Abstract:
An inkjet recording apparatus that records an image on a recording medium including: at least one recording head for unused-ink having a nozzle array made of a plurality of nozzles that selectively ejects unused-ink; at least one recording head for recycled-ink having a nozzle array made of a plurality of nozzles that selectively ejects recycled-ink of an equivalent color to the unused-ink ejected from the recording head for unused-ink; a collector that collects ink discharged from the recording head for unused-ink and the recording head for recycled-ink so as to restore an ejectable state of the recording heads; and a recycled-ink supplier that supplies ink, collected by the collector, to the recording head for recycled-ink as recycled-ink.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of Japanese Patent Application No. 2005-132195 filed Apr. 28, 2005 in the Japan Patent Office, the disclosure of which is incorporated herein by reference.  
       BACKGROUND  
       [0002]     This invention relates to an inkjet recording apparatus. Particularly, the present invention relates to technique for reusing ink ejected when nozzle maintenance is performed.  
         [0003]     An inkjet recording apparatus has already been achieved wherein color recording is possible with a plurality of colors of ink (for example, black (to be referred to as “K”), cyan (to be referred to as “C”), magenta (to be referred to as “M”), and yellow (to be referred to as “Y”)). In such an inkjet recording apparatus, nozzles from which a respective color of ink is ejected are provided on a recording head. Ink is selectively ejected from each nozzle onto a recording medium so as to record an image on the recording medium.  
         [0004]     However, it is known that nozzles of this kind of inkjet recording apparatus go into an unejectable state, wherein nozzles are blocked when dust or air enters the nozzles or when the ink inside of the nozzles becomes dried and solidified. In order to restore a normal state of nozzles from such an unejectable state, various maintenance operations are performed, such as a vacuum purging, purging with positive pressure, and flushing. When such maintenance operations are performed, unused-ink is forcibly ejected for the purpose of removing dust, air, and solidified ink from the inside of the nozzles. The ejected ink is conventionally discarded by being stored in a waste ink reservoir or absorbed into a waste ink absorber.  
         [0005]     If a large amount of ink is discarded without being used for recording, because of the maintenance operations described above, the amount of ink that can be used for recording inevitably decreases. There has been a problem in that the running cost, such as for ink, becomes higher.  
         [0006]     A technique for collecting and reusing waste ink has been devised. In an inkjet recording apparatus with this technique, virgin-inks C, M, and Y, which have not been used yet, are used for recording. As for ink K, a processed ink, wherein C, M, and Y, are blended, is used for recording. This inkjet recording apparatus is provided with recording heads for respective colors of ink C, M, and Y, and a recording head for the processed black ink. When ink is ejected from each recording head due to a maintenance operation, ink is collected by a cap. Dust and air bubbles are removed from the collected ink via a filter. Diluting-fluid is added to the collected ink so as to adjust the viscosity. The diluted ink is supplied to the recording head for the processed black ink and reused.  
         [0007]     However, the above-described inkjet recording apparatus is provided with only one recording head for ink K (i.e. for the processed black ink). Since processed black ink (made of C, M, and Y, blended together) is used as ink K, the actual color of ink K sometimes does not appear black depending on the mixture ratio of each color of ink blended therein. When such blended ink is used for image recording, the quality of an image might be deteriorated.  
         [0008]     Moreover, because the processed black ink is made of ink C, M, and Y, causing a large consumption of processed black ink for black-and-white image recording, such as for text-image formation or facsimile-data image formation, causes the quick consumption of a large amount of ink C, M, and Y. These colors of ink might run out before color image recording is performed. Using color ink for black-and-white image recording might cause an increase in ink cost.  
       SUMMARY  
       [0009]     In one aspect of the present invention, in addition to a recording head for unused-ink (virgin-ink) (to be referred to as head V (virgin-ink)), an inkjet recording apparatus may be preferably provided with another recording head for reused-ink (recycled-ink) of an equivalent color (to be referred to as head R (recycled-ink)). In the inkjet recording apparatus, consumption of ink can be preferably saved by reusing the ink discharged during a maintenance operation.  
         [0010]     In the one aspect of the present invention, an inkjet recording apparatus includes at least one recording head for unused-ink (virgin-ink), and at least one recording head for reused-ink (recycled-ink) of an equivalent color to the unused-ink.  
         [0011]     Both of the above-described recording heads respectively have a nozzle array including a plurality of nozzles from which ink can be selectively ejected. The inkjet recording apparatus described above performs the recording of an image on a recording medium with these recording heads. The recording head for unused-ink (to be referred to as head V) ejects unused-ink. The recording head for recycled-ink (to be referred to as head R) ejects recycled-ink of an equivalent color to the ink ejected from the head V. The inkjet recording apparatus furthermore includes a collector and a recycled-ink supplier. The collector collects ink discharged from the head V and the head R in order to restore an ink-ejectable state of the recording heads. The recycled-ink supplier supplies the ink collected by the collector to the head R as recycled-ink.  
         [0012]     It is to be noted that the “ink discharged in order to restore an ink-ejectable state” mentioned above indicates ink discharged during the various maintenance operations in the recording heads, such as suction purging, purging with positive pressure, or flushing (all together simply referred to as “a maintenance operation”). It is also to be noted that “an equivalent color” mentioned above includes not only the meaning of “an identical color”, but also includes a meaning of “a similar color” that is not exactly identical with an original color but can be used as a substitute for the original color.  
         [0013]     With the above-described inkjet recording apparatus, ink, discharged during a maintenance operation, can be reused and the ink can be saved. Moreover, since the head R for recycled-ink of an equivalent color to the unused-ink contained in the head V is provided, image recording can be performed with the recycled-ink stored in the head R even when the unused-ink runs out. Furthermore, unused-ink and recycled-ink can be selectively used depending on the situation. For example, unused-ink from the head V can be used for high quality image recording. Recycled-ink from the head R can be used for lower quality image recording. Additionally, image recording can be performed with high speed by simultaneous ejection of ink in the equivalent color from the head V and the head R. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     The invention will now be described below, by way of example, with reference to the accompanying drawings, in which:  
         [0015]      FIG. 1  is a perspective view showing a multifunction apparatus to which the present invention is preferably applicable;  
         [0016]      FIG. 2  is a block diagram showing a schematic structure of a main part of an inkjet recording apparatus according to a first embodiment of the present invention;  
         [0017]      FIGS. 3A and 3B  are sectional block diagrams in which  FIG. 3A  shows a head V for ink K, and  FIG. 3B  shows a head R for ink RK;  
         [0018]      FIG. 4  is a schematic view showing a disposition of nozzle arrays of respective recording heads in the inkjet recording apparatus according to the first embodiment  FIG. 5  is a block diagram showing a main part of an electric structure in the inkjet recording apparatus according to the first embodiment;  
         [0019]      FIG. 6  is a block diagram, showing a schematic structure of a main part of an inkjet recording apparatus according to a second embodiment of the present invention;  
         [0020]      FIG. 7  is a block diagram showing a main part of an electric structure in the inkjet recording apparatus according to the second embodiment;  
         [0021]      FIG. 8  is a block diagram showing a schematic structure of a main part of an inkjet recording apparatus according to a third embodiment of the present invention;  
         [0022]      FIGS. 9A and 9B  are schematic views showing examples of the disposition of diluting-fluid nozzles of a diluting-fluid ejection head;  
         [0023]      FIG. 10  is a block diagram showing a main part of an electric structure in the inkjet recording apparatus according to the third embodiment;  
         [0024]      FIG. 11  is a block diagram showing a schematic structure of a main part of an inkjet recording apparatus according to a fourth embodiment of the present invention;  
         [0025]      FIG. 12  is a block diagram showing a main part of an electric structure in the inkjet recording apparatus according to the fourth embodiment;  
         [0026]      FIG. 13  is a flowchart explaining an excessive ink disposal process;  
         [0027]      FIG. 14  is a flowchart explaining a recording mode selection process;  
         [0028]      FIG. 15  is a flowchart explaining a process for a recycled-ink priority recording mode;  
         [0029]      FIG. 16  is a flowchart explaining a process for an unused-ink priority recording mode;  
         [0030]      FIG. 17  is a block diagram showing a schematic structure of a main part of an inkjet recording apparatus according to a fifth embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0000]     [Overall Structure of Inkjet Recording Apparatus  1 ] 
         [0031]     Referring to  FIG. 1 , an inkjet recording apparatus  1  is a multifunction device that serves as a printer, a copier, a scanner, and a facsimile. A sheet of paper or plastic film is used as a recording medium.  
         [0032]     The inkjet recording apparatus  1  is provided with a housing  2 , a paper feed cassette  3 , and a paper discharge unit  21 . The housing  2  is made of synthetic resin. The paper feed cassette  3  is provided in a bottom portion of the housing  2 . The paper feed cassette  3  can be inserted into an opening  2   a  formed in the front side of the housing  2 . The paper discharge unit  21  is provided over the paper feed cassette  3 . Paper on which recording is performed is discharged onto the paper discharge unit  21  in the direction indicated by Arrow A. A paper exit, communicated with the paper discharge unit  21 , is provided in a upper portion of the opening  2   a  in the front side of the housing  2 .  
         [0033]     The paper feed cassette  3  can store a plurality of sheets of paper taht are cut into, for example, A4 size, letter size, legal size, or postcard size. Each sheet of paper is placed in a manner so that the long side of the paper is placed in parallel to a paper conveyance direction (a sub-scanning direction, or an x-axis direction). An auxiliary support member  3   a , which can be extended in the x-axis direction, is attached to the front end of the paper feed cassette  3  so as to support a trailing end of a long sheet of paper, such as for the legal size. When paper can be stored within the paper feed cassette  3 , such as paper in an A4 size, the auxiliary support member  3   a  is stored into the front portion of the paper feed cassette  3  in a manner so that the stored auxiliary support member  3   a  does not interrupt the paper feed.  
         [0034]     An image reading device  23  is provided in the upper portion of the housing  2 . The image reading device  23  is used so as to read an original image when the inkjet recording apparatus  1  works as a copier or a facsimile. The image reading device  23  is rotatable on a shaft (not shown) in an up-and-down direction with respect to one side of the housing  2 , and can be opened and closed. A cover  27  is provided on the top portion of the image reading device  23 . The cover  27  covers an original image placed on the top surface of the image reading device  23 . The cover  27  is rotatable in the up-and-down direction on a shaft (not shown) provided on the rear end of the image reading device  23 .  
         [0035]     For reading an image, the cover  27  is lifted upward and opened. An original image is placed on a glass board for original image placement. While the original image is placed on the glass board, a contact image sensor, which is disposed under the glass board so as to be able to be reciprocated in a y-axis direction (a main scanning direction), scans the original image and reads the image.  
         [0036]     An operation panel  29 , having various operation buttons and a liquid crystal display, is provided in front of the cover  27  on the top surface of the image reading device  23 .  
         [0037]     A recording unit (not shown), constituted with a carriage  112  (see  FIG. 5 ) and other mechanisms, is provided inside of the housing  2 . The carriage  112  carries inkjet recording heads that realize the printing performance of the inkjet recording apparatus  1 . The carriage  112  can be reciprocated in the y-axis direction (the main scanning direction).  
         [0038]     In the recording unit, the carriage is controlled by a control unit  100  (see  FIG. 5 ) constituted with a CPU and the like and reciprocated in the y-axis direction (the main scanning direction) so as to move the recording heads. While the recording heads are being moved, ink is ejected onto paper that is placed stationary under the recording heads. An image is recorded on the paper.  
         [0039]     Moreover, a maintenance unit (not shown) is provided at a position that corresponds to a standby position of the carriage in the recording unit. In the maintenance unit, various maintenance operations, such as wiping for wiping the nozzle surfaces of the recording heads with a blade, purging for forcibly removing dust, air, or solidified ink, and flushing, are performed.  
         [0040]     Furthermore, an ink reservoir unit is provided inside of the housing  2 . Ink cartridges and a recycled-ink tank are provided in the ink reservoir unit. Each ink cartridge stores unused-ink of one of the four colors (black (K), cyan (C), magenta (M) and yellow (Y)) for full-color recording. The recycled-ink tank stores ink collected from the recording heads due to maintenance operations. The ink cartridge can be attachable from above and detachable upwardly with respect to the ink reservoir unit. In order to replenish ink, the entire ink cartridge is replaced.  
       First Embodiment  
       [0041]     Referring now to  FIG. 2 , the inkjet recording apparatus  1  according to a first embodiment is provided with ink cartridges  31 ,  32 ,  33 , and  34 , and a recycled-ink tank  41  in the above-described ink reservoir unit. Each of the ink cartridges  31 - 34  stores one of unused-inks K, C, M and Y. The recycled-ink tank  41  is for storing recycled black ink (to be referred to as “RK”). The inkjet recording apparatus  1  is furthermore provided with recording heads  51 ,  52 ,  53  and  54  respectively for unused-ink K, C, M, and Y (heads V), and a recording head  61  for ink RK (head R) on the carriage in the above-described recording unit. Still furthermore, the inkjet recording apparatus  1  is provided with a cap  71   a , a pump  72   a , a filter  73 , and a collected-ink path  75 , in the above-described maintenance unit. Additionally, the inkjet recording apparatus  1  is provided with ink supply tubes  74 . It is to be noted that all of the unused-inks K, C, M, and Y, are dye ink.  
         [0042]     The cap  71   a  is attached to all the recording heads  51 - 54  and  61  when recording is not performed and covers the nozzle surfaces of recording heads  51 - 54  and  61  so as to inhibit the drying of the ink inside of each recording head. When the pump  72   a  is driven while the cap  71   a  is attached to the recording heads  51 - 54  and  61 , ink can be drawn from nozzles of each recording head. As result of this operation, impure substances, air bubbles, and solidified ink accumulated inside of the nozzles of the recording heads  51 - 54  and  61 , can be discharged from the recording heads  51 - 54  and  61  into the cap  71   a  (purging). Ink ejected from the recording heads  51 - 54  and  61  due to flushing can be received in the cap  71   a . Ink inside of the cap  71   a  can be collected by the pump  72   a . It is to be noted that the cap  71   a  receives, in bulk, all of the ink K, C, M, and RK discharged from the respective recording heads  51 - 54  and  61 .  
         [0043]     Ink discharged into the cap  71   a  is collected by the pump  72   a  when the pump  72   a  is driven, Collected ink of respective colors K, C, M, Y, and RK are mixed together. The amount of ink of the respective colors discharged from each of the recording heads  51 - 54  and  61  when purging and flushing are performed is virtually equivalent to one another. Thus, the mixed ink becomes a black color ink. In the inkjet recording apparatus  1  according to the present embodiment, the mixed ink is recycled and used as ink RK for image recording.  
         [0044]     Collected ink flows in the collected ink path  75  and is filtered through the filter  73 . Impure substances and air bubbles contained in the collected ink are removed. Then, the collected ink is stored in the recycled-ink tank  41  as ink RK.  
         [0045]     The recycled-ink tank  41  and ink cartridges  31 - 34  in the ink reservoir unit are respectively communicated with the head R  61  and the heads V  51 - 54  on the carriage of the recording unit via the ink supply tubes  74 . Ink stored in the recycled-ink tank  41  and the ink cartridges  31 - 34  for unused-ink is supplied to the respective recording heads  51 - 54  and  61  through the ink supply tubes  74 . The ink supply tube  74  for ink RK has a larger diameter as compared to the other ink supply tubes  74  for unused-ink. This is based on an assumption that the viscosity of ink RK increases because ink RK is made of ink that has already been discharged once due to a maintenance operation, and the diluting-fluid contained therein evaporates. In other words, by providing the ink supply tube  74  for ink RK with a larger diameter than the other ink supply tubes  74 , an increase of the flow resistance, which can be caused due to a viscosity increase, can be prevented. Consequently, recycled-ink can flow in the ink supply tube  74  in a stable manner although the viscosity of such ink has been increased.  
         [0046]     As shown in  FIGS. 3A and 3B , sub-tanks  51   b  and  61   b  are respectively incorporated in the recording heads  51  and  61 . The sub-tanks  51   b  and  61   b  store ink supplied through the ink tubes  74  (see  FIG. 2 ). In the lower side of sub-tank  51   b  and  61   b , nozzles  51   a  and  61   a  are respectively aligned for ejecting ink. It is to be noted that the other heads V  52 - 54  have the same structure as the structure of the head V  51  for ink K.  
         [0047]     The diameter (Dr) of the nozzles  61   a  of the head R  61  is larger than the diameter (Dv) of the nozzles  51   a  of the head V  51 . This is based on the assumption that ink RK ejected from the head R  61  has a different ejection characteristic from the characteristics of unused-ink, because the viscosity of ink RK is higher due to the volatilization of the diluting-fluid contained in the ink. By making the diameter (Dr) of the nozzles  61   a  of the head R  61  larger than the diameter (Dv) of the nozzles  51   a  of the head V  51 , the recycled-ink can be ejected in a stable manner although the viscosity of the recycled-ink has been increased. A suitable size for the diameter (Dr) can be calculated according to Hagen-Poiseuille Equation with the expected increased viscosity of the recycled-ink. Specifically, if the diameter (Dv) of the nozzles  51   a  of the head V  51  is 20 μm, the diameter (Dr) of the nozzles  61   a  of the head R  61  can be a few μm to several tens of μm larger than Dv in consideration of the increased viscosity of recycled-ink.  
         [0048]     As shown in  FIG. 4 , the arrays of nozzles of the recording heads  51 - 54  and  61  are disposed along the scanning direction of the recording heads  51 - 54  and  61  in the order of nozzle array Y, M, C, K, and RK, from the left side. The arrays Y, M, C, K, and RK, are disposed in parallel to one another. The positions of nozzles  61   a  in the nozzle array RK of the head R  61  are displaced off of the positions of the nozzles  51   a  in the adjacent nozzle array K of the head V  51  in the direction of the alignment for half (0.5 P) of the interval P between the nozzles  51   a.    
         [0049]     Because of the positions of the nozzles  61   a  being displaced off by 0.5 P, when ink K and ink RK are simultaneously ejected from the head V  51  and the head R  61  for image recording, the image recording can be performed more minutely, as compared to a case wherein ink is ejected from only one of the head V  51  and the head R  61 . The quality of image recording can be substantially as minute as the quality of image recording performed with a recording head having half of the interval P between the nozzles. Moreover, if ink K and ink RK are simultaneously ejected for image recording, image recording can be performed with a higher speed and a higher quality.  
         [0050]     As shown in  FIG. 5 , the inkjet recording apparatus  1  includes a control unit  100 , a carriage  112 , a blade  120 , and drive circuits  114 ,  116  and  118 , and  122  in addition to the constituents shown in  FIG. 2 . The control unit  100  has a CPU  102 , a ROM  104 , and a RAM  106  which are conventionally known.  
         [0051]     The carriage  112  is reciprocated in the y-axis direction upon receipt of a control signal from the control unit  100  via the drive circuit  114 .  
         [0052]     The pump  72   a  is driven upon receipt of a control signal from the control unit  100  via the drive circuit  116 . As a result, the above-described ink suction from the nozzles of the recording heads, and collection of ink, discharged from the recording heads due to flushing, can be performed.  
         [0053]     When a control signal is outputted from the control unit  100  via the drive circuit  118 , ink is ejected from desired nozzles in the head R  61  and the respective heads V  51 - 54 .  
         [0054]     When a control signal is outputted from the control unit  100  via the drive circuit  122 , the blade  120  is driven. Consequently, wiping of the nozzle surfaces of the recording heads is performed by the blade  120 .  
         [0055]     Additionally, the control unit  100  performs various processes based on a control signal inputted from an external device, such as the operation panel  29  or a personal computer (to be referred to as “PC”)  124  connected to the control unit  100  via a specific interface.  
         [0000]     [Effect] 
         [0056]     The following effect can be achieved with the inkjet recording apparatus according to the first embodiment. Ink can be saved by recycling ink discharged from the respective recording heads during a maintenance operation and using the recycled-ink as ink RK. Additionally, image recording can be performed even when ink K runs out by providing a head R for ink RK, which is in an equivalent color to ink K, and using ink RK of the head R. Furthermore, the amount of ink that can be used for ink RK increases because ink RK is not only made of ink K, but also made of ink C, M, Y, K, and RK, collected and mixed together. Therefore, the frequency of replenishing ink K can be reduced.  
         [0057]     In the present embodiment, inks C, M, Y, K, and RK are all collected, mixed together, and reused as ink RK for image recording.  
         [0058]     Alternatively, ink RK can be made of at least inks C, M, and Y, which are discharged once, and used for image recording.  
         [0059]     Specifically, the inkjet recording apparatus  1  may have a structure wherein ink discharged only from the heads V  52 - 54  for ink C, M, and Y, or ink discharged only from the heads V  51 - 54  for ink C, M, Y, and K are collected, mixed together, and reused as ink RK. This structure can be achieved by a configuration wherein the cap  71   a  receives ink discharged only from the heads V  52 - 54  for ink C, M, and Y in bulk, or ink discharged only from the heads V  51 - 54  for ink C, M, Y, and K in bulk, and the collected ink is reserved in the recycled-ink tank  41  through the collected-ink path  75 .  
       Second Embodiment  
       [0060]     In  FIG. 6 , which schematically shows the substantial structure of an inkjet recording apparatus  1  according to a second embodiment, the same reference numbers are given to the same components as in the first embodiment shown in  FIG. 2 .  
         [0061]     As shown in  FIG. 6 , the inkjet recording apparatus  1  according to the second embodiment includes ink cartridges  31 ,  32 ,  33 , and  34 , and recycled-ink tanks  41 ,  42 ,  43  and  44 . Each of the ink cartridges  31 - 34  stores one of unused-inks K, C, M, and Y, in the aforementioned ink reservoir unit. Each of the recycled-ink tanks  41 - 44  stores one of recycled-inks K, C, M, and Y (to be referred to as “RK”, “RC”, “RM”, and “RY”). The inkjet recording apparatus  1  is furthermore provided with recording heads  51 ,  52 ,  53 , and  54  for unused-ink (head V) respectively for ink K, C, M, and Y, and recording heads  61 ,  62 ,  63 , and  64  for recycled-ink (heads R) respectively for ink RK, RC, RM, and RY, on a carriage in the aforementioned recording unit. The inkjet recording apparatus  1  is still furthermore provided with a cap  71   b , pumps  72   a , a pump  72   b , a filter  73 , collected-ink paths  75 , and a waste-ink foam  76 , in the aforementioned maintenance unit. Additionally, the inkjet recording apparatus  1  is provided with ink supply tubes  74 . It is to be noted that all of the unused-inks K, C, M, and Y, are dye ink.  
         [0062]     The cap  71   b  is configured so as to separately receive ink discharged from the respective heads V  51 - 54 , and to receive ink discharged from heads R  61 - 64  together in bulk.  
         [0063]     Ink, discharged into the cap  71   b  from the respective heads V  51 - 54  during a maintenance operation, is collected separately by the pumps  72   a . Collected ink flows in the respective collected-ink paths  75 , is filtered through the filter  73 , and stored in the respective recycled-ink tanks  41 - 44 .  
         [0064]     On the other hand, ink discharged into the cap  71   b  from the heads R  61 - 64  during a maintenance operation is collected together by the pump  72   b . The collected ink is discarded into the waste-ink foam  76  and absorbed therein.  
         [0065]     The recycled-ink tanks  41 - 44  and the ink cartridges  31 - 34  in the ink reservoir unit are respectively communicated with the heads R  61 - 64  and the heads V  51 - 54 , on the carriage in the recording unit, via the ink supply tubes  74 . Recycled-ink, stored in the recycled-ink tanks  41 - 44 , and unused-ink, stored in the ink cartridges  31 - 34 , are respectively supplied to the corresponding recording heads through the ink supply tubes  74 .  
         [0066]     As shown in  FIG. 7 , the inkjet recording apparatus  1  includes a control unit  100 , a carriage  112 , a blade  120 , and drive circuits  114 ,  116 ,  118 ,  122 , and  126  in addition to the constituents shown in  FIG. 6 . The control unit  100  has a CPU  102 , a ROM  104 , and a RAM  106  which are conventionally known.  
         [0067]     The carriage  112  is reciprocated in the y-axis direction upon receipt of a control signal from the control unit  100  via the drive circuit  114 .  
         [0068]     Each of the pumps  72   a  is driven upon receipt of a control signal from the control unit  100  via the drive circuit  116 . The pump  72   b  is driven upon receipt of a control signal from the control unit  100  via the drive circuit  126 . As a result, the above-described collection of ink, discharged from the recording heads, can be performed.  
         [0069]     When a control signal is outputted from the control unit  100  via the drive circuit  118 , ink is ejected from desired nozzles in the respective heads R  61 - 64  and the respective heads V  51 - 54 .  
         [0070]     When a control signal is outputted from the control unit  100  via the drive circuit  122 , the blade  120  is driven. Consequently, wiping of the nozzle surfaces of the recording heads is performed by the blade  120 .  
         [0071]     Additionally, the control unit  100  performs various processes based on a control signal inputted from an external device, such as the operation panel  29  or the PC  124  connected to the control unit  100  via a specific interface.  
         [0000]     [Effect] 
         [0072]     The following effect can be achieved with the inkjet recording apparatus according to the second embodiment. In the present embodiment, ink C, M, Y, and K, discharged from the ink cartridges  31 - 34  during a maintenance operation, is recycled as ink in the original colors and reused in the respective heads R  61 - 64 . Therefore, each color of ink can be effectively saved in a case wherein not only ink K, but also ink C, M, and Y are frequently used, such as for color image recording.  
         [0073]     In the present embodiment, only unused-ink, discharged from the respective heads V  51 - 54 , is recycled. Recycled-ink, discharged from the respective heads R  61 - 64 , is discarded. Thus, recycled-ink does not repeatedly go through a cycle of “being discharged and collected”. That is, recycled-ink, supplied to the respective heads R  61 - 64 , is limited only to unused-ink that is discharged from the respective heads V  51 - 54  and collected. As a result, an excessive increase in the viscosity of recycled-ink due to desiccation associated with ink-discharge can be inhibited. The quality of image recording with recycled-ink can be well maintained.  
         [0074]     In the present embodiment, inks of respective colors discharged from the heads V  51 - 54  are individually collected, and respectively ejected from the heads R  61 - 64  as recycled-inks of respective colors.  
         [0075]     In addition to the inks of respective colors discharged from the heads V  51 - 54 , inks of respective colors discharged from the heads R  61 - 64  can be also individually collected, and respectively ejected from the heads R  61 - 64  as recycled-inks of respective colors.  
         [0076]     Specifically, the cap  71   b  may be configured so as to individually receive each of inks discharged from respective heads V  51 - 54 , and to individually receive each of inks discharged from respective heads R  61 - 64 .  
         [0077]     In this case, a collected-ink path, having the same structure as the collected-ink path  75 , is provided for each of inks of respective colors discharged from the respective heads R  61 - 64 . Inks of respective colors, discharged from the respective heads R  61 - 64  due to a maintenance operation, are individually reserved in the corresponding recycled-ink tanks  41 - 44  through the collected-ink paths (and via pumps, having the same structure as the pumps  72   a , and the filter  73  which are both provided on the paths).  
         [0078]     According to this configuration, inks of respective colors, which are discharged during a maintenance operation, can be reused. Therefore, inks of respective colors can be more effectively saved.  
       Third Embodiment  
       [0079]     In  FIG. 8 , which schematically shows the substantial structure of an inkjet recording apparatus  1  according to a third embodiment, the same reference numbers are given to the same components as in the first embodiment shown in  FIG. 2  or in the second embodiment shown in  FIG. 6 .  
         [0080]     As shown in  FIG. 8 , the inkjet recording apparatus  1  according to the third embodiment includes ink cartridges  31 ,  32 ,  33 , and  34 , a recycled-ink tank  41 , and a diluting-fluid tank  78 . Each of the ink cartridges  31 - 34  stores one of the unused-inks K, C, M, and Y, in the aforementioned ink reservoir unit. The recycled-ink tank  41  stores ink RK. The diluting-fluid tank  78  stores diluting-fluid, which is added into the ink so as to adjust the viscosity of the ink. The inkjet recording apparatus  1  is furthermore provided with heads V  51 ,  52 ,  53 , and  54 , a head R  61 , and a diluting-fluid ejection head  80 , on a carriage in the aforementioned recording unit. Each of the heads V  51 - 54  is used for one of the inks K, C, M, and Y. The head R  61  is used for ink RK. The diluting-fluid ejection head  80  is disposed adjacent to the head R  61 . The inkjet recording apparatus  1  is still furthermore provided with a cap  71   c , pumps  72   a  and  72   b , a filter  73 , a collected-ink path  75 , a waste-ink foam  76 , and a viscosity sensor  77 , in the aforementioned maintenance unit. Additionally, the inkjet recording apparatus  1  is provided with ink supply tubes  74  and a diluting-fluid supply tube  79 . A stirring ball  81  for stirring recycled-ink is stored in a sub-tank  61   b  incorporated in the head R  61 . It is to be noted that all of the unused-inks K, C, M, and Y, are dye ink.  
         [0081]     The cap  71   c  is configured so as to receive ink discharged from the head V  51  for ink K together with the head R  61  for ink RK, and to receive ink discharged from the heads V  52 - 54  for ink C, M, and Y together in bulk separately from the other.  
         [0082]     When a maintenance operation is performed, ink is discharged from the head V  51  for ink K and the head R  61  into the cap  71   c . Diluting-fluid is ejected from the diluting-fluid ejection head  80 , which is adjacent to the head R  61 , into the cap  71   c  so as to be added to the discharged ink. The diluting-fluid ejection head  80  ejects a predetermined amount of diluting-fluid (when, for example, the viscosity of the recycled-ink is equal to or higher than a predetermined value) depending on the viscosity of the recycled-ink detected by the viscosity sensor  77 .  
         [0083]     The ink diluted with diluting-fluid is collected by the pump  72   a . The collected ink flows in the collected-ink path  75 , and is filtered through the filter  73 . The collected ink passes the viscosity sensor  77  and is stored in the recycled-ink tank  41  for ink RK. Instead of disposing the viscosity sensor  77  on the collected-ink path  75 , the viscosity sensor  77  can be disposed at any arbitrary position where recycled-ink passes, such as on the ink supply tube  74  for ink RK or inside of the sub-tank  61   b  incorporated into the head R  61 .  
         [0084]     In the present embodiment, the diluting-fluid ejection head  80  is disposed adjacent to the head R  61 . However, the diluting-fluid ejection head  80  may be disposed at one position among inside of any of the heads V  51 - 54 , inside of the head R  61 , adjacent to any of the heads  51 - 54 , or adjacent to the head R  61  and any of the heads V  51 - 54 .  
         [0085]     On the other hand, ink discharged into the cap  71   c  from the heads V  52 - 54  for ink C, M, and Y, during a maintenance operation is all collected together by the pump  72   b , and discarded into the waste-ink foam  76 .  
         [0086]     The diluting-fluid tank  78  is communicated with the diluting-fluid ejection head  80  via the diluting-fluid supply tube  79 . Diluting-fluid, stored in the diluting-fluid tank  78 , is supplied to the diluting-fluid ejection head  80  through the diluting-fluid supply tube  79 .  
         [0087]     The stirring ball  81 , stored within the sub-tank  61   b  in the head R  61 , is urged as the carriage, carrying the recording heads  51 - 54  and  61  and the like, reciprocates for image recording and the stirring ball  81  moves in the sub-tank  61   b . By the movement of the stirring ball  81  in the sub-tank  61   b , recycled-ink stored in the sub-tank  61   b  can be stirred and well mixed with diluting-fluid that is added to the ink. A metallic or resinous spherical body can be used for the stirring ball  81 .  
         [0088]     In  FIG. 9A , each diluting-fluid nozzle  80   a  is disposed between two nozzles  61   a  in the nozzle array for ink RK. In  FIG. 9B , the nozzle array of the diluting-fluid nozzles  80   a  is disposed adjacent to the nozzle array of the nozzles  61   a  for RK ink. In both disposition examples shown in  FIGS. 9A and 9B , diluting-fluid is ejected in close vicinity of the nozzles  61   a  of the head R  61  from which ink RK is discharged during a maintenance operation. Therefore, discharged ink and ejected diluting-fluid can be quickly mixed together.  
         [0089]     As shown in  FIG. 10 , the inkjet recording apparatus  1  includes a control unit  100 , a carriage  112 , a blade  120 , and drive circuits  114 ,  116  and  118 ,  122 , and  126  in addition to the constituents shown in  FIG. 8 . The control unit  100  has a CPU  102 , a ROM  104 , and a RAM  106  which are conventionally known.  
         [0090]     The carriage  112  is reciprocated in the y-axis direction upon receipt of a control signal from the control unit  100  via the drive circuit  114 .  
         [0091]     The pump  72   a  is driven upon receipt of a control signal from the control unit  100  via the drive circuit  116 . The pump  72   b  is driven upon receipt of a control signal from the control unit  100  via the drive circuit  126 . As a result, the above-described collection of ink, discharged from the recording heads, can be performed.  
         [0092]     When a control signal is outputted from the control unit  100  via the drive circuit  118 , ink is ejected from desired nozzles in the head R  61  and the respective heads V  51 - 54 . Depending on the viscosity of recycled-ink detected by the viscosity sensor  77 , a control signal is outputted from the control unit  100  to the diluting-fluid ejection head  80  via the drive circuit  118 . Consequently, a predetermined amount of diluting-fluid is ejected from the diluting-fluid ejection head  80 .  
         [0093]     When a control signal is outputted from the control unit  100  via the drive circuit  122 , the blade  120  is driven. Consequently, wiping of the nozzle surfaces of the recording heads is performed by the blade  120 .  
         [0094]     Additionally, the control unit  100  performs various processes based on a control signal inputted from an external device, such as the operation panel  29  or the PC  124  connected to the control unit  100  via a specific interface.  
         [0000]     [Effect] 
         [0095]     The following effect can be achieved with the inkjet recording apparatus  1  according to the third embodiment. The viscosity of recycled-ink can be adjusted by adding diluting-fluid from the diluting-fluid ejection head  80 , if the viscosity of recycled-ink detected by the viscosity sensor  77  is equal to or higher than a predetermined value. As a result, deterioration of the image quality, which can be caused by a significant increase in the viscosity of recycled-ink, can be inhibited. In other words, since the viscosity of recycled-ink can be adjustable, recycled-ink discharged from the head R  61  during a maintenance operation can be reused repeatedly without the viscosity of the recycled-ink being increased. Therefore, ink can be saved more effectively.  
         [0096]     Additionally, since the stirring ball  81  is moved within the sub-tank  61   b  of the head R  61  corresponding to the reciprocate movement of the carriage for image recording, recycled-ink, which is stored in the sub-tank  61   b  and in which diluting-fluid is added, is stirred. Therefore, the viscosity of the recycled-ink can be uniform.  
       Fourth Embodiment  
       [0097]     In  FIG. 11 , which schematically shows the substantial structure of an inkjet recording apparatus  1  according to a fourth embodiment, the same reference numbers are given to the same components as in the first embodiment shown in  FIG. 2 , in the second embodiment shown in  FIG. 6 , or in the third embodiment shown in  FIG. 8 .  
         [0098]     As shown in  FIG. 11 , the inkjet recording apparatus  1  according to the fourth embodiment includes ink cartridges  31 ,  32 ,  33 , and  34 , and a recycled-ink tank  41 . Each of the ink cartridges  31 - 34  stores one of the unused-inks K, C, M, and Y, in the aforementioned ink reservoir unit. The recycled-ink tank  41  stores ink RK. The inkjet recording apparatus  1  is furthermore provided with heads V  51 ,  52 ,  53 , and  54 , and a head R  61 , on a carriage in the aforementioned recording unit. Each of the heads V  51 - 54  are used for one of the inks K, C, M, and Y. The head R  61  is used for ink RK. The inkjet recording apparatus  1  is still furthermore provided with a cap  71   d , a first pump  72   c , a second pump  72   d , a filter  73 , a collected-ink path  75 , and a waste-ink foam  76 , in the aforementioned maintenance unit. Additionally, the inkjet recording apparatus  1  is provided with ink supply tubes  74 , an ink remaining amount detection sensor  82 , and an ink level detection sensor  83 . The ink remaining amount detection sensor  82  detects the remaining amount of each ink stored respectively in ink cartridges  31 - 34  and the recycled-ink tank  41 . The ink level detection sensor  83  detects whether or not ink remains in each one of the sub-tanks incorporated in respective recording heads  51 - 54  and  61 . It is to be noted that all of the unused-inks K, C, M, and Y, are dye ink.  
         [0099]     The ink remaining amount detection sensor  82  is constituted with a known optical sensor or the like. The ink level detection sensor  83  optically detects the levels of ink in each sub-tank incorporated in each recording head and detects whether or not ink remains in each sub-tank.  
         [0100]     The cap  71   d  is configured so as to receive ink discharged from the heads V  51 - 54  together in bulk, and to receive ink discharged from the head R  61  separately from the others.  
         [0101]     As shown in  FIG. 12 , the inkjet recording apparatus  1  includes a control unit  100 , a carriage  112 , a blade  120 , and drive circuits  114 ,  116 ,  118 ,  122 , and  126  in addition to the constituents shown in  FIG. 11 . The control unit  100  has a CPU  102 , a ROM  104 , and a RAM  106  which are conventionally known.  
         [0102]     The carriage  112  is reciprocated in the y-axis direction upon receipt of a control signal from the control unit  100  via the drive circuit  114 .  
         [0103]     A control signal is outputted from the control unit  100  to the first pump  72   c  via the drive circuit  116  corresponding to information detected by the ink remaining amount detection sensor  82  and information detected by the ink level detection sensor  83 . The first pump  72   c  is driven upon receipt of the control signal. Moreover, a control signal is outputted from the control unit  100  to the second pump  72   d  via the drive circuit  126  corresponding to information detected by the ink remaining amount detection sensor  82  and information detected by the ink level detection sensor  83 . The second pump  72   d  is driven upon receipt of the control signal. As a result, the above-described collection of ink, discharged from the recording head, can be performed in the present embodiment in a similar manner to the other embodiments.  
         [0104]     A control signal is outputted from the control unit  100  to the head R  61  and the respective heads V  51 - 54  corresponding to information detected by the ink remaining amount detection sensor  82  and information detected by the ink level detection sensor  83 . Ink is ejected from desired nozzles in the head R  61  and the respective heads V  51 - 54  in response to the control signal.  
         [0105]     When a control signal is outputted from the control unit  100  via the drive circuit  122 , the blade  120  is driven. Consequently, wiping of the nozzle surfaces of the recording heads is performed by the blade  120 .  
         [0106]     Additionally, the control unit  100  performs various processes based on a control signal inputted from an external device, such as the operation panel  29  or the PC  124  connected to the control unit  100  via a specific interface.  
         [0107]     It is to be noted that the sequence of collection, reuse and disposal of ink is performed the same as in the other embodiments described above, and that the description thereof is not repeated here.  
         [0108]     In the inkjet recording apparatus  1  according to the present embodiment, an excessive ink disposal process, a recording mode selection process, a process for a recycled-ink priority recording mode, and a process for an unused-ink priority recording mode can be performed. These processes can be performed in accordance with a determination made by the control unit  100  using the ink remaining amount detection sensor  82  and the ink level detection sensor  83 , and a control signal outputted from the control unit  100  based on the determination. Each process will be explained below with reference to the flowcharts shown in  FIGS. 13-16 .  
         [0000]     [Excessive Ink Disposal Process] 
         [0109]     Referring to  FIG. 13 , the excessive ink disposal process is performed based on control by a control unit (not shown) of the inkjet recording apparatus  1 . In this process, excessive recycled-ink is discarded when the amount of collected recycled-ink becomes more than the consumption amount, in order to inhibit the recycled-ink tank  41  from being full, which may end up with an overflow of recycled-ink.  
         [0110]     In Step  10  (to be simply denoted as S 10 , other steps will also be denoted in the same manner), corresponding to an initiation of a maintenance operation in the heads V  51 - 54 , ink suction is initiated by the first pump  72   c . In S 20  it is determined whether or not the recycled-ink tank  41  is full according to information regarding the ink remaining amount in the recycled-ink tank  41 , detected by the ink remaining amount detection sensor  82 . If it is determined that the recycled-ink tank  41  is not full (S 20 :N), the process proceeds to S 30 . In S 30  it is determined whether or not the ink suction amount by the first pump  72   c  has reached a predetermined amount. The predetermined amount mentioned here corresponds to the amount of ink to be discharged from the recording heads  51 - 54  as a result of a maintenance operation.  
         [0111]     The determination whether or not the amount of ink drawn by the first pump  72   c  has reached the predetermined amount may be made based on specific information described below. That is, for example, this determination may be made based on at least one of information detected by the ink remaining amount detection sensor  82  regarding a change in the ink remaining amount in the ink cartridges  31 - 34 , and information detected by the ink level detection sensor  83  regarding a change in the positions of surfaces of ink reserved in the sub-tanks in the heads V  51 - 54 . This determination may alternatively be made based on a result of a determination made by the control unit  100  regarding whether or not the driving duration time of the first pump  72   c  has reached a predetermined length.  
         [0112]     If it is determined that the ink suction amount by the first pump  72   c  has not reached the predetermined amount (S 30 :N), drawing of ink by the first pump  72   c  is continued. If it is determined that the ink drawing amount by the first pump  72   c  has reached the predetermined amount (S 30 :Y), that is, when the collection of ink discharged from the recording heads in a maintenance operation is completed, in S 40  the maintenance operation is completed as the first pump  72   c  is stopped. Then, the excess ink disposal process is finished. Ink collected by the first pump  72   c  flows in the collected-ink path  75 , passes through the filter  73 , and is stored in the recycled-ink tank  41 .  
         [0113]     On the other hand, in S 20  if it is determined that the recycled-ink tank  41  is full (S 20 :Y), ink suction by the second pump  72   d  is initiated in S 50 . As a result of ink suction by the second pump  72   d , ink is forcibly discharged from the head R  61  so as to collect excessive ink in the recycled-ink tank  41 . Subsequently, in S 60  it is determined whether or not the ink suction amounts by the first and the second pumps  72   c  and  72   d  respectively have both reached predetermined amounts. It is to be noted that the predetermined suction amount by the first pump  72   c  corresponds to the amount of ink to be discharged from the recording heads  51 - 54  due to a maintenance operation, and the predetermined suction amount by the second pump  72   d  corresponds to, or more than, the amount of ink to be discharged from the recording heads  51 - 54  due to a maintenance operation.  
         [0114]     The determination whether or not the amount of ink drawn by the first pump  72   c  has reached the predetermined amount may be made based on the specific information described above with regard to S 30 .  
         [0115]     Additionally, the determination whether or not the amount of ink drawn by the second pump  72   d  has reached the predetermined amount may be made based on specific information described below. That is, for example, this determination may be made based on at least one of information detected, by the ink remaining amount detection sensor  82  regarding a change in the ink remaining amount in the recycled-ink tank  41 , and information detected by the ink level detection sensor  83  regarding a change in the position of the surface of the ink reserved in the sub-tank in the head R  61 . Alternatively, this determination may be made based on a result of a determination made by the control unit  100  regarding whether or not the driving duration time of the second pump  72   d  has reached a predetermined length.  
         [0116]     In S 60  if it is respectively determined that the ink suction amounts by the first and the second pumps  72   c  and  72   d  have not reached the predetermined amounts (S 60 :N), ink suction is continued. When it is determined that the ink suction amounts by the first and the second pumps  72   c  and  72   d  respectively have reached the predetermined amounts (S 60 :Y), that is, when the collection of ink discharged from the recording heads  51 - 54  and excessive ink in the recycled-ink tank  41  is completed, the process proceeds to S 70 . In S 70  the first and the second pumps  72   c  and  72   d  are stopped. As a result, the maintenance operation is completed, and the excessive ink disposal process is finished.  
         [0117]     Ink collected by the second pump  72   d  from the recycled-ink tank  41  is discarded into the waste-ink foam  76 . On the other hand, ink collected by the first pump  72   c  flows in the collected-ink path  75 , passes through the filter  73 , and is stored in the recycled-ink tank  41 .  
         [0118]     In the excessive ink disposal process, when the recycled-ink tank  41  is full, ink in the recycled-ink tank  41  is collected for the amount equivalent to the amount of ink to be collected in a maintenance operation or more. As a result, overflow of recycled-ink can be inhibited.  
         [0000]     [Recording Mode Selection Process] 
         [0119]     The purpose of this process, shown in the flowchart in  FIG. 14 , is to select one of the recycled-ink priority recording mode and the unused-ink priority recording mode for image recording wherein ink is ejected from the head R  61  or the respective heads V  51 - 54 .  
         [0120]     In the recycled-ink priority recording mode, recycled-ink is used in preference to unused-ink. This recording mode is to perform image recording wherein ink saving is emphasized more than image quality. In the unused-ink priority recording mode, unused-ink is used in preference to recycled-ink. This recording mode is to perform image recording wherein image quality is emphasized more than ink saving.  
         [0121]     As shown in  FIG. 14 , in S 1  it is determined whether or not selection information to select the recycled-ink priority recording mode or to select the unused-ink priority recording mode is inputted into the control unit  100  by a user with an external device, such as key switches in the operation panel  29 , disposed on the top surface of the inkjet recording apparatus  1 , or the PC  124 .  
         [0122]     If it is determined that the selection information is inputted (S 1 :Y), in S 2  it is determined whether the inputted selection information is to select the recycled-ink priority recording mode or to select the unused-ink priority recording mode.  
         [0123]     In S 2  if it is determined that the inputted selection information is to select the recycled-ink priority recording mode, the process for recycled-ink priority recording mode (S 100 -S 170 ) shown in  FIG. 15  is performed (S 3 ).  
         [0124]     In S 2  if it is determined that the inputted information is to select the unused-ink priority recording mode, the process for unused-ink priority recording mode (S 200 -S 270 ) shown in  FIG. 16  is performed (S 4 ).  
         [0125]     On the other hand, in S 1  if it is determined that the selection information is not inputted (S 1 :N), the process proceeds to S 5 . In S 5  it is determined whether or not a command is received from an external device, such as the PC  124 , so as to operate the inkjet recording apparatus  1  as a printer for initiating text-image recording, or so as to operate the inkjet recording apparatus  1  as a facsimile for initiating image recording. If an affirmative determination is made (S 5 :Y), the process for the recycled-ink priority recording mode (S 100 -S 170 ) shown in  FIG. 15  is performed (S 6 ). If a denial determination is made (S 5 :N), the process proceeds to S 7 .  
         [0126]     In S 7  it is determined whether or not a command is received from the external device, such as the PC  124 , so as to operate the inkjet recording apparatus  1  as a printer for initiating photo-image recording. If an affirmative determination is made (S 7 :Y), the process for unused-ink priority recording mode (S 200 -S 270 ) shown in  FIG. 16  is performed (S 8 ). If a denial determination is made (S 7 :N), the process goes back to S 1 .  
         [0000]     [Process for Recycled-Ink Priority Recording Mode] 
         [0127]     As shown in  FIG. 10 , in S 100 , it is determined whether or not a command to initiate image recording is received by, for example, receiving image data. If it is determined that a command to initiate image recording is not determined to have been received (S 100 :N), this step is repeated.  
         [0128]     When it is determined that a command to initiate image recording is received (S 100 :Y), the process proceeds to S 110 . In S 110  it is determined whether or not recycled-ink (RK) remains, based on information regarding the ink remaining amount in the recycled-ink tank  41 , detected by the ink remaining amount detection sensor  82 , and information regarding the ink level in the sub-tank in the head R  61 , detected by the ink level detection sensor  83 . When it is determined that recycled-ink (RK) remains (S 110 :Y), in S 120  image recording is initiated with the head R  61  wherein recycled-ink (RK) is used.  
         [0129]     If it is determined that recycled-ink (RK) does not remain (S 110 :N), the process proceeds to S 130 . In S 130  it is determined whether or not unused-ink (K) remains, based on information regarding the ink remaining amount in the ink cartridge  31 , detected by the ink remaining amount detection sensor  82 , and information regarding the ink level in the sub-tank in the head V  51 , detected by the ink level detection sensor  83 . When it is determined that unused-ink (K) exists (S 130 :Y), in S 140  image recording is initiated with the head V  51  wherein unused-ink K is used.  
         [0130]     If it is determined that unused-ink (K) does not remain (S 130 :N), the process proceeds to S 150 . In S 150  it is determined whether or not the ink cartridge  31  has been replaced and the ink has been replenished.  
         [0131]     The determination in S 150  may be made based on specific information described below. That is, for example, this determination may be made based on at least one of information detected by the ink remaining amount detection sensor  82  regarding a change in the ink remaining amount inside of the ink cartridge  31 , and information detected by the ink level detection sensor  83  regarding a change in the position of the surface of the ink reserved in the sub-tank inside of the head V  51 .  
         [0132]     When it is determined that the ink cartridge  31  has been replaced and the ink has been replenished (S 150 :Y), in S 160  ink is drawn by the first pump  72   c  respectively from the heads V  51 - 54 . The ink drawn by the first pump  72   c  is supplied to the recycled-ink tank  41 .  
         [0133]     Subsequently, in S 170  it is determined whether or not the recycled-ink tank  41  has become full. When it is determined that the recycled-ink tank  41  has not become full (S 170 :N), ink suction is continued. When it is determined that the recycled-ink tank  41  has become full (S 170 :Y), the process goes back to S 110 .  
         [0134]     On the other hand, if it is determined that the ink cartridge  31  has not been replaced and the ink has not been replenished (S 150 :N), the process is finished.  
         [0135]     In the recycled-ink priority recording mode, image recording is performed with recycled-ink RK when there is stored recycled-ink RK. If there isn&#39;t any recycled-ink RK, image recording is performed with unused-ink K. Recycled-ink RK is used on a priority basis. Therefore, image recording can be performed wherein ink saving is emphasized.  
         [0136]     In the above explanation of the process for the recycled-ink priority recording mode, the inkjet recording apparatus  1  is provided with only one recording head R for ink RK as a recording head for recycled-ink. However, it is possible to apply this process to a case, such as shown in  FIG. 5 , wherein the inkjet recording apparatus  1  is respectively provided with heads R for the recycled-ink of inks K, C, M, and Y.  
         [0000]     [Process for Unused-Ink Priority Recording Mode] 
         [0137]     As shown in  FIG. 11 , in S 200 , it is determined whether or not a command to initiate image recording is received by, for example, receiving image data. If it is determined that a command to initiate image recording has not been received (S 200 :N), this step is repeated.  
         [0138]     When it is determined that a command to initiate image recording has been received (S 200 :Y), the process proceeds to S 210 . In S 210  it is determined whether or not unused-ink (K) remains based on information regarding the ink remaining amount in the ink cartridge  31 , detected by the ink remaining amount detection sensor  82 , and information regarding the ink level in the sub-tank in the head V  51 , detected by the ink level detection sensor  83 . When it is determined that unused-ink (K) remains (S 210 :Y), in S 220  image recording with the head V  51  is initiated wherein unused-ink (K) is used.  
         [0139]     If it is determined that unused-ink (K) does not remain (S 210 :N), the process proceeds to S 230 . In S 230  it is determined whether or not recycled-ink (RK) remains based on information regarding the ink remaining amount in the recycled-ink tank  41 , detected by the ink remaining amount detection sensor  82 , and information regarding the ink level in the sub-tank in the head R  61 , detected by the ink level detection sensor  83 . When it is determined that recycled-ink (RK) remains (S 230 :Y), in S 240  image recording is initiated with the head R  61  wherein recycled-ink RK is used.  
         [0140]     If it is determined that recycled-ink (RK) does not remain (S 230 :N), the process proceeds to S 250 . In S 250  it is determined whether or not the ink cartridge  31  has been replaced and the ink K has been replenished.  
         [0141]     The determination in S 250  may be made based on specific information described below. That is, for example, this determination may be made based on at least one of information detected by the ink remaining amount detection sensor  82  regarding a change in the ink remaining amount inside of the ink cartridge  31 , and information detected by the ink level detection sensor  83  regarding a change in the position of the surface of the ink reserved in the sub-tank inside of the head V  51 .  
         [0142]     When it is determined that the ink cartridge  31  has been replaced and the ink K has been replenished (S 250 :Y), in  260  the ink is drawn by the first pump  72   c  from the respective heads V  51 - 54 . The ink drawn by the first pump  72   c  is supplied to the recycled-ink tank  41 .  
         [0143]     Subsequently, in S 270  it is determined whether or not the recycled-ink tank  41  has become full. When it is determined that the recycled-ink tank  41  has not become full (S 270 :N), ink suction is continued. When it is determined that the recycled-ink tank  41  has become full (S 270 :Y), the process goes back to S 210 .  
         [0144]     In S 250 , if it is determined that the ink cartridge  31  has not been replaced and the ink K has not been replenished (S 250 :N), the process is finished.  
         [0145]     In the unused-ink priority recording mode, image recording is performed with unused-ink K when there is stored unused-ink K. If there isn&#39;t any unused-ink K, image recording is performed with recycled-ink RK. Unused-ink K is used on a priority basis. Therefore, image recording can be performed wherein the image quality is emphasized.  
         [0146]     In the above explanation of the process for unused-ink priority recording mode, the inkjet recording apparatus  1  is provided with only one recording head R for ink RK as a recording head for recycled-ink. However, it is possible to apply this process to a ease, such as shown in  FIG. 5 , wherein the inkjet recording apparatus  1  is respectively provided with heads R for the recycled-ink of ink K, C, M, and Y.  
         [0000]     [Effect] 
         [0147]     The following effect can be achieved with the inkjet recording apparatus  1  according to the fourth embodiment. Excessive ink is timely discarded by the performance of the excessive ink disposal process. Therefore, recycled-ink does not overflow even when the amount of ink discharged and collected as a result of a maintenance operation is larger than the amount of recycled-ink consumed.  
         [0148]     Moreover, the recycled-ink priority recording mode and the unused-ink priority recording mode can be suitably and flexibly selected depending on a situation. When, for instance, photo-image recording is performed, the unused-ink priority recording mode can be selected. When an other type of image recording is performed, such as text-image recording, the recycled-ink priority recording mode can be selected. Even when an ink, which is used in preference to other ink, runs out, the other ink can be conveniently used to perform image recording.  
         [0149]     Furthermore, a user can select either of the recycled-ink priority recording mode and the unused ink priority recording mode by operating key-switches in the operation panel  29  (see  FIG. 1 ). Image recording can be performed wherein various needs can be met when, for example, a user wishes high image quality or wishes to save as much ink as possible.  
         [0150]     Additionally, for recording an image such as a facsimile-image or a text-image containing only text data, which can be sufficiently discriminable without a high image quality, as much as for a photo-image, the recycled-ink priority recording mode is automatically selected. Therefore, ink can preferably be saved.  
       Fifth Embodiment  
       [0151]     In  FIG. 17 , which schematically shows the substantial structure of an inkjet recording apparatus  1  according to a fifth embodiment, the same reference numbers are given to the same components as in the first embodiment shown in  FIG. 2 , the second embodiment shown in  FIG. 6 , the third embodiment shown in  FIG. 8 , and the fourth embodiment shown in  FIG. 11 .  
         [0152]     The inkjet recording apparatus  1  according to the present embodiment is an inkjet recording apparatus wherein dye ink and pigment ink are both used for image recording.  
         [0153]     Specifically, as shown in  FIG. 12 , the inkjet recording apparatus  1  includes ink cartridges  31 ,  32 ,  33 , and  34 , and recycled-ink tanks  41 ,  42 ,  43  and  44 . The ink cartridge  31  stores unused pigment ink K in the aforementioned ink reservoir unit. Each of the ink cartridges  32 - 34  stores one of unused dye inks C, M, and Y. Each of the recycled-ink tanks  41 - 44  stores one of the recycled-inks RK, RC, RM, and RY. The inkjet recording apparatus  1  is furthermore provided with recording heads V  51 ,  52 ,  53 , and  54  respectively for ink K, C, M, and Y, and recording heads R  61 ,  62 ,  63 , and  64  respectively for ink RK, RC, RM, and RY, on a carriage in the aforementioned recording unit. The inkjet recording apparatus  1  is still furthermore provided with a cap  71   e , pumps  72   a , a pump  72   b , a filter  73 , collected-ink paths  75 , and a waste-ink foam  76 , in the aforementioned maintenance unit. Additionally, the inkjet recording apparatus  1  is provided with ink supply tubes  74 .  
         [0154]     The cap  71   e  is configured so as to separately receive ink discharged from the respective heads V  52 - 54  for ink C, M, and Y, and to receive both of ink discharged from the head V  51  for ink K and the head R  61  for ink RK together. The cap  71   e  is also configured so as to receive ink discharged from the respective heads R  62 - 64  for recycled-ink RC, RM, and RY together in bulk.  
         [0155]     Ink C, M, and Y, and, ink K and RK are respectively discharged into the cap  71   e  from corresponding heads V  51 - 54  and head R  61  during a maintenance operation, and collected separately by the pumps  72   a . Collected ink flows in respective collected-ink paths  75 , passes through the filter  73 , and is stored in the respective recycled-ink tanks  41 - 44 .  
         [0156]     On the other hand, ink RC, RM, and RY, discharged into the cap  71   e  from respective heads R  62 - 64  during a maintenance operation, is collected together in bulk by the pump  72   b . The collected ink is discarded into the waste-ink foam  76  and absorbed therein.  
         [0157]     In the inkjet recording apparatus  1  according to the present embodiment, dye ink and pigment ink can be reused independently from each other without being mixed together.  
         [0158]     It is to be noted that the inkjet recording apparatus  1  of the present embodiment has the same electric structure as the electric structure shown in  FIG. 7 .  
         [0159]     Although some embodiments of the present invention are described above, the present invention is not limited to these embodiments. Variations and modifications are possible within the scope of the invention. Specific examples will be given below.  
         [0160]     (1) Recycled-ink is different from unused-ink in various physical properties, such as density or surface tension, as the diluting-fluid contained in the ink volatilizes. In order to perform suitable image recording, the ejection of recycled-ink from the nozzles needs to be controlled differently from the ejection of unused-ink. For this purpose, the frequencies of energy application onto the ink so as to drop the ink from the nozzles (to be referred to as drive frequencies) in the heads R and the heads V may be changed. For example, the frequencies of energy application can be changed by making the control unit  100  control the drive circuit  118  which transmits a control signal to the heads R and the heads V (see  FIGS. 5, 7 ,  10 , and  12 ). Specifically, in the heads R, the drive frequency for the ejection of recycled-ink may be a little less than the drive frequency for the ejection of unused-ink in the heads V. The differences in the drive frequencies may be obtained from an experiment or calculation in consideration of the expected density or viscosity of recycled-ink. The drive frequencies are preferably set in consideration of characteristics of various drive methods, such as a drive method wherein energy to drop ink is applied in the form of heat, or a drive method wherein the energy is applied in the form of pressure by piezoelectric elements.  
         [0161]     (2) In regard to the wiping operation performed in the maintenance unit, the movement of a blade, which wipes the nozzle surfaces of recording heads, may be controlled in a manner so that the wiping of the nozzle surfaces of the heads V is performed prior to the wiping of the nozzle surfaces of the heads R. For example, this kind of wiping becomes possible by making the control unit  100  control the drive circuit  122  which transmits a control signal to the blade  120  (see FIGS.  2 ,  5 - 8 ,  10 - 12 , and  17 ). Specifically, for the disposition of recording heads as shown in  FIG. 2 , the blade  120  may be controlled to wipe the nozzle surfaces in the order of Y, M, C, K, and then RK.  
         [0162]     With this wiping order, it is possible to inhibit the blade from carrying contaminants from the nozzle surfaces of the heads R to the nozzle surfaces of the heads V.  
         [0163]     (3) An ink remaining amount indicator may be provided for both unused-ink and recycled-ink. In this case, a user can check not only the remaining amount of unused-ink, but also the remaining amount of recycled-ink. If a user can check that recycled-ink still remains, even when unused-ink runs out, the user does not need to replenish unused-ink in haste. This is convenient for a user. Specifically, a check window  130 , which enables a visual check of whether or not ink remains, can be provided on each ink cartridge and recycled-ink tank (see  FIGS. 2, 6 ,  8 ,  11 , and  17 ). Alternatively, the remaining amount of each ink can be displayed on the LCD of the operation panel  29  (see  FIG. 1 ) based on information regarding the ink remaining amount detected by the ink remaining amount detection sensor  82  and the ink level detection sensor  83 , shown in  FIG. 12 .  
         [0164]     (4) For test recording, which is performed in order to check the ink ejection state of each recording head, the inkjet recording apparatus  1  may be constituted in a manner so that ink is ejected not only from the heads V but also from the heads R. For example, this kind of test recording can be performed by making the control unit  100  control the drive circuit  118  which transmits a control signal to the heads R and the heads V (see  FIGS. 5, 7 ,  10 , and  12 ). This structure enables a user not only to check the ink ejection state of the heads R, but also to check the coloration of the recycled-ink. Recycled-ink can be checked for whether or not the ink has a suitable quality for use.