Patent Publication Number: US-9422128-B2

Title: Sheet conveying apparatus and image forming apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a sheet conveying apparatus conveying a sheet and an image forming apparatus. 
     2. Description of the Related Art 
     Hitherto, an image forming apparatus such as a copier, a printer, and a facsimile includes a sheet conveying apparatus configured to convey a sheet. 
     The sheet is conveyed to an image forming portion by the sheet conveying apparatus, and a toner image formed on a photoconductive drum is transferred onto the sheet. The sheet on which the toner image has been transferred is conveyed to a fixing portion and is then conveyed to a discharging portion. 
     In conveying a sheet in the conventional sheet conveying apparatus, switching operations of various switching units and a switching operation for switching a direction of rotation of a sheet conveying portion are performed based on detection of a front end of the sheet. Then, in order to detect the front end of the sheet as described above, the sheet conveying apparatus is provided with a sheet detection portion configured to detect passage of the sheet on a sheet conveying path. 
     Examples of such conventional sheet detection portion include one including a sensor flag (moving member) against which a front end of the sheet abuts and is turned and a detection sensor detecting the turned sensor flag and inputting a detection signal to a control portion as disclosed in JP-A-9-183539. In the sheet detection portion, when the sensor flag pressed by the sheet turns from a standby position to a detection position where the detection sensor can detect the flag, the detection sensor detecting the turn of the flag inputs a detection signal to the control portion. 
     In response to the input of the detection signal, the control portion determines that the sheet being conveyed has reached the sheet conveyance path. Subsequently, when the sheet has passed through the sensor flag, the pressure of the sheet is released, and hence the sensor flag is returned back to the original standby position from the detection position, no more detection signal is inputted from the detection sensor. If no more detection signal is inputted, the control portion determines that the sheet has passed through the sheet conveyance path. 
     By the way, lately, the image forming apparatus is required to improve productivity further, i.e., to increase a number of image forming sheets per unit time. To that end, a sheet conveying speed is increased, and a distance from a rear end of a sheet being conveyed to a front end of a successively conveyed next sheet (referred to as an ‘inter-sheet distance’ hereinafter) is shortened. 
     Then, in the sheet detecting apparatus, in order to shorten the inter-sheet distance, it is necessary to return the sensor flag back to the standby position from the detection position within a short time after the preceding sheet has passed. 
     Here, in order for the sheet detection portion to detect the front end of the succeeding sheet, a distance between the rear end of the sheet and the front end of the succeeding sheet, i.e., the inter-sheet distance of Δt·V is required: where Δt is a time required for the sensor flag to return to the standby position from the detection position, and V is a sheet conveying speed. Therefore, if the sheet conveying speed is fast, the inter-sheet distance needs to be increased. That is, if the sheet conveying speed is increased, the inter-space distance cannot be shortened. 
     SUMMARY OF THE INVENTION 
     According to an aspect of the present invention, a sheet conveying apparatus including a first rotator pair conveying a sheet, a second rotator pair provided at downstream, in a sheet conveying direction, of the first rotator pair, and a sheet detecting portion detecting the sheet being conveyed in a sheet conveying path between the first and second rotator pairs. The sheet detecting portion includes a moving member provided to move to a detection state from a standby state in which the moving member protrudes into the sheet conveying path by being pressed by a front end of the sheet conveyed by the first rotator pair and configured such that a rear end of the sheet does not pass within a moving trajectory of the moving member in moving from the detection state to the standby state, and a sensor detecting the sheet based on the move of the moving member from the standby state to the detection state. 
     Further features of the present invention 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 illustrating a configuration of a laser printer as one example of an image forming apparatus provided with a sheet conveying apparatus of a first embodiment of the present invention. 
         FIG. 2  is a side view illustrating a sheet detecting apparatus provided in the sheet conveying apparatus. 
         FIG. 3A  is a side view illustrating a state in which a sheet is being conveyed toward a registration roller pair. 
         FIG. 3B  is a side view illustrating a state in which the sheet abuts against a lever member of the sheet detecting apparatus. 
         FIG. 3C  is a side view illustrating a state in which the lever member turns by being pressed by the sheet. 
         FIG. 3D  is a side view illustrating a state in which the sheet enters a nip portion of the registration roller pair. 
         FIG. 3E  is a side view illustrating a state in which the sheet is conveyed by the registration roller pair. 
         FIG. 3F  is a side view illustrating a state in which a rear end of the sheet passes through the sheet detecting apparatus. 
         FIG. 4  is a schematic diagram illustrating a sheet conveying apparatus of a second embodiment of the present disclosure. 
         FIG. 5A  is a side view illustrating a state in which the sheet is conveyed toward the registration roller pair. 
         FIG. 5B  is a side view illustrating a state in which the sheet abuts against the lever member of the sheet detecting apparatus. 
         FIG. 5C  is a side view illustrating a state in which the lever member turns by being pressed by the sheet. 
         FIG. 5D  is a side view illustrating a state in which the sheet enters the nip portion of the registration roller pair. 
         FIG. 6A  is a side view illustrating a state in which the sheet is conveyed by the registration roller pair. 
         FIG. 6B  is a side view illustrating a state in which the rear end of the sheet passes through the sheet detecting apparatus. 
         FIG. 7  is a schematic diagram illustrating a sheet conveying apparatus of a third embodiment of the present disclosure. 
         FIG. 8A  is a side view illustrating a state in which the sheet is conveyed toward the registration roller pair. 
         FIG. 8B  is a side view illustrating a state in which the sheet abuts against the lever member of the sheet detecting apparatus. 
         FIG. 8C  is a side view illustrating a state in which the lever member turns by being pressed by the sheet. 
         FIG. 8D  is a side view illustrating a state in which the sheet enters the nip portion of the registration roller pair. 
         FIG. 9A  is a side view illustrating a state in which the sheet is conveyed by the registration roller pair. 
         FIG. 9B  is a side view illustrating a state in which the rear end of the sheet passes through the sheet detecting apparatus. 
         FIG. 10  is a schematic diagram illustrating a sheet conveying apparatus of a second embodiment of the present disclosure. 
         FIG. 11A  is a side view illustrating a state in which the sheet is conveyed toward the registration roller pair. 
         FIG. 11B  is a side view illustrating a state in which the sheet abuts against the lever member of the sheet detecting apparatus. 
         FIG. 11C  is a side view illustrating a state in which the lever member turns by being pressed by the sheet. 
         FIG. 11D  is a side view illustrating a state in which the sheet enters the nip portion of the registration roller pair. 
         FIG. 12A  is a side view illustrating a state in which the sheet is conveyed by the registration roller pair. 
         FIG. 12B  is a side view illustrating a state in which the rear end of the sheet passes through the sheet detecting apparatus. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Modes for implementing the present invention will be described with reference to the drawings.  FIG. 1  is a diagram illustrating a schematic configuration of a laser printer as one example of an image forming apparatus provided with a sheet conveying apparatus of a first embodiment of the present invention. In  FIG. 1 , the laser printer includes, a laser printer body (referred to as an ‘apparatus body’ hereinafter)  200 A and an image forming portion  200 B provided in the apparatus body  200 A. The laser printer  200  further includes a sheet feeding apparatus  200 C provided in a lower part of the apparatus body  200 A and a sheet conveying apparatus  200 D conveying a sheet fed from the sheet feeding apparatus  200 C to the image forming portion  200 B. 
     The image forming portion  200 B includes a cartridge unit  203  having a photoconductive drum  202 , i.e., an image carrier, and a laser scanner  201  configured to expose the photoconductive drum  202 . In forming an image, the photoconductive drum  202  is exposed by the laser scanner  201  to forma latent image on a surface of the photoconductive drum  202  and, subsequently, a toner image is formed on the surface of the photoconductive drum  202  by developing the latent image. 
     The sheet feeding apparatus  200 C includes a sheet feeding cassette  204 , i.e., a sheet stacking portion, provided drawably within the apparatus body  200 A, and a sheet feed roller  206  provided above the sheet feeding cassette  204  and delivering a sheet S stored in the sheet feeding cassette  204 . The sheet feeding apparatus  200 C comes into pressure contact with the sheet feed roller  206 , and is provided with a separating roller  206   a  constituting a separating unit separating the sheet S delivered from the sheet feed roller  206 . 
     The sheet feeding apparatus  200 C configured as described above feeds the sheet S stored in the sheet feeding cassette  204  by the sheet feed roller  206  in parallel with a toner image forming operation of the image forming portion  200 B described above. Then, the sheets are separated one by one by the separating roller  206   a . The separated sheet S is conveyed to a registration roller pair  209  by a conveying roller pair (first rotator pair)  208  of the sheet conveying apparatus  200 D provided along a sheet conveyance path R. Then, a skew of the sheet S is corrected by the registration roller pair (second rotator pair)  209  and is conveyed to a transfer portion formed by the photoconductive drum  202  and a transfer roller  205  at a predetermined timing. 
     At the transfer portion, the toner image formed on the surface of the photoconductive drum is transferred to the sheet S conveyed to the transfer portion, and subsequently, the sheet S is fed to a fixing portion  210  including a drive roller  211  and a fixing roller  212  provided with a heater integrated therein. The toner image is heated and pressurized in passing through the drive and fixing rollers  211  and  212 , and hence fixed onto the sheet S. The sheet S after the fixation is discharged onto a discharge tray  215  out of the apparatus by an inner discharge roller pair  213  and an outer discharge roller  214 . 
     Meanwhile, in a case of forming an image also on a second surface, the sheet having the image formed on one surface passes through the fixing portion  210 , and then is subjected to a switch-back conveyance by a reverse rotation of the inner and outer discharge roller pairs  213  and  214 . The sheet S is then conveyed again to the transfer portion by conveying rollers  216  and  220  provided along a reverse conveying path  219  and the registration roller pair  209 . At the transfer portion, an image is formed on the opposite surface, and then the sheet is discharged onto the discharge tray  215 . 
     As illustrated in  FIG. 1 , the apparatus body  200 A is provided, at a predetermined position thereof, with a control portion  250  controlling the image forming operation of the image forming portion  200 B and a sheet conveying operation of the sheet conveying apparatus  200 D. The sheet conveying apparatus  200 D is provided with a sheet detecting apparatus  100  detecting a passage of the sheet at an upstream in a sheet conveying direction of the registration roller pair  209  for example. The sheet detecting apparatus  100  inputs a detection signal to the control portion  250 , and in response to the input of the detection signal from the sheet detecting apparatus  100 , the control portion  250  detects the passage of the sheet. 
     The sheet detecting apparatus  100  includes a lever member  101 , i.e., a moving member, which is turned by the sheet abutting against the lever member and an optical sensor  102  as illustrated in  FIG. 2 . The lever member  101  is configured to be turnable (swingable) about a turnable shaft  105 , and includes a sheet abutting portion  103  against which the sheet abuts, and a light-shielding flag portion  104  blocking an optical path from a light-emitting portion to a light receiving portion of the optical sensor  102 . 
     The lever member  101  is biased in a direction indicated by an arrow p by a bias spring not illustrated, i.e., a bias portion, mounted on the turnable shaft  105 , and the sheet abutting portion  103  is positioned at a detection standby position in which the sheet abutting portion  103  enters the sheet conveyance path R by a stopper  106  provided on the apparatus body  200 A. If a front end of the sheet S being conveyed comes into abutment with the sheet abutting portion  103  located at the detection standby position, the lever member  101  turns in a direction indicated by an arrow q about the turnable shaft  105  against the bias spring, and the light-shielding flag portion  104  blocks the optical path of the optical sensor  102 . It is noted that the lever member  101  is arranged such that a predetermined gap exists between the lever member  101  and a counter conveyance guide (second conveyance guide)  107   z  at the standby position. 
     Thereby, a signal indicating that the optical path is blocked, i.e., a detection signal indicating that an arrival of the sheet S is detected, is inputted from the optical sensor  102  of the sheet detecting apparatus  100  to the control portion  250 . The position of the lever member  101  when the optical path is blocked by the light-shielding flag portion  104  in this manner will be referred to as a ‘detection position’ hereinafter. It is noted that when the sheet S is subsequently conveyed and a rear end of the sheet S passes through the lever member  101 , the pressure applied by the sheet S is released, the lever member  101  turns in the direction indicated by the arrow p by the bias spring, and the optical path is brought into a light-transmitting state. Thereby, no more detection signal is inputted from the optical sensor  102 , and the control portion  250  determines that the sheet has passed through. In this manner, the lever member  101  reciprocates between the detection standby position and the detection position in association with the passage of the sheet S. 
     Thus, the lever member  101  becomes a sensor flag of the optical sensor  102  and reciprocates between the detection standby position where the lever member  101  protrudes into the sheet conveying path R at upstream in the sheet conveying direction of the nip portion N 2  of the registration roller pair  209  and the detection position where the lever member  101  turns centering on the rotary shaft  105  by being pressed by the sheet conveyed by the conveying roller pair  208  in association with the passage of the sheet S. That is, by being put into the detection standby position, the lever member  101  is put into the standby state in which the lever member  101  protrudes into the sheet conveying path R by being pressed by the front end of the sheet conveyed by the conveying roller pair  208  and abuts against the sheet. Then, the lever member  101  is put into the standby state by being moved from the detection standby position to the detection state by being pressed by the sheet conveyed by the conveying roller pair  208 . The optical sensor  102  also detects the sheet based on the move from the standby state to the detection state of the lever member  101 . 
     It is noted that while the moving member transmitting the arrival of the sheet to the sensor is constructed solely by the lever member  101  in the pm, the moving member may be constructed by a combination of a plurality of lever members (turning member) or may be constructed by a rotator having a plurality of protrusions around an outer periphery thereof. Still further, as illustrated in  FIG. 2 , a conveyance guide  107  composing apart of the sheet conveying path R is provided between the registration roller pair  209 , i.e., the first rotator pair, and the registration roller pair  209 , i.e., the second rotator pair. The conveyance guide  107  is a first conveyance guide guiding the sheet to a side of the lever member (moving member)  101  of the sheet conveying path R. the counter conveyance guide (second conveyance guide)  107   z  is also provided so as to face the first conveyance guide. Then, a guide portion  1071  composing the sheet conveying path R between the conveying roller pair  208  and the registration roller pair  209  is constructed by the conveyance guide  107  and the counter guide  107   z.    
     Here, as illustrated in  FIG. 2 , a direction of a nip line indicating a sheet conveying direction of a nip portion N 1  of the conveying roller pair  208  is different from a direction of a nip line indicating a sheet conveying direction of the nip portion N 2  of the registration roller pair  209 . The conveyance guide  107  is curved so as to guide the sheet S conveyed by the conveying roller pair  208  to the registration roller pair  209  whose nip line directions are different from each other. That is, the registration roller pair  209  includes a first rotator  209   a  provided on a side same with the lever member  101  with respect to the nip portion N 2  (nip line) and a second rotator  209   b  provided so as to face the first rotator  209   a . Then, the guide portion  1071 , i.e., the sheet conveying path R between the conveying roller pair  208  and the registration roller pair  209 , is constructed curvedly such that a curvature of the first rotator  209   a  side is larger than the second rotator  209   b  side. It is noted that the nip line refers to a straight line orthogonal to a straight line connecting centers of rotation of the first and second rollers of the rotator pair and is a tangential line of the roller at the nip portion. 
     Here, in the present embodiment, the lever member  101  is arranged such that the sheet abutting portion  103  protrudes from the conveyance guide side (the guide portion side) into the sheet conveyance path and is positioned above the nip line of the registration roller pair  209 . An end of the lever member  101  protruding into the sheet conveyance path is apart from the opposed conveyance guide  107   z  in a direction of thickness of the sheet. By arranging the lever member  101  at the position as described above, the sheet S conveyed while being guided by the conveyance guide  107  comes into abutment with the sheet abutting portion  103  at a position indicated by reference sign t. 
     The position t where the front end of the sheet S conveyed by being guided by the conveyance guide  107  comes into abutment with the sheet abutting portion  103  as described above will be referred to as a ‘front end passing position t’ hereinafter. When the sheet S conveyed by the conveying roller pair  208  as described later is handed to the registration roller pair  209 , the sheet S passes through a conveyance passage route u, which extends on the nip line of the registration roller pair  209 . 
     In other words, after when the sheet S is conveyed while being guided by the conveyance guide  107  and reaches the front end passing position t, the sheet S passes through the registration roller pair  209  by passing through the conveyance passage route u, which is a route different from one until then. Here, according to the present embodiment, the sheet conveying direction in passing through the conveyance passage route u is set such that an obtuse angle is formed with respect to a guide direction of the conveyance guide  107  going in a positive direction (counterclockwise). More specifically, The registration roller pair  209  is arranged such that as the nip line which is the tangential line of the nip portion N 2  advances from the upstream side to the downstream side in the sheet conveying direction, the nip line is inclined in a direction approaching from the second rotator  209   b  to the first rotator  209   a . This arrangement makes it possible to move the sheet away from the lever member  101  before the rear end, i.e., an upstream end in the sheet conveying direction, of the sheet passes through the lever member  101 . Still further, the registration roller pair  209  is arranged such that the nip line, i.e., the tangential line of the nip portion N 2  of the registration roller pair  209 , does not intersect with the lever member  101  in the standby state. 
     Next, a sheet detecting operation of the sheet detecting apparatus  100  constructed as described above will be described.  FIG. 3A  is a diagram illustrating a state before the front end of the sheet S reaches the sheet detecting apparatus  100 , i.e., a state before the sheet S comes into abutment with the sheet abutting portion  103  of the lever member  101 . At this time, the lever member  101  is positioned at the detection standby position. 
     The sheet S conveyed to the conveying roller pair  208  by the sheet feed roller  206  and conveyed along the conveyance guide  107  by the conveying roller pair  208  finally reaches the front end passing position t as illustrated in  FIG. 3B . Subsequently, the sheet S is conveyed while turning the lever member  101  in the direction indicated by the arrow q as illustrated in  FIG. 3C . Accordingly, the lever member  101  moves from the detection standby position to the detection position, and the light-shielding flag portion  104  blocks the optical path of the optical sensor  102 . Thereby, the control portion  250  detects the passage of the sheet S. 
     Next, the sheet S is conveyed in a state in which the sheet abutting portion  103  is moved to the detection position, and the front end of the sheet S is finally conveyed to the nip portion N 2  of the registration roller pair  209  as illustrated in  FIG. 3D . After that, the sheet S passes through the nip portion N 2  in a state of being nipped by the registration roller pair  209 . At this time, a conveyance route of the sheet S is shifted from a route along the conveyance guide  107  up to the front end passing position t to the conveyance passage route u which is positioned on the nip line of the registration roller pair  209  as illustrated in  FIG. 3E . 
     If the conveyance passage route u is shifted, because the sheet conveying direction in passing through the conveyance passage route u is set such that an obtuse angle is formed with respect to the guiding direction of the conveyance guide  107 , the sheet S moves in a direction away from the sheet abutting portion  103 . Thereby, the lever member  101  turns in the direction indicated by the arrow p by the bias spring and returns back to the detection standby position, and in association with it, the light-shielding flag portion  104  retracts from the optical path of the optical sensor  102 , whereby the light-receiving portion receives light from the light-emitting portion again, and the optical sensor  102  turns into a non-detection state. 
     In this manner, when the front end of the sheet S is conveyed to the nip portion N 1  of the registration roller pair  209 , the lever member  101  finally returns back to the detection standby position before the rear end of the sheet S passes through. Thereby, the sheet detecting apparatus  100  is put into a state being able to detect the front end of a succeeding sheet S 2  before the rear end of the sheet S passes through. 
     By the way, according to the present embodiment, the succeeding sheet is started to be fed while the sheet S is being conveyed, and the sheet fed next is conveyed by the conveying roller pair  208  along the conveyance guide  107 . Then, as illustrated in  FIG. 3F , the succeeding sheet S 2  comes into abutment with the lever member  101  that has moved to the detection standby position at the front end passing position t, and then turns the lever member  101 . 
     At this time, the rear end of the preceding sheet S has not passed through the nip portion N 2  of the registration roller pair  209  yet. However, since the lever member  101  has moved to the detection standby position, it is possible to detect the succeeding sheet S 2  by the lever member  101  irrespective of the position of the rear end of the preceding sheet S. Consequently, a distance D 11  between the rear end of the preceding sheet S and the front end of the sheet S 2  can be brought closer to zero limitlessly. 
     As described above, according to the present embodiment, the lever member  101  is arranged such that the rear end of the sheet does not pass within the moving trajectory when the lever member  101  moves from the detection state to the detection standby position. Still further, the sheet conveying direction of the registration roller pair  209  is set to form an obtuse angle with respect to the guiding direction of the conveyance guide  107  going in a positive direction (counterclockwise). Accordingly, this arrangement makes it possible to move the sheet away from the lever member  101  before the rear end of the sheet passes through the lever member  101  and to return the lever member  101  back to the detection standby position during a period until when the rear end of the sheet passes through since the passage of the front end thereof. 
     Then, by arranging the lever member  101  such that it returns to the detection standby position during the period until when the rear end of the sheet passes through since the passage of the front end thereof as described above, it becomes possible to detect the succeeding sheet before the rear end of the sheet passes through the sheet detecting apparatus  100 . Thereby, it becomes unnecessary to consider a time otherwise required for the lever member  101  to return to the detection standby position, so that it becomes possible to detect the sheet with a short inter-sheet distance even if a sheet conveying speed is high. As a result, it becomes possible to shorten the inter-sheet distance and to improve an image forming speed. 
     Still further, because the sheet S is kept in a state of being moved away from the lever member  101  in the course of conveyance, i.e., until when the rear end of the sheet passes through the lever member  101 , it is possible to prevent an occurrence of damage, bending and the like of the sheet S otherwise caused by the lever member  101 . In addition, when a user pulls out the sheet S in clearing a jam or the like, it is possible to prevent the sheet S from being caught by the lever member  101  and from being damaged. 
     Next, a second embodiment of the present invention will be described. 
       FIG. 4  is a diagram illustrating a configuration of the sheet conveying apparatus of the present embodiment. In  FIG. 4 , the same reference signs as those in  FIG. 2  described above indicate the same or corresponding portions. In  FIG. 4 , straight first and second conveyance guides  107   a  and  107   b  are provided between the conveying roller pair  208  and the registration roller pair  209  so as to oppose to each other and compose the sheet conveyance path R. 
     It is noted that in the present embodiment, the direction of the nip line of the conveying roller pair  208  corresponds to a direction in which the conveyed sheet is brought into abutment with the first conveyance guide  107   a . More specifically, the conveying roller pair  208  is arranged such that the nip line of the nip portion N 1  of the conveying roller pair  208  inclines in a direction approaching from the second rotator  209   b  side to the first rotator  209   a  side as the nip line advances from upstream to downstream in the sheet conveying direction. Still further, the direction of the nip line of the registration roller pair  209  runs in parallel with the conveyance guide  107   a , differing from the nip line of the conveying roller pair  208 . The conveyance passage route u is set on a substantially straight line connecting the nip portion N 2  of the registration roller pair  209  and the nip portion N 1  of the conveying roller pair  208 . 
     Still further, according to the present embodiment, a sheet conveying speed of the registration roller pair  209  is set to be higher than a sheet conveying speed of the conveying roller pair  208  at least when the sheet is conveyed while being nipped by both of the nip portions N 1  and N 2  of the conveying roller pair  208  and the registration roller pair  209 . That is, the registration roller pair  209  is set such that a rotational speed thereof is higher than a rotational speed of the conveying roller pair  208  at least when the sheet is nipped and conveyed by both of the nip portions N 1  and N 2  of the conveying roller pair  208  and the registration roller pair  209 . With the provision of a difference of the sheet conveying speeds as described above, the sheet S passes through the conveyance passage route u between the registration roller pair  209  and the conveying roller pair  208  in a stretched state after having been nipped by the registration roller pair  209 . 
     Still further, according to the present embodiment, when the lever member  101  is located at the detection standby position, the lever member  101  is arranged so as not to intersect with an imaginary straight line connecting the nip portion N 2  of the registration roller pair  209  and the nip portion N 1  of the conveying roller pair  208 . Thereby, the lever member  101  is moved away from the sheet S when the sheet S passes through the conveyance passage route u in the stretched state. 
     Next, the sheet detecting operation of the sheet detecting apparatus  100  configured as described above will be described.  FIG. 5A  is a diagram illustrating the state before the front end of the sheet S reaches the sheet detecting apparatus  100 , i.e., the state before the sheet S comes into abutment with the sheet abutting portion  103  of the lever member  101 . At this time, the lever member  101  is positioned at the detection standby position. 
     The sheet S conveyed to the conveying roller pair  208  by the sheet feed roller  206  and conveyed along the conveyance guide  107  in the direction of the nip line of the conveying roller pair  208  finally reaches the front end passing position t as illustrated in  FIG. 5B . Subsequently, the sheet S is conveyed while turning the lever member  101  retained at the detection standby position in abutment with the stopper  106  in the direction indicated by the arrow q as illustrated in  FIG. 5C . Thereby, the lever member  101  moves from the detection standby position to the detection position, and the light-shielding flag portion  104  blocks the optical path of the optical sensor  102 . Accordingly, the control portion  250  detects the passage of the sheet S. 
     Next, the sheet S is conveyed in the state in which the sheet abutting portion  103  is moved to the detection position, and the front end of the sheet S is finally conveyed to the nip portion N 2  of the registration roller pair  209  as illustrated in  FIG. 5D . Subsequently, the sheet S passes through the nip portion N 2  in a state of being nipped by the registration roller pair  209 . 
     At this time, as described above, the sheet conveying speed of the registration roller pair  209  is set to be higher than the sheet conveying speed of the conveying roller pair  208 . Therefore, the sheet S is conveyed on a substantially straight line connecting both of the nip portions N 1  and N 2  between the conveying roller pair  208  and the registration roller pair  209  while maintaining the stretched state. Thereby, the conveyance route of the sheet S is shifted from the route along the conveyance guide  107  until reaching to the front end passing position t to the conveyance passage route u which is positioned on the nip line of the registration roller pair  209  as illustrated in  FIG. 6A . 
     Then, if the conveyance passing route is shifted, the sheet S moves in a direction away from the sheet abutting portion  103 . Thereby, the lever member  101  is turned in the direction indicated by the arrow p by the bias spring and returns back to the detection standby position, and in association with it, the light-shielding flag portion  104  retracts from the optical path of the optical sensor  102 , whereby the light-receiving portion receives light from the light-emitting portion again, and the optical sensor  102  is put into the non-detection state. 
     In this manner, when the front end of the sheet S is conveyed to the nip portion N 1  of the registration roller pair  209 , the lever member  101  returns back to the detection standby position by the difference between the conveying speeds of the registration roller pair  209  and the conveying roller pair  208  and a bias force exerted by the bias spring. In other words, in the present embodiment, if the sheet S passes through the front end passing position t, the lever member  101  returns back to the detection standby position before the rear end of the sheet S passes through. Accordingly, the sheet detecting apparatus  100  is put into a state being able to detect the front end of the succeeding sheet S 2  before the rear end of the sheet S passes through. 
     The sheet fed next is conveyed along the conveyance guide  107  by the conveying roller pair  208 , and finally comes into abutment with the lever member  101  moved to the detection standby position as illustrated in  FIG. 6B , and then turns the lever member  101 . At this time, the rear end of the preceding sheet S has not passed through the nip portion N 2  of the registration roller pair  209  yet. However, since the lever member  101  has moved to the detection standby position, it is possible to detect the succeeding sheet S 2  by the lever member  101  irrespective of the position of the rear end of the preceding sheet S. Consequently, the distance D 11  between the rear end of the preceding sheet S and the front end of the sheet S 2  can be brought closer to zero limitlessly. 
     As described above, according to the present embodiment, the sheet conveying speed of the registration roller pair  209  is set to be higher than the sheet conveying speed of the conveying roller pair  208 . When the lever member  101  is located at the detection standby position, the lever member  101  is arranged so as not to intersect with the imaginary straight line connecting the nip portion N 2  of the registration roller pair  209  and the nip portion N 1  of the conveying roller pair  208 . 
     Thereby, when the sheet S is nipped by the registration roller pair  209  and then passes through the conveyance passage route u in the stretched state, the lever member  101  moves away from the sheet S and returns to the detection standby position. Then, by arranging such that the lever member  101  returns to the detection standby position during a period before when the rear end of the sheet passes through after the passage of the front end of the sheet as described above, it becomes possible to detect the succeeding sheet before the rear end of the sheet passes through the sheet detecting apparatus  100 . Accordingly, it is possible to bring about the same effects and advantages as those in the first embodiment described above by the present embodiment. 
     Next, a third embodiment of the present invention will be described.  FIG. 7  is a diagram illustrating a configuration of the sheet conveying apparatus of the present embodiment. In  FIG. 7 , the same reference signs as those in  FIG. 5  described above denote the same or corresponding portions. 
     In  FIG. 7 , first and second conveyance guides  107   c  and  107   d  are provided between the conveying roller pair  208  and the registration roller pair  209  so as to oppose to each other and compose the sheet conveyance path R. The first conveyance guide  107   c  has a straight shape, and the second conveyance guide  107   d , which is an opposed guide portion provided so as to oppose the first conveyance guide  107   c , has a curved shape bulging outward. That is, the second conveyance guide  107   d  is formed curvedly in a direction away from the first conveyance guide  107   c.    
     It is noted that in the present embodiment, the nip line of the conveying roller pair  208  runs in a direction in parallel with the first conveyance guide  107   c . Unlike the direction of the nip line of the conveying roller pair  208 , a direction of the nip line of the registration roller pair  209  runs in parallel with a downstream part in the sheet conveying direction of the conveyance guide  107   d . That is, the conveying roller pair  208  is arranged such that the nip line, i.e., the tangential line of the nip portion N 1 , of the conveying roller pair  208  intersects with the optical sensor  102  of the lever member  101  in the standby state. 
     Still further, according to the present embodiment, the sheet conveying speed of the registration roller pair  209  is set to be lower than the sheet conveying speed of the conveying roller pair  208 . In this manner, with the provision of a difference of the sheet conveying speeds, the sheet S passes through the conveyance passage route u between the registration roller pair  209  and the conveying roller pair  208  while deflecting toward the second conveyance guide  107   d  after having nipped by the registration roller pair  209 . That is, the registration roller pair  209  is set such that a rotational speed thereof is lower than a rotational speed of the conveying roller pair  208  at least when the sheet is nipped and conveyed by both of nip portions N 1  and N 2  of the conveying roller pair  208  and the registration roller pair  209 . Accordingly, when the sheet S passes through the conveyance passage route u, the lever member  101  is moved away from the sheet S. 
     Next, the sheet detecting operation of the sheet detecting apparatus  100  configured as described above will be described.  FIG. 8A  is a diagram illustrating the state before the front end of the sheet S reaches the sheet detecting apparatus  100 , i.e., the state before the sheet S comes into abutment with the sheet abutting portion  103  of the lever member  101 . At this time, the lever member  101  is positioned at the detection standby position. 
     The sheet S conveyed to the conveying roller pair  208  by the sheet feed roller  206  and conveyed along the first conveyance guide  107   c  by the conveying roller pair  208  finally reaches the front end passing position t as illustrated in  FIG. 8B . Subsequently, the sheet S is conveyed while turning the lever member  101  in the direction indicated by the arrow q as illustrated in  FIG. 8C . Accordingly, the lever member  101  moves from the detection standby position to the detection position, and the light-shielding flag portion  104  blocks the optical path of the optical sensor  102 . Accordingly, the control portion  250  detects the passage of the sheet S. 
     Next, the sheet S is conveyed in a state in which the sheet abutting portion  103  is moved to the detection position, and the front end thereof is conveyed to the nip portion N 2  of the registration roller pair  209  as illustrated in  FIG. 8D . Subsequently, the sheet S passes through the nip portion N 2  in the state of being nipped by the registration roller pair  209 . 
     At this time, the conveying speed of the registration roller pair  209  is set to be lower than the conveying speed of the conveying roller pair  208 . Therefore, the sheet S is conveyed while being deflected toward the second conveyance guide  107   d  between the conveying roller pair  208  and the registration roller pair  209  as illustrated in  FIG. 9A . Accordingly, the conveyance route of the sheet S is shifted from a route along the first conveyance guide  107   c  until reaching to the front end passing position t to the conveyance passage route u which is positioned on the nip line of the registration roller pair  209 . 
     Then, when the conveyance passage route is shifted, the sheet S moves in the direction away from the sheet abutting portion  103 . In association with this movement, the lever member  101  turns in the direction indicated by the arrow p by the bias spring, and starts to return back to the detection standby position, and in association with it, the light-shielding flag portion  104  retracts from the optical path, whereby the light-receiving portion receives light from the light-emitting portion again and the optical sensor  102  is put into the non-detection state. 
     In this manner, when the front end of the sheet S is conveyed to the nip portion N 1  of the registration roller pair  209 , the lever member  101  returns back to the detection standby position by the difference between the conveying speeds of the registration roller pair  209  and the conveying roller pair  208  and the bias force exerted by the bias spring. In other words, according to the present embodiment, when the sheet S passes through the front end passing position t, the lever member  101  returns back to the detection standby position before the rear end of the sheet S passes through. Accordingly, the sheet detecting apparatus  100  is put into a state being able to detect the front end of the succeeding sheet S 2  before the rear end of the sheet S passes through. 
     The sheet fed next is conveyed along the first conveyance guide  107   c  by the conveying roller pair  208 , and finally comes into abutment with the lever member  101  moved to the detection standby position as illustrated in  FIG. 9B , and then turns the lever member  101 . At this time, the rear end of the preceding sheet S has not passed through the nip portion N 2  of the registration roller pair  209  yet. However, since the lever member  101  has moved to the detection standby position, it is possible to detect the succeeding sheet S 2  by the lever member  101  irrespective of the position of the rear end of the preceding sheet S. Consequently, the distance D 11  between the rear end of the preceding sheet S and the front end of the sheet S 2  can be brought closer to zero limitlessly. 
     As described above, according to the present embodiment, the sheet conveying speed of the registration roller pair  209  is set to be lower than the sheet conveying speed of the conveying roller pair  208 . The lever member  101  moves away from the sheet S and returns back to the detection standby position when the sheet S passes through the conveyance passage route u while being deflected toward the second conveyance guide  107   d  after being nipped by the registration roller pair  209  by providing the difference of the sheet conveying speeds as described above. Accordingly, it is possible to bring about the same effects and advantages as those in the first embodiment described above. 
     Next, a fourth embodiment of the present invention will be described.  FIG. 10  is a diagram illustrating a configuration of the sheet conveying apparatus of the present embodiment. In  FIG. 10 , the same reference signs as those in  FIG. 4  described above denote the same or corresponding portions. 
     In  FIG. 10 , a guide member  110 , i.e., a sheet conveying direction regulating member, provided so as to be turnable about a shaft  111  at downstream in the sheet conveying direction of the conveying roller pair  208 , and directs the sheet conveyed by the conveying roller pair  208  toward the first conveyance guide  107   a . The guide member  110  is biased toward a direction indicated by an arrow r to bring the sheet being conveyed into abutment with the first conveyance guide  107   a  by the bias spring. Still further, according to the present embodiment, the sheet conveying speed of the registration roller pair  209  is set to be higher than the sheet conveying speed of the conveying roller pair  208 . In this manner, with the provision of the difference of the sheet conveying speeds, the sheet S passes through the conveyance passage route u between the registration roller pair  209  and the conveying roller pair  208  in the stretched state after having nipped by the registration roller pair  209 . That is, guide member  110  is the sheet conveying direction regulating member being capable of moving the sheet conveyed by the conveying roller pair  208  to a first position from which the sheet is directed to a side of the first conveyance guide  107   a  and to a second position moved to a side of the second conveyance guide  107   d  from the first position. 
     Here, the sheet S which has passed through the conveying roller pair  208  is guided in the direction to come into abutment with the first conveyance guide  107   a  by the guide member  110  until when the sheet S is nipped by the registration roller pair  209 . The sheet S after having abutted with the first conveyance guide  107   a  moves along the first conveyance guide  107   a , and finally comes into abutment with the sheet abutting portion  103 . When the conveyance of the sheet S advances and the sheet S is conveyed between the registration roller pair  209  and the conveying roller pair  208  in the stretched state, the guide member  110  is pressed by the sheet S in the stretched state, and turns in a direction opposite from the arrow r against the bias spring. 
     Next, the sheet detecting operation of the sheet detecting apparatus  100  configured as described above will be described.  FIG. 11A  is a diagram illustrating the state before the front end of the sheet S reaches the sheet detecting apparatus  100 , i.e., a state before the sheet comes into abutment with the sheet abutting portion  103  of the lever member  101 . At this time, the lever member  101  is positioned at the detection standby position, and the guide member  110  is moved to a side of the first conveyance guide  107   a.    
     The sheet S conveyed to the conveying roller pair  208  by the sheet feed roller  206  and guided along the first conveyance guide  107   a  by the guide member  110  finally reaches the front end passing position t as illustrated in  FIG. 11B . Subsequently, the sheet S is conveyed while turning the lever member  101  in the direction indicated by the arrow q as illustrated in  FIG. 11C . Accordingly, the lever member  101  moves from the detection standby position to the detection position, and the light-shielding flag portion  104  blocks the optical path of the optical sensor  102 . Accordingly, the control portion  250  detects the passage of the sheet S. 
     Next, the sheet S is conveyed while moving the sheet abutting portion  103  to the detection position, and the front end of the sheet S is finally conveyed to the nip portion N 2  of the registration roller pair  209  as illustrated in  FIG. 11D . Subsequently, the sheet S passes through the nip portion N 2  while being nipped by the registration roller pair  209 . 
     The sheet conveying speed of the registration roller pair  209  at this time is set to be higher than the conveying speed of the conveying roller pair  208  as described above. Therefore, the sheet S is conveyed on the substantially straight line connecting both of the nip portions N 1  and N 2  between the conveying roller pair  208  and the registration roller pair  209  while maintaining the stretched state. Accordingly, the guide member  110  is pressed by the sheet S in the stretched state, and is turned in the direction opposite from the arrow r against the bias spring as illustrated in  FIG. 12A . Also, the conveyance route of the sheet S is shifted from a route along the conveyance guide  107  until reaching to the front end passing position t to the conveyance passage route u which is positioned on the nip line of the registration roller pair  209 . 
     When the conveyance passage route is moved, the sheet S moves in the direction away from the sheet abutting portion  103 . Accordingly, the lever member  101  turns in the direction indicated by the arrow p by the bias spring and returns back to the detection standby position, and in association with it, the light-shielding flag portion  104  retracts from the optical path of the optical sensor  102 , whereby the light-receiving portion receives light from the light-emitting portion again, and the optical sensor  102  turns into a non-detection state. 
     In this manner, when the front end of the sheet S is conveyed to the nip portion N 1  of the registration roller pair  209 , the lever member  101  returns back to the detection standby position by the difference between the conveying speeds of the registration roller pair  209  and the conveying roller pair  208  and the bias force exerted by the bias spring. In other words, according to the present embodiment, when the sheet S passes through the front end passing position t, the lever member  101  returns to the detection standby position before the rear end of the sheet S passes through. Accordingly, the sheet detecting apparatus  100  is put into the state being able to detect the front end of the succeeding sheet S 2  before the rear end of the sheet S passes through. 
     The sheet fed next is conveyed along the conveyance guide  107  by the conveying roller pair  208 , and finally comes into abutment with the lever member  101  moved to the detection standby position as illustrated in  FIG. 12B , and then turns the lever member  101 . At this time, the rear end of the preceding sheet S has not passed through the nip portion N 2  of the registration roller pair  209  yet. However, since the lever member  101  has moved to the detection standby position, it is possible to detect the succeeding sheet S 2  by the lever member  101  irrespective of the position of the rear end of the preceding sheet S. Consequently, the distance D 11  between the rear end of the preceding sheet S and the front end of the sheet S 2  can be brought closer to zero limitlessly. 
     As described above, in the present embodiment as well, the lever member  101  is configured to return back to the detection standby position after the passage of the front end of the sheet before the rear end passes through. Accordingly, the same effects and advantages as in the first embodiment described already are achieved. 
     While the present invention has been described with reference to the exemplary embodiments, it is to be understood that the invention 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. 2014-076748, filed on Apr. 3, 2014, which is hereby incorporated by reference herein in its entirety.