Abstract:
Ink supplied from an ink source to a filter is guided from a tangential direction with respect to the filter. In addition, a partition wall having a spiral shape reduces the cross-sectional area of an ink passage on the upper surface of the filter and produces a rapid ink flow on the upstream side of the filter. The ink flows from the periphery of the filter to the center of the filter. This ink flow allows air bubbles in the ink to be forced to pass through openings of the filter, thereby being discharged to the exterior of the device. Accordingly, faulty ink supply, due to clogging of the filter with air bubbles, is prevented.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of Invention  
           [0002]    The invention relates to an ink-jet recording apparatus that ejects ink to record on a recording medium.  
           [0003]    2. Description of Related Art  
           [0004]    Ink-jet recording apparatuses are typically provided with actuators formed by piezoelectric elements or heating elements, and eject ink selectively by deforming the piezoelectric elements or by locally heating ink to a boil using the heating elements. Ink is supplied, via a tube or directly from an ink cartridge, to a plurality of actuators through an ink passage. A filter is typically provided in the ink passage to remove foreign matter and air bubbles from the ink flowing into the actuators.  
           [0005]    Occasionally, in such ink-jet recording apparatuses, a number of actuators are simultaneously driven to eject ink, or ink is sucked while a number of nozzles are covered with a cap to perform a recovery operation. In such cases, the ink passage should have a cross-sectional area appropriate for supplying a large amount of ink to the actuators.  
           [0006]    A filter typically has very small openings in its lattice frame. Ink is supplied through the filter to the actuators. Thus, the total area of the openings of the filter should be large enough to allow a large amount of ink to be supplied at any given time. The total area of the openings should be larger than the cross-sectional area of the ink passage.  
           [0007]    Recently, high-resolution and multilevel gray-scale printing has become popular. As the demand for this printing grows, a number of actuators are arranged in a single head, and the diameter of each nozzle is made to be extremely small. In some cases, a plurality of ink droplets are continuously ejected to form a dot. Further reducing the size of openings of the filter is advantageous to remove smaller foreign matter and air bubbles, while further increasing the total area of the openings of the filter is advantageous to allow a larger amount of ink to be supplied at any given time. To achieve these advantages, the ink passage should be enlarged on the upstream and downstream sides of the filter.  
           [0008]    By increasing the velocity of flow of ink passing through the filter in a structure wherein ink is sucked with a number of nozzles that are covered with a cap, when ink is forcibly ejected under high pressure applied from an ink source side, or when all actuators are simultaneously driven to perform flushing (hereinafter, these operations are generically referred to as “recovery operations”), air bubbles are forced to pass through the filter and are discharged through the nozzle.  
           [0009]    However, when the total area of the filter is large, the velocity of flow of ink is reduced on the upstream side of the filter, resulting in a deposition of air bubbles generated in the ink on the upstream side of the filter. Air bubbles deposited on the filter reduce the effective area of the filter. As a result, ink supply becomes insufficient, and faulty ink ejection is caused when a number of actuators are simultaneously driven or when actuators are continuously driven to perform printing.  
         SUMMARY OF THE INVENTION  
         [0010]    According to the invention, air bubbles on the upstream side of a filter are effectively discharged, and excellent ink ejection can be maintained for a long time.  
           [0011]    In the invention, a partition member is provided to define a path of ink passing through a filter.  
           [0012]    In this configuration, the path of ink passing through the filter can be narrowed, and thus the velocity of flow of ink can be increased when recovery operations are performed as described above, or when a number of actuators are simultaneously driven. Consequently, air bubbles in the ink are deformed to easily pass through the filter. Then, air bubbles are discharged through the actuators to the exterior of the device. Accordingly, faulty ink supply due to air bubbles is prevented, and excellent ink ejection can be maintained for a long time.  
           [0013]    The partition member preferably includes a rib extending parallel to the filter. Ink is guided along the rib. Even a partition member that has a complex shape can be easily molded from a resin. Further, a peripheral wall may be provided so as to enclose the periphery of the filter. The peripheral wall and the partition member cooperate to guide the ink, through the effective use of the entire surface of the filter, and produce an ink flow effectively passing over the entire surface thereof.  
           [0014]    When the partition member is configured so as to be appropriately spaced from the peripheral wall, a rapid ink flow is effectively produced and guided in a circumferential direction of the filter. Further, when the partition member is configured so as to extend in a spiral manner, the ink is guided to turn from the periphery to the center of the filter or from the center to the periphery thereof. Accordingly, a rapid ink flow is effectively produced over the entire surface of the filter.  
           [0015]    The partition wall may include two parallel ribs extending substantially from the center of the filter toward a direction approaching the peripheral wall. In this configuration, ink supplied to the center of the filter is guided along the peripheral wall, or ink supplied to the peripheral wall side is guided to the center of the filter. Thus, an ink flow is effectively produced over the entire surface of the filter.  
           [0016]    When the partition member includes a plurality of ribs disposed parallel to each other and each rib is spaced, at at least one of its ends, from the peripheral wall, the ink is guided along the ribs in a zigzag manner. Accordingly, an ink flow can be effectively produced over the entire surface of the filter.  
           [0017]    It is more preferable that a guideway is provided so as to supply the ink in a direction parallel to the filter surface. Such a guideway allows the ink to be supplied over a wider area of the filter and an ink flow can be effectively produced along the filter surface. In this case, the guideway may have a curved surface that redirects the ink gradually from a direction intersecting the filter surface to a direction parallel thereto. Even when the ink passage above the filter extends substantially perpendicularly to the filter surface, the ink flow is redirected by the guideway immediately before the ink is supplied to the filter and, as a result, the ink flows along the filter surface. Accordingly, the ink is supplied over a wider area of the filter without being concentrated into a certain portion thereof.  
           [0018]    When the guideway extends parallel to the filter surface, the ink flows along the filter surface to be supplied over a wider area of the filter. Further, when the guideway extends parallel to a tangent to the periphery of the filter, a rapid ink flow is produced that passes along the periphery of the filter and along the filter surface.  
           [0019]    In this configuration, a rapid ink flow is produced to pass in a spiral manner from the periphery to the center of the filter. Consequently, air bubbles in the ink are deformed to pass through the filter, and then are discharged to the exterior of the device.  
           [0020]    The peripheral wall that encloses the filter may be formed to be round, continuous and integral with a part of a wall defining the guideway. When the width of the guideway is less than the radius of the peripheral wall, the velocity of flow of ink in the guideway is increased. Thus, the ink flows more effectively and rapidly in a spiral manner.  
           [0021]    Further, the ink passage maybe a space defined by joining two members, which extend parallel to a direction of flow of ink, so as to face each other. A port connected to the recording head is integrally formed with one of the two members and covered with the filter, and the partition member is formed integrally with the other of the two members. When the two members are joined to each other, the partition member comes into contact with, or alternatively is disposed close to but not in contact with, the filter. By simply joining the two members so as to sandwich the filter, the ink passage and the partition member can be easily formed. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]    Preferred embodiments of the invention will be described with reference to the following figures wherein:  
         [0023]    [0023]FIG. 1 is a sectional view of a substantial part of an ink-jet printer, according to an embodiment of the invention, taken along plane B-B of FIG. 2;  
         [0024]    [0024]FIG. 2 is a sectional view taken along plane A-A of FIG. 1;  
         [0025]    [0025]FIG. 3 is a partially exploded view of FIG. 1;  
         [0026]    [0026]FIG. 4 is a sectional view of a substantial part according to another embodiment of the invention;  
         [0027]    [0027]FIG. 5 is a sectional view of a substantial part according to another embodiment of the invention;  
         [0028]    [0028]FIGS. 6A and 6B are sectional views of substantial parts according to other embodiments of the invention;  
         [0029]    [0029]FIG. 7 is a sectional view of a substantial part of another embodiment of the invention; and  
         [0030]    [0030]FIG. 8 is a perspective view of an ink-jet printer.  
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0031]    [0031]FIG. 8 shows major components of an ink-jet printer.  
         [0032]    As shown in FIG. 8, an ink-jet head unit  600  is mounted on a carriage  100  and is scanned parallel to a recording medium  700 . The carriage  100  is slidably supported by guide bars  110 ,  120 . The carriage is also fixed to a belt  140  extending parallel to the guide bars  110 ,  120 . The belt  140  is moved by a driving force of a motor  37 . As the belt  140  is moved, the carriage  100  reciprocates along the guide bars  110 ,  120 . An ink cartridge  32  containing ink to be supplied to the head unit  600  is removably attached to the carriage  100 . The recording medium  700  is held by feed rollers  160 ,  170  parallel to the scanning direction of the head unit  600  and is fed perpendicularly to the scanning direction.  
         [0033]    As shown in FIG. 1, a recording head  10 , as the head unit  600 , can be provided with a plurality of actuators having ink channels  11 , and ejects ink from nozzles  11   a  formed at lower ends of the ink channels  11 . One type of such actuator locally heats ink in the ink channel to a boil to eject ink, and another type has ink channel sidewalls formed by piezoelectric elements, which are deformed, upon the application of a voltage, to eject ink.  
         [0034]    A manifold  12  is disposed on the opposite side of the recording head  10  from the nozzles  11   a.  The manifold  12  diverts ink supplied from an ink source to a plurality of ink channels  11 . An ink passage  13  interconnecting the manifold  12  and the ink source is formed by two passage-forming members  21 ,  22 .  
         [0035]    As shown in FIGS. 1 and 3, the ink passage  13  extends along a plane parallel to the direction of an array of a plurality of ink channels  11 . The two passage-forming members  21 ,  22  extend along the direction of flow of ink in the ink passage  13  and are disposed in a direction perpendicular to the flow of ink, that is, in upper and lower positions so as to face each other.  
         [0036]    The upper passage-forming member  21  is provided, on its upper side, with a connecting port  23  that is connected to one end of the ink passage  13  and extends upward in a tubular shape. The upper passage-forming member  21  is provided, on its lower side, with a rib-like peripheral wall  25  that extends downward so as to enclose a periphery of the ink passage  13 . The lower passage-forming member  22  is provided, on its lower side, with a connecting port  24  that is connected to the other end of the ink passage  13  and extends downward in a tubular shape. The passage-forming members  21 ,  22  are molded from a synthetic resin. The lower passage-forming member  22  abuts the lower end of the rib-like peripheral wall  25  and they are ultrasonically joined to each other.  
         [0037]    A portion surrounding the connecting port  24  of the lower passage-forming member  22  is recessed like a funnel, and is tapered from top to bottom. A filter  28  is thermally fixed to a peripheral wall  27  at the upper end of a recess  26  so as to cover the recess  26 . The filer  28  is formed from meshed or sintered metal fibers, and its outer shape is preferably round. The opening area at the upper end of the recess  26  is determined such that the total area of openings of the filter  28  is equal to or larger than the total cross-sectional area of a plurality of ink channels  11 . Areas of portions where the filter  28  makes contact with a rib-like partition wall  30 , to be described later, and with the peripheral wall  27 , are excluded.  
         [0038]    As shown in FIG. 2, a peripheral wall section  25   a  of the peripheral wall  25  is round in shape so as to enclose the filter  28 . The width between peripheral wall sections  25   b,    25   c,  which enclose a linear portion of the ink passage  13  interconnecting the peripheral wall section  25   a  and the connecting port  23 , is less than the radius of the peripheral wall section  25   a.  The linear peripheral wall section  25   b  extends tangentially from the round peripheral wall section  25   a.  Thus, a guideway  13   a,  which connects the ink passage  13  extending from the connecting port  23  to the round peripheral wall section  25   a,  is parallel to the upper surface of the filter  28  and is tangentially connected to the periphery of the filter  28 .  
         [0039]    The filter  28  is partitioned, on its upper surface (on the ink supplying side), by a rib-like partition wall  30  extending along the upper surface. The partition wall  30  integrally projects from the lower surface of the upper passage-forming member  21  so as to come into contact with, or alternatively to be disposed close to but not in contact with, the upper surface of the filter  28 . The partition wall  30  extends from the other peripheral wall section  25   c,  which encloses the linear portion of the ink passage  13 , to the filter  28 , and further extends to the center of the filter  28  in a spiral manner, so as to be spaced from the round peripheral wall section  25   a.  In cooperation with the peripheral wall section  25   a,  the partition wall  30  partitions a space above the filter  28  in a spiral manner. Consequently, an elongated space extending from the periphery to the center of the filter  28  is formed, and the cross-sectional area of the filter  28 , which is perpendicular to the ink flow direction, is reduced compared with the case where no partition wall  30  is provided.  
         [0040]    The connecting port  23  of the upper passage-forming member  21  is provided with a seal  31  so as to receive an ink cartridge  32  containing ink. Alternatively, an ink tank can be connected to the connecting port  23  through a tube (not shown). The connecting port  24  of the lower passage-forming member  22  is connected to the manifold  12  through a tube  33 .  
         [0041]    The passage-forming members  21 ,  22 , recording head  10 , and manifold  12  are secured to a support plate  34  and integrated into a single unit.  
         [0042]    An ink sucking operation can be performed in an ink-jet printer to remove air bubbles and foreign matter. During the ink sucking operation, a pump connected to a cap  40  is driven while all nozzles  11   a  are covered with the cap  40 . When the pump is driven, ink is drawn from the ink cartridge  32  into the ink passage  13  and the manifold  12 . When the ink flows from the guideway  13   a  onto the filter  28 , the partition wall  30  makes the ink rapidly turn along the periphery of the filter  28  and flow into the center of the filter  28 . In other words, the ink passes through the filter while it flows rapidly over the entire surface of the filter  28 . Such ink flow allows air bubbles generated in the ink, even if they are larger than the very small openings of the filter  28 , to deform and pass through the very small openings. Air bubbles having passed through the filter  28  are discharged together with the ink from the nozzles  11   a  through the manifold  12  and the ink channels  11 .  
         [0043]    By performing the sucking operation, air bubbles contained in the ink in the ink channel  13  can be effectively discharged. This prevents the openings of the filter  28  from being clogged with air bubbles over a long period. Accordingly, when a number of actuators are simultaneously driven, ink is sufficiently supplied to the ink channels  11  and excellent ink ejection can be maintained.  
         [0044]    In addition to the above-described sucking operation, other operations can be performed to discharge air bubbles and foreign matter. Ink is ejected under high pressure applied from the ink source side, or ink is forcibly ejected through a flushing operation by simultaneously driving all actuators. When these operations are performed, ink flowing from the guideway  13   a  onto the filter  28  turns rapidly along the periphery of the filter  28  toward the center thereof, in the same manner as described above. Accordingly, air bubbles contained in the ink are deformed by such ink flow and pass through the openings of the filter  28 .  
         [0045]    Although the partition wall  30  is formed into a spiral shape in the above-described embodiment, a partition wall  30   a  may be formed so as to extend from the linear peripheral wall section  25   c,  as shown in FIG. 4. Alternatively, a partition wall  30   b  may be provided away from the linear peripheral wall section  25   c  in the circumferential direction, so as to be spaced from and concentrically with the peripheral wall section  25   a.  Alternatively, both of these partition walls  30   a,    30   b  may be provided. In these configurations, ink also flows from the guideway  13   a  parallel to the surface of the filter  28 , tangentially toward the periphery of the filter  28 , and turns along the periphery of the filter  28  as a rapid ink flow.  
         [0046]    [0046]FIG. 5 shows another embodiment of the invention. A plurality of rib-like partition walls  30   c,    30   d,    30   e  are provided so as to be parallel with each other. The partition wall  30   c  extends from the linear peripheral wall section  25   c  and its end is spaced from the round peripheral wall section  25   a.  The partition wall  30   d  is integrally connected to one point of the round peripheral wall section  25   a  and extends parallel to the partition wall  30   c,  and its end is directed toward another point of the round peripheral wall section  25   a,  and is spaced a certain distance from the round peripheral wall section  25   a.  Also, the partition wall  30   e  is integrally connected to one point of the round peripheral wall section  25   a  and extends parallel to the partition wall  30   c,  and its end is directed toward another point of the round peripheral wall section  25   a  and is spaced a certain distance from the round peripheral wall section  25   a.  The partition walls  30   c,    30   d,    30   e  can alternately extend in the opposite direction from the peripheral wall section  25   a.    
         [0047]    Specifically, the partition walls  30   c,    30   d,    30   e  are formed such that ink flows windingly, in a staggered manner, along the upper surface of the filter  28 . In this configuration, the cross-sectional area of the ink passage is reduced, and the velocity of ink flow passing through the filter  28  is increased, thereby enhancing the ability to eliminate air bubbles.  
         [0048]    [0048]FIG. 6A shows still another embodiment of the invention. As shown in FIG. 6A, two substantially parallel rib-like partition walls  30   f,    30   g  are integrally formed with a passage-forming member  21  Peripheral wall sections  25   b  and  25   c  are disposed such that the center of an ink passage  13 , which is defined by the peripheral wall sections  25   b  and  25   c,  are aligned with the center of a filter  28 . The partition walls  31   f,    30   g  are disposed so as to be aligned with peripheral walls sections  25   b,    25   c,  respectively, and spaced from a peripheral wall section  25   a.  As a guideway  13   a  is directed toward the center of the filter  28 , ink flowing from the guideway  13   a  passes between the partition walls  30   f,    30   g  and strikes the peripheral wall section  25   a.  Then, the ink is diverted outwardly to two directions and flows along the peripheral wall section  25   a.  A triangular protrusion  25   d  is formed, at a portion of the peripheral wall section  25   a  opposed to the guideway  13   a,  so as to divert the ink flow to two directions. By the aid of the protrusion  25   d,  the ink flowing from the guideway  13   a  is easily divided so as to flow in two directions.  
         [0049]    In this configuration also, the cross-sectional area of the ink passage is reduced and the velocity of ink flow passing through the filter  28  is increased, thereby enhancing the ability to eliminate air bubbles.  
         [0050]    Although, in the embodiment shown in FIG. 6A, ink is guided to flow from the guideway  13   a  to a passage between the partition walls  30   f,    30   g,  an alternative configuration is conceivable. As shown in FIG. 6B, each guideway  13   a  may be connected to a portion between a partition wall  30   f  and a peripheral wall section  25   a,  and a portion between a partition wall  30   g  and the peripheral wall section  25   a  so as to allow the ink flowing from a connecting port  23  to be supplied to a filter  28  through two passages. In this configuration, the ink flows along the peripheral wall section  25   a  and is guided to a passage between the partition walls  30   f,    30   g.    
         [0051]    [0051]FIG. 7 shows still another embodiment of the invention.  
         [0052]    A connecting port  23  of an upper passage-forming member  21  is formed so as to face a filter  28 . The direction of ink flow in an ink passage  13  is perpendicular to the filter  28 . In the vicinity of the filter  28 , a curved surface  13   b  is formed at the passage-forming member  21 . The curved surface  13   b  directs a guideway  13   c  to a direction parallel to the surface of the filter  28 , along which ink flows. Ink supplied from a connecting port  23  flows perpendicularly to the surface of the filter  28 , and then the ink is redirected by the curved surface  13   b  and supplied onto the filter  28 .  
         [0053]    Accordingly, the ink is supplied over the entire surface of the filter  28  without being concentrated into a certain portion thereof, and flows along the surface of the filter  28 .  
         [0054]    The guideway  13   c  configured as described above can be applied to any one of the embodiments described above with reference to FIGS. 2, 4,  5 , and  6 A. In the configurations shown in FIGS. 2 and 4, if a guideway  13   c  is disposed at the center of the filter  28 , ink flows from the center of the spiral passage to the periphery of the filter  28 .  
         [0055]    Further, in each of the above-described embodiments, an additional wall, identical or similar to in shape, to a partition wall can be provided at a recess  26  opposed to the partition wall such that a filter is sandwiched by the additional wall and the partition wall.