Patent Publication Number: US-8974040-B2

Title: Liquid droplet ejection head, image forming apparatus including same, and method for cleaning same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present patent application is based on and claims priority pursuant to 35 U.S.C. §119 from Japanese Patent Application Nos. 2010-281266, filed on Dec. 17, 2010, and 2011-103633, filed on May 6, 2011, both in the Japan Patent Office, each of which is incorporated by reference herein in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to a liquid droplet ejection head provided with a filter to remove foreign substances from the liquid, an image forming apparatus including the liquid droplet ejection head, and a method for cleaning the liquid droplet ejection head. 
     2. Description of the Background Art 
     In general, a liquid droplet ejection head such as an inkjet head employed in an inkjet-type image forming apparatus includes liquid chambers and multiple nozzles each having a diameter of 10 μm. In the inkjet-type image forming apparatus, foreign substances that inadvertently enter the inkjet head during manufacture or with a liquid such as ink dispensed from an ink cartridge to the inkjet head can cause clogging of the nozzles and irregular ejection of ink droplets from the nozzles, thereby degrading image quality. At the same time, recent improvements in processing performance of such as personal computers and other information processing devices have increased demand for high-speed inkjet-type image forming apparatuses. One way to attain high speed is increasing the number of nozzles provided to the inkjet head. However, an increase in the number of nozzles also requires an improved cleaning unit that removes foreign substances from the ink to provide reliable ejection of ink droplets from the nozzles. 
     There is known a type of inkjet-type image forming apparatus in which a filter that removes foreign substances and bubbles from ink is provided to a common liquid chamber through which the ink is supplied from an ink cartridge to the nozzles to prevent the nozzles from being clogged. In addition, a cleaning opening from which the foreign substances are discharged is provided downstream from the filter in a direction of flow of the ink. 
     It is known that the clogged nozzles tend to be found at edges of the inkjet head, as evidenced by the graph shown in  FIG. 1 . Further, it is known that the foreign substances found at the edges of the inkjet head come from a portion of the inkjet head provided upstream from individual liquid chambers. 
     The upstream portion of the inkjet head has a three-dimensionally asymmetrical shape that causes stagnation of cleaning liquid during cleaning of the inkjet head. It has been found from fluid simulation results that the inkjet head is filled with the ink from the edges to the center during ejection of ink droplets from the nozzles in the event of irregular cleaning of the upstream portion of the inkjet head. Consequently, foreign substances tend to flow to the edges of the inkjet head, yielding the same results obtained from the past production experiments described above. However, because the cleaning opening is provided to the common liquid chamber in the related-art image forming apparatus, it is difficult to reliably clean inside the inkjet head. 
     Thus, it is required to provide the cleaning opening to each of the individual liquid chambers in place of the common liquid chamber. However, although providing the filter to the individual liquid chambers is well known, foreign substances are trapped within the individual liquid chambers in such a configuration, thereby possibly reducing yield. 
     SUMMARY 
     In view of the foregoing, illustrative embodiments of the present invention provide a novel liquid droplet ejection head in which both a filter and a liquid discharge opening are provided to individual liquid chambers to reliably clean the minimum necessary cleaning range of the liquid droplet ejection head without decreasing yield. The illustrative embodiments also provide an inkjet-type image forming apparatus including the liquid droplet ejection head, and a method for cleaning the liquid droplet ejection head. 
     In one illustrative embodiment, a liquid droplet ejection head includes a common liquid chamber, multiple individual liquid chambers communicating with the common liquid chamber, to which a liquid is supplied via the common liquid chamber, a nozzle plate containing multiple nozzles communicating with the multiple individual liquid chambers to eject the liquid, a filter disposed within a passageway between the common liquid chamber and the multiple individual liquid chambers to remove foreign substances from the liquid, and a through-hole provided adjacent to the filter to communicate with the multiple individual liquid chambers, and sealed by a frame member in which the common liquid chamber is formed. 
     In another illustrative embodiment, an image forming apparatus to eject liquid droplets from nozzles using drive energy generated by an actuator driven based on an image signal to form an image on a recording medium includes at least the one liquid droplet ejection head described above. 
     In yet another illustrative embodiment, a method for cleaning the liquid droplet ejection head described above includes the steps of flowing a cleaning liquid poured from the multiple nozzles in a direction opposite a direction of flow of the liquid, discharging the cleaning liquid via the through-hole, and sealing the through-hole by the frame member after the discharging step. 
     Additional features and advantages of the present disclosure will be more fully apparent from the following detailed description of illustrative embodiments, the accompanying drawings, and the associated claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the disclosure and many of the attendant advantages thereof will be more readily obtained as the same becomes better understood by reference to the following detailed description of illustrative embodiments when considered in connection with the accompanying drawings, wherein: 
         FIG. 1  is a graph showing a relation between number of nozzles clogged with foreign substances and channel positions in a related-art inkjet head; 
         FIG. 2  is a vertical cross-sectional view illustrating an example of a configuration of a liquid droplet ejection head according to illustrative embodiments; 
         FIG. 3  is an exploded perspective view illustrating the configuration of the liquid droplet ejection head illustrated in  FIG. 1 ; 
         FIG. 4A  is a vertical cross-sectional view illustrating an example of a configuration of a liquid droplet ejection head according to a first illustrative embodiment; 
         FIG. 4B  is a partial plan view illustrating an example of a configuration of a vibration plate provided to the liquid droplet ejection head illustrated in  FIG. 4A ; 
         FIG. 5  is a vertical cross-sectional view illustrating an example of a configuration of a liquid droplet ejection head according to a second illustrative embodiment; 
         FIG. 6A  is a vertical cross-sectional view illustrating an example of a configuration of a liquid droplet ejection head according to a third illustrative embodiment; 
         FIG. 6B  is a plan view illustrating the configuration of the liquid droplet ejection head illustrated in  FIG. 6A ; 
         FIG. 7A  is a plan view illustrating an example of a configuration of the vibration plate provided to the liquid droplet ejection head according to the first illustrative embodiment; 
         FIG. 7B  is a plan view illustrating another example of a configuration of the vibration plate; 
         FIG. 8A  is a plan view illustrating an example of a configuration of a channel formation plate provided to the liquid droplet ejection head according to the second illustrative embodiment; 
         FIG. 8B  is a plan view illustrating another example of a configuration of the channel formation plate; 
         FIG. 9  is a plan view illustrating an example of a configuration of a channel plate provided to the liquid droplet ejection head according to the third illustrative embodiment; 
         FIG. 10  is a vertical cross-sectional view describing cleaning of individual liquid chambers provided to the liquid droplet ejection head according to the first illustrative embodiment; 
         FIG. 11  is a vertical cross-sectional view describing cleaning of individual liquid chambers provided to the liquid droplet ejection head according to the second illustrative embodiment; 
         FIG. 12A  is a vertical cross-sectional view describing cleaning of individual liquid chambers provided to the liquid droplet ejection head according to the third illustrative embodiment; 
         FIG. 12B  is a plan view illustrating the configuration of the liquid droplet ejection head illustrated in  FIG. 12A ; 
         FIG. 13  is a vertical cross-sectional view illustrating an example of a configuration of a liquid droplet ejection head employing a side-shooter system; 
         FIG. 14  is a partial perspective view illustrating an example of a configuration of an image forming apparatus employing the liquid droplet ejection head according to illustrative embodiments; and 
         FIG. 15  is a vertical cross-sectional view illustrating the configuration of the image forming apparatus illustrated in  FIG. 14 . 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     In describing illustrative embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected, and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner and achieve a similar result. 
     Illustrative embodiments of the present invention are now described below with reference to the accompanying drawings. 
     In a later-described comparative example, illustrative embodiment, and exemplary variation, for the sake of simplicity the same reference numerals will be given to identical constituent elements such as parts and materials having the same functions, and redundant descriptions thereof omitted unless otherwise required. 
     A configuration of a liquid droplet ejection head  30  according to illustrative embodiments is described in detail below with reference to  FIGS. 2 and 3 .  FIG. 2  is a vertical cross-sectional view illustrating an example of a configuration of the liquid droplet ejection head  30 .  FIG. 3  is an exploded perspective view illustrating the configuration of the liquid droplet ejection head  30  illustrated in  FIG. 2 . 
     The liquid droplet ejection head  30  includes a channel plate  1  constructed of a silicon substrate in which multiple holes and individual liquid chambers  51  each serving as a liquid channel are formed. A nozzle plate  2  having multiple nozzles  11  formed by nickel electroforming or the like is joined to an upper surface of the channel plate  1 . A vibration plate  3  formed by nickel electroforming or the like is joined to a lower surface of the channel plate  1 . An actuator in which two rows of laminate-type piezoelectric elements  5  are provided on a metal base member  4  is joined to a lower surface of the vibration plate  3 . Further, a frame member  6  in which a common liquid chamber  10  is formed is joined to the vibration plate  3  so that a liquid such as ink is supplied to each of the individual liquid chambers  51  from the common liquid chamber  10 . 
     In the liquid droplet ejection head  30  having the above-described configuration, application of a drive voltage to the piezoelectric elements  5  displaces the piezoelectric elements  5  in a direction of lamination, that is, a vertical direction in  FIG. 3 , so that the vibration plate  3  is deformed and displaced toward the individual liquid chambers  51  to reduce a volume of each of the individual liquid chambers  51 . As a result, pressure in each of the individual liquid chambers  51  is increased to eject ink droplets from the nozzles  11  formed in the nozzle plate  2 . 
     The configuration of the liquid droplet ejection head  30  is described in more detail with reference to  FIGS. 4 ,  5 , and  6 .  FIG. 4A  is a vertical cross-sectional view illustrating an example of a configuration of the liquid droplet ejection head  30  according to a first illustrative embodiment, and  FIG. 4B  is a partial plan view illustrating an example of a configuration of the vibration plate  3  provided to the liquid droplet ejection head  30  illustrated in  FIG. 4A .  FIG. 5  is a vertical cross-sectional view illustrating an example of a configuration of the liquid droplet ejection head  30  according to a second illustrative embodiment.  FIG. 6A  is a vertical cross-sectional view illustrating an example of a configuration of the liquid droplet ejection head  30  according to a third illustrative embodiment, and  FIG. 6B  is a plan view illustrating the configuration of the liquid droplet ejection head  30  illustrated in  FIG. 6A . 
     In the first illustrative embodiment illustrated in  FIGS. 4A and 4B , a filter  8  and through-holes serving as cleaning liquid discharge openings  9  are provided to the vibration plate  3 . The cleaning liquid discharge openings  9  are sealed with the frame  6  upon formation of the common liquid chamber  10 . The filter  8  catches foreign substances  12  which are, for example, inadvertently contained in an ink cartridge and flow together with the ink in a direction indicated by arrows  13  in  FIG. 4A , at the common liquid chamber  10 . It is to be noted that the filter  8  may be formed together with the vibration plate  3  as a single integrated member. 
     In the second illustrative embodiment illustrated in  FIG. 5 , the filter  8  is provided to a channel formation plate  7  shown also in  FIG. 3 , whereas the cleaning liquid discharge openings  9  are provided to both the vibration plate  3  and the channel formation plate  7 . Only the cleaning liquid discharge openings  9  provided to the channel formation plate  7  are sealed with the frame  6  upon formation of the common liquid chamber  10 . The filter  8  catches the foreign substances  12  at the common liquid chamber  10 . It is to be noted that the filter  8  may be formed together with the channel formation plate  7  as a single integrated member. 
     Although the cleaning liquid discharge openings  9  are provided to both right and left sides of the filter  8  in the first and second illustrative embodiments as illustrated in  FIGS. 4A and 5 , respectively, alternatively only a single cleaning liquid discharge opening  9  may be provided to the right or left side of the filter  8 . 
     In the third illustrative embodiment illustrated in  FIGS. 6A and 6B , the filter  8  is provided to the channel formation plate  7  and the cleaning liquid discharge openings  9  are provided to the channel plate  1 . The cleaning liquid discharge openings  9  are sealed with an adhesive  52  upon formation of the common liquid chamber  10 . The filter  8  catches the foreign substances  12  at the common liquid chamber  10 . It is to be noted that the filter  8  may be formed together with the channel formation plate  7  as a single integrated member. Alternatively, the filter  8  may be provided to the vibration plate  3  in a manner similar to the configuration of the first illustrative embodiment illustrated in  FIGS. 4A and 4B  and be formed together with the vibration plate  3  as a single integrated member. 
     Although the cleaning liquid discharge openings  9  are provided to both edges of the channel plate  1  as illustrated in  FIG. 6B , alternatively only the single liquid discharge opening  9  may be provided to one of the edges of the channel plate  1 . 
     In the first illustrative embodiment, the filter  8  is provided relatively close to the nozzles  11 . Consequently, fluid resistance of the filter  8  may cause irregular ejection of the ink droplets from the nozzles  11 . By contrast, in the second illustrative embodiment, the filter  8  is provided upstream and closer to the common liquid chamber  10  compared to the first illustrative embodiment, thereby preventing irregular ejection of the ink droplets from the nozzles  11  caused by fluid resistance of the filter  8 . It is to be noted that, in the second illustrative embodiment, irregular ejection of the ink droplets can be prevented by increasing a size of the filter  8  as illustrated in  FIGS. 8A and 8B  in the event of large fluid resistance of the filter  8 . 
       FIG. 7A  is a plan view illustrating an example of a configuration of the vibration plate  3  provided to the liquid droplet ejection head  30  according to the first illustrative embodiment in which the common liquid chamber  10  directly communicates with each of the individual liquid chambers  51  via the filter  8 . In other words, portions downstream from the filter  8  do not communicate with one another in the configuration illustrated in  FIG. 7A .  FIG. 7B  is a plan view illustrating an example of a configuration of the vibration plate  3  provided to the liquid droplet ejection head  30  according to the first illustrative embodiment in which all the individual liquid chambers  51  provided downstream from the filter  8  communicate with one another via the cleaning liquid discharge openings  9 . In other words, a second common liquid chamber is formed downstream from the filter  8  in the configuration illustrated in  FIG. 7B .  FIG. 8A  is a plan view illustrating an example of a configuration of the channel formation plate  7  provided to the liquid droplet ejection head  30  according to the second illustrative embodiment in which the common liquid chamber  10  directly communicates with each of the individual liquid chambers  51  via the filter  8 .  FIG. 8B  is a plan view illustrating an example of a configuration of the channel formation plate  7  provided to the liquid droplet ejection head  30  according to the second illustrative embodiment in which all the individual liquid chambers  51  provided downstream from the filter  8  communicates with one another via the cleaning liquid discharge openings  9 .  FIG. 9  is a plan view illustrating an example of a configuration of the channel plate  1  provided to the liquid droplet ejection head  30  according the third illustrative embodiment. 
     It is preferable that the filter  8  be the first layer of an electroform film having a thickness of not greater than 5 μm, more preferably about 3 μm. Because an increase in the thickness of the electroform film increases the fluid resistance of the film  8  and prevents regular ejection of the ink droplets, the first layer of the electroform film is preferably used for the filter  8 . 
     In the foregoing illustrative embodiments, a size of each of openings formed in the filter  8  is smaller than a size of each of the nozzles  11 . Therefore, the foreign substances  12  do not reach the nozzles  11 , and the ink droplets are reliably ejected from the nozzles  11 . In addition, because the filter  8  is provided close to the nozzles  11 , a range to be cleaned with a cleaning liquid described in detail later can be limited to only the individual liquid chambers  51  upon removal of foreign substances from the liquid droplet ejection head  30 , thereby facilitating cleaning of the liquid droplet ejection head  30 . 
     Further, in the foregoing illustrative embodiments, a size of each of the cleaning liquid discharge openings  9  is larger than a size of each of the nozzles  11 . 
     A description is now given of removal of foreign substances  14  that might be inadvertently contained in the individual liquid chambers  51  during manufacture from the liquid droplet ejection head  30  with reference to  FIGS. 10 ,  11 , and  12 .  FIG. 10  is a vertical cross-sectional view describing cleaning of the individual liquid chambers  51  provided to the liquid droplet ejection head  30  according to the first illustrative embodiment.  FIG. 11  is a vertical cross-sectional view describing cleaning of the individual liquid chambers  51  provided to the liquid droplet ejection head  30  according to the second illustrative embodiment.  FIG. 12A  is a vertical cross-sectional view describing cleaning of the individual liquid chambers  51  provided to the liquid droplet ejection head  30  according to the third illustrative embodiment.  FIG. 12B  is a plan view describing cleaning of the individual liquid chambers  51  illustrated in  FIG. 12A . 
     A cleaning liquid such as acetone or ethanol is poured from the nozzles  11  so that the cleaning liquid flows as indicated by arrows  15  through the individual liquid chambers  51  in a direction opposite the direction of flow of ink shown in  FIGS. 4 ,  5 , and  6 , and is discharged from the cleaning liquid discharge openings  9 . As a result, the foreign substances  14  inadvertently contained in the individual liquid chambers  51  are discharged from the cleaning liquid discharge openings  9  together with the cleaning liquid. 
     However, the foreign substances  14  may be caught by the filter  8  without being discharged from the cleaning liquid discharge openings  9  during cleaning of the individual liquid chambers  51 . In order to solve such a problem, first, the filter  8  and the cleaning liquid discharge openings  9  are filled with the cleaning liquid, and then the cleaning liquid flows as indicated by the arrows  15  in  FIGS. 10 ,  11 , and  12 . As a result, the flow of cleaning liquid can be controlled near the filter  8 , thereby preventing the foreign substances  14  from being caught by the filter  8 . 
     After being cleaned with the cleaning liquid, the liquid discharge openings  9  are sealed with the frame  6  or the adhesive  52  so that no foreign substance is present in the individual liquid chambers  51 . 
     An image forming apparatus employing the liquid droplet ejection head  30  according to the foregoing illustrative embodiments prevents irregular ejection of ink droplets and achieves stable image formation. In addition, stable ejection of ink droplets from the nozzles  11  can be achieved. As a result, ink droplets are simultaneously ejected from the multiple nozzles  11  to perform image formation at high speed. Configuration and operation of an image forming apparatus  21  employing the liquid droplet ejection head  30  are described in detail later. 
     Although the piezoelectric elements  5  are provided to the actuator of the liquid droplet ejection head  30  to generate energy to eject ink droplets from the nozzles  11  in the above-described examples, the configuration of the liquid droplet ejection head  30  is not limited thereto. Alternatively, bubbles may be generated by a heating element to eject the ink or a vibration plate that forms a wall of a liquid channel may be displaced by an electrostatic force generated between the vibration plate and an electrode provided opposite the vibration plate to eject the ink. 
     In addition, although an edge-shooter ejection head in which the ink, to which the ejection energy is supplied from the vibration plate  3 , flows in a direction along axes of the nozzles  11  is employed in the foregoing illustrative embodiments, the configuration of the liquid droplet ejection head  30  is not limited thereto. Alternatively, a side-shooter system may be employed in the liquid droplet ejection head  30 . Thus, in the liquid droplet ejection head  30  employing the side-shooter system illustrated in  FIG. 13 , nozzles  17  are provided in a top board  16 , and a channel  19  formed by the top board  16  and a channel board  18  is provided perpendicular to axes of the nozzles  17  so that the ink, to which the ejection energy is supplied, flows in a direction perpendicular to axes of the nozzles  17  as indicated by arrow  20 . 
     Use of the side-shooter system can more efficiently convert the ejection energy generated by an ejection energy generator such as the vibration plate  3  to kinetic energy to form ink droplets. In addition, a meniscus generated at the nozzles  17  is restored rapidly by supply of the ink. Therefore, the side-shooter system is particularly effective when a heating element is used as the ejection energy generator. Further, the side-shooter system can prevent cavitation which occurs in the edge-shooter system. When cavitation occurs, an impact generated as the bubbles pop in the ink gradually destroys the ejection energy generator. In the side-shooter system, the bubbles grow larger and reach the nozzles  17  to communicate with air, thereby preventing shrinkage of the bubbles caused by a temperature decrease and extending product life of the liquid droplet ejection head  30 . 
     In addition, application of the foregoing illustrative embodiments to a liquid channel can provide a higher-quality liquid droplet ejection head with high ejection accuracy. 
     A description is now given of a configuration of an image forming apparatus  21  according to illustrative embodiment with reference to  FIGS. 14 and 15 . 
     As describe previously, the image forming apparatus  21  employs the liquid droplet ejection head  30 .  FIG. 14  is a partial perspective view illustrating an example of a configuration of the image forming apparatus  21  employing the liquid droplet ejection head  30 .  FIG. 15  is a vertical cross-sectional view illustrating the configuration of the image forming apparatus  21  illustrated in  FIG. 14 . 
     The image forming apparatus  21  includes an image formation mechanism  22  constructed of a carriage  29  movable in a main scanning direction, the liquid droplets ejection head  30  installed in the carriage  29 , an ink cartridge  31  that supplies ink to the liquid droplet ejection head  30 , and so forth. 
     A sheet feed tray  24  capable of storing multiple sheets  23  is detachably attached to the image forming apparatus  21  from the front side of the image forming apparatus  21 . The image forming apparatus  21  further includes a foldably openable manual sheet feed tray  25  from which the sheets  23  can be manually fed. The sheets  23  fed from the sheet feed tray  24  or the manual sheet feed tray  25  are conveyed to the image formation mechanism  22  to form images on the sheets  23 . Thereafter, the sheets  23  having the images thereon are discharged from the image forming apparatus  21  to a discharge tray  26  provided on a back surface of the image forming apparatus  21 . 
     In the image formation mechanism  22 , the carriage  29  is slidably held and reciprocally movable in the main scanning direction, that is, a direction perpendicular to the plane of the sheet of paper on which  FIG. 15  is drawn, by a main guide rod  27  and a sub-guide rod  28  each extended between right and left lateral plates of the image forming apparatus  21 . The liquid droplet ejection head  30  that ejects ink droplets of specific colors, that is, yellow (Y), cyan (C), magenta (M), and black (K), is installed on the carriage  29 . Multiple nozzles  11  provided to the liquid droplet ejection head  30  are arranged in a direction intersecting with the main scanning direction and the ink droplets are ejected downward from the nozzles  11 . The ink cartridge  31  that supplies ink of the specified colors to the liquid droplet ejection head  30  is replaceably attached to the carriage  29 . 
     The ink cartridge  31  has an opening that communicates with air at an upper portion thereof, a supply opening from which the ink is supplied to the liquid droplet ejection head  30  at a lower portion thereof, and a porous body filled with the ink at an inner portion thereof. The ink supplied to the liquid droplet ejection head  30  by capillary action of the porous body is controlled to have a slightly negative pressure. 
     Although the single liquid droplet ejection head  30  that ejects ink droplets of multiple colors is employed in the image forming apparatus  21  in the above-described example, alternatively, multiple liquid droplet ejection heads  30  corresponding to number of colors used may be provided to the image forming apparatus  21 . A piezo-type ejection head in which the ink is energized by an electromechanical converter such as a piezoelectric element via a vibration plate that forms a wall of a liquid chamber, a bubble-type ejection head in which bubbles are generated by a heat resistor to pressurize the ink, or an electrostatic ejection head that displaces a vibration plate forming a wall of a liquid channel by an electrostatic force generated between the vibration plate and electrodes provided opposite the vibration plate to energize the ink, may be used as the liquid droplet ejection head  30 . In illustrative embodiments, an electrostatic ejection head is used as the liquid droplet ejection head  30 . 
     A rear end of the carriage  29  slidably engages the main guide rod  27 , and a front end thereof is slidably placed on the sub-guide rod  28 . The image forming apparatus  21  further includes a main scanning motor  32 , a drive pulley  33  rotatively driven by the main scanning motor  32 , a driven pulley  34 , and a timing belt  49  extended between the drive pulley  33  and the driven pulley  34 . The timing belt  49  is fixed to the carriage  29  so that the carriage  29  is moved reciprocally back and forth in the main scanning direction by normal and reverse rotations of the main scanning motor  32 . 
     The image forming apparatus  21  further includes a sheet feed roller  35  and a friction pad  36 , both of which separate the sheets  23  stored in the sheet feed tray  24  to feed the sheets  23  one by one from the sheet feed tray  24  to the liquid droplet ejection head  30 , a guide member  37  that guides the sheets  23 , a first conveyance roller  38  that reverses the sheets  23  to convey the sheets  23  to the liquid droplet ejection head  30 , a second conveyance roller  39  pressed against the first conveyance roller  38 , and a head roller  40  that sets an angle of conveyance of the sheets  23  conveyed by the conveyance roller  38 . The conveyance roller  38  is rotatively driven by a sub-scanning motor  41  via a gear train. 
     The image forming apparatus  21  further includes a receiver  50  serving as a sheet guide member provided below the liquid droplet ejection head  30  corresponding to a scanning range of the carriage  29  in the main scanning direction to guide the sheets  23  conveyed from the first conveyance roller  38 . A third conveyance roller  42  rotatively driven to convey the sheets  23  in a direction of discharge of the sheets  23 , a conveyance spur  43 , a discharge roller  44  that discharges the sheets  23  to the discharge tray  26 , a discharge spur  45 , and guide members  46  and  47  together defining a discharge passageway along which the sheets  23  travel are provided downstream from the receiver  50  in the direction of conveyance of the sheets  23 . 
     During image formation, the image forming apparatus  21  drives the carriage  29  based on image signals so that ink droplets are ejected from the liquid droplet ejection head  30  to the sheet  23 , which remains stationary, while the carriage  29  is moved to form a single line in an image to be formed on the sheet  23 . Thereafter, the sheet  23  is conveyed by a predetermined amount to perform image formation of the next line. When receiving a completion signal or a signal which indicates that a trailing edge of the sheet  23  reaches an imaging range, the image forming apparatus  21  completes image formation to discharge the sheet  23  to the discharge tray  26 . 
     A servicing device  48  that services the nozzles  11  in the liquid droplet ejection head  30  is provided outside the imaging range of the image forming apparatus  21  at one end of the main scanning direction of the carriage  29  to prevent irregular ejection of the ink droplets from the nozzles  11  of the liquid droplet ejection head  30 . The servicing device  48  includes a cap, a suction unit, and a cleaning unit. The carriage  29  is moved to face the servicing device  48  during standby, and the liquid droplet ejection head  30  is capped with the cap. Accordingly, the nozzles  11  are moisturized during standby, thereby preventing irregular ejection of the ink droplets from the nozzles  11  caused by dried ink. In addition, during image formation, the liquid droplet ejection head  30  ejects ink droplets which are not used for image formation so that ink droplets to be ejected from the nozzles  11  have the same viscosity to maintain stable ejection of the ink droplets. 
     Upon occurrence of irregular ejection of the ink droplets, the nozzles  11  are capped with the cap and bubbles and so forth are sucked out from the nozzles  11  together with the ink by the suction unit via a tube. In addition, ink and foreign substances attaching to a surface of each of the nozzles  11  are removed by the cleaning unit to service the nozzles  11 . As a result, ink droplets are reliably ejected from the nozzles  11 . The ink sucked out from the nozzles  11  by the suction unit is discharged to a waste ink storage container provided at a bottom portion of the image forming apparatus  21  to be absorbed and held by an ink absorber provided within the waste ink storage container. 
     Thus, the minimum necessary cleaning range of the liquid droplet ejection head  30  is reliably and efficiently cleaned without decreasing yield in the image forming apparatus  21  employing the liquid droplet ejection head  30 . 
     In the liquid droplet ejection head  30  according to the first and second illustrative embodiments, the liquid discharge openings  9  are sealed upon formation of the common liquid chamber  10  without using additional members, thereby reducing production costs. 
     In the liquid droplet ejection head  30  according to the foregoing illustrative embodiments, the vibration plate  3  and the filter  8  are formed together as a single integrated member so that the liquid channels can be formed at reduced costs. 
     In addition, the vibration plate  3  having the filter  8  is formed by electroforming Accordingly, holes are accurately provided to the filter  8  and a target fluid resistance value can be reliably obtained. 
     Further, the filter  8  has the same thickness as the first layer of the vibration plate  3 , that is, not greater than 5 μm, thereby reducing fluid resistance of the filter  8 . 
     In the liquid droplet ejection head  30  according to the foregoing illustrative embodiments, a size of each of the holes of the filter  8  is smaller than a size of each of the nozzles  11 . As a result, the foreign substances  12  are reliably caught by the filter  8  at an upstream side in the flow of ink to achieve regular ejection of the ink droplets from the nozzles  11 . 
     In addition, a size of each of the cleaning liquid discharge openings  9  is larger than a size of each of the nozzles  11 . As a result, the foreign substances  14  inadvertently contained in the liquid droplet ejection head  30  during manufacture can be reliably removed to achieve regular ejection of the ink droplets from the nozzles  11 . 
     As described previously, the liquid droplet ejection head  30  according to the foregoing illustrative embodiments employs the side-shooter system. Therefore, a sufficient ejection pressure to eject the ink droplets can be obtained even when the filter  8  is provided near the nozzles  11 . 
     The image forming apparatus  21  employs the liquid droplet ejection head  30  having higher cleaning performance according to the foregoing illustrative embodiments. Accordingly, ink droplets are reliably ejected from the nozzles  11 , thereby providing higher quality images. 
     Elements and/or features of different illustrative embodiments may be combined with each other and/or substituted for each other within the scope of this disclosure and appended claims. 
     Illustrative embodiments being thus described, it will be apparent that the same may be varied in many ways. Such exemplary variations are not to be regarded as a departure from the scope of the present invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims. 
     The number of constituent elements and their locations, shapes, and so forth are not limited to any of the structure for performing the methodology illustrated in the drawings.