Abstract:
Aspects of the disclosure provide an image forming apparatus. The image forming apparatus has a first conveying path and a second conveying path which joins the first conveying path. The image forming apparatus includes an actuator configured to be pivoted by a recording sheet conveyed through the first conveying path. The image forming apparatus further includes ribs disposed adjacent to the actuator in an axial direction of the actuator. The image forming apparatus has a first recess which faces at least one of the ribs and is recessed in a direction opposite to the conveying direction.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Application No. 2013-187102, filed on Sep. 10, 2013, which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     Aspects disclosed herein relate to an image forming apparatus having a first conveying path and a second conveying path which joins the first conveying path. 
     BACKGROUND 
     An image forming apparatus known in the prior art includes a conveying path, through which paper is conveyed to an image forming unit, and a re-conveying path, which joins the conveying path on the upstream side of the image forming apparatus in a conveying direction. This type of image forming apparatus has an actuator that detects paper, the actuator being disposed near the downstream side of the junction between the conveying path and the re-conveying path in the conveying direction. If the conveying path is wide at a position at which the actuator is disposed, the top of paper is likely to pass various positions, so the top is likely to come into contact with the actuator at various positions. This causes the actuator to tend to operate at various times. 
     In view of this, if ribs protruding upward are provided at both sides of the actuator to narrow the conveying path at the position of the actuator by an amount by which the ribs protrude, the conveyed paper is less likely to come into contact the actuator at various positions. This enables the actuator to detect the paper more accurately. 
     If, however, the above rib is provided in an image forming apparatus so that the rib extends to the re-conveying path, it is narrowed at a position immediately before the junction between the conveying path and the re-conveying path. This may cause an increase in a resistance that prevents paper from being easily conveyed through the conveying path on the upstream side of the rib in the conveying direction. 
     SUMMARY 
     Aspects of the disclosure provide an image forming apparatus. The image forming apparatus has a first conveying path and a second conveying path which joins the first conveying path. The image forming apparatus includes an actuator configured to be pivoted by a recording sheet conveyed through the first conveying path. The image forming apparatus further includes ribs disposed adjacent to the actuator in an axial direction of the actuator. The image forming apparatus has a first recess which faces at least one of the ribs and is recessed in a direction opposite to the conveying direction. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present disclosure, needs satisfied thereby, and the objects, features, and advantages thereof, reference now is made to the following descriptions taken in connection with the accompanying drawings. 
         FIG. 1  is a cross sectional view of a laser printer in an embodiment of the present invention. 
         FIG. 2  is an enlarged view illustrating the actuator in  FIG. 1  and its peripheral portions. 
         FIG. 3  is a perspective view of a first guiding portion and a fourth guiding portion when viewed from above. 
         FIG. 4A  is an enlarged perspective view of the actuator and its peripheral portions when viewed from above, and  FIG. 4B  is a view of the actuator and its peripheral portions when viewed directly above. 
         FIG. 5  is a perspective view of a process cartridge when viewed from below. 
         FIG. 6  illustrates how the top of paper enters a rib curved portion. 
         FIG. 7A  is an enlarged perspective view of the actuator in a variation and its peripheral portions when viewed from above, and  FIG. 7B  is a view of the actuator and its peripheral portions when viewed directly above. 
     
    
    
     DETAILED DESCRIPTION 
     Preferred embodiment of the present invention will be described with reference to the attached drawings. The general structure of a laser printer  1  will be described first, after which characteristic parts of the present invention will be described. 
     The laser printer  1  is structured so that an image can be formed on both sides of paper P as illustrated in  FIG. 1 . The laser printer  1  includes a paper feed unit  3 , an image forming unit  4 , a discharging unit  7 , and an inverting unit  8  in a case  2 . 
     Directions in the descriptions below are relative to the user who uses the laser printer  1 . Specifically, the right side in  FIG. 1  is “front”, the left side is “back”, the front is “left”, and the back is “right”. The vertical direction in  FIG. 1  is “vertical”. The conveying direction in the descriptions below is a direction in which paper P is conveyed in a supply path  38 . 
     A front cover  23 , which is pivotable away from and toward the case  2 , is provided on the front of the case  2 . A manually inserted tray  24  is provided inside the front cover  23 . When the front cover  23  is opened toward the front, paper P can be manually placed on the manually inserted tray  24 . 
     The paper feed unit  3 , disposed at the bottom of the case  2 , is structured so that paper P is supplied to the image forming unit  4 . The main components of the paper feed unit  3  are a feed tray  31 , a paper pressing plate  32 , a pickup roller  33 , a separating roller  34 , a separating pad  35 , a conveying roller pair  36 , an actuator  100 , a resist roller pair  37 , and the supply path  38 . 
     The supply path  38  (an example of a first conveying path) guides paper P from the feed tray  31  toward the image forming unit  4 , specifically, toward a clearance between a photosensitive drum  51  and a transfer roller  53 . The supply path  38  extends from the vicinity of the pickup roller  33  toward the conveying roller pair  36  disposed upward at an angle on the front side, is curved backward at a nip position  36 A of the conveying roller pair  36 , and extends toward a clearance between the photosensitive drum  51  and the transfer roller  53 . In other words, the supply path  38  is substantially U-shaped so as to extend from the feed tray  31  toward the image forming unit  4 . 
     Part of the supply path  38  extends toward the photosensitive drum  51  disposed downstream of the nip position  36 A of the conveying roller pair  36  in the conveying direction. The walls of the supply path  38  in this range are mainly formed with a first guide  110 , a second guide  120 , and a third guide  130 . The first guide  110 , second guide  120 , and third guide  130  will be described later in detail. 
     The actuator  100  is provided to detect a pass of paper P in the supply path  38  when the paper P comes into contact with the actuator  100 . The actuator  100  is disposed upstream of the resist roller pair  37  in the supply path  38  in the conveying direction and downstream of a junction  38 A, at which the supply path  38  joins a re-conveying path  81  (an example of a second conveying path), which will be described later, in the conveying direction. The actuator  100  is disposed so as to be pivotable away from and toward the second guide  120 . When conveyed paper P comes into contact with the actuator  100 , it falls backward. When the paper P has completely passed the actuator  100 , it returns to its original position. 
     The actuator  100  is placed substantially at the center of the second guide  120  in the right and left direction as illustrated in  FIG. 3 . Ribs  101 , which extend in the conveying direction, are provided adjacent to the actuator  100  and at both ends of the actuator  100 . 
     Paper P placed on the feed tray  31  is moved by the paper pressing plate  32  toward the pickup roller  33  and is then fed out by the pickup roller  33  to the supply path  38 . Sheets of paper P that have been fed out are separated by the separating roller  34  and separating pad  35  one sheet at a time. The separated paper P is conveyed by the conveying roller pair  36 . The skew of the paper P is corrected by the resist roller pair  37 , after which the paper P is conveyed toward the image forming unit  4 , specifically, toward a clearance between the photosensitive drum  51  and the transfer roller  53 . 
     The image forming unit  4 , disposed above the feed tray  31 , is structured so as to form an image on the supplied paper P. The image forming unit  4  mainly includes an exposing unit  40 , a process cartridge  50 , and a fixing unit  60 . 
     The exposing unit  40  is disposed at an upper portion in the case  2 . The exposing unit  40  mainly includes a laser emitting unit (not illustrated), a polygon mirror  41 , which is rotationally driven, a lens  42 , and a reflecting minor  44 . Laser light is emitted from the laser emitting unit according to image data, passes through the polygon minor  41  and lens  42  in that order, and is reflected at the reflecting mirror  44 , as indicated by the dash-dot lines in  FIG. 1 . The surface of the photosensitive drum  51  is then scanned with the reflected laser light at high speed. 
     The process cartridge  50 , disposed below the exposing unit  40 , can be attached to and removed from the case  2  through an opening that is formed when the front cover  23  attached to the case  2  is opened, enabling the process cartridge  50  to be replaced. The process cartridge  50  mainly includes the photosensitive drum  51 , a charger  52 , the transfer roller  53 , a developing roller  54 , a supply roller  55 , and a toner storage unit  56 , which stores toner. 
     The fixing unit  60 , disposed behind the process cartridge  50 , includes a heating roller  61  and a pressure roller  62 , which is disposed opposite to the heating roller  61  to press it. 
     In the image forming unit  4 , after the surface of the photosensitive drum  51  has been uniformly charged by the charger  52 , the surface is exposed with high-speed scan of laser light emitted from the exposing unit  40 , forming an electrostatic latent image on the photosensitive drum  51 . Toner in the toner storage unit  56  is supplied through the supply roller  55  to the developing roller  54  and is supported on the developing roller  54 . 
     The toner supported on the developing roller  54  is supplied to the electrostatic latent image formed on the photosensitive drum  51  to make the electrostatic latent image visible, forming a toner image on the photosensitive drum  51 . When the paper P supplied from the paper feed unit  3  is conveyed through a clearance between the photosensitive drum  51  and the transfer roller  53 , the toner image is transferred from the photosensitive drum  51  onto the paper P. When the paper P is then conveyed through a clearance between the heating roller  61  and the pressure roller  62 , the toner image transferred onto the paper P is thermally fixed. 
     The discharging unit  7  is structured so as to convey, toward the outside of the case  2 , the paper P on which the toner image has been thermally fixed. The discharging unit  7  mainly includes a discharge path  71 , a conveying roller  72 , an auxiliary conveying roller  73 , and a discharge roller  74 . 
     The discharge path  71  is a path through which the paper P conveyed from the fixing unit  60  is guided toward a discharge tray  22  while the paper P is curved. 
     The discharge roller  74 , disposed in the vicinity of the exit of the discharge path  71 , is structured so as to be rotatable in the normal and reverse directions under known control. Specifically, when rotated in the normal direction, the discharge roller  74  discharges paper P toward the outside of the case  2 ; when rotated in the opposite direction, the discharge roller  74  conveys paper P to the inverting unit  8 . 
     The discharge roller  74  includes a driving roller  74 A, which receives a driving force, and driven rollers  74 B and  74 C, which are disposed below the driving roller  74 A and are driven by the driving roller  74 A. 
     In the discharging unit  7 , the paper P discharged from the image forming unit  4  as indicated by the sold line in  FIG. 1 , an image having been formed on the paper P, is conveyed toward the discharge roller  74  along a path that is curved from the upward orientation at an angle behind the discharge roller  74  toward the front. Upon completion of image forming only on one side or on both sides, the paper P enters the discharge path  71  downstream of the image forming unit  4  in the conveying direction, is curved in a substantially U-shaped form, and is discharged to the discharge tray  22  disposed at an upper portion of the case  2 . 
     When an image is formed on both sides of paper P, it is first conveyed by the discharge roller  74  that is rotated in the normal direction toward the outside of the case  2 . Since the discharge roller  74  is rotated in the reverse direction before the entire paper P is completely discharged to the outside of the case  2 , the paper P is drawn into the case  2  again and is conveyed to the inverting unit  8  as indicated by the broken line in  FIG. 1 . 
     The inverting unit  8  conveys inverted paper P toward the image forming unit  4  again during image forming on both sides of the paper P. The inverting unit  8  mainly includes the re-conveying path  81  and re-conveying roller pairs  82  and  83 . 
     The re-conveying path  81  is a path through which paper P with an image formed on one side is guided toward the supply path  38  by rotating the discharge roller  74  in the reverse direction. Specifically, the re-conveying path  81  branches from the vicinity of the back end of the d discharge path  71 , extends downward, is curved toward the front, extends above the feed tray  31  from its back toward its front, passes the re-conveying roller pair  82  on the back side, and extends to the re-conveying roller pair  83  on the front side. Furthermore, the re-conveying path  81  is curved upward from the nip position  83 A of the re-conveying roller pair  83  on the front side, is U-turned, and joins the junction  38 A of the supply path  38 . 
     In the inverting unit  8 , the paper P conveyed by the reverse rotation of the discharge roller  74  is conveyed along the re-conveying path  81  as indicated by the broken line in  FIG. 1 , feeding out the paper P to the supply path  38  again to convey it to the image forming unit  4 . An image is then formed on the back of the paper P in the image forming unit  4  as indicated by the solid line in  FIG. 1 , after which the paper P is discharged to the outside of the case  2  by the discharging unit  7  and is placed on the discharge tray  22 . 
     As illustrated in  FIG. 2 , the first guide  110  forms the re-conveying path  81  and the supply path  38  starting from the junction  38 A toward the upstream end in the conveying direction, the first guide  110  being disposed below the third guide  130 . The first guide  110  includes a first guiding portion  111 , which guides a surface of paper P conveyed through the supply path  38 , the surface facing the transfer roller  53 , and also has a second guiding portion  112 , which guides a surface of paper P conveyed through the re-conveying path  81 . 
     The first guiding portion  111  is curved backward from above the conveying roller pair  36 , extends backward to the junction  38 A (see also  FIG. 1 ). 
     The second guiding portion  112  is U-shaped; it extends downward at an angle toward the front from the back end of the first guiding portion  111 , that is, the downstream end  110 A of the first guide  110 , and is then curved backward. 
     As illustrated in  FIGS. 2 and 3 , a plurality of guide ribs  113 , which extend in the conveying direction, are provided immediately upstream of the junction  38 A in the first guiding portion  111  in the conveying direction in such a way that the guide ribs  113  are arranged in the right and left direction. Of the plurality of guide ribs  113 , guide ribs  113 A are disposed in a predetermined range W, including a range in which the actuator  100  is placed, in the right and left direction, and guide ribs  113 B are disposed outside the predetermined range W in the right and left direction. Each guide rib  113 A has a rib curved portion  114 , which is recessed downward in such a way that the guide rib  113 A is located more away from the third guide  130  than the guide rib  113 B. 
     The predetermined range W may be about 100 mm to 110 mm to match, for example, the length of a postcard in the right and left direction. 
     As illustrated in  FIGS. 3, 4A, and 4B , the first guide  110  has first recesses  115 , a second recess  116 , and downstream ribs  117  substantially at the center of the downstream end  110 A of the first guide  110 . 
     Each first recess  115  is disposed at a position at which it faces the relevant rib  101  in the conveying direction, specifically, in correspondence to a position at which the relevant rib  101  is placed in the right and left direction. The first recess  115  is recessed toward the upstream side in the conveying direction. The first recess  115  has a bottom  115 A and also has an inclined portion  115 B at one end of the bottom  115 A in the right and left direction. The inclined portion  115 B on the right side in the right and left direction is inclined outward in the right direction as it extends toward the downstream side in the conveying direction. Similarly, the inclined portion  115 B on the left side in the right and left direction is inclined outward in the left direction as it extends toward the downstream side in the conveying direction. 
     The second recess  116  is disposed at a position at which it faces the actuator  100  in the conveying direction inside the bottoms  115 A of the first recess  115 , specifically, in correspondence to a position at which the actuator  100  is placed in the right and left direction. The second recess  116  is more recessed toward the upstream side in the conveying direction than the bottoms  115 A of the first recess  115 . 
     A pair of downstream ribs  117  are provided outside the first recesses  115  in the first guiding portion  111  in the right and left direction so as to extend in the conveying direction. 
     As illustrated in  FIG. 2 , the second guide  120  forms the re-conveying path  81  and the supply path  38  starting from the junction  38 A toward the downstream end in the conveying direction, the second guide  120  being disposed so as to be adjacent to the first guide  110  in the fore-and-aft direction. The second guide  120  has a third guiding portion  121 , which guides a side of paper P on which an image has been formed, the paper P being conveyed through the re-conveying path  81 , and also has a fourth guiding portion  122 , which guides the back of paper P to be conveyed through the supply path  38 . 
     The third guiding portion  121  extends upward at an angle toward the front from the front of the re-conveying roller pair  83  on the front side, is curved backward, and then extends to a position A substantially directly below the downstream end  110 A of the first guide  110  (see also  FIG. 1 ). The third guiding portion  121 , which is disposed opposite to the second guiding portion  112 , forms the re-conveying path  81  together with the second guiding portion  112 . 
     The fourth guiding portion  122  extends backward from the position A in the third guiding portion  121 . 
     The third guide  130  guides a side of paper P that faces the photosensitive drum  51 , the paper P being conveyed through the supply path  38  from the upstream side toward the downstream side in the conveying direction. The third guide  130 , which is disposed opposite to the first guiding portion  111  and fourth guiding portion  122 , forms the supply path  38  together with the first guiding portion  111  and fourth guiding portion  122 . 
     As illustrated in  FIGS. 2 and 5 , the third guide  130  is formed with the bottom surface of the process cartridge  50 . The third guide  130  has a recess  130 A, a ridge  130 B, and a pair of cartridge ribs  130 C at a portion that faces the first guide  110  disposed upstream of the junction  38 A in the conveying direction. The recess  130 A is curved upward so as to be recessed at a portion that faces the first guiding portion  111 . The ridge  130 B, which is formed behind the recess  130 A, is curved in a convex form toward the first guiding portion  111 . The cartridge rib pair  130 C is disposed behind the ridge  130 B. 
     The ridge  130 B is formed at a position at which it faces the rib curved portions  114 . Each of the cartridge rib pair  130 C is disposed at a position at which it faces the relevant rib  101  and first recess  115  in the right and left direction. The cartridge rib  130 C is at the same position as the first recess  115  in the conveying direction. 
     Next, the structure of the actuator  100  and its peripheral portions will be described. As illustrated in  FIG. 2 , the actuator  100  is inclined backward and extends from the fourth guiding portion  122  toward the third guide  130 . The surface of the actuator  100  on the upstream side in the conveying direction is an abutting surface  100 A, which comes into contact with paper P. 
     Each rib  101  bridges the third guiding portion  121  and fourth guiding portion  122  and protrudes upward. Specifically, the rib  101  is disposed in a range from a position B on the third guiding portion  121  disposed substantially directly below the bottom  115 A of the first recess  115  of the first guide  110  to a position, on the fourth guiding portion  122 , that is on the downstream side of the actuator  100  in the conveying direction. Thus, the supply path  38  and re-conveying path  81  at the position at which the rib  101  is disposed is narrowed by an amount by which the rib  101  protrudes. 
     As illustrated in  FIG. 2 , the rib  101  is disposed so that a position C, at which the abutting surface  100 A of the actuator  100  and a surface, of the rib  101 , that faces the third guide  130  cross each other, becomes the same as a position of the upper surface  101 A of the rib  101  at which the rib  101  most protrudes toward the third guide  130 . Accordingly, the actuator  100  comes into contact with paper P at a portion at which the supply path  38  is most narrowed, enabling a position at which paper P comes into contact to be easily fixed. 
     A straight line L that connects the ridge  130 B and the position C, at which the abutting surface  100 A of the actuator  100  and the upper surface  101 A of the rib  101  cross each other, is tangent to the downstream end  110 A of the first guide  110 . In other words, the straight line L, which is tangent to the ridge  130 B and the downstream end  110 A of the first guide  110 , crosses the abutting surface  100 A of the actuator  100 , the abutting surface  100 A protruding toward the third guide  130  beyond the rib  101 , when viewed in the right and left direction. Accordingly, paper P that has been conveyed from the supply path  38  is likely to come into contact with the actuator  100 . 
     If the downstream end  110 A of the first guide  110  further extends toward the downstream end in the conveying direction, the abutting surface  100 A and straight line L become likely to cross each other. In this case, it is possible to more reliably bring paper P into contact with the abutting surface  100 A. 
     Accordingly, effects as described below can be obtained in this embodiment. Since each first recess  115  is disposed at a position at which it faces the relevant rib  101  of the first guide  110 , it is possible to suppress the space of the re-conveying path  81  from being narrowed on the upstream side of the rib  101  in the conveying direction. Therefore, it is possible to suppress an increase in a resistance that prevents paper P from being easily conveyed through the re-conveying path  81  on the upstream side of the rib  101  in the conveying direction. 
     Since a portion, other than the first recesses  115 , of the downstream end  110 A of the first guide  110  can be extended toward the downstream side in the conveying direction, paper P can be easily guided accurately toward the actuator  100 . 
     Since the second recess  116  is disposed at a position at which it faces the actuator  100 , even if the actuator  100  pivots toward the upstream end in the conveying direction, it is possible to suppress the first guide  110  from interfering with the actuator  100 . Therefore, when a portion, other than the second recess  116 , of the downstream end  110 A of the first guide  110  is extended toward the downstream end in the conveying direction, paper P can be easily guided accurately to the actuator  100 . 
     Since paper P is less likely to come into contact with the actuator  100  at different positions, a timing at which the actuator  100  operates in response to the movement of paper P can be brought close to a certain value, so the actuator  100  can more accurately detect paper P. 
     Since the straight line L, which is tangent to both the ridge  130 B and the downstream end  110 A of the first guide  110 , crosses the abutting surface  100 A of the actuator  100 , paper P can be easily guided accurately toward the abutting surface  100 A of the actuator  100  while the paper P is being conveyed. 
     Paper P with a small width such as a postcard may be conveyed while the front end of the paper P is curled downward, as illustrated in  FIG. 6 . Then, the front end of the paper P is likely to collide with the guide ribs  113 B disposed upstream of the ribs  101  in the conveying direction, so the paper P is likely to jam in the supply path  38  at the positions at which the ribs  101  are disposed and the supply path  38  is thereby narrowed. In this embodiment, however, each guide rib  113 A within the predetermined range W has the rib curved portion  114 , enabling the front end of the paper P to escape into the curved portions  114 . Therefore, it is possible to suppress paper P from jamming in the supply path  38  at the positions at which the ribs  101  are disposed and the supply path  38  is thereby narrowed. 
     The cartridge ribs  130 C are disposed on a surface, of the process cartridge  50 , that faces the supply path  38 . The cartridge ribs  130 C restrict the movement of paper P toward the process cartridge  50 , so the paper P is less likely to come into contact with the actuator  100  at different positions. Since the first recesses  115  are disposed at the positions corresponding to the cartridge ribs  130 C in the right and left direction, it is possible to suppress the space of the supply path  38  from being narrowed upstream of the ribs  101  in the conveying direction. The cartridge ribs  130 C also enable the paper P to be easily guided toward the actuator  100 . 
     So far, an embodiment of the present invention has been described, but the present invention is not limited to the embodiment. The specific structures can be appropriately changed without departing from the intended scope of the present invention. 
     Although, in the embodiment described above, the second recess  116  has been disposed in the first recesses  115 , the present invention is not limited to this. As illustrated in  FIGS. 7A and 7B , first recesses  215  and a second recess  216 , which is recessed upstream of the first recesses  215  in the conveying direction, may be independently provided. Alternatively, a second recess may not be provided. 
     Although, in the embodiment described above, the upper surface  101 A of the rib  101  has crossed the abutting surface  100 A of the actuator  100 , the present invention is not limited to this. The upper surface  101 A may not cross the abutting surface  100 A 
     Although, in the embodiment described above, the straight line L, which is tangent to both the ridge  130 B and the downstream end  110 A of the first guide  110 , has crossed the abutting surface  100 A of the actuator  100 , the present invention is not limited to this. The straight line L may not cross the abutting surface  100 A. 
     Although, in the embodiment described above, the third guide  130  has had the ridge  130 B, the present invention is not limited to this. The third guide  130  may not have a ridge. 
     Although, in the embodiment described above, each guide rib  113 A within the predetermined range W of the first guiding portion  111  has had the rib curved portion  114 , the present invention is not limited to this. The guide rib  113 A may not have a rib curved portion. Alternatively, the guide ribs  113 A in the entire range of the first guiding portion  111  may have a rib curved portion. 
     Although, in the embodiment described above, each rib curved portion  114  has faced the ridge  130 B, the present invention is not limited to this. The rib curved portion  114  may not face the ridge  130 B. 
     Although, in the embodiment described above, the process cartridge  50  has been taken as an example of a cartridge, the present invention is not limited to this. A development cartridge attachable to and detachable from a process cartridge may be used. 
     Although, in the embodiment described above, paper P such as thick paper, a postcard, and thin paper has been taken as an example of a recording sheet, the present invention is not limited to this. The recording sheet may be, for example, an overhead projector (OHP) sheet. 
     Although, in the embodiment described above, the laser printer  1  has been taken as an example of an image forming apparatus. The present invention is not limited to this. For example, a color printer, a multi-function peripheral, or another type of image forming apparatus may be used.