Patent Publication Number: US-7901060-B2

Title: Ink-jet recording apparatus

Description:
This is a Continuation-in-Part of International Application No. PCT/JP2006/309467 filed May 11, 2006, which claims the benefits of Japanese Patent Application No. 2005-140494 filed May 13, 2005, Japanese Patent Application No. 2005-360586 filed Dec. 14, 2005, and Japanese Patent Application No. 2005-360587 filed Dec. 14, 2005, the disclosures of which are hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an ink-jet recording apparatus that ejects, from a nozzle thereof, ink toward a recording medium and thereby records an image thereon. 
     2. Discussion of Related Art 
     There has been known an ink-jet recording apparatus that includes a carriage; an ink-jet recording head mounted on the carriage; an ink tank provided at a position remote from the carriage; and a tube that supplies the ink from the ink tank to the ink-jet recording head. 
     In this sort of ink-jet recording apparatus, the carriage is moved with acceleration and accordingly pressure changes are produced in the ink-supply channels. If those pressure changes are directly transmitted to the nozzles of the ink-jet recording head, then the properties of droplets of inks, ejected by the recording head, are changed so that an image may be recorded with a lowered quality because of, e.g., occurrence of white spots. To deal with this problem, Patent Document 1 proposes to employ a method in which an ink-deliver chamber equipped with a damping means that damps the pressure changes is provided above the ink-jet recording head, so as to attenuate the adverse influences of acceleration produced by the movement of the carriage. 
     The damping means, disclosed by Publication of Japanese Patent No. 3520658, includes a damper frame having elliptic pressure-absorb chambers (i.e., ink-deliver chambers), and the inks supplied from the ink tanks via the tubes flow into respective flow passages that are connected to respective inlets of the pressure-absorb chambers from the underside in a tangential direction, and flow from respective outlets formed at respective lower portions of the pressure-absorb chambers toward the ink-jet recording head. Each of the pressure-absorb chambers (i.e., the ink-deliver chambers) has one surface that is defined by a flexible film. 
     SUMMARY OF THE INVENTION 
     To attenuate the pressure changes of the inks supplied via the tubes, it is desirable to form, in each of the pressure-absorb chambers (i.e., the ink-deliver chambers), the ink-flow inlet and the ink-flow outlet such that the inlet and the outlet be distant from each other by the largest possible distance. On the other hand, if air bubbles produced from the inks flowing in the pressure-absorb chambers move into the ink-jet recording head, then the recording head may fail to eject droplets of the inks. Therefore, it is desirable that the inks quickly flow from the ink-flow inlets to the ink-flow outlets before the air dissolved in each of the inks grows into the air bubbles. 
     In addition, in the case where different sorts of inks such as different color inks are used, it is needed to employ the same number of damping means as the total number of the different inks, and accordingly the layout of the damping means and respective connecting devices to connect between those damping means and the ink-jet recording head may be complicated and/or the sizes thereof may be increased. 
     It is therefore an object of the present invention to provide at least one of an ink-jet recording apparatus wherein respective volumes of a plurality of ink-deliver chambers are efficiently utilized to attenuate the pressure changes produced therein, and air bubbles produced in the ink-deliver chambers are effectively prevented from moving into an ink-jet recording head, and an ink-jet recording apparatus wherein a plurality of ink-deliver chambers are provided in a small space. 
     According to a first aspect of the present invention, there is provided an ink-jet recording apparatus, comprising a plurality of ink tanks which store a plurality of sorts of inks, respectively; a plurality of tubes which respectively supply the inks stored by the ink tanks; a buffer tank having a plurality of ink-deliver chambers which respectively accommodate the inks supplied from the ink tanks via the tubes; and an ink-jet recording head to which the ink-deliver chambers deliver the inks, respectively, and which ejects droplets of the inks toward a recording medium while the buffer tank and the ink-jet recording head are moved relative to the recording medium, wherein the ink-deliver chambers have respective inner spaces, respective ink-flow inlets through which the respective inks supplied via the respective tubes flow into the respective inner spaces, and respective ink-flow outlets through which the respective inks flow from the respective inner spaces into respective ink-deliver passages each of which communicates with the ink-jet recording head, and wherein the ink-flow inlet and the ink-flow outlet of each of the ink-deliver chambers are provided at respective positions that are substantially most distant from each other such that almost all portions of the inner space of the each ink-deliver chamber are located between the ink-flow inlet and the ink-low outlet of the each ink-deliver chamber. 
     In the present ink-jet recording apparatus, the ink-flow inlet and the ink-flow outlet of each ink-deliver chamber are provided at the respective positions that are substantially the most distant from each other such that almost all portions of the inner space of the each ink-deliver chamber are located between the ink-flow inlet and the ink-low outlet. Therefore, the respective volumes of the ink-deliver chambers are efficiently utilized to attenuate the pressure changes produced therein. In order that the ink-flow inlet and outlet of each ink-deliver chamber may be provided at the respective positions that are substantially the most distant from each other such that almost all portions of the inner space of the each ink-deliver chamber are located between the ink-flow inlet and the ink-low outlet, it is preferred that assuming that the ink-flow inlet and outlet of each ink-deliver chamber are distant from each other in a first direction, a distance between the ink-flow inlet and outlet be not less than 70% of a maximum dimension of the inner space of the each ink-deliver chamber in the first direction, more preferably, not less than 80% of the maximum dimension. 
     The above-indicated first direction may be perpendicular to a scanning direction in which the ink-jet recording head is moved relative to the recording medium. In many cases, the buffer tank has a plurality of first portions to receive, via the respective tubes, the respective inks stored by the respective ink tanks, and a plurality of second portions to deliver those inks to the ink-jet recording head, such that the first portions and the second portions are distant from each other in a direction perpendicular to the scanning direction. In those cases, generally, the inks flow in directions intersecting the scanning direction, and this is technically preferable. In the particular case where the above-indicated first direction is perpendicular to the scanning direction, the respective volumes of the ink-deliver chambers can be efficiently utilized to attenuate the changes of pressure of the inks. Most preferably, the first direction is perpendicular to not only the scanning direction but also upward and downward directions. 
     It is also preferred that the ink-flow inlet and outlet of each ink-deliver chamber be remote from each other in not only the first direction but also a second direction perpendicular to the first direction. In this case, a proportion of a portion of the inner space of each ink-deliver chamber that is located between the ink-flow inlet and outlet thereof may be increased and accordingly the volume of each ink-deliver chamber may be more efficiently utilized. In another particular case where each ink-deliver chamber has a quadrangular cross-section shape having a first pair of sides parallel to each other in the first direction and a second pair of sides parallel to each other in the second direction, the proportion of the portion of the inner space of each ink-deliver chamber that is located between the ink-flow inlet and outlet thereof may be sufficiently increased by determining, as the distance between the ink-flow inlet and outlet in the second direction, not less than 20% of a maximum dimension of the inner space in the second direction, more preferably, not less than 30% of the maximum dimension, most preferably, not less than 40% of the maximum dimension. 
     In yet another particular case where each ink-deliver chamber has a flat shape wherein a dimension thereof in a third direction perpendicular to the first and second directions is smaller than respective dimensions thereof in the first and second directions, the volume of each ink-deliver chamber may be efficiently utilized by making the ink-flow inlet and outlet thereof remote from each other in only one of the first and second directions. In this case, it is preferred that the second direction be perpendicular to the first direction and the upward and downward directions and that the third direction be the upward and downward directions. Furthermore, the above-indicated condition that the ink-flow inlet and outlet of each ink-deliver chamber are remote from each other in not only the first direction but also the second direction, may be expressed such that the ink-flow inlet and outlet of each ink-deliver chamber are remote from each other in the first direction and a straight line connecting between the ink-flow inlet and outlet is inclined relative to the first direction. In many cases, a length of an ink-flow passage in which ink flows can be increased by inclining the above-indicated straight line relative to the first direction. The above-indicated particular case where each ink-deliver chamber has the quadrangular cross-section shape is a typical one of those cases. Preferably, an angle contained by the first direction and the straight line is not less than 10 degrees, more preferably, not less than 20 degrees. 
     According to a second aspect of the present invention, there is provided an ink-jet recording apparatus, comprising a plurality of ink tanks which store a plurality of sorts of inks, respectively; a buffer tank having a plurality of ink-deliver chambers which respectively accommodate the inks supplied from the ink tanks; an ink-jet recording head which ejects droplets of the inks delivered by the ink-deliver chambers, toward a recording medium; and a moving device which moves the buffer tank and the ink-jet recording head in a direction intersecting a direction in which the recording medium is fed, wherein each of the ink-jet recording head and the ink-deliver chambers has a flat shape in which respective dimensions thereof in a first direction and a second direction that are perpendicular to each other are greater than a dimension thereof in a third direction perpendicular to the first direction and the second direction, and the ink-jet recording head and the ink-deliver chambers are arranged in the third direction. 
     In the present ink-jet recording apparatus, each of the ink-jet recording head and the ink-deliver chambers has the flat shape with respect to the third direction, and the ink-jet recording head and the ink-deliver chambers are arranged in the third direction. Therefore, an overall size of the ink-jet recording apparatus including the buffer tank and the ink-jet recording head can be reduced. 
     The ink-jet recording head and the ink-deliver chambers may be arranged such that the head and the chambers are held in contact with each other, such that the head and the chambers are spaced from each other, or such that some of the head and the chambers are held in contact with each other and the others are spaced from each other. 
     The first, second, and third directions recited with respect to the present, second ink-jet recording apparatus may be the same as those recited in the explanations provided with respect to the first ink-jet recording apparatus in accordance with the first aspect of the present invention. 
     According to a third aspect of the present invention, there is provided an ink-jet recording apparatus, comprising a plurality of ink-deliver chambers which accommodate a plurality of sorts of inks, respectively; a plurality of ink-deliver passages through which the inks are delivered from the ink-deliver chambers, respectively; an ink-jet recording head which has a plurality of ink-supply inlets which communicate with the plurality of ink-deliver passages, respectively; and a plurality of air-discharge valves each of which can be opened and closed, wherein the ink-deliver chambers are arranged in upward and downward directions such that the ink-deliver chambers extend parallel to each other, the ink-deliver passages extend in the upward and downward directions over respective substantially same lengths, each of the ink-deliver chambers communicates with an intermediate portion of a corresponding one of the ink-deliver passages, respective upper portions of the ink-deliver passages provide respective air-collect spaces each of which collects an air, respective lower open ends of the ink-deliver passages provide respective ink-deliver outlets which communicate with the respective ink-supply inlets of the ink-jet recording head, respective upper open ends of the ink-deliver passages provide respective air-discharge outlets which are provided along a plane, and the respective air-discharge outlets communicate with an outer space via the respective air-discharge valves. 
     In the present ink-jet recording apparatus, the ink-deliver chambers are arranged in the upward and downward directions such that the ink-deliver chambers extend parallel to each other. Therefore, the ink-deliver chambers can have substantially same operational characteristics. In addition, the ink-deliver chambers can have respective sufficiently large volumes, while a height of the recording apparatus as a whole need not be increased so much. Thus, the present recording apparatus can effectively attenuate the changes of pressure of the inks and thereby record high-quality images on the recording media. Moreover, since the ink-deliver passages extend in the upward and downward directions over the respective substantially same lengths, each of the ink-deliver passages can effectively promote the separation of air from a corresponding one of the inks flowing into a corresponding one of the ink-supply inlets of the ink-jet recording head, so that the separated air may be collected in the upper portion of the each ink-deliver passage and then discharged into the outside space via the air-discharge outlet of the upper portion. 
     Meanwhile, Japanese Patent Application Publication No. 2005-280075, for example, discloses a conventional ink-jet recording apparatus that ejects droplets of ink toward a recording medium and thereby records an image thereon. More specifically described, the conventional ink-jet recording apparatus includes a plurality of ink-deliver chambers that accommodate a plurality of sorts of inks, respectively; a plurality of ink-deliver passages through which the inks are delivered by the ink-deliver chambers; and an ink-jet recording head having a plurality of ink-supply inlets that communicate with the ink-deliver passages, respectively. The plurality of ink-deliver chambers consist of four ink-deliver chambers that accommodate four sorts of inks, respectively, and three of them are each of an upright type so that an air collected in an upper portion of each of the three upright-type chambers may damp the changes of pressure of the corresponding ink. Since, however, the height of the recording apparatus as a whole is limited, the volume of each of the three upright-type chambers is also limited. Therefore, the respective upper portions of the upright-type chambers cannot collect respective sufficiently large amounts of air and accordingly cannot exhibit respective sufficiently high damping effects. 
     In contrast, in the above-indicated, third ink-jet recording apparatus in accordance with the third aspect of the present invention, the ink-deliver chambers can have respective sufficiently large volumes, while the height of the recording apparatus as a whole need not be increased so much. Thus, the recording apparatus can effectively attenuate the changes of pressure of the inks. 
     In a particular case where respective upper or lower surfaces of the ink-deliver chambers are closed by respective flexible films, the changes of pressure of the inks in the ink-deliver chambers can be more effectively damped by respective deformations of those flexible films, because the flexible films can be easily formed to have respective large areas. 
     According to a fourth aspect of the present invention, there is provided an ink-jet recording apparatus, comprising at least one ink-deliver chamber which accommodates at least one ink; at least one ink-deliver passage which extends in upward and downward directions, through which the at least one ink is delivered from the at least one ink-deliver chamber, and which includes a lower portion that is located at a position lower than the at least one ink-deliver chamber and that has an ink-deliver outlet; an ink-jet recording head having at least one ink-supply inlet to which the at least one ink is supplied through the ink-deliver outlet of the at least one ink-deliver passage; and at least one ink-connect portion which maintains or promotes a connection between the ink delivered from the at least one ink-deliver chamber and the ink present in the lower portion of the at least one ink-deliver passage. 
     In the present, fourth ink-jet recording apparatus, the at least one ink-connect portion maintains or promotes the connection between the ink delivered from the at least one ink-deliver chamber and the ink present in the lower portion of the at least one ink-deliver passage. That is, the connection, i.e., flowing of the ink as a fluid is effectively prevented from being cut, i.e., temporarily stopped by the air gradually accumulated in the upper portion of the ink-deliver passage. Therefore, a probability that the air may be sucked into the ink-jet recording head and the recording head may fail to print characters or may print defective characters is lowered. 
     In the above-indicated conventional ink-jet recording apparatus, when each of the ink-deliver chambers delivers the corresponding ink to the corresponding ink-deliver passage, air bubbles are naturally separated from the ink and the separated air bubbles are collected in the upper portion of the ink-deliver passage. Thus, the air is prevented from flowing into the ink-jet recording head. In addition, the thus collected air is discharged, as needed, via a corresponding air-discharge outlet that can be opened and closed by a corresponding air-discharge valve. However, in this type of ink-jet recording apparatus, if more than a prescribed amount of air is accumulated in the upper portion of each ink-deliver passage, then the accumulated air may cut, i.e., temporarily stop the connection, i.e., flowing of the ink from the ink-deliver chamber to the ink-jet recording head. And, if the connection of the ink is cut, then the probability that the air may be sucked into the ink-jet recording head and the recording head may fail to print characters or may print defective characters is raised. Moreover, if, in that event, a purging operation is carried out for the ink-jet recording head, then the accumulated air may expand before the ink is sucked from the ink-deliver chamber, so that the air may be sucked into the recording head and accordingly the recording head may fail to print characters. In order to prevent the cutting of the connection of the ink, it is needed not to accumulate an excessively large amount of air in the upper portion of each ink-deliver passage. 
     In contrast to the conventional ink-jet recording apparatus, the present, fourth ink-jet recording apparatus enjoys the advantages that the connection of the ink as the fluid is prevented from being cut by the air collected in the upper portion of the ink-deliver passage and that the probability that the collected air may be sucked into the ink-jet recording head and the recording head may fail to print characters or may print defective characters is lowered. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view for explaining relevant elements of an ink-jet recording apparatus as a first embodiment of the present invention. 
         FIG. 2  is a plan view of a head holder  9  of the ink-jet recording apparatus. 
         FIG. 3  is a view of a nozzle-opening surface of the head holder  9  shown in  FIG. 2 . 
         FIG. 4  is a cross-section view taken along Arrows  4 - 4  in  FIG. 2  (or  FIG. 15 ). 
         FIG. 5  is a plan view of ink-introduce passages provided in an extension portion  40   a  of a buffer tank  40  of the head holder  9  shown in  FIG. 2 . 
         FIG. 6  is a top plan view of an upper ink case  71  of the head holder  9 . 
         FIG. 7  is a bottom plan view of the upper ink case  71 . 
         FIG. 8  is a top plan view of a lower ink case  72  of the head holder  9 . 
         FIG. 9  is a bottom plan view of the lower ink case  72 . 
         FIG. 10  is an enlarged top plan view of the upper ink case  71 . 
         FIG. 11  is a cross-section view taken along Arrows Y-Y in FIG.  10 . 
         FIG. 12  is a cross-section view taken along Arrows M-M in  FIG. 10 . 
         FIG. 13  is a cross-section view taken along Arrows C-C in  FIG. 10 . 
         FIG. 14  is a cross-section view taken along Arrows B-B in  FIG. 10 . 
         FIG. 15  is a plan view of a head holder  9  of another ink-jet recording apparatus as a second embodiment of the present invention. 
         FIG. 16  is a top plan view of an upper ink case  71  employed in the second embodiment. 
         FIG. 17  is a bottom plan view of the upper ink case  71  shown in  FIG. 16 . 
         FIG. 18  is a top plan view of a lower ink case  72  employed in the second embodiment. 
         FIG. 19  is a bottom plan view of the lower ink case  72  shown in  FIG. 18 . 
         FIG. 20  is an enlarged top plan view of the upper ink case  71  employed in the second embodiment. 
         FIG. 21  is a cross-section view taken along Arrows Y-Y in  FIG. 20 . 
         FIG. 22  is a cross-section view taken along Arrows M-M in  FIG. 20 . 
         FIG. 23  is a cross-section view taken along Arrows C-C in  FIG. 20 . 
         FIG. 24  is a cross-section view taken along Arrows B-B in  FIG. 20 . 
         FIG. 25  is a cross-section view taken along Arrows  25 - 25  in  FIG. 15 . 
         FIG. 26  is a cross-section view corresponding to  FIG. 21  and showing a head holder of another ink-jet recording apparatus as a third embodiment of the present invention. 
         FIG. 27  is a cross-section view corresponding to  FIG. 22  and showing the head holder employed by the third embodiment. 
         FIG. 28  is a cross-section view corresponding to  FIG. 23  and showing the head holder employed by the third embodiment. 
         FIG. 29  is a cross-section view corresponding to  FIG. 24  and showing the head holder employed by the third embodiment. 
         FIG. 30  is an enlarged cross-section view of a portion of the head holder shown in  FIG. 26 , for explaining a state in which an ink normally flows in that portion. 
         FIG. 31  is an enlarged cross-section view of the portion of the head holder shown in  FIG. 26 , for explaining a state in which the flowing of the ink is temporarily stopped. 
         FIG. 32  is an enlarged cross-section view of a portion of the head holder shown in  FIG. 29 , for explaining a state in which an ink normally flows in that portion. 
         FIG. 33  is an enlarged cross-section view of the portion of the head holder shown in  FIG. 29 , for explaining a state in which the flowing of the ink is temporarily stopped. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, there will be described preferred embodiments of the present invention by reference to the drawings. 
     (Ink-Jet Recording Apparatus) 
     First, there will be described relevant elements of an ink-jet recording apparatus  1  by reference to  FIG. 1 .  FIG. 1  is a plan view for explaining the relevant elements of the ink-jet recording apparatus  1 . 
     Inside the ink-jet recording apparatus  1 , there are provided two guide bars  6 ,  7  that cooperate with each other to support a head holder  9  that also functions as a movable carriage. The head holder  9  holds an ink-jet recording head  30  that ejects droplets of inks toward a recording sheet, P, so as to record an image thereon. The head holder  9  is fixed to an endless belt  11  that is circulated by an electric motor  10  and, when the motor  10  is driven or rotated, the head holder  9  is reciprocated along the two guide bars  6 ,  7 . Thus, the head holder  9 , the electric motor  10 , and the endless belt  11  cooperate with each other to provide a moving device that moves the ink-jet recording head  30  relative to the recording sheet P as a recording medium. 
     In addition, an ink tank  5 M that stores a magenta ink, an ink tank  5 C that stores a cyan ink, an ink tank  5 B that stores a black ink, and an ink tank  5 Y that stores a yellow ink are provided at respective fixed positions in a housing of the ink-jet recording apparatus  1 . The four ink tanks  5 M through  5 Y are connected to a tube joint  20  via four flexible tubes  14 M,  14 C,  14 B,  14 Y, respectively. 
     (Head Holder) 
     Next, there will be described relevant elements of the head holder  9 . 
     In the following description, a surface from, and a direction in, which droplets of the inks are ejected from the head holder  9  will be referred to as the “lower” surface and the “downward” direction, respectively; and a surface opposite to the lower surface and a direction opposite to the downward direction will be referred to as the “upper” surface and the “upward” direction, respectively. In addition, respective directions toward left-hand and right-hand ends of the ink-jet recording apparatus  1 , as seen in  FIG. 1 , will be referred to as the “leftward” and “rightward” directions, respectively; and respective directions toward lower and upper ends of the ink-jet recording apparatus  1 , as seen in  FIG. 1 , will be referred to as the “frontward” and “rearward” directions, respectively. 
     In addition, suffixes M, C, B, Y, given to reference numerals, indicate relations to the magenta ink, the cyan ink, the black ink, and the yellow ink, respectively. 
     As shown in  FIG. 4 , the head holder  9  has a box-like configuration having an upper opening, and the ink-jet recording head  30  is held by a lower surface of a bottom wall  9   c  of the head holder  9 . The ink-jet recording head  30  includes a cavity portion  32  having a multiplicity of ink-flow passages, and a piezoelectric actuator  31  that is stacked on the cavity portion  32  and that selectively applies an ejection pressure to an arbitrary one of the inks present in the ink-flow passages of the cavity portion  32 . The cavity portion  32  has, in a lower surface thereof, nozzle arrays  35 ,  36 ,  37 ,  38  ( FIG. 3 ) corresponding to the four inks, and additionally has, in an upper surface thereof, four ink-supply inlets corresponding to the four inks, respectively. In  FIG. 4 , only the ink-supply inlet  32   a  into which the yellow ink flows is shown. A reinforcing frame  33  having a central opening is fixed, by adhesion, to an upper surface of the ink-jet recording head  30 . The reinforcing frame  33  additionally has four ink-flow openings corresponding to the four ink-supply inlets of the cavity portion  32 , respectively. In  FIG. 4 , only the ink-flow opening  33   a  corresponding to the yellow-ink supply inlet  32   a  is shown. 
     (Buffer Tank  40 ) 
     The buffer tank  40  is provided above the bottom wall  9   c  of the head holder  9 . Regarding the upward and downward directions, the buffer tank  40  has such an arrangement that an upper ink case  71  and a lower ink case  72  extend parallel to each other and are joined to each other. In addition, regarding the frontward and rearward directions, the buffer tank  40  has such an arrangement that an ink-introduce portion  40   e , a buffer portion  40   b , and an ink-output portion  40   d  are arranged in the order of description. 
     In the buffer portion  40   b , the upper ink case  71  has a partition wall  71   c  ( FIGS. 11 and 12 ) that separates an inner space into upper and lower portions. Thus, the upper ink case  71  has an upper, yellow-ink deliver chamber  41  ( FIG. 6 ) that accommodates and delivers the yellow ink, and a lower, magenta-ink deliver chamber  42  ( FIG. 7 ) that accommodates and delivers the magenta ink, such that the two ink-deliver chambers  41 ,  42  are adjacent to each other via the partition wall  71   c.    
     In addition, the lower ink case  72  has a partition wall  72   c  ( FIGS. 13 and 14 ) that separates an inner space into upper and lower portions. Thus, the lower ink case  72  has an upper, cyan-ink deliver chamber  43  ( FIG. 8 ) that accommodates and delivers the cyan ink, and a lower, black-ink deliver chamber  44  ( FIG. 9 ) that accommodates and delivers the black ink, such that the two delivery chambers  43 ,  44  are adjacent to each other via the partition wall  72   c.    
     That is, the four ink-deliver chambers  41 ,  42 ,  43 ,  44  are arranged in the upward and downward directions such that the four chambers  41  through  44  extend parallel to each other and such that the first pair of chambers  41 ,  42  are formed in one, upper ink case  71  and the second pair of chambers  43 ,  44  are formed in the other, lower ink case  72 . Thus, the buffer tank  40  temporarily stores the yellow ink, the magenta ink, the cyan ink, and the black ink in respective layers that are arranged in the order of description in the downward direction. 
     Since the four ink-deliver chambers  41  through  44  extend parallel to each other, and are arranged in the upward and downward directions (i.e., are aligned with each other in the upward and downward directions), the four chambers  41  through  44  have substantially same operational characteristics regarding the delivering of the inks to the ink-jet recording head  30 . In addition, the four ink-deliver chambers  41  through  44  can have respective sufficiently large volumes, without needing to increase a height of the buffer tank  40  or a height of the ink-jet recording apparatus  1  as a whole. Therefore, the ink-jet recording apparatus  1  can effectively damp the changes of pressure of the inks and thereby can record images with a high quality. 
     The ink-output portion  40   d  includes the same number of ink-deliver passages  91 Y,  91 M,  91 C,  91 B as the number of the ink-deliver chambers  41  through  44 , and the ink-deliver passages  91 Y through  91 B are provided in rear of the buffer portion  40   b  such that the ink-deliver passages  91 Y through  91 B are arranged in an array in a scanning direction in which the ink-jet recording head  30  is moved. The ink-deliver passages  91 Y through  91 B each extend in the upper and lower ink cases  71 ,  72 , and have, as respective lower open ends thereof, respective ink-deliver outlets  39 Y,  39 M,  39 C,  39 B that communicate with the respective ink-supply inlets (only the ink-supply inlet  32   a  is shown) of the ink-jet recording head  30  via the respective ink-flow openings (only the ink-flow opening  33   a  is shown) of the reinforcing frame  33 . 
     The four ink-deliver passages  91 Y through  91 B corresponding to the four inks, respectively, are formed by separating, with separation walls  91   g , respective inner spaces of respective tubular walls  91   e ,  91   f  of the upper and lower ink cases  71 ,  72 . When the tubular wall  91   e  and the separation walls  91   g  of the upper ink case  71  and the tubular wall  91   f  and the separation walls  91   g  of the lower ink case  72  are aligned with each other, and are bonded to each other by, e.g., supersonic welding or adhesion, then the ink-deliver passages  91 Y through  91 B are each formed continuously in the upper and lower ink cases  71 ,  72  while the two ink cases  71 ,  72  are joined to, and integrated with, each other. 
     Thus, in the respective rear portions of the upper and lower ink cases  71 ,  72 , the ink-deliver passages  91 Y through  91 B extend in the upward and downward directions. 
     The ink-introduce portion  40   e  includes an extension portion  40   a  that is extended frontward from the buffer portion  40   b . As shown in  FIG. 4 , the extension portion  40   a  is supported by a support arm  9   a  that is extended horizontally frontward from a front end of the head holder  9 . The tube joint  20  is attached to an upper surface of a front portion of the extension portion  40   a . The tube joint  20  includes, as a front end portion thereof, a cable-hold portion  29  that holds a flexible flat cable, not shown, such that the flexible flat cable is passed through a slit of the cable-hold portion  29  in the leftward and rightward directions in  FIG. 1 . 
     As shown in  FIG. 2 , the tube joint  20  includes connection portions  21 M,  21 C,  21 B,  21 Y to which the tubes  14 M through  14 Y are connected, respectively, such that the connection portions  21 M through  21 Y are arranged in an array in the frontward direction, and project in the leftward direction. The connection portions  21 M through  21 Y have respective inner ink-flow passages into which the respective inks flow from the tubes  14 M through  14 Y connected thereto. 
     As shown in  FIG. 5 , in an upper surface of the extension portion  40   a  that corresponds to a lower surface of the tube joint  20 , ink-introduce inlets  22 M,  22 C,  22 B,  22 Y that communicate with the respective inner ink-flow passages of the connection portions  21 M through  21 Y ( FIG. 2 ) are formed to open, and are arranged in an array in the order of description in the frontward direction. 
     The extension portion  40   a  has, in a lower surface thereof, ink-introduce passages  61 M,  61 C,  61 B,  61 Y that are connected, at respective front ends thereof, to the ink-introduce inlets  22 M through  22 Y. The ink-introduce passages  61 M,  61 C,  61 B,  61 Y are each defined by a groove (e.g., a recessed groove employed in the present embodiment) that extends in the frontward and rearward directions, and are arranged, in the lower surface of the extension portion  40   a , in the leftward and rightward directions. 
     The ink-introduce passages  61 M through  61 Y given in the form of the grooves have respective lower openings that are commonly closed by a film  85  ( FIGS. 4 and 11 ). The film  85  cooperates with those grooves to constitute the ink-introduce passages  61 M through  61 Y. 
     The extension portion  40   a  is integrally formed with, and connected to, the partition wall  71   c  of the upper ink case  71 . The ink-introduce passages  61 M through  61 Y are connected, at respective rear ends thereof, to respective ink-introduce passages  63 M,  63 C,  63 B,  63 Y, formed in the upper surface of the extension portion  40   a , via respective ink-introduce holes  62 M,  62 C,  62 B,  62 Y formed through a thickness of the extension portion  40   a  in the upward and downward directions. 
     As will be described later, the left-hand-end ink-introduce passage  63 Y and the right-hand-end ink-introduce passage  63 M ( FIG. 5 ) are connected to the yellow-ink deliver chamber  41  and the magenta-ink deliver chamber  42  of the upper ink case  71 , respectively; and the intermediate, two ink-introduce passages  63 C,  63 B are connected to the cyan-ink deliver chamber  43  and the black-ink deliver chamber  44  of the lower ink case  72 , respectively. 
     A lower surface  71   b  of the upper ink case  71  that is opposed to an upper surface  72   a  of the lower ink case  72  has, at a position that is, in its plan view, aligned with respective rear ends of the intermediate two ink-introduce passages  63 C,  63 B, a tubular wall  92   a  ( FIG. 7 ) projecting downward from the lower surface  71   b  toward the upper surface  72   a ; and the upper surface  72   a  of the lower ink case  72  that is opposed to the lower surface  71   b  of the upper ink case  71  has, at a position that is, in its plan view, aligned with the respective rear ends of the intermediate two ink-introduce passages  63 C,  63 B, a tubular wall  92   b  ( FIG. 8 ) projecting upward from the upper surface  72   a  toward the lower surface  71   b . Two ink-introduce passages  64 B,  64 C are each formed through the two tubular walls  92   a ,  92   b , and are connected, at respective upper open ends thereof, to the respective rear ends of the two ink-introduce passages  63 C,  63 B. 
     If the two tubular walls  92   a ,  92   b  are joined to each other by a bonding means such as supersonic welding or adhesion, then the two ink-introduce passages  63 C,  63 B of the upper ink case  71  are connected to the two ink-deliver chambers  43 ,  44  of the lower ink case  72  via the two ink-introduce passages  64 B,  64 C of the same  72 . In addition, the joining of the two tubular walls  92   a ,  92   b  cooperates with the joining of the two tubular walls  91   e ,  91   f  to connect and integrate the upper and lower ink cases  71 ,  72  to and with each other. 
     (Each Ink-Deliver Chamber  41  through  44 ) 
     Next, relevant elements of each of the ink-deliver chambers  41  through  44  will be described by reference to the drawings. 
     (Ink-Deliver Chamber  41 ) 
     As shown in  FIG. 6 , in the buffer portion  40   b  of the buffer tank  40 , the yellow-ink deliver chamber  41  is formed in the upper surface  71   a  of the partition wall  71   c  ( FIG. 11 ) of the upper ink case  71 , such that the yellow-ink deliver chamber  41  has a flat inner space whose cross section is generally quadrangular, and has an upper opening that is also generally quadrangular. The yellow-ink deliver chamber  41  has four side surfaces that are defined by a left-hand side wall  41   i , a right-hand side wall  41   h , a rear side wall  41   k , and a front side wall  41   m . The yellow-ink deliver chamber  41  has, at a left-hand and front corner contained by the left-hand side wall  41   i  and the front side wall  41   m , an ink-flow inlet  41   b  that communicates with the rear end of the ink-introduce passage  63 Y. 
     The yellow-ink deliver chamber  41  additionally has an ink-flow outlet  41   c  through which the yellow ink flows from the deliver chamber  41 . The ink-flow outlet  41   c  opens, in the deliver chamber  41 , at a position located on the right-hand side of the middle of the rear side wall  41   k  and spaced leftward from a right-hand and rear corner of the deliver chamber  41 . 
     Thus, the yellow-ink flow inlet  41   b  and the yellow-ink flow outlet  41   c  are provided at respective positions that are, in view of their circumstances, as near as possible to respective diagonal positions of the yellow-ink deliver chamber  41 . That is, the yellow-ink flow inlet  41   b  and the yellow-ink flow outlet  41   c  are provided at respective positions that are substantially the most distant from each other such that almost all portions of the inner space of the deliver chamber  41  are located between the two positions. 
     The yellow-ink flow inlet  41   b  and the yellow-ink flow outlet  41   c  are distant from each other in a direction (i.e., an example of a first direction) that is perpendicular to not only the scanning direction but also the upward and downward directions, and a straight line connecting between the inlet  41   b  and the outlet  41   c  is inclined relative to the first direction. These are also true with the other ink-deliver chambers  42 ,  43 ,  44 . 
     The yellow-ink flow outlet  41   c  is connected to the ink-deliver passage  91 Y ( FIGS. 7 and 11 ) via a connection passage  65 Y, formed through a thickness of the partition wall  71   c  of the upper ink case  71 , from a bottom surface  41   a  of the yellow-ink deliver chamber  41  to the lower surface  71   b  ( FIG. 7 ) of the partition wall  71   c . A lower end of the connection passage  65 Y opens in the ink-deliver passage  91 Y at a position lower than an upper end of the passage  91 Y. That is, a lower portion of the connection passage  65 Y is defined by a guide wall  64 Y projecting downward from the lower surface  71   b  of the upper ink case  71 , so that the yellow ink is delivered from the ink-flow outlet  41   c  to a lower portion of the ink-deliver passage  91 Y. The four ink-deliver passages  91 Y,  91 M,  91 C,  91 B are expanded frontward into a space between the yellow-ink deliver chamber  41  and the black-ink deliver chamber  44 , so as to be aligned with the connection passage  65 Y, a connection passage  65 M, a cyan-ink flow outlet  43   c , and a black-ink flow outlet  44   c , respectively, in the upward and downward directions. The connection passage  65 Y can be said as an extension of the yellow-ink flow outlet  41   c , and the connection passage  65 M can be said as an extension of a magenta-ink flow outlet  42   c.    
     Respective upper openings of the yellow-ink deliver chamber  41 , the four ink-introduce passages  63 Y,  63 B,  63 C,  63 M, and four air-discharge passages  93 , described later, are closed by a flexible film  81  as a flexible diaphragm ( FIGS. 2 ,  4  and  11 ). Respective upper surfaces of respective side walls that define the ink-introduce passages  63 Y through  63 M and the air-discharge passages  93  are flush with respective upper surfaces of the four side walls  41   h ,  41   i ,  41   k ,  41   m  of the yellow-ink deliver chamber  41 . The flexible film  81  is bonded to those upper surfaces by a bonding means such as adhesion or thermal welding. Thus, the yellow-ink deliver chamber  41 , the ink-introduce passages  63 Y through  63 M, and the air-discharge passages  93  are formed in the upper ink case  71 . 
     Three ribs  41   d ,  41   e ,  41   f  project upward from the bottom surface  41   a  of the yellow-ink deliver chamber  41 , such that the two ribs  41   d ,  41   f  are located on one side of, and spaced from, the straight line connecting between the yellow-ink flow inlet and outlet  41   b ,  41   c  and the rib  41   e  is located on the opposite side of, and spaced from, the same line. Each of the ribs  41   d ,  41   e  has a quadrangular cross section, and has a height equal to substantially half a depth of the ink-deliver chamber  41  (i.e., a distance between the bottom surface  41   a  and the film  81 ). Thus, the two ribs  41   d ,  41   e  are spaced from the film  81  so as not to restrict displacing of the flexible film  81 . The two ribs  41   d ,  41   e  cooperate with each other to guide a quick flow of the yellow ink from the ink-flow inlet  41   b  to the ink-flow outlet  41   c . The third rib  41   f  bent at an intermediate portion thereof, is located between the two ribs  41   d ,  41   e , and cooperates with the second rib  41   e , also bent at an intermediate portion thereof, to guide the flow of the yellow ink to the ink-flow outlet  41   c.    
     (Magenta-Ink Deliver Chamber  42 ) 
     Next, the magenta-ink deliver chamber  42  will be described by reference to  FIG. 7 . Since  FIG. 7  is a bottom view of the upper ink case  71 , “left” and “right” in  FIG. 6  are reversed in  FIG. 7 , i.e., correspond to—right—and—left—in  FIG. 7 , respectively. In the following description, however, the terms “left” and “right” defined in relation with  FIG. 6  are also used in relation with  FIG. 7 . 
     As shown in  FIG. 7 , in the buffer portion  40   b  of the buffer tank  40 , the magenta-ink deliver chamber  42  is formed in the lower surface  71   b  of the partition wall  71   c  of the upper ink case  71 , such that the magenta-ink deliver chamber  42  has a flat inner space whose cross section is generally quadrangular, and has a lower opening that is also generally quadrangular. The magenta-ink deliver chamber  42  is defined by four side walls, i.e., a left-hand side wall  42   i , a right-hand side wall  42   h , a rear side wall  42   k , and a front side wall  42   m . As shown in  FIG. 12 , the magenta-ink deliver chamber  42  is provided adjacent to the yellow-ink deliver chamber  41  via the partition wall  71   c.    
     The magenta-ink deliver chamber  42  has an ink-flow inlet  42   b  that is formed through the thickness of the upper ink case  71 , is connected to the rear end of the ink-introduce passage  63 M ( FIG. 6 ), and opens in a bottom surface  42   a  of the deliver chamber  41 , at a right-hand and rear corner thereof ( FIG. 7 ). 
     The magenta-ink deliver chamber  42  additionally has an ink-flow outlet  42   c  through which the magenta ink flows from the deliver chamber  42 . The ink-flow outlet  42   c  is formed through the thickness of the upper ink case  71 , and opens, in the bottom surface  42   a  of the deliver chamber  42 , at a left-hand and rear corner thereof that is diagonal relative to the ink-flow inlet  42   b.    
     The upper ink case  71  (or the partition wall  71   c  thereof) has, in the upper surface  71   a  thereof, a connection passage  65 M at a position that is aligned with the ink-flow outlet  42   c  and is located outside the yellow-ink deliver chamber  41 . One end of the connection passage  65 M is connected to the ink-flow outlet  42   c  formed through the thickness of the partition wall  71   c , and the other end of the same  65 M is formed through the thickness of the partition wall  71   c  and is connected to the magenta-ink deliver passage  91 M. 
     A lower end of the connection passage  65 M opens, in the ink-deliver passage  91 M, at a position lower than an upper end of the same  91 M. Thus, a lower portion of the rear end portion of the connection passage  65 M is defined by a guide wall  64 M projecting downward from the upper ink case  71 , so that the magenta ink is delivered from the ink-flow outlet  42   c  to a lower portion of the ink-deliver passage  91 M. 
     As described above, the magenta-ink flow outlet  42   c  is formed through the thickness of the partition wall  71   c  that separates the upper ink case  71  into the two ink-deliver chambers  41 ,  42 , and is connected to the ink-deliver passage  91 M via the connection passage  65 M. Thus, the magenta-ink flow outlet  42   c  is an example of an ink-flow outlet of an ink-deliver chamber, formed in one of opposite surfaces of a case, that is formed through a thickness of the case in a direction from the one surface to the other surface and is connected to an ink-deliver passage. 
     Thus, the magenta-ink flow inlet  42   b  and the magenta-ink flow outlet  42   c  are provided at respective substantially diagonal positions of the magenta-ink deliver chamber  42 . That is, the magenta-ink flow inlet  42   b  and the magenta-ink flow outlet  42   c  are provided at respective positions that are substantially the most distant from each other such that almost all portions of the inner space of the deliver chamber  42  are located between the two positions. 
     That is, the magenta-ink flow inlet  42   b  and the magenta-ink flow outlet  42   c  are provided at respective positions that are substantially the most distant from each other such that almost all portions of the inner space of the deliver chamber  42  where the magenta ink flows are located between the two positions. 
     In addition, the yellow-ink deliver chamber  41  and the magenta-ink deliver chamber  42  are provided adjacent to each other via the partition wall  71   c  of the upper ink case  71 , such that the yellow-ink flow inlet  41   b  and the magenta-ink flow inlet  42   b  are provided at respective different positions along the partition wall  71   c  and the yellow-ink flow outlet  41   c  and the magenta-ink flow inlet  42   c  are provided at respective different positions along the partition wall  71   c . Thus, in a plan view of the upper ink case  71 , a straight line connecting between the yellow-ink flow inlet  41   b  and the yellow-ink flow outlet  41   c  and a straight line connecting between the magenta-ink flow inlet  42   b  and the magenta-ink flow outlet  42   c  have such a positional relationship in which the two straight lines intersect each other like two diagonal lines of a quadrangle. 
     That is, the yellow-ink flow inlet  41   b  and the yellow-ink flow outlet  41   c  are distant from each other, and the magenta-ink flow inlet  42   b  and the magenta-ink flow outlet  42   c  are distant from each other, in the direction (i.e., an example of the first direction) that is perpendicular to not only the scanning directions but also the upward and downward directions, and the straight line connecting between the yellow-ink flow inlet  41   b  and the yellow-ink flow outlet  41   c  and the straight line connecting between the magenta-ink flow inlet  42   b  and the magenta-ink flow outlet  42   c  are inclined, relative to the first direction, in opposite directions each away from the first direction. These are also true with the other pair of ink-deliver chambers  43 ,  44 . 
     A lower opening of the magenta-ink deliver chamber  42  is closed by a flexible film  82  as a flexible diaphragm ( FIG. 12 ). The film  82  is bonded to respective upper surfaces of the side walls  42   h ,  42   i ,  42   k ,  42   m  of the ink-deliver chamber  42 , by a bonding means such as adhesion or thermal welding. Thus, the magenta-ink deliver chamber  42  is formed. 
     Thus, the upper ink case  71  includes a chamber-define wall having upper and lower openings, and the two flexible films  81 ,  82  that close the upper and lower openings, respectively. The chamber-define wall includes the partition wall  71   c  that separates the upper ink case  71  into the upper and lower ink-deliver chambers  41 ,  42 ; the upper, side walls  41   h ,  41   i ,  41   k ,  41   m ; and the lower, side walls  42   h ,  42   i ,  42   k ,  42   m.    
     Two ribs  42   d ,  42   e  project downward from the bottom surface  42   a  of the magenta-ink deliver chamber  42 , such that the two ribs  42   d ,  42  extend parallel to each other and are distant by respective substantially equal distances from a diagonal line connecting between the magenta-ink flow inlet  42   b  and the magenta-ink flow outlet  42   c . Each of the ribs  42   d ,  42   e  has a quadrangular cross section, and has a height equal to substantially half a depth of the deliver chamber  42  (i.e., a distance between the bottom surface  42   a  and the film  82 ). Thus, the ribs  42   d ,  42   e  are spaced from the film  82  so as not to restrict the displacing of the flexible film  82 . The two ribs  42   d ,  42   e  cooperate with each other to guide a quick flow of the magenta ink from the ink-flow inlet  42   b  to the ink-flow outlet  42   c.    
     (Cyan-Ink Deliver Chamber  43 ) 
     Next, the cyan-ink deliver chamber  43  will be described by reference to  FIGS. 8 and 9 . Since  FIG. 9  is a bottom view of the lower ink case  72 , “left” and “right” in  FIG. 8  are reversed in  FIG. 9 , i.e., correspond to—right—and —left—in  FIG. 9 , respectively. In the following description, however, the terms “left” and “right” defined in relation with  FIG. 8  are also used in relation with  FIG. 9 . 
     As shown in  FIG. 8 , the cyan-ink deliver chamber  43  having a shape similar to that of the magenta-ink deliver chamber  42 , is formed in the upper surface  72   a  ( FIG. 13 ) of the partition wall  72   c  of the lower ink case  72 , at a position corresponding to the magenta-ink deliver chamber  42 . The cyan-ink deliver chamber  43  is defined by four side walls, i.e., a left-hand side wall  43   i , a right-hand side wall  43   h , a rear side wall  43   k , and a front side wall  43   m , such that the deliver chamber  43  opens upward. Two ribs  43   d ,  43   e  similar to the two ribs  43   d ,  43   e  project upward from a bottom surface  43   a  of the cyan-ink deliver chamber  43 . 
     Like the lower opening of the magenta-ink deliver chamber  42 , the upper opening of the cyan-ink deliver chamber  43  is closed by a flexible film  83  having a generally rectangular shape. 
     The upper and lower ink cases  71 ,  72  are joined to each other such that the film  82  closing the magenta-ink deliver chamber  42  and the film  83  closing the cyan-ink deliver chamber  43  are spaced from, and opposed to, each other and extend parallel to each other. 
     The cyan-ink deliver chamber  43  has an ink-flow inlet  43   b  that is formed through the thickness of the lower ink case  72 , is connected to one end of an ink-introduce passage  66 C formed in the lower surface  72   b  of the lower ink case  72 , and opens, in the bottom surface  43   a  of the deliver chamber  43 , at a right-hand and front corner thereof. More specifically described, the ink-introduce passage  66 C is formed along the right-hand and front corner of the deliver chamber  43 , outside of the same  43 , such that the passage  66 C has an L-shaped profile, and the other end of the passage  66 C is connected to a lower end of the ink-introduce passage  64 C. 
     Thus, the ink-introduce passage  63 C ( FIG. 6 ) formed in the upper surface  71   a  of the upper ink case  71  communicates with the ink-flow inlet  43   b  of the cyan-ink deliver chamber  43  via the ink-introduce passage  64 C formed through the respective thickness of the upper and lower ink cases  71 ,  72 , and the ink-introduce passage  66 C. 
     The cyan-ink deliver chamber  43  additionally has an ink-flow outlet  43   c  through which the cyan ink flows from the deliver chamber  43 . The ink-flow outlet  43   c  is formed through the thickness of the lower ink case  72 , opens, in the bottom surface  43   a  of the deliver chamber  43 , at a left-hand and rear corner thereof that is diagonal relative to the ink-flow inlet  43   b , and is connected to one end of a connection passage  68 C ( FIG. 9 ) formed in the lower surface  72   b  of the lower ink case  72 . 
     As shown in  FIG. 9 , the connection passage  68 C is formed along a left-hand and rear corner of the black-ink deliver chamber  44 , outside the same  44 , such that the passage  68 C has an L-shaped profile. Respective rear end portions of the connection passage  68 C and the black-ink deliver chamber  44  overlap, in their plan view, respective lengthwise intermediate portions of the ink-deliver passages  91 M,  91 C,  91 Y,  91 B, and an other end  68 Ca of the connection passage  68 C is formed through the thickness of the lower ink case  72  in a direction from the lower surface  72   b  thereof to the upper surface  72   a  thereof and is connected to the ink-deliver passage  91 C. 
     More specifically described, the cyan-ink flow outlet  43   c  is formed through the thickness of the partition wall  72   c  that separates the lower ink case  72  into the two ink deliver chambers  43 ,  44 , and is connected to the ink-deliver passage  91 C via the connection passage  68 C. Thus, the cyan-ink flow outlet  43   c  is an example of an ink-flow outlet of an ink-deliver chamber, formed in one of opposite surfaces of a case, that is formed through a thickness of the case in a direction from the one surface to the other surface and is connected to an ink-deliver passage. This is also true with the ink-flow outlet  44   c  of the black-ink deliver chamber  44 . 
     (Black-Ink Deliver Chamber  44 ) 
     Next, the black-ink deliver chamber  44  will be described by reference to  FIG. 9 . 
     As shown in  FIG. 9 , the black-ink deliver chamber  44  is formed in the lower surface  72   b  of the partition wall  72   c  of the lower ink case  72 , such that the black-ink deliver chamber  44  has a flat inner space whose cross section is generally quadrangular, and has a lower opening that is also generally quadrangular. The black-ink deliver chamber  44  is defined by four side surfaces, i.e., a left-hand side wall  44   i , a right-hand side wall  44   h , a rear side wall  44   k , and a front side wall  44   m . The black-ink deliver chamber  44  is provided adjacent to the cyan-ink deliver chamber  43  via the partition wall  72   c.    
     In addition, the ink-introduce passage  66 C is provided adjacent to the right-hand and front corner of the black-ink deliver chamber  44 , and the connection passage  68 C is provided adjacent to the left-hand and rear corner of the deliver chamber  44 , such that each of the ink-introduce passage  66 C and the connection passage  68 C is separated from the deliver chamber  44 . 
     A front portion of the black-ink deliver chamber  44  overlaps, in its plan view, the ink-introduce passage  64 B, and the ink-introduce passage  64 B is formed through a thickness of the partition wall  72   c  of the lower ink case  72 , in the upward and downward directions, so as to open at a left-hand and front corner of a bottom surface  44   a  of the black-ink deliver chamber  44 . Thus, a lower open end of the ink-introduce passage  64 B defines an ink-flow inlet  44   b  of the black-ink deliver chamber  44 . 
     An ink-flow outlet  44   c  of the black-ink deliver chamber  44  from which the black ink flows opens at a right-hand and rear corner of the bottom surface  44   a  of the deliver chamber  44 , and is formed through the thickness of the partition wall  72   c  of the lower ink case  72 , in the upward and downward directions, so as to communicate with the ink-deliver passage  91 B. 
     Thus, the black-ink flow inlet  44   b  and the black-ink flow outlet  44   c  are provided at respective substantially diagonal positions of the black-ink deliver chamber  44 . That is, the black-ink flow inlet  44   b  and the black-ink flow outlet  44   c  are provided at respective positions that are substantially the most distant from each other such that almost all portions of the deliver chamber  44  are located between the two positions. 
     In addition, the black-ink deliver chamber  44  and the cyan-ink deliver chamber  43  are provided adjacent to each other via the partition wall  72   c  of the lower ink case  72 , such that the black-ink flow inlet  44   b  and the cyan-ink flow inlet  43   b  are provided at respective different positions along the partition wall  72   c  and the black-ink flow outlet  44   c  and the cyan-ink flow inlet  43   c  are provided at respective different positions along the partition wall  72   c.    
     Thus, in a plan view of the lower ink case  72 , a straight line connecting between the black-ink flow inlet  44   b  and the black-ink flow outlet  44   c  and a straight line connecting between the cyan-ink flow inlet  43   b  and the cyan-ink flow outlet  43   c  have such a positional relationship in which the two straight lines intersect each other like two different diagonal lines of a quadrangle. 
     Respective lower openings of the black-ink deliver chamber  44 , the ink-introduce passage  66 C, and the connection passage  68 C are closed by a flexible film  84  as a flexible diaphragm ( FIG. 14 ). Respective lower surfaces of the side walls that define the black-ink deliver chamber  44 , the ink-introduce passage  66 C, and the connection passage  68 C are contained by a same plane, and the flexible film  84  is bonded to those lower surfaces by a bonding means such as adhesion or thermal welding. Thus, the black-ink deliver chamber  44 , the ink-introduce passage  66 C, and the connection passage  68 C are formed in the lower ink case  72 . 
     Two ribs  44   d ,  44   e  project downward from the bottom surface  44   a  of the black-ink deliver chamber  44 , such that the rib  44   d  is located on one side of, and spaced from, a straight line connecting between the black-ink flow inlet and outlet  44   b ,  44   c  and the rib  44   e  is located on the opposite side of, and spaced from, the same line. Each of the ribs  44   d ,  44   e  has a quadrangular cross section, and has a height equal to substantially half a depth of the deliver chamber  44  (i.e., a distance between the bottom surface  44   a  and the film  84 ). Thus, the ribs  44   d ,  44   e  are spaced from the film  84  so as not to restrict the displacing of the flexible film  84 . The two ribs  44   d ,  44   e  cooperate with each other to guide a quick flow of the black ink from the ink-flow inlet  44   b  to the ink-flow outlet  44   c.    
     (Air Discharging Device) 
     The ink-deliver passages  91 Y through  91 B that are provided above the ink-deliver outlets  39 Y through  39 B open in the upper surface  71   a  of the upper ink case  71 , and communicate with an air-discharge valve device  45 , provided in a right-hand side portion of the buffer portion  40   b , via four air-discharge passages  93  ( FIG. 10 ) provided in the form of grooves in the upper surface  71   a  of the upper ink case  71 . The air-discharge valve device  45  includes an air-discharge valve box  45   a  as a container; and four air-discharge valves  47 Y,  47 M,  47 C,  47 B that can close and open the four air-discharge passages  93 , respectively. 
     Normally, the air-discharge valves  47 Y through  47 B are in their closed states, so that when the inks supplied from the tubes  14 Y through  14 B flow through the ink-deliver chambers  41  through  44  and the ink-deliver passages  91 Y through  91 B, respectively, the air bubbles contained in the inks naturally move upward so as to be collected in respective upper portions of the ink-deliver passages  91 Y through  91 B. When each of the air-discharge valves  47 Y through  47 B is placed in its open state, the air collected in the upper portion of a corresponding one of the ink-deliver passages  91 Y through  91 B is discharged into the outside space. 
     (Flow of Ink) 
     The yellow ink flows through a path provided in the cross section, shown in  FIG. 11 , that is taken along Y-Y in  FIG. 10 . More specifically described, the yellow ink first flows into the ink-introduce inlet  22 Y ( FIG. 5 ), then flows through the ink-introduce passages  61 Y,  63 Y, and flows into the ink-deliver chamber  41  via the ink-flow inlet  41   b  ( FIG. 6 ). 
     As shown in  FIG. 6 , the yellow ink, introduced into the ink-deliver chamber  41 , flows from the inlet  41   b  to the outlet  41   c  through almost all portions of the inner space of the chamber  41 . The yellow ink, delivered from the ink-deliver chamber  41 , first flows into the ink-deliver passage  91 Y, and then is supplied to the ink-jet recording head  30  via the ink-deliver outlet  39 Y, as shown in  FIG. 11 . 
     The magenta ink first flows through a path provided in the cross section, shown in  FIG. 12 , that is taken along M-M in  FIG. 10 . More specifically described, the magenta ink flows into the ink-introduce inlet  22 M ( FIG. 5 ), then flows through the ink-introduce passages  61 M,  63 M, and flows into the ink-deliver chamber  42  provided on the opposite side  71   b  of the upper ink case  71  via the ink-flow inlet  42   b  ( FIG. 7 ). 
     As shown in  FIG. 7 , the magenta ink, introduced into the ink-deliver chamber  42 , flows from the inlet  42   b  to the outlet  42   c . The magenta ink, delivered from the ink-deliver chamber  42 , flows into the ink-deliver passage  91 M, and then is supplied to the ink-jet recording head  30  via the ink-deliver outlet  39 M, as shown in  FIG. 12 . 
     The cyan ink flows through a path provided in the cross section, shown in  FIG. 13 , that is taken along C-C in  FIG. 10 . More specifically described, the cyan ink flows into the ink-introduce inlet  22 C ( FIG. 5 ), then flows through the ink-introduce passages  61 C,  63 C, further flows into the ink-introduce passage  64 C formed through the respective partition walls  71   c ,  72   c  of the two ink cases  71 ,  72 , so as to flow into the ink-introduce passage  66 C provided on the lower side  72   b  of the lower ink case  72 , and finally flows into the ink-deliver chamber  43 , provided on the upper side  72   a  of the lower ink case  72 , via the ink-flow inlet  43   b  ( FIG. 8 ). 
     As shown in  FIG. 8 , the cyan ink, introduced into the ink-deliver chamber  43 , flows from the inlet  43   b  to the outlet  43   c . The cyan ink, delivered from the ink-deliver chamber  43 , flows into the ink-deliver passage  91 C, and then is supplied to the ink-jet recording head  30  via the ink-deliver outlet  39 C, as shown in  FIG. 13 . 
     The black ink flows through a path provided in the cross section, shown in  FIG. 14 , that is taken along B-B in  FIG. 10 . More specifically described, the black ink flows into the ink-introduce inlet  22 B ( FIG. 5 ), then flows through the ink-introduce passages  61 B,  63 B, and flows into the ink-deliver chamber  44 , provided on the lower side  72   b  of the lower ink case  72 , via the ink-introduce passage  64 B formed through the respective partition walls  71   c ,  72   c  of the two ink cases  71 ,  72 . 
     As shown in  FIG. 9 , the black ink, introduced into the ink-deliver chamber  44 , flows from the ink-flow inlet  44   b  to the ink-flow outlet  44   c . The black ink, delivered from the ink-deliver chamber  44 , flows into the ink-deliver passage  91 B, and then is supplied to the ink-jet recording head  30  via the ink-deliver outlet  39 B, as shown in  FIG. 14 . 
     Advantages of First Embodiment 
     
         
         (1) As is apparent from the foregoing description of the ink-jet recording apparatus  1  as the first embodiment, each of the ink-deliver chambers  41 ,  42 ,  43 ,  44  is constructed such that a corresponding one of the ink-flow inlets  41   b ,  42   b ,  43   b ,  44   b  and a corresponding one of the ink-flow outlets  41   c ,  42   c ,  43   c ,  44   c  are provided at respective positions that are substantially the most distant from each other such that almost all portions of the inner space of the each ink-deliver chamber are located between the corresponding ink-flow inlet and the corresponding ink-flow outlet. Therefore, each of the inks flows through almost all portions of the inner space of the corresponding ink-deliver chamber  41  through  44 . Thus, the inner space of each ink-deliver chamber  41  through  44  can be efficiently utilized to damp the changes of pressure of the corresponding ink supplied from the corresponding tube  14  and discharge the air bubbles contained in the each ink. In particular, since one surface of each ink-deliver chamber  41  through  44  is closed by the corresponding flexible film  81  through  84  having the large area, the changes of pressure of the corresponding ink can be effectively damped by the displacing of the flexible film. 
       
    
     In addition, since, in each ink-deliver chamber  41  through  44 , the corresponding ink flows substantially linearly from the ink-flow inlet thereof toward the ink-flow outlet thereof, the ink can be quickly delivered from the corresponding ink tank  5  to the ink-jet recording head  30  while only a small amount of air bubbles grows in the ink. In particular, since the ribs  41   d ,  41   e ,  41   f ,  42   d ,  42   e ,  43   d ,  43   e ,  44   d ,  44   e  are provided on either side of the straight line connecting between the ink-flow inlet and the ink-flow outlet, the flowing of the ink is enhanced and the recording head  30  is prevented from failing to eject droplets of the ink because of the air bubbles contained in the ink. 
     Since the black-ink deliver chamber  44  is provided as an outermost one of the ink-deliver chambers  41  through  44  that extend parallel to each other, the deliver chamber  44  can easily have the larger volume than those of the other deliver chambers  41  through  43  so as to compensate for the large amount of consumption of the black ink.
     (2) Each of the ink-deliver chambers  41  through  44  has the inner space flat along the plane containing the straight line connecting between the corresponding ink-flow inlet  41   b  through  44   b  and the corresponding ink-flow outlet  41   c  through  44   c . The four ink-deliver chambers  41  through  44  extend parallel to the corresponding planes, and are arranged in a direction perpendicular to those planes. Therefore, the thickness of the buffer tank  40  in that direction can be decreased.   

     The yellow-ink deliver chamber  41  and the magenta-ink deliver chamber  41  are provided adjacent to each other via the partition wall  71   c  of the upper ink case  71 ; and the cyan-ink deliver chamber  43  and the black-ink deliver chamber  44  are provided adjacent to each other via the partition wall  72   c  of the lower ink case  72 . The upper ink case  71  has the opposite openings that are opposite to each other with respect to the partition wall  71   c  and that are closed by the flexible films  81 ,  82 , respectively; and the lower ink case  72  has the opposite openings that are opposite to each other with respect to the partition wall  72   c  and that are closed by the flexible films  83 ,  84 , respectively. 
     In the first embodiment, the chamber-define wall that constitutes each ink case  71 ,  72  includes the partition wall  71   c ,  72   c  that separates the inner space of the each ink case into two ink-deliver chambers; and the two groups of side walls which are provided on the upper and lower sides of the partition wall, respectively, and each group of which includes the left-hand side wall, the right-hand side wall, the rear side wall, and the front side wall. This chamber-define wall has the upper and lower openings that are closed by the two films, respectively, so as to define the two ink-deliver chambers  41 ,  42 , or  43 ,  44 , respectively. 
     The chamber-define wall of the upper ink case  71  has the upper surface  71   a  in which the ink-introduce passages  63 Y through  63 B and the ink-introduce passages  64 B,  64 C are formed. The rear end portion of the ink-introduce passage  63 M (to which the ink-flow inlet  42   b  is connected) and the ink-introduce passages  64 B,  64 C are formed through the partition wall  71   c  of the upper ink case  71 . Moreover, the respective partition walls  71   c ,  72   c  of the two ink cases  71 ,  72  include the tubular walls  91   e ,  91   f  that define the ink-deliver passages  91 Y through  91 B, and the separation walls  91   g , and the ink-deliver passages  91 Y through  91 B are formed through the respective partition walls  71   c ,  72   c  of the two ink cases  71 ,  72 . 
     The respective ink-flow inlets  41   b ,  42   b  of the two ink-deliver chambers  41 ,  42  are provided at the respective different positions along the partition wall  71   c , and the respective ink-flow outlets  41   c ,  42   c  of the two ink-deliver chambers  41 ,  42  are provided at the respective different positions along the partition wall  71   c . Similarly, the respective ink-flow inlets  43   b ,  44   b  of the two ink-deliver chambers  43 ,  44  are provided at the respective different positions along the partition wall  72   c , and the respective ink-flow outlets  43   c ,  44   c  of the two ink-deliver chambers  43 ,  44  are provided at the respective different positions along the partition wall  72   c . That is, each pair of ink-deliver chambers are provided adjacent to each other via the corresponding partition wall  71   c ,  72   c , and the respective ink-flow inlets of the two ink-deliver chambers are provided at the respective different positions along the partition wall  71   c ,  72   c , and the respective ink-flow outlets of the two ink-deliver chambers are provided at the respective different positions along the partition wall  71   c ,  72   c . Therefore, as compared with the case where four ink-deliver chambers are provided in four ink cases, respectively, the ink-deliver chambers  41  through  44  can be provided in a smaller space. 
     Moreover, in the first embodiment, the buffer tank  40  is constituted by the two ink cases  71 ,  72  that are stacked on each other such that the two cases  71 ,  72  extend parallel to each other and are opposed to each other. Therefore, the ink passages can be provided in the small space and the thickness of the buffer tank  40  in the direction in which the two ink cases  71 ,  72  are stacked on each other can be decreased. 
     The ink-deliver passages  91 Y through  91 B corresponding to the ink-deliver chambers  41  through  44 , respectively, are arranged in one array along one side of the buffer tank  40 , and open to face the ink-jet recording head  30 . At least one of the respective ink-flow outlets of the two ink-deliver chambers respectively formed in the opposite surfaces of each ink case  71 ,  72  is formed through the thickness of the each ink case in the direction from one of the opposite surfaces to the other surface so as to communicate with the corresponding ink-deliver passage  91 . Thus, the ink passages can be provided in the small space and an over-all size of the head holder  9  including the ink-jet recording head  30  and the buffer tank  40  can be reduced.
     (3) One ink case  71  has the four ink-introduce passages  63 Y,  63 M,  63 C,  63 B that are connected, at respective one ends thereof, to the four tubes  14 Y through  14 B, and the two ink-introduce passages  63 C,  63 B are formed through the respective partition walls  71   c ,  72   c  of the two ink cases  71 ,  72  so as to be connected, at the respective other ends thereof, to the cyan-ink deliver chamber  43  and the black-ink deliver chamber  44 . Thus, the ink-introduce passages  63 Y through  63 B can be easily connected, and the two ink cases  71 ,  72  can be stacked on each other in the small space.   

     In addition, since one ink case  71  has the four ink-introduce passages  63 Y,  63 M,  63 C,  63 B that are connected to the four tubes  14 Y through  14 B, respectively, an overall-size of the head holder  9  including the connection portion where the tubes  14  are connected to the ink case  71  can be reduced.
     (4) The ink-flow inlet and outlet  42   b ,  42   c  of the magenta-ink deliver chamber  42 , provided on the lower side  71   b  of the upper ink case  71  opposed to the upper side  72   a  of the lower ink case  72 , are located inside the ink-introduce passages  64 B,  64 C formed through the respective partition walls  71   c ,  72   c  of the two ink cases  71 ,  72  and inside the ink-deliver passages  91 Y through  91 B. Thus, the ink-introduce passages  64 B,  64 C and the ink-deliver passages  91 Y through  91 B are not provided inside the contour of the magenta-ink deliver chamber  42  and accordingly the deliver chamber  42  can have a simple shape such as a quadrangle. Therefore, the flow passage can be easily formed which assures that the magenta ink quickly flows from the ink-flow inlet  42   b  to the ink-flow outlet  42   c . This is also true with the cyan-ink deliver chamber  43 .   

     In addition, the flexible film  82 ,  83  that closes the lower or upper opening of the ink-deliver chamber  42 ,  43  can have a simple shape such as a quadrangle. Therefore, when the pressure of the magenta or cyan ink changes, the film  82 ,  83  can be substantially largely displaced to damp the pressure changes. Moreover, the film  82 ,  83  can be easily obtained by cutting a large sheet of film material into pieces of films having prescribed dimensions. Thus, the films can be uselessly used, and can be bonded to the ink cases  71 ,  72  without needing accurate positioning of the films relative to the ink cases  71 ,  72 . 
     The four ink-introduce passages  63 Y through  63 M are arranged in one array in one surface of one ink case  71 . Therefore, the ink-flow passages can be provided in the small space. In addition, the two ink-flow passages  63 Y,  63 M located at the opposite ends of the array of ink-flow passages  63 Y through  63 M are respectively connected to the two ink-deliver chambers  41 ,  42  of the one ink case  71  having the ink-introduce passages  63 Y through  63 M, and the other, two ink-flow passages  63 C,  63 B located in the middle portion of the array of ink-flow passages  63 Y through  63 M are respectively connected to the two ink-deliver chambers  43 ,  44  of the other ink case  72 . Therefore, the two ink-flow passages  63 Y,  63 M can be easily provided such that those passages  63 Y,  63 M do not interfere with the two ink-deliver chambers  42 ,  43  respectively provided in the respective surfaces of the two ink cases  71 ,  72  that are opposed to each other. Thus, the above-describe advantages can be easily obtained. 
     The black-ink deliver chamber  44  may be modified to have a simpler quadrangular cross-section shape. However, since the black-ink deliver chamber  44  has the quadrangular shape containing the ink-introduce passage  66 C and the connection passage  68 C, as shown in  FIG. 9 , the film  84  that closes not only the deliver chamber  44  but also those passages  66 C,  68 C can advantageously have a simple shape such as a quadrangle.
     (5) The respective upper ends of the ink-deliver passages  91 Y,  91 M,  91 C,  91 B communicate with the atmosphere via the air-discharge valve device  45  that can be opened and closed. Therefore, the air bubbles that grow in the ink-deliver chambers  41  through  44  and the ink-deliver passages  91 Y through  91 B can be discharged into the outside space.   

     In the first embodiment, the direction parallel to the guide shafts  6 ,  7  that cooperate with each other to guide the head holder  9  is defined as the scanning direction; the direction that substantially perpendicularly intersects not only the scanning direction but also the upward and downward directions is defined as a first direction; the leftward and rightward directions parallel to the scanning direction are defined as a second direction; and the upward and downward directions are defined as a third direction. 
     In the first embodiment, a distance between the ink-flow inlet and outlet of each of the ink-deliver chambers  41  through  44  is not less than 90% of a dimension of the inner space of the each ink-deliver chamber in the first direction. With respect to the second direction, a distance between the ink-flow inlet and outlet of the yellow-ink deliver chamber  41  is not less than 30% of a dimension of the inner space of the chamber  41 ; a distance between the ink-flow inlet and outlet of each of the magenta-ink and cyan-ink deliver chambers  42 ,  43  is not less than 80% of a dimension of the inner space the each chamber  42 ,  43 ; and a distance between the ink-flow inlet and outlet of the black-ink deliver chamber  44  is not less than 40% of a dimension of the inner space of the chamber  44 . Thus, in each of the ink-deliver chambers  41  through  44 , a corresponding one of the ink-flow inlets and a corresponding one of the ink-flow outlets are provided at the respective positions that are substantially the most distant from each other such that almost all portions of the inner space of the each ink-deliver chamber are located between the corresponding ink-flow inlet and the corresponding ink-flow outlet. 
     The ink-flow inlet and outlet of each of the ink-deliver chambers  41  through  44  are provided at the respective positions that are as possible as near to the respective diagonal positions of the each ink-deliver chamber. That is, with respect to the first direction, the ink-flow inlet and outlet are distant from each other, and the straight line connecting between the ink-flow inlet and outlet is inclined relative to the first direction. An angle of inclination of the straight line connecting between the ink-flow inlet and outlet of the yellow-ink deliver chamber  41 , relative to the first direction, is not less than 15 degrees; an angle of inclination of the straight line connecting between the ink-flow inlet and outlet of each of the magenta-ink and cyan-ink deliver chambers  42 ,  43 , relative to the first direction, is not less than 40 degrees; and an angle of inclination of the straight line connecting between the ink-flow inlet and outlet of the black-ink deliver chamber  44 , relative to the first direction, is not less than 30 degrees. In addition, the straight line connecting between the ink-flow inlet and outlet of one ink-deliver chamber and the straight line connecting between the ink-flow inlet and outlet of another ink-deliver chamber provided adjacent to the one ink-deliver chamber are inclined, relative to the first direction, in the opposite directions each away from the first direction. This is true with not only the first pair of adjacent ink-deliver chambers  41 ,  42  but also the second pair of adjacent ink-deliver chambers  43 ,  44 . 
     In the first embodiment, each of the ink-deliver chambers  41  through  44  has a flat shape having, in the third direction perpendicular to the first and second directions, a smaller dimension than the respective dimensions thereof in the first and second directions. Only if the ink-flow inlet and outlet of the each ink-deliver chamber are provided at respective positions distant from each other in each of the first and second directions, a large portion of the inner space of the each ink-deliver chamber can be provided between the ink-flow inlet and outlet. Thus, the inner volume of the each ink-deliver chamber can be efficiently utilized. 
     The first embodiment may be modified such that the upward and downward directions are defined as the second direction and the direction parallel to the scanning direction is defined as the third direction. 
     Additional Embodiment 1 
     Regarding the first embodiment, a manner in which the air collected in the respective upper portions of the four ink-deliver passages  91 M through  91 B is discharged has not been described in detail because that manner has no particular limitations and accordingly any known technique may be employed. The following, second embodiment is an example of most preferred techniques with respect to the manner in which the air is discharged. Since the second embodiment relates to an ink-jet recording apparatus having a construction identical with that of the ink-jet recording apparatus as the first embodiment, except for a portion relating to the function of discharging air, the same reference numerals as used in the first embodiment are used to designate the corresponding elements of the second embodiment and the description thereof is omitted. The ink-jet recording apparatus as the second embodiment are shown in  FIGS. 15 through 24  corresponding to  FIGS. 2 and 6  through  14 , respectively. Although  FIGS. 15 through 24  show the same constituent elements as employed in the first embodiment, additional reference numerals such as  46  are used to describe, in detail, the portion relating to the function of discharging air. In addition, a cross-section view taken along Arrows  4 - 4  in  FIG. 15  is the same as the cross-section view shown in  FIG. 4 . 
     Like the buffer tank  40  employed in the first embodiment, a buffer tank  40  employed in the second embodiment has four flat ink-deliver chambers  41  through  44  having respective horizontally extending postures. More specifically described, the four ink-deliver chambers  41  through  44  are arranged in upward and downward directions such that the four chambers extend parallel to each other. The two ink-deliver chambers  41 ,  42  are formed in an upper ink case  71 ; and the other, two ink-deliver chambers  43 ,  44  are formed in a lower ink case  72  ( FIGS. 21 through 24 ). The four ink-deliver chambers  41  through  44  communicate with four ink-deliver passages  91 Y through  91 B, respectively. 
     The four ink-deliver passages  91 Y through  91 B extend in the upward and downward directions such that the four passages have respective substantially same lengths ( FIGS. 21 through 24 ). The four ink-deliver chambers  41  through  44  communicate with respective side surfaces of the four ink-deliver passages  91 Y through  91 B, so that the four chambers deliver respective inks to the four passages. Therefore, respective upper portions of the four ink-deliver passages  91 Y through  91 B function as air-collect spaces that collect respective air that are first contained by, and then separated from, the respective inks. 
     Since the four ink-deliver passages  91 Y through  91 B extend in the upward and downward directions over the respective substantially same lengths, the four passages  91 Y through  91 B can effectively separate the respective air from the respective inks to be supplied to respective ink-supply inlets (only the inlet  32   a  is shown in  FIG. 4 ) of an ink-jet recording head  30 , so that the respective air is temporarily collected in the respective upper portions of the four passages  91 Y through  91 B. The thus collected air can be discharged into an outside space through respective air-discharge outlets  46 M,  46 C,  46 Y,  46 B that can be opened and closed by an air-discharge valve device  45 , described later. 
     The four ink-deliver passages  91 Y through  91 B extend in the upper and lower ink cases  71 ,  72 , parallel to each other, in the upward and downward directions. Respective lower open ends of the four passages  91 Y through  91 B define respective ink-deliver outlets  39 Y through  39 B that communicate with the respective ink-supply inlets (only the inlet  32   a  is shown in  FIG. 4 ) of the ink-jet recording head  30 , via respective ink-flow openings (only the opening  33   a  is shown in  FIG. 4 ) of a reinforcing frame  33 . Meanwhile, respective upper open ends of the four passages  91 Y through  91 B provide the respective air-discharge outlets  46 Y through  46 B that are provided along a single plane. Thus, the four ink-deliver passages  91 Y through  91 B communicate with the outer space via the respective air-discharge outlets  46 Y through  46 B that can be opened and closed by the air-discharge valve device  45 , described later. 
     Thus, respective upper portions of the four ink-deliver passages  91 Y through  91 B are formed in the upper ink case  71  so as to communicate with the respective air-discharge outlets  46 Y through  46 B; and respective lower portions of the four passages  91 Y through  91 B are formed in the lower ink case  72  so as to communicate with the respective ink-deliver outlets  39 Y through  39 B. 
     More specifically described, the respective upper portions of the four ink-deliver passages  91 Y through  91 B corresponding to the four inks, respectively, are formed in the upper ink case  71 , by dividing, with respective upper portions of three separation walls  91   g , an inner space of a tubular wall  91   e  of the upper case  71 ; and the respective lower portions of the four passages  91 Y through  91 B are formed in the lower ink case  72 , by dividing, with respective lower portions of the three separation walls  91   g , an inner space of a tubular wall  91   f  of the lower case  72  ( FIGS. 17 and 18 ). In a state in which the tubular wall  91   e  and the separation walls  91   g  of the upper ink case  71  are aligned with the tubular wall  91   f  and the separation walls  91   g  of the lower ink case  72 , respectively, the respective upper portions of the four ink-deliver passages  91 Y through  91 B are joined to the respective lower portions of the same  91 Y through  91 B, by a bonding means such as supersonic welding or adhesion. Thus, the buffer tank  40  having the four ink-deliver chambers  41  through  44  arranged in the upward and downward directions is obtained. 
     Since the four ink-deliver chambers  41  through  44  are arranged in the upward and downward directions and extend parallel to each other, the four chambers  41  through  44  can enjoy respective substantially uniform characteristics with respect to the function of supplying inks to the ink-jet recording head  30 . In addition, the four chambers  41  through  44  can have respective sufficiently large volumes without having to increase a height of the buffer tank  40  or the printer as a whole. Therefore, the present ink-jet recording apparatus can effectively damp the changes of pressure of the inks and thereby record images with high quality. 
     (Air-Discharge Passages) 
     As shown in  FIGS. 20 through 25 , the respective upper ends of the four ink-deliver passages  91 Y through  91 B, located above the four ink-deliver outlets  39 Y through  39 B, provide the four air-discharge outlets  46 Y through  46 B formed in the upper ink case  71 . The four air-discharge outlets  46 Y through  46 B communicate with four air-discharge passages  93 Y,  93 M,  93 C,  93 B, respectively, that are formed as respective grooves in an upper surface  71   a  of the upper ink case  71 , and the four air-discharge passages  93 Y through  93 B communicate with respective upper open ends of four air-discharge holes of the air-discharge valve device  45  that are provided along one side of a buffer portion  40   b  of a buffer tank  40  and correspond to the four inks, respectively. The air-discharge valve device  45  extends substantially parallel to the four air-discharge passages  93 Y through  93 B. Thus, the four air-discharge outlets  46 Y through  46 B as the respective upper open ends of the four ink-deliver passages  91 Y through  91 B communicate with the air-discharge valve device  45  via the four air-discharge passages  93 Y through  93 B, respectively. Respective upper openings of the four air-discharge passages  93 M through  93 B are closed by a flexible film  81 . 
     In the upper surface  71   a  of the upper ink case  71 , the four air-discharge passages  93 Y through  93 B are formed along an outer periphery of the yellow-ink deliver chamber  41 , such that first the four passages  93 Y through  93 B are curved in the rightward direction from the respective upper open ends of the four ink-deliver passages  91 Y through  91 B and then are extended in the frontward direction to communicate with the air-discharge valve device  45 , more specifically described, four air-discharge valves  47 Y,  47 M,  47 C,  47 B of the valve device  45 , respectively. 
     Normally, the four air-discharge valves  47 Y through  47 B are in their closed states. Therefore, when the inks supplied from the ink tubes  14 Y through  14 B flow through the ink-deliver chambers  41  through  44  and the ink-deliver passages  91 Y through  91 B, the air contained by the inks naturally separates from the inks and additionally the air captured by respective filters (not shown) provided in the four ink-deliver outlets  39 Y through  39 B naturally move upward, so that the air is collected in the respective upper portions of the ink-deliver passages  91 Y through  91 B. The thus collected air can be discharged into the outer space via the air-discharge passages  93 Y through  93 B, when the air-discharge valve device  45  is operated and controlled in an appropriate manner to open one or more of the four air-discharge valves  47 Y through  47 B. 
     (Air-Discharge Valve Device) 
     The air-discharge valve device  45  ( FIG. 20 ) includes an air-discharge valve box  45   a , and the four air-discharge valves  47 M through  47 B that can open and close the corresponding air-discharge passages  93 M through  93 B are accommodated by the box  45   a . Since the four air-discharge valves  47 M through  47 B have an identical construction, only the air-discharge valve  47 M corresponding to the magenta ink is described below by reference to  FIG. 25 . 
     As shown in  FIG. 25 , the air-discharge valve  47 M has an air-discharge hole  101  communicating with the corresponding air-discharge passage  93 M. The air-discharge hole  101  is elongate in the upward and downward directions and has upper and lower open ends. Thus, the air-discharge hole  101  functions as a valve chamber that has an upper port  101   a  and an intermediate port  101   b  and in which a valve member  102  is movable. The air-discharge valve device  45  has the four air-discharge holes  101  corresponding to the four inks, respectively. Each of the four air-discharge holes  101  includes an upper, large-diameter portion  101 A and a lower, small-diameter portion  101 B that communicate with each other via the intermediate port  101   b.    
     An upper portion of the air-discharge valve box  45   a  that includes the upper port  101   a  and an engageable projection  71   d , described later, is formed integrally with the upper ink case  71 ; and a lower portion of the box  45   a  that includes the large-diameter and small-diameter portions  101 A,  101 B is formed integrally with the lower ink case  72 . When the upper and lower cases  71 ,  72  are joined to each other as described above, the upper and lower portions of the air-discharge valve box  45   a  are simultaneously joined to each other. 
     The valve member  102  includes a large-diameter valve portion  102   a ; a small-diameter valve rod  102   b  integrally connected to a lower end of the valve portion  102   a ; and an annular seal member  102   c  fitting on the rod  102   b . The diameter of the valve portion  102   a  is larger than that of the valve rod  102   b , and the seal member  102   c  is supported by the valve rod  102   b  such that the seal member  102   c  is held in contact with the valve portion  102   a . The valve portion  102   a  is opposed, via the seal member  102   c , to an annular surface  101 C (i.e., a valve seat) that functions as a bottom surface of the large-diameter portion  101 A and defines the intermediate port  101   b  as an upper open end of the small-diameter portion  101 B. The large-diameter valve portion  102   a  and the small-diameter valve rod  102   b  of the valve member  102  are inserted into the large-diameter portion  101 A and the small-diameter portion  101 B of the air-discharge hole  101 , respectively, such that respective annular gaps through which air (or gas) can flow are left between the valve portion  102   a  and an inner wall surface defining the large-diameter portion  101 A and between the valve rod  102   b  and an inner wall surface defining the small-diameter portion  101 B. Thus, the valve member  102  is provided in the air-discharge hole  101  such that the valve member  102  is slideable in an axial direction of the hole  101  that is parallel to a centerline of the same  101 . The air-discharge valve  47 M is opened by pushing the small-diameter valve rod  102   b  upward by a corresponding one of four projecting bars  121  of a maintenance unit  120 . To this end, a lower end of the valve rod  102   b  is located in the vicinity of a lower open end of the small-diameter portion  101 B, in the state in which the valve  47 M is closed. The seal member  102   c  is preferably provided by, e.g., a packing member formed of an elastic material such as rubber. In the present embodiment, an O-right is used as the seal member  102   c.    
     The annular surface  101 C that defines the intermediate port  101   b  communicating with the atmosphere, functions as the valve seat, and the seal member  102   c  is provided between the annular surface  101 C and the valve portion  102   a . Therefore, the intermediate port  101   b  can be opened and closed by the valve portion  102   a  via the seal member  102   c  fitting on the valve rod  102   b.    
     A coil spring  103  as a biasing member to bias the valve member  102  (i.e., the valve portion  102   a ) in a direction to close the intermediate port  102   b , is provided in the large- diameter portion  101 A. More specifically described, an upper end portion of the coil spring  103  fits on an outer surface of the engageable projection  71   d  of the upper ink case  71 ; and a lower end portion of the coil spring  103  fits in a recess  102   aa  formed in an upper portion of the valve portion  102   a . The upper port  101   a  consists of a plurality of separate holes provided around the engageable projection  71   d . Thus, the upper end of the coil spring  103  is not contacted with an inner wall surface defining the upper port  101   a . Therefore, an air-flow passage through which the air (or gas) flows is formed around the coil spring  103 . 
     The intermediate port  101   b  is opened to discharge the air, if the valve rod  102   b  is moved upward to compress the coil spring  103 . Therefore, the air flowing from the upper port  101   a  is blocked by the compressed coil spring  103 , and a quick flow of the air is produced between the compressed coil spring  103  and the inner wall surface defining the large-diameter portion  101 A. That is, the gap between an outer surface of the compressed coil spring  103  and the inner wall surface defining the large-diameter portion  101 A provides an air-flow passage having a low flow resistance. This air-flow passage cooperates with an outer surface of the valve portion  102   a  to define a block-free air-discharge passage that connects between the upper port  101   a  and the intermediate port  101   b  and that is free of blocks that may increase its flow resistance. 
     Thus, the coil spring  103  normally biases the valve portion  102   a  in the direction to cause the seal member  102   c  to contact the annular surface  101 C. Therefore, at a normal time when the valve member  102  does not receive the pushing force of the projecting bar  121 , the air-discharge valve  47 M is in its closed state in which the intermediate port  102  is closed by the seal member  102   c.    
     The valve rod  102   b  of the valve member  102  has a plurality of axial grooves  102   d  that extend over an entire length of the rod  102   b . In a state in which the seal member  102  is accidentally separated from the valve portion  102   a , the axial grooves  102   d  of the valve rod  102   b  function as gaps (i.e., air-discharge passages) assuring that the air can flow between the seal member  102   c  and the valve rod  102   b . Therefore, even if such a phenomenon may occur that ink adheres to not only the annular surface  101 C but also the seal member  102   c  that is held, in its closed state, in contact with the same  101 C and accordingly only the valve rod  102   b  is pushed up while the seal member  102   c  remains adhered, with the ink functioning as adhesive, to the annular surface  101 C, the air can flow through the axial grooves  102   d . Thus, the air can be prevented from remaining in the ink-deliver passages  91 M through  91 B, or moving downward to the ink-jet recording head  30 , and accordingly images can be recorded with high quality. 
     The maintenance unit  120  performs a cleaning operation to clean the nozzle-open surface of the ink-jet recording head  30 ; a recovering operation to apply suction to each of the inks; and a removing operation to remove the air accumulated in the buffer tank  40 . To this end, the maintenance unit  120  includes a first cap member  122  that can cover and open the nozzle-open surface of the recording head  30  in which the nozzle arrays  35  through  38  open; and a plurality of second cap members  123  that can cover and open respective portions of a lower surface of the air-discharge valve device  45  (i.e., respective lower surfaces of the air-discharge valves  47 M through  47 B in which the respective lower ends of the small-diameter portions  101 B open). The first and second cap members  122 ,  123  are supported by a vertically moving device  124 , known in the art, such that the cap members  122 ,  123  are vertically movable. When the ink-jet recording head  30  is moved to, and stopped at, a waiting position where the recording head  30  does not perform any recording operations, the cap members  122 ,  123  are moved to their upper positions where the cap members  122 ,  123  closely contact the nozzle-open surface of the recording head  30  and the lower surface of the air-discharge valve device  45 ; and when the recording head  30  is moved to other positions, the cap members  122 ,  123  are moved to their lower positions away from those surfaces. The first cap member  122  is connected to a suction pump  125 , known in the art, and, when the pump  125  is driven, the first cap member  122  removes, by suction, the inks with increased viscosities, and foreign matters, from the nozzle arrays  35  through  38 . 
     Each of the four second cap members  123  includes the projecting bar  121 ; and when the each cap member  123  contacts the lower surface of the air-discharge valve device  45 , the projecting bar  121  pushes up the valve member  102  against the biasing force of the coil spring  103  so as to move the seal member  102   c  away from the annular surface  101 C level with the lower open end of the large-diameter portion  101 A and thereby place the corresponding air-discharge valve  47  in its open state in which the intermediate port  101   b  is opened. 
     The four second cap members  123  are connected via a common flow passage to the suction pump  125  and, when the pump  125  is driven, respective amounts of air collected in the respective upper portions of the ink-deliver passages  91 M through  91 B are simultaneously sucked and discharged into the atmosphere. That is, the inks supplied from the ink tanks  5 M through  5 B to the ink-jet recording head  30  via the ink tubes  14 M through  14 B are temporarily held in the ink-deliver passages  91 M through  91 B, provided midway in the ink-flow passages, so that air is separated from each ink and is collected in the upper portion of the corresponding ink-deliver passage  91 . This air is discharged by the operation of the suction pump  125 . 
     The first cap member  122  and the group of second cap members  123  are selectively connected, by a switching valve  126 , to the suction pump  125 . The first cap member  122  and the group of second cap members  123  are simultaneously contacted, by the vertically moving device  124 , with the nozzle-open surface of the recording head  30  and the lower surface of the air-discharge valve device  45 . Subsequently, first, the second cap members  123 , for example, are used to discharge the air collected in the upper portions of the ink-deliver passages  91 M through  91 B, and then the first cap member  122  is used to suck the deteriorated inks from the nozzle arrays  35  through  38 . If air is discharged from the ink-deliver passages  91 M through  91 B, using the first cap member  122  only, then too large amounts of inks would be uselessly consumed. In contrast thereto, the present embodiment can enjoy such advantages that the air can be reliably discharged, and the recording head  30  can be efficiently restored, without having to uselessly consume much inks. 
     However, an operation to remove deteriorated inks from the nozzle arrays  35  through  38  and an operation to discharge air from the ink-deliver passages  91 M through  91 B may be carried out independent of each other. In addition, the suction of the suction pump  125  may be replaced with the application of positive pressure to the inks present in the ink tanks  5  so as to remove inks with increased viscosities, and foreign matters, from the nozzle arrays  35  through  38  and discharge air from the ink-deliver passages  91 M through  91 B. Alternatively, the suction of the suction pump  125  and the application of positive pressure to the inks may be simultaneously used. 
     (Operation of Air Discharging Device) 
     In the ink-jet recording apparatus constructed as described above, at a normal time when a recording operation is carried out by the ink-jet recording head  30 , each of the four valve members  102  is normally pressed downward by the corresponding coil spring  103 , so that the corresponding seal member  102   c  is held in contact with the corresponding valve portion  102   a  and the corresponding valve seat (i.e., the corresponding seal member  102   c  is sandwiched by the corresponding valve portion  102   a , and the corresponding annular surface  101 C defining the corresponding intermediate port  101   b ) and accordingly the corresponding air-discharge valve  47 M is placed in its closed state. 
     Meanwhile, when the ink-jet recording head  30  is moved to, and stopped at, the waiting position, each of the valve rods  102   b  is pushed up by the projecting bar  121  of the corresponding second cap member  123 , while the corresponding coil spring  103  is compressed. The corresponding seal member  102   c  is moved upward together with the corresponding valve portion  102   a , or remains stuck to the corresponding annular surface  101 C (i.e., the valve seat). In either case, the air can flow through the corresponding air-discharge hole  101  or the axial grooves  102   d  of the each valve rod  102 . That is, the intermediate port  101   b  is opened, and the corresponding air-discharge valve  47  is placed in its open state. Thus, the air collected in the respective upper portions of the ink-deliver passages  91 M through  91 B can be discharged into the atmosphere via the respective intermediate ports  101   b , the respective small-diameter portions  101 B, and the suction pump  125 . 
     The upper port  101   a  of each air-discharge valve  47  consists of the plurality of separate holes that are provided around the corresponding coil spring  103  and through each of which the air can flow into the air-discharge hole  101  as the valve chamber. Therefore, although, in the state in which each air-discharge valve  47  is in its open state, the corresponding coil spring  103  is compressed, the air can smoothly flow into the valve chamber. Thus, the compression of the coil spring  103  does not result in increasing the air-flow resistance of the air-discharge hole  101 , i.e., purging different amounts of air in different air-purging operations. 
     Advantages of Present Embodiment 
     
         
         (1) In the present embodiment, the plurality of ink-deliver passages  91  extend in the upward and downward directions over the substantially same lengths. Therefore, in each of the ink-deliver passages  91 , air can be reliably separated from the corresponding ink before the ink flows into the corresponding ink-supply inlet of the ink-jet recording head  30 , and the separated air can be collected in the upper portion of the each passage  91 . Thus, the collected air can be discharged into the outer space via the corresponding air-discharge outlet  46  that can be opened and closed by the corresponding air-discharge valve  47 . 
         (2) Since the air-discharge outlets  46  and the air-discharge passages  93  are formed in the ink cases  71 ,  72 , the advantages described in the above paragraph (1) can be easily obtained. 
         (3) Since each of the two ink cases  71 ,  72  has the two ink-deliver chambers  41 ,  42 , or  43 ,  44 , and the upper portions ( 91   e ,  91   g ), or the lower portions ( 91   f ,  91   g ), of the ink-deliver passages  91 , the four ink-deliver chambers  41 ,  42 ,  43 ,  44  arranged in the upward and downward directions, and the ink-deliver passages  91  connected to those chambers  41  through  44  can be easily formed by joining the two ink cases  71 ,  72  to each other. 
         (4) Since respective one surfaces of the four ink-deliver chambers  41  through  44  that extend parallel to each other are defined by the respective flexible diaphragms (i.e., the flexible films  81  through  84 ), those diaphragms can enjoy respective large areas without having to increase the overall height of the four chambers  41  through  44  in the upward and downward directions. This arrangement is advantageous for the ink-jet recording apparatus to damp effectively the changes of pressure of the inks and thereby record images with high quality. 
         (5) The ink-deliver passages  91  and the air-discharge valve device  45  extend substantially parallel to each other, and the air-discharge outlets  46  as the respective upper ends of the passages  91  communicate with the air-discharge valve device  45  via the respective air-discharge passages  93  formed in the upper surface  71   a  of the upper ink case  71 . Thus, the advantages described in the above paragraphs (1) through (4) can be easily obtained. 
         (6) In the present embodiment, the buffer tank  40  that is moved with the ink-jet recording head  30 , relative to the recording medium, has the four ink-deliver chambers  41  through  44 . Therefore, the changes of pressure of the inks to be ejected from the recording head  30  can be effectively restrained and accordingly images can be recorded with high quality. 
       
    
     Additional Embodiment 2 
     In each of the above-described two embodiments, the inks flow from the ink-deliver chambers  41  through  44  to the respective lower portions of the ink-deliver passages  91  via respective plane surfaces ( FIGS. 11 through 14 , or  FIGS. 21 through 24 ). In contrast, in the present, third embodiment, respective inks flow from respective ink-deliver chambers  41  through  44  to respective lower portions of respective ink-deliver passages  91  via respective inclined surfaces (i.e., inclined surfaces  48 Ya,  48 Ma,  48 Ca,  48 Ba shown in  FIGS. 26 through 29 ). 
     The present embodiment relates to an ink-jet recording apparatus whose construction is similar to that of the ink-jet recording apparatus to which each of the above-described two embodiments relates. Thus, the same reference numerals as used in the above-described two embodiments are used to designate the corresponding elements of the third embodiment and the description thereof is omitted. The following description relates to only differences between the above-described two embodiments and the third embodiment.  FIGS. 26 through 29  correspond to  FIGS. 11 through 14 , respectively. 
     Like the ink-jet recording apparatus to which each of the above-described two embodiments relates, an ink-output portion  40   d  of a buffer tank  40  of the present ink-jet recording apparatus has, in rear of a buffer portion  40   b , the same number of ink-deliver passages  91 Y,  91 M,  91 C,  91 B as the number of the ink-deliver chambers  41  through  44 , such that the ink-deliver passages  91 Y through  91 B are arranged in an array in a scanning direction in which an ink-jet recording head  30  is moved ( FIG. 15  and  FIGS. 26 through 29 ). The ink-deliver passages  91 Y through  91 B are formed such that in a space between the uppermost yellow-ink deliver chamber  41  and the lowermost black-ink deliver chamber  44 , the passages  91 Y through  91 B are expanded frontward so as to overlap respective ink-flow outlets  41   c ,  44   c  of those two chambers  41 ,  44  in the upward and downward directions ( FIGS. 16 through 19 ). The respective expanded portions of the ink-deliver passages  91 Y through  91 B provide respective ink-guide passages  48 Y,  48 M,  48 C,  48 B ( FIGS. 26 through 29 ). The ink-guide passages  48 Y through  48 B are connected to the ink-deliver chambers  41  through  44 , respectively. 
     The respective inks accommodated by the respective ink-deliver chambers  41  through  44  flow via the respective ink-guide passages  48 Y through  48 B into respective lower portions  94 Y,  94 M,  94 C,  94 B of the ink-deliver passages  91 Y through  91 B which portions are located at respective positions lower than the respective ink-deliver chambers  41  through  44 . Thus, each of the ink-guide passages  48 Y through  48 B constitutes a portion through which a corresponding one of the inks flows from a corresponding one of the ink-deliver chambers  41  through  44  into the lower portion  48  of a corresponding one of the ink-deliver passages  91 Y through  91 B. 
     The ink-guide passages  48 Y,  48 M,  48 C,  48 B correspond to, and communicate with, the ink-deliver chambers  41 ,  42 ,  43 ,  44 , respectively. 
     The four ink-deliver passages  91 Y through  91 B extend in the upward and downward directions over respective substantially same lengths. Therefore, in each of the ink-deliver passages  91 Y through  91 B, air is advantageously separated from the ink flowing into a corresponding one of the ink-supply inlets (e.g.,  32   a ) of the ink-jet recording head  30 , and the thus separated air is collected in an upper portion of the each passage  91 , so that the collected air may be discharged into an outside space via a corresponding one of air-discharge outlets  46  that can be opened and closed by air-discharge valves  47 , respectively. Thus, the respective upper portions of the ink-deliver passages  91 Y through  91 B provide respective air-collect spaces each of which collects the air separated from the ink that flows from a corresponding one of the ink-deliver chambers  41  through  44  into a corresponding one of the ink-deliver passages  91 Y through  91 B via a corresponding one of the ink-guide passages  48 Y through  48 B. 
     Respective bottom walls (i.e., portions of a lower ink case  72 ) defining the respective ink-guide passages  48 Y through  48 B include respective downstream-side portions, i.e., respective ink-deliver-passage-side portions having respective inclined guide surfaces  48 Ya,  48 Ma,  48 Ca,  48 Ba whose heights decrease in respective directions toward the corresponding ink-deliver passages  91 Y through  91 B. The respective inclined guide surfaces  48 Ya through  48 Ba provide respective ink-connect portions each of which maintains or promotes a connection between the ink present in a corresponding one of the ink-deliver chambers  41  through  44  and the ink present in the lower portion  94 Y through  94 B of a corresponding one of the ink-deliver passages  91 Y through  91 B that is located at the position lower than the corresponding ink-deliver chamber  41  through  44 . 
     Therefore, as will be described later, even if respective large amounts of air may be collected in the respective upper portions of the ink-deliver passages  91 Y through  91 B, a probability that the collected air may flow into the ink-jet recording head  30  and accordingly the recording head  30  may fail to print characters or may print defective characters, can be lowered. 
     The ink-deliver passages  91 Y through  91 B are formed in both the upper and lower ink cases  71 ,  72 , such that the ink-deliver passages  91 Y through  91 B extend parallel to each other in the upward and downward directions and have, as respective lower open ends thereof, respective ink-deliver outlets  39 Y,  39 M,  39 C,  39 B that are located at respective positions lower than the respective inclined guide surfaces  48 Ya through  48 Ba and that communicate with the ink-supply inlets (only the inlet  32   a  is shown in  FIG. 4 ) of the ink-jet recording head  30  via ink-flow openings (only the opening  33   a  is shown in  FIG. 4 ) of a reinforcing frame  33 . Meanwhile, respective upper open ends of the ink-deliver passages  91 Y through  91 B provide respective air-discharge outlets  46 Y,  46 M,  46 C,  46 B that are provided along a plane (i.e., an upper surface  71   a  of the upper ink case  71 ) and that communicate with the outside space via the respective air-discharge valves  47 Y through  47 B that can open and close the outlets  46 Y through  46 B, respectively.  FIG. 4  relates to each of the first and second embodiments and accordingly does not show any of the inclined guide surfaces  48 Ya through  48 Ba. However, all the elements shown in  FIG. 4 , except for the inclined guide surfaces  48 Ya through  48 Ba, are identical with the corresponding elements employed in the present, third embodiment. 
     (Communication between Ink-Deliver Chambers  41 - 44  and Corresponding Ink-Deliver Passages  91 ) 
     The ink-deliver chambers  41  through  44  employed in the present embodiment are respectively identical with the ink-deliver chambers  41  through  44  employed in each of the first and second embodiments, but the present embodiment differs from the two embodiments in that the present embodiment employs, as the ink-connect portions, the inclined guide surfaces  48 Ya through  48 Ba that are provided between the respective ink-flow outlets  41   c  through  44   c  of the ink-deliver chambers  41  through  44  and the corresponding ink-deliver passages  91 Y through  91 B. The following description relates to differences between the first and second embodiments and the present, third embodiment that are observed with respect to the communication between the ink-deliver chambers  41  through  44  and the corresponding ink-deliver passages  91 Y through  91 B. 
     The ink-flow outlet  41   c  of the yellow-ink deliver chamber  41  is formed through the upper ink case  71  in a direction from a bottom surface  41   a  of the deliver chamber  41  to a lower surface  71   b  of the case  71 , and is connected to the ink-deliver passage  91 Y ( FIG. 17  or  FIG. 26 ) via the ink-guide passage  48 Y. A lower portion of the ink-flow outlet  41   c  is partially defined by a guide wall  64 Y that projects downward from the lower surface  71   b  and separates the lower portion of the ink-flow outlet  41   c  from the ink-deliver passage  91 Y. A lower end of the guide wall  64 Y is lower than the upper end of the ink-deliver passage  91 Y, and is spaced upward from an upper end of the inclined guide surface  48 Ya. Thus, the lower portion of the ink-flow outlet  41   c  communicates with the lower portion  94 Y (eventually, a bottom portion of the ink-deliver passage  91 Y) via the inclined guide surface  48 Ya. 
     The ink-flow outlet  42   c  of the magenta-ink deliver chamber  42  opens, in a bottom surface  42   a  of the deliver chamber  42 , at a left-hand and rear corner diagonal to the ink-flow inlet  42   b  of the deliver chamber  42 . The ink-flow outlet  42   c  is formed through the upper ink case  71 , and is connected to one end portion of a connection passage  65 M. The other end portion of the connection passage  65 M is formed through the upper ink case  71  in the direction from an upper surface  71   a  of the case  71  to the lower surface  71   b  thereof, and is connected to the ink-deliver passage  91 M via the ink-guide passage  48 M. A lower open end of the other end portion of the connection passage  65 M is partially defined by a guide wall  64 M that projects downward from the lower surface  71   b  and separates the lower end portion of the other end portion of the connection passage  65 M, from the ink-deliver passage  91 M. A lower end of the guide wall  64 M is lower than the upper end of the ink-deliver passage  91 M, and is spaced upward from an upper end of the inclined guide surface  48 Ma. Thus, the lower end portion of the other end portion of the connection passage  65 M communicates with the lower portion  94 M (eventually, a bottom portion of the ink-deliver passage  91 M) via the inclined guide surface  48 Ma. 
     The ink-flow outlet  43   c  of the cyan-ink deliver chamber  43  opens, in a bottom surface  43   a  of the deliver chamber  43 , at a left-hand and rear corner of the same  43 . The ink-flow outlet  43   c  is formed through a thickness of the lower ink case  72 , and is connected to one end portion of a connection passage  68 C ( FIG. 19 ) formed in a lower surface  72   b  of the case  72 . The connection passage  68 C and a rear portion of the ink-deliver chamber  44  overlap, in their plan view, the ink-deliver passages  91 Y through  91 B, and the other end  68 Ca of the connection passage  68 C is formed through the lower ink case  72  in the direction from the lower surface  72   b  of the case  72  to the upper surface  72   a  thereof, and opens in the ink-guide passage  48 C, at a position lower than the upper end of the ink-deliver passage  91 C. Thus, the other end  68 Ca of the connection passage  68 C communicates with the lower portion  94 C (eventually, a bottom portion of the ink-deliver passage  91 C) via the inclined guide surface  48 Ca ( FIG. 28 ). 
     The ink-flow outlet  44   c  of the black-ink deliver chamber  44  from which the black ink flows opens, in a bottom surface  44   a  of the deliver chamber  44 , at a right-hand and rear corner of the same  44 . The ink-flow outlet  44   c  is formed through the lower ink case  72  in the upward and downward directions, and opens in the ink-guide passage  48 B, at a position lower than the upper end of the ink-deliver passage  91 B. Thus, the ink-flow outlet  44   c  communicates with the lower portion  94 B (eventually, a bottom portion of the ink-deliver passage  91 B) via the inclined guide surface  48 Ba. 
     (Flow of Inks) 
     In the present embodiment, the inks flow in the same manner as the manner in which the inks flow in each of the first and second embodiments, except that the inks flow from the respective ink-deliver chambers  41  through  44  into the respective ink-deliver passages  91 Y through  91 B via the respective ink-guide passages  48 Y through  48 B. 
     As shown in  FIG. 26 , the yellow ink flows from the ink-deliver chamber  41  into the ink-deliver passage  91 Y via the ink-guide passage  48 Y, and then flows from the ink-deliver outlet  39 Y into the ink-jet recording head  30 ; as shown in  FIG. 27 , the magenta ink flows from the ink-deliver chamber  42  into the ink-deliver passage  91 M via the ink-guide passage  48 M, and then flows from the ink-deliver outlet  39 M into the ink-jet recording head  30 ; as shown in  FIG. 28 , the cyan ink flows from the ink-deliver chamber  43  into the ink-deliver passage  91 C via the ink-guide passage  48 C, and then flows from the ink-deliver outlet  39 C into the ink-jet recording head  30 ; and, as shown in  FIG. 29 , the black ink flows from the ink-deliver chamber  44  into the ink-deliver passage  91 B via the ink-guide passage  48 B, and then flows from the ink-deliver outlet  39 B into the ink-jet recording head  30 . 
     Thus, the inks flow from the respective ink-deliver chambers  41  through  44  into the respective ink-deliver passages  91 Y through  91 B via the respective ink-guide passages  48 Y through  48 B. Therefore, in each of the ink-deliver passages  91 Y through  91 B, air bubbles can be efficiently separated from the ink flowing into the each passage  91 Y through  91 B, and air bubbles captured by a filter (not shown) provided at a corresponding one of the ink-supply inlets (e.g.,  32   a ) of the ink-jet recording head  30  can naturally move upward, so that the air bubbles are collected in the upper portion of the each passage  91 Y through  91 B. The thus collected air can be discharged into the outside space through a corresponding one of the air-discharge outlets  46 Y through  46 B that can be opened and closed by an air-discharge valve device  45 . 
     (Supply of Inks) 
       FIGS. 30 and 32  show a state in which a large amount of air is collected in the upper portion of each of the ink-deliver passages  91 Y through  91 B. As the amount of air collected in the upper portion of each ink-deliver passage  91 Y through  91 B increases, a level, i.e., an upper surface of the ink present in the each passage  91 Y through  91 B gradually lowers and accordingly a connection between the ink present in the each passage  91 Y through  91 B and the ink present in the corresponding ink-deliver chamber  41  through  44  gradually thins. For example, regarding the yellow ink shown in  FIG. 30  (and also regarding the magenta ink), if the upper surface of the yellow ink present in the ink-deliver passage  91 Y lowers to below the guide wall  64 Y, then the ink delivered from the ink-flow outlet  41   c  of the ink-deliver chamber  41  is pushed toward the ink-guide passage  48 M by the pressure of the air collected in the ink-deliver passage  91 Y. However, even if the upper surface of the yellow ink present in the ink-deliver passage  91 Y may lower to a position somewhat spaced downward from the upper end of the inclined guide surface  48 Ya, the upper surface of the yellow ink can remain at a position sufficiently near to the ink present in the ink-deliver chamber  41  owing to the presence of the inclined guide surface  48 Ya. In addition, owing to a surface tension of the ink and an attraction applied to the ink because of the consumption thereof by the ink-jet recording head  30 , the connection between the ink present in the ink-deliver passage  91 Y and the ink present in the ink-deliver chamber  41  can be maintained or promoted. 
     In addition, regarding the black ink shown in  FIG. 32  (and also regarding the cyan ink), even if the upper surface of the black ink present in the ink-deliver passage  91 B may lower to a position substantially level with the upper end of the inclined guide surface  48 Ba, the ink exposed out of the ink-flow outlet  44   c  of the ink-deliver chamber  44  to the ink-guide passage  48 B can remain sufficiently near to the upper surface of the ink present in the ink-deliver passage  91 B owing to the presence of the inclined guide surface  48 Ba. In addition, owing to a surface tension of the ink and an attraction applied to the ink because of the consumption thereof by the ink-jet recording head  30 , the connection between the ink present in the ink-deliver passage  91 B and the ink present in the ink-deliver chamber  44  can be maintained or promoted. 
     In contrast, if the respective inclined guide surfaces  48 Ya,  48 Ma,  48 Ca,  48 Ba of the ink-guide passages  48 Y,  48 M,  48 C,  48 B are replaced with respective horizontal surfaces, then it would be difficult for the inks to flow from the ink-deliver chambers  41  through  44  to the corresponding ink-deliver passages  91 Y through  91 B via those horizontal surfaces, in a state in which the respective upper surfaces of the inks present in the ink-deliver passages  91 Y through  91 B have lowered to below those horizontal surfaces. Thus, at an early stage, the connection between the ink present in each ink-deliver passage  91 Y through  91 B and the ink present in the corresponding ink-deliver chamber  41  through  44  would be broken. In the present embodiment, however, the connection between the ink present in each ink-deliver passage  91 Y through  91 B and the ink present in the corresponding ink-deliver chamber  41  through  44  can be maintained for a certain time duration thereafter. 
       FIGS. 31 and 33  show a state in which the upper surface of the ink present in each of the ink-deliver passages  91 Y through  91 B has further lowered and the connection between the ink present in the each ink-deliver passage  91 Y through  91 B and the ink present in the corresponding ink-deliver chamber  41  through  44  has been broken (even in this state, characters can be printed with the inks left in the ink-deliver passages  91 Y through  91 B). If a first cap member  122  is used to suck the inks from nozzle arrays  35  through  38 , the upper surface of the ink present in each of the ink-deliver passages  91 Y through  91 B quickly lowers, so that the pressure of the air collected in the upper portion of the each passage  91 Y through  91 B lowers. Thus, regarding the yellow ink shown in  FIG. 31  (and also regarding the magenta ink), the ink present in the ink-guide passage  48 Y is sucked toward the ink-deliver passage  91 Y, so that the ink may flow along the inclined guide surface  48 Ya and quickly join with the ink present in the ink-deliver passage  91 Y. In addition, regarding the black ink shown in  FIG. 32  (and also regarding the cyan ink), the ink exposed out of the ink-flow outlet  44   c  to the ink-guide passage  48 B is sucked up by a negative pressure, so that the ink may flow along the inclined guide surface  48 Ba and quickly join with the ink present in the ink-deliver passage  91 B. 
     In contrast, if the respective inclined guide surfaces  48 Ya,  48 Ma,  48 Ca,  48 Ba of the ink-guide passages  48 Y,  48 M,  48 C,  48 B are replaced with the above-described horizontal surfaces, then it would take a long time for the inks to flow from the ink-deliver chambers  41  through  44  to the ink-deliver passages  91 Y through  91 B via those horizontal surfaces and, for that long time, the air collected in the respective upper portions of the ink-deliver passages  91 Y through  91 B would be sucked toward the ink-jet recording head  30 , so that the recording head  30  may fail to eject droplets of the inks or may eject defective ink droplets. In the present embodiment, the ink present in each ink-deliver chamber  41  through  44  can quickly join with the ink present in the corresponding ink-deliver passage  91 Y through  91 B via the corresponding inclined guide surface  48 Ya through  48 Ba. Therefore, respective sufficient amounts of inks that are needed to carry out the recording-head recovering operation can be supplied to the respective ink-deliver passages  91 Y through  91 B and accordingly the recording-head recovering operation can be carried out with reliability. 
     However, the present embodiment may be modified in the following manners:
     (a) In the present embodiment, the ink-connect portions are provided in the respective bottom walls defining the respective ink-guide passages  48 Y through  48 B, i.e., are constituted by the respective inclined guide surfaces  48 Ya through  48 Ba, each in the form of one inclined plane surface, whose heights decrease in the respective directions toward the corresponding ink-deliver passages  91 Y through  91 B. However, each of the respective inclined guide surfaces  48 Ya through  48 Ba may not be constituted by one inclined plane surface, but may be constituted by two or more inclined plane surfaces that are combined to provide a bent, ridged surface or a bent, recessed surface.   (b) Alternatively, the ink-connect portions may be constructed by such respective inclined guide surfaces each of which is provided by not one or more inclined plane surfaces but one or more inclined, curved surfaces such as a curved, ridged surface(s) or a curved, recessed surface(s). Otherwise, each of the ink-connect portions may be constructed by one or more inclined elongate guide recesses that is or are provided in the bottom wall defining a corresponding one of the ink-guide passages  48 Y through  48 B and that has or have a bottom surface(s) whose height decreases in a direction toward a corresponding one of the ink-deliver passages  91 Y through  91 B.   

     Advantages of the Present Embodiment 
     
         
         (1) The inclined guide surfaces  48 Ya through  48 Ba guide the inks delivered from the ink-deliver chambers  41  through  44  into the ink-guide passages  48 Y through  48 B, so that the inks can easily flow into the ink-deliver passages  91 Y through  91 B. That is, only the inclined guide surfaces  48 Ya through  48 Ba, provided in the bottom walls defining the ink-guide passages  48 Y through  48 B, can easily maintain or promote the respective connections between the inks present in the ink-deliver chambers  41  through  44  and the inks present in the respective lower portions  94 Y through  94 B of the ink-deliver passages  91 Y through  91 B that are located at the respective positions lower than the ink-deliver chambers  41  through  44 . 
         (2) In the modified embodiment wherein one or more inclined elongate guide recesses is or are provided in the bottom wall defining each of the ink-guide passages  48 Y through  48 B, such that the inclined elongate guide recess(es) has or have a bottom surface(s) whose height decreases in a direction toward the corresponding ink-deliver passage  91 Y through  91 B, the ink delivered from the corresponding ink-deliver chamber  41  through  44  is guided by the inclined guide recess(es) and can easily flow into the corresponding ink-deliver passage  91 Y through  91 B. In particular, since the inclined guide recess(es) is or are elongate like grooves, the connection between the ink present in the corresponding ink-deliver chamber  41  through  44  and the ink present in the corresponding ink-deliver passage  91 Y through  91 B can be easily maintained or promoted. 
         (3) In the present ink-jet recording apparatus, the ink-jet recording head  30  ejects droplets of the inks while the plurality of ink-deliver chambers  41  through  44  and the ink-jet recording head  30  are moved relative to a recording medium. However, a probability that the air collected in the respective upper portions of the ink-deliver passage  91 Y through  91 B may be sucked into the recording head  30  and accordingly the recording head may fail to print characters or may print defective characters, can be lowered. 
         (4) Since the upper ink case  71  and the lower ink case  72  are joined to each other to provide the buffer tank  40 , the ink-deliver chambers  41  through  44 , the air-discharge outlets  46 Y through  46   b , the ink-deliver passages  91 Y through  91 B, and the ink-guide passages  48 Y through  48 B can be easily provided. 
       
    
     Additional Embodiment 3 
     
         
         (1) In each of the above-described three embodiments, the yellow ink, the magenta ink, the cyan ink, and the black ink are accommodated by the four ink-deliver chambers  41  through  44 , respectively, in the order of description in the downward direction. However, this order may be changed. In the latter case, too, the same advantages as those of the above-described three embodiments can be obtained. 
         (2) The two ink cases  71 ,  72  may be arranged in the scanning direction, i.e., the leftward and rightward directions. In the latter case, a total dimension of the buffer tank  40  in the leftward and rightward directions can be reduced, and at least one of the advantages of the above-described three embodiments can be obtained.