Abstract:
To reduce a fluctuation in pressure of ink supplied in an ink-jet head due to vibration of an ink tank through movement of a carriage, and to prevent density unevenness due to the pressure fluctuation from being caused in printing, the present invention provides a pressure buffer which is provided in an ink supply path connecting an ink-jet head to an ink supply portion for supplying ink to the ink-jet head, an opening portion is provided in a chamber of the pressure buffer, and the opening portion communicates with an ink flow path provided along a side wall of the chamber and is connected to an ink flow outlet provided in a position lower than the opening portion. In the ink flowpath in the vicinity of the ink flow outlet, a hole which communicates with the chamber is provided.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an ink-jet head and an ink-jet recording apparatus for discharging ink onto a recording medium to be recorded thereon. 
         [0003]    2. Description of the Prior Art 
         [0004]    An ink-jet recording apparatus for recording characters and images on a recording medium by using an ink-jet head having a plurality of nozzles for discharging ink has been conventionally known. 
         [0005]    An outline of the ink-jet recording apparatus will be described below.  FIG. 1  is a schematic diagram of the ink-jet recording apparatus which includes a pressure buffer. The ink-jet recording apparatus includes at least ink supply means  30  for supplying ink, an ink-jet head  20  for discharging ink, an ink supply path  50  which is a path for supplying ink from the ink supply means  30  to the ink-jet head  20 , a pressure buffer  10  provided in the ink supply path  50  in the vicinity of the ink-jet head  20 , and a carriage  40  which includes the ink-jet head  20  and the pressure buffer  10  that are mounted therein. 
         [0006]    The ink-jet recording apparatus performs printing in such a manner that the carriage  40  which includes the ink-jet head  20  mounted therein reciprocates on a recording medium. The arrow of  FIG. 1  indicates the reciprocation of the carriage  40  on the recording medium. In the case of performing printing, when the carriage  40  is accelerated or decelerated, a pressure fluctuation is generated inside the ink-jet head  20  due to an inertia of ink provided in the ink supply path  50  which is filled with the ink. The pressure fluctuation causes deterioration in image quality in the case of recording characters or images on a recording medium, and further causes a discharge failure. For this reason, it is necessary to provide the pressure buffer  10  in the ink supply path  50 , which connects the ink supply means  30  and the ink-jet head  20  to each other, in the vicinity of the ink-jet head  20  so that the pressure fluctuation can be suppressed as much as possible. 
         [0007]    Here, an example of the conventional pressure buffer  10  will be described.  FIG. 2  shows a state where the pressure buffer  10  and the ink-jet head  20  according to the prior art are connected to each other, that is, a structure of the carriage  40  of  FIG. 1 . Note that the arrow X of  FIG. 2  indicates a gravity direction. In other words, a lower side of  FIG. 2  indicated by the arrow X indicates a ground side.  FIG. 3  is a cross-sectional diagram of the pressure buffer  10  of  FIG. 2  taken along the line f-f′. 
         [0008]    In  FIG. 3 , a main body  112  of the pressure buffer  10  has a concave portion  114  on at least one surface thereof, and a flexible film  111  is applied to the concave portion  114  so as to hermetically seal the concave portion, to thereby form a chamber  103 . As shown in  FIG. 2 , the chamber  103  has at least an ink flow inlet  102  through which the ink flows into the chamber  103  from the ink supply means  30 , and an opening portion  101  for supplying the ink to the ink-jet head  20 . The chamber  103  is filled with the ink so as to prevent air bubbles which cause the discharge failure of the ink, from being contained in the chamber  103 , so as to fill the ink through pressurization, and so as to obtain a stable characteristic to buffer pressure. The pressure buffer  10  described above is disclosed in JP 2005-14315 A. 
         [0009]    Next, problems to be solved by the present invention will be described below. 
         [0010]    In the structure according to the prior art, as shown in  FIG. 2 , the opening portion  101  of the pressure buffer  10  is provided at an uppermost portion of the pressure buffer  10 . Accordingly, in order to connect the ink-jet head  20  to the pressure buffer  10  to each other, it is necessary to separately provide an ink supply path  105  such as a tube, between the opening portion  101  and the ink-jet head  20 , outside the pressure buffer  10 . As a result, there arise problems in that the number of components is increased, and manufacturing costs are increased. In addition, in a case of arranging the ink-jet head  20  and the pressure buffer  10  to be closer to each other, for example, it is necessary to separately provide a tube or the like. As a result, there arises a problem in that a peripheral space cannot be effectively used. 
         [0011]    Further, there arises another problem in that, when vibration in the vertical direction is applied to the carriage  40 , a space formed between positions indicated by a-a′, that is, space between an uppermost position of the ink supply path  105  and a lowermost position of a nozzle  106  of the ink-jet head  20  becomes a space which is confined a pressure. As a result, the pressure fluctuation is generated due to the inertia of the ink provided in the space between the positions indicated by a-a′ which is filled with the ink  113 . Therefore, there arise problems in that the pressure fluctuation causes a meniscus  104  to be displaced in a positive or negative direction, and a volume of ink droplets to be discharged, or a discharge rate is modulated, which leads to density unevenness. 
       SUMMARY OF THE INVENTION 
       [0012]    To solve the above-mentioned problems, according to a first aspect of the present invention, there is provided a pressure buffer, which is provided in a vicinity of an ink-jet head in an ink supply path that connects the ink-jet head to ink supply means that supplies ink to the ink-jet head to each other, the pressure buffer including: 
         [0013]    a chamber having a concave portion provided in the pressure buffer, to which a flexible film is applied so as to hermetically seal the concave portion; 
         [0014]    an ink flow outlet which communicates with an opening portion provided in the chamber, is connected to an ink flow path that is formed of a partition wall provided along a side wall of the chamber so as to partition the ink flow path from the chamber, is placed at a position lower than the opening portion, and an ink flow outlet through which ink flows from the chamber to the ink-jet head; and 
         [0015]    an ink flow inlet through which the ink flows into the chamber from the ink supply means. 
         [0016]    According to a second aspect of the present invention, in the pressure buffer according to the first aspect, the chamber is filled with the ink so that air bubbles, which cause an ink discharge failure, are prevented from being contained in the chamber, the ink is filled in the chamber through pressurization, and so that a stable characteristic to buffer pressure is obtained. 
         [0017]    According to a third aspect of the present invention, the pressure buffer of the first or second aspect of the present invention further includes a penetrating opening portion which is provided in the partition wall in the vicinity of the ink flow outlet, and through which the ink flows between the chamber and the ink flow path when pressure fluctuation is generated in the ink flow path. 
         [0018]    According to a fourth aspect of the present invention, in the pressure buffer of the third aspect of the present invention, the opening portion has a flow resistance which is smaller than that of the penetrating opening portion. 
         [0019]    According to a fifth aspect of the present invention, the pressure buffer of the first or second aspect of the present invention further includes an air pocket which is provided in the partition wall in the vicinity of the ink flow outlet for partitioning the chamber and the ink flow path from each other, and which alleviates the pressure fluctuation generated in the ink flow path by using resilience of the air. 
         [0020]    According to a sixth aspect of the present invention, the pressure buffer of the first or second aspect of the present invention, further includes pressure suppressing means which is provided in the ink flow path in the vicinity of the ink flow outlet, and which suppresses a pressure fluctuation when the pressure fluctuation is generated in the ink provided in the ink flow path. 
         [0021]    According to a seventh aspect of the present invention, an ink-jet head is configured to include the pressure buffer of any one of the first to the sixth aspects of the present invention. 
         [0022]    According to an eighth aspect of the present invention, an ink-jet recording apparatus includes the ink-jet head of the seventh aspect of the present invention. 
         [0023]    According to the present invention, in the pressure buffer in which the opening portion of the chamber is provided on the upper portion of the pressure buffer, the ink flow path is provided inside the pressure buffer. With this structure, the ink flow outlet can be provided in the lower portion of the pressure buffer without impairing the function of filling the pressure buffer with ink. Therefore, it is possible to directly connect the pressure buffer to the ink-jet head to each other without using the ink supply path such as the tube shown in  FIG. 2 . As a result, the manufacturing costs can be reduced, and a peripheral space can be effectively used when the ink-jet head and the pressure buffer are to be arranged to be closer to each other. 
         [0024]    Further, in the partition wall in the vicinity of the ink flow outlet, there is provided pressure suppressing means which suppresses the fluctuation in pressure of ink, such as a penetrating opening portion or an air pocket. As a result, even when unnecessary vibration is applied to the ink-jet head, the pressure fluctuation generated in the ink flow path between the opening portion of the chamber and the ink-jet head can be effectively reduced or alleviated, and generation of the density unevenness is suppressed, thereby making it possible to drastically improve the image quality. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    In the accompanying drawings: 
           [0026]      FIG. 1  is a schematic diagram of an ink-jet recording apparatus according to a prior art; 
           [0027]      FIG. 2  is a diagram showing a structure of a carriage shown in  FIG. 1  as a specific example of the prior art; 
           [0028]      FIG. 3  is a cross-sectional diagram of a pressure buffer shown in  FIG. 2  which is a specific example of the prior art; 
           [0029]      FIG. 4  is a diagram showing a structure of a pressure buffer according to a first embodiment of the present invention; 
           [0030]      FIG. 5  is a cross-sectional diagram of the pressure buffer shown in  FIG. 4  according to the first embodiment of the present invention; 
           [0031]      FIG. 6  is a diagram showing an example of the structure according to the first embodiment, in which an ink flow inlet and an opening portion are provided at the same height; 
           [0032]      FIG. 7  is a diagram showing an example of the structure according to the first embodiment, in which the ink flow inlet is provided at a position higher than that of the opening portion; 
           [0033]      FIG. 8  is a diagram showing a specific example of the pressure buffer according to the first embodiment; 
           [0034]      FIG. 9  is a cross-sectional diagram of the pressure buffer shown in  FIG. 8  according to the first embodiment; 
           [0035]      FIG. 10  is diagram showing a structure of a pressure buffer according to a second embodiment of the present invention; 
           [0036]      FIG. 11A  is a view showing an example of directions in which vibration is applied to an ink-jet head, and  FIGS. 11B to 11D  are schematic diagrams each showing the vibration applied to the ink-jet head and a density change in association with vibration; 
           [0037]      FIG. 12  is a diagram showing a specific example of the pressure buffer according to the second embodiment; 
           [0038]      FIGS. 13  are diagrams each showing a state where ink is filled in the pressure buffer which is the specific example according to the second embodiment; 
           [0039]      FIG. 14  is a diagram showing a structure of the pressure buffer according to a third embodiment of the present invention; and 
           [0040]      FIG. 15  is a diagram showing a specific example of a pressure buffer according to the third embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0041]    Hereinafter, embodiments of the present invention will be described. 
       First Embodiment 
       [0042]    A structure of a pressure buffer according to a first embodiment of the present invention will be described in detail. 
         [0043]      FIG. 4  is a diagram showing the structure of the pressure buffer according to the first embodiment of the present invention.  FIG. 5  is a cross-sectional diagram of the pressure buffer of  FIG. 4  taken along the line h-h′. An arrow X of  FIG. 4  indicates a gravity direction. In other words, a lower side of  FIG. 4  indicates a ground side. 
         [0044]    As shown in  FIG. 5 , the pressure buffer has a concave portion  114  formed in at least one surface of a main body  112 , and has a partition wall  110  in the vicinity of a side wall  117  of the concave portion  114 . A flexible film  111  is applied to the concave portion  114  and to the partition wall  110  so as to hermetically seal the concave portion  114 , thereby forming a chamber  115  and an ink flow path  107 . 
         [0045]    The pressure buffer of  FIG. 4  has a lower portion in the gravity direction, and has an upper portion in a direction opposite to the gravity direction. The partition wall  110  of  FIG. 4  is formed upward from an ink flow outlet  108 , which is provided in the lower portion of the pressure buffer, along the inside of the side wall  117 . The ink flow path  107  communicates with the chamber  115  through an opening portion  101  provided in the partition wall  110 . The chamber  115  has the opening portion  101  through which the ink flows from the chamber  115  to the ink flow path  107 , and an ink flow inlet  102  through which the ink flows into the chamber  115  from the ink supply means  30 . 
         [0046]    As regards a positional relationship between the opening portion  101  and the ink flow inlet  102 , as shown in  FIG. 6 , for example, the opening portion  101  and the ink flow inlet  102  may be arranged in parallel with each other and may be positioned at the same height. Further, as shown in  FIG. 7 , the opening portion  101  and the ink flow inlet  102  may be perpendicularly arranged, and the ink flow inlet  102  may be positioned higher than the opening portion  101 . In the first embodiment, any structure may be employed as long as a function of filling the chamber  115  with ink is not impaired. 
         [0047]    Further, the ink flow path  107  communicates with the opening portion  101  of the chamber  115 , and the ink flow outlet  108  and an ink-jet head  20  are connected to each other at a lowermost portion of the ink flow path  107 . In this manner, the ink flow path  107  is provided in the pressure buffer, thereby making it possible to provide the ink flow outlet  108  in the lower portion of the pressure buffer. As a result, even when a tube or the like as shown in  FIG. 2  is not provided, the pressure buffer can be directly connected to the ink-jet head, thereby enabling reduction in manufacturing costs. In addition, in a case where the ink-jet head and the pressure buffer are to be arranged to be closer to each other, a peripheral space can be effectively used. 
         [0048]    The first embodiment as described above will be described in more detail below. 
         [0049]      FIG. 8  shows an example of a case where the first embodiment is materialized as a plastic molding. In  FIG. 8 , the arrow X indicates the gravity direction. In other words, the lower part of  FIG. 8  indicates the ground side.  FIG. 9  is a cross-sectional diagram of the pressure buffer of  FIG. 8  taken along the line b-b′. 
         [0050]    In  FIG. 9 , a main body  6  is formed of plastic, has a concave portion  114  in one surface thereof, and has a partition wall  4  which corresponds to the partition wall  110  of  FIG. 5  and which is provided in the concave portion  114 . A flexible film  8  is applied to the concave portion  114  and to the partition wall  4  by thermo-compression bonding or the like so as to hermetically seal the concave portion  114 , there by forming a chamber  3  and an ink flow path  5  which correspond to the chamber  115  and the ink flow path  107  of  FIG. 5 , respectively. In  FIG. 8 , an ink flow inlet  1  communicates with an ink supply path (not shown), and the ink flows into the chamber  3  from ink supply means (not shown) through the ink flow inlet  1 . The partition wall  4  is formed from an ink flow outlet  7 , which is provided in the lower portion of the pressure buffer, to an upper portion of the concave portion  114  along the inside of the side wall  117 . The ink flow path  5  communicates with the chamber  3  through the opening portion  2  which is provided in the side wall  117 . Further, the ink flow path  5  communicates with the ink flow outlet  7  on an opposite side of the opening portion  2 , and the ink flows into the ink flow outlet  7  through the ink flow path  5 . In addition, by forming the partition wall  4  along the side wall, the ink flow path  5  can be formed without impairing the original shape of the chamber and without largely reducing the volume of the chamber. As a result, it is possible to prevent the characteristics inherent in the pressure buffer from being impaired. 
         [0051]    Note that it is desirable to form the partition wall  4  integrally with the main body  6 , but the partition wall  4  may be formed by using another member to be bonded to the concave portion  114  by using an adhesive, thermo-compression bonding, or the like. In other words, any structure may be employed as long as the ink flow outlet  7  can be disposed at the lower portion of the pressure buffer without impairing the function of filling the pressure buffer with ink. 
       Second Embodiment 
       [0052]    Next, a pressure buffer according to a second embodiment of the present invention will be described in detail. 
         [0053]      FIG. 10  is a diagram showing a structure of the pressure buffer according to the second embodiment of the present invention. The arrow X of  FIG. 10  indicates the gravity direction. In other words, the lower part of  FIG. 10  indicates the ground side. In addition, the pressure buffer has a lower portion in the gravity direction, and has an upper portion in a direction opposite to the gravity direction.  FIG. 11A  is a diagram showing an example of directions in which vibration is applied to the ink-jet head, and specifically shows a vibration direction of each of an ink-jet head  2000  and a pressure buffer  2001 . Arrows indicated by “+ ” and “− ” of  FIG. 10  each indicate the direction in which vibration is applied to the ink-jet head  2000  and the pressure buffer  2001 . In this case, the arrows “+ ” and “− ” each indicate the vibration in the vertical direction.  FIG. 11B  is a diagram showing the vibration applied to the ink-jet head  2000  with respect to a change of elapsed time.  FIGS. 11C and 11D  are diagrams each showing a change of printing density in a case where the vibration is applied to the ink-jet head  2000 . 
         [0054]    The second embodiment is different from the first embodiment in that there is provided a penetrating opening portion  109  in the vicinity of the ink flow outlet  108  in the partition wall  110 , which is pressure suppressing means that suppresses a pressure fluctuation generated in the ink flow path  107  and releasing the pressure fluctuation into the chamber  115 . 
         [0055]    In a case where the penetrating opening portion  109  is not provided in  FIG. 10 , when the vibration shown in  FIG. 11B  is applied in the X direction, the pressure fluctuation is generated due to an inertia of the ink supplied between a space which is confined the pressure indicated by g-g′ of  FIG. 10 . The pressure fluctuation causes a meniscus  104  of the ink-jet head  20  to be displaced, and gives modulation to the volume and the flight of the ink. As a result, the printing density is changed as shown in  FIG. 11C . Note that  FIG. 11C and 11D  each show results obtained by comparing printing materials to be actually printed. 
         [0056]    On the other hand, in the case where the penetrating opening portion  109  is provided, the pressure fluctuation generated in the ink flow path  107  is released into the chamber  115  through the penetrating opening portion  109 . Accordingly, the displacement of the meniscus  104  can be reduced. As a result, as shown in  FIG. 11D , a difference in density is remarkably reduced, which is effective in improving the image quality to a large extent. Further, when the penetrating opening portion  109  is disposed to be as close as possible to ink flow outlet  108 , the change in amount of the ink flowing through the ink flow path  107  due to the inertia of the ink is reduced, thereby increasing the above-mentioned effect. 
         [0057]    The penetrating opening portion  109  allows the pressure fluctuation generated in the ink flow path  107  to be released into the chamber  115 . For this reason, it is desirable to dispose the penetrating opening portion  109  to be as close as possible to the ink flow outlet  108 . Further, it is necessary to regulate an opening width of the penetrating opening portion  109  to be set as a predetermined width which does not impair the function of discharging air provided in the pressure buffer and of filling the pressure buffer with ink, when the ink is filled in the pressure buffer. Specifically, the opening width of the penetrating opening portion  109  is set to be narrower than an opening width of the opening portion  101 , and a flow path resistance of the penetrating opening portion  109  is set to be larger than that of the opening portion  101 . In this manner, the ink and the air supplied in the chamber  115  are discharged through the opening portion  101  with a low flow path resistance, and the chamber  115  can be filled with the ink. 
         [0058]    Note that the penetrating opening portion  109  may have any shape and may be set in any direction as long as the pressure fluctuation generated in the ink flow path  107  can be released into the chamber  115 . 
         [0059]    A specific example of the second embodiment  2  described above will be described below. 
         [0060]      FIG. 12  shows a specific example of a case where the second embodiment is materialized as a plastic molding. 
         [0061]    A penetrating opening portion  9  of  FIG. 12  corresponds to the penetrating opening portion  109  of  FIG. 10  and an opening portion  2  of  FIG. 12  corresponds to the opening portion  101  of  FIG. 10 . The opening width of each of the penetrating opening portion  9  and the opening portion  2  is set such that the flow path resistance of the penetrating opening portion  9  becomes larger than that of the opening portion  2 . The ink flow inlet  1  is provided so as to flow the ink into the chamber therethrough, and the ink flow outlet  7  is connected to the ink-jet head so as to discharge the ink. 
         [0062]      FIGS. 13A to 13D  each show a state where the ink is filled in the pressure buffer shown in  FIG. 12 . In  FIG. 13A , in a case where an ink  113  is introduced into the ink flow inlet  1  from a state where the chamber  3  is vacant, the ink  113  is gradually filled from a bottom portion of the chamber  3 . Further, as shown in  FIGS. 13B ,  13 C, and  13 D in the stated order, the ink  113  and an air  1000  expand to the upper portion of the chamber  3 , and are discharged from the opening portion  2  provided in the chamber  3  through the ink flow path  5 , the ink flow outlet  7 , and the ink-jet head. 
       Third Embodiment 
       [0063]    In the second embodiment  2 , as a method of alleviating the pressure fluctuation, there is illustrated a method in which the penetrating opening portion is provided in the partition wall, which partitions the link flow path from the chamber, so as to release the pressure fluctuation into the chamber. As long as the pressure fluctuation generated in the ink flowpath can be reduced or alleviated as described above, another method can be employed as the pressure suppressing means. For example, an air pocket for retaining the air may be formed by deforming a part of the partition wall provided in the vicinity of the ink flow outlet, and the pressure fluctuation may be absorbed by utilizing the resilience of the air. 
         [0064]    A pressure buffer according to a third embodiment of the present invention which employs the above-mentioned method will be described below. 
         [0065]      FIG. 14  is a diagram showing a structure of the pressure buffer according to the third embodiment. 
         [0066]    In  FIG. 14 , an air pocket  116  having a predetermined size is formed in the vicinity of the ink flow outlet  108 . The air pocket  116  refers to a space for holding the air provided in the pressure buffer, and also refers to a structure for alleviating the fluctuation in pressure of the ink. In the chamber  115 , the ink flow path  107  is formed by providing the partition wall  110 , and the chamber  115  communicates with the ink flow path  107  through the opening portion  101  provided in the upper portion of the chamber  115 . The ink flows into the chamber  115  from the ink flow inlet  102 . The pressure fluctuation generated in the ink flow path  107  is released into the air pocket  116 , and is reduced or alleviated due to the resilience of the air. In the case of providing the air pocket, it is desirable to form the air pocket to be as close as possible to the ink flow inlet  108 . In the same manner as in the case of providing the penetrating opening portion in the second embodiment, when the air pocket  108  is provided, the displacement of the meniscus  104  of the ink-jet head  20  can be alleviated and the generation of the density unevenness can be reduced to a large extent. Note that the arrow X of  FIG. 14  indicates the gravity direction. In other words, the lower side of  FIG. 14  indicates the ground side. In addition, the pressure buffer has a lower portion in the gravity direction, and has an upper portion in the direction opposite to the gravity direction. 
         [0067]    Note that it is desirable to form the air pocket  116  integrally with the pressure buffer main body which forms the chamber, but the air pocket  116  may be formed by another method. 
         [0068]    A specific example of the third embodiment will be described below.  FIG. 15  shows a specific example of a case where the third embodiment is materialized as a plastic molding. The arrow X of  FIG. 15  indicates the gravity direction. In other words, the lower side of  FIG. 15  indicates the ground side. 
         [0069]    In  FIGS. 13 , the partition wall  4  is formed such that a recessed hollow is formed perpendicularly upward in the direction opposite to the gravity direction, to thereby form an air pocket  11 . The air pocket  11  corresponds to the air pocket  116  shown in  FIG. 14 . In the third embodiment, a width and a depth of the air pocket  11  are each in a range from 2 mm to 10 mm, and a height thereof is in a range from 1 mm to 2 mm. 
         [0070]    Note that in the third embodiment, the air pocket is formed by deforming the partition wall  4 , but the air pocket may be formed by employment of another method so that the air can be held in a predetermined space. For example, an air chamber may be formed integrally with the ink flow outlet. 
         [0071]    The embodiments of the present invention have been described above, but the present invention is not limited thereto. Any modification can be made without departing from the scope of the present invention.