Patent Publication Number: US-2013242010-A1

Title: Method for venting air with a membrane

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     Reference is made to commonly assigned U.S. patent application Ser. No. ______ (Docket K000921) filed concurrently herewith by Brian Kwarta, entitled “Ink Supply Having Membrane for Venting Air,” the disclosure of which is herein incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to off-axis inkjet printers having a vent covered with a membrane for venting air out of tubing between a primary ink supply and a secondary ink supply and more particular to an apparatus for venting the air while eliminating degradation of the performance of the membrane due to wetting by ink and to eliminate moisture loss effecting ink concentration and thus system performance. 
     BACKGROUND OF THE INVENTION 
     In many types of fluidic systems a liquid is transferred from one location to another location, and air can sometimes get into the passageways through which liquid is transferred. This can degrade the ability to transfer liquid and even the performance of the system in some instances. A vent is typically provided in such systems for removing air when needed, and in some instances, an air permeable membrane is included in the vent path. Such a membrane allows air to pass through it, but does not allow the particular liquid to pass through it. The membrane can also keep particulates or other contaminants from entering the fluidic system. 
     An example of a fluidic system employing liquid transfer is an inkjet printer having a primary ink supply and a secondary ink supply. In a carriage printing system, for example, (whether for desktop printers, large area plotters, etc.) the printhead or printheads are mounted on a carriage that is moved back and forth past the recording medium in a carriage scan direction as the inkjet nozzles eject droplets of ink to make a swath of dots. At the end of the swath, the carriage is stopped; printing is temporarily halted and the recording medium is advanced. Then another swath is printed so that the image is formed swath by swath. The amount of ink that is stored on the carriage is typically sufficient for printing several hundred documents. For some inkjet carriage printers the nominal usage is on the order of a couple thousand pages per year. In such cases, having replaceable ink tanks on the carriage is a good approach. However, for printing systems that have heavier usage, that typically print high density ink coverage, or that print wide format documents, a better approach is to have a primary ink supply that is stationarily mounted on the printer, and a secondary ink supply that is mounted on the carriage. Ink is transferred from the primary ink supply to the secondary ink supply as needed. In this way, the amount of ink that is moved by the carriage is kept low (so that forces during carriage acceleration and deceleration can be acceptably low) and the user does not need to replace the ink very frequently. 
     To refill the secondary ink supply from the primary ink supply, flexible tubing is used, or alternatively the secondary ink supply can be moved near the primary ink supply on an as-needed basis and ink can be transferred through a needle and septum for example. In any case, sometimes air can get into the passageways between the primary ink supply and the secondary ink supply. For example, when the system is new, the passageways are full of air that needs to be removed for effective ink transfer. A vent is typically provided near the secondary ink supply so that air can be vented out as ink is transferred into the passageways. At other times during the life of the printer, air can also get into the fluid passageways such as during changing the printhead or the primary ink supply. 
     There are shortcomings that can occur in a conventional air vent in a liquid transfer system. First of all, volatile components of the ink can escape through the vent. For the aqueous based inks that are typically used in inkjet printers, water is typically a major component. Other ink components typically include colorants, humectants, surfactants, and sometimes polymers. The water is typically the least viscous component and the most volatile. As the water evaporates, the water vapor can escape through the air permeable membrane. As more moisture evaporates, the remaining ink becomes more viscous, which can affect the jetting performance. A second shortcoming that can occur is that if the ink is allowed to contact the air permeable membrane, it can obstruct the pores so that the ability of the air permeable membrane to let air through it is degraded. 
     Consequently, a need exists for a venting configuration that inhibits the escape of vapor from the volatile components of the liquid and that also inhibits the liquid from wetting the air permeable membrane. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to overcoming one or more of the problems set forth above. Briefly summarized, according to one aspect of the invention, the invention resides in a method for passing a liquid from a first location to a second location in which gas is selectively vented, the method includes passing the liquid from the first location; receiving the liquid in a conduit having a vent covered by a membrane for permitting gas to be vented; an inlet for receiving the liquid from the first location; and an outlet for passing the liquid to the second location; and selectively permitting and inhibiting flow of gas to the vent; wherein when the liquid in the conduit is below a predetermined threshold, a movable element is placed at a venting position that allows flow of gas to the membrane, and when the ink in the conduit is at or above the predetermined threshold, the movable element is placed at a sealing position that does not allow flow of gas to the membrane. 
     These and other objects, features, and advantages of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there is shown and described an illustrative embodiment of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features, and advantages of the present invention will become more apparent when taken in conjunction with the following description and drawings wherein identical reference numerals have been used, where possible, to designate identical features that are common to the figures, and wherein: 
         FIG. 1  is a perspective of an off-axis printing system of the present invention; 
         FIG. 2  is a schematic of the of the ink transfer device of the present invention illustrating ink in the flexible tubing; 
         FIG. 3  is a schematic of the of the ink transfer device of the present invention illustrating air in the flexible tubing; 
         FIG. 4  is a perspective of an ink transfer device of the present invention; 
         FIG. 5   a  is cross-sectional view of the ink transfer device of  FIG. 4 ; 
         FIG. 5   b  is a cross sectional view of  FIG. 5  taken along line  5   b;    
         FIG. 5   c  is a cross sectional view of  FIG. 5  taken along line  5   c;    
         FIG. 6  is a perspective of the ink transfer device of  FIG. 5  with the conduit removed; 
         FIG. 7  is a perspective of the ink transfer device of  FIG. 5  with the conduit and ball float removed; 
         FIG. 8  is a perspective of the ink transfer device of  FIG. 5  with the conduit, vent cap and air membrane removed; 
         FIG. 9  is a perspective of the ink transfer device of  FIG. 5  with the conduit and vent cap removed; 
         FIG. 10  is a perspective view of a plurality of ink interfaces of the present invention; and 
         FIG. 11  is a schematic view of the present invention illustrating a pump used for pumping ink. 
     
    
    
     While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter of the present invention, it is believed that the invention will be better understood from the following description when taken in conjunction with the accompanying drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     As used herein, words such as “upwardly,” “downwardly,” and the like are words of convenience for the position shown in the particular figure, but as easily understood by those skilled in the art, such directional terms are altered when the particular orientation is correspondingly altered. Also in the embodiment of an inkjet printer, air is typically the gas of interest that is being vented, but it is understood that, in the event that the environment contains some other gaseous element or used in an industrial environment application with other gases, such other gas also be vented. Therefore, the term gas as used herein can be either air, air plus one or more other gaseous elements, or some gaseous element without air. 
       FIG. 1  is a perspective of an interior portion of an off-axis printer  301  according to an embodiment of the present invention. Although ink is shown in the preferred embodiment, any liquid is suitable for the present invention. An inkjet printhead  250  is disposed on a carriage  200  and includes at least one nozzle array (not visible from the view of  FIG. 1 ) which directs ink droplets onto a recording medium  371 . A primary ink supply  265  is rigidly mounted on a support base  340 . The carriage  200  moves the printhead  250  back and forth across a print region  303  so that an image (such as letters “Brian”) can be printed on the recording medium  371 . At least one pressure-regulated secondary ink supply  210  is mounted on the printhead  250  which moves in conjunction with the printhead  250 . In this embodiment of  FIG. 1 , the primary ink supply  265  includes four ink supplies, each having a tubing connector  266 , although the number of ink supplies can vary depending on the particular design. The tubing connectors  266  extend inside the primary ink supplies and can extend substantially to the bottom of primary ink supply  265  so that ink can continue to be withdrawn as it is depleted. Alternatively, in other configurations (not shown) tubing connectors  266  can be located near the bottom of primary ink supply  265 , preferably when the primary ink supply  265  is located above the secondary ink supply  210  permitting gravity to transport the fluid. In the example of  FIG. 1 , a pump (not shown) is enclosed within the primary ink supply  265  for pumping the ink since the location of the primary ink supply  265  (at or below the elevation of its destination, secondary ink supplies  210 ) does not lend itself to gravitational flow. 
     Four secondary ink supplies  210  each include a conduit  315  (see  FIG. 2 ) and are mounted on the carriage  200  via the printhead  250  for supplying ink to printhead  250  so that the carriage  200  moves the secondary ink supplies  210  as well as the printhead  250 . As ink is used during printing and maintenance processes, ink is passed from the primary ink supply  265  through flexible tubing  267 , to the conduit  315  and eventually into the secondary ink supplies  210  for replenishing the secondary ink supplies  210 . It is noted for clarity that only one piece of the flexible tubing  267  is shown in  FIG. 1  so as not to obscure other features and that the details of the conduit  315  are omitted due to size constraints of  FIG. 1 , but are discussed in detail herein below. 
     A regulator chamber  212  is disposed extending into the secondary ink supply  210  for regulating the ink back pressure required by the ejector nozzles and in particular for damping out pressure spikes that occur as the carriage  200  is moved back and forth during printing. Pressure regulated secondary ink supply  210  can be integrated as part of printhead  250  or it can be detachable from printhead  250 . 
       FIG. 2  is a schematic illustrating the inkjet printer according to an embodiment of the present invention. The flexible tubing  267  connects the rigidly mounted primary ink supply  265  to the carriage mounted secondary ink supply  210 . The pressure regulator  212  (not shown in  FIG. 2 ) is typically included with the secondary ink supply  210  to maintain the ink pressure within a satisfactory range. If the ink pressure at the nozzle array  305  becomes too high, ink can drool out of the nozzles. If the ink pressure at the nozzle array  305  becomes too low, the nozzles cannot be refilled quickly enough and printing defects can occur. Typically, pressure is maintained between around negative 2 inches and negative 10 inches of water. 
     In the example of  FIG. 2 , the conduit  315  includes an inlet  310  attached to the tubing  267  for receiving the ink, an outlet  325  for passing the ink to the secondary ink supply  210 , a vent  320  for venting gas (typically air) from the conduit  315  and an interior portion  324  for providing a passageway for the ink to flow from the inlet  310  to the outlet  325 . It is noted that some of the components of the interior portion  324  are not discussed relative to  FIGS. 2 and 3  since the scaled size of these components as shown in  FIGS. 2 and 3  are small, but they are discussed later relative to  FIG. 5 . A hollow needle  330  is disposed within the secondary ink supply  210  and displaces the ball of a spring-loaded ball valve  335  in order to permit ink to flow into the secondary ink supply  210  as necessary. If the secondary ink supply  210  is removed, for example, in order to change the printhead  250 , the ball valve  335  provides a seal so that ink does not drain out of the flexible tubing  267 . 
     It is noted that the vent  320  is disposed above the inlet  310  and the outlet  325 , and the vent  320  is covered with an air permeable membrane  350  which is included as a portion of the vent path. A movable element  345 , such as a ball float (shown in this embodiment) a flap or other component capable of performing this function, is provided to inhibit the flow of gas (including air and water vapor from the ink) when the ink at the inlet  310  is at or above a predetermined threshold. In particular, if the ink level is high enough, as it usually will be during operation, the movable element  345  will be raised upwardly by the ink so that the movable element  345  seals against a sealing surface  360  that is below the air permeable membrane  350 . This inhibits the loss of water vapor from the ink through the air permeable membrane  350 . It is noted that, although a spherical ball float is shown, the ball float may be shaped as a cylinder, tapered cone, or any other shape as those skilled in the art can readily determine. It is noted that in the embodiment such as in  FIG. 2  where the primary ink supply  265  is at a higher elevation than the secondary ink supply  210 , the ink flows under the influence of gravity without the need for a pump. 
       FIG. 3  is similar to  FIG. 2 , but represents an instance where there is sufficient air in the flexible tubing  267  that the ink level in the interior portion  324  has dropped below a predetermined threshold. As a result the movable element  345 , which floats atop of the ink in the case of a ball float, is no longer pressed against the sealing surface  360 . As a result, air in the system (tubing  267  and conduit  315  having its inlet  310  and outlet  325 ) can escape through the vent  320 . For example, when an empty primary ink supply  265  is replaced with a full supply, ink flows through the flexible tubing  267 . The ink forces the air out of the flexible tubing  267  and subsequently out of the vent  320  and through membrane  350 . In addition to reduced loss of volatiles such as water vapor, a second advantage of the ink transfer apparatus of  FIGS. 2 and 3  is that as the ink comes through the flexible tubing  267  and displaces the air, ink is prevented from reaching the air permeable membrane  350  by the movable element  345 , such as the ball float, which seals against the sealing surface  350  as the ink level is raised. Thus the air permeable membrane  350  remains dry so that it continues to be optimally effective for venting gas but not the passage of the ink. 
     The ball float  345  is designed such that it will float in the ink. In other words, if the ink has a density of approximately  1  gram per cubic centimeter (similar to water), the ball float  345  is designed to have a density of less than  1  gram per cubic centimeter. To achieve the desire density, the ball float  345  can be hollow and air filled for example. 
     Referring to  FIG. 4 , there is shown the conduit  315  having the inlet  310  and the outlet  325 . An inlet coupling  365  is attached to the inlet  310  for permitting the flexible tubing  267  (see  FIGS. 1-3 ) to be attached to the inlet  310 . A vent cap  370  having a vent opening  375  covers a top portion of the vent  320  and the air permeable membrane  350  (both of which are not visible in  FIG. 4  due to being covered by the vent cap  370 ). An outlet coupling  380  is attached to the outlet  325  for permitting to be coupled to the secondary ink supply  210 . For convenience, the entire apparatus as shown in  FIG. 4  is referred as an ink transfer device  460  so that  FIGS. 6-9 , in which parts are selectively omitted for illustrating various components more clearly, have a point of reference. 
     Referring to  FIG. 5   a , there is shown the interior portion  324  of the conduit  315  for illustrating the air flow when the ball float  345  is in its venting position and components in the lower part of the interior portion  324  for selectively permitting and inhibiting flow to the secondary ink supplies  210 . A spring  385  and a sealing ball  390  function together to form the ball valve  335  (shown in  FIGS. 2 and 3 ). The upper portion of the spring  385  rests against a lip  400  for inhibiting upwardly movement beyond the lip  400 . The lower portion of the spring  385  rests against ball  390 . In  FIG. 5   a , the needle  330  (see  FIGS. 2 and 3 ) has not been inserted, and the sealing ball  390  is disposed on a sealing surface  410  for preventing ink to flow out of the interior portion  324 . When the needle  330  is inserted, the sealing ball  390  moves upwardly with the force of the needle  330  and the force of this upwardly movement urges the lower portion of the spring  385  upwardly overcoming the spring force, and an ink passageway is formed for permitting the ink to flow around the sealing ball  390  and into the pressure regulated secondary ink supplies  210 . 
     In the upper portion of the interior portion  324 , the ball float  345  rests on feet  430 , which are molded into the conduit  315 . As best seen in  FIG. 5   c , notched-out openings  440  are formed so that the gas or air flows therethrough. As best seen in  FIG. 5   b , the ball float  345  (shown in cross section) at its largest diameter is disposed inside an upper portion of the conduit  315  and shows a sufficient air path  450  formed around the ball float  345 . It is to be understood that when the ball float  345  is in the vent position as shown, gas (typically air) enters the inlet  310 , passes into the interior portion  324 , maneuvers through the open space of the spring  385 , through the opening  440  and air path  450 , out of the vent  320 , through the air permeable membrane  350  and finally through the opening  375  in the vent cap. 
     Referring to  FIG. 6 , the conduit  315  is removed so that the sealing position of the ball float  345  against the sealing surface  360  (hidden from view in  FIG. 6 ) is more clearly shown.  FIG. 7  is the same as  FIG. 6  except that the view is altered and the ball float  345  is removed so that the sealing surface  360  is shown. The view of  FIG. 7  also shows an opening  440  in the outlet coupling  380  for permitting the needle  330  to pass through the outlet coupling  380 .  FIG. 8  is the same as  FIG. 6  except that the vent cap  370  is removed and the ball float  345  is installed so that a membrane seat  455  of the vent  320  can be seen. The membrane seat  455  forms a seat upon which is disposed the air permeable membrane  350  as seen in  FIG. 9 . 
     Referring to  FIG. 10 , there is shown an ink interface  465  that includes a plurality of ink transfer devices  460  that are supported by an ink interface housing  468 . In this case, the ink is passed from the plurality of primary ink supplies  265  (as shown in  FIG. 1 ) into a plurality of ink transfer devices  460  each having a conduit with an inlet  310 ; an outlet  325 ; and the vent  320  covered by an air permeable membrane  350  (not visible in  FIG. 10 ). The flexible tubing  267  is used to connect the primary ink supplies  265  to each of the inlets  310 . Each of the outlets  325  respectively connects to a plurality of secondary ink supplies (see  FIG. 1 ). 
       FIG. 11  is the same as  FIGS. 2 and 3  except that the primary ink supply  265  is at an elevation at or lower than the elevation of the secondary ink supply  210  so that a pump  470  is connected to the flexible tubing  267  to pump the ink to the secondary ink supply  210 . 
     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 spirit and scope of the invention. 
     PARTS LIST 
     
         
           200  carriage 
           210  secondary ink supplies 
           212  pressure regulator 
           250  printhead 
           265  primary ink supply 
           266  tubing connector 
           267  tubing 
           301  off-axis printer 
           303  print region 
           305  nozzle array 
           310  inlet 
           315  conduit 
           320  vent 
           324  interior portion 
           325  outlet 
           330  needle 
           335  ball valve 
           340  support base 
           345  movable element (ball float) 
           350  air permeable membrane 
           360  sealing surface 
           365  inlet coupling 
           370  vent cap 
           371  recording medium 
           375  vent opening 
           380  outlet coupling 
           385  spring 
           390  sealing ball 
           400  lip 
           410  sealing surface 
           420  disk 
           430  feet 
           440  opening 
           450  air path 
           455  membrane seat 
           460  ink transfer device 
           465  ink interface 
           468  ink interface housing 
           470  pump