Patent Publication Number: US-6905197-B2

Title: Ink supply device, ink-jet recording device, and method of supplying ink

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This patent application is a continuation application of U.S. application Ser. No. 09/981,218, filed Oct. 16, 2001 now U.S. Pat. No. 6,612,689, entitled “INK SUPPLY DEVICE, INK-JET RECORDING DEVICE, AND METHOD OF SUPPLYING INK”, herein incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an ink supply device that supplies ink into a sub ink tank of a recording head unit, an ink-jet recording device having the ink supply device, and a method of supplying ink. 
     2. Description of the Related Art 
     In the ink-jet recording device that ejects ink drops on a recording medium such as a paper from recording heads on the basis of image information and records the image, there is such a configuration that mounts the sub ink tanks corresponding to each of the recording heads on a carriage to make the recording heads scan, in which there are various types of proposals as to the supply of ink into the sub ink tanks. 
     For example, Japanese Published Unexamined Patent Application No. Hei 6-238911 discloses an ink-jet printer as shown in  FIG. 18 , in which an ink tank  314  is disposed on one end of the shifting range of a recording head  312 . The ink tank  314  has an ink supply outlet  318  formed at a position corresponding to an ink supply inlet  316  of the recording head  312 , and has a bellow portion  320  formed on the middle thereof. And, as the recording head  312  returns to the home position, the ink supply inlet  316  of the recording head  312  is connected with the ink supply outlet  318  of the ink tank  314 , and the recording head  312  is pressed to the ink tank  314  by a drive force of a drive motor not illustrated; thus, the bellow portion  320  of the ink tank  314  shrinks by this pressing force. Accordingly, the content volume of the ink tank  314  varies, and the ink inside the ink tank  314  flows into a common liquid chamber by way of the ink supply outlet  318  and the ink supply inlet  316 . The ink tank  314  that once shrank recovers the original volume by the recording head  312  shifting and releasing the pressure, and by a self-restoring force of the bellow portion  320 . AT this moment, a check valve  322  provided with the ink tank  314  opens, and the air equivalent to the volume of ink supplied into the recording head  312  flows into the ink tank  314  from an air intake  324 . 
     However, in the construction in which the supply of ink is carried out by such pressurization, the supply of ink can take a comparably long time in some cases, which sometime lowers the efficiency of the ink supply. 
     In contrast to this, as shown in FIG.  19  and  FIG. 20 , the Japanese Published Unexamined Patent Application No. Hei 11-240180 discloses an ink-jet recording device that includes a first tank  354  provided with a recording head  352  and a second tank  356  to supply ink into the first tank  354 . A switching hole  362  on a partition wall  360  that separates an ink chamber  358  of the first tank  354  from the recording head  352  can be opened and closed by a check valve  364 ; and as a differential pressure is produced, the switching hole  362  is to open. Supply of ink into the ink chamber  358  needs to couple a suction hole  366  with a suction cap  368 , and thereafter drive a supply pump  370 , thus decompressing the first tank  354 . Next, a rubber seal  372  is made to advance by driving a reversible motor, and a needle  374  projected on the first tank  354  is inserted into the rubber seal  372 , whereby the first tank  354  is connected with the second tank  356 . Since the first tank  354  is in decompression, the ink is supplied from the second tank  356  into the first tank  354  by way of a tube  376 . 
     However, in this construction, since the first tank  354  is not made to communicate with the atmosphere, the check valve  364  is required in order to prevent an ink leakage or air suction through a nozzle  378 , due to a variation of the inner pressure, thereby making the structure complicated. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in view of the above circumstances, and provides an ink supply device that permits supply of ink securely with a simple construction into a sub ink tank having an air communication hole, a method of supplying ink, and an ink-jet recording device provided with the ink supply device. 
     According to one aspect of the invention, the ink supply device possesses an ink supply unit provided in correspondence with a recording head unit including a recording head that ejects ink drops onto a recording medium on the basis of image information, and a sub ink tank provided with an air communication hole, storing the ink supplied to the recording head, which implements ink supply by a pressure reduction part reducing a pressure inside the sub ink tank; and a sealing part that at least permits sealing of the air communication hole while the ink supply unit is reducing the pressure inside the sub ink tank. 
     According to this invention, the sub ink tank that the ink is supplied into is provided with the air communication hole. This air communication hole softens a surge pressure variation inside the sub ink tank, accompanied with ejection&#39;s of ink and/or environmental changes, and so forth, and prevents an unexpected ink leakage from the sub ink tank and a mixture of air (air suction from an ink discharging nozzle of the recording head, and creation of air bubbles inside the sub ink tank). Thus, the recording head maintains an optimum state for discharge of ink drops. 
     Also, since the ink supply device has the sealing part, at least the device is able to seal the air communication hole of the sub ink tank, while the ink supply unit is reducing the pressure inside the sub ink tank. In the sealing state, as the pressure reduction part reduces the pressure inside the sub ink tank, the air does not flow unexpectedly into the sub ink tank, and the ink flows securely into the sub ink tank, thus achieving a smooth ink supply. 
     In addition, the ink supply is carried out not by the pressurization but by the decompression inside the sub ink tank; and the ink supply can securely be carried out in a shorter time. 
     According to another aspect of the invention, the ink supply device further includes a displacement mechanism that displaces the ink supply unit in relation to the sub ink tank between a non-supply position where the ink is not supplied and a supply position where the ink is supplied, wherein the sealing part is provided with the ink supply unit, and it carries out sealing of the air communication hole, based on a displacement from the non-supply position to the supply position by the displacement mechanism. 
     That is, the ink supply unit is displaced by the displacement mechanism from the non-supply position to the supply position in relation to the sub ink tank. The ink supply unit is designed to supply ink into the sub ink tank at the supply position, where the ink is supplied into the sub ink tank. 
     As the ink supply unit displaces from the non-supply position to the supply position, by this displacement, the sealing part seals the air communication hole. In this manner, the utilization of the displacement of the ink supply unit simplifies the construction, and also secures the sealing of the air communication hole, interlocking with the ink supply operation into the sub ink tank. 
     Further, the sealing part is provided integrally with the ink supply unit. 
     Thereby, the ink supply device reduces the number of components, simplifies its construction to diminish the size, and reduces the manufacturing cost. 
     According to another aspect of the invention, the ink supply unit is provided with an air suction member and an ink supply member that are connected to the sub ink tank, and the sealing part is made to seal the air communication hole, after the air suction member and the ink supply member are connected to the sub ink tank. 
     Therefore, after the air suction member and the ink supply member are connected to the sub ink tank, the sealing part seals the air communication hole. In this state, as the air suction member sucks the air inside the sub ink tank, the ink flows into the sub ink tank from the ink supply member, resulting in supplying ink. 
     Now, in this series of operation, if the construction is such that the sealing part seals the air communication hole first, and then the air suction member and the ink supply member are connected to the sub ink tank, there will be apprehensions that a slight variation of pressure created during connection will not be absorbed, because the air communication hole is already sealed. In contract to this, in this invention, since the air suction member and the ink supply member are connected to the sub ink tank first, and then, the sealing part seals the air communication hole, a slight variation of pressure created during connection will be absorbed by the air communication hole that is not sealed. 
     According to another aspect of the invention, the ink supply member is provided with a valve mechanism. 
     This provision of the valve mechanism blocks up the ink supply member except during the ink supply, which precludes unexpected drying of ink, mixture of foreign matters into the ink, and so forth. 
     According to another aspect of the invention, a plural number of ink supply units are provided in correspondence with the plural recording head units, and the displacement mechanism displaces a specific one of the ink supply units and the sealing parts in relation to the corresponding specific one of the recording head units independently from the other ink supply units and sealing parts. 
     Since the plural ink supply units are provided in correspondence with the plural recording head units, for example, an ink-jet recording device capable of color image recording is able to supply ink into the sub ink tank of the recording head unit individually for each color. 
     According to another aspect of the invention, the pressure reduction part includes a suction pump. 
     The suction by the suction pump secures decompression inside the recording head unit in a short time. 
     According to another aspect of the invention, the inkjet recording device includes any one of the foregoing ink supply devices, and a recording head unit including a sub ink tank into which the ink supply device supplies ink, provided with an air communication hole, and a recording head that ejects the ink supplied from the sub ink tank onto a recording medium on the basis of image information as ink drops. 
     In this ink-jet recording device, the ink supplied from the ink supply device into the sub ink tank of the recording head unit is ejected as ink drops onto a recording medium by the recording head, thereby forming an image on the recording medium. The sub ink tank is provided with the air communication hole, which eases a pressure variation due to ejection of ink and environmental changes, and so forth. Thereby, an unexpected ink leakage from the sub ink tank and a mixture of air into the sub ink tank can be prevented, and the recording head maintains an optimum state for discharge of ink drops. 
     And, since this ink-jet recording device includes any one of the foregoing ink supply devices, it is able to seal the air communication hole of the sub ink tank while supplying ink. In the sealing state, the decompression inside the sub ink tank by the pressure reduction part will preclude an unexpected flow of air into the sub ink tank through the air communication hole; and accordingly, the ink securely flows into the sub ink tank. Thus, the ink is supplied by means of the decompression inside the sub ink tank, not by the pressurization, and a secure ink supply can be achieved in a shorter time. 
     According to another aspect of the invention, it is preferable that both a supplying connection portion to which the ink supply member is connected and a sucking connection portion to which the air suction member is connected, in the sub ink tank, include a valve mechanism. 
     Therefore, the valve mechanism is able to block up the supplying connection portion and the sucking connection portion, except while supplying ink into the sub ink tank, whereby unexpected evaporation of ink and leakage of ink and so forth can be prevented. 
     According to another aspect of the invention, the method of supplying ink into a sub ink tank provided with an air communication hole, in which the ink supplied to a recording head is stored includes a connection step of connecting an air suction member and an ink supply member to the sub ink tank, the air suction member capable of sucking air from the sub ink tank and the ink supply member capable of supplying the ink into the sub ink tank; a sealing step of sealing the air communication hole by a sealing part, after the connection step; and an suction step of sucking the air from the sub ink tank by the air suction member, after the sealing step. 
     That is, at the connection step, after the air suction member and the ink supply member are connected to the sub ink tank, at the sealing step, the sealing part seals the air communication hole. Therefore, if there is a slight variation of pressure created during connection, the variation of pressure will be absorbed by the air communication hole that is not sealed. 
     Thereafter, at the suction step, the air suction member sucks the air from the sub ink tank. Thereby, the ink flows into the sub ink tank through the ink supply member. Since the sealing part seals the air communication hole, the ink can be supplied securely into the sub ink tank in a shorter time. 
     In addition, the sub ink tank into which the ink is supplied has the air communication hole, which softens pressure variations inside the sub ink tank resulting from the discharges of ink and environmental changes and so forth. Thereby, an unexpected ink leakage from the sub ink tank and a mixture of air into the sub ink tank can be prevented, and the recording head maintains an optimum state for discharge of ink drops. 
     According to another aspect of the invention, the method of supplying ink further includes a sealing release step of releasing the sealing of the air communication hole by the sealing part, after the suction step; and a disconnection step of disconnecting the air suction member and the ink supply member from the sub ink tank, after the sealing release step. 
     Thus, after the ink supply is completed, first the sealing of the air communication hole is released at the sealing release step, and next at the disconnection step, the air suction member and the ink supply member are disconnected from the sub ink tank. Therefore, if there occurs a slight pressure variation during disconnection, this pressure variation will be absorbed, because the air communication hole is already opened (not sealed) at this moment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred embodiments of the present invention will be described in detail based on the followings, wherein: 
         FIG. 1  is a perspective view illustrating a recording head carriage and its neighboring area of an ink-jet recording device provided with an ink supply device relating to one embodiment of the invention; 
         FIG. 2  is a plan view illustrating the ink supply device relating to the embodiment of the invention; 
         FIG. 3  is a partially broken-out side view illustrating a schematic construction of the ink supply device relating to the embodiment of the invention; 
         FIG. 4  is a partially broken-out side view enlarged, illustrating an ink supply unit of the ink supply device and a sub ink tank of the ink-jet recording device relating to the embodiment of the invention; 
         FIG. 5  is a partially broken-out plan view enlarged, illustrating an ink supply unit of the ink supply device and a sub ink tank of the ink-jet recording device relating to the embodiment of the invention; 
         FIG. 6  is a partially broken-out plan view enlarged, illustrating an ink supply unit of the ink supply device and a sub ink tank of the ink-jet recording device with a positioning arm taking an advanced position, relating to the embodiment of the invention; 
         FIG. 7  is a partially broken-out plan view enlarged, illustrating an ink supply unit of the ink supply device and a sub ink tank of the ink-jet recording device with the ink supply unit on the way of advance, relating to the embodiment of the invention; 
         FIG. 8  is a partially broken-out plan view enlarged, illustrating an ink supply unit of the ink supply device and a sub ink tank of the ink-jet recording device with the ink supply unit reaching a ink supply position, relating to the embodiment of the invention; 
         FIG. 9  is a sectional view illustrating a connection structure of an ink supply port of the ink supply device and an ink supply inlet of the sub ink tank relating to the embodiment of the invention; 
       FIG.  10 A through  FIG. 10D  are sectional views illustrating the process of connecting the ink supply port of the ink supply device to the ink supply inlet of the sub ink tank relating to the embodiment of the invention; 
         FIG. 11  is a sectional view illustrating a connection structure of an exhaust port of the ink supply device and an air outlet of the sub ink tank relating to the embodiment of the invention; 
         FIG. 12  is a partially broken-out plan view illustrating a drive system that displaces the ink supply unit in the ink supply device relating to the embodiment of the invention; 
         FIG. 13  is a partially broken-out plan view illustrating a drive system that drives a pump unit in the ink supply device relating to the embodiment of the invention; 
         FIG. 14  is a graph illustrating a relation between a rotating angle of a cam unit and a position of the positioning arm, and a relation between the rotating angle and a position of the ink supply unit, in the ink supply device relating to the embodiment of the invention; 
         FIG. 15  illustrates a state that each of the ink supply units advances to the corresponding one of recording head units, in which  FIG. 15A  shows the case of the black ink supply unit, and  FIG. 15B  shows the case of the cyan ink supply unit, in the ink supply device relating to the embodiment of the invention; 
         FIG. 16  illustrates a state that each of the ink supply units advances to the corresponding one of recording head units, in which  FIG. 16A  shows the case of the magenta ink supply unit, and  FIG. 16B  shows the case of the yellow ink supply unit, in the ink supply device relating to the embodiment of the invention; 
         FIG. 17  is a timing chart illustrating a connection state of the ink supply port of the ink supply device and the ink supply inlet of the sub ink tank relating to the embodiment of the invention; 
         FIG. 18  is a partial sectional view of a conventional ink supply device; 
         FIG. 19  is an explanatory chart illustrating a schematic construction of the conventional ink supply device; and 
         FIG. 20  is a partial sectional view of the conventional ink supply device illustrated in FIG.  19 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  illustrates an ink-jet recording device  12  of the first embodiment of this invention, in which a recording head carriage  14  and its neighboring area are enlarged. 
     The ink-jet recording device  12  includes a recording medium conveyance member  16  that conveys a recording medium P (for example, paper) in a fixed direction, and a pair of guide members  18  installed along a direction perpendicular to the conveyance direction of the recording medium P so as to face the conveyance route of the recording medium P. These guide members  18  support a recording head carriage  14 . Further, a maintenance station  20  underlies the guide members  18  near the conveyance route of the recording medium P, which comes into contact and becomes disjoined with the recording head carriage  14  (moves up and down in this embodiment) to perform a maintenance operation of capping and suction of ink, etc. A control circuit not illustrated controls this maintenance operation in accordance with a specified condition and timing. 
     The home position of the recording head carriage  14  is set at a position facing the maintenance station  20 , and a position sensor  22  locates this home position. A main housing  24  retains the recording head carriage  14 , recording medium conveyance member  16 , guide members  18 , maintenance station  20 , and position sensor  22 . Picture information is sent to the recording head carriage  14  through signal lines formed on a flexible board. 
     Here, the drawing indicates the moving direction (fast-scanning direction) of the recording head carriage  14  with an arrow M, and the moving direction (slow-scanning direction) of the recording medium P with an arrow S. 
     As illustrated also in FIG.  2  through  FIG. 4 , the recording head carriage  14  is made up with a recording head carriage frame  26  installed movably along the guide members  18 , plural recording heads  28  (four heads, in this embodiment) mounted to project below the bottom (side to face the conveyance route of the recording medium P) of the recording head carriage frame  26 , of which ink discharge openings are formed on the bottom, and sub ink tanks  30  that supply ink to each of the recording heads  28  disposed detachably on the recording head carriage frame  26 . The number of the sub ink tanks  30  corresponds to that of the recording heads  28 , and this embodiment takes on four tanks. Therefore, if the sub ink tanks  30  each supply the recording heads  28  each with different colored inks (black Bk, yellow Y, magenta M, cyan C) and discharge ink drops, it will be possible to record a full-colored picture image. A recording head  28  and a sub ink tank  30  in correspondence constitute a recording head unit  32  relating to this invention. Hereunder, in distinguishing the recording heads  28 , sub ink tanks  30 , and ink supply units  48  described later in correspondence with each of the colors, Bk, Y, M, or C will be put on after the symbol. 
     And, as shown in  FIG. 1 , the ink-jet recording device  12  of this embodiment conveys the recording medium P by means of the recording medium conveyance member  16 , while making a reciprocating movement of the recording head carriage  14 , discharges ink drops in accordance with picture information, and records an image on the recording medium P. 
     Each of the sub ink tanks  30  is, as shown in  FIG. 3 , provided with an exhaust port  34  having an air outlet  42  that permits a discharge of air inside the sub ink tank  30 , and an ink supply port  36  below the exhaust port  34 , having an ink supply inlet  44  that permits taking in ink into the sub ink tank  30 . Further, the sub ink tank  30  has an air communication hole  38  formed above the exhaust port  34 , through which air comes in and goes out of the sub ink tank  30 . The going in and out of air through the air communication hole  38  eases a pressure variation inside the sub ink tank  30 . Further, the sub ink tank  30  has an ink sensor  40  attached, which detects an ink quantity inside. The ink sensor  40  sends the detected information of the ink quantity inside the sub ink tank  30  to a control circuit not illustrated. 
     As shown in  FIG. 1 , the main housing  24  further retains an ink supply device  46  containing plural (four in this embodiment) ink supply units  48  in correspondence with each of the sub ink tanks  30 . The position at which the ink supply unit  48  is to supply ink into the sub ink tank  30  is defined as the ink supply position of the sub ink tank  30 . The ink supply position is also detected by the position sensor  22  in the same manner as the home position. The ink supply position may be set to the same position as the home position; however, in this embodiment, it takes a different position. 
     Further, as shown in FIG.  2  and  FIG. 3 , a main ink tank  50  underlies the ink supply device  46 . The main ink tank  50  contains ink in advance that the ink-jet recording device  12  uses; and the ink supply device  46  supplies the ink into the sub ink tank  30 , which is used for recording images. The main ink tank  50  is disposed to overlap partially with the ink supply device  46  when viewed from the top (in this embodiment, it overlaps substantially completely with the ink supply device  46 ), whereby the ink-jet recording device  12  achieves miniaturization as a whole. 
     As detailed in FIG.  4  and  FIG. 5 , the ink supply device  46  has a fixed frame  52  that is integrally mounted on the main housing  24  of the ink-jet recording device  12 . Further, the fixed frame  52  has a guide frame  54  disposed therein. The guide frame  54  has specific gaps  56  in the cross direction between the fixed frame  52  and the guide frame  54 . The guide frame  54  is movable in the fixed frame  52  within a certain range in the same direction as the moving direction (fast-scanning direction) of the recording head carriage  14 . Further, the gaps  56  have compression coil springs  58  placed therein, which retain the guide frame  54  virtually in the center in the cross direction in the fixed frame  52 . Here, the ‘cross direction’ as simply referred to signifies the same one as the cross direction of the guide frame  54 , which coincides with the fast-scanning direction of the recording head carriage  14  (the direction indicated by the arrow M). 
     The guide frame  54  has a pair of positioning arms  60  installed near the both ends thereof, which can slide toward the recording head carriage  14 . As shown in FIG.  2  and  FIG. 3 , in the normal state, the positioning arms  60  take a position where they will not come in contact with the recording head carriage  14 . The space between inner sides  60 A (opposing faces) of the positioning arms  60  is defined as equal to the breadth of the recording head carriage frame  26  of the recording head carriage  14 . 
     As illustrated in FIG.  2  and  FIG. 5 , the positioning arms  60  have tapered faces  62  cut slant to the recording head carriage  14  formed on the end portions of the positioning arms  60  on the side of the recording head carriage  14 . As illustrated by the solid line in  FIG. 2 , if the recording head carriage  14  is displaced in the cross direction to the guide frame  54  when it stops at the ink supply position (the chain double-dashed line in  FIG. 2  shows the normal position of the recording head carriage frame  26 ), any one of the tapered faces  62  of the positioning arms  60  will come in contact with a corner of the recording head carriage frame  26  when the positioning arms  60  approach toward the recording head carriage  14 . In this state, if the positioning arms  60  further approach toward the recording head carriage  14 , the movement in this approaching direction will be converted into a cross-directional movement of the guide frame  54 . Thereby, the guide frame  54  moves in the cross direction against an elastic force of the compression coil spring  58  (one of the gaps  56  between the fixed frame  52  and the guide frame  54  is expanded and the other one is narrowed). And, if the positioning arms  60  further approach toward the recording head carriage  14 , as shown in  FIG. 5 , sides  26 S of the recording head carriage frame  26  will come in contact with the inner sides  60 A of the positioning arms  60 , and the recording head carriage  14  and the guide frame  54  will be positioned correctly in the cross direction. Thereby, the four ink supply units  48  are to be integrally positioned to the corresponding sub ink tanks  30 . 
     As illustrated in FIG.  5  and  FIG. 6 , the positioning arms  60  have pressing piece housings  64  inside thereof, and the pressing piece housings  64  contain pressing pieces  66  that project out partially from the inner sides  60 A of the positioning arms  60 . The pressing pieces  66  are made slidable in the pressing piece housings  64 , and compression coil springs  68  energize the pressing pieces  66  in the direction approaching to the recording head carriage  14 . In the state that the sides  26 S of the recording head carriage frame  26  come in contact with the inner sides  60 A of the positioning arms  60 , and the recording head carriage  14  and the guide frame  54  are positioned correctly in the cross direction, and further, when the positioning arms  60  further advance toward the recording head carriage  14 , then as shown in  FIG. 6 , the pressing pieces  66  receiving an energizing force by the compression coil springs  68  press the recording head carriage  14 . Thereby, the recording head carriage  14  is held between the pressing pieces  66  and the guide members  18 , which prevents looseness of the recording head carriage  14 . 
     The guide frame  54  has the four ink supply units  48  corresponding to the four sub ink tanks  30  disposed therein. Each of the ink supply units  48  independently slides in each of containers  70 , and approaches and comes off from the corresponding sub ink tank  30 . The area of movement where the ink supply unit  48  approaches and comes off from the recording head carriage  14  (the sub ink tank  30 ) is designed not to overlap with the area of movement where the maintenance station  20  approaches and comes off from the recording head carriage  14 , as understood from FIG.  1 . Accordingly, when any one of the ink supply unit  48  and the maintenance station  20  approaches to and comes off from the recording head carriage  14 , the other one does not have to draw back. 
     As shown in FIG.  3  and  FIG. 4 , each of the ink supply units  48  is provided on an opposing face to the corresponding sub ink tank  30  with an exhaust port  74  at a position corresponding to the air outlet  42  of the sub ink tank  30 , and an ink supply port  76  at a position corresponding to the ink supply inlet  44  of the sub ink tank  30 . When the ink supply unit  48  moves toward the corresponding sub ink tank  30 , the exhaust port  74  is connected to the air outlet  42 , and the ink supply port  76  is connected to the ink supply inlet  44 . 
     Further, each of the ink supply units  48  has a cap  72  attached at a position corresponding to the air communication hole  38  of the sub ink tank  30 . After the ink supply unit  48  approaches to the sub ink tank  30 , and the exhaust port  74  and the ink supply port  76  are connected to the air outlet  42  and to the ink supply inlet  44 , respectively, when the ink supply unit  48  further approaches the sub ink tank  30 , the cap  72  seals the air communication hole  38 , which deters a flow of air through the air communication hole  38  in the sub ink tank  30 . The shape and the mounting position of the cap  72  are designed to fulfill the above function. 
     Further, each of the ink supply units  48  has a positioning pin  78  projected toward the sub ink tank  30 . On the other hand, the sub ink tank  30  has a positioning port  80  formed at a position corresponding to the positioning pin  78 . The positioning pin  78  is made up of a cylindrical positioning portion  82  having a constant diameter, and a conically formed guide portion  84  that is tapered toward the front from this positioning portion  82 . The outer diameter of the positioning portion  82  is virtually equal to the inner diameter of the positioning port  80 . As the ink supply unit  48  approaches the sub ink tank  30 , first the guide portion  84  on the front side of the positioning pin  78  goes into the positioning port  80 . Since the guide portion  84  is tapered toward the front, even if the center of the positioning pin  78  is dislocated from the center of the positioning port  80 , the positioning pin  78  is driven to enter the positioning port  80 . And, as the ink supply unit  48  further approaches the sub ink tank  30 , the guide portion  84  drives the positioning pin  78  and the positioning port  80  to gradually move in such a direction that the centers of both coincide. When the positioning portion  82  reaches the positioning port  80 , the center of the positioning pin  78  coincides with that of the positioning port  80 , whereby the ink supply unit  48  and the sub ink tank  30  are positioned individually. 
     As shown in FIG.  3  through  FIG. 5 , there are specific gaps  86  formed between the upper, lower, right, and left sides of the ink supply unit  48  and the upper, lower, right, and left sides of the container  70  that contains the ink supply unit  48 . The ink supply unit  48  has guide pins  88  projected from these sides, and the guide pins  88  are received in guide grooves  90  formed on these sides of the container  70 . 
     As understood from  FIG. 4 , the guide groove  90  includes a retaining portion  90 A whose outer diameter is formed slightly wider than that of the guide pin  88 , and a divergent portion  90 B that broadens toward the outside, formed on the end near the sub ink tank  30 . The position of the divergent portion  90 B is set such that the guide pin  88  stays in divergent portion  90 B, in the state that the ink supply unit  48  approaches the sub ink tank  30  and the positioning pin  78  goes into the positioning port  80 . Therefore, in the state that the positioning pin  78  does not enter the positioning port  80 , the guide pin  88  moves inside the retaining portion  90 A, and the ink supply unit  48  slides inside the container  70  without looseness. And, in the state that the positioning pin  78  enters the positioning port  80 , the guide pin  88  reaches the divergent portion  90 B, and a gap is formed between the guide pin  88  and the divergent portion  90 B; and therefore, the ink supply unit  48  becomes movable within a certain range in the vertical and cross directions in the container  70 . Therefore, in this state, namely, in the state that the positioning pin  78  goes into the positioning port  80 , the guide of the ink supply unit  48  by the guide pin  88  and the guide groove  90  is substantially released, and the correct positioning by the positioning pin  78  and the positioning port  80  is accomplished. In addition, the gap between the guide pin  88  and the divergent portion  90 B increases, as the guide pin  88  approaches to the sub ink tank  30 ; and the movable range of the ink supply unit  48  in the vertical and cross directions increases accordingly. 
     Each of the ink supply ports  76  provided on each of the ink supply units  48  has an ink supply pipe  92  installed as shown in FIG.  9 . The ink supply pipe  92  has a pipe body  94  that is formed in a substantially cylindrical shape as a whole. The pipe body  94  has a communication hole  96  formed on the front thereof, through which ink flows out into the sub ink tank  30 . The front portion of the pipe body  94  has a tapered shape that the diameter gradually diminishes toward the front. 
     The pipe body  94  contains a valve element  98  that is movable in the longitudinal direction, and a bracket  102  that is press-fit in the rear end through an O-ring  100 . 
     The valve element  98  includes a ring-shaped packing  104  made of an elastic member, a packing holder  106  that holds the packing  104  and is able to slide in the pipe body  94 , and a compression coil spring  108  inserted between the packing holder  106  and the bracket  102 , which energizes the packing holder  106  and the packing  104  toward the communication hole  96 . 
     Normally, the compression coil spring  108  energizes the packing holder  106  and the packing  104  toward the communication hole  96 , and presses the packing  104  onto the circumference of the communication hole  96  to thereby seal the communication hole  96 ; however, as shown in FIG.  10 C and  FIG. 10D , when the packing holder  106  and the packing  104  slide against an energizing force of the compression coil spring  108 , and the packing  104  comes off from the circumference of the communication hole  96 , the ink can be flowed through the communication hole  96 . 
     The packing holder  106  has a valve contact  110  projected therefrom. The valve contact  110  pierces through the packing  104 , and exposes the front end thereof to the outside through the communication hole  96 ; and a valve protrusion  122  described later is designed to press the front end. 
     The rear end of the bracket  102  is connected to one end of an ink supply tube  124  by way of a cover  112 . As shown in  FIG. 3 , the other end of the ink supply tube  124  is connected to the main ink tank  50  that beforehand stores the ink used for image recording. As described later, when the ink supply port  76  is connected to the ink supply inlet  44  of the sub ink tank  30 , a flow passage is made up from the main ink tank  50  to the sub ink tank  30 . 
     On the other hand, the ink supply inlet  44  of the sub ink tank  30  has a gasket  114  placed inside thereof, which a gasket cover  112  retains at a specific position so as not to fall off. A circular swollen portion  114 A is formed on the periphery of the gasket  114 , and the swollen portion  114 A is pressed on the inner face of the ink supply inlet  44 , which deters a flow of ink and air through a gap between them. Further, the gasket  114  has a circular inward-projecting lip  114 B formed thereon, and as shown in FIG.  10 C and  FIG. 10D , the lip  114 B comes in contact with the outside of the inserted pipe body  94  over the whole circumference thereof, which blocks a flow of ink and air through a gap between them. An annular presser ring  116  is placed between the gasket cover  112  and the gasket  114 , which restricts deformation of the lip  114 B within a certain extent while drawing out and putting in the pipe body  94 . This construction, when the pipe body is moved (drawn out and put in) in the ink supply inlet  44 , prevents the lip  114 B from following the drawing out and putting in unexpectedly only to perform as a resistor during that movement, and maintains adhesion of the lip  114 B onto the circumference of the pipe body  94 . 
     In the ink supply inlet  44 , a valve  118  is placed further inside from the gasket  114 . Normally, the valve  118  is energized by a compression coil spring  120  in the ink supply inlet  44 , and is pressed onto a circular projection  114 C formed on the gasket  114  to close a flow passage of ink. However, as shown in FIG.  10 C and  FIG. 10D , when the valve  118  slides against an energizing force of the compression coil spring  120  and comes off from the projection  114 C, the flow passage of ink is formed. Here, in this embodiment, the spring constant of the compression coil spring  120  is set greater than that of the compression coil spring  108 . 
     The valve  118  has the valve protrusion  122  projected therefrom, which faces to the valve contact  110  of the packing holder  106 . As the pipe body  94  is inserted into the ink supply inlet  44 , as shown in  FIG. 10B , the front of the valve contact  110  comes in contact with the front of the valve protrusion  122  to press each other. This pressure slides the valve element  98  and the valve  118  to form the flow passage of ink. In this embodiment, the spring constant of the compression coil spring  120  is set greater than that of the compression coil spring  108 , and the flow passage of ink is formed inside the pipe body  94  first, and then it is formed inside the ink supply inlet  44 . Thereby, the ink supply unit  48  is liquidly coupled to the sub ink tank  30 . Further, the packing holder  106  and the valve  118  both have communication holes  106 D and  118 D formed, which avoids blocking a flow of ink during liquid coupling. 
     The positions and shapes of the valve contact  110  and the valve protrusion  122  are speculated as specific ones to form a flow passage of ink after the insertion of the pipe body  94  into the ink supply inlet  44  and at least after the adhesion of the lip  114 B onto the circumference of the pipe body  94 . 
       FIG. 11  illustrates the exhaust port  74  and the air outlet  42 . The exhaust port  74  and the air outlet  42  are to discharge air inside the sub ink tank  30 , as described later, inside of which ink does not flow. Accordingly, the exhaust port  74  does not contain the valve element  98  inside the pipe body  94 . That is, the communication hole  96  of the pipe body  94  is always open, and the pipe body  94  is provided with the valve contact  110  that can press the valve protrusion  122 . Such a construction also allows forming of a flow passage of air and discharging air inside the sub ink tank  30  from an exhaust tube  126 , since the insertion of the pipe body  94  into the air outlet  42  causes the valve contact  110  to press the valve protrusion  122  to push in the gasket  114 . Here, since the constructions of the exhaust port  74  and the air outlet  42  are stipulated as the same, except the aforementioned, as those of the ink supply port  76  and the ink supply inlet  44  illustrated in  FIG. 9 , the same components and members as those in  FIG. 11  are given the same numeric symbols, and the descriptions will be omitted. 
     As shown in  FIG. 2 ,  FIG. 12 , and  FIG. 13 , on the fixed frame  52  are mounted a drive motor  128  that drives the ink supply device  46 , an ink supply unit shifting gear train  130  that receives a drive force by the drive motor  128  to rotate, a pump driving gear train  132 , and a clutch unit  134  that switches transmission of a rotating force according to the forward rotation and the reverse rotation of the drive motor  128  into the ink supply unit shifting gear train  130  or the pump driving gear train  132 . 
     The clutch unit  134  includes an input-side gear  138  that engages with a drive gear  136  of the drive motor  128 , a swing arm  140  placed swingably about the shaft of the input-side gear  138 , and an output-side gear  142  attached on one front of the swing arm  140 , which engages with the input-side gear  138  to receive a rotating force. As the drive motor  128  makes the forward rotation, as shown in  FIG. 12 , the swing arm  140  swings counterclockwise, and the output-side gear  142  engages with the ink supply unit shifting gear train  130 . On the other hand, as the drive motor  128  makes the reverse rotation, as shown in  FIG. 13 , the swing arm  140  swings clockwise, and the output-side gear  142  engages with the pump driving gear train  132 . 
     As understood from  FIG. 2 ,  FIG. 3 , and  FIG. 12 , on the fixed frame  52  are laid out cam units  144  in correspondence with each of the ink supply units  48  and the positioning arms  60  (six in total, in this embodiment), so as to rotate coaxially integrally by a rotating force transmitted by the ink supply unit shifting gear train  130 . Each of the cam units  144  is made up of a forward cam  146  that advances the corresponding ink supply unit  48  and positioning arm  60 , and a backward cam  148  that retreats them. 
     Further, cam follower units  150  are laid out on the fixed frame  52 . Each of the cam follower units  150  is provided integrally with a forward cam follower  152  and a backward cam follower  154  each corresponding to the forward cam  146  and the backward cam  148 , and is able to slide in the same direction as the slide direction of the ink supply unit  48 . 
     Further, the fixed frame  52  is provided with link mechanisms  158 , each of which is made up of a link  160  capable of swinging about a spindle  156 , and a shifting arm  162  whose one end is pivoted on the front of this link  160 . The other end of the shifting arm  162  is pivoted on the positioning arm  60  or the ink supply unit  48 . Further, the cam follower unit  150  is pivoted on substantially the center of the link  160 . Thereby, as the cam follower unit  150  slides, the link mechanism  158  amplifies the slide, and the result is transmitted to the positioning arm  60  or the ink supply unit  48 . 
     Each of the cam units  144  has predetermined positions and shapes of the forward cam  146  and the backward cam  148 , so as to advance or retreat the corresponding positioning arm  60  or ink supply unit  48  at a specific timing. Further, the fixed frame  52  has a sensor attached thereon to detect a rotating position of the cam unit  144 , which is not illustrated. On the basis of the rotating angle of the cam unit  144  that is detected by this sensor, a control circuit not illustrated drives the drive motor  128 , sets the initial position of the cam unit  144 , and controls the rotating angle thereof. 
     Therefore, as shown in  FIG. 14 , as the cam unit  144  turns, receiving a rotating force by the forward rotation of the drive motor  128 , first, at the moment the rotating angle of the cam unit  144  reaches 10°, the forward cam  146  of the cam unit  144  corresponding to the positioning arm  60  advances the positioning arm  60  (refer to FIG.  5 ). As the rotating angle of the cam unit  144  reaches 40°, as shown in  FIG. 6 , the positioning arm  60  takes the most advanced position; and until the rotating angle reaches 320°, the positioning arm  60  maintains this position. 
     And, when the rotating angle of the cam unit  144  reaches 40°, the forward cam  146  of the cam unit  144  corresponding to the black ink supply unit  48 Bk starts advancing the ink supply unit  48 Bk. When the rotating angle reaches 90°, as shown in  FIG. 15A , the ink supply unit  48 Bk takes the most advanced position, and until the rotating angle reaches 110°, the ink supply unit  48 Bk maintains this position (here, stopping or reversing the rotation of the drive motor  128  will not rotate the cam unit  144 , accordingly the ink supply unit  48 Bk is able to maintain this position, until the drive motor  128  makes the forward rotation next). 
     As the cam unit  114  further rotates, the backward cam  148  starts to retreat the ink supply unit  48 Bk, and when the rotating angle reaches 140°, the ink supply unit  48 Bk retreats to the initial position. And, when the rotating angle reaches 110° (namely, at the same time the ink supply unit  48 Bk starts to retreat), the forward cam  146  of the cam unit  144  corresponding to the cyan ink supply unit  48 C starts advancing the ink supply unit  48 C. When the angle reaches 160°, the ink supply unit  48 C takes the most advanced position. Thereafter, when the angle stays between 160° and 180°, the ink supply unit  48 C maintains this most advanced position (refer to FIG.  15 B); when the angle is at 180°, the backward cam  148  starts to retreat the ink supply unit  48 C, and when the angle reaches 210°, the ink supply unit  48 C retreats to the initial position. Therefore, the cyan ink supply unit  48 C performs the same action with the delay of the rotating angle 70° against the black ink supply unit  48 Bk. Thereafter, in the same manner, the magenta ink supply unit  48 M performs advance and retreat with the delay of the rotating angle 70° against the cyan ink supply unit  48 C (refer to FIG.  16 A); and the yellow ink supply unit  48 Y performs advance and retreat with the delay of the rotating angle 70° against the magenta ink supply unit  48 M (refer to FIG.  16 B). In this manner, since the ink supply device  46  of this embodiment provides a specific phase difference (70° in this embodiment) to each of the cam units  144  corresponding to each of the ink supply units  48 , it is possible to advance and retreat each of the ink supply units  48  independently with regard to each of the corresponding sub ink tanks  30 . 
     As shown in  FIG. 13 , as the drive motor  128  makes the reverse rotation, the swing arm  140  being a constituent of the clutch unit  134  swings clockwise, and the output-side gear  142  engages with the pump driving gear train  132 ; accordingly, the rotating force of the drive motor  128  is transmitted to a pump spindle  166  being a constituent of a pump unit  164 . 
     As shown in  FIG. 2 , the pump unit  164  has four roller pumps  168  in correspondence with the exhaust tubes  126  extending from the ink supply units  48  each. As shown in  FIG. 3 , each of the roller pumps  168  has a rotating disc  170  that rotates integrally with the pump spindle  166 , and one or plural (two in this embodiment) rollers  172  mounted near the periphery of this rotating disc  170 . In contrast to this, the exhaust tube  126  is laid out to partially surround the rotating discs  170 , and the roller  172  pushes to crush the exhaust tube  126  locally. Therefore, as the rotating disc  170  rotates clockwise in  FIG. 3 , the rollers  172  moves to squeeze the exhaust tube  126 , and evacuates the fluid (air in this embodiment) inside the exhaust tube  126  into the atmosphere from the other end of the exhaust tube  126 . Here, in each of the roller pumps  168 , the angle of attaching each of the rotating discs  170  is determined in such a manner that the rollers  172  as a whole are arranged in an equal spacing when viewed from the axial direction of the pump spindle  166 . In this embodiment, the pump unit  164  has the four roller pumps  168  installed, and as understood from  FIG. 3 , the rotating discs  170  each are arranged with a displacement of 45°. Therefore, when viewed along the pump spindle  166 , the rollers  172  as a whole are arranged in an equal spacing of the center angle 22.5°. Thereby, the resistance (especially, the rotational resistance resulting from that the roller  172  is pressed by a reaction of the exhaust tube  126 ) acting on the pump unit  164  is dispersed, and the pump unit  164  rotates smoothly. 
     The advance and retreat of the ink supply units  48  by the drive (forward rotation or reverse rotation) of the drive motor  128  and the drive of the pump unit  164  are controlled by a control circuit not illustrated so as not to overlap in the timing with the maintenance operation by the maintenance station  20 . 
     Next, the function of the ink supply device  46  and the ink-jet recording device  12  of this embodiment, and the method of supplying ink by the ink supply device  46  will be described. 
     Ejecting ink drops in accordance with image information from the recording head  28 , the recording head carriage  14  moves in the fast-scanning direction, and the recording medium P moves in the slow-scanning direction, whereby images are recorded on the recording medium P. Since the ink supplied from the sub ink tank  30  to the recording head  28  produces the ink drops, the ink inside the sub ink tank  30  decreases, accompanied with the image recording. 
     As the recording head  28  reaches a specific state that requires any maintenance, the control circuit not illustrated shifts the recording head carriage  14  to the home position, brings the maintenance station  20  close to the recording head  28 , and makes the maintenance station  20  carry out a specific maintenance operation. Thereby, the recording head  28  recovers the optimum state for ink ejection, and as a consequence, the optimum state for ink ejection is maintained constantly, which achieves a high picture quality recording on the recording medium P. 
     As the ink sensor  40  detects that the ink quantity inside a specific sub ink tank  30  has decreased to a specific quantity, and sends the information detected to the control circuit not illustrated, the control circuit shifts the recording head carriage  14  to the ink supply position. At this moment, the control circuit controls the maintenance station  20  not to operate. 
     Next, the control circuit controls the drive motor  128  to make the forward rotation in such a manner that the cam unit  144  rotates by the angle corresponding to the specific sub ink tank  30 . For example, in the case of supplying a black ink into the sub ink tank  30 Bk, as understood from  FIG. 14 , the control circuit controls the drive motor  128  to make the forward rotation in such a manner that the cam unit  144  comes to the rotating angle between 90° or larger and 110° or smaller. 
     At that moment, first, as the rotating angle of the cam unit  144  reaches 10°, a pair of the positioning arms  60  start advancing; and if the recording head carriage  14  is displaced in the cross direction to the guide frame  54 , any one of the tapered faces  62  of the positioning arms  60  comes in contact with a corner of the recording head carriage frame  26 . And in this state, as the positioning arms  60  further approach toward the recording head carriage  14 , the movement in this approaching direction is converted into a cross-directional movement of the guide frame  54 ; accordingly, the guide frame  54  moves in the cross direction against the elastic force of the compression coil spring  58 . As the positioning arms  60  further approach toward the recording head carriage  14 , as shown in  FIG. 5 , the sides  26 S of the recording head carriage frame  26  come in contact with the inner sides  60 A of the positioning arms  60 , and the recording head carriage  14  and the guide frame  54  are positioned correctly in the cross direction. For example, if the stop position (ink supply position) of the recording head carriage  14  is slightly dislocated, or if there is such a dislocation due to other various factors, this dislocation will be dissolved, and the four ink supply units  48  will integrally be positioned to the corresponding sub ink tanks  30 . 
     As the positioning arms  60  further move forward and the pressing pieces  66  come in contact with the recording head carriage frame  26 , the recording head carriage  14  is pressed by receiving the energizing force of the compression coil springs  68 . Thereby, the recording head carriage  14  is held between the pressing pieces  66  and the guide members  18 , which prevents unexpected plays and/or rattling sounds of the recording head carriage  14 . 
     Here, the rotating angle of the cam unit  144  comes to 40°, which is understood from  FIG. 14 , and since the forward cam follower  152  is pressed to the sub ink tank  30  in the approaching direction by the forward cam  146  of the cam unit  144  corresponding to the black, the ink supply unit  48 Bk advances and starts approaching to the sub ink tank  30 Bk. During the advancement (in the state that the positioning pin  78  is not in the positioning port  80 ), the guide pin  88  moves inside the retaining portion  90 A, and the ink supply unit  48  slides in the container  70  of the guide frame  54  without plays. 
     As shown in  FIG. 7 , the approaching of the ink supply unit  48  to the sub ink tank  30  starts inserting the positioning pin  78  into the positioning port  80 . Here, as understood from  FIG. 17 , in the state before insertion, the packing  104  seals the communication hole  96  in the pipe body  94  (refer to FIG.  10 A), and the inside of the pipe body  94  is sealed. In the same manner, in the inside of the ink supply inlet  44 , the valve  118  adheres onto the projection  114 C of the gasket  114 , which blocks communication with the atmosphere. 
     Since the guide portion  84  of the positioning pin  78  is tapered toward the front thereof, when the positioning pin  78  is inserted into the positioning port  80 , even if the center of the positioning pin  78  is dislocated from the center of the positioning port  80 , the positioning pin  78  is driven to enter the positioning port  80 . At this moment, the guide pin  88  has reached the divergent portion  90 B, and since a gap is formed between the guide pin  88  and the divergent portion  90 B, the ink supply unit  48  becomes movable within a certain range in the vertical and cross directions in the container  70 . As the ink supply unit  48  further approaches the sub ink tank  30 , the guide portion  84  drives the positioning pin  78  and the positioning port  80  to gradually move in such a direction that the centers of both coincide. And, when the positioning portion  82  reaches the positioning port  80 , the center of the positioning pin  78  coincides with that of the positioning port  80 , whereby a specific ink supply unit  48  and the corresponding sub ink tank  30  are positioned with precision. 
     Next, as understood from  FIG. 10B ,  FIG. 10C , and  FIG. 17 , the ink supply port  36  advances, the front of the pipe body  94  enters the ink supply inlet  44  (start of pipe-insertion process), and the front of the valve contact  110  comes into contact with that of the valve protrusion  122 . Here, as the pipe body  94  is further pushed in, the valve contact  110  and the valve protrusion  122  press each other. Since the spring constant of the compression coil spring  108  inside the pipe body  94  is set smaller than that of the compression coil spring  120  inside the ink supply inlet  44 , first-while the compression coil spring  108  is shrinking, the pipe body  94  only advances (the valve element  98  stands still in strict sense), and the valve element  98  opens the communication hole  96 . At this moment, the lip  114 B comes into close contact with the circumference of the pipe body  94  to seal the gap between them. 
     As shown in  FIG. 10C , as the pipe body  94  further goes into the ink supply inlet  44 , the front of the pipe body  94  comes into contact with the valve  118 ; accordingly, the compression coil spring  120 , being pressed by the pipe body  94  through the valve  118 , starts shrinking (the valve element  98  and the pipe body  94 , maintaining a relatively virtually constant positional relation, integrally enter the ink supply inlet  44 ). Thereby, the valve  118  comes off from the projection  114 C of the gasket  114 , and the spacing between them starts expanding. 
     As shown in  FIG. 10D , in the state that the pipe body  94  goes into the innermost, the ink supply unit  48  comes to the ink supply position, the ink supply port  76  and the ink supply inlet  44  of the sub ink tank  30  is completely connected into a liquid coupling, and the flow passage of ink is formed from the main ink tank  50  to the sub ink tank  30 Bk. At the same time, the connection of the exhaust port  34  and the air outlet  42  is completed. Thereafter, as shown in  FIG. 8 , the cap  72  seals the air communication hole  38 , which blocks communication of air between the inside and the outside of the sub ink tank  30  (end of pipe-insertion process). Therefore, to control the drive motor  128  into the forward rotation and to bring the cam unit  144  into a specific rotating angle makes it possible to connect a specific ink supply unit  48  to the corresponding sub ink tank  30 . 
     Here, the control circuit not illustrated brings the drive motor  128  into the reverse rotation. The swing arm  140  of the clutch unit  134  swings clockwise in  FIG. 12 , and as shown in  FIG. 13 , the transmission of a rotating force by the drive motor  128  is switched from the ink supply unit shifting gear train  130  into the pump driving gear train  132 . Thereby, while the position of the ink supply unit  48 Bk is being maintained at the ink supply position, the roller pump  168  being a constituent of the pump unit  164  is driven, and the internal air is ejected through the air outlet  42  of the sub ink tank  30 Bk by the ink supply unit  48 Bk. At this moment, since the air communication hole  38  of the sub ink tank  30 Bk is sealed by the cap  72 , the air will not come into the sub ink tank  30 Bk unexpectedly from the air communication hole  38 , and the air can securely be evacuated from the inside of the sub ink tank  30 Bk. Also, the corresponding roller pump  168  is to be driven with respect to the ink supply unit  48  that has not advanced to the ink supply position; however, since the exhaust port  74  is opened, the roller pump  168  will not produce a resistance in the driving. 
     Since the control circuit brings the drive motor  128  into the reverse rotation for a specific time, a specific quantity of ink is supplied into the sub ink tank  30 . The time for the reverse rotation of the drive motor  128  may be speculated as a preset constant time, or the time for the reverse rotation may be determined by the feedback control on the basis of ink quantity information from the ink sensor  40 . 
     Next, the control circuit brings the drive motor  128  into the forward rotation. The swing link  160  swings counterclockwise in  FIG. 13 , and as shown in  FIG. 12 , the rotating force by the drive motor  128  is transmitted again to the ink supply unit shifting gear train  130 , and the cam unit  144  rotates accordingly. As understood from  FIG. 14 , when the rotating angle of the cam unit  144  reaches 110°, the ink supply unit  48 Bk starts to retreat, and the cap  72  comes off from the air communication hole  38 , which releases the sub ink tank to the atmospheric pressure. 
     Further, as understood from  FIG. 17 , since the pipe body  94  starts to retreat from the ink supply inlet  44  (start of pipe-pulling out process), the valve  118  slides by an elastic force of the compression coil spring  120 , and approaches to the projection  114 C of the gasket  114 . And, as the valve  118  returns to the initial position and adheres onto the projection  114 C, the valve element  98  inside the pipe body  94  receives an elastic force of the compression coil spring  108  to slide, and the valve element  98  advances toward the communication hole  96 . Further, the circumference of the pipe body  94  comes off from the lip  114 B during this movement, and the sealing by these is released accordingly. Thus, the valve element  98  returns to the initial position to seal the communication hole  96 , and the pipe body  94  is pulled out from the ink supply inlet  44  (end of pipe-pulling out process). 
     As the drive motor  128  further makes the forward rotation and the rotating angle of the cam unit  144  comes to 140°, the ink supply unit  48 Bk comes to the end point of retreat, and the ink supply unit  48 Bk returns to the initial position. 
     As mentioned above, the black ink supply into the sub ink tank  30 Bk is completed, and if another color ink supply to another sub ink tank  30  is needed, the control circuit controls to rotate the drive motor  128  further forward, so that the rotating angle of the cam unit  144  comes to the angle corresponding to the sub ink tank  30  required for the ink supply. If the cyan ink is supplied to the cyan sub ink tank  30 C, for example, the drive motor  128  is made to continue the forward rotation until the rotating angle of the cam unit  144  comes to 160° or more to 180° or less, and as shown in  FIG. 15B , the cyan ink supply unit  48 C is set to the ink supply position. In this state, the control is made to bring the drive motor  128  into the reverse rotation, to drive the roller pump  168 , and to supply the ink into the sub ink tank  30 C. After the supply of a specified quantity of ink, the control circuit brings the drive motor  128  into the forward rotation, makes the ink supply unit  48 C retreat to the initial position. If the ink supply into the sub ink tank  30 C is not necessary, the control of the drive motor  128  not making the reverse rotation effects the advance and retreat of the ink supply unit  48 C only, and it does not drive the pump unit  164 , which precludes the ink supply into the sub ink tank  30 C. 
     Thus, as the ink supply into a desired sub ink tank  30  is completed, as understood from  FIG. 14 , in the end (strictly speaking, simultaneously with the retreat operation of the ink supply unit  48 Y), the cam for retreat corresponding to the positioning arm  60  brings the positioning arm  60  in retreat, and returns it to the initial position. With the aforementioned, all the operations of the ink supply into the sub ink tank  30  are completed. 
     As understood from the above explanation, this embodiment moves the ink supply unit  48  that requires ink supply, corresponding to a specific sub ink tank  30  among plural sub ink tanks  30 , selectively to the ink supply position, and achieves the ink supply into the sub ink tank  30  for each color. 
     Further, the sub ink tank unit  30  is provided with the air communication hole  38 , which softens a surge pressure variation inside the sub ink tank  30 . Since this softening prevents an unexpected ink leakage from an ink discharge opening of the recording head  28  and an suction of air, and so forth, the recording head unit  32  is able to maintain an optimum state for discharge of ink. 
     Further, the ink supply into the sub ink tank  30  is achieved by a negative pressurization inside the sub ink tank  30 , and accordingly the inner pressure in the sub ink tank  30  does not rise. Therefore, it is possible to reliably supply a certain quantity of ink into the sub ink tank  30 , in a shorter time without an unnecessary application of load, which is advantageous. Also, the ink supply unit  48  itself can be configured very simply, which achieves a cost reduction. 
     Since the cap  72  seals the air communication hole  38  during the ink supply, when the roller pump  168  is driven and the air inside the sub ink tank  30  is ejected out, the air will not come into the sub ink tank  30  from the air communication hole  38 , which enables secure pressure reduction inside the sub ink tank  30 , and secure ink supply. 
     Especially, in this embodiment, the air outlet  42  and the ink supply inlet  44  of the sub ink tank  30  are each connected to the exhaust port  74  and the ink supply port  76  of the ink supply unit  48 , respectively; and thereafter, the air communication hole  38  is to be sealed, and in addition the air communication hole  38  is opened, and thereafter the exhaust port  74  and the ink supply port  76  come off the air outlet  42  and the ink supply inlet  44 . This construction resolves a pressure variation created inside the sub ink tank  30 , accompanied with the connection or disconnection (connection release) operation of the exhaust port  34  and the ink supply port  36 . 
     The sealing part to seal the air communication hole  38  during the ink supply is not necessarily confined to the cap  72 , and any other measure may be used as long as it can seal the air communication hole  38 . Further, the cap  72  is not necessarily required to be attached to the ink supply unit  48 . For example, a holding member to hold the cap  72  may be provided; however, this embodiment attaches the cap  72  to the ink supply unit  48 , thereby saves such a holding member, reduces the number of components, and lowers the production cost. Further, the displacement (advance and retreat) of the ink supply unit  48  is utilized for sealing the air communication hole  38  or for releasing the sealing, which saves a device to move the cap  72  and simplifies the construction. 
     The ink supply device of the invention includes: an ink supply unit provided in correspondence with a recording head unit including a recording head that ejects ink drops onto a recording medium on the basis of image information, and a sub ink tank provided with an air communication hole, storing the ink supplied the recording head, which implements an ink supply by a pressure reduction part reducing a pressure inside the sub ink tank; and a sealing part that at least implements sealing of the air communication hole, while the ink supply unit is reducing the pressure inside the sub ink tank. Therefore, when the ink supply member is in reducing the pressure inside the sub ink tank, the air communication hole of the sub ink tank can be sealed, and the ink supply can be performed securely in a short time. 
     The entire disclosure of Japanese Patent Application No. 2000-316974 filed on Oct. 17, 2000 including specification, claims, drawings and abstract is incorporated herein by reference in its entirety.