Patent Publication Number: US-8973918-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 and an image forming apparatus, and more particularly, to the structure of a skew feeding correcting portion configured to correct skew feeding of a sheet. 
     2. Description of the Related Art 
     According to the related art, an image forming apparatus such as a copying machine, a printer, and a facsimile machine includes an image forming portion, and a sheet conveying apparatus configured to convey a sheet to the image forming portion by a conveyance roller. In the image forming apparatus according to the related art, due to deformation of the conveyance roller, misalignment of the conveyance roller, and the like, the sheet may sometimes be skewed when the sheet is conveyed. In the image forming apparatus, the position of the sheet with respect to the image forming portion significantly affects accuracy of an image forming position with respect to the sheet, and hence accurate alignment of the position of the sheet with respect to the image forming portion is an important factor to secure image quality. 
     In view of the above, in the image forming apparatus according to the related art, a skew feeding correcting portion is provided to the sheet conveying apparatus, and this skew feeding correcting portion corrects the skew feeding of the sheet, to thereby enhance the accuracy of the image forming position. As the skew feeding correcting portion described above, for example, there is known a skew feeding correcting portion including a shutter biased by a spring or the like in a direction opposite to a sheet conveying direction so as to bring a leading edge of the sheet into abutment against the shutter (Japanese Patent Application Laid-Open No. H09-183539 and International Patent WO2011/048668A). In the shutter-type skew feeding correcting portion described above, the leading edge of the sheet is brought into abutment against an abutment portion of a shutter member positioned perpendicularly to the sheet conveying direction, and the leading edge of the sheet is aligned with the abutment portion, to thereby correct the skew feeding of the sheet. 
     By the way, in recent years, there has been a users&#39; demand to enhance productivity of the image forming apparatus and reduce operation sound. However, in the case where the skew feeding is corrected by bringing the sheet into abutment against the shutter member as in the sheet conveying apparatus according to the related art, when the leading edge of the conveyed sheet is brought into abutment against the shutter member, collision sound is generated. The collision sound becomes louder when the sheet conveying speed increases to enhance the productivity. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in view of the above-mentioned circumstances, and it is therefore an object thereof to provide a sheet conveying apparatus and an image forming apparatus, which is configured to reduce collision sound to be generated due to abutment between a sheet and a shutter member. 
     According to one embodiment of the present invention, a sheet conveying apparatus configured to convey a sheet, comprises: 
     a skew feeding correcting portion configured to correct skew feeding of a sheet, 
     the skew feeding correcting portion including: 
     a rotary member pair configured to convey the sheet; 
     a shutter member configured to abut against a leading edge of a sheet being conveyed, and having a home position; and 
     a moving member arranged with a gap formed between the moving member and the shutter member positioned in the home position, such that the shutter member is moveable independently from the home position up to a point of engagement with the moving member, when the gap is closed, and such that the moving member is movable integrally with the shutter member while the gap is closed, 
     wherein the rotary member pair is arranged to nip a sheet during a period in which the shutter member is configured to move integrally with the moving member. 
     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 an overall structural view of a color laser printer serving as an example of an image forming apparatus including a sheet conveying apparatus according to a first embodiment of the present invention. 
         FIGS. 2A and 2B  are first explanatory views illustrating the structure of a skew feeding correcting portion provided to the sheet conveying apparatus. 
         FIG. 3  is a second explanatory view illustrating the structure of the skew feeding correcting portion. 
         FIG. 4  is an explanatory view illustrating shutter members provided in the skew feeding correcting portion. 
         FIG. 5  is a view illustrating a state at the time when the shutter member is positioned in a home position. 
         FIG. 6  is a view illustrating a state of a shutter cam at the time when the shutter member is positioned in the home position. 
         FIG. 7  is a view illustrating a state at the time when a skewed sheet is conveyed to the skew feeding correcting portion. 
         FIGS. 8A ,  8 B,  8 C, and  8 D are first explanatory views illustrating a skew feeding correcting operation of the skew feeding correcting portion. 
         FIGS. 9A ,  9 B,  9 C, and  9 D are second explanatory views illustrating the skew feeding correcting operation of the skew feeding correcting portion. 
         FIGS. 10A ,  10 B,  10 C, and  10 D are third explanatory views illustrating the skew feeding correcting operation of the skew feeding correcting portion. 
         FIGS. 11A ,  11 B,  11 C, and  11 D are fourth explanatory views illustrating the skew feeding correcting operation of the skew feeding correcting portion. 
         FIG. 12  is a cam diagram illustrating a relationship among a position of the shutter member, a radius of the shutter cam, and an angle of the shutter cam. 
         FIG. 13  is a first view illustrating another structure of the skew feeding correcting portion. 
         FIG. 14  is a second view illustrating still another structure of the skew feeding correcting portion. 
         FIG. 15  is an explanatory view illustrating the structure of a skew feeding correcting portion provided in a sheet conveying apparatus according to a second embodiment of the present invention. 
         FIGS. 16A and 16B  are first explanatory views illustrating a skew feeding correcting operation of the skew feeding correcting portion. 
         FIGS. 17A and 17B  are second explanatory views illustrating the skew feeding correcting operation of the skew feeding correcting portion. 
         FIGS. 18A and 18B  are views illustrating another structure of the skew feeding correcting portion. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Now, exemplary embodiments of the present invention will be described in detail with reference to the attached drawings.  FIG. 1  is an overall structural view of a color laser printer serving as an example of an image forming apparatus including a sheet conveying apparatus according to a first embodiment of the present invention. In  FIG. 1 , a color laser printer  600  has a full-color laser printer main body (hereinafter referred to as “printer main body”)  600 A. The printer main body  600 A includes an image forming portion  600 B configured to form an image on a sheet, a sheet feeding portion  600 C for feeding the sheet, a sheet conveying apparatus  100  configured to convey, to the image forming portion  600 B, the sheet fed from the sheet feeding portion  600 C, and the like. 
     The image forming portion  600 B includes process cartridges  8  ( 8 Y,  8 M,  8 C, and  8 K) removably mounted to the printer main body  600 A, and is configured to form toner images of four colors, specifically, yellow, magenta, cyan, and black, respectively. In this case, the process cartridges  8  include photosensitive drums  1  ( 1 Y,  1 M,  1 C, and  1 K) serving as image bearing members, charging rollers ( 2 Y,  2 M,  2 C, and  2 K), and developing rollers  3  ( 3 Y,  3 M,  3 C, and  3 K), respectively. Further, the image forming portion  600 B includes a scanner unit  4  arranged below the process cartridges  8  in a vertical direction, and configured to radiate laser beams based on image information to form electrostatic latent images on the respective photosensitive drums  1 . 
     Further, in  FIG. 1 , the printer main body  600 A includes an intermediate transfer belt unit  600 D, and the intermediate transfer belt unit  600 D includes an intermediate transfer belt  601 , and primary transfer rollers  7  ( 7 Y,  7 M,  7 C, and  7 K) arranged on an inner side of the intermediate transfer belt  601 . Note that, the intermediate transfer belt  601  is stretched around a secondary transfer opposing roller  602 T, a drive roller  6 , and a tension roller  5 . In this case, the drive roller  6  is a roller configured to drive the intermediate transfer belt  601  in a direction indicated by the arrow B (clockwise) so that the surface speed of the intermediate transfer belt  601  becomes substantially equal to the surface speed of each photosensitive drum  1 . Further, the drive roller  6  is rotationally driven by a drive source (not shown). 
     Further, the primary transfer rollers  7  are arranged to be opposed to the respective photosensitive drums  1  to form primary transfer portions T 1  (T 1 Y, T 1 M, T 1 C, and T 1 K), and a bias applying unit (not shown) applies a transfer bias to the primary transfer rollers  7 . Then, the primary transfer rollers  7  apply a primary transfer bias to the intermediate transfer belt  601 , and hence the toner images of the respective colors on the photosensitive drums are sequentially transferred onto the intermediate transfer belt  601 . In this manner, full-color images are formed on the intermediate transfer belt  601 . Further, the secondary transfer opposing roller  602 T and a secondary transfer roller  602  form a secondary transfer portion T 2  configured to transfer, onto the sheets, the full-color images sequentially formed on the intermediate transfer belt  601 . 
     The sheet feeding portion  600 C includes a sheet feeding cassette  9  removably mounted to the printer main body  600 A, a pickup roller  10  configured to feed sheets S contained in the sheet feeding cassette  9 . The sheet conveying apparatus  100  includes a sheet separating portion  13  configured to separate the sheets S fed by the pickup roller  10  into each single sheet S, and a skew feeding correcting portion  12  configured to correct a leading edge of the sheet S passing through the sheet separating portion to become in parallel to a leading edge of an image region including the toner image on the intermediate transfer belt  601 . Note that, after correcting the skew feeding of the sheet S, the skew feeding correcting portion  12  guides the sheet S into the secondary transfer portion T 2  in synchronization with a timing when the toner images on the intermediate transfer belt  601  arrive at the secondary transfer portion T 2 . 
     Note that, in  FIG. 1 , a fixing portion  604  fixes the toner images by heating and pressurizing the images formed on the sheet S. The fixing portion  604  includes a heating roller  604   a , and a pressure roller  604   b  held in pressure contact with the heating roller  604   a . Further, a control circuit board  605  serving as a control unit controls the color laser printer  600 . Based on a print start signal, the control circuit board  605  causes yellow, magenta, cyan, and black toner images to be formed on the respective photosensitive drums  1 . 
     Next, an image forming operation of the color laser printer  600  having the above-mentioned structure will be described. When image signals are input from a personal computer (not shown) or the like to the scanner unit  4 , the scanner unit  4  irradiates the photosensitive drums  1  with laser beams corresponding to the respective image signals. At this time, the surfaces of the photosensitive drums  1  are uniformly charged at predetermined polarity and potential by the charging rollers  2  in advance, and electrostatic latent images are formed on the surfaces through the irradiation of the laser beams from the scanner unit  4 . After that, those electrostatic latent images are developed and visualized by the developing rollers  3 . 
     In this color laser printer  600 , the scanner unit  4  first irradiates the photosensitive drum  1 Y with a laser beam corresponding to an image signal of a yellow component of an original, to thereby form an electrostatic latent image for yellow on the photosensitive drum  1 Y. Then, the developing roller  3 Y develops the electrostatic latent image for yellow with yellow toner, to thereby visualize the electrostatic latent image as a yellow toner image. After that, along with rotation of the photosensitive drum  1 Y, the yellow toner image arrives at the primary transfer portion T 1 Y formed through abutment between the photosensitive drum  1 Y and the intermediate transfer belt  601 , and then the yellow toner image on the photosensitive drum  1 Y is transferred onto the intermediate transfer belt  601  due to the primary transfer bias applied to the primary transfer roller  7 Y. 
     When a part of the intermediate transfer belt  601  which bears the yellow toner image then moves, a magenta toner image formed on the photosensitive drum  1 M by a method similar to the above-mentioned method by the time of movement of the intermediate transfer belt  601  is transferred onto the intermediate transfer belt  601  while being superimposed on the yellow toner image. Similarly, along with the movement of the intermediate transfer belt  601 , a cyan toner image and a black toner image are transferred at the respective primary transfer portions T 1 C and T 1 K while being superimposed on the yellow toner image and the magenta toner image. In this manner, full-color toner images are formed on the intermediate transfer belt  601 . 
     Further, in parallel with the toner image forming operation, the sheets S contained in the sheet feeding cassette  9  are fed by the pickup roller  10 , and then separated by the sheet separating portion  13  serving as a sheet conveying unit into each single sheet S to be conveyed. After that, the sheet S is conveyed to the skew feeding correcting portion  12 , and the skew feeding is corrected by the skew feeding correcting portion  12 . Then, the sheet S is conveyed to the secondary transfer portion T 2  by the skew feeding correcting portion  12  so that the position of the full-color toner images on the intermediate transfer belt  601  is aligned with the position of the sheet S at the secondary transfer portion T 2 . Then, at the secondary transfer portion T 2 , a bias of a positive polarity is applied to the secondary transfer roller  602 , and hence the four-color toner images on the intermediate transfer belt  601  are secondarily transferred onto the conveyed sheet S. Note that, after the toner images are secondarily transferred onto the sheet S, the toner remaining on the intermediate transfer belt  601  is removed by a transfer belt cleaning device  603 , and the removed toner is collected into a waste toner collecting container (not shown). 
     After the toner images are transferred onto the sheet S, the sheet S is conveyed to the fixing portion  604 , and is heated and pressurized by the heating roller  604   a  and the pressure roller  604   b  so that the full-color toner images are fixed onto the surface of the sheet S as a permanent image. After the full-color toner images are fixed as a permanent image as described above, in a case of forming an image on one side of the sheet S, the sheet S is then delivered by a sheet delivering portion  600 E and stacked onto a sheet stacking portion  600 F. In a case of forming images on both sides of the sheet S, on the other hand, the sheet S is conveyed by a duplex conveying portion  600 G again to the image forming portion  600 B, and after the images are formed on both sides of the sheet S, the sheet S is delivered and stacked onto the sheet stacking portion  600 F. 
       FIGS. 2A and 2B  are explanatory views illustrating the structure of the skew feeding correcting portion  12  provided to the sheet conveying apparatus  100 .  FIG. 2A  is a perspective view of the skew feeding correcting portion  12 , and  FIG. 2B  is a perspective view of the skew feeding correcting portion  12  as seen from an opposite side to that in  FIG. 2A . The skew feeding correcting portion  12  includes a registration roller pair  101 ,  102  serving as a rotary member pair, which is formed of a registration roller  101  having a roller shaft  101   f  arranged in parallel to a rotational axis of each photosensitive drum  1 , and conveying rotatable members  102  ( 102   a ,  102   b ,  102   c ,  102   d  and  102   e ). The registration roller  101  includes the roller shaft  101   f , and a plurality of roller main bodies  101   a ,  101   b ,  101   c ,  101   d  and  101   e  fixed to the roller shaft  101   f  at predetermined intervals. Further, the conveying rotatable members  102   a  to  102   e  are held in pressure contact with the plurality of roller main bodies  101   a  to  101   e  of the registration roller  101 , respectively. 
     Note that, in the embodiment, the conveying rotatable members  102  ( 102   a  to  102   e ) are rotatably supported by bearing portions (not shown) which are supported to be movable along a direction of the registration roller  101  with respect to a conveyance frame  201  serving as a main body of the sheet conveying apparatus  100 . Further, the bearing portions (not shown) are biased toward the registration roller  101  by rotatable member pressing units  501  and rotatable member pressing springs  502  illustrated in  FIG. 3 , and thus the conveying rotatable members  102   a  to  102   e  are brought into pressure contact with the roller main bodies  101   a  to  101   e , respectively. 
     Note that, in  FIG. 3 , a shutter shaft  302  serving as a moving member is supported to be rotatable (movable) with respect to the conveyance frame  201  and to be in parallel to the direction of the rotational axis of each photosensitive drum  1 . As illustrated in  FIG. 4 , the shutter shaft  302  rotatably holds a plurality of shutter members (shutter portion)  301  ( 301 A,  301 B,  301 C, and  301 D). Note that, a shutter cam  303  configured to determine a posture (phase) of each shutter member  301  is provided at one end portion of the shutter shaft  302 . 
     Note that, in  FIG. 4 , a pressing member  304  is supported to be pivotable with respect to the conveyance frame  201 . A cam follower  306  is rotatably supported at a lower end of the pressing member  304 . Further, the cam follower  306 , which is provided on the pressing member  304 , is constantly held in pressure contact with the shutter cam  303  by a shutter spring  305  fixed to the conveyance frame  201 . Note that, in the embodiment, the shutter cam  303 , the cam follower  306 , and the shutter spring  305  serving as a biasing member form a biasing unit  12 A configured to bias the shutter shaft  302 . 
     Note that, as illustrated in  FIG. 3 , the shutter shaft  302  is provided coaxially with a shaft  102   g  of each conveying rotatable member  102  serving as one rotary member of the rotary member pair, and the shaft  102   g  of the conveying rotatable member  102  is supported so as to form a clearance T between the shaft  102   g  and an outer peripheral surface of the shutter shaft  302 . Thus, even when the conveying rotatable member  102  is moved, the conveying rotatable member  102  is not brought into contact with the shutter shaft  302 , and as a result, a biasing force for the conveying rotatable member  102  from the rotatable member pressing unit  501  and the rotatable member pressing spring  502  is not applied to the shutter shaft  302 . Thus, even when the conveying rotatable member  102  is biased, the rotational operation of the shutter members  301 A to  301 D and the shutter cam  303  which are mounted integrally with the shutter shaft  302  is not hindered. 
     As illustrated in  FIG. 5 , on the shutter shaft  302 , there are provided regulating members  401  serving as abutment portions which abut against the plurality of shutter members  301 A to  301 D provided on the shutter shaft  302  to regulate the rotation of the shutter members  301 A to  301 D. Further, the plurality of shutter members  301 A to  301 D are arranged at the same phase on the shutter shaft  302  through an intermediation of the respective regulating members  401 . Still further, gaps “g” are formed between the shutter members  301 A to  301 D and the respective regulating members  401 . Thus, the shutter members  301 A to  301 D are independently rotatable with respect to the shutter shaft  302  by an amount corresponding to a gap angle α between the shutter members  301 A to  301 D and the respective regulating members  401 . Note that, in the embodiment, the gap angle α is set to 5°. Further, on a peripheral surface of each shutter member  301 , three (or a plurality of) retaining surfaces  301   a ,  301   b , and  301   c  which abut against the leading edge of the sheet S to retain the sheet S are provided at regular intervals. 
       FIG. 5  illustrates a state at the time when the shutter member  301  is positioned in a standby position (hereinafter referred to as “home position”), which is a position of the shutter member  301  before the sheet S abuts against the shutter member  301 . At this time, the shutter member  301  takes such a posture that any one of the three retaining surfaces  301   a  to  301   c  is positioned on an upstream side of a nip portion N (see  FIG. 3 ) of the registration roller pair  101 ,  102  in a sheet conveying direction.  FIG. 6  illustrates a state of the shutter cam  303  at this time. The shutter cam  303  is brought into pressure contact with the cam follower  306  of the pressing member  304  which is biased by the shutter spring  305 , and hence the shutter member  301  is held in the home position. The shutter cam  303  includes the same number of depressed portions  303   a  as the number of the retaining surfaces  301   a  to  301   c . When the cam follower  306  engages with one of the depressed portions  303   a , the shutter shaft  302  and the shutter member  301  are positioned in the home position. 
     In general, in the color laser printer  600 , as illustrated in  FIG. 7 , the sheet S fed and conveyed from the sheet feeding cassette  9  may sometimes enter the registration roller pair  101 ,  102  in a posture inclined by ΔS with respect to the registration roller pair  101 ,  102 . In this case, when the plurality of shutter members  301  fixed to the shutter shaft  302  are not provided, the sheet S is conveyed still in the inclined posture to arrive at the secondary transfer portion T 2 , and hence the image to be transferred onto the sheet S is formed while being inclined with respect to the sheet S. However, the plurality of shutter members  301  fixed to the shutter shaft  302  are positioned on the upstream side of the nip portion N of the registration roller pair  101 ,  102  in the sheet conveying direction, and thus the inclination of the sheet S can be corrected. 
     Next, a skew feeding correcting operation of the skew feeding correcting portion  12  having the above-mentioned structure will be described. First, as illustrated in  FIG. 5 , an advancing-side leading edge portion of the sheet S conveyed in the inclined posture approaches the retaining surface  301   a  of the shutter member  301 A which is positioned on the upstream side of the nip portion N of the registration roller pair  101 ,  102  in the sheet conveying direction. At this time, as illustrated in  FIG. 6 , due to a biasing force of the shutter spring  305 , the shutter cam  303  rests in the home position which is an abutment position for aligning the leading edge of the sheet S by the retaining surface  301   a  of the shutter member  301 A. 
     Subsequently, as illustrated in  FIG. 8A , when the leading edge of the sheet S is brought into contact with the retaining surface  301   a , the shutter member  301 A is pushed by the sheet S and rotated in a direction indicated by the arrow z1. At this time, the gap “g” is formed between the shutter member  301 A and the regulating member  401 , and hence the shutter member  301 A is rotated by an amount corresponding to the gap angle α to abut against the regulating member  401 . Thus, the gap “g” is canceled, and the shutter member  301 A and the regulating member  401  form the gap angle α therebetween on the opposite side to that before the rotation. As a result, the rotation is temporarily stopped in such a position that the retaining surface  301   a  is positioned in a position indicated by  301   a ′. At this time, sliding resistance generated between the shutter member  301 A and the shutter shaft  302  due to the rotation of the shutter member  301 A is sufficiently smaller as compared to the biasing force of the shutter spring  305  which determines the posture of the shutter cam  303 , and hence, as illustrated in  FIG. 8B , there is no change in postures of the regulating member  401  and the shutter shaft  302 . 
     When the shutter member  301 A is rotated, the retaining surface  301   a  is moved to the position indicated by  301   a ′. At this time, the position of the retaining surface  301   a  is positioned on the upstream side of the nip portion N of the registration roller pair  101 ,  102  in the sheet conveying direction. When the rotation of the shutter member  301 A is stopped by the regulating member  401 , the sheet S receives a reaction force caused by a force for holding the shutter cam  303  biased by the shutter spring  305 . The biasing force of the shutter spring  305  is set so that the whole shutter members  301  are not rotatable at the time when one shutter member  301 A is pushed by the sheet S as described above. 
     Subsequently, when the sheet separating portion further conveys the sheet S to achieve a state illustrated in  FIG. 8C , the advancing-side leading edge portion of the sheet S conveyed in the inclined posture is still conveyed in a state of being retained by the retaining surface  301   a ′ of the shutter member  301 A. After that, a delaying-side leading edge portion of the sheet S conveyed in the inclined posture is retained by sequentially abutting against the retaining surfaces  301   a  of the plurality of shutter members  301 B,  301 C, and  301 D arranged in the positions corresponding to the leading edge portion of the sheet S. Through this process, the sheet S forms a loop curved in a direction indicated by the arrow y. 
     The loop of the sheet S is larger on an Sr side in  FIG. 7 , on which the sheet S is retained first, than on an Sl side, and then has a predetermined size afterward. When the loop has the predetermined size, due to stiffness (rigidity) of the sheet S, the leading edge of the sheet S is aligned with the retaining surfaces  301   a ′ of the shutter members  301 A to  301 D, with the result that the sheet S becomes in parallel to the direction of the rotational axis of the registration roller pair  101 ,  102  and the inclination ΔS becomes zero. Note that, also when the correction is thus carried out so that the inclination ΔS of the sheet S becomes zero, as illustrated in  FIG. 8D , there is no change in postures of the regulating member  401  and the shutter shaft  302 . That is, the shutter shaft  302  is not rotated. 
     When the sheet S is then aligned with the shutter members  301 A to  301 D, a force for rotating the shutter members  301 A to  301 D and the shutter cam  303  about the shutter shaft  302  in a direction indicated by the arrow z2 in  FIG. 9A  is generated due to the stiffness (rigidity) of the sheet S. Thus, the shutter members  301 A to  301 D and the shutter shaft  302  are integrally rotated and moved to a passage position for allowing the sheet S to enter the nip portion N of the registration roller pair  101 ,  102 . 
     After the sheet S enters the nip portion N of the registration roller pair  101 ,  102  while rotating the shutter members  301 A to  301 D, the sheet S is nipped and conveyed by the registration roller pair  101 ,  102  which starts rotating at a predetermined timing. Note that, when the shutter members  301  are pushed by the sheet S and the shutter shaft  302  is rotated integrally with the shutter members  301 , the shutter cam  303  is also rotated as illustrated in  FIG. 9B . 
     Also, when forming the loop of the sheet S, it is desired to form a larger loop inside a sheet conveyance path which is formed by the conveyance frame  201  and a conveyance guide  202 , to thereby enhance the skew feeding correcting performance. Therefore, as illustrated in  FIG. 9A , it is desired to provide a wide loop forming space  902  in a sheet conveyance path R which is formed by the conveyance frame  201  and the conveyance guide  202 , to thereby form a predetermined loop. Note that, the predetermined loop refers to a loop of the sheet S which is formed inside the loop forming space  902  and partially brought into contact with a conveyance guide  801  so that the stiffness (rigidity) of the sheet S becomes higher enough to push up the shutter members  301 . 
     Subsequently, as illustrated in  FIG. 9C , along with the travel of the leading edge of the sheet S conveyed due to a conveyance force of the registration roller pair  101 ,  102 , the shutter members  301  ( 301 A to  301 D) are rotated in a direction indicated by the arrow z3. When the shutter members  301  are rotated, a top dead center of the shutter cam  303  passes through a contact point between the shutter cam  303  and the cam follower  306  along with the rotation as illustrated in  FIG. 9D . When the top dead center of the shutter cam  303  passes through the contact point between the shutter cam  303  and the cam follower  306 , a rotational force in a direction indicated by the arrow z4 in  FIG. 10A  is generated in the shutter members  301  by the shutter cam  303  and the shutter spring  305 . 
     However, at this time, peripheral surfaces  311   b  serving as abutment surfaces of the shutter members  301  are brought into contact with the sheet S that is being conveyed. In this case, the sheet S has higher stiffness through the loop formation, and when the peripheral surfaces  311   b  are brought into contact with the sheet S thus having higher stiffness, the shutter members  301  are stopped without rotating. Note that, even in the state in which the shutter members  301  are not rotated, as illustrated in  FIG. 10B , the rotational force is applied to the shutter cam  303  due to the shutter spring  305 , and hence the shutter cam  303  and the shutter shaft  302  are rotated by the shutter spring  305 . That is, in the embodiment, the peripheral surfaces  311   b  of the shutter members  301  are brought into abutment against the sheet S which is being conveyed so as to stop the shutter members  301 . In this manner, only the shutter cam  303  and the shutter shaft  302  are rotated. 
     Thus, only the shutter cam  303  and the shutter shaft  302  are rotated by an amount corresponding to the gap angle α in a direction indicated by the arrow z5 in  FIG. 10C , and are then stopped by the regulating members  401  in the state in which the gap angle α is formed. In this manner, during the conveyance of the sheet S, the shutter members  301  are held in such a posture that the sheet S is nipped by the peripheral surfaces  311   b  and the conveyance guide  202 . Further, after the rotation by the amount corresponding to the gap angle α, the shutter members  301  are stopped, and hence the shutter cam  303  is stopped in a position illustrated in  FIG. 10D , in which the top dead center of the shutter cam  303  passes through the contact point between the shutter cam  303  and the cam follower  306 . 
     Subsequently, the sheet S is further conveyed and a trailing edge of the sheet S passes through the sheet separating portion  13 . Then, the stiffness of the sheet S becomes lower. When the stiffness of the sheet S becomes lower, the shutter members  301  are gradually rotated in a direction indicated by the arrow z6 in  FIG. 11A  together with the shutter cam  303  and the shutter shaft  302 . At this time, the shutter cam  303  and the shutter shaft  302  are rotated as illustrated in  FIG. 11B . 
     When the trailing edge of the sheet S is completely separated from the shutter members  301 , as illustrated in  FIG. 11C , the shutter members  301  are brought into a state in which their retaining surfaces  301   b  stand by in the home position for aligning a leading edge of a succeeding sheet S. Further, as illustrated in  FIG. 11D , due to the biasing force of the shutter spring  305 , the shutter cam  303  is brought back into the state in which the shutter members  301  are held in the home position. After that, every time the sheet S passes through the registration roller pair  101 ,  102 , the retaining surfaces are sequentially switched in an order of the retaining surface  301   a , the retaining surface  301   b , the retaining surface  301   c , and the retaining surface  301   a , and the respective retaining surfaces retain a leading edge of a newly fed sheet S, to thereby correct the skew feeding of the sheet S. 
     Note that,  FIG. 12  is a diagram illustrating a relationship among a position of the shutter member  301 , a radius of the shutter cam  303 , and an angle of the shutter cam  303  as described above. As in the cam diagram of  FIG. 12 , in the embodiment, when the shutter cam  303  is rotated at 75°, the shutter cam  303  is set so as to move to the position corresponding to the top dead center. When the shutter cam  303  is then further rotated at 45° from the position corresponding to the top dead center, the shutter member  301  is set so as to move to the home position. 
     As described above, in the embodiment, when the leading edge of the sheet S is brought into contact with the retaining surface  301   a , only the shutter member  301  is rotated by an amount corresponding to the gap angle α while canceling the gap “g”. Through the rotation of only the shutter member  301  described above, it is possible to absorb or reduce a shock received by the skew feeding correcting portion  12  through an intermediation of the shutter member  301 . Thus, it is possible to reduce collision sound that is generated when the sheet S is brought into contact with the shutter member  301 . That is, as in the embodiment, the regulating member  401  is arranged with the gap “g” formed between the regulating member  401  and the shutter member  301 , and the shutter member  301  is brought into abutment against the regulating member  401  during a period in which the shutter member  301  is moved from the abutment position. Thus, it is possible to reduce the collision sound which is generated due to the abutment between the sheet S and the shutter member  301 . 
     Further, in the embodiment, after the shutter member  301  is moved to the passage position, the peripheral surface  311   b  of the shutter member  301  is brought into contact with the sheet S, and then the shutter member  301  is stopped, but the shutter cam  303  and the shutter shaft  302  are rotated by an amount corresponding to the gap angle α. When the shutter member  301  is returned to the home position through the rotational operation of the shutter cam  303  and the shutter shaft  302 , the gap angle α is secured constantly. Thus, it is possible to keep the state in which, even when a succeeding sheet S is subsequently conveyed and brought into abutment against the shutter member  301 , the collision sound generated due to the abutment between the sheet S and the skew feeding correcting portion  12  is reduced constantly. 
     Further, in the embodiment, as described above, a larger loop is formed inside the sheet conveyance path R that is formed by the conveyance frame  201  and the conveyance guide  202 , to thereby increase the stiffness of the sheet S. Thus, even in a case of conveying a sheet having low rigidity, such as a sheet having a basis weight of 60 g/m 2  or less, it is possible to suppress deformation of the leading edge of the sheet when the sheet collides against the shutter member  301 , and to enhance the sheet skew feeding correcting performance as well. 
     The above description is directed to the case where the regulating member  401  is provided on the shutter shaft  302  and the gap “g” is formed between the shutter member  301  and the regulating member  401  so that the shutter member  301  is rotatable by an amount corresponding to the gap angle α, but the present invention is not limited thereto. For example, as illustrated in  FIG. 13 , a depressed portion  403  configured to form a gap between the shutter member  301  and the shutter shaft  302  may be provided in the shutter member  301 . Further, due to the depressed or flattened portion  403 , the shutter member  301  may be set independently rotatable with respect to the shutter shaft  302  by an amount corresponding to the gap angle α. 
     Further, as illustrated in  FIG. 14 , a spring or an elastic member  901  having spring property, which generates a smaller force than the rotational force generated by the shutter spring  305  and the shutter cam  303 , may be provided between the shutter member  301  and the regulating member  401 . The elastic member  901  biases the shutter member  301  in a direction indicated by the arrow z7, and thus, after the shutter member  301  is moved to the passage position, the shutter cam  303  and the shutter shaft  302  can reliably be rotated by an amount corresponding to the gap angle α. That is, the elastic member  901  is provided between the shutter member  301  and the regulating member  401 , and thus the gap angle α between the shutter member  301  and the regulating member  401  can reliably be kept after the passage of the sheet S without deteriorating the sheet skew feeding correcting function. 
     Next, a second embodiment of the present invention will be described.  FIG. 15  is an explanatory view illustrating the structure of a skew feeding correcting portion provided in a sheet conveying apparatus according to the embodiment. Note that, in  FIG. 15 , the same reference symbols as those described above in  FIG. 4  represent the same or corresponding portions. 
     In  FIG. 15 , the conveying rotatable members  102  ( 102   a  to  102   e ) rotate about a rotatable member shaft  175  in a state in which inner peripheral surfaces of the conveying rotatable members  102  and an outer peripheral surface of the rotatable member shaft  175  are held in contact with each other. Further, the conveying rotatable members  102  are pressed against the plurality of roller main bodies  101   a  to  101   e  of the registration roller  101  by rotatable member shaft pressing springs  176  provided at both ends of the rotatable member shaft  175 . 
     Further, shutter members  171  ( 171 A,  171 B,  171 C, and  171 D) are fixed at the same phase to a shutter holding member  172 . A shutter portion in this embodiment is constructed of the shutter members  171 A,  171 B,  171 C, and  171 D and the shutter holding member  172 . The shutter holding member  172  is pivotably supported by the roller shaft  101   f  of the registration roller  101  through an intermediation of a pivotal movement regulating member  173  and a roller bearing  174  serving as the moving members. 
     The shutter holding member  172  includes a regulating portion  172   a . As illustrated in  FIGS. 16A and 16B , the regulating portion  172   a  and the pivotal movement regulating member  173  form the gap “g” therebetween. Further, the shutter holding member  172 , that is, the shutter member  171  is independently rotatable with respect to the pivotal movement regulating member  173  by an amount corresponding to the gap angle α which is an angle of the gap “g”. Note that, in the embodiment, the gap angle α is set to 5°. 
     Further, during a period other than the period in which the sheet S is conveyed, the position of the shutter holding member  172  is kept by the pivotal movement regulating member  173  in such a posture that a retaining surface  171   a  of the shutter member  171  is positioned on the upstream side of the nip portion N of the registration roller pair  101 ,  102  in the sheet conveying direction. Note that, the pivotal movement regulating member  173  is biased in a direction indicated by the arrow z8 by a pivotal spring  177  serving as the biasing unit, and the posture in the home position is regulated by a stopper  181 . 
     Next, a skew feeding correcting operation of the skew feeding correcting portion  12  having the above-mentioned structure will be described. First, as illustrated in  FIG. 16B , the leading edge of the conveyed sheet S is brought into contact with the retaining surface  171   a  of, for example, the shutter member  171 A illustrated in  FIG. 16A  among the plurality of shutter members  171 A to  171 D positioned in the home position. 
     When the leading edge of the sheet S is brought into contact as described above, the shutter member  171 A is pushed by the sheet S and pivoted in a direction indicated by the arrow z9 together with the shutter holding member  172 . When the shutter holding member  172  is pivoted by an amount corresponding to the gap angle α, the regulating portion  172   a  abuts against the pivotal movement regulating member  173 , and the regulating portion  172   a  and the pivotal movement regulating member  173  form the gap angle α therebetween on the opposite side to that before the pivotal movement. As a result, the pivotal movement is stopped in such a position that the retaining surface  171   a  is positioned in a position indicated by  171   a′.    
     At this time, sliding resistance between the roller bearing  174  and the roller shaft  101   f  caused by the pivotal movement of the shutter holding member  172  is sufficiently smaller as compared to the biasing force of the pivotal spring  177 , and hence there is no change in posture of the pivotal movement regulating member  173 . Further, the retaining surface  171   a ′ is positioned on the upstream side of the nip portion N of the registration roller pair  101 ,  102  in the sheet conveying direction. 
     When the pivotal movement of the shutter holding member  172  is stopped by the pivotal movement regulating member  173 , the sheet S receives a reaction force of the pivotal spring  177 . The biasing force of the pivotal spring  177  is set so that the whole shutter members  171  are not rotatable at the time when one shutter member  171 A is pushed by the sheet S as described above. 
     However, after that, the sheet S is further conveyed, and a predetermined loop is formed in the sheet S as described above. Then, the inclination of the leading edge of the sheet S is corrected, and the leading edge of the sheet S pushes up the shutter members  171 . Thus, the sheet S enters the nip portion N of the registration roller pair  101 ,  102 , and is conveyed by the registration roller pair  101 ,  102 . 
     When the shutter members  171  are pushed up, the shutter holding member  172  is pushed up integrally with the shutter members  171 , and further, the pivotal movement regulating member  173  is pivoted together with the shutter holding member  172  through an intermediation of the regulating portion  172   a  of the shutter holding member  172 . Thus, during the conveyance of the sheet S, as illustrated in  FIG. 17A , the sheet S is conveyed in a state in which the ends of the shutter members  171  abut against the sheet S due to the biasing force of the pivotal spring  177 . 
     When the sheet S then passes through the skew feeding correcting portion  12  as illustrated in  FIG. 17B , due to the biasing force of the pivotal spring  177 , the pivotal movement regulating member  173  is moved in a direction opposite to the movement direction to return to the home position illustrated in  FIG. 16A . Note that, in the embodiment, gravity center positions of the shutter holding member  172  and the shutter members  171  are set on the side of the nip portion N instead of the center of the roller shaft  101   f  of the registration roller  101 . Therefore, when the pivotal movement regulating member  173  returns to the home position, due to self-weights of the shutter holding member  172  and the shutter members  171  and the rotational force generated by the pivotal spring  177 , the shutter holding member  172  and the shutter members  171  return to the home position while forming the gap angle α. That is, when the sheet S passes through the shutter members  171 , the pivotal movement regulating member  173  is moved due to the biasing force of the pivotal spring  177  while moving the shutter members  171  in a direction opposite to the movement direction. 
     As described above, in the embodiment, after the leading edge of the sheet S is brought into contact with the retaining surface  171   a , only the shutter holding member  172 , that is, the shutter member  171  is pivoted by an amount corresponding to the gap angle α before the skew feeding correcting operation is started. Through the pivotal movement of the shutter holding member  172  described above, it is possible to absorb a shock received by the skew feeding correcting portion  12  through an intermediation of the shutter member  171  from the leading edge of the sheet S conveyed by the sheet separating portion  13 . Thus, it is possible to reduce collision sound that is generated when the sheet S is brought into contact with the shutter member  171 . 
     Note that, the above description is directed to the case where the shutter holding member  172  (shutter member  171 ) is pivoted about a fulcrum corresponding to the roller shaft  101   f  of the registration roller  101 , but the present invention is not limited thereto. The shutter holding member  172  (shutter member  171 ) may be pivoted about a fulcrum corresponding to the rotatable member shaft  175  of the conveying rotatable member  102 . That is, it is only necessary that the shutter holding member  172  (shutter member  171 ) be provided to be pivotable about any one of the shafts of the registration roller pair  101 ,  102 . 
     Further, as illustrated in  FIG. 18A , a spring or an elastic member  231  having spring property, which generates a smaller spring force than the force of the pivotal spring  177  and biases the regulating portion  172   a  in a direction indicated by the arrow z10, may be provided between the regulating portion  172   a  of the shutter holding member  172  and the pivotal movement regulating member  173 . Thus, the gap angle α between the shutter holding member  172  and the pivotal movement regulating member  173  can reliably be kept after the passage of the sheet S without deteriorating the sheet skew feeding correcting function. 
     Still further, as illustrated in  FIG. 18B , the shutter member  171  may be provided to be movable by an amount corresponding to a gap distance  402   c  with respect to the shutter holding member  172 , and the shutter holding member  172  may be biased directly by the pivotal spring  177 . Thus, when the leading edge of the sheet S abuts against the retaining surface  171   a , only the shutter member  171  is moved by the amount corresponding to the gap distance  402   c , and hence the effect of reducing the collision sound can be attained. Note that, in this structure, the shutter holding member  172  serves as the moving member. 
     In the embodiment, the moving member movable integrally with the shutter member is arranged with the gap formed between the moving member and the shutter member, and the gap is canceled during a period in which the shutter member is moved from the abutment position to the passage position. Thus, it is possible to reduce the collision sound which is generated due to the abutment between the sheet and the shutter member. 
     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. 2012-283306, filed Dec. 26, 2012, which is hereby incorporated by reference herein in its entirety.