Abstract:
An image forming apparatus includes plural medium transport paths that branch at a predetermined branching position and along which a medium is transported in a curved state; a switching member disposed at the branching position and including a guide surface that allows the medium to be transported along one of the medium transport paths, the switching member switching between the medium transport paths; an output unit that outputs the medium toward a stacking portion, on which the medium is to be stacked, while corrugating the medium; and a guide portion that guides the medium from the branching position toward the output unit in a region in which the medium is corrugated.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2015-124431 filed Jun. 22, 2015. 
       BACKGROUND 
       [0002]    Technical Field 
         [0003]    The present invention relates to an image forming apparatus. 
         [0004]    Summary 
         [0005]    According to an aspect of the invention, there is provided an image forming apparatus including plural medium transport paths that branch at a predetermined branching position and along which a medium is transported in a curved state; a switching member disposed at the branching position and including a guide surface that allows the medium to be transported along one of the medium transport paths, the switching member switching between the medium transport paths; an output unit that outputs the medium toward a stacking portion, on which the medium is to be stacked, while corrugating the medium; and a guide portion that guides the medium from the branching position toward the output unit in a region in which the medium is corrugated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein: 
           [0007]      FIG. 1  is a sectional schematic diagram illustrating the inner structure of an image forming apparatus; 
           [0008]      FIG. 2  is a sectional schematic diagram illustrating a sheet transporting operation of a sheet transport device in a state in which a switching gate is switched to a first position; 
           [0009]      FIG. 3  is a sectional schematic diagram illustrating the sheet transporting operation of the sheet transport device in a state in which the switching gate is switched to a second position; 
           [0010]      FIG. 4  is a diagram illustrating how a paper sheet is corrugated in a paper output unit; 
           [0011]      FIG. 5  is a plan schematic diagram illustrating the positional relationship between the switching gate and a first output roller pair; 
           [0012]      FIG. 6  is a sectional schematic diagram illustrating the manner in which the trailing end of a corrugated paper sheet is transported; 
           [0013]      FIG. 7  is a sectional schematic diagram illustrating a sheet transporting operation of a sheet transport device in a state in which a switching gate is switched to a first position; 
           [0014]      FIG. 8  is a plan schematic diagram illustrating the positional relationship between the switching gate and a first output roller pair; and 
           [0015]      FIG. 9  is a plan schematic diagram illustrating the deformation of the switching gate during an offset operation. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    The present invention will be explained in further detail by describing exemplary embodiments and examples with reference to the drawings. However, the present invention is not limited to the exemplary embodiments and examples. 
         [0017]    It is to be noted that the drawings referred to in the following description are schematic, and that dimensional ratios, for example, are not equal to the actual dimensional ratios. Components other than those needed to be explained to facilitate understanding are omitted as appropriate in the drawings. 
       First Exemplary Embodiment 
     1. Overall Structure and Operation of Image Forming Apparatus 
       [0018]      FIG. 1  is a vertical sectional view illustrating the inner structure of an image forming apparatus  1 . 
         [0019]    The overall structure and operation of the image forming apparatus  1  will be described with reference to the drawings. 
         [0020]    The image forming apparatus  1  includes a control device  10 , a sheet feeding device  20 , photoconductor units  30 , developing devices  40 , a transfer device  50 , and a fixing device  60 . A paper output tray unit T, which receives paper sheets having images recorded thereon, is provided on an upper surface (Z-direction-side surface) of the image forming apparatus  1 . 
         [0021]    The control device  10  includes a controller  11  that controls the operation of the image forming apparatus  1 , an image processing unit  12  that performs an operation controlled by the controller  11 , and a power supply device  13 . The power supply device  13  applies a voltage to devices including the photoconductor units  30 , the developing devices  40 , and the transfer device  50 . 
         [0022]    The image processing unit  12  converts print information input thereto from an external information transmission device (for example, a personal computer) into image information used to form a latent image, and outputs a drive signal to an exposure device at a preset timing. 
         [0023]    A sheet feeding device  20  that contains a stack of paper sheets P, which serve as media, is provided at the bottom of the image forming apparatus  1 . The paper sheets P, which are positioned in a width direction by a regulating plate (not shown), are drawn out one at a time in the forward direction (-X direction) by a sheet drawing unit  22 . 
         [0024]    The paper sheets P drawn out by the sheet drawing unit  22  is transported along a first sheet transport path  91  to a nip portion of a registration roller pair  23 . 
         [0025]    The photoconductor units  30  include photoconductor drums  31  that are arranged next to each other in a region above (on the Z-direction side of) the sheet feeding device  20 . Yellow (Y), magenta (M), cyan (C), and black (K) toner images are formed on the photoconductor drums  31  by the respective developing devices  40 . 
         [0026]    The toner images of the respective colors formed on the photoconductor drums  31  of the photoconductor units  30  are successively electrostatically transferred onto an intermediate transfer belt  51 , which is included in the transfer device  50 , in a first transfer process, so that a superposed toner image in which the toners of the respective colors are superposed is formed. The superposed toner image formed on the intermediate transfer belt  51  is transferred, by a second transfer roller  52  onto a paper sheet P that has been transported from the registration roller pair  23  and guided by a transport guide. 
         [0027]    The fixing device  60  includes a fixing nip portion (fixing region) in a region in which a pair of modules, which are a heating module  61  and a pressing module  62 , are pressed against each other. 
         [0028]    The paper sheet P onto which the toner image has been transferred by the transfer device  50  is transported to the fixing nip portion of the fixing device  60  along a transport guide  53  while the toner image is not fixed. The pair of modules, which are the heating module  61  and the pressing module  62 , apply heat and pressure to the toner image to fix the toner image. 
         [0029]    The paper sheet P on which the fixed toner image is formed is guided by a sheet transport device  70  and output to the paper output tray unit T on the upper surface of the image forming apparatus  1  from a first output roller pair  80 . When duplex printing is to be performed, a switching gate  74  switches the transporting direction to a direction toward a second transport path, and a second output roller pair  90  is driven in the reverse direction so that the paper sheet P is transported from a reversing transport path S 2  to the registration roller pair  23 . Then, an image is formed on the back surface of the paper sheet P. 
       2. Structure and Operation of Sheet Transport Device 
       [0030]      FIG. 2  is a sectional schematic diagram illustrating a sheet transporting operation of the sheet transport device  70  in a state in which the switching gate  74  is switched to a first position.  FIG. 3  is a sectional schematic diagram illustrating the sheet transporting operation of the sheet transport device  70  in a state in which the switching gate  74  is switched to a second position.  FIG. 4  is a diagram illustrating how a paper sheet is corrugated in a paper output unit.  FIG. 5  is a plan schematic diagram illustrating the positional relationship between the switching gate  74  and the first output roller pair  80 .  FIG. 6  is a sectional schematic diagram illustrating the manner in which the trailing end of a corrugated paper sheet is transported. 
         [0031]    The structure and sheet transporting operation of the sheet transport device  70  included in the image forming apparatus  1  will be described with reference to the drawings. 
       2.1. Structure of Sheet Transport Unit 
       [0032]    Referring to  FIG. 2 , the sheet transport device  70  of the image forming apparatus  1  includes guides  71   a  and  71   b,  transport roller pairs  72  and  73 , the switching gate  74 , and the first output roller pair  80 . 
         [0033]    The guides  71   a  and  71   b,  which are located downstream of the fixing nip portion of the fixing device  60 , guide the paper sheet P to which the toner image is fixed to the transport roller pair  72 . The sheet transport path that extends from the transport roller pair  72  to the first output roller pair  80  is defined by the switching gate  74 . 
         [0034]    The switching gate  74  is supported by a support shaft  75  so as to be rotatable between a first position for guiding the paper sheet P to the first output roller pair  80 , as illustrated in  FIG. 2 , and a second position for guiding the paper sheet P to the second output roller pair  90 , as illustrated in  FIG. 3 . 
         [0035]    In a state in which the switching gate  74  is at the first position for guiding the paper sheet P to the first output roller pair  80 , the sheet transport path from the transport roller pair  72  to the first output roller pair  80  is curved so that an increase in the height of the apparatus is suppressed. 
         [0036]    The switching gate  74  has first guide surfaces  74   a,  second guide surfaces  74   b,  and third guide surfaces  74   c,  and is supported so as to be rotatable around the support shaft  75 . 
         [0037]    The third guide surfaces  74   c  are integrally connected to the corresponding first guide surfaces  74   a  so as to extend toward a front side (toward the first output roller pair  80 ) to a position where the front ends thereof overlap the first output roller pair  80  when viewed in the axial direction, thereby defining a first transport path that guides the paper sheet P transported by the transport roller pair  72  to a nip portion of the first output roller pair  80 . 
         [0038]    The second guide surfaces  74   b  define a second transport path that guides the paper sheet P transported by the transport roller pair  72  to a nip portion of the transport roller pair  73 . 
         [0039]    The first output roller pair  80  includes drive rollers  81  that are rotated, pinch rollers  82  that are pressed against the drive rollers  81  in a rotatable manner, and corrugation rollers  83  that are disposed between the pinch rollers  822  in a rotatable manner. When the first output roller pair  80  is rotationally driven, the paper sheet P is output to the paper output tray unit T. 
         [0040]    As schematically illustrated in  FIG. 4 , the first output roller pair  80  includes a corrugation unit that forms plural vertically concave portions in the paper sheet P along the direction in which the paper sheet P is output to increase the stiffness of the paper sheet P that is output and improve the travelling stability of the paper sheet P that is output. 
         [0041]    More specifically, central portions of the corrugation rollers  83 , which are disposed between the pinch rollers  82 , have outer diameters greater than those of the pinch rollers  82  so that, when the paper sheet P is output, the paper sheet P is formed into a corrugated shape that undulates in a direction perpendicular to the direction in which the paper sheet P is output, and the stiffness of the paper sheet P is increased. 
         [0042]    Referring to  FIG. 5 , in a region in which the corrugation unit of the first output roller pair  80  is disposed, the switching gate  74  has the third guide surfaces  74   c,  each of which is integrally connected to the corresponding first guide surface  74   a  so as to extend toward the front side (toward the first output roller pair  80 ). The third guide surfaces  74   c  are disposed near the corrugation unit of the first output roller pair  80  in the sheet transporting direction. 
       2.2. Sheet Transporting Operation 
       [0043]    In the sheet transport device  70  having the above-described structure, when the leading end of the paper sheet P is nipped by the first output roller pair  80  and the process of outputting the paper sheet P is started, the paper sheet P is corrugated by the corrugation unit. The paper sheet P is corrugated not only in a region downstream of the first output roller pair  80  but also in a region upstream of the first output roller pair  80 . 
         [0044]    Accordingly, as schematically illustrated in  FIG. 6 , the paper sheet P is transported while the trailing end portion of the paper sheet P is pressed against the first guide surfaces  74   a  and the third guide surfaces  74   c  of the switching gate  74  in such a state that the trailing end portion is curved and corrugated so that the stiffness thereof is increased (see F in  FIG. 6 ). 
         [0045]    In a region between the switching gate  74 , which defines the sheet transport paths and which is supported so as to be rotatable between the first position and the second position, and the nip portion of the first output roller pair  80 , a step is easily formed in the sheet transporting direction. Accordingly, when the trailing end of the paper sheet P passes the first guide surfaces  74   a  of the switching gate  74 , there is a risk that a large impact noise will be caused by flapping of the paper sheet P that is stiff. 
         [0046]    In the sheet transport device  70  according to the present exemplary embodiment, the sheet transport path from the transport roller pair  72  to the first output roller pair  80  is defined by the switching gate  74 . the switching gate  74  includes the first guide surfaces  74   a  that guide the paper sheet P to the nip portion of the first output roller pair  80 , and the third guide surfaces  74   c  that are integrally connected to the corresponding first guide surfaces  74   a  so as to extend toward the front side (toward the first output roller pair  80 ) to a position where the front ends thereof overlap the first output roller pair  80  when viewed in the axial direction. 
         [0047]    As a result, the sheet transport path that is curved between the first guide surfaces  74   a  of the switching gate  74  and the nip portion of the first output roller pair  80  does not have a step portion that is stepped toward the curved side. 
         [0048]    Accordingly, the trailing end of the paper sheet P is guided while being pressed against the third guide surfaces  74   c,  which are connected to the corresponding first guide surfaces  74   a,  until the trailing end of the paper sheet P reaches the nip portion of the first output roller pair  80 . Thus, the large impact noise caused by flapping of the paper sheet P that is stiff is suppressed. 
       Second Exemplary Embodiment 
       [0049]      FIG. 7  is a sectional schematic diagram illustrating a sheet transporting operation of a sheet transport device  70 A in a state in which a switching gate  74 A is switched to a first position.  FIG. 8  is a plan schematic diagram illustrating the positional relationship between the switching gate  74 A and a first output roller pair  80 .  FIG. 9  is a plan schematic diagram illustrating the deformation of the switching gate  74 A during an offset operation. 
         [0050]    The structure and sheet transporting operation of the sheet transport device  70 A included in an image forming apparatus  1  will be described with reference to the drawings. Components similar to those in the sheet transport device  70  according to the first exemplary embodiment are denoted by the same reference numerals, and detailed descriptions thereof are thus omitted. 
         [0051]    As illustrated in  FIG. 7 , the sheet transport device  70 A includes guides  71   a  and  71   b,  transport roller pairs  72  and  73 , the switching gate  74 A, and the first output roller pair  80 . 
         [0052]    The switching gate  74 A is supported so as to be rotatable around a support shaft  75 A at a location downstream of the transport roller pair  72 . The switching gate  74 A has first guide surfaces  74 Aa that guide the paper sheet P transported by the transport roller pair  72  to the nip portion of the first output roller pair  80 ; second guide surfaces  74 Ab that guide the paper sheet P transported by the transport roller pair  72  to the nip portion of the transport roller pair  73 ; and third guide surfaces  74 Ac that are integrally connected to the corresponding first guide surfaces  74 Aa so as to extend toward the front side (toward the first output roller pair  80 ). 
         [0053]    Shaft-receiving portions  74 Ad are formed integrally with the switching gate  74 A at the end of the switching gate  74 A near the third guide surfaces  74 Ac, and are in contact with and supported by a shaft  81   a  of drive rollers  81  included in the first output roller pair  80 . 
         [0054]    The switching gate  74 A includes shaft portions  74 Ae, through which holes having a D-cut surface extend, and is supported so as to be movable in the axial direction of the support shaft  75 A by being guided by a D-cut surface  75 Aa formed on a portion of the support shaft  75 A (see the arrows in  FIG. 8 ). The shape is not limited to the D-cut shape as long as the switching gate is capable of moving in the axial direction while being rotated by the shaft. 
         [0055]    The third guide surfaces  74 Ac of the switching gate  74 A are elastically deformable. There is no particular limitation regarding the material of the switching gate  74 A. The switching gate  74 A is formed integrally with the shaft portions  74 Ae by using a resin material containing a rubber component, an elastomer, or the like. 
         [0056]    In the sheet transport device  70 A having the above-described structure, the sheet transport path from the transport roller pair  72  to the first output roller pair  80  is defined by the switching gate  74 A. The trailing end of the paper sheet P corrugated by the corrugation unit is guided while being pressed against the third guide surfaces  74   c,  which are connected to the first guide surfaces  74   a,  until the trailing end of the paper sheet P reaches the nip portion of the first output roller pair  80 . 
         [0057]    As a result, the sheet transport path that is curved between the first guide surfaces  74 Aa of the switching gate  74 A and the nip portion of the first output roller pair  80  does not have a step portion that is stepped toward the curved side, and the large impact noise caused by flapping of the paper sheet P that is stiff is suppressed. 
         [0058]    In addition, in the present exemplary embodiment, a moving portion (not shown) that moves the first output roller pair  80  in a direction that crosses the transporting direction of the paper sheet P (direction substantially perpendicular to the transporting direction of the paper sheet) is provided. By moving the first output roller pair  80  with the moving unit, an offset operation for outputting the paper sheet P at positions shifted from each other in the direction that crosses the sheet transporting direction may be performed. 
         [0059]    Referring to  FIG. 9 , when the offset operation is performed, the first output roller pair  80  is moved in the direction that crosses the transporting direction of the paper sheet P (see the arrows R1 in  FIG. 9 ). 
         [0060]    The shaft-receiving portions  74 Ad are supported by the shaft  81   a  of drive rollers  81  included in the first output roller pair  80  while being in contact with the shaft  81   a.  Therefore, even when the first output roller pair  80  is moved, the state in which the sheet transport path from the transport roller pair  72  to the first output roller pair  80  is defined by the switching gate  74 A is maintained. 
         [0061]    When the first output roller pair  80  is further moved in the direction that crosses the transporting direction of the paper sheet P and the drive rollers  81  come into contact with the shaft-receiving portions  74 Ad of the switching gate  74 A, the third guide surfaces  74 Ac of the switching gate  74 A are elastically deformed. Since the switching gate  74 A is supported so as to be movable in the axial direction of the support shaft  75 A, the switching gate  74 A moves in the same direction as the direction in which the first output roller pair  80  is moved (see the arrows R2 in  FIG. 9 ). 
         [0062]    As a result, the state in which the sheet transport path from the transport roller pair  72  to the first output roller pair  80  is defined by the switching gate  74 A is maintained, and the large impact noise generated when the stiff paper sheet P is transported is suppressed. 
         [0063]    The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.