Abstract:
An image forming apparatus and a method of forming an image by the image forming apparatus that includes an image forming unit for forming an image onto a recording medium, a supply path for supplying a recording medium to the image forming unit, a first discharge path for discharging the recording medium, a return path, connected with the first discharge path, for returning the recording medium to the image forming unit, a second discharge path, substantially parallel with the supply path, for discharging the recording medium, and a guide member movable from a first position to create the first discharge path and the return path to a second position to create the second discharge path.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The invention relates to an image forming apparatus including a face-up sheet discharging function for discharging a single-sided printed sheet with a printed side thereof facing up, and a double-sided printing function for printing images on both sides of a recording medium. 
     2. Description of Related Art 
     A known image forming apparatus includes a double-sided printing function for printing an image on both sides of a recording medium. When the double-sided printing is performed in the image forming apparatus, the recording medium is discharged with a side of the recording medium which is printed first facing up and with the other side thereof printed next facing down. 
     For double-sided printing, a reverse feeding path is required in a rearward position of a fixing unit, to reversely feed the recording medium having an image printed on one side thereof, back to the image forming unit to form an image on the other side of the recording medium. 
     When an image is formed on a side of a special recording medium, such as thick paper like cardboard, it is required to feed and discharge such special recording medium, with the printed side thereof facing up, through a generally straight discharge path. If the discharge path has a turn, it is difficult to feed the recording medium of the cardboard through the turn, thus inhibiting the printing of an image on the cardboard. 
     To form a generally straight discharge path, a rear-side plate of the image forming apparatus disposed downstream of the fixing unit in a feeding direction of the recording medium is structured to open or close. When an image is formed on the special recording medium, such as cardboard, the rear-side plate of the image forming apparatus is opened to ensure the generally straight discharge path. The recording medium is discharged onto the rear-side plate after an image is printed thereon. 
     As described above, the reverse feeding path is required in the rearward position of the fixing unit for double-sided printing. In addition, a generally straight discharge path is required in a rearward position of the fixing unit for printing on the special recording medium, such as cardboard. Requirements of the reverse feeding path for double-sided printing and the generally straight discharge path for printing on the special recording medium cannot be satisfied at the same time. 
     SUMMARY OF THE INVENTION 
     The invention provides an image forming apparatus including a face-up sheet discharging function for discharging a single-sided printed sheet with a printed side thereof facing up, and a double-sided printing function for printing images on both sides of a recording medium. 
     In various embodiments of the image forming apparatus, the image forming apparatus comprises an image forming unit for forming an image onto a recording medium, a supply path for supplying a recording medium to the image forming unit, a first discharge path for discharging the recording medium, a return path, connected with the first discharge path, for returning the recording medium to the image forming unit, a second discharge path, substantially parallel with the supply path, for discharging the recording medium, and a guide member movable from a first position to create the first discharge path and the return path to a second position to create the second discharge path. 
     In various embodiments of a method of forming an image by an image forming apparatus, the method comprises the steps of supplying a recording medium to the image forming apparatus, forming the image onto the recording medium, and discharging the recording medium to either a first discharge path, a return path connected with the first discharge path or a second discharge path substantially parallel with the supply path, wherein a guide member is movable from a first position to create the first discharge path and the return path to a second position to create the second discharge path. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An exemplary embodiment of the invention will be described in detail with reference to the following figures wherein: 
     FIG. 1 is a side cross-sectional view of a laser beam printer according to an exemplary embodiment of the invention; 
     FIG. 2 is an enlarged view of a face-up sheet discharging unit of the laser beam printer shown in FIG. 1; 
     FIG. 3A is an enlarged top view of the face-up sheet discharging unit in an open state; and 
     FIG. 3B is a partially side view of the face-up sheet discharging unit shown in FIG.  3 A. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     An exemplary embodiment of the invention will be described in detail with reference to the figures. 
     Referring to FIG. 1, configurations of a laser beam printer  1  will be described below. As shown in FIG. 1, the laser beam printer  1  is provided in a case  2  with a feeder unit  4  that feeds sheets  3  of paper. The feeder unit  4  includes a sheet tray  43  that accommodates the sheets  3  therein, a sheet pressure plate  6  that is pressed by a spring (not shown) and pivots as shown by solid lines and dashed lines in FIG. 1, a pick-up roller  7 , a separation pad  8 , and a spring  10  that urges the separation pad  8 . The sheet pressure plate  6  presses the sheets  3  against the pick-up roller  7 . By the rotation of the pick-up roller  7 , the topmost sheet  3  is separated and picked up by the separation pad  8  and the pick-up roller  7 . The sheet  3  is fed at a predetermined timing. 
     First sheet supply rollers  59  are disposed downstream of the pick-up roller  7  in a sheet feeding direction. A pair of register rollers  44 ,  45  are rotatably supported downstream of the first sheet supply rollers  59  in the sheet feeding direction. The sheet  3 , picked up by the pick-up roller  7 , is fed by the first sheet supply rollers  59  to the pair of the register rollers  44 ,  45 , while making a U-turn. The register rollers  44 ,  45  feed the sheet  3  at a predetermined timing to an image transfer position between a photosensitive drum  21  and a transfer roller  26 . 
     The photosensitive drum  21  is formed of an organic photosensitive member including positively chargeable polycarbonate as a main ingredient. More specifically, the photosensitive drum  21  includes a tubular aluminum sleeve, as a main drum, and a hollow drum having an approximately 20-mm-thick light-sensitive layer including a light-sensitive resin dispersed in polycarbonate, formed on an outer surface of the tubular sleeve. The photosensitive drum  21  is rotatably supported in the case  2 , with the tubular sleeve electrically grounded. The photosensitive drum  21  is driven to rotate in the clockwise direction by a driving unit (not shown). 
     A charger  25  is a scorotron charger that uniformly and positively charges the surface of the photosensitive drum  21  by generating corona discharge from a tungsten wire. 
     A scanner unit  11  includes a laser beam generator (not shown) that generates a laser beam to form an electrostatic latent image on the photosensitive drum  21 , a polygon mirror (pentahedron mirror)  14  that is driven to spin lenses  15 ,  16 , and reflecting mirrors  17 ,  18 ,  19 . 
     In a developing unit  12 , a toner containing chamber  27  is formed in a case  36 . In the toner containing chamber  27 , an agitator  29  and a cleaner  39  are rotatably supported by a rotating shaft  28 . The toner containing chamber  27  contains a positively chargeable non-magnetic single component toner having electrical insulation capacity. In a side wall of the toner containing chamber  27 , which is disposed on an end side of the rotating shaft  28 , a light penetration window  40  is provided. The agitator  29  agitates the toner in the toner containing chamber  27  by the rotation thereof. The cleaner  39  wipes the window  40  as the cleaner  39  rotates. 
     Formed adjacent to the toner containing chamber  27  to a side of the photosensitive drum  21  is a developing chamber  23  that communicates with the toner containing chamber  27  through an opening  30 . A toner supply roller  24  and a developing roller  22  are rotatably supported in the developing chamber  23 . The toner on the developing roller  22  is thin layered with a thin-plate-like elastic blade  37  regulating a thickness thereof to a predetermined amount. 
     The developing roller  22  includes a core metal formed of a stainless steel, a tubular base that is formed of conductive silicone rubber including conductive fine carbon particles and provided on the core metal, and a layer which covers the tubular base with a resin material or a rubber material including fluorine. The tubular base of the developing roller  22  may be formed of conductive urethane rubber other than the conductive silicone rubber. 
     The blade  37  includes a supporting portion formed of iron or stainless steel, a plate spring formed of phosphor bronze or stainless steel, and a contact portion  38  formed of silicone rubber and provided at one end of the plate spring. 
     Positively chargeable non-magnetic single component toner contained in the toner containing chamber  27  includes toner particles formed of styrene-acrylic-based resin in a spherical shape using a suspension polymerizationm method, to which a known coloring material, such as a carbon black, and a charge controlling agent, such as nigrosine, triphenylmethane, and quaternary ammonium salt, are added. A toner particle size is approximately 6 to 10 mm with an average toner particle size of 8 mm. Furhtermore, silica is added to a surface of the toner particle. 
     The transfer roller  26  is rotatably supported. The transfer roller  26  is formed of a conductive foam material having elasticity, such as silicone rubber and urethane rubber. A voltage is applied to the transfer roller  26  to transfer the toner on the photosensitive drum  21  onto the sheet  3 . 
     A fixing unit  13  is provided downstream of a pressing portion where the photosensitive drum  21  and the transfer roller  26  are pressed against each other, in the sheet feeding direction. The fixing unit  13  includes a heat roller  32  and a pressure roller  31 . The toner transferred onto the sheet  3  is fixed thereon with the heat and pressure applied while being fed by the heat roller  32  and the pressure roller  31 . 
     A pair of second sheet supply rollers  33  disposed downstream of the heat roller  32  and the pressure roller  31  in the sheet feeding direction. A sheet guiding tray  60  is provided downstream of the second sheet supply rollers  33  in the sheet feeding direction. 
     As will be described below, the sheet guiding tray  60  is rotatably provided. When the sheet guiding tray  60  is in a position shown in FIG. 1, a discharge path  56  is formed to guide the sheet  3  fed by the second sheet supply rollers  33  to a face-down sheet discharging portion  35  therethrough. 
     A guide  61  is rotatably provided in the sheet guiding tray  60 . When the sheet guiding tray  60  is in a position shown in FIG. 1, the guide  61  protrudes over a surface of the sheet guiding tray  60  toward the fixing unit  13 . The guide  61  guides the sheet  3  fed by the second sheet supply rollers  33  to the face-down sheet discharging portion  35 . A plurality of the guides  61  are provided in the width direction of the sheet  3 , with a predetermined spacing therebetween. 
     Provided above the sheet guiding tray  60  is a pair of discharge rollers  34  that discharge the sheet  3  guided by the sheet guiding tray  60  onto the face-down sheet discharging portion  35 . 
     The sheet  3  is discharged onto the face-down sheet discharging portion  35  to face down a side of the sheet  3  having an image formed just before the sheet  3  is discharged. 
     When images are printed on both sides of the sheet  3 , the discharge rollers  34  are rotated opposite to the sheet feeding direction, before the sheet  3 , fed by the discharge rollers  34  toward the face-down sheet discharging portion  35 , is completely discharged onto the discharging portion  35 . Thus, the feeding direction of the sheet  3  is reversed. 
     A reverse feed guiding portion  62  is provided adjacent to the discharge rollers  34 . The sheet  3  is fed along the reverse feed guiding portion  62  into a reverse feeding path  63 . 
     The reverse feeding path  63  is defined by the sheet guiding tray  60  and a rear tray  64 . The rear tray  64  is rotatably provided, similar to the sheet guiding tray  60 . When the rear tray  64  is in a closed position as shown in FIG. 1, the sheet  3  fed into the reverse feeding path  63  is transferred downward to a reverse feeding unit. 
     The reverse feeding unit includes a reverse sheet feeding guide  52  and a plurality of pairs of reverse feeding rollers  55 . The reverse feeding unit conveys the sheet  3 , fed through the reverse feeding path  63 , to the register rollers  44 ,  45 . The sheet  3  is further fed to the pressing portion between the photosensitive drun  21  and the transfer roller  26 . 
     Image forming operations performed by the laser beam printer  1  according to the exemplary embodiment will be described below. 
     The surface of the photosensitive drum  21  is uniformly charged by the charger  25 . As the surface of the photosensitive drun  21  is selectively exposed to a laser beam modulated in accordance with image information emitted from the scanner unit  11 , an electrostatic latent image is formed on the surface of the drum  21 . The electrostatic latent image is made visible by the toner on the developing roller  22 . The visible toner image formed on the photosensitive drum  21  is carried by the photosensitive drum  21  to an image transfer position. The sheet  3  is supplied to the image transfer position, via the first sheet supply rollers  59  and the register rollers  44 ,  45 . The visible toner image on the photosensitive drum  21  is transferred onto the sheet  3  by a transfer bias applied by the transfer roller  26 . The toner remaining on the photosensitive drum  21  after an image transfer, is collected by the developing roller  22  into the developing chamber  23 . 
     The sheet  3 , fed to the fixing unit  13 , is held and passed between the heat roller  32  and the pressure roller  31 . Heat and pressure fuse the toner to the sheet  3 , to fix the image on the sheet  3 . Thereafter, the sheet  3  is conveyed by a pair of the second sheet supply rollers  33 , the guide  61 , the sheet guiding tray  60 , and the discharge rollers  34 , to the face-down sheet discharging portion  35  while making an U-turn. Thus, the image is formed on one side of the sheet  3 . 
     When images are formed on both sides of the sheet  3 , the sheet  3  is held between the discharge rollers  34  after an image is formed on one side thereof. The sheet  3 , held between the discharge rollers  34 , is reversely fed by the rotation of the discharge rollers  34  in the opposite direction, along the reverse feed guiding portion  62  into the reverse feeding path  63  defined by the sheet guiding tray  60  and the rear tray  64 . The sheet  3  fed through the reverse feeding path  63  is guided to the reverse feeding rollers  55  by the reverse sheet feeding guide  52 . The reverse feeding rollers  55  guide the sheet  3  to the register rollers  44 ,  45 . 
     When the sheet  3  is reversely fed between the photosensitive drum  21  and the transfer roller  26 , a side of the sheet  3  having an image formed thereon faces the transfer roller  26  and the other side having no image faces the photosensitive drum  21 . An image is formed, as described above, on the side of the sheet  3  facing the photosensitive drum  21 . This side of the sheet  3  faces down when discharged onto the face-down sheet discharging portion  35 . The sheet  3  having images formed on both sides thereof is discharged onto the face-down sheet discharging portion  35 . Thus, double-sided image forming operations are finished. 
     In addition to the single-sided or double-sided image forming with the face-down sheet discharge, the single-sided image forming with a face-up sheet discharge may be performed in the exemplary embodiment. Structures that enable the single-sided image forming with the face-up sheet discharge will be described below. 
     A manual insertion sheet tray  57  is provided on a front portion of the laser beam printer  1 . The manual insertion sheet tray  57  is pivotally provided to close, or open as illustrated in FIG.  1 . To form an image on a side of a special sheet, such as cardboard or an overhead transparency film that is unsuitable for a curved or U-turned feeding path and to discharge such special sheet with the printed side thereof facing up, the sheet  3  is placed on the manual insertion sheet tray  57 , that is opened as shown in FIG. 1, to supply the sheet  3  therefrom. 
     Provided on an opposite side of the manual insertion sheet tray  57  are the rear tray  64  and the sheet guiding tray  60  that pivot about lower ends thereof. 
     As shown in FIGS. 2-3B, the rear tray  64  includes a main tray  64 A and an extendable tray  64 B. The extendable tray  64   b  is provided to slide over the main tray  64 A. By extending the extendable tray  64 B, a sheet having a large size can be placed on the rear tray  64 . 
     The rear tray  64  is integrally formed with a link plate  70  having an elongated hole  70 A formed thereon, at each side of the main tray  64 A. A link pin  71  that engages in the elongated hole  70 A, is formed at each side of the sheet guiding tray  60 . As the rear tray  64  pivots about the lower end thereof, the link pins  71  slide within the elongated holes  70 A. Accordingly, the sheet guiding tray  60  is turned. 
     As shown in FIG. 3A and 3B, ribs  72  are provided, like teeth of a comb, with a predetermined spacing therebetween on the main tray  64 A of the rear tray  64 . Similarly, the sheet guiding tray  60  has ribs  73  provided, like teeth of a comb, with a predetermined spacing therebetween. The sheet guiding tray  60  also has ribs  74  on an opposite side of the ribs  73 . The ribs  74  are provided, like teeth of a comb, with a predetermined spacing therebetween. 
     When the rear tray  64  and the sheet guiding tray  60  are closed as shown in FIG. 1, parts of the ribs  73  guide the sheet  3  passing through the discharge path  56 , from the second sheet supply rollers  33  to the discharge rollers  34 . The ribs  72  and  74  guide the sheet  3  reversely fed through the reverse feeding path  63  for double-sided printing, to sandwich the sheet  3  between the ribs  72  and  74 . 
     When the rear tray  64  and the sheet guiding tray  60  are in an open state as shown in FIG. 2, the ribs  73  and  72  guide the sheet  3  fed by the second sheet supply rollers  33 . The rear tray  64  and the sheet guiding tray  60  are positioned to keep the sheet  3  substantially flat with the ribs  72  and  73 . 
     The ribs  74  of the sheet guiding tray  60  are disposed to interpose the ribs  72  of the rear tray  64 , as shown FIG.  3 B. Therefore, when the rear tray  64  and the sheet guiding tray  60  are open, the ribs  74  and  72  do not interfere with each other. 
     As described above, the sheet guiding tray  60  is provided with the guide  61 . The guide  61  is urged by a spring (not shown) in a direction such that the guide  61  protrudes over the sheet guiding tray  60 , as shown in FIG.  1 . As shown in FIG. 2, the guide  61  has a lever  61 A to allow the guide  61  to rotate. When the lever  61 A makes contact with a part of the rear tray  64 , the lever  61 A rotates and is situated inward from the surface of the sheet guiding tray  60 , as shown in FIG.  2 . Therefore, the discharged sheet  3  may be placed substantially flat on the rear tray  64  and the sheet guiding tray  60 , without being blocked by the guide  61 , as shown in FIG.  2 . 
     As the rear tray  64  is open, as shown in FIG. 2, the sheet guiding tray  60  correspondingly opens. In this state, the link plates  70  extend upwardly from a sheet guiding surface, so that the sheet  3  is discharged onto the sheet guiding tray  60  while being restricted with respect to a width direction thereof by the link plates  70 . 
     As shown in FIG. 2, an end of the sheet guiding tray  60  is disposed adjacent to an outer wall  75  of the fixing unit  13 . With this structure, the rear edge of the sheet discharged onto the rear tray  64  and the sheet guiding tray  60  is aligned by the outer wall  75 . 
     With the above-described structures according to the exemplary embodiment, a face-up discharge path is formed by opening the rear tray  64  and the sheet guiding tray  60 , as shown in FIG.  2 . Thus, a generally straight discharge path is formed from the manual insertion sheet tray  57  to the sheet guiding tray  60  and the rear tray  64 , for printing on thick paper, such as cardboard, or an overhead transparency film that is unsuitable for curved or U-turned feeding path. 
     When an image is formed on, for example, cardboard, the cardboard is inserted into the manual insertion sheet tray  57 . The cardboard is fed by the first sheet supply rollers  59  and the register rollers  44 ,  45  between the photosensitive drum  21  and the transfer roller  26  where the toner on the photosensitive drum  21  is transferred onto the cardboard. When the cardboard, having the toner transferred thereon, passes through the fixing unit  13 , the toner is fixed onto the cardboard. Thus, the image is formed on the cardboard. The cardboard having the image formed thereon is fed by the second sheet supply rollers  33  and discharged onto the rear tray  64  and the sheet guiding tray  60 , with the printed side of the cardboard facing up. Because the cardboard is fed through a generally straight feeding path, the cardboard is not bent or creased while being conveyed, so that an image may be preferably formed on the cardboard. When the rear tray  64  and the sheet guiding tray  60  are open as shown in FIG. 2, the second sheet supply rollers  33  function as rollers to discharge the sheet  3  onto the rear tray  64  and the sheet guiding tray  60 . When the rear tray  64  and the sheet guiding tray  60  are closed as shown in FIG. 1, the second sheet supply rollers  33  function as rollers to discharge the sheet  3  onto the face-down sheet discharging portion  35 . 
     When the rear tray  64  and the sheet guiding tray  60  are closed as shown in FIG. 1, the reverse feeding path  63  is formed in an area that is defined by the rear tray  64  and the sheet guiding tray  60 . This structure also enables the double-sided printing. 
     In the exemplary embodiment, the rear tray  64  defines the reverse feeding path  63  and serves as a face-up sheet discharging unit. In addition, by simply opening or closing the rear tray  64  and the sheet guiding tray  60 , the double-sided printing mechanism and a face-up sheet discharging mechanism are compatibly provided. 
     When the rear tray  64  and the sheet guiding tray  60  are open as shown in FIG. 2, access to the fixing unit  13  becomes easier, so that maintenance of the fixing unit  13  or clearing paper jams may be easily performed. 
     While the invention has been described with reference to the exemplary embodiment, it is to be understood that the invention is not restricted to the particular forms shown in the foregoing exemplary embodiment. Various modifications and alterations can be made thereto without departing from the scope of the invention.