Patent Publication Number: US-8523466-B2

Title: Image forming apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image forming apparatus with a conveying mechanism configured to preferably clear a paper jam. 
     2. Description of the Related Art 
     An image forming apparatus such as a copy machine, a printer, a fax machine or a complex machine with their functions generally conveys a sheet and forms a toner image in the housing. Such an image forming apparatus typically comprising a removal mechanism configured to remove sheets jammed in the housing. 
     A known removal mechanism includes a sheet feeder and a conveying portion, which are connected with each other by a link mechanism, and allows them to be integrally pulled out from the housing. A user may pull out the sheet feeder and the conveying portion from the housing to remove sheets jammed in the housing. 
     Since the sheet feeder and the conveying portion of the aforementioned removal mechanism are integrally pulled out from the housing, the user may more efficiently remove the sheets jammed in the housing. The link mechanism integrating the sheet feeder and the conveying portion, however, results in increase in size of the entire image forming apparatus. Moreover, appropriate settings for feeding a sheet is likely to change because the sheet feeder is unnecessarily moved, which results in a failure of the sheet feeding process. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an image forming apparatus which allows efficient removal of a sheet without unnecessarily moving a sheet feeding mechanism configured to feed sheets. 
     An image forming apparatus having an image forming portion for forming an image on a sheet according to one aspect of the present invention includes: a housing configured to accommodate the image forming portion; and a conveying mechanism configured to at least partially define a conveying path for guiding the sheet to the image forming portion, wherein the conveying mechanism has a first conveying element including an upstream end on which a feeding assembly for feeding the sheet is formed, and a second conveying element confronting the first conveying element to form the conveying path in cooperation with the first conveying element, the housing includes a rail configured to guide the second conveying element, and the rail guides displacement of the second conveying element from a first position where the second conveying element forms the conveying path along the first conveying element to a second position where the second conveying element is away from the first conveying element. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an image forming apparatus according to an embodiment. 
         FIG. 2  is a diagram schematically showing an internal structure of the image forming apparatus shown in  FIG. 1 . 
         FIG. 3  is a side view showing a conveying mechanism of the image forming apparatus shown in  FIG. 2 . 
         FIG. 4  is a perspective view showing the conveying mechanism of the image forming apparatus shown in  FIG. 2 . 
         FIG. 5  is a perspective view showing the conveying mechanism completely drawn out from a housing. 
         FIG. 6  is a side view showing a positioning mechanism of the conveying mechanism. 
         FIG. 7  is a cross-sectional diagram schematically showing the positioning mechanism of the conveying mechanism. 
         FIG. 8  is a perspective view showing another structure of a rail. 
         FIG. 9  is an enlarged perspective view around a border between a first section and second section of a third rail. 
         FIG. 10  is a bottom view of the conveying mechanism guided by the rail shown in  FIG. 8 . 
         FIG. 11  is a perspective view of the conveying mechanism drawn out from the housing. 
         FIG. 12  is a perspective view of the conveying mechanism drawn out from the housing. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     One embodiment of an image forming apparatus is described hereinafter with reference to the accompanying drawings. It should be noted that directional terms such as “upper,” “lower,” “left” and “right” hereinafter simply aim to clarify the descriptions without limiting a principle of the image forming apparatus. Also, a term “sheet” in the following descriptions means a copy sheet, coated sheet, OHP sheet, cardboard, postcard, tracing paper and other sheet materials subjected to an image forming process. A term “leading edge of a sheet” means a leading edge of the sheet in a sheet conveying direction. Terms “upstream”, “downstream” and other similar terms hereinafter mean concepts of “upstream,” “downstream” and the like in terms of the sheet conveying direction. 
       FIG. 1  is a perspective view showing an appearance of the image forming apparatus according to one embodiment. It should be noted that the image forming apparatus shown in  FIG. 1  is a printer. The image forming apparatus may be any other apparatus configured to form an image on a sheet, such as a copy machine, a fax machine or a complex machine with their functions. 
     An image forming apparatus  1  comprises a substantially rectangular parallelpiped housing  2 , a tray  510  protruding from a front side of the housing  2  and a cassette  300  disposed below the tray  510 . The housing  2  accommodates various equipments necessary to form an image on a sheet (e.g., various elements used in an image forming portion described hereinafter). The tray  510  attached to the housing  2  turns around a lower edge of the tray  510 . The tray  510  shown in  FIG. 1  is located in a protruding position so as to protrude from the housing  2 . A user may place a sheet on the tray  510  located in the protruding position. A feeding assembly, which is described hereinafter, feeds the sheet on the tray  510  toward the image forming portion configured to form an image on the sheet. When the user turns the tray  510  closer to the housing  2  from the protruding position, the tray  510  becomes accommodated in a concave area  21  formed on the housing  2 . The cassette  300  is configured to be inserted into and drawn out from the housing  2 . The user may draw out the cassette  300  from the housing  2  toward the front side to place sheets in the cassette  300 . After placing desired sheets in the cassette  300 , the user may insert the cassette  300  into the housing  2 . In the following descriptions, the sheet on the tray  510  is exemplified as a first sheet, and the sheet accommodated in the cassette  300  is exemplified as a second sheet. The image forming apparatus  1  may selectively convey the first sheet and the second sheet to the image forming portion to form a toner image. 
     An operation panel  22  is disposed above the tray  510 . The user may operate the operation panel  22  to perform a desired operation on the image forming apparatus  1 . The operation panel  22  may includes a button for adjusting, for example, density of the toner image. The image forming apparatus  1  forms a toner image on a sheet in accordance with an input from the user onto the operation panel  22 , as well as an image signal (a signal with information on an image to be printed) sent from an external device (e.g., a personal computer). 
     After the image forming portion forms a toner image on a sheet fed from the tray  510  or the cassette  300 , the sheet is discharged onto a discharge tray  23  formed on an upper surface of the housing  2 . The sheet subjected to the image forming process is stacked in a space in the form of a substantially triangular pole, which is formed on an upper surface of the discharge tray  23 . 
       FIG. 2  schematically shows an internal structure of the image forming apparatus  1 . The image forming apparatus  1  is further described with reference to  FIGS. 1 and 2 . 
     As described above, a sheet is conveyed from the tray  510  or the cassette  300 . Subsequently, the sheet is guided by a conveying path formed in the housing  2  and sent to the image forming portion  410 . The image forming portion  410  forms the toner image on the sheet. The sheet is then conveyed to a fixing portion  430 . The fixing portion  430  fixes the toner image onto the sheet. Thereafter, the sheet is discharged onto the discharge tray  23  through a discharge portion  450 . 
     The conveying path includes a first feed path  530  extending toward a back wall  24  of the housing  2 . A feeding assembly  520  configured to pull the first sheet into the housing and feed it to the image forming portion  410  is disposed at an upstream end of the first feed path  530 . The conveying path further includes a second feed path  310  extending upward from a downstream end of the cassette  300  (the right end in  FIG. 2 ) located below the first feed path  530 . The first feed path  530  and the second feed path  310  join together at an upstream side of a resist roller pair  320  configured to send a sheet to the image forming portion  410  in synchronization with the image forming process performed by the image forming portion  410 . A substantially linear section in the first feed path  530  above the cassette  300  is formed by a conveying mechanism  600 , which is described hereinafter. 
     The conveying path further includes a main conveying path  330  for guiding a sheet from the resist roller pair  320  to the fixing portion  430 , and a discharge conveying path  340  for guiding the sheet from the fixing portion  430  to the discharge portion  450 . The image forming portion  410  forms a toner image on a sheet moving along the main conveying path  330 . The fixing portion  430  then fixes the toner image onto the sheet. If a user performs one-side printing using the image forming apparatus  1 , the discharge portion  450  discharges the sheet, which is sent from the fixing portion  430  to the discharge conveying path  340 , to the outside of the housing  2 . The discharged sheet is stacked on the discharge tray  23 . 
     If the user performs both side printing using the image forming apparatus  1 , the discharge portion  450  carries out a switchback operation so that a certain length of the sheet sent from the fixing portion  430  to the discharge conveying path  340  is further sent outside the housing  2  and then pulled back into the housing  2 . The conveying path further includes a return conveying path  350  for guiding the sheet pulled back by the discharge portion  450 . The return conveying path  350  extends toward the back wall  24  of the housing  2  from the discharge portion  450  and then extends downward. Thereafter, the return conveying path  350  extends toward the second feed path  310  and joins together with the second feed path  310 . 
     A conveying roller pair  360  configured to convey a sheet guided by the first feed path  530 , the second feed path  310 , the main conveying path  330 , the discharge conveying path  340  and the return conveying path  350  is disposed in proper places of these conveying paths. 
     As described above, the feeding assembly  520  sends the first sheet put on the tray  510  to the first feed path  530  formed by the conveying mechanism  600 . The feeding assembly  520  comprises a lift plate  521  configured to lift up a leading edge of the first sheet on the tray  510  which is inclined downward towards the housing  2 , a feed roller  522  configured to come into contact with the leading edge of the first sheet lifted up by the lift plate  521 , and a separating pad  523  disposed below the feed roller  522 . When the feed roller  522  rotates, the first sheet passes between the feed roller  522  and the separating pad  523 , and is then sent into the first feed path  530 . The separating pad  523  applies frictional force to the first sheet passing between the feed roller  522  and the separating pad  523 . Therefore, when the feed roller  522  sends several first sheets to the first feed path  530 , the separating pad  523  applies frictional force acting in a direction opposite to the conveying direction, to the first sheets other than the top first sheet (the first sheet which is in direct contact with the feed roller  522 ), to prevent conveyance of these redundant first sheets into the first feed path  530 . Consequently the first sheets are sent into the first feed path  530  one by one. 
     The cassette  300 , which is used as another sheet feeding source, includes a lift plate  305  configured to support the second sheet. The lift plate  305  inclines so as to lift up a leading edge of the second sheet in the cassette  300 . A pickup roller  311  is disposed above a downstream end of the lift plate  305 . The pickup roller  311  comes into contact with the leading edge of the second sheet lifted up by the lift plate  305 . Consequently the second sheet is sent from the cassette  300  to the downstream as the pickup roller  311  rotates. 
     A feed roller  312  and a separating roller  313  below the feed roller  312  are disposed at a downstream position of the pickup roller  311 . The pickup roller  311  sends the second sheet between the feed roller  312  and the separating roller  313 . The feed roller  312  rotates to send the second sheet further downstream. The separating roller  313 , on the other hand, rotates in a direction for returning the second sheet back to the cassette  300 . Therefore, when the pickup roller  311  sends several second sheets, the separating roller  313  pulls the second sheets other than the top second sheet (the second sheet which is in direct contact with the feed roller  312 ) back to the cassette  300 . Consequently the second sheets are sent to the second feeding path  310  one by one. 
     The sheets conveyed to the second feed path  310  are sent toward the resist roller pair  320  by the conveying roller pair  360  provided in the second feed path  310  with which the aforementioned return conveying path  350  joins together at an upstream position of the conveying roller pair  360  in the second feed path  310 . Therefore, the conveying roller pair  360  in the second feed path  310  similarly sends the sheets fed to the second feed path  310  via the return conveying path  350 , to the resist roller pair  320  as well. The first feed path  530  and the second feed path  310  joins together at the upstream position of the resist roller pair  320 . Thus, the resist roller pair  320  feeds the sheets conveyed through the first feed path  530  or the second feed path  310 , to the image forming portion  410 . 
     The image forming portion  410  comprises a yellow (Y) toner container  900 Y, magenta (M) toner container  900 M, cyan (C) toner container  900 C, and black (Bk) toner container  900 Bk. Developing devices  10 Y,  10 M,  10 C and  10 Bk corresponding to the YMCBk are disposed below these containers, respectively. The image forming portion  410  uses the toner contained in these toner containers  900 Y,  900 M,  900 C and  900 Bk to form an image on a sheet. 
     The image forming portion  410  comprises photosensitive drums  17  (photoreceptors on which latent images are formed by electrophotography) configured to bear toner images thereon. Photosensitive drums using amorphous silicon (a-Si) based materials may be used as the photosensitive drums  17 . The photosensitive drums  17  are supplied with the yellow, magenta, cyan and black toner from the toner containers  900 Y,  900 M,  900 C and  900 Bk, respectively. 
     A charger  16 , the developing device  10  ( 10 Y,  10 M,  10 C or  10 Bk), a transfer roller  19  and a cleaning device  18  are disposed on a circumference of the photosensitive drum  17 . The charger  16  uniformly charges the surface of the photosensitive drum  17 . An exposure unit  94  exposes the surfaces of the charged photosensitive drums  17  to light to form electrostatic latent images on the photosensitive drums  17 , respectively. The exposure unit  94  radiates laser beams based on, for example, image signals (signal with image information) from the external device. The developing devices  10 Y,  10 M,  10 C and  10 Bk use the toner supplied by the toner containers  900 Y,  900 M,  900 C and  900 Bk, to develop (visualize) the electrostatic latent images formed on the photosensitive drums  17 , respectively. The transfer roller  19  and the photosensitive drum  17  sandwich an intermediate transfer belt  921  to form a nip. The transfer roller  19  primarily transfers the toner image formed on the photosensitive drum  17  onto the intermediate transfer belt  921 . The cleaning device  18  cleans the circumferential surface of the photosensitive drum  17  after the transfer of the toner image. 
     The developing devices  10 Y,  10 M,  10 C and  10 Bk comprise developing housings  20 , respectively. The developing housing  20  may store two-component developer with magnetic carrier and toner. Stirring rollers  11  and  12  are disposed near a bottom of the developing housing  20 . The stirring rollers  11  and  12  extending parallel to each other rotate inside the developing housing  20 . 
     A developer circulation path is formed on an inner bottom surface of the developing housing  20 . The stirring rollers  11  and  12  are disposed in the circulation path. The developing housing  20  includes a partition  201  disposed between the stirring rollers  11  and  12 . The partition  201  stands upright from the bottom of the developing housing  20  to partially partition the circulation path. The circulation path surrounds the partition  201 . The two-component developer is stirred by the stirring rollers  11  and  12  and conveyed along the circulation path. 
     The toner is charged while the stirring rollers  11  and  12  stir and circulate the two-component developer in the developing housing  20 . The two-component developer on the stirring roller  11  is attracted by a magnetic roller  14  above the stirring roller  11 . The attracted two-component developer forms a magnetic brush (not shown) on the magnetic roller  14 . A doctor blade regulates thickness of the magnetic brush. A toner layer is formed on a developing roller  15  by potential difference between the magnetic roller  14  and the developing roller  15 . The electrostatic latent image on the photosensitive drum  17  is developed by the toner layer. 
     The exposure unit  94  comprises various optical equipments such as a light source, a polygon mirror, a reflective mirror and a polarizing mirror. The exposure unit  94  irradiates the circumferential surface of the photosensitive drum  17  provided in the image forming portion  410 , with the light based on the image signals to form the electrostatic latent image. 
     An intermediate transfer unit  92  includes the intermediate transfer belt  921 , a driving roller  922  and an idler  923 . The toner images formed by the photosensitive drums  17  are superimposed (primarily transferred) to the intermediate transfer belt  921 . The superimposed toner images are secondarily transferred by a secondary transfer part  98  to the sheet fed from the cassette  300  or the tray  510 . The driving roller  922  and the idler  923  to run the intermediate transfer belt  921  are rotatably supported by the housing  2 . 
     The sheet conveyed from the resist roller pair  320  is sent between the intermediate transfer belt  921  and a transfer roller  981  which configure the secondary transfer part  98 . Subsequently, the sheet bearing the toner image transferred by the secondary transfer part  98  is sent to the fixing portion  430 . 
     The fixing portion  430  comprises a heating roller  432  including a built-in heater  431 , and a pressure roller  433  compressed to the heating roller  432 . The sheet sent from the secondary transfer part  98  is delivered between the heating roller  432  and the pressure roller  433 . The toner on the sheet is melted by heat energy from the heating roller  432  and receives pressure from the pressure roller  433 . Consequently the toner image is fixed onto the sheet. The fixing portion  430  sends the sheet to the discharge portion  450  through the discharge conveying path  340  after fixing the toner images onto the sheet. 
     The discharge portion  450  comprises a discharge roller pair  451 . The discharge roller pair  451  bi-directionally rotates to accomplish the aforementioned switchback operation. 
       FIG. 3  is a side view showing the conveying mechanism  600  forming the first feed path  530 . The conveying mechanism  600  is described with reference to  FIGS. 2 and 3 . 
     The conveying mechanism  600  comprises a first conveying element  610  and a second conveying element  620  disposed below the first conveying element  610 . An upper surface of the second conveying element  620  along a lower surface of the first conveying element  610  at least partially defines the first feed path  530 . In the following description, the position of the second conveying element  620  where the upper surface of the second conveying element  620  extends along the lower surface of the first conveying element  610  is exemplified as a first position. The position of the second conveying element  620  farther away from the first conveying element  610  than the first position is exemplified as a second position. 
     The feeding assembly  520  described in the context of  FIG. 2  is formed at an upstream end of the first conveying element  610 . As described above, the feeding assembly  520  feeds the sheet to the first feed path  530  formed between the first conveying element  610  and the second conveying element  620 . 
     The second conveying element  620  confronting the first conveying element  610  forms the first feed path  530  in cooperation with the first conveying element  610 , as described above. The second conveying element  620  includes an upstream element  622  and a downstream element  621 . The upstream element  622  and the downstream element  621  are aligned along a feed direction in which the first sheet is fed from the feeding assembly  520 . The upstream element  622  and the downstream element  621  are pivotally connected to each other.  FIG. 3  shows a pin  624  configured to pivotally connect the upstream element  622  with the downstream element  621 . Instead of the pin  624 , an appropriate connecting member configured to pivotally connect the upstream element  622  with the downstream element  621  to each other may be used. A first boss  625  protrudes from a side surface of an upstream end of the upstream element  622 . A second boss  623  protrudes from a side surface of a downstream end of the downstream element  621 . 
       FIG. 4  is a perspective view of the second conveying element  620  connected to an inner wall of a side wall  25  of the housing  2 . The second conveying element  620  shown in  FIG. 4  is present in the first position. It should be noted that  FIG. 4  shows neither the first conveying element  610  nor the cassette  300 . The second conveying element  620  is further described with reference to  FIGS. 1 to 4 . 
     Depressed rails  640  are provided in an inner surface of left and right side walls  25  of the housing  2 , respectively. The rail  640  includes a first rail  641  configured to engage with the first bosses  625  protruding from left and right side surfaces of the upstream element  622 , respectively. The first rail  641  guides the upstream element  622  from the first position to the second position. The rail  640  further includes a second rail  642  configured to engage with the second boss  623  protruding from left and right side surfaces of the downstream element  621 , respectively. The second rail  642  guides the downstream element  621  from the first position to the second position. The rail  640  further includes a third rail  643  horizontally extending (a direction in which the cassette  300  is inserted or drawn out). The third rail  643  is connected to lower ends of the first rail  641  and the second rail  642 . The third rail  643  may be configured to guide the cassette  300  to be inserted into and drawn out from the housing  2 . The second conveying element  620  is guided by the first rail  641  and the second rail  642  and displaced from the first position to the second position. Thereafter, the second conveying element  620  is guided by the third rail  643  and is allowed to move in the direction of the insertion or drawing out of the cassette  300 . 
     The first rail  641  includes an upstream wall  644  inclining in an upstream direction from a point where the first position of the upstream element  622  is defined to a point where the second position is defined, as well as a downstream wall  645  inclining in a downstream direction from a point where the first position of the upstream element  622  is defined to a point where the second position is defined. The second rail  642  inclines in an upstream direction from the point where the first position of the downstream element  621  is defined to a point where the second position is defined along the inclined upstream wall  644  of the first rail  641 . 
       FIG. 5  is a perspective view showing the second conveying element  620  completely drawn out from the housing  2  of the image forming apparatus  1 . Operations performed on the second conveying element  620  are described with reference to  FIG. 1  and  FIGS. 3 to 5 . 
     After drawing out the cassette  300  from the housing  2 , a user may completely draw out the second conveying element  620  from the housing  2  as shown in  FIG. 5 . After removing the cassette  300  from the housing  2 , the user displaces the second conveying element  620  downward. When the upstream element  622  is displaced from the first position to the second position, the first boss  625  of the upstream element  622  guided by the upstream wall  644  of the first rail  641  is displaced downward while moving in the upstream direction. When the downstream element  621  is displaced from the first position to the second position, the second boss  623  of the downstream element  621  guided by the second rail  642  is displaced downward while moving in the upstream direction, as with the upstream element  622 . Subsequently, the user may draw out the second conveying element  620  existing in the second position from the housing  2  along the third rail  643 . Consequently sheets jammed in the first feed path  530  formed between the first conveying element  610  and the second conveying element  620  is moved to the outside of the housing  2  along with the second conveying element  620 . Alternatively the sheets jammed in the first feed path  530  are dropped into a space for accommodating the cassette  300 . Thus the user may efficiently remove the sheets jammed in the first feed path  530 . 
     After removing the sheet jammed in the first feed path  530 , the user may push the second conveying element  620  from the downstream element  621  into the housing  2 . The downstream element  621  is guided by the third rail  643  to horizontally moves in the housing  2 . Thereafter the downstream element  621  forms a corner with the upstream element  622  when the second boss  623  is transferred from a downstream end of the third rail  643  to the second rail  642 . After the second boss  623  reaches an upper end of the second rail  642 , the user may push the upstream element  622  upward. Consequently the first boss  625  of the upstream element  622  guided by the downstream wall  645  of the first rail  641  moves in the upstream direction while moving upward. When the first boss  625  reaches the upstream end of the first rail  641 , upper surfaces of the upstream element  622  and the downstream element  621  become substantially flush with each other. Consequently the second conveying element  620  reaching the first position forms the first feed path  530  in corporation with the first conveying element  610 . 
       FIG. 6  is a side view of the conveying mechanism  600  for schematically illustrating a positioning mechanism configured to position the second conveying element  620  in the first position.  FIG. 7  is a cross-sectional view for schematically illustrating the positioning mechanism configured to position the second conveying element  620  in the first position. The positioning mechanism is described with reference to  FIGS. 3 ,  4 ,  6  and  7 . 
     The conveying mechanism  600  has a positioning mechanism  630  configured to position the second conveying element  620  in the first position. The positioning mechanism  630  includes a substantially rectangular frame  631  attached to the side surface of the first conveying element  610 , a biasing member  632  buried in the upstream element  622 , and an engaging piece  633  attached to a tip of the biasing member  632 . An engaging hole  634  is formed in the frame  631 . In the present embodiment, a coil spring is used as the biasing member  632 . Alternatively, any member configured to protrude and retract the engaging piece  633  with respect to a side surface of the upstream element  622  may be used as the biasing member  632 . 
     When the downstream element  621  is in the first position, the upstream element  622  is disposed in the position where the upstream element  622  extends along the first conveying element  610  as described above. At this moment, the engaging piece  633  of the positioning mechanism  630  is inserted into the engaging hole  634 . Consequently the upstream element  622  and the downstream element  621  are positioned with respect to the first conveying element  610  and fixed at the first position. 
     When the user applies downward force to a handle  635  formed at an upstream edge of the upstream element  622 , the engaging piece  633  becomes buried in the upstream element  622 , so that the engaging piece  633  is disengaged from the engaging hole  634 . Thus the user may more easily form a space between the first conveying element  610  and the second conveying element  620 . Therefore, the sheets jammed in the conveying mechanism  600  may be easily removed. 
       FIG. 8  is a perspective view showing another structure of the rail  640 . It should be noted in the embodiment described hereinafter that the structure of the conveying mechanism  600  is substantially similar to the one described in the context of  FIGS. 3 to 7 . The rail  640  is described with reference to  FIGS. 4 and 8 . 
     The third rail  643  of the rail  640  shown in  FIG. 8  is divided into an upstream first section and a downstream second section. The first section is used for guiding the first boss  625  of the upstream element  622 . The second section is used for guiding the second boss  623  of the downstream element  621 . It should be noted in the present embodiment that engagement between the second boss  623  and the third rail  643  is deeper than engagement between the first boss  625  and the third rail  643 . 
       FIG. 9  is an enlarged perspective view around a border between the first section and the second section. The third rail  643  is further described with reference to  FIGS. 4 ,  8  and  9 . 
     As shown in  FIG. 9 , the second section of the third rail  643  may be formed deeper than the first section of the third rail  643 . Consequently a confining portion  646  configured to confine movement of the second boss  623  toward the first section is formed between the first section and the second section. Alternatively, any structure, shape or size for confining the movement of the second boss  623  such as a wall crossing the third rail  643 , a protrusion protruding inward of the third rail  643 , and a part where the width of the third rail  643  is reduced, may be used as the confining portion  646 . 
       FIG. 10  is a bottom view of the second conveying element  620  guided by the rail  640  described in the context of  FIGS. 8 and 9 . The second conveying element  620  is described with reference to  FIGS. 8 to 10 . 
     As shown in  FIG. 10 , the second boss  623  protruding from the side surface of the downstream element  621  is longer than the first boss  625  protruding from the side surface of the upstream element  622 . The difference X in protrusion amount between the first boss  625  and the second boss  623  protruding from the side surface of the second conveying element  620  is substantially equal to the difference in depth between the first section and the second section of the third rail  643 . 
       FIG. 11  is a perspective view showing the second conveying element  620  drawn out from the housing  2 . The movement of the second conveying element  620  is described with reference to  FIGS. 8 to 11 . 
     The second boss  623  moves from the second section toward the first section when a user draws out the second conveying element  620  from the housing  2  along the third rail  643 . When the second boss  623  reaches the upstream end of the second section, the second boss  623  becomes stuck at the confining portion  646 . Consequently the movement of the second conveying element  620  is confined. Thus the second conveying element  620  is partially drawn out from the housing  2 . 
       FIG. 12  is a perspective view showing the second conveying element  620  partially drawn out from the housing  2 . The second conveying element  620  is described with reference to  FIGS. 8 to 12 . 
     The upstream element  622  of the second conveying element  620  partially drawn out from the housing  2 , because of its weight, turns downward around the pin  624  exposed outside the housing  2 . Consequently a user may remove the sheets jammed in the housing  2  without interference with the upstream element  622 . Moreover, since the upstream element  622  does not protrude from the housing  2 , preferably, the user is less likely to apply excessive load to the second conveying element  620 . 
     As shown in  FIG. 12 , the downstream element  621  stays in the housing  2 . Therefore, after removing the sheet inside the housing  2 , the user may guide the second conveying element  620  to the third rail  643  so that the user places the second conveying element  620  into the housing  2 . Subsequently, the second conveying element  620  is guided by the first rail  641  and the second rail  642  and installed in the first position. The second conveying element  620  is then positioned by the positioning mechanism  630 . 
     In the present embodiment, the user may remove sheets from the front surface of the housing  2  as shown in  FIG. 12 . The left and right side walls  25  of the housing  2  may open. In this case, the user may remove the sheets from the lateral side of the conveying mechanism  600 . 
     The embodiment described above creates a sufficiently wide space between the first conveying element  610  and the second conveying element  620  in order to remove sheets. No complicated link mechanism is interposed between the first conveying element  610  and the second conveying element  620 . The third rail  643  guides not only the movement of the cassette  300  but also the movement of the second conveying element  620 . For this reason, no additional element for guiding the second conveying element  620  is required. Therefore, a smaller image forming apparatus is provided. In addition, since the feeding assembly  520  is not unnecessarily moved, the sheet feed settings is less likely to be changed, so that a failure in feeding the sheets is less likely to occur after removal of the sheets, which results in efficient sheet removal. 
     This application is based on Japanese Patent application serial No. 2010-039299 filed in Japan Patent Office on Feb. 24, 2010, the contents of which are hereby incorporated by reference. 
     Although the present invention has been fully described by way of example with reference to the accompanying drawings, it is to be understood that various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the scope of the present invention hereinafter defined, they should be construed as being included therein.