Patent Publication Number: US-8973920-B2

Title: Conveying apparatus and recording apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a conveying apparatus which conveys a sheet via a conveying path including a curved portion and which corrects the direction of the sheet so that a side of a leading end of the sheet is orthogonal to a conveying direction, and a recording apparatus with the conveying apparatus mounted therein. 
     2. Description of the Related Art 
     In a known configuration of recording apparatuses represented by printers, copiers, and facsimile machines, sheets are conveyed using a conveying path with a curved internal space in order to reduce the size of the apparatus. In such a recording apparatus, a sheet may be pushed hard against an outer side of the conveying path due to the rigidity of the sheet and thus conveyed while being subjected to great conveying resistance. This increases the likelihood of causing the sheet to skew. Thus, such a recording apparatus desirably performs an operation of correcting the direction of the sheet so that a side of a leading end of the sheet is orthogonal to a conveying direction, what is called an skew correcting operation, before recording an image on the sheet. A known common skew correcting operation reverses a main conveying roller (roller) engaged with the sheet. During the skew correcting operation, a loop (flexible portion) of the sheet is formed in the internal space of the conveying path. The loop comes into abutting contact with the outer side of curvature of the conveying path. Then, a force is exerted in conjunction with the abutting contact and causes a leading end of the sheet to be pushed into the main conveying roller. Japanese Patent Application Laid-Open No. H08-157107 discloses an apparatus that can adjust the above-described pressing force according to the rigidity of the sheet. The apparatus disclosed in Japanese Patent Application Laid-Open No. H08-157107 includes an upstream guide formed of a thin elastic plate and a downstream plate formed of a rigid plate and biased toward an inner side of the conveying path by a spring; the upstream and downstream guides are arranged on the outer side of a curvature of the conveying path. In this apparatus, during the skew correcting operation, less rigid sheets come into abutting contact with the upstream guide and are pushed into an skew correcting roller by the elastic force of the upstream guide. More rigid sheets come into abutting contact with the downstream guide and are pushed into a registration roller by a downstream elastic force that is greater than that of the upstream guide. During the skew correcting operation, the apparatus disclosed in Japanese Patent Application Laid-Open No. H08-157107 provides a space in the conveying path in which the sheet is deflected or flexed and can push the sheet into the registration roller with an appropriate force according to the rigidity of the sheet. 
     When a conveying operation and an skew correcting operation are performed within a curved conveying path in the same manner as that of the apparatus disclosed in Japanese Patent Application Laid-Open No. H08-157107, a narrow conveying path (a short distance between the inner guide and the outer guide) facilitates the abutting contact of the loop of the sheet with the conveying path and is thus suitable for the skew correcting operation. However, in this case, conveying resistance of the sheet is increased, possibly affecting the conveying operation. In contrast, a wide conveying path (a long distance between the inner guide and the outer guide) serves to reduce the conveying resistance of the sheet and is thus suitable for the conveying operation. However, this makes the abutting contact of the loop of the sheet with the conveying path difficult, possibly hindering the skew correcting operation from being stably achieved. 
     SUMMARY OF THE INVENTION 
     Thus, an object of the present invention is to provide a conveying apparatus that enables both a reduction in conveying resistance and a stable skew correcting operation, and a recording apparatus with the conveying apparatus. 
     To accomplish the object, a conveying apparatus according to the present invention includes a conveying path with a curved path through which a sheet is passed, 
     a roller provided downstream of the conveying path in a conveying direction of the sheet, the roller being rotated in a first direction to enable execution of a conveying operation of conveying the sheet in the conveying direction and being rotated in a second direction opposite to the first direction to enable execution of an skew correcting operation of forming a loop of the sheet, and 
     a guide member which guides the sheet using an inner side of a curvature of the conveying path and which can move toward the inner side of the curvature of the conveying path when subjected by the sheet during the conveying operation to a force stronger than during the skew correcting operation. 
     The present invention enables both a reduction in conveying resistance and a stable skew correcting operation. 
     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 perspective view illustrating an internal configuration of an ink jet recording apparatus that is an embodiment of a recording apparatus according to the present invention. 
         FIG. 2  is a cross-sectional view illustrating a configuration of a conveying apparatus mounted in the ink jet recording apparatus illustrated in  FIG. 1 . 
         FIG. 3  is a perspective view of an inclined surface member provided in the conveying apparatus illustrated in  FIG. 2 . 
         FIG. 4  is a cross-sectional view of the inclined surface member illustrated in  FIG. 3 . 
         FIG. 5A  and  FIG. 5B  are cross-sectional views of an abutting member  103  provided in the conveying apparatus illustrated in  FIG. 2 . 
         FIG. 6  is a perspective view of the surroundings of a separating member extracted from  FIG. 2  illustrating the conveying apparatus. 
         FIG. 7  is a cross-sectional view of the separating member illustrated in  FIG. 6 . 
         FIG. 8A  and  FIG. 8B  are diagrams illustrating, in further detail, a configuration of the separating member illustrated in  FIG. 6  and  FIG. 7 . 
         FIG. 9  is a cross-sectional view of a reverse conveying portion of the conveying apparatus. 
         FIG. 10  is a perspective view of an inner guide unit. 
         FIG. 11  is an exploded perspective view of a conveying roller unit. 
         FIG. 12  is a cross-sectional view of an outer guide unit. 
         FIG. 13  is a perspective view of an auxiliary guide member. 
         FIG. 14  is a cross-sectional view of the auxiliary guide member illustrated in  FIG. 13 . 
         FIG. 15  is a block diagram illustrating electric control components of the ink jet recording apparatus illustrated in  FIG. 1 . 
         FIG. 16  is a flowchart illustrating a procedure for operations of the ink jet recording apparatus illustrated in  FIG. 1 . 
         FIG. 17  is a cross-sectional view illustrating the position and state of a sheet during a conveying operation and an skew correcting operation both of which are performed by a main conveying roller. 
         FIG. 18  is a cross-sectional view illustrating the position and state of the sheet during the conveying operation and the skew correcting operation both of which are performed by the main conveying roller. 
         FIG. 19  is a cross-sectional view illustrating the position and state of the sheet during the conveying operation and the skew correcting operation both of which are performed by the main conveying roller. 
         FIG. 20A  and  FIG. 20B  are cross-sectional views illustrating operations of the auxiliary guide member. 
         FIG. 21  is a cross-sectional view of a conveying apparatus provided in a recording apparatus according to Exemplary Embodiment 2 of the present invention. 
         FIG. 22  is a cross-sectional view illustrating operations of the auxiliary guide member illustrated in  FIG. 21 . 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Preferred embodiments of the present invention will now be described in detail in accordance with the accompanying drawings. 
     (Exemplary Embodiment 1) 
       FIG. 1  is a perspective view illustrating an internal configuration of an ink jet recording apparatus  10  that is an exemplary embodiment of a recording apparatus according to the present invention.  FIG. 1  mainly illustrates a configuration of an image forming portion  914  (see  FIG. 15 ) that forms an image on a sheet. The image forming portion  914  includes a recording head  14 , a platen  15 , a pair of main conveying rollers  16 , a sheet discharging roller  17 , and a carriage  18 . In the ink jet recording apparatus  10 , a sheet conveyed to by a conveying apparatus passes through a conveying path curved in a U shape to the platen  15 . Thereafter, the recording head  14  ejects ink from above the platen  15  to form an image on the sheet. At this time, the recording head  14  ejects the ink while the carriage  18  is moving in a direction orthogonal to an advancing direction of the sheet. The sheet with the image formed thereon is discharged into a sheet discharging tray  13 . 
       FIG. 2  is a cross-sectional view of the conveying apparatus mounted in the recording apparatus illustrated in  FIG. 1 . The conveying apparatus  11  illustrated in  FIG. 2  includes a sheet feeding portion  19  and a reverse conveying portion  20 . First, the sheet feeding portion  19  will be described. 
     As illustrated in  FIG. 2 , the sheet feeding portion  19  includes a sheet feeding tray  101  that can accommodate a plurality of stacked sheets P. In the sheet feeding tray  101 , the side surfaces of the sheets P are aligned with a side guide (not illustrated in the drawings). An inclined surface member  102  is arranged in front of the sheet feeding tray  101  in an advancing direction D of the sheet P to separate one sheet P from the plurality of sheets P. A sheet feeding mechanism  100  is arranged above the sheet feeding tray  101 . The sheet feeding mechanism  100  includes a sheet feeding arm  104 . When rotated around a rotating shaft  105 , the sheet feeding arm  104  can be rotated according to the stack height of the sheets P stacked in the sheet feeding tray  101 . The sheet feeding arm  104  includes a sheet feeding roller  106  attached to a tip thereof to advance the uppermost sheet P. The sheet feeding roller  106  is driven by power transmitted via a rotating shaft  105  and a sheet feeding idler gear  107 . The sheet feeding roller  106  is in abutting contact with the uppermost sheet P. When the sheet feeding roller  106  is driven, a frictional force is exerted between the sheet feeding roller  106  and the sheet P to feed the sheet P in the advancing direction D. Thereafter, one sheet P is separated from the sheets P during passage along the inclined surface member  102  and conveyed to the reverse conveying portion  20 . 
     The inclined surface member  102  will be described below in detail. 
       FIG. 3  is a perspective view of the inclined surface member provided in the conveying apparatus illustrated in  FIG. 2 .  FIG. 4  is a cross-sectional view of the inclined surface member  102  illustrated in  FIG. 3 . The inclined surface member  102  includes a slope  102   a  inclined at an obtuse angle to the advancing direction in order to facilitate the separation of the uppermost sheet P. The slope  102   a  includes an inclined surface guide member  110  that reduces conveying resistance when the sheet P is conveyed along the slope  102   a . A surface of the inclined surface guide member  110  which contacts the sheet P is shaped by flattening a material with a small coefficient of friction. Two openings are formed in the slope  102   a  of the inclined surface member  102 . An abutting member  103  projects from one of the openings, and a separating member  111  projects from the other opening. The abutting member  103  and the separating member  111  will be described below. 
     First, the abutting member  103  will be described.  FIG. 5A  and  FIG. 5B  are cross-sectional views of the abutting member  103  provided in the conveying apparatus  11  illustrated in  FIG. 2 .  FIG. 5A  illustrates that the abutting member  103  is held at a position where the abutting member  103  comes into abutting contact with leading ends of the sheets P.  FIG. 5B  illustrates that the abutting member  103  is held at a position where the abutting member  103  has left the leading ends and retracted with respect to the inclined surface guide member  110 . The abutting member  103  is attached to a rotating shaft  119  provided at a lower side (foot side) of the slope  102   a  of the inclined surface member  102 . A surface of the abutting member  103  is stepped and includes a plurality of curved surfaces. Thus, even if the abutting member  103  runs into abutting contact with the sheets P housed in the sheet feeding tray  101  in order to align the leading ends of the sheets P with the abutting member  103 , damage to the sheets P can be reduced. A back surface of the abutting member  103  is pressed by a cam member  112 . The cam member  112  is attached to a rotating shaft (not illustrated in the drawings) provided inside the inclined surface member  102 . The abutting member  103  is pulled by a spring member  113  attached to the inclined surface member  102  and held as illustrated in  FIG. 5B . When power transmitted to a rotating shaft of the cam member  112  rotates the cam member  112  counterclockwise as seen in  FIG. 5B , the cam member  112  is stopped by a stopper at a position where the surface of the abutting member  103  is substantially perpendicular to the advancing direction D of the sheet P (see  FIG. 5A ). When the cam member  112  rotates clockwise as seen in  FIG. 5A , the cam member  112  is stopped by a stopper at a position where the abutting member  103  is retracted (hidden) from the inclined surface guide member  110 . The cam member  112  thus returns to the state illustrated in  FIG. 5B . 
     Now, the separating member  111  will be described.  FIG. 6  is a perspective view of the surroundings of the separating member  111  extracted from  FIG. 2  illustrating the conveying apparatus  11 .  FIG. 7  is a cross-sectional view of the separating member  111  illustrated in  FIG. 6 .  FIG. 8A  and  FIG. 8B  are diagrams illustrating, in further detail, a configuration of the separating member  111  illustrated in  FIG. 6  and  FIG. 7 .  FIG. 8A  is a perspective view of the separating member  111  extracted from  FIG. 6 .  FIG. 8B  is a cross-sectional view of the separating member  111  illustrated in  FIG. 8A . The separating member  111  comes into abutting contact with the sheets P, and includes a protruding surface  111   a  that is almost parallel to the slope  102   a  of the inclined surface member  102 . The protruding surface  111   a  includes a plurality of protrusions arranged along an inclining direction of the protruding surface  111   a . The separating member  111  is supported by a link mechanism  120  from a side opposite to the protruding surface  111   a.    
     The link mechanism  120  moves the separating member  111  from a projecting position to a retracted position. The projecting position is where the protrusions on the protruding surface  111   a  projects with respect to the slope  102   a  of the inclined surface member  102  and where the uppermost sheet being conveyed comes into abutting contact with the protruding surface  111   a . The retracted position is where the protrusions on the protruding surface  111   a  are retracted (hidden) with respect to the slope  102   a  of the inclined surface member  102 . The link mechanism  120  will be described below. 
     According to the present exemplary embodiment, the link mechanism  120  includes a pair of link members  114  and  115 . A central portion of the link member  114  is pivotally movably coupled to a central portion C of the link member  115 . A fitting hole K 1  formed at an upper end of the link member  114  is fitted over a shaft of the separating member  111 . The link member  114  is rotatably attached to the separating member  111 . The link member  115  includes a fitting hole formed at a lower end thereof and in which a slide shaft K 2  is fitted. The separating member  111  includes a slot  111   c  formed at a position lower than a shaft fitted in the fitting hole K 1 . The slide shaft K 2  can slide along the slot  111   c  in a direction intersecting the advancing direction D. 
     A straight line G 1  (see  FIG. 7 ) joining the fitting hole K 1  in the link member  114  and the slide shaft K 2  is set to be substantially perpendicular to the advancing direction D. Thus, according to the present exemplary embodiment, the slide shaft K 2  is slidable in the direction orthogonal to the advancing direction D (see arrow E in  FIG. 7 ). 
     The link member  114  includes a fitting hole formed at a lower end thereof. The fitting hole is pivotally movably fitted over a slide shaft S 2  that slides in the direction of arrow E in  FIG. 7 . The link member  115  includes a fitting hole S 1  formed at an upper end thereof and pivotally movably fitted over a shaft formed on a main body frame. A straight line G 2  joining the fitting hole S 1  and the slide hole S 2  is set to be substantially perpendicular to the advancing direction D. Thus, like the slide shaft K 2 , the slide shaft S 2  can slide in the direction of arrow E illustrated in  FIG. 7 . According to the present exemplary embodiment, the distance from each of the opposite ends of the link member  114  to the central portion C is equal to the distance from each of the opposite ends of the link member  115  to the central portion C. That is, the following are all equal: the distance from the fitting hole K 1  to the central hole C, the distance from the slide shaft K 2  to the central portion C, the distance from the fitting hole S 1  to the central portion C, and the distance from the slide shaft S 2  to the central portion C (see  FIG. 7 ). 
     The separating member  111  includes a spring member  116  attached to a side thereof opposite to the protruding surface  111   a . The spring member  116  presses the separating member  111  to hold the separating member  111  in the above-described projecting position. The pressing force of the spring member  116  acts in a direction opposite to the direction of the abutting force of the sheet P. 
     If the fed sheet P comes into abutting contact with the separating member  111  located at the projecting position and the abutting force received by the separating member  111  from the sheet P is greater than the pressing force of the spring member  116 , the slide shaft S 2  and the slide shaft K 2  simultaneously slide in the direction of arrow E in  FIG. 7 . As a result, the link mechanism  120  is deformed to move the separating member  111  toward the above-described retracted position. The separating member  111  is hidden in the inclined surface member  102 . The moving operation of the separating member  111  is similar regardless of the stack height of the sheets P stacked in the sheet feeding tray  101 . 
     Now, a configuration of the reverse conveying portion  20  will be described.  FIG. 9  is a cross-sectional view of the reverse conveying portion  20  of the conveying apparatus  11 . The reverse conveying portion  20  includes an inner guide unit  201  and an outer guide unit  202 . First, the inner guide unit  201  will be described.  FIG. 10  is a perspective view of the inner guide unit  201 . 
     The inner guide unit  201  includes an inner guide  204  of a conveying path  200  with a curved internal space through which the sheet is passed, and a conveying roller unit  203  attached to the inner guide  204 . The conveying roller unit  203  will be described.  FIG. 11  is an exploded perspective view of the conveying roller unit  203 . 
     The conveying roller unit  203  includes a conveying roller  207  that is a rotor conveying the sheet in the conveying direction, a conveying arm  208  with a conveying roller  207  and a drive transmitting unit, a conveying shaft  209  that serves to transmit a drive force, and a clutch  210 . An outer peripheral portion of the conveying roller  207  is formed of a high-friction member such as rubber and supported by the conveying arm  208 . A roller  224  (see  FIG. 9 ) is provided upstream of the conveying roller  207  in the conveying direction of the sheet to swing the conveying roller  207  in the conveying direction. The conveying roller  207  is of a swing arm type that revolves along an outer peripheral portion of the roller  224  to swing in the conveying direction. 
     The conveying arm  208  is configured to be able to swing because a shaft integrated with the conveying arm  208  is supported by holes Xa and Xb (see  FIG. 10 ) in the inner guide  204 . A supporting point of the conveying arm  208  is set upstream, in the conveying direction of the sheet, of the point of the contact between the sheet and the conveying roller  207 . One end side of the conveying shaft  209  is supported by the hole Xb so as to be coaxial with a shaft of the conveying arm  208 . The other end side of the conveying shaft  209  is supported by the inner guide  204  via the clutch  210 . The conveying shaft  209  rotates integrally with a conveying input gear  211  connected to a drive source (not illustrated in the drawings). The conveying arm  208  is configured to be rotatable within a predetermined range by engaging with a rotation regulating portion formed on the inner guide  204 . The conveying input gear  211  is fixed to the clutch  210  via a coupling member  230  and an engaging member  231 . The engaging member  231  includes a recessed groove  232  formed therein and with which the coupling member  230  is engaged. A clutch spring  214  is attached between the engaging member  231  and the conveying input gear  211 . One end of the clutch spring  214  is fixed to a drive frame (not illustrated in the drawings) of the inner guide unit  201  so that the engaging member  231  can be rotated only in one direction. 
     Rotation of the conveying input gear  211  releases the clutch spring  214  to allow the conveying shaft  209  to rotate. As a result, the conveying roller gear  212  rotates via the gear  213  fixed to the conveying shaft  209 . In conjunction with the conveying roller gear  212 , the conveying roller  207  rotates counterclockwise as seen in  FIG. 9  to feed the sheet in the conveying direction. At this time, when the sheet being conveyed offers conveying resistance to the conveying roller  207 , the turning force of the gear  213  acts as a torque that revolves the conveying roller gear  212  clockwise around the gear  213 . The torque in turn acts as a pressing force that presses the conveying roller  207  against a conveying pinch roller  215 . The pressing force that presses the conveying roller  207  against the conveying pinch roller  215  increases consistently with the conveying resistance of the sheet. With the conveying input gear  211  stopped, when the conveying roller  207  is rotated counterclockwise, the clutch  210  acts to block the drive transmitted from the conveying shaft  209 . Thus, the clutch spring  214  is released, and the conveying roller  207  rotates at a low torque. With the conveying input gear  211  stopped, when an attempt is made to rotate the conveying roller  207  clockwise, the clutch  210  acts to transmit power to the conveying shaft  209 . However, the clutch spring  214  contracts to preclude the conveying roller  207  from rotating. 
     Now, the outer guide unit  202  will be described.  FIG. 12  is a cross-sectional view of the outer guide unit  202 . The outer guide unit  202  includes an outer guide  205  of the conveying path  200  and a conveying pinch roller unit  206 . The conveying pinch roller unit  206  will be described. 
     The conveying pinch roller unit  206  includes a conveying pinch roller  215  that cooperates with the conveying roller  207  in conveying the sheet and a conveying pinch roller holder  216  to which the conveying pinch roller  215  is rotatably attached. The conveying pinch roller holder  216  is configured to be able to be swing because a shaft integrated with the pinch roller holder  216  is supported by a hole formed in the outer guide  205 . The conveying pinch roller holder  216  includes a conveying pinch roller spring  217  provided on a back surface side thereof. The conveying pinch roller spring  217  presses the conveying pinch roller  215  toward the conveying roller  207  via the conveying pinch roller holder  216 . The position of the conveying pinch roller holder  216  is regulated by a rotation regulating portion Z provided on the outer guide  205 . 
     The conveying pinch roller  215  and the conveying pinch roller holder  216  remain stationary until an abutting force X (see  FIG. 12 ) of the conveying roller  207  exceeds an elastic force Y (see  FIG. 12 ) of the conveying pinch roller spring  217  which acts in a direction opposite to the direction of the abutting force X. When the abutting force X (see  FIG. 12 ) exceeds the spring force X, the conveying pinch roller holder  216  and the conveying pinch roller  215  rotate counterclockwise as seen in  FIG. 12  and retracts. 
     In the conveying roller unit  203 , the conveying arm  208  includes a preload spring  218  attached thereto (see  FIG. 11 ). The preload spring  218  keeps the conveying roller  207  stationary in abutting contact with the conveying pinch roller  215 . The conveying arm  208  includes a supporting point located in a direction in which the conveying force further increases in response to the conveying resistance of the sheet. In a standby state with no conveying resistance (the sheet is not conveyed), the abutting force of the conveying roller  207  is equal to only the force of the preload spring  218 . When the conveying resistance of the sheet increases during conveyance, the abutting force of the conveying roller  207  correspondingly increases. When the abutting force exceeds the elastic force Y of the conveying pinch roller spring  217 , the conveying pinch roller  215  starts to retract. 
     In the above-described inner guide  204 , an auxiliary guide member  220  is provided on an inner side a curvature of the conveying path  200 .  FIG. 13  is a perspective view of the auxiliary guide member  220 .  FIG. 14  is a cross-sectional view of the auxiliary guide member  220 . 
     The auxiliary guide member  220  includes two shafts  220   a  and  220   b  extending in directions that intersect in the conveying direction. The shaft  220   a  is supported by a hole Ya formed in the inner guide  204 . On the other hand, the shaft  220   b  is supported by a hole Yb formed in the inner guide  204 . The auxiliary guide member  220  is attached to the inner guide  204  so as to be rotatable around the shafts  220   a  and  220   b . The shaft  220   b  includes an auxiliary guide spring member  221  attached to an outer peripheral surface thereof and which is a torsion coil spring. The auxiliary guide spring  221  is engaged with the auxiliary guide member  220  at one end thereof. The auxiliary guide spring  221  is engaged with the inner guide  204  at the other end thereof. The auxiliary guide spring  221  biases the auxiliary guide member  220  toward a direction opposite to the conveying direction. The auxiliary guide member  220  includes a protrusion (not illustrated in the drawings) located at a lower end thereof so that the point of the contact between the protrusion and the inner guide  204  serves as a stopper to receive the bias force of the auxiliary guide spring  221 . Thus, while no sheet is conveyed, the auxiliary guide member  220  is held in an upright posture with respect to the inner guide  204 . 
       FIG. 15  is a block diagram illustrating electric control components of the ink jet recording apparatus  10  illustrated in  FIG. 1 . A control portion  901  connects to one of a PC (Personal Computer)  902  that transmits signals to the control portion  901  and an operation panel  903  installed on the apparatus main body. When the control portion  901  receives a predetermined signal from one of the PC  902  and the operation panel  903  or a timer inside the control portion  901  has measured a predetermined elapsed time, the control portion  901  starts an image forming operation. The control portion  901  instructs a conveying motor driver  904  to supply power to the conveying motor  905 . A main drive transmission mechanism  906  is connected to the conveying motor  905 . The conveying motor  905  drives the pair of main conveying rollers  16  via the main drive transmission mechanism  906 . A conveyance drive transmission mechanism  908  is connected to the pair of main conveying rollers  16 . In conjunction with the driving by the pair of main conveying rollers  16 , the conveyance drive transmission mechanism  908  drives the conveying roller  207 . 
     Furthermore, the control portion  901  instructs an image forming portion motor driver  912  to supply power to an image forming portion motor  913 . An image forming portion  914  is connected to the image forming portion motor  913 . A sheet feeding drive transmission mechanism  910  is connected to the image forming portion  914  and the above-described conveying drive transmission mechanism  908 . The sheet feeding drive transmission mechanism  910  selectively switches between transmission and non-transmission of power from the conveyance drive transmission mechanism  908  to a sheet feeding mechanism  500  according to the position of the carriage  18  in the image forming portion  914 . As a result, the sheet feeding mechanism  500  and the conveying roller  207  can be synchronously/asynchronously driven. 
     The rotational state and loading state of each of the above-described motors and the conveying state of the sheet P are detected by sensors of a sensor group  915  including the plurality of sensors, provided at various parts in the ink jet recording apparatus  10 . Information detected by the sensor group  915  is transmitted to the control portion  901 . The control portion  901  controls the motors based on signals received from one of the PC  902  and the operation panel  903  and the detection information received from the sensor group  915 . 
       FIG. 16  is a flowchart illustrating a procedure for operations of the ink jet recording apparatus according to the present exemplary embodiment. When the PC  902  inputs a signal indicating the start of image formation to the control portion  901 , a sheet feeding operation is started (step S 1 ). Specifically, the control portion  901  transmits the above-described instruction to the conveying motor driver  904  to drive the conveying motor  905 . The sheet feeding roller  106  and the conveying roller  207  are sequentially rotated. 
     After a sheet feeding operation is started, the control portion  901  determines whether or not the sheet P has been conveyed by a predetermined amount (step S 2 ). The predetermined amount is the minimum required amount of conveyance which is required for the leading end of the sheet P to reach the pair of main conveying rollers  16 . Then, the control portion  901  determines whether or not a sensor  222  included in the sensor group  915  has detected the arrival of the sheet P at the pair of main conveying rollers  16  before a predetermined time elapses (step S 3 ). If the arrival of the sheet P has not been detected, the control portion  901  allows the operation panel  903  to indicate sheet absence error (step S 11 ), thus urging a user to re-feed a sheet P. Upon receiving the re-fed sheet through an error reset key provided on the operation panel  903  (step S 12 ), the control portion  901  returns to the operation in step S 1 . 
     In step S 3 , when the sensor  222  detects when the leading end of the sheet P is about to reach the pair of main conveying rollers  16 , the control portion  901  allows an skew correcting operation to be performed (step S 4  and step S 5 ). After the skew correcting operation is performed, the control portion  901  allows the pair of main conveying rollers  16  and the image forming portion  914  to perform an image forming operation (step S 6  to step S 8 ). When the image forming operation is terminated (step S 9 ), the control portion  901  allows a discharging operation of discharging the sheet P to be performed (step S 10 ). 
     The contents of the conveying operation and skew correcting operation of the main conveying roller  223 , one of the pair of main conveying rollers  16 , will be described below in detail. 
       FIG. 17  to  FIG. 19  are cross-sectional views illustrating the position and state of the sheet P during the conveying operation and the skew correcting operation. According to the present exemplary embodiment, the speed ratio of each of the sheet feeding roller  106 , conveying roller  207 , and sheet discharging roller  17  to the main conveying roller  223  is set as follows. 
     The main conveying roller:the sheet feeding roller:the conveying roller:the conveying roller:the sheet discharging roller=1:0.65:0.65:1 
     First, the sheet feeding roller  106 , the conveying roller  207 , and the main conveying roller  223  rotate in a direction in which the sheet P is conveyed in the conveying direction, to start a sheet feeding operation. In this case, the direction of rotation of the main conveying roller  223  is referred to as a first direction. 
     The sheet feeding roller  106  and the inclined surface member  102  separate the uppermost sheet P from the sheets P stacked in the sheet feeding tray  101  with recorded surfaces thereof down. The separated uppermost sheet P is conveyed through the inclined surface member  102  to the conveying roller  207  by the sheet feeding roller  106 . 
     Upon reaching the conveying roller  207 , the sheet P is conveyed further downstream in the conveying direction by the sheet feeding roller  106  and the conveying roller  207 . When conveyed by a predetermined amount after passing through the conveying roller  207 , the sheet P leaves the sheet feeding roller  106  and is conveyed only by the conveying roller  207 . Thereafter, when the sheet P passes through the conveying path  200 , the sensor  222  detects the leading end of the sheet P. Thereafter, when the sheet P is conveyed by a predetermined amount after passing a position where the leading end of the sheet P is detected, the conveying roller  207  is stopped. The predetermined amount varies depending on the type of the sheet P such as plain paper or photographic paper. The present exemplary embodiment sets the predetermined amount such that the leading end of the sheet P is positioned 6.5 mm downstream of the conveying roller  223  in the conveying direction for plain paper and 4 mm downstream of the conveying roller  223  in the conveying direction for photographic paper. 
     The sheet P supported by the auxiliary guide member  220  is conveyed along the conveying guide member  108  to the main conveying roller  223  by rotation of the conveying roller  207  (see  FIG. 17 ). According to the present exemplary embodiment, the main conveying roller  223  rotates about 1.5 times as fast as the conveying roller  207 . Thus, upon starting to be conveyed by the main conveying roller  223 , the sheet P in contact with the outer side of the conveying guide member  108  is drawn to the inner guide  204  side (see  FIG. 18 ). 
     Then, when the main conveying roller  223  starts to rotate in a second direction opposite to the first direction, the leading end of the sheet P is returned to upstream of a nip portion between the main conveying roller  223  and a follower rollerfollower, which form the pair of main conveying rollers  16 . Since the conveying roller  207  is stopped, a loop of the sheet P is formed in the internal space of the conveying path  200  (see  FIG. 19 ). As a result, one side of the leading end of the sheet P is pressed against both the main conveying roller  223  and the follower rollerfollower roller of the pair of main conveying rollers  16  on upstream of and in proximity to the nip portion between the main conveying roller  223  and the follower rollerfollower roller. Thus, the orientation of the sheet P is corrected such that the sheet P is orthogonal to the conveying direction. When the loop is in abutting contact with the conveying guide member  108 , the rigidity of the sheet P serves to increase a force that presses the leading end of the sheet P to the nip portion of the pair of main conveying rollers  16 . Therefore, possible skew can be efficiently corrected. If the sheet P is passing obliquely, the loop of the sheet P is twisted. 
     Then, when the main conveying roller  223  starts to rotate in the first direction, the loop formed in the middle of the sheet P is gradually eliminated due to a difference in velocity between the main conveying roller  223  and the conveying roller  207 . Moreover, when tension is applied to the sheet P between the main conveying roller  223  and the conveying roller  207 , the conveying roller  207  is rotated at a speed equal to the speed of the main conveying roller  223  via the sheet P. This eliminates the conveying resistance of the sheet P, which acts on the conveying roller  207 , and the force that brings the conveying roller  207  into abutting contact with the sheet P is exerted only by the preload spring  218 . Hence, only a weak force is exerted by the conveying roller  207  and the conveying pinch roller  215  in sandwiching the sheet between the rollers  207  and  215 . Thus, the sheet is likely to slide with respect to the conveying roller  207  and the conveying pinch roller  215 . A reaction force involved in the twist of the sheet P causes the sheet P to slide against the conveying roller  207  and the conveying pinch roller  215 . This eliminates the twisted loop of the sheet P. 
       FIG. 20A  and  FIG. 20B  are cross-sectional views illustrating operations of the auxiliary guide member  220 . 
     Until the sheet P reaches the main conveying roller  223 , the auxiliary guide member  220  is kept in an upright position by the bias force of the auxiliary guide spring member  221  so as to narrow the conveying path against a force R resulting from the weight of the sheet P and acting in the vertical direction. Also when the sheet P sandwiched between the main conveying roller  223  and the follower roller is conveyed downstream, the auxiliary guide member  220  is kept in the upright position by the bias force of the auxiliary guide spring member  221  so as to narrow the conveying path against the force resulting from the weight of the sheet P and acting in the vertical direction. While the main conveying roller  223  is performing an skew correcting operation (rotating in the second direction), the auxiliary guide member  220  receives, from the sheet P, the force resulting from the weight of the sheet P and acting in the vertical direction (see  FIG. 20A ). When the main conveying roller  223  performs a conveying operation (rotates in the first direction) after the skew correcting operation, the auxiliary guide member  220  receives a force acting in the conveying direction F, from the sheet P as a result of the friction between the auxiliary guide member  220  and the sheet P being moved and the tension applied to the sheet P (see  FIG. 20A ). The auxiliary guide member  220  is configured to rotate around the shafts  220   a  and  220   b  as described above. Thus, given a moment acting around the shafts  220   a  and  220   b , the force in the direction R is stronger than the force in the direction F. Thus, during the conveying operation, the auxiliary guide member  220  is tilted toward the conveying direction, and the portion of the auxiliary guide member  220  which guides the sheet P moves to the inner side of the curvature (see  FIG. 20B ). At this time, because of the above-described rotational configuration, the auxiliary guide member  220  is subjected to only low conveying resistance even with the contact thereof with the sheet P. 
     To move the auxiliary guide member  220 , which is movable as described above, the sheet P needs to come into contact with the auxiliary guide member  220 . However, meeting the following relationship enables improvement of the reliability with which the sheet P comes into contact with the auxiliary guide member  220 .
 
 e×B&gt;D  
 
     The velocity ratio e indicates the velocity ratio of the conveying roller  207  to the main conveying roller  223  during the conveying operation. The conveying distance B indicates the conveying distance over which the sheet P is conveyed in the direction opposite to the conveying direction. The minimum distance D indicates the minimum distance from the outer guide  205  to the upper end of the auxiliary guide member  220 . 
     According to the present exemplary embodiment, during the skew correcting operation, the auxiliary guide member  220  functions to narrow the conveying path  200 . This enables the loop of the sheet P to reliably come into abutting contact with the outer guide  205  to stabilize the skew correcting operation. On the other hand, during the conveying operation, the auxiliary guide member  220  functions to widen the conveying path  200  to enable a reduction in conveying resistance. During the conveying operation, the sheet P is in contact with the auxiliary guide member  220 , but the above-described rotational configuration reduces the conveying resistance. This enables both a reduction in conveying resistance and a stable skew correcting operation to be achieved. 
     (Exemplary Embodiment 2) 
     A recording apparatus according to Exemplary Embodiment 2 will be described. The following description focuses on differences from the ink jet recording apparatus  10  according to the above-described Exemplary Embodiment 1. The present exemplary embodiment is different from Exemplary Embodiment 1 in the auxiliary guide member  220  of the conveying apparatus  11 .  FIG. 21  is a cross-sectional view of the conveying apparatus  11  provided in the recording apparatus according to Exemplary Embodiment 2 of the present invention. In the conveying apparatus  11  according to the present exemplary embodiment, the auxiliary guide member  220  is a flat plate-like elastic member attached to the inner guide  204 . According to the present exemplary embodiment, the auxiliary guide member  220  is formed of two flat plates of polyester films of thickness 0.12 mm, width 23 mm and length 10.5 mm which are laminated together. 
       FIG. 22  is a cross-sectional view illustrating operations of the auxiliary guide member  220 . 
     While the main conveying roller  223  is performing a skew correcting operation, the auxiliary guide member  220  takes an upright posture with respect to the inner guide  204 . After the skew correcting operation, when the main conveying roller performs a conveying operation, the auxiliary guide member  220  is deformed so as to be deflected toward the conveying direction by a force received from the sheet P as illustrated in  FIG. 22 . Thus, the auxiliary guide member  220  is tilted toward the conveying direction after the skew correcting section compared to during the skew correcting operation. The portion of the auxiliary guide member  220  which guides the sheet P moves to the inner side of the curvature. 
     According to the present exemplary embodiment, as is the case with Exemplary Embodiment 1, the auxiliary guide member  220  functions to narrow the conveying path  200  during the skew correcting operation and to widen the conveying path  200  during the conveying operation. This enables both a reduction in conveying resistance and a stable skew correcting operation to be achieved. 
     Moreover, compared to Exemplary Embodiment 1, the present exemplary embodiment simplifies the driving configuration for the auxiliary guide member  220 , enabling a reduction in costs. 
     The above-described exemplary embodiments perform the skew correcting operation by reversing the main conveying roller  223  after conveying the sheet in the conveying direction using the pair of main conveying rollers  16 . The present invention is applicable to any other skew correcting operation. Another skew correcting operation is as follows. The sheet P is conveyed by the conveying roller  207  so that the leading end of the sheet P comes into abutting contact with both the main conveying roller  223  and follower roller of the stopped pair of main conveying rollers  16  upstream of and in proximity to the nip portion between the main conveying roller  223  and the follower roller. The sheet P is further conveyed by the conveying roller  207  so that a loop is formed between the conveying roller  207  and the pair of main conveying rollers  16 . Then, the leading end of the sheet P is pressed against both the main conveying roller  223  and the follower roller. One side of the leading end is aligned with a longitudinal direction of the main conveying roller  223 . Such a method may be used to correct possible skew. Furthermore, at this time, the skew correcting operation can be similarly performed even when the main conveying roller  223  is rotated in the direction opposite to the conveying direction. 
     While the present invention has been described with reference to 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. 2011-179610, filed Aug. 19, 2011, which is hereby incorporated by reference herein in its entirety.