Abstract:
An image reader includes: a read frame; a read guide; and a seal mechanism. The seal mechanism covers a gap between the read frame and the read guide. The seal mechanism includes a rib standing in parallel with a sliding direction of the read guide and a flexible dustproof sheet having an end that is in contact with the rib.

Description:
CROSS REFERENCE 
       [0001]    This Nonprovisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2010-175132 filed in Japan on Aug. 4, 2010, the entire contents of which are hereby incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to an image reader including a read guide unit disposed on both sides of a document conveyance path, the read guide unit having an adjustable space in accordance with a thickness of a document conveyed, and relates to an image forming apparatus including such an image reader. 
         [0003]    At a document reading position for reading a document conveyed is disposed a contact glass configured to come into contact with the document and to guide the conveyance of the document. In general, this contact glass is supported stably by a housing that accommodates an optical system therein. 
         [0004]    In such a configuration, there is a case of dust entering the housing through a gap between the contact glass and a glass supporting portion of the housing and the dust adhering to the optical system in the housing. Such dust adhering to the optical system unfortunately may appear as black streak in a read image. 
         [0005]    To avoid this, some conventional techniques propose a reader including a flexible dustproof member intervening between the lower face of a contact glass and a supporting portion of the contact glass and a restricting part provided at a part of a sheet guide unit to prevent the floating of the contact glass by a pressing force of the flexible member to the contact glass (see JP 2000-180994 A, for example). 
         [0006]    Even with such a configuration in the conventional technique, in the case of an image reader provided with a read guide unit with an adjustable space in accordance with the thickness of a document conveyed, there is a case of dust entering inside a housing through a mechanism to move the read guide unit. 
         [0007]    Such a mechanism adjusting the space in accordance with the thickness of a document conveyed is important for keeping good reading accuracy for both fixed ordinary paper and cards, but has a problem of often generating a gap in the housing corresponding to a moving stroke of the mechanism. 
         [0008]    For dustproofing, the housing has to have an improved sealing property. A mechanism for such an improved sealing property, however, may hinder the smooth movement of members making up the housing, which may cause problems such as a failure in adjusting the space of a read guide unit appropriately or a document being caught at the read guide unit and fed in a slanting direction. 
         [0009]    It is an object of the present invention to provide an image reader and an image forming apparatus capable of achieving an improved sealing property of a housing member to accommodate an optical system therein without impairing a space-adjusting function of a read guide with an adjustable space in accordance with the thickness of a document conveyed. 
       SUMMARY OF THE INVENTION 
       [0010]    An image reader of the present invention includes a read guide disposed on both sides of a document conveyance path, the read guide having a space that is adjustable in accordance with a thickness of a document conveyed. The image reader includes: a read frame member; a read guide member; and a seal mechanism. 
         [0011]    The read frame member is fixed to a document reading unit, and supports an optical system. 
         [0012]    The read guide member makes up a housing member together with the read frame member to accommodate the optical system therein. The read guide member is configured to guide a document to be conveyed to a reading position and support a read glass. The read guide member is supported slidably with respect to the read frame member. 
         [0013]    The seal mechanism covers a gap between the read frame member and the read guide member. The seal mechanism includes a rib standing in parallel with a vertical moving direction of the read guide member and a flexible dustproof sheet having an end that is in contact with the rib. Examples of the dustproof sheet include a urethane sheet of about 0.1 mm in thickness. 
         [0014]    In this configuration, the rib disposed at one of the read frame member and the read guide member is in contact with the dustproof sheet disposed at the other, whereby a gap between the read frame member and the read guide member is covered. 
         [0015]    The rib is provided in parallel with the vertical moving direction of the read guide member, and the end of the flexible dustproof sheet is in contact with the rib, thus sealing the housing member. This configuration enables the sliding operation of the read guide member with less interruption by friction between the dustproof sheet and the rib. As a result, a sealing property of the housing member made up of the read frame member and the read guide member can be improved without inhibiting the smooth sliding operation of the read guide member. 
         [0016]    According to the present invention, a sealing property of a housing member to accommodate an optical system therein can be improved without impairing a space-adjusting function of a read guide with an adjustable space in accordance with the thickness of a document conveyed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a cross-sectional view illustrating a schematic configuration of an image forming apparatus according to one embodiment of the present invention. 
           [0018]      FIG. 2  is a cross-sectional view illustrating a schematic configuration of a document reading section. 
           [0019]      FIG. 3  is a cross-sectional view schematically illustrating the configuration in the vicinity of a first read guide unit and a second read guide unit of the document reading section. 
           [0020]      FIG. 4  is an assembly drawing schematically illustrating the configuration of the second read guide unit. 
           [0021]      FIG. 5  is a cross-sectional view schematically illustrating the configuration of the second read guide unit along the length direction. 
           [0022]      FIG. 6  is a cross-sectional view taken along VI-VI of  FIG. 5 . 
           [0023]      FIG. 7  is a cross-sectional view taken along VII-VII of  FIG. 5 . 
           [0024]      FIG. 8A  and  FIG. 8B  illustrate a movable range of a read guide of the second read guide unit. 
           [0025]      FIG. 9A  and  FIG. 9B  illustrate an operation of the second read guide unit and a state of a sealing unit. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]      FIG. 1  is a schematic cross-sectional view of an image forming apparatus  100  according to one embodiment of the present invention. The image forming apparatus  100  forms a multicolored or single-colored image on a predetermined sheet (recording sheet) in accordance with image data externally transmitted, and includes a document reading section  20  and an image forming section  10 . 
         [0027]    The document reading section  20  is configured capable of simultaneously reading images on both faces of a document conveyed. The document reading section  20  includes a document platen  22  made of transparent glass on which a document is manually placed, and above the document platen  22  is installed an automatic document processor  24 . The automatic document processor  24  is configured to sequentially convey a document on a paper feeding tray  26  via a document conveyance path  36  to a first document output unit  28  to output a document of ordinary paper or to a second document output unit  30  to output a thick document (cards, envelopes or the like). 
         [0028]    On both sides of the document conveyance path  36  are provided a first reading unit  32  configured to read an image on a first face of a document conveyed or an image of a document on the document platen  22  and a second reading unit  34  configured to read an image on a second face of a document conveyed. In this example, the first reading unit  32  and the second reading unit  34  each include an optical reduction system using a CCD, which may be a CIS. The detailed configuration of the document reading section  20  will be described later. 
         [0029]    Below the document reading section  20  is disposed the image forming section  10 . The image forming section  10  includes an optical scanner  210 , a development unit  102 , a photoreceptor drum  103 , a cleaner unit  104 , a charger  105 , an intermediate transfer belt unit  106 , a fixing unit  107 , a paper feeding cassette  181 , a copy receiving unit  191  and the like. 
         [0030]    Image data processed by this image forming apparatus  100  corresponds to a color image including colors of black (K), cyan (C), magenta (M) and yellow (Y). Accordingly, four sets of the development unit  102 , the photoreceptor drum  103 , the charger  105  and the cleaner unit  104  are provided to form four types of latent images corresponding to the respective colors including black, cyan, magenta and yellow, thus configuring four image stations. 
         [0031]    The charger  105  is means to uniformly charge the surface of the photoreceptor drum  103  at a predetermined electrical potential, which may be a contact type charger such as a roller or a brush instead of a non-contact type charger as illustrated in  FIG. 1 . 
         [0032]    The optical scanner  210  is configured to form an electrostatic latent image on the surface of each photoreceptor drum  103  in accordance with image data input. 
         [0033]    Each development unit  102  makes the electrostatic latent image formed on the corresponding photoreceptor drum  103  visible with toner in one of the four colors (YMCK). Each cleaner unit  104  removes and collects toner remaining on the surface of the corresponding photoreceptor drum  103  after development and image transferring steps. 
         [0034]    The intermediate transfer belt unit  106  disposed above the photoreceptor drums  103  includes an intermediate transfer belt  161 , an intermediate transfer belt driving roller  162 , an intermediate transfer belt idle roller  163 , intermediate transfer rollers  164 , and an intermediate transfer belt cleaning unit  165 . Four intermediate transfer rollers  164  are provided corresponding to the respective colors of YMCK. 
         [0035]    The intermediate transfer belt driving roller  162 , the intermediate transfer belt idle roller  163  and the intermediate transfer rollers  164  are configured to stretch the intermediate transfer belt  161  therebetween for rotation driving. Each intermediate transfer roller  164  applies a transfer bias to transfer a toner image on the photoreceptor drum  103  to the intermediate transfer belt  161 . 
         [0036]    The intermediate transfer belt  161  is provided to come into contact with each photoreceptor drum  103 . The intermediate transfer belt  161  has a function to allow a toner image in each color formed on the photoreceptor drum  103  to be transferred and sequentially overlaid thereon, so that a color toner image (multicolored toner image) is formed on the intermediate transfer belt  161 . The intermediate transfer belt  161  is formed as an endless belt using film of 100 μm to 150 μm in thickness, for example. 
         [0037]    Toner images are transferred from the photoreceptor drums  103  to the intermediate transfer belt  161  by the intermediate transfer rollers  164  in contact with the rear side of the intermediate transfer belt  161 . A transfer bias of a high voltage (high voltage with reversed polarity (+) of the polarity (−) of charged toner) is applied to the intermediate transfer rollers  164  for transferring of the toner images. Each of the intermediate transfer rollers  164  is a roller including a metal (e.g., stainless steel) shaft of 8 to 10 mm in diameter as a base that is surrounded by a conductive elastic material (e.g., EPDM or urethane foam). This conductive elastic material enables the uniform application of a high voltage to the intermediate transfer belt  161 . The present embodiment uses the transfer electrodes in a roller shape, but not limited to, and a brush type transfer electrode may be used, for example. 
         [0038]    As stated above, the electrostatic image is made visible on each photoreceptor drum  103  in the corresponding color, and is overlaid on the intermediate transfer belt  161 . Then, as the intermediate transfer belt  161  rotates, the thus overlaid image information is transferred onto a sheet by a transfer roller  110  described below that is disposed at a contact position of the sheet and the intermediate transfer belt  161 . 
         [0039]    At this time, the intermediate transfer belt  161  and the transfer roller  110  are brought into contact with each other under pressure with a predetermined nip, while a voltage (high voltage with reversed polarity (+) of the polarity (−) of charged toner) is applied to the transfer roller  110  for transferring of the toner onto a sheet. In order to allow the transfer roller  110  to give the above-stated nip steadily, any one of the transfer roller  110  and the intermediate transfer belt driving roller  162  may be made of a hard material (e.g., metal), and the other may be an elastic roller made of a soft material (e.g., elastic rubber roller or foaming resin roller). 
         [0040]    As stated above, toner adheres to the intermediate transfer belt  161  in contact with the photoreceptor drums  103  or toner may remain on the intermediate transfer belt  161  without being transferred to a sheet by the transfer roller  110 , and such toner causes the mixture of colors of toner at a following step. In order to avoid this, the intermediate transfer belt cleaning unit  165  is provided to remove and collect such toner. The intermediate transfer belt cleaning unit  165  includes a cleaning blade, for example, as cleaning member coming into contact with the intermediate transfer belt  161 . At a portion of the intermediate transfer belt  161  brought into contact with the cleaning blade, the intermediate transfer belt  161  is supported by the intermediate transfer belt idle roller  163  from the opposite side. 
         [0041]    The paper feeding cassette  181  is a tray for storing sheets (recording sheets) used for image formation, and is disposed below the optical scanner  210  of the image forming section  10 . The sheets used for image formation may be placed on a manual paper feeding cassette  182  as well. The copy receiving unit  191  provided at an upper portion of the image forming section  10  is a tray for piling up sheets subjected to printing while letting the printed side face downward. 
         [0042]    The image forming section  10  is further provided with a substantially vertical sheet conveyance path  200  to send a sheet from the paper feeding cassette  181  or the manual paper feeding cassette  182  to the copy receiving unit  191  via the transfer roller  110  and the fixing unit  107 . In the vicinity of the sheet conveyance path  200  from the paper feeding cassette  181  or the manual paper feeding cassette  182  to the copy receiving unit  191  are disposed pickup rollers  111 A and  111 B, a plurality of conveyance rollers  112 A to  112 D, paper stop rollers  113 , the transfer roller  110  and the fixing unit  107 , for example. 
         [0043]    The conveyance rollers  112 A to  112 D are small rollers to promote and assist the conveyance of a sheet, and a plurality of these rollers are provided along the sheet conveyance path  200 . The pickup roller  111 A is provided in the vicinity of an end of the paper feeding cassette  181  so as to pick up sheets one by one from the paper feeding cassette  181  and supply the sheet to the sheet conveyance path  200 . Similarly, the pickup roller  111 B is provided in the vicinity of an end of the manual paper feeding cassette  182  so as to pick up sheets one by one from the manual paper feeding cassette  182  and supply the sheet to the sheet conveyance path  200 . 
         [0044]    The paper stop rollers  113  hold a sheet being conveyed along the sheet conveyance path  200  once. Then, the paper stop rollers  113  function to convey the sheet to the transfer roller  110  at timing when a front end of a toner image on the photoreceptor drum  103  and a front end of the sheet are aligned. 
         [0045]    The fixing unit  107  includes a heat roller  171  and a pressure roller  172 , and the heat roller  171  and the pressure roller  172  rotate while sandwiching a sheet therebetween. The heat roller  171  is set at a predetermined fixing temperature by a controller on the basis of a signal from a temperature detector not illustrated. The heat roller  171  as well as the pressure roller  172  have a function to heat and pressurize toner with respect to a sheet to melt, mix and pressurize a multicolored toner image transferred on the sheet for heat fixing. An external heating belt  173  is further provided to heat the heat roller  171  externally. 
         [0046]    The following describes the sheet conveyance path in detail. As stated above, the image forming apparatus is provided with the paper feeding cassette  181  for storing sheets beforehand and the manual paper feeding cassette  182 . In order to feed a sheet from these paper feeding cassettes  181  and  182 , the pickup rollers  111 A and  111 B are provided, respectively, so as to guide sheets one by one to the conveyance path  200 . 
         [0047]    A sheet is conveyed from the paper feeding cassette  181  or the manual paper feeding cassette  182  to the paper stop rollers  113  by the conveyance rollers  112 A in the sheet conveyance path  200 . Then, the sheet is conveyed to the transfer roller  110  at timing when a front end of the sheet is aligned with a front end of image information on the intermediate transfer belt  161 , and the image information is written on the sheet. Thereafter, the sheet passes through the fixing unit  107  so that unfixed toner is melt by heat and fixed for adhesion to the sheet, and the sheet is discharged via the conveyance rollers  112 B provided downstream to the copy receiving unit  191 . 
         [0048]    The above-stated conveyance path is for processing a single-sided printing request to a sheet. On the other hand, in the case of a double-sided printing request, a sheet subjected to single-sided printing and passing through the fixing unit  107  as stated above is held at its rear end by the finally disposed conveyance rollers  112 B. Then, the conveyance rollers  112 B rotate reversely so as to guide the sheet to the conveyance rollers  112 C and  112 D. Thereafter the sheet passes through the paper stop rollers  113  and is subjected to printing on the rear face of the sheet. The sheet is then discharged to the copy receiving unit  191 . 
         [0049]    Referring now to  FIG. 2 , the following describes the configuration of the document reading section  20 . As illustrated in this drawing, the document conveyance path  36  is linearly inclined downward from the paper feeding tray  26  to a document guide  38  (in this drawing, inclined downward from right to left). Herein, the document guide  38  is supported swingably. Downstream of the document guide  38  is provided a path changing member  39  configured to guide a document conveyed either to the first document output unit  28  or to the second document output unit  30 . In this embodiment, the path changing member  39  is configured to guide a thick document such as a card (e.g., with a thickness of 0.6 mm or more) to the second document output unit  30  and to guide a document other than thick documents (e.g., with a thickness less than 0.6 mm) to the first document output unit  28 . A document guided by the path changing member  39  to the first document output unit  28  passes through a portion having a U-letter shape in cross section of the document conveyance path  36  and then is conveyed to the first document output unit  28 . 
         [0050]    Upstream of the document guide  38  in the document conveyance path  36  are provided a first read guide unit  40  and a second read guide unit  42  that are inclined substantially in parallel with the document conveyance path  36 . The first read guide unit  40  and the second read guide unit  42  are disposed to sandwich the document conveyance path  36  therebetween and are configured to achieve stable conveyance of a document to be read by the first reading unit  32  and the second reading unit  34 . 
         [0051]    Referring next to  FIG. 3 , the configuration in the vicinity of the first read guide unit  40  and the second read guide unit  42  is described below. The first read guide unit  40  and the second read guide unit  42  are configured to guide a document so that an image on the document is read at a first reading position  50  or a second reading position  52 . The first read guide unit  40  and the second read guide unit  42  are opposed to each other while sandwiching the document conveyance path  36  therebetween, and have a space therebetween adjustable in accordance with a thickness of a document conveyed. In this embodiment, the space between the first read guide unit  40  and the second read guide unit  42  is adjustable in a range, but not limited to, from about 0.6 mm to 1.3 mm. 
         [0052]    The first read guide unit  40  includes a first guide member  400  made up of a transparent plate member such as glass facing a first face of a document and a guide supporting member  402  supporting the first guide member  400 . 
         [0053]    A second read guide unit  42  includes a read frame  420  fixed to a frame in the document reading section  20  and a read guide  422  suspending from the read frame  420  to be movable up and down (i.e., movable vertically). The read frame  420  together with the read guide  422  make up a housing member to accommodate an optical system therein. The read frame  420  includes an open face on one side, and this open face is blocked by the read guide  422 . The read frame  420  has an opening  424  letting light pass therethrough, and all around the opening  424  is provided a moltplane  45 . This moltplane  45  is in intimate contact with the second reading unit  34  so as to prevent the leakage of light through the opening  424 . The read guide  422  includes a transparent plate member  410  such as glass facing a second face of a document. A light beam for document reading emitted from the second reading unit  34  passes through the opening  424  and the plate member  410  and is applied to the second face of a document. 
         [0054]    Referring next to  FIGS. 4 to 8 , the configuration of the second read guide unit  42  is described below. The read frame  420  is provided with an optical system including a LED board  426  with a LED mounted thereon, a light guiding plate  428  disposed around the LED board  426 , a reflector  430  that reflects light toward a document reading position and the like. 
         [0055]    The read guide  422  is supported at one end portion in the length direction (direction orthogonal to the document conveyance direction) by the read frame  420  via a shoulder screw  432 . As illustrated in  FIG. 4 , the shoulder screw  432  is inserted from below the second read guide unit  42  to a boss  445  provided in a protruding manner at a bottom face of the read guide  422 , and is screwed with a screw hole  435  penetrating through a top face of the read frame  420 . The other end portion of the read guide  422  is supported by engagement between an engagement hole  436  formed in a side wall  434  of the read frame  420  and an engagement piece  438  provided at the read guide  422 . 
         [0056]    As illustrated in  FIG. 8 , a sufficient space D 1  is formed between the upper end of the boss  445  and the top face of the read frame  420 . As illustrated in  FIG. 8 , a sufficient space D 2  is formed between the upper face of the engagement piece  438  and the upper edge of the engagement hole  436 . The spaces D 1  and D 2  may have the same size or either one may have a larger size. When the spaces D 1  and D 2  have the same size, the vertical movable range of the read guide  422  is decided by their size. When the spaces D 1  and D 2  have different sizes, the vertical movable range of the read guide  422  is decided by a smaller size. The read guide  422  is supported at the lowest position of the vertical movable range by its own weight, and when a thick document passing gives a lifting force thereto, the read guide  422  can move upward to the highest position of the vertical movable range at maximum as described later. 
         [0057]    In this configuration, although the shoulder screw  432  is provided only at one end portion in the length direction of the read guide  422 , both end portions may be supported using the shoulder screws  432 . Considering the workability for attachment and detachment of the read glide  422 , however, the shoulder screw  432  is preferably provided at only one end portion in the length direction of the read guide  422 . 
         [0058]    The read frame  420  and the read guide  422  are sealed by a seal mechanism  421  so as to prevent dust from entering inside the read frame  420  and the read guide  422 . 
         [0059]    The seal mechanism  421  includes a rib  442  formed along the entire perimeter of the read guide  422  and a thin and flexible dustproof sheet  440  disposed along the entire perimeter of the read frame  420 . The rib  442  stands vertically from the face of the read guide  422  facing the read frame  420 . That is, the rib  442  is provided in parallel with the vertical moving direction of the read guide  422 . 
         [0060]    The dustproof sheet  440  is made of a urethane sheet of about 0.1 mm in thickness, and is disposed so that an end of the dustproof sheet  440  is brought into contact with the rib  442 . In this embodiment, as the dustproof sheet  440 , a urethane sheet produced by Nihon Matai Co., Ltd. “Matai URS surface matte type” is used. The dustproof sheet  440  is attached to the read frame  420  via a sheet attachment member  444  made of urethane foam. In this way, the dustproof sheet  440  is attached via the sheet attachment member  444  made of the same material, whereby the effect of preventing the rippling of the sheet can be obtained due to uniform linear expansion. In this example, the dustproof sheet  440  is attached, but not limited to, using double-faced tape. 
         [0061]    Referring next to  FIGS. 9A and 9B , operations of the first read guide unit  40  and the second read guide unit  42  are described below.  FIG. 9A  illustrates a state of the first read guide unit  40  and the second read guide unit  42  when an ordinary paper document of about 0.1 to 0.2 mm in thickness is conveyed, and  FIG. 9B  illustrates a state of the first read guide unit  40  and the second read guide unit  42  when a card document of about 0.8 mm in thickness is conveyed. 
         [0062]    As illustrated in  FIG. 9A , when the surface and the rear face of a document are read simultaneously, the space between the first read guide unit  40  and the second read guide unit  42  is decreased to about 0.6 mm for a stable focal length. As a result, when an ordinary paper document of about 0.1 to 0.2 mm in thickness is conveyed, both images for the surface and the rear face of the document can have reduced tendency of defocusing. 
         [0063]    As illustrated in  FIG. 9B , when a document exceeding about 0.6 mm in thickness passes, the second read guide unit  42  is lifted upward by a force received from the document, and moves away from the document conveyance path  36 . At this time, the boss  445  at one end portion of the read guide  422  moves upward while being guided by the shoulder screw  432 , and the engagement piece  438  at the other end portion of the read guide  422  moves upward while being guided by the engagement hole  436 , and accordingly the read guide  422  slides upward while keeping the parallel state. As a result, the space between the first read guide unit  40  and the second read guide unit  42  is expanded. 
         [0064]    This embodiment is configured so that the space between the first read guide unit  40  and the second read guide unit  42  is expanded to about 1.3 mm at maximum. Therefore, even when a card-like document of about 0.8 mm in thickness is conveyed, for example, the document can be conveyed in a preferable manner and images on both faces can be read. 
         [0065]    Additionally, the seal mechanism  421  sealing the read frame  420  and the read guide  422  can prevent dust from entering inside the read frame  420  and the read guide  422 . Therefore, even when the read guide  422  moves upward, the seal mechanism  421  keeps the sealing property inside the read guide  422  and the read frame  420 . 
         [0066]    Further, when the read guide  422  moves downward, a bending force is slightly applied to the end of the dustproof sheet  440 , and large friction does not occur between the dustproof sheet  440  and the rib  442 . Accordingly, a dustproof effect can be obtained without inhibiting the vertical moving operation of the read guide  422 . 
         [0067]    Moreover, a focal length for an ordinary paper document having an ordinary thickness is secured, and further a focal length can be secured stably even when both faces of a thick document such as a card document are read. In this way, both faces of a document can be read simultaneously without defocusing irrespective of the thickness of a document. 
         [0068]    A thick document such as a card document passes through a linear portion only in the document conveyance path  36  without passing through a curved portion in the document conveyance path  36  and is discharged to the second document output unit  30 , and therefore a problem such as a conveyance failure can be suppressed. 
         [0069]    The above described embodiments are to be considered in all respects as illustrative and not restrictive. The scope of the invention is indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are intended to be embraced therein.