Abstract:
A droplet ejection apparatus includes a plurality of tanks, a plurality of sub-tanks, a replenishment amount detector, a liquid replenisher and a recording head. Each of the plurality of tanks is capable of storing a different kind of basic liquid. The plurality of sub-tanks includes a first sub-tank that includes a mixed liquid of two or more of the different kinds of the basic liquids from the plurality of tanks. The replenishment amount detector detects amount of each of the different kinds of the basic liquids to be transferred to the first sub-tank. The liquid replenisher transfers the basic liquids stored in the tanks into the sub-tanks until a predetermined amount for each of the basic liquids is detected by the replenishment amount detector. The recording head ejects the liquids supplied from the sub-tanks in a form of droplets.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of Japanese Patent Application No. 2005-313278 filed Oct. 27, 2005, the disclosure of which is incorporated herein by reference. This is a Continuation-in-Part of application Ser. No. 11/385,930 filed Mar. 22, 2006 and Ser. No. 11/386,095 filed Mar. 22, 2006, the disclosure of which are incorporated herein by reference. 
     
    
     BACKGROUND  
       [0002]     This invention relates to a droplet ejection apparatus that ejects liquid supplied from sub-tanks as droplets. Particularly, this invention is effective when it is applied to an inkjet recording apparatus (inkjet printer).  
         [0003]     A known inkjet recording apparatus includes an ejection head that ejects ink as a droplet and an ink tank that supplies ink to the ejection head. The prior inkjet recording apparatus could produce ink with various hues to match user&#39;s taste since a user himself mixes the plurality colors of ink in an ink mixing container, which is provided to the user separately from the inkjet recording apparatus, and the user himself replenishes and supplies mixed ink to the ink tank.  
         [0004]     However, there is a high possibility that the hue of mixed ink is different from that of previous mixed ink every time ink is replenished, since the user himself mixes the plurality colors of ink in the ink mixing container, which is provided to the user separately from the inkjet recording apparatus, and the user himself replenishes and supplies mixed ink to the ink tank.  
         [0005]     In other words, the hue of mixed ink is determined by the original mixing ratio of the plurality colors of basic ink. Therefore, it is necessary to constantly produce mixed ink with a uniform mixed ratio so as to produce the mixed color with a uniform hue.  
         [0006]     However, it is difficult to replicate the amount of ink being injected to the ink mixing container each time a user mixes ink, since the user pours the plurality colors of basic ink in the ink mixing container and mixes them together. Thus, it results in difficulty of producing mixed ink with the uniform mixed ratio all the time.  
         [0007]     Consequently, the prior art has a problem that it is very difficult to replicate the hue since the hue of mixed ink differs every time mixed ink is replenished.  
       SUMMARY  
       [0008]     In consideration of the above and other problems, one purpose of the present invention is to enable the mixing ratio to be easily replicated in the apparatus which includes a droplet ejection apparatus such as an inkjet recording apparatus.  
         [0009]     In one aspect of the present invention, there is provided a droplet ejection apparatus which includes a plurality of tanks, a plurality of sub-tanks, a replenishment amount detector, a liquid replenisher and a recording head. Each of the plurality of tanks is capable of storing a different kind of basic liquid. The plurality of sub-tanks includes a first sub-tank that includes a mixed liquid of two or more of the different kinds of the basic liquids from the plurality of tanks. The replenishment amount detector detects amount of each of the different kinds of the basic liquids to be transferred to the first sub-tank. The liquid replenisher transfers the basic liquids stored in the tanks into the sub-tanks until a predetermined amount for each of the basic liquids is detected by the replenishment amount detector. The recording head ejects the liquids supplied from the sub-tanks in a form of droplets.  
         [0010]     Due to this configuration, in the present invention, plurality kinds of basic liquid is replenished to the first sub-tanks while the replenishment amount of each plurality kinds of basic liquid to be replenished is automatically detected. Consequently, it enables the accurate mixing ratio of the mixed liquid in the first sub-tanks to be stabilized. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The invention will now be described below, by way of example, with reference to the accompanying drawings, in which:  
         [0012]      FIG. 1  is an external view of a multifunction apparatus according to an embodiment of the present invention;  
         [0013]      FIG. 2  is a diagram showing a structure of an inkjet recording apparatus according to an embodiment of the present invention;  
         [0014]      FIG. 3  is a diagram showing a structure of an image recording unit of the inkjet recording apparatus according to an embodiment of the present invention;  
         [0015]      FIG. 4  is a diagram showing the bottom surface of a recording head according to an embodiment of the present invention;  
         [0016]      FIG. 5  is a sectional diagram showing the recording head and a sub-tank according to an embodiment of the present invention;  
         [0017]      FIG. 6  is a sectional diagram showing the recording head and the sub-tank according to an embodiment of the present invention;  
         [0018]      FIG. 7  is a sectional diagram showing the recording head and the sub-tank according to an embodiment of the present invention;  
         [0019]      FIG. 8A and 8B  are sectional diagrams showing a connecting portion of an ink tank according to an embodiment of the present invention;  
         [0020]      FIG. 9  is a diagram showing an electrical structure of the inkjet recording apparatus according to an embodiment of the present invention;  
         [0021]      FIG. 10  is a diagram showing an ink replenishment state in the inkjet recording apparatus according to an embodiment of the present invention;  
         [0022]      FIG. 11  is a flowchart illustrating the ink replenishment operation of the inkjet recording apparatus according to an embodiment of the present invention;  
         [0023]      FIG. 12  is a flowchart illustrating an ink replenishment operation of the inkjet recording apparatus according to the embodiment;  
         [0024]      FIG. 13  is a flowchart illustrating the ink replenishment operation of the inkjet recording apparatus according to an embodiment of the present invention;  
         [0025]      FIG. 14  is a diagram showing the ink replenishment operation of the inkjet recording apparatus according to an embodiment of the present invention;  
         [0026]      FIGS. 15A and 15B  are diagrams showing the ink replenishment operation of the inkjet recording apparatus according to an embodiment of the present invention;  FIGS. 16A and 16B  are diagrams showing the ink replenishment operation of the inkjet recording apparatus according to an embodiment of the present invention;  
         [0027]      FIGS. 17A and 17B  are diagrams showing the ink replenishment operation of the inkjet recording apparatus according to an embodiment of the present invention;  
         [0028]      FIGS. 18A, 18B  and  18 C are diagrams showing the ink replenishment operation of the inkjet recording apparatus according to an embodiment of the present invention; and,  
         [0029]      FIG. 19  is a diagram showing a structure of an ink tank according to a variation of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0030]     According to embodiments of the present invention, an inkjet recording apparatus using a droplet ejection apparatus is applied to a multifunction apparatus, which may include a printer function, a scanner function, a copy function, and a facsimile function.  
         [0031]     [First Embodiment] 
         [0000]     1. Overall Structure of Multi Function Apparatus  10   
         [0032]     Referring to  FIG. 1 , a multifunction apparatus  10  is provided with an inkjet printer unit  11  in the lower portion thereof, and a scanner unit  12  in the upper portion.  
         [0033]     The printer unit  11  is provided with an opening  13 , a paper feed tray  14 , and a paper discharge tray  15 . The opening  13  is disposed in the front surface of the printer unit  11 . The paper feed tray  14  and the paper discharge tray  15  are disposed on top of another so as to be exposed from the opening  13 . The paper feed tray  14  stores recording paper. Recording paper stored in the paper feed tray  14  is fed to the inside of the printer unit  11 . A predetermined image is recorded on the recording paper. Then, the recording paper is discharged onto the paper discharge tray  15 .  
         [0034]     The paper feed tray  14  is provided with a slide tray  16 . The slide tray  16  is slid out, if necessary, so as to enlarge the tray surface. The scanner unit  12  is composed as a so-called flat-bed scanner, and provided with a platen glass (not shown) and an image reading device (not shown) under a cover  17  which covers, from upside, an original to be read. The image reading device includes a CIS (Contact Image Sensor) and a CCD (Charge-Coupled Device).  
         [0035]     The platen glass is used so as to place an original thereon. The image reading device is disposed under the platen glass so as to be able to scan the entire surface of a placed original. The multifunction apparatus  10  is furthermore provided with an operation panel  18 , which is used so as to operate the printer unit  11  or the scanner unit  12 . The operation panel  18  is provided with various operation buttons and a liquid crystal display unit. The multifunction apparatus  10  is operated according to an operation instruction from the operation panel  18  or an instruction sent from a computer via a printer driver.  
         [0000]     2. Structure of Printer Unit  11  (Inkjet Recording Apparatus)  
         [0000]     2.1 Overall Structure  
         [0036]     Referring now to  FIG. 2 , on the bottom of the multifunction apparatus  10  (printer unit  11 ), the paper feed tray  14  is disposed wherein a number of sheets of recording paper is placed. In the back side of the paper feed tray  14  (on the right side in the drawing), an inclined separation board  21  is provided so as to separate sheets of recording paper placed on the paper feed tray  14  and guide the recording paper toward the upside.  
         [0037]     A conveyance path  22  of recording paper is formed upward from the inclined separation board  21 . The conveyance path  22  is firstly extended upward, curved toward the left side in the drawing, furthermore extended from the back side of the multifunction apparatus  10  toward the front side thereof, and reaches the paper discharge tray  15  via an image recording unit  23 .  
         [0038]     As a result, recording paper stored in the paper feed tray  14  is guided to the image recording unit  23  through the conveyance path  22  so as to make a U-turn from the lower side to the upper side. After an image is recorded on the recording paper by the image recording unit  23 , the recording paper is discharged onto the paper discharge tray  15 .  
         [0039]     A paper feed roller  25  is provided so as to separate recording paper stacked on the paper feed tray  14  in a sheet-by-sheet manner and supply the recording paper a sheet by sheet to the conveyance path  22 . The structure of the paper feed roller  25  is the same as that of a known paper feed roller. That is to say, the paper feed roller  25  is, for example, supported on a leading end of a paper feed arm  26 , which moves upward and downward, so that the paper feed roller  25  can be in contact with the paper feed tray  14  and separated therefrom. The paper feed roller  25  is connected to a motor via a drive transmission mechanism. The paper feed arm  26  is disposed so as to be rotatable around an axis  27  of the trailing end. The paper feed arm  26  is flipped upward by a paper feed clutch, a spring, or the like (not shown) when the printer unit  11  is in a standby state, and swung down when recording paper is fed. 2.2 Image Recording Unit  23   
         [0040]     Referring now to  FIG. 3 , the image recording unit  23  is provided with a head unit  28 , a platen  41 , a recording head  43 , sub-tanks  29 - 36 , cartridge-type ink tanks  37 - 40 , and so forth. The platen  41  is disposed so as to face the head unit  28 . The recording head  43  ejects (discharges) ink. The sub-tanks  29 - 36  store ink to be supplied into the recording head  43 . The ink tanks  37 - 40  store ink to be supplied into the sub-tanks  29 - 36 . Although the ink tanks  37 - 40  are shown larger than the sub-tanks  29 - 36  in  FIG. 3  so as to facilitate understanding, the ink tanks  37 - 40  and the sub-tanks  29 - 36  can be approximately the same size in order to facilitate ink supply.  
         [0041]     The image recording unit  23  records an image on recording paper  47 , while the head unit  28  moves in a main scanning direction, by ejecting various colors of inks, such as cyan (C), magenta (M), yellow (Y), black (Bk), and so forth from the head unit  28  onto the recording paper  47  intermittently conveyed on the platen  41 .  
         [0042]     The recording head  43  and the sub-tanks  29 - 36  are held by a scanning carriage  42 . The recording head  43  is disposed so as to be exposed on the bottom surface of the scanning carriage  42 . The sub-tanks  29 - 36  are disposed on the upper side of the recording head  43  of the scanning carriage  42 .  
         [0043]     A guide shaft  44 , extending in the main scanning direction, is included to guide and support the scanning carriage  42  so that the scanning carriage  42  can be moved thereon. An endless belt  45  is disposed in parallel to the guide shaft  44  so that the scanning carriage  42  (head unit  28 ) can be moved thereon. The endless belt  45  is driven by a belt drive motor  46  via a pulley.  
         [0044]     On the bottom surface of the recording head  43 , arrays of ejection nozzles  48  are aligned substantially in one line as shown in  FIG. 4 . The number of these arrays corresponds to the number of sub-tanks  29 - 36 .  
         [0045]     From the ink ejection nozzles  48  in the array disposed in the left end side in the drawing, black ink (to be referred to as ink Bk) is ejected. Hereinafter, in the order of the alignment of the ejection nozzles  48 , cyan ink (to be referred to as ink C), yellow ink (ink Y), magenta ink (ink M), blue ink (ink B), red ink (ink R), green ink (ink G), and Photo Black ink (ink Pb) are ejected from the ejection nozzles  48  in respective arrays.  
         [0046]     The recording head  43  according to the present embodiment is a piezo-type recording head which ejects ink by the use of piezoelectric element (piezo element). As shown in  FIG. 5  to  FIG. 7 , the recording head  43  receives ink supply from the sub-tanks  29 - 36  disposed on the top side of the recording head  43 , and ejects (discharges) ink toward recording paper.  
         [0047]     On the top surface of each of the sub-tanks  29 - 36 , an ink supply hole  50  is disposed for ink supplied from the ink tanks  37 - 40 . In the bottom portion of the ink supply hole  50 , a push rod  50   a  is provided for opening an on-off valve  58  (see  FIG. 8 ) disposed in each of the ink tanks  37 - 40 . On the root portion of the push rod  50   a , communication holes  50   b  are provided so that each supply hole  50  is communicated with one of the sub-tanks  29 - 36 .  
         [0000]     2.3 Ink Tanks  37 - 40   
         [0048]     The ink tanks  37 - 40  are replenishment tanks wherein ink is stored so as to be replenished into the sub-tanks  29 - 36 . Here, the number of the ink tanks  37 - 40  is less than the number of the sub-tanks  29 - 36  as shown in  FIG. 3 . In the ink tanks  37 - 40 , ink to become the basis for basic color (to be referred to as basic ink) is stored respectively.  
         [0049]     The basic ink, mentioned here, is in some colors which compose the basis of the colors of ink stored in respective sub-tanks  29 - 36 . Four colors of ink: ink Bk, ink C, ink Y, and ink M can be employed as the basic ink.  
         [0050]     The ink tanks  37 - 40  are held by a holder  65 . On the bottom portion of respective ink tanks  37 - 40 , a connecting portion  66  is provided so as to be connected to the above-described supply opening  50  of respective sub-tanks  29 - 36 .  
         [0051]     Inside of the connecting portion  66 , the on-off valve  58 , which opens and closes an ink replenishment opening  66   a  disposed within the connecting portion  66 , is provided as shown in  FIGS. 8A and 8B . The on-off valve  58  opens the ink replenishment opening  66   a  by being pressed by the push rod  50   a  when the connecting portion  66  is connected to the supply opening  50 . When the connecting portion  66  is removed from the supply opening  50 , the on-off valve  58  closes the ink replenishment opening  66   a  by the pressure of ink in respective ink tanks  37 - 40  and the resilient force of a spring, which is not shown in the drawing.  
         [0052]     The ink tanks  37 - 40  are respectively provided with a slide cylinder  67  and a pump  68  as shown in  FIG. 3 . The slide cylinders  67  provide driving force so as to individually lower the ink tanks  37 - 40  toward the sub-tanks  29 - 36 . The pumps  68  pressurize inside of the ink tanks  37 - 40 . Respective slide cylinders  67  and the pumps  68  can be fixed to the holder  65 .  
         [0053]     In  FIG. 3 , only one slide cylinder  67  and one pump  68  of the ink tank  40  are shown in order to simplify the drawing. Additionally, in  FIG. 3 , the slide cylinder  67  is disposed so as to provide the driving force of the slide cylinder  67  from the back side of the ink tanks  37 - 40 . However, the driving force of the slide cylinder  67  is provided to link mechanisms or the like, which are not shown in the drawing and respectively provided to each of the ink tanks  37 - 40 . The driving force is converted into driving force which lowers the ink tanks  37 - 40  toward the sub-tanks  29 - 36 , and then, provided to the ink tanks  37 - 40 . Although the connection between the pump  68  and the ink tank  40  is not shown in  FIG. 3  in order to simplify the drawing, pumps  68  are respectively connected to the ink tanks  37 - 40  via, for example, tubes (see  FIGS. 5, 6  and  7 ).  
         [0000]     2.4 Sub-tanks  
         [0054]     There are two kinds of sub-tanks in the sub-tanks  29 - 36 . One is a basic color sub-tank, wherein an identical color of basic ink only is supplementary supplied. The other is a mixed color sub-tank, wherein plural colors of basic ink are mixed and supplied. In this embodiment according to the present invention, the sub-tanks  29 - 32  correspond to the basic color sub-tank, and the sub-tanks  33 - 36  correspond to the mixed color sub-tank.  
         [0055]     Moreover, each sub-tanks  29 - 36 , as shown in  FIG. 5  to  FIG. 7 , has a first electrode  51  (in this configuration the electrode constitutes a pair) to detect whether or not ink stored in the sub-tanks  29 - 36  becomes the predetermined minimum amount, and a second electrode  52  (in this configuration the electrode is a pair of electrodes) to detect whether or not ink replenished in sub-tanks  29 - 36  becomes the predetermined maximum amount.  
         [0056]     More specifically, when the amount of ink (the level of ink liquid surface) in the sub-tanks  29 - 36  conforms with the position (height) where the first electrode  51  is disposed, a electronic resistance value between a pair of the first electrode  51  changes, and the ink surface level determination device  55  detects the change and transmits such signal to the central processing member  70 , which will be explained later.  
         [0057]     Similarly, when the amount of ink (the level of ink liquid surface) in the sub-tanks  29 - 36  conforms with the position (height) where the second electrode  52  is disposed, a electronic resistance value between a pair of the first electrode  52  changes, and the ink surface level determination device  55  detects the change and transmits such signal to the central processing member  70 .  
         [0058]     Moreover, as shown in  FIG. 6 , in addition to the first electrode  51  and the second electrode  52 , a third electrode  53  (in this configuration the electrode constitutes a pair) is disposed at the position (height) which internally divides a space between the first electrode  51  and the second electrode  52  by the mixing ratio of ink to be mixed.  
         [0059]     Furthermore, the first electrode  51 , the second electrode  52  and the third electrode  53  are arranged in the height-wise direction in the sub-tanks  33 - 36  containing the mixture of colors, and the position (height) is set so that the ratio of volume occupied by each spaces between the electrode  51  and the electrode  52  and the electrode  53  is equivalent to the ratio of ink to be mixed.  
         [0060]     More specifically, it is set so that the volume ratio of space A between the first electrode  51  and the second electrode  52  and space B between the second electrode  52  and the third electrode  58  is equivalent to the mixing ratio of basic ink to be replenished and supplied to the mixed color sub-tanks. Consequently, the volume of space A and B, that is, the position (height) of the third electrode  53 , differs by the mixing ratio of basic ink to be replenished and supplied in each sub-tanks  33 - 36 .  
         [0061]     Meanwhile, the tank shown in  FIG. 6  has only a third electrode  53  since it is the mixed color sub-tank  33 - 35  which mixes two colors of basic ink. A fourth electrode  54  (in this configuration the electrode is a pair of electrodes) is disposed on the mixed sub-tank  36 , as shown in  FIG. 7 , where three colors of basic ink are mixed.  
         [0062]     Moreover, the third electrode  53  and the fourth electrode  54  are set so that the distances between the first electrode  51  and the fourth electrode  54 , between the fourth electrode  54  and the third electrode  53 , and between the third electrode  53  and the second electrode  52  become the mixing ratio of three colors of basic ink.  
         [0000]     2.5 Conveyance Mechanism for Recording Paper  
         [0063]     As shown in  FIGS. 2 and 3 , in the upstream side of the image recording unit  23 , a driving roller  60  and a retaining roller  61  are provided. The driving roller  60  and the retaining roller  61  sandwich the recording paper  47  conveyed in the conveyance path  22 , and feed the recording paper  47  onto the platen  41 . The driving roller  60  is driven and rotated by a motor  64 .  
         [0064]     On the other hand, in the downstream side of the image recording unit  23 , a paper discharge roller  62  and a retaining roller  63  are disposed. The paper discharge roller  62  and the retaining roller  63  sandwich the recording paper  47  on which image recording is finished, and feed the recording paper  47 . The paper discharge roller  62  is driven and rotated by a motor (not shown) which is similar to the motor  64  for the driving roller  60 .  
         [0065]     The retaining roller  61  is resiliently pressed against the driving roller  60  so that the retaining roller  61  presses the driving roller  60  with predetermined pressing force. When the recording paper  47  enters between the driving roller  60  and the retaining roller  61 , the retaining roller  61  resiliently recedes by the thickness of the recording paper  47  and holds the recording paper  47  together with the driving roller  60 .  
         [0066]     Similarly, the retaining roller  63  is resiliently pressed against the paper discharge roller  62 . However, since the retaining roller  63  comes in contact with the recording paper  47  on which image recording is finished, the surface of the retaining roller  63  is formed spur-like, in order not to deteriorate the image recorded on the recording paper  47 .  
         [0067]     The recording paper  47 , held by the driving roller  60  and the retaining roller  61 , is intermittently fed in predetermined linefeed widths on the platen  41 . Correspondingly, the recording head  43  is moved (in this configuration it is moved in parallel) every time the recording paper  47  is fed for a new line, and performs image recording from the leading end side of the recording paper  47 . The recording paper  47 , wherein image recording is finished, is discharged onto the paper discharge tray  15 .  
         [0000]     3. Electrical Structure of Multifunction Apparatus  10   
         [0068]     Referring now to  FIG. 9 , a control device of the multifunction apparatus  10  according to one embodiment of the present invention is a micro computer having a central processing unit  70  with a CPU, a ROM, and a RAM. The central processing unit  70  is connected to various sensors, the printer unit  11 , the scanner unit  12 , the operation panel  18 , and so forth via a bus  71  and an ASIC (Application Specific Integrated Circuit)  72  so as to be able to transmit/receive data to/from these components.  
         [0069]     The ROM provided in the central processing unit  70 , stores predetermined computer programs. In accordance with the programs stored in the ROM and based on information from various sensors and signals from the liquid surface level determination device  55 , the CPU performs some control processes. Specifically, the CPU controls the rotation of the motor  64  (LF motor), which is the driving source of the driving roller  60 , and the rotation of the belt driving motor  46  (CR motor) so as to make the head portion  28  slide. The CPU also controls the extension and contraction of the slide cylinder  67  so as to move the ink tanks  37 - 40  toward the head portion  28 , and controls the pump  68  so as to supply the basic ink stored in the ink tanks  37 - 40  into the sub-tanks  29 - 36 .  
         [0070]     The multifunction apparatus  10  according to one embodiment of the present invention includes an interface (I/F) for transmitting/receiving data to/from a personal computer (PC)  73 . When the I/F is connected to the PC  73 , a graphic image or a text image can be recorded on the recording paper  47  based on graphic data or text data transmitted from the PC  73 .  
         [0000]     4. Operation of Printer Unit  11  (Inkjet Recording Apparatus)  
         [0071]     The printer unit  11  (inkjet recording apparatus) according to one embodiment of the present invention is different from a general inkjet recording apparatus in terms of the structure and the operation for replenishing and supplying ink from the ink tanks  37 - 40  into the sub-tanks  29 - 36 . The following describes the operation of the printer unit  11  (inkjet recording apparatus) focusing especially on the ink replenishment operation.  
         [0000]     4.1 Overall Operation of Ink Replenishment  
         [0072]     Firstly, the scanning carriage  42  is moved so that the sub-tanks  29 - 36 , which receive ink supply from the sub-tanks  37 - 40 , are positioned immediately below the ink tanks  37 - 40  which store specific colors to supply.  
         [0073]     Next, the slide cylinders  67  are extended so as to lower the ink tanks  37 - 40  toward the sub-tanks  29 - 36 . The connecting portions  66  of the ink tanks  37 - 40  are inserted into the supply openings  50  of the sub-tanks  29 - 36  and connected thereto.  
         [0074]     At this time, the on-off valves  58  pressed by the push rods  50   a  and open the ink replenishment openings  66   a  (see  FIG. 8B ). The pumps  68  are operated so as to supply ink inside of the ink tanks  37 - 40  into the sub-tanks  29 - 36 .  
         [0075]     In the mixed color sub-tanks  33 - 36 , mixed inks: ink B, ink R, ink G, and ink Pb are respectively stored. Ink B is produced with ink C and ink M mixed together. Ink R is produced with ink Y and ink M mixed together. Ink G is produced with ink Y and ink C mixed together. Ink Pb is produced with ink Y, ink M, and ink C mixed together.  
         [0000]     4.2 Ink Replenishment Operation Control  
         [0076]      FIG. 11  is a flowchart showing the above-described replenishment operation, wherein the basic ink is replenished from the ink tanks  37 - 40  into the sub-tanks  29 - 36 . The replenishment operation is carried out when the remaining ink in the sub-tanks  29 - 36  reaches the predetermined minimum amount based on a signal from one of the electrodes  51 - 54  (in this configuration the signal is from electrode  51 ). Hereinafter, this flowchart will be explained in detail.  
         [0077]     Firstly, the basic inks are supplied from the ink tanks  37 - 40  into respective basic color sub-tanks  29 - 32 . Specifically, in S 1 , it is determined whether or not the scanning carriage  42  of the head unit  28  is positioned at a predetermined position, that is, at an end of a scannable area where the scanning carriage  42  can perform scanning. This determination is made, for example, based on an input signal from a position sensor for the scanning carriage  42 , such as an encoder.  
         [0078]     If it is determined that the scanning carriage  42  is not positioned at the predetermined position (S 1 :NO), in S 2 , the belt drive motor  46  is driven so as to move the scanning carriage  42  to the predetermined position. In S 3 , the slide cylinders  67  are operated. In S 4 , the connecting portions  66  of respective ink tanks  37 - 40  and the supply openings  50  of the sub-tanks  29 - 32  are connected, so that the on-off valves  58  of the connecting portions  66  open the ink replenishment openings  66 . In S 5 , the pumps  68  are operated. As a result, in S 6 , the basic inks are independently supplied into respective sub-tanks  29 - 32 .  
         [0079]     If it is determined that the scanning carriage  42  is positioned at the predetermined position (S 1 :YES), the process in S 2  is skipped and the process in S 3  is executed. Subsequently, it is determined whether or not production of mixed ink is necessary, in other words, the remaining ink in the mixed color sub-tanks  33 - 36  becomes the predetermined minimum amount (S 7 ). Then, if it is determined that production of mixed ink is necessary (S 7 :YES), the mixed color ink supply control which will be discussed later, is executed (S 8 ).  
         [0080]     Subsequently, in S 9 , it is determined whether or not production of another mixed ink is necessary. If it is determined that production of another mixed ink is necessary (S 9 :YES), S 8  is executed. On the other hand, if it is determined that production of another mixed ink is not necessary (S 9 :NO), the flow of the present control finishes.  
         [0000]     4.2.1.2 Mixed Ink Supply Control for Mixing Two Colors  
         [0081]      FIG. 12  is a control flowchart showing a mixed ink supply control when two colors of basic ink are mixed. First, the scanning carriage  42  is scanned so as to position one of the mixed sub-tanks  33 - 36 , subject to replenishment, immediately below one of the ink tanks  37 - 40 , which store basic ink to replenish and supply as a first color (S 21 ).  
         [0082]     When scanning by the scanning carriage  42  is done, the slide cylinder  67  is operated (S 23 ). Then, the connecting portion  66  of the ink tank and the supply opening  50  of the sub-tank are connected, and the on-off valve  58  of the connecting portion  66  is opened (S 25 ). Subsequently, the pump  68  is operated, and supply of the first basic ink to the sub-tank is initiated (S 27 ). It is desirable that the speed of replenishment should be regulated so that the ink liquid surface does not ruffle within the sub-tank when the basic ink is replenished.  
         [0083]     Then, based on a signal from the third electrode  53 , it is determined whether or not the basic ink, which is in the process of replenishment, is reached the predetermined amount (S 29 ). When it is determined that the amount of replenishment is reached the predetermined amount, the pump  68  is stopped and replenishment of the first basic ink finishes (S 31 ).  
         [0084]     Next, the scanning carriage  42  is scanned so as to position one of the mixed sub-tanks  33 - 36 , subject to replenishment, immediately below one of the ink tanks  37 - 40 , which store a basic ink to replenish (supply) as a second color (S 33 ).  
         [0085]     When scanning by the scanning carriage  42  is done, the slide cylinder  67  is operated (S 35 ). Then, the connecting portion  66  of the ink tank and the supply opening  50  of the sub-tank are connected, and the on-off valve  58  of the connecting portion  66  is opened (S 37 ). Subsequently, the pump  68  is operated, and supply of the second basic ink to the sub-tank is initiated (S 39 ).  
         [0086]     Then, based on a signal from the second electrode  52 , it is determined whether or not the basic ink, which is in the process of replenishment, is reached the predetermined amount (S 41 ). When it is determined that the replenishment amount is reached the predetermined amount, the pump  68  is stopped and replenishment of the second basic ink finishes (S 43 ).  
         [0000]     4.2.2.3 Mixed Ink Supply Control for Mixing Three Colors  
         [0087]      FIG. 13  is a control flowchart showing a mixed ink supply control when three colors of basic ink are mixed. First, the scanning carriage  42  is scanned so as to position one of the mixed sub-tanks  33 - 36 , subject to replenishment, immediately below one of the ink tanks  37 - 40 , which store a basic ink to replenish (supply) as a first color (S 51 ).  
         [0088]     When scanning by the scanning carriage  42  is done, the slide cylinder  67  is operated (S 53 ). Then, the connecting portion  66  of the ink tank and the supply opening  50  of the sub-tank are connected, and the on-off valve  58  of the connecting portion  66  is opened (S 55 ). Subsequently, the pump  68  is operated, and supply of the first basic ink to the sub-tank is initiated (S 57 ).  
         [0089]     Then, based on a signal from the fourth electrode  54 , it is determined whether or not the basic ink, which is in the process of replenishment, is reached the predetermined amount (S 59 ). When it is determined that the replenishment amount is reached the predetermined amount, the pump  68  is stopped and replenishment of the first basic ink finishes (S 61 ).  
         [0090]     Next, the scanning carriage  42  is scanned so as to position one of the mixed sub-tanks  33 - 36 , subject to replenishment, immediately below one of the ink tanks  37 - 40 , which store a basic ink to replenish (supply) as a second color (S 63 ).  
         [0091]     When scanning by the scanning carriage  42  is done, the slide cylinder  67  is operated (S 65 ). Then, the connecting portion  66  of the ink tank and the supply opening  50  of the sub-tank are connected, and the on-off valve  58  of the connecting portion  66  is opened (S 67 ). Subsequently, the pump  68  is operated, and supply of the second basic ink to the sub-tank is initiated (S 69 ).  
         [0092]     Then, based on a signal from the third electrode  53 , it is determined whether or not the basic ink, which is in the process of replenishment, is reached the predetermined amount (S 71 ). When it is determined that the replenishment amount is reached the predetermined amount, the pump  68  is stopped and replenishment of the second basic ink finishes (S 73 ).  
         [0093]     Next, the scanning carriage  42  is scanned so as to position one of the mixed sub-tanks  33 - 36 , subject to replenishment, immediately below one of the ink tanks  37 - 40 , which store a basic ink to replenish (supply) as a third color (S 75 ).  
         [0094]     When scanning by the scanning carriage  42  is done, the slide cylinder  67  is operated (S 77 ). Then, the connecting portion  66  of the ink tank and the supply opening  50  of the sub-tank are connected, and the on-off valve  58  of the connecting portion  66  is opened (S 79 ). Subsequently, the pump  68  is operated, and supply of the third basic ink to the sub-tank is initiated (S 81 ).  
         [0095]     Then, based on a signal from the second electrode  52 , it is determined whether or not the basic ink, which is in the process of replenishment, is reached the predetermined amount (S 83 ). When it is determined that the amount of replenishment is reached the predetermined amount, the pump  68  is stopped and replenishment of the second basic ink finishes (S 85 ).  
         [0000]     4.3 Detail of Ink Replenishment Operation  
         [0000]     4.3.1 Basic Ink Replenishment  
         [0096]     In accordance with the processes in S 2  to S 6  of the ink replenishment operation control (see  FIG. 11 ), the scanning carriage  42  is positioned, and respective ink tanks  37 - 40  are connected to the sub-tanks  29 - 32 , as shown in  FIG. 14 .  
         [0097]     At this time, upon the connecting portions  66  of respective ink tanks  37 - 40  being inserted into the supply openings  50  of the sub-tanks  29 - 32 , the pumps  68  are operated and the basic inks are respectively supplied into the sub-tanks  29 - 32 .  
         [0000]     4.3.2 Production of Mixed Ink (ink B)  
         [0098]     Ink B is produced with, among the basic inks, ink C and ink M mixed together. Firstly, as shown in  FIG. 15A , the ink tank  38  is positioned immediately above the sub-tank  33  which is allocated for producing mixed ink (ink B). The ink tank  38  is lowered so as to be connected to the sub-tank  33 . Then, ink C is supplied into the sub-tank  33 .  
         [0099]     Secondly, as shown in  FIG. 15B , the ink tank  40  is positioned immediately above the sub-tank  33 . The ink tank  40  is lowered so as to be connected to the sub-tank  33 . Then, ink M is supplied into the sub-tank  33 . As a result, ink B is produced in the sub-tank  33 .  
         [0100]     The way of producing ink B is not limited to the above-described example. Contrary to the order of ink supply in the above example, ink M can be firstly supplied into the sub-tank  33 , and then ink C can be supplied. In other words, among the plurality of the basic inks to be mixed, inks should be preferably supplied into the sub-tank  33  in the order from a relatively paler color.  
         [0000]     4.3.3 Mixed Ink (Ink R)  
         [0101]     Ink R is produced with, among the basic inks, ink Y and ink M mixed together. Firstly, as shown in  FIG. 16A , the ink tank  39  is positioned immediately above the sub-tank  34  which is allocated for producing mixed ink (ink R). The ink tank  39  is lowered so as to be connected to the sub-tank  34 . Then, ink Y is supplied into the sub-tank  34 .  
         [0102]     Secondly, as shown in  FIG. 16B , the ink tank  40  is positioned immediately above the sub-tank  34 . The ink tank  40  is lowered so as to be connected to the sub-tank  34 . Then, ink M is supplied into the sub-tank  34 . As a result, ink R is produced in the sub-tank  34 .  
         [0103]     The way of producing ink R is not limited to the above-described example. Contrary to the order of ink supply in the above example, ink Y can be firstly supplied into the sub-tank  34 , and then ink M can be supplied.  
         [0000]     4.3.4 Mixed Ink (Ink G)  
         [0104]     Ink G is produced with, among the basic inks, ink Y and ink C mixed together. Firstly, as shown in  FIG. 17A , the ink tank  39  is positioned immediately above the sub-tank  35  which is allocated for producing mixed ink (ink G). The ink tank  39  is lowered so as to be connected to the sub-tank  35 . Then, ink Y is supplied into the sub-tank  35 .  
         [0105]     Secondly, as shown in  FIG. 17B , the ink tank  38  is positioned immediately above the sub-tank  35 . The ink tank  38  is lowered so as to be connected to the sub-tank  35 . Then, ink C is supplied into the sub-tank  35 . As a result, ink G is produced in the sub-tank  35 .  
         [0106]     The way of producing ink G is not limited to the above-described example. Contrary to the order of ink supply in the above example, ink Y can be firstly supplied into the sub-tank  35 , and then ink C can be supplied.  
         [0000]     4.3.5 Mixed Ink (Ink Pb)  
         [0107]     Ink Pb is produced with three colors of inks among the basic inks, that is, ink Y, ink C, and ink M mixed together. Firstly, as shown in  FIG. 18A , the ink tank  39  is positioned immediately above the sub-tank  36  which is allocated for producing mixed ink (ink Pb). The ink tank  39  is lowered so as to be connected to the sub-tank  36 . Then, ink Y is supplied into the sub-tank  36 .  
         [0108]     Secondly, as shown in  FIG. 18B , the ink tank  38  is positioned immediately above the sub-tank  36 . The ink tank  38  is lowered so as to be connected to the sub-tank  36 . Then, ink C is supplied into the sub-tank  36 .  
         [0109]     Furthermore, as shown in  FIG. 18C , the ink tank  40  is positioned immediately above the sub-tank  36 . The ink tank  40  is lowered so as to be connected to the sub-tank  36 . Then, ink M is supplied into the sub-tank  36 . As a result, ink Pb is produced in the sub-tank  36 .  
         [0110]     The way of producing ink Pb is not limited to the above-described example. The inks can be supplied into the sub-tank  36 , for example, in the order from a relatively paler color, that is, in the order of ink Y, ink M, and ink C.  
         [0111]     In the above-described embodiments, the replenishment amount device includes a first electrode  51  to the fourth electrode  54  and the liquid surface level determination device  55 . However, the present invention is not limited to this embodiment. The replenishment amount device can include devices for measuring the amount of ink existing in the mixed color sub-tanks  33 - 36  or of detecting the ink liquid surface optically and so forth.  
         [0112]     Although the connecting portions  66  are disposed in the lower portion of the ink tanks  37 - 40  and the supply holes  50  are disposed in the upper portion of the sub-tanks  29 - 36  in the first embodiment described above, it is not limited to this embodiment. According to the co-pending application Ser. No. 11/386,095 incorporated in the present application, the connecting portions ( 66 ) can be disposed in the side surface of the ink tank and the mating portions ( 56 ) can be disposed in the side surface of the sub-tank. All the disclosure of the co-pending application Ser. No. 11/386,095 is incorporated herein by reference.  
         [0000]     5. Characteristic of Inkjet Recording Apparatus (Printer Unit  11 )  
         [0113]     In the embodiment of the present invention, related to the multifunction apparatus (Inkjet recording apparatus), replenishment of the plurality of colors of basic ink is carried out as it automatically detects the replenishment amount of each of the plurality of colors of basic ink to be replenished to the sub-tanks  33 - 36 , the accurate mixing ratio of mixed ink of the sub-tanks  33 - 36  can be replicated.  
         [0114]     Furthermore, in the present embodiment, the replenishment amount is detected by utilizing a change of the electronic resistance value. Therefore, the replenishment amount can be detected more easily, accurately and inexpensively.  
         [0115]     [Second Embodiment] 
         [0116]     In the first embodiment, the ink tanks  37 - 40  and the sub-tanks  33 - 36  are usually separated from each other, and they become connected each other when ink is supplied from the ink tanks to the sub-tanks. However, in the second embodiment, as it is described in the co-pending application Ser. No. 11/386,930, the ink tanks and the sub-tanks are usually connected each other via the connecting pipes and the ink replenishment from the ink tanks to the sub-tanks is performed by a pump disposed in the ink tank, and switching valve between the pump and the ink tanks and switch valves disposed in the sub-tanks.  
         [0117]     The detailed explanation would be referred to the co-pending application Ser. No, 11/385,930, all the disclosure of which is incorporated herein by reference.  
         [0118]     As described in the first embodiment, the sub-tanks are provided with electrodes in order to supply the predetermined amount of ink from the ink tanks  37 - 40  to the sub-tanks  29 - 36  and replenishInent of ink is controlled based on the signal from the electrodes that are applied to the inkjet recording apparatus of the second embodiment, That is, as shown in  FIGS. 5, 6  and  7 , the sub-tanks are provided with the electrode  51  to measure the minimum amount of ink and the electrode  52  to detect the maximum amount of ink as well. Also, the sub-tanks that store the mixed ink are provided with the electrodes  53 - 54  at the level in accordance with the mixing ratio of the plurality of basic inks in order to make the mixed ink, and the predetermined ink is replenished by detecting the signal from the electrode, more specifically, the change of the resistance value between the pair of electrodes.  
         [0119]     According to the co-pending Ser. No. 11/385,930, as shown in  FIGS. 9A and 9B ,  FIGS. 10A and 10B  and  FIGS. 11A and 11B  (FIGS.  9 A and  9 B: Steps  4  to  6 , FIGS.  10 A and  10 B: Steps  4  to  6  and Steps  10  to  12 , FIGS.  11 A and  11 B: Steps  4  to  6 , Steps  10  to  12  and Steps  16  to  18 ), the predetermined amount of ink is supplied by the pressurizing pump being operated in the predetermined period of time. However, in the second embodiment of the present invention, operation of the pressure pump stops when it is determined that the predetermined amount of ink is replenished based on the change of the resistance value between the pair of electrodes.  
         [0120]     Therefore, according to the second embodiment above, the mixed ink can be supplied stably and accurately as well as the first embodiment.  
         [0121]     There are two kinds of sub-tanks of the co-pending applications Ser. No. 11/386,095 and the Ser. No. 11/385,930: one is to store the basic inks and the other is to store the mixed inks. It should be noted that a number of all the sub-tanks is represented as m in the Ser. No. 11/386,095, whereas the number of the sub-tanks is represented as n+m in the Ser. No. 11/385,930; therefore, the meaning of ‘m’ is different in those applications. In order to avoid confusion, the number of the sub-tanks is indicated as n′ and the number of the sub-tanks that store the mixed liquid is indicated as n″.  
         [0122]     In the first and second embodiments, the detector that detects the amount of ink is disposed in the sub-tanks, however, it can be disposed in the ink tank too. In this case, the amount of ink to be supplied from the ink tank to the sub-tank differs depending on the mixed color to be made; therefore, the height of the ink should be detected closely. For this purpose, it is desirable that the electrodes  100  are arranged closely each other by uniform intervals in the heightwise direction as shown in  FIG. 19 , or an optical sensor is employed to measure the liquid surface level (not shown) when the ink amount detector is disposed in the ink tank.  
         [0123]     Although the embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement that is calculated to achieve the same purpose may be substituted for the specific embodiments shown. This application is intended to cover any adaptations or variations of the present invention. It is to be understood that the above description is intended to be illustrative, and not restrictive. Combinations of the above configurations and other configurations will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention includes any other applications in which the above structures and fabrication methods are used. Accordingly, the scope of the invention should only be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.