Patent Publication Number: US-9840085-B2

Title: Liquid ejecting apparatus and liquid ejecting method

Description:
BACKGROUND 
     1. Technical Field 
     The present invention relates to a technique for ejecting liquid such as ink onto a medium. 
     2. Related Art 
     Various kinds of structure for fixing a cartridge that contains ink such as ink have been proposed. For example, the following structure is disclosed in JP-A-2007-062189. Two connection portions are provided on a cartridge. An ink taking-out opening and an ink filling opening are formed separately in each of the two connection portions. When the cartridge is attached to a cartridge attachment unit, the ink taking-out opening is connected to a flow passage through which ink is supplied to an ink-ejecting head, and the ink filling opening is connected to a flow passage toward a replenishment tank. 
     When plural flow-passage openings connected to respective different flow passages are formed in a cartridge as in the ink taking-out opening and the ink filling opening of JP-A-2007-062189, if these openings are formed in each of plural connection portions separately for connection to the corresponding flow passage of a cartridge attachment unit separately, the positioning of each of these connection portions in relation to the corresponding flow passage of the cartridge attachment unit is necessary, resulting in a complex connection portion structure. 
     SUMMARY 
     An advantage of some aspects of the invention is to simplify the structure of a connection portion for connection of a liquid container and an attachment unit. 
     A liquid ejecting apparatus according to an aspect of the invention comprises: an attachment unit to which a liquid container that contains liquid is attachable; a liquid ejecting head that ejects the liquid; and a connection portion that is provided on the attachment unit and is detachably inserted into a connection port of the liquid container, wherein the connection portion has at least one opening of a first flow passage and at least one opening of a second flow passage separately, wherein the first flow passage is a passage through which the liquid contained in the liquid container is sent to the liquid ejecting head, and wherein the second flow passage is a passage through which the liquid contained in the liquid container is sent, but not to the liquid ejecting head. Since the opening of the first flow passage and the opening of the second flow passage are formed in the connection portion of the attachment unit separately, it is possible to connect both the opening of the first flow passage and the opening of the second flow passage to the inside of the liquid container by attaching the liquid container in such a way that the connection portion of the attachment unit enters the connection port of the liquid container. Therefore, as compared with a case where a connection portion for the opening of the first flow passage and a connection portion for the opening of the second flow passage are provided separately from each other, it is possible to simplify the structure of the connection portion for connection of the liquid container and the attachment unit. 
     Preferably, the level of the opening of the second flow passage is higher than the level of the opening of the first flow passage in a vertical direction. With this preferred mode, the liquid level in the liquid container is never below the level of the opening of the first flow passage when, for example, the liquid is sucked out of the liquid container through the opening of the second flow passage. Therefore, with this structure, it is possible to prevent air bubbles, etc. from entering through the opening of the first flow passage leading to the liquid ejecting head. 
     Preferably, as viewed in the direction of insertion of the connection portion, the opening of the first flow passage and the opening of the second flow passage are arranged to surround the center of the connection portion. With this preferred mode, it is possible to make it easier to insert the connection portion into the connection port of the liquid container by, for example, adopting a pointed tip at the center of the connection portion as compared with a case where an opening is located at the center of the connection portion. 
     Preferably, the connection portion protrudes upward from an inner bottom surface of the attachment unit. With this preferred mode, it is possible to apply the invention to a case where the liquid container is attached to the bottom surface of the attachment unit. 
     Preferably, the connection portion protrudes sideways from an inner side surface of the attachment unit. With this preferred mode, it is possible to apply the invention to a case where the liquid container is attached to the side surface of the attachment unit. 
     Preferably, the liquid ejecting head and the attachment unit are provided on a moving member that reciprocates. With this preferred mode, it is possible to apply the invention to a case where the liquid container is mounted on the moving member on which the liquid ejecting head is provided. 
     Preferably, the liquid ejecting head is provided on a moving member that reciprocates; and the attachment unit is provided on the body of the liquid ejecting apparatus. With this preferred mode, it is possible to apply the invention to a case where the liquid container is mounted on the body of the liquid ejecting apparatus. 
     Preferably, the liquid ejecting head is an elongated line head; and the liquid ejecting head and the attachment unit are fixed. With this preferred mode, it is possible to apply the invention to a case where the liquid ejecting head is a line head. 
     Preferably, the liquid ejecting apparatus further comprises: a third flow passage for collection of the liquid sent through the second flow passage, wherein the third flow passage is detachably connected to the second flow passage. Since the third flow passage for collection of the liquid is detachably connected to the second flow passage of the attachment unit, with this preferred mode, it is possible to provide the third flow passage in other element (e.g., collection unit) that is not the attachment unit, in which the second flow passage is provided. 
     Preferably, a liquid ejecting apparatus comprises: an attachment unit to which a plurality of liquid containers each containing liquid is attachable; a liquid ejecting head that ejects the liquid; and a plurality of connection portions provided on the attachment unit, each of the plurality of connection portions being detachably inserted into a corresponding connection port of the corresponding liquid container, wherein each of the plurality of connection portions has at least one opening of a first flow passage and at least one opening of a second flow passage separately, wherein the first flow passage is a passage through which the liquid contained in the liquid container is sent to the liquid ejecting head, and wherein the second flow passage is a passage through which the liquid contained in the liquid container is sent, but not to the liquid ejecting head. With this preferred mode, for each of the plurality of liquid containers, it is possible to simplify the structure of the connection portion for connection of the liquid container and the attachment unit. 
     Preferably, the liquid ejecting apparatus further comprises: a third flow passage for collection of the liquid sent through the second flow passage, wherein the third flow passage is detachably connected to each of the second flow passages. With this preferred mode, it is possible to collect the liquid through only the second flow passage connected to, among the plurality of liquid containers, the desired liquid container. 
     A liquid ejecting method in a preferred aspect is as follows. A liquid ejecting apparatus includes an attachment unit to which a plurality of liquid containers each containing liquid is attachable, a liquid ejecting head that ejects the liquid, a plurality of connection portions provided on the attachment unit, each of the plurality of connection portions being detachably inserted into a corresponding connection port of the corresponding liquid container, each of the plurality of connection portions having at least one opening of a first flow passage and at least one opening of a second flow passage separately, the first flow passage being a passage through which the liquid contained in the liquid container is sent to the liquid ejecting head, the second flow passage being a passage through which the liquid contained in the liquid container is sent, but not to the liquid ejecting head, a third flow passage for collection of the liquid sent through the second flow passage being connected to each of the second flow passages, a valve being provided between each of the second flow passages and the third flow passage so as to be able to open and close therebetween, and a detector that detects an amount of the liquid left in each of the plurality of liquid containers. The liquid ejecting method comprises: detecting, by the detector, among the plurality of liquid containers, a liquid container in which the amount of the liquid left is not larger than a predetermined amount; opening the valve between the third flow passage and the second flow passage corresponding to the connection portion inserted in the connection port of the detected liquid container; and sucking the liquid out of the liquid container through the second flow passage to which the third flow passage is connected, thereby collecting the sucked liquid through the third flow passage. With this preferred aspect, it is possible to collect the liquid through only the second flow passage connected to, among the plurality of liquid containers, the liquid container whose remaining liquid amount has been detected to be not larger than the predetermined amount. 
     A liquid ejecting method in another preferred aspect is as follows. A liquid ejecting apparatus includes an attachment unit to which a plurality of liquid containers each containing liquid is attachable, a liquid ejecting head that ejects the liquid, a plurality of connection portions provided on the attachment unit, each of the plurality of connection portions being detachably inserted into a corresponding connection port of the corresponding liquid container, each of the plurality of connection portions having at least one opening of a first flow passage and at least one opening of a second flow passage separately, the first flow passage being a passage through which the liquid contained in the liquid container is sent to the liquid ejecting head, the second flow passage being a passage through which the liquid contained in the liquid container is sent, but not to the liquid ejecting head, a third flow passage for collection of the liquid sent through the second flow passage being detachably connected to each of the second flow passages, and a detector that detects an amount of the liquid left in each of the plurality of liquid containers. The liquid ejecting method comprises: detecting, by the detector, among the plurality of liquid containers, a liquid container in which the amount of the liquid left is not larger than a predetermined amount; connecting the third flow passage to the second flow passage corresponding to the connection portion inserted in the connection port of the detected liquid container; and sucking the liquid out of the liquid container through the second flow passage to which the third flow passage is connected, thereby collecting the sucked liquid through the third flow passage. With this preferred aspect, it is possible to collect the liquid through only the second flow passage connected to, among the plurality of liquid containers, the liquid container whose remaining liquid amount has been detected to be not larger than the predetermined amount. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements. 
         FIG. 1  is a structure diagram of a printing apparatus according to a first embodiment. 
         FIG. 2  is an enlarged view of an attachment unit for liquid containers illustrated in  FIG. 1 , and of a collection unit. 
         FIG. 3  is a side view of the attachment unit. 
         FIG. 4  is a sectional view of arbitrary one connection portion of the attachment unit, taken along the Y-Z plane. 
         FIG. 5  is an enlarged view of the connection portion illustrated in  FIG. 4 . 
         FIG. 6  is a perspective view of the connection portion illustrated in  FIG. 4 . 
         FIG. 7  is a top view of the connection portion illustrated in  FIG. 4 . 
         FIG. 8  is view of a variation example of the top portion of the connection portion according to the first embodiment. 
         FIG. 9  is a diagram for explaining the operation of the connection portion illustrated in  FIG. 4 . 
         FIG. 10  is a sectional view of a connection portion according to a variation example of the first embodiment, and a top view. 
         FIG. 11  is a side view of the connection portion illustrated in  FIG. 10 . 
         FIG. 12  is a diagram for explaining the operation of the connection portion illustrated in  FIG. 10 . 
         FIG. 13  is a flowchart that illustrates residual ink collection control performed by a controller. 
         FIG. 14  is a structure diagram of a printing apparatus according to a second embodiment. 
         FIG. 15  is an enlarged view of an attachment unit for liquid containers according to the second embodiment, and of a collection unit. 
         FIG. 16  is a structure diagram of a printing apparatus according to a third embodiment. 
         FIG. 17  is an enlarged view of an attachment unit for liquid containers according to a third embodiment, and of a collection unit. 
         FIG. 18  is a structure diagram of a printing apparatus according to a variation example of the third embodiment. 
         FIG. 19  is a structure diagram of a printing apparatus according to a fourth embodiment. 
         FIG. 20  is a sectional view and a top view of a connection portion according to a variation example. 
         FIG. 21  is a sectional view and a top view of a connection portion according to another variation example. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     First Embodiment 
       FIG. 1  is a partial structure diagram of an ink-jet printing apparatus  10  according to a first embodiment of the invention. The printing apparatus  10  is a liquid ejecting apparatus that ejects ink, which is an example of liquid, onto a medium (ejection target)  12  such as printing paper. In the first embodiment, a so-called off-carriage-type structure, in which a liquid container such as an ink container is mounted on the body of the printing apparatus  10 , is taken as an example. The printing apparatus  10  includes a controller  30 , a transportation mechanism  32 , a movement mechanism  33 , a carriage  34 , and a liquid ejecting head  36 . The carriage  34  is an example of a moving member. 
     An attachment unit (cartridge holder)  40  is provided on the printing apparatus  10 . A plurality of liquid containers (cartridges) C 1  to C 4  is attachable to the attachment unit  40 . Plural types of ink are contained in the respective containers separately. Ink is liquid that contains a colorant such as pigment or dye (color ink). For example, the liquid is ink of four colors, specifically, cyan (C), magenta (M), yellow (Y), and black (K). The ink may contain a resin material. In the present embodiment, the liquid containers C 1  to C 4  contain yellow ink (Y), magenta ink (M), cyan ink (C), and black ink (K) respectively. A collection unit  50  for collection of the ink contained in the liquid containers C 1  to C 4  is connected to the attachment unit  40 . A detailed explanation of the attachment unit  40  and the collection unit  50  will be given later. 
     The controller  30  illustrated in  FIG. 1  centrally controls the elements of the printing apparatus  10 . The controller  30  includes, for example, a control circuit such as a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory), etc. The ROM is, for example, a rewritable flash ROM. Programs that are to be run by the controller  30  and various kinds of data necessary for running the programs are stored in the ROM. Data, etc. used temporarily when the controller  30  runs the programs are stored into the RAM. A management apparatus (not illustrated), for example, a personal computer, is connected to the controller  30 . In accordance with instructions given from the management apparatus, the controller  30  centrally controls the elements of the printing apparatus  10 . 
     Under the control of the controller  30 , the liquid ejecting head  36  ejects ink of the respective colors supplied from the liquid containers C 1  to C 4  onto the medium  12 . Four ink nozzle lines L 1  to L 4  are arranged on the ejecting face (surface that faces the medium  12 ) of the liquid ejecting head  36  illustrated in  FIG. 1 . Each of the ink nozzle lines L 1  to L 4  is a group of plural nozzles N that are in a linear array along the Y direction. Each of the ink nozzle lines L 1  to L 4  may consist of plural columns (for example, zigzag array or staggered array). 
     Yellow ink (Y), which is supplied from the liquid container C 1 , is ejected from the nozzles N of the ink nozzle line L 1 . Magenta ink (M), which is supplied from the liquid container C 2 , is ejected from the nozzles N of the ink nozzle line L 2 . Cyan ink (C), which is supplied from the liquid container C 3 , is ejected from the nozzles N of the ink nozzle line L 3 . Black ink (K), which is supplied from the liquid container C 4 , is ejected from the nozzles N of the ink nozzle line L 4 . 
     Pressure compartments and piezoelectric elements that are not illustrated are provided in the liquid ejecting head  36  correspondingly to the nozzles N of each of the ink nozzle lines L 1  to L 4 . Ink supplied from each of the liquid containers C 1  to C 4  is filled into the corresponding pressure compartments of the liquid ejecting head  36 . A driving signal is supplied so as to cause each piezoelectric element to vibrate. This gives rise to a pressure change in the corresponding pressure compartment. As a result, ink in the corresponding pressure compartment is ejected from the corresponding nozzle N. 
     Under the control of the controller  30 , the transportation mechanism  32  transports the medium  12  in the Y direction (sub scan direction). Under the control of the controller  30 , the movement mechanism  33  causes the carriage  34  to reciprocate in the X direction (main scan direction). Concurrently with the transportation of the medium  12  and the reciprocation of the carriage  34 , the liquid ejecting head  36  ejects ink onto the medium  12 . As a result, a print-instructed image is formed on the surface of the medium  12 . In the description below, the direction perpendicular to the X−Y plane (plane parallel to the surface of the medium  12 ) is denoted as Z direction. The direction in which ink is ejected by the liquid ejecting head  36  (vertically downward) corresponds to the Z direction. 
     Liquid Container Attachment Unit and Collection Unit 
       FIG. 2  is an enlarged view of the attachment unit  40  for the liquid containers C 1  to C 4 , and of the collection unit  50 .  FIG. 3  is a side view of the attachment unit  40  from the positive side +Y in the Y direction. In  FIG. 3 , the illustration of the collection unit  50  is omitted. Each of the liquid containers C 1  to C 4  is an ink-tank-type cartridge made of a box-shaped container. The liquid container C 1  to C 4  is not limited to a box-shaped container. It may be an ink-pack-type cartridge having a bag container structure. 
     The attachment unit  40  in the first embodiment has an open-topped box structure. For example, it is formed integrally by injection-molding a resin material. The liquid containers C 1  to C 4  are arranged toward the positive side +X in the X direction and accommodated in a container-housing space surrounded by the inner bottom surface (floor)  412  of the bottom wall  41  of the attachment unit  40  and the inner side surfaces  422  of the sidewalls  42  thereof. A connection portion  43  is provided inside the container-housing space of the attachment unit  40  correspondingly to each of the liquid containers C 1  to C 4 . In the first embodiment, the connection portions  43  are provided on the inner bottom surface  412 . Each of the liquid containers C 1  to C 4  is detachably attached to the corresponding connection portion  43 . A detailed explanation of the connection portion  43  will be given later. 
     The collection unit  50  includes a collection flow passage (third flow passage)  52 , a suction pump P, and a collection container (collection tank)  54 . The collection container  54  is a box-shaped container that contains collected ink. The collection flow passage  52  is made up of a main flow passage Q, which is in communication with the collection container  54 , and four branch flow passages Q 1  to Q 4 , which branch off from the main flow passage Q. 
     The suction pump P, which is driven by the controller  30 , is provided on the main flow passage Q. Each of the branch flow passages Q 1  to Q 4  is connected to a side of the attachment unit  40 , for example, to the corresponding one of openings O 1  to O 4 , which are formed in a side  411  of a bottom wall portion  41  in the +Y direction. Each of the openings O 1  to O 4  is in communication with the inside of the corresponding one of the liquid containers C 1  to C 4  separately from the others through the corresponding connection portion  43  (described later) where the corresponding liquid container C 1  to C 4  is connected to the attachment unit  40 . On each of the branch flow passages Q 1  to Q 4 , the corresponding one of open/close valves V 1  to V 4  is provided. The opening and closing of the open/close valves V 1  to V 4  is controlled by the controller  30 . With the structure described above, it is possible to individually suck ink of one of the liquid containers C 1  to C 4  for collection into the collection container  54  by controlling, by the controller  30 , the open/close valves V 1  to V 4  so as to open one of the branch flow passages Q 1  to Q 4  and driving the suction pump P. Though a structure example in which the open/close valves V 1  to V 4  are provided on the collection unit  50  is illustrated in  FIGS. 1 and 2 , the open/close valves V 1  to V 4  may be provided on the attachment unit  40 . 
     Connection of Attachment Unit and Liquid Container 
     The connection portion  43  where the liquid container C 1  to C 4  is connected to the attachment unit  40  will now be explained in detail.  FIG. 4  is a sectional view of arbitrary one connection portion of the attachment unit  40  illustrated in  FIG. 2 , taken along the Y-Z plane.  FIG. 5  is an enlarged view of the connection portion  43  illustrated in  FIG. 4 .  FIG. 6  is a perspective view of the connection portion  43 .  FIG. 7  is a view of the connection portion  43  in the Z direction (viewed from above vertically). The same structure applies to the connection portions  43  where the respective liquid containers C 1  to C 4  are connected to the attachment unit  40 . Therefore, in the description below, arbitrary one of the liquid containers C 1  to C 4  is taken as a representative example and is denoted as C. The opening corresponding to the representative liquid container C is denoted as O, and the open/close valve corresponding to the representative liquid container C is denoted as V. With this representative one taken as an example, the connection of the liquid container C and the attachment unit  40  will now be explained. 
     As illustrated in  FIG. 4 , the liquid container C is detachably attached to the inner bottom surface  412  of the attachment unit  40 . The connection portion  43  of the attachment unit  40  has a needle shape, meaning that its tip  431  is pointed. The pointed tip  431  is inserted into the liquid container C. More specifically, a cylindrical connection port  24 , which is in communication with the inside of the liquid container C, is provided on the lower surface  212  of the bottom wall  21  of the liquid container C, and the connection portion  43  is inserted into the connection port  24 . 
     As illustrated in  FIGS. 5 and 6 , the connection portion  43  of the attachment unit  40  protrudes from the inner bottom surface  412  toward the negative side −Z in the Z direction (vertically upward). The cone-shaped tip portion  431  of the connection portion  43  has, in its conical surface (slope), a plurality of inlets (openings)  442  of a first flow passage  44  and a plurality of inlets (openings)  452  of a second flow passage  45  separately. The first flow passage  44  is a passage through which ink contained in the liquid container C is sent to the liquid ejecting head  36  for ink ejection. The second flow passage  45  is a passage through which ink contained in the liquid container C is sent, but not to the liquid ejecting head  36 . In the example described here, the second flow passage  45  is used as an ink collection passage, through which ink contained in the liquid container C is sent to the collection container  54 . 
     As illustrated in  FIG. 7 , when the tip portion  431  of the connection portion  43  is viewed in the Z direction (direction of insertion), the plural flow-passage inlets  442  for ink ejection and the plural flow-passage inlets  452  for ink collection are arranged annularly to surround the center of the tip portion  431 . With this annular arrangement, it is possible to make it easier to insert the connection portion into the connection port  24  of the liquid container C by adopting a center-pointed tip  431  as compared with a case where a flow-passage inlet  452  for ink collection is located at the center of the tip portion  431  (for example, as in  FIG. 20  described later). For example, when a liquid container C with a film-covered connection port  24  in mint condition is designed to be attached to the attachment unit  40  by piercing the needle portion through the film of the connection port  24 , the pointed annular array structure makes the piercing easier. 
     The plural flow-passage inlets  442  for ink ejection are arranged to encircle the plural flow-passage inlets  452  for ink collection. In other words, the flow-passage inlets  442  are located outside in relation to the flow-passage inlets  452 . Therefore, as compared with a case where the flow-passage inlets  442  are located inside in relation to the flow-passage inlets  452  (for example, similarly to  FIG. 21  described later), it is harder for air bubbles, etc. to enter through the flow-passage inlets  452  for ink collection. The flow-passage inlets  442  for ink ejection and the flow-passage inlets  452  for ink collection are not limited to plural annular-array through holes as in  FIG. 7 . For example, as illustrated in  FIG. 8 , the inlet shape may be a ring-groove shape. 
     As illustrated in  FIG. 5 , the plural flow-passage inlets  452  for ink collection are located above the plural flow-passage inlets  442  for ink ejection in the Z direction (vertical direction). With this structure, since the surface of ink (liquid level) is never below the level of the plural flow-passage inlets  442  for ink ejection when the ink is sucked through the flow-passage inlets  452 , it is possible to prevent air bubbles, etc. from entering through the flow-passage inlets  442 . A more detailed explanation of this benefit will be given later. 
     The first flow passage  44  for ink supply is made up of a main flow passage  444  and branch flow passages  445 . The main flow passage  444  is in communication with a flow-passage outlet  443 , which is open at the lower surface  413  of the bottom wall  41  of the attachment unit  40 . The branch flow passages  445  branching off from the main flow passage  444  are in communication with the respective flow-passage inlets  442 . A non-return valve Vs for preventing ink from flowing backward is provided on the main flow passage  444 . A pump (not illustrated) that sends ink to the liquid ejecting head  36  is connected to the flow-passage outlet  443 . On the other hand, the second flow passage  45  for ink collection is made up of a main flow passage  454  and branch flow passages  455 . The main flow passage  454  is in communication with a flow-passage outlet  453 . The branch flow passages  455  branching off from the main flow passage  454  are in communication with the respective flow-passage inlets  452 . The flow-passage outlet  453  is connected to the opening O described earlier. The second flow passage  45  for ink collection is in communication with the collection flow passage  52  of the collection unit  50  through the opening O. 
     A liquid amount detector  47  is provided partially on the liquid container C and partially on the attachment unit  40 . The liquid amount detector  47  detects the amount of ink left in the liquid container C. For example, as illustrated in  FIG. 4 , the liquid amount detector  47  is made up of an optical sensor  472 , which is provided in the attachment unit  40 , and a prism  474 , which is provided in the liquid container C. The prism  474  is a transparent member that has an isosceles-triangular shape with slopes. The liquid container C has a through-hole-type window in the bottom wall  21 , and the prism  474  is hermetically embedded in the window. The apex defined by the slopes of the isosceles triangle is oriented upward in the vertical direction. The optical sensor  472  is embedded in the bottom wall  41  of the attachment unit  40 . The optical sensor  472  and the prism  474  face each other. Under the control of the controller  30 , the optical sensor  472  emits light toward the prism  474  and receives light reflected therefrom. On the basis of the amount of the reflection light received, the amount of ink left in the liquid container C is detected. The structure of the liquid amount detector  47  is not limited to the above example. 
     As illustrated in  FIG. 4 , when the liquid container C is attached to the inner bottom surface  412  of the attachment unit  40  having the above structure, the connection portion  43  enters the connection port  24  of the liquid container C. When this insertion is performed, the tip portion  431  of the attachment unit  40  becomes positioned inside the liquid container C in such a way as to protrude upward from the upper surface (inner bottom surface)  214  of the bottom wall  21  of the liquid container C. By attaching the liquid container C to the attachment unit  40  in such a way that the connection portion  43  of the attachment unit  40  enters the connection port  24  of the liquid container C in this way, it is possible to obtain the fluid connection of both the inlets  442  of the first flow passage  44  and the inlets  452  of the second flow passage  45  to the inside of the liquid container C. Therefore, with a single connection portion  43 , as compared with a case where a connection portion for the inlets  442  of the first flow passage  44  and a connection portion for the inlets  452  of the second flow passage  45  are provided separately from each other, it is possible to simplify the connection structure. To supply ink to the liquid ejecting head  36  from the liquid container C attached to the attachment unit  40 , the pump, which is not illustrated, is driven. When pumped, ink flows out of the liquid container C into the ink-supplying flow-passage inlets  442  of the connection portion  43 , and next through the first flow passage  44 . By this means, it is possible to supply the ink to the liquid ejecting head  36 . 
     For ink collection into the collection container  54 , the suction pump P of the collection unit  50  is driven. When pumped, ink flows out of the liquid container C into the ink-collecting flow-passage inlets  452  of the connection portion  43 , and next through the second flow passage  45 , and finally into the collection container  54 . As illustrated in  FIG. 9 , the surface of ink (liquid level) in the vertical direction drops when ink is sucked out through the ink-collecting flow-passage inlets  452 , and the drop in the liquid level stops at the level h of the ink-collecting flow-passage inlets  452 . Since the level h of the ink-collecting flow-passage inlets  452  is above the level h′ of the ink-supplying flow-passage inlets  442 , the liquid level is never below the level h′ of the ink-supplying flow-passage inlets  442  when the ink is sucked through the flow-passage inlets  452 . Therefore, with this structure, it is possible to prevent air bubbles, etc. from entering through the ink-supplying flow-passage inlets  442 , the flow destination of which is the liquid ejecting head  36 . 
     In the first embodiment, the tip portion  431  of the connection portion  43  (conical surface) slopes downward with respect to the vertical direction from the center toward the circumference. Therefore, the farther the flow-passage inlets  442  for ink ejection are located outside in relation to the flow-passage inlets  452  for ink collection as viewed from above in the vertical direction, the greater the level difference between the flow-passage inlets  452  and the flow-passage inlets  442  is. This makes it harder for air bubbles, etc. to enter through the flow-passage inlets  442  for ink ejection. 
     In the example illustrated in  FIG. 4 , the liquid container C is attached to the inner bottom surface  412  of the attachment unit  40 . However, the scope of the invention is not limited thereto. For example, as illustrated in  FIG. 10 , the liquid container C may be attached to an inner side surface of the attachment unit  40 . The attachment unit  40  illustrated in  FIG. 10  has, on its sidewall  42 , a connection portion  43  that protrudes from an inner side surface  422  of the sidewall  42  toward the negative side −Y in the Y direction. 
     Since the attachment unit  40  illustrated in  FIG. 10  does not have the negative-side −Y sidewall, it is possible to insert the liquid container C into the attachment unit  40  through this wall-less side. Therefore, it is possible to detachably attach the liquid container C to the inner side surface  422  of the attachment unit  40 . The connection portion  43  illustrated in  FIG. 10  has a needle shape, meaning that its tip  431  is pointed. The pointed tip  431  is inserted into the liquid container C to take in ink. More specifically, a connection port  24 , which is in communication with the inside of the liquid container C, is provided on the outer surface  222  (+Y side) of a sidewall  22  of the liquid container C, and the connection portion  43  is inserted into the connection port  24 . 
     The connection portion  43  illustrated in  FIG. 10  protrudes from the inner side surface  422  of the attachment unit  40  toward the negative side −Y in the Y direction. The cone-shaped tip portion  431  of the connection portion  43  has, in its conical surface (slope), a plurality of inlets  442  of a first flow passage  44  for ink ejection and a plurality of inlets  452  of a second flow passage  45  for ink collection separately. 
       FIG. 11  is a Y-directional side view of the tip portion  431  of the connection portion  43  illustrated in  FIG. 10 . As illustrated in  FIG. 11 , the plural flow-passage inlets  452  for ink collection are located above the plural flow-passage inlets  442  for ink ejection in the Z direction (vertical direction). Assuming that a virtual G-G line goes through the center of the tip portion  431  of the connection portion  43  in parallel with the X direction, the plural flow-passage inlets  452  for ink collection are located above the G-G line in the Z direction (thereabove in the vertical direction), and the plural flow-passage inlets  442  for ink ejection are located below the G-G line in the Z direction (therebelow in the vertical direction). In this layout, the area above the G-G line is located at a higher-level position in the vertical direction as compared with the area below the G-G line. Therefore, the level of the flow-passage inlets  452  for ink collection, which are located above the G-G line, is higher than the level of the flow-passage inlets  442  for ink ejection, which are located below the G-G line. The flow-passage inlets  442  for ink ejection and the flow-passage inlets  452  for ink collection are not limited to plural annular-array through holes as in  FIG. 11 . For example, the inlet shape may be a ring-groove shape. Similarly to  FIG. 11 , when such a ring-groove structure is adopted, the flow-passage inlet  452  for ink collection is arranged above the G-G line, and the flow-passage inlet  442  for ink ejection is arranged below the G-G line. Therefore, the level of the flow-passage inlet  452  for ink collection is higher than the level of the flow-passage inlet  442  for ink ejection. Similarly to  FIG. 4 , the ink-supplying first flow passage  44  illustrated in  FIG. 10  is in communication with a flow-passage outlet  443 , which is open at the outer surface  413  of the bottom wall  41  of the attachment unit  40 . In addition, similarly to  FIG. 4 , the downstream end of the second flow passage  45  for ink collection is connected to the opening O. 
     When the liquid container C illustrated in  FIG. 10  is attached to the inner side surface  422  of the attachment unit  40  having the above structure, the connection portion  43  enters the connection port  24  of the liquid container C. When this insertion is performed, the tip portion  431  of the attachment unit  40  becomes positioned inside the liquid container C in such a way as to protrude through the sidewall  22  of the liquid container C toward the negative side −Y in the Y direction. To supply ink to the liquid ejecting head  36 , the pump, which is not illustrated, is driven. When pumped, ink flows out of the liquid container C into the ink-supplying flow-passage inlets  442  of the connection portion  43 , and next through the first flow passage  44 . By this means, it is possible to supply the ink to the liquid ejecting head  36 . 
     For ink collection into the collection container  54 , the suction pump P of the collection unit  50  is driven. When pumped, ink flows out of the liquid container C into the ink-collecting flow-passage inlets  452  of the connection portion  43 , and next through the second flow passage  45 , and finally into the collection container  54 . As illustrated in  FIG. 12 , the surface of ink (liquid level) in the vertical direction drops when ink is sucked out through the ink-collecting flow-passage inlets  452 , and the drop in the liquid level stops at the level h of the ink-collecting flow-passage inlets  452 . Since the liquid level of ink h is above the level h′ of the ink-supplying flow-passage inlets  442 , as in  FIG. 9 , this structure prevents air bubbles from entering through the ink-supplying flow-passage inlets  442 . 
     Some printers are designed to notify a user of an ink-low (near-end) state, that is, a state in which the amount of ink left in the liquid container C is small. For example, a lamp goes ON to let a user know that it is time to replace the liquid container C with new one. If ink is consumed until the liquid container C becomes completely empty, there is a risk that air bubbles might enter the liquid ejecting head  36 , resulting in poor ejection. A near-end notification is made to avoid this from happening. However, in such a case, there exists a small amount of ink left in the liquid container C when the time to replace the liquid container C with new one is detected by the controller  30 . Therefore, if the user detaches and shakes the liquid container C carelessly, there is a risk of the splattering of the ink. 
     In this respect, with the structure of the first embodiment, even if the above-mentioned ink-low near-end state has been programmed in advance in association with the time to replace the liquid container C with new one, it is possible to remove a large part of the residual ink until the residual liquid level becomes very close to the inner bottom surface  214  of the liquid container C. Moreover, air bubbles do not go in through the ink-supplying flow-passage inlets  442 . By performing residual ink collection described above, it is possible to eliminate a risk of the splattering of ink even if a user shakes the liquid container C inadvertently, while ensuring that air bubbles do not go in through the ink-supplying flow-passage inlets  442 . 
     Residual Ink Collection Method 
     Next, a method for collecting ink left in the liquid container C 1  to C 4  according to the first embodiment will now be explained in detail.  FIG. 13  is a flowchart that illustrates residual ink collection control performed by the controller  30 . First, in a step S 101 , the controller  30  causes the liquid amount detector  47  to detect the amount of ink left in each of the liquid containers C 1  to C 4 . In a step S 102 , the controller  30  judges whether, for any of the liquid containers C 1  to C 4 , the ink amount detected by the liquid amount detector  47  is not greater than a predetermined value (near end) or not. By performing ink amount detection processing for each of the liquid containers C 1  to C 4  in this way, the controller  30  detects one or more liquid containers C 1  to C 4  that need to be replaced, if any. Instead of “not greater than a predetermined value”, “less than a predetermined value” may be defined as “near end”. 
     The process returns to the step S 101  if there is no near-end container, specifically, if it is judged by the controller  30  in the step S 102  that, for none of the liquid containers C 1  to C 4 , the ink amount is not greater than the predetermined value. If it is judged by the controller  30  in the step S 102  that the amount of ink left in any of the liquid containers C 1  to C 4  is not greater than the predetermined value (near end) (assume that the amount of ink left in the liquid container C is not greater than the predetermined value), in a step S 103 , among the open/close valves V 1  to V 4  illustrated in  FIG. 2 , one corresponding to the liquid container C is opened. When it is opened, the other valves are kept closed. 
     Next, in a step S 104 , to suck ink out of the liquid container C, the controller  30  drives the suction pump P of the collection unit  50 . As a result, ink is sucked out of the liquid container C only. The sucked ink goes to the collection container  54 . Next, in a step S 105 , the controller  30  judges whether residual ink collection has ended or not. For example, to judge whether residual ink collection has ended or not, it is judged whether predetermined time has elapsed or not. The method of judgment is not limited thereto. It may be judged on the basis of the ink amount detected by the liquid amount detector  47 . Alternatively, an optical sensor for detecting the presence or absence of ink in the collection flow passage  52  may be provided. The controller  30  can judge that residual ink collection has ended when the absence of ink in the collection flow passage  52  is detected by the optical sensor. 
     The processing in the step S 104  continues if the controller  30  judges in the step S 105  that residual ink collection has not ended yet. If the controller  30  judges in the step S 105  that residual ink collection has ended, in a step S 106 , the open/close valve corresponding to the liquid container C is closed to finish the series of collection control steps. 
     With the residual ink collection control illustrated in  FIG. 13 , it is possible to collect residual ink by, under the control of the controller  30 , detecting the amount of ink for each of the liquid containers C 1  to C 4  and opening only the open/close valve corresponding to the liquid container whose ink amount is not greater than the predetermined value. For example, if the amount of ink left in the liquid container C 4  is not greater than the predetermined value, the controller  30  opens the open/close valve V 4 , which corresponds to the liquid container C 4 , and drives the suction pump P. Since the other open/close valves V 1 , V 2 , and V 3  remain closed, it is possible to suck ink out of the liquid container C 4  only. Moreover, if the suction pump P is driven for predetermined time, the drop in the liquid level stops at the level of the ink-collecting flow-passage inlets  452  as illustrated in  FIG. 9 or 12 . Therefore, it is possible to prevent air bubbles, etc. from entering through the ink-supplying flow-passage inlets  442  without any need for precisely setting the predetermined duration of driving the suction pump P. 
     Second Embodiment 
     A second embodiment of the invention will now be explained.  FIG. 14  is a partial structure diagram of a printing apparatus  10  according to a second embodiment. In the first embodiment, a so-called off-carriage-type structure, in which the liquid containers C 1  to C 4  are mounted on the body of the printing apparatus  10 , has been described. In the second embodiment, a so-called on-carriage-type structure, in which the liquid containers C 1  to C 4  are mounted on the carriage  34 , is taken as an example. In each exemplary embodiment described below, the same reference numerals as those used in the description of the first embodiment are assigned to elements that are the same in operation and/or function as those in the first embodiment, and a detailed explanation of them is omitted. 
     The liquid containers C 1  to C 4  illustrated in  FIG. 14  are mounted together with the liquid ejecting head  36  on the carriage  34 . That is, in the structure illustrated in  FIG. 14 , the attachment unit  40  illustrated in  FIG. 2  is provided on the carriage  34 , and the collection unit  50  is provided on the body of the printing apparatus  10 . 
     As illustrated in  FIG. 14 , the collection unit  50  is provided in a non-print area H, for example, at the home position (standby position) of the carriage  34  in the X direction. Specifically, the collection unit  50  is provided in the non-print area H at the positive side in the Y direction with respect to the home position of the carriage  34 . As illustrated in  FIG. 14 , the collection unit  50  is configured to be able to reciprocate from the positive side toward the negative side and vice versa in the Y direction so as to be able to be attached to and detached from the attachment unit  40  mounted on the carriage  34 . 
       FIG. 15  is a diagram for explaining the operation of the collection unit  50  when the carriage  34  stays at the home position. Due to the reciprocation of the collection unit  50  between the positive side and the negative side in the Y direction when the carriage  34  stays at the home position, the branch flow passages Q 1  to Q 4  of the collection flow passage  52  are connected to and disconnected from the respective openings O 1  to O 4  of the attachment unit  40 . The standby position of the collection unit  50  is located at the positive side in the Y direction with respect to the home position of the carriage  34 . 
     In the second embodiment, the same structure as that of the first embodiment can be adopted for the attachment unit  40 , including the connection portion  43 . By this means, in the second embodiment, it is possible to collect the residual ink of the liquid container C 1  to C 4  as in the first embodiment, thereby preventing air bubbles from entering through the ink-supplying flow-passage inlets  442 . The controller  30  of the second embodiment is also capable of performing residual ink collection control illustrated in  FIG. 13 . After the movement of the carriage  34  to the home position, the controller  30  causes the collection unit  50  to move toward the negative side in the Y direction so as to connect the branch flow passages Q 1  to Q 4  of the collection flow passage  52  to the respective openings O 1  to O 4  of the attachment unit  40  and thereafter opens the open/close valve in the step S 103 . After the closing of the open/close valve in the step S 106 , the controller  30  causes the collection unit  50  to move back toward the positive side in the Y direction to its standby position so as to disconnect the branch flow passages Q 1  to Q 4  of the collection flow passage  52  from the respective openings O 1  to O 4  of the attachment unit  40 . By this means, in the second embodiment, the same effects as those of the first embodiment can be expected. 
     Third Embodiment 
     A third embodiment of the invention will now be explained.  FIG. 16  is a partial structure diagram of a printing apparatus  10  according to a third embodiment. As in the second embodiment, the printing apparatus  10  of the third embodiment has a so-called on-carriage-type structure, in which the liquid containers C 1  to C 4  are mounted on the carriage  34 . Unlike the second embodiment, the collection unit  50  of the third embodiment includes a non-branched collection flow passage  52 . In addition, as illustrated in  FIG. 17 , the collection unit  50  of the third embodiment is configured to be able to reciprocate not only in the Y direction but also in the X direction. The structure of the attachment unit  40  of the third embodiment is the same as that of the first embodiment. By this means, in the third embodiment, it is possible to collect the residual ink of the liquid container C 1  to C 4  as in the first embodiment, thereby preventing air bubbles from entering through the ink-supplying flow-passage inlets  442 . Residual ink may be collected from any liquid container C 1  to C 4  by, instead of moving the collection unit  50  in the X direction, moving the carriage  34  in the X direction for X-directional positional adjustment; specifically, the carriage  34  is moved to align one of the openings O 1  to O 4  with the collection flow passage  52  of the collection unit  50 , followed by connection, and collection. 
     The controller  30  of the third embodiment is also capable of performing residual ink collection control illustrated in  FIG. 13 . After the movement of the carriage  34  to the home position, the controller  30  causes the collection unit  50  to move both in the X direction and in the Y direction so as to connect the collection flow passage  52  to, among the openings O 1  to O 4 , only one corresponding to the liquid container from which residual ink is to be collected (in  FIG. 17 , the opening O 4  only) and thereafter opens the open/close valve V in the step S 103 . After the closing of the open/close valve V in the step S 106 , the controller  30  causes the collection unit  50  to move both in the Y direction and in the X direction back to its standby position so as to disconnect the collection flow passage  52  from the opening of the attachment unit  40 . By this means, in the third embodiment, the same effects as those of the first embodiment can be expected. In addition, in the third embodiment, it is sufficient to provide a single open/close valve V on the collection flow passage  52 . As compared with a structure in which the open/close valves V 1  to V 4  corresponding to the respective liquid containers C 1  to C 4  are provided, it is possible to simplify open/close valve control because no selection among the open/close valves V 1  to V 4  is necessary. 
     In the printing apparatus  10  of the third embodiment, after the movement of the liquid ejecting head  36  to the home position H, the ejecting face of the liquid ejecting head  36  may be sealed (capped) with a sealing member (cap) before the collection of residual ink by the collection unit  50 . Specifically, as illustrated in  FIG. 18 , the ejecting face of the liquid ejecting head  36  is sealed with a sealing member  60 , which is provided at the home position H of the printing apparatus  10 . The sealing member  60  is a capping member that is open toward the ejecting face of the liquid ejecting head  36 . The sealing of the ejecting face of the liquid ejecting head  36  with the sealing member  60  makes it easier to withstand pressure fluctuation that occurs inside the liquid ejecting head  36  when residual ink is sucked by the collection unit  50 . Moreover, since the nozzles N are sealed by the sealing member  60 , when residual ink is sucked by the collection unit  50 , the sealing prevents the entering of air bubbles into the ink-supplying flow passage of the liquid ejecting head  36  through the nozzles N effectively. As stated above, it is possible to suck residual ink without an influence on the ink-supplying flow passage of the liquid ejecting head  36 . During the sealing of the liquid ejecting head  36  with the sealing member  60 , the liquid ejecting head  36  cannot be moved in the X, Y direction. In this respect, since the collection unit  50  of the third embodiment is movable not only in the Y direction but also in the X direction, it is possible to connect the collection flow passage  52  to one of the openings O 1  to O 4  even when the liquid ejecting head  36  cannot be moved. Another maintenance member such as a suction pump for the recovery of clogged nozzles N may be provided for the sealing member  60 . 
     Fourth Embodiment 
     A fourth embodiment of the invention will now be explained. The printing apparatus  10  described in the first, second, and third embodiments is a serial-head printer in which the carriage  34 , together with the liquid ejecting head  36  mounted thereon, moves in the X direction. In the fourth embodiment, a line-head printer whose liquid ejecting head  36  is elongated in a direction intersecting with the transportation direction of the medium  12  (elongated in the X direction here) is taken as example. 
       FIG. 19  is a partial structure diagram of a printing apparatus  10  according to a fourth embodiment. The liquid ejecting head  36  of the printing apparatus  10  illustrated in  FIG. 19  is a line head on the ejecting face of which four ink nozzle lines L 11  to L 14  are arranged at Y-directional intervals. Each of the ink nozzle lines L 11  to L 14  is a group of plural nozzles N that are in a linear array along the X direction. Each of the ink nozzle lines L 11  to L 14  may consist of plural rows (for example, zigzag array or staggered array). 
     As in the first embodiment, the printing apparatus  10  illustrated in  FIG. 19  has a so-called off-carriage-type structure, in which the liquid containers C 1  to C 4  are mounted on the body of the printing apparatus  10 . The structure and position of the attachment unit  40  and of the collection unit  50  illustrated in  FIG. 19  is the same as that of the first embodiment. Yellow ink (Y), which is supplied from the liquid container C 1 , is ejected from the nozzles N of the ink nozzle line L 11 . Magenta ink (M), which is supplied from the liquid container C 2 , is ejected from the nozzles N of the ink nozzle line L 12 . Cyan ink (C), which is supplied from the liquid container C 3 , is ejected from the nozzles N of the ink nozzle line L 13 . Black ink (K), which is supplied from the liquid container C 4 , is ejected from the nozzles N of the ink nozzle line L 14 . Since the structure of the attachment unit  40  and of the collection unit  50  in the fourth embodiment is the same as that of the first embodiment, the same effects as those of the first embodiment can be expected in the fourth embodiment. 
     Variation Examples 
     The exemplary embodiments described above can be modified in various ways. Specific variation examples are described below. Two or more variation examples selected arbitrarily from the description below may be combined as long as they are not contradictory to each other or one another. 
     (1) The structure of the connection portion  43  of the attachment unit  40  is not limited to the foregoing examples in the embodiments. For example, the connection portion  43  illustrated in  FIG. 5  may be modified as illustrated in  FIG. 20 . The connection portion  43  illustrated in  FIG. 20  has an inlet  452  of the second flow passage  45  for ink collection at the center of the tip portion  431  of the connection portion  43 , and has an inlet  442  of the first flow passage  44  for ink supply therearound. Though a ring groove is illustrated as an example of the ink-supplying flow-passage inlet  442  in  FIG. 20 , it is not limited thereto. The connection portion  43  may have plural ink-supplying flow-passage inlets  442  that are plural through holes arranged annularly. Though the tip portion  431  of the connection portion  43  illustrated in  FIG. 20  has a convex structure protruding upward in the vertical direction, it may be modified into a concave structure illustrated in  FIG. 21 . In  FIG. 21 , the tip portion  431  of the connection portion  43  is recessed vertically. Similarly to the first embodiment, in the structure illustrated in  FIG. 20  and the structure illustrated in  FIG. 21 , the flow-passage inlet  452  for ink collection is located above the flow-passage inlet  442  for ink ejection in the Z direction (vertical direction). Therefore, when ink is sucked through the flow-passage inlet  452  for ink collection, the entering of air bubbles through the ink-ejecting flow-passage inlet  442  is prevented. However, the convex tip portion  431  of the connection portion  43  illustrated in  FIG. 20  produces a greater effect of preventing air bubbles from entering through the ink-ejecting flow-passage inlet  442  than that of the concave tip portion  431  of the connection portion  43  illustrated in  FIG. 21 . 
     (2) The structure of the liquid ejecting head  36  can be modified. For example, though a piezoelectric liquid ejecting head  36  utilizing a piezoelectric element that applies mechanical vibration to a pressure compartment is disclosed as an example in the foregoing embodiments, a thermal liquid ejecting head utilizing a heat generation element that produces an air bubble inside a pressure compartment by heating may be employed instead. The structure of the plural nozzles N in the liquid ejecting head  36  is not limited to the foregoing examples in the embodiments. 
     (3) The printing apparatus disclosed as examples in the foregoing embodiments can be applied to various kinds of equipment such as facsimiles and copiers, etc. in addition to print-only machines. The scope of application of a liquid ejecting apparatus according to the present invention is not limited to printing. For example, a liquid ejecting apparatus that ejects a colorant solution can be used as an apparatus for manufacturing a color filter of a liquid crystal display device. A liquid ejecting apparatus that ejects a solution of a conductive material can be used as a manufacturing apparatus for forming wiring lines and electrodes of a wiring substrate. 
     The entire disclosure of Japanese Patent Application No. 2015-230470, filed Nov. 26, 2015 is expressly incorporated by reference herein.