Patent Publication Number: US-9403390-B2

Title: Image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This patent application is based on and claims priority pursuant to 35 U.S.C. §119(a) to Japanese Patent Application No. 2014-222638, filed on Oct. 31, 2014, in the Japan Patent Office, the entire disclosure of which is hereby incorporated by reference herein. 
     BACKGROUND 
     1. Technical Field 
     Aspects of the present disclosure relate to an image forming apparatus having recording heads. 
     2. Related Art 
     Of image forming apparatuses such as printers, facsimiles, copiers, plotters, and multifunction peripherals with a combination of these apparatuses, there is known an inkjet recording apparatus as an image forming apparatus of liquid-ejection recording system using a liquid ejection head (droplet ejection head) to discharge droplets, for example. 
     In the case of forming an image by the image forming apparatus of liquid ejection system, the landing accuracy of droplets discharged from a nozzle largely influences image quality. The low landing accuracy of droplets degrades image quality, and the recording heads need to be positioned at high accuracy. 
     Meanwhile, the recording heads need to be easily replaceable under user usage environments in the event of a discharge failure in the recording head. In this case, the reproducibility of positional accuracy needs to be kept high. 
     SUMMARY 
     In an aspect of this disclosure, there is provided an image forming apparatus that includes at least one recording head, at least one head holder, a carriage, a reference member, a sub-reference member, and an adjuster. The at least one recording head includes a plurality of nozzles to discharge droplets. The at least one head holder holds the at least one recording head. The carriage holds the at least one head holder and movable in a main scanning direction. The reference member is provided at the carriage and arranged along the main scanning direction. The sub-reference member is provided at the carriage in separation from the reference member. The adjuster adjusts parallelism of the sub-reference member to the reference member. The at least one head holder is supported by and detachable from the reference member, positioned in contact with the sub-reference member, and held in the carriage. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The aforementioned and other aspects, features, and advantages of the present disclosure would be better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
         FIG. 1  is an entire configuration diagram of an example of an inkjet recording apparatus as an image forming apparatus according to an embodiment of the present disclosure; 
         FIG. 2  is a perspective view of a carriage scanning assembly according to the embodiment of the present disclosure; 
         FIG. 3  is a perspective schematic view of the state where head holders are being mounted to a carriage according to the embodiment of the present disclosure; 
         FIG. 4  is a perspective view of the state where the head holders are mounted to the carriage in a specific mode according to the embodiment of the present disclosure; 
         FIG. 5  is a front view of  FIG. 4  according to the embodiment of the present disclosure; 
         FIG. 6  is a side view of  FIG. 4  according to the embodiment of the present disclosure; 
         FIG. 7  is a perspective view of the state where the head holders are detached from the carriage according to the embodiment of the present disclosure; 
         FIG. 8  is a front view of the carriage according to the embodiment of the present disclosure; 
         FIG. 9  is a diagram illustrating a positioning part for a reference shaft as seen from the right side of  FIG. 8  according to the embodiment of the present disclosure; 
         FIG. 10  is a side view of two head holders according to the embodiment of the present disclosure; 
         FIG. 11  is a perspective view of the two head holders according to the embodiment of the present disclosure; 
         FIG. 12  is a side view of the head holder with a color recording head according to the embodiment of the present disclosure; 
         FIG. 13  is an enlarged view of a hook portion in the head holder according to the embodiment of the present disclosure; 
         FIG. 14  is an enlarged view of another hook portion in the head holder according to the embodiment of the present disclosure; 
         FIG. 15  is a schematic view of a configuration of adjusting the parallel relation between a sub-reference shaft and a reference shaft according to the embodiment of the present disclosure; 
         FIG. 16  is a schematic view of the state where the amounts of inclinations of the two head holders are adjusted according to the embodiment of the present disclosure; 
         FIG. 17  is a schematic view of a configuration of lifting the head holders by the use of an interposer according to the embodiment of the present disclosure; 
         FIG. 18  is a schematic view of the state where the head holders are lifted according to the embodiment of the present disclosure; 
         FIG. 19  is a schematic view of a configuration of lifting directly the head holders according to the embodiment of the present disclosure; 
         FIG. 20  is a schematic view of the state where the head holders are lifted according to the embodiment of the present disclosure; and 
         FIG. 21  is a perspective view of a specific form example of the interposer according to the embodiment of the present disclosure. 
     
    
    
     The accompanying drawings are intended to depict embodiments of the present disclosure and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted. 
     DETAILED DESCRIPTION 
     In describing 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 similar results. 
     Although the embodiments are described with technical limitations with reference to the attached drawings, such description is not intended to limit the scope of the disclosure and all of the components or elements described in the embodiments of this disclosure are not necessarily indispensable. 
     Referring now to the drawings, embodiments of the present disclosure are described below. In the drawings for explaining the following embodiments, the same reference codes are allocated to elements (members or components) having the same function or shape and redundant descriptions thereof are omitted below. 
     Embodiments of the present disclosure will be described with respect to the accompanying drawings.  FIG. 1  is an entire configuration diagram of an inkjet recording apparatus as an example of an image forming apparatus according to the present disclosure.  FIG. 2  is a perspective view of a carriage scanning assembly in the inkjet recording apparatus. 
     Inside an apparatus body  1  of an inkjet recording apparatus  1000  in this embodiment, a guide rod  3  and a guide stay  4  as guides are hung over both side plates, and a carriage  5  is held by the guide rod  3  and the guide stay  4  to be slidable in directions indicated by arrow A. 
     The carriage  5  includes recording heads  6  composed of liquid ejection heads to discharge ink droplets of colors of black (K), yellow (Y), magenta (M), and cyan (C). The recording heads  6  have a plurality of nozzles to discharge droplets. The recording heads  6  also include integrally head tanks to supply the inks to the recording heads. 
     A main scanning assembly  10  moving the carriage  5  for scanning includes: a drive motor  11  disposed at one end in a main scanning direction; a drive pulley  12  rotatable by the drive motor  11 ; a driven pulley  13  disposed at the other end in the main scanning direction; and a timing belt  14  as a drawing member hung between the drive pulley  12  and the driven pulley  13 . The driven pulley  13  is tensioned outward (in a direction away from the drive pulley  12 ) by a tension spring. 
     In a main scanning span of the carriage  5 , a sheet  20  is intermittently conveyed in a recording span by a suction conveyor  7  in a direction perpendicular to the main scanning direction of the carriage  5  (sub-scanning direction or sheet conveyance direction shown by arrow B). 
     In addition, at one end side of the main scanning span, a maintenance device  8  is disposed for maintenance of the recording heads  6 . At the outside of the carriage movement span in the main scanning direction or the other end of the main scanning span, a main cartridge  9  storing color inks to be supplied to sub tanks of the recording heads  6  is removably mounted to the apparatus body  1 . 
     A roll sheet (hereinafter, referred to as sheet)  20  is set in a sheet feeder  21 . Roll sheets with different widths can be set in the sheet feeder  21 . The sheet  20  conveyed from the sheet feeder  21  is then conveyed by a conveyor into the recording span from the back to front sides of the apparatus body  1 . Then, the carriage  5  is moved in the main scanning direction, the sheet  20  is intermittently fed by the suction conveyor  7 , and the recording heads  6  are driven to discharge droplets according to image information, thereby forming a desired image on the sheet  20 . Then, the sheet  20  after the image formation is cut into a predetermined length, and is ejected into a sheet ejection tray disposed at the front side of the apparatus body  1 . 
       FIG. 3  is a perspective schematic view of the state where head holders holding recording heads are being mounted to a carriage. As illustrated in  FIG. 3 , the carriage  5  holds a black head holder  51 A and a color head holder  51 B. 
     The head holder  51 A includes two recording heads  6 A and  6 B that are offset from each other in the sub-scanning direction to discharge black droplets. The head holder  51 B includes three recording heads  6 C,  6 D, and  6 E that are aligned in the sub-scanning direction to the recording head  6 A to discharge yellow, magenta, and cyan droplets. As describe above, the recording heads may be called collectively as recording heads  6  in the case where they do not heed to be differentiated from one another. Each of the head holders  51 A and  51 B may hold one recording head  6 . 
     The carriage  5  is provided with a reference shaft  71  as a reference member along the guide rod  3 . Each of the head holders  51 A and  51 B (hereinafter, referred to as “head holders  51 ” in the case where they do not need to be differentiated from each other) are provided with a hook portion  53  to be detachably fitted onto the reference shaft  71 . The head holders  51 A and  51 B are held by the carriage  5  by hitching the hook portions  53  to the reference shaft  71 . The reference shaft  71  may be cylinder or polygonal in shape. 
     As described above, disposing the reference shaft  71  along the guide (guide rod  3 ) of the carriage  5  improves the positional accuracy of inclination in the sub-scanning direction, the height direction, the tilt direction, and the main scanning direction. 
     In this embodiment, at the time of replacement of heads, for example, the recording heads  6 A and  6 B, the head holder  51  is detached from the reference shaft  71 , and the replacement head holder  51  is hung and held on the reference shaft  71 . Accordingly, the head positional accuracy of the replacement head holder  51  can be reproduced, and the high positional accuracy of the head  6  in the other head holder  51  can be achieved. 
     Specific examples of the carriage and the head holder will further be described.  FIG. 4  is a perspective view of the state where the head holders are mounted to the carriage in a specific mode.  FIG. 5  is a front view of  FIG. 4 .  FIG. 6  is a side view of  FIG. 4 .  FIG. 7  is a perspective view of the state where the head holders are detached from the carriage.  FIG. 8  is a front view of the carriage.  FIG. 7  illustrates the state where the head holders  51  hold the recording heads  6  ( 6 A to  6 E) of each color. 
     The reference shaft  71  is positioned relative to the carriage by adjusting plates  72 A and  72 B disposed on the both side surfaces of the carriage  5 . That is, the adjusting plates  72 A and  72 B are position adjusters to adjust the position of the reference member (reference shaft  71 ) relative to the carriage. In addition, a sub-reference shaft  75  as a sub-reference member is disposed at the carriage  5  under the reference shaft  71 . The head holders  51  supported by the reference shaft  71  are in contact with the sub-reference shaft  75  and held by the carriage  5 . 
     By deciding the postures of the head holders  51  by the two shafts, that is, the reference shaft  71  and the sub-reference shaft  75 , the plurality of head holders  51  can be held in the carriage  5  with high accuracy. In addition, an adjuster is included to adjust the parallelism of the sub-reference shaft  75  with the reference shaft  71 . In this embodiment, the adjuster has one end of the sub-reference shaft  75  (left end in  FIG. 8 ) movable in a front-back direction (a direction vertical to  FIG. 8 , that is, a direction passing through  FIG. 8 ) and an adjusting member (adjusting cum  77 ) adjusting the position of the one end (left end in  FIG. 8 ) of the movable sub-reference shaft  75 . 
     The adjusting cum  77  as the adjusting member is disposed at the end of the sub-reference shaft  75  at the front and left side. The adjusting cum  77  moves the one end of the sub-reference shaft  75  in the front-back direction to adjust the parallelism of the sub-reference shaft  75  with the reference shaft  71 . Accordingly, the parallelism between the reference shaft  71  and the sub-reference shaft  75  can be adjusted on the actual machine. The adjuster to adjust the parallelism of the sub-reference shaft  75  with the reference shaft  71  is not limited to the foregoing one but may be any other appropriate one. 
     As illustrated in  FIG. 8 , an interposer  74  is disposed between the reference shaft  71  at the upper side of the carriage  5  and the sub-reference shaft  75  at the lower side of the carriage  5 . A plurality of lifting cams  112  is fixed and disposed at the sub-reference shaft  75  such that the lifting cams  112  can be rotated by rotating the sub-reference shaft  75  to lift the interposer  74 . The upper surface of the interposer  74  is in abutment with the reference shaft  71 . As the interposer  74  is lifted, the reference shaft  71  and the head holders  51  supported by the reference shaft  71  are also raised. When the head holders  51  are raised, the recording heads  6  become higher in position to widen a printing gap. 
     In the case of printing on a cardboard or wrinkled sheet, the gap between the sheet and the recording heads  6  become narrower than usual and the sheet may touch the recording heads  6 . Raising the recording heads  6  prevents such a situation and keeps the constant printing gap even with differences in sheet thickness to provide the printing accuracy. 
       FIG. 9  is a diagram illustrating a positioning part for the reference shaft  71  as seen from the right side of  FIG. 8 . Although  FIG. 9  illustrates the side of the adjusting plate  72 B, the opposite adjusting plate  72 A is the same as the illustrated side. As illustrated in  FIG. 9 , long cutouts  73  are formed in the adjusting plates  72  ( 72 A and  72 B), and the reference shaft  71  fitted into the cutouts  73  is held by the adjusting plates  72  to be capable of being lifted. That is, the reference shaft  71  is movable in up-down directions in  FIG. 9  that come close to and away from the recording surface (sheet surface). Accordingly, the head holders  51  ( 51 A and  51 B) supported by the reference shaft  71  can come close to and away from the recording surface (sheet surface). 
     Next, a support structure for the head holders  51  will be described in detail with reference to  FIGS. 10 to 14 . In the case of using the two head holders  51 , the two head holders  51  in the sub-scanning direction are positioned by hitching the hook portions  53  of the head holders  51  to the reference shaft  71 . The head holders  51  ( 51 A and  51 B) are provided with contact faces  54  (refer to  FIG. 12 ) to be in abutment with the sub-reference shaft  75 . The sub-reference shaft  75  and the contact faces  54  are brought into abutment with each other by the moment around the reference shaft  71  generated by the weights of the head holders  51 . 
     A pressing member may be provided to press the head holders  51  against the sub-reference shaft  75 . The sub-reference shaft  75  is disposed in parallel to the reference shaft  71 , and the two head holders  51  ( 51 A and  51 B) are held in the same posture by the two shafts. 
     As described above, the reference shaft  71  may not be a shaft member (round bar) but may be a polygonal member (bar of polygonal cross section).  FIG. 14  illustrates an example in which the polygonal reference shaft  71 B is used. In the case where the reference shaft  71 B is square as illustrated in  FIG. 14 , the polygonal reference shaft  71 B can be shaped such that the head holders  51  are in point contact with the polygonal reference shaft  71 B, thereby ensuring the same accuracy as in the case of using the round shaft. 
       FIGS. 15 and 16  are schematic diagrams illustrating a configuration of adjusting the parallelism between the sub-reference shaft  75  and the reference shaft  71 .  FIGS. 15 and 16  are views as seen from the left side of  FIG. 5 . 
     As illustrated in  FIGS. 15 and 16 , when the two head holders  51 A and  51 B are different in the amount of inclination due to weight difference and part accuracy, the adjusting cum  77  disposed at the one end of the sub-reference shaft  75  can adjust the parallelism between the sub-reference shaft  75  and the reference shaft  71  and adjust the difference in amount of inclination. 
     The adjusting cum  77  is in contact with the contact face  62  of the carriage  5  and is disposed to adjust the distance between the one end of the sub-reference shaft  75  and the contact face  62 . The adjusting cum  77  is an oval eccentric cam but may have another shape in cross section. 
     In this embodiment, as described above, the adjusting cum  77  is a member to adjust the parallelism of the sub-reference shaft  75  with the reference shaft  71  and is also a sub-scanning direction position adjuster to adjust the carriage and the sub-reference shaft (sub-reference shaft  75 ) in the sub-scanning direction by moving the one end of the sub-reference shaft  75  in the front-back direction (right-left direction in  FIGS. 15 and 16 ). 
     Disposing the adjusting cum  77  makes it possible to adjust the distance between the carriage  5  and the sub-reference shaft (sub-reference shaft  75 ) in the sub-scanning direction at the one end of the sub-reference shaft  75 , and adjust easily the difference in gap between the head holders  51  ( 51 A and  51 B) on the actual machine. The head holders  51  can be held in the same manner even when the reference shaft  71  and the sub-reference shaft  75  are reversely positioned (configured). 
     Next, a configuration of lifting the head holders  51  will be described with reference to the schematic diagrams of  FIGS. 17 to 20 .  FIGS. 17 to 20  are views as seen from the right side of  FIG. 5 . As illustrated in  FIGS. 17 and 18 , an interposer  74  for lifting is disposed between the reference shaft  71  and the sub-reference shaft  75 . The interposer  74  is movable in the up-down directions in  FIGS. 17 and 18  (that come close to and away from the recording surface, and the reference shaft  71  and the interposer  74  are in abutment with each other.  FIG. 21  illustrates a specific example of the interposer  74 . In the illustrated example, the interposer  74  has two pressing faces  74   a  and  74   a  at the upper part. The pressing faces  74   a  are brought into abutment with the reference shaft  71 . When the lifting cams  112  fixed and disposed at the sub-reference shaft  75  lift the interposer  74 , the interposer  74  lifts the reference shaft  71 , and the head holders  51  ( 51 A and  51 B) are raised to change printing gaps. The lifting cams  112  are oval eccentric cams but may have another shape in cross section. 
     The contact faces  54 A and  54 B (collectively referred to as  54 ) of the head holders  51  relative to the sub-reference shaft  75  ( FIGS. 17 to 20  illustrate only the contact face  54 B of the holder  51 B) are elongated in the height direction. Accordingly, when the head holders  51  are lifted, the reference shaft  71  and the contact faces  54  are kept in contact with each other. 
     As in other configuration examples illustrated in  FIGS. 19 and 20 , each of the head holders  51  has an abutment portion  55  of a shape to allow the lifting cams  112  to abut on the head holders  51  without the use of the interposer  74 , so that the lifting cams  112  can lift directly the head holders  51 . 
     In this case, a drive source to rotate the sub-reference shaft  75  and the lifting cams  112  are not included in the carriage  5  but are disposed at the device body. The drive source connects a drive to the carriage  5  at a predetermined position to rotate the sub-reference shaft  75 . 
     As described above, the image forming apparatus according to at least one embodiment of the present disclosure has the reference member, the sub-reference member, and the adjuster to adjust the parallelism of the sub-reference member with the reference member. The head holders detachably supported by the reference member are positioned in contact with the sub-reference member. Accordingly, it is possible to suppress deformation of the member holding the head holders and adjust the positions of the head holders with high accuracy independently from the reference member. 
     The plurality of head holders can be positioned and held in the carriage with high accuracy, and the positional relation between the two shafts can be adjusted. This allows easy adjustment of the positional relation between the head holders. 
     The carriage includes the position adjuster to adjust the position of the reference member relative to the carriage. This allows high-accuracy positioning of the reference member relative to the carriage. 
     The reference member is movable in directions to come close to and away from the recording surface. Supporting the head holders by the reference member allows the head holder to move in the directions to come close to and away from the recording surface to adjust the printing gap. 
     By moving (lifting) the reference member by the interposer, the head holders can be lifted together with the reference member to keep the positions of the head holders with high accuracy at the time of lifting (when the distance from the recording surface is longer). 
     According to the configuration of moving (lifting) directly the head holders, the printing gap can be adjusted according to a recording medium. The position adjuster is disposed at the one end of the sub-reference member to adjust the distance between the carriage and the sub-reference member in the sub-scanning direction. Accordingly, the simple configuration allows adjustment of the parallelism between the reference member and the sub-reference member on the actual machine. In the case of using a plurality of head holders, the differences in the amount of inclination between the head holders can be adjusted. 
     The above-described embodiments of the present disclosure are described with reference to the drawings. However, the present invention are not limited to the above-described embodiments and numerous additional modifications and variations are possible within the scope of the above teachings. 
     For example, in this disclosure, the term “sheet” used herein is not limited to a sheet of paper and includes anything such as OHP (overhead projector) sheet, cloth sheet, glass sheet, or substrate on which ink or other liquid droplets can be attached. In other words, the term “sheet” is used as a generic term including a recording medium, a recorded medium, a recording sheet, and a recording sheet of paper. The terms “image formation”, “recording”, “printing”, “image recording” and “image printing” are used herein as synonyms for one another. The terms “image formation”, “recording”, “printing”, and “image printing” are used herein as synonyms for one another. 
     The term “image forming apparatus” refers to an apparatus that discharges liquid on a medium to form an image on the medium. The medium is made of, for example, paper, string, fiber, cloth, leather, metal, plastic, glass, timber, and ceramic. The term “image formation” includes providing not only meaningful images such as characters and figures but meaningless images such as patterns to the medium (in other words, the term “image formation” also includes only causing liquid droplets to land on the medium). 
     The term “ink” is not limited to “ink” in a narrow sense, unless specified, but is used as a generic term for any types of liquid usable as targets of image formation. For example, the term “ink” includes recording liquid, fixing solution, DNA sample, resist, pattern material, resin, and so on. 
     The term “image” used herein is not limited to a two-dimensional image and includes, for example, an image applied to a three dimensional object and a three dimensional object itself formed as a three-dimensionally molded image. The term “image forming apparatus” includes both serial-type image forming apparatus and line-type image forming apparatus. The term “image forming apparatus” is not limited to a printer and may be, for example, a copier, a facsimile, a plotter, or a multifunctional periphery having at least one of the foregoing capabilities.