Patent Publication Number: US-8538315-B2

Title: Image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC 119 from Japanese Application No. 2009-071238 filed Mar. 24, 2009 and Japanese Application No. 2009-165428 filed Jul. 14, 2009. 
     BACKGROUND 
     Technical Field 
     This present invention relates to an image forming apparatus. 
     SUMMARY 
     According to an aspect of the present invention, there is provided an image forming apparatus comprising: an image forming apparatus main body, an image forming unit that is provided in the image forming apparatus main body and forms an image on a recording medium, and a transport unit transporting the recording medium, wherein the image forming apparatus main body has a forward port for forwarding the recording medium having the image thereon by the image forming unit to the outside of the image forming apparatus main body, and further has a guide unit by which the recording medium forwarded to the outside of the image forming apparatus main body is guided to be retrieved into the image forming apparatus main body, and to be led toward the transport unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein: 
         FIG. 1  is a side view showing an overview of an image forming apparatus according to a first exemplary embodiment of the invention; 
         FIG. 2  is a front view showing the image forming apparatus shown in  FIG. 1 ; 
         FIG. 3  is a side view showing a status where a guide member in the image forming apparatus shown in  FIG. 1  is put in the image forming apparatus main body; 
         FIG. 4  is a block diagram showing a controller of the image forming apparatus shown in  FIG. 1 ; 
         FIG. 5  is a side view showing an overview of a first modified version of an image forming apparatus according to the first exemplary embodiment, an image forming apparatus  10   a;    
         FIG. 6  is a side view showing an overview of a second modified version of the image forming apparatus according to the first exemplary embodiment, an image forming apparatus  10   b;    
         FIG. 7  is a side view showing an overview of a third modified version of the image forming apparatus according to the first exemplary embodiment, an image forming apparatus  10   c;    
         FIG. 8  is a side view showing an overview of a fourth modified version of the image forming apparatus according to the first exemplary embodiment, an image forming apparatus  10   d;    
         FIG. 9  is a side view showing an overview of a fifth modified version of the image forming apparatus according to the first exemplary embodiment, an image forming apparatus  10   e;    
         FIG. 10  is a side view showing an overview of an image forming apparatus  10   f  according to a second exemplary embodiment of the invention; 
         FIG. 11  is a side view showing an overview of an image forming apparatus  10   g  according to a third exemplary embodiment of the invention; 
         FIG. 12  is a side view showing an overview of an image forming apparatus  10   h  according to a fourth exemplary embodiment of the invention; 
         FIG. 13  is a side view showing an overview of an image forming apparatus  10   i  according to a fifth exemplary embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Next, an exemplary embodiment of the present invention will be described, based on the drawings of the first exemplary embodiment. 
       FIG. 1  and  FIG. 3  are a side view showing an overview of an image forming apparatus  10  according to a first exemplary embodiment of the present invention, and  FIG. 2  is a front view of the image forming apparatus  10 . 
     As shown in  FIG. 1  and  FIG. 2 , the image forming apparatus  10  has an image forming apparatus main body  12 , and in the image forming apparatus main body  12 , a image forming part  13  is disposed, for example, at an approximately central portion thereof, and a sheet feed unit  14  with one stage is disposed, e.g. at the bottom of the image forming apparatus main body  12 . Further the image forming apparatus main body  12  has a transfer device  26  for transferring the image formed by the image forming part  13  on a recording medium, and a fixing device  22  for fixing the image transferred with the transfer device  26  to the recording medium by using, at least, heat. Note that an image forming unit, which forms an image onto a recording medium such as a plain paper, is configured with the image forming part  13  and the transfer device  26 . 
     Further the image forming apparatus main body  12  has a transport device  17  which is used as a transport unit transporting the recording medium toward the image forming part  13  and transports the recording medium, e.g. from the sheet feed unit  14 , toward the image forming part  13 . 
     An user interface device (UI device)  68  such as a touch panel is arranged in a position above the image forming apparatus main body  12 , and a controller  70  controlling each of parts configuring the image forming apparatus  10  is arranged in the image forming apparatus main body  12 . 
     The transport device  17  has a transport path  18 , transport rollers  52  and  56 . The transport device  17  is also used as a transport unit which transports the recording medium from the fixing device  22  to the transfer device  26  for further transferring an image to the recording medium fixed the image onto with the fixing device  22 . 
     The transport path  18  has a main transport path  19  and a repeat path  46 . Along the transport path  18 , the recording medium is capable of becoming transported so as to be forwarded from the forward port  48  to the outside of the image forming apparatus main body  12  with passing around at least a portion of the image forming unit  13 , and be retrieved into the image forming apparatus main body  12 . 
     An exit  20  for ejecting the recording medium toward e.g. the upper side and e.g. a front side of the image forming apparatus main body  12  (the left side on  FIG. 1 ) is formed in the image forming apparatus main body  12 . Further the forward port  48  is shaped on e.g. the front side of the image forming apparatus main body  12 . The forward port  48  is used as a position where the recording medium having the image thereon by the image forming part  13  is forwarded to the outside of the image forming apparatus main body  12 . Further a retrieve port  50  is shaped, e.g., at the front side of the image forming apparatus main body  12 , and, e.g., in a lower part of the forward port  48 . The retrieve port  50  is used as a position where the recording medium, which is forwarded to the outside of the image forming apparatus main body  12  to pass through the forward port  48 , is retrieved into the image forming apparatus main body  12 . 
     A guide member  54  is arranged on the front side of the image forming apparatus main body  12  so as to be placed e.g. on the exterior surface of the image forming apparatus main body  12 . 
     The image forming part  13  has an image carrier  24  such as e.g. a photoreceptor, a charging device  62 , an optical projection device  66 , a rotary development device  57 , and an image carrier cleaner  64 . 
     The charging device  62 , consisting e.g. a charging roller, is arranged in the front side of the image carrier  24 , and evenly charges the image carrier  24 . The optical projection device  66  is arranged above the rotary development device  57 , and projects an electrostatic latent image on the image carrier  24  charged with the charging device  62  with a beam such as a laser beam. The rotary development device  57  is arranged e.g. in a lower part of an approximately central portion, and has four development units  58   a  to  58   d , respectively containing four colors of developers, i.e., yellow, magenta, cyan, and black developers, to sequentially visualize an electrostatic latent image carried on the image carrier  24  with each color developer. The image carrier cleaner  64  abuts on the image carrier  24  upstream relative to the charging device  62  in the direction of rotation of the image carrier  24 , and scrapes off developer particles remaining on the image carrier  24  after transfer. 
     The transfer device  26 , consisting of e.g. a transfer roller having elastic surface, is arranged in the rear side of the image carrier  24 , and sequentially transfers the developer images visualized with the development unit  58   a  to  58   d  to the recording medium in a transfer position T as shown  FIG. 1 . 
     The fixing device  22 , having a heat roller and a pressure roller, is arranged downstream of the transfer position T in the transport direction of the recording medium, and fixes the developer images, which is obtained from the image carrier  24  and transferred to the recording medium with transfer device  26 , on the recording medium by using heat and pressure. 
     A pickup roller  16  for picking up the recording medium from the sheet feed unit  14  is arranged in a position above the sheet feed unit  14 . The pickup roller  16 , driven by a driver (not shown), rotates to supply the recording medium toward a transport path  18 . 
     The main transport path  19  is a recording medium passage from the pickup roller  16  to the exit  20 . The main transport path  19  is in the rear side of the image forming apparatus main body  12  (the right side portion in  FIG. 1 ), and has an approximate vertical part from the sheet feed unit  14  to the exit  20 . Along the main transport path  19 , in upstream side of a fixing device  22 , the above image carrier  24  and the above transfer device  26  are arranged. Further, a registration roller  28  is arranged in the upstream side of the image carrier  24  and the transfer roller  26 . Further, an exit roller  42  is arranged in the vicinity of the exit  20  in the transport path  18 . 
     Downstream of the fixing device  22  in the transfer direction of the recording medium, a switching device  44  is disposed. The switching device  44  switches the recording medium transported from a side of the fixing device  22  to the exit roller  42  or to a side of the repeat path  46  for transporting. 
     The repeat path  46  is a passage where the recording medium is transported to be returned from a position where the switching device  44  is disposed to the registration roller  28 . A part of the repeat path  46  is in an outside of the image forming apparatus main body  12 . That is, along the repeat path  46 , the recording medium is forwarded to the outside of the image forming apparatus main body  12 , and subsequently is retrieved into the image forming apparatus main body  12 . In particular, the recording medium is guided with the switching device  44  to the repeat path  46  to be forwarded with a transport roller  52  from the forward port  48  to the outside of the image forming apparatus main body  12 , and further, the recording medium is guided by a guide member  54  to be retrieved into the image forming apparatus main body  12  at the retrieve port  50 . Furthermore, the recording medium is transported with the transport roller  56  to the registration roller  28 . Note that the recording medium is subjected to a pressure by gravity, thereby goes down while passing through the repeat path  46  in the outside of the image forming apparatus main body  12 . 
     Note that, the guide member  54  consisting of plural wires such as a steel wire may be stored inside the image forming apparatus main body  12  as shown in  FIG. 2  when color printing is not performed. 
       FIG. 4  is a block diagram showing the controller  70 . 
     The controller  70  has a control circuit consisting of e.g. CPU, and as shown in  FIG. 4 , receives image data via a communication interface  71 . Further, the controller  70  receives input data information from a user interface (UI) device  68 . The data information from the UI device  68  includes, e.g. types and thickness of a recording medium which is stored in the sheet feed unit  14  and is formed an image onto. 
     The controller  70  is connected with a data table  69 . The data table  69  stores information for a relation between type, thickness, size or the like, which the recording medium has, and a appropriate heating temperature for heating the recording medium with the fixing device  22  according to the above conditions. The data table  69  further stores a relation between at least one condition of the recording medium type, the recording medium thickness, and heating temperature for heating the recording medium with the fixing device  22 , and an appropriate time where the recording medium, forwarded to the outside of the image forming apparatus main body  12 , has been retrieved into the image forming apparatus main body  12 . 
     The controller  70  connects to the image forming part  13 , the transfer device  26 , the transport device  17 , the fixing device  22 , the switching device  44  and the like to control by transmitting data. In particular, the controller  70  controls the image forming part  13 , the transfer device  26 , the transport device  17 , the fixing device  22 , the switching device  44  and the like so as to forward the recording medium having the image thereon from the forward port  48  to the outside of the image forming apparatus main body  12 , whenever e. the image forming part  13  and the transfer device  26  forms a single-color image onto the recording medium. 
     Further, the controller  70  controls the image forming part  13 , the transfer device  26 , the transport device  17 , the fixing device  22 , the switching device  44  and the like so as to forward the recording medium having a image formed to the outside of the image forming apparatus main body  12  whenever a single-color image transferred onto the recording medium with the transfer device  26  is fixed on the recording medium with the fixing device  22 . Further, the controller  70  controls the image forming part  13 , the transfer device  26 , the transport device  17 , the fixing device  22 , the switching device  44  and the like so as to optimize time until the recoding medium forwarded to the outside of the image forming apparatus main body  12  has retrieved into the image forming apparatus main body  12  according to at least one condition of the recording medium type, the recording medium thickness, and heating temperature for heating the recording medium with the fixing device  22 , with reference to a data table. 
     In the image forming apparatus  10  configured as the above-described, when a single-color such as a black image is formed, under the control of the controller  70 , the recording medium is picked up from the sheet feed unit  14  with the pickup roller  16  and is transported toward the registration roller  28 . Further, when a front edge of the recording medium transported is temporarily stopped with the registration roller  28 , the recording medium is transported between the image carrier  24  and the transfer device  26  at predetermined timing, and is subjected to transfer of e.g. a black developer image on the surface of the recording medium. Further, the black developer image transferred onto the recording medium is fixed on the recording medium with the fixing device  22 , and the recording medium fixed the developer image onto is ejected with an exit roller  42  from the exit  20 . 
     Whereas, in the case of color printing used yellow, magenta, cyan, and black developers, the recording medium is returned to the repeat path  46 , e.g. three times under the control of the controller  70 , and the yellow, magenta, cyan, and black developers image formed onto the image carrier  24  is transferred to the recording medium with each developer superposed. 
     In the case of color printing, the controller  70  controls the switching device  44  to switch a transport passage to the repeat path  46  side. Then, the recording medium is forwarded with the transport roller  52  from the forward port  48  to the outside of the image forming apparatus main body  12 , and further, is guided along a guide member  54  on outside of the image forming apparatus main body  12  to be retrieved into the image forming apparatus main body  12  at the retrieve port  50 . Further the recording medium is transported with the transport roller  56  to the registration roller  28 . Then, the recording medium passes through the registration roller  28 , a portion between the image carrier  24  and the transfer device  26 , and the fixing device  22  four times. The recording medium having transferred four color developer images is ejected from the exit  20  with the switching device  44  controlled for switching. 
     When an image forming signal is sent to the controller  70 , in the image forming part  13 , the image carrier  24  is evenly charged with the charging device  62 , and a light ray corresponding to a yellow image is emitted from the optical projection device  66  to the image carrier  24  charged based on the image signal. The light ray from the optical projection device  66  exposes the surface of the image carrier  24 , thereby an electrostatic latent image is formed. 
     The electrostatic latent image carried on the image carrier  24  is developed with the yellow developer supplied from the development unit  58   a , and is transferred to the recording medium supplied from the sheet feed unit  14 . The recording medium to which the yellow developer image has been transferred is led to the fixing device  22 , and the developer image is fixed on the recording medium with the heating roller and the pressure roller. 
     Note that the recording medium fixed the yellow developer image onto is, as mentioned above, guided to the repeat path  46  with the switching device  44 , and is forwarded from the forward port  48  toward the outside of the image forming apparatus main body  12 , and subsequently is retrieved into the image forming apparatus main body  12  at the retrieved port  50  with guided by the guide member  54 . 
     Developer particles remaining on the image carrier  24  is scraped off with the image carrier cleaner. 
     Then the image carrier  24  is evenly charged again with the charging device  62 , and a light ray corresponding to a magenta image is emitted from the optical projection device  66  to the image carrier  24  charged based on the image signal. The light ray from the optical projection device  66  exposes the surface of the image carrier  24 , thereby an electrostatic latent image is formed. 
     The electrostatic latent image carried on the image carrier  24  is developed with the magenta developer supplied from the development unit  58   b , and is overlay-transferred to the recording medium having passed through the repeat path  46 . 
     The recording medium to which the magenta developer image has been transferred is led to the fixing device  22  to be fixed the developer image thereon with the heating roller and the pressure roller. The recording medium on which the magenta developer image is fixed is, as mentioned above, guided to the repeat path  46  with the switching device  44 . Developer particles remaining on the image carrier  24  is scraped off with the image carrier cleaner  64 . 
     The recording medium is returned toward the registration roller  28  three times, and as in the case of the yellow and magenta developer images, developer images developed with the cyan and the black developers are fixed on the recording medium by the fixing device  22 . Thus a color image is formed with overlaid developer images on the recording medium. The recording medium to which the color image has been fixed is led to the exit roller  42  with the switching device  44  and is ejected. 
     In the image forming apparatus  10 , when the recording medium is transported from the fixing device  22  to the transfer device  26  so that a image may be further transferred on the recording medium on which the image has been fixed with the fixing device  22 , as mentioned above, the transport device  17  forwards the recording medium, on which the image has been fixed with the fixing device  22 , toward the outside of the image forming apparatus main body  12 , and retrieves again the recording medium forwarded into the image forming apparatus main body  12 . Accordingly, the image forming apparatus  10  reduces a problem that the image quality may be reduced when an image is further formed on the recording medium, on which the image has been fixed by heating. 
     In general, when the recording medium is subjected to heating for fixing an image thereon, moisture is evaporated and changes shape. Accordingly, the image may not be formed successfully when overlay-transfer of images on the recording medium fixed the image onto is performed in the status where the recording medium changes shape. Whereas, the image forming apparatus  10  allows the recording medium not to change shape by forwarding the recording medium to the outside of the image forming apparatus main body  12  to expose the recording medium, subjected to heating for fixing, to the air, thereby the recording medium absorbs water in the air. After the deformation of the recording medium has disappeared, the recording medium is transferred next image onto. Accordingly, reduction of image quality due directly to the deformation of the recording medium is hardly caused. 
     Furthermore, in general, when the recording medium is subjected to heating for fixing an image, since moisture in the recording medium is evaporated and resistance value of the recording medium changes because of reduction of the moisture content in the recording medium, i.e. the sheet moisture content thereof. Accordingly, the image may not be formed successfully when overlay-transfer of images on the recording medium fixed the image onto is performed. Whereas, the image forming apparatus  10  allows the recording medium to have a stable moisture content by forwarding the recording medium to the outside of the image forming apparatus main body  12  to expose the recording medium, subjected to heating for fixing, to the air, thereby the recording medium absorbs water in the air. After the moisture content of the recording medium has been stable, the recording medium is transferred next image onto. Accordingly, reduction of image quality due directly to the change of the resistance value in the recording medium is hardly caused. 
     Next, a first modified version according to the first exemplary embodiment of the present invention will be described. 
       FIG. 5  is a side view showing an overview of a first modified version of the image forming apparatus  10  according to the first exemplary embodiment, the image forming apparatus  10   a . Note that the image forming apparatus  10   a  shown in  FIG. 5  indicates the parts substantially similar to the parts configuring the image forming apparatus  10  shown in  FIG. 1  to  FIG. 3  with the same reference numeral as the image forming apparatus  10 . 
     As shown in  FIG. 5 , a retrieve guide member  72  is provided on the retrieve port  50  side in the image forming apparatus main body  12  so that the recording medium on the repeat path  46  may be retrieved into the image forming apparatus main body  12  at the retrieve port  50 . 
     The retrieve guide member  72  is used as a retrieve guide part, consisting of e.g. a platy member. When a color printing is not performed in the image forming apparatus  10   a , the retrieve guide member  72  is capable of being stored inside the image forming apparatus main body  12  by swung around a fulcrum  74  as a center. 
     When color printing is performed in the image forming apparatus  10   a , the controller  70  controls the switching device  44  to switch toward the repeat path  46 . Then, the recording medium is forwarded with the transport roller  52  from the forward port  48  to the outside of the image forming apparatus main body  12 , and further, is guided along the retrieve guide member  72 , placed outside the image forming apparatus main body  12 , to be retrieved into the image forming apparatus main body  12  at the retrieve port  50 . Further the recording medium is transported with the transport roller  56  to the registration roller  28 . Thus the recording medium is passed through the registration roller  28 , a portion between the image carrier  24  and the transfer device  26 , and the fixing device  22  four times and is ejected from the exit  20 . Note that the recording medium is subjected to a pressure by gravity to go down while passing through the repeat path  46  in the outside of the image forming apparatus main body  12   
     The image forming apparatus  10   a  may have a guide member  76  which is arranged in the forward port  48  side of the image forming apparatus main body  12  and guides the recoding medium toward the retrieve port  50 . The guide member  76 , consisting of e.g. a platy member, is capable of being stored inside the image forming apparatus main body  12  by swung around a fulcrum  78  as a center when a color printing is not performed in the image forming apparatus  10   a.    
     Next, a second modified version according to the first exemplary embodiment of the present invention will be described. 
       FIG. 6  is a side view showing an overview of a second modified version of the image forming apparatus  10  according to the first exemplary embodiment, the image forming apparatus  10   b . Note that the image forming apparatus  10   b  shown in  FIG. 6  indicates the parts substantially similar to the parts configuring the image forming apparatus  10  shown in  FIG. 1  with the same reference numerals as the parts of the image forming apparatus  10 . 
     While the image forming apparatus main body  12  has one forward port, i.e. the forward port  48  in the above-described image forming apparatus  10  according to the first exemplary embodiment, in the image forming apparatus  10   b  as the second modified version, the image forming apparatus main body  12  has two forward ports  80   a  and  80   b  arranged in the upper front side of the image forming apparatus main body  12  from the top as shown in  FIG. 6 . Further, the image forming apparatus  10   b  has a switching device  82  for switching the transported recording medium from the forward port  80   a  to the outside of the image forming apparatus main body  12  or from the forward port  80   b  toward outside the image forming apparatus main body  12 . The switching device  82  is controlled by the controller  70  as the switching device  44  and the like. 
     When the recording medium is guided to the repeat path  46  with the switching device  44  in the image forming apparatus  10   b , the recording medium is forwarded to the outside of the image forming apparatus main body  12  from the forward port  80   a  or  80   b  by switched the switching device  82 . Note that the controller  70  controls the switching device  82  for switching based on the recording medium length in the transport direction input via e.g. UI device  68 . For instance, when the recording medium length in the transport direction is equal or more than the predetermined length, the controller  70  controls the switching device  82  for switching to forward the recording medium from the forward port  80   a  to the outside of the image forming apparatus main body  12 . When the recording medium length in the transport direction is less than the predetermined length, in order to shorten the length of the repeat path  46 , the controller  70  controls the switching device  82  for switching to forward the recording medium from the forward port  80   b  to the outside of the image forming apparatus main body  12 . 
     The image forming apparatus  10   b  may have a detection device  67  detecting the recording medium length in the transport direction in the image forming apparatus main body  12 , accordingly, the controller  70  may be input data of the recording medium length in the transport direction detected with the detection device  67 , and controls the switching device  82  for switching based on the recording medium length in the transport direction input. 
     Next, a third modified version according to the first exemplary embodiment of the present invention will be described. 
       FIG. 7  is a side view showing an overview of the third modified version of the image forming apparatus  10  according to the first exemplary embodiment, the image forming apparatus  10   c . Note that the image forming apparatus  10   c  shown in  FIG. 7  indicates the parts substantially similar to the parts configuring the image forming apparatus  10   a  shown in  FIG. 5  with the same reference numerals as the parts of the image forming apparatus  10 . 
     As shown in  FIG. 7 , the image forming apparatus  10   c  has a forward guide member  84  to guide the recording medium forwarded from the forward port  48  toward the predetermined direction switchable. When the recording medium is guided with the switching device  44  to the repeat path  46 , forward angle of the forward guide member  84  is switched by the controller  70 , accordingly, the recording medium is forwarded toward the outside of the image forming apparatus main body  12  with the forward angle switched. Note that the controller  70  controls the forward angle of the forward guide member  84  to switch based on data of the recording medium length in the transport direction input via e.g. UI device  68 . For instance, when the recording medium length in the transport direction is equal or more than the predetermined length, in order to lengthen the length of the repeat path  46 , the controller  70  controls the forward guide member  84  for switching to forward the recording medium to the direction away from the image forming apparatus main body  12 . When the recording medium length in the transport direction is shorter than the predetermined length, in order to shorten the length of the repeat path  46 , the controller  70  controls the forward guide member  84  for switching to forward the recording medium to the direction not far from the image forming apparatus main body  12 . 
     Note that the forward guide member  84 , consisting of e.g. a platy member, in the case where a color printing is performed in the image forming apparatus  10   c , is capable of being stored inside the image forming apparatus main body  12  by swung around a fulcrum  86  as a center. 
     Next, a fourth modified version according to the first exemplary embodiment of the present invention will be described. 
       FIG. 8  is a side view showing an overview of the fourth modified version of the image forming apparatus  10  according to the first exemplary embodiment (the image forming apparatus  10   d ). Note that in the image forming apparatus  10   d  shown in  FIG. 8  indicates the parts substantially similar to the parts configuring the image forming apparatus  10  shown in  FIG. 1  with the same reference numeral as the image forming apparatus  10 . 
     Further to the configuration which the image forming apparatus  10  according to the first exemplary embodiment has, the image forming apparatus  10   d  has a reversing guide member device  180  used as a reversing guide unit which guides the recording medium, on which the image has been formed, for leading to the transport device  17  with reversing the recording medium. The reversing guide device  180  has a reversing transport path  182 , connecting the exit roller  42  and the position at upstream side of the registration roller  28  in the transporting direction, and two reversing transport rollers  184  and  186  transporting the recording medium in the direction of an arrow shown in  FIG. 8 . The image forming apparatus  10   d  controls the exit roller  42  to rotate in the direction opposite to the rotation direction in ejecting the recording medium. 
     In the case that the recording medium formed the image on one surface thereof is further formed the image on another surface thereof, the controller  70  of the image forming apparatus  10   d  controls the exit roller  42  to start rotating in the opposite direction at the time where the trail edge of the recording medium formed the image on the one surface is sandwiched with the exit roller  42 . The exit roller  42  reverses, and then, the recording medium, formed the image on the one surface is passed through a reversing transport path  182  and is transported to the transport path  18  at the position upstream of the registration roller  182  with reversing. 
     The mentioned-above fourth modified version according to the first exemplary embodiment may be combined with the first modified version, the second modified version, or the third modified version. That is, the reversing guide device  180  may be mounted in the image forming apparatus  10   a  of the first modified version, the image forming apparatus  10   b  of the second modified version, or the image forming apparatus  10   c  of the third modified version. 
     Next, a fifth modified version according to the first exemplary embodiment of the present invention will be described. 
       FIG. 9  is a side view showing an overview of the fifth modified version of the image forming apparatus  10  according to the first exemplary embodiment, the image forming apparatus  10   e . Note that the image forming apparatus  10   e  shown in  FIG. 9  indicates the parts substantially similar to the parts configuring the image forming apparatus  10   d  shown in  FIG. 8  with the same reference numeral as the image forming apparatus  10 . 
     In the mentioned-above image forming apparatus  10   d  (Refer to  FIG. 8 ), the reversing transport path  182  is formed inside the image forming apparatus main body  12 . Whereas, in the image forming apparatus  10   e  as the fifth modified version, at least a portion of the reversing transport path  182  is formed on outside of the image forming apparatus main body  12 . In particular, a forward port  194  and a retrieve port  196  are formed in the image forming apparatus main body  12 , and the reversing transport path  182 , along which the recording medium is forwarded to the outside of image forming apparatus main body  12  with the reversing transport roller  184  and is retrieved again at the retrieve port  196  into the image forming apparatus main body  12 , is formed. 
     Further, the image forming apparatus  10   e  has a guide member  198  to guide the recording medium from the forward port  194  to the retrieve port  196 . The guide member  198  consists of e.g. steel materials such as plural wires, and is attached on the exterior surface of the image forming apparatus main body  12 . 
     The mentioned-above fifth modified version of the image forming apparatus  10  according to the first exemplary embodiment may be combined with the first modified version, the second modified version, or the third modified version. That is, the reversing guide device  180 , which forwards the recording medium to the reversing transport path  182  having at least a portion formed in outside of the image forming apparatus main body  12 , may be mounted in the image forming apparatus  10   a  of the first modified version, the image forming apparatus  10   b  of the second modified version, or the image forming apparatus  10   c  of the third modified version. 
     Next, a second exemplary embodiment of the present invention will be described. 
       FIG. 10  is a side view showing an overview of the image forming apparatus  10   f  according to the second exemplary embodiment of the present invention. Note that the image forming apparatus  10   f  shown in  FIG. 10  indicates the parts substantially similar to the parts configuring the image forming apparatus  10  shown in  FIG. 1  with the same reference numeral as the image forming apparatus  10 . 
     In the image forming apparatus  10   f , control by the controller  70  allows the registration roller  90  to be reversible, and to transport the recording medium toward the transfer position T at the predetermined timing. The mentioned-above image forming apparatus  10  according to the first exemplary embodiment has the transport path  18  having the main transport path  19  and the repeat path  46 . Whereas, the image forming apparatus  10   d  has a transport path  18  having the main transport path  19  and a repeat path  92 . 
     Further, the controller  70  of the image forming apparatus  10   f  controls an exit roller  94  to be capable of reversing. Furthermore, the image forming apparatus  10   f  has a switching device  96  between the fixing device  22  and the exit roller  94  in the transport direction. The switching device  96  is controlled by the controller  70 . 
     In the image forming apparatus  10   f , when a color printing is performed, as mentioned above, the recording medium is returned to the repeat path  92 . That is, a position of the transport path  18  in the front of the reversible exit roller  94  is forked, and a switching device  96  is disposed on the fork point. Further, the repeat path  92  returning the recording medium from the forked position to downstream the registration roller  90  is formed. 
     The repeat path  92 , which a part of the repeat path  92  is formed on outside of the image forming apparatus main body  12 , allows the recording medium to be retrieved again into the image forming apparatus main body  12  following forwarding the recording medium to outside of the image forming apparatus main body  12 . That is, in the rear side of the image forming apparatus main body  12  (Right side in  FIG. 6 ), a forward port  98  and a retrieve port  100  are formed in the upper part and the lower part of the image forming apparatus main body  12 , respectively. The exit roller  94  reverses at the time where the retail edge short of the recording medium reaches the exit roller  94 , accordingly, the recording medium is guided to the repeat path  92  with the switching device  96 . Further, the recording medium is forwarded from the forward port  98  to outside of the image forming apparatus main body  12 . Further, by guided with the guide member  102  in outside of the image forming apparatus main body  12 , the recording medium is retrieved at the retrieve port  100  into the image forming apparatus main body  12 , and is transported from downstream side of the transport path  18  to the registration roller  90 . 
     The registration roller  90  reverses to transport the recording medium to the upstream side of the transport path  18 , that is, backward feeds the recording medium, thereby the recording medium is returned to the sheet feed unit  14  side and is transported toward the transfer position T at the predetermined timing. 
     Thus, in the case of color printing, the switching device  96  is switched a transport path to the repeat path  92  side. Then, the recording medium is forwarded by reversing of the exit roller  94  from the forward port  98  to the outside of the image forming apparatus main body  12 , and further, is guided along a guide member  102 , placed on outside of the image forming apparatus main body  12 , to be loaded to the inside of the image forming apparatus main body  12  at the retrieve port  100 . Further the recording medium is transported with the registration roller  28  to the transfer position T at the predetermined timing. Then the recording medium is passed through a position between the image carrier  24  and the transfer device  26  four times and is ejected from the exit  20 . 
     Note that the registration roller  90  does not have to reverse if the repeat path  92  is formed to return the recording medium in the upstream side of the registration roller  90 . 
     Next, a third exemplary embodiment of the present invention will be described. 
       FIG. 11  is a side view showing an overview of the image forming apparatus  10   g  according to the third exemplary embodiment. Note that the image forming apparatus  10   g  shown in  FIG. 11  indicates the parts substantially similar to the parts configuring the image forming apparatus  10  shown in  FIG. 1  with the same reference numeral as the image forming apparatus  10 . 
     The above-mentioned image forming apparatus  10  (Refer to  FIG. 1 ) has the image forming part  13  with the rotary development device  57 , whereas the image forming apparatus  10   g  has a developing device  104  to visualize an electrostatic latent image carried on the image carrier  24  with a black developer. Further, the above-mentioned image forming apparatus  10  has the transport path  18  with the main transport path  19  and the repeat path  46 , whereas the image forming apparatus  10   g  has a transport path  18  with the main transport path  19  and a reverse path  108 . 
     Further, in the image forming apparatus  10   g , the exit roller  106  is capable of reversing, and the recording medium is returned to the reverse path  108  in the case of duplex printing. That is, a position of the transport path  18  short of the exit roller  106  is forked, and a switching device  110  is disposed in the forked point. Further, the reverse path  108  returning from the forked point to the registration roller  28  is formed. The switching device  110  is controlled by the controller  70 . 
     In the case of duplex printing in the image forming apparatus  10   g  configured as mentioned above, the controller  70  controls the switching device  110  to switch a passage to the reverse path  108 . Accordingly, the exit roller  106  reverses at the time where the retail edge short of the recording medium reaches the exit roller  94 , and the recording medium is led to the reverse path  108 . Further, the recording medium is forwarded from the forward port  48  to outside of the image forming apparatus main body  12  with the transport roller  52 . Further, by guided with the guide member  54  to outside of the image forming apparatus main body  12 , the recording medium is retrieved at the retrieve port  50  into the image forming apparatus main body  12 , and is transported with the registration roller  28  at the predetermined timing. Furthermore, the recording medium passes through a position between the image carrier  24  and the transfer device  26  and the fixing device  22 , and is ejected from the exit  20 . 
     Next, a fourth exemplary embodiment of the present invention will be described. 
       FIG. 12  is a side view showing an overview of the image forming apparatus  10   h  according to the fourth exemplary embodiment. Note that the image forming apparatus  10   h  shown in  FIG. 12  indicates the parts substantially similar to the parts configuring the image forming apparatus  10   g  shown in  FIG. 11  with the same reference numeral as the image forming apparatus  10 . 
     The reverse path  108  in the above-mentioned image forming apparatus  10   g  has a portion which is located on outside of the image forming apparatus main body  12 . Whereas, the reverse path  108  in the image forming apparatus  10   h  is located entirely inside the image forming apparatus main body  12 . Further, the exit roller  106  in the image forming apparatus  10   g  is arranged inside the image forming apparatus main body  12 . Whereas, the exit roller  106  in the image forming apparatus  10   h  is arranged on the outside of the image forming apparatus main body  12 . 
     In the image forming apparatus  10   h  configured as the mentioned above, in the case of duplex printing, when the exit roller  106  catches the retail edge of the recording medium and starts rotation, it is a state that whole of the recording medium is placed on the outside of the image forming apparatus main body  12 . Accordingly, even though the moisture content of the recording medium reduces by fixing the image on one surface of the recording medium, since whole of the recording medium is placed on the outside of the image forming apparatus main body  12 , the moisture content of the recording medium becomes stable due to absorbing water consisted in the air on outside of the image forming apparatus main body  12 . Since the image formation is performed on another surface of the recording medium in the stable moisture content state, reduction of image quality is hardly caused in forming the image on the another surface. 
     Next, a fifth exemplary embodiment of the present invention will be described. 
       FIG. 13  is a side view showing an overview of the image forming apparatus  10   i  according to the fifth exemplary embodiment. As shown in  FIG. 13 , the image forming apparatus  10   i  has an image forming apparatus main body  112  with a sheet feed unit  114  having one stage and arranged in the bottom of the image forming apparatus main body  12 . 
     A pickup roller  116 , which picks up the recording medium such as a sheet from the sheet feed unit  114 , is arranged at the upper part of the sheet feed unit  114 . Driven by an unillustrated drive part, the pickup roller  116  rotates to supply the recording medium toward the transport path  118 . 
     The transport path  118  is a recording medium passage from the pickup roller  116  to the exit  120 , and guides the recording medium, picked up from the pickup roller  116 , to a transfer position T to be described later with the switching device  117 . The transport path  118  has a portion approximately horizontally extended in a lower part of the image forming apparatus main body  112 . Along the transport path  118 , the recording medium is transported to the exit  120  located at the upper part of the image forming apparatus main body  112 . An image carrier  124  such as a photoreceptor and a transfer roller  126  having an elastic surface are arranged at the upstream side of the fixing device  122  on the transport path  118 . Further, a registration roller  128  is arranged at the upstream side of the image carrier  124  and the transport roller  126 . 
     Further, an exit roller  142  is arranged in proximity to the exit  120  on the transport path  118 . 
     Accordingly, the recording medium picked up from the sheet feed unit  114  with the pickup roller  116  is led along the transport path  118 , and is suspended with the registration roller  128 . Further, the recording medium passes between the image carrier  124  and the transfer roller  126  at the predetermined timing with e.g. transferred a black developer image. The black developer image transferred is fixed with the fixing device  122  on the recording medium, is ejected from the exit  120  with the exit roller  142 . 
     In the case of color printing, the recording medium is returned e.g. three times to a repeat path  146  to be described later, and a controller  170  to be described later controls an order of forming each color developer image on the image carrier  124 . That is, a position of the transport path  118  in downstream of the fixing device  122  is forked, and a switching device  144  is arranged in the forked point. Further, the repeat path  146  returning the recording medium from the forked position to the registration roller  128  is formed. 
     The repeat path  146  has a portion formed on the top outside of the image forming apparatus main body  112 , accordingly, the recording medium is forwarded to outside of the image forming apparatus main body  112  and is retrieved again inside the image forming apparatus main body  112 . That is, a forward port  148  is formed in a rear side (Left side in  FIG. 8 ), and a retrieve port  150  is formed in front side, respectively, in the upper part of the image forming apparatus main body  112 . Guided with the switching device  144  to the repeat path  146 , the recording medium is forward with the transport roller  152  to the outside of the image forming apparatus main body  112  from the forward port  148 . Further, the recording medium is transported along the top outside of the image forming apparatus main body  112 , and is retrieved into the image forming apparatus main body  112  at the retrieve port  150  by guide of the guide member  154 . Thus the recording medium is transported with the transport roller  155 , and is guided with the switching device  117  to the registration roller  128 . 
     Thus, in the case of color printing, the switching device  144  switches a transport path to the repeat path  146  side. Then, the recording medium is forwarded with the transport roller  152  from the forward port  148  to the outside of the image forming apparatus main body  112 , and further, is guided along the top outside of the image forming apparatus main body  112 , to be retrieved into the image forming apparatus main body  12  at the retrieve port  150  by guide of the guide member  154 . Further the recording medium is transported with the registration roller  128 . Then the recording medium is guided with the switching device  117  to the registration roller  128  to be passed through the registration roller  128  and a position between the image carrier  124  and the transfer device  126 , and the fixing device  122  four times, and is ejected from the exit  120 . 
     Note that the guide member  154 , consisting of e.g. a platy member, in the case that a color printing is not performed in the image forming apparatus  10 , is capable of being stored inside the image forming apparatus main body  12 . 
     In the image forming apparatus main body  112 , development units  158   a  to  158   d  respectively containing four colors of developers, i.e., yellow, magenta, cyan, and black is disposed, e.g. in a front side of an approximately central portion. An electrostatic latent image carried on the image carrier  124  is sequentially visualized with each color developer. 
     In upper of the image carrier  124 , a charging device  162  such as a charging roller, is provided for evenly charging the image carrier  124 . Furthermore, an image carrier cleaner  164  abuts on the image carrier  124 , upstream relative to the charging device  162  in the direction of rotation of the image carrier  124 . The image carrier cleaner  164  scrapes away developer particles remaining on the image carrier  124  after transfer. 
     Above the image carrier cleaner  164 , an optical projection device  166  which projects an electrostatic latent image on the image carrier  124  charged by the charging device  162 , using a beam such as a laser beam is arranged. Down the image carrier  124 , the above-mentioned transfer roller  126  is located. The transfer roller  126  overlay-transfers each developer image made visible with each of the development units  158   a  to  158   d  sequentially onto a recording medium in the transfer position T. 
     Downstream of the transfer position T, a fixing device  122  is arranged. The fixing device  122  has a heating roller and a pressure roller for fixing the developer image, which has been transferred to the recording medium with the image carrier  124  and the transfer roller  126 , on the recording medium with heat and pressure and further transporting them. 
     Furthermore, an user interface (UI) equipment  168  such as a touch panel is disposed in a position above the image forming apparatus main body  112 , and a controller  170 , controlling each of part configuring the image forming apparatus  10   f  is disposed in the image forming apparatus main body  112 . 
     Next, all operations of the image forming apparatus  10   f  in color printing will be described. When a signal to form an image is delivered, the image carrier  124  is evenly charged by the charging device  162 . Toward the image carrier  124  charged, a beam corresponding to a yellow image is emitted from the optical projection device  166  based on the signal. The beam from the optical projection device  166  exposes the surface of the image carrier  124 , thereby forming an electrostatic latent image. 
     The electrostatic latent image carried on the image carrier  124  is developed with a yellow developer supplied by the development unit  158   a , and the developer image is transferred to the recording medium fed from the sheet feed unit  114 . The recoding medium having the yellow developer image transferred thereto is led to the fixing device  122  where the heating roller and the pressure roller apply heat and pressure to the recording medium, thereby fixing the developer image onto the recording medium. 
     The recording medium having the yellow developer image fixed thereto is led to the repeat path  146  with the switching device  144  to be forwarded to outside of the image forming apparatus main body  112  from the forward port  148 . Further, the recording medium is transported to the guide member  154  along top outside of the image forming apparatus main body  112  to be retrieved into the image forming apparatus main body  112  at the retrieve port  150 , thereby is guided to the registration roller  128  with the switching device  117 . 
     Developer particles remaining on the image carrier  124  is scraped off with the image carrier cleaner  164 . 
     Furthermore, the image carrier  124  is evenly charged again with the charging device  162 . Toward the image carrier  124  charged, a beam corresponding to a magenta image is emitted from the optical projection device  166  based on the image signal. The beam from the optical projection device  166  exposes the surface of the image carrier  124 , thereby forming an electrostatic latent image. 
     The electrostatic latent image carried on the image carrier  124  is developed with a magenta developer in the development unit  158   b . The magenta developer image is overlay-transferred to the recording medium having passed through the repeat path  146 . 
     The recording medium having the magenta developer image transferred thereto is led to the fixing device  122  where the heating roller and the pressure roller applies heat and pressure to the recording medium, thereby fixing the developer image onto the recording medium. Then, the recording medium having the magenta developer image fixed thereon is guided to the repeat path  146  with the switching device  144 . Developer particles remaining on the image carrier  124  are scraped off with the image carrier cleaner  164 . 
     The recording medium is returned to the registration roller  128  three times, and as in the case of the yellow and magenta developer images, developer images developed with the cyan and the black developers are fixed on the recording medium. Thus a color image is formed with overlaid developer images on the recording medium. The recording medium to which the color image has been fixed is led to the exit roller  142  with the switching device  144  and is ejected. 
     Further, in the exemplary embodiment mentioned above, the description has been provided for an example in which an image is formed by an image forming unit including the image carrier  24 , the charging device  62 , the optical projection device  66 , the rotary development device  57 , the transfer device  57 , the transfer device  26 , and the fixing device  22 . However, the scope of the present invention is not so limited. The image forming unit may be e.g. an ink jet type. 
     In the image forming apparatus  10   i , the image carrier  124 , the charging device  162 , the optical projection device  166 , the development units  158   a ,  158   b ,  158   c , and  158   d , and the transfer roller  126  are disposed in the image forming apparatus main body  112 , and are used as a image forming unit forming an image on the recording medium as mentioned above. Further, in the image forming apparatus  10   i , as a transport unit transporting the recording medium to the image forming unit including the development unit  158   a , and the like, the transport path  118 , the repeat path  146 , the transport rollers  152  and  155  are used. Furthermore, in the image forming apparatus main body  11 , the forward port  148  at which the recording medium formed the image formed by the image forming unit onto, is forwarded to outside of the image forming apparatus main body  112  is formed. Further, in the image forming apparatus  10   i , the guide member  154 , by which the recording medium, forwarded to outside of the image forming apparatus main body  112  from the forward port  148  is guided to be returned into the image forming apparatus main body  112  and to be led to the above-mentioned transport unit, is formed. 
     In the image forming apparatus  10   i , the image carrier  124 , the charging device  162 , the optical projection device  66 , and the development units  158   a ,  158   b ,  158   c , and  158   d  are disposed in the image forming apparatus main body  112  and are used as the image forming part forming an image. The image formed by the image forming part is transferred to the recording medium with the transfer roller  126 , and is fixed on the recording medium by at least heating with the fixing device  122 . Further, in the image forming apparatus  10   i , the repeat path  146 , the transport rollers  152  and  155  are used as the transport unit which transports the recording medium from the fixing device  122  to the transfer roller  126  so as to further transfer an image on the recording medium fixed the image onto with the fixing device  122 . In the transport unit, the recording medium fixed the image onto with the fixing device  122  is forwarded again to outside of the image forming apparatus main body  112 , and is retrieved into the image forming apparatus main body  112 . 
     As described above, the exemplary embodiment of the present invention is applicable to an image forming apparatus of e.g. a duplicate machine, a printer, a facsimile machine, or the like. 
     The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modification and variations will be apparent to practitioners skilled in the art. The embodiments were 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.