Abstract:
A liquid drop emitter, a method of mixing a liquid, and a method of printing are provided. The liquid emitter includes a structure defining a chamber adapted to provide a liquid having an orifice through which a drop of the liquid can be emitted. A drop forming mechanism is operatively associated with the chamber. A mixing mechanism is associated with the chamber and is operable to create a surface tension gradient on the liquid provided by the chamber such that the liquid flows without being emitted from the chamber.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to the field of inkjet printing but more specifically to the surface tension induced stirring of liquids that are to be ejected by a liquid ejection mechanism.  
       BACKGROUND OF THE INVENTION  
       [0002]     The problems associated with the premature drying of liquids such as inks, within fluid delivery devices such as inkjet printers, are known. The premature drying of liquids causes the plugging of ejection nozzles that will either impede or totally prevent liquids from being delivered through the nozzle and onto a desired delivery medium. The plugging that occurs within liquid ejection nozzles has created a need for methods that remove such blockages, such as purging of the nozzles.  
         [0003]     Those skilled in the art of inkjet printers are aware that software exists to verify the proper operation of liquid ejection nozzles. The software also provides various routines to exercise those nozzles to purge them of dried or drying liquids. A significant drawback to purging of nozzles within fluid ejection systems exists in that the purged fluids must be deposited somewhere. This is typically accomplished by depositing the purged fluids into a sponge. However, purging receptacles such as sponges and the like have limited storage volume and become full requiring costly and often inconvenient service requirements. Service, the replacement of sponges, and the use of cleaning cycles increases the cost of printing and adds to the complexity of printer mechanisms. Additionally, full and saturated receptacles can contaminate the very nozzles that you are trying to clean, by virtue of cross-contaminating wet sponge material into nozzles that are already clean.  
         [0004]     Also, in typical printing applications, the image-wise requirement of placing ink droplets upon a receiver will leave certain nozzles unused. This exacerbates the drying of ink within the unused nozzles, because of the rapid reciprocation of the print head. The additional motion enhances the movement of air over the nozzles, and thus directly increases the rate of the evaporation of the fluids waiting to be ejected. Additionally, inks, including dye and pigment based inks, exhibit unique physical drying properties based upon their individual formulations, with the rate of those drying properties being accelerated when the ink is idle and exposed to the atmosphere at the meniscus of an ejector nozzle.  
         [0005]     U.S. Pat. No. 6,695,441 B2, issued to Asano on Feb. 24, 2004, discloses a stirring device that utilizes an ultrasonic transducer that applies ultrasonic vibrations to ink in order to overcome problems such as molecular over-concentration due to molecular coupling, the sedimentation of suspended particles and the cohesion of particles within an ink. Asano teaches that the molecular-weight distribution of inks increases because of molecular clumping and causes erratic or clogged ink nozzles, and additionally that the practice of simple ink stirring does not sufficiently address problems such as sedimentation or cohesion, those types of problem being solved by the aggressive method of using a complicated and costly ultrasonic device.  
         [0006]     U.S. Pat. No. 6,172,693 B1, issued to Minemoto et al. on Jan. 9, 2001, also discloses a method of stirring a fluid. This method discusses a plurality of electrophoretic electrodes that react with the polarity of particles that are suspended within a fluid. These particles in turn correspond with and react to a plurality of ejecting electrodes whose functions are also based upon the polarity of the suspended particles. Stirring electrodes that are disposed in proximity to the ejecting electrodes serve to stir the polarity-based color particles that are suspended within the fluid carrier that delivers those particles to the ejecting electrodes. This charge-based stirring of the suspended particles promotes proper dispersion of the particles in the area of an ejection port, thus preventing those particles from plugging the ejection port and blocking their ejection, the ejection of a particle being accomplished by virtue of electrophoresis.  
       SUMMARY OF THE INVENTION  
       [0007]     According to one feature of the present invention, a liquid emitter includes a structure defining a chamber adapted to provide a liquid and has an orifice through which a drop of the liquid can be emitted. A drop forming mechanism is operatively associated with the chamber. A mixing mechanism is associated with the chamber and is operable to create a surface tension gradient on the liquid provided by the chamber such that the liquid flows without being emitted from the chamber.  
         [0008]     According to another feature of the present invention, a method of mixing a liquid includes providing a liquid in a chamber having an orifice through which a drop of the liquid can be emitted; and creating a surface tension gradient on the liquid provided by the chamber, wherein the liquid flows without being emitted from the chamber.  
         [0009]     According to another feature of the present invention, a method of printing includes providing a liquid in a chamber having an orifice through which a drop of the liquid can be emitted; providing a drop forming mechanism operatively associated with the chamber; mixing the liquid in the chamber by creating a surface tension gradient on the liquid provided by the chamber such that the liquid flows without being emitted from the chamber; and ejecting a drop of the liquid from the orifice of the chamber using the drop forming mechanism. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     In the detailed description of the preferred embodiments of the invention presented below, reference is made to the accompanying drawings, in which:  
         [0011]      FIG. 1  is a cross-sectional view of an inkjet chamber;  
         [0012]      FIG. 2  is a partial cross-sectional view of the inkjet chamber showing the temperature gradient across a meniscus induced by heater(s);  
         [0013]      FIG. 3  is a partial cross-sectional view of the inkjet chamber showing the surface tension gradient across a meniscus;  
         [0014]      FIG. 4  is a partial cross-sectional view of the inkjet chamber showing the circulation of fluid that is induced within a nozzle;  
         [0015]      FIG. 5  is a partial cross-sectional view of the inkjet chamber;  
         [0016]      FIG. 6  is a partial top view of an inkjet chamber; and  
         [0017]      FIG. 7  is a partial cross sectional view of the nozzle plate of an inkjet chamber. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]     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.  
         [0019]     Referring to  FIG. 1 , the drawing illustrates a cross-sectional view of an inkjet chamber  10 , for an ink jet print head that contains ink  20  to be ejected from a nozzle  30  that is disposed upon a chamber roof  40 . It should be noted at this point in time that the present invention contemplates the ejection of a multiplicity of possible fluids such as medicines, inks, pigments and the like. However, for purposes of clarity and consistency, fluids will be hereafter referred to as inks. Inkjet chamber  10  also contains a plurality of heaters including upper ejection heaters  50  and lower ejection heaters  60  depending upon the type of ejection mechanism used. If upper ejection heaters  50  were activated upper vapor bubbles  70  would be generated. This type of ejection methodology is generally referred to as a back-shooter. If the lower ejection heater  60  were activated a lower vapor bubble  80  would be generated. This type of ejection methodology is generally referred to as a roof-shooter. Upper ejection heaters  50  and lower ejection heater  60  as shown can be configured as a single heater or a plurality of heaters.  
         [0020]     Referring next to  FIG. 2 , the drawing illustrates a partial cross-sectional view of the inkjet chamber  10 . A meniscus  90  of ink  20  that is formed within the nozzle  30  occurs at the interface of the ink  20  to the air  100  that resides outside the confines of the inkjet chamber  10 . The interface that is represented by the meniscus  90  will dries over time when in contact with the air  100 . This drying over time causes the ink  20  at the surface of the meniscus  90  to become progressively more concentrated as time passes until first the skinning and eventually the complete clogging of nozzle  30  occurs. Additionally, variations in viscosity of the ink will occur in layers through the ink (not shown) wherein the viscosity of the ink at the meniscus  90  is the thickest, with a gradual decrease in viscosity as the depth into the nozzle  30  increases. Activation of either or both of the upper ejection heaters  50  will result in the heating of the ink  20  at the meniscus  90  of the inkjet chamber  10 .  
         [0021]     It is instructive to note that those skilled in the art should realize that in the discussion of ink stirring, the present invention deals specifically with ink  20  that is stirred by a flow induced at the meniscus  90  of ink  20 . The stirring of the ink  20  is caused by the application of a sufficient amount of heat to create a sufficient surface tension gradient that in turn causes the ink  20  to flow at the meniscus  90  without the ink  20  being ejected from the inkjet chamber  10 . Heat gradient lines  110  denote the heat gradient formed across the meniscus  90  of inkjet chamber  10 . Upon actuation of either upper ejection heater  50 , a decreasing heat gradient presents itself across the meniscus  90  of ink  20 , with the ink being warmest at the edge of the meniscus  90  and cooler at the center of the meniscus  90 . Heat gradient lines  110  are shown bent away from the decreasing heat gradient that is produced across the meniscus  90 . It should be evident by those skilled in the art that the heaters used to cause stirring can comprise separate upper ejection heaters  50  along with circulation heaters  180  as shown in  FIG. 7 . Additionally the existing upper ejection heaters  50  can have secondary purpose and can be used as stirring elements. The application of a lower power to the upper ejection heaters  50  essentially causes heating at the meniscus  90  without causing ink  20  to be ejected from the inkjet chamber  10 .  
         [0022]     Referring next to  FIG. 3 , the drawing illustrates a partial cross-sectional view of the inkjet chamber  10 . A meniscus  90  of ink  20  that is formed within the nozzle  30  occurs at the interface of the ink  20  to the air  100  that resides outside the confines of the inkjet chamber  10 . It is instructive to remember that as previously discussed in  FIG. 2 , the activation of either or both of the upper ejection heaters  50  will result in the heating of the ink  20  at the meniscus  90  that is present across the nozzle  30  of the inkjet chamber  10 . The vertically diagrammed surface tension gradient arrows  120  denote the surface tension gradient present across the meniscus  90  of inkjet chamber  10 . The gradient in surface tension represented by the surface tension gradient arrows  120  results from the application of the heating gradient represented by the heat gradient lines  110  discussed in  FIG. 2 . The surface tension across the meniscus  90  of inkjet chamber  10  varies as a function of the heat gradient across the meniscus  90  of inkjet chamber  10 . The surface tension decreases in a liquid as temperature increases. That is to say that the heat gradient across the meniscus  90  of the inkjet chamber  10  is the inverse of the surface tension gradient across the meniscus  90  of inkjet chamber  10 . Accordingly, while a heat profile that is induced by the application of the upper ejection heaters  50  across the meniscus  90  of inkjet chamber  10  increases from the edge of the meniscus  90  and decreases towards the center of meniscus  90 , the surface tension gradient that results across the meniscus  90  of inkjet chamber  10  is lessened at the outside edge of meniscus  90  and increases towards the center of the meniscus  90  that is formed across nozzle  30 .  
         [0023]     Referring next to  FIG. 4 , the drawing illustrates a partial cross-sectional view of the inkjet chamber  10 . A meniscus  90  of ink  20  that is formed within the nozzle  30  occurs at the interface of the ink  20  to the air  100  that resides outside the confines of the inkjet chamber  10 . It is instructive to remember that as previously discussed in  FIG. 2 , the activation of either or both of the upper ejection heaters  50  results in the heating of the ink  20  at the meniscus  90  that is present across the nozzle  30  of the inkjet chamber  10 . The circularly drawn circulation arrows  130  denote the circulation of the ink  20  that occurs within the nozzle  30  of inkjet chamber  10 . Flow occurs in the ink  30  by virtue of the existence of a surface tension gradient  120  previously discussed in  FIG. 3 . This region of lower surface tension at the edge of nozzle  30  that gradually increases to a region of higher surface tension towards the center of nozzle  30  causes the flow diagrammed by circulation arrows  130 . This flow occurs in the ink  20  and occurs from the region of lower surface tension at the edge of nozzle  30  to the region of higher surface tension towards the center of nozzle  30  due to heating performed by upper ejection heater  50  at the wall of the nozzle. As the ink  20  flows towards the interior of the meniscus, it results in a pressure increase towards the interior of the meniscus. This reduces the velocity of the ink  20  towards the interior of the meniscus. The ink  20  at this point is diverted towards the bulk interior that also includes ink  20 , where it seeks this lower pressure region, thus creating the circulation pattern denoted by the circulation arrows  130 . If the second upper ejection heater  50  are used on the right wall of nozzle  30 , a plurality of timing sequences could be ultimately employed, a similar phenomenon will be experienced on the right side of the meniscus, thus resulting in a mirrored circulation pattern. The combination of the two circulation patterns or vortices enhances the fluid velocity at the center of the meniscus causing the ink to fall deeper into the bulk interior. It should be noted here that a plurality of heaters can also be employed depending upon engineering requirements.  
         [0024]     Referring now to  FIG. 5 , the drawing illustrates a partial cross-sectional view of the inkjet chamber  10 . A meniscus  90  of ink  20  that is formed within the nozzle  30  occurs at the interface of the ink  20  to the air  100  that resides outside the confines of the inkjet chamber  10 . It should be readily evident to those skilled in the art that various types of mechanisms exist to eject ink  20  onto a medium such as paper. Typical ejection mechanisms such as fluid pumps, piezo-electric mechanisms, bi-metallic mechanisms and the like are all possible schemes that can be utilized for the ejection of ink  20 . Actuator box  140  is attached to output tube  150 . Output tube  150  is in turn affixed about nozzle  90  and connected to the chamber roof  40  of inkjet chamber  10 . Dashed separation line  170  denotes the functional separation between actuator box  140  and output tube  150 . This arrangement allows a flow of ink  20  to be possible through ink port  160 , actuator box  140 , and in turn through output tube  150  and nozzle  30 . Since these various ejection mechanisms can be readily integrated with the mixing mechanism previously described in  FIG. 5 , one of ordinary skill will recognize that these mechanisms all share the benefits of this method of ink circulation.  
         [0025]     Referring next to  FIG. 6 , drawn is a partial top view of inkjet chamber  10 . Chamber roof  40  incorporates nozzle  30 , and upper ejection heaters  50 . Also are shown two additional upper ejection heaters  50  diagrammed at 12:00 and 6:00 respectively. These are shown to illustrate that any plurality of heaters can be used depending on design needs and requirements. Shown within these upper ejection heaters  50  are shown the smaller circulation heaters  180 . The smaller circulation heaters  180  are drawn of smaller size simply for clarity of the figures and could be either bigger, smaller or of identical size to the upper ejection heaters  50 . A transition line  190  details a now permits a transition to  FIG. 7 .  
         [0026]     Referring to  FIG. 7 , detailed is a partial cross sectional view of inkjet chamber  10  that is functionally and descriptively linked to  FIG. 6 . It is understood from the teachings of  FIG. 4  that any plurality of upper ejection heaters  50  can actually be used due to variable design needs and requirements. It is also understood from the teachings of  FIG. 6  that it is possible to also incorporate the any plurality of circulation heaters  180  into a circulation design, and these circulation heaters  180  can exist in variable sizes, along with co-existing concurrently with the upper ejection heaters  50 . Both of these upper ejection heaters  50  and circulation heaters  180  can be placed above or below each other relative to the nozzle  30 . They could additionally be placed in positions that are inside or outside each other relative to the nozzle  30 . However, heaters that are equally placed relative to nozzle  30  are more effective that those that are not, because of the properties of heat transfer and fluid behavior.  
         [0027]     The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the scope of the invention.  
       PARTS LIST  
       [0000]    
       
           10  inkjet chamber  
           20  ink  
           30  nozzle  
           40  chamber roof  
           50  upper ejection heater  
           60  lower ejection heater  
           70  upper vapor bubble  
           80  lower vapor bubble  
           90  meniscus  
           100  air  
           110  heat gradient lines  
           120  tension gradient arrows  
           130  circulation arrows  
           140  actuator box  
           150  output tube  
           160  ink port  
           170  dashed separation line  
           180  circulation heaters  
           190  transition line