Patent Publication Number: US-6213596-B1

Title: Method and apparatus for reducing entrained air in ink for ink jet cartridges used in ink jet printers

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the invention. 
     The present invention relates to ink jet cartridges used in ink jet printers and, more particularly, to the filling of ink jet cartridges with ink. 
     2. Description of the related art. 
     Ink jet printers utilize cartridges that hold ink and which selectively dispense or eject the ink during printing. The cartridges are filled with ink after manufacture. Once the cartridge is filled with ink, the cartridge is sealed and ready for use. 
     Ink jet cartridges typically include a body or housing defining a chamber or cavity for the ink, a printhead in fluid communication with the ink chamber including a plurality of ink emitting nozzles, and circuitry coupled to the printhead and adapted to allow controlled ejection of ink from selected nozzles during printing. The printhead/circuitry includes heating elements associated with each nozzle that allow the ink to be ejected from the nozzle by forming drops. Thus, the ink is naturally heated in a very small, localized manner during the printing process. Ink jet printing is essentially a thermal ink ejecting system. 
     However, historical data shows that ink jet printing with a temperature offset or at a rate of drop ejection that causes a temperature offset may cause individual nozzles to not fire. It has been found that the resulting elevation in printing temperature releases air entrained within the ink which inhibits the formation of the ink drop and thus the ejection of the ink drop from the nozzle. This is due to the fact that the ink was supersaturated with air during the process of filling the ink cartridge. 
     The amount of air that dissolves in ink is a function of the temperature of the ink. The function is an inverse ratio with cooler ink holding or entraining more air than warmer ink. Thus as the printhead heats up during use, air or gas is liberated from the ink in the form of small air bubbles. These air bubbles may clog the nozzles of the printhead. 
     Conventional filling processes for ink cartridges are accomplished with room temperature ink. As a result, the ink becomes supersaturated with air. This further results in visible air bubbles at the nozzles of the printhead even at the point of manufacture let alone during printing. Degassing the ink prior to filling the ink cartridge will not appreciably solve the problem as air quickly re-dissolves into the ink during the fill process. 
     What is needed is a method to reduce the supersaturation of the ink with air during the ink cartridge fill process. 
     What is also needed is a method of reducing the amount of entrained air in ink for ink jet cartridges. 
     What is further needed is an apparatus for reducing the amount of entrained air in ink for ink jet cartridges during the cartridge filling process. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a method and apparatus for reducing the amount of air entrained in ink within ink jet printer cartridges. 
     In one form the present invention is a method for filling an ink jet cartridge with ink. The method includes providing ink suitable for ink jet printing, heating the ink to a temperature above ambient temperature to liberate air entrained in the ink and then filling the ink jet cartridge with the ink while substantially maintaining the elevated temperature of the ink. 
     The method preferably includes heating the ink with a temperature controlled resistance heater within a holding chamber baffled to allow the ink time to reach and maintain an appropriate temperature that is above ambient temperature. Resistance heated fill tubes in fluid communication with the holding chamber and the ink cartridge maintain the elevated temperature of the ink during filling of the ink cartridge. When the ink, now within the ink cartridge, reaches ambient temperature, it will be at or below an air saturation level of the ink for ambient conditions. 
     A target temperature for the ink is a temperature that is high enough such that the resulting supersaturation level for air in the ink is equivalent to the saturation level for air in ambient or room temperature ink. Once the ink cartridge is filled with the heated ink the ink cartridge is sealed. The ink is thereafter allowed to reach ambient temperature without further heating. 
     The method may also include utilizing an ultrasonic generator during heating to assist in the removal of air entrained in the ink. Prior to filling the ink cartridge and after heating the ink, the air evolved ink may also be stored in an accumulator/regulator tank. Such storage must be temporary as evaporation caused by the elevated temperature can change ink composition. Ink must then be re-heated prior to fill, or kept at reduced air pressure. 
     In another form, the present invention is an apparatus for filling an ink jet cartridge with ink. An ink holding tank is in fluid communication via a conduit with an air removal device adapted to elevate the temperature of the ink and liberate air entrained therein. The air removal device is in turn in fluid communication via a second conduit with an ink cartridge which is filled with the heated ink. 
     Preferably, the air removal device includes a temperature controlled resistance heater and a baffled ink holding chamber adapted to allow the ink time to reach and maintain a predetermined temperature. The second conduit may include a second resistance heater to help maintain the elevated temperature of the ink during transfer of the heated ink from the air removal device to the ink cartridge during filling. 
     An advantage of the present invention is that the ink within the ink cartridge will not form as many bubbles due to entrained air during printing. 
     Another advantage of the present invention is that agitation of the ink during the fill process does not result in excess entrained air. 
     Yet another advantage of the present invention is that clogs in ink jet cartridge printhead nozzles due to entrained air during printing are reduced. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawing wherein there is shown a diagrammatic view of an ink jet cartridge being filled with ink in accordance with the principles of the present invention. 
    
    
     The exemplification set out herein illustrates a preferred embodiment of the invention in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawing there is shown apparatus  10  for thermally elevating or heating ink above ambient temperature for ink jet printer cartridge  12  which is used in an ink jet printer (not shown). Ink jet printer cartridge  12  includes body  14  housing ink reservoir  16 . Ink reservoir  16  is in fluid communication with a printhead (not shown) as is known in the art for ejecting ink onto a print medium such as paper when installed into the ink jet printer. The printhead is controlled in a known manner when installed into the ink jet printer. 
     Apparatus  10  includes tank or reservoir  18  that holds ink  20  which is suitable for use in ink jet printing. Ink  20  is held at ambient temperature within tank  18 . Tank  18  is in fluid communication with conduit or tube  22  that is in fluid communication with pump  24 . Pump  24  is in fluid communication with conduit or tube  26  that is in fluid communication with air removal device  28 . Pump  24  is preferably controllable in a manner so as to allow flow rate control of ink  20 . Conduit  26  is in fluid communication with air removal device  28  such that ink  20  from tank  18  may be pumped therein. 
     Air removal device  28  includes tank  30  defining holding area  31  into which ink  20  is driven by pump  24 . Holding area  31  has baffles  33  therein and at least one heater coil  32  that is preferably a resistance type heating coil. Heater coil  32  is preferably coupled to controller/regulator  54  via communication line  56  for controlling and/or regulating the temperature of heater coil  32  and thus the ink held or circulating therein. Baffles  33  provide a circuitous route for the ink to allow the ink time to reach an elevated temperature to drive off or liberate air entrained within the ink as signified by the wavy arrows emanating from screen  34 . Air removal device  28  may include an ultrasonic generator (not shown) to aid in air removal. 
     Tank  30  is in fluid communication with pump  40  via conduit  36  that includes insulation  38 . Pump  40 , via conduit  42 , is in fluid communication with temporary holding or accumulation/regulation tank  46  where temperature elevated ink  48  is held. The heated, and thus air evolved ink may be temporarily stored in tank  46 . The ink is maintained at substantially the same elevated temperature as when it exited air removal device  28 . Conduit  42  includes insulation  44  in like manner as conduit  36 . Pump  40  like pump  24 , is preferably controllable to regulate the amount of ink flow therethrough and thus into tank  46 . Insulation  38  of conduit  36  and insulation  44  of conduit  42  helps maintain the elevated temperature of the ink after exiting air removal device  28 . Likewise, tank  46  may be heated or tank  46  may be thermally insulated to retain the heat in the ink. 
     Tank  46  is in fluid communication with reservoir  16  of ink cartridge  12  via conduit  50  in a known manner. Conduit  50  preferably includes heater coil  52  that is coupled to controller/regulator  54  via communication line  53  to aid in maintaining the elevated temperature of the ink while being carried within conduit  50  during the cartridge filling process. 
     Ink cartridge  12  is thus filled with air evolved ink in the following manner. Tank  18  holds a reserve of ink  20  that is at ambient temperature and thus can be supersaturated with air when pumped or moved. Pump  24  draws ink  20  from tank  18  via conduit  22  and sends ink  20  into air removal device  28  via conduit  26 . Once the ink is within tank  30 , heater coil  32  elevates the temperature of the ink preferably under control of regulator/controller  54 . A target temperature for the ink is one that is high enough such that the supersaturation level of air in the ink is equivalent to the saturation level of air in ink at ambient or room temperature. Baffles  33  impede the flow of ink therethrough to allow enough time for the ink to reach the elevated temperature and liberate the air entrained therein. 
     Pump  40  draws the temperature elevated ink from air removal device  28  through conduit  36  and into tank  46  via conduit  42 . Temperature elevated ink  48  within tank  46  is transferred into ink reservoir  16  of ink cartridge  12  through conduit  50  which maintains the elevated temperature of the ink by heater coil  52 . By maintaining the ink at the elevated temperature, the air driven off by air removal device  28  does not re-dissolve or saturate into the ink during the filling process. Once the ink has been received into ink reservoir  16 , cartridge  12  is removed from the filling position, and allowed to cool at room temperature. 
     During the fill process and cooling, some air will become saturated into the ink. However, the present method and apparatus limits the amount of air entrained in the ink by driving off the entrained air, reducing the amount of re-entrained air by maintaining the temperature of the ink during the filling process of the ink cartridge. assist removal of air from the ink, ultrasonic energy may be applied to the ink. The ultrasound waves speed air removal from the ink and the elevated temperature maintains that saturation level. The use of ultrasonic energy to speed air removal from ink is known, and thus is not described in further detail herein. 
     While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.