Abstract:
A fluid ejection apparatus that ejects fluid from an ejection nozzle in an ejection head includes a fluid receiver that has a concave portion for accommodating the ejected fluid and defines a closed space around the ejection nozzle when the concave portion contacts the ejection head. Suction pumps suck the fluid in the concave portion through suction ports in the concave portion. A fluid suction unit sucks the fluid in the ejection head through the ejection nozzle by operating the suction pumps such that the concave portion contacts the ejection head. An air suction unit sucks the air and the fluid in the concave portion of the fluid receiver after completion of suction of the fluid in the ejection head, by allowing at least one suction pump to reverse the air flow in collaboration with the operation of at least one other suction pump.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present invention relates to an apparatus that ejects a fluid from an ejection head. 
         [0003]    2. Related Art 
         [0004]    An inkjet printer can print an image of high quality by ejecting an accurate amount of ink to an appropriate position from a fine ejection nozzle. Using this technology, an electrode, a sensor, or a bio-chip may be manufactured by ejecting various fluids onto a substrate instead of ink. 
         [0005]    In this technology, a dedicated ejection head is used to eject an accurate amount of fluid such as ink to an appropriate position. Since the viscosity of fluid such as ink supplied to the ejection head increases over time, making it difficult to eject the fluid appropriately, a cap comes in contact with the ejection head to close the periphery of the ejection nozzle when the fluid is not ejected and thus suppresses an increase in the viscosity of the fluid. The state in which the cap is in contact with the ejection head in order to suppress an increase in the viscosity of the fluid is referred to as a “capping state.” 
         [0006]    The viscosity of the fluid in the ejection head gradually increases even in a capping state. As such, if the viscosity of the fluid increases, an operation (cleaning operation) which involves compulsorily drawing out the fluid whose viscosity has increased in the ejection head from the ejection nozzle is performed through negative pressure created in the cap by a suction pump while the cap is in contact with the ejection head. Since the sucked fluid is attached to the periphery of the ejection nozzle after the cleaning operation, the ejection nozzle may be blocked if this state continues. After the cleaning operation, an operation (wiping operation) of wiping the fluid attached to the periphery of the ejection nozzle is performed after the cap is separated from the ejection head. Then, the cap comes in contact with the ejection head, returning to the capping state. 
         [0007]    However, since the cap on which the cleaning operation has been performed is filled with the fluid drawn out from the ejection head, the fluid filled in the cap is leaked out when the cap is separated from the ejection head. Therefore, Japanese Patent Laid-Open No. 2001-342975 suggested that an air opening valve for introducing air into the cap is provided in advance in the cap to suck air by opening the air opening valve after the completion of a cleaning operation, performing an air sucking operation of introducing air by opening the air opening valve with a suction pump being operated, and performing a wiping operation to achieve a capping state. 
         [0008]    Since the viscosity of fluid in the ejection head increases, it is difficult to draw out the fluid. In order to overcome this, it is preferable for the magnitude of the negative pressure of the suction pump to be as large as possible. 
         [0009]    However, if the magnitude of the negative pressure in the cap is increased by the suction pump, air flows in with a rush and generates bubbles in the cap when an air sucking operation is performed by the opening the air opening valve. The bubbles can then be introduced into the ejection nozzle, and in this case the fluid cannot be normally ejected. 
       SUMMARY 
       [0010]    An advantage of some aspects of the invention is that it provides a fluid ejection apparatus that avoids the abnormal ejection of fluid due to bubbles generated during an air sucking operation while also generating a large magnitude of negative pressure in the cap. 
         [0011]    According to a first aspect of the invention, there is provided a fluid ejection apparatus that ejects a fluid from an ejection nozzle formed in an ejection head, comprising: a fluid receiver that has a concave portion for accommodating the fluid from the ejection nozzle, and defines a closed space around the ejection nozzle when the concave portion comes in contact with the ejection head; a plurality of suction pumps that suck the fluid in the concave portion of the fluid receiver through suction ports provided in the concave portion of the fluid receiver; a fluid suction unit that sucks the fluid in the ejection head through the ejection nozzle by operating the suction pumps in a state in which the concave portion of the fluid receiver comes in contact with the ejection head; and an air suction unit that, after completion of suction of the fluid in the ejection head, sucks the air together with the fluid in the concave portion of the fluid receiver by allowing at least one suction pump to reverse the air flow in collaboration with the operating of at least one other suction pump. 
         [0012]    In the fluid ejection apparatus, the fluid from the ejection nozzle can be received into the concave portion provided in the fluid receiver. A plurality of suction ports are provided in the concave portion and are each connected to suction pumps. A fluid sucking operation of sucking fluid in the ejection head from the ejection nozzle is allowed by operating the suction pumps after the concave portion of the fluid receiver comes in contact with the ejection head. The fluid sucking operation is completed by performing an air sucking operation in which at least one suction pump is operated in a state in which air can be reversed by at least one other suction pump. 
         [0013]    Since a large magnitude of negative pressure can be generated in the concave portion of the fluid receiver by simultaneously operating the suction pumps, the fluid can be drawn out from the ejection nozzle even after the viscosity of the fluid in the ejection head has increased. After the completion of the fluid sucking operation, the fluid in at least one suction pump is reversed to reduce the magnitude of the negative pressure in the concave portion of the fluid receiver when the air in the at least one suction pump is reversible. After this, an air sucking operation is performed, such that it is possible to avoid abnormal ejection of the fluid due to bubbles generated during the air sucking operation. 
         [0014]    The fluid ejection apparatus includes a waste fluid tank in which the fluid sucked from the ejection nozzle is gathered. The waste fluid tank and discharge ports of the suction pumps may be connected to each other by a waste fluid tube. 
         [0015]    In this way, the fluid drawn out from the suction pump may be properly introduced into the waste fluid tank. 
         [0016]    The waste fluid tube of the suction pump allowed to reverse air flow when air is being sucked, is inserted into the waste fluid tank in a shallower position than the waste fluid tube of another suction pump. 
         [0017]    In this way, even when the tip end of the waste fluid tube of another suction pump (performing a suction operation) is submerged in the fluid in the waste fluid tank, the tip end of the waste fluid tube of the suction pump through which air is reversible is not submerged in the fluid, which enables the suction of air and the performing of an air sucking operation. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements. 
           [0019]      FIG. 1  is a perspective view schematically illustrating an example of a fluid ejection apparatus, i.e. an inkjet printer according to an embodiment of the invention. 
           [0020]      FIG. 2  is a bottom view of a head assembly of  FIG. 1 . 
           [0021]      FIG. 3  is a perspective view schematically illustrating a maintenance mechanism of  FIG. 1 . 
           [0022]      FIG. 4  is a view illustrating the maintenance mechanism of  FIG. 1  in more detail. 
           [0023]      FIGS. 5A to 5C  are views for explaining the maintenance operation of the inkjet printer according to the embodiment of the invention. 
       
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0024]    Hereinafter, an exemplary embodiment of the invention will be described in detail with reference to the accompanying drawings. 
         [0025]      FIG. 1  is a perspective view schematically illustrating an example of a fluid ejection apparatus, i.e. an inkjet printer according to an embodiment of the invention. As illustrated in  FIG. 1 , the inkjet printer  10  includes a carriage  20  forming ink dots on a printing medium  2  while reciprocating in a main scanning direction, a drive mechanism  30  reciprocating the carriage  20 , a platen roller  40  for feeding paper, i.e. the printing medium  2 , and a maintenance mechanism  100  for maintaining a normal printing operation. The carriage  20  contains an ink cartridge  26  accommodating ink, a carriage case  22  to which the ink cartridge  26  is mounted, and a head assembly  24  mounted to the bottom (facing the printing medium  2 ) of the carriage case  22 . As will be described below, the head assembly  24  includes a plurality of ejection heads for ejecting ink in order to eject only the accurate amount of ink in the ink cartridge  26  to the printing medium  2  from the ejection heads, thereby printing an image. 
         [0026]    The drive mechanism  30  for reciprocating the carriage  20  includes a guide rail  38  installed in the main scanning direction, a timing belt  32  having a plurality of teeth on the inner surface thereof, a driving pulley  34  enmeshed with the timing belt  32 , and a stepping motor  36  for driving the driving pulley  34 . Some portions of the timing belt  32  are fixed to the carriage case  22  in order to move the carriage case  22  along the guide rail  38  when the timing belt  32  is driven. Since the timing belt  32  is enmeshed with the driving pulley  34 , when the driving pulley  34  is driven by the stepping motor  36 , the carriage case  22  can be precisely moved according to the driving amount of the stepping motor  36 . 
         [0027]    The plate roller  40  for feeding the printing medium  2  is driven by a driving motor or gear mechanism (not shown) to feed the printing medium  2  by a predetermined amount in a sub-scanning direction. 
         [0028]    The maintenance mechanism  100  is provided in a region called a home position other than a factor region, and includes a wiper blade  110  wiping out an ejection head provided on the bottom surface of the head assembly  24 , a cap  130  pressed by the bottom surface of the head assembly  24  to define a closed space with the ejection head, a suction pump unit  140  provided under the cap  130 , a waste fluid tank  120  provided under the suction pump unit  140 . When a printing operation is not carried out, a closed space is defined between the cap  130  and the ejection head mounted to the head assembly  24  by moving the carriage  20  to the home position and pressing the cap  130  against the bottom surface of the head assembly  24 . As will be described in detail, although a fine ejection nozzle provided in the ejection head to eject ink is opened, the viscosity of the ink in the ejection head can be prevented from increasing due to the drying of ink by defining a closed space by the pressing of the cap  130 . 
         [0029]    However, even when ink is prevented from being dried by pressing the cap  130 , moisture or volatile substances in the ink gradually decrease over a long period of time which change the property of the ink (in particular, increase the viscosity of the ink). Therefore, when the viscosity of ink minutely increases, the property of the ink in the head assembly  24  is returned to a normal state by moving the head assembly  24  to the position of the cap  130  and performing an operation (flashing operation) of ejecting the ink whose viscosity has increased. Meanwhile, when ink cannot be recovered by a flashing operation or the viscosity of ink has increased due to non use of the inkjet printer  10  over a long period of time, an operation (cleaning operation) of drawing the ink in the head assembly  24  out of an ejection nozzle is performed by operating the suction pump embedded in the suction pump unit  140  and creating negative pressure in the closed space. The ink discharged by a flashing operation or a cleaning operation gathers in the waste fluid tank  120 . Since ink is attached to a surface of an ejection head provided in the head assembly  24  after a cleaning operation, it may cause the blocking of an ejection nozzle or a filthy surface of a printing medium if it is left in that state. Therefore, the ink attached to a surface of an ejection head is wiped off by the wiper blade  110  after a cleaning operation. 
         [0030]      FIG. 2  is a bottom view of a head assembly of  FIG. 1 . As illustrated in  FIG. 2 , a plurality of ejection heads  25  are provided on the bottom surface of the head assembly  24  and small ejection nozzles Nz for ejecting ink are arranged in each ejection head  25  in evenly spaced intervals. A predetermined number of ejection heads  25  (two ejection heads in the illustrated example) forms a set and ink of yellow (Y), magenta (M), cyan (C), and black (K) is ejected from each nozzle Nz. 
         [0031]      FIG. 3  is a perspective view schematically illustrating a maintenance mechanism of  FIG. 1 . As illustrated in  FIG. 3 , a rectangular concave portion  132  is formed on the upper surface of the cap  130  (facing the head assembly  24 ) to allow ink discharged from the ejection head  25  to be received into the concave portion  132  during a flashing operation or a cleaning operation. Two suction ports  134  are provided on the bottom surface of the concave portion  132 . 
         [0032]    Two suction pumps  150  are accommodated in the suction pump unit  140 . One suction pump  150  is connected to a suction port  134  provided in the concave portion  132  of the cap  130  via a suction tube  142 , and the other suction pump  150  is connected to a suction port  134  via a suction tube  142 . The two suction pumps  150  are connected to a motor (not shown) such that when they are simultaneously operated, ink can be sucked from the two suction ports  134  provided in the concave portion  132  of the cap  130 . Meanwhile, only one suction pump  150  may be independently operated. 
         [0033]      FIG. 4  is a view illustrating the maintenance mechanism of  FIG. 1  in more detail. Briefly, a suction pump  150  has a configuration where a suction tube  142  is wound around the outer periphery of a rotary disk  152 , and the rotary disk  152  and the suction tube  142  are accommodated in a case  154 . Although the suction tube  142  does not completely loop around the outer periphery of the rotary disk  152  for clarity in  FIG. 4 , it completely loops around the outer periphery of the rotary disk  152  in reality. 
         [0034]    Disk-shaped top members  156  are rotatably provided in the rotary disk  152  and are supported within guide grooves  158 . Each guide groove  158  has an angle with respect to the outer periphery of the rotary disk  152  such that one end thereof is closer to the outer periphery of the rotary disk  152  and the opposite end thereof is further away from the outer periphery of the rotary disk  152 . Therefore, when each top member  156  is located on one side of the guide groove  158 , it protrudes significantly from the outer periphery of the rotary disk  152 . On the other hand, when the top member  156  is located on the opposite side of the guide groove  158 , it protrudes by a small degree from the outer periphery of the rotary disk  152 . 
         [0035]    The operation of the suction pump  150  will be described in detail. The rotary disk  152  is rotated in the forward direction (indicated by an arrow in the figure) by the operating of a motor (not shown). Then, the two top members  156  provided in the rotary disk  152  are moved to one side of the guide groove  158  by a frictional force from the suction tube  142  and protruding significantly from the outer periphery of the rotary disk  152 .  FIG. 4  illustrates a state in which the top members protruding significantly from the outer periphery of the rotary disk  152 . As illustrated in  FIG. 4 , the suction tube  142  is closed when pressed by a significantly protruding top member  156 . 
         [0036]    In this state, when the rotary disk  152  is rotated in the forward direction, the pressed position of the suction tube  142  is moved as the top member  156  moves. As a result, ink in the suction tube  142  is pushed downward and is discharged into the waste fluid tank  120  through the waste ink tube  146  from the discharge port  144  of the suction pump  150 . Therefore, as illustrated in  FIG. 4 , if the rotary disk  152  is rotated in the forward direction in a state in which the upstream side of the suction tube  142  is connected to the suction port  134  of the cap  130  and the downstream side of the suction tube  142  is connected to the waste tube  146  through the discharge port  144 , the ink gathered in the concave portion  132  of the cap  130  can be discharged into the waste fluid tank  120 . 
         [0037]    On the other hand, when the rotary disk  152  is rotated in the backward direction, the top member  156  is moved to the opposite side of the guide groove  158  by the frictional force from the suction tube  142 . As described above, since the opposite side of the guide groove  158  is further away from the outer periphery of the rotary disk  152 , the top member  156  protrudes by a smaller degree as it moves from the one side to the opposite side of the guide groove  158 . The top member  156  is in contact with the suction tube  142 , but does not close the suction tube  142  on the opposite side of the guide groove  158 . Therefore, the exit of the waste ink tube  146  is linked with the suction port  134  of the cap  130  through the suction tube  142  when the rotary disk  152  is rotated in the backward direction. 
         [0038]    As described above, two suction pumps  150  are mounted to the inkjet printer  10  according to the embodiment of the invention. As a result, as will be described below, the cleaning operation and the air sucking operation are performed in a particular way. Hereinafter, the cleaning operation and the air sucking operation of the inkjet printer  10  will be described in detail. The two operations, i.e. the cleaning operation and the air sucking operation are referred to as a maintenance operation. 
         [0039]      FIGS. 5A to 5C  are views for explaining the maintenance operation of the inkjet printer according to the embodiment of the invention.  FIG. 5A  illustrates an initial operation of the maintenance operation, i.e. the cleaning operation. In the cleaning operation, the suction pump  150  is operated with a closed space being formed by forcing the cap  130  to come in contact with the bottom side of the head assembly  24 . As described above, since two suction pumps  150  are mounted to the inkjet printer  10  according to the embodiment of the invention, they are respectively referred to as suction pump  150   a  and suction pump  150   b  for clarity when they need to be distinguished. 
         [0040]    As illustrated in  FIG. 5A , when the two suction pumps  150   a  and  150   b  are rotated in the forward direction, the negative pressures generated by the suction pumps  150   a  and  150   b  are simultaneously applied to the concave portion  132  of the cap  130  and this sucks ink from the ejection heads  25 . The sucked ink gathers in the concave portion  132  of the cap  130  and is discharged into the waste fluid tank  120  by the suction pumps  150   a  and  150   b . In  FIG. 5   a , the oblique lines in the concave portion  132  of the cap  130  show that the concave portion  132  is filled with ink. 
         [0041]    In this way, since ink is sucked using two suction pumps  150   a  and  150   b , a large magnitude of negative pressure is produced in the concave portion  132  of the cap  130 , and as a result, the head assembly  24  can return to a normal state by the drawing out the ink whose viscosity has increased, even after the viscosity of the ink in the head assembly  24  has increased. 
         [0042]    If the ink whose viscosity has increased in the head assembly  24  is drawn out through the cleaning operation, the cap  130  is separated from the head assembly  24  to perform the wiping operation, and through introduction of air, an air sucking operation of discharging all the ink in the concave portion  132  of the cap  130  is started. However, since two suction pumps  150   a  and  150   b  are simultaneously operated in the inkjet printer  10  to create a large magnitude of negative pressure in the concave portion  132  of the cap  130 , bubbles are generated in the concave portion  132  of the cap  130  by the air introduced during an air sucking operation, mix in the ejection nozzle and hamper normal ejection of ink. Therefore, the inkjet printer  10  according to the embodiment of the invention performs the following air sucking operation. 
         [0043]    First, in a state in which one suction pump  150   a  is being rotated forward, the other pump  150   b  is rotated backward. As described above referring to  FIG. 4 , an upstream side (connected to the concave portion  132 ) of the suction pump  150   b  that has been rotated backward is linked with the downstream side (connected to the waste fluid tank  120 ) thereof. Here, since a large magnitude of negative pressure is generated in the concave portion  132  of the cap  130  and a negative pressure is not generated in the waste fluid tank  120 , the ink in the suction tube  142  and the waste ink tube  146  of the suction pump  150   b  is reversed and introduced into the concave portion  132  of the cap  130 . As a result, the magnitude of the negative pressure of the concave portion  132  is reduced.  FIG. 5B  illustrates the suction pump  150   b  that reduces the magnitude of the negative pressure in the concave portion  132  by reversing the ink when it is rotated backward. In  FIG. 5B , after the upstream side and downstream side of the suction pump  150   b  that has been rotated backward are linked with each other, the rotation of the suction pump  150   b  may be stopped. 
         [0044]    In this way, if one suction pump  150   a  remains rotating forward and the other suction pump  150   b  remains rotating backward (or remains stopped after rotated backward), all the ink in the suction pump  150   b  that is rotated backward is reversed, and the so-called air sucking operation is started by reversing air from the waste fluid tank  120 . That is, if the suction pump  150   a  that is rotating forward sucks out the ink in the concave portion  132  of the cap  130 , the ink is reversed and sucked in through the other suction pump  150   b  by the negative pressure. 
         [0045]    In the inkjet printer  10  according the embodiment of the invention, since the ink in the suction pump  150   b  rotated backward is reversed and the negative pressure in the concave portion  132  of the cap  130  is reduced before an air sucking operation, the air introduced during the air sucking operation does not generate bubbles in the concave portion  132  of the cap  130 . As illustrated in  FIG. 5 , the waste ink tube  146   b  connected to the suction pump  150   b  rotated backward is inserted in a shallower position of the waste fluid tank  120  than the waste ink tube  146   a  of the suction pump  150   a . Therefore, even if the tip end of the waste tube  146   a  of the suction pump  150   a  rotated forward is submerged in the ink, the tip end of the waste ink tube  146   b  of the suction pump  150   b  rotated backward is not submerged in the ink, which allows for the suction of the ink. 
         [0046]      FIG. 5C  illustrates an operation of sucking all the ink in the concave portion  132  of the cap  130 . The dashed lines represents that air reversed from the suction pump  150   b  is drawn out by the suction pump  150   a . In this state, the air sucking operation is completed by stopping the suction pumps  150   a  and  150   b . Thereafter, a wiping operation is performed after the cap  130  is lowered to be separated from the head assembly  24 . 
         [0047]    As described above, in the inkjet printer  10  according to the embodiment of the invention, since a large magnitude of negative pressure can be generated in the concave portion  132  of the cap  130  by operating the two suction pumps  150 , even when the viscosity of the ink in the head assembly  24  has increased, it can be returned to a normal state. Since after the cleaning operation, one suction pump  150   b  can be in a reversible state with the other suction pump  150   a  is being operated, an air sucking operation can be started after the negative pressure in the concave portion  132  is reduced by reversing the ink in the suction pump  150   b . As a result, there will be no problems in the normal ejection of the ink due to the inflow of air with a rush which causes the generation of bubbles in the concave portion  132  and the bubbles being mixed in the ejection nozzle. 
         [0048]    If the suction pump  150   b  is brought into a reversible state to perform an air sucking operation, since the ink in the suction pump  150   b  is automatically reversed to reduce the magnitude of the negative pressure in the concave portion  132  of the cap  130 , a particular operation is not needed to reduce the magnitude of the negative pressure in the concave portion  132  of the cap  130  and the structure and control of the inkjet printer  10  does not become complicated. 
         [0049]    Although the exemplary embodiment of the invention has been described with reference to the accompanying drawings, it should be understood that the invention is not limited to such embodiments. Various shapes or combinations of respective constituent elements illustrated in the above-described embodiments are merely examples, and various changes may be made depending on design requirements or the like without departing from the spirit or scope of the invention. 
         [0050]    For example, the embodiment of the invention illustrates a so-called serial printer that prints an image with a head assembly  24  reciprocating on printing paper. However, the present invention can be applied to so-called line printers that print an image by transporting printing paper with the head assembly  24  not being moved. 
         [0051]    The entire disclosure of Japanese Patent Application No. 2008-189459, filed Jul. 23, 2008 is expressly incorporated by reference herein.