Abstract:
Both a cleaning fluid jet apparatus and method for cleaning an array of inkjet nozzles in a printhead is provided. The fluid jet apparatus includes a cleaning head having an array of cleaning nozzles registrable with the array of inkjet nozzles in the printhead, and a mounting assembly that mounts the cleaning head in opposition to the printhead with the cleaning nozzles in substantial alignment with the inkjet nozzles. A supply of pressurized cleaning fluid is connected to the cleaning nozzles such that the cleaning nozzles discharge a stream of high velocity cleaning droplets that impinges the inkjet nozzles. Both a droplet sizing mechanism and a droplet speed controller are provided so that the size, frequency, and velocity of the cleaning droplets may be selected for maximum cleaning efficiency. The apparatus also includes a mechanism for changing a location of cleaning droplet impingement so that both the inkjet nozzles and the areas immediately surrounding the nozzles may be effectively cleaned.

Description:
BACKGROUND OF THE INVENTION 
     This invention generally relates to devices and methods for cleaning the inkjet nozzles of an inkjet printhead, and is specifically concerned with a fluid jet device that cleans such inkjet nozzles by means of a stream of small, high velocity fluid droplets discharged from a cleaning head mounted in opposition to the printhead. 
     Devices for cleaning the nozzles of either drop-on-demand or continuous inkjet nozzles in a printhead are known in the prior art. Such devices are necessary, as dried ink deposits and other debris tend to accumulate around the orifices of the inkjet nozzles over time. Such deposits and debris may ultimately interfere with the ability of the printhead to achieve high resolution printing by either deflecting the intended trajectory of the ink droplets discharged from the nozzles, or, in extreme cases, blocking the orifices of the nozzles altogether. 
     In many of these prior art devices, a printhead wiper cleans the nozzle surfaces via a mechanical wiping action. Cleaning solvent is applied either to the wiper itself, or onto the surface of the printhead prior to the wiping operation. In another type of prior art cleaning device, cleaning solution is either oscillated or discharged directly through the nozzles of the inkjet printhead itself. In some prior art devices, the printing ink itself is used as a cleaning solvent prior to the initiation of a printing operation to simplify the cleaning operation. 
     While mechanical wiping techniques are effective in the removal of contaminants, they also reduce the lifetime of the printhead due to mechanical wear. They are further time consuming and consequently reduce printer productivity. Even in prior art devices where the cleaning fluid is applied without direct mechanical contact to the printhead (as, for example, via a spray nozzle), such application alone is not effective in dislodging and removing the deposits and debris around the inkjet nozzles, and the use of a mechanical wiper is necessary to complete the cleaning operation. Moreover, in all such prior art cleaning devices, no attempt is made to restrict the application of the cleaning fluid to the bore of the nozzles. Consequently, the entire printhead surface (and possibly other portions of the printer) are completely covered with a cleaning solution, which is not only unnecessary and wasteful, but potentially damaging to fragile and sensitive mechanical and electrical components on and around the printhead. 
     In prior art cleaning devices where the ink itself is the cleaning fluid and is either oscillated within the nozzle or ejected from it, optimal cleaning is not easily achieved due to the fact that neither an oscillatory or a continuously streaming fluid provides much dislodgment force on the contaminants and debris on the interior surfaces of the nozzle. In cases where a cleaning fluid other than ink is used, the cleaning fluid must be completely purged from the printhead and the printhead must be refilled with ink after the cleaning operation. In all cases where the cleaning fluid is ejected from the inkjet nozzles themselves, a large volume of cleaning fluid (whether ink or a special cleaning solution) is necessary. 
     Clearly, there is a need for a cleaning technique that avoids the mechanical wear associated with wiping techniques, and the waste and ineffectiveness associated with techniques which oscillate or eject cleaning fluids through the inkjet nozzles themselves. Ideally, such a technique would concentrate the cleaning action on or around the inkjet nozzles themselves in order to conserve cleaning fluid, and to eliminate contact between the cleaning fluid and fragile electronic and mechanical components located near the vicinity of the inkjet nozzles. Finally, such a technique should be adaptable to both drop-on-demand and continuous inkjet printers, and rapid in operation in order to minimize printing downtime. 
     SUMMARY OF THE INVENTION 
     Generally speaking, the invention is a fluid jet apparatus and method that cleans the inkjet nozzles of a printhead without the aforementioned shortcomings associated with the prior art. To this end, the fluid jet apparatus of the invention comprises a cleaning head having an array of cleaning nozzles registrable with the array of inkjet nozzles in the printhead, a mounting assembly that mounts the cleaning head in opposition to the printhead with the cleaning nozzles in substantial alignment with the inkjet nozzles, and a supply of pressurized fluid connected to the cleaning nozzles such that the cleaning nozzles discharge a stream of fluid droplets that impinge on the inkjet nozzles, wherein at least some of the droplets are about the same size as the orifices of the printhead nozzles. The fluid jet apparatus preferably includes a droplet sizing mechanism that controls the size of the cleaning droplets discharged by the cleaning nozzles. Such a droplet sizing mechanism may have a plurality of electrical resistance heaters adjacent to each of the cleaning nozzles for applying heat pulses at different frequencies to the stream of fluid discharged thereby to thermally “pinch” the stream into droplets of a desired size. 
     The fluid jet apparatus may further have a droplet speed controller that controls the velocity and frequency of solvent droplets discharged by the cleaning nozzle. The supply of pressurized fluid may include a fluid pump and the droplet speed controller may include a circuit for controlling the amount of pressure that the pump generates in fluid connected to the cleaning nozzles. 
     The fluid jet apparatus may also comprise a mechanism for changing a location of impingement of the cleaning droplets with respect to the inkjet nozzles of the printhead. Such a location mechanism may include a cleaning head moving assembly for oscillating the cleaning head relative to the printhead. In another embodiment of the invention, the locating changing mechanism may include a cleaning droplet deflector that deflects a path of cleaning droplets as they are discharged from the cleaning nozzles. Such a deflector may take the form of electrical resistance heaters positioned adjacent to each of the cleaning nozzles for asymmetrically applying heat pulses to the stream of cleaning droplets discharged by the cleaning nozzles. In another embodiment, the location changing mechanism may include a device for generating a fluid stream, such as a stream of air, that traverses the path of the cleaning droplets. The flow rate of the fluid stream varies over time to different areas of the nozzles in order to deflect the cleaning droplets. 
     The fluid jet apparatus also preferably includes a cleaning fluid reclamation system. Such a system may include a gutter for collecting liquid cleaning fluid that impinges and runs off of the inkjet nozzles of the printhead. The reclamation system may further include a pump for generating a negative pressure in the inkjet nozzles during a cleaning operation such that at least some of the cleaning droplets are sucked into the inkjet nozzles and directed back into a reclamation reservoir. 
     In operation, the fluid jet apparatus discharges discrete droplets of cleaning fluid of controlled size and high velocity in and around the orifices of the inkjet nozzles. At least some of the droplets are about the same size as the printhead nozzle orifices. The trajectory of the cleaning droplets may be varied during cleaning by oscillating the cleaning head, applying asymmetric thermal pulses or applying a time-varying fluid stream across the droplets so that droplets impinge on different areas of the printhead nozzles. The cleaning droplets may be discharged continuously during the cleaning operation, or on demand by conducting individual slugs of cleaning fluid to the cleaning head between pulses of compressed air to conserve cleaning fluid. In all cases, the resulting high velocity impingement of small individual cleaning droplets provides a highly effective cleaning action with a minimum amount of cleaning fluid that sharply focuses the cleaning action on the nozzle orifices themselves, and in areas immediately surrounding them, thereby preventing other potentially sensitive areas of the printhead from being unnecessarily exposed to the cleaning fluid. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A is a perspective view of the fluid jet device (shown in phantom) performing a cleaning operation on an inkjet printhead; 
     FIG. 1B is a side view of the cleaning head and inkjet printhead illustrated in FIG. 1A; 
     FIG. 1C is a cross-sectional plan view of the cleaning head and printhead illustrated in FIG. 1B along the line  1   c — 1   c;    
     FIG. 2A is a schematic plan view of the fluid jet device of the invention performing a cleaning operation on a printhead in a continuous cleaning droplet mode; 
     FIG. 2B is an alternative embodiment of the fluid jet device of the invention which, in contrast to the embodiment illustrated in FIG. 2A, is capable of a drop-on-demand type cleaning mode; 
     FIGS. 3A and 3B illustrate different types of orifice plates for inkjet printheads, while FIG. 3C is an orifice plate for the cleaning head of the invention having cleaning jets which are registrable with the inkjets of the printhead illustrated in FIG. 3B; 
     FIG. 4A is a plan, cross-sectional view of the orifice plate of the cleaning head performing a cleaning operation on the orifice plate of a printhead using cleaning droplets of uniform size which are slightly smaller than the nozzles of the printhead; 
     FIG. 4B is a plan, cross-sectional view of the orifice plates of the cleaning head and a printhead wherein the droplet sizing mechanism of the cleaning head generates cleaning droplets of which are both larger and smaller than the printhead nozzle orifices; 
     FIGS. 5A and 5B illustrate the cleaning effect on the orifice plate of the printhead of the different sized drops generated in FIG. 4B; 
     FIG. 6 is a plan, cross-sectional view of the orifice plates of the cleaning head and the printhead illustrating how the cleaning head may be oscillated or dithered during a cleaning operation so that the cleaning droplets impinge on different areas surrounding the nozzles of the inkjet printhead; 
     FIG. 7 illustrates an alternative mechanism for changing the location of impingement of the cleaning droplets relative to the nozzles of the printhead wherein thermal steering is used to change the trajectories of the cleaning droplets during the cleaning operation, and 
     FIG.  8  and FIG. 9 are photographs of an inkjet nozzle before and after the cleaning operation of the invention, respectively. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference now to FIGS. 1A,  1 B, and  1 C, wherein like components are designated by like reference numerals throughout all of the several Figures, the purpose of the fluid jet device  1  of the invention is to clean to inkjet nozzles  3  of inkjet printhead  5 . Each of these nozzles  3  includes an orifice  4  located in an orifice plate  7 . A circuit board  9  mounted adjacent to the orifice plate  7  generates electrical signals which serve either to size or deflect the ink droplets generated by the nozzles  4  or to actuate the individual generation of such ink drops, depending upon whether the printhead  5  is a continuous or drop-on-demand type printhead. Both the orifice plate  7  and circuit board  9  are mounted onto the rectangular housing  11  of the printhead  5 . An inlet  12   a  and outlet  12   b  is provided on the bottom of the housing  11  for circulating a flow of ink through the printhead  5 . The housing  11  of the printhead  5  is movably connected to a mounting assembly  13  for reciprocatory motion with respect to a print medium (not shown). 
     The cleaning head  15  includes an array of cleaning nozzles  17  mounted in an orifice plate  19  as shown. Similar to the printhead  5 , a circuit board  21  is provided adjacent to the orifice plate  19  for generating electrical signals which may either control the size of the cleaning droplets generated by the nozzles  17 , or operate to steer the droplets so that they impinge on different areas on and around the inkjet nozzles  3 . Both the orifice plate  19  and circuit board  21  are mounted on a rectangular housing  23  having an inlet  24   a  and an outlet  24   b  for circulating a flow of cleaning fluid. As is most evident in FIGS. 1A and 1C, the cleaning nozzles  17  present in the orifice plate  19  are a precise mirror image of the inkjet nozzles  3  present in the orifice plate  7  so that there exists a one-to-one alignment between the inkjet nozzles  3  and cleaning nozzles  17  when the printhead  5  and cleaning head  15  are opposed to one another. The cleaning head  15  is connected to a mounting assembly  25  which allows such a one-to-one nozzle alignment to occur. 
     FIG. 2A schematically illustrates a first embodiment of the fluid jet device  1  of the invention wherein the cleaning head  15  continuously generates cleaning droplets  27  that impinge on the orifices  4  of the inkjet nozzles  3  of a printhead  5 . In this embodiment, a supply of pressurized cleaning fluid  30  is connected to the inlet  24   a  of the cleaning head  15 . A cleaning fluid reclamation system  32  is connected to the fluid outlet  24   b  of the cleaning head  15 . The pressurized cleaning fluid supply  30  includes a closed vessel  34  that contains an inventory of cleaning fluid  35 . 
     In this preferred embodiment, the cleaning fluid  35  is the same ink used by the inkjet printhead  5 , since such ink has proven to be a highly effective cleaning solvent for the removal of dried ink and other debris from the nozzles  3 . The use of ink as a cleaning solvent also allows the printhead  5  and the cleaning heat  15  to use the same fluid supply  30  and reclamation system  32 . However, other cleaning fluids may be used, including non-ink cleaning solvents, and even particulate materials such as fine particles of dry ice entrained in a stream of compressed air. 
     An inlet conduit  36  connects the cleaning fluid  35  and the vessel  34  where the inlet conduit  24   a  of the cleaning head  15 . A pump having an outlet connected to the upper end of the closed vessel  34  pressurizes the vessel so that cleaning fluid  35  is forced through the conduit  36  into the cleaning head inlet  24   a . A droplet speed controller in the form of a pressure controller  39  regulates the pump  38  to vary the pressure within the vessel  34  in order to control the velocity of the cleaning droplets discharged from the cleaning nozzles  17 . A distribution plate  40  uniformly distributes the pressurized cleaning fluid to each of the cleaning nozzles  17 . Cleaning fluid that is not discharged through the nozzles  17  is collected in the outlet  24   b , which in turn is connected to the outlet conduit  42 . The end of the outlet conduit  42  is disposed within an open collection vessel  44  of the cleaning fluid reclamation system  32 . 
     A control valve  46  mounted in the outlet conduit  42  determines whether or not cleaning fluid forced through the inlet conduit  36  will flow through the cleaning nozzles  17 , or merely circulate through the distribution plate  40 , the outlet conduit  42 , and into the collection vessel  44 . The reclamation system  32  also includes a gutter  48  for collecting droplets of cleaning fluid that drip from the orifice plate  7  of the printhead  5 . Any such cleaning fluid collected by the gutter  48  flows into the collection vessel  44  via drain conduit  50 . Finally, the reclamation system  32  includes a drain vessel  52  connected to the bottom of the collection vessel  44  by way of a drain valve  54 . A conduit  56  connects the drain vessel  52  to the cleaning fluid supply vessel  34  via a filter  58 . A recycling pump  60  supplies pressurized air to the upper end of the drain vessel  52  to force reclaimed cleaning fluid through the filter  58  and back into vessel  34 . 
     As previously indicated, one advantage of using printhead ink as the cleaning fluid  35  is that the same fluid supply  30  and reclamation system  32  may be used to supply ink to the printhead  5  when the cleaning head  15  is removed from its opposing position after a cleaning operation has been performed. Still another advantage is that the same supply  30  and reclamation system  32  may be used to circulate ink through the printhead  5  in a “back flush” mode of operation in order to generate a small negative pressure in the nozzles  3  which effectively sucks the cleaning droplets  27  down the various orifices  4  where they may be directed into the collection vessel  34 . To this end, the inlet  12   a  of the printhead  5  is connected to the ink being used as a cleaning fluid  35  via inlet conduit  62 . A distribution plate  64  connects the inlet  12   a  to the outlet  12   b . Outlet  12   b  is in turn connected to the collection vessel  44  via outlet conduit  66 . When back flush valve  68  located in outlet  66  is open (as is shown in FIG.  2 A), the ink used as the cleaning fluid  35  will circulate from the inlet  12   a  to the outlet  12   b  through the distribution plate  64  without being ejected through the nozzles  3  due to the larger flow path (and consequent lower fluid resistance) offered by the orifice plate  64  versus the nozzles  3  of the orifice plate  7 . Because lower pressures are generated in areas immediately surrounding the flow of a moving fluid via Bernoulli&#39;s principal, a small amount of negative pressure will be generated in the orifices  4  of the printhead nozzles  3 . 
     In operation, the pump  38  of the fluid supply  30  is actuated while control valve  46  is closed. The printhead may be of any type. As shown printhead  5  contains a return fluid path  66 . It is not necessary to have a return path of fluid and conduit  66  or valve  68  as shown in FIGS. 2A and 2B. The pressure generated by the pump  38  forces the ink used as cleaning fluid  35  through the inlet conduit  36  and out through the nozzles  17  of the cleaning head  15 . At the same time, back flush valve  68  of the outlet conduit  66  of printhead  5  is opened so that the ink used as the cleaning fluid  35  circulates through the printhead  5  as previously described. Operation of valve  68  can be in both the closed and open positions. Fluid in the printhead  5  will be directed out of the nozzles  3  if the valve  68  is closed. Cleaning droplets  27  that impinge directly in and around the orifices  4  of the inkjet nozzles  3  are sucked into the circulating flow of ink through the printhead  5 . Both the back flushed cleaning fluid and the collected cleaning droplets  27  are discharged through the outlet conduit  66 , where they are collected in the vessel  44  of the reclamation system  32 . Periodically, drain valve  54  is opened to allow a flow of the ink used as a cleaning fluid into the drain vessel  52 . Recycling pump  60  is then actuated, forcing the ink used as cleaning fluid through the drain conduit  56 , the filter  58 , and back into the closed vessel  34 . 
     FIG. 2B illustrates an alternative embodiment  70  of the fluid jet device which is identical in all respects to the embodiment  1  illustrated in FIG. 2A, with two exceptions. First, an auxiliary pump outlet  71  is provided between the cleaning fluid supply pump  38  and the inlet conduit  36 . Second, a modulation valve  72  is provided between one end of the inlet conduit  36  and the joint between the auxiliary pump outlet  71  and the balance of the inlet conduit  36 . Such an arrangement allows an individual slug  74  of cleaning fluid to be introduced into the inlet conduit  36  by the rapid opening and closing of the modulation valve  72 . Thereafter, a flow of compressed air  76  generated by the pump  38  propels the slug  74  through cleaning head inlet  24   a , distribution plate  40 , and out through the cleaning head nozzles  17 , as control valve  46  is closed during such a cleaning operation. In all other ways, this alternative embodiment  70  operates in the same manner as described with respect to the first embodiment  1 , the only difference being that a smaller amount of cleaning fluid  35  is used. As such, the embodiment  70  of the invention illustrated in FIG. 2B operates more analogously to a drop-on-demand printhead, in contrast to the continuous drop operation described with respect to the embodiment  1  illustrated in FIG.  2 A. 
     With reference now to FIGS. 3A,  3 B, and  3 C, the orifice plate  7  of the printhead  5  may include an array of inkjet nozzles  3  which are all the same size, and uniformly spaced. Alternatively, as is illustrated in FIG. 3B, the inkjet nozzles  3  may be of different sizes and non-uniformly spaced. In either case, the cleaning nozzles  17  of the cleaning head  15  should reflect the same size and spacing as the nozzles  3  of the printhead  5  in mirror symmetry in the same fashion that the cleaning nozzles  17  illustrated in FIG. 3C correspond with the inkjet printing nozzles  3  illustrated in FIG.  3 B. 
     As previously mentioned, both embodiments  1  and  70  of the invention include a droplet speed controller in the form of a pressure controller  39  which is operably connected to the pump  35  of the cleaning fluid supply  30 . As shown in FIG. 3C, both of these embodiments  1 ,  70  further include a droplet sizing mechanism  77  in the form of annular heaters  78  circumscribing each of the cleaning nozzles  17  in combination with a power pulse source  80  connected to each of the heaters  78 . Each of the heaters  78  includes two semi-annular heaters  79   a ,  79   b , each of which is separately connected to the power pulse source  80 . In operation, the power pulse source  80  supplies pulses of electrical current to both halves of the annular heater  78  surrounding each of the cleaning nozzles  17 . The heater  78  converts these current pulses into thermal pulses which “pinch” the stream of cleaning fluid ejected from the cleaning nozzles  17  into a droplet of a size which is dependent upon the specific frequency of the current pulses supplied by the power pulse source  80 . A specific description of the relationship between frequency, pulse current, and droplet size is given in co-pending U.S. patent Ser. No. 08/954,317 filed Oct. 17, 1997, by the same assignee as this application, Eastman Kodak Company, the entire specification of which is incorporated hereby by reference. Two different modes of operating the embodiments  1 ,  70  are illustrated in FIGS. 4A and 4B, respectively. In FIG. 4A, the frequency of the current pulses generated by the power pulse source  80  is such that each of the cleaning droplets  17  is somewhat smaller than the orifices  8  of each of the nozzles  3  of the printhead  5 . Such a mode of cleaning is particularly effective at dislodging and removing dried ink deposits which may have accumulated in or around the edges of each orifice  4 . However, if the frequency of the current pulses is periodically slowed down, cleaning droplets  27  of a larger size may be generated by the droplet sizing mechanism  77 . Such a mode of operation is illustrated in FIG.  4 B. Here, the cleaning droplets  27  generated are a mixture of small droplets  81   a  having a diameter smaller than that of the orifices  4  of the printing nozzles  3 , and larger droplets  81   b  having a diameter about the same as the orifices  4 . The smaller droplets  81  are useful for dislodging ink deposits and other debris which have accumulated around the interior walls of the orifice  4 . The larger droplets  81   b  are particularly useful for dislodging and removing dried ink deposits and debris which may have accumulated on the surfaces of the nozzles around the edges of the orifices  4 . Each of these particular cleaning actions is illustrated in FIGS. 5A and 5B, respectively. Typically the number of drops may lie in the range of from 3 to 10,000, but is not restricted. 
     In addition to having a droplet sizing mechanism  77 , each of the two embodiments  1 ,  70  of the invention may further include a droplet direction controller  82  as shown in FIG.  6 . Controller  82  may take the form of an oscillating assembly  84  which oscillates or reciprocally moves (or “dithers”) the cleaning head  15  relative to the printhead  5  so that the cleaning droplets  27  impinge different areas surrounding each of the inkjet nozzles  4 . The advantage of such a droplet direction controller  82  is that it allows the narrow streams of high-impact cleaning droplets  27  to more thoroughly clean the areas surrounding the printhead nozzles  4 . Alternatively, as shown in FIG. 7, the droplet direction controller  82  may take the form of a droplet steering circuit  86  connected to the two halves  79   a ,  79   b  of the previously described annular heaters  78  also used in the droplet sizing mechanism  77 . Here, the droplet steering circuit  86  alternately applies pulses of electrical current to the left half  79   a  and then to the right half  79   b  of the annular heaters  78 . The asymmetric application of thermal pulses to the ejected stream of cleaning droplets  27  deflects them first to the left, and then to the right, as indicated. Such thermal steering may also be operated in a manner to better “aim” cleaning droplets which are slightly misdirected due to small misalignments between the printhead  5  and cleaning head  15 , or small faults in the cleaning nozzles. Thermal steering is described in detail in U.S. Pat. No. 6,079,821 by J. Chwalek et al and assigned to Eastman Kodak Company, the entire specification of which is expressly incorporated herein by reference. Of these two types of droplet direction controllers  82 , the use of a droplet steering circuit  86  in combination with annular heaters  78  having two separate halves  79   a ,  79   b  is preferred, since such a controller  82  can be combined with the previously described droplet sizing mechanism  77 , the only difference being that the control circuit connected to the heaters  78  is programmed in one fashion to create cleaning droplets  27  of different sizes when desired, and in another fashion in order to effect the type of thermal steering illustrated in FIG. 7. A third type of droplet direction controller  82  is schematically illustrated in FIG.  1 C. Here, a pair of fluid stream generators  88   a ,  88   b  are provided on either side of the orifice plate  19  of the cleaning head  15 . In this embodiment, each of the fluid stream generators  88   a ,  88   b  may include a plenum for directing a variable flow of air, which flow is alternated in order to deflect the droplets in the side-to-side manner as is illustrated in FIG.  7 . The use of this type of droplet direction controller  82  has the advantages of being relatively easy to implement, and of allowing the heaters  78  to be operated in a droplet sizing mode while simultaneously being deflected from side-to-side, thereby resulting in a somewhat more effective cleaning action than if the heaters  78  are sequentially used as a droplet sizing mechanism  77  in a droplet direction controller  82 . 
     EXAMPLE 1 
     A laboratory prototype of the fluid jet device  1  was used to clean clogged nozzles  3  shown in the enlarged photograph of FIG.  8 . The application of cleaning droplets into the orifice  4  of the nozzle  4  from a cleaning head cleaned the nozzle as shown in FIG.  9 . The delivery of cleaning fluid through conduit  36  to a separate cleaning head  15  was pressurized via a pump  38  while the cleaning head  15  was placed directly opposite to the printhead  5  to be cleaned. The cleaning head  15  sprayed droplets into the orifice  4  of the printhead  5  to be cleaned. The experiment was conducted at a pressure of 30 psi in conduit  36  with valve  46  in the closed position and then increased to 60 psi in the cleaning printhead  15 . Clorox was used as the cleaning fluid. The printhead  5  to be cleaned was operated in a backflush mode using 35 psi water in conduit  62 . Valve  68  was alternatively opened and closed every 2 seconds for 2 minutes. As shown in FIG. 8 at the start of the test, the orifice  4  was blocked by a particulate deposit. The result of the cleaning operation is shown in FIG. 9, where the particulate deposit has been removed. 
     While this invention has been described with respect to several preferred embodiments, persons of skill in the art will recognize that various additions and modifications of the invention might be made to retain or perhaps enhance the advantages associated with the invention. A number of different solvents other than ink may further be used to enhance the cleaning operation, such as a particulate containing liquid, bleach, particulate dry ice, or an organic solvent. All such advantages and modifications are intended to be encompassed within the scope of this invention, which is limited only by the claims appended hereto. 
     
       
         
               
             
               
               
               
             
           
               
                   
               
               
                 PARTS LISTS 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 1. 
                 Fluid jet device 
               
               
                   
                 3. 
                 Inkjet nozzles 
               
               
                   
                 4. 
                 Orifice 
               
               
                   
                 5. 
                 Printhead 
               
               
                   
                 7. 
                 Orifice plate 
               
               
                   
                 9. 
                 Circuit board 
               
               
                   
                 11. 
                 Rectangular housing 
               
               
                   
                 12. 
                 Inlet, outlet a, b 
               
               
                   
                 13. 
                 Mounting assembly 
               
               
                   
                 15. 
                 Cleaning head 
               
               
                   
                 17. 
                 Cleaning nozzles 
               
               
                   
                 19. 
                 Orifice plate 
               
               
                   
                 21. 
                 Circuit board 
               
               
                   
                 23. 
                 Rectangular housing 
               
               
                   
                 24. 
                 Inlet, outlet 
               
               
                   
                 25. 
                 Mounting assembly 
               
               
                   
                 27. 
                 Cleaning droplets 
               
               
                   
                 30. 
                 Supply of pressurized cleaning fluid 
               
               
                   
                 32. 
                 Cleaning fluid reclamation system 
               
               
                   
                 34. 
                 Closed vessel 
               
               
                   
                 35. 
                 Cleaning fluid 
               
               
                   
                 36. 
                 Inlet conduit 
               
               
                   
                 38. 
                 Pump 
               
               
                   
                 39. 
                 Pressure controller 
               
               
                   
                 40. 
                 Distribution plate 
               
               
                   
                 42. 
                 Outlet conduit 
               
               
                   
                 44. 
                 Collection vessel 
               
               
                   
                 46. 
                 Control valve 
               
               
                   
                 48. 
                 Gutter 
               
               
                   
                 50. 
                 Drain conduit 
               
               
                   
                 52. 
                 Drain vessel 
               
               
                   
                 54. 
                 Drain valve 
               
               
                   
                 56. 
                 Conduit 
               
               
                   
                 58. 
                 Filter 
               
               
                   
                 60. 
                 Recycling pump 
               
               
                   
                 62. 
                 Inlet conduit 
               
               
                   
                 64. 
                 Distribution plate 
               
               
                   
                 68. 
                 Back flush valve 
               
               
                   
                 70. 
                 Alternative embodiment 
               
               
                   
                 71. 
                 Auxiliary pump outlet 
               
               
                   
                 72. 
                 Modulation valve 
               
               
                   
                 74. 
                 Solvent slug 
               
               
                   
                 76. 
                 Air 
               
               
                   
                 77. 
                 Droplet sizing mechanism 
               
               
                   
                 78. 
                 Annular heaters 
               
               
                   
                 79. 
                 Heater halves a, b 
               
               
                   
                 80. 
                 Power pulse source 
               
               
                   
                 82. 
                 Droplet direction controller 
               
               
                   
                 84. 
                 Oscillating assembly 
               
               
                   
                 86. 
                 Droplet steering circuit 
               
               
                   
                 88. 
                 Fluid stream generators a, b