Abstract:
An image forming apparatus includes: an image forming unit that forms an image on a first sheet; a fixing unit that fixes the image on the first sheet; a discharging unit that discharges the first sheet and a second sheet; a first transporting path that transports the first sheet on which the image is fixed to the discharging unit; a branch path that is branched from the first transporting path downstream of the fixing unit in a sheet transporting direction, the first sheet being transported to the branch path from the first transported path; a second transporting path that transports the second sheet in a direction opposite to the sheet transporting direction to the discharging unit; a plurality of sheet stock units in which sheets are stocked; a first sheet feed unit that feeds the first sheet from at least one of the plurality of sheet stock units to the first transporting path; and a second sheet feed unit that feeds the second sheet from at least one of the plurality of sheet stock units to the second transporting path.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2009-050437 filed Mar. 4, 2009. 
       BACKGROUND 
     Technical Field 
       [0002]    The present invention relates to an image forming apparatus for forming an image on a sheet. 
       SUMMARY 
       [0003]    According to an aspect of the present invention, there is provided an image forming apparatus including: an image forming unit that forms an image on a first sheet; a fixing unit that fixes the image on the first sheet; a discharging unit that discharges the first sheet and a second sheet; a first transporting path that transports the first sheet on which the image is fixed to the discharging unit; a branch path that is branched from the first transporting path downstream of the fixing unit in a sheet transporting direction, the first sheet being transported to the branch path from the first transported path; a second transporting path that transports the second sheet in a direction opposite to the sheet transporting direction to the discharging unit; a plurality of sheet stock units in which sheets are stocked; a first sheet feed unit that feeds the first sheet from at least one of the plurality of sheet stock units to the first transporting path; and a second sheet feed unit that feeds the second sheet from at least one of the plurality of sheet stock units to the second transporting path. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]    Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein: 
           [0005]      FIG. 1  is a diagram showing the construction of an image forming system to which an exemplary embodiment is applied; 
           [0006]      FIG. 2  is a diagram showing an image forming apparatus according to a first exemplary embodiment; 
           [0007]      FIG. 3  is a diagram showing the image forming apparatus; 
           [0008]      FIG. 4  is a diagram showing a state under which a first transporting unit and a second transporting unit have been installed in the image forming apparatus; 
           [0009]      FIG. 5  is a diagram showing an image forming apparatus according to a second exemplary embodiment; and 
           [0010]      FIG. 6  is a diagram showing the image forming apparatus in which a first transporting unit has been installed. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    Exemplary embodiments according to the present invention will be described hereunder with reference to the accompanying drawings. 
       First Exemplary Embodiment 
       [0012]      FIG. 1  is a diagram showing the construction of an image forming system to which an exemplary embodiment is applied. 
         [0013]    The image forming system  1  of the exemplary embodiment has an image forming apparatus  100  for forming an image on paper as an example of a sheet, a first paper feed apparatus  200  for feeding paper to the image forming apparatus  100 , and a second paper feed device  300  that is disposed at a downstream side of the first paper feed device  200  with respect to the paper transporting direction and feeds paper to the image forming apparatus  100 . Furthermore, the image forming system  1  has a curl correcting device  400  for correcting curl (warp) of paper transported from the image forming apparatus  100 , a paper stack device  500  for stacking paper transported from the curl correcting device  400 , and a paper processing device  600  for executing a predetermined processing on paper passed through the paper stacking device  500 . Here, the first paper feed device  200  and the second paper feed device  300  can be treated as external sheet feed devices for feeding paper (sheets) to a receiving portion  171  (described later) of the image forming apparatus  100 . 
         [0014]    The first paper feed device  200  has a first paper stock unit  210  and a second paper stock unit  220  in which paper (sheets) is stocked. The first paper feed device  200  is further provided with a feed-out roll  230  for feeding out paper stocked in the first stock unit  210  and the second stock unit  220  to a transporting path connected to the image forming apparatus  100 . 
         [0015]    The second paper feed device  300  has the same configuration as the first paper feed device  200 , and is provided with a first paper stock unit  310  and a second paper stock unit  320  in which paper (sheets) is stocked. Furthermore, the second paper feed device  300  is provided with a feed-out roll  330  for feeding out paper stocked in the first stock unit  310  and the second stock unit  320  to the transporting path connected to the image forming apparatus  100 . The second paper feed device  300  has a transporting path  340  for transporting paper fed from the first paper feed device  200  to the image forming apparatus  100 . 
         [0016]    The curl correcting device  400  has a curl correcting unit  410  for correcting curl of paper discharged from the image forming apparatus  100 . Omitting detailed description, the curl correcting unit  410  has an upper-curl correcting unit  411  for correcting an upper curl which occurs in paper (both the end portions of the paper in the paper transporting direction warp face up) when the paper passes through a fixing unit (described later) of the image forming apparatus  100 , and also a down-curl correcting unit  412  for correcting a down curl occurring in paper (both the end portions of the paper in the paper transporting direction warp face down) when the paper passes through the fixing unit. 
         [0017]    When the upper curl occurs in the paper, the upper-curl correcting unit  411  applies force (press force) to the upper-curl paper so that the paper concerned is bent to the opposite side to the upper-curl side, thereby correcting the upper curl. Furthermore, when the down curl occurs in the paper, the down-curl correcting unit  412  applies force (press force) to the down-curl paper so that the paper concerned is bent to the opposite side to the down-curl side, thereby correcting the down curl. 
         [0018]    The paper stack device  500  has a first paper stack unit  510  for stacking paper (sheets) transported from the curl correcting device  400 . The paper stack device  500  has a second paper stack unit  520  at the lower side of the first paper stack unit  510 . The paper stack device  500  has a transporting path  530  for transporting paper from the curl correcting device  400  to the paper processing device  600 . 
         [0019]    The paper processing device  600  has a folding device  610  for subjecting a folding processing such as an internal three-folding (C folding), external three-folding or the like to paper passing through the paper stack device  500 . Furthermore, the paper processing device  600  is provided with a perforating unit  620  for perforating (punching) paper, a side stitching unit  630  for stitching the ends of a stack of paper (sheets) by using a staple to create a booklet, and a saddle-stitching unit  640  for center-folding/saddle stitching a stack of paper (sheets) to create a center-page spread booklet. In this case, for example when plural sheets of paper are subjected to staple processing to create a booklet, plural sheets of paper are stacked on a compile tray  631  provided to the side stitching unit  630 , and the staple processing is executed by a staple head  632 . The paper stack formed as a booklet through the staple processing is discharged to the paper stacking unit  650  provided to the paper processing device  600 . 
         [0020]    Next, the image forming apparatus  100  will be described with reference to  FIG. 2 . 
         [0021]      FIG. 2  is a diagram showing the image forming apparatus  100 . 
         [0022]    As shown in  FIG. 2 , the image forming apparatus  100  has an image forming unit  110  for forming a toner image on paper (a sheet), and also has a fixing unit  120  for fixing the toner image formed on the paper in the image forming unit  110  so that the toner image is fixed onto the paper. The fixing unit  120  heats and pressurizes the paper and the toner image to fix the toner image onto the paper. Furthermore, the image forming apparatus  100  has a receiving unit  171  for receiving paper transported from the first paper feed device  200  or the second paper feed device  300 . The image forming apparatus  100  further has a first paper transporting path  141  for passing the paper received by the receiving unit  171  through the image forming unit  110  and the fixing unit  120  and then transporting the paper to a paper discharge unit  172 . The image forming apparatus  100  also has a paper feeder  130  for feeding paper to the first paper transporting path  141 . 
         [0023]    The image forming apparatus  100  is further provided with a third paper feed path  161  which is provided so as to be branched from the first paper transporting path  141  and transports paper received by the receiving unit  171  to a site at which a third paper stock unit  133 A described later is provided. The image forming apparatus  100  is further provided with a switching gate G 0  (an example of a switching unit) for switching the paper transporting destination to the first paper transporting path  141  or the third paper transporting path  161 , and a driving source (not shown) such as a solenoid or the like for driving the switching gate G 0 . The image forming apparatus  100  is also provided with a transporting roll  162  which is provided in the third paper transporting path  161  and transports paper along the third paper transporting path  161 . 
         [0024]    The image forming unit  110  has a photoconductor drum  111 , an electrifying device  112 , an exposure device  113 , a developing device  114 , a transfer device  115  and a cleaning device  116 . The photoconductor drum  111  has a photoconductive layer on the outer peripheral surface thereof and rotates in the direction of an arrow in  FIG. 2 . The electrifying device  112  electrifies the rotating photoconductor drum  111  so that the potential of the photoconductor drum  111  is set to a predetermined potential. The exposure device  113  selectively exposes to light the photoconductor drum  111  which is electrified at the predetermined potential by the electrifying device  112 , thereby forming an electrostatic latent image. 
         [0025]    The developing device  114  develops the electrostatic latent image formed on the photoconductor drum  111  with toner to form a toner image. The transfer device  115  electrostatically transfers the toner image formed on the photoconductor drum  111  to paper transported along the first paper transporting path  141 . The cleaning device  116  cleans toner, etc. remaining on the photoconductor drum  111  after the transfer. A position at which the photoconductor drum  111  and the transfer device  115  are opposed to each other and a toner image on the photoconductor drum  111  is transferred onto paper by using the transfer device  115  is referred to as transfer position Tp. 
         [0026]    The paper feeding unit  130  has a first paper feeder  131 , a second paper feeder  132  and a third paper feeder  133 . In this exemplary embodiment, the third paper feeder  133  is disposed at the lowermost position, the second paper feeder  132  is disposed above the third paper feeder  133 , and the first paper feeder  131  is disposed above the second paper feeder  132 . Additionally describing, the third paper feeder  133  is disposed at the most upstream side, and the first paper feeder  131  is disposed at the most downstream side with respect to the paper transporting direction. 
         [0027]    The first paper feeder  131  has a first paper stock unit  131 A, a first pull-in roller  131 B and a first handling mechanism  131 C. 
         [0028]    Here, the first paper stock unit  131 A as an example of a sheet stock unit has a rectangular parallelepiped shape opened at the upper portion thereof, accommodates paper (sheets) therein. The first paper stock unit  131 A is provided so that it can be pulled to the front side (forwardly in  FIG. 2 ). Accordingly, when the first paper stock unit  131 A is out of paper or the like, the first paper stock unit  131 A is pulled out from the image forming apparatus  100 , and paper can be replenished to the first paper stock unit  131 A. The first paper stock unit  131 A is further pulled to the front side (forwardly in  FIG. 2 ), whereby the first paper stock unit  131 A can be detached form the image forming apparatus  100  (the device main body  100 A). 
         [0029]    The first pull-in roll  131 B is provided above the first paper stock unit  131 A so as to be movable in the up-and-down direction. The first pull-in roll  131 B comes into contact with the uppermost paper of a stack of paper (sheets) stocked in the first paper stock unit  131 A, and feeds out the uppermost paper to the first handling mechanism  131 C. 
         [0030]    The first handling mechanism  131 C is provided at the downstream side of the first pull-in roll  131 B with respect to the paper transporting direction. The first handling mechanism  131 C is constructed by a rotatable field roll and a rotation-restricted retard roll, and it handles sheets of paper fed out from the first pull-in roll  131 B one by one and feeds out each handled sheet of paper to a first transporting roll  131 D described later. 
         [0031]    The second paper feeder  132  also has the same configuration as the first paper feeder  131 , and is equipped with a second paper stock unit  132 A, a second pull-in roll  132 B and a second handling mechanism  132 C. Furthermore, the third paper feeder  133  as an example of the paper feeder has the same configuration as the first paper feeder  131 , and is equipped with a third paper stock unit  133 A (an example of the sheet stock unit), a third pull-in roll  133 B and a third handling mechanism  133 C. 
         [0032]    Furthermore, the paper feeder  130  is equipped with a first feeding roll  131 D, a second feeding roll  132 D and a third feeding roll  133 D. 
         [0033]    The first feeding roll  131 D is constructed by a pair of roll-shaped members, and provided at the downstream side of the first handling mechanism  131 C with respect to the paper transporting direction. The first transporting roll  131 D temporarily stops paper fed from the first handling mechanism  131 C, and then feeds the paper at a predetermining timing again. The second transporting roll  132 D is also constructed by a pair of roll-shaped members. This second transporting roll  132 D is provided at the downstream side of the second handling mechanism  132 C with respect to the paper transporting direction, and it temporarily stops paper fed from the second handling mechanism  132 C and then feeds the paper at a predetermining timing again. 
         [0034]    Furthermore, the third transporting roll  133 D is also constructed by a pair of roll-shaped members. The third transporting roll  133 D is provided at the downstream side of the third handling mechanism  133 C with respect to the paper transporting direction, and it temporarily stops paper fed from the third handling mechanism  133 C and then feeds the paper at a predetermined timing again. 
         [0035]    When paper is supplied from each of the second paper feeder  132  and the third paper feeder  133 , the first transporting roll  131 D and the second transporting roll  132 D at the upper stage of these second and third paper feeders  132  and  133  function as transporting rolls for transporting this paper along the first paper transporting path  141 . 
         [0036]    Furthermore, in the image forming apparatus  100  of this exemplary embodiment, a pre-registration roll  151  and a registration roll  152  are provided to the first paper transporting path  141  to be located at the downstream side of the first transporting roll  131 D. Here, the pre-registration roll  151  further transports paper transported through the first transporting roll  131 D to the downstream side, and forms a loop in cooperation with the registration roll  152 . Furthermore, the registration roll  152  temporarily stops and thus temporarily stops the transportation of the paper, and resumes its rotation in conformity with the timing, whereby the paper is transported to the transfer position Tp while executing registration adjustment. 
         [0037]    The image forming apparatus  100  is provided with a reversing and feeding mechanism for reversing one-side-fixed paper fixed in the fixing unit  120  and feeding the paper to the transfer position Tp again when the both side mode is selected. This reversing and feeding mechanism has a first branch path  143  downwardly branched from the first paper transporting path  141  at the downstream side of the fixing unit  120  with respect to the paper transporting direction. The reversing and transporting mechanism is provided so as to be connected to the first branch path  143 , and it is equipped with a second paper transporting path  144  which extends downwardly from the connection portion with the first branch path  143  and directs from the above connection portion to a paper discharge unit  172 . Furthermore, the reversing and transporting mechanism is provided with a return path  145  which is connected to the second paper feeding path  144  and joined to the first paper transporting path  141  at the upstream side of the pre-registration roll  151 . 
         [0038]    In the image forming apparatus  100 , a paper discharge roll  153  for discharging paper to the outside of the apparatus is provided in the first paper transporting path  141 . The image forming apparatus  100  has a branch roll  154  that is provided in the first branch path  143  and transports paper transported to the first branch path  143  to the second paper transporting path  144 , and also has a reversing roll  155  that is forwardly and reversely rotatable, temporarily feeds the paper transported to the second paper transporting path  144  downwardly (in one direction), and reversely rotates to feed the paper into the return path  145  or transports the paper along the second paper transporting path  144 . A space (site)  147  in which paper is downwardly fed is formed at the lower side of the reversing roll  155 . This space  147  is provided in proximity to the first paper feeder  131 , the second paper feeder  132  and the third paper feeder  133  of the paper feeder  130 . 
         [0039]    The image forming apparatus  100  has a return roll  156  that is provided in the return path  145  and transports the paper transported by the reversing roll  155  along the return path  145 . The image forming apparatus  100  also has a transporting roll  157  for transporting the paper in the second paper transporting path  144  to the paper discharge unit  172 , and the transporting roll  157  is located so as to be nearer to the paper discharge unit  172  than the connection portion between the first branch path  143  and the second paper transporting path  144 . 
         [0040]    Although omitted from the foregoing description, the image forming apparatus  100  of this exemplary embodiment is configured so that paper (sheet) having an image formed thereon can be discharged to the outside of the apparatus while both the sides thereof are reversed. In this case, the paper passing through the fixing unit  120  is fed through the first branch path  143  into the second paper transporting path  144 . Thereafter, the paper is guided to the second paper transporting path  144  and then transported to the discharge unit  172 . 
         [0041]    A first switching gate G 1  for switching the paper transportation destination to the first paper transporting path  141  and the first branch path  143  is provided between the first paper transporting path  141  or the first branch path  143 . Furthermore, a second switching gate G 2  for switching the paper transportation destination to the return path  145  or the second paper transporting path  144  is provided between the second paper transporting path  144  and the return path  145 . Furthermore, a third switching gate G 3  for transporting paper fed to the second paper transporting path  144  into the paper discharge unit  172  is provided between the first branch path  143  and the second paper transporting path  144 . The image forming apparatus  100  is also provided with a driving source (not shown) such as a solenoid or the like for driving the first switching gate G 1  to the third switching gate G 3 . 
         [0042]    Furthermore, the image forming apparatus  100  of this exemplary embodiment is equipped with a receiver  191  for receiving image data from a personal computer (PC)  2 , an image reader  3  or the like, and an image processor  192  for subjecting the image data received by the receiver  191  to image processing and then outputting the processed image data to the exposure device  113 . The image forming apparatus  100  is also equipped with a controller  193  for controlling the respective devices and the respective units provided to the image forming apparatus  100  and also controlling the overall image forming system  1  of this exemplary embodiment. 
         [0043]    The image forming apparatus  100  has a user interface (UI)  194  (an example of a display unit and an accepting unit) that is constructed by a display panel, accepts an instruction (information) from a user and displays a message or the like for the user). The controller  193  functioning as one of the speed controller and the apparatus controller has CPU (Central Processing Unit), ROM (Read Only Memory) and RAM (Random Access Memory). CPU executes the processing according to the program stored in ROM while receiving/transmitting data from/to RAM, thereby implementing respective functions described later. 
         [0044]    Furthermore, the image forming apparatus  100  of this exemplary embodiment is provided with a first read-out unit  195  that is provided below the third paper stock unit  133 A and reads out information from an EEPROM (Electrically Erasable and Programmable ROM) mounted in a first transporting unit  700  described later. In addition, a second read-out unit  196  for reading out information from EEPROM (Electrically Erasable and Programmable ROM) mounted in a second transporting unit  800  described later is provided above the space  147 . Here, the first read-out unit  195  may be regarded as a type of detecting unit for detecting mounting of the first transporting unit  700 . Furthermore, the second read-out unit  196  may be regarded as a type of detecting unit for detecting mounting of the second transporting unit  800 . 
         [0045]    Here, the image forming system  1  of this exemplary embodiment is provided with the side stitching unit  630  and the saddle-stitching unit  640  as described above, and thus a booklet including plural sheets of paper can be created. There is a case where a printed front cover or a printed rear cover is separately added when such a booklet is created. Furthermore, there is also a case where printed paper is inserted between sheets of paper constituting a booklet. There is also a case where ornamented paper on which gold foil or silver foil is impressed is used as a front cover, a rear cover or insertion paper to be inserted between sheets of paper. In this specification, the front cover, the rear cover, the insertion paper, the ornamented paper, etc. will be referred to as “additional paper” in some cases. 
         [0046]    When such additional paper is added, the paper passing through the fixing unit  120  may be lowered in quality due to heat of the fixing unit  120 . Specifically, the degree of brilliancy of an image may be lowered. When gold foil or silver foil is formed as described above, the degree of brilliancy of this gold foil or silver foil may be lowered. 
         [0047]    Therefore, when additional paper is added, it is possible that the additional paper is fed into the paper transporting path at the downstream side of the image forming apparatus  100 . In such a case, in addition to the paper feeding device for feeding paper (sheets) to the image forming apparatus  1  (corresponding to the first paper feeding device  200  and the second paper feeding device  300  in this exemplary embodiment), a paper feeding device is required to be further provided at the downstream side of the image forming apparatus  100 . As a result, the image forming system must be designed in a large scale. Therefore, the image forming system  1  of this exemplary embodiment adopts the following configuration. 
         [0048]    In the image forming apparatus  100  of the image forming system  1  according to this exemplary embodiment, the third paper stock unit  133 A is detachably mounted as described above. Furthermore, the space  147  for feeding paper downwardly is formed at the lower side of the reversing roll  155 . The space  147  is provided to be adjacent to the first paper feeder  131 , the second paper feeder  132  and the third paper feeder  133  of the paper feeder  130 . Therefore, in the image forming apparatus  100  of this exemplary embodiment, a paper transporting path along which paper (sheets) is not passed through the fixing unit  120  is formed by using a space (site)  148  formed after the third paper stock unit  133 A is detached and the space  147  located below the reversing roll  155 . 
         [0049]      FIG. 3  is a diagram showing the image forming apparatus  100 . 
         [0050]    As shown in  FIG. 3 , when the third paper stock unit  133 A (see  FIG. 2 ) is detached from the image forming apparatus  100 , the space  148  is formed at the position where the third paper stock unit  133 A has been mounted just before. In this exemplary embodiment, a first transporting unit  700  which can be fitted to (inserted into) this space  148  is prepared. 
         [0051]    The first transporting unit  700  has a rectangular parallelepiped unit body  710 . A unit transporting path  720  to which paper is transported is provided in the unit body  710 . Furthermore, the first transporting unit  700  has plural transporting rolls  730  for transporting paper along the unit transporting path  720 . The transporting rolls  730  can be rotated by using the driving force transmitted from the image forming apparatus  100  side. The first transporting unit  700  may be provided with a driving source such as a motor or the like so that the transporting rolls  730  can be rotated by the driving source. The first transporting unit  700  has EEPROM  740  as an example of a memory in which various kinds of information are stored. 
         [0052]    Furthermore, in this exemplary embodiment, a second transporting unit  800  which can be fitted (inserted) in the space  147  formed below the reversing roll  155  is prepared. The second transporting unit  800  has a rectangular parallelepiped unit body  810 . A unit transporting path  820  to which paper is transported is provided in the unit body  810 . The second transporting unit  800  is also equipped with plural transporting rolls  830  for transporting paper along the unit transporting path  820 . 
         [0053]    The transporting rolls  830  can be rotated by using the driving force transmitted from the image forming apparatus  100  side. However, the second transporting unit  800  may be provided with a driving source such as a motor or the like so that the transporting rolls  830  can be rotated by the driving source. The second transporting unit  800  has EEPROM  840  as an example of a memory in which various kinds of information are stored. 
         [0054]    Here,  FIG. 4  shows the image forming apparatus  100  under the state that the first transporting unit  700  and the second transporting unit  800  are mounted in the image forming apparatus  100 . 
         [0055]    As shown in  FIG. 4 , when the first transporting unit  700  is mounted in the image forming apparatus  100 , the unit transporting path  720  in the first transporting unit  700  is set to be connected to the third paper transporting path  161  provided to the image forming apparatus  100 . 
         [0056]    Furthermore, when the second transporting unit  800  is mounted in the image forming apparatus  100 , the unit transporting path  820  in the second transporting unit  800  is set to be connected to the unit transporting path  720  in the first transporting unit  700 . In addition, the unit transporting path  820  in the second transporting unit  800  is set to be connected to the second paper transporting path  144  in the image forming apparatus  100 . 
         [0057]    When the first transporting unit  700  is mounted in the image forming apparatus  100 , information stored in EEPROM  740  is read out by the first read-out unit  195 . When the second transporting unit  800  is mounted in the image forming apparatus  100 , information stored in an EEPROM  840  is read out by the second read-out unit  196 . Accordingly, on the basis of the read-out information, the controller  193  can recognize that the first transporting unit  700  and the second transporting unit  800  are mounted in the image forming apparatus  100 . 
         [0058]    Here, when the controller  193  recognizes that the first transporting unit  700  and the second transporting unit  800  are mounted in the image forming apparatus  100 , the controller  193  displays, on UI  194  , a screen for accepting a condition for adding additional paper from a user. Specifically, the screen for accepting information concerning an insertion position of additional paper, etc. is displayed on UI  194 . Additionally describing, the display of UI  194  is changed to accept the additional-paper adding condition from the user. The controller  193  does not display the above screen when the controller  193  does not recognize that the first transporting unit  700  and the second transporting unit  800  are mounted. 
         [0059]    Furthermore, the controller  193  accepts from the user through UI  194  the information concerning a paper stock unit in which additional paper is stocked (the first paper stock unit  210 , the second paper stock unit  220 , the first paper stock unit  310  or the second paper stock unit  320  (see  FIG. 1 )). Accordingly, the controller  194  can identify the paper stock unit in which the additional paper (sheets) is stocked. 
         [0060]    Furthermore, when the controller  193  recognizes that the first transporting unit  700  and the second transporting unit  800  are mounted, the controller  193  changes the display of UI  194  so as to make it possible to set the condition which has been impossible to be set before the first transporting unit  700  and the second transporting unit  800  are mounted. For example, when various kinds of settings cannot be performed with respect to paper (sheets) having a thickness exceeding some upper limit value because it is difficult to fix such thick paper in the fixing unit  120 , the display of UI  194  is changed so that these various kinds of settings can be performed with respect to paper having a thickness exceeding the upper limit value. That is, even in the case of paper having a thickness larger than some upper limit value, it can be transported while bypassing a bypass transporting path described later. Therefore, the display of UI  194  is changed so that various kinds of settings can be performed with respect to paper having a thickness exceeding the upper limit value. 
         [0061]    As described above, when the first transporting unit  700  and the second transporting unit  800  are mounted in the image forming apparatus  100 , a new paper transporting path is formed by the third paper transporting path  161 , the unit transporting path  720 , the unit transporting path  820  and the second paper transporting path  144 . Additionally describing, the new paper transporting path (hereinafter referred to as “bypass transporting path”) along which paper is not passed through the image forming unit  110  and the fixing unit  120  is formed. Accordingly, the additional paper which should not be passed through the fixing unit  120  can be stocked in the first paper feeding device  200  or the second paper feeding device  300  (see  FIG. 1 ). Additionally describing, paper which should not be passed through the fixing unit  120  can be stocked in the first paper feeding device  200  or the second paper feeding device  300 , and it is unnecessary to further provide a paper feeding device at the downstream side of the image forming apparatus  100 . 
         [0062]    Here, when a booklet is created in the paper processing device  600 , the controller  193  accepts through UI  194  information concerning creation of a booklet such as an insertion position, etc. of additional paper. The controller  193  transmits a control signal to the first paper feeding device  200  and the second paper feeding device  300  on the basis of the accepted information. In response to this control signal, paper (sheets) is successively transported from the first paper feeding device  200  and the second paper feeding device  300 . Specifically, the paper (sheets) is successively transported from the first paper feeding device  200  and the second paper feeding device  300 , and also additional paper (an example of a different sheet) is transported while inserted at the insertion position. When paper on which an image is formed in the image forming unit  110  is transported, the controller  193  drives the switching gate GO and selects the first paper transporting path  141  as a paper transporting destination. Accordingly, the paper is passed through the image forming unit  110  and the fixing unit  120  and also discharged to the outside of the apparatus (the curl correcting device  400 ) by the paper discharging roll  153 . 
         [0063]    When additional paper is transported, the controller  193  drives the switching gate G 0  to switch the transporting destination of the additional paper to the third paper transporting path  161 . Furthermore, the controller  193  drives the switching gate G 2  and the switching gate G 3  to set the second paper transporting path  144  as a paper transporting path to which the additional paper is transported. Accordingly, the additional paper is passed through the third paper transporting path  161 , the unit transporting path  720 , the unit transporting path  820  and the second paper transporting path  144  and discharged to the outside of the apparatus. That is, the additional paper is discharged to the outside of the apparatus without passing through the image forming unit  110  and the fixing unit  120 . 
         [0064]    For example, when there is a difference between the path length of the first paper transporting path  141  (hereinafter referred to as “fixing unit passing transporting path”) passing through the image forming unit  110  and the fixing unit  120  and the path length of the bypass transporting path, the time for which paper passing along the fixing unit passing transporting path is discharged from the image forming apparatus  100  is different from the time for which paper passing along the bypass transporting path is discharged from the image forming apparatus  100 . Additionally describing, when sheets of paper are successively transported under the state that paper passing through the fixing unit passing transporting path and paper passing through the bypass transporting path are mixed with each other, the pitch of the sheets of paper which are successively discharged from the image forming apparatus  100  is not uniform. 
         [0065]    Therefore, in order to make the paper discharge pitch uniform, the paper transporting speed may be controlled. Additionally describing, the paper transporting speed may be controlled so that the time required until paper passing through the fixing unit passing transporting path reaches the paper discharge unit  172  is equal to the time required until paper passing through the bypass transporting path reaches the paper discharge unit  172 . Here, the bypass transporting path side is provided with neither image forming unit  110  nor fixing unit  120 . Therefore, the paper transporting speed at the bypass transporting path side is controlled. 
       Second Exemplary Embodiment 
       [0066]      FIG. 5  is a diagram showing an image forming apparatus  100  according to a second exemplary Embodiment. The same functions as the first exemplary embodiment are represented by the same reference numerals, and the description thereof is omitted. 
         [0067]    In this exemplary embodiment, plural reversing rolls  155  functioning as transporting units are provided. These reversing rolls  155  are provided in the space  147  (see  FIG. 2 ) in the first exemplary embodiment. Additionally describing, the plural reversing rolls  155  are provided along the second paper transporting path  144 . Furthermore, in this exemplary embodiment, a second branch path  149  which is branched from the second paper transporting path  144  and directs to the third paper feeder  133  is provided. The second branch path  149  is branched from the second paper transporting path  144  at the lower side of the reversing roll  155  located at the lowermost position out of the plural reversing rolls  155 . 
         [0068]    The third paper feeder  133  of this exemplary embodiment is provided with a fourth pull-in roll  133 E (an example of a second feeding unit) and a fourth handling mechanism  133 F in addition to the third pull-in roll  133 B (an example of the first feeding unit) and the third handling mechanism  133 C. The fourth pull-in roll  133 E and the fourth handling mechanism  133 F are provided at the opposite side to the side (the left side in  FIG. 5 ) at which the third pull-in roll  133 B and the third handling mechanism  133 C are provided. Paper which is fed out by the fourth pull-in roll  133 E and handled by the fourth handling mechanism  133 F is fed through the second branch path  149  into the second paper transporting path  144 . 
         [0069]    Therefore, in this exemplary embodiment, the paper which is fed out by the fourth pull-in roll  133 E and handled by the fourth handling mechanism  133 F is fed to the second paper transporting path  144 , and then upwardly transported by the reversing rolls  155 . Additionally describing, the paper which is fed out by the fourth pull-in roll  133 E and handled by the fourth handling mechanism  133 F is discharged through the second branch transporting path  149  and the second paper transporting path  144  to the outside of the image forming apparatus  100 . Additionally describing, paper stocked in the third paper feeder  133  can be discharged to the outside of the image forming apparatus without passing through the image forming unit  110  and the fixing unit  120 . 
         [0070]    Therefore, when the additional paper which should not be passed through the fixing unit  120  is stocked in the third paper feeder  133 , the additional paper can be discharged to the outside of the image forming apparatus without passing through the fixing unit  120 . Additionally describing, it is likewise unnecessary to provide a paper feeding device at the downstream side of the image forming apparatus  100 . 
         [0071]    For this exemplary embodiment is also prepared the first transporting unit  700  which can be inserted into the space (site) formed after the third paper stock unit  133 A is detached. 
         [0072]      FIG. 6  is a diagram showing the image forming apparatus  100  when the first transporting unit  700  is mounted. As shown in  FIG. 6 , by mounting the first transporting unit  700 , the third paper transporting path  161  and the second branch path  149  are connected to each other. As a result, paper which is transported from the first paper feeding device  200  and the second paper feeding device  300  can be also discharged to the outside of the image forming apparatus  100  without passing through the image forming unit  110  and the fixing unit  120 . 
         [0073]    When the number of sheets of additional paper which should not be passed through the fixing unit  120  is small, these sheets may be stocked in the third paper feeder  133 . On the other hand, when the number of sheets of additional paper is small, there occurs a situation that all the sheets of additional paper cannot be stocked in the third paper feeder  133 . In such a case, by mounting the first transporting unit  700 , these sheets of additional paper can be stocked in the first paper feeding device  200  having a large volume or the like. 
         [0074]    In this exemplary embodiment, when the third paper stock unit  133 A is detached, the third pull-in roll  133 B (see  FIG. 5 ), the third handling mechanism  133 C and the fourth pull-in roll  133 E are detached together with the third paper stock unit  133 A. Furthermore, in this exemplary embodiment, the second branch path  149  is located at the upper side of the third paper transporting path  161 , and thus the unit transporting path  720  in the first transporting unit  700  is obliquely disposed. 
         [0075]    The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The exemplary embodiments were chosen and described in order to best explain the skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.