Patent Publication Number: US-9845212-B2

Title: Paper delivery device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. 119 to Japanese Patent Application No. 2015-202239 filed on Oct. 13, 2015, which application is hereby incorporated by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a paper delivery device provided in an image forming apparatus for forming an image on a paper and delivers the paper on which the image is formed to the outside. 
     2. Description of the Related Art 
     Conventionally, there has been known an image forming apparatus which delivers papers on which images are formed to a paper exit tray while sorting the papers in accordance with the number of copies. For example, there has been known an image forming apparatus equipped with a shift frame which is slidable back and forth in a roller axis direction of a paper delivery roller. 
     In this image forming apparatus, the shift frame is moved in the direction perpendicular or substantially perpendicular to a paper feeding direction of papers and, thereafter, papers on which images are formed are delivered to a paper exit tray (shift sort). 
     Further, in the image forming apparatus which forms images on papers by electrophotography, at the time of heating a paper for fusing toner to the paper, moisture is evaporated from a heated surface of the paper. It has been known that, as a result of the evaporation of moisture, the heated surface of the paper is contracted so that the paper curls. 
     To prevent such curl, there has been known a paper delivery device equipped with a decurling mechanism which eliminates curl generated on a paper by a plurality of driven rollers which are brought into contact with a curved surface of a drive roller at the time of delivering the paper. 
     Conventionally, in mounting the shift sorting mechanism and the decurling mechanism described above on the image forming apparatus, these mechanisms are mounted separately from each other. As a result, it has been impossible to downsize the image forming apparatus having functions of both mechanisms. 
     SUMMARY OF THE INVENTION 
     Preferred embodiments of the present invention provide a paper delivery device of an image forming apparatus in which a mechanism that performs a shift sorting function and a mechanism that performs a decurling function are housed in a compact manner. 
     A plurality of preferred embodiments of the present invention are described hereinafter. Elements, features, or characteristics of the various preferred embodiments of the present invention can be arbitrarily combined with each other when necessary. 
     According to a preferred embodiment of the present invention, there is provided a paper delivery device which is provided in an image forming apparatus to form an image on a paper, and delivers the paper on which the image is formed to the outside. The paper delivery device includes a shift frame, a driver, a drive roller, a first driven roller, and a second driven roller. 
     The shift frame is movable in a second direction perpendicular or substantially perpendicular to a first direction along which the paper is delivered to the outside. The driver moves the shift frame in the second direction. 
     The drive roller includes a first outer peripheral surface extending in the second direction, and is supported by the shift frame such that the drive roller is rotatable about a first shaft disposed parallel or substantially parallel to the second direction. 
     The first driven roller includes a second outer peripheral surface which extends in the second direction and is brought into contact with the first outer peripheral surface at a first contact position. The first driven roller is supported by the shift frame such that the first driven roller is rotatable about a second shaft disposed parallel or substantially parallel to the second direction following the rotation of the drive roller. The first driven roller is rotated in a state where the paper is nipped between the first outer peripheral surface and the second outer peripheral surface thus transporting the paper in the first direction. “nip” means clamping the paper between two rollers. 
     The second driven roller includes a third outer peripheral surface which extends in the second direction and is brought into contact with the first outer peripheral surface at a second contact position downstream of the first contact position in the first direction. The second driven roller is supported by the shift frame such that the second driven roller is rotatable about a third shaft disposed parallel or substantially parallel to the second direction following the rotation of the drive roller. The second driven roller is rotated in a state where the paper which is nipped between the first outer peripheral surface and the second outer peripheral surface is nipped by the first outer peripheral surface and the third outer peripheral surface thus transporting the paper in the first direction. 
     In the above paper delivery device, at the time of delivering the paper on which an image is formed, the paper which is nipped between the first outer peripheral surface of the drive roller and the second outer peripheral surface of the first driven roller at the first contact position is nipped between the first outer peripheral surface of the drive roller and the second outer peripheral surface of the second driven roller at the second contact position. With such a configuration, it is possible to curve the nipped paper in the direction opposite to the direction of curl formed on the paper. As a result, it is possible to eliminate curl generated on the nipped portion. 
     In the above paper delivery device, the drive roller, the first driven roller and the second driven roller are supported by the same shift frame. With such a configuration, it is possible to realize the compact paper delivery device that performs both a shift sorting function and a decurling function. As a result, an image forming apparatus equipped with the paper delivery device is able to be downsized. 
     In an operation for delivering the paper in the paper delivery device after moving the paper to a different position in the second direction, the paper delivery device may perform an operation in which (i) the paper is transported due to rotation of the drive roller until a rear edge of the paper in the first direction is released from nipping between the first outer peripheral surface and the second outer peripheral surface and the rear edge of the paper is nipped between the first outer peripheral surface and the third outer peripheral surface, (ii) the rotation of the drive roller is stopped in a state where the rear edge of the paper in the first direction is nipped only between the first outer peripheral surface and the third outer peripheral surface, (iii) the driver moves the shift frame in the second direction while the rear edge of the paper in the first direction is nipped between the first outer peripheral surface and the third outer peripheral surface; and (iv) the paper is delivered from between the drive roller and the second driven roller by rotating the drive roller. 
     With such an operation, during the movement of the shift frame in the second direction, the paper is not brought into a curved state due to nipping by three rollers. Accordingly, it is possible to prevent the generation of nip marks on the paper during the movement of the paper in the second direction. 
     Thus, with preferred embodiments of the present invention, a mechanism that performs a shift sorting function and the mechanism that performs a decurling function are housed in the paper delivery device of the image forming apparatus in a compact manner. 
     The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partial cross-sectional view illustrating an image forming portion of an image forming apparatus. 
         FIG. 2  is a front view of the paper delivery device as viewed from a delivery port. 
         FIG. 3  is a perspective view of the paper delivery device. 
         FIG. 4  is a cross-sectional view of the paper delivery device as viewed from a second direction. 
         FIG. 5A  is a view illustrating a state of a home detector when shift frames are not at home positions 
         FIG. 5B  is a view illustrating the state of the home detector when the shift frames are at the home positions. 
         FIG. 6  is a block diagram illustrating the configuration of a controller. 
         FIG. 7  is a flowchart illustrating an image forming process of the image forming apparatus. 
         FIG. 8  is a view illustrating a state where a sheet of paper is nipped by three rollers. 
         FIG. 9  is a flow chart illustrating a process in which a paper is delivered after performing shift sorting. 
         FIG. 10  is a view illustrating a state where a rear edge of the paper is nipped at a second contact position. 
         FIG. 11  is a view illustrating one example of a state of the paper delivery device where the shift frame is shifted in the second direction from the home position. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The preferred embodiments described hereinafter describe preferred specific examples of the present invention. In the preferred embodiments described hereinafter, numerical values, shapes, materials, elements, the arrangement positions and connection states of the elements, operational steps, the order of operational steps and the like are merely examples, and these are not intended to limit the present invention. 
     First Preferred Embodiment 
     Hereinafter, an image forming apparatus according to a first preferred embodiment of the present invention is described. First, the overall configuration of the image forming apparatus  100  according to the first preferred embodiment is described with reference to  FIG. 1 . 
     The image forming apparatus  100  includes a body  1 . The body  1  defines a body of the image forming apparatus  100 . A paper exit tray T is provided on a portion of the body  1 . A paper P transported by a paper delivery device  4  (described later) is delivered to the paper exit tray T. 
     The image forming apparatus  100  includes a paper feed cassette  2 . The paper feed cassette  2  is disposed on a lower portion of the body  1  (below an image former  3 ). Papers P to be transported to the image former  3  for formation of an image are placed in the paper feed cassette  2 . The papers P placed on the paper feed cassette  2  are transported to a first transportation path R 1  due to the rotation of a pickup roller  21 . 
     The image forming apparatus  100  includes the image former  3  inside the body  1 . The image former  3  forms an image on a surface of the paper P transported to the first transportation path R 1  by electrophotography. The image former  3 , after the image is formed on the paper P, delivers the paper P to a second transportation path R 2 . 
     The image forming apparatus  100  includes the paper delivery device  4  inside the body  1  and above the image former  3 . The paper delivery device  4  delivers the paper P which is transported through the second transportation path R 2  and on which an image is formed to the paper exit tray T through a delivery port E ( FIG. 1 ). The configuration of the paper delivery device  4  is described in detail later. The direction along which the paper P is transported to the paper exit tray T from the delivery port E is referred to as a first direction D 1 . 
     The image forming apparatus  100  includes a controller  5  inside the body  1 . The controller  5  controls respective elements of the image former  3 . The configuration of the controller  5  is described in detail later. 
     The image forming apparatus  100  includes an operation panel  6  above the body  1 . The operation panel  6  includes a touch screen and various types of keys, and receives an input operation performed by a user or the like. The operation panel  6  also includes a display which displays a state of the image forming apparatus  100 . 
     The image forming apparatus  100  includes a paper passing detection switch SW in the vicinity of the paper delivery device  4  in the second transportation path R 2  ( FIG. 4 ). The paper passing detection switch SW is a switch equipped with a photointerrupter, and detects that the paper P on which an image is formed approaches to the paper delivery device  4 . 
     To be more specific, when a leading edge of the paper P on which an image is formed passes the paper passing detection switch SW, a lever of the paper passing detection switch SW is moved from a position where the lever blocks light to a position where the lever allows passing of the light and hence, passing of the leading edge of the paper P is able to be detected. The paper passing detection switch SW outputs a signal indicative of the reception of the above-mentioned light to the controller  5 . 
     When a rear edge of the paper P passes the paper passing detection switch SW, the lever of the paper passing detection switch SW returns to the position where the lever blocks light from the position where the lever allows passing of the light and hence, it is possible to detect passing of the rear edge of the paper P. The paper passing detection switch SW outputs a signal indicative of the blocking of the above-mentioned light to the controller  5 . 
     That is, the paper passing detection switch SW detects a signal indicative of the detection of light from the photointerrupter of the paper passing detection switch SW and, thereafter, outputs a signal indicative of the blocking of the light (for example, an output signal of the paper passing detection switch SW is switched to an OFF signal from an ON signal) and hence, the paper passing detection switch SW informs the controller  5  of the fact that the rear edge of the paper P in the first direction D 1  has passed the paper passing detection switch SW. 
     The image forming apparatus  100  may include an image reader  7  above the operation panel  6 . The image reader  7  is an image scanner, for example, and reads an image from a surface of a document or the like. With such a configuration, the image forming apparatus  100  is able to realize a copying function of forming the image read from the surface of the document on the paper P. 
     Next, the details of the configuration of the paper delivery device  4  are described with reference to  FIG. 2 ,  FIG. 3  and  FIG. 4 .  FIG. 2  is a front view of the paper delivery device as viewed from a delivery port.  FIG. 3  is a perspective view of the paper delivery device.  FIG. 4  is a cross-sectional view of the paper delivery device as viewed from a second direction. 
     The paper delivery device  4  includes shift frames  41   a ,  41   b . The shift frames  41   a ,  41   b  are plate-shaped members which are movable in the second direction D 2  which is perpendicular or substantially perpendicular to the first direction D 1  which is a direction along which the paper P is delivered. To be more specific, each of the shift frames  41   a ,  41   b  is supported by a shift frame support member SU fixed to the inside of the body  1  in a state where rod-shaped members BA which extend in the second direction D 2  from the shift frame support member SU penetrate the shift frames  41   a ,  41   b.    
     The paper delivery device  4  includes a driver  42 . The driver  42  moves the shift frames  41   a ,  41   b  in the second direction D 2 . 
     To be more specific, as illustrated in  FIG. 2 , the driver  42  includes: a first gear G 1  connected to an output rotary shaft of a first motor M 1  ( FIG. 6 ); a second gear G 2  which meshes with the first gear G 1  and is axially rotatably supported by the body  1 ; a third gear G 3  which meshes with the second gear G 2  and is axially rotatably supported by the body  1 ; and a fourth gear G 4  which meshes with the third gear G 3  and is axially rotatably supported by the body  1 . The fourth gear G 4  meshes with a drive gear GD extending in the second direction D 2  from either one of the shift frames (the shift frame  41   a ). 
     With such a configuration, the shift frames  41   a ,  41   b  are movable in the second direction D 2  or in the direction opposite to the second direction D 2  due to the rotation of the first motor M 1  ( FIG. 6 ) transmitted through the first to fourth gears. 
     The paper delivery device  4  has a home detector  43 . The home detector  43  detects whether or not the shift frames  41   a ,  41   b  are at home positions. The home detector  43  detects whether or not the shift frames  41   a ,  41   b  are at the home positions by a photointerrupter method. 
     To be more specific, as illustrated in  FIG. 5A  and  FIG. 5B , the home detector  43  includes a light source  431 . The light source  431  is a light emitting element such as an LED (Light Emitting Diode) which applies light (infrared light, for example) toward a detection element  433  described later. 
     The home detector  43  includes the detection element  433 . The detection element  433  is a photodiode which measures a light reception amount of light from the light source  431 . The detection element  433  outputs a detection signal (a voltage value or a current value) indicative of whether or not light is detected to the controller  5  corresponding to intensity of received light. 
     The home detector  43  includes a blocking member  435 . The blocking member  435  is a plate which is mounted on one end on a shift frame  41   b  side of a second shaft A 2  (described later) which penetrates a first driven roller  45  (described later). The blocking member  435  moves following the movement of the second shaft A 2 , and blocks light from the light source  431  or allows the light from the light source  431  to pass therethrough. 
     Since the home detector  43  has the above configuration, when the shift frames  41   a ,  41   b  are not at the home positions in the second direction D 2 , as illustrated in  FIG. 5A , the home detector  43  is able to detect light from the light source  431  by the detection element  433  and output a signal of a predetermined voltage value or current value to the controller  5 . The controller  5  which receives the detection signal is able to determine that the shift frames  41   a ,  41   b  are not at the home positions. 
     On the other hand, when the shift frames  41   a ,  41   b  are at the home positions in the second direction D 2 , as illustrated in  FIG. 5B , light from the light source  431  is blocked by the blocking member  435 . In this case, the detection element  433  does not output the above detection signal of a predetermined voltage value or current value to the controller  5 . The controller  5  which does not receive the detection signal is able to determine that the shift frames  41   a ,  41   b  are at the home positions. 
       FIG. 5A  is a view illustrating a state of the home detector when the shift frames are not at the home positions.  FIG. 5B  is a view illustrating the state of the home detector when the shift frames are at the home positions. 
     The paper delivery device  4  includes the shift frames  41   a ,  41   b , the driver  42  and the home detector  43  described above and hence, the paper delivery device  4  is able to deliver the paper P to be delivered to a predetermined position in the second direction D 2  in the paper exit tray T. 
     The paper delivery device  4  includes a drive roller  44 . The drive roller  44  includes first outer peripheral surfaces F 1  extending in the second direction D 2 , and is supported by the shift frames  41   a ,  41   b  such that the drive roller  44  is rotatable about a first shaft A 1 . As illustrated in  FIG. 3  and the like, the drive roller  44  includes a plurality of circular columnar rollers  44 - 1 ,  44 - 2 , . . .  44 - 8  made of rubber in which the first shaft A 1  penetrates the centers of surfaces of the circular columnar rollers  44 - 1 ,  44 - 2 , . . .  44 - 8  perpendicular or substantially perpendicular to the circular columnar shaft. 
     Both ends of the first shaft A 1  which penetrate the plurality of rollers  44 - 1 ,  44 - 2 , . . .  44 - 8  are rotatably and pivotally supported by holes or grooves formed in the shift frames  41   a ,  41   b  such that the length direction of the first shaft A 1  becomes parallel or substantially parallel to the second direction D 2 . Either one of ends of the first shaft A 1  pivotally supported by the shift frames  41   a ,  41   b  is connected to an output rotary shaft of a second motor M 2  ( FIG. 6 ) by way of a clutch  56  ( FIG. 6 ). With such a configuration, the drive roller  44  is rotated about the first shaft A 1  due to the rotation of the second motor M 2 . 
     The paper delivery device  4  includes the first driven roller  45 . The first driven roller  45  extends in the second direction D 2 , and includes a second outer peripheral surface F 2  which is brought into contact with the first outer peripheral surfaces F 1  at a first contact position TP 1  ( FIG. 4 ). The first driven roller  45  preferably is a resin-made circular cylindrical roller. The first driven roller  45  is supported by the shift frames  41   a ,  41   b  such that the first driven roller  45  is rotatable about the second shaft A 2  disposed parallel or substantially parallel to the second direction D 2  along with the rotation of the drive roller  44 . 
     To be more specific, the first driven roller  45  is supported by the second shaft A 2  such that the first driven roller  45  is rotatable about the second shaft A 2 . Both ends of the second shaft A 2  are supported by the shift frames  41   a ,  41   b  on a side where the second shaft A 2  is disposed closer to the second transportation path R 2  than the first shaft A 1  such that the length direction of the second shaft A 2  becomes parallel or substantially parallel to the second direction D 2 . With such a configuration, a surface (the second outer peripheral surface F 2 ) of the first driven roller  45  which is parallel or substantially parallel to the circular cylindrical shaft is brought into contact with the first outer peripheral surfaces F 1  at the first contact position TP 1  close to the second transportation path R 2  below the drive roller  44  ( FIG. 4 ). 
     As illustrated in  FIG. 4 , the first driven roller  45  may be movable relative to the drive roller  44 , and may be resiliently biased against the drive roller  44  by a biasing member  46 . With such a configuration, for example, when a leading edge of the paper P having a strong curl impinges on the first driven roller  45 , the first driven roller  45  is displaced downward so that the leading edge of the paper P is able to be easily introduced between the drive roller  44  and the first driven roller  45 . 
     The paper delivery device  4  includes a second driven roller  47 . The second driven roller  47  extends in the second direction D 2 , and includes a third outer peripheral surface F 3  which is brought into contact with the first outer peripheral surfaces F 1  at a second contact position TP 2  downstream of the first contact position TP 1  in the first direction D 1 . The second driven roller  47  preferably is a circular columnar roller made of foamed plastics having hardness (ASKER C) of 30 degrees. Hardness of the second driven roller  47  is set lower than hardness of the drive roller  44 . The second driven roller  47  is supported by the shift frames  41   a ,  41   b  such that the second driven roller  47  is rotatable about a third shaft A 3  disposed parallel or substantially parallel to the second direction D 2  along with the rotation of the drive roller  44 . 
     To be more specific, the third shaft A 3  penetrates the center of a surface of the second driven roller  47  perpendicular or substantially perpendicular to the circular columnar shaft such that the second driven roller  47  is rotatable about the third shaft A 3 . Both ends of the third shaft A 3  are supported by the shift frames  41   a ,  41   b  at a position closer to the delivery port E ( FIG. 1 ) than the second shaft A 2  such that the length direction of the third shaft A 3  becomes parallel or substantially parallel to the second direction D 2 . With such a configuration, a surface of the second driven roller  47  parallel or substantially parallel to the circular columnar shaft (the third outer peripheral surface F 3 ) is brought into contact with the first outer peripheral surface F 1  at the second contact position TP 2  with a predetermined contact force. 
     The second driven roller  47  preferably is made of sponge having the above hardness and hence, the second driven roller  47  is resiliently deformed corresponding to a thickness of the paper P and the paper P is able to be nipped with a fixed nipping force regardless of a kind of the paper P. 
     Further, unlike the first driven roller  45 , the second driven roller  47  may be supported by the shift frames  41   a ,  41   b  such that the second driven roller  47  is not movable relative to the drive roller  44 . That is, an inter-shaft distance between the first shaft A 1  of the drive roller  44  and the third shaft A 3  of the second driven roller  47  is fixed. With such a configuration, there is no possibility that a nipping force generated by the second driven roller  47  is weakened or strengthened depending on a thickness of the paper P. As a result, the second driven roller  47  is able to nip the paper P with a fixed or uniform nipping force regardless of a kind of the paper P. 
     The paper delivery device  4  includes the drive roller  44 , the first driven roller  45  and the second driven roller  47  described above. Accordingly, at the time of delivering the paper P to the paper exit tray T due to the rotation of three rollers, it is possible to bend the paper P nipped by three rollers in the direction opposite to the direction of curl generated on the paper P. As a result, curl generated on the paper P is able to be significantly reduced or eliminated. 
     Further, as described above, the drive roller  44 , the first driven roller  45  and the second driven roller  47  are supported by the shift frames  41   a ,  41   b  which are movable in the second direction D 2 . With such a configuration, it is possible to realize the compact paper delivery device  4  that performs both a shift sorting function and a decurling function. As a result, a volume of the body  1  is able to be decreased thus realizing the downsizing of the image forming apparatus  100 . 
     Next, the configuration of the controller  5  which controls respective elements of the image forming apparatus  100  is described with reference to  FIG. 6 .  FIG. 6  illustrates the configuration of the controller. The controller  5  includes a central processing unit (CPU)  51 . The central processing unit  51  preferably is a system on chip in which an information processing circuit, a signal processing circuit (an analog to digital converter, a digital to analog converter) or the like, a communication circuit and the like are preferably formed as one chip. 
     The central processing unit  51  performs information processing to operate respective elements of the controller  5  based on an instruction from a user received by the operation panel  6 , an instruction from a computer (not illustrated in the drawing) which is connected to the image forming apparatus  100  through a network interface  501  such as an Ethernet (registered trademark) card. The central processing unit  51  outputs a signal including information related to a state of the image forming apparatus  100  to the operation panel  6  or the above computer. 
     Further, the central processing unit (CPU)  51  receives inputting of image data from the image reader  7 , the network interface  501  and a modem  502 , and outputs the image data to an image processor  54  (described later). 
     The controller  5  includes a memory  53 . The memory  53  is a device which stores information, such as a RAM (Random Access Memory), a ROM (Read Only Memory) or an HDD (Hard Disk Drive). The memory  53  stores various settings of the image forming apparatus  100 , programs executed by the central processing unit  51  and the like. 
     The controller  5  includes the image processor  54 . The image processor  54  controls the image former  3  based on image data input to the image processor  54  from the image reader  7  or the like through the central processing unit  51 . The above functions of the image processor  54  are preferably realized on hardware by an FPGA (Field Programmable Gate Array). 
     The controller  5  includes motor drivers  55   a ,  55   b . The motor drivers  55   a ,  55   b  are motor control circuits which respectively output drive signals generated based on pulse signals output from the central processing unit  51  to the first motor M 1  and the second motor M 2  (stepping motors), and control the rotation of these motors. 
     The controller  5  includes the clutch  56 . The clutch  56 , based on an instruction from the central processing unit  51 , for example, transmits the rotation of the second motor M 2  to the first shaft A 1  or interrupts the transmission of the rotation by making the gear which is connected to a rotation transmission mechanism (not illustrated in the drawing) from the second motor M 2  and the gear which is connected to the first shaft A 1  mesh with each other or by separating these gears from each other. 
     The controller  5  includes a DIP switch  57 . The DIP switch  57  includes a plurality of switches. The DIP switch  57  sets a transportation time from a point of time when a rear edge of the paper P reaches the paper delivery device  4  to a point of time when only the rear edge of the paper P is nipped at the second contact position TP 2  due to the combination of ON and OFF of the plurality of switches. To be more specific, the transportation time is calculated by the central processing unit  51  as a product of a binary numerical value and a unit time expressed as combination of ON and OFF of the plurality of switches of the DIP switch  57 . The above unit time is stored in the memory  53 . 
     The DIP switch  57  is not limited to a hardware DIP switch and may be a so-called software DIP switch. In this case, a set value of the DIP switch  57  is held in a non-volatile memory (for example, the memory  53 ). For example, binary expressed values where ON of the DIP switch is set as “1” and OFF of the DIP switch is set as “0” can be stored in the memory  53 . Besides the above values, values which are obtained by converting binary expressed value based on ON/OFF of the DIP switch into decimal numbers or hexadecimal numbers can be stored in the memory  53 . 
     By changing the combination of ON and OFF of switches of the DIP switch  57 , that is, by changing magnitude of a numerical value set by the DIP switch  57  corresponding to a state of the image forming apparatus  100  or the like, a transportation time until only a rear edge of the paper P is nipped only at the second contact position TP 2  is able to be arbitrarily set. 
     The above transportation time can be preliminarily decided as a time slightly shorter than a time from a point of time when a rear edge of the paper P passes a mounting position of the paper passing detection switch SW to a point of time when the rear edge of the paper P reaches the second contact position TP 2 , for example. 
     Next, an operation of delivering the paper P on which an image is formed to the paper exit tray T in the image forming apparatus  100  is described with reference to  FIG. 7 .  FIG. 7  is a flow chart illustrating an image forming process of the image forming apparatus. 
     In the following description, an image forming process is described by taking a case where the image formation of a plurality of copies is performed as an example. Further, in performing the image formation of the plurality of copies, it is assumed that second and subsequent sets of copies are delivered to the paper exit tray T after the papers P are shifted and sorted. Further, it is assumed that the shift frames  41   a ,  41   b  are at the home positions at the time of starting the image forming process. 
     When an instruction to form an image on the paper P is issued through an operation of the operation panel  6 , communication from an external computer through the network interface  501  or the like, the central processing unit  51  rotates the pickup roller  21 . Accordingly, the papers P placed on the paper feed cassette  2  are transported to the image former  3  through the first transportation path R 1  (step S 1 ). 
     When the paper P is transported to the image former  3 , the formation of an image on the paper P is started (step S 2 ). To be more specific, first, the central processing unit  51  transmits image data received from the image reader  7  or the modem  502  or image data received from the external computer or the like through the network interface  501  to the image processor  54 . 
     Next, the image processor  54  which receives image data applies light on a surface of a charged photoconductive drum  32  ( FIG. 1 ) based on a gradation value of the received image data or the like while controlling a light quantity of a light source  31  ( FIG. 1 ) of the image former  3 . As a result, an electrostatic latent image which corresponds to the received image data is formed on a surface of the photoconductive drum  32 . 
     Then, a toner feeder  33  ( FIG. 1 ) feeds toner to the photoconductive drum  32  on which the electrostatic latent image is formed. Accordingly, toner is adhered to the surface of the photoconductive drum  32  corresponding to the electrostatic latent image. Then, during the passing of the transported paper P on the surface of the photoconductive drum  32 , toner adhered to the photoconductive drum  32  is transferred to one surface of the paper P. 
     After the toner is transferred to the paper P, the surface of the paper P to which the toner is transferred is heated by a heater roller  34  ( FIG. 1 ) and, at the same time, a pressure is applied to the surface by a press roller  35  ( FIG. 1 ). Accordingly, the toner is fused to the paper P. That is, an image corresponding to image data is formed on the paper P. 
     In fusing the toner to the paper P, moisture evaporates from a surface of the paper P on a heater roller  34  side. Due to the evaporation of moisture from the paper P, the heated surface of the paper P is shrunken first. As a result, there may be a case where the paper P is curled such that a surface of the paper P on which the image is formed by fusing the toner is disposed inside. With respect to curl of the paper P which is generated in the toner fusing step, curl which is generated such that the surface of the paper P on which the image is formed by fusing becomes the inside (concave surface) is referred to as image curl. 
     After an image is formed on the paper P, the central processing unit  51  determines whether or not the paper P on which the image is formed is transported through the second transportation path R 2  and reaches the paper delivery device  4  (step S 3 ). 
     To be more specific, the central processing unit  51  determines that a leading edge of the paper P has reached the paper delivery device  4  when the central processing unit  51  receives a detection signal indicative of the detection of light of the photointerrupter of the paper passing detection switch SW. 
     When the central processing unit  51  determines that the paper P has not reached the paper delivery device  4  (“No” in step S 3 ), the central processing unit  51  stands by until the central processing unit  51  receives the above detection signal from the paper passing detection switch SW. 
     On the other hand, when the central processing unit  51  determines that the paper P has reached the paper delivery device  4  (“Yes” in step S 3 ), the central processing unit  51  delivers the paper P on which the image is formed to a predetermined position of the paper exit tray T. 
     Before starting an operation of delivering the paper P to the paper exit tray T, the central processing unit  51  determines whether the paper P is to be delivered after the paper P is moved (shift sorting) in the second direction D 2  or the paper P is delivered without performing shift sorting (step S 4 ). 
     To be more specific, in the case where the image formation of the plurality of sets of copies is instructed and shift sorting is also instructed, when the formation of the image for second or subsequent set of copies is performed in the image forming process, the central processing unit  51  determines that shift sorting of the papers P is necessary. 
     When the formation of the image for the first set of copies is being performed at that moment and the central processing unit  51  determines that shift sorting of the paper P is unnecessary (“No” in step S 4 ), the central processing unit  51  delivers the paper P to the paper exit tray T without performing shift sorting of the paper P (step S 5 ). 
     To be more specific, the central processing unit  51  issues an instruction to the clutch  56  requesting that the rotation of the second motor M 2  be transmitted to the first shaft A 1  so that the drive roller  44  is rotated. When the rotation of the drive roller  44  is started, the rotation of the first driven roller  45  and the rotation of the second driven roller  47  are started along with the rotation of the drive roller  44 . 
     When the paper P is transported to the first contact position TP 1  of the paper delivery device  4 , the paper P is nipped between the first outer peripheral surfaces F 1  of the drive roller  44  and the second outer peripheral surface F 2  of the first driven roller  45 . 
     Then, due to the rotation of the drive roller  44  and the rotation of the first driven roller  45 , the paper P is transported to the second contact position TP 2  of the paper delivery device  4 . When the paper P reaches the second contact position TP 2 , as illustrated in  FIG. 8 , the paper P is nipped at the first contact position TP 1  and, at the same time, the paper P is nipped between the first outer peripheral surfaces F 1  of the drive roller  44  and the third outer peripheral surface F 3  of the second driven roller  47  at the second contact position TP 2 .  FIG. 8  illustrates a state where the paper is nipped by three rollers. 
     When the paper P is nipped at two positions, that is, at the first contact position TP 1  and the second contact position TP 2 , as illustrated in  FIG. 8 , the paper P is disposed such that a surface of the paper P on a side opposite to the surface of the paper P on which the image is formed (an upper-side surface of the paper P in  FIG. 8 ) is disposed along a curve of the first outer peripheral surfaces F 1  of the drive roller  44 . That is, the paper P nipped by three rollers is curved in the direction opposite to the direction of image curl. By bending the paper P in the direction opposite to the direction of image curl, three rollers are able to eliminate image curl generated on the paper P. 
     The paper P from which image curl is eliminated is transported in the first direction D 1  due to the rotation of the drive roller  44 , the first driven roller  45  and the second driven roller  47 , and is delivered to the paper exit tray T from the delivery port E. 
     On the other hand, when the formation of the image for second or subsequent set of copies is being performed at that moment and the central processing unit  51  determines that shift sorting of the papers P is necessary (“Yes” in step S 4 ), the central processing unit  51  delivers the paper P to the paper exit tray T after performing shift sorting of the paper P (step S 6 ). To be more specific, the paper P is delivered in accordance with the flow of processing illustrated in the flow chart in  FIG. 9 . 
     First, the central processing unit  51  issues an instruction to the clutch  56  requesting that the rotation of the second motor M 2  be transmitted to the first shaft A 1  so that the drive roller  44  is rotated (step S 61 ). With such a step, as described above, the paper P on which an image is formed is transported in the first direction D 1  by the drive roller  44 , the first driven roller  45  and the second driven roller  47 . During the transportation of the paper P in the first direction D 1 , the paper P is nipped by the above three rollers and hence, image curl generated on the paper P is eliminated. 
     During the transportation of the paper P in the first direction D 1 , the central processing unit  51  determines whether or not the rear edge of the paper P in the first direction D 1  has reached the second contact position TP 2  (step S 62 ). 
     To be more specific, the central processing unit  51  determines that the rear edge of the paper P in the first direction D 1  has reached the second contact position TP 2  when a time which has elapsed from a point of time when the rear edge portion of the paper P has passed the paper passing detection switch SW becomes a transportation time set by the DIP switch  57 . 
     When the central processing unit  51  determines that the rear edge of the paper P has not reached the second contact position TP 2  (“No” in step S 62 ), the processing to deliver the paper P after performing shift sorting of the paper P returns to step S 61 . That is, the central processing unit  51  continues the rotation of the drive roller  44 . 
     On the other hand, when the central processing unit  51  determines that the rear edge of the paper P has reached the second contact position TP 2  (“Yes” in step S 62 ), the central processing unit  51  issues an instruction to the clutch  56  requesting that an output rotary shaft of the second motor M 2  and the first shaft A 1  be interrupted from each other so that the rotation of the drive roller  44  is stopped (step S 63 ). 
     By stopping the rotation of the drive roller  44  when the rear edge of the paper P has reached at the second contact position TP 2 , as illustrated in  FIG. 10 , the rear edge of the paper P in the first direction D 1  is released from nipping between the first outer peripheral surfaces F 1  and the second outer peripheral surface F 2  and hence, the rear edge of the paper P in the first direction D 1  is nipped only between the first outer peripheral surfaces F 1  and the third outer peripheral surface F 3 .  FIG. 10  illustrates a state where the rear edge of the paper is nipped at the second contact position. As illustrated in  FIG. 10 , the rotation of the drive roller  44  is stopped in a state where the rear edge of the paper P is nipped only at the second contact position TP 2  and hence, it is possible to prevent the occurrence of nip marks on the rear edge of the paper P. 
     Thereafter, the paper P is moved to a different position in the second direction D 2  (step S 64 ). 
     To be more specific, the central processing unit  51  issues an instruction to the first motor M 1  requesting that the first gear G 1  be rotated in the rotating direction so that the shift frames  41   a ,  41   b  are moved in the direction away from the home positions in the second direction D 2 . Thereafter, the central processing unit  51  outputs a pulse signal having a predetermined number of pulses to a motor driver  55   a  which drives the first motor M 1 . 
     The above number of pulses of the pulse signal which is output to the motor driver  55   a  is decided based on the position in the second direction D 2  in the paper exit tray T to which the paper P is delivered, for example, the number of the set of copies which is under a copying operation at that moment. 
     By performing step S 64 , as illustrated in  FIG. 11 , the shift frames  41   a ,  41   b  are moved in the second direction D 2  from the home positions by an amount of movement corresponding to the above number of pulses of a pulse signal output from the central processing unit  51  due to the rotation of the first motor M 1 . That is, the paper P is moved to the position in the second direction D 2  corresponding to the number of pulses of the pulse signal output from the central processing unit  51 .  FIG. 11  illustrates one example of a state of the paper delivery device where the shift frame is shifted in the second direction from the home position. 
     During the movement of the paper P in the second direction D 2  by performing step S 64 , the rear edge of the paper P in the first direction D 1  is nipped only at the second contact position TP 2 . That is, during the movement of the paper P in the second direction D 2 , the paper P is not brought into a state where the paper P is curved by nipping by three rollers. Accordingly, it is possible to avoid the occurrence of nip marks on the paper P during the movement of the paper P in the second direction D 2 . 
     After the paper P is moved to the predetermined position in the second direction D 2 , the paper P is delivered to the paper exit tray T (step S 65 ). To be more specific, the central processing unit  51  issues an instruction to the clutch  56  requesting that the rotation of the second motor M 2  be transmitted to the first shaft A 1  by a time (stored in the memory  53 ) which is preset based on a transportation speed of the paper P and a transportation distance along which the paper P is delivered. Accordingly, the rear edge of the paper P in the first direction D 1  is released from nipping between the first outer peripheral surfaces F 1  and the third outer peripheral surface F 3 , and the paper P is delivered to the paper exit tray T from the delivery port E. 
     After the paper P is delivered to the paper exit tray T, the central processing unit  51  returns the shift frames  41   a ,  41   b  to the home positions (step S 66 ). 
     To be more specific, first, the central processing unit  51  issues an instruction to the first motor M 1  requesting that the first gear G 1  be rotated in the rotating direction so that the shift frames  41   a ,  41   b  are moved in the direction opposite to the direction away from the home positions in the second direction D 2 . 
     Thereafter, the central processing unit  51  outputs a pulse signal to drive the first motor M 1  to the motor driver  55   a  until the central processing unit  51  no longer receives a detection signal having a predetermined voltage value or current value from the detection element  433  of the home detector  43 . Accordingly, the shift frames  41   a ,  41   b  are moved to the home positions from the present positions due to the rotation of the first motor M 1 . 
     As described above, in step S 66 , the home detector  43  detects whether or not the shift frames  41   a ,  41   b  have reached the home position. Accordingly, the central processing unit  51  is able to detect with certainty that the shift frames  41   a ,  41   b  have returned to the home positions. As a result, the central processing unit  51  is able to stop the rotation of the first motor M 1  with proper timing at the time of returning the shift frames  41   a ,  41   b  to the home positions. 
     After a sheet of the paper P is delivered to the paper exit tray T by performing step S 5  or step S 6 , the central processing unit  51  determines whether or not image forming process is to be finished (step S 7 ). To be more specific, when the central processing unit  51  determines that steps S 1  to S 6  are repeatedly performed the number of times corresponding to a product of the instructed number of sets of copies and the number of pages per one copy, the central processing unit  51  determines that the image forming process is to be finished. 
     When the central processing unit  51  determines that the image forming process is not to be finished (“No” in step S 7 ), the image forming process returns to step S 1 . That is, steps S 1  to S 6  are repeatedly performed the number of times corresponding to a product of the instructed number of sets of copies and the number of pages per one copy. On the other hand, when the central processing unit  51  determines that the steps S 1  to S 6  are performed corresponding to the instructed number of sets of copies and the image forming process is to be finished (“Yes” in step S 7 ), the central processing unit  51  finishes the image forming process. 
     The above paper delivery device according to the first preferred embodiment preferably has the following configurations and functions. 
     The paper delivery device (for example, the paper delivery device  4 ) is provided in an image forming apparatus (for example, the image forming apparatus  100 ) to form an image on a paper (for example, the paper P), and delivers the paper on which an image is formed to an outside (for example, the paper exit tray T). The paper delivery device includes the shift frames (for example, the shift frames  41   a ,  41   b ), the driver (for example, the driver  42 ), the drive roller (for example, the drive roller  44 ), the first driven roller (for example, the first driven roller  45 ), and the second driven roller (for example, the second driven roller  47 ). 
     The shift frame is movable in the second direction (for example, the second direction D 2 ) perpendicular or substantially perpendicular to the first direction (for example, the first direction D 1 ) along which the paper is delivered to the outside. The driver moves the shift frame in the second direction. 
     The drive roller includes the first outer peripheral surface (for example, the first outer peripheral surfaces F 1 ) extending in the second direction, and is rotatable about the first shaft (for example, the first shaft A 1 ) disposed parallel or substantially parallel to the second direction. 
     The first driven roller includes the second outer peripheral surface (for example, the second outer peripheral surface F 2 ) which extends in the second direction and is brought into contact with the first outer peripheral surface at the first contact position (for example, the first contact position TP 1 ). The first driven roller is supported by the shift frames such that the first driven roller is rotatable about a second shaft (for example, the second shaft A 2 ) disposed parallel or substantially parallel to the second direction following the rotation of the drive roller. The first driven roller is rotated in a state where the paper is nipped between the first outer peripheral surfaces and the second outer peripheral surface thus transporting the paper in the first direction. 
     The second driven roller includes the third outer peripheral surface (for example, the third outer peripheral surface F 3 ) which extends in the second direction and is brought into contact with the first outer peripheral surfaces at the second contact position (for example, the second contact position TP 2 ) downstream of the first contact position in the first direction. The second driven roller is supported by the shift frame such that the second driven roller is rotated about the third shaft (for example, the third shaft A 3 ) disposed parallel or substantially parallel to the second direction following the rotation of the drive roller. The second driven roller is rotated in a state where the paper which is nipped between the first outer peripheral surfaces and the second outer peripheral surface is nipped between the first outer peripheral surface and the third outer peripheral surface thus transporting the paper in the first direction. 
     Other Preferred Embodiments 
     Although preferred embodiments of the present invention have been described heretofore, the present invention is not limited to the above preferred embodiments, and various modifications are conceivable without departing from the gist of the present invention. Particularly, a plurality of preferred embodiments and modifications described in this specification may be arbitrarily combined with each other when necessary. 
     In the above first preferred embodiment, the DIP switch  57  preferably sets a time from a point of time when passing of the rear edge of the paper P on the paper passing detection switch SW is detected to a point of time when only the rear edge of the paper P in the first direction D 1  is nipped only at the second contact position TP 2 . 
     However, it is sufficient for the DIP switch  57  to set an amount of rotation of the second motor M 2  corresponding to a transportation distance of the paper P necessary for allowing nipping of only the rear edge of the paper P in the first direction D 1  only at the second contact position TP 2  after the paper P reaches the paper delivery device  4  and hence, a set value set by the DIP switch  57  is not limited to the above-mentioned time. 
     For example, the DIP switch  57  may set the number of pulses of a pulse signal which the central processing unit  51  outputs to the motor driver  55   b  and which is necessary to nip only the rear edge of the paper P in the first direction D 1  at only the second contact position TP 2  after the paper P reaches at the paper delivery device  4 . 
     In this case, the central processing unit  51  may issue an instruction to the clutch  56  requesting that the rotation of the second motor M 2  be not transmitted to the first shaft A 1  at a timing that the number of pulses of a pulse signal output to the motor driver  55   b  becomes a value set by the DIP switch  57 . 
     In the above first preferred embodiment, all of the plurality of small rollers  44 - 1 ,  44 - 2 , . . .  44 - 8  of the drive roller  44  preferably have the same length in the second direction D 2 . However, the drive roller  44  is not limited to such a configuration. To enable stable nipping of an end portion of the paper P in the second direction D 2 , among the plurality of small rollers  44 - 1 ,  44 - 2 , . . .  44 - 8 , the length in the second direction D 2  of the small rollers  44 - 1 ,  44 - 8  which form end portions of the drive roller  44  in the second direction D 2  may be set larger than the length in the second direction D 2  of other small rollers  44 - 2 ,  44 - 3 , . . .  44 - 7 . 
     In the above first preferred embodiment, nothing is disposed in a gap between the first driven roller  45  and the second driven roller  47 . However, the present invention is not limited to such a configuration. For example, a belt having a predetermined width with respect to the second direction D 2  may be arranged such that the belt extends between and over the first driven roller  45  and the second driven roller  47 . 
     With such a configuration, the paper P nipped at the first contact position TP 1  is able to be moved to the second contact position TP 2  with certainty without being moved in the direction which differs from the direction along which the paper P is transported to the second contact position TP 2 . As a result, the paper P is able to be nipped with certainty at the second contact position TP 2 . 
     While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.