Patent Publication Number: US-7901061-B2

Title: Liquid discharge device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Patent Application No. 2006-181778, filed on Jun. 30, 2006, the contents of which are hereby incorporated by reference into the present application. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to liquid discharge device that discharges liquid from a main tank to a sub tank that is arranged on a carriage. 
     2. Description of the Related Art 
     Ink jet printers having a so-called stationary supply mechanism are known. With the stationary supply mechanism, a sub tank that is capable of storing small amount of ink is arranged on a carriage. A print head used to print on the printing medium is also arranged on the carriage. Ink is supplied to the print head from the sub tank. A main tank that is capable of storing a large amount of ink is attached to a position separate from the carriage. The carriage is capable of moving. The movement of the carriage can be controlled easier with lighter load burdened onto the carriage. The sub tank and the main tank are separated in order to lighten the carriage load. 
     When the carriage moves to an ink supply position, the sub tank and the main tank are temporarily connected with a supply nozzle. The supply nozzle is inserted into the sub tank via a connecting position arranged on the sub tank, and the ink inside the main tank is replenished to the sub tank via the supply nozzle. The aforementioned configuration of the so-called stationary supply mechanism is disclosed in the Japanese Patent Application Publication No. 2001-162830. 
     In the aforementioned publication, a cover that can be rotated is arranged on the connecting position of the sub tank by using a spring. The supply nozzle is able to push the cover towards its opening direction, and be inserted into the sub tank. After the ink is replenished, as the supply nozzle is withdrawn from the sub tank, the cover is rotated towards its closing direction by the force of the spring. 
     Furthermore, a technique to connect the supply nozzle by arranging a rubber at the connecting position is taught in the U.S. Pat. No. 6,880,925. In the aforementioned publication, a joint rubber with a cleavage at its center is arranged on a print head. The ink tank, on the other hand, has a supply nozzle to supply ink to the print head. In the course of connecting the supply nozzle to the print head, the supply nozzle is inserted into the cleavage of the joint rubber. The elasticity of the joint rubber maintains the sealing of the print head, even in the course of inserting and withdrawing the supply nozzle. 
     BRIEF SUMMARY OF THE INVENTION 
     With the above-mentioned configurations, however, the construction of the connecting position may be degraded by the process of repeatedly inserting and withdrawing the supply nozzle. If the connecting portion of the sub tank is damaged, broken particles from the construction of the connecting position may be transferred into the sub tank in the course of connecting the supply nozzle to the sub tank. Such foreign substances give rise to undesirable conditions such as clogging of filter inside the sub tank, which often consequently blocks discharge from the print head. 
     Furthermore, the construction of the connecting position of the sub tank may be fatigued due to the repetition of the process of inserting and withdrawing the supply nozzle. For example, the spring that is supporting the cover towards the closing direction may be broken or fatigued, or the rubber may be torn and the cleavage thereof may be enlarged, due to the repetitive insertion of the supply nozzle. If such conditions occur, the sealing of the connecting position may be loosened. If the sealing of the connecting position is demeaned, the ink inside the sub tank may be exposed to air, and the viscosity of ink is increased from drying. Such undesirable condition also gives rise to clogging of filter inside the sub tank and blocking of discharge from the print head, and the like. 
     The present specification discloses a technique that is capable of inhibiting undesirable phenomenon from occurring by repeatedly inserting the supply nozzle into the sub tank. 
     A liquid discharge device disclosed in the present specification includes a casing, a carriage, a discharge head, a sub tank, a supply nozzle, and a moving device. The casing has a space for housing a main tank. The carriage is capable of moving. The discharge head is arranged on the carriage. The sub tank is also arranged on the carriage. The sub tank communicates with the discharge head. The supply nozzle is to be communicated with the main tank. The moving device is capable of moving the supply nozzle with respect to the carriage such that the supply nozzle pierces through a first position of the sub tank and is inserted into the sub tank. Furthermore, the moving device is capable of moving the supply nozzle with respect to the carriage such that the supply nozzle pierces through a second position of the sub tank and is inserted into the sub tank, and the second position is a different position from the first position. 
     With the aforementioned configuration, the moving device is capable of changing a piercing position of the supply nozzle with respect to the sub tank. Such configuration may inhibit undesirable phenomenon from occurring at the piercing position of the sub tank. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic plan view of an ink jet printer utilizing an ink supply device. 
         FIG. 2A  shows a schematic view of a sub tank and a supply nozzle connected at a first position, and  FIG. 2B  shows a schematic view of the sub tank and the supply nozzle connected at a second position. 
         FIG. 3A  shows a schematic view of the sub tank and the supply nozzle disconnected at the first position, and  FIG. 3B  shows a schematic view of the sub tank and the supply nozzle disconnected at the second position. 
         FIG. 4A  shows a schematic view of the supply nozzle and the carriage in the printing area, and  FIG. 4B  shows a schematic view of the supply nozzle and the carriage in the printing area. 
         FIG. 5  shows a schematic view of the ink supply device performing a preliminary discharge. 
         FIG. 6A  shows a schematic view of the ink supply device replenishing ink to the sub tank at the first position, and  FIG. 6B  shows a schematic view of the ink supply device replenishing ink to the sub tank at the second position. 
         FIG. 7  shows a schematic view of the electrical system of the ink jet printer. 
         FIG. 8A  and  FIG. 8B  show a flow chart of a replenishing process. 
         FIG. 9  shows a variant of the ink supply device. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a schematic plan view of an ink jet printer  100  utilizing an ink supply device  200 . The ink jet printer  100  has a casing  62  that houses the ink supply device  200 , which comprises the components as described below. 
     Within the casing  62 , the ink supply device  200  has a print head  1 , which is of an ink jet type. The print head  1  utilizes piezoelectric elements or thermoelectric elements to discharge ink drops onto the printing medium  2  that is fed underneath the print head  1 . An image is printed on the printing medium  2 , such as a paper, in accordance with data input to the ink jet printer  100 . 
     The print head  1  is mounted onto a carriage  4 . The carriage  4  is moved using a carriage driving mechanism  6 . The carriage driving mechanism  6  includes a timing belt  10  that is arranged along a guide member  8 . The timing belt  10  is connected to the carriage  4 , and is driven by a motor  12  arranged on the guide member  8 . The driving force of the motor  12  is exerted on the timing belt  10 , and rotates the timing belt  10 . The carriage  4  can thus be moved back and forth along the guide member  8 . Moreover, a sub tank  30  is also mounted on the carriage  4  with the print head  1 . The sub tank  30  stores ink inside, and provides the ink to the print head  1 . 
     The printing medium  2  is fed by a paper feeding mechanism  14  in a perpendicular direction to the moving direction of the carriage  4 . The paper feeding mechanism  14  includes roller shafts  16 ,  18  that are arranged parallel to the guide member  8 . Two pairs of supply rollers  20 ,  21  and  22 ,  23  are arranged on the roller shafts  16 ,  18  in such a manner that the printing medium  2  can be caught and fed between the supply rollers  20  and  21 , and also between the supply rollers  22  and  23 . In the course of sending the printing medium  2  through the paper feeding mechanism  14 , the roller shafts  16 ,  18  are rotated by a feeding motor  24 . 
     The carriage  4  is moved by the carriage driving mechanism  6  in its moving direction, through a flushing area, a printing area, and an ink supply area. The flushing area and the ink supply area are arranged on either side of the printing area which is an area the printing medium  2  occupies during the printing process. When the carriage  4  is in the flushing area or the ink supply area, the print head I is also outside the printing area. Even when ink is discharged within the flushing area or the ink supply area, the printing medium  2  is not within the marking range of the ink. When the carriage  4  is moved into the flushing area, a compulsory flushing of ink from the print head  1  is processed. 
     When data to process printing is input to the ink jet printer  100  and printing process is performed, the carriage  4  moves within the printing area. The carriage  4  is at its printing position during printing, and the print head  1  discharges ink onto the printing medium  2  in accordance with the printing data. The carriage  4  moves to the ink supply area when replenishing ink to the sub tank  30  and also when the ink jet printer  100  is not performing printing process. 
     In the ink supply area, a cap  26  is arranged. The cap  26  covers discharge nozzles (not shown in the figures) of the print head  1 , to prevent the ink inside the print head  1  from drying when the carriage  4  is in the ink supply area. The cap  26  can be moved by a moving mechanism, not shown in the figures, between a sealing position and a stand-by position. The cap  26  covers the discharge nozzles in the sealing position, and when the cap  26  is retracted lower with respect to the print head  1  to the stand-by position, it is separated from the print head  1 . 
     In the ink supply area, a main tank  32  is detachably housed in the casing  62 . The main tank  32  is houses separately from the sub tank  30 . The main tank  32  is communicated with a supply nozzle  34  when it is set at a predetermined position within the casing  62 . When the carriage  4  moves into the ink supply area and stops at a predetermined ink supply position, sub tank  30  and the main tank  32  are temporarily connected, and the ink inside the main tank  32  is replenished to the sub tank  30  via the supply nozzle  34 . 
     In the ink supply area, a foam  48  is also arranged under the supply nozzle  34 . The foam  48  is arranged at a position where the ink discharged from the supply nozzle  34  drips. In the case when the cap  26  is in its stand-by position and the carriage  4  is not within the ink supply area, the ink discharged from supply nozzle  34  falls onto the foam  48  placed below. 
       FIG. 2A  shows a schematic view of the sub tank  30  and the supply nozzle  34  connected at a first position  102 , and  FIG. 2B  shows a schematic view of the sub tank  30  and the supply nozzle  34  connected at a second position  104 .  FIG. 3A  shows a schematic view of the sub tank  30  and the supply nozzle  34  disconnected at the first position  102 , and  FIG. 3B  shows a schematic view of the sub tank  30  and the supply nozzle  34  disconnected at the second position  104 .  FIG. 4A  shows a schematic view of the supply nozzle  34  and the carriage  4  in the printing area, and  FIG. 4B  shows a schematic view of the supply nozzle  34  and the carriage  4  in the printing area.  FIG. 5  shows a schematic view of the ink supply device  200  performing a preliminary discharge.  FIG. 6A  shows a schematic view of the ink supply device  200  replenishing ink to the sub tank  30  at the first position  102 , and  FIG. 6B  shows a schematic view of the ink supply device  200  replenishing ink to the sub tank  30  at the second position  104 . The print head  1  and sub tank  30  in  FIGS. 4A and 4B  are shown with dotted lines, to accentuate that the carriage  4  is in the printing area in  FIGS. 4A and 4B . 
     As shown in  FIGS. 2A and 2B , in the present embodiment, a connecting mechanism  36  and a connecting position adjusting mechanism  41  are arranged to move the supply nozzle  34  and the main tank  32  so that the supply nozzle  34  pierces through one of the connecting position among the first position  102  and the second position  104 , and is inserted into the sub tank  30 . The connecting positions, the first position  102  and the second position  104 , are located at different positions. The connecting mechanism  36  and the connecting position adjusting mechanism  41  are capable of changing the connecting position of the supply nozzle  34  and the sub tank  30 , from the first position  102  to the second position  104 , or from the second position  104  to the first position  102 . 
     The connecting mechanism  36  is driven by a motor  38 , and moves the supply nozzle  34  and the main tank  32  in the up and down direction, that is, the direction orthogonal to the printing surface of the printing medium  2 . As shown in  FIGS. 2A ,  2 B and  FIGS. 6A ,  6 B, with the aforementioned connecting mechanism  36 , the supply nozzle  34  is moved downward. With the carriage  4  at the ink supply position, the supply nozzle pierces through a connecting member  39  at one of the aforementioned connecting positions. 
     The connecting position adjusting mechanism  41 , on the other hand, is driven by a motor  43  and moves the supply nozzle  34  and the main tank  32  parallel to the surface of the connecting member  39 ; that is, in the left and right direction shown with arrow in  FIGS. 3A and 3B . The position of which the supply nozzle  34  pierces through the seal member  40  is adjusted by the connecting position adjusting mechanism  41 . For example, when the connecting position adjusting mechanism  41  moves the main tank  32  and the supply nozzle  34  from the position shown in  FIG. 3A  to the position shown in  FIG. 3B , the connecting position where the supply nozzle  34  pierces the connecting member  39  is adjusted from the first position  102  as shown in  FIG. 2A  to the second position  104  as shown in  FIG. 2B . 
     The connecting member  39  is arranged on a main body  31  of the sub tank  30 . The connecting member  39  has a connecting hole (not shown in the figures) and a seal member  40 . The connecting hole is formed on the main body  31  of the sub tank  30 . The seal member  40  is made of elastomeric material. It may also be made of other elastic materials. The seal member  40  is arranged to cover the connecting hole. The seal member  40  is detachably coupled to the main body  31  of the sub tank  30 , for example, using a double-sided adhesive tape. The first position  102  and the second position  104 , through which the supply nozzle  34  pierces, are located on the seal member  40 . 
     When the carriage  4  is at the ink supply position within the ink supply area, the supply nozzle  34  can be lowered so as to pierce through one of the aforementioned connecting positions on the seal member  40  and into the connecting hole by the connecting mechanism  36  and the connecting position adjusting mechanism  41 . As a result of the lowering movement, the supply nozzle  34  is pierced through one of the connecting positions, thus the supply nozzle  34  and the sub tank  30  are connected. In  FIG. 2A , for example, the supply nozzle  34  is inserted into the sub tank  30  by piercing through the seal member  40  at the first position  102 . 
     Furthermore, in the case shown in  FIG. 2A , by moving the supply nozzle  34  in the upward direction using the connecting mechanism  36 , the supply nozzle  34  is pulled out from the seal member  40 . As shown in  FIG. 3A , the supply nozzle  34  and the sub tank  30  are disconnected at the first position  102 , while, simultaneously, a hole formed at the first position  102  by the supply nozzle  34  is clogged by the restoration force of the elastomeric material. As a result, the sub tank  30  is sealed, and the transfer of dust therethrough and the drying of ink are prevented. 
     The connecting hole (not shown) and the seal member  40  are formed large enough for the supply nozzle  34  to be inserted at at least two different positions, that is, the first position  102  and the second position  104  in this embodiment. The connecting hole can consist of one large hole, or a hole elongated in the left-right direction in  FIG. 3 , and the seal member  40  can be formed large enough to cover such hole. Furthermore, a plurality of connecting holes and a plurality of seal members  40  can be arranged on the sub tank  30 , where each seal member  40  covers the corresponding connecting hole. In such case, the first position  102  and the second position  104  may or may not be located within the same sealing member  40 , provided that the first position  102  and the second position  104  are located at different positions. Furthermore, the supply nozzle  34  may also pierce through the seal member  40  at positions other than the aforementioned positions. 
     In the present embodiment, the connecting mechanism  36  moves the main tank  32  and the supply nozzle  34  in the up and down direction to connect or disconnect the supply nozzle  34  and the sub tank  30 . However, the connecting mechanism  36  is not restricted to such construction. For example, the main tank  32  and the supply nozzle  34  can be connected by an elastic tube or the like, and the connecting mechanism  36  may only move the supply nozzle  34 . Moreover, the connecting mechanism  36  may move the supply nozzles  34  in a rotating direction rather than in a straight direction. In this case, the supply nozzle  34  can be swung around a shaft pin arranged at its rotating center to connect and disconnect with the sub tank  30 . Furthermore, the supply nozzle  34  can be moved in a horizontal direction or the left-right direction, or in an angled direction. In all of the aforementioned cases, the connecting mechanism  36  is able to connect and disconnect the supply nozzle  34  and the sub tank  30 . 
     In the present embodiment, the connecting position adjusting mechanism  41  moves the main tank  32  and the supply nozzle  34  in a direction parallel to the surface of the connecting member  39  to determine the connecting position. However, the configuration of the connecting position adjusting mechanism  41  is not restricted to the above. The direction in which the connecting position adjusting mechanism  41  moves the main tank  32  and the supply nozzle  34  is determined in accordance with the form of the seal member  40 . If the seal member  40  is elongated in the moving direction of the carriage  4 , the connecting position adjusting mechanism  41  may move the main tank  32  and the supply nozzle  34  in the corresponding direction to adjust the position which the supply nozzle  34  pierces, so that the sub tank  30  and the supply nozzle  34  can be connected at different positions. Furthermore, the connecting position adjusting mechanism  41  may move the supply nozzle  34  solely without moving the main tank  32 . 
     Furthermore, a pump mechanism  42  is arranged to supply energy to the ink inside the main tank  32 . The pump mechanism  42  includes a filter  44 , and a pump  46 . The pump mechanism  42  draws in air through the filter  44 , which is compressed and driven into the main tank  32  by the pump  46 . When the compressed air is pumped into the main tank  32 , according amount of ink stored inside the main tank  32  are discharged from the supply nozzle  34 . The pump mechanism  42  is not restricted to the aforementioned construction. For example, a pump may be arranged at the ink passage between the main tank  32  and the supply nozzle  34 , and compress the ink thereof. Furthermore, the device that supplies energy to the ink inside the main tank  32  may include constructions other than the pump mechanism  42 . 
     The sub tank  30  and the main tank  32  may each distinctively store ink of plurality of colors: cyan, yellow, magenta, and black. The tanks of the aforementioned colors of ink may be formed as one component, or the colored ink may be stored in separate tanks. In the present embodiment, one set of the supply nozzle  34  and the pump mechanism  42  is arranged for each of the colored ink. The connecting mechanism  36  and the connecting position adjusting mechanism  41  may move the sets for the aforementioned four types of colored ink simultaneously in the same direction. Furthermore, the aforementioned sets may also be moved separately. 
       FIG. 7  shows a schematic view of the electrical system of the ink jet printer  100 . As shown in  FIG. 7 , the aforementioned print head  1 , carriage driving mechanism  6 , paper feeding mechanism  14 , connecting mechanism  36 , connecting position adjusting mechanism  41 , pump mechanism  42 , and a counter  45  are connected to a controller  50 . The controller  50  includes a CPU  52 , a ROM  54  and a RAM  56  as the main components of the logic operation circuit. The aforementioned components of the logic operation circuit are connected to an input/output circuit  58  via a common bus  60 . The input/output circuit  58  inputs signal from and outputs signal to the exterior mechanisms connected thereof. The CPU  52  controls the print head  1 , carriage driving mechanism  6  and paper feeding mechanism  14  via the input/output circuit  58  so that the carriage  4  is moved back and forth in the moving direction while the print head  1  discharges ink onto the printing medium  2  that is fed into the printing area. Furthermore, the CPU  52  controls the carriage driving mechanism  6 , the connecting mechanism  36 , the connecting position adjusting mechanism  41 , the pump mechanism  42 , and the counter  45  in order to replenish ink to the sub tank  30 . These controls are operated according to the data and control program stored in the ROM  54  and RAM  56 . 
       FIGS. 8A and 8B  show flow chart of the replenishing process. As shown in  FIG. 8A , when the replenishing process is carried out, whether or not a printing signal has been input is determined (S 100 ). If the printing signal is not input (“NO” in S 100 ), the controller  50  maintains the stand-by status until such signal is input. In the present embodiment, during the stand-by status, the carriage  4  is at its ink supply position within the ink supply area, and the cap  26  is at the sealing position and as such sealing the discharge nozzles of the print head  1 . Furthermore, the sub tank  30  and the supply nozzle  34  are connected at the first position  102  during the stand-by status (see  FIG. 2A ). With such a configuration, the adhesion of impurities such as dust and drying of ink within the supply nozzle  34  is prevented. 
     When the printing signal is input (“YES” in S 100 ), the connecting mechanism  36  is controlled so that the main tank  30  and the supply nozzle  34  are moved upward, and the supply nozzle  34  and the sub tank  30  are disconnected at the first position  102  as shown in  FIG. 3A  (S 110 ). Along with the above-mentioned disconnection, the cap  26  is moved from the sealing position to the stand-by position. 
     Then, as shown in  FIG. 4A , the print head  1 , carriage driving mechanism  6  and paper feeding mechanism  14  are controlled so that the carriage  4  is moved to the printing area to begin the printing process (S 120 ). In accordance with the printing data, the carriage  4  moves back and forth as ink is discharged from the print head  1 , while the printing medium  2  is fed through the printing area. 
     Then, during printing, whether or not the sub tank  30  needs ink replenishment is determined (S 130 ). This determination can be done, for example, based on the data detected by an ink remainder sensor (not shown in the figures) arranged on the sub tank  30 . The ink remainder sensor detects the amount of ink remaining inside the sub tank  30 . The remaining amount of ink can also be calculated from the ink consumption according to the printing data. In this step, it is determined whether the amount of ink inside the sub tank  30  is less than the predetermined limit amount, and if replenishment of ink is necessary. At the beginning of the printing process, for example, there is plenty of ink inside each of the sub tank  30 , so it will be determined that replenishment of ink is unnecessary (“NO” in S 130 ). 
     Then, it is determined whether or not the printing data has been completely printed and the printing has been completed (S 240 ). If printing has not been completed (“NO” in S 240 ), steps of S 130 , S 240  and other necessary steps are repeatedly performed, and depending on the determination of the aforementioned steps, other necessary steps as will be described below are performed. 
     If the remaining ink inside the sub tank  30  is less than the predetermined limit, and it was determined that the replenishment of ink is necessary (“YES” in S 130 ) during the process of repeating the steps of S 130  and S 240 , a preliminary ink discharge is executed (S 140 ). In the case where the replenishment has not been carried out for a while during printing, the ink inside the supply nozzle  34  may potentially be dehydrated. Hence, the pump mechanism  42  is controlled so that the pump  46  drives air into the main tank  32 . The air driven into the main tank  32  compels the ink to discharge from the supply nozzle  34 . Thus, impurities that may have adhered inside the supply nozzle  34 , such as the drying ink and dust, are washed off along with the ink liquid that is discharged by the process of step S 140 . In this step, the ink inside the supply nozzle  34  is preliminarily discharged before the supply nozzle  34  is connected to the sub tank  30 . Thus, the transfer of such impurities into the sub tank  30  is prevented. 
     When the process of step S 140  is carried out, the print head  1  and the sub tank  30  are located within the printing area, as shown in  FIGS. 4A and 4B . The above mentioned preliminary discharge from the supply nozzle  34  occurs within the ink supply area, hence the ink drips and impurities (if any) that are discharged by the preliminary ink discharge motion fall onto the foam  48  that is placed under the main tank  32 , and absorbed therein (see  FIG. 5 ). The ink discharged in the preliminary discharge from the supply nozzle  34  will not contaminate the sub tank  30  and the print head  1 . Furthermore, when the print head  1  is processing printing, the cap  26  is in its stand-by position. Therefore, the cap  26  will likewise not be contaminated by the ink discharged in the preliminary ink discharge. It is also possible to strain the ink absorbed by the foam  48  by using filters, and return it to the main tank  32 . 
     Not much ink needs to be discharged in the step S 140 . The amount of ink only needs to be sufficient enough to wash out the impurities that may exist in the distal end of the supply nozzle  34 . 
     While the preliminary discharge of step S 140  is being processed, the printing process is still continuing. Thus, the printing motion of the print head I is temporarily stopped, and the printing process is paused (S 150 ). Then, the carriage driving mechanism  6  is controlled in order to move the carriage  4  to the ink supply position within the ink supply area (S 160 ). 
     Then, it is determined whether the number of times which the supply nozzle  34  and the sub tank  30  has been connected at the connecting position that is presently used is within the predetermined number (S 170 ). If the number of connection made at the first position  102  is within the predetermined number (“YES” in S 170 ), the connecting mechanism  36  is controlled in order to connect the supply nozzle  34  to the sub tank  30  (S 180 ). The motor  38  is driven to move the supply nozzle  34  downward so as to pierce through the first position  102 . In this case, the count value counted by the counter  45  is incremented. 
     On the other hand, if the number of connection made at the first position  102  exceeds the predetermined number (“NO” in S 170 ), there is a substantial possibility that the first position  102  is degraded from the repetitive insertion of the supply nozzle  34 . The first position  102  may be damaged, or fatigued, and further usage thereof may result in undesirable conditions such as contamination of the ink inside the sub tank  30 , clogging of the filters therein, and demeaning of the sealing thereof. 
     Thus, in such case, the connecting position adjusting mechanism  41  is controlled to move the supply nozzle  34  so as to adjust the connecting position of the supply nozzle  34  from the first position  102  to the second position  104  (S 175 ). Then, the supply nozzle  34  is moved so as to pierce through the second position  104  by the control of the connecting mechanism  36  (S 180 ). 
     In the process of step S 175 , the position of which the supply nozzle  34  pierces through the sealing member  40  is changed from the first position  102  to the second position  104 . After processing the step of S 175 , the supply nozzle  34  is inserted into the sealing member  40  at the adjusted connecting position, the second position  104 , which has not yet fatigued nor degraded. Even in the case where the former connecting position (that is, the first position  102  in the present embodiment) is fatigued, or the material of the sealing member  40  therearound is degraded, the transfer of foreign substances therefrom, and the undesirable condition due to such transfer is prevented. Furthermore, the fatigued first position  102  will not be used, so as not to demean the sealing thereof. The sealing of the sealing member  40  is thus maintained, preventing the increase of viscosity of the ink inside the sub tank  30 . 
     In the present embodiment, the supply nozzle  34  and the sealing member  40  are repeatedly connected at the same connecting position (that is, the first position  102  or the second position  104 ) within the predetermined number of connection. However, the connecting position can be adjusted each time the connection is necessary. For example, first position  102  and the second position  104  may be orderly used. As mentioned earlier, the sealing member  40  is detachably coupled to the main body  31  of the sub tank  30 . If the number of times which the supply nozzle  34  and the sub tank  30  has been connected exceeds the predetermined number with both of the positions  102  and  104 , the sealing member  40  can be exchanged to a new one. The whole of the sub tank  30  does not need to be exchanged. 
     After the sub tank  30  and the supply nozzle  34  are connected in the process of step S 180 , the pump mechanism  42  is controlled in order to replenish ink into the sub tank  30  (S 190 ). The pump  46  is driven so that air is driven into the main tank  32 . As shown in  FIG. 6A , the air driven into the main tank  32  forces the ink therein to be discharged from the supply nozzle  34 , and the ink is replenished into the sub tank  30 . 
     Moreover, even in the case where the connecting position of the supply nozzle  34  has been adjusted to the second position  104  by the process of step S 175 , as shown in  FIG. 6B , the air is likewise driven into the main tank  32 , and the ink is replenished to the sub tank  30 . 
     Then, it is determined if the sub tank  30  has been replenished with the necessary amount of ink (S 200 ). If the sub tank  30  has not been replenished sufficiently (“NO” in S 200 ), the process of step S 190  is continued and the pump  46  is driven until the sub tank  30  is replenished with the necessary amount of ink. 
     In the case where a sensor is used to detect the amount of ink inside the sub tank  30 , the above-mentioned determination for step S 200  can be done based on the amount of ink detected by the sensor. Furthermore, the amount of ink replenished into the sub tank  30  is determined by the driving rate of the pump  46 , hence the determination for step S 200  can also be done by detecting the driving rate of the pump  46 . 
     When the sub tank  30  is replenished with the necessary amount of ink (“YES” in S 200 ), the driving of the pump  46  is ceased (S 210 ). Then, the connecting mechanism  36  is controlled in order to drive the motor  38  so that the supply nozzle  34  is moved upward so as to disconnect the supply nozzle  34  from the sub tank (S 220 ). As a result, the supply nozzle  34  is withdrawn from the seal member  40  of the sub tank  30 , as shown in  FIGS. 3A and 3B . 
     Then, the printing process is resumed (S 230 ). The print head  1 , carriage driving mechanism  6  and the paper feeding mechanism  14  are controlled so that the carriage  4  is moved back into the printing area, and ink is discharged from the print head  1  in accordance with the printing data. 
     After the printing process is resumed, the determination of whether or not the printing has completed is carried out (S 240 ). If printing has not completed (“NO” in S 240 ), the processes of step S 130  through step S 240  are repeated. During the repetition of the aforementioned steps, the preliminary ink discharge is carried out if the sub tank  30  needs to be replenished (“YES” in S 130 ). In such a case, the pump  46  is driven in order to discharge ink from the main tank  32 , and washes away the impurities adhering inside the supply nozzles  34  prior to the replenishment process of S 190 . 
     Also during the repetition of the aforementioned steps, the number of times which the supply nozzle  34  and the sub tank  30  has been connected at the connecting position presently used is determined before connecting the supply nozzle  34  with the sub tank  30 . If the number of the connecting times is within the predetermined number (“YES” in S 170 ), it is assumed that the seal member  40  has not been fatigued at the presently used position, and the normal function thereof can be expected. If the number of the connecting times exceeds the predetermined number (“NO” in S 170 ), it is assumed that the seal member  40  has been fatigued, and further usage of the presently used position may result in aforementioned undesirable conditions. The connecting position is thus adjusted so that the supply nozzle  34  can be connected to the sub tank  30  through another position. Then, the printing process is resumed after ink has been replenished. 
     On the other hand, as shown in  FIG. 8B , if it is determined during step S 240  that the printing process is complete (“YES” in S 240 ), the preliminary ink discharge is processed (S 250 ). In the process of preliminary discharge, the pump mechanism  42  is controlled. Air is driven into the main tank  32  by the pump  46 , and the ink from the main tank  32  is preliminarily discharged from the supply nozzle  34 . During the process of step S 250 , the carriage  4  remains within the printing area, and not within the ink supply area. 
     As in the case of step S 140 , before connecting the supply nozzle  34  with the sub tank  30 , the impurities within the supply nozzle  34  are washed out with the preliminary discharge in the process of step S 250 . Hence, the transfer of such impurities into the sub tank  30  can be prevented. The sub tank  30  and the print head  1  will not be contaminated. 
     Then, the carriage driving mechanism  6  is controlled in order to move the carriage  4  to the ink supply position within the ink supply area (S 260 ). Simultaneously, the cap  26  is moved from the stand-by position to the sealing position. 
     The timing of which the preliminary discharge is processed is not restricted to the timing shown in  FIGS. 8A and 8B , as long as it is performed before the carriage  4  moves to the ink supply position. For example, it is also possible to execute the preliminary discharge while the carriage  4  is being moved to the ink supply position. 
     Then, it is determined whether the number of times which the supply nozzle  34  and the sub tank  30  has been connected at the presently used connecting position is within the predetermined number (S 270 ). If the number of connection made is within the predetermined number (“YES” in S 270 ), the connecting mechanism  36  is controlled in order to connect the supply nozzle  34  with the sub tank  30  (S 280 ). For example, if the first position  102  is presently used as the connecting position, the motor  38  is driven to move the supply nozzle  34  downward, and pierce through the first position  102  as shown in  FIG. 2A . In this case, the count value counted by the counter  45  is incremented. 
     On the other hand, if the number of connection made exceeds the predetermined number (“NO” in S 270 ), the connecting position adjusting mechanism  41  is controlled to adjust the connecting position (S 275 ). If the first position  102  is presently used as the connecting position, the motor  43  is driven to move the supply nozzle  34  along the sealing member  40  to a position which the supply nozzle  34  is located above the second position  104  (see  FIG. 3B ). Then, the connecting mechanism  36  is controlled that the supply nozzle pierces through the second position  104 , and be connected to the sub tank  30  (S 280 ). 
     In the process of step S 275 , the position of which the supply nozzle  34  pierces through the sealing member  40  is changed. After processing the step of S 275 , the supply nozzle  34  can be inserted into the sub tank  30  at a connecting position that has not yet fatigued nor degraded. The undesirable condition due to transfer of foreign substances that may occur at the formerly used connecting position is prevented. The sealing of the sealing member  40  thereof is also maintained, preventing the increase of viscosity of the ink inside the sub tank  30 . 
     After the sub tank  30  and the supply nozzle  34  are connected, the pump mechanism  42  is controlled in order to replenish ink to the sub tank  30  (S 290 ). The pump  46  is driven so that air is driven into the main tank  32 . As shown in  FIGS. 6A and 6B , the air driven into the main tank  32  forces the ink therein to be discharged from the supply nozzle  34 , and the sub tank  30  is replenished with ink. 
     Then, it is determined if the sub tank  30  has been replenished with the necessary amount of ink (S 300 ). If the sub tank  30  is not yet replenished sufficiently (“NO” in S 300 ), the process of step S 290  is continued and the pump  46  is driven until the sub tank  30  is replenished with the necessary amount of ink. 
     When the sub tank  30  has been replenished with the necessary amount of ink (“YES” in S 300 ), the driving of the pump  46  is ceased (S 310 ). The controller  50  returns to the process of step S 100 , and again determines if printing signal is input, while the ink jet printer  100  maintains its stand-by status. 
     In the stand-by status until the printing data is input, the supply nozzle  34  is maintained connected with the seal member  40  at the connecting position at which it pierced in the process of S 280 . Thus, the supply nozzle  34  and the sub tank  30  are maintained connected. Such configuration prevents the supply nozzle  34  to be exposed to air. The drying of ink inside the supply nozzle  34  can be effectively prevented during the stand-by status. Then, if printing data is input (“YES” in S 100 ), the whole cycle of steps S 110  to S 310  is repeated. 
     Furthermore, in the present embodiment, the supply nozzle  34  and the sub tank  30  are connected during the stand-by status of the ink jet printer  100 . However, the supply nozzle  34  may be covered by a cap not shown in the figures, so as to be sealed thereof. In such a case, the supply nozzle  34  and the sub tank  30  are disconnected during the stand-by status. 
     Furthermore, in the present embodiment, the connecting position adjusting mechanism  41  moves the supply nozzle  34  to change the connecting position from the first position  102  to the second position  104 . However, the connecting position adjusting mechanism  41  is not restricted to such configuration. The connecting position adjusting mechanism  41  should be able to move the supply nozzle  34  with respect to the carriage  4 , so as to adjust the relative spatial relationship regarding the connecting position of the seal member  40  and the supply nozzle  34 . 
       FIG. 9  shows a variant of the ink jet printer  100 . As shown in  FIG. 9 , the sealing member  40  is arranged so that its lengthwise direction (that is, the direction in which the sealing member is elongated) is parallel to the moving direction of the carriage  4 . The supply nozzle  34  can be moved in the up and down direction (shown with an arrow) by the connecting mechanism  36  to pierce through the seal member  40 . 
     Furthermore, the carriage  4  is capable of stopping at different stopping positions within the ink supply area. For example, if the carriage  4  is stopped at a first stopping position  4   a  shown with dotted line, the supply nozzle  34  and the sub tank  30  are connected at the first position  102 . If the carriage  4  is stopped at a second stopping position  4   b  shown with solid line, the supply nozzle  34  and the sub tank  30  are connected at the second position  104 . Even with such configuration, the sealing member  40  can be used under healthy condition by changing the connecting position in which the supply nozzle  34  is inserted in accordance with the number of times the connection has been made. The transfer of foreign substances into the sub tank  30  can be prevented, and, at the same time, the durability of the sealing member  40  can be efficiently maintained. 
     With the aforementioned configuration, the relative spatial relationship of the supply nozzle  34  and the sealing member is adjusted by the control of the stopping position of the carriage  4 . Moreover, in such case, the carriage driving mechanism  6  functions as the connecting position adjusting mechanism. The construction of the ink jet printer  100  is simplified. 
     In the embodiment as described above, sheets of paper are assumed as the printing medium  2 . However, the printing medium  2  is not restricted to such medium. The printing medium  2  may be a glass substrate, a silicon substrate, resin film, or the like. In such cases, corresponding change in the construction of the paper feeding mechanism  14  is required. Furthermore, the printing medium  2  may have a curved surface, instead of a flat surface as is described in the embodiment above. 
     Moreover, in the embodiment as described above, the present invention is applied to an ink jet printer which discharges ink to print images onto the printing medium  2 . However, the present invention can be adequately applied to other liquid discharge devices that discharges liquids other than ink, for example, reagent liquid, biological solution, electrical wiring material solution, electronic material solution, adhesive solution, resinous liquid for geometric molding, or the like.