Patent Publication Number: US-2023152735-A1

Title: Sheet conveyance apparatus and image forming system

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a sheet conveyance apparatus and an image forming system including the same. 
     Description of the Related Art 
     Hitherto, an image forming apparatus configured to form an image onto a sheet serving as a recording material such as a copier, a printer and a facsimile is provided with a sheet conveyance apparatus configured to convey the sheet. In the image forming apparatus, there is a case where a so-called jam occurs and the sheet stagnates in a sheet conveyance apparatus. To deal with such a case, Japanese Patent Application Laid-open No. 2016-204142 discloses a sheet conveyance apparatus that is provided with a pair of guide plates disposed openably and so as to face with each other to nip the sheet to enable a user to remove the sheet stagnating in the sheet conveyance apparatus. Then, one of the guide plates is provided with a jam releasing lever that enables the user to hold and to operate to be able to open a sheet conveyance path by manually operating the lever. That is, the user can operate the jam releasing lever while opening a door openably attached to an apparatus body. 
     In a case where a jam occurs as described above, the user can remove the sheet stagnated in the sheet conveyance apparatus by moving one of the guide plates to an open position where the sheet conveyance path is opened by opening the door and by operating the jam releasing lever. At this time, the moved guide plate is held at the open position so as not to return to a close position where the sheet conveyance path is not opened during when the user removes the sheet. Therefore, the user is required to close the door after returning the guide plate to the close position after removing the sheet. According to the apparatus disclosed in above-described Japanese Patent Application Laid-open No. 2016-204142, the door is hardly closed in a case where the guide plate is not returned to the close position. However, in a case where the user forgets to return the guide plate to the close position and the door is forcibly closed while keeping the guide plate at the open position, there is a possibility that the guide plate or the like is damaged by being strongly pressed by the door. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, a sheet conveyance apparatus includes a conveyance portion configured to convey a sheet, a first guide plate configured to guide one surface of the sheet being conveyed by the conveyance portion, a second guide plate provided so as to face the first guide plate, the second guide plate being pivotable between a first position in which a sheet conveyance path is formed together with the first guide plate by guiding another surface opposite from one surface of the sheet and a second position by which the sheet conveyance path is opened, an operation portion provided on the second guide plate and configured to be operated for pivoting the second guide plate, a holding portion configured to hold the second guide plate at the second position, a door composing a part of an appearance of the sheet conveyance apparatus, being provided to be pivotable between an open state and a close state and permitting to access to the operation portion when the door is opened, a releasing portion provided on the door, configured to abut with the operation portion on the second guide plate positioned at the second position along with a move of the door from the open state to the close state and release the second guide plate held by the holding portion, a pressing portion provided on the door and configured to press the operation portion such that the second guide plate is positioned at the first position, and a retraction portion provided on the door and configured to retract the pressing portion from a moving locus of the operation portion in moving the second guide plate from the first position to the second position by abutting with the operation portion of the second guide plate moving from the second position to the first position and swinging. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic diagram illustrating a configuration of an image forming system according to a present exemplary embodiment. 
         FIG.  2    is a schematic diagram illustrating an image forming unit. 
         FIG.  3    is a partial perspective view illustrating an external cooling unit from which a front door is opened. 
         FIG.  4    is an upper section view illustrating the external cooling unit. 
         FIG.  5    is a schematic diagram illustrating a sheet cooling unit. 
         FIG.  6 A  is a perspective view illustrating an upstream conveyance unit viewed from an obliquely upward direction. 
         FIG.  6 B  is a perspective view illustrating the upstream conveyance unit viewed from an obliquely downward direction. 
         FIG.  7    is a perspective view illustrating a guide holding member. 
         FIG.  8    is an enlarged perspective view illustrating an upstream holding releasing portion. 
         FIG.  9    is an enlarged top view illustrating the upstream holding releasing portion. 
         FIG.  10 A  is a schematic diagram illustrating an upstream guide portion in a state in which the front door is closed. 
         FIG.  10 B  is a schematic diagram illustrating the upstream guide portion in a state in which the front door is closed halfway through. 
         FIG.  10 C  is a schematic diagram illustrating the upstream guide portion in a state in which the front door is closed still halfway through. 
         FIG.  10 D  is a schematic diagram illustrating the upstream guide portion in a state in which the front door is closed. 
         FIG.  11    is an enlarged perspective view illustrating a downstream holding releasing portion. 
         FIG.  12    is an enlarged top view illustrating the downstream holding releasing portion. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Image Forming System 
     A configuration of an image forming system of the present exemplary embodiment will be schematically described with reference to  FIGS.  1  and  2   . The image forming system  1 X illustrated in  FIG.  1    includes an image forming apparatus  100 , an external cooling apparatus  110  and a sheet processing apparatus  310 . 
     Image Forming Apparatus 
     The image forming apparatus  100  is an electro-photographic tandem type full-color printer. The image forming apparatus  100  includes image forming units PY, PM, PC and PK configured to form yellow, magenta, cyan and black images, respectively. The image forming apparatus  100  is configured to form and fix the toner images onto a sheet S corresponding to image signals transmitted from an image reading apparatus and connected to an apparatus body  100 A or from an external unit such as a personal computer communicably connected with the apparatus body  100 A. The sheet S includes various sheet members such as a plain sheet of paper, a thick paper, a rough paper, an uneven paper, a coated paper, a plastic film and a cloth. In a case of the present exemplary embodiment, an image forming unit  200  configured to form the toner images onto the sheet S has the image forming units PY, PM, PC and PK, a primary transfer roller  5 , an intermediate transfer belt  8 , a secondary transfer inner roller  9 , a secondary transfer outer roller  10  and tension rollers  121  and  122 . 
     As illustrated in  FIG.  1   , the image forming units PY, PM, PC and PK are disposed side by side along a moving direction of the intermediate transfer belt  8  within the apparatus body  100 A. The intermediate transfer belt  8  is configured to run in a direction of an arrow R 2  in  FIG.  1    by being stretched by a plurality of rollers. The intermediate transfer belt  8  bears and conveys the toner images transferred from a photosensitive drum  1  (see  FIG.  2   ). The secondary transfer outer roller  10  is disposed at a position facing the secondary transfer inner roller  9  stretching the intermediate transfer belt  8  across the intermediate transfer belt  8  and forms a secondary transfer portion T 2  for transferring the toner images on the intermediate transfer belt  8  onto the sheet S. 
     A cassette  12  storing the sheets S is disposed at an under part of the image forming apparatus  100 . The sheet S is conveyed out of the cassette  12  by a conveyance roller  13  to a registration roller  14 . Then, the sheet S is conveyed to the secondary transfer portion T 2  as the registration roller  14  starts to rotate in synchronism with the toner images formed on the intermediate transfer belt  8  as described later. Note that while one cassette  12  is illustrated here, a plurality of cassettes  12  may be disposed so as to store different sheets S having different sizes and thicknesses. In such a case, the sheet S may be conveyed selectively from any one of the plurality of cassettes  12 . Still further, not only the sheet S stored in the cassette  12 , the sheet S may be conveyed from a manual feed portion not illustrated or from an external sheet feed unit not illustrated and connected to the apparatus body  100 A. 
     The image forming units PY, PM, PC and PK have substantially the same configuration except of that their developing colors are different. Therefore, the image forming unit PK configured to form a black image will be typically described and the other image forming units will not be described here. 
     As illustrated in  FIG.  2   , the cylindrical photosensitive drum  1  serving as a photosensitive member is disposed in the image forming unit PK. The photosensitive drum  1  is rotated in a direction of an arrow R 1  at a predetermined processing speed. Disposed around the photosensitive drum  1  are a charging unit  2 , an exposure unit  3 , a developing unit  4 , a primary transfer roller  5  and a cleaning unit  6 . 
     A process for forming a full-color image by the image forming apparatus  100  will now be described. A surface of the photosensitive drum  1  is homogeneously charged by the charging unit  2  when an image forming operation starts. The charging unit  2  is a corona charger for example that irradiates the surface of the photosensitive drum  1  with charged particles generated along corona discharge for example to homogeneously charge the photosensitive drum  1  with a negative dark potential. Next, the photosensitive drum  1  is scanned and exposed by a laser light L corresponding to image signals emitted from the exposure unit  3 . Thereby, an electrostatic latent image corresponding to the image signals is formed on the surface of the photosensitive drum  1 . The electrostatic latent image formed on the photosensitive drum  1  is then developed and visualized by toner stored within the developing unit  4 . 
     The toner image formed on the photosensitive drum  1  is then transferred onto the intermediate transfer belt  8  at a primary transfer portion T 1  configured between the photosensitive drum  1  and the primary transfer roller  5  disposed across the intermediate transfer belt  8 . At this time, a primary transfer voltage is applied to the primary transfer roller  5 . Toner left on the surface of the photosensitive drum  1  after the primary transfer is removed by the cleaning unit  6 . 
     Returning to the description of  FIG.  1   , such operation is sequentially conducted in each of the image forming units PY, PM, PC and PK of yellow, magenta, cyan and black, and the four toner images are superimposed on the intermediate transfer belt  8 . After that, the sheet S stored in the cassette  12  is conveyed to the secondary transfer portion T 2  in synchronism with the toner image forming timing. Then, the full-color toner image formed on the intermediate transfer belt  8  is secondarily and collectively transferred onto the sheet S as a secondary transfer voltage is applied to the secondary transfer outer roller  10 . 
     The sheet S onto which the toner image has been secondarily transferred is conveyed to a fixing unit  11 . The fixing unit  11  includes a rotatably disposed fixing roller  11   a  and a pressure roller  11   b  that rotates while being in pressure contact with the fixing roller  11   a . The fixing roller  11   a  is rotated by a driving motor not illustrated while being in pressure contact with the pressure roller  11   b . A halogen heater  11   c  is disposed within the fixing roller  11   a  to heat the fixing roller  11   a.    
     The fixing unit  11  is configured to fix the toner image onto the sheet S on which the toner image has been formed by heating and pressurizing the sheet S by nipping and conveying at the fixing nip portion T 3  by the fixing roller  11   a  and the pressure roller  11   b . That is, the toner of the toner image formed onto the sheet S is molten and blended by the heat and pressure and is fixed onto the sheet S as the full-color image. The series of image forming process thus ends. Then, the sheet S onto which the toner image has been fixed is conveyed by the conveyance unit  170 . 
     In a case of the present exemplary embodiment, the image forming apparatus  100  can perform duplex printing. In a case of simplex printing, the sheet S onto which the toner image has been fixed is discharged by a sheet discharge roller  15  out of the apparatus body  100 A. In a case of the duplex printing, the sheet S onto which the toner image has been fixed is conveyed to a duplex reverse conveyance path  600  to be reversed such that a front surface and a back surface of the sheet S are switched. The reversed sheet S is conveyed to the registration roller  14  and is conveyed toward the secondary transfer portion T 2  such that the back surface of the sheet not printed faces the intermediate transfer belt  8 . A full-color toner image formed onto the intermediate transfer belt  8  is secondarily and collectively transferred onto the back surface of the sheet S at the secondary transfer portion T 2 . Then, the toner image of the sheet S is fixed by the fixing unit  11  and the sheet S is discharged out of the apparatus body  100 A. 
     The image forming apparatus  100  is linked with the external cooling apparatus  110  and the sheet processing apparatus  310  so as to be able to pass the sheet S sequentially from an upstream side of a conveyance path of the sheet S. The external cooling apparatus  110  and the sheet processing apparatus  310  are configured to be able to link with the image forming apparatus  100  as retrofitting peripheral apparatuses or optional units for extending functions of the image forming apparatus  100 . The image forming apparatus  100 , the external cooling apparatus  110  and the sheet processing apparatus  310  are connected among each other so as to be able to transmit/receive data through communication cables not illustrated that allow serial communication or parallel communication. The image forming apparatus  100  controls the external cooling apparatus  110  and the sheet processing apparatus  310  through the communication cables connected so as to be able to communicate with each other. 
     The external cooling apparatus  110  of the present exemplary embodiment includes a sheet cooling unit  20  serving as a sheet cooling portion for cooling the sheet S and upstream and downstream conveyance units  40  and  60  that passes and receives the sheet S to/from the sheet cooling unit  20 . The upstream conveyance unit  40  conveys and passes the sheet S discharged out of the image forming apparatus  100  to the sheet cooling unit  20 . The downstream conveyance unit  60  receives the sheet S from the sheet cooling unit  20  and conveys toward the sheet processing apparatus  310 . The upstream conveyance unit  40 , the downstream conveyance unit  60  and the sheet cooling unit  20  form a series of sheet conveyance paths  210  within the external cooling apparatus  110 . The external cooling apparatus  110  serving as the sheet conveyance apparatus or as the sheet cooling unit will be described in detail later. 
     The sheet S cooled by the external cooling apparatus  110  is conveyed to the sheet processing apparatus  310 . The sheet S conveyed to the sheet processing apparatus  310  undergoes a punching process through which the sheet S is punched by the sheet processing apparatus  310  or a stapling process through which a bundle of sheets S is stapled. In a case of performing the punching process, the sheet processing apparatus  310  executes the punching process by temporarily stopping the sheet S at a punching processing portion  314 . Then, a conveyance path is switched by a discharge destination switching portion  311  and the punched sheet S is discharged onto an upper sheet discharge tray  312 . Meanwhile, in a case of performing the stapling process, the sheet processing apparatus  310  switches the conveyance path by the discharge destination switching portion  311  to convey the sheets S to a stapling processing tray  315 . Then, when a predetermined number of sheets S are loaded on the stapling processing tray  315 , stapling is conducted by a stapler  316 . After that, the bundle of the stapled sheets S is discharged onto a lower sheet discharge tray  313 . 
     External Cooling Apparatus 
     Next, the external cooling apparatus  110  will be described with reference to  FIGS.  3  through  12   .  FIG.  3    is a schematic diagram illustrating the external cooling unit  110  from which a front door  120  is opened.  FIG.  4    is an upper section view illustrating the external cooling apparatus  110  from which the front door  120  is opened. 
     As illustrated in  FIGS.  3  and  4   , an apparatus body  110 A of the external cooling apparatus  110  is provided with the front door  120  so as to be pivotable to an open state and to a close state. The front door  120  composes a part of an appearance of the external cooling apparatus  110  in the close state. A user can access to the sheet cooling unit  20 , the upstream conveyance unit  40 , the downstream conveyance unit  60  and the like within the apparatus body  110 A from outside of the apparatus body  110 A by opening the front door  120 . In a case of the present exemplary embodiment, the front door  120  is configured to be openable with respect to the apparatus body  110 A, e.g., a frame  112 , serving as a support frame member centering on a pivot shaft  125  extending in a perpendicular direction. The pivot shaft  125  is provided downstream in the sheet conveyance direction close to the downstream conveyance unit  60  rather than the upstream conveyance unit  40 . In a case where a jam occurs, the user can manually operate the upstream conveyance unit  40  or the downstream conveyance unit  60  by opening the front door  120  to remove the sheet S stagnated therein. Note that an upstream closing unit  50  and a downstream closing unit  70  are provided at positions on an inner surface of the front door  120  facing the upstream conveyance unit  40  and the downstream conveyance unit  60 , respectively, in a state in which the front door  120  is closed. Their details will be described later. 
     Sheet Cooling Unit 
       FIG.  5    illustrates one example of the sheet cooling unit  20 . The sheet cooling unit  20  in  FIG.  5    is a belt cooling type cooling unit. As illustrated in  FIG.  5   , the sheet cooling unit  20  roughly includes a first cooling unit  21 U and a second cooling unit  25 U. The first cooling unit  21 U includes a first belt  21 , and the second cooling unit  25 U includes a second belt  25  that conveys the sheet S while nipping with the first belt  21 . The first and second belts  21  and  25  are endless belts formed into a shape of film by using high strength polyimide for example. 
     The first belt  21  is wrapped around a plurality of first belt stretching rollers  22   a , 22   b , 22   c  and  22   d , and at least one of the first belt stretching rollers  22   a , 22   b , 22   c  and  22   d  is rotated by a driving motor not illustrated. Thereby, the first belt  21  rotates in a direction of an arrow B in  FIG.  5   . Meanwhile, the second belt  25  is wrapped around a plurality of second belt stretching rollers  26   a , 26   b , 26   c  and  26   d  and is in contact with an outer circumferential surface of the first belt  21 . Therefore, the second belt  25  is driven and is rotated by the first belt  21 . Note while the first belt  21  is rotated such that the second belt  25  is driven following to the first belt  21  here, the second belt  25  may be rotated such that the first belt  21  is driven following to the second belt  25  in contrary. Or, both of the first belt  21  and the second belt  25  may be rotated by the driving motor. 
     The sheet S discharged out of the image forming apparatus  100  is nipped between the first and second belts  21  and  25  and is conveyed in a conveyance direction, i.e., in a direction of an arrow C in  FIG.  5   . At this time, the sheet S passes through a cooling nip T 4  formed by the first and second belts  21  and  25  being in contact with each other. In a case of the present exemplary embodiment, the first cooling unit  21 U includes a heat sink  30 , and the first belt  21  is cooled by the heat sink  30 . In order to efficiently cool the sheet S, the heat sink  30  is disposed so as to come into contact with an inner circumferential surface of the first belt  21  at a part where the cooling nip T 4  is formed. The sheet S is cooled through the first belt  21  in passing through the cooling nip T 4 . As the sheet S is cooled, the toner on the sheet S is cooled and is more adhered onto the sheet S. 
     The heat sink  30  serving as a cooling portion is a heat radiating plate made of metal such as aluminum. The heat sink  30  includes a heat receiving portion  30   a  for drawing heat out of the first belt  21  by being in contact the first belt  21 , a heat radiating portion  30   b  for radiating heat and a fin base  30   c  for conducting heat from the heat receiving portion  30   a  to the heat radiating portion  30   b . The heat radiating portion  30   b  is formed of a large number of heat radiating fins to gain a more contact area with air and to accelerate efficient heat radiation. Still further, in order to forcefully cool the heat sink  30  itself, there is provided a cooling fan  140  for blowing air to the heat radiating portion  30   b . The cooling fan  140  is driven by a motor not illustrated, and its air quantity is set at 2 m 3 /min, for example. Note that the heat sink  30  may be cooled by means other than the cooling fan  140 . 
     It is also noted that while the heat sink  30  is brought into contact with the first belt  21  to cool the first belt  21  in the exemplary embodiment described above, the present disclosure is not limited to such configuration and the heat sink  30  may be brought into contact with the second belt  25  to cool the second belt  25 . Or, the heat sinks  30  may be provided per the first and second cooling units  21 U and  25 U to cool both of the first belt  21  and the second belt  25 . Still further, the first and second belts  21  and  25  may be cooled not only by the heat sink  30  but also by a belt cooling fan for blowing air to the belt or by a water cooling unit in which a pipe or like in which cold liquid circulates is brought into contact with the belt. 
     Returning to the description of  FIG.  3   , the sheet cooling unit  20  described above is provided such that the first cooling unit  21 U is pivotable with respect to the second cooling unit  25 U. According to the present exemplary embodiment, the pivot shaft  125  (see  FIG.  4   ) extending along the sheet conveyance direction is provided at a rear position on an opposite side from the front door  120  in a front-back direction which is a direction orthogonal to the perpendicular direction and the sheet conveyance direction. Then, the first cooling unit  21 U is configured such that a front side thereof facing the front door  120  in the front-back direction is openable/closable in a vertical direction. The user can disengage a hocked-end latch portion  201  and the second cooling unit  25  by operating a grip  202  of the first cooling unit  21 U, and can lift up the first cooling unit  21 U. This arrangement is made to enable the user to remove the sheet S stagnating in the sheet cooling unit  20  in a case where a jam occurs. Note that although no illustration is made, the first cooling unit  21 U adopts a so-called free-stop configuration in which a damper is provided at a hinge part of the pivot shaft so that the first cooling unit  21 U can stay at arbitrary position while being opened. 
     Conveyance Unit 
     Still further, as illustrated in  FIG.  3   , the external cooling apparatus  110  is configured such that the upstream conveyance unit  40  is disposed upstream in the sheet conveyance direction and the downstream conveyance unit  60  is disposed downstream, i.e., on a side close to a rotational axis of the front door  120  here, so as to sandwich the sheet cooling unit  20 . The upstream and downstream conveyance units  40  and  60  are also configured to be pivotable such that the user can remove the sheet S stagnated in the upstream and downstream conveyance units  40  and  60 . The upstream and downstream conveyance units  40  and  60  will now be described with reference to  FIGS.  6 A and  6 B . 
     Note that because the upstream and downstream conveyance units  40  and  60  have substantially the same configuration, though they are partly different, the following description will be made by exemplifying the downstream conveyance unit  60 . As for the upstream conveyance unit  40 , reference signs of corresponding components will be described within parentheses in  FIGS.  6 A and  6 B . Still further,  FIGS.  6 A and  6 B  illustrate a case where an upper guide portion  60 A is located, with respect to a lower guide portion  60 B, at an open position where no sheet conveyance path is formed within the sheet cooling unit  20 . 
     As illustrated in  FIGS.  6 A and  6 B , the downstream conveyance unit  60  includes the lower guide portion  60 B and the upper guide portion  60 A. According to the present exemplary embodiment, the lower and upper guide portions  60 B and  60 A form a part of the sheet conveyance path  210  within the external cooling apparatus  110  (see  FIG.  1   ) and can convey the sheet S in a case where the upper guide portion  60 A is located at a close position where the upper guide portion  60 A is closed with respect to the lower guide portion  60 B. 
     The lower guide portion  60 B is provided with a first guide plate  65  and driving rollers  64  serving as first rollers and the upper guide portion  60 A is provided with a second guide plate  62  and driven rollers  63  serving as second rollers. In a case where the upper guide portion  60 A is located at the abovementioned close position, the lower guide portion  60 B and the upper guide portion  60 A face with each other so as to nip the sheet S. The first guide plate  65  is disposed along the sheet conveyance path so as to guide one surface of the sheet S and the second guide plate  62  is disposed along the sheet conveyance path so as to guide another surface of the sheet S opposite from one surface. 
     The first guide plate  65  is provided with opening portions perforated therethrough and driving rollers  64  rotationally driven by a motor not illustrated are rotatably provided so as to expose out of the opening portions. In the same manner, the second guide plate  62  is provided with opening portions perforated therethrough and driven rollers  63  are rotatably provided so as to expose out of the opening portions and to come into contact with the driving rollers  64 . The driven rollers  63  press the driving rollers  64  by an urging force of a compression spring not illustrated, so that the driving and driven rollers  64  and  63  serving as a rotating conveyance portion can nip and convey the sheet S. 
     The upper guide portion  60 A described above is provided to be pivotable with respect to the lower guide portion  60 B so as to move between the close position, i.e., a first position, where the upper and lower guide portions  60 A and  60 B form the sheet conveyance path to convey the sheet S and the upper open position, i.e., a second position, where the upper and lower guide portions  60 A and  60 B open the sheet conveyance path and do not convey the sheet S. The second guide plate  62  of the upper guide portion  60 A is pivotable between the close position and the open position centering on a pivot shaft extending in a horizontal direction. Then, the upper guide portion  60 A is provided with a jam releasing lever  61  serving as an operation portion which is to be held and operated by the user such that the user can pivotably and manually operate the upper guide portion  60 A between the close position and the open position. The jam releasing lever  61  is projectively provided toward the front side facing the front door  120  from an end portion of the second guide plate  62  in a width direction, i.e., in a direction crossing with the sheet conveyance direction (see  FIG.  4   ) such that the user can operation while opening the front door  120  (see  FIG.  3   ). In a case where the user is to move the upper guide portion  60 A from the close position to the open position, the user can bring up the upper guide portion  60 A while holding the jam releasing lever  61 . Meanwhile, in a case where the user is to move the upper guide portion  60 A from the open position to the close position, the user can bring down the upper guide portion  60 A while holding the jam releasing lever  61 . Note that the jam releasing lever  61  is provided projecting toward the side of the front door  120  more than the sheet cooling unit  20  such that the user can readily operation while holding the jam releasing lever  61  (see  FIG.  4   ). 
     The second guide plate  62  is also provided with a pin  68  projecting toward the side of the first guide plate  65 . In a case where the upper guide portion  60 A is moved to the close position, the pin  68  is inserted through a pin fitting hole  67  perforated through the first guide plate  65 . Thereby, a move of the pin  68  in the sheet conveyance direction is restricted by the pin fitting hole  67  and relative positions in the sheet conveyance direction of the upper and lower guide portions  60 A and  60 B are determined. These pin  68  and pin fitting hole  67  are formed respectively in a vicinity of the rotational axis of the driven roller  63  and the driving roller  64  in the sheet conveyance direction. Thereby, it is possible to suppress a deflection amount of alignment of the driven roller  63  and the driving roller  64  that rotate in contact with each other in the downstream conveyance unit  60  configured to be openable. It is possible to suppress a skew of the sheet S in conveying the sheet S by suppressing the alignment deflection amount of the driven roller  63  and the driving roller  64  because a rotational axis of the driven roller  63  and a rotational axis of the driving roller  64  can be kept in parallel. 
     Still further, a lengthy magnet  69  serving as a guide holding magnet which is long in the sheet conveyance direction is attached to the surface where the pin  68  is formed on the second guide plate  62  as illustrated in  FIG.  6 B  in order to keep the upper guide portion  60 A at the close position. Still further, as illustrated in  FIG.  6 A , the first guide plate  65  is provided with a magnet attracting portion  66  formed at a place where the magnet  69  faces when the upper guide portion  60 A is located at the close position. In a case where the upper guide portion  60 A is moved to the close position, the upper guide portion  60 A is held at the close position as the magnet  69  sticks with the magnet attracting portion  66  by its magnetic force. The pin  68 , the magnet  69 , the pin fitting hole  67  and the magnet attracting portion  66  are provided outside, i.e., on the side of the end portion, of a widthwise area W which permits a maximum size sheet among the sheets S to be conveyed to pass so as not to hamper the conveyance of the sheet S by the driven roller  63  and the driving roller  64 . 
     Note that it is preferable to provide at least a part of the magnet  69  at a position overlapping with a rotational axis N of the driven roller  63  in the sheet conveyance direction and to provide at least a part of the magnet attracting portion  66  at a position overlapping with a rotational axis M of the driving roller  64 . This arrangement makes it possible to suppress a sheet conveyance force from being dispersed because the driven roller  63  and the driving roller  64  come into contact with each other with a uniform and adequate pressure in the rotational axis direction, i.e., in the width direction, by the magnetic force of the magnet  69  when the upper guide portion  60 A is located at the close position. 
     Because the free-stop configuration is not adopted for the upper guide portion  60 A, differing from the first cooling unit  21 U, in the case of the present exemplary embodiment, the upper guide portion  60 A cannot stay at an arbitral position in the open state. However, if the upper guide portion  60 A is not kept at the open position and falls down by itself to the close position by own weight, it is hard for the user to remove the sheet S. 
     Then, according to the present exemplary embodiment, two guide holding members  130  are provided on frames  112  of the apparatus body  110 A as illustrated in  FIG.  3    to be able to hold the upper guide portion  40 A ( 60 A) of the respective upstream and downstream conveyance units  40  and  60  at the open position. The guide holding member  130  will now be described with reference to  FIG.  3    and by using  FIG.  7   . 
     Guide Holding Member 
     As illustrated in  FIG.  7   , the guide holding member  130  includes a magnet  131  serving as a holding portion and a magnet attaching portion  132 . The magnet  131  is attached to the magnet attaching portion  132  such that a tip thereof faces the upper guide portion  60 A, i.e., downward in  FIG.  7   . The guide holding member  130  is fixed to the frame  112  of the apparatus body  110 A through the magnet attaching portion  132 . A magnet attracting portion  61   a  formed of a sheet metal is provided at a widthwise tip of the second guide plate  62 . The magnet attracting portion  61   a  may be formed integrally with the jam releasing lever  61  described above. 
     The magnet  131  is disposed on a locus along which the magnet attracting portion  61   a  moves along with the pivot of the second guide plate  62  and sticks with the magnet attracting portion  61   a  by its magnetic force as the second guide plate  62  pivots and arrives at the open position. This arrangement makes it possible to hold the upper guide portion  60 A at the open position and to prevent the upper guide portion  60 A from moving from the open position to the close position by its own weight. In this case, it is necessary to release the second guide plate  62  held by the magnet  131  in order to move the upper guide portion  60 A from the open position to the close position. Here, the user can release the second guide plate  62  held by the magnet  131  by holding and lowering the jam releasing lever  61 . 
     Note that although the present exemplary embodiment has been arranged such that the upper guide portion  60 A is held at the open position by the magnet  131 , the present disclosure is not limited to such configuration. For instance, instead of the magnet  131 , a hook-like engaging projection may be provided on the frame  112  of the apparatus body  110 A and an engagement hole may be formed on the upper guide portion  60 A instead of the magnet attracting portion  61   a . In such a case, the upper guide portion  60 A is held at the open position by engaging the engaging projection with the engagement hole. Still further, the upper guide portion  60 A is held at the close position by the magnet  69 , the present disclosure is not limited to such configuration. However, it is preferable to hold the upper guide portion  60 A at the close position by the magnet  69  in order to suppress dispersion of the sheet conveyance force as described above. 
     It is noted that a projection amount, i.e., a length, of the pin  68  from the second guide plate  62  is set such that the tip of the pin  68  is inserted into the pin fitting hole  67  before the magnet  69  arrives at the magnet attracting portion  66  in moving the upper guide portion  60 A from the open position to the close position. That is, as illustrated in  FIG.  6 B , the tip of the pin  68  projects more to the side of the lower guide portion  60 B than the magnet  69 . That is, the pin  68  is inserted into the pin fitting hole  67  before the upper guide portion  60 A arrives at the close position. This arrangement makes it possible to position the upper and lower guide portions  60 A and  60 B in a plane direction by the pin  68  and the pin fitting hole  67  when the upper guide portion  60 A moving from the open position to the close position arrives at a position where the pin  68  engages with the pin fitting hole  67 . Accordingly, because the upper guide portion  60 A moves to the close position while being guided by the pin  68  and the pin fitting hole  67 , the magnet  69  provided on the upper guide portion  60 A can be steadily attracted with the magnet attracting portion  66  provided on the lower guide portion  60 B. This arrangement makes it possible to bring the driven roller  63  and the driving roller  64  adequately into contact with each other. 
     By the way, when a jam occurs, the user opens the front door  120  at first and then performs a work of removing the sheet S stagnated in the upstream conveyance unit  40  or the downstream conveyance unit  60 . For instance, in a case where the sheet S is jammed in the downstream conveyance unit  60 , the user brings up the jam releasing lever  61  to move the upper guide portion  60 A from the close position to the open position. Then, after removing the sheet S, the user presses down the jam releasing lever  61  to move the upper guide portion  60 A from the open position to the close position. Then, after moving the upper guide portion  60 A to the close position, the user closes the front door  120 . However, in a case where the user closes the front door  120  without returning the upper guide portion  60 A to the close position, there is a possibility that the downstream conveyance unit  60  is damaged by being pressed by the front door  120 . There is also a possibility of damaging the upstream conveyance unit  40  in the similar condition. 
     Then, the present exemplary embodiment is arranged such that the upstream conveyance unit  40  or the downstream conveyance unit  60  is not damaged even if the user closes the front door  120  without returning the upper guide portion  40 A or the upper guide portion  60 A. A configuration of the present exemplary embodiment for realizing such a situation will be described below. 
     As illustrated in  FIG.  3   , upstream and downstream closing units  50  and  70  are provided on an inner surface of the front door  120 . According to the present exemplary embodiment, the downstream closing unit  70  comes into contact with the jam releasing lever  61  of the downstream conveyance unit  60  at first along with a closing operation of the front door  120 , and then the upstream closing unit  50  comes into contact with the jam releasing lever  41  of the upstream conveyance unit  40  along with the closing operation of the front door  120 . 
     Upstream Closing Unit 
     The upstream closing unit  50  will be described with reference to  FIG.  3    and  FIGS.  8  through  10 D . As illustrated in  FIG.  3   , the upstream closing unit  50  includes an upstream holding releasing portion  51  serving as a releasing portion and an upstream guide portion  52  serving as a guide portion. 
     Upstream Holding Releasing Portion 
     Firstly, the upstream holding releasing portion  51  will be described. The upstream holding releasing portion  51  is provided so as to form an inclined surface  51   a  that projects out of the inner surface of the front door  120  and is inclined in a gravity direction. The inclined surface  51   a  is formed such that an upper side thereof, in the perpendicular direction, intrudes deeply into the apparatus body  110 A more than a lower side thereof. Along with the closing operation of the front door  120 , the upstream holding releasing portion  51  butts against the jam releasing lever  41  of the upstream conveyance unit  40  and releases the second guide plate  42  held at the open position by the guide holding member  130  or specifically by the magnet  131  (see  FIG.  7   ). 
     That is, as illustrated in  FIGS.  8  and  9   , the upstream holding releasing portion  51  of the front door  120  butts against the tip of the jam releasing lever  41  serving as the operation portion when the front door  120  is closed. Note that the downstream closing unit  70  is not illustrated in  FIG.  9   . When the front door  120  is closed further from when the upstream holding releasing portion  51  has butted against the tip of the jam releasing lever  41 , the jam releasing lever  41  is pressed by the front door  120  and is moved downward in the gravity direction along the inclined surface  51   a  of the upstream holding releasing portion  51 . Thereby, the upper guide portion  40 A moves downward and the magnet attracting portion  41   a  separates from the guide holding member  130 , so that the upper guide portion  40 A, i.e., the second guide plate  42 , held by the magnet  131  (see  FIG.  7   ) is released. 
     The upper guide portion  40 A after being released from the held condition moves downward by being pressed by the front door  120  in the condition in which the jam releasing lever  41  butts against the upstream holding releasing portion  51 . That is, the upstream holding releasing portion  51  is formed such that a force in the width direction applied to the upper guide portion  40 A along with the closing operation of the front door  120  of the user is separated into components of force in the width direction and in a downward direction by the inclined surface  51   a . This arrangement makes it possible to suppress the upper guide portion  40 A from being damaged along with the closing operation of the front door  120  during when the upper guide portion  40 A is contact with the upstream holding releasing portion  51 . Still further, even if the force is separated, because the force in the width direction is applied to the upper guide portion  40 A, the upper guide portion  40 A will not fall at once down to the close position by its own weight. 
     It is noted in a case of the present exemplary embodiment, one end portion of the upper guide portion  40 A in the sheet conveyance direction is in contact with the guide holding member  130  and a move in the sheet conveyance direction thereof is regulated by the guide holding member  130  during the move of the upper guide portion  40 A while the jam releasing lever  41  is in contact with the upstream holding releasing portion  51 . To that end, the magnet attaching portion  132  is provided with a regulating plane extending in the gravity direction or in an opening/closing direction of the upper guide portion  40 A here. That is, the guide holding member  130  also functions as a regulating portion that comes into contact with the second guide plate  42  on the side of the pivot shaft  125  (see  FIG.  4   ) of the front door  120  in the sheet conveyance direction and regulates the second guide plate  42  from moving to the side of the pivot shaft  125  of the front door  120 . 
     Upstream Guide Portion 
     Next, the upstream guide portion  52  will be described. As described above, as the upper guide portion  40 A after being released from the holding condition is moved downward along the inclined surface  51   a  of the upstream holding releasing portion  51 , the jam releasing lever  41  is moved downward in the perpendicular direction and arrives at an upstream guide portion  52  continuously provided under the upstream holding releasing portion  51 . The upstream guide portion  52  guides the second guide plate  42  to the close position, i.e., the first position, through the jam releasing lever  41  while suppressing the move in the sheet conveyance direction of the jam releasing lever  41  of the second guide plate  42  that has been released by the upstream holding releasing portion  51 . 
     As illustrated in  FIG.  3   , the upstream guide portion  52  is formed into a shape of a rectangular box having a hollow space inside and is provided with a retraction member  52   a  serving as a retraction portion therein. The upstream guide portion  52  is provided with an opening portion perforated on a surface of a same side with the inclined surface  51   a  of the upstream holding releasing portion  51 , and the retraction member  52   a  is provided on an inner side of the upstream guide portion  52  and is exposed out of the opening portion. Then, the retraction member  52   a  is provided movably in a direction opposite from a direction in which the front door  120  is closed by butting against the jam releasing lever  41  along with the closing operation of the front door  120  as described later. 
     As illustrated in  FIG.  10 A , the retraction member  52   a  is provided pivotably with respect to the upstream guide portion  52 . In a case of the present exemplary embodiment, the retraction member  52   a  has a pivot shaft  53  located higher than an elastic member  52   b , i.e., a pressing portion, in the perpendicular direction and pivots centering on the upper side and by setting a side of the elastic member  52   b , i.e., a side of the pressing portion, as a free end. The retraction member  52   a  and the elastic member  52   b  are integrally provided. The retraction member  52   a  is urged by a torsion spring  54  serving as an urging portion toward the opening portion of the upstream guide portion  52  or in other words, in a same direction with a direction in which the front door  120  is closed. 
     As described above, when the upstream holding releasing portion  51  of the front door  120  butts against the tip of the jam releasing lever  41  along with the closing operation of the front door  120 , a force F 1  in the width direction is applied to the upper guide portion  40 A. The force F 1  in the width direction applied to the upper guide portion  40 A is separated into components in the width direction and the downward direction by the inclined surface  51   a  of the upstream holding releasing portion  51  (resultant force f 1 ). Then, the upper guide portion  40 A held by the magnet  131  is released by the resultant force f 1 , and the upper guide portion  40 A falls down while frictionally sliding the jam releasing lever  41  with the inclined surface  51   a.    
     As the front door  120  is continuously closed, the tip of the jam releasing lever  41  arrives at the upstream guide portion  52  as illustrated in  FIG.  10 B  and the tip of the jam releasing lever  41  intrudes into the upstream guide portion  52  through the opening portion and butts against the retraction member  52   a . When the front door  120  is closed further as it is, the retraction member  52   a  is pressed by the jam releasing lever  41  and pivots centering on the pivot shaft  53  in a direction R 3  opposite from the urging direction of the torsion spring  54 . That is, the retraction member  52   a  swings in the R 3  direction by abutting with the jam releasing lever  41  along with the move of the upper guide portion  40 A moving from the open position to the close position. Then, the retraction member  52   a  retracts the elastic member  52   b  from a moving locus of the jam releasing lever  41 . 
     As illustrated in  FIG.  10 C , the upper guide portion  40 A is moved to the close position as the jam releasing lever  41  slides with the retraction member  52   a . At this time, because the force F 1  in the width direction is applied to the upper guide portion  40 A through the retraction member  52   a , the upper guide portion  40 A does not fall at once to the close position by its own weight. Still further, because the retraction member  52   a  operates so as to retract from the jam releasing lever  41  toward the outside of the front door  120 , the upper guide portion  40 A is suppressed from being damaged along with the closing operation of the front door  120 . That is, because the retraction member  52   a  swings so as to retract from the pivoting locus of the jam releasing lever  41 , the upper guide portion  40 A is suppressed from being damaged along with the closing operation of the front door  120 . It is noted that because the state in which the jam releasing lever  41  intrudes into the upstream guide portion  52  from the opening portion is maintained until when the upper guide portion  40 A is moved to the close position, the move of the upper guide portion  40 A in the sheet conveyance direction is limited while being moved by the upstream guide portion  52 . 
     When the upper guide portion  40 A is moved to the close position, the driven roller  43  of the upper guide portion  40 A comes into contact with the driving roller  44  of the lower guide portion  40 B, and the magnet  49 , i.e., the guide holding magnet, of the upper guide portion  40 A sticks with the magnet attracting portion  46  of the lower guide portion  40 B. However, because the driven roller  43  is urged by a compression spring not illustrated, a reaction force O acts by the urging force of the compression spring when the driven roller  43 , i.e., a second roller, comes into contact with the driving roller  44 , i.e., a first roller. Therefore, when the upper guide portion  40 A arrives at the close position, the magnet  49  does not immediately stick with the magnet attracting portion  46  and there is a case where the magnet  49  sticks with the magnet attracting portion  46  after the upper guide  40 A has bounced for a while. Then, it is preferable to stick the magnet  49  with the magnet attracting portion  46  without bouncing the upper guide portion  40 A by generating a force f 3  by own weight of the retraction member  52   a  and an operation of the torsion spring  54 . To that end, according to the present exemplary embodiment, the elastic member  52   b  such as a rubber plate is provided at a lower end portion of the retraction member  52   a . The elastic member  52   b  elastically deforms by butting against the jam releasing lever  41  and presses the second guide plate  42  toward the first guide plate  45  through the jam releasing lever  41 . That is, the elastic member  52   b  is one example of a pressing portion configure to press the jam releasing lever  41 . The elastic member  52   b  presses the second guide plate  42  toward the first guide plate  45  and causes the magnet  49  to stick with the magnet attracting portion  46  by pressing the jam releasing lever  41  of the second guide plate  42  on a way when the second guide plate  42  moves from the open position to the close position. Still further, the second guide plate  42  is positioned at the close position as the elastic member  52   b  keeps pressing the jam releasing lever  41  of the second guide plate  42  at the close position. It is noted that because the elastic member  52   b  swings so as to retract from the pivoting locus of the jam releasing lever  41  together with the retraction member  52   a , the upper guide portion  40 A is suppressed from being damaged along with the closing operation of the front door  120 . 
     However, the elastic member  52   b  needs not to be always in contact with the jam releasing lever  41  in a case where the front door  120  is closed. Even in a configuration in which the elastic member  52   b  is not in contact with the jam releasing lever  41  in the case where the front door  120  is closed, the magnet  49  may be caused to stick with the magnet attracting portion  46  without bouncing the upper guide portion  40 A by increasing the urging force of the torsion spring  54 . Still further, the elastic member  52   b  may be noncontact with the jam releasing lever  41  in the case where the front door  120  is closed as long as an arrangement is made such that a force that causes the magnet  49  to stick with the magnet attracting portion  46  can be applied in a process of shifting from the open state to the closed state of the front door  120 . It is noted that in a case of the configuration in which no magnet  49  is provided, it is possible to adopt a configuration in which the elastic member  52   b  is always in contact with the jam releasing lever  41  and presses the second guide plate  42  to the first guide plate  45  in the case where the front door  120  is closed. 
     As illustrated in  FIG.  10 D , the upper guide portion  40 A is held at the close position as the magnet  49  sticks with the magnet attracting portion  46  by the force f 3  generated on the elastic member  52   b  of the retraction member  52   a  due to the force applied by own weight of the retraction member  52   a  and to the urging force of the torsion spring  54 . Thus, the upstream guide portion  52  moves the upper guide portion  40 A along with the closing operation of the front door  120  while retracting the second guide plate  42  which has been released from the magnet  131  so as not to be damaged by being pressed by the front door  120  and such that the second guide plate  42  does not fall at once to the close position by its own weight. 
     Downstream Closing Unit 
     Next, the downstream closing unit  70  will be described with reference to  FIGS.  3 ,  11  and  12   . As illustrated in  FIG.  3   , the downstream closing unit  70  includes a downstream holding releasing portion  71  serving as a releasing portion and a downstream guide portion  72  serving as a guide portion. The downstream guide portion  72  is formed into a shape of a rectangular box having an internal hollow, and a retraction member  72   a  serving as a retraction portion is provided therein. A configuration of the downstream guide portion  72  is the same with that of the upstream guide portion  52  of the upstream closing unit  50  described above, its description will be omitted here. 
     Downstream Holding Releasing Portion 
     The downstream holding releasing portion  71  releases a second guide plate  62  held by the downstream guide holding member  130  or specifically the magnet  131  (see  FIG.  7   ). While a same inclined surface with the inclined surface  51   a  of the upstream holding releasing portion  51  described above may be formed also on the downstream holding releasing portion  71 , or as illustrated in  FIG.  3   , an inclined member  71   a  forming an inclined surface inclined also in the width direction in addition to the gravity direction is provided in the present exemplary embodiment. It is because the downstream conveyance unit  60  is disposed on a side close to the rotational axis of the front door  120 , it is difficult to release the second guide plate  62  held by the guide holding member  130  corresponding to the closing operation of the front door  120  if the same inclined surface with the inclined surface  51   a  of the upstream holding releasing portion  51  is adopted. That is, in a case where the downstream conveyance unit  60  is disposed on the side close to the rotational axis of the front door  120  and the same inclined surface with that of the upstream closing unit  50  disposed on the side far from the rotational axis is adopted, a great force needs to be applied to separate the magnet  131  from the magnet attracting portion  61   a  (see  FIG.  7   ). Therefore, a possibility of damaging the downstream conveyance unit  60  increases. 
     Then, according to the present exemplary embodiment, the downstream holding releasing portion  71  is provided with the inclined member  71   a  as illustrated in  FIGS.  11  and  12   .  FIGS.  11  and  12    illustrate a state in which the inclined member  71   a  of the downstream holding releasing portion  71  starts to come into contact with the jam releasing lever  61  of the upper guide portion  60 A located at the open position by being held by the guide holding member  130 . 
     The inclined member  71   a  is provided so as to face the pivot shaft  125  of the front door  120 . A disposed position and an orientation of the inclined surface of the inclined member  71   a  are determined based on a pivot direction, i.e., an arrow V 11 , of the front door  120 , and a disposed position of the guide holding member  130  with respect to the upper guide portion  60 A. As the position of the downstream holding releasing portion  71  comes closer to the rotational axis of the front door  120 , ease of application of a necessary force for separating the magnet  131  from the magnet attracting portion  61   a  changes. Then, the ease of application of the necessary force for separating the magnet  131  from the magnet attracting portion  61   a  is adjusted by the orientation of the inclined surface of the inclined member  71   a.    
     In the case of the present exemplary embodiment, the inclined surface serving as a butting portion of the inclined member  71   a  is formed obliquely such that a lower part thereof is closer to the inner surface of the front door  120 , rather than the upper part thereof in the perpendicular direction. Still further, the inclined surface of the inclined member  71   a  is formed obliquely such that a part thereof closer to the pivot shaft of the front door  120 , rather than a part far from the pivot shaft of the front door  120 , is closer to the inner surface of the front door  120 . Then, it is preferable to provide the inclined member  71   a  such that an angle θ formed by “a straight line Z which is a perpendicular line with respect to the rotational axis X of the upper guide portion  60 A positioned at the open position and which passes through a butting point Q of the inclined surface of the inclined member  71   a  against which the jam releasing lever  61  butts” and “a straight line Y that passes through the butting point Q and an abutment point T of the guide holding member  130  with which the second guide plate  62  abuts” is equal to or more than 3° and equal to or less than 10°. It is preferable to provide the inclined member  71   a  such that the abovementioned angle θ to be formed is around 3.5°, though it depends on a distance between the downstream holding releasing portion  71  and the rotational axis of the front door  120 . 
     While the downstream holding releasing portion  71  has been mainly described here, the same relationship holds also for the inclines surface  51   a  of the upstream holding releasing portion  51 . However, the shape of the inclined surface  51   a  of the upstream holding releasing portion  51  is different from that of the inclined surface of the inclined member  71   a  because a positional relationship of the upper guide portion  40 A and the upstream guide holding member  130  is opposite from a positional relationship of the upper guide portion  60 A and the downstream guide holding member  130 . Because the upstream holding releasing portion  51  is provided at the position separated further from the pivot shaft of the front door  120  than the downstream holding releasing portion  71 , the inclined surface  51   a  may take a state inclined also in the width direction with respect to the jam releasing lever  41  along with the closing operation of the front door  120 . Accordingly, the inclined surface  51   a  can release the upper guide portion  60 A by the upstream holding releasing portion  51  even if the inclined surface  51   a  has the inclined surface different from the inclined member  71   a.    
     In closing the front door  120 , the inclined member  71   a  pressurizes the upper guide portion  60 A in the pivot direction, i.e., in the direction of the arrow V 11 , of the front door  120  through the jam releasing lever  61  at the point, i.e., the butting point Q, where the inclined member  71   a  comes into contact with the jam releasing lever  61 . This pressurizing direction, i.e., the direction of the arrow V 11 , is set in a direction having an angle equal to or more than 3° and equal to or less than 10° with respect to the direction, i.e., the straight line Z, perpendicular to the rotational axis X of the pivot shaft (see  FIG.  12   ) of the upper guide portion  60 A pivoting between the open position and the close position. The inclined member  71   a  is thus provided. 
     In such a case, the upper guide portion  60 A may move in a direction of an arrow V 12  when the inclined member  71   a  pressurizes the upper guide portion  60 A in the pivot direction, i.e., in the direction of the arrow V 11 , of the front door  120  through the jam releasing lever  61  by the force of closing the front door  120 . Then, an edge of the upper guide portion  60 A comes into contact with the regulating surface of the guide holding member  130  fixed to the frame  112  of the apparatus body  110 A (see  FIG.  3   ) from a direction of the arrow V 12 . Then, the widthwise force F 1  applied to the upper guide portion  60 A as the downstream holding releasing portion  71  of the front door  120  butts against the tip of the jam releasing lever  61  is separated into components in the width direction and the downward direction by the inclined surface of the inclined member  71   a  (resultant force f 1 ). Then, the upper guide portion  60 A held by the guide holding member  130  is released by the resultant force f 1 , and the upper guide portion  60 A falls downward while frictionally sliding the jam releasing lever  61  with the inclined surface of the inclined member  71   a . Therefore, the upper guide portion  60 A may have rigidity necessary for the normal operation of the user. 
     As described above, according to the present exemplary embodiment, the upstream closing unit  50  and the downstream closing unit  70  are provided on the inner surface of the front door  120 . The downstream closing unit  70  includes the downstream holding releasing portion  71  ( 51 ) (the same applies to the upstream closing unit  50 ) that butts against the jam releasing lever  61  ( 41 ) when the front door  120  is closed and releases the upper guide portion  60 A ( 40 A) held by the guide holding member  130 . Still further, the downstream closing unit  70  ( 50 ) includes the downstream guide portion  72  ( 52 ) which is provided with the retraction member  72   a  ( 52   a ) pivotably. Along with the closing operation of the front door  120 , the jam releasing lever  61  ( 41 ) butts against the retraction member  72   a  ( 52   a ). When the front door  120  is closed further as it is, the retraction member  72   a  ( 52   a ) is pressed by the jam releasing lever  61  ( 41 ) and retracts in the direction opposite from the direction in which the front door  120  is closed while sliding with the jam releasing lever  61  ( 41 ). This arrangement makes it possible to prevent the downstream conveyance unit  60  or the upstream conveyance unit  40  from being damaged even if the user closes the front door  120  while forgetting to close the upper guide portion  60 A ( 40 A). 
     Note that while the configuration in which the retraction member  52   a  is urged by the torsion spring  54  has been illustrated concerning the upstream conveyance unit  40  as illustrated in  FIGS.  10 A through  10 D , the present disclosure is not limited to such configuration. For instance, an equal force f 3  with the case where the torsion spring  54  is provided on the retraction member  52   a  may be applied by increasing a weight of the retraction member  52   a  or specifically a lower end side, without providing the torsion spring  54 . Note that the same applies to the downstream conveyance unit  60 . 
     Note that although the configuration in which the upstream guide holding member  130  is provided upstream in the sheet conveyance direction with respect to the upstream upper guide portion  40 A and the guide holding member  130  is provided downstream of the sheet conveyance direction with respect to the downstream upper guide portion  60 A, the present disclosure is not limited to such configuration. The positional relationship of the guide holding member  130  with the upper guide portion  40 A ( 60 A) may be opposite from the exemplary embodiment described above as long as such configuration is adopted that the angle θ formed by “the straight line Z which is a perpendicular line with respect to the rotational axis X of the upper guide portion  60 A positioned at the open position and which passes through the butting point Q of the inclined surface of the inclined member  71   a  against which the jam releasing lever  61  butts” and “the straight line Y that passes through the butting point Q and the abutment point T of the guide holding member  130  with which the second guide plate  62  abuts” is equal to or more than 3° and equal to or less than 10°. 
     Note that the present disclosure may be applied not only to the external cooling apparatus  110  as described in the exemplary embodiment but also to the conveyance unit  170  (see  FIG.  1   ) or the like for conveying the sheet S within the apparatus body  100 A of the image forming apparatus  100  for example. Still further, the abovementioned embodiment is applicable also to a sheet conveyance apparatus capable of passing the sheet S with the sheet cooling unit  20  which is provided within the apparatus body  100 A of the image forming apparatus  100 . That is, the sheet conveyance apparatus of the present exemplary embodiment may be disposed at any place within the apparatus body  100 A of the image forming apparatus  100  or within the apparatus body  110 A of the external cooling apparatus  110 . 
     Other Embodiments 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2020-91179, filed on May 26, 2020, Japanese Patent Application No. 2020-91180, filed on May 26, 2020, and Japanese Patent Application No. 2021-39766, filed on Mar. 12, 2021, which are hereby incorporated by reference herein in its entirety.