Abstract:
A printing apparatus to form an image on a recording medium is provided. The printing apparatus includes a recording head, an ink cartridge, which contains the ink therein, an ink cartridge storage to store the ink cartridge, an ink conveyer tube, which connects the recording head and the ink cartridge to convey the ink, and a maintenance system having an aspirator to aspirate the ink to be drawn in the recording head and the ink conveyer tube and a cap to cover a nozzle surface of the recording head, and a releasing system, which is arranged in the ink conveyer tube to switch an open state and a closed state. The releasing system is arranged in a position higher than a position of the ink cartridge so that the releasing system and the ink cartridge have a predetermined water head difference therebetween.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Application No. 2008-093060, filed on Mar. 31, 2008, the entire subject matter of which is incorporated herein by reference. 
     BACKGROUND 
     1. Technical Field 
     An aspect of the present invention relates to a printing apparatus, specifically to a printing apparatus to print in ink containing solid component, which may be deposited in the ink, and concentration gradient may occur therein. 
     2. Related Art 
     Conventionally, an inkjet printer to form an image in white ink, in addition to the other colored inks (e.g., cyan, magenta, yellow, and black), has been suggested. The white ink generally contains oxidized titanium and therefore has specifically higher density of colorant with respect to densities of colorants in the other colored inks. Further, a particle size of the white colorant is larger. Therefore, the colorant in the white ink can be easily deposited inside an ink tube. 
     Accordingly, the densities of the white ink may vary within the tube, and troubles such as irregular ejection of the ink from an inkjet head, insufficient flow of the ink flow to the inkjet head, or uneven densities of the color in a formed image can be caused due to the uneven distribution of the ink within the tube. 
     Therefore, an inkjet printer with white ink is generally provided with a mechanism to prevent deposition of the colorant in the white ink. For example, Japanese Patent Provisional Publication No. 2004-009685 discloses an inkjet printer having an ink path, in which ink inside an ink cartridge is circulated so that the ink is stirred and smoothly conveyed. 
     For another example, Japanese Patent Provisional Publication No. 2003-39690 discloses an ink cartridge for an inkjet printer having an stirrer equipment and a vibrator equipment to periodically stir the ink therein. 
     SUMMARY 
     In the above inkjet printing apparatuses, however, the dedicated equipments and controlling systems to control behaviors of the equipments often require a large space and may increase cost for the entire printing apparatuses. If the deposition of the colorant in the ink is to be prevented without such equipments, instead, a head cleaning operation to replace the ink remaining in an ink supplying system with freshly stirred ink in the ink cartridge is required. However, such an operation to replace the remaining ink in the entire ink supplying system including tubes and an inkjet head waste a large amount of ink, which is not beneficial in cost-effectiveness and an ecological reason. 
     In view of the above drawbacks, the present invention is advantageous in that a printing apparatus, in which unevenness of the ink in the ink supplying system can be reduced and concentration gradient of the ink within the ink supplying system can be smaller, without a space-consuming equipment, is provided. 
     According to an aspect of the present invention, a printing apparatus to form an image on a recording medium according to print data representing the image is provided. The printing apparatus includes a recording head, which ejects ink onto the recording medium, an ink cartridge, which contains the ink therein, an ink cartridge storage to store the ink cartridge, an ink conveyer tube, which connects the recording head and the ink cartridge to convey the ink, a maintenance system having an aspirator to aspirate the ink to be drawn in the recording head and the ink conveyer tube and a cap to cover a nozzle surface of the recording head when the ink in the recording head and the ink conveyer tube is aspirated, and a releasing system, which is arranged in the ink conveyer tube to switch an open state in which air flow in the ink conveyer tube is released and a closed state in which the air flow in the ink conveyer tube is shut down. The releasing system is arranged in a position higher than a position of the ink cartridge so that the releasing system and the ink cartridge have a predetermined water head difference therebetween. 
     According to the above configuration, when the air flow in the ink conveyer tube is released by the releasing system, the water head difference between the releasing system and the ink cartridge substantially large to collect the ink remaining in the ink conveyer tube to be withdrawn in the ink cartridge. Thus, the ink in the ink conveyer tube can be prevented from being left in the ink conveyer tube to be deposited. 
    
    
     
       BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS 
         FIG. 1  is a plane view of an inkjet printer according to an embodiment of the present invention. 
         FIG. 2  is a front view of the inkjet printer according to the embodiment of the present invention. 
         FIG. 3  is a front view of inkjet heads and a release valve in the inkjet printer according to the embodiment of the present invention. 
         FIGS. 4A and 4B  illustrate an ink collecting operation of the release valve in the inkjet printer according to the embodiment of the present invention. 
         FIG. 5  is a block diagram to illustrate an electric configuration of the inkjet printer according to the embodiment of the present invention. 
         FIG. 6  is a flowchart to illustrate a main flow of the operation of the inkjet printer according to the embodiment of the present invention. 
         FIGS. 7A and 7B  are diagrams to illustrate an operation indicator panel in the inkjet printer according to the embodiment of the present invention. 
         FIG. 8  is a flowchart to illustrate an ink withdrawal operation to be executed in the inkjet printer according to the embodiment of the present invention. 
         FIGS. 9A and 9B  are diagrams to illustrate the operation indicator panel during an ink reloading operation in the inkjet printer according to the embodiment of the present invention. 
         FIG. 10  is a flowchart to illustrate the ink reloading operation to be executed in the inkjet printer according to the embodiment of the present invention. 
         FIGS. 11A and 11B  are diagrams to illustrate the operation indicator panel during a cleaning and ink reloading operation in the inkjet printer according to the embodiment of the present invention. 
         FIG. 12  is a flowchart to illustrate the cleaning and ink reloading operation to be executed in the inkjet printer according to the embodiment of the present invention. 
         FIGS. 13A and 13B  are diagrams to illustrate an ink stirring operation to be executed in the inkjet printer according to the embodiment of the present invention. 
         FIG. 14  is a flowchart to illustrate the ink stirring operation to be executed in the inkjet printer according to the embodiment of the present invention. 
         FIGS. 15A and 15B  are diagrams to illustrate manually-operable release valves according to the embodiment of the present invention. 
         FIGS. 16A and 16B  are diagrams to illustrate a descendible configuration in the inkjet printer according to the embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, an embodiment according to an aspect of the present invention will be described with reference to the accompanying drawings.  FIG. 1  is a plane view of an inkjet printer  1  according to the embodiment of the present invention.  FIG. 2  is a front view of the inkjet printer  1  according to the embodiment of the present invention.  FIG. 3  is a front view of inkjet heads and a release valve in the inkjet printer  1  according to the embodiment of the present invention.  FIGS. 4A and 4B  illustrate an ink collecting operation of the release valve in the inkjet printer  1  according to the embodiment of the present invention.  FIG. 5  is a block diagram to illustrate an electric configuration of the inkjet printer  1  according to the embodiment of the present invention.  FIG. 6  is a flowchart to illustrate a main flow of the operation of the inkjet printer  1  according to the embodiment of the present invention. 
     The inkjet printer  1  in the present embodiment is configured to be an inkjet printer having first inkjet heads  21  and second inkjet heads  22  to form an image on a recording medium in inks ejected from nozzle surfaces of the first and the second inkjet heads  21 ,  22  according to image data. In the inkjet printer  1 , a piece of fabric can be used as a recording medium, and the piece of fabric may be, for example, a T-shirt. As shown in  FIGS. 1 and 2 , the inkjet printer  1  is provided with a flat base plate  2  at a bottom and a chassis  10  to cover the entire body of the inkjet printer  1 . 
     The first inkjet heads  21  are mounted on a carriage  13 , which is reciprocated in a right-and-left direction in  FIG. 1  along a guide rail  11 . In the vicinity of a right-hand end of the guide rail  11 , a first carriage motor  24  ( FIG. 5 ) to carry the first inkjet heads  21  is provided. Further, a pulley (not shown) is provided in the vicinity of a left-hand end of the guide rail  1 , and a carriage belt (not shown) is drawn between the first carriage motor  24  and the pulley. The carriage belt is fixed to the carriage  13  so that the carriage  13  is reciprocated along the guide rail  11  in the right-and-left direction (i.e., the main scanning direction) when the first carriage motor  24  is activated. At one of the right-hand end and the left-hand end of the reciprocative range of the carriage  13 , a maintenance mechanism (not shown) such as a capping unit and a purge unit for the first inkjet heads  21  is provided. 
     On the right-hand end of the chassis  10 , first ink cartridges  31  containing white ink therein are detachably attached. The first ink cartridges  31  are connected to each of the inkjet heads  21  by flexible ink conveyer tubes  34  so that the inks stored in the first ink cartridges  31  are conveyed to each channel of the inkjet heads  21 . According to the present embodiment, all of the inkjet heads  21  are provided to discharge white ink therefrom, and the first ink cartridges  31  respectively contain white ink. 
     The ink conveyer tubes  34  to supply the ink to the first inkjet heads  21  are moved along with first inkjet heads  21  when the carriage  13  with the first inkjet heads  21  is reciprocated in the main scanning direction. Therefore, the ink conveyer tubes  34  are formed to be longer than a length of the guide rail  11 . The ink conveyer tubes  34  with the length are held by a first arm  36  to extend there-along so that the ink conveyer tubes  34  can smoothly move to follow the carriage  13 . 
     The first arm  36  includes a rear portion, which is a thin and elongated plate rotatable about a supporting point  36   a , and a supporting point  36   b  is provided at an end of the rear portion. The first arm  36  further includes a front portion, which is a thin and elongated plate rotatable about the supporting point  36   b  and is coupled to the carriage  13  at a supporting point  36   c.    
     The inkjet printer  1  according to the embodiment is equipped with a guide rail  12  ( FIG. 1 ), which is arranged in parallel with the guide rail  11 , to guide a carriage  14  with a second inkjet head  22  being mounted. As shown in  FIG. 2 , the guide rail  12  is arranged in a position higher than the guide rail  11 . 
     In the vicinity of a left-hand end of the guide rail  12 , a second carriage motor  25  ( FIG. 5 ) to carry the second inkjet heads  22  is provided. Further, a pulley (not shown) is provided in the vicinity of the right-hand end of the guide rail  12 , and a carriage belt (not shown) is drawn between the second carriage motor  25  and the pulley. The carriage belt is fixed to the carriage  14  so that the carriage  14  is reciprocated along the guide rail  12  in the left-and-right direction (i.e., the main scanning direction) when the second carriage motor  25  is activated. At one of the right-hand end and the left-hand end of the reciprocative range of the carriage  14 , a maintenance mechanism (not shown) such as a capping unit and a purge unit for the second inkjet heads  22  is provided. 
     On the left-hand end of the chassis  10 , second ink cartridges  32  containing CMYK (cyan, magenta, yellow, and black) colored inks respectively therein are detachably attached. The second ink cartridges  32  are connected to each of the inkjet heads  22  by flexible ink conveyer tubes  35  so that the inks stored in the second ink cartridges  32  are conveyed to each channel of the inkjet heads  22 . According to the present embodiment, each of the inkjet heads  22  discharges C, M, Y, K inks therefrom respectively. 
     The ink conveyer tubes  35  to supply the ink to the second inkjet heads  22  are moved along with second inkjet heads  22  when the carriage  14  with the second inkjet heads  22  is reciprocated in the main scanning direction. Therefore, the ink conveyer tubes  35  are formed to be longer than a length of the guide rail  12 . The ink conveyer tubes  35  with the length are held by a second arm  37  to extend there-along so that the ink conveyer tubes  35  can smoothly move to follow the carriage  14 . 
     The second arm  37  includes a rear portion, which is a thin and elongated plate, rotatable about a supporting point  37   a , and a supporting point  37   b  is provided at an end of the rear portion. The second arm  37  further includes a front portion, which is a thin and elongated plate, rotatable about the supporting point  37   b  and is coupled to the carriage  14  at a supporting point  37   c.    
     It is to be noted that the guide rail  12  is arranged in the position vertically higher than the guide rail  11 ; therefore, movements of the first arm  36  and the second arm  37  do not interfere each other even when the second arm  37  moves to cross over the first arm  36 . 
     The inkjet printer  1  is equipped with a platen  5 . The platen  5  is formed to have a substantially rectangular-shaped plate, on which the recording medium (e.g., a T-shirt) is placed in a printable posture in the inkjet printer  1 . The platen  5  is supported by a platen feed unit  7 , which includes a guide rail (not shown) and a platen feed motor  40  ( FIG. 4 ) being a stepping motor arranged at a rear end portion (i.e., upper end in  FIG. 1 ) of the guide rail. When the platen feed motor  40  is activated, the platen  5  is reciprocated along the guide rail in the front- and-rear direction (i.e., up-and-down direction) in  FIG. 1 . The inkjet printer  1  may have a plurality of sizes of platen  5 , which can be selected according to, for example, sizes and shapes of the recording media. 
     At right-hand front of the inkjet printer  1  is provided an operation panel  28 , through which a user inputs an instruction for the inkjet printer  1 . The operation panel  28  includes print buttons  29  and a display  30 . 
     Next, a fluid releasing mechanism according to the present embodiment will be described with reference to  FIG. 3 . The inkjet printer  1  in the present embodiment is equipped with an air release valve  44 , which releases and shuts down air flow in the ink conveyer tubes  34 . As has been mentioned above, the ink conveyer tubes  34  connect the first ink cartridges  31  and the channels of the inkjet heads  21  to convey the white ink. The air release valve  44  is an electromagnetic valve, which is switched from an open position and a closed position, and vice versa, to release and shut down the air flow in between the first inkjet heads  21  and the first ink cartridges  31  in the ink conveyer tubes  34 , according to electric signals. When the air release valve  44  is opened to release the air flow in the ink conveyer tubes  34  with the first inkjet heads  21  being covered with caps  45  (see  FIG. 4A ) in the maintenance unit, the ink remaining in the ink conveyer tubes  34  is withdrawn in the first ink cartridges  31 . 
     As shown in  FIG. 4A , when the caps  45  cover the nozzle surfaces of the first inkjet heads  21 , and the air release valve  44  is switched to shut down the air flow in the ink conveyer tubes  34 , a water head difference between a level of the nozzle surfaces of the first inkjet heads  21  and an ink supplying level (i.e., vertical positions of the first ink cartridges  31 ) is substantially small so that the ink remaining in the ink conveyer tubes  34  is not withdrawn in the first ink cartridges  31 . 
     However, as shown in  FIG. 4B , when the caps  45  cover the nozzle surfaces of the first inkjet heads  21 , and the air release valve  44  is switched to release the air flow in the ink conveyer tubes  34 , the water head difference between a level of the air release valve  44  and the ink supplying level of the first ink cartridges  31  is substantially large so that the ink remaining in the ink conveyer tubes  34  is withdrawn in the first ink cartridges  31 . The air release valve  44  is switched to be opened and closed according to predetermined timings in an ink reloading process, which will be described later in detail. 
     In the present embodiment, the water head difference between the levels of the air release valve  44  and the ink supplying level of the first ink cartridges  31  is approximately 100 mm. Therefore, when the air release valve  44  is switched to release the air flow in the ink conveyer tubes  34 , the water head difference grows to be larger so that the remaining ink can be substantially withdrawn. However, it is to be noted that the water head difference is not limited to 100 mm, but may be any height greater than 20 mm with respect to the ink supplying level of the first ink cartridges  31 . 
     It is to be noted in the present embodiment that the first ink cartridges  31  are provided with filters  51 b, and the first inkjet heads  21  are provided with filters  51   a  at positions indicated by dotted lines in  FIGS. 4A and 4B . These filters  51   a ,  51   b  serve to catch obstacles flowing in the ink when the ink is collected. 
     Next, referring to  FIG. 5 , an electrical configuration of the inkjet printer  1  will be described.  FIG. 4  is a block diagram showing the electrical configuration of the inkjet printer  1  according to the present embodiment of the invention. As shown in  FIG. 5 , the inkjet printer  1  is provided with a control unit  100 , and the control unit  100  includes a CPU  110  that controls the entire operation in the inkjet printer  1 . The CPU  110  is connected with a ROM  120 , a RAM  130  through a bus  115 . The ROM  120  stores various controlling programs to be executed in the CPU  110 . The RAM  130  temporarily stores data concerning the operations in the inkjet printer  1 . 
     The CPU  110  is further connected with a communication unit  150  and with a PC (personal computer)  170  through a communication cable  160 . Furthermore, the CPU  110  is connected with a print control unit  140  to control printing operations in the inkjet printer  1  through the bus  115 . 
     The print control unit  140  includes a head controller  141 , which drives piezoelectric actuators for each of the channels in the first inkjet heads  21  and the second inkjet heads  22 . The print control unit  140  further includes a head drive controller  142  to activate the first carriage motor  24  and the second carriage motor  25 , and a platen feed motor controller  143  to activate the platen feed motor  40 . 
     The print control unit  140  further includes a sensor input unit  144 , which receives input signals provided by a print start key  29   a , a cancel key  29   b , a maintenance key  29   c , and a cartridge detective sensor  43 . The print start key  29   a , the cancel key  29   b , and the maintenance key  29   c  are provided on the operation panel  28  (see also  FIG. 7A ). The operation panel  28  further includes a data reception indicator  30   a , an error indicator  30   b , and the display  30 , which are controlled by a display control unit  145 . The print control unit  140  further includes a fluid release controller  145  to control motions of the air release valve  44 . 
     The inkjet printer  1  in the present embedment includes a first maintenance mechanism and a second maintenance mechanism respectively on either (right or left) side of the guide rail  11  and the guide rail  12 . The first and the second maintenance mechanisms serve to maintain operating conditions of the first inkjet heads  21  and the second inkjet heads  22  respectively. The first maintenance mechanism includes a first maintenance motor  41 , and the second maintenance mechanism includes a second maintenance motor  42 . The print control unit  140  is provided with a maintenance controller  147  to activate the first maintenance motor  41  and the second maintenance motor  42 . 
     Next, a main flow of the operation of the inkjet printer  1  according to the embodiment of the present invention will be described with reference to  FIG. 6 . When the inkjet printer  1  is powered on and the operation starts in S 1 , the inkjet printer  1  is initialized. The initialization includes, for example, a flushing operation to prepare the nozzles of the first and the second inkjet heads  21 ,  22  in condition for ejecting ink drops. In S 2 , determination is made as to whether the initialization successfully completed. When the initialization fails (S 2 : NO), in S 11 , the error indicator  30   b  is activated. When the error indicator  30   b  is activated, for example, an indicator lamp is lit and/or an error indicating sound is generated. 
     Following S 11 , in S 12 , it is examined as to whether one of operation menus, which exclude “print,” “ink withdrawal,” and “head cleaning,” is selected. When one of the operation menus is selected (S 12 : YES), in S 13 , an operation corresponding to the selection is performed. Thereafter, the inkjet printer  1  waits for next input to select an operation menu. 
     In S 12 , if no operation menu is selected (S 12 : NO), in S 14 , it is examined as to whether power to the inkjet printer  1  is shut off. If power to the inkjet printer  1  is shut off (S 14 : YES), the operation is terminated. If the power supply to the inkjet printer  1  is maintained (S 14 : NO), the process repeats S 12 . 
     In S 2 , when the initialization successfully completes (S 2 : YES), the inkjet printer  1  waits for selection of an operation menu to be entered. In S 3 , it is examined as to whether the print start key  29   a  has been operated. If the print start key  29   a  has been operated (S 3 : YES), in S 4 , it is examined as to whether the inkjet printer  1  is provided with print data. If no print data has been provided (S 4 : NO), in S 6 , an error is indicated, and the process returns to S 3 . If the inkjet printer  1  is provided with print data (S 4 : YES), in S 5 , a printing operation to print an image according to the print data is performed. The process returns to S 3  thereafter. 
     In S 3 , if the print start key  29   a  has not been operated (S 3 : NO), in S 7 , it is examined as to whether an ink withdrawal operation is selected through a menu window displayed in the operation panel  28 . If selection for the ink withdrawal operation is made (S 7 : YES), in S 8 , the ink remaining in the ink conveyer tubes  34  is withdrawn in the first ink cartridges  31 . The process returns to S 3  thereafter. The ink withdrawal operation will be described later in detail. 
     In S 7 , if selection for the ink withdrawal operation is not made (S 7 : NO), in S 9 , it is examined as to whether selection for a head cleaning operation is made. If selection for the head cleaning operation is made (S 9 : YES), in S 10 , an ink reloading operation is performed, and the ink conveyer tubes  34 , from which the remaining ink has been unloaded, is reloaded. The process returns to S 3  thereafter. The ink reloading operation will be described later in detail. 
     Next, the ink withdrawal operation in the inkjet printer  1  according to the present embodiment will be described with reference to  FIGS. 7A ,  7 B, and  8 .  FIGS. 7A and 7B  are diagrams to illustrate the operation indicator panel  28  in the inkjet printer  1  according to the embodiment of the present invention.  FIG. 8  is a flowchart to illustrate the ink withdrawal operation to be executed in the inkjet printer  1  according to the embodiment of the present invention. 
     The operation indicator panel  28  in the inkjet printer  1  according to the present embodiment includes the display  30 , the print start key  29   a , the cancel key  29   b , the maintenance key  29   c , a cursor (up) key  29   d , a cursor (down) key  29   e , and an OK key  29   f  When the maintenance key  29   c  is pressed, the display  30  shows a menu screen as shown in  FIG. 7A . Specifically, menu options “Head Cleaning,” “Test Print,” and “Ink Unloading” are displayed. When the menu options are displayed, a background of an option being currently selected (i.e., “Head Cleaning” in  FIG. 7A ) is inverted. An option to be selected can be specified by up and down motions of a cursor, which can be shifted by the cursor (up) key  29   d  and the cursor (down) key  29   e . Thus, when the option “Ink Unloading” is selected with the OK key  29   f , the display  30  shows the option “Ink Unloading” inverted as shown in  FIG. 7B , and the ink withdrawal operation is started. 
     Next, the ink withdrawal operation will be described with reference to  FIG. 8 . When the ink withdrawal operation starts, in S 20 , it is examined as to whether an error condition is detected in the inkjet printer  1 . The error condition may include, for example, that the first ink cartridges  31  is not set in a predetermined set position. When an error condition is detected (S 20 : YES), in S 27 , the error indicator  30   b  is activated, and information to indicate the ink withdrawal is inexecutable is provided to the user. More specifically, the error indicator lamp is lit, and/or an error indicating sound is generated. Thereafter, the operation is terminated. 
     In S 20 , when no error condition is detected (S 20 : NO), in S 21 , a message (e.g., “Unloading ink from the nozzles.”) to indicate the ink is to be withdrawn is presented in the display  30 . Further, the air release valve  44  is switched to release the air flow in between the first inkjet heads  21  and the first ink cartridges  31  in the ink conveyer tubes  34 . In S 22 , it is examined as to whether the air release valve  44  is switched to release the air flow. If the air release valve  44  is switched (S 22 : YES), in S 23 , a message (e.g., “Unloading . . . ”) to indicate that the ink is being withdrawn is presented in the display  30 . In S 24 , it is examined as to whether a predetermined time period, which is substantially long to withdraw the remaining ink from the ink conveyer tubes  34 , has elapsed. When the predetermined time period elapses (S 24 : YES), in S 25 , the air release valve  44  is switched to shut down the air flow in the ink conveyer tubes  34 . Thus, because the air release valve  44  is switched to shut down the air flow in the ink conveyer tubes  34  after the predetermined time period, the inner surface of the ink conveyer tubes  34  is prevented from being exposed to open air so that even the minimum amount of ink remaining in the ink conveyer tubes  34  should not be dried out. 
     In S 26 , a message (e.g., “Ink withdrawn”) to indicate completion of the ink withdrawal is presented in the display  30 . In this regard, predetermined sound to indicate the completion of the ink withdrawal can be generated optionally. The operation is terminated thereafter. 
     According to the above operation, the ink remaining in the ink conveyer tubes  34  can be withdrawn and collected in the first ink cartridges  31  by utilizing the water head difference. Once the ink is collected, the ink can be stirred when the first ink cartridges  31  are removed from the inkjet printer  1  and shaken. When the first ink cartridges  31  containing the stirred ink are set again in the inkjet printer  1 , the well-conditioned white ink can be ejected smoothly from the nozzles, and the remaining ink can be prevented from being wasted. According to the above configuration, removal of the ink conveyer tubes  34  in order to collect the remaining ink is not required, or branch structures to collect the remaining ink are not specifically required in the ink conveyer tubes  34 . 
     Next, an ink reloading operation in the inkjet printer  1  according to the present embodiment will be described with reference to  FIGS. 9A ,  9 B, and  10 .  FIGS. 9A and 9B  are diagrams to illustrate the operation indicator panel  28  during the ink reloading operation in the inkjet printer  1  according to the embodiment of the present invention.  FIG. 10  is a flowchart to illustrate the ink reloading operation to be executed in the inkjet printer  1  according to the embodiment of the present invention. 
     When the operation indicator panel  28  presents the screen shown in  FIG. 7A , and a user operates the cursor (down) key  29   e  to select a menu option “Ink Reloading,” as shown in  FIG. 9A , the “Ink Reloading” option is selected, and a screen presenting a submenu as shown in  FIG. 9B  is presented. When the OK key  29   f  is operated with the cursor on “Ink” option, the ink reloading operation is started. 
     The ink reloading operation will be described with reference to  FIG. 10 . When the ink reloading operation starts, in S 30 , it is examined as to whether an error condition is detected in the inkjet printer  1 . When an error condition is detected (S 30 : YES), in S 38 , the error indicator  30   b  is activated, and information to indicate the ink reloading is inexecutable is provided to the user. More specifically, the error indicator lamp is lit, and/or an error indicating sound is generated. Thereafter, the operation is terminated. 
     In S 30 , if no error condition is detected (S 30 : NO), in S 31 , a message (e.g., “Shake the cartridges”) to prompt the user to shake the first ink cartridges  31  is presented on the screen of the display  30 . Thereafter, in S 32 , it is examined as to whether the first ink cartridges  31  are placed back in the predetermined set position in the inkjet printer  1 . When the first ink cartridge  31  being set in the predetermined set position is detected (S 32 : YES), in S 33 , a message (e.g., “Reloading . . . ”) to indicate that the ink is reloaded in the ink conveyer tubes  34  is presented in the display  30 . Further, the ink is reloaded in the ink conveyer tubes  34 . More specifically, the first inkjet heads  21  are moved to a predetermined maintenance position, in which the nozzle surfaces of the first inkjet heads  21  are covered with the caps  45  and the ink is drawn from the first ink cartridges  31 . The caps  45  are connected to an aspirator (see  FIGS. 4A ,  4 B) which aspirates through the nozzle surfaces of the first inkjet heads  21  so that the ink in the first ink cartridges  31  is drawn through the ink conveyer tubes  34  to the first inkjet heads  21 . In this regard, it is to be noted that the ink can be aspirated from the first ink cartridges  31  through the ink conveyer tubes  34  even when the air release valve  44  is in the closed position to shut down the air flow. 
     When the ink conveyer tubes  34  and the first inkjet heads  21  are reloaded, an amount of the ink to be aspirated is smaller than an amount of the ink loaded in the ink conveyer tubes  34  for the first time. This is because a small amount of ink remains in the ink conveyer tubes  34  and the first inkjet heads  21 , and fluid resistance in the ink conveyer tubes  34  and the first inkjet heads  21  is smaller. Therefore, upon reloading, an amount of the ink to be aspirated is adjusted to be smaller so that an amount of the ink to be wasted is reduced. 
     More specifically, in S 34 , it is examined as to whether the first maintenance motor  41  has rotated for a predetermined number of times, which is smaller than a number of times of rotation for the first maintenance motor  41  to initially load the ink. When the number of times of rotation reached to the predetermined number (S 34 : YES), in S 35 , the first maintenance motor  41  is stopped to cease aspiration. Further, the caps  45  are removed from the nozzle surfaces. In S 36 , the nozzle surfaces are wiped, the ink is flushed out of the nozzle surfaces, and the nozzle surfaces are covered with the caps  45 . In S 37 , a message (e.g., “Ready”) to indicate that the inkjet printer  1  is ready for a printing operation is presented in the screen of the display  30 . In this regard, predetermined sound to indicate the completion of the ink reloading can be generated optionally. The operation is terminated thereafter. 
     According to the above operation, the ink collected in the first ink cartridges  31  can be reloaded in the ink conveyer tubes  34  and the first inkjet heads  21  to be used, and an amount of the ink to be wasted can be reduced. 
     Next, a cleaning and ink reloading operation in the inkjet printer  1  according to the present embodiment will be described with reference to  FIGS. 11A ,  11 B, and  12 . 
       FIGS. 11A and 11B  are diagrams to illustrate the operation indicator panel  28  during the cleaning and ink reloading operation in the inkjet printer  1  according to the embodiment of the present invention.  FIG. 12  is a flowchart to illustrate the cleaning and ink reloading operation to be executed in the inkjet printer  1  according to the embodiment of the present invention. 
     When the operation indicator panel  28  presents the screen shown in  FIG. 7B , and the user operates the cursor (down) key  29   e  to select a menu option “Ink Reloading,” as shown in  FIG. 11A , the “Ink Reloading” option is selected, and a screen presenting a submenu as shown in  FIG. 11B  is presented. When the OK key  29   f  is operated with the cursor on “Flush+ink” option, the cleaning and ink reloading operation is started. 
     The cleaning and ink reloading operation will be described with reference to  FIG. 12 . When the cleaning and ink reloading operation starts, in S 40 , it is examined as to whether an error condition is detected in the inkjet printer  1 . When an error condition is detected (S 40 : YES), in S 52 , the error indicator  30   b  is activated, and information to indicate the ink reloading is inexecutable is provided to the user. More specifically, the error indicator lamp is lit, and/or an error indicating sound is generated. Thereafter, the operation is terminated. 
     In S 40 , if no error condition is detected (S 40 : NO), in S 41 , a message (e.g., “Set cleaner cartridges”) to prompt the user to set cleaner cartridges (not shown), which contain cleaner liquid, in the inkjet printer  1  is presented on the screen of the display  30 . Thereafter, in S 42 , it is examined as to whether the cleaner cartridges are placed in the predetermined set position in the inkjet printer  1 . When the cleaner cartridges being set in the predetermined set position is detected (S 42 : YES), in S 43 , a message (e.g., “Reloading . . . ”) to indicate that the cleaner liquid is loaded in the ink conveyer tubes  34  is presented in the display  30 . Further, the cleaner liquid is loaded in the ink conveyer tubes  34 . More specifically, the first inkjet heads  21  are moved to a predetermined maintenance position, in which the nozzle surfaces of the first inkjet heads  21  are covered with the caps  45  and the cleaner liquid is drawn from the cleaner cartridges. 
     In this regard, when the ink conveyer tubes  34  and the first inkjet heads  21  are loaded, an amount of the cleaner liquid to be aspirated is smaller than an amount of the ink loaded in the ink conveyer tubes  34  for the first time. This is because a small amount of ink remains in the ink conveyer tubes  34  and the first inkjet heads  21 , and fluid resistance in the ink conveyer tubes  34  and the first inkjet heads  21  is smaller. Therefore, upon loading the cleaner liquid, an amount of the cleaner liquid to be aspirated is adjusted to be smaller so that an amount of the cleaner liquid to be wasted is reduced. 
     More specifically, in S 44 , it is examined as to whether the first maintenance motor  41  has rotated for a predetermined number of times, which is smaller than a number of times of rotation for the first maintenance motor  41  to initially load the ink. When the number of times of rotation reached to the predetermined number (S 44 : YES), in S 45 , the first maintenance motor  41  is stopped to cease aspiration. Further, a message (e.g., “Set cartridges with white ink”) to prompt the user to set the first ink cartridges  31  containing white ink in the predetermined set position is presented on the screen of the display  30 . 
     In S 46 , it is examined as to whether the first ink cartridges  31  are placed back in the predetermined set position in the inkjet printer  1 . When the first ink cartridge  31  being set in the predetermined set position is detected (S 46 : YES), in S 47 , a message (e.g., “Reloading . . . ”) to indicate that the ink is reloaded in the ink conveyer tubes  34  is presented in the display  30 . Further, the ink is reloaded in the ink conveyer tubes  34 . More specifically, the first inkjet heads  21  are moved to a predetermined maintenance position, in which the nozzle surfaces of the first inkjet heads  21  are covered with the caps  45  and the ink is drawn from the first ink cartridges  31 . 
     In this regard, when the ink conveyer tubes  34  and the first inkjet heads  21  are reloaded, an amount of the ink to be aspirated is smaller than an amount of the ink loaded in the ink conveyer tubes  34  for the first time. More specifically, in S 48 , it is examined as to whether the first maintenance motor  41  has rotated for a predetermined number of times, which is smaller than a number of times of rotation for the first maintenance motor  41  to initially load the ink. When the number of times of rotation reached to the predetermined number (S 48 : YES), in S 49 , the first maintenance motor  41  is stopped to cease aspiration. Further, the caps  45  are removed from the nozzle surfaces. In  50 , the nozzle surfaces are wiped, the ink is flushed out of the nozzle surfaces, and the nozzle surfaces are covered with the caps  45 . In S 51 , a message (e.g., “Ready”) to indicate that the inkjet printer  1  is ready for a printing operation is presented in the screen of the display  30 . In this regard, predetermined sound to indicate the completion of the ink reloading can be generated optionally. The operation is terminated thereafter. 
     According to the above operation, the ink remaining in the ink conveyer tubes  34  can be removed to clean the ink conveyer tubes  34 . The ink collected in the first ink cartridges  31  can be reloaded in the ink conveyer tubes  34  and the first inkjet heads  21  to be used. Thus, the inkjet printer  1  can be operated with the ink conveyer tubes  34  and the first inkjet heads  21  in a cleaned condition. 
     Next, an ink stirring operation in the inkjet printer  1  according to the present embodiment will be described with reference to  FIGS. 13A ,  13 B, and  14 . 
       FIGS. 13A and 13B  are diagrams to illustrate an ink stirring operation to be executed in the inkjet printer  1  according to the embodiment of the present invention.  FIG. 14  is a flowchart to illustrate the ink stirring operation to be executed in the inkjet printer  1  according to the embodiment of the present invention. 
     When the operation indicator panel  28  presents the screen shown in  FIG. 7B , and the user operates the cursor (down) key  29   e  to select a menu option “Ink Reloading,” as shown in  FIG. 13A , the “Ink Reloading” option is selected, and a screen presenting a submenu as shown in  FIG. 13B  is presented. When the OK key  29   f  is operated with the cursor on “Mixing” option, the stirring operation is started. 
     The stirring operation will be described with reference to  FIG. 14 . When the stirring operation starts, in S 60 , it is examined as to whether an error condition is detected in the inkjet printer  1 . When an error condition is detected (S 60 : YES), in S 73 , the error indicator  30   b  is activated, and information to indicate the ink reloading is inexecutable is provided to the user. More specifically, the error indicator lamp is lit, and/or an error indicating sound is generated. Thereafter, the operation is terminated. 
     In S 60 , if no error condition is detected (S 60 : NO), in S 61 , it is examined as to whether the first ink cartridges  31  are placed in the predetermined set position in the inkjet printer  1 . When the first ink cartridges  31  being set in the predetermined set position is detected (S 61 : YES), in S 62 , a message (e.g., “Reloading . . . ”) to indicate that the ink is reloaded in the ink conveyer tubes  34  is presented in the display  30 . Further, the ink is reloaded in the ink conveyer tubes  34 . More specifically, the first inkjet heads  21  are moved to a predetermined maintenance position, in which the nozzle surfaces of the first inkjet heads  21  are covered with the caps  45  and the ink is drawn from the first ink cartridges  31 . 
     In this regard, the amount of the ink to be aspirated is smaller than the amount of the ink loaded in the ink conveyer tubes  34  for the first time so that an amount of the ink to be wasted is reduced. 
     Therefore, in S 63 , it is examined as to whether the first maintenance motor  41  has rotated for the predetermined number of times, which is smaller than the number of times of rotation for the first maintenance motor  41  to initially load the ink. When the number of times of rotation reached to the predetermined number (S 63 : YES), the first maintenance motor  41  is stopped to cease aspiration. Thus, the ink conveyer tubes  34 , from which the remaining ink has been once withdrawn, are reloaded. 
     In the stirring operation, next, the ink reloaded in the ink conveyer tubes  34  is once again withdrawn. More specifically, in S 64 , a message (e.g., “Unloading ink from the nozzles.”) to indicate the ink is to be withdrawn is presented in the display  30 . In S 65 , the air release valve  44  is switched to release the air flow in between the first inkjet heads  21  and the first ink cartridges  31  in the ink conveyer tubes  34 . In S 66 , a message (e.g., “Unloading . . . ”) to indicate that the ink is being withdrawn is presented in the display  30 . In S 67 , it is examined as to whether the predetermined time period, which is substantially long to withdraw the remaining ink from the ink conveyer tubes  34 , has elapsed. When the predetermined time period elapses (S 67 : YES), in S 68 , the air release valve  44  is switched to shut down the air flow in the ink conveyer tubes  34 . Thus, the recollecting operation of the ink is terminated. 
     In the stirring operation according to the present embodiment, the ink reloading operation (S 61 -S 63 ) and the ink recollecting operation (S 64 -S 68 ) are repeated for a predetermined times (e.g., three times). Therefore, in S 69 , it is examined as to whether the above steps (S 61 - 64 ) have been repeated for three times. If the steps S 61 - 64  have not been repeated for three times (S 69 : NO), the process returns to S 61  to repeat the steps S 61 -S 64 . When the steps S 61 -S 64  have been repeated for three times (S 69 : YES), the process proceeds to S 70 , which corresponds to the operation in the steps S 40 -S 48  in the cleaning and ink reloading operation shown in  FIG. 12 . It is to be noted that the predetermined times for the ink reloading operation and the ink recollecting operation are repeated is not limited to three, but may be twice, or four times or more. 
     When the cleaning and ink reloading operation is completed, in S 71 , the nozzle surfaces of the inkjet heads  21  are wiped, the ink is flushed out of the nozzle surfaces, and the nozzle surfaces are covered with the caps  45 . In S 72 , a message (e.g., “Ready”) to indicate that the inkjet printer  1  is ready for a printing operation is presented in the screen of the display  30 . In this regard, predetermined sound to indicate the completion of the ink reloading can be generated optionally. The stirring operation is terminated thereafter. 
     According to the stirring operation as described above, the ink is reloaded and withdrawn repeatedly in the ink conveyer tubes  34 ; therefore, the white ink in the first inkjet heads  21  and the ink conveyer tubes  34  can be stirred. Accordingly, uneven concentration of the colorant in the white ink can be prevented from occurring, and concentration gradient of the white ink within the ink conveyer tubes  34  and the first inkjet heads  21  can be sustained to be smaller. 
     Although an example of carrying out the invention has been described, those skilled in the art will appreciate that there are numerous variations and permutations of the printing apparatus that fall within the spirit and scope of the invention as set forth in the appended claims. It is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or act described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims. 
     For example, the air release valve  44  may not necessarily be an electromagnetic valve, but may be a manually-operable valve.  FIG. 15A  illustrates manually-operable valves  44 a provided in the ink conveyer tubes  34 .  FIG. 15B  is an enlarged view of one of the manually-operable valves  44   a . As shown in  FIG. 15B , the manually-operable valve  44   a  is provided with joint portions  44   c  and a knob  44   b  which can be rotated manually. When the knob  44   b  is in an orientation perpendicular to the ink conveyer tube  34 , as shown in  FIG. 15B , the valve  44   a  is closed to shut down the air flow in the ink conveyer tube  34 . When the knob  44   b  is turned by the user to orient in parallel with the ink conveyer tube  34 , the valve  44   a  is open so that the air in the ink conveyer tube  34  is released to flow. Accordingly, the ink remaining in the ink conveyer tube  34  is withdrawn in the first ink cartridge  31 . The user is required to turn the knobs  44   b  in the orientation shown in  FIG. 15B  after a predetermined time period to shut down the air flow in the ink conveyer tubes  34 . When the ink reloading operation is conducted, the user is required to confirm that the manually-operable valves  44   a  are in the releasing orientation prior to aspiration of the ink. 
     Thus, according to the manually-operable valves  44   a , the ink remaining in the ink conveyer tubes  34  can be collected, and the ink conveyer tubes  34  can be reloaded with the ink without electricity or other larger-volumed equipment. 
     For another example, a descendible structure, which is for example configured with segmented arms to lower the position of the first ink cartridges  31 , may be provided to the inkjet printer  1 .  FIGS. 16A and 16B  are diagrams to illustrate a descendible mechanism  50  in the inkjet printer  1  according to the embodiment of the present invention. When the inkjet printer  1  is in a normal printing operation, an ink cartridge container  31   a  containing the first ink cartridges  31  is in an uplifted position with the segmented arms extended as shown in  FIG. 16A . When the ink remaining in the ink conveyer tubes  34  is collected, the segmented arms are folded to descend the position of the position of the ink cartridge container  31  a in a lower position as shown in  FIG. 16B . 
     According to the descending movement of the first ink cartridges  31 , the water head difference in the ink conveyer tubes  34  is enlarged so that the ink can be collected in a shorter period of time. The descendible mechanism  50  may be manually or electrically driven. 
     In addition to the air release valve  44  in the ink conveyer tubes  34  for white ink, air release valves in a similar configuration can be provided to the ink conveyer tubes  35  for the CMYK inks. Optionally or alternatively, a descendible mechanism similar to the descendible mechanism  50  can be provided to the second ink cartridges  32  for the CMYK inks. 
     Further, it is to be noted that the fluid releasing mechanism may be provided to other ink conveyer tubes to convey ink other than white ink, containing solid component which may be deposited in the ink, to prevent concentration gradient.