Abstract:
An image forming apparatus to perform duplex printing, including a duplex printing unit selectively detached and mounted with respect to a main body thereof, a pivotable duplex printing unit cover to form a document circulation path for a recording medium, a pivotable guide, and a door openably mounted to the main body to correspond to the guide.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of Korean Application No. 2005-45426, filed May 30, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the invention  
         [0003]     An aspect of the present invention relates to an image forming apparatus. More particularly, an aspect of the present invention relates to an image forming apparatus for duplex printing, capable of relatively efficiently removing jam of a recording medium.  
         [0004]     2. Description of the Related Art  
         [0005]     General image forming apparatuses such as a copier, a printer, and a facsimile comprise an image carrying medium usually implemented by a photoconductive drum, an electrostatic-latent-image formation unit which forms an electrostatic latent image on the photoconductive drum, a developing unit which develops the electrostatic latent image formed on the photoconductive drum to a visible image by a developer, a transfer unit which transfers the visible image formed on the photoconductive image onto an intermediate transfer belt or onto a recording medium, and a fixing unit which fuses permanently the image transferred onto the recording medium by heat and pressure. With the above structure, image formation processes including formation of the electrostatic latent image, developing, transfer, and fusing are repeatedly performed.  
         [0006]     Generally, such image forming apparatuses are equipped with a duplex printing unit capable of printing desired information respectively and sequentially on both sides of one sheet of the recording medium.  
         [0007]      FIG. 1  schematically shows the structure of an image forming apparatus having a conventional duplex printing unit, as disclosed in U.S. Patent Publication No. 2002/0114634 A1 (Aug. 22, 2002). Referring to  FIG. 1 , the image forming apparatus comprises a main body  100  including therein an image formation unit  2 , and a duplex printing unit  200  detachably mounted to the main body  100 .  
         [0008]     The duplex printing unit  200  comprises a door panel  210  and a cover panel  220 , which face each other to form a document returning path  201  therebetween and which rotate relative to each other.  
         [0009]     According to the above structure, the recording medium bearing an image fixed on one side thereof through a fixing unit  3  is reversed and returned through the document returning path  201  and enters the image formation unit  2  again.  
         [0010]     The duplex printing unit  200  is separably formed from the main body  100  as aforementioned, so that when the recording medium becomes jammed (hereinafter, referred to as ‘paper jam’), the recording medium may be easily removed.  
         [0011]     However, in the above-structured conventional image forming apparatus, if the paper jam occurs before the recording medium enters the duplex printing unit  200 , especially if the paper jam occurs at the fixing unit  3 , a correction of the paper jam becomes relatively difficult because the main body  100  may not be opened enough to draw out the jammed recording medium.  
       SUMMARY OF THE INVENTION  
       [0012]     An aspect of the present invention is to solve at least the above problems and/or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of the present invention is to provide an image forming apparatus for duplex printing, capable of efficiently removing a jam of a recording medium by improving the structure of a duplex printing unit.  
         [0013]     In order to achieve the above-described aspects of the present invention, there is provided an image forming apparatus to perform duplex printing, comprising a main body including a recording medium supply unit, an image formation unit that produces an image on a recording medium supplied through the recording medium supply unit, a fixing unit that fuses the image on the recording medium, and a discharge unit that ejects the recording medium where the image is fused by the fixing unit; a duplex printing unit removably mounted to the main body to reinsert the recording medium, on which the image is fused onto one side thereof, into the image formation unit; and a door openably mounted to one side of the main body to correspond in position to a position of the duplex printing unit, wherein the duplex printing unit comprises, a duplex printing unit cover pivotably mounted by one end thereof, a first guide pivotably mounted by one end thereof to direct the duplex printing unit cover, and a second guide to convey the recording medium, as conveyed to a document circulation path formed between the duplex printing unit cover and the first guide, to the image formation unit.  
         [0014]     The second guide comprises a first document reversing path to convey by a predetermined distance the recording medium, having been conveyed through the document circulation path; and a second document reversing path to reinsert the recording medium, having been conveyed by the predetermined distance along the first document circulation path, in the image formation unit.  
         [0015]     The document feeding path formed between the image formation unit and the fixing unit is substantially parallel with a bottom of the main body, the document circulation path formed by the duplex printing unit cover and the first and the second guides are substantially perpendicular to the document feeding path formed by the image formation unit and the fixing unit, and the first and the second document reversing paths are substantially parallel with the document feeding path formed by the image formation unit and the fixing unit.  
         [0016]     The recording medium supply unit is disposed at a lower part of the main body, and the second guide is disposed at a lower part of the recording medium supply unit.  
         [0017]     The first guide comprises a lower guide formed at the second guide; and an upper guide pivotably mounted to the lower guide.  
         [0018]     The image forming apparatus may further comprise a reversing roller at a converging point of the first and the second document reversing paths to reverse an advancing direction of the recording medium.  
         [0019]     The image forming apparatus may further comprise a reverse sensor at an upper stream of the converging point of the first and the second document reversing paths to detect a reversing time point of the recording medium.  
         [0020]     The image forming apparatus may further comprise a cooling fan in the document circulation path formed proximate to the duplex printing unit cover and the first and the second guides and/or adjacent to the first and the second document reversing paths in order to reduce a temperature of the recording medium.  
         [0021]     The cooling fan is disposed at the converging point of the first and the second document reversing paths.  
         [0022]     The second guide has an air suction port at one side near the converging point of the first and the second document reversing paths to draw in external air, and an air exhaust port at the opposite side to discharge the external air.  
         [0023]     According to the above-described image forming apparatus to perform duplex printing, since the duplex printing unit cover and the guides are configured rotatably, jam of the recording medium may be relatively easily removed by simply opening the duplex printing unit cover and the upper guide even before entering the duplex printing unit.  
         [0024]     Therefore, paper jam generated in the main body may be efficiently removed without having to totally separating the duplex printing unit. As a result, systemic errors generated by misassembling of the duplex printing unit after separation may be prevented.  
         [0025]     Additional and/or other aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]     These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:  
         [0027]      FIG. 1  illustrates the structure of a conventional image forming apparatus;  
         [0028]      FIG. 2  is a sectional view illustrating the structure of an image forming apparatus according to an embodiment of the present invention;  
         [0029]      FIG. 3  is a perspective view illustrating a duplex printing unit applied to the image forming apparatus according to an embodiment of the present invention; and  
         [0030]      FIG. 4  is a perspective view showing another side of  FIG. 3 .  
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0031]     Reference will now be made in detail to the present embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures.  
         [0032]      FIG. 2  schematically illustrates the operation of an image forming apparatus according to an embodiment of the present invention. According to  FIG. 2 , an image forming apparatus  300 , according to an embodiment of the present invention, comprises a recording medium supply unit  310 , an image formation unit  330 , a fixing unit  350 , a discharge unit  370 , and a duplex printing unit  390 .  
         [0033]     The recording medium supply unit  310  comprises a recording medium supply cassette  311 , in which plural sheets of recording medium  312  are stacked, a pickup roller  313  to pick up the recording medium  312  from the recording medium supply cassette  311  sheet by sheet, and a plurality of supply rollers  315  and  316  to convey the picked-up recording medium  312  to the image formation unit  330 .  
         [0034]     The image formation unit  330  produces a predetermined image on the recording medium fed from the recording medium supply unit  310 . For this purpose, the image formation unit  330  comprises a laser scanning unit  331 , a photoconductive drum  333  where an electrostatic latent image is formed by a light projected by the laser scanning unit  331 , a developing roller  335  to develop the electrostatic latent image formed on the photoconductive drum  333  into a visible image using developer, and a transfer roller  337  to transfer the visible image developed by the developing roller  335  onto the recording medium  312 .  
         [0035]     The fixing unit  350  fuses the image transferred on the recording medium  312  through the image formation unit  330  by heat and pressure. The fixing unit  350  comprises a heating roller  351  and a pressing roller  353 .  
         [0036]     The discharge unit  370  ejects the recording medium  312  bearing thereon the image fused by the fixing unit  350  to the outside of the main body  301 . To this end, the discharge unit  370  comprises a plurality of discharge rollers  371  and  373 .  
         [0037]     The image formation unit  330  and the fixing unit  350  are positioned horizontally and substantially parallel with respect to a bottom  301   a  of the main body  301 , such that a document feeding path P 1 , formed by the image formation unit  330  and the fixing unit  350 , is also substantially parallel with the bottom  301   a  of the main body  301 . Accordingly, a path along which the recording medium  312  travels through the recording medium supply cassette  311 , the image formation unit  330 , the fixing unit  350  and the discharge unit  370  up to the outside of the main body  301 , substantially forms an “S” shape.  
         [0038]     The duplex printing unit  390 , as a single module, is selectively mountable to and separable from the main body  301 . The duplex printing unit  390  forms a document circulation path P 2 , through which the recording medium  312  having an image already fixed on one side thereof is circulated through the fixing unit  350 , between a printing cover  391  and a first guide  393 . The printing cover  391  and the first guide  393  face each other. In addition, the duplex printing unit  390  further comprises a second guide  395 , to reinsert the recording medium  312  when the recording medium is returned through the document circulation path P 2  into the image formation unit  330 , in contact with a lower part of the main body  301 .  
         [0039]     The duplex printing unit cover  391  and the first guide  393  are each rotatably supported at respective ends thereof by hinge shafts  401  and  403 , respectively. When passing by the hinge shaft  401  and  403 , the document circulation path P 2  is arranged substantially perpendicularly to the bottom  301   a  of the main body  301 .  
         [0040]     A door  303  is pivotably mounted at one side of the main body  301 , corresponding to the first guide  393 , in order to prevent the inside of the main body  301  from being exposed to the outside when using the image forming apparatus  300  with the duplex printing unit  390  separated therefrom.  
         [0041]     The first guide  393  is divided into a lower guide  393   a  formed at an upper surface of the second guide  395 , and an upper guide  393   b  pivotably mounted to the lower guide  393   a  by the hinge shaft  403 .  
         [0042]     The second guide  395  comprises a first document reversing path P 3  through which the recording medium  312  having been conveyed through the document circulation path P 2  by a predetermined distance is conveyed, and a second document reversing path P 4  to reverse an advancing direction of a following end of the recording medium  312  that has been conveyed by the predetermined distance along the first document reversing path P 3  so as to reinsert the recording medium  312  into the image forming unit  330 . The second guide  395  is laterally formed in contact with the lower part of the main body  301 . The first and the second document reversing paths P 3  and P 4  are substantially parallel with the bottom  301   a  of the main body  301 .  
         [0043]     Consequently, the recording medium  312  is conveyed along an oval track which is longer in a lateral direction, sequentially through the document circulation path P 2 , the first and the second document reversing paths P 3  and P 4 , and then the document feeding path P 1 .  
         [0044]     The first guide  393  is provided with first and second feeding rollers  411   a  and  413   a  while the duplex printing unit cover  391  is correspondingly provided with first and second backup rollers  411   b  and  413   b.  A reversing roller  415   a  to reverse the advancing direction of the recording medium  312  and a reverse backup roller  415   b  are mounted at a converging point N of the first and the second document reversing paths P 3  and P 4 . Further, a reverse sensor  431  is mounted at an upper stream of the reversing roller  415   a  and the reverse backup roller  415   b  to detect a reversing time point of the recording medium  312 .  
         [0045]     A plurality of returning rollers  417   a  and return backup rollers  417   b  that correspond to the returning rollers  417   a  are provided on the first and the second document reversing paths P 3  and P 4 .  
         [0046]     According to an embodiment of the invention, a cooling fan  451  to cool the recording medium  312  is provided adjacent to the first and the second document reversing paths P 3  and P 4  in order to prevent a deterioration of a transferring operation by heat from the recording medium  312 . More specifically, the cooling fan  451  is disposed near a converging point N of the first and the second document reversing paths P 3  and P 4  so that the recording medium  312  may be continuously supplied with a cooling air flow.  
         [0047]     As shown in  FIG. 2 , a recording medium reversing unit  461  selects between a discharge path P 5  and the document circulation path P 2 , and a plurality of sensors  432  to  435  detects the recording medium  312  being conveyed to thereby check for an occurrence of a jam of the recording medium  312  (hereinafter, referred to as ‘paper jam’).  
         [0048]     The rollers provided in the duplex printing unit  390 , such as the first and the second feeding rollers  411   a  and  413   a,  the reversing roller  415   a,  and the returning roller  417   a  are transmitted with a power of a motor  491  through a belt pulley  471  or a gear train (not shown).  
         [0049]     Hereinbelow, the operation of the duplex printing unit cover  391  and the first guide  393  will be described in greater detail with reference to  FIGS. 3 and 4 .  FIG. 3  is a perspective view of the duplex printing unit according to an embodiment of the present invention, and  FIG. 4  is a perspective view showing another side of  FIG. 3 .  
         [0050]     Referring to  FIGS. 3 and 4 , the duplex printing unit cover  391  is pivotably connected to one side of the second guide  395 . A plurality of guide ribs  391   c  are vertically formed within the duplex printing unit cover  391 . The first guide  393  comprises the upper guide  393   b  and the lower guide  393   a  respectively having a plurality of ribs, that is, lower ribs  393   a ′ and upper ribs  393   b ′ corresponding to the guide ribs  391   c  of the duplex printing unit cover  391 . The lower guide  393   a  is integrally formed with an upper part of the second guide  395 . The upper guide  393   b  is pivotably mounted to the lower guide  393   a  by the hinge shaft  403 . However, the upper guide  393   b  may pivot on other parts using a dedicated member, instead of on the lower guide  393   a.    
         [0051]     Regarding the relative operational structure between the duplex printing unit cover  391  and the first guide  393   a,  as shown in  FIGS. 3 and 4 , after the duplex printing unit cover  391  is opened, the upper guide  393   b  may also be opened. Alternatively, the upper guide  393   b  may be opened in association with the duplex printing unit cover  391 . However, according to an embodiment of the invention the duplex printing unit cover  391  may be opened independently.  
         [0052]     The cooling fan  451  is provided at the converging point N of the first and the second document reversing paths P 3  and P 4  of the second guide  395 , as shown in  FIG. 2 . An air suction port  395   a  through which external air is drawn in is formed on one side of the second guide  395 , whereas an air exhaust port  395   b  is formed on the opposite side of the air inhaling hole  395   a,  of the second guide  35 , as shown in  FIG. 4 .  
         [0053]     Hereinbelow, processes of forming an image will be explained. Operations for simple printing will be described first. The recording medium  312 , having been picked up by the pickup roller  201  from the recording medium supply cassette  311 , is fed to the image formation unit  330  by the supply rollers  315  and  316 . A toner image is transferred on one side of the fed recording medium  312  by the photoconductive drum  333  and the transfer roller  337 . The transferred toner image is fused on the recording medium  312  by the heating roller  351  and the pressing roller  353  of the fixing unit  350 . Then, the recording medium  312 , having had a desired image formed thereon, is discharged to the outside of the main body  301  through the discharge unit  370 . Here, the recording medium reversing unit  461  restricts the advancing direction of the recording medium  312  to the discharge path P 5 .  
         [0054]     Next, operations for duplex printing will be described. Upon a setup of a duplex printing mode, the recording medium  312 , having been passed through the simple printing processes, enters the document circulation path P 2  formed between the duplex printing unit cover  391  and the first guide  393 , as a result of being restricted by the recording medium reversing unit  461 . The recording medium  312  is then conveyed by the first and the second feeding rollers  411   a  and  413   a  to the reversing roller  415   a.  Since high temperature of the recording medium  312  heat may cause a deterioration of an efficiency of the transferring operation, the cooling fan  451  is driven to reduce a temperature of the recording medium  312 . Being disposed at the converging point N of the first and the second document reversing paths P 3  and P 4 , the cooling fan  451  is positioned to be able to blow the external air to the first and the second document reversing paths P 3  and P 4  so as to improve cooling efficiency.  
         [0055]     The recording medium  312 , having been conveyed to the reversing roller  415   a,  is moved along the first document reversing path P 3  of the second guide by the reversing roller  415   a  by a predetermined distance. As the following end of the recording medium  312  advances beyond a sensing range of the reverse sensor  431  by being continuously moved along the first document reversing path P 3 , the motor  491  rotates backwards so as to convey the following end of the recording medium  312  to the second document reversing path P 4 . As the advancing direction of the recording medium  312  is reversed at this point, the image-printed side of the recording medium  312  is directed upward with respect to  FIG. 2 .  
         [0056]     The recording medium  312 , having been conveyed to the second document reversing path P 4 , is then fed by the plurality of returning rollers  417   b  back to the image formation unit  330 . Then the recording medium  312 , having been conveyed into the main body  301 , repeats the above-described image forming processes to complete the duplex printing.  
         [0057]     Now, operations to correct a paper jam occurring especially near the duplex printing unit  390  will be explained. First, operations to remove the paper jam generated before the recording medium  312  enters the document circulation path P 2  of the duplex printing unit  390  will be described. The duplex printing unit cover  391  and the upper guide  393   b  are opened sequentially. The door  303  of the main body  301  is then opened. In this state, the recording medium  312 , jammed in the fixing unit  350 , for example, may be drawn out. After the jammed recording medium  312  is removed, the door  303 , the upper guide  393   b  and the duplex printing unit  391  may be closed in the opposite order as before.  
         [0058]     If the paper jam is generated in the document circulation path P 2  between the duplex printing unit  391  and the first guide  393 , the recording medium  312  may be drawn out by opening only the duplex printing unit cover  391 .  
         [0059]     Although the document feeding path P 1 , formed by the image formation unit  330  and the fixing unit  350  is horizontally arranged in this exemplary embodiment, the present invention does not limit the structure so. It will be sure understood that the present invention may be applied in the conventional image forming apparatus ( FIG. 1 ) where the image formation unit and the fixing unit are vertically arranged, with a different configuration of the second guide  395  and the first and the second document reversing paths P 3  and P 4 .  
         [0060]     Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.