perform the maintenance operation. An exemplary technique for cleaning with fluids (including air) is given in U.S. Pat. No. 4,970,535 to Oswald et al. in 1990. This method includes enclosing the print head with a cavity having an inlet and an outlet such that a fluid is directed through the inlet and cavity at an angle that is substantially tangential to the nozzle aperture. Ink disposed around the nozzles is thusly carried away through the outlet. Other prior art techniques require the use of a wiping device for dried ink from the nozzles. For instance physical wipers, such as squeegees and cloth wipes are moved across or blotted against the face. 
     A final printhead reliability problem is caused by the storage of printheads between periods of use wherein ink dries out in and adjacent to the nozzles. One solution is to keep a moist or solvent rich environment proximate to the nozzles during storage. For example, U.S. Pat. No. 4,626,869 to Piatt in 1985 describes a system wherein the critical components of the printhead assembly are stored in a wet condition. 
     To provide for the maintenance operations necessary to prevent the aforementioned reliability problems, the printer may include a built-in start-up station, also called a home station, which is located at the side of the printhead. The printhead is moved over and into sealed relation with a chamber of the home station where various cleaning, drying and diagnostic operations are performed. While the procedures performed by such start-up stations are quite effective, the addition of such stations add considerable complexity and cost to the printing apparatus. 
     Clearly, there is a need for a mechanism that effectively provides the needed maintenance and cleaning operations on the printhead of an ink jet printer without the need for a dedicated start-up maintenance station. Ideally, such operations could be implemented by structures easily integrated into the printhead itself to simplify the printer structure and reduce printer fabrication costs. Finally, it would be desirable if at least some of the maintenance operations could be implemented or facilitated by preexisting structures within the printer that are normally used for other purposes to further lower printer construction costs. 
     SUMMARY OF THE INVENTION 
     A primary feature of the current invention is the shared use of air plenum structures in a droplet deflector to provide the integrated functions of startup cleaning, shut-down cleaning, maintenance and storage, in addition to the usual function of droplet separation. In this implementation, provision is made to either direct air or cleaning fluids over the surface of the print head. 
     To this end, the invention is an ink jet printing apparatus for printing an image that comprises an ink droplet forming mechanism including a printhead having at least one nozzle for ejecting a stream of ink droplets having a selected one of at least two different volumes; a droplet deflector for producing a flow of gas that separates ink droplets having different volumes from one another, and a cleaning station formed at least in part from the droplet deflector for providing a flow of fluid over the printhead to clean and maintain it. 
     The droplet deflector includes a pressurized gas source for producing a flow of gas and a plenum for conducting the gas flow across the stream of ink droplets to separate them from one another. Advantageously, the cleaning station is formed at least in part from the plenum and the gas source of the droplet deflector, and further includes a source of liquid cleaning fluid (which may be water) connected to the plenum via a valve. In operation, the valve may be opened to admit a flow of cleaning fluid over the printhead. Afterwards, the source of pressurized gas (which may be an air blower) may be actuated to dry excess cleaning fluid from the surface of the printhead. 
     The ink jet printing apparatus may further comprise an ink catcher for catching ink droplets not used to produce an image, and a recovery reservoir for collecting ink droplets caught by the catcher for recycling. Advantageously, the cleaning station may also be formed in part from the recovery reservoir, which serves the additional function of collecting used liquid cleaning fluid directed across the face of the printhead during a cleaning operation. Preferably, the liquid cleaning fluid used is the same type of solvent used as the basis of the ink forming the droplets so that the collection of used cleaning fluid will not interfere with the recycling of ink collected from the ink catcher. 
     Finally, the ink jet printing apparatus may comprise a parking mechanism linked to the printhead for withdrawing and extending it from a parking position to an operating position with respect to the droplet deflector and an imaging medium. During storage, the parking mechanism withdraws the printhead into a parking position where it may be stored for relatively long periods of non-use with a moistening sponge placed over the ink jet nozzles of the printhead. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features and advantages of the present invention will become apparent from the following description of the preferred embodiments of the invention and the accompanying drawings, wherein: 
         FIG. 1  is a schematic plan view of a printhead made in accordance with a preferred embodiment of the present invention; 
       FIGS.  2 ( a ) and  2 ( b ) show diagrams illustrating a frequency control of a heater used in the preferred embodiment of FIG.  1  and the resulting ink droplets; 
         FIG. 3  is a cross-sectional view of an ink jet printhead made in accordance with the preferred embodiment of the present invention; 
         FIG. 4  is a schematic representation of an ink jet printhead made in accordance with a another embodiment of the present invention; 
       FIGS.  5 ( a )- 5 ( c ) are schematic representations of electrical activation waveforms and ink drops produced from the waveforms; and 
         FIG. 6  is an alternative embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present description will be directed in particular to elements forming part of, or cooperating more directly with, apparatus in accordance with the present invention. It is to be understood that elements not specifically shown or described may take various forms well known to those skilled in the art. 
     Referring to  FIG. 1 , an ink droplet forming mechanism  10  of a preferred embodiment of the present invention is shown. Ink droplet forming mechanism  10  includes a printhead  20 , at least one ink supply  30 , and a controller  40 . Although ink droplet forming mechanism  10  is illustrated schematically and not to scale for the sake of clarity, one of ordinary skill in the art will be able to readily determine the specific size and interconnections of the elements of the preferred. 
     In a preferred embodiment of the present invention, printhead  20  is formed from a semiconductor material (silicon, etc.) using known semiconductor fabrication techniques (CMOS circuit fabrication techniques, micro-electro mechanical structure (MEMS) fabrication techniques, etc.). However, it is specifically contemplated and, therefore within the scope of this disclosure, that printhead  20  may be formed from any materials using any fabrication techniques conventionally known in the art. 
     Again referring to  FIG. 1 , at least one nozzle  25  is formed on printhead  20 . In an example presented here, nozzles  25  are 9 micrometers in diameter. Nozzle  25  is in fluid communication with ink supply  30  through ink passage  50  also formed in printhead  20 . It is specifically contemplated, therefore within the scope of this disclosure, that printhead  20  may incorporate additional ink supplies in the manner of  30  and corresponding nozzles  25  in order to provide color printing using three or more ink colors. Additionally, black and white or single color printing may be accomplished using a single ink supply  30  and nozzle(s)  25 . 
     Heater  60  is at least partially formed or positioned on printhead  20  around corresponding nozzle  25 . Although heater  60  may be disposed radially away from the edge of corresponding nozzle  25 , heater  60  is preferably disposed close to corresponding nozzle  25  in a concentric manner. In a preferred embodiment, heater  60  is formed in a substantially circular or ring shape and consists principally of an electric resistive heating element electrically connected to electrical contact pads  55  via conductors  45 . 
     Conductors  45  and electrical contact pads  55  may be at least partially formed or positioned on printhead  20  and provide an electrical connection between controller  40  and heater  60 . Alternatively, the electrical connection between controller  40  and heater  60  may be accomplished in any well-known manner. Additionally, controller  40  is typically a logic controller, programmable microprocessor, etc. operable to control many components (heater  60 , ink droplet forming mechanism  10 , etc.) in a desired manner. 
     Referring to FIG.  2 ( a ), a schematic example of the electrical activation waveform provided by controller  40  to heater  60  is shown. In general, a rapid pulsing of the heater  60  forms small ink droplets, while slower pulsing creates larger drops. In the example presented here, small ink droplets are to be used for marking the image receiver, while larger droplets are captured for ink recycling. 
     In a preferred implementation, multiple drops per nozzle per image pixel are created. In FIG.  2 ( a ), P is the time associated with the printing of an image pixel, and the subscript indicates the number of printing drops to be created during the pixel time. The schematic illustration in (b) shows the drops that are created as a result of the application of waveform (a). A maximum of two small printing drops is shown for simplicity of illustration, however, it must be understood that the reservation of more time for a larger count of printing drops is clearly within the scope of this invention. In the drop formation for each image pixel, a non-printing large drop  95 ,  105 , or  110  is always created, in addition to a variable number of small, printing drops. The waveform of activation of heater  60  for every image pixel begins with electrical pulse time  65 , typically from 0.1 to 10 microseconds in duration, and more preferentially 0.5 to 1.5 microseconds. The further (optional) activation of heater  60 , after delay time  83 , with an electrical pulse  70  is conducted in accordance with image data wherein at least one printing drop  100  is required as shown for interval P 1 . For cases where the image data requires that still another printing drop be created as in interval P 2 , heater  60  is again activated after delay  83 , with a pulse  75 . Heater activation electrical pulse times  65 ,  70 , and  75  are substantially similar, as are all delay times  83 . Delay time  83  is typically 1 to 100 microseconds, and more preferentially, from 3 to 6 microseconds. Delay times  80 ,  85 , and  90  are the remaining times after pulsing is over in a pixel time interval P and the start of the next image pixel. All small, printing drops  100  are the same volume, however the volume of the larger, non-printing drops  95 ,  105 , and  110  varies depending on the number of small drops  100  created in the pixel time interval P; the creation of small drops takes mass away from the large drop during the pixel time interval P. The delay time  90  is chosen to be significantly larger than the delay time  83 , so that the volume ratio of large non-printing-drops  110  to small printing-drops  100  is preferentially a factor of 4 or greater 
     Referring to  FIG. 3 , the operation of printhead  20  in a manner such as to provide an image-wise modulation of drop volumes, as described above, is coupled with an gas-flow discrimination means which separates droplets into printing or non-printing paths according to drop volume. Ink is ejected through nozzle  25  in printhead  20 , creating a filament of working fluid  120  moving substantially perpendicular to printhead  20  along axis X. The physical region over which the filament of working fluid is intact is designated as r 1 . Heater  60  is selectively activated at various frequencies according to image data, causing filament of working fluid  120  to break up into a stream of individual ink droplets. Coalescence of drops often occurs in forming non-printing drops  95 ,  105  and  110 . This region of jet break-up and drop coalescence is designated as r 2 . Following region r 2 , drop formation is complete in region r 3  and small, printing drops and large, non-printing drops are spatially separated. Beyond this region in r 4 , aerodynamic effects can cause merging of adjacent small and large drops, with concomitant loss of imaging information. A discrimination force  130  is provided by a gas flow perpendicular to axis X. The force  130  acts over distance L, which is less than or equal to distance r 3 . Large, non-printing drops  95 ,  105 , and  110  have greater masses and more momentum than small volume drops  100 . As gas force  130  interacts with the stream of ink droplets, the individual ink droplets separate depending on individual volume and mass. Accordingly, the gas flow rate can be adjusted to sufficient differentiation D in the small droplet path S from the large droplet path K, permitting small drops  100  to strike print media W while large, non-printing drops  95 ,  105 , and  110  are captured by a ink guttering structure described in the apparatus below. 
     Referring to  FIGS. 3 and 4 , a printhead  20  used in a preferred implementation of the current invention is shown schematically along with associated fluidic connections. Large volume ink drops  95 ,  105  and  110  and small volume ink drops  100  are formed from ink ejected from printhead  20  substantially along ejection paths X a stream. A droplet deflector  315  contains upper plenum  345  and lower plenum  335  which facilitate a laminar flow of gas in droplet deflector  315 . Pressurized air from blower  150  enters lower plenum  335  which is disposed opposite plenum  345  and promotes laminar gas flow while protecting the droplet stream moving along path X from external air disturbances. In the center of droplet deflector  315  is positioned proximate path X. The application of force  130  due to gas flow separates the ink droplets into small-drop path S and large-drop paths K. 
     An ink collection structure  325 , disposed adjacent to plenum  335  near path X, intercepts path K of large drops  95 ,  105 , and  110 , while allowing small ink drops  100  traveling along small droplet paths S to continue on to a recording media. Large, non-printing ink drops  95 ,  105 , and  110  strike ink catcher  320  in ink collection structure  325 . Ink recovery conduit  327  returns ink to recovery reservoir  180  through normally-open valve  200 . Negative pressure in conduit  327 , communicated from blower  150  through line  340  and normally-open value  195 , facilitates the motion of recovered ink to the recovery reservoir  180 . The pressure reduction in conduit  327  is sufficient to draw in recovered ink, however it is not large enough to cause significant air flow to substantially alter drop paths S. 
     A small portion of the gas flowing through upper plenum  345  is re-directed by plenum  330  to the entrance of ink collection structure  325 . The positive gas pressure in supply plenum  165  is controlled by pressure regulator  170 , wherein excess pressure is released to the external environment. In a complementary way, the negative gas pressure in plenum  160  is controlled by regulator  155 . Regulators  170  and  155  are adjusted so that the gas pressure in the print head assembly near ink catcher  320  is positive with respect to the ambient air pressure external to the printhead assembly. Environmental dust and paper fibers are thusly discouraged from approaching and adhering to ink catcher  320  and are additionally excluded from entering ink recovery conduit  327 . 
     “O” ring seals  202  and spill channel  310  provide a means to capture and recycle ink that comes from mis-directed nozzles in printhead  20  which fail to properly enter droplet deflector  315 . 
     During all times when not printing (jets not running), the print assembly is translated to a parking position where a non-porous elastomeric pad (not shown) is pressed over the exit port of the print assembly near ink catcher  320 . This pad provides a fluidic seal to keep any ink or cleaning solvents from leaking out of the printhead assembly. 
     Prior to initiation of the start-up sequence, the printhead assembly is in the “parked” position, and the exit port is sealed. The printhead is stored in a wet state, to be discussed in more detail later. Valves  185 ,  195 , and  200  are closed so that channel  310  and plenum  335 , and conduit  327  contain a cleaning/storage solvent. At startup, valves  185 ,  195 , and  200  open, allowing fluid from channel  310 , plenum  335  and conduit  327  to drain into recovery reservoir  180 . Valve  190  closes and blower  150  reverses direction, so that the pressure in plenum  160  is greater than in plenum  165 . Since pressure regulators  170  and  155  do not open under reverse-pressure conditions, the air flow rate near the printhead, in droplet deflector  315  is substantially higher than during printing conditions, thus facilitating the removal of cleaning solvent from the surface of printhead  20 . The toggling of valve  300  sends pressurized air from plenum  160  alternately into plenum  345  and conduit  305 . With the air flowing in this manner, the ink supply pressure to printhead  20  is gradually increased, and jetting begins. The air flow assists in stabilizing the jets. 
     In order to prepare for printing, blower  150  is operated in the mode first described, where the pressure in plenum  165  is greater than in plenum  160 . Valve  300  moves to the position that allows plenum  345  to communicate with plenum  160 . The printhead assembly is then moved from the “park” to a printing location, facing the receiver media and normal printing activity resumes. 
     Periodically, a maintenance cycle is carried out by again returning to the “park” position and sealing the head assembly exit port. Three-way valve  205  and valve  300  are moved to positions which allow solenoid pump  303  to communicate with channel  305 . A cleaning solvent (e.g. water) is drawn from reservoir  350  by pump  303  and caused to flow across the printhead  20  surface. Dried ink is removed and is carried through channel  310  into recycling reservoir  180 . Following this flushing of the printhead, valve  205  is moved so that plenum  345  again communicates with plenum  160 . Blower  150  is operated in reverse mode as previously described for blowing air across the printhead as in start-up conditions. 
     For printhead storage, the printhead assembly is moved to the “park” position where the head assembly exit port is sealed. Ink pressure to the printhead is removed causing jetting to cease and blower  150  is turned off. Valves  185 ,  195  and  200  are closed. Valves  205  and  300  are moved to a position which allows solvent pump  303  to communicate with channel  305 . Solvent from tank  350  is allowed to flow and accumulates in channel  310 , plenum  165 , and conduit  327 , submersing the nozzles in printhead  20  until level F is reached. 
     In an alternate implementation of the current invention the principle of the printing operation is reversed, where the larger droplets are used for printing, and the smaller drops recycled. An example of this mode is presented here. In this example, only one printing drop is provided for per image pixel, thus there are two states of heater  60  actuation, printing or non-printing. The electrical waveform of heater  60  actuation for the printing case is presented schematically as FIG.  5 ( a ). The individual large ink drops  95  resulting from the jetting of ink from nozzles  25 , in combination with this heater actuation, are also shown schematically in FIG.  5 ( a ). Heater  60  activation time  65  is typically 0.1 to 5 microseconds in duration, and in this example is 1.0 microsecond. The delay time  80  between heater  60  actuations is 42 microseconds. The electrical waveform of heater  60  activation for the non-printing case is given schematically as FIG.  5 ( b ). Electrical pulse  65  is 1.0 microsecond in duration, and the time delay  83  between activation pulses is 6.0 microseconds. The small drops  100 , as diagrammed in FIG.  5 ( b ), are the result of the activation of heater  60  with this non-printing waveform. 
     FIG.  5 ( c ) is a schematic representation of the electrical waveform of heater  60  activation for mixed image data where a transition is shown for the non-printing state, to the printing state, and back to the non-printing state. Schematic representation of the resultant droplet stream formed is also shown in FIG.  5 ( c ). It is apparent that heater  60  activation may be controlled independently based on the ink color required and ejected through corresponding nozzles  25 , movement of printhead  20  relative to a print media W, and an image to be printed 
     Referring to  FIG. 6 , an alternative embodiment of the present invention is shown schematically with like elements being described using like reference signs. Large volume ink drops  95  and small volume ink drops  100  are formed from ink ejected from printhead  20  substantially along ejection paths X a stream. A droplet deflector  315  contains upper plenum  345  and lower plenum  335  which facilitate a laminar flow of gas in droplet deflector  315 . Pressurized air from blower  150  enters upper plenum  160  which communicates with plenum  345 . Plenum  345  is disposed opposite plenum  335  and promotes laminar gas flow while protecting the droplet stream moving along path X from external air disturbances. In the center of droplet deflector  315  is positioned proximate path X. The application of force  130  due to gas flow separates the ink droplets into small-drop path S and large-drop paths K. 
     Plenum  335 , near path X, serves as a droplet collector as well as an air flow director for droplet deflector  315 . One wall of plenum  335  intercepts path S of small drops  100 , while allowing large ink drops  95  traveling along large droplet path K to continue on to a recording media. Plenum  335  communicates with ink recovery reservoir  180  through normally-open valve  365 . Negative pressure in plenum  335 , communicated from blower  150  through line  165  and ink recovery reservoir  180 , facilitates the motion of recovered ink to the recovery reservoir  180 . The pressure reduction in conduit  327  is sufficient to draw in recovered ink, however it is not large enough to cause significant air flow to substantially alter drop path K. 
     Bleed port and filter  360  allow some external air to be drawn into ink recovery reservoir  180 . This action causes the air pressure near the droplet path K to be slightly positive with respect to the atmosphere external to the printhead assembly. Environmental dust and paper fibers are thusly discouraged from approaching and adhering to the walls of plenum  335 . 
     Spill channel  310  provides a means to capture and recycle ink that comes from mis-directed nozzles in printhead  20  which fail to properly enter droplet deflector  315 . 
     In operation, a recording media W is transported in a direction transverse to axis X by print drum  400  in a known manner. Transport of recording media W is coordinated with movement of print mechanism  10 . This can be accomplished using controller  40  in a known manner. Recording media W may be selected from a wide variety of materials including paper, vinyl, cloth, other fibrous materials, etc. 
     During all times when not printing (jets not running), the print assembly is translated to a parking position where a non-porous elastomeric pad (not shown) is pressed over the exit port of the print assembly near ink path K. This pad provides a fluidic seal to keep any ink or cleaning solvents from leaking out of the printhead assembly. 
     Prior to initiation of the start-up sequence, the printhead assembly is in the “parked” position, and the exit port is sealed. The printhead is stored in a wet state, as in the previous example of FIG.  4 . Valve  365  is closed so that channel  310  and plenum  335  contain a cleaning/storage solvent. At startup, valve  365  opens, allowing fluid from channel  310  and plenum  335  to drain into recovery reservoir  180 . Blower  150  is capable of two-speed operation, and the higher speed is selected, so that the air flow rate near the printhead, in droplet deflector  315  is substantially higher than during printing conditions, thus facilitating the removal of cleaning solvent from the surface of printhead  20 . With the air flowing in this manner, the ink supply pressure to printhead  20  is gradually increased, and jetting begins. 
     In order to prepare for printing, blower  150  is operated in the slower-speed mode. The printhead assembly is then moved from the “park” to a printing location, facing the receiver media and is prepared for normal printing operation. 
     A maintenance cycle is carried out by returning to the “park” position and sealing the head assembly exit port. Pump  303  draws in external air through filter  353  and pressurizes the cleaning fluid in reservoir  350 . Valve  205  opens which allows a cleaning solvent in reservoir  350  to flow into channel  305 . Fluid is directed across the surface of printhead  20  and dried ink is removed and is carried through channel  310  into recycling reservoir  180 . In addition, a portion of the cleaning fluid is directed into plenum  345  and removes dried ink from the walls of lower plenum  335 . Following this flushing of the printhead, valve  205  is closed and valve  203  is opened. Compressed air from pump  303  enters channel  305  and blows excess fluid off the surface of printhead  20 . Air flow from blower  150  aids in drying plenum  345  and plenum  335 . 
     For printhead storage, the printhead assembly is moved to the “park” position where the head assembly exit port is sealed. Ink pressure to the printhead is removed causing jetting to cease and blower  150  is turned off. Valve  365  is closed. Valve  205  is opened allowing solvent from tank  350  to flow and accumulate in channel  310  and in plenum  335 , submersing the nozzles in printhead  20  until level F is reached. 
     While the foregoing description includes many details and specificities, it is to be understood that these have been included for purposes of explanation only, and are not to be interpreted as limitations of the present invention. Many modifications to the embodiments described above can be made without departing from the scope of the invention, as is intended to be encompassed by the following claims and their legal equivalents. 
     Parts List 
     
         
         
           
               10  ink droplet forming mechanism 
               20  printhead 
               25  small nozzle 
               30  ink supply 
               35  large nozzle 
               40  controller 
               45  electrical connection 
               50  ink passage 
               55  electrical contact pad 
               60  heater 
               65  electrical pulse time 
               70  electrical pulse time 
               75  electrical pulse time 
               80  delay time 
               85  delay time 
               90  delay time 
               95  large drop 
               100  small drop 
               105  large drop 
               110  large drop 
               120  working fluid 
               130  force 
               150  blower 
               155  negative pressure regulator 
               160  plenum 
               165  plenum 
               170  positive pressure regulator 
               180  ink recovery reservoir 
               185  valve 
               190  valve 
               195  valve 
               200  valve 
               202  “O” ring seal 
               203  valve 
               205  valve 
               300  valve 
               303  pump 
               305  upper channel 
               310  spill channel 
               315  droplet deflector 
               320  ink catcher 
               325  ink catcher structure 
               327  ink recovery conduit 
               330  plenum 
               335  plenum 
               340  air line 
               345  plenum 
               350  cleaning solvent reservoir 
               355  air filter 
               360  air filter 
               400  print drum ink re
           W print media   F fill level   L interaction distance   D separation distance   X ejection path   S small droplet path   K large droplet path

Technology Category: b