Patent Publication Number: US-7717548-B2

Title: Ink container and ink jet recording apparatus

Description:
FIELD OF THE INVENTION 
     The present invention relates to an ink container for supplying ink to an ink jet type recording head, and an ink jet recording apparatus using the ink container. 
     BACKGROUND ARTS 
     An ink jet recording apparatus has been known, which has a recording head for discharging ink as droplets onto a recording paper to print an image. The ink jet recording apparatus is provided with at least an ink container containing ink, to supply the ink from the ink container to the recording head. In an example, the recording head is provided with at least a nozzle and an oscillation plate driven by a piezoelectric element. Making use of pressure change in the nozzle, which is caused by oscillating the oscillation plate, the recording head sucks the ink from the ink container into the nozzle, and discharges the ink through an ink outlet of the nozzle. 
     Because the ink is a consumable material, the ink container is often formed as a cartridge that is removably attached to the ink jet recording apparatus, so the ink may be supplied conveniently. When the ink contained in the cartridge type ink container, hereinafter called the ink cartridge, is used up, the empty ink cartridge is replaced with another that is fully filled with the ink. In an ink cartridge loading section of the recording apparatus, an ink supply needle is disposed for supplying the ink from the ink cartridge to the recording head. The ink cartridge is connected to the nozzles of the recording head through an ink supply path, including the ink supply needle. 
     An ink jet recording apparatus disclosed in Japanese laid-open Patent Application No. 2003-300331 uses an ink cartridge that consists of a flexible ink bag and a case protecting the ink bag. If the ink is exposed to the air, the air will be solved in the ink, forming air bubbles in the ink, or some components of the ink react with oxygen, deteriorating the ink. To keep the air out of the ink, the ink cartridge uses the air-tight ink bag. 
     It is known in the art that the pressure inside the nozzle of the recording head, hereinafter called the nozzle internal pressure, is kept negative relative to the atmosphere, in order to prevent the ink leakage through the nozzle, which would otherwise be caused by the weight of the ink. Where the ink cartridge is placed above the recording head, the nozzle internal pressure is so raised by the weight of the ink contained in the ink cartridge, that it cannot keep the negative value relative the atmospheric pressure without any countermeasure. According to the above prior art, the air in a room between the ink bag and the case is sucked by a suction pump to reduce the pressure in the room, so that the nozzle internal pressure is kept negative relative to the atmospheric pressure. 
     As the ink in the ink bag is consumed, the pressure applied to the nozzle by the ink weight decreases, so the negative pressure in the nozzle would become too large if the case internal pressure is kept at the initial negative value. In that case, the ink discharged from the nozzle would be improperly reduced, lowering the print density improperly. To avoid this problem, the above-mentioned prior art suggests providing a pressure sensor for measuring the nozzle internal pressure, and controlling the amount of suction by the suction pump depending upon the measured nozzle internal pressure. Thereby, the nozzle internal pressure is kept in a proper range. 
     However, because the conventional method of controlling the nozzle internal pressure by controlling the pressure of the room between the ink bag and the case needs the suction pump, the apparatus for this method tends to have a complicated structure. So an alternative device that ensures stability of ink discharging property of the recording head without complicating the structure of the ink container has been desired. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, a primary object of the present invention is to provide an ink container that is simple in structure and useful for stabilizing the ink discharging operation of the ink jet recording apparatus. 
     Another object of the present invention is to provide an ink jet recording apparatus for use with the ink container. 
     To achieve the above and other objects in an ink container containing ink in a case having an ink outlet at its bottom, the present invention suggests an ink container that comprises a negative pressure generator chamber that contains a negative pressure generator and has the ink outlet formed through a bottom portion, the negative pressure generator absorbing and holding the ink by its capillary force, to keep pressure inside the nozzles negative to atmospheric pressure while the ink outlet is connected to the recording head; a storage chamber that is separated from said negative pressure generator chamber by a partition wall and contains an air-tight ink bag storing the ink; an ink port formed through the partition wall and joined to an ink spout of the ink bag to connect the ink bag to the negative pressure generator chamber; a first air introduction hole for introducing air into the negative pressure generator chamber as the ink in the negative pressure generator chamber decreases; and a second air introduction hole for introducing air into the storage chamber as the ink in the ink bag decreases. 
     The case of the ink container preferably comprises a case body having the negative pressure generator chamber and the storage chamber, and a top lid for closing an open top of the case body, wherein the first and second air introduction holes are formed through the top lid. 
     According to a preferred embodiment, an ink bag has accordion folds that extend substantially horizontally, so that the ink bag is folded down along the accordion folds as the ink in the ink bag decreases and the air is introduced into the storage chamber. 
     Preferably, the ink port may be switched over between an opening position to permit the ink flowing through the ink port, and a closing position to stop the ink from flowing through the ink port, by use of an ink port opening closing mechanism. 
     According to the present invention, an ink jet recording apparatus comprises an ink jet type recording head discharging ink through nozzles in accordance with image data to print an image; an ink container for supplying the recording head with the ink, the ink container being disposed above the recording head, and comprising a negative pressure generator chamber containing a negative pressure generator that absorbs and holds the ink by its capillary force to keep pressure inside the nozzles negative to atmospheric pressure, a storage chamber storing the ink to be supplied to the negative pressure generator chamber, and an ink port for supplying the ink from the storage chamber to the negative pressure generator chamber; an ink port opening closing mechanism for switching over the ink port between an opening position to permit the ink flowing through the ink port, and a closing position to stop the ink from flowing through the ink port; and a control device for controlling the ink port opening closing mechanism. 
     According to a preferred embodiment, the ink jet recording apparatus further comprises an ejected ink amount detecting device for detecting an ejected amount of ink from the recording head, wherein the control device controls the ink port opening closing mechanism to supply the ink to the negative pressure generator chamber by an amount according to the ejected amount of the ink. 
     According to another preferred embodiment, the ink jet recording apparatus further comprises an ink level detector for detecting that the ink contained in the negative pressure generator chamber goes below a predetermined reference level, wherein the control device controls the ink port opening closing mechanism to supply the ink by a given amount to the negative pressure generator chamber when the ink level goes below the reference level in the negative pressure generator chamber. 
     Providing the ink container with the negative pressure generator chamber and the storage chamber containing the ink bag suppresses variations in pressure inside the nozzles and thus stabilizes ink discharging operation of the recording head. 
     Providing the ink port opening closing mechanism still more suppresses variations in pressure inside the nozzles and thus improves stability of the ink discharging operation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects and advantages of the present invention will be more apparent from the following detailed description of the preferred embodiments when read in connection with the accompanied drawings, wherein like reference numerals designate like or corresponding parts throughout the several views, and wherein: 
         FIG. 1  is an explanatory diagram illustrating essential elements of an ink jet recording apparatus according to an embodiment of the invention; 
         FIG. 2  is an exploded perspective view of an ink cartridge used in the ink jet recording apparatus of  FIG. 1 ; 
         FIG. 3  is an exploded perspective view of a cartridge case of the ink cartridge; 
         FIGS. 4A and 4B  are sectional views of the ink cartridge; 
         FIG. 5  is a flow chart illustrating a sequence of manufacturing the ink cartridge; 
         FIG. 6  is a flow chart illustrating a sequence of filling the ink cartridge with ink; 
         FIG. 7  is an explanatory diagram illustrating an ink cartridge having a valve mechanism for opening or closing an ink port from an ink bag to a negative pressure generator chamber, and an ink jet recording apparatus having a valve controller for controlling the valve mechanism; 
         FIG. 8  is an explanatory sectional diagram illustrating the valve mechanism mounted in an ink port section; 
         FIG. 9  is a fragmentary perspective view of the ink port section; 
         FIG. 10  is a graph illustrating a relationship between flow rate of the ink through the ink port and ink level in the ink bag; 
         FIG. 11  is a graph illustrating a relationship between the ink viscosity and the temperature; 
         FIG. 12  is a flow chart illustrating a printing sequence of the ink jet recording apparatus of  FIG. 7 ; 
         FIG. 13  is a flow chart illustrating a sequence of calculating the flow rate of the ink through the ink port; 
         FIG. 14  is an explanatory diagram illustrating an ink cartridge having an ink level sensor, and an ink jet recording apparatus that controls an ink port opening closing mechanism in cooperation with the ink level sensor; and 
         FIG. 15  is a flow chart illustrating a printing sequence of the ink jet recording apparatus of  FIG. 14 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An ink jet recording apparatus  10  shown in  FIG. 1  is provided with a recording head  12  that discharges ink toward a paper sheet  11  to print images thereon. The recording head  12  is provided with a plurality of nozzles  12   a  for discharging the ink from individual outlets. The outlets of the nozzles  12   a  are aligned in a plane to form a discharging surface, and the discharging surface is placed in face to a recording surface of the paper sheet  11 . The recording head  12  is mounted in a carriage  13  that is movable in a widthwise direction of the paper sheet  11 , that is, a main scanning direction X. The discharging surface is exposed through an opening formed through a bottom of the carriage  13 . While reciprocating in the widthwise direction of the paper sheet  11  together with the carriage  13 , the recording head  12  records an image in a line sequential fashion. Each time the recording head  12  makes one lap to record a line of the image, the recording paper  11  is fed by not-shown conveyer rollers in a sub scanning direction Y, that is orthogonal to the main scanning direction X, by a length corresponding to a width of each image line as recorded by the recording head  12 . Thus, a frame of image is recorded line after line. 
     The carriage  13  is mounted on a pair of guide rods  14   a  and  14   b  to slide thereon, and is driven by a belt mechanism  18  consisting of a belt  16  and a pair of pulleys  17 . The carriage  13  carries ink cartridges  20 , e.g. four cartridges containing inks of four different colors: yellow, magenta, cyan and black. 
     The carriage  13  is provided with not-shown slots, into which the ink cartridges  20  are plugged. In each slot, there is provided an ink supply needle  36 , see  FIG. 2 , having a through-hole as a path for supplying the ink to the recording head  12 . When the ink cartridge  20  is plugged in the slot, the ink supply needle  36  is stuck into an ink outlet  31  that is formed on a bottom of the ink cartridge  20 , so the ink contained in the ink cartridge  20  is supplied through the ink supply nozzle  36  to the recording head  12 . In the recording head  12 , not-shown pressure rooms and oscillation plates are provided in one-to-one relationship with the nozzles  12   a . The oscillation plates are driven individually by piezoelectric elements, to change volume of the pressure room. Thereby, the ink in the ink cartridge  20  is sucked into the nozzles  12   a , and is ejected from the outlets of the nozzles  12   a.    
     As shown in  FIG. 2 , a case  21  of the ink cartridge  20  consists of a case body  22  formed with ink chambers  24  for storing the ink, and a top lid  23  for closing an open top of the case body  22 . After the case body  22  is filled with the ink, the top lid  23  is affixed to the case body  22 , for example, by welding. Thereby, the ink is prevented from leaking through the open top of the case body  22 . The case body  22  is formed from a transparent plastic or the like, so the remaining amount of the ink in the ink cartridge  20  is visible from outside. 
     The ink chambers  24  consist of an negative pressure generator chamber  26  holding a negative pressure generator  28  that absorbs and holds the ink by its capillary force, and a storage chamber  25  for storing the ink. The negative pressure generator chamber  26  and the storage chamber  25  are partitioned by a partition wall  27 . 
     As shown in  FIG. 3 , the case body  22  consists of a main body portion  22   a , the partition wall  27 , and a bottom lids  22   b  that is attached to close an open bottom of the main body portion  22   a . Thus, the bottom lid  22   b  constitutes a bottom wall of the ink chambers  24 . The partition wall  27  has an ink port  27   a  formed integrally at a lower near the bottom wall of the ink chambers  24 . Through the ink port  27   a , the ink is supplied from the storage chamber  25  to the negative pressure generating chamber  26 . The ink port  27   a  is formed as a tube protruding into the storage chamber  25 . The bottom lid  22   b  and the partition wall  27  are affixed to the main body portion  22   a  by welding. 
     An ejection opening  26   a  for ejecting the ink from the negative pressure generator chamber  26  out of the case body  22  is formed through a bottom portion of the negative pressure generator chamber  26 . The ejection opening  26   a  and an ejection tube  29  extending downward from the ejection opening  26   a  constitute the ink outlet  31 . In the ejection tube  29 , a filter  33  for filtering the ink and a porous member  34  to insert the ink supply needle  36  are provided. The porous member  34  absorbs the ink past through the filter  33 , to conducts the ink to the ink supply needle  36 . 
     The negative pressure generator  28  is a spongy material having micro holes that generate the capillary force. Concretely, the negative pressure generator  28  is made of a porous material, including a foamed material like urethane foam, or a fibrous material like felt. The filter  33  is a spongy member that generates a capillary force like the negative pressure generator  28 . A top surface of the filter  33  is in tight contact with a bottom surface of the negative pressure generator  28 , and a bottom surface of the filter  33  is in tight contact with a top surface of the porous member  34 . The filter  33  and the porous member  34  absorb the ink from the negative pressure generator  28  and hold the ink therein by their capillary force. 
     As the ink cartridge  20  is attached to the carriage  13 , the negative pressure generator chamber  26  is connected to the recording head  12  that is placed under the carriage  13 . More specifically, as the ink cartridge  20  is attached to the carriage  13 , the ink supply needle  36  in the slot of the carriage  13  is stuck from the bottom into the porous member  34 , providing the ink supply path from the ink chambers  24  through the ink supply needle  36  to the associated nozzles  12   a  of the recording head  12 . 
     The negative pressure generator  28  generates a negative pressure due to its capillarity, which keeps the pressure of the ink in the negative pressure generator chamber  26  negative to the atmosphere. Keeping the ink pressure in the negative pressure generator chamber  26  negative to the atmosphere makes an ink pressure in the nozzles of the recording head  12  negative to the atmosphere, which forms meniscuses of the ink in the nozzles, preventing leakage of the ink from the nozzles. 
     For printing, the recording head  12  generates such a suction force against the negative pressure of the ink in the negative pressure generator chamber  26  that the ink is sucked from the negative pressure generator chamber  26  and is ejected from the outlets of the nozzles  12   a . The ink contained in the negative pressure generator chamber  26  is thus consumed, and the ink contained in the storage chamber  25  is used for refilling the negative pressure generator chamber  26 . 
     The storage chamber  25  holds an ink bag  37  containing the ink. The ink bag  37  consists of a bag body  38  made of an air-tight material, and an ink spout  39  provided at a lower position of the bag body  38 . The ink spout  39  is fitted on the ink port  27   a , to cover an open end of the ink port  27   a . An outer periphery of the ink port  27   a  and an inner periphery of the ink spout  39  are bonded together by welding, so the ink bag  37  is fixed to the partition wall  27 . 
     The ink bag  37  contains the ink air-tightly to isolate the ink from the atmosphere, so that the amount of air dissolved the ink is kept low in the ink bag  37 . If the amount of air dissolved in the ink increases, air bubbles are generated in the ink, or the ink deteriorates due to chemical reaction on oxygen, causing malfunctions of the recording head  12 . The ink bag  37  suppresses such troubles. As the ink bag  37  keeps the amount of air dissolved in the ink low, the ink is preserved in good condition, so the ink contained in the ink bag  37  may be preserved for a longer time, enabling the ink cartridge  20  to contain a larger volume of ink. 
     The bag body  38  is made of a flexible material, so it shrinks as the contained ink decreases. The bag body  38  has accordion folds  38   a  with substantially horizontal folding lines. Thanks to these accordion folds  38   a , with the consumption of the ink contained in the ink bag  37 , the ink bag  37  is folded along the accordion folds  82   a  to reduce its height while keeping its top surface approximately horizontal. Because the ink bag  37  will not irregularly shrink, the contained ink moves less with the shrinkage of the bag body  38 , and the liquid surface of the ink inside the bag body  38  changes relatively continuously. Since the ink bag  37  is connected to the nozzles  12   a  through the ink port  27   a  and the negative pressure generator chamber  26 , the weight of the ink in the ink bag  37  effects as a positive pressure on the nozzles  12   a . The positive pressure applied to the nozzles  12   a  fluctuates less where the ink in the ink bag  37  moves less, and the liquid surface of the ink in the ink bag  37  changes continuously. As a result, fluctuation of internal pressure in the nozzles  12   a  is suppressed, so the stability of ink discharging operation of the recording head  12  is improved. 
     The top lid  23  is provided with first and second air introduction holes  41  and  47 . The first air introduction hole  41  is located above the negative pressure generator chamber  26 , to introduce the air into the negative pressure generator chamber  26  as the ink in the negative pressure generator chamber  26  decreases, whereas the second air introduction hole  47  is located above the storage chamber  25 , to introduce the air into the storage chamber  25  as the ink in the storage chamber  25  decreases, 
     The top lid  23  has a meander groove  42  formed in its top surface. One end  42   a  of the groove  42  is connected to the first air introduction hole  41 , and a liquid sink  43  is formed on a path from the end  42   a  to a second end  42   b  of the groove  42 . The groove  42  is covered from the top with a seal  45 , exclusive of the second end  42   a , so the second end  42   b  alone is exposed to the atmosphere. The groove  42  leads the ink to the liquid sink  43  if the ink leaks out of the negative pressure generator chamber  26  through the first air introduction hole  41 . So the ink is prevented from leaking out of the ink cartridge  20 . The air is introduced from the second end  42   b  into the first air introduction hole  41 . 
     A number of ribs  46  are formed on the bottom side of the top lid  23  in an area facing to the negative pressure generator chamber  26 . As the top lid  23  is attached to the case body  22 , the ribs  46  protrude into the negative pressure generator chamber  26  and come into contact with a top side of the negative pressure generator  28 , thereby pressing down the negative pressure generator  28  onto the bottom of the negative pressure generator chamber  26 . Thereby, the negative pressure generator  28  is fixedly positioned to space the negative pressure generator  28  apart from the top lid  23 , so the negative pressure generator  28  is prevented from being displaced to close the first air introduction hole  41 . 
     Now the operation of the above embodiment will be described with reference to  FIG. 4 . 
     When the ink cartridge  20  is attached to the ink jet recording apparatus  10 , the ink supply needle  36  is connected to the ink outlet  31 , so the ink supply path from the ink cartridge  20  to the recording head  12  is established. As the ink cartridge  20  is provided with the negative pressure generator chamber  26 , the internal pressure of the nozzles  12   a  is kept negative to the atmosphere, so the ink will not accidentally leak from the outlets of the nozzles  12   a . Unlike the conventional ink cartridge, any suction pump is not necessary for generating the negative pressure, so that the ink cartridge  20  is simple in structure. Since the ink  49  is contained in the ink bag  37 , the amount of air dissolved in the ink  49  is kept low, which contributes to ensuring stable discharging operation of the recording head  12 . 
     When the recording head  12  starts recording an image in response to a print command, the ink is supplied to the recording head  12  from the negative pressure generator chamber  26  through the ink supply needle  36 . As a result, the pressure inside the negative pressure generator chamber  26  goes down, so the negative pressure generator chamber  26  introduce the air through the first air introduction hole  41 , and at the same time, the ink  49  is supplied from the ink bag  37  to the negative pressure generator chamber  26  through the ink port  27   a . The ink  49  is consumed in this way, and the residual amount of the ink  49  in the ink bag  37  reduces from the full level shown in  FIG. 4A . With the ink  49  being consumed, the bag body  38  of the ink bag  37  shrinks as shown in  FIG. 4B . As a result, the pressure inside the storage chamber  25  goes down, so the storage chamber  25  introduces the air through the second air introduction hole  47 . As having the accordion folds, the ink bag  37  reduces its volume by reducing its height while keeping its horizontal contour. Therefore, the fluctuation in nozzle internal pressure with the reduction of the ink is suppressed. 
       FIG. 5  illustrates the sequence of manufacturing the ink cartridge  20 . First, the ink spout  38  of the ink bag  37  is joined to the ink port  27   a  of the partition wall  27 , and the joint is fixed by welding. The partition wall  27  having the ink bag  37  attached thereto, and the bottom lid  22   b  are mounted and welded to the main body portion  22   a , to assemble the case body  22 . While assembling the case body  22 , the filter  33  and the porous member  34  are mounted in the ink outlet  31 . After the case body  22  is thus assembled, the negative pressure generator  28  is inserted from the open top into the negative pressure generator chamber  26 . Thereafter, the top lid  23  is attached and welded to the case body  22 , to assemble the case  21 . 
     Thereafter, the ink is injected through the ink outlet  31  into the case  21 , in a manner as set forth later. After the case  21  is fully filled with the ink, the seal  45  is stuck on the top surface of the top lid  23 , to cover the first air introduction hole  41  and the groove  42  except the second end  42   b . The second air introduction hole  47  may also be covered with a seal or the like. The ink cartridge  20  assembled in this way is shipped for sale. Before the ink cartridge  20  is attached to an ink jet recording apparatus, the seals or the like are removed to uncover the first and second air introduction holes  41  and  47 . 
       FIG. 6  shows the sequence of filling the case  21  with the ink. First, the air remaining in the ink bag  37  is ejected. For this purpose, the first air introduction hole  41  is closed with a seal  51  or another sealing member, and a hollow needle  52  is stuck into the ink outlet  31 , to establish an air ejection duct. Then, a pressing pump  53  is connected to the second air introduction hole  47 , to raise the pressure inside the storage chamber  25  up to a high level that is a number of times, e.g. twice or triple, the atmospheric pressure. The high pressure crushes the ink bag  37  down, to push the remaining air out of the ink bag  37  through the ink port  27   a , the negative pressure generator chamber  26  and the hollow needle  52 . If the case  21  is new, any ink does not remain in the ink bag  37 . But if the case  21  is a reused or recycled one, the ink or other residues than the air can remain in the ink bag  37 . In that case, such residues are pushed out together with the air through the ink outlet  31 . 
     After the air is completely exhausted out of the ink bag  37 , a filling pump  56 , which is connected to an ink supply tank  55 , is joined to the ink outlet  31  to inject the ink from the ink tank  55  into the case  21 . As described above, the ink chambers  24  consist of the negative pressure generator chamber  26  and the storage chamber  25 , and the negative pressure generator chamber  26  contains the negative pressure generator  28 . In an initial stage where the negative pressure generator  28  does not absorb any ink at all, there is a greater flow resistance to the ink on penetrating the ink into the negative pressure generator  28  than a flow resistance through the ink port  27   a , so the ink injected through the ink outlet  31  flows more easily through the ink port  27   a  into the ink bag  37 . To hinder the ink from flowing into the ink bag  37 , the second air introduction hole  47  is sealed up with a seal  57  or another sealing member to close the storage chamber  25  air-tightly while keeping the pressure inside the storage chamber  25  at the high level, when the ink begins to be injected through the ink outlet  31  into the negative pressure generator chamber  26 . Instead, the first air introduction hole  41  is opened before the filling pump  56  is activated to start injecting the ink. Since the internal pressure of the storage chamber  25  is high, the ink injected by the filling pump  56  does not flow into the ink bag  37 , but penetrates into the negative pressure generator  28  to fill the negative pressure generator chamber  26 . 
     When the negative pressure generator chamber  26  is filled with the ink  49  up to a predetermined amount, e.g. about a half of the total volume of the negative pressure generator chamber  26 , the filling pump  56  stops for a moment to seal up the first air introduction hole  41  again and open the second air introduction hole  47 . Thereafter, the filling pump  56  is reactivated to restart injecting the ink. As the second air introduction hole  47  is opened, the pressure inside the storage chamber  25  is reduced, so the injected ink flows through the ink port  27   a  into the ink bag  37 . Since the negative pressure generator  28  already absorbs the ink, the negative pressure generator  28  has a lower flow resistance to the ink than in the initial stage, so that the negative pressure generator  28  still absorbs the ink. In this way, the ink is injected till the negative pressure generator chamber  26  and the storage chamber  25  are filled up with the ink. Then, the filling pump  56  is removed, and the second air introduction hole  47  of the storage chamber  25  is sealed up again, completing the ink filling. 
     In the ink cartridge  20  of the first embodiment, the negative pressure generator chamber  26  and the storage chamber  25  are always interconnected to each other, so the ink can flow from the storage chamber  25  into the negative pressure generator chamber  26  at any time. In order to keep the nozzle internal pressure negative to the atmosphere, a positive pressure due to the ink weight in the storage chamber  25  must be kept lower than a negative pressure generated by the negative pressure generator  28 . To keep such a relationship, certain restrictions are imposed on the ink capacity of the negative pressure generator chamber  26  and that of the storage chamber  25 . 
     In an ink cartridge  61  shown in  FIG. 7 , a valve mechanism  66  is disposed in an ink port  64  that connects a storage chamber  62  to a negative pressure generator chamber  63  that is parted by a partition wall  65  from the storage chamber  62 . The valve mechanism  66  is an ink port opening closing mechanism, and is switched over between a closed position to close the ink port  64 , and an open position to open the ink port  64 . In the opening position of the valve mechanism  66 , the ink  49  can flow from an ink bag  69  of the storage chamber  62  to the negative pressure generator chamber  63 . The valve mechanism  66  prevents continual affection of the positive pressure, which is caused by the ink weight in the storage chamber  62 , onto the nozzles  12   a . Thus, the ink capacity of the storage chamber  62  and that of the negative pressure generator chamber  63  of the ink cartridge  61  are released from such restriction as imposed on the first embodiment. Accordingly, it becomes possible to make the ink capacity of the storage chamber  62  greater than that of the negative pressure generator chamber  63 . 
     Because the negative pressure generator chamber  63  contains a negative pressure generator  67 , the ink capacity of the negative pressure generator chamber  63  is reduced correspondingly. Therefore, the ratio of the ink capacity to the volume of the negative pressure generator chamber  63  is lower than the ratio of the ink capacity to the volume of the storage chamber  62 . Thanks to the valve mechanism  66 , the storage chamber  62  may be made larger than the negative pressure generator chamber  63 . For example, as shown in  FIG. 7 , the storage chamber  62  may be higher than the negative pressure generator chamber  63 . Then, the total ink capacity and thus the ratio of the total ink capacity to the total volume of a case  68  of the ink cartridge  61  is improved. 
     As the valve mechanism  66  disconnects the negative pressure generator chamber  63  from the storage chamber  62 , the nozzle internal pressure depends on the volume of the ink contained in the negative pressure generator chamber  63 . In view of this fact, the amount of ink supplied from the ink bag  69  of the storage chamber  62  is controlled according to the consumed amount of ink, such that the ink volume in the negative pressure generator chamber  63  would not largely vary. Thereby, fluctuation of the nozzle internal pressure is suppressed. 
     A controller  71  totally controls components of an ink jet recording apparatus  10 . The controller  71  controls a head driver  73  in accordance with image data read out from a frame memory  72 . The head driver  73  drives a recording head  12  to eject the ink through nozzles  12   a  in accordance with the image data. The controller  71  is provided with an ink ejection counter  74  to count the number of ejections through each of the nozzles  12   a . The nozzles  12   a  are determined to eject a constant amount of ink at a time, so that the total amount of ink ejected from the recording head  12  may be calculated from the count of the ink ejection counter  74 . The controller  71  calculates the ejected ink amount at regular time intervals, while measuring the time by a timer  76 . 
     Instead of detecting the ejected ink amount based on the number of ink ejections, the controller  71  can detect the ejected ink amount by estimation based on the image data. 
     A valve controller  78  controls the valve mechanism  66 . The valve controller  78  calculates an amount of ink to supply to the negative pressure generator chamber  63  in accordance with the ejected ink amount as detected by the controller  71 , and controls the time to open and close the valve mechanism  66  so as to supply the ink from the ink bag  69  to the negative pressure generator chamber  63  by the calculated amount. 
     As shown in  FIGS. 8 and 9 , the valve mechanism  66  consists of an ink port block  81  having the ink port  64  formed through it, a valve  82  disposed in the ink port  64 , and an actuator  83  for driving the valve  82  to open or close the ink port  64 . The ink port  64  consists of a tubular introduction channel  64   a  that is joined to the ink bag  69 , a round chamber  64   b , a first opening  64   c  formed through a bottom of the round chamber  64   b , and a second opening  64   d  formed through the partition wall  65 . The first opening  64   c  extends vertically, whereas the second opening  64   d  extends horizontally. An opening is formed through a bottom wall of the case  68  at a position corresponding to the first and second openings  64   c  and  64   d , and the valve  82  is mounted to bung up the opening of the bottom wall. 
     The valve  82  is an elastic film made of rubber or the like, and opens the first and second openings  64   c  and  64   d  in its opening position, as shown by solid lines in  FIG. 8 , allowing the ink to flow from the first opening  64   c  to the second opening  64   d . When a pushing member  83   c  of the actuator  83  pushes up the valve  82 , the valve  82  is elastically deformed to move to its closing position, as shown by phantom lines in  FIG. 8 . In the closing position, the valve  82  closes the first and second openings  64   c  and  64   d , thereby to stop the ink flow from the first opening  64   c  to the second opening  64   d . Thus, the valve  82  opens or closes the ink port  64 . For example, the actuator  83  contains a solenoid, which is not shown but consists of a coil and an iron core, in a housing  83   b , so that the actuator  83  drives the valve  82  when the solenoid is powered. 
     The ink  49  flows through the ink port  64  at a flow rate Q, i.e. a volume per unit time of the flown ink, which is dependent upon a length L and an internal diameter D of the introduction channel  64   a  that provides the maximum flow resistance. Besides that, as shown in  FIG. 10 , the flow rate Q is proportional to the ink level H 1  in the ink bag  69 . Consequently, the flow rate Q may be calculated according to the following formula:
 
 Q=ρ×g×H 1×(π× D   4 )/(128 ×μ×L )
 
wherein ρ represents an ink density, μ represents an ink viscosity, and g represents an acceleration due to gravity.
 
     As seen from the formula (1), the flow rate Q decreases as the ink level H 1  gets lower. Accordingly, time for opening the valve  82  to supply the same amount of ink through the ink port  64  gets longer as the ink level H 1  gets lower. It is found by experiments that, assuming the ink viscosity μ is constant, the ink pressure is about 4.5 times greater at the surface height H 1  of 50 mm than at the surface height H 1  of 11 mm. Therefore, when the surface height H 1  is 50 mm, the valve opening time for supplying the same amount of ink is about one-fourth the valve opening time required when the surface height H 1  is 11 mm. 
     The controller  71  is connected to a non-volatile memory, e.g. EEPROM  85 . The EEPROM  85  memorizes the ink level H 1 . During the manufacture, the EEPROM  85  memorizes a maximum value of the ink level H 1  where the ink bag  69  is filled up with the ink. The memorized ink level H 1  is revised with the consumption of the ink. When the ink level H 1  gets lower than a predetermined value, the controller  71  judges that the ink cartridge  61  is running out of the ink  49 , and displays a warning on a display device  89 , to notice the user of the ink run-out. The valve controller  78  reads the ink level H 1  through the controller  71  from the EEPROM  85 . 
     The valve controller  78  calculates the flow rate Q based on the above formula (1), and calculates a time for opening the valve  82  in accordance with an ejected amount of the ink  49 . Instead of calculating the flow rate Q based on the above formula, it is possible to determine the flow rate Q with reference to a lookup table stored in a memory. 
     Meanwhile, the ink viscosity μ is inverse-proportional to the ink temperature Th, so the ink viscosity μ gets higher as the ink temperature Th gets lower. According to experiments, when the ink temperature Th falls from 35 C to 15 C, the ink viscosity μ approximately doubles. As a result, the flow rate Q is reduced by half, so the time for opening the valve  82  to supply the same amount of ink approximately doubles. In view of this, the ink jet recording apparatus  10  is provided with a temperature sensor  86  to measure the ink temperature in the ink cartridge  61 . The temperature sensor  86  may be mounted on a carriage for the recording head  12 . The valve controller  78  reads through the controller  71  the ink temperature as measured by the temperature sensor  86 , to calculate the ink viscosity μ. 
     Now the printing operation of the embodiment shown in  FIG. 7  will be described with reference to  FIGS. 12 and 13 . When a print command is entered, the controller  71  reads the ink level H 1  from the EEPROM  85 . If the ink level H 1  is less than the predetermined level, the controller  71  judges that the ink cartridge  61  is running out of the ink, and gives the warning through the display device  78 . If not, the controller  71  stars printing a frame of image. The recording head  12  is driven based on the image data, to eject the ink. At the start of printing, the ink port  64  is closed, so the ink ejection is done stably regardless of the residual amount of the ink in the ink bag  69 . 
     A given time after the start of discharging the ink, the controller  71  commands the valve controller  78  to start supplying the ink from the ink bag  69  to the negative pressure generator chamber  63  in accordance with the ejected amount of the ink. Then, the valve controller  78  calculates the flow rate Q of the ink through the ink port  64 . As shown in  FIG. 13 , the valve controller  78  calculates the ink viscosity μ based on the ink temperature Th measured by the temperature sensor  86 , and reads the ink level H 1 , to calculate the flow rate Q according to the above formula (1). 
     Based on the flow rate Q, the valve controller  78  calculates a valve opening time necessary for supplying the ink by the amount calculated by the controller  71 , i.e. the ejected amount of the ink. Then the actuator  83  switches the valve  82  to the open position, so the ink flows from the ink bag  69  to the negative pressure generator chamber  63 . Since the valve  82  is opened for the calculated valve opening time, the ink is supplied to the negative pressure generator chamber  63  by the amount corresponding to the amount ejected from the negative pressure generator chamber  63 . Consequently, variations in the ink volume in the negative pressure generator chamber  63  is suppressed, so is the nozzle internal pressure. Therefore, the stability of ink discharging operation is improved. 
     As the ink is supplied from the ink bag  69  to the negative pressure generator chamber  63 , the ink level H 1  in the ink bag  69  comes down. Then the controller  71  revises the value memorized as the ink level H 1  in the EEPROM  78 . The sequence as above is cyclically executed till the printing of one frame is finished. 
     Although the valve  82  of the valve mechanism  66  is mounted in the ink cartridge  61 , and the actuator  83  is mounted in the ink jet recording apparatus in the above embodiment, it is possible to mount an actuator in the ink cartridge. 
     An ink cartridge  91  shown in  FIG. 14  is provided with a surface level sensor  92  for detecting if an ink level H 2  in a negative pressure generator chamber  63  is lower than a predetermined reference level. So an ink jet recording apparatus can supply the ink from an ink bag  69  to the negative pressure generator chamber  63  when it detects through the surface level sensor  92  that the ink level H 2  gets lower than the reference level. Thus, the ink volume in the negative pressure generator chamber  63  is kept around a certain level, so the nozzle internal pressure varies less, ensuring the stability of ink discharging operation. In the illustrated embodiment, the surface level sensor  92  consists of a pair of conductive metal strips that protrude into the negative pressure generator chamber  63 . The metal strips are arranged vertically to each other. While the ink level H 2  in the negative pressure generator chamber  63  is above the metal strips, the metal strips are electrically connected through the ink. When the ink level H 2  goes below the upper metal strip, the metal strips are electrically disconnected from each other. Thereby, a controller  71  of the ink jet recording apparatus detects that the ink level H 2  gets lower than the reference level. 
     As an ink port opening closing mechanism for an ink port  94  between the ink bag  69  and the negative pressure generator chamber  63  of the ink cartridge  91 , a suction pump  96  is used in place of the valve mechanism. The suction pump  96  can suck the ink from the ink bag  69  and send it to the negative pressure generator chamber  63 , so the ink left unused in the ink bag  69  is reduced in comparison with the case using the valve mechanism. 
     The controller  71  controls the suction pump  96  through a pump driver  97 . While the suction pump  96  is activated, the ink port  94  is set in an open position. When the suction pump  96  is deactivated, the ink port  94  is closed. That is, the opening time of the ink port  94  is decided by the operating time of the suction pump  96 . The suction pump  96  may be mounted in a case of the ink cartridge  91 , or in the ink jet recording apparatus. The suction pump  96  is preferably a micro pump, especially where it is mounted to the ink cartridge  91 . 
     As shown in  FIG. 15 , when a print command is entered, the ink jet recording apparatus starts printing a frame of image. A recording head  12  ejects the ink in accordance with image data. A timer  76  measures the time from the start of printing. Each time a given time has passed, the controller  71  makes a decision as to whether the suction pump  96  is to be activated to refill the negative pressure generator chamber  63  with the ink in accordance with the ejected amount of the ink. For this purpose, the controller  71  checks the ink level H 2  through the surface level sensor  92 . If the ink level H 2  is higher than the reference level, the controller  71  continues printing without executing the ink refill. On the contrary, if the ink level H 2  is lower than the reference level, the controller  71  drives the suction pump  96  through the pump driver  97  to refill the negative pressure generator chamber  63  with the ink. The amount of the ink to be supplied is calculated on the basis of the ejected amount of the ink as measured during the given time. For example, about five times the ejected amount of the ink is supplied. 
     After the negative pressure generator chamber  63  is thus refilled, the ink level H 2  is checked again. If it is confirmed that the ink level H 2  is above the reference level, the printing is continued. In this way, the image of one frame is printed. If the ink level H 2  is still below the reference level even after the ink refill, the ink is supplied again from the ink bag  69  to the negative pressure generator chamber  63 . If the ink level H 2  does not go above the reference level even after a number of times of ink supplying operation, the controller  71  regards that there is little or no ink left in the ink bag  69 , and gives a corresponding warning on a display device  78 . 
     The ink cartridges  61  and  91  of the second and third embodiment may be assembled fundamentally in the same sequence as the ink cartridge  21  of the first embodiment, but appropriately including additional steps for mounting the valve, the suction pump or the surface level sensor. 
     Concerting the ink filling process for the ink cartridge having the ink port opening closing mechanism, like the valve or the suction pump, the ink port opening closing mechanism opens the ink port while the remaining air is being exhausted from the ink bag through the ink port, as well as while the ink is being fed into the ink bag through the in port. On injecting the ink into the negative pressure generator chamber before feeding the ink into the ink bag, the ink port is closed. 
     Although the present invention has been described with respect to the embodiment wherein the inks of different colors are supplied from the ink cartridges that are removably connected to the recording head, the present invention is applicable to an ink jet recording apparatus using a single ink cartridge for supplying ink of one color. The present invention is also applicable to an ink cartridge where a recording head is integrated with an ink container, or an ink container fixedly mounted in an ink jet recording apparatus. 
     Thus the present invention is not to be limited to the above-described embodiments, but various modifications will be possible without departing from the scope of claims as appended hereto.