Patent Publication Number: US-7905483-B2

Title: Transport device and image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2008-142096 filed May 30, 2008. 
     BACKGROUND 
     Technical Field 
     The present invention relates to a transport device and an image forming apparatus. 
     SUMMARY 
     According to an aspect of the invention, there is provided a transport device including: a positioning member provided in a sheet transport path, used for positioning of a print sheet in a direction orthogonal to a sheet transport direction; and a skewed roller that transports the print sheet while skewing the print sheet toward a direction of the positioning member, a transport roller being provided in a position different from the skewed roller in the sheet transport direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An exemplary embodiment of the present invention will be described in detail based on the following figures, wherein: 
         FIG. 1  is a left-side cross-sectional view schematically showing the structure of an image forming apparatus according to an exemplary embodiment of the present invention; 
         FIG. 2  is a cross-sectional view of the image forming apparatus according to the exemplary embodiment of the present invention along a line A-A in  FIG. 1 ; 
         FIG. 3A  is a perspective view of a guide member of the image forming apparatus according to the exemplary embodiment of the present invention viewed from a front left side; 
         FIG. 3B  is a cross-sectional view along a line B-B in  FIG. 1 ; 
         FIG. 4  is a cross-sectional view showing transport of a print sheet in the exemplary embodiment of the present invention, along a line C-C in  FIG. 1 ; 
         FIG. 5A  is an explanatory view showing transport of the print sheet with a first skewed roller of the image forming apparatus according to the exemplary embodiment of the present invention; 
         FIG. 5B  is an explanatory view showing transport of the print sheet with a second skewed roller of the image forming apparatus according to the exemplary embodiment of the present invention; and 
         FIG. 6  illustrates a modification of the first skewed roller and the second skewed roller used in the exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Next, an exemplary embodiment of the present invention will be described based on the drawings. 
       FIGS. 1 and 2  show an image forming apparatus  10  according to the exemplary embodiment of the present invention. The image forming apparatus  10  has an image forming apparatus main body  12 . A sheet supply device  14  and an image forming unit  100  are attached in the image forming apparatus main body  12 . Further, an upper part of the image forming apparatus main body  12  is used as a exit unit  30  to which a print sheet where image formation has been completed is output. 
     The sheet supply device  14  has a sheet container  16  where print sheets are stacked and a feed roller  18  to feed the print sheets from the sheet container  16  toward the image forming unit  100 . 
     The image forming unit  100  has a photoreceptor  104  which is used as an image carrier, and which has e.g. a drum shape, a charging device  106  to uniformly charge the surface of the photoreceptor  104 , a writing device  108  to irradiate the photoreceptor  104  charged by the charging device  106  with a laser beam thereby to write a latent image, a developing device  150  to develop the latent image written by the writing device  108  on the photoreceptor  104  and form a developer image on the surface of the photoreceptor  104 , a transfer device  110  to transfer the developer image formed by the developing device  150  on the surface of the photoreceptor  104  to a print sheet, and a cleaning device  112  to remove developer and the like remaining on the surface of the photoreceptor  104  after the transfer of the developer image to the print sheet. 
     The developing device  150  has a developing device main body  160 . 
     The developing device main body  160  is rotatably supported with a rotation shaft  158 . In the developing device main body  160 , four developer cartridges  164   y ,  164   m ,  164   c  and  164   b  are removably attached. The developer cartridge  164   y  contains a yellow developer; the developer cartridge  164   m  contains a magenta developer; the developer cartridge  164   c  contains a cyan developer; and the developer cartridge  164   b  contains a black developer. These developers are supplied to the surface of the photoreceptor  104 , and used for development of a latent image formed on the surface of the photoreceptor  104 . 
     Further, as the developing device main body  160  is rotated about the rotation shaft  158 , one of the developer cartridges  164  provided in a position opposite to the photoreceptor  104  can be selected from the developer cartridges  164   y ,  164   m ,  164   c  and  164   b . Then the developer is supplied to the photoreceptor  104  from the developer cartridge  164  provided in the position opposite to the photoreceptor  104 . 
     Further, a transport path  200  having a main transport path  202  and a return path  204  is formed in the image forming apparatus main body  12 . 
     The main transport path  202  is used for transport of a print sheet from a lower position toward an upper position in the gravitational direction. A registration roller  206 , the above-described transfer device  110  and the photoreceptor  104 , a fixing device  34 , and a exit roller  208  are provided along the main transport path  202  sequentially from the upstream side in a sheet transport direction. The registration roller  206  is used for supply of a print sheet or the like sent from the feed roller  18  toward a contact portion between the photoreceptor  104  and the transfer device  110  at timing of image formation by the image forming unit  100 . 
     The fixing device  34  is used for fixing a developer image transferred to a print sheet by the transfer device  110  to the print sheet using e.g. heat and pressure. The exit roller  208  is used for discharging the print sheet on which the developer image has been fixed by the fixing device  34  to the exit unit  30 . The exit roller  208  is also used for supply of the print sheet on which the developer image has been fixed by the fixing device  34  to the return path  204 . 
     The return path  204  is used to return a print sheet supplied by the exit roller  208  from the main transport path  202  to a position of the main transport path  202  in which the registration roller  206  is provided. 
     The return path  204  has a first curved area  214  positioned on the downstream side of the exit roller  208  in the sheet transport direction, in which a print sheet is transported in a curved state, a straight area  216  provided on the downstream side of the first curved area  214  in the sheet transport direction, in which the print sheet is transported approximately straight, and a second curved area  218  positioned on the downstream side of the straight area  216  in the sheet transport direction, in which the print sheet is transported in a curved state. 
     A positioning member  222  used for positioning is provided in plural different positions in the sheet transport direction on the right side of the transport path  200 . The positioning member  222  is e.g. a plate member having a positioning surface  224  used as a reference surface for positioning of a print sheet in a direction orthogonal to the sheet transport direction, formed on the side opposite to the transport path  200 . 
     In the present exemplary embodiment, the positioning member  222  is provided in one position on the right side of the straight area  216  and the second curved area  218  in the return path  204 . It may be arranged such that total two positioning members are provided in the straight area  216  and the second curved area  218 , and these two positioning members are used as the positioning members in plural different positions in the sheet transport direction. 
     The first curved area  214  of the return path  204  is provided with a pair of guide plates  230  used as a guide member to guide a print sheet. The pair of guide plates  230  have an outside guide plate  232  positioned outside a transported print sheet and an inside guide plate  234  positioned inside the transported print sheet. In the first curved area  214 , a print sheet P is transported so as to be guided in space formed between the outside guide plate  232  and the inside guide plate  234 . The details of the pair of guide plates  230  will be described later. 
     In the return path  204 , a first skewed roller  240  used as a skewed roller to transport a print sheet while skewing the print sheet in the direction of the positioning member  222  and a first contact roller  242  opposite to the first skewed roller  240  and in contact with the first skewed roller  240 , are provided in the straight area  216 . Further, in the second curved area  218  of the return path  204 , a second skewed roller  244  used as a skewed roller to transport a print sheet while skewing the print sheet in the direction of the positioning member  222 , and a second contact roller  246  opposite to the second skewed roller  244  and in contact with the second skewed roller  244  are provided in the second curved area  218 . As described above, the image forming apparatus  10  has plural skewed rollers, the first skewed roller  240  and the second skewed roller  244 . The first skewed roller  240  and the second skewed roller  244  are provided in different positions in the sheet transport direction. 
     The first skewed roller  240  is used as a skewed roller in contact with a position of a print sheet on a straight line. The first skewed roller  240  is positioned on the upstream side in the sheet transport direction. On the other hand, the second skewed roller  244  is used as a skewed roller in contact with a curved portion of the print sheet. The second skewed roller  244  is positioned on the downstream side in the sheet transport direction. 
     In the image forming apparatus  10  having the above structure, a monochrome (black and white) image with the black developer and a multi-color image with the yellow, magenta, cyan and black developers, can be formed. 
     In formation of a monochrome image with the black developer, the surface of the photoreceptor  104  is uniformly charged by the charging device  106 , then a latent image corresponding to a single color black image is written by the writing device  108  on the uniformly charged surface of the photoreceptor  104 , and the latent image corresponding to the single color black image formed on the surface of the photoreceptor  104  is developed by the developing device  150  using the black developer. 
     That is, the developing device main body  160  is rotated about the rotation shaft  158  such that the developer cartridge  164   b  is provided in the position opposite to the photoreceptor  104 . Then developer contained in the developer cartridge  164   b  is supplied to the photoreceptor  104 , and the latent image corresponding to the black image written on the photoreceptor  104  is developed using the black developer. 
     Further, a print sheet is sent with the feed roller  18  toward the registration roller  206 , and the print sheet is supplied to the contact portion between the photoreceptor  104  and the transfer device  110  at timing of image formation by the image forming unit  100 . Then a black developer image formed on the surface of the photoreceptor  104  is transferred by the transfer device  110  to the supplied print sheet, then the developer image transferred on the print sheet is fixed by the fixing device  34  to the print sheet, and the print sheet on which the black developer image has been transferred is output by the exit roller  208  to the exit unit  30 . 
     On the other hand, in formation of a multi-color image with the yellow, magenta, cyan and black developers, first, through approximately the same process as that of the above-described formation of the single color black image, a yellow developer image is formed on a print sheet. Note that in formation of the above-described single color black image, the black developer is supplied to the photoreceptor  104 ; in the case, however, the yellow developer contained in the developer cartridge  164   y  is supplied to the photoreceptor  104  and used for development. 
     The print sheet, on which the yellow developer image transferred by the transfer device  110  has been fixed by the fixing device  34 , is not output by the exit roller  208  to the exit unit  30 , but transported by the exit roller  208  to the return path  204 . The print sheet transported to the return path  204  is guided with the pair of guide plates  230 , then transported with the first skewed roller  240  and then transported with the second skewed roller  244 , thus again supplied to the registration roller  206 . Then, the print sheet supplied to the registration roller  206  is supplied to the contact portion between the photoreceptor  104  and the transfer device  110  at timing of formation of a magenta image by the image forming unit  100 . Then, a magenta developer image is transferred onto the print sheet so as to be overlaid on the yellow developer image, and the magenta developer image is fixed by the fixing device  34  to the print sheet. Then, the print sheet on which the magenta developer image overlaid on the yellow developer image has been fixed is supplied through the return path  204  to the registration roller  206 . 
     Hereinbelow, similarly, a cyan developer image is fixed, and further, a black developer image is fixed to the print sheet. Thereafter, the print sheet is output by the exit roller  208  to the exit unit  30 . 
     As described above, the first skewed roller  240  and the second skewed roller  244  transport a print sheet while the rollers are both in contact with a surface of the print sheet on which a developer image (a yellow developer image, a magenta developer image and a cyan developer image) is transferred. 
       FIGS. 3A and 3B  show the pair of guide plates  230 . 
     As shown in  FIGS. 3A and 3B , in the interval between the outside guide plate  232  and the inside guide plate  234 , a right interval L 1  is wider than a left interval L 2 . In this arrangement, when e.g. the rear end side of the print sheet P is pushed with the exit roller  208  (see  FIG. 1 ) frontward in the sheet transport direction in a state where at least the front end of a print sheet P is inserted between the outside guide plate  232  and the inside guide plate  234 , the front end of the print sheet P is twisted to the left side along the surface of the inside guide plate  234 , and transported in a state where the print sheet P is skewed leftward as shown in  FIGS. 3A and 3B  and  FIG. 2 . Accordingly, the print sheet P is gradually moved away from the positioning member  222  provided on the right side in the direction orthogonal to the sheet transport direction. 
       FIG. 4  shows the print sheet P transported in the return path  204 , and shows the first skewed roller  240  and the second skewed roller  244 . Further,  FIG. 5A  shows the first skewed roller  240  transporting the print sheet, and  FIG. 5B , the second skewed roller  244  transporting the print sheet. 
     As shown in  FIG. 4 , the first skewed roller  240  and the second skewed roller  244  are provided in an inclined state at respectively rightward angles θ 1  and θ 2  with respect to the sheet transport direction. The angles θ 1  and θ 2  are the same angles, within e.g. the range of 2° to 5°. In this manner, since the first skewed roller  240  and the second skewed roller  244  are inclined to the right side with respect to the sheet transport direction, the first skewed roller  240  and the second skewed roller  244  skew a print sheet to the right side, i.e., to the side of the positioning member  222 . 
     The first skewed roller  240  has a main body  240   a  and a shaft  240   b . The main body  240   a  having flexibility in the direction of the shaft  240   b , is formed with an elastic material. 
     For example, as rubber which is a particular material of the main body  240   a , ethylene-propylene diene rubber (EPDM), butadiene rubber, isoprene rubber, chloroprene rubber, natural rubber, acrylonitrile-butadiene rubber, styrene butadience rubber, styrene rubber, butyle rubber, haloid butyle rubber, polyisobutylene rubber, chlorosulfonated polyethylene rubber, acrylic rubber, urethane rubber, silicon rubber, polyether copolymer, epichlorohydrin copolymer, and the like, can be used. These rubbers may be used as the material of the main body  240   a  as a single material, or two or more types of these rubbers may be blended as the material of the main body  240   a . Further, the elastic modulus of the main body  240   a  is set to e.g. 1.5 to 10 Mpa (megapascal) as a Young&#39;s modulus. 
     As the main body  240   a  has elasticity, when the right end of a print sheet transported while skewed rightward is brought into contact with the positioning member  222 , the first skewed roller  240  is pushed with the print sheet P pushed with the positioning member  222 , and a portion in contact with the print sheet P is distorted to the left side as shown in  FIG. 5A . The force of the positioning member  222  to push the print sheet P and the force of the first skewed roller  240  to press the print sheet P against the positioning member  222  at this time are F 1 . Further, the transport force of the first skewed roller  240  to transport the print sheet P in the direction of the positioning member  222  is F 11 . 
     The second skewed roller  244  has a main body  244   a  and a shaft  244   b  as in the case of the first skewed roller  240 . The main body  244   a  having flexibility in the direction of the shaft  244   b , is formed with an elastic material. 
     For example, as in the case of the first skewed roller  240 , as rubber which is a particular material of the main body  244   a , ethylene-propylene diene rubber (EPDM), butadiene rubber, isoprene rubber, chloroprene rubber, natural rubber, acrylonitrile-butadiene rubber, styrene butadience rubber, styrene rubber, butyle rubber, haloid butyle rubber, polyisobutylene rubber, chlorosulfonated polyethylene rubber, acrylic rubber, urethane rubber, silicon rubber, polyether copolymer, epichlorohydrin copolymer, and the like, can be used. These rubbers may be used as the material of the main body  244   a  as a single material, or two or more types of these rubbers may be blended as the material of the main body  244   a . Further, the elastic modulus of the main body  244   a  is set to e.g. 1.5 to 10 Mpa (megapascal) as a Young&#39;s modulus. 
     It is understood from a comparison between the first skewed roller  240  and the second skewed roller  244  that the Young&#39;s modulus of the main body  244   a  of the second skewed roller  244  is higher than that of the main body  240   a  of the first skewed roller  240 , and in the second skewed roller  244 , the elastic modulus in its axial direction is higher than that of the first skewed roller  240 . 
     As in the case of the first skewed roller  240 , when the right end of the transported print sheet P while it is skewed rightward is brought into contact with the positioning member  222 , the second skewed roller  244  is pushed with the print sheet P pushed with the positioning member  222 , and a portion of the second skewed roller  244  in contact with the print sheet P is distorted to the left side as shown in  FIG. 5B . The force of the positioning member  222  to push the print sheet P and the force of the second skewed roller  244  to press the print sheet P against the positioning member  222  at this time are F 2 . Further, the transport force of the second skewed roller  244  to transport the print sheet P in the direction of the positioning member  222  is F 21 . 
     The elastic modulus of the main body of the first skewed roller  240  is lower than that of the second skewed roller  244 . Accordingly, in comparison with the second skewed roller  244 , distortion occurred in the first skewed roller  240  is greater. Even when the force F 21  is set to a higher level than the force F 11 , twist of a print sheet between the skewed rollers and/or slip of the print sheet can be prevented by the distortion of the first skewed roller  240 . Further, as the force F 1  is set to a low level, buckling of the print sheet can be prevented. 
     In the image forming apparatus  10  having the above arrangement, when the print sheet P, pushed with the exit roller  208 , is inserted from its front end between the outside guide plate  232  and the inside guide plate  234 , the print sheet P is moved while it is skewed leftward in the return path  204  along the inside guide plate  234  as indicated with an alternate long and two short dashes line in  FIG. 4  as a position P 1 . 
     Then, when the front end of the print sheet P arrives at the position of the first skewed roller  240 , the print sheet P moved while skewed leftward is transported with the first skewed roller  240  while it is skewed rightward toward the direction of the positioning member  222 . Then the print sheet P is brought into contact with the positioning member  222  from the rear end of its right side, and as indicated with an alternate long and two short dashes line in  FIG. 4  as a position P 2 , pressed against the positioning member  222 . 
     In this manner, since the print sheet is in contact with the first skewed roller  240  and the second skewed roller  244  simultaneously in the position P 2 , the position can be stably controlled. 
     Next, when the front end of the print sheet P arrives at the second skewed roller  244 , the print sheet P is transported with the second skewed roller  244  while it is skewed rightward toward the direction of the positioning member  222 , and pressed against the positioning member  222 . As the print sheet P is pressed against the positioning member  222  with the plural skewed rollers, i.e., the first skewed roller  240  and the second skewed roller  244 , the print sheet P is positioned in a direction orthogonal to the sheet transport direction of the print sheet P as indicated with an alternate long and two short dashes line in  FIG. 4  as a position P 3 . 
     As described above, in the image forming apparatus  10  according to the present exemplary embodiment, as the print sheet P is pressed against the positioning member  222  using the plural skewed rollers, the force of the first skewed roller  240  to transport the print sheet P in the direction of the positioning member  222  (the transport force F 11 ), and the force of the second skewed roller  244  to transport the print sheet P in the direction of the positioning member  222  (the transport force F 21 ), can be set to a lower level in comparison with a case where the print sheet P is pressed against the positioning member  222  using only one skewed roller. As the transport force F 11  and the transport force F 21  can be set to a low value, the pressing forces F 1  and F 2  can be set to low values, and buckling of the print sheet P can be reliably prevented. 
     Further, in the image forming apparatus  10  according to the present exemplary embodiment, the transport force F 21  of the second skewed roller  244  provided in the second curved area  218  in the return path  204  and in contact with a curved position of the print sheet P is higher than the transport force F 11  of the first skewed roller  240  provided in the straight area  216  in the return path  204  and in contact with the straight position of the print sheet P. Accordingly, the probability of failure of positioning of the print sheet P and/or damage to the right end of the print sheet P such as buckling is low. On the other hand, in a case where the right end of the print sheet P is pressed against the positioning member  222  with the same force regardless of position and/or print sheet state, when the force pressing the print sheet P against the positioning member  222  is insufficient, the positioning of the print sheet P fails, while when the pressing force is too strong, damage such as buckling occurs in the right end of the print sheet P. 
     Further, the distortion that occurs in the first skewed roller  240  is larger in comparison with the distortion that occurs in the second skewed roller  244 . Since the first skewed roller  240  absorbs twist of the print sheet P between the skewed rollers and and/or slip of the print sheet, damage such as a napped state of the print sheet P can be suppressed. Further, although the first skewed roller  240  and the second skewed roller  244  come into contact with a surface of the print sheet on which a developer image has been transferred, degradation of image quality of the developer image transferred on the print sheet is suppressed. 
     Particularly, in the present exemplary embodiment, in which images in respective colors are transferred and fixed onto a print sheet in formation of an image in multiple colors, the amount of transferred and fixed image differs by each color on the print sheet transported to the return path  204 . However, it is found in the above arrangement that the degradation of image quality is suppressed in every transport process. 
       FIG. 6  shows a modification of the first skewed roller  240  and the second skewed roller  244 . In the modification, plural grooves  240   c  and  244   c , for example, are formed in the main bodies  240   a  and  244   a  of the first skewed roller  240  and the second skewed roller  244  in e.g. a direction orthogonal to the shaft  240   b  and the shaft  244   b . In this arrangement, the first skewed roller  240  and the second skewed roller  244  are easily elastic-deformed in the axial direction. 
     In the above-described image forming apparatus  10 , the transport force F 11  of the first skewed roller  240  and the transport force F 21  of the second skewed roller  244  are set to mutually different values. To set the transport force F 21  to a value greater than the transport force F 11 , the inclination θ 2  (see  FIG. 4 ) of the second skewed roller  244  is set to a wider angle than the inclination θ 1  (see  FIG. 4 ) of the first skewed roller  240 . Further, the transport force F 21  may be set to a greater value than the transport force F 11  by setting a friction coefficient on the surface of the main body  244   a  of the second skewed roller  244  to a greater value than that of the main body  240   a  of the first skewed roller  240 . 
     Further, in the exemplary embodiment, the first skewed roller  240  and the second skewed roller  244  are both skewed rollers. However, it may be arranged such that one of these rollers is a transport roller as long as the other roller, namely the skewed roller, has a strong transport force to skew the print sheet. 
     As described above, the present invention is applicable to an image forming apparatus such as a duplicator, a facsimile apparatus, a copier and the like and a transport device used in e.g. these image forming apparatuses. 
     The foregoing description of the exemplary embodiment of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The exemplary embodiment was chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.