Patent Publication Number: US-11661299-B2

Title: Conveyance guide unit

Description:
INCORPORATION BY REFERENCE 
     This application is based upon and claims the benefit of priority from the corresponding Japanese Patent Application No. 2020-090844 filed on May 25, 2020 the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     The present disclosure relates to a conveyance guide unit that guides sheets from an image forming apparatus to a post-processing device. 
     There is known a post-processing device that performs post-processing on sheets discharged from an image forming apparatus, such as punching, stapling, and folding. Such a post-processing device is provided with a cabinet that contains a post-processing mechanism that executes post-processing. 
     The cabinet has a sheet carrying-in port; the sheet carrying-in port communicates with a sheet discharge port of an image forming apparatus by way of a relay conveyance device. The relay conveyance device is installed in an internal paper discharge space of the image forming apparatus. The post-processing device supplies, one by one, printed sheets coming through the sheet carrying-in port of the cabinet to the post-processing mechanism. 
     The post-processing mechanism executes post-processing on the sheets and discharges the finished sheets onto a discharge tray through a sheet discharge port. The sheet discharge port is formed in a side surface of the cabinet, which is opposite to a side surface adjacent to the image forming apparatus. 
     The discharge tray is attached to a position adjacent to a lower end edge of the sheet discharge port. The sheets discharged from the sheet discharge port are accumulated on the discharge tray. The printed sheets discharged from the image forming apparatus can be directly supplied to the post-processing device, not by way of the relay conveyance device. 
     SUMMARY 
     A conveyance guide unit according to one aspect of the present disclosure is disposed in a space between an image forming apparatus that forms images on sheets and a post-processing device that is attached to a side surface of the image forming apparatus in a detachable manner and performs post-processing on the sheets subjected to image forming. The post-processing device has a cabinet, a sheet carrying-in port, a discharge housing part, a discharge tray part, and a sheet discharge port. The cabinet contains a post-processing mechanism. The sheet carrying-in port is formed in a side surface of the cabinet, which is adjacent to the image forming apparatus. The discharge housing part protrudes upward from a top surface of the cabinet and contains a sheet discharge mechanism. The discharge tray part is formed toward the image forming apparatus from the discharge housing part protruding from the top surface of the cabinet. The sheet discharge port is formed in a side surface of the discharge housing part, which is adjacent to the image forming apparatus. The post-processing device is configured to perform post-processing on sheets coming through the sheet carrying-in port by the post-processing mechanism, then discharge the sheets through the sheet discharge port toward the image forming apparatus by the sheet discharge mechanism. The conveyance guide unit is provided with a guide member, a supporting frame, and an external cover. The guide member guides a sheet, which is discharged from the sheet discharge port of the image forming apparatus or a sheet discharge port of the relay conveyance device, to the sheet carrying-in port of the post-processing device. The supporting frame supports the guide member. The external cover is fixed to the supporting frame; the external cover covers an upper part of the guide member and side parts of the guide member in a traverse direction of a sheet conveyance path, which is perpendicular to a sheet conveyance direction. The external cover has an upper surface serving as an extension part of the discharge tray part of the post-processing device, which is extended downstream, in a sheet discharge direction. 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description with reference where appropriate to the accompanying drawings. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Furthermore, the claimed subject matter is not limited to implementations that solve any or all disadvantages noted in any part of this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    illustrates a schematic configuration of an image forming system including a conveyance guide unit according to an embodiment, an image forming apparatus, and a post-processing device. 
         FIG.  2    is a perspective view of an exterior of the image forming system. 
         FIG.  3    is an enlarged perspective view of a front region of a main body of the image forming apparatus. 
         FIG.  4    is a perspective view of an exterior of the post-processing device and the conveyance guide unit including a coupling mechanism attached to the post-processing device. 
         FIG.  5    is a perspective view of an exterior of the post-processing device and the coupling mechanism attached to the post-processing device. 
         FIG.  6    is a perspective view of an exterior of the coupling mechanism attached to the post-processing device. 
         FIG.  7    is a perspective view of a left-side surface of the main body of the image forming apparatus. 
         FIG.  8    is an enlarged perspective view of the periphery of a coupled member, located on the left-side surface of the main body of the image forming apparatus. 
         FIG.  9    is a horizontal sectional view of the coupling member and the coupled member of the coupling mechanism in a state of being engaged with each other. 
         FIG.  10    is a perspective view of an exterior of an external cover of the conveyance guide unit. 
         FIG.  11    is a side view of a cover member when viewed from a back side of a front-back direction. 
         FIG.  12    is a side view of the cover member when viewed from a front side of the front-back direction. 
         FIG.  13    is a perspective view of an exterior of the cover member. 
         FIG.  14    is an enlarged perspective view of a first end part of the cover member in an extension direction of the cover member. 
         FIG.  15    is a perspective view of the cover member when viewed in a direction XV indicated in  FIG.  13   . 
         FIG.  16    is an enlarged perspective view of a first fitting portion at the first end part of one of the two cover members and a second fitting portion at a second end part of the other one of the two cover members, when viewed from the front side of the front-back direction. 
         FIG.  17    is an enlarged perspective view of the first fitting portion at the first end part of one of the two cover members and the second fitting portion at the second end part of the other one of the two cover members. 
         FIG.  18    is a plan view of the two cover members coupled in line with each other with the first and second fitting portion being in a linear fitting state, when viewed from the front side of the front-back direction. 
         FIG.  19    is a perspective view of the first coupling and second fitting portion coupled with each other as illustrated in  FIG.  18   , when viewed from the back side of the front-back direction. 
         FIG.  20    is an enlarged section view of an upper half part of the external cover of the conveyance guide unit when cut widthwise in the middle. 
         FIG.  21    is an enlarged view of an upper-front corner of the external cover of  FIG.  20   . 
         FIG.  22    is an enlarged perspective view of a first fixing position of the external cover of the conveyance guide unit. 
         FIG.  23    is an enlarged perspective view of a second fixing position of the external cover the conveyance guide unit. 
         FIG.  24    is an enlarged perspective view of a third fixing position of the external cover of the conveyance guide unit. 
         FIG.  25    is an enlarged plan view of a discharge tray part of the post-processing device and an upper end part of the external cover of the conveyance guide unit wen viewed from the front side. 
         FIG.  26    is an enlarged plan view of upper end parts of the post-processing device, the image forming apparatus, and the external cover of the conveyance guide unit along with a reclosable cover of an automatic document feeder being opened, when viewed from the front side. 
         FIG.  27    is an enlarged plan view of front end parts of the post-processing device, the image forming apparatus, and the external cover of the conveyance guide unit. 
         FIG.  28    is a perspective view of the post-processing device and the image forming apparatus when viewed from the left back side. 
         FIG.  29    is an enlarged plan view of back end parts of the post-processing device, the image forming apparatus, and the external cover of the conveyance guide unit. 
         FIG.  30    is an enlarged plan view of the discharge tray part of the post-processing device and an upper end part of the image forming apparatus in a comparison example when viewed from the front side. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, one or more embodiments of the present disclosure will be described in detail with reference to the drawings. The present disclosure should not be limited to any embodiment described below. 
     Embodiment 
       FIG.  1    illustrated an image forming system M including: a conveyance guide unit  900  according to the present embodiment; an image forming apparatus  1 ; and a post-processing device  400  attached to the image forming apparatus by the conveyance guide unit  900 . 
     Hereinafter, “front” and “back” means the front and back of the image forming apparatus  1 , and “right” and “left” means the right and left of the image forming apparatus  1 , unless otherwise noted. 
     [Configuration of the Image Forming Apparatus  1 ] 
     The image forming apparatus  1  is a copier that is configured to internally discharge paper. The image forming apparatus  1  is provided with a main body  100 , a scanner housing portion  200 , and a coupling housing portion  150 . 
     The scanner housing portion  200  is located above the main body  100 . The scanner housing portion  200  is coupled with the main body  100  by the coupling housing portion  150 . 
     An internal paper discharge space E is provided between the main body  100  and the scanner housing portion  200 . The coupling housing portion  150  is provided with a back side fitting part (not shown) and a right side fitting part  150   a . The back side fitting part is attached to a back end part of the main body  100 . The right side fitting part  150   a  is attached to a right end part of the main body  100 . 
     The right side fitting part  150   a  is provided with a vertical wall  155  that faces the internal paper discharge space E (see  FIG.  1   ). The vertical wall  155  has an upper discharge port  151  and a lower discharge port  152  that are vertically arranged. 
     In the internal paper discharge space E, a relay conveyance device  300  is installed in a detachable manner. After a sheet S is subjected to image forming and discharged from the lower discharge port  152 , the relay conveyance device  300  delivers the sheet S to the post-processing device  400 . 
     A contact glass plate  200   a  is provided on the top of the scanner housing portion  200 . An upper surface of the contact glass plate  200   a  is closed by a document cover  202  such that it can be opened and closed. 
     An automatic document feeding device  30  is integrally attached to the top of the document cover  202 . A reading unit  201  is loaded inside the scanner housing portion  200 . 
     The reading unit  201  optically reads an image on a document sheet G by a flatbed scanning method or a sheetfed scanning method to be described later. The reading unit  201  is provided with a CIS sensor that reads a document image by a photoelectric conversion; the reading unit  201  is configured to slide in a right-left direction. 
     The automatic document feeding device  30  is supported by a back end part of the scanner housing portion  200  with a pair of hinge mechanisms such that it can be turned. In the sheetfed scanning method, the automatic document feeding device  30  delivers the document sheet G to a document reading position R of an upper surface of the contact glass plate  200   a.    
     Specifically, the automatic document feeding device  30  is provided with a document feed tray  31 , a document output tray  32 , a document conveyance path  33 , multiple pairs of conveying rollers  34 , and a casing  35 . 
     The document output tray  32  is provided below the paper feed tray  31 . The document conveyance path  33  is U-shaped, extending from the document feed tray  31  to the document output tray  32 . The multiple pairs of the conveying rollers  34  are arranged along the document conveyance path  33 . The multiple pairs of the conveying rollers  34  constitute an example of a paper conveyance mechanism that conveys the document sheet G through the document conveyance path  33 . The casing  35  contains the multiple pairs of the conveying rollers  34 . 
     The casing  35  has an opening part  35   b  for removing jammed paper; the opening part  35   b  extends from a top wall surface  35   c  of the casing  35  to a side wall surface  35   d  of the casing  35 , which is adjacent to the post-processing device  400  (see  FIGS.  2  and  26   ). The opening part  35   b  is closed by a reclosable cover  35   a  such that it can be opened and closed. 
     The reclosable cover  35   a  is supported by the casing  35 . An end edge part  35   e  of the reclosable cover  35   a , which is adjacent to the post-processing device  400 , is supported such that the reclosable cover  35   a  can be turned about an axis  36  extending in a front-back direction (see  FIG.  26    to be described later). 
     The reclosable cover  35   a  is configured to turn about the axis  36 , moving between a closed position at which the opening part  35   b  is closed and a wide-open position at a predetermined angle upward from the close position. 
     In the sheetfed scanning method, the automatic document feeding device  30  sends document sheets G set on the document feed tray  31  downstream one by one, with the multiple pairs of the conveying rollers  34 . Subsequently, the automatic document feeding device  30  conveys the document sheet G to the document output tray  32  through the document reading position R. In the sheetfed scanning method, the reading unit  201  is disposed immediately below the document reading position R and reads an image on the document sheet G passing through the document reading position R. 
     In contrast, in the flatbed scanning method, the document cover  202  is turned up from a closed position with respect to the hinge mechanisms in a back end part of the document cover  202 , prior to image reading. After the document sheet G is set on the upper surface of the contact glass plate  200   a , the document cover  202  is returned to the closed position such that the document sheet G is kept in place on the upper surface of the contact glass plate  200   a . In this state, the reading unit  201  performs photoelectric conversion of a reflection from the document sheet G by the ICS sensor provided in the reading unit  201  while sliding in a right-left direction, and thereby generates document image data. 
     [Configuration of the Main Body  100  of the Image Forming Apparatus  1 ] 
     The main body  100  is shaped in an approximately rectangular prism. Casters  102  for moving are attached to a bottom of the main body  100 . An image forming portion  20  is provided in the main body  100 . In the main body  100 , a fixing portion  40  is provided above the image forming portion  20 ; two paper feed portions  10  are vertically arranged and disposed below and diagonally left to the image forming portion  20 . 
     Each paper feed portion  10  is provided with: a paper cassette  10   a  that loads sheets S inside; and paper pickup rollers  10   b . The paper pickup rollers  10   b  pick up the sheet S from the paper cassettes  10   a  and send it out. Being sent out from the paper cassette  10   a , the sheet S is supplied to the image forming portion  20  by a pair of conveying rollers  11 . 
     Furthermore, in the main body  100 , large-capacity paper cassettes  15  are disposed side by side below the two paper feed portions  10 . The sheet S loaded in the large-capacity paper cassettes  15  is picked up by paper pickup rollers (not shown) and sent out toward the image forming portion  20 . 
     The image forming portion  20  is provided with a photoconductor drum  21 , a charging device  23 , an exposure device  25 , a developing device  27 , and a transfer device  29 . 
     In the image forming portion  20 , the charging device  23  charges a peripheral surface of the photoconductor drum  21 , then the exposure device  25  forms an electrostatic image on the surface of the photoconductor drum  21  by emitting a laser light with reference to the document image data. The document image data is image data generated by the reading unit  201  from a document image. 
     The developing device  27  forms a toner image on the surface of the photoconductor drum  21  by developing the electrostatic image. The transfer device  29  transfers the toner image onto the sheet S supplied from the paper feed portion  10 , then supplies the sheet S carrying the toner image to the fixing portion  40 . The code  24  indicates a cleaner that removes toner remaining on the surface of the photoconductor drum  21 . 
     The fixing portion  40  applies pressure and heat to the sheet S supplied from the image forming portion  20  while the sheet S passes through an interface between a fixing roller  40   a  and a pressure roller  40   b . The fixing portion  40  thereby fixes the toner image onto the sheet S. Having the toner image fixed hereon by the fixing portion  40 , the sheet S is conveyed upward by the fixing roller  40   a  and the pressure roller  40   b.    
     The sheet S passes through a conveyance path that branches at a position above the fixing portion  40  into a first conveyance path T 1  and a second conveyance path T 2 . Being conveyed by the fixing roller  40   a  and the pressure roller  40   b , the sheet S passes through the first conveyance path T 1  or the second conveyance path T 2 . 
     The first conveyance path T 1  has a bend immediately above the fixing portion  40  and continues leftward to the lower discharge port  152 . A pair of first discharge rollers  12  is disposed immediately upstream of the lower discharge port  152 . The pair of the first discharge rollers  12  constitutes an example of a discharge mechanism. 
     The second conveyance path T 2  has a bend above the fixing portion  40  and continues leftward to the upper discharge port  151 . A pair of second discharge rollers  13  is disposed immediately upstream of the upper discharge port  151 . The second conveyance path T 2  further continues to a duplex-printing conveyance path T 3 . The duplex-printing conveyance path T 3  is a conveyance path for duplex printing, through which the sheet S is turned upside down and resupplied to the image forming portion  20 . 
     In a state not shown in the drawings, in which the relay conveyance device  300  is not installed in the internal paper discharge space E, the sheet S is discharged onto a sheet tray  101  from the lower discharge port  152 . The upper discharge port  151  is used essentially for turning the sheet S upside down. 
     In contrast, in the state shown in  FIG.  1   , in which the relay conveyance device  300  is installed in the internal paper discharge space E, the sheet S is discharged onto a relay conveyance path T 4  in the relay conveyance device  300  from the lower discharge port  152 . 
     The relay conveyance device  300  is disposed on the sheet tray  101 , which defines the bottom of the internal paper discharge space E. The relay conveyance device  300  is provided with a body case  303  formed in an approximately rectangular prism. 
     The body case  303  has a sheet carrying-in port  301  on a right wall of the body case  303  itself; the sheet carrying-in port  301  communicates with the upper discharge port  151 . The body case  303  has a sheet discharge port  302  on a left wall of the body case  303  itself; the sheet discharge port  302  communicates with a sheet carrying-in port  401   c  of the post-processing device  400 . The relay conveyance path T 4  is provided in the relay conveyance device  300 . 
     The relay conveyance path T 4  extends from the sheet carrying-in port  301  to the sheet discharge port  302  in an approximately horizontal direction. Four pairs of conveying rollers  304  are arranged along the relay conveyance path T 4 . A paper discharge tray part  305  is formed on the top of the relay conveyance device  300 ; the paper discharge tray part  305  receives the sheet S from the upper discharge port  151 . 
     [Configuration of the Front Region of the Main Body  100  of the Image Forming Apparatus  1 ] 
     Referring to  FIGS.  2  and  3   , the two paper cassettes  10   a  and the two large-capacity paper cassettes  15  are disposed in a lower region of the main body  100  such that they can be pulled open frontward. A front cover  103  is provided to cover a part of a front region of the main body  100  located higher than the two paper cassettes  10 . 
     The front cover  103  is shaped in a rectangle that is horizontally long when viewed from the front. The front cover  103  has recessed handle parts  103   a  on a right end part and a left end part of the front cover  103  itself. Only one of the recessed handle portions  103   a  is shown in  FIGS.  2  and  3   . 
     The front cover  103  is attached to the main body  100  in a detachable manner. For maintenance, users can detach the front cover  103  therefrom by pulling the recessed handle parts  103   a  with the fingers frontward. The maintenance includes replacing toner containers (not shown), for example. 
     [Configuration of the Post-Processing Device  400 ] 
     The post-processing device  400  is attached to a left-side surface of the main body  100  in a detachable manner, with a conveyance guide unit  900  to be described later. 
     The post-processing device  400  performs post-processing on the sheet S subjected to image forming. The post-processing is stapling, sorting, and center folding, for example. The sheet S subjected to image forming means a printed sheet. 
     Specifically, the post-processing device  400  is provided with a cabinet  404  that is long in an up-down direction as illustrated in  FIG.  1   . Casters  402  for moving are attached to a bottom of the cabinet  401 . A post-processing mechanism  403  is provided inside and in a lower region of the cabinet  401 . 
     The cabinet  401  has the sheet carrying-in port  401   c  on a right-side surface of the cabinet  401  itself; the sheet carrying-in port  401   c  receives the sheet S having been printed from the image forming apparatus  1 . The cabinet  401  has a discharge housing part  401   a  in a left end part of an upper region of the cabinet  401  itself; the discharge housing part  401   a  is shaped in a rectangular prism protruding upward. 
     The discharge housing part  401   a  has a first discharge port  401   d  on a right-side surface of the discharge housing part  401   a  itself. A part of a top region of the cabinet  401 , adjacent to the right of the discharge housing part  401   a  is formed as a discharge tray part  401   b  on which the sheet S is stacked. 
     The cabinet  401  has a second discharge port  401   e  on a left-side surface of the cabinet  401  itself; the second discharge port  401   e  is disposed on an opposite side surface of the cabinet  401  to the sheet carrying-in port  401   c . A lead-in conveyance path H 0 , a first discharge conveyance path H 1 , and a second discharge conveyance path H 2  are provided in the cabinet  401 . 
     The lead-in conveyance path H 0  is a conveyance path extending from the sheet carrying-in port  401   c  to the post-processing mechanism  403 . The first discharge conveyance path H 1  is a conveyance path stretching from the post-processing mechanism  403  to the first discharge port  401   d . The second discharge conveyance path H 2  is a conveyance path stretching from the post-processing mechanism  403  to the second discharge port  401   e . Multiple pairs of rollers are arranged along the conveyance paths H 0 , H 1 , and H 2 . 
     Referring to  FIG.  1   , a pair of lead-in rollers  406 , a pair of first discharge rollers  407  (as an example of a discharge mechanism), and a pair of second discharge rollers  408  are arranged along the conveyance paths H 0 , H 1 , and H 2 , respectively. The other pairs of rollers are omitted from the drawing. 
     The pair of the lead-in rollers  406  is disposed adjacent to the sheet carrying-in port  401   c . The pair of the first discharge rollers  407  is disposed adjacent to the first discharge port  401   d . The pair of the second discharge rollers  408  is disposed adjacent to the second discharge port  401   e.    
     The pair of the first discharge rollers  407  is disposed in the discharge housing part  401   a , discharging the sheet S from the first discharge port  401   d  in a direction X 1  indicated in  FIG.  1   . The direction X 1  is a direction in which the post-processing device  400  and the image forming apparatus  1  face each other, and is the direction from the post-processing device  400  toward the image forming apparatus  1 . 
     The conveyance path of the sheet S subjected to post-processing by the post-processing mechanism  403  is controlled by a controller of the post-processing device  400 . Specifically, the controller switches the position of a conveyance path switch (not shown) provided in the cabinet  401  according to a command from the image forming apparatus  1 . The controller thereby switches the conveyance path of the sheet S subjected to post-processing between the first discharge conveyance path H 1  and the second discharge conveyance path H 2 . 
     The first discharge conveyance path H 1  serves to convey the sheet S subjected to post-processing from the first discharge port  401   d  to the discharge tray part  401   b . The second discharge conveyance path H 2  serves to convey the sheet S subjected to post-processing to another post-processing device (not shown) to be provided to the left of the cabinet  401 . Alternatively, the second discharge conveyance path H 2  serves to convey the sheet S to another discharge tray that is to be provided below the second discharge port  401   e  when the sheet S is a large sheet of paper relatively long in a conveyance direction. 
     [Configuration of the Conveyance Guide Unit  900 ] 
     The conveyance guide unit  900  (see  FIG.  1   ) is a unit that guides the sheet S, which is discharged from the sheet discharge port  302  of the relay conveyance device  300  installed in the image forming apparatus  1 , to the sheet carrying-in port  401   c  of the post-processing device  400 . The conveyance guide unit  900  ensures that the sheet S be delivered from the relay conveyance device  300  to the post-processing device  400  even when the sheet discharge port  302  of the relay conveyance device  300  and the sheet carrying-in port  401   c  of the post-processing device  400  are different in height. In the present example, the conveyance guide unit  900  is unified into a coupling mechanism  500  to be described later, by which the post-processing device  400  is attached to the main body  100 . 
     Referring to  FIGS.  1  and  5   , the conveyance guide unit  900  is provided with a pair of lead-in guide plates  515  and an external cover U. Each lead-in guide plate  515  constitutes a guide member. The lead-in guide plates  515  are spaced in an up-down direction to allow a space between themselves; the space serves as a part of a sheet conveyance path. Each lead-in guide plate  515  is shaped in a rectangular extending in a front-back direction when viewed in plan. The front-back direction is a traverse direction of the sheet conveyance path, which is perpendicular to a sheet conveyance direction. The lead-in guide plates  515  have upstream end parts that are disposed one above the other and face in-between space becoming wider toward the sheet discharge port  302  of the relay conveyance device  300 . A front end part and a back end part of the lead-in guide plate  515   s  are respectively supported by a front vertical frame  512  and a back vertical frame  513 . The front vertical frame  512  and the back vertical frame  513  constitute the supporting frame. The front vertical frame  512  and the back vertical frame  513  are fixed to the post-processing device  400  with screws. 
     Referring to  FIG.  10   , the external cover U is provided with: an upper portion u 1  that extends in a front-back direction and covers an upper part of the pair of the lead-in guide plates  515 ; a front portion u 2  that extends in an up-down direction and covers a front part of the pair of the lead-in guide plates  515 ; and a back portion u 3  that extends in an up-down direction and covers a back part of the pair of the lead-in guide plates  515 . The external cover U serves as an external cover to cover the coupling mechanism  500  to be described later as well as the lead-in guide plates  515 . 
     [Configuration of the Coupling Mechanism  500 ] 
     Hereinafter, a configuration of the coupling mechanism  500  will be described with reference to  FIGS.  4  to  9   . The coupling mechanism  500  is provided with: a recessed attachment member  510  disposed on a right-side surface of the post-processing device  400 ; and a protruding attachment member  520  disposed on the left-side surface of the main body  100  (see  FIG.  7   ). 
     Referring to  FIG.  4   , the recessed attachment member  510  is extended to the right of the external cover U and can be engaged with the protruding attachment member  520  of the image forming apparatus  1 . 
     Referring to  FIGS.  5  and  6   , the recessed attachment member  510  is supported by an upper end part of a rectangular vertical plate  511  that is vertically fixed, such that the recessed attachment member  510  can slide in a front-back direction. 
     A front end part and a back end part of the vertical plate portion  511  are respectively fixed to the front vertical frame  512  and the back vertical frame  513  that both extend in an up-down direction. The front vertical frame  512  and the back vertical frame  513  are fixed to a right-side surface of the cabinet  401  of the post-processing device  400  with screws, for example. 
     An upper part of the front vertical frame  512  and an upper part of the back vertical frame  513  are coupled with each other by a stay  514  and the lead-in guide plates  515 . 
     The vertical plate  511  has a positioning hole  511   a  in the upper part of the vertical plate  511  itself (see  FIG.  6   ); the positioning hole  511   a  is drilled across a thickness direction of the vertical plate  511 . The positioning hole  511   a  is to be engaged with a positioning pin  522  that protrudes from the protruding attachment member  520  of the image forming apparatus  1 . Thickness directions of the vertical plate  511  are right-left directions indicated in  FIG.  6   . 
     The recessed attachment member  510  is a sheet metal shaped by bending and extends in a front-back direction. The recessed attachment member  510  has a U-shaped fitting sliding part  510   a  that fits in the upper part of the vertical plate  511  in a slidable manner. 
     A pair of rectangular aperture parts  510   b  and a pair of long holes  510   e  are formed in a plate part of the recessed attachment member  510 , which faces the right-side surface of the vertical plate  511 . The rectangular aperture parts  510   b  are arranged separately in a front-back direction. Each long hole  510   e  is disposed to the front of each rectangular aperture part  510   b.    
     The long hole  510   e  is constituted by a slit-like hole extending in a front-back direction. The recessed attachment member  510  is fixed to the vertical plate  511  with screws  518  extending through the long holes  510   e , such that the recessed attachment member  510  can slide in a front-back direction. A protruding plate part  510   d  protrudes to the right from an upper end edge of the rectangular aperture part  510   b . Furthermore, a latching part  510   c  protrudes to the right from a front end edge of the rectangular aperture part  510   b.    
     Referring to  FIGS.  7  and  8   , the protruding attachment member  520  is a sheet metal shaped by bending and extends in a front-back direction. The protruding attachment member  520  is fixed to a left-side surface of the main body  100  with two screws  521  that are arranged separately on a diagonal line of the protruding attachment member  520 . 
     A pair of protruding plate portions  520   a  protrudes from the left-side surface of the main body  100  to the left; the protruding plate portion  520   a  is shaped by bending. Each protruding plate portion  520   a  has a slit-like groove part  520   b  that extends in a front-back direction and is open to the front. 
       FIG.  9    is a horizontal sectional view of the recessed attachment member  510  fixed to the post-processing device  400  and the protruding attachment member  520  fixed to the main body  100 , being engaged with each other. To attach the post-processing device  400  to the main body  100 , the pair of the protruding plate portions  520   a  of the protruding attachment member  520  is inserted through the pair of the rectangular apertures part  510   b  of the recessed attachment member  510  in a direction indicated by an arrow C of  FIG.  6   . The pair of the protruding plate portions  520   a  is inserted through the pair of the rectangular aperture parts  510   b  of the recessed attachment member  510  when the recessed attachment member  510  is at a detached position. The recessed attachment member  510  is then slid to the tack until a predetermined attached position. 
     In this state, the latching part  510   c  of the recessed attachment member  510  is engaged with the groove part  520   b  of the protruding plate portion  520   a  of the protruding attachment member  520 . The latching part  510   c  is formed at the front end edge of the rectangular aperture part  510   b  of the recessed attachment member  510 . When the recessed attachment member  510  is slid back to the front until the detached position, the latching part  510   c  is released from the slit-like groove part  520   b , and thereby the recessed attachment member  510  and the protruding attachment member  520  are disengaged from each other. 
     When the recessed attachment member  510  is slid again to the back until the attached position, the recessed attachment member  510  and the protruding attachment member  520  are again engaged with each other. Users can slide the recessed attachment member  510  manually. 
     Furthermore, after the recessed attachment member  510  and the protruding attachment member  520  are engaged with each other, a U-shaped frame portion  512   a  of the front vertical frame  512  is slid from the front and engaged with a latching part  510   f  of the recessed attachment member  510 , and then fixed thereto with a screw  517  (see  FIG.  6   ). This will prevent the recessed attachment member  510  from being accidentally moved to the front and detached from the protruding attachment member  520 . 
     [Configuration of the Front Vertical Frame  512  and the Back Vertical Frame  513 ] 
     Referring to  FIG.  6   , the front vertical frame  512  is provided with the U-shaped frame portion  512   a  and a flat frame portion  512   b . The U-shaped frame portion  512   a  is shaped in a U-shape that is open to the left. The flat frame portion  512   b  extends in an up-down direction and is coupled with a back end edge of the U-shaped frame portion  512   a.    
     The flat frame portion  512   b  has a rectangular plate part  512   c  that is formed in the upper end part and is long in a right-left direction. The rectangular plate part  512   c  has a tapped hole  512   d  that is drilled across a thickness direction of the rectangular plate part  512 . The tapped hole  512   d  is used for fixing the external cover U as to be described later. 
     The back vertical frame  513  is flat, facing to the flat frame portion  512   b  of the front vertical frame  512 . Referring to  FIG.  5   , the back vertical frame  513  has a bent plate part  513   d  that is formed in the upper end part and horizontally extends to the front. The bent plate part  513   d  has a tapped hole  513   e  that is drilled through the bent plate part  513   d  in an up-down direction. 
     The tapped hole  513   e  is used for fixing the external cover U as to be described later. The back vertical frame  513  has a horizontal plate part  513   a  and a vertical plate part  513   b  that are formed in the lower end part. The horizontal plate part  513   a  extends to the front horizontally, and the vertical plate part  513   b  extends from a front end edge of the horizontal plate part  513   a . The vertical plate part  513   b  has a tapped hole  513   c  that is drilled across a thickness direction of the vertical plate part  513   b . The tapped hole  513   c  is used for fixing the external cover U as to be described later. 
     [Detailed Configuration of the External Cover U] 
     Hereinafter, a configuration of the external cover U will be described with reference to  FIGS.  10  to  21   . The external cover U is composed of a combination of the identically shaped cover members  600 . In the present embodiment, the external cover U includes four cover members  600 . 
     For a better understanding of the combined structure of the cover members  600 , in these drawings, a character “A” is given to a first end part of the cover member  600 , and a character “B” is given to a second end part of the cover member  600 . 
     The external cover U includes an upper portion u 1 , a front portion u 2 , and a back portion u 3 . The upper portion u 1  horizontally extends in a front-back direction of the image forming apparatus  1  and is disposed such that it covers an upper part of the coupling mechanism  500  including the lead-in guide plates  515 . The front portion u 2  extends downward from a front end part of the upper portion u 1  and is disposed such that it covers a front part of the coupling mechanism  500  including the lead-in guide plates  515 . 
     The back portion u 3  extends downward from a back end part of the upper portion u 1  and is disposed such that it covers a back part of the coupling mechanism  500  including the lead-in guide plates  515 . It is less necessary to cover the back part of the coupling mechanism  500  because it is in a blind spot for users standing to the front of the image forming apparatus  1 . So, the back portion u 3  of the external cover U includes only one cover member  600 . The back portion u 3  is shorter in length than the front portion u 2  which is constituted by the two cover members  600  arranged in series. 
     Referring to  FIGS.  11  and  12   , the cover member  600  is a resin member that extends in an up-down direction of  FIGS.  11  and  12   . The cover member  600  is a molding produced by injection molding. The cover member  600  should not be limited to a resin member; the cover member  600  may be a metallic member. The cover member  600  should not be limited to a molded member; the cover member  600  may be a sheet metal member subjected to bending or pressing. 
     The cover member  600  has a long wall  601  that extends in a predetermined direction of the cover member  600 . Referring to  FIGS.  12  and  13   , the long wall  601  has an outer surface  601   a ; the outer surface  601   a  has a rectangular flat part  601   b  and an inclined surface  601   c  that extends smoothly from a traverse end edge of the flat part  601   b . The outer surface  601   a  of the long wall  601  is a designed surface. 
     The long wall  601  has a flat side wall  602  that extends from an end edge of the long wall  601  to the back of the cover member  600  (see  FIG.  11   ). The side wall  602  has an approximately rectangular cutout part  602   a  at an intermediate position of the side wall  602  in an extension direction thereof (see  FIG.  10   ). The long wall  601  and the side wall  602  are coupled with multiple inner ribs  606  that are arranged at intervals in an extension direction of the cover member  600  (see  FIG.  11   ). 
     The cover member  600  has a first fitting portion K 1  at the first end and a second fitting portion K 2  at the second end in an extension direction of the cover member  600  itself. Any two of the cover members  600  can be coupled with each other by the first fitting portion K 1  of one of the two cover members  600  and the second fitting portion K 2  of the other one of the two cover members  600 , being coupled with each other. 
     In the present embodiment, any two of the cover members  600  are configured such that the first fitting portion K 1  of one of the two cover members  600  and the second fitting portion K 2  of the other one of the cover members  600  can be re-coupled to be in a linear fitting state or a right-angle fitting state selectively. In the linear fitting state, the two cover members  600  are coupled to form a line so that their extension directions are the same (see  FIG.  18    to be described later). In the right-angle fitting state, the two cover members  600  are coupled to form an L-shape so that their extension directions are perpendicular to each other (see  FIG.  21    to be described later). 
     As described above, any two of the cover members  600  are configured to be re-coupled to be in the linear fitting state or the right-angle fitting state. The external cover U thereby can be flexibly reshaped, not only into the shape illustrated in  FIG.  10   . 
     [Configuration of the First Fitting Portion K 1 ] 
     A configuration of the first fitting portion K 1  will be described with reference to  FIGS.  11  to  15   . The first fitting portion K 1  has a recessed part  604  that is recessed from the outer surface  601   a  to the back of the cover member  600 . The recessed part  604  is open to an extension direction of the cover member  600  and is open to a traverse direction of the cover member  600  without being closed by the side wall  602 . Referring to  FIG.  12   , the recessed part  604  is open to the top and to the right. 
     The recessed part  604  is shaped by a base surface  604   a  and a side surface  604   b . The base surface  604   a  is a flat surface that is perpendicular to a front-back direction of the cover member  600 . The front-back direction of the cover member  600  is perpendicular to the surface of the sheet of  FIG.  12   . The side surface  604   b  rises from an end edge of the base surface  604   a  in an extension direction of the cover member  600 . A surface opposite to the base surface  604   a  has a U-shaped wall  605  that rises from a peripheral part of the base surface  604   a  and is continued to the side wall  602  (see  FIG.  11    and other drawings). 
     The base surface  604   a  has positioning holes  604   c  and  604   d  that are arranged in a traverse direction of the cover member  600 . The base surface  604   a  further has a through hole  604   e  between the positioning holes  604   c  and  604   d . The base surface  604   a  still further has a rectangular idle hole  604   f  that is long in a traverse direction of the cover member  600 . The idle hole  604   f  is located toward the first end part of the cover member  600  in the extension direction from the positioning holes  604   c  and  604   d.    
     Referring to  FIGS.  14  and  15   , the side surface  604   b  has a flat surface  604   j  and an inclined surface  604   k . The flat surface  604   j  extends in a traverse direction of the cover member  600 . The inclined surface  604   k  extends smoothly from a traverse end edge of the flat surface  604   j  at a predetermined angle. The side surface  604   b  is formed in an approximate shape of the letter J when viewed from the front of the cover member  600 . The side surface  604   b  serves as a shaped-to-fit part. 
     Referring to  FIG.  15   , the side surface  604   b  of the recessed part  604  has a rectangular latching hole  604   g  that is long in a traverse direction of the cover member  600  and further has positioning holes  604   h  and  604   i . The positioning holes  604   h  and  604   i  are located toward the front of the front-back direction of the cover member  600  from the latching hole  604   g.    
     [Configuration of the Second Fitting Portion K 2 ] 
     Hereinafter, a configuration of the second fitting portion K 2  will be described with reference to  FIGS.  11  to  13 ,  16  and  17   . 
     Referring to  FIG.  11   , the second fitting portion K 2  has an end wall  603  and a rectangular base plate  610  (also see  FIG.  21    to be described later). The end wall  603  extends from an end edge of the long wall  601  in an extension direction of the cover member  600  to the back of the long wall  601 . The base plate  610  extends along an internal surface of a protruding part of the end wall  603  and an internal surface of the side wall  602 . A surface of the base plate  610 , which is to the back of the cover member  600 , constitutes a contact surface  610   a  to be in contact with the base plate  604   a  when the cover members  600  are coupled in line. To the back of the cover member  600  means to the front of the surface of the sheet of  FIG.  11   . 
     The base plate  610  has positioning projections  611  and  612  arranged in a traverse direction of the cover member  600 . The positioning projections  611  and  612  are both cylindrically shaped. The base plate  610  further has a tapped hole  613  between the positioning projections  611  and  612 . 
     The base plate  610  still further has a latching hook  614  that protrudes from the contact surface  610   a  to the back of the cover member  600 . In  FIG.  11   , the latching hook  614  protrudes toward the surface of the sheet of  FIG.  11   . The latching hook  614  is located toward the first end part (the middle) of the cover member  600  in an extension direction of the cover member  600  from the tapped hole  613 . The latching hook  614  is constituted by a flexible extended plate that faces in an extension direction of the cover member  600  and has a hook part at an outermost end of the extended plate itself. The extension direction of the cover member  600  is an up-down direction of  FIG.  11   . 
     Referring to  FIGS.  12 ,  13 ,  16 , and  17   , the end wall  603  has a flat surface  603   b  that extends in a traverse direction of the cover member  600  and an inclined surface  603   c  continued from the flat surface  603   b . The inclined surface  603   c  extends smoothly from a traverse end edge of the flat surface  603   b  at a predetermined angle. The end surface  603  serves as a shaped-to-be-fitted part in which the side surface  604   b  of the recessed part  604  of the first fitting portion K 1  can fit. The end surface  603  is a shaped-to-fit part to fit in the side surface  604   b  of the recessed part  604 . 
     [Description of the Linear Fitting State] 
       FIGS.  16  and  17    show any two of the cover members  600 ; the side surface  604   b  of the first fitting portion K 1  of one of the two cover members  600  and the end surface  603  of the second fitting portion K 2  of the other one of the two cover members  600  are fitted to each other. The first fitting portion K 1  and the second fitting portion K 2  are thereby in the linear fitting state. 
     The two cover members  600  are thereby coupled in line with each other as illustrated in  FIG.  18   . In the linear fitting state, the positioning hole  604   c  of the first fitting portion K 1  is engaged with the positioning projection  611  of the second fitting portion K 2 , and the positioning hole  604   d  of the first fitting portion K 1  is engaged with the positioning projection  612  of the second fitting portion K 2  as illustrated in  FIG.  19   . The two cover members  600  are thereby set in place to each other. When they are coupled in place in this manner, a screw  650  is inserted through the through hole  604   e  of the first fitting portion K 1  and tightened into the tapped hole  613  of the second fitting portion K 2  (see  FIG.  11   ). The two cover members  600  are thereby fixed to each other such that they cannot be separated. In the linear fitting state, the latching hook  614  of the second fitting portion K 2 , which is used when they are coupled at a right angle, takes refuge in the idle hole  604   f  of the first fitting portion K 1  with sufficient clearance. 
     [Description of the Right-angle Fitting State] 
     Hereinafter, the right-angle fitting state of the first fitting portion K 1  and the second fitting portion K 2  will be described with reference to  FIGS.  20  and  21   .  FIG.  20    illustrates the external cover U when cut widthwise in the middle. As Shown in the figure, the first fitting portion K 1  and the second fitting portion K 2  in the right-angle fitting state serve at upper-front and upper-back corners of the external cover U, for example. 
       FIG.  21    is an enlarged view of an upper-front corner of the external cover U of  FIG.  20   . As shown in an example of the figure, in the right-angle fitting state, the side surface  604   b  of the first fitting portion K 1  of the cover member  600  extending in an up-down direction is in contact with the contact surface  610   a  of the second fitting portion K 2  of the cover member  600  extending in a right-left direction; and the two cover members  600  are thereby perpendicular to each other. 
     The latching hook  614  of the second fitting portion K 2  is engaged with the latching hole  604   g  of the side surface  604   b  of the first fitting portion K 1 . Specifically, the hook part of the latching hook  604  is engaged with an edge part of the latching hole  604   g , and the two cover members  600  are thereby fixed to each other at a right angle. The latching hole  604   g  is an example of a catch. 
     Furthermore, in the right-angle fitting state, although it is not shown, the positioning projection  611  shown in  FIG.  11    is engaged with the positioning hole  604   h  shown in  FIG.  15   , and the positioning projection  612  shown in  FIG.  11    is engaged with the positioning hole  604   i  shown in  FIG.  15   . The two cover members  600  are thereby set in place to each other. The positioning projections  611  and  612  project from the contact surface  610   a  of the second fitting portion K 2 . The positioning holes  604   h  and  604   i  are formed in the side surface  604   b  of the first fitting portion K 1 . 
     [Configuration of the External Cover U being Fixed in Place] 
     Referring to  FIG.  4   , the external cover U is fixed to the coupling mechanism  500  at three positions: a first fixing position F 1 , a second fixing position F 2 , and a third fixing position F 3 . 
       FIG.  22    is an enlarged perspective view of the first fixing position F 1 . The first fixing position F 1  is a position where a back end of the cover member  600  constituting the upper portion u 1  of the external cover U is fixed to an upper end of the back vertical frame  513 . 
     Specifically, a screw  651  is inserted through the through hole  604   e  formed in the base surface  604   a  of the first fitting portion K 1 . The base surface  604   a  of the first fitting portion K 1  is in a back end part of the cover member  600 . The screw  651  is further tightened into the tapped hole  513   e  of the bent plate part  513   d  shown in  FIG.  5   . The bent plate part  513   d  is at the upper end of the back vertical frame  513 . 
       FIG.  23    is a perspective view of the second fixing position F 2 . The second fixing position F 2  is a position where an upper end part of the upper cover member  600  constituting the front portion u 2  of the external cover U is fixed to an upper end part of the front vertical frame  512 . 
     Specifically, a screw  652  is inserted through the through hole  604   e  of the first fitting portion K 1  that is at the upper end part of the upper cover member  600 . The screw  652  is further tightened into the tapped hole  512   d  of the rectangular plate part  512   c  that is formed in the upper end part of the front vertical frame  512 . 
       FIG.  24    is a perspective view of the third fixing position F 3 . The third fixing position F 3  is a position where a lower end part of the cover member  600  constituting the back portion u 3  of the external cover U is fixed to a lower end part of the back vertical frame  513 . 
     Specifically, a screw  653  is inserted through the through hole  604   e  of the first fitting portion K 1  that is located at the lower end part of the cover member  600 . The screw  653  is further tightened into the tapped hole  513   c  of the vertical plate part  513   b  that is formed in the lower end part of the back vertical frame  513  (see  FIG.  5   ). 
     [Positions of the External Cover U in Relation to the Image Forming Apparatus  1  and the Post-Processing Device  400 ] 
     The upper surface of the external cover U serves as an extension part of the discharge tray part  401   b  of the post-processing device  400  as illustrated in  FIG.  25   . 
     The discharge tray part  401   b  has an inclined surface  401   f  and a flat surface  401   g . The inclined surface  401   f  is inclined upward from the left to the right. The flat surface  401   g  horizontally extends from an upper end edge of the inclined surface  401   f  to the right. 
     The upper surface of the external cover U includes the outer surface  601   a  of the cover member  600  constituting the upper portion u 1 . Specifically, the upper surface of the external cover U includes the inclined surface  601   c  and the flat surface  601   b . The inclined surface  601   c  is inclined upward from the left to the right at an angle of 45 degrees approximately. A lower end edge of the inclined surface  601   c  is located lower than the flat surface  401   g  of the discharge tray part  401   b , and an upper end edge of the inclined surface  601   c  is located higher than the flat surface  401   g  of the discharge tray part  401   b.    
     In the example of  FIG.  25   , the flat surface  401   g  of the discharge tray part  401   b  is located in the middle of the vertical length of the inclined surface  601   c  of the cover member  600  constituting the upper portion u 1 . The inclined surface  601   c  of the cover member  600  guides the sheet S, which is discharged onto the discharge tray part  401   b , such that the leading end of the sheet S keeps oriented upward to the right. The inclined surface  601   c  further guides the sheet S such that the leading end of the sheet S reaches the flat surface  601   b.    
     Being discharged from the first discharge port  401   d , the sheet S is smoothly delivered through the discharge tray part  401   b  to the upper surface of the external cover U without being interfered with the movement by the external cover U as illustrated in  FIG.  25   . The configuration should not be limited to the present embodiment in which there is a groove-like recession part between the discharge tray part  401   b  and the upper surface of the external cover U. The groove-like recession part is formed in an approximate shape of the letter V. Alternatively, the discharge tray part  401   b  and the upper surface of the external cover U may be aligned to be even with each other, for example. In other words, an upper surface edge part  601   d  of the external cover U may be aligned with an end part  401   h  of the discharge tray part  401   b  in a sheet discharge direction without a step. The upper surface edge part is an edge part of the upper surface of the external cover U, which is adjacent to the discharge tray part  401   b.    
     Referring to  FIG.  26   , a horizontal width W of the external cover U is greater than an extending range Z extending to the left when the reclosable cover  35   a  is at a wide-open position. The relationship is expressed by W&gt;Z. The extending range Z extending to the left is the range of the reclosable cover  35   a  extending from a left-side surface of the main body  100  toward the post-processing device  400 . The left-side surface of the main body  100  is a surface of the main body  100 , to which the protruding attachment member  520  is fixed. 
     Referring to  FIG.  27   , a reclosable door  404  is provided in a front region of the post-processing device  400 . The reclosable door  404  is shaped in a rectangular case that is open toward the back in the closed state of the door. The reclosable door  404  has a recessed handle part  404   a . The recessed handle part  404   a  is formed at an upper end part of a right end edge of the reclosable door  404  in the closed state. 
     A left end edge of the reclosable door  404  is supported by the cabinet  401  on an axis  405  extending in an up-down direction so that the reclosable door  404  can turn about the axis  405 . For maintenance of the post-processing device  400 , users can open the reclosable door  404  by turning the handle parts  404   a  about the axis  405  with the fingers frontward. An end edge part of the reclosable door  404 , which is adjacent to the front portion u 2  of the external cover U, includes an inclined surface that is inclined frontward as is closer to the image forming apparatus  1 . The inclined surface is composed of: the inclined surface  603   c  of the end wall  603  of the cover member  600  constituting the upper portion u 1  of the external cover U; and the inclined surface  601   c  of the outer surface  601   a  of the cover member  600  constituting the front portion u 2  of the external cover U (see  FIG.  25   ). 
     The cover member  600  constituting the front portion u 2  of the external cover U is located toward the back of the handle part  103   a  of the front cover  103  of the main body  100  as illustrated in  FIG.  27   . 
     The image forming apparatus  1  has a rectangular breather  100   a  in a back end part of a left-side surface of the image forming apparatus  1  as illustrated in  FIGS.  28  and  29   . The breather  100   a  is a hole for air exhaust that allows cooling air, taken inside the main body  100  by a supply fan (not shown), go out through. 
     The cover member  600  constituting the back portion u 3  of the external cover U is located toward the front of the breather  100   a  as illustrated in  FIG.  29   . The breather  100   a  should not be limited to a hole for air exhaust; it may be a hole for air intake alternatively. 
     [Effectiveness of the Present Embodiment] 
     As described above, in the present embodiment, the conveyance guide unit  900  is provided with a pair of the lead-in guide plates  515  that guides the sheet S, which is discharged from the sheet discharge port  302  of the relay conveyance device  300  installed in the image forming apparatus  1 , to the sheet carrying-in port  401   c  of the post-processing device  400 ; the front vertical frame  512  and the back vertical frame  513  that support the pair of the lead-in guide plates  515 ; and the external cover U that is fixed to the front vertical frame  512  and the back vertical frame  513  and covers the upper part of the pair of the lead-in guide plates  515  and side parts of the pair of the lead-in guide plates  515  in traverse directions of the sheet conveyance path. The external cover U is configured such that the upper surface of the external cover U serves as an extension part of the discharge tray part  401   b  of the post-processing device  400 , which is extended downstream, in a sheet discharge direction (see  FIG.  25   ). 
     According to this configuration, the upper surface of the external cover U, which covers the conveyance guide unit  900 , can be used as the discharge tray part  401   b , successfully enhancing the capacity of stacking the sheets S by increasing a space for the sheets S to be stacked on, without the need for upsizing of the post-processing device  400 . Furthermore, costs can be reduced by the use of the conveyance guide unit  900  in comparison with the use of a special extension tray. 
     Furthermore, in the present embodiment, the upper surface of the external cover U has an upper face edge part adjacent to the discharge tray part  401   b , and the upper face edge part is inclined upward in a right-left direction (in a direction of facing), from the post-processing device  400  toward the image forming apparatus  1 . In other words, the upper surface edge part of the external cover U is inclined upward from the post-processing apparatus  400  toward the image forming apparatus  1 . In this case, the sheet S is not interfered with being discharged onto the discharge tray part  401   b  (see  FIG.  25   ). 
     This configuration will prevent the sheet S from being interfered and turned by the external cover U when the sheet S is discharged onto discharge tray part  401   b . In other words, this configuration will further enhance the capacity of stacking the sheets S. 
     Furthermore, in the present embodiment, a front end surface of the external cover U in the front-back direction is located toward the back of the handle part  103   a  of the front cover  103  of the image forming apparatus  1  (see  FIG.  27   ). This configuration allows users to open and close the front cover  103  easily without being interfered by the external cover U. 
     Furthermore, in the present embodiment, a surface (left-side surface) of the image forming apparatus  1 , which is a side surface adjacent to the post-processing device  400 , has the breather  100   a , and a back end surface of the external cover U in the front-back direction is located toward the front of the breather  100   a  (see  FIG.  29   ). 
     This configuration will prevent the breather  100   a  from being blocked by the external cover U. In other words, this configuration will ensure a proper flow of air through the breather  100   a.    
     Furthermore, in the present embodiment, the horizontal width W of the external cover U, which extends in a direction in which the image forming apparatus  1  and the post-processing device  400  face each other (see  FIG.  26   ), is greater than the extending range Z, which extends to the left of the main body  100  when the reclosable cover  35   a  of the automatic document feeding device  30  is at the wide-open position. 
     This configuration keeps the space between the post-processing device  400  and the image forming apparatus  1  large enough for the reclosable cover  35   a  to be turned up to the wide-open position. This configuration allows users to open the front cover  103  easily for maintenance and removing jammed paper. 
     Furthermore, in the present embodiment, the front vertical frame  512  and the back vertical frame  513 , which support the pair of the lead-in guide plates  515 , further serve as frame members of the coupling mechanism  500  which attaches the post-processing device  400  to the image forming apparatus  1 . Similarly, the external cover U further serves as a cover to cover the coupling mechanism  500 . Costs can be reduced by commonality of these parts. 
     Another Embodiment 
     In the above-described embodiment, the relay conveyance device  300  is installed in the internal paper discharge space E of the image forming apparatus  1 , and the conveyance guide unit  900  is configured to guide the sheet S from the relay conveyance device  300  to the post-processing device  400 ; the present disclosure, however, should not be limited to the above-described embodiment. For example, the conveyance guide unit  900  may be configured to guide the sheet S from a sheet discharge port of a rectangular image forming apparatus that does not have the internal paper discharge space E, to the post-processing device  400 . 
     Furthermore, in the above-described embodiment, the external cover U is composed of a combination of the cover members  600 ; alternatively, the external cover U may be composed of one member. 
     In the above-described embodiment, the conveyance guide unit  900  is unified into the coupling mechanism  500 ; alternatively, the conveyance guide unit  900  may be separate from the coupling mechanism  500 . 
     Although the image forming apparatus  1  is a copier in the above-described embodiment, it should not be limited thereto. Alternatively, the image forming apparatus  1  may be a printer, a facsimile, or a multifunctional peripheral (MFP), for example. 
     As described above, the present disclosure serves for a conveyance guide unit that guides sheets from an image forming apparatus to a post-processing device, especially when the image forming apparatus is a printer, a facsimile, a copier, or a multifunctional peripheral (MFP). 
     It is to be understood that the embodiments herein are illustrative and not restrictive, since the scope of the disclosure is defined by the appended claims rather than by the description preceding them, and all changes that fall within metes and bounds of the claims, or equivalence of such metes and bounds thereof are therefore intended to be embraced by the claims.