Patent Publication Number: US-11649129-B2

Title: Sheet discharge apparatus and image forming apparatus

Description:
BACKGROUND 
     Field 
     The present disclosure relates to a sheet discharge apparatus that discharges sheets and an image forming apparatus including the same. 
     Description of the Related Art 
     Image forming apparatuses, such as a printer, a copying machine, and a multi-functional machine, include a sheet discharge apparatus that discharges sheets on which images are formed outside the apparatus main body. In many cases, the sheet discharge apparatus includes a discharge roller pair at an opening (discharge port) of the apparatus main body. The sheet discharge apparatus nips and conveys a sheet with the discharge roller pair to discharge the sheet onto a discharge tray. At that time, the trailing end of the discharged sheet can lean on the vicinity of the discharge port (hereinafter referred to as “trailing-end leaning”). If the trailing-end leaning occurs, the leaning sheet can block the discharge port to obstruct the discharge of the following sheet or disorder the sheets stacked on the discharge tray. 
     Japanese Patent Laid-Open No. 2006-306536 discloses a sheet discharge apparatus including a first flat for detecting that the sheets loaded on a discharge tray reaches a predetermined height (a full-loaded state) and a second flag for detecting a sheet leaning on the discharge port. The second flag comes into contact with the sheet at a position closer to the discharge roller than the first flag. These flags are operably connected via a stopper. The sheet discharge apparatus is configured to detect that at least one of the flags has rotated more than a predetermined angle with a photo-interrupter. 
     However, the apparatus disclosed in Japanese Patent Laid-Open No. 2006-306536 is configured to raise the second flag together with the first flag as a result of the sheet being discharged by the discharge roller pressing the first flag. In other words, the first flag presses the sheet downward at a position farther from the discharge roller than the second flag, and the weight of the second flag acts on the sheet via the first flag. This can cause the sheet to be pressed downward at a position distant from the discharge roller, with the trailing end of the sheet immediately after being discharged from the discharge roller left in the vicinity of the discharge roller, so that the sheet is curved, resulting in sufficient reduction of trailing-end leaning. 
     SUMMARY 
     The present disclosure provides a sheet discharge apparatus configured to electively reduce occurrence of trailing-end leaning and an image forming apparatus including the same. 
     According to an aspect of the present disclosure, a sheet discharge apparatus includes a discharge unit configured to nip a sheet and discharge the sheet in a sheet discharge direction, a sheet support unit configured to support the sheet discharged from the discharge unit, a rotation member having a first abutting portion positioned above the sheet support unit, wherein the rotation member is configured to rotate when the first abutting portion is pressed by the sheet, a detection unit configured to detect a position of the rotation member, and a pressing member having a second abutting portion configured to abut against the sheet at a position downstream from a position at which the discharge unit nips the sheet and upstream from the first abutting portion in the sheet discharge direction, wherein the pressing member is provided rotatably independent of the rotation member and presses the sheet discharged from the discharge unit downward using the second abutting portion, regardless of a position of the rotation member. 
     Further features of the present disclosure 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 of an image forming apparatus according to a first embodiment of the present disclosure. 
         FIG.  2    is a perspective view of a sheet discharge unit according to the first embodiment. 
         FIG.  3    is a side view of the sheet discharge unit according to the first embodiment. 
         FIG.  4    is a cross-sectional view of the sheet discharge unit according to the first embodiment. 
         FIG.  5    is a cross-sectional view of the sheet discharge unit according to the first embodiment during execution of a sheet discharge operation. 
         FIG.  6    is a cross-sectional view of the sheet discharge unit according to the first embodiment during execution of the sheet discharge operation. 
         FIG.  7    is a cross-sectional view of the sheet discharge unit according to the first embodiment during execution of the sheet discharge operation. 
         FIG.  8    is a perspective view of a sheet discharge unit according to a second embodiment of the present disclosure. 
         FIG.  9    is a side view of the sheet discharge unit according to the second embodiment. 
         FIG.  10    is a cross-sectional view of the sheet discharge unit according to the second embodiment. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Embodiments of the present disclosure will be described hereinbelow with reference to the drawings. 
     First Embodiment 
       FIG.  1    is a schematic diagram illustrating a cross-sectional configuration of an image forming apparatus  100  according to a first embodiment. The image forming apparatus  100  forms an image on a sheet S used as a printing medium based on image information input from an external PC or image information scanned from an original. Examples of the sheet S include paper, such as plain paper and cardboard, plastic film, such as a sheet for an overhead projector, sheets of special shapes, such as envelopes and index paper, and cloth. 
     The apparatus main body  101  of the image forming apparatus  100  houses an electrophotographic image forming section  102 . The image forming section  102  is a so-called intermediate transfer type tandem electrophotographic unit in which four image forming units  140  that form toner images of four colors of yellow (Y), magenta (M), cyan (C), and black (Bk) are disposed along an intermediate transfer belt  145 . 
     The image forming section  102  includes the image forming units  140 , the intermediate transfer belt  145 , an inner secondary transfer roller  131 , and an outer secondary transfer roller  132 . The intermediate transfer belt  145  functions as an image bearing member (an intermediate transfer member) of the present embodiment. The outer secondary transfer roller  132  in the present embodiment functions as a transfer unit that transfers toner images from the image bearing member to a printing medium. 
     An image forming process performed by the image forming section  102 , which is an image forming unit of the present embodiment. Each image forming unit  140  includes a photosensitive drum  141 , which is an electrophotographic photosensitive member, a developing unit  143 , and a primary transfer unit  144 . The photosensitive drum  141  of each image forming unit  140  is configured to emit a laser beam from an exposure unit  142  provided at a lower part in the apparatus main body  101 . When the image forming process is started, a laser beam is emitted from the exposure unit  142  to the photosensitive drum  141  whose surface is uniformly charged in advance by a charging unit, such as a charging roller, to expose the photosensitive drum  141 . At that time, the exposure unit  142  receives a signal (a video signal) corresponding to the image data for printing and applies a laser beam modulated according to the video signal to the photosensitive drum  141  via a scanning optical system including a polygon mirror. Thus, an electrostatic latent image corresponding to the image data is formed on the surface of the photosensitive drum  141 . 
     The developing unit  143  supplies toner to the electrostatic latent image formed on the photosensitive drum  141  to visualize (develop) the latent image to a toner image. Thereafter, predetermined pressure and electrostatic load bias are applied by the primary transfer unit  144 , so that the toner image is primarily transferred from the photosensitive drum  141  to the intermediate transfer belt  145 . 
     The intermediate transfer belt  145  is rotationally driven in the direction of arrow R 1  in  FIG.  1   . The above toner image forming operation is performed in parallel in the individual image forming units  140 . The primary transfer is performed on the intermediate transfer belt  145  so that toner images formed by downstream image forming units  140  are put on toner images formed by upstream image forming units  140 . As a result, a full-color toner image is formed on the intermediate transfer belt  145  and conveyed to a secondary transfer unit  130  while being carried on the intermediate transfer belt  145 . 
     The secondary transfer unit  130  is a nip formed by the inner secondary transfer roller  131  and the outer secondary transfer roller  132  facing each other. The secondary transfer unit  130  transfers the toner image from the intermediate transfer belt  145  to the sheet S while conveying the nipped sheet S. In other words, the toner image is transferred from the intermediate transfer belt  145  to the sheet S as a result of the outer secondary transfer roller  132  applying predetermined pressure and electrostatic load bias. Thereafter, the sheet S is conveyed to a fixing unit  150 , which is a heater that applies heat to the toner image. The fixing unit  150  applies heat and pressure to the toner image while conveying the sheet S nipped by a rotating body pair, such as a roller pair and a belt. Thus, the toner is melted and thereafter solidified to be firmly fixed to the sheet S, so that the image is fixed to the sheet S. 
     A process for conveying the sheet S is executed in parallel to the above image forming process. First, the sheet S used as a printing medium is supplied to the image forming section  102  by a sheet feeding unit  110 . The sheet feeding unit  110  includes a cassette including an elevator that is raised or lowered, with the sheets S loaded on the cassette, and a feeding unit that feeds the sheets S from the cassette one by one. The sheet S fed by the feeding unit is conveyed to a skew correction apparatus  120  through a conveying path. The skew correction apparatus  120  corrects the skew of the sheet S and conveys the sheet S to the secondary transfer unit  130  at the timing determined in accordance with the toner image forming operation performed by the image forming section  102 . 
     The sheet S on which the toner image is transferred by the secondary transfer unit  130  and is then fixed by the fixing unit  150  reaches a junction point at which a first switch flap  151  is disposed. The first switch flap  151  guides the sheet S to either of a sheet conveying path to a first discharge unit  190  and a sheet conveying path to a second discharge unit  191 . The sheet S guided to the first discharge unit  190  is discharged by a first discharge roller pair  160  onto a first discharge tray  170  disposed at an upper part in the apparatus main body  101 . 
     The sheet S guided to the second discharge unit  191  is discharged by a second discharge roller pair  161  onto a second discharge tray  171  disposed above the first discharge tray  170  or reversely conveyed by the reversing operation of a second discharge roller pair  161 . For duplex printing, the reversed sheet S is guided to a duplex conveying path  180  by a second switch flap  152  and is again conveyed to the skew correction apparatus  120  through the duplex conveying path  180 . The sheet S that has reached the skew correction apparatus  120  is subjected to the same process as the process on the first side on which the image is formed and is thereafter discharged to the discharge tray  170  or  171 . 
     An image scanning apparatus  181  is disposed at the top of the apparatus main body  101 . The image scanning apparatus  181  includes a platen on which a sheet (an original) is set and a scanning unit that optically scans the sheet set on the platen, and converts image information in the original to an electronic signal. The image data obtained in this way is transmitted to a control unit in the apparatus main body  101  and, for a copying operation, the image data is converted to a video signal and transmitted to the exposure unit  142 . 
     Sheet Discharge Unit 
     The configuration of the first discharge unit  190 , which is a sheet discharge apparatus of the present embodiment, will be described with reference to  FIGS.  2  to  4   . FIG.  2  is a perspective view of the first discharge unit  190 .  FIG.  3    is a diagram of the first discharge unit  190  viewed from the downstream side in the sheet discharge direction (a view through the first discharge tray  170 ).  FIG.  4    is a cross-sectional view of the first discharge unit  190  taken along line IV-IV in  FIG.  3   . 
     As illustrated in  FIG.  2   , the first discharge unit  190  includes the first discharge roller pair  160 , the first discharge tray  170 , and an alignment wall  210 . The first discharge roller pair  160  is a discharge unit of the present embodiment, and the first discharge tray  170  is a sheet support unit of the present embodiment. The terms “discharge roller pair  160 ” and “discharge tray  170 ” hereinafter respectively refer to the first discharge roller pair  160  and the first discharge tray  170 . 
     The discharge tray  170  is part of the casing of the apparatus main body  101  (see  FIG.  1   ) and constitutes the upper surface of the apparatus main body  101 . The image forming apparatus  100  of the present embodiment has a so-called in-drum discharge configuration in which sheet discharge space is provided in the space of the apparatus main body  101  in top view. The discharge tray  170  is inclined with respect to the horizontal plane so as to rise downstream in the sheet discharge direction. The first discharge unit  190  may be fitted with an accessary unit, such as a sheet processing unit, for example, for binding the sheets S, or a relay unit for conveying the sheets S to another sheet processing unit. In this case, the discharge roller pair  160  discharges the sheets S to the accessary unit. 
     As illustrated in  FIG.  3   , the discharge roller pair  160  includes a driving roller  160   a  connected to a drive source and a driven roller  160   b  driven to rotate by the driving roller  160   a . The driving roller  160   a  is a first roller of the present embodiment, and the driven roller  160   b  is a second roller of the present embodiment, which nips the sheet S together with the first roller to convey the sheet S. The driving roller  160   a  and the driven roller  160   b  are disposed at multiple portions in the widthwise direction D 2  of the sheet S (a direction perpendicular to the sheet discharge direction). Each driving roller  160   a  includes a rubber outer rim and is in contact with the roller main body of the opposing driven roller  160   b . Each driven roller  160   b  has kicker units  203  and  203  with outside diameters larger than the outside diameter of the roller main body on both sides in the axial direction. The kicker units  203  and  203  are made of an elastic material, such as rubber or sponge. The kicker units  203  and  203  push out the trailing end of the sheet S (the upstream end in the sheet discharge direction) so that the sheet S completely comes out of the nip between the driving roller  160   a  and the driven roller  160   b . The kicker unit  203  is an elastic unit of the present embodiment. 
     A stiffness imparting roller  202  is disposed between each pair of the driving roller  160   a  and the driven roller  160   b  in the widthwise direction. Each stiffness imparting roller  202  is disposed so as to protrude from one side to the other side (from above to below in the example in  FIG.  3   ) in the thickness direction with respect to the nip between the driving roller  160   a  and the driven roller  160   b . In other words, the stiffness imparting roller  202  is a stiffness imparting member of the present embodiment that enhances the stiffness of the sheet S that is being discharge by the discharge roller pair  160  by curving the sheet S viewed from the downstream side in the sheet discharge direction. 
     Each stiffness imparting roller  202  is rotatably supported by a lever member that is rotatable with respect to the apparatus main body  101  and is urged in the sheet pressing direction by a spring provided between the lever member and the apparatus main body  101 . The configuration in which the stiffness imparting roller  202  can be displaced in the sheet thickness direction improves/refines the capability to respond to various sheets. In other words, in discharging a high-stiffness sheet, such as cardboard, the stiffness imparting roller  202  retracts upward in  FIG.  3    to prevent a decrease in the abutment pressure between the driving roller  160   a  and the sheet S, thereby preventing conveyance failure. In discharging a low-stiffness sheet S, such as recycled paper or thin paper, the pressing force of the spring is higher than the stiffness of the sheet S, so that the stiffness imparting roller  202  curves the sheet S to enhance the stiffness of the sheet S. This reduces the possibility that the sheet S being discharged sags to disorder the sheets stacked on the discharge tray  170 . 
     In discharging a high-stiffness sheet S, the sheet S is curved a little. However, the sheet S being discharged is unlikely to sag because of its high stiffness. In discharging a low-stiffness sheet S, the stiffness imparting roller  202  is retracted a little. However, a sufficient abutment pressure between the driving roller  160   a  and the sheet S is ensured because of the flexibility of the sheet S. The stiffness imparting roller  202  of the present embodiment is disposed so as to abut on a surface of the sheet S opposite to a surface on which an image is formed immediately before (a print surface) by the image forming section  102  (see  FIG.  1   ). This prevents the stiffness imparting roller  202  from scraping the print surface to leave a mark on the image. 
     As illustrated in  FIG.  4   , the discharge roller pair  160  is disposed so as to discharge the sheet S in a sheet discharge direction D 1  inclined with respect to the horizontal direction to move upward with an increasing distance from the alignment wall  210  as viewed in the widthwise direction. Specifically, a straight line perpendicular to a straight line connecting the axes of the driving rollers  160   a  and the axes of the driven rollers  160   b  is inclined with respect to the horizontal direction, as described above. 
     The alignment wall  210  is a wall surface extending upward from the upstream end of the discharge tray  170  in the sheet discharge direction D 1  and constitutes part of the casing of the apparatus main body  101  together with the discharge tray  170 . The sheet S discharged onto the discharge tray  170  slides along the inclination of the discharge tray  170  and abuts at the trailing end against the alignment wall  210  so that its position in the sheet discharge direction D 1  is regulated. 
     The first discharge unit  190  includes an upper discharge guide  204  and a lower discharge guide  205  that guide the sheet S toward the discharge roller pair  160 . The sheet conveying path that the upper discharge guide  204  and the lower discharge guide  205  form extends from the nip of the discharge roller pair  160  upstream in the sheet discharge direction D 1  along the inclination of the sheet discharge direction D 1  with respect to the horizontal direction. This guide shape reduces resistance in conveying the sheet S discharged by the discharge roller pair  160  and stabilizes the posture of the sheet S being discharged. 
     Full-Load Detection Flag and Pressing Member 
     As illustrated in  FIGS.  2  and  3   , the first discharge unit  190  further includes a full-load detection flag  200 , a full-load detection sensor  206 , and a pressing member  201 . The full-load detection flag  200  is a detection flag of the present embodiment. The full-load detection sensor  206  is a detection unit of the present embodiment. The pressing member  201  is a pressing unit of the present embodiment. 
     The full-load detection flag  200  includes a rotary shaft  200   b  that is rotatably supported by the apparatus main body  101  and an abutting portion  200   a  and a light-shielding portion  200   c  which are mounted to the rotary shaft  200   b . The abutting portion  200   a  is a first abutting portion of the present embodiment. The rotary shaft  200   b  extends in the widthwise direction. The abutting portion  200   a  is disposed within the range of the discharge tray  170  in the widthwise direction. The light-shielding portion  200   c  is disposed outside the discharge tray  170  in the widthwise direction. In the present embodiment, the abutting portion  200   a  is disposed at a conveying center C 0  of the discharge roller pair  160  in the widthwise direction D 2 . The conveying center C 0  is a central position in the range in which the discharge unit nips the sheet S, and in the present embodiment, a symmetry center in the widthwise direction of the four sets of driving roller  160   a  and driven roller  160   b.    
     The full-load detection sensor  206  is a photo-interrupter configured to detect the position of the full-load detection flag  200 . In other words, the full-load detection sensor  206  includes a light-emitting part and a light-receiving part that detects light emitted from the light-emitting part, and is configured to detect that the light-shielding portion  200   c  enters the optical path from the light-emitting part to the light-receiving part and blocks the light. The full-load detection sensor  206  is one example of a detection unit, for example, a sensor that detects the mechanical contact of a detection flag. The full-load detection flag  200  is configured to rest at a position where the abutting portion  200   a  is at a predetermined height h 1  when not in contact with the sheet S, as illustrated in  FIG.  4   . When the sheets S are loaded beyond height h 1 , the full-load detection flag  200  rotates upward because the abutting portion  200   a  is pressed by the upper surface of the top sheet S. The full-load detection sensor  206  is disposed so as to be shielded by the light-shielding portion  200   c  when the full-load detection flag  200  rotates a predetermined angle from the rest position. The height of the abutting portion  200   a  when the detection signal from the full-load detection sensor  206  switches is the full-load height of the discharge tray  170  in the present embodiment. 
     As illustrated in  FIGS.  2  and  3   , the pressing member  201  includes a rotary shaft  201   b  that is rotatably supported by the apparatus main body  101  and an abutting portion  201   a  ( FIG.  4   ) mounted to the rotary shaft  201   b . The abutting portion  201   a  is a second abutting portion in the present embodiment. The pressing member  201  is disposed so as to rotate around the rotation center common to the full-load detection flag  200  (coaxially with the full-load detection flag  200 ). When the above accessary unit is mounted, the pressing member  201  and the full-load detection flag  200  are unmounted. The pressing member  201  may be detachably mounted to the apparatus main body  101  together with the full-load detection flag  200  by using, for example, a configuration in which the rotary shaft  201   b  has a boss shape that loosely fits on the rotary shaft  200   b  of the full-load detection flag  200 . 
     The rotation radius of the pressing member  201  is smaller than the rotation radius of the full-load detection flag  200 . The pressing member  201  is disposed so as to be aligned with the abutting portion  200   a  of the full-load detection flag  200  in the widthwise direction. In the present embodiment, the pressing member  201  is disposed at the conveying center C 0  of the discharge roller pair  160  ( FIG.  3   ). One of the stiffness imparting rollers  202  is also disposed at the conveying center C 0 . In other words, the abutting portion  201   a  of the pressing member  201 , the abutting portion  200   a  of the full-load detection flag  200 , and the stiffness imparting roller  202  are aligned in the widthwise direction. 
     As illustrated in  FIG.  4   , the pressing member  201  is configured to rest at a position where the abutting portion  201   a  is located at a predetermined height h 2  when not in contact with the sheet S. The height h 2  of the pressing member  201  at the resting position is set lower than the height h 3  of the rotation center of the driven roller  160   b  of the discharge roller pair  160 . In the present embodiment, the height h 2  of the pressing member  201  at the resting position is set lower than the lower end of the driven roller  160   b  and the height h 1  of the full-load detection flag  200  in the resting position. The distance from the loading surface of the discharge tray  170  to the pressing member  201  in the resting state is set larger than the distance from the loading surface to the full-load detection flag  200  at the resting position. This prevents the pressing member  201  from coming into contact with the sheets S on the tray before the discharge tray  170  becomes a full-loaded state to impede the rotation of the pressing member  201 , hindering the discharge of the sheet S. 
     The pressing member  201  at the resting position overlaps with the driven roller  160   b  of the discharge roller pair  160  as viewed in the widthwise direction. Specifically, the pressing member  201  overlaps with the kicker units  203  of the driven roller  160   b . The fact that two members overlap as viewed in a predetermined direction means that at least part of the projection range of one member overlaps with the projection range of the other member when the members are projected on a virtual plane perpendicular to a predetermined direction using parallel rays in the predetermined direction. 
     Sheet Discharge Operation 
     The operations of the components when the thus-configured first discharge unit  190  performs a sheet discharge operation will be described.  FIGS.  4  to  7    are respective cross-sectional views taken along lines IV-IV, V-V, VI-VI, and in  FIG.  3   .  FIG.  4    illustrates a standby state and  FIGS.  5 ,  6 , and  7    illustrate states during the sheet discharge operation. 
     First, the standby state will be described with reference to  FIG.  4   . The full-load detection flag  200  is at the resting position (a standby position), and the end of the abutting portion  200   a  is at a position a predetermined distance away from the loading surface of the discharge tray  170 . The abutting portion  200   a  extends in a direction intersecting the sheet discharge direction D 1  at an angle of θ other than the right angle. In the present embodiment, θ is set at 45 (degrees) and may be set in the range of 30 to 60 (degrees). The pressing member  201  also stands by at the resting position (a standby position). The abutting portion  201   a  extends in the vertical direction. The angle that the abutting portion  201   a  of the pressing member  201  forms with the sheet discharge direction D 1  viewed in the widthwise direction is nearer to 90 degrees than the angle θ that the abutting portion  200   a  of the full-load detection flag  200  forms with the sheet discharge direction D 1 . 
     As illustrated in  FIG.  5   , when the discharge roller pair  160  nips the sheet S and starts to discharge the sheet S, the leading end of the sheet S abuts against the abutting portion  201   a  of the pressing member  201  and then abuts against the abutting portion  200   a  of the full-load detection flag  200 . The sheet S fed out of the discharge roller pair  160  is given stiffness by the operation of the stiffness imparting roller  202 . The pressing member  201  and the full-load detection flag  200  are raised by the sheet S to rotate upward from the resting position. However, the upward rotation of the full-load detection flag  200  is restricted by a stopper (not illustrated) and is held at a posture in which the abutting portion  200   a  is substantially horizontal. This causes the leading end of the sheet S fed out of the discharge roller pair  160  to be guided toward the discharge tray  170  by the abutting portion  200   a . The pressing member  201  presses the upper surface of the sheet S downward with its own weight. As the discharge of the sheet S proceeds, the stiffness imparting action at a position away from the stiffness imparting roller  202  becomes weak, so that the leading end of the sheet S deviates downward from the sheet discharge direction D 1  onto the discharge tray  170 . 
       FIG.  6    illustrates a state immediately after the trailing end of the sheet S comes out of the nip of the discharge roller pair  160 . The trailing end of the sheet S is in contact with the kicker units  203  and receives friction from the kicker units  203  rotating in a rotational direction (counterclockwise in  FIG.  6   ) along the sheet discharge direction D 1 . The pressing member  201  continuously presses the sheet S downward before the trailing end of the sheet S passes through the nip of the discharge roller pair  160 . For this reason, when the trailing end of the sheet S passes through the nip of the discharge roller pair  160 , the trailing end of the sheet S is pressed against the kicker units  203  by the pressing member  201 . In other words, the pressure of the pressing member  201  increases the friction acting on the sheet S from the kicker units  203 . 
     As illustrated in  FIG.  7   , when the trailing end of the sheet S moves downward to come away from the kicker units  203 , there is nothing to support the trailing end of the sheet S, so that a portion of the sheet S near the trailing end falls toward the discharge tray  170 . At that time, the sheet S is pressed downward by the full-load detection flag  200  and the pressing member  201  rotating in their resting positions. In particular, the pressing member  201  rotates to the resting position at which the end of the abutting portion  201   a  is lower than the kicker units  203 , which prevents the trailing end of the sheet S from leaning against the nip of the discharge roller pair  160  or its periphery. 
     The above sheet discharge operation is repeated on the following discharged sheets S, so that the sheets S are stacked on the discharge tray  170 . When the height of the sheets S stacked on the discharge tray  170  exceeds a predetermined height, the full-load detection flag  200  rotates, so that the full-load state is detected by the full-load detection sensor  206 . 
     Beneficial Effects of Present Embodiment 
     As described above, the present embodiment includes the pressing member  201  that abuts on the sheet S at a position nearer to the discharge roller pair  160  than the full-load detection flag  200 , in addition to the full-load detection flag  200  that abuts against the sheet S above the discharge tray  170 . The pressing member  201  is configured to rotate independently of the full-load detection flag  200  so as to press the sheet S being discharged by the discharge roller pair  160  downward regardless of the position of the full-load detection flag  200 . In other words, the pressing unit that is rotatable independently of the detection flag is configured to press the sheet S discharged from the discharge unit downward with the second abutting portion regardless of the position of the detection flag. 
     This configuration provides a state in which the pressing member  201  presses the sheet S downward at a position closer to the discharge roller pair  160  than the abutting portion  200   a  of the full-load detection flag  200  at the point in time the trailing end of the sheet S passes through the nip of the discharge roller pair  160 . This allows the trailing end of the sheet S that has passed through the nip of the discharge roller pair  160  to quickly move downward away from the discharge roller pair  160 , thereby efficiently reducing occurrence of trailing-end leaning. 
     In the present embodiment, the discharge roller pair  160  discharges the sheet S in the obliquely upward sheet discharge direction D 1 , and the stiffness imparting roller  202  imparts stiffness on the sheet S discharged by the discharge roller pair  160 . This stabilizes the posture of the sheet S being discharged using the stiffness imparting working of the stiffness imparting roller  202  and reduces the occurrence of trailing-end leaning immediately after the discharging by the working of the pressing member  201 . In particular, the present embodiment is configured such that the pressing member  201  presses the sheet S from the same direction as the direction of the stiffness imparting roller  202  (from above) and that the positions of the pressing member  201  and the central stiffness imparting roller  202  are aligned in the widthwise direction. This minimizes the influence of the pressing member  201  on the posture of the sheet S being discharged. 
     In the present embodiment, the pressing member  201  overlaps with the kicker units  203  (elastic portions) provided at the driven roller  160   b  as viewed in the axial direction of the discharge roller pair  160 . This allows the trailing end of the sheet S that has passed through the nip of the discharge roller pair  160  to be pressed against the kicker units  203  by the pressure of the pressing member  201 , increasing the friction of the kicker units  203  on the sheet S. As a result, as the kicker units  203  rotate, the trailing end of the sheet S is separated from the nip of the discharge roller pair  160  while being kept in contact with the kicker units  203 , which prevents the occurrence of trailing-end leaning more reliably. 
     In the present embodiment, the abutting portion  200   a  the full-load detection flag  200  and the abutting portion  201   a  of the pressing member  201  are disposed at the conveying center C 0  of the discharge roller pair  160 . This prevents the conveying resistance to the sheet S from being uneven on one side and the other side of the conveying center C 0  in the widthwise direction. Furthermore, this allows the full-load detection flag  200  and the pressing member  201  to give a certain effect to the sheet S regardless of the width of the sheet S. 
     In the present embodiment, the pressing member  201  for pressing the sheet S is disposed at a position closer to the discharge roller pair  160  than the full-load detection flag  200 . Moving the abutting portion  200   a  of the full-load detection flag  200  itself to the position of the abutting portion  201   a  of the pressing member  201  is disadvantageous in the following points. First, moving the abutting portion  200   a  of the full-load detection flag  200  close to the discharge roller pair  160  makes the angle θ (see  FIG.  4   ) between the abutting portion  200   a  in the resting position and the sheet discharge direction D 1  close to a right angle, which can increase the sheet conveying resistance. Furthermore, since it is necessary to detect the full-load state before the sheets S loaded on the discharge tray  170  blocks the discharge roller pair  160 , the rotation radius of the full-load detection flag  200  has to be set somewhat large, for example, the abutting portion  200   a  is extended lower than the discharge roller pair  160 . This causes the abutting position of the abutting portion  200   a  against the sheet S to be more separated from the discharge roller pair  160  than the abutting portion  201   a  of the pressing member  201  of the present embodiment, so that the effect of quickly separating the trailing end of the sheet S that has passed through the discharge roller pair from the discharge roller pair is not provided. Furthermore, even if the rotation radius is set small using a light-weight full-load detection flag that will not increase the conveying resistance, the sheet height for detecting a full-load state and the height of the discharge roller pair come close to each other, leading to the risk of blocking the discharge roller pair. The configuration of the present embodiment prevents such inconveniences because of the pressing member  201  that rotates independently of the full-load detection flag  200 . 
     In the present embodiment, the rotation range of the full-load detection flag  200  is limited, as described above, so that the upward rotation of the abutting portion  200   a  beyond the substantially horizontal position is restricted (see  FIG.  5   ). This is for the purpose of preventing the sheet S discharged by the discharge roller pair  160  from being continuously discharged at the obliquely upward posture. If the rotation range of the full-load detection flag  200  is not limited, when the sheet S that has passed through the discharge roller pair  160  falls, the sheet S can be moved by receiving a force opposite to the sheet discharge direction D 1  due to air resistance to lean against the nip of the discharge roller pair  160  or the periphery thereof. Such behavior tends to occur when a sheet that has certain stiffness, such as thin paper, and that can easily be curved by the stiffness imparting roller  202  (in other words, a sheet whose leading end is hard to sag) is discharged. Since the present embodiment is configured to guide the leading end of the sheet S with the full-load detection flag  200  whose rotation range is limited, the sheet S can be landed on the discharge tray  170  before the trailing end of the sheet S passes through the discharge roller pair  160 , thus preventing such inconvenience. 
     In order to prevent the behavior of the sheet S that has passed through the discharge roller pair  160  moving opposite to the sheet discharge direction D 1 , the stiffness imparting working of the stiffness imparting roller  202  may be weakened (for example, a spring for urging the stiffness imparting roller  202  is weakened). However, this configuration may reduce the stiffness imparted to a low-stiffness sheet, such as recycled paper, making it difficult to maintain the posture of the sheet being discharged, for example, causing the sheet to come into contact with the discharge tray  170  to be bent. It is also possible to apply air to the lower surface of the low-stiffness sheet S being discharged from a fan provided in the apparatus main body so as to support the posture of the sheet S. This however has an issue in terms of cost and noise. Furthermore, decreasing the space in the vertical direction between the discharge tray  170  and the discharge roller pair  160  leads to a short fall length, allowing the above behavior of the sheet S to be reduced. However, this reduces the load capacity of the discharge tray  170  because it is necessary to determine that the discharge tray  170  is full of sheets S before the loaded sheets S block the discharge roller pair  160 . The configuration of the present embodiment reduces the trailing-end leaning of the sheet S while avoiding these inconveniences. 
     Modification 
     Although the present embodiment uses, as a stiffness imparting member, the stiffness imparting roller  202  provided independently of the discharge roller pair  160 , another configuration may be used. For example, a roller whose outside diameter is larger than the outside diameter of the driving roller  160   a  or the driven roller  160   b  may be disposed on the roller shaft of the driving roller  160   a  or the driven roller  160   b . Although the stiffness imparting roller  202  in the present embodiment is disposed opposite to the print surface of the sheet S, the stiffness imparting roller  202  may be disposed on the same side as the print surface. 
     The discharge roller pair  160  is one example of the discharge unit. Another configuration may be used. For example, two pairs of driving roller  160   a  and driven roller  160   b  forming a nip may be provided. The discharge roller pair may be configured such that a plurality of driving rollers and a plurality of driven rollers are alternately disposed in the axial direction and that the outer circumferential surfaces of the driving rollers and the driven rollers are aligned viewed in the axial direction. In this case, the discharge roller pairs also serve as stiffness imparting members for imparting stiffness to the sheet S. 
     Second Embodiment 
     A sheet discharge apparatus according to a second embodiment will be described with reference to  FIGS.  8  to  10   .  FIG.  8    is a perspective view of a first discharge unit  190 B, which is the sheet discharge apparatus of the present embodiment.  FIG.  9    is a diagram of the first discharge unit  190 B viewed from the downstream side in the sheet discharge direction.  FIG.  10    is a cross-sectional view of the first discharge unit  190 B taken along line X-X in  FIG.  9   . The first discharge unit  190 B is a sheet discharge apparatus that discharges sheets S from the apparatus main body  101  of the image forming apparatus  100 , like the first discharge unit  190  of the first embodiment, and differs in the configuration of a pressing member  211  from the configuration of the pressing member  201  of the first embodiment. The other components having the same configuration and operations as those of the first embodiment are given the same reference numerals as those of the first embodiment and descriptions thereof will be omitted. 
     As illustrated in  FIGS.  8  and  9   , the pressing member  211 , which is a pressing unit of the present embodiment, is rotationally supported by apparatus main body  101 . The pressing member  211  is disposed at the conveying center C 0  of the discharge roller pair  160  in the widthwise direction ( FIG.  9   ). 
     As illustrated in  FIG.  10   , the pressing member  211  includes a rotary shaft  211   b  rotatably supported by the apparatus main body  101  and an abutting portion  211   a  mounted to the rotary shaft  211   b . The pressing member  211  is configured to rest at a position where the abutting portion  211   a  is located at a predetermined height h 4  when not in contact with the sheet S. The height h 4  of the pressing member  211  at the resting position is set lower than the height h 5  of the rotation center of the driven roller  160   b  of the discharge roller pair  160 . The pressing member  211  at its resting position overlaps with the driven roller  160   b  of the discharge roller pair  160  as viewed in the widthwise direction. 
     Also the use of the pressing member  211  allows the pressing member  211  to press the sheet S downward at a position closer to the discharge roller pair  160  than the abutting portion  200   a  of the full-load detection flag  200  at the time the trailing end of the sheet S passes through the nip of the discharge roller pair  160 . This allows the trailing end of the sheet S that has passed through the nip of the discharge roller pair  160  to quickly move downward away from the discharge roller pair  160 , thereby efficiently reducing occurrence of trailing-end leaning, as in the first embodiment. 
     Unlike the first embodiment, the pressing member  211  of the second embodiment is disposed so as to rotate about the rotation center of the driving roller  160   a  of the discharge roller pair  160  (in other words, coaxially with the driving roller  160   a ). This allows the abutting portion  211   a  of the pressing member  211  to abut against the sheet S at a position closer to the nip of the discharge roller pair  160 , thereby pressing the trailing end of the sheet S that has passed through the nip downward. This makes it easy to press the trailing end of the sheet S against the kicker units  203  of the driven roller  160   b , thereby applying friction. Furthermore, since the abutting position of the pressing member  211  against the sheet S being discharged is close to the stiffness imparting roller  202 , the probability that the pressing force of the pressing member  211  causes the sheet S to sag can be reduced. 
     Although the present embodiment has a configuration in which the pressing member  211  is disposed coaxially with the driving roller  160   a  of the discharge roller pair  160 , a pressing unit that has a rotation center at another position may be used. Also this configuration provides the same beneficial advantages as those of the first and second embodiments by providing a pressing unit that presses the sheet S at a position closer to the discharge roller pair  160  than the full-load detection flag  200 . 
     OTHER EMBODIMENTS 
     Although the first and second embodiments illustrate sheet discharge apparatuses that discharge sheets from the apparatus main body  101  of the image forming apparatus  100 , this technique is also applicable to another sheet discharge apparatus. The second discharge unit  191  in the first embodiment is an example of another sheet discharge apparatus. Other examples include a sheet discharge apparatus for discharging an original from which image information is read by an image scanning apparatus and a sheet discharge apparatus for discharging a sheet processed by a sheet processing apparatus. 
     Embodiment(s) of the present disclosure can also be realized by a computer of a system or apparatus that reads out and executes computer executable instructions (e.g., one or more programs) recorded on a storage medium (which may also be referred to more fully as a ‘non-transitory computer-readable storage medium’) to perform the functions of one or more of the above-described embodiment(s) and/or that includes one or more circuits (e.g., application specific integrated circuit (ASIC)) for performing the functions of one or more of the above-described embodiment(s), and by a method performed by the computer of the system or apparatus by, for example, reading out and executing the computer executable instructions from the storage medium to perform the functions of one or more of the above-described embodiment(s) and/or controlling the one or more circuits to perform the functions of one or more of the above-described embodiment(s). The computer may include one or more processors (e.g., central processing unit (CPU), micro processing unit (MPU)) and may include a network of separate computers or separate processors to read out and execute the computer executable instructions. The computer executable instructions may be provided to the computer, for example, from a network or the storage medium. The storage medium may include, for example, one or more of a hard disk, a random access memory (RAM), a read-only memory (ROM), a storage of distributed computing systems, an optical disk (such as a compact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™), a flash memory device, a memory card, and the like. 
     While the present disclosure has been described with reference to exemplary embodiments, it is to be understood that the disclosure 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. 2018-122286, filed Jun. 27, 2018, which is hereby incorporated by reference herein in its entirety.