Abstract:
Plural auxiliary rotating members abut at different positions in a circumferential direction of a roller-shaped rotating member that is configured to rotate in a forward direction and a reverse direction. Diameters of a portion of the roller-shaped rotating member where a first auxiliary rotating member abuts and a portion of the roller-shaped rotating member where a second auxiliary rotating member abuts are different from each other. Conveying speeds of sheets conveyed by the first auxiliary rotating member and the second auxiliary rotating member with the roller-shaped rotating member in different directions at the same time are different from each other.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority to and incorporates by reference the entire contents of Japanese priority document 2007-228787 filed in Japan on Sep. 4, 2007. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a sheet conveying device that conveys sheet such as paper using a roller-shaped rotating member such as a roller and an image forming apparatus equipped with the sheet conveying device. 
         [0004]    2. Description of the Related Art 
         [0005]    With typical electro-photographic method image forming apparatus, a latent image is formed on a photosensitive member. The latent image is then developed using toner. The developed toner image is then transferred to a recording medium such as paper either directly or via an intermediate transfer member. The image is then fixed to the recording medium using heat (and pressure). The latent image, image, and recording medium are typically conveyed by rotating respective roller-shaped rotating members. A drive source such as a motor is provided to rotate the rollers. Coupling then takes place as far as the roller-shaped rotating members using a drive transmission mechanism such as a gear or a timing belt. 
         [0006]    The diameters etc. of each of the roller-shaped rotating members are set to appropriate values so that the recording medium is not subjected to sagging or tensioning to a greater extent than is necessary as a result of recording medium conveying force of the roller-shaped rotating members sandwiching and tensioning the recording medium while conveying the recording medium. An appropriate value is typically set for the recording medium conveying at the time when the recording medium is at the roller-shaped rotating member. 
         [0007]    During duplex printing of a recording medium, there are two recording medium conveying paths for when the recording medium fixed with the image is discharged to outside. Equipment is then widely adopted having a mechanism where the recording medium is reversed within the machine to print to the other surface of the recording medium while discharging the recording medium to outside. Such equipment has been disclosed in Japanese Patent Application Laid-open No. H8-59046 and Japanese Patent Application Laid-open No. H6-250463. It is typical for the discharge roller to be rotated forwards and in reverse so that parts can be common for the conveying of the recording medium. Such a discharge roller is shown in Japanese Patent Application Laid-open No. 2006-017988. 
         [0008]    However, a separate conveying unit is usually required to convey the recording medium to the respective paths on the downstream side in the conveying direction of the recording medium in the vicinity of a divergence point of the recording medium conveying paths. This increases the number of parts. Such a situation is shown in Japanese Patent Application Laid-open No. H8-59046 and Japanese Patent Application Laid-open No. H6-250463. 
         [0009]    On the other hand, when the discharge roller is made to go in forwards and reverse so that conveying for reversing the recording medium can adopt the same number of parts to reduce the number of parts, the recording medium is reversed after one side of the recording medium is printed. It is therefore not possible to print the next recording medium until the reverse surface is printed and discharged. This reduces the number of pages that can be printed per unit time. Such a situation is disclosed in Japanese Patent Application Laid-open No. 2006-017988. 
         [0010]    A structure is also well-known where discharging and reversing of the recording medium can take place at the same time by installing two rotated auxiliary rollers that abut with the discharge roller and reversing the orientation of the recording medium conveying direction at each respective point of contact in order that reverse printing can also take place during reversing of the recording medium. Here, a recording medium conveying speed the recording medium is discharged by the discharge roller at is to be set so that the recording medium is not subjected to sagging or tensioning to a greater extent than is necessary between a discharge unit and a fixing unit upstream from the discharge unit. However, in this structure the reverse conveying speed of the recording medium is equal to an arbitrary discharge speed. The time required to reverse the conveying of the recording medium therefore cannot be made shorter other than by shortening the reverse conveying path length. 
         [0011]    Technology also exists that reduces size and price by performing paper discharge and reversal at one location using three rollers. There is also technology for increasing productivity during duplex printing by discharging and reversing two pieces of paper at the same time using three rollers (one piece of paper is reversed while the other piece of paper is discharged). 
         [0012]    However, with this image forming apparatus, printing productivity is improved by making the speed for the reverse path as fast as possible regardless of the transferring. However, when there are three rollers as in the art, one roller is used for both discharging and reversing. The speeds of discharging and reversing are therefore always the same. This means that productivity cannot be improved during reversing and discharging of two pieces of paper at the same time. 
       SUMMARY OF THE INVENTION 
       [0013]    It is an object of the present invention to at least partially solve the problems in the conventional technology. 
         [0014]    According to an aspect of the present invention, there is provided a sheet conveying device that is configured to convey a sheet in different directions at a time. The sheet conveying device includes a roller-shaped rotating member that is rotated by a driving force from a drive unit; and a plurality of auxiliary rotating members including a first auxiliary rotating member and a second auxiliary rotating member, abutting at different positions in a circumferential direction of the roller-shaped rotating member. The roller-shaped rotating member is configured to rotate in a forward direction and a reverse direction. A diameter of a first portion of the roller-shaped rotating member where the first auxiliary rotating member abuts and a diameter of a second portion of the roller-shaped rotating member where the second auxiliary rotating member abuts are different from each other. A conveying speed of a sheet conveyed in a first nip formed by the first auxiliary rotating member and the roller-shaped rotating member and a conveying speed of a sheet conveyed in a second nip formed by the second auxiliary rotating member and the roller-shaped rotating member in different directions at a time are different from each other. 
         [0015]    Furthermore, according to another aspect of the present invention, there is provided an image forming apparatus including a sheet conveying device that includes a roller-shaped rotating member that is rotated by a driving force from a drive unit; and a plurality of auxiliary rotating members including a first auxiliary rotating member and a second auxiliary rotating member, abutting at different positions in a circumferential direction of the roller-shaped rotating member. The roller-shaped rotating member is configured to rotate in a forward direction and a reverse direction. A diameter of a first portion of the roller-shaped rotating member where the first auxiliary rotating member abuts and a diameter of a second portion of the roller-shaped rotating member where the second auxiliary rotating member abuts are different from each other. A conveying speed of a sheet conveyed in a first nip formed by the first auxiliary rotating member and the roller-shaped rotating member and a conveying speed of a sheet conveyed in a second nip formed by the second auxiliary rotating member and the roller-shaped rotating member in different directions at a time are different from each other. 
         [0016]    The above and other objects, features, advantages and technical and industrial significance of this invention will be better understood by reading the following detailed description of presently preferred embodiments of the invention, when considered in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a cross-sectional view of an outline of a color printer that is an example of an image-forming apparatus equipped with a sheet conveying device of the present invention; 
           [0018]      FIG. 2  is an enlarged diagram of the vicinity of a discharging/reversing unit of the printer; 
           [0019]      FIG. 3  is a perspective view of essential parts of a paper conveying device according to a first embodiment of the present invention; 
           [0020]      FIG. 4  is a schematic drawing illustrating the operation of a discharging/reversing unit; 
           [0021]      FIG. 5  is a schematic drawing explaining drive control of a paper conveying device according to the first embodiment of the present invention; 
           [0022]      FIG. 6  is a perspective view of a second embodiment of a paper conveying device according to the present invention; 
           [0023]      FIG. 7  is a side view of a third embodiment of a paper conveying device according to the present invention; and 
           [0024]      FIG. 8  is an enlarged diagram showing an example of a drive system for a paper conveying device and shows the vicinity of a discharging/reversing unit. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0025]    Exemplary embodiments of the present invention are explained in detail below with reference to the accompanying drawings. 
         [0026]      FIG. 1  is a cross-sectional view showing an outline of a color printer that is an example of an image forming apparatus equipped with a sheet conveying device of the present invention. A color printer  50  shown in the drawing is a color printer adopting a tandem method that is capable of forming full-color images. Four image-forming units  10  (Y, C, M, Bk) are disposed at a substantially central part of the device body. Each image-forming unit  10  (Y, C, M, Bk) is lined up along an upper conveying edge of an intermediate transfer belt  11 . The intermediate transfer belt  11  wrapped around the support rollers  13 ,  14  is driven to be conveyed in an anti-clockwise direction in the drawings. A cleaning unit  16  that cleans the intermediate transfer belt  11  is disposed at the transfer opposing roller  14  that is a support roller for the right side. 
         [0027]    Toner colors handled by each image-forming unit  10  are different but the structure is the same. Photosensitive drums  1  are provided as image carriers. A charging unit  2 , developing apparatus  3 , and a cleaning unit  4  are disposed about the photosensitive drums  1 . Transfer rollers  12  are provided as primary transfer units on the inside of the intermediate transfer belt  11  so as to face each photosensitive drum  1 . To keep the drawings simple, numerals for each item of equipment constituting the image-forming unit are only given to unit  10 Bk that is the image-forming unit for the color black, and are omitted for image-forming units of other colors. 
         [0028]    An optical writing unit  20  is provided above the four image-forming units  10 . The optical writing unit  20  has a polygon mirror and a mirror group etc. and modulated laser light is irradiated onto the photosensitive drums  1  of the image-forming units for each color. 
         [0029]    A paper feed tray  17  loaded with paper is disposed at the lower part of the device body. A paper feed roller  18  that sends out paper loaded at the paper feed tray  17  is provided at the right side of the paper feed tray  17 . A separation pad  19  that separates the paper one sheet at a time is pressure-fused at the paper feed roller  18 . Paper stop rollers  21  are provided above the paper feed roller  18  and the separation pad  19  (on the downstream side in a paper conveying direction). A transfer roller  22  taken as a secondary transfer unit is provided above the paper stop rollers  21  facing the transfer opposing roller  14  so as to form a secondary transfer unit. 
         [0030]    A fixing unit  23  is provided above the secondary transfer unit. The fixing unit  23  includes a fixing roller and a pressure roller. Paper that the unfixed toner images have been transferred to is then fixed at the secondary transfer unit by heating and applying pressure to the transferred paper. A paper discharging/reversing roller  24  is provided above the fixing unit  23 . Paper after fixing is then discharged onto a copy receiving tray  25  formed at the upper surface of the device. 
         [0031]    A duplex conveying unit  26  is provided at the right side of the device in the drawing. When duplex printing is carried out, paper with images formed on a surface is passed through the fixing unit  23 . The paper is then switched back by the paper discharging/reversing roller  24  and sent to the duplex conveying unit  26 . The front and reverse surfaces are then reversed and the paper is again fed to the paper stop rollers  21 . A pair of conveyor rollers  27  is disposed at the duplex conveying unit  26 . 
         [0032]    A brief description is now given of an image-forming operation occurring at the color printer  50  constructed in the above manner. The photosensitive drums  1  of the image-forming units  10  are rotated in a clockwise direction in the drawings by a drive unit (not shown). Laser light from the optical writing unit  20  is irradiated onto charged photosensitive surfaces. This causes latent images to be formed on the surfaces of the photosensitive drums  1 . At this time, image information exposed at each of the photosensitive drums  1  is unitary color image information where a desired full color image is broken down into color information of yellow, magenta, cyan, and black. Toner for each color is provided from the developing apparatus  3  to the electrostatic latent images formed in this manner so as to make the latent images visible as toner images. 
         [0033]    The intermediate transfer belt  11  is driven in an anti-clockwise direction in the drawings. Toner images for each color are then transferred so as to be sequentially overlaid from the photosensitive drums  1  at the intermediate transfer belt  11  as a result of the action of the transfer rollers  12  at each image-forming unit  10 . A full-color toner image is therefore supported at the surface of the intermediate transfer belt  11 . 
         [0034]    It is therefore possible to use just one of the image-forming units  10  to form a single color image, or to form images using two or three colors. Images are formed using just the unit Bk furthest to the right side of the drawing of the four image-forming units during monochrome printing. 
         [0035]    Residual toner affixed to the surface of the photosensitive drum after transfer of a toner image is then removed from the surface of the photosensitive drum by the cleaning unit  4 . The surface is then subject to the action of a charge remover, surface potential is initialized, and the next image is formed. 
         [0036]    On the other hand, paper is fed from the paper feed tray  17 . The paper is then sent to a secondary transfer position by the pair of paper stop rollers  21  while ensuring that the timing coincides with the toner images supported on the intermediate transfer belt  11 . In this example, a transfer voltage of a reverse polarity to the toner electrification polarity of the toner images at the surface of the intermediate transfer belt is applied to the secondary transfer roller  22 . As a result, toner images at the surface of the intermediate transfer belt are collectively transferred onto the paper. When the paper toner images are transferred to pass through the fixing unit  23 , the toner images are fused to the paper using heat and pressure. The fixed paper is then discharged to the copy receiving tray  25  formed on the upper surface of the device body by the paper discharging/reversing roller  24 . 
         [0037]    During duplex printing, the paper with a toner image fixed on one side is switched back by the paper discharging/reversing roller  24  and sent to the duplex conveying unit  26 . The front and reverse sides of the paper are then reversed and the paper is fed again to the pair of paper stop rollers  21 . A toner image is then transferred from the intermediate transfer belt  11  to the reverse surface of the re-fed paper. The reverse surface image is then fixed at the fixing unit  23 . Duplex printing is then completed by discharging the paper supporting the image at the front and reverse surfaces to the copy receiving tray  25 . 
         [0038]    At the color printer  50  of this example, when duplex printing is carried out consecutively for a plurality of pieces of paper, the preceding paper (paper for which printing of one side is complete) is sent to the duplex conveying unit  26 . While the preceding paper is being reversed, subsequent paper or reversed paper is printed. It is therefore possible to prevent lowering of productivity during consecutive duplex printing. 
         [0039]      FIG. 2  is an enlarged view of the vicinity of the discharging/reversing unit.  FIG. 3  is a perspective view showing essential parts of the first embodiment of the paper conveying device of the present invention. As shown in  FIG. 2 , a paper conveying device  100  taken as the paper discharging/reversing roller  24  includes a two-stage roller  101  (roller-shaped rotating member) capable of being rotated in both forward and reverse directions by a drive source (not shown), a paper discharge auxiliary roller  102  (one auxiliary rotating member) abutting with the two-stage roller  101  and rotated by the two-stage roller  101 , and a paper reversing auxiliary roller  103  (other one auxiliary rotating member) abutting with the two-stage roller  101  at a different position to the paper discharge auxiliary roller  102  and rotated by the two-stage roller  101 . 
         [0040]    Two paper conveying paths, a first conveying path  34  linking with the fixing unit  23  and a second conveying path  35  linking with the duplex conveying unit  26 , are formed taking the vicinity of the two-stage roller  101  as a divergence point. A switching unit  36  that switches between the paper conveying paths is then installed at this divergence point. The switching unit  36  is provided at a position so as to be moveable between a depiction of the switching unit  36  using a solid line and that using a virtual line. The forward and reverse rotation of the two-stage roller  101  and a reciprocating operation of the switching unit  36  are typically enacted by forward and reverse rotation of a drive source such as a motor or by the action of a reciprocating action generating unit such as a solenoid. 
         [0041]    As shown in  FIG. 3 , the two-stage roller  101  of the paper conveying device  100  is split-level with differing diameters of D 1  and D 2  (D 1 &lt;D 2 ) . The paper discharge auxiliary roller  102  abuts with the upper periphery of a small diameter section  101   a  having a diameter D 1  and the paper reversing auxiliary roller  103  abuts with the periphery of a large diameter section  101   b  having a diameter D 2 . In this example, four two-stage rollers  101  are fixed at a shaft  101   c  so as to constitute a drive roller. 
         [0042]    The operation of the discharging/reversing unit is explained with reference to  FIG. 4 . During single-side printing, after passing through the fixing unit  23 , the paper is discharged by the paper discharging/reversing roller  24  as is to the copy receiving tray  25  ( FIG. 1 ). The switching unit  36  then switches over to the position denoted by the virtual line. The two-stage roller  101  is then rotated in the direction of an arrow Q. The paper therefore passes through the first conveying path  34  and is discharged to outside using a paper conveying path h 1 . 
         [0043]    During duplex printing, first, it is necessary to reverse the paper after fixing while printing on one side of the paper. This is the same as explained for the image forming operation of the color printer  50 . The switching unit  36  is then switched over to the position denoted by the solid line. The paper is therefore conveyed to the two-stage roller  101  using a paper conveying path h 2 . At this time, the two-stage roller  101  is rotated in the direction of an arrow P. The paper is then conveyed to a point of contact X of (the large diameter section  101   b  of) the two-stage roller  101  and the paper reversing auxiliary roller  103 . The paper is then conveyed from the point of contact X in a discharge direction. When the vicinity of the trailing end of the paper reaches the point of contact X, the two-stage roller  101  is reversed in the direction Q. At the same time, the switching unit  36  is switched over to the position denoted by the virtual line. The paper then passes through the second conveying path  35  using a paper conveying path h 3 , is carried to the duplex conveying unit  26 , and returns to an operation that prints the other side of the paper. There are also cases where the operation of conveying the returned paper back to a position where execution of a printing operation is possible again is repeated a number of times. 
         [0044]    The returned paper is then conveyed back again to the position where printing is possible. Next, paper fed by the paper feed tray  17  (in this case, two pieces of paper) continues, and the returned paper (taken to be one sheet of paper here) is conveyed to the secondary transfer unit. The second sheet of paper is then conveyed to (the point of contact X with) the paper discharging/reversing roller  24  using the paper conveying path h 2  after fixing. The previous piece of paper (second piece of paper) is in the process of being carried to the duplex conveying unit  26  at the time where the returned piece of paper (first piece of paper) is being conveyed to the paper discharging/reversing roller  24  by the fixing unit  23 . The two-stage roller  101  is then rotated in the direction Q and the switching unit  36  is switched over to the position denoted by the virtual line. The paper (first sheet of paper) is then conveyed to a point of contact Y of (the small diameter section  101   a  of) the two-stage roller  101  and the paper discharge auxiliary roller  102  using the paper conveying path h 1 . The paper is then discharged to outside from the point of contact Y. 
         [0045]    Next, drive control of the paper conveying device  100  (paper discharging/reversing roller  24 ) is explained with reference to  FIG. 5 . In the single-side printing operation, the paper is discharged from the fixing unit  23  using the paper conveying path h 1 . During this time, the two-stage roller  101  rotates in the direction of the arrow Q. However, the two-stage roller  101  is driven at a rotational speed N 1  at this time. The paper is therefore sandwiched between the section of the two-stage roller  101  of the diameter D 1  (small diameter section  101   a ) and the paper discharge auxiliary roller  102 . The paper is then conveyed at a speed of V 1 =π·N 1 ·D 1 . The conveying speed V 1  is set so that paper discharged by the fixing unit  23  does not experience sagging or tensioning more that is necessary with respect to the conveying speed. 
         [0046]    On the other hand, in the duplex printing operation (consecutive duplex printing), paper that is printed on one side continues, printing for one side concludes, and the paper is conveyed so as to be adjusted using a reversing operation in preparation for printing on the other side. The two-stage roller  101  is rotated in a direction P while paper printed on one side is conveyed from the fixing unit  23  using the paper conveying path h 2 . However, the two-stage roller  101  is driven at a rotational speed N 2  at this time. The paper is therefore sandwiched between the section of the two-stage roller  101  of the diameter D 2  (the large diameter section  101   b ) and the paper reversing auxiliary roller  103 . The paper is then conveyed at a speed of V 2 =π·N 2 ·D 2 . 
         [0047]    When the trailing end of the paper printed on one side then reaches the two-stage roller  101 , the two-stage roller  101  is reversed in the direction Q, while at the same time the switching unit  36  is shifted to the position of the virtual line. At this time, the two-stage roller  101  is driven at a rotational speed N 1 . As a result of this operation, the paper is carried to the duplex conveying unit  26  using the paper conveying path h 3  at a conveying speed of V 3 =π·N 1 ·D 2 . An operation of printing the other side of the paper is then returned. At the same time, paper that continued to be conveyed by the fixing unit  23  for which the printing operation for the other side is complete (duplex-printed paper) passes through the paper conveying path h 1 . The duplex-printed paper is then sandwiched between the section of the two-stage roller  101  of diameter D 1  (small diameter section  101   a ) and the paper discharge auxiliary roller  102  and is discharged to outside at the speed V 1 =π·N 1 ·D 1 . 
         [0048]    As a result of the above operation it is possible to discharge and reverse the paper at the same time. However, if the rotational speed of the two-stage roller  101  is set to N 2 =(D 1 /D 2 )·N 1 , then V 1 =V 2 =π·N 1 ·D 1 . It is therefore possible to make the conveying speed V 1  of paper discharged from the fixing unit  23  and the conveying speed in the paper discharge direction intended for maintaining an appropriate relationship V 2  equal (V 1 =V 2 ) . It is also possible to make just the conveying speed V 3  for reversing the paper fast by making D 2 &gt;D 1 . In this example, the conveying speed V 1  (and V 2 ) is set to a speed ensuring that paper is not subjected to sagging or tensioning to a greater extent than is necessary with respect to the conveying speed of paper discharged by the fixing unit  23 . 
         [0049]    With the paper conveying device  100  of this example, portions of the drive roller are formed with different diameters (D 1 , D 2 ) to increase productivity by making the conveying speed (V 3 ) after reversing faster than the discharging speed (V 1 ) while conveying after discharging and reversing two pieces of paper at the same time with a structure having three rollers (two driven rollers abutting with one drive roller) . Further, D 1  is made less than D 2 , with discharging taking place using D 1  (small diameter section) and reversing taking place at D 2  (large diameter section). 
         [0050]    The speed (V 1 ) of discharging the paper to outside and the speed (V 2 ) of conveying the paper in the discharge direction before reversing have to be the same because of the relationship with the fixing unit. However, D 2  (the large diameter section) is used in conveying before reversing. The rotational speed is therefore controlled and V 1 =V 2  is implemented. In this case, the relationship between the rotational speed and radius is taken to be N 2 =(D 1 /D 2 )·N 1 . 
         [0051]      FIG. 6  is a perspective view showing a second embodiment of a paper conveying device that can be utilized as the paper discharging/reversing roller  24  of the color printer  50 . The basic structure of a paper conveying device  200  of the second embodiment shown in the drawings is the same as the paper conveying device  100  of the first embodiment. In the first embodiment, the drive roller of the three rollers constituting the paper conveying device is a two-stage roller ( 101 ) having a small diameter section and a large diameter section. However, in the second embodiment, the drive roller is a pair roller constituted by a small diameter roller and a large diameter roller. 
         [0052]    As shown in  FIG. 6 , a pair roller  201  has a small diameter roller  201   a  and a large diameter roller  201   b  fixed to a shaft  201   c.  In this example, four (four sets of) pair rollers  201  are fitted to the shaft  201   c  as the drive roller. The drive roller (pair roller  201 ) can be rotated both forwards and in reverse by a drive source (not shown). A paper discharge auxiliary roller  202  abuts with the small diameter roller  201   a  of the pair roller  201 . The paper reversing auxiliary roller  103  abuts with the large diameter roller  201   b.  The paper discharge auxiliary roller  202  and the paper reversing auxiliary roller  103  are then rotated by the pair roller  201 . A diameter of the small diameter roller  201   a  of the pair roller  201  is D 1  and is the same as the diameter of the small diameter section  101   a  of the two-stage roller  101  in the first embodiment. A diameter of the large diameter roller  201   b  of the pair roller  201  is D 2  and is the same as the diameter of the large diameter section  101   b  of the two-stage roller  101  of the first embodiment. The paper discharge auxiliary roller  202  is the same as the paper discharge auxiliary roller  102  of the first embodiment. The paper reversing auxiliary roller  103  is the same as the paper reversing auxiliary roller  103  of the first embodiment. 
         [0053]    The operation when the paper conveying device  200  of the second embodiment used as the paper discharging/reversing roller  24  of the color printer  50  is the same as the case for the paper conveying device  100  in the first embodiment and is not explained. 
         [0054]    The configuration of parts is simplified and the costs are reduced in the paper conveying device  200  of the second embodiment by using the pair roller  201  having the small diameter roller  201   a  and the large diameter roller  201   b  of a simple shape as the drive roller of the three rollers constituting the paper conveying device rather than using a two-stage roller. 
         [0055]      FIG. 7  is a side view of a third embodiment of a paper conveying device that can be utilized as the paper discharging/reversing roller  24  of the color printer  50 . A paper conveying device  300  of the third embodiment adopts a two-stage roller  301  where a tapered section  301   d  is provided between a small diameter section  301   a  and a large diameter section  301   b  as a drive roller of the three rollers constituting the paper conveying device. Other aspects of the configuration are substantially the same as for the paper conveying device  100  of the first embodiment. The paper discharge auxiliary roller  102  abuts with the small diameter section  301   a  of the two-stage roller  301 . The paper reversing auxiliary roller  103  abuts with the large diameter section  301   b.  The paper discharge auxiliary roller  102  and the paper reversing auxiliary roller  103  are then rotated by the two-stage roller that is the drive roller. The diameter of the small diameter section  301   a  of the two-stage roller  301  is D 1  and is the same diameter as the small diameter section  101   a  of the two-stage roller  101  of the first embodiment. The diameter of the large diameter section  301   b  of the two-stage roller  301  is D 2  and is the same diameter as the large diameter section  101   b  of the two-stage roller  101  of the first embodiment. The two-stage roller  301  can be rotated both forwards and in reverse by a drive source (not shown). 
         [0056]    The operation when the paper conveying device  300  of the third embodiment is used as the paper discharging/reversing roller  24  of the color printer  50  is the same as the case for the paper conveying device  100  in the first embodiment and is not explained. 
         [0057]    It is possible to suppress deformation such as bending of the paper at the paper conveying device  300  of the third embodiment by providing the tapered section  301   d  between the small diameter section  301   a  and the large diameter section  301   b  of the two-stage roller  301 . A taper angle (angle with respect to a roller axis) θ of the tapered section  301   d  is preferably set to thirty degrees or less. 
         [0058]    For example, at the paper conveying device  100  of the first embodiment, the paper also comes into contact with the large diameter section  101   b  of the two-stage roller  101  while conveyed sandwiched by (the small diameter section  101   a  of) the two-stage roller  101  and the paper discharge auxiliary roller  102 . At the paper conveying device  200  of the second embodiment, the paper also comes into contact with the large diameter roller  201   b  of the pair roller  201  while conveyed sandwiched by (the small diameter roller  201   a  of) the pair roller  201  and the paper discharge auxiliary roller  202 . It is therefore possible that deformation of the paper such as bending can occur as a result of the stepped portion of the two-stage roller  101  or the differences in diameter of the pair roller  201 . However, it is possible to suppress deformation such as bending of the paper at the paper conveying device  300  of the third embodiment by providing the tapered section  301   d  between the small diameter section  301   a  and the large diameter section  301   b  of the two-stage roller  301 . 
         [0059]    An explanation is given in the three embodiments of a paper conveying device of the present invention. In each embodiment, the relationship of the discharging speed V 1 , the speed V 2  of conveying before reversing, and the speed V 3  of conveying after reversing of the drive rollers  101  ( 202 , and  301 ) is V 1 =V 2 &lt;V 3 . An explanation is also given where the rotational speed of the drive roller  101  ( 201 , and  301 ) during discharging and during conveying after reversing are controlled to be N 1  and N 2  respectively to implement V 1 =V 2 . It is possible to achieve this difference in rotational speed by controlling the rotational speed of a drive source (for example, a motor) that drives the drive roller  101  ( 201 ,  301 ). However, it is also possible to achieve V 1 =V 2  by fixing the rotational speed of the drive source (or a rotating member driven by the drive source) and switching over between two drive transmission paths having different reduction ratios. In the following, an explanation is given of an example configuration where two drive transmission paths having different reduction ratios are switched between. 
         [0060]      FIG. 8  is an enlarged diagram of the vicinity of a discharging/reversing unit and shows an example drive system for when a paper conveying device of any one of the first to third embodiments is used as the paper discharging/reversing roller  24  of the color printer  50 . An explanation is given using the paper conveying device  100  of the first embodiment as the paper discharging/reversing roller  24 . The three rollers constituting the paper conveying device are the drive roller of the two-stage roller  101 , and two driven rollers of the paper discharge auxiliary roller  102  and the paper reversing auxiliary roller  103 . 
         [0061]    In the drive system of the example shown in the drawings, drive force is transmitted to the two-stage roller  101  by a drive source or by a rotating member  400  driven by a drive source (not shown) using drive transmission means such as gears depicted as dotted-and-dashed circles in the drawing. Dashed lines are shown in the drawing as virtual lines only depicting when a rotary gear  402  moves. A link member  409  is fitted to a shaft of a gear  401  above the rotating member  400 . The rotary gear  402  is then axially supported at the other end (free end) of the link member  409 . The two gears  401  and  402  then constitute a pendulum gear. An arm of a switching unit  410  such as a solenoid is then fitted to the center of the link member  409 . The rotary gear  402  of the pendulum gear then moves between a position (first position) depicted by an alternate dotted and dashed lines and a position (second position) depicted by a virtual line (dashed line) as a result of operation/non-operation of the switching unit  410 . 
         [0062]    When the rotary gear  402  is switched over to the first position shown by the alternate long and short dash line in the drawing, a transmission gear  403  is arranged so as to mesh with the rotary gear  402 . Drive force is then transmitted from the transmission gear  403  via a two stage gear  404  and a transmission gear  405  to a drive dear (gear installed at the shaft of the two-stage roller  101 )  406  (this transmission path is referred to as a first path). When the rotary gear  402  is switched over to the second position shown by the virtual line (dashed line) in the drawing, a two stage gear  407  is arranged so as to mesh with the rotary gear  402 . Drive force is then transmitted from the two stage gear  407  via a transmission gear  408  to the drive dear  406  (this transmission path is referred to as a “second path”). In this example, a transmission path for a second system that is a drive force transmission system from the rotating member  400  to the two-stage roller  101  is provided. When the rotating member  400  is rotated at a fixed rotational speed N in a clockwise direction in the drawing so as to be driven using the first path, the two-stage roller  101  rotates in the, direction of an arrow Q. The two-stage roller  101  is rotated in the direction of an arrow P when driven using the second path. 
         [0063]    The two transmission gears  405  and  408  meshing with the drive gear  406  have different reduction ratios η 1  and η 2 . The two-stage roller  101  is therefore driven at different speeds and in different directions when driven by the first path and the second path. In this example, the conveying speed the paper is discharged at after the completion of duplex printing is V 1 =π·N/η 1 ·D 1 . The conveying speed before the paper is reversed V 2 =π·N/η 2 ·D 2 . The conveying speed after reversing the paper V 3 =π·N/η 1 ·D 2 . By then setting η 2 =(D 2 /D 1 )·η 1 , then V 1 =V 2 =π·N/η 1 ·D 1 . It is then possible to make the speeds V 1  and V 2  that are conveying speeds in the discharge direction of the paper equal to maintain an appropriate relationship for the paper conveying speed. It is also possible to make just the conveying speed V 3  the paper is reversed at fast by making D 2 &gt;D 1 . 
         [0064]    It is also possible to provide the switching unit  36  switching the paper conveying path in unison with the switching of the pendulum gear (movement of the rotary gear  402 ) using the switching unit  410  so as to move between a position denoted by a solid line and a position denoted by a virtual line. 
         [0065]    The present invention is explained using examples in the drawings but the present invention is not limited. For example, in each of the embodiments, a drive roller with four of the two-stage rollers  100  and  300 , or the pair rollers  200  on one shaft (drive shaft) is adopted but the number of rollers is not limited to four and can be an arbitrary number. The orientation etc. of each roller can also be set as appropriate. The diameter of each roller (the diameter of the large diameter section and the small diameter section, or the diameter of the large diameter roller and the small diameter roller) and the rotational speed of the drive roller can also be set as appropriate to give a desired conveying speed. The structure for driving the drive roller can also be designed as appropriate. 
         [0066]    Appropriate structures can also be adopted for switching structures and switching units etc. when switching of the rotational speed of the drive rollers is implemented by switching drive systems. The reduction ratio of each drive system can also be appropriately set so as to obtain the desired conveying speed. 
         [0067]    The structure of the image-forming section of the image forming apparatus is also arbitrary as is the order of arrangement of image-forming units for each color in a tandem method. This is also not limited to a tandem method, and arranging a plurality of developing apparatus so as to surround one photosensitive member or using revolver-type developing apparatus is also possible. The sheet conveying device of the present invention can also be applied to a full-color machine using toner for three colors, a multiple-color machine using toner for two colors, or a monochromatic apparatus. The image-forming apparatus is not limited to a printer, and can also be a copier, a facsimile, or a multifunction product having a plurality of functions. 
         [0068]    The sheet conveying device is also not limited to paper conveying device of an image forming apparatus and can also be broadly applied to machines where sheet-shaped material is conveyed in a plurality of directions at the same time. 
         [0069]    According to an aspect of the present invention, it is possible for a plurality of sheet to be conveyed in different directions at the same time. In this event, the conveying speeds of each sheet-shaped member are different. It is therefore possible to convey the sheet efficiently. When the present invention is applied to a discharging/reversing roller of, for example, an image forming apparatus, it is then possible to raise productivity during duplex printing. 
         [0070]    Furthermore, according to another aspect of the present invention, it is possible to implement a roller-shaped rotating member using a simple structure. Conveying at different speeds in a plurality of directions is also possible. According to the present invention, it is possible to suppress deformation such as bending of sheet due to a difference in diameter between the small diameter section and the large diameter section. 
         [0071]    Moreover, according to another aspect of the present invention, it is possible to suppress deformation of paper and to appropriately convey the sheet. According to the present invention, it is possible to implement the roller-shaped rotating member using simpler members and it is possible to convey in a number of directions at different speeds at the same time. 
         [0072]    Furthermore, according to another aspect of the present invention, it is possible to set the sheet conveying speed of one auxiliary rotating member and the other auxiliary rotating member in the same direction to be the same during forward rotation and reverse rotation of the roller-shaped rotating member. When, for example, the present invention is then applied to a discharging/reversing roller of an image forming apparatus, it is possible to set the discharging speed and the conveying speed before reversing to be equal to maintain an appropriate relationship with the conveying speed from the fixing unit. 
         [0073]    Moreover, according to another aspect of the present invention, when two drive transmission path systems that transmit driving force to the roller-shaped rotating member are provided and the drive transmission paths of the two systems can be switched over, it is possible to set the sheet conveying speeds due to the one auxiliary rotating member and the other one auxiliary rotating member in the same direction to be the same during forward rotation and reverse rotation of the roller-shaped rotating member. When, for example, the present invention is then applied to a discharging/reversing roller of an image forming apparatus, it is possible to set the discharging speed and the conveying speed before reversing to be equal to maintain an appropriate relationship with the conveying speed from the fixing unit. 
         [0074]    Furthermore, according to another aspect of the present invention, it is possible to make the conveying speed fast when the sheet is conveyed in the reverse direction by using the large diameter portion of the roller-shaped rotating member. For example, when the present invention is applied to the discharge/reversing roller of an image forming apparatus, it is possible to make just the conveying speed after reversal fast. 
         [0075]    Moreover, according to another aspect of the present invention, a plurality of sheet can be conveyed in different directions at the same time. In this case, the conveying speed is different for each sheet-shaped member. It is therefore possible to convey the sheet efficiently. 
         [0076]    Furthermore, according to another aspect of the present invention, it is possible to discharge the sheet to outside using the roller-shaped rotating member and it is possible to reverse the conveying direction. According to the present invention, it is possible to improve productivity during duplex printing. 
         [0077]    Although the invention has been described with respect to specific embodiments for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art that fairly fall within the basic teaching herein set forth.