Patent Publication Number: US-9403651-B2

Title: Image forming apparatus

Description:
INCORPORATION BY REFERENCE 
     The present application is based on Japanese Patent Application No. 2014-085961 filed at the Japanese Patent Office on Apr. 18, 2014, the contents of which are incorporated herein by reference. 
     BACKGROUND ART 
     The present disclosure relates to an image forming apparatus that forms an image on a sheet. 
     A conventionally known image forming apparatus that forms an image on a sheet includes a sheet feeding section, an image forming section, a fixing section, and a sheet discharging section. A sheet from stacked sheets in the sheet feeding section is delivered to a sheet conveying path by a sheet feeding roller, and then, an image forming section forms an image on the sheet. Thereafter, the fixing section executes a fixing process on the sheet, and then the sheet is discharged into the sheet discharging section. 
     In such a technique, a timing when the sheet is delivered from the sheet feeding section is different from a timing when the sheet passes through the image forming section or the fixing section. Thus, driving sections specific to the respective timings are needed. 
     SUMMARY OF INVENTION 
     An image forming apparatus according to an aspect of the present disclosure includes an apparatus main body, a sheet feeding cassette, an image forming section, a sheet conveying path, a reverse conveying path, a delivery member, a conveying member, a lift plate, a driving section, a first switching section, a second switching section, and a driving control section. The sheet feeding cassette is removable from the apparatus main body, and sheets are stacked inside the sheet feeding cassette. The image forming section forms an image on the sheet. The sheet conveying path extends from the sheet feeding cassette so as to pass through the image forming section, and the sheet is conveyed through the sheet conveying path. The reverse conveying path is formed downstream of the image forming section in a conveying direction of the sheet so as to branch from the sheet conveying path. At the time of duplex image formation in which an image is formed on each of opposite surfaces of the sheet, the reverse conveying path allows the sheet to be loaded again into an upstream side portion of the sheet conveying path with respect to the image forming section in the conveying direction. The delivery member is disposed opposite the sheet feeding cassette and rotationally driven to deliver the sheet. The conveying member is disposed in the reverse conveying path and rotationally driven to convey the sheet. The lift plate is disposed in the sheet feeding cassette, and the sheet is stacked on an upper surface of the lift plate. The lift plate is enabled to change a position thereof between a sheet feeding position where the stacked sheet is brought into abutting contact with the delivery member and a retracting position where the sheet is retracted from the delivery member. The driving section generates a driving force. The first switching section transmits the driving force generated by the driving section to the delivery member and the conveying member to rotate or stop the delivery member and the conveying member. The second switching section transmits the driving force generated by the driving section to the lift plate to change the position of the lift plate. The driving control section controls the first switching section and the second switching section. The driving control section controls the first switching section, with the lift plate being placed in the sheet feeding position, to rotate the delivery member to feed the sheet into the sheet conveying path, and when the sheet is conveyed through the reverse conveying path, controls the second switching section to move the lift plate from the sheet feeding position to the retracting position. 
     Furthermore, an image forming apparatus according to another aspect of the present disclosure includes an apparatus main body, a first sheet feeding cassette and a second sheet feeding cassette, an image forming section, a sheet conveying path, a first delivery member, a second delivery member, a first lift plate, a second lift plate, a driving section, a first switching section, a second switching section, a third switching section, and a driving control section. The first sheet feeding cassette and the second sheet feeding cassette are removable from the apparatus main body, and sheets are stacked inside the first sheet feeding cassette and the second sheet feeding cassette. The image forming section forms an image on the sheet. A portion of the sheet conveying path extends from the first sheet feeding cassette and another portion of the sheet conveying path extends from the second sheet feeding cassette, and the portion from the first sheet feeding cassette and the portion from the second sheet feeding cassette then join together, and the sheet is conveyed through the sheet conveying path so as to pass through the image forming section. The first delivery member is disposed opposite the first sheet feeding cassette and rotationally driven to deliver the sheet. The second delivery member is disposed opposite the second sheet feeding cassette and rotationally driven to deliver the sheet. The first lift plate is disposed in the first sheet feeding cassette, and the sheet is stacked on an upper surface of the first lift plate. The first lift plate is enabled to change a position thereof between a sheet feeding position where the stacked sheet is brought into abutting contact with the first delivery member and a retracting position where the sheet is refracted from the first delivery member. The second lift plate is disposed in the second sheet feeding cassette, and the sheet is stacked on an upper surface of the second lift plate. The second lift plate is enabled to change a position thereof between a sheet feeding position where the stacked sheet is brought into abutting contact with the second delivery member and a retracting position where the sheet is retracted from the second delivery member. The driving section generates a driving force. The first switching section transmits the driving force generated by the driving section to the first and second delivery members, and rotates or stops the first and second delivery members. The second switching section transmits the driving force generated by the driving section to the first lift plate to change the position of the first lift plate. The third switching section transmits the driving force generated by the driving section to the second lift plate to change the position of the second lift plate. The driving control section controls the first switching section, the second switching section, and the third switching section. The driving control section controls the second switching section or the third switching section to place the lift plate in one of the first and second sheet feeding cassettes in the sheet feeding position, while placing the lift plate in the other of the first and second sheet feeding cassettes in the retracting position, and in this state, controls the first switching section to rotate the first and second delivery members to load the sheet into the sheet conveying path. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a cross-sectional view depicting the internal structure of an image forming apparatus according to an embodiment of the present disclosure; 
         FIG. 2A  and  FIG. 2B  are perspective views of a sheet feeding cassette according to the embodiment of the present disclosure; 
         FIG. 3  is a perspective view of a mechanism that moves a lift plate of the sheet feeding cassette according to the embodiment of the present disclosure up and down; 
         FIG. 4A  and  FIG. 4B  are perspective views depicting how the lift plate of the sheet feeding cassette according to the embodiment of the present disclosure moves up and down; 
         FIG. 5A  and  FIG. 5B  are cross-sectional views of periphery of a cam that moves the lift plate of the sheet feeding cassette according to the embodiment of the present disclosure up and down; 
         FIG. 6A  and  FIG. 6B  are perspective views of periphery of an opposite member and a returning member according to the embodiment of the present disclosure; 
         FIG. 7A  and  FIG. 7B  are cross-sectional views of periphery of a cam that projects and retracts the returning member according to the embodiment of the present disclosure; 
         FIG. 8A  and  FIG. 8B  are cross-sectional views depicting how the opposite member according to the embodiment of the present disclosure moves; and 
         FIG. 9A  and  FIG. 9B  are electrical block diagrams of the image forming apparatus according to the embodiment of the present disclosure. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     An embodiment of the present disclosure will be described below based on the drawings.  FIG. 1  is a cross-sectional view depicting the internal structure of an image forming apparatus  1  according to an embodiment of the present disclosure. As the image forming apparatus  1 , a printer is illustrated herein. However, the image forming apparatus may be a multifunction printer with a printer function and a copy function, a copier, or a facsimile apparatus. 
     &lt;Description of the Image Forming Apparatus&gt; 
     An image forming apparatus  1  includes an apparatus main body  10  with a housing structure shaped generally like a rectangular parallelepiped. A sheet discharging section  12  is disposed in an upper surface portion of the apparatus main body  10 . A sheet with an image formed thereon is discharged on the sheet discharging section  12 . The apparatus main body  10  internally houses a sheet feeding cassette  11  (first sheet feeding cassette), an image forming section  14  that forms a toner image (developer image) on the sheet, an intermediate transfer section  15 , and a fixing section  16  that fixes the toner image to the sheet. Furthermore, a manual tray  13  is provided on a front side surface of the apparatus main body  10  so as to be freely opened and closed. Sheets can be placed on an upper surface of the manual tray  13 . 
     The sheet feeding cassette  11  is removable from the apparatus main body  10 , and sheets are stacked inside the sheet feeding cassette  11 . In the present embodiment, the sheet feeding cassette  11  is installed in an installation direction that is rearward with respect to the apparatus main body  10  (arrow DC in  FIG. 1 ). Inside the sheet feeding cassette  11 , a first lift plate  111  (lift plate) is provided. Sheets are stacked on an upper surface of the first lift plate  111 . The first lift plate  111  enables its position to be changed between a sheet feeding position where a leading end of the uppermost one of the stacked sheets is brought into abutting contact with a first pickup roller  112  described below and a retracting position where the sheet is retracted from the first pickup roller  112 . A bias spring not depicted in the drawings is disposed between the first lift plate  111  and a bottom of the sheet feeding cassette  11 . The bias spring biases the first lift plate  111  upward so as to place the first lift plate  111  in the sheet feeding position. Movement of the first lift plate  111  will be described below in detail. 
     The image forming section  14  is disposed above the sheet feeding cassette  11 . The image forming section  14  includes a plurality of photosensitive drums and developing apparatuses corresponding to a yellow color, a magenta color, a cyan color, and a black color, respectively. An electrostatic latent image according to image data is formed on the photosensitive drum by an exposure apparatus. A toner image on the photosensitive drum developed by the developing apparatus is primarily transferred to an intermediate transfer belt  151  in the intermediate transfer section  15  so as to be superimposed on the intermediate transfer belt  151 . 
     The intermediate transfer section  15  includes the intermediate transfer belt  151 , a belt driving roller  152 , and a tension roller  153 . The intermediate transfer belt  151  is an endless belt stretched between the belt driving roller  152  and the tension roller  153 . The belt driving roller  152  is rotationally driven by a motor M described below to circumferentially move the intermediate transfer belt  151 . At a position opposite the belt driving roller  152  across the intermediate transfer belt  151 , a secondary transfer roller  154  is disposed. The secondary transfer roller  154  forms a secondary transfer nip portion between the secondary transfer roller  154  and the belt driving roller  152 . A secondary transfer voltage applied to the belt driving roller  152  or the secondary transfer roller  154  allows the toner image to be transferred from the intermediate transfer belt  151  to the sheet. 
     The fixing section  16  executes a fixing process for the toner image on the sheet. The fixing section  16  includes a fixing roller  161  and a pressuring roller  162 . The fixing roller  161  internally includes a heat source. The fixing roller  161  is rotationally driven by the motor M described below. The pressuring roller  162  is pressed against a peripheral surface of the fixing roller  161  to rotate in conjunction with the fixing roller  161 . 
     Inside the apparatus main body  10 , a main conveying path  10 A (sheet conveying path), a discharge conveying path  10 B, a reverse conveying path  10 C, and a manual conveying path  10 D are arranged. The main conveying path  10 A is a conveying path which extends from the sheet feeding cassette  11  so as to pass through the image forming section  14  and the fixing section  16  in the apparatus main body  10  and through which the sheet is conveyed. An inlet side of the main conveying path  10 A extends along the installation direction from the sheet feeding cassette  11 . Then, the main conveying path  10 A extends upward and then forward again to an area above the sheet discharging section  12 . Thus, when the image forming apparatus  1  is viewed from left (a cross-sectional view corresponding to  FIG. 1  as viewed from the back side of the sheet of the drawing), the main conveying path  10 A extending from the sheet feeding cassette  11  appears to be generally C-shaped. The discharge conveying path  10 B is a conveying path disposed on a downstream side of the main conveying path  10 A in the conveying direction and through which the sheet is conveyed toward the sheet discharging section  12 . The reverse conveying path  10 C is a conveying path formed on the downstream side with respect to the fixing section  16  in the conveying direction of the sheet so as to branch from the main conveying path  10 A. At the time of duplex image formation in which an image is formed on the opposite surfaces of the sheet, the reverse conveying path  10 C allows the sheet to be loaded again into a portion of the main conveying path  10 A that lies on an upstream side with respect to the image forming section  14 . The manual conveying path  10 D is a conveying path extending rearward from the manual tray  13  and a conveying-direction downstream side of the manual conveying path  10 D is coupled to the main conveying path  10 A. 
     Moreover, the image forming apparatus  1  includes the first pickup roller  112  (delivery member or first delivery member), a first sheet feeding roller  113  (sheet feeding member), a first retard roller  114  (opposite member), a manual lift plate  131 , and a manual sheet feeding roller  132 . Furthermore, the image forming apparatus  1  includes a first conveying roller pair  171 , a registration roller pair  172 , a first driven roller  173 , an opposite driving roller  174 , a discharge roller pair  175 , a second driven roller  176 , a second conveying roller pair  177  (conveying member), a third conveying roller pair  178  (conveying member), a fourth conveying roller pair  179 , a fifth conveying roller pair  180 , and a sixth conveying roller pair  181 . 
     The first pickup roller  112  is disposed on the inlet side of the main conveying path  10 A opposite the sheet feeding cassette  11 . The first pickup roller  112  is rotated to deliver the sheet toward the main conveying path  10 A. The first sheet feeding roller  113  is disposed on the downstream side with respect to the first pickup roller  112  in the conveying direction at a distance from the first pickup roller  112 . The first sheet feeding roller  113  is rotated to convey the sheet delivered by the first pickup roller  112  further downstream along the main conveying path  10 A. The first retard roller  114  is disposed opposite the first sheet feeding roller  113  to form, between the first retard roller  114  and the first sheet feeding roller  113 , a nip portion through which the sheet passes. 
     The manual lift plate  131  is disposed at a downstream-side end of the manual tray  13  in the conveying direction. A lower end of the manual lift plate  131  can be moved up and down by a cam not depicted in the drawings. The manual sheet feeding roller  132  is a roller disposed inside the apparatus main body  10  opposite the manual lift plate  131 . The manual sheet feeding roller  132  is rotated by the motor M described below. When the manual lift plate  131  moves upward, the leading end of the sheet disposed on the manual tray  13  comes into abutting contact with the manual sheet feeding roller  132 , and the sheet is loaded into the manual conveying path  10 D. A solenoid not depicted in the drawings is coupled to the above-described cam. A driving control section  80  described below controls the solenoid to move the manual lift plate  131  up and down to control a delivery operation for the sheet on the manual lift plate  131 . Thus, the manual sheet feeding roller  132  is constantly rotationally driven by the motor M. 
     The first conveying roller pair  171  is disposed at a rear, lower end of the apparatus main body  10 . The first conveying roller pair  171  conveys the sheet delivered by an additional cassette  50  described below toward the registration roller pair  172 . The registration roller pair  172  is a roller pair disposed in the main conveying path  10 A between the first sheet feeding roller  113  and the secondary transfer roller  154 . When the leading end of the sheet arrives immediately in front of the nip portion of the registration roller pair  172 , conveyance of the sheet is temporarily stopped. Then, the registration roller pair  172  conveys the sheet toward the secondary transfer nip portion in association with an image formation timing in the image forming section  14 . Furthermore, the registration roller pair  172  has a function to correct skews in the sheet. 
     The first driven roller  173 , the opposite driving roller  174 , and the second driven roller  176  are three rollers disposed above the fixing section  16  adjacently to one another. The opposite driving roller  174  forms a nip portion between the opposite driving roller  174  and the first driven roller  173  and between the opposite driving roller  174  and the second driven roller  176 . When the opposite driving roller  174  is rotationally driven by the motor M described below, the first driven roller  173  and the second driven roller  176  rotate in conjunction with the opposite driving roller  174 . The sheet passing through the nip portion between the first driven roller  173  and the opposite driving roller  174  is conveyed toward the discharge roller pair  175  along the discharge conveying path  10 B. 
     The discharge roller pair  175  is a roller pair disposed near an outlet of the discharge conveying path  10 B. The discharge roller pair  175  is rotationally driven by the motor M described below. Furthermore, the discharge roller pair  175  is controlled to be driven so as to rotate forward and backward. A forward rotating operation of the discharge roller pair  175  allows the sheet to be discharged on the sheet discharging section  12 . On the other hand, when the discharge roller pair  175  performs a reverse operation with the sheet held at the nip portion of the discharge roller pair  175 , the sheet passes through the nip portion between the second driven roller  176  and the opposite driving roller  174  and is loaded into the reverse conveying path  10 C. 
     The second conveying roller pair  177  and the third conveying roller pair  178  are roller pairs disposed in the reverse conveying path  10 C. The second conveying roller pair  177  and the third conveying roller pair  178  are rotationally driven by the motor M described below. The roller pairs load the sheet into the main conveying path  10 A again. 
     The fourth conveying roller pair  179 , the fifth conveying roller pair  180 , and the sixth conveying roller pair  181  are roller pairs disposed in the manual conveying path  10 D. The roller pairs load the sheet from the manual conveying path  10 D into the main conveying path  10 A. 
     Moreover, the image forming apparatus  1  includes the additional cassette  50  (second sheet feeding cassette). The additional cassette  50  is selectively installed in a lower surface portion of the apparatus main body  10 , and sheets are stacked inside the additional cassette  50 . When the additional cassette  50  is installed in the apparatus main body  10 , an additional conveying path  10 E (sheet conveying path) is formed which extends from the additional cassette  50  and which joins the main conveying path  10 A. The additional conveying path  10 E joins the main conveying path  10 A inside the apparatus main body  10 . The additional cassette  50  includes a second lift plate  511 , a second pickup roller  512  (second delivery member), a second sheet feeding roller  513  (second delivery member), a second retard roller  514  (opposite member). Sheets are stacked on an upper surface of the second lift plate  511 . The second lift plate  511  enables its position to be changed between a sheet feeding position where the leading end of the uppermost one of the stacked sheets is brought into abutting contact with the second pickup roller  512  and a retracting position where the sheet is retracted from the second pickup roller  512 . 
     The second pickup roller  512  is disposed on an inlet side of the additional conveying path  10 E opposite the second lift plate  511 . The second pickup roller  512  is rotated to deliver the sheet toward the additional conveying path  10 E. The second sheet feeding roller  513  is disposed on the downstream side with respect to the second pickup roller  512  in the conveying direction at a distance from the second pickup roller  512 . The second sheet feeding roller  513  is rotated to convey the sheet delivered by the second pickup roller  512  further downstream along the additional conveying path  10 E. The second retard roller  514  is disposed opposite the second sheet feeding roller  513  to form, between the second retard roller  514  and the second sheet feeding roller  513 , a nip portion through which the sheet passes. 
     Now, the structure of periphery of the sheet feeding cassette  11  in the image forming apparatus  1  will further be described in detail with reference to  FIGS. 2A to 8B . The following configuration is also applied to the additional cassette  50 .  FIG. 2A  and  FIG. 2B  are perspective views of the sheet feeding cassette  11  according to the present embodiment.  FIG. 3  is a perspective view of a mechanism that moves the first lift plate  111  of the sheet feeding cassette  11  up and down.  FIG. 4A  and  FIG. 4B  are perspective views depicting how the first lift plate  111  of the sheet feeding cassette  11  moves up and down.  FIG. 5A  and  FIG. 5B  are cross-sectional views of periphery of a first cam  601  that moves the first lift plate  111  of the sheet feeding cassette  11  according to the embodiment of the present disclosure up and down.  FIG. 6A  and  FIG. 6B  are perspective views of periphery of the first retard roller  114  and a returning member  62  described blow according to the embodiment of the present invention.  FIG. 7A  and  FIG. 7B  are cross-sectional views of periphery of a second cam  602  that projects and retracts the returning member  62 .  FIG. 8A  and  FIG. 8B  are cross-sectional views depicting how the first retard roller  114  moves. 
     As seen in  FIG. 2A , the image forming apparatus  1  includes a conveyance guide section  100 . The conveyance guide section  100  is a unit which is a part of the apparatus main body  10  and which is disposed behind the sheet feeding cassette  11 . An upper surface portion of the conveyance guide section  100  includes a curved surface  100 A that defines a part of the main conveying path  10 A. In a central portion of the curved surface  100 A in a lateral direction, the first retard roller  114  described above is disposed. The first retard roller  114  is supported by a holder  70  described below. Furthermore, the curved surface  100 A has a pair of slits  100 G such that the first retard roller  114  is sandwiched between the slits  100 G in the lateral direction ( FIG. 6A  and  FIG. 6B ). 
     As seen in  FIG. 3 , the image forming apparatus  1  includes an interlocking section  60 . The interlocking section  60  is a mechanism that serves to allow for an up-down movement of the first lift plate  111 , a projecting and retracting operation of the returning member  62  described below, and a moving operation of the first retard roller  114 . The interlocking section  60  includes a first shaft  600  (shaft), a pressing arm  61 , the returning member  62 , and the holder  70  (support member). The first shaft  600  has a first cam  601 , a second cam  602 , a third cam  603  each disposed on a circumferential surface of the first shaft  600 . 
     The first shaft  600  is a rotating shaft extending in the lateral direction. In  FIG. 2A , the first shaft  600  is disposed inside the conveyance guide section  100 . A shaft gear  600 A is fixed to a right end of the first shaft  600 . The shaft gear  600 A is coupled to the motor M via a transmission mechanism not depicted in the drawings. Thus, the first shaft  600  is rotationally driven by the motor M. As depicted in  FIG. 4A  and  FIG. 4B , the right end of the first shaft  600  including the shaft gear  600 A is exposed to the right of the conveyance guide section  100 . 
     As seen in  FIG. 3 , the first cam  601  is a pair of cams fixed to the right and left ends of the first shaft  600 . The first cam  601  allows the first lift plate  111  to be moved up and down between the sheet feeding position and the retracting position via the pressing arm  61 . The second cam  602  is a pair of cams located inside the first cam  601  at a distance from the first cam  601  in the lateral direction and fixed to the first shaft  600 . The second cam  602  allows the returning member  62  to pivot and allows the returning member  62  to perform an operation of projecting into and retracting from the main conveying path  10 A. The third cam  603  is a cam located adjacently to the right second cam  602  and fixed to the first shaft  600 . The third cam  603  has a function to move the first retard roller  114  between an opposite position and retracting position via the holder  70 . As depicted in  FIG. 5A ,  FIG. 7A , and  FIG. 8 , the first cam  601 , the second cam  602 , and the third cam  603  are formed such that outer diameters of the cams  601 ,  602 , and  603  partly differ in a circumferential direction. 
     The pressing arm  61  is a pair of arm members disposed opposite the respective cams of the first cam  601 . The pressing arm  61  includes an arm pressing section  61 A, an arm opening  61 B, an arm fulcrum section  61 C, and an arm pressed section  61 D ( FIG. 5A  and  FIG. 5B ). The arm pressing section  61 A is disposed in a front side of the pressing arm  61  and tapered forward. The arm pressing section  61 A has a function to press a lift plate protruding portion  111 A ( FIG. 2A  and  FIG. 2B ) of the first lift plate  111 . The arm opening  61 B is a slot-like opening formed in a central portion of the pressing arm  61  and shaped like a circular arc. As depicted in  FIG. 4A  and  FIG. 4B , the first shaft  600  is inserted through the arm opening  61 B. The arm fulcrum section  61 C serves as a fulcrum portion for pivoting of the pressing arm  61 . The arm fulcrum section  61 C is pivotally supported by the conveyance guide section  100 . The arm pressed section  61 D is a part of the bottom of the pressing arm  61 . The arm pressed section  61 D is formed to have a predetermined width in the lateral direction and is pressed by the first cam  601 . As depicted in  FIG. 4A  and  FIG. 4B , a rectangular opening  11 H is formed at a rear end of a right sidewall of the sheet feeding cassette  11 . The first lift plate  111  includes the lift plate protruding portion  111 A. The lift plate protruding portion  111 A is a protruding portion provided on the first lift plate  111  so as to protrude rightward through the cassette opening  11 H. The pressing arm  61  is supported by the conveyance guide section  100  so as to dispose that arm pressing section  61 A above the lift plate protruding portion  111 A. 
     As seen in  FIG. 3 ,  FIG. 7A , and  FIG. 7B , the returning member  62  is a bar-like member rotatably supported inside the conveyance guide section  100 . The returning member  62 , protruding, around the first sheet feeding roller  113  (first retard roller  114 ), into the main conveying path  10 A, has a function of pushing the sheet, delivered from the sheet feeding cassette  11  to the main conveying path  10 A, back toward the sheet feeding cassette  11 . The returning member  62  includes a returning member fulcrum portion  62 A, a first extending portion  62 B, a sheet abutting contact portion  62 C, and a second extending portion  62 D ( FIG. 7A ). The returning member fulcrum portion  62 A serves as a fulcrum point for pivoting of the returning member  62 . The returning member fulcrum portion  62 A is rotatably pivotally supported by the conveyance guide section  100 . A coil spring not depicted in the drawings is provided around the returning member fulcrum portion  62 A. The coil spring biases the returning member  62  around the returning member fulcrum portion  62 A so as to allow the sheet abutting contact portion  62 C of the returning member  62  to protrude into the main conveying path  10 A. The first extending portion  62 B is a portion extending in one direction from the returning member fulcrum portion  62 A. The sheet abutting contact portion  62 C is formed by bending a tip of the first extending portion  62 B. Pivoting of the returning member  62  around the returning member fulcrum portion  62 A causes the sheet abutting contact portion  62 C to protrude into the main conveying path  10 A through the slit  100 G ( FIG. 6A ). The second extending portion  62 D is a portion extending in a direction opposite to the first extending portion  62 B from the returning member fulcrum portion  62 A. The second extending portion  62 D is pressed by the second cam  602 . 
     As seen in  FIG. 3  and  FIG. 8A , the holder  70  pivotally supports the first retard roller  114 . The first retard roller  114  is supported by a pair of sidewalls of the holder  70  in which the sidewalls are arranged at a distance from each other in the lateral direction. The holder  70  can have its position changed between an opposite position where the first retard roller  114  forms a nip portion between the first retard roller  114  and the first sheet feeding roller  113  and a retracting position where the first retard roller  114  is retracted from the first sheet feeding roller  113 . The holder  70  includes a holder fulcrum portion  70 A and a holder protruding portion  70 B. The holder fulcrum portion  70 A is a fulcrum portion for pivoting of the holder  70 . The holder fulcrum portion  70 A protrudes in the lateral direction from each of the sidewalls of the holder  70 . The holder fulcrum portion  70 A is rotatably pivotally supported by the conveyance guide section  100 . The holder protruding portion  70 B ( FIG. 8A ) is a protruding piece protruding downward from a right end of the holder  70 . On the other hand, as seen in  FIG. 8A , the conveyance guide section  100  includes a guide inner wall portion  100 H and a holder bias spring  100 K. As depicted in  FIG. 6A , an installation portion in which the holder  70  can be installed is disposed on an upper surface portion (curved portion  100 A) of the conveyance guide section  100 . The guide inner wall portion  100 H is an inner wall portion of the conveyance guide section  100  which defines the installation portion and which lies opposite the holder  70 . The holder bias spring  100 K is a spring compressively disposed between the guide inner wall portion  100 H and the holder protruding portion  70 B. The holder bias spring  100 K biases the holder  70  around the holder fulcrum portion  70 A so as to bring the first retard roller  114  into abutting contact with the first sheet feeding roller  113 . Furthermore, as depicted in  FIG. 8A , an idler gear  113 A is disposed between the first sheet feeding roller  113  and the first pickup roller  112 . The idler gear  113 A engages simultaneously with the first sheet feeding roller  113  and the first pickup roller  112 . When a driving force generated by the motor M described above is transmitted to the first sheet feeding roller  113 , the first pickup roller  112  is rotated via the idler gear  113 A. Furthermore, the first retard roller  114  can rotate in conjunction with the first sheet feeding roller  113 , and rotation of the first retard roller  114  stops when the sheets are handled one by one. 
     As depicted in  FIG. 4A  and  FIG. 5A , when the first shaft  600  is placed at a predetermined rotational angle, a first cam large-diameter portion  601 A of the first cam  601  presses the arm pressed section  61 D of the pressing arm  61  downward. As a result, the pressing arm  61  pivots around the arm fulcrum section  61 C, and the arm pressing section  61 A presses the lift plate protruding portion  111 A downward. As a result, the first lift plate  111  is moved downward and placed in the retracting position against the bias force of the above-described bias spring provided below the first lift plate  111  ( FIG. 2A ). On the other hand, when the first shaft  600  is rotated through a predetermined angle from the state depicted in  FIG. 4A  and  FIG. 5A , the first shaft  600  is placed at a rotational angle depicted in  FIG. 4B  and  FIG. 5B . Specifically, a portion of the first cam  601  that comes into abutting contact with the arm pressed section  61 D changes from the first cam large-diameter portion  601 A to a first cam small-diameter portion  601 B. As a result, the bias force of the bias spring causes the first lift plate  111  to be moved upward and placed in the sheet feeding position while causing the pressing arm  61  to pivot around the arm fulcrum section  61 C ( FIG. 2B ). Thus, in response to rotation of the first shaft  600 , the first lift plate  111  is periodically placed in the sheet feeding position and in the retracting position. 
     Furthermore, at a predetermined rotational angle of the first shaft  600 , the second cam small-diameter portion  602 B of the second cam  602  is placed opposite the second extending portion  62 D of the returning member  62  as depicted in  FIG. 7A . At this time, the sheet abutting contact portion  62 C of the returning member  62  protrudes into the main conveying path  10 A via the slit  100 G ( FIG. 6A ). When the first shaft  600  is rotated from the state depicted in  FIG. 7A , as depicted by an arrow, a second cam step portion  602 B of the second cam  602  presses the second extending portion  62 D, and the returning member  62  rotates around the returning member fulcrum portion  62 A. At this time, the returning member  62  rotates against the bias force of the coil spring provided around the returning member fulcrum portion  62 A. As a result, a second cam large-diameter portion  602 C of the second cam  602  comes into contact with the second extending portion  62 D and the first extending portion  62 B to regulate rotation of the returning member  62 , as depicted in  FIG. 7B . As a result, the sheet abutting contact portion  62 C of the returning member  62  is retracted downward from the slit  100 G ( FIG. 6B ). Thus, in response to rotation of the first shaft  600 , the sheet abutting contact portion  62 C of the returning member  62  periodically projects into and retracts from the main conveying path  10 A. 
     Moreover, at a predetermined rotational angle of the first shaft  600 , a third cam large-diameter portion  603 A of the third cam  603  presses the holder protruding portion  70 B of the holder  70  against the bias force of the holder bias spring  100 K, as depicted in  FIG. 8A . As a result, the holder  70  pivots around the holder fulcrum portion  70 A, and the first retard roller  114  separates from the first sheet feeding roller  113 . Furthermore, when the first shaft  600  is rotated from the state depicted in  FIG. 8A , as depicted by an arrow, a third cam small-diameter portion  603 B of the third cam  603  is placed opposite the holder protruding portion  70 B as depicted in  FIG. 8B . At this time, a predetermined gap is formed between the third cam small-diameter portion  603 B and the holder protruding portion  70 B, and thus, the bias force of the holder bias spring  100 K causes the holder protruding portion  70 B to be biased leftward. Therefore, the holder  70  pivots around the holder fulcrum portion  70 A, bringing the first retard roller  114  into abutting contact with the first sheet feeding roller  113 . Thus, in response to rotation of the first shaft  600 , the first retard roller  114  periodically contacts and leaves the first sheet feeding roller  113 . 
     In the present embodiment, when the first shaft  600  is rotated through a predetermined angle from the sheet feeding position of the first lift plate  111  depicted in  FIG. 2B  and  FIG. 4B , the first lift plate  111  is placed in the retracting position ( FIG. 4A ), and the first retard roller  114  is placed in the retracting position of the holder  70  so as to retract from the first sheet feeding roller  113  ( FIG. 8A ). Moreover, when the first shaft  600  is rotated through the predetermined angle, the sheet abutting contact portion  62 C of the returning member  62  protrudes from the downstream side toward the upstream side in the conveying direction of the sheet, that is, toward the sheet feeding cassette  11 , into the main conveying path  10 A ( FIG. 4A ). Then, when the first shaft  600  further rotates, the first retard roller  114  comes into abutting contact with the first sheet feeding roller  113  to retract the sheet abutting contact portion  62 C of the returning member  62  from the main conveying path  10 A, substantially simultaneously with the re-placement of the first lift plate  111  in the sheet feeding position. The outer circumferential shapes of the first cam  601 , the second cam  602 , and the third cam  603  around the first shaft  600  are set so as to achieve the above-described operation during one rotation of the first shaft  600 . Thus, rotating the first shaft  600 , a single shaft, enables a plurality of members to be driven. 
     Now, a driving mechanism in the image forming apparatus  1  will be described.  FIG. 9A  and  FIG. 9B  are electrical block diagram of the image forming apparatus  1  according to the present embodiment.  FIG. 9A  and  FIG. 9B  depict one block diagram, and reference numerals  1  to  5  corresponding to solid or dashed lines in  FIG. 9A  are connected to reference numerals  1  to  5  corresponding to solid or dashed lines in  FIG. 9B , respectively. The image forming apparatus  1  includes the driving control section  80  and the motor M (driving section) ( FIG. 9A ). The driving control section  80  rotationally drives the motor M and controls a feed clutch  106 , a registration clutch  107 , a first solenoid  108 , a second solenoid  109 , and a third solenoid  110  described below. The motor M is a motor that generates a rotational driving force. The driving force generated by the motor M enables a plurality of members (for example, conveying rollers including the fixing section  16 ) to be driven. Moreover, the image forming apparatus  1  includes a first driving mechanism  101  ( FIG. 9A ), a second driving mechanism  102  ( FIG. 9A ), a third driving mechanism  103  ( FIG. 9B ), a fourth driving mechanism  104  ( FIG. 9B ), and a fifth driving mechanism  105  ( FIG. 9B ). Furthermore, the image forming apparatus  1  includes the feed clutch  106  (first switching section) ( FIG. 9A ), the registration clutch  107  ( FIG. 9B ), the first solenoid  108  ( FIG. 9A ), the second solenoid  109  (second switching section) ( FIG. 9B ), and the third solenoid  110  (third switching section) ( FIG. 9B ). 
     The first driving mechanism  101  is a driving row including a group of gears coupled to the motor M. The first driving mechanism  101  is coupled to the above-described belt driving roller  152 , fixing roller  161 , opposite driving roller  174 , and discharge roller pair  175 . That is, driving of the motor M allows the group of rollers to be constantly rotated. As described above, the secondary transfer roller  154 , the pressuring roller  162 , the first driven roller  173 , and the second driven roller  176  are simultaneously driven in conjunction with the above-described rollers. Furthermore, one roller of the discharge roller pair  175  is driven by the motor M, whereas the other roller rotates as a driven roller. This also applies to the following other roller pairs. 
     The second driving mechanism  102  is similarly a driving row including a group of gears coupled to the motor M. The second driving mechanism  102  is coupled, via the feed clutch  106 , to the above-described first sheet feeding roller  113 , second sheet feeding roller  513 , first conveying roller pair  171 , second conveying roller pair  177 , third conveying roller pair  178 , fourth conveying roller pair  179 , fifth conveying roller pair  180 , sixth conveying roller pair  181 , and manual sheet feeding roller  132 . When the motor M is driven, the group of rollers is rotated if the feed clutch  106  is turned on. As described above, the first pickup roller  112 , the first retard roller  114 , the second pickup roller  512 , and the second retard roller  514  are simultaneously rotated in conjunction with the above-described rollers. 
     The third driving mechanism  103  is similarly a driving row including gears coupled to the motor M. The third driving mechanism  103  is coupled to a first roller of the above-described registration roller pair  172  via the registration clutch  107 . A second roller of the registration roller pair  172  rotates in conjunction with the first roller. When the motor M is driven, the rollers are rotated if the registration clutch  107  is turned on. 
     The fourth driving mechanism  104  is similarly a driving row including gears coupled to the motor M. The fourth driving mechanism  104  is coupled to the shaft gear  600 A of the above-described first shaft  600  via the second solenoid  109 . When the motor M is driven, the first shaft  600  is rotated if the second solenoid  109  is turned on. 
     The fifth driving mechanism  105  is similarly a driving row including gears coupled to the motor M. The fifth driving mechanism  105  is coupled to a second shaft  700  via the third solenoid  110 . The second shaft  700  is a shaft disposed in the additional cassette  50  in association with the first shaft  600  in the sheet feeding cassette  11 . Around the second shaft  700 , a first cam, a second cam, a third cam, a pressing arm, a returning member, and a holder (support member), which are not shown in figures, are provided as is the case with the above-described interlocking section  60 . When the motor M is driven, the second shaft  700  is rotated if the third solenoid  110  is turned on. This allows implementation of up-down movement of the second lift plate  511  ( FIG. 1 ), an operation of allowing the second retard roller  514  to contact and leave the second sheet feeding roller  513 , and an operation of projecting and retracting the returning member provided around the second sheet feeding roller  513  and not depicted in the drawings. 
     The feed clutch  106  (first switching section) transmits the driving force generated by the motor M to the first sheet feeding rollers  113  and  177  and the like to synchronously rotate or stop these rollers. Similarly, the registration clutch  107  transmits the driving force generated by the motor M to the registration roller pair  172  to synchronously rotate or stop these rollers. The first solenoid  108  controls the rotating direction of the discharge roller pair  175  rotated by the motor M. This allows switching between discharge of the sheet into the sheet discharging section  12  ( FIG. 1 ) and loading of the sheet into the reverse conveying path  10 C. The second solenoid  109  transmits the driving force generated by the motor M to the first lift plate  111  via the interlocking section  60  ( FIG. 3 ) to change the position of the first lift plate  111 . Furthermore, the second solenoid  109  transmits the driving force generated by the motor M to the returning member  62  and the holder  70  via the interlocking section  60  to perform an operation of projecting and retracting the returning member  62  and an operation of moving the holder  70 . The third solenoid  110  is controlled by the driving control section  80  to transmit the driving force generated by the motor M to the second lift plate  511  to change the position of the second lift plate  511  as is the case with the second solenoid  109 . Additionally, the third solenoid  110  allows performance of an operation of allowing the second retard roller  514  provided in the additional cassette  50  to contact and leave the second sheet feeding roller  513  and an operation of projecting and retracting the returning member not depicted in the drawings. 
     As described above, in the present embodiment, the driving force generated by the motor M is utilized to drive the plurality of members. In particular, a common driving section is used to drive the first pickup roller  112 , the second pickup roller  512 , the second conveying roller pair  177 , the third conveying roller pair  178 , the first lift plate  111 , and the second lift plate  511 , which are distributed over a wide range in the image forming apparatus  1 . Therefore, compared to a case where more motors are provided in order to individually drive these members, the present embodiment reduces the size of the apparatus main body  10  of the image forming apparatus  1  and the weight of the image forming apparatus  1 . Moreover, the present embodiment reduces the number of driving transmission mechanisms such as clutches and solenoids which transmit the driving force of the motor M to the rollers. Furthermore, the sharing of the same driving section and driving transmission mechanism enables a reduction in the costs of the image forming apparatus  1 . 
     On the other hand, the sharing of the same driving source as described above is likely to pose problems described below. First, a problem may occur at the time of duplex image formation utilizing the reverse conveying path  10 C. The image forming section  14  forms an image on the first sheet delivered from the sheet feeding cassette  11  by the first pickup roller  112 . Then, for duplex image formation, the sheet is switched back by means of the discharge roller pair  175  and loaded into the reverse conveying path  10 C. Then, the second conveying roller pair  177  and the third conveying roller pair  178  convey the sheet toward the main conveying path  10 A again. However, when the second conveying roller pair  177  and the third conveying roller pair  178  are rotationally driven in this manner, the first pickup roller  112  and first sheet feeding roller  113  coupled to the second driving mechanism  102  ( FIG. 9A ), to which the second conveying roller pair  177  and the third conveying roller pair  178  are also coupled, also rotate. Thus, another sheet is delivered into the main conveying path  10 A from the sheet feeding cassette  11 . In this case, disadvantageously, a plurality of sheets overlap in the main conveying path  10 A. 
     In the present embodiment, to solve such a problem, the driving control section  80  controls the feed clutch  106  to rotate the first pickup roller  112  with the first lift plate  111  placed in the sheet feeding position to load the sheet into the image forming section  14 . Subsequently, when the sheet is loaded into the reverse conveying path  10 C through the main conveying path  10 A and the discharge conveying path  10 B, the driving control section  80  controls the second solenoid  109  to rotate and move the first shaft  600 , thereby moving the first lift plate  111  from the sheet feeding position to the retracting position. 
     Thus, when the preceding sheet is conveyed through the reverse conveying path  10 C, the sheets stacked on the first lift plate  111  are prevented from being delivered by the first pickup roller  112 . Then, at a timing when a predetermined sheet interval is formed between a trailing end of the sheet being conveyed through the reverse conveying path  10 C and the leading end of the succeeding sheet, the driving control section  80  places the first lift plate  111  in the sheet feeding position again. The first pickup roller  112  then loads the succeeding sheet into the main conveying path  10 A. 
     Moreover, in the present embodiment, rotation of the first shaft  600  causes, in addition to lowering of the first lift plate  111 , separation of the first retard roller  114  from the first sheet feeding roller  113  and protrusion of the returning member  62  into the main conveying path  10 A as described above. When the first retard roller  114  is retracted from the first sheet feeding roller  113 , the nip portion formed between the first retard roller  114  and the first sheet feeding roller  113  is opened. This prevents the first sheet feeding roller  113  and the first retard roller  114  from braking the trailing end of the sheet conveyed by the registration roller pair  172  located on the downstream side of the first sheet feeding roller  113 . Furthermore, opening of the nip portion prevents the succeeding sheet delivered to the vicinity of the first sheet feeding roller  113  from being conveyed downstream. Additionally, the protrusion of the returning member  62  also prevents the succeeding sheet from being erroneously delivered. These manners of control also performed when the sheet is delivered from the additional cassette  50 . 
     Moreover, in the present embodiment, the sheet feeding cassette  11  and the additional cassette  50  are installed in an installation direction depicted by arrow DC in  FIG. 1 , and the inlet sides of the main conveying path  10 A and the additional conveying path  10 E extend along the installation direction, as described above. Thus, when the sheet feeding cassette  11  or the additional cassette  50  is pulled out from the apparatus main body  10  with the sheet held at the nip portion between the first sheet feeding roller  113  and the first retard roller  114  or between the second sheet feeding roller  513  and the second retard roller  514 , the sheet remains inside the apparatus main body  10 . 
     In the present embodiment, to solve such a problem, the driving control section  80  controls the second solenoid  109  and the third solenoid  110  to move the first lift plate  111  and the second lift plate  511  to the retracting positions when a series of image formation operations (print job) ends. At this time, the first retard roller  114  and the second retard roller  514  are retracted downward from the first sheet feeding roller  113  and the second sheet feeding roller  513 , respectively. Moreover, the returning member  62  and the returning member provided in the additional cassette  50  and not depicted in the drawings protrude into the main conveying path  10 A and the additional conveying path  10 E, respectively. Thus, the leading end of the sheet held at the nip portion as described above is quickly pushed back to the sheet feeding cassette  11  or additional cassette  50  located on the upstream side in the conveying direction. As a result, even when the user pulls the sheet feeding cassette  11  or the additional cassette  50  out from the apparatus main body  10 , the sheet is prevented from remaining inside the apparatus main body  10 . 
     Furthermore, in the present embodiment, when the additional cassette  50  is installed in the apparatus main body  10 , a plurality of cassettes (sheet feeding cassette  11  and additional cassette  50 ) is provided in the image forming apparatus  1 . The first pickup roller  112  corresponding to the sheet feeding cassette  11  and the second pickup roller  512  corresponding to the additional cassette  50  are coupled to the common second driving mechanism  102  and switched by the feed clutch  106  so that the start of rotation of one of the rollers synchronizes with the stop of the other. Thus, when sheets from both cassettes are inadvertently loaded into the main conveying path  10 A, sheet jam occurs in the main conveying path  10 A. 
     In the present embodiment, to prevent such a problem, the driving control section  80  places the lift plate of a first one of the sheet feeding cassette  11  and additional cassette  50  in the sheet feeding position, while placing the lift plate of a second cassette in the retracting position when the sheet is delivered from the first cassette to the image forming section  14 . Thus, even when the first pickup roller  112  and the second pickup roller  512  are simultaneously rotationally driven, the sheet is prevented from coming into abutting contact with the pickup roller in the cassette on which the sheet feeding operation is not performed. This prevents sheets from being inadvertently fed from both cassettes. Furthermore, also in this case, the driving control section  80  controls the second solenoid  109  to change the position of the holder  70  corresponding to the lift plate for the position change from the opposite position to the retracting position and to allow the returning member  62  to protrude into the main conveying path  10 A or the additional conveying path  10 E, using the driving force generated by the motor M. 
     The image forming apparatus  1  according to the embodiment of the present disclosure has been described. However, the present disclosure is not limited to this, and for example, such variations as described below may be adopted. 
     (1) In the above-described embodiment, the aspect has been described in which the image forming apparatus  1  includes the reverse conveying path  10 C and in which the additional cassette  50  can be selectively installed. However, the present disclosure is not limited to this. In a variation, an aspect is possible in which the image forming apparatus  1  does not have the reverse conveying path  10 C or the additional cassette  50 . Even when the image forming apparatus  1  does not include the reverse conveying path  10 C, the main conveying path  10 A and additional conveying path  10 E extending from the sheet feeding cassette  11  or the additional cassette  50  join together on the upstream side with respect to the registration roller pair  172 . Thus, to prevent the sheet feeding operation from being simultaneously performed on both cassettes, the lift plate of one of the cassettes may be placed in the retracting position as described above. 
     Furthermore, even when the image forming apparatus  1  does not include the additional cassette  50 , the main conveying path  10 A and reverse conveying path  10 C extending from the sheet feeding cassette  11  join together on the upstream side with respect to the registration roller pair  172 . Thus, to prevent the sheet from being fed from the sheet feeding cassette  11  while another sheet is being conveyed through the reverse conveying path  10 C, the first lift plate  111  of the sheet feeding cassette  11  may be placed in the retracting position as described above. 
     (2) Furthermore, in the above-described embodiment, the aspect has been described in which, in response to movement of the first lift plate  111  to the retracting position, the first retard roller  114  is refracted from the first sheet feeding roller  113  to allow the sheet abutting contact portion  62 C of the returning member  62  to protrude into the main conveying path  10 A. However, the present disclosure is not limited to this. In a variation, an aspect is possible in which the operation of refracting the first retard roller  114  and the operation of allowing the sheet abutting contact portion  62 C to protrude are not performed. 
     Although the present disclosure has been fully described by way of example with reference to the accompanying drawings, it is to be understood that various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the scope of the present disclosure hereinafter defined, they should be construed as being included therein.