Patent Publication Number: US-8123328-B2

Title: Ink tank and ink jet printer incorporating the same

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 11/341,538, filed Jan. 30, 2006, now U.S. Pat. No. 7,708,369, which is a continuation of U.S. patent application Ser. No. 10/635,915, filed Aug. 7, 2003, now U.S. Pat. No. 7,021,736, which claims the benefit of Japanese Patent Application No. 2002-233885, filed Aug. 9, 2002, the entire contents of each of which are hereby incorporated by reference in this application. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     (NOT APPLICABLE) 
     BACKGROUND OF THE INVENTION 
     The present invention relates to an ink tank for containing ink and an ink jet printer incorporating the ink tank as an ink supply source, and more particularly to an ink tank having a mechanism capable of precisely detecting a condition where ink has run out (an ink end). 
     Among those for use in ink jet printers is a known ink tank of such a type having the ink absorbed by and held in an ink absorbent material such as foam and felt. A foam-type ink tank, for example, has a container in which foam that has absorbed and held ink is contained therein, an ink outlet communicating with the foam container, and an vent port communicating with the atmosphere for opening the foam container into the atmosphere. When ink is sucked from the ink outlet by the ejection pressure of an ink jet head, air corresponding to the sucked amount of ink is caused to flow into the foam container. 
     In the case of such a foam-type ink tank, the calculation of the consumed amount of ink is carried out according to the number of ink dots ejected from the ink jet head, the sucked amount of ink through an ink pump for sucking ink from the ink jet head and so forth, so that the detection of the presence or absence of ink therein is made according to the calculated results. 
     Incidentally, a condition where ink in the ink tank has almost run out is generally called a “real end” and a condition where a residual amount of ink in the ink tank has decreased to an amount smaller than the predetermined amount is called a “near end.” However, an “ink end” used in this specification includes both the conditions above unless otherwise specified. 
     However, the method of detecting the ink end by calculating the consumed amount of ink and the like has the following problem. Since the ejected amount of ink from the ink jet head and the sucked amount of ink through the ink pump undergo wide variation, the consumed amount of ink that has been calculated according to the above amounts also shows a variation far greater than that of the actually consumed amount of ink. Therefore, a great margin needs setting in order to settle the ink end. Consequently, a greater amount of ink may be left at a point of time that the ink end is detected, whereby ink may often be wasted. 
     Therefore, with a back surfaces of a reflective face of a prism as an interface with respect to ink, it is conceivable to directly detect the ink end by an optical detection system utilizing optical characteristics in that the reflective face of the prism is restored as its was when ink is used. For example, Japanese Patent Publication No. 10-323993A and U.S. Pat. No. 5,616,929 disclose such a detection system. 
     In the case of a foam-type ink tank, however, ink absorbed by and held in the ink absorbent material (foam) is always kept in contact with the reflective face of the prism even though the back surfaces of the reflective face of the prism is so arranged as to be exposed in the foam container, the reflective characteristics of the prism remain unchanged even when ink has run out. Consequently, the above disclosed detection system is not directly applicable to the foam-type ink tank. 
     It is also conceivable to adopt an arrangement wherein air is introduced into a sub ink chamber under pressure control with ink in the main ink chamber consumed to a certain degree by forming such a sub ink chamber that is small in capacity and capable of storing ink between the main ink chamber (foam container) and an ink outlet, and by disposing the reflective face of the prism in the sub ink chamber to make the back surfaces of the reflective face an interface with respect to ink. 
     Accordingly, when the amount of ink left in the main ink chamber decreases, bubbles become introduced from the main ink chamber into the sub ink chamber every time ink is supplied from the ink outlet into the ink jet head. When ink in the main ink chamber is completely used, the residual amount of ink in the ink tank comes to be substantially equal to only the amount of ink left in the sub ink chamber. As the residual amount of ink in the sub ink chamber decreases in amount further, the back surfaces of the reflective face of the prism as the interface with respect to ink is exposed from the liquid level of ink and the reflective condition of the reflective face changes. In other words, the reflective face kept from serving as a reflective face while the back surfaces thereof is covered with ink gradually recovers its reflective function with the liquid level of ink going down. Therefore, the condition where the residual amount of ink has decreased to the predetermined amount or smaller is detectable according to the amount of reflected light on the reflective face. Consequently, the ink end is detectable at a point of time the residual amount of ink has substantially completely used by making the capacity of the sub ink chamber sufficiently small. 
     However, the air introduced into the sub ink chamber causes bubbles to be generated in the sub ink chamber. In case there exists a condition where bubbles are adhered to or floating around the back surfaces of the reflective face of the prism, a condition where the reflective face of the prism is covered with the ink held among bubbles is maintained even when the liquid level of ink becomes lower than the reflective face of the prism. Consequently, the reflective condition of the reflective face of the prism will not change even though the liquid level of ink lowers. As it takes much time until bubbles covering the reflective face of the prism fade out, there occurs nonconformity in that the ink end is not detected until then. Hence, the detection timing of the ink end is delayed and this causes a harmful effect such as dot missing because bubbles are sent to an ink jet head as a result of lost suction of ink. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the invention is to provide an ink tank capable of obviating a harmful influence caused by the fact that the reflective condition of a reflective face of a prism remains unchanged immediately after the liquid level of ink lowers because of bubbles in a sub ink chamber. 
     It is also an object of the invention is to provide an ink jet printer which makes it possible to immediately recognize a condition where an ink end is brought about by detecting the reflective condition of the reflective face of an ink tank. 
     In order to achieve the above object, according to the invention, there is provided an ink tank, comprising: 
     an ink chamber, formed with a vent port allowing atmospheric air to enter therein and an ink outlet from which ink is taken out; 
     an optical member, having an ink contact face capable of contacting with ink contained in the ink chamber, the ink contact face including a detection face at which a remaining amount of ink in the ink chamber is optically detected in accordance with an amount of air entered into the ink chamber via the vent port; and 
     a first ink absorbing member, disposed in the vicinity of the ink contact face, and capable of absorbing the ink in the ink chamber. 
     In such a configuration, as ink is supplied from the ink outlet, air enters the ink chamber from the vent port so that the liquid level of ink lowers. The detection face of the optical member is gradually exposed from the liquid level of ink accordingly. As a result, the optical property of the detection face (e.g., reflectivity or transmissivity) changes. 
     More specifically, in the case where the reflectivity of the detection face changes, the detection face that has not served as a reflective face while the ink contact face is covered with ink gradually regains the reflective function as the liquid level of ink lowers. In the case where the transmissivity of the detection face changes, as transmission of ink that has been impossible while the detection face is covered with ink is restored, a condition where the residual amount of ink decreases to a predetermined amount or smaller comes to be detectable according to the amount of reflected light or transmitted light. 
     When the residual amount of ink becomes smaller, bubbles are often generated. The bubbles thus generated stick to the detection face or become afloat in the vicinity of the detection face. In a case that the detection face is covered with such bubbles, even though the liquid level of ink lowers, the optical property of the detection face remains unchanged, which may result in making the detection of the ink end impossible. 
     According to the invention, however, since the first ink absorbing member is disposed in a position adjacent to the ink contact face, the ink held in the bubbles generated in the detection face is sucked into the first ink absorbing member by the capillary force thereof. Therefore, bubbles are quickly extinguished so that the optical property of the detection face is immediately changed as the liquid level of ink in the ink chamber lowers, in order to ensure that the ink end is quickly detected. 
     Preferably, the ink chamber includes: a first chamber, formed with the vent port and containing a second ink absorbing member capable of holding ink therein; and a second chamber, disposed between the first chamber and the ink outlet and containing the first ink absorbing member and the optical member. 
     Since the optical member is disposed in the second chamber, the ink end is detectable at a point of time the residual amount of ink has substantially completely used by making the capacity of the second chamber sufficiently small. Moreover, air together with ink enters the second chamber from the first chamber as the residual amount of ink decreases, so that the influence of the bubbles generated in the second chamber can be removed by the first ink absorbing member. 
     Preferably, the first ink absorbing member is placed at an ink flow passage between the optical member and the ink outlet. In such a configuration, bubbles are efficiently extinguished because the ink held in the bubbles is sucked by the first ink absorbing member as the consumption of ink continues. 
     Preferably, the first ink absorbing member is placed away from the detection face. In such a configuration, bubbles sticking to the detection face can quickly be sucked and extinguished by the first ink absorbing member without interfering the optical detection. 
     Preferably, the ink tank further comprises: a first filter, partitioning the first chamber and the second chamber, the first filter comprised of a first porous material having a first porousness so as to allow ink and air bubbles to pass therethrough; and a second filter, partitioning the second chamber and the ink outlet, the second filter comprised of a second porous material having a second porousness finer than the first porousness so as to allow only ink to pass therethrough. Here, the first ink absorbing member has a third porousness coarser than the first porousness. 
     For example, the first ink absorbing member is comprised of at least one of a foam material and a felt material. 
     Preferably, the optical member is a prism provided with a pair of reflective faces serving as the detection face. 
     Preferably, the ink tank further comprises a partition member which partitions the second chamber into a bubble storage located in the vicinity of the first chamber and an ink reservoir located in the vicinity of the ink outlet, the partition member formed with an introduction port which introduces ink from the bubble storage to the ink reservoir. Here, the detection face of the optical member is placed in the ink reservoir. 
     In such a configuration, ink flowing from the first chamber into the bubble storage is passed through the introduction hole of the partition member before being introduced into the ink reservoir. When ink in the first chamber is completely used, air enters bubble storage of the second chamber from the first chamber communicating with the atmosphere, thus causing bubbles to be formed. Consequently, the bubbles are gradually gathered in the bubble storage, which is then filled with bubbles. As the amount of bubbles increases, the residual amount of ink in the second chamber gradually decreases and the liquid level of ink gradually lowers from the inside height position of the bubble storage. 
     When the bubble storage is filled with bubbles and after the liquid level of ink lowers up to the inside height position of the second chamber, ink for use in newly generating bubbles is nonexistent because the bubble storage is filled with bubbles when air enters from the first chamber. Consequently, bubbles filling up the bubble storage are crushed into large bubbles little by little as the entrance of air continues and bubbles in the bubble storage disappear by degrees, whereas a layer containing only air is gradually formed from the upper end side of the bubble storage. 
     In other words, the bubble storage is separated by the partition member from the ink reservoir but communicates with only the introduction hole. Consequently, ink necessary for forming bubbles can be blocked by the partition member from being supplied to the bubble storage. Thus the partition member serves as what separates the liquid level of ink from bubbles and when the liquid level of ink lowers, the separation of bubbles in the bubble storage from the liquid level of ink is facilitated. 
     Therefore, the bubbles gathered in the bubble storage are extinguished little by little in the bubble storage because ink for use in forming bubbles is stopped from being supplied from the ink reservoir, and the formation of the layer containing only air in the upper end portion is started. This layer containing only air gradually spreads toward the ink reservoir as the liquid level of ink in the second chamber lowers, that is, as the entrance of air from the first chamber continues. As bubbles in the bubble storage are then extinguished and replaced with air, the liquid level of ink in the ink reservoir lowers with no bubbles formed. 
     Hence, bubbles are restrained from entering the ink reservoir and covering the detection face. Moreover, according to the invention, since the first ink absorbing member is disposed in a position adjacent to the ink contact face disposed in the ink reservoir, the ink held in the bubbles floating in the vicinity of the detection face are sucked by the capillary force of the first ink absorbing member, whereby the bubbles generated in the detection face are quickly extinguished. Accordingly, the optical property of the detection face changes at excellent response timing as the liquid level of ink lowers, so that the ink end can be detected precisely without delay. 
     Here, it is preferable that the detection face is placed in the vicinity of the introduction port. In such a configuration, detecting precision can be enhanced by utilizing the effect of forcing out bubbles sticking to the detection face with ink supplied from the introduction hole toward the first ink absorbing member. 
     It is also preferable that the introduction port is located at a corner portion defined by wall faces of either the partition member or the second chamber. In such a configuration, bubbles entering from the introduction hole are mainly concentrated on the corner portion by the surface tension and moved along the wall faces to the first ink absorbing member, so that floating bubbles can be decreased. 
     It is also preferable that the partition member is provided with pieces projecting into the ink reservoir to retain the first ink absorbing member therebetween. 
     It is also preferable that the partition member defines an ink flow passage extending from the introduction port to the first ink absorbing member via the detection face. In such a configuration the ink held in the bubbles generated on the detection face can efficiently be absorbed by the first ink absorbing member and the bubbles are also quickly extinguished. 
     According to the invention, there is also provided an ink jet printer, comprising: 
     an ink jet print head; 
     the above ink tank, which supplies ink to the ink jet print head via the ink outlet; and 
     a detector, which optically detects the remaining amount of ink in the ink tank based on a condition of the detection face. 
     In such a configuration, the optical property of the detection face changes at excellent response timing as the liquid level of ink lowers, whereby the ink end of the ink tank is quickly detectable. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above objects and advantages of the present invention will become more apparent by describing in detail preferred exemplary embodiments thereof with reference to the accompanying drawings, wherein: 
         FIG. 1A  is a plan view of a foam-type ink tank according to a first embodiment of the invention; 
         FIG. 1B  is a front view of the ink tank of the first embodiment; 
         FIG. 2  is a bottom perspective view of the ink tank of the first embodiment; 
         FIG. 3  is an exploded perspective view of the ink tank of the first embodiment; 
         FIG. 4  is a sectional view of the ink tank of the first embodiment, taken on the line IV-IV of  FIG. 1A ; 
         FIG. 5  is a sectional view of the ink tank of the first embodiment, taken on the line V-V of  FIG. 1B ; 
         FIG. 6A  is an enlarged sectional view of a sub ink chamber in the ink tank of the first embodiment; 
         FIG. 6B  is a section view of the ink tank of the first embodiment, taken along the line b-b in  FIG. 6A ; 
         FIG. 7  is a perspective view of a partition member in the ink tank of the first embodiment; 
         FIG. 8  is an enlarged sectional view of an essential part of an ink tank according to a second embodiment of the invention; 
         FIG. 9A  is a perspective view of a partition member in the ink tank of the second embodiment; 
         FIG. 9B  is a top view of the partition member of  FIG. 9A ; 
         FIG. 9C  is a front view of the partition member shown in  FIG. 9A ; 
         FIG. 10  is an enlarged sectional view of an essential part in an ink tank according to a third embodiment of the invention; 
         FIG. 11  is a transverse sectional view of the essential part in the ink tank of the third embodiment; 
         FIG. 12  is a transverse sectional view of the essential part in the ink tank of the third embodiment, viewed from the opposite side of  FIG. 11 ; 
         FIG. 13  is a schematic illustration showing an essential part of an ink jet printer; 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Preferred embodiments of the invention will now be described by reference to the accompanying drawings. More specifically, the following refers to embodiments of the invention applied to an ink tank detachably fitted to a tank mounting portion of an ink jet printer. However, the invention is similarly applicable to an ink tank prearranged in an ink jet printer. 
     As shown in  FIG. 13 , an ink jet printer  91  according to a first embodiment of the invention is of a serial type wherein an ink jet head  94  is loaded on a carriage  93  reciprocating along a guide shaft  92  in the direction of arrows A. Ink is supplied from an ink tank  1  mounted in a tank mounting portion  95  via a flexible tube  96  to the ink jet head  94 . 
     The ink tank  1  for use according to this embodiment of the invention is detachably mounted in the tank mounting portion  95  formed in the ink jet printer  91 . As shown in  FIGS. 1A ,  1 B,  2 , and  3 , the ink tank  1  has a container body  2  in the form of a rectangular parallelepiped with its upper side opened and a container cover  4  used to block up an upper-side opening  3 . A main ink chamber  5  is formed inside and a rectangular parallelepiped foam  6  is contained in the main ink chamber  5 , ink being absorbed by and held in the foam  6 . 
     An ink outlet  7  is formed in the base of the container body  2  and disc-shaped rubber packing  8  is mounted in the ink outlet  7  and a through-hole  8   a  bored in the center of the rubber packing  8  serves as an ink outlet hole. In the rear portion of the rubber packing  8  in the ink outlet  7 , a valve  9  capable of closing the ink outlet hole  8   a  is arranged and is usually pressed by a coil spring  10  against the rubber packing  8  so as to block up the ink outlet hole  8   a.    
     The main ink chamber  5  communicates with the ink outlet hole  8   a  via a sub ink chamber  20  partitioned by a first filter  11  and a second filter  12 . The main ink chamber  5  is also opened to a vent port  13  communicating with the atmosphere formed in the container cover  4 . When the ink absorbed by and held in the foam  6  mounted in the main ink chamber  5  is sucked via the ink outlet hole  8   a , air corresponding in quantity to the ink thus sucked is introduced into the main ink chamber  5  from the ports  13  communicating with the atmosphere. 
     The inside of the sub ink chamber  20 , which will be described in detail with reference to  FIGS. 4 to 7 , is partitioned by a partition member  30  into a bubble storage  21  on the main ink chamber side and an ink reservoir  22  on the ink outlet hole side, the storage  21  and the reservoir  22  communicating with each other via an introduction hole  33  formed in the partition member  30 . A bubble-extinguishing porous member  40  is incorporated in the ink reservoir  22 . 
     The vent port  13  communicating with the atmosphere in the container cover  4  is linked with a winding groove  13   a  engraved in the surface of the container cover and the end  13   b  of the groove  13   a  is extended up to the vicinity of the edge end of the container cover  4 . When the ink tank  1  is shipped, a seal  14  is adhered to the portion where the vent port  13  and the groove  13   a  of the container cover  4  are formed. On the other hand, when the ink tank  1  is used, part  14   b  of the seal  14  is torn off along cutting lines  14   a  of the seal  14  whereby to expose the end  13   b  of the groove  13   a , thus setting the ports  13  open to the atmosphere. 
     Moreover, a seal  15  is also adhered to the portion of the ink outlet hole  8   a  in the bottom of the container so that an ink supply needle (not shown) attached to the tank mounting portion  95  is made to break the seal  15  before being thrust into the ink outlet hole  8   a  when the ink tank  1  is mounted in the tank mounting portion  95  of the ink jet printer  91 . 
     As shown in  FIG. 3 , the partition member  30  is provided with a partition panel  31  for partitioning the sub ink chamber  20  and a cylindrical frame  32  perpendicularly projecting from the center of the ink reservoir side of the partition panel  31 . Further, the introduction hole  33  for introducing ink from the bubble storage  21  into the ink reservoir  22  is formed in the one end side portion of the partition panel  31 . 
     The ink tank  1  is provided with a detected portion having a right prism  51  for use in optically detecting whether the ink tank  1  is mounted in the tank mounting portion  95  of the ink jet printer  91  and a right prism  52  for use in optically detecting the ink end of the ink tank  1 . The back surfaces of the reflective face of the right prism  52  is exposed in the ink reservoir  22  of the sub ink chamber  20  to serve as an interface with respect to ink. 
     More specifically, as shown in  FIG. 4 , a frame  202  rectangular in cross section is passed through the bottom plate  201  of the container body  2  and extended vertically and perpendicularly. A rectangular opening of an upper frame portion  203  perpendicularly uprighted in the main ink chamber  5  forms a communication port  205  on the main ink chamber side. The first rectangular filter  11  is fitted to the communication port  205 . 
     The lower end of a lower frame portion  204  projecting perpendicularly downward from the bottom plate  201  is blocked up by a bottom plate  206  continued from the bottom plate  201 , and the ink outlet  7  is formed in the center of the bottom plate  206 . The ink outlet  7  has a cylindrical projected portion  207  projecting perpendicularly upward (within the ink reservoir  22 ) from the center of the bottom plate  206  and the central hole of the projected portion  207  forms an ink passage  208  communicating with the ink outlet hole  8   a . The rubber packing  8 , the valve  9  and the coil spring  10  are mounted in the ink passage  208 . A spring holder  209  for the coil spring  10  is formed integrally with the inner peripheral face of the projected portion  207 . The upper-side opening of the projected portion  207  forms a circular communication port  210  on the outlet hole side and the second filter  12  is fitted to the communication port  210 . 
     The first filter  11  is made of porous material that passes ink and is simultaneously capable of causing bubbles to pass therethrough by ink sucking force acting on the ink outlet hole  8   a . In other words, the filter  11  is made of porous material whose pore size corresponds to capillary gravitation by which the meniscus is destroyed because of the ink sucking force. In this case, the first filter  11  is formed of unwoven fabric, a mesh filter or the like. 
     On the other hand, the second filter  12  is made of porous material whose pore size is smaller than that of the first filter  11 , so that the filter  12  allows no bubbles, but only ink to pass therethrough when the ink sucking force acts on the ink outlet hole except that an ink pump is being operated. The pore size of the second filter  12  should be large enough to capture alien substances mingling in ink. The second filter  12  may also be formed of unwoven fabric, a mesh filter or the like. 
     In this case, the “ink sucking force” means force acting on ink outlet hole  8   a  by the ink ejection pressure of the ink jet head  94  or the sucking force of the ink pump. 
     Further, the right prisms  51  and  52  will now be described with reference to mainly  FIGS. 3 through 5 . An elongated rectangular plate  54  is fixedly welded to the lower end portion of a side plate portion  53  of the container body  2 . The right prisms  51  and  52  are formed integrally with the inner side of the rectangular plate  54  with a predetermined space held therebetween. The right prism  51  has a pair of reflective faces  51   a  and  51   b  crossing at right angles and the right prism  52  has a pair of reflective face  52   a  and  52   b  crossing at right angles. 
     The right prism  51  faces the side plate portion  53  via an air layer  55  having a predetermined gap. In other words, a recessed portion  56  corresponding in configuration to the right prism  51  is formed in the side plate portion  53 , whereby the reflective faces  51   a  and  51   b  face the side plate portion  53  via the air layer  55  having the predetermined gap. 
     On the other hand, the right prism  52  for detecting the ink end is directly exposed in the inside of the ink reservoir  22  from an opening  202   b  opened in the frame  202  defining the ink reservoir  22 , and the back surfaces of each of the reflective faces  52   a  and  52   b  serves as an interface with respect to ink. 
     As shown in  FIGS. 4 and 5 , reflection type optical sensors  57  and  58  are installed on the side of the ink jet printer  91  provided with the ink tank  1 . The optical sensors  57  and  58  are respectively provided with light emitting elements  57   a  and  58   a  and light receiving elements  57   b  and  58   b . The position of the optical sensor  57  is set so that the optical sensor  57  makes the light emitted from the light emitting element  57   a  incident at an angle of 45 degrees with the reflective face  51   a  and also makes the light receiving element  57   b  receive the return light reflected from the reflective face  51   a  and the reflective face  51   b . Similarly, the position of the optical sensor  58  is set so that the optical sensor  58  makes the light emitted from the light emitting element  58   a  incident at an angle of 45 degrees with the reflective face  52   a  and also makes the light receiving element  58   b  receive the return light reflected from the reflective face  52   a  and the reflective face  52   b.    
     As shown in  FIGS. 6A and 7 , an outer face  302   a  of a peripheral frame portion  302  is connected liquid-tightly to an inner peripheral side  205   a  of the communication port  205  in the rectangular frame  202  forming the sub ink chamber  20 . 
     The surface of a panel body  301  (the surface on the side of the bubble storage  21 ) is formed as an uneven surface  303 . The uneven surface  303  serves as a bubble trap for capturing bubbles formed by the air introduced from the main ink chamber  5  via the first filter  11  into the bubble storage  21  so as to prevent the bubbles from flowing toward the introduction hole  33 . 
     The uneven surface  303  is so constituted that recessed portions  304  and protruded portions  305 , having a fixed width and extending in the direction of the short side of the panel body  301 , are formed alternately at predetermined intervals in the direction of the long side of the panel body  301 . On the surface of each protruded portion  305 , protrusions  306  having a predetermined length are formed discretely at predetermined intervals. When seen from along the direction of the long side of the panel body  301 , the protrusions  306  discretely formed on the surface of each protruded portion  304  are alternately arranged. With the recessed portion  304  as a reference, each protruded portion  305  is 0.1 mm in height, for example, and the protrusions  306  formed on the surface of the protruded portion  305  is 0.2 mm in height, for example. The recessed portion  304  and the protruded portion  305  are 0.5 mm in width, for example. 
     The elliptic introduction hole  33  that is longer in the direction of the short side of the panel body  301  is formed in the central portion of the end portion on the side where the right prism  52  is disposed in the long side direction of the panel body  301 . The perimeter of the introduction hole  33  is surrounded with a protruded frame portion  307  equal in height to the protrusions  306 . Moreover, recessed portions  308  and protruded portions  309  extending in the long side direction of the panel body  301  are alternately formed at predetermined intervals in the direction of the short side of the panel body  301  at regions between the protruded frame portion  307  and the long-side edges of the panel body  301 . The protruded portion  309  is equal in height to the protrusion  305 . 
     A circular recessed portion  310  is formed in the center of the panel body  301 . The partition member  30  is an injection-molded part made of resin material and this circular recessed portion  310  is a gate mark. Further, a drop wall  311  projecting downward further than the central position in the vertical direction of the right prism  52  is formed on a lower face (surface on the side of the ink reservoir  22 ) of the panel body  301 . The drop wall  311  is formed over the whole width in the short side direction of the panel body  301 . 
     The cylindrical frame  32  perpendicularly extended from the center of the undersurface of the panel body  301  is used to suck up ink accumulated on the bottom of the ink reservoir  22  up to the communication port  210  fitted with the second filter  12  positioned upward. 
     As shown in  FIGS. 6A through 7 , a plurality of projections  322  formed at intervals of predetermined angles are perpendicularly projected from a circular edge face  321  of the lower end opening of the cylindrical frame  32 . In this embodiment, there are formed four projections  322  of the same height at intervals of 90 degrees. The inner peripheral face of the cylindrical frame  32  is provided with a lower part  323 , a tapered part  324  that is continuous to the lower part  323  and slightly protruded inward, and an upper part  325  that is continuous to the tapered part  324 . 
     The partition member  30  provided with the cylindrical frame  32  is mounted with capping applied from the upper side to the cylindrical projected portion  207 . Ribs  207   a  projecting outside at intervals of predetermined angles are formed in the lower-side portion of the outer peripheral face of the projected portion  207 . Four ribs  207   a  are formed at intervals of 90 degrees and the projected amount of each rib  207   a  is set so that these ribs  207  are just fitted in the outer peripheral face  323  on the lower end side of the cylindrical frame  32 . 
     When the cylindrical frame  32  of the partition member  30  is fitted to the projected portion  207  with capping, four gaps  220  that are arcuate in cross section and used for sucking up ink are formed by the four ribs  207   a  between the inner peripheral face of the cylindrical frame  32  and the outer peripheral face of the projected portion  207 . Consequently, there is formed an ink sucking passage led from a gap  221  to the second filter  12  positioned upward via the gaps  220  formed between the projected portions  322  at the lower end of the cylindrical frame  32 . In so doing, the amount of ink left in the ink reservoir  22  decreases and even when the liquid level becomes lower than the second filter  12 , the ink left in the ink reservoir  22  is sucked up to the position of the second filter  12  and can be supplied from the ink passage  208  to the ink outlet hole  8   a.    
     The bubble-extinguishing porous member  40  disposed in the ink reservoir  22  of the sub ink chamber  20  will be described by reference to  FIGS. 3 through 6B . The rectangular parallelepiped porous member  40  is made of flexible material such as felt and foam and disposed beneath the introduction hole  33  and in a position adjacent to the right prism  52 . In this embodiment, the porous member  40  is arranged in such a condition as to be kept in contact with a corner portion  52   c  on the back surfaces of the reflective faces  52   a  and  52   b  of the right prism  52 . 
     In other words, the porous member  40  is stuffed in between an inner side face  202   c  of the frame  202  fitted with the right prism  52  and the cylindrical frame  32  of the partition member  30 . The porous member  40  is retracted with respect to the reflective faces  52   a  and  52   b  so that its upper edge face  40   a  is positioned in the middle of the height of the reflective faces  52   a  and  52   b.    
     As shown in  FIG. 5 , a side  40   b  facing the right prism  52  of the porous member  40  is in a depressed condition as its central portion is brought into contact with the corner portion  52   c . Any side portion other than that central portion is separated from the reflective faces  52   a  and  52   b , so that the porous member  40  is prevented from contacting reflective areas  52 A and  52 B in particular where the detection light is reflected therefrom. Further, the upper edge faces  52   d  and  52   e  of the right prism  52  are also separated from vertical edge faces  202   d  and  202   e  of an opening  202   b  formed in the frame  202 . Consequently, a space A is formed between the reflective faces  52   a  and  52   b  and the porous member  40  so as to surround the reflective faces  52   a  and  52   b.    
     In this case, the porous member  40  is capable of absorbing and holding ink, and is made of material with larger meshes than those of the first filter  11 . 
     The detection of whether the ink tank  1  has been mounted in the tank mounting portion  95  of the ink jet printer  91  as well as the ink end of the ink tank  1  are made as follows. 
     When the ink tank  1  is mounted in the tank mounting portion  95  of the ink jet printer  91 , the front end portion of the ink supply needle (not shown) disposed on the side of the ink jet printer  91  passes through the through-hole of the rubber packing  8  mounted in the ink outlet  7  of the ink tank  1  and pushes up the valve  9  positioned in the ink passage  208 . Consequently, as the ink outlet hole  8   a  is left open, the ink absorbed by and held in the foam  6  in the main ink chamber  5  is caused to flow into the ink passage  208  via the first filter  11  and the sub ink chamber  20  and to pass along the ink supply needle inserted into the ink outlet hole  8   a , whereby the ink can be supplied to the ink jet head  94  on the side of the ink jet printer  91 . Since such an ink supply mechanism is known in the art, further description will be omitted. 
     When the ink tank  1  is thus installed, the right prism  51  formed on the side of the ink tank  1  is made to face the optical sensor  57  on the side of the ink jet printer  91 . Therefore, the light emitted from the optical sensor  57  is reflected by the reflective faces  51   a  and  51   b  of the right prism  51  before being received by the optical sensor  57 , whereby it is detected that the ink tank  1  has been installed. 
     When the ink jet printer  94  is driven to perform ink ejection, the ink sucking force acts on the ink outlet hole  8   a  due to the ink ejection pressure, so that ink is supplied to the ink jet printer  94 . As the ink held in the foam  6  decreases after it is supplied, air is introduced into the main ink chamber  5  via the vent port  13 . As the consumption of ink continues, the ink infiltrated into the foam  6  gradually decreases and then bubbles enter the foam  6  instead. When the residual amount of ink in the foam  6  decreases further, air from the main ink chamber  5  passes through the first filter  11 , thus forming bubbles, which are introduced into the bubble storage  21  of the sub ink chamber  20 . However, the second filter  12  used to separate the ink reservoir  22  of the sub ink chamber  20  from the ink outlet hole  8   a  passes no bubbles through. Therefore, the bubbles are gradually gathered in the small-capacity bubble storage  21  formed in the uppermost portion of the sub ink chamber  20 . 
     When the residual amount of ink further decreases, the liquid level of ink left in the main ink chamber  5  and the sub ink chamber  20  gradually lowers and the pair of prism reflective faces  52   a  and  52   b  of the right prism  52  is gradually exposed from the liquid level of ink. Consequently, the pair of the reflective faces  52   a  and  52   b  start serving as reflective members. When the liquid level of ink in the sub ink chamber  20  becomes lower than a predetermined detection position (e.g., position L shown in  FIG. 4 ), the amount of received light of the light receiving element  58   b  of the optical sensor  58  exceeds a threshold amount. The detection of the absence of ink (the ink end state) in the ink tank  1  is based on an increase in the amount of received light at the light receiving element  58   b.    
     As the ink end is detected at a point of time the residual amount ink becomes very small by making the capacity of the sub ink chamber  20  sufficiently small, the ink end is detectable with the residual amount of ink being as small as possible, whereby ink is prevented from being wasted. In this case, the ink end detected by the reflective faces  52   a  and  52   b  of the prism is regarded as the near end, whereupon the following process is performed, whereby ink is prevented from being wasted more certainly. That is, the near end of ink is detected by the optical sensor  58  first and then an amount of ink to be used thereafter is calculated and the real end is decided when the value obtained reaches an amount equivalent to the capacity of the ink reservoir  22  of the sub ink chamber  20 , so that ink is usable until the residual amount of ink is substantially used up. 
     In the case where bubbles generated in the sub ink chamber  20  are floating in the vicinity of the reflective faces  52   a  and  52   b  of the right prism  52 , the reflective faces  52   a  and  52   b  of the prism come to be substantially covered with ink. Even though the liquid level of ink becomes lower than the reflective faces  52   a  and  52   b  of the prism in the condition above, the reflective faces  52   a  and  52   b  of the prism remain covered with ink and the reflective condition also remains unchanged, so that the ink end is impossible to detect. 
     In this embodiment of the invention, however, the bubble storage  21  is formed by the partition panel  31  in the upper-end portion of the sub ink chamber  20  and the liquid level of ink drops with the liquid level of ink separated from bubbles when the residual amount of ink becomes smaller than the predetermined amount. It is therefore possible to suppress the generated amount of bubbles that are introduced into the ink reservoir  22  and floating in the vicinity of the reflective faces  52   a  and  52   b  of the prism. 
     The ink introduced from the bubble storage  21  via the introduction hole  33  into the ink reservoir  22  flows along the reflective faces  52   a  and  52   b  of the right prism  52  before being absorbed by the porous member  40 . The ink is then sucked from the bottom portion of the ink reservoir  22  along the gap between the cylindrical frame  32  and the projected portion  207 , and led to the ink outlet hole  8   a  through the second filter  12 . 
     The bubbles together with the ink introduced from the introduction hole  33  into the ink reservoir  22  are gathered in the upper-side portion of the upper edge face  40   a  of the porous member  40  and in the space A between the porous member  40  and the reflective faces  52   a  and  52   b  of the right prism  52 . However, the ink held in the bubbles gathered in these sites is sucked into the porous member  40  because of the capillary action of the porous member  40 . 
     More specifically, the ink absorbed by and held in the porous member  40  is taken out with the ink sucking operation accompanied after the liquid level of ink becomes lower than the upper edge face  40   a  of the porous member  40  as the residual amount of ink decreases. When ink is taken out of the porous member  40 , the ink held in the upper-side portion of the upper edge face  40   a  and what is held in the bubbles in the portion on the back surfaces of the reflective faces  52   a  and  52   b  are sucked by the capillary force. Consequently, the bubbles are quickly extinguished. When the liquid level of ink lowers in the ink reservoir  22 , the reflective condition of the reflective faces  52   a  and  52   b  changes at excellent response timing. The ink end is thus detectable precisely and promptly. 
     In the ink tank  1  according to this embodiment, the sub ink chamber  20  is partitioned by the partition member  30  into the bubble storage  21  and the ink reservoir  22 , which communicate with each other via only the introduction hole  33 . Accordingly, ink necessary for the formation of bubbles is blocked by the partition member  30  from being supplied from the bubble storage  21  to the ink reservoir  22  as much as possible. Therefore, the partition member  30  serves as a separator so that bubbles in the bubble storage  21  are readily separated from ink as the liquid level of ink lowers. Moreover, the bubbles generated in the ink reservoir  20  are quickly extinguished because of the suction of ink by the capillary force of the porous member  40  disposed in the ink reservoir  22 . 
     Consequently, the reflective condition of the reflective faces  52   a  and  52   b  is changed at excellent response timing based on which the ink end is detectable quickly and surely. 
     In the ink jet printer  91  with the ink tank  1  as an ink supply source according to this embodiment, the reflective condition of the reflective faces  52   a  and  52   b  provides the basis for making certain the detection of the ink end of the ink tank. 
     As shown in  FIGS. 8 through 9C , an ink tank  1 A according to a second embodiment of the invention is basically similar in structure to the ink tank  1  described above. As such, like corresponding parts are given like reference characters and the description thereof will be omitted. The ink tank  1 A according to this embodiment is characterized in that a porous-member holder  34  for holding a bubble-extinguishing porous member  40 A is provided in a partition member  30 A. Moreover, the partition member  30 A is used to form an ink passage through which ink introduced from the introduction hole  33  is led into the ink reservoir  22  flow via the back sides of the reflective faces  52   a  and  52   b  and the porous member  40 A. 
     The partition member  30 A of the ink tank  1 A is provided with the partition panel  31 , the cylindrical frame  32  projecting from the back surfaces of the ink reservoir  22  and the porous-member holder  34  in a side closer to the side of the right prism  52  than the cylindrical frame  32 . The porous-member holder  34  is provided with a drop wall  35  having the same width as that of partition panel  31  and perpendicularly projecting from a bottom face of the partition panel  31  so that the lower end of the drop wall  35  is extended up to a position in the vicinity of the bottom of the ink reservoir  22 . At the lower end of the drop wall  35 , holding pieces  36   a  and  36   b  are perpendicularly projected from both the lateral end portions of the drop wall  35  toward the right prism  52 . In the respective upper positions of these holding pieces, holding pieces  36   c  and  36   d  are also projected from the drop wall  35  toward the right prism  52 . The holding ability for the porous member  40 A is realized with the pair of upper holding pieces  36   c  and  36   d  and the pair of lower holding pieces  36   a  and  36   b.    
     The porous member  40 A is a rectangular parallelepiped having the same width as that of the drop wall  35  and is slightly greater in height than a vertical interval between the holding pieces so that the porous member  40 A is stuffed between the holding pieces while being slightly compressed. 
     With the porous member  40 A held between the holding pieces, the surface  41  of the porous member  40 A on the side of the right prism  52  is kept in contact with the inner side face  202   c  of the frame  202 . The upper end face  42  of the porous member  40 A is positioned so that it is substantially the same in height as the lower end face  52   e  of the right prism  52 . Therefore, the upper half portion of the surface  41  of the porous member  40 A is in such a condition that it faces the space A adapted to surround the reflective faces  52   a  and  52   b  of the right prism  52 . 
     Incidentally, the surface of the partition panel  31  of the partition member  30 A is not an uneven surface but a flat one, and two ribs  38  and  39  for introducing ink toward the introduction hole  33  are formed on the surface. 
     Even in the ink tank  1 A in this embodiment, the partition member  30 A serves as a separator for promoting the separation of ink from bubbles. 
     Further, ink flowing from the introduction hole  33  into the ink reservoir  22  flows down between the drop wall  35  of the partition member  30 A and the reflective faces  52   a  and  52   b , and is absorbed by the porous member  40 A. The ink is then directed to the second filter  12  via the partition member  30 A. In other words, ink is made to flow along the ink passage regulated by the drop wall  35  as shown by arrows in  FIG. 8 . 
     The porous member  40 A serves to quickly extinguish the bubbles introduced into the ink reservoir  22 . More specifically, when the residual amount of ink decreases and when the consumption of the ink soaked into the porous member  40 A of the ink reservoir  22  increases, bubbles enter the space A formed between the reflective faces  52   a  and  52   b  of the prism and the porous member  40 A. The lower-side portion of the right prism  52  in the space A is in contact with the porous member  40 A. When ink is taken out of the porous member  40 A, the ink held in the bubbles gathered in the space A is sucked into the porous member  40 A by the capillary force of the porous member  40 A. Consequently, bubbles sticking to the back surfaces of the reflective faces  52   a  and  52   b  of the prism and those floating in the vicinity of the back surfaces are quickly extinguished by the porous member  40 A. 
     With the ink tank  1 A thus arranged, bubbles sticking to the back surfaces of the reflective faces  52   a  and  52   b  of the prism and those floating in the vicinity of the back thereof are quickly extinguished by the porous member  40 A. Therefore, the ink end condition can immediately be detected without being obstructed by bubbles at a point of time the ink end condition is established. 
     Since the capacity of the partition panel  31  is small, the residual amount of ink in the porous member  40 A can be decreased and the advantage is that the amount of ink to be wasted is reducible as well. 
     In the above embodiments, each of the partition members  30  and  30 A is arranged so that the inside of the sub ink chamber  20  is partitioned into the bubble storage  21  and the ink reservoir  22 . It is also adoptable to dispose the porous member in a position adjacent to the back surfaces of the reflective faces  52   a  and  52   b  with the omission of the partition members  30  and  30 A. Even in this case, the bubbles generated in the portion on the back sides of the reflective faces are quickly extinguishable. 
     As the material of the porous members  40  and  40 A, any material capable of absorbing and holding ink can be used. For example, porous material formed by intertwining natural or synthetic fibers or bundling fibers may be adopted. However, the use of felt and foam as the material is not particularly effective. 
     Although a smaller space A is needless to say better, it is further preferable to obviate the space A by bringing the upper end face  42  of the porous member  40 A into contact with the lower end face  52   e  of the right prism  52 . 
       FIGS. 10 through 12  show an ink tank  1 B according to a third embodiment of the invention which is basically similar in structure to the ink tank  1  above. As such, like corresponding parts are given like reference characters and the description thereof will be omitted. 
     As shown in  FIG. 11 , the ink tank  1 B in this embodiment is characterized in that a circular introduction hole  61  is formed at a corner of the panel body  301  in the side where the right prism  52  is disposed. The perimeter of the introduction hole  61  is surrounded with the protruded frame portion  307  equal in height to the protrusions  306 . Moreover, the recessed portions  308  and the protruded portions  309  extending in the long side direction of the panel body  301  are alternately formed at predetermined intervals in the direction of the short side in a region between the protruded frame portion  307  and the long side edge of the panel body  301 . The protruded portion  309  is equal in height to the protrusions  306 . 
     As shown in  FIGS. 10 and 12 , a drop wall  62  and rib portions  62   a  and  62   b  projecting downward further than the central position in the vertical direction of the right prism  52  is formed on a bottom face of the panel body  301 , the ribs  62   a  and  62   b  are directed from the drop wall  62  to the right prism  52 . The rib portion  62   a  on one side and the drop wall  62  are formed so as to surround the introduction hole  61 . 
     A porous member  60  is stuffed in between the inner side face  202   c  of the frame  202  fitted with the right prism  52  and a rib portion  32   a  protruded from the cylindrical frame  32  toward the right prism  52  such that the porous member  60  is kept in contact with the drop wall  62  and the lower ends of the rib portions  62   a  and  62   b . The porous member  60  is placed in the position retracted down the direction of flow of ink with respect to the reflective faces  52   a  and  52   b  of the right prism  52 . 
     With the ink tank  1 B thus arranged, the ink caused to flow into the ink reservoir  22  from the introduction hole  61  flows downward between the drop wall  62  of the partition member  30 B and the reflective faces  52   a  and  52   b . The ink is then absorbed by the porous member  60 , so that ink is directed to the second filter  12  via the porous member  60 . In other words, ink flows along the ink passage regulated by the drop wall  62  and the rib  62   a . In this case, it is preferable to provide not only the introduction hole  61  in a position separated from the reflective faces  52   a  and  52   b  but also a labyrinth wall so that floating bubbles existing between the introduction hole  61  and the reflective faces  52   a  and  52   b  are readily caught thereon. 
     With the arrangement above, the bubbles caused to flow from the introduction hole  61  into the ink reservoir  22  are caught on the corner portion between wall faces  62   c  and  62   d  of the drop wall  62  due to the surface tension generated thereon. Then the bubbles are moved downward along the wall faces  62   c  and  62   d  and absorbed by the porous member  60  which is in contact with the lower ends of the wall faces before being extinguished. 
     Consequently, with the ink tank  1 B according to this embodiment, bubbles sticking to or floating around the back surfaces of the reflective faces  52   a  and  52   b  of the right prism  52  are quickly extinguished by the porous member  60  as in the second embodiment. Moreover, the bubbles caused to move from the introduction hole  61  are caught on the corner portion between the wall faces  62   c  and  62   d  so as to be guided to the porous member  60 , whereby the floating bubbles can be decreased. 
     Therefore, the ink end condition can immediately be detected without being obstructed by bubbles at a point of time the ink end condition is established. As bubbles flowing out of the introduction hole  61  flow along the wall faces  62   c  and  62   d  after the detection of the ink end condition, the bubbles are prevented from sticking to the right prism  52  again, so that detection accuracy is improved as the presence of ink is never detected incorrectly. 
     The invention is not limited to the above-described embodiments but may be changed in various manners. Although a description has been given of a case where the ink chamber including the main ink chamber and the sub ink chamber that are separated from each other is employed by way of example, only an ink chamber corresponding to the sub ink chamber may be employed without using an ink chamber corresponding to the main ink chamber. Even in this case, the same effect is achievable because the bubbles thus generated are extinguished by the porous member in the position where they are subjected to the detection. 
     Although the reflection type detected portion has been described as the embodiments, a transmission type photosensor as described in Japanese Patent Publication No. 6-115089A may be employed. Even in this case, because bubbles in the position subjected to the detection are extinguishable, transmissivity is improved at the time ink has run out, which results in improving accuracy in detecting the presence or absence of ink, particularly black ink whose transmissivity is low. 
     Further, instead of the utilization of the wall faces provided on the partition panel body in the vicinity of the introduction hole, the inner wall of the main ink chamber may be used to define the ink flow passage.