Patent Publication Number: US-7585063-B2

Title: Filter device and liquid drop ejecting device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims priority under 35 USC 119 from Japanese patent document, 2005-329946, the disclosure of which is incorporated by reference herein. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a filter device and a liquid drop ejecting device, and in more detail, to a filter device that removes refuse and foreign matter from liquid, and to a liquid drop ejecting device that ejects, from nozzles of a liquid drop ejecting head, liquid which has passed through the filter device and been supplied. 
   2. Description of the Related Art 
   In an inkjet recording device carrying out printing onto a recording medium by ejecting ink drops from nozzles of a recording head, in order to prevent deterioration in the ink ejecting performance or clogging of the nozzles due to refuse and foreign matter existing in the ink, a filter which removes the refuse and foreign matter in the ink is provided on the path by which ink is supplied to the recording head. 
   On the other hand, in inkjet recording heads in recent years, for the purpose of high-speed printing, there has been the trend to increase the number of nozzles provided at a single recording head, or to make the repetition frequency of ink jetting larger. Further, for the purpose of high image quality printing, the trend toward making the diameter of the nozzle smaller in order to make the jetted ink drop smaller has progressed. 
   For these reasons, the ability to remove even finer refuse and foreign matter, and a configuration having a small pressure loss, have been required of the aforementioned filter. To this end, trends toward making the mesh of the filter finer and making the surface area of the filter larger have advanced. However, if the surface area of the filter is made to be large, the inkjet recording head becomes large due to the placement of the filter. As a measure for addressing this, it has been thought to suppress the increase in the size of the inkjet recording head by dividing the filter into plural sections and placing the plural sections in parallel. 
   However, in the above-described structure, the flow path at the downstream side of the filter branches off in plural directions. Therefore, in a case in which an air bubble which has arisen in the ink stops in one of the flow paths, the flow speed in the other flow path increases. The ability to remove (ability to discharge) the air bubble in the flow path in which the air bubble has stopped worsens, which leads to a deterioration in the ink ejecting performance. 
     FIG. 14  is a drawing which shows, schematically and in a simplified manner, a filter unit (filter device). 
   As shown in  FIG. 14 , a filter unit  910  is provided at an ink flow path between an ink tank (not shown) and an inkjet recording head  902 . The inkjet recording head  902  ejects ink drops from nozzles (not shown) formed in a nozzle surface  904  onto a recording sheet which is a recording medium, so as to form an image on the recording sheet. 
   The filter unit  910  has a first ink chamber  912  and a second ink chamber  914 . The first ink chamber  912  and the second ink chamber  914  are partitioned by a filter  916 . 
   An ink supply path  924  and an ink circulating path  926  communicate with the first ink chamber  912 . An ink feed-out path  930  communicates with the second ink chamber  914 . The ink in the ink tank (not shown) is supplied from the ink supply path  924 , and is fed to the inkjet recording head  902  from the ink feed-out path  930 . Further, the ink in the first ink chamber  912  can circulate to the ink tank from the ink circulating path  926 . 
   Note that the first ink chamber  912  corresponds to an outer chamber, whereas the second ink chamber  914  corresponds to an inner chamber. 
   First, the discharging of air at the time when ink is initially filled into the filter unit  910  will be described. 
   As shown in  FIGS. 15(   a ) and ( b ), ink is poured into the first ink chamber  912  from the ink supply path  924 , and the ink is gradually filled into the first ink chamber  912  and the second ink chamber  914 . 
   At this time, when the lower end portion of the filter  916  which partitions the first ink chamber  912  and the second ink chamber  914  is submerged in the ink, the ink seeps toward the upper portion of the filter  916  due to capillary action. The entire surface of the filter  916  is wet by the ink before the first ink chamber  912  and the second ink chamber  914  are filled with ink. 
   When the entire surface of the filter  916  is wet by ink, the entry and exit of air between the first ink chamber  912  and the second ink chamber  914  via the filter  916  is impeded. Therefore, air within the second ink chamber  914  cannot be discharged-out through the ink circulating path  926 . Accordingly, the air within the second ink chamber  914  can only be discharged-out through the inkjet recording head  902  which has a high discharge resistance. 
   Thus, as shown in  FIG. 15(   c ), the liquid surfaces of the first ink chamber  912  and the second ink chamber  914 , which had been maintained the same until then, are no longer the same. The first ink chamber  912 , from which air is discharged from the ink circulating path  926  which has low resistance, is filled with ink first. 
   As shown in  FIG. 15(   d ), when the first ink chamber  912  is filled with ink, the pouring of ink into the second ink chamber  914  begins again. 
   Then, as shown in  FIG. 15(   e ), when the liquid surface reaches the height of a feed-out path entrance  930 A of the ink feed-out path  930 , ink is discharged from the ink feed-out path  930 , and the supply of ink to the inkjet recording head  902  begins. 
   At this time, because the cross-sectional surface area of the ink feed-out path  930  is large, the ink goes along the wall surface of the ink flow path  930  (like a waterfall), and flows into the inkjet recording head  902 . In other words, the ink flows into the inkjet recording head  902  in a state in which no meniscus is formed. 
   Therefore, as shown in  FIG. 15(   f ), the ink is fed to the inkjet recording head  902  in a state in which ink and air are mixed together. 
   A large amount of air K remains at the ceiling portion of the second ink chamber  914 . Due to the filter  916 , it is difficult for this air K to move to the first ink chamber  912 , and therefore, the air K continues to remain in the filter unit  910 . 
   As shown in  FIG. 16 , because the feed-out path entrance  930 A of the ink feed-out path  930  opens in a vicinity of the ceiling portion, the air K which is remaining is in a vicinity of the feed-out path entrance  930 A. 
   Thus, at the time of an ink suction operation which sucks the ink from the nozzles of the inkjet recording head  902 , or the like, due to the ink which is flowing as shown by arrow Y 9 , the air which is remaining becomes fine air bubbles which enter into the ink feed-out path  930  from the feed-out path entrance  930 A and flow into the inkjet recording head  902 . 
   When air flows into the inkjet recording head  902  together with the ink in this way, the reliability of the inkjet recording head  902  markedly deteriorates. 
   Accordingly, it is desirable to make it difficult for air remaining in a filter unit to flow-out. 
   SUMMARY OF THE INVENTION 
   The present invention has been made in view of the aforementioned, and provides a filter device and a liquid drop ejecting device which make it difficult for air remaining within the filter device to flow-out. 
   A filter device of an aspect of the present invention has: a supply path into which liquid flows; a first liquid chamber communicating with the supply path; a second liquid chamber communicating with the first liquid chamber; a first discharge path which communicates with the second liquid chamber, and from which liquid is discharged; and a filter provided between the first liquid chamber and the second liquid chamber, wherein an intermediate portion of the first discharge path between an entrance and an exit of the first discharge path is higher than the entrance and the exit, and the entrance of the first discharge path opens in a vicinity of a floor portion of the second liquid chamber. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An exemplary embodiment of the present invention will be described in detail based on the following figures, wherein: 
       FIG. 1  is a drawing schematically showing the structure of a filter unit relating to an exemplary embodiment of the present invention, and schematically showing main portions of an inkjet recording device using the filter unit; 
       FIG. 2  is a drawing schematically showing the structure of the filter unit relating to the exemplary embodiment of the present invention; 
       FIG. 3  is a drawing showing, in order, states at a time of filling ink into the filter unit of  FIG. 1 ; 
       FIG. 4  is a drawing showing the flow of ink in the filter unit of  FIG. 1  into which ink has been filled; 
       FIG. 5  is a table comparing the performances of the filter unit of  FIG. 1  and a conventional filter unit with respect to various types of conditions; 
       FIG. 6  is a drawing showing a first modified example of the filter unit relating to the exemplary embodiment of the present invention; 
       FIG. 7  is a drawing showing a second modified example of the filter unit relating to the exemplary embodiment of the present invention; 
       FIG. 8  is a perspective view showing the exterior of a filter unit of a first example; 
       FIG. 9  is an exploded perspective view showing a disassembled state of the filter unit of  FIG. 8 ; 
       FIG. 10A  is a cross-sectional view taken along line A-A of  FIG. 10B , and showing a cross-section of the filter unit of  FIG. 8 ; 
       FIG. 10B  is a cross-sectional view taken along line B-B of  FIG. 10A , and showing a cross-section of the filter unit of  FIG. 8 ; 
       FIG. 11  is a perspective view showing the exterior of a filter unit of a second example; 
       FIG. 12  is an exploded perspective view showing a disassembled state of the filter unit of  FIG. 11 ; 
       FIG. 13A  is a cross-sectional view taken along line A-A of  FIG. 13B , and showing a cross-section of the filter unit of  FIG. 11 ; 
       FIG. 13B  is a cross-sectional view taken along line B-B of  FIG. 13A , and showing a cross-section of the filter unit of  FIG. 11 ; 
       FIG. 14  is a drawing schematically showing the structure of a conventional filter unit; 
       FIG. 15  is a drawing showing, in order, states at a time of filling ink into the conventional filter unit of  FIG. 14 ; and 
       FIG. 16  is a drawing showing the flow of ink in the conventional filter unit of  FIG. 14  into which ink has been filled. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   An exemplary embodiment of the present invention will be described in detail hereinafter with reference to the drawings. 
   As shown in  FIG. 1 , in an inkjet recording device  01 , a filter unit  10  is provided at an ink flow path between an ink tank (not shown) and an inkjet recording head  02 . The inkjet recording head  02  ejects ink drops (represented by the dotted-line arrows in  FIG. 1 ) from nozzles (not shown) formed in a nozzle surface  04 , onto a recording sheet P which is a recording medium, so as to form an image on the recording sheet P. 
   The filter unit  10  has a first ink chamber  12  and a second ink chamber  14 . The first ink chamber  12  and the second ink chamber  14  are partitioned by a filter  16 . 
   The filter  16  vertically partitions the region between a floor portion  10 A and a ceiling portion  10 B. Accordingly, the filter  16  is disposed at an orientation substantially orthogonal to the nozzle surface  04  of the inkjet recording head  02  in which the nozzles are formed. Therefore, even though the surface area of the filter  16  is made to be large, the surface area projected onto the nozzle surface  04  is not large. 
   The filter  16  is formed from a lower filter  18  and an upper filter  20 , and a partitioning portion  22  is provided therebetween. Note that the partitioning portion  22  is positioned slightly downward from the ceiling portion  10 B. 
   An ink supply path  24  and an ink circulating path  26  communicate with the first ink chamber  12 . An ink feed-out path  30  communicates with the second ink chamber  14 . Ink of an ink tank (not shown) is supplied from the ink supply path  24 , passes through the first ink chamber  12 , the filter  16 , and the second ink chamber  14 , and thereafter, is fed from the ink feed-out path  30  to the inkjet recording head  02 . Further, the ink of the first ink chamber  12  can be circulated to the ink tank from the ink circulating path  26 . 
   A supply path exit  24 B of the ink supply path  24  opens in a vicinity of above the floor portion  10 A. Further, a flow regulating plate  36  stands erect from the floor portion  10 A, between the ink supply path  24  and the filter  16 . A top portion  36 A of the flow regulating plate  36  extends further upward than the supply path exit  24 B of the ink supply path  24 . Further, a circulating path entrance  26 A of the ink circulating path  26  opens in the ceiling portion  10 B. 
   The ink feed-out path  30  is formed overall in the shape of an upside-down “U”. A feed-out path entrance  30 A of the ink feed-out path  30  opens in a vicinity of above the floor portion  10 A. The cross-sectional surface area of the ink feed-out path  30  is greater than or equal to 3 mm 2  and less than or equal to 12 mm 2 . 
   The ceiling portion  10 B is an inclined surface which rises from the second ink chamber  14  toward the first ink chamber  12 . The circulating path entrance  26 A of the ink circulating path  26  opens at the highest position of the ceiling portion  10 B. 
   The height of a convex peak portion  30 C of the ink feed-out path  30  (the highest position of the ink feed-out path  30 ) is higher than the circulating path entrance  26 A of the ink circulating path  26 . 
   Accordingly, as shown in  FIG. 2 , the order of heights, from the highest, is as follows: (1) the convex peak portion  30 C of the ink feed-out path  30 &gt;(2) the circulating path entrance  26 A of the ink circulating path  26 &gt;(3) a bottom end portion  20 A of the upper filter  20 , and separated greatly therefrom, (4) the top portion  36 A of the flow regulating plate  36 &gt;(5) the supply path exit  24 B of the ink supply path  24 =the feed-out path entrance  30 A of the ink feed-out path  30 . 
   Operation of the present exemplary embodiment will be described next. 
   First, the discharging of air bubbles at the time when ink is initially filled into the filter unit  10  (initial filling) will be described. 
   As shown in  FIGS. 3(   a ) and ( b ), ink is poured into the first ink chamber  12  of the filter unit  10  from the ink supply path  24 , and the ink is gradually filled into the first ink chamber  12  and the second ink chamber  14 . 
   At this time, when the lower end portion of the filter  16  which partitions the first ink chamber  12  and the second ink chamber  14  is submerged in the ink, the ink seeps toward the upper portion of the filter due to capillary action. However, the filter  16  is formed from the upper filter  20  and the lower filter  18 , and the partitioning portion  22  is provided therebetween. Accordingly, the lower filter  18  is wet by the ink, but because the seeping of the ink stops at the partitioning portion  22 , the upper filter  20  is maintained in a state of not being wet. Therefore, air can enter and exit between the first ink chamber  12  and the second ink chamber  14  via the upper filter  20 . Accordingly, the air within the second ink chamber  14  is discharged from the ink circulating path  26  via the first ink chamber  12 . 
   Accordingly, as shown in  FIG. 3(   c ), the first ink chamber  12  and the second ink chamber  14  are gradually filled in a state in which the same liquid surfaces are maintained therein. Further, ink is filled into the ink feed-out path  30  as well in a state in which the substantially the same liquid surface as in the first ink chamber  12  and the second ink chamber  14  is maintained therein. Note that the air discharge resistance of the ink feed-out path  30 , which is connected to the inkjet recording head  02  (see  FIG. 1) , is greater than that of the ink circulating path  26 . Because the air within the ink feed-out path  30  comes-out through the inkjet recording head  02 , the liquid surface is slightly lower than in the first ink chamber  12  and the second ink chamber  14 . 
   As shown in  FIG. 3(   d ), when the liquid surface of the ink exceeds the partitioning portion  22  and reaches the bottom end of the upper filter  20 , the ink seeps toward the upper portion of the upper filter  20  due to capillary action, and the entire surface of the upper filter  20  is wet with ink before the first ink chamber  12  and the second ink chamber  14  are filled with ink. At this time, for the first time, the flow of air between the first ink chamber  12  and the second ink chamber  14  is cut-off. 
   However, as shown in  FIG. 3(   e ), ink is already sufficiently filled in the second ink chamber  14  at this time, and the amount of air K remaining within the second ink chamber  14  is very small (compare  FIG. 3(   e ) and  FIG. 15(   e )). 
   As shown in  FIG. 3(   f ), when the first ink chamber  12  and the second ink chamber  14  are filled with ink, the supply of ink from the ink feed-out path  30  to the inkjet recording head  02  begins. At this time, because the cross-sectional surface area of the ink feed-out path  30  is greater than or equal to 3 mm 2  and less than or equal to 12 mm 2 , the ink is fed with a meniscus M thereof being maintained as is. Therefore, ink is poured into the inkjet recording head  02  in a state in which hardly any air is mixed therein (compare  FIGS. 3(   e ), ( f ), and ( g ) with  FIGS. 15(   e ) and ( f )). Moreover, as shown in  FIGS. 3(   g ) and ( h ), only a slight amount of the air K remains. 
   The flow of the ink after filling will be described next. 
   As shown in  FIG. 4 , because the feed-out path entrance  30 A of the ink feed-out path  30  opens in a vicinity of the floor portion  10 A, the remaining air K is very far from the feed-out path entrance  30 A of the ink feed-out path  30 . Therefore, at the time of an ink suction operation which sucks ink from the nozzles of the inkjet recording head  02 , or the like, there are hardly any cases in which the air bubble K remaining in the second ink chamber  14  enters into the ink flow path  30  from the flow path entrance  30 A. 
   In this way, there is very little of the air which remains in the filter unit  10 , and moreover, there are very few occurrences of air (air bubbles) flowing-out together with the ink to the inkjet recording head  02 . Accordingly, reliability does not deteriorate due to air remaining in the filter unit  10  flowing-out and flowing into the inkjet recording head  02 . 
   Further, it is best that the ink be fed from the first ink chamber  12  to the second ink chamber  14  through as wide of a region of the filter  16  as possible. Accordingly, in the present exemplary embodiment, by creating a rising flow in the flow of the ink by the flow regulating plate  36  as shown by arrow Y, the ink can be prevented from flowing from the supply path exit  24 B of the ink supply path  24  along the floor portion  10 A to the feed-out path entrance  30 A of the ink feed-out path  30 , and the ink is fed from the first ink chamber  12  to the second ink chamber  14  through as wide a region of the filter  16  as possible. 
     FIG. 5  is a table which compiles various conditions required of a filter unit (filter device) for the inkjet recording head  02  (ink drop ejecting head). Note that FU in  FIG. 5  is an abbreviation for filter unit, and JS is an abbreviation for inkjet recording head. 
   As can be understood from this table, the conventional filter unit cannot sufficiently satisfy some of these various conditions. In contrast, the filter unit  10  of the present exemplary embodiment can sufficiently satisfy all of these conditions. As a result, the reliability and maintainability of the inkjet recording head  02  can be greatly improved. 
   Note that the present invention is not limited to the above-described exemplary embodiment. 
   For example, as shown in  FIG. 6 , a filter unit  810  of a first modified example, which uses the conventional filter  916  which is not separated into an upper portion and a lower portion, may be used. 
   In this structure, when the lower end portion of the filter  916  which partitions the first ink chamber  12  and the second ink chamber  14  is submerged in the ink, the ink seeps toward the upper portion of the filter  916  due to capillary action. The entire surface of the filter  916  is wet by the ink before the first ink chamber  12  and the second ink chamber  14  are filled with ink. When the entire surface of the filter  916  is wet by ink, the entry and exit of air between the first ink chamber  12  and the second ink chamber  14  via the filter  916  is impeded. Therefore, air within the second ink chamber  14  cannot be discharged-out through the ink circulating path  26 . Accordingly, the air within the second ink chamber  14  can only be discharged-out through the inkjet recording head  02  which has a high discharge resistance. 
   Accordingly, the first ink chamber  12 , from which air is discharged from the ink circulating path  26  which has little resistance, is filled with ink first. Therefore, the second ink chamber  14  is filled with ink after the first ink chamber  12  is filled with ink. Accordingly, the amount of air remaining in the second ink chamber  14  increases more than in the filter unit  10  of the above-described exemplary embodiment. 
   However, as described above, because the feed-out path entrance  30 A of the ink feed-out path  30  opens in a vicinity of the floor portion  10 A, the remaining air K is very far from the feed-out path entrance  30 A of the ink feed-out path  30 . Accordingly, at the time of an ink suction operation which sucks ink from the nozzles of the inkjet recording head  02 , or the like, there are hardly any cases in which the air K remaining in the second ink chamber  14  enters into the ink flow path  30  from the flow path entrance  30 A (see  FIG. 4 ). 
   Moreover, as shown in  FIG. 7 , a filter unit  710  of a second modified example, which does not have the ink circulating path  26 , may be used. In this case, the discharging of the air of the first ink chamber  12  is carried out from an ink supply path  724 . 
   Examples of the present invention will be described next. 
   FIRST EXAMPLE 
   As shown in  FIG. 8 , a filter unit  110  of a first example is formed overall in the shape of a flat, substantially trapezoidal box. The filter unit  110  is structured as a unit by the respective structural members thereof being assembled integrally. In this state of being made into a unit, the filter unit  110  is used by being connected to an ink flow path between an inkjet recording head and an ink cartridge which are installed in an inkjet recording device. 
   As shown in  FIG. 9  as well, the filter unit  110  has a case main body  150 , two side plate members  172 , and two filters  116 . 
   The both side surfaces of the case main body  150  are open, and the interior thereof is hollow. The left portion and the right portion at the top surface of the case main body  150  are substantially horizontal surfaces, and the right portion is slightly higher than the left portion. An inclined surface, which is inclined upwardly from the left side toward the right side, is formed between the left portion and the right portion. 
   A partitioning wall  152  is formed within the case main body  150 , with predetermined intervals between the partitioning wall  152  and a ceiling portion  150 B and between the partitioning wall  152  and a front inner wall surface portion  150 C. The width of the partitioning wall  152  is narrower than the width of the case main body  150 . The filters  116  are affixed to the partitioning wall  152 . Accordingly, the two filters  116  are disposed so as to oppose one another and be substantially parallel to one another. The side plate members  172  are affixed to the both side surfaces of the case main body  150 . Note that  FIG. 9  illustrates a state in which only one of the filters  116  and only one of the side plate members  172  are affixed. 
   Due to such a structure, as shown in  FIGS. 10A and 10B  as well, an inner chamber  114  which is sandwiched between the filters  116  is formed, and an outer chamber  112  is formed at the outer side of the inner chamber. Namely, the inner chamber  114  is sandwiched by the outer chamber  112 . Further, the filters  116  are provided at the boundary surfaces of the inner chamber  114  and the outer chamber  112 . Note that the outer chamber  112  corresponds to the first ink chamber  12  described in the above-described exemplary embodiment, whereas the inner chamber  114  corresponds to the second ink chamber  14  (refer to  FIG. 1 ). 
   The filter  116  is structured by an upper filter  120  and a lower filter  118 , and a partitioning portion  122  which partitions the upper filter  120  and the lower filter  118 . 
   A partitioning wall  154  is provided between the front portion of the partitioning wall  152  and the front inner wall surface portion  150 C. The partitioning wall  154  is suspended downward from the ceiling portion  150 B, and is formed such that there is an interval between a floor portion  150 A and the bottom end of the partitioning wall  154 . The width of the partitioning wall  154  is the same as the width of the case main body  150 . The space between the partitioning wall  154  and the front inner wall surface portion  150 C is an ink supply path  124 . A supply path exit  124 B is the gap between the bottom end of the partitioning wall  154  and the floor portion  150 A. 
   A flow regulating plate  136  is provided between the partitioning wall  152  and the partitioning wall  154 . The flow regulating plate  136  stands upright from the floor portion  150 A, and the top end of the flow regulating plate  136  is positioned higher than the supply path exit  124 B. 
   A cylindrical tube portion  160  projects at the left portion of the top surface of the case main body  150 . The tube portion  160  communicates with the ink supply path  124 . 
   A cylindrical tube portion  162  projects at the right portion of the top surface of the case main body  150  as well. The tube portion  162  opens at the ceiling portion  150 B. The tube portion  162  is an ink circulating path  126 , and the opening of the ceiling portion  150 B is a circulating path entrance  126 A. 
   An ink feed-out path  130 , which is configured as a pipe being bent in an upside-down U-shape, is disposed in a vicinity of the substantial center of the inner chamber  114 . A feed-out path entrance  130 A, which is one end portion of the ink feed-out path  130 , opens slightly above the floor portion  150 A. The other end portion of the ink feed-out path  130  passes through the floor portion  150 A and projects-out, and is connected to an inkjet recording head (not shown). Further, a convex portion of the ink feed-out path  130  passes through the ceiling portion  150 B and projects-out. Accordingly, a height of a convex peak portion  130 C of the ink feed-out path  130  (the highest position of the ink feed-out path  130 ) is higher than the circulating path entrance  126 A of the ink circulating path  126 . 
   Note that the cross-sectional surface areas of the ink supply path  124 , the ink circulating path  126 , and the ink feed-out path  130  are 4.9 mm 2 . (The ink feed-out path  130  is a circular conduit of an inner diameter of 2.5 mm.) A meniscus is stably maintained in the ink flowing therethrough. 
   The flow of ink of the filter unit  110  will be described next, although some of the description will be redundant with that of the exemplary embodiment. 
   Ink of an ink tank (not shown) is fed to the ink supply path  124  from the tube portion  160 . The ink exits from the supply path exit  124 B of the ink supply path  124 . The flow of the ink is changed to an upward flow by the flow regulating path  136  (refer to arrow Y 1  in  FIG. 10A ). Then, the inner chamber  114  and the outer chamber  112  are filled with ink. At this time, when the lower end portions of the filters  116  which separate the inner chamber  114  and the outer chamber  112  are immersed in the ink, the ink seeps toward the upper portions of the filters due to capillary action. However, the filters  116  are formed from the upper filters  120  and the lower filters  118 , and the partitioning portions  122  are provided therebetween. Accordingly, although the lower filters  118  are wet by ink, because the seepage of ink stops at the partitioning portions  22 , the upper filters  120  are maintained in a state of not being wet. Thus, air can enter and exit between the inner chamber  114  and the outer chamber  112  via the upper filters  120 . Accordingly, the air within the inner chamber  114  is discharged-out from the ink circulating path  126  via the outer chamber  112  (corresponding to  FIGS. 3(   a ) and ( b ) of the exemplary embodiment). 
   Accordingly, the inner chamber  114  and the outer chamber  112  are gradually filled in a state in which the liquid surfaces thereof are maintained the same. Further, ink is filled in the ink feed-out path  130  as well, in a state in which the liquid surface thereof is maintained substantially the same as in the inner chamber  114  and the outer chamber  112  (corresponding to  FIG. 3(   c ) of the exemplary embodiment). 
   When the liquid surface of the ink exceeds the partitioning portions  122  and reaches the lower ends of the upper filters  120 , the ink seeps toward the upper portions of the upper filters  120  due to capillary action, and the entire surfaces of the upper filters  120  are wet with ink before the inner chamber  114  and the outer chamber  112  are filled with ink. This is the first time that the flow of air between the inner chamber  114  and the outer chamber  112  is cut-off (corresponding to  FIG. 3(   d ) of the exemplary embodiment). 
   However, ink is already sufficiently filled in the inner chamber  114  at this time, and the amount of air remaining in the inner chamber  114  is very small (corresponding to  FIG. 3(   e ) of the exemplary embodiment). 
   When the outer chamber  112  and the inner chamber  114  are filled with ink, the supply of ink from the ink feed-out path  130  to the inkjet recording head begins. At this time, because the cross-sectional surface area of the ink feed-out path  130  is 4.9 mm 2  (an inner diameter of 2.5 mm), the ink is fed with the meniscus of the ink maintained as is. Therefore, the ink is poured into the inkjet recording head in a state in which hardly any air is mixed therein (corresponding to  FIG. 3(   f ) of the exemplary embodiment). Moreover, only a slight amount of air remains in the inner chamber  114  (corresponding to  FIGS. 3(   g ) and ( h ) of the exemplary embodiment). 
   The feed-out path entrance  130 A of the ink feed-out path  130  opens in a vicinity of the floor portion  150 A. Accordingly, the air which remains in a vicinity of the ceiling portion  150 B of the inner chamber  114  is very far from the feed-out path entrance  130 A of the ink feed-out path  130 . Therefore, at the time of an ink suction operation which sucks ink from the nozzles of the inkjet recording head, or the like, there are hardly any cases in which the remaining air enters into the ink feed-out path  130  from the feed-out path entrance  130 A. 
   Further, due to the structure in which the inner chamber  114  is sandwiched by the outer chamber  112 , the surface area of the filters  116  can be made to be large. 
   SECOND EXAMPLE 
   As shown in  FIG. 11 , a filter unit  210  of a second example is formed overall in the shape of a cylindrical tube. Further, in the same way as in the first example, the filter unit  210  is structured as a unit by the respective structural members thereof being assembled integrally. In this state of being made into a unit, the filter unit  210  is used by being connected to an ink flow path between an inkjet recording head and an ink cartridge which are installed in an inkjet recording device. 
   As shown in  FIGS. 12 ,  13 A and  13 B, the filter unit  210  is formed from a lid member  270 , a case main body portion  250 , and a filter  216 . 
   The bottom surface of the lid member  270  opens in a circular shape, and the interior of the lid member  270  is shaped as a hollow cylindrical tube. A tube portion  260  and a tube portion  262  project from the top portion of the lid member  270 . The tube portion  260  extends to the interior, and is an ink supply path  224 . The opening thereof is a supply path exit  224 B. The tube portion  262  is an ink circulating path  226 , and an opening of a ceiling portion  270 B is a circulating path entrance  226 A. 
   The case main body portion  250  has a disc-shaped floor portion  250 A. A cylindrical tube portion  254 , in whose side surface are formed plural rectangular openings  252  which are long in the vertical direction, is provided at the floor portion  250 A. The top portion of the cylindrical tube portion  254  is lower than the ceiling portion  270 B of the lid member  270 . 
   An ink feed-out path  230 , which is configured as a pipe which is bent in an upside-down U-shape, is disposed within the cylindrical tube portion  254 . A feed-out path entrance  230 A, which is one end portion of the ink feed-out path  230 , opens slightly above the floor portion  250 A. The other end portion of the ink feed-out path  230  passes through the floor portion  250 A and projects-out, and is connected to an inkjet recording head (not shown). Further, a flow regulating plate  236  stands erect from the floor portion  250 A in the form of a concentric circle at the outer side of the cylindrical tube portion  254 . 
   After the filter  216  is affixed around the cylindrical tube portion  254 , the lid member  270  is placed on and joined to the case main body portion  250 . 
   When assembly has been carried out in this way, an inner chamber  214  of the interior of the cylindrical tube portion  254  is within an outer chamber  212  which is between the cylindrical tube portion  254  and the lid member  270 . Note that the inner chamber  214  corresponds to the second ink chamber  14  of the exemplary embodiment, whereas the outer chamber  212  corresponds to the first ink chamber  12  of the exemplary embodiment. 
   The filter  216 , which separates the inner chamber  214  and the outer chamber  212 , is structured from an upper filter  220  and a lower filter  218 , and a partitioning portion  222  which partitions the upper filter  220  and the lower filter  218 . 
   Description of the flow of ink will be omitted as it would be redundant with that of the exemplary embodiment and the first example. 
   Due to such a structure, the ink of the ink supply path  224  creates an upward flow due to the flow regulating plate  236  as shown by arrow Y 5  of  FIG. 13A , and the ink flows over the entire periphery of the outer chamber  212  as shown by arrows Y 6  in  FIG. 13B . Moreover, the ink flows from the openings  252  through the filter  216  to the inner chamber  214  as shown by arrows Y 7 . 
   Due to the cylindrical configuration, the ink flows-in from the outer chamber  212  through the filter  216  into the inner chamber  214 , and the flow speed of the ink heading toward the ink feed-out path  230  is the same in all directions. In this way, there are fewer stagnant portions which arise at the time when the ink flows, and the ability to discharge air is good. 
   Note that the present invention is not limited to the above-described exemplary embodiment and examples. 
   For example, the filter device is not limited to an inkjet recording device, and can also be applied to other liquid drop ejecting devices such as a pattern forming device which ejects liquid drops in order to form a pattern of a semiconductor or the like, or the like. 
   In the filter device of the present invention, the liquid flows from the supply path into the first liquid chamber, and then flows into the second liquid chamber. At this time, when the liquid flows from the first liquid chamber to the second liquid chamber, the liquid passes through the filter provided between the first liquid chamber and the second liquid chamber. Foreign matter, such as refuse or the like, existing in the liquid is thereby caught by the filter, and is removed from the liquid. Then, the liquid is discharged from the first discharge path. 
   The intermediate portion of the first discharge path between the entrance and the exit of the first discharge path, is higher than the entrance and the exit. Further, the entrance of the first discharge path opens in a vicinity of the floor portion of the second liquid chamber. Because the air remaining in the second liquid chamber is at the ceiling portion at the upper portion, the entrance is far from the remaining air. Accordingly, there are hardly any cases in which the air remaining in the second liquid chamber flows-in from the entrance of the first discharge path. 
   If the entrance is simply positioned below, i.e., if the entrance is positioned upper than the intermediate portion, in a case in which the flow of liquid stops, the liquid surface of the liquid in the filter device falls to a vicinity of the entrance. Accordingly, the filter device returns to a state in which hardly any liquid is filled in the filter device. 
   However, because the intermediate portion is higher than the entrance, the liquid surface only falls to the highest position portion of the intermediate portion. Accordingly, even if the entrance of the first discharge path is positioned below, a state in which liquid is filled in the filter device can be maintained. 
   The filter device of the present invention may have a second discharge path which communicates with the first liquid chamber. 
   In the above-described filter device, the second discharge path communicates with the first liquid chamber. Accordingly, because the air of the first liquid chamber can be discharged-out from the second discharge path, there is little remaining of air in the first liquid chamber. 
   Further, in the filter device of the present invention, an entrance of the second discharge path may open at one of a ceiling portion of the first liquid chamber and a vicinity of the ceiling portion. 
   In the above-described filter device, the entrance of the second discharge path opens at the ceiling portion of the first liquid chamber, or in a vicinity of the ceiling portion. Because air remains in a vicinity of the ceiling portion of the second liquid chamber, it is easy for the air to be discharged-out from the entrance of the second discharge path. 
   In the filter device of the present invention, the first discharge path may be formed overall in an upside-down U-shape. 
   In the above-described filter device, by forming the first discharge path overall in an upside-down U-shape, it is easy to form a structure in which the intermediate portion between the entrance and the exit is higher than the entrance. 
   Further, in the filter device of the present invention, an exit of the supply path may open in a vicinity of a floor portion of the first liquid chamber. 
   In the above-described filter device, because the exit of the supply path opens in a vicinity of the floor portion of the first liquid chamber, liquid is gradually filled from the floor portion of the first liquid chamber. Accordingly, there is little air which remains. 
   Moreover, in the filter device of the present invention, a cross-sectional surface area of the first discharge path may be made to be greater than or equal to 3 mm 2  and less than or equal to 12 mm 2 . 
   In the above-described filter device, the cross-sectional surface area of the first discharge path is made to be greater than or equal to 3 mm 2  and less than or equal to 12 mm 2 . Therefore, the liquid flowing through the first discharge path flows while maintaining a meniscus. Accordingly, air is not mixed-in with the liquid flowing through the first discharge path. 
   In the filter device of the present invention, a highest position portion of the intermediate portion of the first discharge path may be made to be higher than a ceiling portion of the second liquid chamber. 
   In the above-described filter device, because the highest position portion of the intermediate portion of the first discharge path is higher than the ceiling portion of the second liquid chamber, even at times when the flow of liquid stops, the second liquid chamber is filled with liquid without the liquid surface falling. 
   Moreover, in the filter device of the present invention, the second liquid chamber may be provided at an inner side of the first liquid chamber. 
   In the above-described filter device, by using a structure in which the outer side surface of the second liquid chamber is surrounded by the first liquid chamber, the surface area of the outer side surface is made to be large. Therefore, the surface area of the filter provided along the outer side surface can be made to be large. 
   In the filter device of the present invention, the first liquid chamber may be provided so as to surround an outer side surface of the second liquid chamber, and the filter may be provided along the outer side surface. 
   In the above-described filter device, by using a structure in which the outer side surface of the second liquid chamber is surrounded by the first liquid chamber, the surface area of the outer side surface can be made to be large. Accordingly, the surface area of the filter provided along the outer side surface also can be made to be even larger. 
   Moreover, in the filter device of the present invention, the second liquid chamber and the filter may be cylindrical-tube-shaped, and the first discharge path may be disposed at a substantially axially central position of the cylindrical-tube-shaped filter. 
   In the above-described filter device, the second liquid chamber and the filter are shaped as cylindrical tubes. By placing the flow-out path at the substantially axially central position of the filter, the flow speed of the ink, which passes through the filter and flows into the second liquid chamber and heads toward the first discharge path, is the same in any direction. In this way, there are fewer stagnant portions which arise when the ink flows, and the ability to discharge air bubbles is good. Further, when such a cylindrical-tubular filter is used, the shape of the filter is simple and manufacturing thereof is easy as compared with a case in which, for example, the outer side surface is a polygonal surface and the filter is made to be a polygonal tube, or the like. 
   In the filter device of the present invention, the first liquid chamber may be provided so as to sandwich the second liquid chamber, and the filter may be provided at a boundary surface of the first liquid chamber and the second liquid chamber. 
   In the above-described filter device, by using a structure in which the second liquid chamber is sandwiched by the first liquid chamber, the surface area of the boundary surface between the first liquid chamber and the second liquid chamber can be made to be larger. Therefore, the surface area of the filter provided at this boundary surface also can be made to be larger. 
   A liquid drop ejecting device of the present invention may have: a liquid drop ejecting head ejecting liquid drops from nozzles toward an object of discharge; a liquid storing section in which liquid, which is to be supplied to the liquid drop ejecting head, is stored; and a filter device which has any of the above-described structures and which is provided between the liquid drop ejecting head and the liquid storing section. 
   Because the above-described liquid drop ejecting device is equipped with the filter device which makes it difficult for remaining air to flow-out, deterioration in the liquid drop ejecting performance is prevented. 
   Further, in the liquid drop ejecting device of the present invention, the filter may be disposed at an orientation substantially orthogonal to a nozzle surface of the liquid drop ejecting head in which the nozzles are formed. 
   In the above-described liquid drop ejecting device, by disposing the filter at an orientation substantially orthogonal to the nozzle surface, the projected surface area of the filter onto the nozzle surface does not become large even if the surface area of the filter is made to be large.