Abstract:
A method and system for purging bubbles from a fluid chamber of a micro-fluid ejection head containing a plurality of fluid chambers, an ejection actuator respectively associated with each of the fluid chambers, and a common fluid supply area for the fluid chambers. According to this exemplary method, one or more of the ejection actuators are pulsed with energy sufficient to expand a bubble present in one of the fluid chambers without substantially boiling the fluid in the common fluid supply area. A first temperature of the ejection head is maintained for a first period of time during bubble expansion so that the bubble in the fluid chamber is urged away from the fluid chamber. The ejection head temperature is decreased over a second period of time to lower the ejection head temperature to a second temperature lower then the first temperature.

Description:
FIELD 
     The disclosure relates to a system and method for purging gas bubbles from a micro-fluid ejection head which, in some embodiments, may improve operating characteristics of a micro-fluid ejection device. 
     BACKGROUND AND SUMMARY 
     As micro-fluid ejection devices become smaller and the frequency of ejection of fluid from ejection heads for the devices becomes greater, the ejection heads have become more susceptible to a variety of occurrences which may lead to misfiring of certain ejection actuators on the ejection heads. One such occurrence is the presence of a gas bubble in a fluid chamber of the ejection head. Because of the small size of the fluid chambers and associated ejection orifices, even minute gas bubbles in the fluid chambers may be effective to block fluid flow from the ejection orifices. There are a number of sources that may lead to the formation of gas bubbles in the fluid chambers. For example, impact of the ejection head on a hard surface may form gas bubbles in the fluid chambers. Another source of gas bubbles may be dissolved air or oxygen in the fluid. 
     In order to reduce the occurrence of gas bubbles in the fluid chambers, impact of the ejection head may be minimized. Another method for reducing the occurrence of gas bubbles may be to provide an ejection head design which is less susceptible to retaining gas bubbles in the fluid chambers. However, neither of these solutions is completely satisfactory. Accordingly, there remains a need for an improved system and method for purging bubbles from a micro-fluid ejection head. 
     With regard to the foregoing, the disclosure provides in one exemplary embodiment a method for purging bubbles from a fluid chamber of a micro-fluid ejection head containing a plurality of fluid chambers, an ejection actuator respectively associated with each of the fluid chambers, and a common fluid supply area for the fluid chambers. According to this exemplary method, one or more of the ejection actuators are pulsed with energy sufficient to expand a bubble present in one of the fluid chambers without substantially boiling the fluid in the common fluid supply area. A first temperature of the ejection head is maintained for a first period of time during bubble expansion so that the bubble in the fluid chamber is urged away from the fluid chamber in the absence of applying a pressure to the fluid chamber. The ejection head temperature is decreased over a second period of time to lower the ejection head temperature to a second temperature lower then the first temperature. 
     In another exemplary embodiment, there is provided a micro-fluid ejection device including a micro-fluid ejection head containing a plurality of fluid chambers, fluid actuator devices associated with the fluid chambers, a fluid supply inlet, and fluid supply channels in fluid flow communication with the fluid supply inlet and each of the fluid chambers. A fluid supply reservoir is in fluid flow communication with the fluid supply inlet. The ejection actuators are capable of being pulsed with an energy sufficient to expand any bubbles present in the fluid chambers, without substantially boiling the fluid in the fluid supply inlet, and to force the bubbles present in the fluid chambers away from the fluid chambers. 
     An advantage of the exemplary embodiments can be that boiling the fluid in a common fluid supply area of the ejection head is substantially avoided. Furthermore, the system can use existing ejection actuators without the need for additional ejection head heaters to effect a temperature rise of the ejection head. Since individual ejection actuators can be used for the bubble purging procedure, heat may be directed specifically to chambers containing bubbles thereby enabling lower ejection head temperatures to be used to effectuate removal of the bubbles. Specific elements of the bubble purging procedure can enable bubbles to be purged and/or shrunk to the point where they disappear from the fluid chamber. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features and advantages of exemplary embodiments disclosed herein may become apparent by reference to the detailed description when considered in conjunction with the figures, which are not to scale, wherein like reference numbers indicate like elements through the several views, and wherein: 
         FIG. 1  is a perspective view, not to scale, of an exemplary micro-fluid ejection device according to the disclosure; 
         FIG. 2  is a perspective view, not to scale, of a fluid cartridge and ejection head for a micro-fluid ejection device according to the disclosure; 
         FIG. 3  is a cross-sectional view, not to scale, of a portion of a micro-fluid ejection head taken through lines  3 - 3  of  FIG. 4 ; 
         FIG. 4  is a plan view, not to scale, of a portion of a micro-fluid ejection head for a micro-fluid ejection device according to the disclosure; 
         FIG. 5  is a plan view, not to scale, of a portion of a micro-fluid ejection head having air bubbles trapped in fluid chambers and in a fluid supply channel; 
         FIG. 6  is a graphical representation of a heating and cooling sequence for a purging sequence of an exemplary embodiment of the disclosure; 
         FIG. 7  is graphical representation of a bubble growth multiplier versus bubble temperature for a purging sequence as disclosed; and 
         FIGS. 8-9  are plan views, not to scale of a portion of an ejection head during a bubble purging procedure. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     For the purposes of this disclosure, unless indicated otherwise, “temperature” means the temperature of an ejection head structure rather than of the fluid as it is difficult to measure and control fluid temperatures within ejection head structures as set forth herein. 
     With reference to  FIGS. 1 and 2  there are shown in perspective views, a fluid micro-fluid ejection device  10  including one or more fluid cartridges  12  for ejecting fluids, such as inks, therefrom onto a substrate or print media  14 . The fluid cartridge  12  includes an ejection head  16  disposed on an ejection head area  18  of the fluid cartridge  12 . As described in more detail below, the ejection head  16  is provided by a nozzle plate  20  containing ejection orifices  22  attached to a semiconductor substrate  24  containing fluid ejection actuators. Power may be provided to the ejection actuators on the substrate  24  as by electrical tracing  26  and a flexible circuit  28  containing electrical contact pads  30  which are in electrical communication with a controller in the micro-fluid ejection device  10 . Fluid ejected by the ejection head  16  may be contained in the fluid cartridge  12  in a fluid reservoir  32  or in other ways, such as by a separate fluid supply reservoir remote from the ejection head  16 . 
       FIG. 3  is a cross-sectional view and  FIG. 4  is a partial plan view, not to scale, of a portion of an exemplary ejection head  16 . The ejection head  16  is provided by the semiconductor substrate  24  containing a plurality of fluid ejection actuators such as heater resistor  34  and the nozzle plate  20 . The heater resistor  34  is defined on a silicon substrate  36  by a resistive layer  38  deposited on a first insulating layer  40 . A first metal layer  42  provides anode and cathode conductors for the heater resistor  34 . A second insulating layer  44  insulates the first metal layer  42  from a second metal layer  46  providing power to the heater resistor  34 . One or more passivation layers  48  and  50  and a cavitation layer  52  may be deposited over the heater resistor  34  to protect the heater resistor  34  from fluid corrosion and mechanical damage caused by collapsing of vapor bubbles during a fluid ejection sequence. 
     During a fluid ejection sequence, fluid, such as ink, is provided to a fluid chamber  54  through a fluid channel  56  that is in fluid flow communication with a common fluid supply area  58 . When energy is provided to the heater resistor  34 , fluid in the fluid chamber  54  adjacent the heater resistor  34  is superheated causing a vapor bubble to form which urges fluid in the chamber  54  through the ejection orifice  22 . After ejection of fluid from the fluid chamber  54 , the bubble collapses enabling fluid to refill the fluid chamber  54  by fluid flow through the fluid channel  56  from the common fluid supply area  58 . 
     During manufacturing or handling of the fluid cartridges  12 , air bubbles may form in the fluid channels  56  and fluid chambers  54  when the cartridge  12  is impacted on a hard surface, shaken, or otherwise moved in a manner sufficient to form air bubbles in the fluid channels  56  and fluid chambers  54 . If the air bubbles are not eliminated, they may block or inhibit the flow of fluid to the chambers  54  from the common fluid supply area  58  or may block or inhibit ejection of fluid from the orifices  22 . The elimination of air bubbles is expected to be even more critical as the size of the ejection heads  16  and resulting fluid passages continues to decrease. 
     Problematic air bubbles  60 ,  62 , and  64  are illustrated in an enlarged portion of the ejection head illustrated in  FIG. 5 . Air bubble  60  is shown in a fluid chamber  54 A blocking exit of fluid through an orifice  22 A adjacent the chamber  54 A. Air bubble  62  is shown blocking fluid flow through a fluid channel  56 C to a fluid chamber  54 C. Multiple small air bubbles  64  are shown in a fluid chamber  54 F and fluid channel  56 F while there are no air bubbles blocking fluid flow through orifices  22 B,  22 D,  22 E, and  22 G and fluid channels  56 B,  56 D,  56 E, and  56 G in this illustration. While the air bubbles  64  are not sufficiently large to block fluid flow in channel  56 F and orifice  22 F, the bubbles  64  may easily combine to form one or more bubbles large enough to block or otherwise inhibit fluid flow through the channel  56 F or orifice  22 F. 
     In order to substantially eliminate air bubbles from the ejection heads  16  that may cause fluid flow problems through the fluid channels  56  and ejection orifices  22 , a bubble elimination scheme can be used. An aspect of such a scheme can include that boiling of fluid in the common fluid supply area  58  is not required, and, in fact, can be substantially avoided by a procedure described in more detail below. 
     Test data showed that non-nucleate heating (NNH) of a fluid, such as ink, for an appropriate period of time and at a predetermined temperature worked well at eliminating or at least substantially reducing the presence of air bubbles in the fluid chambers  54  and fluid channels  56 . In order to create air bubbles in the ejection heads  16 , the ejection heads  16  were impacted multiple times on a hard surface. A condition corresponding to the presence of air bubbles in the ejection heads  16  sufficient to block ink flow was confirmed by observation of print tests which demonstrated that a number of ejection orifices  22  were incapable of ejecting fluid, hereinafter referred to as “missing nozzles.” For a first series of test, the average number of missing nozzles was about 100 per test, with a low of 36 and a high of 346 missing nozzles. For these tests, several different types of ink jet print heads containing different types of fluids were tested. The ejection heads  16  were not wiped and a controlled amount of fluid was not ejected after the heating and cooling sequence. The ejection heads  16  were heated at the indicated temperatures for the indicated period of time and the number of missing nozzle was determined for each temperature and period of time. Results of the bubble elimination tests are contained in the following Tables. 
     
       
         
               
             
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Dye type ink jet print head 
               
             
          
           
               
                   
                 Temperature (° C.) 
                   
               
             
          
           
               
                 Time (msec) 
                 90 
                 95 
                 100 
                 105 
               
               
                   
               
             
          
           
               
                 1 
                 2 
                 0 
                 4 
                 1 
               
               
                 100 
                 5 
                 0 
                 1 
                 2 
               
               
                 2000 
                 2 
                 0 
                 1 
                 — 
               
               
                 5000 
                 0 
                 3 
                 1 
                 — 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 General purpose type ink jet print head 
               
             
          
           
               
                   
                 Temperature (° C.) 
                   
               
             
          
           
               
                 Time (msec) 
                 90 
                 95 
                 100 
                 105 
               
               
                   
               
             
          
           
               
                 1 
                 45 
                 0 
                 4 
                 3 
               
               
                 100 
                 46 
                 6 
                 3 
                 3 
               
               
                 2000 
                 34 
                 9 
                 3 
                 — 
               
               
                 5000 
                 40 
                 21 
                 3 
                 — 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Photographic type ink jet print head 
               
             
          
           
               
                   
                 Temperature (° C.) 
                   
               
             
          
           
               
                 Time (msec) 
                 90 
                 95 
                 100 
                 105 
               
               
                   
               
             
          
           
               
                 1 
                 19 
                 4 
                 2 
                 0 
               
               
                 100 
                 29 
                 4 
                 3 
                 0 
               
               
                 2000 
                 37 
                 5 
                 2 
                 — 
               
               
                 5000 
                 15 
                 7 
                 2 
                 — 
               
               
                   
               
             
          
         
       
     
     The foregoing results indicate effective levels of bubble elimination from the print heads. It was observed, however, that the heating time at each of the indicated temperatures had more variability than desired. The test also indicated that the general purpose ink jet print head and the photographic ink jet print head may be more susceptible to bubble formation than an ink jet print head containing a dye type ink. 
     In another series of bubble elimination tests, nine dye type ink jet print heads and nine general purpose ink jet print heads were subjected to a standard installation maintenance algorithm for aligning and priming the print heads after creating air bubbles in the print heads by impacting the print heads on a hard surface. In this test, the average number of missing nozzles decreased to 44.8 from an initial average number of 205 missing nozzles. The standard installation maintenance algorithm includes activating an ejection head so that about 800 droplets of fluid are ejected from each nozzle at an ejection frequency ranging from about 9 to about 12 kHz, then the ejection head is wiped to remove any excess fluid from the ejection head. 
     In yet another series of bubble elimination tests, nine dye type ink jet print heads and nine general purpose ink jet print heads were subjected to a procedure in accordance with an embodiment of the disclosure. According to this procedure, the print heads were heated to 100° C. and held at this temperature for two seconds. The print heads were then cooled for 10 seconds, 800 drops of fluid were ejected from the print heads at a frequency of 24 kHz and the print heads were wiped to remove excess fluid from the print heads. Using this procedure, the average number of missing nozzles decreased from 176 to 1.7 missing nozzles. 
     Based on the results of the foregoing bubble elimination test, a procedure was devised which was found to be suitable for eliminating air bubbles in most of the tested color ink jet print heads. According to the procedure, the print heads are heated to about 95° C. for about 2.5 seconds and are cooled for about ten seconds. The print heads are then wiped and a predetermined amount of fluid is ejected from the print heads at a frequency ranging from about 5 to about 30 kHz. A graphical representation of the heating and cooling cycle for the ejection head  16  is illustrated in  FIG. 6  by curve  70 . 
     Without desiring to be bound by theoretical considerations, it is believed that the foregoing bubble elimination procedure is effective to expand air bubbles in the fluid chambers  54  until they are too large for the chambers  54  and are forced out of either the orifice  22  or through the channel  56  into the common fluid area  58 . As illustrated by  FIG. 7 , an air bubble reaches its maximum growth rate at a temperature of from about 90 to about 100° C. Accordingly, maintaining a temperature below the normal fluid boiling point of 100° C. for a predetermine period of time is effective in expanding the air bubble so that the bubble will be forced from the chamber  54  or channel  56 . The bubble expansion illustrated in  FIG. 7  is primarily based on bubble growth due to water vapor. Dissolved air in the fluid may contribute to bubble expansion, but to much lower bubble growth levels. 
     In  FIG. 8 , the bubbles  60 ,  62  and  64  have been expanded by the foregoing procedure. Expansion of bubble  62  has resulted in movement of the bubble  62  out of the fluid channel  56 C into the common fluid supply area  58 . Expansion of bubble  64  has caused bubble  64  to form a larger bubble  64 , which will move out of the fluid channel  56 F and fluid chamber  54 F either through the orifice  22 F or into the common fluid supply area  58 .  FIG. 9  is an illustration of a portion of the fluid ejection head  16  after conducting the procedure described above. 
     Occasionally a bubble may split in two or otherwise divided with part of the bubble remaining in the chamber  54 , or a small bubble will grow and become large enough to block an orifice  22 . Such bubbles tend to shrink and disappear when the fluid cools down during the cooling cycle. 
     While the foregoing procedure is typically conducted upon the installation of a fluid cartridge  12  in a fluid ejection device  10 , the procedure may also be conducted to remove air bubbles or reduce the number of missing nozzles as part of a routine maintenance procedure for the ejection head  16 . Bubble elimination routines may be activated during manufacture of the fluid cartridges or upon use of the fluid cartridge by a user. 
     Having described various aspects and exemplary embodiments of the disclosure and several advantages thereof, it will be recognized by those of ordinary skills that the exemplary embodiments are susceptible to various modifications, substitutions and revisions within the spirit and scope of the appended claims.